JPH0457181B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for relaxing heat treatment of a thermoplastic resin film, and more particularly to a method for stably and reliably performing relaxation heat treatment of a thermoplastic resin film heat-set with a tenter. .

(Prior Art) After a thermoplastic resin film is stretched, it is slit as necessary and subjected to secondary processing. At that time, the film may be subjected to reheat treatment, and dimensional stability is required. If the film undergoes heat shrinkage during secondary processing, problems such as problems in the processing process and a decrease in product yield will occur, so normally,
A method has been adopted in which a dimensional stabilization treatment, such as a relaxation heat treatment, is performed in the film forming process to reduce the thermal shrinkage rate of the film.

As for the relaxation heat treatment in the longitudinal direction of the film, for example, there is a method in which a heating device is provided between the rolls in the longitudinal direction of the film, and the speed of the take-off roll is slightly reduced relative to the supply roll. A method of slowing down to a relaxation heat treatment (Japanese Patent Publication No. 44-20240) is known. In the former case, a heating device is usually provided between the rolls to reheat the cooled film, resulting in a large energy loss and requiring additional heat treatment time.
On the other hand, in the latter case, the film side edges are also heat-treated in the tenter at the same time, so there is a difference in heat shrinkage between the thick end portions and the thin center portion, causing the film to sag, resulting in poor flatness, etc. On the contrary, there is a problem that the clip speed decreases, and furthermore, means for gradually decreasing the clip speed in the direction of propagation within the tenter complicates the equipment and is disadvantageous in terms of maintenance and cost.

Another method using a tenter is to cut both ends (clip gripping parts) of the film behind the tenter heat treatment zone, and then loosen only the central part of the film in the longitudinal direction between the tenter and the winder. For example, Special Publication No. 57-54290) is known. However, with this method, not only is it difficult to cut smoothly due to the hot air circulating inside the tenter, but also the film temperature at the cutting position is high, and the distance from the cutting position to the take-off system is long, so the film in the central part may be sagging. This causes problems such as a lack of running stability and, in some cases, wrinkles in the film running direction.

(Objective of the Invention) An object of the present invention is to provide a method for relaxing heat treatment of a thermoplastic resin film, which improves the above-mentioned problems and also provides a large thermal shrinkage.

(Structure of the Invention) The present invention heat-sets a stretched film made of a thermoplastic resin at a temperature 100 to 180°C higher than the glass transition temperature (Tg) of the resin in a heat treatment zone of a tenter,
Both ends of the heat-set film are cut and separated in a film-processing wind-free zone provided between the heat treatment zone and the cooling zone, and the heat-set film with both ends cut off is gradually cooled in the cooling zone and collected. This is a relaxation heat treatment method for a thermoplastic resin film, which is characterized by relaxing by reducing the speed, then cooling the film subjected to the relaxation heat treatment to room temperature, and winding it up.

Here, the glass transition temperature (Tg: °C) is the glass transition temperature of an unstretched film of thermoplastic resin. Usually determined by DSC (differential scanning calorimeter), for example, the Tg of polyethylene terephthalate is 69 to 70.
It is ℃.

The first feature of the present invention is that a zone free from film processing wind is provided between the heat treatment (heat setting) zone and the cooling zone of the tenter, and both ends of the heat set film are cut and separated in this zone. Thereby, both ends of the heat-set film can be stably cut without being affected by the film circulation wind. Moreover, since the film at the cutting position is relatively hot, it is possible to sufficiently relax the film in the longitudinal direction by slowing down the film take-up speed, and as a result, a low thermal shrinkage rate can be imparted. Furthermore, there is an advantage that a difference can be created between the longitudinal heat shrinkage start temperature and the transverse heat shrinkage start temperature, so that the heat shrinkage rate of the film in the transverse direction can be controlled to some extent. The difference in thermal contraction start temperature in both axial directions is thought to be due to the following reason.

The film traveling inside the tenter is held at both ends by clips, and both ends are cut and then loosened by decelerating the film take-up speed.
The influence of the longitudinal relaxation extends to the front of the cut position, that is, the heat fixation zone, while the transverse heat contraction is completely parasitic by the clip, so heat contraction begins from the cut position, and the temperature at that cut position The thermal shrinkage rate characteristics are determined by:

The cutting position may be placed either on the heat fixing zone side or on the cooling zone side, depending on the case.

The second feature is that the heat-set film with both ends cut is slowly cooled to a predetermined temperature in a cooling zone, or in some cases in a take-up roll system. Since the temperature at which both ends of the film are cut is relatively high, vertical wrinkles will occur if the film is rapidly cooled during the subsequent cooling process. To prevent this, it is effective to slowly cool the film.In order to cool the film in stages, the temperature in the cooling zone is controlled in stages, and in order to prevent rapid cooling due to contact with the roll in the take-up system. It is preferable to use a temperature control roll. The temperature of the cooling air in the cooling zone is preferably higher than Tg.
During cooling in the cooling zone, the film temperature from this temperature ranges from Tg to (Tg+80)℃ and furthermore from Tg to (Tg+60)
℃, especially Tg to (Tg+40)℃, and it is preferable to keep the temperature difference between the take-up roll and the film within 40°C until the film temperature becomes lower than Tg. One or more take-up rolls can be provided, but in the case of two or more take-up rolls, it is preferable that the temperature of each roll satisfies the above temperature conditions.

In addition, in order to ensure constant and reliable film relaxation, the film is prevented from slipping on the roll, and to prevent the tension of the subsequent take-up system and the tension that winds the film from reaching the tenter side.
It is preferable to provide a nip roll. In this case as well, the temperature of the nip roll is preferably the same as that of the take-up roll.

The film made of thermoplastic resin 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, the stretched film may be a uniaxially stretched film stretched only in the vertical direction or only in the horizontal direction, or may be a biaxially stretched film stretched in the vertical direction and the horizontal direction. Further, the heat setting temperature of the stretched film is 100 to 180°C higher than the glass transition temperature (Tg) of the thermoplastic resin. As the stretching method, conditions, etc., conventionally known methods or those accumulated in the art can be used.

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

FIG. 1 is a schematic cross-sectional view showing the main parts of a conventional device from a tenter to a take-up roll. The longitudinally stretched thermoplastic resin film 1 is preheated in a preheating zone 3 with its side ends held by the clips of a tenter rail 2, and then laterally stretched in a stretching zone 4. Subsequently, it is heat-set in a heat treatment zone (heat-setting zone) 5, cooled in a cooling zone 6, taken up by take-up rolls 10, 11, and then wound up by a winding equipment (not shown).

FIG. 2 is a schematic sectional view showing the main parts from the tenter to the cooling roll to which the present invention is applied. The longitudinally stretched thermoplastic resin film 1 is preheated in a preheating zone 3 with its side ends held by the clips of a tenter rail 2, and then laterally stretched in a stretching zone 4. Subsequently, in heat treatment zone (heat setting zone) 5, the material is heat fixed at a temperature of at least glass transition temperature (Tg) + 100°C and below glass transition temperature (Tg) + 180°C, and in cooling zone 6, it is heated with cooling air at a temperature above glass transition temperature (Tg). In some cases, the cooling zone is divided into multiple zones (6', 6'') to achieve independent cooling (above the glass transition temperature, 6' zone temperature ≧ 6'' zone temperature). cooled down. At that time,
A zone 7 is provided between the heat treatment zone 5 and the cooling zone 6, which has cutter equipment 8, 8' for cutting the ends of the film without substantially blowing out hot air. The cutter equipment 8, 8' cuts and separates both sides of the heat-set film. The film (center part) with both ends cut off is slowly cooled in the cooling zone 6 while being clipped at the take-up speed of the take-up roll 10 whose temperature is adjusted to a temperature within 40° C. to avoid rapid cooling. By slightly decreasing the running speed, the cutter (8, 8')
It travels while being relaxed between the rollers 10 and 10. In this case, if the temperature of the film is high and the film remains above the glass transition temperature even after passing through the take-up roll 10,
It is advisable to further adjust the temperature of the take-up roll.

Furthermore, the film is held down in the width direction by the nip roll 9 in order to keep the take-up roll 10 and the film traveling speed constant and constant, and to prevent the tension of the following take-up system and winding system from reaching the film relaxation zone. The position of the nip roll 9 may be set at the time when the temperature of the film becomes below the glass transition temperature. The film is then cooled to room temperature and rolled up.

(Example) The present invention will be explained below with reference to Examples.

Example 1 Polyethylene terephthalate (intrinsic viscosity determined at 35°C using O-chlorophenol solvent:
. 230℃ in heat treatment zone 5
After cutting both ends of the heat-set film in zone 7, which has cutter equipment that does not blow out hot air, the film is relaxed by reducing the take-up speed by 1.5%, and then cut in cooling zone 6 with cooling air at 100℃. Cool gradually;
The slowly cooled film leaving the cooling zone at a film temperature of 80°C was taken up by a take-up roll 10 at a temperature of 65°C equipped with a nip roll 9, cooled to room temperature, and then wound. The resulting biaxially oriented film with a thickness of 100 μm was
The longitudinal heat shrinkage rate when held at 150°C for 30 minutes was 0.1%. Moreover, the flatness of this film was good with no wrinkles.

Comparative Example 1 Polyethylene terephthalate (intrinsic viscosity 0.72) was formed into a film in the same manner as in Example 1, stretched longitudinally, stretched 3.6 times in the transverse direction using the conventional method shown in Figure 1, and then heat-set at 230°C. I picked up the film.
The resulting biaxially oriented film with a thickness of 100 μm was heated at 150°C.
The heat shrinkage rate when held for 30 minutes was 1.20%, which is a high value for a heat shrinkage rate.

(Effects of the Invention) In the present invention, both ends of the stretched thermoplastic resin film are cut in a zone between the heat treatment (heat fixing) zone and the cooling zone of the tenter that does not blow out hot air. In addition, since the longitudinal heat shrinkage start position is different (vertical heat shrinkage starts upstream of the film from the cutting position), the longitudinal heat shrinkage is increased. It also has the advantage that the heat shrinkage characteristics in the lateral direction can be brought close to the heat shrinkage characteristics in the longitudinal direction to some extent.Furthermore, since no hot air is blown into this zone during film cutting, the film runs stably and the film It also has the advantage of allowing smooth cutting.

By controlling the cooling air in the relaxation zone and avoiding rapid cooling with the take-up roll, it has the effect of suppressing vertical wrinkles that occur in the film.

In addition, if a nip roll is provided to keep the take-up roll and film running speed constant and consistent and to prevent the tension of the following take-up and winding systems from reaching the film relaxation zone, the longitudinal heat shrinkage characteristics of the film can be further improved. It has the advantage of being stable and uniform.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the main parts of a conventional device from a tenter to an auxiliary roll. FIG. 2 is a schematic sectional view showing the main parts from the tenter to the cooling roll to which the present invention is applied. 1... Thermoplastic resin film, 2... Tenter rail, 3... Preheating zone, 4... Stretching zone,
5...Crystallization zone, 6...Cooling zone, 6',
6″...Multi-divided cooling zone, 7...Zone without film processing wind, 8, 8'...Cutting blade, 9
...Nitspro roll, 10...Takeover roll, 11...
…Takeover roll.

Claims (1)

[Claims] 1. A stretched film made of a thermoplastic resin is heated to a temperature lower than the glass transition temperature of the resin in a heat treatment zone of a tenter.
A heat-set film that is heat-set at a high temperature of 100 to 180 degrees Celsius, then cut and separated on both sides of the heat-set film in a film processing wind-free zone provided between the heat treatment zone and the cooling zone. A method for relaxing heat treatment of a thermoplastic resin film, characterized in that the film is gradually cooled in the cooling zone and relaxed by slowing down the take-up speed, and then the film subjected to the relaxation heat treatment is cooled to room temperature and wound up. 2. The relaxation heat treatment method according to claim 1, characterized in that the temperature of the cooling air supplied to the cooling zone is equal to or higher than the glass transition temperature of the thermoplastic resin. 3. The relaxed heat-treated film that has come out of the tenter is taken up using one or more take-up rolls whose temperature difference with the film is adjusted to within 40°C until the temperature of the film becomes lower than the glass transition temperature of the thermoplastic resin. 2. The relaxation heat treatment method according to claim 1, wherein the relaxation heat treatment method is performed by withdrawing the material. 4. The relaxation heat treatment method according to claim 3, characterized in that a nip roll is combined with the take-up roll.