JPS6412213B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an extrusion device for molding thermoplastic resin. In this type of extrusion device, various inventions and ideas have been made for the purpose of increasing the amount of extrusion.One method is to deepen the screw groove in the feed section of the screw and to roughen the inner wall surface of the cylinder in the feed section. This makes it possible to reliably transport pellets, powder, etc. without the bridge effect, that is, the raw materials do not rotate together with the screw. Therefore, compared to a cylinder in which the supply section has a normal smooth circular wall surface, the material can be absorbed better, even a cylinder with a smaller diameter can extrude a large amount, and the temperature of the cylinder can be easily controlled. Research has been conducted in various fields regarding the melting morphology of thermoplastic resins, and many theories and experimental data have been reported. It is typically explained using a melting model. In FIG. 1, numeral 1 indicates a solid bed (unmelted material) at the front of the screw groove, 2 indicates a molten material at the rear of the screw groove, and 3 indicates a melt film formed along the inner wall surface of the cylinder 5. Also, 4 is Skrill Flight. At the initial stage of melting, the morphology as shown in this model is clearly maintained, but as melting progresses and the melting ratio increases, an unsteady phenomenon called destruction of the solid bed due to interference of the melt occurs. This causes unfavorable results such as extrusion fluctuations, contamination of unmelted substances, or entrainment of air bubbles. This phenomenon becomes particularly noticeable during extrusion at high speeds, and is therefore the biggest factor regulating the performance of extruders. As shown in Figure 2A, according to the screw proposed in Japanese Patent Publication No. 11505/1973, the solid bed and the molten material are separated by the second flight during the melting process, so that the solid bed as described above is Destructive phenomena are easily prevented and good operation cannot be continued under certain conditions. However, in general, there are a wide range of conditions such as the composition of materials handled by extruders, physical properties, types of molded products, and required production volume, and it is important to note that the melting forms of resins corresponding to each are also infinitely different. must not. Under such circumstances, if the solid side passage groove is blocked at its end, it lacks adaptability to various conditions and, for example, a relatively large amount of resin in the form of a solid may reach the vicinity of the end. It has been confirmed that under such severe conditions, the resin often becomes clogged in the channel grooves, resulting in a sharp drop in extrusion performance. In order to prevent the above-mentioned clogging phenomenon, it is possible to assist melting by external heating, but resin is generally a poor conductor of heat, and much cannot be expected due to the structural limitations of the heating system. In addition, it can be improved by preparing several types of screws with different shapes and selecting and operating the screw that suits each condition, but this is not economical. On the other hand, as shown in FIG. In this case, resin clogging phenomenon can be prevented, but on the other hand, since it is an open type, it has characteristics similar to conventional (full-flight) screws, and complete melting cannot be achieved under all of the various extrusion conditions described above. cannot be guaranteed. In other words, some or a considerable amount of unmelted material flows out to the next process,
This may have an unfavorable effect on the extruded product. Although it is possible to improve the degree of melting to some extent by changing the cross-sectional area of the solid side passage groove, it is fundamentally difficult to achieve both complete melting of the resin and non-occlusion. The more complex the process, the less significant the effect will be. Also, since the fluids flowing out from different passages to the next process naturally have different state quantities such as resin temperature, it will be difficult to maintain the homogeneity of the extruded product unless there is an appropriate device to mix the two fluids. . The object of the present invention is to provide an extrusion device that eliminates the above-mentioned drawbacks, increases the extrusion rate by improving the feeding section, and makes the extruded product homogeneous using a relatively simple screw structure. Next, with reference to FIGS. 3 to 9, 1 according to the present invention
To explain the embodiment, reference numeral 11 denotes an extrusion device, and a screw 14 is rotatably inserted into a heating cylinder 12 and a feed section cylinder 13 by a drive device (not shown). The feed section cylinder 13
A plurality of taper grooves 15 extending in the axial direction are provided on the inner wall surface, and the grooves become shallower in the direction of the material flow, to prevent the material input from the material supply port 16 from rotating together with the screw 14. ing. Of course, the inner wall surface does not have to be a groove as described above, but it is sufficient that the inner wall surface is roughened so that frictional action can be effectively performed so that the material does not rotate together with the rotation of the screw 14. Further, the feed portion cylinder 13 is provided with a spiral circular groove 17, and cooling by air or water is possible by flowing a heat medium into the groove 17 as necessary. As shown in the detailed view of FIG. 5, the screw 14 is located between the supply section F starting from the raw material input port and the final measuring section M, and sequentially includes a melting promotion section A, a mixing section B, and a melting completion section from the supply section F. It is composed of C. If the screw diameter is D, then approximately
The melting promoting section A has a length of about 5D and extends from near the end of the supply section F to near the starting point of the mixing section B. The second flight 18 has a smaller outer diameter than the first flight 18.
The second flight 19 divides the inside of the screw groove into a groove 19a in which the solid part mainly passes in the front and a molten material passage 19b in the rear. It is also 30 to 80% wide at certain points, and is open to prevent stagnation in any part. As shown in the detailed view of FIG. 6, the mixing section B is located in the downstream area adjacent to the melting promotion section A, and contains a large amount of molten resin transferred from the melting promotion section A and a relatively small amount of unmixed resin. It has a relatively deep groove and an auxiliary mixing function such as a beat or pin 20 for uniformly mixing the molten material and sending it to the next process. The melting completion section C completely melts the resin flow containing the unmelted material sent out from the mixing section B and equalizes the resin temperature. A plunger 21 is provided to maintain a small gap d between the plungers 21 and a stopper groove 21a that does not penetrate through the outer peripheral surface of the plunger 21.
are arranged alternately in opposite directions so that they do not communicate with each other. 22 is a heater provided on the outer periphery of the heating cylinder 12. The extrusion device according to the present invention is equipped with the feed section cylinder and screw as described above. Next, its operation will be explained. The material resin supplied from the material supply port 16 at room temperature or slightly preheated passes through the supply section A. During this process, the friction coefficient with the inner wall surface of the feed cylinder 13 is increased by the groove 15 provided on the inner wall surface of the feed cylinder 13. The spiral circular groove 17
Humidity increases due to the heat medium inside and the frictional heat generated between the heater 22 and the inner wall surface of the feed section cylinder 13, and the position is determined depending on various conditions, that is, the supply section F.
A melt film 5 as shown in FIG.
is generated. These are scraped off by the top of the flight 4 to form a melt pool 2 on the front side of the flight, and the melt pool 2 gradually increases in volume and advances until it reaches the starting point of the melt promotion zone A. That is, a predetermined amount of melting has already progressed at the starting point of part A. In order to satisfy this condition, the starting point of part A must be at least upstream of the point where the solid bed begins to break and downstream of the expected slowest melting start point. In reality, it is preferable to study various possible operating conditions by theory, experience, or experiments using a small test extruder, and to set the volume melting ratio at a position that reaches about 13 to 18%. In addition, the degree of opening (wm/w x 100% in Fig. 7) at the starting point of the molten material side passage is, in principle, slightly lower than the melting ratio, that is, the ratio is 10 to 15%. However, even if a situation occurs where the melting form is quite different from the initially designed value due to unexpected operating conditions, for example, the melting ratio is lower than the opening of the melt side gutter at the starting point of the melt promotion zone A, a portion of the solid Even if particles just enter the melt side passage, the basic function of the screw is not impaired, and it is possible to continue operating at least better than conventional screws. Now, as mentioned above, the solid side passage in the melting promotion section A has a screw groove width of 85 to 90 mm near the starting position.
Since the resin has a relatively large contact area with the heating cylinder 12, the resin is moderately compressed and its melting is promoted by frictional action with the inner surface of the heating cylinder 12 and heat transfer from the outside. In this part, the resin (melt film) in the part in contact with the inner surface of the heating cylinder 12, which has been completely melted, gradually passes over the mountain part of the second flight 19, which has a smaller outer diameter than the first flight 18, and flows into the molten material passage groove 19b. Therefore, the phenomenon of destruction of the solid bed as described above does not occur, and a good steady state can be maintained. The screw 14 according to the present invention is intended to prevent the phenomenon of destruction of the solid bed under all various operating conditions in the melting promotion section A, and also to prevent the phenomenon of material clogging in the solid side passage 19. Therefore, complete separation of solid and melt is not required. Therefore, as a general rule, the cross-sectional area of the solid side passage, especially the passage width, should always be designed to be slightly larger than the actual width of the remaining solid. For exactly the same reason, the solid side passage 19 is made open at the end point of the melting promotion section A, and the groove depth at this point is slightly larger than the particle size of the material passing through, and the opening degree (solid section groove width / total width × 100%) is usually set to a high value of 30 to 80%. For this reason, during high-speed extrusion, as a matter of course, the melting of the resin is incomplete at the end point of the melt-promoting zone A, and unmelted particles of approximately several to 15% by volume remain.However, the screw according to the present invention This does not prevent these parts from flowing to the next process. However, these unmelted portions are 100% melted in the next mixing section B and melting completion section C defined by the screw according to the present invention, and at the same time it is possible to equalize the resin temperature. Next, the operation in the mixing section B will be explained in detail with reference to FIG. In the melting promotion zone A, the solid bed is not destroyed and is sufficiently heated under normal action, and the group of unmelted particles, which have a temperature at least above the secondary dislocation point and just below the melting point, and have undergone considerable softening, enter the solid side passage. It is unevenly distributed on the back side of the flight of 19a. After flowing into the mixing section B, these are finely divided by an auxiliary stirring mixer such as a beat or pin 20 shown in the attached Fig. 6 in relatively deep grooves, and are uniformly dispersed and mixed within a large amount of melt, while being separated from the surroundings. As heat is supplied and the temperature rises, albeit slightly, a portion of the surface layer melts and enters each inlet side groove 21a of the melting completion section C. The flow path 21a is formed by alternately arranging grooves with one side closed so as not to penetrate between the mixing portion B and the measuring portion M, so that the resin flow flowing into the flow path 21a flows through a relatively narrow gap δ. The adjacent flow path 21a passing through
reach. In this process, a momentary but very effective shear stress is generated only in the unmolten material, which is still quite viscous (elastic), so the particles are deformed and stretched thin, and at the same time frictional heat is added, so that the melting point is quickly exceeded. Melting is complete. According to the screw according to the present invention, as described above, the shear in the melted part acts more strongly on the unmelted material side, so the temperature of the already melted part does not rise much, and the excellent kneading action is achieved, so the resin temperature increases. The whole is uniform, and it is possible to perform extremely good extrusion. Such ideal melting can only be achieved by the plunger 21 in the melting completion section C, as described in Japanese Patent Publication No. 43-24493 adopted in the present invention. This is not guaranteed with dalmage or ring valves. Moreover, it cannot be expected that the melted part C alone can sufficiently exhibit its function. That is, it is clear that it is not effective against the destruction or clogging phenomenon of solid beds, and that its performance deteriorates when unmelted particles concentrate in some grooves. In other words, the extrusion apparatus that achieves the ideal effect of the present invention, that is, increases the extrusion rate and produces a product with excellent physical properties, is a screw system that has a comprehensive combination of the melt accelerating section A, the mixing section B, and the melting completion section C; This is achieved by improving the feeding of material in the feed section cylinder 13 by increasing the material feed rate. The results of a comparative test between the extrusion apparatus according to the present invention and a conventional apparatus, which were conducted using an extruder with a 65 mm L/D=28, are shown below. Example 1

【table】 Example 2

[Table] In the above experiment, no unmelted substances or bubbles were observed in the extruded product. Further, none of the above embodiments indicates an upper limit of performance. As described above, the screw according to the present invention has a reduction rate of at least 150% and even 200% of that of the conventional screw.
It is possible to hope for the above performance improvement.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the state of the resin at the initial stage of melting, and FIG. 2 is a diagram of a screw used in a conventional device.
FIG. 3 is a diagram showing one embodiment according to the present invention. FIG. 4 is an explanatory diagram thereof, and is a cross-sectional view of FIG. 3. Figure 5 is a detailed view of the screw, Figure 6 is a detailed view of the "A" part in Figure 5, Figure 7 is an explanatory diagram showing the state of resin distribution at the starting point of the melt promoting part, and Figure 8 is a detailed view of the melt promoting part. An explanatory diagram showing the resin distribution state at the end point, and FIG. 9 is a diagram showing another kneading device. 13...Feed section cylinder, 14...Screw, 18...First flight, 19...Second flight, 20...Pin, 21...Plunger.

Claims (1)

[Claims] 1. In an extrusion device for molding thermoplastic resin, the following steps (1), (2), and (3) are performed sequentially from the supply section between the supply section starting from the material input port and the final measuring section. An extrusion device for molding a thermoplastic resin, comprising a screw having a portion constituted by a melting promotion section A, a mixing section B, and a melting completion section C defined as follows, and a feed cylinder defined in (4) below. (1) A second flight having a smaller outer diameter than the first flight starts from near the end of the supply section and extends to near the start of the mixing section B, and the second flight allows the resin passage groove to move forward. The proportion of the solid part mainly divided into the solid part passage groove and the rear melt passage groove is approximately 85 to 90% at the starting point position (solid part groove width/total width x 100%, the same applies hereinafter) at the end point position. 30 to 80% of the melting promoted part A is characterized in that it is clear in any part. (2) Located in the downstream area adjacent to the melt promotion section A, a large amount of molten resin flowing out from the previous process and a relatively small amount of unmelted material are uniformly mixed and then sent to the next process. Mixing section B has a relatively deep groove and has an auxiliary mixing function such as a beat or pin. (3) In order to instantaneously completely melt the resin flow containing unmelted material flowing from the mixing section B, and at the same time equalize the resin temperature, a small gap is provided downstream of the mixing section B between the inner wall surface of the cylinder and the resin flow including unmelted material. A melting completion part C is provided with a plunger part that has a plunger part, and has first-stop grooves that do not penetrate the outer peripheral surface of the plunger and are alternately arranged in opposite directions so that they do not communicate with each other. (4) The area corresponding to 5 pitches from the starting point of the feeding section of the screw is defined as a forced feed area, and the inner wall surface of the cylinder in this area is provided with a plurality of taper grooves or grooves extending in the axial direction that gradually become shallower in the flow direction of the raw materials. Feed cylinder with arbitrary rough surface.