JPH0515009B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a waterproof communication cable provided with flame retardancy.

[Prior art and its problems]

A waterproof communication cable is one in which a waterproofing mixture is filled in the void in a cable core made up of a large number of insulated core wires or optical fiber cores, and the outer periphery of the cable core is covered with a sheath. Normally, this type of cable has a sheath made of polyethylene and a waterproofing compound made of petroleum-based or polybdenum-based jewelry, so it is flammable, and if part of it burns in a fire,
There is a risk of fire spreading.

In order to impart flame retardancy to cables to prevent the spread of fire, it is common to use flame retardant plastic in the sheath. However, in the case of waterproof communication cables, when the temperature rises, the viscosity of the waterproofing mixture decreases,
There was a problem in that it was difficult to make flame retardant because it flowed out from the burnt part of the sheath and burned.

[Means for solving problems and their effects]

In order to solve the problems of the prior art as described above, the present invention provides a cable core consisting of a large number of core wires, a waterproofing mixture filled in the voids in the cable core, and a waterproof mixture that covers the outer periphery of the cable core. In the waterproof communication cable equipped with a sheath, the sheath is made of flame-retardant plastic, and the waterproofing mixture is made of a gel-like compound whose viscosity is temperature-independent and whose main component is tetrafluoroethylene or It is characterized by the use of a gel-like compound containing silicone oil as a main component and adding silica or carbon black.

In this way, even if the cable becomes hot, the viscosity of the waterproofing mixture will be maintained at the same level as when it is at room temperature, so it will not leak out to the outside, and the flame retardant properties of the sheath will make the connection of the cable easier. This can prevent serious combustion.

In order to make the sheath flame retardant, a sheath material containing a halogen-based substance, or a material to which an endothermic substance such as aluminum hydroxide or antimony trioxide is added may be used.

Further, as a waterproof mixture whose viscosity is not temperature dependent, a gel-like compound containing tetrafluoroethylene as a main component can be used. It has no melting point and maintains a viscosity of about 1000 centipoise in the range -30°C to 200°C. In addition, silicone grease made by adding silica to dimethyl silicone oil and silicone grease made by adding carbon black to methyl silicone oil with many phenyl groups can also be used because they have no melting point. Note that a waterproof mixture whose viscosity does not depend on temperature is a waterproof mixture whose viscosity is maintained at the same level as at room temperature even at high temperatures and does not flow.

Note that in order to further improve flame retardancy, the waterproof mixture should also be made flame retardant. To this end, it is recommended to add to the waterproofing mixture a substance that causes an endothermic reaction during combustion, such as aluminum hydroxide, magnesium hydroxide, antimony trioxide, and antimony pentoxide. Further, if the waterproofing mixture forms a carbonized layer upon combustion, the flame retardance will be even better. This is because the carbonized layer prevents the material melted by heating from flowing.

〔Example〕

We prototyped the following waterproof communication cable,
Tests specified in IEEE383 were conducted.

Cable core: 0.4 mm x 100 pairs Polyethylene insulation and waterproof mixture: Gel-like compound mainly composed of tetrafluoroethylene Viscosity 1000 centibore core wrap: Insulating paper Metal shielding layer: Aluminum tape sheath: OI (oxygen index) 32 As a result, there was no phenomenon of the waterproofing mixture melting down and burning on the floor, and the damaged sheath length was 1800 mm.
1500mm passed the following standards.

It is desirable to use a material with an OI of 27 or higher for the sheath. In addition, if there is an intervening or tension member sheath within the sheath, their OI
It is also desirable that the number is 27 or higher. Furthermore, it is desirable to use a corelap that forms a char layer after combustion.

By the way, if the above-mentioned waterproof mixture whose viscosity is not temperature-dependent is used, it is easy to construct a high-temperature waterproof cable used in high-temperature areas.

If a petroleum-based or polybdenum-based waterproofing mixture is used in the past, in order to prevent the waterproofing mixture from flowing out at high temperatures, it is necessary to increase the viscosity so that it does not flow even at high temperatures, and then the cable core It becomes necessary to fill the container at a high temperature. However, high-temperature filling softens the cable core insulation, making the cable core surface more susceptible to damage during manufacturing, and requires high-temperature work, so there are many safety considerations. Furthermore, in order to prevent insufficient filling due to a drop in temperature (increase in viscosity) of the mixture during filling, it is necessary to warm the cable core in advance, which is extremely complicated.

On the other hand, if a waterproof mixture whose viscosity is not temperature dependent is used, it becomes possible to fill the cable at room temperature, and stable production is possible without damaging the cable core. For example, gel-like compounds mainly composed of tetrafluoroethylene, silicone greases made by adding silica to dimethyl silicone oil, silicone greases made by adding carbon black to methyl silicone oil with many phenyl groups, etc., have a viscosity of about 700 to 1000 centipoise. This material does not flow under its own weight and can be press-fitted into the cable core.
Cables filled with a 600-pair cable core and covered with a regular polyethylene sheath are REA standard PE
-39 test (65℃), passed without melting or dripping of the mixture.

〔Effect of the invention〕

As explained above, according to the present invention, a gel compound whose viscosity is temperature-independent and whose main component is tetrafluoroethylene, or a gel whose main component is silicone oil and silica or carbon black is used as a waterproofing mixture. Since the waterproofing compound is used, even if exposed to high temperatures due to a fire, the waterproofing mixture will not leak out and burn. Therefore, by making the sheath flame retardant, the spread of fire in the event of a fire is reliably prevented. can do.

Claims (1)

[Scope of Claims] 1. A cable core consisting of a large number of core wires, and a waterproofing mixture filled in the void within the cable core,
A waterproof communication cable comprising a sheath that covers the outer periphery of the cable core, wherein the sheath is made of flame-retardant plastic, and the waterproofing mixture is mainly composed of tetrafluoroethylene whose viscosity is not temperature dependent. A flame-retardant and waterproof communication cable characterized by being made of a gel-like compound or a gel-like compound containing silicone oil as a main component and adding silica or carbon black. 2. The communication cable according to claim 1, characterized in that the waterproof mixture contains a substance that causes an endothermic reaction when burned.