JPH09302230A - Silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-quality silicone rubber composition which has the excellent properties inherent in silicone rubbers, has a significantly improved long-lasting resistance to dynamic fatigue by, e.g. repeated loading, is highly homogeneous, and has high reliability. SOLUTION: This composition comprises 100 pts.wt. organopolysiloxane (A) represented by the formula, Ra SiO(4-a)/2 (wherein R is an (un)substituted monovalent hydrocarbon group and (a) is 1.95-2.04) and having a degree of polymerization of 100 or higher, 5-80 pts.wt. precipitated silica filler (B) which has a specific surface area of 100m<2> /g or larger and an average secondary particle diameter of 10μm or smaller, and at least 15wt.% of which is accounted for by particles each having a diameter of 16μm or larger, and a hardener (C) in an amount sufficient to cure the component (A).

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 having improved rubber properties. More specifically, the silicone rubber composition maintains excellent rubber properties originally possessed by silicone rubber.
The present invention relates to a silicone rubber composition having dramatically improved durability against dynamic fatigue such as repetitive load and suitable for keyboard materials (rubber contacts), automobile constant velocity joint boots, diaphragm materials and the like.

[0002]

2. Description of the Related Art Conventionally, silicone rubber has been widely used in various fields because of its excellent heat resistance, cold resistance, weather resistance and electric insulation due to its siloxane structure having a unique skeleton. It is applied.

However, silicone raw rubber (eg, dimethylpolysiloxane) alone is only 3 kgf / c.
Since it only exhibits a tensile strength of about m ² , it is common to add a reinforcing filler in order to increase it to a practical strength.

Out of the silicone rubber compositions containing such a reinforcing filler, excellent elasticity (click property)
Precipitated silica-containing silicone rubber, which gives a good compression set and has a cost advantage, is often used as a keyboard material (rubber contact) for calculators and personal computers. Although excellent dynamic fatigue durability is required for use in this application, there is an increasing demand for improvement in fatigue durability as the application range of rubber contacts is expanded. In order to improve this fatigue durability, it is important to reduce the occurrence of stress concentration parts due to silica as much as possible. For that reason, silica having a large specific surface area, that is, fine primary particle silica is used. The precipitating silica-containing silicone rubber has not been able to sufficiently meet the increasing demand.

For this reason, various attempts have been made to improve the silica filler, for example, JP-A-2-289649.
The publication, by controlling the average particle size of the secondary particles formed by binding and aggregating the primary particles to a certain particle size or less,
It has been proposed to improve dynamic fatigue durability.

However, although the above-mentioned proposal can achieve a certain level of improvement in dynamic fatigue durability, it is still not sufficient, resulting in a large variation and a low yield.
It was unreliable.

The present invention has been made in view of the above circumstances, and in addition to the excellent properties inherent to silicone rubber such as heat resistance, cold resistance, compression recovery, and rubber elasticity, the dynamic fatigue resistance is further increased. It is an object of the present invention to provide a high-quality silicone rubber composition which is improved, has less variation, and has high reliability.

[0008]

Means for Solving the Problems and Modes for Carrying Out the Invention As a result of intensive studies conducted by the present inventors in order to achieve the above object, the following average composition formula (1) R _a SiO _{(4-a) / 2} (1) (wherein R is an unsubstituted or substituted monovalent hydrocarbon group, a
Is a positive number from 1.95 to 2.04. ), The organopolysiloxane having a degree of polymerization of 100 or more has a specific surface area of 100 m ² / g or more, and the average particle diameter of secondary particles formed by binding and aggregation of primary particles is 10 μm or less,
It is possible to unexpectedly and effectively disperse the stress concentration part by adding a certain amount of a precipitating silica-based filler in which coarse particles having a particle size of 16 μm or more are 15% by weight or less of the whole silica. It was found that the dynamic fatigue durability is dramatically improved, the yield is improved because the variation is small, and a high-quality silicone rubber composition having high reliability can be obtained.

The silicone rubber obtained by curing the silicone rubber composition has dynamic fatigue resistance in addition to excellent rubber properties such as heat resistance, cold resistance, compression recovery property and rubber elasticity which are inherent in silicone rubber. The present invention has led to the present invention by finding that it can be suitably used as a keyboard material (rubber contact), a constant velocity joint boot for automobiles, a diaphragm material and the like because it is also excellent.

Therefore, the present invention comprises (A) 100 parts by weight of an organopolysiloxane represented by the above average composition formula (1) and having a degree of polymerization of 100 or more, and (B) a specific surface area of 100 m ² / g or more, Precipitable silica-based filler having secondary particles having an average particle size of 10 μm or less and coarse particles having a particle size of 16 μm or more in an amount of 15% by weight or less based on the total amount of silica. (C) The above (A) A silicone rubber composition comprising a curing agent in an amount sufficient to cure the components.

The present invention will be described in more detail below. The silicone rubber composition of the present invention contains (A) an organopolysiloxane, (B) a precipitable silica-based filler, and (C) a curing agent as main components. It is a thing.

Here, the organopolysiloxane as the component (A) is represented by the following formula (1) R _a SiO _{(4-a) / 2} (1).

In this formula, R is a substituted or unsubstituted monovalent hydrocarbon group, preferably having 1 to 12 carbon atoms, more preferably having 1 to 10 carbon atoms, such as methyl group, ethyl group and propyl group. , Alkyl groups such as butyl groups, cycloalkyl groups such as cyclohexyl groups, vinyl groups, allyl groups, butenyl groups, alkenyl groups such as hexenyl groups, aryl groups such as phenyl groups and tolyl groups, or carbon atoms of these groups It is selected from a chloromethyl group, a trifluoropropyl group, a cyanoethyl group and the like in which a part or all of the bonded carbon atoms is substituted with a halogen atom, a cyano group or the like. In addition, n is a positive number of 1.95 to 2.04, and this organopolysiloxane has its molecular chain terminal blocked with a trimethylsiloxy group, a dimethylphenylsiloxy group, a dimethylvinylsiloxy group, a trivinylsiloxy group, or the like. It is preferably one.

In this case, the organopolysiloxane is not particularly limited, but specifically,
Dimethyl polysiloxane, methyl vinyl polysiloxane, methyl vinyl phenyl polysiloxane, 3,3,3
Examples thereof include polysiloxanes such as trifluoropropylmethylvinylpolysiloxane. The organopolysiloxane is basically a linear diorganopolysiloxane, but may partially contain a branched structure. This organopolysiloxane contains at least 2 in one molecule.
It is preferable to contain 0.01 to 5 mol% of alkenyl groups such as vinyl groups and allyl groups.

The degree of polymerization of the above-mentioned organopolysiloxane must be 100 or more, and preferably 30 in order to make the physical properties of the obtained rubber elastic body sufficient.
It is 0 to 50,000. If the degree of polymerization is less than 100, the dispersion of silica may be insufficient or the mechanical strength may be insufficient. It should be noted that the polymerization degree is preferably 3,000 to 10,000 for the millable type rubber and 300 to 1,200 for the liquid type rubber.

The viscosity of this organopolysiloxane is 25.
At 100C, it is 100 to 100,000,000 cs, more preferably 300 to 10,000,000 cs.
The organopolysiloxane as the component (A) may be used alone or in combination of two or more.

The organopolysiloxane of this type is usually obtained by cohydrolytically condensing one or more selected organohalogenosilanes, or a cyclic polysiloxane (trimer or tetramer of siloxane). Etc.) can be obtained by ring-opening polymerization using an alkaline or acidic catalyst.

Next, the component (B) of the precipitated silica filler is prepared by a method generally called a wet method, for example, water glass (N).
a ₂ O · 3.3SiO ₂₎ of acid (sulfuric acid, a silica which is synthesized by the hydrochloric acid or the like) process. Since this silica imparts a preferable reinforcing effect to the silicone rubber elastic body and the dynamic fatigue durability characteristic of the present invention, its specific surface area by the BET method is 100 m ² / g or more, and the average secondary particle diameter is 10
It is necessary that the coarse particles having a particle diameter of 16 μm or more and having a particle diameter of 16 μm or more account for 15% by weight or less of the entire silica.

The component (B) of the precipitated silica-based filler has all of the following conditions, that is, a specific surface area of 100 m ² / g or more, more preferably 100 to 600 m ^2.
/ G, the average secondary particle size is 10 μm or less, more preferably 0.1 to 8 μm, and the particle size is 16 μm.
15% by weight or less, more preferably 10% by weight or less, still more preferably 5% by weight of coarse particles having a particle size of m or more based on the entire silica.
From the viewpoint of achieving the object of the present invention, it is necessary to satisfy the condition of being in the following range.

In this case, if the specific surface area is less than 100 m ² / g, sufficient reinforcement cannot be obtained, and the average secondary particle size is 1
If it is larger than 0 μm, the dynamic fatigue durability becomes insufficient. Particularly, coarse particles having a particle size of 16 μm or more account for 15% by weight of the entire silica
If it exceeds, even if the average secondary particle diameter of silica is made small, it is impossible to obtain the expected silicone rubber excellent in dynamic fatigue durability.

Such precipitated silica with few coarse particles or small average particle diameter can be obtained by pulverizing and classifying the agglomerated silica obtained by the above standard production method.

The pulverizing step may be carried out by using an ordinary apparatus usually used for pulverizing agglomerated silica, for example, a ball mill,
Examples include hammer mills, jet mills, and florate fans. Also, the classification process may be standard, and a shifter or cyclone can be used.

In these pulverizing and classifying steps, the average particle size and coarse particle cut point are adjusted by controlling factors such as processing speed, air flow rate, residence time, number of times, and sieve according to the degree of aggregation of agglomerated silica. You can

The amount of the precipitating silica filler as the component (B) is 5 to 80 parts by weight, more preferably 10 to 70 parts by weight, based on 100 parts by weight of the organopolysiloxane as the component (A). When the component (B) is less than 5 parts by weight, practical rubber strength cannot be obtained, and when it exceeds 80 parts by weight, compounding becomes difficult and dynamic fatigue durability is deteriorated due to occurrence of stress concentration part of silica. There is.

As the curing agent as the component (C), various known ones can be used depending on the organopolysiloxane as the component (A). Specifically, when an organic peroxide is used as the component (C), it is usually, for example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, 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 (t-butylperoxy) hexyne,
1,1-bis (t-butylperoxy) -3,3,5-
Trimethylcyclohexane, etc. are mentioned, and these are 1
Species may be used alone or in combination of two or more. The addition amount is usually 1 part (A) of organopolysiloxane 1
The amount is 0.1 to 10 parts by weight, more preferably 0.5 to 3 parts by weight, relative to 00 parts by weight. If it is less than 0.1 parts by weight, a sufficient curing reaction cannot be obtained, and if it exceeds 10 parts by weight, the mechanical strength of the obtained cured product may decrease.

On the other hand, when the organopolysiloxane of the component (A) has two or more alkenyl groups in one molecule, the organohydrogenpolysiloxane can be used as the component (C). In this case, a known platinum group metal-based catalyst is used in combination as the catalyst (addition reaction catalyst). Here, the organohydrogenpolysiloxane may be an organopolysiloxane having two or more SiH groups in one molecule and may be linear, cyclic or branched, but has a degree of polymerization of Those of 1,000 or less are preferable. Further, such SiH group may be at the end of the polysiloxane chain or may be in the middle thereof.
Such an organohydrogenpolysiloxane is
The hydrogen atom (≡Si—H) directly bonded to the silicon atom in the hydrogen siloxane is 0.0.1 per mole of the alkenyl group (eg (≡Si—CH═CH ₂ )) in the organopolysiloxane of the component (A). It is preferable to use an amount in the range of 5 to 3 mol. When using a platinum group metal-based catalyst as the catalyst, the total amount of the organopolysiloxane and the organohydrogenpolysiloxane of the component (A) is And usually 5 to 1,000 p as a platinum group metal
It may be in the range of pm. Examples of such platinum group metal-based catalysts include fine powder metal platinum catalysts described in US Pat. No. 2,970,150 and US Pat. No. 2,823.
218, chloroplatinic acid catalysts, platinum-hydrocarbon complex compounds described in U.S. Pat. Nos. 3,159,601 and 3,159,662, U.S. Pat.
Chloroplatinic acid-olefin complex compounds described in 516,946, platinum-vinyl siloxane complexes described in US Pat. Nos. 3,775,452 and 3,814,780 can be used. it can.

The composition of the present invention includes the above (A) to (C).
In addition to the components, ultrafine silica such as fumed silica, filler such as diatomaceous earth, clay, CaCO ₃ , titanium dioxide, carbon black, silane having alkoxy group, silanol group, vinyl group, etc., low molecular weight Wetting agents such as siloxane, heat improvers such as iron oxide, cerium oxide, iron octylate, mold release agents such as fatty acid metal salts and fatty acid-modified siloxane polymers, various carbon functional silanes, flame retardants, etc. Can be added as required.

The composition of the present invention can be obtained by kneading the above-mentioned components (A) to (C) and optional components with a mixer such as a roll, a kneader or a Banbury mixer, and usually (A), ( The component (B) and, if necessary, the optional components are uniformly mixed in advance, and after the heat treatment, if necessary, the component (C) is added and mixed.

The composition of the present invention is used for pressure molding, transfer molding,
It is molded into a rubber elastic body by injection molding or the like. The molding conditions may be selected depending on the molding method and the shape of the molded product, but generally, after vulcanizing at a temperature of 80 to 200 ° C. for about 10 seconds to 15 minutes under pressure, 180 to 2 are further added as necessary.
If the secondary vulcanization is carried out at 50 ° C. for 30 minutes to 24 hours, it can be cured to obtain a silicone rubber elastic body having excellent dynamic fatigue durability.

Since the composition of the present invention gives a rubber elastic body having excellent dynamic fatigue durability in addition to the original properties of silicone rubber, it is suitable for rubber contacts, and also a roll material to which repeated stress is applied. It is also suitable for use in automotive parts such as joint boots and diaphragm materials that are subject to vibration fatigue.

[0031]

EFFECTS OF THE INVENTION The silicone rubber composition of the present invention has the excellent characteristics inherent to silicone rubber, and has significantly improved durability against dynamic fatigue such as repeated load, with little variation and high reliability. It is of quality.

[0032]

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. All parts in each example are parts by weight.

[Examples 1 to 3, Comparative Examples 1 and 2] (C
H ₃ ) ₂ SiO 60 parts of (CH ₃ ) ₂ SiO and 60 parts of an organopolysiloxane having a polymerization degree of 8,000 in which both ends of the molecular chain are blocked with dimethylvinylsiloxy groups (hereinafter abbreviated as organopolysiloxane A) Unit 99.5 mol%
And (CH ₃ ) (CH ₂ ═CH) SiO unit 0.5 mol%
40 parts of the precipitable silica shown in Table 1 in a mixture of 40 parts of organopolysiloxane (hereinafter abbreviated as organopolysiloxane B) having a polymerization degree of 8,000 in which both ends of the molecular chain are blocked with dimethylvinylsiloxy groups. Then, 6 parts of dimethyldimethoxysilane was added, and the mixture was uniformly kneaded in a kneader and then heat-treated at 170 ° C. for 2 hours to obtain a silicone rubber compound.

To 100 parts of the silicone rubber compound thus obtained, 0.5 part of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane was added and mixed using a two-roll mill, and the molding temperature was adjusted. After press vulcanization at 165 ° C for 10 minutes, secondary vulcanization at 200 ° C for 4 hours, thickness 2m
m sheet, press vulcanization at a molding temperature of 165 ° C. for 15 minutes, and then secondary vulcanization at 200 ° C. for 4 hours,
A columnar sample having a thickness of 12.7 mm and a diameter of about 28 mm was prepared.

Various rubber physical properties of the obtained sheet and columnar sample were measured in accordance with JIS K-6301. The results are also shown in Table 1.

Regarding the dynamic fatigue durability, a DeMatcha flexural fatigue tester was used for measurement and JIS 3 was used at room temperature.
The dumbbell piece was repeatedly stretched at 0 to 100% at 5 Hz, and an average value of the number of times of breakage by 5 test pieces was obtained, and this value was defined as 100% elongation fatigue durability. The results are also shown in Table 1.

[0037]

[Table 1]

[Examples 4 to 6 and Comparative Example 3] Examples 1 to 3
Using the same amount of organopolysiloxanes A and B as above, 38 parts of the precipitated silica shown in Table 2 and 5 parts of dimethyldimethoxysilane were added, and after kneading with a kneader, 170
A silicone rubber compound was obtained by heat treatment at ℃ for 2 hours.

A curing agent was added to the obtained silicone rubber compound in the same manner as in Example 1 and molding was performed, and the rubber physical properties of the prepared sample were measured in the same manner. The results are also shown in Table 2.

[0040]

[Table 2]

From the results of Tables 1 and 2, in Comparative Examples 1 to 3, since the amount of coarse particles of 16 μm or more in the precipitating silica filler exceeds 15% by weight of the whole silica, the specific surface area and average secondary Compared to Examples 1 to 6 using a precipitable silica filler having a particle size (the amount of coarse particles of 16 μm or more is 15% by weight or less of the total silica), 100% elongation durability, that is, dynamic fatigue durability It is inferior.

On the other hand, in Examples 1 to 6, in addition to the excellent rubber characteristics originally possessed by silicone rubber, it was recognized that the dynamic fatigue durability was further improved.

Claims (1)

[Claims] (A) The following average composition formula (1) R _a SiO _{(4-a) / 2} (1) (wherein R is an unsubstituted or substituted monovalent hydrocarbon group, and a is 1) 100 parts by weight of organopolysiloxane having a degree of polymerization of 100 or more, and (B) having a specific surface area of 100 m ² / g or more and an average of secondary particles. Precipitable silica-based filler having a particle size of 10 μm or less and coarse particles having a particle size of 16 μm or more in an amount of 15% by weight or less of the entire silica, (C) curing the component (A) A silicone rubber composition comprising a sufficient amount of a curing agent.