Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-12-02
2002-05-21
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S208000, C525S176000, C525S438000, C525S528000
Reexamination Certificate
active
06391970
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to clear coat systems based on acid epoxy-isocyanate chemistry wherein one or more of the components can be modified such that the system is adapted for different applications.
More particularly, the clear coat systems exhibit dual cross links of ester and urethane which give the system enhanced advantages over clear coats exhibiting only one type of cross linking.
BACKGROUND OF THE INVENTION
Clear coats have become increasingly popular as coatings for painted articles such as automobiles. Not only do clear coats generally have excellent gloss, but they also generally offer enhanced resistance to etching and scratching. While clear coats are desirable, those employing polyisocyanates have presented certain problems in that they are sensitive to moisture. In an attempt to address many of the problems associated with employing polyisocyanates in clear coat systems, U.S. Pat. No. 4,650,718 discloses a cross-linkable coating composition based on polyepoxides and polyacid curing agents. While the resulting compositions are purported to produce cured coatings with excellent adhesion, gloss and the ability to reflect images, they generally fail to provide good humidity and mar resistance. In an attempt to address these concerns, U.S Pat. No. 4,927,868 discloses a curable, liquid coating composition containing an organic solvent and a resinous binder comprising a polyepoxide and a copolymer of an alpha-olefin or cyclolefin and an olefinically unsaturated monoanhydride which may include a partial ester thereof and preferably a polyacid.
In contrast to the present invention, it appears that the compositions of the above-mentioned patents exhibit significant secondary hydroxyl formation during the acid-epoxy reaction which, in turn, may result in the perceived humidity failures. The final thermoset polymer, i.e. clear coat composition, formed under the present invention will have both ester and urethane cross links which will synergistically enhance the properties of each other. As a result, higher equivalent weight epoxides, isocyanates and acid cross linkers can be utilized under the present invention which will generally result in significant cost savings.
Thus, the present invention fulfills a need in the art for coating compositions and, more particularly, clear coat systems which have good mar and etch resistance, a relatively high microhardness, good shelf life stability and are relatively inexpensive to produce.
SUMMARY OF THE INVENTION
The present invention provides for resinous binders useful in clear coat compositions comprising: a) a polyepoxide; b) a polyacid containing at least two carboxyl groups per molecule; and c) a polyisocyanate, wherein said resinous binder exhibits at least ester or urethane cross-linking. The invention further relates to clear coat compositions including an organic solvent and a resinous binder comprising: a) the reaction product of a polyepoxide and a polyacid; and b) an isocyanate reacted with the product of a), wherein said resinous binder exhibits both ester and urethane cross-linking. The invention also provides a process for applying a clear coat composition to a substrate wherein the dual cross-linkable system described above is in the clear coat.
The resinous binders of the clear coat compositions of the present invention are preferably obtained by the reaction of an epoxide with a polyacid to obtain a hydroxy ester which is subsequently reacted with an isocyanate in accordance with the following reaction mechanism:
The resulting resinous binder thereby allows for extensive cross-linking including at least ester or urethane cross-linking sites, and preferably both.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The essential components of the dual cross-linkable compositions of the present invention are the reaction product of a polyepoxide and a polyacid, and the polyisocyanate.
Among the polyepoxides which can be used are epoxy-containing acrylic polymers such as copolymers of an ethylenically unsaturated monomer having at least one epoxy group and at least one ethylenically unsaturated monomer which is free from epoxy groups. In general, ethylenically unsaturated monomers containing epoxy groups are those including 1,2 epoxy groups such as glycidyl acrylates, glycidyl methacrylates and alkyl glycidyl ethers, among others.
Examples of ethylenically unsaturated monomers which do not contain epoxy groups are alkyl esters of acrylic and methacrylic acid containing from 1 to 20 atoms in the alkyl group. Specific examples of these acrylates and methacrylates are methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate.
Examples of other copolymerizable ethylenically unsaturated monomers are vinyl aromatic compounds such as styrene and vinyl toluene; nitrites such as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl acetate. Acid group-containing copolymerizable ethylenically unsaturated monomers such as acrylic and methacrylic acid are preferably not used because of the possible reactivity of the epoxy and acid group.
The epoxy group-containing ethylenically unsaturated monomer(s) is preferably used in amounts of from about 5.0 to 60.0, more preferably from 20.0 to 50.0 percent by weight of the total monomers used in preparing the epoxy-containing acrylic polymer. Of the remaining polymerizable ethylenically unsaturated monomers, preferably from 95.0 to 40.0 percent, more preferably from 80.0 to 50.0 percent by weight of the total monomers are the alkyl esters of acrylic and methacrylic acid.
In preparing the epoxy-containing acrylic polymer, the epoxide functional monomers and the other ethylenically unsaturated monomers can be mixed and reacted by conventional free radical initiated organic solution polymerization.
The epoxy-containing acrylic polymer typically has a number average molecular weight between about 1,000 and 30,000, preferably 2,000 to 20,000, more preferably 2,000 to 10,000 with an epoxy equivalent weight of typically from 50-2,000, preferably 100-1,000, and more preferably 200-600. The molecular weight is determined by gel permeation chromatography using a polystyrene standard.
In determining molecular weights in this fashion, it is not the actual molecular weights which are measured but an indication of the molecular weight as compared to polystyrene. The values which are obtained are commonly referred to as polystyrene numbers. However, for the purposes of this invention, they are referred to as molecular weights.
The epoxy condensation polymers which are useful are polyepoxides, i.e., those having a 1,2-epoxy equivalency greater than 1 and up to about 3.0. Examples of such epoxides are polyglycidyl ethers of polyhydric phenols and of aliphatic alcohols. These polyepoxides can be produced by etherification of the polyhydric phenol or aliphatic alcohol with an epihalohydrin such as epichlorohydrin in the presence of alkali.
Examples of suitable polyphenols are 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 1,1-bis(4-hydroxyphenyl)ethane and 2-methyl-1, 1-bis(4-hydroxyphenyl)propane. Examples of suitable aliphatic alcohols are ethylene glycol, diethylene glycol, 1,2-propylene glycol and 1,4-butylene glycol. Also, cycloaliphatic polyols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-bis(hydroxymethyl)cyclohexane and hydrogenated bisphenol A can also be used.
Besides the epoxy-containing polymers described above, certain polyepoxide monomers and oligomers can also be used. Examples of these materials are those containing the cyclohexane oxide moiety. These polyepoxides are of relatively low molecular weight and of relatively high reactivity, thus, enabling the formation of high solids coating compositions with excellent cure response. The polyepoxides should have an average 1,2-epoxy equivalency of greater than one. The preferred polyepoxides are diepoxides, that is, having a 1,2-epoxy equivalency of two.
Various
Gupta Manoj K.
Ramesh Swaminathan
BASF Corporation
Sellers Robert E. L.
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