JP2616284B2 - Method for producing silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a silicone rubber having excellent fatigue durability, and thus has improved elongation and bending fatigue characteristics required for dynamic applications. The present invention relates to a method for producing a silicone rubber composition useful for applications such as boots, diagrams, and medical pump tubes.

[0002]

2. Description of the Related Art A silicone rubber composition is obtained by blending a filler, a processing aid, a vulcanizing agent, etc., with a silicone polymer (raw rubber). Silicone rubber has heat resistance, cold resistance, weather resistance, and electric resistance. It excels in insulation, compression set, rubber elasticity, etc. and is non-toxic.
Not only static applications from electronic parts, office equipment, automobiles, aircraft, food, medical products to leisure products, but also rubber contacts in calculators and push phones, keyboards, constant velocity joint cover boots for automobiles, diagrams, medical pumps It is also widely used in dynamic applications such as tubes.

[0003]

However, when silicone rubber is used for the above-mentioned dynamic applications, the results of dynamic fatigue properties such as elongation and flexural fatigue properties are not always satisfactory, so that general synthetic rubber is not used. Dynamically adopting means such as uniform cross-linking, low cross-link density, low modulus, low filling of filler, uniform dispersion, and removal of coarse filler used to improve the dynamic fatigue characteristics of rubber Although the fatigue properties are improved, the elongation and bending fatigue properties of such treatments are reduced by 50% according to the most common Demasher type fatigue test method.
The limit is the 10,000th level.

A method of adding an organohydrogenpolysiloxane to a silicone polymer in order to improve the dynamic fatigue characteristics (JP-A-62-197452, JP-A-62-197452).
JP-A-2-197454), a method of adding a fluorine-containing low polymer (see JP-A-63-150350), and a method of adding a phosphorus-containing organic compound (JP-A-62).
The silicone rubbers produced by these methods have improved flex fatigue properties by the Demasher type fatigue test method up to 10 million times, but further improve flex fatigue properties. Therefore, there is a strong demand for the development of a silicone rubber having further improved bending fatigue characteristics.

[0005] The present invention has been made in view of the above circumstances,
In particular, it is an object of the present invention to provide a method for producing a silicone rubber composition that gives a silicone rubber having improved elongation and bending fatigue properties.

[0006]

The present inventors have made intensive studies to achieve the above object, and as a result, the dispersion state of the finely divided silica in the silicone rubber composition has been found to affect the elongation and bending fatigue characteristics of the silicone rubber. In order to improve the state of dispersion of the fine silica powder, a raw rubber (organopolysiloxane) having an average degree of polymerization of 3000 or more represented by the following composition formula (1) was added.
First, one of the two organopolysiloxane raw rubbers, which is divided into two as a first step, has a specific surface area of at least 50 m ² /
g of the finely divided silica and a silica dispersant to form a very good dispersion state of the silica fine powder in the silicone rubber composition. By adopting a production method in which 1 to 30 parts by weight of the organopolysiloxane raw rubber is added to 100 parts by weight of the component (A) and kneaded, the elongation, It has been found that the bending fatigue life is extended 1.5 to 3 times, and the life can exceed 30 million cycles in the absolute value of the Demasher type fatigue test. High hardness,
The inventors have found that they have characteristics such as high elasticity and high tear, and have accomplished the present invention.

[0007]

Embedded image (In the formula, R ¹ is a monovalent organic group or a hydroxyl group excluding the same or different fluorine-containing groups, and a is a positive number from 1.90 to 2.05.)

Accordingly, the present invention provides (A) an organopolysiloxane having an average degree of polymerization of 3000 or more represented by the above average composition formula (1), (B) finely divided silica having a specific surface area of 50 m ² / g or more, and C) After kneading the silica dispersant uniformly, the above (A)
The same organopolysiloxane as component (A) component 10
A method for producing a silicone rubber composition, characterized in that after 1 to 30 parts by weight are added to 0 parts by weight and kneading, a curing catalyst is added to the silicone rubber composition obtained by the above-mentioned production method. A method for producing a silicone rubber characterized by being cured.

Hereinafter, the present invention will be described in more detail. The method for producing a silicone rubber composition of the present invention comprises mixing a mixture of (A) an organopolysiloxane, (B) finely divided silica, and (C) a silica dispersant. After kneading, the same organopolysiloxane as the component (A) is added later.

In this case, the organopolysiloxane of the component (A) is represented by the following formula (1).

[0011]

Embedded image

Here, R ¹ is a monovalent organic group or a hydroxyl group excluding the same or different fluorine-containing groups, and the organic group preferably has 1 to 10, particularly preferably 1 to 8, carbon atoms.
Specifically, alkyl groups such as methyl group, ethyl group, propyl group and butyl group; alkenyl groups such as vinyl group and allyl group; aryl groups such as phenyl group and tolyl group; cycloalkyl groups such as cyclohexyl group; , An aralkyl group such as a β-phenylethyl group, or a chloromethyl group in which part or all of the hydrogen atoms bonded to the carbon atoms of these groups have been substituted with a halogen atom (excluding a fluorine atom), a cyano group, or the like; And the like. A is a positive number from 1.90 to 2.05.

The organopolysiloxane is basically preferably a linear diorganopolysiloxane, and may have a partially branched structure. The organopolysiloxane has an average degree of polymerization of 300 from the viewpoint that silicone rubber has sufficient hardness for practical use.
It is 0 or more, preferably 4000 to 6000.

In the above R ¹ , 50 mol% or more is a methyl group, and when an organic group other than a methyl group is used, a phenyl group is 50 mol% or less and a vinyl group is 0.01 to 6 mol%.
It is preferable that the organopolysiloxane contains a trialkylsilyl group containing a lower alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, or one or more of these alkyl groups. A silyl group in which two or more groups are substituted with an alkoxy group such as a hydroxyl group, a methoxy group, an ethoxy group, a propoxy group and a butoxy group; a dialkylmonoalkenyl group containing the above-mentioned alkyl group and a lower alkyl group such as a vinyl group, an allyl group or a butenyl group; What is necessary is just to block with the silyl group, the alkyl dialkenyl silyl group, and the trialkenyl silyl group.

The finely divided silica as the component (B) is for imparting appropriate hardness and mechanical strength to the silicone rubber, and has a specific surface area of 50 m ² / g or more, preferably 130 m ² / g or more.
Finely powdered silica ~250m ² / g is preferably used.
As such finely divided silica, specifically, conventionally known fillers for silicone rubber, such as fumed silica, precipitated silica, and silica airgel, can be used alone or in combination of two or more. These silicas may be surface-treated with silane, siloxane, silazane or the like containing trimethylsilyl group, dimethylsilyl group, diphenylmethylsilyl group or the like.

The amount of the fine powdered silica is based on 100 parts (parts by weight, hereinafter the same) of the total of the organopolysiloxane (A) used in the first step and the organopolysiloxane used in the second step. 10-100 parts, especially 2
It is preferable that the amount be 0 to 70 parts. If the amount is less than 10 parts, the reinforcing properties of the silicone rubber may be insufficient, and if it exceeds 100 parts, the processability of the silicone rubber composition may be extremely difficult.

The dispersant of the component (C) is represented by the following formula (2)
The organopolysiloxane represented by is preferably used.

[0018]

Embedded image

Here, R ² and R ³ are the same monovalent organic groups as R ¹ (however, they may be fluorine-substituted hydrocarbon groups).
And b is a number of 4 to 100, preferably 4 to 20. The amount of the organopolysiloxane is 0.5 to 15 parts, preferably 1 to 10 parts, based on 100 parts of the total of the organopolysiloxane (A) used in the first step and the organopolysiloxane used in the second step. It is preferable to use a part. If the compounding amount is less than 0.5 part, there is a possibility that the processability is remarkably impaired, such as an increase in plastic reversion. If the compounding amount exceeds 15 parts, the silicone composition has tackiness and may also impair the processability.

The composition of the present invention may contain, if necessary, pigments, dyes, antioxidants, antioxidants, antistatic agents, flame retardants such as antimony oxide and paraffin chloride, and boron nitride, aluminum oxide and the like. A thermal conductivity improver and the like may be blended. Also, various known rubber compounding agents appropriately compounded in the silicone rubber composition, for example, pulverized silica, diatomaceous earth, iron oxide, zinc oxide, titanium oxide, carbon black, barium oxide, magnesium oxide, cerium hydroxide, carbonate Calcium, magnesium carbonate, zinc carbonate, asbestos, glass wool, fine powdered mica, fused silica powder and the like may be added and blended to such an extent that the object of the present invention is not impaired.

In the method for producing the silicone rubber composition of the present invention, first, the above components (A), (B) and (C) are kneaded as a first step, and then the same as the above component (A) is carried out as a second step. Is added afterwards as the component (A ') and kneaded. In this case, the amount of the post-added organopolysiloxane added as the component (A ') in the second step is 1 to 30 parts, preferably 100 parts, per 100 parts of the organopolysiloxane of the component (A) used in the first step. 10 to 20 parts. If the amount of the component (A ') is less than 1 part, the effect of kneading is insufficient, and if it exceeds 30 parts, the tensile strength, the tear strength, and the like are deteriorated.

In the production of the silicone rubber composition of the present invention, the method of adding the component (A ') and heat-treating is as follows.
The mixture of the components (B) and (C) is kneaded with a mixer such as a kneader, and after the mixture becomes uniform, the component (A ′) is added.
A method of performing heat treatment at a temperature of 00 to 200 ° C, preferably 150 to 180 ° C for 0.5 to 5 hours, preferably 1 to 3 hours, and mixing the components (A), (B) and (C) in the same manner as described above. Kneading, heat treatment at the same temperature and time as described above, and then addition of the component (A ') can be employed. These heat treatments may be performed in the same kneader as the kneading, or may be further compounded by a roll.

To cure the silicone rubber composition produced as described above, a curing catalyst is used as the component (D). As a curing catalyst, a silicone rubber composition is heat-cured by addition of a conventionally known organic peroxide,
Curing may be carried out by any method of addition reaction by addition of organohydrogenpolysiloxane and a platinum-based compound, or method by condensation reaction, and therefore, what is necessary for these reactions can be used. Usually, a heat curing method by adding an organic peroxide is employed. Examples of the organic peroxide include benzoyl peroxide, monochlorobenzoyl peroxide, p-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide ,
t-butylbenzoyl peroxide, dicumylbenzoyl peroxide, 2,5-bis (t-butylperoxy) -2,5-dimethylhexane, 2,5-bis (t
-Butylperoxy) -2,5-dimethylhexine, and dicarbonates such as dimyristyl peroxycarbonate and dicyclododecylperoxydicarbonate;
Examples thereof include t-butyl monooxycarbonates, compounds represented by the following formula (3), and these may be used alone or
It can be used in combinations of more than one species.

[0024]

Embedded image (In the formula, R ⁴ is a monovalent hydrocarbon group having 3 to 10 carbon atoms.)

These organic peroxides are blended in an amount of 0.1 to 5 parts per 100 parts of the diorganopolysiloxane of the component (A) + (A ') usually used in the first step.

When the organopolysiloxane of the component (A) contains an alkenyl group such as a vinyl group or an allyl group in the molecule, one molecule of a silicon-bonded hydrogen atom that undergoes an addition reaction with the alkenyl group is used. A combination of an organohydrogenpolysiloxane having two or more components therein and a platinum group metal-based addition reaction catalyst can be used as a curing agent.

As such a platinum group metal-based addition reaction catalyst, for example, there are platinum-based, palladium-based, and rhodium-based catalysts, and among them, platinum-based catalysts are preferably used. Examples of the platinum-based catalyst include solid platinum supported on a carrier such as platinum black, alumina, and silica, chloroplatinic acid, alcohol-modified chloroplatinic acid, a complex of chloroplatinic acid and an olefin, and platinum-vinylsiloxane. Complexes are exemplified.

These platinum group metal-based addition reaction catalysts are used in an amount of 0.1 to 500 ppm, particularly preferably in the range of 0.1 to 500 ppm in terms of platinum group metal, based on the organopolysiloxane (A) + (A ′).
It is preferable to mix at a ratio of 0.5 to 200 ppm.

The organohydrogenpolysiloxane to be combined with the platinum group metal-based addition reaction catalyst includes:
For example, those represented by the following average composition formula (4) are exemplified.

[0030]

Embedded image

In the formula, R ⁵ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, c and d are each a positive number and 1
Those satisfying ≦ c + d ≦ 3 and having at least two silicon-hydrogen bonds in the molecule are used. Preferred examples of R ⁵ include alkyl groups such as methyl group, ethyl group, propyl group and butyl group, aryl groups such as phenyl group and tolyl group, and 3,3,3-trifluoropropyl group. it can.

The degree of polymerization of the organohydrogenpolysiloxane is preferably 300 or less, particularly preferably 10 to 100, and its molecular structure can be any of conventionally known linear, cyclic and branched. It may be.

The amount of the organohydrogenpolysiloxane to be added is 0.5 to 10, especially 1.0 to 3, based on the alkenyl group content (molar number) of the component (A) + (A ').
It is preferably set to 0.

[0034]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. Prior to the description of the examples, methods of measuring physical properties in each example will be described. (Method of measuring 100% elongation fatigue life) Measured using a Demasher-type bending fatigue tester (Toyo Seiki Co., Ltd.), and using a No. 3 dumbbell specified in JIS K-6301, Section 3 at 5 Hz at room temperature. Operate continuously and display the number of cycles until breakage. (Measurement Method of Keying Durability) A rubber contact having the shape shown in FIG. 1 is formed, and a change with time of the keying force of the restoring force when the stroke and the stress pattern are repeated is determined. The keying durability life was determined. The measurement is
The keying stroke was 1 mm and the keying speed was 5 times / second.

Examples 1 and 2, Comparative Example 1 (CH ₃ ) ₂ S
99.85 mol% of iO units and (CH ₃ ) (CH ＝ CH ₂ )
It consists of 0.15 mol% of SiO units and has a degree of polymerization of about 70.
00, the molecular chain ends are (CH ＝ CH ₂ ) (CH ₃ ) ₂ Si
86 parts of methylvinylpolysiloxane (raw rubber) blocked with _0.5 unit of O, 25 parts of fumed silica having a specific surface area of 200 m ² / g [Aerosil-200 (manufactured by Nippon Aerosil Co., Ltd.)], and a silica dispersant 2 parts of dimethylpolysiloxane having a degree of polymerization of about 20 and both ends of the molecule blocked with silanol groups, (CH ₃ ) (CH ＝ CH ₂ ) SiO
Dimethylpolysiloxane 4 containing 10 mol% units and having a degree of polymerization of about 20 and having both ends of molecular chains blocked with silanol groups
Parts were blended and kneaded with a kneader (formulation A).

After the composition A becomes uniform, (C
H _{3) 2} consists of SiO unit 100 mol%, polymerization degree of about 4
000 and the molecular chain end is (CH = CH ₂ ) (CH ₃ ) ₂ Si
_Oxygen- blocked methylvinylpolysiloxane _0.5
4 parts were added, kneaded for 30 minutes, and then heat-treated at 170 ° C. for 2 hours to obtain a silicone rubber composition I (Example 1).

Further, the same compound A as in Example 1 was kneaded and homogenized, and then heat-treated at 170 ° C. for 2 hours, and (C)
H _{3) 2} consists of SiO unit 100 mol%, polymerization degree of about 4
000 and the molecular chain end is (CH = CH ₂ ) (CH ₃ ) ₂ Si
_Oxygen- blocked methylvinylpolysiloxane _0.5
4 parts were added and kneaded for 30 minutes to obtain a silicone rubber composition II (Example 2).

In Example 1, 86 parts of methylvinylpolysiloxane (raw rubber) at the time of the first charge was added to 10 parts.
A silicone rubber composition III was prepared in the same manner except that the amount was 0 part, and the raw rubber was not added later (Comparative Example 1).

Next, 0.5 parts of 2,5-bis (t-butylperoxy) -2,5-dimethylhexane was added as a curing agent to these silicone rubber compositions I, II and III, and the mixture was heated at a temperature of 170 ° C. The sheet was press-cured at a pressure of 20 kg / cm ² for 10 minutes to produce a sheet having a thickness of 2 mm, and the 100% elongation fatigue life of the sheet was measured. Table 1 shows the results.

The silicone rubber compositions I, I
The rubber contact shown in FIG. 1 was prepared from I and III, and the keying durability of the rubber contact was examined. The results are also shown in Table 1.

[0041]

[Table 1]

Example 3, Comparative Example 2 (CH ₃ ) ₂ SiO
99.85 mol% of the unit and (CH ₃ ) (CH ＝ CH ₂ ) Si
O unit consists of 0.15 mol% and the degree of polymerization is about 7000
In 86 parts of methyl vinyl polysiloxane, the molecular chain ends of which are blocked with _0.5 units of (CH = CH ₂ ) (CH ₃ ) ₂ SiO,
Wet silica having a BET specific surface area of 190 m ² / g [N
ipsil-LP (manufactured by Nippon Silica Industry Co., Ltd.)] 35
5 parts of dimethylpolysiloxane containing 10 parts by mole of (CH ₃ ) (CH ＝ CH ₂ ) SiO units, having a degree of polymerization of about 20 and having both ends of the molecular chain blocked by silanol groups, and kneading with a kneader. did.

Then, heat treatment was performed at 170 ° C. for 2 hours,
H _{3) 2} consists of SiO unit 100 mol%, polymerization degree of about 4
000 and the molecular chain end is (CH = CH ₂ ) (CH ₃ ) ₂ Si
_Oxygen- blocked methylvinylpolysiloxane _0.5
4 parts were added and kneaded for 30 minutes to obtain a silicone rubber composition IV (Example 3).

In Example 3, 86 parts of methylvinylpolysiloxane (raw rubber) at the time of the first preparation was added to 10 parts.
A silicone rubber composition V was prepared in the same manner except that the amount was 0 part, and the raw rubber was not added later (Comparative Example 2).

Next, these silicone rubber compositions I
V and V were prepared in the same manner as in Examples 1 and 2, and a rubber contact was formed in the same manner as in Examples 1 and 2.
The same test was performed. Table 2 shows the results.

[0046]

[Table 2]

[0047]

As described above, according to the present invention,
It is possible to obtain a fatigue-resistant silicone rubber composition that gives a silicone rubber excellent in dynamic fatigue durability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a rubber contact used in a characteristic test in Examples and Comparative Examples of the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masayuki Yoshida 1-10 Hitomi, Matsuida-machi, Usui-gun, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Technology Laboratory (56) References JP-A-3-39360 ( JP, A) JP-A-63-207854 (JP, A)

Claims (2)

(57) [Claims] (A) an organopolysiloxane having an average degree of polymerization of 3000 or more represented by the following average composition formula (1): (In the formula, R ¹ is a monovalent organic group or a hydroxyl group excluding the same or different fluorine-containing groups, and a is a positive number of 1.90 to 2.05.) (B) Specific surface area is 50 m ² / g After uniformly kneading the finely divided silica and the silica dispersant (C), the above (A)
The same organopolysiloxane as component (A) component 10
A method for producing a silicone rubber composition, comprising adding 1 to 30 parts by weight to 0 part by weight and kneading the mixture. 2. A method for producing a silicone rubber, comprising adding a curing catalyst to the silicone rubber composition obtained in claim 1 and curing the composition.