JPH10158518A - Silicone rubber composition for automobile joint cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition excellent in the characteristics of bending fatigue resistance and stretching fatigue resistance by compounding a specified organopolysiloxane, a specified organohydrogenpolysiloxane, etc. SOLUTION: This composition is composed of (A) 100 pts.wt. of an organopolysiloxane expressed by average composition formula I [R is a (substituted) monovalent hydrocarbon; (a)=1.95-2.05] and containing at least two aliphatic unsaturated hydrocarbon groups in a molecule, (B) an organohydrogenpolysiloxane expressed by formula II [A is H or R; B is SiRH2 , SiR2 H, etc.; (m)>=0, (n)>=0 and 5<=(m+n)<=100] and containing at least two H atoms bonding to a silicon atom in a molecule in such an amount that the molar ratio of H atoms in the component B to the aliphatic unsaturated hydrocarbon groups in the component A becomes 1.0-2.5, (C) 10-100 pts.wt. of reinforcing silica and (D) a platinum-based catalyst in a catalytic amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition for an automobile joint cover boot.

[0002]

2. Description of the Related Art Silicone rubber is excellent in heat resistance, cold resistance, weather resistance, electrical insulation, compression set and rubber elasticity, and has no toxicity. , Aircraft parts, food production equipment parts,
It is used in a wide range of applications, from medical device parts to leisure goods, such as rubber contacts in calculators, touch phones, keyboards, constant velocity joint cover boots for automobiles, diaphragms, medical pump tubes, etc. It is often used for various dynamic applications. However, this silicone rubber does not always show satisfactory results of elongation resistance and bending fatigue resistance in dynamic applications, and is used as a measure against these to improve the dynamic fatigue resistance of general synthetic rubber. As for uniform crosslinking, low crosslinking density, low modulus, and filler, means such as reduction of the amount used, uniform dispersion, and removal of coarse-grained filler are appropriately adopted. The improvement of elongation and bending fatigue resistance was insufficient.
In other words, the most common Demasher type fatigue test method is 300 to 4
Since the millionth level was the limit, improvement of these characteristics has been strongly demanded. Other methods for improving the fatigue resistance include a method of adding an organohydrogenpolysiloxane (see JP-A-62-197454) and a method of adding a fluorine-containing low-molecular-weight polymer (see JP-A-63-197454). 150
No. 350) has also been proposed.

[0003]

However, the above method alone is excellent in elongation fatigue resistance, but is remarkable in crack growth due to compression fatigue of an object having a crack in advance, as in the bending test of JIS K6301. Some compositions have short lifespans and are unsuitable for materials of structures that are subject to repeated compression and expansion, such as automotive boot materials.

[0004] The present invention provides a silicone rubber composition for automobile joint cover boots which solves the above-mentioned problems and has excellent bending fatigue resistance, in particular, very low crack growth rate and excellent extension fatigue resistance. .

[0005]

Means for Solving the Problems The present invention provides the following a),
A silicone rubber composition for automotive joint cover boots comprising (b), (c) and (d). B) 100 parts by weight of an organopolysiloxane represented by the average composition formula R _a SiO _{(4-a) / 2} and having at least two aliphatic unsaturated hydrocarbon groups in one molecule, wherein R is A is a substituted or unsubstituted monovalent hydrocarbon group, a is a positive number from 1.95 to 2.05) b) is represented by the following general formula (Chemical Formula 2) and has at least two hydrogen atoms bonded to a silicon atom in one molecule Organohydrogenpolysiloxane "where the ratio of the number of moles of hydrogen atoms in b) to the number of moles of aliphatic unsaturated hydrocarbon groups in b) is 1.0 to 2.5", wherein R is the same as defined above. , a is H or R, B is SiRH _2, SiR _{2 H,} a group selected from SiR _3, m is an integer of m ≧ 0, n is and 5 ≦ an integer n ≧ 0 (m + n) ≦ 100 "

Embedded image C) Reinforcing silica 10 to 100 parts by weight, d) Platinum catalyst Catalyst amount. That is, the present inventors have found that a molded article of an addition-vulcanization-type silicone rubber composition using a platinum catalyst has a low crack growth rate and excellent elongation fatigue resistance, and is particularly suitable for a joint boot material of an automobile. The present invention has been completed.
In particular, molded articles made of the composition of the present invention have an excellent 100% elongation fatigue life of more than 4 million times, and the number of times of bending at which a crack doubles in a bending test of a previously cracked object is 40,000 times or more. It has characteristics.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The organopolysiloxane of component (a) in the present invention may be any of those conventionally known as main raw materials for room-temperature-curable or heat-curable silicone rubbers, and has an average composition formula of R _a SiO _{(4- a) / 2} , having at least two aliphatic unsaturated hydrocarbon groups in one molecule. Here, R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, such as an alkyl group such as methyl, ethyl, propyl and butyl; an alkenyl group such as vinyl and allyl; Aryl groups such as phenyl and tolyl; cycloalkyl groups such as cyclohexyl group; benzyl, β
-Aralkyl groups such as phenylethyl, or 3,3,3-trifluoropropyl, chloromethyl, cyanoethyl in which part or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms, cyano groups, etc. A is a positive number from 1.95 to 2.05, and is basically a linear diorganopolysiloxane, but may have a partially branched structure.

The organopolysiloxane in the present invention may be a liquid having a low degree of polymerization, but the cured elastomer obtained from the composition of the present invention is required to have a practical hardness. A polymer having a degree of polymerization of 300 or more is preferable.
In the case of 3,000 or millable, the degree of polymerization is preferably 3,000 to 10,000. About R, it is preferable that 50 mol% or more is a methyl group, and about 0.01 to
It is preferably contained in an amount of 5 mol%, more preferably 0.02 to 5 mol%.

In the above organopolysiloxane, R
It is preferable to mix two types of organopolysiloxanes having different aliphatic unsaturated hydrocarbon group contents in order to improve the elongation fatigue resistance. In particular, the terminal of the molecular chain is an aliphatic unsaturated group, and R is 0.25. 1010 mol% (preferably 0.5〜5 mol%) of an organopolysiloxane having an unsaturated hydrocarbon group is 0.53030% by weight [A] of organopolysiloxane 100
0.5 to 30 parts by weight in weight parts]. The remainder is preferably dimethylpolysiloxane having both ends blocked with a dimethylvinylsiloxy group.

The organohydrogenpolysiloxane (b) in the present invention is an organohydrogenpolysiloxane having at least two hydrogen atoms bonded to a silicon atom in one molecule. m + n) is from 5 to 100, preferably from 10 to 30,
And the ratio of the number of moles of hydrogen atoms bonded to silicon atoms in one molecule to the number of moles of unsaturated hydrocarbon groups contained in one molecule of the organopolysiloxane a) is 1.0 to 2.5, preferably 1.5 to 2.0. Use an amount in the range of Polymerization degree is 5
If it is less than 100 or more than 100, the bending fatigue resistance becomes insufficient. If the molar ratio is less than 1.0, the physical properties and elongation fatigue resistance of the cured rubber are reduced, and if it exceeds 2.5, the growth rate of cracks due to bending increases. When it is in the range of 1.0 to 2.5, the effects of improving the elongation fatigue resistance and suppressing the crack growth are remarkably exhibited.

The reinforcing silica (c) in the present invention may be any of those conventionally known as silicone rubber fillers such as fumed silica, precipitated silica, silica aerogel and the like, which imparts reinforcing properties to the rubber. Because there is a specific surface area
50 m ² / g or more, particularly 150 meters ² / g or more is preferable, more preferably a specific surface area of 200 m ² / g or more fumed silica. The silica may be one whose surface is treated with chlorosilane, alkoxysilane, silane coupling agent, siloxane, silazane or the like. The compounding amount is less than 10 parts by weight per 100 parts by weight of the organopolysiloxane of a). If the reinforcing effect is insufficient, and if it exceeds 100 parts by weight, the processability of the rubber is remarkably deteriorated. Therefore, it is necessary to set the range of 10 to 100 parts by weight, but the preferable range is 20 to 70 parts by weight.

The platinum-based catalyst according to the present invention d) includes solid platinum supported on a carrier such as platinum black, alumina or silica, chloroplatinic acid, alcohol-modified chloroplatinic acid, or chloroplatinic acid and olefin. Examples of the complex include a complex of platinum and vinyl siloxane. The amount of the platinum-based catalyst used may be a catalytic amount, but is usually 0.1 to 2,000 p in terms of platinum element per 100 parts by weight of the organopolysiloxane of a).
It is preferable to mix at a ratio of pm, especially 0.5 to 200 ppm. It is optional to add a control agent for maintaining the pot life in the addition reaction using a platinum-based catalyst, for example, acetylene alcohol.

The silicone rubber composition of the present invention has the above-mentioned a)
This method can be obtained by uniformly mixing a predetermined amount of the above (2) to (4), which may be kneaded with a two-roll mill, a kneader, a Banbury mixer or the like used for compounding a general silicone rubber composition. It is optional to add a metal oxide as a heat resistance improver, a coloring agent, a processing aid, and the like, and further include an organosilicon compound represented by the following general formula (Formula 3) as a silica dispersant. 10 parts by weight or less, preferably 0.5 to 10 parts by weight, may be added to 100 parts by weight of the organopolysiloxane of the component (a).

Embedded image (Here, R ^c and R ^d are the same unsubstituted or substituted monovalent hydrocarbon groups having 1 to 10 carbon atoms as R, provided that they are aliphatic unsaturated hydrocarbon groups or fluorine-substituted hydrocarbon groups. And especially methyl, vinyl, phenyl, 3,3,3
-A trifluoropropyl group is preferred. b is 1 to 100. )

[0013]

The following examples will be given, in which all parts are by weight. The measured physical properties were measured by the following methods.

(Measurement method for 100% elongation fatigue life) Measured using a Demasher-type bending fatigue tester (manufactured by Toyo Seiki Co., Ltd.). The operation was continued at 5 Hz, and the number of cycles until breakage was displayed. (Measurement method of crack growth rate due to bending fatigue) JIS K6301
A bending test was performed according to the specified bending fatigue test, and the number of bendings until a 2.5 mm crack generated beforehand became 10 mm in a 5 Hz bending test at room temperature was determined.

(Examples 1 to 5; Comparative Examples 1 to 6) Both ends of the molecular chain are (CH ₃ ) ₂ (CH ₂ CHCH) SiO—, and all of the molecular main chains are — (CH ₃ ) _2.
95 parts by weight of an organopolysiloxane composed of SiO- units, both ends of the molecular chain being (CH ₃ ) ₂ (CH ₂ = CH) SiO-, and the molecular main chain being-(C
90 mol% of H ₃ ) ₂ SiO-units, 10-(CH ₃ ) (CH ₂ = CH) SiO-units
5% by weight of an organopolysiloxane consisting of mol% and a specific surface area of 200 m ² / g fumed silica Aerosil 20
0 [trade name, manufactured by Nippon Aerosil Co., Ltd.] 30 parts by weight, and 8 parts by weight of dimethylpolysiloxane having a polymerization degree of about 20 in which both ends of a molecular chain are blocked with silanol groups as a silica dispersing agent are kneaded with a kneader, and the mixture is mixed at 170 ° C./2 hours Heat treatment was performed to prepare a silicone rubber composition.

Further, as a cross-linking agent, both terminals are blocked with a dimethylhydrogensilyl group, and 20 mol% of the main chain is
Organohydrogenpolysiloxanes each having -H (CH ₃ ) SiO- units and-(CH ₃ ) ₂ SiO- units having the degree of polymerization shown in Table 1 were prepared. The number of moles of a vinyl group contained in one molecule of the organopolysiloxane in the silicone rubber composition is defined as (SiVi), and the number of moles of SiH contained in one molecule of the organohydrogenpolysiloxane is defined as (SiVi).
When the number of moles of the group was (SiH), the organohydrogenpolysiloxane was added to the composition in such an amount that the molar ratio (SiH) / (SiVi) became the value shown in Table 1. However, only the comparative example 5 did not contain the organohydrogenpolysiloxane.

In Comparative Examples 5 and 6, each of the peroxides shown in Table 1 was added in an amount of 0.5 part by weight as peroxide vulcanization. However, only the platinum catalyst was not added in Comparative Example 6.

The amount of platinum was 2% by weight in the octyl alcohol-modified solution of chloroplatinic acid with respect to the compositions of Examples and Comparative Examples.
Was added to the composition of the present invention and the composition of the comparative example by adding 0.2 parts by weight of a platinum catalyst and 0.05 part by weight of ethynylcyclohexanol as a control agent. Pressed for minutes and vulcanized. A sheet having a thickness of 2 mm was formed under the above-mentioned conditions for elongation fatigue resistance measurement, and was formed in accordance with JIS K6301 for bending fatigue resistance measurement. These two types of tests were performed on these, and the obtained results are shown in Table 2. It became clear that the cured product of the composition of the present invention was excellent in elongation fatigue resistance and flex fatigue resistance.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As described above, it is possible to provide a silicone rubber composition for automobile joint cover boots having excellent bending fatigue resistance, particularly a very low crack growth rate, and excellent extension fatigue resistance.

Claims (2)

[Claims] 1. A silicone rubber composition for automobile joint cover boots comprising the following a), b), c) and d). A) 100 parts by weight of an organopolysiloxane represented by the average composition formula R _a SiO _{(4-a) / 2} and having at least two aliphatic unsaturated hydrocarbon groups in one molecule, wherein R is A is a substituted or unsubstituted monovalent hydrocarbon group, a is a positive number from 1.95 to 2.05) b) is represented by the following general formula (Formula 1) and has at least two hydrogen atoms bonded to silicon atoms in one molecule Organohydrogenpolysiloxane "where the ratio of the number of moles of hydrogen atoms in b) to the number of moles of aliphatic unsaturated hydrocarbon groups in b) is 1.0 to 2.5", wherein R is the same as defined above. , a is H or R, B is SiRH _2, SiR _{2 H,} a group selected from SiR _3, m is an integer of m ≧ 0, n is and integer of n ≧ 0 5 ≦ (m + n) ≦ 100 "embedded 1) C) Reinforcing silica 10 to 100 parts by weight, d) Platinum catalyst Catalyst amount. 2. The organopolysiloxane of a) wherein the molecular chain terminal is an aliphatic unsaturated hydrocarbon group and 0.25 to 10 mol% of R in the average composition formula is an aliphatic unsaturated hydrocarbon group. 2. The silicone rubber composition for automobile joint cover boots according to claim 1, wherein parts by weight are contained in 100 parts by weight of the organopolysiloxane.