Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-06-02
2002-04-23
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S405000, C428S407000, C427S212000, C427S213360, C427S387000
Reexamination Certificate
active
06376078
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to spherical fine particles of a silicone resin or, more particularly, to spherical fine particles of a silicone resin having usefulness as an additive in plastic resins to impart slipperiness, antiwearing resistance and light-diffusibility, as a blocking inhibitor in plastic films, as a surface lubricity improver in coating compositions, as an extender, lubricity improver and water repellent agent in cosmetic preparations and polishing waxes, polisher agent in cleaning compositions and so on.
As is known, various methods have been proposed heretofore for the preparation of fine particles of a polyorganosilsesquioxane resin. Some of the methods therefor include a method disclosed in Belgian Patent 572412 in which ethyl trichlorosilane is hydrolyzed and subjected to a hydrolysis-condensation reaction in water, a method disclosed in Japanese Patent Publication 40-16917 in which a methyl trialkoxy silane is hydrolyzed and subjected to a condensation reaction in an aqueous solution of an alkaline earth hydroxide or an alkali carbonate, a method disclosed in Japanese Patent Publication 2-22767 in which a methyl trialkoxy silane is hydrolyzed and subjected to a condensation reaction in an aqueous solution of ammonia or an organic amine compound followed by heating of the reaction mixture at 70 to 80° C. to promote the condensation reaction and then the product is washed with water and finely pulverized, a method disclosed in Japanese Patent Kokai 1-217039 in which an alkyl trialkoxysilane, of which the alkyl group has
1
to
6
carbon atoms, is hydrolyzed in the presence of an organic acid and then subjected to a condensation reaction in an alkaline aqueous solution and a method disclosed in Japanese Patent Kokai 4-202325 for the preparation of a polyorganosilsesquioxane resin having, besides methyl groups, long-chain alkyl groups, phenyl groups and alkyl groups substituted by a functional group.
The fine particles of the polyorganosilsesquioxane resins disclosed above are currently under practical use as an additive in plastic resins to impart slipperiness, antiwearing resistance and light-diffusibility, as a blocking inhibitor in plastic films, as a surface lubricity improver in coating compositions, as an extender, lubricity improver and water repellent agent in cosmetic or toiletry preparations and polishing waxes, polisher agent in cleaning compositions and so on. While some problems are left to be solved that incorporation of the particles is detrimental against transparency of the base material, whitening of the base material is unavoidable due to irregular reflection of light on the particle surfaces and, in certain applications, the efficiency of light reflection is decreased on the surface of the base material.
On the other hand, improvements for these defects are proposed heretofore. For example, Japanese Patent Kokai 2-163127 discloses spherical fine particles of a polymethylsilsesquioxane resin having modified surfaces in which organic groups having functional groups such as alkenyl groups, phenyl groups, epoxy groups, acryloxy groups and amino groups are bonded to the polymethylsilsesquioxane molecules on the surface of the resin particles. Further, Japanese Patent Kokai 4-122731 discloses fine particles of a polyorganosilsesquioxane consisting of a core portion formed from polymethylsilsesquioxane units and a surface layer formed from perfluoroalkyl silsesquioxane units. The improvements obtained in these products, however, are limited because the modification is effected only in the composition of the surface portion so that the problems above mentioned relative to the optical properties of the particles remain unsolved.
SUMMARY OF THE INVENTION
The present invention accordingly has an object, in view of the above described problems and disadvantages relative to the conventional fine silicone resin particles, to provide novel spherical fine particles of a silicone resin free from the problems that, when incorporated into a variety of base materials, the transparency of the base material is decreased and the base material is imparted with a whitened appearance due to irregular reflection of light on the silicone resin particles or, in some cases, the efficiency of light reflection is rather decreased as well as to provide a method for the preparation of such improved spherical fine particles of a silicone resin.
Thus, the present invention completed as a result of the extensive investigations undertaken by the inventor with the above mentioned objects, provides spherical fine particles of a silicone resin consisting of methyl silsesquioxane units and phenyl silsesquioxane units and having an average particle diameter in the range from 0.1 to 50 &mgr;m, of which each particle has a composite structure consisting of a core portion of a first silsesquioxane resin and a cladding layer of a second silsesquioxane resin, the molar proportions relative to the methyl silsesquioxane units and phenyl silsesquioxane units in the first and second silsesquioxane resins being different each from the other by a factor of at least 0.02.
In consideration of the optical properties of the particles, in particular, it is preferable that the diameter of the core portion of each particle is in the range from 35% to 90% of the overall diameter of the whole particle and that the difference in the average refractive indices between the core portion and the cladding layer of the particles is in the range from 0.02 to 0.20 as a result of the difference in the molar proportion of the methyl silsesquioxane units and phenyl silsesquioxane units in the first and second silsesquioxane resins. Typically, for example, it is preferable that the first silsesquioxane resin forming the core portion consists of the methyl silsesquioxane units alone and the second silsesquioxane resin forming the cladding layer consists of the phenyl silsesquioxane units alone or vice versa so that the cladding layer has a refractive index larger or smaller than that of the core portion.
The above described unique spherical fine particles of a silicone resin having a composite core-cladding structure of the particle can be prepared by a method comprising the steps of dropwise addition of methyl trialkoxysilane, e.g., methyl trimethoxysilane, phenyl trialkoxysilane, e.g., phenyl trimethoxysilane, or a mixture thereof into an aqueous alkaline medium having a pH in the range from 10.0 to 12.5 at a temperature in the range from 0 to 40° C. to effect hydrolysis and condensation reaction of the silane compound or compounds, in which addition of the silane compound is conducted in two successive steps including a first step and a second step each with the silane compound or a mixture of the silane compounds different relative to the molar proportion of the methyl trialkoxysilane and the phenyl trialkoxysilane from the other.
In particular, for example, the first step addition of the silane compound is performed with a methyl trialkoxysilane only and the second step addition is performed with a phenyl trialkoxysilane only so that each of the thus obtained spherical particles consists of a core portion of methyl silsesquioxane resin and a cladding layer of phenyl silsesquioxane resin.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is described above, the most characteristic feature of the inventive spherical fine particles of a silicone resin is the composite core-cladding structure of the particles while the particles as a whole consists of the siloxane units comprising methyl silsesquioxane units and phenyl silsesquioxane units expressed by the unit formulas of MeSiO
3/2
and PhSiO
3/2
, respectively, in which Me is a methyl group and Ph is a phenyl group. It is optional that the siloxane units forming the particles further comprise siloxane units of other types such as Me
3
SiO
1/2
, Me
2
PhSiO
1/2
, MePh
2
SiO
1/2
, Ph
3
SiO
1/2
, Me
2
SiO
2/2
, MePhSiO
2/2
, Ph
2
SiO
2/2
and SiO
4/2
in a relatively small proportion, for example, not exceeding 20% by moles.
While
Kiliman Leszek
Millen, White, Zelano & Branigan, Plc.
Shin-Etsu Chemical Co., Ltd
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