JP5686530B2 - Silicone rubber composition - Google Patents

Description

  The present invention relates to a silicone rubber composition that provides a cured product (silicone rubber) having both excellent tear strength and compression set resistance.

  In general, when the silicone rubber is intended to improve its tear strength, it can be considered to increase the surface area of the reinforcing silica. When looking at the polymer, it has been proposed to blend two or more types of silicone polymers with different viscosities and vinyl group contents to make the dispersion of the cross-linking points non-uniform and increase the tear strength. .

However, in the method using silica having a large surface area and high activity, even if a sufficient tear strength is obtained, the compression set has an adverse effect due to the surface activity. Further, non-uniform cross-linking points are easily affected by polymer cutting due to oxidative degradation at the time of heat resistance, resulting in adverse effects on heat resistance and compression set. As a countermeasure, a method of adding a vinyl group-containing three-dimensional network silicone resin has been proposed, but it has not been sufficient.
In addition, the following literature is mentioned as a prior art relevant to this invention.

Japanese Patent Publication No. 47-18419 JP-A-4-283265 Japanese Patent No. 3106917

  The present invention has been made to overcome the above-described problems, and an object of the present invention is to provide a silicone rubber composition that provides a cured product having both high tear strength and compression set resistance.

  As a result of intensive studies to achieve the above object, the present inventor has found that it is preferable to use a silicone rubber compound in which a raw rubber-like dimethyl silicone polymer and preferably a raw rubber-like phenyl group-containing silicone polymer are blended. The present inventors have found out that it is optimal for achieving both strength and compression set resistance, and have made the present invention.

（式中、Ｒ ³ 、Ｒ ⁴ は同一又は異種の非置換もしくは置換の１価炭化水素基であり、Ｒ ³ 基及びＲ ⁴ 基全体の少なくとも１モル％はフェニル基であり、ｎは１〜３０の整数である。）
で示される両末端シラノール基封鎖シリコーンオリゴマー
（ａ）成分と（ｂ）成分の合計１００質量部に対して０．１〜２０質量部
を含有してなるシリコーンゴム組成物を提供する。 Therefore, the present invention
(A) The following general formula (1)
R ¹ _a SiO _{(4-a) / 2} (1)
(Here, R ¹ is the same or different unsubstituted or substituted aliphatic monovalent hydrocarbon group, and 0.001 to 20 mol% in all R ¹ groups is an alkenyl group. A is 1.90. It is a positive number of ~ 2.05.)
1 to 99 parts by mass of an organopolysiloxane represented by
(B) The following general formula (2)
R ² _b SiO _{(4-b) / 2} (2)
(Here, R ² is a monovalent hydrocarbon radical unsubstituted or substituted in the same or different, 1 to 20 mol% of the total R ² group is phenyl group, 0.001 in all R ² groups ˜20 mol% is an alkenyl group, b is a positive number of 1.90 to 2.05.)
1 to 99 parts by mass of a phenyl group-containing organopolysiloxane represented by
However, the sum total of (a) component and (b) component is 100 mass parts.
(C) 10 to 100 parts by mass of reinforcing silica having a specific surface area of at least 50 m ² / g,
(D) necessary amount of vulcanizing agent for silicone rubber ,
(E) As a silica dispersant

(Wherein R ³ and R ⁴ are the same or different unsubstituted or substituted monovalent hydrocarbon group, at least 1 mol% of the entire R ³ group and R ⁴ group are phenyl groups, and n is 1 to 1) (It is an integer of 30.)
Silanol group-blocked silicone oligomers represented by
A silicone rubber composition containing 0.1 to 20 parts by mass with respect to a total of 100 parts by mass of the component (a) and the component (b) is provided.

  According to the present invention, by blending an organopolysiloxane containing an alkenyl group and a phenyl group-containing organopolysiloxane into a silicone rubber compound, a silicone rubber molded article having excellent tear strength and simultaneously excellent compression set. Can be obtained.

Hereinafter, the present invention will be described in more detail.
(A) Organopolysiloxane In the present invention, the organopolysiloxane of the component (a) used as the base component is represented by the following general formula (1).
R ¹ _a SiO _{(4-a) / 2} (1)
A linear alkenyl group-containing organopolysiloxane which contains an aliphatic hydrocarbon group as a monovalent hydrocarbon group bonded to a silicon atom in the molecule and does not contain an aryl group such as a phenyl group. It is.

Here, R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, a cycloalkyl group such as a cyclohexyl group, an alkenyl group such as a vinyl group, an allyl group, a butenyl group or a hexenyl group, or a group thereof. The same or different, preferably 1 to 10 carbon atoms, selected from a chloromethyl group, a trifluoropropyl group, a cyanoethyl group, or the like in which some or all of the hydrogen atoms bonded to the carbon atom are substituted with a halogen atom, a cyano group, More preferably an unsubstituted or substituted aliphatic monovalent hydrocarbon group having 1 to 8 carbon atoms. In this case, R ¹ must have at least two aliphatic unsaturated groups (alkenyl groups), but the content of aliphatic unsaturated groups in R ¹ is 0.001 to 20 mol%. In particular, 0.025 to 10 mol% is preferable. The R ¹ group other than the aliphatic unsaturated group (alkenyl group) is preferably an alkyl group, particularly a methyl group, and the component (a) is preferably an alkenyl group-containing dimethylpolysiloxane.

  Moreover, a is a positive number of 1.90 to 2.05. The organopolysiloxane of the above formula (1) is preferably basically linear, but may be one or a mixture of two or more having different molecular structures.

  Further, the organopolysiloxane has a raw rubber-like component (that is, non-liquid without self-fluidity) at room temperature (25 ° C. ± 10 ° C.) having an average degree of polymerization of 100 to 10,000, particularly 3,000 to 8,000. Component). In addition, this average degree of polymerization can be normally calculated | required as a weight average degree of polymerization of polystyrene conversion in a gel permeation chromatography (GPC) analysis (hereinafter the same).

The organopolysiloxane of component (b) is represented by the following general formula (2)
R ² _b SiO _{(4-b) / 2} (2)
Is a linear alkenyl group-containing organopolysiloxane containing 1 to 20 mol% of a phenyl group as a monovalent hydrocarbon group bonded to a silicon atom.

R ² is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group; a cycloalkyl group such as a cyclohexyl group; an alkenyl group such as a vinyl group, an allyl group, a butenyl group or a hexenyl group; The same or different groups selected from a chloromethyl group, a trifluoropropyl group, a cyanoethyl group, etc. in which a part of or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with a halogen atom, a cyano group, etc. Preferably it is a C1-C10, More preferably, it is a C1-C8 unsubstituted or substituted monovalent hydrocarbon group. R ² needs to contain 1 to 20 mol%, preferably 2 to 10 mol% of a phenyl group. Further, R ² must have at least two aliphatic unsaturated groups (alkenyl groups), and the content of aliphatic unsaturated groups in R ² is 0.001 to 20 mol%, particularly It is preferable that it is 0.025-5 mol%.
The R ² group other than the phenyl group and the aliphatic unsaturated group (alkenyl group) is preferably an alkyl group, particularly a methyl group, and the component (b) is an alkenyl group-containing phenylmethylpolysiloxane. preferable.

  B is a positive number of 1.90 to 2.05. The organopolysiloxane of the above formula (2) is preferably basically linear, but may be one or a mixture of two or more having different molecular structures.

  Further, the organopolysiloxane has a raw rubber-like component (that is, non-liquid without self-fluidity) at room temperature (25 ° C. ± 10 ° C.) having an average degree of polymerization of 100 to 10,000, particularly 3,000 to 8,000. Component).

  The (b) component phenyl group-containing organopolysiloxane is essentially incompatible with the organopolysiloxane (particularly dimethylpolysiloxane) of the component (a) to some extent, and this low compatibility. As a result, it is considered that the tear strength can be improved since the crack growth is inhibited in the tear strength test in the cured rubber after vulcanization.

  The blending ratio of the component (a) to the component (b) is such that the component (a) is 1 to 99 parts by weight, preferably 10 to 90 parts, based on a total of 100 parts by weight of the components (a) and (b). Parts by mass, more preferably 20-80 parts by mass, still more preferably 30-70 parts by mass, with the remainder being component (b) (ie 99-1 parts by mass, preferably 90-10 parts by mass, more preferably 80 -20 mass parts, more preferably 70-30 mass parts) from the viewpoint of tear strength and compression set resistance.

(C) Reinforcing silica having a specific surface area of at least 50 m ² / g has a specific surface area by a BET adsorption method of at least 50 m in order to improve mechanical strength such as moderate hardness and tensile strength of silicone rubber. ² / g, in particular 100 to 400 m ² / g of silica are used. As such silica, fumed silica, calcined silica, precipitated silica, or the like is used alone or in combination of two or more. These silicas may be surface-treated with chain organopolysiloxane, cyclic organopolysiloxane, hexamethyldisilazane, dichlorodimethylsilane or the like.

  Such silica is blended in a proportion of 10 to 100 parts by weight, particularly 10 to 50 parts by weight, based on a total of 100 parts by weight of the organopolysiloxanes of component (a) and component (b). Moreover, even if it is blended in a small amount, the processability of the silicone rubber is deteriorated, and sufficient mechanical strength is hardly obtained.

  As the component (d) silicone rubber vulcanizing agent (curing agent), a known organic peracid peroxide vulcanizing agent or platinum addition type vulcanizing agent used when vulcanizing and molding silicone rubber can be used. .

  Examples of the organic peroxide include benzoyl peroxide, orthomethylbenzoyl peroxide, paramethylbenzoyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, and the like. A combination of the above may also be used. In addition, it is preferable that the compounding quantity shall be 0.1-5 mass parts with respect to 100 mass parts in total of the organopolysiloxane of (a) component and (b) component.

  When curing by addition reaction, a combination of an organohydrogenpolysiloxane and a platinum catalyst is used as a vulcanizing agent (curing agent). Examples of platinum-based catalysts include platinum element alone, platinum compounds, platinum complexes, chloroplatinic acid, alcohol compounds of chloroplatinic acid, aldehyde compounds, ether compounds, and complexes with various olefins. The addition amount of the platinum-based catalyst may be in the range of 1 to 2,000 ppm, particularly 2 to 1,000 ppm in terms of the mass of platinum atoms with respect to the sum of the organopolysiloxanes of the components (a) and (b). desirable.

On the other hand, the organohydrogenpolysiloxane may have a linear, branched, cyclic, or three-dimensional network structure, but the degree of polymerization (number of silicon atoms in the molecule) is 300 or less ( Usually, 2 to 300) are preferable, more preferably 3 to 200, and still more preferably about 4 to 150. The organohydrogenpolysiloxane contains at least 2 (usually 2 to 300), preferably 3 to 200, more preferably 4 to 150 hydrogen atoms (SiH groups) bonded to silicon atoms in the molecule. This silicon atom-bonded hydrogen atom (SiH group) is bonded to a silicon atom in the middle of the molecular chain (non-terminal), even if it is bonded to the silicon atom at the end of the molecular chain. Or both of them.
Moreover, as an organo group (unsubstituted or substituted monovalent hydrocarbon group) bonded to a silicon atom other than a silicon atom-bonded hydrogen atom, the same as R ² in the general formula (2) of the component (b) In particular, an unsubstituted or substituted monovalent hydrocarbon group excluding an aliphatic unsaturated bond may be mentioned.

Examples of the organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogensiloxane cyclic polymer, and methylhydrogensiloxane.・ Dimethylsiloxane cyclic copolymer, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, trimethylsiloxy-blocked methylhydrogenpolysiloxane, trimethylsiloxy-blocked methylhydrogensiloxane / dimethylsiloxane copolymer Coalesced, dimethylhydrogensiloxy-blocked dimethylpolysiloxane, dimethylhydrogensiloxy-blocked methylhydrogenpolysiloxane, dimethylhydrogen Proxy group blocked methylhydrogensiloxane-dimethylsiloxane copolymer, dimethyl siloxane units _{(H (CH 3) 2 SiO} 0.5 units) and the low viscosity fluid consisting of SiO ₂ units, 1-propyl -3,5,7 -Trihydrogen-1,3,5,7-tetramethylcyclotetrasiloxane, 1,5-dihydrogen-3,7-dihexyl-1,3,5,7-tetramethylcyclotetrasiloxane The

  The addition amount of the organohydrogenpolysiloxane as the curing agent is an organohydrogenpolysiloxane with respect to the total of aliphatic unsaturated groups (alkenyl groups) in the organopolysiloxanes of the components (a) and (b). It is desirable that silicon atom-bonded hydrogen atoms (SiH groups) are used in a proportion of 50 to 500 mol%.

（式中、Ｒ³、Ｒ⁴は同一又は異種の非置換もしくは置換の１価炭化水素基であり、Ｒ³基及びＲ⁴基全体の少なくとも１モル％はフェニル基であり、ｎは１〜３０の整数である。） In the present invention, as a silica dispersant, both ends silanol groups (hydroxyl groups bonded to silicon atoms) blocked silicone oligomers of the component (e) represented by the following general formula (3) (that is, both ends silanol group blocked diorganosiloxane) An appropriate amount of oligomer) can be added as required.

(Wherein R ³ and R ⁴ are the same or different unsubstituted or substituted monovalent hydrocarbon group, at least 1 mol% of the entire R ³ group and R ⁴ group are phenyl groups, and n is 1 to 1) (It is an integer of 30.)

Here, examples of R ³ and R ⁴ include those similar to R ² in the general formula (2) of the component (b), preferably those excluding aliphatic unsaturated bonds such as alkenyl groups. . Particularly, as the R ^3, R ^4, a methyl group, typically such as ethyl group, 1 to 6 carbon atoms, in particular the recommended lower alkyl group having 1 to 4 carbon atoms, R ³ groups and R ⁴ groups It is desirable that at least 1 mol% (usually about 1 to 50 mol%, particularly about 10 to 50 mol%) of the total of these is a phenyl group. Although n is an integer of 1-30, Preferably it is 2-20, More preferably, it is 3-15, Most preferably, it is 4-10. Thus, it is considered that the component (a) (for example, dimethylsiloxane polymer) and the component (b) (phenyl group-containing organopolysiloxane) can have a certain degree of compatibility. Specifically, the following structures (4) to (6) are conceivable.

（但し、Ｍｅ、φはそれぞれ、メチル基、フェニル基を示す。）

(However, Me and φ represent a methyl group and a phenyl group, respectively.)

  (E) When adding a component, the addition amount is 0.1-20 mass parts with respect to a total of 100 mass parts of (a) component and (b) component, Preferably it is 0.5-10 mass parts, More preferably Is preferably 1 to 10 parts by mass. If the addition amount is less than 0.1 parts by mass, the silica may not be sufficiently dispersed. If the addition amount is more than 20 parts by mass, the handling of the rubber composition is deteriorated.

  Moreover, it is optional to add various additives such as a colorant, a reaction control agent, a mold release agent, or a filler dispersant to the composition of the present invention as necessary.

  In the silicone rubber composition according to the present invention, the components (a) to (c) and (e) described above are uniformly mixed using a rubber kneader such as a two-roll, Banbury mixer, or dough mixer (kneader). And it can obtain by heat-processing as needed and adding (d) component with a 2 roll or a dough mixer after that.

  The silicone rubber composition thus obtained can be molded by a conventional molding method according to the required application. That is, compression molding, injection molding, transfer molding, normal pressure hot air vulcanization, steam vulcanization, and the like are not particularly limited. In addition, although hardening conditions can be suitably selected according to the hardening method and the thickness of a molding, it can carry out on the conditions for 10 second-30 days normally at 80-600 degreeC.

  Examples and Comparative Examples are given below, but the present invention is not limited thereto. In addition, in the following example, an average polymerization degree shows the weight average polymerization degree of polystyrene conversion in a gel permeation chromatography (GPC) analysis, and a part shows a mass part.

（但し、Ｍｅ、φはそれぞれ、メチル基、フェニル基を示す。） [Preparation of rubber composition]
(Example 1 and Comparative Examples 1 and 2)
The following were prepared as components (a) to (e).
(A) (CH ₃ ) ₂ SiO units 99.95 mol%, (CH ₃ ) (CH ₂ ═CH) SiO units 0.05 mol%, and both ends of the molecular chain are (CH ₂ ═CH) (CH ₃ ) ₂ average polymerization degree of which is blocked with SiO _1/2 units containing about 7,000 vinyl linear dimethylpolysiloxane gum _{(b) (CH 3) 2} SiO units 89.85 mol%, (CH ₃₎ It consists of 0.15 mol% of (CH ₂ ═CH) SiO units and 10 mol% of (CH ₃ ) (C ₆ H ₅ ) SiO units, and both ends of the molecular chain are (CH ₂ ═CH) (CH ₃ ) ₂ SiO Vinyl group-containing linear phenylmethylpolysiloxane raw rubber capped with _1/2 units and having an average degree of polymerization of about 7,000 (c) Fumed silica having a specific surface area of 200 m ² / g by BET adsorption method (e) Contains hydroxyl groups at both ends of the molecular chain represented by formula (5) Methylphenylsiloxane oligomer (polymerization degree: 10) ... Silica dispersant

(However, Me and φ represent a methyl group and a phenyl group, respectively.)

  The above components (a), (b), (c), and (e) were uniformly mixed in the kneader in the addition amounts shown in Table 1, and heat treated at 150 ° C. for 2 hours to prepare a silicone rubber compound.

[Test sheet preparation and physical property measurement]
(D) C-25A (platinum catalyst) / C-25B (organohydrogenpolysiloxane) (both manufactured by Shin-Etsu Chemical Co., Ltd.) respectively 1.0 parts / 2.0 parts as an addition crosslinking curing agent After kneading with two rolls and adding, and uniformly mixing, press curing was performed at 150 ° C./10 minutes, followed by post curing at 200 ° C. for 4 hours to prepare a test sheet having a thickness of 2 mm.
Based on this sheet, hardness (durometer type A), tensile strength, elongation at break, tear strength (crescent type), and compression set (180 ° C./22 hours) were measured based on JIS K6249.
The results are shown in Table 1.

Claims (5)

(A) The following general formula (1)
R ¹ _a SiO _{(4-a) / 2} (1)
(Here, R ¹ is the same or different unsubstituted or substituted aliphatic monovalent hydrocarbon group, and 0.001 to 20 mol% in all R ¹ groups is an alkenyl group. A is 1.90. It is a positive number of ~ 2.05.)
1 to 99 parts by mass of an organopolysiloxane represented by
(B) The following general formula (2)
R ² _b SiO _{(4-b) / 2} (2)
(Here, R ² is a monovalent hydrocarbon radical unsubstituted or substituted in the same or different, 1 to 20 mol% of the total R ² group is phenyl group, 0.001 in all R ² groups ˜20 mol% is an alkenyl group, b is a positive number of 1.90 to 2.05.)
1 to 99 parts by mass of a phenyl group-containing organopolysiloxane represented by
However, the sum total of (a) component and (b) component is 100 mass parts.
(C) 10 to 100 parts by mass of reinforcing silica having a specific surface area of at least 50 m ² / g,
(D) necessary amount of vulcanizing agent for silicone rubber ,
(E) As a silica dispersant

(Wherein R ³ and R ⁴ are the same or different unsubstituted or substituted monovalent hydrocarbon group, at least 1 mol% of the entire R ³ group and R ⁴ group are phenyl groups, and n is 1 to 1) (It is an integer of 30.)
Silanol group-blocked silicone oligomers represented by
0.1 to 20 parts by mass with respect to 100 parts by mass in total of component (a) and component (b)
A silicone rubber composition comprising: 2. The silicone rubber composition according to claim 1 , wherein in formula (3) of component (e), 10 to 50 mol% of the total of R ³ groups and R ⁴ groups is a phenyl group, and n is an integer of 3 to 30. object. The silicone rubber composition according to claim 1 or 2, wherein the component (e) is contained in an amount of 1 to 20 parts by mass with respect to a total of 100 parts by mass of the components (a) and (b). The silicone rubber composition according to any one of claims 1 to 3, wherein the organopolysiloxanes of component (a) and component (b) are raw rubber-like components having an average degree of polymerization of 3,000 or more. (D) a silicone rubber vulcanizing agent component, any one of claims 1 to 4, characterized in that an addition curing type vulcanizing agent consisting of a combination of organohydrogenpolysiloxane and platinum catalyst The silicone rubber composition as described.