JP5085582B2 - Twin screw extruder for devolatilization - Google Patents

Description

  The present invention relates to a devolatilizing twin screw extruder used for removing volatile components contained in plastic raw materials.

  A conventional example of a devolatilizing twin screw extruder used for removing volatile components contained in a plastic raw material will be described.

As shown in FIG. 10, the twin screw extruder disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2006-1252) includes a cylinder 101 and two screws 102 that are rotatably disposed in the cylinder, A rotation drive mechanism (not shown) for rotating the screw 102 is provided. The plastic raw material supplied from the supply port 103 provided on the upstream side of the cylinder 101 is transported to the downstream side of the cylinder 101 by the two screws 102 rotating in the same direction, and is melted by applying a shearing force in the kneading unit 104. Then, the volatile components are transported to the devolatilization region 105 and separated in the devolatilization region 105 that has become negative pressure by the vacuum suction force from the vacuum vent port 107, and are removed to the outside through the vacuum vent port 107.

  In Patent Document 2 (Japanese Patent No. 3857411), in a meshing type co-rotating twin screw extruder, a kneading part and a devolatilization part are alternately provided, so that a plastic is provided at a site corresponding to a vacuum vent port. A kneading unit is disclosed in which a screw piece having a high ability to stir the raw material is provided to reflow the plastic raw material from the downstream side to the upstream side to renew the surface.

JP 2006-1252 A Japanese Patent No. 3857411

  The extruder disclosed in Patent Document 1 is provided with a kneading flight twisted so that the plastic raw material can be transported in the downstream direction in the devolatilization region, and updates the surface of the plastic raw material while mixing.

  However, in order to increase the number of surface renewals, it is necessary to lengthen the residence time of the plastic raw material in the devolatilization region, so that the filling rate of the plastic raw material in the devolatilization region increases. As a result, the exposed surface area of the plastic raw material exposed under reduced pressure decreases, and conversely, the devolatilization ability may decrease. Therefore, in order to obtain sufficient devolatilization capability, a screw piece with high transport capability that does not fill the plastic material inside the cylinder is installed so that the exposed surface area of the plastic raw material in the devolatilization area does not decrease. There is a problem that the area must be set long.

  In the invention disclosed in Patent Document 2, a surface renewal screw is provided at a portion corresponding to the vacuum vent port. Therefore, there is a possibility that the plastic raw material swells up and closes the vent port so that the vent port does not function.

  The present invention has been made in view of the above-described problems of the conventional example, and by increasing the number of surface renewals without reducing the exposed surface area of the plastic raw material, the volatile components contained in the plastic raw material can be efficiently removed. An object of the present invention is to provide a devolatilizing twin screw extruder.

In order to achieve the above object, a devolatilizing twin-screw extruder according to the present invention includes a temperature-adjustable cylinder, two screws rotatably disposed in the cylinder, and a rotational drive that rotates the screw. In the devolatilization twin screw extruder comprising a kneading section, a devolatilization area having a vacuum vent port, and a raw material filling section in order from the upstream side to the downstream side where the supply port is provided. In the volatilization area, an expansion cylinder having an expansion amount equivalent to 0.01 to 0.15 times the inner diameter of the cylinder in the kneading part or the raw material filling part is arranged on the upper side of the inner wall surface of the cylinder, and In the expansion cylinder, a screw piece having a surface renewability is provided in an upstream side portion avoiding the portion immediately below the opening of the vacuum vent port .

  Since this invention is comprised as mentioned above, there exists an effect as described below.

  By providing a cylinder with an enlarged internal space volume in the devolatilization region, it is possible to increase the number of surface renewals without reducing the exposed surface area of the plastic raw material. As a result, the contained volatile components can be efficiently removed.

It is explanatory drawing which shows the principal part of the twin-screw extruder for devolatilization by one Embodiment of this invention. An example of a surface renewal screw piece is shown, (a) is a side view, (b) is a front view seen from the axial direction. An example of a surface renewal screw piece is shown, (a) is a side view, (b) is a front view seen from the axial direction. It is a perspective view which shows an example of the expansion cylinder segment which concerns on this invention. It is a perspective view which shows the other example of the expansion cylinder segment which concerns on this invention. FIG. 3 is an explanatory view showing a main part of a devolatilizing twin screw extruder according to Example 1; 6 is an explanatory view showing a main part of a devolatilizing twin screw extruder according to Example 2. FIG. It is explanatory drawing which shows the principal part of the twin-screw extruder for devolatilization by a comparative example. It is a graph which shows devolatilization ability about Example 1, 2 and a comparative example. 2 shows a devolatilizing twin screw extruder according to a conventional example, in which (a) is a schematic side view of a cylinder, and (b) is a schematic side view of a screw.

  An embodiment of a devolatilizing twin screw extruder according to the present invention will be described.

  FIG. 1 is an explanatory view showing a main part of a devolatilizing twin screw extruder according to an embodiment. The devolatilizing twin-screw extruder 11 includes a temperature-adjustable cylinder 12, two meshing screws 14 rotatably disposed in a hollow portion of the cylinder 12, and two screws 14 rotating in the same direction. A rotation drive mechanism is provided. And the kneading part 17, the devolatilization area | region 16, and the raw material filling part 15 are arrange | positioned sequentially toward the downstream from the upstream of the cylinder 12 provided with the supply port (not shown).

  The cylinder 12 is configured by connecting a plurality of cylinder segments in the axial direction, and a evacuation region 16 is provided with a vacuum vent port 13 and an enlarged cylinder segment 19 on the upstream side of the vacuum vent port.

  The screw 14 is configured by connecting a plurality of screw pieces in the axial direction, and a surface renewal screw piece 18 is provided in the devolatilization region 16 at an upstream side portion avoiding directly under the opening of the vacuum vent port 13. Yes.

  The vacuum vent port 13 is connected to an unillustrated evacuation device, and when evacuated by the evacuation device, the devolatilization region 16 is in a negative pressure state, and volatile components contained in the plastic raw material are gasified and separated. However, it is configured to be removed outside the machine.

  When a plastic raw material is supplied from a supply port (not shown) of the twin screw extruder, it is transported to the kneading section 17 downstream of the two screws 14 rotating in the same direction in the cylinder 12 and filled with the kneading section 17. The devolatilization region 16 is kept airtight and transported to the devolatilization region 16. The plastic raw material transported to the devolatilization region 16 is transported downstream while the surface renewal screw piece 18 exchanges the surface portion and the inside, and the volatile components contained in the plastic raw material are separated and removed. It is discharged through the part 15.

In the present invention, the surface renewal screw piece 18 may be of any kind as long as it is a kneading piece having a transport ability in the downstream direction, but FTKD (Forward Twist) shown in FIG.
Kneading Disk) and FKD (Forward Kneading Disk) shown in FIG. 3 are preferable.

  As shown in FIG. 2, the FTKD has five disks arranged with a phase angle θ (45 °) around the screw axis, and each disk is substantially elliptical when viewed from the axial direction of the screw. The flight chip (chip lead angle α) protrudes from both ends on the long axis side. Further, as shown in FIG. 3, the FKD has five discs arranged with a phase angle θ (45 °) around the screw axis.

  The phase angle θ is not limited to 45 °, and can be set to an angle of 30 °, 60 °, etc. depending on operating conditions.

  An expanded cylinder segment 29 having an inner diameter larger than the inner diameter of the cylinder 12 in the kneading part 17 and the raw material filling part 15 is provided in the devolatilization region 16 in which the surface renewal screw piece 18 is provided. As shown in FIG. 4, the expanded cylinder segment 19 is formed by scraping the upper side of the inner wall surface of the cylinder of the kneading part 17 and the raw material filling part 15 (hereinafter referred to as “standard cylinder”) to expand the inner diameter. It is preferable that the ratio δ / D of the cutting amount δ with respect to the inner diameter D of the cylinder is in the range of 0.01 to 0.15.

  In addition, as shown in FIG. 5, the shape which scraped off the upper side of the inner wall surface of the standard cylinder by the cutting amount δ may be used.

  In the present invention, by expanding the cylinder internal space volume like the enlarged cylinder segments 19 and 29, the plastic raw material is not excessively filled in the cylinder, and the volatile components contained in the plastic raw material are efficiently separated and removed. Is done.

(Extrusion conditions)
Raw material: LDPE (M1 = 2) [Texct manufactured by Nippon Steel Works]
Contained volatile components: n-Hex (3000 ppm)
Cylinder inner diameter: 69φmm
Raw material throughput Q: 150-250 Kg / h
Screw rotation speed: 100-250rpm
The structure of the cylinder screw used in the experiment is shown in FIGS.

  In Example 1 shown in FIG. 6, an expansion cylinder segment 19 in which δ / D = 0.01 was provided in the devolatilization region 16.

  In Example 2 shown in FIG. 7, an expansion cylinder segment 19 in which δ / D = 0 · 15 was provided in the devolatilization region 16.

  The surface renewal screw piece 18 was provided with three sets of FTKD (L / D = 0.2D × 5 sets, phase angle θ = 45 ° thrust in the forward direction, chip lead = 6.0 × D).

  The comparative example shown in FIG. 8 is different from the example in that the standard cylinder is used instead of the expansion cylinder of the example in the devolatilization region. The shaving amount (enlargement amount) δ / D is preferably in the range of 0.01 to 0.15.

  When δ / D is smaller than 0.01, since it is almost the same as the space volume of the standard cylinder, a large increase in the exposed surface area cannot be expected, and an effect commensurate with the effort and cost of scraping the cylinder cannot be expected.

  On the other hand, when δ / D is larger than 0.15, the plastic raw material may stay in the extruder for a long time and burns may occur.

  FIG. 9 shows the experimental results. FIG. 9 shows the devolatilization ability in Examples 1 and 2 and the comparative example. As evaluation of the devolatilization ability, the devolatilization rate of the raw material throughput (Q) = 150 kg / h in the comparative example was set to 1, and the devolatilization rate in Examples 1 and 2 was compared.

  The devolatilization rate is 1-Cout / Cin.

Where Cout = concentration of volatile components contained in the raw material discharged from the extruder
Cin = Concentration of volatile components contained in raw material before being supplied to the pressing machine From FIG. 9, by using an expansion cylinder as in Examples 1 and 2, it is possible to improve the devolatilization capacity over the standard cylinder. did it. In Example 2 (θ / D = 0.15 expansion cylinder), compared with the comparative example, about 9% at the raw material throughput Q = 150 kg / h, about 14% at the raw material throughput Q = 250 kg / h, devolatilization Ability improved.

  Moreover, since the devolatilization capability at the raw material throughput Q = 250 kg / h in Example 2 is equal to or higher than the devolatilization capability at the raw material throughput Q = 150 kg / h in the comparative example, the surface renewal screw piece By deploying an expansion cylinder at the position where it is located, even if the raw material throughput was increased by about 67% compared to the conventional configuration, the devolatilization capability equal to or higher was obtained.

  In addition, in the said Example, although the result when the devolatilization area | region is one place is shown, when devolatilizing with a twin screw extruder, a devolatilization area | region may be arranged in multiple places, Even in that case Similar effects can be obtained.

DESCRIPTION OF SYMBOLS 11 Devolatilization twin screw extruder 12 Cylinder 13 Vacuum vent port 14 Screw 15 Raw material filling part 16 Volatilization area 17 Kneading part 18, 28 Surface renewal screw piece 19, 29 Expansion cylinder segment

Claims (1)

A temperature-adjustable cylinder, two screws rotatably disposed in the cylinder, and a rotation drive mechanism that rotates the screw, and sequentially from the upstream side to the downstream side where the supply port is provided In a devolatilization twin screw extruder equipped with a kneading part, a devolatilization area having a vacuum vent, and a raw material filling part,
In the devolatilization area, an expansion cylinder having an expansion amount corresponding to 0.01 to 0.15 times the inner diameter of the cylinder in the kneading part or the raw material filling part is arranged on the upper side of the inner wall surface of the cylinder . A devolatilizing twin screw extruder , wherein a screw piece having a surface renewability is provided in an upstream portion of the expansion cylinder so as to avoid directly under the opening of the vacuum vent port .

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