JP2003137530A - Method for surface treatment of minute powder silica and polyorganosiloxane composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for completely silylating a silanol group on the surface of a minute powder silica by using a silazane compound in a process for kneading polyorganosiloxane and minute powder silica, and also to provide a polyorganosiloxane composition in which the silanol group on the surface of the minute powder silica is eliminated. SOLUTION: This method comprises treating the surface of the minute powder silica by using the silazane compound while kneading the mixture of polyorganosiloxane and the silica, and is characterized by supplying the silazane compound and/or its hydrolysate to the silica surface for treatment under a reflux condition. The polyorganosiloxane composition includes both polyorganosiloxane and minute powder silica treated by the above method.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating the surface of fine powder silica, and more specifically, in the step of kneading polyorganosiloxane and fine powder silica, the surface of the fine powder silica is treated with an organosilicon compound. The present invention relates to a method for silylation treatment. The present invention also relates to the polyorganosiloxane composition obtained by such surface treatment.

[0002]

BACKGROUND OF THE INVENTION Polyorganosiloxane compositions, especially polyorganosiloxane compositions that cure to give silicone rubbers, include addition reactions between polyorganosiloxanes containing aliphatically unsaturated hydrocarbon groups and polyorganohydrogensiloxanes. Crosslinking is carried out in the presence of a platinum compound to form a rubber-like elastic material, and an addition reaction-curable polyorganosiloxane composition; and linear high-polymerization polydiorganosiloxane are blended with an organic peroxide and heated. By doing so, there is a radical reaction curable polyorganosiloxane composition that crosslinks to form a rubber-like elastic body, and together with a polyorganosiloxane composition by another curing mechanism,
Each is widely used. In any case, in order to impart processability to the composition and to give the resulting silicone rubber excellent mechanical properties and other properties depending on the purpose, it is possible to add an inorganic filler such as silica. Is widely practiced.

Among these inorganic fillers, it is fine powder silica having a specific surface area of 50 m ² / g or more that gives silicone rubber particularly high mechanical strength. However, such finely divided silica has a large amount of silanol groups on the surface depending on its specific surface area. Therefore, the polyorganosiloxane composition containing the finely divided silica undergoes pseudo-crosslinking between the silanol groups and the siloxane bonds of the polyorganosiloxane during storage, causing a change in the state of the system. That is, the base polymer is a liquid polyorganosiloxane, and the composition also exhibits appropriate fluidity and is used for casting, injection molding, transfer molding, and the like.
In the case of a so-called liquid silicone rubber composition, the apparent viscosity increases remarkably during storage, and in an extreme case, the fluidity is lost. Further, even in the case of a so-called millable type silicone rubber composition in which the base polymer is a linear polydiorganosiloxane having a high degree of polymerization and mastication is performed by roll work, the roll workability is significantly impaired by long-term storage.

In addition, the presence of the silanol groups makes the surface of the finely powdered silica hydrophilic and contains adsorbed water, which adversely affects the electrical properties and heat resistance of the cured silicone rubber.

Therefore, depending on the method of molding and curing the silicone rubber and the purpose of use, the surface of the fine powder silica is treated with various organosilicon compounds to silylate the silanol groups. Examples of such organosilicon compounds are cyclic oligosiloxanes such as hexamethylcyclotrisiloxane and oritamethylcyclotetrasiloxane, organohalosilanes such as dimethyldichlorosilane and trimethylchlorosilane; organoalkoxys such as trimethylmethoxysilane. Examples of silanes include silazane compounds such as hexamethyldisilazane. In particular, it has been found that the use of finely powdered silica surface-treated with a silazane compound makes it possible to obtain a polyorganosiloxane composition having a low apparent viscosity of the system and a small change with time.

However, it is complicated to subject the fine powder silica to such a treatment, and the productivity is poor. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 7-238228, when the liquid polyorganosiloxane and the finely powdered silica are heated and kneaded, hexamethyldisilazane is added and kneaded to obtain the same as above. Is obtained, the apparent viscosity of the system is low, and the polyorganosiloxane composition whose change with time is small is obtained with good productivity.

However, when the silazane treatment is carried out in such a kneading process, the silanol groups on the surface of the fine powder silica cannot be completely removed, and a small amount of silanol groups remains. Therefore, a liquid polyorganosiloxane having an aliphatic unsaturated hydrocarbon group such as a vinyl group is used as a base polymer, a platinum compound is used as a catalyst, and a polyorganohydrogensiloxane is compounded as a crosslinking agent immediately before use. In the polyorganosiloxane composition to be cured, the silazane-treated fine powder silica obtained as described above is used, and the silanol group remaining on the surface and the hydrosilyl group in the polyorganohydrogensiloxane form a platinum compound The catalytic action causes dehydrogenative condensation at room temperature to form a crosslinked structure of the polyorganohydrogensiloxane through the finely divided silica, thus increasing the apparent viscosity of the system. For example, even in a composition which is cured by heating at 100 to 200 ° C. after molding, when left at room temperature, the above-mentioned cross-linking reaction by the finely divided silica proceeds to give a gel or a cured product. Therefore, when such a composition is used to mass-produce a molded product by a molding machine such as an injection molding machine,
When the molding machine is stopped for a long time, it is necessary to completely remove the remaining uncured composition and discard it. This restricts the flexibility of the process schedule in the molding process of such an addition reaction type silicone rubber and generates a large amount of waste, which hinders the rationalization of the process.

The same cross-linking reaction with finely powdered silica having silanol groups remaining on the surface is also observed in a millable silicone rubber composition which is cured by an addition reaction in the presence of a platinum compound as described above. I'm losing sex.

In order to completely remove the silanol group on the surface of the fine powder silica by silylation, a large excess of silazane compound with respect to the fine powder silica may be used. However, when the polyorganosiloxane and the finely divided silica are heated and kneaded, if a large excess of the silazane compound is present in the system, the mixture becomes wet with the silazane compound and becomes slippery, and a uniform mixture can be obtained. Can not.

[0010]

The object of the present invention is to knead polyorganosiloxane and finely divided silica,
It is to provide a method for completely sililating silanol groups on the surface of finely divided silica with a silazane compound.
Another object of the present invention is to provide a polyorganosiloxane composition containing finely divided silica having surface silanol groups removed, obtained by such a method.

[0011]

As a result of repeated studies to solve the above problems, the present inventors have found that an organosilicon compound, particularly a silazane compound, and / or its hydrolysis product is released to the outside of the system. The inventors have found that the object can be achieved by subjecting the finely powdered silica to a surface treatment under conditions under which it does not occur, especially under reflux conditions, and have completed the present invention.

That is, according to the present invention, an organosilicon compound is kneaded while kneading a mixture of a polyorganosiloxane having at least two monovalent aliphatic unsaturated hydrocarbon groups bonded to a silicon atom in one molecule and finely divided silica. A method of silylating the surface of finely divided silica with a compound, comprising the organosilicon compound, preferably a silazane compound and / or
Or a method for treating the surface of finely divided silica, characterized in that the hydrolysis product thereof is subjected to a surface treatment of the finely divided silica under conditions that prevent the product from escaping out of the system, preferably under reflux conditions; It relates to the obtained polyorganosiloxane composition.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The polyorganosiloxane used in the present invention is a component which becomes a base polymer in silicone rubber. The polyorganosiloxane has at least two monovalent aliphatic unsaturated hydrocarbon groups bonded to a silicon atom in one molecule in order to form a network structure by various curing reactions.

As the monovalent aliphatic unsaturated hydrocarbon group,
Examples include vinyl, allyl, 3-butenyl, 5-hexenyl, etc., which are easy to synthesize and have excellent fluidity of the composition before curing and excellent heat resistance of the composition after curing. Most preferred.

Other organic groups bonded to a silicon atom include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl and dodecyl; aryl groups such as phenyl; 2-phenylethyl,
Aralkyl groups such as 2-phenylpropyl; chloromethyl, chlorophenyl, 2-cyanoethyl, 3,3,3-
Substituted hydrocarbon groups such as trifluoropropyl are exemplified. Of these, a methyl group is most preferable because it is easy to synthesize and has an excellent balance of properties such as mechanical strength and fluidity before curing.

The monovalent aliphatic unsaturated hydrocarbon group may be present either at the terminal or in the middle of the molecular chain of the polyorganosiloxane, or at both of them, but in the composition after curing. In order to give excellent mechanical properties, in the case of a linear chain, it is preferable that they are present at least at both ends thereof. On the basis of the above-mentioned premise, the amount of the unsaturated hydrocarbon group is preferably 2 mol% or less on the average in the case of liquid polyorganosiloxane, based on the total organic groups bonded to silicon atoms, and the polyorgano with a high degree of polymerization is preferably used. 0.05 for siloxane
.About.0.5 mol% is preferred.

The siloxane skeleton of the polyorganosiloxane is substantially linear when the resulting polyorganosiloxane composition is a millable silicone composition, and linear or branched when it is a liquid silicone rubber composition. It may be a shape. In order to improve the mechanical properties of the liquid silicone composition after curing and to use it for molding a complicated shape, a linear polydiorganosiloxane and a branched polyorganosiloxane are mixed. It is preferable to use. When these mixtures are used, in order to increase the mechanical strength and elastic modulus of the cured product, R ₃ SiO _1/2 units and SiO ₂ units and, if necessary, R ₂ SiO units (R Represents an organic group as described above, of which at least two are present in one molecule,
2 to 5 branched polyorganosiloxanes composed of preferably 3 or more monovalent aliphatic unsaturated hydrocarbon groups)
It is more preferable to use a mixture containing 0% by weight of polydiorganosiloxane with the balance being linear and the both ends being blocked with monovalent aliphatic unsaturated hydrocarbon groups.

The average degree of polymerization may be any as long as it can form a silicone rubber having good rubber elasticity and mechanical properties upon curing, and is preferably 100 to 10,000. In the case of a liquid silicone rubber composition, in order for the composition before curing to have good flowability and workability, and for the composition after curing to have appropriate elasticity and excellent mechanical properties, it is necessary to use 25% of polyorganosiloxane. Viscosity at 0 to 5
Those of 00 Pa · s are preferable, and those of 1-100 Pa · s are particularly preferable. On the other hand, in the case of the millable silicone rubber composition, the one having an average degree of polymerization of 3,000 to 10,000 is particularly preferable so that the composition after curing has excellent physical properties. These polyorganosiloxanes may be used alone or in combination of two or more.

The finely powdered silica used in the present invention is used as a reinforcing filler and has a specific surface area of usually 50.
m ² / g or more, preferably 130~400m ² / g. Examples of such fine powder silica include fumed silica, dry process silica such as arc silica; and precipitated silica, wet process silica such as silica aerogel. The finely divided silica may be pretreated with another organosilicon compound, for example, octamethylcyclotetrasiloxane.

Organosilicon compounds used for silylation of finely divided silica in the present invention include hexamethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, octamethyltrisilazane, Silazane compounds such as hexamethylcyclotrisilazane; aminosilanes such as trimethylsilyldimethylamine, trimethylsilyldiethylamine; chlorosilanes such as trimethylchlorosilane; trimethylmethoxysilane,
Examples thereof include alkoxysilanes such as trimethylethoxysilane; and cyclic siloxane compounds such as hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane. A silazane compound is preferable, a hexaorganodisilazane compound is more preferable, and hexamethyldisilazane is particularly preferable because of its excellent silylation effect. The silazane compounds may be used alone or in combination of two or more.

Such an organosilicon compound directly reacts with a silanol group on the surface of fine powder silica by heating, or is formed by a condensation reaction between silanol groups with water present in the system as adsorbed water and by heating. It is hydrolyzed by water and / or added water to produce a silanol compound, which is dehydrated and condensed with a hydroxyl group (silanol group) on the surface of fine powder silica to be converted into a hydrophobic group. For example, when hexamethyldisilazane is used, hydrolysis of the silazane produces trimethylsilanol, which is dehydrated and condensed with a hydroxyl group on the surface of fine powder silica to convert the hydroxyl group into a trimethylsiloxy group.

The surface treatment of the finely divided silica with the organosilicon compound is carried out during the kneading step of the aforementioned polyorganosiloxane as the base polymer and the finely divided silica. The processing apparatus used is a normal closed kneading apparatus, that is, depending on the degree of polymerization of the base polymer and the fluidity of the system,
A universal kneader, a paddle mixer, a screw mixer, a kneader, a dough mixer, a Banbury mixer, etc. can be illustrated. The kneading is usually performed while flowing an inert gas such as nitrogen or argon. The surface treatment is usually performed at a temperature of 30 to 200 ° C., preferably 80 to 150 ° C., usually for 0.5 to 10 hours. The system pressure may be normal pressure or may be slightly pressurized.

While efficiently kneading the polyorganosiloxane as the base polymer and the fine powder silica,
In order to completely sililate the silanol groups on the surface of the silica, the amount of finely divided silica is preferably 30 to 200 parts by weight, preferably 40 to 40 parts by weight, based on 100 parts by weight of polyorganosiloxane.
-80 weight parts is more preferable. The amount of the organosilicon compound used for the silylation treatment is preferably 5 to 40% by weight, more preferably 10 to 25% by weight, based on the fine powder silica. The fine powder silica and the organosilicon compound to be subjected to the kneading and the surface treatment may be charged into the treatment apparatus at once, or may be fed in several times or continuously added.

In the surface treatment of the finely divided silica according to the present invention, a non-reinforcing filler having a large particle size, a silane coupling agent, and the like may be coexisted, if necessary, as long as the surface treatment is not hindered. Good.

A feature of the present invention is that the above-mentioned surface treatment which is carried out simultaneously with kneading is carried out by discharging the by-product such as ammonia when the surface treatment agent is a silazane compound, while discharging the organosilicon compound and / or the same. Hydrolysis products,
It is to be performed under the condition that it does not escape to the outside of the system. Examples of such a method include a method in which the above compound is refluxed, absorbed in a high boiling point solvent and returned to the system, and the like, and reflux is preferred. Reflux, for example, in the above kneading device,
This can be done by providing a reflux condenser at the outlet of the inert gas. Under such a reflux condition, the surface treatment of finely powdered silica with an organosilicon compound, in particular a silazane compound and / or a hydrolysis product thereof, causes them to be entrained in an inert gas or by-product, particularly by-product ammonia. Therefore, it is possible to completely silylate the silanol groups on the surface of the fine powder silica while performing sufficient kneading without using a large excess of an organosilicon compound, for example, a silazane compound. .

After completion of the surface treatment, the unreacted organosilicon compound and / or its hydrolysis product can be removed by further heating under reduced pressure, if necessary. The heating under reduced pressure is performed, for example, at 0.5 to 0.5 without reflux.
It can be performed by heating at 80 to 150 ° C. at 20 kPa.

By the surface treatment method of the present invention, a polyorganosiloxane composition containing polyorganosiloxane and fine powder silica in which silanol groups have been completely silylated and sufficiently mixed can be obtained.

The polyorganosiloxane composition of the present invention is prepared by preparing the composition as described above, and further, if necessary, in order to control the hardness and other physical properties of the desired silicone rubber. You may add the polyorganosiloxane which is a base polymer. The polyorganosiloxane added in this step may be the same as or different from the one used in the kneading involving the silylation treatment with the organosilicon compound.

The polyorganosiloxane composition of the present invention is prepared by adding a polyorganohydrogensiloxane as a cross-linking agent and a platinum compound as a catalyst to an unsaturated hydrocarbon group bonded to a silicon atom of a base polymer constituting the composition, and adding it. By the reaction, the silicone rubber can be obtained by curing with good working efficiency. In the case of such a reaction system,
A composition containing all of these components generally has poor storage stability at room temperature, so one of the polyorganosiloxane compositions of the present invention may be mixed with polyorganohydrogensiloxane and the other with a platinum compound, and the composition may be used immediately before use. It is general that both are mixed and the curing reaction is carried out under heating. It is also possible to appropriately select the amount and type of the catalyst, and / or to add a curing retarder, and to mix and store all components necessary for curing, if necessary.

The polyorganohydrogensiloxane functions as a crosslinking agent by the addition reaction of the hydrosilyl group contained in the molecule with the monovalent aliphatic unsaturated hydrocarbon group in the polyorganosiloxane. In order to reticulate the cured product, it has at least three hydrogen atoms bonded to the silicon atom involved in the addition reaction. The siloxane skeleton may be linear, branched or cyclic. Moreover, you may use these mixtures. Although the degree of polymerization is not particularly limited, it is preferable that the polyorganohydrogensiloxane in which two or more hydrogen atoms are bonded to the same silicon atom is composed of three or more siloxane units. When the polyorganosiloxane composition is heated and cured, it is more preferable that the polyorganosiloxane composition is composed of 10 or more siloxane units so as not to volatilize at the curing temperature.

Examples of the organic group bonded to the silicon atom of the siloxane unit include those similar to the organic groups other than the monovalent unsaturated aliphatic hydrocarbon group in the above polyorganosiloxane, and among them, the synthesis is From an easy point,
Most preferred is the methyl group.

The amount of the polyorganohydrogensiloxane blended is such that when the polyorganosiloxane is in a liquid state, it is completely cured and has a low compression set and an excellent surface condition, particularly an injection molded product. Therefore, the hydrogen atom bonded to the silicon atom in the polyorganohydrogensiloxane is preferably 0.5 to 5 with respect to one monovalent aliphatic unsaturated hydrocarbon group in the siloxane.
The amount is such that the number is one, more preferably one to three.
If the polyorganosiloxane has a high molecular weight, then an excess of hydrosilyl hydrogen atoms may be present.

The platinum compound is a catalyst for promoting the addition reaction between the monovalent aliphatic unsaturated hydrocarbon group in the polyorganosiloxane and the hydrosilyl group in the polyorganohydrogensiloxane. Examples of the platinum compound include chloroplatinic acid, a reaction product of chloroplatinic acid and an alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, a platinum-phosphine complex, a platinum-phosphite complex and the like. Among them, since the catalytic activity is good, the reaction product of chloroplatinic acid and alcohol and platinum-
Vinyl siloxane complexes are preferred.

The content of the platinum compound is 1 to 100 ppm by weight, preferably 2 to 50 ppm by weight in terms of platinum atom, based on the polyorganosiloxane in the composition, since an appropriate curing rate can be obtained. .

In order to impart desired physical properties to the polyorganosiloxane composition of the present invention, various non-reinforcing fillers may be added in appropriate amounts, if necessary. Fillers used include diatomaceous earth, crushed quartz, fused silica, aluminum oxide, iron oxide, zinc oxide, titanium oxide, cerium oxide and other oxides; calcium carbonate, magnesium carbonate, zinc carbonate and other carbonates; talc. Complex oxides such as clay, glass beads, and fine powder of mica; conductive fillers such as carbon black, copper powder, and nickel powder; and polymethylsilsesquioxane powder. These may be used by hydrophobizing the surface by a method such as coexisting in the surface treatment step of fine powder silica, if necessary.

When the polyorganosiloxane composition of the present invention is mixed with a polyorganohydrogensiloxane and a platinum compound in order to cure by an addition reaction,
In particular, when a liquid polyorganosiloxane having a monovalent aliphatic unsaturated hydrocarbon group is used as a base polymer, and when it is used in mass production techniques such as injection molding, in order to improve its storage stability at room temperature and workability, Compounded with acetylene alcohols, alkynyl group-containing silanes, vinyl group-containing low-molecular-weight siloxane compounds, diallyl maleate, triallyl isocyanurate, nitrile compounds, triphenyl phosphite, or curing retarders such as organic peroxides. May be.

Furthermore, if necessary, the composition of the present invention may include pigments, dyes, flame retardants, heat resistance improvers, thermal conductivity improvers, adhesion improvers and cups which have been conventionally compounded in silicone rubber. You may mix | blend a ring agent, a thixotropy imparting agent, a processing aid, a plasticizer, etc.

To obtain a silicone rubber by curing,
The composition of the present invention in which a cross-linking agent, a curing catalyst and other necessary components are blended, if necessary, is kneaded by a known method depending on the degree of polymerization of the base polymer, the cross-linking mechanism, and the shape of the composition. It can be prepared by mixing. Depending on the crosslinking mechanism, when a composition containing the base polymer and the crosslinking means is prepared, the crosslinking reaction proceeds even at room temperature. Therefore, in such a system, at least one component constituting the base polymer and the crosslinking means is placed in a separate container. Save it
Immediately before use, mix both; store in the presence of a set retarder; or if moisture in the air is involved in the crosslinking reaction, store it in a moisture-tight container to block it, and press immediately before use. A well-known method such as putting out can be adopted.
The cross-linking reaction is allowed to proceed at room temperature or by heating to a known predetermined temperature after molding by various molding methods such as casting, compression molding, injection molding, transfer molding, and extrusion molding depending on the cross-linking mechanism. You can For example, in the case of an addition reaction type liquid silicone rubber composition, injection molding is possible under the molding conditions of a temperature of 80 to 170 ° C. and a curing time of 10 seconds to 10 minutes.

[0039]

The present invention will be described in more detail with reference to the following examples. In these examples, parts indicate parts by weight, and all physical properties such as viscosity are values at 23 ° C. The invention is not limited by these examples. The following abbreviations are used in the chemical formulas of polyorganosiloxanes and silazane compounds. Me: methyl group; Vi: vinyl group

In the polyorganosiloxanes, the following symbols are used for siloxane units, and the intermediate unit indicates the number average unit number. When more than one type of intermediate siloxane unit is present, it is merely an indication of the number of intermediate units in the random copolymer and not a block copolymer. M: Me ₃ SiO _1/2 −; ^MH : HMe ₂ SiO _1/2 −;
^{_{M V: ViMe 2 SiO 1/2 -}} ; D: -Me 2 SiO-; D H: -MeHSiO-; D
^V : -MeViSiO-; Q: SiO4 _{/ 2} (tetravalent)

Example 1 Heating / cooling and depressurization are possible, a vertical butterfly blade is provided, a powder introduction port, a silazane compound introduction port, a nitrogen introduction port, an exhaust port, and necessary instruments are provided. the mixer is installed with a reflux condenser outlet, after purging the air by nitrogen was charged with 100 parts of liquid polymethylvinylsiloxane represented by average formula M ^V D ₇₈₀ M ^V. To this, 10 parts of hexamethyldisilazane was added, and water 5
And the mixture was thoroughly stirred. Then the specific surface area 300m ² / g
50 parts of fumed silica of (1) was added by extruding with nitrogen from the powder introduction port, and kneaded for 1 hour. During kneading, the system temperature rose to about 50 ° C. Then, it heated at 150 degreeC for 5 hours, and completed the reaction. Meanwhile, keep flowing nitrogen,
Moreover, hexamethyldisilazane and trimethylsilanol volatilized from the reaction system were totally refluxed into the system by the reflux condenser.

After the completion of the reaction, the condenser was switched so that the distillate was discharged to the outside of the system, the pressure was gradually reduced to 6.5 kPa, the temperature was raised to 150 ° C., and the reduced pressure heating was performed for 3 hours. Hexamethyldisilazane and other low boilers of the reaction were removed. Then, 60 parts of liquid polymethylvinylsiloxane represented by the average formula M ^V D ₇₈₀ M ^V was blended and mixed until uniform to obtain a fluid polyorganosiloxane composition.

The composition thus obtained was divided into two equal parts, and one composition contained 0.1% by weight of platinum-tetramethyltetravinylcyclotetrasiloxane complex containing 2% by weight of platinum atom.
The parts were blended and stirred to homogeneity to prepare Formulation A, which was sealed and stored. In the other composition, the average formula MD ^H ₂₀ D
1.5 parts of polymethyl hydrogen siloxane represented by ₁₀ M and 0.35 part of 2-methyl-3-butyn-2-ol are mixed and stirred until they are homogeneous to prepare a compound B, which is sealed. saved.

Comparative Example 1 In the same manner as in Example 1 except that a reflux condenser was not installed at the exhaust port, liquid polymethylvinylsiloxane and fumed silica were heated and kneaded, and the surface of the silica was treated with hexamethyldisilazane. Then, Formulation A and Formulation B were prepared in the same manner as in Example 1 and stored in a sealed manner.

Comparative Example 2 Kneading and surface treatment of silica were attempted in the same manner as in Comparative Example 1 except that the amount of hexamethyldisilazane was 50 parts, but the entire mixture of polyorganosiloxane and fumed silica was hexagonal. The paste was wet with methyldisilazane and trimethylsilanol and could not be sufficiently kneaded.

Evaluation Example 1 Equivalent amounts of the respective blends A and B obtained in Example 1 and Comparative Example 1 were uniformly mixed and defoamed under reduced pressure to obtain respective molding composition samples. It was This was evaluated as follows. The results are shown in Table 1. (1) Viscosity: Measured at 23 ° C. using a rotational viscometer. (2) Pot life: The pot life was defined as the time at which the viscosity was doubled by sealing and leaving at 23 ° C. (3) Physical properties after curing: A molding composition sample was cast in a mold and heated at 150 ° C. for 10 minutes to be cured to obtain a sheet having a thickness of 2 mm. Using this sheet, JISK 6249
The physical properties were measured by. However, the tensile strength and the elongation were measured by making a test piece with JIS K 6251 dumbbell No. 2 type.

[0047]

[Table 1]

As a result, in Example 1 in which the treating agent was returned to the system by total reflux during the heat kneading and the surface treatment, the silanol groups on the surface of the finely powdered silica were substantially completely silylated and obtained. The polyorganosiloxane composition obtained sufficient stability at room temperature even in the presence of a platinum catalyst. On the other hand, Comparative Example 1 in which the treating agent was not refluxed
However, the silanol groups on the surface of the finely powdered silica remained, resulting in poor stability, and gelation occurred within a few hours after mixing both formulations, making casting impossible. Moreover, when an excessive amount of the treating agent was used as in Comparative Example 2, the kneading could not be sufficiently performed.

[0049] Using the same mixer as that used in Example 1, after purging the air by nitrogen, charged with 100 parts of liquid polymethylvinylsiloxane represented by average formula M ^V D ₅₆₀ M ^V It is. To this, consists of M units, M ^V and Q units,
10 parts of branched polymethylvinylsiloxane containing M ^V units corresponding to an amount of 0.1 mol of vinyl group per 100 g and having an M / Q molar ratio of 0.7 were charged, and hexamethyldisilazane 7 was added thereto. Parts, and further 3 parts of water were added and stirred. Next, fumed silica 3 with a specific surface area of 140 m ² / g
0 part was added by extruding with nitrogen from the powder introduction port, and kneaded for 3 hours. During kneading, the system temperature rose to 40 ° C. Then, it heated at 150 degreeC for 5 hours, and completed the reaction. In the meantime, nitrogen flow was continued and the reflux condenser completely refluxed hexamethyldisilazane and trimethylsilanol volatilized from the reaction system into the system.

After completion of the reaction, the cooler was switched so that the distillate was discharged to the outside of the system, the pressure was gradually reduced to 6.5 kPa, the temperature was raised to 150 ° C., and the reduced pressure heating was performed for 3 hours. Hexamethyldisilazane and other low-boiling substances in the reaction were removed to obtain a fluid polyorganosiloxane composition.

The composition thus obtained was divided into two equal parts, and one part of the composition was mixed with 0.05 part of an isopropanol solution of chloroplatinic acid containing 5% by weight of platinum atom and stirred until uniform. Formulation A was prepared and stored sealed. In the other composition, 1 part and 2-methyl of branched polymethyl hydrogen siloxane comprising ^MH units and Q units and having ^MH units corresponding to 1 mol of hydrogen atoms bonded to silicon atoms per gram. 0.35 part of -3-butyn-2-ol was blended and stirred until it was homogeneous to prepare a blend B, which was sealed and stored.

Comparative Example 3 The surface treatment of hexamethyldisilazane with hexamethyldisilazane was carried out in the same manner as in Example 2 except that a reflux condenser was not installed at the exhaust port while heating and kneading liquid polymethylvinyl siroquine and fumed silica. Then, Formulation A and Formulation B were prepared in the same manner as in Example 2 and stored in a sealed manner.

Evaluation Example 2 The viscosity, pot life and physical properties after curing were measured in the same manner as in Evaluation Example 1 except that the curing conditions were 60 ° C. and 2 hours. The results are shown in Table 2.

[0054]

[Table 2]

As is clear from Table 2, the composition obtained in Example 2 exhibited excellent storage stability at room temperature. On the other hand, the composition obtained in Comparative Example 3 gelled within a few hours after mixing.

Example 3 A reflux condenser was installed at the exhaust port of a horizontal type 2 kneader equipped with the same elements as used in Example 1, and an average formula MD _{5990 was used.}
100 parts of high molecular weight polymethylvinylsiloxane represented by D ^V ₁₂ M was charged and the air was purged with nitrogen. To this, 20 parts of hexamethyldisilazane was added, 10 parts of water was further added and mixed well, and then a specific surface area of 200 m ²
50 parts of fumed silica of / g was added by extruding with nitrogen from the powder inlet and kneading for 2 hours. During kneading, the system temperature rose to 80 ° C. Then, it heated at 150 degreeC for 3 hours, and completed the reaction. During that time, nitrogen flow was continued, and the volatilized hexamethyldisilazane and trimethylsilanol were totally refluxed into the system by a reflux condenser.

After the reaction was completed, the condenser was switched so that the distillate was discharged to the outside of the system, the pressure was gradually reduced to 6.5 kPa, the temperature was raised to 150 ° C., and the reduced pressure heating was performed for 3 hours. A polyorganosiloxane composition was obtained by removing hexamethyldisilazane and other low-boiling substances in the reaction.

Comparative Example 4 In the same manner as in Example 3 except that a reflux condenser was not installed at the exhaust port, while heating and kneading the high molecular weight polymethylvinylsiloxane and fumed silica, the surface of the silica by hexamethyldisilazane was used. Treatment was carried out, and then heating under reduced pressure was carried out in the same manner as in Example 3 to obtain a polyorganosiloxane composition.

Evaluation Example 3 100 parts of each of the polyorganosiloxane compositions obtained in Example 3 and Comparative Example 4 were taken, and 5 parts of polymethylhydrogensiloxane represented by the average formula MD ^H ₂₈ M and platinum -Triphenyl phosphite complex 3 ppm, triphenyl phosphite 9 ppm and 2,5-dimethyl-2,5-di-t-butylperoxyhexane 20
ppm was blended and mixed until uniform to obtain a molding composition sample. This was evaluated as follows. The results are shown in Table 3. (1) Storage stability: The sample was sealed and stored at 50 ° C., and the time until gelation due to crosslinking was determined. (2) Physical properties after curing: A composition sample for molding was masticated and packed in a mold, and press vulcanization was performed at a temperature of 180 ° C for 10 minutes, and then at a temperature of 200 ° C in an air circulation heater. Thermal vulcanization was performed for 4 hours to obtain a sheet having a thickness of 2 mm. Using this sheet, physical properties were measured as in Evaluation Example 1.

[0060]

[Table 3]

The composition obtained in Example 3 showed excellent storage stability. On the other hand, the composition obtained in Comparative Example 4 showed gelation within several hours.

[0062]

INDUSTRIAL APPLICABILITY According to the present invention, when the polyorganosiloxane and the fine powder silica are kneaded, the silanol group on the surface of the fine powder silica can be completely removed by the silazane compound while effectively performing the kneading. . As a result, a polyorganosiloxane composition having excellent storage stability can be obtained even in the presence of fine powder silica and a platinum compound.

According to the present invention, a silicone rubber which is cured by an addition reaction can be stably produced with good workability, and particularly when a molding composition containing a catalyst is prepared in advance, such as injection molding, Even if the molding apparatus is temporarily stopped, the composition can be stably stored during that time, which is advantageous in process control. Further, even in a system that cures by a radical reaction, a system containing a platinum compound as a flame retardant can be stably stored.

Therefore, the present invention is cured by an addition reaction by various molding methods such as injection molding (LIM) using liquid silicone rubber for electronic parts, automobile parts, packing, gaskets, rolls, nipples of baby bottles and the like. It is extremely effective in rationalizing the production process of liquid silicone rubber and millable silicone rubber products.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Shinoki             6-2-1 Roppongi, Minato-ku, Tokyo             -Toshiba Silicone Co., Ltd. (72) Inventor Koji Nagumo             6-2-1 Roppongi, Minato-ku, Tokyo             -Toshiba Silicone Co., Ltd. F term (reference) 4G072 AA25 BB05 GG03 HH14 HH28                       QQ06 RR05 RR07 UU08                 4J002 CP042 CP131 DA117 DD077                       DJ016 FB146

Claims (10)

[Claims] 1. A mixture of a polyorganosiloxane having at least two monovalent aliphatic unsaturated hydrocarbon groups bonded to a silicon atom in one molecule and finely divided silica while kneading the mixture with an organosilicon compound. A method for silylating the surface of fine powder silica, which comprises subjecting the organosilicon compound and / or its hydrolysis product to fine powder silica surface treatment under conditions that do not escape to the outside of the system. , A method of surface treatment of fine powder silica. 2. The surface treatment method according to claim 1, wherein the organosilicon compound is a silazane compound. 3. The surface treatment method according to claim 2, wherein the silazane compound is hexamethyldisilazane. 4. The method according to claim 1, wherein 30 to 200 parts by weight of finely divided silica is used with respect to 100 parts by weight of polyorganosiloxane, and the silazane compound is used at 5 to 40% by weight of the finely divided silica. The surface treatment method according to item 1. 5. The surface treatment method according to claim 1, wherein the organosilicon compound and / or its hydrolysis product is subjected to a surface treatment of fine powder silica under reflux conditions. 6. A polyorganosiloxane composition containing a polyorganosiloxane and a silazane-treated finely divided silica obtained by the surface treatment method according to claim 1. 7. The composition according to claim 6, wherein the polyorganosiloxane has a viscosity at 25 ° C. of 0.5 to 500 Pa · s. 8. The composition according to claim 6, wherein the polyorganosiloxane has an average degree of polymerization of 3,000 to 10,000. 9. The method according to claim 6, further comprising a platinum compound.
The composition according to any one of 1. 10. The composition according to claim 9, further comprising a polyorganohydrogensiloxane having 3 or more hydrogen atoms bonded to silicon atoms in one molecule.