JPH09169910A - Radiation-curable silicone rubber composition and radiation-cured silicone rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of giving, through its radiation curing, a silicone rubber excellent in mechanical properties and surface characteristics with no need of any secondary treatment for removing by- products and/or low-molecular weight siloxanes in the resultant cured product, with no particular limitation of the silicone rubber's applicability. SOLUTION: This radiation-curable silicone rubber composition comprises an organopolysiloxane >=100 in average degree of polymerization expressed by the average composition formula: R<1> a R<2> b SiO(4-a-b)/2 [R<1> is a (substituted) monovalent hydrocarbon group; R<2> is a radiation-cross-linkable functional group; (a) and (b) are each positive number satisfying the relationship: (a+b)=1.98-2.02] and reinforcing silica powder >=50m<2> /g in specific surface area. The other objective silicon rubber is obtained by radiation-curing this composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel radiation-curable silicone rubber composition having good vulcanization characteristics and production efficiency, and a silicone rubber excellent in surface characteristics obtained by curing the composition with radiation.

[0002]

2. Description of the Related Art Silicone rubber has excellent weather resistance, electrical characteristics, low compression set, heat resistance, and cold resistance. Therefore, in recent years, it has been used in a variety of electronic devices, automobiles, construction, medical care, foods, etc. Widely used in the field. Specific applications include, for example, packing for various home electric appliances such as electric rice cookers, refrigerators, electric kettles, packing used for food storage cases, various medical tubes such as catheters, and electric wire tubes. Conventionally, as one of methods for obtaining such a silicone rubber, a method of heating and vulcanizing a millable silicone composition is known. The millable silicone composition includes an organic peroxide crosslinkable type and an addition reaction crosslinkable type. The organic peroxide cross-linking type is one in which a silicone composition containing an organic peroxide is heated to generate radicals by the organic peroxide to cross-link the silicone raw rubber. And the addition reaction cross-linking type is, for example, in a composition containing a vinyl group-containing organopolysiloxane raw rubber, a hydrogensilyl group-containing organosiloxane and a platinum-based catalyst,
It is crosslinked by a hydrosilylation reaction. However, the organic peroxide cross-linking composition requires a secondary treatment of heating at a high temperature of about 200 ° C. for a long time in order to remove decomposition by-products from the silicone rubber obtained by curing the composition. Therefore, such a composition has a problem that the production efficiency of the obtained rubber product is poor. Further, the addition-reaction cross-linking composition has a drawback in that, even when an extremely small amount of the amine or sulfide is present during the addition reaction, these become catalyst poisons and inhibit vulcanization. Therefore, the addition reaction cross-linking type has a problem that its application range is limited only when there is no vulcanization inhibiting substance such as amine or sulfide that can be a catalyst poison. In addition, since the addition reaction cross-linking type contains a low molecular weight siloxane in the obtained silicone rubber, it is necessary to carry out a secondary treatment to remove them so that they do not bleed to the surface of the silicone rubber.

Further, the conventional silicone rubber has a higher frictional resistance than other synthetic rubbers, and cannot be said to have excellent surface characteristics (sliding property). Therefore, development of a silicone rubber having a low surface friction resistance is desired.

[0004]

The object of the present invention is that by-products are not formed during curing and the amount of low-molecular-weight siloxane in the silicone rubber is extremely small. Therefore, it is necessary to carry out a secondary treatment to remove them. Radiation-curable silicone rubber capable of obtaining a silicone rubber excellent in mechanical strength and surface characteristics, since the application range is not particularly limited because amine and sulfide do not become a catalyst poison. It is to provide a composition and a silicone rubber cured by irradiation.

[0005]

The present invention provides (A) the following average composition formula (1): R ¹ _a R ² _b SiO _{(4-ab) / 2} (1) (wherein R ¹ is independently It is an unsubstituted or substituted monovalent hydrocarbon group, R ² is a radiation-crosslinkable functional group, and a and b are positive numbers satisfying a + b = 1.98 to 2.02). A radiation-curable silicone rubber composition containing the organopolysiloxane of (1) and (B) a reinforcing silica powder having a specific surface area of 50 m ² / g or more.

The present invention also provides a silicone obtained by irradiating the radiation-curable silicone rubber composition with at least one radiation selected from electron beam, γ-ray and ultraviolet ray to cure the composition. Provide rubber.

Hereinafter, the present invention will be described in detail.

[0008]

DETAILED DESCRIPTION OF THE INVENTION Radiation-curable silicone rubber composition (A) used in the component present invention component (A) organopolysiloxane are those represented by the above-described average compositional formula (1). In the formula (1), examples of the unsubstituted or substituted monovalent hydrocarbon group represented by R ¹ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-
Butyl group, pentyl group, neopentyl group, hexyl group,
Alkyl group such as heptyl group, octyl group, nonyl group, decyl group, dodecyl group; cycloalkyl group such as cyclopentyl group, cyclohexyl group, cycloheptyl group; vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, Alkenyl groups such as isobutenyl group, hexenyl group and cyclohexenyl group; aryl groups such as phenyl group, tolyl group, xylyl group, naphthyl group and biphenylyl group;
Benzyl group, phenylethyl group, phenylpropyl group,
Aralkyl group such as methylbenzyl group; alkaryl group;
And some or all of the hydrogen atoms bonded to the carbon atoms of these groups are halogen atoms such as fluorine, chlorine and bromine,
Groups substituted with a cyano group, for example, chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, 3,
3,3-trifluoropropyl group, chlorophenyl group,
Fluorophenyl group, cyanoethyl group, 3,3,4
4,5,5,6,6,6-nonafluorohexyl group and the like, preferably having 1 to 10 carbon atoms, more preferably having 1 to 8 carbon atoms, Particularly preferably, a methyl group, a vinyl group, a phenyl group,
It is a trifluoropropyl group, most preferably a methyl group.

Examples of the radiation-crosslinkable functional group represented by R ² in the formula (1) include acryloylalkyl groups such as acryloylmethyl group, β-acryloylethyl group and γ-acryloylpropyl group; methacryloylmethyl group and β
-Methacryloylalkyl groups such as methacryloylethyl group and γ-methacryloylpropyl group; and mercaptoalkyl groups such as mercaptomethyl group, β-mercaptoethyl group and γ-mercaptopropyl group.

The ratio of the radiation-crosslinkable functional group (R ² ) to all the substituents (R ¹ and R ² ) is preferably about 0.005 to 15 mol%, more preferably 0.05 to 5 mol%. It is preferably 0.25 to 2.5 mol%. If this ratio is too low, the composition of the present invention may not be able to sufficiently absorb energy from radiation. On the contrary, if the amount is too large, it may not be possible to obtain the organopolysiloxane of component (A) having a sufficiently high degree of polymerization.

In the equation (1), a and b are a + b = 1.98 to 2.
It is a positive number that satisfies 02.

The organopolysiloxane represented by the formula (1) has an average degree of polymerization of 100 or more, preferably 3000 or more, and more preferably 4,000 to 4,000.
20,000 organopolysiloxane gums. Also,
The viscosity at 25 ° C is preferably 100 cSt or more, more preferably 100,000 to 100,000,000 cSt.
The component (A) is not particularly limited as long as it is represented by the above formula (1), and may be any of linear, cyclic, or three-dimensional network-like organopolysiloxanes. It may be a mixture of the above. In particular, a typical component (A) is a linear one in which both ends of the molecular chain are terminated with a triorganosilyl group, preferably a trimethylsilyl group. A linear organopolysiloxane in which both ends of the molecular chain are terminated with a triorganosilyl group is
For example, it can be obtained as follows. That is,
(A) General formula (2) below:

[0013]

Embedded image (In the formula, R ³ is independently an unsubstituted or substituted monovalent hydrocarbon group, and n is an integer of 1 to 3000.) At least one selected from organosilanes and organosiloxanes having a silanol group. Seed, (b) the following general formula (3):

[0014]

Embedded image (In the formula, R ⁴ is an unsubstituted or substituted monovalent hydrocarbon group, R ⁵ is a radiation-crosslinkable functional group, and m is 1 to 300.
At least one selected from an organosilane and an organosiloxane having a silanol group represented by the following general formula (4):

[0015]

Embedded image (Wherein R ⁶ and R ⁷ are independently an unsubstituted or substituted monovalent hydrocarbon group) are premixed with each other, and the mixture is allowed to exist in the presence of an acidic compound having _a pK _{a of} 3 or less. By heating below, these components can be polymerized to obtain the above-mentioned radiation-crosslinkable functional group-containing organopolysiloxane gum.

Component (a) An unsubstituted or substituted 1 represented by R ³ in the general formula (2)
Examples of the valent hydrocarbon group are the same as those of R ¹ . N in the general formula (2) is an integer of 1 to 3000,
From the viewpoint of economy, an integer of 10 to 1000 is preferable.

In the component (a), n in the general formula (2) is 1
Or an organosiloxane having n of 2 to 3000, or a mixture of two or more thereof.

The organosiloxane as the component (a) can be obtained, for example, by ring-opening polymerization of a cyclic organosiloxane. The organosiloxane usually has the following general formula (5):

[0019]

Embedded image (In the formula, R ³ is the same as above, and L is an integer of 3 to 25) and contains a low molecular weight cyclic organosiloxane (hereinafter, referred to as low molecular weight cyclic organosiloxane) as an impurity.

As the component (a), it is preferable that the content of the low molecular weight cyclic organosiloxane is 5000 ppm or less, particularly 2000 ppm or less. Thus, the content of low molecular weight cyclic organosiloxane was reduced (a).
By using the component, the content of the low molecular weight cyclic organosiloxane contained as an impurity in the organopolysiloxane of the component (A) used in the composition of the present invention can be reduced to 6000 ppm or less. Examples of the method for removing the low molecular weight cyclic organosiloxane in the component (a) include a stripping method and the like. Further, when the low molecular weight cyclic organosiloxane in the component (a) is sufficiently removed, specifically, when the content of the low molecular weight cyclic organosiloxane is 1000 ppm or less, the low molecular weight cyclic organosiloxane in the component (A) is reduced. The molecular weight cyclic organosiloxane content can be 2000 ppm or less.
Further, as the component (a), the following general formula:

[0021]

Embedded image By using a ring-opening polymerized cyclic trisiloxane represented by the formula (wherein R ³ is the same as above), the content of the low molecular weight cyclic organosiloxane can be further reduced.

Component (b) Component (b) is an organosilane or organosiloxane having a silanol group represented by the general formula (3). An unsubstituted or substituted 1 represented by R ⁴ in the general formula (3)
Examples of the valent hydrocarbon group are the same as those of R ¹ .

As the radiation-crosslinkable functional group represented by R ⁵ in the general formula (3), the same as the above R ² can be mentioned.

M in the general formula (3) is an integer of 1 to 300, preferably 1 to 100, and more preferably 1 to 10.

The component (b) may be an organosilane in which m is 1 in the general formula (3), an organosiloxane in which m is 2 to 300, or a mixture of two or more thereof.

The amount of the component (b) used is 100 parts of the component (a).
It is usually 0.01 to 50 parts by weight, preferably 0.1 to 30 parts by weight per part by weight, but it is preferable that the ratio of the radiation-crosslinkable functional group falls within the above range.

Component (c) The component (c) is a monoacyloxysilane represented by the general formula (4). The component (c) terminates the end of the organopolysiloxane of the component (A) with a triorganosilyl group. In addition to introducing an organic group at both ends of the molecular chain of the organopolysiloxane, the organopolysiloxane. It controls the degree of polymerization of.

As the unsubstituted or substituted monovalent hydrocarbon group represented by R ⁶ and R ⁷ in the general formula (4), those similar to R ¹ can be mentioned. Further, R ⁷ is preferably a methyl group because it is easily available.

Specific examples of the monoacyloxysilane as the component (c) include trimethylacetoxysilane and dimethylvinylacetoxysilane. (C)
The component monoacyloxysilane may be used alone or in combination of two or more.

The amount of the component (c) used can be appropriately determined by calculating it from the degree of polymerization of the target organopolysiloxane gum. For example, in the case of obtaining an organopolysiloxane gum having a degree of polymerization of 5000, 2 × 10 ⁻⁴ per 1 mol of the total amount of the components (a) and (b).
A molar amount of the component (c) is used [the larger the amount of the component (C) (stopper), the smaller the degree of polymerization].

Acidic Compound The acidic compound acts as a catalyst. Examples of the acidic compound include the acidic catalyst disclosed in JP-A-3-179027. Specifically, for example,
CF ₃ COOH, FCH ₂ COOH, C ₃ F ₇ COO
H, C ₃ F ₇ OCF (CF ₃ ) COOH, C ₃ F ₇ OC
F (CF ₃ ) CF ₂ OCF (CF ₃ ) COOH, ClC
H ₂ COOH, BrCH ₂ COOH, CH ₂ (COO
H) _{2 and the} like.

[0032] The acidic compound is usually a value of pK _a at 20 ° C. is in a range of -3 to 3, and more preferably from 0-3. When the value of the pK _a is too high reduced the rate of polycondensation reaction takes a long time to completion of the polymerization. On the other hand, if it is too low, the siloxane bond of the polymer is cleaved, and a low-molecular weight siloxane is by-produced, which is not preferable.

The amount of the acidic compound used is usually 0. 0 per 100 parts by weight of the total amount of the components (a) and (b).
001 to 10 parts by weight, preferably 0.1 to 10 parts by weight.

When the mixture of the above-mentioned components (a), (b) and (c) is heated in the presence of an acidic compound, radiation-crosslinkable functional groups are protected from polymerization reaction in addition to these components. Di (t-butyl) hydroxytoluene (hereinafter referred to as BHT), N N′-diphenyl-
It is desirable to add a polymerization inhibitor such as p-phenylenediamine (Antage Dp) to the mixture. The addition amount of these polymerization inhibitors is usually 0.0001 to 0.1 per 100 parts by weight of the total amount of the components (a) and (b).
Parts by weight, preferably 0.001 to 0.01 parts by weight. If this addition amount is too small, the above-mentioned protective effect is not recognized and gelation may proceed. On the contrary, if the amount is too large, it may hinder the polymerization of the components (a), (b) and (c). These polymerization inhibitors may be used alone or in combination of two or more.

The heating temperature is usually 20 to 200 ° C.
And preferably 100 to 150 ° C. If the heating temperature is too low, it will take a long time to complete the polymerization. The heating temperature is preferably below the boiling point of the raw material used. The polymerization time is usually 1 to 72 hours, but the reaction time can be shortened by increasing the addition amount of the acidic compound. The polymerization method may be a batch process or a continuous process.

The organopolysiloxane obtained by such a method is represented by the following formula:

[0037]

[Chemical 6] (Wherein R ³ , R ⁴ , R ⁵ , R ⁶ , n and m are the same as above, p and q are positive integers), and the degree of polymerization is 100 or more. is there. In addition, when this method is used, a low-molecular-weight siloxane is not produced as a by-product, and if necessary, a gum-like substance having a degree of polymerization of 3000 or more, which is conventionally difficult, typically 4000 to 20000, can be produced. it can.

Component (B) The reinforcing silica powder as the component (B) used in the composition of the present invention is essential to obtain a silicone rubber having excellent mechanical strength. The reinforcing silica powder has a specific surface area (BET value, the same applies hereinafter) of 50 m ² / g or more,
It should preferably be 100 to 400 m ² / g. If this specific surface area is too small, the mechanical strength of the resulting silicone rubber will decrease.

Examples of such reinforcing silica include fumed silica and precipitated silica.

The amount of the reinforcing silica powder used is the same as in the above (A).
It is usually 5 to 70 parts by weight, preferably 30 to 50 parts by weight, per 100 parts by weight of the component. If the amount used is too small, a sufficient reinforcing effect of the silicone rubber may not be obtained, and if it is too large, the processability of the silicone rubber may deteriorate and the mechanical strength of the obtained silicone rubber may decrease.

Other Components In addition to the above-mentioned essential components, a filler such as ground quartz, diatomaceous earth or calcium carbonate may be added as a bulking agent to the composition of the present invention, if necessary.

In the composition of the present invention, if necessary, a sensitizer, a colorant, a heat resistance improver and a conductive filler (for example,
Various additives such as carbon black), reaction control agents,
A release agent, a filler dispersant, etc. can be added.
The amounts of diphenylsilanediol, various alkoxysilanes, carbon functional silanes, silanol group-containing low molecular weight siloxanes and the like used as the filler dispersant are kept to a minimum so as not to impair the effects of the present invention. It is preferable.

Production of Composition The composition of the present invention is prepared by uniformly mixing the above-mentioned components using a rubber kneader such as a two-roll mill, a Banbury mixer, a dough mixer (kneader), and if necessary heat treatment. Can be obtained by applying. In this case, for example,
The base compound may be prepared by previously mixing the organopolysiloxane as the component (A) and the reinforcing silica as the component (B), and the optional components may be mixed therein.

The silicone rubber composition of the present invention thus obtained can be molded into a desired shape of silicone rubber by various molding methods such as cast molding, mold pressure molding and extrusion molding. .

Silicone Rubber The silicone rubber of the present invention can be obtained by irradiating the above silicone rubber composition with radiation to cure it. The silicone rubber of the present invention thus obtained has excellent surface characteristics such as a coefficient of dynamic friction of 0.5 or less.

Radiation includes a beam of particles (including photons) emitted by radiation decay,
Specific examples include α-rays, β-rays, γ-rays, X-rays, electron beams, ultraviolet rays, infrared rays, visible light, proton rays, and neutron rays, and these may be used in combination of two or more. Among them, electron beams, γ rays, and ultraviolet rays are preferable from the viewpoint of equipment, productivity, and economics. For example, as a method of curing a composition using an electron beam, the electron beam is irradiated using an electron beam generator corresponding to the shape of the silicone rubber to be obtained. For example, in order to obtain a silicone rubber having a specific thickness, the output of the electron beam may be fixed and cured. The electron dose to be irradiated can be appropriately selected depending on the shape of the silicone rubber to be obtained, but it is usually 1 kGy to 500 kGy,
It is preferably 10 to 300 kGy.

[0047]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

The gum-like organopolysiloxane used in each of the examples is a dimethylpolysiloxane having silanol groups at both ends of the molecular chain (silanol group content 0.0195 mol, low molecular weight cyclic organosiloxane having D unit of 3 to 25 as impurities). 1080 ppm is included.) For 500 g, a corresponding amount of γ-acryloylpropylmethylsilanediol was charged in a separable flask and stirred at room temperature for 30 minutes,
Then, in the separable flask, 0.1 g of trimethylacetoxysilane, C ₃ F ₇ CF (CF ₃ ) CF ₂ OCF- (CF ₃ ) COOH (2
0.50 pKa at 0 ° C and BHT
(Polymerization inhibitor) 0.3 g was added and stirred for 30 minutes, and 1
It was prepared by heating to 00 ° C. and conducting a polycondensation reaction for 10 hours while stirring.

EXAMPLE 1 99.475 mol% of dimethylsiloxane units, 0.5 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxy units, having an average degree of polymerization of about
100 parts by weight of 8,000 gum-like organopolysiloxane (containing 1200 ppm of cyclic organosiloxane having D unit of 3 to 25) as a dispersant, dimethylpolysiloxane having silanol groups at both ends of the molecular chain (degree of polymerization: 10) 4 50 parts by weight of fumed silica having a specific surface area of 200 m ² / g (manufactured by Nippon Aerosil Co., Ltd.),
These were kneaded with a two-roll to prepare a compound. Then, this compound is press molded at room temperature,
A 2 mm thick sheet was obtained. Then, the sheet was irradiated with an electron beam using an electron curtain type manufactured by ES (irradiation conditions: 50 kGy, applied voltage 2 MV, current 2 mA) to obtain a silicone rubber sheet. The following rubber physical properties of the obtained silicone rubber sheet were measured. Table 1 shows the results.

(Physical Properties of Rubber) Hardness (Scale): Measured according to JIS K 6301. In addition, the measurement used the A type of a spring type hardness tester.

Tensile strength (kgf / cm ² ): JIS K 630
1 was measured.

Elongation (%): Measured according to JIS K 6301.

Tear strength (kgf / cm): JIS K 6301
It measured according to. A type A test piece was adopted.

Dynamic friction coefficient: 250 gf, 500 gf, 1
The dynamic friction coefficient at each load of 000 gf was measured with a HEIDON type surface property measuring device.

Example 2 Instead of the gum-like organopolysiloxane used in Example 1, 98.975 mol% of dimethylsiloxane units, 1.0 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxy units were used. Gum-like organopolysiloxane having a degree of about 8,000 (containing 980 ppm of cyclic organosiloxane having D unit of 3 to 25)
A silicone rubber sheet was obtained in the same manner as in Example 1 except that the amount of D units 3 to 25 contained in the compound was changed as shown in Table 1. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1.
Table 1 shows the results.

Examples 3 to 4 Instead of the gum-like organopolysiloxane used in Example 1, 96.975 mol% of dimethylsiloxane units, 3.0 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxane units were used. A gum-like organopolysiloxane with an average degree of polymerization of about 8,000 (D
A silicone rubber sheet was obtained in the same manner as in Example 1 except that 1320 ppm of a unit of 3 to 25 cyclic organosiloxane was used and the amount of D units 3 to 25 contained in the compound was as shown in Table 1. It was Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1. Table 1 shows the results.

Example 5 A gum-like organopolysiloxane having 96.975 mol% of dimethylsiloxane units, 3.0 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxane units and having an average degree of polymerization of about 8,000 (D unit 3). Contains 1320ppm of ~ 25 cyclic organosiloxanes)
In addition, 4 parts by weight of dimethylpolysiloxane having a silanol group at both ends of a molecular chain (polymerization degree: 10) as a dispersant, 50 parts by weight of fumed silica having a specific surface area of 200 m ² / g [manufactured by Nippon Aerosil Co., Ltd.] and 2.0 parts by weight of 2,2-diethoxyacetophenone was added as a sensitizer, and these were kneaded with a two-roll to prepare a compound. Then
This compound was press-molded at room temperature to obtain a 2 mm thick sheet. Then, the sheet is irradiated with ultraviolet rays using an ultraviolet irradiation device manufactured by Suga Test Instruments Co., Ltd. (irradiation condition: 10
00 mJ / cm ² ) and a silicone rubber sheet were obtained. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 1 Dimethylsiloxane unit 99.475 mol%, vinylmethylsiloxane unit 0.5 mol%, dimethylvinylsiloxy unit
100 parts by weight of a gum-like organopolysiloxane having an average degree of polymerization of about 8,000 (D unit: 3 to 25)
Containing 15600 ppm of cyclic organosiloxane of
As a dispersant, 4 parts by weight of dimethylpolysiloxane having a silanol group at both ends of a molecular chain (degree of polymerization: 10) and 50 parts by weight of fumed silica having a specific surface area of 200 m ² / g [manufactured by Nippon Aerosil Co., Ltd.] are added. Then, these were heated and kneaded for 7 hours at 180 ° C. using a two-roll to prepare a compound. To this compound was mixed 1 part of an 80% paste of 2,4-dichlorobenzoyl peroxide / fumed silica manufactured by Nippon Aerosil Co., Ltd. Next, this mixture was press-cured at 120 ° C. for 10 minutes and then post-cured at 200 ° C. for 4 hours to obtain a silicone rubber sheet. About the obtained silicone rubber sheet,
Rubber properties were measured in the same manner as in Example 1. Table 2 shows the results
Shown in

Comparative Example 2 99.475 mol% of dimethylsiloxane unit, 0.5 mol% of vinylmethylsiloxane unit, dimethylvinylsiloxy unit
100 parts by weight of a gum-like organopolysiloxane having an average degree of polymerization of about 8,000 (D unit: 3 to 25)
Containing 15600 ppm of cyclic organosiloxane of
As a dispersant, 4 parts by weight of dimethylpolysiloxane having a silanol group at both ends of a molecular chain (degree of polymerization: 10) and 50 parts by weight of fumed silica having a specific surface area of 200 m ² / g [manufactured by Nippon Aerosil Co., Ltd.] are added. Then, these were heated and kneaded for 7 hours at 180 ° C. using a two-roll to prepare a compound. 0.2 part by weight of 1,3,5,7-tetrahydrogen-1,3,5,7-tetramethylcyclotetrasiloxane was added to this compound, and a vinyldimethylsiloxane solution of a vinylsiloxane platinum chloride complex (viscosity at 25 ° C;
600 cSt) 0.05 parts by weight were mixed. The mixture was then press cured at 165 ° C for 10 minutes, then 20 more minutes.
Post-cure was performed at 0 ° C. for 4 hours to obtain a silicone rubber sheet. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1. Table 2 shows the results.

When the surface of each silicone rubber sheet was touched with a finger, a tackiness was felt in Comparative Examples 1 and 2, but no tackiness was felt in the others.

[0061]

[Table 1] In the table, the amount of D3 to D25 represents the content of the cyclic organosiloxane having D units of 3 to 25 (the same applies hereinafter).

[0062]

[Table 2] Example 6 Instead of the gum-like organopolysiloxane used in Example 1, 98.975 mol% of dimethylsiloxane units, 1.0 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxane units were used, and the average degree of polymerization was about 8,000 gum-like organopolysiloxane (D
2) in the same manner as in Example 1 except that 1180 ppm of a unit of 3 to 25 cyclic organosiloxane was used and the amount of D units of 3 to 25 contained in the compound was as shown in Table 3.
An uncured sheet having a thickness of mm was obtained. Two sheets of this sheet were prepared. Then, each sheet was irradiated with an electron beam using an electron curtain type manufactured by ES Co. (irradiation conditions: 50 kGy or 100 kGy, applied voltage 2 MV, current 2 mA) to obtain a silicone rubber sheet. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1. Table 3 shows the results.

Example 7 Instead of the gum-like organopolysiloxane used in Example 1, 96.975 mol% of dimethylsiloxane units, 3.0 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxane units were used. Gum-like organopolysiloxane with a degree of about 8,000 (D
A silicone rubber sheet was prepared in the same manner as in Example 6 except that 1020 ppm of a unit 3 to 25 cyclic organosiloxane was used and the amount of D units 3 to 25 contained in the compound was as shown in Table 3. Obtained. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1.
Table 3 shows the results.

Example 8 Instead of the gummy organopolysiloxane used in Example 1, 94.975 mol% of dimethylsiloxane units, 5.0 mol% of γ-acryloylpropylmethylsiloxane units and 0.025 mol% of trimethylsiloxane units were used. Gum-like organopolysiloxane with a degree of about 8,000 (D
A silicone rubber sheet was prepared in the same manner as in Example 6 except that the amount of the D units 3 to 25 contained in the compound was as shown in Table 3 by using 1260 ppm of the unit 3 to 25 cyclic organosiloxane). Obtained. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1.
Table 3 shows the results.

Example 9 In the production of the silicone rubber sheet, except that the UV irradiation (irradiation condition: 1000 mJ / cm ² ) was performed using an UV irradiation device manufactured by Suga Test Instruments Co., Ltd. instead of electron beam irradiation. A silicone rubber sheet was obtained in the same manner as in Example 8. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1. Table 3 shows the results. Comparative Example 3 Dimethylsiloxane unit 99.475 mol%, vinylmethylsiloxane unit 0.5 mol%, dimethylvinylsiloxy unit
100 parts by weight of a gum-like organopolysiloxane having an average degree of polymerization of about 8,000 (D unit: 3 to 25)
Containing 15600 ppm of cyclic organosiloxane of
As the dispersant, 4 parts by weight of dimethylpolysiloxane having a silanol group at both ends of the molecular chain (degree of polymerization: 10), 35 parts by weight of fumed silica [made by Nippon Aerosil Co., Ltd.] having a specific surface area of 200 m ² / g, and spherical silica [Manufactured by Micron Co., Ltd.] 20 parts by weight were added, and these were heated and kneaded at 180 ° C. for 7 hours using a double roll to prepare a compound. To this compound, 1 part by weight of 80% paste of 2,4-dichlorobenzoyl peroxide / fumed silica [manufactured by Nippon Aerosil Co., Ltd.] was added, and the mixture was heated at 120 ° C.
After press-curing for 10 minutes at 200 ° C., post-curing was further performed at 200 ° C. for 4 hours to obtain a silicone rubber sheet. Rubber properties of the obtained silicone rubber sheet were measured in the same manner as in Example 1. Table 4 shows the results.

When the surface of each of the silicone rubber sheets of Examples 6 to 9 and Comparative Example 3 was touched with a finger, there was a tack feeling in Comparative Example 3 but no tack feeling in the other cases.

[0067]

[Table 3]

[0068]

[Table 4]

[0069]

The composition of the present invention does not require a secondary treatment to remove by-products and low molecular weight siloxanes in the cured silicone rubber, so that the production of products using the silicone rubber is not required. A silicone rubber having excellent efficiency and mechanical strength can be obtained. Moreover, since there is no particular curing inhibitor, the range of use is not limited. Furthermore, the silicone rubber obtained by curing the composition of the present invention by irradiation with radiation has a low dynamic friction coefficient of 0.5 or less and excellent surface characteristics.

Claims (5)

[Claims] 1. (A) The following average composition formula (1): R ¹ _a R ² _b SiO _{(4-ab) / 2} (1) (In the formula, R ¹ is independently unsubstituted or substituted monovalent carbon. A hydrogen group, R ² is a radiation-crosslinkable functional group, and a and b are positive numbers satisfying a + b = 1.98 to 2.02), and an organopolysiloxane having an average degree of polymerization of 100 or more, and (B ) A radiation-curable silicone rubber composition containing a reinforcing silica powder having a specific surface area of 50 m ² / g or more. 2. The radiation curable silicone rubber composition according to claim 1, wherein the organopolysiloxane as the component (A) is an organopolysiloxane gum having an average degree of polymerization of 3000 or more. 3. The radiation-crosslinkable functional group represented by R ² of the average composition formula (1) is at least one selected from an acryloylalkyl group, a methacryloylalkyl group and a mercaptoalkyl group. The radiation-curable silicone rubber composition described. 4. The radiation-curable silicone rubber composition according to any one of claims 1 to 3 is irradiated with at least one type of radiation selected from electron beams, γ rays and ultraviolet rays to cure the composition. The silicone rubber thus obtained. 5. The silicone rubber surface has a coefficient of dynamic friction of 0.
The silicone rubber according to claim 4, which is 5 or less.