JPH06262675A - Production of plastic film - Google Patents

Abstract

PURPOSE:To produce a laterally stretched plastic film reduced in bowing phenomenon and uniform in physical properties in the lateral direction thereof by cooling a film to a predetermined value or less before the heat treatmet process after lateral stretching and setting the temp. rising speed in the heat treatment process to a predetermined value or more. CONSTITUTION:In the production of a plastic film heat-treated after stretched at least in the lateral direction thereof by a tenter, a cooling process cooling a laterally stretched film to 70 deg.C or lower before a heat treatment process is provided and the temp. rise speed of the film in the heat treatment process is set to 1000 deg.C/sec or more. The longitudinal shrink stress of the film is cut at a time of lateral stretching by providing the cooling process but, since the thermal shrinkage of the film at a time of the application of heat is generated before the heat treatment process, a bowing phenomenon can not be prevented only by providing the cooling process. However, since thermal shrinkage stress becomes low by increasing the temp. rising speed, the thermal shrinkage stress can be prevented by setting the temp. rising speed to 1000 deg.C/sec or more.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing at least a transversely stretched plastic film. More specifically, the present invention relates to a method for producing a plastic film stretched at least in the transverse direction in which the bowing phenomenon and the anisotropy of physical properties in the width direction, which are caused by performing transverse stretching with a tenter and heat treatment, are reduced.

[0002]

2. Description of the Related Art Plastic films are
It is used in various fields depending on its thermal characteristics.
In particular, a plastic film stretched in the machine direction, the transverse direction, or its biaxial direction is more preferably used because it has excellent mechanical properties. However,
In a transversely stretched or biaxially stretched film, it is said that anisotropy of physical properties occurs in the width direction of the film due to a so-called bowing phenomenon in the production process of stretching in the transverse direction, that is, in the transverse stretching in the tenter, and the heat treatment step. There's a problem. The bowing phenomenon referred to here is a phenomenon in which a straight line drawn in the width direction before entering the tenter is curved in a bow shape with a delay in the central portion of the film when exiting the tenter. Due to this bowing phenomenon, the principal axis of molecular orientation is tilted in the width direction, and thus strength, dimensional stability, etc. are changed in the width direction. This causes troubles such as misalignment during printing, meandering and curling, and deterioration of recording characteristics due to warpage in the apparatus as a base film of a floppy disk.

This bowing phenomenon is due to the fact that the transverse stretching and the heat treatment, which are the conventional processes for producing a stretched film, are continuously performed with the same tenter. For this,
Technology for relaxation between transverse stretching and heat treatment (Japanese Patent Publication No. 35-
No. 11774), a technique for forcibly advancing the central part of the film by a narrow nip roll (Japanese Patent Publication No. 63-24).
459), a technique of providing a nip roll group between the lateral stretching and the heat treatment process (Japanese Patent Laid-Open No. 50-73978), and the like.

Among them, as disclosed in JP-A-3-193328 and JP-A-3-216326, bowing is caused by a method of providing a cooling step of a certain length or more between the transverse stretching and the heat treatment step. Although it is considered to be considerably reduced, the results of our investigation show that the effect is not yet sufficient.

[0005]

As described above, although there is a strong demand for improving the anisotropy of the physical properties in the width direction by bowing, there is a problem that the bowing reduction effect by various studies is not sufficient. .

In order to solve such problems, the present invention provides a method for producing a plastic film stretched at least in the transverse direction to reduce the bowing phenomenon and obtain a film having uniform physical properties in the width direction. It is intended.

[0007]

The method for producing a plastic film according to the present invention, which meets this object, is a method for producing a plastic film by stretching at least in the transverse direction with a tenter and then performing heat treatment. Before the above, a cooling step of cooling the film to 70 ° C. or less is provided, and the temperature rising rate in the heat treatment step is 1000 ° C. /
It is a method for producing a plastic film, which is characterized in that the time is at least 2 seconds.

The present invention will be described in detail below.

The plastic referred to in the present invention is a so-called thermoplastic resin, that is, a resin which is softened by applying heat and can be plastically processed. For example, polyolefin resin represented by polyethylene, polypropylene, polymethylpentene, etc., polyamide resin represented by nylon 66, nylon 6, etc.,
Vinyl resins such as polyvinyl chloride and polyvinyl acetate, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and other acrylic resins, styrene resins, polycarbonate resins, polyacetal resins, polyphenylene Examples thereof include oxide resins, polyphenylene sulfide resins, polyurethane resins, polyvinylidene chloride resins and the like. Further, homopolymers of these resins may be used, but copolymers may also be used.

Various known additives such as antioxidants, antistatic agents, crystal nucleating agents, and inorganic particles may be added to the plastic.

The film stretched in at least the transverse direction in the present invention means a film stretched in a direction perpendicular to the longitudinal direction of the film by a tenter. Needless to say, it may be biaxially stretched, and it may be stretched in the longitudinal direction and the transverse direction a plurality of times. Specifically, a melt-extruded, substantially non-oriented film is stretched in the transverse direction, or stretched in the longitudinal direction and then stretched in the transverse direction, and also stretched in the longitudinal direction and stretched in the transverse direction. May be combined multiple times. Further, stretching may be performed simultaneously in the machine direction and the transverse direction. After these stretching steps, heat treatment is performed to impart dimensional stability and flatness. Usually, this heat treatment step is carried out subsequently in the tenter after lateral stretching or simultaneous biaxial stretching in the tenter. In the present invention, the term "lateral stretching" hereinafter refers to stretching with a tenter, including simultaneous biaxial stretching.

In the present invention, in order to reduce the bowing phenomenon, it is necessary to cool the film to 70 ° C. or less after the transverse stretching by the tenter and before the heat treatment step. It is preferably 50 ° C or lower, more preferably 30 ° C or lower. The bowing phenomenon is a force that pulls back from the heat treatment process side to the lateral stretching side due to the thermal contraction stress when heat is applied and the longitudinal contraction stress during lateral stretching, but both ends of the film are gripped by clips. Therefore, it is not pulled back, and is caused by pulling back only the central portion of the softened film in the heat treatment step. Therefore, by providing a cooling process between the transverse stretching process and the heat treatment process, and once cooling the film to a temperature of 70 ° C. or less to give the film rigidity, it is possible to prevent only the central part from being pulled back. To do.

However, as a result of earnest studies by the authors, it was found that a sufficient effect for reducing the bowing phenomenon cannot be obtained only by providing the cooling step as described above.
That is, by providing a cooling step, the shrinking stress in the machine direction during transverse stretching can be cut, but the heat shrinking stress when heat is applied occurs when entering the heat treatment step. The bowing phenomenon due to shrinkage stress cannot be prevented. However, as a result of intensive studies by the authors, it was surprisingly found that this heat shrinkage stress becomes smaller as shown in FIG. 1 by increasing the temperature rising rate during film heating. That is, in the present invention, the temperature rising rate in the heat treatment step is 1000 ° C /
It must be more than a second. Preferably 2000
C./second or higher, more preferably 2500.degree. C./second or higher. If the rate of temperature increase is less than 1000 ° C./second, the heat shrinkage stress is large and bowing cannot be prevented, as described above.

The method for obtaining the temperature rising rate is not particularly limited, but a method using a combination of hot air having a high wind speed and an infrared heater is recommended. Heat treatment with a roll has a large heat transfer coefficient, but since it is heated from one side, the rate of temperature rise is not as large as expected, and if it is not in close contact with the roll, the temperature rise effect will be significantly worse. Due to unevenness, it is difficult to heat-treat uniformly, which is not preferable.

In the present invention, it is preferable that after the transverse stretching, the film is once removed from the clip of the tenter and then passed through the cooling step. As described above, in the transverse stretching step, longitudinal shrinkage stress occurs. Therefore, when the film is gripped by the clip at this time, both ends of the film are fixed and the central part of the film is in a free state, so that different strains are accumulated in the central part and both ends of the film.
Therefore, after the transverse stretching, the film is once removed from the clip and then passed through a cooling step, whereby such strain is eliminated, which is preferable.

Further, in the present invention, it is preferable that the heat treatment step is performed while being held by a clip.
It is also preferable to apply without gripping the clip. When it is gripped by a clip, it is a heat treatment under some tension, which is preferable for improving the flatness of the film. At this time, it is also preferable to perform a relaxing process in the lateral direction by shortening the interval between the clips in order to impart dimensional stability. On the other hand, when the film is not gripped by the clip, the film is heat-treated under no tension, which is particularly preferable for improving dimensional stability. The heat treatment at this time is also preferably carried out while being supported by rolls in an oven, but more preferably, a so-called floating-type floating heat treatment, which is supported by hot air. In addition, the heating method is preferably an oven method using hot air that is uniformly heated from both sides, rather than heating with a roll.

Further, according to the studies made by the authors, it is preferable that the traveling speed V1 during transverse stretching and the traveling speed V2 during heat treatment are V1> V2. That is, if high tension is applied between the transverse stretching step and the heat treatment step, strain will be accumulated in the film. In addition, by setting V1> V2, it is possible to combine the relaxation processing in the vertical direction,
It is preferable for improving dimensional stability.

Further, in the present invention, after the transverse stretching, before the cooling step, the transverse stretching temperature is not less than (transverse stretching temperature + 50 ° C.).
It is also preferable to perform preliminary heat treatment below. This preliminary heat treatment relaxes the heat shrinkage stress generated, improves the flatness,
In addition, it is preferable because it can be subjected to a relaxation treatment and the like. The preliminary heat treatment may be performed in the tenter, may be removed from the clip with a heating roll, or may be an oven heat treatment with hot air.

Next, the manufacturing method of the present invention will be explained.
It is not limited to such an example.

An example in which polypropylene is used as the plastic is shown, but the stretching conditions such as temperature differ depending on the resin. Polypropylene pellets at 270-300 ° C
It is supplied to the extruder heated to the temperature of and is extruded into a sheet form from the T die.

The melted sheet is adhered and solidified on a drum cooled to a drum surface temperature of 25 ° C. to obtain an amorphous unstretched film. When biaxially stretching, the unstretched film is heated by a heating roll group of 120 to 150 ° C. and longitudinally stretched in a single stage or in multiple stages 5 to 8 times in the longitudinal direction,
It cools with a roll group of 20-50 degreeC.

Then, transverse stretching is performed. The both ends of the longitudinally stretched film or the unstretched film are introduced into a tenter while holding both ends with clips, and transversely stretched 7 to 10 times in the transverse direction in a hot air atmosphere heated to 130 to 150 ° C.

The biaxially stretched film is subjected to a heat treatment at 150 to 160 ° C. in order to impart flatness and dimensional stability, but before that, it is subjected to a cooling step of cooling to room temperature to 60 ° C. At this time, the clip may be removed once. Next, by using a high-speed hot air and an infrared heater in combination, a heating rate of 1000 ° C./sec or more and a heating rate of 150 to 160
The temperature is raised to ℃, after the heat treatment, it is cooled gradually to room temperature and wound up.

[0024]

[Physical property evaluation method]

1. Temperature rising rate A thermocouple is attached on the film, it is passed through the heat treatment process, the temperature change at that time is recorded on the recording paper, and the temperature T1 (° C) at the time of entering the heat treatment process becomes (T1 + 100 ° C) From the time t (seconds) up to, the rate of temperature rise (° C./second)=100/t.

2. Glass transition point and melting point Using a differential scanning calorimeter DSC3100 manufactured by Mac Science Co., the sample was held at 300 ° C. for 5 minutes, liquid nitrogen was rapidly cooled, and then the glass transition point and melting point were measured at a temperature rising rate of 20 ° C./minute. did.

3. Heat Shrinkage Stress The film is sampled in a width of 10 mm and fixed on a chuck connected to a strain gauge at 20 mm intervals. A thermocouple is attached on this film, and hot air is blown onto the film from a hot air generator. At this time, the stress is recorded on the recording paper by the strain gauge, and the temperature is recorded on the recording paper. Measurements were performed by changing the wind speed and temperature of hot air, the temperature increase rate was calculated from the recorded temperature, and the change in stress with respect to temperature was obtained from the recorded stress and recorded temperature.

4. Heat shrinkage rate of film The film is sampled in a width of 10 mm and a length of 250 mm, and marks are provided at intervals of about 200 mm. This gauge length is accurately measured and is referred to as To (mm). The sample is left unloaded in a hot air oven at 100 ° C. for 30 minutes and then cooled at room temperature. After sufficiently cooling, the distance between the gauge points was measured again and was set to T (mm), the heat shrinkage rate (%) = (To−T) / To × 100.

5. A straight line in the transverse direction was drawn with a marker on the film before entering the bowing transverse stretching process, and the distortion of the line after the transverse stretching and heat treatment was evaluated. That is, both ends of the line on the film after the heat treatment were connected by a straight line, and the maximum value of the distance between the distorted line and the straight line drawn after was defined as the bowing amount (mm).

[0029]

EXAMPLES The present invention will be described based on examples.

Example 1 Nylon 6 pellets were vacuum dried at 150 ° C. for 3 hours, then fed to an extruder heated to 270 ° C. to 300 ° C., and molded into a sheet from a T die. Furthermore, an unstretched film obtained by closely adhering and solidifying this film on a cooling drum having a surface temperature of 25 ° C. by electrostatic force was obtained.

The unstretched film was introduced into a simultaneous biaxially stretched tenter heated to 120 ° C. while gripping with a clip, and stretched 3.0 times in the longitudinal direction and 3.3 times in the lateral direction.

Then, after removing from the clip and once cooling to 50 ° C., the clip is gripped again and heated to 180 ° C. at a heating rate of 2200 ° C./sec by a high-velocity hot air and an infrared heater in the tenter to perform heat treatment. After uniform cooling,
It was cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 12 μm.

The physical properties of the obtained film are shown in Table 1. The Boeing amount was 5 mm, and a small Boeing film could be obtained.

Example 2 The film stretched in the same manner as in Example 1 was removed from the clip and once cooled to 50 ° C., the temperature was raised to 1800 ° C./sec by using an infrared heater together with a floating heat treatment apparatus. Then, it was heat-treated at 180 ° C., uniformly cooled gradually, cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 12 μm.

The physical properties of the obtained film are shown in Table 1. The Boeing amount was 4 mm, and a small Boeing film could be obtained. Furthermore, the heat shrinkage rate is 0.
A film excellent in dimensional stability of 7% could be obtained.

Comparative Example 1 A film stretched in the same manner as in Example 1 was heat-set as it was at 180 ° C. in a tenter at a temperature rising rate of 550 ° C./sec. After cooling and winding, a biaxially stretched film having a thickness of 12 μm was obtained.

The physical properties of the obtained film are shown in Table 1. The Boeing amount was 33 mm, which was a big Boeing film. In addition, the film had a heat shrinkage rate of 1.5% and was poor in thermal dimensional stability.

Comparative Example 2 The film stretched in the same manner as in Example 1 was removed from the clip, once cooled to 50 ° C., again held by the clip and passed through a tenter, at a heating rate of 700 ° C./sec. 1
It was heat-set at 80 ° C., uniformly cooled gradually, cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 12 μm.

The physical properties of the obtained film are shown in Table 1. The bowing amount was 16 mm, and although the bowing was smaller than that of Comparative Example 1, the film was still insufficient. In addition, the film had a heat shrinkage ratio of 1.6% and was poor in thermal dimensional stability.

Example 3 The film stretched in the same manner as in Example 1 was removed from the clip, cooled once to 50 ° C., again held by the clip, passed through a tenter, and heated at a rate of 2200 ° C./sec. Then, it was heat-treated at 180 ° C., uniformly cooled gradually, cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 12 μm. At this time, the traveling speed V2 at the time of heat treatment was 118 m / min and V1> V, while the traveling speed V1 at the transverse stretching was 120 m / min.
There was a relationship of 2.

The physical properties of the obtained film are shown in Table 1. The Boeing amount was 3 mm, and a very small Boeing film could be obtained. Furthermore, a film having a heat shrinkage of 0.3% and excellent dimensional stability could be obtained.

Example 4 A film obtained by transverse stretching in the same manner as in Example 1 was used.
After preliminary heat treatment at 0 ℃, remove from the clip,
After once cooling to 50 ° C, it is again gripped by a clip and passed through a tenter, subjected to heat treatment at 180 ° C at a heating rate of 2200 ° C / sec, uniformly cooled slowly, and then cooled to room temperature and wound up. A 12 μm biaxially stretched film was obtained.

The physical properties of the obtained film are shown in Table 1. The Boeing amount was 5 mm, and a small Boeing film could be obtained. Furthermore, the heat shrinkage rate is 0.4%
In addition to being a film excellent in dimensional stability, it was possible to obtain a film excellent in flatness.

Example 5 Polypropylene pellets were fed to an extruder heated to 270 ° C. to 300 ° C. and molded into a sheet from a T die. Further, an unstretched film obtained by closely adhering and solidifying this film on a cooling drum having a surface temperature of 25 ° C. was obtained.

This unstretched film is heated to 120 to 150 ° C.
After heating with a heating roll group of 6 and stretching 6 times in the machine direction,
It cools with a roll group of 20-50 degreeC.

Subsequently, this uniaxially stretched film was introduced into a tenter heated to 150 ° C. while being gripped by a clip, and stretched 8 times in the transverse direction.

Then, after removing from the clip and once cooling to 50 ° C., the clip is gripped again and heated to 155 ° C. at a heating rate of 2200 ° C./sec by a high-velocity hot air and an infrared heater in the tenter to perform heat treatment. After uniform cooling,
It was cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 12 μm.

The physical properties of the obtained film are shown in Table 1. The Boeing amount was 3 mm, and a small Boeing film could be obtained.

[0049]

[Table 1]

[0050]

According to the method for producing a plastic film of the present invention, a plastic film with markedly improved bowing can be obtained, and various troubles due to the anisotropy in the width direction due to bowing can be eliminated. Therefore, it is possible to contribute to improvement of quality and productivity such as improvement of yield. In addition, it is possible to obtain other quality improvement effects on physical properties such as a smaller heat shrinkage rate.

[Brief description of drawings]

FIG. 1 is a biaxially stretched film of nylon 6 (thickness 12 μ
3 is a curve of the temperature rising rate dependency of the heat shrinkage stress with respect to the temperature in the vertical direction in (m).

Claims (6)

[Claims] 1. A method for producing a plastic film by stretching the film at least in the transverse direction with a tenter and then subjecting it to a heat treatment.
A method for producing a plastic film, comprising: providing a cooling step of cooling to 0 ° C. or lower, and setting a temperature rising rate in the heat treatment step to 1000 ° C./second or higher. 2. The method for producing a plastic film according to claim 1, wherein after the transverse stretching, the film is once removed from the clip of the tenter and then subjected to a cooling step. 3. The method for producing a plastic film according to claim 2, wherein the heat treatment is performed by again gripping the film with a clip of the tenter. 4. The method for producing a plastic film according to claim 2, wherein the heat treatment is performed without gripping the film with a clip of the tenter. 5. The plastic film according to claim 1, wherein the traveling speed V1 of the film during transverse stretching and the traveling speed V2 of the film during heat treatment have a relationship of V1> V2. Production method. 6. The plastic film according to claim 1, wherein after the transverse stretching, before the cooling step, a preliminary heat treatment is performed at a transverse stretching temperature or higher and a (transverse stretching temperature + 50 ° C.) or lower. Manufacturing method.