Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-29
2002-02-05
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06344503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preparing low VOC, water-based polyester-acrylic graft emulsion copolymer resin compositions.
2. Discussion of the Prior Art
Protective surface coatings are organic compositions applied to substrates to form continuous films which are cured or otherwise hardened to provide protection as well as a decorative appearance for the substrate. Protective surface coatings ordinarily comprise an organic polymeric binder, pigments, inert fillers and other additives, where the polymeric binder acts as a fluid vehicle for the pigments and imparts rheological properties to the fluid paint coating. Upon curing, the polymeric binder hardens and functions as a binder for the pigments and provides adhesion of the dried paint film to the substrate.
Increasingly stringent policies and regulations for the protection of the environment have increased the need for protective coatings having very low contents of volatile organic components, that is, having very low VOCs (“volatile organic contents”). For example, polyester-acrylic graft copolymeric binders are utilized in coating compositions of various types. Since the polyester-acrylic-graft copolymeric resinous material, typically employed as the binder in such compositions, often makes up a substantial part of the composition as a whole, the volatile organic solvent content of the resin utilized as the binder is quite important with respect to achieving a low VOC for the composition as a whole.
However, it has been difficult to achieve low VOC in water-borne systems employing solution polymerized acrylic resins, for example, in systems employing a combination of acrylic and polyester resins. The removal of organic solvents from resinous compositions containing solution polymerized acrylic copolymers in attempting to achieve a low VOC generally is accompanied by the significant drawback of causing the viscosity of the resin compositions to increase to an undesirable extent and may even result in gelation.
Craun, U.S. Pat. No. 5,464,885, which issued on Nov. 7, 1995, discloses that high quality aqueous dispersed epoxy coatings can be produced with no organic solvent by esterifying a low molecular weight epoxy resin with low molecular weight carboxyl functional polyester to produce a carboxyl functional low molecular weight epoxy-ester, mixing the epoxy ester with ethylenic monomers and dispersing the mixture in water, and then copolymerizing the ethylenically unsaturated monomers to produce an emulsion polymer useful as a polymeric binder. The aqueous emulsion dispersions of the epoxy-ester addition copolymer are prepared and maintained dispersed in water by ammonia neutralization of the epoxy-ester carboxyl groups without the use of surfactants or any volatile organic solvents. Copolymerization of the ethylenic monomers produces a stable small particle size polymeric dispersion.
Maska, et al., U.S. Pat. No. 4,927,875, which issued on May 22, 1990, discloses an aqueous composition of a water-borne resin comprising a polyester polymer and a solution polymerized acrylic copolymer which has been at least partially neutralized by a base. The water-borne resin comprises: (I) from 10 to 50 percent by weight of a polyester polymer, and (II) from 90 to 50 percent by weight of a solution polymerized acrylic copolymer. The aqueous composition has an organic solvent content of less than or equal to 15 percent by weight and a viscosity at 25 degrees Celsius (° C.) of less than or equal to 5,000 centipoise when the total solids content of the aqueous composition is greater than or equal to 40 percent by weight. The aqueous composition disclosed is prepared by a method which comprises: (A) addition polymerizing in solution (i.e., solution polymerizing in an organic medium) a first monomer composition containing from 1 percent to 15 percent by weight of an epoxy-functional vinyl monomer and from 99 percent to 85 percent by weight of at least one other copolymerizable vinyl monomer in the presence of a polyester polymer having an acid value on solids of from 10 to 85 milligrams KOH/gram (mg KOH/g) and a weight average molecular weight of from 500 to 2,000 until the epoxy functionality of the epoxy-functional vinyl monomer has been essentially completely reacted, to form a first product (1), and thereafter, (B) addition polymerizing in the aforesaid first product (1), a second monomer composition containing from 3 to 50 percent by weight, based on the total weight of vinyl monomers from parts (A) and (B), of an ethylenically unsaturated carboxylic acid and at least one other copolymerizable vinyl monomer different from the epoxy-functional vinyl monomer, to form a second product (2), and thereafter, (C) dispersing the aforesaid product (2) in water utilizing a basic neutralizing agent.
Falk, U.S. Pat. No. 4,252,704, which issued on Feb. 24, 1981, discloses graft polymers that are prepared by graft polymerizing one or more vinyl monomers in the presence of a suitably cross-linked, aliphatic polyester elastomer and that are high impact thermoplastic resins possessing a useful balance of physical properties. The vinyl monomers that are suitable for the purposes of preparing the disclosed graft polymers include vinyl aromatic monomers and acrylic monomers. The cross-linked polyester elastomers that are suitable for the purposes of this invention are linear, high molecular weight, aliphatic, polyester rubbers which have been converted to a latex, and then cross-linked. The latex may be employed in blending directly, or coagulated to form free-flowing rubber particles. The elastomeric polyesters may be described as copolymers of aliphatic dicarboxylic acids and glycols wherein from about 0 to about 20% of the glycol and/or the dicarboxylic acid is ethylenically unsaturated. In preparing the cross-linked polyester latex, the polyester is first dissolved in a suitable organic solvent. The organic solvent must be immiscible with water, and be sufficiently volatile to be readily stripped from an aqueous emulsion. An emulsion of the polyester is then prepared by mixing the solution of polyester with approximately an equal volume of water containing a surfactant. The solvent is then stripped from the emulsion by heating the mixture and distilling the solvent. The resulting solvent-free latex comprises finely dispersed, uncross-linked polyester in aqueous emulsion. Cross-linking of the polyester in latex form is accomplished by adding a suitable peroxide catalyst such as benzoyl peroxide, lauryl peroxide or the like, and heating the mixture to effect decomposition of the peroxide and cross-linking of the polyester. The graft polymer is prepared by polymerizing the vinyl monomer in the presence of the cross-linked, polyester elastomer substrate. The polymerization may be accomplished by a variety of conventional graft polymerization techniques including latex and suspension processes. The resulting graft polymer composition will comprise from 90 to 30 wt. % of the superstrate vinyl monomer component polymerized in the presence of from 10 to 70 wt. % of the substrate cross-linked, polyester elastomer.
OBJECTS OF THE INVENTION
It is therefore a general object of the present invention to provide an improved process for producing polyester-acrylic graft copolymers which overcomes the aforesaid problems of prior art methods.
More particularly, it is an object of the present invention to provide an improved aforesaid process that affords the production of polyester-acrylic graft copolymers having low VOCs.
It is a related object of the present invention to provide an improved aforesaid process that involves production of the graft copolymer by emulsion polymerization in water.
Other objects and advantages will become apparent upon reading the following detailed description and appended claims.
SUMMARY OF THE INVENTION
The objects are achieved by the process of the present invention for producing a water-based graft copolymer of a carboxyl functional polyester and an acrylic monomer co
Curry-Nkansah Maria
Desai Ajaykumar
McKee Catherine T.
Nkansah Asare
BP Corporation North America Inc.
Henes James R.
Michl Paul R.
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