JP3077496B2 - Silicone rubber composition - Google Patents

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 having improved creep hardening and excellent storage stability.

[0002]

BACKGROUND OF THE INVENTION When a large amount of a silica filler is added to a silicone polymer, the composition is made to have excellent physical properties such as tensile strength, tear strength, elongation and heat resistance. Is known to be.
However, in order to incorporate a large amount of silica filler into the silicone polymer, it is necessary to add a large amount of a wetter (dispersant) in order to improve the dispersibility of the silica filler.

Heretofore, as a wetter, an α, ω-siloxane diol having a degree of polymerization of 10 to 20 represented by the following formula HO [(CH ₃ ) ₂ SiO] _x H (x = 10 to 20) is generally used. (U.S. Pat. No. 3,795)
9,962).

Further, RO [(CH ₃ ) ₂ SiO] _y H
Also known are α-alkoxy-ω-siloxanols (R: short-chain alkyl group, y = 3 to 5), and furthermore, an anti-structure using a mixture of hexamethyltrisiloxanediol and methoxyhexamethyltrisiloxanol. Agents have also been proposed (US Pat. No. 3,925,285).
No.).

However, in conventional wetters, if the silicone rubber composition is added in a relatively large amount in order to reduce creep hardening, the silicone rubber composition becomes sticky, the workability deteriorates, and the mechanical properties of the cured product are reduced, and the stickiness is suppressed. Therefore, if the addition amount is reduced, the tackiness is eliminated, but there are problems such as remarkable creep hardening.
Therefore, the development of a wetter which has little creep hardening, has no stickiness, and improves the mechanical properties of a cured product has been desired.

That is, the silicone rubber composition is moistened between the silica and the polymer when it is compounded. However, if it is kept unvulcanized, the silicone rubber composition has hydrogen bonds and van der Waals forces between the silica and the polymer. Pseudo-crosslinking proceeds due to physical bonding of. This is a phenomenon called creep hardening, and when this phenomenon occurs, the workability becomes very poor. In this case, if the mixture is sufficiently kneaded again by applying a shearing force, it returns to the original state completely, but such re-kneading is industrially disadvantageous.

The conventional wetter has room for improvement in compression set and mechanical strength of silicone rubber vulcanized by adding a vulcanizing agent.

Further, the conventional wetter has a problem in providing a silicone rubber having excellent transparency.

The present invention has been made in order to improve the above-mentioned disadvantages, and has improved creep hardening, excellent storage stability, small compression set, and excellent mechanical strength.
Another object of the present invention is to provide a silicone rubber composition that gives a silicone rubber having excellent transparency.

[0010]

The present inventors have made intensive studies to achieve the above object, and as a result, have found that the following general composition formula (1) R ¹ _a SiO _{(4-a) / 2} (1 ₎ (In the formula, R ¹ represents a substituted or unsubstituted monovalent hydrocarbon group, and 0.001 to 0.5 mol% of R ¹ is an alkenyl group. A is 1.95 to 2. A positive number of 0.05) is added to a silicone rubber composition containing an organopolysiloxane having an average degree of polymerization of 100 or more and a reinforcing silica filler having a specific surface area (BET method) of 50 m ² / g or more. It has been found that it is effective to mix the compound represented by the formula (2) or (3).

[0011]

Embedded image (However, R ² represents a methyl group, a trimethylsiloxy group, a vinyl group or a trifluoropropyl group, and b represents 0, 1, 2
Or 3 is shown. )

That is, by blending the compound of the above formula (2) or (3), the creep hardening can be remarkably improved, and the increase in plasticity is significantly reduced even after long-term storage. The compound of the formula (2) or (3) is
Since the silanol content is high, the amount used for compound adjustment is small, so that there is no stickiness on the surface, and the processability is improved.Moreover, since the activity of the silanol group is high, the filler such as silica can be used. It has been found that it also gives the advantage of being very easy to mix.

It has also been found that a silicone rubber composition containing the compound of the formula (2) or (3) gives a highly transparent silicone rubber having a small compression set, good mechanical strength, and good mechanical strength.

That is, as described above, conventionally known α, ω
-Although siloxane diol oil is widely used as a wetter, it has disadvantages such as remarkably weakening the green strength to reduce the plasticity (mooney viscosity) of the compound, and retains the shape of the green body, roll releasability, and suppresses foaming. However, conventional α, ω-siloxane diols have a degree of polymerization of 5 to 5, such as impairing processability, such as an increase in compression set and a decrease in mechanical strength.
100 is generally used, and particularly those having a degree of polymerization of 10 to 20 are often used as wetters. However, by using the compound of the formula (2) or (3), the conventional problems can be solved. This has led to the achievement of the present invention.

Accordingly, the present invention provides a compound represented by the following general composition formula (1): R ¹ _a SiO _{(4-a) / 2} (1) wherein R ¹ is a substituted or unsubstituted monovalent hydrocarbon group. As shown, 0.001 to 0.5 mol% of R ¹ is an alkenyl group. A is a positive number of 1.95 to 2.05.) 100 parts by weight of siloxane and specific surface area (BET method) of 50 m ² /
g of the reinforcing silica filler and 5 to 100 parts by weight of the reinforcing silica filler, wherein the compound of the formula (2) or (3) is blended in an amount of 1 to 30% by weight based on the reinforcing silica filler. A silicone rubber composition is provided.

Now, the present invention will be described in more detail. The organopolysiloxane of the first component of the present invention has the following general composition formula (1): R ¹ _a SiO _{(4-a) / 2} (1) , R ¹ represents a substituted or unsubstituted monovalent hydrocarbon group, wherein 0.001 to 0.5 mol% of R ¹ is an alkenyl group, and a is a positive number of 1.95 to 2.05. Is an organopolysiloxane having an average degree of polymerization of 100 or more.

Here, in the formula (1), R ¹ represents a substituted or unsubstituted monovalent hydrocarbon group, and preferably has 1 to 10, more preferably 1 to 6 carbon atoms. In this case, it is necessary that the alkenyl group is contained in a ratio of 0.001 to 0.5 mol% in all R ¹ groups, and more preferably 0.01 to 0.3 mol%. Examples of such an alkenyl group include a vinyl group, an allyl group and a butenyl group, and a vinyl group is preferable. If the proportion of this alkenyl group is too small, the curability of the resulting composition will be reduced, and if it is too large, the resulting cured product will have reduced physical properties such as tensile strength, tear strength and elongation. I do.

The R ¹ group other than the alkenyl group includes, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl,
Alkyl groups such as dodecyl group, aryl groups such as phenyl group and tolyl group, hydrocarbon groups such as aralkyl group such as β-phenylethyl group, and some or all of the hydrogen atoms in these hydrocarbon groups are halogen atoms And substituted hydrocarbon groups such as a 3,3,3-trifluoropropyl group and a cyanoethyl group substituted with a cyano group and the like. Of these, a methyl group is generally preferred, but in order to impart cold resistance, radiation resistance and transparency, a phenyl group may be substituted with all R groups.
It is preferable to contain it in a ratio of 2 to 20 mol% in ^one group. When oil resistance and gasoline resistance are imparted, all R
It is preferable that ^one group contains a cyanoethyl group, a 3,3,3-trifluoropropyl group and the like at a ratio of 5 to 70 mol%.

A must be in the range of 1.95 to 2.05, more preferably 1.98 to 2.02.
It is. When a is outside the above range, the polymerization degree is 10
Difficulties arise when synthesizing zero or more organopolysiloxanes.

In the organopolysiloxane of the first component used in the present invention, most of the constituent units are diorganosiloxane units, but triorganosiloxane units and SiO ₂ units are contained in an amount of 1 mol% in the organopolysiloxane. It may be included to the extent. Further, the terminal of the molecular chain may be blocked with a hydroxyl group or a triorganosiloxy group. Further, the degree of polymerization of the organopolysiloxane is required to be 100 or more in order for the cured product of the obtained composition to obtain sufficient mechanical strength, preferably 100 to 10,000, more preferably 2000 to 10000.
0000.

Examples of the reinforcing silica filler having a specific surface area (BET method) of 50 m ² / g or more as the second component include, for example, fumed silica, calcined silica, precipitated silica and the like. Or a combination of two or more. Moreover, those silica fillers whose surfaces are treated with, for example, a chain organopolysiloxane, a cyclic organopolysiloxane, hexamethyldisilazane or the like may be used.

Particularly, in terms of transparency and reinforcing property of the obtained silicone rubber composition, the specific surface area is 100 to 400 m ^2.
/ G of fumed silica is preferred. In addition, in terms of physical properties such as cost and elasticity of the obtained silicone rubber composition, reinforcing silica having a specific surface area of 50 to 800 m ² / g is particularly preferable.

The amount of the silica filler is 5 to 100 parts by weight based on 100 parts by weight of the first component organopolysiloxane.
The ratio by weight is preferably, more preferably, 10 to 50 parts by weight. If the compounding amount is too large or too small, the processability of the obtained silicone rubber composition is reduced, and the cured product obtained by curing the silicone rubber composition has sufficient tensile strength, tear strength and the like. It has no mechanical strength.

According to the present invention, in a silicone rubber composition containing the above-mentioned organopolysiloxane and silica filler, a compound represented by the following formula (2) or (3) is blended as a wetter (dispersant). Thus, the creep hardening is remarkably improved.

[0025]

Embedded image (However, R ² represents a methyl group, a trimethylsiloxy group, a vinyl group or a trifluoropropyl group, and b represents 0, 1, 2
Or 3 is shown. )

Here, the compound of the formula (3) can be obtained by a known method as shown below.

[0027]

Embedded image

On the other hand, the compound of the formula (2) can also be obtained by a known method, for example, 1,1,1,3,5,
7,7,7-octamethyltetrasiloxane and 3,5-
Bis (trimethylsiloxy) -1,1,1,7,7,7
-Can be obtained by a method such as hydrolysis of hexamethyltetrasiloxane with a Pd / C catalyst.

The compound of the formula (2) or (3) may be used alone or in combination of two or more. The compounding amount is based on the silica filler. 1-3
It is desirable to add 0% by weight, but more preferably 1 to
When the amount is less than 1% by weight, the activity of the silica is strong, so that the creep hardening is not improved. When the amount is more than 30% by weight, the composition becomes sticky and the body falls down, resulting in high cost. turn into.

When the silicone rubber composition of the present invention is obtained, it can be produced by mixing the above-mentioned organopolysiloxane, silica filler and the compound of the formula (2) or (3) by using a kneading device such as a kneader. . Other suitable kneading devices include a two-roll mill, a Banbury mixer (continuous kneader), and a pressure kneader.

The composition thus obtained may be left at room temperature for 1 hour to 24 hours to improve the familiarity and dispersion of each component, or may be mixed at 40 to 70 ° C. in some cases. Dispersion may be performed for several minutes to several hours. If necessary, a solvent such as alcohol, toluene, or xylene, or a compatible silane or siloxane may be used in combination to increase the dispersibility of the compound of the formula (2) or (3).

By subjecting these compositions to a heat treatment as required, the affinity between the silica and the organopolysiloxane in the composition can be increased. For this purpose, preferably 50 to 300 ° C, more preferably 100 to 25 ° C.
It is desirable to perform a heat treatment in a temperature range of 0 ° C. for 10 to 120 minutes.

Thus, a silicone rubber composition having improved creep hardening, which is the object of the present invention, is obtained.

[0034] The silicone rubber composition of the present invention may contain a compounding agent which is usually compounded in silicone rubber. For example, ground silica, diatomaceous earth, iron oxide, zinc oxide, titanium oxide, carbon black, barium oxide, magnesium oxide, cerium hydroxide, calcium carbonate, magnesium carbonate, zinc carbonate, asbestos, glass wool, fine mica, fused silica powder Etc. may be blended. If necessary, pigments, dyes, antioxidants, antioxidants, antistatic agents, flame retardants (for example, antimony oxide,
Paraffin chloride) and a thermal conductivity improver (for example, boron nitride, aluminum oxide, etc.).

The silicone rubber composition of the present invention can be cured into a silicone rubber by using a curing agent. In this case, as the curing agent, when the composition is cured by a hydrosilylation reaction, an organohydrogenpolysiloxane and a platinum group metal-based catalyst are used,
In the case of peroxide crosslinking, peroxide is used,
Known ones are used.

More specifically, in the case of curing by a hydrosilylation reaction, an organohydrogenpolysiloxane and a platinum group metal-based catalyst are used as a curing agent.
The composition can be cured by heating at a temperature of 200C for 0.5 minute to 5 hours. As the organohydrogenpolysiloxane to be used, the following average composition formula (4) R ⁴ _{c Hd} SiO _{(4-cd) / 2} (4) (wherein, R ⁴ is a substituted or unsubstituted carbon atom having 1 carbon atom) Represents a monovalent hydrocarbon group of 10 to 10, and 0 ≦ c <3 and 0 <d ≦ 3
Where c + d satisfies 1.0 to 3.0. ) And having two or more -SiH groups in the molecular chain. The -SiH group may be at the terminal of the molecular chain or may be in the middle. In the above average composition formula (4), R ⁴ is, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, an aryl group such as a phenyl group or a tolyl group, or 3,3,3-trifluoro. Examples include a hydrocarbon group in which a hydrogen atom such as a propyl group is substituted.

The organohydrogenpolysiloxane used as the curing agent preferably has a degree of polymerization of not more than 200, and may be in any of a linear, cyclic or branched state. Examples of such an organohydrogenpolysiloxane include the following.

[0038]

Embedded image (In the formula, Me is a methyl group, i and j are integers of 0 or more, and k is an integer of 1 or more.)

The amount of the above-mentioned organohydrogenpolysiloxane is such that the amount of the ≡SiH group in the organohydrogenpolysiloxane is 0.5 to 3 mol per 1 mol of the alkenyl group in the organopolysiloxane (a). Is more preferable, and is more preferably an amount of 1 to 2 mol.

Examples of the platinum group metal-based catalyst include platinum-based, palladium-based and rhodium-based catalysts, and among them, platinum-based catalysts are preferred. As such a platinum-based catalyst, for example, a fine powdered metal platinum catalyst (for example, US Pat.
70150), chloroplatinic acid catalysts (e.g., those described in U.S. Pat. No. 2,823,218), platinum-hydrocarbon complex compounds (e.g., those described in U.S. Pat. No. 3,159,601 or U.S. Pat. No. 3,159,662), Chloroplatinic acid-olefin complex compounds (for example, U.S. Pat.
946), platinum-vinylsiloxane complexes (e.g. U.S. Pat. No. 3,775,452 or U.S. Pat.
No. 814780). The amount used is usually 0.1 to 1000 ppm (in terms of platinum) with respect to the total amount of the organopolysiloxane (a) and the above-mentioned organohydrogenpolysiloxane.
More preferably, it is 1 to 100 ppm (in terms of platinum).

In the case of curing by such a hydrosilylation reaction, in order to maintain the storage stability at room temperature and an appropriate pot life of the obtained silicone rubber composition, for example, a reaction with methylvinylcyclotetrasiloxane, acetylene alcohol, etc. Control agents may be added.

On the other hand, in the case of curing with an organic peroxide, usually 0.01 to 3 parts by weight of an organic peroxide is blended with respect to 100 parts by weight of an organopolysiloxane. More preferably, it is 0.05 to 1 part by weight. The resulting silicone rubber composition is usually 10 to 500 ° C. at 10 ° C.
It can be cured by heating for seconds to 5 hours.

The organic peroxide as a curing agent may be any one which is usually used in a peroxide-curable silicone rubber composition, such as benzoyl peroxide,
Monochlorobenzoyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-di-tert-butyl peroxide, p-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, tert-butyl perbenzoate, Tertiary butyl peroxy isopropyl carbonate, dimyristyl peroxy carbonate, dicyclododecyl peroxy dicarbonate, 2,
5-bis- (tert-butylperoxy) -2,5
-Dimethylhexane, 2,5-bis- (tert-butylperoxy) -2,5-dimethylhexine, etc., and these may be used alone or in combination of two or more.

[0044]

Industrial Applicability The silicone rubber composition of the present invention has improved creep hardening, excellent preservability, good workability, and low compression set, and has good mechanical properties. It is suitable as a material for extrusion molding of, for example, building gaskets, medical tubing, etc., and is also suitable as a material for rubber contacts, nipples, joint boots, plug boots, anode caps, electric wires, etc. It is.

[0045]

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. The middle part in the examples indicates parts by weight.

Examples 1-4, Comparative Example 1 (CH ₃ ) ₂ S
99.825 mol% of iO units, (CH ₃ ) (CH ₂ ＣC
H) SiO unit is 0.15 mol%, (CH ₂ ＣＨCH)
(CH ₃ ) ₂ methylvinylpolysiloxane 1 comprising 0.025 mol% of SiO _1/2 units and having an average degree of polymerization of 3000
A fumed silica having a specific surface area of 200 m ² / g (produced by Nippon Aerosil Co., Ltd., trade name Erosil 200) is added to 00 parts
7 parts and 6 parts of the compound represented by the following formula (A) were charged into a kneader mixer and uniformly mixed.

When this was left at room temperature overnight, a transparent compound was obtained. This compound was heat-treated in a kneader at 100 ° C. for 30 minutes to obtain a base compound 1.

[0048]

Embedded image

A base compound 2 was obtained in the same manner as above except that 6 parts of the compound represented by the following formula (B) was used instead of the compound of the above formula (A).

[0050]

Embedded image

Further, base compounds 3 and 4 were obtained in the same manner as described above except that 4 parts of the compound represented by the following formula (C) or (D) was used instead of the compound of the formula (A).

[0052]

Embedded image

For comparison, α, ω-siloxanediol 4 having an average degree of polymerization of 10 was used in place of the compound of formula (A).
The base compound 5 (comparative example) was obtained when parts and 10 parts were used. In this case, it was difficult to blend silica with 4 parts of α, ω-siloxane diol.

The appearance and plasticity of the obtained silicone rubber composition over time were evaluated according to JIS-C-2123.

The above silicone rubber compound 1
Then, 1.5 parts of 2,4-dichlorobenzoyl peroxide (50% product) as a vulcanizing agent was added to 00 parts, and the mixture was cured under the conditions of press cure at 120 ° C. for 10 minutes and post cure at 200 ° C. for 2 hours. A sheet was obtained, and its physical properties were evaluated according to JIS-K-6301. Table 1 shows the results.

[0056]

[Table 1]

From the results shown in Table 1, it was confirmed that the compositions of the examples were improved in transparency and less in creep hardening.

[Examples 5 and 6] In place of the fumed silica of Example 1, 40 parts of precipitated silica (Nipsil Lp, trade name, manufactured by Nippon Silica Co., Ltd.) and a compound of the formula (A) or (C) Compounds 6 and 7, respectively, were prepared in the same manner as in Example 1 except that the addition amount of was 2 parts. The workability of the obtained compound was good, and the physical properties were as shown in Table 2.

[0059]

[Table 2]

[Examples 7 and 8] Using the base compounds 1 and 3 used in Example 3, addition vulcanization was performed. To 100 parts of the base compound were added 1.0 part of an organohydrogenpolysiloxane (the molar ratio of SiH groups / vinyl groups was 1.3) and 1000 ppm of a platinum-based catalyst,
As a control agent, 0.02 parts of 1-ethynylcyclohexane-1-ol was added by a two-roll mill and mixed uniformly. This was vulcanized at 165 ° C. for 10 minutes to form a 2 mm thick sheet. Thereafter, secondary curing was performed at 200 ° C. for 4 hours. Table 3 shows the results. From the results shown in Table 3, this compound was excellent in transparency and physical properties.

[0061]

[Table 3]

Continued on the front page (72) Inventor Masaharu Takahashi 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Silicon Electronic Materials Research Laboratories Shin-Etsu Chemical Co., Ltd. (58) Field surveyed (Int.Cl. ⁷ , DB name) ) C08L 83/04 C08L 83/06 C08L 83/07 C08K 3/36 C08K 5/541

Claims (2)

(57) [Claims] (A) The following general composition formula (1): R ¹ _a SiO _{(4-a) / 2} (1) (wherein, R ¹ represents a substituted or unsubstituted monovalent hydrocarbon group) Wherein 0.001 to 0.5 mol% of R ¹ is an alkenyl group; a is a positive number of 1.95 to 2.05), and the average degree of polymerization is 100 or more. A silicone rubber composition containing 100 parts by weight and (B) 5 to 100 parts by weight of a reinforcing silica filler having a specific surface area (BET method) of 50 m ² / g or more: (C) the following formula (2) or (C) A silicone rubber composition comprising the compound (3) in an amount of 1 to 30% by weight based on the component (B). Embedded image (However, R ² represents a methyl group, a trimethylsiloxy group, a vinyl group or a trifluoropropyl group, and b represents 0, 1, 2
Or 3 is shown. ) 2. The silicone rubber composition according to claim 1, wherein an organohydrogenpolysiloxane and a platinum group metal-based catalyst or an organic peroxide are blended as a curing agent.