Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-04-30
2003-12-02
Sellers, II, Robert E. (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S407200, C427S408000, C427S410000, C525S111000, C525S166000, C525S172000
Reexamination Certificate
active
06656531
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a curable resin composition which is suitable for an automotive top coating composition and a coil coating composition.
BACKGROUND OF THE INVENTION
A top coating composition for an automobile generally comprises, as a binder component, a combination of a hydroxyl group-containing polymer and a melamine resin curing agent. However, a coated film obtained by using a melamine resin as a curing agent generally has poor acid resistance. Accordingly, such a coated film is liable to be damaged by an acid rain which has recently become a serious problem, and an appearance of the coated film is deteriorated.
The poor acid resistance which is provided by using a melamine resin is believed to originate from a triazine nucleus in the melamine resin. Accordingly, a drawback of poor acid resistance occurs, so far as a melamine resin is used as a curing agent.
In Japanese Laid-Open Patent Publication Nos. 2-45577 and 3-287650, there is suggested a novel coating composition without using a melamine resin. The coating composition comprises an acid group and an epoxy group therein, and the acid group and the epoxy group reacts to form a crosslinking point of an ester bond, and therefore, acid resistance of the resulting coated film is excellent.
The coating composition, however, has high functional group content and high viscosity. Therefore, a large amount of solvent must be used for controlling viscosity, and it is difficult to prepare a high-solid type coating composition.
On the other hand, in order to reduce the harmful influence on the environment, a high-solid coating composition which volatilizes a small amount of solvent into air has recently been required.
In Japanese Laid-Open Patent Publication No. 6-166741, there is disclosed a high-solid coating composition using a silicone polymer. In this reference, a hydroxyl group functional silicone polymer is reacted with an acid anhydride group-containing compound in order to impart acid functionality, and incorporated into the coating composition. Accordingly, an amount of functional group of the composition can not be increased, Tg of the resulting resin becomes low, and therefore, Tg of the resulting coated film can not be increased.
In Japanese Laid-Open Patent Publication No. 6-41575, there is disclosed a high-solid coating composition comprising a polyepoxide (a) and a polyester polycarboxylic acid (b). However, solid content of the coating composition is not sufficiently high in order to prevent the harmful influence on the environment, and the coated film formed has poor acid resistance.
OBJECTS OF THE INVENTION
An object of the present invention is to solve the above conventional problem, and provide a high-solid curable resin composition which forms a coated film having excellent acid rain resistance, mar resistance and appearance, as well as a high-solid coating composition and a method for forming a coated film using the same.
SUMMARY OF THE INVENTION
That is, the present invention provides a high-solid curable resin composition, comprising:
(a) 10 to 70% by weight of an acrylic polycarboxylic acid having 2 or more carboxyl groups per molecule on an average, an acid value of 5 to 300 mg KOH/g (solid) and a number-average molecular weight of 500 to 8000;
(b) 5 to 70% by weight of a polyester polycarboxylic acid having an acid value of 50 to 350 mg KOH/g (solid), a number-average molecular weight of 400 to 3500 and a ratio of weight-average molecular weight to number-average molecular weight of 1.8 or less, which is obtained by reacting a polyester polyol having 3 or more hydroxyl groups with an acid anhydride group-containing compound; and
(c) 10 to 80% by weight of a polyepoxide having an epoxy equivalent of 50 to 700 and a number-average molecular weight of 200 to 10000; provided that the amounts of the components (a) to (c) are based on the weight of the total solid contained in the curable resin composition.
DETAILED DESCRIPTION OF THE INVENTION
An acrylic polycarboxylic acid (a) to be used in the present invention has 2 or more carboxyl groups per molecule on an average, an acid value of 5 to 300 mg KOH/g, preferably 25 to 250 mg KOH/g, more preferably 50 to 200 mg KOH/g, and a number average-molecular weight of 500 to 8000, preferably 800 to 6000, more preferably 1500 to 4000.
The acrylic polycarboxylic acid is obtained by copolymerizing 5 to 80% by weight of a carboxyl group-containing ethylenically unsaturated monomer with 20 to 95% by weight of an ethylenically unsaturated monomer having no carboxyl group according to a method known to the art. For example, the copolymerization can be carried out at a polymerization temperature of 80 to 200° C. for a polymerization time of 3 to 10 hours under normal or applied pressure, using an azo or peroxide initiator as a radical polymerization initiator in an amount of 0.5 to 20 parts by weight, based on 100 parts by weight of the total ethylenically unsaturated monomers. Conventional polymerization controlling agents such as a chain transfer agent, a color protection agent and the like may be added during the polymerization.
Examples of the carboxyl group-containing ethylenically unsaturated monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, an adduct of these with &egr;-caprolactone (e.g. “Allonix M-5300”, manufactured by Toa Gosei Kagaku Co., Ltd., etc.), an adduct of an ethylenically unsaturated monomer having a hydroxyl group represented by the formula (I) with an acid anhydride group-containing compound, and an adduct of an acid anhydride group-containing ethylenically unsaturated monomer with a monoalcohol. The ethylenically unsaturated monomer having a carboxyl group can be used alone or in combination thereof.
The acid anhydride group-containing compound is half-esterified by a hydroxyl group to provide a carboxy functional group in an ambient reaction condition such as room temperature to 150° C. under normal pressure. It is preferred to use an acid anhydride group-containing compound having 4 to 12 carbon atoms, particularly 8 to 10 carbon atoms, which has a (unsaturated or saturated) cyclic group. Such a component may improve compatibility of the resulting resin.
Examples of the preferred acid anhydride group-containing compound include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl hexahydrophthalic anhydride, trimellitic anhydride, succinic anhydride, etc.
Examples of the acid anhydride group-containing ethylenically unsaturated monomer to be used herein include itaconic anhydride, maleic anhydride, citraconic anhydride, etc.
Examples of the monoalcohol to be used herein include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-hexyl alcohol, lauryl alcohol, methyl cellosolve, ethyl cellosolve, methoxypropanol, ethoxypropanol, furfuryl alcohol, dimethylamino ethanol, diethylamino ethanol, acetol, allyl alcohol, propargyl alcohol, etc.
Examples of the ethylenically unsaturated monomer having no carboxyl group include styrene, &agr;-methylstyrene, p-t-butylstyrene, (meth)acrylate (e.g. methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-, i- and t-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, cyclohexyl(meth)acrylate, isobornyl(meth)acrylate), etc.), VeoVa-9 and VeoVa-10 manufactured by Shell Co., etc. When styrene or a styrene derivative is used as the ethylenically unsaturated monomer having no carboxyl group, it is preferred to use it in an amount of 5 to 40% by weight.
A preferred acrylic polycarboxylic acid (a) of the curable resin composition of the present invention, has a carboxyl group and a carboxylate group, which bond to adjacent carbon atoms each other, because acid resistance of the resulting coated film is improved. The acrylic polycarboxylic acid (a) having a carboxyl group and a carboxylate group is obtained, for example, by reacting an acrylic polyacid anhydride (a)(i) with a monoalcohol (a)(ii).
The acrylic polyacid anhydride (a)(i) is obtained by copolymerizing 15
Eguchi Yoshio
Fushimi Akira
Inoue Masanobu
Miyazoe Seigo
Yoshioka Manabu
Nippon Paint Co. Ltd.
Sellers II Robert E.
Wenderoth , Lind & Ponack, L.L.P.
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