Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-14
2001-12-25
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S411000, C523S412000, C523S414000, C523S415000, C523S423000, C525S065000
Reexamination Certificate
active
06333367
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an electrodeposition coating composition, more particularly to a cationic electrodeposition coating composition which is free of lead and capable of forming a coating film showing good properties in both corrosion resistance and weather resistance.
(2) Description of Background Art
The electrodeposition coating method makes it possible to form a coating film showing good properties in durability, corrosion resistance, and the like, and has widely been used in an automobile, domestic article, other apparatus, etc. Taking the above advantages of the electrodeposition coating method, demand on an electrodeposition coating composition for use in one coating finish has recently been increased.
As the electrodeposition coating composition for use in one coating finish, an electrodeposition coating composition prepared by adding an acrylic resin to an epoxy resin, particularly a bisphenol type epoxy resin, is known in the art. However, the above electrodeposition coating composition has such drawbacks that a decreased epoxy resin content makes it impossible to obtain a satisfactory corrosion resistance, and an increased epoxy resin content so as to increase corrosion resistance makes it impossible to obtain a satisfactory weather resistance, resulting in making it impossible to obtain a satisfactory properties in both corrosion resistance and weather resistance.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cationic electrodeposition coating composition which has a good coating bath stability and is capable of forming a coating film showing good properties in corrosion resistance, weather resistance and finish appearance.
That is, the present invention provides a cationic electrodeposition coating composition containing (A) an acrylic resin obtained by subjecting a mixture of 10 to 60% by weight of a hydroxyl group-containing acrylic monomer (a), 5 to 35% by weight of an amino group-containing acrylic monomer (b), 5 to 55% by weight of an aromatic vinyl monomer (c) and optionally another acrylic monomer (d) to a radical copolymerization reaction; (B) a hydroxyl group-containing acrylic resin-modified epoxy resin obtained by reacting 65 to 95% by weight of a resin mixture consisting of 10 to 90% by weight of an epoxy resin (e) and 90 to 10% by weight of a hydroxyl group-containing acrylic resin (f) with 5 to 35% by weight of an amine compound (g); (C) a aliphatic and/or alicyclic blocked polyisocyanate compound, and (D) a bismuth compound component, a mixing ratio of the components (A), (B) and (C) being such that the component (A) is in the range of 40 to 90% by weight, the component (B) is in the range of 5 to 55% by weight and the component (C) is in the range of 5 to 40% by weight based on a total weight of solid contents in the components (A), (B) and (C), the component (D) being contained in such an amount as to be in the range of 0.01 to 10 parts by weight as a bismuth content per 100 parts by weight of a resin solid content in the electrodeposition coating composition.
DETAILED DESCRIPTION OF THE INVENTION
Comonomers of the acrylic resin (A) used in the present invention comprises a hydroxyl group-containing acrylic monomer (a), an amino group-containing acrylic monomer (b), an aromatic vinyl monomer (c), and optionally another acrylic monomer (d).
Examples of the hydroxyl group-containing acrylic monomer (a) may include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, addition products of 2-hydroxyethyl(meth)acrylate with caprolactone such as Placcel FA-2, Placcel FM-3 and the like, and the like. These may be used alone or in combination. An amount of the hydroxyl group-containing acrylic monomer (a) is in the range of 10 to 60% by weight, preferably 30 to 50% by weight based on a total amount of monomer components of the acrylic resin (A). When the amount of the acrylic monomer (a) is more than 60% by weight, an increased hydrophilic property of the acrylic resin (A) results poor corrosion resistance of the electrodeposition coating film. On the other hand, when less than 10% by weight, a reduced water dispersibility due to the acrylic resin (A) results poor stability of the coating composition, and poor coating film performances due to an insufficient crosslinking density after heat curing.
Examples of the amino group-containing acrylic monomer (b) may include N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-di-t-butylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylamide, and the like. An amount of the amino group-containing acrylic monomer (b) is in the range of 5 to 35% by weight, preferably 10 to 25% by weight based on a total amount of the comonomers of the acrylic resin (A). The amount of the amino group-containing acrylic monomer (b) more than 35% by weight results an electrodeposition coating film showing poor properties in weather resistance, corrosion resistance and the like due to the acrylic resin (A). On the other hand, when less than 5% by weight, a seriously reduced water dispersibility due to the acrylic resin (A) results poor stability of the coating composition.
An amount of the aromatic vinyl monomer (c) is in the range of 5 to 55% by weight, preferably 10 to 45% by weight based on a total amount of the comonomers of the acrylic resin (A). The aromatic vinyl monomer (c) more than 55% by weight makes it impossible to obtain an electrodeposition coating film having a smooth coating surface, and reduces weather resistance. When less than 5% by weight, a shortage of oxygen permeability makes it impossible to obtain a satisfactory corrosion resistance.
Examples of another acrylic monomer (d) may include methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, and the like. An amount of another acrylic monomer (d) is in the range of 0 to 80% by weight, preferably 0 to 50% by weight.
The acrylic resin (A) may be prepared by subjecting the comonomers (a), (b), (c) and (d) to a radical copolymerization reaction according to a known process. Examples of an organic solvent used in the radical copolymerization reaction may include aromatic hydrocarbons such as toluene, xylene and the like; ketones such as methyl isobutyl ketone, cyclohexanone and the like; alcohols such as n-butanol, ethyl cellosolve, butyl cellosolve, methoxypropanol, ethylene glycol monobutyl ether and the like, and the like. These solvents may be used alone or in combination.
The radical copolymerization reaction may be carried out by reacting a mixture of the above comonomers in an organic solvent at a temperature in the range of about 50° C. to about 300° C., preferably about 60° C. to 250° C. for about one hour to about 24 hours, preferably about 2 hours to about 10 hours under an inert gas such as nitrogen gas.
The acrylic resin (A) has a hydroxy value in the range of 10 to 300 mg KOH/g, preferably 50 to 200 mg KOH/g. A hydroxy value more than 300 mg KOH/g increases hydrophilic properties of the resin (A) and results poor corrosion resistance of the electrodeposition coating film. On the other hand, a hydroxy value less than 10 mg KOH/g results poor coating film performances because of reduction in water dispersibility and reduction in crosslinking density due to the resin (A).
The acrylic resin (A) has an amine value in the range of 10 to 125 mg KOH/g, preferably 15 to 80 mg KOH/g. An amine value more than 125 mg KOH/g increases hydrophilic properties of the resin (A), resulting an electrodeposition coating film showing poor properties in weather resistance, corrosion resistance and the like. On the other hand, when less than 10 mg KOH/g, water dispersibility of an emulsion due to the resin (A) may seriously be reduced.
The acrylic resin (A) has a number average molecular weight in the range of 2
Haneishi Hidehiko
Kato Akiko
Miyatake Shinji
Nishida Reijiro
Nishiguchi Shigeo
Aylward D.
Dawson Robert
Fisher Christen & Sabol
Kansai Paint Co. Ltd.
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