JPS62199427A - Method for stretching polymer film - Google Patents

Abstract

PURPOSE:To certainly prevent the generation of folded wrinkles on a film caused by the air bank generated on a roll, in stretching the film between rolls different in a peripheral speed, by applying an electrostatic field to the side of the low speed roll. CONSTITUTION:A polyethylene terephthalate film 1 with a thickness of 20mum biaxially oriented under a stretching condition of 3.5 times in both longitudinal and lateral directions is sent between a low speed roll 2 having a hard chromium plating surface and an electrode 6. The electrode 6 to be used comprises an elastomer roll with hardness of 70 deg. and volume inherent resistivity of 10<5>OMEGA.cm and the contact pressure with the low speed roll is set to 0.5kg/cm<2> and voltage to be applied is set to 1.0kV. An opposed roll comprises an elastomer roll with hardness of 80 deg.. Subsequently, the film 1 is stretched while closely contacted with a high speed roll 3. Even if a stretching magnification reaches 1.4-1.8, folded wrinkles and scratch are not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for stretching a polymer film.

(Prior Art) A method of stretching a polymer film between rolls having different circumferential speeds is generally well known.

For example, as shown in FIG. 3, there is a method in which the conveying film is stretched between a low speed roll 2 and a high speed roll 3 at a stretching ratio determined by a circumferential speed ratio. At this time, when the film is stretched on the roll, there is a difference between the peripheral speed of the roll surface and the speed of the film surface in contact with the roll, that is, the film slips on the roll surface, resulting in the problem of scratches on the film surface. Generally, in order to avoid the above-mentioned problem, in order to prevent the stretching tension from propagating to the film on the roll, as shown in Fig. Opposing rolls 4 and 5 are provided so as to be in contact with each other as close as possible to each contact line, and pressure is applied between the rolls 2 and 4 and 3.5 to cut the propagation of tension to the film on the rolls.

[Problem that the invention seeks to solve]

However, in the above method, as shown in FIG. 4, the air flow accompanying the film tends to accumulate between the film and the roll, resulting in a so-called "air bank". This air bank causes wrinkles in the film, and when the wrinkles are compressed, they are fixed as creases, which is a drawback. Furthermore, the air bank rubs between the rolls, making the desired tension cut insufficient and causing defects such as scratches on the film surface.

In many cases, the low-speed roll is a heated roll, and there are problems such as uneven heat transfer due to air banks between the film and the roll, resulting in uneven physical properties of the film.

As shown in Figure 5, one possible way to eliminate the air bank is to provide opposing rolls on both the contact and separation lines of the film, but the problem of wrinkles and folds due to fixation still remains. , the equipment becomes complicated, which is disadvantageous when there are space constraints. Generally speaking, this method of contacting the rolls is
Problems such as contamination of the film from the contacting rolls occurred, which is not desirable in the film manufacturing process where contamination due to deposits is disliked.

It is an object of the present invention to provide a method for preventing the formation of air banks when stretching polymer films.

Yet another object of the present invention is to provide a method for preventing creases from forming during stretching of a polymer film.

Still another object of the present invention is to provide a method for preventing the occurrence of air banks without contaminating the film mentioned above.

[Means for Solving the Problems] The present invention provides a method for stretching a polymer film between rolls having different peripheral speeds, in which a voltage is applied between an electrode provided on the low-speed roll side and the low-speed roll. , characterized in that the film is electrostatically brought into close contact with the low speed roll, and the film is stretched while being brought into close contact with the low circumferential speed roll by means of an opposing roll provided on the downstream side of the electrode with respect to the transport direction of the film. The present invention relates to a method for stretching a polymer film.

The polymer film used in the present invention means that the volume resistivity of the transport film is 109Ω・in order to obtain an electrostatic adhesion effect.
It is particularly preferable to use one with a diameter of cm or more. Therefore, the method of the present invention is applicable to many types of electrically insulating thermoplastic polymer films, including polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyamides such as nylon, polyimides, Includes many polymeric materials that are formed into films.

In the present invention, stretching between rolls having different circumferential speeds means stretching between at least a pair of rolls consisting of a low circumferential speed roll (low speed roll) and a high circumferential speed roll (high speed roll) according to the circumferential speed ratio. Refers to a known method of stretching a film at a magnification. The peripheral speed ratio, that is, the magnification can be set to any target value, and varies depending on the film, but is from 1.0 times to 10.
It takes a value of about 0 times.

The low-speed rolls are heated as necessary by passing a heat medium through them or electrically, and the high-speed rolls after the end of stretching are cooled as necessary. That is, when the film is stretched between two rolls, it is heated on the first day and cooled on the second day. When stretched with 0 rolls, 1
~n-1 Until today, the n-th grain is heated, the n-th grain is cooled, and the circumferential speed increases sequentially from the 1st to the n-th grain.

In the present invention, the electrodes are: (1) ionizes the atmosphere near the electrode without contacting the film, and applies the ions to the film to electrostatically bring the film into close contact with the roll and entrain it; These include: (1) those that cut airflow, and (2) those that contact the film and maintain a high potential difference between them and the rolls with the film sandwiched between them to electrostatically adhere the film to the rolls.

The former non-contact electrode shape includes known wires, knives, bands, etc., and the latter contact electrode shape is preferably roll-shaped. FIG. 1 shows an example using roll-shaped electrodes, and FIG. 2 shows an example using wire-shaped electrodes.

The material of the electrode needs to be conductive.

Here, conductivity refers to a volume resistivity of 10 8 Ω·cm or less.

Therefore, the non-contact electrode is preferably made of metal, carbon, etc., and the contact roll-shaped electrode is preferably made of an elastic material with excellent abrasion resistance from the viewpoint of damage and contamination to the film surface. Hardness of 90 degrees or less is good. In addition, non-contact electrodes are preferable due to the problem of film contamination mentioned above, but in the case of non-contact electrodes, there are problems such as difficulty in adjusting the gap between the electrode and the roll due to the widening of the width. Since a roll-shaped electrode has a better ability to impart electrostatic adhesion, it is better to select the electrode depending on the situation.

In this case, even when the rolled electrodes are in contact with each other, it is the electrostatic adhesion between the film and the roll that cuts the accompanying airflow, and problems such as contamination are significantly reduced. When using a roll-shaped electrode, the contact pressure between the electrode and the low circumferential speed roll is preferably 11 i/cm or less per width.

The electrode position in the present invention ranges from a position 30° further upstream from the tangent line (tangent line ■) where the film starts contacting the low-speed roll to the line where the opposing roll contacts the film (tangent line ■) (Fig. 6A ) is preferred.

More preferably, 30' upstream and downstream from the tangent I.
(FIG. 6B), more preferably a range of 15° upstream and downstream from the tangent I (FIG. 6C).

In the case of non-contact electrodes such as wires, bands, knives, etc., the distance between the electrode and the roll surface is preferably 5 to 20 mm, and the applied voltage is preferably 3 to 20 KV. In any case, it is preferable to appropriately adjust the speed, stretching ratio, film thickness, etc. under conditions that do not cause spark discharge.

In the case of contact electrodes such as rolls, the applied voltage is preferably 0
．． 1KV or more, 10KV or less, more preferably 0.3
KV or more and 3KV or less. However, as mentioned above, it is better to appropriately adjust this according to various conditions.

Generally known rolls can be used without regard to the material of the low speed roll and the counter roll in the present invention, but it is preferable that the surface of the low speed roll is a rigid body and the surface of the counter roll is an elastic body. Here, the rigid body refers to one with a Vickers hardness of 500 or more, and the elastic body refers to one with a hardness of 90 degrees or less according to JIS K6301-1975.

In general, the surface of the slow roll needs to be conductive in order for the film to adhere electrostatically.

The above-mentioned applied voltage refers to the potential difference between the electrode and the surface of the stretching roll.

〔Example〕

EXAMPLES Hereinafter, the effects of the present invention will be specifically explained with reference to Examples.

Example 1 A polyethylene terephthalate film with a thickness of 20 μm, which had been biaxially stretched under the conditions of 3.5 times in the machine direction and 3.5 times in the transverse direction, was fed into the apparatus shown in FIG.

The low speed roll 2 has a hard chrome plated surface, and the electrode 6 has a hardness of 70° and a volume resistivity of 105Ω・C.
Using an Ex 1 to Mar roll of 1.0 m, the contact pressure with the low speed roll was 0.5 ki/cm, and the applied voltage was 1.5 ki/cm. OK, set it to V.

As the opposing roll, an elastomer roll having a hardness of 80' was used.

At this time, the stretching ratio, the occurrence of folding wrinkles, and the occurrence of scratches on the film surface were as shown in the table.

Comparative Example When the same stretching was carried out using the same equipment and conditions as in the Example except that the electrode was removed, the occurrence of scratches was as shown in the table.

As is clear from these results, it can be seen that the method of the present invention is an excellent stretching method that does not cause scratches or creases compared to conventional methods.

Front surface folding wrinkles present: × 〃 Front 20** scratches (more than 500 μ) O pieces / 100ri 201 to 20 pieces / 100 I: △ More than 20 lines / 100 (d: x (effect of the invention) of the present invention By using this method, the occurrence of air banks on the roll is prevented, and the polymer film can be stretched without folding wrinkles, scratches on the film surface, or uneven physical properties.

In particular, the method of the present invention is effective when troubles due to air banks are likely to occur, that is, when re-stretching a wide thin film that has already been stretched in the width direction.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing another practical embodiment of the present invention, FIG. 3 is a diagram showing a conventional stretching method, and FIG. 4 is a diagram showing a conventional stretching method. FIG. 5 is a diagram showing another conventional stretching method, and FIG. 6 is an explanatory diagram of electrode positions provided in the present invention. 1: Film 2: Stretching roller 3: Cooling roll 4, 5: Opposing roller 6: Electrode

Claims (1)

[Claims] In a method of stretching a polymer film between rolls having different circumferential speeds, a voltage is applied between an electrode provided on the low-speed roll side and the low-speed roll to electrostatically adhere the film to the low-speed roll. A method for stretching a polymer film, which comprises stretching the film while bringing the film into close contact with the low-speed rolls using opposing rolls provided downstream from the electrodes in the film transport direction.