JPH0452895Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a flame-retardant, low-smoke multicore cable that has excellent flame retardancy, generates little smoke during combustion, and is highly flexible.

[Background of the idea]

In recent years, with the development of electronic devices, OA devices such as computers and facsimile machines have become rapidly popular. Since these OA devices are installed in offices and buildings, consideration must be given to fire safety for the electric wires and cables used in these devices.
These electric wires and cables are now required not only to prevent the spread of fire, but also to reduce smoke generation during combustion.

In general, fluororesins such as FEP and PVDF are often used as wire coating materials with excellent flame retardancy and low smoke properties. Although these fluororesins have excellent flame retardancy, low smoke properties, and heat resistance, they have the drawback of being very expensive. However, when a fluororesin is used as an outer coating layer for a thick cable such as a multi-core cable, the cable becomes extremely hard, making installation difficult and resulting in poor workability. Furthermore, the purpose of using a fluororesin for the outer coating layer is that flame retardancy and low smoke properties are often required rather than heat resistance. Therefore, we investigated a multi-core cable that is flame retardant, has low smoke, and is easy to work with using a general-purpose resin. A well-known method for reducing smoke in polymeric materials generally used for wire coating materials is to add a large amount of hydrated metal oxides such as aluminum hydroxide and magnesium hydroxide. As a method for evaluating flame retardancy, the oxygen index of the resin filled with hydrated metal oxides and metal carbonates was measured by the oxygen index method (JIS-K-7201) and is shown in FIG. In Figure 1,
1 shows the change in oxygen index with respect to the filler amount: magnesium carbonate, 2 magnesium hydroxide, 3 aluminum hydroxide, and 4 zinc borate. In general, when flame retardancy is expressed by an oxygen index, it is said that horizontal flame retardance has an oxygen index of 22 to 25, and vertical flame retardance has an oxygen index of 27 to 30 or higher. Now, the oxygen index which is the flame retardant degree of vertical flame retardant
If the amount of filler required to achieve 30% is calculated from FIG. 1, it is necessary to add 100 parts by weight or more. Smoke production was measured using an NBS smoke density chamber, and the maximum smoke density (Dm) at framing was determined.

The Dm of fluororesin framing, which is used as a low smoke material, is approximately 40 for FEP and approximately 125 for PVDF. On the other hand, ethylene-tetrafluoroethylene conjugate (ETFE), which is a type of fluororesin, is said to be unusable as a low-smoke material due to its high amount of smoke, and the Dm of this resin is approximately 150. From this, it can be seen that a material that can replace these fluororesins needs to have a Dm of 125 or less.

Now, in the framing of polyolefin resin compositions filled with hydrated metal oxides and metal carbonates,
Dm is shown in Figure 2. The symbols in Figure 2 are:
As is clear from this figure, which shows the same filler as in Figure 1, the amount of smoke emission decreases as the amount of filler added increases. Therefore, in order to obtain a large smoke reduction effect, it is necessary to add a large amount of filler.

From this point of view, it is desirable that the polymer used be one that can add a large amount of filler, and examples of the polymer include rubbers such as EP rubber, ethylene-vinyl acetate copolymer, ethylene-α-olefin copolymer, and the like. Among these polymers, ethylene-vinyl acetate copolymers with a vinyl acetate content of 50% or more can be molded even with a high loading of 200 to 300 parts by weight, and are highly flexible, making them suitable as highly filled filler polymers. ing. As the base polymer, it is preferable to use ethylene-vinyl acetate copolymer alone, but depending on the required properties, other polymers may be used, such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer (vinyl acetate content less than 50%). , ethylene-ethyl acrylate copolymer, ethylene-α-olefin copolymer, EP rubber (EPDM), butyl rubber, polybutadiene, polyurethane, and the like.

Against this background, we investigated the development of a flame-retardant, low-smoke multicore cable using inexpensive flame-retardant, low-smoke materials as an alternative to expensive fluororesins.

[Specific explanation of the idea]

This invention uses a fluororesin with low smoke generation as the insulating layer, and the coating layer has a vinyl acetate content of 50%.
% or more of a polyolefin resin composition mainly composed of ethylene-vinyl acetate copolymer,
It consists of a resin composition in which hydrated metal oxide or metal carbonate and zinc borate are added in a total of 100 weight or more, and the ratio of zinc borate in the filler is 0.25 to 0.75, and cross-linked by radiation irradiation. The invention relates to flexible, inexpensive, flame-retardant, low-smoke multicore cables.

Fluorine resins used as the insulating layer include FEP, PVDF, and FEP because they emit little smoke.
When a flame-retardant, low-smoke polyolefin resin composition is used as an insulating layer, the dielectric constant becomes large, making it unsuitable for applications with strict requirements.

Ethylene-vinyl acetate copolymers with a vinyl acetate content of 50% or more are suitable for the base polymer of flame-retardant, low-smoke, polyolefin resin compositions for the outer coating layer because they allow for high filler filling. There is. It is also possible to blend it with other polymers depending on the required properties.

The reason why the amount of filler added is 100 parts by weight or more is as follows.
This is to make the oxygen index 30 or higher. The reason why the ratio of zinc borate in the filler is 0.25 to 0.75 is the third reason.
As can be seen from Fig. 4, when the ratio is less than 0.25,
This is because when Dm exceeds 125 and exceeds 0.75, the oxygen index becomes less than 30.

The reason why crosslinking by radiation is necessary is that adding a large amount of filler causes a large decrease in strength, and the aim is to improve mechanical strength by crosslinking. The reason why radiation crosslinking is suitable is that in chemical crosslinking using organic peroxides, the decomposition temperature of the organic peroxide is low.
This is because the temperature is 120°C to 200°C, and the large amount of filler causes molding to be impossible at temperatures lower than the decomposition temperature due to the large torque during extrusion. The reason why polyimide film is used as the presser tape is that it has excellent flame retardancy.
This is because it has low smoke properties.

The present invention will be explained below with specific examples.

FIG. 5 shows one embodiment of the present invention. Outer diameter
Extrude an FEP insulating layer 2 onto a 0.7 mm (12/0.18) tinned conductor 1, twist 12 insulated wires 3, and cover it with a polyimide film 4 with a thickness of 25 μ and a width of 30 mm.
Press and wrap with a wrap. Then an ethylene-vinyl acetate copolymer with a vinyl acetate content of 60% by weight
A resin composition consisting of 100 parts by weight of zinc borate, 150 parts by weight of magnesium carbonate, and 0.5 parts by weight of an antioxidant was extruded and coated as the outer coating layer 5 to a thickness of 1.5 mm, and then irradiated with 20 Mrad using an electron beam accelerator. Cross-linked. The 25% modulus of the coating layer of the multicore cable thus obtained is 0.35Kg/ ^mm2 ,
25% modulus 1.2 when FEP is used as the coating layer
Kg/mm ² compared, the cable was highly flexible and easy to install. Moreover, it was found that the cost of the outer coating layer was 1/4 to 1/5 of that of fluororesin.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of various fillers added and the oxygen index. FIG. 2 is a graph showing the relationship between the amount of various fillers added and the amount of smoke generated. FIG. 3 is a graph showing the relationship between the addition ratio of zinc borate in the filler and the amount of smoke generated. FIG. 4 is a graph showing the relationship between the addition ratio of zinc borate in the filler and the oxygen index. FIG. 5 is a cross-sectional view of a multicore cable, in which 1 is a metal conductor, 2 is an insulating layer, 3 is an FEP insulated wire, 4 is a polyimide tape, and 5 is an external insulating layer.

Claims (1)

[Scope of claim for utility model registration] (1) Two or more insulated wires using fluororesin for the insulation layer are twisted together, and a polyimide film pressure tape is wrapped over the strands, and the vinyl acetate content is 50%.
A total of 100 parts by weight or more of a hydrated metal oxide or metal carbon salt and zinc borate as a filler is added to 100 parts by weight of a polyolefin resin composition mainly composed of ethylene-vinyl acetate copolymer in an amount of 100 parts by weight or more. A flame-retardant, low-smoke multicore cable characterized in that the cable is coated with a resin composition in which the ratio of zinc borate in the filler is 0.25 to 0.75, and is crosslinked by radiation. (2) Utility model registration where the fluororesin is polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) A flame-retardant, low-smoke multicore cable according to claim (1). (3) The flame retardant according to claim 1, wherein the hydrated metal oxide is selected from the group consisting of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium hydroxide. , low smoke multicore cable. (4) Flame retardant and low smoke according to claim 1, wherein the metal carbonate is selected from the group consisting of magnesium carbonate, magnesium calcium carbonate, calcium carbonate, zinc carbonate, and barium carbonate. multicore cable.