阅读说明：本技术 自熔合高介电性硅橡胶组合物和自熔合高介电性带 (Self-fusing highly dielectric silicone rubber composition and self-fusing highly dielectric tape ) 是由 大石和弘 小池义明 于 2018-03-23 设计创作，主要内容包括：本发明提供自熔合高介电性硅橡胶组合物和自熔合高介电性带。可通过挤出成型或采用压延辊的压延成型进行常压热空气硫化的自熔合高介电性硅橡胶组合物,其含有：(A)由下述平均组成式(1)表示、在1分子中含有至少2个与硅原子键合的烯基的有机聚硅氧烷：100质量份,R<Sup>1</Sup><Sub>n</Sub>SiO<Sub>(4-n)/2</Sub> (1)(式中,R<Sup>1</Sup>为相同或不同的未取代或取代的1价烃基,n为1.95～2.04的正数。)(B)采用BET吸附法得到的比表面积为50m<Sup>2</Sup>/g以上的疏水性气相法二氧化硅：10～100质量份,(C)导电性复合氧化物：100～300质量份,(D)硼酸或硼酸化合物：0.1～50质量份,(E)分子链两末端用烷氧基封端的二有机聚硅氧烷：1～10质量份,和(F)由酰基系有机过氧化物构成的固化剂：0.01～10质量份。(The invention provides a self-fusing highly dielectric silicone rubber composition and a self-fusing highly dielectric belt. A self-fusing highly dielectric silicone rubber composition which can be subjected to atmospheric hot air vulcanization by extrusion molding or calender molding using calender rolls, comprising: (A) an organopolysiloxane containing at least 2 silicon atom-bonded alkenyl groups in 1 molecule, represented by the following average compositional formula (1): 100 parts by mass of R 1 n SiO (4‑n)/2 (1) (in the formula, R 1 Are identical or different unsubstituted or substituted 1-valent hydrocarbon groups, and n is a positive number of 1.95 to 2.04. ) (B) a specific surface area of 50m by BET adsorption 2 A hydrophobic fumed silica per gram or greater: 10 to 100 parts by mass of (C) a conductive composite oxide: 100 to 300 parts by mass of (D) boric acid or a boric acid compound: 0.1 to 50 parts by mass of (E) a diorganopolysiloxane capped at both ends of the molecular chain with alkoxy groups: 1 to 10 parts by mass, and (F) a curing agent comprising an acyl organic peroxide: 0.01 to 10 parts by mass.)

1. A self-fusing highly dielectric silicone rubber composition comprising:

(A) an organopolysiloxane containing at least 2 silicon atom-bonded alkenyl groups in 1 molecule, represented by the following average compositional formula (1): 100 parts by mass of a water-soluble polymer,

R¹ _nSiO_(4-n)/2 (1)

in the formula, R¹Are identical or different unsubstituted or substituted 1-valent hydrocarbon radicals, n is a positive number from 1.95 to 2.04,

(B) the specific surface area obtained by the BET adsorption method is 50m²A hydrophobic fumed silica per gram or greater: 10 to 100 parts by mass of a water-soluble polymer,

(C) conductive composite oxide: 100 to 300 parts by mass of a water-soluble polymer,

(D) boric acid or a boric acid compound: 0.1 to 50 parts by mass of a stabilizer,

(E) diorganopolysiloxane capped at both molecular chain terminals with alkoxy groups: 1 to 10 parts by mass, and

(F) curing agent comprising acyl organic peroxide: 0.01 to 10 parts by mass;

the atmospheric hot air vulcanization can be carried out by extrusion molding or calender molding using calender rolls.

2. The self-fusing highly dielectric silicone rubber composition according to claim 1, wherein the conductive composite oxide of component (C) is a solid solution of zinc oxide and aluminum oxide and/or a solid solution of zinc oxide and titanium oxide, and the composite oxide has a resistivity value of 0.1 to 10.0 Ω -m.

3. The self-fusing highly dielectric silicone rubber composition according to claim 1 or 2, wherein the average particle diameter of the conductive composite oxide of component (C) is 0.8 μm or less.

4. The self-fusing highly dielectric silicone rubber composition as claimed in any one of claims 1 to 3, wherein component (D) is a polyorganoboroxane.

5. The self-fusing highly dielectric silicone rubber composition according to any one of claims 1 to 4, wherein a cured product of the silicone rubber composition has an elongation at break of 500 to 1200%.

6. The self-fusing highly dielectric silicone rubber composition according to any one of claims 1 to 5, wherein a cured product of the silicone rubber composition has a relative dielectric constant of 10 or more and a volume resistivity of 1.0 x 10¹²～1.0×10¹⁷Ω·cm。

7. The self-fusing highly dielectric silicone rubber composition according to any one of claims 1 to 6, which is used for a self-fusing highly dielectric tape that is wound around an end portion of a power cable and that alleviates an electric field concentrated at the end portion of the power cable.

8. A self-fusing highly dielectric tape comprising a cured product of the self-fusing highly dielectric silicone rubber composition according to any one of claims 1 to 7.

Technical Field

The present invention relates to a self-fusing highly dielectric silicone rubber composition and a self-fusing highly dielectric tape which can be cured well by normal pressure Hot Air Vulcanization (HAV) and give a high dielectric insulating rubber cured product having high airtightness and rubber strength while maintaining a high relative dielectric constant.

Background

In the case of connecting CV cables (Cross-linked polyethylene insulated PVC sheathed cables), transformers, overhead lines, and the like, the outer semiconductive layer at the end of the CV Cable must be treated to a predetermined length. However, if only the outer semiconductive layer is removed, an electric field concentrates on an end portion of the outer semiconductive layer, and the electric characteristics are impaired, and therefore, in order to alleviate or suppress the concentration of the electric field, an electric field alleviation layer formed of a dielectric having a higher relative permittivity than the permittivity of the cable insulator is provided in a cut-out portion of the cable shield layer. This utilizes the principle that equipotential lines and electrical stress are refracted when they pass through substances having different dielectric constants (patent document 1: Japanese patent laid-open No. 2015-153514). Examples of the rubber composition for improving the relative dielectric constant include those obtained by blending a base polymer of polyolefin, ethylene-propylene rubber, ethylene-propylene-diene copolymer, acrylic rubber and nitrile rubber with a dielectric substance such as a metal oxide, a dielectric ceramic including barium titanate, carbon black or the like (patent document 2: Japanese patent laid-open publication No. 2017-002218). Further, the cable end is often exposed outdoors, and a high dielectric material in which a high dielectric substance is blended with a silicone rubber having excellent weather resistance has been developed (patent document 3: Japanese patent laid-open publication No. 2013-177558). On the other hand, if a power cable terminal is inserted while spreading out a molded rubber product, there are problems of artificial workability such as air layer mixing, characteristic fluctuation due to individual differences of workers, and time taken for insertion, which can cause insulation breakdown during construction.

Therefore, a highly dielectric tape has been developed in which a high dielectric rubber is formed into a tape shape to impart air tightness and resistance to damage by contamination to the structure of a power cable terminal and to improve the efficiency of workability (patent document 4: Japanese patent laid-open No. 2015-076168).

Further, a self-fusing highly dielectric silicone rubber composition which maintains a high relative permittivity, has airtightness and rubber strength, and is obtained by adding an electrically conductive composite oxide and a boric acid compound to an alkyl peroxide as a curing agent has been proposed (patent document 5: Japanese patent laid-open No. 2017-039833), and when the composition is vulcanized by ordinary pressure hot air vulcanization, vulcanization inhibition by oxygen occurs, so that curing becomes insufficient and the desired rubber properties cannot be obtained. Or a step of sufficiently removing oxygen in advance becomes necessary.

In order to increase the relative permittivity of rubber materials used for these applications, pi electron-transporting conductive materials such as carbon black and carbon fibers are often used as materials for imparting conductivity. However, when a silicone rubber composition using carbon black as a material imparting electrical conductivity is molded and vulcanized continuously by extrusion molding or the like of a long material, there are very large restrictions on the vulcanization system. That is, in the case of organic peroxide vulcanization, if an acyl peroxide such as benzoyl peroxide or 2, 4-dichlorobenzoyl peroxide, which is generally used in ordinary pressure Hot Air Vulcanization (HAV) of a silicone rubber composition, is used in a system containing carbon black, vulcanization is not sufficiently performed due to the influence of carbon black, and a satisfactory molded product cannot be obtained. Further, alkyl peroxides such as di-t-butyl peroxide and dicumyl peroxide can be press-molded using a mold, but are affected by oxygen in the air in atmospheric hot air vulcanization, and the surface vulcanization is not sufficient, and there is a problem that they are not satisfactory products.

Therefore, when a silicone rubber composition containing carbon black is subjected to atmospheric hot air vulcanization, a method using addition vulcanization has been generally employed. The method comprises adding a platinum-based catalyst for addition reaction to an organopolysiloxane having an alkenyl group and an organohydrogenpolysiloxane having a silicon-bonded hydrogen atom which is addition-reacted with the alkenyl group, and curing the resulting mixture. However, this addition reaction system has a drawback that the production range is limited due to the fact that the hydrosilylation reaction is easily inhibited by catalyst poisoning and the reaction proceeds even at room temperature, and therefore, the storage life is short, which has a great problem in molding.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a self-fusing highly dielectric silicone rubber composition which can be cured well by normal pressure Hot Air Vulcanization (HAV) and gives a high dielectric insulating rubber cured product having high airtightness and rubber strength while maintaining a high relative dielectric constant, and a self-fusing highly dielectric tape.

Means for solving the problems

The present inventors have made extensive studies to achieve the above object, and as a result, have found that: by using a silicone rubber composition containing (A) a specific organopolysiloxane, (B) fumed silica having a surface hydrophobized with chlorosilane, hexamethyldisilazane, or the like, (C) a conductive composite oxide, (D) a boric acid or boric acid compound, (E) a diorganopolysiloxane having both molecular chain ends capped with alkoxy groups, and (F) a curing agent comprising an acyl organic peroxide, there is no cure inhibition of catalyst poisoning due to addition vulcanization, a sufficient shelf life is obtained, a good self-weldability is obtained, and a high dielectric insulating rubber cured product having high air impermeability and rubber strength while maintaining a high relative dielectric constant can be obtained by curing well with normal pressure Hot Air Vulcanization (HAV) at the time of extrusion molding and calender molding, and therefore, the concentration of an electric field can be effectively alleviated, and the silicone rubber composition is suitable as a material for a power cable connection part, a power cable connection, The present invention has been completed based on a tape member of an electric field relaxation layer such as a terminal connection portion.

Accordingly, the present invention provides a self-fusing highly dielectric silicone rubber composition and a self-fusing highly dielectric tape that can be subjected to atmospheric pressure Hot Air Vulcanization (HAV) by the following extrusion molding or calender molding using calender rolls.

[1] A self-fusing highly dielectric silicone rubber composition comprising:

(A) an organopolysiloxane containing at least 2 silicon atom-bonded alkenyl groups in 1 molecule, represented by the following average compositional formula (1): 100 parts by mass of a water-soluble polymer,

R¹ _nSiO_(4-n)/2 (1)

(in the formula, R¹Are identical or different unsubstituted or substituted 1-valent hydrocarbon groups, and n is a positive number of 1.95 to 2.04. )

(B) The specific surface area obtained by the BET adsorption method is 50m²A hydrophobic fumed silica per gram or greater: 10 to 100 parts by mass of a water-soluble polymer,

(C) conductive composite oxide: 100 to 300 parts by mass of a water-soluble polymer,

(D) boric acid or a boric acid compound: 0.1 to 50 parts by mass of a stabilizer,

(E) diorganopolysiloxane capped at both molecular chain terminals with alkoxy groups: 1 to 10 parts by mass, and

(F) curing agent comprising acyl organic peroxide: 0.01 to 10 parts by mass;

the atmospheric hot air vulcanization can be carried out by extrusion molding or calender molding using calender rolls.

[2] [1] the self-fusing highly dielectric silicone rubber composition, wherein the conductive composite oxide of component (C) is a solid solution of zinc oxide and aluminum oxide and/or a solid solution of zinc oxide and titanium oxide, and the composite oxide has a resistivity value of 0.1 to 10.0 Ω · m.

[3] [1] the self-fluxing highly dielectric silicone rubber composition according to [1] or [2], wherein the conductive composite oxide of component (C) has an average particle diameter of 0.8 μm or less.

[4] The self-fusing highly dielectric silicone rubber composition according to any one of [1] to [3], wherein the component (D) is a polyorganoboron siloxane.

[5] The self-fusing highly dielectric silicone rubber composition according to any one of [1] to [4], wherein a cured product of the silicone rubber composition has an elongation at break of 500 to 1200%.

[6][1]～[5]The self-fusing highly dielectric silicone rubber composition as described in any of the above, wherein a cured product of the silicone rubber composition has a relative dielectric constant of 10 or more and a volume resistivity of 1.0X 10¹²～1.0×10¹⁷Ω·cm。

[7] The self-fusing highly dielectric silicone rubber composition according to any one of [1] to [6], which is used for a self-fusing highly dielectric tape that is wound around an end portion of a power cable and that alleviates an electric field concentrated at the end portion of the power cable.

[8] A self-fusing highly dielectric tape comprising a cured product of the self-fusing highly dielectric silicone rubber composition according to any one of [1] to [7 ].

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a self-fusing highly dielectric silicone rubber composition which can be cured well by normal pressure Hot Air Vulcanization (HAV), gives a high dielectric insulating rubber cured product maintaining a high relative permittivity and having high airtightness and rubber strength, and a self-fusing highly dielectric tape which can efficiently alleviate the concentration of an electric field and can be used as an electric field alleviation layer in a power cable connection part, a terminal connection part, and the like can be provided.

Detailed Description

The present invention will be described in detail below. In the present invention, the specific surface areas of the reinforcing filler and the conductive composite oxide are values measured by the BET adsorption method. The kneading-type silicone rubber composition is a high-viscosity, non-liquid silicone rubber composition which does not normally have self-fluidity at room temperature (25 ℃), and means a silicone rubber composition which can be kneaded uniformly under shear stress by a kneading machine such as a roll kneader (for example, a two-roll kneader or a triple roll kneader). The organopolysiloxane raw rubber is a non-liquid organopolysiloxane component having a high polymerization degree (high viscosity) of 100 to 100000 and generally having no self-fluidity at room temperature (25 ℃).

The silicone rubber composition of the present invention contains components (A), (B), (C), (D), (E) and (F).

[ (A) organopolysiloxane ]

(A) The organopolysiloxane of component (a) is a main agent (base polymer) of the present composition, and is represented by the following average composition formula (1), and contains at least 2, preferably 2 to 10000, alkenyl groups bonded to silicon atoms in 1 molecule.

R¹ _nSiO_(4-n)/2 (1)

(in the formula, R¹Are identical or different unsubstituted or substituted 1-valent hydrocarbon groups, and n is a positive number of 1.95 to 2.04. )

In the formula (1), R¹Is a 1-valent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, and more preferably 1 to 8 carbon atoms. As a group consisting of R¹Examples of the 1-valent hydrocarbon group include alkyl groups such as methyl, ethyl, propyl and butyl, cycloalkyl groups such as cyclohexyl, alkenyl groups such as vinyl, allyl, butenyl and hexenyl, and aryl groups such as phenyl and tolylAralkyl groups such as a beta-phenylpropyl group, and the like. Some or all of the hydrogen atoms bonded to carbon atoms of these groups may be substituted with halogen atoms, and examples thereof include 3, 3, 3-trifluoropropyl groups. Of these, methyl, vinyl, phenyl and trifluoropropyl are preferred, and methyl and vinyl are more preferred. Of these, R in the molecule is particularly preferable¹In the 1-valent hydrocarbon group, 50 mol% or more of the groups are methyl groups, more preferably 80 mol% or more of the groups are methyl groups, and further preferably all R's other than alkenyl groups¹Is methyl.

In the formula (1), n is a positive number of 1.95 to 2.04, preferably a positive number of 1.98 to 2.02. If the n value is not in the range of 1.95 to 2.04, the resulting cured product may not exhibit sufficient rubber elasticity.

The organopolysiloxane of component (A) must have at least 2 alkenyl groups in 1 molecule, and in formula (1), R is preferably R¹0.001 to 10 mol%, particularly 0.01 to 5 mol% of (A) is an alkenyl group. The alkenyl group is preferably a vinyl group or an allyl group, and particularly preferably a vinyl group.

(A) The organopolysiloxane of component (A) has an average polymerization degree of usually 100 to 100000, preferably 1000 to 100000, more preferably 3000 to 50000, and particularly preferably 4000 to 20000. When the average polymerization degree is less than 100, the silicone rubber composition does not satisfy the properties as a kneaded rubber, and the roll kneading property and the like are significantly deteriorated, which is not preferable. The average polymerization degree can be determined as a weight-average polymerization degree in terms of polystyrene in GPC (gel permeation chromatography) analysis measured under the following conditions.

[ measurement conditions ]

Developing solvent: toluene

Flow rate: 1mL/min

The detector: differential refractive index detector (RI)

Column: KF-805 Lx 2 root (made by Shodex Co., Ltd.)

Column temperature: 25 deg.C

Sample injection amount: 30 μ L (0.2 mass% toluene solution)

(A) The organopolysiloxane of component (A) is not particularly limited as long as it satisfies alkenyl groups in one moleculeThe number and average polymerization degree are not particularly limited, but the main chain is preferably composed of diorganosiloxane units (R)¹ ₂SiO_2/2，R¹Same as above, the same applies hereinafter) and triorganosiloxy groups (R) at both ends of the molecular chain¹ ₃SiO_1/2) The blocked linear diorganopolysiloxane is preferably blocked at both molecular chain terminals with trimethylsiloxy, dimethylvinylsiloxy, dimethylhydroxysiloxy, methyldiethylsilyloxy, trivinylsiloxy and the like, and particularly preferably blocked with siloxy having at least one vinyl group. These organopolysiloxanes may be used alone in 1 kind, or 2 or more kinds different in polymerization degree and molecular structure may be used in combination.

[ (B) hydrophobic fumed silica ]

(B) The hydrophobic fumed silica of component (a) functions as a filler imparting excellent mechanical properties to the silicone rubber composition, and is a product subjected to hydrophobic treatment with Silanol (SiOH) groups present on the surface. (B) The specific surface area of the hydrophobic fumed silica of component obtained by the BET method must be 50m²A ratio of 100 to 400 m/g or more²(ii) in terms of/g. If the specific surface area is less than 50m²In some cases, the reinforcing effect of the component (B) may be insufficient.

(B) As the hydrophobic fumed silica as the component (B), one surface-treated with an organic silicon compound such as organopolysiloxane, chlorosilane, alkoxysilane or the like is used. These silicas may be used alone in 1 kind, or in combination of 2 or more kinds. From the viewpoint of hydrophobicity of the surface of the fumed silica, a reinforcing fumed silica surface-treated with an organosilicon compound in advance is preferable, and foaming due to volatilization of moisture at the time of vulcanization in hot air under normal pressure can be suppressed. (B) The components may be used singly or in combination of 2 or more.

As the hydrophobic fumed silica as the component (B), commercially available products can be used, and examples thereof include fumed silicas subjected to surface hydrophobic treatment such as AEROSIL series (manufactured by AEROSIL R-972, AEROSIL R-974, Japan), Rheorosil DM-20S, 30S (manufactured by Deshan Co., Ltd.).

The amount of the hydrophobic fumed silica of component (B) is 10 to 100 parts by mass, preferably 15 to 80 parts by mass, and more preferably 15 to 60 parts by mass, based on 100 parts by mass of the organopolysiloxane of component (A). If the amount of the silicone rubber composition is outside the above range, not only the processability of the obtained silicone rubber composition is reduced, but also mechanical properties such as tensile strength and tear strength of a silicone rubber cured product obtained by curing the silicone rubber composition may become insufficient.

[ (C) conductive composite oxide ]

Examples of the conductive composite oxide include zinc oxide (ZnO) and aluminum oxide (Al)₂O₃) Solid solution of (3), zinc oxide (ZnO) and titanium oxide (TiO)₂) Solid solutions of (2), and the like. Among these, a solid solution of zinc oxide and aluminum oxide is preferable, and a conductive composite oxide in which aluminum atoms are doped in zinc oxide is particularly preferable. The reason for this is that the powder has good dispersibility in a polymer such as a resin, excellent processability, and relatively low hardness of the powder itself represented by mohs hardness or the like, and the following advantages are mentioned: since the commercial products are available in a large number of grades, the selection range for particle size, dispersibility, and shape is wide, and the cost is stable.

As an example of the method for producing the conductive composite oxide, the following method can be mentioned: 1 or 2 or more different kinds of metal ions are dispersed in crystal particles of a certain metal oxide, and fired in a reducing atmosphere. For example, in the case of a conductive composite oxide which is a solid solution of zinc oxide and aluminum oxide, zinc oxide and an aluminum salt may be treated in an aqueous ammonium salt solution, dehydrated, and then fired in a hydrogen atmosphere (see japanese patent publication No. 62-41171). Further, as the conductive composite oxide, a commercially available product can be used, and for example, as conductive zinc oxide in which aluminum atoms are doped to zinc oxide, conductive zinc oxide (manufactured by shinkanji chemical corporation), conductive zinc oxide 23-K (manufactured by ハ ク ス イ テ ッ ク corporation), and the like can be used.

Many of such conductive composite oxides have conductivity as n-type semiconductors, and have a characteristic that the conductivity is hardly affected by humidity or environmental factors. The mechanism of generating conductivity is considered to be that a surplus or deficiency of electron pairs of metal atoms of different atomic valence, which are doped to replace a part of them, cause conductivity of a semiconductor.

When a solid solution of zinc oxide and aluminum oxide and/or a solid solution of zinc oxide and titanium oxide is used as the conductive composite oxide of component (C), the composite oxide preferably has a resistivity value of 0.1 to 10.0 Ω · m.

The resistivity value can be adjusted to 1.0X 10 by adjusting the relative permittivity of a cured product of the composition described later to 10 or more and the volume resistivity to 1.0X 10 by using a blend of (C-1) having a resistivity value of 0.1 or more and less than 1.0. omega. m and (C-2) having a resistivity value of 5.0 to 10.0. omega. m, for example, as a solid solution of zinc oxide and aluminum oxide and/or a solid solution of zinc oxide and titanium oxide as the component (C)¹²～1.0×10¹⁷Range of Ω · cm.

The mass ratio of (C-1) to (C-2) in the conductive composite oxide is preferably (C-1)/(C-2) 5/95 to 95/5, more preferably 10/90 to 90/10. If a relative permittivity of 10 or more is to be obtained only with (C-1) having a resistivity value of 0.1 or more and less than 1.0. omega. m, the amount of blending must be increased as described later, and as a result, the rubber strength and rubber elasticity of the cured rubber may be lowered. Further, if the resistivity value is only 5.0 to 10.0. omega. m (C-2), the relative permittivity increases, and the insulation may be deteriorated because of exhibiting semiconductivity.

The average particle diameter of the conductive composite oxide of component (C) is preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. The lower limit is not particularly limited, but is usually about 0.001. mu.m. If the particle diameter of the conductive composite oxide is too large, the rubber elasticity may be reduced. The average particle diameter can be determined as the cumulative volume average value D using a particle size distribution measuring device using a laser diffraction method or the like₅₀And (4) obtaining.

The amount of the conductive composite oxide of component (C) is 100 to 300 parts by mass, preferably 150 to 280 parts by mass, and more preferably 170 to 250 parts by mass, based on 100 parts by mass of component (A). When the amount is less than 100 parts by mass, the intended high dielectric constant characteristics may not be obtained, and when it exceeds 300 parts by mass, the rubber strength and rubber elasticity of a cured rubber obtained by curing the composition may be lowered.

[ (D) boric acid or boric acid compounds ]

(D) The boric acid or boric acid compound as the component (b) is used as a component for imparting self-weldability to a cured product of the composition, and 1 kind of the boric acid or boric acid compound can be used alone or 2 or more kinds can be used in combination as appropriate. Specific examples of the boric acid compound include boric acids such as anhydrous boric acid, pyroboric acid and orthoboric acid, boric acids such as trimethyl borate, triethyl borate and trimethoxyboroxine, derivatives of anhydrous boric acid, and polyorganoborosiloxane obtained by heat-condensing organoalkoxysilane such as dimethyldimethoxysilane and dimethyldiethoxysilane with anhydrous boric acid.

The amount of the component (D) is 0.1 to 50 parts by mass, preferably 0.5 to 40 parts by mass, and more preferably 1 to 35 parts by mass, based on 100 parts by mass of the organopolysiloxane of the component (A). When the amount is less than 0.1 part by mass, sufficient self-weldability cannot be imparted to the cured product, and when it exceeds 50 parts by mass, it causes deterioration in heat resistance and mechanical strength of the cured product.

[ (E) diorganopolysiloxane capped at both ends of molecular chain with alkoxy group ]

In the silicone rubber composition of the present invention, a diorganopolysiloxane having both ends of the molecular chain blocked with alkoxy groups is preferably blended from the viewpoint of self-adhesiveness.

The diorganopolysiloxane capped at both ends of the molecular chain with alkoxy groups includes a diorganopolysiloxane capped at both ends with alkoxy groups represented by the following formula (2).

R³O(SiR² ₂O)_mR³ (2)

(in the formula, R²Are identical or different unsubstituted or substituted alkyl or alkoxy radicals having a valency of 1, R³Are the same or different unsubstituted or substituted alkyl radicals having a valence of 1, and m is an integer from 1 to 100. ) In the formula (2), R²The same or different unsubstituted or substituted alkyl or alkoxy group having a valence of 1, and usually, a group having 1 to 8 carbon atoms, particularly 1 to 4 carbon atoms is preferable. Specific examples thereof include methyl, ethyl, propyl, butyl, methoxy, ethoxy, propoxy and butoxy, and methyl, ethyl, methoxy and ethoxy are preferred. R³The same or different unsubstituted or substituted 1-valent alkyl groups are preferred, and those having 1 to 8 carbon atoms, particularly 1 to 4 carbon atoms, are generally preferred. Specific examples thereof include methyl, ethyl, propyl, and butyl, with methyl and ethyl being preferred. m is an integer of 1 to 100, preferably an integer of 1 to 50. In particular, the organopolysiloxane as the component (E) is preferably an organopolysiloxane having 4 or more alkoxy groups in 1 molecule.

The amount of component (E) is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of component (A). If the amount is too small, the adhesion strength by fusion may be lowered, and if it is too large, it may be precipitated from the rubber surface, resulting in poor moldability.

[ (F) curing agent comprising acyl organic peroxide ]

In the present invention, a curing agent comprising an acyl organic peroxide is used.

When the curing is carried out using an alkyl peroxide, vulcanization is inhibited by oxygen, and therefore, vulcanization may not be sufficiently carried out in processing (calender molding) using a calender roll or extrusion molding. Further, in addition reaction in which a platinum-based catalyst for addition reaction is added to an organopolysiloxane having an alkenyl group which is conventionally addition-vulcanized and an organohydrogenpolysiloxane having a silicon-bonded hydrogen atom which is addition-reacted with the alkenyl group to cure the organopolysiloxane, there is a disadvantage that the hydrosilylation reaction is easily inhibited by catalyst poisoning, the reaction proceeds even at room temperature, the storage period is short, and the production range is limited. Further, even when the curing is carried out by a combination of a platinum-based catalyst and an organohydrogenpolysiloxane, sufficient self-fusibility may not be obtained in some cases.

The curing agent comprising an acyl organic peroxide improves these curing agents.

Examples of the acyl organic peroxide include benzoyl peroxide, 2, 4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, and o-methylbenzoyl peroxide.

The amount of component (F) is 0.01 to 10 parts by mass, preferably 0.05 to 8 parts by mass, per 100 parts by mass of component (A), and is used in an amount effective for curing. If the amount is less than 0.01 part by mass, the vulcanization reaction does not proceed sufficiently, and there are cases where the physical properties deteriorate, such as a decrease in hardness or an insufficient rubber strength, and if the amount is more than 10 parts by mass, not only is it economically disadvantageous, but also a large amount of decomposition products of the curing agent are produced, and a sufficient relative dielectric constant cannot be obtained.

[ other ingredients ]

In the silicone rubber composition used in the present invention, in addition to the above components, if necessary, fillers such as ground quartz, diatomaceous earth, and calcium carbonate, colorants, tear strength improvers, heat resistance improvers, flame retardancy improvers such as platinum compounds, acid acceptors, thermal conductivity improvers such as alumina and silicon nitride, and known fillers and additives in heat-curable silicone rubber compositions such as mold release agents may be added as other components as long as the object of the present invention is not impaired. The other components may be used alone in 1 kind, or 2 or more kinds may be used in combination.

Process for the preparation of compositions

The kneading type silicone rubber composition of the present invention can be obtained by mixing the components constituting the composition using a known kneading machine such as a kneader, a banbury mixer, or a twin roll. When a composition containing the above-mentioned components (a) to (F) is obtained as the silicone rubber composition, it is preferable that the conductive composite oxide of component (C), the boric acid or boric acid compound of component (D), and the diorganopolysiloxane blocked at both molecular chain terminals of component (E) are mixed with each other in the mixture after the organopolysiloxane of component (a) and the hydrophobic fumed silica of component (B) are mixed to obtain a mixture, and the curing agent of component (F) is added to the mixture. When the composition containing the above-mentioned components (a) to (F) further contains other components, it is preferable that the organopolysiloxane of component (a), the hydrophobic fumed silica of component (B), the conductive composite oxide of component (C), the boric acid or boric acid compound of component (D), the diorganopolysiloxane blocked at the molecular chain end with an alkoxy group of component (E), and other components are mixed to obtain a mixture, and then the curing agent of component (F) is added to the mixture.

Method for molding silicone rubber

As the molding method, a known molding method can be selected according to the shape and size of the target molded article. For example, a self-fusing highly dielectric tape is produced by extrusion molding, calender molding using calender rolls, etc., molding into a tape or sheet, cutting as needed, winding into a roll, and curing by an atmospheric Hot Air Vulcanization (HAV) system.

The obtained self-fusing highly dielectric tape is used for a connection portion of a power cable. Specifically, since the electric field relaxing layer can be formed by winding the self-fusing highly dielectric tape around the terminal portion such as the intermediate connection portion or the terminal connection portion of the power cable, the electric stress (electric line of force) is not concentrated on the connection portion and can be uniformly dispersed.

Curing conditions

The curing conditions may be any known conditions in the molding method used, and may be preferably 100 to 500 ℃ for 10 seconds to 10 minutes, more preferably 110 to 450 ℃ for 0.2 to 60 minutes, and still more preferably 1 to 45 minutes. In addition, in order to reduce the residual low molecular weight siloxane component in the obtained silicone rubber, and to remove the organic peroxide decomposition products in the silicone rubber, post-curing (2-time curing) may be performed in an oven at 200 ℃ or higher, preferably 200 to 250 ℃ or the like for 1 hour or longer, preferably 1 to 70 hours, more preferably 1 to 10 hours.

The obtained silicone rubber cured product has a relative dielectric constant of preferably 10 or more, more preferably 10 to 50, and even more preferably 11 to 30, in the measurement method described below. If the relative dielectric constant is less than 10, the concentration is concentrated at the terminal part of the high-voltage power cableThe electric field relaxing effect of the electric field dispersion may become insufficient. Further, the volume resistivity is preferably 1.0X 10¹²～1.0×10¹⁷Omega. cm, more preferably 1.0X 10¹²～5.0×10¹⁶Omega. cm, more preferably 1.0X 10¹³～1.0×10¹⁶Omega cm. If the volume resistivity is less than 1.0X 10¹²Ω · cm is insufficient in insulation, and therefore, there is a possibility that dielectric breakdown due to electric field concentration may occur. In addition, if the volume resistivity exceeds 1.0X 10¹⁷Omega cm, the target high dielectric properties cannot be obtained.

The elongation at break of the obtained silicone rubber cured product (processed product) is preferably 500 to 1200%, more preferably 600 to 1100%, and still more preferably 700 to 1000%. By setting the above range, a highly dielectric tape having high airtightness can be obtained without cracking or breaking after elongation.