JPH06166818A - Silicone rubber composition - Google Patents

Abstract

PURPOSE:To reduce the stickiness, thus improve the processibility, and facilitate the adjustment of surface properties of a silicone rubber compsn. by compounding a silicon rubber compsn. with a specific low-mol.-wt. polyethylene. CONSTITUTION:A silicone rubber compsn. is compounded with a low-mol.-wt. polyethylene having a density at 20 deg.C of not higher than 0.95g/cm<3> obtain an improved silicone rubber compsn. having a decreased stickiness, i.e., an improved processibility, and surface properties adjustable simply without detriment to the physical properties and without any limitation on compounding.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a silicone rubber composition having excellent processability and capable of adjusting the surface characteristics (sliding property, gloss, adsorption ability, etc.) of a vulcanized product.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION AND ITS PROBLEMS Conventional silicone rubber compositions, in particular compositions of the type called millable, which take the step of molding and vulcanizing the compound,
It is known that the tackiness and green strength of the unvulcanized compound have a great influence on the physical properties of the molded product, and compared to other elastomers, silicone rubber with less crystallinity and lower molecular weight Many of them had large tackiness and had difficulty in roll workability, extrusion workability, and calendering workability. In order to solve such a problem of workability, conventionally, a low molecular weight polyorganosiloxane in which a polar group such as a phenyl group is introduced is blended,
Use the difference in the SP value to migrate,
The tackiness was improved by means such as blending fatty acids such as stearic acid and metal salts thereof. In addition, to adjust the surface characteristics (sliding property, gloss, adsorption capacity, etc.) of the vulcanizate, a (true) spherical filler is blended to reduce its friction coefficient, or the properties and shape of the filler to be blended. In consideration of this, a means such as designing a composition or applying the above-described migration action was used. However, the above-mentioned conventional tackiness improver cannot be said to be a general technique because the width of its applicable range is narrow, and further, the tackiness improving effect is low, and on the contrary, it may reduce the physical properties of the silicone rubber. there were. Also, the adjustment of the surface characteristics,
It is difficult to say that this is a technique that can be applied to all formulations, and its effect is poor in sustainability, which is also a cause of deterioration of the physical properties of silicone rubber.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and there is no compounding limitation, and the workability is improved by reducing the tackiness of the silicone rubber compound without lowering the physical properties of the silicone rubber. Another object of the present invention is to provide a silicone rubber composition capable of easily adjusting surface characteristics.

[0004]

As a result of intensive studies to achieve the above object, the present inventors have found that low-density low-molecular-weight polyethylene is effective, and completed the present invention. That is, the present invention is a silicone rubber composition characterized by being blended with a low-molecular-weight polyethylene whose density at 20 ° C. does not exceed 0.95.

The silicone rubber composition of the present invention will be described in detail below. The main component of the silicone rubber composition of the present invention is (a) a polyorganosiloxane base polymer,
(b) A curing agent and, if necessary, various additives and the like are mixed and uniformly dispersed. Among various components used in such a polyorganosiloxane composition, (a) a silicone-based polymer and (b) a curing agent are appropriately selected according to a reaction mechanism for obtaining a rubber-like elastic body. is there. As the reaction mechanism, (1) a crosslinking method with an organic peroxide vulcanizing agent, (2) a method by an addition reaction, etc. are known, and depending on the reaction mechanism, the component (a) and the component (b), namely, It is well known that the preferred combination with a curing catalyst or crosslinking agent will be determined. That is, in the case of applying the crosslinking method of (1) above, the base polymer of the component (a) is usually a polydiene in which at least two of the organic groups bonded to silicon atoms in one molecule are vinyl groups. Organosiloxane is used. Further, as the curing agent of the component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,
Various organic peroxide vulcanizing agents such as 5-di-t-butylperoxyhexane and di-t-butylperoxide are used. Since they give particularly low compression set, dicumyl peroxide and cumyl-t-butyl are used. Peroxide, 2,
5-Dimethyl-2,5-di-t-butylperoxyhexane and di-t-butylperoxide are preferred. In addition,
These organic peroxide vulcanizing agents are used alone or as a mixture of two or more. The blending amount of the organic peroxide which is the curing agent of the component (b) is 100% based on the silicone base of the component (a).
The range of 0.05 to 15 parts by weight is preferable with respect to parts by weight. If the content of the organic peroxide is less than 0.05 parts by weight, the vulcanization will not be sufficiently carried out, and if it is blended in excess of 15 parts by weight, there will be no further significant effect, and the physical properties of the obtained silicone rubber will not be improved. This is because it may have an adverse effect. As the base polymer of the component (a) when the addition reaction of the above (2) is applied, the same base polymer as that of the above (1) is used. Further, as the curing agent of the component (b), a platinum catalyst such as chloroplatinic acid, a platinum olefin complex, a platinum vinyl siloxane complex, platinum black, or a platinum triphenylphosphine complex is used as a curing catalyst. A polydiorganosiloxane having an average number of hydrogen atoms bonded to silicon atoms of at least 2 per molecule is used. In the curing agent as the component (b), the compounding amount of the curing catalyst is preferably such that the platinum element amount is in the range of 1 to 1000 ppm with respect to the base polymer as the component (a). If the compounding amount of the curing catalyst is less than 1 ppm as the amount of platinum element, the curing does not proceed sufficiently, and if it exceeds 1000 ppm, no particular improvement in the curing rate can be expected. The amount of the cross-linking agent to be added is preferably such that 0.5 to 4.0 hydrogen atoms bonded to silicon atoms in the cross-linking agent are present per one alkenyl group in the component (a), and more preferably, The amount is such that it becomes 1.0 to 3.0 pieces. When the amount of hydrogen atoms is less than 0.5, curing of the composition does not proceed sufficiently, and the hardness of the composition after curing becomes low. The physical properties and heat resistance of the composition are reduced. The organic groups other than the alkenyl groups in the polyorganosiloxane as the base polymer of the component (a) used in the above various reaction mechanisms are monovalent substituted or unsubstituted hydrocarbon groups such as methyl group, ethyl group and ethyl group. Group, propyl group,
An unsubstituted hydrocarbon group such as an alkyl group such as a butyl group, a hexyl group and a dodecyl group, an aryl group such as a phenyl group, an aralkyl group such as a β-phenylethyl group and a β-phenylpropyl group, and a chloro group. Methyl group, 3,3,3
-Substituted hydrocarbon groups such as a trifluoropropyl group are exemplified. In addition, a methyl group is generally used because of its ease of synthesis.

A filler, a pigment, a heat resistance improver, a flame retardant, etc. may be optionally added to the silicone rubber composition of the present invention, as long as the effect of the present invention is not impaired. You may use together polyorganosiloxane. Examples of such substances are usually reinforcing fillers such as diatomaceous earth, titanium oxide, aluminum oxide, zinc oxide, iron oxide, cerium oxide, mica, clay, zinc carbonate, manganese carbonate, cerium hydroxide and glass beads. , Polydimethylsiloxane, alkenyl group-containing polysiloxane, and the like.

Next, the low molecular weight polyethylene having a density at 20 ° C. not exceeding 0.95, which is a feature of the present invention, will be described. The low molecular weight polyethylene having a density at 20 ° C. of not more than 0.95 according to the present invention is included in what is generally called polyethylene waxes. Such low molecular weight polyethylene whose density at 20 ° C does not exceed 0.95 is classified as a low density type. In the present invention, as long as these conditions are satisfied, hue, viscosity,
There are no limitations on various properties such as softening point, penetration, acid value, and average molecular weight. When a low-molecular-weight polyethylene having a density at 20 ° C. of more than 0.95 is blended, the physical properties of the silicone rubber are deteriorated, and the plasticity of the compounded compound is increased to deteriorate the processability, which is not preferable. The compounding amount is not particularly limited, but is appropriately 0.01 to 20 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the silicone rubber. In addition, the kneading and compounding method to the compound is also the usual method, procedure,
A kneading device may be used. It should be noted that when the temperature of the low molecular weight polyethylene is increased above the softening point, the dispersion will be good, but since environmental problems due to the generation of fumes occur, the above temperature should not be increased above the softening point. It has no effect on the effect of the invention.

[0008]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
In the following examples, parts are parts by weight. Example 1 and Comparative Examples 1 and 2 Polydimethylsiloxane having a phenyl group (viscosity 20 cSt) in 100 parts of polydimethylsiloxane (polymerization degree of about 7000) having 0.21 mol% of methylvinylsiloxane units blocked at the ends by trimethylsilyl groups. ) 1.5 parts, as low molecular weight polyethylene "trade name: Sun Wax 131-P,
Density 0.93 at 20 ° C, manufactured by Sanyo Kasei Co., Ltd. "0.1 part was charged in a kneader, and the fumed silica was spun at a rotation speed of 30 rpm" Product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd. "
40 parts were gradually added and kneaded to prepare a silicone rubber compound. Then, 1.0 part of 2,4-dichlorobenzoyl peroxide was uniformly mixed as a vulcanizing agent to obtain a silicone rubber composition. The obtained silicone rubber composition was extruded using an extruder (L / D = 10) onto a 1 mmφ copper wire so that the outer diameter was 2.4 mm (thickness 0.7 mm),
Increasing the line speed, the appearance of the compound, wrinkles, lines,
The linear velocity at the time of appearance defects such as rough skin was measured, and the influence on workability was investigated. For comparison, a silicone rubber composition (Comparative Example 1) was prepared in the same manner as in Example 1 except that low-molecular-weight polyethylene was not added.
The same as in Example 1 except that a low-molecular-weight polyethylene having a density at 20 ° C. of more than 0.95, “trade name: Sunwax LEL-400 P, density at 20 ° C., 0.96, manufactured by Sanyo Kasei Co., Ltd.” was used. A silicone rubber composition (Comparative Example 2) was prepared by using the same, and the same characteristic evaluation as in Example 1 was performed on these. The result shows that the composition of Example 1 is 79 m
/ Min, the composition of Comparative Example 1 was 24 m / min, and the composition of Comparative Example 2 was 19 m / min.

Example 2, Comparative Examples 3 to 4 100 parts of polydimethylsiloxane (polymerization degree of about 6600) having 0.07 mol% of methylvinylsiloxane units blocked at the ends by trimethylsilyl groups, and 30 parts of light calcium carbonate
As a low molecular weight polyethylene, "trade name: Sunwax 165-P, density at 20 0.91, Sanyo Chemical Industry Co., Ltd.
2 parts of "made" were charged into a kneader and kneaded to prepare a silicone rubber compound. Then, to this was added 2,5-dimethyl-2,5-di-t-butylperoxyhexane 0.5.
The parts were uniformly mixed to obtain a silicone rubber composition. This silicone rubber composition was formed into a sheet with an 8-inch roll, and it was investigated to what thickness the rubber sheet could be reasonably dispensed. For comparison, a silicone rubber composition (Comparative Example 3) was prepared in the same manner as in Example 2 except that no low-molecular-weight polyethylene was added, and a low-molecular-weight polyethylene having a density of more than 0.95 at 20 ° C. : Sunwax LEL-800, density 0.9 at 20 ℃
6. Silicone rubber composition (Comparative Example 4) in the same manner as in Example 2 except that "6, Sanyo Kasei Co., Ltd." was used.
Were prepared, and the same characteristic evaluation as in Example 2 was performed. Since the compounds of Comparative Examples 3 and 4 have high adhesiveness, the sheet thicknesses of 2.8 mm and 2.5 mm, respectively, would not stick to the roll and prevent peeling if they were not thick to some extent. The compound could be dispensed to an ultra-thin sheet of 0.4 mm.

[0010]

As described above, in the silicone rubber composition of the present invention, since the low molecular weight polyethylene having a density at 20 ° C. of not exceeding 0.95 is blended, it has excellent extrusion processability. , The compound is
Since the tackiness is reduced, roll processability and the like are also excellent due to this.

Claims (1)

[Claims] 1. A silicone rubber composition comprising a low molecular weight polyethylene having a density at 20 ° C. not exceeding 0.95.