JPH11277604A - Extruder screw - Google Patents

Abstract

(57) [Problem] To suppress an increase in resin temperature of an extruder having a degassing part and to obtain good degassing performance. SOLUTION: A plurality of deaeration sections D1 to D3 are formed in a screw 2 of an extruder with a plurality of kneading sections C1 to C3 interposed therebetween. The side walls on both sides of the screw 2 of the screw flight of the deaeration sections D1 to D3 are continuous from the flight top to the groove bottom. Of these two side walls,
The surface of the screw 2 on the upstream side in the lead direction is
The flight top side and the groove bottom side have a curved surface shape that connects smoothly, and the surface on the downstream side with respect to the lead direction of the screw 2 has a vertical plane shape orthogonal to the groove bottom surface. I have.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw for an extruder, and more particularly to a screw for an extruder having a deaeration section at the rear of a kneading section of a co-rotating twin screw extruder.

[0002]

2. Description of the Related Art As a conventional screw of an extruder having a deaeration section, there is one disclosed in Japanese Patent Application Laid-Open No. Hei 7-164509. In the vacuum vent portion (degassing portion) of the cylinder of the extruder, the screw fitted to the cylinder hole is a two-shaft that meshes and rotates in the same direction as shown in FIG. At the same time, the flight of the screw is formed in a shape called full flight as shown in FIG. FIG. 7 shows a line FF orthogonal to the lead direction of the screw flight in FIG.
2 shows a cross section along the line. That is, the side wall on both sides of the screw flight has a curved R2 shape on the left side (upstream side) in FIG. 7 and smoothly connects to the groove bottom 2d, and the side wall on the right side (downstream side) in FIG. The curve R1 is smoothly connected to 2d. As the screw, a plurality of screw segments 2a as shown in FIG. 6 (a) are axially fitted to a central shaft (involute spline shaft), and each meshes with a mating side to form a complete mesh type full. A flight screw is formed. As a result, as shown in FIG. 6A, the gap between the meshing portions 2c for each segment 2a becomes substantially uniform over the entire length in the left-right direction in the figure, and the resin can be strongly conveyed. The performance of removing volatile components contained in the resin, that is, the so-called degassing performance is enhanced.

[0003]

However, in the screw of the conventional extruder as described above, the resin receives a large shearing force at the meshing portion 2c of the deaeration portion.
There is a problem that the resin temperature becomes higher than a predetermined value due to heat generation due to shear friction, which may adversely affect the physical properties of the resin product. If the rotation speed of the screw is reduced to suppress such a rise in the resin temperature, the conveyance force is reduced and deaeration is not sufficiently performed.
The concentration of volatile components remaining in the resin product increases, which adversely affects the physical properties and shape accuracy of the resin product. An object of the present invention is to solve such a problem.

[0004]

According to the present invention, in the degassing zone of an extruder, the resin temperature is kept from becoming too high without lowering the rotation speed of the screw, and the residence time of the resin is made longer than before. By doing so, the above-mentioned problem is solved. That is, the screw of the extruder of the present invention is intended for the one in which the deaeration section (D) is provided at the rear of the kneading section of the meshing co-rotating twin screw extruder. In addition, gaps (S1, S2) are provided in the meshing portion (2C) of the screws (2, 2) of the degassing portion (D) so as to suppress shear friction and increase the residence time of the molten resin. And According to the second aspect of the present invention, the deaeration section (D) is provided at a plurality of locations, and the screw (2) of the screw transport section corresponding to the deaeration section (D) includes: Screw flight on the downstream side in the lead direction (2
B) A feature is that a flight-shaped screw zone is provided in which the side wall surface is a vertical plane orthogonal to the groove bottom (2D) surface. In addition, the code | symbol in a parenthesis shows the corresponding member of embodiment.

[0005] The raw material supplied from the raw material supply section of the extruder is melted and kneaded into a molten state, and then water is supplied into the cylinder in the kneading section, where the resin and water are kneaded and dispersed, and then degassed. In the section (degassing zone), volatile components in the resin are vaporized and removed together with water and discharged to the outside. At this time, in the degassing section, the resin conveyed from the upstream side to the downstream side suppresses the shear friction by the gap actively provided in the meshing section, and partially passes through the gap in the meshing section. Therefore, the gas flows backward from the downstream side to the upstream side. Therefore, it is possible to prevent the temperature from excessively increasing due to the shear friction, and it is possible to sufficiently deaerate the resin in the deaeration section longer than before, without increasing the resin temperature as in the conventional case. it can. Further, the resin surface degassed can be improved by the behavior of the resin due to the rotation of the screw in the gap. That is, by providing the gaps (S1, S2), the resin does not need to be excessively sheared, so that the resin is less likely to be denatured and deteriorated, and the surface shape when extruded into a molded product is improved.

[0006]

1 to 3 show an embodiment of the present invention. FIG. 1 shows a twin-screw 2 in a case where the present invention is applied to a water injection foaming twin-screw extruder (in the figure, the back screw is hidden behind the front screw and is not visible). From the upstream side on the left side in the figure, the pressure reducing section A, the raw material supply section B, the first kneading section C1, the first deaeration section D1, the second kneading section C2, and the second
Through the zones of the deaeration section D2, the third kneading section C3, and the third deaeration section D3, they are pushed to the outside from the downstream side on the left side in the figure. In the water injection foaming twin screw extruder, water is supplied to the resin that has been melt-kneaded in the kneading section, and after being kneaded and dispersed, volatile components in the resin are vaporized and removed together with water in the deaeration section. After that, foaming of the resin is performed. The first degassing section D1 and the second degassing section D
2. The third deaeration section D3 (hereinafter simply referred to as "deaeration section D" unless otherwise specified) is formed by fitting a plurality of screw segments 2A as shown in FIG. The number of segments is slightly different (in the present embodiment, D
1 = 4, D2 = 3, and D3 = 3). Others have the same shape.

As shown in FIG. 2A, a meshing portion 2C of the two screw segments 2A, 2A in the degassing portion D is provided.
Is a gap S1 on each side of the screw flight 2B,
S2 is formed. That is, the screw flight 2B of the deaeration section D is viewed from a cross section along the line EE perpendicular to the flight lead direction, and as shown in FIG. A curved line R smoothly connects to the groove bottom 2D, and a vertical line L perpendicular to the groove bottom 2D is formed on the right (downstream) side wall in the figure. That is, when viewed from the direction of the resin flow, the front portion of the flight is formed in a square flight shape.
Such a flight shape (conventional “full flight”
Let's call it "half-width flight." By using such a half-width flight, the shearing action that the resin undergoes when passing through the meshing portion 2C can be made smaller than before, and accordingly, the amount of heat generated by the shearing is small so that the resin temperature does not become too high. be able to.
Further, since a part of the resin flows backward from the downstream side to the upstream side through the gaps S1 and S2, the residence time of the resin can be made longer than before, and sufficient deaeration is performed during this residence. be able to. Further, the resin surface degassed can be improved by the behavior of the resin due to the rotation of the screw in the gap. That is, since the gaps S1 and S2 are provided, the resin does not need to be excessively sheared.
It is less likely to be denatured and deteriorated, and the surface shape when extruded into a molded product is improved.

Next, the operation of this embodiment will be described.
In FIG. 1, a raw material is supplied in a raw material supply unit B. In the exhaust part A, volatile matter separated during the supply of the raw material is removed.
Next, the raw materials are melt-kneaded to be in a molten state. Next, water is supplied into the cylinder in the first kneading section C1, and the resin and water are kneaded and dispersed. Then, in the first deaeration section D1, volatile components in the resin are vaporized and removed together with the water, and the resin is discharged to the outside. Is discharged. The same operation is sequentially repeated in the second kneading section C2, the second deaeration section D2, the third kneading section C3, and the third deaeration section D3 to perform kneading and deaeration of the resin. On this occasion,
The resin is subjected to a shearing action only at the top of the screw flight 2B in the degassing section D, and the gaps S1,
Since almost no shearing action is applied to the portion S2, the shearing friction is suppressed. Therefore, in the degassing section D, there is no danger that the temperature of the resin becomes too high and impurities due to denaturation increase. The resin conveyed from the upstream side to the downstream side has a portion of the resin from the gap S1 side through the gap on the top side of the screw flight 2B in the gap S2 side in the meshing portion 2C in FIG. Therefore, the residence time of the resin in the degassing section D is set to be longer than in the conventional case. Volatiles can be degassed. In addition, the resin surface degassed is improved by the behavior of the resin due to the rotation of the screw in the gap. The resin thus degassed is extruded from the extrusion port on the right side in the figure, not shown.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 6 (and FIG. 7), a conventional full flight screw (abbreviated as "FF" in FIGS. 4 and 5) and a half-width flight (abbreviated as "HSF": flight) of the present invention. An extrusion test of the resin was performed using a screw having a front part in a square flight shape), and the concentration of volatile components contained in the resin product and the resin temperature were measured. The extruder used was a model number: TEX65XC manufactured by Japan Steel Works, Ltd.
T-38.5PW-4V. The L / D (length / diameter) and lead of the screw were the same for "FF" and "HSF". The raw material used was L-LDPE, and the hexane (volatile content) concentration in the raw material was 5 wt%. FIG. 4 shows a comparison diagram of the concentration of volatile components remaining in the resin product, and FIG. 5 shows a comparison diagram of the resin temperature. It can be seen that the volatile matter concentration of the product according to the present invention is almost halved over the entire range of the screw rotation speed as compared with the conventional product, and the degassing performance is improved about twice. In addition, the resin temperature at the time of extrusion is approximately 10% over the entire range of the screw rotation speed in the present invention as compared with the conventional one.
° C lower. That is, as compared with the conventional temperature range in which the physical properties of the resin may be adversely affected, the temperature range has shifted to a safer temperature range, and the risk of generation of impurities due to denaturation and deterioration of the resin has been reduced.

In the description of the above embodiment,
Although the present invention was implemented in a water injection foaming twin-screw extruder, the present invention is not limited to this, and it is clear that the present invention can be applied to other types of extruders that require degassing. It is. Further, in the description of the above embodiment, the kneading section and the deaeration section are provided at three places, respectively, but the number of the kneading sections and the deaeration section is determined according to the required kneading degree and the deaeration degree. It may be increased or decreased.

[0011]

As described above, according to the present invention, when extruding a resin with a twin-screw extruder, the degassing performance can be enhanced without increasing the temperature of the resin as in the conventional case. it can. Therefore, it is not necessary to prevent the temperature of the resin from becoming too high, thereby increasing impurities due to denaturation and deterioration, or to adversely affect the physical properties of the resin due to insufficient degassing. In addition, the surface of the resin to be degassed can be improved by the behavior of the resin in the gap.
That is, by providing the gaps (S1, S2), the resin does not need to be excessively sheared, so that the resin is less likely to be denatured and deteriorated, and the surface shape when extruded into a molded product is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a screw corresponding to a deaeration unit according to an embodiment of the present invention.

FIGS. 2A and 2B are external views showing a segment corresponding to a deaerating portion of the meshing screw according to the present invention, wherein FIG. 2A is a plan view and FIG. 2B is a side view.

FIG. 3 is a cross-sectional view taken along line EE in FIG. 2 (a), showing a shape (half-width flight) of a screw flight corresponding to a degassing portion.

FIG. 4 is a diagram showing the product volatile content concentration with respect to the screw rotation speed in comparison between a conventional screw flight and that of the present invention.

FIG. 5 is a diagram showing the resin temperature with respect to the screw rotation speed in comparison between a conventional screw flight and that of the present invention.

6A and 6B are external views showing segments of a conventional fully meshing screw, in which FIG. 6A is a plan view and FIG. 6B is a side view.

FIG. 7 is a cross-sectional view taken along the line FF of FIG. 6 (a), showing a screw flight shape (full flight).

[Explanation of symbols]

 2 Screw 2A Screw segment corresponding to deaeration section 2B Screw flight corresponding to a deaeration section 2C Engagement section 2D Groove bottom 3 Center axis B Raw material supply section C1, C2, C3 Kneading section D1, D2, D3 Deaeration section L Vertical Line R curve

Claims (2)

[Claims] An extruder screw (2) provided with a deaeration section (D) at the rear of a kneading section of an interlocking co-rotating twin screw extruder, wherein the screw (2) of the deaeration section (D) is provided. 2) A screw for an extruder, wherein gaps (S1, S2) are provided in a meshing portion (2C) of the two to suppress shear friction and increase a residence time of a molten resin. 2. A screw (2) of an interlocking co-rotating twin-screw extruder in which a deaeration section (D) is provided at a rear portion of a kneading section, the deaeration section (D) is provided at a plurality of positions. In addition, a screw flight (2B) side wall surface on the downstream side with respect to the lead direction is provided on the screw (2) of the screw transport unit at a position corresponding to the deaeration unit (D). Groove bottom (2
D) A screw of an extruder, wherein a flight-shaped screw zone having a vertical plane perpendicular to the plane is provided.