JPH0655890B2 - Silicone rubber composition with excellent mold releasability - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silicone rubber composition having excellent releasability such as roll releasability and mold releasability.

(Prior Art) Generally, unless a special adhesion treatment is applied to silicone rubber, it does not have adhesiveness at the time of molding, has excellent releasability from mold materials, and the surface of the cured rubber is also low. Because of its excellent releasability with energy, it is used as a base material for molding various impression materials such as epoxy resin and urethane resin.

However, with the progress of molding technology in recent years, when molding a heat-vulcanizing type silicone rubber, in order to separate the compound from the roll during roll work and to remove from the mold during heat and pressure molding, Under the present circumstances, excellent releasability is required.

As a means for further improving the releasability, a mold is coated with an appropriate mold release agent, or various additives such as various waxes, fatty acid esters, metal soaps and lubricants are mixed in the rubber compound. Method has been tried.

(Problems to be Solved by the Invention) The means of applying a mold releasing agent to the mold requires a preheating or an extension of the molding time because the temperature of the heated mold is lowered. However, there is a problem that productivity is reduced.

On the other hand, although the purpose of improving the releasability is achieved to some extent by the means of incorporating an additive, the characteristics inherent to the silicone rubber such as mechanical strength, heat resistance, and compression recovery are impaired. In addition, there are problems such as coloring.

Therefore, an object of the present invention is to provide a silicone rubber composition in which various problems of these conventional techniques are effectively solved.

(Means for Solving Problems) The present invention has succeeded in effectively avoiding the above-mentioned various problems and improving releasability by blending a specific fluorine-containing silicon compound. .

That is, the silicone rubber composition of the present invention is obtained by adding the silicone rubber compound to the following general formula [I], The fluorine-containing silicon compound represented by

Silicone Rubber Compound The silicone rubber compound used in the present invention comprises (a) a siloxane component as a base component, and (b) a silica filler, and an appropriate vulcanizing agent and various compounding agents. .

(a) Siloxane component The base organosiloxane component has the following general unit formula [II], And the degree of polymerization is preferably such that the silicon atom in one molecule is
It is composed of a liquid or gum-like organopolysiloxane having 1000 or more and a viscosity (25 ° C.) of 10 ⁵ cst or more, preferably 10 ⁷ cst or more.

Further, as the group R ² , specifically, a methyl group, an ethyl group,
Alkyl group such as propyl group; Aliphatic or alicyclic unsaturated hydrocarbon group such as vinyl group, allyl group, cyclopentenyl group, cyclohexenyl group; aromatic group such as phenyl group, tolyl group, benzyl group and styryl group Hydrocarbon groups; substituted hydrocarbon groups such as chloropropyl group, trifluoropropyl group, heptadecafluorooctylethyl group, cyanoethyl group and methoxyethyl group; and the like.

The above-mentioned polysiloxane is usually less than the molecule blocked with a SiOH group or an R ² ₃ Si- group, but it is vulcanized by having an alkenyl group such as a vinyl group at the side chain or terminal in the molecule. The characteristics are remarkably improved.

Such a polysiloxane generally hydrolyzes dichlorosilane represented by the following formula [III], R ² ₂ SiCl ₂ [III] (in the formula, R ² has the above-mentioned meaning, and the same applies hereinafter), and Subsequently, the following formula [IV] by a method known per se such as cracking with an alkali catalyst, (In the formula, n is a number of 3 to 6) and is prepared by synthesizing a cyclic oligomer and subjecting it to ring-opening polymerization or equilibrium reaction using an acid catalyst or a base catalyst. At this time, if necessary, as a catalyst, (Me represents a methyl group, the same applies hereinafter) is used to polymerize a three-membered ring, or It is also possible to introduce a vinyl group at the terminal of the molecule by adding and carrying out an equilibrium reaction. After the polymerization, the catalyst is neutralized with a suitable neutralizing agent, and the remaining volatile components such as low molecular weight oligomers are removed by means such as heating or depressurization to obtain the target polysiloxane. It is also possible to prepare the target polysiloxane by hydrolyzing the dichlorosilane of the above formula [III] and immediately polymerizing it.

The above-mentioned vulcanization of the organopolysiloxane of the base component (a) can be carried out by a radical reaction or a hydrosilylation reaction (addition reaction). Vulcanizing agents can be included in the compound.

In the case of vulcanization by radical reaction, an organic peroxide which is a radical initiator is used as a vulcanizing agent. Such organic peroxides are not limited to these, but typical ones include benzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, bis-
p-chlorobenzoyl peroxide, dicumyl peroxide, t-butyl peroxybenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t
-Butylperoxy) hexane, γ-hexylene glycol perbenzoate, t-alkylperoxyalkyl carbonate, hydroxymethyl-t-butylperoxide, t-butyl-β-hydroxyethylperoxide and the like can be exemplified. Such an organic peroxide is usually added in an amount of 0.01 to 100 parts by weight per 100 parts by weight of the component (a) siloxane.
Used in a proportion of 5 parts by weight.

Vulcanization by hydrosilylation reaction is particularly applied when the organopolysiloxane of component (a) has an alkenyl group such as a vinyl group in its molecule, and in this case, the catalyst (vulcanization accelerator ) And a crosslinking agent are used.

As the catalyst, all known per se such as chloroplatinic acid or a modified product thereof or a complex thereof with vinyl siloxane can be used, and the amount thereof is generally a platinum weight relative to the organopolysiloxane of the component (a). It is about 0.5 to 300 ppm.

As the cross-linking agent, an organohydrogensiloxane or polysiloxane having two or more SiH groups in one molecule is used. Generally, the following formula [IV], Is a binary or ternary copolymer of methylhydrogenpolysiloxane consisting of repeating units represented by or dimethylpolysiloxane, diphenylpolysiloxane or perfluoroalkylpolysiloxane.
The molecular end is R ² ₃ SiO−, or A polymer blocked with, for example, is used. This cross-linking agent is usually 0.1 to 3 per 100 parts by weight of component (a) siloxane.
It is blended at a ratio of 0 part by weight.

(b) Silica-based filler: The silicone rubber compound used in the present invention contains 5 to 300 parts by weight, preferably 10 to 100 parts by weight of 100 parts by weight of the siloxane of the component (a) in order to reinforce the strength of the cured product.
The silica filler is used in a ratio of 100 parts by weight. As this silica-based filler, natural products such as quartz powder and diatomaceous earth may be used, but in order to obtain high strength,
Synthetic silica having a specific surface area of 50 m ² / g or more, which is called reinforced silica, is suitable. Examples of such synthetic silica include dry silica such as fumed silica, Aerosil-130, 200, 300, 380 manufactured by Degussa, MS-5 manufactured by Cabot.
There are commercially available products such as MS-7, and as wet silica, there are commercially available products such as Nipsil VN-3, LP, E220 and A-300 manufactured by Nippon Silica. These reinforcing silica because it has a large amount of silanol groups on the surface, and _{^{which, R 2 3 SiX, R 2}} 2 SiX 2, R 2 S
So-called treated silica obtained by reacting silane such as iX ₃ (X is a negative group such as halogen or alkoxy group) or a silazane compound such as [R ² ₃ Si] ₂ NH can also be used.

Other compounding agents: In addition, various compounding agents usually used in this field may be appropriately compounded in the silicone rubber compound. For example, in a vulcanization system by a hydrosilylation reaction, N-containing compounds such as amine and benzotriazole, hydroperoxides, and acetylene alcohols are used as reaction retarders in order to adjust the curing rate and prevent scorching during roll work. Can be blended in an appropriate amount.

Further, in order to uniformly disperse the filler such as silica, as a wetting agent (wetting agent), diphenylsilanediol, a siloxane oligomer having silanols at both ends, or the like can be used. An oil resistance improver, a pigment, a flame retardant and the like may be appropriately mixed.

Fluorine-containing silicon compound In the present invention, the above-mentioned silicone rubber compound is added to the above-mentioned general formula [I], that is, The fluorine-containing silicon compound represented by By blending such a fluorine-containing compound, roll releasability and releasability during hot vulcanization molding are significantly improved.

In the above general formula [I], a is a number of 0 or 1, b is an integer of 1 to 3, and c is a number of 0 or 1.

The group R _f is a perfluoroalkyl group or a perfluoropolyether group, and the perfluoroalkyl group preferably has 4 to 12 carbon atoms, specifically, C ₄ F ₉ —, C ₆ F _{13 -, C 8 F 17 -,} C 10 F 20 -, C 12 F 25 - , and the like _{-, (CF 3) 2 CFCF} 2 4, (CF 3) 2 CFCF 2 6, (CF 3) 2 CFCF 2 8 The perfluoropolyether group preferably has 5 to 15 carbon atoms, specifically, Etc. can be illustrated.

Further, the group Q may be either a homopolymer chain of ethylene glycol, a homopolymer chain of propylene glycol or a copolymer chain of both of them. When the copolymer chain of both is used, it may be in the form of either a block polymer chain or a random polymer chain. However, since this polyether group Q is introduced for the purpose of imparting hydrophilicity to this fluorosilicon compound, its polymerization degree is balanced with that of the organosilicon compound having the above-mentioned hydrophobic fluorine-containing organic group. Must be taken into consideration when making a decision. For example, propylene glycol is relatively less hydrophilic than ethylene glycol, and therefore, when a homopolymer chain of propylene glycol is used as the polyether group Q, it is necessary to use a polymer chain having a relatively high degree of polymerization. . When a copolymer chain of ethylene glycol and propylene glycol is used, the content of propylene glycol in the whole is not particularly limited, but is preferably about 2 to 10 mol%, for example.

When the terminal group R ¹ bonded to the polyether group Q becomes an excessively large organic group, it may exhibit a function as a hydrophobic group, and the hydrophilicity of this compound is impaired. For example, a hydrogen atom, an allyl group, An alkyl group having 1 to 4 carbon atoms and an acyl group having 2 to 4 carbon atoms are used. Of these, a methyl group and an acetyl group are preferable.

Such a fluorine-containing silicon compound can be changed from a liquid to a solid one depending on the molecular weight and structure of the fluorine-containing organic group and polyether group, but an appropriate structure and molecular weight may be selected according to the application. Specific examples of the fluorine-containing silicon compound include, but are not limited to, the following.

The above-mentioned fluorine-containing silicon compound is synthesized by subjecting the corresponding fluorine-containing hydrogen silane or siloxane and a terminal allyl polyether compound to a hydrosilylation reaction in the presence of a platinum catalyst.

The fluorine-containing silicon compound is preferably added in an amount of 0.01 part by weight or more, particularly 0.05 to 3 parts by weight, based on 100 parts by weight of the siloxane of the component (a) of the compound. When this blending amount is small, it becomes difficult to achieve the object of the present invention of improving releasability,
In addition, if it is blended in too large an amount, there is a case that the strength of the cured product is lowered and the fluorine-containing silicon compound is bleed out.

Silicone Rubber Composition The composition of the present invention is easily prepared by uniformly mixing the above-mentioned silicone rubber compound and the fluorine-containing silicon compound with a mixer such as a roll mill, a kneader, a Banbury mixer or the like.

Such mixing may be done just before use of the composition, for example, the siloxane of the base component (a) and a filler,
Pigment and other compounding agents such as heat resistance improver in one package form, and further make vulcanizing agent (component (b)) into paste with silicone oil or siloxane component into one package form, and use them with fluorine The silicon compound can be uniformly mixed with a two-roll mill or the like before use. Of course, the fluorine-containing silicon compound may be kneaded in the silicone rubber in advance.

(Effect of the invention) According to the present invention, in the silicone rubber composition, the roll releasability and the mold release property at the time of heat vulcanization are remarkably improved, and as is clear from the results of Examples described later,
The above effects can be achieved without deteriorating the properties inherent to silicone rubber such as compression set properties.

Further, the fluorine-containing silicon compound used in the present invention,
Since it does not contain an element that inhibits an addition reaction such as N, P, S heavy metal ions, the present invention can be applied not only to a vulcanization system by a radical reaction but also to a vulcanization system by a hydrosilylation reaction. The utility of the invention is extremely large.

The excellent effect of the present invention will be described in the following example.

(Examples) Examples 1 and 2 and Comparative Examples 1 to 4 As the silicone rubber compound, KE961U manufactured by Shin-Etsu Chemical Co., Ltd., which is a mixture of silicone raw rubber and wet silica, was used, and 2,5-dimethyl- was used as a vulcanizing agent. A paste of 2,5-bis (t-butylperoxy) hexane (C-8A manufactured by Shin-Etsu Chemical Co., Ltd.) is used.

Further, the compound (A) represented by the following formula is used as the fluorine-containing silicon compound, and the compound (B) represented by the following formula is used as the silicon compound for comparison.

Fluorine-containing silicon compound (A); Silicon compound (B); A rubber composition was prepared by blending 0.5 part by weight of a vulcanizing agent C-8A and 0.1 part by weight or 1.0 part by weight of a fluorine-containing silicon compound (A) per 100 parts by weight of the silicone rubber compound KE961U (Examples 1 and 2). ).

For comparison, in the above-mentioned examples, those containing no fluorine-containing silicon compound (A) (Comparative Example 1), zinc stearate powder was used in place of the fluorine-containing silicon compound (A).
A mixture containing 0.5 parts by weight (Comparative Example 2) or a mixture containing 0.5 parts by weight or 1.0 part by weight of the silicon compound (B) (Comparative Examples 3 and 4) was prepared.

The normal physical properties of these compositions are shown in Table 1, and the state of peeling from the two rolls during the preparation thereof was observed, and the results are also shown in Table 1.

In addition, each of these compositions was heat-pressed in a mold at 170 ° C for 10 minutes, and a sheet of 13 × 17 × 0.2 cm and 1.25 × 2.
A sample of 80 cm was molded. The observation results of the mold releasability at this time are shown in Table 1, and the physical properties of the rubber were measured according to JIS K6301 after post-curing this sample at 200 ° C. for 4 hours, and the results are shown in Table 1.

From the results shown in Table 1, in the rubber compositions (Examples 1 and 2) in which the fluorine-containing silicon compound (A) was blended according to the present invention, the roll settability and the mold release were maintained without lowering the compression set. It is understood that the sex is improving. Furthermore,
In the composition of the present invention, the impact resilience and strength physical properties were not deteriorated, and the change in hardness after the heat resistance test at 230 ° C. × 72 hours was 0 point.

On the other hand, in the compositions containing conventional internal release agents (Comparative Examples 2, 3, 4), the compression set was significantly deteriorated.

Further, regarding the compositions of Examples 1 and 2 and Comparative Example 1,
When a hat-shaped rubber part having a size of 7.6φ × 6.3 (height) × 0.6 (wall thickness) mm was press-molded with a mold of 20 pieces at 170 ° C. × 10 minutes, the composition of Examples 1 and 2 showed that Although molding could be continuously performed up to 15 times without abnormalities, the composition of Comparative Example 1 exhibited insufficient mold releasability after 2 times, and part of the phenomenon of tearing occurred during demolding.

Front Page Continuation (72) Inventor Takashi Matsuda 2-13-1, Isobe, Annaka City, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (72) Shinichi Sato Isobe, Annaka City, Gunma Prefecture 2-13-1 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory

Claims (1)

[Claims] (A) The following general unit formula: And (b) 5 parts by weight per 100 parts by weight of the organopolysiloxane of (a) above.
To 300 parts by weight of a silica filler, a silicone rubber compound containing the following general formula [I], The silicone rubber composition is characterized in that the fluorine-containing silicon compound represented by the formula (1) is blended in an amount of 1 part by weight or more per 100 parts by weight of the organopolysiloxane (a).