JPH101611A - Silicone rubber composition and method for improving silicone rubber compression set - Google Patents

Abstract

(57) [Problem] To improve compression set characteristics of a silicone rubber composition. SOLUTION: (1) The following average composition formula (1) R ¹ SiO _{(4-n) / 2} (1) (where R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group) 100 parts by weight of a diorganopolysiloxane represented by the following formula (2): 10 to 70 parts by weight of a reinforcing silica powder having a specific surface area of 100 m ² / g or more. 3) A silicone rubber composition containing 0.1 to 50 parts by weight of titanium oxide having a crystal form of anatase type and a primary particle diameter of 10 nm or less (4) a releasing agent of 0 to 10 parts by weight. The composition described above can be suitably used as a seal, packing, gasket material, industrial roll material, office machine roll material, electrical insulating material, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention provides a cured product having excellent compression set characteristics, and is suitably used as a seal, packing, gasket material, industrial roll material, office machine roll material, electric insulating material and the like. And a method for improving the compression set properties of silicone rubber.

[0002]

2. Description of the Related Art In general, silicone rubber is excellent in weather resistance, durability, heat resistance, physiological inertness, coloring property, etc., and is therefore used for building materials, electric / electronic parts, office machine parts. It is used in various fields such as automobile parts, medical equipment and the like.

[0003] Silicone rubber moldings used for such applications are usually used under compressive deformation, and it is required to quickly restore the initial shape after removing the stress that causes deformation. You.

[0004] On the other hand, silicone rubber is generally said to have excellent compression set characteristics as compared with other synthetic rubbers. In recent years, however, seal, packing, gasket materials, industrial roll materials, and office machine rolls have been developed. The use of materials, furthermore, electric insulating materials such as anode caps and plug boots, which require a lower compression set characteristic than ever before, is increasing, and it is desired to meet this demand.

[0005] In this case, a release agent is often added to the silicone rubber composition in order to facilitate moldability of the silicone rubber. However, the addition of the release agent deteriorates the compression set characteristics of the silicone rubber. Therefore, improvement of this point is also desired.

The present invention has been made in view of the above circumstances, and provides a silicone rubber composition which provides a cured product having significantly improved compression set characteristics, and a method for improving the compression set characteristics of silicone rubber. With the goal.

[0007]

Means for Solving the Problems and Embodiments of the Invention The present inventors have made intensive studies to achieve the above object, and as a result, the following average composition formula (1) R ¹ SiO _{(4-n) / 2} ( 1) wherein R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a number from 1.98 to 2.02. A silicone rubber composition containing a reinforcing silica powder having a specific surface area of 100 m ² / g or more and, if necessary, a releasing agent, wherein the crystalline form is anatase type and the primary particle diameter is 10 nm.
It has been found that by adding the following titanium oxide, the compression set characteristic of the obtained cured silicone rubber is remarkably improved.

[0008] That is, it is known that titanium oxide is blended with silicone rubber. However, conventionally used titanium oxide is a wet type titanium oxide having a crystal type of rutile type or anatase type, or a fumed product prepared by a dry method. Titanium has a large primary particle size, and its compression set characteristics were hardly improved even when compounded with silicone rubber.However, when a specific amount of the above-mentioned special titanium oxide is mixed, it has excellent low compression set characteristics. It has been found that a silicone rubber composition giving a cured product can be obtained, and the present invention has been accomplished.

Accordingly, the present invention provides (1) 100 parts by weight of a diorganopolysiloxane represented by the above average composition formula (1), and (2) 10 to 70 parts by weight of a reinforcing silica powder having a specific surface area of 100 m ² / g or more. Part (3): a silicone rubber composition comprising: 0.1 to 50 parts by weight of titanium oxide having an anatase type crystal form and a primary particle diameter of 10 nm or less; and (4) a releasing agent of 0 to 10 parts by weight. A silicone rubber composition comprising: (1) a diorganopolysiloxane represented by the above average composition formula (1); and (2) a reinforcing silica powder having a specific surface area of 100 m ² / g or more. When curing in the presence of a silicone rubber, titanium oxide having an anatase crystal type and a primary particle diameter of 10 nm or less is added to the silicone rubber composition, and the pressure of the silicone rubber is reduced. To provide an improved method of compression set of the silicone rubber, characterized in that to reduce the permanent set values.

Hereinafter, the present invention will be described in more detail. The silicone rubber composition of the present invention comprises (1) a diorganopolysiloxane, (2) a reinforcing silica powder, (3) a specific titanium oxide, and if necessary. (4) It contains a release agent.

Here, the diorganopolysiloxane of the first component constituting the silicone rubber composition of the present invention has the following average composition formula (1) R ¹ SiO _{(4-n) / 2} (1) Wherein R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a number from 1.98 to 2.02).

R ¹ in the above formula (1) is the same or different and preferably has 1 to 10 carbon atoms, more preferably 1 to 10 carbon atoms.
8 is a substituted or unsubstituted monovalent hydrocarbon group, specifically a methyl group, an ethyl group, a propyl group, an isopropyl group,
Alkyl groups such as butyl group, isobutyl group, tert-butyl group, hexyl group and octyl group; cycloalkyl groups such as cyclohexyl group; alkenyl groups such as vinyl group, allyl group, butenyl group and hexenyl group; phenyl group and tolyl group , An aryl group such as a xylyl group, or a chloromethyl group, a chloromethyl group, a trifluoromethyl group, a cyanoethyl group, or the like, in which some or all of the hydrogen atoms bonded to carbon atoms of these groups are substituted with a halogen atom, a cyano group, or the like. You.
n is a number from 1.98 to 2.02. In addition, each substituent may be different or the same.

The organopolysiloxane of the above formula (1) may be such that the molecular chain ends are blocked with a trimethylsilyl group, dimethylphenylsilyl group, dimethylhydroxysilyl group, dimethylvinylsilyl group, trivinylsilyl group or the like. It is suitable.

The organopolysiloxane of the above formula (1) can be prepared by (co) hydrolytic condensation of one or more selected organohalogenosilanes, or a cyclic polysiloxane (trimer of siloxane or 4
And the like) can be obtained by ring-opening polymerization using an alkaline or acidic catalyst, and is basically a linear diorganopolysiloxane, but is a mixture of two or more kinds having different molecular structures. There may be.

The organopolysiloxane has 2
Although those having a viscosity at 5 ° C. of 100 cs or more are suitable, usually 100,000 to 100,000,000 c
s, the degree of polymerization is preferably 3,000 to 20,000.

The reinforcing silica powder as the second component is an essential component for obtaining a silicone rubber having excellent mechanical strength. For this purpose, the specific surface area is 100 m ² / g or more, preferably 150 to 200 m ² / g. It needs to be 400 m ² / g. Representative examples of the reinforcing silica powder include fumed silica, precipitated silica, and silica obtained by hydrophobizing the surface thereof with silane, siloxane, silazane, or the like.

The amount of the reinforcing silica powder added is 100 parts by weight of the first component organopolysiloxane (parts by weight, hereinafter the same).
When the amount is less than 10 parts, the amount is too small to obtain a sufficient reinforcing effect, and when the amount exceeds 70 parts, the workability deteriorates.

Next, the third component, titanium oxide, is an essential component of the present invention, and the crystal type is anatase type.
In addition, the primary particle diameter needs to be 10 nm or less. When the crystal type is anatase type and the primary particle diameter is 10 nm or less, the specific effect of improving compression set characteristics is exhibited. When the primary particle size exceeds 10 nm, the compression set characteristic of the present invention is not improved. There is almost no improvement effect.

Examples of such anatase type titanium oxide include ST-01 and ST-31 of Taipaque ST series manufactured by Ishihara Sangyo Co., Ltd.

The amount of the above-mentioned titanium oxide as the third component is from 0.1 to 50 parts, preferably from 1 to 50 parts, per 100 parts of the first component. When the amount exceeds 50 parts, the plastic reversion of the compound is large, the processability is poor, and the economy is disadvantageous.

The release agent of the fourth component is added for facilitating the moldability of the silicone rubber, and for example, improves the releasability of the unvulcanized rubber from a roll and the releasability from a mixer. For the purpose of facilitating mold release during mold vulcanization molding, it is added. Although this release agent may deteriorate the compression set property, the compression set property is compounded even when the release agent is mixed by the specific anatase type titanium oxide of the third component. If you can not keep it at the level.

Examples of the release agent used for such purposes include fatty acids, fatty acid metal salts, fatty acid amide compounds, waxes, and polyhydric alcohols such as polyethylene glycol. In this case, as the fatty acid, the fatty acid metal salt, and the fatty acid amide compound, generally, those having a hydrocarbon portion of 10 or more carbon atoms are preferably used. Specifically, stearic acid, lauric acid, palmitic acid, myristic acid And monovalent carboxylic acids such as behenic acid, polyvalent carboxylic acids such as dodecane diacid and eicosane diacid, and metal salts thereof. In addition, as a metal salt,
For example, salts of calcium, magnesium, zinc, nickel, barium, aluminum and the like can be mentioned. The compounding amount is 0 to 10 parts, particularly 0.01 to 5 parts, per 100 parts of the organopolysiloxane of the first component.

In the silicone rubber composition of the present invention, the above-mentioned first to fourth components are uniformly mixed using a two-roll, rubber mixer such as a Banbury mixer or a dough mixer (kneader mixer). However, if necessary, a filler such as crushed quartz, diatomaceous earth, or calcium carbonate may be added as an extender.

Further, the composition of the present invention may contain various additives such as a colorant, a heat resistance improver, a flame retardant aid, an antistatic agent and the like, a reaction control agent, a filling dispersant, and the like, if necessary. The addition is optional. As the filler dispersant, for example, addition of diphenylsilanediol, various alkoxysilanes, carbon functional silane, silanol group-containing low molecular weight siloxane, etc. is also optional.

[0025] The silicone rubber composition thus obtained is added with a curing agent and cured to form a silicone rubber.

As the curing agent, an organic peroxide or a combination of an organohydrogenpolysiloxane having two or more SiH groups in one molecule and a platinum-based catalyst (addition reaction curing agent) can be used. In the present invention, an organic peroxide is suitably used as a curing agent, and a conventionally known curing agent can be used. As organic peroxides,
Specifically, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5
-Dimethyl-bis (2,5-t-butylperoxy) hexane, di-t-butylperoxide, t-butylperbenzoate, 1,1-bis- (t-butylperoxy) 3,3,5- Trimethylcyclohexane and the like can be exemplified.

The amount of the organic peroxide is 0.5 to 5 parts based on 100 parts of the organopolysiloxane of the first component, or 0.1 to 3 parts based on the silicone rubber composition.
Parts may be added.

The silicone rubber composition to which the curing agent has been added is molded by various molding methods using a mold such as pressure molding, transfer molding and injection molding. The vulcanization conditions are room temperature to 400 ° C., especially 100 ° C.
The temperature can be from 1 minute to 2 hours at ~ 300 ° C. Also,
If necessary, secondary vulcanization may be performed at 100 to 200 ° C. for 30 minutes to 24 hours.

According to the present invention, the compression set characteristics of silicone rubber can be improved by blending the specific anatase type titanium oxide. That is, JIS K6 is compared with that in which the anatase type titanium oxide is not blended.
The compression set by No. 301 can be remarkably reduced, and the compression set characteristic is particularly deteriorated when a release agent is added, but the same except that the release agent is not added by the addition of anatase type titanium oxide. The compression set value can be equal to or less than that of the silicone rubber having the composition.

[0030]

According to the present invention, the compression set of silicone rubber can be remarkably improved. Therefore, seals, packings, gasket materials, industrial roll materials, office machine roll materials, and anode caps can be obtained. It can be effectively used for applications that require lower compression set characteristics than ever before, such as electrical insulating materials such as plugs and plug boots.

[0031]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. All parts in each example are parts by weight.

[Examples 1 to 4, Comparative Examples 1 to 7] Consisting of 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units. Is 8:00
100 parts of a rubbery organopolysiloxane No. 0, 3 parts of diphenylsilanediol as a dispersant, 1 part of dimethylpolysiloxane having a terminal silanol group (degree of polymerization 10), and fumed silica having a specific surface area of 200 m ² / g (Nippon Aerosil) Mix 40 parts with a kneader and mix
Heat treatment was performed for a time to produce a base compound.

Next, various base compounds 100
As shown in Table 1, 2,5-bis (t-
(Butylperoxy) -2,5-dimethylhexane, zinc stearate and various titanium oxides as a release agent were mixed and crosslinked, and the compression set was measured based on JIS K6301. The results are shown in Tables 1 and 2.

[0034]

[Table 1]

[0035]

[Table 2]

From the results in Tables 1 and 2, it can be seen that when the crystal type is rutile or titanium oxide having a primary particle size of more than 10 nm is used, there is no satisfactory effect on the reduction of compression set. When anatase type titanium oxide having a primary particle diameter of 10 nm or less was used, it was found that a clear decrease in compression set was recognized.

Examples 5 to 7, Comparative Examples 8 to 9
Using the same base compound as in Examples 1 to 4, titanium oxide as shown in Table 3, a vulcanizing agent, and further using palmitic acid in place of zinc stearate, and molding a silicone rubber in the same manner as in Examples 1 to 4. Made and measured for compression set.
As a comparative example, the compression set was measured when the amount of titanium oxide ST01 was changed. Table 3 shows the results.

[0038]

[Table 3]

From the results shown in Table 3, it was found that ST01 had almost no effect when added in an amount exceeding 50 parts, but rather resulted in a compound having a large plasticization return and poor roll processability.

Claims (3)

[Claims] (1) R ¹ SiO _{(4-n) / 2} (1) wherein R ¹ is the same or different, unsubstituted or substituted monovalent hydrocarbon group And n is a number from 1.98 to 2.02.) 100 parts by weight of a diorganopolysiloxane represented by the following formula (2): 10 to 70 parts by weight of a reinforcing silica powder having a specific surface area of 100 m ² / g or more. (3) A silicone rubber composition comprising 0.1 to 50 parts by weight of titanium oxide having a crystal form of anatase type and a primary particle diameter of 10 nm or less. (4) 0 to 10 parts by weight of a release agent. . (1) R ¹ SiO _{(4-n) / 2} (1) wherein R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group And n is a number from 1.98 to 2.02.) (2) A silicone rubber composition comprising a reinforcing silica powder having a specific surface area of 100 m ² / g or more. When the product is cured in the presence of a curing agent to obtain a silicone rubber, a titanium oxide having an anatase crystal type and a primary particle size of 10 nm or less is added to the silicone rubber composition, and the compression set value of the silicone rubber is added. A method for improving the compression set characteristics of silicone rubber, characterized by lowering the compression set. 3. The method according to claim 2, wherein a release agent is further added to the silicone rubber composition.