JPS62149414A - Cooling of film made of thermoplastic resin - Google Patents

Abstract

PURPOSE:To prevent curling from developing and consequently obtain a film with favorable flatness by a method wherein the temperature of cooling rolls are set in two specified steps in a method to cool the thick-gage film, which is made of thermoplastic resin and the thickness after orientation of which lies within the specified range, with the cooling rolls. CONSTITUTION:The temperature of a first cooling roll is set at a temperature comparatively higher than the normal cooling temperature of within the range of Tg-10-Tg-30 deg.C (where Tg is the glass transition temperature of a film) so as to hold down the gradient of the cooling rate of the surface layer of the film, with the side of which the first cooling roll comes into contact. The thickness of the film is 150-1,500mum. The temperature drop in the interior part of the film while being carried by winding on the cooling roll is not so much larger. The temperature of a second cooling roll is set lower than that of the first cooling roll by 10-40 deg.C. As a result, the gradient of the cooling rate of the surface layer of the film, with the side of which the second cooling roll comes into contact, becomes nearly equal to the gradient of the cooling rate of the surface layer of the film in case of the first cooling roll and the densities of the surface layers becomes nearly the same as each other and consequently curling is prevented from developing at the film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of cooling a thick film made of a thermoplastic resin after stretching or heat treatment using a cooling roll.

[Prior Art] Generally, in the manufacturing process of a film made of a thermoplastic resin, a plurality of cooling rolls are used to forcibly cool the film to a predetermined temperature after it has been stretched or heat treated. Then, the film is sequentially wound around a plurality of cooling rolls and conveyed, and is cooled alternately from the front side and the back side. Conventionally, in this film cooling, all of the plurality of cooling rolls are set to approximately the same temperature, and the film is cooled from the front and back surfaces under the same conditions.

[Problems to be Solved by the Invention] However, when the film has a thickness of 150 μm to 1500 μm just before cooling, that is, after orientation, the method of simply cooling the front and back sides of the film alternately does not allow the front side of the film to There is a difference in cooling rate between the front and back sides, and the density of the film surface layer on the front and back sides differs due to the difference in cooling rate.
A problem of poor flatness may occur where the film curls on the higher density side. When such a curling phenomenon occurs, it not only deteriorates the quality of the film but also causes trouble in the process after cooling. For example, in a manufacturing process in which a thick film is uniaxially stretched, it is immediately cooled with a cooling roll, and the -axis oriented film is stretched in the width direction with a tenter device holding both sides of the film with clips. This leads to the problem that it becomes difficult to fit the film into the clip.

The present invention focuses on the above-mentioned problems in roll cooling of thick films, and aims to prevent the occurrence of curling due to the difference in cooling speed between the front and back surfaces of the film, and to obtain a film with good flatness. shall be.

[Means for Solving the Problems] A method for cooling a film made of a thermoplastic resin according to the present invention in accordance with this purpose is a film made of a thermoplastic resin oriented in at least one axis, with a thickness of 150 μm after orientation.
A thick film in the range of ~1500μ is placed in the cooling port,
- In the method of cooling using a film, the temperature of the cooling roll is set in two stages, and the temperature of the first cooling roll is set to the glass transition temperature of the film (Tq > -10°C to the glass transition temperature (Tg)). -30'C, and the temperature of the second cooling roll is 10° higher than the temperature of the first cooling roll.
It consists of a method in which the film is cooled at a temperature of 'C to 40'C.

Here, if a large number of cooling rolls are provided, the third
Although the temperature of the cooling roll after the second cooling roll is not particularly specified, it is preferably set to approximately the same temperature as the second cooling roll.

[Operation] In such a cooling method, the temperature of the first cooling roll is relatively high as a cooling temperature (TCI)-1
Since it is set in the range of 0℃~(Tq)-30'C,
First, the cooling rate gradient of the film surface layer on the side that contacts the first cooling roll is suppressed to a small level. Since the film is thick, the temperature of the inner layer of the film does not increase even while the film is being wound around the first cooling roll and being conveyed, and depending on the first cooling roll, the temperature of the inner layer of the film does not increase. Cooling of the surface layer of the film on the opposite side is hardly expected, or at least very little. . However, even during this time, since the surface opposite to the contact surface is exposed to the atmosphere, it is cooled by the atmosphere. Therefore, when the film passes through the first cooling roll and enters the second cooling roll,
The temperature of the surface in contact with the second chill roll is lower than the film surface temperature when the film enters the first chill roll. From this state, the surface opposite to the surface cooled by the first cooling roll is cooled by the second cooling roll, but the temperature of the second cooling roll is the same as that of the first cooling roll. 10'C~40'C than
This temperature difference is exactly the difference between the film surface temperature when it enters the first cooling roll and the film temperature at the contact surface to the second cooling roll when it enters the second cooling roll. If the temperature of the second cooling roll is set to correspond to the cooling rate of the film surface layer on the side that contacts the second cooling roll, the cooling rate gradient of the film surface layer on the first cooling roll The slope will be almost the same.

By making the cooling rate gradients of both film surfaces almost the same, the densities of the film surface layers are also almost the same, and curling is prevented.

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an apparatus for carrying out a method according to an embodiment of the present invention, in which the present invention is applied to a cooling process after longitudinal stretching (longitudinal stretching) of a film made of a thermoplastic resin. It shows.

In the figure, F indicates a continuously conveyed film made of thermoplastic resin, and in this example, a particularly thick film made of polyethylene terephthalate. It is in the range of 150μ to 1500μ. However, the film targeted by the present invention is not limited to the film oriented in the uniaxial direction as described above, but also includes the film oriented in the biaxial direction, and the thermoplastic resin Ih is not limited to simply polyethylene terephthalate. .

1 to 5 indicate preheating rolls before the stretching process that heats the film to the stretching temperature, and 6 indicates a rubber-lined nip roll. Immediately after the preheating roll 5 and the nip roll 6, a stretching section is provided. A heater 7.87) is installed in the stretching section to increase the amount of heat.

Immediately after this stretching section, a cooling roll as used in the present invention is provided. In this embodiment, the first cooling roll 9, the second
In addition to the first cooling roll 10, a third and fourth cooling roll 11, 12, a total of four cooling rolls are provided. In addition, in this example, the number of cooling rolls was set to four, or
The present invention is not limited to this, and any suitable number may be used depending on the speed, thickness, cooling capacity, etc. of the film, and the present invention can be implemented as long as there are at least a first cooling roll and a second cooling roll.

When the present invention was implemented using the apparatus configured as described above, the following results were obtained compared to the conventional case where all the cooling rolls were kept at the same temperature.

The test conditions were all the same for both the conventional method and the present invention method, except for the temperature of the cooling roll. In the test, the film thickness of polyethylene terephthalate before Ml stretching was 2.5#,
Set the temperature of preheating rolls 1 to 4 to 82℃ 1 preheating roll 5
After heating to a temperature of 90'C, stretching at a longitudinal stretching ratio of 3 times (heater capacity ω is 8 Kw on the upper side and 4 Kw on the lower side) L,
Next, the film was stretched laterally (stretched in the width direction of the film) at a magnification of 3.5 times and a temperature of 140°C, and then tension heat-set was performed at 200'C, and the film was wound up with a winder.

The film forming speed was 20 m/min after longitudinal stretching.

The temperature conditions for cooling rolls 9 to 12 were set as shown in Table 1, J: Sea urchin.

When evaluating the curl of the obtained biaxially stretched film,
Curl hanging, which was 11m in the conventional method, is reduced to 1m in the method of the present invention.
decreased to m. To measure the curl, as shown in FIG. 2, the method is to take 10 cm of the most severely curled part, place this film fragment 20 on a flat surface 21, and measure the height H of the film apex 22 from the flat surface 21. According to In addition,
Regarding the surface defects of the obtained films, there were no defects in both the conventional method and the method of the present invention.

In addition, although the above-mentioned example applies the present invention to a cooling roll after longitudinal stretching of a film, the present invention is not limited thereto, and the present invention is not limited to this, and the present invention is applied to a cooling roll after longitudinal re-stretching of an already oriented film, or a cooling roll after longitudinal stretching of an already oriented film, or a suitable heat treatment process. The present invention can also be applied to cooling rolls and the like.

[Effects of the Invention] As explained above, when using the method for cooling a film made of a thermoplastic resin of the present invention, a thick film is cooled at two temperatures, and the first cooling roll cools the surface layer of the film. Since the cooling speed and the cooling speed of the second cooling roll are set to be almost the same speed, the density of the surface layer of the film after cooling can be made almost the same on both sides, and the occurrence of curling can be prevented. The effect is that the flatness of the film can be improved.

Moreover, as a result of being able to prevent the occurrence of curling, in addition to the above-mentioned improvement in quality, it is also possible to prevent troubles in the manufacturing process such as poor clip biting in the tenter device.

[Brief explanation of drawings]

FIG. 1 is a side view of a longitudinal film stretching apparatus for carrying out a method according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram showing a curl evaluation method. F...Film 1.2.3.4.5...Preheating roll 6...
...Nip roll 7.8...Heater

Claims (1)

[Claims] (1) A film made of thermoplastic resin oriented in at least one axis, with a thickness of 150μ to 1500 after orientation.
In a method of cooling a film with a thickness in the range of μ using a cooling roll, the temperature of the cooling roll is set in two stages, and the temperature of the first cooling roll is set to the glass transition temperature (Tg) of the film - 10℃～Glass transition temperature (Tg
) -30°C, and the temperature of the second cooling roll is 10°C to 40°C lower than the temperature of the first cooling roll to cool the film. Cooling method.