JPH07207161A - Autohesive silicone rubber composition - Google Patents

Abstract

PURPOSE:To obtain an autohesive silicone rubber composition compounded with a specific amount of a specific tin compound, giving a rubbery elastomer having excellent autohesivity by thermal curing, having excellent initial autohesivity, resistant to the lowering of autohesivity even after leaving for a long period at a high temperature in the presence of moisture and useful for electrical insulation and protection material, etc. CONSTITUTION:This autohesive silicone rubber composition contains (A) 100 pts.wt. of a polyorganosiloxane expressed by average unit formula I [R is a (substituted)univalent hydrocarbon group; (a) is 1.90-2.70] and optionally having a small amount of silanol groups, (B) 0.1-30 pts.wt. of a boron compound selected from boric acids, boric acid derivatives and polyorganoborosiloxanes, (C) 0.01-10 pts.wt. of a tin compound selected from tin oxide, organic acid tin salt and organic tin compound and (D) 0.1-10 pts.wt. of an organic peroxide.

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, and more particularly to a heat curable silicone rubber composition which is cured to give a self-fusing silicone rubber. The silicone rubber composition of the present invention is excellent in heat resistance and cold resistance in addition to the above self-fusing property, and is useful as a contact material, a hose, a sealing material, etc. in addition to various electrical insulation protective materials.

[0002]

2. Description of the Related Art Silicone rubber has excellent heat resistance and cold resistance, and is therefore preferably used in various fields. Those containing silica as the inorganic filler are particularly widely used as an electrical insulating material or a protective material because they have excellent electrical insulating properties and retain the electrical insulating properties even when they are oxidized or burned. On the other hand, the one using carbon as the inorganic filler is useful as a rubbery electrical contact material having excellent heat resistance. Further, by taking advantage of its heat resistance and cold resistance, it is also used as a material for hoses, sealing materials and the like.

Among such silicone rubbers, those containing a boron compound are known to have self-bonding properties after curing. For example, Japanese Patent Publication No. 34-1004
5, Japanese Patent Publication No. 35-18190, Japanese Patent Publication No. 35
-18191, Japanese Patent Publication No. 38-26280,
Japanese Patent Publication No. 40-10117 and Japanese Patent Publication No. 49-43
699 publication. Among them, the special public Sho 40-
Japanese Patent No. 10117 exemplifies the structure of a typical heat-curable self-fusing silicone rubber made of organic peroxide.

The term "self-melting property" as used herein means a property in which cured and hardened rubbers are brought into contact with each other or are pressure-bonded to each other, and the contacting and pressure-bonding surfaces are fused and integrated with each other by heating at room temperature or if necessary. Say. Such a property is, as described above,
It is obtained by compounding the silicone rubber with a boron compound, which is due to the coordination bond of the boron atom.

However, such a self-fusing silicone rubber has a problem that the self-fusing property deteriorates when left in the presence of water or at a high temperature. In the above Japanese Patent Publication No. 40-10117, the self-adhesive silicone rubber has a self-adhesive property when it is vulcanized at too high temperature for a long time (which means formation of an elastic body of the silicone rubber) during heat curing. It is described that the sheet surface loses its self-fusion property and the sheets no longer stick even when they are brought into contact with each other.
In the rubber molding industry, this phenomenon is called the "Kabuki" phenomenon,
This term will be used hereafter in this specification.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the self-fusing property of a heat-curable self-fusing silicone rubber from occurring, that is, the deterioration of the self-fusing property when left at high temperature or high humidity. It is to provide a self-bonding silicone rubber.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the object is achieved by adding a specific amount of a specific tin compound. After finding out, the present invention was completed.

That is, the present invention provides (A) an average unit formula: R _a SiO _{(4-a) / 2} (wherein R represents the same or different substituted or unsubstituted monovalent hydrocarbon group; a is 1.90 to 2.70
100 parts by weight of a polyorganosiloxane in which some silanol groups may be present; (B) at least one boron compound selected from boric acids, boric acid derivatives and polyorganoborosiloxanes. To 30 parts by weight; (C) at least one tin compound selected from tin oxide, organic acid tin salt and organic tin compound 0.01 to 10
And (D) 0.1 to 10 parts by weight of an organic peroxide, the present invention relates to a silicone rubber composition having self-fusing property after curing.

The polyorganosiloxane of component (A) in the present invention is a base polymer and has an average composition formula:
R _a SiO _{(4-a) / 2} (in the formula, R and a are as described above). R is an alkyl group such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl or decyl; a cycloalkyl group such as cyclohexyl; an alkenyl group such as vinyl or allyl; an aryl group such as phenyl or naphthyl; or chloromethyl Substituted hydrocarbon groups such as 1,1,1-trifluoropropyl are exemplified, and in order to obtain excellent heat resistance, cold resistance, and processability as a silicone rubber, 50 mol% except for the alkenyl group described below. More preferably, 85 mol% or more is a methyl group. Especially when radiation resistance, heat resistance or cold resistance is required, a phenyl group; when oil resistance or chemical resistance is required, the desired amount of 1,1,1-trifluoropropyl group may be introduced into the molecule. It is valid.

The radicals generated from the organic peroxide of the component (D), which will be described later, can also act on the methyl group in the component (A) to form a crosslink, depending on the type of the component (D).
A wide variety of components (D) are made to work effectively in a small amount,
In order to obtain a silicone rubber having good heat resistance and mechanical properties, it is preferable that some alkenyl groups, especially vinyl groups, are present in R. From the heat resistance of the polyorganosiloxane, the content of vinyl groups is preferably 1 mol% or less, more preferably 0.02 to 0.2 mol% of the total R. Furthermore, it is preferable that the polymer end is blocked with a group containing a silanol group, for example, a dimethylhydroxysilyl group, since excellent self-fusion property is obtained.

A is in the range of 1.90 to 2.70, preferably 1.99 to 2.01.

The viscosity of component (A) at 25 ° C. is preferably 10-200,000,000 cSt. When the self-bonding silicone rubber composition is a liquid silicone rubber, the above viscosity is preferably 10 to 500,000 cSt. When the viscosity is less than 10 cSt, not only sufficient rubber elasticity is not obtained after curing, but also the base polymer and the inorganic filler are separated during storage. On the other hand, when it exceeds 500,000 cSt, the uncured silicone rubber composition becomes too viscous and workability is significantly impaired. On the other hand, when the self-fusing silicone rubber composition is a millable silicone rubber, the viscosity is 3,000,000 to 20,000.
A range of 000 cSt is preferred. Viscosity is 3,000,00
If it is less than 0 cSt, it is difficult to obtain sufficient mechanical properties,
If it exceeds 0,000 cSt, it becomes difficult to mix and knead the filler and the like.

The boron compound as the component (B) is an important component which imparts self-fusing property after curing to the composition of the present invention. As the component (B), boric acid such as boric acid anhydride, pyroboric acid, orthoboric acid; derivatives of boric acid or boric acid anhydride such as trimethyl borate, triethyl borate, and trimethoxyboroxine; and polysiloxane chain Examples thereof include polyorganoborosiloxanes having a boroxane bond introduced therein, such as polymethylborosiloxane.
Such a polyorganoborosiloxane can be obtained by heating and condensing an organoalkoxysilane such as dimethyldimethoxysilane or dimethyldiethoxysilane and boric anhydride. These may be used alone or in combination of two or more. From the compatibility with the polyorganosiloxane of the component (A), polyorganoborosiloxane is preferable.

The blending amount of the component (B) is 100 parts of the component (A).
The amount is 0.1 to 30 parts by weight, and preferably 1 to 15 parts by weight, depending on the molecular structure of the boron compound. If it is less than 0.1 part by weight, the self-fusion property after curing will not be developed, and if it exceeds 30 parts by weight, the silicone rubber obtained by curing will not show sufficient heat resistance and the mechanical properties will deteriorate.

The tin compound as the component (C) is an important component for improving the self-fusion property of the composition of the present invention and for preventing the above-mentioned phenomenon. As component (C), tin oxide such as stannous dioxide; stannous butyrate, stannous octoate, stannous decanoate, stannous naphthenate, stannous octoate, stannous oleate. Organic acid tin salts such as; and hydrocarbons directly bound to tin atoms such as dibutyltin diacetate, dibutyltin dioctate, dibutyltin di-2-ethylhexoate, dibutyltin dilaurate, dibutyltin dimethylate, dibutyltin dioxide An organic tin compound having a group is exemplified. From the compatibility with the component (A), a tin compound useful as a condensation catalyst for a room temperature curable silicone rubber is also preferable as a compounding agent of the present invention.

The blending amount of the component (C) is 100 parts of the component (A).
The amount is 0.01 to 10 parts by weight, and preferably 0.1 to 5 parts by weight, depending on the molecular structure of the tin compound. If the amount is less than 0.01 part by weight, the effect of suppressing the cracking phenomenon is not exerted, and if the amount exceeds 10 parts by weight, the curing of the silicone rubber is inhibited, and the silicone rubber obtained by curing does not show sufficient heat resistance. Quality also deteriorates.

The organic peroxide of the component (D) generates radicals by heating to cause a crosslinking reaction of the component (A),
This is a curing agent that cures the composition of the present invention. As the component (D), benzoyl peroxide,
Acyl peroxides such as bis (p-chlorobenzoyl) peroxide, bis (2,4-dichlorobenzoyl) peroxide; di-tert-butyl peroxide,
Alkyl peroxides such as 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, tert-butylcumyl peroxide and dicumylperoxide; and ester organic peroxides such as tert-butylperbenzoate. An oxide is illustrated.

The blending amount of the component (D) is 100 parts of the component (A).
0.1 to 10 parts by weight with respect to parts by weight, 0.3 to 5
Parts by weight are preferred. In order to handle the component (D) safely and easily, the component (D) may be blended with silicone oil to form a paste or adsorbed on an inorganic fine powder to be blended.

If desired, an inorganic filler may be added to the self-fusing silicone rubber composition of the present invention. Inorganic fillers provide the silicone rubber composition with the necessary hardness and mechanical properties, such as reinforcing fillers such as fumed silica, silica airgel, precipitated silica; and quartz powder, fused silica, diatomaceous earth, Examples are non-reinforcing fillers such as calcium carbonate, titanium oxide, iron oxide, ferrite and carbon. As other fillers, for example, "Practical Handbook of Additives for Supplementary Plastics and Rubbers"
(Chemical Industry Co., Ltd., issued in July, 1989), pp. 487-787, those described as fillers and reinforcing materials are cited. These may be used alone or in combination of two or more.

It is preferable that the surface of the above-mentioned filler, particularly the reinforcing filler, is treated with various silane compounds, silazane compounds or siloxane compounds to make it hydrophobic, and then used. This can improve workability, storage stability of the uncured composition, and electrical properties of the silicone rubber obtained by curing. Further, the silicone rubber composition of the present invention is dissolved or dispersed in an organic solvent such as toluene or xylene,
When applying / coating on fiber etc. and processing into tape etc.,
By such treatment, it is possible to facilitate the dispersion of the filler in the system, reduce the apparent viscosity of the obtained liquid material, and improve the floating stability of the filler. Examples of such treating agents include trimethylchlorosilane, dimethyldichlorosilane, trimethylmethoxysilane, hexamethyldisilazane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, linear polydimethylsiloxane and polymethylhydrogensiloxane. Therefore, one kind may be used, or two or more kinds may be used in combination.

The inorganic filler has a good balance between physical properties of the rubber obtained after curing and various properties to be imparted.
It is appropriately and selectively compounded. Generally, the upper limit is 1,000 parts by weight with respect to 100 parts by weight of the component (A), and in view of processability and the like, the amount is 1 to 500 parts by weight.

The self-fusing silicone rubber composition of the present invention has been conventionally known as a compounding agent for silicone rubber,
Pigments, heat resistance improvers, antioxidants, processing aids, organic solvents and the like may be added. Also, to prevent pseudo-crosslinking,
Alcohols such as methanol, ethanol, isopropyl alcohol, propylene glycol and glycerin may be added.

The composition of the present invention comprises a Banbury mixer,
It can be prepared by cold kneading or heating kneading at a temperature of 300 ° C. or lower using an arbitrary kneading device such as a kneader or roll. The mixing order of the components (A) to (D) and the inorganic filler to be blended as necessary is arbitrary, but when heat kneading is used, the components (B), (C) and (D) are used.
In any case, the mixture should be added after cooling the mixture after kneading by heating.

The composition of the present invention can be molded into a desired shape and then heated at 50 to 500 ° C. for several tens of seconds to several hours to be cured and converted into a rubber-like elastic body.

The silicone rubber molded product obtained by curing the silicone rubber composition of the present invention exhibits excellent self-fusion properties only by pressing the molded product at room temperature.

[0026]

EFFECT OF THE INVENTION The self-fusing silicone rubber composition of the present invention can be cured by heating to obtain a rubber-like elastic body having excellent self-fusing property. This silicone rubber is not only superior in self-fusing property at the initial stage as compared with the self-fusing silicone rubber obtained by the conventional technique, but also left for a long time in the presence of moisture or humidity or at a high temperature. Even after that, the self-bonding property does not decrease (so-called phenomenon).
Moreover, its mechanical properties and electrical properties are also excellent.

Therefore, the silicone rubber composition of the present invention is used for various electrical insulation protective materials which require self-bonding property.
It is extremely useful as a material for contact materials, hoses, and sealing materials.

[0028]

The present invention will be described in more detail with reference to the following examples and comparative examples. In these examples and comparative examples, all parts are parts by weight. The invention is not limited by these examples.

Base Polymer In the following examples and comparative examples, as component (A), that is, the base polymer, A-1 to A-3 shown in Table 1 were used.
The polyorganosiloxane of was used.

[0030]

[Table 1]

Compounding Agents In the following Examples and Comparative Examples, the compounding agents to be compounded with the above base polymer were as follows.

Component (B) B-1: trimethyl borate; B-2: dimethyldimethoxysilane and boric anhydride are mixed at a molar ratio of 2: 1 and condensed by heating at 130 to 170 ° C. for 2 hours. Polymethylborosiloxane obtained by the above (viscosity 200 cSt at 25 ° C.). Component (C) C-1: dibutyltin dilaurate; C-2: dibutyltin dioctate; C-3: stannous octoate. Component (D) D-1: Blended with benzoyl peroxide and silicone oil to prepare a paste having a concentration of 50%; D-2: 2,5-Dimethyl-2,5-di-tert-butyl peroxide, blended with silicone oil And concentration 50%
Formulated as a paste. Inorganic filler F-1: Fume-like silica whose surface is hydrophobized with dimethyldichlorosilane; F-2: Precipitated silica whose surface is hydrophobized with polydimethylsiloxane.

Examples 1 to 3 and Comparative Examples 1 to 3 These compounding agents were compounded into the above-mentioned base polymers A-1 to A-3 by a kneader and uniformly kneaded, and the compounding ratios shown in Table 2 were used. The compositions of Examples 1-3 according to the present invention were prepared. However, although the component (D) was blended in the form of a paste containing each of them, it is shown in Table 2 as the amount of the organic peroxide. Further, for comparison, Comparative Example 1 having the same composition as the compositions of Examples 1 to 3 except that the component (C) was not used.
~ 3 compositions were prepared.

From these compositions, by hot pressing,
Under the curing conditions shown in Table 2, a rubber sheet having a thickness of 2 mm was prepared, and JIS K6301 and JIS C21 were prepared.
In accordance with No. 23, rubber physical properties and electrical properties were measured. The results are shown in Table 2.

Next, the fusion force of the rubber obtained from the composition by curing was measured. That is, Examples 1 and 2,
In addition, in Comparative Examples 1 and 2, a sheet having a thickness of 1 mm and a width of 25 mm obtained by the above press vulcanization was produced.
Further, in Example 3 and Comparative Example 3, a liquid having a solid content concentration of 30% obtained by dissolving and dispersing the composition in xylene was applied to a glass cloth, and xylene was volatilized, followed by drying at 150 ° C. Curing was carried out for 10 minutes in a ribbon-shaped sample having a coating thickness of 0.4 mm and a width of 25 mm.

Each pair of these samples is
A fusion-bonded sample was prepared by overlapping over mm and pressure bonding for 10 minutes at a pressure of 0.3 kgf / cm ² . A shearing force was applied to the sample at a speed of 50 cm / min to measure the fusion force. However, the measurement of the fusion force was performed for the following.
The results are also shown in Table 2. (1) Initial stage: Measurement was performed immediately after curing. (2) After leaving: After curing, left for 1 month in a thermo-hygrostat at room temperature (25 ° C.) and 80% RH, and then measured.

[0037]

[Table 2]

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Claims (1)

[Claims] 1. An average unit formula (A): R _a SiO _{(4-a) / 2} (wherein R represents the same or different substituted or unsubstituted monovalent hydrocarbon group; a is 1) .90 to 2.70
100 parts by weight of a polyorganosiloxane in which some silanol groups may be present; (B) at least one boron compound selected from boric acids, boric acid derivatives and polyorganoborosiloxanes. To 30 parts by weight; (C) at least one tin compound selected from tin oxide, organic acid tin salt and organic tin compound 0.01 to 10
Parts by weight; and (D) 0.1 to 10 parts by weight of an organic peroxide, which is self-fusing after curing.