JP2002018948A - Method for manufacturing stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a stretched film having almost no physical property difference along its lateral direction. SOLUTION: In the method for manufacturing the stretched film by thermally fixing a film stretched at least in one direction at temperature not less than the glass transition temperature of the film, a difference is provided between temperature raising speeds corresponding to the positions in the lateral direction of the film in a process for raising the temperature of the film to the thermal fixing temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially stretched polyester film having uniform physical properties along the width direction of the film. The present invention relates to a method for producing a film having excellent properties.

[0002]

2. Description of the Related Art Conventionally, biaxially stretched films have been used for industrial purposes. Among them, films are widely used for optical applications such as polarizing plate separators, magnetic recording, photography, drafting, packaging, capacitors and the like. It is required that the optical properties, mechanical properties, coefficient of humidity expansion, coefficient of thermal expansion, coefficient of thermal shrinkage, and the like be uniform in the width direction of.

However, in the prior art, a normal biaxial stretching method,
That is, it was extremely difficult to make the physical properties in the width direction of the product film uniform in the method of performing transverse stretching using a tenter after longitudinal stretching.

The reason is as follows. Since both ends of the film are gripped by the gripping means in the tenter, the contraction stress in the vertical direction accompanying the transverse stretching is restrained by the gripping means. On the other hand, since the binding force of the gripping means is relatively weak in the central portion of the film, the central portion tends to move due to the contraction stress. If a straight line is drawn in the horizontal direction on the film surface before the horizontal stretching,
This straight line is transformed into a concave curve in the direction of film advance. This phenomenon is called Boeing.
This bowing causes unevenness in the physical properties of the film in the width direction, particularly, optical properties such as orientation angle distribution, mechanical properties, humidity expansion coefficient, thermal expansion coefficient, and heat shrinkage rate.

Several proposals have been made to eliminate such physical property differences in the width direction.

For example, a method in which a uniaxially stretched film is horizontally stretched by a tenter, a clip is released once, the film is gripped again by a clip, and heat-fixed while raising the temperature in a temperature range of 120 to 240 ° C. JP-A-57-87331), a method in which an unstretched film is preheated at a stretching temperature or higher, then simultaneously biaxially stretched in the machine and transverse directions, and then is heated in multiple stages at equal temperatures and reheated. Japanese Patent Application Laid-Open No. 54-137076 discloses a method of immediately lowering the film temperature to a temperature below the glass transition temperature immediately after transverse stretching to increase rigidity and to prevent the film in the heat treatment chamber from being drawn into the stretching chamber. -13
027, Japanese Unexamined Patent Publication No. Hei 3-216326), a method in which a nip roll is provided between transverse stretching and heat treatment to forcibly advance a central portion instead of a cooling step (for example,
Japanese Patent Publication No. Sho 63-24459) and a method in which a film is biaxially stretched and then heated so that the temperature at the edge is higher than that at the center of the film (for example, JP-A-61-23352).
No. 3, JP-A-62-183327, JP-A-6-183327
No. 2-183328) has been proposed.

However, in such a method, even if the bowing phenomenon can be controlled to some extent, the optical characteristics,
Problems such as insufficient dimensional stability in the film width direction without impairing thermal dimensional stability, mechanical properties, flatness, and the like are insufficient, and the apparatus becomes large.

[0008]

SUMMARY OF THE INVENTION The present invention solves such a problem, and there is almost no difference in physical properties along the film width direction.
An object of the present invention is to provide a method for producing a film having excellent uniformity.

[0009]

Means for Solving the Problems In view of the above-mentioned problems, the present inventors have made intensive studies and as a result elucidated the process of occurrence of bowing, and found means for suppressing this bowing, and reached the present invention.

That is, the present invention relates to a method for producing a stretched film, in which a film stretched in at least one direction is heat-set at a temperature not lower than a glass transition temperature. A method for producing a stretched film, characterized in that the rate of temperature rise of the film is made different depending on the position.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The stretched film of the present invention is a film stretched in at least one direction. The stretching direction is not particularly limited, and examples thereof include a film uniaxially stretched in the longitudinal direction or the transverse direction, and a film stretched biaxially in both the longitudinal direction and the transverse direction.

The stretched film of the present invention preferably comprises a resin composition having crystallinity. As the resin composition having crystallinity, for example, a thermoplastic resin is preferable. As the thermoplastic resin, for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate,
Polyamides such as nylon 6 and nylon 66, polyolefins such as polypropylene and polyethylene, polyphenylene sulfide, and the like can be used. The thermoplastic resin may be a single substance, a mixture, or a copolymer. They may also contain small amounts of inorganic or organic additives.

The stretching method of the stretched film of the present invention is not particularly limited, but the resin composition is heated and melted at a temperature not lower than its melting point, and is extruded from an extrusion means including a slit die into a film on a cooling drum surface. After obtaining an unoriented unstretched film, a method of stretching the unstretched film in one direction in a longitudinal direction or a transverse direction at a temperature equal to or higher than the glass transition temperature of the resin composition, stretching in the longitudinal direction, and then stretching in the transverse direction After stretching in the transverse direction, a method of stretching in the longitudinal direction, or a method of stretching in the longitudinal direction and the transverse direction simultaneously,
The stretching in the longitudinal direction and the stretching in the width direction may be performed in combination a plurality of times.

In the production method of the present invention, in order to obtain a stretched film excellent in uniformity with little difference in physical properties in the film width direction, the stretched film stretched by the above-mentioned method is heated to a temperature equal to or higher than its glass transition temperature, preferably. When the glass transition temperature is equal to or higher than + 20 ° C., and more preferably equal to or higher than the stretching temperature, for example, when heat setting is performed using an oven-type heat treatment apparatus such as a tenter method, the longitudinal restraining force of the film center portion and the edge portion is made equal. Alternatively, in order to reduce the difference, in the process of raising the film temperature to the heat setting temperature, it is important to heat-set the film at a different rate depending on the position in the film width direction. Preferably, the rate of temperature rise at the end portion in the film width direction is higher than at the center portion.

The specific method of making the temperature rise rate different according to the position in the film width direction of the present invention is not particularly limited. For example, when heat is fixed by hot air, the amount, speed and temperature of hot air are adjusted. It is preferred to do so.

For heating, it is preferable to use hot water, steam, a heating medium, or an electric heater such as far infrared rays or near infrared rays. Actually, for example, in the case of a tenter type oven, the hot air blowing nozzles are subdivided in the film width direction and the longitudinal direction from the initial part of the heat fixing zone to the time when the film temperature is raised to the heat fixing temperature, and the air volume of each nozzle A method of adjusting the wind speed and temperature, that is, a method of attaching windmills of different sizes to the tip of the hot air blowing nozzle so that the wind speed changes, the inside of the hot air blowing nozzle installed in the tenter type oven in a laterally elongated manner. A method of changing the wind speed by an inverter, a method of covering the tip of the nozzle so that the wind speed changes, and an infrared ray in the film width direction and the longitudinal direction from the initial portion of the heat fixing zone until the film temperature is raised to the heat fixing temperature. A method of changing the temperature of each heater by installing several to hundreds of heaters such as heaters, or The combination of al like, film width direction, but most preferably be provided a difference in heating rate in the longitudinal direction is not limited to these methods. Further, the manner of providing the difference in the heating rate may be continuous or stepwise.

The length in the longitudinal direction of raising the film temperature up to the heat setting temperature of the present invention depends on the running speed or thickness of the film. It is preferable that the length is not less than 0.1 second. In addition, the shape in the film width direction and the longitudinal direction of the portion which makes a difference in the heating rate is a fan-shaped, triangular, trapezoidal, etc. in the film running direction as shown in FIG. It is preferable to make a difference in the heating rate so as to fall within the range.

In addition, lateral stretching using two stenters
In the case of performing the heat treatment separately, the film width direction of the portion that makes a difference in the heating time of the heat setting by the second stenter,
The shape in the longitudinal direction is preferably a range obtained by taking out only the heat setting zone in FIG. 1, and the shape is set so as to be a sector, a triangle, a trapezoid, or the like in the film running direction as in FIG. 1. It is preferable to make a difference in the heating rate.

Here, a more detailed description will be given with reference to FIG. 1. FIG. 1 shows a tenter-type horizontal stretching and heat fixing apparatus, which is used in a process of raising the film temperature from the initial part of the heat fixing zone to the heat fixing temperature. It shows a range in which a difference in the heating rate is provided depending on the position in the film width direction. Here, the upper figure has a fan-shaped area, and the lower figure has a triangular shape and a trapezoidal shape. Further, each range preferably satisfies the following expression.

0.1 ≦ L2 / L1 <1.0 0.1 ≦ L3 / L1 <1.00 ≦ W2 / W1 <1.0 The difference between the temperature rising rate between the film edge and the film center is 0.01.
Second or more is the most preferable, and the difference between the slowest part and the fastest part in the longitudinal direction from the heat-setting initial part to the heat-setting temperature is also 0.0
It is most preferable that the heating time is 1 second or longer, and it is most preferable that the rate of temperature rise at the edge of the film is higher than that at the center of the film. In the longitudinal direction of the film, it is most preferable to increase the speed from the initial portion of the heat setting toward the running direction of the film.

In the present invention, the difference in the temperature rising rate is obtained by symmetrically raising and lowering the film in the film width direction symmetrically with respect to the film center in the film width direction in order to obtain a film having uniform physical properties in the film width direction. It is preferable to make a difference in the heating rate.

In the present invention, the difference between the heating rates is that the film width can be set at the initial portion of each zone, for example, when the heat setting is performed in multiple stages, for example, when the heat setting temperature is gradually increased. This is preferable because the physical properties in the directions can be made uniform. Further, even in the case of heat setting using a plurality of heat fixing devices, it is preferable to provide the heat fixing device in the initial portion of each heat fixing device or the initial portion of each heat fixing zone because a film having uniform properties in the film width direction can be obtained.

FIG. 2 shows an embodiment of the present invention, in which in the process of raising the film temperature from the initial portion of the heat setting zone to the heat setting temperature, a difference is made in the rate of temperature increase depending on the position in the film width direction. FIG. 7 is a schematic plan view schematically showing an example in which the tip of a hot-air nozzle is covered as a measure, and an example of a mode adopted in Example 1 described later.

FIG. 3 shows an embodiment of the present invention, in which the temperature is raised from the initial part of the heat-setting zone to the heat-setting temperature in the process of raising the film temperature depending on the position in the film width direction. FIG. 9 is a schematic plan view schematically showing an example in which the tip of a hot air nozzle is covered as a means, and an example of a mode adopted in Example 2 described later.

FIG. 4 shows an embodiment of the present invention, in which the temperature is raised from the initial part of the heat-setting zone to the heat-setting temperature by a difference in the temperature-raising rate depending on the position in the film width direction. Example 3 shows an example in which the tip of a hot-air nozzle is covered as an effective means.
FIG. 5 is a schematic plan view schematically showing an example of the mode adopted in the embodiment.

FIG. 5 shows an embodiment of the present invention, in which the temperature is raised from the initial portion of the heat setting zone to the heat setting temperature by a difference in the rate of temperature increase depending on the position in the film width direction. FIG. 9 is a schematic plan view schematically showing an example in which the tip of a hot air nozzle is covered as a means, and an example of a mode adopted in Example 4 described later.

FIG. 6 shows one example of carrying out the present invention, in which the heat is fixed from the initial part of the heat fixing zone in the heat fixing by the second stenter when the transverse stretching and the heat treatment are separately performed using two stenters. In the process of raising the film temperature to a fixed temperature, as a specific means for providing a difference in the temperature raising rate depending on the position in the film width direction, an example in which the tip of a hot air nozzle is covered is shown.
FIG. 5 is a schematic plan view schematically showing an example of the mode adopted in the embodiment.

[0029]

[Method of measuring characteristics] (1) Glass transition point (Tg), melting point (Tm): Differential scanning calorimeter RDC manufactured by Seiko Denshi Co., Ltd.
Using a Model 220, 5 mg of a resin composition sample was sampled, and the melting point (Tm) was determined from the temperature of the endothermic peak when the temperature was raised from room temperature at a rate of temperature rise of 20 ° C./min. The glass transition temperature (Tg) of the film sample was raised to 280 ° C.
After maintaining at 0 ° C. for 5 minutes, the temperature was rapidly cooled with liquid nitrogen, and the temperature was measured again from room temperature at a rate of temperature increase of 20 ° C./min. (2) Boeing amount (mm): Heat fixing is performed by drawing a straight line with Magic (registered trademark) or the like over the entire width in the width direction of the stretched film before heat fixing. The film after heat setting was taken out, and the maximum distance (mm) between a straight string and an arc deformed by bowing was measured. (3) Film width direction, orientation angle distribution: automatic refractive index measuring device (KOBRA-21ADH manufactured by Oji Scientific Instruments)
Measured using The measurement was performed at a position 200 mm from the center of the film and the end of the film. The measurement temperature is 2
Performed at 5 ° C. The transverse direction of the film was set to 0 °.

[0030]

EXAMPLES Examples 1, 2, and 3 Polyethylene terephthalate resin was melted, extruded from a T-die, formed into a film on the surface of a quenching drum, cooled, and then stretched three times in the machine direction by a roll type longitudinal stretching machine. And
At 95 ° C., both ends of the film are gripped with a stenter clip and stretched 3.7 times in the transverse direction to form a 45 μm biaxially stretched film. 2 While holding both ends as it is
A 4 m long heat fixation zone maintained at 20 ° C.
After passing at a speed of 1 minute, it was cooled to room temperature and wound up.

Here, in the process of raising the film temperature from the initial part of the heat setting zone to the heat setting temperature, the tip of the hot air nozzle is so positioned as to be different in the rate of temperature increase depending on the position in the film width direction, as shown in FIGS. As shown in FIG. 4, they were covered, and they were respectively named Example 1, Example 2, and Example 3 in order. In order to increase the heating rate from the center to the edge of the film,
The longitudinal direction of the film was shaped such that the rate of temperature rise increased in the direction of film advance.

Each of the films thus obtained had a film width of 900 mm and, as shown in Table 1, had a small bowing amount and uniform physical properties along the film width direction. Example 4 A polyethylene terephthalate resin was melted, extruded from a T-die, formed into a film on the surface of a quenching drum, cooled, and then stretched three times in a longitudinal direction by a roll-type longitudinal stretching machine.
At 95 ° C., both ends of the film are gripped with a stenter clip and stretched 3.7 times in the transverse direction to form a 45 μm biaxially stretched film. 1 while holding both ends as it is
A 4 m long heat fixation zone maintained at 20 ° C.
Min. To complete the low temperature heat setting in the first stenter. Next, the clips at both ends of the film are released, and at room temperature, the roll group is passed at a constant speed with both sides of the film open, and the film is gripped at both ends again and led to the second stenter. Second Stenter is 4
The temperature is divided into zones, and the set temperature is selected so as to increase sequentially. That is, a 1.5 m zone maintained at 120 ° C., a 1.5 m zone maintained at 160 ° C., a 1.5 m zone maintained at 180 ° C., and 2
It consisted of a 1.5 m zone maintained at 00 ° C. After heat setting with this second stenter, it was cooled to room temperature and wound up. Here, each of the four zones of the second stenter is assigned to one of the zones from the initial zone.
The tip of the hot air nozzle was covered as shown in FIG. 5 so that the heating rate was different depending on the position in the film width direction up to the portion of / 3. The shape was such that the rate of temperature rise was increased from the center of the film toward the end, and the rate of temperature rise was increased in the longitudinal direction of the film in the direction of film advance.

The film thus obtained had a film width of 900 mm and, as shown in Table 1, had a small bowing amount and uniform physical properties along the film width direction. Comparative Examples 1 and 2 In Examples 1 and 3, heat-fixing was performed without covering the hot-air nozzle so that the rate of temperature rise varies depending on the position in the film width direction in the heat-fixing zone.

Each of the films thus obtained had a film width of 900 mm and, as shown in Table 1, had a large bowing amount and had non-uniform physical properties along the film width direction.

[0035]

[Table 1]

[0036]

According to the method for producing a stretched film of the present invention, it is possible to produce a film having almost no difference in physical properties along the film width direction and excellent in uniformity.

[Brief description of the drawings]

FIG. 1 is a schematic model diagram showing a range in which a difference in the rate of temperature rise is provided depending on a position in a film width direction in a process of raising a film temperature from an initial portion of a heat setting zone to a heat setting temperature according to the present invention.

FIG. 2 is a specific means for implementing the present invention as a specific means for providing a difference in the heating rate depending on the position in the film width direction in the process of increasing the film temperature from the initial part of the heat setting zone to the heat setting temperature. FIG. 4 is a schematic model diagram showing an example in which the tip of a hot air nozzle is covered.

FIG. 3 shows a specific means for implementing the present invention as a specific means for providing a difference in the rate of temperature increase depending on the position in the film width direction in the process of raising the film temperature from the initial part of the heat setting zone to the heat setting temperature. FIG. 4 is a schematic model diagram showing an example in which the tip of a hot air nozzle is covered.

FIG. 4 is a specific means for implementing the present invention as a specific means for providing a difference in the rate of temperature increase depending on the position in the film width direction in the process of raising the film temperature from the initial portion of the heat setting zone to the heat setting temperature. FIG. 4 is a schematic model diagram showing an example in which the tip of a hot air nozzle is covered.

FIG. 5 is a specific example of an embodiment of the present invention, in which a difference in the heating rate is provided depending on a position in a film width direction in a process of increasing a film temperature from an initial portion of a heat setting zone to a heat setting temperature. FIG. 4 is a schematic model diagram showing an example in which the tip of a hot air nozzle is covered.

FIG. 6 shows a second example in which lateral stretching and heat treatment are separately performed using two stenters as one example of implementing the present invention.
An example in which the tip of a hot air nozzle is covered as a specific means for providing a difference in the temperature rising rate depending on a position in a film width direction in a process of raising a film temperature from an initial portion of a heat fixing zone to a heat fixing temperature in a heat setting by a stenter. FIG.

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Claims (3)

[Claims] 1. A method for producing a stretched film, wherein a film stretched in at least one direction is heat-set at a temperature not lower than a glass transition temperature, wherein the film temperature is raised to the heat-setting temperature by a position in a film width direction. A method for producing a stretched film, characterized in that the rate of temperature rise is varied. 2. The method for producing a stretched film according to claim 1, wherein the heating rate is made different depending on the position in the film width direction symmetrically with respect to the center of the film with respect to the longitudinal direction of the film. A method for producing a biaxially stretched polyester film. 3. The method for producing a biaxially stretched polyester film according to claim 1, wherein in the method for producing a stretched film, the rate of temperature rise at the edge of the film is made faster than at the center of the film.