JPS6130893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synthetic resin extrusion device used in an extruder or injection molding machine.

Conventionally, regardless of whether the extruder or injection molding machine is used, a single-thread screw as shown in FIG. 1 is used to plasticize, knead, and homogenize synthetic resin. That is, in Fig. 1, A is a screw with a single-thread shape, and B is a cylinder. The synthetic resin is transported to the front part while moving in a spiral along the threaded part by the rotation of screw A. During this time, heat is transferred from the cylinder. As a result, the material is plasticized and melted, and shear is applied between the screw bottom and the cylinder B to achieve kneading and homogenization.

By the way, the performance of an extruder or injection molding machine is usually determined by the quality of kneading, and the conditions that determine the quality of kneading include uniformity of discharge temperature, stirring effect, shearing effect, etc. If the synthetic resin material is simply transported in a spiral motion using a screw, it will lack stirring and shearing effects, but if these effects can be imparted more effectively to the resin, not only will the quality of molded products improve, but the production volume will also increase. It becomes possible to increase the number of In other words, in general, the relationship between screw rotation speed and quality is as shown in the graph in Figure 2, as the screw rotation speed increases, the amount of extrusion increases, but the quality decreases.
In this graph, if curve 1 is used with a single-thread screw, if the kneading effect is increased further, the quality curve will move to curve 2, and compared to curve 1, the quality will improve at the same screw rotation speed, and the quality will be the same. At the level, the production volume can be increased by the increase in screw rotation speed.

For this reason, various attempts have been made in recent years to improve the kneading effect.In addition to providing a barrier (dam) in a part of the screw to separate the molten resin from the unmolten resin, the resin is sheared when it passes through this barrier. A number of devices have been developed that aim to provide agitation and mixing effects using protrusions such as pins. However, with the barrier type, the extrusion amount decreases due to the resistance caused by the barrier, and there is a problem of thermal deterioration of the resin due to heat generation in the barrier part, and with the protrusion, there are problems such as retention and deterioration of the resin. The reality is that overall, the effects of improving quality and increasing production have not been sufficient.

In view of these circumstances, the present invention provides a synthetic resin extrusion device that improves conditions such as shearing action, stirring action, uniformity of discharge temperature, etc., significantly enhances the kneading effect, and achieves sufficient quality improvement and production increase. Its features are the feed section,
A screw having a compression section and a metering section has a feeding wing section which has a lead angle in the direction of feeding the synthetic resin material toward the tip of the screw in a part ahead of the compression section, and a feeding wing section which continues in front of the feeding wing section and carries the material. A mixing section with an irregular cross-sectional shape is provided with a plurality of raised kneading blades consisting of a return wing section having a lead angle in the push-back direction, and a gap between the outermost part of this mixing section and the inner circumferential surface of the cylinder is provided. 1/10 of cylinder inner diameter
The reason is that it was formed from 0 to 1/10.

Hereinafter, the present invention will be explained with reference to drawings of embodiments.

In FIG. 3, 1 is a screw, 2 is a cylinder, and 3 is a hopper. The figure exemplifies the structure of a screw for an extruder, and the screw 1 has a feed section 4, a compression section 5, and a metering section 6 in order from the hopper 3 side. Part 7
Equipped with. The feed section 4, the compression section 5, and the metering section 6 are formed with screw flights in a fixed direction, similar to conventional screws, and feed the synthetic resin toward the tip of the screw while making a spiral motion.

The mixing section 7 includes a continuous feeding blade section 8a.
A plurality of kneading blades 8 consisting of a return blade part 8b...
In the illustrated example, it is composed of four kneading blades 8... This mixing part 7 is different from the shape of the screws constituting the other feed part 4, compression part 5, and metering part 6, and is formed into an irregular cross-sectional shape, such as a substantially rectangular shape with tops on all sides.
The top portion forms a kneading blade 8. The kneading blades 8 are twisted at a relatively gentle lead angle in the direction of feeding the material toward the screw tip side over the range from the starting end to the middle part of the mixing part 7, and from the tip to the mixing part 7. On the other hand, by continuously twisting the lead angle with a relatively gentle lead angle in the direction of pushing back the material over the range up to the end, the sending wing section 8a and the returning wing section 8b are It consists of The lengths and lead angles of the sending wing portion 8a and the returning wing portion 8b may be the same or different from each other, and can be arbitrarily selected in terms of design. In addition, by setting the gap 8 between the outermost layer of the mixing part 7 and the inner peripheral surface of the cylinder 2 to 1/100 to 1/10 of the inner diameter of the cylinder 2,
While the synthetic resin material passes through this portion, it is effectively subjected to shearing action. The value of this gap 8 corresponds to about 5 to 10 times the gap value between the outermost diameter of the screw and the inner diameter of the cylinder in a normal extruder.

This mixing portion 7 may be separately machined in advance as shown in FIG. 5 and the tip of the screw 1 may be inserted into it, or it may be formed integrally with the screw 1. Further, the location of the mixing part 7 in the screw 1 can be selected as appropriate within the range beyond the compression part 5 where the resin begins to melt, but it can be placed at the tip of the screw 1 as shown in FIG. 3, or at the tip of the screw 1 as shown in FIG. It is appropriate to provide it between the compression section 5 and the metering section 6 as shown in FIG.

The operation of the screw of the present invention as described above will be explained next. By rotating the screw 1 in a certain direction, the synthetic resin material supplied from the hopper 3 is moved toward the tip of the screw 1 by the feeding action of the screws of the feed section 4, compression section 5, and metering section 6. Compression section 5 or metering section 6
At the time when the resin flows into the mixing section 7 from
The resin has been completely melted or is in a state where unmelted resin and molten resin are mixed. In the mixing section 7, the kneading blades 8 shear and stir the resin. In this case, the mixing section 7 has a higher shearing and stirring effect than a single-threaded one, and also keeps the molten resin at a relatively low and uniform temperature to prevent deterioration due to heat generation, and also prevents unmelted resin from deteriorating due to heat generation. If it is mixed in, it also has the effect of accelerating its melting.

In other words, shear force has a great effect on kneading molten resin, but with conventional screws that only have a single-thread shape, it is the groove of the screw that attempts to homogenize the molten resin, and there is a gap between the bottom of the screw and the cylinder. Shearing is applied, and the thread top only has the function of extruding the resin, so it has a poor shearing effect, and since the resin only moves in a laminar flow in the helical direction, it also has a poor stirring effect.

On the other hand, according to the structure of the mixing part 7 in the present invention, the top part of the kneading blade 8 is called the kneading flight part 9, and the part with a wide distance from the inner wall of the cylinder 2 is called the open part 10. When the resin passes through, a large shearing force is applied to the resin, improving kneading. In this case, the resin generates heat due to the shearing force, but the time it takes to pass through the kneading flight section 9 is short and the amount of heat generated is very small.On the other hand, only a low shearing force is applied in the release section 10, so the amount of heat generated is small. Therefore, the heat of the resin that has passed through the kneading flight section 9 is absorbed by the low-temperature resin that is passing through the release section 10, and the resin as a whole generates almost no heat. Therefore, the temperature of the resin is kept uniform,
Moreover, even if the rotational speed of the screw 1 is increased, an unnecessary rise in the temperature of the resin can be avoided. Also,
The resin flowing through the mixing section 7 undergoes vortex motion as shown by the arrows in Figure 6, and is mixed in the depth direction, resulting in a much more effective stirring effect than laminar flow mixing using conventional screws. be enhanced. Furthermore, the resin is mixed into the kneading flight section 9 and the release section 1.
The kneading effect is further enhanced by repeatedly compressing and releasing the material. Mixing section 7
If the unmelted resin and molten resin are in a mixed state when the resin is introduced into the compressor, the heat of the molten resin permeates into the unmolten resin during the compression, thereby completing the melting process quickly.

Further, since the kneading blades 8 of the mixing section 7 have a sending blade part 8a and a return blade part 8b, it is possible to prevent the molten resin from flowing in a short circuit along the release part 10 to the tip of the screw 1, and to ensure that Since the resin passes through the kneading flight section 9 many times, sufficient kneading is achieved.

The device of the present invention is not limited to an extruder, but can also be applied as an injection molding machine by changing the design such that the screw 1 can be moved in a fixed stroke in the axial direction.

The apparatus of the present invention configured as described above is provided with a plurality of kneading blades each consisting of a sending blade part and a return blade part, in front of the compression part of the screw having a feed part, a compression part, and a metering part. A mixing section with an irregular cross-sectional shape is provided, and a gap of 1/100 to 1/10 of the cylinder inner diameter is provided between the outermost part of the mixing section and the inner peripheral surface of the cylinder with a circular cross section. It is designed to receive sufficient shearing action while passing through. For this reason, while having sufficient extrusion capacity, the shearing effect and stirring effect are greatly increased,
Furthermore, it promotes the melting of the resin, which also promotes the above effects, and also avoids deterioration due to temperature unevenness and heat generation, which increases the kneading effect and improves quality. Even if the rotation speed is increased to increase the extrusion amount, it is possible to obtain an extrudate that is homogeneous both in temperature and physical properties at a low temperature.
Therefore, as a screw for a synthetic resin extruder or an injection molding machine, it has a great effect on improving quality and increasing production.

[Brief explanation of the drawing]

Figure 1 is a vertical side view showing a conventional screw.
Fig. 2 is a graph showing the relationship between the screw rotation speed and the quality of molded products in a synthetic resin extruder or injection molding machine, and Figs. 3 to 7 show examples of the screw of the present invention. 4 is an enlarged sectional view taken along the - line in FIG. 3, FIG. 5 is an enlarged side view of the mixing section, and FIG. 6 is an enlarged sectional view showing the flow state of the resin in the mixing section. 7 are overall longitudinal sectional side views showing another embodiment. 1...screw, 7...mixing department, 8...
...Kneading blade, 8a...Feeding blade section, 8b...Returning blade section.

Claims (1)

[Claims] 1 Consisting of a screw having a feed section, a compression section, and a metering section in order from one end in the axial direction, in which a screw flight is formed, and a cylinder surrounding the screw with an inner peripheral surface having a circular cross section. In the synthetic resin extrusion device, the screw has a feed wing section which has a lead angle in a direction to feed the synthetic resin material toward the tip of the screw, in a portion beyond the compression section of the screw, and a feed wing section that continues in front of the feed wing section and pushes the material back. A mixing section with an irregular cross-sectional shape is provided, which is equipped with a plurality of raised kneading blades consisting of a return wing section having a lead angle in the direction, and a gap between the outermost part of the mixing section and the inner circumferential surface of the cylinder is provided. A synthetic resin extrusion device characterized in that the cylinder has a diameter of 1/100 to 1/10 of the inner diameter.