JPH0221926B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a thermoplastic resin foam manufacturing apparatus. (Conventional technology) For uniformly mixing synthetic resins,
There is an extrusion mixer described in JP-A-57-87344. This has a hollow cylindrical stator and a cylindrical rotor rotatably supported within the stator. It is attached to a normal extruder, and the stator is connected to the barrel of the extruder, and the rotor is connected to the barrel of the extruder.
Connected to the screw tip of the extruder. When the resin is extruded into the extruder 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-described conventional structure, resin can be efficiently kneaded, but there is a problem when producing a resin foam by adding a blowing agent to the resin. That is, the proper foaming temperature range of the foaming agent is relatively narrow, and temperatures lower than that range will only result in insufficient foaming, while 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 described above can efficiently knead the resin, it easily generates heat, and the appropriate foaming temperature of the blowing agent cannot be adjusted. There is a risk of exceeding the range.
In particular, when a readily volatile foaming agent that is liquid at room temperature is used, its adverse effects are significant. The present inventor has discovered that if the resin and foaming 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. discovered. The present invention is based on this discovery. (Means for Solving the Problems) In order to solve the above problems, the thermoplastic resin foam manufacturing apparatus of the present invention rotatably supports a screw in a barrel in a cantilevered manner, and the tip of the screw in the barrel In an extruder with a resin discharge port, a pre-kneading shaft and a main kneading shaft are connected concentrically in this order at the tip of the screw in the barrel, and the pre-kneading shaft has many protrusions, and the main kneading shaft The outer circumferential surface of the 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 inner circumferential surface of the barrel opposite thereto. The blowing agent injection port is provided on the upstream side of the pre-kneading shaft of the barrel, and the length of the main kneading shaft is 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 pushed out by the rotation of the screw,
The foaming agent is added through the foaming agent injection port, and after being preliminarily kneaded by the protrusion of the pre-kneading shaft, it is pushed into the gap between the main kneading shaft and the barrel, and is then mixed by the cavity of the main kneading shaft and the barrel. After being efficiently kneaded and cooled in a cooler, the resin is 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, 2 is a cooler, and the extruder 1
The extruder 1 is arranged in parallel with the extruder 1, and is 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 screw rotatably inserted into the barrel 6, and 8 and 9 are screws 7.
A pre-kneading shaft and a main kneading shaft are concentrically connected at the tip of the shaft, 10 is a large number of protrusions implanted on the pre-kneading shaft 8,
Reference numerals 11 and 12 denote a number of isolated hemispherical depression-shaped cavities formed on the outer circumferential surface of the main kneading shaft 9 and the inner circumferential surface of the barrel 6 opposite thereto. cavity 1
It is located across 1. The main kneading shaft 9
The outer peripheral surface of the barrel 6 is close to the inner peripheral surface of the barrel 6. 1
Reference numeral 3 denotes a blowing agent injection port provided at a location opposite to the boundary between the pre-kneading shaft 8 and the screw 7 of the barrel 6;
4 is a resin inlet formed at the end of the screw supporting side of the barrel 6, and 15 is a heater provided on the outer peripheral surface of the barrel 6. The cooler 2 is composed of the following:
Reference numeral 17 is an outer cylinder having 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 bearing 2 on the outer cylinder 17.
3, the proximal large diameter portion 19 is rotatably supported through
A, a central small diameter portion 19B, and a tip large diameter portion 19C, and an annular protrusion 19D is provided at a location slightly downstream from a portion of the central small diameter portion 19B facing the injection port 5. 24 is the central small diameter portion 19B
These are hurdle-shaped kneading rods that are protruded in large numbers on the downstream side of the annular protrusion 19D. The length of the main kneading shaft 9 is set to 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 set to 1 to 7 times (preferably 2 to 5 times) the diameter of the screw.
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. The resin passage cross-sectional area of the pre-kneading shaft 8 is made larger than the resin passage cross-sectional area of the tip of the screw 7 (preferably 1.5 to 3 times). If it is the other way around, the amount of resin supplied onto the pre-kneading shaft 8 will be excessive, making it impossible to perform sufficient pre-kneading. Further, a protrusion 10 provided on the pre-kneading shaft 8
Examples include cylindrical pins, screw lights with notches, and dalmage shapes. The operation of the above configuration will be explained below. Skrillyu 7
Then, the main shaft 19 is 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 a foaming agent injection port 13, and the foaming agent and resin are preliminarily mixed by a protrusion 10. Next, the foaming agent-containing resin is mixed into the main kneading shaft 9
The foaming agent is pushed into the gap between the resin and the barrel 6, and is kneaded by the cavities 11 and 12, so that the foaming agent is evenly dispersed in the resin. The principle of kneading will be explained using wires using the schematic diagrams shown in FIGS. 3a to 3h. First, the cavity 12 on the left side of Figure a.
The filaments that come out from the bottom extend along the inner circumferential surface of the cavity 12, and as shown in FIG. It is pulled by the edge A and changes its direction, reaching the state shown in Figure c, and the tip of the filament is bent by the Edge Lo, as shown in Figure d, and the Edge Lo and barrel form as shown in Figure E. 6, the tip of the filament is cut off, and the tip of the filament is bent by the edge C, as shown in figure f, and as shown in figure g,
The tip of the filament is cut by the edge C and the barrel 6, and the tip of the filament is bent by the edge D, as shown in FIG. 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,
Based on 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 resin with the foaming agent evenly dispersed passes through the supply pipe 3 and enters the outer cylinder 17 of the cooler 2, and enters the annular protrusion 1.
9D in the direction of arrow D, kneaded by the hurdle-shaped kneading rod 24 rotating in the direction of arrow B, and cooled appropriately at the same time, the gap between the large diameter portion 19C at the tip and the outer cylinder 17 is through the outlet 2
It is extruded from 1 and foams. Next, a first concrete example will be described. Barrel 6
The inner diameter of the screw 7 is 50 mm, the length of the pre-kneading shaft 8 is 250 mm, the length of the main kneading shaft 9 is 250 mm, and the gap between the main kneading shaft 9 and the barrel 6 is 0.4 mm. mm, the main kneading shaft 9 and the barrel 6 are provided with 6 cavities 11, 12 in the circumferential direction and 7 rows in the axial direction, the diameter of the cavity 11 is 24.5 mm, the depth is 8 mm, and the cavities 12 The diameter is 23mm, the depth is 9.5mm,
The distance between the cavities 11 and 12 was set to 22 mm, the rotation speed of the screw 7 was set to 106 rpm, the temperature of the molten material passing through the cooler 2 was adjusted to 123°C, and the width of the outlet 21 of the mouthpiece 20 was set to 100 mm. Its height is 1mm
And so. 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 hexabromocyclododecane as a flame retardant are added to 100 parts by weight of the base resin. A uniform mixture of 2.0 parts by weight was supplied as a raw material to an extruder 1, and the extruder 1 was operated to extrude the raw material at a rate of 55 kg per hour. In addition, dichlorodifluoromethane is added to the base resin as a foaming agent from the foaming agent injection port 13.
12.5 parts by weight was press-fitted to 100 parts by weight. As a result, a plate-shaped foam having a width of about 250 mm, a thickness of about 25 mm, and a density of 40 Kg/m ³ was obtained through the sizer attached to the nozzle 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.

[Table] As is clear from the attached table, according to the specific examples of the present invention, uniformly foamed foams could be obtained. (Effects of the Invention) As described above, according to the present invention, the resin and foaming agent extruded by the screw are preliminarily kneaded by the protrusions of the pre-kneading shaft, so that the length of the main kneading shaft can be reduced. Screw diameter 2 to 8
It can be made shorter than the conventional one, and the heat generated by the main kneading shaft and barrel cavity can be suppressed to a low level. 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 foaming will occur as specified. A foam can be obtained. Moreover, 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 drawings]

The drawings show an 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. 3 a
-h are schematic explanatory diagrams showing the principle of kneading using cavities. In each figure, 1 is an extruder, 2 is a cooler, 6 is a barrel, 7 is a screw, 8 is a preliminary kneading shaft, 9 is a main kneading shaft, 10 is a protrusion, 11 and 12 are cavities,
13 is a blowing agent injection port.

Claims (1)

[Scope of 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 shaft are attached to the tip of the screw in the barrel. The kneading shafts are arranged concentrically in this order, the pre-kneading shaft has a large number of protrusions, the outer peripheral surface of the main kneading shaft is brought close to the inner peripheral surface of the barrel, and the outer peripheral surface of the main kneading shaft and this A large number of isolated cavities are formed on the inner circumferential surfaces of opposing barrels, and the cavities on the inner circumferential surfaces of the barrels are positioned astride between the cavities of the main kneading shaft, and the blowing agent injection inlet is located upstream of the pre-kneading shaft of the barrel. 1. An apparatus for producing a thermoplastic resin foam, characterized in that the length of the main kneading shaft is 2 to 8 times the screw diameter, and the length of the pre-kneading shaft is 1 to 7 times the screw diameter. 2. The apparatus for producing a thermoplastic resin foam according to claim 1, characterized in that the cross-sectional area of the 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.