JPH10166441A - Method for molding inflation film and bag body using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that in a conventional inflation molding, when molding speed is increased to enhance the productivity, insufficient a cooling and deterioration of molding stability occurs so that production cannot be containued for a long period of time. SOLUTION: In an inflation molding method wherein the inner surface of a tubular molten thermoplastic resin extruded, in a molten state, from an annular die makes contact with the surface of a cooling device to form a tubular film, a cooling device 5, which is disposed coaxially with an annular die 1 and in which a surface to be in contact with a tubular molten resin 10 is made from ceramics, is disposed in a tubular molten resin 10, extruded from the die 1 into an annular form, so as to be displaced from an expansion start point 2, between an annular die 1 and the point 2 where the resin begins to expand, by a distance 50mm or more and from the annular die 1 by a distance 35mm or more, and a cooling medium 8 is fed into the device 5 so that the resin 10 is brought into contact with the device 5 to cool the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to an improved method for producing a tubular film. More specifically, in the present invention, a tubular film of a polyolefin resin is formed by inflation molding at a speed of 1.5 times or more, that is, 60 m / min. In order to enable stable molding at high speed for two days or more at high speed,
The present invention relates to a high-speed inflation molding method which enhances a cooling effect and improves a slip property between a cooling body and a molten resin.

[0002]

2. Description of the Related Art Conventionally, thermoplastic resin films, particularly polyolefin resin films, produced by an inflation molding method are used for packaging, agricultural and industrial materials,
It is widely used for shopping bags and the like. For the production of such polyolefin resin films,
Conventionally, 40 m / min. It is produced at the following speeds. In recent years, in order to increase productivity, there has been a demand for an inflation molding method at high speed. In order to increase the molding speed of the inflation molding method, development of an efficient cooling method in the inflation molding process during which the molten resin is extruded from the annular die and undergoes expansion deformation to form a tubular film, and long-term stable molding Method development is required. Conventionally, when a film is obtained by inflation molding with a polyolefin-based resin, as a general cooling method, cooling air is blown in the same direction as the molten tubular resin extruded from the annular die near the annular die surface, to the extruded tubular resin. A cooling method that blows out toward has been performed. However, in such a cooling method, 40 m / min. Although there is no problem in performing inflation molding at the following low speed, if the molding speed is increased and a large amount of cooling air needs to be blown, molding stability decreases, and it is difficult to perform inflation molding. Become.

[0003] In order to improve the cooling effect, for example, a method of blowing cooling air over a plurality of stages from the vicinity of a frost line (end point of expansion deformation) to an internal stabilizer (Japanese Patent Publication No. 1-52171). Various external cooling methods have been studied so far. However, these methods have poor heat removal efficiency due to the use of gas as a cooling medium in any of the methods, and have a limited cooling effect.
Therefore, in order to improve the heat removal efficiency,
Attempts have been made to cool with aerosolized water as proposed in US Pat. No. 7224. But,
Since the apparatus around the tubular molten resin extruded from the annular die becomes large-scale, there is a tendency that the operation of pulling up the tubular molten resin at the time of the molding start operation becomes difficult. JP-A-48-23666, JP-A-55-34911, JP-A-2-34324, and JP-A-4-254.
No. 19 discloses a method of cooling by installing a stabilizer passing through a cooling medium inside a bubble (expanded tubular resin). However, these techniques still have significant problems. The biggest problem is that the slip between the stable body and the molten tubular resin through the cooling medium deteriorates with time, and the film is cut in a few hours, so that long-term production cannot be performed.

[0004]

As described above, various cooling methods for inflation molding have been developed so far, but with these methods, there are insufficient cooling and long cooling caused by high-speed inflation molding. It cannot sufficiently solve the problem of molding stability during the period. The present invention has been made in view of the above-mentioned drawbacks, and is intended to stably produce a high-quality tubular film at 60 m / min. An object of the present invention is to provide an improved inflation molding method for manufacturing at a high speed as described above.

[0005]

According to the present invention, there is provided an inflation molding method in which a tubular molten thermoplastic resin melt-extruded from an annular die contacts a cooling device surface to form a tubular film. Inside the tubular molten resin (10), a thermoplastic resin is filled with an annular die (1).
A distance of at least 50 mm from the inflation start point (2) during the period from when the tube is extruded into a tube to when the inflation start point (2) is reached,
A cooling device (5) which is coaxially arranged with the annular die (1) and whose surface in contact with the tubular molten resin (10) is made of ceramics is installed in a range at least 35 mm away from the annular die (1). Producing a tubular film, characterized in that the tubular molten resin (10) is brought into contact with the cooling device (5) and cooled by passing a cooling medium (8) into the cooling device (5). The present invention relates to an inflation molding method.

The thermoplastic resins used in the present invention include polyolefin resins, polystyrene resins, polystyrene resins such as copolymers of acrylonitrile and styrene, copolymers of acrylonitrile, butadiene and styrene, and polyvinyl chloride. Resin, polyvinylidene chloride resin,
Examples thereof include polyamide resins such as nylon 6 and nylon 66, polyester resins such as polyethylene terephthalate, and polyvinyl alcohol resins. These resins may be used alone or in combination of two or more. You may mix and use. The polyolefin resin is a high-density polyethylene resin, a high-pressure low-density polyethylene resin, a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, a polypropylene resin, a copolymer of ethylene and propylene, and ethylene and vinyl acetate. And the like. For the copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, examples of the α-olefin having 3 to 12 carbon atoms include propylene, 1-butene, 1-pentene and 1-hexene. And 4-methylpentene-1,1-octene and 1-decene.

The resin used in the present invention is preferably a polyolefin resin among these resins. More preferably, among the polyolefin resins, a high-density polyethylene resin, a high-density low-density polyethylene resin, a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, and a copolymer of ethylene and vinyl acetate. From the viewpoint of the melt flow rate, the melt flow rate (AST
MD1238) 0.01 g / 10 min. ~ 5.0
g / 10 min. Is preferred. More preferably,
Melt flow rate 0.01 g / 10 min. ~ 0.1
g / 10 min. Is preferred. More preferably,
Melt flow rate 0.01 g / 10 min. ~ 0.1
g / 10 min. High density polyethylene resin is preferred.

[0008] The expansion starting point described in the present invention means that when inflation molding is performed, the thermoplastic molten resin is extruded from an annular die to form a tubular film. (4) The point at which the expansion starts at (TD) and the frost line (ie, the molten thermoplastic resin extruded into a tubular shape from the annular die passes through the expansion start point and undergoes expansion deformation, and then the horizontal expansion deformation ends). ) Shows the position (2) where the expansion starts.

The cooling device (5) according to the present invention is arranged coaxially with the annular die as shown in FIG.
It is preferable to use a cylindrical shape according to the shape of the extruded annular molten resin, but it is not particularly limited, and a cylindrical shape, a polygonal column shape, a conical shape, a polygonal pyramid shape, and the like can be used, and further, these are combined. Shapes can also be used. With the above-described shape and arrangement, the cooling device (5) can have a function of further contributing to stabilization of the tubular molten resin during inflation molding.

It is necessary that the surface in contact with the tubular molten resin (10) is made of ceramics. When the surface in contact with the tubular molten resin (10) is not made of ceramics, the sliding of the tubular molten resin (10) and the cooling device (5) is insufficient, and it is difficult to form the resin stably for a long period of several hours or more. . Preferably the tubular molten resin (10) of the cooling device (5)
If the roughness of the ceramic surface of the surface in contact with the surface is from 1 to 50 microns in Ra surface roughness by the DIN method, and if the Ra surface roughness is less than 1 micron, the tubular molten resin (10)
And the sliding of the cooling device (5) may be insufficient.
If the surface roughness is larger than 50 microns, a clog occurs between the tubular molten resin (10) and the cooling device (5),
Molding may become unstable in a few hours. Furthermore, the thickness of the ceramic surface that contacts the tubular molten resin (10) is:
The thickness is preferably 0.05 to 2.00 mm, and when the thickness is less than 0.05 mm, the heat transfer is too large, so that the tubular molten resin (10) may be solidified in the cooling device (5), If the molding is difficult, on the other hand, if the thickness is more than 2.00 mm, the cooling effect is reduced because the heat transfer is too small, and 50 m / min. The above high-speed molding may not be possible.

Further, the material of the ceramic surface in contact with the tubular molten resin (10) is preferably a sprayed ceramic, and when the material of the ceramic surface is a combination of ceramic blocks or the like, the tubular molten resin is formed at the block boundary surface. (10) may be scratched, resulting in defects of the formed film. Further, the average particle size of the ceramic powder of the sprayed ceramic is preferably from 1 to 200 μm. If the average particle size is less than 1 μm, the surface of the sprayed ceramic becomes too smooth and the tubular molten resin (1
0), the molding may become unstable in several hours, and if the average particle size is larger than 200 microns, smooth contact with the tubular molten resin (10) becomes impossible, The surface of the molten resin (10) may be damaged.

The ceramics on the surface which comes into contact with the tubular molten resin (10) are oxide-based ceramics such as white alumina, gray alumina, alumina titania, alumina zirconia, spinel, mullite, magnesia spinel, zirconia mullite, chromia, and chromia. There are titania, titania, nickel oxide, magnesia silica, zircon, CaO stabilized zirconia, MgO stabilized zirconia, Y ₂ O ₃ stabilized zirconia, and the like. Tungsten carbide cermet, titanium carbide cermet, chromium carbide cermet, silicon carbide cermet and the like as carbide ceramics. Other ceramics include graphite cermet, silicon nitride cermet, boron nitride cermet, and silicon nitride whisker.

The maximum diameter of the cooling device used in the present invention is:
There is no particular limitation as long as a high-quality film can be stably produced at a high speed for a long period of time.
It is preferably at most twice. If the diameter is less than one time,
The contact between the cooling device (5) and the tubular molten resin (10) may not be uniform, and if the diameter is more than 2.5 times, the molding start operation may be difficult. Regarding the contact area between the cooling device (5) and the tubular molten resin (10), the molding stability is not limited uniformly since it varies depending on the inflation molding conditions. It is preferable that the cooling device (5) and the tubular molten resin (10) are brought into contact with the entire contact area where they can come into contact under the molding conditions at that time. Further, depending on the conditions, it is sufficient that the contact area is three-quarters or more of the contact area that can make contact.

The cooling medium (8) used in the present invention is not particularly limited, but includes, for example, air, water,
Examples include oils and antifreeze. The cooling medium may be used alone or as a mixture.

In the inflation molding method described in the present invention, in addition to using the cooling device (5), a well-known air cooling device (6) conventionally used outside may be used in combination. The number of air cooling devices is not limited and may be used alone or a plurality of air cooling devices may be used. Further, a bubble stabilizing device such as a Wiris ring, an iris ring, a bubble basket, or the like may be used during a period from the time when the tubular film is completed to be expanded and deformed in the lateral direction until the tubular film is taken up by the pinch roll (3). The high-quality film in the present invention refers to a film having a small variation in the width of the film, a small thickness unevenness in the circumferential direction of the die, and excellent mechanical properties of the film.

Next, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 shows an example of an inflation molding method of the present invention, FIG. 2 shows an example of a cooling device of the present invention, and FIG. 3 shows a schematic diagram of an example of a conventional inflation molding method. In FIG. 1, a molten resin is extruded into a tube from an annular die (1) connected to an extruder, and after passing an expansion start point (2), undergoes expansion deformation and a frost line (4).
To form a tubular film, which is taken up by a pinch roll.

In the present invention, a cooling device (5) whose surface in contact with the tubular molten resin (10) is made of ceramic is installed inside the extruded tubular molten resin (10).
Further, a cooling medium (8) is passed through the cooling device (5),
The tubular molten resin (10) is taken out while being brought into contact with the cooling device (5), the inside of the tubular molten resin (10) is cooled, and the outside is cooled by an external air cooling device (6) such as an air ring. Inflation molding method. When cooling is performed by an external air cooling device (6) such as an air ring, the cooling air is preferably injected toward the cooling device (5). Even when strong cooling air is injected into the tubular molten resin (10), since the cooling device (5) is supported inside, the tubular molten resin (10) is not deformed inward and the inflation molding method is stably performed. It becomes possible.

In FIG. 2, (A) is a surface of the cooling device (5) which comes into contact with the tubular molten resin (10) and is made of ceramics, and (B) is a surface of the cooling device (5). (C) is a passage of a cooling medium in the cooling device (5), and (D) is a structure formed of aluminum.
(E) is a pipe for introducing air into the bubble, and is a pipe for discharging the cooling medium to the outside of the cooling device (5).
(F) indicates a pipe for introducing a cooling medium into the cooling device (5).

In the conventional well-known inflation molding method in which only air cooling is performed from the outside (FIG. 3), when high-speed inflation molding is performed, the cooling becomes insufficient, and 40 m / mi.
n. In the above-described molding, the frost line (4) rises to make molding difficult. Further, in order to improve the insufficient cooling, if the amount of cooling air is increased, the vibration of the bubble becomes large, and it is difficult to obtain a normal product. However, in the inflation molding method of the present invention as shown in the example of FIG. 1, since the tubular molten resin (10) is cooled by contact with the cooling device (5) inside, the cooling effect is high. When used together, cooling is performed from both the inside and the outside, so that the cooling effect is extremely high. However, due to contact cooling, slippage between the tubular molten resin (10) and the inner cooling body deteriorates after several hours of molding, and there is a disadvantage that molding is difficult in several hours. In the present invention, the use of ceramics on the surface of the cooling body enables stable molding for a long period of two days or more. In a conventionally known air-type internal cooling method, the inside of a bubble is an open system, and cooling air is constantly taken in and out from the outside. Therefore, it is necessary to finely adjust the amount of cooling air flowing in and out. For this reason, it was not possible to cope with some change in external factors, and there was a drawback that the film width was likely to fluctuate during long-term operation. However, in the inflation molding method of the present invention, since the inside of the bubble is a closed system, air does not flow into and out of the outside, the bubble is stable, and therefore a high-quality film having good dimensional accuracy can be obtained. Longer than 60 days, 60 m / min. It is possible to easily obtain at the above high speed. As described above, according to the present invention, fills of various thicknesses and widths are set to 60 m / min. It is possible to manufacture stably at such a high speed for a long period of two days or more.

The diameter L1 of the expansion start point (2) cannot be uniformly defined because it differs depending on the inflation molding speed and other conditions, but is preferably smaller than the diameter L0 of the annular die. The cooling device (5) includes a cooling medium (8).
As shown in FIGS. 1 and 2, a cooling medium (8) is put into a lower part outside a cooling medium supply pipe (F), and a cooling medium is sent from a cooling medium discharge pipe (D) from an upper part as shown in FIGS. The method of (8) is preferable.

The temperature of the cooling medium (8) communicating with the inside of the cooling device (5) varies depending on the amount of molten resin to be extruded and cannot be uniformly defined. The temperature is preferably in the range of -10 to + 140 ° C. Depending on molding conditions, it may be in the range of -10 to + 70 ° C. Further, the flow rate of the cooling medium (8) cannot be uniformly defined for the same reason, but is not more than 1 liter / sec.
It may be 2 liters / second or less.

The inflation molding method of the present invention can be effectively applied not only to the formation of a single-layer film, but also to the formation of a multilayer film having two or more layers. The inflation molding method of the present invention has a molding speed of 60 m / min. Above, preferably 80 m / min. A great effect is exhibited by the above molding.

In the inflation molding method of the present invention, an ordinary internal stabilizer may be installed near the expansion start point (2) to perform inflation molding depending on conditions.
The internal stabilizer used at this time is not particularly limited, but the surface is covered with felt, knitting, woven fabric, nonwoven fabric, or the like, or coated with Teflon resin or the like to improve the slipperiness of the molten resin and the internal stabilizer. It is preferred to use a stable internal stabilizer. The diameter of the internal stabilizer is preferably 1.0 to 1.5 times the diameter (L1) of the tubular molten resin (10) at the expansion start point (2). As a method for producing a bag from a film formed by the inflation molding method of the present invention, there is a method in which heat sealing is performed at one or several places. Generally, the strength of the heat sealing portion tends to be inferior to the film strength, and the heat sealing portion The smaller the number, the more the strength of the bag tends to be stable.

[0024]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Example 1 As raw material resin, density (ASTM D1505) 0.9
54 g / cm ³ , melt flow rate (ASTM D
1238) 0.06 g / 10 min. Was molded using an inflation molding apparatus having an extruder having a screw diameter of 70 mm, a die having a die diameter of 100 mm, and a die having a die gap of 1.2 mm. Also,
An internal stabilizer whose surface was covered with felt was installed near the expansion start point, and the extruder and the die were molded at a set temperature of 200 ° C.

As shown in FIG. 1, cooling devices (5) and (6) were mounted on an inflation molding device. The cooling device (5) uses aluminum as a structural member, and uses white alumina having an average particle size of 50 microns on the contact surface with the tubular molten resin so that the Ra surface roughness by DIN method becomes 9 microns and the thickness becomes 0.5 mm. Into a cylindrical shape. An air ring device was used for the cooling device (6). The cooling device (5) was cooled using water as a cooling medium, and the cooling device (6) was cooled using air as a cooling medium. As shown in FIG. 1, the cooling device (5) was installed such that its lower end was at a position of 40 mm from the die and its upper end was at 415 mm from the expansion start point (2). The size of the cooling device (5) is 105 mm in diameter,
A 145 mm high columnar one was used. The cooling device (6) was installed such that the lower end of the cooling outlet was located 50 mm above the annular die. First, only the cooling device (6) was operated to perform normal inflation molding, and then the cooling device (5) was operated to form an expansion start point (2) at a position 600 mm above the die. Then, the film size was adjusted to a thickness of 20 microns and a film width of 350 mm.
min for 48 hours, and the molding stability was measured.

Example 2 The cooling device (5) was installed at a position such that its lower end was 10 mm from the die.
The same operation as in Example 1 was performed except that the position was set to 0 mm. Comparative example 1 It carried out similarly to Example 1 except having removed the cooling device (5). Comparative Example 2 The same operation as in Example 1 was performed except that the surface of the cooling device (5) was not subjected to the ceramics treatment.

Comparative Example 3 The installation position of the cooling device (5) was such that the lower end was 30
The procedure was performed in the same manner as in Example 1 except that the position was set at the position of mm. Comparative Example 4 Example 1 except that the installation position of the cooling device (5) was set such that the upper end thereof was located at a position 30 mm from the expansion start point.
The same was done. Comparative Example 5 The same procedure as in Example 1 was carried out except that the surface of the cooling device (5) was wound with a felt without performing the ceramics treatment. The results are shown in Table 1 below.

[0028]

[Table 1]

[0029]

According to the inflation molding method of the present invention, insufficient cooling is eliminated, and since the inside of the bubble is a closed system, a high-quality film can be produced at 60 m / mi for a long time.
n. The above-mentioned high-speed and stable production is possible.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of an inflation molding method of the present invention.

FIG. 2 is a schematic view showing one example of a cooling device of the present invention.

FIG. 3 is a schematic view showing one example of a conventional inflation molding method.

[Explanation of symbols]

 (1) Annular die (2) Expansion start point (3) Pinch roll (4) Frost line (5) Cooling device (6) External air cooling device such as air ring (7) Guide plate (8) Cooling medium (9) Hole for ventilation (10) Tubular molten resin (A) Ceramics (B) Cooling device structure (C) Cooling medium passage (D) Cooling medium discharge pipe (E) Air pipe for film size adjustment (F) Cooling medium supply pipe

Claims (6)

[Claims] In an inflation molding method, an inner surface of a tubular molten thermoplastic resin melt-extruded from an annular die comes into contact with a surface of a cooling device to form a tubular film. Between the point at which the resin is extruded into a tube from the annular die (1) and the point at which the resin reaches the expansion start point (2), a distance of 50 mm or more from the expansion start point (2) and at least 35 mm from the annular die (1). A cooling device (5), which is arranged coaxially with the annular die (1) and whose surface in contact with the tubular molten resin (10) is made of ceramic, is provided with a cooling medium inside the cooling device (5). (8) The blown molding method for producing a tubular film, wherein the tubular molten resin (10) is brought into contact with the cooling device (5) to be cooled. 2. A surface in contact with the tubular molten resin (10),
2. A cooling device (5) comprising a ceramic surface having a Ra surface roughness of 1 to 50 microns by a DIN method.
Molding method. 3. The surface in contact with the tubular molten resin (10),
The molding method according to any one of claims 1 to 2, further comprising a cooling device (5) comprising a ceramic surface having a thickness of 0.05 to 2.00 mm. 4. A surface in contact with the tubular molten resin (10),
The molding method according to any one of claims 1 to 3, further comprising a cooling device (5) made of sprayed ceramics. 5. The sprayed ceramic has an average particle size of 1 to 2
5. The molding method according to claim 4, comprising ceramic particles of 00 microns. 6. A bag comprising a film obtained by the molding method according to claim 1 and having one heat-sealed portion.