Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-04-05
2002-10-01
Beck, Shrive P. (Department: 1762)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S447000, C428S448000, C427S407100, C427S409000, C525S063000
Reexamination Certificate
active
06458463
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for forming, on automotive bodies, a multilayer coating film having weathering resistance, acid resistance, car wash-free stain resistance and storage stability and excellent in recoat adhesion in non-sand recoating (NSR) and in water resistance and to an automotive body.
PRIOR ART
A clear coating for top coating for automobiles is required to have decorativeness, weathering resistance and like qualities as key performance characteristics in addition to the minimum requirement to be met by any coating, namely storage stability, since said coating constitutes the outermost layer of coating films on automotive bodies. In recent years, from the viewpoint of decorativeness producing a good appearance, it has been further desired that such coatings should maintain their decorativeness, namely their resistance to staining and their giving no unpleasant feeling even after repeated use.
Generally, the outermost layer of automotive coating films is washed with water by the user to remove stains and, where necessary, further treated with wax to remove surface stains. In the case of luxury cars, it is very important from the decorativeness viewpoint to wax for polishing whereas, in the case of cars of practical use, for example passenger cars, it is important from the decorativeness viewpoint that any unpleasant feeling will not be awakened even in repeated use.
Thus, a function such that surface stains will not be left without particularly removing stains by washing with water becomes more important. In other words, if clear coating films which have sufficient hydrophilicity to allow surface contaminants to be washed away by rainwater and the like and thus make the coatings car-wash-free without requiring any work to remove the contaminants are provided, the user will be no more required to waste time and labor for car washing and, thus, a clear coating for automobiles which has such hydrophilicity and is excellent in decorativeness has been desired.
In the pamphlet (1994) on International laid-open Patent Application No. 94/06870, there is disclosed a coating which comprises a hydroxyl-containing organic base resin with an organosilicate and/or a condensation product derived therefrom incorporated therein plus an amino resin curing agent or a (blocked) polyisocyanate compound crosslinking agent as a reaction-curable organic resin. As specific examples preferred as the organosilicate, there are mentioned tetrahydroxysilane, tetramethoxysilane, tetraethoxysilane and the like.
In Japanese Kokai Publication Hei-07-331165, there is disclosed a method of forming top coating films using a curable coating comprising an acid/epoxy-curable coating and a silicon compound having at least one silanol group and/or a hydrolyzable group directly bonded to a silicon atom in each molecule.
In Japanese Kokai Publication Hei-09-220516, there is disclosed a method of forming multilayer coating films for automobiles which comprises applying a water-based coating containing, as a base coat, a water-based tertiary amino- and/or acid group-containing resin, and a compound having an epoxy group and a hydrolyzable silyl group in each molecule.
In Japanese Kokai Publication Hei-10-67844, there is disclosed a heat-curable resin composition which comprises a polyol resin, a blocked polyisocyanate curing agent or an amino resin, a silane coupling agent-treated silicate Condensate derived from a partial hydrolyzate-condensate of an alkoxysilane compound by treatment with a silane coupling agent. These technologies are to solve the problems mentioned above about stain resistance by incorporating a relatively low-molecular silicate compound.
In Japanese Kokai Publication Hei-10-140077, there is disclosed a top coating for automobiles which comprises an acid/epoxy-curable coating with a low condensate (low silicate condensate), with a degree of condensation of 2 to 10, of tetramethyl silicate and/or tetraethyl silicate incorporated therein. This technology, too, is to solve the problems mentioned above about stain resistance.
By using a low condensate of tetramethyl silicate and/or tetraethyl silicate as the low silicate condensate, namely by restricting the number of carbon atoms in the alkoxyl group, this technology contrives to retain the reactivity with water. And, as a basic principle, coating films obtained from this coating show high hydrophilicity resulting from the hydroxyl groups formed by the reaction of methoxy or ethoxy groups of the low silicate condensate as occurring in large amounts in the vicinity of the surface of coating films with water upon exposure or treatment with an acid and thus show stain resistance.
However, when a low condensate of tetramethyl silicate, which has highly reactive methoxy groups alone, is used as the low silicate condensate, coating films formed by using the coating at an early stage of storage show high hydrophilicity and good stain resistance whereas, however, during a long period of storage, low silicate condensate molecules may react with one another or the low silicate condensate may react with hydroxyl groups in the epoxy resin in the coating, resulting in viscosity increases and marked worsening in storage stability and/or in insufficient hydrophilicity and insufficient stain resistance of coating films when formed from the coating after storage. Such problems still remain.
When a low condensate of tetraethyl silicate having ethoxy groups alone is used as the low silicate condensate, the reactivity of the ethoxy group is lower than that of the methoxy group, so that the coating shows relatively improved storage stability; however, coating films obtained will not show good hydrophilicity, hence cannot show satisfactory stain resistance.
When a low condensate derived from tetramethyl silicate and one derived from tetraethyl silicate are used as the low silicate condensate, too, the fact that the silicon atoms in the low silicate condensates have methoxy or ethoxy groups alone as functional groups raises the same storage stability problem; coating films obtained from the coating after storage tend to show unsatisfactory hydrophilicity.
Furthermore, such low silicate condensates provide coating film surfaces with high hydrophilicity, so that the surfaces may possibly take up moisture into the coating films to thereby cause whitening (blushing) and thus worsen the coating film appearance.
When an abnormality in the coating film appearance due to settling of dust, for instance, occurs in an automobile coating line, that portion is locally repaired by polishing with a sandpaper or the like, or the unit block of the automotive panel is recoated again with the corresponding base coating and clear coating for top coating.
It is known, in such cases, that when the recoating anew with the base coating and the clear coating for top coating (for second coat) is carried out-without polishing the existing (first coat) clear coating film, the adhesion between the first coat clear coating film and second coat base coating film is generally inferior to that adhesion attainable when the (second coat) base coating and clear coating for top coating are reapplied after polishing the existing (first coat) clear coating film prior to recoating.
Since, when the first coat clear Rating film is not polished, the adhesion of the (second coat) base coating film is inferior, as mentioned above, it has become a general practice to apply the second coat base coating and clear coating for top coating after polishing the first coat clear coating film.
If the adhesion of the second coat base coating film shows equally good adhesion even when the second coat base coating and clear coating for top coating are reapplied without polishing the first coat clear coating film, the trouble of polishing the first coat clear coating film will be saved and the cost of repairing or recoating in an automobile coating line will be reduced. Therefore, it has been desired that, on the occasion of applying the second coat base coating and clear coating for
Toui Teruzo
Yoshioka Manabu
Beck Shrive P.
Fletcher, III William Phillip
Nippon Paint Co., LTD
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