JPS598343B2 - Stretching method for thermoplastic resin film or sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for stretching a thermoplastic resin film or sheet (hereinafter collectively referred to as "film"), particularly a method for producing a stretched film with few or no scratches on the surface. related to.

Films made of polyolefins such as polyethylene and polypropylene, linear polyesters such as polyethylene terephthalate, polyamides such as nylon, and other thermoplastic resins such as polyvinyl chloride and polystyrene are stretched using low-speed heating stretching rolls and high-speed cooling stretching. The method of stretching the film at a desired magnification in the longitudinal direction, that is, the machine direction, by using rolls and appropriately selecting the speed ratio of both rolls is well known and is widely practiced industrially.

In such a stretching process, the film is displaced on the stretching roll surface, causing damage to the film surface.

Such scratches generally impair the appearance of the film and reduce its commercial value. It is particularly unsuitable for applications that require transparency. Furthermore, when polyester films are used for materials that require highly demanding performance, such as tape recorders, other recording tapes, and insulating materials for capacitors, this can become a fatal flaw. Therefore, it is desired to establish a method for suppressing the occurrence of such scratches as much as possible and obtaining a scratch-free stretched film. In order to prevent scratches, it is possible to consider means to prevent the film from shifting on the stretching rolls during the stretching operation.

On the other hand, when stretching is performed between low speed rolls and high speed rolls,
A method has been proposed in which charges are deposited on the film on a low-speed roll using a charged electrode, and the film is brought into close contact with the roll surface to prevent neck-in (film width shrinkage) (Japanese Patent Publication No. 37-7143). (Refer to the publication), it is conceivable that this method can bring the film into close contact with the roll surface to prevent the film from shifting and causing scratches. However, in this type of conventional method, the point where static electricity is applied is near the point where the film enters the low-speed roll and starts coming into contact with it. It prevents air from being entrained between the film and roll, and also applies an electric charge to the film at the point where it starts contacting the slow roll to achieve the purpose of making the film stick to the roll and improve heat conduction. This is because it is necessary.
However, the static electricity on the applied film dissipates within a short time, and this dissipation is accelerated as the temperature increases. The film on the low-speed stretching rolls is usually heated to a temperature suitable for stretching, so the temperature is high. In particular, when polyester films are highly oriented, the film is stretched biaxially and then stretched again. The temperature is higher than the temperature during the first longitudinal stretching, and the film on the rolls is generally heated to at least 110°C, preferably 130°C or higher. In this way, the adhesion force due to the electrical charge cannot be maintained until the exit of the film on the low-speed stretching roll (the point where the roll and the film no longer contact each other), and as a result, the film sag near the exit on the low-speed stretching roll, resulting in scratches. It was found that this occurs. In general, scratches are most likely to occur near the exit of the film (this is thought to be due in part to the stretching stress of the film), so conventional methods cannot sufficiently achieve the purpose of preventing scratches. In view of the above-mentioned background, the present inventors have completed the present invention through extensive research to solve the problems in the conventional methods. The present invention provides a method for producing a stretched film with few or no scratches such as scratches when a thermoplastic resin film is stretched in the longitudinal direction of the film using low-speed stretching rolls and high-speed stretching rolls. This purpose is to set a circumferential angle of 25 degrees with the point A where the film leaves the low-speed stretching roll, and the above-mentioned point A on the upstream side of the moving flow of the film on this low-speed stretching roll. This is achieved by providing a charging electrode between the point B and the film on the low-speed stretching roll to deposit an electric charge on the film and bring the film into close contact with the roll. explain.

The accompanying drawings are explanatory diagrams illustrating embodiments of the method of the present invention. In the figure, 1 is a low speed roll for stretching, 2 is a high speed roll, 3 is a thermoplastic resin film, and 4 is a charging electrode. The film 3 advances in the direction of the arrow, is heated by low-speed rolls 1 to a temperature suitable for stretching, and is cooled by high-speed rolls 2. The film is then stretched in the longitudinal direction due to the speed difference between the two rolls. A is the location where the film 3 leaves the low speed roll 1, ie, the film exit on the low speed roll, and D is the location where the film 3 contacts the high speed roll 2, ie, the film inlet on the high speed roll. Geometrically speaking, A and D are the points of contact when tangent lines are drawn to both the circumference of the low-speed roll and the circumference of the high-speed roll. B is the intersection of the circumference and a line that makes an angle of 250 on the upstream side of the film movement flow with respect to the AO line, with the center of the circle of the slow roll being o.

Similarly, C is the intersection of a line making an angle of 100 with respect to the AO line and the circumference. In carrying out the method of the present invention, a charging electrode 4 is provided above the roll between A and B.

However, it is more preferable to provide an electrode between C and B. The charging electrode 4 may be of any conventionally known form, such as wire, knife edge, needle, etc.Although its auxiliary equipment is not particularly shown, conventionally known devices may be used. Furthermore, the conditions such as the discharge voltage of the electrode and the distance between the film and the electrode do not need to be special, and can be implemented according to conventional methods. Further, as the stretching device, any type of longitudinal stretching device including low speed rolls and high speed rolls can be used.

In the method of the present invention, it is more preferable to provide a charging electrode on the high-speed stretching roll so that charges can be deposited on the film on the roll, since it is possible to prevent the film from shifting on the high-speed roll. In this case, the charging electrode is connected from the film entrance, that is, slightly upstream of the film flow from point D (the distance at which the charged charge can remain even if the film is placed on a high-speed roll), and from the point D. It is preferable to provide it slightly downstream of the film flow.

In the method of the present invention, as mentioned above, it is essential to provide an electrode between point A and point B of the low-speed roll in the figure, and even if the electrode is placed upstream of point B in the film flow, The effect of reducing scratches that occur is small.

However, a charging electrode is provided between point A and point B, and in addition... '(, There is no problem in depositing electrical charges upstream of point B. According to the method of the present invention, it is possible to not only suppress the occurrence of scratches on the stretched film surface, but also to prevent neck-in, which is likely to occur during stretching. can also be suppressed.

Since neck-in tends to occur near the film exit of the low-speed roll due to stretching stress, it is effective to deposit electrical charges near the exit. The method of the present invention can be applied to any type of electrically insulating thermoplastic resin film that is longitudinally stretched.

In particular, when re-stretching a biaxially stretched film of polyester such as polyethylene dried phthalate, the diameter of the stretching roll increases, which tends to cause scratches, and the film is exposed to high temperatures (more than 110°C, most commonly is 130℃
(above), the charge is likely to disappear, so this method is particularly effective.Next, embodiments of the method of the present invention will be described.

Example A polyethylene terephthalate film (thickness 15μ, width 1.5m) biaxially stretched 4 times in the longitudinal direction and 3.4 times in the transverse direction.
) was supplied at a speed of 1.0 m/s and heated to 150°C by a low-speed roll (diameter 250 mm) and a high-speed roll (diameter 250 mm) at 40°C.
250 mm in diameter), and was further stretched 1.2 times in the longitudinal direction.

At this time, a needle electrode was placed above the film at a distance of 5 mm, and a charge was deposited on the film using a DC voltage of 5 KV. The positions of the needle electrodes are, from point A in the attached drawing, on the upstream side of the film flow: (a) a position corresponding to a circumferential angle of 100, (b) a position corresponding to a circumferential angle of 20, and a circumference of ←→30. I went to each of the three positions that hit the corner. The result is (a)
No scratches were observed in F- and Naka), but f-
), scratches occurred. What has been explained above and shown in the drawings are representative examples to help the understanding of the present invention, and the present invention is not limited to these cases, and other changes and modifications may be made within the gist of the invention. It is something that can be taken.

[Brief explanation of drawings]

The accompanying drawings are explanatory diagrams for explaining embodiments of the method of the present invention. 1...Low speed roll for stretching, 2...
High-speed roll for stretching, 3... thermoplastic resin film, 4...' charging, electrode.

Claims (1)

[Claims] 1. When stretching a thermoplastic resin film or sheet in the length direction of the film or sheet using a low-speed stretching roll and a high-speed stretching roll, the location A where the film or sheet leaves the low-speed stretching roll and this low-speed stretching On the upstream side of the moving flow of the film or sheet in the roll, the above A
A method characterized in that a charging lightning pole is provided between the location and location B forming a circumferential angle of 25° to deposit charges on the film on the low-speed stretching roll.