Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-01-16
2002-12-17
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S010000, C528S012000, C528S014000, C528S021000, C528S032000
Reexamination Certificate
active
06495649
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to spherical silicone fine particles and the process for producing the same. More specifically, the present invention relates to spherical silicone fine particles having an average particle diameter of 0.1 to 5 &mgr;m and the process for effectively producing the same.
BACKGROUND OF THE INVENTION
A process described in JP-A-63-77940 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) has conventionally been known as a process for producing spherical silicone fine particles. This production process obtains spherical silicone fine particles wherein the shape of the respective particles is independently truly spherical, by subjecting organotrialkoxy silane and/or partial hydrolyzed product thereof to hydrolysis and polycondensation at the interface between the organotrialkoxy silane and/or the partial hydrolyzed product thereof, or a mixed liquid of the organotrialkoxy silane and/or the partial hydrolyzed product thereof and an organic solvent as an upper layer, and a mixed liquid of ammonia and/or amine and an organic solvent as a lower layer.
Silicone fine particles obtained by this process have characteristics such that the particle shape is spherical, the hydrophobic property is high, the condensation ability is low, and the specific gravity is small. In view of those characteristics, the silicone fine particles are used as modification additives for imparting lubricating property to paints, plastic, rubber, cosmetics and paper, improving dispersibility, and giving light-scattering function.
However, the production process of such spherical silicone fine particles is complicated to maintain a reaction interface where the organotrialkoxysilane and/or the partial hydrolyzed product thereof are subjected to hydrolysis and polycondensation. As a result, there was the problem that productivity to time and the capacity of an apparatus is low.
In order to solve these problems, the present inventors proposed a process for producing spherical silicone fine particles comprising optionally diluting an aqueous/alcohol solution of an organosilane triol obtained by hydrolyzing an organoalkoxysilane and/or the partial condensation product thereof, adding an aqueous alkaline solution thereto, followed by mixing, and then keeping the resulting mixture in a stationary state (JP-A-2000-186148). According to this process, the hydrolysis and the polycondensation are effected in a uniform reaction state so that spherical silicone fine particles are obtained. Thus, complicated keeping of an interface where hydrolysis and polycondensation are effected is not required as in the conventional art and, therefore, productivity to time and the capacity of an apparatus can greatly be improved.
According to this process, an average particle diameter of spherical silicone fine particles obtained can be controlled in a range of 1 to 10 &mgr;m and the spherical silicone fine particles obtained have a characteristic such that the particle size distribution of the resulting particles is sharp as compared with the conventional art. The spherical silicone fine particles are compounded with plastics and used for a light diffuser panel of a liquid crystal display and for imparting lubricating property for enhancing running stability of a video tape for a high-quality image.
This process, however, has a problem in that it is difficult to obtain fine particles having an average particle size of less than 1 &mgr;m. Namely, according to this process, for obtaining particles having a relatively small average particle size, the concentration of a reaction product is required to decrease or a dilution step is required. Thus, in the production of particles having a relatively small average particle size, the productivity thereof to time and the capacity of an apparatus is low as compared with a case of obtaining particles having a relatively large average particle size.
SUMMARY OF THE INVENTION
The present invention has been made to solve these conventional problems.
Accordingly, one object of the present invention is to provide spherical silicone fine particles having an average particle diameter of 0.1 to 5 &mgr;m, which can be produced without decreasing the yield and also without a dilution step.
Another object of the present invention is to provide a process for effectively producing such spherical silicone fine particles.
As a result of extensive investigations to achieve the above-described objects, it has been found that the above-described objects could be achieved by adding an aqueous alkaline solution to an aqueous/alcohol solution of silanol (obtained by hydrolyzing a mixed silane comprising an organotrialkoxysilane and an organotetraalkoxysilane wherein four hydrolyzable groups are bonded to Si) and/or the partial condensation product thereof, mixing the resulting mixture rapidly and uniformly, and allowing the mixture obtained to stand. The present invention has been completed based on this finding.
The spherical silicone fine particles of the present invention is obtained by polycondensation reaction of an organotrialkoxysilane represented by the following formula (I):
R
1
Si(X)
3
(I)
wherein R
1
represents a monovalent group selected from a group consisting of a substituted or unsubstituted alkyl group, alkenyl group and phenyl group; X represents the same or different hydrolyzable group, and an organosilane represented by the following formula (II):
SiX
4
(II)
wherein X represents the same or different hydrolyzable group, with a R
1
/Si ratio being in a range of 0.9 to less than 1.0.
The process for producing spherical silicone fine particles of the present invention comprises:
(A) a step of mixing an organotrialkoxysilane represented by the following formula (III):
R
1
Si(OR
2
)
3
(III)
wherein R
1
represents a monovalent group selected from a group consisting of a substituted or unsubstituted alkyl group, alkenyl group and phenyl group; R
2
represents the same or different substituted or unsubstituted alkyl group; and
a tetraalkoxysilane represented by the following formula (IV):
Si(OR
2
)
4
(IV)
wherein R
2
represents the same or different substituted or non-substituted alkyl group such that a ratio of R
1
/Si is 0.9 to less than 1.0, adding thereto water in an amount of 20 to 150 moles per mole of the silane of the resulting mixture to conduct hydrolysis under an acidic condition, thereby obtaining an aqueous or alcohol solution of an organosilanol and/or the partial hydrolyzed product thereof; and
(B) a step of adding an aqueous alkaline solution to the aqueous or alcohol solution of an organosilanol and/or the partial hydrolyzed product thereof obtained above, followed by mixing and mixed, and subjecting the organosilanol and/or the partial hydrolyzed product thereof to polycondensation under a stationary state to form spherical silicone fine particles.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
Examples of R
1
in an organotrialkoxysilane represented by the formula (I) used in the present invention include an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms and a phenyl group. Those can be used alone or as mixtures thereof. Methyl group is preferable because of good reactivity.
Example of X in the general formula (I) or (II) is an alkoxy group represented by OR
2
, which can be an organosiloxane partially comprising a halogen such as chlorine. Examples of R
2
of the alkoxy group represented by the above OR
2
include an alkyl group such as methyl, ethyl or butyl; and an alkoxy-substituted hydrocarbon group such as 2-methoxyethyl, or 2-ethoxyethyl. Methyl, ethyl and 2-methoxyethyl are preferable because of high hydrolysis rate. Examples of such a methyltrialkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, methyltri-n-propoxysilane, methyltriisopropoxysilane, and methyltris(2-methoxyethoxy)silane. Those can be used alone or as mixtures thereof.
In the reac
Harada Yukinobu
Takagi Akira
GE Toshiba Silicones Co., Ltd.
Moore Margaret G.
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