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...
Patent
1996-11-14
1999-08-10
Cain, Edward J.
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...
C08L 5100
Patent
active
059360267
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an improved aqueous composition for coating a variety of substrates. In particular, this invention is directed to a coating composition comprising a graft copolymer, referred to as a self-stabilized latex, having neutralized carboxylic-acid or amine functionality in a graft segment thereof which stabilizes the aqueous graft copolymer dispersion. The invention involves preparing the graft copolymer in an aqueous carrier.
BACKGROUND OF THE INVENTION
Automobiles and trucks receive exterior finishes for several well known reasons. First, such finishes provide barrier protection against corrosion. Second, consumers prefer an exterior finish 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 polymers. Most commonly, acrylic polymers are linear in structure and cure, upon application, by reaction with crosslinking agents. However, the use of non-linear graft copolymers has been disclosed. For example, U.S. Pat. No. 4,801,653 to Das et al. describes the use of hydroxy functional graft copolymers. Das et al. disclose grafting by a condensation reaction between epoxy groups of a glycidyl ester, contained in an acrylic polymer, and carboxy groups on at least a portion of vinyl monomers which are polymerized in the presence of the acrylic polymer.
In preparing graft polymers in general, various living polymerization methods have been disclosed for obtaining functional ended polymers by selective termination of living ends. Such functionally ended polymers may subsequently be attached to another polymer, that is, as so-called macromonomer "arms" on a polymeric backbone to form a comb or graft copolymer. Webster, in "Living Polymerization Methods,"251 SCIENCE 887 (Feb. 22, 1991) generally discloses living polymerization methods for preparing architectural forms of polymers, including graft and comb copolymers.
U.S. Pat. No. 4,680,352 to Janowicz et al., U.S. Pat. No. 4,722,984 to Janowicz, and PCT WO 87/03605 disclose the use of cobalt (Co) chelates as chain transfer agents in free radical polymerization. The latter patents disclose that macromonomers prepared by cobalt chain transfer can be polymerized to produce graft copolymers which are useful in coating and molding resins, including high solid finishes and aqueous or solvent based finishes. The use of such polymers, however, have so far found only limited use in the automotive finishes area, as for example disclosed in U.S. Pat. No. 5,010,140.
The present invention relates to aqueous coating compositions. 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. Graft copolymers containing carboxyl groups and the preparation of these polymers is
REFERENCES:
patent: 5231131 (1993-07-01), Chu et al.
Bruylants Paul
Fryd Michael
Huybrechts Jozef
Stranimaier Kerstin
Cain Edward J.
Costello James A.
Deshmukh Sudhir G.
E. I. Du Pont de Nemours and Company
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