JPS634287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic sheath provided over a cable core, the sheath comprising two materials.

Generally, a plastic sheath provided on a cable core, also called a protective coating, has the role of protecting the internal cable core from various external factors.

External factors include things such as rainwater and chemicals that can make it impossible to obtain the desired characteristics of the cable if they enter the cable core, things that can deteriorate the plastic sheath such as sunlight, and things that can damage the plastic sheath such as mechanical shock. Items that may be physically destroyed,
Or bending or twisting during cable installation.
There are various mechanical forces such as tension and external pressure, and to protect the cable core from these various external factors, a plastic sheath of vinyl chloride, polyethylene, etc. with a thickness of 1 mm to 4 mm is usually provided.

When these factors are analyzed and considered, they can be divided into dynamic and static factors.For dynamic factors, especially mechanical factors, the tensile strength, rigidity, hardness of the plastic sheath, etc. The strength of will counter it. In order to ensure the strength of this material, it is important to select the material and design the thickness, and the thickness of conventional plastic sheaths is determined from these points of view. Also, there are some things such as impact force that cannot be covered simply by thickness.

On the other hand, it also protects the cable core from static factors such as chemicals, sunlight, and outside air, but the only important factor for these factors is the selection of the material of the plastic sheath, and the thickness It is sufficient to have the minimum necessary thickness, and the thickness of conventional plastic sheaths is too thick from this point of view.

In order to protect the cable core from these various external factors, plastic sheaths are designed for material selection and thickness, but in order to satisfy all requirements with one plastic sheath, certain specific Even if it is sufficient for one request, it may far exceed the necessary limit for other requests.

Let's take a look at this example.

Carbon black is mixed into materials such as vinyl chloride and polyethylene to prevent sunlight from passing through, but if this is the only purpose, the thickness of the plastic sheath will be lower than the current thickness. Approximately one-tenth of the size or less is sufficient.

In addition, anti-aging agents are added to the plastic sheath material to prevent aging, but the same amount is applied to the areas that are exposed to outside air such as oxygen and the areas that are not exposed to outside air such as the side that contacts the internal cable core. Although it is mixed, there is little need for it inside.

In particular, the major factors that determine the thickness of current plastic sheaths are mechanical factors such as external pressure, twisting, bending, and vibration. Considering these factors alone, the materials currently used for plastic sheaths are of extremely high quality. It can be said that even something of low quality is sufficient.

A possible method of manufacturing a plastic sheath at a lower cost than before while fully satisfying the requirements arising from the external factors mentioned above is to create a composite sheath using two or three types of materials. For example, as shown in Figure 1, an inner sheath 2 made of a material on top of a cable core 1 and an outer sheath 3 made of a different material are provided, and the inner layer is made of a low-grade material and the outer layer is made of a high-grade material. However, in this case, since there is a clear intervening surface 4 between the inner and outer layers, the mechanical strength is particularly poor compared to a single-layer plastic sheath with a thickness corresponding to the total thickness of the inner and outer layers. It is weak against bending, impact, twisting, etc., and therefore has the disadvantage that mechanical strength equivalent to that of a single layer cannot be secured unless the total thickness of the entire structure is thicker than that of a single layer.

The present invention solves the shortcomings of the conventional two-layer plastic sheath, and provides a plastic sheath structure that is inexpensive and highly reliable while providing sufficient protection against external factors. The plastic sheath of the present invention is characterized in that it consists of an inner layer material constituting the inner layer and an outer layer material constituting the outer layer, and the ratio of the inner and outer layer materials changes continuously at the interface between the inner layer and the outer layer. It is.

FIG. 2 shows an embodiment of the present invention, in which an inner layer 2 made of an inner layer material and an outer layer 3 made of an outer layer material are provided on the cable core 1, and the intervening surfaces 5 of the inner and outer layers are arranged as they go from the inside to the outside. The proportion of the inner layer material is continuously smaller than the proportion of the outer layer material, and the proportion of the inner layer material is 100% in the section 5-1 and 0% in the section 5-2. In this example, the outer diameter of the cable core 1 is 20 mm, and the thickness of the inner layer 2 is 0.5 mm.
~1.5 mm, the thickness of the intervening surface 5 is approximately 0.5 mm, and the thickness of the outer layer 3 is 0.5 to 1.5 mm.

Furthermore, unlike the conventional plastic sheath cable shown in Fig. 1, the material of the plastic sheathed cable of the present invention changes continuously at the interface 5, and there is no discontinuity in the material at the portions 5-1 and 5-2. Therefore, buckling of the cable is less likely to occur when the cable is bent or twisted. Therefore, it has the advantage that it can be bent with a small radius of curvature and can be installed in places where twisting operations are required. Furthermore, since there is no sudden change in the material at the intervening surface, the intervening surface portion will not peel off due to repeated bending or the like.

Examples of inner layer materials and outer layer materials are listed below.

Vinyl chloride or polyethylene that does not contain carbon black is used as the inner layer material, vinyl chloride or polyethylene that contains carbon black is used as the outer layer material, or a material that contains less anti-aging agent than before is used as the inner layer material. It is also possible to use the same material as before as the outer layer material, or use a low-grade material with low requirements for carbon dispersion, amount of foreign matter, etc. as the inner layer material and use the same material as before as the outer layer material. However, in a cable with a colored sheath, the inner layer material is colorless and only the outer layer is colored.

It is also possible to make the inner layer a foam material to increase the cushioning effect against impact.

Next, an example of how to manufacture such a plastic sheathed cable will be described.

One method is the 2
Using a screw-type extruder with heavy grooves, the material for the inner layer is supplied from the hopper 11 and the material for the outer layer is supplied from the hopper 11', so that the material for the inner layer is placed in one groove 12 of the screw and the material for the outer layer is placed in the other. There is a method in which the two materials are guided into one groove 12' of the cable core 14, and while being kneaded, the two materials are brought together in the die section 13 and extruded onto the cable core 14.

Since the plastic sheathed cable of the present invention as described above has two layers, it is easy to select the material, and it is possible to select a material that is cheaper than a single-layered cable.
In addition, since the interface changes continuously from the inner layer material to the outer layer material, and there is no clear interface, even if mechanical force is applied, it will separate at that part and the overall resistance between the inner and outer layers will deteriorate. Therefore, the scope of application is very wide. In addition, in the past, a cushion layer was separately provided under the plastic sheath for what was required, but if a foam layer is combined as an inner layer, there is an advantage that the need for such a special cushion layer is reduced.

[Brief explanation of the drawing]

Figure 1 shows a conventional double plastic sheath;
The figure shows an embodiment of the plastic sheath of the present invention, and FIG. 3 shows a method of manufacturing the plastic sheath of the present invention, in which 1 is a cable core, 2 is an inner layer, 3 is an outer layer, and 5 is an intervening surface.

Claims (1)

[Claims] 1. In a cable in which a plastic sheath is placed on a cable core, the plastic sheath consists of an inner layer material constituting the inner layer and an outer layer material separate from it, and the ratio of the inner and outer layer materials is the same at the interface between the inner layer and the outer layer. A plastic sheathed cable characterized by a continuous change in .