Ultrafine reactive silica particles, suspension containing the s

Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...

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423338, 423339, C09D 100

Patent

active

058006060

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a reactive ultrafine particulate silica, a suspension containing the same and a hard coating composition.


BACKGROUND ART

A resin coating, a silicone coating or an inorganic coating is used as a means for forming a hard thin film on glass, resin or metal surface for preventing occurrence of scratches, invasion by various chemicals and permeation of water, air and other gases.
Among these coating materials, a resin thin film is flexible but is easily damaged. A silicone thin film is water-repellent but is easily damaged. On the other hand, an inorganic thin film is hardly damaged but is breakable and it is difficult to form a uniform thin film.
Particularly, a tetraethoxysilane oligomer is used as an inorganic type hard coating composition, but the hardness of its thin film is insufficient and the storage stability as a hard coating composition is unsatisfactory and it is difficult to effect mass production.


DISCLOSURE OF INVENTION

The present inventors have studied and discovered as the result of the study that a composition obtained by blending tetramethoxysilane with water has a satisfactory storage stability and provides a very thin coating film excellent in hardness and flexibility, and that a reactive ultrafine particulate silica having a radius of gyration of at most 10 .ANG. can be obtained by hydrolysis condensation of tetramethoxysilane and a suspension containing the reactive ultrafine particulate silica provides a hard coating composition having excellent properties.
Thus, the essential feature of the present invention resides in a reactive ultrafine particulate silica, a suspension containing the same and a hard coating composition obtained by blending tetramethoxysilane with water.


BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows measurement data of scattering intensity of composition A obtained in Example 1 illustrating one example of a suspension of the present invention; FIG. 2 shows measurement data of scattering intensity of composition B obtained in Example 1 illustrating another example of a suspension of the present invention; FIG. 3 shows point beam data after slit amendment of composition A; FIG. 4 shows point beam data after slit amendment of composition B; FIG. 5 shows distribution of radius of gyration of fine particles in composition A; FIG. 6 shows distribution of radius of gyration of fine particles in composition B; FIG. 7 shows distribution of sphere-assumed radius of fine particles in composition A; FIG. 8 shows distribution of sphere-assumed radius of fine particles in composition B; and FIG. 9 shows measurement data of scattering intensity of a tetramethoxysilane oligomer obtained in Example 1 (synthesis of tetramethoxysilane oligomer).


DETAILED DESCRIPTION OF THE INVENTION

The present invention is described hereinafter in details.
The hard coating composition of the present invention is a hard coating composition obtained by blending tetramethoxysilane with water. Thus, in the present invention, a tetramethoxysilane is used as an alkoxysilane. The tetramethoxysilane used in the present invention is a monomer (Si(OCH.sub.3).sub.4) obtained by such a process as reaction of silicon tetrachloride and methanol or reaction of metallic silicon and methanol and/or an oligomer which is a partly hydrolyzed condensate of these monomers. Since impurities can be easily removed by purifying this starting material and this material does not by-produce hydrochloric acid which is liable to corrode an apparatus, it is preferable to employ a monomer of tetramethoxysilane obtained by reacting silicon and methanol and/or its oligomer particularly for use which requires removal of impurities.
It is indicated that a tetramethoxysilane monomer is remarkably poisonous and attacks cornea of eyes and even its vapor brings damages. Also, since it is highly active, it sometimes generates heat and causes bumping during operation. Further, a hard coating composition containing a large amount of the tetramethoxysilane monomer is liable to gradually

REFERENCES:
patent: 5011669 (1991-04-01), Tsuchiya et al.
CA 94:161236, Yamane, "Gelling of silicon methoxide solution", 1980.
CA 110:119944, Ziemath et al., "Light scattering of silica monodisperse microspheres", 1988.
Database WPI, Derwent Publications, AN 83-841316, JP-A-58 189 263, (Nov. 4, 1983).
Database WPI, Derwent Publications, AN 93-261870, JP-A-05 179 201, (Jul. 20, 1993).
Database WPI, Derwent Publications, AN 93-148965, JP-A-05 085 714, (Apr. 6, 1993).
Database WPI, Derwent Publications, AN 89-344255, JP-A-01 256 576, (Oct. 13, 1989).

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