JPS5913329B2 - Biaxially stretched film manufacturing method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for producing a homogeneous biaxially stretched film with uniform thickness from a tubular thermoplastic film.

The conventional method for biaxially stretching a tubular thermoplastic film is to sandwich the tube between 2 pairs of nip rolls located above and below, increase the circumferential speed of the lower nip roll than the upper nip roll, and stretch the tube between the two nip rolls. In general, the tube is heated from the outside with an air sinter, while gas is previously sealed inside the tube, so that the tube is stretched simultaneously in the longitudinal and lateral directions in the heating section.

One way to seal gas inside the tube is to use a ventilation needle to pump the gas between the upper pair of nip rolls. In this case, the nip roll has a groove in the center for the needle to pass through. . 5. Another method of gas entrapment is to spread out the lower pair of nip rolls, insert a tube therein, blow in gas, and then quickly close the nip rolls together as soon as the tube is pulled out.

In order to uniformly heat the film and prevent the film from wobbling, various ideas have been proposed for heating methods, including a method of surrounding the outer periphery of the melon tube with a cover, and a method of blowing a laminar flow onto the outer surface of the film using an air ring. Several improved methods have also been proposed.

However, in the method of venting from between the upper nip rolls, the ventilation needle must pass through the annular die during inflation molding and reach the nip rolls, which makes the equipment extremely complicated. Because of the cut, uneven force is applied to the film at this partb1.As a result, the stretching does not proceed completely uniformly,
Unevenness in the stretching ratio in the lateral direction could not be avoided. In addition, if the method of sealing gas between the lower Nippuro rolls is unsuccessful, the drawing ratio is likely to change due to leakage of the sealed gas, and the lower Nitsuzu rolls must be opened again to compensate for the leaked gas. In addition to requiring time and skill, there was a problem in that a large amount of film was lost each time the gas was replenished. In addition, in these gas containment methods, when tube-shaped films such as polyvinyl alcohol films contain a certain amount of volatile matter due to their nature, the proportion of volatile vapor in the trapped gas gradually increases and the transparent luster of the film is impaired. Furthermore, when the temperature drops after the stretching is completed, condensation of volatile vapor occurs on the film surface, which sometimes causes trouble when secondary processing such as coating or lamination is performed later.

However, the present inventors thought that they could obtain a good stretched film by heating the tube from the inside and outside and displacing the gas inside the tube, instead of adopting the conventional method of confining gas inside the tube. The nip roll is a grooved roll, a double pipe is inserted into the groove, and gas is continuously introduced from the inner pipe of the double pipe and continuously discharged from the outer pipe. Various attempts were made to tear the folded film into two pieces with a cutter and wind each piece onto separate winding rolls, but the stretching point of the tube was not consistent and it was not possible to achieve the desired result. I couldn't reach my goal.

However, as a result of further studies, the present invention found that in this gas introduction/exhaust method, the inner tube for gas introduction has a diameter slightly smaller than the diameter of the tube after stretching, at or near the tip thereof, in a direction perpendicular to the inner tube. Attach the disk and press this disk to D
When the tip of the inner tube is placed in the center of the tube near the stretching point, biaxial stretching proceeds extremely smoothly and a high-quality stretched film with uniform thickness can be obtained. The present invention has been completed based on the discovery that the present invention can be suitably used not only for raw material films that do not contain chlorine, but also for raw material films that contain some volatile matter, such as polyvinyl alcohol films. The method and apparatus of the present invention will be explained with reference to the drawings.

1 is a thermoplastic film formed by inflation molding and folded flat.

Types of thermoplastic films include polyethylene film, polypropylene film, polyester film, polyamide film, polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film,
Various types of films can be used, including saponified ethylene monovinyl acetate copolymer films. This film 1 is supplied to a nip roll 2, and the nip roll 2
After passing through, the tube is expanded into a tube shape by the gas introduced through the inner tube 4, while being heated from the outside by a heater 7 provided along the outer periphery of the tube. At this time, the film may be preheated before or after passing through the nip roll 2. The lower nip roll 3 is a grooved nip roll, into which a double pipe for introducing and discharging gas is inserted. The double-pipe inner tube 4 is a tube for blowing gas, and is positioned so that its tip reaches the stretching point of the tubular film. A disk 6 having a diameter slightly smaller than the diameter of the tube after stretching is installed at the tip (at or near the tip) of the inner tube 4. It is convenient to be able to adjust the positions of the inner tube 4 and disk 6 up and down. The double tube inner tube 5 is shorter in length than the inner tube 4, and it is only necessary to penetrate the groove of the nip roll 3 and insert it slightly into the tube. The gas sent from the blower 13 is blown into the tube from the tip of the inner tube 4 through the heater 14, which can be adjusted to any temperature as needed, and then passed through the narrow gap between the disk 6 and the tube. The liquid then moves downward and is discharged to the outside through the outer tube 5. The stretching location is precisely defined by the disk 6, and the diameter of the stretched tube is also kept exactly the same, and as a result, the thickness unevenness of the film becomes unimaginably small in this type of biaxial stretching method. After the stretching is completed, the cheese 8 is placed on the guide roll 9
, 9', and folded flat by the nip roll 3. The folded tube is torn into two pieces, the front and the back, by a cutter 10 (not shown in the drawing), and the torn film pieces 11 and 11' are wound up on take-up rolls 12 and 12', respectively. It will be done. As is clear from the above description, in this system, the gas continuously blown into the inner tube 4 is continuously discharged through the outer tube 5.

Therefore, even if the film 1 supplied from the Nipprol 2 contains some moisture or other volatile matter, it will be dried from the inside, so there will be no trouble during stretching, and there will be no problems during secondary processing later. There is no obstacle to this. The stretching ratio can be controlled to a desired degree by changing the gas introduction and discharge speeds and the difference in peripheral speed between the nip rolls 2 and 3.

In actual stretching, as shown in the drawing, the inner tube 4
A diaphragm valve 15 is provided at the tube, and a detector 16 is provided below the nip roll 3 in a folded film, or a detector 16' is provided to detect the circumference of the tube before folding, and these are controlled by a controller 17. It is practical to connect them and control the stretching ratio to a predetermined level.

Although the above description has been made regarding the case where the film is run downward, it is also possible to run the film upward. Next, the present invention will be further explained with reference to Examples.

Example 1 A polyvinyl alcohol tubular film with a folding width of 300 mm, a thickness of 150 μm, and a water content of 8% by weight was fed to the Nippro roll 2 at a rate of 10rn/MiO, and the lower grooved Nipprol 3 was fed at a rate of 30m/MllO. The film was sent out and wound onto winding rolls 12, 12'.

Then, hot air at a temperature of 180°C is blown onto the outer circumference of the tube from the air ring 7 installed on the outside of the tube below the Nipprol 2, while air at a temperature of 6°C is blown from inside the tube towards the inner tube 4.
Heated air at 0°C was blown in at a ratio of 2I/MIO. The inner diameter of the inner tube 4 is 1.5.21! $j wall thickness is 2m1! ,
The inner diameter of the outer tube 5 is 25.4 m, L1, and wall thickness 2! ! W! The diameter of the disk 6 was 550 mm. After the stretching, the tube 8 is crushed by guide rolls 9, 9' and folded flat by the nip roll 3, and after passing through the nip roll 3, it is cut into a cutter 10.
(not shown in the drawings), the sheet was torn into two sheets each having a width of 900 m and 1 L, and then wound onto winding rolls 12 and 12' as described above. The stretching ratio was set to 3 times in both length and width, that is, 9 times in terms of area magnification. The film thickness of the thus produced stretched film was measured at a number of locations, and the average thickness was 17 μm, and the thickness deviation was only ±5%.

Control example 1 A polyvinyl alcohol tube was sandwiched between upper and lower nip rolls, and air at a temperature of 180°C was blown from the outer periphery of the nip rolls between the two nip rolls using an air ring. ) The film was stretched 3 times in length and width using a stretching device that previously blows air through the gap with a ventilation needle to seal in the air.

However, from about 30 minutes after the start of stretching, stable D stretching became impossible due to the drastic fluctuations in the stretching point. Furthermore, the thickness of the stretched film at the beginning of stretching was as high as 40 to 50%. Example 2 A polypropylene film having a folding width of 300 m, 1 L, and a thickness of 200 μm was stretched according to Example 1 under the following conditions.

The thickness of the stretched film thus obtained was as follows.

Comparative Example 2 A polypropylene film was stretched 3 times in length and width using the apparatus of Comparative Example 1, but from about 30 minutes after the start of stretching, the stretching point began to fluctuate so much that stable stretching became impossible.

Also, the thickness of the stretched film at the beginning of stretching has a thickness deviation ratio of ±4.
It was also 0-50 (f).

[Brief explanation of drawings]

The drawings are explanatory diagrams showing one example of the apparatus used in the present invention and for explaining the method of the present invention.

Claims (1)

[Claims] 1. A thermoplastic film 1 in the form of a tube folded flat is run between a nip roll 2 on the supply side and a nip roll 3 on the take-up side, which has a higher circumferential speed than the nip roll 2, and the two nip rolls 2, 3 When simultaneously biaxially stretching the film by expanding it in between, the nip roll 3 on the winding side is used as a nip roll with a groove, and the inner tube 4 and the length from this are passed through the groove from the direction opposite to the tube traveling direction. Insert a double tube consisting of a short outer tube 5 and position it so that the tip of the inner tube 4 reaches the stretching point of the tubular film. A disk 6 having a diameter slightly smaller than the diameter of the stretched tube is attached to the distal end of the inner tube 4, and a heater provided along the outer circumference of the tube is attached to the outer surface of the tube. 7
The tube 8 biaxially stretched by this operation is folded flat by the nip roll 3 with the help of the guide rolls 9 and 9', and then folded into a flat shape by the cutter 10.
A method for producing a biaxially stretched film, which comprises cutting the film into pieces, and then winding the cut film pieces 11 and 11' onto take-up rolls 12 and 12'. 2 A nip roll 2 on the supply side for running the flat folded tubular film and a grooved nip roll 3 on the take-up side, inserted from the groove of the nip roll 3 to expand the film between both nip rolls 2 and 3. A double pipe consisting of an inner pipe 4 and an outer pipe 5 shorter in length,
A heater 7 for externally heating the film that has passed through the nip roll 2, and guide rolls 9 and 9' that help fold the stretched tubular film flat again.
, cutter 10 for cutting the folded film
, and winding rolls 12, 12' for winding the film.
The inner tube 4 is installed so that its tip is located near the tube stretching point, and a disk 6 having a diameter slightly smaller than the tube diameter after stretching is attached to the tip of the inner tube 4. Axial stretched film manufacturing equipment.