Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2000-05-26
2002-09-03
Dawson, Robert (Department: 1712)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S140000, C427S142000, C428S416000, C428S418000, C523S463000, C525S523000, C525S529000, C528S119000, C528S339000, C528S407000
Reexamination Certificate
active
06444272
ABSTRACT:
The present invention relates to a single-packaged epoxy resin coating composition which does not bring about lifting of an old coating film when recoated on the old coating film and a recoating method using the composition.
Epoxy resins have so far been used in the respective fields such as sealants, adhesives and the like including paints since it is excellent in various characteristics, particularly an adhesive strength. However, almost all of epoxy resin coating materials usually used are of a two-packaged composition comprising a principal component and a hardener component, and immediately after mixing, a curing reaction goes on. Accordingly, usable time is very short, so that there has been a problem in terms of a workability.
Accordingly, a method for extending usable time includes a method in which a latent curing agent such as a blocked isocyanate-modified epoxy resin is used, but the above curing agent is originally a thermosetting type and is not satisfactory in terms of practical use.
Further, investigated are single-packaged epoxy resin coating materials such as an epoxy ester resin having an air drying property without using a curing agent. However, this coating material is an air-oxidation type, and therefore if a coating film has a large film thickness, the surface of the coating film is dried before the inside of the coating film is dried, so that liable to be caused is a so-called “uncured inner portion” that a solvent remains in the inside of the coating film, so that the inside of the coating film is not sufficiently cured. Further, in general, involved is the problem that the coating film is inferior in a solvent resistance as compared with a coating film formed from a two-packaged epoxy resin coating material and shrinkage is caused depending on the kind of a top coating material applied thereon, so that top coating materials capable of being used are restricted to a large extent.
Further, a single-packaged epoxy resin coating material comprising an epoxy resin, a ketimine compound, a dehydrating agent and an added resin (a modified epoxy resin, a xylene resin, a petroleum resin and the like) is disclosed in Japanese Patent Application Laid-Open No. 217859/1996 (EP-A-846,710) as a method by which these problems can be solved. It is described therein that a large amount of a strong solvent such as a ketone base solvent is added in order to improve the storage stability. However, there is the problem that when this coating material containing a large amount of the strong solvent is applied on an old coating film, the old coating film is attacked by the solvent contained in the above coating material to cause lifting of the old coating film. In the specification, “an old coating film” means “a coating film allowed to repair”.
An object of the present invention is to provide a single-packaged epoxy resin coating composition which is excellent in a storage stability and a workability and can form a coating film having an excellent curing property, top coating applicability and adhesive property and which does not cause lifting of an old coating film also when it is applied thereon.
Intensive researches repeated by the present inventors have resulted in finding that the object described above can be achieved by using a specific ketimines compound as a curing agent and employing a solvent composition comprising primarily an aliphatic hydrocarbon base solvent and/or a specific aromatic hydrocarbon base solvent, and they have come to complete the present invention.
Thus, the present invention provides a single-packaged epoxy resin coating composition comprising:
(A) an epoxy resin having at least one epoxy group in a molecule and capable of being dissolved in the following organic solvent (D),
(B) a ketimines compound having at least two primary amino groups blocked with a carbonyl compound and having substantially no other amino groups than the above blocked amino groups,
(C) a dehydrating agent and
(D) an organic solvent,
wherein the above organic solvent (D) comprises a hydrocarbon base solvent selected from the group consisting of an aliphatic hydrocarbon base solvent and an aromatic hydrocarbon base solvent having a boiling point of 148° C. or higher in a proportion of at least 95% by weight based on the above organic solvent (D).
Further, the present invention provides a recoating method characterized by applying the single-packaged epoxy resin coating material described above on an old coating film.
The present invention shall be explained below in further details.
Epoxy Resin (A)
The epoxy resin which is the component (A) in the present invention is a resin having at least one epoxy group, preferably at least two epoxy groups on an average and more preferably at least 2 to 5 epoxy groups on an average in a molecule, and it has a number average molecular weight falling preferably in a range of 350 to 2000, particularly 500 to 1500 and an epoxy equivalent falling preferably in a range of 80 to 1000, particularly 200 to 800. Used as the component (A) is an epoxy resin capable of being dissolved in the organic solvent (D) described later which is the solvent component in the coating composition of the present invention.
The epoxy resin described above includes, for example, glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, other glycidyl type epoxy resins and alicyclic epoxy resins; modified epoxy resins prepared by modifying these epoxy resins with at least one modifying agent selected from the group consisting of alkylphenols, alkylphenol novolak type resins and fatty acids, and epoxy group-introduced alkylphenol or alkylphenol novolak type resins prepared by reacting alkylphenol or alkylphenol novolak type resins with epichlorohydrin.
Among them, the modified epoxy resins described above are suitable for the epoxy resin which is the component (A) in the coating material of the present invention.
The glycidyl ether type epoxy resins described above include, for example, epoxy resins having a glycidyl ether group which can be obtained by reacting polyol compounds such as polyhydric alcohols and polyhydric phenols with epihalohydrin or alkylene oxide. Examples of the polyhydric alcohols described above include, for example, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, neopentyl glycol, butylene glycol, hexanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerin and sorbitol. Examples of the polyhydric phenols described above include, for example, 2,2-bis(4-hydroxyphenyl) propane[bisphenol A], 2,2-bis(2-hydroxyphenyl)propane, 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane, halogenated bisphenol A, bis(4-hydroxyphenyl)methane[bisphenol F], tris(4-hydroxyphenyl)-propane, resorcin, tetrahydroxyphenylethane, 1,2,3-tris(2,3-epoxypropoxy) propane, novolak type polyhydric phenols and cresol type polyhydric phenols.
The glycidyl ester type epoxy resins described above include diglycidyl phthalate, diglycidyl hexahydrophthalate, diglycidyl tetrahydrophthalate and diglycidyl dimerate.
The other glycidyl type epoxy resins described above include, for example, tetraglycidyl aminodiphenylmethane and triglycidyl isocyanurate.
The alicyclic epoxy resins described above include, for example, (3,4-epoxy-6-methylcyclohexyl)methyl-3,4-epoxy -6-methylcyclohexanecarboxylate, (3,4-epoxycyclohexyl)methyl-3, 4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, bis(3, 4-epoxy-6-methylcyclohexylmethyl)adipate, Epolead GT300 (trade name, trifunctional alicyclic epoxy resin manufactured by Daicel Chemical Industries Ltd.), Epolead GT400 (trade name, tetrafunctional alicyclic epoxy resin manufactured by Daicel Chemical Industries Ltd.) and EHPE (trade name, multifunctional alicyclic epoxy resin manufactured by Daicel Chemical Industries Ltd.).
The modified epoxy resins described above include epoxy resins prepared by modifying non-modified epoxy resins such as the glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, other glycidyl ether type epoxy resins and
Adachi Yoshimitsu
Iida Shinji
Matsuda Koji
Nakano Tadashi
Aylward D.
Dawson Robert
Kansai Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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