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
2000-02-25
2002-05-28
Tucker, Philip (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...
C525S208000, C106S287220
Reexamination Certificate
active
06395835
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermocurable resin composition for coating with good storage stability and capable of forming a coating film excellent in low temperature curability, acid resistance, scratch resistance etc.
2. Description of the Prior Art
As a topcoat paint for motorcar body, paints containing a hydroxyl group-containing resin and melamine resin are widely used. The coating film formed by using said paints, however, has a defect of insufficient acid resistance. Therefore, an “acid-epoxy type paint”, without using a melamine resin, applying a crosslinking reaction between carboxyl group and epoxy group has been proposed. The coating film formed by using this type of paint has an improved acid resistance, but has a defect of being prone to generate scratches on the coating surface during car washing and improvement of these defects has been strongly demanded.
The main purpose of the present invention is to provide a thermocurable resin composition for coating useful as a novel “acid-epoxy type paint” capable of forming a coating film excellent in acid resistance and scratch resistance and excellent in storage stability, low temperature curability of the coating film, etc. The present inventors found out, this time, that the above-mentioned purpose could be achieved by conducting the introduction of a carboxyl group into the base resin by using a polymerizable monomer obtained by half-esterification of a hydroxyl group-containing, polymerizable unsaturated monomer and an acid anhydride group-containing compound in a prescribed proportion and have completed the present invention.
SUMMARY OF THE INVENTION
Thus, according to the present invention, there is provided a thermocurable resin composition for coating characterized by containing
(i) a polymer (B), obtained by copolymerizing
(a) a polymerizable, unsaturated, half-esterified product obtained by half-esterification of a hydroxyl group-containing, polymerizable unsaturated monomer and an acid anhydride group-containing compound in the proportion of 1-1.5 moles of acid anhydride group per 1 mole of hydroxyl group,
(b) an acid anhydride group-containing, polymerizable unsaturated monomer, and
(c) another polymerizable unsaturated monomer, to form an acid anhydride group-containing polymer (A) and half-esterifying the acid anhydride group of the polymer (A) with
(d) a monohydric alcohol, and
(ii) a polymer (C) having both hydroxyl group and epoxy group in the molecule.
Then the thermocurable resin composition for coating of the present invention (hereinafter referred to as the present composition) will be described in more detail.
DETAILED DESCRIPTION OF THE INVENTION
Polymer (A)
The polymer (A) used in the present invention is an acid anhydride group-containing polymer obtained by copolymerizing a polymerizable, unsaturated, half-esterified product (a) obtained by half-esterification of a hydroxyl group-containing, polymerizable unsaturated monomer and an acid anhydride group-containing compound in the proportion of 1-1.5 moles of acid anhydride group per 1 mole of hydroxyl group, an acid anhydride group-containing, polymerizable unsaturated monomer (b) and another polymerizable unsaturated monomer (c).
The hydroxyl group-containing, polymerizable unsaturated monomer used for the preparation of the above-mentioned polymerizable, unsaturated, half-esterified product (a) is a compound having each one of hydroxyl group and polymerizable, unsaturated carbon-carbon double bond in the molecule and there can be mentioned, for example, a monoesterified product (for example, a hydroxyalkyl ester) of a polymerizable, unsaturated carboxylic acid such as acrylic acid or methacrylic acid and a dihydric alcohol (diol) of a carbon number of 2-24. Particularly, in order to improve the scratch resistance of the coating film to be formed, monoesterified products with dihydric alcohols of a carbon number of 3-10 are preferred. Moreover, as a hydroxyl group-containing, polymerizable unsaturated monomer, an addition product of an endocyclic ester group-containing compound (lactone) such as &egr;-caprolactone to a polymerizable unsaturated aliphatic carboxylic acid such as acrylic acid or methacrylic acid can be preferably used.
As specific examples of such a hydroxyl group-containing, polymerizable unsaturated monomer, there can be mentioned hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, PLACCEL FM or FA series (made by Daicel Chemical Industries Ltd., trade name; ring-open esterified products of &egr;-caprolactone with acrylic acid or methacrylic acid, etc.
The acid anhydride group-containing compound is a linear or cyclic compound, having an acid anhydride group
but containing no polymerizable unsaturated bond, which easily half-esterifies with a hydroxyl group in the above-mentioned hydroxyl group-containing, polymerizable unsaturated monomer to form each one mole of carboxyl group and ester group per 1 mole of acid anhydride group, and includes, for example, succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, Himic® anhydride, trimellitic anhydride, methylcyclohexenetricarboxylic anhydride, pyromellitic an hydride etc. Particularly succinic anhydride is preferred, because the reactivity of the carboxyl group formed by its half-esterification is high.
The polymerizable, unsaturated, half-esterified product (a) is obtained by half-esterification of the above-mentioned hydroxyl group-containing, polymerizable unsaturated monomer and the acid anhydride group-containing compound in the proportion of 1 mole of the hydroxyl group in the former unsaturated monomer and 1-1.5 moles, preferably 1.02-1.3 moles, particularly preferably 1.05-1.25 moles of the acid anhydride group of the latter compound. When the proportion of the acid anhydride group per 1 mole of the hydroxyl group here is less than 1 mole, unreacted hydroxyl group-containing, polymerizable unsaturated monomer remains and the storage stability of the present composition tends to lower and, on the other hand, when it is more than 1.5 moles, the water resistance of the cured coating film formed from the present composition may be deteriorated.
By reacting the hydroxyl group-containing, polymerizable unsaturated monomer and the acid anhydride group-containing compound in the proportion in the above-mentioned range in the preparation of the polymerizable, unsaturated, half-esterified product (a), there remains almost no unreacted hydroxyl group-containing, polymerizable unsaturated monomer or at all and there is no lowering of the storage stability. On the other hand, there may remain unreacted acid anhydride group-containing compound, which is reacted with a monohydric alcohol and half-esterified at the next step, and the product participates in the crosslinking reaction with the polymer (C) and therefore it is not a factor to deteriorate the performance of the coating film.
The half-esterification reaction of the hydroxyl group-containing, polymerizable unsaturated monomer and the acid anhydride group-containing compound can be conducted by a usual process, for example, at the temperture of room temperature to about 150° C., suitably in an organic solvent inert to the reaction.
The acid anhydride group-containing, polymerizable unsaturated monomer (b) is a compound having each one acid anhydride group capable of easily half-esterifying with a monohydric alcohol and polymerizable unsaturated carbon-carbon double bond in the molecule and there can be specifically mentioned, for example, maleic anhydride, itaconic anhydride, citraconic anhydride etc.
Other polymerizable unsaturated monomer (c) is a compound having at least one polymerizable unsaturated bond in the molecule and copolymerizable with the above-mentioned half-esterified product (a) and the unsaturated monomer (b) and there can be specifically mentioned, for exam
Nakamura Shigeru
Nakao Yasushi
Kansai Paint Co. Ltd.
Tucker Philip
Wenderoth , Lind & Ponack, L.L.P.
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