JPH04359057A - Production of silicone rubber composition and silicone rubber - Google Patents

Abstract

PURPOSE:To obtain a composition, cured by adding a curing catalyst and capable of providing a silicone rubber excellent in fatigue durability by kneading part of crude rubber with fine powdery silica and a silica dispersing agent, then adding the residual crude rubber and further kneading the resultant mixture. CONSTITUTION:A silicone rubber composition is composed of (A) 100 pts. wt. organopolysiloxane having an average composition formula expressed by formula I [R<1> is monofunctional organic group except fluorine atom or OH; (a) is a positive number of 1.9-2.05], (B) 10-100 pts.wt. fine powdery silica (e.g. aerosol silica) having >=50m<2>/g, especially 130-250m<2>/g specific surface area and the optionally treated surface and (C) 0.5-15 pts.wt. silica dispersing agent, preferably an organosiloxane expressed by formula II (R<2> and R<3> are monofunctional organic group same as R<1>, but may be a fluorine-substituted hydrocarbon group; (b) is 4-100]. The aforementioned composition is obtained by kneading part of the component (A) with the components (B) and (C), then adding the residual component (A) and kneading the resultant mixture. A silicone rubber is prepared by adding a curing catalyst (e.g. an organic peroxide) to the above-mentioned composition and curing the composition.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a silicone rubber with excellent fatigue durability, and therefore improves the elongation and bending fatigue properties required in dynamic applications. The present invention relates to a method of producing silicone rubber compositions useful for applications such as boots, diagrams, medical pump tubes, etc., and a method of producing silicone rubber from the silicone rubber compositions.

0002

[Prior Art] Silicone rubber compositions are made by blending silicone polymers (raw rubber) with fillers, processing aids, vulcanizing agents, etc. Silicone rubber has heat resistance, cold resistance, weather resistance, and electrical resistance. It has excellent insulation properties, compression set, rubber elasticity, etc., and is also non-toxic, so it is used for static applications ranging from electrical and electronic parts, office equipment, automobiles, aircraft, food, medical products, and leisure goods. It is also widely used in dynamic applications such as rubber contacts in calculators and touch phones, keyboards, constant velocity joint cover boots in automobiles, diagrams, medical pump tubes, etc.

0003

[Problems to be Solved by the Invention] However, when silicone rubber is used for the above-mentioned dynamic applications, dynamic fatigue properties such as elongation and bending fatigue properties do not necessarily show satisfactory results. The dynamic fatigue characteristics of rubber are improved by appropriately adopting measures such as uniform crosslinking, low crosslinking density, low modulus, low filler loading, uniform dispersion, and removal of coarse fillers. However, with this type of treatment, the elongation and bending fatigue properties are 500% by the most common demasher fatigue test method.
The limit is 10,000 times level.

[0004] Furthermore, a method of adding organohydrogenpolysiloxane to a silicone polymer in order to improve dynamic fatigue properties (Japanese Patent Application Laid-open No. 197452/1983,
2-197454), a method of adding a fluorine-containing low polymer (see JP-A-63-150350)
, a method of adding a phosphorus-containing organic compound (Japanese Patent Application Laid-Open No. 62-4
1263 (see Publication No. 1263)), and silicone rubbers manufactured by these methods have improved bending fatigue properties up to 10 million cycles using the demasher fatigue test method, but the bending fatigue properties have not been improved beyond that. Therefore, there is a strong demand for the development of silicone rubber with further improved bending fatigue properties.

[0005] The present invention has been made in view of the above circumstances.
In particular, it is an object of the present invention to provide a method for producing a silicone rubber composition that provides silicone rubber with improved elongation and bending fatigue properties.

[0006]

[Means and effects for solving the problem] As a result of intensive studies to achieve the above object, the present inventors found that the state of dispersion of finely powdered silica in a silicone rubber composition affects the elongation and bending fatigue properties of silicone rubber. Therefore, in order to improve the dispersion state of this fine powder silica, raw rubber (organopolysiloxane) shown by the following composition formula (1) was divided into two parts, and as a first step, After kneading one of the organopolysiloxane raw rubbers with finely powdered silica having a specific surface area of at least 50 m2/g and a silica dispersant, the finely dispersed silica powder is brought into a very well dispersed state in the silicone rubber composition. By adopting a manufacturing method in which the other (remaining) organopolysiloxane raw rubber divided into two parts is added and kneaded in the second step, the silicone rubber obtained by the conventional manufacturing method has a higher elongation, It was discovered that the bending fatigue life was extended by 1.5 to 3 times, and in terms of absolute values, a life of over 30 million cycles was obtained in a demasher fatigue test, and furthermore, the original properties of silicone rubber were not impaired at all. It was discovered that the material has characteristics such as high hardness, high elasticity, and high tearability, and this led to the present invention.

[0007]

embedded image (In the formula, R1 is a monovalent organic group or hydroxyl group excluding the same or different fluorine-containing groups, and a is a positive number from 1.90 to 2.05.)

Therefore, the present invention provides (A) an organopolysiloxane represented by the above average composition formula (1), (B) finely powdered silica having a specific surface area of 50 m2/g or more, and (C) a silica dispersant that is uniformly dispersed. A method for producing a silicone rubber composition, which comprises kneading the silicone rubber composition, and then adding and kneading the same organopolysiloxane as the component (A) above, and a silicone rubber composition obtained by the above production method. Provided is a method for producing silicone rubber, which is characterized by adding a curing catalyst to a product and curing it.

[0009] To explain the present invention in more detail below, the method for producing a silicone rubber composition of the present invention involves mixing a blend of (A) organopolysiloxane, (B) fine powder silica, and (C) a silica dispersant. After kneading, the same organopolysiloxane as component (A) is added afterwards.

In this case, the organopolysiloxane of component (A) is represented by the following formula (1).

[0011]

[Chemical 3]

Here, R1 is a monovalent organic group or a hydroxyl group excluding the same or different fluorine-containing groups, and the organic group preferably has 1 to 10 carbon atoms, particularly 1 to 8 carbon atoms. Specifically, alkyl groups such as methyl group, ethyl group, propyl group, butyl group, alkenyl groups such as vinyl group and allyl group, aryl groups such as phenyl group and tolyl group, cycloalkyl groups such as cyclohexyl group, benzyl group, etc. aralkyl groups such as β-phenylethyl groups, or chloromethyl groups and cyanoethyl groups in which some or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms (excluding fluorine atoms), cyano groups, etc. Examples include groups. Note that a is a positive number from 1.90 to 2.05.

[0013] The organopolysiloxane is preferably a basically linear diorganopolysiloxane, and may partially contain a branched structure. Note that this organopolysiloxane may be a liquid material with a low degree of gravity, but from the viewpoint of imparting sufficient hardness to silicone rubber for practical use, it is preferable that the average degree of polymerization is 3000 or more, particularly 4000.
It is preferable that it is 6000-6000.

Regarding R1, 50 mol% or more is a methyl group, and if an organic group other than a methyl group is used, the phenyl group is 50 mol% or less, and the vinyl group is 0.01 to 6 mol%.
The molecular chain terminal of this organopolysiloxane is preferably a trialkylsilyl group containing a lower alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, or one or more of these alkyl groups. Silyl group in which two or more sets are substituted with alkoxy groups such as hydroxyl group, methoxy group, ethoxy group, propoxy group, butoxy group, dialkyl monoalkenyl containing the above alkyl group and lower alkyl group such as vinyl group, allyl group, butenyl group It is sufficient if it is blocked with a silyl group, an alkyldialkenylsilyl group, or a trialkenylsilyl group.

The finely powdered silica as component (B) is used to impart appropriate hardness and mechanical strength to silicone rubber, and has a specific surface area of 50 m2/g or more, preferably 130 m2/g or more.
~250 m2/g of finely powdered silica is preferably used. As such fine powder silica, specifically, those conventionally known as fillers for silicone rubber, such as fumed silica, precipitated silica, and silica aerogel, can be used alone or in combination of two or more. Further, these silicas may be surface-treated with silane, siloxane, silazane, etc. containing trimethylsilyl group, dimethylsilyl group, diphenylmethylsilyl group, etc.

The blending amount of the fine powder silica is based on 100 parts (parts by weight, the same applies hereinafter) of the organopolysiloxane component (A) used in the first step and the organopolysiloxane used in the second step. 10-100 parts, especially 2
It is preferable to set it as 0-70 parts. If the amount is less than 10 parts, the reinforcing properties of the silicone rubber may be insufficient, and if it exceeds 100 parts, the processability of the silicone rubber composition may become extremely difficult.

[0017] As the dispersant for component (C), the following formula (2) is used.
An organopolysiloxane represented by is preferably used.

[0018]

[C4]

Here, R2 and R3 are 1 similar to R1.
It is a valent organic group (however, it may be a fluorine-substituted hydrocarbon group), and b is a number of 4 to 100, preferably 4 to 20. The blending amount of this organopolysiloxane is the organopolysiloxane of component (A) used in the first stage and the organopolysiloxane of component (A) used in the first stage.
Total amount of organopolysiloxane used in step 100
The amount is preferably 0.5 to 15 parts, particularly 1 to 10 parts. If the amount is less than 0.5 parts, there is a risk that the processability will be significantly impaired, such as increased plastic reversion, and if it exceeds 15 parts, the silicone composition will become sticky, which may also impair the processability.

The composition of the present invention may also contain pigments, dyes, antioxidants, antioxidants, antistatic agents, flame retardants such as antimony oxide and chlorinated paraffin, boron nitride, aluminum oxide, etc., as necessary. A thermal conductivity improver or the like may be added. In addition, various known rubber compounding agents that are appropriately blended into the silicone rubber composition, such as ground silica, diatomaceous earth, iron oxide, zinc oxide, titanium oxide, carbon black, barium oxide, magnesium oxide, cerium hydroxide,
Calcium carbonate, magnesium carbonate, zinc carbonate, asbestos, glass wool, fine mica powder, fused silica powder, etc. may be added and blended to the extent that the object of the present invention is not impaired.

[0021] In the method for producing the silicone rubber composition of the present invention, first, in the first step, the above components (A), (B), and (C) are kneaded, and then, in the second step, the same as the above component (A) is kneaded. The organopolysiloxane (A') is subsequently added and kneaded. In this case, the amount of organopolysiloxane to be added as component (A') in the second stage should be 1 to 30 parts per 100 parts of organopolysiloxane as component (A) used in the first stage. is preferable, and more preferably 10 to 20 parts. If the amount of component (A') added after addition is less than 1 part, the kneading effect will be insufficient, and if it exceeds 30 parts, tensile strength, tear strength, etc. may deteriorate.

[0022] The method of adding component (A') and heat treatment when producing the silicone rubber composition of the present invention includes (A), (
The mixture of components B) and (C) is kneaded with a mixer such as a kneader, and after it becomes homogeneous, component (A') is added, and 10
at a temperature of 0 to 200°C, preferably 150 to 180°C,
A method of heat treatment for 0.5 to 5 hours, preferably 1 to 3 hours, after kneading components (A), (B), and (C) in the same manner as above, and heat treating at the same temperature and time as above, ( A') Two methods of adding the component can be adopted. Note that these heat treatments may be performed in the same kneader as the kneading, or may be further blended using rolls.

To cure the silicone rubber composition produced as described above, a curing catalyst is used as component (D). As a curing catalyst, a silicone rubber composition can be heated and cured by adding a conventionally known organic peroxide;
Curing may be performed by either an addition reaction by adding an organohydrogenpolysiloxane and a platinum-based compound or a condensation reaction, and therefore, materials necessary for these reactions can be used. Usually, a heat curing method is adopted by adding an organic peroxide, and examples of the organic peroxide include benzoyl peroxide, monochlorobenzoyl peroxide, p-methylbenzoyl peroxide, 2,4-benzoyl peroxide, t -Butylbenzoyl peroxide, dicumylbenzoyl peroxide, 2,5-bis(t-butylperoxy)-
2,5-dimethylhexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexyne, and dicarbonates such as dimyristylperoxycarbonate and dicyclododecylperoxydicarbonate, t- Examples include butyl monooxycarbonates, compounds represented by the following formula (3), and these can be used alone or in combination of two or more types.

[0024]

[Image Omitted] (In the formula, R4 is a monovalent hydrocarbon group having 3 to 10 carbon atoms.)

These organic peroxides are usually blended in an amount of 0.1 to 5 parts per 100 parts of the diorganopolysiloxane (A)+(A') used in the first step.

In addition, when the organopolysiloxane of component (A) contains an alkenyl group such as a vinyl group or an allyl group in the molecule, one molecule of silicon-bonded hydrogen atoms that undergoes an addition reaction with this alkenyl group is added. A combination of two or more organohydrogenpolysiloxanes and a platinum group metal addition reaction catalyst can be used as the curing agent.

Such platinum group metal addition reaction catalysts include, for example, platinum-based, palladium-based, and rhodium-based catalysts, among which platinum-based catalysts are preferably used. Examples of platinum-based catalysts include solid platinum supported on carriers such as platinum black, alumina, and silica, chloroplatinic acid, alcohol-modified chloroplatinic acid, complexes of chloroplatinic acid and olefins, and platinum-vinylsiloxane complexes. A complex is exemplified.

These platinum group metal addition reaction catalysts (A
)+(A') component organopolysiloxane,
0.1 to 500 ppm in terms of platinum group metal, especially 0.5
It is suitable to mix in a proportion of ~200 ppm.

[0029] Furthermore, as the organohydrogenpolysiloxane to be combined with the platinum group metal addition reaction catalyst,
For example, those represented by the following average compositional formula (4) are exemplified.

[0030]

[C6]

In the formula, R5 is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, c and d are each positive numbers, and 1
A compound that satisfies ≦c+d≦3 and has at least two silicon-hydrogen bonds in its molecule is used. Suitable examples of R5 include alkyl groups such as methyl, ethyl, propyl, and butyl, aryl groups such as phenyl and tolyl, and 3,3,3-trifluoropropyl. .

The degree of polymerization of this organohydrogenpolysiloxane is preferably 300 or less, particularly 10 to 100, and its molecular structure may be any of the conventionally known linear, cyclic, and branched structures. It may be.

The amount of the organohydrogenpolysiloxane to be blended is 0.5 to 10, particularly 1.0 to 3.0, based on the alkenyl group content (number of moles) of components (A)+(A').
It is preferable to set it to 0.

[0034]

[Examples] The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. Note that, prior to describing the examples, a method for measuring physical properties in each example will be described. (100% elongation fatigue life measurement method) Measurement was performed using a demasher type bending fatigue tester [manufactured by Toyo Seiki Co., Ltd.]. Operates continuously and displays the number of cycles until breakage. (Method for measuring keystroke durability) A rubber contact with the shape shown in Figure 1 is formed, and when the stroke and stress pattern is repeated, the change in return force due to keystrokes is determined, and the number of keystrokes to reach 50% of the initial value is determined. It is defined as the keystroke durability life. The measurement is
The measurement was carried out under the following conditions: a keystroke stroke of 1 mm and a keystroke speed of 5 times/second.

[Examples 1 and 2, Comparative Example 1] (CH3)2
99.85 mol% of SiO units and (CH3)(CH=CH
2) It consists of 0.15 mol% of SiO units, the degree of polymerization is about 7000, and the molecular chain terminals are (CH=CH2) (CH3).
86 parts of methyl vinyl polysiloxane (raw rubber) blocked with 0.5 units of 2SiO has a specific surface area of 200 m2/g.
25 parts of fumed silica [Aerosil-200 (manufactured by Nippon Aerosil Co., Ltd.)], 2 parts of dimethylpolysiloxane as a silica dispersant with a degree of polymerization of about 20 and both molecular ends capped with silanol groups, (CH3) (CH=CH2
) 4 parts of dimethylpolysiloxane containing 10 mol % of SiO units, having a degree of polymerization of approximately 20, and having both molecular chain ends blocked with silanol groups was blended and kneaded in a kneader (Blend A
).

After this formulation A becomes homogeneous, (CH3
)2SiO unit 100 mol%, the degree of polymerization is about 40
00, the molecular chain terminal is (CH=CH2)(CH3)2Si
Add 14 parts of methylvinylpolysiloxane blocked with 0.5 units of O, mix for 30 minutes, then heat to 170°C.
Heat treatment was carried out for 2 hours to obtain silicone rubber composition I (
Example 1).

[0037] Further, the same blend A as in Example 1 was kneaded and made uniform, and then heat treated at 170°C for 2 hours to form (CH3
)2SiO unit 100 mol%, the degree of polymerization is about 40
00, the molecular chain terminal is (CH=CH2)(CH3)2Si
14 parts of methylvinylpolysiloxane blocked with 0.5 units of O was added and kneaded for 30 minutes to obtain silicone rubber composition II (Example 2).

Further, in Example 1, 86 parts of methylvinylpolysiloxane (raw rubber) was added to 10
A silicone rubber composition III was obtained by blending in the same manner except that the raw rubber was not added later (Comparative Example 1).

Next, these silicone rubber compositions I
, II, and III were added with 0.5 part of 2,5-bis(t-butylperoxy)-2,5-dimethylhexane as a curing agent, and the temperature was 170°C and the pressure was 20kg/cm2.
Sheets with a thickness of 2 mm were prepared by press curing for 0 minutes, and the 100% elongation fatigue life of these sheets was measured. The results are shown in Table 1.

[0040] Also, these silicone rubber compositions I and II
, III to produce the rubber contact shown in FIG. 1,
We investigated the durability of this keystroke. The results are also listed in Table 1.

[0041]

[Table 1]

[Example 3, Comparative Example 2] (CH3)2Si
99.85 mol% O units and (CH3) (CH=CH2)
It consists of 0.15 mol% of SiO units, and the degree of polymerization is about 70.
00, the molecular chain terminal is (CH=CH2)(CH3)2Si
35 parts of wet silica [Nipsil-LP (manufactured by Nippon Silica Kogyo Co., Ltd.)] having a BET specific surface area of 190 m2/g, (CH3) (CH= CH2) SiO unit 1
5 parts of dimethylpolysiloxane containing 0 mol %, having a degree of polymerization of approximately 20, and having both molecular chain ends blocked with silanol groups was blended and kneaded using a kneader.

[0043] Next, heat treatment was performed at 170°C for 2 hours to obtain (C
H3) Consists of 100 mol% of 2SiO units, the degree of polymerization is approximately 4000, and the molecular chain terminal is (CH=CH2)(CH3)2
14 parts of methylvinylpolysiloxane blocked with 0.5 units of SiO was added and kneaded for 30 minutes to obtain silicone rubber composition IV (Example 3).

In addition, in Example 3, 86 parts of methylvinylpolysiloxane (crude rubber) used in the initial charging was replaced with 10
A silicone rubber composition V was obtained by blending in the same manner except that the raw rubber was not added later (Comparative Example 2).

Next, these silicone rubber compositions I
A sheet was prepared using V and V in the same manner as in Examples 1 and 2, and a rubber contact was made in the same manner as in Examples 1 and 2.
A similar test was conducted. The results are shown in Table 2.

[0046]

[Table 2]

[0047]

[Effects of the Invention] As explained above, according to the present invention,
It is possible to obtain a fatigue-resistant silicone rubber composition that provides a silicone rubber with excellent dynamic fatigue resistance.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a rubber contact used in characteristic tests in examples and comparative examples of the present invention.

Claims (2)

[Claims] Claim 1: (A) Organopolysiloxane represented by the following average compositional formula (1): [Formula 1] (wherein R1 is a monovalent organic group or hydroxyl group excluding the same or different fluorine-containing groups, a is a positive number from 1.90 to 2.05.) After uniformly kneading (B) fine powder silica having a specific surface area of 50 m2/g or more and (C) a silica dispersant, the above (A) component A method for producing a silicone rubber composition, which comprises post-adding and kneading an organopolysiloxane similar to the above. 2. A method for producing silicone rubber, which comprises adding a curing catalyst to the silicone rubber composition obtained in claim 1 and curing it.