JP2000052410A - Molding method for tubular film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a tubular film in which even when molding velocity is made higher, the high-quality tubular film can be obtained at a low cost and also even when molding velocity is made lower, abnormal tension in not caused. SOLUTION: While a parison P extruded from a ring extrusion die and being in a molten state is cooled by internal cooling water W held in the upper part of a sizing part 2 and kept at a prescribed water level, the parison P is passed through the sizing part 2 and a tubular film F having prescribed inside diameter is formed. At this time, when molding velocity is high, the water level H of internal cooling water is made deep. When molding velocity is low, the water level H is made shallow. Thereby, the water level H of internal cooling water is controlled so that a frost line of the parison H is positioned in the vicinity of the sizing part 2 and molding is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a parison in a molten state, which is extruded from an annular extrusion die, is passed through a sizing section while being cooled by internal cooling water at a predetermined water level maintained above the sizing section, and is provided with a predetermined inner diameter. And a method for forming a tubular film.

[0002]

2. Description of the Related Art An unstretched tubular film is subjected to an extrusion step of extruding a parison in a molten state from an annular extrusion die, a sizing step of sizing the parison obtained in this extrusion step to obtain a raw film having a predetermined diameter, ie, a tubular film. It is molded by. An extruder used for such an extrusion step and a sizing step, and a sizing mandrel are shown in FIG. As is well known in the art, an extruder includes a hopper A for storing a resin material, an extrusion cylinder B for kneading and melting the resin material,
And a circular extrusion die C provided at the downstream end of the extrusion cylinder B, and the like. A sizing mandrel D for forming a tubular film is provided below the annular extrusion die C.

The details of a conventional sizing mandrel D are shown in FIG. Sizing mandrel D
Has a sizing portion E having a maximum diameter at the upper side. And
Below that is a small-diameter seal ring portion F. A groove is formed on the outer peripheral portion of the sizing mandrel D between the sizing portion E and the seal ring portion F to form an internal cooling portion G. A water case H is attached to the outer peripheral portion of the sizing mandrel D thus configured at a predetermined interval from the outer peripheral portion. Thus, between the water case H and the parison P, the external cooling water W '
The internal cooling water W is stored inside the parison P. The sizing mandrel D configured as described above is attached to the mandrel C ′ of the annular extrusion die C via the support member J. The mandrel C ′ is mounted concentrically with the ring member K by a spider, and the internal cooling water W is supplied from the spider to the upper part of the sizing section E in a conventional manner,
The water level h is kept constant.

Since the extruder and the sizing mandrel D are configured as described above, when the resin material is supplied from the hopper A to the extrusion cylinder B and the screw is driven to rotate, the resin material is kneaded and melted, and the annular extrusion die is formed. A cylindrical parison P is extruded from the die slit of C. The extruded parison P is drawn toward the sizing mandrel D, in which the inside is cooled by the internal cooling water W and the outside is cooled by the external cooling water W ′.
And then sized and continuously taken up by a pair of pinch rolls R, R as shown by the dashed line in FIG.
A tubular film F is obtained. Further, a stretched film can be obtained by stretching this tubular film F.

[0005]

As described above, the inner surface of the molten parison is cooled by the internal cooling water, and the outer surface thereof is cooled by the external cooling water. There is an advantage that the tubular film can be formed at a relatively high speed. However, the conventional level of the internal cooling water is maintained at a constant level, so that there is a drawback that it cannot cope with a change in the molding speed. For example, when the molding speed changes, chatter vibration may occur in the parison or the tubular film, and the inner diameter of the obtained tubular film may not be constant. Furthermore, abnormal tension may occur in the tubular film. The reason why this phenomenon occurs is that if the molding speed is increased to increase molding efficiency, the inner peripheral surface of the parison comes into frictional contact with the sizing part before reaching the solidification point, that is, the frost line, and the inner peripheral surface of the parison This is probably because smoothness cannot be obtained due to the viscosity. In addition, when solidifying after passing through the sizing section, in other words, when passing through the sizing section in a softened state, the inner diameter of the tubular film is not constant. On the other hand, when the molding speed is reduced, the material is solidified before passing through the sizing portion, and a large tension is required to pass through the sizing portion having the maximum diameter. When such chatter vibration occurs, a stripe pattern is formed on the obtained tubular film, and the quality of the film is deteriorated. In addition, the wear of the sizing portion is significantly increased, the life of the sizing mandrel is shortened, and as a result, the cost is increased. Further, the tubular film may break due to abnormal tension. The present invention provides a method for forming a tubular film that has solved the above-described disadvantages, that is, even if the forming speed of the tubular film is increased, a high-quality tubular film can be obtained at a low cost, and the forming speed is reduced. It is another object of the present invention to provide a method for forming a tubular film that does not cause abnormal tension.

[0006]

The above object of the present invention is achieved by controlling and shaping the internal cooling water so that the frost line of the parison is located near the sizing portion. That is, in order to achieve the above object, according to the present invention, the parison in a molten state extruded from an annular extrusion die is provided with internal cooling water at a predetermined water level maintained above a sizing part. When passing through the sizing portion while cooling at a time, when forming a tubular film of a predetermined inner diameter, when the forming speed of the tubular film is low, the water level of the internal cooling water is lowered, when it is large, it is raised, It is configured so that the parison is kept in contact with the internal cooling water for a constant time regardless of the molding speed. The invention according to claim 2 is that the parison in the molten state extruded from the annular extrusion die is passed through the sizing section while being cooled by internal cooling water at a predetermined water level maintained above the sizing section, and the parison has a predetermined inner diameter. When chatter vibration is generated at a desired forming speed of the tubular film when forming the tubular film, the water level of the internal cooling water is gradually increased, and molding is performed at the water level immediately after the chatter vibration disappears. According to the third aspect of the present invention, the parison in a molten state extruded from the annular extrusion die is passed through the sizing section while being cooled by internal cooling water at a predetermined water level maintained above the sizing section. When forming a tubular film having an inner diameter, when chatter vibration does not occur at a desired forming speed of the tubular film, the water level of the internal cooling water is gradually lowered, and the water is formed at a water level immediately before chatter vibration occurs. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a tubular film forming apparatus used for carrying out the method of the present invention will be described below with reference to FIG. The tubular film forming apparatus generally supplies a sizing mandrel 1 for forming a tubular film, a pair of pinch rolls 37 provided below the sizing mandrel 1, and cooling water to the sizing mandrel 1. Cooling water supply device 30 to be drained, control device 40
It is composed of The sizing mandrel 1 for forming a tubular film is connected to an annular extrusion die of an extruder as is well known in the art, and the level of cooling water inside the sizing mandrel 1 is controlled by a control device 40. .

The sizing mandrel 1 according to the present embodiment also has the same appearance or shape as a conventionally known mandrel. In FIG. 1, the upper part is the sizing part 2 having the maximum diameter, and the lower part is the sizing part 2. Are also small-diameter seal ring portions 10. The sizing portion 2 and the seal ring portion 10 are connected by a guide member 15 selected to have a predetermined length in the axial direction, and a cooling water recovery container 12 is disposed further below the seal ring portion 10.

Inside the sizing mandrel 1 thus constructed, the lower end of the sizing mandrel 1 extends through the sizing mandrel 1 in the axial direction.
, A cooling water supply pipe 4 and a cooling water return pipe 7 are provided. The cooling water supply pipe 4 has a plurality of branch pipes 5, 5, ... branched radially outward in the vicinity of the sizing section 2, and these branch pipes 5, 5, ... are located near the top of the sizing section 2. It is connected to an open ring-shaped water supply nozzle 3. Therefore, the internal cooling water W is maintained at a predetermined depth water level “H” above the sizing section 2 in accordance with the amount of the cooling water supplied from the water supply nozzle 3. In addition, the cooling water supply pipe 4 further includes a plurality of second branch pipes 6 that are further branched radially outward below the sizing section 2,
, And these branch pipes 6, 6, ... open into an annular gap 16 between the skirt portion 8 of the sizing portion 2 and the upper portion of the guide member 15. Thereby, the internal cooling water W is supplied to the outer peripheral portion of the skirt portion 8. At the lower end of the guide member 15, a plurality of pores 17,
, And a plurality of pores 11, 11,... Are also formed in the bottom plate of the seal ring portion 10. Therefore,
Cooling water supplied from the annular gap 16 and the sizing part 2
The cooling water flowing down from above through the skirt 8 of
, 18, 18,... Are collected in the cooling water recovery container 12.

A water case 18 is attached to the outer peripheral portion of the sizing mandrel 1 at a predetermined interval from the outer peripheral portion. The upper end of the water case 18 is
The upper portion extends upward, and the lower portion extends close to the seal ring portion 10. A ring-shaped seal member 19 is provided at the center of the bottom of the water case 18, and the seal member 19 is pressed against the outer peripheral surface of the seal ring portion 10 via the parison P or the tubular film F. Therefore, the external cooling water W ′ is stored between the water case 18 and the parison P, and the internal cooling water W is stored inside the parison P.

The sizing mandrel 1 configured as described above is attached via a suspension member 21 to the mandrel 20 of the annular extrusion die described with reference to FIG. The mandrel 20 is mounted concentrically with the ring member 22 by a plurality of spiders 20 'as is well known in the art. The spider 20 'is provided with a cooling water supply pipe 23 and a cooling water return pipe 24, and these pipes 23 and 24 are connected to the cooling water supply pipe 4 and the cooling water return pipe 7, respectively. Have been. In addition, the mandrel 20
A die slit 25 is formed between the outer peripheral surface of the ring member 22 and the inner peripheral surface of the ring member 22 as is well known.

The cooling water supply device 30 has a water tank 31. A suction pipe 32 and a return pipe 34 are provided in connection with the water tank 31. The suction pipe 32 is connected to the cooling water supply pipe 23 provided in the spider 30 ′.
The return pipes 34 are also connected to the cooling water return pipes 24 similarly provided in the spider 30 '. A water pump 33 driven by a motor not shown in FIG. 1 is interposed in the suction pipe 32. The water tank 31
Since the inside water temperature needs to be maintained at a predetermined temperature or a constant temperature, temperature controllers such as a refrigeration cycle are provided, but these temperature controllers are not shown in FIG. Further, a water pump for returning the cooling water to the water tank 31 is not shown for the sake of simplicity.

The control device 40 controls the water level H of the internal cooling water W. The control device 40 calculates the number of rotations of the motor for driving the water pump 33 from the forming speed of the tubular film F and the water level H, and adjusts the temperature. It has various functions such as a vessel control function. The control device 40 includes the pinch roll 3
A signal relating to the rotation speed of the pinch roll 37 measured by the tachometer 41 attached to the motor 7 and thus to the forming speed of the tubular film F is input through a signal line a. In addition, a water level sensor 42 is attached in association with the sizing mandrel 1, and the water level sensor 42
The signal relating to the water level H of the internal cooling water W measured at the step (b) is input to the control device 40 through the signal line b. In the embodiment shown in FIG. 1, the water level sensor 42 includes a U-shaped sensor tube 43,
The tip 44 extends from the spider 20 'into the internal cooling water W. Then, a U-shaped portion 45 is formed outside the spider 30 ', and the water level H of the internal cooling water W is measured at the U-shaped portion 45.

The water tank 31 is provided with a temperature sensor 46, and the temperature of the cooling water measured by the temperature sensor 46 is input to the control device 40 via a signal line c so that the cooling water is maintained at a predetermined temperature. It has become. Although not shown in FIG. 1, the sizing mandrel 1 is provided with a vibrometer for measuring or detecting chatter vibration of the parison P, and this vibration is also input to the control device 40. . The control device 40 and the motor driving the water pump 33 are connected by a signal line d.

Next, an example of forming a tubular film F using the tubular film forming apparatus according to the above embodiment will be described. As is well known, when the resin material is supplied from the hopper to the extrusion cylinder and the screw is driven to rotate, the resin material is kneaded and melted, and the cylindrical parison P is extruded from the die slit 25 of the mandrel 20 of the annular extrusion die. It is. The extruded parison P is pulled toward the sizing mandrel 1, where the inside is cooled by the internal cooling water W, the outside is cooled by the external cooling water W ′, and the sizing is performed in the sizing section 2. Then, when a pair of pinch rolls 37, 37 are continuously pulled in a direction indicated by an arrow at a predetermined speed and wound around a drum, a tubular film F having a predetermined diameter is obtained as conventionally known. Further, a stretched film can be obtained by stretching this tubular film F.

When the tubular film F is thus obtained, the cooling water in the water tank 31 is supplied to the suction pipe 32, the cooling water supply pipe 23, the cooling water supply pipe 4, the branch pipe 5,
5, water is supplied from the water supply nozzle 3 so that the water level above the sizing section 2 becomes the predetermined water level H. .. Are also supplied to the annular gap 16 from the second branch pipes 6, 6,. The cooling water thus supplied is supplied to the guide member 1.
, And the pores 11, 11,... Of the seal ring portion 10 are collected in the cooling water recovery container 12. Then, the cooling water returns to the water tank 31 through the cooling water return pipe 7, the cooling water return pipe 24, and the return pipe 34. Thereafter, circulation is performed in the same manner. In addition, the external cooling water W 'at a predetermined temperature is also maintained at a predetermined water level.

The tubular film F is formed as described above, but is first formed at a desired forming speed. At this time, when chatter vibration is detected, the chatter vibration is
Is input to When chatter vibration occurs, the cooling effect needs to be enhanced because the inner peripheral surface of the parison P passes through the sizing portion 2 before reaching the frost line as described above. Since the water temperature in the water tank 31 is maintained at a constant temperature, the water pump 33 is controlled by the control device 40 to increase the rotation speed, and the water level H of the internal cooling water W is controlled.
Gradually rises. Since the water level H rises, the time of contact with the internal cooling water W becomes longer, and the degree of cooling advances. When chatter vibration is no longer detected, the frost line of the parison P is located upstream of or near the sizing portion 2 having the maximum diameter. Thereby, the relationship between the forming speed of the tubular film F measured by the tachometer 41 and the water level H of the internal cooling water W measured by the water level sensor 42 is obtained, and stored in the control device 40.

On the other hand, when molding is performed at a desired molding speed and chatter vibration is not detected, the frost line on the inner peripheral surface of the parison P is located on the upstream side of the sizing section 2 and has the maximum diameter. Excessive tension is acting on the tubular film F to pass through the tube film 2. This time, the water pump 33 is controlled by the control device 40 so as to decrease the rotation speed, and the water level H of the internal cooling water W gradually decreases. When chatter vibration is detected, the water pump 33
Is controlled by the control device 40 to increase the rotation speed.
The water level H of the internal cooling water W gradually rises. When chatter vibration is no longer detected, the frost line of the parison P is located upstream or near the sizing portion 2 having the largest diameter. Similarly, the tachometer 41
The relationship between the forming speed of the tubular film F measured by the above and the water level H of the internal cooling water W measured by the water level sensor 42 is obtained and stored in the control device 40.

If the molding speed is increased or the molding speed is set to a large value, the controller 40 determines whether the frost line of the parison P is in the vicinity of the sizing section 2 or the relationship between the measured or set molding speed and the water level H. The water level H of the internal cooling water W located immediately upstream is calculated. And
The control device 40 controls the water pump by, for example, feedback control so that the calculated water level becomes H. By this control, the water level H becomes deep. Similarly, when the molding speed is reduced, the control device 40 calculates the water level H at which the frost line is located near the sizing section 2 from the measured or set molding speed, and controls the water pump so that the calculated water level H is reached. It is controlled by feedback control. At this time, the water level H becomes shallow.

As described above, according to the present embodiment, even if the molding speed changes, the water level H of the internal cooling water W also changes, and the time during which the parison P passes through the internal cooling water W, or the internal cooling water Since the time of contact with W becomes constant, that is, the same cooling is performed even if the molding speed changes, the frost line of the parison P is located immediately upstream or in the vicinity of the sizing part 2, and chatter vibration occurs. And no abnormal tension is generated in the tubular film F.

Next, a second embodiment of the present invention will be described with reference to FIG. The same components as those of the embodiment shown in FIG. 1 are denoted by the same reference numerals and will not be described repeatedly. According to the present embodiment, there is neither a water level meter for measuring the water level of the internal cooling water W nor a speed meter for measuring the forming speed of the tubular film, but only a vibration meter 50 for detecting the vibration of the sizing part 2 or the parison P. The chatter vibration of the parison P detected by the vibrometer 50 is input to the control device 40 via the signal line e.

It is clear that the second embodiment operates in substantially the same manner. That is, molding is performed at a desired molding speed. At this time, when the vibration meter 50 detects chatter vibration,
This chatter vibration is input to the control device 40. And
The water pump 33 is controlled by the control device 40 to increase the rotation speed, and the water level H of the internal cooling water W gradually increases.
When the water level H rises and chatter vibration is no longer detected, the frost line of the parison P is located immediately upstream of the maximum diameter sizing section 2 or in the vicinity of the sizing section 2. Therefore, the molding is performed while maintaining the water level H.

On the other hand, when molding is performed at a desired molding speed and chatter vibration is not detected, the frost line of the parison P is located on the upstream side of the sizing section 2. The rotation speed is controlled so as to decrease, and the water level H of the internal cooling water W gradually decreases. When chatter vibration is detected, the frost line is located downstream of the sizing section 2, so that the water pump 33 is again controlled by the control device 40 to increase the rotation speed, and the internal cooling is performed. Water level H of water W
Gradually rises. When chatter vibration is no longer detected, the frost line of the parison P is located immediately upstream of the sizing section 2 having the largest diameter. Similarly, molding is performed while maintaining this water level. Also according to the present embodiment, the frost line of the parison P is formed at a water level located immediately upstream or in the vicinity of the sizing portion 2 having the largest diameter, so that chatter vibration does not occur, and There is no occurrence of abnormal tension in the film F.

[0024]

As described above, according to the first aspect of the invention, the molten parison extruded from the annular extrusion die is cooled by the internal cooling water at a predetermined water level maintained above the sizing portion. While passing through the sizing section, when forming a tubular film of a predetermined inner diameter, when the forming speed of the tubular film is small, the water level of the internal cooling water is lowered, when it is large, it is increased, and the forming speed of the tubular film is increased. Irrespective of whether the parison is in contact with the internal cooling water or not, the parison is formed at a constant time. Is gradually increased, and molded at the water level immediately after the chatter vibration disappears. According to the invention of claim 3, when chatter vibration does not occur at a desired tubular film forming speed, The water level of the part coolant gradually lowered,
Since the molding is performed at the water level just before chatter vibration occurs, the parison frost line is located near the sizing part, regardless of the forming speed of the tubular film, and neither parison chatter vibration nor abnormal tension occurs in the tubular film . Therefore, according to the present invention, even if the molding speed is increased, the striped pattern does not appear on the tubular film, the inner diameter is constant, the wear of the sizing portion is small, and a high-quality tubular film can be obtained at low cost. The effect that can be obtained is obtained. Further, even if the molding speed is reduced, the tubular film does not break.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing a first embodiment of a tubular film forming apparatus used for carrying out the present invention.

FIG. 2 is a front view schematically showing a second embodiment of the tubular film forming apparatus used for carrying out the present invention.

FIG. 3 is a view showing a conventional tubular film forming apparatus, in which (a) is a front view showing the whole, and (b) is a front view of a sizing mandrel.

[Explanation of symbols]

1 Sizing mandrel 2
Sizing part 30 Cooling water supply device 40
Control device 41 Tachometer 42
Water level meter 10 Annular extrusion die 50
Vibrometer P Parison F
Tubular film W Internal cooling water H
Internal cooling water level

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F207 AG08 AH00 AK02 AP07 AP11 AP20 AQ04 AR07 AR09 KA01 KA17 KK63 KK76 KK77 KM02 KM15 KM22

Claims (3)

[Claims] 1. A molten parison extruded from an annular extrusion die is passed through the sizing section while being cooled by internal cooling water at a predetermined water level held above the sizing section to form a tubular film having a predetermined inner diameter. When the forming speed of the tubular film is low, the water level of the internal cooling water is lowered, and when it is large, the water level is set high and the time for the parison to contact the internal cooling water is constant regardless of the forming speed of the tubular film. A method for forming a tubular film, characterized by forming. 2. A molten parison extruded from an annular extrusion die is passed through the sizing section while being cooled by internal cooling water at a predetermined water level held above the sizing section, to form a tubular film having a predetermined inner diameter. When chatter vibration is generated at a desired tubular film forming speed, the water level of the internal cooling water is gradually increased, and forming is performed at a water level immediately after the chatter vibration disappears. Method. 3. A parison in a molten state extruded from an annular extrusion die is passed through the sizing section while being cooled by internal cooling water at a predetermined water level held above the sizing section to form a tubular film having a predetermined inner diameter. When chattering does not occur at the desired tubular film forming speed, the level of the internal cooling water is gradually lowered, and the forming is performed at the water level immediately before chattering occurs. .