Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-02-16
2002-03-12
Tucker, Philip (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C523S407000, C523S411000, C523S412000, C524S839000, C524S840000, C525S920000
Reexamination Certificate
active
06355351
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cationically electrodepositable coating composition, more specifically to a cationically electrodepositable coating composition having an excellent chipping resistance and impact resistance and capable of forming a cured coating film which is excellent in a corrosion resistance.
2. Description of the Prior Art
A cationically electrodepositable coating composition is used for wide uses including undercoating for automobiles, and those having various characteristics have so far been developed. Usually, a cationically electrodepositable coating composition comprises an amine-modified epoxy resin as a base resin and a blocked polyisocyanate as a curing component.
On the other hand, salts for melting snow are scattered for preventing freezing in the winter season in cold districts such as North America and Canada. Coating film damage due to stones striking against outside plates such as doors and bonnets is liable to be caused in running of cars in such cold districts. In addition thereto, coating films are exposed to severe corrosive environment originating in scattered salts for melting snow, so that rusts produced on damaged parts become a serious problem. Thus, strongly desired to be developed is a coating material capable of forming a coating film which is excellent in coating film physical properties such as a chipping resistance and an impact resistance and which has a high corrosion resistance.
Proposed as a method for solving the problems described above are a method in which in a cationically electrodepositable coating composition usually used as an undercoating material for a car body, a modifying agent for providing flexibility is introduced into an epoxy resin used as a base resin and/or (blocked) polyisocyanate used as a curing agent; and a method in which coating components are blended with a plasticizing component such as polyol, a soft resin such as a xylene resin and an organic solvent having a high boiling point as additives. However, in the modifying agent-introducing method and the additive-blending method each described above, it is difficult to obtain a cationically electrodepositable coating composition capable of forming a coating film which is excellent in both of coating film physical properties such as a chipping resistance and an impact resistance and a corrosion resistance.
SUMMARY OF THE INVENTION
Intensive researches repeated by the present inventors in order to solve the problems described above have resulted in finding that an electrodepositable coating film is provided with flexibility and elasticity by adding a cationic urethane-modified polymer emulsion to a cationically electrodepositable coating composition and that obtained is a cationically electrodepositable coating composition capable of forming a coating film which is excellent in both of coating film physical properties such as a chipping resistance and an impact resistance and a corrosion resistance by allowing the emulsion to melt in a base resin, a curing agent and other components in baling and allowing it to partially cross-linking with other resin components.
Thus, according to the present invention, provided is a cationically electrodepositable coating composition comprising an amine-modified epoxy resin (A) and a blocked polyisocyanate (B), further comprising 5 to 50 parts by weight of a cationic urethane-modified polymer emulsion (C) per 100 parts by weight of the total of the amine-modified epoxy resin (A) and the blocked polyisocyanate (B) in terms of a solid matter.
The cationically electrodepositable coating composition of the present invention shall be explained below in further details.
DETAILED DESCRIPTION OF THE INVENTION
Amine-modified epoxy resin (A):
Those usually used as a base resin for a cationically electrodepositable coating material can be used as well for the amine-modified epoxy resin (A) in the cationically electrodepositable coating composition of the present invention. To be specific, capable of being given are, for example, (i) an adduct of a polyepoxide compound to primary mono- or polyamine, secondary mono- or polyamine or primary and secondary mixed-polyamine (refer to, for example, U.S. Pat. No. 3,984,299); (ii) an adduct of a polyepoxide compound to secondary mono- or polyamine having a primary amino group which is reduced to ketimine (refer to, for example, U.S. Pat. No. 4,017,438); and (iii) a reaction product obtained by etherification of a polyepoxide compound with a hydroxy compound having a primary amino group which is reduced to ketimine (refer to, for example, Japanese Patent Application Laid-Open No. 43013/1984).
The polyepoxide compound used for producing the amine-modified epoxy resin (A) described above is a compound having at least two epoxy groups in a molecule and is suitably a compound having a number average molecular weight falling in a range of usually at least 200, preferably 400 to 4000 and more preferably 800 to 2000 and an epoxy equivalent falling in a range of usually at least 100, preferably 200 to 2000 and more preferably 400 to 1000. In particular, a compound obtained by reacting a polyphenol compound with epichlorohydrin is preferred. The polyphenol compound which can be used for producing the above polyepoxide compound includes, for example, 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-butyl-phenyl)-2,2-propane, bis(2-hy-droxynaphthyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4′-dihydroxydiphenylsulfone, phenol novolak and cresol novolak.
The above polyepoxide compound may be those reacted partly with polyols, polyetherpolyols, polyesterpolyols, polyamide-amines, polycarboxylic acids and polyisocyanate compounds. Further, it may be those graft-polymerized with &egr;-caprolactone and acryl monomers.
On the other hand, the amine compound which can be added to the polyepoxide compound described above includes, for example, diethylamine, dibutylamine, methybutylamine and diethanolamine. Further, ketimine-reduced blocked products of amine compounds such as diethylenetriamine can be used as well. They each can be used alone or in combination of two or more kinds thereof.
Blocked Polyisocyanate (B):
The blocked polyisocyanate (B) used as a curing agent in the cationically electrodepositable coating composition of the present invention is a compound obtained by blocking substantially all isocyanate groups of polyisocyanate with a volatile blocking agent.
Polyisocyanate is a compound having at least two free isocyanate groups in a molecule and includes aromatic, aliphatic or alicyclic polyisocyanates. To be specific, it includes, for example, 2,4-or 2,6-toluylenediisocyanate or a mixture thereof, p-phenylenediisocyanate, diphenylmethane-4,4′-diisocyanate, polymethylenepoly-phenylisocyanate, tetramethylene-diisocyanate, hexamethylenediisocyanate, isophorone-diisocyanate; polyisocyanates obtained by linking a part of the isocyanate groups of the polyisocyanates described above with low molecular diols such as ethylene glycol propylene glycol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol and 1,4-cyclohexanediol and oligomer diols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and polylactonediol or mixtures thereof; adducts of the polyisocyanates described above to polyhydric alcohols such as trimethylolethane and trimethylolpropane, polyester resins (including oil-modified types) of low molecular weights having a functional group which reacts with an isocyanate group, acryl base copolymers and water; buret products of the polyisocyanates described above and copolymers (oligomers) of diisocyanates themselves; equimolar adducts of 2-hydroxypropyl (meth)acrylate to hexamethylenediisocyanate and copolymers comprising as an essential component, vinyl monomers having an isocyanate group and a copolymerizable unsaturated group such as isocyanateethyl methacrylate; and
Kamikado Koji
Nishiguchi Shigeo
Sawada Hidenori
Aylward D.
Kansai Paint Co. Ltd.
Tucker Philip
Wenderoth Lind & Ponack LLP
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