Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-04-27
2003-04-01
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C528S029000, C528S028000, C528S031000, C528S025000, C525S479000, C525S474000, C525S453000, C427S389000
Reexamination Certificate
active
06541119
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to curable compositions, particularly to curable film-forming compositions, comprising a functional group-containing organic polysiloxane component, which is a chain-extended reaction product, the compositions being characterized in that they provide cured compositions having high crosslink densities. More particularly, the invention relates to curable film-forming compositions which exhibit improved scratch resistance.
BACKGROUND OF THE INVENTION
Color-plus-clear coating systems involving the application of a colored or pigmented base coat to a substrate followed by application of a transparent or clear top coat over the base coat have become increasingly popular as original finishes for automobiles. The color-plus-clear systems have outstanding appearance properties such as gloss and distinctness of image due in large part to the clear coat.
Clear film-forming compositions, particularly those used to form the transparent top coat in color-plus-clear systems for automotive applications, are subject to damage from numerous environmental elements. Such elements include acidic precipitation, exposure to ultraviolet radiation from sunlight, high relative humidity and temperatures, and defects due to impact with small, hard objects resulting in chipping and scratching of the coating surface.
Typically, a harder more highly crosslinked film may exhibit improved scratch resistance, but it is much more susceptible to chipping and/or thermal cracking due to embrittlement of the film resulting from a high crosslink density. A softer, less crosslinked film, while not prone to chipping or thermal cracking, is susceptible to scratching, water spotting and acid etch due to a low crosslink density of the cured film.
U.S. patent Ser. No. 08/904,597, filed Aug. 1, 1997 discloses curable compositions based on functional polysiloxanes, particularly hydroxyl functional group-containing polysiloxanes, which are suitable for use as clear coats in color-plus-clear systems for automotive applications. The functional group-containing polysiloxanes provide clear coatings with, inter alia, improved mar and acid etch resistance.
U.S. Pat. No. 5,853,809 discloses clear coats in color-plus-clear systems which have improved scratch resistance due to the inclusion in the coating composition of surface reactive inorganic microparticles such as colloidal silicas which have been modified with a reactive coupling agent. There, nonetheless, remains a need in the automotive coatings art for top coats having improved initial scratch resistance as well as enhanced post-weathering (“retained”) scratch resistance without embrittlement of the film due to the high crosslink density.
SUMMARY OF THE INVENTION
In accordance with the present invention, multi-component composite coating compositions are provided which comprise a base coat deposited from a pigmented film-forming composition and a transparent top coat, or top coats, applied over the base coat in which the transparent top coat is deposited from a film-forming composition comprising:
(a) one or more ungelled organic polysiloxanes having reactive functional groups, said polysiloxane comprising at least one unit of the following structure (I):
wherein R
1
and R
2
are independently selected from the group consisting of OH and monovalent hydrocarbon groups; X is an organic polyvalent linking group selected from the group consisting of alkylene, oxyalkylene, and alkylene aryl, which is derived from a material having two or more unsaturated bonds capable of undergoing hydrosilylation reaction; and n has a value ranging from 2 to 4 such that n is equal to the number of unsaturated bonds capable of undergoing hydrosilylation reaction; and
(b) one or more curing agents having functional groups reactive with the functional groups of (a). A method for applying the multi-component composite coating composition to a substrate and coated substrates are also provided.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Also, as used herein, the term “polymer” is meant to refer to oligomers and both homopolymers and copolymers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As aforementioned, the transparent top coat of the multi-component composite coating of the present invention is deposited from a film-forming composition comprising: (a) an ungelled organic polysiloxane having reactive functional groups of the formula (I) above; and (b) a curing agent having functional groups reactive with the functional groups of the polysiloxane (a).
Preferably, the polysiloxane (a) comprises the ungelled reaction product of the following reactants (i) and (ii):
(i) one or more polysiloxanes containing silicon hydride having the structure (II):
wherein the R groups are independently selected from the group consisting of H, OH, and monovalent hydrocarbon groups connected to the silicon atoms, provided at least one of the groups represented by R is H; and m has a value ranging from 0 to 100, preferably 0 to 5, such that the mole percent of hydrogen-bonded silicon atoms to non-hydrogen-bonded silicon atoms ranges from 10 to 100; and
(ii) one or more materials having two or more, preferably two, unsaturated bonds capable of undergoing hydrosilylation reaction with the silicon hydride group (Si—H) of the polysiloxane. Preferably, reactant (ii) contains functional groups, most preferably, hydroxyl functional groups.
By “ungelled” is meant that the reaction products are substantially free of crosslinking and have an intrinsic viscosity when dissolved in a suitable solvent, as determined, for example, in accordance with ASTM-D1795 or ASTM-D4243. The intrinsic viscosity of the reaction product is an indication of its molecular weight. A gelled reaction product, on the other hand, since it is of essentially infinitely high molecular weight, will have an intrinsic viscosity too high to measure.
It should be appreciated that the various R groups can be the same or different and it is usually the case that the R groups will be mixed groups or entirely monovalent hydrocarbon groups.
As used herein and in the claims, “monovalent hydrocarbon groups” means organic groups containing essentially carbon and hydrogen. The hydrocarbon groups can be branched or unbranched, aliphatic, aromatic, cyclic, or acyclic and can contain from 1 to 24 (in the case of aromatic from 3 to 24) carbon atoms. The hydrocarbon groups can be substituted with heteroatoms, for example, oxygen. Examples of such monovalent hydrocarbon groups include alkyl, alkoxy, aryl, alkaryl or alkoxyaryl groups.
By “alkylene” is meant acyclic or cyclic alkylene groups having a carbon chain length of from C
2
to C
25
. Examples of suitable alkylene groups include those derived from propene, butene, pentene, 1-decene, isoprene, myrcene, and 1-heneicosene. By “oxyalkylene” is meant an alkylene group containing at least one ether oxygen atom and having a carbon chain length of from C
2
to C
25
, preferably from C
2
to C
4
. Examples of suitable oxyalkylene groups include those derived from trimethylolpropane monoallyl ether, pentaerythritol monoallyl ether, trimethylolpropane diallylether, polyethoxylated allyl alcohol, and polypropoxylated allyl alcohol. By “alkylene aryl” is meant an acyclic alkylene group containing at least one aryl group, preferably phenyl, and having an alkylene carbon chain length of from C
2
to C
25
. The aryl group can be substituted, if desired. Suitable substituent groups include hydroxyl, benzyl, carboxylic acid, and aliphatic groups. Examples of suitable alkylene aryl groups include those derived from styrene and 3-isopropenyl-&agr;,&agr;-dimethylbenzyl isocyanate.
It should be understood that the ratio of reactants (i) and (ii) and reaction conditions are selected to produce a “chain extended” polysiloxane reaction product. The term “chain
Anderson Lawrence G.
Hockswender Thomas R.
Nakajima Masayuki
Sadvary Richard J.
Simpson Dennis A.
Dawson Robert
Peng Kuo-Liang
PPG Industries Ohio Inc.
Uhl William J.
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