JPH04202479A - Production of hydrophobic silica - Google Patents

Abstract

PURPOSE:To obtain the title silica with excellent reinforcing properties as a filler for a rubber, etc., by providing a process wherein a specified alkali metal salt of an organosilanol is incorporated in an aq. suspension of a silica while keeping the pH of the suspension at a specified value. CONSTITUTION:A process wherein an alkali metal salt of an organosilanol of the formula (wherein M is an alkali metal; a and x are each 1-3 and 2<=a+x<=4; R is a 1-10C (substd.) monovalent hydrocarbon group) is added to an aq. suspension of a silica while keeping the pH of the suspension at 6-10 is provided.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing hydrophobic silica.

(Prior Art) Silicone rubber produced by vulcanizing polydiorganosiloxane gum raw rubber generally has low ultimate elongation and ultimate tensile strength values. One way to improve this physical property is to add silica filler to the polydiorganosiloxane gum before vulcanization. However, the silica filler gradually bonds with the polydiorganosiloxane, and as the bond increases, the hardness of the compound also increases (creep hardening). Therefore, in order to reduce or eliminate the creep hardening tendency and at the same time improve the physical properties of the vulcanized silicone rubber, attempts have been made to hydrophobize the surface of the silica filler to be added.

U.S. Pat. No. 3,024,126, issued March 6, 1962, discloses that silica fillers are prepared in an organic solvent with a total of 0.1 to 2 hydroxyl groups per silicon atom and/or
Methods of hydrophobization by treatment with small amounts of organosilicon compounds such as organosilanes containing alkoxyl groups, low molecular weight organosiloxanes, certain amines, quaternary ammoniums or organometallic compounds are described.

(Problems to be Solved by the Invention) The above method has the drawback that the operation is complicated because the silica must be once dispersed in a solvent and converted into an organogel, and then hydrophobized.

Therefore, the object of the present invention is to develop a method for producing hydrophobic silica that can hydrophobize silica as it is without converting the aqueous suspension of silica (hydrokel) obtained in the wet silica production process into an organogel. It is about providing.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a silica aqueous suspension containing the general formula (1): % formula % () (where M represents an alkali metal and a is a number from 1 to 3, X is a number from 1 to 3, and 2≦a+X
The number satisfies ≦4. Further, R represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms. ) The present invention provides a method for producing hydrophobic silica, which includes the step of adding an organosilanol alkali metal salt represented by the following formula while maintaining the pH of the suspension at 6 to 10.

Silica Aqueous Suspension The method for producing hydrophobic silica of the present invention can be applied to a wet silica aqueous suspension obtained in a wet silica production process by a known method, and can also be applied to a wet silica aqueous suspension obtained in a wet silica production process using a known method. It can also be applied to an aqueous suspension obtained by dispersing it in. As a method for producing wet silica, for example, US Pat. No. 2,601,235 issued on June 24, 1952
For example, the method described in Japanese Patent Publication No. 39-1207.

Organosilanol alkali metal salt R in the general formula (I) represents a substituted or unsubstituted monovalent hydrocarbon group, such as an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, etc. basis,
Examples include cycloalkyl groups such as cyclopentyl group and cyclohexyl group, aralkyl groups such as 2-phenylethyl group and 2-phenylpropyl group, aryl groups such as phenyl group and tolyl group, and alkenyl groups such as vinyl group and allyl group. It will be done. Among these, methyl group is preferred.

M in general formula (I) represents an alkali metal, such as sodium, lithium, and potassium, with sodium being preferred.

The organosilanol alkali metal salt represented by general formula (I) is, for example, methylsilanetriol sodium salt,
Ethylsilanetriol sodium salt, propylsilanetriol sodium salt, butylsilanetriol sodium salt, dimethylsilanetriol sodium salt, diethylsilanediol sodium salt, trimethylsilane monool sodium salt, triethylsilane monool sodium salt, Examples include sodium salts such as vinylsilanetriol sodium salt, phenylsilanetriol sodium salt, and diphenylsilanediol sodium salt. Among them, methylsilanol sodium salt is preferred.

The organosilanol alkali metal salt represented by the general formula (I) improves the hydrophobicity of the silica filler by binding the organosilyl group to the silanol group on the surface of the wet silica fine powder.

Solvent In the method of the present invention, the organosilanol alkali metal salt can be added to the aqueous suspension of silica in the form of a solution diluted with a solvent. The solvent used for diluting the organosilanol alkali metal salt is, for example, water, or one or more hydrophilic solvents such as ethanol, alcohols such as propatool, and ketones such as acetone. , or a mixed solvent used in combination.

Reaction conditions in the addition step The number of moles of silicon in the organosilanol alkali metal salt solution is 5 to 30 of the number of moles of silicon in the silica aqueous suspension.
% or so is preferable. If it is less than 5%, the hydrophobic effect will be weakened, and if it exceeds 30%, the structure of silica will be damaged and its dispersibility will be reduced.

The concentration of the organosilanol alkali metal salt solution is preferably 1 to 50 g/100 cc in terms of organic silicic acid concentration.

The rate of addition of the organosilanol alkali metal salt solution is not particularly limited; if the rate is too high, the entire solution may gel or the hydrophobization effect may be uneven.

During the above process, the pH of the aqueous silica suspension gradually increases with the addition of the organosilanol alkali metal salt. When the pH exceeds IO, the generated organic silicic acid exists stably and loses its effectiveness as a hydrophobizing agent, so the pl is adjusted to 6 to 10
It is particularly preferable to keep the value between 7 and 9. For this reason, an acid is added together if necessary. Examples of the acids used include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, sulfurous acid, formic acid, and carbonic acid, and one or more of them may be used as an aqueous solution or gas.

The reaction temperature may be between 0 and 100″C, and between 80 and 100°C.
C is preferred.

After the addition process is complete, acid is added to the aqueous silica suspension again to make the PL of the wet silica suspension 6 or less. At this time, when using a weak acid such as carbonic acid, the pH will not drop, so the mother liquor Separate and add strong acid. Next, with or without aging, add acid to adjust pf (to the desired pH of the product,
Filter, remove, wash and dry.

Applications The hydrophobic silica obtained by the method of the present invention is useful as a filler for various rubbers including silicone rubber, as a matting agent for various paints, as a flow modifier, as a coating agent for special papers, and the like.

(Example 1) Wet silica aqueous suspension 63 with specific surface area 340rrf/g
4cc (silicic acid concentration 5.3g/100cc),
Methylsilanetriol sodium salt aqueous solution 130cc
(silicic acid concentration 12.5 g/100 cc) was added over about 20 minutes with vigorous stirring while maintaining the temperature of the wet silica aqueous suspension at 80-90°C. At this time,
41 cc of a 4.7N sulfuric acid aqueous solution was also added at the same time to maintain the PL of the suspension at 8-9. Next, the above sulfuric acid aqueous solution was further added to adjust the suspension to pH 2, and the suspension was filtered, washed, and dried to obtain 50 g of hydrophobic silica.

The carbon content of this hydrophobic silica was 4.5%, the specific surface area by BET method was 315rrf'/g, and no creep hardening was observed when it was blended into silicone raw rubber.

(Example 2) Wet silica aqueous suspension 330 with a specific surface area of 65 rrr/g
0cc (silicic acid concentration 5.5g/100cc), 500cc of methylsilanetriol sodium salt aqueous solution
(silicic acid concentration 10 g/100 cc) was added over about 80 minutes with vigorous stirring while maintaining the temperature of the wet silica suspension at 80-90°C. At this time, 163 cc of a 4.8N sulfuric acid aqueous solution was also added at the same time to maintain the pH of the suspension at 8 to 9.

Next, the above sulfuric acid aqueous solution is further added to adjust the pH of the suspension.
2, filtered, washed, dried, hydrophobic silica 220
I got g.

The apparent specific gravity of this hydrophobic silica is 0.14g/cnr, the carbon content is 4.5%, and the specific surface area by BET method is 60r.
It was rr/g. When blended with silicone raw rubber, no creep hardening was observed.

〔evaluation〕

The hydrophobic silica obtained in Example 2 was blended into silicone rubber as follows.

Organopolysiloxane: 68 parts by weight Organopolysiloxane: 32 parts by weight At least 40 parts by weight of the hydrophobic silica obtained in Example 2 were blended and kneaded in a two-roll mill, and then kneaded in a three-roll mill to give 5 parts by weight.
A base compound was obtained by kneading twice.

Next, for 100 parts by weight of the above base compound,
3 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane was added as a peroxide vulcanizing agent, and kneaded using a two-roll mill.

The kneaded rubber produced by the above operations was heated to 165°C.
Press vulcanization was performed under the following conditions: primary curing for 10 minutes at 200°C, and secondary curing for 4 hours at 200°C, resulting in a thickness of 2mm.
A sheet with a size of 150 mm x 200 mm was obtained.

Using this as a sample, vulcanized rubber physical test (JIS K630
1) was performed. The results are shown in Table-1.

Table 1 (Effects of the Invention) According to the method of the present invention, hydrophobic silica having excellent hydrophobicity and sufficient reinforcing properties as a filler for rubber etc. can be easily produced. The hydrophobic silicas produced according to the invention are suitable as fillers, for example in silicone rubbers.

Claims (1)

[Claims] A silica aqueous suspension containing the general formula (I): R_aSi(OM)_xO_(_4_-_a_-_x_
)_/_2(I) (In the formula, M represents an alkali metal, and a
is a number from 1 to 3, and x is a number from 1 to 3, and satisfies 2≦a+x≦4. Further, R represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms. ) A method for producing hydrophobic silica, comprising the step of adding an organosilanol alkali metal salt represented by the following formula while maintaining the pH of the suspension at 6 to 10.