A process for preparing trimethylhydroquinone diacetate, with subsequent hydrolysis to give trimethylhydroquinone, the process including reacting 2,2,6-trimethylcyclohexane-1,4-dione under oxidative conditions, in the presence of a sulfonating agent and a strong acid, and in the presence of an acylating agent.

1. Field of the Invention
The invention relates to a process for preparing 2,3,5-trimethylhydroquinone diesters (TMHQ-DA) by the oxidative aromatization of 2,6,6-trimethylcyclohexane-1,4-dione (dihydro-ketoisophorone=DH-KIP), by reaction with a sulfonating agent in the presence of an acylating agent, and in the presence of an acid catalyst which may be present in the reaction medium either in dissolved form or else as a heterogeneous solid catalyst. The trimethyl-hydroquinone diesters obtained may be converted directly to vitamin E acetate by reaction with phytol derivatives, in particular isophytol (IP), or may instead be first hydrolyzed in the presence of suitable catalysts to give trimethylhydroquinone (TMHQ), which can then be converted into vitamin E by condensation with isophytol derivatives followed by acylation to give vitamin E acetate.
2,3,5-trimethylhydroquinone and 2,3,5-trimethylhydroquinone diesters are very important intermediates in the synthesis of vitamin E and other chromane compounds which are pharmaceutically active substances and which are used, inter alia, as antioxidants. Vitamin E-acetate, in turn, is used in the form of special formulations as an animal feedstuffs additive in addition to applications in the human sector.
2. Description of the Related Art
To produce 2,3,5-trimethylhydroquinone diesters, 4-oxoisophorone (KIP) is normally used as the initial reactant, which can be rearranged in the presence of strong acid catalysts and an acylating agent such as carboxylic anhydrides or acyl halides. The rearrangement of ketoisophorone (KIP) is described in U.S. Pat. No. 4,247,720, which describes rearrangement in the gas phase under hydrogenating conditions. With maximum conversions of 30%, a selectivity to give a TMHQ yield of only 50% is achieved.
Bull. Korean Chem. Soc. 1991, 12, pages 253 et seq., discloses the rearrangement of KIP in a 5% strength solution in acetanhydride, with the addition of 5 equivalents of concentrated sulfuric acid. The TMHQ-DA yields achieved are only 30%.
DE-OS 2 149 159 discloses the rearrangement of KIP in the presence of acetanhydride, in a rearrangement reaction catalyzed by proton or Lewis acids, to give trimethylhydroquinone diacetate, which is then saponified to give TMHQ. In order to achieve complete conversion, large excesses of acid have to be used. The resulting isolation yields (maximum 66%, with respect to the ketoisophorone used) are unsatisfactory because costly recrystallization procedures are required due to the presence of secondary products.
DE-OS 196 27 977 discloses the rearrangement of KIP in the presence of stoichiometric amounts of acetanhydride and catalytic amounts of various acids (trifluoromethanesulfonic acid, chlorosulfonic acid, and oleum, in various concentrations).
Other processes which describe basically the same procedure, that is, the reaction of ketoisophorone with acetanhydride or acetic acid in the presence of a proton acid to give trimethylhydroquinone diacetate, are described in EP 0 850 912 and EP 0 916 642 A1 and JP OS 11-49712. (Suyama et al., 23.2.99; rearrangement of KIP in the gas phase in the presence of a heterogeneous acidic solid catalyst).
A common feature of all these processes is that the trimethylhydroquinone ester, and the trimethylhydroquinone obtainable therefrom by hydrolysis, are prepared starting from a non-aromatic starting compound, that is 2,6,6-trimethylcyclohex-2-ene-1,4-dione. In this reaction, the initial reactant (KIP) already has the same oxidation state as the product, TMHQ-DA, which means that the reaction can be explained by a simple Wagner-Meerwein rearrangement. The diagram given below reproduces the reaction normally used to prepare TMHQ-DA:
The KIP enolester can be detected when following the course of the reaction using gas chromatography, from which it is assumed that the enolester is the intermediate product of the reaction.
However, the ketoisophorone used for the synthesis is relatively expensive as a starting material. It is obtained using known processes by the oxygen oxidation of xcex2-isophorone. The mixture obtained is then worked up by distillation.
To prepare TMHQ-DA, 2,2,6-trimethylcyclohexane-1,4-dione (DH-KIP=dihydro-KIP) is especially interesting, this being obtainable by oxidation, starting from xcex2-isophorone, via xcex2-isophorone epoxide and 4-hydroxyisophorone. The preparation of the aliphatic 1,4-diketone (DH-KIP) or its precursor 4-hydroxyisophorone (HIP) is described, for example, in the following references:
Journal Mol. Cat. 172, 427-435, (1997) discloses the epoxidation of xcex2-isophorone with tert-butyl-hydroperoxide as oxidizing agent, in the presence of a heterogeneous catalyst (SiO2-TiO2 solid catalyst), giving xcex2-isophorone epoxide (xcex2-IPO) and 4-hydroxy-isophorone (HIP).
Tetrahedron Lett., Suppl. 8, Part I, 1-7, discloses the oxidation of xcex2-isophorone to xcex2-IP epoxide by oxidation with meta-chlorobenzoic acid, followed by isomerization in basic medium, to give HIP, which is rearranged to give DH-KIP (yield: 78%), in the presence of an apolar solvent and in the presence of catalytic amounts of p-toluenesulfonic acid.
Helv. Chim. Acta 39, 2041 (1956) discloses the oxidation of xcex2-IP with peracetic acid as oxidizing agent, followed by treatment of the reaction product with NaOH, and the formation of HIP in 57% yield.
DP 38 06 835 discloses the oxidation of xcex2-IP by reaction with aqueous hydrogen peroxide in the presence of formic acid to give HIP, with simultaneous back-isomerization of xcex2-IP to alpha-isophorone.
The object of the present invention is to find alternative aliphatic initial reactants for TMHQ-DA synthesis which are readily obtainable, and to find a process for the efficient reaction of this alternative initial reactant to give TMHQ diesters.
The present invention relates to the use of dihydro-ketoisophorone (DH-KIP) as an alternative initial reactant for the synthesis of TMHQ-DA. The invention relates also to an economically viable process for this reaction. It is intended that both the requisite oxidation reaction as well as the rearrangement reaction involving aromatization be performed in a single process step.
The present invention thus relates to a process for preparing trimethylhydroquinone diesters of the general formula (2)
wherein R represents an optionally substituted aliphatic, alicyclic or aromatic hydrocarbon group,
and to a process for preparing 2,3,5-trimethyl-hydroquinone of the general formula (3)
by reacting 2,2,6-trimethyl-cyclohexane-1,4-dione of the general formula (1)
xe2x80x83with an acylating agent, the reaction being performed under oxidative conditions, with a sulfonating agent, and in the presence of a proton acid and/or a Lewis acid, at a temperature between xe2x88x9250xc2x0 C. and 200xc2x0 C., wherein the ratio between acylating agent and 2,2,6-trimethyl-cyclohexane-1,4-dione is at least 1.
The reaction of DH-KIP as an initial reactant in the preparation of TMHQ-DA has not heretofore been used because the saturated 1,4-diketone does not have the appropriate oxidation state to ensure successful reaction by a simple rearrangement to TMHQ-DA.
By means of the process according to the invention, however, it is now possible to use DH-KIP as an initial reactant for the synthesis of trimethylhydroquinone diesters and trimethylhydroquinone. The reaction according to the invention is shown in the following diagram:
As shown in the reaction scheme given above, the reaction also leads to trimethyl-pyrocatechol diacetate (TMBC-DA) and to 3,4,5-trimethylphenol acetate (TMP-Ac), in addition to trimethylhydroquinone diacetate, depending on the reaction conditions.
The invention provides a new process for preparing 2,3,5-trimethylhydroquinone diesters, and trimethylhydroquinone, by the rearrangement of 2,2,6-trimethyl-cyclohexane-1,4-dione (dihydroketoisophorone=DH-KIP) by reaction with an acylating agent in the presence of an acid proton-containing catalyst with a pKa value or 3 or less, and/or a Lewis acid, under oxidizing conditions. In a straightforward example of the process according to the invention, the catalyst acid used for rearrangement is also the oxidizing agent, in particular sulfuric acid or oleum. According to a further variant, however, the oxidative rearrangement of DH-KIP in the presence of an acylating agent may also be catalyzed by a non-oxidizing Brxc3x6nsted or Lewis acid, wherein in this case a sulfonating agent such as, for example, sulfuric acid/oleum, must also be present.
The reaction takes place at temperatures from xe2x88x9250 to 200xc2x0 C., wherein the ratio of acylating agent to DH-KIP is at least 1:1. The reaction is preferably performed in the temperature interval from xe2x88x9220 to 120xc2x0 C. At higher temperatures, the selectivity for TMHQ diester formation decreases in favor of the formation of secondary products such as trimethylphenol acetate and trimethylpyrocatechol diesters. At lower temperatures, high product selectivity can be achieved, but the rate of reaction decreases.
The TMHQ diester obtained at the end of the reaction can be reacted directly with isophytol to give vitamin E acetate, after isolation and under suitable conditions. As an alternative to this procedure, the diester obtained as an intermediate product is hydrolyzed to give trimethyl hydroquinone, with the addition of water to the reaction mixture.
The acylating agent used in the process is preferably a carboxylic anhydride, carboxylic acid halide, enolester, ketene or some other acylating agent known in the art. Carboxylic anhydrides with the general formula (4) given below are particularly preferred:
wherein R and Rxe2x80x2 are identical or different substituents and represent an optionally substituted aliphatic, alicyclic or aromatic group having from 1-10 carbon atoms, which may optionally be halogenated.
In the context of the invention, acetanhydride is particularly preferred for use as an acylating agent. Another advantage of using acetanhydride is the production of acetic acid during the reaction, this being a suitable phase-promoter for the subsequent hydrolysis reaction with water to give TMHQ. Other suitable acid anhydrides are the anhydrides of propionic acid, butyric acid, isobutyric acid, cyclohexanoic acid, benzoic acid, or the anhydrides of monohalogenated or polyhalogenated carboxylic acids. Chloroacetic acid and trifluoroacetic acid, for example, may be mentioned. Cyclic anhydrides such as, for example, maleic anhydride or succinic anhydride are also suitable as acylating agents in the reaction. Also, there are no restrictions on the use of carboxylic acid halides, wherein good results are obtained in particular with the chlorides corresponding to the carboxylic acids listed above. The use of acetyl chloride as an acylating agent is particularly preferred.
The acylating agent should preferably be present in a molar ratio of at least 1:1 with respect to the DH-KIP used, preferably in a molar ratio of 1:1 to 1:10. The use of higher concentrations of acylating agent does not interfere with the reaction, but no further improvement in reaction is produced by these high dilutions. In this case, the excess acylating agent is used as a solvent which can be separated from the product and recycled in a simple manner by distillation after production of the TMHQ diester required as the target product.
When using carboxylic acid halides, the same data with regard to molar ratios apply as were mentioned in the case of using anhydrides. The use of acetyl chloride, propionyl chloride and butyryl chloride may be mentioned, for example, for use as carboxylic acid chlorides. As an example of the use of enolesters, isopropenyl acetate and structurally related compounds of the following general formula (5) may be mentioned here:
wherein R1, to R4 represent H atoms or hydrocarbon groups having 1-10 carbon atoms, or a 5 or 6-membered alicyclic hydrocarbon, and R5 represents an aliphatic, alicyclic or aromatic hydrocarbon group, optionally substituted, having 1 to 10 carbon atoms.
In the process according to the invention, rearrangement of the 1,4-dione has to be performed under oxidative conditions. In the simplest case, the catalyst acid used also takes on the function of the oxidizing agent. According to the invention, oxidizing acids with a pKa value of 3 or less are suitable for rearranging DH-KIP to give TMHQ diesters, in particular sulfuric acid and oleum, with a variety of SO3 concentrations.
Particularly suitable for the process according to the invention are sulfonating reagents, such as sulfuric acid or oleum, with a variety of SO3 concentrations. Also suitable are mixtures of sulfuric acid with boric acid and oleum with boric acid. When using these reagents, the reaction takes place with sulfonation occurring in situ, wherein SO2 is given off in a subsequent step.
When using sulfuric acid, oleum, and similar sulfonating reagents, additional non-oxidizing acid catalysts may also be added in order to accelerate the reaction. In principle, both proton acids and Lewis acids are suitable. Examples of Brxc3x6nsted acids which can be used are mineral or organic acids with a pka value of 3 or less, including aliphatic or aromatic sulfonic acids such as para-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, hydrohalic acids (HX; X=F, Cl, Br, I), phosphoric acid and aliphatic and aromatic phosphonic acids, haloacetic acids (XCH2CO2H; X=F, Cl, Br) or the corresponding polyhalogenated derivatives such as trichloroacetic acid or trifluoroacetic acid, nitroterephthalic acid or corresponding aryl carboxylic acids which are activated by electron-attracting substituents.
Particularly preferred proton acids which can be used in addition to the sulfonating reagents are catalyst systems which contain, on the one hand, boric acid, and, on the other hand, carboxylic acids or other chelating ligands. The action of these catalyst systems is based on the catalyst species being formed in situ from the boron-containing compound, on the one hand, and the carboxylic acid used, on the other hand, the pKa value of this species being lower than the pKa value of boric acid. Particularly suitable in this regard are mixtures of boric acid or appropriate boric acid derivatives and oxalic acid, wherein the ratio of the catalyst components is between 1:10 and 10:1.
In another variant, the process is performed in the presence of a proton acid having a Hammett constant H0 less than xe2x88x9211.9. Acids covered by this classification include the so-called superacids such as perchloric acid, halosulfonic acids (chlorosulfonic acid, fluorosulfonic acid, etc), and perhaloalkanesulfonic acids such as, for example, perfluoroalkanesulfonic acids of the general formula (6):
CnF2n+1SO3Hxe2x80x83xe2x80x83(6)
wherein n may be from 1-8.
Solid catalysts, which have advantages over homogeneously dissolved proton acids during the working up procedure due to the ease of separation after the end of reaction, may also be used as acids. These solid catalysts include strongly acidic and superacidic ion exchangers, various acidic mixed oxides, zeolites (Y, X, A, or xcex2type), and heteropolyacids (heteropolyacids which are composed, inter alia, from the elements P, Mo, V, W and Si). Acidic ion exchangers are, in particular, common ion exchangers in which the acidity is produced by xe2x88x92SO3H groups on a suitable support (for example Amberlyst catalysts, or Deloxane; Degussa AG). The sulfonic acid groups may be bonded, inter alia, covalently to an organic or inorganic supportmaterial. Superacidic solid acids may also be used (for example those of the Nafion type, such as Nafion NR50 from Aldrich or Nafion H from Dupont), wherein the acidity here is produced by perfluoroalkanesulfonic acid groups which are bonded to various support materials. Insoluble sulfates which are acidic under the reaction conditions, e.g. CaSO4, Fe2(SO4)3, CuSO4, NiSO4, (Al)2(SO4)3, MnSO4, BaSO4, CoSO4, ZnSO4, (NH4)SO4, may also be used. Examples of acidic mixed oxides which may be mentioned include SiO2xe2x80x94Al2O3, SiO2xe2x80x94TiO2, TiO2xe2x80x94ZrO2, SiO2xe2x80x94ZrO2, and related compounds. Also suitable are zeolites, including ZSM-5, mordenite, and acidic aluminium phosphate systems. Various Lewis acids and proton acids, which have already been mentioned above, fixed to a support material, are also suitable as solid catalysts. Examples which may be mentioned here are SbF5, TaF5, BF3, AlX3 (X=Cl, Br, F), SbF5xe2x80x94HF, SbF5xe2x80x94FSO3H, SbF5xe2x80x94CF3SO3H, SO42xe2x88x92, and compounds with equivalent acidity. The previously specified compounds also include superacids which have a Hammett constant H0 less than xe2x88x9211.9.
The solid catalyst may be used as a slurry or else, in an appropriate form, introduced into a fixed bed reactor.
The process may be performed in the presence of an organic solvent which behaves in an inert fashion under the reaction conditions. The concentration of reactants in the solvent has only a minor effect on the product mixture for the reaction, and has an effect only on the ratio between trimethylhydroquinone diesters and the corresponding pyrocatechol diesters. The reaction is preferably performed without any solvent, so that solvent distillation and separation from the product are not required.
If the rearrangement takes place in the presence of organic solvents, in particular aliphatic and cyclic esters, for example ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, gamma-butyrolactone, ethylene carbonate, their derivatives and homologues; aliphatic, alicyclic and aromatic hydrocarbons, for example pentane, hexane, heptane, octane and other homologues, benzene, toluene or xylene are used. Ketones are also suitable as solvents in the context of the invention, such as, for example, acetone, methyl-ethyl ketone, diethyl ketone or isophorone. Furthermore, aliphatic, aromatic or mixed ethers such as diethyl ether, methyl-tert-butyl ether may be used.
In one embodiment of the process, the trimethylhydroquinone diester being produced is crystallized directly from the carboxylic acid being produced during reaction, without needing to add another solvent. However, it is also possible to achieve isolation of the product (and thus the removal of secondary products such as trimethylphenol esters and pyrocatechol diesters) by adding a suitable solvent after distilling off the free carboxylic acid being produced. In another embodiment, the reaction is performed in one of the solvents mentioned, and product isolation is performed by crystallization directly from the solvent for the reaction. The purity of the TMHQ-DA isolated in this way corresponds to the product quality which is required for use as an initial reactant in vitamin E acetate synthesis.
In another embodiment, the TMHQ diacetate being produced is saponified without isolation, by adding water to the crude mixture from the reaction. The presence of the carboxylic acid produced during TMHQ-DA formation, in this case acetic acid, is advantageous because it acts as a phase promoter and ensures efficient hydrolysis of the diester. The same catalyst may be used as a saponification catalyst as was used for the oxidative rearrangement of DH-KIP. Free trimethyl-hydroquinone TMHQ is isolated in a manner known per se by crystallization from an appropriate medium. TMHQ may also be synthesized after the intermediate isolation of TMHQ-DA, wherein hydrolysis is then performed in the presence of a basic or acidic catalyst, optionally in the presence of a phase-promoting compound such as, for example, acetic acid, n-butanol or n-butyl acetate. It is also possible to convert TMHQ-DA into TMHQ by hydrolysis under pressure in the presence of a catalyst.

Process for preparing trimethylhydroquinone diacetate and trimethylhydroquinone


A coating composition containing an emulsion polymer prepared with up to about 20% by weight, based on total polymerizable monomers, of addition polymerizable esters of the glycidyl esters of tertiary acids having 9 or more carbon atoms, preferably up to 18 carbon atoms, and particularly having 9 to 11 carbon atoms has improved application properties and produces coatings with better appearance and less water sensitivity. The emulsion polymerization process of the invention produces less coagulum without having to increase the amount of surfactant.

This invention relates to latex polymer dispersions and coating compositions containing such lattices, particularly automotive coatings.
Increasing environmental concerns initiated an evolution in the automotive coatings industry in the last decades of the twentieth century. The push towards zero volatile organic compound-containing coatings brought more reliance on polymerization techniques limiting use of organic solvents, such as aqueous emulsion polymerization. Emulsion polymerization is carried out by addition polymerization of generally hydrophobic monomer in micelles stabilized by a surfactant in the water. The resulting polymer dispersion is referred to as a latex.
Common variations of the emulsion polymerization process include one-step (batch) and two-step polymerization techniques. In the one-step technique, all the monomers are combined and polymerized in a single step. In the two-step technique, two distinct monomer compositions are added sequentially, forming a first polymer and then polymerizing a second polymer in the presence of the first polymer. The product of the two-step emulsion polymer may be termed a two-stage polymer. A two-stage emulsion polymer offers more opportunity to tailor the emulsion particle properties as well as the properties of the coating obtained form the coating composition.
Coating compositions may be formulated with emulsion polymers, whether one-stage or two-stage, to achieve lower volatile organic content. Automotive coatings must meet rigorous performance requirements, and the polymer and other vehicle components must be able to provide the necessary application characteristics and film properties, including the rheology to achieve excellent appearance. It is important for the cured coating layers to provide a smooth surface so that the vehicle finish will have a mirror-like quality. One problem that has been encountered for automotive coatings made with emulsion polymers has been sagging when the composition is applied to the vehicle. Sagging causes unacceptable distortions of the vehicle finish.
It is believed that increased polymer hydrophobicity will reduce or eliminate sagging by increasing the rate of water release when the coating composition is applied by air-atomized spraying onto the vehicle. If the coating composition contains less water by the time it reaches the vehicle surface, then it will form a coating layer with less tendency to sag. It has been found that more hydrophobic monomers are more difficult to emulsify than more hydrophilic monomers. Mini-emulsion and micro-emulsion techniques, which use shear to form very small monomer droplets, have been employed for emulsion polymerization of more hydrophobic monomer mixtures. These techniques are explained in more detail in U.S. Pat. Nos. 5,969.030, 5,786,420, and 5,569,715, incorporated herein by reference. The mini-emulsion technique provides droplets in the range of 50 to 500 nanometers, while the micro-emulsion technique uses a co-surfactant to achieve monomer droplets in the range of 50 to 100 nm.
While the mini- and micro-emulsion techniques can produce more hydrophobic lattices, the increase in cost is substantial. The equipment for providing the high shear necessary to form the small droplet sizes of mini- and micro-emulsion is much more expensive than traditional emulsion polymerization equipment. The larger amount of surfactant and co-surfactant used in mini-emulsion and micro-emulsion techniques increase the cost of the emulsion polymer even more. Additionally, the added equipment and processing increases the opportunity for coagulum to form. Coagulum is a problem for a number of reasons. Coagulum must be filtered from the product polymer because the coagulated particles will cause imperfections in the coating layer. Coagulum reduces usable product. Coagulum also collects in the equipment so that eventually production must be stopped and the equipment cleaned, which is even more of a problem in mini- and micro-emulsion polymerizations because of additional equipment to clean.
It would be desirable, therefore, to have a method of preparing a more hydrophobic emulsion polymer that would not require the high shear and high surfactant/co-surfactant content necessary for the mini-emulsion and micro-emulsion techniques.
The invention provides a hydrophobic emulsion polymer prepared with up to about 20% by weight, based on total polymerizable monomers, of addition polymerizable esters of the glycidyl esters of tertiary acids having 9 or more carbon atoms, preferably up to 18 carbon atoms, and particularly having 9 to 11 carbon atoms. The emulsion polymerization process of the invention produces less coagulum without having to increase the amount of surfactant.
While xe2x80x9cemulsionxe2x80x9d generally refers to a liquid-in-liquid stable suspension and xe2x80x9cdispersionxe2x80x9d to a solid-in-liquid stable suspension, the products of emulsion polymerization have traditionally been called xe2x80x9cemulsionsxe2x80x9d or xe2x80x9cemulsion polymersxe2x80x9d regardless of whether their glass transition temperature is such that they are in fact solids. xe2x80x9cEmulsionxe2x80x9d or xe2x80x9cdispersionxe2x80x9d will be used interchangeably to refer to dispersions and emulsions.
The invention further provides a coating composition containing the hydrophobic emulsion polymer described. The coating composition also provides better handling properties and better appearance (e.g., improved resistance to pinholing) because of its quicker release of water during application to the substrate.
The invention still further provides a coating formed by applying the coating composition to a substrate and, optionally, curing the applied coating to form a cured coating, and a composite coating having at least one layer formed by applying and optionally curing the coating composition of the invention. The coating composition advantageously contains less surfactant that would tend to increase water sensitivity in the coating prepared from it. The coating also has improved impact resistance and chip resistance.
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Specific preferred addition polymerizable esters of the glycidyl esters of tertiary acids having 9 or more carbon atoms may be represented by the formula:
in which R1, R2, and R3 are alkyl groups, preferably at least one of which is methyl, having a total of at least 8 carbon atoms, preferably up to about 16 carbon atoms preferably from 8 carbons to about 10 carbon atoms; and R4 and R5 are either both H or one of R4 and R5 is a methyl group and the other is H.
In one preferred embodiment, the polymerizable ester is the condensation product of a polymerizable acid and glycidyl esters of a mixture of tertiary acids having 9 to 11 carbon atoms having at least one methyl group on the xcex1-carbon (e.g., R1, R2, and R3 of the above structure are alkyl groups having a total of from 8 carbons to 10 carbon atoms. at least one of which is a methyl group). Mixtures of tertiary acids having 9 to 11 carbon atoms having at least one methyl group on the xcex1-carbon are available under the trademark VERSATIC(copyright) acid, and the glycidyl ester of VERSATIC(copyright) acid (also commonly called neodecanoic acid) is available under the brand name CARDURA(trademark) Resin E-10 from Resolution Performance Products, Houston, Tex. Examples of polymerizable acids include, without limitation, acrylic acid, methacrylic acid, and crotonic acid. The glycidyl esters may also be reacted with fumaric, maleic, and itaconic anhydrides, fumaric, maleic, and itaconic acids, and monoalkyl esters of these acids.
The emulsion polymer preferably includes crosslinkable functionality such as, without limitation, active hydrogen groups, oxirane groups, carbodiimide groups, and acetoacetoxy groups. The emulsion polymer may be polymerized from a monomer mixture that includes an active hydrogen-functional monomer and, when the active hydrogen-functional monomer is not an acid-functional monomer, preferably also includes an acid-functional monomer. Examples of active hydrogen-functional monomers include, without limitation, hydroxyl-functional monomers such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylates, and hydroxybutyl methacrylates; acid-functional monomers including acrylic acid, methacrylic acid, and crotonic acid; and carbamate- and urea-functional monomers or monomers with functional groups that are converted to carbamate or urea groups after polymerization such as, without limitation, those disclosed in U.S. Pat. No. 5,866,259, xe2x80x9cPrimer Coating Compositions Containing Carbamate-Functional Acrylic Polymers,xe2x80x9d the entire disclosure of which is incorporated herein by reference. Examples of other monomers that can be used to provide crosslinkable functionality include, without limitation, glycidyl acrylate, glycidyl methacrylate, acetoacetoxybutyl methacrylate, acetoacetoxyethyl acrylate, and carbodiimide methacrylate. Preferably, a sufficient amount of active hydrogen-functional monomer is included to produce an equivalent weight of 1000 or less grams per equivalent, more preferably 800 or less grams per equivalent, and even more preferably 600 or less grams per equivalent.
In one preferred embodiment, the emulsion polymer forms an anionic dispersion. Examples of suitable acid-functional monomers include, without limitation, xcex1,xcex2-ethylenically unsaturated monocarboxylic acids containing 3 to 5 carbon atoms, xcex1,xcex2-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms and the anhydrides and monoesters of these. Examples include, without limitation, acrylic acid, methacrylic acid, crotonic acid, maleic acid or maleic anhydride, itaconic acid or itaconic anhydride, and so on. A sufficient amount of acid-functional monomer is included to produce an emulsion polymer with an acid number of at least about 1, and preferably the emulsion polymer has an acid number of from about 1 to about 10.
In addition to the one or more polymerizable esters of glycidyl esters of tertiary acids, one or more other ethylenically unsaturated monomers are employed as comonomers in forming the emulsion polymers of the invention. Examples of such copolymerizable monomers include, without limitation, derivatives of xcex1,xcex2-ethylenically unsaturated monocarboxylic acids containing 3 to 5 carbon atoms, including esters, nitriles, or amides of those acids; diesters of xcex1,xcex2-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms; vinyl esters, vinyl ethers, vinyl ketones, vinyl amides, and aromatic or heterocyclic aliphatic vinyl compounds. Representative examples of acrylic and methacrylic acid amides and aminoalkyl amides include, without limitation, such compounds as acrylamide, N-(1,1-dimethyl-3-oxobutyl)-acrylamide, N-alkoxy amides such as methylolamides; N-alkoxy acrylamides such as n-butoxy acrylamide; N-aminoalkyl acrylamides or methacrylamides such as aminomethylacrylamide, 1-aminoethyl-2-acrylamide, 1-aminopropyl-2-acrylamide, 1-aminopropyl-2-methacrylamide, N-1-(N-butylamino)propyl-(3)-acrylamide and 1-aminohexyl-(6)-acrylamide and 1-(N,N-dimethylamino)-ethyl-(2)-methacrylamide, 1-(N,N,-dimethylamino)-propyl-(3)-acrylamide and 1-(N,N-dimethylamino)-hexyl-(6)-methacrylamide.
Representative examples of esters of acrylic, methacrylic, and crotonic acids include, without limitation, those esters from reaction with saturated aliphatic and cycloaliphatic alcohols containing 1 to 20 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl, lauryl, stearyl, cyclohexyl, trimethylcyclohexyl, tetrahydrofurfuryl, stearyl, sulfoethyl, and isobornyl acrylates, methacrylates, and crotonates; and polyalkylene glycol acrylates and methacrylates.
Representative examples of vinyl monomers that can be copolymerized include, without limitation, such compounds as vinyl acetate, vinyl propionate, vinyl ethers such as vinyl ethyl ether, vinyl and vinylidene halides, and vinyl ethyl ketone. Representative examples of aromatic or heterocyclic aliphatic vinyl compounds include, without limitation, such compounds as styrene, xcex1-methyl styrene, vinyl toluene, tert-butyl styrene, and 2-vinyl pyrrolidone.
Representative examples of other ethylenically unsaturated polymerizable monomers include, without limitation, such compounds as fumaric, maleic, and itaconic anhydrides (which would provide acid functionality in the emulsion polymer), monoesters (also providing acid functionality), and diesters. Polyfunctional monomers may also be included to provide a partially crosslinked dispersion. Examples of polyfunctional compounds include, without limitation, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol diacrylate and dimethacrylate, 1,6-hexanediol diacrylate and dimethacrylate, divinylbenzene, trimethylolpropane triacrylate and trimethacrylate, pentaerythritol tetaacrylate and tetramethacrylate, and so on.
The monomers may be emulsion polymerized in a single-stage or two-stage polymerization according to well-known methods. In a two-stage polymerization, the first stage monomers are added and polymerized first in the aqueous medium, followed by addition and polymerization of the second stage monomers. The aqueous medium may contain a portion of organic solvent, but preferably less than about 5% of the aqueous medium is organic solvent, and preferably no organic solvent is included in the aqueous medium. Suitable examples of water-miscible organic solvent include, without limitation, esters, alkylene glycol ethers, alkylene glycol ether esters, lower molecular weight aliphatic alcohols, and so on.
Ionic or amphoteric surfactants, such as sodium lauryl sulfate, nonionic surfactants based on polyethoxylated alcohols or polyethoxy-polyalkoxy block copolymers, polyoxyethylenenonylphenyl ethers, polyoxyethylenealkylallyl ether sulfuric acid esters, amino and alkali salts of dodecylbenzenesulfonic acid such as the dimethylethanolamine salt of dodecylbenzenesulfonic acid and sodium dodecylbenzenesulfonic acid, and sodium dioctylsulfosuccinate, are preferably included. The reactor is charged with water and a surfactant. It is preferred to charge from about 0.08% by weight to about 0.5% by weight, preferably from about 0.15% by weight to about 0.35% by weight, based on the total weight of monomers polymerized in the first and second stages, of an anionic surfactant. The combination of monomers to be polymerized in each stage may be pre-emulsified in water and 1% to 5% by weight surfactant, based on monomer weight, before being added to the reactor. The emulsion polymerization is preferably carried out in the presence of a nonionic or an anionic surfactant. Suitable surfactants include, without limitation, polyoxyethylenenonylphenyl ethers, polyoxyethylenealkylallyl ether sulfuric acid esters, amino and alkali salts of dodecylbenzenesulfonic acid such as the dimethylethanolamine salt of dodecylbenzenesulfonic acid and sodium dodecylbenzenesulfonic acid, and sodium dioctylsulfosuccinate.
In general, polymerization is carried out at temperatures from about 30xc2x0 C. to about 95xc2x0 C., preferably from about 50xc2x0 C. to about 90xc2x0 C.
A suitable initiator capable of producing free radicals is used in the polymerization. Examples of suitable initiators include, without limitation, azo compounds and peroxy compounds such as azodiisobutyronitrile, 4,4-azobis(4-cyanovaleric acid), benzoyl peroxide, lauroyl peroxide, diisopropyldicarbonate, t-butyl peroxy-2-ethylhexanoate, peroxyisopivalate, persulfate initiators such as ammonium persulfate, potassium persulfate, and sodium persulfate, and alkali metal peroxydiphosphates, in some cases in combination with reducing agents such as sodium disulfite, hydrazine, hydroxylamine and catalytic amounts of accelerators such as iron, cobalt, cerium, and vanadyl salts, preferably alkali metal or ammonium peroxydisulfates. Chain transfer agents may be added, if desired, to control molecular weight. Typical chain transfer agents include, without limitation, mercaptan compounds such as alkyl mercaptans, e.g., octyl mercaptan and dodecyl mercaptan, mercaptopropionic acid, and esters of mercaptopropionic acid. The polymerization typically proceeds by free radical polymerization. The free radical source is typically supplied by a redox initiator or by an organic peroxide or azo compound. Useful initiators include, without limitation, ammonium peroxydisulfate, potassium peroxydisulfate, sodium metabisulfite, hydrogen peroxide, t-butyl hydroperoxide, dilauryl peroxide, t-butyl peroxybenzoate, 2,2xe2x80x2-azobis(isobutyronitrile), and redox initiators such as ammonium peroxydisulfate and sodium metabisulfite with ferrous ammonium sulfate. Optionally, a chain transfer agent may be used. Typical chain transfer agents include mercaptans such as octyl mercaptan, n- or tert-dodecyl mercaptan, thiosalicylic acid, mercaptoacetic acid, and mercaptoethanol; halogenated compounds; and dimeric alpha-methyl styrene.
After polymerization, the acid functionality (if present) may be salted, preferably with an alkali or base, preferably an amine. Example of suitable salting materials include, without limitation, ammonia, monoethanolamine, ethylamine, dimethylamine, diethylamine, triethylamine, propylamine, dipropylamine, isopropylamine, diisopropylamine, triethanolamine, butylamine, dibutylamine, 2-ethylhexylamine, ethylenediamine propylenediamine, ethylethanolamine, dimethylethanolamine, diethylethanolamine, 2-amino-2-methylpropanol, and morpholine. Preferred salting materials include 2-amino-2-methylpropanol and dimethylethanolamine.
The emulsion polymer typically can have weight average molecular weights of one million or more.
The theoretical glass transition temperature of the emulsion polymer can be adjusted according to methods well-known in the art through selection and apportionment of the comonomers. The preferred glass transition temperature for the emulsion polymer will depend upon the kind of automotive or industrial coating composition it will be used in. If the emulsion polymer is included in an automotive primer composition, the theoretical glass transition temperature is preferably not more than about 0xc2x0 C.; in a basecoat composition, the theoretical glass transition temperature is preferably from about 0xc2x0 C. to about 20xc2x0 C.; and in a clearcoat composition, the theoretical glass transition temperature is preferably from about 20xc2x0 C. to about 60xc2x0 C. A two-stage polymer gives further opportunity to customize the emulsion polymer to the particular type of coating composition in which it will be used.
The automotive coating compositions of the present invention preferably also include a crosslinker component. The crosslinker component includes one or more crosslinkers reactive with the active hydrogen functionality or other crosslinkable functionality of the emulsion polymer. Examples of crosslinkers reactive with active hydrogen functionality include, without limitation, materials having active methylol or methylalkoxy groups, including aminoplast resins or phenol/formaldehyde adducts; blocked polyisocyanate curing agents; tris(alkoxy carbonylamino) triazines; with acid groups, curing agents with oxirane functionality; and combinations thereof. Suitable aminoplast resins are amine/aldehyde condensates, preferably at least partially etherified, and most preferably fully etherified. Melamine and urea are preferred amines, but other triazines, triazoles, diazines, guanidines, or guanamines may also be used to prepare the alkylated amine/aldehyde aminoplast resins crosslinking agents. The aminoplast resins are preferably amine/formaldehyde condensates, although other aldehydes, such as acetaldehyde, crotonaldehyde, and benzaldehyde, may be used. Non-limiting examples of preferred aminoplast resins include monomeric or polymeric melamine formaldehyde resins, including melamine resins that are partially or fully alkylated using alcohols that preferably have one to six, more preferably one to four, carbon atoms, such as hexamethoxy methylated melamine; urea-formaldehyde resins including methylol ureas and siloxy ureas such as butylated urea formaldehyde resin, alkylated benzoguanimines, guanyl ureas, guanidines, biguanidines, polyguanidines, and the like. Monomeric melamine formaldehyde resins are particularly preferred. The preferred alkylated melamine formaldehyde resins are water miscible or water soluble. Examples of blocked polyisocyanates include isocyanurates of toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate blocked with a blocking agent such as an alcohol, an oxime, or a secondary amine such as pyrazole or substituted pyrazole.
The crosslinker component preferably is from about 2% by weight to about 30% by weight, and more preferably from about 5% by weight to about 20% by weight, and particularly preferably about 5% to about 15% by weight of the combined nonvolatile weights of the film-forming components, including the emulsion polymer, the crosslinking component, and any other film-forming polymer or resin.
The compositions may include one or more catalysts to enhance the cure reaction. The type of catalyst depends upon the particular crosslinker component composition utilized. For example, when aminoplast compounds, especially monomeric melamines, are used as a curing agent, a strong acid catalyst, typically blocked with an amine, may be utilized to enhance the cure reaction. Useful catalysts include, without limitation, blocked acid catalysts, such as para-toluene sulfonic acid, dodecylbenzene sulfonic acid, and dinonylnaphthylene disulfonic acid blocked with amines; phenyl acid phosphate, monobutyl maleate, and butyl phosphate, hydroxy phosphate ester; Lewis acids, zinc salts, and tin salts, including dibutyl tin dilaurate and dibutyl tin oxide.
The coating compositions according to the invention may further include pigments such as are commonly used in the art, including organic and inorganic color pigments, metallic or other inorganic flake materials such as pearlescent mica flake pigments or metallic flake pigments such as aluminum flak pigments, corrosion inhibiting pigments, and conductive pigments, as well as fillers. Illustrative examples of these are metal oxides, chromates, molybdates, phosphates, and silicates, carbon black, titanium dioxide, sulfates, and silicas. The amount of pigment may vary widely depending upon the desired color and the specific pigments used, e.g. a pigment-to-solid binder ratio of 0.01 to 2.
Other conventional materials, such as dyes, flow control or rheology control agents, stabilizers, wetting agents, dispersing agents, adhesion promoters, UV absorbers, hindered amine light stabilizers, etc. may be incorporated into the coating composition. While such additives are well-known in the prior art, the amount used must be controlled to avoid adversely affecting the coating characteristics.
The coating composition has a very low content of volatile organic solvent, and is preferably a solvent free or substantially solvent free dispersion. By xe2x80x9csubstantially solvent freexe2x80x9d it is meant that the dispersion has a volatile organic content of less than about 5% by weight of the coating composition. The coating composition preferably has a volatile organic content of less than about 1.5, more preferably less than about 1.3, and even more preferably less than about 0.7. The volatile organic content of a coating composition is typically measured using ASTM D3960.
The coating compositions of the invention are preferably formulated as thermosetting automotive or industrial coatings. The coating composition can be formulated as electrodeposition primer, primer surfacer, basecoat, or clearcoat compositions
Coating compositions can be coated on the article by any of a number of techniques well-known in the art. These include, for example, spray coating, dip coating, roll coating, curtain coating, and the like. For automotive body panels, spray coating is preferred.
The automotive or industrial coating compositions of the present invention can be applied over substrates including metals, plastic, and elastomers. The compositions may be formulated as primers for automotive articles, such as metal or plastic automotive bodies or elastomeric fascia. When the article is a metallic article, it is preferred to have a layer of electrocoat primer before application of the primer coating composition of the invention.
In a preferred embodiment, the primer composition further includes a polyurethane dispersion. The polyurethane polymer of the dispersion preferably has a glass transition temperature of about 0xc2x0 C. or less, preferably about xe2x88x9220xc2x0 C. or less, and more preferably about xe2x88x9230xc2x0 C. or less. The glass transition temperature of the polyurethane is in the range of from about xe2x88x9280xc2x0 C. to about 0xc2x0 C., more preferably from about xe2x88x9265xc2x0 C. to about xe2x88x9210xc2x0 C., still more preferably from about xe2x88x9265xc2x0 C. to about xe2x88x9230xc2x0 C., and even still more preferably from about xe2x88x9260xc2x0 C. to about xe2x88x9235xc2x0 C.
The weight average molecular weight of the polyurethane is preferably from about 15,000 to about 60,000, more preferably from about 15,000 to about 60,000, and even more preferably from about 20,000 to about 35,000.
Polyurethanes are prepared by reaction of at least one polyisocyanate and at least one polyol. The reactants used to prepare the polyurethane are selected and apportioned to provide the desired glass transition temperature. Suitable polyisocyanates include, without limitation, aliphatic linear and cyclic polyisocyanates, preferably having up to 18 carbon atoms, and substituted and unsubstituted aromatic polyisocyanates. Illustrative examples include, without limitation, ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-methylene bis(cyclohexyl isocyanate), isophorone diisocyanate, toluene diisocyanates (e.g., 2,4-toluene diisocyanate and 2,6-toluene diisocyanate) diphenylmethane 4,4xe2x80x2-diisocyanate, methylenebis-4,4xe2x80x2-isocyanatocyclohexane, 1,6-hexamethylene diisocyanate, p-phenylene diisocyanate, tetramethyl xylene diisocyanate, meta-xylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, and combinations of two or more of these. Biurets, allophonates, isocyanurates, carbodiimides, and other such modifications of these isocyanates can also be used as the polyisocyanates. In a preferred embodiment, the polyisocyanates include methylenebis-4,4xe2x80x2-isocyanatocyclohexane, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, and combinations thereof. It is particularly preferred to use at least one xcex1,xcfx89-alkylene diisocyanate having four or more carbons, preferably 6 or more carbons, in the alkylene group. Combinations of two or more polyisocyanates in which one of the polyisocyanates is 1,6-hexamethylene diisocyanate are especially preferred.
The polyol or polyols used to prepare the polyurethane polymer can be selected from any of the polyols known to be useful in preparing polyurethanes, including, without limitation, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,6-hexanediol, neopentyl glycol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol, propylene glycol, dipropylene glycol, glycerol, cyclohexanedimethanols, 2-methyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, thiodiglycol, 2,2,4-trimethyl-1,3-pentanediol, cyclohexanediols, trimethylolpropane, trimethylolethane, and glycerin; polyester polyols such as the reaction products of any of the foregoing alcohols and combinations thereof with one or more polycarboxylic acids selected from malonic acid, maleic acid, succinic acid, glutaric acid adipic acid, azelaic acid, anhydrides thereof, and combinations thereof; polyether polyols, such as polyethylene glycols and polypropylene glycols; and combinations of such polyols. Polyols having two hydroxyl groups are preferred. The polyurethane is preferably prepared using one or more polyester polyols. In a preferred embodiment, the polyester polyol is the reaction product of a mixture that comprises neopentyl glycol and adipic acid.
While it is possible to prepare a nonionic dispersion of the polyurethane, the polyurethane dispersion is preferably anionic. Acid-functional polyurethanes that can be salted to form anionic dispersions or emulsions may be synthesized by including a monomer having acid functionality, such as, without limitation, dialkylpropionic acids including dimethylolpropionic acid, and alkali metal salts of amino acids such as taurine, methyl taurine, 6-amino caproic acid, glycine, sulfanilic acid, diamino benzoic acid, ornithine, lysine and 1:1 adducts of sultones, such as propane sultone or butane sultone, with diamines, such as ethylene diamine, hydrazine, or 1,6-hexamethylene diamine. The hydroxyl groups react to form the urethane linkages while the acid group remains unreacted in the polyurethane polymerization.
Suitable polyurethane polymers can be prepared by any of the known methods. In one method for preparing polyurethane polymers, the polyisocyanate component is reacted with an excess of equivalents of the polyol component to form a hydroxyl-functional polyurethane polymer. Alternatively, an excess of equivalents of the polyisocyanate component can be reacted with the polyol component to form an isocyanate-functional prepolymer. The prepolymer can then be reacted further in different ways. First, the prepolymer can be reacted with a mono-functional alcohol or amine to provide a non-functional polyurethane polymer. Examples of mono-functional alcohols and amines that may be used include polyethylene oxide compounds having one terminal hydroxyl group, lower mono-functional alcohols having up to 12 carbon atoms, amino alcohols such as dimethylethanolamine, and secondary amines such as diethylamine and dimethylamine. Secondly, the prepolymer can be reacted with a polyfunctional polyol, polyamine, or amino alcohol compound to provide reactive hydrogen functionality. Examples of such polyfunctional compounds include, without limitation, the polyols already mentioned above, including triols such as trimethylolpropane; polyamines such as ethylenediamine, butylamine, and propylamine; and amino alcohols, such as diethanolamine. Finally, the prepolymer can be chain extended by the water during emulsification or dispersion of the prepolymer in the aqueous medium. The prepolymer is mixed with the water after or during neutralization.
The polyurethane may be polymerized without solvent. Solvent may be included, however, if necessary, when the polyurethane or prepolymer product is of a high viscosity. If solvent is used, the solvent may be removed, partially or completely, by distillation, preferably after the polyurethane is dispersed in the water. The polyurethane may have nonionic hydrophilic groups, such as polyethylene oxide groups, that serve to stabilize the dispersed polyurethane polymer. In a preferred embodiment, however, the polyurethane polymer is prepared with pendant acid groups as described above, and the acid groups are partially or fully salted with an alkali, such as sodium or potassium, or with a base, such as an amine, before or during dispersion of the polyurethane polymer or prepolymer in water.
The primer coating composition of the invention is applied directly to the substrate or over one or more other layers of primer, such as the electrocoat primer. The applied primer coating composition is then cured to form a primer coating layer. The electrocoat primer or other first layer of primer may be cured at the same time as the primer coating layer of the invention in a process known as xe2x80x9cwet-on-wetxe2x80x9d coating. The primer coating layer formed from the primer coating composition of the invention is the outermost primer layer of the composite coating.
A topcoat composition is applied over the primer coating layer and cured to form a topcoat layer. The substrate at that point is then covered with a composite coating that has at least one layer of primer coating derived from the inventive compositions and at least one layer of topcoat. In a preferred embodiment, the coating composition of the present invention is overcoated with a topcoat applied as a color-plus-clear (basecoat-clearcoat) topcoat. In a basecoat-clearcoat topcoat, an underlayer of a pigmented coating, the basecoat, is covered with an outer layer of a transparent coating, the clearcoat. Basecoat-clearcoat topcoats provide an attractive smooth and glossy finish and generally improved performance.
Crosslinking compositions are preferred as the topcoat layer or layers. Coatings of this type are well-known in the art and include waterborne compositions as well as solventborne compositions. For example, the topcoat may be a clearcoat according to U.S. Pat. No. 5,474,811, applied wet-on-wet over a layer of a basecoat composition. Polymers known in the art to be useful in basecoat and clearcoat compositions include, without limitation, acrylics, vinyl, polyurethanes, polycarbonates, polyesters, alkyds, and polysiloxanes. Acrylics and polyurethanes are preferred. Thermoset basecoat and clearcoat compositions are also preferred, and, to that end, preferred polymers comprise one or more kinds of crosslinkable functional groups, such as carbamate, hydroxy, isocyanate, amine, epoxy, acrylate, vinyl, silane, acetoacetate, and so on. The polymer may be self-crosslinking, or, preferably, the composition may include a crosslinking agent such as a polyisocyanate or an aminoplast resin of the kind described above. In one embodiment, waterborne basecoat compositions and/or clearcoat compositions having low volatile organic content are used. The waterborne basecoat and waterborne clearcoat compositions each preferably has a volatile organic content of less than about 1.5, more preferably less than about 1.3, and even more preferably less than about 0.7.
When the coating composition according to the invention is used as the basecoat of a composite basecoat-clearcoat coating, the basecoat coating is typically applied over one or more layers of primer coating, which are preferably cured before the basecoat is applied. A clearcoat composition is then applied over the basecoat, typically before the basecoat is cured in what is generally known as a xe2x80x9cwet-on-wetxe2x80x9d application, with the basecoat and clearcoat being cured at the same time. The clearcoat composition may any of a number of types well-known in the art, including. Polymers known in the art to be useful in clearcoat compositions include acrylics, vinyls, polyurethanes, polycarbonates, polyesters, alkyds, and polysiloxanes. Preferred polymers include acrylics and polyurethanes. Clearcoat polymers may be thermoplastic, but are preferably crosslinkable and comprise one or more type of crosslinkable functional groups. Such groups include, for example, hydroxy, isocyanate, amine, epoxy, acrylate, vinyl, silane, and acetoacetate groups. These groups may be masked or blocked in such a way so that they are unblocked and available for the crosslinking reaction under the desired curing conditions, generally elevated temperatures. Useful crosslinkable functional groups include hydroxy, epoxy, acid, anhydride, silane, and acetoacetate groups. Preferred crosslinkable functional groups include hydroxy functional groups and amino functional groups. Clearcoat compositions are preferably thermosetting and include one or more suitable crosslinkers, such as those already mentioned.
Each layer of the composite coatings of the invention can be applied to an article to be coated according to any of a number of techniques well-known in the art. These include, for example, spray coating, dip coating, roll coating, curtain coating, and the like. If an initial electrocoat primer layer is applied to a metallic substrate, the electrocoat primer is applied by electrodeposition. For automotive applications, the primer coating composition of the invention and the topcoat layer or layers are preferably applied by spray coating, particularly electrostatic spray methods. Coating layers of one mil or more are usually applied in two or more coats, separated by a time sufficient to allow some of the solvent or aqueous medium to evaporate, or xe2x80x9cflash,xe2x80x9d from the applied layer. The flash may be at ambient or elevated temperatures, for example, the flash may use radiant heat. The coats as applied can be from 0.5 mil up to 3 mils dry, and a sufficient number of coats are applied to yield the desired final coating thickness.
The outermost primer layer, which is formed by reacting the primer compositions of the invention, may be cured by reaction of curing component with at least one the polyurethane resin or the acrylic resin. before the topcoat is applied. The cured primer layer may be from about 0.5 mil to about 2 mils thick, preferably from about 0.8 mils to about 1.2 mils thick.
Color-plus-clear topcoats are usually applied wet-on-wet. The compositions are applied in coats separated by a flash, as described above, with a flash also between the last coat of the color composition and the first coat the clear. The two coating layers are then cured simultaneously. Preferably, the cured basecoat layer is 0.5 to 1.5 mils thick, and the cured clear coat layer is 1 to 3 mils, more preferably 1.6 to 2.2 mils, thick.
Alternatively the primer layer of the invention and the topcoat can be applied xe2x80x9cwet-on-wet.xe2x80x9d For example, the primer composition of the invention can be applied, then the applied layer flashed; then the topcoat can be applied and flashed; then the primer and the topcoat can be cured at the same time. Again, the topcoat can include a basecoat layer and a clearcoat layer applied wet-on-wet.
The coating compositions described herein are preferably subjected to conditions so as to cure the coating layers. The coating compositions described are preferably cured with heat. Curing temperatures are preferably from about 70xc2x0 C. to about 180xc2x0 C., and particularly preferably from about 170xc2x0 F. to about 200xc2x0 F. for a composition including an unblocked acid catalyst, or from about 240xc2x0 F. to about 275xc2x0 F. for a composition including a blocked acid catalyst. Typical curing times at these temperatures range from 15 to 60 minutes, and preferably the temperature is chosen to allow a cure time of from about 15 to about 30 minutes. In a preferred embodiment, the coated article is an automotive body or part.
The invention is further described in the following examples. The examples are merely illustrative and do not in any way limit the scope of the invention as described and claimed. All parts are by weight unless otherwise indicated.

Hydrophobic lattices and coating compositions containing them


Process for obtaining a ceramic coating on the surface of a metal having semiconducting properties, such as aluminium, titanium, magnesium, hafnium, zirconium and their alloys, by a physico-chemical transformation reaction of the treated metal. This process consists in immersing the metal workpiece to be coated in an electrolytic bath composed of an aqueous solution of an alkali metal hydroxide, such as potassium hydroxide or sodium hydroxide, and of an oxyacid salt of an alkali metal, the metal workpiece forming one of the electrodes, and in applying a signal voltage of overall triangular waveform to the electrodes, that is to say a signal having at least a rising slope and a falling slope, with a form factor that can vary during the process, generating a current which is controlled in its intensity, its waveform and its ratio of positive current to negative current.

The subject of the present invention is an electrical oxidation process using a microarc plasma for the purpose of obtaining a ceramic coating on the surface of a metal having semiconducting properties.
Aluminium, titanium, their alloys and all metals which exhibit valve (diode) properties have a beneficial strength/weight ratio and are suitable for a wide range of applications such as in aeronautics, automobiles and mechanical engineering (especially for moving parts, with high mechanical loads and strains), etc.
However, as these materials do not naturally exhibit suitable tribological and mechanical properties (hardness, friction coefficient, abrasion resistance, etc.), coatings are often used to improve the limited characteristics of the coatings on these materials.
They often allow complementary requirements to be met, such as the corrosion resistance in acid medium and/or alkaline medium, the possibility of momentarily withstanding high temperatures, or the obtaining of dielectric properties.
Several electrolytic coating processes are currently employed. The process most used, for wear and/or corrosion protection, is hard anodizing. However, this quite rapidly reaches its operating limits.
This anodizing process is used to form protective oxide layers on aluminium workpieces. However, the coatings produced by this method are limited in terms of thickness and have only a moderate hardness (a maximum of about 500 Hv).
A number of other techniques have been developed to produce coatings of higher performance, especially ceramic coatings, so as to meet severer operating requirements, namely arch-discharge plasma spraying, flame spraying or vacuum deposition techniques.
However, the drawback is that, to obtain good adhesion of the coating, these techniques require a high substrate temperature and prior processes for preparing the surface.
Moreover, these processes cannot compete with conventional anodizing in terms of coating uniformity and/or production costs.
A relatively old (1932) anodic oxidation process using anodic spark discharges or microarc discharges has been developed so as to obtain ceramic coatings for workpieces made of aluminium, titanium, magnesium and their alloys, as a means of protection against severe abrasion and corrosion.
Owing to the valve effect, microarc oxidation forms an insulating barrier film on the metals such as aluminium and titanium. By increasing the anodic potential to more than 200 V, the barrier film is broken and microarcs appear. If a high voltage is maintained, many microarcs are initiated and they move rapidly over the entire immersed surface of the specimen.
These dielectric breakdowns create tracks which pass through the oxide (barrier) layer formed. Complex compounds are synthesized within these tracks. They are composed of substrate material, surface oxides and addition elements from the electrolyte. Chemical interactions in the plasma phase occur in the multiple surface discharges and result in the formation of a coating which grows in two directions from the surface of the substrate. This causes a gradual change in the composition of the properties of the coating from the metal alloy within the substrate to a complex ceramic compound in the coating.
According to the historical description of this process, Gunterschulze and Betz were the first to mention, in 1932, the anodic spark deposition (ASD) process. They observed that the material underwent deposition of the electrolyte during the dielectric breakdown of an insulating film growing on the anode.
This dielectric breakdown causes sparks which appear and disappear while being distributed over the entire surface of the anode, giving the effect of movement.
The first practical applications of ASD were their use as anticorrosion coatings on magnesium alloys, dating from 1936, and these were included in a military specification in 1963.
Since then, the main research efforts have been pursued by Gruss, McNeill and coworkers at the Frankford Arsenal in Philadelphia, and by Brown, Wirtz, Kriven and coworkers at the University of Illinois in Urbana-Champaign.
At the same time, research was carried out in East Germany, mainly by Krysmann, Kurze, Dittrich and coworkers. The German process is called xe2x80x9canodic oxidation by spark dischargesxe2x80x9d (the German acronym for which is ANOF [Anodische Oxidation an Funkenanladung]). The reports of this work in the international literature make reference to patents in the German language.
It is clear that this research has made significant progress, yet it remains, despite everything, superficial and the compounds of the coating formed have not been clearly identified (only the xcex1-Al2O3 and xcex3-Al2O3 (OH) (bohemite) have been identified by X-ray diffraction).
One process, patented in 1974, was developed in order to compete with coatings on aluminium for architectural purposes. The method allows the aluminium substrate to act as an anode in a potassium silicate solution so that an aluminosilicate coating of olive-grey colour is applied by using a 400 V half-wave rectified DC current. The process takes place by dielectric breakdown of the barrier layer, causing sparks or scintillations visible on the anodic substrate, while Bakovets, Dolgoveseva and Nikoforova postulate three parallel mechanisms during formation of the film, namely electrochemical, plasma oxidation and chemical oxidation mechanisms.
Several modifications have been made to this process, called xe2x80x9csilicodisantxe2x80x9d, comprising the addition of carboxylic acids and of vanadium components in the bath. Ceramic or tetrafluoroethylene resins have also been added to the bath so as to provide the coating with hardness or lubrication properties.
The drawback with such processes is the use, in terms of signal waveform, of a DC current of a few mA at voltages of less than 500 V. This results in the sparking being stopped after a few minutes (most of the deposit is formed in the first few minutes). Such operating conditions make it possible to produce only very small coating thicknesses and thus limit its physical properties.
Other processes describe the use, in electrolytic baths of variable composition, of AC voltages which may exceed 1000 V combined with a DC or AC current.
It should also be noted that the use in certain cases of high voltages with high current densities means that these processes cannot easily be exploited on an industrial scale.
On the other hand, the excellent adhesion to the substrate of this type of coating, the physical and tribological characteristics (high hardness, thermal resistance, electrical resistance, abrasion resistance, corrosion resistance, etc.), the wide variety of aluminosilicate mixtures for coating purposes and the fact that the coating can be performed within narrow surfaces of complex geometry are among the many advantages of this process.
We describe below a different type of microarc process capable of monitoring, imposing and controlling the change in a ceramic coating process in its various phases. A suitable device is used to achieve optimum programming according to various parameters (nature of the alloy or of the metal of the workpieces to be treated, characteristics of the ceramic that it is desired to obtain, etc.).
Three main process phases may be identified, according to the descriptions that may be found in the numerous scientific works and other publications on the subject generally called microarc oxidation and described above.
The workpieces to be treated and the electrodes immersed in the electrolyte constitute a dipole, to which the electrical energy delivered by a generator is applied.
The electrolyte is an aqueous solution, preferably based on demineralized water, and includes at least one oxyacid salt of an alkali metal and a hydroxide of an alkali metal. A wide variety of solutions are described in the numerous publications on the subject.
In the first phase, which lasts from a few seconds to a few minutes depending on the alloys, an insulating layer consisting of a hydroxide is formed, this thin layer being a dielectric.
In the second phase, breakdown of this dielectric layer is observed with microarc activity which increases with the electrical energy applied.
According to the aforementioned parameters, this second phase lasts between 15 and 30 minutes.
The third phase sees the gradual formation of a thick ceramic layer. The composition and the physical properties of the coating change during this formation. The predominant presence of components of the xcex3-Al2O3 (bohemite) and xcex1-Al2O3 (corundum) have been identified by X-ray diffraction.
When a generator delivering DC or AC electrical power with fixed parameters is used, a drop in the current during the process is observed, with differentiation of the voltage versus current curves recorded on the oscilloscope.
This is the result of the process itself, independently of any intervention. In this case, one of the key factors is the dielectric property and the thickness of the ceramic layer formed.
The generators used and described in the various publications deliver either a rectified and/or DC current or a sinusoidal single-phase or three-phase AC current. Series-connected capacitors are interposed, especially to limit the current in the secondary operating circuit and a particular waveform of the current ensues. Also described are AC generators supplied with three-phase current and using the three phases sequentially by means of thyristors or equivalent electronic devices. The waveform of the current is merely the result of the process itself and its shape cannot be modified.
Document U.S. Pat. No. 5,616,229 relates to a process for producing a ceramic coating by this technique, in which the voltage applied to the electrodes is at least 700 V. Below this voltage value, it is not possible to obtain a coherent ceramic, but rather a powder. There is therefore a very high energy consumption, especially when the workpieces to be coated with ceramic have a large area.
An electrolyte process is provided for plasma microarc oxidation for the purpose of obtaining a ceramic coating on the surface of a metal workpiece having semiconducting properties, such as aluminium, titanium, magnesium, hafnium, zirconium and their alloys by a physico-chemical transformation reaction of the treated metal. The porosity of the ceramic layer is decreased, obtaining a very dense and uniformly thick layer over the entire surface of the workpiece. Furthermore, the time to grow the ceramic on the surface of the metal workpiece is reduced, while decreasing the electrical energy consumed.
For this purpose, the process of the invention is characterized in that it consists in:
immersing the metal workpiece to be coated in an electrolytic bath composed of an aqueous solution of an alkali metal hydroxide, such as potassium hydroxide or sodium hydroxide, and of an oxyacid salt of an alkali metal, the metal workpiece forming one of the electrodes; and
applying a signal voltage of overall triangular waveform to the electrodes, that is to say a signal having at least a rising slope and a falling slope, with a form factor that can vary during the process, generating a current which is controlled in its intensity, its waveform and its ratio of positive intensity to negative intensity.
It is thus possible to tailor the voltage waveform to the various steps of the process as well as to the type of alloy and to the various electrolytic bath solutions. This waveform has, in addition and jointly, a frequency-variable parameter. This improves to a great extent the quality of the ceramic coating compared with that obtained by known processes.
Various methods of implementing this process are possible. Thus, the rising and falling slopes of the voltage signal may be approximately symmetric or asymmetric and have angles which vary during the process. It is also possible, during the process, to make the frequency of the triangular signal change between about 100 and 400 Hz.
According to one method of implementing this process, it consists in making the value of the triangular voltage change during the electrolysis between about 300 and 600 Vrms.
The value of the current may also be modified or fixed independently of the voltage. The various parameters (the form factor, the value of the potential, the frequency, the value of the current and the UA/IC ratio) may be modified simultaneously or independently of one another during the process.
According to another of these characteristics, this process consists in separately controlling its waveforms and the electrical power VI values in the positive phase and/or in the negative phase.
An electronic generator of the current source type for implementing this process, comprising a unit for connection to a single-phase or three-phase electrical supply from the mains and a unit for connection to the electrolysis tank, is characterized in that it comprises:
a module for converting the sinusoidal AC signal delivered by the mains into a trapezoidal or sawtooth signal;
a module for modifying the slope and the form factor of the signal;
a module for varying the frequency in various types of cycle; and
a module for managing the electrical energy according to the parameterized energy and the energy used.
Advantageously, this generator includes, at the output, an isolating transformer with series-connected capacitors in the primary or the secondary, in order to filter the DC component so as to prevent the magnetic circuit from saturating, while introducing optimum operating safety in respect of electrical protection, with connection of one of the poles to earth.
According to another characteristic of the invention, this generator is controlled by a PC-type processor used to manage the various parameters during execution of the process.
The conjugate variations in the frequency, voltage and form factor of the signal and of the current play an essential role in the process according to the invention.
The frequency scan conjugate with the variations in the rising slope of our triangular signal makes it possible to excite, in turn, internal regions which are not very active and external regions having high levels of natural excitation.
The steep rising slope makes it possible to induce microarc initiation very actively without a rise in the mean voltage. The gentle slope maintains a constant current for the time needed to carry out the physico-chemical reaction within the plasma. Controlling the falling slope also has repercussions on the negative current. The negative current peak helps to diffuse the Al ions needed for continuity of formation of the ceramic layer in certain phases of the process. It also serves to reduce the residual porosity at the end of the process.
Symmetric slopes of the signal favour a rapid and uniform growth of the ceramic layer and allow the inclusion of additive elements that can be added to the bath, according to the characteristics of the ceramic coating that it is desired to obtain for the optimum use of the workpieces.
This situation is much more effective than that obtained using a sinusoid or a DC current described in the documents of the prior art.
Implementation of the process according to the invention has the following main advantages:
optimum formation of the hydroxide layer;
significant reduction in the roughness of the surface of the layer;
improvement in the adhesion of the coating to the substrate;
progressive growth of the oxide layer;
rapid growth of the ceramic layer of the xcex1-Al2O3 (corundum) type;
capability of effective control and reduction of the residual level of porosity inherent in the basic microarc process itself, and above all with certain alloys;
improvement in the treatment on highly alloyed aluminium grades;
formation of a thicker and denser layer in a time reduced by more than half (50%);
capability of restarting the microarcs in the advanced phase of the treatment in order to obtain greater thicknesses from 40 xcexcm to 300 xcexcm (depending on the alloys) without destruction of the existing layer;
reduction in the energy consumption by more than 50%;
reduction in the thermal power emitted by a factor of 35%;
better homogeneity obtained apart from the current creep paths due to the corners and the contours of the workpieces to be treated; and
possibility of impregnating, under vacuum, by dipping, by spraying or other means, an elastomeric polymer resin or other organic compound.
For an identical compared capacity per dm2 of area treated, it is possible with this new process to use a 50% smaller supply cable cross section.
The energy power of the mains which delivers the electrical supply is reduced in the same proportions along with the fixed meter band charge for the electrical energy consumed.
It follows that there is a major saving and a substantial reduction in the manufacturing cost of the treatment, with increased quality. Knowing that one of the main industrial drawbacks lies in such high electrical energy consumption, the current process already provides a major advantage in this field.
From another standpoint, this same plant is capable, based on a certain value of electrical energy, of doubling the treatment capacity compared with a conventional generator using the sinusoidal signal of the distribution mains. The voltage versus current curves obtained show the fundamental differences in the positive and negative energy peaks obtained by the process. Complete control of these parameters means that it is possible to obtain the desired current values and waveforms at whatever step in the growth of the layer during the treatment.

Oxidizing electrolytic method for obtaining a ceramic coating at the surface of a metal


A decorative light tree with an elongate pipe retained in a three-dimensional spiral shape is disclosed. One end of the elongate pipe is supported on a top end of a central post, and the other end is spirally suspended around the central post. A number of ropes extend at a predetermined angle with respect to the central post and angularly spaced from each other about the central post, binding on the pipe thereby securely retaining the pipe in a three-dimensional spiral shape. A plurality of lightening members are electrically connected in series and arranged inside the hollow inner tube of the elongate pipe in a manner equally spaced from each other. Further, a number of clips clip on the pipe and then the ropes binding on the clips. Each of the ropes has a downward extended section for being fixed in a location by a fixing member.

1. Field of the Invention
The present invention generally relates to a decorative light tree and in particular to a decorative light tree with a three-dimensional spiral shape. The decorative light tree mainly comprises a supporting frame and an elongate pipe supported thereon, incorporating with a number of ropes to form a three-dimensional spiral light tree that is easily assembling.
2. Description of the Prior Art
Decorative light strings are widely used in holidays and festivals, especially in Christmas. A light string usually is composed of a plurality of bulb sockets and an electrical wire for connecting the bulb sockets. Each of the bulb sockets may receive and hold a light bulb thereon. Typically, the light bulbs arranged on the light string are electrically connected in series to form a series circuit loop. An electric plug may be provided at one end of the light string for connection with an external power source. Further, an electric socket may be connected at the other end of the light string to provide an electrical connection to another light string to form an extendible long light string.
Conventionally, the light string is arranged on a tree directly and randomly for decorating purpose. The light string may be tangled on the tree easily and taking off the light string from the tree becomes a terrible task. The light string that has been taken off often tangles together and becomes a chaotic mass, and the sockets or bulbs will easily drop out at this time. It is really a trouble to arrange the light string into a box for storing.
Thus, it is desired to have an improved decorative light tree that can be easily assembled and stored for overcoming the problems discussed above.
Accordingly, a primary object of the present invention is to provide a decorative light tree with three-dimensional spiral construction.
Another object of the present invention is to provide a spiral decorative light tree easy to be assembled and stored.
One more object of the present invention is to provide a decorative light tree including a light string mounted in an elongate pipe and supported by a supporting frame so as to retain the decorative light tree in a three-dimensional spiral shape.
To achieve the above objects, in accordance with the present invention, there is provided a spiral decorative light comprising a supporting frame having an upright central post mounted on a stand. A support ring is attached to a section near the top end of the central post for an elongate pipe attached thereon. A star-shape member is attached to the top end of the central post for the star-shape surround section of the elongate pipe may be attached thereon. The elongate pipe is transparent and with a hollow inner tube formed therein. A plurality of lighting members electrically connected in series and arranged inside the hollow inner tube of the elongate pipe in a manner equally spaced from each other. When spreading the elongate pipe to arrange on the supporting frame, the first end of the elongate pipe is supported on the supporting ring and the free second end is spirally suspended around the central post. A number of ropes extend at a predetermined angle with respect to the central post and angularly spaced from each other about the central post, binding on the pipe thereby securely retaining the pipe in a three-dimensional spiral shape. Further, a number of clips clip on the pipe and then the ropes binding on the clips. Each of the ropes has a downward extended section for being fixed in a location by a fixing member.


A plant for producing semiconductor products is described and has a plurality of production and measuring units in at least one clean room. Provided there is a configuration of processing stations, which has at least one production unit or measuring unit, a production buffer disposed at the latter for the deposition of semiconductor products and a handling device for the automatic delivery and outward transport of the semiconductor products. The processing stations are interconnected via a conveyor system.

The invention relates to a plant for producing semiconductor products.
Plants of this type can be constructed in particular as a plant for processing wafers. These plants contain a large number of production units, with which different production processes can be carried out. The production processes are, in particular, etching processes, wet chemical methods, diffusion processes and different cleaning processes, such as a chemical mechanical polishing (CMP) process. For each of the processes, one or more production units are provided, in which various production steps in a production process are carried out.
In addition, plants of this type contain a large number of measuring units. In the measuring units, the quality of processing of one or more production steps in a production process is checked.
The entire production process is subject to strict cleanness requirements, so that the production units and the measuring units are disposed in a clean room or in a system of clean rooms.
The wafers are supplied to the individual production units by a transport system, in predetermined batch sizes in cassettes. In addition, the outward transport of the cassettes following the processing of the wafers is carried out by the transport system.
The transport system typically has a conveyor system that, for example, is constructed in the form of roller conveyors. Here, the cassettes with the wafers are transported lying on the roller conveyors. Alternatively, the conveyor system can also contain continuous conveyors, suspension conveyors or the like.
Such conveyor systems run linearly through the clean room. In order to ensure the supply of the cassettes with the wafers to the production units, the conveyor systems branch in a suitable way. In this way, a more or less self-contained network of roller conveyors is produced within the clean room.
In order to ensure an adequate supply of wafers to the production units and the measuring units, the transport system additionally has a storage system, which has a specific number of storage units that are distributed suitably over the clean room. Storage units of this type are typically constructed as stockers, which are attached to the conveyor system. Temporarily stored in the stockers in each case is a predefined number of cassettes with wafers. The cassettes with wafers are removed from the stockers in a suitable number as required and, via the conveyor system, are supplied to the production units and the measuring units.
The disadvantage in this case, however, is that storing the cassettes with wafers in the stockers is very time-consuming and costly.
In the publication titled xe2x80x9cWhat Gain from Small Batch Manufacturingxe2x80x9d, by George Horn and William A. Podgorski in xe2x80x9cSemiconductor Fabtechxe2x80x9d, 8th Edition, a plant structure is proposed with which the number of stockers can be reduced.
The transport system described there contains, in addition to a conveyor system, a plurality of local process buffers. In this case, a process buffer is in each case assigned to a plurality of identical production units that in each case process the same production steps in a production process. In addition, storage units with larger storage capacities are provided for a plurality of production units and measuring units supplementing a production process, if corresponding storage capacities are required for such production processes. The production processes include, for example, diffusion processes.
Although, in a plant of this type, stockers are no longer needed, the expenditure of time for storing the cassettes with wafers and removing them again is still considerable. Depending on the processing capacities of the production unit and measuring units, cassettes have to be stored temporarily in a sufficient number in the local process buffers and in the storage units that are used to supply the production units and measuring units of a production process. The cassettes have to be removed from the storage unit again and assigned to the respective production units and measuring units, in order that they can be supplied to the production units and the measuring units via the conveyor system.
It is accordingly an object of the invention to provide a plant for producing semiconductor products which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which provides the simplest, most efficient and cost-effective supply of semiconductor products possible to the individual production and measuring units.
With the foregoing and other objects in view there is provided, in accordance with the invention, a plant for producing semiconductor products such as wafers. The plant includes at least one clean room and a plurality of processing stations disposed in the clean room. Each of the processing stations contains at least one unit selected from the group consisting of production units and measuring units, and a production buffer for storing the semiconductor products. The production buffer is disposed directly at the unit. Each of the processing stations also has a handling device for automatic delivery and outward transport of the semiconductor products to and from the production buffer. A conveyor system interconnects the processing stations.
The plant according to the invention has the configuration of processing stations. Each of the processing stations has at least one production or measuring unit and also a production buffer, disposed on the latter, for the storage of semiconductor products. Also provided is a handling device, which is likewise a constituent part of the processing station. By the handling device, the delivery of the semiconductor products to the production buffer, and the outward transport of the products from the buffer are respectively carried out automatically.
The individual processing stations are interconnected via a conveyor system, via which the semiconductor products are transported between the individual processing stations.
The significant advantage of the plant according to the invention is that the semiconductor products are delivered to production buffers that are disposed directly at the production or the measuring units. From the production buffers, the semiconductor products can therefore be fed directly into the production or measuring units, without any further removal from the storage unit and supply via further transport devices being necessary. Saving transport devices of this type leads to a significant saving in costs. It is particularly advantageous here that, in the process station, no storage systems such as stockers or local process buffers are provided, from which temporarily stored semiconductor products have to be removed, sorted out and supplied to the various production or measuring units. Instead, the semiconductor products on the production buffers can already be assigned to the respective production or measuring units.
Storing the semiconductor products in the production buffers therefore leads to a considerable saving in costs and to simplification of the material flow in the plant, as a result of omitting stockers and local process buffers.
A further advantage can be seen in the fact that the production buffers can be attached directly to the production or measuring units, in a space-saving way, which leads to a low requirement for space for the plant.
Finally, it is advantageous that the transport of the semiconductor products within a processing station can be carried out very quickly and without the use of any personnel. The handling device, which can be constructed in particular as a robot or rack server, automatically supplies the semiconductor products delivered by the conveyor system to the production buffers and also ensures that they are transported away to the conveyor system. In addition, the removal of semiconductor products from a production buffer, subsequent insertion into the production or measuring unit and the subsequent removal are preferably carried out automatically by robots, grippers or the like.
In a particularly advantageous embodiment, the production buffers are constructed in the form of storage racks. Storage racks of this type are cost-effective and, in addition, can be populated with semiconductor products simply and rapidly by the rack server. The storage racks are particularly advantageously disposed immediately in front of or above loading and unloading stations on the respective production or measuring units.
Therefore, not only that an extremely space-saving installation of the production buffer on the respective production or measuring unit is provided, but also that the production buffers are disposed in the immediate vicinity of the loading and unloading station which is used to supply the semiconductor products to the respective production unit and measuring unit. By this configuration, the expenditure on the transport of the semiconductor products between the loading and unloading stations and the storage rack is reduced to a minimum.
Finally, the capacities of the storage racks can advantageously be matched in a straightforward way to the requirement for semiconductor products, by a suitable selection of the size of the storage racks. It is, moreover, advantageous that the semiconductor products can be supplied to the individual storage racks on the Kanban principle. If the filling level of a storage rack falls below a predefined desired value, the storage rack is repopulated with a predefined number of semiconductor products by the rack server.
In accordance with an added feature of the invention, the handling device is a rack server.
In accordance with an additional feature of the invention, the rack server has at least two set-down surfaces. It being possible for the cassettes with the semiconductor products to be supplied to the production buffer to be set down on a first of the set-down surfaces and for the cassettes with the semiconductor products for outward transport from the unit to be set down on a second of the set-down surfaces.
In accordance with another feature of the invention, the rack server has grippers with which the cassettes with the semiconductor products can be supplied to the production buffer and removed from the production buffer.
In accordance with a further feature of the invention, drive-to positions of the unit of a respective one of the processing stations are stored as parameter values in the rack server belonging to the respective processing station.
In accordance with another added feature of the invention, a plurality of the production units and the measuring units for carrying out a production process are disposed in a respective one of the processing stations.
In accordance with another additional feature of the invention, the production units and the measuring units are each formed of at least device selected from the group consisting of machines and staff workplaces.
In accordance with another further feature of the invention, the production buffer has a level control for determining a quantity of semiconductor products stored in the production buffer. The production buffer is refilled as soon as a filling level of the production buffer falls below a predefined desired value.
In accordance with a further added feature of the invention, at least one further production buffer is provided and functions as a transfer station for the semiconductor products for a bi-directional exchange of the semiconductor products with the conveyor system.
In accordance with a concomitant feature of the invention, the further production buffer forming the transfer station has a storage rack with a predefined number of rack compartments. The rack compartments are accessible to the handling device of the processing stations and via the transfer station the semiconductor products are transported from and to the conveyor system.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a plant for producing semiconductor products, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

Plant for producing semiconductor products