JPH0452894Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of the invention] The invention is a flame-retardant, low-smoke multicore cable that has excellent flame retardancy, does not generate any harmful corrosive gas when burned, and generates little smoke. Regarding.

[Background of the idea]

In recent years, the requirements for flame retardancy for building wiring and internal wiring in equipment have become increasingly strict.
Furthermore, it is required that no harmful gases are generated that have an adverse effect on the human body and equipment.

Fluororesin, which has excellent flame retardancy and low smoke properties, is often used as a wire coating material for internal wiring in buildings. However, multicore cables coated with fluororesin have the problem of being hard and difficult to wire. Moreover, fluorine-based resins
It is known that when burned, it generates highly corrosive and harmful gases such as hydrofluoric acid.

In addition, there is an economical problem in that fluororesins are expensive. Therefore, it has excellent flame retardant and low smoke properties,
In addition, a highly flexible material that does not generate corrosive gases is required. Since no harmful corrosive gas is emitted, it is inappropriate to add resins containing halogen in the molecule, such as polyvinyl chloride, or halogen-based flame retardants. Generally, it is well known to add a large amount of a hydrated metal oxide such as aluminum hydroxide or magnesium hydroxide to a halogen-free polyolefin resin.

We have now measured the oxygen index of a polyolefin resin composition filled with hydrated metal oxides and metal carbonates using the oxygen index method (JIS-K-7201), which is one of the methods for evaluating flame retardancy. It is shown in Figure 1.

In Figure 1, 1 is magnesium carbonate, 2 is magnesium hydroxide, 3 is aluminum hydroxide,
4 shows the change in oxygen index with respect to the amount of zinc borate filler. 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, if we calculate the amount of filler necessary to achieve an oxygen index of 30, which is the degree of flame retardance for vertical flame retardation, from Figure 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 fluororesins used as low smoke materials is about 40 for tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and about 125 for polyvinylidene fluoride (PVDF). On the other hand, ethylene-tetrafluoroethylene copolymer (ETFE), which is also a fluororesin, is said to have a high smoke-emitting property and cannot be used as a low-smoke material, and its Dm is 150
That's about it. Therefore, it is necessary as a low smoke material.
Dm can be said to be 125 or less.

FIG. 2 shows the Dm in framing of a polyolefin resin composition filled with hydrated metal oxides and metal carbonates. The numbers in FIG. 2 indicate the same fillers as in FIG. As is clear from this figure, the amount of smoke generated decreases as the amount of filler added increases. Therefore, in order to obtain a large smoke reduction effect,
The addition of large amounts of filler is required. Furthermore, it can be seen from Figure 2 that zinc borate has the highest smoke reduction effect. However, it was found from the oxygen index in Figure 1 that zinc borate has poor flame retardancy and cannot be used alone.

The polymer to be used next is preferably one that can contain a large amount of filler and does not contain substances that cause the generation of corrosive gases, such as halogens.
Such polymers include rubbers such as EP rubber,
Ethylene-vinyl acetate copolymer, ethylene-α-
Examples include olefin copolymers. Among these polymers, ethylene-vinyl acetate copolymers with a vinyl acetate content of 50% by weight or more can be molded even with the addition of 200 to 300 parts by weight of filler and have excellent flexibility. Therefore, it is suitable as a base polymer. It is preferable to use ethylene-vinyl acetate copolymer alone as the base polymer, but
Depending on the required properties, other polymers such as polyethylene, polypropylene, ethylene-vinyl acetate copolymers (vinyl acetate content less than 50% by weight) may be used.
It can also be used in a blend with ethylene-ethyl acrylate copolymer, ethylene-α-olefin copolymer, EP rubber (EPDM), butyl rubber, polybutadiene, etc.

Against this background, we are considering flame-retardant, low-smoke multicore cables that are easy to work with when installing electric wires, have excellent flame retardant properties, do not generate harmful corrosive gases when burned, and emit less smoke. did.

[Specific explanation of the idea]

In the present invention, 100 parts by weight of a polyolefin resin composition mainly composed of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 50% by weight or more is added to the insulating layer, and a hydrated metal oxide or metal carbonate is added as a filler. Adding 100 parts by weight or more of zinc borate,
After cross-linking an insulated wire using a resin composition with a ratio of zinc borate in the filler of 0.25 to 0.75 by irradiation with radiation, two or more cores are twisted or stretched, and then a polyimide film press tape is applied over the wire. A flame retardant method, characterized in that a resin composition having the same composition as the insulating layer is coated on the insulated wire by extrusion, and then crosslinked by radiation.
Regarding low smoke multicore cables.

The reason for using an ethylene-vinyl acetate copolymer with a vinyl acetate content of 50% by weight or more as the base polymer for a flame-retardant, low-smoke resin composition is that it allows high filler filling and is highly flexible. .
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 increase the oxygen index to 30 or higher. The reason why the ratio of zinc borate in the filler is 0.25 to 0.75 is because
If it is less than 0.25, Dm will be 125 or more from Figure 3, and if it exceeds 0.75, the oxygen index will be from Figure 4.
This is because the number is less than 30.

The reason why crosslinking by radiation irradiation is necessary is because the strength is low as it is because a large amount of filler is added, and the mechanical strength is improved by crosslinking.
The reason why radiation crosslinking is suitable is that chemical crosslinking using organic peroxides requires a large amount of filler and high torque during extrusion, and molding is difficult at temperatures below the decomposition temperature of organic peroxides (120°C to 200°C).

Further, the reason why polyimide film is used for the presser tape is that it has excellent flame retardancy and heat resistance, and generates little smoke when burned.

The present invention will be explained below using specific examples.

FIG. 5 shows one embodiment of the present invention. Outer diameter
The 0.7 mm (12/0.18) tinned conductor 1 has a vinyl acetate content of 60% by weight. A resin composition consisting of 100 parts by weight of ethylene-vinyl acetate copolymer, 100 parts by weight of zinc borate, 100 parts by weight of magnesium carbonate, and 0.5 parts by weight of antioxidant was extrusion coated as the insulating layer 2 to a thickness of 0.4 mm, and then Twelve insulated wires 3 crosslinked by wire irradiation are twisted together and wrapped with a polyimide film 4 having a thickness of 25 μm and a width of 30 mm in a 1/2 wrap.
A resin composition having the same composition as the insulating layer 2 is extrusion coated onto the twisted wire to a thickness of 1.5 mm to form a coating layer 5. After that, it is irradiated with an electron beam to cause crosslinking. The 25% modulus of the coating layer of the multicore cable thus obtained was measured and was found to be 0.35 Kg/mm ² . For comparison,
The 25% modulus of tetrafluoroethylene-hexafluoropropylene copolymer of the same thickness was measured to be 1.2.
It was confirmed that the ^multi -core cable of this invention has excellent flexibility and is easy to install.
Further, as a result of combustion tests, it was found to have excellent flame retardancy, emit little smoke during combustion, and did not generate any harmful corrosive gases.

[Brief explanation of drawings]

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. Figure 5 is a cross-sectional view of a multicore cable, where 1 is a metal conductor, 2 is an insulating layer, 3 is an insulated wire,
4 is a pressure tape, and 5 is an outer coating layer.

Claims (1)

[Claims for Utility Model Registration] (1) The insulating layer contains 100 parts by weight of a polyolefin resin composition mainly composed of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 50% by weight or more, and a hydrated metal oxide as a filler. Adding 100 parts by weight or more of carbonate or metal carbonate and zinc borate,
and the ratio of zinc borate in the filler is 0.25~0.75
An insulated wire made of a resin composition is cross-linked by radiation irradiation, two or more cores are twisted or straightened, a polyimide film pressure tape is wrapped over the wire, and then an insulating layer is formed on the insulated wire. A flame-retardant, low-smoke multicore cable characterized by being extruded and coated with a resin composition having the same composition and then crosslinked by radiation. (2) The hydrated metal oxide is selected from the group consisting of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium hydroxide.
A flame-retardant, low-smoke multicore cable according to claim 1 of the utility model registration claim. (3) The flame-retardant, low-smoke multicore according to claim 1 of the utility model registration claim, wherein the metal carbonate is selected from the group consisting of magnesium carbonate, magnesium calcium carbonate, calcium carbonate, zinc carbonate, and barium carbonate. cable.