Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Patent
1998-07-21
2000-10-24
Dudash, Diana
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
4274071, 427409, 4284242, 428414, 428515, B05D 136
Patent
active
061364495
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for applying a base finishing coat and a top finishing coat wet-on-wet on to a substrate surface to form a thermosetting paint film, and to painted objects obtained by this means. More specifically, the present invention relates to a method for forming thermosetting paint films of outstanding acid resistance, finished appearance, water-resistance, adhesion and bending resistance, etc., suitable for finishing coat paint films, and painted objects obtained by this means.
PRIOR ART
Thermosetting paints which form a hardened paint film by applying a base finishing coat and top finishing coat wet-on-wet and stoving the resulting paint films at the same time are widely used as finishing coats for painting the outer skins of automobiles. However, the fact that top finishing coat paint films are prone to water staining by acid rain of low pH due to atmospheric pollution, which lowers their appearance, has become a problem in recent years.
In order to solve this problem, paint compositions with increased water resistance due to crosslinking of the principal resin of the top finishing coat with a hardener to form a composite, etc., have been investigated: for example, in Japanese Unexamined Patent 3-275780 paint compositions are proposed in which the principal components are an acrylic resin containing hydroxyl groups and carboxyl groups, an acrylic resin containing hydroxyl groups and epoxy groups, an amino resin and a quaternary phosphonium salt.
However, if the concentration of carboxyl groups and epoxy groups in such paint compositions is increased in order to obtain a high degree of acid resistance, the finished appearance of the paint film is lowered; and raising the glass transition temperature of the hardened paint film invites decreases in recoat adhesion and bending resistance. Thus, it is extremely difficult to obtain finishing coat paint films which have acid resistance and finished appearance balanced at a high level, and have outstanding adhesion resistance and bending resistance by painting prior finishing coats.
The purpose of the present invention is to solve this problem by offering a method for forming a paint film which can form hardened paint films with outstanding acid resistance, finished appearance, water resistance, adhesion, and bending resistance, etc., in forming a paint film by painting a base finishing coat and a top finishing coat painted wet-on-wet, and offering painted objects obtained with this method.
SUMMARY OF THE INVENTION
The present invention provides the following method for forming a paint film, and painted objects.
(1) A method for forming a paint film, which is a method for forming a hardened paint film in which a solvent-based thermosetting base finishing coat is painted onto the surface of an object to be painted, a thermosetting top finishing coat is painted on top of this wet-on-wet, and the resulting paint films are hardened at the same time, characterized in that the aforementioned top finishing coat contains as the principal resin a copolymer which is a copolymer of a vinyl monomer which has a ring structure and (an)other vinyl monomer(s) in which the proportion of vinyl monomers having a ring structure in the total quantity of monomers is 20-50 wt %, and the proportion of other vinyl monomer(s) is 80-50 wt %, and which has a glass transition temperature of 0-60.degree. C., a solubility parameter of 9.0-11.0, and a weight-average molecular weight of 4000-30,000.
(2) A method for forming a paint film according to (1), characterized in that the base finishing coat contains as the principal resin a resin which has a glass transition temperature of -50 to +40.degree. C., a solubility parameter of 10.0-12.0 and a surface tension of 30-50 mN/m.
(3) Painted objects obtained by the method of (1) above.
DETAILED DESCRIPTION OF THE INVENTION
The glass transition temperatures (Tg) in the present invention are values found by Equation (1) below, of T. G. Fox (Bull. Am. Phys. Soc. No. 3, 123 (1956)).
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WO9409916 A; (BASF Lacke & Farben); Shibato Kishio (JP); Kawamura Masataka; May 11, 1994(see whole document).
Database WPI sec. Ch., Week 9527, Derwent Publications Ltd., London, GB; AN 95-204098 XPoo2o26639 (No month, date).
Database WPI sec. Ch., Week 9527, Derwent Publications Ltd., London, GB; Cladd A14, AN 95-363057 (No month, date).
Furuuchi Kazuyoshi
Mori Souichi
BASF Coatings AG
Dudash Diana
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