Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-19
2002-01-29
Mayekar, K. (Department: 1741)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C204S489000, C204S499000
Reexamination Certificate
active
06342546
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a cationic electrodeposition coating composition having a low volatile organic solvent content that is, having a low content of a volatile organic compound (hereinafter may be referred to as VOC).
(2) Description of Background Art
The cationic electrodeposition coating composition has a high throwing power and is capable of forming a coating film showing good properties in durability, corrosion resistance and the like, and has widely been used as a primer coating composition coated on an electrically conductive metal such as an automobile body, electrical All articles and the like, in which the above coating film properties are required.
The electrodeposition coating composition in the prior art needs to contain 2% by weight or more of a volatile organic solvent such as monoalcohols, glycols, cellosolves, ketones and the like, so that a satisfactory film-forming properties may be maintained. On the other hand, demand on reducing a content of a volatile component in the electrodeposition coating composition, for example, an organic solvent from the standpoints of prevention of environmental disruption, saving of resources and the like has been increased.
In view of the above, it may be proposed to simply remove the volatile component in the electrodeposition coating composition so that a content of the volatile component may be 1% by weight or less, resulting in that reduction in film-forming properties makes it difficult to form a cured coating film having a film thickness of 15 &mgr;m or more, and reduces smoothness and corrosion resistance. On the other hand, in the application of the electrodeposition coating composition to a galvanized alloy, for example, an automobile body as widely used as a substrate, a high energized voltage for the purpose of thickening the electrodeposition coating film develops pinholes due to generation of gas, resulting in undesirably reducing smoothness of the coating film.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cationic electrodeposition coating composition having a volatile organic solvent content in the range of 1% by weight or less without reducing throwing power, corrosion resistance, etc. and showing good film-forming properties, and is capable of forming a coating film showing good smoothness.
It is another object of the present invention to provide a cationic electrodeposition coating composition capable of applying to a galvanized alloy to form a thick coating film having a film thickness of 15 &mgr;m or more without developing pinholes due to generation of gas.
That is, the present invention provides a cationic electrodeposition coating composition comprising (A) a cationic resin having a crosslinkable functional group and a cationic group in one molecule, (B) a crosslinking agent, and (C) polyether polyol, said cationic electrodeposition coating composition having a volatile organic solvent content in the range of 1% by weight or less.
DETAILED DESCRIPTION OF THE INVENTION
The cationic electrodeposition coating composition of the present invention may include a water-based coating composition which essentially contains a cationic resin (A) having a crosslinkable functional group such as hydroxyl group and a cationic group in one molecule, a crosslinking agent (B) and polyether polyol (C), and optionally contains color pigments, anti-corrosive pigments, extender pigments, organic solvents, acids for use in neutralization, anti-cissing agents, surface active agents, catalysts, inhibitors, rheology-controling agents, pigment dispersants and the like.
The cationic resin (A) has a crosslinkable functional group such as hydroxyl group and a cationic group in one molecule, and may include, as a resin skelton, epoxy resin, acrylic resin, polybutadiene, alkyd resin, polyester resin and the like. Of these, a cationic resin prepared by addition of an amine to the epoxy resin is preferable from the standpoint of good corrosion resistance.
Examples of the cationic resin prepared by addition of the amine to the epoxy resin may include (1) adducts of an epoxy compound with primary mono or polyamine, secondary mono or polyamine, primary and secondary mixed polyamine or the like (see U.S. Pat. No. 3984299 Specification); (2) adducts of an epoxy compound with a ketiminized, primary amino group-containing mono or polyamine (see U.S. Pat. No. 4017438 Specification); (3) reaction products obtained by etherification between an epoxy compound and a ketiminized, primary amino group-containing hydroxyl compound (see Japanese Patent Application Laid-Open No. 43013/84), and the like. These may be modified with a modifier such as polyamide resin and the like.
The above epoxy compound has at least two epoxy groups in one molecule and a number average molecular weight in the range of 400 to 4000, and may be prepared by a reaction between a polyphenol compound and epichlorohydrin. Examples of the polyphenol compound may include bis (4-hydroxyphenyl)2,2-propane, 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butylphenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene, bis(2,4-dihydroxyphenyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4-dihydroxyphenylsulfone, phenol novolak, cresol novolak, and the like.
The crosslinking agent (B) may include known crosslinking agents such as blocked polyisocyanate compound, amino resin and the like. The blocked polyisocyanate compound may include a reaction product obtained by subjecting all of isocyanate groups to addition reaction of a blocking agent to the isocyanate groups. The polyisocyanate compound is a compound having at least two isocyanate groups in one molecule, and may include known aromatic, alicyclic and aliphatic polyisocyanate compounds, and isocyanate group-terminated prepolymers obtained by reacting a low molecular weight active hydrogen-containing compound such as glycol or triol with an excess amount of the above polyisocyante compounds. Examples of the blocking agent may include lactams, oximes, phenols, aliphatic alcohols, aromatic alkyl alcohols, ether alcohols, and the like.
A mixing ratio of the cationic resin (A) to the crosslinking agent (B) is such that the cationic resin (A) is in the range of 50 to 90% by weight, preferably 65 to 80% by weight, and the crosslinking agent (B) is in the range of 50 to 10% by weight, preferably 35 to 20% by weight based on a total weight of solid contents of both components (A) and (B) respectively.
The cationic resin (A) may be neutralized with a water-soluble organic acid such as formic acid, acetic acid, lactic acid and the like so as to be water-soluble or water-dispersible.
Examples of the anti-corrosive pigment may include zinc dust, zinc phosphate, calcium phosphate, aluminum phosphate, aluminum polyphosphate such as aluminum tripolyphosphate, aluminum orthophosphate, calcium orthophosphate, boric acid based anti-corrosive pigment, alkaline earth metal, zinc oxide and the like, compound oxides of iron oxides with at least one of the above compounds, tungstic acid based anti-corrosive pigments, phosphite based anti-corrosive pigments, hypophosphous acid based anti-corrosive pigments, nitrite based anti-corrosive pigments, vanadic acid based anti-corrosive pigments, zinc formate, zinc acetate, zinc octenate and the like, and further may include compounds represented by chemical formulas such as Zr(OH)
4
, Mg
4
Al
2
(OH)
12
CO
3
·3H
2
O, Mg
6
Al
2
(OH)
16
CO
3
·5H
2
O and Mg
6
Al
7
(OH)
16
CO
3
·4H
2
O; and bismuth-containing compounds such as bismuth lactate, bismuth silicate, triphenylbismuth, bismuth gallate, bismuth hydroxide, bismuth trioxide, bismuth nitrate, bismuth benzoate, bismuth citrate, bismuth oxycarbonate, and the like.
The above anti-corrosive pigments may usually be used as a powder having a particle size of 10 &mgr;m or less, particularly 0.01 to 3 &mgr;m, and may suitably be used in the range of 0. 5 to 100 parts by weight, part
Kato Kiyoshi
Sugisaki Katsuhisa
Fisher Christen & Sabol
Kansai Paint Co. Ltd.
Mayekar K.
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