JPS6111772B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for extrusion molding resins such as plastics and rubber using a screw extruder.
More specifically, a molten liquid additive such as a crosslinking agent is directly pressed into the extruder through a liquid injection port formed in a cylinder or screw, and the main raw material resin such as plastic or rubber fed from a hopper and the liquid additive are The present invention relates to an extrusion method in which these are mixed in an extruder. As is well known, in extrusion molding of crosslinked polyethylene, etc., it is necessary to add and mix additives such as a crosslinking agent in addition to the main raw material such as polyethylene. The conventional method of adding and mixing additives and extrusion molding is to knead the main raw material such as polyethylene with additives such as a crosslinking agent in advance and form it into a pellet.
A common method was to charge the additive-containing mixture pellets into the hopper of an extruder and extrude them. However, with this method, it is necessary to knead additives such as cross-linking agents into the main raw material resin in advance, which increases manufacturing costs and also reduces the quality of extruded products due to the introduction of foreign substances during kneading. Additionally, if volatile additives are used, they may evaporate during kneading, resulting in insufficient blending of crosslinking agents and other additives, which may impair the quality of the extruded product. , loss of additives may occur. In order to solve the above-mentioned problems, as shown in Fig. 1, the main raw material resin introduced from the cylinder 1 or screw 2 of the extruder (usually from the hopper 4) is in a semi-molten or molten state. A liquid inlet 3 is formed at a position such that the main body is injected from the hopper 4. A method has been developed in which raw materials and liquid additives are kneaded in an extruder. According to this method, there is no need for a step to knead additives such as crosslinking agents with the main raw material resin in advance, reducing manufacturing costs and reducing the risk of foreign substances getting mixed in during kneading. Therefore, a high quality extrusion molded product can be obtained, and even when volatile additives are used, various effects such as reducing the risk of the additives volatilizing can be obtained. However, when carrying out the method of pressurizing the liquid additive separately from the main raw material through the liquid injection port as described above, conventional extruders simply provided a liquid injection port in the screw or cylinder of an ordinary extruder. However, the actual situation is that no particular consideration is given to the shape of the screw itself, which causes various problems in actual operation. In other words, the flow of resin in the screw groove is generally as shown by arrow A in Figure 2, and when a low viscosity liquid is directly injected into such a state, the liquid flows from the bottom of the screw groove. It has a tendency to stay near the portion 2D rising up to the mountain portion 2B behind it. This is the rising part 2
This phenomenon is caused by the small curvature of D, and in extrusion where a low viscosity liquid is not injected, this problem of stagnation does not occur due to the high viscosity of the molten resin. Ta. However, when injecting a liquid additive with low viscosity, the liquid additive 6 injected from the liquid injection port 3 is not immediately and uniformly dispersed into the molten resin 7, as shown in FIG. , the above-mentioned screw flight remains in the rising part of the small curvature and is extruded as it is, and as a result, the product 8 obtained by extrusion has the additive 6 in the center as shown in FIG. A problem arises in that the particles are concentrated, making it impossible to obtain a product with uniform characteristics. Additionally, a portion of the liquid additive added from the liquid inlet may remain attached to the surface of the screw groove without being extruded, which may impede operations or adversely affect product quality. There is. The purpose of this invention is to solve the above-mentioned inconvenience caused by injection of liquid additives, and it uses an extruder with an improved screw shape so that liquid additives do not remain in the screw grooves. An extrusion method is provided. That is, the extrusion method of the present invention uses a single screw type extruder, in which the groove depth of the screw groove near the liquid inlet provided in the compression section of the screw extruder is set to be shallower than the groove depth of the screw groove in the metering section. This method is characterized by performing extrusion using a liquid additive injection method using a type extruder. To explain the method of the present invention in more detail below, FIG. 5 is a diagram showing the main parts of an example of a single-screw extruder used in the method of the present invention.
In FIG. 5, a liquid inlet 3 is formed on the wall surface of the cylinder 1 at a position corresponding to the compression section B of each section of the screw 2, that is, the supply section A, the compression section B, and the metering section C. Further, among the screw groove portions 2A of the screw 2, the groove portions in the range P for three to four circumferences in the front and rear including the position corresponding to the liquid inlet 3 have a groove depth W equal to the depth of the screw groove portion of the measuring portion C.
It is set to be shallower than W′. Here, the groove depths W' and W'' of the portions other than the range P may be approximately the same as the groove depth of a conventional conventional extruder.The present invention uses an extruder configured as described above. ,
If the liquid additive is directly pressurized into the extruder from the liquid inlet 3 and the main raw material resin is introduced from the hopper, the resin introduced from the hopper is transported forward as the screw 2 rotates and is fed to a heater (not shown). is gradually melted by being heated by
A liquid additive is mixed with the resin which is in a semi-molten or molten state. Here, since the screw groove near the position where the liquid additive is press-fitted has a shallow groove depth W, the flow rate of the resin is extremely high, and therefore the liquid additive flows from the bottom of the groove to the rear. It is evenly dispersed and mixed into the resin without staying in the rising part of the resin. Therefore, it is effectively possible to prevent the additive from concentrating in the center of the extruded product or from causing a portion of the liquid additive to remain attached to the surface of the screw groove without being extruded. In the above explanation, if the range P in which the screw groove depth is set to be shallow is shorter than two circumferences of the groove, the liquid additive is not sufficiently dispersed in the resin within the groove in the range P, and the area in front of the groove is The above-mentioned range P is At least two rounds are required. On the other hand, if the groove depth is set to be shallow throughout the screw 2 from the rear end to the tip, sufficient extrusion force and sufficient kneading effect will not be obtained, so the groove depth should be made shallow. The range P is limited to several laps around the liquid inlet 3,
As mentioned above, it is desirable that the groove depths of the groove portions of the screw 2 near the tip and the rear end be set to be equal to the groove depth of a conventional extruder. In order to sufficiently obtain the effect of uniformly dispersing the liquid additive, as well as to obtain sufficient extrusion force and kneading effect, it is most desirable to set the range P to 3 to 4 times around the groove. Note that if the liquid inlet 3 is provided at a position close to the hopper of the supply section A, the liquid additive is added and mixed while the resin introduced from the hopper is still solid, so the resin may slip. This may result in smooth extrusion, and if the liquid inlet 3 is provided in the metering section C, the distance to the extruder outlet may be short, so the liquid additive may not be sufficiently absorbed into the resin. There is a risk that the liquid will be extruded before it is dispersed, and therefore the liquid inlet 3
It is desirable to provide it in the compression part B or in a part near the compression part B in the supply part A. Furthermore, in some cases, the liquid inlet 3 may be formed in the screw 2, and the liquid additive may be press-fitted from the inside of the screw 2 into the screw groove 2A. Examples and comparative examples of this invention are described below. Example A liquid inlet was formed in the middle of the compression section of a commercially available single-screw extruder with L/D = 22 and 150 mmφ, and the depth of the screw groove in the range of three circumferences around the liquid inlet was 4 mm. It was set to Further, the screw grooves in ranges other than the above range were set to be 6 mm in the supply section and 6 mm in the metering section. This extruder was used to extrude polyvinyl chloride. In addition, n-DOP is used as a plasticizer, and this plasticizer is added to the raw material vinyl chloride.
30wt% was injected through the liquid injection port. Comparative Example A conventional single-screw extruder with L/D = 22 and 150 mmφ (same as the one used in the example except that the depth of the screw groove near the liquid inlet was 11 mm) was used. Extrusion molding of polyvinyl chloride was carried out in the same manner as in the examples. When the extrusion amount when the screw rotation speed was 30 rpm in Examples and Comparative Examples and the content of plasticizer in the center and near the surface of the extruded products obtained in each example were measured, the results shown in the following table were obtained. Ta.

[Table] As is clear from this table, there is almost no difference in the amount of extrusion. It is also clear that in the Comparative Examples, the plasticizer is concentrated in the center of the extruded product, whereas in the Examples, the plasticizer is uniformly dispersed. Furthermore, when we observed the surface condition of the screws used in the above Examples and Comparative Examples, we found that in the screws used in the Comparative Examples, plasticizer remained in the screw grooves attached to the liquid inlet, whereas in the Examples No residual plasticizer was observed in the screws used. As is clear from the above explanation, according to the method of the present invention, liquid additives can be uniformly dispersed in the main raw material resin for extrusion molding, and the additives are not concentrated in the center of the extruded product. Because there is no additive, it is possible to obtain an extruded product with homogeneous and good properties, and there is no risk that part of the liquid additive will remain in the screw groove, so it will not interfere with the operation or adversely affect the quality of the product. You can obtain various beneficial effects such as not having to do anything.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view showing a general example of a conventional single-screw extruder, and Figures 2 and 3 are parts of the extruder for explaining the operation of a conventional single-screw extruder. FIG. 4 is a sectional view showing a cross section of a product extruded by a conventional method, and FIG. 5 is a sectional view showing an example of an extruder used in the extrusion method of the present invention. 1...Cylinder, 2...Screw, 3...Liquid inlet, 4...Hopper.

Claims (1)

[Claims] 1. A liquid inlet is formed in the cylinder or screw of the compression part in a single-screw extruder, and the groove depth of the screw groove within a predetermined range including the position corresponding to the liquid inlet is set to the extruder. Using a single-screw extruder that is made to have a groove depth shallower than that of the screw groove in the metering section, the liquid additive is press-fitted into the extruder from the liquid injection port, and the resin is charged from the hopper. A plastic extrusion method characterized by mixing a resin and a liquid additive in an extruder and extruding the mixture.