Bridged molding body, wire sheathing material and wire

Abstract

To provide a crosslinked molding, a wire coating material and a wire having high-level flame retardancy while maintaining heat resistance.SOLUTION: A crosslinked molding comprises a flame-retardant polyolefin resin composition comprising (A) silane-modified polyolefin, (B) metal hydroxide, and (C) siloxane component-containing rubber, wherein, the (A) silane-modified polyolefin has been crosslinked. A wire coating material comprising the crosslinked molding is used to coat a conductor to be used as a wire.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a crosslinked molded article, and a wire covering material and a wire using the same. [Background technology]

[0002] Polyolefins have superior electrical properties compared to flexible polyvinyl chloride resins and are also economically advantageous, making them widely used in a variety of molded products, including electrical wire and cable coverings. However, polyolefin resins are flammable solids, and once a fire breaks out, it is difficult to prevent the fire from spreading. Therefore, in applications requiring high flame retardancy, such as electrical wire coverings, metal hydroxides, bromine-based flame retardants, and phosphorus-based flame retardants are added to improve flame retardancy. Furthermore, a technique for improving flame retardancy by using metal hydroxides in combination with composite rubber is also known (Patent Documents 1 and 2). Furthermore, methods that have been proposed to further enhance the heat resistance and flame retardancy of polyolefins include adding a flame retardant and composite rubber, followed by electron beam irradiation crosslinking and water crosslinking (Patent Documents 3 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-26664 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-338755 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-50287 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-241548 [Patent Document 5] Japanese Patent Application Laid-Open No. 2005-255994 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the inventions that combine the method of cross-linking polyolefins, the method of adding flame retardants and composite rubber and then cross-linking has shown improvements in heat resistance, but has not yet reached the level of flame retardancy required for electric wire products, etc. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cross-linked molded article, a wire covering material, and an electric wire that have high flame retardancy while maintaining heat resistance. [Means for solving the problem]

[0005] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that a crosslinked molded article made from a flame-retardant polyolefin resin composition containing (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber can significantly improve flame retardancy while maintaining heat resistance, provided that the crosslinked molded article is made from the flame-retardant polyolefin resin composition containing (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber. That is, the present invention has the following features.

[0006] [1] A molded article made of a flame-retardant polyolefin resin composition containing (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber, wherein the (A) silane-modified polyolefin is crosslinked. [2] The crosslinked molded article according to [1], wherein the (A) silane-modified polyolefin is water-crosslinked. [3] The crosslinked molded article according to [1] or [2], wherein the metal hydroxide (B) is synthetic magnesium hydroxide. [4] A wire covering material comprising the crosslinked molded article according to any one of [1] to [3]. [5] An electric wire in which a conductor is covered with the electric wire covering material described in [4]. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a cross-linked molded article, a wire covering material, and an electric wire that have high flame retardancy while maintaining heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following description and can be modified and implemented as desired within the scope that does not deviate from the gist of the present invention. In this specification, when "~" is used to express a numerical value or a physical property value, the values ​​before and after the "~" are included.

[0009] The crosslinked molded article of the present invention is a molded article made of a flame-retardant polyolefin resin composition containing (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber, and is a crosslinked molded article in which at least the silane-modified polyolefin (A) is crosslinked. The crosslinked molded article of the present invention will be described in detail below.

[0010] <(A): Silane-modified polyolefin> In the present invention, the silane-modified polyolefin (sometimes referred to herein as "(A) silane-modified polyolefin" or "component (A)") is believed to finely disperse the (B) metal hydroxide and (C) siloxane component-containing rubber described below in the resin composition. It is also necessary for the polyolefin to exhibit the mechanical and electrical properties required. Additionally, it can form a crosslinked product by reacting with water in the presence of a specific condensation catalyst.

[0011] (A) Silane-modified polyolefin can be obtained, for example, by grafting an unsaturated silane compound onto a raw material polyolefin resin such as those listed below to modify it.

[0012] The polyolefin resin used as a raw material for (A) silane-modified polyolefin (hereinafter, sometimes referred to as "raw material polyolefin resin") is not particularly limited, but examples include homopolymers of α-olefins having about 3 to 8 carbon atoms, such as ethylene, propylene, and 1-butene, and copolymers of these α-olefins with other α-olefins having about 3 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene, as well as copolymers of vinyl acetate, (meth)acrylic acid, and (meth)acrylic acid esters. Here, "(meth)acrylic acid" refers to either or both of "acrylic acid" and "methacrylic acid." The same applies to "(meth)acryloyl," which will be described later.

[0013] Specific examples of the raw material polyolefin resin include ethylene homopolymers such as branched or linear low-density polyethylene, branched or linear medium-density polyethylene, and branched or linear high-density polyethylene; ethylene-based resins such as ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-1-hexene copolymers, ethylene-1-octene copolymers, ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid copolymers, and ethylene-ethyl (meth)acrylate copolymers; propylene-based resins such as propylene homopolymers, propylene-ethylene copolymers, propylene-1-butene copolymers, propylene-ethylene-1-butene copolymers, and propylene-4-methyl-1-pentene copolymers; and 1-butene-based resins such as 1-butene homopolymers, 1-butene-ethylene copolymers, and 1-butene-propylene copolymers. These raw material polyolefin resins may be used alone or in combination of two or more.

[0014] Here, the ethylene-based resin, propylene-based resin, and 1-butene-based resin refer to resins containing ethylene units, propylene units, and 1-butene units, respectively, in a proportion of 50% by mass or more, preferably more than 50% by mass, of all monomer units constituting the resin. Among these, ethylene-based resins are preferred as the polyolefin resins used as the raw material for (A) silane-modified polyolefin.

[0015] The silane-modified polyolefin (A) in the present invention can be obtained by, for example, grafting an unsaturated silane compound onto a raw polyolefin resin by a graft reaction using a free radical generator, as described below, and it is preferable that the raw polyolefin resin is an ethylene-based resin, since grafting can be carried out efficiently.Furthermore, it is preferable that the raw polyolefin resin is an ethylene-based resin, since the heat resistance is good when the resin composition of the present invention is used for electric wire coating. Among the above ethylene-based resins, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, ethylene-vinyl acetate copolymer, and ethylene-methyl (meth)acrylate copolymer are particularly preferred.

[0016] To obtain (A) the silane-modified polyolefin by graft-modifying a raw polyolefin resin with an unsaturated silane compound, the raw polyolefin resin is usually subjected to a graft reaction step of an ethylenically unsaturated silane compound in the presence of a free radical generator such as an organic peroxide, thereby graft-modifying the raw polyolefin resin by a known method. For example, a method can be used in which a predetermined amount of an unsaturated silane compound and a free radical generator are mixed with a raw material polyolefin resin, and the mixture is melt-kneaded at a temperature of 80 to 250° C. In this case, if water is present, a water crosslinking reaction will proceed, so it is preferable to melt-knead the mixture in a water-free state.

[0017] The unsaturated silane compound used for the graft modification includes an ethylenically unsaturated silane compound represented by the following general formula (I). R 1 SiR 2 n Y 3-n …(I)

[0018] In the above formula (I), R 1represents an ethylenically unsaturated hydrocarbon group or a hydrocarbonoxy group, and R 2 represents a hydrocarbon group, Y represents a hydrolyzable organic group, and n is an integer of 0 to 2.

[0019] where R 1 Examples of R include ethylenically unsaturated hydrocarbon groups or hydrocarbonoxy groups having 2 to 6 carbon atoms, such as vinyl groups, propenyl groups, butenyl groups, cyclohexenyl groups, and γ-(meth)acryloyloxypropyl groups. 2 Examples of Y include hydrocarbon groups having 1 to 10 carbon atoms, such as a methyl group, an ethyl group, a propyl group, a decyl group, and a phenyl group. Examples of Y include a methoxy group, an ethoxy group, a formyloxy group, an acetoxy group, a propionyloxy group, an alkylamino group, and an arylamino group.

[0020] Specific examples of such ethylenically unsaturated silane compounds include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, and γ-methacryloyloxypropyltrimethoxysilane. Among these, vinyltrimethoxysilane is preferably used from the viewpoint of odor, etc. The unsaturated silane compounds may be used alone or in combination of two or more.

[0021] The amount of the unsaturated silane compound used is not limited, and a larger amount is desirable to obtain a sufficient dispersion effect of the flame retardant and obtain the flame retardancy of the resin composition of the present invention, but a smaller amount is desirable from the viewpoint of processability. Specifically, the amount is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the raw material polyolefin resin.

[0022] The free radical generator is not limited as long as it can graft an unsaturated silane compound onto the raw polyolefin resin, but organic peroxides such as dicumyl peroxide, 2,5-(tert-butylperoxy)hexyne-3,1,3-bis(tert-butylperoxyisopropyl)benzene, etc. These organic peroxides may be used alone or in combination of two or more.

[0023] The amount of the free radical generator used is not limited, and a larger amount is desirable in order to sufficiently graft copolymerize the unsaturated silane compound with the raw polyolefin resin to obtain a sufficient crosslinking effect, but a smaller amount is desirable from the viewpoint of processability. Specifically, the amount is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and preferably 0.2 parts by mass or less, more preferably 0.1 parts by mass or less, per 100 parts by mass of the raw polyolefin resin.

[0024] The silane-modified polyolefin (A) used in the present invention has a density of 0.850 to 0.960 g / cm 3 is preferably 0.870 to 0.920 g / cm 3 The higher the density, the better the heat resistance, chemical resistance, abrasion resistance, flex resistance, etc. of the resulting coated electric wire, while the lower the density, the better the flexibility. By setting the density within the above range, the heat resistance, chemical resistance, abrasion resistance, and flex resistance of the resulting coated electric wire are sufficiently improved, and sufficient flexibility can be obtained.

[0025] The melt flow rate (MFR) of the silane-modified polyolefin (A) measured in accordance with JIS K7210 at 190°C under a load of 2.16 kg is preferably high in terms of moldability, but low in terms of mechanical properties. Specifically, the MFR of the silane-modified polyolefin (A) at 190°C under a load of 2.16 kg is preferably 0.1 g / 10 min or more, more preferably 1 g / 10 min or more, and is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less. By keeping the MFR within these ranges, a good balance between moldability and mechanical properties can be achieved.

[0026] The (A) silane-modified polyolefin may be used alone or in combination of two or more different types having different monomer compositions, physical properties, and the like. As the (A) silane-modified polyolefin, a commercially available product can be used, and for example, a product under the trade name "Linkron" manufactured by Mitsubishi Chemical Corporation can be suitably used.

[0027] In the present invention, the silane-modified polyolefin (A) can be used in any amount, but is preferably 10 wt% or more, more preferably 20 wt% or more, of the total composition. On the other hand, it is preferably 80 wt% or less, more preferably 70 wt% or less. If the blending ratio of the silane-modified polyolefin (A) is above the lower limit, the metal hydroxide (B) and the siloxane-containing rubber (C) tend to be easily dispersed. On the other hand, if the blending ratio is below the upper limit, the content of the metal hydroxide (B) and the siloxane-containing rubber (C) increases, which tends to improve flame retardancy.

[0028] As a commercially available product of the component (A), for example, the Linkron (registered trademark) series manufactured by Mitsubishi Chemical Corporation can be appropriately used.

[0029] <(B): Metal hydroxide> In the present invention, the metal hydroxide (sometimes referred to in this specification as "(B) metal hydroxide" or "(B) component") is a component that mainly imparts flame retardancy to the resin composition, molded article, and wire coating material of the present invention.

[0030] The type of (B) metal hydroxide is not limited, but specific examples include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, hydrotalcite, etc., with magnesium hydroxide being preferred. Among these, synthetic magnesium hydroxide is particularly preferred. Synthetic magnesium hydroxide refers to magnesium hydroxide produced by the hydration reaction of magnesium oxide or by reacting a magnesium-containing aqueous liquid with a strongly basic compound such as magnesium hydroxide. The mechanism by which these hydroxides function favorably in the present invention is unclear, but it is thought that their fine particle size and fewer impurities may play a role compared to natural magnesium hydroxide obtained by crushing brucite (hydrotalcite). These (B) metal hydroxides may be used alone or in combination of two or more types.

[0031] The (B) metal hydroxide may be surface-treated with a surface treatment agent. Examples of the surface treatment agent include silane coupling agents, titanate coupling agents, fatty acids, and fatty acid metal salts. Known methods such as wet methods, dry methods, and direct kneading methods can be used to treat the (B) metal hydroxide with these surface treatment agents. The use of a surface-treated (B) metal hydroxide may improve dispersibility in the resulting resin composition, thereby improving mechanical properties.

[0032] The average particle size of the (B) metal hydroxide is preferably 2.0 μm or less, more preferably 0.5 to 1.2 μm, from the viewpoints of mechanical properties, dispersibility, and flame retardancy. If the particle size is below the upper limit, the actual area where interaction occurs between the (B) metal hydroxide and the (C) component (a siloxane component-containing rubber, which will be described later) increases, resulting in a significant improvement in flame retardancy. If the particle size is above the lower limit, the torque during kneading and molding can be reduced, resulting in improved molding processability. Here, the average particle size of (B) the metal hydroxide is the particle size at a volume-based cumulative distribution of 50 vol%.

[0033] In the present invention, the blending ratio of (B) metal hydroxide is preferably 20 wt% or more, more preferably 40 wt% or more, and is preferably 80 wt% or less, more preferably 70 wt% or less, based on the total composition. If the blending ratio of (B) metal hydroxide is equal to or greater than the above-mentioned lower limit, sufficient flame retardancy can be obtained. On the other hand, if the blending ratio of (B) metal hydroxide is equal to or less than the above-mentioned upper limit, a decrease in productivity due to an increase in extrusion load and a decrease in mechanical properties can be prevented.

[0034] As a commercially available product of the component (B), for example, the corresponding product in the Magseeds (registered trademark) series manufactured by Kyowa Chemical Industry Co., Ltd. can be appropriately used.

[0035] <(C): Siloxane-containing rubber> In the present invention, the siloxane component-containing rubber (sometimes referred to in this specification as "(C) siloxane component-containing rubber" or "component (C)") is added mainly for the purpose of improving the flame retardancy of the metal hydroxide, and is a component that ultimately imparts flame retardancy to the resin composition, molded article, and wire coating material of the present invention.

[0036] The (C) siloxane component-containing rubber is not particularly limited as long as it contains a polyorganosiloxane rubber component, but a composite rubber containing a polyorganosiloxane rubber component is preferred. As a composite rubber containing a polyorganosiloxane rubber component, a composite rubber composed of a polyorganosiloxane rubber component and a polyalkyl (meth)acrylate component, the main component of which is a copolymer in which one or more vinyl monomers are graft-polymerized, can be suitably used.

[0037] The polyorganosiloxane rubber component and polyalkyl(meth)acrylate component that make up the composite rubber are preferably in the range of 1 to 99 mass% for the polyorganosiloxane rubber component and 99 to 1 mass% for the polyalkyl(meth)acrylate component (however, the total of all components is 100 mass%), and from the standpoints of flame retardancy and flexibility, the polyorganosiloxane rubber component is more preferably in the range of 30 to 95 mass%, and even more preferably 50 to 90 mass%. The composite rubber may be produced by any method, but emulsion polymerization is the most suitable method. It is preferable to first prepare a polyorganosiloxane latex, then impregnate the polyorganosiloxane latex particles with a synthesis monomer of alkyl (meth)acrylate, and then polymerize the synthesis monomer.

[0038] The polyorganosiloxane rubber component constituting the composite rubber can be prepared by emulsion polymerization using the organosiloxane and crosslinking agent (CI) shown below, and a grafting agent (GI) can also be used in combination. Examples of organosiloxanes include various cyclic compounds with three or more members, with three- to six-membered rings being preferred. Examples include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, trimethyltriphenylcyclotrisiloxane, tetramethyltetraphenylcyclotetrasiloxane, and octaphenylcyclotetrasiloxane. These can be used alone or in combination of two or more. The amount of these compounds used is preferably 50% by weight or more, and more preferably 70% by weight or more, of the polyorganosiloxane component.

[0039] As the crosslinking agent (CI), a trifunctional or tetrafunctional silane-based crosslinking agent such as trimethoxymethylsilane, triethoxyphenylsilane, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, or tetrabutoxysilane is used. Tetrafunctional crosslinking agents are particularly preferred, and among these, tetraethoxysilane is particularly preferred. The amount of the crosslinking agent used is preferably in the range of 0.1 to 30% by weight of the polyorganosiloxane component.

[0040] As the grafting agent (GI), compounds capable of forming units represented by the following formulae (GI-1 to GI-4) and the like are used. In the formula, R 3 is a methyl group, an ethyl group, a propyl group, or a phenyl group, R 4 represents a hydrogen atom or a methyl group, m represents 0, 1 or 2, and p represents 1 to 6.

[0041] [ka]

[0042] (Meth)acryloyloxysiloxanes capable of forming the unit of the above formula (GI-1) have high grafting efficiency, so they can form effective graft chains, and are advantageous in terms of expressing flexibility, and methacryloyloxysiloxanes are particularly preferred.Specific examples of methacryloyloxysiloxanes include β-methacryloyloxyethyldimethoxymethylsilane, γ-methacryloyloxypropylmethoxydimethylsilane, γ-methacryloyloxypropyldimethoxymethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylethoxydiethylsilane, γ-methacryloyloxypropyldiethoxymethylsilane, and γ-methacryloyloxybutyldiethoxymethylsilane. Examples of compounds capable of forming the unit of the above formula (GI-2) include vinyl siloxanes, and a specific example thereof is tetramethyltetravinylcyclotetrasiloxane.

[0043] Examples of compounds that can form the unit of formula (GI-3) include p-vinylphenyldimethoxymethylsilane, and examples of compounds that can form the unit of formula (GI-4) include γ-mercaptopropyldimethoxymethylsilane, γ-mercaptopropylmethoxydimethylsilane, and γ-mercaptopropyldiethoxymethylsilane. The amount of the grafting agent used is preferably 0 to 10% by weight, more preferably 0.5 to 5% by weight, of the polyorganosiloxane component.

[0044] This polyorganosiloxane component latex can be produced by methods described, for example, in U.S. Pat. Nos. 2,891,920 and 3,294,725. In the practice of the present invention, a mixed solution of organosiloxane, crosslinking agent (CI), and optionally grafting agent (GI) is preferably produced by shear mixing with water using a homogenizer or the like in the presence of a sulfonic acid emulsifier such as alkylbenzenesulfonic acid or alkylsulfonic acid. Alkylbenzenesulfonic acid is preferred because it acts as an emulsifier for organosiloxane and also as a polymerization initiator. In this case, the use of a metal alkylbenzenesulfonate or metal alkylsulfonate is preferred, as it is effective in maintaining the stability of the polymer during graft polymerization.

[0045] The polyalkyl(meth)acrylate component constituting the composite rubber can be synthesized using the following alkyl(meth)acrylate, crosslinking agent (CII), and grafting agent (GII): Examples of alkyl(meth)acrylates include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, and alkyl methacrylates such as hexyl methacrylate, 2-ethylhexyl methacrylate, and n-lauryl methacrylate, with n-butyl acrylate being particularly preferred.

[0046] Examples of the crosslinking agent (CII) include ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,4-butylene glycol dimethacrylate. Examples of the grafting agent (GII) include allyl methacrylate, triallyl cyanurate, triallyl isocyanurate, etc. Allyl methacrylate can also be used as a crosslinking agent.

[0047] These crosslinking agents and graft crosslinking agents may be used alone or in combination of two or more. The total amount of these crosslinking agents and graft crosslinking agents used is preferably 0.1 to 20% by weight of the polyalkyl(meth)acrylate component. Polymerization of the polyalkyl(meth)acrylate component is carried out by adding the alkyl(meth)acrylate, crosslinking agent, and graft crosslinking agent to a latex of the polyorganosiloxane component neutralized with an aqueous alkali solution such as sodium hydroxide, potassium hydroxide, or sodium carbonate, impregnating the polyorganosiloxane particles, and then reacting with a conventional radical polymerization initiator. As the polymerization progresses, a composite rubber latex of the polyorganosiloxane component and the polyalkyl(meth)acrylate component is obtained.

[0048] In carrying out the present invention, a composite rubber in which the main skeleton of the polyorganosiloxane rubber component has a repeating unit of dimethylsiloxane and the main skeleton of the polyalkyl (meth)acrylate component has a repeating unit of n-butyl acrylate is preferably used as the composite rubber.

[0049] Examples of vinyl monomers to be graft-polymerized onto this composite rubber include aromatic alkenyl compounds such as styrene, α-methylstyrene, and vinyltoluene; methacrylic acid esters such as methyl methacrylate and 2-ethylhexyl methacrylate; acrylic acid esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; and vinyl cyanide compounds such as acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more. Among these vinyl monomers, methacrylic acid esters are preferred, with methyl methacrylate being particularly preferred.

[0050] The ratio of the composite rubber to the vinyl monomer in the (C) siloxane component-containing rubber is preferably 5 to 95 mass% composite rubber and 5 to 95 mass% vinyl monomer, more preferably 25 to 90 mass% composite rubber and 10 to 75 mass% vinyl monomer. If the vinyl monomer content is less than 5 mass%, the dispersibility of the graft copolymer in the resin composition will be poor, and if it exceeds 95 mass%, the flexibility will be significantly reduced.

[0051] The (C) siloxane component-containing rubber is obtained by adding a vinyl monomer to a composite rubber latex and polymerizing it in one or multiple stages using a radical polymerization technique. The graft copolymer latex can be separated and recovered by adding it to hot water containing a metal salt, such as calcium chloride, calcium acetate, or magnesium sulfate, followed by salting out and coagulation. The composite rubber graft copolymer, in which one or more vinyl monomers are grafted onto the composite rubber composed of the polyorganosiloxane component and the polyalkyl (meth)acrylate rubber component, can be blended. This allows for high flame retardancy without impairing flexibility and while significantly reducing the amount of metal hydroxide (B) added. If necessary, polyorganosiloxane can be mixed with the resulting composite rubber graft copolymer.

[0052] In the present invention, the blending ratio of (C) siloxane component-containing rubber is preferably 2 wt% or more, more preferably 4 wt% or more, and is preferably 20 wt% or less, more preferably 15 wt% or less, based on the total composition. If the blending ratio of (C) siloxane component-containing rubber is above the above-mentioned lower limit, sufficient flame retardancy can be obtained. On the other hand, if the blending ratio of (C) siloxane component-containing rubber is below the above-mentioned upper limit, deterioration of mechanical properties due to a relative decrease in the resin component can be prevented.

[0053] The effect of the (C) siloxane component-containing rubber is presumed to be as follows: (C) siloxane component-containing rubber itself has no flame retardant effect, and mixing it alone with a polyolefin resin does not change the flame retardancy of the resin composition. When a resin composition having (A) silane-modified polyolefin as the base resin is introduced into a combustion field in the presence of (B) metal hydroxide in the vicinity, the high temperature causes the formation of a composite with (B) metal hydroxide, thereby exhibiting high flame retardancy.

[0054] It is presumed that the (A) silane-modified polyolefin has electrical polarity in the modifying group, which allows the (B) metal hydroxide and (C) siloxane component-containing rubber to be dispersed and arranged in close proximity to each other. On the other hand, when only a polyolefin resin, which has lower polarity than the (A) silane-modified polyolefin, is used, the (B) metal hydroxide and (C) siloxane component-containing rubber are each compounds with electrical polarity, so they tend to self-aggregate, making it difficult to achieve the synergistic flame retardancy effect.

[0055] As a commercially available product of (C), for example, the corresponding product in the Metablen (registered trademark) series manufactured by Mitsubishi Chemical Corporation can be appropriately used.

[0056] <Flame-retardant polyolefin resin composition> The flame-retardant polyolefin resin composition of the present invention contains (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber. The flame-retardant polyolefin resin composition preferably has a ratio of component (A) / component (C) of 10 / 1 to 2 / 1. By keeping the ratio within this range, it tends to be easier to obtain improved flame retardancy.

[0057] <Other ingredients> The flame-retardant polyolefin resin composition may contain, as necessary, resins and additives other than the above-mentioned components (A) to (C) as "other components" within the scope of not significantly impairing the effects of the present invention. The other components may be used alone or in any combination and ratio of two or more. The resin components other than the silane-modified polyolefin (A) are not particularly limited, but unmodified polyolefins such as unmodified polyethylene resins can be used as components for improving the mechanical properties and moldability of the resin composition, as well as the molded articles and wire coating materials using the resin composition.

[0058] The unmodified polyolefins refer to polyethylene-based resins such as various polyethylenes and ethylene copolymers into which functional groups have been introduced by copolymerization, and polypropylene-based resins such as polypropylene and propylene copolymers into which functional groups have been introduced by copolymerization, and are resins that have not been modified by a silane coupling agent, functional groups, or the like. Here, the ethylene-based resin and the propylene-based resin refer to resins containing ethylene units and propylene units, respectively, in a proportion of 50% by mass or more, preferably more than 50% by mass, of all monomer units constituting the resin.

[0059] Examples of the polyethylene resin include copolymers of ethylene with other α-olefins having about 3 to 20 carbon atoms, such as propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene; and copolymers of ethylene with vinyl acetate, (meth)acrylic acid, and (meth)acrylic acid esters.

[0060] The unmodified polyethylene resin has a density of 0.850 to 0.970 g / cm 3 The density is preferably 0.850 g / cm. 3 If the density is 0.970 g / cm or more, the heat resistance, chemical resistance, abrasion resistance, bending resistance, etc. of the obtained electric wire will be good. 3 If it is less than this, the flexibility is good. The unmodified polyethylene resin preferably has an MFR of 1 to 10 g / 10 min under a load of 2.16 kg at 190°C, measured in accordance with JIS K 7210. As with the MFR of (A) silane-modified polyolefin, a larger MFR of the unmodified polyethylene is preferable in terms of moldability, enabling an improvement in production volume per unit time, and a smaller MFR is preferable in terms of mechanical properties and heat resistance.

[0061] The unmodified polyethylene resin may be used alone or in combination of two or more types having different monomer compositions, physical properties, etc.

[0062] The upper limit of the content of the unmodified polyolefin is usually 500 parts by mass or less, preferably 100 parts by mass or less, more preferably 75 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 25 parts by mass or less, per 100 parts by mass of the silane-modified polyolefin (A), from the viewpoint of heat resistance.

[0063] (A) Examples of the resins other than silane-modified polyolefins and unmodified polyethylene-based resins include, in addition to the unmodified polypropylene-based resins described above, thermoplastic resins such as polyphenylene ether-based resins; polycarbonate resins; polyamide-based resins such as nylon 66 and nylon 11; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; styrene-based resins such as polystyrene; and (meth)acrylic resins such as polymethyl (meth)acrylate-based resins, as well as various thermoplastic elastomers.

[0064] Specific examples of the additives include process oils, processing aids, plasticizers, crystal nucleating agents, impact modifiers, flame retardants other than component (B), flame retardant aids, crosslinking catalysts, crosslinking aids, antistatic agents, antioxidants, lubricants, fillers, compatibilizers, heat stabilizers, light stabilizers, ultraviolet absorbers, carbon black, and colorants.

[0065] In the present invention, the crosslinking catalyst is a component that can water-crosslink the silane-modified polyolefin (A). Since (A) silane-modified polyolefin is a modified polyolefin graft-modified with an unsaturated silane compound, a compound that can form a crosslinked structure in the polyolefin resin when contacted with moisture in the presence of the crosslinking catalyst, i.e., a silanol condensation catalyst, is preferably used. Specific examples of the silanol condensation catalyst include metal fatty acid salts such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dioctaate, stannous acetate, stannous caprylate, zinc caprylate, lead naphthenate, and cobalt naphthenate. The crosslinking catalyst may be used alone or in any combination and ratio of two or more kinds.

[0066] In the present invention, the blending ratio of the crosslinking catalyst is preferably 0.0001% by weight or more, more preferably 0.0002% by weight or more, and is preferably 0.02% by weight or less, more preferably 0.01% by weight or less, based on the total resin. If the blending ratio of the crosslinking catalyst is above the lower limit, crosslinking of the silane-modified polyolefin proceeds sufficiently, and sufficient crosslinking properties can be obtained. On the other hand, if the blending ratio of the crosslinking catalyst is below the upper limit, deterioration of moldability due to excessive crosslinking can be prevented.

[0067] When crosslinking by electron beam irradiation, general conditions can be used. In this case, it is desirable to add a crosslinking aid. A multifunctional compound is used as the crosslinking aid. Specifically, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylpropyl acrylate, tripropylene glycol diacrylate, polyethylene polypropylene glycol diacrylate, dioxane glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol polyacrylate, polypentaerythritol polyacrylate, 1,6-hexanediol dimethacrylate, 1, Examples of crosslinking aids include 9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, neopentyl glycol dimethacrylate, 2-hydroxy-1,3-dimethacryloxypropane, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tripropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polyethylene polypropylene glycol dimethacrylate, tricyclodecane dimethanol dimethacrylate, ethoxylated bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, ditrimethylolpropane tetramethacrylate, and triallyl isocyanurate. The crosslinking aids may be used alone or in any combination and ratio of two or more.

[0068] In the present invention, the blending ratio of the crosslinking aid is preferably 0.1 wt% or more, more preferably 0.5 wt% or more, and is preferably 5.0 wt% or less, more preferably 3.0 wt% or less, of the total resin. If the blending ratio of the crosslinking aid is above the above lower limit, crosslinking of the resin components proceeds sufficiently, and sufficient crosslinking properties can be obtained. On the other hand, if the blending ratio of the crosslinking aid is below the above upper limit, unreacted crosslinking aid can be reduced, making it less likely that the physical properties of the crosslinked product will deteriorate.

[0069] Flame retardants other than component (B) are broadly classified into halogen-based flame retardants and non-halogen-based flame retardants, with non-halogen-based flame retardants being preferred. Examples of non-halogen-based flame retardants other than (B) metal hydroxides include phosphorus-based flame retardants, nitrogen-containing compound (melamine-based, guanidine-based) flame retardants, and inorganic compound (borate, molybdenum compound) flame retardants.

[0070] Examples of the heat stabilizer and antioxidant include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, and alkali metal halides.

[0071] The fillers are broadly classified into organic fillers and inorganic fillers. Examples of organic fillers include naturally occurring polymers such as starch, cellulose fine particles, wood flour, soybean pulp, rice husks, and bran, as well as modified products thereof. Examples of inorganic fillers include talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fibers, metal whiskers, ceramic whiskers, potassium titanate, boron nitride, graphite, and carbon fibers.

[0072] The resin composition of the present invention may also contain a hydrocarbon-based rubber softener. As the hydrocarbon-based rubber softener, a mineral oil-based or synthetic resin-based softener is preferred, and a mineral oil-based softener is more preferred. The mineral oil-based softener is generally a mixture of aromatic hydrocarbons, naphthenic hydrocarbons, and paraffinic hydrocarbons, and those in which 50% or more of the total carbon atoms are paraffinic hydrocarbons are called paraffinic oils, those in which approximately 30 to 45% or more of the total carbon atoms are naphthenic hydrocarbons are called naphthenic oils, and those in which 35% or more of the total carbon atoms are aromatic hydrocarbons are called carbon-aromatic oils.

[0073] The synthetic resin softener is preferably any one selected from paraffinic oil, naphthenic oil, and carbon atom aromatic oil. Of these, paraffinic oil is more preferably used because of its good color. Examples of the synthetic resin softener include polybutene and low molecular weight polybutadiene.

[0074] When the resin composition of the present invention contains other components such as these additives and resins, their content is not limited, but it is preferable that the total content of components (A) to (C) is in a range such that it accounts for 50 mass% or more of the resin composition of the present invention, more preferably 60 mass% or more, and even more preferably 70 mass% or more.

[0075] <Method of producing flame-retardant polyolefin resin composition> There are no particular limitations on the method for producing the flame-retardant polyolefin resin composition of the present invention, as long as it can be produced so as to contain (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber. The flame-retardant polyolefin resin composition of the present invention can be produced, for example, by mixing the respective components simultaneously or in any order. Other components such as antioxidants and colorants may be added at any time as long as they can be uniformly dispersed.

[0076] There are no limitations on the equipment used to mix the raw material components, and general-purpose equipment such as a kneader, a Banbury mixer, a roll, a single-screw extruder, a twin-screw extruder, etc. The temperature during melt mixing may be any temperature at which at least one of the raw material components is in a molten state, but a temperature at which all of the components used are melted is usually selected, and the mixture is generally carried out at 150 to 250°C.

[0077] <Molded article of flame-retardant polyolefin resin composition> Molded articles of the flame-retardant polyolefin resin composition can be obtained by known molding methods, including but not limited to extrusion molding, compression molding, and injection molding. However, extrusion molding is preferred from the viewpoint of the fluidity of the flame-retardant polyolefin resin composition in a molten state. The molding temperature is not particularly limited as long as it is higher than the melting temperature of the flame-retardant polyolefin resin composition, but is preferably 150 to 200°C. If the molding temperature is above the lower limit, the fluidity of the molten resin composition is high, making it easy to obtain molded articles of the desired shape. On the other hand, if the molding temperature is below the upper limit, deterioration of the appearance due to foaming caused by decomposition of (B) metal hydroxide is less likely to occur.

[0078] <Crosslinked molded body> In a molded article made from a flame-retardant polyolefin resin composition containing at least (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber, there are no particular limitations on the crosslinking method used to form a crosslinked molded article in which the silane-modified polyolefin (A) is crosslinked. Examples include water crosslinking and electron beam irradiation crosslinking. Because the resin composition of the present invention contains the silane-modified polyolefin (A) as an essential component, a water crosslinking method in which a crosslinking catalyst is simply added or applied to the molded article is preferred. When water crosslinking is to be performed, the formation of a crosslinked structure is promoted by further contacting the molded article with liquid or vapor water at room temperature to about 200°C, usually room temperature to about 100°C, for about 10 seconds to 1 week, usually 1 minute to 1 day, after molding. It is preferable to mold the flame-retardant polyolefin resin composition into a desired shape before crosslinking to obtain a molded product, and then perform crosslinking to obtain a crosslinked molded product.This method makes it possible to obtain a crosslinked molded product with a smooth surface and a good appearance free of scorch (burn marks), for example, when extrusion molding is performed.

[0079] <Application> The uses of the crosslinked molded article of the present invention are not particularly limited, but because it has excellent heat resistance, mechanical properties, and flame retardancy, as well as an excellent appearance, it can be suitably used as an insulator or sheath for electric wires and cables. Furthermore, it can be suitably used for tubes for bundling electric wires, various insulating films, insulating pipes, power supply boxes, etc. Among the above, it is particularly preferable to use the crosslinked molded article of the present invention as an electric wire coating material. This electric wire coating material can be used to coat a conductor to produce an electric wire or cable. [Example]

[0080] Specific embodiments of the present invention will be described in more detail below using examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. Note that the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limit values ​​in the embodiments of the present invention, and preferred ranges may be defined by a combination of the above-mentioned upper or lower limit values ​​and the values ​​in the following examples or values ​​between the examples.

[0081] [Raw materials] In the following examples and comparative examples, the following raw materials were used. <Component (A): Silane-modified polyolefin> Silane-grafted polyolefin-1: Product name: Linkron SH710N (manufactured by Mitsubishi Chemical Corporation, MFR: 2 g / 10 min, density: 0.892 g / cm 3 , the content of ethylene units in all constituent monomer units: 50 mass% or more, ethylene-1-butene copolymer), hereinafter referred to as "SH710N".

[0082] <Component (B): Metal hydroxide> Metal hydroxide-1: Synthetic magnesium hydroxide, trade name Magseeds S-6 (manufactured by Konoshima Chemical Co., Ltd., average particle size: 1.0 μm, silane surface treatment), hereinafter referred to as “S-6.”

[0083] <Component (C): Siloxane-containing rubber> Siloxane-containing rubber-1: Trade name: Metablen SX-005 (manufactured by Mitsubishi Chemical Corporation), alkyl methacrylate-alkyl acrylate-dimethylsiloxane copolymer, hereinafter referred to as "SX-005."

[0084] <Other ingredients: resins> Polyethylene resin: ethylene-1-butene copolymer, trade name: ENGAGE 7256 (manufactured by Dow Chemical Japan, MFR: 2.5 g / 10 min, density: 0.885 g / cm 3 ), hereinafter referred to as "ENGAGE7256". <Other ingredients: additives> Antioxidant: pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], trade name: Irganox 1010 (manufactured by BASF Japan Ltd.), hereinafter referred to as "Irganox 1010". Crosslinking aid: trimethylolpropane triacrylate, trade name: A-TMPT (manufactured by Shin-Nakamura Chemical Co., Ltd.), hereinafter referred to as "A-TMPT."

[0085] <Other ingredients: Other> Brominated flame retardant: ethylenebis(pentabromophenyl), trade name: Seitex 8010 (manufactured by Albemarle Japan Co., Ltd.), hereinafter referred to as "Seitex 8010." Antimony-based flame retardant synergist: antimony trioxide, trade name: PATOX-KN (manufactured by Nippon Seiko Co., Ltd.), hereinafter referred to as "PATOX-KN." Crosslinking catalyst: dioctyltin dilaurate (manufactured by Nitto Kasei Co., Ltd.), hereinafter referred to as "crosslinking catalyst."

[0086] [evaluation] <Heat aging> The resulting flame-retardant polyolefin resin composition pellets were extruded into 1.0 mm thick tapes using a 20 mm extruder, and then punched out with a forging blade to prepare test specimens. A crosslinking catalyst was applied to the surface of the test specimen, which was then left to stand at 85°C and 85% humidity for 24 hours to obtain a crosslinked test specimen. Using these test specimens, a post-heat tensile test was performed according to the method of JIS K 6723. For tensile strength retention and elongation retention, the closer the numbers are to 100, the better the heat aging resistance.

[0087] <Flame retardancy> The oxygen index was measured as an evaluation index of flame retardancy. The obtained pellets of the flame-retardant polyolefin resin composition were compression molded at 180°C and then punched with a forging blade to prepare test specimens. As a post-processing step, a crosslinking catalyst was applied to the surface of the test specimen, and the specimen was then left to stand at 85°C and 85% humidity for 24 hours to obtain a crosslinked test specimen. The oxygen index was measured using this test specimen according to the method of JIS K 7201-2. The higher the oxygen index number, the better the flame retardancy.

[0088] <Heat resistance> The heat deformation rate was measured as an evaluation index for heat resistance. The obtained flame-retardant polyolefin resin pellets were compression molded at 180°C to prepare test specimens. As a post-processing step, a crosslinking catalyst was applied to the surface of the test specimen, and then crosslinked using the following crosslinking method to obtain a test specimen. Using this test specimen, the heat deformation rate was measured according to the method of JIS K 6723. The smaller the heat deformation rate, the better the heat resistance.

[0089] <Preparation of Resin Composition> Example 1 In a pressure kneader with a capacity of 1.0 L, 50 parts by mass of silane graft polyolefin-1 (SH710N) as component (A), 100 parts by mass of metal hydroxide-1 (S-6) as component (B), 5 parts by mass of siloxane component-containing rubber-1 (SX-005) as component (C), 50 parts by mass of polyethylene resin (ENGAGE7256) and 0.5 parts by mass of antioxidant (Irganox 1010) were added and kneaded for 15 minutes at a set temperature of 100 ° C. The resulting kneaded product was further sheeted with a roll and then pelletized with a pelletizer to produce a flame-retardant polyolefin resin composition. Various test pieces were prepared using pellets of the resulting flame-retardant polyolefin resin composition. After applying a crosslinking catalyst to the surface, the pellets were left to stand at 85°C and 85% humidity for 24 hours to obtain crosslinked molded articles. Various physical properties were then evaluated. The results are shown in Table 1.

[0090] <Examples 2 to 8, 10> According to the formulation shown in Table 1, a crosslinked molded article was obtained in the same manner as in Example 1.

[0091] Example 9 According to the formulation shown in Table 1, a flame-retardant polyolefin resin composition was prepared in the same manner as in Example 1. Various test specimens were prepared using pellets of the resulting flame-retardant polyolefin resin composition. As a post-processing step, the specimens were irradiated with an electron beam at an acceleration voltage of 650 kV and a dose of 100 kGy to obtain crosslinked molded articles. Various physical properties were then evaluated. The results are shown in Table 1.

[0092] Example 11 A flame-retardant polyolefin resin composition was obtained in the same manner as in Example 1 according to the formulation shown in Table 1, and various test pieces were then prepared using pellets of the resulting flame-retardant polyolefin resin composition. As post-processing, a crosslinking catalyst was applied to the surface, and the resulting pellets were allowed to stand at 85°C and 85% humidity for 24 hours, after which they were irradiated with an electron beam at an acceleration voltage of 650 kV and a dose of 100 kGy to obtain crosslinked molded articles. Various physical properties were then evaluated.

[0093] <Comparative Examples 1 to 6> According to the formulation shown in Table 2, a crosslinked molded article was obtained in the same manner as in Example 9. In Comparative Examples 1 to 5, component (A) was not used, and in particular, post-treatment to form a crosslinked molded article was not carried out in Comparative Example 5. In Comparative Example 6, component (B) was not used, and further, post-treatment to form a crosslinked molded article was not carried out.

[0094] [Table 1]

[0095] [Table 2]

[0096] (result) It was confirmed that all of Examples 1 to 11, in which the components (A), (B) and (C) were blended and then crosslinked into molded articles, had high flame retardancy while maintaining heat resistance. In contrast, the comparative examples gave the following results.

[0097] No improvement in flame retardancy was observed in Comparative Examples 1 to 4, which did not contain component (A), presumably because the dispersion of components (B) and (C) in the resin composition was insufficient. In Comparative Example 5, which is a non-crosslinked molded article containing no component (A), not only was no improvement in flame retardancy observed, but also the heat resistance was significantly poor, similar to Comparative Examples 1 to 4. In Comparative Example 6, a non-crosslinked molded article containing a brominated flame retardant and an antimony-based flame retardant synergist instead of component (B), not only was no improvement in flame retardancy observed, but heat resistance was also significantly poor. Comparative Example 6 contains a brominated flame retardant and an antimony-based flame retardant synergist as a flame retardant other than component (B), but no synergistic effect with component (C) was observed, suggesting that the coexistence of components (B) and (C) contributes to a dramatic improvement in flame retardancy.

[0098] It is known that halogen-antimony flame retardants exhibit the same level of flame retardancy as metal hydroxides when added in smaller amounts (Reference: Fundamentals of Flame Retardant Technology and the Latest Development Trends (Author: Nishizawa Hitoshi)). In Comparative Example 6, an investigation was conducted using an amount of addition at which the halogen-antimony flame retardant exhibited the same level of flame retardancy as metal hydroxides (same level of flame retardancy as in Comparative Example 1). As a result, it was confirmed that no significant improvement in flame retardancy was observed even when the halogen-antimony flame retardant coexisted with (A) silane-modified polyolefin and (C) siloxane component-containing rubber. This behavior is different from that in the case of (B) metal hydroxide.

[0099] From the above results, it is clear that the present invention can provide a crosslinked molded article that has high flame retardancy while maintaining heat resistance.

Claims

1. A molded article made of a flame-retardant polyolefin resin composition containing (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber, The (A) silane-modified polyolefin is crosslinked, The component (C) is a copolymer in which one or more vinyl monomers are graft-polymerized onto a composite rubber composed of a polyorganosiloxane rubber component and a polyalkyl(meth)acrylate component, A crosslinked molded article, wherein the blending ratio of the (A) component is 10 wt % or more and 70 wt % or less, the blending ratio of the (B) component is 20 wt % or more and 80 wt % or less, and the blending ratio of the (C) component is 2 wt % or more and 20 wt % or less, based on the entire flame-retardant polyolefin resin composition.

2. The crosslinked molded article according to claim 1 , wherein the silane-modified polyolefin (A) is water-crosslinked.

3. 3. The crosslinking method according to claim 1, wherein the metal hydroxide (B) is synthetic magnesium hydroxide. Molded body.

4. A wire covering material comprising the crosslinked molded article according to any one of claims 1 to 3.

5. An electric wire having a conductor covered with the electric wire covering material according to claim 4.

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