JPH08290456A - Multistage extruding apparatus for thermoplastic resin - Google Patents

Abstract

PURPOSE: To provide a multistage extruding apparatus for a thermoplastic resin which can obtain adequate mixing of the resin with an additive and prevents inadequate dispersion of the additive. CONSTITUTION: In a multistage extruding apparatus for a thermoplastic resin in which extruders are connected in sequence so that the resin is supplied from the front stage extruder 1 to the rear stage extruder 11, and an additive is 13 is added into the resin in the extruder 11 latter than the initial stage, a high shear kneading part 20 for kneading the resin and the additive 13 is formed between the first thread and tenth thread of a screw on the feed part side of a place where the, additive 13 is injected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-stage thermoplastic resin extruder for extruding a thermoplastic resin by sequentially connecting a plurality of extruders.

[0002]

2. Description of the Related Art A conventional multi-stage thermoplastic resin extruding device of this type is shown in FIG. 3 (FIG. 3 shows a conventional multi-stage thermoplastic resin extruding device applied to an insulating coating device for a plastic insulated cable. The pellets of the thermoplastic resin are fed from the hopper 3 into the cylinder 2 of the first-stage extruder 1, and the pellets are heated and melted in the cylinder 2 while being kneaded by the screw 4 to the outlet side. Transport. In the course of this transportation, the additive 5 may be injected into the extruder 1 from the container 6 by the pump 7. The molten thermoplastic resin conveyed to the outlet side of the extruder 1 passes through a breaker plate 9 and a screen pack 8 composed of an ultrafine mesh screen provided for the purpose of removing fine foreign matter. .

The molten thermoplastic resin extruded from the first-stage extruder 1 is continuously guided to the resin temperature control tube 10 and controlled to an appropriate resin temperature, and then the second-stage extruder 11 is controlled. It is supplied into the cylinder 12. In the second-stage extruder 11, after the additive 13 is injected from the container 14 into the cylinder 12 of the extruder 11 by the pump 15, the additive 13 is kneaded with the molten thermoplastic resin by the screw 16 and extruded, Supply to 17. In the crosshead 17, the outer periphery of the conductor 18 is extrusion-coated with the molten thermoplastic resin to manufacture the plastic insulated cable 19.

Further, in such a multi-stage type thermoplastic resin extruder, the second stage extruder screw 16 does not need to melt the resin on the way and the density does not change greatly, so that the entire length of the screw is improved. Generally, the groove depth (valley diameter) is constant. As the additives 5 and 13, those which are liquid at room temperature can be used as they are,
A solid material at room temperature is heated to be in a liquid state.

[0005]

However, in such a conventional thermoplastic resin extruder, the resin pressure distribution in the cylinder 12 of the second-stage extruder 11 is as shown in FIG. Since the side is high and the feed side is low, a part of the injected additive, which has a large viscosity difference from the molten thermoplastic resin, flows in the cylinder 12 without being sufficiently mixed with the molten thermoplastic resin. It will flow back to the feed side. If the additive flowing back is stagnated in a part of the cylinder 12, poor dispersion of the additive occurs,
If this part gets mixed into the extruded product, the electrical quality will be remarkably inferior.

An object of the present invention is to solve the above problems and to provide a multi-stage thermoplastic resin extruder capable of obtaining a sufficient mixed state of a thermoplastic resin and an additive and preventing defective dispersion of the additive. And

The present invention has the following means in order to solve the above problems.

In the multi-stage type thermoplastic resin extruder according to claim 1 of the present invention, a plurality of extruders are sequentially connected so as to supply the thermoplastic resin from the former stage extruder to the latter stage extruder. In a multi-stage type thermoplastic resin extruder in which an additive is added to the thermoplastic resin in the extruder after the eye and kneading is performed, from the position where the additive is injected, from one screw of the screw on the feed section side. A high-shear kneading section for kneading the molten thermoplastic resin and the additive is provided between the 10 mountains.

The multistage thermoplastic resin extruder according to claim 2 of the present invention is characterized in that the high-shear kneading section is formed by a protrusion projecting on a screw in the extruder.

[0009]

According to the multi-stage thermoplastic resin extruder of the present invention, a plurality of extruders are sequentially connected so as to supply the thermoplastic resin from the former extruder to the latter extruder, and the second and subsequent extruders are connected. In a multi-stage thermoplastic resin extruder in which an additive is added to a thermoplastic resin in an extruder and kneading is performed, at least 1 to 10 threads of a screw on the feed side from the position where the additive is injected from the position where the additive is injected. Since a high shear kneading section for kneading the molten thermoplastic resin and the additive is provided in the molten thermoplastic resin exiting the former extruder, the additive is added in the extruder thereafter, and the additive is added. Even if a part of the backflow occurs on the feed side due to the resin pressure gradient, the backflowed additive and molten thermoplastic resin are uniformly kneaded by the high-shear kneading section and are conveyed by the rotation of the screw. Prevent dispersion failure Rukoto can. That is, the high shear kneading section for kneading the molten thermoplastic resin and the additive is provided between 1 to 10 threads of the screw on the feed section side from the position where the additive is injected, for the following reason. .
Since the additive flowing back is still present on the cylinder surface between the injection position of the additive or less than one screw of the feed part, providing the high shear kneading part has no effect. Further, at a position separated by 10 or more peaks, an excessive amount of the additive remains at a certain point on the screw before the reverse flow of 10 or more peaks, and the additive flowing back cannot be completely kneaded. Therefore, as the position of the high-shear kneading part, the optimum position is to be provided between 1 and 10 ridges of the screw on the feed part side from the position where the additive is injected.

[0010]

The present invention will be described below in detail with reference to examples. The same parts as the conventional ones are designated by the same reference numerals, and detailed description thereof will be omitted.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a multistage thermoplastic resin extruder according to the present invention. In this embodiment,
1 shows an example in which a two-stage extruder according to the present invention is applied to an insulation coating line of a plastic insulated cable. As shown in the figure, in the multi-stage thermoplastic resin extruder of this embodiment, the screw 16 of the second-stage extruder 11 that supplies the additive 13 is fed to the screw 16 on the feed section side from the injection position of the additive 13. A high-shear kneading section 21 for kneading with a higher shearing force than the other portions of the screw 16 is provided between the first and the tenth peaks.

The high-shear kneading section 21 is formed of a projection 21a composed of a large number of pins projecting on the circumference of the screw 16 as shown in FIG. Alternatively, FIG.
As shown in (b), it is formed by a columnar protrusion 21b projecting on the screw 16 so as to reduce the gap between the screw 16 and the cylinder 12.

Next, an example of manufacturing a plastic insulated cable with such a multi-stage type thermoplastic resin extruder will be described. A hopper 3 is provided in the cylinder 2 of the first-stage extruder 1.
The thermoplastic resin pellets are supplied from the above, and the pellets are heated and melted in the cylinder 2 while being kneaded by the screw 4 and conveyed to the outlet side. In the course of this transportation, an additive 5 such as an antioxidant may be injected from the container 6 into the extruder 1 by the pump 7 and kneaded with the molten thermoplastic resin by the screw 4. The molten thermoplastic resin conveyed to the outlet side of the extruder 1 is a screen pack (in this example, 100 mesh, 200 mesh) composed of an ultrafine mesh screen provided for the purpose of removing fine foreign matter. , 500 mesh, 1000 mesh screen mesh) 8 and the breaker plate 9.

In this way, the first-stage extruder 1 has a high resin temperature (in the case of low-density polyethylene, a viscosity that allows the molten thermoplastic resin in which the antiaging agent is kneaded to pass through the ultrafine mesh without difficulty. Extrusion temperature 2 for melting point 110 ° C
Extrude at 00 ° C). After cooling this high temperature molten thermoplastic resin to an appropriate resin temperature by the resin temperature control cylinder 10, the second
It is fed into the cylinder 12 of the extruder 11 of the stage. In the second-stage extruder 11, the cross-linking agent as the additive 13 is supplied from the container 14 by the pump 15 in the process of conveying the molten thermoplastic resin supplied while kneading with the screw 16. Inject into the cylinder 12. The cross-linking agent is
Immediately after being injected into the cylinder 12, the screw 1 has a viscosity difference from that of the molten thermoplastic resin and a flow characteristic of the cross-linking agent.
Gathered on the surface of No. 6 and not kneaded with the molten thermoplastic resin. Cylinder 1 with molten thermoplastic
2 The cross-linking agent conveyed to the outlet side is kneaded with the molten thermoplastic resin by the kneading section 20 provided on the tip side of the screw 16, but is partially affected by the resin pressure gradient and flows backward to the screw feed section side. The cross-linking agent (1) remains unkneaded with the molten thermoplastic resin.

However, in the present invention, the screw 1 is provided with respect to the screw 16 at the position of 1 to 10 ridges of the screw on the feed side from the injection position of the additive 13.
Since a high-shear kneading section 21 for kneading at a higher shearing force than the other portions of 6 is provided, the cross-linking agent which flows backward is uniformly mixed with the molten thermoplastic resin, and then the screw 1
By 6, it will be conveyed. In the present embodiment, the inner diameter of the extruder 11 of the second stage extruder is 200 mm, the groove depth of the normal flight part is constant at 2 mm, the additive is injected into the eighth ridge from the feed side, and the second to fifth to sixth ridges from the feed side. A high shear kneading section 21 for the pile was formed. In other words, high shear kneading section 2
No. 1 was provided at 2 to 3 peaks on the feed section side from the injection position of the additive 13. The clearance between the crest of the screw 16 of the high shear kneading section 21 and the inner wall of the cylinder 12 is 0.8 mm.
Is. In this way, the molten thermoplastic resin in which the additive 13 is uniformly dispersed and mixed is extruded by the screw 16 and supplied to the crosshead 17, and the conductor 1
The outer circumference of 8 is extruded to cover the plastic insulated cable 19
To manufacture.

A multi-stage thermoplastic resin extruder according to the prior art (using a screw without a high-shear kneading section on the feed side from the additive injection position) and a multi-stage thermoplastic resin extruder according to the present invention (additive injection) Table 1 shows a comparison of the degree of cross-linking of the extrusion-coated cable insulator in which the high-shear kneading section is located closer to the feed section than the position).

[Table 1] In this Table 1, after injecting 2.0 parts of the cross-linking agent DCP as an additive into 100 parts of low-density polyethylene in the second-stage extruder 11, the degree of cross-linking of the insulator cross-linked under the same conditions was investigated. The results are shown. The low degree of cross-linking means
This means that the amount of the crosslinking agent is small, that is, the injected crosslinking agent is uniformly kneaded with the molten thermoplastic resin and is not extruded.

Further, Table 2 is a comparison of continuous extrusion time in which extrusion can be carried out without causing trouble such as stagnation of resin in the extruder, but the present invention also has a continuous extrusion possible time several times longer than the conventional one. It shows that there is a step effect.

[Table 2]

In the above embodiment, the case where the extruder has two stages is shown, but the present invention is not limited to this, and the same applies to a multistage thermoplastic resin extruder having three or more stages of extruder. Can be applied as

Further, as equipment for supplying the molten thermoplastic resin to the second and subsequent extruders, equipment other than the extruder of the first embodiment (for example, Banbury mixer, continuous kneader, etc.) can be used. The same can be naturally applied to the case where the equipment capable of supplying the molten thermoplastic resin is used.

Further, in the above embodiment, the high-shear kneading section 21 is located 2 to 3 peaks on the feed section side from the injection position of the additive 13.
However, even if the high-shear kneading section is provided between 1 to 10 threads of the screw on the feed section side from the position where the additive is injected, the high shear kneading section can be applied for the following reason. . That is, since the additive that flows backward is still present on the screw surface between the injection position of the additive or less than one screw of the feed part, providing the high shear kneading part has no effect. Further, at a position separated by 10 or more peaks, an excessive amount of the additive remains at a certain point on the screw before the reverse flow of 10 or more peaks, and the additive flowing back cannot be completely kneaded. Therefore, as the position of the high-shear kneading part, the optimum position is to be provided between 1 and 10 ridges of the screw on the feed part side from the position where the additive is injected.

As described above, according to the multi-stage thermoplastic resin extruder of the present invention, a plurality of extruders are sequentially fed from the former extruder to the latter extruder. In a multi-stage type thermoplastic resin extruder in which an additive is added to a thermoplastic resin in the extruder after the second stage and kneading is performed, in the screw on the feed section side at the position where the additive is injected, Since a high-shear kneading section for kneading the molten thermoplastic resin and the additive is provided between 1 and 10 threads, the additive can be added to the thermoplastic resin discharged from the former extruder in the subsequent extruders. When added, part of the additive, even when it flows backward in the screw feed direction due to the influence of the resin pressure distribution in the extruder cylinder, the thermoplastic resin and the additive are added by the high shear kneading part of the extruder. It can be kneaded uniformly and does not disperse. It can be eliminated. Therefore,
High quality extrusion molding can be stably performed for a long time.

[Brief description of drawings]

FIG. 1 is a longitudinal section showing an embodiment of a multi-stage thermoplastic resin extrusion apparatus of the present invention.

FIG. 2 is a detailed view showing an example of a high-shear kneading section provided on the screw of the apparatus shown in FIG.

FIG. 3 is a vertical cross-sectional view showing an example of a conventional multi-stage thermoplastic resin extruder.

FIG. 4 is a resin pressure distribution diagram in a second-stage extruder cylinder in a general multistage thermoplastic resin extruder.

[Explanation of symbols]

 1 First Stage Extruder 2 Cylinder 3 Hopper 4 Screw 5 Additive 6 Storage Container 7 Pump 8 Screen Pack 9 Breaker Plate 10 Resin Temperature Control Cylinder 11 Second Stage Extruder 12 Cylinder 13 Additive 14 Storage Container 15 Pump 16 Screw 17 Crosshead 18 Conductor 19 Plastic insulated cable 20 High shear kneading part 21 Kneading part 21a Projection 21b Projection

Claims (2)

[Claims] 1. A plurality of extruders are sequentially connected so as to supply a thermoplastic resin from a former extruder to a latter extruder, and an additive is added to the thermoplastic resin in the second and subsequent extruders. In a multi-stage thermoplastic resin extruder that is kneaded by kneading, the molten thermoplastic resin and the additive are kneaded between 1 to 10 ridges of the screw on the feed section side from the position where the additive is injected. A multi-stage thermoplastic resin extruder, which is provided with a high-shear kneading section. 2. The multistage thermoplastic resin extruder according to claim 1, wherein the high-shear kneading section is formed by a protrusion protruding on a screw in the extruder.