Polyolefin resin composition and wiring material

Abstract

Provided are: a polyolefin resin composition comprising a base resin containing a polyolefin resin, a halogen-based flame retardant including a bromine-based flame retardant having a phthalimide structure, and a flame retardant containing antimony trioxide and melamine cyanurate, wherein, with respect to 100 parts by mass of the base resin, the content of the bromine-based flame retardant having a phthalimide structure is at least 25 parts by mass, the content of the antimony trioxide is at least 10 parts by mass, the content of the melamine cyanurate is 5-30 parts by mass, and the total content of the flame retardants is at most 95 parts by mass; and a wiring material having, on an outer peripheral surface of a conductor, a coating layer formed of said polyolefin resin composition.

Description

Polyolefin resin composition and wiring material

[0001] This invention relates to a polyolefin resin composition and a wiring material using the same.

[0002] Electrical and electronic equipment and vehicles (including railway vehicles, industrial vehicles, automobiles, etc.) typically have wiring materials (insulated wires or cables, (electrical) cords, optical fiber cores, optical fiber cords, optical cables, etc.) installed to transport power or transmit information. In addition to flame retardancy, such wiring materials are required to have various properties depending on the application, such as mechanical properties (e.g., tensile elongation and tensile strength), heat resistance, and appearance properties (surface smoothness). For example, Patent Document 1 proposes the following wire coating material composition, which is described as being able to provide a wire with good heat resistance, light weight, flexibility, and ease of handling. "A wire coating material composition characterized by containing the following (A) to (D). (A) Density of 0.860 to 0.950 g / cm³ ３ A silane-grafted polyolefin in which a silane coupling agent is grafted onto a polyolefin. (B) Density of 0.860–0.950 g / cm³ ３ (C) Unmodified polyolefin. (D) Phosphate compound and / or melamine compound. (E) Crosslinking catalyst batch in which the crosslinking catalyst is dispersed in a binder resin.

[0003] Furthermore, Patent Document 2 describes a material obtained by mixing "a polyolefin (a), a silane compound, a free radical generator, and a flame retardant (B) containing at least three of the following: an antimony compound, a brominated flame retardant, a melamine-based flame retardant, magnesium hydroxide, and aluminum hydroxide, and then dispersing the flame retardant (B) in the polyolefin (a) while graft polymerizing the silane compound onto the polyolefin (a) in the presence of the free radical generator to form a silane-grafted polyolefin (A)" and "a silane batch containing a silane-grafted polymer in which a silane compound has been graft polymerized onto a polymer." Electric wires and cables with a coating layer formed from this material are said to have less aggregation of the flame retardant and excellent flame retardancy.

[0004] Japanese Patent Publication No. 2016-103414 Japanese Patent Publication No. 2017-186416

[0005] Flame retardancy is an important characteristic for the safety and reliability of wiring materials, and the required level of flame retardancy is increasing as electrical and electronic equipment becomes more complex and sophisticated. For example, a high level of flame retardancy, such as passing the vertical combustion test (VW-1) specified in UL 1581, is sometimes required. Furthermore, due to the recent increase in performance and / or the expansion of applications of electrical and electronic equipment, the environments in which wiring materials are used are also wide-ranging. For example, wiring materials may be used in low-temperature environments such as cold regions, refrigeration facilities, and freezing facilities, for example, at temperatures of around -60°C. Wiring materials used in such low-temperature environments require, from the standpoint of safety and reliability, flexibility that allows the covering layer to be bent without damaging it during installation work in low-temperature environments, and characteristics that suppress deterioration and damage to the covering layer over time in the installed state (sometimes referred to as "low-temperature flexibility" in this invention). In wiring materials, one effective way to achieve a high degree of flame retardancy is to incorporate a large amount of flame retardant. However, incorporating a large amount of flame retardant impairs not only insulation but also low-temperature flexibility. Thus, high flame retardancy, insulation, and low-temperature flexibility are mutually exclusive properties, and it is generally difficult to achieve a balance between them. However, the wire covering compositions and materials described in Patent Documents 1 and 2 not only fail to achieve the aforementioned high degree of flame retardancy, but also fail to consider the possibility of achieving a balance between insulation and low-temperature flexibility.

[0006] The present invention aims to provide a polyolefin resin composition that exhibits high flame retardancy while also exhibiting excellent low-temperature flexibility and high insulation properties. Furthermore, the present invention aims to provide a wiring material comprising a coating layer formed from the above polyolefin resin composition, exhibiting high flame retardancy, excellent low-temperature flexibility, and high insulation properties.

[0007] The inventors of this invention have diligently studied flame retardants to be included in resin compositions that form the coating layer of wiring materials. They discovered that, among various flame retardants (including those referred to as flame retardant aids), the combined use of halogen-based flame retardants and melamine cyanurate has the potential to simultaneously improve flame retardancy, insulation, and low-temperature flexibility. Based on this finding, further investigations revealed that by selecting at least a bromine-based flame retardant having a phthalimide structure from among halogen-based flame retardants and using it in combination with melamine cyanurate and antimony trioxide in specific proportions (contents), it is possible to achieve a high level of flame retardancy that can pass the vertical combustion test (VW-1). Furthermore, they found that while maintaining such a high level of flame retardancy, it is possible to reduce the total content of the flame retardant, thereby achieving excellent low-temperature flexibility and high insulation. Finally, they found that by using a resin composition containing these flame retardants in specific proportions to form the coating layer of wiring materials, the wiring material can be given a high level of flame retardancy, excellent low-temperature flexibility, and high insulation. Based on this finding, the inventors conducted further research and arrived at the present invention.

[0008] In other words, the object of the present invention has been achieved by the following means: <1> A polyolefin resin composition comprising a base resin containing a polyolefin resin, a halogen-based flame retardant containing a brominated flame retardant having a phthalimide structure, antimony trioxide, and melamine cyanurate, wherein, per 100 parts by mass of the base resin, the content of the brominated flame retardant having a phthalimide structure is 25 parts by mass or more, the content of the antimony trioxide is 10 parts by mass or more, the content of the melamine cyanurate is 5 to 30 parts by mass, and the total content of the flame retardant is 95 parts by mass or less. <2> The polyolefin resin composition according to <1>, wherein the ratio of the content of the halogen-based flame retardant to the content of the antimony trioxide [content of halogen-based flame retardant: content of antimony trioxide] is in the range of 1:1 to 5:1. <3> The polyolefin resin composition according to <1> or <2>, which is a crosslinked product. <4> The polyolefin resin composition according to <3>, wherein the crosslinked material is a crosslinked material formed by irradiation with an electron beam. <5> A wiring material having a coating layer on the outer surface of a conductor, wherein the coating layer is formed of the polyolefin resin composition according to any one of <1> to <4>.

[0009] The present invention can provide a polyolefin resin composition that exhibits high flame retardancy while also possessing excellent low-temperature flexibility and high insulation properties. Furthermore, the present invention can provide a wiring material comprising a coating layer formed from the above polyolefin resin composition, exhibiting high flame retardancy, excellent low-temperature flexibility, and high insulation properties. The above and other features and advantages of the present invention will become clearer from the following description.

[0010] In the present invention, when describing the content, physical properties, etc. of components by indicating numerical ranges, if the upper and lower limits of the numerical range are described separately, either upper or lower limit can be appropriately combined to form a specific numerical range. On the other hand, when multiple numerical ranges expressed using "~" are set and described, the upper and lower limits forming the numerical range are not limited to the specific combination of upper and lower limits described before and after "~" as a specific numerical range, but can be a numerical range formed by appropriately combining the upper and lower limits of each numerical range. In the present invention, a numerical range expressed using "~" means a range that includes the numbers described before and after "~" as the lower and upper limits. Also, in the present invention, "(meth)acrylic" represents either acrylic or methacrylic, or both. For example, "(meth)acrylate" represents either alkyl acrylate or alkyl methacrylate, or both.

[0011] [Polyolefin Resin Composition] The polyolefin resin composition of the present invention (hereinafter sometimes simply referred to as "the resin composition of the present invention") contains a base resin containing a polyolefin resin and a halogen-based flame retardant containing a brominated flame retardant having a phthalimide structure as an essential component, antimony trioxide, and melamine cyanurate. Furthermore, the content of the flame retardants is limited to a specific range. Specifically, per 100 parts by mass of the base resin, the content of the brominated flame retardant having a phthalimide structure is 25 parts by mass or more, the content of antimony trioxide is 10 parts by mass or more, the content of melamine cyanurate is 5 to 30 parts by mass, and the total content of the above flame retardants is 95 parts by mass or less.

[0012] The resin composition of the present invention having the above-described composition exhibits excellent low-temperature flexibility and high insulation properties while also exhibiting high flame retardancy, regardless of the presence or type of crosslinking. Therefore, for example, by using the resin composition of the present invention as a material for forming a coating layer, it is possible to realize (manufacture) a coating layer and wiring material that exhibit high flame retardancy, excellent low-temperature flexibility, and high insulation properties. Thus, the resin composition of the present invention is suitable as a material for forming a coating layer of wiring material, for example, as a material for forming insulated electric wires for automobiles, and is particularly suitable as a material for forming wiring materials used in low-temperature environments, such as insulated electric wires for automobiles designed for cold climates, and electric wires for robots used in freezers, etc., where the above-described excellent properties can be utilized.

[0013] The resin composition of the present invention may be either a non-crosslinked polyolefin resin composition (also referred to as a "non-crosslinked polyolefin resin composition") or a crosslinked polyolefin resin composition (also referred to as a "crosslinked polyolefin resin composition"), and the necessity of crosslinking is appropriately selected according to the application and required characteristics. When used as a material for forming the coating layer of wiring materials, a crosslinked polyolefin resin composition is preferable because it exhibits high heat resistance in addition to high flame retardancy, excellent low-temperature flexibility, and high insulation properties. Of the resin compositions of the present invention, those intended for crosslinking are referred to as "crosslinkable polyolefin resin compositions" and are distinguished from the above-mentioned non-crosslinked polyolefin resin compositions that are not intended for crosslinking.

[0014] In the present invention, the crosslinkable polyolefin resin composition and the non-crosslinkable polyolefin resin composition are resin compositions in which a crosslinking reaction has not been actively carried out, and the base resin is usually not crosslinked, but a portion of the base resin may be crosslinked inevitably or to the extent that it does not impair the effects of the present invention. The crosslinkable polyolefin resin composition is a resin composition in which a crosslinking reaction has been actively carried out, and the base resin is usually crosslinked, but a portion of the base resin may not be crosslinked depending on the crosslinking conditions or the content of the crosslinking catalyst or crosslinking agent. In the present invention, unless otherwise specified, the term "polyolefin resin composition" is used as a general term that includes non-crosslinkable polyolefin resin compositions, crosslinkable polyolefin resin compositions and crosslinkable polyolefin resin compositions.

[0015] A crosslinked polyolefin resin composition (crosslinked product) is a crosslinked product in which a base resin has been crosslinked, and is prepared by performing a crosslinking reaction treatment on a crosslinkable polyolefin resin composition. The crosslinking reaction (crosslinking method) is not particularly limited, and known resin crosslinking methods, such as crosslinking reactions for polyolefins, can be applied. Specifically, electron beam crosslinking, organic peroxide crosslinking, and silane crosslinking methods can be used. Among these, the silane crosslinking method is preferred from the viewpoint of enabling crosslinking reaction treatment with high productivity without requiring special equipment, and the electron beam crosslinking method is preferred from the viewpoint of being able to further improve heat resistance, in particular the property of suppressing foaming and melting of the coating layer in secondary processing such as soldering (hereinafter sometimes referred to as "solder resistance") to a higher level while maintaining high flame retardancy, excellent low-temperature flexibility, and high insulation properties. In the present invention, electron beam crosslinking refers to a method of crosslinking a resin, etc., by irradiating a crosslinkable polyolefin resin composition with an electron beam. On the other hand, the organic peroxide crosslinking method is a type of chemical crosslinking method in which a crosslinkable polyolefin resin composition containing an organic peroxide as a crosslinking catalyst is heated to a temperature above the decomposition temperature of the organic peroxide, and the radicals generated from the organic peroxide directly cause a crosslinking reaction between the resins. Furthermore, the silane crosslinking method, which is a different chemical crosslinking method from the organic peroxide crosslinking method, is a method in which a silane graft resin, preferably a crosslinkable polyolefin resin composition containing a silane coupling agent that has undergone a grafting reaction with a silane coupling agent as a crosslinking agent, is brought into contact with water, causing a silane coupling agent to undergo a silanol condensation reaction and crosslink the resin via the silane coupling agent.In the present invention, a crosslinkable polyolefin resin composition suitably applicable to the electron beam crosslinking method, the organic peroxide crosslinking method, or the silane crosslinking method may be referred to as an electron beam crosslinkable polyolefin resin composition, a peroxide crosslinkable polyolefin resin composition, or a silane crosslinkable polyolefin resin composition, respectively.

[0016] Crosslinked polyolefin resin compositions have a crosslinked structure in which at least the base resin (or the resin constituting the (co)polymer, etc.) is crosslinked directly or via a crosslinking agent, etc., and exhibit excellent heat resistance while maintaining high flame retardancy, excellent low-temperature flexibility, and high insulation properties. Electron beam crosslinked materials, in particular, also exhibit even higher solder resistance. The crosslinked structure varies depending on the type of crosslinking reaction (crosslinking method) and cannot be clearly and generally defined. For example, a crosslinked polyolefin resin composition obtained by irradiating an electron beam crosslinkable polyolefin resin composition with an electron beam (also called "electron beam crosslinked polyolefin resin composition" or "electron beam crosslinked material") has a crosslinked structure in which the base resin (or the resin constituting it, etc.) is directly crosslinked. A crosslinked polyolefin resin composition obtained by crosslinking a peroxide crosslinkable polyolefin resin composition (also called "peroxide crosslinked polyolefin resin composition" or "peroxide crosslinked material") has a crosslinked structure in which the base resin (or the resin constituting it, etc.) is directly crosslinked, preferably via a crosslinking agent and / or crosslinking aid, etc. A crosslinked polyolefin resin composition obtained by crosslinking a silane-crosslinkable polyolefin resin composition (also referred to as a "silane-crosslinked polyolefin resin composition" or "silane-crosslinked product") has a crosslinked structure via a silane coupling agent or its silanol condensate in at least the base resin (or the resins constituting it). Components such as flame retardants and inorganic fillers may be incorporated into a part of this crosslinked structure.

[0017] The resin composition of the present invention preferably further contains, in addition to the above components, components essential for or suitable for the crosslinking method described later, depending on whether or not crosslinking is performed and the crosslinking method applied.

[0018] The resin composition of the present invention may be in a formless (unmolded) state, such as strands or pellets, or it may be in a molded state (molded article). When the resin composition of the present invention is made into a molded article, the resin composition of the present invention can be molded into an appropriate shape and dimensions depending on the application, etc. The molding method is not particularly limited, and various molding methods that can be normally applied to resin compositions, etc., can be cited, and specifically, the molding methods described below can be cited.

[0019] The content of each component in the resin composition of the present invention will be described later. However, the content of the base resin contained in the crosslinked polyolefin resin composition shall be the value converted to the content of the base resin before crosslinking, that is, the content of the base resin in the crosslinkable polyolefin resin composition.

[0020] The components used in this invention are described below. Each component can be used individually or in combination of two or more types.

[0021] [Base Resin] The resin composition of the present invention may contain a polyolefin resin as its base resin, but may also contain other resins, elastomers, oils, etc. In the present invention, even if the resin composition contains various rubbers such as ethylene rubber or styrene-based elastomers, it will be referred to as a resin composition, etc. for convenience, but this does not exclude elastomer compositions from the technical scope of the present invention.

[0022] By including a polyolefin resin in the base resin, the flame retardant effect of the flame retardant can be effectively expressed, and the total content of the flame retardant can be reduced. The resin or elastomer other than the polyolefin resin that may be included in the base resin (also referred to as "other resins" in this invention) can be any resin or elastomer commonly used in various resin compositions, without any particular limitations. Examples of other resins include acid-modified copolymer resins, fluororesins, chlorinated polyethylene resins, ethylene rubber, silicone rubber, acrylic rubber, fluororubber, synthetic rubber, styrene-based elastomers, ethylene-α-olefin copolymer rubber, oils, and the like.

[0023] In a crosslinkable polyolefin resin composition, it is preferable that at least one of the resins (including elastomers) that may be included in the base resin is a resin having crosslinkable moieties. Examples of resins having crosslinkable moieties include polyolefin resins. The crosslinkable moieties only need to have a structure suitable for each crosslinking method, and examples include unsaturated bond sites in a carbon chain and carbon atoms having hydrogen atoms.

[0024] <Polyolefin Resin> The polyolefin resin is not particularly limited as long as it is a polymer obtained by polymerizing or copolymerizing compounds having ethylenically unsaturated bonds (also called olefin compounds, excluding carboxylic acid compounds and acid ester compounds described later), and known resins used in various resin compositions can be used. Examples include polyethylene, polypropylene, ethylene-α-olefin copolymer, block copolymer of polypropylene and ethylene-α-olefin copolymer, copolymer having an acid copolymer component, and copolymer having an acid ester copolymer component. Also, rubber or elastomers of these copolymers (excluding ethylene rubber and styrene-based elastomers) can be mentioned. The polyolefin resin preferably contains at least one of the following resins: polyethylene, polypropylene, copolymer having an acid copolymer component, and copolymer having an acid ester copolymer component. In order to effectively exhibit the flame retardant effect of the flame retardant and achieve a good balance of high flame retardancy, excellent low-temperature flexibility, and high insulation, the first embodiment, which contains at least one resin of a copolymer having an acid copolymer component and the second embodiment, which contains polyethylene resin and polypropylene resin, is preferred, and the first embodiment is more preferred. In the first embodiment, a form comprising at least a copolymer resin having an acid ester copolymer component is preferred, and a form comprising the copolymer resin having an acid ester copolymer component alone, or a form comprising the copolymer resin having an acid ester copolymer component and a polyethylene resin is more preferred.

[0025] (Polyethylene Resin) Polyethylene resin (PE) is not particularly limited as long as it is a polymer resin mainly composed of ethylene. Examples include ultra-high molecular weight polyethylene (UHMW-PE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and very low-density polyethylene (VLDPE). Among these, high-density polyethylene, low-density polyethylene, and linear low-density polyethylene are preferred.

[0026] (Polypropylene resin) Polypropylene resin (PP) is not particularly limited as long as it is a polymer resin mainly composed of propylene. Examples include propylene homopolymers, as well as random polypropylene and block polypropylene resins.

[0027] (Ethylene-α-olefin copolymer resin) Preferably, the ethylene-α-olefin copolymer resin is a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms (excluding those included in polyethylene and polypropylene mentioned above).

[0028] (Copolymer resins having acid copolymer components) The compounds used to introduce the acid copolymer components in copolymer resins having acid copolymer components are not particularly limited, and examples include carboxylic acid compounds such as (meth)acrylic acid. Examples of copolymer resins having acid copolymer components (excluding those contained in polyethylene resins) include ethylene-(meth)acrylic acid copolymer resins.

[0029] (Copolymer resins having acid ester copolymer components) The compounds used to derive the acid ester copolymer components in copolymer resins having acid ester copolymer components are not particularly limited, and examples include vinyl acetate and acid ester compounds such as (meth)acrylic acid esters. The (meth)acrylic acid esters are not particularly limited, but examples include alkyl (meth)acrylates. The alkyl group of the alkyl (meth)acrylate has 1 to 12 carbon atoms, which is preferable. Examples of copolymer resins having acid ester copolymer components (excluding those contained in polyethylene resins) include ethylene-vinyl acetate copolymers (EVA) and ethylene-alkyl (meth)acrylate copolymers. Specifically, examples of ethylene-alkyl (meth)acrylate copolymer resins include ethylene-methyl acrylate copolymers (EMA), ethylene-ethyl acrylate copolymers (EEA), ethylene-butyl acrylate copolymers (EBA), and ethylene-methyl methacrylate copolymers (EMMA). Among these, ethylene-vinyl acetate copolymers and ethylene-ethyl acrylate copolymers are preferred.

[0030] <Other Resins> Other resins can be used without particular limitation as any of the above-mentioned resins or elastomers (including rubber) used in resin compositions or elastomer compositions, as described above.

[0031] (Composition of base resin) In the present invention, the base resin may contain a polyolefin resin, and may also contain other resins depending on the physical properties and applications of the polyolefin resin composition. The composition (components and their content) of the base resin in this case is appropriately selected and determined. Preferably, the content of each component of the base resin is appropriately determined from the following range so that the total content of each component is 100% by mass.

[0032] In 100% by mass of the base resin, the total content of the polyolefin resin can be appropriately determined, and is preferably 90 to 100% by mass, and more preferably 95 to 100% by mass, in which the flame retardant effect of the flame retardant can be effectively expressed while reducing its total content.

[0033] In 100% by mass of the base resin, the polyethylene content can be appropriately determined considering the total content of the polyolefin resin, etc., and for example, it is preferable that it be 0 to 90% by mass in terms of effective expression of the flame retardant's flame retardant effect and reduction of the total content. In the first embodiment, the polyethylene content is preferably 0 to 50% by mass, and more preferably 0 to 30% by mass, in terms of effective expression of the flame retardant's flame retardant effect and reduction of the total content. On the other hand, in the second embodiment, the polyethylene content is preferably 50 to 95% by mass, and more preferably 70 to 90% by mass, in terms of effective expression of the flame retardant's flame retardant effect and reduction of the total content.

[0034] In 100% by mass of the base resin, the content of polypropylene can be appropriately determined considering the total content of the polyolefin resin, etc. For example, in terms of effective expression of the flame retardant effect and reduction of the total content, it is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and even more preferably 5 to 10% by mass. In 100% by mass of the base resin, the content of copolymer resin having an acid copolymer component can be appropriately determined considering the total content of the polyolefin resin, etc. For example, in terms of effective expression of the flame retardant effect and reduction of the total content, it is preferably 50 to 100% by mass, and more preferably 70 to 100% by mass. In 100% by mass of the base resin, the content of copolymer resin having an acid ester copolymer component can be appropriately determined considering the total content of the polyolefin resin, etc. For example, in terms of effective expression of the flame retardant effect and reduction of the total content, it is preferably 50 to 100% by mass, and more preferably 70 to 100% by mass. The content of ethylene-α-olefin copolymer resin in 100% by mass of the base resin can be appropriately determined considering the total content of the polyolefin resin, etc.

[0035] In 100% by mass of the base resin, the total content of other resins is not particularly limited and can be, for example, 0 to 10% by mass, and preferably 0 to 5% by mass.

[0036] [Flame Retardant] The resin composition of the present invention contains a halogen-based flame retardant, antimony trioxide, and melamine cyanurate as flame retardants, wherein the halogen-based flame retardant contains at least a bromine-based flame retardant having a phthalimide structure as an essential component. By using these flame retardants in combination in specific proportions described later, a high degree of flame retardancy is achieved while also exhibiting excellent low-temperature flexibility and high insulation properties. In the present invention, "flame retardant" includes components that can function as flame retardant aids in the resin composition.

[0037] <Halogen-based Flame Retardant> The halogen-based flame retardant is not particularly limited as long as it is a flame retardant having at least one halogen atom in one molecule. For example, preferred examples include chlorine-based flame retardants containing at least one chlorine atom in one molecule, and bromine-based flame retardants containing at least one bromine atom in one molecule, with bromine-based flame retardants having a high flame retardancy enhancing effect being preferred. In the present invention, the halogen-based flame retardant includes at least one bromine-based flame retardant having a phthalimide structure described below among bromine-based flame retardants, and may further contain a bromine-based flame retardant having no phthalimide structure and a chlorine-based flame retardant.

[0038] (Bromine-based Flame Retardant) The bromine-based flame retardant is not particularly limited as long as it is a flame retardant having at least one bromine atom in one molecule, and those commonly used in resin compositions can be used without particular limitation. Examples of bromine-based flame retardants include bromine-based flame retardants having at least one phthalimide structure (sometimes referred to as "bromine-based phthalimide flame retardants" in the present invention) and bromine-based flame retardants having no phthalimide structure (sometimes referred to as "bromine-based non-phthalimide flame retardants" in the present invention). By using a bromine-based flame retardant in combination with melamine cyanurate and further allowing antimony trioxide to coexist, high-level flame retardancy sufficient to pass the vertical combustion test (VW-1) can be achieved even if the total content of the flame retardant is reduced. As the bromine-based flame retardant, a bromine-based phthalimide flame retardant is preferred from the viewpoint of expressing high flame retardancy, excellent low-temperature flexibility and high insulation properties.

[0039] As a brominated phthalimide flame retardant, any flame retardant having at least one phthalimide structure among brominated flame retardants is acceptable, and it is preferable that the flame retardant has two phthalimide structures. By using a brominated phthalimide flame retardant in combination with melamine cyanurate and further coexisting with antimony trioxide, a high level of flame retardancy that passes the vertical combustion test (VW-1) can be achieved even with a reduced total content of the flame retardant. As a brominated phthalimide flame retardant, those commonly used in resin compositions, etc., can be used without particular limitation, and examples include brominated ethylene bisphthalimide compounds (brominated ethylene bisphthalimide and its derivatives), brominated phthalimide compounds (brominated phthalimide and its derivatives), etc., with brominated ethylene bisphthalimide compounds being preferred. Examples of brominated ethylene bisphthalimide compounds include ethylene bistetrabromophthalimide and ethylene bistribromophthalimide. In the present invention, "derivative" refers to a compound having an organic group such as an alkyl group as a substituent, or a compound having a different number of bromine atoms.

[0040] As the bromine-based non-phthalimide flame retardant, any bromine-based flame retardant that does not have a phthalimide structure may be used, and those ordinarily used for resin compositions and the like can be used without particular limitation. Examples of the bromine-based non-phthalimide flame retardant include N,N'-bis(bromophenyl)terephthalamide compounds (N,N'-bis(bromophenyl)terephthalamide and derivatives thereof), brominated bisphenol compounds (brominated bisphenol and derivatives thereof), 1,2-bis(bromophenyl)alkanes, polybromodiphenyl ether compounds (e.g., decabromodiphenyl ether), polybromobiphenyl compounds (e.g., tribromophenyl), hexabromocyclododecane, brominated polystyrene, and hexabromobenzene. Among these, N,N'-bis(bromophenyl)terephthalamide compounds, brominated bisphenol compounds, or 1,2-bis(bromophenyl)alkanes (the number of carbon atoms constituting the alkane is not particularly limited, and may be, for example, 1 or 2) are preferred, and 1,2-bis(bromophenyl)ethane is more preferred. The number of bromine atoms contained in each of the above bromine-based non-phthalimide flame retardants is not particularly limited, and a larger number is preferred. For example, in 1,2-bis(bromophenyl)alkane, the number of bromine atoms contained in one phenyl group may be 1 to 5, and preferably 3 to 5.

[0041] The chlorine-based flame retardant is not particularly limited, and those ordinarily used in resin compositions can be used without particular limitation. Examples include decachlorododecahydrodimethanocyclooctene compounds, 1,6,7,8,9,14,15,16,17,17,18,18-dodecachloropentacyclo[12.2.1.1⁶,⁹.0²,¹³.0⁵,¹⁰]octadeca-7,15-diene (Dechlorane Plus), and the like.

[0042] <Antimony Trioxide> Antimony trioxide is a type of antimony oxide-based flame retardant additive that exhibits a high degree of flame retardancy in the resin composition of the present invention while maintaining low-temperature flexibility and insulation properties. Specifically, by using antimony oxide in combination with halogen-based flame retardants, particularly brominated phthalimide flame retardants, it can synergistically improve the flame retardant effect of halogen-based flame retardants, particularly brominated phthalimide flame retardants, by reacting stepwise with halogen-based flame retardants, particularly brominated phthalimide flame retardants, without inhibiting the flame retardancy exhibited by using it in combination with melamine cyanurate, as described later.

[0043] <Melamine Cyanurate> Melamine cyanurate is a compound composed of melamine and cyanuric acid. When used in combination with halogenated flame retardants, especially brominated phthalimide flame retardants, melamine cyanurate can synergistically improve the flame retardant effect of halogenated flame retardants, especially brominated phthalimide flame retardants, and can also reduce the total amount of flame retardant required to maintain a high level of flame retardancy.

[0044] <Other Flame Retardants> The resin composition of the present invention may contain flame retardants other than the above-mentioned flame retardants (referred to as "other flame retardants" in the present invention). Examples of other flame retardants include aluminum hydroxide, magnesium hydroxide, boehmite, calcium carbonate, magnesium carbonate, fluorine compounds, red phosphorus, phosphate esters, metal hydrates such as zinc borate and zinc stannate, melamine compounds other than melamine cyanurate, and also silicates and phosphite compounds. Examples of silicates include calcium silicate and magnesium silicate, and specifically, the compounds described in Patent Document 1 are included, and this description is incorporated herein by reference as part of the description. Examples of phosphite compounds include the compounds described in Patent Document 1, and this description is incorporated herein by reference as part of the description.

[0045] Other flame retardants are preferably free of silicates and / or phosphite compounds. Specifically, aluminum hydroxide, magnesium hydroxide, boehmite, calcium carbonate, and magnesium carbonate are more preferred, and aluminum hydroxide, magnesium hydroxide, and calcium carbonate are even more preferred. Here, "free of silicates and / or phosphite compounds" means that the total content of silicates and phosphite compounds is 1 part by mass or less per 100 parts by mass of the base resin.

[0046] [Other Components] In addition to the base resin and flame retardant, the resin composition of the present invention may contain various components such as additives commonly used in resin compositions ("other components"), to the extent that they do not impair the purpose of the present invention. Examples of other components include antioxidants, lubricants, metal deactivators, plasticizers, crosslinking agents, crosslinking aids, and inorganic fillers. Furthermore, for the crosslinkable polyolefin resin composition used to prepare the resin composition of the present invention, it is preferable to appropriately include crosslinking agents, crosslinking aids, crosslinking catalysts, crosslinking accelerators, etc., depending on the type of crosslinking reaction applied, and these components will also be described. The other components that the polyolefin resin composition may contain may be one or two or more of each type.

[0047] <Anti-aging agents (oxidants)> Anti-aging agents are not particularly limited, but examples include amine anti-aging agents, phenol anti-aging agents, benzimidazole anti-aging agents, sulfur anti-aging agents, etc., with phenol anti-aging agents and benzimidazole anti-aging agents being preferred. Phenol anti-aging agents are not particularly limited, but examples include pentaerythritol-tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, etc. Benzimidazole anti-aging agents are not particularly limited and include benzimidazole compounds and their metal salts, such as 2-mercaptobenzimidazole, zinc salt of 2-mercaptobenzimidazole, 2-methylmercaptobenzimidazole or its zinc salt, 1,3-dihydro-1-phenyl-2H-benzimidazole-2-thion or its zinc salt.

[0048] <Lubricant> Lubricants are not particularly limited, but examples include silicone compounds, fatty acid metal salts, and fatty acid amides, with silicone compounds being preferred.

[0049] <Crosslinking Agents and Crosslinking Auxiliaries> When the crosslinkable polyolefin resin composition is an electron beam crosslinkable polyolefin resin composition or a peroxide crosslinkable polyolefin resin composition, it may contain one or more crosslinking agents and crosslinking aids. The crosslinking agents and crosslinking aids can be those commonly used in electron beam crosslinking or peroxide crosslinking without particular limitation. Typically, polyfunctional compounds are used, for example, (meth)ate polyfunctional compounds such as polypropylene glycol di(meth)acrylate and trimethylolpropane tri(meth)acrylate, allyl polyfunctional compounds such as triallyl cyanurate, maleimide polyfunctional compounds, and divinyl polyfunctional compounds.

[0050] <Silane Coupling Agents> When the crosslinkable polyolefin resin composition is an electron beam crosslinkable polyolefin resin composition, it is preferable to include one or more silane coupling agents as crosslinking agents. On the other hand, when the crosslinkable polyolefin resin composition is a silane crosslinkable polyolefin resin composition, one or more silane coupling agents are used when preparing the silane graft resin, and the silane crosslinkable polyolefin resin composition contains one or more silane coupling agents as crosslinking agents. Silane coupling agents (including silane coupling agents before graft bonding to the base resin) have graft reaction sites (groups or functional groups such as ethylenically unsaturated groups) that can react to crosslinkable sites of the base resin in the presence of radicals generated by electron beam irradiation or decomposition of organic peroxides. Silane coupling agents used in the silane crosslinking method further have hydrolyzable silyl groups (e.g., alkoxysilyl groups) as reaction sites that can undergo silanol condensation.

[0051] Such silane coupling agents are not particularly limited and include silane coupling agents conventionally used in electron beam crosslinking or silane crosslinking methods. Preferred silane coupling agents include those having an ethylenically unsaturated group and a hydrolyzable silyl group (e.g., an alkoxysilyl group). Specific examples of silane coupling agents include vinyl alkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinyldimethoxyethoxysilane, vinyldimethoxybutoxysilane, vinyldiethoxybutoxysilane, allyltrimethoxysilane, allyltriethoxysilane, and vinyltriacetoxysilane, and (meth)acryloxysilanes such as methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, and methacryloxypropylmethyldimethoxysilane. Among these, vinyltrimethoxysilane or vinyltriethoxysilane are particularly preferred.

[0052] <Organic Peroxide> When the crosslinkable polyolefin resin composition is a peroxide-crosslinkable polyolefin resin composition, the composition preferably contains one or more organic peroxides as a crosslinking catalyst. Further, when the crosslinkable polyolefin resin composition is a silane-crosslinkable polyolefin resin composition, it is preferable to use one or more organic peroxides when preparing the silane-grafted resin. Organic peroxides generate radicals through thermal decomposition, and act as catalysts to initiate and progress crosslinking reactions between resins, or to initiate and promote grafting reactions via radical reactions between a silane coupling agent and a base resin. There are no particular limitations on the organic peroxide, and those used in radical polymerization reactions or conventional silane crosslinking methods can be used without particular restriction. Examples of such organic peroxides include those 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 compounds represented by the above formula are preferred. Here, R １ to R ６ each independently represent an alkyl group, an aryl group or an acyl group. Among R １ to R ６ , compounds in which all groups are alkyl groups, or compounds in which one group is an alkyl group and the remaining groups are acyl groups are preferred. The decomposition temperature (exothermic onset temperature) of the organic peroxide, measured by the method described in Japanese Patent Laid-Open No. 2016-121203, is preferably 80 to 195°C, and particularly preferably 125 to 180°C. Examples of such organic peroxides include the organic peroxides described in paragraph

[0036] of Japanese Patent Laid-Open No. 2016-121203, the content of which is incorporated herein by reference as part of the description of the present specification. Among these, benzoyl peroxide, 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.

[0053] <Silanol Condensation Catalyst> When the crosslinkable polyolefin resin composition is a silane crosslinkable polyolefin resin composition, it is preferable to contain one or more silanol condensation catalysts. The silanol condensation catalyst has the function of promoting the condensation reaction of the silanol condensation-capable reaction sites of the silane coupling agent grafted to the base resin in the presence of water (moisture). Such silanol condensation catalysts are not particularly limited, and examples include organotin compounds, metal soaps, platinum compounds, etc., with organotin compounds being preferred. Examples of organotin compounds include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctiate, and dibutyltin diacetate.

[0054] <Carrier Resin> When the crosslinkable polyolefin resin composition is a silane crosslinkable polyolefin resin composition, it is preferable to use a resin or rubber (referred to as a carrier resin) to form a mixture with the silanol condensation catalyst in its production. That is, it is preferable that the silanol condensation catalyst is used mixed with the carrier resin. The carrier resin is not particularly limited, but the components described for the base resin can be used. In terms of compatibility with the base resin, the carrier resin is preferably at least one of the components constituting the base resin, and preferably contains the same components as the base resin.

[0055] <Inorganic Fillers> The resin composition of the present invention may contain inorganic fillers. The inorganic fillers can be any that are commonly used as fillers in resin compositions, without any particular limitations. Examples of inorganic fillers include calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whiskers, and basic magnesium carbonate. Other examples include boron nitride, silica (crystalline silica, amorphous silica, etc.), carbon black, clay (calcined clay), tin oxide, titanium oxide, molybdenum oxide, silicone compounds, quartz, and white carbon. Inorganic fillers can be surface-treated with silane coupling agents or the like. Examples of surface treatment agents include silane coupling agents, titanate coupling agents, phosphate esters, fatty acids, and fatty acid metal salts.

[0056] [Composition of Polyolefin Resin Composition] In the resin composition of the present invention, the total content of the flame retardant is preferably 95 parts by mass or less per 100 parts by mass of the base resin, in that it exhibits high flame retardancy while also exhibiting excellent low-temperature flexibility and high insulation properties, more preferably 75 to 95 parts by mass, and even more preferably 80 to 90 parts by mass, in that it exhibits a good balance of high flame retardancy, excellent low-temperature flexibility and high insulation properties.

[0057] The content of halogen-based flame retardant per 100 parts by mass of base resin can be determined considering the total content of the above flame retardants, etc., and is preferably 25 parts by mass or more (less than 95 parts by mass) in order to exhibit a high degree of flame retardancy while reducing the total content. In order to exhibit a good balance of high flame retardancy, excellent low-temperature flexibility, and high insulation, the content of halogen-based flame retardant is preferably 25 to 50 parts by mass, and more preferably 30 to 45 parts by mass, per 100 parts by mass of base resin. The content of brominated phthalimide flame retardant per 100 parts by mass of base resin can be determined considering the total content of the above flame retardants, the content of the above halogen-based flame retardants, etc., and can be set to the same range as the content of the above halogen-based flame retardants, for example. The content of brominated non-phthalimide flame retardant per 100 parts by mass of base resin can be determined considering the total content of the above flame retardants, the content of the above halogen-based flame retardants, etc., and can be set to the same range as the content of the above halogen-based flame retardants, for example. The chlorine-based content per 100 parts by mass of the base resin can be determined by considering the total content of the above-mentioned flame retardant, the content of the above-mentioned halogen-based flame retardant, etc., and can be set to the same range as the content of the above-mentioned halogen-based flame retardant, for example.

[0058] The antimony trioxide content per 100 parts by mass of base resin can be determined considering the total content of the above-mentioned flame retardants, and is preferably 10 parts by mass or more (less than 95 parts by mass) in that it is possible to exhibit a high level of flame retardancy while reducing the total content. The antimony trioxide content is preferably 10 to 30 parts by mass, and more preferably 15 to 25 parts by mass, per 100 parts by mass of base resin in that it exhibits a good balance of high flame retardancy, excellent low-temperature flexibility, and high insulation. The melamine cyanurate content per 100 parts by mass of base resin can be determined considering the total content of the above-mentioned flame retardants, and is preferably 5 to 30 parts by mass, in that it is possible to exhibit a high level of flame retardancy while reducing the total content, while maintaining excellent insulation. The melamine cyanurate content is preferably 5 to 25 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of base resin in that it is possible to achieve an even higher level of both flame retardancy and insulation while maintaining excellent low-temperature flexibility.

[0059] The ratio of halogenated flame retardant content to antimony trioxide content [halogenated flame retardant content: antimony trioxide content] can be appropriately determined considering the total content, individual content, etc., and is preferably in the range of 1:1 to 5:1, more preferably in the range of 1.5:1 to 4:1, and even more preferably in the range of 1.5:1 to 3:1, in order to further improve flame retardancy while maintaining excellent low-temperature flexibility and high insulation properties.

[0060] The total content of other flame retardants per 100 parts by mass of the base resin can be appropriately determined considering the above total content. For example, in order to reinforce high flame retardancy while maintaining the excellent low-temperature flexibility and high insulation properties exhibited by the above three types of flame retardants, the total content of other flame retardants is preferably 0 to 40 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of the base resin. The content of aluminum hydroxide, magnesium hydroxide, boehmite, calcium carbonate, and magnesium carbonate, which are preferred flame retardants among the other flame retardants, and the total content of each can be appropriately determined considering the above total content and the total content of other flame retardants, and can be set within the range described above for the total content of other flame retardants. The content (total amount) of silicates and phosphite compounds among the other flame retardants can be appropriately determined considering the above total content and the total content of other flame retardants, and for example, it is preferably 1 part by mass or less per 100 parts by mass of the base resin.

[0061] The total content of other components and the content of each component in the resin composition of the present invention are not particularly limited and can be appropriately set within a range that does not impair the effects of the present invention. For example, the content of the antioxidant in the resin composition of the present invention is not particularly limited and can be, for example, 0.5 to 15 parts by mass per 100 parts by mass of the base resin. The content of the lubricant in the resin composition of the present invention is set within a range that does not impair the effects of the present invention and can be, for example, 0 to 5 parts by mass per 100 parts by mass of the base resin.

[0062] The content of the crosslinking agent and crosslinking aid (used in the electron beam crosslinking method or the organic peroxide crosslinking method) in the resin composition of the present invention (converted to the content before the crosslinking reaction) can be set appropriately, for example, to 1 to 8 parts by mass per 100 parts by mass of the base resin, and preferably to 2 to 6 parts by mass.

[0063] The content of the silane coupling agent in the resin composition of the present invention is preferably 2 to 15 parts by mass, more preferably 2.5 to 12 parts by mass, and even more preferably 3 to 10 parts by mass, per 100 parts by mass of the base resin. Here, in the silane crosslinkable polyolefin resin composition, the silane coupling agent is graft-bonded to the base resin, but for convenience, the above content of the silane coupling agent is the content converted to the mass before the graft reaction with the base resin (content of the silane coupling agent used in combination with the base resin).

[0064] The content of the organic peroxide (used in the organic peroxide crosslinking method or the silane crosslinking method) in the resin composition of the present invention can be appropriately determined depending on the crosslinking method. For example, the content in the peroxide crosslinkable polyolefin resin composition can be 0.003 to 3 parts by mass per 100 parts by mass of the base resin. The content of the organic peroxide used in the silane crosslinkable polyolefin resin composition and in its preparation is preferably 0.003 to 0.5 parts by mass, more preferably 0.005 to 0.5 parts by mass, and even more preferably 0.005 to 0.2 parts by mass per 100 parts by mass of the base resin.

[0065] The content of the silanol condensation catalyst (used in the silane crosslinking method) in the resin composition of the present invention is not particularly limited and can be determined as appropriate. The content of the silanol condensation catalyst is preferably 0.0001 to 0.5 parts by mass, and more preferably 0.001 to 0.2 parts by mass, per 100 parts by mass of the base resin.

[0066] The content of inorganic filler in the resin composition of the present invention is not particularly limited and can be determined as appropriate. The content of inorganic filler is preferably 0 to 30 parts by mass, and more preferably 0 to 20 parts by mass, per 100 parts by mass of the base resin.

[0067] When the resin composition of the present invention is a crosslinked product, the composition of this crosslinked product is usually the same as the types and content of each component in the resin composition of the present invention described above. However, the content of the base resin is converted to the content before crosslinking. In addition, in the silane crosslinked resin composition, the content of the silane coupling agent is converted to the content before the grafting reaction and the silanol condensation reaction. Note that the organic peroxide and the silanol condensation catalyst are usually decomposed.

[0068] [Preparation of Polyolefin Resin Composition] The resin composition of the present invention can be prepared by appropriate methods, and if necessary, by molding and / or crosslinking. A detailed explanation follows below.

[0069] [Preparation of Non-Crosslinked Polyolefin Resin Composition and Crosslinked Polyolefin Resin Composition] Both of the above compositions can be prepared by mixing or melt-mixing a (uncrosslinked) base resin, a flame retardant, and, as appropriate, other components, particularly components depending on the crosslinking method. The mixing method is not particularly limited as long as it is a method normally used in the preparation of rubber or resin compositions. For example, mixing can be done using various mixing devices such as a single-screw extruder, a twin-screw extruder, rolls, a Banbury mixer, and various kneaders. The mixing conditions, such as the temperature and time of melt mixing (also called melt kneading), are not particularly limited and can be appropriately set within a temperature range above the melting temperature of the base resin. The mixing temperature is preferably, for example, the melt mixing conditions (80 to 250°C) of step (1) described later. The mixing order of each component is not particularly limited, and each component can be mixed (melted) all at once, or each component can be mixed sequentially in an appropriate order. In this way, a non-crosslinked or crosslinked (uncrosslinked) polyolefin resin composition in which each component is dispersed (mixed) can be prepared. Furthermore, regardless of the above preparation method, it is preferable to prepare the silane-crosslinkable polyolefin resin composition by step (1) described later.

[0070] The resin composition of the present invention can also be molded into appropriate shapes and dimensions. When preparing the crosslinkable polyolefin resin composition, it is possible to mold the crosslinked product after the crosslinking treatment, but it is preferable to mold it before the crosslinking treatment (during or after preparation). The molding method and molding conditions are selected appropriately depending on the shape and form after molding. For example, molding methods include extrusion molding using an extrusion molding machine, extrusion molding using an injection molding machine, and molding using other molding machines. Extrusion molding is preferred when forming a coating layer for wiring materials due to its productivity and the fact that it can be co-extruded with the conductor.

[0071] [Preparation of Crosslinked Polyolefin Resin Composition] The resin composition (crosslinked product) of the present invention can be prepared by performing the crosslinking reaction treatment described later on the crosslinkable polyolefin resin composition described above. The crosslinkable polyolefin resin composition may be crosslinked in an unmolded state, but it is preferable to perform the crosslinking treatment after molding by, for example, the molding method described above.

[0072] When a crosslinkable polyolefin resin composition is subjected to a crosslinking reaction by electron beam crosslinking, the crosslinkable polyolefin resin composition prepared as described above is preferably molded into an appropriate shape before being irradiated with an electron beam. The electron beam irradiation conditions are not particularly limited as long as the crosslinkable polyolefin resin composition (resin) can be crosslinked. For example, the electron beam irradiation dose can be 1 to 30 Mrad, and the acceleration voltage during irradiation can be 500 to 750 keV.

[0073] When a crosslinkable polyolefin resin composition is subjected to a crosslinking reaction using an organic peroxide crosslinking method, the crosslinkable polyolefin resin composition prepared as described above is preferably molded into an appropriate shape and then heated to a temperature above the decomposition temperature of the organic peroxide. The heating conditions should be above the decomposition temperature of the organic peroxide contained in the crosslinkable polyolefin resin composition, and the heating time is not particularly limited. As heating conditions, for example, the melt mixing conditions of step (1) described later can be applied.

[0074] When a crosslinkable polyolefin resin composition is subjected to a crosslinking reaction by the silane crosslinking method, it is preferable to mold the silane crosslinkable polyolefin resin composition, which contains a base resin that has undergone a grafting reaction with a silane coupling agent, into an appropriate shape, and then bring it into contact with moisture. As a method for producing a silane crosslinked polyolefin resin molded article as a crosslinked product (molded article) by the silane crosslinking method, a method having the following steps (1), (2), and (3) (hereinafter sometimes referred to as "method for producing a molded article by the silane crosslinking method") is preferred.

[0075] Step (1): A process to obtain a molten mixture (silane crosslinkable polyolefin resin composition) by melt-mixing a base resin containing a polyolefin resin, a halogenated flame retardant containing a brominated phthalimide flame retardant, a flame retardant containing antimony trioxide and melamine cyanurate, a silane coupling agent, an organic peroxide, a silanol condensation catalyst, and other components as appropriate. Step (2): A process to obtain a molded body by molding the molten mixture obtained in step (1). Step (3): A process to obtain a molded body of a crosslinked polyolefin resin composition (silane crosslinked product) by contacting the molded body obtained in step (2) with water.

[0076] Step (1) described above can be performed by mixing all the above components at once, but it is preferable to perform it in the following steps (a) to (c). When performing the following steps (a) to (c), step (1) preferably includes steps (a) and (c) if all of the base resin is melted and mixed in step (a), and preferably includes steps (a), (b), and (c) if only a portion of the base resin is melted and mixed in step (a). The manner in which the flame retardant is mixed in the following steps (a) to (c) will be described later. Step (a): A step to prepare a silane masterbatch (silane MB) by melt-mixing all or part of the base resin, a silane coupling agent, an organic peroxide, and other components as appropriate at a temperature above the decomposition temperature of the organic peroxide. Step (b): A step to prepare a catalyst masterbatch (catalyst MB) by melt-mixing the remaining base resin and a silanol condensation catalyst. Step (c): A step to melt-mix the silane MB and the silanol condensation catalyst or catalyst MB.

[0077] When the remaining portion of the base resin is melt-mixed as a carrier resin in step (b), preferably 80 to 99 parts by mass, more preferably 94 to 98 parts by mass of the base resin is melt-mixed in step (a), and preferably 1 to 20 parts by mass, more preferably 2 to 6 parts by mass of the base resin is melt-mixed in step (b). The base resins to be mixed in steps (a) and (b) can be appropriately selected from the resins used as base resins.

[0078] In the silane crosslinking method for manufacturing molded articles, the mixing amounts of each component used as the base resin shall be the same as the content percentages described above as the composition of the base resin. Furthermore, the mixing amounts of the flame retardant, silane coupling agent, silanol condensation catalyst, and other components shall be the same as the content percentages in the resin composition of the present invention described above. Moreover, in the silane crosslinking method for manufacturing molded articles, the mixing amount of organic peroxide shall be the same as the amount of organic peroxide used in the grafting reaction between the silane coupling agent and the base resin described above.

[0079] The melt mixing in steps (1) and (a) can be carried out by appropriately selecting a method commonly used for rubber, plastics, etc., for example, by using various mixing devices such as a single-screw extruder, twin-screw extruder, rolls, Banbury mixer, or various kneaders. The melt mixing temperature (also called the mixing temperature) is above the decomposition temperature of the organic peroxide, preferably at the decomposition temperature of the organic peroxide + (1 to 80) °C. Here, the decomposition temperature of the organic peroxide used as the reference for the melt mixing temperature is the temperature under normal pressure (approximately 0.1 MPa). It is difficult to uniquely determine the melt mixing temperature, but as an example, 80 to 250 °C is preferred, and 100 to 240 °C is more preferred. Other conditions can be set as appropriate. The mixing time is not particularly limited, for example, the mixing time can be 1 to 25 minutes, preferably 3 to 20 minutes. In step (a), it is preferable to melt and mix each of the above-mentioned components in the absence of a silanol condensation catalyst (for example, in a ratio of 0.01 parts by mass or less per 100 parts by mass of the base resin) to suppress the condensation reaction of the silane coupling agent.

[0080] In steps (1) and (a), the mixing order of each component during melt-mixing is not particularly limited, and all components can be melt-mixed at once. It is preferable that the silane coupling agent is mixed with a flame retardant, and further with an inorganic filler, and optionally with an organic peroxide, before being melt-mixed with the base resin. This pre-mixing (pre-mixing) can be performed using a known mixer, kneader, etc., at a temperature below the decomposition temperature of the organic peroxide, preferably 10 to 60°C, more preferably near room temperature (20 to 35°C), by dry or wet mixing for several minutes to several hours. Preferably, dry blending is performed at a temperature below the decomposition temperature of the organic peroxide. Pre-mixing allows for good dispersion of the flame retardant in the base resin. Furthermore, when an inorganic filler is mixed, a good balance can be formed between a silane coupling agent that strongly bonds with the inorganic filler and a silane coupling agent that weakly bonds with the inorganic filler. In the pre-mixing method, the obtained mixture and all or part of the base resin and the remaining components are then melt-mixed, for example, under the melt-mixing conditions described above.

[0081] The flame retardant may be mixed in at least one of steps (a) and (b), or it may be mixed in both steps. For example, halogenated flame retardants (especially brominated flame retardants having a phthalimide structure) are preferably mixed in step (b), while antimony trioxide and melamine cyanurate are preferably mixed in step (a).

[0082] The melt mixing in steps (b) and (c) can be carried out in the same manner as the melt mixing in step (a). However, in step (c), it is preferable that the silane MB and silanol condensation catalyst are not kept at a high temperature for a long time in a mixed state in order to avoid the silanol condensation reaction. In step (c), prior to melt mixing, the resin can be mixed (e.g., dry blended) under non-melting conditions, for example, under the conditions of the pre-mixing described above.

[0083] In step (1), other components may be mixed in any of the steps. In step (1), steps (a) to (c) may be carried out simultaneously or sequentially. Step (1) prepares a silane crosslinkable polyolefin resin composition (unmolded body) as a molten mixture.

[0084] Next, step (2) is performed to mold the obtained molten mixture to obtain a molded body. The molding in step (2) only needs to be able to mold the molten mixture, and an appropriate molding method and molding conditions are selected according to the form of the molded body. The molding method is as described above. This step (2) can be performed simultaneously with or in succession to step (c) above, for example, using an extrusion molding machine. For example, a series of steps can be adopted in which silane MB and silanol condensation catalyst or catalyst MB are mixed by dry blending or the like just before the coating device (extruder), and then melt-mixed in the coating device (extruder) (step (c)), or silane MB and silanol condensation catalyst or catalyst MB are separately introduced into the coating device and then melt-mixed (step (c)), and then molded (step (2)). As for the molding conditions, for example, the melt-mixing method and conditions of step (a) can be applied.

[0085] Step (3) is performed to bring the molded article of the crosslinkable polyolefin resin composition obtained in this way into contact with water, thereby causing the silane coupling agent to undergo a silanol condensation reaction (crosslinking reaction). This step (3) can be carried out by a conventional method, and the above crosslinking reaction will proceed even if left at room temperature, for example, in a temperature environment of about 20 to 25°C, but the molded article can also be actively brought into contact with water to promote the crosslinking reaction. In this way, a polyolefin resin composition (molded article) containing a base resin crosslinked via a silane coupling agent can be prepared.

[0086] Regarding the silane crosslinking method described above, the components other than the base resin used (silane coupling agent, organic peroxide, silanol condensation catalyst, inorganic filler, etc.), each step (1) to (3) in the molded article manufacturing method by the silane crosslinking method, and furthermore, the reactions in the silane crosslinking method and the form of the resulting condensation cured product can be appropriately applied from, for example, International Publication No. 2016 / 140253 or Japanese Patent Application Publication No. 2017-145370, and the contents described in these publications are incorporated as is as part of the description in this specification.

[0087] <Applications of the Polyolefin Resin Composition> Because the resin composition of the present invention exhibits the above-mentioned excellent properties, it can be suitably used as a material for forming the coating layer of wiring materials, particularly wiring materials. It can also be applied to general molded products (sealants, gaskets, etc.). In particular, taking advantage of the above-mentioned excellent properties, it is suitable as a material for forming the coating layer of wiring materials used in the low-temperature environment described above.

[0088] [Wiring Material] The following describes a wiring material that uses a tubular molded body formed from the resin composition of the present invention as a covering layer. The wiring material of the present invention has a covering layer (including an insulating layer, sheath, etc.) formed from the resin composition of the present invention on the outer surface of a conductor. This wiring material exhibits high flame retardancy, excellent low-temperature flexibility and high insulation, and preferably also exhibits high heat resistance and / or excellent solder resistance.

[0089] The wiring material of the present invention only needs to have at least one coating layer made of the resin composition of the present invention on the outer surface of the conductor, and the other components can be the same as those of a normal wiring material. Examples include insulated wires having at least one coating layer on the outer surface of the conductor, and cables in which a sheath as a coating layer is formed on the outer surface of such insulated wires or a bundle of multiple such insulated wires. Examples of wiring materials include insulated wires or cables, (electrical) cords, optical fiber cores, optical fiber cords, and optical cables. These include wiring materials used for internal or external wiring of electrical and electronic equipment, wiring materials installed indoors, and wiring materials installed outdoors.

[0090] [Coating Layer] The coating layer in the wiring material of the present invention is the same as the coating layer in ordinary wiring materials, except that it is formed of the resin composition of the present invention. Since the resin composition of the present invention includes both a non-crosslinked polyolefin resin composition and a crosslinked polyolefin resin composition, the wiring material of the present invention includes wiring materials having a coating layer formed of a non-crosslinked polyolefin resin composition and wiring materials having a coating layer formed of a crosslinked polyolefin resin composition. The coating layer made of the resin composition of the present invention may be provided directly on the outer surface of the conductor or indirectly via other layers such as an adhesive layer. The coating layer may be single-layered or multi-layered, and in the case of multi-layered, it is sufficient that at least one layer is formed of the resin composition of the present invention. Furthermore, the sheath of the cable may be formed of the resin composition of the present invention. The thickness (wall thickness) of the coating layer is appropriately determined according to the application, etc., but can be set to the same thickness as ordinary wiring materials used for each application. For example, in insulated wires, it is usually set to about 0.15 to 10 mm (0.4 mm or less for ultra-thin wires), and in optical fiber cables, it is usually set to about 0.1 to 10 mm.

[0091] [Conductor] Various conductors and cores can be used as conductors depending on the type and application of the wiring material. Such conductors and cores can be those that are normally used in wiring materials. Examples of conductors used in wiring materials such as insulated wires include single or stranded wires of soft copper, copper alloy, or aluminum (with tensile fibers attached longitudinally or twisted together). In addition to bare wires, tin-plated wires or those with an enamel coating insulation layer can also be used. Examples of cores used in wiring materials such as cables include optical fiber cores, single-core cores consisting of a single insulated wire, or double-core cores made by bundling multiple insulated wires, as well as single insulated wires or bundles of multiple insulated wires covered with an insulation layer or wrapped with insulating tape. The outer diameter of the conductor is not particularly limited and is appropriately determined according to the type, application, and characteristics of the wiring material. For example, it can be 0.5 to 20 mm for insulated wires, and 1.0 to 25 mm for various cables. The conductor may have layers other than the cross-linked coating layer, reinforcing tape, etc., on its surface.

[0092] [Method for Manufacturing Wiring Material] The wiring material of the present invention can be manufactured by any suitable method, but it is preferable to manufacture it by placing the resin composition of the present invention on the outer surface of a conductor (forming it into a tubular shape) and then performing a crosslinking reaction treatment as appropriate. The method for placing the resin composition of the present invention on the outer surface of a conductor can be any method that can cover the conductor with the resin composition of the present invention, and any suitable molding method can be used, such as the molding method described above. The method for placing the resin composition of the present invention on the outer surface of a conductor (placement of the polyolefin resin composition) can also be performed as a series of steps (in one go) in succession with the method for preparing the resin composition of the present invention (preparation of the polyolefin resin composition in the extrusion molding machine) using an extrusion molding machine. If the resin composition of the present invention is a crosslinkable polyolefin resin composition, then the crosslinkable polyolefin resin composition placed on the outer surface of the conductor is subjected to a crosslinking reaction treatment. This crosslinking reaction treatment can be applied without particular limitation to methods and conditions that are normally applied to each crosslinking method suitable for the crosslinkable polyolefin resin composition, and specifically as described above. When the resin composition of the present invention is crosslinked by the silane crosslinking method, the manufacturing method is the same as the above-described method for manufacturing a molded article by the silane crosslinking method, except that step (2) is performed by molding the molten mixture obtained in step (1) onto the outer surface of a conductor using, for example, an extrusion molding machine.

[0093] In this way, by forming a coating layer using the resin composition of the present invention, a wiring material exhibiting high flame retardancy, excellent low-temperature flexibility, and high insulation, preferably further exhibiting heat resistance, can be manufactured. In particular, by forming the coating layer with an electron beam crosslinked material, a wiring material exhibiting high solder resistance in addition to high flame retardancy, excellent low-temperature flexibility, high insulation, and heat resistance can be manufactured.

[0094] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0095] Details of each compound used in the examples and comparative examples are shown below. <Base Resin> (Polyolefin Resin) Linear low-density polyethylene (LLDPE1): Evolu SP0540 (trade name, manufactured by Prime Polymer) Linear low-density polyethylene (LLDPE2): Evolu SP2520 (trade name, manufactured by Prime Polymer) High-density polyethylene (HDPE): Hyzex 5305E (trade name, high-density polyethylene resin, manufactured by Sun Allomer) Ethylene-vinyl acetate copolymer (EVA): Evaflex V5274R (trade name, manufactured by Mitsui Dow Polychemicals) Ethylene-ethyl acrylate copolymer (EEA): NUC-6510 (trade name, manufactured by NUC) Random polypropylene (r-PP): PB222A (trade name, manufactured by Sun Allomer) Ethylene-methyl methacrylate copolymer (EMMA): Aclift WH102 (trade name, manufactured by Sumitomo Chemical)

[0096] <Flame Retardants> Brominated flame retardant: Scytex 8010 (trade name, brominated flame retardant without a phthalimide structure, ethylenebis(pentabromophenyl), manufactured by Albemarle) Brominated flame retardant (BT-93W): Scytex BT-93W (trade name, brominated flame retardant with a phthalimide structure, ethylenebistetrabromophthalimide, manufactured by Albemarle) Antimony trioxide: Sb ２ O ３ (Manufactured by Nippon Seikou Co., Ltd.) Magnesium hydroxide: Kisma 5A (product name, manufactured by Kyowa Chemical Co., Ltd.) Aluminum hydroxide: BF013S (product name, manufactured by Nippon Light Metal Co., Ltd.) Phosphite: PX200 (product name, aromatic condensed phosphate ester, manufactured by Daihachi Chemical Co., Ltd.) Silicate: Kunipia F (product name, montmorillonite, manufactured by Kunimine Industries Co., Ltd.) Calcium carbonate: Softon 1200 (product name, manufactured by Bihoku Funka Kogyo Co., Ltd.) Melamine cyanurate: MC-6000 (product name, manufactured by Nissan Chemical Corporation)

[0097] <Other ingredients> Primary antioxidant: Irganox 1010 (trade name, Pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), phenol antioxidant, manufactured by BASF) Secondary antioxidant: Nocrac MBZ (trade name, zinc salt of 2-mercaptobenzimidazole, benzimidazole antioxidant, manufactured by BASF) Crosslinking agent (TMPT): Ogmont T200 / 01 (trade name, trimethylolpropane trimethacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) Silane coupling agent: KBM-1003 (trade name, vinyltrimethoxysilane, manufactured by Shin-Etsu Silicone Co., Ltd.) Organic peroxide: Permil D (trade name, dicumyl peroxide, decomposition temperature 145°C, manufactured by NOF Corporation) Silanol condensation catalyst: ADEKA stab OT-1 (product name, dioctyl tin dilaurate, manufactured by ADEKA Corporation)

[0098] [Examples 1-16 and Comparative Examples 1-18] Examples 1-16 and Comparative Examples 1-18 were carried out using the components shown in Tables 1 and 2, respectively. Specifically, crosslinkable polyolefin resin compositions having the compositions shown in Tables 1 and 2 were prepared by the following manufacturing methods, and insulated wires having a coating layer formed by extrusion molding (extrusion coating) and crosslinking treatment were manufactured on the outer surface of a conductor. In Tables 1 and 2, the numerical values ​​for the mixing amount (content) of each example are in parts by mass unless otherwise specified. Also, a blank space for each component means that the mixing amount of the corresponding component is 0 parts by mass. The "Total Flame Retardant Content" column in Tables 1 and 2 represents the total content of each flame retardant in each example and comparative example. Also, the "Content Ratio" column in Tables 1 and 2 represents the ratio of the content of halogen-based flame retardant to the content of antimony trioxide [Halogen-based flame retardant content / Antimony trioxide content] in each example and comparative example.

[0099] <Examples 1-14 and Comparative Examples 14-18> Insulated wires were manufactured by the following electron beam crosslinking method (referred to as "electron beam" in the "Crosslinking Method" column of Table 1). The components shown in Tables 1 and 2 were added to a Banbury mixer in the amounts shown in Tables 1 and 2, melted and mixed at 170°C for 10 minutes, then discharged at a material discharge temperature of 180°C and passed through a feeder-luder to obtain pellets of electron beam crosslinkable polyolefin resin composition. Using the obtained pellets, an insulating coating was formed as follows to manufacture wire precursors. That is, the obtained pellets were introduced into an extrusion molding machine equipped with a screw with a diameter of 25 mm (ratio of effective screw length L to diameter D: L / D = 25, compression section screw temperature 170°C, head temperature 180°C). In this extrusion molding machine, pellets were melted and extruded at a speed of 100 m / min (screw rotation speed of 40 rpm) to coat the outer circumference of a stranded conductor (outer diameter 0.80 mm) made by concentrically twisting 19 soft copper wires with a diameter of 0.16 mm, resulting in a finished outer diameter of 1.40 mm (thickness 0.30 mm), thereby producing a wire precursor. Next, an electron beam crosslinkable polyolefin resin composition placed on the outer surface of the conductor was irradiated with an electron beam at an acceleration voltage of 500 kV to an irradiation dose of 10 Mrad. In this way, insulated wires having a tubular molded body (electron beam crosslinked product) of the electron beam crosslinkable polyolefin resin composition as a coating layer were produced.

[0100] <Examples 15 and 16> Insulated wires were manufactured by the silane crosslinking method described below (referred to as "Silane 1" in the "Crosslinking Method" column of Table 1). In each example, a portion of the base resin was used in step (a), and 5 parts by mass of LLDPE as the remainder of the base resin was used as the carrier resin for catalyst MB in step (b).

[0101] Specifically, using 100 parts by mass of the base resin as the mixing ratio, antimony trioxide and melamine cyanurate as flame retardants, a silane coupling agent, an organic peroxide, and an antioxidant were dry-mixed at room temperature (25°C) in the mass ratios shown in Table 1. The resulting mixture and a portion of the base resin were melt-mixed for 5 minutes at a temperature above the decomposition temperature of the organic peroxide (170°C) using a 2L Banbury mixer (manufactured by Nippon Roll Co., Ltd.) in the mass ratios shown in Table 1, and then discharged at a material discharge temperature of 180°C to obtain silane MB (step (a)). In addition, the remaining base resin, a silanol condensation catalyst, and a bromine-based flame retardant having a phthalimide structure as a flame retardant were melt-mixed at 170°C using a Banbury mixer (manufactured by Nippon Roll Co., Ltd.) in the mass ratios shown in Table 1, and then discharged at a material discharge temperature of 180°C to obtain catalyst MB (step (b)). Next, the silane MB obtained in step (a) and the catalyst MB obtained in step (b) were dry-blended at 25°C for approximately 1 minute directly above an extruder (screw diameter: 25 mm, L / D (ratio of effective screw length L to diameter D): 25) in the mass ratios shown in Tables 1 and 2 to obtain a dry blend. The obtained dry blend was fed into the extruder and extruded onto the outer circumference of a stranded conductor (outer diameter 0.80 mm) consisting of 19 concentric strands of soft copper wire with a diameter of 0.16 mm, at a line speed of 100 m / min (screw rotation speed 40 rpm) under the extrusion temperature conditions described below, so that the finished outer diameter would be 1.40 mm (thickness 0.30 mm), thereby producing a wire precursor (step (2)). At this time, the dry blend is melt-mixed in the extruder before extrusion molding (step (c)), thereby preparing a silane crosslinkable polyolefin resin composition (step (1)). The extrusion temperature conditions were set to 170°C in the cylinder section of the extrusion molding machine, and further set to 180°C for the die temperature (molding temperature). The wire precursor obtained in this way was left in a 25°C, 50% RH environment for 24 hours (step (3)), and a silanol condensation reaction was carried out by contacting the tubular molded body of the crosslinkable polyolefin resin composition with water, thereby producing insulated wires having a tubular molded body of the silane crosslinked polyolefin resin composition (silane crosslinked product) as a coating layer.

[0102] <Comparative Examples 1-13> Insulated wires were manufactured using the silane crosslinking method described below (referred to as "Silane 2" in the "Crosslinking Method" column of Table 1). Specifically, the base resin, flame retardant, silane coupling agent, organic peroxide, silanol condensation catalyst, and antioxidant were dry-blended at 25°C for approximately 1 minute directly above an extruder (screw diameter: 25 mm, L / D (ratio of effective screw length L to diameter D): 25) in the mass ratios shown in Table 1 to obtain a dry blend. The obtained dry blend was fed into the extruder and extruded onto the outer circumference of a stranded conductor (outer diameter 0.80 mm) consisting of 19 concentric strands of soft copper wire with a diameter of 0.16 mm, at a line speed of 100 m / min (screw rotation speed 40 rpm) under the extrusion temperature conditions described below, so that the finished outer diameter was 1.40 mm (thickness 0.30 mm), thereby producing a wire precursor. The extrusion temperature conditions were set to 170°C in the cylinder section of the extrusion molding machine, and further set to 180°C for the die temperature (molding temperature). Using each of the obtained wire precursors, insulated wires having a tubular molded body (silane crosslinked product) of a silane crosslinked polyolefin resin composition as a coating layer were manufactured in the same manner as in Example 15.

[0103] The following tests were performed on each insulated wire manufactured, and the results are shown in Tables 1 and 2.

[0104] <Evaluation 1: Flame Retardancy> As a flame retardancy test, the UL 1581 VW-1 test (vertical combustion test) was performed on each of the five samples (N=5) prepared for each manufactured insulated wire. Whether or not each sample passed the VW-1 test was checked, and the flame retardancy was evaluated based on the evaluation criteria below. - Evaluation Criteria - ○ (Pass): All five samples passed consecutively. × (Fail): None of the five samples passed consecutively (even one of the five samples failed).

[0105] <Evaluation 2: Low Temperature Flexibility> A low temperature winding test was conducted in accordance with JIS C 3005 as a cold resistance test. The test temperature was set to -60°C, and each manufactured insulated wire was left at the respective test temperature for one hour. Next, the insulated wire was wound around a mandrel with the same outer diameter as the wire itself at least six turns, and the presence or absence of cracks in the insulated wire was visually checked. Low temperature flexibility was then evaluated based on the evaluation criteria below. - Evaluation Criteria - ○ (Pass): No cracks occurred in the wound insulated wire × (Fail): Cracks occurred in the wound insulated wire

[0106] <Evaluation 3: Insulation Resistance> In accordance with JIS C 3005, 10m of each manufactured wiring material was used as a test piece. This test piece was immersed in a 20°C water bath for 24 hours, and the insulation resistance value was measured. The measurement voltage, charging time, and measurement time were 500V, 10 seconds, and 50 seconds, respectively. The measurement was performed 1 hour after immersion in water. The insulation performance was evaluated from the measured values ​​based on the following evaluation criteria. - Evaluation Criteria - ○ (Pass): Insulation resistance value was 5000 MΩ·km or higher × (Fail): Insulation resistance value was less than 5000 MΩ·km

[0107] <Evaluation 4: Solder Resistance (Reference Test)> The insulation layer up to 5 mm from the tip of the manufactured insulated wire was stripped to create a test specimen. This test specimen was immersed in a solder bath set to 350°C and held there for 5 seconds. After that, the test specimen was removed from the solder bath and its solder resistance was evaluated by checking for foaming based on the evaluation criteria below. - Evaluation Criteria - ○ (Pass): No significant foaming was observed that caused visible irregularities on the surface of the test specimen. × (Fail): Significant foaming was observed that caused visible irregularities on the surface of the test specimen.

[0108] In Tables 1 and 2, in the "Crosslinking Method" column, "Electron beam" refers to the electron beam crosslinking method, "Silane 1" refers to the silane crosslinking method in Example 15, etc., and "Silane 2" refers to the silane crosslinking method in Comparative Examples 1 to 13.

[0109]

[0110]

[0111] The results shown in Tables 1 and 2 indicate the following: The comparative polyolefin resin compositions that did not use halogenated flame retardants containing brominated phthalimide flame retardants, antimony trioxide, and melamine cyanurate in specific proportions failed to achieve a balance of high flame retardancy, excellent low-temperature flexibility, and high insulation. Furthermore, the comparative polyolefin resin compositions containing flame retardants with a total content exceeding 95 parts by mass exhibited inferior low-temperature flexibility, even when multiple flame retardants were used in combination.

[0112] In contrast, the polyolefin resin compositions of the examples containing a halogenated flame retardant including a brominated phthalimide flame retardant, antimony trioxide, and melamine cyanurate in specific proportions (content of each flame retardant and total content) all exhibit high flame retardancy, excellent low-temperature flexibility, and high insulation properties. Therefore, by using the resin composition of the present invention as a coating layer forming material, wiring materials exhibiting high flame retardancy, excellent low-temperature flexibility, and high insulation properties can be manufactured. Furthermore, the electron beam crosslinked polyolefin resin composition exhibits high solder resistance in addition to high flame retardancy, excellent low-temperature flexibility, and high insulation properties. Therefore, by using the resin composition of the present invention as a coating layer forming material, wiring materials exhibiting high flame retardancy, excellent low-temperature flexibility, and high insulation properties, preferably wiring materials also exhibiting high solder resistance, can be manufactured. It has been confirmed that the insulated wires manufactured in each example exhibit higher heat resistance than insulated wires with a coating layer formed from a non-crosslinked polyolefin resin composition having the same composition except for the crosslinking agent.

[0113] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting the spirit and scope of the invention as set forth in the appended claims.

[0114] This application claims priority based on Japanese Patent Application No. 2025-052900, filed in Japan on 27 March 2025, which are incorporated herein by reference as part of this specification.

Claims

1. A polyolefin resin composition comprising a base resin containing a polyolefin resin, a halogenated flame retardant containing a brominated flame retardant having a phthalimide structure, antimony trioxide, and melamine cyanurate, wherein, per 100 parts by mass of the base resin, the content of the brominated flame retardant having a phthalimide structure is 25 parts by mass or more, the content of the antimony trioxide is 10 parts by mass or more, the content of the melamine cyanurate is 5 to 30 parts by mass, and the total content of the flame retardant is 95 parts by mass or less.

2. The polyolefin resin composition according to claim 1, wherein the ratio of the content of the halogen-based flame retardant to the content of the antimony trioxide [content of halogen-based flame retardant: content of antimony trioxide] is within the range of 1:1 to 5:

1.

3. The polyolefin resin composition according to claim 1, which is a crosslinked product.

4. The polyolefin resin composition according to claim 3, wherein the crosslinked material is a crosslinked material obtained by irradiation with an electron beam.

5. A wiring material having a coating layer on the outer surface of a conductor, wherein the coating layer is formed of the polyolefin resin composition described in any one of claims 1 to 4.

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