JP2014005373A - Thermoplastic elastomer composition and extra-high voltage cable for railway vehicle using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic elastomer composition having excellent mechanical properties, heat resistance, oil resistance, flexibility and flame retardance, as well as high production efficiency.SOLUTION: A thermoplastic elastomer composition comprises: (A) silane-grafted ethylene-vinyl acetate with a vinyl acetate content of 20 wt.% or more and (B) crystalline polyolefin-based resin with a melting point of 80°C or higher at a ratio within a range from 50:50 to 80:20 as a resin component; and (C) 50-200 pts.mass of a silane-treated metal hydroxide based on the resin component of 100 pts.mass. In the composition, the component (A) is crosslinked through silane crosslinking, a tensile strength is 7 MPa or more, an elongation at break is 125% or more, residual rates of tensile strength and elongation at break after heating are both 70% or more, residual rates of tensile strength and elongation at break after immersion in a test oil are both 70% or more, a flexural modulus of elasticity is 90 MPa or more, and a char length in the vertical flame test according to BS4066-3 is 2.5 m or less.

Description

  The present invention relates to a thermoplastic elastomer composition, and more particularly to a thermoplastic elastomer composition used for a coating layer of a special high-voltage cable for railway vehicles.

  In railway vehicles, in order to further improve the traveling speed, higher voltage electric power is taken into the vehicle from the overhead line via the pantograph. At this time, a so-called special high voltage cable is used as the cable (see, for example, Patent Document 1). Cables are classified into three stages of low voltage, high voltage, and special high voltage according to the rated voltage in the “Ministerial Ordinance (Electrical Equipment Standard) that establishes technical standards concerning electric equipment”, and the special high voltage cable corresponds to a cable exceeding 7000V. Such a special high-voltage cable is mainly used as a lead-in cable connecting a pantograph and a transformer installed in the lower part of the vehicle floor, or a vehicle crossover cable that connects vehicles and supplies electric power.

  In this type of special high-voltage cable for railway vehicles, not only electrical characteristics, but also mechanical characteristics against damage and abrasion, environmental resistance such as heat resistance, oil resistance, flame resistance, and each device under the train floor Flexibility is required because wiring is performed between the two. These characteristics are mainly attributed to the sheath material (resin composition) used for the coating layer (sheath) of the cable.

  Conventionally, chloroprene rubber has been used as the resin component for the sheath material of the extra high voltage cable. Special high-pressure cables using chloroprene rubber generate a large amount of non-flammable halogen-based gases during combustion, thereby blocking the oxygen around the special high-pressure cables and preventing combustion, thereby exhibiting flame retardancy. However, the halogen-based gas generated during combustion has a problem of generating a large amount of smoke containing a toxic gas.

  In this regard, there is a resin composition in which a polyolefin resin is used instead of the chloroprene rubber and a metal hydroxide such as magnesium hydroxide or aluminum hydroxide is mixed with the resin. In this resin composition, the resin component is crosslinked by an electron beam irradiation apparatus or the like so as to have heat resistance and oil resistance.

JP 2004-32852 A

  However, in a sheath material using a polyolefin-based resin, the elastic modulus increases due to crosslinking, so that the formed sheath becomes hard and it is difficult to obtain the flexibility of the cable.

  In addition, in the sheath material (resin composition) using a polyolefin-based resin, it is not only necessary to separately provide a cross-linking step, but large-scale equipment such as an electron beam irradiation device is required for the cross-linking, The cable production efficiency will decrease.

  The present invention has been made in view of such problems, and its purpose is to provide excellent mechanical properties, heat resistance, oil resistance, flexibility, flame retardancy, and high production efficiency. It is an object of the present invention to provide a plastic elastomer composition and a special high-voltage cable for railway vehicles using the same.

  According to the first aspect of the present invention, a silane-grafted ethylene-acetic acid obtained by graft-copolymerizing a silane coupling agent to an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass or more as a resin component. The vinyl copolymer (A) and the crystalline polyolefin resin (B) having a melting point of 80 ° C. or higher are contained at a mass ratio (A: B) in a ratio within the range of 50:50 to 80:20, And 50 mass parts or more and 200 mass parts or less of the metal hydroxide (C) by which the surface was silane-treated with respect to 100 mass parts of said resin components, The said silane grafted ethylene-vinyl acetate among the said resin components The copolymer (A) is silane-crosslinked and has a tensile strength of 7 MPa or more, an elongation at break of 125% or more, and a tensile strength after heating at 120 ° C. for 240 hours in a test according to JIS C3005. In the test according to JIS K7171, the residual ratio of tensile strength and residual elongation at break are 70% or more, and the residual tensile strength and residual elongation at break after 70 hours of immersion in a test oil at 70 ° C. are 70% or more, respectively. There is provided a thermoplastic elastomer composition having a flexural modulus of 90 MPa or more and a carbonization length of 2.5 m or less in a vertical combustion test based on BS4066-3.

  According to the second aspect of the present invention, in the first aspect, the silane-crosslinked silane-grafted ethylene-vinyl acetate copolymer (A) is dispersed in the crystalline polyolefin resin (B). A thermoplastic elastomer composition is provided.

  According to the third aspect of the present invention, the crystalline polyolefin resin (B) is polypropylene, high density polyethylene, linear low density polyethylene, ultra low density polyethylene, ethylene-butene-1 copolymer, ethylene. -One type of resin selected from hexene-1 copolymer, ethylene-octene-1 copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, or a mixed resin of two or more types There is provided a thermoplastic elastomer composition according to a first aspect or a second aspect.

  According to a fourth aspect of the present invention, there is provided the thermoplastic elastomer composition according to the first to third aspects, wherein the metal hydroxide (C) is magnesium hydroxide or aluminum hydroxide.

  According to the fifth aspect of the present invention, the coating layer made of the thermoplastic elastomer composition according to the first to fourth aspects is an insulated wire having an insulating layer on a conductor or a core formed by twisting a plurality of the insulated wires. A special high-voltage cable for railway vehicles formed on top is provided.

  According to the present invention, a thermoplastic elastomer composition having excellent mechanical properties, heat resistance, oil resistance, flexibility, and flame retardancy, and high production efficiency, and a special high-voltage cable for a railway vehicle using the same. Is obtained.

It is process drawing which shows the manufacturing method of the thermoplastic elastomer composition which concerns on one Embodiment of this invention. It is sectional drawing of the special high voltage cable for rail vehicles which concerns on one Embodiment of this invention.

  In order to achieve the above object, the present inventors have paid attention to a dynamically crosslinked thermoplastic elastomer composition. Dynamic cross-linking is a method in which a specific resin component is cross-linked while kneading a mixture containing two or more kinds of resin components. As the dynamic cross-linking thermoplastic elastomer composition, for example, a polyolefin which is a fluid component And a composition in which a crosslinked rubber component is dispersed in a continuous phase of a resin.

  In this regard, the present inventors diligently studied the crosslinking method of the crosslinked rubber component and found that silane crosslinking with a silane coupling agent is effective.

  Conventionally, since silane crosslinking has a slower crosslinking reaction than a system using sulfur or organic peroxide, a step of crosslinking by contact with moisture in the presence of a silanol condensation catalyst after molding has been required. However, olefin crosslinking is promoted by kneading a polyolefin resin, a rubber component obtained by graft copolymerization of an ethylene-vinyl acetate copolymer with a silane compound, a metal hydroxide, and a silanol condensation catalyst, and rubber It has been found that the components can be dynamically crosslinked. Furthermore, it has been found that various properties such as flexibility of the resin composition can be improved by silane-crosslinking only the rubber component to form a dispersed phase of the rubber component in the polyolefin resin. Based on the above findings, the inventor has created the present invention.

  Below, the thermoplastic elastomer composition which concerns on one Embodiment of this invention, and the cable using the same are demonstrated. First, the manufacturing method of the thermoplastic elastomer composition which concerns on this embodiment is demonstrated using FIG. FIG. 1 is a process diagram showing a method for producing a thermoplastic elastomer composition according to an embodiment of the present invention.

(1) Method for Producing Thermoplastic Elastomer Composition The method for producing the thermoplastic elastomer composition of the present embodiment is obtained by adding a silane cup to an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass or more as a resin component. A silane grafted ethylene-vinyl acetate copolymer (A) in which a ring agent is graft copolymerized with a crystalline polyolefin resin (B) having a melting point of 80 ° C. or more in a mass ratio of 50:50 to 80:20. A step of forming a mixture obtained by adding 50 parts by mass or more and 200 parts by mass or less of a metal hydroxide (C) whose surface is silane-treated to 100 parts by mass of the resin component, kneading the mixture and resin And silane-crosslinking the silane-grafted ethylene-vinyl acetate copolymer (A) among the components.

[Additive]
First, the silane-grafted ethylene-vinyl acetate copolymer (A), the crystalline polyolefin resin (B), and the metal hydroxide (C) used in the production method will be described.

(Silane-grafted ethylene-vinyl acetate copolymer)
The silane-grafted ethylene-vinyl acetate copolymer is obtained by graft copolymerizing an ethylene-vinyl acetate copolymer with a silane coupling agent and has a crosslinkable structure. The silane grafted ethylene-vinyl acetate copolymer is one of the base polymers of the thermoplastic elastomer composition and mainly improves the flexibility of the thermoplastic elastomer composition.

Since ethylene-vinyl acetate copolymer has high crystallinity when the vinyl acetate content (hereinafter also referred to as VA amount) is low, it tends to be excellent in heat resistance. On the other hand, since the crystallinity is high, the flexibility and flexibility are inferior. Moreover, since the polarity is small, the oil resistance is also poor. The ethylene-vinyl acetate copolymer has lower crystallinity as the vinyl acetate content increases, so that the heat resistance is lowered, while the flexibility and flexibility are improved. Moreover, since the polarity increases as the vinyl acetate content increases, the oil resistance is also improved. In this respect, in the present embodiment, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass or more is used. The degree of crosslinking of the ethylene-vinyl acetate copolymer is determined in relation to the amount of the silane coupling agent added and the production conditions described below. For this reason, although the upper limit of vinyl acetate content of an ethylene-vinyl acetate copolymer is not specifically limited, It is preferable that it is 90 mass% or less in the point of availability. More preferably, it is preferable to use an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass to 30% by mass. Since the ethylene-vinyl acetate copolymer having a VA amount of less than 20% by mass has high crystallinity and is hard, the properties such as flexibility of the thermoplastic elastomer composition are deteriorated. In addition, as long as it is in the range of the said VA amount as an ethylene-vinyl acetate copolymer, there is no limitation in molecular weight and melt viscosity, Arbitrary things can be used.

  The ethylene-vinyl acetate copolymer may be obtained by copolymerizing an unsaturated carboxylic acid or a derivative thereof in part. In an ethylene-vinyl acetate copolymer copolymerized with an unsaturated carboxylic acid or derivative thereof, a reaction occurs between the unsaturated carboxylic acid or derivative thereof and the metal hydroxide (C), thereby improving adhesion. As a result, mechanical properties such as mechanical strength of the thermoplastic elastomer composition can be further improved. Although unsaturated carboxylic acid or its derivative (s) is not particularly limited, maleic anhydride is preferred. The amount of copolymerization is arbitrary, but it is preferably 0.5% by mass or more and 10% by mass or less with respect to the ethylene-vinyl acetate copolymer.

  The silane coupling agent introduces a crosslinkable structure into the ethylene-vinyl acetate copolymer, and is capable of reacting with the ethylene-vinyl acetate copolymer (reactive functional group) and silanol condensation. It has a silane-crosslinking group (hydrolyzable group). Examples of the reactive functional group include a vinyl group, an amino group, an epoxy group, an acrylic group, and a mercapto group. Examples of the hydrolyzable group include alkoxy groups such as a methoxy group and an ethoxy group. Examples of the silane coupling agent include vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxylane, and vinyltris (β-methoxyethoxy) silane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- aminosilane compounds such as β- (aminoethyl) γ-aminopropyltrimethoxysilane, β- (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, β- (3,4 epoxy) (Cyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, epoxysilane compounds such as γ-glycidoxypropylmethyldiethoxysilane, and acrylic silane compounds such as γ-methacryloxypropyltrimethoxysilane Mercapto such as bis (3- (triethoxysilyl) propyl) disulfide, polysulfide silane compounds such as bis (3- (triethoxysilyl) propyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane A silane compound etc. can be mentioned.

(Crystalline polyolefin resin)
The crystalline polyolefin resin (B) is a resin having a crystalline state in its structure and having a predetermined melting point. The crystalline polyolefin resin (B) is a resin mixed with the silane-grafted ethylene-vinyl acetate copolymer and mainly improves the mechanical properties, heat resistance, and oil resistance of the thermoplastic elastomer composition. . In the present embodiment, a crystalline polyolefin resin (B) having a melting point of 80 ° C. or higher is used. When the melting point is less than 80 ° C., it becomes difficult not only to obtain a predetermined heat resistance but also to obtain oil resistance. Here, melting | fusing point shows the temperature measured on the conditions of the temperature increase rate of 10 degrees C / min by differential scanning calorimetry (DSC method).

As the crystalline polyolefin resin (B) having a melting point of 80 ° C. or higher, known resins can be used, such as polypropylene, high density polyethylene, linear low density polyethylene, ultra low density polyethylene, ethylene-butene- 1 type of resin selected from 1 copolymer, ethylene-hexene-1 copolymer, ethylene-octene-1 copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, or 2 It is preferable that it is a mixed resin of more than one type. In addition to homopolymers, the above polypropylene includes block copolymers and random copolymers copolymerized with α-olefins typified by ethylene, and polypropylene having a rubber component typified by ethylene propylene rubber introduced in the polymerization stage. Shall be. As the ethylene-vinyl acetate copolymer, those having a crystalline vinyl acetate content of less than 20 wt% can be used. Other usable materials include low density polyethylene, polybutene, poly-4-methyl-pentene-1, ethylene-butene-hexene terpolymer, ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer. And an ethylene-glycidyl methacrylate copolymer.

  The upper limit of the melting point of the crystalline polyolefin-based resin (B) is not particularly limited, but is preferably 200 ° C. or lower in consideration of the melting points of the resins listed above.

  Further, the crystalline polyolefin resin (B) may be obtained by copolymerizing an unsaturated carboxylic acid or a derivative thereof in part. In a crystalline polyolefin resin copolymerized with an unsaturated carboxylic acid or derivative thereof, a reaction occurs between the unsaturated carboxylic acid or derivative thereof and the metal hydroxide (C), thereby improving adhesion. Further, mechanical properties such as mechanical strength of the thermoplastic elastomer composition can be further improved. Although unsaturated carboxylic acid or its derivative (s) is not particularly limited, maleic anhydride is preferred. Moreover, although the quantity to copolymerize is arbitrary, it is preferable to set it as 0.5 to 10 mass% with respect to crystalline polyolefin resin (B).

(Metal hydroxide)
The metal hydroxide (C) is a flame retardant that imparts flame retardancy to the thermoplastic elastomer composition. Furthermore, silane crosslinking is promoted together with the silanol condensation catalyst, and silane crosslinking (dynamic crosslinking) during kneading is enabled. The mechanism for promoting the silane crosslinking of the metal hydroxide is not known in detail, but the moisture contained in the metal hydroxide is contained in the silane coupling agent obtained by graft copolymerization with the ethylene-vinyl acetate copolymer. It is considered that the hydrolysis of a hydrolyzable group (for example, an alkoxy group) is promoted, and the silanol condensation catalyst promotes the dehydration condensation of the silanol group.

  Moreover, in this embodiment, the metal hydroxide by which the surface was processed is used from a dispersible viewpoint to a thermoplastic elastomer composition. Surface treatment includes surface treatment with a surface treatment agent such as a silane coupling agent, titanate coupling agent, fatty acid or fatty acid metal salt, etc., but improves the adhesion between the resin and the metal hydroxide and improves the heat resistance. In view of this, a metal hydroxide whose surface is silane-treated with a silane coupling agent is used. In the case of a metal hydroxide that has not been surface-treated or a metal hydroxide that has been surface-treated other than a silane coupling agent, the heat resistance of the thermoplastic elastomer composition will be degraded, and significant deformation will occur at high temperatures. .

  Examples of the metal hydroxide include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, etc. Among them, magnesium hydroxide and aluminum hydroxide having a high flame retardant effect are preferable.

  The average particle diameter of the metal hydroxide is preferably 4 μm or less from the viewpoint of mechanical properties, dispersibility, and flame retardancy.

  As a surface treatment method of the metal hydroxide, a known method such as a wet method, a dry method, a direct kneading method, or the like can be used.

  The surface treatment amount of the silane coupling agent is not particularly limited, but is preferably 0.1% by mass or more and 0.5% by mass or less with respect to the metal hydroxide.

  Examples of the silane coupling agent for treating the surface of the metal hydroxide include vinyl silane compounds such as vinyl trimethoxy silane, vinyl triethoxy lane, vinyl tris (β-methoxy ethoxy) silane, γ-aminopropyl trimethoxy silane, γ-aminopropyltriethoxysilane, N-β- (aminoethyl) γ-aminopropyltrimethoxysilane, β- (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, etc. Aminosilane compounds, epoxy-silane compounds such as β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxy Acrylic silane compounds such as silane, polysulfide silane compounds such as bis (3- (triethoxysilyl) propyl) disulfide, bis (3- (triethoxysilyl) propyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercapto Mercaptosilane compounds such as propyltriethoxysilane can be used.

[Manufacturing process]
(Silane grafted ethylene-vinyl acetate copolymer preparation step S10)
First, a silane-grafted ethylene-vinyl acetate copolymer (A) having a predetermined VA amount is prepared. As shown in S10 in FIG. 1, a silane-grafted ethylene-vinyl acetate copolymer is mixed by mixing a silane coupling agent with an ethylene-vinyl acetate copolymer (EVA) having a predetermined VA amount and graft copolymerizing the mixture. A coalescence (silane grafted EVA) is produced. Specifically, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass or more, a silane coupling agent, and a free radical generator are mixed and melt-kneaded at a temperature of 80 ° C. to 200 ° C. Graft copolymerization. In the graft copolymerization, the free radical generator is thermally decomposed by heating to generate radicals, and the radicals graft copolymerize the silane coupling agent to the ethylene-vinyl acetate copolymer.

  In the graft copolymerization, the addition amount of the silane coupling agent is not particularly limited, but is preferably 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. In the case of less than 0.5 part by mass, it is difficult to obtain a sufficient effect of silane crosslinking because there are few introductions of hydrolyzable groups into the ethylene-vinyl acetate copolymer. On the other hand, if it exceeds 10 parts by mass, the processability of the silane-grafted ethylene-vinyl acetate copolymer tends to decrease.

  In the graft copolymerization, as a free radical generator to be added, for example, an organic peroxide such as dicumyl peroxide can be used. The amount of the free radical generator added is preferably 0.001 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. When the amount is less than 0.001 part by mass, it becomes difficult to graft copolymerize the silane coupling agent with respect to the ethylene-vinyl acetate copolymer, and it becomes difficult to obtain a sufficient effect of silane crosslinking. If it exceeds 3.0 parts by mass, scorch of the ethylene-vinyl acetate copolymer tends to occur.

(Mixing step S20)
Next, as shown in S20 of FIG. 1, as a resin component, a silane-grafted EVA (A) having a vinyl acetate content of 20% by mass or more and a crystalline polyolefin resin (B) having a melting point of 80 ° C. or more, A metal hydroxide (C) whose surface is silane-treated and a silanol condensation catalyst are mixed to form a mixture.

In the present embodiment, as a resin component, a mass ratio (A: B) of the silane-grafted ethylene-vinyl acetate copolymer (A) and the crystalline polyolefin resin (B) is 50:50.
The ratio is in the range of 80:20. That is, the content of the component (A) is 50 to 80 parts by mass and the content of the component (B) is 50 to 20 parts by mass so that the resin component is 100 parts by mass. When the content of the component (A) is less than 50 parts by mass and the content of the component (B) exceeds 50 parts by mass, it is difficult to obtain good flexibility of the thermoplastic elastomer composition. On the other hand, when the content of the component (A) exceeds 80 parts by mass and the content of the component (B) is less than 20 parts by mass, the moldability of the thermoplastic elastomer composition is lowered and the extruded appearance is deteriorated. .

  In the said resin component, as long as mass ratio (A: B) of (A) component and (B) component is in the said range, other polymers other than (A) component and (B) component should be contained. Is also possible.

  The addition amount of the metal hydroxide (C) is 50 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the resin component. When the addition amount is less than 50 parts by mass, the flame retardancy of the thermoplastic elastomer composition is lowered. On the other hand, when it exceeds 200 parts by mass, flexibility and mechanical properties (such as mechanical strength) are lowered.

  The silanol condensation catalyst is a catalyst that improves the crosslinking rate of the silane-grafted ethylene-vinyl acetate copolymer. Examples of the silanol condensation catalyst include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, stannous acetate, stannous caprylate, zinc caprylate, lead naphthenate, cobalt naphthenate, and the addition amount is a catalyst. Depending on the type, it is preferable that the amount is 0.001 to 0.1 parts by mass relative to 100 parts by mass of the resin component. As a method for adding the silanol condensation catalyst, there is a method of using a masterbatch previously mixed with an ethylene-vinyl acetate copolymer or a crystalline polyolefin resin in addition to the method of adding the silanol as it is.

  In addition to the above additives, process oil, processing aid, flame retardant aid, crosslinking agent, crosslinking aid, antioxidant, lubricant, inorganic filler, compatibilizer, stabilizer, carbon black as necessary It is also possible to add additives such as colorants.

  The order of kneading the three components of the silane-grafted ethylene-vinyl acetate copolymer (A), the crystalline polyolefin resin (B) and the metal hydroxide (C) is arbitrary, and (1) ( A) component and (C) component are kneaded first, (B) component is added later, (2) (A) component and (B) component are kneaded first, and (C) component is added later And (3) kneading all together. The silanol condensation catalyst is optimally added last. In addition, compounding agents such as antioxidants and colorants may be added at any timing.

(Kneading / Silane cross-linking step S30)
Next, as shown in S30 of FIG. 1, the above mixture is kneaded and, among the resin components, the silane-grafted ethylene-vinyl acetate copolymer (A) is silane-crosslinked.

In kneading the mixture, by dispersing the silane-grafted ethylene-vinyl acetate copolymer (A) in the crystalline polyolefin resin (B), the component (B) is used as the continuous phase, A dispersed phase dispersed in the continuous phase is preferable. In the present embodiment, a method for kneading the above mixture is not particularly limited, but general-purpose ones such as a kneader, a Banbury mixer, a roll, a twin screw extruder can be used. Among these, it is preferable to knead with a kneader. According to the kneader, the kneading time can be adjusted, and the kneading can be performed for a long time as compared with the twin-screw extruder. For this reason, the crosslinkable degree can be improved by arranging the hydrolyzable groups of the silane coupling agents close to each other. Further, according to the kneader, the blade clearance is larger than the screw of the twin screw extruder. For this reason, it is hard to produce the malfunction that an additive is crushed and forms a lump, dispersibility can be improved, and a mechanical characteristic and a flame retardance can be improved. Further, according to the kneader, kneading at a low speed becomes possible. For this reason, the shearing force which acts on material and the mechanical damage to a polymeric material can be suppressed low. In addition, heat generation due to kneading is suppressed and temperature adjustment is facilitated, so that thermal degradation of the polymer material can also be suppressed.

  As kneading conditions, for example, the heating temperature is preferably 160 ° C. or more and 250 ° C. or less, the number of rotations of the screw is 10 rpm or more and 50 rpm or less, and the kneading time after addition of the catalyst is preferably 5 minutes or more and 30 minutes or less.

  Furthermore, silane crosslinking is performed while the mixture is kneaded. In silane crosslinking, the silane-grafted ethylene-vinyl acetate copolymer (A) having a crosslinkable structure is crosslinked. Since the silane coupling agent is graft copolymerized with the component (A), a hydrolyzable group such as an alkoxy group is introduced. The hydrolyzable group is hydrolyzed to become a silanol group, causing silanol condensation (dehydration condensation) and crosslinking. On the other hand, the crystalline polyolefin resin (B) into which the crosslinked structure is not introduced exists as non-crosslinked. That is, in the thermoplastic elastomer composition, the silane-crosslinked (A) component is a rubber component, while the non-crosslinked (B) component is a fluid component. As a result, the component (B) becomes a continuous phase (sea phase), and the component (A) becomes a dispersed phase (island phase) dispersed in the continuous phase. Moreover, in this embodiment, by kneading with a kneader, the dispersed phase becomes fine and is uniformly distributed in the continuous phase.

In this embodiment, the crystalline polyolefin resin (B) is prepared by previously graft copolymerizing an ethylene-vinyl acetate copolymer and a silane coupling agent to prepare a silane-grafted ethylene-vinyl acetate copolymer. Graft copolymerization of the silane coupling agent on the surface can be prevented. For this reason, at the time of silane crosslinking, crosslinking of the crystalline polyolefin resin (B) can be prevented, and a decrease in fluidity of the elastomer composition can be suppressed.
In addition, before the silane-crosslinking of the silane-grafted ethylene-vinyl acetate copolymer (A), the crystalline polyolefin resin (B) and the metal hydroxide (C) are added and kneaded so that the crystalline polyolefin Dispersibility of the silane-grafted ethylene-vinyl acetate copolymer (A) to the resin (B) can be improved. Moreover, with the improvement in dispersibility, the coarsening of the silane-grafted ethylene-vinyl acetate copolymer (A) due to crosslinking can be suppressed, and the extrusion appearance and various characteristics of the elastomer composition can be suppressed from decreasing.
Moreover, since silane crosslinking can be performed simultaneously during kneading, the manufacturing process can be simplified. Furthermore, since silane crosslinking with a silane coupling agent does not require a large facility such as an electron beam irradiation apparatus that has been conventionally required, production efficiency can be improved.

  In the above embodiment, the case where the graft copolymerization step and the kneading / silane crosslinking step are separately performed has been described. However, the two steps can be performed at a time.

(2) Thermoplastic elastomer composition The thermoplastic elastomer composition obtained by the above-described production method includes, as a resin component, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass or more and a silane coupling agent. The graft-copolymerized silane-grafted ethylene-vinyl acetate copolymer (A) and the crystalline polyolefin resin (B) having a melting point of 80 ° C. or higher are 50:50 to 80 in mass ratio (A: B). : It contains in the ratio within the range of 20, and the metal hydroxide (C) whose surface was silane-treated with respect to 100 parts by mass of the resin component contains 50 parts by mass or more and 200 parts by mass or less of the resin component. Of these, the silane-grafted ethylene-vinyl acetate copolymer (A) is silane-crosslinked.

And when the thermoplastic elastomer composition of this embodiment is used for the coating layer of a cable, the tensile strength in a test based on JIS C3005 is 7 MPa or more, and elongation at break is 1
It is 25% or more, and has predetermined mechanical characteristics. The test conditions are a sample shape of dumbbell No. 3 and a crosshead speed of 200 mm / min.

  Further, the tensile strength residual rate and the fracture elongation residual rate after heating at 120 ° C. for 240 hours in a test based on JIS C3005 are each 70% or more, and have predetermined heat resistance. The test conditions are a sample shape of dumbbell No. 3 and a crosshead speed of 200 mm / min.

  Moreover, in the test based on JIS C3005, the tensile strength residual ratio and the breaking elongation residual ratio after immersion for 4 hours in a test oil at 70 ° C. are each 70% or more, and have predetermined oil resistance. The test conditions are a sample shape of dumbbell No. 3 and a crosshead speed of 200 mm / min.

  Moreover, the bending elastic modulus in the test based on JISK7171 is 90 Mpa or more, and it has predetermined flexibility. As test conditions, the sample shape is a strip of 80 mm × 10 mm × 4 mm, a compression test is performed at a crosshead speed of 1 mm / min, and the elastic modulus is calculated from the elastic region of the obtained stress-strain curve.

  Moreover, the carbonization length in the vertical flame-retardant test based on BS4066-3 is 2.5 m or less, and has a predetermined flame retardance. In the present embodiment, a vertical flame retardant test based on BS4066-3 is performed, but the sample to be installed, the installation method, and the determination are based on BS6853. Specifically, one cable having a length of 3.5 m and an outer diameter of 54 mm is laid, and the combustion distance from the bottom edge of the burner is measured.

  According to the thermoplastic elastomer composition of the present embodiment, predetermined mechanical properties, heat resistance, oil resistance, flexibility, and flame retardancy can be obtained. In addition, since a resin containing no halogen as a resin component and a metal hydroxide as a flame retardant are used, generation of toxic gas accompanying combustion can be prevented. The thermoplastic elastomer composition can be easily melted and molded by heating during extrusion molding.

  In the thermoplastic elastomer composition of the present embodiment, the silane-crosslinked silane-grafted ethylene-vinyl acetate copolymer (A) is preferably dispersed in the crystalline polyolefin resin (B). According to this configuration, the silane-crosslinked (A) component is dispersed in the non-crosslinked (B) component which is a fluid component, so that the extrusion appearance during extrusion molding is improved.

(3) Special high voltage cable Next, a special high voltage cable provided with the coating layer (sheath) which consists of the said thermoplastic-elastomer composition is demonstrated. FIG. 2 shows a cross-sectional view of an extra high voltage cable according to an embodiment of the present invention. As shown in FIG. 2, the extra high voltage cable 1 includes an insulated electric wire 10 having an insulating layer 13 formed on a conductor 11 through an internal semiconductive layer 12, and an outer semiconductive layer on the outer periphery of the insulated wire 10. 20, a shielding layer 30, a pressing tape 40, and a sheath 50.

As the conductor 11, for example, an aggregate stranded wire in which tin-plated annealed copper wires having a diameter of 0.45 mm are stranded can be used. As the internal semiconductive layer 12, for example, a semiconductive tape wound or a semiconductive rubber can be used. As the insulating layer 13, EP rubber, vinyl chloride, cross-linked polyethylene, silicone rubber, and fluorine-based material can be used, but EP rubber is preferable in consideration of electrical characteristics and flexibility. As the external semiconductive layer 20, for example, a tape obtained by winding semiconductive rubber can be used. As the shielding layer 30, for example, a braided structure in which tin-plated annealed copper wires are alternately knitted can be used, but a lateral winding structure in which the annealed copper wires are laterally wound in a spiral shape may be used. As the presser tape 40, a tape made of cloth or non-woven fabric can be used. And as the sheath 50, the said thermoplastic elastomer composition is used.

  As a method for manufacturing the special high-voltage cable, the insulator 13 is extrusion-coated on the conductor 11 coated with the inner semiconductive layer 12, and the outer semiconductive layer 20, the shielding layer 30, and the pressing tape 40 are formed on the insulating layer 13. Are formed in this order. Then, the heated thermoplastic elastomer composition is extrusion-coated at a predetermined thickness on the presser tape 40 thus formed to form a sheath 50, and the special high-voltage cable of this embodiment is manufactured.

  The thermoplastic elastomer composition of the present embodiment can also be applied to the insulating layer 13, but by applying it to the sheath 50, particularly excellent moldability, high mechanical properties, heat resistance, oil resistance, good A special high voltage cable having flexibility and flame retardancy can be formed. In addition, in FIG. 2, an example in which one insulated wire 10 is used has been described, but the present invention is not limited to this, and a plurality of insulated wires are used instead of one insulated wire. A core formed by twisting can also be used.

  The thermoplastic elastomer composition and cable according to the present invention were produced by the following method and conditions. These examples are examples of the thermoplastic elastomer composition and cable according to the present invention, and the present invention is not limited to these examples.

  First, a silane-grafted ethylene-vinyl acetate copolymer (A), a crystalline polyolefin resin (B), and a metal hydroxide (C) are prepared.

  As the silane-grafted ethylene-vinyl acetate copolymer (A), a silane coupling agent mixed with the ethylene-vinyl acetate copolymer and graft copolymerized was used. Specifically, 100 parts by mass of an ethylene-vinyl acetate copolymer having a predetermined vinyl acetate content (hereinafter referred to as VA amount), a silane coupling agent vinyltrimethoxysilane and an organic peroxide dichloride. 3 parts by mass, 0.01 part by mass, 5 parts by mass, and 0.02 parts by mass of milperoxide were added and mixed, and these mixtures were mixed into a 40 mm extruder at 200 ° C. (L / D = 24). ) And a graft reaction to obtain a residence time of about 5 minutes to obtain a silane-grafted ethylene-vinyl acetate copolymer having a predetermined VA amount. In this example, an ethylene-vinyl acetate copolymer (EV360, manufactured by Mitsui DuPont Polychemical) having a VA amount of 25% by mass and an ethylene-vinyl acetate copolymer (EV260, Mitsui DuPont polychemicals) having a VA amount of 28% by mass are used. A silane-grafted ethylene-vinyl acetate copolymer (silane-grafted EVA) having a predetermined VA amount was obtained.

  The crystalline polyolefin resin (B) includes an ethylene-vinyl acetate copolymer having a melting point of 94 ° C. (P1007, manufactured by Mitsui DuPont Polychemical, VA amount: 10% by mass), and an ethylene-acetic acid having a melting point of 84 ° C. A vinyl copolymer (EV450, manufactured by Mitsui DuPont Polychemicals, VA amount: 19% by mass) was used.

Further, as the metal hydroxide (C), Mg (OH) ₂ (Magics S4, manufactured by Kamishima Chemical Co., Ltd.) whose surface was silane-treated, Al (OH) ₂ (B1403-ST) whose surface was silane-treated Manufactured by Nippon Light Metal Co., Ltd.).

Example 1
In Example 1, as shown in Table 1 below, 80 parts by mass of a silane-grafted ethylene-vinyl acetate copolymer having a VA amount of 28% by mass as component (A) and ethylene having a melting point of 94 ° C. as component (B) -20 parts by weight of vinyl acetate copolymer, magnesium hydroxide Mg (C) as component (C)
OH) ₂ (Silane treatment) 60 parts by mass, silanol condensation catalyst di-n-butyltin dilaurate (manufactured by Showa Chemical Co., Ltd.) 0.2 part by mass, and antioxidant pentaerythritol tetrakis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate] (IRGANOX 1010, manufactured by Nagase Sangyo Co., Ltd.) was added in a batch to a 55 L wonder kneader and mixed. The introduced raw material was kneaded at a temperature of 200 ° C. and a rotation speed of 30 rpm with a 55 L wonder kneader, and only the component (A) was crosslinked to obtain the thermoplastic elastomer composition of Example 1.

  Moreover, the cable was manufactured using the thermoplastic elastomer composition of Example 1 obtained. Specifically, using a 40 mm extruder (L / D = 24) preheated to 180 ° C., the cable core was extrusion coated with the thermoplastic elastomer composition at a thickness of 1.5 mm, and a coating layer (sheath) The cable of Example 1 was manufactured. As the cable core, a copper conductor having a 2 mm outer diameter coated with polyethylene at a thickness of 0.8 mm was twisted together with an intervening material with four cores twisted and pressed with kraft paper tape.

(Examples 2 to 8)
In Examples 2-8, as shown in Table 1 above, heat was changed in the same manner as in Example 1 except that the types and addition amounts of the components (A), (B), and (C) were changed. Plastic elastomer compositions and cables were produced.

(Evaluation method)
With respect to the obtained cables of Examples 1 to 8, various characteristics of the sheath were evaluated by the test methods shown below.

<Formability>
The moldability of the thermoplastic elastomer composition was determined by the appearance when the sheath was extruded on the cable core, and the pass was evaluated as “◯” and the reject as “X”.
When the moldability of the thermoplastic elastomer compositions of Examples 1 to 8 was evaluated, it was a good appearance and was a pass “◯”.

<Mechanical properties, heat resistance, oil resistance>
Only the sheath was sampled from the cables of Examples 1 to 8, cut into a sheet having a thickness of 1 mm, and mechanical properties, heat resistance, and oil resistance were evaluated in accordance with JISC3005.
As mechanical properties, those having a tensile strength of 7 MPa or more and an elongation at break of 125% or more were regarded as acceptable.
As heat resistance, the sheath was heated at 120 ° C. for 240 hours in a thermostatic bath, and the one having a residual tensile strength ratio and a residual elongation at break of 70% or more was regarded as acceptable.
As oil resistance, the sheath was immersed in test oil 1RM902 oil at 70 ° C. for 4 hours, and the one having a residual tensile strength ratio and a residual elongation at break of 65% or more was determined to be acceptable.

When the sheaths of Examples 1 to 8 were evaluated, it was found that in any of the sheaths, the tensile properties were 7 MPa or more, the elongation at break was 125% or more, and the mechanical properties were excellent. .
Similarly, in terms of heat resistance, the residual tensile strength and the residual elongation at break were 70%, indicating that the film had excellent heat resistance.
Moreover, also in oil resistance, the tensile strength residual rate and the breaking elongation residual rate were 70% or more, and it turned out that it has the outstanding oil resistance.

<Flexibility>
The flexibility was evaluated according to JlS K7171, and the one having a flexural modulus of 90 MPa or less was accepted.
When the cables of Examples 1 to 8 were evaluated, the bending elastic modulus was 90 MPa or less, and it was found to have excellent flexibility.

<Flame retardance>
The flame retardancy was subjected to a vertical combustion test (1 line laying) in accordance with BS4066-3, and a carbonization length of 2.5 m or less was accepted. However, in the vertical combustion test, the sample to be laid, the laying method, and the determination were based on BS6853.
When the cables of Examples 1 to 8 were evaluated, the carbonization length was 2.5 m or less, and it was found to have excellent flame retardancy.

<With / without cross-linking>
About the sheath of Examples 1-8, the presence or absence of silane bridge | crosslinking was confirmed. Specifically, the sheath material is extracted in hot xylene at 130 ° C. for 24 hours, and if there is a residual insoluble polymer, it is determined that crosslinking has been introduced. It was determined that there was no “x”.
In the cables of Examples 1 to 8, residual insoluble polymer was confirmed, and it was confirmed that the silane-grafted ethylene-vinyl acetate copolymer (A) was crosslinked.

<Morphology>
The degree of mixing (dispersibility) of the silane-grafted ethylene-vinyl acetate copolymer (A) and the crystalline polyolefin resin (B) in the sheaths of Examples 1 to 8 was evaluated. Specifically, after staining a thin film section of the sheath, the microstructure of the sheath is observed with a transmission electron microscope. When the morphology of the silane-grafted ethylene-vinyl acetate copolymer (A) is a dispersed phase, “○ “,” For the continuous phase, “×”.
In the cables of Examples 1 to 8, it was confirmed that the silane-grafted ethylene-vinyl acetate copolymer (A) was in a dispersed phase in the crystalline polyolefin resin (B).

  The evaluation results of the characteristics by the above test are shown in Table 2 below. As shown in Table 2, it was found that the cables of Examples 1 to 8 were excellent in moldability, mechanical properties, heat resistance, oil resistance, flexibility, and flame retardancy. Further, in the cables of Examples 1 to 8, the silane-grafted ethylene-vinyl acetate copolymer (A) was confirmed to be cross-linked, and the silane-grafted ethylene- It was confirmed that the vinyl acetate copolymer (A) was dispersed to form a dispersed layer.

(Comparative Example 1 and Comparative Example 2)
In Comparative Example 1 and Comparative Example 2, as shown in Table 3, the thermoplastic elastomer was the same as in Example except that the mass ratio of the component (A) and the component (B) was changed to be outside the scope of the present invention. Compositions and cables were produced. Note that, in Table 3, the configuration deviating from the scope of the present invention is underlined.

(Comparative Example 3)
In Comparative Example 3, as shown in Table 3, a thermoplastic elastomer composition and a cable were produced in the same manner as in Example except that a silane-grafted ethylene-vinyl acetate copolymer having a VA amount of 19% by mass was used. . A silane-grafted ethylene-vinyl acetate copolymer having a VA amount of 19% by mass is obtained by adding a silane coupling agent to an ethylene-vinyl acetate copolymer (EV450, manufactured by Mitsui DuPont Polychemical) having a VA amount of 19% by mass. Graft copolymerized.

(Comparative Example 4)
In Comparative Example 4, as shown in Table 3, an ethylene-vinyl acetate copolymer was prepared using an ethylene-vinyl acetate copolymer (VA amount: 28% by mass) in which the silane coupling agent was not graft-copolymerized. A thermoplastic elastomer composition and a cable were produced in the same manner as in the Examples except that they were not crosslinked.

(Comparative Example 5)
In Comparative Example 5, as shown in Table 3, as the crystalline polyolefin resin, an ethylene-vinyl acetate copolymer having a melting point of less than 80 ° C. (VA amount: 25 mass%, melting point: 77 ° C.) was used. A thermoplastic elastomer composition and a cable were produced in the same manner as in the examples.

(Comparative Example 6)
In Comparative Example 6, as shown in Table 3, the same as in Example except that Mg (OH) ₂ whose surface was treated with fatty acid (Magsees N4, manufactured by Kamishima Chemical Co., Ltd.) was used as the metal hydroxide. A thermoplastic elastomer composition and a cable were produced.

(Comparative Example 7 / Comparative Example 8)
In Comparative Example 7 and Comparative Example 8, as shown in Table 3, the thermoplastic elastomer composition and the cable were changed in the same manner as in Example except that the content of the component (C) was changed to be out of the scope of the present invention. Manufactured.

  Further, the characteristics of Comparative Examples 1 to 8 were evaluated in the same manner as in Example 1. The results are shown in Table 4 below. In Table 4, items for which characteristics were not obtained are underlined.

  As shown in Table 4, in Comparative Example 1, the mass ratio of the component (A) is larger than the range defined by the present invention, and the structure is such that the component (B) is dispersed in the crosslinked component (A). Since the extrusion appearance became uneven, the characteristics could not be measured.

  In Comparative Example 2, since the mass ratio of the component (A) was smaller than the range defined by the present invention, the flexural modulus was large and sufficient flexibility could not be obtained.

  In Comparative Example 3, since a silane-grafted ethylene-vinyl acetate copolymer having a vinyl acetate content of less than 20% by mass was used, the flexural modulus was large and sufficient flexibility could not be obtained.

  In Comparative Example 4, an ethylene-vinyl acetate copolymer having no crosslinked structure was used, and the ethylene-vinyl acetate copolymer was not silane-crosslinked in the thermoplastic elastomer composition. And the sample deform | transformed in the case of evaluation of heat resistance, and sufficient heat resistance was not able to be obtained. In addition, sufficient oil resistance could not be obtained.

  In Comparative Example 5, since a crystalline polyolefin resin having a melting point of less than 80 ° C. was used, the sample was deformed by heating, and sufficient heat resistance was not obtained.

  In Comparative Example 6, since metal hydroxide whose surface was treated with fatty acid was used, sufficient heat resistance and oil resistance could not be obtained as in Comparative Example 5.

  In Comparative Example 7, since the content of the component (C) was less than the amount specified by the present invention, sufficient flame retardancy was not obtained.

  In Comparative Example 8, since the content of the component (C) was larger than the amount specified by the present invention, sufficient mechanical properties and flexibility could not be obtained.

  As described above, in the cable including the sheath made of the thermoplastic elastomer composition of the present invention, not only is it excellent in flexibility and flame retardancy, but also high mechanical properties, heat resistance, and oil resistance can be obtained. . For this reason, it can be used as a special high-voltage cable for railway vehicles that requires high characteristics.

DESCRIPTION OF SYMBOLS 1 Special high voltage cable 10 Insulated electric wire 11 Conductor 12 Internal semiconductive layer 13 Insulating layer 20 External semiconductive layer 30 Shielding layer 40 Pressing tape 50 Covering layer (sheath)

Claims (5)

As a resin component, a silane-grafted ethylene-vinyl acetate copolymer (A) obtained by graft-copolymerizing a silane coupling agent to an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20% by mass or more, and a melting point Containing a crystalline polyolefin resin (B) of 80 ° C. or higher in a mass ratio (A: B) within a range of 50:50 to 80:20, and
50 parts by mass or more and 200 parts by mass or less of a metal hydroxide (C) whose surface is silane-treated with respect to 100 parts by mass of the resin component,
Among the resin components, the silane-grafted ethylene-vinyl acetate copolymer (A) is silane-crosslinked,
In a test based on JIS C3005,
Tensile strength is 7 MPa or more,
Breaking elongation is 125% or more,
The residual tensile strength and the residual elongation at break after heating at 120 ° C. for 240 hours are each 70% or more, and the residual tensile strength and the residual elongation at break after 70 hours of immersion in a test oil at 70 ° C. are 70%, respectively. That's it,
The bending elastic modulus in the test based on JIS K7171 is 90 MPa or more,
A thermoplastic elastomer composition having a carbonization length of 2.5 m or less in a vertical combustion test based on BS4066-3. The thermoplastic elastomer composition according to claim 1, wherein the silane-grafted ethylene-vinyl acetate copolymer (A) crosslinked with silane is dispersed in the crystalline polyolefin resin (B). . The crystalline polyolefin resin (B) is polypropylene, high density polyethylene, linear low density polyethylene, ultra low density polyethylene, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-octene. 1 type resin selected from -1 copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, or two or more types of mixed resin. The thermoplastic elastomer composition described in 1. The thermoplastic elastomer composition according to any one of claims 1 to 3, wherein the metal hydroxide (C) is magnesium hydroxide or aluminum hydroxide.   The coating layer comprising the thermoplastic elastomer composition according to any one of claims 1 to 4 is formed on an insulated wire having an insulating layer on a conductor or a core formed by twisting a plurality of the insulated wires. Special high-voltage cable for railway vehicles.