JP2001214062A - Silicone rubber composition and method for producing the same - Google Patents

Abstract

(57) [Abstract] (with correction) [PROBLEMS] To provide a silicone rubber composition which does not undergo heat treatment, has little plasticization return, has excellent storage stability, and does not cause physical change with time. SOLUTION: (A) Average composition formula: R ¹ _a SiO
_{2 (4a-a) / 2} (R ¹ is a monovalent hydrocarbon group, a is 1.98 to 2.0
2) 100 parts of polyorganosiloxane, (B) average composition formula: R ² _b H _c SiO _{(4-bc) / 2} (R ² is a monovalent hydrocarbon group, b and c are positive numbers and b + c = 1.0 to 3.0) polyorganohydrogensiloxane 0.1-10 parts, (C) the average composition _{^{formula: R 3 d Z e SiO (}} 4-de) / 2 (R 3 is a monovalent hydrocarbon group, Z is 1 Valence polyether chain-containing groups, d and e are 0 <
d ≦ 2, 0 <e ≦ 1, 1.9 ≦ d + e ≦ 2.1)
Of polyether-modified polyorganosiloxane 0.1 to 10
Parts (D) 5 to 200 parts of finely divided wet silica.

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 and a method for producing the same. The present invention relates to a silicone rubber composition that hardly changes, and a method for producing such a silicone rubber composition.

[0002]

2. Description of the Related Art Silicone rubber has excellent heat resistance,
It is widely used in various fields due to its cold resistance, weather resistance, electrical characteristics and the like. In such a silicone rubber, a reinforcing silica powder such as fumed silica or finely powdered silica is usually blended in order to increase the mechanical strength.

[0003] Among the reinforcing silica powders, silica produced by a wet method (hereinafter referred to as wet silica) is particularly used.
Since the silicone rubber is very inexpensive, the silicone rubber in which it is blended has a great cost advantage. In addition, wet silica has been widely used as a general-purpose silicone rubber filler since it gives excellent elasticity in terms of rubber properties.

However, wet silica is about 1 to 15%
It is known that since the surface is covered with the adsorbed water, the compatibility with the silicone rubber having high water repellency is very poor as compared with the fumed silica having almost no adsorbed water. Therefore, simply blending wet silica with silicone raw rubber changes the rubber properties over time or greatly increases the plasticity over time due to poor affinity between the two. Cured)
Caused a problem.

[0005] As measures to prevent this plasticization return, for example, (1) chain or cyclic polyorganosiloxane, hexamethyldisilazane, reactive silane, or the like is added and heat-treated, so that silicone raw rubber and wet silica are mixed. And (2) using wet silica which has been treated with an appropriate polyorganosiloxane, hexamethyldisilazane, reactive silane, etc., and then hydrophobized to obtain a raw silicone rubber. Methods for increasing the affinity with, for example, have been conventionally implemented.

[0006]

However, in the above-mentioned method (1), heat treatment is required, which is a major factor that hinders improvement in productivity and cost reduction of silicone rubber. I was

That is, in the method (1), the water adsorbed on the surface of the wet silica is forcibly heated by heating at a temperature of at least 100 ° C., preferably at least 150 ° C. under normal pressure, or by heating under reduced pressure. In this method, the affinity between wet silica and raw silicone rubber, linear or cyclic polyorganosiloxane, hexamethyldisilazane, reactive silane, or the like is increased.

Japanese Patent Application Laid-Open No. Hei 7-133356 also proposes a heat treatment at a higher temperature condition (200 to 225 ° C.) in order to obtain a silicone rubber composition with little plasticization return over a long period of time. Have been. Further, JP-A-10-120905
Japanese Patent Application Laid-Open Publication No. H11-163873 discloses a method for reducing the difference in physical properties between primary vulcanization and secondary vulcanization of silicone rubber, in which a polyorganohydrogensiloxane is blended as a silica filler treating agent, and a temperature of 100 ° C. or higher is used. There has also been proposed a method of heating the material.

As described above, heat treatment is indispensable in order to reduce the time-dependent property change and plasticization return (crepe hardening) of the silicone rubber kneaded material (compound). There has been a problem that not only productivity is remarkably reduced, but also price reduction is hindered.

Further, in the above method (2), when the heat treatment is not carried out, a sufficient effect is not obtained in preventing a change in characteristics over time and a prevention of plasticization return. In addition, wet silica has the property of absorbing moisture over time, even if it is once hydrophobicized by surface treatment.
Even when using wet silica surface-treated by the method (2), heat treatment is substantially performed. Further, in this method, since it is necessary to perform a surface treatment of wet silica in advance, there is a problem that productivity of silicone rubber is lowered and price is increased.

The present invention has been made to address such problems, and contains finely powdered wet silica, has little plasticization reversion, has excellent storage stability, and hardly changes in physical properties over time. No silicone rubber compound,
An object of the present invention is to provide a silicone rubber composition that can be obtained without performing a heat treatment, and a method for producing the same.

[0012]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that, when mixing fine powdered wet silica into silicone rubber raw rubber, polyorganohydrogensiloxane and polyether-modified It has been found that the use of a polyorganosiloxane in combination is effective for increasing the affinity between the two, and the present invention has been completed.

That is, the silicone rubber composition of the present invention comprises: (A) an average composition formula: R ¹ _a SiO _{(4-a) / 2} (where R ¹ is a substituted or unsubstituted monovalent hydrocarbon group) And a represents a number in the range of 1.98 to 2.02.) Polyorganosiloxane 100 having an average degree of polymerization of 3000 to 20000
(B) average composition formula: R ² _b H _c SiO _{(4-bc) / 2} (wherein R ² is a substituted or unsubstituted monovalent hydrocarbon group) , b, c is a polyorganohydrogensiloxane 0.1-10 parts represented by each represent a positive number number b + c = 1.0 to a 3.0), (C) the average composition formula:. R ³ _d Z _e SiO _{(4-de) / 2} (wherein, R ³ represents a substituted or unsubstituted monovalent hydrocarbon group, and each R ³ may be the same or different from each other. ^{formula: -R 4 O- (R 5 O} ) n -R 6
Is a monovalent polyether chain-containing group. In the formula, R ⁴ represents an alkylene group, R ⁵ represents one or more alkylene groups having 2 to 4 carbon atoms, and R ⁶ represents a hydrogen atom or an alkylene group having 1 to 18 carbon atoms and containing no unsaturated bond. Represents a monovalent hydrocarbon group, and n represents a number of 3 to 100. Further, d,
e satisfies 0 <d ≦ 2 and 0 <e ≦ 1, respectively; and
Indicates a number that satisfies 1.9 ≦ d + e ≦ 2.1. ), And 0.1 to 10 parts of a polyether-modified polyorganosiloxane represented by the formula (D), and (D) 5 to 200 parts of finely divided wet silica.

Further, the method for producing a silicone rubber composition of the present invention is characterized in that the above silicone rubber composition is mixed at room temperature without heating.

In the present invention, a silicone rubber composition which has little plasticization reversion, has excellent storage stability, and hardly changes in physical properties over time can be easily prepared without heat-treating the composition containing wet silica. Can be obtained. And since it is not necessary to perform a heat treatment, high productivity can be obtained and the cost reduction of silicone rubber can be achieved.

Hereinafter, the present invention will be described in more detail.

(A) The average degree of polymerization represented by the following formula (A): R ¹ _a SiO _{(4-a) / 2}
The polyorganosiloxane of 00 to 20000 serves as a base polymer of the curable silicone rubber composition. Primarily linear ones are used, but a part thereof may form a branched or three-dimensional structure, or may be a homopolymer, a copolymer or a mixture thereof.

In this polyorganosiloxane, the substituted or unsubstituted monovalent hydrocarbon group (R ¹ ) bonded to a silicon atom includes, for example, an alkyl group such as a methyl group, an ethyl group and a propyl group; a vinyl group; Alkenyl groups such as allyl group and butadienyl group; aryl groups such as phenyl group, xenyl group and naphthyl group; cycloalkyl groups such as cyclohexyl group; cycloalkenyl groups such as cyclohexenyl group; aralkyl groups such as benzyl group. A group; an alkylaryl group such as a tolyl group or a xylyl group;

In general, these hydrocarbon groups are preferably methyl groups, but from the viewpoint of mechanical strength and crosslinkability,
For example, the vinyl group may contain about 0 to 5% of the total number of R ¹ . The content ratio of the vinyl group is particularly 0.05 to
A range of 3% is preferred.

The molecular chain terminal of the polyorganosiloxane is exemplified by a hydroxyl group, an alkoxy group or a triorganosilyl group, and a triorganosilyl group is more preferable. Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, and a methyldiphenylsilyl group.

The average degree of polymerization of the above component (A) is from 3000 to 2
0000, preferably 5000-10000, more preferably 6000-7000. (A) The average degree of polymerization of the component is 30.
If it is less than 00, it is difficult to obtain a sufficient mechanical strength, and if the average polymerization degree is more than 20000, it becomes difficult to incorporate it into the system.

The (B) polyorganohydrogensiloxane represented by the average composition formula: R ² _b H _c SiO _{(4-bc) / 2} used in the present invention is a polyether of the component (C) described later. It acts on finely powdered wet silica synergistically with the modified polyorganosiloxane and is an important component for achieving the object of the present invention.

The component (B) may be any polyorganohydrogensiloxane having at least one silicon-hydrogen bond in one molecule, and may be branched from low-molecular-weight compounds to high-molecular-weight compounds. Various types of compounds and cyclic compounds such as resinous compounds can be used. As a substituted or unsubstituted monovalent hydrocarbon group (R ² ) bonded to a silicon atom,
Can be selected from the same hydrocarbon group as R ¹ described above, it is particularly preferable to be methyl group.

The amount of the component (B) is based on the amount of silicon-
Depending on the content of hydrogen bonds, based on 100 parts of component (A)
It can be changed in the range of 0.1 to 10 parts. If the amount of the component (B) is less than 0.1 part, the desired effect cannot be obtained.
On the other hand, if it exceeds 10 parts, the surface of the vulcanized rubber becomes sticky, which is not preferable.

The polyether-modified polyorganosiloxane which is the component (C) used in the present invention is (D)
The component (C) itself has a function of being compatible with both water contained in the finely divided wet silica as the component and the polyorganosiloxane as the component (A), and the finely divided wet silica as the component (D) and (A) ) At the same time as being a binder for the polyorganosiloxane as the component, it facilitates the binding reaction of the polyorganohydrogensiloxane as the component (B) to the component (D) and promotes surface treatment without applying heat energy by heating. It will be possible to do so.

It is necessary that both the component (B) and the component (C) be blended together, and the desired effect cannot be obtained if either one is missing. That is, when either one of the component (B) and the component (C) is lacking, without heat treatment, there is little plasticization return, excellent storage stability, and physical properties over time. It is not possible to obtain silicone rubber compounds with little change.

The component (C) has an average composition formula: R^Three _dZ
_eSiO_{(4-de) / 2}In the molecule, a siloxy unit represented by
Having at least one polyether-modified polyorgano
Siloxane. Substituted or non-bonded to the silicon atom
A substituted monovalent hydrocarbon group (R ^Three) Is the above-mentioned R
¹Can be selected from the same hydrocarbon groups as
Preferably, it is a tyl group. Z is a general formula: -R
^FourO- (R^FiveO)ⁿ-R⁶Monovalent polyether represented by
A chain-containing group.

Here, R ⁴ represents an alkylene group, and examples thereof include a methylene group, an ethylene group and a trimethylene group.
Preferably it is a trimethylene group. R ⁵ is, -R ⁵ O-
Represents an alkylene group having 2 to 4 carbon atoms constituting a polyether chain, ethylene group, trimethylene group, linear alkylene group such as tetramethylene group, and methylethane-1,2-diyl group, ethylethane-1,2 And a branched alkylene group such as -diyl group. Although the same polyether chain may have only one kind of alkylene group,
A copolymerized polyether chain containing at least one kind of alkylene group may be formed. In this case, a random copolymerized chain or a block copolymerized chain may be used. Further, the degree of polymerization n of the polyether chain is 3 to 100, more preferably 3 to 30.
The degree of polymerization n is a purpose of the polyether modified polyorganosiloxane, hydrophobicity / hydrophilicity ratio and viscosity required, depending on the physical properties such as interfacial tension, it is selected along with the kind or the combination of R ^5. R ⁶ is a hydrogen atom or a carbon atom 1
To 18, preferably a monovalent hydrocarbon group containing no unsaturated bond of 1 to 6, specifically, an alkyl group such as a methyl group, an ethyl group, a butyl group, an octyl group and an octadecyl group; a benzyl group And the like; an aralkyl group such as phenyl; an aryl group such as phenyl; and an arylaryl group such as octylphenyl and nonylphenyl.

In order to achieve the object of the present invention, it is desirable to use (C) the polyether-modified polyorganosiloxane having an average molecular weight of 500 to 500,000. If the average molecular weight of the component (C) is out of the above range, the ability to treat the surface of the wet silica is insufficient, which is not preferable. The compounding amount of the polyether-modified polyorganosiloxane as the component (C) can be an appropriate amount in the range of 0.1 to 10 parts depending on the content of the polyether. If the amount of the component (C) is too small, the desired effect cannot be obtained.
Roll workability deteriorates, which is not preferable.

The (D) finely divided wet silica used in the present invention is finely divided silica produced by a wet method, that is, a method of reacting sodium silicate with a mineral acid and salts in an aqueous solution. A known filler generally used as a reinforcing filler such as silicone rubber can be used. Commercial products include Nipsil LP, Nipsil HD, Nipsil VN3 and Nipsil SS manufactured by Nippon Silica Kogyo Co., Ltd.
And Toksil series such as Toksil US, Toksil USA and Toksil US-F manufactured by Tokuyama Soda Co., Ltd.

It is preferable to use (D) the finely powdered wet silica having a particle diameter of 20 μm or less. In addition, from the viewpoint of cost reduction, it is preferable that the surface treatment is not performed. However, it is also possible to use one that is surface-treated with organosilane, organosiloxane, organosilazane, or the like. Furthermore, in order to achieve the object of the present invention, the water content of the component (D) is preferably from 1 to 9%, more preferably from 2 to 7%.

If the amount of the component (D) is too large, it is difficult to mix it. If the amount is too small, mechanical strength such as tensile strength cannot be imparted.
It is preferable to add 5 to 200 parts with respect to 00 parts.

The silicone rubber composition of the present invention is obtained by mixing the above-mentioned components (A) to (D) using a twin roll, Banbury mixer, kneader mixer, single-shaft or twin-shaft continuous mixer or the like. It is obtained by doing. And
Since there is no need to perform a heat treatment after mixing, the silicone rubber composition can be prepared in a short time. If necessary, additives such as known fillers such as titanium oxide, carbon black, iron oxide and glass fiber, heat-resistant agents and pigments may be added.

The silicone rubber composition thus obtained can be cured by further blending a curing agent. As the curing method, there are two methods, a curing method using an organic peroxide and a curing method using an addition type crosslinking agent and a catalyst.

Here, as a curing agent using an organic peroxide, conventionally known benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, ditertiary butyl peroxide, dicumyl peroxide, 2,5-dimethyl- Examples thereof include 2,5-di (tert-butylperoxy) hexane. These curing agents are used in the range of 0.1 to 5 parts based on 100 parts of the silicone rubber composition of the present invention.

Further, an addition type reaction (hydrosilylation reaction)
As a curing agent, a polyorganosiloxane having an average of two or more hydrogen atoms bonded to silicon atoms in one molecule is used as a crosslinking agent, and a platinum-based catalyst is used as a curable catalyst. The compounding amount of the polyorganosiloxane having a hydrogen atom is 0.5 to 5 hydrogen atoms bonded to a silicon atom with respect to one alkenyl group bonded to a silicon atom in the polyorganosiloxane in the silicone rubber composition of the present invention. Is preferable. When a polyorganosiloxane having an average of two or more hydrogen atoms bonded to silicon atoms in one molecule is blended as the component (B) of the present invention, the amount of the crosslinking agent can be reduced. It is. The platinum-based catalyst is preferably used in an amount of about 1 to 1000 ppm based on the component (A).

Further, a specific silicone rubber molded product such as a keypad can be obtained by molding the above-described silicone rubber composition by a known molding method such as press molding or injection molding using a mold.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In addition, all parts in the examples represent parts by mass.

Example 1 99.86 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (C
H ₂ ＣＨCH) 100 parts of a polyorganosiloxane having a polymerization degree of 7000, which is composed of 0.14 mol% of SiO units and whose terminals are blocked with dimethylvinylsilyl groups, and a dimethylsiloxane unit and a methylhydrogensiloxane unit in a molar ratio of 1: 9. 2 parts of methyl hydrogen polysiloxane (1) with a viscosity of 1000 cSt and a polyether group content of 30%
Then, 3 parts of polyether-modified polyorganosiloxane (1) having an average molecular weight of 8,000, 45 parts of Tokusil USA, a finely powdered wet silica, and 0.07 part of magnesium stearate were kneaded with a kneader mixer until uniform. Thus, a silicone rubber composition (compound) was obtained. At this time, no heating was performed. Then, the time required to obtain this silicone rubber composition was measured. Immediately, the plasticity of the obtained silicone rubber composition was measured.

Next, the obtained silicone rubber composition 100
Parts of organic peroxide (2,5-dimethyl
-2,5-di (tert-butylperoxy) hexane
0.3 parts was added, and press vulcanization was performed for 10 minutes at a temperature of 170 ° C. and a pressure of 100 kgf / cm ² to prepare a 130 mm × 130 mm × 2 mm silicone rubber sheet. Then, this sheet was subjected to at-vulcanization (secondary vulcanization) at 200 ° C. for 4 hours using an air circulation dryer, and the hardness was measured the next day.

Further, the obtained silicone rubber composition was left in a room at 40 ° C. for one month, taken out, put into a 16-inch roll, observed the degree of plasticization return, and produced a silicone rubber sheet. And the hardness was measured. Table 1 shows the results.

Example 2 In place of the methyl hydrogen polysiloxane (1), the molar ratio of the dimethyl siloxane unit to the methyl hydrogen siloxane unit was 1: 1 and the viscosity was 200 cSt. And a silicone rubber composition was obtained in the same manner as in Example 1 except that the amount was 3 parts. At this time, the time required to obtain the silicone rubber composition was measured. A test similar to that of Example 1 was performed using this silicone rubber composition. Table 1 shows the results.

Example 3 In place of the polyether-modified polyorganosiloxane (1), the content of polyether groups was 70%, and the average molecular weight was 2%.
0000 polyether modified polyorganosiloxane
A silicone rubber composition was obtained in the same manner as in Example 2, except that (2) was used, and the amount was further changed to 2 parts. At this time, the time required to obtain the silicone rubber composition was measured. Also, using this silicone rubber composition,
The same test as in Example 1 was performed. Table 1 shows the results.

Comparative Example 1 A silicone rubber composition was obtained in the same manner as in Example 1 except that the polyether-modified polyorganosiloxane (1) was not blended. At this time, the time required to obtain the silicone rubber composition was measured. A test similar to that of Example 1 was performed using this silicone rubber composition.
Table 1 shows the results.

Comparative Example 2 A silicone rubber composition was obtained in the same manner as in Example 1 except that the methylhydrogenpolysiloxane (1) was not blended. At this time, the time required to obtain the silicone rubber composition was measured. A test similar to that of Example 1 was performed using this silicone rubber composition. Table 1 shows the results.

Comparative Example 3 In the silicone rubber composition of Example 1, neither methyl hydrogen polysiloxane (1) nor polyether-modified polyorganosiloxane (1) was blended.
The terminal is blocked with a silanol group and the viscosity at 25 ° C is 9
3 parts of 0 cSt polyorganosiloxane was blended. Otherwise in the same manner as in Example 1, a silicone rubber composition was obtained. At this time, the time required to obtain the silicone rubber composition was measured. A test similar to that of Example 1 was performed using this silicone rubber composition. Table 1 shows the results.

Comparative Example 4 The silicone rubber composition obtained in Comparative Example 3 was subjected to a heat treatment at 150 ° C. for 3 hours while kneading. At this time,
The time required to obtain the silicone rubber composition was measured, but a considerable time other than the heating time was required, such as the time required to reach a predetermined temperature and the cooling time after heating. Example 1 was prepared using the obtained silicone rubber composition.
The same test was performed. Table 1 shows the results.

Comparative Example 5 The silicone rubber composition obtained in Comparative Example 1 was subjected to a heat treatment at 150 ° C. for 3 hours while kneading. At this time,
The time required to obtain the silicone rubber composition was measured, but a considerable time other than the heating time was required, such as the time required to reach a predetermined temperature and the cooling time after heating. Example 1 was prepared using the obtained silicone rubber composition.
The same test was performed. Table 1 shows the results.

[0049]

[Table 1] As shown in Table 1, in Examples 1 to 3, by using a combination of methyl hydrogen polysiloxane and polyether-modified polyorganosiloxane, the plasticization reversion is small similarly to the composition obtained by the heat-kneading formulation. A silicone rubber composition having a small change in hardness over time was obtained. Moreover, since the heating and kneading process can be omitted,
The production time can be greatly reduced, and the price of silicone rubber can be significantly reduced.

[0050]

As is apparent from the above description, according to the present invention, from the compounding ingredients containing finely divided wet silica,
Without heat treatment, a silicone rubber composition with little plasticization return, excellent storage stability, and little change in physical properties over time can be easily obtained. And
Since there is no need to perform a heat treatment, it is possible to realize unprecedented high productivity and to reduce the cost of silicone rubber.

Claims (3)

[Claims] (A) Average composition formula: R ¹ _a SiO
_{(4-a) / 2} (wherein, R ¹ represents a substituted or unsubstituted monovalent hydrocarbon group, and a represents a number in the range of 1.98 to 2.02.) Polyorganosiloxane 100
(B) average composition formula: R ² _b H _c SiO _{(4-bc) / 2} (wherein R ² is a substituted or unsubstituted monovalent hydrocarbon group) , b, c is a polyorganohydrogensiloxane 0.1-10 parts represented by each represent a positive number number b + c = 1.0 to a 3.0), (C) the average composition formula:. R ³ _d Z _e SiO _{(4-de) / 2} (wherein, R ³ represents a substituted or unsubstituted monovalent hydrocarbon group, and each R ³ may be the same or different from each other. ^{formula: -R 4 O- (R 5 O} ) n -R 6
Is a monovalent polyether chain-containing group. In the formula, R ⁴ represents an alkylene group, R ⁵ represents one or more alkylene groups having 2 to 4 carbon atoms, and R ⁶ represents a hydrogen atom or an alkylene group having 1 to 18 carbon atoms and containing no unsaturated bond. Represents a monovalent hydrocarbon group, and n represents a number of 3 to 100. further,
d and e satisfy 0 <d ≦ 2 and 0 <e ≦ 1, respectively.
And a number that satisfies 1.9 ≦ d + e ≦ 2.1. ) Represents a polyether-modified polyorganosiloxane 0.1 to 10
(D) 5 to 200 parts of finely divided wet silica. 2. The silicone rubber composition according to claim 1, wherein the polyether-modified polyorganosiloxane (C) has an average molecular weight of 500 to 500,000. 3. A method for producing a silicone rubber composition, comprising mixing the silicone rubber composition according to claim 1 at room temperature without heating.