JP7748890B2 - Flame-retardant polyolefin resin composition and wiring material using the same - Google Patents

Description

The present invention relates to a flame-retardant polyolefin resin composition and a wiring material using the same.

Electrical and electronic devices, vehicles, etc. are usually equipped with wiring materials (insulated wires or cables, (electric) cords, optical fiber cores, optical fiber cords, optical cables, etc.) that transport power or transmit information. Depending on the application, such wiring materials are required to satisfy required properties such as sufficient flame retardancy, while also being abrasion resistant enough to prevent exposure of the conductor due to damage (cracks, tears, etc.) to the coating layer even when repeatedly contacted with or rubbed against other components or other wiring materials.
The abrasion resistance of wiring materials can be improved by providing (attaching) a protective member to the wiring material. However, this method is not necessarily applicable to recent electrical and electronic devices, etc., where installation space is gradually becoming smaller due to the need for space for the protective member. Therefore, it is desirable to ensure that the coating layer of the wiring material itself (the material forming the coating layer) exhibits sufficient abrasion resistance while still satisfying the required characteristics. For example, Patent Document 1 proposes a wiring material with an abrasion-resistant coating layer, which is a heat-resistant crosslinked electric wire comprising: "a coating layer covering the periphery of a conductor formed with a resin composition containing a resin consisting of high-density polyethylene, low-density polyethylene, an ethylene copolymer, and an ethylene copolymer modified with an unsaturated carboxylic acid anhydride, a brominated flame retardant, and magnesium hydroxide, wherein the total amount of the brominated flame retardant and magnesium hydroxide is 30 to 55 parts by mass per 100 parts by mass of the resin, and the coating layer is crosslinked," and the hardness and specific gravity of the resin composition are within specific ranges.

JP 2014-132530 A

In recent years, as electrical and electronic devices, vehicles, and the like have become increasingly complex and sophisticated, the number of wiring materials being installed is increasing, and the installation space is becoming increasingly narrow. Furthermore, there is a demand for even thinner (lighter) wiring materials themselves. Therefore, installed wiring materials frequently come into contact with and rub against other components, and thinner wiring materials, in particular, experience reduced abrasion resistance as the coating layer becomes thinner. Therefore, there is a demand for the development of materials for forming coating layers that exhibit high abrasion resistance even when thinned (materials that themselves exhibit high abrasion resistance). However, Patent Document 1 does not consider achieving such high abrasion resistance that exceeds conventional abrasion resistance, nor does it consider balancing this with the required characteristic (flame retardancy).

However, when a resin such as high-density polyethylene is used for the coating layer to improve abrasion resistance, problems arise, such as the coating shrinking after formation, exposing the conductor. As a result, electric wires with such a coating layer have poor dimensional stability, making the conductor more likely to become exposed after installation, undermining the reliability of the electric wire and its installation. This issue can be resolved by cutting the cut wire to the specified length again before installation. However, this leads to poor installation workability and increased manufacturing costs.

The present invention aims to provide a flame-retardant polyolefin resin composition that can form a molded article (coating layer) that exhibits high abrasion resistance while maintaining excellent flame retardancy and suppressing excessive shrinkage. Another objective of the present invention is to provide wiring material that exhibits high abrasion resistance while also having excellent flame retardancy and dimensional stability.

After extensive research into materials for forming the coating layer of wiring material, the inventors discovered that by using a resin that forms the base of the material and that satisfies specific compositions [A] to [C], which specify the type and content of copolymers, etc., and then adding a flame retardant to this resin, it is possible to form a molded article (coating layer) that exhibits high abrasion resistance while maintaining excellent flame retardancy, while suppressing excessive shrinkage. They also discovered that a composition containing the above resin and flame retardant can form a molded article (coating layer) that exhibits high abrasion resistance while also having excellent flame retardancy and dimensional stability, and is therefore suitable as a material for forming the coating layer (molded article) of wiring material. Based on this finding, the inventors conducted further research and arrived at the present invention.

That is, the object of the present invention has been achieved by the following means.
<1> A flame-retardant polyolefin resin composition containing a resin and a flame retardant,
The flame-retardant polyolefin resin composition, wherein the resin satisfies the following compositions [A] to [C].

[A] A resin containing high-density polyethylene polymerized using a metallocene catalyst at a content of 15 to 70 mass %. [B] An ethylene-vinyl acetate copolymer, an ethylene copolymer having an acid copolymerization component, an acid-modified copolymer thereof, an ethylene rubber, and a styrene-based elastomer are contained in the resin at a content of 15 to 70 mass %.
[C] Polymers having a density of less than 0.90 g/ ^cm3 are not essential.

<2> The flame-retardant polyolefin resin composition according to <1>, wherein the content of the high-density polyethylene in the resin is 25 to 70 mass%.
<3> The flame-retardant polyolefin resin composition according to <1> or <2>, containing a total of 120 parts by mass or less of components having a melting point exceeding 200°C per 100 parts by mass of the resin.
<4> The flame-retardant polyolefin resin composition according to any one of <1> to <3>, wherein the total content of the composition [B] is 5 mass% or less.
<5> The flame-retardant polyolefin resin composition according to any one of <1> to <4>, which is a crosslinked product.
<6> A wiring material having a coating layer on the outer peripheral surface of a conductor,
A wiring material, wherein the coating layer is formed from the flame-retardant polyolefin resin composition according to any one of <1> to <5> above.
<7> The wiring material according to <6>, which is an insulated wire for use in a vehicle.

The flame-retardant polyolefin resin composition of the present invention can form a molded article (coating layer) that exhibits high abrasion resistance while suppressing excessive shrinkage and maintaining excellent flame retardancy. Furthermore, the wiring material of the present invention comprises a tubular molded article of the flame-retardant polyolefin resin composition of the present invention as a coating layer, and exhibits high abrasion resistance while also exhibiting excellent flame retardancy and dimensional stability.

In this specification, a numerical range expressed using "to" means a range that includes the numerical values written before and after "to" as the upper and lower limits. In the present invention, when multiple numerical ranges are set in stages for content, etc., the upper and lower limits forming the numerical range are not limited to the specific combination written before and after "to" as a specific numerical range, and the upper and lower limits forming each numerical range can be combined as appropriate.

[Flame-retardant polyolefin resin composition]
The flame-retardant polyolefin resin composition of the present invention contains a resin and a flame retardant. Furthermore, the resin satisfies the following compositions [A], [B], and [C]. By combining a resin and a flame retardant that satisfy these specific compositions [A] to [C], it is possible to form a molded product, particularly a coating layer for wiring materials, that exhibits higher abrasion resistance than conventional molded products while suppressing excessive shrinkage and maintaining excellent flame retardancy. Therefore, for example, by using the flame-retardant polyolefin resin composition of the present invention as a material for forming a coating layer, it is possible to realize (produce) a wiring material that exhibits high abrasion resistance while also having excellent flame retardancy and dimensional stability.

Composition [A]: High density polyethylene polymerized using a metallocene catalyst is added to the resin in an amount of 15 to 70%.
Composition [B] contained in a content of mass %: ethylene vinyl acetate copolymer, ethylene copolymer having an acid copolymerization component,
These acid-modified copolymers, ethylene rubber, and styrene elastomer resins
Composition [C] whose total content in the fat is 10 mass% or less: A polymer having a density of less than 0.90 g/ ^cm3 is not required.

Thus, the flame-retardant polyolefin resin composition of the present invention is suitable as a material for forming a coating layer for wiring materials, for example, an insulated electric wire for an automobile, particularly as a material for forming a thin-walled coating layer for a thin-walled electric wire.

The flame-retardant polyolefin resin composition of the present invention may be a non-crosslinked flame-retardant polyolefin resin composition (also referred to as a flame-retardant non-crosslinked polyolefin resin composition) or a crosslinked flame-retardant polyolefin resin composition (also referred to as a flame-retardant crosslinked polyolefin resin composition), and the necessity of crosslinking is appropriately selected depending on the application and required properties. When used as a material for forming a coating layer of a wiring material, a flame-retardant crosslinked polyolefin resin composition is preferred.
Among the flame-retardant polyolefin resin compositions of the present invention, compositions intended to be crosslinked are referred to as crosslinkable flame-retardant polyolefin resin compositions, and are distinguished from the above-mentioned flame-retardant non-crosslinked polyolefin resin compositions that are not intended to be crosslinked.
In the present invention, unless otherwise specified, the term "flame-retardant polyolefin resin composition" is used as a general term including flame-retardant non-crosslinked polyolefin resin compositions, flame-retardant crosslinked polyolefin resin compositions, and crosslinkable flame-retardant polyolefin resin compositions.

The flame-retardant crosslinked polyolefin resin composition (crosslinked product) of the present invention is prepared by subjecting a crosslinkable flame-retardant polyolefin resin composition to a crosslinking reaction. The flame-retardant crosslinked polyolefin resin composition has a crosslinked structure in which at least the resin (constituting (co)polymers, etc.) is crosslinked directly or via a crosslinking agent, etc., and exhibits a high level of suppression of excessive shrinkage, flame retardancy, and abrasion resistance in a well-balanced manner. The crosslinked structure varies depending on the type of crosslinking reaction (crosslinking method), and cannot be clearly and unambiguously defined.
The crosslinking method (crosslinking reaction) is not particularly limited, and any known resin crosslinking method, such as a crosslinking method using polyolefins, can be used. Examples include an electron beam crosslinking method, an organic peroxide crosslinking method, and a silane crosslinking method. The silane crosslinking method is preferred because it does not require special equipment and allows for a crosslinking reaction treatment with high productivity.
In the present invention, the organic peroxide crosslinking method is a chemical crosslinking method in which a crosslinkable flame-retardant polyolefin resin composition containing an organic peroxide as a crosslinking catalyst is heated to a temperature equal to or higher than the decomposition temperature of the organic peroxide, and the resins are directly crosslinked by radicals generated from the organic peroxide. The silane crosslinking method, which is a chemical crosslinking method different from the organic peroxide crosslinking method, is a method in which a crosslinkable flame-retardant polyolefin resin composition containing a silane coupling agent as a crosslinking agent, which has undergone a grafting reaction, and preferably further contains a silanol condensation catalyst, is brought into contact with moisture, and the silane coupling agent undergoes a silanol condensation reaction, thereby crosslinking the resin via the silane coupling agent.

The components and their contents used in the present invention will be described below.
<Resin>
The resin includes the polymers (including resins, elastomers, and rubbers) defined in the above compositions [A] to [C], as well as other polymers.
In the present invention, the density of the polymer is a value measured in accordance with "Method A (water displacement method)" specified in Japanese Industrial Standards (JIS) K 7112 (1999).
In the present invention, the polymer includes homopolymers and copolymers, and generally means a resin thereof, but also includes an elastomer and a rubber thereof.

(High density polyethylene polymerized using a metallocene catalyst: m-HDPE)
The flame-retardant polyolefin resin composition of the present invention contains a specific amount of high-density polyethylene polymerized using a metallocene catalyst (hereinafter, sometimes referred to as metallocene high-density polyethylene (m-HDPE)). This allows the flame-retardant polyolefin resin composition of the present invention to exhibit high abrasion resistance.
Metallocene high-density polyethylene is the same as ordinary high-density polyethylene, for example, high-density polyethylene obtained by a low-pressure process or a medium-pressure process using a Ziegler-Natta catalyst, a titanium catalyst, or the like, except that it is a polymer obtained by polymerizing at least ethylene using a metallocene catalyst.
The m-HDPE used in the present invention is polyethylene having a density of 0.940 g/cm or ^more , and is also called crystalline hard polyethylene. This m-HDPE includes homopolymers of ethylene (homopolyethylene) and copolymers of ethylene with α-olefins other than ethylene. The α-olefin is not particularly limited, but examples include α-olefins having 3 to 12 carbon atoms. The density and molecular weight of the m-HDPE are not particularly limited and may be set appropriately.
m-HDPE can be produced by polymerizing ethylene or the like using a metallocene catalyst, and commercially available products can also be used. For example, the polymerization method for linear low-density polyethylene (LLDPE) using a metallocene catalyst can be used as a reference. Examples of commercially available products include Evolue (registered trademark)-H SP5505 (trade name, manufactured by Prime Polymer Co., Ltd.).
The flame-retardant polyolefin resin composition may contain one or more types of m-HDPE.

(Ethylene vinyl acetate copolymer: EVA)
The ethylene-vinyl acetate copolymer may be any copolymer of ethylene and vinyl acetate, and may be an alternating copolymer formed by alternating polymerization of ethylene and vinyl acetate components, a block copolymer formed by combining a polymerized block of an ethylene component and a polymerized block of a vinyl acetate component, or a random copolymer formed by randomly polymerizing an ethylene component and a vinyl acetate component. When the flame-retardant polyolefin resin composition of the present invention contains an ethylene-vinyl acetate copolymer, the flame retardancy of the composition is improved. The vinyl acetate content (also referred to as the VA content) of the ethylene-vinyl acetate copolymer is not particularly limited and may be appropriately determined taking into consideration the flame retardancy, etc. Furthermore, the density and molecular weight of the ethylene-vinyl acetate copolymer are also not particularly limited and may be appropriately determined.
The ethylene vinyl acetate copolymer contained in the flame-retardant polyolefin resin composition may be one type or two or more types.

(Ethylene copolymer having an acid copolymerization component)
The acid copolymerization component constituting the ethylene copolymer having an acid copolymerization component is not particularly limited, but examples thereof include carboxylic acid compounds such as (meth)acrylic acid, and (meth)acrylic acid alkyl ester compounds. Here, the alkyl group of the (meth)acrylate preferably has 1 to 12 carbon atoms. Examples of polyolefin copolymers having an acid copolymerization component include ethylene-(meth)acrylic acid copolymers and ethylene-(meth)alkyl(meth)acrylate copolymers. More specifically, examples include the copolymers described in paragraph [0017] of Patent Document 1. For information on ethylene copolymers having an acid copolymerization component, reference can be made to the disclosure of Patent Document 1, which is incorporated herein by reference. Note that, in the present invention, the ethylene copolymer having an acid copolymerization component does not include the ethylene-vinyl acetate copolymer.
The flame-retardant polyolefin resin composition may contain one or more types of ethylene copolymers having an acid copolymerization component.

(Acid-modified copolymer)
Acid-modified copolymers include acid-modified copolymers of the above-mentioned ethylene-vinyl acetate copolymer and acid-modified copolymers of the above-mentioned ethylene copolymer having an acid copolymerization component. Specific examples include polymers obtained by modifying the above-mentioned ethylene-vinyl acetate copolymer or the above-mentioned ethylene copolymer having an acid copolymerization component with an unsaturated carboxylic acid compound (also simply referred to as unsaturated carboxylic acid) or its anhydride. Such acid-modified copolymers have unsaturated carboxylic acid-derived groups, typically as side chains (pendant chains, graft chains, etc.), resulting from the reaction of the unsaturated group of the unsaturated carboxylic acid with the above-mentioned copolymer. The amount of modification with the unsaturated carboxylic acid in the acid-modified polyolefin polymer is not particularly limited, but is preferably 0.1 to 2.0 mass% and more preferably 0.2 to 1.0 mass% relative to the copolymer (before modification). The acid-modified copolymer may be synthesized as needed, or a commercially available product may be used. When synthesizing the acid-modified copolymer, the copolymer and the above-mentioned unsaturated carboxylic acid are typically mixed and heated in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide, thereby modifying the copolymer (reacting with the unsaturated carboxylic acid).
The unsaturated carboxylic acid (including anhydride) is not particularly limited, and suitable examples include carboxylic acids having an unsaturated bond capable of reacting with the copolymer (e.g., radical addition reaction). The unsaturated carboxylic acid may have one or more carboxy groups. Specific examples of preferred unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, itaconic acid, and fumaric acid, as well as metal salts or organic salts thereof, and unsaturated carboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, and fumaric anhydride. The unsaturated carboxylic acid used to modify the copolymer may be one or more types. Maleic anhydride or acrylic acid is preferred as the unsaturated carboxylic acid.
The flame-retardant polyolefin resin composition may contain one or more types of acid-modified copolymers.

(ethylene rubber)
The ethylene rubber is not particularly limited as long as it is a rubber (including elastomers) made of a copolymer obtained by copolymerizing a compound having an ethylenically unsaturated bond, and known rubbers can be used. Preferred examples of the ethylene rubber include a binary copolymer rubber of ethylene and an α-olefin, and a ternary copolymer rubber of ethylene, an α-olefin, and a diene. The diene compound constituting the terpolymer may be a conjugated diene compound or a non-conjugated diene compound, but a non-conjugated diene compound is preferred.
As the α-olefin, an α-olefin having 3 to 12 carbon atoms is preferred. As the conjugated diene compound, for example, butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc. are mentioned, and butadiene compounds are preferred. As specific examples of the non-conjugated diene compound, for example, dicyclopentadiene (DCPD), ethylidene norbornene (ENB), 1,4-hexadiene, etc. are mentioned.
As the binary copolymer rubber, ethylene-propylene rubber (EPM) is preferred, and as the ternary copolymer rubber, ethylene-propylene-diene rubber (EPDM) is preferred.
The flame-retardant polyolefin resin composition may contain one or more types of ethylene rubber.

(styrene elastomer)
Styrenic elastomers refer to polymers containing components derived from aromatic vinyl compounds within the molecule. Examples of such styrene elastomers include block copolymers and random copolymers of conjugated diene compounds and aromatic vinyl compounds, as well as hydrogenated products thereof. Examples of such styrene elastomers include styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-isoprene-styrene block copolymers (SIS), hydrogenated SIS, styrene-butadiene-styrene block copolymers (SBS), hydrogenated SBS, styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-butadiene rubber (SBR), and hydrogenated styrene-butadiene rubber (HSBR).
The flame-retardant polyolefin resin composition may contain one or more types of styrene-based elastomer.

(Polymers with a density of less than 0.90 g/ ^cm3 )
The flame-retardant polyolefin resin composition of the present invention does not necessarily require (does not contain) a polymer having a density of less than 0.90 g/ ^cm3 as a resin. In the present invention, "not requiring a polymer" includes both an embodiment in which no polymer is contained and an embodiment in which a polymer may be contained within a range that does not impair the effects of the present invention. The range in which the effects of the present invention are not impaired is not uniquely determined depending on the composition of the flame-retardant polyolefin resin composition, but is, for example, 1 mass% or less relative to 100 mass% of the resin.
The polymer having a density of less than 0.90 g/ ^cm3 is not particularly limited, but examples thereof include ultra-low density polyethylene (VLDPE, ULDPE) that satisfies the above density, and polyolefin elastomers that satisfy the above density (for example, CAS No. 25087-34-7).
When the flame-retardant polyolefin resin composition contains a polymer having a density of less than 0.90 g/cm ³ , the polymer may be one type or two or more types.

(Other polymers)
The flame-retardant polyolefin resin composition of the present invention may contain a polymer other than the above polymers. Examples of such a polymer include polyethylene other than m-HDPE and having a density of 0.90 g/cm or ^more (e.g., high-density polyethylene, low-density polyethylene (LDPE), ultra-high-molecular-weight polyethylene (UHMW-PE), linear low-density polyethylene (LLDPE) described below), polypropylene, halogenated resins, and acid-modified polymers thereof.
When the flame-retardant polyolefin resin composition contains other polymers, the polymers may be one kind or two or more kinds.

(High density polyethylene: HDPE)
High-density polyethylene as another polymer is a (co)polymer obtained by polymerizing ethylene or the like without using a metallocene catalyst, and examples thereof include (ordinary) high-density polyethylene obtained by a low-pressure process or a medium-pressure process using a Ziegler-Natta catalyst, a titanium catalyst, or the like.
The flame-retardant polyolefin resin composition may contain one or more types of high-density polyethylene.

(Polypropylene: PP)
The polypropylene may be any polymer (composition) containing a propylene constituent as the main component, and includes propylene homopolymers (homopolypropylene: h-PP), random propylene (also referred to as ethylene-propylene random copolymer, r-PP), block propylene (also referred to as ethylene-propylene block copolymer, b-PP), etc. The ethylene-propylene random copolymer refers to a copolymer containing an ethylene component of approximately 1 to 10% by mass, in which the ethylene component is randomly incorporated into the propylene chain. Here, the ethylene component content is a value measured in accordance with the method described in ASTM D3900. The ethylene-propylene block copolymer refers to a copolymer containing an ethylene or ethylene-propylene rubber (EPR) component of approximately 5 to 20% by mass, in which the ethylene or EPR component is independently present within the propylene component, forming a sea-island structure. When the flame-retardant polyolefin resin composition of the present invention contains polypropylene, homopolypropylene and block polypropylene are preferred from the viewpoint of abrasion resistance.
The flame-retardant polyolefin resin composition may contain one or more types of polypropylene.

As the other polymers, high-density polyethylene, low-density polyethylene or linear low-density polyethylene, and polypropylene are preferred, and high-density polyethylene, linear low-density polyethylene, and polypropylene are more preferred, in that they can achieve a high level of both shrinkage and abrasion resistance, which are in a trade-off relationship.
When two or more types of polymers are contained as the other polymers, it is preferable that the polymer contains two types of polymers, namely, linear low-density polyethylene and polypropylene (particularly homopolypropylene), or three types of polymers including these two types and high-density polyethylene.
As the other polymer, ultra-low density polyethylene having a density of 0.90 g/cm ³ or more may be contained, but it is preferable not to contain it (it is not essential) from the viewpoint of abrasion resistance.

(organic mineral oil)
In order to achieve high abrasion resistance, the flame-retardant polyolefin resin composition of the present invention preferably does not require (does not contain) organic mineral oil. The term "not requiring" is as described above. Examples of organic mineral oils include those typically used in resin compositions, such as paraffinic oils and naphthenic oils. While organic mineral oils may include those (polymers) with a density of less than 0.90 g/cm ³ , in the present invention, those with a density of 0.90 g/cm ³ or more are also classified as organic mineral oils.

(Resin Composition)
The resins contained in the flame-retardant polyolefin resin composition of the present invention are set to a proportion that totals 100 mass % and satisfy the following compositions [A] to [C]. When the resin satisfies compositions [A] to [C], a molded article can be formed that exhibits high abrasion resistance while maintaining excellent flame retardancy and suppressing excessive shrinkage. Therefore, by using the resin as a material for forming a coating layer for wiring material, the coating layer can be made thinner (the diameter of the wiring material can be reduced), and the attachment of a protective member after the wiring material is installed is not necessary.

Composition [A]: m-HDPE contained in a resin at a content of 15 to 70 mass %. Composition [B]: ethylene vinyl acetate copolymer, ethylene copolymer having an acid copolymerization component,
These acid-modified copolymers, ethylene rubber, and styrene elastomer resins
Composition [C] whose total content in the fat is 10 mass% or less: A polymer having a density of less than 0.90 g/ ^cm3 is not required.

(Composition [A])
The resin (the flame-retardant polyolefin resin composition of the present invention) contains 15 to 70% by mass of m-HDPE based on 100% by mass of the resin. This, combined with the effects of compositions [B] and [C], allows for a high level of both excessive shrinkage suppression and abrasion resistance, which are in a trade-off relationship, to be achieved while maintaining excellent flame retardancy. The m-HDPE content is preferably 25 to 70% by mass, and more preferably 30 to 60% by mass, in order to highly improve abrasion resistance and achieve a well-balanced high level of excessive shrinkage suppression, flame retardancy, and abrasion resistance.

(Composition [B])
The resin contains ethylene-vinyl acetate copolymer, ethylene copolymer having an acid copolymerization component, acid-modified copolymer thereof, ethylene rubber, and styrene-based elastomer in a total content of 10% by mass or less per 100% by mass of resin. This, combined with the effects of composition [A] and composition [C], allows for a high level of both excessive shrinkage suppression and abrasion resistance, which are in a trade-off relationship, while maintaining excellent flame retardancy. The total content is preferably 5% by mass or less (0 to 5% by mass), in order to achieve a good balance between excessive shrinkage suppression, flame retardancy, and abrasion resistance at a high level.

The composition [B] may satisfy the above-mentioned composition, but it is also preferable that the composition [B] satisfies the following composition.
The content of the ethylene-vinyl acetate copolymer in 100% by mass of the resin is determined appropriately taking into consideration the above-mentioned composition [B]. For example, from the viewpoints of flame retardancy, abrasion resistance, etc., it is preferably 10% by mass or less, and more preferably 0 to 5% by mass.
The content of the ethylene copolymer having an acid copolymerization component in 100% by mass of the resin is determined appropriately taking into consideration the above-mentioned composition [B]. For example, from the viewpoint of abrasion resistance, etc., it is preferably 10% by mass or less, and more preferably 0 to 5% by mass.
The content of the acid-modified copolymer in 100% by mass of the resin is determined appropriately taking into consideration the above-mentioned composition [B]. For example, from the viewpoints of abrasion resistance and flame retardancy, it is preferably 10% by mass or less, and more preferably 0 to 5% by mass.
The content of ethylene rubber in 100% by mass of the resin is determined appropriately taking into consideration the above-mentioned composition [B]. For example, from the viewpoint of abrasion resistance, etc., it is preferably 10% by mass or less, and more preferably 0 to 5% by mass.
The content of the styrene-based elastomer in 100% by mass of the resin is determined appropriately taking into consideration the above-mentioned composition [B]. For example, from the viewpoint of abrasion resistance, etc., it is preferably 10% by mass or less, and more preferably 0 to 5% by mass.

(Composition [C])
The resin does not necessarily include a polymer having a density of less than 0.90 g/ ^cm3 . This, combined with the effects of composition [A] and composition [B], can highly improve abrasion resistance. The meaning of "the resin does not necessarily include this polymer" is as described above.

(Composition of other polymers)
The resin contained in the flame-retardant polyolefin resin composition of the present invention may be any resin as long as it satisfies the above-mentioned compositions [A] to [C]. However, when the resin contains the above-mentioned other polymers, the content of the other polymers in 100 mass% of the resin is appropriately determined taking into consideration the above-mentioned compositions [A] to [C].
The total content of the other polymers is, for example, preferably from 20 to 85% by mass, more preferably from 30 to 80% by mass, and even more preferably from 40 to 60% by mass.

When the resin contains, as the other polymer, a polyethylene other than m-HDPE and having a density of 0.90 g/cm or ^more , the total content of this polyethylene in 100% by mass of the resin is appropriately determined in consideration of the above-mentioned total content, and is, for example, preferably 10 to 60% by mass, and more preferably 15 to 50% by mass.
The content of LLDPE among polyethylenes is determined as appropriate taking into consideration the total content, and is preferably 10 to 50% by mass, and more preferably 15 to 40% by mass, from the viewpoints of compound manufacturability, low-temperature flexibility, etc. The content of high-density polyethylene in 100% by mass of resin is determined as appropriate taking into consideration the total content, and is preferably 0 to 40% by mass, and more preferably 0 to 20% by mass, from the viewpoints of further enhancing abrasion resistance without impairing flame retardancy and suppressing excessive shrinkage.

When the resin contains polypropylene as another polymer, the total content of polypropylene in 100% by mass of the resin is determined appropriately taking into account the above total content. For example, in terms of suppressing excessive shrinkage, it is preferably 60% by mass or less, more preferably 0 to 50% by mass, and even more preferably 20 to 50% by mass. The total polypropylene content is the sum (total amount) of the homopolypropylene content, random propylene content, and block propylene content.
The content of each of the homopolypropylene, random propylene, and block propylene is appropriately determined in consideration of the total content of polypropylene. For example, the content of each of the homopolypropylene and random propylene is preferably 0 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 5 to 20% by mass.

<Flame retardants>
The flame-retardant polyolefin resin composition of the present invention contains a flame retardant, which allows the composition to effectively exhibit a high flame-retardant effect.
The flame retardant is not particularly limited, and examples thereof include those typically used in resin compositions, such as halogen-based flame retardants, phosphorus-based flame retardants, metal hydrates, etc. Among these, halogen-based flame retardants and metal hydrates are preferred in terms of exhibiting excellent flame retardancy.
The flame retardant contained in the flame retardant polyolefin resin composition may be one type or two or more types.

(Halogen-based flame retardant)
The halogen-based flame retardant is not particularly limited as long as it is a flame retardant having a halogen atom, but preferred examples include chlorine-based flame retardants containing chlorine atoms and bromine-based flame retardants containing bromine atoms, and bromine-based flame retardants that have a high flame retardancy enhancing effect due to the flame retardant auxiliary described below are preferred.
The brominated flame retardant is not particularly limited, and any of those typically used in flame-retardant compositions can be used without particular limitation. Examples include brominated ethylene bisphthalimide compounds, bisbrominated phenyl terephthalamide compounds, brominated bisphenols (e.g., tetrabromobisphenol A) compounds, 1,2-bis(bromophenyl)ethane compounds, polybromodiphenyl ethers (e.g., decabromodiphenyl ether) compounds, polybromobiphenyls (e.g., tribromophenyl) compounds, hexabromocyclododecane, brominated polystyrene, and hexabromobenzene. Other examples include those described in paragraph [0020] of Patent Document 1. For details of brominated flame retardants, please refer to the contents of Patent Document 1 as appropriate, and the contents thereof are incorporated herein by reference.
The chlorine-based flame retardant is not particularly limited, and any chlorine-based flame retardant commonly used in flame-retardant compositions can be used without particular limitation, such as decachlorododecahydrodimethanocyclooctene compounds and 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).

(phosphorus-based flame retardant)
The phosphorus-based flame retardant is not particularly limited as long as it is a flame retardant having a phosphorus atom in the molecule, and known flame retardants can be used. Examples include phosphorus oxides such as red phosphorus, phosphorus trioxide, phosphorus tetroxide, and phosphorus pentoxide, phosphoric acid compounds such as phosphoric acid, phosphorous acid, hypophosphorous acid, metaphosphoric acid, pyrophosphoric acid, and polyphosphoric acid, ammonium phosphates such as monoammonium phosphate, diammonium phosphate, and ammonium polyphosphate, melamine phosphate salts such as melamine monophosphate, melamine diphosphate, and melamine polyphosphate, metal phosphates such as lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate, and magnesium phosphate, aliphatic phosphate ester compounds such as trimethyl phosphate and triethyl phosphate, and aromatic phosphate ester compounds such as triphenyl phosphate and tricresyl phosphate.
In the present invention, when a phosphorus-based flame retardant contains a halogen atom in the molecule, it is classified as a halogen-based flame retardant rather than a phosphorus-based flame retardant.

(metal hydrate)
The metal hydrate refers to a compound having a hydroxyl group or crystal water that functions as a flame retardant. The metal hydrate is not particularly limited, and examples thereof include metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and boehmite, as well as calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whisker, hydrated aluminum silicate, hydrated magnesium silicate, basic magnesium carbonate, hydrotalcite, and talc.
As the metal hydrate, a metal hydroxide is preferred, and magnesium hydroxide is more preferred.

The flame retardant may be surface-treated with a silane coupling agent or the like. Examples include Kisuma 5L and Kisuma 5P (both trade names, magnesium hydroxide, manufactured by Kyowa Chemical Industry Co., Ltd.). The amount of the silane coupling agent used to surface treat the flame retardant is not particularly limited, but is preferably 3 mass % or less.
The flame retardant is usually contained as a powder or particles. The average particle size is not particularly limited, but is preferably 0.2 to 10 μm. If the average particle size is within the above range, secondary aggregation can be suppressed. The average particle size is determined by dispersing the flame retardant in alcohol or water and using an optical particle size analyzer such as a laser diffraction/scattering particle size distribution analyzer.

<Flame retardant synergist>
In the present invention, when a halogen-based flame retardant is contained as the flame retardant, it is preferable to further contain a flame retardant aid for the halogen-based flame retardant. This flame retardant aid is used because, when used in combination with the halogen-based flame retardant, it exerts a synergistic effect that exceeds the flame retardant effect exhibited by the halogen-based flame retardant alone. Such a flame retardant aid can be any of those commonly used in flame-retardant compositions, and is selected appropriately depending on the halogen-based flame retardant. For example, antimony oxide such as antimony trioxide is preferred. Antimony trioxide can react stepwise with the halogen-based flame retardant to exhibit a high flame retardant effect. The flame-retardant polyolefin resin composition may contain one or more flame retardant aids.

<Flame retardant and flame retardant synergist content>
The flame-retardant polyolefin resin composition of the present invention preferably contains 15 to 160 parts by mass of flame retardant per 100 parts by mass of resin (total content). This allows the composition to exhibit high flame retardancy and, in combination with the resin composition, to exhibit remarkable abrasion resistance. The total content of the flame retardant is preferably 25 to 120 parts by mass, more preferably 30 to 100 parts by mass.
Of the flame retardants, the content of each of the halogen-based flame retardant and the phosphorus-based flame retardant is preferably 0 to 55 parts by mass, more preferably 10 to 50 parts by mass, and even more preferably 15 to 40 parts by mass, relative to 100 parts by mass of the resin.
The content of the metal hydrate among the flame retardants is, for example, preferably 0 to 150 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 20 to 75 parts by mass, relative to 100 parts by mass of the resin, in order to achieve a good balance between flame retardancy and abrasion resistance.

When the flame-retardant polyolefin resin composition of the present invention contains a halogen-based flame retardant and a flame-retardant aid, the total content of the halogen-based flame retardant and the flame-retardant aid is not particularly limited and is appropriately determined as the sum of the above content of the halogen-based flame retardant and the below content of the flame-retardant aid. The content of the flame-retardant aid is preferably 0 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 5 to 20 parts by mass, per 100 parts by mass of the resin, in order to enhance the flame-retardant effect of the halogen-based flame retardant and achieve a good balance between flame retardancy and abrasion resistance.
The mass ratio of the content of the halogenated flame retardant to the total content of the halogenated flame retardant and the flame retardant synergist [content of halogenated flame retardant/total content] is usually determined appropriately taking into consideration the flame retardancy enhancing action of the halogenated flame retardant and the flame retardant synergist (e.g., the above-mentioned reaction). The mass ratio [content of halogenated flame retardant/total content] is, for example, preferably 1 to 3, and more preferably 1.5 to 2.5.

<Other ingredients>
In addition to the resin, flame retardant, and flame retardant aid described above, the flame-retardant polyolefin resin composition of the present invention may contain various components (referred to as "other components"), such as additives commonly used in resin compositions, within the scope of the present invention. Examples of other components include inorganic fillers (excluding those that act as flame retardants), antioxidants (antioxidants), lubricants, crosslinking agents, crosslinking aids, etc.
The crosslinkable flame-retardant polyolefin resin composition preferably further contains a crosslinking agent, a crosslinking aid, a crosslinking catalyst, a crosslinking accelerator, etc., depending on the type of crosslinking reaction to be applied.
The flame-retardant polyolefin resin composition may contain one or more of each of the other components.

(inorganic filler)
As the inorganic filler, any filler that is usually used as a filler in a resin composition can be used without any particular limitation.
Examples of inorganic fillers include boron nitride, silica (crystalline silica, amorphous silica, etc.), carbon, clay (calcined clay), zinc oxide, tin oxide, titanium oxide, silicone compounds, quartz, zinc borate, white carbon, zinc borate, zinc hydroxystannate, and zinc stannate.

The inorganic filler may be surface-treated with a silane coupling agent, etc. The amount of the silane coupling agent used to treat the surface of the inorganic filler is not particularly limited, but is preferably, for example, 3 mass % or less.
The inorganic filler is usually contained as a powder or particles. The average particle size is not particularly limited, but is preferably 0.2 to 10 μm in order to suppress secondary aggregation. The average particle size of the inorganic filler can be measured in the same manner as for the flame retardant.

The content of inorganic filler in the flame-retardant polyolefin resin composition is not particularly limited and can be determined as appropriate, but it is preferably determined taking into account the content (total amount) of components with melting points exceeding 200°C, as described below. The content of inorganic filler is, for example, preferably 100 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 70 parts by mass or less.

(anti-aging agent)
The antioxidant (antioxidant) is not particularly limited, but examples thereof include amine antioxidants, phenol antioxidants, and sulfur antioxidants, with phenol antioxidants being preferred.
The content of the antioxidant in the flame-retardant polyolefin resin composition is set within a range that does not impair the effects of the present invention, and can be, for example, 0.5 to 15 parts by mass per 100 parts by mass of the resin.

(lubricant)
The lubricant is not particularly limited, but examples thereof include silicone compounds, fatty acid metal salts, and fatty acid amides, with silicone compounds being preferred.
The content of the lubricant in the flame-retardant polyolefin resin composition 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 resin.

(Components with melting points exceeding 200°C)
The flame-retardant polyolefin resin composition of the present invention preferably contains 160 parts by mass or less of components having a melting point exceeding 200°C. Examples of components having a melting point exceeding 200°C include components (compounds) other than the resins described above that have a melting point exceeding 200°C. Specifically, these components are those that can exist in a solid state (particles, powder) during melt-mixing to prepare the flame-retardant polyolefin resin composition (without changing the component itself, specifically, without melting, decomposing (thermal decomposition), or deteriorating (removal of hydration water, etc.)). The melting point may be above 200°C, but is preferably at least the melt-mixing temperature described below, and can be, for example, at least 250°C or at least 270°C.
Such components are not particularly limited, but examples thereof include inorganic compounds and organic compounds, more specifically the inorganic fillers described above, and further include flame retardants (e.g., halogen-based flame retardants, phosphorus-based flame retardants, metal hydrates, etc.), flame retardant assistants, etc.
When the total content of components having a melting point exceeding 200°C is 160 parts by mass or less relative to 100 parts by mass of the resin, abrasion resistance can be further improved without impairing the excellent suppression of excessive shrinkage and flame retardancy. The total content of the above components is, for example, preferably 120 parts by mass or less relative to 100 parts by mass of the resin, more preferably 30 to 100 parts by mass, and even more preferably 45 to 100 parts by mass.
In the present invention, the melting point is a value measured in an environment of normal pressure (1 atm) in accordance with the method specified in JIS K 0064.

(Silane coupling agent)
In the present invention, when the crosslinkable flame-retardant polyolefin resin composition is crosslinked by an electron beam crosslinking method or a silane crosslinking method, the crosslinkable flame-retardant polyolefin resin composition preferably contains one or more silane coupling agents as a crosslinking agent. The silane coupling agent has a grafting reaction site (group or atom) that can undergo a grafting reaction to the resin in the presence of radicals generated by electron beam irradiation or decomposition of an organic peroxide. The silane coupling agent used in the silane crosslinking method further has a hydrolyzable group capable of silanol condensation, and this hydrolyzable group preferably can react with the above-mentioned metal hydrate or inorganic filler. Preferred examples of the grafting reaction site of the silane coupling agent include ethylenically unsaturated groups, and preferred examples of the hydrolyzable group include alkoxysilyl groups.

The silane coupling agent having the above-mentioned moiety is not particularly limited, and can be the silane coupling agent that has been used in conventional electron beam crosslinking method or silane crosslinking method.Specifically, can be vinyl alkoxysilane such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tributoxysilane, vinyl dimethoxyethoxysilane, vinyl dimethoxybutoxysilane, vinyl diethoxybutoxysilane, allyl trimethoxysilane, allyl triethoxysilane, vinyl triacetoxysilane, etc., methacryloxypropyl trimethoxysilane, methacryloxypropyl triethoxysilane, methacryloxypropyl methyl dimethoxysilane, etc. (meth) acryloxy alkoxysilane etc.
The content of the silane coupling agent in the flame-retardant polyolefin resin composition 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 resin.

(organic peroxide)
When the crosslinkable flame-retardant polyolefin resin composition is crosslinked by an organic peroxide crosslinking method or a silane crosslinking method, the crosslinkable flame-retardant polyolefin resin composition preferably contains one or more organic peroxides. The organic peroxide generates radicals at least by thermal decomposition and acts as a catalyst to induce a crosslinking reaction between resins or a grafting reaction of a silane coupling agent to a resin by a radical reaction.
The organic peroxide is not particularly limited, and those used in radical polymerization reactions or conventional silane crosslinking methods can be used without any particular limitation. Preferred examples of such organic peroxides include benzoyl peroxide, dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, and 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3.
The content of the organic peroxide in the flame-retardant polyolefin resin composition is not particularly limited and can be determined appropriately depending on the crosslinking method. For example, it 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 resin.

(Silanol condensation catalyst)
When a crosslinkable flame-retardant polyolefin resin composition is crosslinked by a silane crosslinking method, the crosslinkable flame-retardant polyolefin resin composition preferably contains one or more silanol condensation catalysts. The silanol condensation catalysts function to promote the condensation reaction of the silane coupling agent grafted onto the resin in the presence of moisture. This condensation reaction crosslinks the resin via the silane coupling agent and, optionally, an inorganic filler.
Examples of silanol condensation catalysts include organotin compounds, metal soaps, platinum compounds, etc. Organotin compounds are preferred, such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctiate, and dibutyltin diacetate.
The content of the silanol condensation catalyst in the crosslinkable flame-retardant polyolefin resin composition is not particularly limited, but 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 resin.

(Crosslinking aid)
When the crosslinkable flame-retardant polyolefin resin composition is crosslinked by an electron beam crosslinking method, the crosslinkable flame-retardant polyolefin resin composition may contain one or more crosslinking aids. As the crosslinking aid, any crosslinking aid commonly used in the electron beam crosslinking method can be used without any particular limitation. Examples of crosslinking aids include polyfunctional compounds, such as (meth)acrylate compounds such as polypropylene glycol diacrylate and trimethylolpropane triacrylate, allyl compounds such as triallyl cyanurate, maleimide compounds, and divinyl compounds.
The content of the crosslinking aid in the crosslinkable flame-retardant polyolefin resin composition is appropriately set, and can be set, for example, from 1 to 8 parts by mass per 100 parts by mass of the resin.

(Preparation of flame-retardant non-crosslinked polyolefin resin composition and crosslinkable flame-retardant polyolefin resin composition)
Both of the above compositions can be prepared by melt mixing the above ingredients.
The kneading method is not particularly limited as long as it is a method commonly used in preparing rubber or resin compositions. For example, mixing can be performed using various mixing devices such as a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, and various kneaders. The kneading conditions, such as the kneading temperature and kneading time, are not particularly limited and can be appropriately set within a temperature range equal to or higher than the melting temperature of the resin. The kneading temperature is preferably set to, for example, the melt mixing conditions of step (1) described below. The order in which the components are mixed is not particularly limited, and the above components can be mixed all at once (melt) or sequentially in an appropriate order. In this way, a non-crosslinked or crosslinked (uncrosslinked) flame-retardant polyolefin resin composition in which the components are dispersed (mixed) can be obtained.
Regardless of the above preparation method, the crosslinkable flame-retardant polyolefin resin composition to be applied to the silane crosslinking method is preferably prepared by the step (1) described below.

Both of the above compositions can also be molded into appropriate shapes. When preparing the crosslinkable flame-retardant polyolefin resin composition, 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 of the molded product. For example, molding methods include extrusion molding using an extruder, extrusion molding using an injection molding machine, and molding using other molding machines. Extrusion molding is preferred when forming a coating layer for wiring material because of its productivity and the ability to be co-extruded with the conductor.

(Preparation of Flame-Retardant Crosslinked Polyolefin Resin Composition)
The flame-retardant crosslinked polyolefin resin composition (crosslinked product) of the present invention can be prepared by subjecting the above-mentioned crosslinkable flame-retardant polyolefin resin composition to the above-mentioned crosslinking reaction treatment. The flame-retardant crosslinked polyolefin resin composition may be crosslinked in an unmolded state, but is preferably molded by, for example, the above-mentioned molding method and then crosslinked to form a crosslinked molded product.

When crosslinking a crosslinkable flame-retardant polyolefin resin composition using an electron beam crosslinking method, the crosslinkable flame-retardant polyolefin resin composition prepared as described above is preferably molded into an appropriate shape and then irradiated with electron beams. The electron beam irradiation conditions are not particularly limited as long as they are capable of crosslinking the crosslinkable flame-retardant polyolefin resin composition (resin). 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.

When a crosslinkable flame-retardant polyolefin resin composition is subjected to a crosslinking reaction using an organic peroxide crosslinking method, the crosslinkable flame-retardant polyolefin resin composition prepared as described above is preferably molded into an appropriate shape and then heated to a temperature equal to or higher than the decomposition temperature of the organic peroxide. The heating conditions are not particularly limited as long as they are equal to or higher than the decomposition temperature of the organic peroxide contained in the crosslinkable flame-retardant polyolefin resin composition, and the heating time is not particularly limited.

When a crosslinkable flame-retardant polyolefin resin composition is subjected to a crosslinking reaction treatment by a silane crosslinking method, a method is preferred in which the crosslinkable flame-retardant polyolefin resin composition containing a resin grafted with a silane coupling agent is molded, preferably into an appropriate shape, and then brought into contact with moisture.
The method for producing a crosslinked molded article by the silane crosslinking method is preferably a production method comprising the following steps (1), (2) and (3).

Step (1): A resin, a flame retardant, a silane coupling agent, an organic peroxide, and a silanol
The molten mixture (crosslinking agent) is melt-mixed with a condensation catalyst and an appropriate inorganic filler.
Step (2): A step of molding the molten mixture obtained in Step (1) to obtain a molded article; Step (3): A step of contacting the molded article obtained in Step (2) with water to obtain a flame-retardant crosslinked polyolefin resin composition.
A step of obtaining a molded body of the resin composition

When carrying out the above step (1), if all of the resin is melt-mixed in the following step (a), the process includes steps (a) and (c), and if only a part of the resin is melt-mixed in the following step (a), the process includes steps (a), (b), and (c).

Step (a): Mixing all or part of the resin, a flame retardant, a silane coupling agent, and an organic peroxide
The material, optionally an inorganic filler, is melted at a temperature above the decomposition temperature of the organic peroxide.
Step (b): Melt-mixing the remaining resin and the silanol condensation catalyst to prepare a catalyst master batch.
Step (c): A step of preparing a silane master batch and a silanol condensation catalyst or the above catalyst master batch.
A process of melting and mixing

When the remainder of the resin is melt-mixed as a carrier resin in step (b), the resin is melt-mixed in an amount of preferably 80 to 99% by mass, more preferably 94 to 98% by mass in step (a), and in step (b), the resin is melt-mixed in an amount of preferably 1 to 20% by mass, more preferably 2 to 6% by mass.

The content of each component melt-mixed in step (1) is the same as the content in the flame-retardant polyolefin resin composition described above.

The melt mixing in step (1) and step (a) can be carried out by appropriately selecting a method commonly used for rubber, plastics, etc., and examples include mixing using various mixing devices such as a Banbury mixer or various kneaders. The melt mixing temperature is equal to or higher than the decomposition temperature of the organic peroxide, preferably a temperature of the decomposition temperature of the organic peroxide + (1 to 80)°C. Although it is difficult to uniquely determine the melt mixing temperature, for example, 80 to 250°C is preferred, and 100 to 240°C is more preferred. Other conditions can be set as appropriate. In step (a), it is preferable to melt mix the above-mentioned components in the absence of a silanol condensation catalyst (e.g., a ratio of 0.01 parts by mass or less per 100 parts by mass of the resin) to suppress the condensation reaction of the silane coupling agent.
In steps (1) and (a), the order of mixing the components during melt mixing is not particularly limited, and the above components can be melt mixed all at once. Among flame retardants, metal hydrates are preferably premixed with a silane coupling agent before being melt mixed with the resin. Furthermore, when an inorganic filler is used, the silane coupling agent is preferably premixed with the inorganic filler and, optionally, with an organic peroxide before being melt mixed with the resin. This premixing (premixing) can be carried out, for example, at 20 to 35°C, preferably by dry blending. Premixing allows for a well-balanced mixture of silane coupling agents that bond strongly to the metal hydrate or inorganic filler and silane coupling agents that bond weakly to the metal hydrate or inorganic filler. In the premixing method, the resulting mixture, all or part of the resin, and the remaining components are then melt-kneaded, for example, under the melt mixing conditions described above.

The melt mixing in steps (b) and (c) can be carried out in the same manner as in step (a) above. However, in step (c), to avoid a silanol condensation reaction, it is preferable not to maintain the silane MB and silanol condensation catalyst in a mixed state at a high temperature for a long period of time. Prior to melt mixing in step (c), the resins can be mixed (e.g., dry blended) while they are not melted, for example, under the premixing conditions described above.

In step (1), steps (a) to (c) can be carried out simultaneously or successively.
In step (1), a crosslinkable flame-retardant polyolefin resin composition is prepared as a molten mixture.

Next, the resulting molten mixture is molded to obtain a molded product (step (2)). The molding in step (2) can be performed by any molding method and conditions appropriate to the shape of the molded product, as long as the molten mixture can be molded. The molding method is as described above. This step (2) can be performed simultaneously with or consecutively to the above step (c), for example, using an extrusion molding machine.
The resulting molded article of the crosslinkable flame-retardant polyolefin resin composition is brought into contact with water in step (3), whereby the silane coupling agent undergoes a silanol condensation reaction (crosslinking reaction). This step (3) can be carried out by a conventional method, and the crosslinking reaction proceeds simply by leaving the molded article at room temperature, but the molded article can also be brought into active contact with water in order to promote the crosslinking reaction.
In this way, a flame-retardant crosslinked polyolefin resin composition (molded article thereof) containing a resin crosslinked via a silane coupling agent can be prepared.

Regarding the above-mentioned silane crosslinking method, the components other than the resin and flame retardant used (silane coupling agent, organic peroxide, silanol condensation catalyst, etc.), steps (1) to (3) in the above-mentioned manufacturing method, and the reactions in the silane crosslinking method and the form of the resulting condensation-cured product can be appropriately described in, for example, WO 2016/140253 or JP 2017-145370 A, and the contents of these publications are incorporated herein by reference.

<Uses of the flame-retardant polyolefin resin composition>
The flame-retardant polyolefin resin composition of the present invention exhibits the above-mentioned excellent properties and can therefore be suitably used as a material for forming a coating layer of wiring materials, particularly wiring materials. It can also be used for general molded products (sealing materials, packings, etc.). Taking advantage of the above-mentioned excellent properties, it is particularly suitable for applications requiring extremely high abrasion resistance, such as wiring materials, and is therefore suitable as a material for forming a coating layer of automotive insulated wires, particularly (very) thin-walled wires, as described below.

[Wiring material]
A wiring material using a tubular molding formed from the flame-retardant polyolefin resin composition of the present invention as a covering layer will be described below.
The wiring material of the present invention has a coating layer (including an insulating layer, sheath, etc.) formed on the outer surface of a conductor using the flame-retardant polyolefin resin composition of the present invention. This wiring material is prevented from excessive shrinkage of the coating layer, suppresses exposure of the conductor, and has excellent dimensional accuracy. It also exhibits flame retardancy and remarkable abrasion resistance.
The wiring material of the present invention may have at least one coating layer made of the flame-retardant polyolefin resin composition of the present invention on the outer surface of the conductor, and the remaining configuration may be the same as that of a typical wiring material. Examples include an insulated wire having at least one coating layer on the outer surface of the conductor, and a cable in which a sheath serving as a coating layer is formed on the outer surface of such an insulated wire or a bundle of such insulated wires. The coating layer made of the flame-retardant polyolefin resin composition of the present invention may be formed directly on the outer surface of the conductor, or indirectly via another layer such as an adhesive layer. The coating layer may be a single layer or multiple layers. In the case of multiple layers, at least one layer must be formed from the flame-retardant polyolefin resin composition of the present invention. The sheath of the cable may also be formed from the flame-retardant polyolefin resin composition of the present invention.

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 devices, wiring materials installed indoors, and wiring materials installed outdoors. The wiring material of the present invention can preferably be used as insulated wires or cables for vehicles (onboard automobiles, railway vehicles, etc.), communication wires or cables, communication optical fibers or optical cables, or power wires or cables. Among these, it is particularly suitable as insulated wires for vehicles, particularly (ultra) thin-walled wires (e.g., AESSX class).

As the conductor, an appropriate conductor can be used depending on the wiring material. For example, a solid-wire conductor or a stranded-wire conductor (including a stranded wire in which tensile strength fibers are longitudinally aligned or twisted together) can be used as appropriate. For example, the conductor used in an insulated electric wire or the like may be a bare wire, a tin-plated wire, or an enamel-coated wire. Examples of metal materials forming the conductor include soft copper, copper alloy, and aluminum. The outer diameter of the conductor is determined appropriately depending on the application, and can be set similarly to that of ordinary wiring materials used for each application. For example, it can be 0.5 to 4.0 mm. On the other hand, examples of conductors used in optical fiber cores and optical fiber cables include conductors made of quartz glass, various plastics, and the like.
The thickness (wall thickness) of the coating layer is determined appropriately depending on the application, etc., and can be set to the same thickness as that of ordinary wiring materials used for each application. For example, for insulated electric wires, etc., it is usually set to about 0.15 to 10 mm (0.4 mm or less for ultra-thin-wall electric wires), and for optical fiber cables, etc., it is usually set to about 0.1 to 10 mm.

<Method of manufacturing wiring material>
The wiring material of the present invention can be produced by any suitable method, but is preferably produced by disposing the flame-retardant polyolefin resin composition of the present invention on the outer peripheral surface of a conductor and then subjecting it to a suitable crosslinking reaction treatment.
The method for disposing the flame-retardant polyolefin resin composition of the present invention on the outer peripheral surface of a flame-retardant polyolefin resin composition conductor may be any method capable of covering the conductor with the flame-retardant polyolefin resin composition, and may be any suitable molding method, such as the molding method described above. The method for disposing the flame-retardant polyolefin resin composition of the present invention on the outer peripheral surface of a conductor (disposing the flame-retardant polyolefin resin composition) can also be carried out as a series of steps (all at once) using an extrusion molding machine, consecutively to the method for preparing the flame-retardant polyolefin resin composition of the present invention (preparing the flame-retardant polyolefin resin composition in the extrusion molding machine).
When the flame-retardant polyolefin resin composition of the present invention is a crosslinkable flame-retardant polyolefin resin composition, the crosslinkable flame-retardant polyolefin resin composition disposed on the outer peripheral surface of the conductor is then subjected to a crosslinking reaction treatment. This crosslinking reaction treatment can be carried out by any method or under any conditions normally applied to crosslinking methods suitable for crosslinkable flame-retardant polyolefin resin compositions, without any particular limitations, and is specifically as described above.
When the flame-retardant polyolefin resin composition of the present invention is crosslinked by the silane crosslinking method, the production method is the same as the above-mentioned production method except that the molten mixture obtained in step (1) is molded onto the outer surface of the conductor using, for example, an extrusion molding machine.

In this way, the flame-retardant polyolefin resin composition of the present invention can be used to manufacture wiring materials with a coating layer that has excellent dimensional accuracy, flame retardancy, and abrasion resistance.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
In the following Tables 1-1 and 1-2 (collectively referred to as Table 1), the numerical values relating to the blending amounts of each example are based on mass unless otherwise specified. In Table 1, a blank space for each component means that the blending amount (content) of the corresponding component is 0 parts by mass. The composition of each composition is also clearly stated. Here, the units for compositions [A] to [C] and "other polymers" are % by mass, and the units for "flame retardant" and "component with a melting point exceeding 200°C" are parts by mass, but these are omitted in Table 1.

Details of each compound used in the examples and comparative examples are shown below.
<Resin>
m-HDPE: Evolue (registered trademark)-H SP5505 (trade name, high-density polyethylene polymerized using a metallocene catalyst, density 0.951 g/cm ³ , manufactured by Prime Polymer Co., Ltd.)
LLDPE: Evolue (registered trademark) 1540 (trade name, linear low-density polyethylene, density 0.91 g/cm ³ , manufactured by Prime Polymer Co., Ltd.)
HDPE: Hi-Zex (registered trademark) 5305E (trade name, high-density polyethylene, density 0.950 g/cm ³ , manufactured by SunAllomer Co., Ltd.)
h-PP: SunAllomer PM600A (trade name, homopolypropylene, manufactured by SunAllomer Co., Ltd.)
r-PP: SunAllomer PB222A (trade name, random polypropylene, manufactured by SunAllomer Co., Ltd.)
Styrene-based elastomer: Kraton FG1901X (product name, SEBS, manufactured by Kraton Corporation)
Ethylene vinyl acetate copolymer: Evaflex EV560 (trade name, EVA, manufactured by Dow Mitsui Polychemicals)
Polymer with a density of less than 0.90 g/cm ³ : Kernel KS240T (trade name, very low density polyethylene (VLDPE), density 0.88 g/cm ³ , manufactured by Japan Polyethylene Corporation)
<Flame retardants>
Brominated flame retardant: Cytex 8010 (trade name, ethylene bis(pentabromophenyl), melting point over 200°C, manufactured by Albemarle)
Magnesium hydroxide: Magseeds FK-621 (trade name, magnesium hydroxide, melting point over 200°C, manufactured by Konoshima Chemical Co., Ltd.)
<Flame retardant synergist>
Antimony trioxide (melting point over 200°C, manufactured by Nippon Seiko Co., Ltd.)
<Other ingredients>
Silane coupling agent: KBM-1003 (trade name, trimethoxyvinylsilane, melting point 200°C or less, manufactured by Shin-Etsu Silicones Co., Ltd.)
Organic peroxide: Perhexa 25B (trade name, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, manufactured by NOF Corporation)
Silanol condensation catalyst: Adekastab OT-1 (trade name, dioctyltin dilaurate, melting point 200°C or less, manufactured by ADEKA Corporation)
Crosslinking aid: Ogmont T200 (trade name, trimethylolpropane trimethacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.)
Antioxidant: Irganox 1010 (trade name: Pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), melting point 200°C or less, manufactured by BASF)
Lubricant: X-22-2125H (trade name, silicone mixture, melting point 200°C or less, manufactured by Shin-Etsu Silicones Co., Ltd.)

[Examples 1 to 17 and Comparative Examples 1 to 6]
Flame-retardant polyolefin resin compositions having the compositions shown in Table 1 were prepared by the following production method, and these were extrusion-molded (extrusion coating) onto the outer peripheral surface of a conductor to produce insulated wires (AESSX-0.3SQf, compliant with Japan Automotive Engineering Society (JASO) D 625) having a coating layer formed thereon.

In the examples and comparative examples, the following other components were used depending on the crosslinking method.
<Silane crosslinking method>
2.8 parts by mass of silane coupling agent, 0.1 part by mass of organic peroxide, 0.1 part by mass of silanol condensation catalyst, 1 part by mass of antioxidant, and 1 part by mass of lubricant <electron beam crosslinking method>
3 parts by mass of a methacrylate-based polyfunctional compound as a crosslinking aid, 1 part by mass of an antioxidant, and 1 part by mass of a lubricant <Non-crosslinked (Example 3)>
Antioxidant 1 part by mass and lubricant 1 part by mass. In Table 1, other components and their respective mixed amounts are omitted, and the total content of each mixed amount is shown in the "Other Components" column.

<Examples 1, 4, 6, 8 to 17 and Comparative Examples 1 to 6>
An insulated wire was produced by the following silane crosslinking method.
In the Examples and Comparative Examples, a portion of the resin (95% by mass) was used in step (a), and the remaining portion of the resin (5% by mass) was used as a carrier resin for catalyst MB in step (b).
The remainder of the resin used in step (b) was LLDPE in each of the Examples and Comparative Examples.

Specifically, 100 parts by mass of resin were mixed at room temperature (25°C) with the parts by mass of magnesium hydroxide and antimony trioxide shown in Table 1, 2.8 parts by mass of a silane coupling agent, and 0.1 parts by mass of an organic peroxide. The resulting mixture, a portion of the resin, and the contents of a brominated flame retardant, 1 part by mass of an antioxidant, and 1 part by mass of a lubricant shown in Table 1 were melt-mixed in a 2L Banbury mixer (manufactured by Nippon Roll Co., Ltd.) at a temperature equal to or higher than the decomposition temperature of the organic peroxide (200°C) for 5 minutes, and then discharged at a material discharge temperature of 130°C and pelletized to obtain Silane MB (step (a)).
The remainder of the resin and 0.1 parts by mass of a silanol condensation catalyst were melt-mixed at 150°C in a Banbury mixer (manufactured by Nippon Roll Co., Ltd.), and the mixture was discharged at a material discharge temperature of 130°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 immediately above an extruder (screw diameter: 25 mm, L/D (ratio of effective screw length L to diameter D): 25) at 25°C for about 1 minute to obtain a dry blend. The obtained dry blend was charged into the extruder and extrusion-coated around a stranded conductor (outer diameter: 0.80 mm) made of 19 concentrically twisted annealed copper wires, each 0.16 mm in diameter, at a wire speed of 100 m/min (screw rotation speed: 40 rpm) to a finished outer diameter of 1.40 mm (thickness: 0.30 mm) under the following extrusion temperature conditions (step (2)), thereby producing an electric wire precursor.
In this case, the dry blend is melt-mixed in the extruder before extrusion (step (c)), thereby preparing a crosslinkable flame-retardant polyolefin resin composition. The extrusion temperature conditions were as follows: the temperature control in the cylinder part of the extruder was divided into three zones C1, C2, and C3 from the feeder side to the die side; the C1 zone was set to 150°C, the C2 zone to 170°C, and the C3 zone to 190°C; and the die temperature (molding temperature) was set to 200°C.
The wire precursor thus obtained was left in an environment of 25°C and 50% RH for 24 hours (step (3)), thereby bringing the tubular molded body of the crosslinkable flame-retardant polyolefin resin composition into contact with water and causing a silanol condensation reaction, thereby producing an insulated wire having a tubular molded body of the flame-retardant crosslinked polyolefin resin composition as a coating layer.

<Examples 2, 5 and 7>
An insulated wire was produced by the following electron beam crosslinking method.
Each component shown in Table 1, 3 parts by mass of crosslinking coagent, 1 part by mass of antioxidant, and 1 part by mass of lubricant were charged into a Banbury mixer in the amounts shown in Table 1 and melt-mixed at 120 to 200°C for 10 minutes, and then discharged at a material discharge temperature of 200°C and passed through a feeder rudder to obtain pellets of a crosslinkable flame-retardant polyolefin resin composition.
The obtained pellets were used to form an insulating coating to produce an electric wire precursor as follows: That is, the obtained pellets were introduced into an extruder equipped with a screw having a diameter of 25 mm (ratio of effective screw length L to diameter D: L/D = 25, compression section screw temperature 190°C, head temperature 200°C). While melting the pellets in the extruder, the pellets were extrusion coated at a wire speed of 100 m/min (screw rotation speed 40 rpm) around the outer periphery of a stranded conductor (outer diameter 0.80 mm) formed by concentrically twisting 19 soft copper wires having a diameter of 0.16 mm, to a finished outer diameter of 1.40 mm (thickness 0.30 mm), thereby producing an electric wire precursor.
Next, the crosslinkable flame-retardant polyolefin resin composition placed on the outer peripheral surface of the conductor was irradiated with an electron beam at an acceleration voltage of 500 kV to a dose of 10 Mrad.
In this way, an insulated wire having a tubular molding of the flame-retardant crosslinked polyolefin resin composition as a covering layer was produced.

Example 3
In Example 2, an insulated wire having a tubular molding of a flame-retardant non-crosslinked polyolefin resin composition as a coating layer was produced in the same manner as in Example 2, except that the flame-retardant crosslinked polyolefin resin composition (but not containing 3 parts by mass of crosslinking aid) placed on the outer peripheral surface of the conductor was not irradiated with electron beams.

The following tests were conducted on each of the manufactured insulated wires, and the results are shown in Table 1.

<Wear resistance test>
A scrape abrasion test was conducted under severe conditions in accordance with Japan Automotive Engineering Society (JASO) standard D 625, in which a 0.45 mm diameter stainless steel (SUS) wire was reciprocated on the surface of the insulated wire with a load of 10 N. The test was conducted at four test points on the surface of the insulated wire, forming a central angle of 90°. The number of reciprocating abrasions was recorded at the point where the coating layer peeled off and electrical continuity with the conductor was established. The minimum number of reciprocating abrasions among the four was regarded as the abrasion count of the insulated wire.
The abrasion resistance of the insulated wire was evaluated based on whether the number of abrasion cycles fell within any of the following criteria. In this test, an evaluation rank of "C" indicates sufficient abrasion resistance for an insulated wire, but an evaluation rank of "B" or higher is considered acceptable, as it represents the high abrasion resistance achieved by the present invention.

-Evaluation criteria-
A: 250 times or more B: 200 times or more, but less than 250 times C: 100 times or more, but less than 200 times D: Less than 100 times

<Flame retardancy test>
The flame retardancy test was conducted in accordance with JASO D 625, by carrying out the following 45-degree inclined burning test and the following horizontal burning test. As a result, samples that passed both the 45-degree inclined burning test and the horizontal burning test were rated as "Good", samples that passed only the horizontal burning test were rated as "Good", and samples that did not pass either the horizontal burning test were rated as "Poor" (failed the test).

(Horizontal burning test)
The prepared insulated wire was fixed horizontally and exposed to a flame from a burner with an outer flame length adjusted to 20 mm for 5 seconds. The test piece was then burned, and the time from the start of flame exposure to extinction (extinction time) was measured. If the extinction time was within 30 seconds, the test piece was deemed to have passed the horizontal combustion test.
(45 degree inclined combustion test)
The prepared insulated wire was fixed at a 45° inclination with respect to the vertical direction and exposed to a flame from a burner with an outer flame length adjusted to 20 mm for 15 seconds. The test piece was then burned, and the time from the start of flame exposure to extinction (extinction time) was measured. If the extinction time was within 70 seconds and the burning portion was more than 50 mm below the top end of the insulated wire, the wire was deemed to have passed the 45° inclined combustion test.

<Contractility test>
The insulated wire cut to a length of 3000 mm was left in a horizontal position for 24 hours under an environment of normal temperature and humidity (25°C, 50% RH). The lengths of the conductors protruding from the ends of the coating layer at both ends of the insulated wire were measured, and the protruding lengths at each end and the shrinkage of the insulated wire were evaluated.
When each protrusion length was 0.5 mm or less, it was evaluated as "◯" (pass), and when it exceeded 0.5 mm, it was evaluated as "×" (fail).

In Table 1, in the column "Crosslinking method,""Silane" indicates silane crosslinking method, "Electron beam" indicates electron beam crosslinking method, and "None" indicates no crosslinking (non-crosslinking).
The "other components" in Table 1 are selected depending on the crosslinking method, and are specifically as described above.
The column "Composition [B]" in Table 1 shows the total content of the styrene elastomer and the ethylene vinyl acetate copolymer in the resin.

As is clear from the results shown in Table 1, none of the compositions of Comparative Examples 1 to 5, in which the resin does not satisfy the compositions [A] to [C], and the composition of Comparative Example 6, which does not contain flame retardancy, can form a coating layer (molded article) that combines flame retardancy, shrinkage properties (dimensional stability and reliability), and abrasion resistance.
In contrast, the flame-retardant polyolefin resin composition of the present invention, which contains a resin satisfying the compositions [A] to [C] and a flame retardant, can form a coating layer that is excellent in flame retardancy and shrinkage properties (dimensional stability and reliability) and exhibits extremely high abrasion resistance, regardless of whether it is crosslinked or not, and regardless of the crosslinking method.

Claims (7)

A flame-retardant polyolefin resin composition containing a resin and a flame retardant,
The flame-retardant polyolefin resin composition, wherein the resin satisfies the following compositions [A] to [C].

[A] High-density polyethylene polymerized using a metallocene catalyst , having a density of 0.940 g
[B] an ethylene-vinyl acetate copolymer, wherein the resin contains a high-density polyethylene having a viscosity of 15 to 70% by mass of polyethylene terephthalate or higher ^; an ethylene copolymer having a (meth)acrylic acid component ; an ethylene copolymer having a ( meth )acrylic acid alkyl ester compound component ;
acid-modified copolymer of ethylene vinyl acetate copolymer, ethylene vinyl acetate copolymer having (meth)acrylic acid component,
Acid-modified copolymer of ethylene copolymer, (meth)acrylic acid alkyl ester compound
[C] The resin contains an acid-modified copolymer of an ethylene copolymer having a molecular weight of 10% or less, an ethylene rubber, and a styrene-based elastomer in a total content of 10% by mass or less. [D] The resin contains a polymer having a density of less than 0.90 g/ ^cm3 in a content of 1% by mass or less.
have The flame-retardant polyolefin resin composition according to claim 1, wherein the content of the high-density polyethylene in the resin is 25 to 70 mass%. The flame-retardant polyolefin resin composition according to claim 1 or 2, containing a total of 120 parts by mass or less of components having a melting point exceeding 200°C per 100 parts by mass of the resin. The flame-retardant polyolefin resin composition according to any one of claims 1 to 3, wherein the total content of component [B] is 5 mass% or less. The flame-retardant polyolefin resin composition according to any one of claims 1 to 4, which is a crosslinked product. A wiring material having a coating layer on the outer peripheral surface of a conductor,
A wiring material, wherein the coating layer is formed from the flame-retardant polyolefin resin composition according to any one of claims 1 to 5. The wiring material according to claim 6, which is an insulated wire for use in a vehicle.