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
2002-06-04
2004-03-30
Sellers, Robert (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...
C525S423000, C525S438000
Reexamination Certificate
active
06713560
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of ammonia and organic amines as catalysts in epoxy hybrid powder coatings.
TECHNICAL BACKGROUND
Powder coatings are dry polymer powders that are coated onto a substrate and then heated to coalesce the particles and create the final coating. The technical demands on such coatings are significant: the powder must be able to be applied and cured to give a smooth coating which is strong and flexible. The binder resin must possess a rapid cure rate, at as low a temperature as possible, to allow high production throughput and minimum energy expenditure. Additionally, the powder must be non-tacky at temperatures up to 40° C. so that the particles do not clump on prolonged storage before use.
Resin curing is often catalyzed by the addition of quaternary ammonium salt or phosphonium salt catalysts. In order to be effective, these salts must be compatible with the resin and have sufficient mobility in the resin melt to diffuse to and contact the reactive groups of the resin polymer components in order to catalyze the reaction. These catalysts introduce mobile ions into the resin coating that may compromise hydrolytic and electrochemical stability. Moreover, the act of blending the catalyst into the resin composition, typically by melt extrusion, can induce premature curing of the composition. Finally, a significant amount of catalyst by weight is required in the formulation due to the typically high molecular weight of the catalyst.
A significant portion of the powder coatings market is represented by carboxyl-functional polymer-epoxy hybrids, which are combinations of epoxy resins with carboxylic acid-ended oligomers, such as polyester oligomers. The use of quaternary ammonium or amine salts or phosphonium salts as catalysts for polyester-epoxy films is well known. These materials are generally added in either melt-blending or dry compounding before application to the article to be coated. However, generally larger amounts of amine or quaternary ammonium salts must be added to allow for full curing, resulting in excess materials to be used, which subsequently stay in the cured film as a potential impurity.
GB 1,474,140 discloses the use of nitrogenous bases, or thermally decomposable salts thereof, to catalyze the reaction of an oligomeric ester or a polyester containing free hydroxyl groups but substantially no free carboxyl groups with a compound containing at least two epoxy groups.
Japanese Patent Application 50-85632 describes a heat curable coating composition comprising a polyepoxy compound and a polycarboxy compound, at least one of which is a film-forming polymer, or a film-forming polymeric compound having both epoxy groups and carboxyl groups, in combination with ammonia or an organic amine; wherein at least some of the carboxyl groups are included in the form of a salt with the ammonia or organic amine. The compositions are prepared by conventional melt mixing of the components of the heat curable composition at 80-150° C., followed by pulverizing the composition to a particle size of not more than about 200 &mgr;m.
SUMMARY OF THE INVENTION
The present invention relates to a process for preparing heat curable coating compositions, comprising exposing a powder comprising a carboxyl-functional polymer and a polyepoxy compound to an amine chosen from the group consisting of organic amines and ammonia under mild conditions.
The present invention also relates to the products made by the process described herein.
DETAILS OF THE INVENTION
It has been found that the rate of crosslinking in carboxyl-functional polymer-epoxy blends for powder coating can be greatly increased by catalytically reacting the carboxyl-functional polymer carboxylic acid end groups with ammonia or organic amines. Surprisingly, it has also been found that this reaction requires no additional compounding and may be carried out with pre-compounded epoxy-carboxyl-functional polymer powder by simply exposing the powder to ammonia or an organic amine, or mixtures thereof.
This exposure is done at a relatively mild temperature, i.e. a temperature that is not so high that it could induce premature cross-linking of the components of the coating composition. Temperatures between −30° C. and +50° C., and preferably between −10° C. and +10° C., are suitable for providing such mild conditions.
Suitable carboxyl-functional polymers for use in the process of this invention include carboxyl-functional polyester resins, carboxyl-functional polyacrylate resins, carboxyl-functional polymethacrylate resins, carboxyl-functional polyamide resins, carboxyl-functional polyimide resins and carboxyl-functional polyolefin resins. Preferred carboxyl-functional polymers are carboxylic-functional polyesters.
Suitable carboxyl functional polyester resins can be obtained by condensation polymerization of a dicarboxyl- or polycarboxyl-containing monomer with a dihydroxy or polyhydroxy monomer such that the carboxylic groups are in excess. Examples of suitable carboxyl-containing monomers are terephthalic acid, isophthalic acid, trimellitic acid, adipic acid, sebacic acid, maleic acid, and the like. Useful hydroxy compounds include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, bis(hydroxyethyl)terephthalate, trimethylolpropane, glycerol, pentaerythritol, and the like.
Suitable carboxyl-functional acrylic resins can be obtained by polymerizing or copolymerizing a carboxyl-containing monomer such as acrylic acid, methacrylic acid or the like. Examples of monomers capable of copolymerizing with monomers such as acrylic acid, methacrylic acid and the like include acrylic acid esters, methacrylic acid esters, and other ethylene-based unsaturated monomers such as acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate and the like.
Suitable carboxyl-functional polyolefin resins can be obtained by copolymerizing a carboxyl-containing monomer such as acrylic acid, methacrylic, or the like with an ethylenic monomer capable of copolymerization such as ethylene, propylene, butene, butadiene, chloroprene, vinyl chloride, styrene and the like.
Suitable carboxyl-functional polyamide resins can be obtained by condensation polymerization of a dicarboxyl- or polycarboxyl-containing monomer with a diamino or polyamino monomer such that the carboxylic groups are in excess. Examples of carboxyl-containing monomers are terephthalic acid, isophthalic acid, trimellitic acid, adipic acid, sebacic acid, maleic acid, and the like. Useful amino monomers include ethylenediamine, hexamethylenediamine, dodecamethylenediamine, xylylenediamine, m-phenylenediamine, p-phenylenediamine, and the like.
Suitable carboxyl-functional polyimide resins can be obtained by condensation polymerization of a biscarboxylic anhydride-containing monomer with a diamino or polyamino monomer such that the carboxylic groups are in excess. This can be accomplished either by using the bisanhydride monomer in excess or by effecting only partial condensation such that free carboxyl groups adjacent to amidized carboxyls remain un-imidized. Examples of carboxylic anhydride-containing monomers include pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride and biphenyl tetracarboxylic dianhydride. Useful amino monomers include ethylenediamine, hexamethylenediamine, dodecamethylenediamine, xylylenediamine, m-phenylenediamine, p-phenylenediamine, and the like.
Suitable polyepoxy compounds include epoxy compounds or resins having two or more glycidyl groups in one molecule. Such compounds, often used as curing agents, are a reaction product of a phenolic compound such as bisphenol A, phenol novolac, or the like with epichlorohydrin; a reaction product of a cresolic compound such as cresol novolac or the like with epichlorohydrin; a glycidyl ether obtained from a reaction of an alcoholic compound such as ethylene glycol, propylene glycol, 1,4-butanediol, polyethylene glycol, polypropyl
E. I. du Pont de Nemours and Company
Sellers Robert
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