JPH04286626A - Inflation molding method and device - Google Patents

Abstract

PURPOSE:To manufacture a smooth film without generating creases on the film even when thermoplastic resin of comparatively high rigidity such as polyolefin resin is used in the inflation molding. CONSTITUTION:A ring film 4 is formed by extruding resin in the molten state out of a ring die 4, and while the ring film 4 is expanded by gas blown into its inner space 4a while bing cooled, and then its downstream side is immersed in a liquid path 8 to seal the space 4a without using a nip roll. After that, the film is cut along the extrusion direction in the liquid path 8 through slitters 9a and 9b and taken off through guide rolls 10a and 10b.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] This invention is applicable to extrusion moldable materials such as polyolefin resins such as polyethylene and polypropylene, ethylene-vinyl alcohol copolymer resins, liquid crystal polymers, etc. The present invention relates to a method and an apparatus for forming a film from a thermoplastic resin by an inflation method. [0002] The inflation molding method is widely used in the production of films made of thermoplastic resins including polyolefin resins such as low-density polyethylene and high-density polyethylene because the equipment is simple and inexpensive. has been done. [0003] In the general inflation molding method, a molten thermoplastic resin is extruded through an annular die of an extruder.
While the outer surface of the extruded annular film is cooled by air blown out from the cooling ring, a gas such as air is simultaneously supplied to the inner space of the annular film to expand it to a predetermined size by internal pressure, and then, A film is formed by pressing an annular film together using a pair of nip rolls, dividing it into two pieces by cutting both ends with a slitter, and then winding up each of the divided flat films separately or at the same time. be. [0004] In the production of film by the conventional inflation molding method as described above, a pair of closely-contacted nip rolls seals a gas such as air supplied to the inner space of the annular film. It plays the role of maintaining the internal pressure at a predetermined pressure, and when the annular film is pressed one on top of the other by this pair of nip rolls, it is particularly effective against polyolefin resins, ethylene-vinyl alcohol copolymer resins, liquid crystal polymers, and other various types. When using highly rigid thermoplastic resins such as engineering plastics, if the diameter of the annular film extruded from the annular die varies slightly or if the film thickness is uneven, the above-mentioned problems may occur. Wrinkles are likely to occur on the film when it passes through the nip rolls, and these wrinkles are a factor in lowering the commercial value of the film. [0005] This invention was made in view of the above-mentioned circumstances, and it is possible to form a smooth film without wrinkles even when using a relatively rigid thermoplastic resin. The object of the present invention is to provide an inflation molding method and apparatus. Means for Solving the Problems In order to achieve the above object, the inflation molding method according to the present invention extrudes a molten resin to form an annular film, and while cooling the film, the inner space is In the inflation molding method, the material is supplied with gas and expanded by internal pressure.
Gas is sealed in the inner space by immersing the downstream side of the annular film in a liquid, and the annular film is cut along the extrusion direction in the liquid to produce a flat film. This method is characterized by taking off a membranous film. Further, the inflation molding apparatus according to the present invention includes an extrusion means for extruding the molten resin in an annular shape, a cooling means for cooling and solidifying the extruded annular film, and a gas injecting into the inner space of the annular film. an internal pressure applying means for supplying and expanding the internal pressure; an enclosing means for enclosing gas in the inner space by immersing the downstream side of the annular film in liquid; and an enclosing means for cutting the annular film along the extrusion direction in the liquid The present invention is provided with a cutting means for producing a flat film using the same method, and a taking-off means for taking off the flat film. Next, the inflation molding method and apparatus of the present invention will be explained in more detail based on drawings showing embodiments thereof. FIG. 1(a) shows a schematic cross-sectional view of an example of an inflation molding apparatus of the present invention. Further, FIG. 1(b) is a plan view showing the slitter of FIG. 1(a). In FIG. 1(a), the thermoplastic resin that has been melted and kneaded into a fluid state inside the extruder 1 is
An annular film 4 is formed by being extruded downward in an annular shape from an annular die 3 through an adapter 2 at the tip. This annular film 4 is cooled and solidified by a gas a such as air blown out from a cooling ring 5 disposed around the annular die 3, and a gas b such as expansion air is introduced into the inner space 4a. is supplied from the gas inlet 6 and expanded to a predetermined size by its internal pressure. The annular film 4 (bubble) expanded and solidified in this way gradually deforms from a cylindrical shape to an elliptical shape along the stabilizer plates 7a and 7b, which are arranged to be inclined so that the width becomes narrower toward the lower end. While moving, from its bottom end,
It is immersed in a liquid bath 8 such as water. As a result, the inner space 4a of the annular film 4 is filled with a gas b such as air. Next, in the liquid bath 8, the annular film 4 is passed through a slitter 9 as shown in FIG. 1(b).
Both ends are cut along the extrusion direction by a and 9b to produce flat films 4Aa and 4Ab, which are then wound onto take-up rolls 11a and 11b via separate guide rolls 10a and 10b, respectively. To be taken away by being taken. Here, the flat films 4Aa, 4Ab after being cut by the slitters 9a, 9b may be wound up in an overlapping state by the same guide roll. The cooling ring 5 and the gas inlet 6 are connected to the same gas supply source 14 such as a compressor via pressure regulating valves 12 and 13, respectively.
A relatively low pressure gas (air) a is supplied from the gas inlet 6, and a relatively high pressure gas (air) b is supplied from the gas inlet 6. The extruder 1, the adapter 2, and the annular die 3 constitute extrusion means of the present invention, the cooling ring 5, the pressure regulating valve 12, and the gas supply source 14 constitute the cooling means, and the gas inlet 6, the pressure regulating valve 13 and gas supply source 14 serve as internal pressure applying means, liquid bath 8 and guide rolls 10a, 1
0b is the enclosing means, slitters 9a and 9b are the cutting means,
The take-up rolls 11a and 11b each constitute a take-up means. FIG. 2 is a schematic sectional view showing an example of another molding apparatus for carrying out the inflation molding method of the present invention, and the difference from FIG. The annular film 4, which is cooled and solidified by the gas a blown out from the ring 5, is not deformed into an elliptical shape by the stabilizing plate, but is immersed in the liquid bath 8 while keeping the cylindrical shape, so that the inner space 4a is filled with air like air. gas b
Since the other parts are the same as those in FIG. 1, the same reference numerals are given to the corresponding parts and the explanation thereof will be omitted. In this device as well, the flat films 4Aa, 4Ab after being cut by the slitters 9a, 9b may be wound up in an overlapping state by the same guide roll. In the inflation molding method and apparatus of the present invention, there is no particular restriction on the thermoplastic resin that can be extruded, and usable thermoplastic resins include low-density polyethylene, medium-density polyethylene, high-density polyethylene, and polypropylene. , olefin resins such as α-olefin copolymers and ethylene-unsaturated ester copolymers; ethylene-vinyl alcohol copolymer resins; soft vinyl chloride resins; soft vinylidene chloride resins;
Liquid crystal polymer; various engineering plastics, etc. can be exemplified. [Function] According to the present invention, in order to expand the annular film by internal pressure, gas to be supplied to the inner space of the annular film is filled, instead of using a pair of nip rolls as in the conventional method. Since the downstream side is immersed in a liquid such as water to form a liquid seal, there is no need for the film to pass through narrow and frictional areas, so the diameter of the annular film extruded from the annular die can be reduced. Even if there is slight variation or unevenness in film thickness, it is possible to form a smooth film without wrinkles. Especially high-density polyethylene,
Since highly rigid resins such as liquid crystal polymers tend to wrinkle when pressed together with nip rolls, the molding method and apparatus according to the present invention are extremely effective. EXAMPLES Examples of the present invention will be explained in more detail below. Example 1 Using a 40 mmφ extruder 1 shown in FIG.
00SF) was extruded from a ring die 3 having a diameter of 40 mm and a lip interval of 0.5 mm to form an annular film 4. Solidifying air was blown from the cooling ring 5, and the temperature and volume of the cooling air were controlled so that a frost line was formed at a predetermined distance from the tip of the ring die 3. The extruded annular film 4 is guided into water 8, and both ends of the film 4 are cut by slitters 9a and 9b installed in the water to divide it into two pieces, and each film 4Aa and 4Ab is guided by guide rolls 10a and 10b. Take-up roll 11a
, 11b. When the annular film 4 is extruded stably, the expansion air inlet 6
Air was introduced into the inner space 4a to form a bubble 4. At this time, the width of the films 4Aa and 4Ab after passing through the slitters 9a and 9b is 200 mm, respectively.
and the thickness of each was 50 μm. Films 4Aa and 4Ab formed in this manner had no visually observed vertical or horizontal wrinkles, and smooth films were obtained. In addition, high-density polyethylene ring die 3
By changing the amount of extrusion from
A film of m was wound up. In this case as well, no wrinkles were observed. Furthermore, when similar molding was performed using the apparatus shown in FIG. 2, smooth films with no wrinkles were obtained in both cases of 50 μm and 75 μm thick films, as in the above. Example 2 The apparatus in Example 1, ie, FIGS. 1(a) and (
Using the apparatus shown in b) or the apparatus shown in FIG. 2, a liquid crystal polymer (Novaculate E310, manufactured by Mitsubishi Kasei) was extruded to form films with thicknesses of 50 μm and 75 μm, respectively. In any case, as in Example 1, no vertical or horizontal wrinkles were observed. Comparative Example In the apparatus shown in FIGS. 1(a) and 1(b), the guide rolls 10a and 10b were replaced with a pair of nip rolls,
Using a device that eliminates the liquid bath 8, high-density polyethylene (
Hyzex 5000SF manufactured by Mitsui Petrochemical Industries) or liquid crystal polymer (Novaculate E310 manufactured by Mitsubishi Kasei)
) film was molded. That is, after extruding the resin from the ring die 3, the expanded and cooled bubbles 4 were pressed together using nip rolls, both ends of the folded tubular film were cut with a slitter, and the film was wound up. A large number of vertical and horizontal wrinkles were observed in the film thus formed. The number of wrinkles per unit area visually observed in the wound film was as follows. For high-density polyethylene film with a thickness of 50 μm: 1
15 films/m2 For high-density polyethylene film with a thickness of 75 μm: 6
0 lines/m2 For liquid crystal polymer with a thickness of 50 μm: 130 lines/m2
For liquid crystal polymer with a thickness of 75 μm: 70 lines/m2 [
As is clear from the above Examples 1 and 2 and the comparative example, the nip roll is not used, but instead the downstream side of the annular film is immersed in a liquid such as water to seal the inner space. By this, wrinkles do not occur in the formed film, and a smooth film can be obtained. [0020] As described above, according to the method and apparatus of the present invention, rigidity can be improved by simply employing a simple means of immersing the downstream side of the annular film in a liquid instead of using nip rolls. Even when using a thermoplastic resin with a high viscosity, a smooth film without wrinkles can be produced, and the commercial value can be improved.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic sectional view of an example of an inflation molding apparatus for carrying out the inflation molding method according to the present invention, and FIG. 1(b) is a plan view showing the slitter of FIG. 1(a). be.

FIG. 2 is a schematic cross-sectional view showing an example of another inflation molding apparatus for carrying out the method of the present invention.

[Explanation of symbols]

1... Extruder, 3... Annular die, 1-3... Extrusion means, 4... Annular film (bubble), 5... Cooling ring, 5, 12, 14... Cooling means, 6... Gas blowing port, 6, 13, 14 ...Internal pressure adding means, 8...
Liquid bath, 9a, 9b... slitter (cutting means),
10a, 10b...guide roll, 8, 10a, 10
b... Enclosing means, 11a, 11b... Winding roll (take-up means).

Claims (2)

[Claims] 1. An inflation molding method in which a molten resin is extruded to form an annular film, and while cooling the film, gas is supplied to the inner space of the film and the film is expanded by internal pressure, the downstream side of the annular film being expanded. Filling the inner space with gas by immersing it in a liquid,
An inflation molding method comprising: cutting the annular film in a liquid along the extrusion direction to produce a flat film, and then taking the flat film. 2. Extrusion means for extruding molten resin in an annular shape, cooling means for cooling and solidifying the extruded annular film, and internal pressure application for supplying gas to the inner space of the annular film to expand it due to internal pressure. means for sealing gas into the inner space by immersing the downstream side of the annular film in a liquid; and cutting for cutting the annular film along the extrusion direction in the liquid to produce a flat film. and a taking-off means for taking off the flat film.