JP2008222849A - Curable silicone rubber composition giving cured product with excellent fatigue resistance and cured product thereof - Google Patents

Abstract

[PROBLEMS] To provide a curable silicone rubber composition that provides a cured product having improved fatigue resistance such as elongation fatigue resistance and bending fatigue resistance without introducing a forced dispersion step by a three-roll mill, and the cured product thereof. To do.
(A) The following average composition formula (1): R ¹ _a SiO _{4 -a / 2} (wherein R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is 100 parts by mass of an organopolysiloxane having an average degree of polymerization in the range of 3,000 to 30,000, and (B) a specific surface area by the BET method of 120 to 350 m ² / g. A curable silicone rubber composition containing 10 to 100 parts by mass of a reinforcing filler having a bulk density of 15 g / L or more and less than 40 g / L, and (C) a curing agent, and a cured product thereof.
[Selection figure] None

Description

  The present invention relates to a curable silicone rubber composition that provides a cured product having improved fatigue resistance such as elongation fatigue resistance and flexural fatigue resistance, and the cured product thereof.

  Silicone rubber is excellent in properties such as electrical properties, heat resistance, cold resistance, weather resistance, compression set resistance, rubber elasticity, etc., and it is not toxic, so electric and electronic parts, various office equipment, automobiles, It is used in a wide range of fields such as aircraft parts, food production equipment parts, medical instrument parts, and leisure goods. In that case, it is often used not only for static applications but also for dynamic applications such as rubber contacts in calculators and push phones, keyboards, constant velocity joint cover boots for automobiles, diaphragms, pump tubes and the like.

  However, conventionally known silicone rubbers are not necessarily satisfactory in fatigue resistance such as elongation fatigue resistance and flexural fatigue resistance, particularly in dynamic applications, and improvement thereof is desired.

As countermeasures, means generally employed for improving the dynamic fatigue resistance of synthetic rubber, such as uniform cross-linking, low cross-linking density, low modulus, reduction of filler usage, uniform packing Dispersion, removal of coarse particles in the filler, and the like are also employed for silicone rubber. However, even with such means, the fatigue resistance of silicone rubber is still not satisfactory. In addition to this, a method of adding an organohydrogenpolysiloxane (see Patent Document 1), a method of adding a fluorine-containing low molecular weight polymer (see Patent Document 2), and a method of using an acid strength modifier (see Patent Document 3) ), And a method of adding an alkoxy group-containing organopolysiloxane (see Patent Document 4) has also been proposed.
Japanese Patent Laid-Open No. 62-197454 JP-A 63-150350 JP-A-3-281572 JP-A-4-108857

  Among the above-mentioned means, examples of particularly effective means for uniformly dispersing the filler, removing coarse particles in the filler, and the like include introduction of a forced dispersion step by a three-roll mill. However, from the viewpoint of improving the productivity and the quality of the resulting cured silicone rubber, it is desired to improve the fatigue resistance of the silicone rubber without introducing such a forced dispersion step. Therefore, the object of the present invention is to provide a curable silicone rubber composition that gives a cured product having improved fatigue resistance such as elongation fatigue resistance and bending fatigue resistance without introducing a forced dispersion step by a three-roll mill, and It is to provide the cured product.

  As a result of intensive studies, the present inventors have replaced the normally used filler with a bulk density of 40 to 70 g / L as the reinforcing filler used in the curable silicone rubber composition. By using a material in a lower range of 15 g / L or more and less than 40 g / L, a cured product obtained by introducing the forced dispersion step without introducing the forced dispersion step by a three-roll mill, The inventors have found that a cured product having excellent fatigue resistance such as elongation fatigue resistance and flexural fatigue resistance can be obtained, and the present invention has been completed.

That is, the present invention firstly
(A) The following average composition formula (1):
R ¹ _a SiO _{4-a / 2} (1)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.95 to 2.05.)
100 parts by mass of an organopolysiloxane having an average degree of polymerization in the range of 3,000 to 30,000,
(B) 10 to 100 parts by mass of a reinforcing filler having a specific surface area by BET method of 120 to 350 m ² / g and a bulk density of 15 g / L or more and less than 40 g / L, and
(C) A curable silicone rubber composition containing a curing agent is provided.

  Secondly, the present invention provides a cured silicone rubber obtained by curing the curable silicone rubber composition.

  According to the present invention, a curable silicone rubber composition that gives a cured product with improved fatigue resistance such as elongation fatigue resistance and bending fatigue resistance without introducing a forced dispersion step by a three-roll mill, and its A cured product can be obtained. The cured product of the present invention can be widely used not only for static applications but also for dynamic applications.

  Hereinafter, the present invention will be described in detail.

[(A) component]
The organopolysiloxane of component (A) has the following average composition formula (1):
R ¹ _a SiO _{4-a / 2} (1)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and a is a positive number from 1.95 to 2.05. .)
And an average degree of polymerization in the range of 3,000 to 30,000.

In the average composition formula (1), as R ¹ , for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, pentyl group, hexyl group, octyl group, decyl group, dodecyl group, etc. Alkyl group; cycloalkyl group such as cyclopentyl group and cyclohexyl group; alkenyl group such as vinyl group, allyl group, butenyl group and hexenyl group; aryl group such as phenyl group, tolyl group, xylyl group and naphthyl group; benzyl group, 2 An aralkyl group such as a phenylethyl group or a β-phenylpropyl group; a chloromethyl group, a bromoethyl group, wherein a part or all of the hydrogen atoms bonded to carbon atoms of these hydrocarbon groups are substituted with a halogen atom, a cyano group, or the like; Trifluoropropyl group, 2- (nonafluorobutyl) ethyl group, 2- (heptadecafluorooctyl) ) Ethyl group, p-chlorophenyl group, cyanoethyl group and the like.

  The a is a positive number from 1.95 to 2.05.

  The (A) component organopolysiloxane is basically a linear diorganopolysiloxane whose molecular chain (main chain) is composed of repeating diorganosiloxane units, but may be partially branched.

  Examples of the group blocking the molecular chain end of the organopolysiloxane include a trimethylsilyl group, a dimethylvinyl group, a methyldivinyl group, and a trivinylsilyl group.

The average degree of polymerization of the organopolysiloxane of component (A) is usually in the range of 3,000 to 30,000, preferably 4,000 to 20,000, more preferably 5,000 to 15,000. The average degree of polymerization was determined by measuring the number average molecular weight of the component (A) by GPC (gel permeation chromatography) using polystyrene as a molecular weight marker.
Average degree of polymerization = number average molecular weight of component (A) / molecular weight of repeating unit of component (A). When a plurality of types of repeating units are contained in the component (A), the “molecular weight of the repeating unit of the component (A)” in the above formula is the number average molecular weight of these types of repeating units.

In addition, when the organopolysiloxane of component (A) is in a liquid state, its average polymerization degree is in the above range, and its kinematic viscosity measured at 25 ° C. using an Ostwald viscometer is 100 mm ² / It is preferably s or more, and more preferably 100,000 to 10,000,000 mm ² / s.

  (A) A component may be used individually by 1 type, or may be used in combination of 2 or more types from which average polymerization degree and molecular structure differ.

  These organopolysiloxanes can be selected optimally depending on the curing type of the composition as described below.

  When the composition of the present invention is of an addition reaction curable type, the component (A) includes, for example, an organopolysiloxane having at least 1, preferably at least 2, silicon-bonded alkenyl groups in one molecule. It is done. Examples of the silicon atom-bonded alkenyl group include a vinyl group and an allyl group, and a vinyl group is preferable.

  Examples of the organopolysiloxane having a silicon atom-bonded alkenyl group include, for example, molecular chain both ends dimethylvinylsiloxy group-blocked dimethylpolysiloxane, molecular chain both ends dimethylvinylsiloxy group-blocked dimethylsiloxane / methylvinylsiloxane copolymer, Examples thereof include a dimethylsiloxane / methylvinylsiloxane copolymer blocked with a trimethylsiloxy group blocked at both molecular chains, and a methyl (3,3,3-trifluoropropyl) polysiloxane blocked with a molecular chain both ends dimethylvinylsiloxy group.

  When the composition of the present invention is of an organic peroxide curable type, the component (A) is not limited, but preferred examples thereof include at least 1, preferably at least 2, silicon atom-bonded alkenyl in one molecule. An organopolysiloxane having a group may be mentioned. Examples of the silicon atom-bonded alkenyl group include a vinyl group and an allyl group, and a vinyl group is preferable.

  Examples of the organopolysiloxane having a silicon atom-bonded alkenyl group include, for example, molecular chain both ends dimethylvinylsiloxy group-blocked dimethylpolysiloxane, molecular chain both ends dimethylvinylsiloxy group-blocked dimethylsiloxane / methylvinylsiloxane copolymer, Examples thereof include a dimethylsiloxane / methylvinylsiloxane copolymer blocked with a trimethylsiloxy group blocked at both molecular chains, and a methyl (3,3,3-trifluoropropyl) polysiloxane blocked with a molecular chain both ends dimethylvinylsiloxy group.

  The organopolysiloxane of component (A) can be produced by a conventionally known method. For example, depending on the proportion of siloxane units contained in the structure of the target organopolysiloxane, one or more of the corresponding organohalogenosilanes may be co-presented in the presence of an alcohol having 1 to 4 carbon atoms. The desired product can be obtained by hydrolytic condensation to remove by-produced hydrohalic acid and low-boiling components. The catalyst used after ring-opening polymerization of a cyclic polysiloxane (such as a siloxane trimer or tetramer) with an alkaline or acidic catalyst, optionally in the presence of water for hydrolysis. Alternatively, the target organopolysiloxane can also be obtained by removing low-boiling components.

[(B) component]
The reinforcing filler (B) is used to obtain a cured product having excellent mechanical strength and improved fatigue resistance such as elongation fatigue resistance and bending fatigue resistance. For this purpose, the reinforcing filler has a specific surface area according to the BET method of 120 to 350 m ² / g, preferably 180 to 350 m ² / g, and a bulk density of 15 g / L or more and less than 40 g / L, Preferably it is 20-35 g / L.

  When a reinforcing filler is blended in a rubber compound, it has been generally considered that the bulk density of the reinforcing filler is preferably 40 to 70 g / L. When the bulk density is within this range, the blending time of the reinforcing filler is shortened, and the productivity is improved. However, if the bulk density is in this range, the secondary agglomerated reinforcing filler becomes difficult to disperse, so that a cured product having excellent fatigue resistance such as elongation fatigue resistance and bending fatigue resistance can be obtained. Not suitable.

  As described above, in the present invention, the reinforcing filler of the component (B) has a bulk density of 15 g / L or more and less than 40 g / L. When the bulk density is within this range, there is no great difference in blending time and productivity as compared with the case where a reinforcing filler having a bulk density of 40 to 70 g / L is used. Even if a forced dispersion step is not introduced, a cured product having excellent fatigue resistance can be obtained.

The bulk density is measured according to the bulk density measurement method described in AEROSIL (registered trademark) Technical Report, No. 15, p.1. Specifically, it is as follows. The reinforcing filler placed on the paper is slowly added to a 100 ml graduated cylinder to bring the bulk volume occupied by the reinforcing filler to 100 ml. This operation is performed without hitting or dropping the reinforcing filler. The mass of the entire graduated cylinder is measured before and after adding the reinforcing filler, and the difference is defined as the reinforcing filler mass. The bulk density is obtained from the following formula.
Bulk density (g / L) = Mass of reinforcing filler (g) /0.1 (L)

  Examples of the reinforcing filler (B) include fine powder silica. Specific examples of the component (B) include fumed silica (dry silica) and precipitated silica (wet silica), and fumed silica (dry silica) is preferable. Further, these surfaces may be hydrophobized with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like. The reinforcing filler of component (B) may be used alone or in combination of two or more.

  The amount of the reinforcing filler (B) added is usually 10 to 100 parts by weight, preferably 15 to 90 parts by weight, particularly preferably 30 to 80 parts by weight based on 100 parts by weight of the organopolysiloxane (A). Part by mass. When the addition amount is less than 10 parts by mass, it is difficult to obtain a sufficient reinforcing effect. When the amount added is more than 100 parts by mass, the processability of the resulting silicone composition tends to be poor, and the physical properties of the resulting silicone rubber cured product tend to deteriorate.

[(C) component]
The curing agent of component (C) is appropriately selected according to the reaction for curing the curable silicone rubber composition of the present invention to obtain a rubbery elastic body. Preferred examples of the reaction include (1) a crosslinking reaction with an organic peroxide, and (2) a curing agent for addition reaction of a curable silicone rubber composition, that is, a combination of an organohydrogenpolysiloxane and an addition reaction catalyst. Examples thereof include a crosslinking reaction and a combination of the crosslinking reactions (1) and (2). That is, preferable examples of the component (C) include (i) an organic peroxide, (ii) a combination of an organohydrogenpolysiloxane and an addition reaction catalyst, and a combined system of (i) and (ii). It is done.

(I) Organic peroxide Examples of the organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 4-methylbenzoyl peroxide, 2-methylbenzoyl peroxide, and 2,4-dimethylbenzoyl peroxide. Oxide, 1,4-bis (para-toluoylperoxycarbonyloxy) butane, 1,6-bis (2,4-dimethylbenzoylperoxycarbonyloxy) hexane, 2,5-dimethyl-2,5-di ( and organic peroxides such as t-butylperoxy) hexane, t-butylperoxybenzoate, dicumyl peroxide, cumyl-t-butyl peroxide. When performing normal pressure hot air vulcanization, diacyl organic peroxides such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and 4-methylbenzoyl peroxide are generally used. In addition, these organic peroxides may be used alone or in combination of two or more.

  The compounding amount of the organic peroxide is preferably 0.05 to 15 parts by mass, more preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the organopolysiloxane as the component (A). If the blending amount is within this range, crosslinking is likely to be sufficient, and the curing rate is likely to increase as the addition amount increases, so that it is economically advantageous. Reactants and decomposition residues can be removed in a short time.

(Ii) Combination / addition reaction catalyst of organohydrogenpolysiloxane and addition reaction catalyst The addition reaction catalyst comprises an alkenyl group in component (A) and a silicon atom bond of organohydrogenpolysiloxane in the curing agent of (ii). It is a catalyst that causes an addition reaction with a hydrogen atom (that is, SiH group). The addition reaction catalyst may be used alone or in combination of two or more.

  As the addition reaction catalyst, any conventionally known catalyst can be used, and examples thereof include platinum group metal catalysts such as platinum group metals alone and their compounds. Specific examples thereof include particulate platinum metal adsorbed on a support such as silica, alumina or silica gel, platinum chloride, chloroplatinic acid, chloroplatinic acid hexahydrate and a complex of olefin or divinyldimethylpolysiloxane, Examples thereof include an alcohol solution of chloroplatinic acid hexahydrate, a palladium catalyst, and a rhodium catalyst.

  The addition amount of the addition reaction catalyst may be an effective amount that can promote the above addition reaction. For example, when a platinum group metal catalyst is used as the addition reaction catalyst, the component (A) is usually converted into the platinum group metal amount. 1 to 1,000 ppm (based on mass, hereinafter the same), preferably 10 to 100 ppm with respect to the organopolysiloxane. When the addition amount is within this range, the addition reaction is likely to be sufficiently promoted, the curing is likely to be sufficient, and the rate of the addition reaction is easily improved as the addition amount increases. It tends to be advantageous.

Organohydrogenpolysiloxane Organohydrogenpolysiloxane is used as a cross-linking agent for addition reaction, and it can be either linear or cyclic as long as it contains 2 or more, preferably 3 or more SiH groups in one molecule. Or may be branched. Organohydrogenpolysiloxanes may be used singly or in combination of two or more. As such an organohydrogenpolysiloxane, a known organohydrogenpolysiloxane can be used as a crosslinking agent for an addition reaction curable silicone rubber composition. For example, the following average composition formula (2):
R ² _x H _y SiO _{(4-xy) / 2} (2)
(Wherein R ² is an identical or different unsubstituted or substituted, monovalent hydrocarbon group having preferably 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, excluding aliphatic unsaturated groups, x and y are positive numbers satisfying 1 ≦ x ≦ 2.2, 0.002 ≦ y ≦ 1, and 1.002 ≦ x + y ≦ 3.)
The thing shown by is mentioned. Specific examples of R ² include those exemplified above for R ¹ and those similar to those other than unsubstituted or substituted alkenyl groups.

When the organohydrogenpolysiloxane is linear, the SiH group may be present only at one or both of the molecular chain terminal and the non-molecular chain terminal. The kinematic viscosity of the organohydrogenpolysiloxane measured with an Ostwald viscometer at 25 ° C. is preferably 300 mm ² / s or less.

  The amount of the organohydrogenpolysiloxane is preferably 0.5 to 10 mol, more preferably 1 to 4 in terms of the amount of SiH groups in the organohydrogenpolysiloxane with respect to 1 mol of alkenyl groups in the component (A). This is the amount to make a mole. When the blending amount is within this range, crosslinking is likely to be sufficient, and after curing, mechanical strength is likely to be sufficient, and other physical characteristics, particularly heat resistance and compression set resistance, are easily maintained. Such a compounding amount can be realized, for example, by blending 0.01 to 10 parts by mass of the organohydrogenpolysiloxane with respect to 100 parts by mass of the organopolysiloxane of the component (A).

[Other ingredients]
In the curable silicone rubber composition of the present invention, if necessary, non-reinforcing silica such as pulverized quartz and diatomaceous earth, carbon black such as acetylene black, furnace black and channel black, filler such as calcium carbonate, colorant , Heat improver, flame retardant improver, acid acceptor, thermal conductivity improver, etc .; mold release agent; alkoxysilane, diphenylsilanediol, carbon functional silane, molecular chain both ends silanol-blocked low molecule A dispersant such as siloxane may be added. Further, when a curing agent containing a platinum group metal catalyst is used as the component (C), the curable silicone rubber composition of the present invention includes a polymethylvinylsiloxane cyclic compound, an acetylene group-containing alcohol, a peroxide and the like. It is preferable to add a known platinum group metal catalyst inhibitor.

[Production method]
The curable silicone rubber composition of the present invention can be obtained by uniformly mixing the above components using a rubber kneader such as a two-roll mill, a Banbury mixer, or a dough mixer (kneader).

[Curing method]
By curing the curable silicone rubber composition thus prepared with heat, a cured silicone rubber can be easily obtained. The curing method is not particularly limited as long as heat for vulcanization can be sufficiently applied to the curable silicone rubber composition. Further, the molding method of the curable silicone rubber composition of the present invention is not particularly limited, and examples thereof include continuous vulcanization by extrusion molding, mold molding by press or injection, etc., and mold molding by press is particularly preferable. Adopted. The heating temperature is preferably 100 to 500 ° C, and particularly preferably 200 to 400 ° C. The heating time is preferably several seconds to 1 hour, and particularly preferably 10 seconds to 30 minutes. If necessary, secondary vulcanization may be performed at 180 to 250 ° C. for about 1 to 10 hours.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to the following Example.

(Example 1)
Raw rubber-like organopolysiloxane consisting of dimethylsiloxane units and methylvinylsiloxane units, with both ends of the molecular chain blocked with dimethylvinylsiloxy groups and an average degree of polymerization of about 5,000 (vinyl group content: all organic bonded to silicon atoms) About 0.15 mol% relative to the group), 100 parts by mass as a dispersing agent of formula (3):

（式中、ｎは２〜６の整数である。）
で示される化合物10質量部、充填剤としてＢＥＴ法による比表面積が200m²/gであり、且つ嵩密度が30g/Ｌである乾式シリカ60質量部を添加し、得られた混合物を190℃において1時間、ニーダーを用いて混練りしてコンパウンドAを調製した。

(In the formula, n is an integer of 2 to 6.)
10 parts by mass of the compound represented by the formula, 60 parts by mass of dry silica having a specific surface area of 200 m ² / g by the BET method and a bulk density of 30 g / L as a filler, and the resulting mixture at 190 ° C. Compound A was prepared by kneading for 1 hour using a kneader.

(Comparative Example 1)
As the filler, dry silica (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g by the BET method and a bulk density of 50 g / L was used instead of the dry silica of Example 1. Compound B was prepared in the same manner as Example 1 except for the above.

(Comparative Example 2)
Compound B ′ was prepared by subjecting compound B prepared in Comparative Example 1 to a forced dispersion step once in a three-roll mill.

(Comparative Example 3)
Compound B ″ was prepared by subjecting compound B prepared in Comparative Example 1 to a forced dispersion step three times with a three-roll mill.

(Comparative Example 4)
Mainly composed of dimethylsiloxane alone, methyl vinyl siloxane unit, 100 parts by mass of rubber-like organopolysiloxane having an average degree of polymerization of about 5,000 consisting of about 0.15 mol% of vinyl derived from dimethylvinylsiloxane unit, 15 parts by weight of the compound represented by 2), 60 parts by weight of dry silica (trade name: Aerosil 300, manufactured by Nippon Aerosil) having a specific surface area (BET method) of 300 m ² / g and a bulk density of 50 g / L as a filler Compound C was prepared by heat treatment at 190 ° C. for 1 hour.

(Evaluation)
1 part by mass of a paste containing 40% by mass of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as a curing agent is added to 100 parts by mass of each compound obtained in Examples and Comparative Examples The resulting mixture was kneaded using a two-roll mill at 25 ° C. for 5 minutes to obtain a composition. The obtained composition was molded and cured to obtain a 150 mm square, 2 mm thick sheet-like elastic body. The molding / curing temperature was 165 ° C., the time was 10 minutes, and the pressure was 8 MPa. The obtained sheet-like elastic body was further subjected to secondary vulcanization at 200 ° C. for 4 hours to obtain the desired cured product. The obtained cured product was subjected to an elongation fatigue test by a demature fatigue test method. The demach type fatigue test method was performed under the following conditions.
Equipment used: Demacha bending fatigue testing machine manufactured by Toyo Seiki Temperature: Room temperature (21-25 ℃)
Elongation condition: 100% after increasing the ratio of the elongation (length when the cured product is elongated-initial length of the cured product) to the initial length (150 mm) of the cured product from 0% to 100% The operation of decreasing from 0 to 0% was taken as 1 cycle and repeated 5 cycles per second.

  The number of times the test piece reached until it broke was defined as 100% elongation fatigue life. The cured product is more excellent in elongation fatigue resistance as this value is larger. The obtained results are shown in Table 1. It has been revealed that the cured product of the composition of the present invention is excellent in elongation fatigue resistance. Therefore, according to the present invention, it is possible to provide a curable silicone rubber composition that provides a cured product excellent in elongation fatigue resistance and a cured product thereof.

Claims (2)

(A) The following average composition formula (1):
R ¹ _a SiO _{4-a / 2} (1)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.95 to 2.05.)
100 parts by mass of an organopolysiloxane having an average degree of polymerization in the range of 3,000 to 30,000,
(B) 10 to 100 parts by mass of a reinforcing filler having a specific surface area by BET method of 120 to 350 m ² / g and a bulk density of 15 g / L or more and less than 40 g / L, and
(C) A curable silicone rubber composition containing a curing agent.   A cured silicone rubber obtained by curing the curable silicone rubber composition according to claim 1.