JPH0457182B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for relaxing heat treatment of a thermoplastic resin film, and more specifically, the present invention relates to a method for relaxing heat treatment of a thermoplastic resin film, and more specifically, a stretched thermoplastic resin film is actively treated to prevent wrinkles from forming in the running direction (lengthwise direction of the film). It relates to a method of relaxing heat treatment while suppressing the

Prior Art After a thermoplastic resin film is stretched, it is slit and subjected to secondary processing, if necessary. At that time, the film may be subjected to heat treatment,
Dimensional stability is required.

As a means for improving this dimensional stability, a method of subjecting a stretched film to a relaxation heat treatment is known, and for example, it is known to carry out this relaxation heat treatment in the film forming process. At that time, when the film is heated and cooled, vertical wrinkles occur in the film, and these are fixed by heat, or in extreme cases, are pressed on the take-up roll, causing the film to overlap twice at the wrinkled part. This may result in severe creases, which may worsen the film's flatness and dimensional stability.

Conventionally, as a method to suppress the occurrence of wrinkles,
When heating or cooling a film without contact using air or other media, or when heating or cooling a film using a roll, etc., take time to avoid rapid heating or cooling of the film. A method of gradually heating and cooling is known. However, this method takes too much time to heat and cool the film, and it also requires heating and cooling to be done gradually and in stages, requiring a lot of equipment and requiring more precise temperature control. It's coming.

In addition, in conventional relaxation technology, thermal shrinkage in the longitudinal direction is controlled by the heating temperature and relaxation rate of the film, but at the same time, the thermal shrinkage rate characteristics in the transverse direction (width direction) are uniquely determined by this heating temperature. determined by
There is a problem in that the heat shrinkage in the lateral direction (width direction) cannot be controlled independently of the heat shrinkage conditions in the longitudinal direction. In other words, unlike the vertical direction, there is nothing to regulate the film dimensions in the horizontal direction, and there is nothing to apply tension in the horizontal direction. In cases where the maintenance of thermal shrinkage rates is different and further two-dimensional dimensional stability is required, that is, when it is necessary to bring the vertical and horizontal thermal contraction rate characteristics close to each other, it becomes difficult to cope with the conventional technology.

OBJECT OF THE INVENTION The object of the present invention is to improve the above-mentioned problems, eliminate wrinkles in the longitudinal direction of the film during relaxation heat treatment, and, if necessary, reduce the wrinkles in the lateral direction without affecting the heat shrinkage characteristics in the longitudinal direction. An object of the present invention is to provide a method for relaxing heat treatment of a thermoplastic resin film for controlling heat shrinkage characteristics.

Composition of the Invention The present invention provides a processing method for thermally relaxing a heated stretched thermoplastic resin film by utilizing a speed difference between film supply and take-off. At least one set of film tentering devices each having a nip roll for gripping the film, the axis of which is inclined at an angle of 5 to 30 degrees with respect to the width direction of the film, is provided at each end of the film,
Both ends of the film with the nip roll are measured using the following formula (1): F≧200/μ×D/t ² [However, F: Nip force (Kg) μ: Coefficient of friction between the film and roll D: Film thickness (μ) t: This is a relaxation heat treatment method for a thermoplastic resin film, which is characterized by applying a tensile force in the width direction to the film by gripping it with a nipping force F that satisfies the film temperature (°C) at the time of nipping.

The thermoplastic resin film in the present invention is a film made of thermoplastic resin such as polyester, polyamide, polyolefin, etc. Among these, a film made of polyester, particularly polyethylene terephthalate, is preferred.

Further, a stretched film is a film stretched in at least one axis, and may be, for example, a film stretched uniaxially in the longitudinal direction or a film stretched uniaxially in the transverse direction, or a biaxially stretched film stretched in the longitudinal and transverse directions. It may be. This stretched film can be produced by any method known or accumulated in the art, but preferably by a method using a tenter.

In the present invention, the thermoplastic resin stretched film can be heated by any arbitrary means, such as contact heating with a roll, radiation heating with an electric heater, infrared heater, steam heater, etc., convection heating with a heated gas, etc. This can be carried out by a well-known method such as a heating method or a combination thereof.

In the present invention, the thermal relaxation of a stretched film is achieved by running a heated thermoplastic resin stretched film and utilizing the speed difference between the film supply speed and take-up speed, that is, the speed difference that occurs when the take-up speed is slower than the supply speed. Let's do it. This method is well known in the art. Conventional film feeding devices, take-up devices, etc. can be used.

A feature of the present invention is that a film tentering device is provided in the zone where the speed difference occurs to apply a tensile force in the width direction (lateral direction) of the running film to smooth out wrinkles in the film and control the transverse heat shrinkage characteristics. It's about doing. This film tentering device has a nip roll for gripping (nipping) the edge of the film, and the roll axis of the nip roll is inclined at an angle of 5 to 30 degrees with respect to the width direction of the film.
Since the nip roll is not parallel to the film width direction but is tilted at the above angle, a force is applied to the running film whose end is gripped by the nip roll in a direction perpendicular to the roll axis, and the width direction component of this force is acts to pull the film in the width direction.

In order for the nip roll to sufficiently exhibit a tensile action, the nip force (F: Kg) of the roll must satisfy the following formula (1).

F≧200/μ×D/t ² ...(1) However, F: Nipping force (Kg) μ: Friction coefficient between the film and roll D: Film thickness (μ) t: Film temperature during nipping (℃) One or more sets of film width adjusting devices (hereinafter sometimes referred to as cross guiders) are installed at both ends of the film.

The relaxation heat treatment of the present invention may be performed during the stretched film manufacturing process, or may be performed at a location separate from the manufacturing process. The former is inline processing, and the latter is online processing. Among these, inline processing is preferred. In particular, after a stretched thermoplastic film is heat-set in a heat treatment zone of a tenter, both ends of the film are cut and separated at a suitable location inside the tenter or outside the take-off side, and then the film is cooled and at the same time both ends are separated. This is useful in the method of loosening the film at the center of the film by slowing down the take-up speed. It suppresses film relaxation and vertical wrinkles that occur in the film during cooling, and controls lateral heat absorption. In this method, it is preferable to provide a film tenter between the tenter outlet and the take-up roll.

Next, the present invention will be explained based on the drawings.

FIG. 1 illustrates a method of heating and relaxing a stretched thermoplastic resin film using a roll, and shows the main part of a take-up roll that heat-treats the film using a roll, relaxes it due to a speed difference, and further cools it. It is a schematic sectional view. The stretched thermoplastic resin film 1 is heated by rolls 2 and 3, thermally relaxed by the speed difference between rolls 3 and 4, and then cooled by cooling rolls 4 and 5 for post-rolling. taken. At this time, a cross guider consisting of nip rolls 6 and 6' for gripping both ends of the film is rolled in the relaxation zone between the rolls 3 and 4 to suppress vertical wrinkles caused by cooling and relaxation of the film. 3,4
It is set in between. The materials of the nip rolls of the cross guider may be the same or different materials (for example, one is a rubber roll and the other is a metal roll). In the case of nip rolls made of different materials, in order to provide a predetermined nip force (F), it is preferable that the nip rolls have a high coefficient of friction with the film. The nip roll of the cross guider can be shaped as shown in Figures 2 (1) and (2) to increase the film gripping force. 1 in Figure 2
1 shows the held film, 6 and 6' a pair of nip rolls, and 9 a support for the nip rolls.

FIG. 3 shows that it can be used to prevent wrinkles that may occur on the heated side when heat is applied to the stretched film of the cross guider. FIG. 2 is a schematic cross-sectional view in which a cross guider is provided.

FIG. 4(1) is a plan view showing the mounting position of the cross guider, and FIG. 4(2) is a side view thereof. The nip rolls 6A and 6B in FIG. 4(1), like the rolls 6 and 6' in FIG. 4(2), nip both ends of the film and form an angle θ with the width direction (lateral direction) of the film. installed on. Angle θ is 5~30°
It is.

FIG. 5 is a schematic sectional view showing the main parts from the tenter to the take-up roll. The longitudinally stretched thermoplastic resin film 11 is preheated in a preheating zone 13 held by a clip of a tenter rail 12, and then laterally stretched in a stretching zone 14. Subsequently, it is heat-set in the crystallization zone 15, slowly cooled in the cooling zone 16, and then taken off by take-up rolls 20, 21 whose speed is slightly reduced. Then, in order to separate the film 11 from the grip of the clip, both ends of the film are cut off by cutters 17, 17' provided in the cooling zone 16, and the cut central film is then cut off by the nip rolls 18, 1 of the cross guider.
8' and the nip rolls 19, 19' receive a tensile force in the lateral direction, and the deceleration take-up roll nip roll 20
It is thermally relaxed between. This nituprol 18,
18', 19, and 19' suppress the occurrence of wrinkles and control the transverse heat shrinkage characteristics. FIG. 6 is a plan view of FIG. 5, showing the state in which the cross guidance nip rolls 18A, 18B, 19A, and 19B are attached. Here, the positions of the cutters 17, 17' vary depending on the desired heat yield value, but the cutters 17, 17' may be omitted depending on the case, and the relaxation zone in this case runs on the tenter rail 12. It is formed between the location (position) where the clip releases the gripped film and the deceleration take-up roll 20. In this way, even if you do not cut and separate both ends of the film, roll both ends of the film with one roll.
8, 18' or nip rolls 19, 19' to give a tentering effect to the film to prevent wrinkles from occurring.

Relaxation in the present invention is usually achieved by heat shrinkage of 5% or less, preferably 2 to 3%, although it depends on the film properties.

Examples The present invention will be explained below with reference to Examples. In addition,
The properties in the examples were determined by the following methods.

1 Coefficient of friction between film and roll 5 with a fixed, non-rotating nip roll of 5 cm length
Nip a cm-wide film with a nipping force of 10 kg, pull the spring scale attached to the other end of the film in a direction perpendicular to the axis of the nip roll, read the load on the spring scale just before the roll starts to slide, and calculate the friction coefficient using the formula below. Find (μ).

μ=Spring scale load (Kg)/Nip force (=10Kg) Example 1 A polyethylene terephthalate film with a thickness of 100 μm that had been biaxially stretched by a conventional method was subjected to relaxation heat treatment using the apparatus shown in FIG. heating roll 2,
The temperatures of the cross guider rolls 6 and 6' are 150℃ and 200℃, respectively. The temperatures in No. 5 were 50°C and 20°C, respectively. The speed relaxation rate between roll 3 and roll 4 was set to 1.0%. The resulting heat-treated film had good flatness without any wrinkles. In addition, when the film is held at 150°C for 30 minutes, the heat shrinkage rates in the vertical and horizontal directions are respectively
It was 0.1%, 0.1%.

Example 2 Polyethylene terephthalate (intrinsic viscosity 0.72)
A film was formed by a conventional method, stretched in the longitudinal direction, and then subjected to relaxation heat treatment using the apparatus shown in FIG. The temperature of crystallization zone 15 was 220°C, and the temperature of cooling zone 16 was 120°C. 2 installed after cooling zone 16
Cross guider rolls 18, 18' and 1
The nipping forces for 9 and 19' are 5Kg and 10Kg, respectively (the film temperatures at the time of nipping are 120℃ and 80℃, respectively, and the coefficient of friction between the film and the nip roll is
0.6). After cutting both ends of the film in cooling zone 16, the center film was thermally relaxed by reducing the take-off speed by 1.5%. obtained thickness
The 100 μm heat-treated film had good flatness without any wrinkles. In addition, the film was heated at 150℃ for 30 minutes.
The heat shrinkage rates in the longitudinal and transverse directions when held for minutes were 0.2% and 0.2%, respectively.

Comparative example 1 Example 1 except that no cross guider is installed
Relaxation heat treatment was carried out in the same manner as above. The flatness of the heat-treated film obtained was in a poor state with wrinkles visible at first glance. In addition, the film was heated to 150°C.
The heat shrinkage rates in the longitudinal and transverse directions when held for 30 minutes were 0.1% and -0.2%, respectively, indicating a large difference in the heat shrinkage rates in the longitudinal and transverse directions.

Comparative Example 2 A film was formed, biaxially stretched, and subjected to relaxation heat treatment in the same manner as in Example 2 except that a cross guider was not installed. The flatness of the obtained heat-treated film with a thickness of 100 μm was in a poor state with wrinkles visible at first glance. Furthermore, when the film is held at 150°C for 30 minutes, the heat shrinkage rate in the longitudinal and transverse directions is 0.2 each.
%, -0.3%, and there was a large difference in the heat shrinkage rates in the longitudinal and transverse directions.

Effects of the Invention According to the present invention, it is possible to suppress the occurrence of wrinkles in the longitudinal direction due to thermal relaxation and cooling of a thermoplastic resin stretched film, and to obtain a heat-treated film with good flatness and high winding quality. can. The heat treated film can also meet the dimensional stability required in secondary processing heat treatment.
In addition, sometimes there is a demand to bring the longitudinal and lateral heat shrinkage rates closer together, and in response to this, it is necessary to change the nip force of the cross guider, adjust the lateral tensile force, and improve the lateral heat loss. This can be handled by controlling it.

[Brief explanation of drawings]

1 and 3 are schematic cross-sectional views of a relaxation heat treatment process applicable to the present invention. FIG. 2 is a sectional view showing an example of the nip roll shape of the tentering device.
FIG. 4(1) is a plan view showing how the nip roll of the tentering device is installed, and FIG. 4(2) is a side view thereof. FIG. 5 is a schematic sectional view showing the main parts of the film forming equipment applicable to the present invention from the tenter to the take-up roll, and FIG. 6 is a plan view thereof. 1... Thermoplastic resin stretched film, 2, 3...
Heating roll, 4, 5... Cooling roll, 6, 6,
7, 7'...Nip roll of the tentering device (cross guider), 8...Film running direction, 9...
Nipprol support, 11... thermoplastic resin stretched film, 12... tenter rail, 13...
Preheating zone, 14... Stretching zone, 15... Crystallization zone, 16... Cooling zone, 17, 17'...
...Cutter for cutting off the end of the film, 18, 18',
19,19'...Cross Guider's Nitprol,
20, 21...Takeover roll.

Claims (1)

[Claims] 1. In a processing method in which a heated thermoplastic resin stretched film is thermally relaxed by utilizing the difference in speed between supplying and taking off the film, the edge of the film is placed in the zone where this speed difference occurs. At least one set of film tentering devices each having a nip roll for gripping the film and whose axis is tilted at an angle of 5 to 30 degrees with respect to the width direction of the film is installed at both ends of the film, and the nip rolls are used to set both ends of the film according to the following formula. F≧200/μ×D/t ² [However, F: Nipping force (Kg) μ: Coefficient of friction between the film and roll D: Film thickness (μ) t: Film temperature during nipping (℃)] A method for relaxing heat treatment of a thermoplastic resin film, which is characterized by gripping the film with a nip force F and applying a tensile force in the width direction to the film. 2. Claims characterized in that the zone where the speed difference occurs is between a position provided in the tenter where both ends of the film are cut and separated and a take-up roll that takes the film in the center part under deceleration. The relaxation heat treatment method according to item 1. 3. The relaxation heat treatment method according to claim 2, wherein the heated thermoplastic resin stretched film is a stretched heat-set film that has exited a heat-set zone of a tenter. 4. The relaxation heat treatment method according to claim 2, characterized in that a film tentering device is provided between the tenter outlet and the take-up roll.