JP2966596B2 - Polyorganosiloxane coated fine particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polyorganosiloxane-coated fine particles exhibiting stable dispersion stability in a non-aqueous solvent, especially in silicone oil. More specifically, when used as a non-aqueous suspension in which the fine particles are dispersed,
In addition to the fields of paints and cosmetics, display devices using electrophoresis (see, for example, JP-A-48-31096), which require long-term dispersion stability, and suspensions of anisotropic dipole fine particles The present invention relates to polyorganosiloxane-coated fine particles particularly useful for electro-optical devices (hereinafter, referred to as DPS devices) (see, for example, JP-A-2-118619).

[0002]

2. Description of the Related Art As a method of dispersing fine particles in a non-aqueous solvent, a method of adsorbing a surfactant or a polymer on the surface of the fine particles is generally used. There has been a great deal of research on these to date, and it has been found that the dispersibility can be considerably improved by selecting a suitable surfactant and adsorbing polymer according to the type of fine particles and dispersion medium.

[0003] Among the fine particles, carbon black has long been used to improve the dispersibility thereof by chemically bonding a polymer to the surface (so-called grafting) (for example, JB Donnet). , Carbon, Volume 6, 1968
Year, p. 161).

Recently, Tsubokawa et al. Reported that a stable dispersion system in water can be obtained by grafting a water-soluble polymer such as polyacrylamide onto the surface of oxide fine particles. Abstracts of the Special Meeting on Chemistry, 1987, p. 111).

[0005]

As described above, conventionally, when dispersing fine particles in a non-aqueous solution, various surfactants and dispersants such as polymers have been used, but almost all of them are used. This utilizes physical adsorption of the dispersant on the surface of the fine particles. Therefore, there is a drawback that the adsorbing power is small and the particles are easily desorbed and the dispersion state is easily affected by the temperature.

On the other hand, in the method utilizing the grafting, the fine particles in the dispersion have a large dispersion stabilizing effect due to the entropy repulsion between the polymers. Further, since the polymer is fixed to the surface of the fine particles by a covalent bond, the polymer has a feature that the bonding force is extremely large. However, conventionally, since many graft polymers having a functional group at both terminals have been used, there has been a problem that a part of the graft polymer acts as a cross-linking agent between the fine particles and conversely causes aggregation.

On the other hand, a method of grafting fine particles using a polymer having a functional group at one end as a graft polymer is effective as a method for solving the above-mentioned problem. In particular, a condensation reaction between an OH group on the surface of the fine particles and the graft polymer can be used for the graft reaction of the fine particles having at least a surface made of an oxide. However, the reaction rate of the OH groups on the surface of the fine particles varies depending on various conditions such as the type of the graft polymer, the molecular weight, the reaction temperature, and the reaction time.
Because of the following, a large amount of unreacted OH groups remains on the surface of the fine particles after the grafting treatment. Since the residual OH groups on the surface of the fine particles form hydrogen bonds with the polar group, when a graft polymer containing a polar group is used, the residual OH group on one fine particle and the residual OH on the other fine particle surface are used. Hydrogen bonds formed between groups cause cross-linking and aggregation between particles (Tada et al., Coloring Materials, Vol. 64, 19
1991, p. 12).

[0008] Since the entropy repulsion acting between the graft polymers increases with the molecular weight of the polymer, considering only this point, the use of a polymer having a large molecular weight is more effective for stabilizing the dispersion. However, the high molecular weight polymer has a large occupied cross-sectional area on the surface of the fine particles, and the unreacted O
The number of H groups will increase.

Therefore, in order to further improve the dispersion stability, it is necessary to graft a high molecular weight polymer on the surface of the fine particles and at the same time minimize the number of unreacted OH groups.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, have found that at least one OH
Having a reactive silicon group containing a group or a hydrolyzable group, and treating the fine particles composed of an oxide at least on the surface with a polyorganosiloxane having a trimethylsilyl ester group at the other end, having a functional group at one end At the same time that the polyorganosiloxane is grafted onto the fine particles, the trimethylsilanol formed by hydrolysis of the trimethylsilyl ester binds the remaining OH groups by trimethylsilylation (the above-mentioned reaction is referred to as endcapping) and disperses in a non-aqueous solvent. The inventors have found that the stability is significantly improved, and have reached the present invention.

That is, the present invention provides a compound represented by the general formula (I):

[0012]

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(1 ≦ y ≦ 3, 10 ≦ m ≦ 100, 1 ≦ n ≦ 2
0, R is an oxygen atom or an alkylene chain having 2 to 10 carbon atoms,
X represents an OH group or a hydrolyzable group) having at least one reactive silicon group containing an OH group or a hydrolyzable group at one end and a trimethylsilyl ester group at the other end. The present invention relates to polyorganosiloxane-coated fine particles obtained by the reaction of siloxane with the surface of fine particles comprising at least an oxide.

[0014]

The polyorganosiloxane represented by the general formula (I) used in the present invention has at least one reactive silicon group containing an OH group or a hydrolyzable group at one terminal, It is a polymer having a terminal trimethylsilyl ester group.

In the general formula (I), the OH group or the hydrolyzable group represented by X is a functional group which reacts with the OH group present on the surface of the oxide. An atom, an amino group, an alkoxyl group and the like are preferred. In addition, the number of the functional groups may be at least one in one molecule, and those having a range of 1 ≦ y ≦ 3 can be used.

If the degree of polymerization of the polydimethylsiloxane portion is too small, the effect of stabilizing the dispersion due to the entropy repulsion of the polymer cannot be obtained. OH
Crosslinking adsorption by the group occurs, and the dispersibility decreases. Therefore, the degree of polymerization (m) of the polydimethylsiloxane moiety is
Those in the range of 10 ≦ m ≦ 100 are used.

Further, if the number (n) of methylene groups in one molecule is too large, the graft density of the polymer is also lowered, so that a polymer having a number of 20 or less (1 ≦ n ≦ 20) is used.

Further, considering the restrictions on synthesis and the graft density of the polymer, R represents an oxygen atom or a compound having 2 to 10 carbon atoms.
Are used.

The polyorganosiloxane has the following general formula (II) having hydrogen at one end:

[0020]

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(Wherein m, y, X and R are the same as described above) and an unsaturated fatty acid (H
(CH ₃ ) ₃ which is a trimethylsilylated product of OOC— (CH ₂ ) _n-2 CH ＝ CH ₂ (where n is as defined above)
SiOOC (CH ₂₎ a _n-2 CH = CH ₂ by using a platinum catalyst such as chloroplatinic acid, further aromatic optionally using a solvent ether or ketone 50 to 15
It can be synthesized by reacting at 0 ° C. for 2 to 20 hours.

The fine particles used in the reaction with the polyorganosiloxane in the present invention are fine particles having at least a surface made of an oxide.

Since the surface of the fine particles is made of an oxide,
An OH group is present on the surface, and a condensation reaction with an OH group or a hydrolyzable group of the polyorganosiloxane represented by the general formula (I) proceeds, and the polyorganosiloxane is grafted.

Specific examples of the fine particles include titania fine particles and fine particles composed of oxides such as silica, alumina, zirconia, and iron oxide. The fine particles are coated with silica, alumina, titania, zirconia, or the like. May be.

The reaction between the polyorganosiloxane represented by the general formula (I) and the fine particles having at least a surface of an oxide is carried out, for example, by charging the fine particles into the polyorganosiloxane and heating and stirring the mixture under an inert gas atmosphere. It is done by doing.

The grafting amount of the polyorganosiloxane increases with the reaction temperature. However, since the reactivity is high, a sufficient dispersion stabilizing effect can be obtained even at about 50 ° C. Also,
The reaction time may be about 2 hours. In the reaction,
It is preferable to use fine particles in a proportion of 1 to 20 parts with respect to 100 parts (parts by weight, hereinafter the same) of polyorganosiloxane. Further, in order to avoid side reactions such as oxygen and moisture in the air, it is desirable to carry out the reaction while flowing dry nitrogen.

In the polyorganosiloxane-coated fine particles of the present invention obtained by the above reaction, the ratio of the polyorganosiloxane to the fine particles before coating is preferably 5 to 10%.

When the above-mentioned polyorganosiloxane-coated fine particles of the present invention are dispersed in a non-aqueous solvent such as silicone oil, the dispersed state is stabilized by the entropy repulsion of the polyorganosiloxane as a graft polymer. You.

Further, trimethylsilanol generated by hydrolyzing the trimethylsilyl ester portion of the graft polymer acts as an endcapping reagent, and the OH group on the surface of the fine particles is trimethylsilylated, so that a more stable dispersion effect can be obtained. . Further, the electrostatic repulsion effect of the carboxylic acid group generated by hydrolysis of the trimethylsilyl ester portion of the graft polymer also contributes to dispersion stabilization.

Example 1 A polyorganosiloxane represented by the general formula (I), wherein one end has a reactive silicon group containing a methoxy group (X = O
CH ₃ , y = 3), a polyorganosiloxane in which the other end is a trimethylsilyl ester group and R is an oxygen atom (n = 10, m = 18, GP-X manufactured by Shin-Etsu Chemical Co., Ltd.) 20
After adding 400 mg of silica-coated titania fine particles (average particle size 0.2 μm) to a three-necked flask containing g, the mixture was dispersed by stirring at room temperature for 15 minutes using a disperser.

The suspension after dispersion is further stirred at 50 ° C. to 75 ° C. in the range of 50 ° C. to 200 ° C. while stirring with a disperser.
The grafting reaction was allowed to proceed by changing the reaction temperature to 200 ° C., 150 ° C., and 200 ° C. for 2 hours each. In addition, in order to prevent a side reaction, the reaction was performed while flowing dry nitrogen through a calcium chloride tube.

The fine particles after the reaction were washed five times with about 30 ml of toluene, and then dried by heating to 50 ° C. in a vacuum dryer.

After adding 40 mg of the obtained fine particles to 280 mg of KBr and kneading them in an agate mortar, a diffuse reflection FT-IR measurement (JIR 5500 manufactured by JEOL Ltd.) was carried out to obtain a methyl group of 2960 cm ^-1 . The amount of the graft polymer was determined from the absorbance of the absorption based on the stretching vibration.

The results of this example are shown in FIG.

Comparative Example 1 Formula (III):

[0036]

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A polyorganosiloxane (GP-S manufactured by Shin-Etsu Chemical Co., Ltd.) having a reactive silicon group containing a methoxy group at one end and a trimethylsilyl group at the other end is used in Example 1. Example 1 except that the same silica-coated titania fine particles were heated at a reaction temperature of 200 ° C. for 2 hours.
Grafting was performed in the same manner as described above, and the amount of the graft polymer was determined. The results of this comparative example, which were performed twice under the same conditions, are shown in FIG.
Indicated by

FIG. 1 shows that the amount of the graft polymer increases as the reaction temperature increases. Same reaction temperature
Comparing at 200 ° C., it can be seen that GP-X used in Example 1 was grafted about 4.5 times as much as GP-S used in Comparative Example 1.

This indicates that, together with the grafting of the polydimethylsiloxane moiety, the endcapping by trimethylsilanol, which is a low molecular weight substance produced by the hydrolysis of the trimethylsilyl ester, occurs efficiently.

Example 2 Using the same method as in Example 1, GP-X manufactured by Shin-Etsu Chemical Co., Ltd. was grafted onto the same silica-coated titania fine particles as used in Example 1 at a reaction temperature of 150 ° C. A sample was prepared. 4 mg of the fine particles treated as above
Add to 7.4g of polydimethylsiloxane (20cst)
By stirring for 15 minutes using an Ultra Death Parser, a dispersion having a fine particle concentration of 0.023% was prepared.

In order to evaluate the dispersion stability of the dispersion liquid thus obtained, the change with time of turbidity at 540 nm was traced using a spectrophotometer (330, manufactured by Hitachi, Ltd.).

The results of this example, which were performed twice under the same conditions, are indicated by squares in FIG. In FIG. 2, the vertical axis is the reciprocal of turbidity.

Comparative Example 2 The same raw material as in Comparative Example 1 (GP-produced by Shin-Etsu Chemical Co., Ltd.)
Using S), a grafted sample was prepared in the same manner (reaction temperature: 200 ° C.), and a dispersion was prepared in the same manner as in Example 2 to evaluate dispersion stability. The results of this comparative example, which were performed twice under the same conditions, are indicated by a circle in FIG.

From this, it can be seen that an almost linear relationship is established between the reciprocal of turbidity and time in the system treated with any of the graft polymers. This slope gives the apparent aggregation rate, and the smaller this value is, the better the dispersion stability is. The slope of the straight line was determined by the least square method.

From the results shown in FIG. 2, it was found that the sample treated with GP-X described in Example 2 (slope 0.029 cm / day) was more than the sample treated with GP-S described in Comparative Example 2 (slope 0.065 cm / day). It can be seen that ()) has better dispersion stability.

[0046]

The polyorganosiloxane-coated fine particles of the present invention are more non-aqueous than the conventional fine particles treated with a surfactant or an adsorptive polymer, as well as the conventional polydimethylsiloxane-grafted fine particles. The dispersion stability in a solvent, especially in silicone oil, is further enhanced.

Accordingly, non-aqueous suspensions in which the polyorganosiloxane graft fine particles of the present invention are dispersed include, for example, pigments, paints, electrophoretic devices, DPS devices, and the like, which require long-term dispersion stability. It is extremely useful as

[Brief description of the drawings]

FIG. 1 is a graph showing the results of quantification of graft polymers of fine particles obtained by the methods described in Example 1 and Comparative Example 1.

FIG. 2 is a graph showing the dispersion stability of fine particles in the dispersion described in Example 2 and Comparative Example 2.

Continued on the front page (72) Inventor, Tomoaki Ono 1-10 Hitomi, Matsuidacho, Usui-gun, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (72) Inventor Hiroshi Yoshioka 1 Hitomi, Matsuidacho, Usui-gun, Gunma Prefecture −10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (58) Field surveyed (Int. Cl. ⁶ , DB name) C08L 83/04

Claims (1)

(57) [Claims] [Claim 1] General formula (I): (1 ≦ y ≦ 3, 10 ≦ m ≦ 100, 1 ≦ n ≦ 20, R represents an oxygen atom or an alkylene chain having 2 to 10 carbon atoms, and X represents an OH group or a hydrolyzable group) By reacting a polyorganosiloxane having at least one reactive silicon group containing an OH group or a hydrolyzable group and having a trimethylsilyl ester group at the other end with a fine particle surface having at least a surface made of an oxide. Polyorganosiloxane-coated fine particles.