JPS60176304A - Flame resistant high frequency coaxial cable - Google Patents

Abstract

To improve the flame-resistance of coaxial radio-frequency cables, the space between the inner and outer conductor is filled to less than 70% with a halogen-free material, the outer conductor has a number of shells from metal foil and mesh, and the protective sleeve is produced from a material whose oxygen index at 20 DEG C is at least 35%. <IMAGE>

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a cylindrical inner conductor, an insulating material surrounding the inner conductor, a flexible cylindrical outer conductor surrounding the insulating material,
A flame-resistant high frequency coaxial cable comprising a protective sheath surrounding the outer conductor.

It is.

In many applications, strict requirements are placed on high frequency recessed coaxial cables regarding their behavior in the event of a fire. In addition to the halogen-free requirements imposed on all materials used, flame-resistant cables must pass the following tests: δ, i.e., lying on vertically oriented metal conductors. This test involves contacting a cable attached with a flame for 20 minutes at 860°C in a special furnace equipped with forced draft. In this test, the cable must not spread or burn off after contact with the flame.

In order to meet the strict requirements for cables,
It is common to use materials with relatively high filling ratios in telecommunications and power supply cables, which fillings are mostly based on hydrated aluminum oxide for the insulating and protective sheathing of the conductors. Furthermore, wrappings of glass, mica or a combination thereof are frequently applied between the so-called cable core and the protective sheath.

It is more common in telecommunications and power supply cables to interpose between the cable core and the protective sheath an intermediate sheath of very high fill material, which intermediate sheath has mechanical and electrical properties. Particularly high requirements are imposed on the filling material, which cannot be used for cable insulation in high-frequency coaxial cables.

The cross-sectional area of the insulation between this inner and outer conductor is significantly large compared to the cross-sectional area of the insulation in telecommunications and power supply cables. Furthermore, the usual methods of wrapping bands of glass or mica, for example, are useless because they do not present a sufficient oxygen barrier to the insulating materials used for electrical purposes. Such insulating material consists of polyethylene which expands and vaporizes when heated to high temperatures, causing rupture of the sheath.

It is an object of the invention to satisfy the electrical requirements and to increase the flame resistance to such an extent that the cable satisfies the aforementioned test conditions, but without unacceptably increasing the cost of the cable and reducing the dimensions of the cable, i.e. It is an object of the present invention to provide a high frequency coaxial cable structure that does not essentially increase the cross-sectional area of the cable.

The flame-resistant high-frequency coaxial cable of the present invention has long flame-resistant properties even when polyethylene is used as the insulating material between the inner conductor and the outer conductor, if the following conditions a-b are satisfied. : a. said fringe material is comprised of a rogen-free material, said material filling less than 70% of the space between the inner conductor and the outer conductor; b. The cylindrical outer conductor has a multi-layered form, and is a foil that is adjacent to and surrounds the insulating material over its entire periphery, and extends parallel to the axis, and has an inner side that overlaps both edges of the band. Spinning a foil and a metal wire surrounding the foil and having a visual coverage of 80% or more
ing) and an outer metal foil concentrically wrapping said wire spinning, said outer wrapping overlapping said bands edges by at least 26% of each other, said protection surrounding said outer conductor; The sheath is at 20℃
The flame-resistant halogen-free material has an oxygen index of at least 86%.

The following formula: (where d - diameter of the insulation, LOI - oxygen index of the protective sheath at -20 °C, % F - space factor of the insulation between the inner and outer conductors W - of the protective sheath It is advantageous to take a wall thickness W of the protective sheath according to the wall thickness S.

As a result according to the invention, first of all it is achieved that the insulation between the inner conductor and the outer conductor can expand. This ensures that very high internal pressures do not automatically and immediately build up during heating. The reason for this is that at least 80% of the spatial volume between the inner and outer conductors favors expansion. If it is not possible to prevent evaporation of the insulation material and to prevent rupture of the outer conductor at all in the case of sealing, that is to say in the case of significant shrinkage, this conductor is constructed in multiple layers that produce a high-strength, high-tight seal. Finally, the protective sheath, together with the aluminum foil on the outer conductor, contributes to reducing the effect of heat on the insulation. Such outer aluminum foil reflects heat that would cause the protective sheath to burst and peel.

Regarding the insulating material of the inner and outer conductors, cellular polyethylene with a space factor of approximately 60% is preferably selected in order to achieve a small outer diameter while the damping constant remains unchanged. The longitudinally overlapping metal foils on the insulation provide further diameter reduction compared to cables that use only braiding as the outer conductor. The longitudinally overlapping metal foils exhibit a long seal against oxygen ingress and polymer emigration along with relatively dense wire spinning. The reason for this is that the expanded insulating material presses the foil against the dense braid.

When crosslinked materials are used as insulation, the flow of molten material is significantly reduced. In this case, the material is preferably crosslinked by high-energy radiation. The insulation burns only slowly or decomposes locally, ie it does not escape into the flame area.

Next, the invention will be explained by way of example with reference to the drawings.

The drawing shows a longitudinal section of a high frequency coaxial cable.

The high frequency cable consists of an inner conductor l, an insulating material 2, an outer conductor 8 and a protective sheath 4.

The insulating material 2 consists of a material having a suitable dielectric constant, preferably cellular polyethylene. Instead of a homogeneous cellular polyolefin, any other suitable configuration can also be selected.

The outer conductor 2 is a longitudinally applied foil 31. Preferably, the ends overlap and consist of aluminum coated with spinning 82. Although the spinning 82 is comprised of aluminum wire, such spinning could also be comprised of zinc coated copper wire. In order to achieve sufficiently high strength, the visual coverage area of the above spinning is 8.
It is necessary to set it to 0% or more. Preferably, the spinning 82 is wrapped in a foil 88, and the foil 88 is successively constructed as a composite foil consisting of two types of metal foils and a synthetic resin foil interposed therebetween. The thickness of the metal foil is 9 μm to 26 μm.
It is advantageous to choose a thickness of .mu.m and to provide between the foils a synthetic resin foil with a thickness of 10 .mu.m to 40 .mu.m. - the protective sheath 4 comprises two constituent sheaths 41 and 42;
It consists of a slitting cord 48 sandwiched between them.

The construction sheath 41 is a complete protective sheath that can be inserted into standard plug connectors without any modifications due to its normal wall thickness. The outer constructional sheath 42 can be easily removed by means of an intervening slitting cord 48 in areas where the cable must have minimum dimensions and where there is little danger from a technical point of view of contact with the flame. .

Construction of the protective sheath 4 The sheath 42 is a crosslinked or thermoplastic material with an oxygen index of >85%. A liquid blowing agent can be added to at least one material of the sheath forming the protective sheath, which acts against contact with the flame. When a liquid blowing agent is added to the constituent sheath 42, the flame blast preferably
It decomposes immediately within a temperature range of 200° C., creating bubbles in the molten sheath material, resulting in substantially increased thermal insulation.

The use of a composite metal foil instead of a single metal foil has the advantage of increasing the expandability. Copper foil can be used instead of aluminum foil as the outer conductor, but aluminum is more flexible and less expensive.

[Brief explanation of drawings]

The drawing is a longitudinal sectional view of an example cable of the present invention. 1... Inner conductor 2... Insulating material 8... Outer conductor 4... Protective sheath 81... Foil 8
2... Spinning 88 composite foil 41.42... Constituent sheath 48...
Slitting code special n M person N.B. Philips Fluiran pen 7 application

Claims (1)

[Scope of Claims] L A flame-resistant device comprising a cylindrical inner conductor, an insulating material surrounding the inner conductor, a flexible cylindrical outer conductor surrounding the insulating material, and a protective sheath surrounding the outer conductor. 1. In a high frequency coaxial cable, a. the insulating material is made of a halogen-free material, and the material fills less than 70% of the gap between the inner conductor and the outer conductor; b. the cylindrical outer conductor is in a multilayered form; An inner foil that is in contact with the insulating material and surrounds it over its entire periphery, and that extends parallel to the axis and overlaps both edges of the band, and an inner foil that surrounds the foil and surrounds it by 80% or more. consisting of a spinning metal wire having a visual coverage area of 0, an outer metal foil concentrically wrapping the spinning wire, the outer wrapping overlapping the edges of the band by at least 25% of each other; The protective sheath surrounding the outer conductor is 20°
A flame-resistant high-frequency coaxial cable, characterized in that it consists of a flame-resistant, halogen-free material having an oxygen index at C of at least 86%. & the following formula; (where d - diameter of the insulation material, - LOI - oxygen index of the protective sheath material at 20 ° C, % F - space factor of the insulation material between the inner and outer conductors W - the protective sheath 2. The flame-resistant high-frequency coaxial cable according to claim 1, characterized in that the wall thickness (W) of the protective sheath is in accordance with the wall thickness (W). & Flame-resistant high-frequency coaxial cable according to claim 1, in which the insulation material and/or protective sheath of the cable is made of a cross-linked synthetic resin. A flame-resistant high-frequency coaxial cable according to any one of claims 1 to 8, which is provided under the sheath. Flame-resistant high-frequency coaxial cable according to claim 1, characterized in that at least one of the metal foils is made of a synthetic resin-metal composite foil... Oa composite foil is 9 μm to 2
Claim No. 1, characterized in that it has at least two kinds of metal foils each having a thickness within the range of 6 μm, and a synthetic resin foil having a thickness within the range of 10 μm to 40 μm is provided between these metal foils. The flame-resistant high frequency coaxial cable described in item 6. 7. The flame-resistant high-frequency coaxial cable according to claim 6, wherein the wrapping metal foil for the outer conductor is made of aluminum or an aluminum alloy.