JPH09143375A - Silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicone rubber compsn. which is excellent in sheetability with rolls, releasability from a metal mold, and impact resiliency after curing and gives a molded item with a low compression set by compounding a specific raw rubber with a silicone rubber powder, a filler, and a curative. SOLUTION: This compsn. comprises 100 pts.wt. raw organopolysiloxane rubber having at least two units represented by the formula: R<1> a R<2> b SiO(4-a-b)/2 (wherein R<1> is a monovalent hydrocarbon group except an alkenyl; R<2> is an alkenyl; (a) is 0, 1, or 2; and (b) is 1 or 2 provided a+b is 1, 2, or 3) in the molecule and having a content of alkenyl group of 0.01-5wt.% 1-100 pts.wt. reinforcing filler, 110-300 pts.wt. spherical silicone rubber powder having an average particle size of 0.5-30μm and a curative in an amt. enough to cure the compsn. Pref., the rubber powder has a JIS A hardness (according to JIS K 6301) of 40 degrees or lower.

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 in particular, it has excellent roll dispensing properties and mold releasability.
The present invention relates to a silicone rubber composition which, after being cured, has excellent impact resilience and can be a silicone rubber molded product having a small compression set.

[0002]

2. Description of the Related Art Silicone rubber is used in a wide variety of fields because of its excellent heat resistance and weather resistance. Among them, as the silicone rubber used for packing, rolls, etc., a silicone rubber having a relatively low hardness (a silicone rubber having a JIS A hardness of 50 degrees or less) is used.
As a method of obtaining such a low hardness silicone rubber, there are a method of reducing the compounding amount of the reinforcing silica compounded in the silicone rubber composition, a method of compounding an expanding filler such as quartz powder, and the like. However, the low-hardness silicone rubber composition obtained by these methods generally has low plasticity and high tackiness, and thus is inferior in roll kneading workability,
There has been a problem that it is difficult to take out rolls in preform molding. Further, these silicone rubber compositions have a problem in that they easily adhere to the wall surface of the mold and the silicone rubber after curing has a strong adhesive property, so that the mold release property from the mold is poor. Further, a method of reducing the crosslink density of the silicone rubber to obtain a low-hardness silicone rubber has also been attempted, but if the crosslink density is reduced, the recoverability against deformation such as compression set and permanent elongation becomes extremely poor, and the long-term There was a problem that it cannot be used for packing, rolls, etc., which are required to have a low compression set due to deformation during a period of time. On the other hand, a method of adding 5 to 100 parts by weight of a spherical silicone rubber powder to a silicone rubber composition to improve molding processability such as roll processability has been proposed (JP-A-2-
No. 102263), when this method is applied to a low-hardness silicone rubber composition, there is a problem that it cannot be used depending on the intended use because of insufficient roll dispensing property, mold release and impact resilience. It was

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies for solving the above-mentioned problems, the present inventors unexpectedly found that if a large amount of a specific silicone rubber powder is blended with a silicone rubber composition, the roll is unexpectedly processed. The present invention has been accomplished by finding that a dispensing property and mold releasability are remarkably improved, and a silicone rubber molded product having an extremely high impact resilience can be obtained. That is, an object of the present invention is to provide a silicone rubber composition which is excellent in rubber molding processability, has a low hardness after curing, is excellent in impact resilience, and can be a silicone rubber molded product having a small compression set.

[0004]

Means for Solving the Problems The present invention provides (A) a general formula: R ¹ _a R ² _b SiO _{(4-ab) / 2} (wherein R ¹ is a monovalent hydrocarbon group excluding an alkenyl group, R ² is an alkenyl group, a is an integer of 0 to 2, b is an integer of 1 to 2, and a + b is an integer of 1 to 3). 100 parts by weight of organopolysiloxane raw rubber having a group content within the range of 0.01 to 5% by weight, (B) 1 to 100 parts by weight of a reinforcing filler, (C) spherical particles having an average particle diameter of 0.5 to 30 μm. Silicone rubber powder 110 to 300 parts by weight, and (D) curing agent The present invention relates to a silicone rubber composition comprising an amount sufficient to cure the composition.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The organopolysiloxane raw rubber of the component (A) used in the present invention is the main ingredient of the composition of the present invention, wherein R ¹ is a methyl group, an ethyl group,
Examples thereof include an alkyl group exemplified by a propyl group; an aryl group exemplified by a phenyl group and a tolyl group; and a substituted alkyl group exemplified by a 3,3,3-trifluoropropyl group and a 3-chloropropyl group. R ² is a vinyl group, an allyl group,
An alkenyl group exemplified by a propenyl group and the like. This organopolysiloxane has two or more alkenyl groups in one molecule, and the content of the alkenyl groups must be within the range of 0.01 to 5% by weight. It is preferably in the range of 3 wt%. The molecular structure of this organopolysiloxane raw rubber is preferably linear, but it may be linear with branching.

The reinforcing filler of the component (B) used in the present invention is a known filler which has been conventionally used for silicone rubber, and its type is not particularly limited. Examples of such a reinforcing filler include finely powdered silica such as fumed silica and precipitated silica, silica having the surface of the finely powdered silica hydrophobized with organosilane or organosiloxane, fused silica, and carbon black. To be done.

The component (C) silicone rubber powder used in the present invention functions to reduce the tackiness of the silicone rubber molded product and improve the rubber processability. The silicone rubber powder has an average particle diameter of 0.1 to 30 μm and needs to be spherical in shape. Further, the hardness of this silicone rubber powder is preferably 40 degrees or less in JISA hardness specified in JIS K6301.
More preferably, it is in the range of 0 to 5 degrees.

A method for producing such a silicone rubber powder is known, for example, a method of spraying a liquid addition reaction type silicone rubber composition into hot air and curing it in a spray state, a liquid condensation reaction type or It is produced by a method of dispersing an addition reaction type silicone rubber in water or water containing a surfactant as a discontinuous phase and spraying it in hot air to cure the silicone rubber and at the same time remove water (Patent Publication 7). -81080, Japanese Patent Publication No. 4-17986). Also, the surface of the silicone rubber powder obtained by the above method may be treated with various treatment agents such as a silane coupling agent.

The blending amount of this component is 110 to 300 parts by weight, preferably 120 parts by weight, relative to 100 parts by weight of the component (A).
２５０250 parts by weight. When the compounding amount of the component (C) is less than 110 parts by weight, the effect of improving the roll dispensing property and the mold releasability is not recognized, and when it is more than 300 parts by weight, the silicone rubber composition is kneaded or molded. Becomes extremely difficult.

The curing agent as the component (D) is a component for curing the composition of the present invention, and those generally known as curing agents for silicone rubber compositions can be used. One of such curing agents is organic peroxide. Here, as the organic peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 1, 1-bis (t-butylperoxy)
Examples include 3,3,5-trimeryl cyclohexa, benzoyl peroxide and the like. Also, a combination of an organohydrogenpolysiloxane and a platinum-based catalyst can be used,
Two or more kinds of these curing agents may be used in combination for use. The blending amount of this component is an amount sufficient to cure the composition of the present invention. Specifically, when an organic peroxide is used as a curing agent, with respect to 100 parts by weight of the component (A),
The amount is in the range of 0.1 to 10 parts by weight, and when the combination of the organohydrogenpolysiloxane and the platinum catalyst is used, the amount of the organohydrogenpolysiloxane is 0.5 to 100 parts by weight of the component (A). It is used in an amount of 10 parts by weight, and a platinum-based catalyst as platinum metal in the range of 0.001 to 0.1 parts by weight.

The composition of the present invention can be easily prepared by uniformly mixing the above-mentioned components (A) to (D), which includes quartz powder, diatomaceous earth, calcium carbonate powder, alumina powder and the like. Various additives such as non-reinforcing fillers, carbon black, metal powders, metal oxide powders and other conductivity imparting agents, red iron oxide, titanium oxide and other pigments, heat-resistant agents, flame retardants, adhesion imparting agents, etc. It may be added and blended as long as the purpose is not impaired.

[0012]

Next, the present invention will be described by way of examples. In the examples, "parts" means "parts by weight", and the viscosity is 2
This is a measured value at 5 ° C.

[0013]

[Reference Example 1] Both ends of a molecular chain were capped with dimethylvinylsiloxy groups. 100 parts of dimethylpolysiloxane with a viscosity of 500 centipoise (vinyl group content: 0.5% by weight) were capped with trimethylsiloxy groups at both ends. Viscosity 1
A mixture a was obtained by adding 6 parts of 0 centipoise of methyl hydrogen polysiloxane (content of silicon atom-bonded hydrogen atoms: 1.5% by weight). On the other hand, 100 parts of the same dimethylpolysiloxane as described above was added with isopropyl alcohol solution of chloroplatinic acid (platinum content 3% by weight) 0.6
Parts were added and mixed to obtain a mixture b. A mixture of the mixture a and the mixture b in a weight ratio of 1: 1 was sent to a colloid mill, and ion-exchanged water and a surfactant were added at the same time to obtain an aqueous dispersion of a silicone rubber composition. An aqueous dispersion of this silicone rubber composition was sprayed into a spray dryer set at 200 ° C. to cure in a spray state and at the same time remove water to obtain a silicone rubber powder. The obtained silicone rubber powder was a true spherical powder and had an average particle diameter of 5 μm. Moreover, the hardness was 30 degrees in terms of JIS A hardness specified in JIS K6301. The hardness of the mixture a and the mixture b is 1:
1 The mixture was cured into a sheet and measured.

[0014]

Example 1 100 parts by weight of dimethylpolysiloxane raw rubber having an average degree of polymerization of 3,000 consisting of 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methylvinylsiloxane units, 10 parts by weight of fumed silica and a viscosity of 80 centipoise. After uniformly mixing 3 parts of dimethylpolysiloxane having silanol groups at both ends, the mixture was heated and mixed at 150 ° C. for 1 hour to obtain a silicone rubber base compound. The silicone rubber powder obtained in Reference Example 1 was added to the silicone rubber base compound in the amount shown in Table 1. Subsequently, 0.5 part of 2,5-dimethylbis (2,5-t-butylperoxy) hexane was added and uniformly mixed on a two-roll mill to obtain silicone rubber compositions 1 to 3. Here, the dispensability during kneading on the two rolls was evaluated. This composition was press-molded for 10 minutes under conditions of a temperature of 170 ° C. and a pressure of 25 kg / cm ² to obtain a silicone rubber sheet-shaped molded product having a thickness of 2 mm. The hardness and impact resilience of the obtained sheet-shaped molded product were measured according to the method specified in JIS K6301, and the measurement results are shown in Table 1.

[0015]

[Table 1]

[0016]

Example 2 100 parts of dimethylpolysiloxane raw rubber having an average degree of polymerization of 3,000 consisting of 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methylvinylsiloxane units was mixed with 100 parts of acetylene black [manufactured by Denki Kagaku Co., Ltd.,
Conductive carbon black] 30 parts were uniformly mixed to obtain a silicone rubber base compound. The silicone rubber base compound was blended with the silicone rubber powder obtained in Reference Example 1 in the amounts shown in Table 2. Then 2,5-
Dimethylbis (2,5-t-butylperoxy) hexane (1.0 part) was blended and uniformly mixed on a two-roll mill to obtain a silicone rubber composition 4 and a silicone rubber composition 5. . Here, the dispensability during kneading on the two rolls was evaluated. This composition is used at a temperature of 170 ° C. and a pressure of 25 kg /
Press molding was carried out for 10 minutes under the condition of cm ² to obtain a sheet-shaped molded product of silicone rubber having a thickness of 2 mm. The hardness and impact resilience of the obtained sheet-shaped molded product were measured according to the method specified in JIS K6301, and the measurement results are shown in Table 2.

[0017]

[Table 2]

[0018]

Example 3 113 parts of the silicone rubber base compound used in Example 1 was mixed with 120 parts of the silicone rubber powder obtained in Reference Example 1, and at the same time, a dimethylsiloxane / methylhydrogensiloxane block-capped with trimethylsiloxy groups at both ends was added. Polymer (silicon atom-bonded hydrogen atom content 0.8% by weight) 1.0 part, 1-ethynyl-1-cyclohexane 0.3 part, complex catalyst of chloroplatinic acid and 1,3-divinyltetramethyldisiloxane (Platinum content: 0.6% by weight) 0.4 part was added and uniformly mixed to obtain an addition reaction curable silicone rubber composition 6. This composition 6 at a temperature of 1
Press molding was carried out at 50 ° C. under a pressure of 25 kg / cm ² for 5 minutes to obtain a silicone rubber sheet-shaped molded product having a thickness of 2 mm. The hardness of the obtained sheet-shaped molded product is 25 (JIS
A), impact resilience was 81 (%). Further, the two-roll dispensing property and the mold releasability were both good.

[0019]

The silicone rubber composition for rolls of the present invention comprises components (A) to (C), and in particular, the silicone rubber powder of component (C) is used in an amount of 110 to 100 parts by weight of component (A).
Since it is blended in a large amount of 300 parts by weight, it is excellent in processability such as roll dispensing property and mold releasing property, and after curing, it can be a silicone rubber molded product having excellent rubber elasticity.

Claims (3)

[Claims] 1. (A) General formula: R ¹ _a R ² _b SiO _{(4-ab) / 2} (wherein R ¹ is a monovalent hydrocarbon group excluding an alkenyl group, R ² is an alkenyl group, a Is an integer of 0 to 2, b is an integer of 1 to 2, and a + b is an integer of 1 to 3). In one molecule, at least two units are represented, and the alkenyl group content is 0. 100 parts by weight of organopolysiloxane raw rubber in the range of 0.01-5% by weight, (B) 1-100 parts by weight of reinforcing filler, (C) spherical silicone rubber powder having an average particle diameter of 0.5-30 μm 110-300 parts by weight, and (D) curing agent A silicone rubber composition comprising sufficient amount to cure the composition. 2. The hardness of the spherical silicone rubber powder as the component (C) is 40 in terms of JIS A hardness specified in JIS K6301.
The silicone rubber composition according to claim 1, wherein the silicone rubber composition has a hardness of not more than 100 degrees. 3. The hardness of the silicone rubber after curing is JIS
The silicone rubber composition according to claim 1, which has a JIS A hardness defined by K6301 of 45 degrees or less and a rebound resilience of 75% or more.