Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1997-10-23
1999-08-17
Yoon, Tae
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523205, 523216, 524493, 524789, C08K 902, C08K 336
Patent
active
059394714
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to composite materials comprising fine silica particles and organic polymers, and to molded articles made by using such composite materials.
BACKGROUND ART
Generally, many organic polymers have low rigidity, low hardness and low thermal resistance. As an attempt to improve these properties, the formation of composite materials by combination with inorganic materials has frequently been investigated until now.
As composite materials containing colloidal silica, for example, coating compositions comprising an aqueous emulsion of an acrylic polymer having alkoxysilyl or hydroxyl groups and colloidal silica are disclosed in Japanese Patent Publication Nos. 41180/'89, 48832/'92 and 40796/'93, Japanese Patent Laid-Open Nos. 287217/'93, 199917/'94 and 26165/'95, and Japanese Patent Publication No. 94620/'95. These coating compositions are effective in modifying the surface properties of plastic moldings, but cannot improve the rigidity, toughness and thermal resistance of the moldings themselves.
Moreover, thermoplastic resins containing a core/shell material having colloidal silica as the core and polyorganosiloxane as the shell, and a vinyl monomer graft-copolymerized thereto are disclosed in Japanese Patent Laid-Open Nos. 223333/'91, 231925/'91, 270710/'92 and 117338/'93. The process disclosed in these patents comprises polymerizing a siloxane in an aqueous dispersion of colloidal silica to prepare a silica core/silicone shell material and then effecting the emulsion polymerization of a vinyl monomer thereon to obtain a vinyl polymer-grafted core/shell material. Consequently, this process has the disadvantage that, unless a high proportion of a silicone component is added, a large amount of undesired solid matter (cullets) may be formed in the polymerization system and that, depending on the type of the vinyl monomer, the components within the polymerization vessel may solidify during polymerization and fail to yield a stable emulsion. That is, this process involves considerable limitations on composition. Moreover, this process allows colloidal silica to assume only a morphology in which it is completely covered with silicone rubber, and fails to achieve an effect anticipated by incorporating colloidal silica in a resin (i.e., an improvement in the rigidity and thermal resistance of molded articles). Actually, it is theoretically and experimentally shown in J. Mat. Sci., Vol. 29, p. 4651 (1994) that high rigidity cannot be achieved in a structure in which an inorganic filler is coated with a rubber component.
Furthermore, Japanese Patent Laid-Open No. 322036/'94 discloses a process for the preparation of a silica-containing acrylic polymer composition which comprises subjecting a (meth)acrylate and a crosslinkable monomer to emulsion polymerization or suspension polymerization and, when a predetermined degree of polymerization is reached, adding fine silica particles that have previously been treated with a silane coupling agent. In this process, however, a crosslinkable monomer is indispensably used in order to disperse silica satisfactorily and to crosslink the polymer thermally by subsequent addition of a crosslinking agent. Moreover, fine particles of silica powder must previously be dispersed in water and treated with a silane coupling agent. Thus, this process inevitably requires a complicated procedure. Furthermore, since the fine particles of silica powder dispersed in the acrylic polymer have a size greater than a submicron order, it is impossible to obtain highly transparent molded articles which are desired in the present invention.
In addition, Japanese Patent Publication No. 50881/'81 and Japanese Patent Laid-Open Nos. 213839/'87, 53727/'95 and 53728/'95 each disclose dispersions and powders of a composite material comprising charged inorganic particles and oppositely charged polymer particles and having a structure in which the polymer particles are coated with the inorganic particles, as well as a process for preparing the same. These patents are direc
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Ige Hitoshi
Watanabe Hiroyuki
Yanagase Akira
Mitsubishi Rayon Co. Ltd.
Yoon Tae
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