JP2992088B2 - Silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition and, more particularly, to a silicone rubber composition having excellent durability against repeated deformation such as bending and elongation after curing.

[0002]

2. Description of the Related Art Silicone rubber is used for various applications because of its excellent heat resistance, cold resistance and the like. However, silicone rubber is inferior in durability against repeated deformation such as bending and elongation, and is not a sufficiently satisfactory material for applications requiring durability against repeated deformation such as keyboards and automotive constant velocity joint boots. Conventionally, in order to improve such durability, it has been good to reduce the amount of the filler to be added to the silicone rubber composition, improve the dispersion of the filler, enhance the filtration, and remove as much foreign matter as possible. However, silicone rubber compositions having sufficiently satisfactory durability have not been obtained by these methods.

[0003]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, if a small amount of a special silicone compound is added to a silicone rubber composition, the durability against repeated deformation is reduced. The inventors have found that the improvement is remarkable and arrived at the present invention.

[0004] That is, an object of the present invention is to provide a silicone rubber composition capable of forming a silicone rubber molded article having excellent durability against repeated deformation such as bending and elongation after curing.

[0005]

SUMMARY OF THE INVENTION The present invention provides
(A) General formula: R ¹ _a SiO _{(4-a) / 2} (wherein R ¹ is a monovalent hydrocarbon group, and a is a number from 1.90 to 2.05). 100 parts by weight of organopolysiloxane, (B)
5 to 100 parts by weight of reinforcing filler, (C) general formula:

Wherein R ² and R ³ are monovalent hydrocarbon groups containing no alkenyl group, R ⁴ is a monovalent hydrocarbon group,
Is a divalent hydrocarbon group, b is 0 or 1, and n is an integer of 1 to 30. The present invention relates to a silicone rubber composition comprising 0.05 to 20 parts by weight of a silanol group-containing organosilicone compound represented by the formula (1) and (D) a curing agent (a sufficient amount for curing the composition of the present invention). Hereinafter, these will be described in detail.

The organopolysiloxane of the component (A) is a main component of the composition of the present invention, wherein R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group; a vinyl group or an allyl group. Alkenyl groups such as phenyl group, tolyl group, etc .; cycloalkyl groups such as cyclohexyl group, or chloromethyl in which part or all of the carbon-bonded hydrogen atoms of these groups have been substituted with halogen atoms, cyano groups, etc. And unsubstituted or substituted monovalent hydrocarbon groups exemplified by a trifluoropropyl group, a cyanomethyl group and the like.
A is a number from 1.90 to 2.05. Examples of such organopolysiloxanes include methylvinylpolysiloxane having trimethylsiloxy groups at both ends, a methylvinylsiloxane / dimethylsiloxane copolymer having trimethylsiloxy groups at both ends, and dimethylsiloxane / methyl having dimethylvinylsiloxy groups at both ends. Phenylsiloxane copolymer, dimethylsiloxane / diphenylsiloxane copolymer with dimethylvinylsiloxy groups at both ends blocked,
Dimethylsiloxane / methylphenylsiloxane / methylvinylsiloxane copolymer with trimethylsiloxy groups at both ends, methyl (3,3,3-trifluoropropyl) polysiloxane with dimethylvinylsiloxy groups at both ends, dimethylvinylsiloxy group at both ends Blocked dimethylsiloxane methyl (3,3,3-trifluoropropyl)
Siloxane copolymer, CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 unit, (CH ₃ ) ₃
Examples thereof _include organopolysiloxanes composed of SiO _1/2 units and SiO _4/2 units. The degree of polymerization of component (A) is 100 to 3
It is preferably in the range of 0000, more preferably in the range of 1,000 to 20,000. In the present invention,
The above-mentioned various organopolysiloxanes may be used in combination.

[0007] The reinforcing filler of the component (B) is a component for improving the mechanical strength of the silicone rubber molded product obtained by curing the composition of the present invention. Examples of such reinforcing fillers include precipitated silica, fumed silica, calcined silica, fumed titanium oxide, and those fillers whose surface is coated with an organosilicon compound such as hexamethyldisilazane, trimethylchlorosilane, or polymethylsiloxane. The processed one is exemplified. The amount of this component is in the range of 5 to 100 parts by weight per 100 parts by weight of component (A).

The silanol group-containing organosilicone compound (C) is essential for imparting durability to repeated deformation such as bending and elongation to a silicone rubber molded product obtained by curing the composition of the present invention. Component. In the above formula, R ² and R ³ are R ¹ described in the description of the component (A).
And R ⁴ is a monovalent hydrocarbon group similar to R ¹ described in the description of the component (A) above. And A are divalent hydrocarbon groups exemplified by alkylene groups such as ethylene group, propylene group, butylene group and pentylene group. B is 0 or 1, and n is an integer of 1 to 30. Such a silanol group-containing organosilicone compound also acts as a plasticizer that reduces the interaction between the polymer component of the silicone rubber composition before curing and the reinforcing filler, and therefore, as the silanol group content increases, good. Component (C) is added in an amount of 0.05 to 20 parts by weight per 100 parts by weight of component (A). Such a compound can be synthesized by the following method. That is, an organosilicone compound in which tetrakis (dimethylsiloxy) silane and dimethylvinylchlorosilane or one end of a molecular chain is blocked with a silicon-bonded vinyl group and the other end is blocked with a silicon-bonded chlorine atom in the presence of a platinum-based catalyst. By the addition reaction, an adduct having (4-b) silicon-bonded chlorine atoms at the molecular chain terminals is obtained. The silicon-bonded chlorine atoms of the adduct are then obtained by careful hydrolysis with a dilute aqueous basic solution. The reaction formulas are shown below.

(Equation 1)

The component (D) is a curing agent for curing the composition of the present invention. Typical examples of the component (D) include organic peroxides. Specifically, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, 2,5-dimethyl-2 , 5-Di (t-butylperoxy) hexane, 2,5-dimethyl-2,5
-Di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) -3,3,5
-Trimethylcyclohexane, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, parachlorobenzoyl peroxide and the like. (D)
The amount of the component added is sufficient to cure the composition of the present invention, and is usually 0.1 to 100 parts by weight of the component (A).
The range is preferably from 15 to 15 parts by weight.

As the component (D), there is a curing agent obtained by using an organohydrogenpolysiloxane containing three or more silicon-bonded hydrogen atoms in one molecule together with a platinum catalyst. Here, examples of the organohydrogenpolysiloxane containing three or more silicon-bonded hydrogen atoms include a dimethylsiloxane / methylhydrogensiloxane copolymer capped at both ends with a trimethylsiloxy group, and the degree of polymerization is 3 to 700. It is desirable to be within the range. The ratio of the total number of moles of silicon-bonded hydrogen atoms in component (D) to the total number of moles of alkenyl groups in component (A) is (0.5: 1) to (20: The amount is such that 1) is obtained. In this case, a platinum-based catalyst is used in combination as the addition reaction promoting catalyst. Platinum-based catalysts include chloroplatinic acid and its solution dissolved in alcohol, ketone, ether, etc., complex compounds of chloroplatinic acid and olefins,
Examples thereof include a complex compound of chloroplatinic acid and alkenylsiloxane, platinum black and a compound in which platinum is held on a carrier.
The amount of the platinum-based catalyst to be added is preferably 0.1 to 500 parts by weight based on 1 million parts by weight of the total weight of the components (A) and (D). A known curing retarder such as an acetylene-based compound, a hydrazine-based compound, a triazole-based compound, a phosphine-based compound, or a mercaptan-based compound may be used together with such a curing agent to secure working time.

The composition of the present invention can be easily obtained by uniformly mixing the above components (A) to (D). If necessary, the known additives for silicone rubber, such as ground quartz and diatom, are used. Increasing fillers such as soil, asbestos, calcium carbonate, aluminosilicic acid and the like; heat-resistant agents such as iron oxide, cerium oxide, aluminum oxide, zinc oxide, manganese carbonate and the like, and flame retardants may be added.

[0012]

The present invention will be described below in more detail with reference to examples. In the examples, “parts” means “parts by weight”. In the examples, the measurement of the constant elongation fatigue durability was measured according to the following method. -Constant elongation fatigue durability test A 2 mm thick sheet as a test piece was punched out of a silicone rubber sheet as a dumbbell No. 3 specified in JIS K6301. This test piece was subjected to JIS K6301, 15
Set on the Deathmatcher type testing machine shown in the item 3 and set the gauge so that the marked line distance is 40 mm at the maximum and 20 mm at the minimum.
The specimen was reciprocated at a rate of ± 10 times / min, and the number of reciprocations until the test piece was broken was quantified as a constant elongation fatigue durability. In this test method, the test piece held between the gripping jigs is repeatedly stretched with an elongation of 0 to 100%.

[0013]

Reference Example 1 In a four-necked flask equipped with a stirrer, 10.89 parts of tetrakis (dimethylsiloxy) silane was prepared by the following formula:

Embedded image 50 parts of an organosilicone compound represented by the following formula, 100 parts of toluene, and a complex of chloroplatinic acid and tetramethyldivinyldisiloxane were added so that the platinum concentration was 40 ppm with respect to the total amount of the two organosilicon compounds. The reaction was carried out for 2 hours under reflux. Infrared spectroscopic analysis of the sampled reaction mixture confirmed that the characteristic absorption of silicon-bonded hydrogen atoms had disappeared. Then excess formula under reduced pressure:

After distilling off the low-boiling substances and the compound having the formula:

Embedded image An organosilicone compound represented by the formula was obtained. 250 parts of water, 250 parts of ice, 125 parts of diethyl ether and 15 parts of sodium hydrogencarbonate are put into a four-necked flask equipped with a stirrer, and the mixture of 53.9 parts of the adduct and 50 parts of diethyl ether is cooled and stirred. The mixture was added dropwise. After hydrolysis, liquid separation was performed, and anhydrous sodium sulfate was added to the ether layer, followed by drying. After drying, the ether was distilled off under reduced pressure at room temperature to give the formula:

Embedded image A silanol group-containing organosilicone compound represented by the formula (Silicone A) was obtained. It was confirmed by the following method that silicone A had the above structure. That is, after silanol groups of the silicone A were silylated with tetramethyldisilazane, excess tetramethyldisilazane was distilled off by heating under reduced pressure. The residue was determined to have a silicon-bonded hydrogen atom content of 0.214 weight percent and a calculated value of 0.215.
It was in good agreement with the weight percentage. The reaction formula is as follows.

(Equation 2)

[0014]

[Reference Example 2] In a four-necked flask equipped with a stirrer, 50.0 parts of tetrakis (dimethylsiloxy) silane was prepared.

Embedded image 81 parts of chlorosilane represented by the formula, 100 parts of toluene,
A complex of chloroplatinic acid and tetramethyldivinyldisiloxane was added so that the platinum concentration was 20 ppm with respect to the total amount of the two organosilicone compounds, and the mixture was reacted under heating and refluxing for 2 hours. By infrared spectroscopic analysis of the sampled reaction mixture, it was confirmed that the characteristic absorption of silicon-bonded hydrogen atoms had disappeared, and excess dimethylvinylchlorosilane and low-boiling substances were distilled off under reduced pressure.
formula:

Embedded image An organosilicone compound represented by the formula was obtained. 300 parts of water, 300 parts of ice, 300 parts of diethyl ether and 35 parts of sodium hydrogencarbonate are put into a four-necked flask equipped with a stirrer, and a mixture of 65 parts of the adduct and 50 parts of diethyl ether is added thereto while cooling and stirring. It was dropped. After hydrolysis, liquid separation was performed, and anhydrous sodium sulfate was added to the ether layer, followed by drying. After drying, the ether is distilled off at room temperature under reduced pressure to give the formula:

Embedded image 55 parts of an organosilicone compound (Silicone B) represented by the following formula: It was confirmed in the same manner as in Reference Example 1 that silicone B had the above structure. That is, after silanol groups of silicone B were silylated with tetramethyldisilazane, excess tetramethyldisilazane was distilled off by heating under reduced pressure. The residue had a silicon-bonded hydrogen atom content determination of 0.40 weight percent, which was in good agreement with the calculated value of 0.41 weight percent. The reaction formula is as follows.

(Equation 3)

[0015]

Example 1 100 parts of an organopolysiloxane having an average degree of polymerization of 7000 consisting of 99.92 mole percent of dimethylsiloxy units and 0.18 mole percent of methylvinylsiloxy units, 25 parts of dry-processed silica having a specific surface area of 300 square meters / gram, Silicone A obtained in Example 1
Was added as shown in Table 1, kneaded with a kneader mixer, and heat-treated at 170 ° C. for 1 hour to obtain a silicone rubber base. 2,5 parts of this silicone rubber base
-Dimethyl-2,5-di (t-butylperoxy) hexane (0.7 parts) was added and uniformly mixed to obtain a silicone rubber composition. Then, the composition was press-molded under the conditions of a temperature of 170 ° C., a pressure of 20 kg / cm ² and a heating time of 10 minutes to obtain a molded silicone rubber sheet having a thickness of 2 mm. The sheet was placed in a thermal circulating oven set at 200 ° C. and left for 4 hours. Dumbbells for evaluation tests were prepared from the sheets thus obtained, and 100% constant elongation fatigue properties were measured using a Desmatcher fatigue tester. The results shown in Table 1 were obtained. For comparison, the viscosity at 25 ° C. was 4
A silicone rubber composition (composition of Comparative Example 1) was obtained in the same manner as above except that dimethylpolysiloxane (silicone C) having both ends silanol groups of 0 centistokes was used. This composition was tested for physical properties and constant elongation fatigue durability of the silicone rubber sheet in the same manner as described above. These measurement results are also shown in Table 1 as Comparative Example 1. From these results, in the composition of the present invention, the cured silicone rubber sheet withstands elongation of 2,000,000 times or more, and showed a constant elongation fatigue durability superior to the silicone rubber composition of Comparative Example 1.

[Table 1] 1) Organopolysiloxane 100 having an average degree of polymerization of 7000
Parts by weight per part

[0016]

Example 2 100 parts of an organopolysiloxane having an average degree of polymerization of 7000, consisting of 99.92 mole percent of dimethylsiloxy units and 0.18 mole percent of methylvinylsiloxy units, 40 parts of wet-process silica having a specific surface area of 200 square meters / gram, Silicone B obtained in Example 2
Was mixed as shown in Table 2, kneaded with a kneader mixer, and heat-treated at 170 ° C. for 1.5 hours to obtain a silicone rubber base. To 100 parts of this silicone rubber base,
2,5-dimethyl-2,5-di (t-butylperoxy)
Hexane (0.6 part) was added and mixed uniformly to obtain a silicone rubber composition. The composition is then heated at 170 ° C.
Press molding was performed under the conditions of a pressure of 20 kg / cm ² and a heating time of 10 minutes to obtain a 2 mm-thick silicone rubber molded sheet. This sheet was placed in a thermal circulating oven set at 200 ° C. and left for 4 hours. A dumbbell for evaluation test was prepared from the silicone rubber sheet thus obtained, and the constant elongation fatigue durability was examined in the same manner as in Example 1.
The results in Table 2 were obtained. For comparison, a silicone rubber composition was produced in the same manner as in Example 1 except that silicone C used in Comparative Example 1 was added instead of silicone B in the above. A silicone rubber composition was produced in the same manner as above except that neither silicone B nor silicone C was added. These silicone rubber compositions were evaluated in the same manner as described above. These results are shown in Table 2. From these results, in the composition of the present invention, the cured silicone rubber endured 1.5 million or more elongations, and showed a constant elongation fatigue durability superior to the composition of Comparative Example 2.

[Table 2] 1) Organopolysiloxane 100 having an average degree of polymerization of 7000
Parts by weight per part

[0017]

Example 3 100 parts of an organopolysiloxane having an average degree of polymerization of 7000, consisting of 99.92 mole percent of dimethylsiloxy units and 0.18 mole percent of methylvinylsiloxy units, 25 parts of dry-processed silica having a specific surface area of 300 square meters / gram, Silicone A obtained in Example 1
Was mixed as shown in Table 3, kneaded with a kneader mixer, and heat-treated at 170 ° C. for 1 hour to obtain a silicone rubber base. 25 parts of this silicone rubber base
Formula with a viscosity of 5 centistokes:

Embedded image The silicon-bonded hydrogen atom content represented by
0.5 parts by weight of dimethylsiloxane / methylhydrogensiloxane copolymer, 0.06 parts of monomethyltris (monomethylbutynoxy) silane, and a complex of chloroplatinic acid and tetramethylvinyldisiloxane as platinum, based on the total weight. The silicone rubber composition was obtained by adding an amount of 15 ppm to the mixture and uniformly mixing the mixture with two rolls. This composition was heated at a temperature of 150 ° C. and a pressure of 20 kg /
Press molding under the condition of cm ² and heating time of 5 minutes, thickness 2
A millimeter molded silicone rubber sheet was obtained. A dumbbell for evaluation test was prepared from the silicone rubber sheet thus obtained, and the physical properties and the constant elongation fatigue durability were measured in the same manner as in Example 1. Table 3 shows the results of these measurements. For comparison, a silicone rubber composition was produced in the same manner as in Example 1 except that silicone C used in Comparative Example 1 was added instead of silicone A in the above. Further, a silicone rubber composition was produced in the same manner as described above except that silicone A and silicone C were not added. The properties of these silicone rubber compositions were measured in the same manner as described above. The results are shown in Table 3. From these results, in the composition of the present invention, the cured silicone rubber withstands elongation of 2.5 million times or more, and exhibited a constant elongation fatigue durability superior to the silicone rubber composition of Comparative Example 3.

[Table 3] 1) Organopolysiloxane 100 having an average degree of polymerization of 7000
Parts by weight per part

[0018]

The silicone rubber composition of the present invention comprises (A)
It is composed of the components (D) to (D), and particularly contains a special silanol group-containing organosilicone compound of the component (C), so that it exhibits excellent durability against repeated deformation such as bending and elongation after heat curing. It has the characteristic that it can be a silicone rubber molded product.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C08L 83/04 C08K 3/00 C08K 5/14 C08K 5/54 C08L 83/14

Claims (1)

(57) [Claims] (A) General formula: R ¹ _a SiO _{(4-a) / 2} (wherein R ¹ is a monovalent hydrocarbon group, and a is 1.90 to 2.0)
Number 5 ), 100 parts by weight of an organopolysiloxane represented by the formula (B), 5 to 100 parts by weight of a reinforcing filler,
(C) General formula: (Wherein, R ² and R ³ are monovalent hydrocarbon groups not containing an alkenyl group, R ⁴ is a monovalent hydrocarbon group, A is a divalent hydrocarbon group, and b is 0 or 1. Yes, n is 1 to 30
Is an integer. A silicone rubber composition comprising 0.05 to 20 parts by weight of a silanol group-containing organosilicone compound represented by the formula (1) and (D) a curing agent (a sufficient amount to cure the composition of the present invention).