JPWO2019189469A1 - Flame-retardant resin composition, flame-retardant heat-shrinkable tube and flame-retardant insulated wire - Google Patents

Abstract

A resin composition containing a resin component A composed of polyethylene, an ethylene ethyl acrylate copolymer and an acid-modified polyethylene, a metal hydroxide, and silicone, wherein the content ratio of polyethylene in the resin component A is 25% by mass or more. 70% by mass or less, the content ratio of the ethylene ethyl acrylate copolymer is 25% by mass or more and 70% by mass or less, and the content ratio of the acid-modified polyethylene is 5% by mass or more and 35% by mass or less. On the other hand, a flame-retardant resin composition having a metal hydroxide content of 100 parts by mass or more and 200 parts by mass or less and a silicone content of 1 part by mass or more and 8 parts by mass or less, said flame-retardant. A flame-retardant heat-shrinkable tube formed of a resin composition, and a flame-retardant insulated wire having an insulating layer formed of the flame-retardant resin composition.

Description

The present disclosure relates to a flame-retardant resin composition used as a material for a heat-shrinkable tube, a flame-retardant heat-shrinkable tube formed of the flame-retardant resin composition, and a flame-retardant insulated electric wire.

The heat-shrinkable tube is a resin tube that shrinks in the radial direction by heating. When the object to be coated is coated with a heat-shrinkable tube and heated, the resin layer shrinks along the shape of the coated portion to form a resin layer in close contact with the portion. Therefore, the heat-shrinkable tube is used for forming an insulating layer of an insulated electric wire, protecting a binding portion of an electric wire and a terminal of a wiring, insulating, waterproofing, and the like.

Since the heat-shrinkable tube is sufficiently adhered to the portion covered by shrinkage, an excellent shrinkage rate (large radial shrinkage due to heating) is required.
The heat-shrinkable tube is formed by extruding a resin composition containing a flame retardant or the like in a thermoplastic resin to form a tubular molded body (hollow extruded molded body), and then cross-linking the resin and expanding the diameter of the tube. Obtained by imparting heat shrinkage. Therefore, it is desired that the resin composition as a material for forming a heat-shrinkable tube has a small variation in the diameter of the tube extruded during extrusion processing, that is, excellent extrusion processability (dimensional stability).

Furthermore, for heat-shrinkable tubes used for insulation protection of insulated wires used for internal wiring of railway vehicles, automobiles, etc., and for heat-shrinkable tubes used for insulation protection of busbars used in electrical junction boxes installed in buildings, factories, etc. Is required to be halogen-free and to have high flame retardancy and excellent mechanical strength such as tensile strength and tensile elongation. For example, a heat-shrinkable tube used in a railroad vehicle is required to have an oxygen index, which is an index of flame retardancy, of a predetermined value or more, and the flame retardancy includes a property that combustion is difficult to propagate, specifically. In many cases, it is required that the flame propagation index is small and that there is no drip (drop) of combustibles during combustion. Further, excellent oil resistance is often required.

As a halogen-free flame-retardant resin composition having both high flame retardancy and excellent mechanical strength, a composition obtained by blending a thermoplastic resin such as polyolefin with a metal hydroxide as a flame retardant is widely known. There is. For example, Patent Document 1 discloses a heat-shrinkable tube made of a halogen-free flame-retardant resin composition in which magnesium hydroxide is mixed with a polyolefin resin such as ethylene-vinyl acetate copolymer (EVA).

Japanese Unexamined Patent Publication No. 63-77958

However, the conventional flame-retardant resin composition such as the flame-retardant resin composition disclosed in Patent Document 1 has a flame-retardant resin composition for forming a heat-shrinkable tube for insulating protection of the internal wiring of a railway vehicle. The above-mentioned requirements for a material, that is, the ability to form a heat-shrinkable tube having an excellent shrinkage rate, excellent extrusion workability, an oxygen index of a predetermined value or more, a flame propagation index of a predetermined value or less, and a combustible product during combustion. There is no one that has high flame retardancy such as no drip, excellent mechanical strength such as tensile strength and tensile elongation, and excellent oil resistance, and all of the above requirements are satisfied. The development of a flame-retardant resin composition has been desired.

The present disclosure is a halogen-free resin composition containing a metal hydroxide as a flame retardant, which is excellent in extrusion processability, has a high oxygen index, a small flame propagation index, and drip (drops) of combustibles during combustion. It is an object of the present invention to provide a flame-retardant resin composition which has excellent flame retardancy in the absence of metal, has excellent mechanical strength and oil resistance, and can form a heat-shrinkable tube having an excellent shrinkage rate.

The present disclosure is also a halogen-free flame-retardant heat-shrinkable tube formed from the flame-retardant resin composition, which has excellent mechanical strength, excellent oil resistance, and excellent shrinkage rate, and is also flame-retardant. It is also an object to provide a flame-retardant heat-shrinkable tube having excellent properties, a high oxygen index, a small flame propagation index, and no drip (drop) of combustibles during combustion.

The present disclosure further comprises an insulating layer formed from a conductor and the flame-retardant resin composition, which has excellent mechanical strength, excellent oil resistance, a high oxygen index, and a small flame. It is also an issue to provide an insulated wire having a propagation index and no drip (drop) of combustibles during combustion.

As a result of diligent research to solve the above problems, the present inventor has made polyethylene (PE), ethylene ethyl acrylate copolymer (EEA), acid-modified polyethylene (acid-modified PE), metal hydroxide, and silicone. The present disclosure has been found that the above-mentioned problems can be achieved by a resin composition containing PE, EEA, acid-modified PE, metal hydroxide, and silicone having a content within a predetermined range. Completed the invention of.

The first aspect of the present disclosure is
A resin composition containing a resin component A composed of PE, EEA and acid-modified PE, a metal hydroxide, and silicone, wherein the content ratio of PE in the resin component A is 25% by mass or more and 70% by mass or less. The content ratio of EEA is 25% by mass or more and 70% by mass or less, and the content ratio of acid-modified PE is 5% by mass or more and 35% by mass or less, and the content of the metal hydroxide is relative to 100 parts by mass of the resin component A. Is 100 parts by mass or more and 200 parts by mass or less, and the content of the silicone is 1 part by mass or more and 8 parts by mass or less.

The second aspect of the present disclosure is a molded product obtained by molding the flame-retardant resin composition of the first aspect into a tube shape, and the flame-retardant property is imparted by expanding the diameter of the molded product. It is a heat-shrinkable tube.

A third aspect of the present disclosure is an insulated wire having a conductor and an insulating layer covering the conductor, wherein the insulating layer is a flame-retardant insulated wire made of the flame-retardant resin composition of the first aspect. is there.

According to the first aspect of the present disclosure, it is halogen-free, has a high oxygen index, a small flame propagation index, and has excellent flame retardancy and excellent extrusion workability without dripping of combustibles during combustion. At the same time, a flame-retardant resin composition capable of forming a heat-shrinkable tube having excellent mechanical strength, oil resistance and shrinkage rate is provided.

According to the second aspect of the present disclosure, it is halogen-free, has a high oxygen index, a small flame propagation index, has excellent flame retardancy without drip (drop) of combustibles during combustion, and is mechanical. A flame-retardant heat-shrinkable tube having excellent strength, oil resistance and shrinkage rate is provided.

According to the third aspect of the present disclosure, it is halogen-free, has a high oxygen index, a small flame propagation index, excellent flame retardancy with no drip of combustibles during combustion, and mechanical strength and mechanical strength. Provided is a flame-retardant insulated electric wire in which a conductor is coated with an insulating layer having excellent oil resistance.

Hereinafter, embodiments for carrying out the invention of the present disclosure will be specifically described. The invention of the present disclosure is not limited to the following embodiments, and includes all modifications within the scope of the claims and in the same meaning and scope as the claims.

The first aspect of the present disclosure is
A resin composition containing a resin component A composed of PE, EEA and acid-modified PE, a metal hydroxide, and silicone, wherein the content ratio of PE in the resin component A is 25% by mass or more and 70% by mass or less. The content ratio of EEA is 25% by mass or more and 70% by mass or less, the content ratio of acid-modified PE is 5% by mass or more and 35% by mass or less, and the content of the metal hydroxide is contained in 100 parts by mass of the resin component A. A flame-retardant resin composition having an amount of 100 parts by mass or more and 200 parts by mass or less and a silicone content of 1 part by mass or more and 8 parts by mass or less.

First, each composition constituting the flame-retardant resin composition of the first aspect will be described.
As the PE, any of various PEs such as high-density polyethylene, medium-density polyethylene, and linear low-density polyethylene can be used.
Among PEs, PE having a melt flow rate (melt mass flow rate (g / 10 min) according to JIS K 7210-1999) of 0.08 or more can be preferably used. When PE having a melt flow rate of 0.08 or more is used, the appearance of the extruded tube becomes good when a heat-shrinkable tube is produced by extrusion molding, and when used for forming an insulating layer of an insulated wire, the insulating layer This is preferable because it improves printability.
Further, PE having Mw / Mn of 8 or more when the number average molecular weight measured by gel permeation chromatography (GPC) is Mn and the weight average molecular weight is Mw is preferable. Mw / Mn is an index showing the breadth of the molecular weight distribution of PE. However, when PE having a wide molecular weight distribution of Mw / Mn of 8 or more is used, when a heat-shrinkable tube is produced by extrusion molding, the extruded tube is used. It is preferable because the appearance is good and the printability of the insulating layer is improved when it is used for forming the insulating layer of the insulated wire.

The EEA is a copolymer of ethylene and ethyl acrylate. The range of the copolymerization ratio of ethylene and ethyl acrylate is not particularly limited, but usually, one having a mass ratio of ethyl acrylate in all the constituent monomers of about 5 to 25% is used. The melting point decreases as the ratio of ethyl acrylate increases, but those with a melting point of 83 to 107 ° C. are usually used. The range of the molecular weight and the range of the density (specific gravity) of the EEA are not particularly limited, but usually, the melt flow rate (MFR) measured at 190 ° C. and a load of 21.6 kg is 0.3 to 25 (g / 10 min). Those having a specific gravity of 0.92 to 0.95 are used.

The acid-modified PE is a PE in which an acid such as maleic anhydride is grafted on the polymer chain or a carboxylic acid group is present at the end of the polymer chain.

Examples of the metal hydroxide include magnesium hydroxide, aluminum hydroxide, calcium hydroxide and the like. Of these, magnesium hydroxide and aluminum hydroxide are preferable, and magnesium hydroxide is more preferable. The metal hydroxide preferably has a particle size in the range of 0.1 μm or more and 5.0 μm or less, and the particle size is particularly large from the viewpoint of dispersibility in the resin, flame retardancy when dispersed, and mechanical strength. Those in the range of 0.5 μm or more and 2.0 μm or less are preferably used. If the particle size is larger than the above range, the tensile elongation of the resin tends to decrease, and if it is smaller than the above range, the metal hydroxide tends to aggregate. Further, a metal hydroxide surface-treated with a silane coupling agent or a metal hydroxide surface-treated with an anionic surfactant can also be used.

The type of silicone is not particularly limited, but modified silicone is preferable from the viewpoint of compatibility with the resin component. The modified silicone means a silicone having one or more functional groups at at least one of the terminal and side chains of the polymer chain of the silicone. Examples of the modified silicone include vinyl-modified silicone and alkyl-modified silicone.

The vinyl-modified silicone is a silicone in which a functional group having one or more carbon-carbon double bonds is bonded to at least one of the terminal and side chains of the polymer chain of the silicone. Examples of the functional group having a carbon-carbon double bond bonded to the terminal or side chain of the polymer chain include -CH = CH ₂ , -OCO-C (CH ₃ ) = CH ₂ (methacrylate group), and -OCO-CH =. CH ₂ (acrylate group) and the like can be mentioned. Of these, an acrylate group and a methacrylate group are preferable. Examples of the vinyl-modified silicone include those described in JP-A-2005-132855. Further, a commercially available product such as TEGOMER V-Si4042 (manufactured by EVONIK) can also be used.
The alkyl-modified silicone is a silicone in which one or more alkyl groups having three or more carbon atoms are bonded to at least one of the terminal and side chains of the polymer chain of the silicone.

The flame-retardant resin composition of this embodiment contains an ethylene methyl acrylate copolymer (EMA), an ethylene methyl methacrylate copolymer (EMMA), and ethylene for the purpose of improving various properties as long as the gist of the invention is not impaired. -Various resins such as propylene diene rubber (EPDM), ethylene butyl acrylate (EBA), ethylene acrylic rubber, polyolefin elastomer, and styrene elastomer may be blended. Further, as long as the gist of the invention is not impaired, antioxidants, lubricants, processing stabilizers, colorants (color pigments), foaming agents, reinforcing agents, fillers such as calcium carbonate and talc, and polyfunctional monomers (crosslinking aids) ) And other various additives can be blended.

The flame-retardant resin composition of the first aspect is characterized in that the above-mentioned essential constituent components are blended within a specific composition range. Next, this specific composition range will be described.
The content ratio of PE is 25 parts by mass or more and 70 parts by mass or less, that is, 25 in the resin component A, when the total amount of PE, EEA and acid-modified PE (that is, the amount of the resin component A is mixed) is 100 parts by mass. It is mass% or more and 70 mass% or less.
The blending of PE improves the oil resistance of the insulating layer of the heat-shrinkable tube and the insulated wire formed from the flame-retardant resin composition. If the PE content is less than 25% by mass, sufficient oil resistance cannot be obtained. On the other hand, when the content ratio of PE exceeds 70% by mass, drip is likely to occur in the flame propagation test, and the tensile elongation and the shrinkage rate of the tube are also likely to be lowered to be insufficient. It is preferably 30% by mass or more and 50% by mass or less, and more excellent oil resistance can be obtained within this range, drip is further suppressed, and tensile elongation and tube shrinkage are also sufficient.

The content ratio of EEA is 25 parts by mass or more and 70 parts by mass or less, that is, 25 in the resin component A, when the total amount of PE, EEA and acid-modified PE (that is, the amount of the resin component A is mixed) is 100 parts by mass. It is mass% or more and 70 mass% or less.
The EEA formulation suppresses drip in flame propagation tests. When EVA used in the prior art is used instead of EEA, drip is likely to occur. In the case of EVA, the cohesive force between the resins due to the metal hydroxide is weak because the hydroxyl group remains in the main chain when the ester bond is broken during combustion, but in the case of EEA, the ester bond is broken during combustion. It is considered that the carboxy group remains in the main chain, so that the cohesive force between the resins due to the metal hydroxide is strong, and as a result, drip is suppressed.
When the content ratio of EEA is less than 25% by mass, a sufficient drip suppressing effect cannot be obtained. On the other hand, when the content ratio of EEA exceeds 70% by mass, the oil resistance is lowered and the shrinkage rate of the tube is insufficient. It is preferably 30% by mass or more and 50% by mass or less, and a more excellent drip suppressing effect can be obtained within this range, and oil resistance and tube shrinkage are also sufficient.

The content ratio of the acid-modified PE is 5 parts by mass or more and 35 parts by mass or less, that is, in the resin component A, when the total amount of PE, EEA and the acid-modified PE (that is, the amount of the resin component A) is 100 parts by mass. It is 5% by mass or more and 35% by mass or less.
By blending the acid-modified PE, the dispersibility of the metal hydroxide is improved, and as a result, the tensile strength and the tensile elongation are improved. Also, the shrinkage rate of the tube is improved.
If the content ratio of the acid-modified PE is less than 5% by mass, the tensile strength and tensile elongation may decrease, and sufficient mechanical strength (tensile characteristics) may not be obtained. Also, the shrinkage rate of the tube becomes insufficient. On the other hand, when the content ratio of the acid-modified PE exceeds 35% by mass, drip is likely to occur in the flame propagation test, and the oil resistance is also lowered, which is likely to be insufficient. It is preferably 10% by mass or more and 30% by mass or less, and more excellent tensile strength, tensile elongation, and tube shrinkage can be obtained within this range, drip in the flame propagation test is suppressed, and sufficient oil resistance is also obtained. Be done.

The metal hydroxide is blended in an amount of 100 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the resin component A (that is, the total amount of PE, EEA and acid-modified PE). Metal hydroxides improve flame retardancy represented by oxygen index, flame propagation index, etc., and meet various standards for in-vehicle insulated wires used for internal wiring of railway vehicles, automobiles, etc. Formulated to achieve.
When the blending amount of the metal hydroxide is less than 100 parts by mass with respect to 100 parts by mass of the resin component A, the flame propagation index becomes high, the oxygen index, etc. becomes insufficient, and various types of insulating electric wires for vehicles are used. It becomes difficult to obtain flame retardancy that meets the above standards.
On the other hand, when the blending amount of the metal hydroxide exceeds 200 parts by mass, the tensile strength and the tensile elongation are lowered to be insufficient, and the shrinkage rate of the tube is also lowered to be insufficient.

The silicone is blended in an amount of 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the resin component A (that is, the total amount of PE, EEA and acid-modified PE).
Silicone is blended to improve the flame retardancy represented by the oxygen index or the like, but when the blending amount of silicone is less than 1 part by mass with respect to 100 parts by mass of the resin component A, the oxygen index is high. It decreases and the flame retardancy becomes insufficient. On the other hand, if it exceeds 8 parts by mass, the extrusion processability is lowered, and the tube diameter becomes unstable when extrusion molding into a tube shape, so that sufficient dimensional stability cannot be obtained.

The flame-retardant resin composition of this embodiment can be obtained by mixing the above-mentioned essential components and optionally blended components by a known method using a known mixer and kneader.

The flame-retardant resin composition of this embodiment is halogen-free, has a high oxygen index, a small flame propagation index, and has excellent flame retardancy with no drip (drop) of combustibles during combustion, and is extruded. It is a flame-retardant resin composition capable of forming a heat-shrinkable tube having excellent properties, mechanical strength, oil resistance, and shrinkage rate.

The second aspect of the present disclosure is a molded product obtained by molding the flame-retardant resin composition of the first aspect into a tube shape, and the flame-retardant property is imparted by expanding the diameter of the molded product. It is a heat-shrinkable tube.

The flame-retardant heat-shrinkable tube of the present embodiment is a step of molding the flame-retardant resin composition of the first aspect into a tube shape (molding step), and a resin tube (molded product) obtained in the molding step in the radial direction. It can be manufactured by a method having a step of expanding (diameter expanding step). The molding step can be carried out by extrusion molding, which can be carried out in the same manner as a known method usually used when producing a conventional heat-shrinkable tube.

Preferably, a cross-linking step of cross-linking the resin is performed before the diameter-expanding step. By cross-linking the resin, the shrinkage characteristics as a heat-shrinkable tube are more exhibited. As a method for cross-linking the resin, a method of irradiating the resin with radiation (irradiation cross-linking of the resin) is preferable. Since molding becomes difficult after the resin material is crosslinked by irradiation with radiation, irradiation with radiation (crosslinking step) is performed after extrusion molding (molding step). By irradiating radiation after extrusion molding, molding is easy and the effect of irradiation with radiation can be sufficiently obtained.

Examples of the radiation used for irradiation cross-linking of the resin include high-energy electromagnetic waves such as X-rays and γ-rays, and particle beams such as electron beams. Since the electron beam generator has a low running cost, can obtain a high output electron beam, and is easy to control, the electron beam is preferably used in radiation.

The irradiation amount is not particularly limited, but when the irradiation amount is too large, the decomposition reaction becomes dominant over the cross-linking reaction, and conversely, the degree of cross-linking may decrease and the intensity may decrease. On the other hand, when the irradiation amount is too small, the degree of cross-linking required to sufficiently exhibit the shrinkage characteristics of the heat-shrinkable tube may not be obtained. Therefore, it is preferable to select a radiation irradiation amount as small as possible within the range in which the contraction characteristics are sufficiently exhibited, and usually, the range of 10 kGy to 300 kGy is preferable.

As a method for expanding the diameter of the crosslinked tubular molded product, a known diameter-expanding method usually used for producing a conventional heat-shrinkable tube can be used. For example, a method may be mentioned in which a resin tube is heated to a temperature equal to or higher than the melting point, an internal pressure (pressure inside the tube) is applied to expand the tube, and then the tube is cooled.

The flame-retardant heat-shrink tubing of the second aspect of the present disclosure is halogen-free and has excellent flame retardancy with a high oxygen index, a small flame propagation index, and no drip of combustibles during combustion. At the same time, it is a heat-shrinkable tube having excellent mechanical strength, oil resistance and shrinkage rate.

A third aspect of the present disclosure is an insulated wire having a conductor and an insulating layer covering the conductor, wherein the insulating layer is a flame-retardant insulated wire made of the flame-retardant resin composition of the first aspect. is there.

A conductor is a wire made of a conductor such as copper. Examples of the method for forming the insulating layer of the flame-retardant insulated electric wire of the present embodiment include a method of extrusion-coating the flame-retardant resin composition of the first aspect on a conductor. Since the internal wiring of railway vehicles and automobiles may be exposed to high temperatures during use, the flame-retardant resin composition should be extruded and coated, and then cross-linked by irradiating with electron beams to suppress deformation at high temperatures. Is preferable. The insulating layer can also be formed by a method of coating the conductor with the flame-retardant heat-shrinkable tube of the second aspect and heat-shrinking it.

The third flame-retardant insulated wire of the present disclosure is halogen-free, has a high oxygen index, a small flame propagation index, excellent flame retardancy with no drip of combustibles during combustion, and a machine. It is an insulated wire whose conductor is coated with an insulating layer having excellent strength and oil resistance. Therefore, it can be suitably used for internal wiring of railway vehicles, automobiles, and the like.

Examples 1 to 15 and Comparative Examples 1 to 11
(Material used)
-High-density polyethylene: Novatec HD320, manufactured by Mitsubishi Chemical Corporation, melt flow rate = 0.3, Mw / Mn = 44, density 0.947 g / mL, represented by "HDPE" in the table.
-Medium density polyethylene: Novatec SD911, manufactured by Mitsubishi Chemical Corporation, melt flow rate = 0.1, Mw / Mn = 38, density 0.937 g / mL, represented by "MDPE" in the table.
Linear low density polyethylene: DFDJ7540, manufactured by NUC, melt flow rate = 0.8, Mw / Mn = 10, density 0.920 g / mL, represented by "LLDPE" in the table.
-EEA: Lexpearl A4250, manufactured by Mitsubishi Chemical Corporation, EA amount 25 wt%, melt flow rate = 5, density 0.934 g / mL, expressed as "EEA" in the table.
-EVA: EVAflex EV360, manufactured by Mitsui DuPont Polychemical Co., Ltd., VA amount 25 wt%, melt flow rate = 2, density 0.94 g / mL, represented by "EVA" in the table.
-Acid-modified PE: Toughmer MH5020, acid-modified VLDPE with a density of 0.860 g / mL, represented as "acid-modified PE" in the table.
・ Magnesium hydroxide: Kisuma 5L (manufactured by Kyowa Chemical Industry Co., Ltd.)
-Aluminum hydroxide: Heidilite H42STM (manufactured by Showa Denko)
-Antioxidant: Irganox 1010 (manufactured by BASF Japan Ltd.)
-Lidant: Zinc stearate / Vinyl-modified silicone: TEGOMER V-Si4042 (manufactured by EVONIK)
-Alkyl-modified silicone: TSF4421 (manufactured by Momentive Performance Materials)

The materials used were kneaded in an open roll at 180 ° C. with the formulations (mass ratio) shown in Tables 1 to 5, and then pelletized by a pelletizer. Then, it was extruded into a tube shape having an inner diameter of 3 mmφ and an outer diameter of 4 mmφ (thickness 0.5 mm) with a 50 mmφ extruder. After irradiating the obtained tube with an electron beam of 60 kGy, air was blown into the tube at 150 ° C. to pressurize the tube and expand it in the radial direction until the outer diameter became 6 mmφ to obtain a tubular molded product.

Evaluation of extrusion processability, oxygen index (flame retardancy), flame propagation property (flame propagation index and presence / absence of drip), tensile strength, tensile elongation, oil resistance, and shrinkage rate of expanded tube for the obtained tube. Was done. The evaluation method is as follows.

(Extrusion workability)
The outer diameter fluctuation width was measured with a laser outer diameter measuring device, and the case where the outer diameter fluctuation width was within ± 10% of the design value was regarded as acceptable.

(Oxygen index)
The oxygen index indicates the minimum oxygen concentration (volume%, minimum oxygen concentration in a mixture of oxygen and nitrogen that can maintain the combustion of the material) required to sustain the combustion of the material, and is standardized in JIS K 7201: 2007. It is an indicator of the flammability of the material. In Examples and Comparative Examples, the oxygen index was measured according to JIS K 7201: 2007 (combustion test method for polymer materials by the oxygen index method). As a high flame retardant material, an oxygen index of 30 or more is generally desired. In particular, the BS6853 material standard for passenger cabins for railway vehicles has an oxygen index of 34 or more, so an oxygen index of 34 or more is passed. Is determined.

(Flame propagation test)
This was done according to ASTM E162: 2016 (Surface flammability of material by radiant heat energy source). Specifically, the following test was performed using six samples having a size of 152 mm × 457 mm.
The sample is set at an angle of 30 ° with respect to a vertically installed radiant panel (radiant plate), the radiant plate is preheated to 670 ° C., and the sample is ignited using the pilot frame at the top of the sample. After ignition, the flame spreads downward on the surface of the sample, but progresses to the point where the radiant heat from the radiant panel gradually decreases and the flame cannot continue to propagate. The speed at which the flame propagated on the surface of the sample (flame diffusion coefficient: Fs) and the heat release coefficient (Q) of the exhaust pipe at the top of the device were obtained, and the flame propagation index Is was obtained from the following equation.
Is = Fs × Q
The presence or absence of falling (drip) of combustibles during flame propagation was visually observed.
When the flame propagation index Is was 35 or less and there was no drip of combustibles, it was judged to be acceptable.

(Tensile strength, tensile elongation)
A tube having a length of 120 mm was cut out, and tensile strength (strength at break) and tensile elongation (elongation at break) were measured at a tensile speed of 500 mm / min. If the tensile strength is 7.0 MPa or more and the tensile elongation is 200% or more, it is judged to be acceptable.

(Oil resistance)
After immersing in light oil at 70 ° C. for 168 hours, the tensile strength and tensile elongation were measured, and the case where the tensile strength after immersion was 4.9 MPa or more and the tensile elongation was 120% or more was judged to be acceptable.

(Tube shrinkage rate)
The inner diameter of the tube before expansion, the inner diameter of the tube before shrinkage, and the inner diameter of the tube after shrinkage were measured. The shrinkage rate of the tube is a value (%) calculated by the following equation.
{[(Inner diameter of tube before contraction)-(Inner diameter of tube after contraction)] / [(Inner diameter of tube before contraction)-(Inner diameter of tube before expansion)]} x 100

From the evaluation results shown in Tables 1 to 5 above,
The content ratio of PE in the resin component is 25% by mass or more and 70% by mass or less, the content ratio of EEA is 25% by mass or more and 70% by mass or less, and the content ratio of acid-modified PE is 5% by mass or more and 35% by mass or less. The amount of the metal hydroxide compounded is 100 parts by mass or more and 200 parts by mass or less, and the amount of the silicone compounded is 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the resin component (first). The flame-retardant resin compositions of Examples 1 to 15 (which have a composition within the range of aspects) have passed the dimensional stability (extrusion processability) at the time of extrusion molding, and the difficulty obtained from this resin composition. The flammable heat-shrinkable tube has an oxygen index and a flame propagation index that are above the acceptance criteria, has excellent flame retardancy without drip (drop) of combustibles during combustion, mechanical strength, oil resistance, and It has also been shown to have excellent shrinkage.

On the other hand, in Comparative Example 1 in which the PE content is less than 25% by mass, the oil resistance is unacceptable. Further, in Comparative Example 7 in which the PE content exceeds 70% by mass, drip occurs in the flame propagating test, and the flame propagating test is determined to be unacceptable. The tensile elongation is 80%, which is much lower than the acceptance standard of 200% or more, and the shrinkage rate of the tube is 78% of the acceptance standard of 90% or more, both of which are insufficient results.

In Comparative Example 2 in which the content ratio of EEA is less than 25% by mass, drip occurs in the flame propagation test, and the flame transmission test is determined to be unacceptable. On the other hand, in Comparative Example 8 in which the content ratio of EEA exceeds 70% by mass, the judgment of oil resistance is unacceptable, and the shrinkage rate of the tube is 83%, which is 83% of the acceptance standard of 90% or more, which is an insufficient result. It has become.
In Comparative Example 3, which is the same as in Example 1 except that EVA is blended in an amount of 50% by mass instead of EEA, drip occurs in the flame propagation test, and the flame propagation test is determined to be unacceptable.

In Comparative Example 6 in which the content ratio of the acid-modified PE is less than 5% by mass, the tensile strength and the tensile elongation are lower than the values of the acceptance criteria, and sufficient mechanical strength (tensile characteristics) is not obtained. In addition, the shrinkage rate of the tube is 73%, which is insufficient compared to 90% or more of the acceptance standard. On the other hand, in Comparative Example 2 in which the content ratio of the acid-modified PE exceeds 35% by mass, drip occurs in the flame propagation test, and in Comparative Example 9, the oil resistance is determined to be unacceptable.

In Comparative Example 10 in which the content of the metal hydroxide is less than 100 parts by mass with respect to 100 parts by mass of the resin component, the flame propagation index exceeds the acceptance standard, and the flame propagation test is determined to be unacceptable. The oxygen index is less than the acceptance standard, and flame retardancy that meets various standards for in-vehicle insulated wires has not been obtained. On the other hand, in Comparative Example 11 in which the content of the metal hydroxide exceeds 200 parts by mass, the tensile strength and tensile elongation are lower than the values of the acceptance standard, and the shrinkage rate of the tube is also lower than 90% of the acceptance standard, which is insufficient. ..

In Comparative Example 4 in which the silicone content is less than 1 part by mass with respect to 100 parts by mass of the resin component, the oxygen index is less than the acceptance standard, and flame retardancy satisfying various standards for in-vehicle insulated wires is obtained. Not done. On the other hand, in Comparative Example 5 in which the content of silicone (vinyl-modified silicone) exceeds 8 parts by mass, the extrusion processability is low, and when extrusion molding into a tube shape, the tube system becomes unstable and sufficient dimensional stability is obtained. Not done.

Claims (8)

A resin composition containing a resin component A composed of polyethylene, an ethylene ethyl acrylate copolymer and an acid-modified polyethylene, a metal hydroxide, and silicone, wherein the content ratio of polyethylene in the resin component A is 25% by mass or more. 70% by mass or less, the content ratio of the ethylene ethyl acrylate copolymer is 25% by mass or more and 70% by mass or less, and the content ratio of the acid-modified polyethylene is 5% by mass or more and 35% by mass or less. On the other hand, a flame-retardant resin composition in which the content of the metal hydroxide is 100 parts by mass or more and 200 parts by mass or less, and the content of the silicone is 1 part by mass or more and 8 parts by mass or less. The flame-retardant resin composition according to claim 1, wherein the polyethylene is polyethylene having a melt flow rate of 0.08 or more. The flame-retardant resin composition according to claim 1 or 2, wherein the polyethylene has a molecular weight distribution (Mw / Mn) of 8 or more. The flame-retardant resin composition according to any one of claims 1 to 3, wherein the metal hydroxide is magnesium hydroxide or aluminum hydroxide. The flame-retardant resin composition according to any one of claims 1 to 4, wherein the silicone is a modified silicone. The flame-retardant resin composition according to claim 5, wherein the modified silicone is a vinyl-modified silicone or an alkyl-modified silicone. A molded product obtained by molding the flame-retardant resin composition according to any one of claims 1 to 6 into a tube shape, and heat shrinkage is imparted by expanding the diameter of the molded product. Flame-retardant heat-shrinkable tube. An insulated wire having a conductor and an insulating layer covering the conductor, wherein the insulating layer is a flame-retardant insulated wire made of the flame-retardant resin composition according to any one of claims 1 to 6. ..