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
2002-11-15
2004-05-11
Metzmaier, Daniel S. (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...
C525S403000, C525S406000, C525S390000, C525S398000, C525S399000, C528S103000, C528S107000, C528S110000, C528S113000, C428S413000, C205S317000
Reexamination Certificate
active
06734260
ABSTRACT:
The present invention relates to a cationic coating composition, more specifically to a cationic coating composition capable of forming a cured coating film which is excellent in a corrosion resistance and a rust preventive steel plate aptitude.
A cationic coating composition is used mainly as an electrodepositable coating composition for wide-ranged uses including an undercoating composition for car bodies, and those having various characteristics have so far been developed. Proposed as a conventional cationic coating composition is, for example, a coating composition having an excellent corrosion resistance and improved in an electrodepositable coating aptitude and an adhesive property toward a rust preventive steel plate, in which used as a vehicle component is a modified epoxy resin obtained by internally plasticizing an epoxy resin having an amino group and/or a quaternary ammonium salt group as a hydrophilic group with a plasticizer, such as polyamide, polyester and polyether and blended is a rust preventive pigment such as lead chromate, basic lead silicate and strontium chromate. In recent years, however, hazardous compounds such as lead compounds and chromium compounds are restricted in use thereof from a viewpoint of pollution problems, and techniques which can improve a corrosion resistance of the coating film without blending such hazardous compounds are expected to be developed.
On the other hand, an epoxy resin which is internally plasticized with a plasticizer tends to reduce a corrosion resistance of the coating film, and therefore it is considered to use as a base resin an epoxy resin containing no plasticizing modifier to thereby elevate the corrosion resistance. However, this provides the problem that the electrodepositable coating aptitude against a rust preventive steel plate is reduced. In order to solve such problems, it is proposed that added as a plasticizer for an epoxy resin are, for example, polyol resins such as polyesterpolyols, polyetherpolyols, polyurethanepolyols and acrylpolyols; and polymers including polyolefins such as polybutadiene and polyethylene. Involved therein, however, is the problem that these materials not only do not have a sufficiently high compatibility with epoxy resins and are not effective so much for improving the electrodepositable coating aptitude against a rust preventive steel plate but also reduce a corrosion resistance of the coating film when added in a large amount.
An object of the present invention is to provide a cationic coating composition based on an epoxy resin and capable of forming a coating film which is excellent both in a corrosion resistance and the electrodepositable coating aptitude against a rust preventive steel plate without using hazardous compounds such as lead compounds and chromium compounds.
Intensive researches repeated by the present inventors have resulted in finding that the object described above can be achieved by using as a vehicle component in a cationic coating composition, a xylene-formaldehyde resin-modified, amino group-containing epoxy resin obtained by reacting an epoxy resin with a xylene-formaldehyde resin and an amino group-containing compound, and they have come to complete the present invention.
Thus, the present invention provides a cationic coating composition comprising as a vehicle component, a xylene-formaldehyde resin-modified, amino group-containing epoxy resin obtained by reacting an epoxy resin (A) having an epoxy equivalent of 180 to 2500 with a xylene-formaldehyde resin (B) and an amino group-containing compound (C).
The cationic coating composition of the present invention shall be explained below in further details.
Epoxy Resin (A)
An epoxy resin obtained by the reaction of a polyphenol compound with epihalohydrin, for example, epichlorohydrin is particularly suited as an epoxy resin used as a starting material in the production of the modified epoxy resin used as the vehicle component in the coating composition of the present invention from a corrosion resistance of the coating film.
The polyphenol compounds which can be used for producing the above epoxy resin include, for example, bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)methane (bisphenol F), bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4-dihydroxy-diphenylsulfone (bisphenol S), phenol novolak and cresol novolak.
Particularly suited as the epoxy resin obtained by the reaction of a polyphenol compound with epihalohydrin is a compound derived from bisphenol A, which is represented by the following formula:
wherein n is 1 to 8.
The epoxy resin (A) can have an epoxy equivalent falling in a range of generally 180 to 2,500, preferably 200 to 2,000 and more preferably 400 to 1,500. Further, it has suitably a number average molecular weight falling in a range of generally at least 200, particularly 400 to 4,000 and more particularly 800 to 2,500.
Commercially available products of such epoxy resin include, for example, products which are marketed from Japan Epoxy Resin Co., Ltd. in the trade names of Epikote 828EL, ditto 1002, ditto 1004 and ditto 1007.
Xylene-formaldehyde Compound (B)
In the present invention, the xylene-formaldehyde resin (B) has preferably a phenolic hydroxyl group capable of reacting with an epoxy group and is useful for plasticization (modification) of the epoxy resin (A) described above, and it can be produced, for example, by subjecting xylene, formaldehyde and, if necessary, phenols to condensation reaction in the presence of an acid catalyst.
Capable of being given as examples of the formaldehyde described above are compounds which generate formaldehyde such as formalin, paraformaldehyde and trioxane which are readily available in an industrial scale. When a polymer such as paraformaldehyde and trioxane is used in the present invention, a blending amount thereof is regulated based one molecule of formaldehyde.
Further, the phenols described above include monovalent or divalent phenol compounds having two or three reaction sites, and to be specific, they include, for example, phenol, cresols (o-cresol, m-cresol and p-cresol), paraoctylphenol, nonylphenol, bisphenolpropane, bisphenolmethane, resorcin, pyrocatechol, hydroquinone, para-tert-butylphenol, bisphenolsulfone, bisphenol ether and paraphenylphenol. They can be used alone or in combination of two or more kinds thereof. Among them, phenol and cresols are particularly suited.
The acid catalyst used for condensation reaction of xylene, formaldehyde and, if necessary, phenols includes, for example, sulfuric acid, hydrochloric acid, paratoluenesulfonic acid and oxalic acid, and usually sulfuric acid is particularly suited. A use amount thereof, as usually diluted with water contained in a formaldehyde aqueous solution, can be controlled in a range of 10 to 50% by weight in terms of a concentration in the aqueous solution.
The condensation reaction can be carried out, for example, by heating at a temperature at which xylene, phenols, water and formalin present in the reaction system are refluxed, usually about 80 to about 100° C., and it can be finished in 2 to 6 hours.
Xylene, formaldehyde and, optionally and preferably, phenols are reacted by heating under the condition described above in the presence of the acid catalyst, whereby the xylene-formaldehyde resin can be produced. The xylene-formaldehyde resin can be produced as well by reacting a xylene-formaldehyde resin produced in advance with phenols in the presence of the acid catalyst.
The xylene-formaldehyde resin thus obtained has preferably a phenolic hydroxyl group and can have a viscosity falling in a range of usually 20 to 50,000 centipoise (25° C.), preferably 30 to 15,000 centipoise (25° C.). It has preferably a phenolic hydroxyl group equivalent falling in a range of usually 100 to 50,000, particularly 200 to 10,000.
Amino Group-containing Compound (C)
In the present invention, the a
Iijima Hideki
Kamikado Koji
Midogochi Susumu
Nishiguchi Shigeo
Shimasaki Akihiko
Kansai Paint Co. Ltd.
Keehan Christopher
Metzmaier Daniel S.
Wenderoth Lind & Ponack LLP
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