JP2999379B2 - Relaxation heat treatment method for stretched film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for relaxing heat treatment of a stretched film. More specifically, when a heated stretched thermoplastic resin film is subjected to a relaxation heat treatment using a difference in running speed, it is prevented that wrinkles are formed in a running direction (longitudinal direction) of the film in a cooling process of the film, or wrinkles that have been formed are removed. The present invention also relates to a method for heat treatment for relaxation of a stretched film, in which the longitudinal tension of the film is prevented from increasing due to its own weight and the relaxation efficiency is increased.

[0002]

2. Description of the Related Art After a thermoplastic resin film is stretched,
Secondary processing is performed by slitting as necessary. At that time, the film may be subjected to a reheat treatment, and dimensional stability is required. As a method for improving the dimensional stability, a method of performing a relaxation heat treatment on a stretched film is known. For example, it is known that the relaxation heat treatment is performed in a film forming process. In that case, wrinkles in the vertical direction are generated at the stage of heating and cooling the film, and the wrinkles are thermally fixed to deteriorate the flatness of the film.

[0003] In order to improve this problem and remove the vertical wrinkles generated in the film during the relaxation heat treatment, a nip roll that applies a horizontal tensile force to the film while holding both ends of the film in the relaxation zone in the tenter is used. A method of installation has been devised (Japanese Patent Publication No. 3-80620, Japanese Patent Publication No. 4-5718)
Issue 2). However, according to this method, wrinkles in the vertical direction can be suppressed, but it is impossible to prevent the film between the nip rolls from hanging down by its own weight. If the sagging of the film is excessive, the film comes into contact with the heated air nozzle in the tenter and scratches the film. In order to reduce the sagging of the film, it is necessary to apply a certain amount of longitudinal tension to the film, but if the tension is too large, the dimensional stability of the film in the longitudinal direction will not be improved, but may worsen. obtain.

As a method for solving this problem, there is known a method of gradually slowing the progress of a clip in a tenter and performing a relaxation heat treatment (Japanese Patent Publication No. 44-20240). However, in this method, heat treatment is performed at the same time including the film edge while the edge is restrained in the tenter.
There is a difference in the amount of heat shrinkage between the thick edge portion and the thin central portion, which causes the film to be loosened, resulting in a difficult surface such that the flatness is deteriorated and the heat yield is not completely reduced. There is also a problem that the equipment cost is very high.

On the other hand, in order to improve productivity, it is required to heat-treat a wide film at a high speed. In this case, it is necessary to increase the length of the zone required for heating and cooling the film in order to obtain a sufficient processing time, and the tension in the vertical and horizontal directions is inevitably increased by the weight of the film. There is a problem that the dimensional stability cannot be improved.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the wrinkles in the longitudinal direction of a film, and to perform a flattening heat treatment with a low tension even in a high-speed heat treatment of a wide-width film without sagging due to the weight of the film. It is an object of the present invention to provide a method for relaxing and heat-treating a stretched film to obtain a low heat shrinkable film having good heat resistance.

[0007]

According to the present invention, there is provided a heat treatment method for thermally relaxing a heated stretched thermoplastic resin film by utilizing a speed difference between supply and take-off. (B) the width of the film is 3 to 8 m;
One or more sets of tentering devices having a nip roll for gripping the edge of the film and applying a tensile force in the width direction of the film in the relaxation zone where the speed difference is generated are installed along the film running direction, and the width direction of the film is set in the width direction of the film. (C) providing a means for supporting the weight of the film in the relaxation zone to reduce or prevent sagging of the film, and (c) achieving a relaxation heat treatment method for a stretched film having a thickness of 40 to 300 μm. Is done.

Hereinafter, the present invention will be described in detail.

[0009] The thermoplastic resin film in the present invention is a film made of a thermoplastic resin such as polyester, polyamide and polyolefin. Among these, a film made of polyester, especially polyethylene terephthalate is preferred. The stretched film is a film stretched in at least one direction, such as a film stretched uniaxially in a longitudinal direction and a film stretched biaxially in a longitudinal direction and a transverse direction. The production of the stretched film can be performed by a known method or a technique accumulated in the art, but a method using a tenter is particularly preferable.

In the present invention, the stretched thermoplastic resin film needs to have a width of 3 to 8 m . The technique of the present invention can be applied even if the film width is small, but the effect is small. In particular the film width Ru very large effect on the obtained when more than 3m.

The thickness of the stretched thermoplastic resin film is 4
0 to 300 μm. When the thickness of the film is thin, the film loses its rigidity and it is difficult to stably transport the film. The upper limit of the thickness of the Ru 300μm der.

In the present invention, the stretched thermoplastic resin film can be heated by any means, for example, a method of directly heating with a roll or the like, a method of radiant heating with an electric heater, an infrared heater, a steam heater, or the like, a heating gas, and the like. And convection heating by a well-known method such as a combination of these methods. Among them, convection heating in a tenter is preferable because the stretched film heat-set in the tenter can be subjected to relaxation heat treatment as it is, and air can be floated by applying a heated gas to the film.

The stretched film is 100 ° C. below the glass transition temperature (Tg: ° C.) of the thermoplastic resin constituting the film.
Or higher temperature, preferably (Tg + 100) to (Tg +
180) Heat to a temperature range of ° C.

In the present invention, the thermal relaxation of the stretched film utilizes the difference between the film supply speed and the take-up speed, ie, the speed difference caused by making the take-up speed slower than the supply speed, by running the heated thermoplastic resin stretched film. Do it. This method is well known in the art,
Conventional devices can be used for the film supply device and the take-up device. In the present invention, the length of the relaxation zone having the speed difference is not limited, but the length required for cooling the film needs to be secured. The processing speed is not particularly limited as long as the temperature of the film can be raised, but 20 to 20 times.
0 m / min is practical, and preferably 150 m / min or less.

The film tentering device in the present invention is:
It has a nip roll for gripping both ends of the film, and the nip roll is set such that the roll axis has an angle of 1 to 5 ° in a horizontal plane with respect to the film width direction. Since the nip roll is not parallel to the film but is inclined at the above angle, a force is applied to the running film, the end of which is fixed by the nip roll, in a direction perpendicular to the roll axis. It acts to pull the film in the width direction. In the film tentering apparatus, one set provided at both ends of the film is set as one set, and one or more sets are provided in the film running direction. The installation pitch in the film running direction of the film tentering device is not particularly limited because there is a means for supporting the film's own weight, but is preferably 10 m or less, and is preferably 5 m or less from the viewpoint of film running stability, and more preferably the film's own weight is reduced. It is advisable to shorten the support as long as it can be installed without difficulty. The nip roll may be made of any material such as rubber and metal, but it is preferable to use a heat-resistant material such as silicone rubber or viton rubber because the temperature of the film and the surroundings is high.

The relaxation heat treatment of the present invention may be performed during the stretching step of the stretched film, or may be performed at a place separated from the manufacturing step. The former is inline processing, and the latter is offline processing. Of these, in-line processing is preferred. In particular, after heat-setting the stretched thermoplastic resin film in the heat treatment zone of the tenter, cut and separate both ends of the film at an appropriate place in the oven of the tenter or outside the oven on the side where the tenter is taken out, and then simultaneously cool the film. It is useful in a method in which the film at the central portion with both ends cut off is relaxed by reducing the take-off speed. A film tentering device should be installed between the point where both ends of the film were cut off and the take-up roll.
More than two sets are provided to suppress the loosening of the central film and the vertical wrinkling of the film during cooling.

In the present invention, the running film is forcibly cooled by applying a lateral force to the running film in one or more sets of film tentering devices in a relaxation zone having a speed difference between the film supply and the film take-up. This cooling is preferably performed until the film temperature after passing through the final film tentering device becomes (Tg + 50) ° C. or lower, more preferably (Tg + 30) ° C. or lower, particularly Tg or lower.

In the present invention, means is provided for supporting the film's own weight in the relaxation zone where there is a difference in the speed of film supply and take-off. As a means for supporting the film's own weight, a method in which the film is floated by air whose temperature has been adjusted can be preferably applied. Further, the film may be supported by a transport roll, and the transport roll and air floating may be used in combination. As a method of air floating, a floating dryer method often used in a coating line can be applied. In the present invention, since the edge nip is performed, it is not necessary to blow the floating air over the entire width of the film, and it is sufficient to blow the film at a width of 1/2 or more with respect to the film width around the center of the film. Preferably, it is good to spray with a width of 2/3 or more. It is necessary to change the flow rate of the floating air depending on the thickness of the film to be subjected to the relaxation treatment.
Air floating equipment may be newly installed,
Modification of only the tip of the plenum duct attached to the existing tenter is enough. In this case, the blower, the temperature control equipment and the like can be used as they are, and the remodeling cost can be greatly reduced.

The transport roll may be a free roll or may be driven. If you make a freeroll,
It is necessary to reduce the rotational inertia in order to prevent slippage with the film. However, since little force is applied to this transport roll, there is no problem since a small diameter and thin structure can be achieved. The material may be rubber or metal, but from the viewpoint of durability, a metal roll is preferably subjected to surface plating.

The longitudinal tension in the film can be measured by detecting a well-known dancer roll or a reaction force applied to the roll from the film. The longitudinal tension of the film in the relaxation zone may be ² to 50 kg / cm ² , preferably 5 to 20 kg / cm ² , more preferably 10 to 15 kg / c.
m ² is good. If the tension is less than this range, the film is loosened and sags. In the case of air floating, the film is blown up and disturbs the flatness. On the other hand, if the tension is higher than this, improvement in dimensional stability cannot be expected. Although the tension in the transverse direction of the film does not need to be set as accurately as in the longitudinal direction, it is preferable that the tension in the transverse direction is the same as that in the longitudinal direction.

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing a state in which a film tentering device (hereinafter referred to as a cross guider) and a means for supporting the film's own weight (in this case, an air floating nozzle) are installed in a tenter. FIG. 2 shows A-
It is arrow A sectional drawing. Both ends of the stretched film 1 running in the direction of arrow 6 are cut by fixed cutters 2 and 2 ', and the film is separated into edge films 3 and 3' and a center film 4, and the separated center film 4 is a tenter in a tenter. The clip cannot be gripped. The cross guiders 5, 5 'are nip rolls 5 (a), respectively.
(B) nipping both ends of the central film 4 and attaching it so as to form an angle θ with the lateral direction of the film;
Remove vertical wrinkles in the center film. Further, the central film 4 is subjected to relaxation heat treatment by means of supporting the film's own weight (in this case, temperature-controlled air blown out from the air floating nozzle 7) without sagging.

FIG. 3 shows the positional relationship between two sets of cross guiders installed to prevent wrinkles generated during relaxation heat treatment in a tenter and air floating nozzles installed as means for supporting the film's own weight. It is a schematic plan view from a tenter to a take-up roll.
FIG. 4 is this side view. The longitudinally stretched thermoplastic resin film 11 is gripped by clips of a tenter rail 12, preheated in a preheating zone 13, and horizontally stretched in a stretching zone 14. Subsequently, it is heat-fixed in the heat treatment zone 15, cooled in the cooling zone 16, passes through the tension detecting means 22 (in this case, a dancer roll), and is then taken up by the take-off rolls 23 and 24 which have been slightly decelerated. In addition, the film 11 is provided with a cutter 1 provided for separating the clip from the grip.
The edge films 25, 25 'and the center film 26 are separated by 7, 17', and only the center film 26 is passed through the dancer roll, and only the tension of the center film is accurately measured.

At least one set of cross guiders (in this case, set 1) for gripping both ends of the separated central film 26
8, 18 'and 19, 19') are provided with the cooling zone 16 interposed therebetween. Means for supporting the film's own weight (in this case, air floating nozzles 20 and 21) are provided between the two sets of cross guiders. This prevents speed relaxation and vertical wrinkles generated during the cooling process,
Even if the tension in the longitudinal direction of the film is kept low, it is possible to produce a stable and flat heat-reduced film without sagging.

FIG. 5 is a schematic plan view of the rear part of the tenter, showing the positional relationship between two sets of cross guiders and free rolls installed as means for supporting the weight of the film. FIG. 6 is a side view of this. Except that the means for supporting the film's own weight are the free rolls 27, 28 and 29, the structure is the same as that of the apparatus shown in FIGS. 3 and 4, and the same effects can be obtained.

The installation position of the cross guider does not have to strictly sandwich the cooling zone as shown in FIGS.
If the main cooling section is provided between at least two sets of cross guiders, it is effective in preventing wrinkles. For example, the cooling zone may start before the cross guiders 18, 18 ', and the cross guiders 19, 19' may be provided. The cooling zone may continue further behind. Further, the cooling zone provided between the cross guiders can be extended before the cutting position for separating both ends of the film in some cases.

The relaxation in the present invention depends on the film properties, but is usually obtained by heat shrinkage of 5% or less, preferably 0.1 to 3%, particularly preferably 0.2 to 2%.

[0028]

The present invention will be further described with reference to the following examples. In the examples, each property value was measured by the following method.

(1) Thermal Shrinkage A film marked at a distance of 30 cm in the vertical and horizontal directions was placed in a furnace controlled at 150 ° C. for 30 minutes.
Hold for one minute and measure shrinkage.

(2) Planarity A flat, two-dimensional table is provided with many fine air vent holes.
The film cut into a size of 2 × 2 m is spread and evaluated from the wavy state of the film. A level having no problem in quality is represented by ○, and a level having problem is represented by ×.

(3) Glass transition temperature (Tg) Measured using a DSC (differential scanning calorimeter).

(4) Intrinsic viscosity Determined at 35 ° C. using an o-chlorophenol solvent.

Example 1 Intrinsic viscosity = 0.72, Tg =
A film of polyethylene terephthalate at 69 to 70 ° C. is formed by a conventional method to obtain an unstretched film, which is stretched in the longitudinal direction, and then subjected to transverse stretching, heat fixing and relaxation heat treatment by a tenter shown in FIGS. Was. The film speed after longitudinal stretching was 150 m / min. The temperature of the heat setting zone was 220 ° C., and the temperature of hot air in the cooling zone (zone length 3 m, distance from the edge cut position to the take-up roll 9 m) was 60 ° C. The center film cut at both ends in the heat setting zone reduces the take-off speed, keeps the tension at 7 to 9 kg / cm ² by dancer rolls, and sets the film running direction in the horizontal direction using two sets of film tentering devices with a 3 m spacing in the film running direction. And subjected to relaxation heat treatment. As means for supporting the film's own weight, two air floating nozzles were installed between film tentering devices at intervals of 60 cm and used. A slit 4 whose width is 70% of the width at the center of the film and whose opening is 3 mm
Heated air with a wind speed of 10 m / sec was blown from a floating nozzle having two locations to float the film.

The film in the zone having a speed difference during the relaxation treatment was running stably without vertical wrinkles, sagging, and flapping.

The flatness of the obtained biaxially oriented film having a thickness of 60 μm was good without wrinkles, and the heat shrinkage in the vertical and horizontal directions was 0.2% and 0.2%, respectively.

Example 2 A film was formed and heat-treated in the same manner as in Example 1 except that four transport rolls were installed at intervals of 30 cm as means for supporting the film's own weight. The transport roll had a diameter of 40 mm and was a free roll. The roll was made of stainless steel and hard chrome plated on the surface. The length of the roll was set to cover the entire width of the central film.

Although the film in the zone having a speed difference during the relaxation treatment was slightly sagged between the transport rolls,
There was no contact with the tenter's plenum duct, and it was running stably without vertical wrinkles and flapping.

The flatness of the obtained biaxially oriented film having a thickness of 60 μm was good without wrinkles, and the heat shrinkage in the vertical and horizontal directions was 0.3% and 0.2%, respectively.

Comparative Example 1 A film was formed and heat-treated in the same manner as in Example 1 except that no means for supporting the weight of the film was provided. As the take-up speed of the central film was reduced, the film dripped drastically with the tension being 10 to 15 kg / cm ² and came into contact with the plenum duct of the tenter. As a result, the film was scratched and did not become a product.

[Comparative Example 2] In the state of Comparative Example 1, the take-up speed was increased until the film droop did not touch the duct. As a result, the tension could not be reduced below 20 kg / cm ² .

The flatness of the obtained biaxially oriented film was such that the central portion was slackened and wrinkles were formed in the lateral direction. The heat shrinkage in the vertical and horizontal directions was 0.9% and 0%, respectively, and the heat shrinkage in the vertical direction hardly decreased.

The results are summarized in Table 1.

[0043]

[Table 1]

[0044]

According to the present invention, when a heated stretched thermoplastic resin film is thermally relaxed by using a speed difference, wrinkles generated in the longitudinal direction can be suppressed, and a film having good flatness can be obtained. be able to. Further, by supporting the film's own weight, a large speed difference can be obtained without worrying about sagging of the film, and a low tension heat treatment can be performed, so that a very low heat shrinkage can be obtained. Also, even under low tension, drooping can be prevented, so that the rejection rate due to abrasion can be reduced. In particular, in the case of a film forming heat treatment machine having a wider width and a higher speed, the effect of the film's own weight increases due to the increase in the width and the zone length of the apparatus, so that the utility of the present invention further increases.

[Brief description of the drawings]

FIG. 1 is a plan view showing an attached state of a film tentering device (cross guider) and a film self-weight supporting means (here, an air floating nozzle).

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a schematic plan view showing a positional relationship between a cross guider and an air floating nozzle from a tenter to a take-up roll.

FIG. 4 is a side view of FIG. 3;

FIG. 5 is a schematic plan view of a rear part of a tenter showing a positional relationship between a cross guider and a film transport roll.

FIG. 6 is a side view of FIG. 5;

[Explanation of symbols]

1: Thermoplastic resin film 2, 2 ': Fixed cutter 3, 3': Edge film after cut 4: Central film after cut 5, 5 ': Nip roll of cross guider 5 (a), 5 (b): 1 One cross guider has
A pair of nip rolls 6: View in the direction of film movement 7: Air floating nozzle 11: Thermoplastic resin film 12: Tenter rail 13: Preheating zone 14: Stretching zone 15: Heat treatment zone 16: Cooling zone 17, 17 ': Fixed cutter 18, 18 ', 19, 19': Nip roll of cross guider 18 (a), 18 (b), 19 (a), 19 (b): 1
A pair of nip rolls of two cross guiders 20, 21: air floating nozzle 22: dancer roll 23, 24: take-up roll 25, 25 ': edge film after cutting 26: central film after cutting 27, 28, 29: film Transport roll

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B29C 55/02-55/28 B29C 71/02

Claims (7)

(57) [Claims] 1. A heat treatment method for thermally relaxing a heated stretched thermoplastic resin film by utilizing a difference in speed between supply and take-off of the film, wherein (a) the width of the film is 3 to 8
and m, installed (b) 1 or more pairs along the ends of the occur are relaxed zone film speed difference gripping and tentering apparatus having a nip roll which gives a tensile force to the film width direction in the film running direction (C) providing a means for supporting the film's own weight in the relaxation zone to reduce or prevent sagging of the film, wherein the thickness is 40 to 300 μm.
Relaxation heat treatment method of the stretched film that. 2. The relaxation heat treatment method according to claim 1, wherein pneumatic force is used as a means for supporting the weight of the film. 3. The relaxation heat treatment method according to claim 1, wherein a rotatable film transport roll is used as a means for supporting the film's own weight. 4. The relaxation heat treatment method according to claim 1, wherein the tension in the running direction of the film in the relaxation zone is ² to 50 kg / cm ² . 5. The relaxation heat treatment method according to claim 1, wherein a relaxation zone is provided between a position provided in the tenter for cutting and separating both end portions of the film and a take-off roll for drawing the film at the center portion under reduced speed. 6. The relaxation heat treatment method according to claim 1, wherein the heated stretched thermoplastic resin film is a biaxially stretched heat set film that has exited a heat setting zone of a tenter. 7. The temperature of the heated stretched thermoplastic resin film is 100 ° C. or more higher than the glass transition temperature (Tg) of the resin, the film is forcibly cooled in the relaxation zone, and the film at the end position of the relaxation zone is formed. Temperature is Tg + 50
2. The relaxation heat treatment method according to claim 1, wherein the temperature is lower than ℃.