Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-06-24
2002-04-23
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S493000, C524S497000, C524S507000, C524S538000, C524S539000, C525S124000, C525S424000, C525S440030
Reexamination Certificate
active
06376589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating composition capable of forming a thick coating film which has excellent hardness, processibility, corrosion resistance and blocking resistance, and a coated metal plate coated by using coating composition.
2. Description of the Prior Art
As a topcoat paint for precoated steel plate for vessels processing or building materials which are coated by a continuous coating such as coil coating, paints comprising polyester type resin system, having polyester resin as a base resin and combining methyletherified methylolmelamine resin or polyisocyanate compound as a crosslinking agent, are being largely used up to the present. As the baking of the coating film with these polyester resin type topcoat paints at the production of precoated steel plate is conducted usually at a high temperature for a short time, the popping (bubbling of the coating film) tends to occur, if the coating film thickness is thick. Therefore, it was difficult to form a thick coating film of film thickness of more than 25 &mgr;m with a polyester resin type topcoat paint by one coating/baking operation.
For a coating film on a precoated steel plate, further improvement of durability such as corrosion resistance, in addition to hardness and processibility, is required. If it is possible to make a thick topcoating film, it will be advantageous in view of durability. However, it was difficult to form a thick film by one topcoat coating/baking operation up to the present in respect of popping resistance at a high temperature short time baking. Therefore it was necessary for making a thick film to coat topcoat paints several times in layers. However, for coating topcoat paints several times in layers it is necessary to wind up the coated plate in a coil shape after the first top coating and baking and to repeat the same operation afterwards. It will increase the number of coating/baking steps, increase the costs and generate problems concerning equipment.
Moreover, if the curability is lowered in order to form a thick film without generating a popping by one operation of top coating and high temperature short time baking, the curing of the coating film is insufficient and causes problems such that the coating film surface becomes tacky or the coating film is prone to generate blocking.
The main purpose of the present invention is to provide a polyester resin type topcoat paint, in a polyester resin type paint for precoated steel plate, capable of forming a coating film having excellent hardness, processibility, alkali resistance, corrosion resistance, anti-tackiness of the coating surface, blocking resistance, curability etc. and having an excellent coating film appearance without generation of popping by coating in one operation of top coating and high temperature short time baking for a film thickness of more than 25 &mgr;m.
As a result of an intensive study the present inventors found that the above-mentioned purpose can be achieved by using a specific polyester resin, specific blocked polyisocyanate compound and resin fine particles in combination in a polyester resin type paint and completed the present invention.
SUMMARY OF THE INVENTION
According to the present invention there is provided a coating composition comprising a binder component consisting of
(A) hydroxyl group-containing polyester resin having a number average molecular weight of 2,000-5 20,000, glass transition temperature of −40° C. to 30° C. and hydroxyl value of 5-95 mgKOH/g and
(B) blocked polyisocyanate compound blocked with &egr;-caprolactam, and the equivalent ratio of the blocked isocyanate groups in said blocked polyisocyanate compound (B)/the hydroxyl groups in said polyester resin (A) being in the range of 0.7-1.2, and
(C) resin fine particles with an average particle diameter of 8-70 &mgr;m which do not completely melt at the time of coating film curing and containing 0.5-30 parts by weight of said resin fine particles (C) per 100 parts by weight of said binder component.
According to the present invention there is provided also a coated metal plate having a topcoat cured coating film of the film thickness of more than 30 &mgr;m formed of the above-mentioned coating composition on the metal plate through the intermediary of a polyester type primer coating film or an epoxy type primer coating film.
The coating composition of the present invention is described hereinafter in more detail.
DETAILED DESCRIPTION OF THE INVENTION
Hydroxyl Group-containing Polyester Resin (A):
The hydroxyl group-containing polyester resin (A) used as one of the binder components in the coating composition of the present invention is a polyester resin having at least one hydroxyl group in the molecule and includes, for example, oil-free polyester resin, oil-modified alkyd resin, and modified substances of these resins, for example, urethane-modified polyester resin, urethane-modified alkyd resin, epoxy-modified polyester resin etc.
The above-mentioned oil-free polyester resin consists of an esterified product of a polybasic acid component and a polyhydric alcohol component. As a polybasic acid component there is used mainly. for example, one or more dibasic acid selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic acid etc. and lower alkyl esterified products of these acids, and, as necessary, a monobasic acid such as benzoic acid, crotonic acid, p-t-butylbenzoic acid etc. and a polybasic acid higher than tribasic acid such as trimellitic anhydride, methylcyclohexenetricarboxylic acid, pyromellitic anhydride etc. can be jointly used. As a polyhydric alcohol component there is used mainly, for example, a dihydric alcohol such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, 1,6-hexanediol etc., and, as necessary, a polyhydric alcohol higher than trihydric alcohol such as glycerol, trimethylolethane, trimethylolpropane, pentaerythritol etc. can be jointly used. These polyhydric alcohols can be used singly or in mixing more than two. Esterification or ester exchange reaction between these two components can be conducte by a per se known method, in adjusting the reaction ratios of the acid component and the alcohol component so that the polyester resin to be formed would contain a hydroxyl group(s). As an acid component isophthalic acid, terephthalic acid and lower alkyl esters of these acids are particularly preferable.
Oil-modified alkyd resin is prepared by reacting an oil fatty acid in addition to the acid component and alcohol component described about the above-mentioned oil-free polyester resin by a per se known method so that the resin to be formed would contain a hydroxyl group(s). As an oil fatty acid there can be mentioned, for example, coconut oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, tung oil fatty acid etc. Preferable oil length of an alkyd resin is less than 30%, particularly about 5-20%.
As a urethane-modified polyester resin there can be mentioned a reaction product of the above-mentioned oil-free polyester resin, or an oil-free polyester resin of a low molecular weight obtained by reacting an acid component and an alcohol component used in the preparation of the above-mentioned oil-free polyester resin, with a polyisocyanate compound made by a per se known method. Moreover, a urethane-modified alkyd resin includes a reaction product of the above-mentioned alkyd resin, or an alkyd resin of a low molecular weight obtained by reacting individual components used in the preparation of the above-mentioned alkyd resin, with a polyisocyanate compound made by a per se known method. As a polyisocyanate compound usable in the preparation of the urethane-modified polyester resin and the urethane-modified alkyd resin there can be mentioned, for
Abe Hideyuki
Tanaka Shoichi
Kansai Paint Co. Ltd.
Short Patricia A.
Wenderoth , Lind & Ponack, L.L.P.
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