JPH0154182B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an air ring of a thermoplastic resin extrusion molding apparatus used for cooling resin during thermoplastic resin extrusion molding such as inflation film molding and pipe molding. In recent years, high-speed molding has been desired from the viewpoint of improving productivity in extrusion inflation film molding of thermoplastic resins such as high-density polyethylene, low-density polyethylene, and polypropylene. The traditional inflation film forming method is
The molten resin is extruded into a tube shape from an extrusion die, expanded by internal pressure, and cooled by cooling air discharged in the direction of resin extrusion from an air ring arranged in an annular shape on the outside. I'm trying to wind it up. However, with such an air ring, when high-speed molding is performed,
This results in insufficient cooling or uneven cooling, which causes a significant rise in the frost line, bubble breathing, and steering, which causes uneven thickness, uneven width, or wrinkles in the film, and even causes blocking in the nip roll. This had the disadvantage that it could lead to suspension of operation due to bubble breakage. Also, if you increase the amount of air discharged from the air ring to compensate for the lack of cooling,
Although the frost line descended, the bubble became unstable due to the increase in wind speed, and the bubble vibrated violently, making it difficult to expect a film of uniform and good quality. Therefore, in order to increase the cooling capacity without simply increasing the air discharge amount, an air ring (Japanese Patent Application Laid-open No. 77258/1983, which has double air discharge slits facing the resin extrusion direction) was developed. 53−
No. 137261, No. 54-150473, etc.), and those that rectify the air by installing a cylinder on the top of the air ring (Tokuko Showa).
53-8339 etc.) are known. However, in these cases, the air ring is installed on a high-temperature extrusion die, so when air is discharged from the air ring in the direction of resin extrusion, the air ring is heated by the heated air at the top of the extrusion die. The discharged air is heated, and the upper part of the extruded resin is particularly insufficiently cooled. In addition, the flow velocity of the air discharged from the air ring gradually decreases as it advances from the air ring in the extrusion direction, so that the cooling effect necessary for high-speed molding cannot be expected. Furthermore, in addition to the air ring provided on the extrusion die, there is also known a device in which another air ring is provided at a predetermined height position (Japanese Patent Laid-Open No. 52
-101260, 52-128955, etc.). In this type of product, the airflow that is discharged from the lower air ring and raised in temperature on the outer peripheral surface of the resin flows upward along the outer peripheral surface of the resin, so that it is discharged from the upper air ring. The air does not have a sufficient cooling effect, and furthermore, when the upper air ring is brought close to the bubble expansion part, the bubble becomes unstable. In any case, conventional air rings are insufficient for molding materials such as high-density polyethylene, that is, molding materials using a core under conditions of relatively high frost lines. Therefore, not only is it not possible to perform high-speed molding, but it is also not possible to produce films of various thicknesses, especially thick films, by varying the blowing ratio. An object of the present invention is to provide an air ring that has an excellent cooling effect and enables stable high-speed extrusion molding. The air ring according to the present invention is arranged above an extrusion die that extrudes and molds a thermoplastic resin into a tubular shape, and has a central hole in an annular hollow body through which cooling air for cooling the thermoplastic resin passes. An air ring for an apparatus for extrusion molding a thermoplastic resin, which is provided with first and second discharge slits above and below an inner peripheral portion of the center hole, and the first discharge slit is configured to extrude the thermoplastic resin. The second discharge slit is characterized in that it opens diagonally upward toward the thermoplastic resin, and the second discharge slit opens diagonally downward toward the thermoplastic resin. Therefore, first, the molten tubular resin extruded into a tubular shape from the extrusion die can be cooled by the cooling air discharged diagonally downward from the second discharge slit. At this time, the heated air in the upper part of the extrusion die is removed from the outer periphery of the tubular resin by the cooling air from the second discharge slit, surrounds the outer periphery of the resin, and is entrained in the resin flow. Never. Further, the cooling air discharged diagonally upward from the first discharge slit cools the tubular resin that has passed through the discharge slit, but the cooling air from the second discharge slit has already cooled the resin on the die. Since the heated air does not surround the outer periphery of the tubular resin and the tubular resin is pre-cooled by the cooling air from the second discharge slit, the resin can be cooled quickly and efficiently. Can be done. Therefore, since the cooling effect is excellent, stable high-speed extrusion molding is possible. Embodiments of the present invention will be described below based on the drawings. FIG. 1 shows a blown film forming apparatus using the air ring of the present invention. In this figure, molten resin is extruded from an extrusion die 1 in an annular shape to form a tubular resin 2. A cylindrical core 3 fixed to the extrusion die 1 is provided inside the tubular resin 2 . The core 3 is, for example, the one shown in Japanese Patent Publication No. 55-46296. Further, compressed air is sealed inside the tubular resin 2,
The core 3 is expanded at a predetermined blow-up ratio on the extrusion direction side, and is formed into bubbles 4. At the same time, a frost line F is formed at a predetermined position of this bubble 4. At an intermediate position between the extrusion die 1 and the frost line F, an air ring 5 is arranged so as to surround the tubular resin 2 and to be variable in height. As shown in an enlarged view in FIG. 2, the air ring 5 is provided with an annular hollow body 7 as an air ring main body having a substantially rectangular cross section and having an annular air flow path 6. Tubular resin 2 in the center
It has a central hole 19 through which it passes. An air supply pipe 8 is connected to the annular hollow body 7 , and air for cooling the thermoplastic resin is supplied from the air supply pipe 8 into the annular air passage 6 . The inner circumferential edge 9 of the annular hollow body 7 is provided with a threaded portion 10 along its entire circumference.
An air outlet 11 with a predetermined width is provided at the center of the inner peripheral edge 9.
are perforated along the circumferential direction. Of the threaded parts 10, a screw carved on the outer peripheral edge of the annular upper wing 12 is screwed into the threaded part 10 on the side in the resin extrusion direction, that is, on the upper side in the figure, from the air outlet 11. A screw carved on the outer peripheral edge of the annular lower wing 13 is screwed into the threaded portion 10 on the extrusion direction side. Thereby, the air flowing out from the air outlet 11 is configured to be guided toward the inner center of the annular hollow body 7. An annular partition plate 14 is provided between the upper wing 12 and the lower wing 13. The inner peripheral edge of the partition plate 14 is a protruding edge 14A that protrudes slightly from the upper wing 12 and the lower wing 13 toward the center of the annular hollow body 7, and protrudes by a predetermined length in the vertical direction.
has. On the other hand, the outer peripheral edge of the partition plate 14 is fixed to the annular hollow body 7 by a plurality of fixing parts 15 located at the center of the air outlet 11 and provided at predetermined intervals along the circumferential direction. This results in
Air flowing out from the air outlet 11 is separated by a partition plate 14. That is, the air passing between the partition plate 14 and the upper wing 12 passes through the inner peripheral side edge of the upper wing 12 and the protruding edge 14A in the center hole 19 of the annular hollow body 7.
The resin is discharged toward the tubular resin 2 from an upward slit 16 that is opened diagonally upward and serves as a first discharge slit. On the other hand, the partition plate 14
The air passing between the lower wing 13 and the lower wing 1
The resin is discharged toward the tubular resin 2 through a downward slit 17 that is opened obliquely downward and serves as a second discharge slit formed by the inner circumferential edge of No. 3 and the protruding edge 14A. Further, the widths, that is, the opening degrees of the upward slits 16 and the downward slits 17 can be continuously changed to wide or narrow by respectively adjusting the screwing positions of the threaded portions 10 of the upper wings 12 and lower wings 13. Can be done. Therefore, the amount of air discharged from the upward slit 16 and the downward slit 17 is configured to be adjusted continuously, that is, steplessly. Next, the operation of this embodiment will be explained. The tubular resin 2 extruded from the extrusion die 1 is
The air ring 5 is cooled by being blown onto the thermoplastic resin cooling air discharged obliquely downward from the downward slit 17 of the air ring 5. At this time, the heated air in the upper part of the extrusion die 1 is expelled from the vicinity of the outer periphery of the tubular resin 2 by the air discharged diagonally downward from the downward slit 17. Therefore, the heated air does not surround the outer periphery of the tubular resin 2 and be entrained in the flow of the tubular resin 2. The tubular resin 2 immediately after being extruded from the extrusion die 1 has a low melt tension, but since it is efficiently cooled by the downward slit 17, the tension gradually increases as it moves in the resin extrusion direction, making it stable even during high-speed formation. The state is maintained. The tubular resin 2 that has passed through the downward slit 17 of the air ring 5 is further cooled and expanded into a bubble 4 by thermoplastic resin cooling air discharged diagonally upward from the upward slit 16. At the same time, a frost line F is formed at a predetermined position of this bubble 4. On the upper side of the air ring, the air that has already been heated by the tubular resin 2 on the lower side of the air ring 5 does not surround the outer periphery of the tubular resin 2 or the bubble 4, so that it is discharged from the upward slit 16. The tubular resin 2 and bubbles 4 are efficiently cooled by the cooling air. In this way, since the tubular resin 2 is efficiently cooled in the upper and lower directions of the air ring 5, the frost line F can be maintained at a predetermined position even during high-speed molding. In addition, since the arrangement position of the air ring 5 is variable at the intermediate position between the extrusion die 1 and the frost line F, the type of resin to be extruded,
It may be placed at an appropriate position depending on the molding conditions, etc., but if it is too close to the extrusion die 1, the cooling by the downward slit 17 will not be achieved sufficiently, and if it is too close to the frost line F, there is a risk that the stability of the bubble in the expansion region will be impaired. Generally, it is desirable that the height from the extrusion die 1 to the frost line F be within the range of 1/10H to 9/10H, where H is the height from the extrusion die 1 to the frost line F. In addition, in order to adjust the amount of thermoplastic resin cooling air discharged diagonally upward and diagonally downward from the air ring 5, the upper blade 12 and the lower blade 13 are rotated with respect to the annular hollow body 7, and the upward slit is adjusted. The slit widths of the slits 16 and 17 may be adjusted respectively. According to this embodiment, the resin can be cooled extremely efficiently, and even during high-speed molding, there is no insufficient cooling or uneven cooling, and the bubble 4 is prevented from breathing or steering. Therefore, there is an effect that a high quality film, that is, a film free from uneven thickness, uneven width, wrinkles, etc., can be produced stably and with high productivity. Furthermore, even during high-speed molding, the resin can be sufficiently cooled, so the frost line F can be maintained at a predetermined position. Therefore, there is no risk of blocking occurring due to nipprol. In addition, the resin used in this example is a general thermoplastic resin, but in particular low-density polyethylene, polypropylene, etc., which have low melt tension and which have traditionally been difficult to mold at high speeds or thick materials, and frost line resins. Even high-density polyethylene and the like that require a high position can be cooled sufficiently, and these resins can also be molded at high speed stably and with good productivity. Furthermore, the air volume and discharge angle of the thermoplastic resin cooling air discharged diagonally upward and diagonally downward can be adjusted independently by adjusting the screwing positions of the threaded portions 10 of the upper blades 12 and lower blades 13. It can be easily adjusted steplessly. Therefore, the height position of the air ring 5 is set depending on the type of resin, molding conditions, molding purpose, etc.
By changing the ratio of the amount of air from diagonally above to the amount of air from diagonally below, high-speed extrusion molding can always be performed stably regardless of the type of resin. Moreover, in order to change the air volume ratio, it is sufficient to simply adjust the slit width, that is, the opening degree, by adjusting the upper blade 12 and the lower blade 13, so the structure is simple and inexpensive. In addition, in the above-mentioned embodiment, the air ring 5
The upper wing 12 and the lower wing 13 both have a threaded portion 10.
Although the attachment position to the annular hollow body 7 is made to be movable through the annular hollow body 7, only one side may be displaceable, or both may be displaceable as in an embodiment other than the above shown in FIG. It may be fixed so that it cannot be displaced. In this case, the tips of the adjusting screws 20 are rotatably but immovably attached to the partition plate 14 at predetermined intervals along the circumferential direction, and the adjusting screws 20
0 is screwed onto the upper wing 12, the upward slit 16 and the downward slit 17 can be adjusted simultaneously by rotating the adjustment screw 20, so that the resin is discharged in the resin extrusion direction and in the anti-resin extrusion direction. The air volume and discharge angle can be adjusted at the same time. In addition, the amount of air for cooling thermoplastic resin discharged diagonally upward and diagonally downward can be adjusted by
The width of the upward slit 16 and the downward slit 17 is not limited to the means for adjusting the slit width, but a valve mechanism may be provided to adjust the width. In addition, the upward slit 16 and the downward slit 1
7 are both provided in the same annular hollow body 7, in other words, not only when both the upward slit 16 and the downward slit 17 are provided in one air ring body, but also when they are adjacent to each other. It is also possible to have different air ring bodies disposed close to each other, with an upward slit 16 provided on one side and a downward slit 17 provided on the other side. Further, in the above embodiment, the core 3 is provided within the annular resin 2, but the core 3 is not necessarily required. However, if the core 3 is provided, the molding stability will be extremely high even in high-speed inflation molding of ultra-thin films and thick films. Further, in the above embodiment, the air ring 5 is applied to top-blown inflation film forming, but it can of course also be applied to bottom-blown inflation film forming. Further, the air ring according to the present invention is applicable not only to inflation film molding but also to a wide range of tubular resin extrusion molding fields such as thick pipes and sheets.
However, especially in the case of inflation film molding, the effect of improving stability in high-speed molding and thick molding is remarkable. As described above, according to the present invention, it is possible to provide an air ring that has an excellent cooling effect and is capable of stable high-speed extrusion molding. The invention will be explained in more detail by the following examples. Examples 1 to 3 High-density polyethylene (density 0.955 g/cm ³ , melt index 0.05 g/10 min) was used at a temperature of 200°C using an extruder diameter of 55 mm, extrusion die diameter of 80 mm, and a center core of 95 mmφ500 mmH. Folding width 550mm thickness
A 25 μm inflation film was molded, and at this time, an air ring (inner diameter 130 mm) according to the present invention was formed.
The amount of resin that can be stably molded was investigated by changing the height of the resin. The results are shown in Table 1. Comparative Example 1 The resin extrusion amount was examined in the same manner as in Examples 1 to 3 under the same conditions as in Examples 1 to 3. However, a conventional air ring (inner diameter 130 mm) that discharges air only in the extrusion direction was installed on the extrusion die.
The results are shown in Table 1.

[Table] 1 Examples 4 to 6 Using high-density polyethylene (density 0.955 g/cm ³ , melt index 0.05 g/10 min), temperature was measured from the center of extruder diameter 55 mm, extrusion die diameter 80 mm, 95 mm φ 500 mmH. Inflation films of different thicknesses with a fold width of 400 mm were molded under the conditions of 200°C and resin extrusion of 40 kg/h, and at this time, the height of the air ring (inner diameter 130 mm) according to the present invention was changed to mold various thicknesses. Stability was investigated. The results are shown in Table 2. Comparative Example 2 Molding stability was investigated in the same manner as in Examples 4 to 6 above under the same conditions as in Examples 4 to 6 above. however,
A conventional air ring (inner diameter 130 mm) that discharges air only in the extrusion direction was installed on the extrusion die.
The results are shown in Table 2.

[Table] Thus, it can be seen that the air ring according to the present invention has an excellent cooling effect and enables stable high-speed extrusion molding.

[Brief explanation of drawings]

Fig. 1 is a front view showing the main parts of a blown film device to which the air ring of the present invention is applied, Fig. 2 is a partially enlarged sectional view showing the air ring used in the device, and Fig. 3 is a FIG. 7 is a partially enlarged sectional view showing another embodiment of the ring. 1... Extrusion die, 2... Tubular resin, 3... Core, 4... Valve, 5... Air ring, 7...
Annular hollow body as air ring body, 10...
Threaded portion, 12... Upper wing, 13... Lower wing, 14
...Bullet plate, 16...Upward slit as a discharge slit, 17...Downward slit as a discharge slit, 19...Center hole, 20...Adjustment screw,
F...Frost line.

Claims (1)

[Claims] 1. Thermoplastic resin extrusion, which is arranged above an extrusion die that extrudes and molds a thermoplastic resin into a tubular shape, and in which cooling air for cooling the thermoplastic resin is discharged from a center hole of an annular hollow body through which the thermoplastic resin passes. The air ring of the molding device is provided with first and second discharge slits above and below the inner periphery of the center hole, and the first discharge slit opens obliquely upward toward the thermoplastic resin. , said second
An air ring characterized in that the discharge slit is opened diagonally downward toward the thermoplastic resin.