JPH03254016A - Flame retardant cable - Google Patents

Abstract

PURPOSE:To strengthen the resistance to damages from outside and prevent generation of a large amount of harmful gases and smoke at the time of burning by forming a bilayered coating composed of a mixture of mainly olefin-based resin having a prescribed oxygen index and tensile strength on the outer circumference of a cable. CONSTITUTION:A coating having a bilayered structure composed of an inner layer of a mixture containing mainly olefin-based resin with an oxygen index of 27 or more and tensile strength of 0.7kgf/mm<2> or more and an inorganic hydrate compound and an outer layer of a mixture containing olefin-based resin with oxygen index of 22 or more and tensile strength of 1.2kgf/mm<2> or more and an inorganic hydrate compound, is formed on the outer circumference of a flame retardant cable. The thickness of the inner layer is 50-90% of the whole thickness. As the olefin-based resin, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, etc., are used. As the inorganic hydrate compounds, aluminum hydroxide, calcium hydroxide, hydromagnesites are used, and besides them, a lubricating agent, a pigment, a flame retarding agent, an antioxidant, and a cross-linking agent may be added.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is characterized by excellent flame retardancy and resistance to external damage, and also does not produce harmful gases such as halogen gas or large amounts of smoke when burned. Concerning flame-retardant cables that do not generate

[Prior Art] Thermoplastic resins such as olefin resins and vinyl chloride resins, which have excellent extrusion processability and electrical insulation properties, have been used as cable sheath materials.

In recent years, there has been an increasing demand for these materials to be flame retardant, and in particular, there is a demand for non-halogen mixtures that do not contain any halogens, since they do not emit harmful gases such as halogen gas or large amounts of smoke when burned. and is partially used.

These non-halogen mixtures include polyethylene, ethylene,
It can be obtained by mixing an inorganic hydrous compound such as magnesium hydroxide or aluminum hydroxide with an olefin resin such as ethyl acrylate copolymer or ethylene/vinyl acetate copolymer.

[The mystery that the invention attempts to solve]

However, the method of using the above-mentioned non-halogen mixture as a cable sheath material has the following problems.
A solution is needed.

In other words, in order to improve the flame retardance of a cable, a large amount of an inorganic water-containing compound must be added to the olefin resin as a non-halogen mixture, and as a result, the tensile strength of the resulting mixture decreases. There was a problem that the extrusion processability deteriorated. In particular, a decrease in tensile strength means that when the weight of the cable is heavy, such as a high-voltage cable, the cable is susceptible to damage during installation, and in severe cases, the sheath may be damaged and come off.

[Means and actions to solve the problem]

The present invention has been made to solve the above-mentioned IU, and provides a flame-retardant cable whose outer periphery is coated with a flame-retardant sheath, in which the flame-retardant sheath has an oxygen index of 27 or more and a tensile strength of 0.7 kgf. /m” or more, an inner layer made of a mixture of an olefin resin and an inorganic water-containing compound mainly;
It has a two-layer structure with an outer layer made of a mixture of an olefin resin with an oxygen index of 22 or more and a tensile strength of 1.2 kgf nom or more and an inorganic water-containing compound, and the thickness of the inner layer is equal to or less than the H fuel. The flame retardant cable is characterized in that the thickness of the entire sheath is 50% or more and less than 90%.

The flame-retardant cable of the present invention is the same as conventional cables except for the sheath. That is, the present invention utilizes electrical cables, communication cables, and optical fibers using cross-linked polyethylene, oil-impregnated paper, etc. as insulators. It can be used for any cable etc. Of course, the flame retardance of the cable can be further improved by wrapping it with flame retardant tape or the like.

The flame-retardant sheath in the flame-retardant cable of the present invention has a two-layer structure including an inner layer and an outer layer coated thereon.

First, the inner layer should not be a mixture of an olefin resin and an inorganic water-containing compound, and should have an oxygen index of 27 or more and a tensile strength of 0.7 kgf/m" or more, more preferably an oxygen index of 30 or more. It is.

As the olefin resin, ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer, ultra-low density polyethylene, linear low density polyethylene, etc. are suitably used. As the inorganic hydrous compound, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, a mixture of hydromagnesite and huntite, etc. are preferably used.

In addition to these, admixtures include metal salts such as stearic acid and oleic acid, lubricants such as fatty acid amides, pigments such as carbon black and titanium white, and flame retardants such as red phosphorus, zinc borate, zinc sulfide, and antimony dioxide. , various antioxidants, crosslinking agents such as organic peroxides, etc. may be added in desired amounts.

The outer layer formed on this inner layer should not be a mixture mainly composed of an olefin resin and an inorganic water-containing compound, and should preferably have an oxygen index of 22 or more and a tensile strength of 1.2 kgf/kaku2 or more. is 1.4 kgf/-2 or more. Regarding the olefin resin, inorganic water-containing compound, and other compounding agents, the same ones used for the inner layer mixture are used.

The mixture in the inner layer must have an oxygen index of 27 or higher, preferably 30 or higher, to provide the flame retardancy required for the cable, and if the tensile strength is not 0.7 kgf/m or higher, it may cause injury during cable installation, etc. It becomes easier to receive.

Similarly, the outer layer mixture has an oxygen index of 22 or more and a tensile strength of 1.2 kgf/m or more, preferably 1.4 kgf/m'' or more.
11111" or more is used. If the 0M prime index is less than 22, the H flammability necessary for the cable cannot be obtained, and the tensile strength is 1.2 kgf/wttr" or more, preferably 1.2 kgf/wttr" or more.
If it is less than 4 kgf/m", it will be more likely to be damaged during cable installation, etc.

In the flame-retardant sheath formed as described above, the thickness of the inner layer is 50% to 90% of the thickness of the entire sheath.
Preferably it is set in the range of 60% to 80%. Therefore, the thickness of the outer layer is 10% to 50%, preferably 20% to
It is set to 40%.

If the thickness of the inner layer is less than 50% of the total thickness (therefore, the thickness of the outer layer is 50% or more), the flame retardance of the cable cannot be ensured, and the ratio of the thickness of the outer layer is 10%.
This is because if the thickness of the inner layer is less than 90% (therefore, the thickness of the inner layer is 90% or more), the flame-retardant sheath is likely to be damaged during cable installation.

[Effect]

The flame-retardant sheath of the present invention ensures flame retardancy with its inner layer and trauma resistance with its outer layer. As a result, the cable becomes both flame retardant and trauma resistant.

[Examples of the Invention] Examples 1 to 3, Comparative Examples 1 to 4 A conductor with a cross-sectional area of 250 m was extruded and coated with an internal semiconductive layer, an insulating layer, and an external semiconductive layer with a thickness of 11 cm. A cross-linked polyethylene insulated cable core was produced.A metal tape was then wound around the cable core, and an inner layer and an outer layer having the properties shown in Table 1 were sequentially extruded and coated thereon to form a sheath.

Each of the obtained electric cables was subjected to a vertical tray combustion test specified by IEEE383 to examine its flame retardance.

Further, the cable was passed over an iron vibrator at a speed of 10 m/min with a load of 900 kg/m placed on the cable, and damage to the sheath, peeling, etc. at that time was visually observed. The following results are collectively shown in Table 1.

(Blank below) [Effects of the Invention] As is clear from the above explanation, the flame-retardant cable of the present invention has both flame-retardant and trauma-resistant properties, making it extremely useful as an electric power cable or communication cable. be.

Claims (1)

[Claims] In a flame-retardant cable whose outer periphery is coated with a flame-retardant sheath, the flame-retardant sheath has an oxygen index of 27 or more and a tensile strength of 0.
．． An inner layer consisting of a mixture of an olefin resin with an oxygen index of 22 or more and a tensile strength of 1.2 kgf/mm^2 or more containing an inorganic hydrate compound. A flame-retardant cable having a two-layer structure with an outer layer mainly consisting of a blended mixture, wherein the thickness of the inner layer is 50% or more and less than 90% of the total thickness of the flame-retardant sheath.