JPH0515011B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a flame-retardant electric cable that does not generate toxic halogen gas when burned, especially a flame-retardant electric cable that has a high degree of flame retardancy and passes the vertical tray combustion test (VTFT). It is related to. [Prior Art] Polyolefin, which has excellent electrical insulation properties, has been widely used as insulation materials and sheath materials for electric wires and cables. As a recent trend, there has been a strong demand for flame retardancy for electric wires and cables for nuclear power plants, electric wires for vehicles, and electric wires for wiring inside panels and machines. As a method of making polyolefin flame retardant, a method of mixing a halogen-containing compound, a phosphorus-containing compound, etc. has generally been adopted. However, these produce a large amount of smoke when burned, causing problems such as corrosiveness to equipment and toxicity to the human body. In particular, recently there has been a strong demand for not generating such halogen gases from the standpoint of safety. In light of this situation, inorganic compounds such as metal hydroxides and carbonates, which have very low smoke generation and toxicity, have been attracting attention. [Problems to be solved by the invention] On the other hand, the flame retardance of electric cables is often required to pass VTFT in consideration of fire during installation. This is a very severe test for electrical cables whose bodies are not flame retardant at all. In particular, it is extremely difficult for small single-core cables to pass this test. The present invention has been made based on the above,
The purpose of this invention is to provide a flame-retardant electric cable that has a high degree of flame retardancy that passes VTFT and does not emit toxic halogen gas when burned. [Means for Solving the Problems] The flame-retardant electric cable of the present invention has two inner and outer sheath layers on the outer periphery of the insulated wire core, and the inner coating layer is made by adding 50 to 50 parts of magnesium hydroxide to 100 parts by weight of polyolefin. Formed by a composition containing 400 parts by weight,
The outer coating layer is characterized in that it is formed from a composition containing 50 to 400 parts by weight of aluminum hydroxide based on 100 parts by weight of polyolefin. In the present invention, the insulated wire core is constructed by providing an insulator around the outer periphery of the conductor, and may be a single thread or a plurality of threads twisted together. The insulator is made of a halogen-free polymer, such as polyethylene, polypropylene, poly4-methylpentene-1, polybutene, cross-linked polyethylene, cross-linked polypropylene, ethylene-propylene copolymer, ethylene-propylene terpolymer, ethylene-ethyl acrylate copolymer. Combined ethylene・
Examples include butene copolymers, ethylene/vinyl acetate copolymers, natural rubber, butyl rubber, styrene-butadiene rubber, and silicone rubber. In the present invention, the polyolefin forming the coating layer for protecting the insulated wire core in the event of a fire includes ethylene propylene copolymer, ethylene propylene diene terpolymer, polyethylene, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, ethylene butene copolymer, ethylene Examples include butene diene terpolymers, which can be used alone or in combination of two or more. The present inventor has discovered that if the outer coating layer is first decomposed and foamed by heat during combustion, and then the inner coating layer is further decomposed and foamed as the temperature rises, the coating layer will form a hard carbonized layer. We discovered that the insulator of the insulated wire core can be effectively protected, and from this point of view, the inner coating layer contains hydroxide, which has a relatively high decomposition temperature (endothermic peak temperature determined by differential scanning calorimeter (DSC)) of 432°C. Magnesium was used as a flame retardant, and aluminum hydroxide, which has a relatively low decomposition temperature of 313°C, was used as a flame retardant in the outer coating layer. The flame retardant must be contained in an amount of 50 to 400 parts by weight per 100 parts by weight of the polyolefin. If it is less than 50 parts by weight, the desired flame retardancy cannot be imparted, and if it exceeds 400 parts by weight, extrusion processability will be significantly reduced. In the present invention, in addition to the above components, crosslinking agents, antioxidants, lubricants, softeners, dispersants, etc. may be added as appropriate. As a crosslinking agent, dicumyl peroxide, 3
- Organic peroxides represented by bis(t-butylperoxyisopropyl)benzene are suitable;
Sulfur, ethylene dimethacrylate, diacrylphthalate, p-quinone dioxime, etc. may be used in combination with this as a crosslinking aid. As antioxidants, amine antioxidants such as phenyl-α-naphthylamine, N,N'-di-β-naphthyl-p-phenylenediamine, 2,6
Examples include phenolic antioxidants such as -di-t-butyl-4-methylphenol and hindered phenol. [Example] Various ingredients were put into a 12-inch roll kept at 130°C according to the compounding ratio shown in Table 1, and roll kneading was performed.
Using m/m extruder (L/D=25), outer diameter 3.0mm
An inner layer and an outer layer each having a thickness of 1.5 mm were coated by extrusion on the outer periphery of three twisted cross-linked polyethylene insulated wire cores. The evaluation results for each example are shown in the lower column of Table 1. Flame retardancy evaluation was carried out as follows: 8 cables 2.4m long were arranged vertically on a vertical tray at intervals of 1/2 the outer diameter, and 70,000 cables were placed from the bottom.
After exposing the burner to a BTU/hr flame for 20 minutes, the burner was extinguished, and if the flame self-extinguished, it passed, and if it burns to a height of 1.8 m, it was judged to have failed.

[Table] As is clear from Table 1, in Examples 1 to 4 according to the present invention, good effects were obtained in both flame retardancy and extrusion processability. On the other hand, Comparative Example 1, in which the content of inorganic compounds in the outer layer is below the specified value, fails the flame retardant test, and Comparative Example 2, in which the content of inorganic compounds in the material forming the inner layer is above the specified value, is extruded. It is necessary to create a cable due to poor workability, and in Comparative Examples 3 and 4, which used a flame retardant different from the flame retardant specified in the present invention, the flame retardance was rejected, and the inorganic compound content of the inner layer was Comparative Example 5, which was below the specified value, failed in terms of flame retardancy. [Effects of the Invention] As explained above, the present invention forms an inner coating layer with a composition containing magnesium hydroxide in polyolefin, and forms an outer coating layer with a composition containing aluminum hydroxide in polyolefin. This makes it possible to create electrical cables that have a high degree of flame retardancy that passes VTFT and do not emit toxic halogen gas when burned.

Claims (1)

[Claims] 1. A flame-retardant electric cable having an inner coating layer and an outer coating layer on the outer periphery of the insulated wire core, wherein the inner coating layer is formed from a composition containing 50 to 400 parts by weight of magnesium hydroxide based on 100 parts by weight of polyolefin, A flame-retardant electric cable, wherein the outer coating layer is formed from a composition containing 50 to 400 parts by weight of aluminum hydroxide based on 100 parts by weight of polyolefin.