JPH0533481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improved manufacturing method capable of making the degree of foaming of a highly foamed insulated wire uniform in the longitudinal direction.

[Conventional technology and problems] The performance of information-related equipment, with computers at its peak, is increasing rapidly, and performance requirements such as higher speeds, higher density packaging, and noise reduction are becoming increasingly severe. . Moreover, the electric wires and cables used in these applications are now required to have a high level of performance.

Highly foamed insulated wire was developed to meet the above situation by reducing the inductivity of the insulator and solving transmission problems, especially at high frequencies. In order to achieve this, it is necessary to increase the degree of foaming to 70-80%, and maintain a uniform degree of foaming over the entire length so that there is no variation in performance in the longitudinal direction.As the above-mentioned required characteristics become more sophisticated, Controlling this foaming is becoming a major issue.

Conventionally, the general method for manufacturing foam insulated wire is
A pyrolytic chemical blowing agent is kneaded into the insulating material, a volatile foaming liquid is impregnated into the insulation material, or a gas for forming bubbles is directly injected into the insulation material. The material was extruded and coated inside, and foaming was caused by the effect of reduced pressure at that time. However, with such a method, a large degree of foaming cannot be expected, and the degree of foaming tends to vary, making it difficult to maintain a uniform degree of foaming over the entire length.

Therefore, foaming does not depend on the above-mentioned pressure difference between the inside of the extruder and the atmosphere, and instead a pyrolyzable foaming agent is used as the foaming agent, and the extrusion temperature during extrusion coating is kept below the decomposition temperature of the foaming agent. A method of foaming by coating the foam in a heating furnace and then passing it through a heating furnace has become available, which has made it possible to significantly improve the degree of foaming and make it more uniform.

The figure is an explanatory diagram showing how a highly foamed insulated wire is manufactured by such a method, and 1 is a core before foaming, and 10 is a core after foaming. In the figure, an unfoamed core 1 coated with an unfoamed insulator by extrusion is passed through a heating furnace 3 and foamed to obtain a foamed core 10, which is continuously taken off by a take-off machine 5.

At this time, as a means to eliminate variations in the degree of foaming, conventional methods have been used to keep the temperature of the heating furnace and the take-up speed of the take-off machine 5 constant, and to supply unfoamed cores 1 with as little variation in outer diameter as possible. Ta. but,
It is very difficult to maintain the same extrusion conditions for each lot, and it is the fate of this type of manufacturing method that variations occur even in the same lot, resulting in changes in the outer diameter. It was nearly impossible to control the variation in foaming degree only by controlling the outer diameter.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to achieve uniform foaming over the entire length even if the diameter of the unfoamed core before heating varies. The purpose of the present invention is to provide a method for producing highly foamed insulated wires.

[Summary of the Invention] That is, the gist of the present invention is that in a heating furnace passage method foaming method, measuring machines are arranged to measure the outer diameter of an unfoamed core and the outer diameter of a foamed core, and the outer diameter of the foamed core is measured. The measurement results are fed back to the take-up speed of the take-up machine, and the take-up speed can be controlled by changing the core diameter. This makes it possible to control the foaming degree and always maintain the desired uniform foaming degree. This makes it possible to stably manufacture foam insulated wires.

[Examples] The present invention will be described below based on Examples.

If you want to pass an unfoamed core through a heating furnace at a constant temperature and a constant furnace length to obtain the desired degree of foaming, it is necessary to pass the core with a large outer diameter slowly and the core with a small outer diameter quickly. It is logical that there is.

Therefore, if the outer diameter can be made uniform over the entire length,
By passing at the same speed, a product with the same foaming degree over the entire length can be obtained. This is a foaming degree control method based on the above-mentioned conventional knowledge. However, with this method, if the outer diameter of the unfoamed core fluctuates for some reason, the degree of foaming will change accordingly, making it difficult to control the outer diameter as described above. Considering this, it must be said that the control method always includes unstable elements, and as the demands on wire characteristics become more and more severe due to the development of today's equipment, this becomes a serious problem.

Now, if the cross-sectional area of the insulator before foaming is A, the diameter of the conductor is d, and the outer diameter of the unfoamed core at that time is _D1 , then A = π/4 (D ₁ ² - ^{d 2} )... (1) becomes.

Next, if the insulator with the above cross-sectional area A is foamed and the outer diameter of the core after foaming is _D2 , and the degree of foaming at that time is x%, D can be calculated by a simple method. ₂ can be expressed by equation (2).

Here, since the diameter d of the conductor can be considered constant, it can be seen from equation (2) that the desired degree of foaming x% is determined by D ₁ and D ₂ .

In the present invention, as shown in the figure, an outer diameter measuring device 2 is installed before passing through the heating furnace 3, and the outer diameter _D1 of the unfoamed core 1 is measured. Next, an outer diameter measuring device 4 is used to measure the outer diameter D ₂ of the foamed core 10 at a position on the movement path of the core that is the exact length L from the outer diameter measuring device 2 and has passed through the heating furnace 3. Set it up.

If installed in this way and the separation length L of both measuring instruments 2 and 4 on the core moving path is determined in advance, the outer diameter D ₁ and
Since D ₂ is automatically measured and it is immediately known whether the desired degree of foaming x in equation (2) above has been obtained, if the respective outer diameters that directly vary the degree of foaming If fluctuations occur in D ₁ and D ₂ , this can be fed back and the take-up speed of the take-up machine 5 can be controlled accordingly, making it possible to always maintain a constant degree of foaming and ensure uniform foaming over the entire length. Highly foamed insulated wires having a degree of foaming are available.

As the insulator for the above-mentioned highly foamed insulated wire, polyolefin, especially polyethylene, which has a low dielectric constant and is easy to mix with foaming agents and extrude, is widely used, but it is difficult to crosslink because of its strength and heat resistance. There are many examples of this. Although there are various crosslinking methods, it is preferable to use a method of irradiating ionizing radiation such as an electron beam for this kind of electric wire, which is generally thin in size. That is, after extruding an unfoamed core, it is passed through an ionizing radiation irradiation device to be crosslinked, and then passed through a heating furnace to be foamed, thereby making it possible to easily obtain a highly foamed crosslinked insulated wire in one step. It can be done.

In addition, as a method for continuously measuring the degree of foaming, a method of continuously measuring capacitance can also be considered, but 1.
In the case of this type of electric wire, which is a long piece with a length of 10 km, even if the wire is grounded, the distance from the measuring device changes, making it impossible to obtain accurate values. Therefore, the method according to the present invention can be said to be a truly excellent method.

[Effects of the Invention] As described above, according to the method according to the present invention, a highly uniform foaming product with a beautiful appearance and uniform foaming characteristics, such as a fluctuation in foaming degree of 2% or less and a capacitance of ±1.5 pF/m or less, can be obtained. This makes it possible to obtain foam insulated wires, and its industrial value is extremely large.

[Brief explanation of drawings]

The figure is an explanatory diagram showing the implementation status of the manufacturing method according to the present invention. 1... Unfoamed core, 2, 4... Core outer diameter measuring device, 3... Heating furnace, 5... Taking machine, 10... Foamed core.

Claims (1)

[Scope of Claims] 1. Extrusion coating of a foamable composition comprising a thermoplastic resin and a pyrolyzable blowing agent at a temperature lower than the decomposition temperature of the blowing agent, and passing the coated wire through a heating furnace. In the method for manufacturing a foamed insulated wire that is foamed by foaming, an outer diameter measuring machine capable of measuring the outer diameter of the core before and after foaming is placed before and after passing through the heating furnace, respectively, and the outer diameter measurement results are fed back. A method for producing highly foamed insulated wire that controls the speed of passage through a heating furnace and uniformizes the degree of foaming. 2. The manufacturing method according to claim 1, wherein the foamable composition is crosslinked by irradiation with ionizing radiation after extrusion coating and before passing through a heating furnace. 3. The manufacturing method according to claim 1 or 2, wherein the thermoplastic resin is polyolefin.