JP7374079B2 - Flame retardant resin composition, flame retardant heat shrinkable tube and flame retardant insulated wire - Google Patents

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 from the flame-retardant resin composition, and a flame-retardant insulated wire.

A heat shrinkable tube is a resin tube that shrinks in the radial direction when heated. When an object to be coated is covered with a heat-shrinkable tube and heated, a resin layer is formed that shrinks along the shape of the covered portion and adheres to the covered portion. Therefore, heat shrink tubes are used for forming insulation layers of insulated wires, protecting wire bundles and wiring terminals, insulating them, waterproofing them, and the like.

The heat-shrinkable tube is required to have an excellent shrinkage rate (large radial shrinkage due to heating) in order to sufficiently adhere to the portion covered by the shrinkage.
Heat-shrinkable tubes are made by extruding a resin composition containing a thermoplastic resin and a flame retardant, etc. to form a tubular molded product (hollow extrusion molded product), and then crosslinking the resin and expanding the diameter of the tube. Obtained by imparting heat shrinkability. Therefore, the resin composition used as the material for forming the heat-shrinkable tube is desired to have small fluctuations in the diameter of the extruded tube during extrusion processing, that is, to have excellent extrusion processability (dimensional stability).

Furthermore, heat shrinkable tubes are used to protect the insulation of insulated wires used in the internal wiring of railway vehicles and automobiles, and heat shrinkable tubes are used to protect the insulation 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, heat-shrinkable tubes used in railway vehicles are required to have an oxygen index, which is an indicator of flame retardancy, of a predetermined value or higher. In many cases, it is required that the flame spread index be small and that there be no dripping (falling) of burning material during combustion. Furthermore, excellent oil resistance is often required.

As a halogen-free flame-retardant resin composition that achieves both high flame retardancy and excellent mechanical strength, compositions in which metal hydroxide, which is a flame retardant, is blended with thermoplastic resin such as polyolefin are 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 blended with a polyolefin resin such as ethylene-vinyl acetate copolymer (EVA).

Japanese Unexamined Patent Publication No. 63-77958

However, conventional flame-retardant resin compositions such as the flame-retardant resin composition disclosed in Patent Document 1 do not include flame-retardant resin compositions that are used to form heat-shrinkable tubes for insulation protection of internal wiring of railway vehicles. The above-mentioned requirements for products include the ability to form heat-shrinkable tubes with excellent shrinkage, excellent extrusion processability, oxygen index above a certain value, flame spread index below a certain value, and the ability to produce combustible materials during combustion. There is no material that satisfies all of the following requirements: high flame retardancy such as no dripping (dropping), excellent mechanical strength such as tensile strength and tensile elongation, and excellent oil resistance. The development of flame-retardant resin compositions has been desired.

The present disclosure is a halogen-free resin composition containing a metal hydroxide as a flame retardant, which has excellent extrusion processability, has a high oxygen index, a small flame spread index, and has a high oxygen index, a low flame spread index, and no dripping of combustion materials during combustion. An object of the present invention is to provide a flame-retardant resin composition that can form a heat-shrinkable tube with excellent mechanical strength, oil resistance, and excellent shrinkage rate.

The present disclosure also provides 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 flame-retardant. Another object of the present invention is to provide a flame-retardant heat-shrinkable tube that has excellent properties, a high oxygen index, a small flame spread index, and does not cause any burning material to drip during combustion.

The present disclosure further includes an insulating layer formed from a conductor and the flame-retardant resin composition, and the insulating layer has excellent mechanical strength, excellent oil resistance, high oxygen index, and small flame resistance. Another object of the present invention is to provide an insulated wire that has a propagation index and does not drip (fall) of combustion materials during combustion.

As a result of intensive research to solve the above problems, the present inventors have discovered that polyethylene (PE), ethylene ethyl acrylate copolymer (EEA), acid-modified polyethylene (acid-modified PE), metal hydroxide, and silicone It 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 in a predetermined content, and the present disclosure completed the invention.

A first aspect of the present disclosure includes:
A resin composition containing a resin component A consisting of PE, EEA and acid-modified PE, a metal hydroxide, and silicone, wherein the content of PE in the resin component A is 25% by mass or more and 70% by mass or less, The content of EEA is 25% by mass or more and 70% by mass or less, the content of acid-modified PE is 5% by mass or more and 35% by mass or less, and the content of the metal hydroxide is based on 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.

A second aspect of the present disclosure is a flame-retardant molded article formed by molding the flame-retardant resin composition of the first aspect into a tube shape, the flame-retardant resin composition being imparted with heat shrinkability by expanding the diameter of the molded article. It is heat shrink tubing.

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. be.

According to the first aspect of the present disclosure, it is halogen-free, has a high oxygen index, a low flame spread index, and has excellent flame retardancy and excellent extrusion processability without dripping (falling) of combustion materials during combustion. Additionally, a flame-retardant resin composition is provided that can form a heat-shrinkable tube with excellent mechanical strength, oil resistance, and shrinkage rate.

According to the second aspect of the present disclosure, it is halogen-free, has a high oxygen index, a low flame spread index, has excellent flame retardancy with no dripping (falling) of combustion materials during combustion, and has a mechanical A flame-retardant heat-shrinkable tube with excellent strength, oil resistance, and shrinkage rate is provided.

According to a third aspect of the present disclosure, the present invention is halogen-free, has excellent flame retardancy such as a high oxygen index, a small flame spread index, and no dripping of combustion materials during combustion, and has excellent mechanical strength and A flame-retardant insulated wire in which a conductor is coated with an insulating layer having excellent oil resistance is provided.

Hereinafter, embodiments for carrying out the invention of the present disclosure will be specifically described. Note that the invention of the present disclosure is not limited to the embodiments described below, and includes all changes within the scope of the claims and within the meaning and range equivalent to the scope of the claims.

A first aspect of the present disclosure includes:
A resin composition containing a resin component A consisting of PE, EEA, and acid-modified PE, a metal hydroxide, and a silicone, wherein the content 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 based on 100 parts by mass of the resin component A. The present invention is a flame-retardant resin composition in which the amount of silicone 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.

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

EEA is a copolymer of ethylene and ethyl acrylate. Although the range of the copolymerization ratio of ethylene and ethyl acrylate is not particularly limited, one in which the mass ratio of ethyl acrylate to all constituent monomers is about 5 to 25% is usually used. As the ratio of ethyl acrylate increases, the melting point decreases, but those having a melting point of 83 to 107°C are usually used. The molecular weight range and density (specific gravity) range of 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 with a specific gravity of 0.92 to 0.95 are used.

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

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

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

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 end and side chain of the silicone polymer chain. Functional groups having a carbon-carbon double bond bonded to the end or side chain of a polymer chain include -CH=CH ₂ , -OCO-C(CH ₃ )=CH ₂ (methacrylate group), -OCO-CH= CH ₂ (acrylate group) and the like can be mentioned. Among these, acrylate groups and methacrylate groups are preferred. Examples of vinyl-modified silicones include those described in JP-A No. 2005-132855. Furthermore, commercially available products 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 3 or more carbon atoms are bonded to at least one of the terminal and side chain of the silicone polymer chain.

The flame retardant resin composition of this embodiment contains ethylene methyl acrylate copolymer (EMA), ethylene methyl methacrylate copolymer (EMMA), ethylene - Various resins such as propylene diene rubber (EPDM), ethylene butyl acrylate (EBA), ethylene acrylic rubber, polyolefin elastomer, and styrene elastomer may be blended. In addition, antioxidants, lubricants, processing stabilizers, colorants (coloring pigments), blowing agents, reinforcing agents, fillers such as calcium carbonate and talc, and polyfunctional monomers (crosslinking aids) may be used as long as they do not impair the spirit of the invention. ) and other various additives can be added.

The flame-retardant resin composition of the first aspect is characterized in that the above-mentioned essential components are blended within a specific composition range. Next, this specific composition range will be explained.
The content ratio of PE is 25 parts by mass or more and 70 parts by mass or less, that is, 25 parts by mass or less, when the total amount of PE, EEA, and acid-modified PE (i.e., the amount of resin component A) is 100 parts by mass. It is not less than 70% by mass and not more than 70% by mass.
The addition of PE improves the oil resistance of the heat-shrinkable tube or insulating layer of 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, if the PE content exceeds 70% by mass, drips are likely to occur in the flame propagation test, and the tensile elongation and shrinkage rate of the tube are also likely to decrease, resulting in insufficient results. It is preferably 30% by mass or more and 50% by mass or less, and within this range, better oil resistance can be obtained, dripping can be further suppressed, and the tensile elongation and shrinkage rate of the tube can be sufficient.

The content ratio of EEA is 25 parts by mass or more and 70 parts by mass or less, i.e., 25 parts by mass or less, when the total blending amount of PE, EEA, and acid-modified PE (i.e., the blending amount of resin component A) is 100 parts by mass. It is not less than 70% by mass and not more than 70% by mass.
The EEA formulation suppresses drips in flame spread tests. When EVA, which is used in the prior art, is used instead of EEA, drips are 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. In this case, since the carboxy group remains in the main chain, the cohesive force between the resins due to the metal hydroxide is strong, and as a result, it is thought that dripping is suppressed.
If the content of EEA is less than 25% by mass, a sufficient drip suppression effect cannot be obtained. On the other hand, if the content of EEA exceeds 70% by mass, the oil resistance will decrease and the shrinkage rate of the tube will be insufficient. Preferably, it is 30% by mass or more and 50% by mass or less, and within this range, a better drip suppression effect can be obtained, and the oil resistance and shrinkage rate of the tube will also be sufficient.

The content ratio of acid-modified PE is 5 parts by mass or more and 35 parts by mass or less, i.e., 5 parts by mass or more and 35 parts by mass or less, when the total amount of PE, EEA, and acid-modified PE (i.e., the amount of resin component A) is 100 parts by mass. It is 5% by mass or more and 35% by mass or less.
By blending acid-modified PE, the dispersibility of metal hydroxide is improved, resulting in improved tensile strength and tensile elongation. Moreover, the shrinkage rate of the tube is also improved.
If the content of acid-modified PE is less than 5% by mass, tensile strength and tensile elongation may decrease, and sufficient mechanical strength (tensile properties) may not be obtained. Also, the shrinkage rate of the tube becomes insufficient. On the other hand, if the content of acid-modified PE exceeds 35% by mass, drips are likely to occur in the flame propagation test, and the oil resistance is also likely to decrease and become insufficient. Preferably, it is 10% by mass or more and 30% by mass or less, and within this range, better tensile strength, tensile elongation, and tube shrinkage can be obtained, dripping in the flame spread test is also suppressed, and sufficient oil resistance can be obtained. It will 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 blended amount of PE, EEA, and acid-modified PE). Metal hydroxide improves flame retardancy expressed by oxygen index, flame spread index, etc., and has flame retardancy that meets various standards for automotive insulated wires used for internal wiring of railway vehicles, automobiles, etc. It is formulated to achieve the following.
If the amount of metal hydroxide is less than 100 parts by mass per 100 parts by mass of resin component A, the flame spread index will be high and the oxygen index etc. will be insufficient, resulting in various problems regarding insulated wires for vehicles. It becomes difficult to obtain flame retardancy that meets the standards.
On the other hand, if the amount of metal hydroxide exceeds 200 parts by mass, the tensile strength and tensile elongation will decrease and become insufficient, and the shrinkage rate of the tube will also decrease and tend to become 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 flame retardancy expressed by oxygen index, etc., but if the amount of silicone blended is less than 1 part by mass per 100 parts by mass of resin component A, the oxygen index flame retardancy becomes insufficient. On the other hand, if the amount exceeds 8 parts by mass, extrusion processability deteriorates, and when extruded into a tube, the tube diameter becomes unstable and 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 optional components by a known method using a known mixer or kneader.

The flame-retardant resin composition of this embodiment is halogen-free, has excellent flame retardancy such as a high oxygen index, a small flame spread index, and no dripping of combustion materials during combustion, and can be processed by extrusion. It is a flame-retardant resin composition that can form a heat-shrinkable tube with excellent properties, mechanical strength, oil resistance, and shrinkage rate.

A second aspect of the present disclosure is a flame-retardant molded article formed by molding the flame-retardant resin composition of the first aspect into a tube shape, the flame-retardant resin composition being imparted with heat shrinkability by expanding the diameter of the molded article. It is heat shrink tubing.

The flame-retardant heat-shrinkable tube of this embodiment includes a step of molding the flame-retardant resin composition of the first embodiment 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 including an expansion step (diameter expansion step). The molding process can be performed by extrusion molding, and this extrusion molding can be performed in a manner similar to a known method commonly used in producing conventional heat shrinkable tubes.

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

Examples of the radiation used for irradiation crosslinking of the resin include high-energy electromagnetic waves such as X-rays and γ-rays, and particle beams such as electron beams. Among radiation sources, electron beams are preferably used because electron beam generators have low running costs, can produce high-output electron beams, and are easy to control.

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

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

The flame-retardant heat shrink tube of the second aspect of the present disclosure is halogen-free and has excellent flame retardancy with high oxygen index, small flame spread index, and no dripping of combustion materials during combustion. In addition, it is a heat-shrinkable tube with 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. be.

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 wire of this embodiment include a method of extrusion coating the flame-retardant resin composition of the first embodiment onto the conductor. The internal wiring of railway vehicles and automobiles is sometimes exposed to high temperatures during use, so after extrusion coating a flame-retardant resin composition, cross-linking is performed using electron beam irradiation, etc. to suppress deformation at high temperatures. is preferred. Further, the insulating layer can also be formed by the method of covering the conductor with the flame-retardant heat-shrinkable tube of the second embodiment and heat-shrinking the conductor.

The third flame-retardant insulated wire of the present disclosure is halogen-free, has excellent flame retardancy such as a high oxygen index, a small flame spread index, and no dripping of combustion materials during combustion, and This is an insulated wire in which the conductor is coated with an insulating layer that has excellent physical strength and oil resistance. Therefore, it can be suitably used for internal wiring of railway vehicles, automobiles, etc.

Examples 1 to 15 and Comparative Examples 1 to 11
(Materials used)
- High-density polyethylene: Novatec HD320, manufactured by Mitsubishi Chemical Corporation, melt flow rate = 0.3, Mw/Mn = 44, density 0.947 g/mL, expressed as "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, expressed as "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, expressed as "LLDPE" in the table.
- EEA: Lexpar 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 DuPont Mitsui Polychemicals, VA amount 25 wt%, melt flow rate = 2, density 0.94 g/mL, expressed as "EVA" in the table.
- Acid-modified PE: Tafmer MH5020, acid-modified VLDPE with a density of 0.860 g/mL, expressed as "acid-modified PE" in the table.
・Magnesium hydroxide: Kisuma 5L (manufactured by Kyowa Chemical Co., Ltd.)
・Aluminum hydroxide: Higilite H42STM (manufactured by Showa Denko)
・Antioxidant: Irganox 1010 (manufactured by BASF Japan)
・Lubricant: Zinc stearate ・Vinyl modified silicone: TEGOMER V-Si4042 (manufactured by EVONIK)
・Alkyl-modified silicone: TSF4421 (manufactured by Momentive Performance Materials)

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

The obtained tube was evaluated for extrusion processability, oxygen index (flame retardancy), flame spread property (flame spread index and presence or absence of drip), tensile strength, tensile elongation, oil resistance, and shrinkage rate of the expanded tube. I did it. The evaluation method is as follows.

(Extrusion processability)
The outer diameter variation range was measured using a laser outer diameter measuring device, and a case where the outer diameter variation range was within ±10% of the design value was considered to be a pass.

(oxygen index)
The oxygen index indicates the minimum oxygen concentration (volume %, the minimum concentration of oxygen 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 polymeric materials by oxygen index method). Generally speaking, highly flame-retardant materials are desired to have an oxygen index of 30 or more, and in particular, the BS6853 material standard for railroad vehicle cabins requires an oxygen index of 34 or more, so an oxygen index of 34 or more is acceptable. It is determined that

(Flame spread test)
The test was conducted in accordance with ASTM E162:2016 (Surface combustibility of materials using radiant heat energy sources). Specifically, the following test was conducted using six samples with a size of 152 mm x 457 mm.
The sample is set at a 30° inclination to a vertically installed radiant panel (radiant plate), the radiant plate is preheated to 670°C, and the sample is ignited using a pilot flame above the sample. After ignition, the flame spreads downward across the surface of the sample, but the radiant heat from the radiant panel gradually decreases until the flame can no longer continue propagating. The speed of flame propagation 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 determined, and the flame spread index Is was determined from the following formula.
Is=Fs×Q
The presence or absence of dripping of burning material during the propagation of the flame was visually observed.
A case where the flame spread index Is was 35 or less and there was no dripping of combustible material was determined to be acceptable.

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

(Oil resistance)
After being immersed in light oil at 70° C. for 168 hours, the tensile strength and tensile elongation were measured, and a 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 contraction, and the inner diameter of the tube after contraction were measured. The shrinkage rate of the tube is a value (%) calculated by the following formula.
{[(Tube inner diameter before contraction) - (Tube inner diameter after contraction)] / [(Tube inner diameter before contraction) - (Tube inner diameter before expansion)]} x 100

From the evaluation results shown in Tables 1 to 5 above,
The content of PE in the resin component is 25% by mass or more and 70% by mass or less, the content of EEA is 25% by mass or more and 70% by mass or less, and the content of acid-modified PE is 5% by mass or more and 35% by mass or less, With respect to 100 parts by mass of the resin component, the amount of the metal hydroxide is 100 parts by mass or more and 200 parts by mass or less, and the amount of the silicone is 1 part by mass or more and 8 parts by mass or less (the first The flame-retardant resin compositions of Examples 1 to 15 (having compositions within the range of the embodiments) had to pass the dimensional stability during extrusion molding (extrusion processability), and the flame-retardant resin compositions obtained from the resin compositions The flammable heat shrink tube has an oxygen index and a flame spread index that are above the acceptance criteria, and has excellent flame retardancy with no dripping of combustion materials during combustion, as well as mechanical strength, oil resistance, and It has also been shown that the shrinkage rate is excellent.

On the other hand, in Comparative Example 1 in which the PE content is less than 25% by mass, the oil resistance is rejected. Moreover, in Comparative Example 7 in which the PE content exceeds 70% by mass, dripping occurs in the flame propagation test, and the flame propagation test is determined to fail. The tensile elongation was also 80%, which was much lower than the acceptance standard of 200% or more, and the shrinkage rate of the tube was 78%, which was 90% or more, which was the acceptance standard, both of which were unsatisfactory results.

In Comparative Example 2 in which the content of EEA is less than 25% by mass, dripping occurs in the flame propagation test, and the flame propagation test is determined to fail. On the other hand, in Comparative Example 8, in which the content of EEA exceeds 70% by mass, the oil resistance was judged as failing, and the shrinkage rate of the tube was 83%, compared to the passing standard of 90% or more, indicating an unsatisfactory result. It has become.
In addition, in Comparative Example 3, which is the same as Example 1 except that 50% by mass of EVA was blended instead of EEA, dripping occurred in the flame propagation test, and the flame propagation test was determined to fail.

In Comparative Example 6 in which the content of acid-modified PE was less than 5% by mass, the tensile strength and tensile elongation were lower than the values of the acceptance criteria, and sufficient mechanical strength (tensile properties) was not obtained. Furthermore, the shrinkage rate of the tube was 73%, which was an unsatisfactory result, compared to the acceptance standard of 90% or more. On the other hand, in Comparative Example 2 in which the content of acid-modified PE exceeds 35% by mass, dripping occurred in the flame propagation test, and in Comparative Example 9, the oil resistance was determined to fail.

In Comparative Example 10, in which the content of the metal hydroxide was less than 100 parts by mass based on 100 parts by mass of the resin component, the flame spread index exceeded the passing standard and the flame spread test was determined to fail, and The oxygen index was below the acceptance standard, and the flame retardance that met various standards for insulated wires for vehicles was not achieved. On the other hand, in Comparative Example 11, in which the metal hydroxide content exceeds 200 parts by mass, the tensile strength and tensile elongation are lower than the acceptance criteria, and the shrinkage rate of the tube is also lower than 90% of the acceptance criteria, which is insufficient. .

In Comparative Example 4, in which the content of silicone is less than 1 part by mass per 100 parts by mass of the resin component, the oxygen index is less than the acceptance standard, and the flame retardance that meets various standards for insulated wires for vehicles is not obtained. It has not been done. On the other hand, in Comparative Example 5 in which the content of silicone (vinyl-modified silicone) exceeds 8 parts by mass, extrusion processability is low, and when extruded into a tube, the tube system becomes unstable and sufficient dimensional stability cannot be achieved. It has not been done.

Claims (5)

A resin composition containing a resin component A consisting of polyethylene, an ethylene ethyl acrylate copolymer and an acid-modified polyethylene, a metal hydroxide, and a vinyl-modified silicone or an alkyl-modified silicone, wherein the resin component A contains polyethylene. The proportion is 25% by mass or more and 70% by mass or less, the content of the ethylene ethyl acrylate copolymer is 25% by mass or more and 70% by mass or less, and the content of acid-modified polyethylene is 5% by mass or more and 35% by mass or less, and With respect to 100 parts by mass of resin component A, 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 vinyl-modified silicone or alkyl-modified silicone is 1 part by mass or more and 8 parts by mass or less. A flame-retardant resin composition , wherein the polyethylene has a molecular weight distribution (Mw/Mn) of 38 or more and a density of 0.937 g/mL or more . The flame-retardant resin composition according to claim 1, wherein the polyethylene has a melt flow rate of 0.08 or more. The flame-retardant resin composition according to claim 1 or 2, wherein the metal hydroxide is magnesium hydroxide or aluminum hydroxide. A molded product obtained by molding the flame-retardant resin composition according to any one of claims 1 to 3 into a tube shape, the molded product being imparted with heat shrinkability by expanding its diameter. Flame retardant heat shrink tubing. A flame-retardant insulated wire having a conductor and an insulating layer covering the conductor, wherein the insulating layer is made of the flame-retardant resin composition according to any one of claims 1 to 3. .