JPH064275B2 - Horizontal stretching method of film - Google Patents

Description

The present invention relates to a transverse stretching apparatus and a transverse stretching method for thermoplastic polymer films, particularly polyester films. In the present invention, transverse stretching is used as a concept including a step of stretching a film in the width direction and a step of subsequently performing a heat treatment.

[Conventional technology and problems to be solved]

Polymer films, especially polyester films, have very good properties and are widely used for magnetic tapes, electrical applications and the like. In video tape applications among magnetic tape applications, the required characteristics have become more and more stringent in recent years.
One of them is the problem of oligomer deposition on the film surface. If the oligomer adheres to the film surface, it causes dropout and is not preferable.

Various methods have been proposed for preventing contamination by this oligomer, but they can be roughly divided into two.
One of them is a method of using a polyester raw material having a small amount of oligomer, and the second is a method of preventing the oligomer sublimated from the film from adhering to the film in the film forming step, especially in the transverse stretching step.

The transverse stretching of a polyester film is usually called a tenter method and is a method as shown in FIG. 1 in FIG.
Is a polyester film, 2 is a housing for transverse stretching and heat treatment, and the inside of the housing is A to D.
Each zone is an oven in which hot air is circulated. A is a preheating zone, B is a transverse stretching zone,
C is a heat treatment zone, and D is a cooling zone, and temperature control is performed in each zone. In FIG. 1, the transverse stretching zone of B is further divided into two, and the heat treatment zone of C is 1
Although it is composed of two zones, each zone may be partitioned by providing a larger number of partitions. This also applies to the A and D bands. The zones A to D are usually formed in one housing, but they may be appropriately separated into two or more. In the present invention, the device comprising the zones A to D is referred to as a transverse stretching device. The film 1 is grasped at the side of the film with a clip (not shown) and stretched in the width direction.

In such a tenter system, an oligomer which is a low polymer contained in the polymer sublimates depending on the type of the thermoplastic polymer. The air containing a high concentration thereof becomes associated air of the film and flows to the downstream side in the film traveling direction, and is particularly deposited in the communication zone following the heat treatment zone or in the winding step outside the tenter. These deposits become linear or powdery and contaminate the film, significantly reducing the value of the product.

In order to deal with these phenomena, the following measures have been taken.

An air supply / exhaust system is installed above the heat treatment zone to reduce the concentration of sublimate in the zone, thereby reducing the amount of sublimate in the associated air.

A catalytic combustion device is provided in the heat treatment zone, and the sublimate is burned by passing circulating air to reduce the concentration of the sublimate in the zone.

A cooling zone is provided after the heat treatment zone, and the internal air is exhausted with a panwath to increase the number of ventilations, and the associated air is vented and contaminated air is exhausted from the system.

Between the cooling zone and the heat treatment zone, a zone called a neutral zone which does not have an air supply device is arranged, and the air is exhausted there to discharge the accompanying air from the system.

Another zone is installed following the heat treatment zone, and air is supplied and exhausted there to reduce the concentration of sublimate in the accompanying air.

Suction nozzles, etc. are installed in various places so as to be close to the film, and the amount of accompanying air is reduced.

However, these measures have the following drawbacks.

Although the amount of sublimate is reduced by the air supply / exhaust device in the heat treatment zone, a sufficient effect cannot be obtained. When trying to improve the effect further, a huge heat loss occurs, which is not practical.

Although the catalytic combustion device is effective in reducing the concentration of sublimates, it is necessary to replace and reactivate the catalyst periodically. Also,
The effect decreases at low temperatures.

If a cooling zone is installed immediately after the heat treatment zone and exhaust is performed in one pass, the film will be rapidly cooled and the flatness will deteriorate. In addition, sublimate accumulation occurs before the cooling zone where air is rapidly cooled, and film contamination is unavoidable.

When the neutral zone is provided, the cooling zone is less contaminated, but the sufficient effect cannot be obtained.

If another zone is installed following the heat treatment zone, the effect of removing sublimates will be higher than that in the neutral zone, but the cost of the apparatus will be higher. Also, there is a large amount of heat loss, which is not practical.

A suction nozzle is effective for blowing out air from the heat treatment zone, but has little effect of reducing entrained air. Further, when the nozzle is brought close to the film to try to enhance the effect, the film comes into contact with the film and is scratched.

Therefore, none of these methods is industrially satisfactory.

[Means for solving problems]

As a result of earnest research on a method for preventing the precipitation of sublimates generated in the heat-treated zone of the film, the present inventors have blown fresh heated air to the film at a certain place in at least a part of the zone to make a housing. The present invention has been completed by finding that it is possible to efficiently suppress the contamination of the film by the oligomer by forming an air curtain near the inner partition.

That is, the present invention has a lateral stretching zone in which lateral stretching is carried out while restraining the side portions of the film while the film is running, and a heat treatment zone in which heat treatment is subsequently carried out, and the boundary between the lateral stretching zone and the heat treatment zone is a partition. In a method of performing lateral stretching and heat treatment of a film by using a lateral stretching device that is divided into two or more zones in each zone, the film running downstream side of at least one zone And / or upstream, heated air substantially free of oligomers taken in from the outside of the stretching device is blown against the film surface in the width direction of the film to form an air curtain. The present invention relates to a lateral stretching method.

The present invention will be described in detail below.

The polymer film applicable to the present invention is not particularly limited, but it is effective for polyester, especially polyethylene terephthalate film, polyethylene naphthalate film and the like.

A transverse stretching apparatus, which is one of the constitutions of the present invention, has been conventionally known, and is divided into a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone as described above, and a film runs in each zone. It is partitioned except for a gap, and heated air whose temperature is adjusted to a temperature suitable for each zone is circulated in each zone.

2 and 3 are front and cross-sectional views, respectively, showing one zone. The lateral stretching device is composed of a plurality of such unit bands that are continuous to form one device.

Reference numeral 1 is a film, 2 is a housing, 3 is a film clip, and 4 is a heater. Air is circulated in the direction shown by the arrow in the drawing by the fan 6 driven by the motor 5 and heated by the air heater 4 in the zone, and hot air is blown onto the film 1 from the hot air blowing nozzle 7. Reference numeral 8 is an intake / exhaust motor, and 9 is an intake / exhaust duct. This duct may or may not be installed. 10
Is a partition plate that partitions the band.

In the transverse stretching device, a neutral zone in which hot air is not circulated may be provided in the middle of each zone.

The temperature of each zone varies depending on the stretching conditions of the film, but it is usually 80 ° C. to 150 ° C. in the stretching zone and 150 ° C. to 250 ° C. in the heat treatment zone, and when further subdividing each zone, usually go to the latter stage. The higher the temperature is set. The preheating zone is naturally set at a lower temperature than the stretching zone, but it is preferable that this zone is also divided into a plurality of zones and gradually set to a high temperature. The cooling zone is a zone for preventing the film that has passed through the heat treatment zone from being exposed to the outside air at one time, and is preferably divided into a plurality of zones to gradually lower the temperature.

The present invention has a mechanism capable of forming an air curtain by blowing heated air across a film width direction with respect to a film surface on a plurality of downstream sides and / or upstream sides of at least one partitioned zone. The zone having the configuration may be any of the preheating zone to the cooling zone, and when each zone is partitioned into two or more zones, the configuration of the present invention may be set in only one zone among them. good. Since the oligomer is generated in a large amount as the film is heated to a high temperature, the structure of the present invention is most efficiently provided in the heat treatment zone. Furthermore, setting the composition of the present invention in a zone before the zone in which the temperature is set lower in the successive zones prevents the oligomers from being deposited on the film in the next zone. Is highly effective.

The method of blowing air is preferably performed by providing a nozzle over the entire width direction of the film, but even if this nozzle has a rectangular blowout opening extending over the entire width of the film, a circular nozzle is extended over the entire width of the film. It may be provided, but in short, it suffices if the air curtain can be efficiently stretched on the partition portion of the band. The nozzle may be provided on one or both of the downstream side and the upstream side in the traveling direction of the film, but it is efficient to provide the nozzle on the downstream side.

When heated air is blown in, the balance of the air in the entire band is disturbed, so it is desirable to install an air outlet, but it is not essential. For example, in the band, 9 in FIG. 2 and FIG.
If there is an intake / exhaust duct like this, this may be used for exhaust.

In a preferred embodiment, when the air supply nozzle is installed on the downstream side of the zone, it is preferable to provide an exhaust duct as an exhaust area immediately upstream thereof. Therefore, when the air supply nozzle is provided at the upstream end of the zone, the exhaust duct can be set immediately downstream thereof.

A preferred embodiment of the present invention is shown in FIG. The numbers 1 to 10 indicate the same parts as the numbers used in FIGS.

The heated air flows through the air supply duct 17 by the fan 18 driven by the motor 19 and is heated by the heater 16 and blown from the air supply nozzle 15 onto the film surface.
Create an air curtain near the partition. The blown air passes through the exhaust nozzle 11 through the exhaust duct 14, and is discharged to the outside by the force of the fan 12 driven by the drive motor 13.

The shape of the intake nozzle is preferably inclined toward the upstream side in the film running direction. FIG. 5 is a diagram showing the nozzle shape. The air supply nozzle inclination angle (θ) in the figure is 5 ° to the upstream side when the nozzle is installed on the downstream side of the film, and 5 ° to the downstream side when the nozzle is installed on the upstream side. It is better to tilt it by -50 °.

In the transverse stretching device having the above-described configuration, the temperature of the air blown from the air supply nozzle needs to be the set temperature of the zone. When air that is substantially free of oligomer or has a lower oligomer content than the oligomer concentration in the zone is blown out from the air supply nozzle, this is replaced with air having a high oligomer content in the zone on the upper surface of the film, and The action of the air curtain near the partition can prevent the oligomer from flowing out to the downstream or upstream zone.

As the air to be used, the air which does not substantially contain the oligomer taken in from the outside of the stretching apparatus as described above is used.

The amount of air blown out from the air-supply nozzle is the distance between the nozzle tip and the film, (the distance from the nozzle tip to the film is preferably in the range of 5 cm to 20 cm, and varies depending on the inclination angle of the nozzle tip, but the film is wavy. The amount should not be moderate, specifically 3 to ²⁰ m ² per 1 m width
/ Mm range. Further, it is preferable to make it faster than the wind speed from the hot air blowing nozzle (FIG. 2) that circulates hot air in the zone.

〔Example〕

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

Examples 1 to 10 and Comparative Example 1 Polyethylene terephthalate melt-extruded, cooled and solidified, and then longitudinally stretched 3.7 times at 100 ° C., laterally stretched 3.7 times by a tenter method, and then heat treated to a width of 2000 m.
A film having m and a thickness of 6 μm was obtained.

In the tenter, the preheating zone temperature is 80 ° C and the transverse stretching zone temperature is 10
The temperature was 0 ° C., the heat treatment zone temperature was 230 ° C., and the cooling zone temperature was 60 ° C. The film running speed was 100 m / min, and the heat treatment time was 3 seconds.

An air supply nozzle was provided on the entire surface in the film width direction at a position 30 cm upstream from the downstream partition of the heat treatment zone. The shape of the nozzle and the air supply amount are shown in Table 1. The distance between the tip of the nozzle and the film was 120 mm. If an exhaust area is provided,
A duct having a shape as shown in FIG. 4 is installed in contact with the air supply nozzle on the upstream side of the air supply nozzle, and the amount of air blown out from the partition opening on the downstream side is similar to that in the case of normal stretching. The displacement was adjusted so that The sublimate concentration is measured 10 mm from the film surface at a position 500 mm downstream of the air supply nozzle.
An air suction port was installed at the position, air was sucked from the air suction port, trapped with methanol, and then the concentration was measured by an ultraviolet absorption method. A hot-wire anemometer was used for the air velocity.

The measurement results are shown in Table 1.

[Effect of the present invention] In the present invention, by supplying hot air to the downstream side and / or the upstream side of the film in at least one zone of the transverse stretching device, the adhesion of oligomers to the film is greatly reduced. be able to.

[Brief description of drawings]

FIG. 1 is a plan view of the housing of the transverse stretching device, and FIG.
Figures and 3 are a front sectional view and a transverse sectional view of one zone of the transverse stretching apparatus, FIG. 4 is a transverse sectional view showing one embodiment of the present invention, and FIG. 5 shows a nozzle shape. It is a figure.
1 to 5, 1 is a film, 7 is a hot air blowing nozzle, 9 is an intake / exhaust duct, 10 is a partition in the housing, 11 is an exhaust nozzle, 14 is an exhaust duct, 15 is an air supply nozzle, Reference numeral 17 indicates an air supply duct.

Claims (2)

[Claims] 1. A lateral stretching zone for laterally stretching the film while restraining the side portions of the film while running the film, and a thermal treatment zone for subsequent heat treatment, wherein the boundaries between the lateral stretching zone and the thermal treatment zone are partitioned. In the method of performing lateral stretching and heat treatment of a film by using a transverse stretching device that may be divided into two or more zones within each zone, the film running downstream side of at least one zone divided And / or upstream, heated air substantially free of oligomers taken in from the outside of the stretching device is blown against the film surface in the width direction of the film to form an air curtain. Lateral stretching method 2. Heated air is blown to the downstream side of the film and air is exhausted from an air exhaust area provided on the upstream side in the arbitrarily stretched zone in the transverse stretching zone and / or the heat treatment zone. Claim 1 characterized in that
Method described in section