JPH0741562A - Production of liquid silicone rubber base compound - Google Patents

Abstract

PURPOSE:To produce a liquid silicone rubber base compd. of which the viscosity is low and hardly changes with time. CONSTITUTION:The compd. is produced by mixing 30-60 pts.wt. diorganopolysiloxane having a viscosity at 25 deg.C of 300-50,000cP with 25-50 pts.wt. silica filler having a hydrophobic surface treatment and a bulk density of 100-200g/l and then with 70-40 pts.wt. the diorganopolysiloxane on a mixing machine.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a liquid silicone rubber base compound. More specifically, it relates to a method for producing a liquid silicone rubber base compound having a low viscosity and a small viscosity change with time.

[0002]

2. Description of the Related Art Conventionally, a silicone rubber molded article is obtained by kneading a silicone rubber base compound containing a diorganopolysiloxane raw rubber and a reinforcing silica filler as a main component with an organic peroxide as a curing catalyst, and curing the mixture. Was there. However, in the case of this method, complicated steps such as mastication by a two-roll machine and dispensing are required before the molding process. Recently, a liquid silicone rubber base compound comprising a diorganopolysiloxane having a silicon atom-bonded vinyl group having a relatively low degree of polymerization and a fine powder silica filler has been used as a curing agent or a curing catalyst for a silicon atom-bonded hydrogen atom-containing organopolysiloxane. A method in which a siloxane and a platinum-based catalyst are added and blended and cured and molded to obtain a silicone rubber molded article is widely used. In the case of this method, the liquid silicone rubber base compound before curing has fluidity, the process is simple, and it is easy to apply to injection molding and automation, and it is possible to simplify the whole process from kneading to molding. There are advantages. However, this liquid silicone rubber base compound is required to maintain fluidity while containing a large amount of reinforcing filler, and therefore, as a plasticizer, for example, hexamethyldisilazane, a low degree of polymerization at both ends is used. Addition of silanol group-blocked dimethylpolysiloxane or low degree of polymerization both-end alkoxy group-blocked dimethylpolysiloxane was essential. As a result, the composition and process are complicated, and the manufacturing cost is high. In order to solve this drawback, a method of producing a liquid silicone rubber base compound having fluidity by a simple process without adding a plasticizer has been proposed (Japanese Patent Publication No. 28008/1992).
-39487 gazette). However, the liquid silicone rubber-based compound obtained by these methods has a drawback that its viscosity changes with time.

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors in order to solve the above-mentioned drawbacks, as a result of using a surface-hydrophobized silica filler having a remarkably large bulk density and employing a specific kneading method, the above-mentioned drawbacks are The present invention has been achieved by finding that the above is solved. That is, an object of the present invention is to provide a method for producing a liquid silicone rubber base compound having a low viscosity and a small viscosity change with time.

[0004]

MEANS FOR SOLVING THE PROBLEMS AND ACTION THEREOF The present invention provides a kneading machine having (A) a viscosity of 300 to 5 at 25 ° C.
30 to 60 parts by weight of diorganopolysiloxane having a 000 centipoise and (B) a bulk density of 100 to 200 g /
25 to 50 parts by weight of the surface-hydrophobicized silica filler which is 1 is supplied and kneaded, and then 70 to 40 parts by weight of the diorganopolysiloxane of the component (A) is added to the kneaded product and kneaded. , A method for producing a liquid silicone rubber base compound.

To explain this, it is used in the present invention.
The diorganopolysiloxane as the component (A) is a raw material for the liquid silicone rubber base compound, and the conventionally known diorganopolysiloxane used in the liquid silicone rubber base compound is used. This diorganopolysiloxane has a viscosity of 3 at 25 ° C.
If it is less than 00 centipoise, excellent physical properties as a silicone rubber elastic body cannot be obtained after curing,
When it exceeds 00 centipoise, it becomes difficult to handle it. Therefore, it is necessary that the viscosity at 25 ° C. is 300 to 50,000 centipoise. The molecular structure of this diorganopolysiloxane is linear, but if it is a small amount, it may contain branched ones. A substituted or unsubstituted monovalent hydrocarbon group is generally used as the organic group bonded to the silicon atom, and a methyl group, an ethyl group, a propyl group or a butyl group is used as the substituted or unsubstituted monovalent hydrocarbon group. Alkyl groups such as; alkenyl groups such as vinyl group, allyl group, 1-propenyl group; aryl groups such as phenyl group, tolyl group; 2-phenylmethyl group, 2-phenylethyl group, 3,3,3-trifluoro Substituted alkyl groups such as propyl group are exemplified, but at least 50 mol% is preferably methyl group. Further, this diorganopolysiloxane preferably contains two or more silicon-bonded alkenyl groups in one molecule, and in addition to the above-mentioned monovalent hydrocarbon group, a hydroxyl group, an alkoxy group or a hydrogen atom is contained at the end of the polymer. May be combined. Typical examples of such a diorganopolysiloxane include dimethylvinylsiloxy group-capped dimethylsiloxane / methylvinylsiloxane copolymers having both ends, dimethylvinylsiloxy group-capped dimethylpolysiloxanes having both terminals dimethylvinylsiloxy group-capped dimethylsiloxane. -Methyl vinyl siloxane-Methyl phenyl siloxane copolymer, both ends trimethylsiloxy group blocked dimethyl siloxane-Methyl vinyl siloxane copolymer, both ends trimethyl siloxy group blocked dimethyl siloxane-Methyl phenyl siloxane-
Examples thereof include a methyl vinyl siloxane copolymer and methyl (3,3,3-trifluoropropyl) polysiloxane capped with dimethyl vinyl siloxy groups at both ends.

The component (B) surface-hydrophobicized silica filler used in the present invention is a reinforcing filler for a liquid silicone rubber base compound. Typical types of this silica filler are wet silica and dry silica.
The specific surface area thereof is preferably 130 m ² / g or more. As a method for hydrophobizing the surface, a reflux method, a suspension method, a normal method, a surface treatment agent such as an organoalkoxysilane, an organohalogenosilane, an organosilazane, or a linear or cyclic low-polymerization organopolysiloxane is used. Examples of the method include hydrophobizing treatment by a method such as a pressure fluidized bed method or a pressure method. Although the surface-hydrophobicized silica filler obtained by this method is commercially available, it has no bulk density and is not useful for the present invention. The bulk density of the surface-hydrophobized silica filler used in the present invention needs to be 100 to 200 g / l. It has a bulk density of 100 g / l
If it is less than 200 g / l, the viscosity of the obtained liquid silicone rubber-based compound changes greatly with time.
This is because it is difficult to uniformly disperse the surface-hydrophobized silica filler in the liquid silicone rubber-based compound if it exceeds the range. The silica filler having such a high bulk density is obtained by compressing and deaerating the surface-hydrophobicized silica filler obtained by the above method with a vacuum roll, or by putting the above-mentioned surface-hydrophobicized silica filler in a sealed bag. It is obtained by compressing and degassing. Here, the value of this bulk density is measured according to the following method. The surface-hydrophobized silica filler is put into a graduated cylinder of 1000 cc up to a scale of 1 liter. At this time, since the surface-hydrophobized silica filler precipitates,
For 3 minutes after the addition, the surface-hydrophobized silica filler is replenished so that the volume is maintained at 1000 cc. Then 3
After a lapse of minutes, the weight (g) of the surface-hydrophobicized silica filler in the measuring cylinder is measured. The measured value is g / l
Is displayed as the bulk density.

The liquid silicone rubber-based compound obtained by the production method of the present invention contains the above-mentioned components (A) and (B) as the main ingredients, and it has a low degree of polymerization and has silanol groups at both ends and dimethyl poly-terminal. Plasticizers such as siloxane, low polymerization degree both ends alkoxy group-blocked dimethylpolysiloxane, quartz fine powder, diatomaceous earth powder, rouge, cerium oxide, cerium fatty acid salt, titanium oxide, carbon black, etc. Addition of agents may be carried out as long as the object of the present invention is not impaired.

In the present invention, the above-mentioned kneader is used.
30 to 60 parts by weight of the component (A) and 5 to 50 parts by weight of the component (B) are supplied to uniformly knead, and then 70 to 40 parts by weight of the component (A) is added to this kneader to uniformly knead. . Examples of the kneader used at this time include a biaxial continuous kneading extruder, a kneader mixer, a Banbury mixer, and a universal mixer. Although this kneading can be carried out at room temperature, it is generally carried out under heating conditions of 100 ° C to 300 ° C, more preferably under heating conditions of 200 ° C to 300 ° C.

According to the production method of the present invention, the viscosity is low,
Further, it is possible to manufacture a liquid silicone rubber base compound having a small change in viscosity with time. Such a liquid silicone rubber base compound has a low viscosity and can be stored for a long period of time because the viscosity changes little with time, and is easy to handle and used as a liquid silicone rubber base compound for injection molding or transfer molding. It is extremely effective.

As a curing agent for the liquid silicone rubber-based compound obtained by the production method of the present invention, it is preferable to use a combination of an organohydrogenpolysiloxane and a platinum catalyst, but in some cases, an organic peroxide may be used. Good. The amount of the curing agent added is preferably in the range of 0.5 to 30 parts by weight with respect to 100 parts by weight of the liquid silicone rubber base compound, and the platinum catalyst is the weight of the diorganopolysiloxane of the component (A). On the other hand, the range of 1 to 300 ppm in terms of platinum is preferable. When using an organic peroxide, the addition amount is (A)
The range of 0.5 to 10 parts by weight is preferable with respect to 100 parts by weight of the component diorganopolysiloxane. The liquid silicone rubber base compound obtained in the present invention can be obtained by adding the above-mentioned curing agent to the liquid silicone rubber base compound and heating and curing it to obtain a silicone rubber elastic body. At this time, if necessary, additives well known to be added to the liquid silicone rubber-based compound, such as an addition reaction retarder, a heat-resistant agent, a flame retardant, and a coloring agent, may be added. Examples of the molding method include compression molding, injection molding, transfer molding and cast molding.

[0011]

EXAMPLES The present invention will now be described with reference to examples. In the examples, "parts" means "parts by weight", and the viscosity is a value at 25 ° C. In the examples, the time-dependent change in viscosity of the obtained liquid silicone rubber-based compound [Viscosity increase rate
(%)] Was measured as follows. ○ Method for measuring change with time of viscosity of silicone rubber base compound The viscosity of the obtained liquid silicone rubber base compound immediately after production was measured with a rotary viscometer (Vismetron B type), and the liquid silicone rubber base compound was further measured at room temperature. The viscosity after standing for 4 weeks was measured in the same manner, and the viscosity increase rate (%) was calculated according to the following formula. Viscosity increase rate (%) = [(viscosity after 4 weeks-viscosity immediately after production) / viscosity immediately after production] × 100 In addition, the dispersibility of the surface-hydrophobicized silica filler in the obtained liquid silicone rubber base compound was measured. It was measured visually and evaluated in the following two stages. Good: The surface-hydrophobicized silica filler was uniformly dispersed in the liquid silicone rubber base compound. Poor: The surface-hydrophobicized silica filler was tentatively dispersed in the liquid silicone rubber base compound, but was partially aggregated. The physical properties of the obtained liquid silicone rubber base compound after curing were measured according to the method specified in JIS K6301 Vulcanized Rubber Physical Property Measurement Method.

[0012]

[Reference Example 1] Preparation of surface-hydrophobized silica filler having a bulk density of 150 g / l Dry silica filler surface-hydrophobized with hexamethyldisilazane (bulk density 50 g / l, specific surface area 150 m ²
/ G) was placed on two vacuum rolls (rolls in which the inside of the roll is hollow and the pressure can be reduced), and the roll was rotated in a vacuum state. Here, the clearance between the two rolls was 5 mm. The dry silica filler on the roll adhered to the roll surface and was consolidated. Then
The compacted dry silica filler was peeled off from the roll surface and placed in a polyethylene bag for storage. The bulk density of this dry silica filler was 150 g / l.

[0013]

[Reference Example 2] Preparation of surface-hydrophobicized silica filler having a bulk density of 80 g / l Dry silica filler surface-hydrophobicized with hexamethyldisilazane (bulk density 50 g / l, specific surface area 150 m ²
/ G) was placed in a polyethylene bag, which was inserted between compression presses and pressed under a pressure of 9 kg / m ² .
The bulk density of the obtained dry silica filler was 80 g / l.

[0014]

[Example 1] In a rigid container moving type multi-axis mixer, a viscosity of 2,
5,000 centipoise dimethylpolysiloxane blocked with dimethylvinylsiloxy groups at both ends and 36 parts of surface-hydrophobized silica filler having a bulk density of 150 g / l obtained in Reference Example 1 were supplied, and kneaded at a temperature of 200 ° C. did.
Then, 50 parts of the above dimethylpolysiloxane was further added to this kneaded product and kneaded until uniform, and after 2 hours, a liquid silicone rubber base compound was obtained. Viscosity increase rate of the obtained liquid silicone rubber base compound
(%) And the dispersibility of the surface-hydrophobized silica filler in the liquid silicone rubber base compound were measured, and the results are shown in Table 1. Further, to 100 parts of this liquid silicone rubber base compound, 2 parts of methylhydrogenpolysiloxane having a viscosity of 7 centipoise and having trimethylsiloxy groups at both ends blocked (a silicon atom-bonded hydrogen atom content of 0.75% by weight), chloroplatinic acid and tetrachloride were added. A silicone rubber composition was prepared by adding a complex salt of methyltetravinylsiloxane to dimethylpolysiloxane in the liquid silicone rubber base compound in an amount such that the platinum weight was 10 ppm and mixing them uniformly. This silicone rubber composition was compression molded for 30 minutes at a temperature of 120 ° C. and a pressure of 30 kg / cm ² to prepare a silicone rubber sheet having a thickness of 2 mm. The physical properties of this silicone rubber were measured, and the results are shown in Table 2.

[0015]

[Comparative Example 1] In Example 1, in place of the silica filler having a bulk density of 150 g / l obtained in Reference Example 1, a surface hydrophobic treatment having a bulk density of 80 g / l obtained in Reference Example 2 was used. A liquid silicone rubber base compound was prepared in the same manner as in Example 1 except that the silica filler was used. The viscosity increase rate (%) of this liquid silicone rubber base compound and the dispersibility of the surface-hydrophobicized silica filler in the liquid silicone rubber base compound were measured, and the results are shown in Table 1. Further, to 100 parts of this liquid silicone rubber base compound, 2 parts of methylhydrogenpolysiloxane having a viscosity of 7 centipoise and having trimethylsiloxy groups at both ends blocked (a silicon atom-bonded hydrogen atom content of 0.75% by weight), chloroplatinic acid and tetrachloride were added. A silicone rubber composition was prepared by adding a complex salt of methyltetravinylsiloxane to dimethylpolysiloxane in the liquid silicone rubber base compound in an amount such that the platinum weight was 10 ppm and mixing them uniformly. The physical properties of this silicone rubber were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0016]

Comparative Example 2 In Example 1, the surface-hydrophobicized silica filler used in the preparation of this silica filler was replaced with the surface-hydrophobicized silica filler having a bulk density of 150 g / l obtained in Reference Example 1. A liquid silicone rubber base compound was prepared in the same manner as in Example 1 except that only dry silica filler having a bulk density of 50 g / l was used. The viscosity increase rate (%) of the obtained liquid silicone rubber base compound and the dispersibility of the surface-hydrophobicized silica filler in the liquid silicone rubber base compound were measured, and the results are shown in Table 1.
Furthermore, this liquid silicone rubber base compound 1
To 00 parts, 2 parts of methylhydrogenpolysiloxane having a viscosity of 7 centipoise and blocked with trimethylsiloxy groups at both ends (silicon atom-bonded hydrogen atom content of 0.75% by weight), and a complex salt of chloroplatinic acid and tetramethyltetravinylsiloxane are added. A liquid silicone rubber composition was prepared by adding an amount of platinum of 10 ppm to dimethylpolysiloxane in the liquid silicone rubber base compound and mixing them uniformly. The physical properties of this silicone rubber were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0017]

[Comparative Example 3] In a rigid container moving type multi-axis mixer, Example 1 was used.
Dimethylpolysiloxane 100 capped at both ends with dimethylvinylsiloxy groups and having a viscosity of 2,000 centipoise
And 36 parts of dry silica filler having a bulk density of 50 g / l just surface-hydrophobized with hexamethyldisilazane used when preparing a silica filler having a bulk density of 150 g / l in Reference Example 1 Was kneaded until uniform, and after 2 hours, a liquid silicone rubber base compound was obtained. The dispersibility of the surface-hydrophobicized silica filler in the obtained liquid silicone rubber base compound was measured, and the results are shown in Table 1. Further, the viscosity of this liquid silicone rubber base compound immediately after its production was measured. Furthermore, when this was left to stand at room temperature for 4 weeks, the fluidity was lost after 4 weeks to form a gel-like substance, and its viscosity could not be measured. The results are shown in Table 1. Further, 100 parts of the liquid silicone rubber base compound immediately after the production was added to a methylhydrogenpolysiloxane having a viscosity of 7 centipoise and having trimethylsiloxy groups at both ends blocked (silicon atom-bonded hydrogen atom content:
75 parts by weight) and 2 parts of a complex salt of chloroplatinic acid and tetramethyltetravinylsiloxane are added to the dimethylpolysiloxane in the liquid silicone rubber base compound in an amount such that the platinum weight is 10 ppm and mixed uniformly. A liquid silicone rubber composition was prepared. The physical properties of this silicone rubber were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

Example 2 A twin-screw type continuous kneading extruder was used, and the viscosity was 5,000.
60 parts of dimethylpolysiloxane capped with dimethylvinylsiloxy groups at both ends of centipoise, and surface-hydrophobicized silica filler 30 having a bulk density of 150 g / l obtained in Reference Example 1
Parts were fed and these were kneaded until uniform. Next, 40 parts of the above dimethylpolysiloxane was added to this kneaded product and kneaded until uniform, and after 3 hours, a liquid silicone rubber base compound was obtained. Viscosity increase rate (%) of the obtained liquid silicone rubber base compound
The dispersibility of the surface-hydrophobicized silica filler in the liquid silicone rubber base compound was measured, and the results are shown in Table 3. Furthermore, 100 parts of this liquid silicone rubber base compound was added to a methylhydrogenpolysiloxane having a viscosity of 7 centipoise and blocked at both ends with trimethylsiloxy groups (content of silicon atom-bonded hydrogen atoms of 0.7).
5 parts by weight) and 2 parts of chloroplatinic acid and a tetramethyltetravinylsiloxane complex salt are added to the dimethylpolysiloxane in the liquid silicone rubber base compound in an amount of 10 ppm as platinum weight and mixed uniformly. A liquid silicone rubber composition was prepared. This silicone rubber composition was compression molded for 30 minutes at a temperature of 120 ° C. and a pressure of 30 kg / cm ² to prepare a silicone rubber sheet having a thickness of 2 mm. The physical properties of this silicone rubber were measured, and the results are shown in Table 4.

[0021]

[Comparative Example 4] In Example 2, in place of the silica filler having a bulk density of 150 g / l obtained in Reference Example 1, the silica filler having a bulk density of 80 g / l obtained in Reference Example 2 was used instead of the silica filler. A liquid silicone rubber base compound was prepared in the same manner as in Example 2 except that the silica filler was used. The viscosity increase rate (%) of the obtained liquid silicone rubber base compound and the dispersibility of the surface-hydrophobicized silica filler in the liquid silicone rubber base compound were measured, and the results are shown in Table 3. Further, to 100 parts of this liquid silicone rubber base compound, 2 parts of methylhydrogenpolysiloxane having a viscosity of 7 centipoise and having trimethylsiloxy groups at both ends blocked (a silicon atom-bonded hydrogen atom content of 0.75% by weight), chloroplatinic acid and tetrachloride were added. A liquid silicone rubber composition was prepared by adding a complex salt of methyltetravinylsiloxane to dimethylpolysiloxane in the liquid silicone rubber base compound in an amount such that the platinum weight was 10 ppm, and mixing them uniformly. This silicone rubber composition was treated at a temperature of 120 ° C. and a pressure of 3
A silicone rubber sheet having a thickness of 2 mm was prepared by compression molding for 30 minutes under the condition of 0 kg / cm ² . The physical properties of this silicone rubber were measured, and the results are shown in Table 4.

[0022]

[Comparative Example 5] In Example 2, instead of the surface-hydrophobicized silica filler having a bulk density of 150 g / l obtained in Reference Example 1, a bulk density of 50 g / l obtained by surface-hydrophobicizing treatment with hexamethyldisilazane. A liquid silicone rubber base compound was prepared in the same manner as in Example 2 except that the dry silica filler in Example 1 was used. The viscosity increase rate (%) of the obtained liquid silicone rubber base compound and the dispersibility of the surface-hydrophobicized silica filler in the liquid silicone rubber base compound were measured, and the results are shown in Table 3. Further, to 100 parts of this liquid silicone rubber base compound, 2 parts of methylhydrogenpolysiloxane having a viscosity of 7 centipoise and having trimethylsiloxy groups at both ends blocked (a silicon atom-bonded hydrogen atom content of 0.75% by weight), chloroplatinic acid and tetrachloride were added. A complex salt with methyltetravinylsiloxane is added to the dimethylpolysiloxane in the liquid silicone rubber base compound as platinum weight of 10 ppm.
A liquid silicone rubber composition was prepared by adding an amount such that This silicone rubber composition was compression molded for 30 minutes at a temperature of 120 ° C. and a pressure of 30 kg / cm ² to prepare a silicone rubber sheet having a thickness of 2 mm.
The physical properties of this silicone rubber were measured, and the results are shown in Table 4.

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

EFFECTS OF THE INVENTION The production method of the present invention is characterized in that it is possible to efficiently produce a liquid silicone rubber base compound having a low viscosity and a small viscosity change with time.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsuo Hamada 12-12 Yachi, Kanazu-cho, Sakai-gun, Fukui Toray Dow Corning Silicone Co., Ltd. Fukui factory

Claims (1)

[Claims] 1. A kneader has (A) a viscosity of 3 at 25 ° C.
30 to 60 parts by weight of a diorganopolysiloxane having a density of 0 to 50,000 centipoise and (B) a bulk density of 100 to 2
Surface-hydrophobized silica filler 25, which is 00 g / l
50 parts by weight are kneaded and kneaded, and then the kneaded product is mixed with (A).
A method for producing a liquid silicone rubber base compound, which comprises adding 70 to 40 parts by weight of a component diorganopolysiloxane and kneading.