Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
2001-06-08
2004-01-13
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Silicon containing other than solely as silicon dioxide or...
C106S287130, C106S287140, C106S287160
Reexamination Certificate
active
06676740
ABSTRACT:
This invention relates to coating compositions for forming mar and weather-resistant protective coatings on plastic substrates, typically polycarbonate resin substrates, a method for coating plastic substrates with the coating compositions, and coated articles having coatings thereof.
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 can adversely affect the adhesion to the substrate. 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.
On the other hand, Japanese Patent Nos. 2,938,458 and 2,924,018, JP-A 11-286652 and JP-A 10-324827 attempt to enhance the curing properties and weather and abrasion resistance of coating compositions by adding thereto titanium chelate compounds or partial hydrolyzates thereof which play the catalytic role of promoting cure. Undesirably, these attempts rather detract from crack resistance by reason of over-curing, and tend to adversely affect storage stability.
SUMMARY OF THE INVENTION
An object of the invention is to provide a coating composition and method for forming a protective coating having improved mar and weather resistance. Another object is to provide a coated article having a mar and weather-resistant coating.
The inventors have found that a coating composition capable of achieving the above objects is obtained by blending an organosilicon compound having a hydrolyzable group-bearing silyl group with a hydrolytic condensate (sometimes referred to as final reaction product) of a reaction product and/or a mixture of a &bgr;-diketone with a mixture (b-1) containing a titanium tetraalkoxide and a metal alkoxide of the formula: M(OR)
n
wherein M is at least one metal selected from among Zr, Fe, Al, Zn, In, Cu, Si, Sn, W, and Mg, n is the valence of the metal, and R is an alkyl group of 1 to 10 carbon atoms or hydrogen.
Studying a coating composition for improving the mar and weather resistance of molded parts of thermoplastic resins such as polycarbonate, the inventors have discovered that when the final reaction product is added to the organosilicon compound, the resulting composition remains very stable over a long term. Especially the final reaction product is (1) the reaction product obtained by reacting in a solvent the mixture (b-1) of the titanium tetraalkoxide as a main component and the metal alkoxide with a &bgr;-diketone, followed by hydrolytic condensation, or (2) the reaction product obtained by subjecting the mixture (b-1) of the titanium tetraalkoxide as a main component and the metal alkoxide to hydrolytic condensation in a solvent containing a &bgr;-diketone. Unlike customary titanium oxide sol, the final reaction product is soluble in solvents, does not settle with the lapse of time, and remains stable in the mixture. When a coating is formed from the composition, very good transparency is provided as compared with the titanium oxide sol. Since the final reaction product takes a microparticulate structure and has &bgr;-diketone ligands left on particle surfaces, it imparts lubricity to the coating surface, significantly improving abrasion resistance as compared with the conventional titanium oxide sol-added coatings. Moreover, the final reaction product can act as a crosslinking catalyst to achieve nearly full-cure crosslinkage even under moderate curing conditions, leaving few uncrosslinked portions. Crack resistance is improved since the undesirable phenomenon that micro-cracks generate as a result of slow progress of crosslinking with time is eliminated.
Additionally, the final reaction product itself has a ultraviolet radiation absorbing capability, which eliminates the addition of or reduces the amount of an organic UV absorber, thereby removing the detrimental effects by bleeding-out of such absorber. Since there is no loss of UV absorbing capability which is otherwise caused by decomposition of organic UV absorbers, satisfactory weather resistance is kept over a long period of time. Continuing further study on the ratio and amounts of distinct components in the coating composition, the inventors has arrived at the present invention.
In one aspect, the invention provides a coating composition as defined below.
I) A coating composition comprising
(A) 100 parts by weight of an organosilicon compound having a hydrolyzable group-bearing silyl group, and
(B) 0.1 to 50 parts by weight of a hydrolytic condensate of a reaction product and/or a mixture of a &bgr;-diketone with a mixture (b-1) containing a titanium tetraalkoxide and a metal alkoxide of the formula: M(OR)N wherein M is at least one metal selected from the group consisting of Zr, Fe, Al, Zn, In, Cu, Si, Sn, W, and Mg, n is the valence of the metal, and R is an alkyl group of 1 to 10 carbon atoms or hydrogen.
II) The coating composition of I wherein component (A) is a silane compound of the formula (1):
R
3
a
Si(R
4
)
4-a
(1)
wherein R
3
is an alkyl, aryl, halogenated alkyl, halogenated aryl or alkenyl group of 1 to 10 carbon atoms or an organic group having an epoxy, (meth)acryloxy, mercapto, amino or cyano group, R
4
is an alkoxy, alkenyloxy, acyloxy or alkoxyalkoxy group of 1 to 10 carbon atoms, and “a” is 0, 1 or 2, and/or a hydrolyzate thereof.
III) The coating composition of I wherein component (A) is an organic copolymer of an alkoxysilyl group-containing acrylic and/or vinyl monomer and another monomer copolymerizable therewith, the content of the alkoxysilyl group-containing acrylic and/or vinyl monomer in the organic copolymer being 0.1 to 50% by weight.
IV) The coating composition of any one of I to III wherein component (B) is a hydrolytic condensate obtained by reacting in a solvent the mixture (b-1) with a &bgr;-diketone of the general formula: R
1
COCH
2
COR
2
wherein R
1
and R
2
are alkyl groups of 1 to 6 carbon atoms and may be the same or different, followed by hydrolytic condensation.
V) The coating composition of any one of I to III wherein component (B) is a hydrolytic condensate obtained by subjecting the mixture (b-1) to hydrolytic condensation in a solvent containing a &bgr;-diketone of the general formula: R
1
COCH
2
COR
2
wherei
Higuchi Koichi
Matsumura Kazuyuki
Yamaya Masaaki
Brunsman David
Shin-Etsu Chemical Co. , Ltd.
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