This description addresses ionic compositions of matter comprising positively charged cations [Ct]+ and negatively charged anions [A]xe2x88x92, said anion comprising a central core Group 13 element to which are bound fluoroaryl ligands, at least one of said fluoroaryl ligands being substituted with a siloxy group represented by the symbolsxe2x80x94SiOR3, wherein R is a C1-C30 hydrocarbyl or hydrocarbylsilyl substituent. [Ct]+ may be. selected from any capable of use with olefin polymerization catalysts and typically will be from the group consisting of anilinium and ammonium cations, trityl carbenium cations, Group 11 metal cations, silylium cations, the cations of the hydrated salts of Group 1 or 2 metals, and derivatives of the foregoing anilinium, ammonium, trityl carbenium, and silylium cations containing C1-C20 hydrocarbyl, hydrocarbylsilyl, or hydrocarbylamine substituents for one or more hydrogen atoms of said cations. The ionic compositions described can be used to activate olefin polymerization catalysts, and can be prepared so as to be soluble in aliphatic solvents. Syntheses and polymerization are illustrated.

This invention relates to polymerization cocatalyst compounds containing weakly coordinating Group 13 element anions and to the preparation of olefin polymers using ionic catalyst systems based on organometallic transition metal cationic compounds stabilized by these anions.
The term xe2x80x9cnoncoordinating anionxe2x80x9d is now accepted terminology in the field of olefin and vinyl monomer polymerization, both by coordination or insertion polymerization and carbocationic polymerization. See, for example, EP 0 277 003, EP 0 277 004, U.S. Pat. Nos. 5,198,401, 5,278,119, and Baird, Michael C., et al, J. Am. Chem. Soc. 1994, 116, 6435-6436. The noncoordinating anions are described to function as electronic stabilizing cocatalysts, or counterions, for essentially cationic metallocene complexes which are active for polymerization. The term noncoordinating anion as used here applies both to truly noncoordinating anions and coordinating anions that are at most weakly coordinated to the cationic complex so as to be labile to replacement by olefinically or acetylenically unsaturated monomers at the insertion site. These noncoordinating anions can be effectively introduced into a polymerization medium, or premixed with an organometallic catalyst compound prior to introduction into the polymerization medium, as Bronsted acid salts containing charge-balancing countercations, ionic cocatalyst compounds. See also, the review articles by S. H. Strauss, xe2x80x9cThe Search for Larger and More Weakly Coordinating Anionsxe2x80x9d, Chem. Rev., 93, 927-942 (1993).
Olefin solution polymerization processes are generally conducted in aliphatic solvents that serve both to maintain reaction medium temperature profiles and solvate the polymer products prepared. However, aryl-group containing activators, such as those having phenyl derivatives and other fused or pendant aryl-group substituents, are at best sparingly soluble in such solvents and typically are introduced in aryl solvents such as toluene. Solution polymerization processes in aliphatic solvents thus can be contaminated with toluene that must be removed to maintain process efficiencies and to accommodate health-related concerns for both industrial manufacturing processes and polymer products from them. Alternatively, relatively insoluble catalyst components can be introduced via slurry methods, but such methods required specialized handling and pumping procedures that complicate and add significant costs to industrial scale plant design and operation. Low solubility can also become disadvantageous should the process involve low temperature operation at some stage such as in typical adiabatic processes run in areas subject to low ambient temperatures. Additionally, separating or counteracting the build up in the recycle system of aromatic catalyst solvents may become another problem. At the same time means of maintaining high molecular weights in olefin polymers while operating at economically preferable high polymerization reaction temperatures and high polymer production rates is highly desirable. It is therefore desirable to identify olefin polymerization cocatalyst activators which are active for polymerization, particularly at elevated temperatures, which are more soluble in aliphatic solvents.
U.S. Pat. No. 5,502,017 addresses ionic metallocene catalysts for olefin polymerization comprising, as a cocatalyst component, a weakly coordinating anion comprising boron substituted with halogenated aryl substituents preferably containing silylalkyl substitution, such as tert-butyldimethyl-silyl. This substitution is said to increase the solubility and thermal stability of the resulting metallocene salts. Examples 3-5 describes the synthesis and polymerization use of the cocatalyst compound triphenylcarbenium tetrakis(4-dimethyl-t-butylsilyl-2,3,5,6-tetrafluorophenyl)borate.
In view of the above there is a continuing need for activating cocatalyst compounds both to improve the industrial economics of solution polymerization and to provide alternative activating compounds for ionic, olefin polymerization catalyst systems.
The invention provides anion-containing cocatalyst precursor compounds which can be combined with organometallic catalyst precursor compounds to form active catalysts for olefin polymerization by insertion, or coordination, and by carbocationic methods. Olefin polymerization can be conducted by subsequent contacting, or in situ catalyst formation essentially concurrent with said contacting, with polymerizable monomers, those having accessible olefinic, acetylenic unsaturation, or with monomers having olefinic unsaturation capable of cationic polymerization. The catalysts according to the invention are suitable for preparing polymers and copolymers from olefinically and acetylenically unsaturated monomers. The anions [A]xe2x88x92 of the cocatalyst precursor compounds are those containing a central Group 13 core element to which are bound fluoroaryl ligands, at least one of said fluoroaryl ligands being substituted in the para-position with a siloxy group represented by the symbol, xe2x80x94OSiR3, R representing one or more alkyl or alkylsilyl groups. When the anions are to be used with anilinium or ammonium cations, R groups are secondary, or even tertiary alkyl or alkylsilyl groups when capable of use in view of steric hindrance problems.
Preferred invention cocatalyst activator compounds can be represented by the following formula:
[Ct]+[M(ArF)n((ArF)OSiR3)4xe2x88x92n]xe2x88x92,
where [Ct]+ is a cation capable of abstracting an alkyl group, or breaking a carbon-metal bond from organometallic compounds containing such , M is a Group 13 element, preferably boron or aluminum, ArF is a fluorinated aryl group, and each R is independently selected from C1-C30 hydrocarbyl or hydrocarbylsilyl substituents, preferably attached to the Si atom through a secondary or tertiary carbon atom.
Exemplary ArF ligands and substituents of the above invention specifically include fluorinated aryl groups, preferably perfluorinated aryl groups, and include substituted ArF groups having substituents additional to the fluorine substitution, such as fluorinated hydrocarbyl groups. Preferred fluorinated aryl groups include phenyl, biphenyl, napthyl and derivatives thereof. The disclosures of U.S. Pat. Nos. 5,198,401, 5,296,433, 5,278,119, 5,447,895, 5,688,634, 5,895,771, WO 93/02099, WO 97/29845, WO 99/43717, WO 99/42467 and copending U.S. application Ser. No. 09/261,627, filed Mar. 3, 1999, and its equivalent WO 99/45042 are particularly instructive as to suitable ArF chemical groups and are incorporated by reference for purposes of U.S. patent practice. It is preferred that at least one third of hydrogen atoms on carbon atoms of the aromatic ligands be replaced by fluorine atoms, and more preferred that the aryl ligands be perfluorinated ligands. Perfluorinated means that each aryl hydrogen atom, other than those substituted with the siloxy substituents of the invention, should be substituted with fluorine or fluorcarbyl substituents, e.g., trifluoromethyl. The term xe2x80x9cperfluorinatedxe2x80x9d also encompasses those aryl ligands in which all but one hydrogen atom in the para position is replaced with fluorine and the para-position hydrogen is replaced with a siloxy group according to the invention.
Essentially any of the defined R groups will be effective for olefin polymerization such as by solution, bulk, slurry and gas phase polymerization processes. Exemplary R groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl, cyclohexyl, benzyl, methyltrimethylsilyl, methyltriethylsilyl, etc. The R groups may be the same or different, in other words mixed alkyl groups may be located on the siloxy silicon atom. In one embodiment, each R is a C1-20 hydrocarbyl or hydrocarbylsilyl substituent, preferably attached to the Si of the xe2x80x94Oxe2x80x94Sixe2x80x94 group through a secondary or tertiary carbon atom. Tertiary-carbon containing substituents can be advantageously employed where the two other R groups are less bulky, that is lower alkyl (C1-C4) primary or secondary alkyl substituents so as to minimize steric hindrance problems. Particular advantage in solution polymerization can be realized by selecting R such that solubility in aliphatic solvents is effectively achieved. The term xe2x80x9ceffective solubilityxe2x80x9d, and equivalent phraseology, is used here to mean having sufficient solubility such that amounts of cocatalyst reagent dissolved in an aliphatic solvent such as hexane are capable of activating industrially useful amounts of organometallic catalyst compounds without the use of aromatic solvents or slurry techniques. For example the selection of C2, or higher carbon-number alkyl or silylalkyl groups on the silicon atom, provides effective solubility.
Effective cations (Ct+) can be any of those known to be suitable for the abstraction of any of monoanionic hydride, alkyl, or other hydrocarbyl or hydrocarbylsilyl ligands on organometallic compounds suitable as insertion polymerization catalysis, or scission of covalent metal-carbon xcex71 or xcex72 bonds in such organometallic compounds. Preferably the cation is essentially non-interfering with the ionic catalyst complexes formed with the organometal catalyst precursor compounds. Such include nitrogen-containing cations such as the anilinium and ammonium salts of U.S. Pat. No. 5,198,401, and WO 97/35893, the trityl carbenium cations of U.S. Pat. No. 5,387,568, metal cations, e.g., Ag+, the silylium cations of WO 96/08519, and the cations of the hydrated salts of Group 1 or 2 metals of U.S. Pat. No. 5,767,208. Additionally suitable cations include nitrogen and carbon based cations described in WO 97/35893, and in copending U.S. applications serial No. 60/160,942, filed Oct. 22, 1999, and No. 60/169,768, filed Dec. 9, 1999. Thus hydrocarbyl, hydrocarbyl-amine, hydrocarbyl-silyl, preferably C1-C20, and Group 1, 2, 11 and 12 metal based cations, are suitable in accordance with the invention. An example of a hydrocarbyl-amine is [N-pentafluorophenyl pyrrolidinium]. The teachings of these references are referred to for information and incorporated by reference for the purposes of U.S. patent practice.
The ionic activator cocatalyst compositions of the invention may be prepared by synthetic methods well within the skills of organic and organometallic chemists. In a typical procedure, bromo-tetrafluorophenol is converted to the siloxy substituted counterpart by reacting with a trialkylchlorosilane in the presence of a strong base such as potassium hydride. The reaction product is then converted by reaction with BuLi and appropriate amount of a trihalylborane or aluminane. The resulting lithium salt can then be converted to an activating cocatalyst salt by cation exchange reaction with a halide salt, for example aninilinium or ammonium salts. This reaction sequence is illustrated below.
Organometallic precursors compounds suitable as olefin polymerization catalysts by coordination or insertion polymerization in accordance with the invention will include the known organometallic, transition metal compounds useful in traditional Ziegler-Natta coordination polymerization, particularly the metallocene compounds known to be useful in coordination polymerization, when such compounds are capable of catalytic activation by the cocatalyst activators described for the invention. These will typically include Group 3-10 transition metal compounds wherein at least one metal ligand can be abstracted by the cocatalyst activators, particularly those ligands including hydride, hydrocarbyl, and hydrocarbylsilyl, and lower alkyl-substituted (C1-C10) derivatives of those. Examples include hydride, methyl, benzyl, dimethyl-butadiene, etc. Ligands capable of being abstracted and transition metal compounds comprising them include those metallocenes described in the background art, see for example U.S. Pat. No. 5,198,401 and WO 92/00333. Syntheses of these compounds is well known from the published literature. Additionally, where the metal ligands include halogen, amido or alkoxy labile ligands (for example, biscyclopentadienyl zirconium dichloride) which not allow for ready abstraction with the activating cocatalysts of the invention, they can be converted into suitable ligands via known alkylation reactions with organometallic compounds such as lithium or aluminum hydrides or alkyls, alkylalumoxanes, Grignard reagents, etc. See also EP 0 500 944 and EP 0 570 982 for the reaction of organoaluminum compounds with dihalo-substituted . metallocene compounds prior to addition of activating anion compounds. All documents are incorporated by reference for purposes of U.S. patent practice.
Additional description of metallocene compounds which comprise, or can be alkylated to comprise, at least one ligand capable of abstraction to form a catalyticly active transition metal cation appear in the patent literature, e.g., EP-A-0 129 368, U.S. Pat. Nos. 4,871,705, 4,937,299, 5,324,800, 5,470,993, 5,491,246, 5,512,693, EP-A-0 418 044, EP-A-0 591 756, WO-A-92/00333, WO-A-94/01471 and WO 97/22635. Such metallocene compounds can be described for this invention as mono- or biscyclopentadienyl substituted Group 3, 4, 5, or 6 transition metal compounds wherein the ancillary ligands may be themselves substituted with one or more groups and may be bridged to each other, or may be bridged through a heteroatom to the transition metal. The size and constituency of the ancillary ligands and bridging elements are not critical to the preparation of the ionic catalyst systems of the invention but should be selected in the literature described manner to enhance the polymerization activity and polymer characteristics being sought. Preferably the cyclopentadienyl rings (including substituted cyclopentadienyl-based fused ring systems, such as indenyl, fluorenyl, azulenyl, or substituted analogs of them), when bridged to each other, will be lower alkyl-substituted (C1-C6) in the 2 position (without or without a similar 4-position substituent in the fused ring systems) and may additionally comprise alkyl, cycloalkyl, aryl, alkylaryl and or arylalkyl substituents, the latter as linear, branched or cyclic structures including multi-ring structures, for example, those of U.S. Pat. Nos. 5,278,264 and 5,304,614. Such substituents should each have essentially hydrocarbyl characteristics and will typically contain up to 30 carbon atoms but may be heteroatom containing with 1-5 non-hydrogen/carbon atoms, e.g., N, S, O, P, Ge, B and Si. All documents are incorporated by reference for purposes of U.S. patent practice.
Metallocene compounds suitable for the preparation of linear polyethylene or ethylene-containing copolymers (where copolymer means comprising at least two different monomers) are essentially any of those known in the art, see again WO-A-92/00333 and U.S. Pat. Nos. 5,001,205, 5,198,401, 5,324,800, 5,304,614 and 5,308,816, for specific listings. Selection of metallocene compounds for use to make isotactic or syndiotactic polypropylene, and their syntheses, are well-known in the art, specific reference may be made to both patent literature and academic, see for example Journal of organometallic Chemistry 369, 359-370 (1989). Typically those catalysts are stereorigid asymmetric, chiral or bridged chiral metallocenes. See, for example, U.S. Pat. Nos. 4,892,851, 5,017,714, 5,296,434, 5,278,264, WO-A-(PCT/US92/10066) WO-A-93/19103, EP-A2-0 577 581, EP-A1-0 578 838, and academic literature xe2x80x9cThe Influence of Aromatic Substituents on the Polymerization Behavior of Bridged Zirconocene Catalystsxe2x80x9d, Spaleck, W., et al, Organometallics 1994, 13, 954-963, and xe2x80x9cansa-Zirconocene Polymerization Catalysts with Annelated Ring Ligands-Effects on Catalytic Activity and Polymer Chain Lengthsxe2x80x9d, Brinzinger, H., et al, Organometallics 1994, 13, 964-970, and documents referred to therein. Though many above are directed to catalyst systems with alumoxane activators, the analogous metallocene compounds will be useful with the cocatalyst activators of this invention for active coordination catalyst systems, when the halogen, amide or alkoxy containing ligands of the metals (where occurring) are replaced with ligands capable of abstraction, for example, via an alkylation reaction as described above, and another is a group into which the ethylene group xe2x80x94Cxe2x95x90Cxe2x80x94 may insert, for example, hydride, alkyl, alkenyl, or silyl. See additional description in G. G. Hlatky, xe2x80x9cMetallocene catalysts for olefin polymerization Annual review of 1996xe2x80x9d, Coordination Chemistry Reviews, 181, 243-296 (Elsevier Science, 1999). All documents are incorporated by reference for purposes of U.S. patent practice.
Representative metallocene compounds can have the formula:
LALBLCiMcDE
where, Mc is a Group 3-6 metal; LA is a substituted or unsubstituted cyclopentadienyl or heterocyclopentadienyl ancillary ligand xcfx80-bonded to Mc; LB is a member of the class of ancillary ligands defined for LA, or is J, a heteroatom ancillary ligand "sgr"-bonded to Mc; the LA and LB ligands may be covalently bridged together through one or more Group 13-16 element-containing linking groups; LCi is an optional neutral, non-oxidizing ligand having a dative bond to Mc (i equals 0 to 3); and, D and E are independently labile ligands, each having a metal-carbon bond to Mc, optionally bridged to each other or LA or LB, which bond can be broken for abstraction purposes by a suitable activator and into which a polymerizable monomer or macromonomer can insert for coordination polymerization. Also, the use of hetero-atom containing rings or fused rings, where a non-carbon Group 13, 14, 15 or 16 atom replaces one of the ring carbons is considered for this specification to be within the terms xe2x80x9ccyclopentadienylxe2x80x9d, xe2x80x9cindenylxe2x80x9d, and xe2x80x9cfluorenylxe2x80x9d. See, for example, the background and teachings of WO 98/37106, having common priority with U.S. Ser. No. 08/999,214, filed Dec. 29, 1997, and WO 98/41530, having common priority with U.S. Ser. No. 09/042,378, filed Mar. 13, 1998, both incorporated by reference for purposes of U.S. patent practice. Substituted cyclopentadienyl structures means that one or more hydrogen atoms is replaced with hydrocarbyl, hydrocarbylsilyl, or heteroatom-containing like structures. The hydrocarbyl structures specifically include C1-C30 linear, branched, cyclic alkyl and cycloaromatic fused and pendent rings. These rings may also be substituted with similar structures.
Non-limiting representative metallocene compounds include monocyclopentadienyl compounds such as pentamethylcyclopentadienyltitanium isopropoxide, pentamethylcyclopentadienyltribenzyl titanium, dimethylsilyltetramethylcyclopentadienyl-tert-butylamido titanium dichloride, pentamethylcyclopentadienyl titanium trimethyl, dimethylsilyltetramethylcyclopentadienyl-tert-butylamido zirconium dimethyl, dimethylsilyltetramethylcyclopentadienyl-dodecylamido hafnium dihydride, dimethylsilyltetramethylcyclopentadienyl-dodecylamido hafnium dimethyl, unbridged biscyclopentadienyl compounds such as bis(1,3-butyl, methylcyclopentadienyl)zirconium dimethyl, pentamethylcyclopentadienyl-cyclopentadienyl zirconium dimethyl, (tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconium dimethyl; bridged bis-cyclopentadienyl compounds such as dimethylsilylbis(tetrahydroindenyl)zirconium dichloride and silacyclobutyl(tetramethylcyclopentadienyl)(n-propyl-cyclopentadienyl)zirconium dimethyl; bridged bisindenyl compounds such as dimethylsilylbisindenyl zirconium dichloride, dimethylsilylbisindenyl hafnium dimethyl, dimethylsilylbis(2-methylbenzindenyl)zirconium dichloride, dimethylsilylbis(2-methylbenzindenyl)zirconium dimethyl; and fluorenyl ligand-containing compounds, e.g., diphenylmethyl(fluorenyl)(cyclopentadienyl)zirconium dimethyl; and the additional mono- and biscyclopentadienyl compounds such as those listed and described in U.S. Pat. Nos. 5,017,714, 5,324,800, WO 92/00333 and EP-A-0 591 756. Particular advantage in solution polymerization can be achieved by the use of aliphatic solvent-soluble precursor compounds, e.g., bis(para-triethylsilyl-phenyl)methylene (2,7-(di-tert-butyl)fluorenyl)(cyclopentadienyl)hafnium dimethyl, however, the solubilizing effect of the aliphatic solvent-soluble anion compounds of the invention will tend to offset the lack of solubility for typical organometallic compound cations useful in olefin polymerization. See, copending applications U.S. Ser. No. 09/426,099, filed Oct. 22, 1999, and No. 60/160,942, filed Oct. 22, 1999 for background as to soluble catalysts and specific metallocene and precursor cocatalyst cations useful with the current invention. All documents are incorporated by reference for purposes of U.S. patent practice.
Representative traditional Ziegler-Natta transition metal compounds include tetrabenzyl zirconium, tetra bis(trimethylsiylmethyl)zirconium, oxotris(trimethlsilylmethyl)vanadium, tetrabenzyl hafnium, tetrabenzyl titanium, bis(hexamethyldisilazido)dimethyl titanium, tris(trimethylsilylmethyl)niobium dichloride, tris(trimethylsilylmethyl)tantalum dichloride. The important features of such compositions for coordination polymerization are the ligand capable of abstraction and that ligand into which the ethylene (olefinic) group can be inserted. These features enable the ligand abstraction from the transition metal compound and the concomitant formation of the ionic catalyst composition of the invention.
Additional organometallic transition metal compounds suitable as olefin polymerization catalysts in accordance with the invention will be any of those Group 3-10 that can be converted by ligand abstraction or "sgr"-bond scission into a catalyticly active cation and stabilized in that active electronic state by a noncoordinating or weakly coordinating anion sufficiently labile to be displaced by an olefinically unsaturated monomer such as ethylene.
Exemplary compounds include those described in the patent literature. International patent publications WO 96/23010, WO 97/48735 and Gibson, et. al., Chem. Comm., pp. 849-850 (1998), disclose diimine-based ligands for Group 8-10 metal compounds shown to be suitable for ionic activation and olefin polymerization. See also WO 97/48735. Transition metal polymerization catalyst systems from Group 5-10 metals wherein the active transition metal center is in a high oxidation state and stabilized by low coordination number polyanionic ancillary ligand systems are described in U.S. Pat. No. 5,502,124 and its divisional U.S. Pat. No. 5,504,049. See also the Group 5 organometallic catalyst compounds of U.S. Pat. No. 5,851,945 and the tridentate ligand containing Group 5-10 organometallic catalyst compounds of copending U.S. application Ser. No. 09/302,243, filed Apr. 29, 1999, and its equivalent PCT/US99/09306. Group 11 catalyst precursor compounds, capable of activation with ionizing cocatalysts, useful for olefins and vinyl group-containing polar monomers are described and exemplified in WO 99/30822 and its priority document, including U.S. patent application Ser. No. 08/991,160, filed Dec. 16, 1997. Each of these documents is incorporated by reference for the purposes of U.S. patent practice.
U.S. Pat. No. 5,318,935 describes bridged and unbridged bisamido transition metal catalyst compounds of Group 4 metals capable of insertion polymerization of xcex1-olefins. Bridged bis(arylamido) Group 4 compounds for olefin polymerization are described by D. H. McConville, et al, in Organometallics 1995, 14, 5478-5480. Synthesis methods and compound characterization are presented. Further work appearing in D. H. McConville, et al, Macromolecules 1996, 29, 5241-5243, described bridged bis(arylamido) Group 4 compounds that are active catalysts for polymerization of 1-hexene. Additional transition metal compounds suitable in accordance with the invention include those described in WO 96/40805. Cationic Group 3 or Lanthanide metal complexes for coordination polymerization of olefins is disclosed in copending U.S. application Ser. No. 09/408,050, filed Sep. 29, 1999, and its equivalent PCT/US99/22690. The precursor metal compounds are stabilized by a monoanionic bidentate ancillary ligand and two monoanionic ligands and are capable of activation with the ionic cocatalysts of the invention. Each of these documents is incorporated by reference for the purposes of U.S. patent practice.
Additional description of suitable organometallic or organometalloid catalyst precursor compounds may be found in the literature, any of such will be suitable where comprising, or where capable of alkylation to comprise, ligands capable of ionizing abstraction. See, for instance, V. C. Gibson, et al, xe2x80x9cThe Search for New-Generation Olefin Polymerization Catalysts: Life Beyond Metallocenesxe2x80x9d, Angew. Chem. Int. Ed, 38, 428-447 (1999).
When using the above catalysts of the invention, the total catalyst system will generally additionally comprise one or more organometallic compound scavenging agent. Such compounds as used in this application and its claims is meant to include those compounds effective for removing polar impurities from the reaction environment and for increasing catalyst activity. Impurities can be inadvertently introduced with any of the polymerization reaction components, particularly with solvent, monomer and catalyst feed, and adversely affect catalyst activity and stability. It can result in decreasing or even elimination of catalytic activity, particularly when ionizing anion pre-cursors are used to activate the catalyst systems. The polar impurities, or catalyst poisons include water, oxygen, metal impurities, etc. Preferably steps are taken before provision of such into the reaction vessel, for example by chemical treatment or careful separation techniques after or during the synthesis or preparation of the various components, but some minor amounts of organometallic compound will still normally be used in the polymerization process itself.
Typically these compounds will be organometallic compounds such as the Group-13 organometallic compounds of U.S. Pat. Nos. 5,153,157, 5,241,025 and WO-A-91/09882, WO-A-94/03506, WO-A-93/14132, and that of WO 95/07941. Exemplary compounds include triethyl aluminum, triethyl borane, triisobutyl aluminum, methylalumoxane, and isobutyl aluminumoxane. Those compounds having bulky or C6-C20 linear hydrocarbyl substituents covalently bound to the metal or metalloid center being preferred to minimize adverse interaction with the active catalyst. Examples include triethylaluminum, but more preferably, bulky compounds such as triisobutylaluminum, triusoprenylaluminum, and long-chain linear alkyl-substituted aluminum compounds, such as tri-n-hexylaluminum, tri-n-octylaluminum, or tri-n-dodecylaluminum. When alumoxane is used as activator, any excess over the amount needed to activate the catalysts present can act as a poison scavenger compound and additional organometallic compounds may not be necessary. Alumoxanes also may be used in scavenging amounts with other means of activation, e.g., methylalumoxane and triisobutyl-aluminoxane with boron-based activators. The amount of such compounds to be used with catalyst compounds of the inventions is minimized during polymerization reactions to that amount effective to enhance activity (and with that amount necessary for activation of the catalyst compounds if used in a dual role) since excess amounts may act as catalyst poisons.
The catalyst compounds of the invention are useful in polymerization of unsaturated monomers conventionally known to be polymerizable under coordination polymerization using metallocenes. Such conditions are well known and include solution polymerization, slurry polymerization, gas-phase polymerization, and high pressure polymerization. The catalyst of the invention may be supported on inorganic oxide or polymeric supports and as such will be particularly useful in the known operating modes employing fixed-bed, moving-bed, fluid-bed, slurry or solution processes conducted in single, series or parallel reactors. Pre-polymerization of supported catalyst of the invention may also be used for further control of polymer particle morphology in typical slurry or gas phase reaction processes in accordance with conventional teachings. A preferred method of supporting the invention catalysts for gas phase or slurry polymerization is described in WO 98/55518, incorporated by reference for purposes of U.S. patent practice.
In alternative embodiments of olefin polymerization methods for this invention, the catalyst system is employed in liquid phase (solution, slurry, suspension, bulk phase or combinations thereof), in high pressure liquid or supercritical fluid phase, or in gas phase. Each of these processes may also be employed in singular, parallel or series reactors. The liquid processes comprise contacting olefin monomers with the above described catalyst system in a suitable diluent or solvent and allowing said monomers to react for a sufficient time to produce the invention copolymers. Hydrocarbyl solvents are suitable, both aliphatic and aromatic, hexane is preferred. Bulk and slurry processes are typically done by contacting the catalysts with a slurry of liquid monomer, the catalyst system being supported. Gas phase processes typically use a supported catalyst and are conducted in any manner known to be suitable for ethylene homopolymers or copolymers prepared by coordination polymerization. Illustrative examples may be found in U.S. Pat. Nos. 4,543,399, 4,588,790, 5,028,670, 5,382,638, 5,352,749, 5,408,017, 5,436,304, 5,453,471, and 5,463,999, 5,767,208 and WO 95/07942. Each is incorporated by reference for purposes of U.S. patent practice.
Generally speaking, the polymerization reaction temperature can vary from about 40xc2x0 C. to about 250xc2x0 C. Preferably the polymerization reaction temperature will be from 60xc2x0 C. to 220xc2x0. The pressure can vary from about 1 mm Hg to 2500 bar, preferably from 0.1 bar to 1600 bar, most preferably from 1.0 to 500 bar.
For homogenous solution polymerization best results may be obtained when the quantity and type of solvent used to introduce the catalyst is controlled as well as the manner of introduction. Generally it is believed preferable to achieve full solution and avoid slurried systems, and hence fairly high concentrations of the catalyst, at low temperatures and use low solvent amounts. The ease with which these objectives can be achieved may vary with the solubility of the non-coordinating anion and transition metal components. Some of the more active catalysts or those likely to give a higher molecular weight at a given temperature, may have reduced solubility or may be modified for increased solubility.
The invention is especially suitable for use with solution polymerization using bridged fluorenyl metallocene hafnium compounds with naphthyl group-containing non-coordinating anions at polymerization temperatures in excess of 110xc2x0 C., for elastomeric olefin copolymers, and more preferably more than 160xc2x0 C. and up to 250xc2x0 C. for plastomeric ethylene copolymers.
Linear polyethylene, including high and ultra-high molecular weight polyethylenes, including both homo- and copolymers with other alpha-olefin monomers, alpha-olefinic and/or non-conjugated diolefins, for example, C3-C20 olefins, diolefins or cyclic olefins, are produced by adding ethylene, and optionally one or more of the other monomers, to a reaction vessel under low pressure (typically  less than 50 bar), at a typical temperature of 40-250 xc2x0 C. with the invention catalyst that has been slurried with a solvent, such as hexane or toluene. Heat of polymerization is typically removed by cooling. Gas phase polymerization can be conducted, for example, in a continuous fluid bed gas-phase reactor operated at 2000-3000 kPa and 60-160 xc2x0 C., using hydrogen as a reaction modifier (100-200 PPM), C4-C8 comonomer feedstream (0.5-1.2 mol %), and C2 feedstream (25-35 mol %). See, U.S. Pat. Nos. 4,543,399, 4,588,790, 5,028,670 and 5,405,922 and 5,462,999, which are incorporated by reference for purposes of U.S. patent practice.
Ethylene-xcex1-olefin (including ethylene-cyclic olefin and ethylene-xcex1-olefin-diolefin) elastomers of high molecular weight and low crystallinity can be prepared utilizing the catalysts of the invention under traditional solution polymerization processes or by introducing ethylene gas into a slurry utilizing the xcex1-olefin or cyclic olefin or mixture thereof with other monomers, polymerizable and not, as a polymerization diluent in which the invention catalyst is suspended. Typical ethylene pressures will be between 10 and 1000 psig (69-6895 kPa) and the polymerization diluent temperature will typically be between 40 and 160xc2x0 C. The process can be carried out in a stirred tank reactor, or more than one operated in series or parallel. See the general disclosure of U.S. Pat. No. 5,001,205 for general process conditions. See also, international application WO 96/33227 and WO 97/22639. All documents are incorporated by reference for description of polymerization processes, metallocene selection and useful scavenging compounds.
Other olefinically unsaturated monomers besides those specifically described above may be polymerized using the catalysts according to the invention, for example, styrene, alkyl-substituted styrenes, isobutylene and other geminally disubstituted olefins, ethylidene norbornene, norbornadiene, dicyclopentadiene, and other olefinically-unsaturated monomers, including other cyclic olefins, such as cyclopentene, norbornene, alkyl-substituted norbornenes, and vinyl group-containing polar monomers capable of coordinating polymerization. See, for example, U.S. Pat. Nos. 5,635,573, 5,763,556, and WO 99/30822. Additionally, alpha-olefinic macromonomers of up to 1000 mer units, or more, may also be incorporated by copolymerization yielding branch-containing olefin polymers. Additionally oligomerization, dimerization, hydrogenation, olefin/carbon monoxide copolymerization, hydroformulation, hydrosilation, hydroamination and related catalytic reactions employing organometallic cationic complexes can be accomplished using the cocatalyst complexes of the invention with selected organometallic compounds suitably selected as known in the art.
The catalyst compositions of the invention can be used as described above individually for coordination polymerization or can be mixed to prepare polymer blends with other known olefin polymerization catalyst compounds. By selection of monomers, blends of coordination catalyst compounds, polymer blends can be prepared under polymerization conditions analogous to those using individual catalyst compositions. Polymers having increased MWD for improved processing and other traditional benefits available from polymers made with mixed catalyst systems can thus be achieved.
The formation of blended polymers can be achieved ex situ through mechanical blending or in situ through the use of a mixed catalyst system. It is generally believed that in situ blending provides a more homogeneous product and allows the blend to be produced in one step. The use of mixed catalyst systems for in situ blending involves combining more than one catalyst in the same reactor to simultaneously produce multiple distinct polymer products. This method requires additional catalyst synthesis and the various catalyst components must be matched for their activities, the polymer products they generate at specific conditions, and their response to changes in polymerization conditions.

Siloxy substituted cocatalyst activators for olefin polymerization


A composition comprising finely divided particles of (a) an electrically-conductive material; (b) one or more inorganic binders; and (c) tin, wherein components (a), (b) and (c) are in a liquid vehicle, said composition being suitable for use in the manufacture of an electrically-conductive pattern on a substrate.

The present invention relates to conductor compositions and their use in the manufacture of components, particularly heating elements, in microelectronic circuits. These compositions are of particular use in the manufacture of demisting elements in heated windows, for example in automotive glazing, particularly automotive backlights.
The use of thick-film conductors as components in hybrid microelectronic circuits is well known in the electronics field. Compositions for the manufacture of such components usually take the form of a paste-like solid-liquid dispersion, where the solid phase comprises finely divided particles of a noble metal or a noble metal alloy or mixtures thereof and an inorganic binder. The liquid vehicle for the dispersion is typically an organic liquid medium, but may also be an aqueous-based liquid medium. Additional materials may be added in small quantities (generally less than about 3% by weight of the composition) to modify the properties of the composition and these include staining agents, rheology modifiers, adhesion enhancers and sintering modifiers.
The metals used in the preparation of thick-film conductor compositions are typically selected from silver, gold, platinium and palladium. The metal can be used either in isolation or as a mixture which forms an alloy upon firing. Common metal mixtures include platinum/gold, palladium/silver, platinum/silver, platinum/palladium/gold and platinum/palladium/silver. The most common systems used in the manufacture of heating elements are silver and silver/palladium. The inorganic binder is typically a glass or glass-forming material, such as a lead silicate, and functions as a binder both within the composition and between the composition and substrate onto which the composition is coated. Due to environmental considerations the use of lead-containing binders is becoming less common and lead-free binders such as zinc or bismuth borosilicates are now often employed. The role of the organic medium is to disperse the particulate components and to facilitate the transfer of the composition onto the substrate.
The consistency and rheology of the composition is adjusted to the particular method of application which may comprise screen printing, brushing, dipping, extrusion, spraying and the like. Typically, screen printing is used to apply the composition. The pastes are usually applied to an inert substrate, such as an alumina, glass, ceramic, enamel, enamel-coated glass or metal substrate, to form a patterned layer. The thick-film conductor layer is normally dried and then fired, usually at temperatures between about 600 and 900xc2x0 C., to volatilise or burn off the liquid vehicle and sinter or melt the inorganic binder and the metal components. Direct wet-firing, i.e. wherein the thick film layer is not dried before fig, has also been used to generate the patterned layer.
It is, of course, necessary to connect the conductive pattern to the other components of the electronic circuit, such as the power source, resistor and capacitor networks, resistors, trim potentiometers, chip resistors and chip carriers. This is generally achieved by using metal clips, typically comprising copper, which are soldered either directly adjacent to or on top of the conductive layer. Where the clips are soldered on top of the conductive layer, attachment is either directly onto the conductive pattern itself or onto a solderable composition which is overprinted onto the pattern (an xe2x80x9cover-printxe2x80x9d). An over-print is generally applied only in the region of the conductive pattern to which the metal clips are attached by solder, which region is generally referred to as the xe2x80x9cclip areaxe2x80x9d. The ability to solder onto the electrically-conductive layer is an important parameter in the manufacture of heating elements since it removes the requirement for an over-print. However, the inorganic binder, which is important for binding the paste onto the substrate, can interfere with solder wetting and result in poor adhesion of the soldered metal clips to the conductive layer. The requirements of high substrate adhesion and high solderability (or adhesion of the metal clips to the conductive pattern) are often difficult to meet simultaneously. U.S. Pat. No. 5,518,663 provides one solution to this problem by incorporating into the composition a crystalline material from the feldspar family.
An important application of patterned electrically-conductive layers is in the automobile industry, and particularly in the manufacture of windows which can be defrosted and/or demisted by an electrically-conductive grid permanently attached to the window and capable of producing heat when powered by a voltage source. In order for the window to defrost quickly, the circuit must be capable of supplying large amounts of power from a low voltage power source, typically 12 volts. For such power sources the resistivity requirement of the conductive pattern is generally in the range of from about 2 to about 5 xcexcxcexa9 cm (5 mxcexa9/xe2x96xa1 at 10 xcexcm after firing). This requirement is readily met by conductors containing noble metals, particularly silver which is the most commonly-used material for this application.
In certain applications, a conductive composition having a higher resistivity is required. In particular, it is anticipated that the resistance requirements of window-heating elements in automobiles will shortly need to change since the automotive industry is expected to adopt the use of a 42 and 48 volt power supply in the near future. As a result, the conductive composition used to manufacture the window-heating elements will be required to exhibit higher values of resistivity, typically greater than about 10 xcexcxcexa9 cm, preferably greater than about 12 xcexcxcexa9 cm, particularly in the range from about 20 to about 70 xcexcxcexa9 cm.
A number of different materials may be added to adjust the specific resistivity of a conductive composition. For example, metal resinates such as rhodium and manganese resinates have been used to increase resistivity, as disclosed in U.S. Pat. No. 5,162,062 and U.S. Pat. No. 5,378,408. In addition, an increase in the content of precious metals, particularly the platinum group metals such as platinum and palladium, has also been used to increase the specific resistivity. Silver/palladium and silver/platinum compositions can achieve resistivity values from about 2 xcexcxcexa9 cm (that of a composition comprising only silver and binder) up to around 100 xcexcxcexa9 cm (for a 70:30 Pd:Ag blend). Systems comprising platinum and/or palladium are, however, significantly more expensive and their use would be prohibitive in applications requiring coverage of a large surface area, such as the window-heating elements used in the automotive industry. In addition, an over-print of a composition containing a high amount of silver (and typically small amounts of filler) is generally required for certain metal blends, such as compositions containing high palladium levels, in order to achieve adequate solder adhesion. Conventional conductive compositions which typically operate at resistivity values of 2 to 5 xcexcxcexa9 cm and which are comprised predominantly of silver do not require an over-print since acceptable levels of solder adhesion can be achieved by adjusting the levels of inorganic binder.
Other, lower-cost approaches for achieving a high resistivity involve blending large amounts of filler into a silver-containing conductive composition to block the conductive path. Fillers are typically inorganic materials and those commonly used are glass (which may be the same or different as that used for the binder) and alumina (or other metal oxides). However, such approaches tend to result in a loss of solder acceptance and solder adhesion. For example, adequate solder adhesion can be maintained only up to a level of about 10% alumina by weight of the composition but this level is generally too low for an appreciable rise in resistivity. For glass-type fillers, loss of solder adhesion occurs at even lower levels and, again, this level is too low for an appreciable rise in resistivity. In addition, this problem can not normally be ameliorated by the use of silver over-prints owing to glass migration between the layers during firing, specifically from the conductive coating into the over-print.
A further requirement of the conductor compositions is that they must be chemically durable and resilient to exposure to varying environmental conditions such as temperature, humidity, acid and salt. Compositions comprising large amounts of glass filler, particularly lead-free glass filler, are often relatively unstable to such factors.
An additional consideration is that it is desirable for the resistance of the coating composition to be substantially independent of the temperature of firing used in the manufacture of the patterned conductive layer. For instance, in the case of the application of a conductive composition to a glass substrate, the behaviour of the composition under sintering and melting should remain substantially constant between the temperatures of about 620 and 680xc2x0 C. Nevertheless, a change in resistance of up to about 10% between these two temperatures, which corresponds to the behaviour of a pure silver composition, is generally tolerated. The use of large amounts of filler to significantly increase resistivity results in compositions which do not generally satisfy this requirement
A further additional consideration is that it is desirable for the relationship between the resistivity and the amount of resistivity modifier added to the composition to be relatively predictable and/or substantially linear within the target range of desired resistivities. The resistivity of compositions comprising large amounts of filler generally increases in an almost linear manner until a critical concentration is reached. At this critical concentration, the resistivity may rise very rapidly, often by an order of magnitude, when the level of resistivity modifier is increased by only a fraction of a weight percent. As a result, it is difficult to target specific values of resistivity for such compositions.
It is an object of this invention to provide higher-resistivity electrically-conductive compositions which do not suffer from the afore-mentioned disadvantages. In particular, it is an object of this invention to provide an economical electrically-conductive coating composition having increased resistivity while at the same time exhibiting good solderability.
Accordingly, the present invention provides a composition comprising finely divided particles of (a) an electrically-conductive material; (b) one or more inorganic binders; and (c) tin, wherein components (a), (b) and (c) are dispersed in a liquid vehicle, preferably an organic medium.
The composition of the present invention preferably exhibit higher values of resistivity of greater than about 10 xcexcxcexa9 cm, preferably greater than about 12 xcexcxcexa9 cm, preferably in the range from about 20 to about 70 xcexcxcexa9 cm, and more preferably in the range from about 20 to about 50 xcexcxcexa9 cm. In one embodiment, the resistivity is in the range from about 30 to about 40 xcexcxcexa9 cm.
The compositions of the present invention are suitable for use as paste compositions for forming thick-film conductive patterns on a substrate, for instance, by the process of screen-printing. The compositions of the present invention are of particular use as components in the manufacture of windows which can be defrosted and/or demisted by an electrically-conductive grid attached to the window, particularly for use in the automotive industry.
As used herein, the term xe2x80x9cfinely dividedxe2x80x9d is intended to mean that the particles are sufficiently fine to pass through a 400-mesh screen (US standard sieve scale). It is preferred that at least 50%, preferably at least 90%, and more preferably substantially all of the particles are in the size range of 0.01 to 20 xcexcm. Preferably, the largest dimension of substantially all particles is no more than about 10 xcexcm and desirably no more than about 5 xcexcm.
Preferably, the components are present in amounts such that the total amount of components (a), (b) and (c) is about 50 to about 95% by weight of the composition, with the liquid vehicle being present in amounts of about 5 to about 50% by weight of the composition. In a preferred embodiment, the total amount of components (a), (b) and (c) is in the range from about 60 to about 90%, preferably from about 70 to about 85% by weight of the composition.
Compounds (a), (b) and (c) generally comprise substantially all of the solid phase material used to prepare the compositions of the invention. Preferably component (a) is present in amounts of from about 30 to about 99.4%, preferably from about 50 to about 98%, more preferably from about 60 to about 90%, and more preferably from about 65 to about 75%, by weight of the total solids present in the composition. Preferably component (b) is present in amounts of from about 0.5 to about 40%, preferably from about 2 to about 25%, by weight of the total solids present in the composition. In one embodiment, component (b) is present in amounts from about 10 to about 25% and more preferably from about 15 to about 25%, by weight of the total solids present in the composition. In an alternative embodiment, component (b) is present in amounts from about 2 to about 20% and more preferably from about 5 to about 15%, by weight of the total solids present in the composition. Preferably component (c) is present in amounts of about 0.1 to about 30%, preferably from about 2 to about 20%, more preferably from about 4 to about 16%, and more preferably from about 6 to about 12%, by weight of the total solids present in the composition.
The electrically-conductive particles of component (a) can be in any form suitable for the production of the compositions of the present invention. For example, electrically-conductive metallic particles may be in the form of either metal powders or metal flakes or blends thereof. In one embodiment of the invention, the metallic particles are a blend of powder and flake. The particle size of the metal powder or flake is not by itself narrowly critical in terms of technical effectiveness. However, particle size does affect the sintering characteristics of the metal in that large particles sinter at a lower rate than small particles. Blends of powders and/or flakes of differing size and/or proportion can be used to tailor the sintering characteristics of the conductor formulation during firing, as is well-known in the art. The metal particles should, however, be of a size that is appropriate to the method of application thereof, which is usually screen printing. The metal particles should therefore generally be no larger than about 20 xcexcm in size and preferably less than about 10 xcexcm. The minimum particle size is normally about 0.1 xcexcm.
The preferred metal for the electrically-conductive component (a) of the conductor composition of the present invention is silver. Silver particles larger than about 1.0 xcexcm impart greater colouring to the composition. It is preferred that the compositions of the invention contain at least 50% weight silver particles larger than 1.0 xcexcm. The silver will ordinarily be of high purity, typically greater than 99% pure. However, less pure materials can be used depending on the electrical requirements of the conductive layer or pattern. In an embodiment of the invention, component (a) comprises a mixture of silver and nickel and/or suitable derivatives. A preferred nickel derivative suitable for use in this embodiment of the invention is nickel boride (Ni3B). Typically, the Ag:Ni ratio will be about 1:1 to about 25:1, preferably at least about 1.5:1 and more preferably about 1.5:1 to about 3:1.
Component (c) in the compositions of the present invention comprises tin in one or more of the following forms:
(i) metallic tin particles;
(ii) particles of a tin-containing alloy;
(iii) a derivative of tin which is substantially converted to the metal under the action of heat.
Preferably, the particles of component (c) are metallic tin particles and/or particles of a tin-containing alloy. More preferably, the particles of component (c) are metallic tin particles. In the embodiment of the invention wherein component (c) comprises a tin-containing alloy, it is preferred that said alloy is a tin/silver alloy, particularly a eutectic tin/silver alloy, particularly a tin/silver alloy containing between about 94 and 99% and particularly about 97% by weight tin.
The size of the particles should generally be no larger than about 20 xcexcm and preferably less than 10 xcexcm. The minimum particle size is normally about 0.1 xcexcm. The particles may be spherical or spheroid or irregular in shape, in the form of a flake or a powder, or in any other suitable morphology.
The use of metallic tin-containing particles as an additive according to the present invention provides compositions which exhibit (i) high resistivity; (ii) high solder adhesion; (iii) a more uniform rise in resistivity with increasing concentration of the additive in relation to compositions in which large amounts of filler are used to increase resistivity; and (iv) low variation of resistance with firing temperature. In addition, tin is a relatively inexpensive material and is an economical method of increasing resistivity.
Suitable inorganic binders for use in the present invention are those materials which upon sintering serve to bind the metal to a substrate such as a glass (including toughened and laminated glass), enamel, enamel-coated glass, ceramic, alumina or metal substrate. The inorganic binder, also known as a frit, comprises finely-divided particles and is a key component in the compositions of the present invention. The softening point and viscosity of the frit during firing, as well as its wetting characteristics for the metal powder/flake and the substrate, are very important factors. The particle size of the frit is not narrowly critical and frits useful in the present invention will typically have an average particle size from about 0.5 to about 4.5 xcexcm, preferably from about 1 to about 3 xcexcm.
It is preferred that the inorganic binder is a frit having a softening point of between about 350 and 620xc2x0 C. in order that the compositions can be fired at the desired temperatures (typically 300 to 700xc2x0 C., particularly 580 to 680xc2x0 C.) to effect proper sintering, wetting and adhesion to the substrate, particularly a glass substrate. It is known that mixtures of high and low melting frits can be used to control the sintering characteristics of the conductive particles. In particular, it is believed that the high temperature frit dissolves in the lower melting frit and together they slow the sintering rate of the conductive particles as compared to pastes containing only low melting frit. This control of the sintering characteristics is especially advantageous when the composition is printed and fired over decorative enamels. (Decorative enamels are normally pastes comprised of one or more pigment oxides and opacifiers and glass frit dispersed in an organic medium.) A high melting frit is considered to be one having a softening point above 500xc2x0 C. and a low melting frit is considered to be one having a softening point below 500xc2x0 C. The difference in the melting temperatures of the high and low melting frits should be at least 100xc2x0 C. and preferably at least 150xc2x0 C. Mixtures of three or more frits having different melting temperatures can also be used. When mixtures of high and low melting frits are used in the invention, they are normally used in ratios by weight from 4:1 to 1:4.
As used herein, the term xe2x80x9csoftening pointxe2x80x9d refers to softening temperatures obtained by the fibre elongation method of ASTM C338-57.
Suitable binders include lead borates, lead silicates, lead borosilicates, cadmium borate, lead cadmium borosilicates, zinc borosilicates, sodium cadmium borosilicates, bismuth silicates, bismuth borosilicates, bismuth lead silicates and bismuth lead borosilicates. Typically, any glass having a high content of bismuth oxide, preferably at least 50% and more preferably at least 70% by weight bismuth oxide, is preferred. Lead oxide as a separate phase may also be added, if necessary. However, due to environmental considerations, lead-free binders are preferred. Examples of glass compositions (compositions A to I) are given in Table 1 below; the oxide components are given in weight percent.
The glass binders are prepared by conventional glass-making techniques, by mixing the desired components (or precursors thereof, e.g. H3BO3 for B2O3) in the desired proportions and heating the mixture to form a melt. As is well known in the art, heating is conducted to a peak temperature and for a time such that the melt becomes entirely liquid, yet gaseous evolution has ceased. The peak temperature is generally in the range 1100xc2x0 C.-1500xc2x0 C., usually 1200xc2x0 C.-1400xc2x0 C. The melt is then quenched by cooling the melt, typically by pouring onto a cold belt or into cold running water. Particle size reduction can then be accomplished by milling as desired.
Other transition metal oxides may also be employed as part of the inorganic binder, as is well known to those skilled in the art. Oxides or oxide precursors of zinc, cobalt, copper, nickel, manganese and iron are commonly used, particularly with substrates other than glass substrates, such as alumina substrates. These additives are known to improve soldered adhesion.
The inorganic binder can also contain up to approximately 4 parts by weight basis paste of a pyrochlore-related oxide having the general formula:
(MxMxe2x80x22xe2x88x92x)Mxe2x80x32O7xe2x88x92Z
wherein
M is selected from at least one of Pb, Bi, Cd, Cu, Ir, Ag, Y and rare earth metals having atomic numbers of 57-71 and mixtures thereof,
Mxe2x80x2 is selected from Pb, Bi and mixtures thereof,
Mxe2x80x3 is selected from Ru, Ir, Rh and mixtures thereof,
X=0-0.5, and Z=0-1.
Pyrochlore materials have been described in detail in U.S. Pat. No. 3,583,931, the disclosure of which is incorporated herein by reference. The pyrochlore materials act as adhesion promoters for the compositions of this invention. Copper bismuth ruthenate (Cu0.5Bi1.5RU2O6.75) is preferred.
Traditionally, conductive compositions have been based on lead frits. The elimination of lead from glass compositions to meet current toxicity and environmental regulations may limit the types of binder that can be used to achieve the desired softening and flow characteristics, while simultaneously meeting wettability, thermal expansion, cosmetic and performance requirements. U.S. Pat. No. 5,378,406, the disclosure of which is incorporated herein by reference, describes a series of low-toxicity lead-free glasses based upon the constituents Bi2O3, Al2O3, SiO2, CaO, ZnO and B2O3, all of which may be used in the compositions of the present invention.
In a preferred embodiment of the invention, the frit is composition I in Table 1 herein.
The components (a) to (c) of the composition hereinbefore described will ordinarily be dispersed into a liquid vehicle to form a semi-fluid paste which is capable of being printed in a desired circuit pattern. The liquid vehicle may be an organic medium or may be aqueous-based. Preferably the liquid vehicle is an organic medium. Any suitably inert liquid can be used as an organic medium. The liquid vehicle should provide acceptable wettability of the solids and the substrate, a relatively stable dispersion of particles in the paste, good printing performance, dried film strength sufficient to withstand rough handling, and good firing properties. Various organic liquids with or without thickening agents, stabilising agents and/or other common additives are suitable for use in the preparation of the compositions of the present invention. Exemplary of the organic liquids which can be used are alcohols (including glycols); esters of such alcohols such as the acetates, propionates and phthalates, for instance dibutyl phthalate; terpenes such as pine oil, terpineol and the like; solutions of resins such as polymethacrylates of lower alcohols; or-solutions of ethyl cellulose in solvents such as pine oil and monobutyl ether of diethylene glycol. The vehicle can also contain volatile liquids to promote fast setting after application to the substrate.
A preferred organic medium is based on a combination of a thickener consisting of ethyl cellulose in terpineol (typically in a ratio of 1 to 9), optionally combined for instance with dibutyl phthalate or with the monobutyl ether of diethylene glycol (sold as butyl CARBITOL(trademark)). A further preferred organic medium is based on ethyl cellulose resin and a solvent mixture of alpha-, beta- and gamma-terpineols (typically 85-92% alpha-terpineol containing 8-15% beta and gamma-terpineol).
The ratio of liquid vehicle to solids in the dispersion can vary considerably and is determined by the final desired formulation viscosity which, in turn, is determined by the printing requirements of the system. Normally, in order to achieve good coverage, the dispersions will contain about 50 to about 95%, preferably about 60 to about 90%, by weight solids, and about 5 to about 50%, preferably about 10 to about 40%, by weight liquid vehicle, as noted above.
The compositions of the present invention may additionally comprise further additives known in the art, such as colorants and staining agents, rheology modifiers, adhesion enhancers, sintering inhibitors, green-state modifiers. surfactants and the like.
In the preparation of the compositions of the present invention, the particulate inorganic solids are mixed with the liquid vehicle and dispersed with suitable equipment, such as a three-roll mill or a power-mixer, according to conventional techniques well-known in the art, to form a suspension. The resulting composition has a viscosity generally in the range of about 10-500, preferably in the range of about 10-200, more preferably in the range of about 15-100 Pa.s at a shear rate of 4 secxe2x88x921, for instance, as measured on a Brookfield HBT viscometer using #5 spindle at 10 rpm and 25xc2x0 C. The general procedure for preparing the composition of the invention is set out below.
The ingredients of the paste are weighed together in a container. The components are then vigorously mixed by a mechanical mixer to form a uniform blend; then the blend is passed through dispersing equipment, such as a three-roll mill, to achieve a good dispersion of particles to produce a paste-like composition having a suitable consistency and rheology for application onto a substrate, for instance by screen-printing. A Hegnan gauge is used to determine the state of dispersion of the particles in the paste. This instrument consists of a channel in a block of steel that is 25 xcexcm deep (1 mil) on one end and ramps up to zero depth at the other end. A blade is used to draw down paste along the length of the channel. Scratches appear in the channel where the agglomerates"" diameter is greater than the channel depth. A satisfactory dispersion will give a fourth scratch point of typically 10-18 xcexcm. The point at which half of the channel is uncovered with a well-dispersed paste is between 3 and 8 xcexcm typically. Fourth scratch measurements of greater than 20 xcexcm and xe2x80x9chalf-channelxe2x80x9d measurements of greater than 10 xcexcm indicate a poorly dispersed suspension.
The compositions are then applied to a substrate using conventional techniques known in the art, typically by the process of screen printing, to a wet thickness of about 20-60 xcexcm, preferably about 35-50 xcexcm. The compositions of this invention can be printed onto the substrates either by using an automatic printer or a hand printer in the conventional manner. Preferably, automatic screen printing techniques are employed using a 200- to 325-mesh per inch screen. The printed pattern is optionally dried at below 200xc2x0 C., preferably at about 150xc2x0 C., for a time period between about 30 seconds to about 15 minutes before firing. Firing to effect sintering of both the inorganic binder and the finely divided particles of metal is preferably done in a well-ventilated belt conveyor furnace with a temperature profile that will allow burn-off of the vehicle at about 200-500xc2x0 C., followed by a period of maximum temperature of about 500-1000xc2x0 C., preferably about 600-850xc2x0 C., lasting for about 30 seconds to about 15 minutes. This is followed by a cooldown cycle, optionally a controlled cooldown cycle, to prevent over-sintering, unwanted chemical reactions at intermediate temperatures or substrate fracture which can occur from too rapid cooldown. Alumina substrates are particularly susceptible to fracture resulting from too rapid cooldown. The overall firing procedure will preferably extend over a period of about 2-60 minutes, with about 1-25 minutes to reach the firing temperature, about seconds to about 10 minutes at the firing temperature and about 5 seconds to about 25 minutes in cooldown. For the manufacture of a toughened glass substrate, a controlled cooldown cycle is generally used wherein the overall firing procedure typically extends over a period of about 2 to 5 minutes, with about 1 to 4 minutes to reach the firing temperature, followed by a rapid cooldown.
Typical thicknesses of the thick-films after firing are from about 3 xcexcm to about 40 xcexcm preferably from about 8 xcexcm to about 20 xcexcm.
The compositions of the invention are primarily intended for use in the manufacture of heating elements in windows such as defogging or defrosting elements in automotive glazing, particularly backlights. The compositions may also be used to incorporate other conductive functions into the window, such as a printed aerial or antenna. However, the coating compositions can be employed in various other applications, including printed circuits and heating elements generally. For instance, the compositions of the present invention may be used as base plates in hot water heating appliances. There is a general need within the electronics and electrical industry for lower-cost heating elements, particularly screen-printable heating elements.
According to a further aspect of the invention, there is provided a composition comprising finely divided particles of (a) an electrically-conductive material; (b) one or more inorganic binders; and (c) tin, wherein components (a), (b) and (c) are dispersed in a liquid vehicle, preferably an organic medium, for use in the manufacture of an electrically-conductive pattern on a substrate.
According to a further aspect of the invention, there is provided a process for the preparation of a composition comprising finely divided particles of (a) an electrically-conductive material; (b) one or more inorganic binders; and (c) tin, said process comprising the step of dispersing components (a), (b) and (c) in a liquid vehicle, preferably an organic medium.
According to a further aspect of the invention there is provided a process for the manufacture of an electrically-conductive pattern, said process comprising applying to a substrate a composition comprising finely divided particles of (a) an electrically-conductive particles; (b) one or more inorganic binders; and (c) tin, said components (a), (b) and (c) being dispersed in a liquid vehicle, preferably an organic medium, and firing the coated substrate to effect sintering of the finely-divided particles to the substrate. Preferably the process is a screen printing process.
According to a further aspect of the present invention there is provided a substrate, typically a rigid substrate such as a glass (including toughened and laminated glass), enamel, enamel-coated glass, ceramic, alumina or metal substrate, having on one or more surfaces thereof an electrically-conductive pattern, said conductive pattern comprising (a) an electrically-conductive material; (b) one or more inorganic binders; and (c) tin.
The following test procedures were used to evaluate the compositions of the present invention.
Adhesion
Copper clips (obtained from Quality Product Gen. Eng. (Wickwar), UK) are soldered to the fired conductive pattern on a glass substrate (dimensions 10.2 cmxc3x975.1 cmxc3x973 mm) using a 70/27/3 Pb/Sn/Ag solder alloy at a soldering iron temperature of 350 to 380xc2x0 C. A small quantity of a mildly active rosin flux, such as ALPHA 615-25(copyright) (Alpha Metals Limited, Croydon, UK) may be used to enhance solder wetting and to keep the solder and clip in place during assembly of parts, in which case the flux is applied to the solder using a shallow tray containing a thin film of fresh flux. Adhesion was measured on a CHATTILLON(copyright) pull tester Model USTM at a pull speed of 0.75xc2x10.1 inches per minute (1.91xc2x10.25 cm per minute) and the pull strength recorded at adhesion failure. The average value of adhesion failure over 8 samples was determined: The adhesion should preferably be greater than 10 kg, more preferably greater than 15 kg and more preferably greater than 20 kg. The principal failure modes of adhesion are as follows:
(a) clip separates from the conductive pattern (i.e. poor solder adhesion).
(b) the conductive pattern separates from the substrate (i.e. poor substrate adhesion).
(c) glass pullout/fracture (i.e. the bonding strengths between the clip and the conductive layer and between the conductive layer and the substrate is greater than the strength of the substrate).
(d) failure within the solder.
Resistance and Resistivity
The resistance of the fired conductive pattern on a glass substrate (dimensions 10.2 cmxc3x975.1 cmxc3x973 mm) was measured using a GenRad Model 1657 RLC bridge calibrated for use between 1 and 900 xcexa9 or equivalent The thickness of the conductive layer is measured using a thickness measuring device such as a surf-analyser (e.g. TALYSURF(trademark), which is a contact measuring device which analyses the surface of the substrate in 2 dimensions using a spring loaded stylus; any change in height will deflect the stylus and this change will then be registered on a recorder, such as a chart recorder; the difference between the base line and average height gives the print thickness). Resistance of the pattern is determined by placing the probe tips at the point where the conductive track meets the solder pads. The bulk resistivity (thickness-normalised) of the layer is determined by dividing the measured resistance for the pattern by the number of squares therein where the number of squares is the length of the conductive track divided by the width of the track. The resistivity value is obtained as mxcexa9/xe2x96xa1 at any normalised thickness, typically 10 xcexcm.
Particle Size
Particle size in the composition is measured according to ASTM D1210-79 using a large Hegman type fineness of grind gauge.
Chemical Durability
A solution of 1% glacial acetic acid in deionised water is used in this test. The glass substrate (50xc3x97100 mm) having thereon a fired conductive pattern was inserted into a plastic container half-filled with the test solution. The container is then sealed and left to stand at ambient temperature. The test substrates are removed after 96, 168 and 336 hours, dried and then analysed by a lift test. The lift test comprises application of a 0.75 inch (19.1 mm) wide masking tape (NICEDAY(trademark)) onto the substrate and then removing sharply in approximately xc2xd second. The results of the lift test are given as the approximate percentage of film area removed by the tape.
The invention will now be described with reference to the following examples. It will be appreciated that the examples are not intended to be limiting and modification of detail can be made without departing from the scope of the invention.


Coated articles having improved chemical resistance comprising an article formed from a moldable polymer coated on at least one surface with a coating composition comprising at least one vinyl ether oligomer compound, and at least one photoinitiator are disclosed. Coatings which also contain at least one acrylate compound and/or at least one epoxy compound are also disclosed. The articles are preferably made from polyesters. Methods for coating such articles are also disclosed.

The present invention relates generally to polyester articles coated with a bendable and stress crack resistant photocured coating. The polyesters contain dibasic acid moieties comprising at least 80 mole % terephthalic, naphthalene dicarboxylic, isophthalic and/or 1,4-cyclohexanedicarboxylic acid and glycol moieties derived from ethylene glycol and 1,4-cyclohexanedimethanol.
Environmental stress cracking is the crazing and/or cracking that may occur when a thermoplastic under a tensile stress is exposed to aggressive chemicals. It is undesirable because it detracts from the aesthetic appearance of the plastic and, more importantly, could lead to mechanical failure of the molded article formed from the plastic. The potential for environmental stress cracking is of paramount concern when plastics are used in applications as diverse as injection-molded medical packaging and parts and blow-molded carbonated soft drink containers, where mechanical failure can have unwelcome ramifications.
Thermoplastics commonly coated for the purpose of improving stress crack resistance include polyethylene and polycarbonate. Poly(ethyelene terephthalate) (PET) and other polyesters are less commonly coated for this purpose. Heat cured siloxane systems, which are disclosed in U.S. Pat. No. 4,348,431 and commonly applied to polycarbonate plastics do not work on PET because the curing temperature is too high. This coating system is also expensive since it requires drying ovens and a curing time which may be as long as 4 hours. Polyurethane coatings, such as those disclosed in U.S. Pat. Nos. 5,300,334 and 5,681,628, also require undesirably long curing times and high temperatures for use on PET carbonated soft drink containers). The photocurable acrylate siloxane system disclosed in U.S. Pat. No. 4,197,173 and supplied by GE Plastics exhibits poor adhesion to PET copolyesters and the coating is brittle. The photocurable acrylate used by Yoshino Kogyosho for PET bottles require a primer coating in order to achieve adhesion of the acrylate to the substrate (U.S. Pat. No. 4,569,869). Acrylate coatings in general are stiff films and even if they adhere to PET, they result in the loss of impact properties and bendability.
xe2x80x9cUV and EB Curing Formulation for Printing Ink, Coatings and Paintsxe2x80x9d edited by R. Holman, published by SITA-Technology Ltd., 203 Gardiner House, Broomhill Road, London SW18, England (1984) and xe2x80x9cChemistry and Technology of UV and EB Formulation for Coatings, Inks and Paintsxe2x80x9d, Volumes I-IV, edited by P. K. T. Oldring, published by SITA Technology Ltd., (1991) disclose general methods and compositions for coating plastic substrates.
U.S. Pat. Nos. 5,300,334 and 5,681,628 describe a pressurizable thermoplastic container having an exterior polyurethane layer and its method of making. The solvent -based polyurethane was cured at 60xc2x0 C. for 10 minutes.
U.S. Pat. No. 4,569,869 discloses a saturated polyester bottle-shaped container with hard coating and method of fabricating the same. The hard coating is a UV-cured methyl methacrylate resin. The polyester bottle was coated with a primer layer prior to coating with the hard coat in order to promote adhesion of the hard coat to the container.
U.S. Pat. No. 4,348,431 discloses a continuous coating process for plastic films including polycarbonates, polyesters (PET and PBT), acrylic resins and others in which an aqueous dispersion of colloidal silica in an aliphatic alcohol-water solution of an organosilicon compound is applied and cured at elevated temperatures.
U.S. Pat. No. 5,086,087 describes a coating composition containing UV curable unsaturated monomers and/or oligomers, a photoinitiator and colloidal silica with an organosilane compound. The examples illustrate putting the coatings on polycarbonate samples.
U.S. Pat. No. 4,557,975 describes curing of a photocurable coating mixture containing polyfunctional acrylates, acrylonitrile, and a photoinitiator on polymeric substrates, especially the polycarbonates.
Many coatings have been disclosed as useful for coating polycarbonates. For example, U.S. Pat. No. 5,571,570 describes using a UV curable blend of three acrylic modified aliphatic polyurethanes, U.S. Pat. No. 4,197,173 describes a photocurable composition containing a polythiol, a polyene, and a silicone modified polyester copolymer, U.S. Pat. No. 4,198,465 describes a photocured coating containing the photoreaction products of certain multifunctional acrylate ester monomers or mixtures thereof and resorcinol monobenzoate, U.S. Pat. No. 4,384,026 describes photocured coatings containing the reaction of certain multifunctional acrylate ester monomers and certain acrylate modified polymers, U.S. Pat. No. 4,929,506 describes a hard, abrasion and chemical resistant coating which is the photoreaction product of an acrylated urethane oligomer, a difunctional acrylate monomer and preferably also a monofunctional olefinic monomer and U.S. Pat. No. 5,236,968 describes a UV hardenable lacquer.
Therefore, there remains a need in the art for solventless coating compositions which would adhere well to PET and other polyesters, be bendable, and provide good resistance to environmental stress cracking.
It has been found that UV-curable coatings can be applied to the surface of films, sheeting, and molded objects of certain polyesters to provide bendable, stress crack resistant coatings with good adhesion to the substrate.
More specifically the present invention relates to improving stress crack performance of a polyester article by applying an UV-curable, stress crack resistant topcoat to one or more sides. By increasing the resistance of the surface to stress cracking, the polyester can be used more safely in existing applications as well as find applications in more aggressive environments.
Polyesters which are suitable for use in the present invention include crystallizable polyester homopolymer or copolymer that are suitable for use in packaging, and particularly food packaging. Suitable polyesters are generally known in the art and may be formed from aromatic dicarboxylic acids, esters of dicarboxylic acids, anhydrides of dicarboxylic esters, glycols, and mixtures thereof. More preferably the polyesters are formed from repeat units comprising terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl-2,6-naphthalenedicarboxylate, 2,6-naphthalenedicarboxylic acid, ethylene glycol, diethylene glycol, 1,4-cyclohexane-dimethanol, 1,4-butanediol, and mixtures thereof.
The dicarboxylic acid component of the polyester may optionally be modified with up to about 15 mole percent of one or more different dicarboxylic acids. Such additional dicarboxylic acids include aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms. Examples of dicarboxylic acids to be included with terephthalic acid are: phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4xe2x80x2-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, mixtures thereof and the like.
In addition, the glycol component may optionally be modified with up to about 15 mole percent, of one or more different diols other than ethylene glycol. Such additional diols include cycloaliphatic diols preferably having 6 to 20 carbon atoms or aliphatic diols preferably having 3 to 20 carbon atoms. Examples of such diols include: diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 3-methylpentanediol-(2,4), 2-methylpentanediol-(1,4), 2,2,4-trimethylpentane-diol-(1,3), 2-ethylhexanediol-(1,3), 2,2-diethylpropane-diol-(1,3), hexanediol-Q1,3), 1,4-di-(hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane, 2,2-bis-(3-hydroxyethoxyphenyl)-propane, 2,2-bis-(4-hydroxypropoxyphenyl)-propane, mixtures thereof and the like. Polyesters may be prepared from two or more of the above diols.
The resin may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride, pentaerythritol, and other polyester forming polyacids or polyols generally known in the art.
The polymers may be prepared from the dibasic acids or their synthetic equivalents such as their lower alkyl esters. If esters are used, the methyl esters are preferred. The polyesters will generally have inherent viscosity values of about 0.5 to about 1.5, but those with values of about 0.6 to about 1.0 are preferred.
Polyesters suitable for use in the present invention may be made by the generally known three-stage polyesterification process. The three polymerization stages are hereinafter referred to as the esterification stage, the prepolymer stage, and the polycondensation stage. Conditions for these stages are well known in the art, and summarized below.
In the first stage of the melt-phase process, a mixture of polyester monomer (diglycol esters of dicarboxylic acids) and oligomers are produced by conventional, well-known processes. The ester exchange or esterification reaction is conducted at a temperature between about 220xc2x0 C. to about 250xc2x0 C. and a pressure of about 0 to about 20 psig in the presence of suitable ester exchange catalysts such as lithium, magnesium, calcium, manganese, cobalt and zinc, or esterification catalysts such as hydrogen, titanium or suitable forms of which are generally known in the art. The catalysts can be used alone or in combination. Preferably the total amount of catalyst is less than about 100 ppm on an elemental basis. The reaction is conducted for about 1 to about 4 hours. It should be understood that generally the lower the reaction temperature, the longer the reaction will have to be conducted.
Generally at the end of the esterification, a polycondensation catalyst is added. Suitable polycondensation catalysts include salts of titanium, gallium, germanium, tin, antimony and lead, preferably antimony or germanium or a mixture thereof. Preferably the amount of catalyst added is between about 90 and 150 ppm when germanium or antimony is used. Suitable forms such as, but not limited to antimony oxide are well known in the art. The prepolymer reaction is conducted at a temperature less than about 280xc2x0 C., and preferably between about 240xc2x0 C. and 280xc2x0 C. at a pressure sufficient to aid in removing undesirable reaction products such as ethylene glycol. The condensation stage may be conducted either continuously or in one or more batch reactors.
Next, the mixture of polyester monomer and oligomers undergoes melt-phase polycondensation to produce a low molecular weight precursor polymer. The precursor is produced in a series of one or more reactors operating at temperatures between about 240xc2x0 C. to about 280xc2x0 C. and a pressure between about 0 and 2 mm Hg. The reactors may be purged with an inert gas. Inert gas is any gas that does not cause unwanted reaction or product characteristics. Suitable gases include, but are not limited to CO2, argon, helium and nitrogen.
Once the desired inherent viscosity is reached, the polymer is pelletized. Precursor I.V. is generally below about 0.7. Inherent viscosity (I.V.) was measured at 25xc2x0 C. using 0.50 grams of polymer per 100 ml of a solvent consisting of 60% by weight phenol and 40% by weight tetrachloroethane.
The polyesters used in the present invention may also include a variety of additives depending on the end use for the polymer. Such additives include, but are not limited to colorants, toners, pigments, carbon black, glass fibers, fillers, impact modifiers, antioxidants, slip agents, denesting agents, stabilizers, barrier enhancing compounds, flame retardants, reheat aids, acetaldehyde reducing compounds and the like.
The polymers are formed into articles. Articles suitable for coating in the present invention include sheet, film, tubing, profiles, preforms, fiber, woven and shaped articles, such as containers, thermoformed articles such as trays and the like. The articles are formed by conventional processes such as extrusion, thermoforming, injection and stretch blow molding, injection molding, spinning. drawing and the like. These processes are known in the art.
The coatings may be applied to all or part of at least one surface. For example, where stress crack or scuff resistance is desired the coatings may be beneficially applied to all or part of the outside of the article. Some applications may require coatings in high contact areas, such as the base region of a container, while other applications may benefit from coating the entire interior or exterior of the article. Containers displaying improved stress crack resistance and scuff resistance are an example. In other application, the coating may be beneficially applied to the inside of the article to provide chemical resistance to chemicals which the article comes in contact with during use.
Suitable coating compositions for use in the present invention comprise at least one vinyl ether compound and at least one photoinitiator. Coating compositions of the present invention may also include, acrylate, urethane, or epoxy, monomers or oligomers and mixtures thereof, and photoinitiators. The selection of the coating composition components and their amounts will depend on the composition of the article to be coated and the properties which are critical for the end use application. The preferred components of the coating compositions are those that provide adequate wetting of the polymer matrix surface during application. Without being bound by any particular theory, it is believed that monomer compounds which are compatible with the polymer and act as a solvent and diffuse into the matrix upon coating are preferred. Curing causes the monomer compounds to polymerize into the matrix, thereby providing excellent adhesion between the coating and the matrix polymer.
It is preferred that the liquid coating is cured immediately after application by irradiation with UV light or other suitable radiation source. The thickness of the cured coating will generally range from about 0.05 to about 5 mil. The preferred coating thickness is about 0.1 to about 1.0 mil, although thinner coatings may be effective in improving stress crack resistance to chemicals such as alcohols, surfactants and lubricants.
Vinyl ether compounds which are suitable for use in the present invention include vinyl ether monomer and oligomers which are generally known in the art and may be described as:
(Rxe2x80x2CHxe2x95x90CRxe2x80x3xe2x80x94-OZ)n-A
where Rxe2x80x2 and Rxe2x80x3 may be the same or different and are independently selected from H or an alkyl group having 1 to 10 carbon atoms; A is a moiety derived from urethanes, phenols, polyesters, polyethers, polycarbonates, or polysiloxanes and has a molecular weight of about 400 to 10,000; Z is a moiety derived from a saturated aliphatic or cycloaliphatic hydrocarbon or a polyalkylene ether and has a molecular weight of about 28 to 250; n is an integer from 2 to 6, preferably 2 or more.
Examples of preferable vinyl ether monomers and oligomers used in the present invention are 1-Butanol-4-(ethenyloxy)-benzoate (VE3010), Pentanedioic acid bis[[4-[(ethenyloxy)methyl]ester(VE4020), Butanedioic acid bis [4-(ethynyloxy)butyl]ester(VE4030), Carbamic acid (methylene di-4,1-phenylene) bis-bis[4-(ethynyloxy)butyl]ester(VE4210), Carbamic acid (methyl-1,3-phenylene)bis-, bis[4-(ethynyloxy)butyl]ester(VE4220), mixtures thereof and the like. All of the foregoing compounds are commercially available from AlliedSignal, Inc.
Among the most desirable vinyl ether monomers used in the present invention are Cyclohexane methanol 4-[(ethenyloxy) methyl]- benzoate(VE3040), 1,3-Benzenedicarboxylic acid bis[4-(ethenyloxy) butyl]ester(VE4010), Hexanedioic acid bis[4-ethynyloxy) butyl]ester(VE4060), and 1,2,4-Benzenetricarboxylic acid tris[4-(ethynyloxy) butyl]ester(VE5015).
The vinyl ether compounds may be present in amounts up to about 100 weight %, preferably from about 5 to about 100 weight % and in some embodiments more preferably between about 20 to about 100 weight %. In addition, the mono-, di- and trifunctional vinyl ether monomers are used for diluency, as generally known in the art.
Suitable acrylates include acrylate oligomers. Examples of acrylate oligomers include acrylated aliphatic urethane oligomers such as Ebecryl 8804 (UCB Chemical), and ethoxylated bisphenol A diacrylate, SR 349, (Sartomer), mixtures thereof and the like. Such coatings containing vinyl ether/acrylate exhibit excellent abrasion resistance, flexibility and high modulus when cured. (Sitzmann et. al., RadTech98 Conf. Proc. (1998). The acrylates may be present in amounts up to about 100 weight %, preferably from about 10 to about 100 weight % and in some embodiments more preferably between about 50 to about 90 weight %.
Epoxies, when combined with vinyl ethers, are most useful for the present invention when they display as many of the following properties as possible. Epoxies should have a functionality of at least two, i.e., they should have at least two oxirane moieties for each molecule, have a low cure rate, i.e., cure at least about 5 times slower (at least about 5 seconds), relative to the vinyl ethers used in the formulation, provide a low viscosity to the formulation, and are completely miscible with selected vinyl ethers. In general, the vinyl ether will rapidly set up an initial polymer network, while the slower curing epoxies react to form a secondary network within the vinyl ether network structure.
Epoxies derived from phenols, particularly bisphenol A, novolacs, linear and cycloaliphatic polyols, polyether polyols and siloxanes are preferred. Examples of epoxies that are most preferable in the present invention are bisphenol A diglycidyl ethers (such as DER 331, 332, Dow Chemical and Epon 828, Shell Chemical), epoxy novolacs (such as DEN 431, Quatrex 240, Dow Chemical), epoxy cresols (such as Quatrex 3310, Dow Chemical), and cycloaliphatic epoxides (such as ERL 4221, ERL 4299, ERL 4234, Union Carbide). The epoxies, when present, may be present in amounts up to about 80 weight %, preferably from about 10 to about 80 weight % and in some embodiments more preferably between about 10 to about 70 weight %. It should be appreciated that coating compositions with high epoxy contents (greater than about 60 weight %) will have slower cure times than those with lower epoxy contents.
An important aspect for selection of composition is the viscosity of the final formulation. A general range of viscosity for use as polymer coating is in the range from about 50 to about 50,000 mPas, and preferably about 50 to about 5000 mPas, (as measured with a Brookfield (DV-I) viscometer). The viscosity of the formulation should be low in order to facilitate spray coating, as in certain embodiments this process is preferable over roll coating, rod coating, brushing or dipping. In certain embodiments it is preferred that the coating change the optical properties of the article being coated as little as possible. This is particularly important in packaging applications, such as food and medical, where seeing the contents is important. In these applications it is preferred that the clarity and color of the article be changed no more than 5%, and preferably not at all. Percent haze measurements are obtained according to ASTM D- 1003 using a Hunter Lab Ultrascan Colorimeter. The b* values (a measure of yellowness) are measured in accordance with ASTM D-2244-93 using 4xe2x80x3 by 4xe2x80x3 sections of the article (for example a bottle sidewall) on a Hunter Lab Ultrascan Instrument.
The proportion of vinyl ethers and epoxies used in formulations of the present invention is disclosed in U.S. Pat. No. Pat. No. 5,705,116, the disclosure of which is incorporated herein by reference. The proportions of vinyl ethers and epoxides is defined by the formula: M=F/E. Where M is the vinyl ether equivalent weight of the composition, F is the total weight of the composition, in grams, which includes both vinyl and epoxy compounds, and E is the number of ether equivalents in the composition. The vinyl ether equivalent may be calculated by the molecular weight of the vinyl ether by the number of reactive groups. Accordingly, the vinyl ether equivalent weight (M) should be between about 80 and about 800 and preferably between about 120 and about 450.
The coating formulation of the present invention also includes at least one photoinitiator for cationic curing of vinyl ethers and vinyl ether/epoxy formulations. Cationic polymerization conditions are required for epoxies, as epoxies cure by a cationic mechanism rather than radical conditions, while vinyl ethers can cure by either cationic or radical mechanisms. Suitable photoinitiators are known in the art and disclosed in U.S. Pat. No. 4,058,400, the disclosure of which is incorporated herein by reference. Preferred cationic photoinitiators include the onium salts of Group V, VI and VII elements. More preferred photoinitiators include triarylsulfonium salts, diaryliodonium salts and mixtures thereof. Preferred anions are hexafluorophosphate and hexafluoroantimonate. Examples of commercial sources of triarylsulfonium hexafluoroantimonates are CD 1010 (Sartomer), and UVI 6974 (Union Carbide) and triarylsulfonium hexafluorophosphate UVI-6990 (Union Carbide). Sulfonium salts are preferred as photoinitiators for cationic cure, because of their excellent thermal stability and high quantum yield to produce strong Bronsted acids. Accordingly, photoinitiators are usually required in amounts from about 0.1 to 5 wt % in the blended formula of vinyl ethers and epoxides.
The physical properties of the resulting coating, such as, modulus, elongation, adhesion, shrinkage, and abrasion resistance, etc., can be ascribed to the degree of crosslinking, chain length and the intrinsic properties of the chemical moeity that comprise the bulk of the repeat unit chain.
The coatings are readily applied by techniques well known in the art. Such methods include roll coating, rod coating, spray coating, brushing, dipping and the like. For many articles spray coating will be preferred. It is preferred that the liquid coating is cured immediately after application with UV light or other suitable radiation source. The thickness of the cured coating will generally range from about 0.05 to about 5 mil. The preferred coating thickness is about 0.1 to about 1.0 mil, although thinner coatings may be effective in improving stress crack resistance to chemicals such as alcohols, surfactants and lubricants. The preferred coating is also optically clear.
Examples of photocuring equipment and conditions used to cure film compositions described in the present invention include RPC model QC- 1202 processor equipped with two medium pressure mercury arc lamps and variable conveyor speed from about 50 to about 500 ft/min. The most preferred equipment used for photocuring coatings employ microwave-powered lamps, D-type bulb in particular, supplied by Fusion UV Systems. Although a variety of bulb types are available, D-type bulbs are preferred due to their high energy output and wide spectral range, from about 275 to about 445 run. This spectral range includes the spectral frequency range, about 300 to about 350 nm, required for optimum response for cationic photoinitiators most commonly employed in coatings that are the subject of the present invention. This combination of high-energy output and narrow band emission are useful for providing cure times of about 1 sec. and less.
Sitzrnann et. al., RadTech98 Conf. Proc. (1998) reported a correlation between lamp dose and conveyor belt speed which was expressed as dose (mJ/cm2)=25987/(belt speed, ft/min) and having a correlation of R2 greater than 0.99. Tack-free cure doses for vinyl ether/acrylate coatings up to about 6 mil thick was measure to be less than about 22 mJ/cm2. Conveyor belt speeds of about 1200 ft/min are preferred to produce such tack-free coatings. Typical doses required to reach an ultimate modulus for vinyl ether/acrylate hybrid formulations was about 400 to about 1000 mJ/cm2. The dose required to cure vinyl ether-polyesters was typically from up to about 75 mJ/cm2 and up to about 400 mJ/cm2, for the vinyl ether-polyurethane compositions.
Adhesion of the fully cured coating to the polyester substrate as measured by Test Method B of ASTM D3359 Standard Test Methods for Measuring Adhesion by Tape Test is such that zero area is removed from the substrate using Permacel 99 tape manufactured by Permacel, New Brunswick, N.J. The test results reported in Table 9 show that although all examples pass the environmental stress-cracking test, examples 1 and 6 fail the adhesion test. The preferred coating compositions should therefore meet the following criteria of no crazing and 0% (None) of the coating removed using Test Method B of ASTM D3359 Standard Test Methods for Measuring Adhesion by Tape Test.
The elongation to break of the fully cured film should exceed about 10%, and preferably 10% as measured by ASTM D882 Standard Test Method for Tensile Properties of Thin Plastic Sheeting.

Photocurable coatings for polyester articles