A molding composition comprising (a) from 10 to 90 weight percent of a polyester resin; (b) from 90 to 10 weight percent of an aromatic polycarbonate, polyarylate, polyester carbonate resin or blend thereof; and (c) a flow improving amount of lignin and/or a compound having a phosphonium sulfonate group.

This invention relates to polycarbonate-polyester compositions having a flow enhancing additive.
Polyester resins derived from terephthalic acid and reactive derivatives thereof, such as dimethyl terephthalate, and alkanediols have been known for some time and have become important constituents for moldable compositions. Workpieces molded from such polyester resin compositions, alone, or combined with reinforcements, offer a high degree of surface hardness, solvent resistance, abrasion resistance, and high gloss. More recently, blends of such polyester resins with one or more second resins have become of significant commercial interest because such second resins, carefully selected, can greatly improve impact strength, as well as tensile strength, modulus, dimensional stability and distortion temperature under load in parts molded from such compositions. Such second resins can comprise aromatic polycarbonate resins as described for example, in Kawase et al, U.S. Pat. No. 3,953,539 and related polyester-carbonate and polyarylate resins.
Impact-modified PC/PBT blends are very suitable materials for exterior automotive applications (e.g. as bumpers). A good flowing material during molding is a necessity for that molding cycles while the mechanical properties as impact of the molded part should be excellent in order to pass the application specifications. Improvement of the impact/flow balance cannot be simply done by changing the PC/PBT-ratio or polymer molecular weights or by reducing the impact modifier content. So, the problem to be solved is to increase the flow behavior of an impact modified PC/PBT blend without major effects on ductility.
Hence, it is desirable to increase the flow behavior of an impact modified PC/PBT blend without major effects on ductility.
None of following referenced patents describe the use of lignin-type of compounds or phosphonium sulfonate type of compounds as a flow improver in a blend of PC with PBT, while the other properties as impact and heat resistance stay for the major part the same.
U.S. Pat. No. 4,209,427; GE-Patent filed 1977: flame-retardant polycarbonate composition. This patent describes that the use of lignin or lignosulfonates can be used as a flame-retardant additive. Typical amounts are 0.5-1.0 part per 100 parts PC.
U.S. Pat. No. 4,943,380; Patent from Takemoto Yushi Kabushiki Kaisha, filed 1989: anti-static resin composition with transparency containing phosphonium sulphonate. The use of 0.1-10% of phosphonium sulphonate is described.
U.S. Pat. No. 4,038,258; Patent from DuPont, filed 1976: anti-static composition containing an aliphatic polyester or polyetherester and a phosphonium salt. Polyesters having a Tg less than 25 C., containing 0.02-35% of a phosphonium salt.
PAJ-08059975 (publ.no.); Patent from Teijin, filed 1994: To obtain a PC, excellent in high temp. stability, melt moldability, hydrolytic resistance, a (phosphonium) sulfonate is added (0.01-500 ppm) during the reaction system to obtain a PC with desired viscosity.
PAJ-07304942; Patent from Mitsubishi Chem.Corp., filed 1994: Blend of PC with 0.1-20 pts. wt phosphonium sulfonate. Mentioned advantages: flowability, mechanical properties, anti-static properties.
PAJ-06089499 and 07292234; Patents from Teijin, filed 1994: Blend of PC (45-93%), polyalkyleneglycol (12-15%) and polyester with groups attached to it (5-40%) in order to get anti-static properties.
PAJ-07188539; Patent from Nippon GII Plast KK, filed 1993: Blend of a specific copolycarbonate (eg based on BPA and resorcinol) with 0.1-10% of a phosphonium sulfonate to get ant-static properties.
PAJ-07165905; Patent from Teijin, filed 1993: Production of stabilized PC-resin by adding a phosphonium sulfonate on and after the completion of a reaction in solution polymerization.
PAJ-07062215 and 05171024; Patents from Mitsubishi Chem. (Kasei) Corp., filed 1993: Blends of 100 pts PC with 0.1-20 pts phosphonium sulfonate and 0.01-3 pts sulfur containing ester compound to get antistatic properties.
PAJ-08092819; Patent from Asahi Chem.Ind.Co., filed 1994: Blend of a polyester copolymerized with 1 mol % isophthalic acid component containing a metal sulfonate group with 0.01-0.3% of P-cpd as viscosity reducing agent. P-cpd is pref. a phosphonium phosphonate.
PAJ-06279658 and 06263855; Patents from Teijin, filed 1993: Modified polyester (polyester-ionomer), synthesized through copolymerization using a phosphonium sulfonate compound.
PAJ-06041408 and -06041407: Patents from Toray Ind., filed 1991: Modified polyester: polyester (eg PET) and incorporated therein 1-30% ester-forming phosphonium sulfonate compound and 1-20% polyalkyleneglycol.
It has been found that the presence of lignin or phosphonium sulfonate compounds provides highly improved flow properties in a PC/PBT blend, while mechanical and physical properties are remained for a major part.
A molding composition comprising (a) from 10 to 90 weight percent of a polyester resin; (b) from 90 to 10 weight percent of an aromatic polycarbonate, polyarylate, polyester carbonate resin or blend thereof; and (c) a flow improving amount of lignin and/or a compound having a phosphonium sulfonate group.
The phosphonium sulfonate flow enhancing additive is preferably a compound of the formula
(R1-SO3-P(-R3,-R4,-R5,-R6)), wherein R1 is 1-40 Carbon alkyl or aryl or alkylaryl; and R3-R6 are each H, 1-10 Carbon, alkyl, or aryl. More preferably the phosphonium is a tetrabutylphosphonium dodecylbenzene sulfonate. Typical phosphonium salts include methyltributylphosphonium xylenesulfonate, tetrabutylphosphonium benzenesulfonate, methyltricyclohexylphosphonium xylenesulfonate, benzyltriphenylphosphonium xylenesulfonate, tetraoctylphosphonium phenyl sulfonate, and di(methyltribenzylphosphonium) phenyl sulfonate.
The lignin flow enhancing additive is selected from the group consisting of a lignin, kraft lignin, lignosulfonates and mixtures thereof. As set froth in U.S. Pat. No. 4,209,427, while complete determination of the structure of lignosulfonates apparently as not been achieved, it is known that the basic lignin monomer unit is a substituted phenyl-propane. The lignosulfonates are metallic sulfonate salts prepared commercially from the lignin of sulfite pulp-mill liquors as known in the art. They are described as anionic polyelectrolytes whose molecular weights vary between 1,000 and 20,000. Additionally, the lignosulfonates can be substituted with the substituent consisting of an electron withdrawing radical. Preferably the electron withdrawing radical or substituent is the halo-, nitro-, trihalomethyl or cyano withdrawing radical or mixtures thereof. The electron withdrawing phenomenon, or as it is also referred to as electronegativity, is defined in Basic Principles of Organic Chemistry by Roberts and Caserio, 1964 (pages 185-186), and Physical Organic Chemistry by Jack Hine, McGraw-Hill Book Company, Inc. 1962 (pages 5, 32 and 85-93). Briefly, the electron withdrawing phenomenon is where the radical has a strong affinity for a negative charge, namely electrons, but still remains covalent and does not form an ion. It is considered that a section of polymeric lignosulfonates can have the structure shown in U.S. Pat. No. 4,209,427 wherein M is an alkali or alkaline earth metal in the lignosulfonate.
The lignin additive is preferable present in an amount of 0.1-5 wt %, more preferably in an amount of 0.3-3 wt %, and most preferably in an amount of 0.5-2.0 wt %. The phosphoniun sulfonate compound is preferable present in an amount of 0.03-3 wt %, preferably in an amount of 0.05-1.5 wt %, most preferably in an amount of 0.1-1.0 wt %.
In a preferred molding composition, polycarbonate is present in an amount of 5-95 wt % and the polyester in an amount of 95-5 wt %, more preferably the polycarbonate and polyester are present in an amount of 40-75 wt %, respectively 25-60 wt %. The polycarbonate may be a polycarbonate ester based on bisphenolacetone, and the polyester is a polyester based on terephthalic units and a C2-C15 diol. The molding composition may include impact modifiers and stabilizers. Preferred impact modifiers include methacrylate butadiene rubber, acrylic rubber and polyolefin copolymers containing acrylic, methacrylic, vinyl ester or vinyl ether derived units.
Polyester components include crystalline polyesters such as polyesters derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, containing from 2 to about 15 carbon atoms and at least one aromatic or aliphatic dicarboxylic acid. Preferred polyesters are crystalline thermoplastics derived from an aliphatic diol and an aromatic dicarboxylic acid having repeating units of the following general formula:
wherein n is an integer of from 2 to 15. R is a C6-C20 radical comprising a dicarboxylated residue derived from a dicarboxylic acid.
Examples of aromatic dicarboxcylic acids represented by the dicarboxylated residue R are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4xe2x80x2-dicarboxydiphenyl ether, 4,4xe2x80x2 bisbenzoic acid and mixtures thereof. All of these acids contain at least one aromatic nucleus. Acids containing fused rings can also be present, such as in 1,4-1,5- or 2,6-naphthalenedicarboxylic acids. Aliphatic dicarboxylic acids, especially cyclic dicarboxylic acids or derivatives may be used. The preferred dicarboxylic acids are terephthalic acid, isophthalic acid, cyclohexane dicarboxylic or mixtures thereof.
The most preferred polyesters are poly(ethylene terephthalate) xe2x80x9cPETxe2x80x9d, and poly(butylene terephthalate), xe2x80x9cPBTxe2x80x9d and poly(propylene terephthalate) xe2x80x9cPPTxe2x80x9d.
Also contemplated herein are the above polyesters with minor amounts, e.g., from about 0.5 to about 25 percent by weight, of units derived from aliphatic acids, diamines and/or aliphatic polyols to form copolyesters. The aliphatic polyols include glycols, such as poly(ethylene glycol) and poly(butylene glycol). Such polyesters can be made following the teachings of, for example, U.S. Pat. Nos. 2,465,319 and 3,047,539.
The preferred poly(1,4-butylene terephthalate) resin used in this invention is one obtained by polymerizing a glycol component of at least 70 mole %, preferably at least 80 mole %, of which consists of tetramethylene glycol and an acid component at least 70 mole %, preferably at least 80 mole %, of which consists of terephthalic acid, and polyester-forming derivatives therefore.
The polyesters used herein have an intrinsic viscosity of from about 0.4 to about 2.0 dl/g. as measured in a 60:40 phenol/tetrachloroethane mixture or similar solvent at 23-30xc2x0 C. VALOX Registered TM 315 polyester is particularly suitable for this invention. Preferred PBT resins have an intrinsic viscosity of 1.1 to 1.4 dl/g.
Typically polycarbonates are prepared by reacting a dihydric phenol with a carbonate precursor, such as phosgene, a haloformate or a carbonate ester. Generally speaking, such carbonate polymers may be typified as possessing recurring structural units of the formula
wherein A is a divalent aromatic radical of the dihydric phenol employed in the polymer producing reaction. Preferably, the carbonate polymers used to provide the resinous mixtures of the invention have an intrinsic viscosity (as measured in methylene chloride at 25xc2x0 C.) ranging from about 0.30 to about 1.00 dl/g. The dihydric phenol which may be employed to provide such aromatic carbonate polymers are mononuclear or polynuclear aromatic compounds, containing as functional groups two hydroxy radicals, each of which is attached directly to a carbon atom of an aromatic nucleus. Typical dihydric phenols are: 2,2-bis(4-hydroxyphenyl) propane; hydroquinone; resorcinol; 2,2-bis(4-hydroxyphenyl) pentane; 2,4xe2x80x2-(dihydroxydiphenyl) methane; bis(2 hydroxyphenyl) methane; bis(4-hydroxyphenyl) methane; bis(4-hydroxy-5-nitrophenyl) methane; 1,1-bis(4-hydroxyphenyl) ethane; 3,3-bis(4-hydroxyphenyl) pentane; 2,2-dihydroxydiphenyl; 2,6-dihydroxynaphthalene; bis(4-hydroxydiphenyl)sulfone; bis(3,5-diethyl-4-hydroxyphenyl)sulfone; 2,2-bis(3,5-dimethyl4-hydroxyphenyl)propane; 2,4xe2x80x2-dihydroxydiphenyl sulfone; 5xe2x80x2-chloro-2,4xe2x80x2-dihydroxydiphenyl sulfone; bis-(4hydroxyphenyl)diphenyl sulfone; 4,4xe2x80x2-dihydroxydiphenyl ether; 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dichlorodiphenyl ether; 4,4-dihydroxy-2,5-dihydroxydiphenyl ether; and the like.
Other dihydric phenols which are also suitable for use in the preparation of the above polycarbonate resins are disclosed in U.S. Pat Nos. 2,999,835; 3,038,365; 3,334,154; and 4,131,575.
These aromatic polycarbonates can be manufactured by known processes, such as, for example and as mentioned above, by reacting a dihydric phenol with a carbonate precursor, such as phosgene, in accordance with methods set forth in the above-cited literature and in U.S. Pat. No. 4,123,436, or by transesterification processes such as are disclosed in U.S. Pat. No. 3,153,008, as well as other processes known to those skilled in the art.
It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with a hydroxy- or acid-terminated polyester or with a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired for use in the preparation of the polycarbonate mixtures of the invention. Branched polycarbonates are also useful, such as are described in U.S. Pat. No. 4,001,184. Also, there can be utilized blends of linear polycarbonate and a branched polycarbonate. Moreover, blends of any of the above materials may be employed in the practice of this invention to provide the aromatic polycarbonate.
These polycarbonates may be branched or linear and generally will have a weight average molecular weight of from about 10,000 to about 200,000, preferably from about 20,000 to about 100,000 as measured by gel permeation chromatography. The polycarbonates of the invention can employ a variety of end groups to improve performance. Bulky mono phenols, such as cumyl phenol, are preferred.
Preferred resins for enhanced weatherabilty and UV resistance are esters of aromatic dicarboxylic acids and bisphenols known as polyarylates. Polyarylate copolymers, with carbonate linkages in addition to the aryl ester linkages, known as polyester-carbonates, are also preferred. These resins may be used alone or in combination with each other or more preferably in combination with bisphenol polycarbonates. These resins can be prepared in solution or by melt polymerization from aromatic diacarboxylic acids or their ester forming derivatives and bis phenols and their derivatives. Suitable dicarboxylic acids are iso and terephthalic acid, their esters or acid chlorides. A preferred bisphenol is bis phenol A or its diacetate derivative. Polyester carbonates and polyarylates may also contain linkages derived from hydroxy carboxylic acids such as hydroxy benzoic acid. The most preferred polyester carbonate and polyarylates are derived from bisphenol A and mixture of iso and tere phthalic acid and are amorphous resins. U.S. Pat. No. 4,663,421 describes suitable polyarylates and U.S. Pat. Nos. 3,169,121; 4,156,069 and 4,269,731 describe suitable polyester-carbonates. All 4 patents are hereby incorporated by reference.
The aromatic polycarbonate, polyarylate, polyester carbonate resin can comprise a polyester carbonate to polycarbonate or polyarylate to polycarbonate ratio of 90:10 to 10:90.
Additional resin components may include, an effective amount of any of the known impact modifiers useful for polyesters and polyester blends. These may be added to the compositions by themselves or in combination with the aforementioned aromatic polycarbonates or polyesters. Useful impact modifiers generally comprise an acrylic or methacrylic grafted polymer of a conjugated diene or an acrylate elastomer, alone or co-polymerized with a vinyl aromatic compound. Other grafted polymers are the core-shell polymers of the type available from Rohm and Haas, for example ACRYLOID EXL2691 and ACRYLOID EXL3330. In general these impact modifiers contain units derived from butadiene in combination with a vinyl aromatic compound, acrylate, or akylacrylate ester such as methacrylate. The aforementioned impact modifiers are believed to be disclosed in Fromuth, et al., U.S. Pat. No. 4,180,494; Owens, U.S. Pat. No. 3,808,180; Farniham, et al., U.S. Pat. No. 4,096,202; and Cohen, et al., U.S. Pat. No. 4,260,693, all incorporated herein by reference. The impact modifier may comprise a two stage polymer having either a butadiene or n-butyl acrylate based rubbery core and a second stage polymerized from methylmethacrylate alone or in combination with styrene. Also present in the first stage are cross linking monomers and graft linking monomers. Examples of the cross linking monomers include 1,3-butylene diacrylate, divinyl benzene and butylene dimethacrylate. Examples of graft linking monomers are allyl acrylate, allyl methacrylate and diallyl maleate.
Additional preferred impact modifiers are of the type disclosed in U.S. Pat. No. 4,292,233, incorporated by reference. These impact modifiers comprise, generally, a relatively high content of a partially cross-linked butadiene polymer grafted base having grafted thereon acrylonitrile and styrene copolymers.
The most preferred impact modifiers are polyolefin copolymers with vinyl epoxide derived units. Such epoxide functional copolymers may be prepared from an olefin, such as ethylene and glycidyl acrylate or methacrylate. Other non functionalized vinyl containing monomers may also be incorporated such as alkyl acrylate or methacrylate, vinyl esters and vinyl ethers. Suitable epoxy containing polyolefin copolymers and terpolymers are described in U.S. Pat. No. 5,907,026 (herein incorporated by reference). The most preferred impact modifiers are ethylene-alkyl methacrylate-glycidyl methacrylate (EMA-GMA) terpolymers. Such epoxy olefin impact modifiers are preferred to be used at 1 to 5% loading.
The UV resistance and weathering performance of the blends of the invention can be enhanced by addition of ultraviolet radiation absorbers. Benzotriazole UV absorbers are preferred for instance commercially available TINUVIN 234, MIXXIM BB/200 and CYASORB 5411. Other suitable UV absorbers are described in U.S. Pat. No. 5,907,026 hereby incorporated by reference. UV absorbers are used at any effective concentration generally from 0.1-2.0 wt.% of the entire mixture.
When combining polycarbonate, polyarylates or polyester-carbonates with polyester resins it is very desirable to use special stabilizers, often referred to as quenchers, to suppress polycarbonate polyester reaction. These stabilizers are used at a level of 0.01-10 weight percent and preferably at a level of from 0.05-2.0 weight percent. The stabilizers include an effective amount of an acidic phosphate salt; an acid, alkyl, aryl or mixed phosphite having at least one hydrogen or alkyl group; a suitable metal phosphate salt, preferably a Li, Na, K, Mg, Ca or Zn salt; a phosphorus oxo acid, a metal acid pyrophosphate or a mixture thereof. The suitability of a particular compound for use as a stabilizer and the determination of how much is to be used as a stabilizer may be readily determined by preparing a mixture of the polyester component and the polycarbonate with and without the particular compound and determining the effect on melt viscosity or color stability or the formation of interpolymers. These stabilizers are further described in U.S. Pat. No. 5,441,997 in column 6, line 48 to column 7, line 10. This text is incorporated by reference into the present application.
In order to achieve the full benefits of this invention the type and amount of quencher should be chosen so that the colored resin composition is substantially free of particulates. Organic substituted quenchers like; partially esterified phosphorous acid, an acid, alkyl, aryl or mixed phosphite having at least one hydrogen or alkyl group, phosphoric or phosphorous acids are preferred. Mineral quenchers that will act as a particulate filler in the blend are less preferred but may be acceptable at a low level. Similarly any significant level of a particulate additive such as carbon black or titanium dioxide may be detrimental to gloss retention depending on the severity of the weathering conditions and the nature of the polyester blend matrix. The appropriate level of particles allowed into the blend will depend on the matrix and the length of weathering and can be determined using the process of our invention. Polyester blends of the invention with UV stabilizer and further containing at least some level ( greater than 5% preferred,  greater than 10% more preferred) of polyester-carbonate or polyarylate resins will have the best gloss retaining capability under severe weathering conditions. Such polyester polyarylate or polyester-carbonate blends will better tolerate the presence of low levels of particulates than blends of polyester with just aromatic polycarbonate (for examples Bis Phenol A-PC). In any event the gloss retention of all compositions of the invention will benefit from the absence of particulates.
The blends of the invention comprise less than 5 percent by weight additional ingredients which may be added to contribute to additional desirable properties such as: good mechanical properties, oxidation resistance, good processability, i.e. short molding cycle times, good flow, and easy release from the molding tool. Preferred are antioxidants such as hindered phenols, thioesters, phosphonites and phosphites. Mold release agents, especially low molecular weight polyesters such as pentaerythritol tetrastearate (PETS), are also preferred.
The method of blending the compositions can be carried out by conventional techniques. One convenient method comprises blending the polyester, polycarbonate, colorants and other ingredients in powder or granular form, extruding the blend and comminuting into pellets or other suitable shapes. The ingredients are combined in any usual manner, e.g., by dry mixing or by mixing in the melted state in an extruder, on a heated mill or in other mixers. Colorants or other portions of the blend may be added to the extruder downstream of the throat feed port.
Although it is not essential, best results are obtained if the ingredients are pre compounded, pelletized and then molded. Pre compounding can be carried out in conventional equipment. For example, after predrying the polyester and polycarbonate resins, the resins may be blended with other ingredients and melt mixed on a single or twin screw extruder. The ingredients can be added all together or fed in portions into different areas of the melt mixing device. It may be advantageous to pre compound some ingredients of the blend before mixing with the remainder of the blend for example as described in U.S. Pat. No. 5,814,712 hereby incorporated by reference.
In the most preferred case using BPA polycarbonate, a polyester-carbonate and PBT or PET, a generally suitable machine temperature will be from about 240xc2x0 C. to about 300 xc2x0 C. The pre-compounded composition can be extruded and cut or chopped into molding compounds, such as conventional granules, pellets, etc. by standard techniques. The compositions can be molded in any equipment conventionally used for thermoplastic compositions. For example, good results will be obtained in an injection molding machine, with conventional cylinder temperatures, e.g., 250xc2x0 C. to 275xc2x0 C., and conventional mold temperatures, e.g., 65xc2x0 to 90 xc2x0 C.
The following examples are designed to illustrate the scope of the invention and should not be construed to limit the claims in any manner whatsoever.

Polycarbonate-polyester compositions with enhanced flow


A pressurized fluid dispenser includes a base unit and a reservoir. The base unit includes a pump and a battery compartment including electrical contacts electrically connected with the pump. The reservoir is supported by and selectively removable from the base unit. The reservoir includes an internal compartment that is in fluid communication with the pump when the reservoir is connected to the base unit. A female panel mount for an electrically operated unit is also disclosed.

This disclosure generally relates to a pressurized fluid dispenser, which can also be referred to as a power washer or pressure washer. However, the present disclosure also describes a female panel mount for an electrically operated unit, which need not be used in association with a pressurized fluid dispenser.
Small and portable power washers are an increasingly popular outdoor power tool; however, some drawbacks to exist with regard to the mobility of known power washers. Known portable power washers are typically not suitable for use remote from electrical outlets that are connected with an electrical utility grid. Typically, power washers include an electric pump that is operated by electrical power that is received from a wall outlet through an electrical cord that is plugged into the wall outlet. This can require the power washer to be used near buildings and other structures that include these wall outlets, or it requires a very long extension cord to be used with the power washer. This limits where these power washers can be used.
Moreover, known power washers are not configured for easy refilling. To refill the reservoir of these known washer units, the operator typically must move the entire unit, including the electrical components for the power washer (e.g. the electric pump), and carry these components to a fluid source for filling the reservoir. This requires the operator to carry unnecessary components, e.g. the electric pump and other electrical components, to a fluid source, e.g. a spigot, to fill the reservoir. This can limit the available water sources for filling the reservoir, especially where electrical components are attached to the reservoir. For example, the operator of the power washer may not want to dunk a power washer that includes an attached electric pump into a pond or stream to fill the reservoir. Moreover, this results in added weight that must be carried around by the operator when filling the reservoir.

Techtronic Floor Care Technology Limited


A coating composition for forming a water-resistant coating on fiber-reinforced articles such as rods or cables. The composition comprises an aqueous solution of a superabsorbent water-soluble polymer, a viscosity modifying agent, and optionally a lubricant. the coating formed by applying the composition effectively prevents the treated surface from water-permeation damage by absorbing water that contacts the layer containing the superabsorbent component.

The present invention relates to a high strength superabsorbent coating capable of rapidly absorbing water, which is suitable for coating reinforcing fibers, or for coating articles comprising reinforcing fibers, such as reinforced rods and cables. More specifically, the coating is formed from a composition comprising a superabsorbent polymer precursor which, upon cure, forms a polymer with a high water swelling ability; and a film-forming polymer. As a modification to adapt the coating to pultruded articles, the coating composition may also include a viscosity-modifying agent.
The inventive concept also relates to articles coated with the superabsorbent coating composition, such as glass rods; and methods of applying such coatings. The novel coating of this invention demonstrates a high level of water absorption in fresh and salt-water environments, and excellent spreading and coating ability when applied to a substrate.
Deterioration caused by the invasion of moisture beneath the exposed surfaces of articles used in outdoor environments is a well-known problem. This deterioration includes oxidative deterioration caused by reaction of water with the surfaces of reinforcing fibers used in these articles, as well as water-induced corrosion. In marine environments, the problems associated with waterlogging are particularly compounded by the salinity of the environment. The presence of salt in such aqueous environments hastens the oxidative decomposition.
Articles affected by the deterioration described above include reinforced fibers made of glass, carbon, polymer or mixtures thereof, or items containing such reinforcing fibers. The term xe2x80x9carticlesxe2x80x9d, as used herein, is specifically intended to include reinforcing fiber materials known in the art, as well as products made using one or more of these fibers collectively or dispersed within a matrix of any type. The term also includes articles manufactured using reinforced fiber products, such as structural materials or in equipment. Examples of such articles include such as reinforced rods and cables, such as fiber optic or telecommunications cables. These telecommunications cables are often used in situations where they are buried underground or submerged in water over long periods. As such, protection from water damage is critical to the structural integrity of these cables and to the success of the functions they are intended to perform. A telecommunications cable, for example, may include a core comprising a glass rod that acts as a stiffening or reinforcing member. This rod contributes to the rigidity of the cable. When water penetrates to contact the core element of the cable, corrosion or chemical deterioration of the cable infrastructure may result.
In order to combat the problems associated with this waterlogging damage, several strategies have been devised in an attempt to provide water resistance to cables and other reinforced articles, and to protect their sensitive inner surfaces from contact with water or water vapor present in the surrounding environment. These techniques for making water-repellent articles have included wrapping the articles in a protective sheathing material; or sealing the surface to be protected. Sealing techniques may include chemically manipulating the surface layer of the article to render it resistant to water-absorption, or applying a repellent coating.
The technique of covering the surface with a protective sheathing material is conventional. It includes for example, using a wrap or tape made of an impervious polymer with water-blocking ability, or treating the wrapping material with an emulsion or solution of a water-blocking polymer. The sheathing process does not require application of a chemical compound or treatment to the surface of the article, rather the protection is derived only from the coverage by the sheathing material.
Coatings used to repel water traditionally have been composed of substances that are both insoluble and impenetrable to water, and therefore presented a physical barrier to encroaching moisture. Such barrier coatings have included materials such as greases or gels. In the case of cables, for example, these coatings are applied by extrusion under pressure. There are however, certain drawbacks associated with this type of coating. Greases or gels are difficult to handle because of their slipperiness, and they contribute an unpleasant feel to the coated article. This is an important factor to be considered in the manufacturing process, particularly because it affects the ease of handling of the cable during splicing operations. Greases and gels also undergo changes in viscosity at low or high temperatures. These viscosity changes may affect the freeze/thaw performance and therefore the stability of the coating. Poor performance in these respects therefore affects the stable performance of the cables.
More recently, greaseless, water-resistant dry coatings have been devised which, of themselves, have some degree of water-absorbing capacity. This ability to absorb water allows the coating to absorb the moisture contacting the article, while preventing direct contact with the sensitive surfaces. The absorbent component in these dry waterblocking coatings is a dry, granulated superabsorbent polymer that swells and absorbs upon contact with water. The superabsorbent polymers are usually characterized in terms of their swell rate, swell capacity and gel strength. Traditional uses for these dry superabsorbent polymers have primarily included personal hygiene product articles, food packaging articles and chemical spill cleanup compositions, however recent experimentation has included using these dry polymers to form coatings for other articles such as reinforced cables. For example, U.S. Pat. No. 5,689,601 to Hager, herein incorporated by reference, discloses a dry waterblocking coating for reinforcing fiber articles using a powdered or granulated water-soluble dry blocking ingredient encased in one or more thin layers of a sheathing polymer. This casing restricts the degree of water absorption that can be achieved by the granular polymer, and accordingly the swell capacity of this coating is limited.
The superabsorbent polymers traditionally used in dry waterblocking cable coating applications are dry, granular polymers that are incorporated into various substrates such as yarn, binders and tape. The substrates typically also contain glass fibers as a form of reinforcement. However, as discussed above, the coatings formed with dry granulated blocking agents suffer the limitations of limited water swelling ability and swell rate as a necessary consequence of optimizing the gel strength. In the context of surface coatings, gel strength is defined as the ability to prevent water from wicking down the cable axis, particularly when the cables are used in aqueous environments where they are exposed to elevated water pressures. The swelling ability is directly related to the degree of cross-linking of the superabsorbent polymer. As the degree of cross-linking increases, so does the gel strength, but there is a related decrease in the swell rate and swell capacity of the polymer. The swell rate defines the amount of water that the coating absorbs over a fixed period of time. The swell capacity denotes the maximum amount of water or fluid absorbed by the coating, based on a measure of its dry weight. Consequently, coatings made of dry, granular, water-insoluble polymer are limited in their water-absorbing performance, as measured in terms of the swell rate and swell capacity.
Generally, coatings for reinforced fibers, strands and articles such as cables that are made from these fibrous materials are applied to the surface of the fibrous material and then cured before further processing, if any, occurs. The means of applying coatings, in general, differs depending on whether a fluid coating is used or whether a solid particulate coating is being applied.
In the case of powdered coatings, the coating process using granulated water-blocking agents involves several time-consuming and labor- and equipment-intensive steps that are directly related to the use of a granulated polymer. These steps include the need for one or more treatments with a binding resin, and one or more applications of powdered resin at the powder-coating stations using apparatus such as a fluidized bed.
The means for applying fluid coatings may include flooding, or dipping the fibers or cables, for example in a resin bath and then removing excess resin and form a consistent layer on the treated surface. In the case of strands, rovings or cables, the product is in the form of a continuous filament and therefore it can be passed through a stripper die to remove the excess resin. Alternatively, the coating may be sprayed onto the surface of the article. In order to form a coating layer that is thick enough to provide good coverage and protection from water penetration, the coating composition must be thick enough that it can adequately coat the article in one pass through the coating apparatus. In addition to thickness however, the composition must also have sufficient flowing ability to allow ready formation of a uniform coating on the surface of the article, and to prevent clogging of the coating apparatus, dye orifices or other machinery used to make polymer-coated fibrous articles. Traditionally in the art, in order to modify the viscosity of the fluid coating composition, dry particulate ingredients such as a flocculent polymer or starch have been used. The difficulty with such compositions is that the resulting composition after this solid ingredient is added is not homogenous. Rather, the composition contains varying levels of a particulate material, which makes handling difficult and also compromises the spreadability of the composition.
There exists in the art then, a need for a waterblocking coating composition which possesses excellent gel strength and wicking ability, as well as a high degree of water absorption and a concurrent, rapid swell rate. At the same time, a further need exists in the art for a coating composition that does not contain powdered polymer, and which, as a result, would not require a costly and labor intensive application process. At the same time it is desired that such a coating composition exhibit good spreading and surface performance characteristics.
It has now surprisingly been discovered that highly absorbent waterblocking coatings having an excellent water swelling capacity and a rapid swell rate can be formed by incorporating a solution of a superabsorbent polymer precursor into an aqueous solution used to coat glass fiber reinforced articles such as cables or rods. The polymer precursor, when cured, forms a superabsorbent polymer. The novel coatings containing this superabsorbent polymer are capable of substantially instantaneous water absorption when exposed to aqueous environments.
Depending on the intended application, the absorbent coating may be enhanced by adding a viscosity-modifying agent. For example, where the coating composition is applied to rods comprising glass, carbon, polymer or mixtures thereof, including a viscosifier imparts excellent spreading ability to the formulation. This viscosity-modifying agent is not an insoluble powdered component, rather it is a polymeric solution or dispersion that can be easily incorporated into the coating composition. Hence, unlike waterblocking coatings previously known in the art, the coating composition of this invention is in the form of a true solution having substantially no particulate components.
In one aspect, this invention also relates to a process of forming a coating onto fibers or strands of a reinforcing material. The process of coating may further be applied to products containing reinforced fiber materials, such as rods or cables formed from a composite making process such as pultrusion or injection molding. Generally, this process includes the steps of applying the coating composition to the surface of the fibers, strands or articles, passing it through a stripper die to remove excess coating, followed by a drying or curing step.
The inventive concept further relates to articles containing reinforcing fibers made of glass, polymer, carbon or natural fibers that are made using the water-absorbent coatings of the present invention. Such articles include reinforcing fibers, strands, rods, rovings etc., either in continuous form or as chopped fibers, strands, or pellets; fabrics comprised of glass, polymer or natural fibers; and pultruded articles such as rods or cables. The pultruded articles may be comprised of glass, carbon, one or more polymers, and mixtures thereof. Also, the coating can be applied to corrugated metallic tubes and tapes used for rodent protection in fiber optic cables.
The composition of this invention is suitable for forming a superabsorbent coating on the surface of fiber reinforcements and fibrous products or articles made using these reinforcements. The products to which the composition may be applied can be divided into the broad categories of fiber reinforcements, such as continuous strands, or composited articles comprising fiber reinforcements and one or more other components. The ingredients included in the superabsorbent coating formulation depend on the type of product to which the composition will be applied.
As one embodiment, examples of fibrous reinforcement products in the first category mentioned above include strands or rovings made from fiber-forming materials such as glass, carbon, polymers or mixtures thereof. The coating formulation for these products will preferably include a small amount of a lubricant.
In another embodiment, the composited articles in the second category include articles that comprise a reinforcing fiber material as at least one component thereof. Examples include articles formed in a pultrusion operation. For example, the coatings of this invention can be successfully applied to a pultruded rod or cable comprised at least partially of reinforcing glass fiber/polymer composite. The polymers that may be used to form these pultruded articles include thermosetting resins, such as epoxies, polyesters and vinyl esters. The polymer component of the pultruded article may also be a thermoplastic resin that has been heat-treated, however a thermosetting resin is preferred. As an example, a thermosetting epoxy resin such as a vinyl ester may be combined with glass strands in a pultrusion operation to form a rod that can be used as the stiffening member in a telecommunications cable.
The water resistant properties of the coatings of the present invention are obtained by combining a solution of a non-toxic, environmentally safe superabsorbent polymer precursor with the binder resin used to coat the substrate articles. The superabsorbent polymer formed by this precursor possesses a surprisingly high capacity for absorbing water, and at the same time maintains a high gel strength in the cured coating as a result of increased cross-linking. As mentioned previously, this polymer uniquely provides water resistance by absorbing large quantities of water. As water contacts the coated surface of the article to be protected, the coating absorbs water and swells in volume. By absorbing the water, the coating effectively wicks away the moisture and thus prevents it from contacting the inner surfaces of the protected article. As a result, the sensitive inner surfaces remain dry and are protected from waterlogging deterioration. The coatings of this invention uniquely achieve water resistance protection by absorbing water to prevent moisture penetration beneath the coating layer. This function is distinctly different from the type of protection accomplished by the barrier coatings more commonly known in the art, which protect the substrate by forming an impermeable barrier.
The non-toxic, environmentally safe superabsorbent polymer precursor used in the coatings of this invention may be selected from any such polymer capable of forming an aqueous solution for use in the coating mixture, and which, upon cure, has a swell capacity and swell rate that enables rapid absorption of large amounts of water followed by desorption without loss of the polymer itself when the coating is dried. A polymer precursor suitable for use in the present coating will demonstrate a swell capacity of up to about 400 times its initial dry weight when the coating is applied to reinforcing fibers or strands and cured.
The superabsorbent polymer precursor for use in the present invention may, for example, be selected from the group of water-soluble polyacrylates possessing the required ability to absorb and desorb large quantities of water, as has been previously mentioned. The superabsorbent polymer precursor is preferably used in its anionic form as a salt of a corresponding alkali or alkali metal salt. The polymer salt is in the form of an aqueous solution that is either c dear or slightly cloudy in appearance. A desirable solids content is in the range of from 30-35% weight. The solution also has a specific gravity of about 1.1 grams per milliliter and a viscosity of about 1000 mPas at about 20xc2x0 C. The solution is typically slightly anionic, having a pH of from about 6 to about 8. One example of an acceptable superabsorbent polymer precursor is a water-soluble anionic polyacrylate in aqueous solution.
If the coating is to be applied to pultruded articles, a viscosity-modifying agent may also be added to the coating composition. The role of this viscosifier is to create a spreading consistency that will enable adequate coating of the pultruded article after it has been passed through a stripper die. The viscosifier also provides good flowing ability and prevents c dogging of the coating apparatus and die orifices. Viscosity modifying agents capable of forming a true solution, such as alkyl cellulose or acrylamide polymers, may be used in the coatings of this invention. A preferred viscosifier for use in the present coatings is a polyacrylamide in aqueous solution. The polyacrylamide solution is particularly suitable because of its compatibility with the superabsorbent polymer precursor solution and the film-forming binder component.
The binder component used in the coating compositions of this invention can include any polymeric material customarily used as a binder in coating compositions for reinforced fiber-containing products. The binder preferably comprises a film-forming polymer or polymer latex that is a thermosetting resin or a thermosetting resin with some thermoplastic properties to enhance the flexibility of the coating. The film-forming binder is also necessarily compatible with the water-absorbing polymer and with the viscosity-modifying agent, in that it promotes combination of the ingredients in the coating composition, and also facilitates adherence of the coating to the surface once it is applied. The film-former further provides a tough film with preferably no surface tackiness or flaking of the coating after it is cured. The film-forming polymer comprised in the binder may for example be a polyester, urethane, epoxy, latex or mixtures thereof. The latex may in turn be selected from an acrylic latex, a styrene-butadiene latex, or mixtures thereof. Preferably, the binder is a film-forming urethane that promotes adherence of the water-absorbing polymer to the treated surface after it is dried. An example of a desirable film-forming binder is Witcobond W320, which is a polyurethane film-former available from Witco Chemical Co.
Optionally, the coating composition may also include one or more additives selected from the group consisting of lubricants and wetting agents. Lubricants are added to enhance the handling of the polymer-impregnated strand in subsequent processing. Where the coating is applied to fiber reinforcements such as glass strands, a lubricant is preferably added to improve adherence of the coating to the strand.
The wetting agent is added to facilitate contact between the dispersion and the fiber surface. Any conventional wetting agent that is compatible with the other ingredients of the sizing composition can be used.
When the coatings of the invention are applied to the surfaces of reinforcing fiber strands and cured, they demonstrate a swell capacity of from about up to about 400 times the initial dry weight of the water-swellable polymer. Preferably, the swell capacity for this type of application is from about 200 to about 400 times the initial dry weight of the water-swellable polymer. Where the coatings are applied and cured on the surface of articles such as rods or cables, the swell capacity ranges up to 120 times the initial dry weight of the water-swellable polymer. In this context, preferably the swell capacity is from about 50 to about 100 times the initial dry weight of the water-swellable polymer.
The swell rate of the coating should also be high. The coatings of this invention demonstrate an exceptionally high swell rate, in the order of from about 300% to about 2000% weight in the first minute, based on the total weight of the polymer and the fiber substrate. The rate of water uptake varies depending on the salinity of the aqueous environment in which the coating is used. In fresh water, the swell rate is higher than can be achieved in a saline solution such as a marine environment. However, whether the coating is used in either a fresh or salt-water environment, its performance, as measured by the swell rate, is demonstrably higher than has been previously achieved by dry waterblocking coatings known in the art.
In the method of making the coating compositions of this invention, the ingredients are combined in liquid form to prepare the coating solution. A solution of the superabsorbent polymer precursor is first stirred to ensure homogeneity, then added to a mixing tank. Deionized water is then added to the tank, and the lubricant, if desired, is then introduced. Next, the polyurethane in the form of an aqueous emulsion is pumped into the tank. The viscosity-modifying agent is first premixed to form a 1% aqueous solution, and a sufficient amount of this aqueous solution is added to the mixing tank. As a final step, the mixture is then stirred, without heating, and the resulting composition is ready for application.
The composition is contacted with the surface of the articles to be coated by a means suitable for applying a liquid coating. For example, the coating composition can be applied by passing reinforcing fiber strands through a resin bath. Alternatively, the composition is applied to an article to be coated by spraying, flooding, or by any other means which permits the liquid coating to be contacted with the entire surface of the article. A further processing means may then be used to ensure an even and adequate distribution of the coating layer. For example, fiber strands or rods coated with the coating composition are passed through a stripper die.
The coated articles are then dried and cured. The article coated with the superabsorbent polymer precursor is heated to 212xc2x0 F. for a period sufficient to volatilize a substantial portion of the water. The polymer precursor-coated article is then heated to approximately 280xc2x0 F. to cure the polymer by cross-linking. Typically, polymers heated to above approximately 300xc2x0 F. lose the desired superabsorbent quality. The drying/curing step may be performed in an in-line oven. In a 25 foot long oven set to approximately 600xc2x0 F. the polymer is cured at 380-490 feet per minute, and preferably at 440-465 feet per minute.
Glass fiber reinforced articles having the water resistant coating herein described may be used in applications where exposure to water or water vapor is likely, and where the formation of a durable, resilient, flexible coating with good waterproofing properties is desired. The following examples are representative, but are in no way limiting as to the scope of this invention.

Superabsorbent water-resistant coatings for fiber-reinforced articles

Owens Corning Fiberglas Technology, Inc.


A manufacturing method comprising the steps of forming at first solidified wax layer of a desired shape, depositing onto the first solidified wax layer at least one layer of a liquid resin formulation, solidifying the layer of liquid resin formulation, depositing a second wax layer on to the combination of the first solidified wax layer and the layer of solidified resin formulation, solidifying the second wax layer, and separating the solidified resin formulation from first and second wax layers. Preferably, the resin formulation comprises at least one monofunctional water soluble vinyl or acrylic monomer in combination with a low molecular weight aliphatic polymer having acrylic or methacrylic acid functionality. The solidified wax and resin formulation layers can be machined as may be desired to form mold of a given shape comprising wax layers when the layer of formulation is separated from the wax layers.

This invention relates to shape deposition manufacturing of products having a complex configuration from using a liquid resin formulation that may be deposited in layers, polymerized (preferably photopolymerized) and precision machined.
Shape Deposition Manufacturing (SDM) technology comprises fabrication of parts or products by the sequential deposition, solidification, and precision Computer Numeric Controlled (CNC) machining of wax layers which are deposited upon one another until a desired product mold results. See e.g., U.S. Pat. Nos. 5,207,371; 5,286,573; 5,301,415 and 5,301,863. A liquid resin (i.e., polyurethane, epoxy, or ceramic gelcasting slurry) is subsequently cast into the wax mold and cured to produce a desired polymer or green ceramic part or product having a complex shape.
Unfortunately, many parts or products have complex geometries (i.e., internal chambers or overhang features) that make it difficult to accurately fabricate wax molds in successive layers without causing slumpage and remelting of previously deposited and CNC machined wax layer features. In particular, the highly fluid nature of the molten wax coupled by its slow solidification rate often causes a newly deposited layer of wax to slump considerably prior to its solidification on an adjacent or previously deposited layer. This can detract from product dimensional accuracy of the wax mold and thus the product will have imperfections. The problem of casting or molding complex parts or products using a layer by layer wax technique to form the complex mold has perplexed those of skill in the art.
Briefly, in accordance with the present invention, one is able to prepare accurate parts or products by depositing and photocuring liquid resin layers within each solidified and machined wax layer prior to the deposition of a subsequent wax layer. In other words, parts are fabricated by the deposition, solidification, and machining of successive wax and cured resin layers until the final mold encapsulating a resin formulated part results. The wax and resin layer solidification is accomplished by cooling and UV photopolymerization (e.g., photocuring) respectively. By following the described steps, a completed wax mold results with an internal core or cavity filled with a photocured resin product. The photocured resin product has the dimensions of the final desired molded part or product. Thus, the resin core may be washed from the mold by immersion in a neutral or weakly alkaline aqueous solution (preferably a solution having a pH of greater than about 8).
The resin which is preferred for use in the process is composed of at least one monofunctional water soluble vinyl or acrylic monomer (e.g., N-Vinyl pyrrolidone or N,Nxe2x80x2-Dimethylacrylamide) combined with a low molecular weight aliphatic polymer having acrylic acid (AA) or methacrylic acid (MA) functionality. A major advantage of the cured resin of the present invention is that it has dimensional stability even after exposure to high ambient humidity, yet readily dissolves in aqueous solutions. This provides an attractive means for fabricating fugitive parts or products, support materials, or soluble cores for wax molds constructed using Shape Deposition Manufacturing technology.
An object of the present invention is to provide formulations that have the ability to photocure as very thick layers, e.g. a 3 millimeter resin layer, as opposed to thin wax layers (e.g., 100 micronmeter wax layers typically encountered in accordance with conventional Shape Deposition Manufacturing technology) over a 2 minute period in a single pass using ultraviolet (UV) radiation.
Another object of the present invention is to provide techniques and formulations that enable casting or molding parts and products that have smooth surfaces and with minimal chipping.
A further objection of the present invention is to provide techniques and formulations that provide the ability to fabricate positive image structures.
Another object of the present invention is to provide techniques and formulations that have the ability to fill fine crevices and machine features in a wax mold as it is being manufactured.
A further object of the present invention is to provide techniques and formulations that result in higher strength molds than conventional Shape Deposition Manufacturing technology.
Yet another object of the present invention is to provide techniques and formulations that enable manufacture of a completely soluble, organic molded product with no mineral filler.
Additional objects of the present invention include the provision of techniques and formulations for making molds that incorporate the use of sucrose, which reduces shrinkage and reduces exotherm (i.e., energy) on curing, resulting in less bubbling and smoother surfaces in the part and/or mold. Notably, the refractive index of sucrose is similar to the resin monomers of the present invention. Further, it has been discovered that sucrose has minimal effect upon UV transmission and resin curing.

Machinable positive image model material for shape deposition manufacturing


A process for the vapor phase preparation of vinyl acetate in the presence of a catalyst of 0.2 to 1.3% by weight of gold or a gold compound, 0.3 to 10% by weight of an alkali metal compound, 0.5 to 2.0% by weight of a palladium compound and 0.01 to 1% by weight of a lanthanoid compound.

The present invention relates to a catalyst which comprises palladium and/or its compounds, gold and/or its compounds, alkali metal compounds and at least one lanthanoid metal and/or its compounds, and to its use for preparing vinyl acetate from acetic acid, ethylene and oxygen or oxygen-containing gases.
It is known that ethylene can be converted in the gas phase with acetic acid and oxygen or oxygen-containing gases on palladium/gold/alkali metal-containing fixed bed catalysts into vinyl acetate.
The palladium/gold/alkali metal-containing catalysts have a particular noble metal distribution, with the noble metals being present in a shell on the carrier particles, while the core of the particles is substantially free of noble metals. Catalysts with this noble metal distribution are distinguished by an increased specific productivity (g of vinyl acetate/g of noble metal). The noble metal compound in shell form is achieved by impregnation and subsequent precipitation of the noble metals using alkaline compounds.
The process disclosed in U.S. Pat. No. 4,048,096 for preparing palladium, potassium and gold-containing catalysts entails initial impregnation of the carrier material with an aqueous solution which comprises a mixture of palladium and gold salts. The metal salts are then converted by treatment with alkalis into water-insoluble compounds and are fixed on the carrier material in this way. Subsequent treatment with a reducing agent reduces the palladium and gold compounds to the corresponding metals. Finally, the carrier material loaded with palladium and gold is treated with an alkali metal acetate solution and dried. The impregnation step with the aqueous solution containing palladium and gold salts is characterized by the volume of the impregnation solution corresponding to the pore volume of the carrier material. The resulting catalyst has a shell structure in which palladium and gold are dispersed in a shell thickness of about 0.5 millimeter over the surface of the carrier material.
U.S. Pat. No. 3,775,342 also discloses a process for preparing palladium, potassium and gold-containing catalysts by impregnation with a solution of palladium and gold salts, by subsequent treatment with an alkali solution, which results in water-insoluble palladium and gold compounds precipitating on the carrier, and by subsequent reduction of the metal compounds to the corresponding noble metals. Treatment of the carrier material with an alkali metal acetate solution can take place before or after the reduction step.
U.S. Pat. No. 5,185,308 discloses a palladium, potassium and gold-containing shell catalyst in which the noble metals are dispersed in a shell thickness of 1 millimeter over the carrier material. The known catalyst has a ratio of gold to palladium in the range from 0.6 to 1.25 by weight.
It is further known to prepare a palladium, potassium and gold-containing shell catalyst by washing a carrier material, which has been provided with a binder, for example an alkali metal or alkaline earth metal carboxylate, before the impregnation with an acid, and treating with a base after the impregnation (EP-A-0 519 435).
In the process disclosed in U.S. Pat. No. 5,332,710 for preparing a palladium, gold and potassium-containing shell catalyst, the carrier impregnated with an aqueous palladium and gold salt solution is immersed in an aqueous fixing solution containing sodium hydroxide or potassium hydroxide and agitated therein for at least 0.5 h.
It has now been found, surprisingly, that catalysts of this type can be distinctly improved by adding at least one lanthanoid metal and/or a lanthanoid metal compound, i.e. provide a higher space-time yield with identical or higher selectivity for vinyl acetate.
The invention accordingly relates firstly to a process for preparing vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst which comprises 0.5-2.0% by weight of palladium and/or its compounds, 0.2-1.3% by weight of gold and/or its compounds, and 0.3-10% by weight of alkali metal compounds on a carrier, wherein the catalyst additionally comprises 0.01-1% by weight of at least one lanthanoid metal and/or its compounds, the percentages relating to the metal contents, based on the total mass of the catalyst.
The invention secondly relates to a catalyst which comprises 0.5-2.0% by weight of palladium and/or its compounds, 0.2-1.3% by weight of gold and/or its compounds, and 0.3-10% by weight of alkali metal compounds on a carrier, wherein the catalyst additionally comprises 0.01-1% by weight of at least one lanthanoid metal and/or its compounds, the percentages relating to the metal contents, based on the total mass of the catalyst.
The procedure for preparing the catalysts according to the invention is preferably as follows (U.S. Pat. No. 3,775,342, U.S. Pat. No. 4,048,096, U.S. Pat. No. 5,332,710):
(1) First the carrier particles are impregnated one or more times by being intimately mixed with at least one solution of at least one salt of the elements palladium and gold, and of at least one salt of at least one lanthanoid metal.
(2) The pretreated carrier is treated with a fixing solution with an alkaline reaction, which results in the noble metals and the lanthanoid metals being precipitated in the form of water-insoluble compounds on the surface of the carrier particles, and thus being fixed.
(3) The noble metal compounds deposited on the carrier particles are reduced to the corresponding metals by treatment with a reducing agent. A noble metal shell doped with at least one lanthanoid metal is produced in this way on the surface of the carrier particles.
(4) Interfering anions are removed by washing the treated catalyst.
(5) The treated catalyst is dried at not above 150xc2x0 C.
(6) The dried carrier is treated with a solution which contains at least one alkali metal compound.
(7) Finally, the treated carrier is dried at not above 150xc2x0 C.
The procedure in step (1) can also be to apply the salt solutions containing catalytically active substances to the carrier by single or multiple spraying on, vapor deposition or immersion.
The term xe2x80x9clanthanoid metalsxe2x80x9d means the 14 rare earth elements cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, and the elements scandium, yttrium and lanthanum because their chemical behavior resembles that of the rare earth elements.
Suitable carriers are the known inert carrier materials such as silica, alumina, aluminosilicates, silicates, titanium oxide, zirconium oxide, titanates, silicon carbide and carbon. Particularly suitable carriers of this type are those with a specific surface area of 40 to 350 m2/g (measured by the BET method) and an average pore radius of 50 to 2000 xc3x85 (Angstrom) (measured by mercury porosimetry), especially silica (SiO2) and SiO2/Al2O3 mixtures. These carriers can be used in any form such as, for example, in the form of beads, tablets, rings, stars or particles of other shapes, with a diameter or length and thickness generally of 3 to 9 mm.
Carriers of these types can be prepared, for example, from aerogenic SiO2 or an aerogenic SiO2/Al2O3 mixture which can be prepared, for example, by flash hydrolysis of silicon tetrachloride or a silicon tetrachloride/aluminum trichloride mixture in an oxyhydrogen flame (U.S. Pat. No. 3,939,199).
Suitable solvents for the palladium, gold, alkali metal and lanthanoid metal salts are all compounds in which the selected salts are soluble and which can easily be removed again after the impregnation by drying. Suitable for the acetates are, in particular, unsubstituted carboxylic acids having 2 to 10 carbon atoms such as acetic acid, propionic acid, n- and iso-butyric acid and the various valeric acids. Among the carboxylic acids, acetic acid is preferred because of its physical properties and also for economic reasons. Water is particularly suitable for the chlorides and chloro and acetato complexes. Additional use of another solvent is expedient if the salts are insufficiently soluble in acetic acid or in water. Thus, for example, palladium chloride can be dissolved considerably better in an aqueous acetic acid than in glacial acetic acid. Suitable additional solvents are those which are inert and are miscible with acetic acid or water. Those which may be mentioned as additions for acetic acid are ketones such as acetone and acetylacetone, also ethers such as tetrahydrofuran or dioxane, but also hydrocarbons such as benzene.
It is possible to apply a plurality of salts of palladium, gold, alkali metal and the particular lanthanoid metal, but generally exactly one salt of each of these elements is applied.
The elements palladium and gold which are to be applied in each case in the procedure of step (1), and the lanthanoid metal to be applied in each case, can be applied in the form of salt solutions, singly or else in any suitable combination in any suitable sequence, preferably using a single solution which contains these elements to be applied in the form of salts. It is particularly preferred to use a single solution which contains exactly one salt of each of these elements to be applied.
This solution preferably contains a salt of a single lanthanoid metal, but it is also possible to use a solution which contains one salt of each of different lanthanoid metals.
Where the following speaks generally of xe2x80x9cthe solution of the saltsxe2x80x9d, the same applies analogously to the case where a plurality of solutions are employed in sequence, each of which contains only part of the totality of salts to be applied, in which case the total of the individual parts amounts to the total quantity of the salts to be applied to the carrier.
For the procedure of step (1), the solution of the salts is applied to the carrier particles by impregnating the latter one or more times with this solution, employing the total volume of the solution all at once or divided into two or more part-volumes. However, it is expedient to use the total volume of the salt solution all at once, so that the carrier particles are impregnated with the required amount of elements to be applied by a single impregnation, in which case drying can follow immediately. In the case of impregnation sequentially with a plurality of part-volumes, drying is carried out immediately after each impregnation.
xe2x80x9cImmediatexe2x80x9d drying means in this connection that drying the impregnated particles must start without delay. It is generally sufficient for this case to start drying the particles no later than half an hour after the end of an impregnation.
The impregnation of the carrier particles with the solution of the salts to be applied is carried out by covering the carrier particles with the solution and, where appropriate, then pouring off or filtering off excess solution. It is advantageous, with regard to losses of solution, to employ only the quantity of solution corresponding to the integral pore volume of the catalyst carrier.
It is expedient to mix the carrier particles intimately during the impregnation, for example in a rotating or agitated flask or a mixing drum, in which case drying can follow immediately. The speed of rotation or intensity of the agitation must, on the one hand, be sufficient to ensure good mixing and wetting of the carrier particles but must, on the other hand, not be so great that there is considerable abrasion of the carrier material.
The solution of the salts should have a temperature which is high enough to prevent the salts precipitating during the application to the carrier. The temperature should, however, generally not be much above 70xc2x0 C. in order to avoid excessive evaporation of the solvent and decomposition of the noble metal compounds.
The treatment of the carrier particles impregnated in step (1) with a solution with an alkaline reaction converts the salts of the applied elements into water-insoluble compounds, and they are thus fixed to the surface of the carrier (step (2)).
Examples of fixing solutions which can be used are aqueous solutions with an alkaline reaction. Examples of such solutions are aqueous solutions of alkali metal silicates, alkali metal carbonates and bicarbonates or alkali metal hydroxides.
An aqueous solution of the alkali metal hydroxides, in particular potassium or sodium hydroxide, is preferred. Aqueous solutions which contain boron compounds can also be used as solutions with an alkaline reaction. Particularly suitable in this case are aqueous solutions of borax, potassium tetraborate or mixtures of alkali metal hydroxide solution and boric acid. The alkaline solution may have buffering properties.
The amount of the compound with an alkaline reaction present in the fixing solution is expediently such that it is at least sufficient for stoichiometric conversion of the applied palladium, gold and lanthanoid metal salts into water-insoluble compounds.
However, it is also possible to use an excess of the compound with an alkaline reaction present in the fixing solution, the excess generally being 1 to 10 times the amount required by the stoichiometry.
The volume of the fixing solution must be at least sufficient to cover the impregnated carrier completely with the fixing solution. The fixing preferably takes place by the rotation immersion technique disclosed in U.S. Pat. No. 5,332,710, which is incorporated herein by reference. This technique comprises agitating the carrier which is completely covered by the fixing solution by rotation from the start of the treatment with the fixing solution.
Every type of rotation or similar treatment which keeps the carrier particles agitated can be used, because the exact manner is not critical. The intensity of the agitation is important, however. It should be sufficient for the entire surface area of the impregnated carrier to be wetted uniformly with the alkaline fixing solution.
The treated carrier is then left to stand in the fixing solution at room temperature for up to 16 hours in order to ensure that the applied palladium, gold and lanthanoid metal salts are completely precipitated in the form of water-insoluble compounds on the catalyst carrier.
The reaction on the carrier can, however, also be carried out at elevated temperature, for example at 70xc2x0 C.
After the fixation is complete, the supernatant fixing solution is poured away. This can be followed, where appropriate, by washing the treated carrier in order to remove the soluble compounds present on the treated carrier, for example the alkali metal chlorides liberated in the fixing step and any excess which is present of the compound with an alkaline reaction present in the fixing solution, by washing.
For this purpose, the treated carrier is continuously washed with the washing liquid, preferably with running demineralized water, at room temperature. The washing is continued until interfering anions, for example chlorides, are substantially removed from the carrier.
The moist impregnated catalyst carrier can then be dried, which is expedient if the subsequent reduction of the deposited noble metal compounds to the corresponding metals (step (3)) is carried out in the gas phase.
Reduction of the water-insoluble compounds fixed on the catalyst carrier to the corresponding metals can be carried out with a gaseous reducing agent (step (3)).
The reduction temperature is generally between 40 and 260xc2x0 C., preferably between 70 and 200xc2x0 C. It is generally expedient to use for the reduction a reducing agent which is diluted with inert gas and contains 0.01 to 50% by volume, preferably 0.5 to 20% by volume, of reducing agent. It is possible to use as inert gas, for example, nitrogen, carbon dioxide or a noble gas. Examples of suitable reducing agents are hydrogen, methanol, formaldehyde, ethylene, propylene, isobutylene, butylene or other olefins. The reduction can also be carried out in liquid phase at a temperature from 0xc2x0 C. to 90xc2x0 C., preferably from 15 to 25xc2x0 C. Examples of reducing agents which can be used are aqueous solutions of hydrazine, formic acid or alkali metal borohydrides, preferably sodium borohydride. The amount of reducing agent depends on the amount of the noble metals; the reduction equivalent should be at least equal to oxidation equivalent in quantity, but larger amounts of reducing agent are not harmful.
It is essential to select the reduction conditions in the reduction step so that the fixed water-insoluble noble metal compounds are reduced to the corresponding noble metals. It is, on the other hand, immaterial whether the fixed water-insoluble lanthanoid metal compounds are also converted under the selected reduction conditions into the corresponding lanthanoid metals, because it is not critical for the suitability of the novel catalysts for preparing vinyl acetate whether the lanthanoid metals are present as elements and/or their compounds in the noble metal shell of the novel catalysts.
If no washing step takes place after the fixation is complete (step (2)), or if the reduction takes place with an aqueous solution of a reducing agent, the treated catalyst carrier must, after the reduction is complete, be washed several times to remove interfering compounds, for example to remove chloride residues derived from the impregnation step and released due to the fixation and reduction of the noble metals (step (4)).
For this purpose, the treated carrier is washed continuously with the washing liquid, preferably with running demineralized water, at room temperature until interfering anions, for example chlorides, are removed.
If an aqueous solution of a reducing agent is used in step (3), residues of the reducing agent used can also be removed with the washing step.
The catalyst is then dried at temperatures not exceeding 150xc2x0 C. (step (5)).
In step (6), the dried catalyst carrier is then treated, preferably impregnated, one or more times with a solution of an alkali metal compound, the total volume of the solution being employed all at once or divided into part-volumes. However, it is expedient to use the total volume of the solution all at once, so that the carrier particles are impregnated with the required amounts of alkali metal compound to be applied by a single impregnation. The volume of the solution of the alkali metal compound is, in the case of single or multiple impregnation, generally between 60 and 110%, preferably between 80 and 100%, of the pore volume.
The solution of the alkali metal compound can also be applied to the carrier by single or multiple spraying on, vapor deposition or immersion.
After the treatment with a solution of an alkali metal compound, the catalyst carrier is finally dried at no higher than 150xc2x0 C. (step (7)).
The alkali metal compound is used in an amount such that the catalyst carrier contains 0.1 to 10% by weight of alkali metal after the drying.
The drying of the treated catalyst carrier to be carried out in steps (5) and (7) takes place in a stream of hot air or in a stream of inert gas, for example in a stream of nitrogen or carbon dioxide. The temperature during this drying should generally be 60 to 150xc2x0 C., preferably 100 to 150xc2x0 C. Drying is moreover carried out, where appropriate, under reduced pressure, generally from 0.01 MPa to 0.08 MPa.
If the drying forms part of step (1) and, where appropriate, the other steps, the procedure is the same.
The finished shell catalysts containing palladium, gold, alkali metal and at least one lanthanoid metal have the following metal contents:
If more than one lanthanoid metal is used to dope the palladium, gold and alkali metal-containing shell catalysts, the term xe2x80x9clanthanoid metal contentxe2x80x9d means the total content of all the lanthanoid metals present in the finished catalyst. The stated percentages always relate to the amounts of the elements palladium, gold, alkali metal and lanthanoid metal present in the catalyst, based on the total mass of the catalyst (active elements plus anions plus carrier material).
Suitable salts are all salts of palladium, gold, an alkali metal and a lanthanoid element which are soluble; the acetates, the chlorides, and the acetato and chloro complexes are preferred. However, in the case of interfering anions such as, for example, in the case of chlorides, it must be ensured that these anions are substantially removed before use of the catalyst. This takes place by washing the doped carrier, for example with water, after, for example, the palladium and gold which have been applied as chloride have been converted into an insoluble form, for example through the fixation with compounds having an alkaline reaction and/or by reduction (steps (2) and (3)).
Particularly suitable salts of palladium and gold are chloride, chloro complexes and carboxylates, preferably the salts of aliphatic monocarboxylic acids having 2 to 5 carbon atoms, for example the acetate, propionate or butyrate. Further suitable examples are the nitrate, nitrite, oxide hydrate, oxalate, acetylacetonate or acetoacetate. Because of the good solubility and availability, preferred palladium and gold salts are in particular the chlorides and chloro complexes of palladium and gold.
The alkali metal compound preferably employed is at least one sodium, potassium, rubidium or caesium compound, in particular a potassium compound. Particularly suitable compounds are carboxylates, in particular acetates and propionates. Compounds which are converted under the reaction conditions into the alkali metal acetate, such as, for example, the hydroxide, the oxide or the carbonate, are also suitable.
The lanthanoid metal compound employed is preferably at least one praseodymium, neodymium, samarium, europium or dysprosium compound. However, it is also possible to employ mixtures of these compounds.
The chlorides, nitrates, acetates and acetylacetonates are particularly suitable as lanthanoid metal compound.
In the novel catalysts, the noble metals and the particular lanthanoid metals and/or their compounds are applied in a shell on the carrier particle.
Vinyl acetate is generally prepared by passing acetic acid, ethylene and oxygen-containing gases at temperatures from 100 to 220xc2x0 C., preferably 120 to 200xc2x0 C., under pressures from 0.1 to 2.5 MPa, preferably 0.1 to 2.0 MPa, over the finished catalyst, it being possible to circulate unreacted components. It is also advantageous in some circumstances to dilute with inert gases such as nitrogen or carbon dioxide. Carbon dioxide is particularly suitable for the dilution because it is formed in small amounts during the reaction.
With the same reaction conditions it is possible with the aid of the novel catalysts to prepare more vinyl acetate per reactor volume and time with, at the same time, improved selectivity by comparison with known catalysts.
This facilitates the workup of the resulting crude vinyl acetate because the vinyl acetate content in the gas discharged from the reactor is higher, which further results in a saving of energy in the workup part. A suitable workup is described, for example, in U.S. Pat. No. 5,066,365.
If, on the other hand, it is wished to keep the space-time yield constant, it is possible to reduce the reaction temperature and thus carry out the reaction more selectively, with the same total productivity, in which case there is a saving of precursors. This is also associated with a decrease in the amount of carbon dioxide, which is formed as byproduct and therefore must be removed, and in the loss of entrained ethylene which is associated with this removal. In addition, this procedure results in an increase in the useful life of the catalyst.
The following examples are intended to illustrate the invention but do not restrict it. The percentages of the elements palladium, gold, potassium and of the lanthanoid element are percent by weight based on the total mass of the catalyst.
The catalyst carrier used was the SiO2 carrier available from Sxc3xcd-Chemie with the name KA 160 in the form of beads with a diameter of 5 mm. The pore volume of 1 l of carrier was 335 ml.

Catalyst based on palladium, gold, alkali metal and lanthanoid and process for preparing vinyl acetate