JPH11148016A - Heat-curable silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat-curable silicon rubber composition having rapid curing rate and capable of providing a silicone rubber free from discoloration and having small compression set. SOLUTION: This rubber composition comprises (A) 100 pts.wt. alkenyl group- containing organopolysiloxane raw rubber, (B) 10-100 pts.wt. reinforcing filler, (C) 0.01-10 pts.wt. organic pigment and (D) 0.05-5 pts.wt. t- butylperoxyisopropylmonocarbonate or t-butylperoxyacetate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-curable silicone rubber composition, and more particularly, to a heat-curable silicone rubber composition having a high curing rate and not causing discoloration.

[0002]

2. Description of the Related Art Silicone rubber is excellent in heat resistance, weather resistance and electrical insulation, and is therefore widely used in fields requiring such characteristics. Among these uses, a silicone rubber colored by adding a pigment is used for a key of a calculator or a lamp cap. In general, an organic peroxide is used for curing silicone rubber. The organic peroxide used in silicone rubber is
Each has a different decomposition temperature and each imparts a different cure rate to the silicone rubber. In general, it is desirable that the curing speed is high. However, in view of various physical properties, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is most widely used although the curing speed is low.
On the other hand, as a technique for increasing the curing speed while using 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, a method of blending an organohydrogenpolysiloxane with a silicone rubber composition has been proposed. (See JP-A-9-95612). This method has recently been widely used as a method that does not significantly affect various physical properties while increasing the curing speed. However, this method
When applied to a silicone rubber colored with an organic pigment, there has been a problem that the organohydrogenpolysiloxane added for the purpose of increasing the curing speed reacts with the organic pigment, causing discoloration of the silicone rubber. Accordingly, there has been a demand for a silicone rubber composition which can be a silicone rubber having a high curing speed, no discoloration, and excellent physical properties such as a small compression set and the like.

[0003]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that a specific organic peroxide is used as a curing agent for a heat-curable organopolysiloxane composition containing an organic pigment. Thus, the present inventors have found that the curing rate of the silicone rubber composition can be increased without adding and blending an organohydrogenpolysiloxane, and reached the present invention. That is, an object of the present invention is to provide a silicone rubber composition which can be a silicone rubber having a high curing rate, no discoloration, and a small compression set.

[0004]

The present invention provides (A) 100 parts by weight of an alkenyl group-containing organopolysiloxane raw rubber, (B) 10 to 100 parts by weight of a reinforcing filler, (C) 0.01 to 10 parts by weight of an organic pigment, and (D) A heat-curable silicone rubber composition comprising 0.05 to 5 parts by weight of t-butylperoxyisopropyl monocarbonate or t-butylperoxy ciacetate.

[0005]

The alkenyl group-containing organopolysiloxane raw rubber (A) used in the composition of the present invention has an average composition formula of R ¹ _a SiO _{(4-a) / 2.}
An organopolysiloxane represented by the formula: wherein R ¹
Is a substituted or unsubstituted monovalent hydrocarbon group, for example,
Alkyl groups such as methyl group, ethyl group and propyl group; alkenyl groups such as vinyl group, allyl group, butynyl group and hexenyl group; aryl groups such as phenyl group;
Trifluoropropyl group, 2-phenylethyl group, 2-
And a cyanoethyl group. In the formula, a is 1.95 to 2.
05 is the number. The molecular structure of this component is a straight chain or a straight chain partially having a branch. The polymerization degree of this component is usually in the range of 1,000 to 20,000. This component may be a homopolymer or a copolymer, or may be a mixture of these polymers. Specific examples of the unit constituting this component include a dimethylsiloxane unit, a methylvinylsiloxane unit, a methyl (3,3,3-trifluoropropyl) siloxane unit, and a methylphenylsiloxane unit. Examples of the molecular terminal group of the component include a trimethylsiloxy group, a silanol group, a dimethylvinylsiloxy group, and a methylvinylhydroxysiloxy group.
Such organopolysiloxane raw rubber includes dimethylvinylsiloxy-terminated dimethylsiloxane / methylvinylsiloxane copolymer raw rubber, dimethylvinylsiloxy-terminated dimethylpolysiloxane raw rubber, and silanol-terminated dimethylsiloxane / methylvinyl at both ends. Examples include siloxane copolymer raw rubber and dimethylsiloxane / methylvinylsiloxane copolymer raw rubber having both ends methylvinylhydroxysiloxy groups blocked.

The reinforcing filler (B) is a component essential for imparting excellent mechanical strength to the silicone rubber molded product obtained by curing the composition of the present invention. Examples of such reinforcing fillers include dry-process silica such as fumed silica and wet-process silica such as precipitated silica, and furthermore, the surface thereof has an organochlorosilane, hexaorganodidisilazane, or silanol group-containing organosiloxane. Fine powdered silica that has been hydrophobized with an organosilicon compound such as an oligomer or diorganocyclopolysiloxane can also be used. This component has a particle size of 50 μm or less, and a specific surface area of preferably 50 m ² / g or more, and more preferably 100 m ² / g or more. Conventionally known reinforcing fillers such as organopolysiloxane resin powder and carbon black can also be used. The amount of this component is 1 to 100 parts by weight of component (A).
It is in the range of 0 to 100 parts by weight. This is because if the amount is less than 10 parts by weight, the mechanical strength of the composition of the present invention after curing is insufficient, and if it exceeds 100 parts by weight, it becomes difficult to mix the component (A).

The organic pigment of the component (C) is added for the purpose of coloring the present composition. Examples of such organic pigments include dye pigments, azo pigments, phthalocyanine pigments, condensed polycyclic pigments, nitro pigments, nitroso pigments, and fluorescent pigments.Further, as dye pigments, basic dyes, Acid dyes, vat dyes, and mordant dyes are exemplified, and azo pigments include soluble azo, insoluble azo, condensed azo, azo complex salts, and benzimidazolone azo. The amount of this component is within a range that does not affect the properties of the silicone rubber.
It is within the range of parts by weight. In addition, this organic pigment may be directly blended into the silicone rubber composition, but is previously mixed with low-viscosity dimethylpolysiloxane to form a paste,
It is recommended to add this to the silicone rubber composition and mix it.

[0008] The component (D) t-butylperoxyisopropyl monocarbonate or t-butylperoxyacetate is a curing agent and is a component that characterizes the composition of the present invention. By using such a curing agent, the curing rate of the composition of the present invention is increased, and after curing, a silicone rubber having a small compression set can be obtained. The amount of the component (D) is 0.05 to 5 parts by weight, preferably 0.1 to 2 parts by weight, per 100 parts by weight of the component (A). This is because if it is less than 0.05 part by weight, sufficient curing as a rubber cannot be obtained, and if it exceeds 5 parts by weight, physical properties of the cured silicone rubber are adversely affected.

The composition of the present invention comprises the above-mentioned component (A)
(D) component, but in addition to these components,
Various additives known to be incorporated into the silicone rubber composition, for example, a surface treatment agent for silica filler, a non-reinforcing filler, an inorganic pigment, a heat-resistant agent, a flame retardant, an internal mold release agent,
Incorporation of a plasticizer or the like may be used as long as the object of the present invention is not impaired. Here, as the non-reinforcing filler,
Examples thereof include calcium carbonate, mica, magnesium oxide, aluminum oxide, and magnesium hydroxide. Examples of the inorganic pigment include iron oxide and titanium dioxide. Rare earth oxides, rare earth hydroxides,
Cerium silanolate and cerium fatty acid salt are exemplified. Examples of the flame retardant include a platinum compound, fumed titanium dioxide, manganese carbonate, and zinc carbonate. Examples of the internal release agent include higher fatty acid salts such as calcium stearate.

The composition of the present invention comprises the components (A) to (D) described above.
The components are easily produced by uniformly mixing the respective predetermined amounts of the components. As a means for mixing the components (A) to (D), a kneader mixer known as a method for producing a silicone rubber composition is used. A twin-screw continuous kneading extruder, a mixing machine such as a two-roll mill or a kneading machine can be used.

In order to cure the composition of the present invention, the composition of the present invention is used at a temperature not lower than the decomposition temperature of the organic peroxide (D) and not causing scorch, that is,
Under a temperature condition of 130 to 200 ° C., preferably 140 to 200 ° C.
What is necessary is just to heat under 170 degreeC temperature conditions. As a method for molding the composition of the present invention, a conventionally known molding method for molding a thermosetting silicone rubber, such as compression molding or injection molding, can be applied.

The heat-curable silicone rubber composition of the invention as described above is characterized by having a high curing speed, and is a silicone rubber having no discoloration and a small compression set. It is useful for various applications.

[0013]

Next, the present invention will be described with reference to examples. In the examples, “parts” means “parts by weight”. The physical properties, curing speed and color of the silicone rubber were measured as described below. ○ Physical properties: Measured according to JIS K6301. The silicone rubber composition was compression-molded at 170 ° C. for 10 minutes to produce a silicone rubber sheet having a thickness of 2 mm. The hardness, tensile strength, and elongation of this sheet were measured. The silicone rubber composition was filled in a compression set mold, compression-molded at 170 ° C. for 10 minutes, and cured in a heating oven at 200 ° C. for 4 hours. A cylindrical test piece having a thickness of 29 mm and a thickness of 12.7 mm was prepared, and the compression set of these test pieces was measured. -Curing speed: Measured according to JIS K6300. As the curast meter, JSR Curast Meter III type [manufactured by Orientec Co., Ltd.] was used, and the time at which the torque value reached 90% of the maximum torque value at a temperature of 170 ° C. was defined as T ₉₀ . ○ Hue Observed with the naked eye.

[0014]

Example 1 99.85 mol% of dimethylsiloxane units
Dimethylsiloxane-methylvinylsiloxane copolymer raw rubber having both ends dimethylvinylsiloxy group-capped and 0.15 mol% of methylvinylsiloxane units (degree of polymerization: 5,
000) 100 parts, 45 parts of fumed silica having a specific surface area of 200 m ² / g, and 6 parts of a dimethylsiloxane oligomer having silanol groups at both ends and having a viscosity of 40 centistokes are charged into a kneader mixer and kneaded under heating to obtain a silicone rubber base. A compound was prepared. A silicone rubber base compound was prepared by mixing 100 parts of this base compound with 1 part of a red organic pigment (soluble monoazo pigment, manufactured by Sanyo Pigment Co., Ltd., Pigment Scarlet BL). This red organic pigment has a viscosity of 100
100 parts of red organic pigment was mixed with 100 parts of centistokes dimethylpolysiloxane, and mixed in a paste state. Further, 0.4 parts of t-butylperoxyisopropyl monocarbonate was added to 100 parts of the silicone rubber base compound, and the mixture was uniformly mixed on a two-roll mill to prepare a silicone rubber composition. The curing properties, physical properties, and changes in color of this silicone rubber composition were measured, and the evaluation results are shown in Table 1.

[0015]

Comparative Example 1 In Example 1, instead of 0.4 part of t-butylperoxyisopropyl monocarbonate, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane
A silicone rubber composition was prepared in the same manner as in Example 1 except that 4 parts were compounded. Then, the characteristics of this composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0016]

Comparative Example 2 Example 1 was repeated except that 0.4 part of dicumyl peroxide was blended in place of 0.4 part of t-butylperoxyisopropyl monocarbonate.
A silicone rubber composition was prepared in the same manner as described above. The properties of this composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0017]

Comparative Example 3 In Example 1, instead of 0.4 part of t-butylperoxyisopropyl monocarbonate, 2,5-
A silicone rubber composition was prepared in the same manner as in Example 1 except that 0.4 part of dimethyl-2,5-di (t-butylperoxy) hexane was blended. Next, 1.0 part of organohydrogenpolysiloxane was added to the composition on a two-roll mill and kneaded. The properties of this composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0018]

Example 2 99.85 mol% of dimethylsiloxane units
And dimethylvinylsiloxy-group-blocked dimethylsiloxane-methylvinylsiloxane copolymer raw rubber comprising 0.15 mol% of methylvinylsiloxane units (degree of polymerization 5,000)
0) 100 parts, 45 parts of fumed silica having a specific surface area of 200 m ² / g, and 6 parts of a dimethylsiloxane oligomer having a silanol group at both ends and having a viscosity of 40 centistokes, were mixed in a kneader mixer and kneaded under heating to obtain a silicone rubber base. A compound was prepared. 100 parts of the base compound is coated with a red organic pigment (soluble monoazo pigment, manufactured by Sanyo Dyeing Co., Ltd., Pigment Scarlet B, trade name).
L) 1 part was mixed to prepare a silicone rubber-based compound. The red pigment was previously mixed with 100 parts of dimethylpolysiloxane having a viscosity of 100 centistokes and 100 parts of a red organic pigment, and mixed in a paste state. Furthermore, this silicone rubber base compound 1
To 100 parts, 0.4 part of t-butylperoxyacetate was added and uniformly mixed on a two-roll mill to prepare a silicone rubber composition. Curing properties of this silicone rubber composition,
Changes in physical properties and color tone were measured, and the evaluation results are shown in Table 1.

[0019]

Example 3 99.85 mol% of dimethylsiloxane units
And dimethylvinylsiloxy-group-blocked dimethylsiloxane-methylvinylsiloxane copolymer raw rubber comprising 0.15 mol% of methylvinylsiloxane units (degree of polymerization 5,000)
0) 100 parts, 45 parts of fumed silica having a specific surface area of 200 m ² / g, and 6 parts of a dimethylsiloxane oligomer having silanol groups at both ends were charged into a kneader mixer and kneaded under heating to prepare a silicone rubber-based compound. 100 parts of this base compound contains a yellow organic pigment
(Soluble diazo pigment, Pigment Yellow, trade name, manufactured by Sanyo Dyeing Co., Ltd.) was mixed with 1 part to prepare a silicone rubber-based compound. This red pigment has a viscosity of 1
00 centistoke dimethylpolysiloxane 100
Was mixed with 100 parts of a yellow organic pigment in a paste state. Further, 0.4 parts of t-butylperoxyisopropyl monocarbonate was added to 100 parts of the silicone rubber base compound, and the mixture was uniformly mixed on a two-roll mill to prepare a silicone rubber composition. The curing properties, physical properties, and changes in color of this silicone rubber composition were measured, and the evaluation results are shown in Table 2.

[0020]

Comparative Example 4 In Example 3, instead of 0.4 part of t-butylperoxyisopropyl monocarbonate, 2,5-
A silicone rubber composition was prepared in the same manner as in Example 3, except that 0.4 part of dimethyl-2,5-di (t-butylperoxy) hexane was blended. The properties of this composition were measured in the same manner as in Example 3. The results are shown in Table 2.

[0021]

Comparative Example 5 Example 3 was repeated except that 0.4 part of dicumyl peroxide was used instead of 0.4 part of t-butylperoxyisopropyl monocarbonate.
A silicone rubber composition was prepared in the same manner as described above. The properties of this composition were measured in the same manner as in Example 3. The results are shown in Table 2.

[0023]

Comparative Example 6 In Example 3, instead of 0.4 part of t-butylperoxyisopropyl monocarbonate, 2,5-
A silicone rubber composition was prepared in the same manner as in Example 3, except that 0.4 part of dimethyl-2,5-di (t-butylperoxy) hexane was blended. Then, 1 part of the organohydrogenpolysiloxane was mixed with 2 rolls of this composition. The properties of this composition were measured in the same manner as in Example 3. The results are shown in Table 2.

[0024]

Example 4 99.85 mol% of dimethylsiloxane units
And dimethylvinylsiloxy-group-blocked dimethylsiloxane-methylvinylsiloxane copolymer raw rubber comprising 0.15 mol% of methylvinylsiloxane units (degree of polymerization 5,000)
0) 100 parts, 45 parts of fumed silica having a specific surface area of 200 m ² / g, and 6 parts of a dimethylsiloxane oligomer having a silanol group at both ends and having a viscosity of 40 centistokes, were mixed in a kneader mixer and kneaded under heating to obtain a silicone rubber base. A compound was prepared. A silicone rubber base compound was prepared by mixing 100 parts of this base compound with 1 part of a yellow organic pigment (soluble diazo pigment, Pigment Yellow, trade name, manufactured by Sanyo Dyeing Co., Ltd.).
This yellow organic pigment was previously added to 100 parts of dimethylpolysiloxane having a viscosity of 100 centistokes by adding the yellow organic pigment 1
00 parts were mixed and mixed in a paste state. Further, 0.4 part of t-butylperoxy acetate was added to 100 parts of the silicone rubber base compound,
A silicone rubber composition was prepared by uniform mixing on two rolls. Changes in the curing properties, physical properties, and hue of the silicone rubber composition were measured, and the results of the evaluation are shown in Table 2.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

The silicone rubber composition of the present invention comprises (A)
Component-(D) component, especially, because it contains a special organic peroxide of the component (D) as a curing agent, curing fast,
In addition, it has no discoloration and can be a silicone rubber having a small compression set.

Claims (1)

[Claims] (A) 100 parts by weight of an alkenyl group-containing organopolysiloxane raw rubber, (B) 10 to 100 parts by weight of a reinforcing filler, (C) 0.01 to 10 parts by weight of an organic pigment, and (D) t- A heat-curable silicone rubber composition comprising 0.05 to 5 parts by weight of butylperoxyisopropyl monocarbonate or t-butylperoxy siacetate.