JP2000063673A - Silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicone rubber compsn. which gives a homogeneous soln. contg. no microgel by compounding an organopolysiloxane having at least two alkenyl groups in the molecule with a fine silica powder, a wetter, and a polymn. inhibitor in a specified wt. ratio. SOLUTION: This compsn. comprises (A) 100 pts.wt. organopolysiloxane, (B) 0.1-100 pts.wt. fine silica powder, (C) 0.1-30 pts.wt. wetter, and (D) 0.01-10 pts.wt. polymn. inhibitor and may further contain 0.1-100 pts.wt. organohydrogenpolysiloxane and an arbitrary amt. of an org. solvent. An example of ingredient A is a polysiloxane having at least two vinyl groups; examples of ingredient C are silane and a siloxane; and ingredient D has at least one phenyl group in the molecule and its example is 2,6-di-t-butyl-p-hydroxytoluene. While ingredient B is slowly added to ingredient A, ingredient C is added thereto, and then the whole is mixed and kneaded. Ingredient D is added before heat treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a silicone rubber composition capable of preventing an increase in viscosity of a silicone rubber composition during heat treatment, preventing an increase in viscosity of a melt of the silicone rubber composition, and stabilizing production of the silicone rubber composition. .

[0002]

2. Description of the Related Art Silicone rubber is used for paper, due to its excellent weather resistance, heat resistance, low surface tension and flame retardancy.
It is used as a raw material for plastic films, fibers, and surface coating agents for concrete. When silicone rubber is required to have mechanical strength, or when it is coated on paper, fibers, or the like, which has large bleeding, it is often practiced to incorporate fine powder silica. Further, when forming a thin silicone rubber film, it is difficult to coat the silicone rubber composition by itself. Therefore, it is often performed by dissolving the silicone rubber composition in a solvent such as toluene or xylene. These methods have been put to practical use as coating agents for airbags and varnishes for sleeves.

As a method for producing this silica-containing silicone rubber composition, a method in which a silicone base polymer, silica and a wetter are pre-blended to form a composition is generally used, but the silica surface is not sufficiently wetted. Since the increase in rubber viscosity occurs due to the aggregation of silica particles in the rubber, which is called plasticity reversion, it is essential to introduce a heat treatment step (usually 150 ° C to 180 ° C) after compounding to prevent this. However, it has been confirmed that excessive heat treatment causes an increase in viscosity (plasticity), especially when using a siloxane with a high vinyl group content containing 0.3 mol% or more of vinylmethylsiloxy units, or at 180 ° C or higher. The tendency is remarkable when heat treatment is performed.

[0004]

When a silicone rubber composition having an increased viscosity is dissolved in a solvent, not only a remarkable increase in solution viscosity but also generation of microgel is observed, and a suitable product cannot be obtained. This phenomenon of viscosity increase is caused by a) radicals generated from a trace amount of the metal compound and oxygen contained in the filler during heat treatment cause a partial crosslinking reaction of the alkenyl groups of the alkenyl group-containing dimethylpolysiloxane, or It is considered to be generated by reacting with the hydroxyl groups present on the surface of the filler. b) When a silicone rubber composition that has not been heat-treated is used, the wetting of the hydroxyl groups on the silica surface is insufficient, and since silica is not sufficiently dispersed, the silicone rubber composition and its dissolved product have a high initial viscosity. Not only that, but there was a problem that the viscosity increased with time. The increase in viscosity due to the crosslinking reaction as described above causes the viscosity of the product to fluctuate, and it has been difficult to manufacture a product of stable quality by the conventional technology.

[0005]

DISCLOSURE OF THE INVENTION In the present invention, as a result of intensive studies for solving these problems of viscosity increase, it was found that a silicone rubber composition containing a specific polymerization inhibitor solves these problems. did. That is, the present invention is as follows (A)
To (D) are silicone rubber compositions. (A) 100 parts by weight of organopolysiloxane containing at least two alkenyl groups in one molecule, (B) 0.1 to 100 parts by weight of finely divided silica, (C) 0.1 to 30 parts by weight, (D) polymerization Inhibitor 0.01 to 10 parts by weight.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Each component used in the present invention will be described in detail below. The organopolysiloxane containing at least two alkenyl groups in one molecule as the component (A) in the present invention is represented by the average unit formula R _a SiO _{(4-a) / 2} .
In the formula, a is a value of 1.95 to 2.05, R is a substituted or unsubstituted monovalent hydrocarbon group, and is methyl, ethyl, propyl, vinyl, phenyl, 3,3,3-trifluoropropyl. And the like, of which at least 80% is a methyl group. A vinyl group is particularly preferred as the alkenyl group contained in the molecule by being directly bonded to at least two silicon atoms. The alkenyl group may be present only at the end of the molecular chain, only in the molecular chain, or both. This organopolysiloxane is a fluid, gum-like substance with a degree of polymerization of 1,000 or more, and its molecular chain ends have trimethylsilyl groups, dimethylvinyl groups, trivinylsilyl groups,
Examples thereof include a methylphenylvinyl group, a hydroxyl group, and an alkoxy group, but are not limited thereto. The term “substantially linear” means a linear or partially branched one.

The finely divided silica as the component (B) in the present invention is used for reinforcing the silicone rubber and for increasing the amount of the composition, and may be produced by either a dry method or a wet method. The diameter is not limited, and the surface may be treated with an organic compound or the like. As these silicas, commercially available ones can be used, and those obtained by the dry method include A-130 and A-20.
0, A-300, A-380 [Japan Aerosil Co., Ltd.
], Cab-O-Sil [manufactured by Cabot], Nipseal LP [manufactured by Nippon Silica Industry Co., Ltd.] as a wet method, and R-972, R- as examples of treated silica.
974 [manufactured by Nippon Aerosil Co., Ltd.] and the like.
The reinforcing effect of the fine powdery silica of the component (B) is that an adsorption layer of rubber molecules is formed on the surface of the silica fine particles, which brings about a crystallization effect in the silicone raw rubber, and the intermolecular attractive force between the adsorption layers is increased. By forming a physical or chemical bond between a siloxane bond or a terminal silanol group and a silanol (Si-OH) group on the surface of silica.
If the amount of the finely divided silica as the component (B) is less than 0.1 parts by weight relative to 100 parts by weight of the component (A), the effect is not sufficient to reinforce the rubber compound and prevent penetration of the solution. If it exceeds 0.1, the plasticity of the rubber compound is excessively increased, molding becomes difficult, and the fluidity when made into a solution is significantly impaired, so 0.1 to 100 parts by weight is necessary.

The component (C) wetter (wetting agent) in the present invention is added for the purpose of preventing secondary bonding due to active points on the surface of the finely powdered silica (B). Since fine powder silica has a strong cohesive force among particles, it is difficult to disperse it in raw rubber.
Therefore, the reinforcing effect of the fine powder silica is not sufficiently exhibited. In addition, it causes "Crepe Hardening", which is inconvenient for processing. When a wetter as the component (C) is added, it reacts with silanol groups on the silica surface, or the wetter covers the silica surface to prevent "Crepe Hardening", and
It functions to uniformly disperse the finely divided silica as the component (B) in the raw rubber. As a result, the reinforcing effect of the fine powder silica is sufficiently exerted, and the storage stability of the silicone rubber composition is improved. As the component (C) wetter usable in the present invention, silicone resins, alkoxysilanes and siloxanes, hydroxysilanes and siloxanes, silazanes, organic acid esters, polyhydric alcohols and the like are used. Of these, silanes and siloxanes are preferable from the viewpoint of compatibility with silicone raw rubber and heat resistance of the wetter itself. Specifically, dimethyldimethoxysilane,
α, ω-dihydroxypolysiloxane, 1,1,1,
3,3,3-hexamethyldisilazane and the like can be mentioned.
If the amount of the component (C) wetter is less than 0.1 parts by weight per 100 parts by weight of the component (A), it is not sufficient to impart wettability to the silica surface, which makes formulation difficult, and if it exceeds 30 parts by weight. 0.1 to 30 parts by weight is required because the rubber compound becomes sticky.

The polymerization inhibitor as the component (D) in the present invention forms the basis of the present invention, and is specifically a compound having the ability to trap radicals generated during heat treatment. A typical example of such a compound is a compound having a hydroxyl group and an amino group directly bonded to a phenyl group.
In such a compound, protons of a hydroxyl group and an amino group react with a radical, and the radical is chain-transferred to an oxygen atom and a nitrogen atom. This radical is delocalized due to the presence of the phenyl group, and works effectively through a process of trapping the radical. This polymerization inhibitor traps radicals generated from a trace amount of metal compounds and oxygen contained in the filler during heat treatment to suppress an increase in viscosity, and when a silicone rubber composition not subjected to heat treatment is used, the silica surface Wetting of the hydroxyl groups is insufficient.

As an example of such a polymerization inhibitor, as an example of a compound having a hydroxyl group directly bonded to a phenyl group,
2,6-di-t-butyl-p-hydroxytoluene (B
HT), hydroquinone, p-methoxyphenol,
2,5-di-t-butylhydroquinone, 2,5-di-
t-amyl hydroquinone, 4,4′-butylidene bis (6-t-butyl-m-cresol), 2,2′-methylene bis (4-methyl-6-t-butylphenol),
There are 2,2'-methylenebis (4-ethyl-6-t-butylphenol) and styrene-modified phenol.

Examples of the compound having an amino group directly bonded to the phenyl group include N, N'-diphenylamine, N,
There are N'-diphenyl-p-phenylenediamine, 6-ethoxy-2,2,4-triethyl-1,2-dihydroquinoline, 2-methylcaptobenzimidazole, phenothiazine.

These compounds are used in large amounts as stabilizers and polymerization inhibitors in the polymer chemistry industry, and are commercially available. Of these, when a compound having an amino group directly bonded to a phenyl group is used, the rubber may be colored depending on the addition amount, and therefore it is preferable to use a compound having a hydroxyl group directly bonded to the phenyl group. The addition amount of the polymerization inhibitor in the present invention is in the range of 0.01 to 10 parts by weight. If it is less than 0.01 parts by weight, the effect as a polymerization inhibitor cannot be sufficiently exerted, and if it exceeds 10 parts by weight, the physical properties are adversely affected. A particularly preferred addition amount is 0.1 to 2.0 parts by weight.

As a method of compounding the rubber composition in the present invention, the finely powdered silica of the component (B) is gradually added to the component (A) and kneaded in advance, in order to facilitate the mixing of the two. A component (C) wetter is used for. The polymerization inhibitor as the component (D) may be added before the heat treatment, and the addition timing is arbitrary.

The organohydrogenpolysiloxane as the component (a) in the present invention contains at least two hydrogen atoms in one molecule, and it may be linear, branched or cyclic. May be Specifically, α, ω-bis (dimethylhydrogensiloxy)
Polydimethylsiloxane, α, ω-bis (trimethylsiloxy) polymethylhydrogenpolysiloxane,
Examples include α, ω-bis (trimethylsiloxy) poly (methylhydrogen) (dimethyl) siloxane copolymer and the like. The addition amount is such that the molar ratio of SiH / alkenyl groups to the component (A) is 0.5 to 50, and preferably 1.5 to 8. The silicone rubber composition 10 according to claim 1.
0.1 to 100 parts by weight is necessary with respect to 0 parts by weight, and less than 0.1 parts by weight or more than 100 parts by weight results in poor curability, which is not preferable.

The organic solvent as the component (b) in the present invention basically has only to dissolve the silicone rubber composition according to claim 1 and the component (a), and an aromatic hydrocarbon such as toluene or xylene. Examples thereof include aliphatic hydrocarbons such as pentane and hexane, and ester compounds such as methyl acetate and ethyl acetate, with toluene being most preferred from the viewpoint of solubility and safety.

A composition obtained by adding an organohydrogenpolysiloxane (a) containing at least two Si--H in one molecule to the silicone rubber composition of claim 1 of the present invention is crosslinked by addition reaction. It is possible. As the catalyst, for example, a noble metal type such as platinum black, chloroplatinic acid, chloroplatinic acid-olefin complex, and rhodium type complex can be used, and these are usually 5 to 1,000 in terms of platinum or rhodium with respect to the composition of claim 1. Used in the ppm (weight ratio) range. This can be increased or decreased depending on reactivity, economy, desired curing speed and the like. Further, peroxide vulcanization with peroxide is also possible, and as the peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 2,5-bis (t-butylperoxy) hexane or the like can be used. These are usually 50 to 1,00 relative to the silicone rubber composition of the above claim 1.
Used in the range of 0 ppm (weight ratio). This can be increased or decreased depending on reactivity, economy, desired curing speed and the like. Furthermore, the silicone rubber composition of claim 2 can also be cured with the same precious metal-based catalyst as the silicone rubber composition of claim 1, and is applied to a substrate such as paper or cloth using a wire bar coater, a gravure coater or the like. It can then be heated or cured at room temperature.

[0017]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
All parts in the examples are parts by weight. The plasticity and solution viscosity of the silicone rubber composition were measured by the following methods. (Plasticity) 10 g of the rubber composition was passed through a triple roll 10 times, and then measured according to JIS-K-6249. (Solubility viscosity) The silicone rubber composition was made into a 30 wt% uniform toluene solution, and the dissolution viscosity was based on JIS-K-7117.
It was measured with a rotational viscometer.

(Examples 1 to 4) Dimethylpolysiloxane 653.6 having an average degree of polymerization of 8,000 and having both ends blocked with trivinyl groups and containing 0.5 mol% of methylvinylsiloxy groups.
Parts, 326.7 parts of dry treated silica R-972, and 1.97 parts of a wetter represented by the following average structural formula were kneaded with a kneader until uniform.

[Chemical 1] Next, the polymerization inhibitor BHT (2,6-ditert-Butyl-p-Hyd
5.0 parts of roxyToluene) was added, and when the temperature reached 170 ° C., the rubber was taken out and the plasticity was measured. Further 30.0 parts of the above rubber composition, 0.33 parts of a crosslinking agent represented by the following average structural formula

[Chemical 2] 69.67 parts of toluene and toluene were mixed until uniform, and the solution viscosity of this solution was measured. Also, visually observing the appearance,
The presence or absence of a gel-like substance was observed (Example 1). Similarly 170 ℃
Similarly, the viscosity of the toluene solution and the appearance were observed for the ones that were heat-treated for 1 hour, 2 hours, and 4 hours after reaching the temperature (Examples 2, 3, and 4).

(Comparative Examples 1 to 4) Corresponding to Examples 1 to 4, similar experiments were carried out for those to which BHT was not added, and these were designated as Comparative Examples 1, 2, 3 and 4, respectively.

[0020]

[Table 1]

[0021]

The composition of the present invention has excellent viscosity stability, and further provides a uniform solution containing no microgel when dissolved in an organic solvent. The inventors have succeeded in suppressing an increase in viscosity by using a polymerization inhibitor in a composition manufacturing process and trapping radicals generated during heat treatment. This technique not only provides a method for stably producing a silicone rubber melt, but also provides a silicone rubber composition which suppresses an increase in the plasticity of the silicone rubber and has excellent processability.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Isobe             Gunma Prefecture Usui District, Matsuida Town             Shin-Etsu Chemical Co., Ltd. Silicone electronic materials             Inside the technical laboratory F-term (reference) 4J002 CP041 CP06X DJ016 EC047                       EC057 EE058 EH007 EJ028                       EJ038 EJ068 EN078 EX007                       EX037 EX077 FD016 FD20X                       FD207 FD208 GH00 GK02                       GK04 GN00

Claims (3)

[Claims] 1. A silicone rubber composition comprising the following (A) to (D): (A) 100 parts by weight of organopolysiloxane containing at least two alkenyl groups in one molecule, (B) 0.1 to 100 parts by weight of finely divided silica, (C) 0.1 to 30 parts by weight, (D) polymerization Inhibitor 0.01 to 10 parts by weight. 2. A silicone rubber composition comprising 100 parts by weight of the silicone rubber composition of claim 1 and the following (a) and (b) added thereto. (A) 0.1 to 100 parts by weight of organohydrogenpolysiloxane containing at least two Si-H in one molecule, (b) an arbitrary amount of organic solvent. 3. The silicone rubber composition according to claim 1 or 2, wherein the polymerization inhibitor contains at least one phenyl group in one molecule.