JPH0124057B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a blown film, and particularly to an improvement in a method for cooling a molten resin extruded into a tubular shape from an extrusion die. When forming inflation film,
In order to improve productivity by performing high-speed (high extrusion rate) molding and to obtain a high-quality film, it is required to sufficiently cool the molten resin. The most common conventional method for forming blown film is to place a single air ring near the top of the extrusion die that discharges cooling air in the direction of extrusion of the resin. The method involved blowing cooling air onto the outer peripheral surface of the resin. However, in such a molding method, the hot air flow heated to a high temperature by heat exchange with the high-temperature molten resin immediately after being extruded from the extrusion die hits the outer peripheral surface of the resin along the flow of the resin. It was not possible to obtain a sufficient cooling effect because the person was accompanied by the person for an indefinite period of time. Furthermore, if the amount of cooling air discharged is increased in an attempt to increase the cooling effect, the molding stability will be significantly impaired, so there is naturally a limit to the improvement of the cooling effect by such a method. By the way, a method has already been proposed in which cooling is performed by providing two air rings, upper and lower, that discharge cooling air along the extrusion direction of the resin (Japanese Unexamined Patent Application Publication No. 1983-1999).
146764, Special Publication No. 57-14295). however,
Even with these previously proposed methods, the hot air flow heated to a high temperature is not excluded from the outer peripheral surface of the resin. We also proposed a method using a mechanism in which a vacuum suction mechanism is provided in the middle of the two-stage air ring, and this vacuum suction mechanism removes the high-temperature hot air flow heated at the outer periphery of the molten resin from the outer periphery of the resin. (Japanese Patent Laid-open No. 54-29370), however, when installing such a vacuum suction mechanism, large-scale equipment is required, and operation control is also difficult, making it difficult to easily perform high-speed stable molding. It was not something I could do. In addition, as methods other than these, for example, external water cooling of tubular resins and internal cooling methods are already known, but the equipment is similarly very complicated and operation control is also difficult. The object of the present invention is to avoid the need for complicated equipment, and to
To provide a method for forming a blown film that is easy to operate, has a high cooling effect, and can easily form a high-quality film at high speed. In the present invention, cooling air is first blown onto the tubular resin at a predetermined position between the top surface of the extrusion die and the film expansion end point, and the resin is extruded at a position near the film expansion end point. A second blowing of cooling air is performed, and in the second blowing, cooling air is discharged in the opposite direction to the extrusion direction of the resin, and this cooling air in the opposite extrusion direction is applied to the outer peripheral surface of the tubular resin. The shape of the tubular resin is improved by keeping the hot air flow heated by heat exchange with the molten resin from flowing along with the resin, and by blowing cooling air in two stages. The purpose is to achieve the above object by effectively cooling the molten resin by constantly bringing the low-temperature cooling air into contact with the molten resin, no matter what the cooling air is. The present invention will be explained in detail below. FIG. 1 shows a first example of an apparatus to which the method for forming a blown film according to the present invention is applied. The tubular resin 4 is extruded into a tubular resin 4, and compressed air at a predetermined pressure is sealed from the air sealing passage 5 of the extrusion die 1 into the tubular resin 4, and the internal pressure of this compressed air causes the tubular resin 4 to blow up at a predetermined blow-up ratio. After being expanded and cooled and solidified, it is nipped by a nip roller (not shown) located on the upper side of the figure and is continuously wound up at a predetermined speed. Here, examples of the molten resin 3 include thermoplastic resins such as low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, polystyrene, ethylene-vinyl acetate copolymer, and polyvinyl chloride. A first air ring 6 is disposed near the top surface of the extrusion die 1, and a discharge port 6A of the first air ring 6 is directed from the resin extrusion direction toward the radially inner side of the tubular resin 4 (see Fig. 1). (see middle sign β) 20 degrees ~
Cooling air is discharged in a direction inclined at 70 degrees, thereby performing the first blowing of cooling air. Further, the tubular resin 4 extruded from the extrusion die 1 ends its expansion at a predetermined height position from the extrusion die 1, and a second air ring 7 is disposed near this expansion end point. Cooling air is discharged from the discharge port 7A of the air ring 7 in the direction opposite to the direction in which the resin is extruded.
Cooling air is being blown. Discharge port 7
The direction of the cooling air blown from A depends on the arrangement position of the second air ring 7 and the shape of the expanded part of the tubular resin 4, but normally the direction of the cooling air blowing from A is zero, and the direction is exactly opposite to the direction in which the resin is extruded. When the direction facing inward along the radial direction of the resin 4 is 90 degrees (see symbol α in FIG. 1), it is preferably 10 degrees to 70 degrees,
The cooling air blown in this way flows downward in the figure along the outer circumferential shape of the tubular resin 4. Note that the surface of the tubular resin 4 that is directly blown with the cooling air discharged from the second air ring 7 has already been solidified to a certain extent, so even if the discharge amount of cooling air is considerably increased, the surface of the tubular resin 4 is not directly blown. 4 does not cause breathing or meandering, and the molding stability is not easily impaired. However, if there is a risk that the molding stability will be impaired, the inclination angle of the discharge port 7A may be reduced by an appropriate amount. The cooling air discharged from the first and second air rings 6 and 7 collides with each other at an intermediate height from the top surface of the extrusion die 1 to the end point of film expansion, and flows outward in the radial direction of the tubular resin 4. The hot air flow generated when the cooling air is heated by heat exchange with the tubular resin 4 is expelled from the outer circumference of the tubular resin 4. An example of the molding method according to the present invention has the following effects. The cooling air discharged from the first air ring 6 is blown onto the high-temperature tubular resin 4 immediately after being extruded from the extrusion die 1, exchanges heat, and becomes high in temperature. Since the heated air collides with the cooling air discharged downward from the air ring 7 and is removed from the outer periphery of the tubular resin 4, the hot air flow does not accompany the flow of the tubular resin 4. Therefore, the tubular resin 4 is always exposed to low-temperature cooling air, and the cooling effect is great. Furthermore, unlike the conventional example described above, the hot air flow can be eliminated without the need to provide a decompression suction mechanism for the hot air flow in the middle of the two-stage air ring, so there is no need for large-scale equipment and operation control is easy. It is. Furthermore, the surface of the tubular resin 4 is solidified to some extent at the position where the second air ring 7 is disposed, and even if the amount of cooling air discharged from the second air ring 7 is increased, the tubular resin 4 will remain solid. Molding stability is not easily inhibited, and the amount of cooling air discharged can be increased, and from this point of view as well, the cooling effect can be increased, and therefore,
High-quality films can be formed at high speed. FIG. 2 shows a second example of an apparatus to which the molding method of the present invention is applied, and in this figure, the discharge port 8A of the first air ring 8 is a double slit and is used for extruding resin. The tubular resin 4 is tilted radially outward from the direction. If such a first air ring 8 is used, even if resin such as linear low-density polyethylene, high-density polyethylene, or polypropylene is used, the first air ring 8 can be used in a tubular shape immediately after being extruded from the extrusion die 1. Since it has the effect of pulling and fixing the resin 4 outward in the radial direction, it has the effect that stable molding is more easily performed.
Moreover, the second air ring 9 has a discharge port 9A that blows cooling air on the opposite side to the direction in which the resin is extruded.
In addition to the above, an auxiliary discharge port 9B is provided that blows cooling air in the extrusion direction.
The stability of the tubular resin 4 is further improved by the cooling air blown from B along the flow of the resin. FIG. 3 shows a third example of an apparatus to which the molding method according to the present invention is applied, and in this figure, the tubular resin 4 extruded from the extrusion die 1 is placed at a predetermined height position from the extrusion die 1. The diameter up to this point is approximately the same, but the diameter is rapidly expanded at the resin expansion portion. Further, a mandrel 10 is provided on the extrusion die 1 as a stable body. In such a third example, since the diameter changes rapidly at the resin expansion portion, it is not possible to change the outer peripheral shape of the tubular resin 4 by only blowing downward cooling air from the second air ring 7. Although it is difficult to flow cooling air sufficiently downward in the figure along The resin 4 can be effectively cooled. A fourth example is shown in FIG. In this figure, the first air ring 11 is placed at a predetermined height from the top of the extrusion die 1, and cooling air is supplied to the first air ring 11 in the direction of resin extrusion. It has an upward discharge port 11A for discharging cooling air and a downward discharge port 11B for discharging cooling air in the counter-extrusion direction. According to this fourth example, in addition to having the same effect as the third example, the hottest air flow near the top surface of the extrusion die 1 is cooled by the cooling air blown downward from the downward discharge port 11B. Since it is removed from around the tubular resin 4 more quickly, the cooling effect is even higher. A fifth example is shown in FIG. 5, in which an upward air ring 12 having an upward discharge port 12A and a downward discharge port 13A are provided at a predetermined height position from the top surface of the extrusion die 1. A downward air ring 13 is disposed, and the cooling air discharged from these air rings 12 and 13 performs the first blowing of cooling air. Even in such a case, the same effects as in the fourth example can be achieved. Also, the second air ring 7 in Figures 3, 4, and 5
By using the second air ring 9 shown in FIG. 2 instead, more stable molding can be achieved. Furthermore, in the present invention, a chamber is provided above the expansion start point of the tubular resin 4 to prevent the collision between the cooling air flow discharged in the resin extrusion direction and the cooling air flow discharged in the counter-extrusion direction. By avoiding the collision and removing it from the outer periphery of the resin, or by moderately relaxing the collision and removing it from the outer periphery of the resin, stable molding, cooling efficiency can be improved, and molding with excellent high-speed stable moldability can be performed. Although the above explanation was given as a method for forming a single layer film, the method can also be applied to forming a multilayer film, and the method is not limited to top blowing, but may also be bottom blowing or side blowing, and the tubular resin 4 is cooled from the inside. An internal cooling mechanism may also be provided. As described above, according to the present invention, it is possible to form a blown film that does not require complicated equipment, is easy to operate, has a high cooling effect, and can easily form a high-quality film at high speed. method can be provided. Next, the present invention will be explained in more detail using the following examples and comparative examples. Example 1 High-density polyethylene (density...0.955 g/cm ³ , melt index...0.05 g/10 minutes) was made of 55 mm diameter.
Using a screw extruder with L/D=28, the film was continuously extruded through an 80 mm diameter annular slit with a lip interval of 1.3 mm to form an inflation film with a fold diameter of 550 mm and a thickness of 25 μm. In addition, a mandrel with a diameter of 90 mm and a height of 700 mm was used as an internal stabilizer. Molding temperature...200℃ Cooling method...The first air ring (130mm diameter) is placed at a height of 200mm from the top surface of the extrusion die, and from this first air ring, from the resin extrusion direction to the inside of the tubular resin in the radial direction The first blow of cooling air is performed by discharging the cooling air in an inclined direction, and the second air ring (390mm diameter)
is placed at a height of 700mm from the top of the extrusion die,
A second blowing of cooling air was performed by discharging cooling air from this second air ring in a direction inclined at 45 degrees from the anti-extrusion direction toward the inside of the tubular resin in the radial direction. The evaluation results of moldability etc. are shown in Table 1. Example 2 The height of the first air ring is determined from the top of the extrusion die.
Molding was carried out under substantially the same conditions as in Example 1 except that the diameter was 300 mm. The results are shown in Table 1. Example 3 The height of the first air ring is determined from the top of the extrusion die.
Molding was carried out under substantially the same conditions as in Example 1 except that the diameter was 400 mm. The results are shown in Table 1. Comparative Example 1 Except that only one air ring (130 mm diameter) was placed at a height of 50 mm from the top surface of the extrusion die, and cooling air was blown from this air ring in a direction inclined at 45 degrees inward from the resin extrusion direction. Molding was carried out in substantially the same manner as in Example 1 above. The results are shown in Table 1. Comparative Example 2 A first air ring (130 mm diameter) was placed at a height of 50 mm from the top surface of the extrusion die, a second air ring (390 mm diameter) was placed at a height of 300 mm, and these first,
Molding was carried out in substantially the same manner as in Comparative Example 1, except that cooling air was blown from the second air ring in a direction inclined at 45 degrees inward from the resin extrusion direction. The results are shown in Table 1.

[Table] From the above-mentioned Examples and Comparative Examples, it can be seen that according to the present invention, the cooling effect is large and high extrusion rate molding can be performed stably. Example 4 Low-density polyethylene (density...0.92 g/cm ³ , melt index...2.4 g/10 minutes) with a diameter of 50 mm,
Using a screw type extruder with L/D=28, the film was continuously extruded through a 200 mm diameter annular slit with a lip interval of 2 mm to form an inflation film with a fold diameter of 470 mm and a thickness of 30 μm. Molding temperature...170℃ Cooling method...The first air ring (300mm diameter) was placed near the top surface of the extrusion die, and the first air ring was tilted 45 degrees inward in the radial direction of the tubular resin from the resin extrusion direction. performing a first blowing of cooling air by discharging cooling air in the direction;
A second air ring (390 mm diameter) is placed at a height of 550 mm from the extrusion die, and cooling air is discharged from this second air ring in a direction tilted 45 degrees inward in the radial direction of the tubular resin from the anti-extrusion direction. A second blow of cooling air was applied. The evaluation results of moldability etc. are shown in Table 2. Comparative Example 3 Same as Example 4 except that only one air ring (300 mm diameter) was placed near the top surface of the extrusion die, and cooling air was blown from this air ring in a direction inclined 45 degrees inward from the resin extrusion direction. Molding was carried out in substantially the same manner. The results are shown in Table 2. Comparative Example 4 A first air ring (300 mm diameter) is placed near the top surface from the extrusion die, a second air ring (390 mm diameter) is placed at a height of 550 mm, and air from these first and second air rings is In both cases, molding was carried out in substantially the same manner as Comparative Example 3, except that the cooling air was blown in a direction inclined at 45 degrees inward from the extrusion direction of the resin. The results are shown in Table 2.

[Table] Example 5 Low-pressure process ethylene-4-methylpentene-1 copolymer (density...0.923 g/cm ³ , melt index...2.4 g/10 minutes) was prepared using a screw type with a diameter of 50 mm and L/D = 28. Using an extruder, it is continuously extruded through a 125 mm diameter annular slit with a lip spacing of 2.0 mm, with a fold diameter of 300 mm.
An inflation film with a thickness of 30 μm was molded. Molding temperature: 170℃ Cooling method: A double slit type first air ring (150mm diameter) is placed near the top of the extrusion die, and the outer slit is tilted 20 degrees outward in the radial direction of the tubular resin from the extrusion direction. from the inner slit perpendicularly along the extrusion direction.
The first blow of cooling air was performed by discharging the cooling air. In addition, a second air ring is placed at a height of 500 mm from the extrusion die, and this second air ring is placed at a height of 500 mm from the extrusion die.
A second blowing of cooling air was performed by discharging cooling air in both the extrusion direction and the counter-extrusion direction using the air ring. The evaluation results of moldability etc. are shown in Table 3. Comparative Example 5 Molding was carried out in accordance with Example 5, except that the cooling air was sprayed by the second air ring by discharging the cooling air only in the extrusion direction. The results are shown in Table 3. Comparative Example 6 The first air ring (300 mm diameter) is placed near the top of the extrusion die, the second air ring is placed at a height of 500 mm from the extrusion die, and both the first and second air rings Molding was carried out in accordance with Example 5, except that the first and second blows of cooling air were performed by discharging cooling air in a direction inclined at 45 degrees inward in the radial direction of the tubular resin from the extrusion direction. . The results are shown in Table 3.

【table】

[Table] From the above-mentioned Examples and Comparative Examples, it is clear that according to the present invention, the cooling effect is large, high extrusion rate molding can be performed stably, and the height of the second air ring is strictly controlled. It can be seen that the operation is easy because accurate positioning is not required because there is no need for precision.

[Brief explanation of drawings]

1 to 5 are cross-sectional views showing first to fifth examples of apparatuses to which the blown film forming method according to the present invention is applied, respectively. 1... Extrusion die, 2... Annular slit, 3...
Molten resin, 4... Tubular resin, 6, 8, 11... First air ring, 7, 9... Second air ring, 12... Upward air ring, 13... Downward air ring.

Claims (1)

[Claims] 1 In a method of forming a blown film in which a molten resin is extruded into a tubular shape from an extrusion die, expanded by internal pressure, and then continuously wound, the tubular resin is placed at a predetermined position between the top surface of the extrusion die and the end point of film expansion. At the same time, a first blowing of cooling air is performed in the extrusion direction of the resin, and a second blowing of cooling air is performed at a position near the end point of film expansion, and in the second blowing, the extrusion of the resin is A method for forming an blown film characterized by discharging cooling air in the opposite direction.