JPH0510214B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL FIELD OF APPLICATION The present invention relates to a method for re-stretching a stretched film or sheet made of a thermoplastic resin that has already been stretched in at least one direction. PRIOR ART It is generally well known that re-stretching a stretched film or sheet made of a thermoplastic resin can further improve the mechanical properties 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, the stretched film or stretched sheet conveyed at a constant wrapping angle is pulled by the downstream high-speed rotating roll, slides on the roll, and is re-stretched on the roll. be. When re-stretched on the rolls, scratches or ridge-like defects 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, and if the accompanying air current intervenes during this time, the stretched film or sheet will be supported floating on the roll, so that the stretched film or sheet will not move in the width direction. As the position changes and the stretching position is not fixed, a problem arises in that the width of the re-stretched film or sheet itself varies. 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 which presses the film or sheet together with the rolls. Rubber-lined rollers are usually used for nip rolls to enhance the nipping effect, but uneven nips are likely to occur due to nip defects due to rubber friction and roll bending due to the clamping force, and it is not always possible to obtain a good re-stretching condition. I can't get it. Therefore, a non-contact method is desired as an alternative to Nipprol. As a non-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 just before the stretched film or sheet leaves the roll (Japanese Patent Laid-Open No. 55-27270
(No. 3, No. 3, No. 1, No. 2003-11-11), scratches and width fluctuations sometimes occurred in the portion wrapped around the roll on the upstream side of the addition position. There is also a method of applying static electricity to almost the entire area of the stretched film or sheet wrapped around a roll (Japanese Patent Publication No. 50-27073), but according to this method, the electrode for applying static electricity is attached to the roll. Since it is necessary to provide it at a position quite far from the surface, the amount of applied static electricity is reduced, and there is a problem that it is difficult to obtain strong adhesion to the roll surface of the stretched film or stretched sheet. Therefore, there is a lack of certainty in preventing scratches and width fluctuations. Purpose of the Invention The purpose of the present invention is to reliably prevent scratches, ridge-like defects, fluctuations in the width direction, and fluctuations in the width of the film or sheet itself when re-stretching a stretched film or sheet. . Composition of the Invention The method of re-stretching a stretched film or stretched sheet of the present invention in accordance with this purpose comprises a thermoplastic resin, preferably a linear polyester, stretched in at least one direction, preferably 2 to 4 or 5 times. In a method for re-stretching a stretched film or sheet, the stretched film or sheet is re-stretched, preferably by 1.1 to 4 times, by a difference in the circumferential speed of a group of rolls, in the flow direction of the stretched film or sheet of the roll group. With respect to the starting point of contact between the roll on the upstream side and the stretched film or sheet, in the range of 30 degrees on the upstream side and 15 degrees on the downstream side, preferably 10 degrees on the upstream side and 5 degrees on the downstream side, in terms of the circumferential angle of the roll. This method is characterized in that the stretched film or sheet is re-stretched while applying static electricity. If the electrode is set at a position more than 30 degrees 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. Further, the applied static electricity is attenuated, and when the film comes into contact with the roll, sufficient static electricity is not obtained to make the film adhere to the roll, resulting in scratches and width fluctuations. On the other hand, if the electrode position is more than 15 degrees downstream, it will be difficult to cut off 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,
They are conveyed in close contact with each other at a fixed wrapping angle on rolls. Therefore, no relative speed is generated between the stretched film or sheet and the roll surface on the roll, preventing scratches and ridge-like defects, and the film or sheet is tightly attached to the roll surface from the point where it starts contacting with the roll. Therefore, the accompanying airflow is blocked at the contact start position and does not come between the film or sheet on the subsequent rolls, so that fluctuations in the width direction of the stretched film or sheet and fluctuations in the width of the stretched film or sheet itself are caused by the roll. This is prevented by close contact with the 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 placed 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 application position is set at the contact start point to the heating roll where no relative velocity occurs between the stretched film or sheet and the roll and where the accompanying airflow can be reliably blocked. Since re-stretching is carried out in a limited area in the vicinity and maintaining good contact with the rolls, it is possible to reliably prevent surface defects of the film or sheet, as well as positional and width fluctuations caused by re-stretching. The effect of being able to do this is obtained. As a result, it is possible to improve the product acceptance rate and productivity. Embodiments Below, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an apparatus for carrying out a method for re-stretching a stretched film or sheet according to a 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. 1 roll, 3 is No. 2 roll, 4 is No.
Three rolls are shown, all of which are heating rolls. 5
is the No. 4 roll, which is a cooling roll. And No. 1 roll 2 and No. 4 roll 5 are drive rolls,
No. 2 roll 3 and No. 3 roll 4 are free rolls. The stretched film 1 is inserted from the No. 1 roll 2 and is re-stretched in the traveling direction due to the difference in circumferential speed between the No. 1 roll 2 and the No. 4 roll 5. Contact start point 6 of stretched film 1 of No. 2 roll 3
An electrode 7 for applying static electricity to the stretched film 1 being conveyed is provided above, and the No. 2 roll 3 itself is grounded. The electrode 7 is a high voltage generator 8
It is connected to the. 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 of the contact starting point 6 when viewed from the circumferential angle θ of the No. 2 roll 3. In this embodiment, it is provided at a position of 25 degrees on the upstream side. Using the apparatus configured as described above, the method for stretching a stretched film or sheet of the present invention is carried out as follows. Stretched film 1 inserted into the re-stretching roll group
is heated by No. 1 roll 2, No. 2 roll 3, and No. 3 roll 4, which are heating rolls, and cooled by No. 4 roll 5. Then, while conveying the No. 2 roll 3 and No. 3 roll 4, which are mainly free rolls, the film is re-stretched between the rolls. Static electricity is applied to the stretched film 1 by the high voltage generator 8 and the electrode 7 just before the contact start point 6 to the No. 2 roll 3, so the stretched film 1 wound around the No. 2 roll 3 is No. 2 is charged with static electricity from its initial position on roll 3. Due to this electrostatic charge, the stretched film 1 is brought into close contact with the surface of the No. 2 roll 3. Since the stretched film 1 is in close contact with the No. 2 roll 3 from the beginning due to static electricity, the stretched film 1 is in close contact with the No. 2 roll 3 over the entire contact area with the No. 2 roll 3. This prevents slipping on the No. 2 roll 3 due to the tensile force. When slipping is prevented, stretched films 1 and No. 2
Since there is no relative speed between the stretched film 1 and the roll 3, scratches and scaly defects on the surface of the stretched film 1 are prevented from occurring. Also, since it is in close contact from the contact starting point 6, No. 2
Airflow accompanying the stretched film 1 that attempts to enter between the roll 3 and the stretched film 1 being conveyed is blocked at the contact starting point 6. Therefore, the stretched film 1 is not supported floatingly on the No. 2 roll 3 due to the intervention of the accompanying air current, and the stretched film 1 is not supported floatingly on the No. 2 roll 3.
The position is fixed at the top, and positional fluctuations and fluctuations in the stretching state between No. 2 roll 3 and No. 3 roll 4 are prevented. As a result, the positional variation in the width direction of the stretched film 1 and the width variation of 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 and 2 times in the direction of film advance and 3 and 2 times in the width direction) Re-stretching ratio: 1.45 times (No. 1 roll 2 and No. 4 roll 5) Roll temperature conditions: No. 1 roll 92℃ No. 2 roll 130℃, No. 3 roll 130℃ No. 4 roll 40℃ Film take-up speed: 50, 100, 150, 200, 250
m/min As a comparative example, a test was conducted using an apparatus as shown in FIG. That is, as in the first embodiment, No. 1 roll 2 is a drive roll and a heating roll, No. 2 roll 3 is a free roll and a heating roll, No. 3 roll 4,
A No. 4 roll 5, which is a driving roll and a cooling roll, is provided, and the electrode 10 connected to the high voltage generator 9 is positioned at a point 11 that is 80 degrees away from the point 6 where the stretched film 1 contacts the No. 2 roll 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.

[Table] However, the scratch grades are A: 2 or less, B: 3 to 10, C: 11 to 30, and D: 31 or more per cm of film length. 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 embodiment, No. 1 roll 12 and No. 5 roll 16 are drive rolls, No. 2 roll 13, No. 3 roll 14, and No. 5 roll are drive rolls.
4 rolls 15 are free rolls. And the stretched film 1 is No. 3 roll 14, No. 4 roll 1
The film is strongly heated by a radiation heater 17 provided between the film 5 and re-stretched mainly in this region. The electrodes 18, 19, and 20 are each No.
1 roll 12, No. 2 roll 13, No. 3 roll 14
are arranged near the contact start points 21, 22, 23,
30 degrees upstream to 15 degrees downstream of each contact start point
installed within the range of Electrodes 18, 19, 20
are connected to high voltage generators 24 and 25. Using this device, a test was conducted under the following conditions. Stretched film: 20μ thick polyester biaxially stretched film Electrodes 18, 19: Electrode made of wire (applies positive charge) Electrode 20: Electrode made of wire (applies negative charge) Roll temperature conditions: No. 1 roll 90°C No. .2 roll, No. 3 roll 125℃ No. 4 roll 43℃, No. 5 roll 43℃ Re-stretch ratio: 1.35 times Take-up speed: 200 m/min As a result, the obtained re-stretched film has no width fluctuation. There were almost no scratches, and good results were obtained.

[Brief explanation of drawings]

FIG. 1 is a side view of a re-stretching device for implementing 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, and FIG. 3 is a side view of a re-stretching device of the present invention. FIG. 7 is a side view of a re-stretching device for carrying out the method according to the second embodiment. 1...Stretched film, 2, 3, 4, 5, 12,
13, 14, 15, 16...rolls for re-stretching,
6, 21, 22, 24... connection starting point, 7, 1
8, 19, 20...electrode, θ...circumference angle of roll.

Claims (1)

[Claims] 1. In a method for re-stretching a stretched film or sheet made of a thermoplastic resin stretched in at least one axial direction, the stretched film or sheet is re-stretched by a difference in circumferential speed between roll groups. Static electricity is applied to the stretched film or stretched sheet within a range of 30 degrees upstream and 15 degrees downstream, as viewed from the circumferential angle of the roll, relative to the contact start point between the roll and the stretched film or sheet located upstream in the flow direction. 1. A method for re-stretching a stretched film or sheet, the method comprising re-stretching a stretched film or sheet.