JPS6054110A - Method of replacing color of foamable insulated wire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field] The present invention provides a foam insulation chamber +1i! The present invention relates to a method for changing the color of foamed insulators during the manufacture of foamed insulators.

[Prior art]

Foamed insulated wires used as core wires of communication cables are manufactured by passing a copper wire through the crosshead of an extruder and extruding a foamed insulating material thereon. To make it easier to identify individual foam-insulated wires when they are made into cables,
When manufacturing foam insulated wires, it is necessary to extrude and coat the same size foam insulators in different colors.
Colors are often changed. This color change is performed by switching the resin material supplied to the extruder from one color to another, but since defective products are produced when performing this color change, it is necessary to minimize the number of defective products. It is also important to minimize the time required for color changes.

To change the color in the manufacturing process of foam insulated wire, generally, the running of the wire is stopped, the over 7'0-cock in the crosshead of the extrusion wall is opened, and the resin material of the previous color remaining in the extruder is extracted. The procedure is to restart operation once the new colored resin material has been used.

By the way, there are two methods for manufacturing foam insulated wires: a chemical foaming method in which a thermally decomposed chemical foaming agent is mixed into the resin material supplied to an extruder, and the mixture is heated and foamed; There is a gas injection foaming method in which gas is injected into the material and the gas is used as a foaming agent. In the chemical foaming method, the extrusion conditions (e.g. temperature, etc.) to obtain a constant foaming rate vary depending on the type of colorant (pigment) used, so it is necessary to change the extrusion conditions each time the color is changed. There are five problems that require a lot of time, for example 30 to 40 minutes. In contrast, the Vegas injection foaming method has the advantage that since the foaming agent is originally a gas, there is no need to change the extrusion conditions even if the type of colorant changes. However, even in the case of the gas injection foaming method, the foaming rate changes when the line speed is changed or the overflow cock is opened/closed, so it takes time to stabilize the foaming rate after restarting operation. The problem is that there are few (or no) good products.

[Purpose of the invention]

An object of the present invention is to provide a method that takes advantage of the above-mentioned gas injection foaming method and can change colors in a short time during the manufacturing process of foamed insulated wires.

[Structure of the invention]

In order to achieve the above object, the present invention provides a method for changing the color of a foamed insulator extruded when manufacturing a foamed insulated wire using a gas injection foaming method, in which the wire speed is changed from the operating wire speed to the color change wire speed. It is characterized by adjusting the opening of the overflow cock so that the resin pressure in the crosshead remains constant from the start of the color change or from the middle of the color change to the end of the color change. It is something to do.

Normally, foam insulated wires are manufactured at a line speed of about 1000 to 30001 η/tray, which is the so-called operating line speed, but when changing colors, this is increased to, for example, 300 m
Reduce the color change line speed to around 7 minutes. Then, at the end of the color change, the original operating line speed is restored. Also, when changing colors, the overflow cock on the crosshead must be opened, and the resin material of the previous color must be discharged. In this way, changing the linear speed or opening and closing the overflow cock causes the resin pressure in the crosshead to fluctuate. Generally, when the linear speed is reduced, the resin pressure in the crosshead increases, and when the overflow cock is opened, the resin pressure decreases. In the gas injection foaming method, such fluctuations in the resin pressure within the loss head lead to fluctuations in the foaming rate. That is, in general, extrusion JuQ is expressed by the following formula.

Q=αN-βΔP・・・・・・・・・(1N Niscrew rotation speed ΔP: Differential pressure, resin pressure in the crosshead and at a certain position in the axial direction of the extruder (e.g. gas injection part) Differences from resin pressure α and β: When constant N = constant, the fact that the resin pressure in the crosshead fluctuates means that ΔP fluctuates, and therefore the extrusion amount Q fluctuates.On the other hand, when the gas In the case of the injection foaming method, the amount of gas injected (per unit time) is constant regardless of changes in resin pressure inside the extruder, so if the amount of extrusion changes, the ratio of resin to gas changes and the foaming rate changes. I will do it.

For this reason, the present invention adjusts the opening degree of the oval flow cock so that the resin pressure in the crosshead becomes the same constant pressure as in the operating state during the color change, and immediately returns to the operating state after the color change is completed. This is what I did.

〔Example〕

FIG. 1 shows an example of the apparatus used to carry out the method of the invention. Reference numeral 1 is a screw set for extrusion, 3 is a hopper for supplying a resin material mixed with a colorant, 5 is a gas inlet, 1 is a valve for setting the gas flow rate, and 9 is a crosshead. The wire runs within the crosshead 9 in a direction perpendicular to the plane of the paper. 11 is an overflow cock for removing resin attached to the crosshead 9; 13 is a pulse motor that adjusts the opening of the overflow cock 11; 15 is a pressure detector that detects the resin pressure inside the crosshead 9; 17 is a color This is a controller that drives the pulse motor according to the pressure detected at the time of replacement.

Next, the order in which colors are changed in this device will be explained with reference to the time chart shown in FIG. The overflow cock 11 is fully opened at t1 at the start of color change.

At the same time or prior to this, the material supplied to the hopper 3 is also switched to another color. Overflow cock 11
(as the resin pressure inside the crosshead 9 decreases,
After a short time, the linear velocity is decreased from time t2. Up until now, it has been the operating line speed.

The line speed is gradually reduced, and when the line speed reaches a predetermined color change speed, the line speed is kept constant from time t4 to time t15. The color change line speed is, for example, about 1/10 of the operating line speed. The time from t4 to ts'i' is determined by taking into consideration the time until all of the resin in the extruder 1 and crosshead 9 is replaced with a new color.

When the resin replacement is completed, the linear speed is increased from the time point 15, and when the operating linear speed is reached, the operating linear speed is kept constant from that time point t6 onwards. On the other hand, the resin pressure in the crosshead 9 decreases due to the opening of the overflow cock 11, but is controlled to maintain the same constant pressure as in the operating state from an appropriate time t3 until the color change end time t6. Ru. In this control, the pressure detector 15 detects the resin pressure in the crosshead 9, and when the detected value is higher than the set value in the controller 1γ, the pulse motor 13 is switched to the overflow cock 11.
This is done by driving the pulse motor 13 in the opposite direction when it is low. Therefore, the overflow cock 11 has a fine opening degree from t3 to t6.
Change.

If the resin pressure in the crosshead 9 is kept constant at °C while the color is being changed in this way, the extrusion amount will be kept approximately constant during that time, and the foaming rate will also be approximately constant. Therefore, a product with a stable foaming rate can be obtained immediately after returning to the operating line speed.

In the above embodiment, the pressure in the crosshead was controlled from t3 during the color change, but it would still take one step to control the pressure from 11 at the start of the color change.

Furthermore, in the above embodiment, the case where gas is injected from the middle of a single screw extruder is explained, but the present invention is equally applicable to the case where two extruders are connected and gas is injected from the connection part. be.

〔Effect of the invention〕

As explained above, according to the present invention, since the resin pressure in the crosshead is controlled to be kept constant from the time when the linear speed is reduced and the color change is performed, the operating line is changed from the color change linear speed to the operating line. By the time the foaming rate is returned to high speed, the foaming rate is already stable and a good product can be obtained immediately thereafter, which has the advantage that the time required for color change is short.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of a device used for the method of the present invention, and FIG. 2 is a time chart showing an embodiment of the method of the present invention. 1... Extruder, 5... Gas inlet, 9
...Crosshead, 11...Open low cock, 13...Pulsmoke, 15.
...Pressure detector, 17...Controller.

Claims (1)

[Claims] (1) In a method of changing the color of the foamed insulator extruded during the production of foamed insulated wire by the gas injection foaming method, the color change is performed by lowering the wire speed from the operating wire speed to the color changing wire speed. At the same time, the opening degree of the overflow cock is adjusted so that the resin pressure in the crosshead is constant from the start of the color change or from the middle of the color change to the end of the color change. Color change method.