Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-07-21
2002-12-24
Dawson, Robert (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S412000, C427S164000, C427S204000, C427S387000, C524S588000, C524S858000, C524S859000, C528S012000, C528S021000, C528S029000, C106S287100
Reexamination Certificate
active
06497964
ABSTRACT:
This invention relates to coating compositions for forming mar and weather-resistant protective coatings on plastic substrates, typically polycarbonate resin substrates, and a method for the surface protection of plastic substrates.
BACKGROUND OF THE INVENTION
As glazing substitutes, shatterproof or highly shatter resistant transparent materials have been widely utilized for these decades. For example, plastic substrates, especially polycarbonate resins have superior transparency, impact resistance and heat resistance and are currently used as structural members instead of glass in a variety of applications including building and vehicle windows and instrument covers.
The polycarbonate resins, however, are inferior to glass in surface properties such as mar resistance and weather resistance. It is desired to improve the surface properties of polycarbonate resin parts. Nowadays, polycarbonate resin parts for use as vehicle windows and acoustic barrier walls along highways are required to withstand more than 10 years of weathering.
Known means for improving the weather resistance of polycarbonate resin parts include the lamination of a weather resistant acrylic resin film on the surface of a polycarbonate resin substrate and the formation of a ultraviolet absorber-containing resin layer on the resin surface, for example, by co-extrusion.
For improving the mar resistance of polycarbonate resin parts, it is known to coat thermosetting resins such as polyorganosiloxanes and melamine resins and to coat photo-curable resins such as polyfunctional acrylic resins.
As to the manufacture of transparent articles having both weather resistance and mar resistance, JP-A 56-92059 and JP-A 1-149878 disclose ultraviolet-absorbing transparent substrates having a primer layer loaded with a large amount of UV absorber added and a protective coating of colloidal silica-containing polysiloxane paint overlying the primer layer. However, several problems arise with this approach. The addition of a large amount of UV absorber, especially to the primer layer can adversely affect the adhesion to the substrate and to the protective coating of colloidal silica-containing polysiloxane paint to be applied on the primer layer. During heat curing step, the UV absorber can volatilize off. On outdoor use over a long period of time, the UV absorber will gradually bleed out, causing whitening. From the mar resistance standpoint, it is impossible to add a large amount of UV absorber to the protective coating of colloidal silica-containing polysiloxane.
From these considerations, it was also attempted to fix a UV absorber by silyl modification. For example, JP-A57-21476 discloses alkylcarbamyl addition products of alkoxysilyl or alkanoylsilyl. This method, however, involves complex steps and is uneconomical.
It is also proposed to produce silyl-modified UV absorbers by reacting aromatic UV absorbers such as 2,4-dihydroxybenzophenone with silane compounds containing hydroxyl and epoxy groups. The reaction is effected between hydroxyl groups in the former and epoxy groups in the latter in the presence of tetramethylammonium chloride as disclosed in JP-A 58-10591 and JP-A 58-8766 or an aluminum chelate as disclosed in JP-B 3-62177.
Since these silyl-modified UV absorbers have alkoxysilyl groups which undergo condensation reaction during the heat curing step, the absorbers are advantageously fixed within the coating during the heat curing step so that the absorbers might not bleed out. However, these UV absorbers are less resistant to weathering, probably because the conjugated system of the UV absorber is altered by silyl modification. In general, the silyl-modified UV absorbers are added to the outermost protective coating layer. In the prior art, it has never been attempted to add the silyl-modified UV absorbers to primer or undercoating compositions.
SUMMARY OF THE INVENTION
An object of the invention is to provide a coating composition having improved long-term weather resistance and surface protection performance on a plastic substrate, and suited as an outermost coating on such a substrate. Another object is to provide an article having a coating of the coating composition on a substrate.
A further object is to provide an undercoating composition comprising a silyl-modified UV absorber and capable of forming a protective coating having improved mar and weather resistance. A still further object is to provide a method for protecting a surface of a plastic substrate using the undercoating composition.
We have found that significant improvements are made when a protective coating composition comprising (1) the reaction product of a hydroxyl group-containing benzophenone compound with a silane and/or a (partial) hydrolyzate thereof, preferably the reaction product obtained by reacting a compound of the following general formula (A) with an epoxy group-containing silane of the following general formula (B) in the presence of a catalyst, and/or a (partial) hydrolyzate thereof, (2) a silane of the following general formula (C) and/or a (partial) hydrolyzate thereof, and optionally and preferably, (3) a microparticulate inorganic oxide containing titanium, cerium or zinc, and capable of absorbing light with a wavelength of up to 400 nm, or a protective coating composition comprising a co-hydrolyzate of components (1) and (2), and optionally and preferably, component (3) is applied and cured onto plastic substrates, typically polycarbonate resins. The benzophenone organic UV absorber does not bleed out because of silyl modification or detract from mar resistance because of good compatibility with component (2). The benzophenone organic UV absorber containing at least three OH groups in a molecule maintains a UV absorbing capability substantially unchanged despite silyl modification. The use of benzophenone organic UV absorber in combination with the microparticulate inorganic oxide capable of absorbing light with a wavelength of up to 400 nm achieves the synergistic effect of effectively absorbing light in a wide UV region for significantly improving the weather resistance of plastic substrates, typically polycarbonate resins.
In formula (A), X, which may be the same or different, is hydrogen or a hydroxyl group, and at least one X is a hydroxyl group.
R
1
a
SiR
2
b
(OR
3
)
4-a-b
(B)
In formula (B), R
1
is an epoxy group-containing organic group, R
2
is an alkyl group of 1 to 10 carbon atoms or aryl group, R
3
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group of 1 to 10 carbon atoms which may contain an oxygen atom, “a” is equal to 1 or 2, “b” is equal to 0 or 1, and the sum of a and b is equal to 1 or 2.
R
4
m
SiR
2
n
(OR
3
)
4-m-n
(C)
In formula (C), R
4
is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 10 carbon atoms, R
2
is an alkyl group of 1 to 10 carbon atoms or aryl group, R
3
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group of 1 to 10 carbon atoms which may contain an oxygen atom, m and n each are equal to 0, 1 or 2, and the sum of m and n is equal to 0, 1 or 2.
Seeking for an undercoating composition capable of improving the adhesion and weather resistance of molded parts of thermoplastic resins such as polycarbonate which are subsequently coated with an organopolysiloxane coating, we have found that when the reaction product of a hydroxyl group-containing benzophenone compound with a silane and/or a (partial) hydrolyzate thereof, preferably the reaction product obtained by reacting a compound of the general formula (A) with an epoxy group-containing silane of the general formula (B) and/or a (partial) hydrolyzate thereof is added to the undercoating composition, the reaction product is so compatible with other components in the undercoating composition owing to the effect of silyl groups that a large amount of the reaction product may be added without detracting from the adhesion of the undercoating composition to the substrate or the protective coating. The UV absorber is firmly fixed in the undercoat, elim
Higuchi Koichi
Kudo Muneo
Matsumura Kazuyuki
Sato Kazuharu
Yamaya Masaaki
Birch & Stewart Kolasch & Birch, LLP
Dawson Robert
Feely Michael J
Shin-Etsu Chemical Co. , Ltd.
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