Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-03-02
2002-04-09
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S414000, C525S165000, C528S093000, C528S094000
Reexamination Certificate
active
06369133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to crosslinkable aqueous coating compositions which exhibit excellent film-forming and curing characteristics, in terms of processability and safety. The compositions can be used for coating the interior surfaces of cans. Moreover, these crosslinkable aqueous coating compositions are capable of forming films having excellent hardness, and accordingly can be used as primers or finish coats for automotive or industrial applications.
2. Description of the Prior Art
In the past, aqueous coating compositions have been made from the reaction product of a high acid value acrylic resin and a high molecular weight bisphenol A based epoxy resin. These compositions have been used for coating the interior surface of cans. However, recently questions have been raised about bisphenol A, and effort has been directed to coating compositions in which bisphenol A does not elute.
Polyester resins have previously been proposed for use as a base resin in aqueous coatings. Japanese Laid-Open Patent Application No. 61-37811 discloses a thermosetting resin composition prepared by emulsifying a water-soluble polyester resin and an epoxy resin. The composition contains hydrophilic solvent for polyester resin, and exhibits increased dispersion power. However, the film forming ability and processability for coating the interior surface of cans is inadequate. In addition, attempts to improve processability often result in reduction of the stability of an emulsion of this type.
Compositions for coating substrates other than cans have been prepared from polyester resin obtained by using hydrophilic materials such as those having sulfonic acid metal salt, polyalkylene glycol, aliphatic dicarboxylic acid and the like. These compositions exhibit good solubility and dispersibility in water. However, the water resistance of the resulting coating was not satisfactory. Japanese Laid-Open Patent Application No. 57-40525 and No. 61-37811 disclose a technique to raise water dispersion capacity in which a hydrophilic solvent is used in the polyester resin having a content of hydrophilic material reduced. However, the hardness and physical properties of the resulting coating were inadequate.
Aqueous coating compositions have also been proposed containing a polyester resin having hydroxyl group and carboxyl group, an alicyclic epoxy resin and a quaternary ammonium compound. These are described in Japanese Laid-Open Patent Application No. 4-359075. These compositions provided good storage stability and film properties. Continuing effort has been directed toward further improvement of stain resistance and scratch resistance in the final finish. In addition, it has been difficult to provide a good balance between a high hardness in the coating s made using the polyester resin and emulsion stability after dispersion in water.
SUMMARY OF THE INVENTION
The present invention is provides polyester-based aqueous coating compositions which exhibit good emulsion stability after dispersing in water, excellent processability, film forming ability, and cost performance when used in coating the interior surface of cans.
The invention also provides polyester-based aqueous coating compositions which exhibit good emulsion stability after dispersing in water, excellent curability, film forming ability and film hardness when used as either an undercoating or finish coating on automobile bodies or industrial products.
Specifically, the present invention provides a polyester-based aqueous coating composition comprising a mixture of carboxyl-functional polyester resin (A) which is a condensation product of at least one polyalcohol of which ethylene glycol comprises at least about 60 mol % based on the total polyalcohol component and at least one polybasic acid of which polyvalent aromatic carboxylic acid comprises at least about 80 mol % based on the total polybasic acid component, and which has a number average molecular weight of about from 1,000 to 20,000 and an acid value of about from 10 to 170 mgKOH/g;
DETAILED DESCRIPTION OF THE INVENTION
The carboxyl-functional polyester resin (A) used in the present invention is a condensation product of a polyalcohol component comprising at least about 60 mol ethylene glycol, based on the total polyalcohol components, and a polybasic acid component comprising at least about 80 mol %, based on the total polybasic acid components, of a polyvalent aromatic carboxylic acid, and contains carboxyl groups in the resin. The polyester resin has a number average molecular weight of about from 1,000 to 20,000 and an acid value of about form 10 to 170 mgKOH/g.
The polyester resin can be prepared by any of the following methods (1), (2), or (3). Method (1) involves esterifying polybasic acid components and polyalcohol components using an excess of the former over the latter. Method (2) involves reacting an acid anhydride with a polyester polyol which is obtained by reaction of polybasic acid components and polyalcohol components with a molar excess of the polyalcohol components. Method (3) involves a first step of preparing a hydroxyl-functional polyester by alcoholysis of a high molecular weight polyester such as polyethylene terephthalate or polybutylene terephthalate; then esterifying the resulting hydroxyl-functional polyester with polybasic acid components, and if necessary, polyalcohol components, under conditions in which the polybasic acid components are in molar over the hydroxyl-functional components.
Examples of polybasic acids which can be used in the present invention, mainly in the preparation of the polyester resin, include dicarboxylic acids such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, hexahydroisophthalic acid, hexahydroterephthalic acid, 4-carbonylhexahydrophthalic acid, 4-carbonylhexahydrophthalic anhydride, 3-carbonyltetrahydrophthalic acid, 3-carbonyltetrahydrophthalic anhydride, succinic acid, succinic anhydride, fumaric acid, adipic acid, azelaic acid, sebacic acid, maleic acid, maleic anhydride and lower alkyl esters of these dicarboxylic acids. In addition to these dicarboxylic acids, monobasic acids such as benzoic acid, crotonic acid, p-t-butyl benzoic acid and other various fatty acids can be used. Further, trivalent or higher polycarboxylic acids such as trimellitic acid, trimellitic anhydride, methylcyclohexene tri-carboxylic acid, pyromellitic acid, pyromellitic anhydride and butane tricarboxylic acid can also be used. Among these polybasic acids, it is important that the polyvalent aromatic carboxylic acid comprise at least about 80 mol %, preferably more than 90 mol %, based on the total polybasic acid components. This high concentration of the polyvalent aromatic carboxylic acid has been found to contribute good hydrolysis stability resistance.
Examples of the polyalcohols which can be used in the present invention, mainly in the preparation of the polyester resin, include dihydric alcohols including aliphatic glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,2 butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 2-methylpropane diol, 3-methylpentane diol, 1,4-hexane diol, 1,6-hexane diol, 1,5-pentane diol, 1, 9-nonane diol, diethyl pentane diol, and 2-butyl ethyl propanediol; alicyclic glycols such as cyclohexane dimethanol and spiro glycol; aromatic glycols such as ethylene oxide or propylene oxide addition product of bisphenol compound; polyether polyol such as polyethylene glycol, polypropylene glycol, polybutylene glycol; polyurethane polyol obtained by the reaction of glycol and polyisocyanate compound. In addition to these dihydric alcohols, trivalent or higher polyhydric alcohol such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and the like can be used. These polyalcohols can be used singly or as a mixture of two or more. Further, a glycol including ester functionality in the molec
Aylward D.
Huntley & Associates
Kansai Paint Co. Ltd.
Moore Margaret G.
LandOfFree
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