KR20050045904A - Silicone rubber composition - Google Patents

Abstract

The present invention provides a silicone rubber composition which is excellent in storage stability because of little plasticization conversion over time and excellent in workability because of low adhesion to a roll, and can obtain a silicone rubber having improved resilience after curing.

The silicone rubber composition is

(A) 100 parts by mass of the organopolysiloxane represented by the following formula (1),

(B) 0.1 to 50 parts by mass of the organopolysiloxane or organosilane represented by the following formula (2), or a mixture thereof,

(C) the specific surface area is at least 50 m 2 / g, the pH of the 4 mass% aqueous suspension is 7 to 11, contains Al ₂ O ₃ and Na ₂ O, and the mass ratio of Al ₂ O ₃ / Na ₂ O is 1.2; 5 to 100 parts by mass of precipitated silica which is less than or equal to, and

(D) An effective amount of a curing agent is contained.

R ¹ _n SiO _{(4-n) / 2}

In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04.

R ² O (SiR ¹ ₂ O) _m R ²

In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, m is a positive number from 1 to 50, and R ² is an alkyl group or a hydrogen atom.

Description

Silicone Rubber Composition

The present invention relates to a silicone rubber composition which is excellent in storage stability because of little plasticization conversion over time and excellent in workability because of low adhesion to a roll, and can obtain a silicone rubber having improved resilience after curing.

Silicone rubber is widely used in various fields such as electrical appliances, automobiles, construction, medical, food, etc. because it has excellent weather resistance, electrical properties, low compression permanent distortion, heat resistance, cold resistance, and the like. For example, rubber contacts used as contacts in remote controllers, typewriters, word processors, computer terminals, musical instruments and the like; Construction gaskets; Various rolls such as a copying machine roll, a developing roll, a transfer roll, a charging roll, and a paper feed roll; Anti-vibration rubber such as an audio device; Uses, such as the packing for compact discs used for a computer, are mentioned. At present, the demand of silicone rubber is increasing and development of silicone rubber which has the outstanding characteristic is calculated | required. Generally these silicone rubbers are used in the form of compositions containing high degree of polymerization of polyorganosiloxanes (base polymers) and reinforcing fillers. This composition is manufactured by mixing a reinforcing filler and various dispersing agents with a base polymer using mixing apparatuses, such as a dough mixer and a biaxial roll mill, for example.

Silicone rubber compositions incorporating fine powder silica as reinforcing fillers are known to cause plasticization conversion over time. As a method for preventing this phenomenon, a method of treating the surface of the reinforcing fine powder silica with an organosilazane, an organopolysiloxane having a hydroxyl group at the molecular terminal, or an organosiloxane having an alkoxy group at the molecular chain terminal is known. .

Japanese Patent Application Laid-Open No. 59-176325 discloses a method for producing a silicone rubber compound with little change over time, by mixing a low-viscosity hydroxyl terminal polyorganosiloxane and a filler, adding sulfuric acid, sulfonic acid, and the like to the polyorgano. A method for obtaining a high molecular weight silicone rubber compound by polycondensation of siloxane is presented. According to this method, it is easy to mix filler with organosiloxane certainly, but it was difficult to adjust the degree of polymerization by the influence of moisture or the filler. In addition, this method has a problem that the amount of low molecular siloxane produced when polycondensation increases, or that the heat resistance deteriorates due to residual catalyst.

Japanese Patent Laid-Open No. 59-176326 discloses a method for polycondensing a low viscosity hydroxyl terminal polyorganosiloxane in the presence of an alkaline catalyst. This method had the same problem as above.

Moreover, the presence or absence of adhesiveness to a roll etc. is mentioned as an operation | movement important characteristic of the unvulcanized silicone rubber composition. If the adhesiveness to a roll etc. is high, workability in a biaxial roll mill will fall, and calender shaping | molding etc. become difficult. In addition, there is a problem that the adhesion is increased simply by increasing the silica treatment to prevent plasticization conversion.

Japanese Patent Laid-Open No. 63-207854 describes a method of adding a basic substance to a composition as a method of producing a silicone rubber composition capable of obtaining a cured rubber having high tear strength. Zinc stearate, calcium stearate, and the like exemplified therein do not significantly change the molecular weight of the polymer, and are effective in preventing adhesion. However, these have a problem of increasing plasticization conversion. Moreover, in this method, basic substances, such as ammonia water, can be used, which became the cause of coloring of a silicone rubber composition.

In Japanese Patent Laid-Open No. 62-199652, the chemical composition of the organopolysiloxane component in the compound, provided that the acid strength of the mixture of the silicone rubber compound and the particulate silica or organopolysiloxane is in the range of 4.0 ≦ pKa ≦ 9.2 in the nonpolar solvent. It has been reported that it does not change at any time during manufacture and after long term storage. However, no workability is described here.

In addition, in Japanese Unexamined Patent Application Publication No. 6-1878, precipitated silica having a pH of 7.5 to 9, which is less colored when blended with silicone rubber, has been proposed as a filler. However, there was no base for their existence ratio of the dispersant or Al ₂ O ₃ and Na ₂ O.

It is an object of the present invention to provide a silicone rubber composition which is excellent in storage stability because of little plasticization conversion over time and excellent in workability because of low adhesion to a roll, and can obtain a silicone rubber having improved resilience after curing. It is.

The present inventors earnestly examined in order to achieve the said objective. As a result, the following silicone rubber composition was found to be excellent in storage stability because of little plasticization conversion over time and excellent in workability because of little adhesion to rolls.

That is, the present invention

(A) 100 parts by mass of the organopolysiloxane represented by the following formula (1),

(B) 0.1 to 50 parts by mass of the organopolysiloxane or organosilane represented by the following formula (2), or a mixture thereof,

(C) the specific surface area is at least 50 m 2 / g, the pH of the 4 mass% aqueous suspension is 7 to 11, contains Al ₂ O ₃ and Na ₂ O, and the mass ratio of Al ₂ O ₃ / Na ₂ O is 1.2; 5 to 100 parts by mass of precipitated silica which is less than or equal to, and

(D) It provides the silicone rubber composition characterized by containing an effective amount of a hardening | curing agent.

<Formula 1>

R ¹ _n SiO _{(4-n) / 2}

In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04.

<Formula 2>

R ² O (SiR ¹ ₂ O) _m R ²

In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, m is a positive number from 1 to 50, and R ² is an alkyl group or a hydrogen atom.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

[(A) component]

The organopolysiloxane of (A) component is a main component of the silicone rubber composition of this invention, and is represented by following General formula (1).

<Formula 1>

R ¹ _n SiO _{(4-n) / 2}

In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04.

In formula (1), R ¹ represents the same or different unsubstituted or substituted, preferably a monovalent hydrocarbon group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. Examples of the monovalent hydrocarbon group represented by R ¹ include an alkyl group such as methyl group, ethyl group, propyl group, butyl group, cycloalkyl group such as cyclohexyl group, alkenyl group such as vinyl group, allyl group, butenyl group, hexenyl group, and phenyl group. , Aryl groups such as tolyl groups, aralkyl groups such as β-phenylpropyl groups, or chloromethyl groups and trifluoropropyl groups in which part or all of the hydrogen atoms bonded to carbon atoms of these groups are replaced with halogen atoms, cyano groups, and the like. And cyanoethyl group. Especially, a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable, and a methyl group and a vinyl group are especially preferable.

In addition, n is a positive number of 1.95 to 2.04, preferably 1.98 to 2.02. If n is not in this range, the hardened | cured material obtained may not show sufficient rubber elasticity. Therefore, although the said organopolysiloxane is substantially linear, it may be branched in the range which does not impair rubber elasticity.

In addition, the molecular chain terminal of the organopolysiloxane is preferably sealed with triorganosilyl groups such as trimethylsilyl group, dimethylvinylsilyl group, dimethylhydroxysilyl group, methyldivinylsilyl group, trivinylsilyl group, It is especially preferable that it is sealed with the triorganosilyl group which has one or more vinyl groups.

In the present invention, the organopolysiloxane preferably has two or more alkenyl groups in the molecule. Moreover, it is preferable that 0.01-5 mol%, especially 0.02-0.5 mol% in R <^1> is an alkenyl group in terms of sclerosis | hardenability of the composition, rubber elasticity, etc. of the hardened | cured material. As an alkenyl group, a vinyl group is especially preferable.

The lower limit of the degree of polymerization is preferably 100, more preferably 3000, further preferably 4000, and the upper limit of the degree of polymerization is preferably 100,000, more preferably 20,000, even more preferably 10,000. These can also use together 2 or more types from which a polymerization degree and molecular structure differ according to the objective.

As a more specific example of the organopolysiloxane represented by the said Formula (1), what is represented by following formula (3) and (4) is mentioned.

In formula, a is an integer of 100 or more, b is an integer of 0 or more, and c is an integer of 2 or more.

Especially, what is represented by the said Formula (3) is especially preferable.

[(B) component]

The component (B) is an organopolysiloxane or organosilane represented by the following formula (2), or a mixture thereof, and has an alkoxy group or a hydroxyl group at the terminal of the molecular chain. Component (B) is used as a treatment agent for treating the reinforcing silica of component (C) and as a dispersant.

<Formula 2>

R ² O (SiR ¹ ₂ O) _m R ²

In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, m is a positive number from 1 to 50, and R ² is an alkyl group or a hydrogen atom.

In formula (2), R ¹ represents the same or different unsubstituted or substituted, preferably a monovalent hydrocarbon group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. Examples of the monovalent hydrocarbon group represented by R ¹ include an alkyl group such as methyl group, ethyl group, propyl group, butyl group, cycloalkyl group such as cyclohexyl group, alkenyl group such as vinyl group, allyl group, butenyl group, hexenyl group, and phenyl group. , Aryl groups such as tolyl groups, aralkyl groups such as β-phenylpropyl groups, or chloromethyl groups and trifluoropropyl groups in which part or all of the hydrogen atoms bonded to carbon atoms of these groups are replaced with halogen atoms, cyano groups, and the like. And cyanoethyl group. Especially, a methyl group, a vinyl group, and a phenyl group are preferable, and a methyl group and a vinyl group are especially preferable. Further, R ¹ in component (B) to ensure the compatibility with the organopolysiloxane of component (A) is preferably the same as R ¹ in the component (A).

In formula (2), R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms. As an example of R <^2> , alkyl groups, such as a hydrogen atom or a methyl group, an ethyl group, a propyl group, a butyl group, are mentioned. In particular, a hydrogen atom, a methyl group, and an ethyl group are preferable.

When the degree of polymerization (m in the formula (2)) of the component (B) exceeds 50, the effect as a treatment agent for treating the reinforcing silica of the component (C) is reduced. Thus m is 1 to 50, preferably 1 to 30, more preferably 2 to 25.

When the compounding quantity of (B) component exceeds 50 mass parts per 100 mass parts of (A) component, adhesion of the silicone rubber composition obtained will generate | occur | produce. On the other hand, when the compounding quantity of (B) component is less than 0.1 mass part per 100 mass parts of (A) component, kneading becomes difficult and plasticization conversion becomes large. Therefore, the compounding quantity of (B) component is 0.1-50 mass parts per 100 mass parts of (A) component, Preferably it is 0.5-20 mass parts, More preferably, it is 1-10 mass parts.

[(C) component]

Precipitated silica of component (C) imparts properties such as mechanical strength. Precipitated silica of (C) component has a specific surface area of 50 m <2> / g or more, Preferably it is 100-400 m <2> / g. If necessary, silica whose surface is surface-treated with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like may be used.

The pH of the 4 mass% aqueous suspension of precipitated silica is 7 to 11, preferably 7.5 to 9.5, more preferably 8 to 9 (hereinafter the pH of the precipitated silica represents the pH in a 4 mass% aqueous suspension). In addition, if the pH is too high, the specific surface area of the precipitated silica decreases with time, and the plasticity is lowered.

In addition, some precipitates exist in precipitated silica as a result of the production method. In the present invention, the mass ratio (hereinafter referred to as Al ₂ O ₃ / Na ₂ O) of the Al ₂ O ₃ content to the Na ₂ O content is 1.2 or less. , Preferably 0.1 to 1.0, particularly preferably 0.2 to 0.9. When it exceeds 1.2, plasticization conversion etc. become large.

Al ₂ O ₃ in the precipitated silica of component (C) 0.01-0.7 mass% is preferable, as for content, 0.02-0.5 mass% is more preferable, 0.03-0.4 mass% is more preferable. The content of Na ₂ O of the precipitated silica of the component (C) is from 0.05 to 0.8% by mass is preferable, and more preferably 0.08 to 0.6 mass%, and more preferably, 0.1 to 0.5% by weight.

These precipitated silicas can be obtained from silica manufacturers such as Doso and Silica.

The compounding quantity of (C) component is 5-100 mass parts with respect to 100 mass parts of organopolysiloxane which is (A) component, Preferably it is 10-70 mass parts, More preferably, it is 20-70 mass parts. When the compounding quantity of (C) component exceeds 100 mass parts with respect to 100 mass parts of (A) component, the workability of the silicone rubber composition obtained falls. Moreover, when the compounding quantity of (C) component is less than 5 mass parts with respect to 100 mass parts of (A) component, the hardened | cured material obtained by hardening | curing this silicone rubber composition will not have sufficient mechanical strength, such as sufficient tensile strength and tear strength.

[(D) component]

(D) component is a hardening | curing agent for hardening the composition (base compound) which consists of said (A)-(C) component. As a hardening | curing agent, the combination of an organic peroxide, an addition crosslinking agent (organohydrogenpolysiloxane), and a hydrosilylation catalyst etc. are mentioned, for example.

As an organic peroxide used as a hardening | curing agent, benzoyl peroxide, paramethyl benzoyl peroxide, orthomethyl benzoyl peroxide, 2, 5- dimethyl- 2, 5- di- t-butyl peroxy hexane, t-butyl per, for example Oxybenzoate, dicumyl peroxide, cumyl-t-butyl peroxide and the like. Among these, acyl organic peroxides such as benzoyl peroxide, paramethylbenzoyl peroxide and orthomethylbenzoyl peroxide are preferably used for atmospheric pressure hot air vulcanization. These organic peroxides may be used individually by 1 type, and may use 2 or more types together. The addition amount of these organic peroxides is 0.1-10 mass parts with respect to 100 mass parts of organopolysiloxane which is (A) component, Preferably it is 0.3-5 mass parts. It is because bridge | crosslinking fully advances in these ranges, and a hardening rate can be improved with addition amount. Silicone rubber can be easily obtained by adding and hardening these organic peroxides to a base compound.

When using the combination of an addition crosslinking agent (organohydrogenpolysiloxane) and a hydrosilylation catalyst as a hardening | curing agent, what has two or more alkenyl groups as organopolysiloxane which is (A) component is selected.

As organohydrogenpolysiloxane, what has 2 or more of hydrogen atoms couple | bonded with the silicon atom in a molecule | numerator is mentioned, for example.

As a hydrosilylation catalyst, a platinum type compound, a rhodium type compound, etc. are mentioned, for example.

The amount of organohydrogenpolysiloxane added is 0.5 to 5, preferably the ratio (SiH / Si-alkenyl group) of the number of hydrogen atoms bonded to the silicon atom in the organohydrogenpolysiloxane and the number of alkenyl groups in component (A). Preferably in an amount of 0.7 to 2. The amount of the hydrosilylation catalyst added is 0.1 to 2000 ppm, preferably 1 to 1000 ppm, more preferably 5 to 500 ppm relative to the organopolysiloxane of component (A).

[Other Ingredients]

In addition to the above components, the composition of the present invention includes, as necessary, non-reinforced silicas such as crushed quartz and crystalline silica, carbon blacks such as acetylene black, furnace black, channel black, fillers such as calcium carbonate, colorants, and tear strength enhancers. Various additives, such as a heat resistance improving agent, a flame retardant improving agent, a hydroxyl agent, and a thermal conductivity improving agent, a mold release agent, a carbon function silane, etc. can also be added.

[Production and Curing of Compositions]

A rubbery elastic body can be obtained by mixing and hardening the said (D) component with the base compound manufactured from the said (A)-(C) component.

The said base compound can be obtained by mixing uniformly using rubber kneading machines, such as a biaxial roll mill, a Benbury mixer, and a dough mixer (kneading machine), heating the said (A)-(C) component. 80-250 degreeC is preferable, as for the temperature of heat processing, 100-200 degreeC is more preferable, and 140-180 degreeC is still more preferable. Moreover, 30 minutes-10 hours are preferable, as for heat processing time, 1 to 4 hours are more preferable, and 1 to 2 hours are still more preferable.

The curing method of the silicone rubber composition of the present invention is not particularly limited as long as it is a method of applying sufficient heat to decomposition of the curing agent and vulcanization of the silicone rubber. Moreover, the shaping | molding method is not restrict | limited in particular, For example, continuous vulcanization by press molding, pressurization, injection, etc. are mentioned. In addition, as necessary, secondary vulcanization may be performed at 150 ° C to 250 ° C for about 1 to 10 hours.

<Example>

Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to a following example.

<Example 1>

(A) 100 parts by mass of an organopolysiloxane containing 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units, and having an average degree of polymerization of about 6000, and (B) silanol groups at both ends 4.4 parts by mass of dimethylpolysiloxane having an average degree of polymerization of 15 and a viscosity of 30 cs at 25 ° C, and (C) pH 8.9, Al ₂ O ₃ / Na ₂ O = 0.77, Al ₂ O ₃ content 0.33 mass% , 0.43 mass% of Na ₂ O content, and 40 mass parts of precipitated silica (manufactured by Nippon Silica Co., Ltd.) having a BET specific surface area of 164 m 2 / g were mixed and kneaded with a kneader. This was heat-processed at 180 degreeC for 2 hours, and compound 1 was manufactured.

In addition, the average degree of polymerization here is calculated from the composition of the monomer used for organopolysiloxane synthesis | combination.

2 parts by mass of 2,5-dimethyl-2,5-di-t-butylperoxyhexane was added as a crosslinking agent with respect to 100 parts by mass of the base compound, and mixed uniformly. Press hardening for minutes. Subsequently, secondary vulcanization was carried out at 200 ° C. for 4 hours to prepare test sheets and test specimens for compressive permanent distortion and rebound elasticity measurements. Resilience was measured by JIS-K6255 and other mechanical characteristics in the method according to JIS-K6249.

Plasticization conversion test

The silicone rubber compound was left to stand for 16 hours under the condition of 120 ° C. After cooling, this was put into a 6-inch biaxial roll mill to observe the plasticization conversion state. The time until the surface was smooth was measured. The shorter this time is, the smaller the plasticization conversion can be.

Adhesive evaluation

The adhesiveness at the time of kneading a rubber compound with a biaxial roll mill was evaluated for good workability (without stickiness) in two stages called ○ and bad (tackiness).

<Example 2>

(C) component as _{pH 8.55, Al 2 O 3 /} Na 2 O = 0.84, Al 2 O 3 content of 0.26 mass%, Na ₂ O content of 0.31 mass%, BET precipitated silica (available from Nippon silica of specific surface area 193 ㎡ / g ( Note) The rubber compound was manufactured by the method similar to Example 1 except having used 40 mass parts of manufacture).

<Example 3>

Component (C) as _{pH 8.0, Al 2 O 3 /} Na 2 O = 0.32, Al 2 O 3 content of 0.06 mass%, Na ₂ O content of 0.19 mass%, BET precipitated silica (available from Nippon silica of specific surface area 188 ㎡ / g ( Note) The rubber compound was manufactured by the method similar to Example 1 except having used 40 mass parts of manufacture).

Comparative Example 1

Component (C) as _{pH 6.1, Al 2 O 3 /} Na 2 O = 1.44, Al 2 O 3 content of 0.26 mass%, Na ₂ O content of 0.18 mass%, BET precipitated silica (available from Nippon silica of specific surface area 201 ㎡ / g ( Note) The rubber compound was manufactured by the method similar to Example 1 except having used 40 mass parts of manufacture).

Comparative Example 2

A rubber compound was prepared in the same manner as in Comparative Example 1 except that 0.09 part of zinc stearate was added.

The silicone rubber composition of the present invention has excellent storage stability because of little plasticization conversion over time, and excellent workability because of low adhesion to the roll, and after curing, a silicone rubber having improved resilience can be obtained. Therefore, the silicone rubber composition of the present invention is a silicone rubber having excellent properties and can be widely used in various fields including electric appliances, automobiles, construction, medical care, and food.

Claims (2)

(A) 100 parts by mass of the organopolysiloxane represented by the following formula (1), (B) 0.1 to 50 parts by mass of the organopolysiloxane or organosilane represented by the following formula (2), or a mixture thereof, (C) the specific surface area is at least 50 m 2 / g, the pH of the 4 mass% aqueous suspension is 7 to 11, contains Al ₂ O ₃ and Na ₂ O, and the mass ratio of Al ₂ O ₃ / Na ₂ O is 1.2; 5 to 100 parts by mass of precipitated silica which is less than or equal to, and (D) Silicone rubber composition containing an effective amount of a hardening | curing agent. <Formula 1> R ¹ _n SiO _{(4-n) / 2} In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04. <Formula 2> R ² O (SiR ¹ ₂ O) _m R ² In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, m is a positive number from 1 to 50, and R ² is an alkyl group or a hydrogen atom. After mixing 100 mass parts of (A) component, 0.1-50 mass parts of (B) component, and 5-100 mass parts of (C) component of Claim 1, heat-processing at 80-250 degreeC, the effective amount of (D) The manufacturing method of the silicone rubber composition of Claim 1 which mixes components.