JP2001055511A - Silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicone rubber composition which allows little reduction of plasticity with time and therefore shows an excellent shelf stability and yields a silicone rubber showing a low compression set. SOLUTION: The objective composition comprises (A) 100 pts.wt. organopolysiloxane of formula I: RnSiO(4-n)/2 (wherein multiple R are identical to or different from each other and are each a non-substituted or substituted monovalent hydrocarbon group; and (n) is a positive number of from 1.98 to 2.02) having a polymerization degree of 100 or larger and at least two alkenyl groups per molecule, (B) from 0.5 to 50 pts.wt. organopolysiloxane or organosilane of formula II: R2O(SiR12O)mR2 (wherein multiple R1 are identical to or different from each other and are each a non-substituted or substituted monovalent hydrocarbon group; R2 is an alkyl group or hydrogen atom; and (m) is a positive number of from 1 to 50), (C) from 5 to 100 pts.wt. reinforcing silica having a specific surface area of 50 m2/g or larger and (D) from 0.1 to 10 pts.wt. alkali metal salt of phosphoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a silicone rubber which has little storage reversion over time, has excellent storage stability, has excellent compression set characteristics, and has improved yellowing after secondary vulcanization. The present invention relates to a silicone rubber composition.

[0002]

2. Description of the Related Art Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance and the like. It is widely used in various fields, including construction, medical care, and food. For example, rubber contacts used as rubber contacts for remote controllers, typewriters, word processors, computer terminals, musical instruments, etc .; gaskets for construction; various rolls such as copy machine rolls, developing rolls, transfer rolls, charging rolls, and paper feed rolls Anti-vibration rubber for audio devices and the like; and applications such as packing for compact discs used in computers. Further, at present, demand for silicone rubber is increasing more and more, and development of silicone rubber having excellent properties is desired.

[0003] These silicone rubbers are generally used in the form of a composition containing a polyorganosiloxane having a high degree of polymerization and a reinforcing filler. This composition, for example, using a dough mixer, a mixing device such as a two-roll,
It is prepared by mixing a raw material polymer with a reinforcing filler and various dispersants.

[0004] However, it is known that a silicone rubber composition in which reinforcing silica is blended causes plasticization return with time. As a method for preventing this phenomenon, the surface of the reinforcing fine powder silica is treated with organosilazane,
A method of treating with an organopolysiloxane having a hydroxyl group at a molecular terminal or an organosiloxane having an alkoxy group at a molecular chain terminal has been known, but it has not been said to be a satisfactory method.

Japanese Patent Application Laid-Open No. Sho 59-176325 discloses a method for producing a silicone rubber composition which has little change over time, which comprises mixing a low-viscosity hydroxyl-terminated polyorganosiloxane with a filler and adding sulfuric acid, sulfonic acid, or the like. Then, a method has been proposed in which the above organosiloxane is polycondensed to increase the molecular weight.

[0006] According to this method, it is easy to mix the filler with the organosiloxane. However, this method is disadvantageous in that it is difficult to control the degree of polymerization due to the influence of moisture and fillers, and furthermore, the problem that the amount of low-molecular siloxane generated during polycondensation increases, There was also a problem that heat resistance deteriorated due to residual catalyst.

JP-A-59-176326 describes a method of polycondensing a low-viscosity hydroxyl-terminated polyorganosiloxane in the presence of an alkaline catalyst. However, this method also has the same problem as described above.

Japanese Patent Laid-Open Publication No. Hei 1-203465 discloses that the presence of a small amount of an alkali metal salt of phosphoric acid in silicone rubber improves flame retardancy. There was little effect on plastic reversion.

Therefore, in a silicone rubber composition containing reinforcing silica, a more effective measure for improving plasticization return is desired.

The present invention has been made in view of the above circumstances, and has little plasticization return over time, excellent storage stability, excellent compression set characteristics, and improved yellowing after secondary vulcanization. It is an object to provide a silicone rubber composition that provides a silicone rubber.

[0011]

Means for Solving the Problems and Embodiments of the Invention The present inventors have conducted intensive studies to achieve the above object, and as a result, (A) the degree of polymerization represented by the following average composition formula (1) 1
An organopolysiloxane having at least two alkenyl groups in one molecule of at least 00, (B) an organopolysiloxane or an organosilane having an alkoxy group or a hydroxyl group at a molecular chain terminal represented by the following general formula (2),
(C) A silicone rubber composition containing a reinforcing silica having a specific surface area of 50 m ² / g or more is added with (D) an alkali metal salt of phosphoric acid in an amount of 0.1 to 100 parts by weight based on the component (A).
By blending 10 parts by weight, the reinforcing silica as the component (C) is uniformly dispersed in the base compound, so that the plasticization return with time is extremely reduced, and excellent storage stability is obtained, and furthermore, such a storage stability is obtained. By curing the silicone rubber composition with an organic peroxide-based curing agent and an addition-reaction-based curing agent, a silicone rubber composition having excellent compression set properties and giving a silicone rubber with less yellowing after secondary vulcanization is obtained. The inventors have found out what can be obtained, and have accomplished the present invention.

Accordingly, the present invention provides: (A) 100 parts by weight of an organopolysiloxane having a degree of polymerization represented by the following average composition formula (1) of at least 100 and having at least two alkenyl groups in one molecule: R _n SiO _{(4-n) / 2} (1) (wherein R is the same or different, unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number from 1.98 to 2.02.) (B) organopolysiloxanes or organosilanes 0.5 to 50 parts by weight represented by the general formula ^{(2) R 2 O (SiR} 1 2 O) m R 2 (2) ( wherein R ¹ is the same or different unsubstituted or Substituted monovalent hydrocarbon group, m is a positive number of 1 to 50. R ² is an alkyl group or a hydrogen atom.) (C) Reinforcing silica having a specific surface area of 50 m ² / g or more 5 to 100 parts by weight ( D) 0.1 to 10 parts by weight of an alkali metal salt of phosphoric acid. A silicone rubber composition.

Hereinafter, the present invention will be described in more detail. The organopolysiloxane (A) of the silicone rubber composition of the present invention contains at least two organopolysiloxanes in one molecule represented by the following average composition formula (1). It has an alkenyl group. R _n SiO _{(4-n) / 2} (1)

In the above formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group.
For example, a methyl group, an ethyl group, a propyl group, an alkyl group such as a butyl group, a cycloalkyl group such as a cyclohexyl group,
Vinyl group, allyl group, butenyl group, alkenyl group such as hexenyl group, phenyl group, aryl group such as tolyl group, benzyl group, aralkyl group such as β-phenylpropyl group,
Or the same or different preferably selected from the group consisting of a chloromethyl group, a trifluoropropyl group, a cyanoethyl group and the like, in which some or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms, cyano groups, etc. Number 1
12, more preferably 1 to 8 unsubstituted or substituted monovalent hydrocarbon groups. Further, the organopolysiloxane of the formula (1) needs to have at least two alkenyl groups in one molecule, and 0.001 to 10 mol%, particularly 0.01 to 5 mol%, of R is an alkenyl group. And particularly preferably a vinyl group. The organopolysiloxane is blocked with a triorganosilyl group or a diorganohydroxysilyl group, for example, the molecular chain ends are blocked with a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like. And those having at least one vinyl group are particularly preferred. n is a positive number from 1.98 to 2.02.

The degree of polymerization of the organopolysiloxane of the formula (1) is 100 or more, preferably 100 to 1
It is preferably in the range of 00,000, especially 3000 to 20,000. As the component (A), two or more organopolysiloxanes having different degrees of polymerization and different structures may be used in combination.

The component (B) is an organopolysiloxane or an organosilane having an alkoxy group or a hydroxyl group at the molecular chain terminal represented by the following general formula (2), which is a treating agent for the reinforcing silica of the component (C). It acts synergistically with the component (D) described below to reduce plastic reversion and reduce yellowing after secondary vulcanization. _{^{R 2 O (SiR 1 2 O}} ) m R 2 (2)

In the formula (2), R ¹ is the same or different and is an unsubstituted or substituted monovalent hydrocarbon group, preferably having 1 to 1 carbon atoms.
12, more preferably 1 to 8, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group, a butenyl group, a hexenyl group, etc. An alkenyl group, a phenyl group, an aryl group such as a tolyl group, an aralkyl group such as a benzyl group or a β-phenylpropyl group, or a halogen atom, a cyano group, or a part of or all of the hydrogen atoms bonded to carbon atoms of these groups. Selected from a chloromethyl group, a trifluoropropyl group, a cyanoethyl group, and the like, and a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable. From the viewpoint of compatibility with the organopolysiloxane of the component (A), the R ¹ group is more preferably the same as the monovalent hydrocarbon group of the R group of the component (A).

R ² is an alkyl group or a hydrogen atom. The alkyl group preferably has 1 to 8 carbon atoms, particularly 1 to 6 carbon atoms, and examples thereof include a methyl group, an ethyl group, a propyl group and a butyl group. You. Preferred are a hydrogen atom, a methyl group and an ethyl group. m is a positive number from 1 to 50.

The degree of polymerization (m) of the organopolysiloxane of the formula (2) is from 1 to 50, preferably from 1 to 30, in particular from 1 to
A range of 10 is preferred. If the degree of polymerization is too high, (C)
In some cases, a satisfactory effect cannot be obtained as a treating agent for the reinforcing silica component.

The amount of the component (B) is 100 parts (A)
0.5 to 50 parts by weight, preferably 1 to 1 part by weight
0 parts by weight. If the amount is too large, the resulting silicone rubber composition will exhibit tackiness. If the amount is too small, kneading becomes difficult, and the plastic reversion of the composition increases.

The reinforcing silica as the component (C) is used for obtaining a silicone rubber having excellent mechanical strength, and has a specific surface area (BET method) of 50 m ² / g or more, preferably 100 to 400 m ^2. / G is used.
Examples of such reinforcing silica include fumed silica, calcined silica, precipitated silica, and the like. These may be used alone or in combination of two or more. If necessary, the surface of these reinforcing silicas may be treated with an organopolysiloxane, an organopolysilazane,
Surface-treated silica treated with a surface treatment agent such as chlorosilane or alkoxysilane may be used. In this case, precipitated silica is effectively used as the reinforcing silica. That is,
Although precipitated silica is inexpensive, it has a large yellowing after secondary vulcanization. According to the present invention, even when precipitated silica is used, its yellowing can be significantly prevented.

The amount of the component (C) is 5 to 100 parts by weight, preferably 10 to 70 parts by weight, based on 100 parts by weight of the organopolysiloxane of the component (A). If the amount is too large or too small, the processability of the obtained silicone rubber composition is reduced, and the obtained cured product does not have sufficient mechanical strength such as tensile strength and tear strength.

As the alkali metal salt of phosphoric acid as the component (D), mono-, di- and tri-alkali metal salts of phosphoric acid are used, and alkali metal salts such as sodium salt and potassium salt are used. Can be. Specific examples include monosodium dihydrogen phosphate, monopotassium dihydrogen phosphate, disodium monohydrogen phosphate, dipotassium monohydrogen phosphate, sodium phosphate, potassium phosphate and the like. The types may be used alone or two or more types may be used in combination. Furthermore, the addition form of the alkali metal salt of phosphoric acid is not particularly limited, and the phosphate may be added as it is in a solid state, or these salts may be added as an aqueous solution.

The compounding amount of the alkali metal salt of phosphoric acid of the component (D) is 0.1 to 10 parts by weight, preferably 0.15 to 100 parts by weight of the organopolysiloxane of the component (A).
To 5 parts by weight, and particularly preferably 0.1 to 5% by weight based on the whole silicone rubber composition. If the amount is too large, the heat resistance may decrease. If the amount is too small, reversion of the composition to plasticization increases, and the effect of preventing yellowing is lost.

In the present invention, in addition to the above essential components, other optional components can be added in desired amounts as needed. Specifically, non-reinforcing silicas such as crushed quartz and crystalline silica, carbon blacks such as acetylene black, furnace black and channel black, fillers and coloring agents other than the reinforcing silica of component (C) such as calcium carbonate Various additives such as a tear strength improver, a heat resistance improver, a flame retardant improver, an acid acceptor, a thermal conductivity improver and a release agent, or an organosilazane such as hexamethylsilazane as a filler dispersant. It is optional to add a dispersant other than the organopolysiloxane or the organosilane of the above formula (2).

In the present invention, the above components are uniformly mixed using a rubber kneader such as a two-roll mill, a Hanbury mixer or a dough mixer (kneader) and, if necessary, subjected to a heat treatment under normal pressure or reduced pressure. In this manner, a silicone rubber composition can be obtained, and an appropriate curing agent is added to the silicone rubber composition and cured to give a rubber-like elastic body having excellent compression set characteristics. In this case, as the curing method, a curing method using an organic peroxide and an addition curing method using an addition crosslinking agent and a catalyst are employed.

In the curing method using an organic peroxide, an organic peroxide-based curing agent is used. Specifically, benzoyl peroxide, paramethylbenzoyl peroxide, orthomethylbenzoyl peroxide, 2,5-dimethyl-2 , 5-di-t-butylperoxyhexane, t-
Organic peroxides containing no chlorine atom, such as butylperoxybenzoate, dicumyl peroxide and cumyl-t-butyl peroxide, are preferably used. In particular, for normal pressure hot air vulcanization, acyl-based organic peroxides such as benzoyl peroxide, paramethylbenzoyl peroxide, and orthomethylbenzoyl peroxide are preferred.

These organic peroxides can be used alone or
Two or more kinds may be used in combination.
It is preferably 0.1 to 10 parts by weight, particularly 0.3 to 5 parts by weight based on parts by weight. If the added amount is too small, the crosslinking may be insufficient, and if it is too large, the curing speed may not be improved.

In the curing method by the addition reaction, a usual addition reaction type curing agent is used as a curing agent, and an organohydrogenpolysiloxane having two or more, preferably three or more, Si-H groups in one molecule is used. be able to.
Examples of such an organohydrogenpolysiloxane include R ³ _{a Hb} SiO _{(4-ab) / 2} (where R ³ is the same group as R,
Preferred are a methyl group, a phenyl group and a trifluoropropyl group, and particularly preferred is a methyl group. a and b are 0 ≦ a
<3, 0 <b ≦ 3, 0 <a + b ≦ 3. ), Specifically, methyl hydrogen polysiloxane, a copolymer of methyl hydrogen polysiloxane and dimethyl polysiloxane, and the like. As the organohydrogenpolysiloxane, usually, those having 400 or less silicon atoms in one molecule are suitably used.

The amount of the above-mentioned organohydrogenpolysiloxane is preferably such that the Si-H group is 0.5 to 3 mol per 1 mol of the alkenyl group of the component (A) of the silicone rubber composition.

Further, chloroplatinic acid, an alcohol-modified chloroplatinic acid, a complex of chloroplatinic acid and ethylene or propylene, a complex of chloroplatinic acid and vinylsiloxane, etc. are compounded as a catalyst together with the above-mentioned addition reaction curing agent. Is preferred. The blending amount of the addition reaction catalyst is 0.1 part as platinum metal with respect to 100 parts by weight of the organopolysiloxane (A).
A range of 1 to 1000 ppm, particularly 1 to 500 ppm is preferred.

Further, the curing conditions of the composition of the present invention may be a method of applying sufficient heat to the decomposition of the curing agent and the vulcanization of the silicone rubber, and the molding method may be continuous vulcanization by extrusion molding, pressing. , Injection and the like are not particularly limited. The curing conditions are selected depending on the molding method, but are usually at 80 to 400 ° C. for 5 seconds to 30 minutes. Also, if necessary, the temperature may be 1 to 1 at 150 to 250 ° C.
Secondary vulcanization may be performed for about 0 hours.

[0033]

Industrial Applicability The silicone rubber composition of the present invention gives a silicone rubber having little storage reversion over time, excellent storage stability, and excellent compression set characteristics. It can be widely used in various fields such as foods and foods.

[0034]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1] Dimethylsiloxane unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxane units, 100 parts by weight of organopolysiloxane having an average degree of polymerization of about 8000, and 40 parts by weight of precipitated silica (NlPSIL-LP, manufactured by Nippon Silica Co., Ltd.) 3. It has a silanol group at both terminals as a dispersant, and has an average degree of polymerization of 4.
1. 4 parts by weight of dimethylpolysiloxane having a viscosity of 15 cs at 25 ° C.
1 part by weight of a 20% aqueous solution prepared at a ratio of 2 was added,
After kneading in a kneader, a heat treatment was performed at 180 ° C. for 1 hour to prepare a base compound 1.

To the above base compound 1, 0.4 parts by weight of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as a crosslinking agent was added, and the mixture was mixed uniformly. Press curing was performed for 10 minutes under the condition of / cm ² . Then at 200 ° C. for 4 hours
Secondary vulcanization was performed to prepare a test sheet and a test piece for measuring compression set.

Using the obtained test sheet and a test piece for measuring compression set, hardness (JISA) and compression set characteristics (150 ° C./22 hours) were measured.

The hardness after press curing was 50, and the compression set (150 ° C./22 hours) was 22%.
The hardness after post cure was 51, and the compression set (150 ° C./22 hours) was 7%.

Further, the base compound 1 was allowed to stand for 16 hours under the condition of 100 ° C., and after cooling, was put into a 6-inch 2-roll, and the state of plasticization return was observed. The time was 15 seconds.

[Example 2] Phosphoric acid 1 of phosphate to be added
A base compound 2 was obtained and cured in the same manner as in Example 1 except that the weight ratio of disodium hydrogen / sodium dihydrogen phosphate was set to 2/8.

The hardness after press curing was 50, and the compression set (150 ° C./22 hours) was 25%.
The hardness after post cure was 52, and the compression set (150 ° C./22 hours) was 10%.

Further, the base compound 2 was allowed to stand at 100 ° C. for 16 hours, cooled, then put into a 6-inch two-roll mill, and the state of plasticization return was observed. The time was 10 seconds.

Example 3 A base compound 3 was prepared in the same manner as in Example 1, except that disodium monohydrogen phosphate / monosodium dihydrogen phosphate was added as a phosphate. And cured in the same manner and evaluated.

The hardness after press curing was 49, and the compression set (150 ° C./22 hours) was 21%.
The hardness after post cure was 52, and the compression set (150 ° C./22 hours) was 9%.

Further, the base compound 3 was allowed to stand for 16 hours under the condition of 100 ° C., and after cooling, was put into a 6-inch two-roll mill, and the state of plasticization return was observed. The time was 10 seconds.

Example 4 The procedure of Example 1 was repeated, except that the amount of the aqueous phosphate solution was changed to 2.0 parts by weight, to obtain a base compound 4, which was similarly cured and evaluated.

The hardness after press curing was 49, and the compression set (150 ° C./22 hours) was 20%.
The hardness after post cure was 50, and the compression set (150 ° C./22 hours) was 5%.

Further, the base compound 3 was allowed to stand at 100 ° C. for 16 hours, cooled, and then put into a 6-inch two-roll mill, and the state of plasticization returned was observed. The time was 5 seconds.

Comparative Example 1 A base compound 5 was obtained in the same manner as in Example 1 except that no phosphate was added, and cured and evaluated in the same manner.

The hardness after press curing was 50, and the compression set (150 ° C./22 hours) was 35%.
The hardness after post cure was 55, and the compression set (150 ° C./22 hours) was 15%.

Further, the base compound 4 was allowed to stand at 100 ° C. for 16 hours, cooled and then put into a 6-inch two-roll mill, and the state of plasticization return was observed. The time was 80 seconds.

Comparative Example 2 A base was prepared in the same manner as in Example 1 except that no phosphate was added and the amount of dimethylpolysiloxane having silanol groups at both ends used as a dispersant was changed to 5 parts by weight. Compound 6 was obtained and similarly cured.

The hardness after press curing was 49, and the compression set (150 ° C./22 hours) was 36%.
The hardness after post cure was 55, and the compression set (150 ° C./22 hours) was 14%.

Further, the base compound 5 was allowed to stand for 16 hours under the condition of 100 ° C., cooled, and then put into a 6-inch two-roll mill, and the state of plasticization return was observed. The time was 30 seconds. In addition, as for this compound, the roll adhesiveness was recognized compared with Examples 1-4 and Comparative Example 1.

Comparative Example 3 A base compound 7 was obtained in the same manner as in Example 1 except that the amount of the aqueous phosphate solution was changed to 0.15 parts by weight, and cured and evaluated.

The hardness after press curing was 50, and the compression set (150 ° C./22 hours) was 33%.
The hardness after post cure was 54, and the compression set (150 ° C./22 hours) was 14%.

Further, the base compound 3 was allowed to stand at 100 ° C. for 16 hours, cooled, and then put into a 6-inch two-roll mill, and the state of plasticization return was observed. The time was 70 seconds.

[Comparative Example 4] A base compound 8 was obtained in the same manner as in Example 1 except that dimethylpolysiloxane having a terminal hydroxyl group was not added, and cured and evaluated in the same manner.

The hardness after press curing was 52, and the compression set (150 ° C./22 hours) was 20%.
The hardness after post cure was 54, and the compression set (150 ° C./22 hours) was 5%.

Further, the base compound 3 was allowed to stand at 100 ° C. for 16 hours, cooled, and then put into a 6-inch two-roll mill, and the state of plasticization return was observed. The time was 105 seconds.

Next, the cured products of the above Examples and Comparative Examples after press curing and after post curing (secondary vulcanization) were visually evaluated for yellowing. Table 1 shows the results.

[0062]

[Table 1] ：: slight yellowing is observed slightly ×: considerable yellowing is observed

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J002 CP032 CP131 CP141 DE179 DH048 DJ017 EK039 EK049 EX036 EZ009 FD010 FD017 FD149

Claims (4)

[Claims] (A) 100 parts by weight of an organopolysiloxane having a degree of polymerization represented by the following average composition formula (1) of at least 100 and having at least two alkenyl groups in one molecule: R _n SiO _{(4-n ) / 2} (1) (In the formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.98 to 2.02.) (B) The following general formula (2) in represented organopolysiloxane or organosilane 0.5 to 50 parts by weight _{^{R 2 O (SiR 1 2 O}} ) m R 2 (2) ( substituted or unsubstituted monovalent hydrocarbon of formula wherein R ¹ may be the same or different R ² is an alkyl group or a hydrogen atom, m is 1 to
It is a positive number of 50. (C) 5 to 100 parts by weight of a reinforcing silica having a specific surface area of 50 m ² / g or more (D) 0.1 to 10 parts by weight of an alkali metal salt of phosphoric acid . 2. The silicone rubber composition according to claim 1, wherein the reinforcing silica as the component (C) is precipitated silica. 3. The silicone rubber composition according to claim 1, wherein an organic peroxide-based curing agent is blended as the curing agent. 4. The silicone rubber composition according to claim 1, wherein an addition reaction type curing agent is blended as the curing agent.