Coating processes – Particles – flakes – or granules coated or encapsulated – Applying superposed diverse coatings or coating a coated base
Reexamination Certificate
1999-05-17
2003-02-18
Mulcahy, Peter D. (Department: 1713)
Coating processes
Particles, flakes, or granules coated or encapsulated
Applying superposed diverse coatings or coating a coated base
C427S215000, C427S220000, C524S261000, C524S262000
Reexamination Certificate
active
06521290
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fine silica particles treated with a silane, and more particularly to a fine silica particles having a high dispersibility and low aggregative properties, a process for their production, and an organic resin composition containing such fine silica particles.
2. Description of the Prior Art
As methods for the surface treatment of silica with silane, commonly available methods are those in which silane is made to adhere to silica particle surfaces by treatment with silicone oil and those in which silane is chemically bonded to silica particle surfaces by treatment with hexamethydisilazane.
Properties required in organic resins, in particular, organic resin films, include transparency, blocking resistance, slip properties, scratch resistance and so forth. Adding spherical fine silica particles in organic resin films is proposed and is reported to bring about an improvement in transparency of the resultant film (Japanese Pre-examination Patent Publication (Kokai) No. 4-348147).
The silica obtained by such surface treatment can be made hydrophobic appropriately, but reactive groups such as silanol groups or alkoxyl groups remaining on the silica particle surfaces may make the silica unable to be dispersed in organic solvents of various types, or may make it highly aggregative. Accordingly, it has been sought to provide fine silica particles having a high dispersibility and low aggregative properties.
Japanese Pre-examination Patent Publication (Kokai) No. 2-160613 discloses fine silica particles having a superior dispersibility, which, however, have a problem that any heating for evaporating solvents may result in a poor primary-particle retention.
When the spherical fine silica particles disclosed in Japanese Pre-examination Patent Publication (Kokai) No. 4-348147 are compounded as a component of a heat-curable or ultra-violet-curable resin composition which is liquid in a relatively low viscosity, the fine silica particles can be dispersed with difficulty in various resins and solvents because they are inorganic matter and hence have so large a specific gravity (larger than 2.0) that they may have a great difference in specific gravity from other materials (components) of the composition, and also because the fine silica particles tend to aggregate on account of the polarity or hydrogen bond of the silanol groups they have. Thus, they have a disadvantage of sedimentation with time during the storage of the composition.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide fine silica particles having a high dispersibility and low aggregative properties, and a process for their production.
Another object of the present invention is to provide an organic resin composition which is an organic resin composition which contain fine silica particles having a high dispersibility and a high stability with time, and hence can form a film having a good transparency and superior blocking resistance, slip properties and scratch resistance.
The present invention provides silane-surface-treated fine silica particles having primary particles having a particle diameter of from 0.01 to 5 &mgr;m, which fine silica particles fulfill the following conditions (i) and (ii).
(i) When an organic compound which is liquid at room temperature and has a dielectric constant of from 1 to 40 F/m and fine silica particles are mixed in a weight ratio of 5:1 and shaken, the fine silica particles disperse uniformly in the organic compound.
(ii) The quantity of primary particles remaining as primary particles when methanol is evaporated under heating by means of an evaporator from a dispersion prepared by dispersing the fine silica particles in methanol and thereafter the particles are held at a temperature of 100° C. for 2 hours, is in a percentage of at least 20% based on the quantity of primary particles originally present.
As a process for producing the above silane-surface-treated fine silica particles, the present invention also provides a process for producing silane-surface-treated fine silica particles, comprising the steps of:
(A) introducing an R
2
SiO
3/2
unit (wherein R
2
represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) to the surfaces of hydrophilic fine silica particles comprising an SiO
2
unit to obtain hydrophobic fine silica particles; and
(B) introducing an R
1
3
SiO
1/2
(wherein R
1
's may be the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms) to the surfaces of the resultant hydrophobic fine silica particles.
This process can provide highly dispersible and low aggregative hydrophobic fine silica particles having a particle diameter of from 0.01 to 5 &mgr;m.
The present invention further provides an organic resin film comprising (a) 100 parts by weight of an organic resin and (b) from 0.01 to 10 parts by weight of the above silane-surface-treated fine silica particles.
The silane-surface-treated fine silica particles obtained by the present invention have a high dispersibility and low aggregative properties any conventional ones do not have. The present fine silica particles can preferably be used to modify properties (slip properties, wear resistance, lubricity, and anti-blocking flexibility) of various rubbers and synthetic resins, to improve properties of coating materials and ink coating agents and to impart lubricating properties and water repellency to cosmetics, and also as a fluidity-providing agent for various powders such as abrasive particles for abrasives, and powdery resins.
In particular, the organic resin composition of the present invention is formed using the above highly dispersible fine silica particles as a material, and may hardly cause the settlement of fine silica particles even with time. Hence, it can form a film having a good transparency and superior blocking resistance, slip properties and scratch resistance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described below in detail.
A process for producing the fine silica particles of the present invention will be described in the order of steps.
Step (A)
In the process of the present invention, there are no particular limitations on hydrophilic fine silica particles used in the step (A) as a starting material. They may include, e.g., those obtained by a process comprising the step of subjecting a tetrafunctional silane compound represented by the general formula (I):
Si(OR
3
)
4
(I)
(wherein R
3′
s may be the same or different and each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms) or a partial hydrolysis-condensation product thereof or a mixture of these, to hydrolysis and condensation in a mixed solvent of water and a hydrophilic organic solvent containing a basic substance, to obtain a hydrophilic fine silica particle mixed-solvent dispersion, and subsequently the step of converting the dispersion medium of the hydrophilic fine silica particle mixed-solvent dispersion into water to prepare an aqueous hydrophilic fine silica particle dispersion.
As specific examples of the tetrafunctional silane compound represented by the general formula (I), it may include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and tetrabutoxysilane. As specific examples of the partial hydrolysis-condensation product of the tetrafunctional silane compound represented by the general formula (I), it may include methyl silicate and ethyl silicate. Any of these may be used alone or in combination of two or more.
There are no particular limitations on the hydrophilic organic solvent so long as it dissolves the compound of the general formula (I) or partial hydrolysis-condensation product and the water. It may include alcohols, cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve and cellosolve acetate, ketones such as acetone and methyl ethyl ketone, and ethers su
Asai Mitsuo
Asami Atsushi
Ichinohe Shoji
Kudo Muneo
Matsumura Kazuyuki
Mulcahy Peter D.
Shin-Etsu Chemical Co. , Ltd.
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