JP2004106534A - Manufacturing method for inflation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a smooth film without causing slackening or wrinkles. <P>SOLUTION: In this air cooling type manufacturing method for the inflation film, a raw material resin is extruded from an annular die in a molten state to form an annular film, air is supplied into the inner space of the annular film under cooling to inflate the film and the annular film solidified by cooling is taken over while flatly folded through a guide member. The temperature Tf(°C) of the annular film solidified at the time of contact with the guide member satisfies a relational expression [Tf≤Tr(5)]. Tr(5) shows a temperature at which a thermal deformation ratio of the solidified annular film becomes 5% when measurement is made by applying stress having magnitude same to frictional force receiving from the guide member under the condition at the time of production of the film. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for producing an inflation film that suppresses film slack and wrinkles.

The inflation molding method is widely used for the production of films made of thermoplastic resins including polyolefin resins such as low density polyethylene and high density polyethylene because the apparatus is simple and inexpensive.

FIG. 1 shows an outline of a general inflation film forming apparatus. According to this apparatus, the molten thermoplastic resin is extruded from the annular die 2 of the extruder, the extruded annular film 4 is taken out while being cooled, and at the same time, a gas such as air is supplied to the inner space of the annular film. Inflated to a predetermined size by internal pressure. The annular film 4 is solidified to reach the final diameter, and is then gradually flattened by being guided by a pair of guide members 11 that are inclined so that the downstream sides in the resin extrusion direction are close to each other. Thereafter, the film is folded flat by a pair of nip rolls 5 disposed on the downstream side and taken outward, and both ends of the folded film are cut with a slitter or the like to be taken up as two flat films. Or as it is wound up as a bag-like film.
Many proposals have been made regarding inflation molding. For example, Japanese Patent Laid-Open No. 9-109274 (Patent Document 1) is a water-cooled inflation molding method in which the outer surface of an annular film expanded to a predetermined size is rapidly cooled with water, and the inner surfaces of the annular film are melted together. The manufacturing method of the inflation film which adjusts a cooling rate so that it may become the temperature range which can be adhere | attached, and folds with a nip roll, fuse | melting inner surfaces mutually is disclosed. According to this method, blocking of the resulting film is prevented, and high-speed take-up is possible. In the water-cooled inflation molding method, a film with good transparency is generally obtained by rapid cooling.
Japanese Patent Application Laid-Open No. 2001-239583 (Patent Document 2) describes a method for producing a blown film excellent in transparency at high speed and with a stable thickness of a film to be molded by a (μm), Inflation molding is performed so that a × b ≧ 1600 and a × c ≧ 720 are satisfied, where b (m / min) is the molding speed and c (° C./second) is the peak cooling rate of the molten resin. is suggesting.
Furthermore, Japanese Patent Laid-Open No. 10-29243 (Patent Document 3) discloses that an aromatic crystalline thermoplastic resin having a melt flow rate of 3 to 8 is made near the melting point of the aromatic crystalline thermoplastic resin to below the melting point. Disclosed is a method for producing an air-cooled blown film, which is extruded downward from a die having a set die temperature. According to the description of the publication, it is said that a film having a small apparatus and a low cost for molding and having excellent transparency can be obtained from an aromatic crystalline thermoplastic resin. Further, as an apparatus useful for carrying out the method, an apparatus for producing an inflation film is described in which a stabilizer and a pinch roll are integrated and movable in the vertical direction.

In such inflation film molding, it has been pointed out that when the formed film is rigid, slack and wrinkles are generated in the film and the commercial value is lowered.
JP-A-9-109274 Japanese Patent Laid-Open No. 2001-239583 JP-A-10-29243

Therefore, the present invention generates slack and wrinkles even when a thermoplastic resin such as engineering plastic having a relatively high rigidity, that is, a high elastic modulus and a low elongation at break is used as a raw material resin. It is an object of the present invention to provide an inflation molding method capable of obtaining a smooth film.

As a result of intensive studies, the present inventors have found that the above problem can be solved by sufficiently reducing the temperature when the annular film solidified by cooling is produced by air-cooled inflation molding and the annular film solidified by cooling is in contact with the guide member. The present invention has been completed.
That is, the present invention melts and extrudes the raw material resin from an annular die to form an annular film, and blows a cooling gas on the outer surface of the annular film to cool and cool the inner space to supply and expand the gas, A method for producing an air-cooled inflation film comprising pulling an annular film solidified by cooling while being folded into a flat shape through a guide member, wherein the temperature Tf of the solidified annular film at the time of first contact with the guide member ( (° C.) provides a method for producing an inflation film satisfying the following relational expression.
Tf ≦ Tr (5)
Tr (5): a temperature at which the thermal deformation rate of the solidified annular film becomes 5% when measured by applying a stress having the same magnitude as the frictional force received from the guide member under the conditions for film production.

In the inflation molding, studies have been made from various viewpoints for the purpose of preventing the occurrence of slack and wrinkles on the film, and various methods have been proposed as improvement measures. Such improvement measures include, for example, (1) a method of disposing a heat retaining cylinder for retaining the film between the expansion start portion of the melt-extruded annular film and the guide member (Japanese Patent Laid-Open No. 4-53728), ( 2) A method for providing a gas blowing port in a take-up stabilizing plate (guide member) and taking it out while deforming the annular film inward (Japanese Patent Laid-Open No. 4-7120), (3) via a roller having a vibration absorbing mechanism A method of reducing the frictional resistance that the annular film receives from the guide member and taking it out while absorbing the vibration generated in the film (Japanese Patent Laid-Open No. 2000-289106), (4) The molten resin contacts the molten resin extruded from the die A method of cooling and folding the portion to be flattened by wrapping it with a pair of flexible guide members made of a gas-permeable member (Japanese Patent Laid-Open No. 2001-162667) Gazette). However, the present invention is completely different from these previously proposed improvements in the solution principle.

According to the present invention, a good inflation film with less slack and wrinkles can be obtained.

Examples of the raw material resin that can be used in the present invention include low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene, α-olefin polymer, and ethylene-unsaturated ester copolymer. In addition to olefinic resins such as polymers, ethylene-vinyl alcohol copolymers, soft polyvinyl chloride, soft polyvinylidene chloride, polyamide, polystyrene, polyarylate, thermoplastic liquid crystal polymers such as thermoplastic liquid crystal polyester, etc. .

As the thermoplastic liquid crystal polymer, those having a melting point in the range of 200 to 400 ° C., preferably 250 to 350 ° C. are used in terms of processability and heat resistance of the obtained film.

The present invention is characterized in that the temperature Tf (° C.) of the solidified annular film at the first contact with the guide member is equal to or lower than the temperature Tr (5).
In the manufacturing method of the present invention, the annular film is sufficiently cooled when it comes into contact with the guide member, and deformation due to frictional resistance from the guide member is sufficiently suppressed. Therefore, it is possible to obtain a film having good quality without occurrence of slack and wrinkles.

It is known that in the production of an inflation film, blocking of the film obtained by folding it with a nip roll after sufficiently cooling can be prevented. For this purpose, it has been widely practiced to adjust the cooling rate of the molten resin extruded from the die. However, the temperature at which the film after being extruded from the die, cooled, and solidified is brought into contact with the guide member that guides the film to the nip roll has not been sufficiently studied so far. By adjusting the temperature at which the solidified film comes into contact with the guide member to the specific range described above, a film free from slack and wrinkles can be obtained for the first time by the inventors' examination. It has become.

The magnitude of the frictional force that the annular film receives from the guide member varies depending on conditions such as the type of raw resin, the material of the guide member, the surface properties of the guide member, temperature, humidity, and the pressure of the gas supplied to the inside of the film. To do. In the manufacturing method of the present invention, taking into account all of these various factors, the magnitude of the frictional force (Fd) that the annular film solidified during film manufacturing receives from the guide member is obtained in advance by calculation. Then, the thermal deformation rate of the film when the same stress as the frictional force (Fd) is applied is measured by a preliminary experiment, and a temperature (Tr (5)) at which this becomes 5% is obtained. . Based on this temperature, adjustment is performed so that the temperature of the solidified annular film is within a predetermined range.

FIG. 2 is a schematic view showing an embodiment of the present invention. In the figure, a case where a thermoplastic liquid crystal polyester is used as a raw material resin is shown, and the molten raw material resin is extruded from the die 2 to form an annular film 4. A gas is supplied to the inner space of the molten annular film 4, and the molten annular film 4 is expanded by the action of the gas, and the diameter gradually increases. The molten annular film 4 is cooled by a cooling gas blown to the outer surface from a cooling ring provided close to the annular die, and reaches the frost line 10 to be solidified. The solidified annular film 4 comes into contact with the pair of guide members 11 and is folded flat. In the figure, a pair of flat plate-like members are used as the guide member 11 and are arranged so that the downstream side based on the raw material resin extrusion direction has a narrow width. In addition, as the guide member 11, a plurality of rolls can be used instead of the flat plate. Examples of the guide member 11 include those made of a metal such as aluminum and stainless steel, those made of a fabric made of cotton and chemical fibers, those made of a polymer compound such as polytetrafluoroethylene, and cardboard. What was comprised with various materials, such as what was comprised with papers and what was comprised with the glass-like inorganic substance, can be used. In addition, the guide member 11 may be formed by combining various materials described above, such as a plate made of a polymer compound and a metal, or a plastic roll wound with a woven fabric. Further, the guide member 11 may have a smooth surface, or may have fine unevenness on the surface.

In FIG. 2, an air ring 31 is installed on the upstream side (lower side) of the guide member 11 so as to face the outer peripheral portion of the annular film 4, and a gas (for example, air) for cooling the solidified annular film 4. Is configured to be sprayed onto the outer surface of the annular film 4. Further, a temperature sensor 32 such as an infrared type for detecting the temperature of the solidified annular film is provided downstream of the air ring 31 and upstream of the guide member 11.

The temperature sensor 32 is connected to the input side of the CPU 33, and the regulator 34 and the valve 35 are connected to the output side of the CPU 33. The CPU 33 controls the regulator 34 and the valve 35 to control the air from the ring 31 so that the temperature of the solidified annular film 4 is equal to or lower than the Tr (5) described above when contacting the guide member 11. Adjust the supply amount.

The control mode of the temperature of the annular film 4 when the film is manufactured by the method shown in FIG. 2 is as follows. First, the temperature Tr (5) obtained by a preliminary experiment in the CPU 33 is set (step 1), and the temperature of the annular film 4 when contacting the guide member 11 is the temperature sensor 32. And the detected value is read by the CPU 33 (step 2). Next, the CPU 33 determines whether or not the read temperature of the annular film 4 is below the temperature [Tr (5)] set in step 1 (step 3). At this time, if the temperature of the annular film 4 is higher than the predetermined temperature, the amount of gas blown from the air ring 31 to the outer surface of the annular film 4 is increased by the output from the CPU 33 (step 4). If the temperature of the annular film 4 is below the set temperature [Tr (5)], step 4 is omitted and the operation from step 2 is repeated. In this way, the temperature of the annular film 4 when contacting each guide member 11 is controlled to be equal to or lower than the set temperature.

In FIG. 2, the raw material resin is extruded upward from the die 2 to form the annular film 4. However, in the present invention, when the raw material resin is extruded downward, further in the lateral direction. It can also be applied when extruding.

Further, in the embodiment described above, the air volume from the air ring 31 is controlled to adjust the temperature of the annular film 4 to be equal to or lower than a predetermined temperature [Tr (5)]. In the adjustment, (A) the position of the guide member 11 is moved in the drawing direction of the annular film 4 (vertical direction in this embodiment), (B) the temperature of the atmosphere around the annular film 4 is adjusted, (C) A method of adjusting the temperature of the gas blown out from the air ring 31 can also be adopted.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples. In the following examples, the thermal deformation rate, appearance, and film thickness variation of the film were measured or evaluated by the following methods.

(1) Thermal deformation rate A test piece having a width of 5 mm and a length of 20 mm was cut out from the film, and the change in length at a predetermined temperature was measured using a thermomechanical analyzer [TMA-50; manufactured by Shimadzu Corporation]. In the measurement, a constant tensile load is applied to one end of the test piece, and a stress (N / mm) of the same magnitude as the frictional force received from the guide member during film production is loaded in the length direction of the test piece. did. Based on this measured value, the thermal deformation rate at a predetermined temperature was calculated. Measurements were made at various temperatures, and graphs showing the relationship between temperature and thermal deformation rate were obtained. From this graph, the temperature at which the thermal deformation rate was 5% was read.
(2) Appearance of film The appearance of the obtained film was visually observed at a length of 1000 m and evaluated in the following four stages.
A: No generation of soot is observed. O: 1-10 occurrences of soot are observed. Δ: 11-50 occurrences of soot are observed. X: 51 or more generations of soot are observed. (3) Film Thickness variation The obtained film was sampled 4 m in the take-up direction (machine axis direction: MD direction), 20 points in the take-off direction (20 cm interval), 24 points in the direction perpendicular to the take-off direction (TD direction), a total of 480 points The film thickness was measured at (20 × 24), and the difference between the maximum value and the minimum value was defined as the film thickness variation.

Using the molding apparatus shown in FIG. 2, a thermoplastic liquid crystalline polyester (Polyplastics, Vectra A950) is used as a raw material resin, and inflation molding is performed under the following conditions. A film having an average film thickness of 25 μm and an average folding width of 314 mm Got. The die 2 used at this time has an outer diameter of 49.5 mm and an inner diameter of 50.0 mm. Further, the discharge amount of the molten resin was set to 13 kg / hr, the film take-up speed was set to 9.9 m / min, and adjustment was made so that the frost line 10 was formed at a position 300 mm (height) from the die 2. In addition, an air ring 31 is installed at a position 1000 mm (height) from the die 2, and the guide member 11 [a member having a length of 2 m, made of stainless steel plate (SUS304), has a lower end at a position 2000 mm from the die 2; Lower end opening: 200 mm, upper end opening: 20 mm]. The air volume from the air ring 31 was adjusted so that the temperature (Tf) of the film 4 when it first contacted the guide member 11 was 100 ° C. The appearance and film thickness variation of the obtained film are as shown in Table 1.
The frictional force that the annular film 4 receives from the guide member 11 when the film is manufactured is calculated to be 0.32 N / mm.
From the obtained film, a rectangular test piece was cut out to have a length of 20 mm in the take-up direction (MD) and a width of 5 mm in the direction (TD) perpendicular to the take-up direction, and the above-described friction force and The thermal deformation rate was measured in a state where stress of the same magnitude was applied.
The temperature [Tr (5)] at which the thermal deformation rate was 5% was 120 ° C.

Comparative Example 1
A film having an average film thickness of 25 μm and an average folding width of 314 mm was obtained in the same manner as in Example 1 except that the air ring 31 was not installed. The temperature of the annular film 4 when first contacting the guide member 11 was 160 ° C., and the temperature of the annular film 4 when reaching the upper end of the guide member 11 was 140 ° C. The appearance and film thickness variation of the obtained film are as shown in Table 1.
In this example, the magnitude of the frictional force that the annular film 4 receives from the guide member 11 during the film production is calculated to be 0.32 N / mm.
From the obtained film, a rectangular test piece was cut out to have a length of 20 mm in the take-up direction (MD) and a width of 5 mm in the direction (TD) perpendicular to the take-up direction, and the above-described friction force and The thermal deformation rate was measured in a state where stress of the same magnitude was applied.
The temperature [Tr (5)] at which the thermal deformation rate was 5% was 120 ° C.

Comparative Example 2
The average film thickness is 25 μm in the same manner as in Example 1 except that the air volume blown from the air ring 31 is changed and the temperature of the film 4 when it first contacts the guide member 11 is adjusted to 130 ° C. A film having an average folding width of 314 mm was obtained. In this example, the temperature of the annular film 4 when it reached the upper end of the guide member 4 was 110 ° C. The appearance and film thickness variation of the obtained film are as shown in Table 1.
In this example, the magnitude of the frictional force that the annular film 4 receives from the guide member 11 during film production is calculated to be 0.32 N / mm.
From the obtained film, a rectangular test piece was cut out to have a length of 20 mm in the take-up direction (MD) and a width of 5 mm in the direction (TD) perpendicular to the take-up direction, and the above-described friction force and The thermal deformation rate was measured in a state where a stress of the same magnitude was applied.
The temperature [Tr (5)] at which the thermal deformation rate was 5% was 120 ° C.

Using the molding apparatus of FIG. 2, a thermoplastic liquid crystal polyester (Polyplastics, Vectra C950) is used as a raw material resin, and inflation molding is performed under the following conditions. The film has an average film thickness of 50 μm and an average folding width of 314 mm. Got. The die 2 used at this time has an inner diameter of 39.0 mm and an outer diameter of 40.0 mm. The discharge amount of the molten resin was set to 26 kg / hr, the film take-up speed was set to 10 m / min, and the frost line 10 was adjusted to be formed at a position 350 mm (height) from the die 2. In addition, an air ring 31 is installed at a position 1000 mm (height) from the die 2, and the guide member 11 [a member having a length of 2 m, made of stainless steel plate (SUS304), has a lower end at a position 2000 mm from the die 2; Lower end opening: 200 mm, upper end opening: 20 mm]. The air volume from the air ring 31 was adjusted so that the temperature (Tf) of the film 4 when it first contacted the guide member 11 was 120 ° C. The appearance and film thickness variation of the obtained film are as shown in Table 2.
The frictional force that the annular film 4 receives from the guide member 11 during film production is calculated as 0.3 N / mm.
From the obtained film, a rectangular test piece was cut out to have a length of 20 mm in the take-up direction (MD) and a width of 5 mm in the direction (TD) perpendicular to the take-up direction, and the above-described friction force and The thermal deformation rate was measured in a state where stress of the same magnitude was applied.
The temperature [Tr (5)] at which the thermal deformation rate was 5% was 140 ° C.

As the guide member 11, a 2 m long plate-shaped member made of a stainless steel plate (SUS304) coated with a glass woven cloth reinforced Teflon (registered trademark) sheet [manufactured by Chukoh Chemical Industry Co., Ltd., FGF-500-4 (product number)] The opening (200 mm, opening of the upper end: 20 mm) of the lower end is used, and the temperature (Tf) of the film 4 when it first comes into contact with the guide member 11 by adjusting the air volume from the air ring 31 becomes 130 ° C. Except for the above adjustment, inflation molding of a thermoplastic liquid crystal polyester (Polyplastics Corp., Vectra A950) was performed in the same manner as in Example 1 to obtain a film having an average film thickness of 25 μm and an average folding width of 314 mm. The appearance and film thickness variation of the obtained film are as shown in Table 2.
The frictional force that the annular film 4 receives from the guide member 11 during film production is calculated to be 0.15 N / mm.
From the obtained film, a rectangular test piece was cut out to have a length of 20 mm in the take-up direction (MD) and a width of 5 mm in the direction (TD) perpendicular to the take-up direction, and the above-described friction force and The thermal deformation rate was measured in a state where stress of the same magnitude was applied. The temperature [Tr (5)] at which the thermal deformation rate was 5% was 145 ° C.

It is the schematic which shows an example when shape | molding the conventional inflation film. It is the schematic which shows the shaping | molding apparatus used for the manufacturing method which concerns on one Embodiment of this invention. It is a graph for demonstrating the film obtained in Example 1, 3 and the comparative examples 1 and 2 about the relationship of the temperature-thermal deformation rate obtained based on the measurement result by a thermomechanical analyzer.

Explanation of symbols

2 annular die 4 annular film 5 nip roll 10 frost line 11 guide member 31 air ring 32 temperature sensor

Claims (2)

Raw material resin is melt-extruded from an annular die to form an annular film, and a cooling gas is blown to the outer surface of the annular film to cool and supply the gas to the inner space to expand it. A method for producing an air-cooled inflation film comprising drawing a film through a guide member while folding it into a flat shape,
A method for producing an inflation film, wherein the temperature Tf (° C.) of the solidified annular film upon first contact with a guide member satisfies the following relational expression.
Tf ≦ Tr (5)
Tr (5): a temperature at which the thermal deformation rate of the solidified annular film becomes 5% when measured by applying a stress having the same magnitude as the frictional force received from the guide member under the conditions for film production. The method for producing an inflation film according to claim 1, wherein the annular film is formed by extruding a raw material resin upward from the annular die.

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