JPH0733250B2 - Method for producing hydrophobic silica - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing hydrophobic silica.

(Prior Art) The values of ultimate elongation and ultimate tensile strength of a silicone rubber produced by vulcanizing a polydiorganosiloxane gum raw rubber are generally low. One way to improve this physical property is to add a silica filler to the polydiorganosiloxane gum prior to 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 tendency of creep curing and at the same time improve the physical properties of the vulcanized silicone rubber, attempts have been made to make the surface of the silica filler to be hydrophobized.

U.S. Pat. No. 3,024,126, issued Mar. 6, 1962, contains a silica filler in organic solvent for a total of 0,0 per silicon atom.
Organosilanes containing 1-2 hydroxyl groups and / or alkoxyl groups, organosilicon compounds such as low molecular weight organosiloxanes, by treatment with small amounts of certain amines, quaternary ammonium or organometallic compounds, A method of hydrophobizing is described.

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

Therefore, an object of the present invention is to provide a method for producing a hydrophobic silica capable of hydrophobizing silica as it is without converting an aqueous silica suspension (hydrogel) obtained in a wet silica production step into an organogel. To provide.

(SUMMARY for a) the present invention is to solve the above problems, the silica aqueous suspension, the general formula _{(I): R a Si (} OM) x O (4-ax) / 2 ( I) (wherein M represents an alkali metal, a is a number of 1 or more and 3 or less, x is a number of 1 or more and 3 or less, and 2 ≦ a + x
It is a number that satisfies ≦ 4. 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 comprises a step of adding the organosilanol alkali metal salt represented by the formula (4) while keeping 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 the wet silica aqueous suspension obtained in the wet silica production step by a known method, and already produced wet silica can be used as an aqueous medium. It can also be applied to an aqueous suspension obtained by dispersing in. As a method for producing wet silica, for example, US Patent No. 2601235 issued on June 24, 1952, and Japanese Patent Publication No. 39
-1207 and the like.

Organosilanol alkali metal salt R in the general formula (I) represents a substituted or unsubstituted monovalent hydrocarbon group, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group or a hexyl group. Group, cyclopentyl group, cycloalkyl group such as cyclohexyl group, aralkyl group such as 2-phenylethyl group and 2-phenylpropyl group, aryl group such as phenyl group and tolyl group, and alkenyl group such as vinyl group and allyl group Is mentioned. Of these, a methyl group is preferable.

M in the general formula (I) represents an alkali metal, and examples thereof include sodium, lithium, and potassium. Among them, sodium is preferable.

The organosilanol alkali metal salt represented by the general formula (I) is, for example, methylsilanetriol sodium salt,
Ethylsilanetriol sodium salt, propylsilanetriol sodium salt, butylsilanetriol sodium salt, dimethylsilanediol sodium salt, diethylsilanediol sodium salt, trimethylsilanemonool sodium salt, triethylsilanemonool sodium salt, vinylsilanetriol sodium salt, phenyl Examples thereof include silanetriol sodium salt and sodium salt such as diphenylsilanediol sodium salt. Among them, methylsilanol sodium salt is preferable.

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

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

Reaction conditions in 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.
A degree is preferable. If it is less than 5%, the effect of hydrophobization will be weakened, and if it exceeds 30%, the structure of silica will be impaired 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 the concentration of organic silicic acid.

The addition rate of the organosilanol alkali metal salt solution is not particularly limited, but if the rate is too fast, the whole gels or the effect of hydrophobizing becomes 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 10, the generated organic silicic acid stably exists and loses its effectiveness as a hydrophobizing agent, so that the pH is 6 to 10, particularly 7 to
It is preferably kept at 9. Therefore, an acid is added together if necessary. Examples of the acid used include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, sulfurous acid, formic acid, and carbonic acid, and one or more kinds may be used as an aqueous solution or gas.

The reaction temperature may be between 0 and 100 ° C, preferably 80-100 ° C.

After the addition step is completed, the acid is added again to the aqueous silica suspension to adjust the pH of the wet silica suspension to 6 or less. At this time, when a weak acid such as carbonic acid is used, the pH does not decrease, so the mother liquor is separated and a strong acid is added. Next, with or without aging, further add an acid to adjust the pH to the pH of the target product, filter, wash and dry.

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

(Example 1) A wet silica aqueous suspension 634 cc (silicic acid concentration 5.3 g / 100 cc) having a specific surface area of 340 m ² / g was added with merylsilanetriol sodium salt aqueous solution 130 cc (silicic acid concentration 12.5 g / 100 cc). The temperature of the aqueous suspension was kept at 80-90 ° C and added with vigorous stirring in about 20 minutes. At this time, 41 cc of a 4.7 N sulfuric acid aqueous solution was also added at the same time to keep the pH of the suspension at 8-9. Next, the suspension was adjusted to pH 2 by further adding the sulfuric acid aqueous solution, filtered, washed, and dried to obtain 50 g of hydrophobic silica.

The carbon content of this hydrophobic silica was 4.5%, and the specific surface area by the BET method was 315 m ² / g. Creep hardening was not observed when blended with silicone raw rubber.

(Example 2) To 3300 cc of a wet silica aqueous suspension having a specific surface area of 65 m ² / g (silicic acid concentration of 5.5 g / 100 cc), 500 cc of a methylsilanetriol sodium salt aqueous solution (silicic acid concentration of 10 g / 100 cc) was added. While maintaining the temperature of the suspension at 80 to 90 ° C, the suspension was added with vigorous stirring in about 80 minutes. 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 8-9. Next, the above-mentioned sulfuric acid aqueous solution is further added to form a suspension.
pH2, filtered, washed, dried, hydrophobic silica 220g
Got

The apparent specific gravity of this hydrophobic silica was 0.14 g / cm ³ , the carbon content was 4.5%, and the specific surface area by the BET method was 60 m ² / g. Creep hardening was not observed when compounded with silicone raw rubber.

[Evaluation]

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

The above components were mixed and kneaded with a two-roll mill, and then kneaded five times with a three-roll mill to obtain a base compound.

Next, to 100 parts by weight of the above base compound, 3 parts by weight of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as a peroxide vulcanizing agent were added and mixed with a two-roll mill. Kneaded

The kneaded rubber produced by the above operation was press-vulcanized under the vulcanization conditions of a primary cure of 165 ° C. for 10 minutes and a secondary cure of 200 ° C. for 4 hours to give a thickness of 2 mm and a size of 150 mm ×
A 200 mm sheet was obtained.

Using this as a sample, a vulcanized rubber physical test (JIS K6301) was performed. The results are shown in Table-1.

(Effect of the Invention) According to the method of the present invention, hydrophobic silica having excellent hydrophobicity and having sufficient reinforcing properties as a filler such as rubber can be easily produced. The hydrophobic silica produced according to the invention is suitable as a filler, for example silicone rubber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Hayashida 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (56) Reference JP-A-50-51494 (JP, A)

Claims (1)

[Claims] To 1. A silica aqueous suspension, the general formula _{(I): R a Si (} OM) x O (4-ax) / 2 (I) ( wherein M represents an alkali metal, a is 1 or more Is a number of 3 or less, x is a number of 1 or more and 3 or less, and 2 ≦ a + x
It is a number that satisfies ≦ 4. R represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms. ) The method for producing hydrophobic silica, which comprises the step of adding the organosilanol alkali metal salt represented by the formula (4) while keeping the pH of the suspension at 6 to 10.