JPH0247338B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for forming a tubular film by an air-cooled inflation method, and more specifically, a method for forming a tubular film by continuing the operation of a forming machine without interrupting the operation of the forming machine. The present invention relates to a method for maintaining stable operation by expanding and contracting the maximum outer diameter of a cylindrical stabilizer of the molding machine according to changes in the diameter of the constriction of a bubble, and a cylindrical stabilizer used therein. It is something.

Conventionally, polyolefin synthetic resin such as polyethylene is melt-extruded from a molding die into a tubular shape using the air-cooled inflation method, cooled with air, and taken out while maintaining the same shape as the annular lip of the die. The method of manufacturing a film by expanding and molding a resin bubble into a funnel shape is widely used because it provides a film with good balance of mechanical strength in both vertical and horizontal directions and excellent impact strength. However, when a tubular film is formed using this forming method, the resin bubbles tend to oscillate, resulting in uneven thickness, wrinkles, or sag in the resulting tubular film, and the folded diameter of the tubular film becomes uneven. There was a drawback. As a way to solve this drawback, the diameter of the annular lip of the die,
A cylindrical stabilizer with approximately the same outer diameter is installed,
A method is adopted in which the molten resin bubbles extruded from the die and before the start of expansion are made to follow the outer surface of the side wall of the stabilizer to prevent the resin bubbles from shaking.

The factors that determine the diameter of the bubble neck are the folding diameter of the film, the thickness of the film, the shape of the die,
Possible factors include the film take-up speed, the temperature of the molten resin, and the physical properties of the resin. Therefore, the shape of the stabilizer must be changed each time depending on the required folding diameter and thickness of the film, but conventionally the method was to temporarily stop the operation and replace it with a separate stabilizer. This required a lot of operational effort and unavoidable loss of a large amount of product.

The present invention overcomes the above-mentioned drawbacks, expands and contracts the maximum outer diameter of the cylindrical stabilizer at any time according to the diameter of the neck of the bubble without interrupting operation, and achieves a balanced vertical and horizontal strength. The purpose of the present invention is to provide an inflation film forming method that can produce films at high speed.

That is, in the method of the present invention, when molding a film using synthetic resin, an expandable cylindrical stabilizer has an airtight structure and is fixed so that its central axis is coaxial with the inflation die. is,
Also, use a structure that allows the maximum outer diameter of the stabilizer to be varied by adjusting the air pressure inside the stabilizer through an air inlet installed along its axis. It is characterized by

Furthermore, in order to avoid direct contact between the resin bubble and the outer periphery of the side wall of the cylindrical stabilizer, the outer periphery of the side wall of the cylindrical stabilizer is wrapped around the coil panel in multiple stages along the circumference. The second feature is that it has been constructed in such a way that there is no problem with the removal of bubbles.

Next, the present invention will be specifically explained with reference to the drawings.

In FIG. 1, the molten resin extruded from an extruder 1 is extruded from an inflation die 2 into a tube shape through a die lip 2a, and an air cooling ring 3
While cooling from the side, air is blown from the blow-up air supply pipe 9 to expand the bubble 5. At this time, the maximum outer diameter of the cylindrical stabilizer 7 is expanded or contracted by the air pressure supplied from the air supply pipe 8 for the cylindrical stabilizer so that the constriction 4 of the bubble 5 comes into contact with the bubble 5 while adjusting the contact area. 5 to prevent shaking and maintain stable operations.

In FIG. 2, the cylindrical stabilizer 7 is made of a material that can withstand the temperature of the molten resin during molding, and is suitably made of, for example, synthetic rubber, which has a heat resistance temperature of around 230°C. Further, the cylindrical stabilizer 7 can be uniformly expanded and contracted in the radial direction, and its maximum outer diameter can be freely selected depending on the internal air pressure.

3 and 4 both show coil springs, and the outer periphery of the side wall of the cylindrical body stabilizer 7 to be wound is grooved so that the spring can be easily attached and difficult to come off. It is attached.
The dimensions of the coil spring 10 can be selected depending on the purpose.

In FIG. 5, a holder tube 6 passes through the cylindrical stabilizer 7 along its central axis to vertically fix the stabilizer body and to supply air into the stabilizer. There are no particular limitations on the diameter of the holder tube 6, as the diameter may be selected to facilitate construction. This holder tube 6 is connected to an air supply tube 8 for the cylindrical stabilizer. The maximum outer diameter of the stabilizer is adjusted by a stabilizing control valve 13 and expanded or contracted by air pressure fed through an air inlet 11.

The expansion of the bubble is carried out by air passed through a blow-up air supply pipe 9 and regulated by a blow-up control valve 12. The air cooling ring 3 is installed so that air uniformly flows upward from the periphery of the bubble 5. Here, the blow-up air for expanding the bubble, the air for expanding and contracting the stabilizer, and the air for bubble cooling are each supplied from different sources, and are characterized in that they can be adjusted independently of each other.

Examples of resins that can be used to form blown films using the method and apparatus of the present invention include polyolefin resins, such as low density and high density polyethylene or polypropylene. Moreover, the operation is extremely stable even at a maximum take-up speed of 80 m/sec.

Examples are listed below to explain more specific embodiments of the present invention.

Example 1 High-density polyethylene (Nissan Polyethylene (registered trademark) 3001) with a melt flow rate of 0.05 (JIS K6760, test temperature 190°C, test load 2.16 kg) was processed using an extruder made by Plako Co., Ltd. with a cylinder inner diameter of 50 mm.
The die slip with the tip of the extruder attached has an inner diameter of 75
mm, upward from a spiral die with a lip clearance of 1.0 mm, resin temperature 215℃, extrusion amount
It was melt extruded at 25 kg/h. A cylindrical stabilizer made of synthetic rubber with a diameter of 60 mm and a length of 300 mm was fixed to the die concentrically with its central axis such that the distance from the top surface of the die to the bottom surface of the stabilizer was 250 mm.
Additionally, the following coil spring was attached around the stabilizer.

Spring coil outer diameter 7 mm Coil wire diameter 1 mm Coil pitch 2 mm Stabilizer side wall step spacing 10 mm Number of steps 28 steps Adjust the blow-up air amount and cooling air amount so that the constriction position is approximately 400 mm from the top of the die. Adjustments were made so that the bubbles were generated at points, and bubbles having the shape shown in FIG. 1 were formed. The bubble is in contact with a cylindrical stabilizer, without shaking, with a thickness of 1.5 μm and a fold diameter of 450 mm.
The film was operated at a take-up speed of 36 m/min. The dart impact strength (ASTM D1709) of the tubular film obtained was 246 g.

Example 2 Following the molding in Example 1, the size of the film product was reduced to a thickness of 20μ without interrupting the molding in the middle of the operation.
When changing the fold diameter to 450 mm, the diameter of the constriction became larger than the diameter of the cylindrical stabilizer, so the bubbles did not come into contact with the stabilizer, making the molding unstable and making it impossible to obtain a product. . Therefore, the internal air pressure of the cylindrical stabilizer was increased to increase the maximum outer diameter of the stabilizer.
When the diameter was changed to 70 mm, the constriction was able to conveniently contact the stabilizer and the operation could be continued. The dart impact strength of the obtained tubular film is
It weighed 257g.

Example 3 Following the molding in Example 2, the product size of the film was changed to 20 μm in thickness without interrupting the molding in the middle of the operation.
When the folding diameter was changed to 500 mm, the molding became unstable and the product could not be obtained.

Therefore, by increasing the internal air pressure of the cylindrical stabilizer and changing the maximum outer diameter of the stabilizer to 78 mm, the constriction was able to conveniently contact the stabilizer, allowing operation to continue as is. The dart impact strength of the resulting tubular film was 282 g.

Comparative example: The main body of the cylindrical stabilizer is made of felt and the outer diameter is 70 mm.
The following three types of films were molded under the same conditions as in the above examples except that:

Film thickness (μm) Fold diameter (mm) (A) 20 500 (B) 20 450 (C) 15 450 In the case of (A), the neck of the bubble does not contact the cylindrical stabilizer and the fold diameter changes. I couldn't get the product.
In the case of (b), the operation was good and a product similar to that of Example 2 was obtained, with a dart impact strength of 253 g. (c)
Although operation was possible in the case of Example 3, the dart impact strength of the obtained film was 132 g, which was significantly lower than that of Example 3.

As described above, in order to increase the strength of the product film while maintaining the stability of the bubble, it is necessary to select a cylindrical stabilizer suitable for each product size. However, according to the method and apparatus of the present invention, the maximum diameter of the constriction of the stabilizer can be expanded or contracted simply by operating the control valve of the air supply pipe without interrupting the operation at all, so there is no product loss. It can be seen that high-quality products can be stably produced.

[Brief explanation of the drawing]

FIG. 1 shows an explanatory diagram of the air-cooled inflation film forming method, FIG. 2 shows an external view of the cylindrical stabilizer of the present invention, FIG. 3 shows a plan view of the spring coil, and FIG. This is a cross-sectional view taken in the A--A direction of FIG. 3, and FIG. 5 is a schematic cross-sectional view of a molding machine including an inflation die and a cylindrical stabilizer. 1... Extruder, 2... Inflation die, 2a... Die slip, 3... Air cooling ring,
4...Neck of bubble, 5...Bubble, 6...
Holder pipe, 7... Cylindrical stabilizer, 8... Air supply pipe for cylindrical stabilizer, 9... Air supply pipe for blow-up, 10... Coil spring, 11... Air inlet, 12... Adjustment for blow-up Valve, 13...Control valve for stabilizer.

Claims (1)

[Claims] 1. When molding a blown film using synthetic resin, a telescopic device is attached to the upper center of a die, has an airtight structure, and has an outer diameter adjusted by internal air pressure. The narrow part of the bubble extruded from an inflation die is brought into contact with the outer periphery of a coil spring that is wound in multiple stages along the circumference of the side wall of a cylindrical stable body, and the bubble is taken out while being expanded. Inflation film molding method. 2. A telescopic cylindrical stabilizer is fixed so that its central axis is coaxial with the inflation die, and the air pressure inside the stabilizer is adjusted through an air inlet installed along the axis. The method according to claim 1, characterized in that the method has a structure such that its maximum outer diameter is variable.