Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-01-29
2001-01-16
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S543000, C524S507000, C524S591000, C524S839000, C524S840000, C525S066000, C525S123000, C525S455000
Reexamination Certificate
active
06174953
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an aqueous (meth)acrylate copolymer composition and process for preparation of such composition and the use of such composition in water-borne coatings with improved properties. In particular, this invention is directed to a (meth)acrylate copolymer composition with a hydroxy value above 200, acid value below 50 and weight average molecular weight less than 20,000 comprising a block or graft copolymer prepared directly in water, solvent or water/solvent blend in the presence of a water-soluble macromonomer substantially free of any acid groups so that the final emulsion has a high solids content at low viscosity. This invention also involves coating compositions based on such aqueous copolymer compositions.
Automobiles and trucks receive exterior finishes for several reasons. First, such finishes provide barrier protection against corrosion. Second, consumers prefer an exterior having an attractive aesthetic finish, including high gloss and excellent DOI (distinctness of image). A typical automobile steel panel or substrate has several layers of finishes or coatings. The substrate is typically first coated with an inorganic rust-proofing zinc or iron phosphate layer over which is provided a primer which can be an electrocoated primer or a repair primer. Optionally, a primer surfacer can be applied to provide for better appearance and/or improved adhesion. A pigmented basecoat or colorcoat is next applied over the primer. A typical basecoat or colorcoat comprises a pigment, which may include metallic flakes in the case of a metallic finish. In order to protect and preserve the aesthetic qualities of the finish on the vehicle, it is well known to provide a clear (unpigmented) topcoat over the colored (pigmented) basecoat, so that the basecoat remains unaffected even on prolonged exposure to the environment or weathering. Coating compositions comprise one or more film-forming copolymers and for topcoats acrylic copolymer are preferred. Most commonly, acrylic polymers are linear in structure and cure upon application by reacting with crosslinking agents. The use of non-linear copolymers for coating compositions has also been disclosed, but the use of such polymers, however, have so far found only limited use in the automotive finishes area. See U.S. Pat. No. 5,010,140.
The evolution of environmental regulations has led to the need for products with lower volatile organic content (VOC). However, it is far from trivial to develop aqueous products with desirable properties for automotive finishes. As mentioned above, such finishes must be high performance in terms of aesthetic qualities and durability. Water dispersible polymers are well known in the art and have been used to form waterbased coating compositions, pigment dispersions, adhesives and the like.
The use of cobalt chelates in the preparation of macromonomers for aqueous copolymer dispersions is limited so far to graft copolymers in which either graft or backbone contain ionizable groups in the form of acid or amine. Most of the applications also teach the preparation of such graft copolymers first in a solvent before inverting into a water dispersion.
SUMMARY OF THE INVENTION
We have now found that aqueous graft or block copolymers can be prepared in water, solvent, or a water/solvent blend using a water-soluble macromonomer substantially free of any acid groups to produce coating compositions with a high solids content at a low viscosity. Dispersions and solutions containing such copolymers show excellent compatibility with polyisocyanates in water-borne two-package formulations.
The aqueous graft or block copolymers comprise 20 to 98%, preferably 50 to 85%, of a water-soluble macromonomer with a weight average molecular weight of below 6000, preferably below 2,000, a hydroxyl value of more than 300, preferably more than 400, and containing less than 10% of an acid functional and/or amine functional unsaturated monomer. The remaining 2-80%, preferably 15-50%, of the copolymer comprises a backbone (in the graft copolymer embodiment) or a B block (in the block copolymer embodiment). The graft or block copolymer has a weight average molecular weight of less than 20,000, preferably between 1500 and 8000, a hydroxy value of at least 200, an acid value of less than 50 and preferably no more than 5% of an ionizable monomer.
The water-soluble macromonomer is preferably prepared using a free radical initiator in water or solvent or blend with a Co(II) or Co(III) chelate chain transfer agent.
DETAILED DESCRIPTION
The backbone or the B block, as the case may be, of the graft or block copolymer has a lower OH value relative to the side chains (or the A block) and can contain polymerized ethylenically unsaturated acid or amine monomers or salts thereof. The backbone or B block can contain polymerized monomers which are preferably methacrylates, but which can contain up to 500% of acrylates or vinyl aromatics. Such monomers can comprise alkylmethacrylates and acrylates, cycloaliphatic methacrylates and acrylates and aryl methacrylates and acrylates as listed hereinafter. It can contain up to 50% by weight based on the weight of the copolymer, of polymerized ethylenially unsaturated non-hydrophobic monomers which may contain reactive functional groups. Other vinyl monomers can be incorporated into the backbone or B block, e.g., ethylenically unsaturated sulfonic, sulfinic, phosphoric or phosphonic acid and esters thereof also can be used such as styrene sulfonic acid, acrylamido methyl propane sulfonic acid, vinyl phosphonic acid and its esters and the like.
In one embodiment, the graft copolymer emulsion contains 50 to 85% of poly 2-hydroxy ethyl methacrylate macromonomer and 15 to 50% of backbone (or B block) monomers essentially being polymethacrylates. Examples of methacrylate monomers are alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate 2-ethyl hexyl methacrylate, nonyl methacrylate, lauryl methacrylate, stearyl methacrylate and the like. Examples of other methacrylates can be used such as trimethyl cyclohexyl methacrylate, isobornyl methacrylate, benzyl methacrylate and the like.
Ethylenically unsaturated monomers containing hydroxy functionality include hydroxy alkyl acrylates and hydroxy alkyl methacrylates, wherein the alkyl has 1 to 12 carbon atoms. Suitable monomers include 2-hydroxy ethyl acrylate, 2-hydroxy propyl acrylate, 4-hydroxy butyl acrylate, 2-hydroxy ethyl methacrylate, 2-hydroxy propyl methacrylate, 4-hydroxy butyl methacrylate, and the like, and mixtures thereof. Reactive functionality can also be obtained from monomer precursors, for example, the epoxy group of a glycidyl methacrylate unit in a polymer. Such an epoxy group can be converted, in a post condensation reaction with water or a small amount of acid, to a hydroxy group, or with ammonia and/or a primary amine to give a hydroxy amine. Suitable other olefinically unsaturated comonomers include: acrylamide and methacrylamide and derivatives as alkoxy methyl (meth)acrylamide monomers, such as N-isobutoxymethyl methacrylamide and N-methylol methacrylamide; maleic, itaconic and maleic anhydride and its half and diesters; vinyl aromatics such as styrene and vinyltoluene; polyethylene glycol monoacrylates and monomethacrylates; aminofunctional (meth)acrylates as, e.g., diethylaminoethylmethacrylate and t-butylaminoethylmethacrylate; glycidyl functional (meth)acrylates as glycidylmethacrylate. Other functional monomers as acrylonitrile, acrolein, allyl methacrylate, aceto acetoxyethyl methacrylate, methylacryl amidoglycolate methylether, ethylene ureaethyl methacrylate, 2-acrylamide-2methyl propanesulfonic acid, trialkoxy silyl propyl methacrylate, reaction products of mono epoxyesters or monoepoxy ethers with alpha-beta unsaturated acids and reaction products of glycidyl (meth)acrylate with mono functional acids up to 22 carbon atoms can be used. The above monomers also can be used in the backbone or B block of the copolymer. They also can be used in the macromonomer
E. I. Du Pont de Nemours and Company
Niland Patrick D.
Tessari Joseph A.
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