JPS6021228A - Extruding machine for foamy extrusion forming - Google Patents

Abstract

PURPOSE:To obtain a foamed resin product of high extrusion rate which is fine and uniform in quality by designing each of those units such as the supply unit of a screw, compression unit, No.1 weighing unit, mixer and No.2 weighing unit to be of special construction respectively. CONSTITUTION:Foam generative thermoplastic resin in a hopper 1 enters a cylin der 3 through the hopper's outlet 2. A screw 4 in the cylinder is equipped with the following units in sequence. In other words, they are a supply unit 5 wherein the clearance between the cylinder and the screw is gradually reduced in order, No.1 weighing unit 7 of which compression ratio is between 1 and 2.5 times, having a barrier flight 7a which separates liquid resin from solid resin and No.2 weighing unit of which groove is deeper than that of a groove for solid resin of the No.1 weighing unit 7 by 10-50%, which is equipped, at its top end, with a torpedo 9b of which length is 0.5-3 times the inner diameter of the cylinder, and of which clearance between the cylinder is 0.3-3mm.. Resin is uniformly extruded by said units of the screw at a low temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extruder for foam extrusion molding that can obtain fine and uniform foaming at a high throughput of thermoplastic resin.

Conventionally, in the extrusion of thermoplastic resin, the inner diameter of the cylinder is the same from the bottom of the hopper to the tip, and the feed section of the screw has a deep groove 2.5 to 4 times as deep as the metering section to feed unmolten thermoplastic resin pellets and powder. etc., making it easier to transport. However, in the case of foam extrusion molding, the volume of the bubbles is kept very small and the bubbles are released under atmospheric pressure immediately after extrusion to obtain uniform and high foaming, so the molten resin is molded in a highly viscous state, so a large torque is required to rotate the screw. Furthermore, since a correspondingly sufficient screw strength is required, there is a limit to the depth of the groove in the feeding section, and therefore a high extrusion needle cannot be expected.

The present invention was achieved as a result of second-by-second detection in order to improve this problem, and provides an extruder for foam extrusion molding with a high throughput. The present invention will be explained below using the drawings.

FIG. 1 is a cross-sectional view of an example of an extruder of the present invention (only the screw is a side view), and the foamable thermoplastic resin in the hopper 1 enters the cylinder 3 through the hopper opening 2. The inside diameter of the cylinder 3 is first larger than that of the screw 4, and the clearance gradually decreases from the supply section 5 to the compression section 6, ensuring a large space around the supply section 5 of the screw and contributing to a high extrusion rate. In order to ensure screw strength, it is preferable that the depth of the feed section groove is relatively shallow, and if the groove is relatively deep or if the extrusion amount can be satisfied, the clearance may be gradually reduced only in the feed section 5. Also, this gradual decrease is not limited to straight Te/-bars; on the other hand, the shaft diameter of the screw itself may change and the inner wall of the cylinder may be straight, but the point is that the cylinder and screw do not come into contact with each other under the hopper. , it is necessary that the space gradually decreases,
This progresses the conveyance and filling of the thermoplastic resin.

Further, it is preferable to provide a concave groove with a rectangular cross section, a half-T+, etc. in the axial direction on the inner surface of the cylinder corresponding to the supply section of the screw, since this improves the biting of the raw resin and increases the extrusion amount.

Referring to the side groove depth, the first groove depth Hf of the supply section 5
The ratio of the groove depth Hat of the measuring part 1, that is, the compression ratio is 1 to 2.
．． It is preferably 5 times, preferably 1 to 1.5 times. If it is less than 1 time, the extrusion rate will not improve much, and if it exceeds 2.5 times, there will be concerns about the screw strength.

The resin that has passed through the supply section 5 and compression section 6 enters the first ilffi section 1 where melting is promoted, but in foam molding, this is done to increase resin viscosity and to prevent bubbles from becoming coarse and gas dissipation due to decomposition of the blowing agent. Therefore, the cylinder temperatures of the supply section 5 and compression section 6 are set to be low. Therefore, the resin fed into the first and deepest portion contains a large amount of unmelted portion. In order to efficiently melt this unmelted resin and prevent heat generation due to applying extra shearing force to the melted resin, the first section 1 part 1 is constructed as shown in the partially enlarged cross-sectional view of Fig. 2. It has an IM structure with barrier flights 7a for separating the same phase and the liquid phase, and the height difference δ between the barrier flights 1a and the main flights 7b is preferably 0.3 to 1.51. Preferably, it is on the solid phase, and the groove width for the same phase is wide on the compression part side, becomes gradually narrower on the screw tip side as melting progresses, and the groove width on the liquid phase part becomes wider.

When the resin enters the mixing section 8, almost all of the resin is in a melted state, but there may be a small amount of unmelted resin remaining, or there may be a distribution of resin temperature, resulting in a uniform viscosity. Therefore, a mixing section 8 is provided to ensure sufficient mixing. Various structures for the mixing section have been proposed and can be used as appropriate, but a combination of a pin section and a fruity rad section as shown in FIG. 1 is preferred.

The resin that has been completely melted in the first metering section 7 enters the second measuring section 8 consisting of a measuring section 9a and a torpedo 9b.

The groove depth H1113 of the measuring section 9a is 10 to 50% deeper than the groove depth H111 for the solid phase of the first measuring section 7, which prevents excessive shearing from the resin and at the same time maintains a stable extrusion amount. It has the structure obtained. Further, the second design portion 9 has a torpedo 9b at its tip. The length of the torpedo 9b is 0.5 to 3 times the inner diameter of the cylinder, and if it is less than 0.5 times, it is difficult to make the flow vessel uniform, and if it is more than 3 times, the pressure drop will be large, leading to a coarse ratio of bubbles.

On the other hand, if the clearance with the cylinder is 0.3 to 31m, and if it is less than 0.3ms+, the torque will be excessive and the 3m
If it exceeds m, it becomes difficult to achieve uniformity, leading to coarsening of the bubbles.

Here, thermoplastic resins include polystyrene, polyethylene,
Boria 0 pyrene, polyvinyl chloride, A 13S, As,
Polycarbonate, nylon, and other resins that can be continuously extruded using an extruder include solid foaming agents,
Any gas blowing agent may be used, and colorants and additives may be added as appropriate.

By using the extruder according to the present invention, it is possible to extrude the thermoplastic resin sufficiently uniformly and at a low temperature, and an extremely good foaming state can be obtained.

FIG. 1 is a partially enlarged sectional view of one measuring section.

1... Hopper 2... Hopper mouth 3... Cylinder 4... Screw 5... Supply section 6... Compression section 1... First measuring section 7a... Barrier flight 7b.
...Main flight 8...Mixing section 9...Second weighing 8II 9a...Total 1 part 9b...
Torvid

Claims (1)

[Claims] The screw sequentially includes a supply section, a compression section, a first metering section, a mixing section, and a second metering section, and the clearance between the cylinder and the screw gradually decreases at least in the supply section of the screw,
The first metering section has a compression ratio of 1 to 2.5 times and has a barrier flight that separates the liquid phase resin and solid phase resin, and the groove depth of the second metering section is the same as that of the first metering section. 10 to 50% of the groove depth
Deep and the length at the tip is 0.5 to 3 times the inner diameter of the cylinder, and the clearance with the cylinder is 0.3 to 3III+
An extruder for foam extrusion molding, characterized by having a torpedo.