JPH02212116A - Method for extruding foaming resin - Google Patents

Abstract

PURPOSE:To make it possible to stably extrude foaming material by a method wherein the pellet-shaped foaming material is housed in a hopper having the specified ambient temperature or higher and fed with chlorofluorocarbon(CFC) gas so as to bring the amount of chlorofluorocarbon gas infiltrated into the foaming material to the specified percentage of the amount of CFC gas saturated in the foaming material or higher and, after that, the resultant foaming material is extruded from the cylinder of an extruder. CONSTITUTION:It is known that the percentage of CFC gas impregnated in fluoroplastic is improved by using high temperature saturated chlorofluorocarbon gas vapor. Since chlorofluorocarbon gas is fed in a hopper 2 having an ambient temperature of 40 deg.C or higher, the gas easily infiltrates into foaming material 1. Even in case of unmolten pellet-like foaming material 1, the amount of chlorofluorocarbon gas infiltrated into the foaming material easily becomes uniform and, in addition, reaches the desired amount of infiltration in a short period of time. Further, since the foaming material 1 is extruded under the condition that the amount of CFC gas infiltrated into the foaming material 1 reaches 80% or higher of the amount of CFC gas saturated in the foaming material, the expansion ratio of the foaming material is also enhanced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to the production of a foamed fluororesin insulated wire d in which the outer periphery of a conductor a is covered with foamed fluororesin as shown in FIG. Related to a method for extruding and covering the outer periphery of a conductor a with a foamed fluororesin (prior art) A conventional method for manufacturing a foamed fluororesin insulated cable uses a fluoride gas as a foaming agent (for example, fluorocarbon gas: DuPont trademark). As shown in Figure 3, the gas is injected from the middle of the extruder cylinder C to impregnate the fluororesin that is the foamed material in the cylinder C, and the resin is decompressed by the depressurizing effect when the resin is discharged from the die. It is foaming.

Methods for injecting this fluorocarbon gas include a constant pressure injection method as shown in FIG. 3, and a metered pump injection method as shown in the same figure.

Before. The neck is a pressure reducing valve B that removes the fluorocarbon gas from the fluorocarbon gas cylinder A.
The nitrogen gas in the nitrogen cylinder D is injected into the extruder cylinder C through the pressure reducing valve E.
The fluorocarbon gas in the cylinder F is injected into the extruder cylinder C by the pump G.

Both of these methods are used depending on the resin pressure of the gas injection part H of the extruder cylinder C.

In any of the above methods, the foaming of the fluororesin is very delicate, and in order to obtain a foaming rate of 60% or more, it is necessary to inject fluorocarbon gas at a point in the extruder cylinder C where the pressure is stable.

Moreover, unless the fluorocarbon gas is injected into the molten resin that is completely melted, the amount of gas impregnated into the resin will be uneven, resulting in non-uniform foaming.

(Problems with the prior art) However, if the fluorocarbon gas is not injected under the molten resin, it will escape from the material supply section such as the hopper, so the gas inlet J has to be installed closer to the crosshead of the extruder cylinder C. As a result, the time required for the resin to reach the crosshead K is shortened, and there is a problem in that the fluorocarbon gas cannot be sufficiently diffused into the fluororesin within that time, making foaming of the resin unstable.

Furthermore, in the metered pump injection method among the above methods, the injection amount depends on the pump precision, and the fluorocarbon gas discharged into the extruder cylinder C cools the fluororesin in the cylinder C. The temperature of the resin in the same cylinder C,
There were also problems in that the viscosity became non-uniform and extrusion of the resin became unstable.

(Objective of the Invention) An object of the present invention is to provide a method for extruding a foamed fluororesin in which fluorocarbon gas is sufficiently diffused into the fluororesin, the foaming of the fluororesin is stabilized, and stable extrusion is possible.

Means for Solving the Problems 1 and 3) The foamed resin extrusion method according to claim 1 of the present invention is as shown in FIG. The foamed material 1 is placed in a hopper 2 at a temperature of ℃ or higher, and fluorocarbon gas is supplied into the hopper 2. After the amount of fluorocarbon gas impregnated into the foamed material 1 reaches 80% or more of the saturated amount, the foamed material 1 is extruded. It is characterized by being extruded from cylinder C.

The second aspect of the present invention is such that the fluorocarbon gas in the first aspect is heated and supplied to the hopper 2, and the gas is pressurized in the hopper 2 and used as saturated steam. be.

(Function) The impregnation rate of fluorocarbon gas into fluororesin is as shown in Figure 4.
It is known that the improvement can be achieved by using fluorocarbon gas as high temperature saturated steam. DF-22, DF- in Figure 4
113 uses Class J4 fluorocarbon gas at 50℃, 20 kg/
cm'', 50°C, 1,5 kg/c+m'', etc. indicate the temperature and pressure of saturated fluorocarbon vapor.

Claims of the Invention In the first foamed resin extrusion method, since the fluorocarbon gas is supplied into the honper 2 at an ambient temperature of 40°C or higher, the gas easily impregnates the foamed material 1, resulting in unmolten pellets. Even if the foamed material 1 has a shape, the amount of fluorocarbon gas impregnated can be easily made uniform, and the desired amount of fluorocarbon gas can be achieved in a short time. Furthermore, since the foamed material 141 is extruded after the amount of fluorocarbon gas impregnated into the foamed material 1 reaches 80% or more of the saturated impregnated amount, the foaming rate is also improved.

Claims of the Invention In the second foamed resin extrusion method, freon gas is heated to, for example, about 50°C and supplied to the hopper 2, and the gas is pressurized in the hopper 2 to become saturated steam, so that the gas foams. It becomes easier to impregnate the material 1 (and the impregnation time is further shortened).

(Example) The extrusion apparatus shown in FIG. 1 is for implementing the extrusion method of the present invention.

In the present invention, in order to be able to heat the fluorocarbon gas supplied to the hopper 2 and turn it into saturated steam, the hopper 2 is made into a pressurized pressure-resistant container. Further, the hopper 2 is provided with a heat-retaining property such as by pasting a heat insulating material on the inner surface in order to keep the heated and supplied fluorocarbon gas warm.

In the present invention, Freon 22 (D
F-22) was used to efficiently impregnate the foamed material in the hopper 2 with g/cae at 50°C and 20°C.
In this case, the gas cylinder 3 of DF-22 was heated to 50°C (rj temperature) in a constant temperature bath 4, and the hopper 2 and piping section 5 were further heated with a heater 6 to bring the temperature to 1 (not shown). The temperature inside the hopper 2 is adjusted to 50°C by adjusting the cylinder temperature once, and then the inside of the hopper 2 is heated to 20g/kg.
cyr'' to obtain saturated steam.

In this state, the foamed material 1 was left in the hopper 2 for about 10 hours, and the foamed material 1 was sufficiently impregnated with chlorofluorocarbon gas.

At this time, the impregnation rate of fluorocarbon gas was about 3.0% by weight. This impregnation rate is determined by the temperature of saturated freon vapor, and experiments have shown that sufficient impregnation for foaming can be obtained if the temperature is 40°C or higher.

In addition, if the amount of fluorocarbon gas impregnated into the pellet-shaped foam material is approximately 80% of the saturated amount, the amount of subsequent impregnation will be small and will take a long time to impregnate, so it will not affect the stability of extrusion. I also learned that.

In addition, in the apparatus shown in FIG. 1, a gear box behind the screw 7 and a power transmission section to the screw 7 (both (not shown).

(Effects of the Invention) In the foamed resin extrusion method of the present invention, fluorocarbon gas can be stably supplied to 1 foamed material 1, and the fluorocarbon gas impregnates the same foamed material 1 in a sufficient amount for foaming.
The foaming of the foaming material 1 is stabilized, and the foaming rate is improved.

As a result, if the outer periphery of the conductor a shown in FIG. 2 is coated with the foamed material 1 by extrusion using the extrusion method of the present invention, the foamed fluororesin insulation type 1i1d can be easily obtained, and productivity is improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an extrusion device embodying the present invention, FIG. 2 is an explanatory diagram of a foamed fluororesin insulated wire,
FIG. 3 is an explanatory diagram of a conventional extrusion device, and FIG. 4 is an explanatory diagram showing the relationship between the impregnation rate of fluorocarbon gas into the fluororesin and the impregnation time. 1 is foam material 2 is hopper

Claims (2)

[Claims] (1) Pellet-shaped foamed material 1 is placed in a hopper 2 with an ambient temperature of 40°C or higher, and fluorocarbon gas is supplied into the hopper 2, so that the amount of fluorocarbon gas impregnated into the foamed material 1 is 80% or more of the saturated impregnated amount. A method for extruding a foamed resin, characterized in that the foamed material 1 is extruded after the foamed material 1 is formed. (2) heating the fluorocarbon gas and supplying it to the hopper 2;
2. A foamed resin extrusion method according to claim 1, characterized in that said gas is pressurized in said hopper and used as saturated steam.