JPH0139602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for changing the color of a foam insulator during the manufacture of a foam insulated wire.

[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. In order 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 cover the foam insulation with several different colors even if they are the same size, and the color is often changed. is being carried out. 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 important to minimize the time required for color changes.

To change the color during the manufacturing process of foam insulated wire, generally, the running of the wire is stopped, the overflow kettle in the crosshead of the extruder 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 pyrolytic 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 foam 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. However, there is a problem in that it takes a long time, for example, 30 to 40 minutes. In comparison, the gas 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 tank is opened or closed, so it takes time to stabilize the foaming rate after restarting operation, and this can cause problems. There is a problem in that there are not a small number of non-defective 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.
The line speed is lowered from the operating line speed to the color change line speed to perform the color change, and an overflow control is applied to keep the resin pressure in the crosshead 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 characterized by adjusting the opening degree of the opening.

Normally, foam insulated wires are manufactured at a line speed of about 1000 to 3000 m/min, which is the so-called operating line speed, but when changing colors, for example,
Reduce the color change line speed to around 300m/min. Then, at the end of the color change, the original operating line speed is restored. Also, when changing colors, the overflow tank attached to 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 line speed is reduced, the resin pressure in the crosshead increases, and when the overflow stock is opened, the resin pressure decreases. In the gas injection foaming method, such fluctuations in the resin pressure within the crosshead lead to fluctuations in the foaming rate. That is, the extrusion amount Q is generally expressed by the following formula.

Q = αN - βΔP ... (1) N: Screw rotation speed ΔP; Differential pressure, that is, the difference α, β between the resin pressure in the crosshead and the resin pressure at a certain position in the axial direction of the extruder (e.g. gas injection part) :Constant When 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,
In the case of the gas injection foaming method, the amount of gas injected (per unit time) is constant regardless of fluctuations in the resin pressure inside the extruder, so if the extrusion amount changes, the ratio of resin to gas changes and the foaming rate changes. It will change.

For this reason, the present invention adjusts the opening degree of the overflow cock so that the resin pressure in the crosshead remains at 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. It is something.

〔Example〕

FIG. 1 shows an example of the apparatus used to carry out the method of the invention. 1 is a screw type extruder, 3 is a hopper for supplying a resin material mixed with a colorant, 5 is a gas inlet, 7 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
13 is a pulse motor for adjusting the opening degree of the overflow socket 11; 15 is an overflow socket for removing resin attached to the crosshead 9
A pressure detector 17 detects the resin pressure in the crosshead 9, and a controller 17 drives a pulse motor in accordance with the pressure detected at the time of color change.

Next, the order in which color change is performed by this device will be explained with reference to the time chart of FIG. First, at _t1 at the start of color change, the overflow cock 11 is fully opened.
At the same time or prior to this, the material supplied from the hopper 3 is switched to another color. When the overflow stock 11 is opened, the resin pressure in the crosshead 9 decreases, so the linear speed is reduced from time _t2 after a short delay. 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 _t5 . The color change line speed is, for example, about 1/10 of the operating line speed. The time from t ₄ to t ₅ is determined by taking into account the time required for all of the resin in the extruder 1 and crosshead 9 to be replaced with new colors.
When the resin replacement is completed, the linear speed is increased from time t ₅ , and when the operating linear speed is reached, the operating linear speed is kept constant from that point t ₆ onwards. On the other hand, the resin pressure inside the crosshead 9 decreases due to the opening of the overflow cock 11, but from an appropriate time _t3 until the color change end time _t6 , the pressure is controlled to be the same as the operating state. be done. 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 17, the pulse motor 13 is driven in the direction in which the overflow cock 11 opens; is performed by driving the pulse motor 13 in the opposite direction. Therefore, the opening degree of the overflow socket 11 changes minutely from t ₃ to t ₆ .

If the resin pressure in the crosshead 9 is kept constant 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 inside the crosshead was controlled from _t3 during the color change, but this pressure control may also be performed from _t1 at the start of the color change.

Furthermore, in the above embodiment, a case was explained in which gas was injected from the middle of the screw type extruder.
The present invention is similarly applicable to the case where two extruders are connected and gas is injected from the connection.

〔Effect of the invention〕

As explained above, according to the present invention, the resin pressure in the crosshead is controlled to be kept constant even when the color change is performed at a reduced linear speed, so that the linear speed of the color change changes to the operating linear speed. The foaming rate is already stable at the time of return, 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 drawings]

FIG. 1 is a front view showing an example of an apparatus used to carry out the method of the present invention, and FIG. 2 is a time chart showing an example of the method of the present invention. 1...Extruder, 5...Gas inlet, 9...Crosshead, 11...Overflow stock, 13
...Pulse motor, 15...Pressure detector, 17...
...Controller.

Claims (1)

[Claims] 1. In a method of changing the color of a foamed insulator extruded during the production of foamed insulated wire by a gas injection foaming method, the wire speed is lowered from the operating wire speed to the color changing wire speed and the color is changed, A method for changing the color of a foam insulated wire, characterized by adjusting the opening degree of an overflow socket so that the resin pressure in the crosshead remains constant from the start of color change or from the middle of color change to the end of color change.