JPS6256114A - Manufacturing device for thermoplastic resin foam - Google Patents

Abstract

PURPOSE:To permit to shorten the length of a main kneading shaft and restrict the generation of heat due to cavities in the main kneading shaft and a barrel to a low degree by a method wherein a resin and a foaming agent, which are extruded by a screw, is kneaded preliminarily by the protuberance of a preliminary kneading shaft. CONSTITUTION:The length of a main kneading shaft 9 is 2-8 times of the diameter of a screw and the length of a preliminary kneading shaft 8 is 1-7 times of the diameter of the screw. The screw 7 and a main shaft 19 are rotated into arrow sign directions A, B while resin is supplied into a barrel 6 through a throwing port 14. Then, the resin is sent to an arrow sign direction C by the screw 7 and is molten by heating by a heater 15 during sending. Foaming agent is injected into the molten resin from a foaming agent injecting port 13 and the resin is mixed with the foaming agent preliminarily by a protuberance 10 provided on the preliminary kneading shaft 8. The resin, including the foaming agent, is forced into gap between the main kneading shaft 9 and the barrel 6 and is kneaded by cavities 11, 12, therefore, the foaming agent is dispersed uniformly into the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for producing thermoplastic resin foam.

(Prior art) As a method for uniformly mixing synthetic m fat, JP-A No. 5
There is an extrusion mixer described in Japanese Patent No. 7-87844.

This has a hollow cylindrical stator and a cylindrical rotor rotatably supported within the stator. The cavity is located between the cavities of the rotor, and is attached to a normal extruder.
The stator is connected to the barrel of the extruder, and the rotor is
Connected to the extruder screw tip.

When the resin is extruded into the extrusion mixer by the rotation of the screw, the resin is sheared by the cavities of the rotor and stator and is efficiently kneaded.

(Problems to be Solved by the Invention) According to the above-mentioned conventional configuration, resin can be kneaded efficiently, but there is a problem when producing a resin foam by adding a blowing agent to the resin. .

In other words, the appropriate foaming temperature range for the foaming agent is relatively narrow, and at temperatures lower than that range, only insufficient foaming occurs.
Temperatures higher than that range will result in premature foaming. Therefore, a heater is usually installed around the outer periphery of the barrel to control the temperature. However, while the extrusion mixer mentioned above can efficiently knead the greaseproofing material, it easily generates heat and does not allow the foaming agent to properly foam. There is a risk of exceeding the temperature range.

In particular, when using an easily volatile foaming agent that is liquid at room temperature,
The negative effects are noticeable.

The present inventor has discovered that if the resin and blowing agent are pre-kneaded, the resin can be sufficiently kneaded even if the length of the rotor and stator is shortened, and on the other hand, the heat generation can be kept low. I discovered that it is possible. The present invention is based on this discovery.

(Means for solving the problem) In order to solve the above problem, the thermoplastic resin foam production equipment of the present invention rotatably supports a screw in a barrel in a cantilevered manner, so that the tip of the screw in the barrel is In an extruder with a resin discharge port, a pre-kneading shaft and a main kneading shaft are arranged concentrically in this order at the tip of the screw inside the barrel, and the pre-mixing shaft has many protrusions, and the main kneading shaft has many protrusions. The outer circumferential surface of the kneading shaft is brought close to the inner circumferential surface of the barrel, and a number of isolated cavities are formed on the outer circumferential surface of the main kneading shaft and the opposing inner surface of the barrel, and the cavities on the inner circumferential surface of the barrel are brought close to the inner circumferential surface of the main kneading shaft. The blowing agent pressure inlet is provided on the upstream side of the pre-mixing shaft of the barrel, and the length of the main kneading shaft is 2 to 8 times the screw diameter, and the length of the pre-mixing shaft is set to be 2 to 8 times the screw diameter. It is 1 to 7 times that of

In the above configuration, the resin supplied into the barrel is extruded by the rotation of the screw, the foaming agent is added from the foaming agent injection port, and after being preliminarily kneaded by the protrusion of the pre-mixing shaft, The resin is pushed into the gap between the main kneading shaft and the barrel, is efficiently kneaded by the main kneading shaft and the cavity of the barrel, is cooled by a cooler, and then discharged from the die and foamed to produce a resin foam.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. 1 is an extruder, and 2 is a cooler, which are arranged parallel to the extruder 4111 and off-center from the extruder 1.

3 is a resin supply pipe connecting the outlet 4 of the extruder 1 and the inlet 5 of the cooler 2.

The extruder 1 is comprised of the following:

6 is a barrel, 7 is a cantilever type screw rotatably inserted into the barrel 6, 8.9 is a pre-kneading shaft and a main kneading shaft that are concentrically connected to the tip of the screw 7, and 10 is a spare. Kneading shaft 8
A large number of protrusions 11 and 12 are implanted in the main kneading shaft 9 and the opposing inner circumferential surface of the barrel 6 are formed in a large number of isolated hemispherical pain-shaped cavities,
The cavity 12 of the barrel 6 is connected to the cavity 11 of the main kneading shaft.
It is positioned straddling between the two. The outer peripheral surface of the main kneading shaft 9 is close to the inner peripheral surface of the barrel/I/6. Reference numeral 13 indicates a blowing agent pressure inlet provided at a location opposite to the boundary between the pre-kneading shaft 8 and the screw 7 of the barrel 6, 14 indicates a resin inlet formed at the end of the screw support side of the barrel 6, and 15 indicates a barrel. 6
This is a heater provided on the outer peripheral surface of the

The cooling device 2 includes the following: The device 17 is an outer cylinder, and has a spiral refrigerant passage 18. 19 is a cantilevered main shaft rotatably inserted into the outer cylinder 17, 20 is a base with a discharge port 21 provided at the tip of the outer cylinder 17, and 22 is a refrigerant in the cooling space formed in the main shaft 19. This is a refrigerant supply pipe for supplying refrigerant. The main shaft 19 has a base end large diameter portion 19A rotatably supported by the outer cylinder 1 via a bearing 23.
It is composed of a central small diameter part 19B and a tip large diameter part 19C, and an annular protrusion 19D is provided at a location slightly downstream from the location of the central small diameter part 19B facing the injection port 5. Reference numeral 24 designates a large number of hurdle-shaped kneading rods protruding from the annular protrusion 19D of the central small diameter portion 19B.

The length of the main kneading shaft 9 is 2 to 8 times (preferably 4 to 6 times) the diameter of the screw.

If it is less than 2 times, kneading will be insufficient, and if it is more than 8 times, heat generation will be too large.

The length of the pre-kneading shaft 8 is 1 to 7 times the screw diameter (
(preferably 2 to 5 times).

If it is less than 1 times, preliminary kneading will be insufficient, and if it is more than 7 times, the kneading effect will not be improved any further.

If the resin passing cross-sectional area of the pre-mixing shaft 8 is larger than the resin passing cross-sectional area of the tip of the screw 7 (preferably 15 to 3 times), and vice versa, the pre-mixing shaft 8 The amount of resin supplied on top becomes excessive, making it impossible to perform sufficient preliminary kneading. The protrusion 10 provided on the pre-mixing shaft 8 may be a cylindrical bottle, a screw slide cut out, or a dalmage.

The operation of the above configuration will be explained below. The screw 7 and the main shaft 19 are rotated in the directions of arrows A and B, respectively, and raw material, that is, resin, is supplied into the barrel 6 from the input port 14. Then, the resin is sent in the direction of arrow C by the screw 7, during which time it is heated and melted by the heater 15. A foaming agent is press-injected into the molten resin from the foaming agent injection port 18, and the foaming agent and resin are preliminarily mixed by the projections 10. Next, the foaming agent-containing resin is forced into the gap between the main kneading shaft 9 and the barrel 6, and is pushed into the cavity 11.1.
2, the blowing agent is evenly dispersed within the resin. The principle of kneading will be explained using wires using the schematic diagrams shown in FIGS. 3a to 3h. First, the filament that comes out from the bottom of the cavity 12 on the forgetting side in Figure A extends along the inner circumferential surface of the cavity 12, and as shown in Figure A, the tip of the filament is directed in the direction of the arrow. It is pulled by the edge (a) between the cavities 11 of the rotating main kneading shaft 9 and changes its direction, resulting in the state shown in figure C, and the tip of the filament is bent by the edge (b) as shown in figure d. As shown in Figure C,
The tip of the filament is cut by the rim (f) and the barrel 6, and as shown in figure f, the tip of the filament is bent by the edge (c), and as shown in figure g, the edge (c) and The tip of the filament is cut off by the barrel 6, and as shown in the figure, the tip of the filament is bent by the edge. Thereafter, the same operation is repeated, the tips of the filaments are cut one after another, and the cut filament portions accumulate in the cavity 12. Therefore, according to this principle, the resin is stretched thin like the above-mentioned filaments and cut into small pieces, and the foaming agent is evenly dispersed within the resin. Next, the foam with the foaming agent evenly dispersed passes through the supply W3 to the outer cylinder 17 of the cooler 2.
The large diameter portion 19C and the outside are kneaded by the hurdle-shaped kneading rod 24 that rotates in the direction of arrow B. Pass through the gap between the cylinder 17 and the discharge port 21
It is then extruded and foamed.

Next, a first concrete example will be explained. The inner diameter of the barrel 6 is 50 m, the diameter of the screw 7 is 50 + 1 m, the length of the pre-kneading shaft 8 is 250 m, and the length of the main kneading shaft 9 is 2 m.
50m, and the gap between the main kneading shaft 9 and the barrel 6 is α4.
For cod, six cavities 11 and 12 were provided in the circumferential direction and seven rows in the axial direction on the main kneading shaft 9 and the barrel 6, respectively, and the diameter of cavity 1 was 245 mm, the depth was 8 m, and The diameter of 12 is 28m, and the depth is 9
．． 5 sheaths, the spacing between the cavities 11 and 12 was set to 22 mm, the rotational speed of the screw 7 was set to 106 rprn, the temperature of the melt passing through the cooler 2 was adjusted to 123°C, and the discharge port of the cap 20 was adjusted to 123 °C. The width of 21 was 100 fl, and the height was INrIl.

In this configuration, polystyrene (Stylon 679 (M-17) manufactured by Asahi Kasei Corporation) is used as the base resin, and 0.3 parts by weight of talc as a bubble regulator and hexabromo as a flame retardant are added to 100 parts by weight of the base resin. Cyclododecane2. ．． A uniformly mixed mixture of 0 parts by weight is supplied as a raw material to extruder 1, and the extrusion 1!11 is carried out at a rate of 5 parts per hour.
It was operated so that the raw material was extruded at a rate of 5 kg. Further, 1245 parts of difluoromethane as a foaming agent was press-injected into 100 parts by weight of the base resin through the foaming agent injection port 13.

As a result, it was possible to obtain a plate-shaped foam having a width of about 250 fl, a thickness of about 25+ am, and a density of 40 to 7/- throughout the sizer attached to the cap 20 (see the attached table).

Note that the comparative example in the attached table shows the case where the main kneading shaft 9 was removed and the cavity 12 of the barrel 6 was eliminated.

As is clear from the attached table, according to the specific examples of the present invention, it was possible to obtain a uniformly foamed foam.

(Effects of the Invention) As described above, according to the present invention, since the resin and blowing agent extruded by the screw are preliminarily kneaded by the protrusions of the premixing shaft, the length of the main kneading shaft can be reduced. The screw diameter can be limited to 2 to 8 times the diameter of the screw, making it shorter than conventional screws, and the heat generated by the main kneading shaft and the cavity of the barrel can be kept low. Therefore, the temperature of the resin passing through the barrel can be maintained within the appropriate foaming temperature range, and even if an easily volatile foaming agent is used, there is no risk of premature foaming, and the foam can be foamed as specified. You can get a body.

Further, problems such as a decrease in the molecular weight of the resin and decomposition of additives such as flame retardants do not occur.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Fig. 1 is a longitudinal sectional view, Fig. 2 is a view taken along the ■-■ arrow in Fig. 1, and Fig. 8 a to h are schematic diagrams showing the principle of kneading using cavities. It is an explanatory diagram. In each figure, l is an extruder, 2 is a cooler, 6 is a barrel,
7 is a screw, 8 is a pre-kneading shaft, 9 is a main kneading shaft, IO is a protrusion, 11.12 is a cavity, and 18 is a blowing agent injection port.

Claims (2)

[Claims] (1) In an extruder in which a screw is rotatably supported in a cantilever type in a barrel, and the tip of the screw in the barrel is used as a resin discharge port, a pre-kneading shaft and a main kneading shaft are attached to the tip of the screw in the barrel. They are arranged concentrically in this order, have a large number of protrusions on the pre-kneading shaft, and bring the outer peripheral surface of the main kneading shaft close to the inner peripheral surface of the barrel. A number of isolated cavities are formed on the circumferential surface, and the cavities on the inner circumferential surface of the barrel are located across the cavities of the main kneading shaft, and a blowing agent pressure inlet is provided upstream of the pre-kneading shaft of the barrel. 1. An apparatus for producing thermoplastic resin foam, characterized in that the length of the kneading shaft is 2 to 8 times the diameter of the screw, and the length of the pre-kneading shaft is 1 to 7 times the diameter of the screw. (2) The apparatus for producing a thermoplastic resin foam according to claim 1, characterized in that the cross-sectional area of resin passing through the pre-kneading shaft portion is larger than the cross-sectional area through which the resin passes through the screw tip portion.