| PATENT ASSIGNEE'S COUNTRY | Japan |
| UPDATE | 09.99 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 07.09.99 |
| PATENT TITLE |
Method for preparing silicone rubber particulates coated with metal oxide microparticles |
| PATENT ABSTRACT |
A novel method for preparing silicone rubber particulates coated with metal oxide microparticles, wherein the metal oxide microparticles are derived from a sol, is disclosed. The silicone rubber particulate so prepared has the advantage of reducing aggregation of the particulate mass. The silicone rubber particulate has particular utility as an additive to organic resins for modifying the properties thereof. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 19.05.92 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | Japanese Abstract, 63309565, 88/12/16, Toray Silicone. |
| PATENT CLAIMS |
What is claimed is: 1. A method of coating silicone rubber particles with metal oxide particles comprising the steps of: forming a water-based dispersion of silicone rubber particles; adding to said dispersion a water-based metal oxide sol; and removing the water from the above mixture by spray-drying. 2. A method in accordance with claim 1 wherein said silicone particles have an average diameter of 0.1 to 200 micrometers. 3. A method in accordance with claim 1 wherein said metal oxide sol has an average particle size between 0.001 and 0.1 micrometers. 4. A method in accordance with claim 2 wherein said metal oxide sol is formed from metals of the group consisting of silicon, titanium, aluminum, zirconium and antimony. 5. A method in accordance with claim 1 wherein said silicone ribber particle dispersion is formed from an addition-reaction-curing of an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms in each molecule and an organopolysiloxane having at least 2 alkenyl groups in each molecule. 6. A method in accordance with claim 1 wherein said silicone rubber particle dispersion is formed from a condensation reaction curing of an hydroxy-terminated diorganopolysiloxane and an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms in each molecule. 7. A method in accordance with claim 1 wherein said step of removing water from the mixture by spray-drying is carried out at a temperature sufficient to remove said water by evaporation and simultaneously cause said silicone rubber to cure. 8. A method in accordance with claim 1 wherein the average particle size of said metal oxide particles is about one-tenth the average particle size of said silicone rubber particles. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to silicone rubber particulate and more specifically to silicon rubber particulate coated with metal oxide. 2. Description of the Prior Art Silicone rubber particulates, water-based dispersions of silicone rubber particulates, and methods for the preparation thereof are known from Japanese Patent Application Laid Open ›Kokai or Unexamined! Numbers 63-77942 ›77,942/88!, 64-70558 ›70,558/89!, and 63-309565 ›309,565/88!. It is also known that silicone rubber particulates are useful as additives for improving or modifying the physical properties of various types of organic resins. However, the particles in the silicone rubber particulates of the prior art have a strong tendency to combine with one another and aggregate. This prevents the development of the properties associated with the silicone rubber particulate in and of itself and thus limits the applications of these silicone rubber particulates. For example, due to their ease of aggregation and poor dispersibility, the prior art silicone rubber particulates cannot be homogeneously dispersed in organic resins of a different type and therefore cannot satisfactorily manifest their properties or characteristics. BRIEF SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a silicone rubber particulate and a method of making the same, wherein the surface of the silicone rubber particles is coated with metal oxide microparticles. Because the surface of the particles is coated, the silicone particulate of the invention resists aggregation to the extent it occurs with prior art silicone particulate. The coated silicone particulate of the invention is particularly useful as an additive to organic resins to improving or modify the physical properties of the resins. Preferably, the silicone rubber particulate has average particle diameter of 0.1 to 200 micrometers and the metal oxide microparticles used to coat the same have an average particle size between 0.001 and 0.1 micrometers. In the preferred embodiment of the invention, the coated silicone particulate is formed from a homogeneous mixture of: (A) a water-based dispersion of a silicone rubber particulate with an average particle diameter of 0.1 to 200 micrometers; and (B) a metal oxide sol. When the water fraction is removed from the above mixture by evaporation, the result is that the silicone rubber particles are coated with the metal oxide. DETAILED DESCRIPTION OF THE INVENTION The silicone rubber particulate of the present invention comprises a particulate having an average particle diameter of 0.1 to 200 micrometers and wherein the surface of the particles is coated with metal oxide microparticles. Silicone rubbers as known from the art can be used as the silicone rubber component of this silicone rubber particulate. Examples of such silicone rubbers include: silicone rubbers afforded by the cure of organoperoxide-curing silicone rubber compositions whose basic components are organoperoxide and alkenyl-containing diorganopolysiloxane, and which optionally contain reinforcing filler; silicone rubbers afforded by the cure of addition-reaction-curing silicone rubber compositions whose basic components are a platinum-type compound, SiH-containing organopolysiloxane, and diorganopolysiloxane containing Si-bonded alkenyl groups, and which optionally contain reinforcing filler; silicone rubbers afforded by the cure of condensation-reaction-curing silicone rubber compositions whose basic components are silanol-terminated diorganopolysiloxane, SiH-containing organopolysiloxane, and organontin compound, and which optionally contain reinforcing filler; and silicone rubbers afforded by the cure of condensation-reaction-curing silicone rubber compositions whose basic components are silanol-terminated diorganopolysiloxane, hydrolyzable organosilane, and organotin compound or titanate ester, and which optionally contain reinforcing filler. The latter two types, i.e., silicone rubbers afforded by the cure of addition-reaction-curing silicone rubber compositions and by the cure of condensation-reaction-curing silicone rubber compositions, are preferred for the present invention due to their ease of preparation and ease of handling. The average particle diameter of the silicone rubber particulate prepared from silicone rubber as described above should fall within the range of 0.1 to 200 micrometers and preferably falls within the range of 0.5 to 80 micrometers. When the average particle diameter falls below 0.1 micrometers, the metal oxide will not uniformly coat the surface of the silicone rubber particulate and the silicone rubber particulate will itself form granules. On the other hand, average particle diameters in excess of 200 micrometers are too large; for example, such a silicone rubber particulate cannot be employed as a physical property-modifying additive for organic resins. The metal oxide microparticles are exemplified by microparticles of silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, and antimony oxide. The particle diameter of the metal oxide should assume values suitable for coating the surface of the aforesaid silicone rubber particulate, and metal oxide particles useful for this purpose will have sizes no larger than one-tenth the particle diameter of the silicone rubber particulate to be coated. In general, average particle diameters within the range of 0.001 to 0.1 micrometers are used. The method for preparing the particulate according to the present invention will now be considered in greater detail. The component (A) employed in the present invention's preparative method comprises a water-based dispersion of silicone rubber particulate with an average particle diameter of 0.1 to 200 micrometers. The same silicone rubber compositions known from the art as described hereinbefore are applicable as compositions useable for this invention. The latter two types, i.e., silicone rubbers afforded by the cure of addition-reaction-curing silicone rubber compositions and silicone rubbers afforded by the cure of condensation-reaction-curing silicone rubber compositions, are again preferred for the present invention due to their ease of preparation and ease of handling. Several methods are available for the preparation of component (A) (water-based dispersion of silicone rubber particulate), and concrete examples of its preparation are provided as follows: (1) An addition-reaction-curing silicone rubber composition is first prepared from a platinum-type compound catalyst, organohydrogenpolysiloxane containing at least 2 silicon-bonded hydrogen atoms in each molecule, and organopolysiloxane containing at least 2 alkenyl groups (typically vinyl) in each molecule. This addition-reaction-curing silicone rubber composition is introduced into water or surfactant-conitaining water and dispersed into particles by stirring the water or surfactant-containing water. Curing is then carried out with heating or merely by maintenance as such. (2) A condensation-reaction-curing silicone rubber composition is first prepared from a platinum-type catalyst, diorganopolysiloxane containing 2 hydroxyl groups (at the two molecular chain terminals), and organohydrogenpolysiloxane containing at least 3 silicon-bonded hydrogen atoms in each molecule; this condensation-reaction-curing silicone rubber composition is introduced into water or surfactant-containing water and dispersed into particles by stirring the water or surfactant-containing water; and curing is then carried out with heating or merely by maintenance as such. The extent of cure in the silicone rubber particulate is not specifically restricted within the context of the present invention, and the present invention encompasses silicone rubber particulates with cures ranging from partial to complete. The metal oxide sol comprising the component (B) employed by the present invention's preparative method is the component which equips the silicone rubber particulate according to the present invention with dispersibility and lubricity. This metal oxide sol is exemplified by silicon oxide sols, titanium oxide sols, aluminum oxide sols, zirconium oxide sols, and antimony oxide sols. The quantity of use of component (B) is not specifically restricted as long as (i) it is present in a quantity which will afford a homogeneous mixture, i.e., a homogeneous water-based dispersion, when preparing the mixture of components (A) and (B), and (ii) it is present in a quantity sufficient for coating the surface of component (A). However, component (B) is preferably employed at 0.1 to 100 weight parts per 100 weight parts component (A) and particularly preferably at 1 to 50 weight parts per 100 weight parts component (A). The silicone rubber particulate in this case should have an average particle diameter of 0.1 to 200 micrometers and preferably 0.5 to 80 micrometers. When this average particle diameter falls below 0.1 micrometers, the metal oxide will not uniformly coat the surface and the silicone rubber particulate will itself form granules. Furthermore, the water-based dispersion of silicone rubber particulate is advantageously prepared by a method such as (1) or (2) above by preliminarily calculating and adjusting the quantity of water, quantity of silicone rubber particulate, quantity of emulsifying agent, etc., taking into consideration the nature of the mixture after the addition of component (B). In the preparative method according to the present invention, the water is then removed from this mixture of components (A) and (B) as described hereinbefore. The water can be easily removed using a thermal dryer as known in the art, for example, a hot-air circulation oven or spray dryer. The present invention's silicone rubber particulate as described hereinbefore in and of itself has an excellent lubricity and in particular an excellent dispersibility in various types of organic resins. It can therefore be used, for example, as an additive for modifying the physical properties of organic resins. The present invention will be explained in greater detail below through illustrative and reference examples, in which parts are by weight. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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