JPH01296512A - Manufacture of electromagnetic wave shielding heat-contracting tube - Google Patents

Abstract

PURPOSE:To reduce breakage of conductive fibers and improve their dispersion by melting speedily and steadily a converging agent for converting conductive fibers and a covering resin during heating phase in molding process of a tube. CONSTITUTION:A conductive fiber bundle 3 is formed by converging long conductive fibers 1 with a converging agent 2 that utilizes a thermoplastic resin having a softening temperature lower than that of a base resin used as the base of a conductive shield layer. Then, after applying coating resin 4 to the conductive fiber bundle 3 with a thermoplastic resin having a softening temperature higher than that of converging agent 2 but lower than that of the base resin, the conductive fiber bundle 3 is cut into pieces of a given length to form conductive resin pellets 5. Then, the pellets 5 and the base resin are mixed together and heated and kneaded in an extrusion mold to form a melted conductive resin, and the resin is extruded through an extrusion outlet so as to be shaped in a tube.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to the manufacture of heat-shrinkable tubes for electromagnetic shielding, which cover electric wires such as cables to protect internal conductors from external harmful effects, mainly electromagnetic waves. Regarding the method.

(Prior art) As described in Japanese Patent Application Laid-open No. 63-2399, a conventional method for manufacturing a heat-shrinkable tube for electromagnetic shielding involves inserting a conductive resin extrusion port and an insulating resin extrusion concentrically from the inside. Using an extrusion molding machine with an outlet, a conductive resin made of thermoplastic resin mixed with conductive powder and an insulating resin made only of thermoplastic resin are simultaneously extruded to form a conductive shield concentrically. A method of molding a heat-shrinkable tube for electromagnetic shielding having a resin layer and an insulating sheath resin layer is known.

(Problems to be Solved by the Invention) However, in such conventional methods, since conductive powder is used as the conductive material, it is difficult to ensure the shielding effect of the conductive shield resin layer. , the conductive powder must be incorporated in a high proportion of approximately 20 wt:% of the total conductive resin. That is, the heat shrinkable tube manufactured by this conventional method has the following problems.

■It is heavy due to its large specific gravity.

■Because it is rigid and hard, it requires a long time to coat cables etc. with heat shrinkage.

■Due to the lack of flexibility, handling after covering cables, etc. is also difficult.

■ Varnish l- is expensive.

The present invention focuses on the above-mentioned problems and aims to develop a manufacturing method for manufacturing a heat-shrinkable tube for electromagnetic shielding that has an excellent shielding effect with a small amount of conductive material.

The purpose of the present invention is to solve this problem by the following means using conductive fibers as a conductive material, and to provide a manufacturing method for manufacturing a heat-shrinkable tube for electromagnetic shielding that is lightweight, flexible, and inexpensive. .

(Means for Solving the Problems) In order to solve the above problems and achieve the above objects, in the method for manufacturing a heat shrinkable tube for electromagnetic shielding of the present invention, a hollow cylindrical tube made of a heat shrinkable resin is manufactured. On the inside, a conductive shielding resin layer is formed using a conductive resin in which conductive fibers are mixed into thermoplastic resin, and on the outside, an insulating sheath resin layer is formed using an insulating resin consisting only of thermoplastic resin. In the manufacturing method of the heat-shrinkable tube for electromagnetic shielding, long conductive fibers are formed using a sizing agent using a thermoplastic resin whose softening temperature is lower than that of the base resin that forms the base of the conductive shielding resin layer. a long fiber convergence step of converging to form a conductive fiber bundle;
After coating the conductive fiber bundle with a thermoplastic resin whose softening temperature is higher than the softening temperature of the sizing agent and lower than the softening temperature of the base resin, the conductive fiber bundle is cut into a predetermined length. A resin pellet forming step in which the conductive resin pellets are cut to form conductive resin pellets, and the conductive resin pellets and base resin are mixed, heated and kneaded in an extruder to form a conductive resin in a molten state, and the conductive resin is The method is characterized by comprising a tube forming step of extruding the plastic resin from an extrusion port and forming it into a tube shape.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

First, the structure of the heat-shrinkable tube to be manufactured in this example will be explained with reference to FIG. 4.

This heat-shrinkable tube T is a cylindrical tube made of heat-shrinkable resin, and has a two-layer structure including a conductive shield resin layer 100 and an insulating sheath resin layer 200.

The conductive shield resin layer 100 is made of a conductive resin in which conductive fibers 1 are mixed into a thermoplastic resin, and is formed inside the tube.

The insulating sheath resin layer 200 is made of an insulating resin consisting only of thermoplastic resin, and is formed on the outside of the tube.

A base resin that is the base of the thermoplastic resin in the conductive resin that forms the conductive shield resin layer 100 and a conductive resin (thermoplastic resin) that forms the insulating sheath resin layer 200.
Both use a medium density ethylene vinyl acetate copolymer (flame retardant pigment, lubricant, etc.) with a softening temperature of 125°C.

As the base resin and the insulating resin, other than ethylene vinyl acetate copolymer, thermoplastic resins such as ethylene-ethyl acrylate copolymer, polyethylene, polyvinyl chloride, crosslinked polyethylene, ethylene propylene rubber, and butyl rubber can be used. Furthermore, the base resin and the insulating resin do not have to be the same resin, and different resins may be used as long as they are a mutually compatible combination.

Next, a method for manufacturing this heat-shrinkable tube T will be explained.

This manufacturing method is divided into a thick (fiber bundle step), a resin pellet forming step, and a tube forming step.

First, in the fiber bundling process, as shown in FIG.
C
In this step, the fibers are dried, cooled, and bundled to produce a long conductive fiber bundle 3.

Specifically, 100 parts by weight of edylene-vinyl acetate copolymer (softening temperature 90°C) was dissolved in 900 parts by weight of trichlorethylene to form liquid sizing agent 2, and this sizing agent 2 was heated to 50'C. Soak in 8μ
5t JS304 series stainless steel fiber of 2850m is bundled.

In addition, as the conductive fiber 1, 5US304 styrene-free steel fiber (81tm ~ 15 LLm, 700 ~ 5
000 pieces), nickel-plated glass fiber (lOum-2
3um, 500 to 4000 pieces, N1GF), nickel-plated carbon fiber (Ni-CF).

8um-1.5um, 700 to 5000 pieces), etc. can be used.

As the sizing agent 2, thermoplastic resins (with a softening temperature of 60° C. to 100° C.) such as ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyethylene, and polyvinyl chloride, l.luene, xylene, trichloroethylene, 10W for solvents such as cycloethylene
A solution of t% to 30wt% can be used.

Here, when binding the conductive fibers 1 with the binding agent 2,
The amount of resin impregnated into the conductive fiber bundle 3 is adjusted to be 10 W% of the conductive fiber bundle 3, for example. Note that the amount of resin impregnated into the conductive fiber bundle 3 does not have to be strictly 10 wt%, but it is 3 wt% to 30 wt% of the conductive fiber bundle 3.
(Most preferably 7 wt% to 12 wt%). By the way, if it is less than 3wt%, the tow of the conductive fiber bundle 3 will fall apart or become fluffy and the fibers will break, and if it is more than 20wt%, the viscosity of the resin liquid will increase, making the work difficult. It becomes difficult.

In the next step of forming resin pellets, as shown in FIG. This is the step of manufacturing a conductive resin pellet 5 as shown in FIG. 2 by applying the coating resin 4) with a pressing roll C and cutting it into an appropriate length using a cutting machine.

Note that the thermoplastic resin used for the sizing agent 2 and the thermoplastic resin used for the coating resin 4 are not necessarily the same resin, but as long as the condition that the softening temperatures are equal is met and they are compatible with each other. , different types of resins may be used.

The amount of coating resin 4 is based on the entire conductive resin pellet 5.
The amount of conductive fiber 1 excluding sizing agent 2 is 10 wt% to 4
The content is adjusted to 0 wt% (most preferably 20 wt% to 30 wt%). By the way, conductive fiber 1 is 10wt.
% or less, the amount of coating resin 4 increases compared to the conductive fibers, so the outer diameter of the conductive resin pellet 5 increases, making molding difficult.
Since the blending amount of the coating resin 4 is small, dispersion is poor when it is heated and melted in the subsequent tube forming step, resulting in variations in conductivity as a whole.

The length of each conductive resin pellet 5 is 1 mm to 10 m.
m (most preferably 4 mm to 6 mm).

The next tube forming step is a step of forming a tube by coextrusion using an extrusion molding machine E, as shown in FIG.

The head of the extrusion molding machine E used here is provided with a nipple 11, an inner tie 12, and an outer tie I3 concentrically, and an air flow path 14 is provided at the center of the nipple 11, and the nipple 11 and the inner tie are arranged concentrically. A first resin flow path 15 is formed between the inner die 12 and the outer die 13, and a second resin flow path 16 is formed between the inner die 12 and the outer die 13. Also, on the outside of the head,
A first hopper 17 that supplies resin to the first resin flow path 15
and a second hopper 18 that supplies resin to the second resin flow path 16.
is established.

Therefore, when molding a tube, the cylinder temperature is set to 30°C to 70°C higher than the softening temperature (125°C) of the base resin pellet 1, and the first resin flow path is 15, a mixture of conductive resin pellets t-5 and base resin pellets 1-0, which are pelletized base resin, is supplied from the second hopper 18 to the second hopper 15.
Insulating resin pellets 1 to 7, which are pelletized insulating resin, are supplied to the resin flow path 16.

Here, conductive resin pellet 5 and base resin pellet 6
Here, 100 parts by weight of conductive resin pellets 5 and 400 parts by weight of base resin pellets 6 are mixed so that the conductive fibers 1 account for 5 wt% of the entire conductive resin. Further, the conductive resin pellets 1 to 5 are mixed almost evenly into the base resin pellet 6.

In addition, conductive resin pellets 1 to 5 and base resin pellets]・6
The mixture of conductive fiber l is 4 to 10w of the whole conductive resin.
It may be adjusted to t%, and does not need to be strictly 5wt%. Incidentally, when the conductive fiber 1 is 4 wt% or less, the volume resistivity value ρ (shielding effect dβ) varies, and when it is 10 wt% or more, the volume resistivity value ρ (shielding effect dβ) does not change much.

The supplied conductive resin pellets 5 and base resin pellets 6 are heated in the first resin flow path 16 and kneaded by a screw (not shown) to become a molten conductive resin 19. is extruded from the first extruder 171 at the tip of the first resin channel 17. At the same time, the insulating resin pellets 7 are also heated and kneaded to become a molten insulating resin 20, and this insulating resin 20 is extruded from the second extrusion port 181 at the tip of the second resin channel 18.

The extruded conductive resin 19 and insulating resin 20 are integrally molded into a cylindrical tube shape by the air blown out from the air flow path 14, and the conductive resin 19 forms a conductive shield resin layer 100, and also forms an insulating resin layer 100. The resin 20 forms an insulating sheath resin layer 200.

The extrusion conditions are such that the conductive shield resin layer 100 is at 220°.
The temperature of the C1 insulating sheath resin layer 200 is 200°C.

Since the softening temperature of the sizing agent 2 and coating resin 4 of the conductive resin pellet 5 is 10 to 70'C lower than that of the base resin pellet 6, the cylinder temperature is lower than that of the base resin pellet 6 as described above.
When the softening temperature is 30 DEG C. to 70 DEG C. or higher, the sizing agent 2 and coating resin 4 begin to melt faster than the base resin bellets 1-6 melt. When the base resin pellets 1-0 are melted, the sizing agent 2 and the coating resin 4 are surely melted, and the conductive fiber bundle 3 is in a state where it can be easily unbundled by the shearing force of the screw. That is, while being kneaded, the conductive fiber bundle 3 becomes individual short conductive fibers 1 and is dispersed in the molten resin.

In this way, the conductive fibers 1 are first dispersed in a bundle when the conductive resin pellets 5 and the base resin pellets 6 are mixed, and later dispersed as individual fibers when mixed. Therefore, it is evenly dispersed and a sufficient shielding effect can be obtained with a small amount.

A tube is formed as described above, and the tube is later enlarged in diameter and shaped through a drying process, a secondary cooling process, a heating stretching process, and a secondary cooling process. The details are as described in Japanese Unexamined Patent Publication No. 63-2399, and will therefore be omitted.

However, the electron beam irradiation dose was 20 M r a d, and the stretching was]
The outer diameter is doubled at 50°C, and the cooling condition is to maintain the strain while keeping the tension constant and allowing it to cool.

The performance of the heat-shrinkable tube T manufactured by the manufacturing method of the present example described above will be described below.

[Volume resistance] Initially 3 x 10-' Ωcm After heat cycle, 2 x 10° Ωcm (Heat cycle: -1 hour at 40°C, 5 minutes at room temperature, 1 hour at 90°C, 5 minutes at room temperature for 6 ) [Tube shrinkage time] 1 to 2 minutes at 200'C, i.e., the amount of conductive material blended is small (about 4 minutes compared to the conventional method)
Despite this, a sufficient shielding effect can be obtained, and it has been revealed that the time required for covering cables etc. due to heat shrinkage is short (approximately one-fifth of the conventional method). Furthermore, since the amount of conductive material blended is small, it is lightweight, has good flexibility, and is easy to handle. It is also possible to reduce costs.

Next, a comparative experiment conducted to clarify the effects of this example and its results will be described.

The conductive fiber bundle 3 that is not coated with resin is cut into 5 mm pieces and mixed with the same resin as the coating resin 4 to form conductive fibers 1.
When the mixture was adjusted so that it was 5 wt% of the total and extruded under the same conditions as in the example, a heat shrinkable tube was produced as a prototype.
The conductive fiber 1 has poor dispersion and the volume resistance is 5X106Ωc.
m, and there was no shielding effect.

]5 Hereinafter, embodiments of the present invention have been described in detail with reference to the drawings, but
The specific configuration is not limited to this embodiment, and any design changes or the like that do not depart from the gist of the present invention are included in the present invention.

For example, in the example, the sizing agent and coating resin of the conductive resin pellet were made of thermoplastic resin with the same softening temperature.
As the coating resin, a resin having a softening temperature higher than that of the sizing agent may be used as long as it does not satisfy the condition that the softening temperature is lower than the softening temperature of the base resin.

Furthermore, if a thermoplastic resin whose softening temperature is lower than that of the sizing agent is selected, the coating resin and the base resin can be made of the same resin or different resins having the same softening temperature.

Further, in the examples, the conductive shield resin layer and the insulating sheath resin layer were simultaneously molded by coextrusion, but they may be molded in separate steps starting from the conductive shield resin layer.

(Effects of the Invention) As explained above, in the method for manufacturing a heat-shrinkable tube for electromagnetic shielding of the present invention, the binding agent and coating resin that bundles conductive fibers are quickly released during heating in the tube forming process. Moreover, by reliably melting the conductive fibers, the conductive fibers are less likely to be cut and have good dispersibility. That is, it is possible to manufacture a heat-shrinkable tube for electromagnetic shielding with excellent shielding effect by reducing the amount of conductive fibers.

Furthermore, as mentioned above, by reducing the amount of conductive fiber in the mix, ■ it is light due to its low specific gravity, and ■ it is highly flexible, which reduces the time needed to coat cables etc. using their heat shrink properties. It is possible to produce heat-shrinkable tubes for electromagnetic shielding that are short, (1) easy to handle after coating cables, etc., and (2) inexpensive.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a fiber convergence step and a resin pellet forming step in the method for manufacturing a heat-shrinkable tube for electromagnetic shielding according to the present invention, FIG. 2 is a perspective view showing a conductive resin pellet, and FIG. 3 is a diagram showing the present invention. FIG. 4 is a partially cutaway perspective view showing a heat-shrinkable tube for electromagnetic shielding manufactured by the manufacturing method of the present invention. T... Heat shrink tube 100... Conductive shield resin layer 200... Insulating sheath resin layer 1... Conductive fiber 2... Bundling agent 3... Conductive fiber bundle 4... Coating resin 5... Conductive resin pellet E... Extrusion molding machine 171... First extrusion port (extrusion port) 19... Conductive resin 20... Insulating resin

Claims (1)

[Claims] 1) A hollow cylindrical tube made of heat-shrinkable resin, with a conductive shielding resin layer formed of a conductive resin in which conductive fibers are mixed into thermoplastic resin on the inside. In the manufacturing method of a heat shrink tube for electromagnetic wave shielding, in which an insulating sheath resin layer made of an insulating resin made of only thermoplastic resin is formed on the outside, the softening temperature of the base resin is the base of the conductive shield resin layer. a long fiber bundling step of bundling long conductive fibers to form a conductive fiber bundle with a sizing agent using a thermoplastic resin whose softening temperature is lower than the softening temperature of the sizing agent; , forming a resin pellet by coating the conductive fiber bundle with a thermoplastic resin having a softening temperature below the softening temperature of the base resin, and then cutting the conductive fiber bundle into a predetermined length to form a conductive resin pellet. A tube in which the conductive resin pellets and base resin are mixed, heated and kneaded in an extruder to form a molten conductive resin, and the conductive resin is extruded from an extrusion port to form a tube. A method for manufacturing a heat-shrinkable tube for electromagnetic shielding, comprising a molding process.