Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1998-10-23
2001-01-30
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S407100
Reexamination Certificate
active
06180175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating composition capable of being cured by crosslinking by a urethanization reaction of a hydroxyl group and an isocyanate group and being made to a high solid content type having more than 70% by weight of solid content at the time of coating, and relates to a multilayer coating film formation process using the composition.
2. Description of the Prior Art
In the field of coating materials, the reduction of amount of usage of organic solvents is an urgent matter from a viewpoint of environmental conservation against atmospheric pollution and saving of resources etc.
As one of the countermeasures, there is mentioned the development of so-called “high solid content coating materials” in which the amount of usage of organic solvents in the coating materials is reduced to obtain a high solid content concentration in the organic solvent type coating materials.
Most of the high solid content coating materials currently under development contain as resin component a hydroxyl group-containing resin compounded with a melamine resin as a curing agent. Such coating materials, however, have the following disadvantages.
Firstly, it is necessary to make the viscosity of hydroxyl group-containing resin and melamine resin lower in order to achieve a high solid content concentration. However, when the molecular weight of these resins is made lower, there arises a problem that the properties of the coating film are lowered. In order to realize lower molecular weight of resins and sufficient properties of the coating film at the same time, it is necessary to have a higher content of crosslinking functional groups, such as hydroxyl group, methylol group etc. in the resin. However, crosslinking functional groups generally increase the viscosity due to a mutual action among functional groups, and there arises a problem that the lowering of viscosity becomes difficult, if the content of functional groups is higher.
Secondly, in case a high solid content coating material is a coating material using melamine resin as curing agent, a large amount of by-products such as alcohol at the time of curing by heating are generated and there arises a problem that popping caused by baking happens in the coating film quite often.
Moreover, in the top coating film of automobile outer plates etc. to be used outdoors, etching and stains caused by the acid rain are worldwide problems. Another problem is scratches caused by a car-washing machine as the machine has been popularized. Therefore, there has been demanded a development of a coating material for top coat, especially a clear coating for top coat which can form a coating film having both enough acid resistance against acid rain etc. and scratch resistance. The coating film obtained from the coating material containing resins of a combination of the above-mentioned hydroxyl group-containing acrylic resin and a melamine resin has a problem of inferior acid resistance and scratch resistance.
Urethane type coating materials, which are crosslinked and cured by a urethanization reaction between a hydroxyl group and an isocyanate group, can form a cured coating film excellent in acid resistance, scratch resistance, coating appearance (for example, gloss, fatness, image sharpness) etc. and are widely used. However, it is difficult for the urethane type coating materials to bring the solid content at the time of coating to a higher solid content concentration of more than 70% by weight, without deteriorating these properties and therefore their applications are limited in recent years where prevention of atmospheric pollution and saving resources are seen as important, without being able to sufficiently utilize the above-mentioned advantages.
The purpose of the present invention is to propose a urethane type coating composition capable of being made the solid content at the time of coating to more than 70% by weight, without deteriorating good properties, which a urethane type coating material has, such as acid resistance, scratch resistance, finishing appearance etc. and a multilayer coating film formation process using the coating composition.
As a result of an extensive study, the present inventors have found that the above-mentioned purpose can be achieved by a coating material comprising a vinyl type polymer having both silylated hydroxyl groups and alkoxysilyl groups, low molecular weight polyol, polyisocyanate compounds and a silanol group forming catalyst, and optionally containing a small amount of an organotin compound, and completed the present invention.
SUMMARY OF THE INVENTION
Thus the present invention proposes an organic solvent-based coating composition comprising
(A) a vinyl polymer having hydroxyl groups and alkoxysilyl groups in the molecule and having a number-average molecular weight in a range of 2,000 to 10,000;
(B) a polyol compound having a number-average molecular weight of not more than 1,000 and having a hydroxyl value in a range of 120 to 1,000 mgKOH/g;
(C) a polyisocyanate compound having a number-average molecular weight of not more than 2,000;
(D) a silanol group-forming catalyst; and
(E) 0 to 0.1 part by weight of a urethanization catalyst per 100 parts by weight of the total of the above-mentioned polymer (A), polyol compound (B) and polyisocyanate compound (C).
The present invention also proposes a coating film-formation process characterized by using the above-mentioned coating composition as the clear coating material of at least top layer in a process of forming a multilayer coating film by coating by turns at least one color coating material and at least one clear coating material.
DETAILED DESCRIPTION OF THE INVENTION
Each component of the coating composition of the present invention etc. are hereinafter described in more detail.
Vinyl polymer (A)
The vinyl polymer (A) used in the present invention is a vinyl polymer having both hydroxyl groups and alkoxysilyl groups in the molecule.
The above-mentioned vinyl polymer (A) may easily be obtained, for example, by copolymerizing a vinyl monomer having a hydroxyl group(s), a vinyl monomer having a hydrolyzable alkoxysilyl group(s), and optionally another vinyl monomer.
As the above-mentioned vinyl monomer having a hydroxyl group(s), there can be mentioned, for example, C
2
-C
8
, hydroxyalkyl esters of acrylic acid or methacrylic acid, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate etc.; monoesters of a polyether polyol such as polyethylene glycol, polypropylene glycol, polybutylene glycol etc. with an unsaturated carboxylic acid such as (meth)acrylic acid etc.; monoethers of a polyether polyol such as polyethylene glycol, polypropylene glycol, polybutylene glycol etc. with an unsaturated monomer having a hydroxyl group(s) such as 2-hydroxyethyl (meth)acrylate etc.; monoesters or diesters of an unsaturated compound having an acid anhydride group(s) such as maleic anhydride, itaconic anhydride etc. with a glycol such as ethylene glycol, 1,6-hexanediol, neopentyl glycol etc.; hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether; allyl alcohol; adducts of an &agr;,&bgr;-unsaturated carboxylic acid with a monoepoxy compound such as Cardura E10 (Made by Shell Chemicals, Co., Ltd., Trade name) and &agr;-olefin epoxide; adducts of glycidyl (meth)acrylate with a monobasic acid, such as acetic acid, propionic acid, p-tert-butylbenzoic acid and fatty acid; adducts of an above-mentioned monomer having a hydroxyl group(s) with a lactone (for example, &egr;-caprolactone, &ggr;-valerolactone etc.).
A vinyl monomer having a hydrolyzable alkoxy-silyl group(s) is a monomer which forms a silanol group(s) by hydrolysis and includes compounds having each one or more alkoxysilyl groups and polymerizable unsaturated groups in the molecule, specifically, for example, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyltris(2-methoxyethoxy)silane, &ggr;-(meth)acryloyloxy-prop
Noura Kohsuke
Okumura Yasumasa
Saika Masaaki
Wada Seiji
Yabuta Motoshi
Cameron Erma
Kansai Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Coating composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coating composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coating composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492959