Heat-resistant silane-crosslinked resin molded body, silane-crosslinkable resin composition, methods for producing the same, and wiring material

Abstract

To provide a heat-resistant silane crosslinked resin molded body which exhibits high heat resistance at 150°C or higher while using a polyolefin resin, and is excellent in appearance characteristics such as a smooth surface and no foam, and a method for producing the heat-resistant silane crosslinked resin molded body, a silane crosslinked resin composition which enables formation of a heat-resistant silane crosslinked resin molded body and a method for producing the silane crosslinked resin composition, and wiring material using a heat-resistant silane crosslinked resin molded body.SOLUTION: A silane crosslinked resin composition is provided which contains boehmite, a silane coupling agent portion, a silanol condensation catalyst, a hindered phenolic antioxidant, and a benzimidazole-based antioxidant with respect to a base resin including at least one ethylene copolymer of an ethylene-vinyl acetate vinyl copolymer and an ethylene-(meth)acrylate copolymer, in specific ratios, and does not contain aluminum hydroxide. A heat-resistant silane crosslinked resin molded body using the silane crosslinked resin composition, and methods for producing the silane crosslinked resin composition and the heat-resistant silane crosslinked resin molded body, and wiring material having a coating layer formed of the heat-resistant silane crosslinked resin molded body are also provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-resistant silane-crosslinked resin molded article, a silane-crosslinkable resin composition, methods for producing the same, and a wiring material using the heat-resistant silane-crosslinked resin molded article. [Background technology]

[0002] Wiring materials such as insulated wires, cables, cords, optical fiber cores, and optical fiber cords (optical fiber cables) used in the fields of electrical and electronic equipment and industrial fields require heat resistance and other properties for safety and reliability. In recent years, advances in the performance and functionality of electrical and electronic devices have led to demands for even higher heat resistance from the wiring materials used in these devices. For example, automotive wiring materials (particularly cables and cross-linked wires installed in the engine compartment of automobiles) are required to withstand extremely high heat temperatures. Specifically, the Japan Automotive Standards Organization (JASO) stipulates that wiring materials must have a tensile elongation of 100% or more (elongation rate of 100% or more) after 10,000 hours at 150°C in a heat resistance test (aging resistance test), and these materials must meet this requirement. Conventional wiring materials that meet such high heat resistance requirements include wiring materials in which the insulating coating layer around the conductor is formed from a composition containing silicone, fluororubber, fluororesin, or other base materials. However, silicone materials have problems with resistance to oil and solvents, making them unsuitable for applications where they may come into contact with engine oil or battery fluid. Furthermore, fluororubber and fluororesin are very expensive and have high material density, which increases the mass of the wiring material, making them unsuitable for wiring materials that require lightweight and low cost. In consideration of the above problems, a method has been developed for producing wiring materials (crosslinked electric wires) with excellent heat resistance by forming a coating layer by crosslinking an inexpensive and lightweight polyolefin resin as a base material. For example, Patent Document 1 describes a method for producing a non-halogen insulated electric wire by irradiating and crosslinking a resin composition containing a base resin mainly composed of polyethylene or the like, a sulfur-based antioxidant, a hindered phenol-based antioxidant, a metal hydroxide, and zinc oxide with an electron beam. Furthermore, Patent Document 2 describes a method for producing a heat-resistant silane-crosslinked resin molded body that forms a coating layer for wiring material, in which a crosslinkable resin molded body containing a base resin, an organic peroxide, a metal hydrate, a bromine-based flame retardant, antimony trioxide, a silane coupling agent, and a silanol condensation catalyst in specific proportions is silane-crosslinked. Furthermore, Patent Document 3 describes a method for producing a flame-retardant crosslinked resin molded article that forms a coating layer for wiring material, in which a flame-retardant crosslinkable resin composition containing a base resin containing a specific resin component such as ethylene rubber, an organic peroxide, boehmite, a silane coupling agent, and a silanol condensation catalyst in specific proportions is silane-crosslinked. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-207642 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-121203 [Patent Document 3] Japanese Patent Application Publication No. 2017-179235 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacturing method described in Patent Document 1, achieving high heat resistance at 150°C for 10,000 hours requires the combined use of aluminum hydroxide or its composite as a metal hydroxide and 2-mercaptobenzimidazole as a sulfur-based antioxidant, in addition to a hindered phenol-based antioxidant and zinc oxide. However, when a large amount of aluminum hydroxide is used, the resin composition is prone to foaming during the melt-mixing and molding processes, making it impossible to produce a coating layer (wiring material) with the desired appearance. In particular, the silane crosslinking method, which requires the melt-mixing and molding processes to be carried out at higher temperatures than the electron beam crosslinking method, is prone to poor appearance due to a decrease in surface smoothness (rough appearance) and the occurrence of bumps (agglomerates). Furthermore, unless manufacturing conditions such as melt-mixing and molding conditions are strictly controlled, foaming becomes significant. Furthermore, the heat-resistant silane-crosslinked resin molded articles or flame-retardant crosslinked resin molded articles produced by the production methods described in Patent Documents 2 and 3 exhibit a certain degree of heat resistance, but there is room for further study to achieve both excellent appearance and high heat resistance.

[0005] The present invention aims to solve the above problems and to provide a heat-resistant silane-crosslinked resin molded article that uses a polyolefin resin but exhibits high heat resistance, for example, at 150°C or higher, and has a smooth surface and excellent appearance properties, free of bumps and bubbles, as well as a production method for producing this molded article while suppressing foaming. Another object of the present invention is to provide a silane-crosslinkable resin composition capable of forming this heat-resistant silane-crosslinked resin molded article and a production method thereof. A further object of the present invention is to provide a wiring material having, as a coating layer, a heat-resistant silane-crosslinked resin molded article obtained by the production method for the heat-resistant silane-crosslinked resin molded article. [Means for solving the problem]

[0006] The present inventors have discovered that a silane-crosslinkable resin composition prepared by a specific process using a base resin essentially containing a polyolefin resin, a specific ethylene copolymer as the polyolefin resin, boehmite as the inorganic filler, and specific amounts of two antioxidants, a hindered phenol antioxidant and a benzimidazole antioxidant, while avoiding the inclusion of aluminum hydroxide as the inorganic filler, can suppress the generation of lumps and bubbles during the melt-mixing and molding processes, and can also form a silane-crosslinked resin molded article with a smooth surface and high heat resistance. Based on this finding, the present inventors conducted further research and have completed the present invention.

[0007] That is, the object of the present invention has been achieved by the following means. <1> A method for producing a heat-resistant silane-crosslinked resin molded product, comprising silane-crosslinking a silane-crosslinkable resin composition containing, relative to 100 parts by mass of a base resin containing at least one ethylene copolymer selected from ethylene-vinyl acetate copolymer and ethylene-(meth)acrylic acid ester copolymer, 9 to 80 parts by mass of boehmite, 1 to 15 parts by mass of a silane coupling agent graft-bonded to the base resin, 0.01 to 0.5 parts by mass of a silanol condensation catalyst, a hindered phenol-based antioxidant, and a benzimidazole-based antioxidant, and which does not contain aluminum hydroxide, the method comprising: A method for producing a heat-resistant silane-crosslinked resin molded product, comprising the following steps (a), (b), (c), (d), and (e), wherein the hindered phenol-based antioxidant or the benzimidazole-based antioxidant is mixed in at least one of steps (a) and (b): Step (a): A part of the base resin, the boehmite, and a grafted polymer to the base resin a silane coupling agent having a reactive grafting reaction site and the base 0.01 to 0.5 parts by mass of an organic peroxide relative to 100% by mass of the resin, The organic peroxide is melt-mixed at a temperature equal to or higher than the decomposition temperature thereof to form a silane mass. Preparing the tar batch Step (b): Melt-mixing the remainder of the base resin with the silanol condensation catalyst to form a catalyst mixture. Preparing the star batch Step (c): dry-blending the silane masterbatch and the catalyst masterbatch and obtaining a silane-crosslinkable resin composition. Step (d): A step of molding the silane-crosslinkable resin composition to obtain a molded product. Step (e): A step of contacting the molded product with water to obtain a heat-resistant silane-crosslinked resin molded product. <2> The hindered phenol-based antioxidant is contained in an amount of 0.5 to 5 parts by mass per 100 parts by mass of the base resin. <1> The manufacturing method described in <3> The benzimidazole antioxidant is contained in an amount of 4 to 12 parts by mass per 100 parts by mass of the base resin. <1> or <2> The manufacturing method described in <4> The ethylene copolymer is contained in a proportion of 10 to 70% by mass relative to 100% by mass of the base resin. <1> ~ <3> The manufacturing method according to any one of the above. <5> Each ethylene copolymer contained in the base resin contains vinyl acetate or (meth)acrylic acid ester in an amount of 10 to 30% by mass based on the ethylene copolymer. <1> ~ <4> The manufacturing method according to any one of the above. <6> The boehmite is contained in an amount of 9 to 50 parts by mass relative to 100 parts by mass of the base resin. <1> ~ <5> The manufacturing method according to any one of the above. <7> The base resin contains a styrene-based elastomer and an organic oil. <1> ~ <6> The manufacturing method according to any one of the above. <8> A method for producing a silane-crosslinkable resin composition containing, relative to 100 parts by mass of a base resin containing at least one ethylene copolymer selected from ethylene-vinyl acetate copolymer and ethylene-(meth)acrylic acid ester copolymer, 9 to 80 parts by mass of boehmite, 1 to 15 parts by mass of a silane coupling agent graft-bonded to the base resin, 0.01 to 0.5 parts by mass of a silanol condensation catalyst, a hindered phenol-based antioxidant, and a benzimidazole-based antioxidant, and containing no aluminum hydroxide, comprising: A method for producing a silane-crosslinkable resin composition, comprising the following steps (a), (b), and (c), wherein the hindered phenol-based antioxidant or the benzimidazole-based antioxidant is mixed in at least one of steps (a) and (b): Step (a): A part of the base resin, the boehmite, and a grafted polymer to the base resin a silane coupling agent having a reactive grafting reaction site and the base 0.01 to 0.5 parts by mass of an organic peroxide relative to 100% by mass of the resin, The organic peroxide is melt-mixed at a temperature equal to or higher than the decomposition temperature thereof to form a silane mass. Preparing the tar batch Step (b): Melt-mixing the remainder of the base resin with the silanol condensation catalyst to form a catalyst mixture. Preparing the star batch Step (c): dry-blending the silane masterbatch and the catalyst masterbatch and obtaining a silane-crosslinkable resin composition. <9> the above <1> ~ <7> 1. A heat-resistant silane-crosslinked resin molded article produced by the method according to any one of claims 1 to 9. <10> the above <8> 1. A silane-crosslinkable resin composition produced by the production method described in 1. <11> A wiring material having a coating layer on the outer periphery of a conductor, The coating layer <9> A wiring material comprising a layer of the heat-resistant silane-crosslinked resin molded product according to claim 1. <12> Heat-resistant wire or cable, <11> The wiring material according to claim 1.

[0008] In the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In the present invention, when multiple numerical ranges are set for the content of a component, physical properties, etc., the upper and lower limits forming the numerical range are not limited to the specific combination written before and after "to" as a specific numerical range, but can be a numerical range obtained by appropriately combining the upper and lower limits of each numerical range. [Effects of the Invention]

[0009] The present invention provides a heat-resistant silane-crosslinked resin molded article that uses a polyolefin resin but exhibits high heat resistance, for example, at 150°C or higher, has a smooth surface, and is free of bumps and bubbles, resulting in an excellent appearance, and a method for producing this molded article while suppressing foaming.The present invention also provides a silane-crosslinkable resin composition that can form this heat-resistant silane-crosslinked resin molded article, and a method for producing the same.Furthermore, the present invention provides a wiring material that includes, as a coating layer, the heat-resistant silane-crosslinked resin molded article obtained by the method for producing the heat-resistant silane-crosslinked resin molded article. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Heat-resistant silane cross-linked resin molding] The heat-resistant silane-crosslinked resin molded article of the present invention is a crosslinked resin molded article (molded article made of a silanol condensate of a silane-crosslinkable resin composition) obtained by silane crosslinking (silanol condensation reaction) after molding a silane-crosslinkable resin composition described below. The heat-resistant silane-crosslinked resin molded article of the present invention can be produced while suppressing the occurrence of causes that cause poor appearance, particularly the occurrence of bumps and bubbles, and has an excellent appearance with a smooth surface and no bumps or bubbles. In the present invention, the occurrence of bubbles mainly generates bubbles (voids) inside the molded article, which leads to a deterioration in the properties of the molded article, and the presence or absence of such bubbles due to foaming is also considered one of the appearance characteristics of the molded article. The heat-resistant silane-crosslinked resin molded article of the present invention not only exhibits the above-mentioned excellent appearance, but also, despite containing a polyolefin resin, can achieve high heat resistance, for example, at 150°C or higher, specifically, high heat resistance sufficient to satisfy the heat resistance test specified in JASO regarding tensile elongation after 10,000 hours at 150°C. Details of the heat resistance test will be explained in the Examples section.

[0011] Although details will be described later, this heat-resistant silane-crosslinked resin molded article has a crosslinked structure (a crosslinked structure via a silane coupling agent or a silanol condensate thereof) in which a base resin, usually at least one ethylene copolymer selected from ethylene-vinyl acetate copolymer and ethylene-(meth)acrylic acid ester copolymer, is silane-crosslinked. As will be described later, this crosslinked structure may incorporate boehmite and optionally an inorganic filler, and it is preferable that boehmite is incorporated as part of the crosslinked structure. The heat-resistant silane-crosslinked resin molded article of the present invention does not contain aluminum hydroxide, a bromine-based flame retardant, or zinc oxide. Even without these components, the excellent properties described above are exhibited. In the heat-resistant silane-crosslinked resin molded article, "not containing any of the components" has the same meaning as in the silane-crosslinkable resin composition described below.

[0012] The heat-resistant silane-crosslinked resin molded article of the present invention is used in products (including semi-finished products, parts, and components) that require heat resistance. Examples of such products include various wiring materials, heat-resistant sheets, and heat-resistant films. Other examples include power plugs, connectors, sleeves, boxes, tape substrates, tubes, sheets, packing, cushioning materials, and vibration-proofing materials. Among these, the molded article is particularly suitable for use as an insulating coating material for automotive wiring materials that require high heat resistance, particularly for cables or crosslinked electric wires installed in the engine compartment of an automobile.

[0013] [Silane-crosslinkable resin composition] The silane-crosslinkable resin composition of the present invention contains, relative to 100 parts by mass of a base resin containing at least one ethylene copolymer selected from the group consisting of ethylene-vinyl acetate copolymer and ethylene-(meth)acrylic acid ester copolymer, 9 to 80 parts by mass of boehmite, 1 to 15 parts by mass of a silane coupling agent grafted to the base resin, 0.01 to 0.5 parts by mass of a silanol condensation catalyst, a hindered phenol-based antioxidant, and a benzimidazole-based antioxidant, but is free of aluminum hydroxide. This silane-crosslinkable resin composition is a dry blend prepared by the method for producing a silane-crosslinkable resin composition of the present invention, which will be described later. As will be described in detail later, the silane-crosslinkable resin composition of the present invention contains a silane-crosslinkable resin obtained by grafting a silane coupling agent bonded or dissociated with boehmite and, optionally, an inorganic filler to a base resin, particularly an ethylene copolymer. This silane-crosslinkable resin composition can be used by a silane crosslinking method (silanol condensation reaction) to produce a heat-resistant silane-crosslinked resin molded article exhibiting the above-mentioned excellent properties while suppressing volatilization of the silane coupling agent and foaming during melt mixing, and is therefore suitable for use in the method for producing a heat-resistant silane-crosslinked resin molded article of the present invention.

[0014] The silane-crosslinkable resin composition of the present invention contains boehmite as an inorganic filler but does not contain aluminum hydroxide. This effectively suppresses foaming during the preparation and molding processes of the silane-crosslinkable resin composition, improving the appearance characteristics without impairing the high heat resistance of the heat-resistant silane-crosslinked resin molded article. In the present invention, "a composition free of aluminum hydroxide" includes not only an embodiment in which the aluminum hydroxide content is 0 parts by mass per 100 parts by mass of base resin in the composition, but also an embodiment in which a certain amount of aluminum hydroxide is contained. In this case, the content cannot be determined unambiguously because the foaming suppression effect varies depending on the manufacturing conditions, etc.; however, for example, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less per 100 parts by mass of base resin in the composition. In the present invention, the aluminum hydroxide contained in the composition includes not only aluminum hydroxide used as an optional inorganic filler, but also aluminum hydroxide remaining in or compounded with boehmite, which will be described later.

[0015] In one preferred embodiment, the silane-crosslinkable resin composition of the present invention does not contain a brominated flame retardant. In this embodiment, a halogen-free resin molded product can be obtained without impairing the high heat resistance of the heat-resistant silane-crosslinked resin molded product. The brominated flame retardant is not particularly limited, and examples thereof include the brominated flame retardants described in Patent Document 2. In the present invention, the composition not containing a brominated flame retardant includes an embodiment in which the content of the brominated flame retardant per 100 parts by mass of the base resin in the composition is 0 parts by mass, as well as an embodiment in which the content is 10 parts by mass or less. Preferably, this content is 5 parts by mass or less.

[0016] In one preferred embodiment, the silane-crosslinkable resin composition of the present invention does not contain zinc oxide. In the present invention, the absence of zinc oxide in the composition includes an embodiment in which the zinc oxide content per 100 parts by mass of the base resin in the composition is 0 parts by mass, as well as an embodiment in which the content is 5 parts by mass or less. Preferably, this content is 3 parts by mass or less.

[0017] Each component used in the present invention will be described below. One or more of each component can be used. <Base resin> The base resin used in the present invention may be any resin containing at least one ethylene copolymer selected from the group consisting of ethylene-vinyl acetate copolymer and ethylene-(meth)acrylic acid ester copolymer. When the base resin contains an ethylene copolymer, it becomes possible to form a silane-crosslinked resin molded product exhibiting high heat resistance by using the ethylene copolymer in combination with boehmite and two antioxidants. In addition to the ethylene copolymer, the base resin may contain a polyolefin resin, a rubber or elastomer such as a polymer that forms a polyolefin resin, and an organic oil, etc. Among these, it is preferable to contain at least one of polyethylene, polypropylene, ethylene rubber, a styrene-based elastomer, and an organic oil, more preferable to contain a styrene-based elastomer and an organic oil, still more preferable to contain a styrene-based elastomer and an organic oil and at least one of polyethylene, polypropylene, and ethylene rubber, and particularly preferable to contain polyethylene, polypropylene, ethylene rubber, a styrene-based elastomer, and an organic oil. Each resin component constituting the base resin usually has a graftable site, such as an unsaturated bond site in a carbon chain or a carbon atom having a hydrogen atom, in the main chain or at its terminal, which is capable of undergoing a grafting reaction with the grafting site of a silane coupling agent. However, since the present invention uses an ethylene copolymer having a graftable site, a resin component not having a graftable site can also be used as the other resin component.

[0018] (ethylene copolymer) The ethylene copolymer may be at least one selected from the group consisting of ethylene-vinyl acetate copolymer (EVA) and ethylene-(meth)acrylic acid ester copolymer, with ethylene-vinyl acetate copolymer being more preferred. By using an ethylene copolymer in combination with boehmite and an antioxidant (described below), a silane-crosslinked resin molded article exhibiting excellent appearance characteristics and high heat resistance can be produced. The ethylene copolymer contained in the base resin may be two or more types, or two to three types, but one or two types are preferred. As the two or more types of ethylene copolymers, EVA and ethylene-(meth)acrylic acid ester copolymers may be used in combination, or EVA and ethylene-(meth)acrylic acid ester copolymers may be combined.

[0019] - Ethylene-vinyl acetate copolymer - The ethylene-vinyl acetate copolymer may be an alternating copolymer in which an ethylene component and a vinyl acetate component are alternately polymerized, a block copolymer in which a polymerized block of an ethylene component and a polymerized block of a vinyl acetate component are bonded, or a random copolymer in which an ethylene component and a vinyl acetate component are randomly polymerized, as long as the ethylene-vinyl acetate copolymer is a copolymer of ethylene and vinyl acetate. The content of the vinyl acetate component (EV content) in each ethylene-vinyl acetate copolymer used as the base resin is not particularly limited and can be set appropriately. In terms of being able to produce molded articles that exhibit excellent appearance characteristics and high heat resistance, the content of the vinyl acetate component is preferably 10 to 30 mass%, more preferably 15 to 25 mass%. When multiple ethylene-vinyl acetate copolymers are used, the content of the vinyl acetate component in the entire ethylene-vinyl acetate copolymer is not particularly limited and can be set appropriately. This vinyl acetate content can be determined in accordance with Japanese Industrial Standards (JIS) K 7192.

[0020] - Ethylene-(meth)acrylic acid ester copolymer - As with the ethylene-vinyl acetate copolymer, the ethylene-(meth)acrylic acid ester copolymer may be any of an alternating copolymer, a block copolymer, or a random copolymer, so long as it is a copolymer of ethylene and a (meth)acrylic acid ester. The (meth)acrylic acid ester is not particularly limited, but is preferably a (meth)acrylic acid alkyl ester, and the number of carbon atoms in the alkyl group is preferably 1 to 12, more preferably 1 to 4. Examples of the ethylene-(meth)acrylic acid ester copolymer include ethylene-methyl(meth)acrylate copolymer (EMA), ethylene-ethyl(meth)acrylate copolymer (EEA), and ethylene-butyl(meth)acrylate copolymer (EBA). The content of the (meth)acrylic acid ester component (EA content) in each ethylene-(meth)acrylic acid ester copolymer used as the base resin is not particularly limited and can be set appropriately. The content of the (meth)acrylic acid ester component is preferably 10 to 30% by mass, more preferably 15 to 25% by mass, in order to effectively suppress the generation of lumps and produce a molded article with excellent appearance characteristics. When multiple ethylene-(meth)acrylic acid ester copolymers are used, the content of the (meth)acrylic acid ester component in the entire ethylene-(meth)acrylic acid ester copolymer is not particularly limited and can be set appropriately. In the case of a manufactured product, this (meth)acrylic acid ester content can be determined from the polymerization amount during production, etc.; in the case of a commercially available product, the value listed in the manufacturer's or distributor's materials (catalog, product information, etc.) can be used.

[0021] (Polyolefin resin) The polyolefin resin is not particularly limited as long as it is a resin consisting of a polymer obtained by homopolymerizing or copolymerizing a compound having an ethylenically unsaturated bond, and any known polyolefin resin that has been conventionally used in heat-resistant resin compositions can be used. Examples include polyethylene (PE), polypropylene (PP), ethylene-α-olefin copolymers, and polyolefin copolymers having an acid copolymer component or an acid ester copolymer component (excluding the above ethylene copolymers).

[0022] The polyethylene (PE) is not particularly limited as long as it is a polymer containing ethylene as the main component, and examples thereof include high-density polyethylene (HDPE), low-density polyethylene (LDPE), ultra-high molecular weight polyethylene (UHMW-PE), linear low-density polyethylene (LLDPE), and very low-density polyethylene (VLDPE). The polypropylene (PP) is not particularly limited as long as it is a polymer containing propylene as a main component, and examples thereof include propylene homopolymers, random polypropylenes, and block polypropylenes. The ethylene-α-olefin copolymer is preferably a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms (excluding those contained in polyethylene and polypropylene). Examples thereof include an ethylene-propylene copolymer (excluding those contained in polypropylene), an ethylene-butylene copolymer, and an ethylene-α-olefin copolymer synthesized in the presence of a single-site catalyst. In the polyolefin copolymer having an acid copolymerization component or an acid ester copolymerization component, the compound that leads to the acid copolymerization component or the acid ester copolymerization component is not particularly limited, and examples thereof include carboxylic acid compounds such as (meth)acrylic acid, etc. Examples of the polyolefin copolymer having an acid copolymerization component or an acid ester copolymerization component include ethylene-(meth)acrylic acid copolymer, etc.

[0023] The polyolefin resin may be acid-modified with a commonly used unsaturated carboxylic acid or a derivative thereof.

[0024] (rubber or elastomer) The rubber or elastomer is not particularly limited, and preferred examples thereof include ethylene rubber and styrene-based elastomers. - Ethylene rubber - The ethylene rubber is not particularly limited as long as it is a copolymer rubber obtained by copolymerizing a compound having an ethylenically unsaturated bond, and known rubbers can be used. Preferred examples of the ethylene rubber include a binary copolymer rubber of ethylene and an α-olefin, and a ternary copolymer rubber of ethylene, an α-olefin, and a diene compound. The α-olefin is not particularly limited, and preferred examples include α-olefins having 3 to 12 carbon atoms. The diene compound constituting the terpolymer is not particularly limited, and examples thereof include conjugated diene compounds such as butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene, and non-conjugated diene compounds such as dicyclopentadiene (DCPD), ethylidene norbornene (ENB), and 1,4-hexadiene, among which non-conjugated diene compounds are preferred. As the binary copolymer rubber, ethylene-propylene rubber (EPM) is preferred, and as the ternary copolymer rubber, ethylene-propylene-diene rubber (EPDM) is preferred.

[0025] - Styrene-based elastomer - Styrenic elastomers refer to elastomers made of polymers containing components derived from aromatic vinyl compounds within the molecule. Examples of such styrenic elastomers include block copolymers and random copolymers of conjugated diene compounds and aromatic vinyl compounds, as well as hydrogenated products thereof. More specific examples include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS), hydrogenated SIS, styrene-butadiene-styrene block copolymer (SBS), hydrogenated SBS, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-butadiene rubber (SBR), and hydrogenated styrene-butadiene rubber (HSBR).

[0026] (organic oil) The base resin may contain various oils, and it is particularly preferable to contain them together with an elastomer. When the base resin contains an elastomer and an organic oil, the moldability of the silane-crosslinkable resin composition is improved, reinforcing the improvement of appearance characteristics. Examples of such oils include oils used as plasticizers in polyolefin resins or mineral oil softeners for rubber. The mineral oil softener is a mixed oil containing three oils: an oil made of a hydrocarbon having an aromatic ring, an oil made of a hydrocarbon having a naphthenic ring, and an oil made of a hydrocarbon having a paraffin chain. Among these, paraffin oil and naphthenic oil are preferably used, and paraffin oil is particularly preferably used.

[0027] (Base Resin Composition) The total content of the ethylene copolymer in 100% by mass of the base resin is not particularly limited, but from the viewpoint of achieving both appearance properties and heat resistance, it is preferably 10 to 70% by mass, more preferably 15 to 50% by mass, and even more preferably 20 to 40% by mass. The total content of polyolefin resins in 100% by mass of the base resin is not particularly limited, but from the viewpoint of achieving both appearance properties and heat resistance, it is preferably 10 to 70% by mass, more preferably 15 to 50% by mass, and even more preferably 20 to 40% by mass. The content of polyethylene in 100% by mass of the base resin is not particularly limited and may be appropriately determined taking into account the total content of the polyolefin resins, and is preferably 10 to 70% by mass, and more preferably 15 to 40% by mass. Similarly, the content of polypropylene in 100% by mass of the base resin is not particularly limited and may be appropriately determined taking into account the total content of the polyolefin resins, and is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass. The contents of the ethylene-α-olefin copolymer and the polyolefin copolymer having an acid copolymerization component or an acid ester copolymerization component in 100% by mass of the base resin are not particularly limited and may be appropriately determined taking into account the total content of the polyolefin resins, and may each be, for example, 0 to 20% by mass.

[0028] The content of the rubber in 100% by mass of the base resin is not particularly limited, but is preferably 0 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass, from the viewpoint of reinforcing the improvement of appearance characteristics, particularly increasing the viscosity of the material and suppressing foaming. The content of the elastomer in 100% by mass of the base resin is not particularly limited, but is preferably 0 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass, from the viewpoint of the moldability of the silane-crosslinkable resin composition. The content of the organic oil in 100% by mass of the base resin is not particularly limited, but from the viewpoint of moldability of the silane-crosslinkable resin composition, it is preferably, for example, 0 to 30% by mass, more preferably 5 to 20% by mass. When the base resin contains an elastomer and an organic oil, the total content of the elastomer and the organic oil is determined appropriately depending on the content of each, but is, for example, preferably more than 0 parts by mass and 50% or less by mass, more preferably 10 to 30% by mass.

[0029] <Boehmite> The boehmite used in the present invention is aluminum oxide hydrate (Al2O3·H2O). Boehmite functions as a filler or flame retardant, but in order to retain a silane coupling agent and contribute to improving mechanical properties and heat resistance, it is preferable that the boehmite has sites (e.g., oxygen atoms) on its surface that can chemically bond with the silanol condensation-capable reactive sites of the silane coupling agent via hydrogen bonds, covalent bonds, or intermolecular bonds. Boehmite can usually be synthesized by hydrothermal treatment of aluminum hydroxide, and commercially available products can also be used. The boehmite used in the present invention can be boehmite composed of aluminum oxide hydrate obtained by completing the hydrothermal treatment, or a composite with aluminum hydroxide obtained by terminating the hydrothermal treatment midway. However, in the present invention, the aluminum hydroxide contents in the silane-crosslinkable resin composition and the heat-resistant silane-crosslinked resin molded product are set to satisfy the above-mentioned ranges. In the present invention, depending on whether or not aluminum hydroxide is used as an inorganic filler and the amount used, the amount of aluminum hydroxide present in the boehmite (composite) is appropriately determined taking into account the allowable aluminum hydroxide content in the heat-resistant silane-crosslinked resin molded product. For example, the amount measured in the "Method for Measuring Aluminum Hydroxide Content" in the Examples described below is preferably 0 to 15% by mass, more preferably 0 to 10% by mass. The boehmite may or may not be surface-treated. It is also preferable that the boehmite is in a particulate form. The surface treatment agent for the boehmite is not particularly limited, and any surface treatment agent for inorganic fillers can be used, including, for example, various fatty acids and various coupling agents such as silane coupling agents. The amount of the surface treatment of the boehmite is not particularly limited, but is, for example, 3% by mass or less.

[0030] <Silane coupling agent> The silane-crosslinkable resin composition contains a silane coupling agent grafted to a base resin. The base resin to which the silane coupling agent is grafted is preferably prepared by a grafting reaction between the silane coupling agent and the base resin in step (a) described below. The silane coupling agent used in the present invention (before the grafting reaction) has a grafting reaction site (atom or functional group such as an ethylenically unsaturated group) that can undergo a grafting reaction with a grafting reaction site of the base resin in the presence of radicals generated by the decomposition of the organic peroxide. Furthermore, it preferably has a hydrolyzable silyl group as a silanol condensation reaction site, which can react with the chemically bondable site of boehmite or an inorganic filler. The silane coupling agent that can be used in the present invention is not particularly limited, and examples thereof include silane coupling agents used in conventional silane crosslinking methods. Suitable silane coupling agents include silane coupling agents having an ethylenically unsaturated group and a hydrolyzable silyl group, and specific examples thereof include vinylalkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinyldimethoxyethoxysilane, vinyldimethoxybutoxysilane, vinyldiethoxybutoxysilane, allyltrimethoxysilane, allyltriethoxysilane, and vinyltriacetoxysilane, and (meth)acryloxyalkoxysilanes such as methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, and methacryloxypropylmethyldimethoxysilane. Among these, vinyltrimethoxysilane or vinyltriethoxysilane is particularly preferred.

[0031] <Silanol condensation catalyst> The silanol condensation catalyst functions to promote the condensation reaction of the silanol condensation-capable reactive sites of the silane coupling agent grafted onto the base resin in the presence of moisture, thereby crosslinking the base resin via the silane coupling agent. Such silanol condensation catalysts are not particularly limited and include, for example, organotin compounds, metal soaps, platinum compounds, etc. Examples of organotin compounds include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctiate, dibutyltin diacetate, etc.

[0032] <Hindered phenol antioxidant> The hindered phenol-based antioxidant is not particularly limited as long as it is an antioxidant having a hindered phenol structure, and known antioxidants, for example, those commonly used in the field of wiring materials, etc., can be used. Examples thereof include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1010, manufactured by BASF), 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearyl propionate (trade name: Irganox 1076, manufactured by BASF), N,N'-bis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionyl]hexamethylenediamine (Irganox 1098 (trade name), manufactured by BASF), and N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine (ADEKA STAB CDA-10 (trade name), manufactured by ADEKA)).

[0033] <Benzimidazole antioxidant> The benzimidazole antioxidant is not particularly limited as long as it has a benzimidazole structure, and known antioxidants, such as those commonly used in the field of wiring materials, can be used. Examples include 2-mercaptobenzimidazole or its zinc salt (Nocrac MBZ, trade name, 1,3-dihydro-2H-benzimidazole-2-thione·0.5zinc, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 2-methylmercaptobenzimidazole or its zinc salt, and 1,3-dihydro-1-phenyl-2H-benzimidazole-2-thione or its zinc salt.

[0034] <Inorganic fillers other than boehmite> In the present invention, inorganic fillers other than boehmite may be used. The inorganic filler preferably has a surface containing a site (e.g., hydroxyl group, water molecules of hydrated or crystalline water, OH groups such as carboxyl groups, amino groups, SH groups, etc.) that can chemically bond with the silanol condensation-capable reactive site of the silane coupling agent. Examples of suitable inorganic fillers include metal hydrates such as aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate, whiskers, hydrated aluminum silicate, hydrated magnesium silicate, basic magnesium carbonate, and compounds having hydroxyl groups or crystalline water, such as hydrotalcite; boron nitride, silica (crystalline silica, amorphous silica, etc.), carbon, clay, zinc oxide, tin oxide, titanium oxide, molybdenum oxide, antimony trioxide, silicone compounds, quartz, talc, zinc borate, white carbon, zinc borate, zinc hydroxystannate, and zinc stannate. The inorganic filler may be surface-treated with a surface treatment agent.

[0035] <Organic peroxide> In the present invention, an organic peroxide is used in preparing the silane-crosslinkable resin composition. The organic peroxide generates radicals by thermal decomposition and functions to promote the grafting reaction of the silane coupling agent to the base resin (a covalent bond-forming reaction between the grafting reaction site of the silane coupling agent and the grafting reaction site of the base resin, also called a (radical) addition reaction). There are no particular limitations on the organic peroxide, and examples thereof include compounds represented by the general formula: R 1 -OO-R 2 , R 3 -OO-C(=O)R 4 , R 5 C(=O)-OO(C=O)R 6 Preferably, a compound represented by the formula: 1 ~R 6 Each independently represents an alkyl group, an aryl group, or an acyl group. 1 ~R 6 Among these, it is preferable that all of them are alkyl groups, or that one of them is an alkyl group and the other is an acyl group. The decomposition temperature of the organic peroxide, as measured by the method described in Patent Document 2, is preferably 80 to 195°C, and particularly preferably 125 to 180°C. As such organic peroxides, for example, the following paragraph of Patent Document 2

[0036] , the contents of which are incorporated herein by reference as part of the present specification. Among these, dicumyl peroxide, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane (Perhexa 25B), and 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3 are preferred.

[0036] <Additives> In the present invention, various additives that are commonly used in electric wires, electric cables, electric cords, etc. can also be used. Examples of such additives include lubricants, metal deactivators, plasticizers, flame retardants, flame retardant assistants, and (co)polymers other than those described for the base resin. Examples of flame retardant (assistant) agents include brominated flame retardants and / or antimony trioxide.

[0037] (Composition of Silane-Crosslinkable Resin Composition) The content of boehmite in the silane crosslinkable resin composition is not particularly limited, but is 9 to 80 parts by mass, preferably 9 to 50 parts by mass, and more preferably 20 to 40 parts by mass, relative to 100 parts by mass of the base resin, in order to achieve a good balance between excellent appearance characteristics (surface smoothness) and high heat resistance and to form a sufficient crosslinked structure. The content of the silane coupling agent grafted to the base resin in the silane cross-linkable resin composition (converted into the mass before the grafting reaction to the base resin) is not particularly limited, but is 1 to 15 parts by mass, preferably 2 to 10 parts by mass, and more preferably 2.5 to 6 parts by mass, relative to 100 parts by mass of the base resin, in order to suppress the formation of agglomerates (lumps) and the occurrence of foaming due to evaporation and to produce a heat-resistant silane-cross-linked resin molded product having a smooth surface and a sufficiently cross-linked structure. The content of the silanol condensation catalyst in the silane cross-linkable resin composition is not particularly limited, but in order to achieve a good balance between excellent appearance characteristics (suppression of bump formation) and high heat resistance, and also to enable excellent surface smoothness, the content is 0.01 to 0.5 parts by mass, preferably 0.03 to 0.2 parts by mass, and more preferably 0.05 to 0.15 parts by mass, relative to 100 parts by mass of the base resin.

[0038] The content of the hindered phenol-based antioxidant in the silane-crosslinkable resin composition is not particularly limited, but from the viewpoint of realizing high heat resistance and further improving appearance characteristics (surface smoothness and suppression of the occurrence of bumps), the content is preferably 0.2 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, relative to 100 parts by mass of the base resin. The content of the benzimidazole antioxidant in the silane crosslinkable resin composition is not particularly limited, but from the viewpoint of realizing high heat resistance and further improving appearance characteristics (surface smoothness and suppression of the occurrence of bumps), the content is preferably 2 to 15 parts by mass, more preferably 4 to 12 parts by mass, and even more preferably 6 to 10 parts by mass, relative to 100 parts by mass of the base resin.

[0039] The content of inorganic fillers other than boehmite in the silane-crosslinkable resin composition is not particularly limited and can be appropriately set within a range that does not impair the effects of the present invention. For example, it is preferably 0 to 100 parts by mass, more preferably 0 to 50 parts by mass, per 100 parts by mass of the base resin. However, when aluminum hydroxide is contained, it should be within the above content range. The content of the additives in the silane-crosslinkable resin composition is not particularly limited and can be appropriately set within a range that does not impair the effects of the present invention. However, when a brominated flame retardant is contained, it is preferable that the content be within the above-mentioned range, and antimony trioxide may or may not be contained.

[0040] (Composition of heat-resistant silane-crosslinked resin molded body) Since the heat-resistant silane-crosslinked resin molded article is formed by subjecting a silane-crosslinkable resin composition to a silanol condensation reaction after molding, the contents of the above-mentioned components in this molded article are usually the same as those in the silane-crosslinkable resin composition, except that in the heat-resistant silane-crosslinked resin molded article, the content of the silane coupling agent is the content before the silanol condensation reaction, and the content of the base resin is the content before crosslinking.

[0041] [Method for producing heat-resistant silane-crosslinked resin molded body] The method for producing the heat-resistant silane-crosslinked resin molded article of the present invention will be described below. In the method for producing a heat-resistant silane-crosslinked resin molded article of the present invention, the silane-crosslinkable resin composition of the present invention is produced by carrying out the following steps (a) to (c). The method for producing a heat-resistant silane-crosslinked resin molded article and the method for producing a silane-crosslinkable resin composition of the present invention may be collectively referred to as the production method of the present invention.

[0042] The method for producing a heat-resistant silane-crosslinked resin molded article of the present invention comprises the following steps (a) to (e), and the method for producing a silane-crosslinkable resin composition of the present invention comprises the following steps (a) to (c), which make it possible to produce a heat-resistant silane-crosslinked resin molded article exhibiting the above-mentioned properties while suppressing foaming during melt mixing and molding. Step (a): A part of the base resin, boehmite, and a graftable graft compound capable of grafting onto the base resin are mixed together. A silane coupling agent having a rafting reaction site and an organic peroxide are reacted with each other to form a silane coupling agent. The silane masterbatch is melted and mixed at a temperature above the decomposition temperature of the organic peroxide. Preparing the sachet Step (b): The remainder of the base resin and the silanol condensation catalyst are melt-mixed to form a catalyst masterbatch. Preparing the mixture Step (c): Mix the silane masterbatch prepared in step (a) with the catalyst masterbatch prepared in step (b). A step of dry blending with the star batch to obtain a silane-crosslinkable resin composition. Step (d): A step of molding the silane-crosslinkable resin composition obtained in step (c) to obtain a molded article. Step (e): The molded product obtained in step (d) is brought into contact with water to produce a heat-resistant silane-crosslinked resin molded product. The process of obtaining

[0043] The hindered phenol-based antioxidant and the benzimidazole-based antioxidant may be mixed in either step (a) or step (b), but mixing in step (b) is preferred because it allows the grafting reaction in step (a) to proceed efficiently. Both antioxidants, particularly the hindered phenol-based antioxidant, can also be mixed in step (a) as long as they are present in an amount that does not inhibit the grafting reaction (for example, 1 part by mass or less per 100 parts by mass of the base resin).

[0044] In the manufacturing method of the present invention, the amounts of the components used as the base resin are the same as those described above for the composition of the base resin, and the amounts of the boehmite, silane coupling agent, silanol condensation catalyst, hindered phenol antioxidant, benzimidazole antioxidant, inorganic filler other than boehmite, and additives are the same as those contained in the silane-crosslinkable resin composition. The amount of organic peroxide mixed in step (a) is 0.01 to 0.5 parts by mass, preferably 0.1 to 0.2 parts by mass, per 100 parts by mass of the base resin. By keeping the amount of organic peroxide mixed within this range, a heat-resistant silane-crosslinked resin molded product with a smooth surface can be obtained without generating agglomerates (lumps) due to crosslinked gel, etc. In the production method of the present invention, the portion of the base resin mixed in step (a) is not particularly limited and may be a specific resin component or two or more resin components, and is selected appropriately. Examples include ethylene copolymers, polyolefin resins, ethylene rubber, styrene-based elastomers, organic oils, etc. The remainder of the base resin (carrier resin) mixed in step (b) is determined depending on the portion of the base resin mixed in step (a), but preferably contains an ethylene copolymer, and more preferably further contains a styrene-based elastomer and an organic oil. The proportion of the base resin mixed in step (a) is preferably 60 to 95 mass%, more preferably 70 to 85 mass%, of 100 mass% of the base resin mixed in steps (a) and (b).

[0045] <Process (a)> Step (a) is a step of preparing a silane master batch (silane MB) containing a silane cross-linkable resin in which the silane coupling agent is grafted onto the base resin by a grafting reaction between a base resin (particularly an ethylene copolymer) and a silane coupling agent in the presence of boehmite. In this process, the base resin is mixed with boehmite and a silane coupling agent in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide, thereby obtaining a molten mixture of silane MB.

[0046] In step (a), the mixing temperature for melt-mixing (also referred to as melt-kneading) the above-mentioned components is equal to or higher than the decomposition temperature of the organic peroxide, preferably equal to or higher than the decomposition temperature of the organic peroxide + (25 to 110)°C, and more preferably 150 to 230°C. Mixing conditions such as mixing time can be set appropriately. For example, the mixing time can be 1 to 40 minutes. By melt-mixing at a temperature equal to or higher than the decomposition temperature of the organic peroxide, the organic peroxide thermally decomposes to generate radicals, which allows the grafting reaction to proceed.

[0047] The mixing method may be any method commonly used for mixing rubber, plastics, etc. The mixing apparatus may be, for example, a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, or various kneaders, and is preferably an internal mixer such as a Banbury mixer or various kneaders.

[0048] In the present invention, the order of mixing is not limited, and the above components may be mixed in any order. For example, the above components may be melt-mixed all at once. In the production method of the present invention, the step (a) is preferably carried out by the following steps (a-1) and (a-2) in the following mixing order. Step (a-1): A step of mixing boehmite and a silane coupling agent to prepare a mixture Step (a-2): The mixture obtained in step (a-1) and a part of the base resin are mixed with an organic peroxide. The mixture is melted and mixed in the presence of an organic peroxide at a temperature above the decomposition temperature of the organic peroxide. Process

[0049] In step (a-1), by premixing boehmite and a silane coupling agent, a good balance of silane coupling agent weakly bonded or adsorbed to the boehmite and silane coupling agent strongly bonded or adsorbed to the boehmite can be achieved. This makes the silane coupling agent less likely to volatilize during melt mixing in step (a-2), and prevents condensation reactions between unadsorbed silane coupling agents, resulting in the production of molded articles with excellent appearance. Examples of weak bonds with boehmite include interactions due to hydrogen bonds, interactions between ions, partial charges or dipoles, and adsorption. Examples of strong bonds with boehmite include chemical bonds with sites on the boehmite surface that can form chemical bonds.

[0050] The mixing method and conditions for step (a-1) are not particularly limited, but examples include a method and conditions in which a known mixer is used to mix the components by dry or wet mixing, typically at a temperature below the decomposition temperature of the organic peroxide, preferably 10 to 60°C, more preferably around room temperature (20 to 25°C), for several minutes to several hours. Of these, dry mixing at a temperature below the decomposition temperature of the organic peroxide is preferred. Other conditions for dry mixing are determined appropriately.

[0051] In step (a-1), a base resin can also be mixed as long as the temperature is maintained below the decomposition temperature. The organic peroxide may be present during the melt mixing in step (a-2), and may be mixed in step (a-2), but is preferably mixed in step (a-1).

[0052] Next, the mixture obtained in step (a-1) and a portion of the base resin are melt-mixed in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide to prepare a silane MB (step (a-2)). This produces a silane master batch containing a silane crosslinkable resin. The melt-mixing in this step can prevent excessive crosslinking between the base resins while suppressing the volatilization and self-condensation of the silane coupling agent. Furthermore, the melt-mixing can be performed while effectively suppressing foaming of the molten mixture. As a result, a heat-resistant silane-crosslinked resin molded product with a smooth surface, no lumps, and no foaming, and excellent appearance characteristics, can be produced. The melt-mixing method and conditions for this step (a-2) are not particularly limited, and the melt-mixing method and conditions for the above step (a) can be applied.

[0053] In step (a-2), the silane coupling agent may undergo a grafting reaction onto the base resin in at least the following manner: In other words, the silane coupling agent weakly bonded to or adsorbed on the boehmite is released from the boehmite and then grafted onto the base resin. The crosslinked structure formed in step (e) described below from this manner does not incorporate boehmite, but is typically a crosslinked structure formed via a silanol condensate between the silane coupling agents. Alternatively, the silane coupling agent strongly bonded to or adsorbed on the boehmite undergoes a grafting reaction onto the resin while maintaining its bond or adsorption to the boehmite. The crosslinked structure formed in step (e) described below from this manner incorporates boehmite, and is a crosslinked structure formed from the boehmite as the starting point via the silane coupling agent bonded to it.

[0054] In step (a), antioxidants, inorganic fillers other than boehmite, additives, etc. may also be mixed. However, it is preferable that a silanol condensation catalyst is not substantially mixed in step (a). This can suppress the silanol condensation reaction of the silane coupling agent. Here, "substantially not mixed" does not exclude the unavoidable presence of a silanol condensation catalyst, but means that it may be present within a range that suppresses the silanol condensation reaction, for example, within a range of 0.01 parts by mass or less per 100 parts by mass of the base resin.

[0055] The Silane MB prepared in step (a) contains a reaction mixture of a base resin, boehmite, and a silane coupling agent, and contains a silane crosslinkable resin (silane graft polymer) in which the silane coupling agent is grafted to the base resin to an extent that it can be molded in step (b) described below. The silane coupling agent grafted to the base resin includes boehmite and inorganic fillers other than boehmite that are optionally present and bonded to or adsorbed thereto at their silanol condensation reactive sites. Silane MB is preferably in pellet or powder form.

[0056] <Process (b)> In the production method of the present invention, the remainder of the base resin and a silanol condensation catalyst are melt-mixed to prepare a catalyst masterbatch (catalyst MB). The melt-mixing method and conditions in step (b) are not particularly limited, and the melt-mixing method and conditions in step (a) can be applied. For example, the melt-mixing temperature may be equal to or higher than the melting temperature of the base resin, and is preferably 120 to 200°C, more preferably 140 to 180°C. The catalyst MB is preferably in the form of pellets or powder.

[0057] <Process (c)> In the production method of the present invention, the silane masterbatch and the catalyst masterbatch are then dry-blended to prepare a silane-crosslinkable resin composition. The mixing method and conditions are not particularly limited, but from the viewpoint of suppressing the occurrence or progression of the silanol condensation reaction, it is preferable to adopt a method and conditions for dry blending under non-high temperature conditions, such as the method and conditions for dry mixing in step (a-1).

[0058] In this manner, the silane-crosslinkable resin composition of the present invention is produced. This silane crosslinkable resin composition contains a silane crosslinkable resin, boehmite, a silanol condensation catalyst, etc. In this silane crosslinkable resin, the silane coupling agent's reactive site capable of silanol condensation may be bonded to or adsorbed on the boehmite, but is not silanol condensed. Therefore, the silane crosslinkable resin includes a silane crosslinkable resin in which the silane coupling agent bonded to or adsorbed on the boehmite is grafted to a base resin, and a silane crosslinkable resin in which the silane coupling agent not bonded to or adsorbed on the boehmite is grafted to a base resin.

[0059] <Process (d)> In the production method of the present invention, the silane-crosslinkable resin composition is then molded to obtain a molded article. In step (d), the silane-crosslinkable resin composition, which is usually a dry blend, is melt-mixed and molded. The molding method is not particularly limited and may be appropriately selected depending on the desired product shape. Examples of molding methods include extrusion molding using an extruder, extrusion molding using an injection molding machine, and molding using other molding machines. When producing a wiring material, extrusion molding is preferred in terms of productivity and the ability to co-extrude with a conductor. The molding conditions (melt-mixing conditions) are not particularly limited as long as they allow for uniform mixing. For example, the melt-mixing method and conditions of step (a) can be applied. For example, the melt-mixing temperature in this step is set to a temperature higher than the melting point of the base resin, preferably 80 to 250°C, more preferably 100 to 240°C, and even more preferably 120 to 200°C. In this melt-mixing, the melt-mixing method and conditions are set so as to maintain the moldability of the melt mixture of the silane-crosslinkable resin composition. The silane-crosslinkable resin in the melt mixture is an uncrosslinked product in which the silane coupling agent has not undergone silanol condensation. In practice, when melt-mixing in step (d), partial crosslinking is unavoidable, but the resulting melt mixture maintains its moldability. For example, to avoid the occurrence or progression of a silanol condensation reaction, it is preferable that the melt-mixed silane-crosslinkable resin composition is not kept at a high temperature for a long period of time.

[0060] Step (d) can be carried out simultaneously with step (c) or consecutively, for example, by dry-blending the silane MB and catalyst MB in a coating device (extruder), melt-mixing them, and then molding (co-extrusion) them onto the outer surface of a conductor or the like.

[0061] <Process (e)> In the manufacturing method of the present invention, the molded article obtained in step (d) is then contacted with water to produce a heat-resistant silane-crosslinked resin molded article. Because the molded article obtained in step (d) is an uncrosslinked article, this step initiates and advances (accelerates) a silanol condensation reaction at the silanol condensable reactive sites of the silane coupling agent grafted to the base resin, resulting in a finally crosslinked molded article. The uncrosslinked molded article can be brought into contact with water by a conventional method. The silanol condensation reaction proceeds simply by leaving the molded article at room temperature, for example, at a temperature of about 20 to 25°C. However, it is preferable to actively bring the molded article into contact with water to promote the silanol condensation reaction (crosslinking reaction). Examples of the contact method include methods (conditions) commonly used in silane crosslinking methods, such as immersion in warm water, placement in a moist heat bath, and exposure to high-temperature steam.

[0062] In this manner, the heat-resistant silane-crosslinked resin molded article of the present invention is produced. This heat-resistant silane-crosslinked resin molded article contains a crosslinked resin formed by condensing a base resin via a siloxane bond. The heat-resistant silane-crosslinked resin molded article also contains boehmite, which may be bonded to a silane coupling agent of the crosslinked resin. Therefore, the crosslinked resin is considered to include a crosslinked resin formed by bonding (crosslinking) multiple base resins to or adsorbing them on the boehmite via the silane coupling agent, and a crosslinked resin formed by crosslinking via the silane coupling agent (siloxane bond) (without via boehmite) due to hydrolysis of the hydrolyzable groups of the silane coupling agent grafted to the base resin and undergoing a silanol condensation reaction with each other.

[0063] In the method for producing a heat-resistant silane-crosslinked resin molded article of the present invention, the kneaded product contains the above-mentioned boehmite and antioxidant in the melt-mixing step, thereby reducing the viscosity of the kneaded product (improving kneadability (fluidity)) and suppressing the volatilization and self-condensation reaction of the silane coupling agent, as well as foaming during melt-mixing. Therefore, even though the method for producing a heat-resistant silane-crosslinked resin molded article of the present invention is a simple silane crosslinking method that has problems with appearance characteristics, it is possible to produce a heat-resistant silane-crosslinked resin molded article that exhibits high heat resistance of, for example, 150°C or higher and has a smooth surface free of bumps and foams and excellent appearance characteristics, using a lightweight and inexpensive polyolefin resin. The heat-resistant silane-crosslinked resin molded product of the present invention not only exhibits high heat resistance, as specified by JASO, with an estimated 40,000-hour lifespan temperature of 125°C or higher, but also exhibits the even higher heat resistance that has been required in recent years, with an estimated 10,000-hour lifespan temperature of 150°C or higher.

[0064] [Wiring material] The wiring material of the present invention is a wiring material having a coating layer around the conductor, and this coating layer is formed from the heat-resistant silane-crosslinked resin molded product of the present invention by molding and crosslinking the silane-crosslinkable resin composition of the present invention into a layer. Therefore, the wiring material of the present invention exhibits high heat resistance, for example, at 150°C or higher, and has excellent appearance characteristics. It is also inexpensive and lightweight. The wiring material of the present invention is the same as conventional wiring materials used in various electrical and electronic equipment fields and industrial fields, except that the coating layer is formed from the heat-resistant silane-crosslinked resin molded product of the present invention. The coating layer formed from the heat-resistant silane-crosslinked resin molded product of the present invention is provided on the outer surface of the conductor directly or via another layer. The presence or absence of other layers and the materials thereof are appropriately determined depending on the type, application, required characteristics, etc. of the wiring material. Conventional conductors can be used, such as copper or aluminum single wires or stranded wires (wires in which tensile strength fibers are longitudinally attached or twisted). In addition to bare wires, tin-plated wires and wires with enamel-coated insulating layers can also be used. The thickness of the coating layer formed from the heat-resistant silane-crosslinked resin molded product of the present invention is not particularly limited, but is usually about 0.15 to 5 mm. The wiring material of the present invention can be produced by disposing the silane-crosslinkable resin composition of the present invention in a layer around the conductor, followed by a crosslinking reaction (silanol condensation reaction). For example, in the above-described method for producing a heat-resistant silane-crosslinked resin molded article of the present invention, the molding step (d) can be replaced by a step of co-extrusion molding the silane-crosslinkable resin composition around the conductor using a coating device (extruder). Specific examples of co-extrusion molding are as described above. [Example]

[0065] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0066] The compounds used in the examples and comparative examples are shown below. <Base resin> (1) Evolue SP0540: Product name, manufactured by Prime Polymer, linear metallocene polyethylene (LLDPE) (2) VF120T: Product name, manufactured by Ube Maruzen Polyethylene Co., Ltd., EVA, VA content 20% by mass (3) Evaflex EV170: Trade name, manufactured by Mitsui Dow Polychemicals, EVA, VA content 33% by mass (4) Rexpearl A1150: Trade name, manufactured by Mitsubishi Chemical Corporation, EEA and EA content 15% by mass (5) EPT3092PM: Product name, manufactured by Mitsui Chemicals, Inc., EPDM (6) PB222A: Product name, manufactured by SunAllomer, Random PP (7) Tuftec N504: Product name, manufactured by Asahi Kasei Corporation, SEBS (8) Diana Process Oil PW-90: Trade name, manufactured by Idemitsu Kosan Co., Ltd., organic oil (paraffin oil)

[0067] <Boehmite> Boehmite FKB104: Product name, manufactured by Konoshima Chemical Co., Ltd., boehmite, residual aluminum hydroxide content of 10% by mass as measured by the following content measurement method <Inorganic fillers other than boehmite> (1) BF 013: Trade name, manufactured by Nippon Light Metal Co., Ltd., aluminum hydroxide (2) Kisuma 5: Trade name, manufactured by Kyowa Chemical Industry Co., Ltd., magnesium hydroxide (3) Boehmite composite aluminum hydroxide (synthesized from BF 013 by the following wet hydrothermal treatment)

[0068] (Synthesis of boehmite composite aluminum hydroxide) 4 kg of aluminum hydroxide powder (BF 013) was weighed and placed in a 30 L polyethylene container, and 16 L of pure water was added and stirred to prepare an aluminum hydroxide slurry. This slurry was poured into an autoclave with a liquid-contacting portion made of Hastelloy (registered trademark) C-276 and subjected to hydrothermal treatment at 170°C for approximately 6 hours while stirring, thereby synthesizing boehmite composite aluminum hydroxide. The boehmite slurry after hydrothermal treatment was cooled to room temperature and then dried and pulverized to obtain a boehmite composite aluminum hydroxide powder. The aluminum hydroxide content in the obtained boehmite composite aluminum hydroxide was 47 mass%.

[0069] (Method for measuring aluminum hydroxide content) The content (remaining amount) of aluminum hydroxide in boehmite or boehmite composite aluminum hydroxide was quantified by the following method. First, the ignition loss of the target sample was measured in accordance with JIS R 9301-3-2. However, the ignition loss was measured between 105 and 900°C. Note that "ignition loss" refers to the amount of mass loss of the target sample measured when heated, and "ignition loss between 105 and 900°C" means "the mass loss when heated at 900°C minus the mass loss when heated at 105°C." Thereafter, the content of aluminum hydroxide was calculated using the following formula. R = (I1 - I2) / (I3 - I2) × 100 The symbols in the above formula have the following meanings: R: Aluminum hydroxide content (%) I1: Ignition loss (%) of the target sample obtained by the above method I2: Theoretical value of ignition loss of boehmite (%) = 15.0 I3: Theoretical value of ignition loss of aluminum hydroxide (%) = 34.6

[0070] <Antioxidants> (1) Irganox 1076: Trade name, manufactured by BASF, hindered phenolic antioxidant (2) Irganox 1010: Trade name, manufactured by BASF, hindered phenolic antioxidant (3) Adekastab CDA-10: Trade name, manufactured by ADEKA Corporation, hindered phenol-based antioxidant (4) Nocrac MBZ: Trade name, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., benzimidazole-based antioxidant

[0071] <Silane coupling agent> KBM-1003: Product name, manufactured by Shin-Etsu Chemical Co., Ltd., vinyltrimethoxysilane <Silanol condensation catalyst> ADK STAB OT-1: Product name, manufactured by ADEKA Corporation, dioctyltin dilaurate <Organic peroxide> "Perhexa 25B" (trade name, manufactured by NOF Corporation, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, decomposition temperature 154°C) <Lubricant> X-21-3043: Product name, manufactured by Shin-Etsu Chemical Co., Ltd., silicone gum

[0072] Examples 1 to 13 (Except for Example 8. The same applies below.) Reference Example 8 and Comparative Examples 1 to 12) Examples 1 to 13 , Reference example 8 Comparative Examples 1 to 12 were carried out using the components shown in Tables 1 and 2, respectively. In Tables 1 and 2, the numerical values ​​relating to the blending amount (content) of each example are in parts by mass unless otherwise specified. Furthermore, blank spaces for each component mean that the blending amount of the corresponding component is 0 parts by mass. In each example and comparative example, a portion of the base resin (specifically, the "carrier resin" shown in the "Catalyst MB" column in Tables 1 and 2) was used as the carrier resin for catalyst MB in the mass ratio shown in the same column.

[0073] First, boehmite or an inorganic filler other than boehmite, a silane coupling agent, and an organic peroxide were added to a rotary blade mixer (Mazera PM: product name, manufactured by Mazera Co., Ltd.) in the mass ratios shown in the "Silane MB" column of Tables 1 and 2, and stirred (premixed) at room temperature (25°C) at a rotation speed of 10 rpm for 1 minute (step (a-1)). Thus, a powder mixture was obtained. Next, the powder mixture and the base resin, antioxidant, and lubricant shown in the "Silane MB" column of Tables 1 and 2 were added to a kneader (75 L capacity) preheated to 150°C in the weight ratios shown in the same column. The mixture was mixed at 40 rpm for 5 minutes, followed by a final melt-mixing step at 30 rpm for 3 minutes. After confirming that the resin temperature (mixture temperature) had reached 180-200°C, above the decomposition temperature of the organic peroxide, the molten mixture was pelletized using a feeder-ruder and pelletizer to obtain Silane MB (step (a-2), step (a-1), and step (a)).

[0074] Separately, the carrier resin, antioxidant, and silanol condensation catalyst were sequentially charged into a kneader (75 L capacity) preheated to 130°C in the mass ratios shown in the "Catalyst MB" column of Tables 1 and 2, and mixed at 30 rpm for 5 minutes, followed by finish kneading (melt mixing) at 25 rpm for 3 minutes. After the resin temperature (mixture temperature) reached approximately 160°C and it was confirmed that the carrier resin was fully melted, the mixture was pelletized using a feeder-ruder and pelletizer to obtain Catalyst MB (step (b)).

[0075] Next, the pellets of Silane MB and Catalyst MB were dry-blended in a tumbler mixer at room temperature (25°C) for 2 minutes immediately before extrusion to obtain a silane-crosslinkable resin composition (step (c)). The mixing ratio of Silane MB to Catalyst MB was the mass ratio shown in the "Silane MB" and "Catalyst MB" columns of Tables 1 and 2.

[0076] The obtained silane-crosslinkable resin composition was then introduced into a 40 mm (screw diameter) extruder (compression section screw temperature 160°C, head temperature 180°C) with an L / D (ratio of effective screw length L to diameter D) of 24, and coated onto the outer surface of a 1 / 0.8A conductor to form a coating with a thickness of 1 mm, thereby obtaining an uncrosslinked electric wire with an outer diameter of 2.8 mm (step (d)).

[0077] The obtained uncrosslinked electric wire was left standing in an atmosphere at a temperature of 60° C. and a humidity of 95% RH for 24 hours to bring the silane crosslinkable resin composition into contact with water (step (e)). In this manner, insulated crosslinked electric wires each having a coating layer formed from a heat-resistant silane crosslinked resin molded article were produced.

[0078] The insulated crosslinked electric wires thus produced were evaluated as follows, and the results are shown in Tables 1 and 2.

[0079] <Appearance characteristics> The appearance characteristics of the insulated cross-linked wire were tested. The evaluation items were surface smoothness, the presence or absence of lumps, and the presence or absence of bubbles inside the coating layer. (Surface smoothness) For 5m-long wire specimens cut from each insulated cross-linked wire, the surface smoothness of the entire surface of the coating layer (presence or absence of irregularities) was evaluated visually and by touch. As a result, if the surface of the coating layer was smooth to the touch, it was given an "A", if the surface of the coating layer felt slightly rough to the touch but was good to the visual eye, it was given a "B", and if roughness was confirmed visually, it was given a "C". "A" and "B" were considered to be acceptable products. (Whether or not there is something) For 5m-long wire specimens cut from each insulated cross-linked wire, the entire surface of the coating layer was visually inspected and tactilely evaluated for the presence or absence of lumps. As a result, if no lumps (protruding agglomerates) were found on the entire surface by visual inspection or tactile inspection, the grade was "A." If no lumps were found by visual inspection but by tactile inspection, the grade was "B." If lumps were found by visual inspection, the grade was "C." "A" and "B" were deemed to be acceptable products. (Presence or absence of foaming) A 1m-long piece of the coating layer of each insulated cross-linked electric wire was sliced ​​into two (semi-cylindrical) pieces along a plane that included the axis of the insulated cross-linked electric wire. The entire cross-section of one of the cut coating layers was observed under a binocular stereo microscope at 10x magnification, and the presence or absence of bubbles (voids) within the cross-section was evaluated. In this evaluation, bubbles were deemed to be present within the cross-section if at least one void with a longest dimension of 0.05mm or greater could be identified (existed) within the entire cross-section as measured by shape measurement, or if five or more voids, regardless of size, could be identified (existed). As a result, cases where no bubbles were identified within the cross-section were given an "A," and cases where bubbles were identified within the cross-section were given a "C." An "A" was deemed to be a passing grade for the product.

[0080] <Heat resistance> The heat resistance of each manufactured insulated cross-linked electric wire was evaluated based on the estimated 10,000-hour and 40,000-hour life temperatures. Specifically, each manufactured insulated cross-linked electric wire was heated to 170°C, 180°C, or 200°C, and the tensile strength and elongation at break were measured after heating. The tensile strength and elongation at break were measured in accordance with JIS C 3005 (2014) (4.16 Tensile strength of insulators and sheaths) by pulling the coating layer of a tubular piece taken from each manufactured insulated cross-linked electric wire at a gauge length of 20 mm and a pulling speed of 500 mm / min. At each temperature, the heating time at which the tensile strength reached 3.92 MPa and the elongation at break reached 100% or 50% were determined. Arrhenius plots were created for the tensile strength and elongation at break from the heating times and temperatures. From these plots (by extrapolation), the estimated 10,000-hour and 40,000-hour life temperatures were determined. In the present invention, "10,000-hour life" means that the elongation at break of an insulated cross-linked electric wire reaches 100% after being heated at a specific temperature for 10,000 hours, and "40,000-hour life" means that the tensile strength of an insulated cross-linked electric wire reaches 3.92 MPa or the elongation at break reaches 50% after being heated at a specific temperature for 40,000 hours. Since the present invention achieves higher heat resistance than conventional ones, a 10,000-hour estimated life temperature of 150°C or higher was deemed to pass, and a 10,000-hour estimated life temperature of less than 150°C was deemed to fail. Note that the 40,000-hour estimated life temperature is a relatively high temperature used to evaluate long-term heat resistance, and was determined for reference purposes in the present invention. Therefore, no pass or fail criteria were established. In Tables 1 and 2, the "10,000-hour estimated life temperature" and "40,000-hour estimated life temperature" are expressed as "10,000-hour heat resistance temperature" and "40,000-hour heat resistance temperature," respectively.

[0081] <Crosslinkability evaluation (heat deformation test)> Each of the produced insulated crosslinked electric wires was evaluated by a heat deformation test to determine whether the coating layer (heat-resistant silane crosslinked resin molded article) was sufficiently crosslinked. This heat deformation test was conducted in accordance with JASO D 625-2 (2020) (4.4 Heat Deformation Test). Specifically, a loaded insulated cross-linked electric wire was placed in a thermostatic chamber heated to 150°C for four hours, and then quickly cooled within 10 seconds by placing it in cold water. The insulated cross-linked electric wire was then immersed in salt water for 10 minutes, after which a voltage of 1 kV was applied for one minute. Test pieces that did not break down the coating layer by the end of the voltage application were deemed to have passed, and those that broke down the cross-linking were deemed to have failed.

[0082] [Table 1]

[0083] [Table 2]

[0084] As is clear from the results in Tables 1 and 2, Comparative Examples 1, 5, 7, and 8, which did not contain an ethylene copolymer, boehmite, a benzimidazole-based antioxidant, or a hindered phenol-based antioxidant, had an estimated 10,000-hour lifespan temperature of less than 150°C, and were unable to achieve high heat resistance. Furthermore, Comparative Examples 4 and 6, which contain excessive aluminum hydroxide, are unable to suppress foaming during melt mixing, resulting in poor appearance characteristics. Comparative Example 2, which contains too little boehmite, and Comparative Example 3, which contains too much boehmite, are unable to achieve high heat resistance, and Comparative Example 2 also exhibits poor surface smoothness. Note that Comparative Example 3 contains 10 parts by mass of aluminum hydroxide, but also 90 parts by mass of boehmite, which is thought to have relatively reduced the impact of foaming from aluminum hydroxide. Comparative Examples 9 and 11, which contain too little organic peroxide or silanol condensation catalyst, are unable to achieve high heat resistance, fail the heat distortion test, and are unable to form sufficient crosslinks. On the other hand, Comparative Example 10, which contains too much silane coupling agent, is unable to suppress foaming and has poor appearance characteristics. Furthermore, Comparative Example 12, which contains too much silanol condensation catalyst, is unable to suppress the generation of lumps, is poor in appearance characteristics, and is unable to achieve high heat resistance.

[0085] In contrast, Examples 1 to 13, which contain ethylene copolymer, boehmite, a hindered phenol-based antioxidant, or a benzimidazole-based antioxidant in specific proportions but do not contain aluminum hydroxide, all exhibit excellent appearance characteristics and high heat resistance, exhibiting an estimated 10,000-hour lifespan temperature of 150° C. or higher. Furthermore, they also passed the heat distortion test (sufficient crosslinking was formed), and satisfy the properties required for, for example, the coating layer of an insulated crosslinked electric wire.

Claims

1. A method for producing a heat-resistant silane-crosslinked resin molded product, comprising silane-crosslinking a silane-crosslinkable resin composition containing 9 to 50 parts by mass of boehmite, 1 to 15 parts by mass of a silane coupling agent graft-bonded to the base resin, 0.01 to 0.5 parts by mass of a silanol condensation catalyst, a hindered phenol-based antioxidant, and a benzimidazole-based antioxidant, with respect to 100 parts by mass of a base resin containing at least one ethylene copolymer selected from ethylene-vinyl acetate copolymers and ethylene-(meth)acrylic acid ester copolymers (provided that, if the base resin contains an organic oil, the content of the organic oil is included), and the silane-crosslinkable resin composition contains 10 parts by mass or less of aluminum hydroxide, A method for producing a heat-resistant silane-crosslinked resin molded product, comprising the following steps (a), (b), (c), (d), and (e), wherein the hindered phenol-based antioxidant or the benzimidazole-based antioxidant is mixed in at least one of steps (a) and (b): Step (a): A part of the base resin, the boehmite, and a grafted polymer to the base resin a silane coupling agent having a reactive grafting reaction site and the base 0.01 to 0.5 parts by mass of an organic peroxide relative to 100% by mass of the resin, The organic peroxide is melt-mixed at a temperature equal to or higher than the decomposition temperature thereof to form a silane mass. Preparing the tar batch Step (b): The remainder of the base resin and the silanol condensation catalyst are melt-mixed to form a catalyst mixture. Preparing the star batch Step (c): dry-blending the silane masterbatch and the catalyst masterbatch and obtaining a silane-crosslinkable resin composition. Step (d): A step of molding the silane-crosslinkable resin composition to obtain a molded product. Step (e): A step of contacting the molded product with water to obtain a heat-resistant silane-crosslinked resin molded product.

2. 2. The method according to claim 1, wherein the hindered phenol-based antioxidant is contained in an amount of 0.5 to 5 parts by mass per 100 parts by mass of the base resin.

3. 3. The method according to claim 1, wherein the benzimidazole antioxidant is contained in an amount of 4 to 12 parts by mass per 100 parts by mass of the base resin.

4. The method according to any one of claims 1 to 3, wherein the ethylene copolymer is contained in an amount of 10 to 70% by mass relative to 100% by mass of the base resin.

5. The method according to any one of claims 1 to 4, wherein each ethylene copolymer contained in the base resin contains vinyl acetate or a (meth)acrylic acid ester in an amount of 10 to 30% by mass based on the ethylene copolymer.

6. A manufacturing method described in any one of claims 1 to 5, wherein the base resin contains a styrene-based elastomer and an organic oil.

7. A method for producing a silane-crosslinkable resin composition containing 9 to 50 parts by mass of boehmite, 1 to 15 parts by mass of a silane coupling agent graft-bonded to the base resin, 0.01 to 0.5 parts by mass of a silanol condensation catalyst, a hindered phenol-based antioxidant, and a benzimidazole-based antioxidant, relative to 100 parts by mass of a base resin containing at least one ethylene copolymer selected from ethylene-vinyl acetate copolymer and ethylene-(meth)acrylic acid ester copolymer (however, if the base resin contains an organic oil, the content of the organic oil is included), and wherein the content of aluminum hydroxide is 10 parts by mass or less, A method for producing a silane-crosslinkable resin composition, comprising the following steps (a), (b), and (c), wherein the hindered phenol-based antioxidant or the benzimidazole-based antioxidant is mixed in at least one of the steps (a) and (b): Step (a): A part of the base resin, the boehmite, and a grafted polymer to the base resin a silane coupling agent having a reactive grafting reaction site and the base 0.01 to 0.5 parts by mass of an organic peroxide relative to 100% by mass of the resin, The organic peroxide is melt-mixed at a temperature equal to or higher than the decomposition temperature thereof to form a silane mass. Preparing the tar batch Step (b): The remainder of the base resin and the silanol condensation catalyst are melt-mixed to form a catalyst mixture. Preparing the star batch Step (c): dry-blending the silane masterbatch and the catalyst masterbatch and obtaining a silane-crosslinkable resin composition.

8. A heat-resistant silane-crosslinked resin molded body produced by the manufacturing method described in any one of claims 1 to 6.

9. A silane-crosslinkable resin composition produced by the manufacturing method described in claim 7.

10. A wiring material having a coating layer on the outer periphery of a conductor, A wiring material, wherein the coating layer is a layer of the heat-resistant silane-crosslinked resin molded product according to claim 8.

11. The wiring material described in claim 10, which is a heat-resistant wire or cable.

Images