JPS60212326A - Restretching of oriented film or sheet - Google Patents

Abstract

PURPOSE:To obtain the titled film free of a scratch, fuzzy defect and widthwise variation by restretching an oriented film of thermoplastic resin with a static electricity being applied to the contact start point between the film and a roll on the upstream of the flow thereof in a specified range viewed from the circumferential angle of the roll. CONSTITUTION:When an oriented film or sheet 1 comprising a thermoplastic resin stretched at least uniaxially is restretched depending on the difference in the circumferential velocity between rolls, the oriented film or sheet 1 is restretched by applying a static electricity from an electrode 7 to the contact start point 6 between the film or sheet 1 and the roll 3 on the upstream of the flow thereof among the rolls 2-5 in the range of 30 deg. on the upstream and 15 deg. on the downstream viewed from the circumferential angle theta of the roll 3 to obtain the desired restretched film or sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for re-stretching a stretched film or sheet of thermoplastic resin that has already been stretched in at least one direction.

BACKGROUND OF THE INVENTION It is generally well known that re-stretching a stretched film or sheet made of a thermoplastic resin can significantly improve the mechanical properties, etc. of the film or sheet. This re-stretching is normally carried out using the difference in peripheral speed between the roll groups.

In this method of re-stretching using the roll circumferential speed difference, the following problems may occur.

That is, on the upstream roll, a stretched film or stretched sheet conveyed at a constant wrapping angle may be pulled by the downstream high-speed rotation roll, slide on the roll, and be re-stretched on the roll. When the film is re-stretched on the rolls, defects such as scratches or ridges may occur on the surface of the stretched film or sheet due to the relative speed difference with the roll surface. In addition, an accompanying air current may be caught between the stretched film or sheet being conveyed and the roll surface. As the stretching position changes and the stretching position is not fixed, the film or sheet must be re-stretched. This causes a problem in that the width of the film or sheet itself fluctuates.

In order to bring the stretched film or sheet into close contact with the rolls and to fix the stretching position, a nip roll is usually used that presses the film or sheet together with the rolls. Rubber-lined rollers are usually used for nip rolls to enhance the nip effect, but uneven nips tend to occur due to nip defects due to rubber wear and roll bending due to squeezing force, and good re-stretching conditions are not always obtained. . Therefore, a non-contact method is desired as an alternative to nip rolls.

As a means of the potato contact method, a method is known in which static electricity is applied to a stretched film or sheet and the film or sheet is brought into close contact with a roll.

However, in the conventional method of applying static electricity, the main purpose was to fix the stretching position, and static electricity was applied at the position immediately before the stretched film or sheet was separated from the roll (Japanese Patent Laid-Open No. 55-27270). In the part wrapped around the roll upstream of the addition position, scratches and width fluctuations may still occur. Another method is to apply static electricity to almost the entire area of the stretched film or sheet wrapped around a roll (Japanese Patent Publication No. 50-270
According to this method, it is necessary to provide an electrode for applying static electricity at a position quite far from the roll surface, so the amount of static electricity applied is reduced, and the roll surface of the stretched film or sheet is There is a problem in that it is difficult to obtain strong adhesion to.

Therefore, there is a lack of certainty in preventing scratches and small fluctuations.

OBJECTS OF THE INVENTION The object of the present invention is to reliably prevent scratches, ridge-like defects, variations in the width direction, and variations in the width of the film or sheet itself when re-stretching a stretched film or sheet.

Structure of the Invention The method of re-stretching a stretched film or stretched sheet of the present invention in accordance with this purpose is to use a thermoplastic resin, preferably linear A stretched film or sheet made of polyester is re-stretched using a peripheral speed difference between the roll groups, preferably 1.1
In a method for re-stretching a stretched film or sheet that is stretched to ~4 times, the contact point between the roll on the upstream side in the flow direction of the stretched film or sheet and the stretched film or sheet among the roll groups is It is characterized by re-stretching while applying static electricity to the stretched film or sheet within the range of 30 degrees upstream and 15 degrees downstream, preferably 10 degrees upstream and 5 degrees downstream, in terms of the circumferential angle of the roll. Consists of methods.

If the electrode is set at a position exceeding 30' upstream and an electrostatic charge is applied from this position, sufficient charge will not be applied as the electrode moves away from the metal roll directly under the film. There is also a decay of the applied electrostatic charge,
When the film comes into contact with the roll, sufficient electrostatic charge is not obtained to make the film adhere to the roll, resulting in scratches and width fluctuations. On the other hand, if the position of the electrode exceeds 15 degrees on the downstream side, it will be difficult to cut the accompanying airflow on the roll, and the relative movement between the film and the roll will increase scratches and width fluctuations.

Effect of the Invention In such a re-stretching method, static electricity is applied near the position where the stretched film or sheet starts contacting the heating roll located upstream of the roll group for re-stretching. The sheet is conveyed on the roll while being charged with static electricity from the beginning. Therefore, the stretched film or sheet adheres well to the roll surface from the beginning, and is conveyed through a certain wrapping angle on the roll while being in close contact with the roll surface. Therefore, there is no relative velocity between the stretched film or sheet and the roll's surface on the roll;
Scratches and mold-like defects are prevented, and since the roll surface is in close contact with the roll from the contact start position, the accompanying airflow is blocked at the contact start position and there is no space between the film or sheet on the roll after that. Since there is no intervention, fluctuations in the width direction of the stretched film or sheet and small fluctuations of the stretched film or sheet itself are prevented by close contact with the rolls. Further, since the static electricity application position is limited to a limited range near the point where contact with the roll starts, the electrode can be easily brought close to the film or sheet surface, and a large amount of static electricity can be easily obtained.

Effects of the Invention Therefore, according to the present invention, the static electricity is applied at a position near the point of contact with the heating roll where no relative velocity occurs between the stretched film or sheet and the roll and where accompanying airflow can be reliably blocked. Since re-stretching is carried out within a limited range and while maintaining good adhesion with the rolls, surface defects of the film or sheet, as well as positional fluctuations and small fluctuations caused by re-stretching can be reliably prevented. This has the effect of being able to. As a result, it is possible to improve the product acceptance rate and productivity.

EXAMPLES Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an apparatus for implementing the method for re-stretching a stretched film or sheet according to the first embodiment of the present invention, and shows an apparatus applied to a polyester stretched film re-stretching apparatus.

In the figure, 1 indicates a stretched film to be re-stretched. 2 is No. 10-le, 3 is No. 20-le, 4 is No.
30 rolls, both of which are heating rolls. 5 is no
40-roll and is a cooling roll. And N010
-Role 2 and No. 40-Rule 5 are driving rolls, No. 20-Rule 3
And No. 3 day - Rule 4 Lee roll.

Stretched film 1 is inserted into No. 10-ru 2, and No.
Due to the difference in circumferential speed between the 10-rule 2 and the NO40-rule 5, the sheet is re-stretched in the advancing direction.

Above the contact start point 6 of the NO2O-ru 3 heel film 1, there is an electric current 1 that adds static electricity to the stretched film 1 being conveyed.
1x7 is provided, and the NO2O-ru 3 itself is grounded. Electrode 7 is connected to high voltage generator 8 .

The high voltage generator 8 consists of a DC high voltage power source, one of which is grounded.

The position of the electrode 7 is set within a range from 30 degrees upstream of the contact starting point 6 to 15 degrees downstream from the contact starting point 6 when viewed from the NO2O-ru3 heel angle θ. In this embodiment, it is provided at a position of 25 degrees on the upstream side.

The method for stretching a stretched film or sheet of the present invention using the apparatus configured as described above is carried out as follows.

The stretched film 1 inserted into the re-stretching roll group is heated by a heating roll N'o 10-roll 2,N.

Heated by 20-ru 3, No 30-ru 4, No.
Cooled by 40-ru 5. Then, while conveying the NO2O-Rule 3 Heel 30-Role 4, which is mainly a free roll, it is re-stretched between the rolls.

Stretched film 1 has No. 20 contact start point 6 to rule 3.
Immediately before, static electricity is applied by the high voltage generator 8 and the electrode 7, so the stretched film 1 that is heated by the NO2O-ru 3 is charged with static electricity from its initial position on the No. 20-ru 3. Due to this charged static electricity, the stretched film 1 is brought into close contact with the surface of the No. 20 roll 3. Since the stretched film 1 is closely attached by static electricity from the beginning, the NO2
The entire area of the O-ru 3 heel contact area is heeled, and slipping on the No. 20-ru 3 due to the tensile force from the No. 30-ru 4 and No. 4 roll 5 is prevented.

When slipping is prevented, stretched film 1 and No. 20-Rule 3
Since there is no relative speed between the stretched film 1 and the stretched film 1, it is possible to prevent defects such as scratches and cavities from occurring on the surface of the stretched film 1.

Further, since the contact starts from the contact starting point 6, the accompanying airflow of the stretched film 1 that tries to enter between the stretched film 1 that is heeled by the NO2O-ru 3 is blocked at the contact starting point 6. Therefore, the stretched film 1 is not supported floatingly on the No. 20-ru 3 due to the intervention of the accompanying air current, but its position is fixed on the No. Fluctuations in the stretching state between the layers 4 are prevented. As a result, positional fluctuations in the width direction of the stretched film 1 and fluctuations in the stretched film 1 itself are also prevented.

Using this first example device, a test was conducted under the conditions shown below.

Stretched film: Polyester film with a thickness of 12μ (a film that has been stretched 3.2 times in the film traveling direction and 3.2 times in the width direction) Re-stretching ratio: 1.45 times (No. 10-Rule 2 and No. 4-day)
Circumferential speed ratio of rule) Roll temperature condition 2N010-Rule 92℃No20-Rule
130℃ No. 30-ru 130℃ No. 40-ru 40℃ Film take-up speed/rate: 50.100, 150.200
．． 250 m/min As a comparative example, a test was conducted using an apparatus as shown in FIG.

Namely, as in the first embodiment, 9, drive roll and heating roll No. 20-Role 2, free roll and heating roll No. 20-Role 3, N030-Role 4, drive roll and cooling roll No. 040-Role. 5, and the position of the electrode 10 connected to the high voltage generator 9 is set at a point 11 that is 80 degrees away from the point 6 where the stretched film 1 contacts No. 2 Day-Rule 3.
The position is 20 degrees upstream of the

The thickness of the stretched film, re-stretching ratio, roll heating conditions, etc. were tested under the same conditions as in the first example.

The results are shown in the table below.

A: Within 2 pieces B: 3 to 10 pieces C: 11-30 pieces D: 31 or more It is.

As is clear from the table, according to this example, the width variation of the stretched film 1 during film formation is small, and the occurrence of scratches is also small, and this effect is particularly noticeable as the speed increases.

Next, FIG. 3 shows an apparatus for carrying out a method according to a second embodiment of the present invention. In this example, No. 10-
No. 12 and No. 50-No. 16 are drive rolls, and No. 2
Day-Rule, N.

3 roll 14 and NO40 roll 15 are free rolls. The stretched film 1 is No. 30-14, N.
Radiation heater 1 installed between O40 and 15
7, and re-stretching occurs mainly in this area. The electrodes 18, 19, and 20 are placed near the contact starting points 21, 22, and 23 of NO1 day rule, No. 20 rule 13, and NO 30 rule 14, respectively, and are 30 degrees upstream of the contact starting point of each of them. It is installed within a range of 15 degrees downstream. The electrodes 18.19.20 are connected to a high voltage generator 24.25.

Using this device, tests were conducted under the following conditions.

Stretched film: Biaxially stretched polyester film with a thickness of 20 μm Electrode 18.19: Electrode made of wire (applied with positive charge) Electrode 20: Electrode made of wire (applied with negative charge) Roll temperature conditions 2 No. 2010-R 90°C No.20- Le, NO3
0-Rule 125°C No. 40-Rule 43°C No. 50-Rule 43°C Re-stretching ratio: 1.35 times Take-up speed: 200 m/min As a result, the obtained re-stretched film has almost no fluctuation in the medium and has no scratches. and good results were obtained.

[Brief explanation of the drawing]

FIG. 1 shows re-stretching for carrying out the method according to the first embodiment of the present invention! ! FIG. 2 is a side view of a conventional re-stretching device as a comparative example; FIG. 3 is a side view of a re-stretching device for carrying out the method according to the second embodiment of the present invention. , is. 1...Stretched film 2.3.4.5. 12.13.14. 15.16... Roll for re-stretching 6.21.2
2.23... Contact start point 7.18.19.20
・・・・・・Electrode θ・・・・・・Roll circumference angle

Claims (1)

[Claims] (1) In a method for re-stretching a stretched film or stretched sheet, in which a stretched film or stretched sheet made of a thermoplastic resin stretched in the axial direction is re-stretched by a peripheral speed difference between roll groups, Stretched film in a range of 30 degrees on the upstream side and 15 degrees on the downstream side when viewed from the circumferential angle of the roll with respect to the contact start point between the roll and the stretched film or sheet on the upstream side in the flow direction of the stretched film or sheet. Or a method for re-stretching a stretched film or sheet, which comprises re-stretching the stretched sheet while applying static electricity.