Non-halogen resin composition, production method of silane cross-linkable resin composition, electric wire / cable and production method thereof

Abstract

To provide: a non-halogen resin composition which can form a coating layer capable of achieving both suppression of fusion of resin cured products at a used environmental temperature and high flexibility of the resin cured product; and an electric wire / cable using the same.SOLUTION: A resin cured product formed of a non-halogen resin composition includes a base polymer containing a high melting point non-halogen resin having a melting point higher than 90°C and containing an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or lower, aluminum hydroxide as a flame retardant, and a silane compound to impart silane cross-linkability to the base polymer, and contains 35 mass% or more and 65 mass% or less respectively of the high melting point non-halogen resin and the an ethylene-α-olefin copolymer in the base polymer, in which the high melting point non-halogen resin is a cross-linked product, the ethylene-α-olefin copolymer is a silane cross-linked product, and 30 pts.mass or more and 150 pts.mass or less of the aluminum hydroxide is contained based on 100 pts.mass of the base polymer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a halogen-free resin composition, a method for producing a silane-crosslinkable resin composition, an electric wire / cable, and a method for producing the same. [Background technology]

[0002] In recent years, with growing awareness of environmental issues, non-halogen materials that do not contain halogen elements such as fluorine, chlorine, and bromine, which may generate harmful gases when burned, have become widely used as covering materials for electric wires and cables. Furthermore, electric wires and cables generally require flexibility for ease of handling. Because cables are structurally larger than electric wires and can withstand heavy loads depending on the conductor size, it is preferable to use flexible, low-melting-point, non-halogen resins as covering materials. Known examples of such low-melting-point, non-halogen resins include ethylene-vinyl acetate copolymer and ethylene-α-olefin copolymer.

[0003] Furthermore, in order to impart heat resistance and toughness to the coating materials for electric wires and cables, crosslinking processes that chemically bond molecules are generally used. Practical methods for this crosslinking process include the continuous crosslinking extrusion method, which connects a coating extruder to a crosslinking tube; the electron beam crosslinking method, which uses electron beams; and the silane crosslinking method, which uses moisture to bond a silane coupling agent grafted onto a resin. Of these, the silane crosslinking method is extremely useful from both an economical and environmental perspective, as it does not require large, dedicated facilities or large amounts of energy.

[0004] For example, a method for crosslinking a polyolefin resin is known in which a composition to which a radical generator and a silane compound have been added is subjected to a graft reaction with a polyolefin resin, and the resulting mixture is brought into contact with water under the action of a silanol condensation catalyst to cause crosslinking (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 60-17353 Summary of the Invention [Problem to be solved by the invention]

[0006] Meanwhile, cables with large conductor cross-sectional areas carry a relatively large current during use, and in some cases, the conductor heats up significantly, causing the temperature around the cable to rise to approximately 90°C. For this reason, cables whose outer surfaces are coated with a low-melting-point, halogen-free resin that has a melting point lower than the ambient temperature of use may experience fusion between the surfaces of the cables (between hardened resins) when multiple cables with large weights are installed and a large current is passed through them.

[0007] One possible solution to this problem is to replace the low-melting-point non-halogen resin that causes fusion with a non-halogen resin that has a melting point above the ambient temperature of use. However, while such a simple substitution can prevent fusion between cured resins within the ambient temperature of use, it usually results in a significant loss of flexibility of the cured resin.

[0008] An object of the present invention is to provide a halogen-free resin composition capable of forming a coating layer that can suppress fusion between cured resins at temperatures below the ambient temperature (90°C or below) and that can provide the cured resin with high flexibility, and to provide an electric wire or cable having a coating layer using the same. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0009] A brief summary of a representative embodiment of the present invention will be given below.

[0010] The cured resin product made from the halogen-free resin composition of the present invention comprises a base polymer containing a high-melting-point halogen-free resin having a melting point above 90°C, including an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or lower, aluminum hydroxide as a flame retardant, and a silane compound for imparting silane crosslinkability to the base polymer, wherein the high-melting-point halogen-free resin and the ethylene-α-olefin copolymer are each contained in the base polymer in an amount of 35% by mass to 65% by mass, the high-melting-point halogen-free resin is crosslinked, and the ethylene-α-olefin copolymer is silane crosslinked, and the aluminum hydroxide is contained in an amount of 30 parts by mass to 150 parts by mass per 100 parts by mass of the base polymer.

[0011] The method for producing a silane-crosslinkable resin composition of the present invention comprises the steps of: kneading a base polymer containing a high-melting-point halogen-free resin having a melting point above 90°C, including an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or lower, aluminum hydroxide as a flame retardant, a silane compound, and a peroxide at a temperature equal to or higher than the melting point of the base polymer and lower than the decomposition temperature of the peroxide; and, after the kneading, heating the mixture to a temperature equal to or higher than the decomposition temperature of the peroxide to introduce the silane compound into the base polymer by a graft reaction. The base polymer contains 35 to 65% by mass of the halogen-free resin and the ethylene-α-olefin copolymer, respectively, and 30 to 150 parts by mass of the aluminum hydroxide per 100 parts by mass of the base polymer.

[0012] The electric wire or cable of the present invention comprises a conductor and a covering layer that covers and protects the conductor, and the covering layer is a cured resin product of the resin composition described above.

[0013] The method for producing an electric wire or cable of the present invention is characterized by comprising the steps of: grafting a silane compound in the non-halogen resin composition onto a base polymer to introduce the silane compound thereinto, thereby obtaining a silane crosslinkable resin composition; and extrusion coating the outer periphery of a conductor with the silane crosslinkable resin composition and a resin composition containing a silane crosslinking catalyst, and curing the silane crosslinkable resin composition by silane crosslinking in the presence of the silane crosslinking catalyst and moisture. [Effects of the Invention]

[0014] The non-halogen resin composition, electric wire / cable, and method for producing the same of the present invention can provide a non-halogen resin composition capable of forming a coating layer that can suppress fusion between cured resins at the ambient temperature of use (90°C or lower) and achieve high flexibility of the cured resin, as well as an electric wire / cable using the same.

[0015] Furthermore, according to the method for producing a silane-crosslinkable resin composition of the present invention, it is possible to provide a silane-crosslinkable resin composition capable of forming the coating layer of the above-mentioned electric wire / cable. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view of a cable according to an embodiment of the present invention; [Figure 2] FIG. 1 is a diagram showing a schematic configuration of an extruder used in the examples to carry out a cable production (extrusion) step. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. In the following embodiments, explanations of the same or similar parts will not be repeated unless particularly necessary.

[0018] [Halogen-free resin composition] The halogen-free resin composition according to the present embodiment is a halogen-free resin composition comprising a base polymer containing a high-melting-point halogen-free resin having a melting point above 90°C, including an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or lower, aluminum hydroxide as a flame retardant, and a silane compound for imparting silane crosslinkability to the base polymer. Each of the components constituting this halogen-free resin composition will be described in detail below.

[0019] (Base polymer) The base polymer in this embodiment comprises a high-melting-point halogen-free resin having a melting point above 90°C, including an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or less.

[0020] The high-melting-point non-halogen resin used herein has a melting point exceeding 90°C and may be a non-halogen resin containing at least an ethylene-ethyl acrylate copolymer. Here, "having a melting point exceeding 90°C" means that the resin that constitutes this high-melting-point non-halogen resin has a melting point exceeding 90°C. The melting point of the high-melting-point non-halogen resin here is preferably in the range of 90 to 110°C.

[0021] Ethylene-ethyl acrylate copolymer is a component whose crystalline components do not melt at 90°C and whose melting point is not excessively high (approximately 100°C), so it is a component that suppresses fusion in an environment of about 90°C and prevents the entire resin composition from becoming excessively hard. In addition, since it contains a polar acrylic group in the molecule, it is expected to have improved oil resistance.

[0022] Furthermore, by using ethylene-ethyl acrylate copolymer as the main component, it is possible to reduce the odor derived from the acetic acid component, which is the case with conventionally known ethylene-vinyl acetate copolymers, and it is expected to be possible to use it comfortably even in applications involving human contact. In the present embodiment, it is preferable that ethylene-vinyl acetate copolymer is not included.

[0023] Here, the high-melting-point non-halogen resin may be any non-halogen resin material having a melting point above 90°C, in addition to ethylene-ethyl acrylate copolymer, and examples thereof include resins that have hydrocarbons in part of their molecular structure, such as the molecular skeleton or molecular side chains, and that do not contain halogen elements such as fluorine, chlorine, or bromine in their molecular structure.

[0024] Examples of high-melting point halogen-free resins other than ethylene-ethyl acrylate copolymers include ethylene-methyl acrylate copolymers, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, thermoplastic elastomers, polyamide polymers, and modified products thereof (for example, those whose molecular structure is partially modified with maleic acid, a silane coupling agent, or the like), and these can be used alone or in combination of two or more types.

[0025] It is preferable to use an ethylene-ethyl acrylate copolymer alone as the high-melting-point non-halogen resin. When a high-melting-point non-halogen resin other than the ethylene-ethyl acrylate copolymer is used in combination as the high-melting-point non-halogen resin, the high-melting-point non-halogen resin preferably contains 50% by mass or more of the ethylene-ethyl acrylate copolymer, and more preferably contains 80% by mass or more of the ethylene-ethyl acrylate copolymer.

[0026] Next, the ethylene-α-olefin copolymer having a melting point of 70°C or less contained in the base polymer is a copolymer of ethylene and an α-olefin, and is a compound having a melting point of 70°C or less.

[0027] The α-olefin component in this ethylene-α-olefin copolymer is not particularly limited as long as it is an α-olefin, and examples thereof include propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Among these, non-polar monomers such as 1-butene and 1-octene are preferred for use as a coating material for electric wires and cables. This is because, for example, when a polar group such as vinyl acetate is contained, as in the case of conventionally known ethylene-vinyl acetate copolymers (EVA), the polar group content becomes high, and therefore attention must be paid to electrical insulation properties.

[0028] The high-melting-point non-halogen resin and the ethylene-α-olefin copolymer are each contained in the base polymer in an amount of 35% by mass to 65% by mass. By maintaining the content within this range, fusion can be suppressed at temperatures below the operating temperature (90°C), ensuring the desired flexibility and electrical insulation. Furthermore, it is preferable to use a high-melting-point non-halogen resin content of 35 to 50% by mass and an ethylene-α-olefin copolymer content of 50 to 65% by mass, which will result in even higher flexibility and electrical insulation.

[0029] (Flame retardant) The flame retardant used in this embodiment is aluminum hydroxide, which is preferable because it has a high flame retardant effect and does not generate deliquescent metal salts even when nitrogen oxides (NOx) and sulfur oxides (SOx) are present in the usage environment atmosphere.

[0030] The aluminum hydroxide is not particularly limited as long as it can be used as a known flame retardant, and may be either surface-treated or untreated. Examples of surface treatments include treatment with a fatty acid and treatment with a silane coupling agent, with fatty acid treatment being preferred.

[0031] Aluminum hydroxide whose surface has been treated with a fatty acid generally exhibits improved affinity and dispersibility with the base polymer, thereby improving the flame retardancy and mechanical properties of the resin composition. The fatty acid used for the surface treatment may be any higher fatty acid having approximately 10 or more carbon atoms, and either saturated or unsaturated fatty acids can be used. Specific examples of higher saturated fatty acids include lauric acid, palmitic acid, stearic acid, and arachidic acid. Examples of higher unsaturated fatty acids include monounsaturated fatty acids such as oleic acid, myristoleic acid, palmitoleic acid, and eicosenoic acid, diunsaturated fatty acids such as linoleic acid, and triunsaturated fatty acids such as linolenic acid. Stearic acid and oleic acid are particularly preferred because they are widely used. These fatty acids are not particularly limited, and they can be used alone or in combination.

[0032] The amount of aluminum hydroxide added is preferably 30 to 150 parts by mass, more preferably 50 to 100 parts by mass, per 100 parts by mass of the base polymer. By setting the content within this range, it is possible to achieve high levels of flame retardancy, flexibility, and electrical insulation required for a wire / cable coating material.

[0033] (Silane compounds) The silane compound in this embodiment is a compound that is bonded to the resin that constitutes the base polymer by a graft reaction to impart silane crosslinkability.

[0034] The silane compound is not particularly limited as long as it can be bonded to the base polymer by a graft reaction and can impart silane crosslinking properties, and examples thereof include silane coupling agents.

[0035] The silane coupling agent may be any agent having a carbon-carbon double bond in its molecular structure, and specific examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane.

[0036] As the silane coupling agent, those containing a methacryl group are effective, particularly from the viewpoint of safety during production (high flash point) and excellent economy. Specific examples of this silane coupling agent include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane, and 3-methacryloxypropyltrimethoxysilane is particularly preferred from the viewpoint of reactivity.

[0037] The amount of the silane compound added is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the base polymer. By setting the content within this range, the silane compound can be introduced into the base polymer and sufficiently cured by silane crosslinking, which will be described later.

[0038] To graft the silane compound onto the base polymer, for example, a peroxide may be added. The peroxide may have a relatively high hydrogen abstraction ability and a one-minute half-life temperature of 120°C to 200°C (preferably 150°C to 200°C for manufacturing reasons). Specific examples of the peroxide include dicumyl peroxide, 1,1-di(t-butylperoxy)cyclohexane, 1,3-bis(t-butylperoxyisopropyl)benzene, t-butylperoxyisopropyl carbonate, t-amylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, di-t-amyl peroxide, 1,1-di(t-amylperoxy)cyclohexane, and t-butylperoxy-2-ethylhexyl carbonate, which may be used alone or in combination. However, the peroxide is not limited to these.

[0039] The amount of peroxide added is preferably 0.01 to 1 part by mass relative to 100 parts by mass of the base polymer, and more preferably 0.1 to 0.8 parts by mass, particularly when a silane coupling agent containing a methacrylic group is used. By setting the content within this range, the base polymer can be sufficiently cured by silane crosslinking, which will be described later, and the silane compound can be introduced.

[0040] Furthermore, in order to improve the crosslinking rate when the base polymer obtained by the graft reaction (grafted) is subjected to silane crosslinking, a crosslinking catalyst can be contained in the resin composition. Note that, since the presence of a crosslinking catalyst initiates crosslinking, it is preferable to add the catalyst at the timing when the crosslinking reaction is carried out.

[0041] Specific examples of the crosslinking catalyst include elements containing Group II elements such as magnesium and calcium, Group VIII elements such as cobalt and iron, or metals such as tin, zinc, and titanium, metal compounds, metal salts of octylic acid or adipic acid, amine compounds, and acids. More specific examples include dioctyltin dineodecanoate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctaate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, dibutylamine, hexylamine, pyridine, inorganic acids such as sulfuric acid, and hydrochloric acid, and organic acids such as toluenesulfonic acid, acetic acid, stearic acid, and maleic acid.

[0042] The amount of the crosslinking catalyst added is preferably 0.01 to 0.5 parts by mass, more preferably 0.02 to 0.1 parts by mass, relative to 100 parts by mass of the base polymer. By setting the content within this range, the silane compound introduced into the base polymer can be efficiently crosslinked to obtain a cured resin.

[0043] Furthermore, the halogen-free resin composition of the present embodiment may contain known additives, such as antioxidants, lubricants, flame retardants, and colorants, as long as they do not impair the effects of the present embodiment.

[0044] Examples of antioxidants include phenol-based antioxidants, sulfur-based antioxidants, phenol / thioester-based antioxidants, amine-based antioxidants, and phosphorous-based antioxidants.

[0045] Examples of lubricants include fatty acid amides, zinc stearate, silicones, hydrocarbons, esters, alcohols, and metal soaps.

[0046] The flame retardant is a flame retardant other than the above aluminum hydroxide, and examples thereof include metal hydroxides other than aluminum hydroxide, halogen-based, phosphorus-based, and antimony-based flame retardants.

[0047] When applied to electric wires and cables, the colorant is often selected from black, yellow, and green, and in this case, the colorant may be blended so as to achieve the above-mentioned color. Examples of such colorants that can be used include carbon black, inorganic pigments, organic pigments, and dyes.

[0048] [Silane-crosslinkable resin composition] The silane-crosslinkable resin composition of the present embodiment is a resin composition obtained by grafting a silane compound onto a base polymer in the above-described halogen-free resin composition.

[0049] This grafting treatment can be carried out, for example, by kneading a resin composition containing a base polymer containing a high-melting-point halogen-free resin having a melting point above 90°C, including an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or less, aluminum hydroxide as a flame retardant, a silane compound for imparting silane crosslinkability to the base polymer, and a peroxide at a temperature above the melting point of the base polymer and below the decomposition temperature of the peroxide, and after kneading, heating to a temperature above the decomposition temperature of the peroxide to introduce the silane compound into the base polymer by a graft reaction.

[0050] When producing a silane-crosslinkable resin composition by the above-mentioned grafting treatment, first, the base polymer is melted, and aluminum hydroxide as a flame retardant, a silane compound, and a peroxide are kneaded in advance at a temperature lower than the decomposition temperature of the peroxide. Then, the mixture is heated to a temperature higher than the decomposition temperature of the peroxide and kneaded to graft the silane compound onto the base polymer, thereby avoiding the application of excessive heat to the resin composition during and after the grafting treatment.

[0051] If aluminum hydroxide were mixed in at high temperatures during or after grafting, it could cause premature crosslinking in the resin composition (which would normally occur during the coating of electric wires and cables), significantly reducing moldability during extrusion coating. Kneading aluminum hydroxide in a separate process after grafting or mixing aluminum hydroxide during extrusion coating is not economical, and is also not practical from the standpoint of homogeneous dispersion of aluminum hydroxide.

[0052] The decomposition temperature of the peroxide is defined as a temperature 30°C lower than the one-minute half-life temperature of the peroxide. That is, by kneading the components at a temperature below the decomposition temperature of the peroxide, the components are thoroughly kneaded at a temperature where thermal decomposition of the peroxide is unlikely to occur, and then the components are heated to the decomposition temperature of the peroxide or higher to initiate the grafting reaction, whereby the peroxide is decomposed and the base polymer is efficiently grafted.

[0053] The grafting temperature is preferably equal to or higher than the one-minute half-life temperature of the peroxide, and the grafting time is preferably at least three times, more preferably at least four times, even more preferably at least five times, and particularly preferably at least six times the time it takes for the peroxide to decrease by half at the grafting temperature (the half-life time of the peroxide).

[0054] [Cured resin] The silane-crosslinkable resin composition obtained as described above can be further converted into a cured resin by silane crosslinking the base polymer grafted with a silane compound. Silane crosslinking can be formed by reacting the silyl groups of the silane compound introduced into the base polymer with a silane crosslinking catalyst in the presence of moisture, thereby crosslinking (curing) the polymer molecules to obtain a cured resin.

[0055] Therefore, the cured resin product obtained here is a cured resin product obtained by crosslinking, by a silane crosslinking method, a so-called non-halogen resin composition (the above-mentioned non-halogen resin composition), in which halogen elements such as chlorine and bromine are not intentionally added to the resin itself or to the compounded additives.

[0056] This cured resin is a mixture of appropriate amounts of a high-melting-point, halogen-free resin containing ethylene-ethyl acrylate copolymer with a melting point above 90°C, an ethylene-α-olefin copolymer with a melting point of 70°C or below that offers particularly excellent flexibility, and aluminum hydroxide, which has high flame retardancy and does not generate deliquescent metal salts even in the presence of nitrogen oxides (NOx) or sulfur oxides (SOx) in the operating environment. Therefore, when applied to a cable, even when the operating temperature of the cable's outer periphery reaches around 90°C, the cured resin maintains its flexibility, flame retardancy, and deliquescence resistance while highly suppressing fusion at that operating temperature.

[0057] Furthermore, by suppressing the tensile peel strength of this cured resin to 5N or less after heat and pressure adhesion treatment at 90°C, even if fusion occurs between the cured resin pieces, they can be peeled off with very little force, and no fusion marks remain on the surface of the cured resin after peeling, so the appearance is not marred. Therefore, this resin composition does not pose any problems in practical use as a cable covering layer.

[0058] Here, the specific pressure conditions shown in this example are sufficient at about 3 MPa, and no change in adhesion was observed even when processing was performed at a pressure higher than this. Since pressures exceeding 5 MPa cause the cured resin to become extremely thin and there is a risk of rupture, molding at 3 to 5 MPa is considered appropriate. Note that the tensile peel strength referred to in this specification is the tensile peel strength of a sample obtained by pressure-welding the cured resin in a press under conditions of 90°C, 3 MPa, and 1 hour.

[0059] The tensile strength of this cured resin at 100% elongation is preferably 7 MPa or less, more preferably less than 6.5 MPa. This tensile strength is calculated by punching out a JIS No. 3 dumbbell specimen from the cured resin cut to a thickness of 1 mm, marking the center of the specimen at intervals of 20 mm, and measuring the tensile load at the point where the specimen is elongated to 100% between the marks at a tension speed of 200 mm / min, using the following formula: δ=F / A (δ: tensile strength (MPa), F: tensile load (N), A: cross-sectional area of ​​the test piece (mm 2 ))

[0060] The oxygen index of this cured resin is preferably 21 or more, and more preferably 22 or more. The oxygen index represents the minimum oxygen concentration (volume %) required to sustain combustion of a material, and is used as an index for evaluating the flammability of a material. This oxygen index is determined in accordance with JIS K 7201-2 (2007).

[0061] Furthermore, the volume resistivity of this cured resin was 5.0 × 10 14 Ω·cm or more is preferable, and 1.0×10 15 Ω·cm or more is more preferable. This volume resistivity is used to evaluate the electrical insulation properties of the cured resin, and can be determined from the current value after applying a voltage under specified conditions using an ultra-high insulation resistance measuring device.

[0062] As described above, by adjusting the compounding recipe of the resin composition to a predetermined value, it is possible to obtain the flame retardancy and electrical insulation properties required for a coating material for electric wires and cables. It is preferable that these properties, specifically, the oxygen index and volume resistivity, are within the specified ranges.

[0063] [Wires and cables] The electric wire / cable of this embodiment has a conductor and a covering layer that covers and protects the conductor, and the covering layer is a cured resin product of the non-halogen resin composition of this embodiment described above. The covering layer can be formed by directly covering the conductor to form an electric wire, or can be formed by indirectly covering the conductor and an insulating layer that covers the conductor to form a cable.

[0064] A cross-sectional view of a cable according to an embodiment of the present invention is shown in Fig. 1. As shown in Fig. 1, the cable 1 is configured to have a conductor 2, an insulating layer 3, and a covering layer 4.

[0065] The conductor 2 may be any commonly used metal wire, such as a copper wire, a copper alloy wire, an aluminum wire, a gold wire, or a silver wire. Alternatively, a metal wire plated with a metal such as nickel may be used as the conductor 2. Furthermore, a twisted conductor made by twisting metal wires may also be used as the conductor 2.

[0066] The insulating layer 3 is not particularly limited as long as it is made of an insulating material that is normally used for cables, such as polyvinyl chloride, fluororesin, cross-linked polyethylene, natural rubber, synthetic rubber, etc.

[0067] The coating layer 4 is formed from a cured resin product of the halogen-free resin composition described in the present embodiment.

[0068] This cable can be manufactured by using an extruder to coat the outer periphery of the insulating layer 3 formed on the conductor 2 with the above-described halogen-free resin composition to produce the cable 1. More specifically, the extrusion coating process can use a so-called two-shot silane crosslinking method in which a silane-crosslinkable resin composition grafted with a silane compound is mixed with a resin composition containing a crosslinking catalyst. After the extrusion coating process, the cable can be stored naturally or placed in a steam chamber at 100°C or below to supply moisture to the coating material, thereby promoting the silane crosslinking reaction and producing the final product.

[0069] Fig. 2 is a diagram showing a schematic configuration of an example of an extruder for producing a cable according to the present embodiment. As shown in Fig. 2, extruder 11 includes a cylinder 20, a screw 13 rotatably provided within cylinder 20, a hopper 12 for supplying material into cylinder 20, and a crosshead 16. Extruder 11 also includes a neck 15 between crosshead 16 and screw 13, and a breaker plate 14 between neck 15 and screw 13. Crosshead 16 has a die 17, and an electric wire 18 (a conductor covered with an insulator) passing through crosshead 16 is covered with a sheath within crosshead 16, passes through die 17, and is drawn out from within crosshead 16 as cable 19.

[0070] The resin composition containing the crosslinking catalyst used here may be formed by mixing the crosslinking catalyst with a base resin. The base resin used here is not particularly limited as long as it does not impair the effects of the present invention, and is preferably selected from the high-melting-point non-halogen resins and ethylene-α-olefin copolymers described above in the resin composition. In addition to the base resin and crosslinking catalyst, antioxidants, copper inhibitors, etc. may also be included.

[0071] Examples of antioxidants include phenolic compounds such as 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (CAS No. 27676-62-6), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (CAS No. 6683-19-8), and n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenyl)propionic acid (CAS No. 2082-79-3), poly(1,2-dihydro-2,2,4-trimethylquinoline) (CAS No. 26780-96-1), and ethoxyquin (CAS No. 91-53-2), 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (CAS No. 10081-67-1), N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine (CAS No. 793-24-8), and other amine compounds; pentaerythritol tetrakis[3-(dodecylthio)propionic acid] (CAS No. 29598-76-3), ditridecyl 3,3'-thiobispropionate (CAS No. 10595-72-9), didodecyl 3,3'-thiobispropionate (CAS No. 123-28-4), dioctadecyl 3,3'-thiobispropionate (CAS No. 693-36-7), and other sulfur compounds; 4,4'-thiobis(6-tert-butyl-m-cresol) (CAS Examples include phenol-sulfur compounds such as 2-mercaptobenzimidazole (CAS No. 583-39-1), benzimidazole compounds such as 2-mercaptobenzimidazole (CAS No. 583-39-1), and thiourea compounds such as 1,3,3-tributylthiourea (CAS No. 2422-88-0). There are no restrictions on how these compounds can be added; they can be used alone, in combination with two or more types, as a mixture, or as a masterbatch mixed with a non-halogen resin.

[0072] As the copper inhibitor, a common heavy metal deactivator can be used, and specific examples include compounds such as N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine (CAS No. 32687-78-8), N-(2H-1,2,4-triazol-5-yl)salicylamide (CAS No. 36411-52-6), and dodecanedioic acid bis[N2-(2-hydroxybenzoyl)hydrazide] (CAS No. 63245-38-5). These compounds may be used alone or in mixtures with other compounds, and the conditions for use are not critical.

[0073] The cable obtained in this manner has the configuration shown in Fig. 1, and its size is not particularly limited. For example, the diameter of the conductor 2 is 10.4 mm, the diameter including the insulating layer 3 is 13.4 mm, and the diameter of the cable 4 is 36 mm. [Example]

[0074] Next, the present embodiment will be described in detail with reference to examples and comparative examples.

[0075] [Examples 1 to 10, Comparative Examples 1 to 5] The following procedures were carried out: mixing a silane coupling agent and various additives into a base polymer, silane grafting, preparation of a crosslinking catalyst masterbatch, and then manufacturing cables using the prepared compounds, followed by crosslinking. The following conditions are examples and are not intended to be limiting.

[0076] (Preparation of Resin Composition and Grafting Treatment) The base polymer, silane coupling agent, peroxide, flame retardant, antioxidant, lubricant, and colorant were added to a 25-liter pressure kneader (the kneader tank was set to a temperature above the melting point of the base polymer but below the decomposition temperature of the peroxide) based on the formulations shown in Tables 2 and 3, and the mixture was kneaded under pressure at a rotor speed of 10 rpm for 10 minutes. Dissolving the peroxide in the silane coupling agent beforehand improves the dispersibility of the peroxide in the polymer. The silane coupling agent (dissolving the peroxide) can be impregnated into fillers such as flame retardants during addition to the kneader tank to reduce adsorption of the silane coupling agent to the kneader tank. These conditions are merely examples and are not limiting. Additives such as fillers and plasticizers may also be added to develop desired properties in the resin composition.

[0077] Grafting of the silane coupling agent is carried out continuously after pressurized kneading. Specifically, kneading is performed to raise the temperature above the decomposition temperature of the peroxide (practically, above the one-minute half-life temperature), and kneading is continued until the peroxide is fully decomposed. The time required for the peroxide to fully decompose should be at least six times the half-life of the peroxide at the kneading temperature. In this example and comparative example, the grafting was performed by raising the temperature to 180°C to decompose the peroxide and maintaining this temperature for 4 minutes. After the grafting, the material was promptly discharged from the kneader tank, extruded into a strand, cooled with water, and pelletized to produce pellets of the silane graft composition. The granulation method is not limited to the above; for example, pellets may be produced using a hot cut machine without water cooling. A release agent can also be used to prevent adhesion between pellets. The release agent can be of any composition or form, such as powder, liquid, or mist. However, for economic reasons, it is effective to use talc, for example.

[0078] (Preparation of crosslinking catalyst masterbatch) The crosslinking catalyst masterbatches in Tables 2 and 3 were prepared in the formulation shown in Table 4 as follows.

[0079] The polymer (non-halogen resin), crosslinking catalyst (silanol condensation catalyst), antioxidant, and copper inhibitor were mixed in a 25L pressure kneader (the kneader tank was above the melting point of the base polymer) at a rotor speed of 20 rpm for 5 minutes, and the mixed material was discharged from the kneader tank, extruded into strands, cooled with water, and pelletized to produce crosslinking catalyst masterbatch pellets.

[0080] Here, the granulation method is not limited to the above, and for example, pellets may be produced using a hot cut facility without water cooling. A release agent may also be used to prevent the pellets from sticking together.

[0081] (Cable manufacturing and cross-linking) In this example and comparative example, cables were produced as follows using the extruder 11 shown in Figure 2. Table 1 shows the extrusion conditions for the cable extrusion process. At this time, cylinders 1 to 5 are connected in this order from the hopper side to the head side to form cylinder 20, and the relationship between the length (L) and inner diameter (D) of cylinder 20 is expressed as L / D.

[0082] Conductor cross section of 100mm, consisting of multiple strands of tin-plated annealed copper wire 2 A cable core was extrusion-coated to a thickness of 2.0 mm with an ethylene-propylene rubber copolymer blend as an insulator on a conductor (outer diameter 15.2 mm) and crosslinked, and then a dry blend of the resin composition after grafting (silane-crosslinkable resin composition) obtained above, a crosslinking catalyst masterbatch, and a pigment masterbatch for colors other than black was extrusion-coated to a thickness of 2.6 mm using a single-screw extruder with a screw diameter of 90 mm, to produce a cable with the configuration shown in Figure 1. After fabrication, the cable was stored at 60°C in a saturated steam atmosphere for 24 hours to undergo a crosslinking treatment and produce the final product.

[0083] To achieve the above-mentioned kneading and grafting treatment, any commonly used kneading or reaction device such as a roll mill, extruder, mixer, or autoclave may be used other than a kneader, and the kneading and grafting conditions are not limited to those described above. Similarly, cable production is also an example, and an electric wire shape may be obtained by extrusion coating directly onto a conductor, and the extruder, cable core, cable structure, and crosslinking conditions are not limited to those described above.

[0084] [Table 1]

[0085] [Characteristics evaluation] The prepared compound after kneading and the cable after crosslinking treatment were evaluated as follows. The evaluation results are shown in Tables 2 and 3.

[0086] <Peeling between materials and cables> Here, the peelability of the material and the cable surface is evaluated by the peelability when they are brought into contact at 90°C (the material exposure temperature under normal use conditions).

[0087] The silane-grafted silane-crosslinkable resin composition, crosslinking catalyst masterbatch, and pigment masterbatch were kneaded in a roller mill and molded into a 1 mm thick sheet using a press. The resulting sheet was crosslinked by storing it for 24 hours in a saturated steam atmosphere at 60°C, the same crosslinking conditions as for cables. The crosslinked sheet was cut into 10 mm x 100 mm strips, and two sheets were stacked together. A 10 mm x 60 mm section was pressure-fused in a press at 90°C, 3 MPa, and 1 hour to prepare a sample for tensile peel testing (the unfused 10 mm x 40 mm section was used as the gripping part for the tensile test).

[0088] The tensile peel test was carried out using a Tensilon tensile testing machine, measuring the maximum load (tensile peel force) when the sample was peeled at a tensile speed of 200 mm / min. The sheet surface after peeling was visually inspected, and those that showed no change before and after peeling were rated as "none" (pass), and those that showed whitening of the sheet surface after peeling (change in the refractive index of the material due to fusion) were rated as "yes" (fail).

[0089] For the cross-linked cables, two sets of cables were prepared by cutting two cables to a length of 300 mm and fixing (contacting) them with wire, which were then stacked at right angles to each other and stored in a thermostatic chamber at 90°C for 24 hours to prepare samples for checking inter-cable peelability. After removing them from the thermostatic chamber and leaving them at room temperature (23°C) for one hour, samples were rated as "good" (passed) if the contact points of the stacked cables had manually peeled off without fusion and no visible traces of fusion at the contact points after peeling, and "poor" (failed) if the contact points had fused or if whitening marks were visible after peeling.

[0090] <Flexibility (tensile strength at 100% elongation)> The cured resin was peeled off from the crosslinked cable sheath, and a 1mm thick piece was cut from the sheath surface. This was then punched into the shape of a JIS No. 3 dumbbell piece, and benchmark lines were marked at 20mm intervals in the center to prepare tensile test specimens. The tensile load was measured at the point where the test piece was elongated to 100% between the benchmark lines at a tension speed of 200mm / min, and the tensile strength was calculated using the following formula. δ=F / A (δ: tensile strength (MPa), F: tensile load (N), A: cross-sectional area of ​​the test piece (mm 2 ))

[0091] The evaluation was carried out with the following markings: a tensile strength at 100% elongation of less than 6.5 MPa was deemed to have sufficient flexibility and marked with "◎", a tensile strength of 6.5 MPa to 7.0 MPa was deemed to be at a level that is acceptable for practical use, such as wiring work, and a marking with "○", and a marking with more than 7.0 MPa was deemed to have insufficient flexibility and marked with "×". The evaluation criteria were "◎" and "○" as pass, and "×" as fail.

[0092] <Flame retardancy (oxygen index)> A 3 mm thick crosslinked sheet was prepared using the same method as the sample for the inter-sheet peel test. The oxygen index of this sheet was measured using a Toyo Seiki Oxygen Indexer according to JIS K 7201-2 (2007). An oxygen index of 22 or higher was designated as having sufficient flame retardancy and marked with a double circle. An oxygen index of 21 to 22 was designated as having sufficient flame retardancy for practical applications requiring flame retardancy in a cable flame retardancy test under horizontal or 60-degree inclined test conditions and marked with a circle. An oxygen index of less than 21 was designated as having insufficient flame retardancy and marked with an x. The evaluation criteria were as follows: x and x were considered pass, and x was considered fail.

[0093] <Electrical insulation (volume resistivity)> A 1 mm thick crosslinked sheet was prepared using the same method as the sample for the inter-sheet peel test. The volume resistivity of this sheet was calculated from the current value after applying DC 500 V for 1 minute at room temperature (23°C) using an ultra-high insulation resistance measuring instrument R8340A manufactured by ADVANTEST. The volume resistivity was found to be 1.0 x 10 15 Those with a volume resistivity of 5.0×10 Ω·cm or more are considered to have sufficient insulation and are marked with a "◎" 14 Ω cm or more 1.0×10 15 A value of "○" indicates that a resistance of less than Ω·cm is generally applicable without any problems unless a high level of insulation is required, and a value of "○" indicates that a volume resistivity of 5.0×10 14 Those with a value of less than Ω·cm were deemed to have insufficient insulation and were marked with an "×". The evaluation criteria were "◎" and "○" as pass, and "×" as fail.

[0094] The overall evaluation was that a product that passed all evaluation items was considered to be a pass, and a product that failed even one item was considered to be a fail.

[0095] [Table 2]

[0096] [Table 3]

[0097] Of the products shown in Tables 2 and 3, "Rexpearl A3100" (melting point 104°C, vinyl acetate content 20% by mass) is manufactured by Ube Maruzen Polyethylene Co., Ltd., "Tafmer DF840" (melting point 66°C, ethylene-1-butene copolymer) and "Tafmer DF940" (melting point 77°C, ethylene-1-butene copolymer) are manufactured by Mitsui Chemicals, Inc., "Evolue SP2520" (linear low-density polyethylene) is manufactured by Japan Polyethylene Co., Ltd., "KBM-503" (3-methacryloxypropyltrimethoxysilane) is manufactured by Shin-Etsu Chemical Co., Ltd., "DCP" (dicumyl peroxide) is manufactured by NOF Corporation, "Antioxidant A" (sulfur-based secondary antioxidant) is manufactured by ADEKA Corporation, "Crodamide EBO" (ethylene bisoleamide) is manufactured by CRODA, and "BF-013 "S" (aluminum hydroxide (fatty acid surface treatment grade) is manufactured by Nippon Light Metal Co., Ltd., "carbon black" (Asahi Thermal Carbon) is manufactured by Asahi Carbon Co., Ltd., "pigment masterbatch (yellow)" (masterbatch containing condensed azo pigment) and "pigment masterbatch (green)" (masterbatch containing a mixture of phthalocyanine blue and monoazo yellow pigment) are manufactured by Dainichiseika Chemicals Co., Ltd.

[0098] [Table 4]

[0099] Of the products shown in Table 4, "Elvalloy 1125AC" is manufactured by DOW, "Antioxidant B" (hindered phenol primary antioxidant) and "Heavy Metal Deactivator" are manufactured by ADEKA, and "Neostan U-830" (dioctyltin dineodecanoate) is manufactured by Nitto Denko.

[0100] The examples showed that if the base polymer contains 35 to 65 mass% of a high-melting-point halogen-free resin with a melting point above 90°C and 35 to 65 mass% of an ethylene-α-olefin copolymer with a melting point of 70°C or less, and if the flame retardant aluminum hydroxide is blended in a ratio of 30 to 150 mass parts per 100 mass parts of base polymer, the practically problematic fusion phenomenon between sheath materials will not occur at 90°C, which is the exposure temperature of the cable sheath in the usage environment, and the flexibility, flame retardancy, and electrical insulation required for the cable will be satisfied.

[0101] Furthermore, Example 4 showed that high-melting-point non-halogen resins with a melting point above 90°C can be made not only from ethylene-ethyl acrylate copolymer alone, but also from a mixture of multiple polymers, and Examples 9 and 10 showed that in addition to the black color that is commonly used as a coating material for electric wires and cables, it is also possible to make them yellow or green.

[0102] In particular, Examples 1 to 3 showed that higher flexibility, flame retardancy, and electrical insulation can be achieved by using 35 to 50 mass% of a high-melting-point halogen-free resin having a melting point above 90°C and 50 to 65 mass% of an ethylene-α-olefin copolymer having a melting point of 70°C or less, and Examples 5 to 8 showed that higher flexibility, flame retardancy, and electrical insulation can be achieved by using 50 to 100 mass parts of aluminum hydroxide.

[0103] It was also found that even when cables come into contact with each other at 90°C, they can be used without any problems in practice as long as the tensile peel strength between the materials is around 5.0 N or less.

[0104] The polymers and additives used in this example are merely examples and are not intended to be limiting. Furthermore, the resin composition is not limited to use in cables in which a sheath is applied to the outer periphery of an insulator, as produced in this example, but can also be used as a material for the coating of so-called insulated wires or wires, which are made up of only a conductor and a coating (insulator).

[0105] From Comparative Example 1, it was found that when the high-melting-point non-halogenated resin having a melting point above 90°C is 30% by mass or less and the ethylene-α-olefin copolymer having a melting point below 70°C is 70% by mass or more, the materials fuse together when heated at 90°C, causing the cables to stick together, and when peeled off, the fused parts turn white, causing a significant impairment of the appearance.On the other hand, as in Comparative Example 2, it was found that when the base polymer having a melting point above 90°C is 70% by mass or less and the ethylene-α-olefin copolymer having a melting point below 70°C is 30% by mass or more, the flexibility as a cable coating material is significantly reduced.

[0106] From Comparative Example 3, it can be seen that when the melting point of the ethylene-α-olefin copolymer exceeds 70°C, flexibility decreases even if an appropriate amount is blended, and therefore, in the present invention, it is important that the melting point of the ethylene-α-olefin copolymer is 70°C or less.

[0107] From Comparative Examples 4 and 5, it was found that when the amount of aluminum hydroxide added as a flame retardant was 20 parts by mass or less, the flame retardancy was significantly reduced, and conversely, when it was added in an amount of 180 parts by mass or more, the flexibility and electrical insulation properties were significantly reduced.

[0108] When manufacturing large-diameter electric wires and cables, continuous crosslinking extrusion and electron beam crosslinking methods require large-scale equipment and a huge amount of applied energy, making the application of the silane crosslinking method particularly effective in terms of equipment maintenance and the environment. This invention makes it possible to manufacture a halogen-free, environmentally friendly material composition using a process that employs the silane crosslinking method. This not only offers economic benefits, but also enables the widespread development of environmentally friendly products, which will become increasingly important in the future.

[0109] The invention made by the present inventors has been specifically described above based on an embodiment, but it goes without saying that the present invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention. [Explanation of symbols]

[0110] 1, 19 Cable 2 conductors 3. Insulation layer 4 Covering layer 11 Extruder 12 Hopper 13 Screw 14 Breaker plate 15 neck 16 Crosshead 17 Dice 18 Electric wire 20 cylinders

Claims

1. The flame retardant comprises a base polymer containing a high-melting-point halogen-free resin having a melting point of more than 90°C, including an ethylene-ethyl acrylate copolymer, and an ethylene-α-olefin copolymer having a melting point of 70°C or less, aluminum hydroxide as a flame retardant, and a silane compound for imparting silane crosslinkability to the base polymer; the high-melting-point halogen-free resin and the ethylene-α-olefin copolymer are each contained in the base polymer in an amount of 35% by mass or more and 65% by mass or less; The high-melting-point halogen-free resin is a crosslinked product, the ethylene-α-olefin copolymer is a silane-crosslinked product, A cured resin product comprising a halogen-free resin composition containing 30 parts by mass or more and 150 parts by mass or less of the aluminum hydroxide per 100 parts by mass of the base polymer.

2. The cured resin material according to claim 1, A cured resin product characterized in that the maximum tensile peel strength between the cured resin products when pressed and adhered at 90°C is 5 N or less, and the tensile strength at 100% elongation is 7 MPa or less.

3. The cured resin material according to claim 1 or 2, The high-melting-point non-halogen resin has a melting point of 100°C or higher.

4. The cured resin material according to any one of claims 1 to 3, The cured resin has an oxygen index of 21 or more and a volume resistivity of 5.0×10 １４ A cured resin having a resistivity of Ω·cm or more.

5. The cured resin material according to any one of claims 1 to 4, The cured resin has a color that is either black, yellow, or green.

6. A conductor and a covering layer that covers and protects the conductor, An electric wire or cable, wherein the coating layer is the cured resin product according to any one of claims 1 to 5.

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