JPS5843254B2 - 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 two 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. A common method is to heat the tube from the outside by nearing, while preliminarily filling the inside of the tube with gas, thereby simultaneously biaxially stretching the tube in the longitudinal and lateral directions in the heating section.

As a means of sealing gas inside the tube, there is a method of introducing gas from between the upper pair of nip rolls using a ventilation needle, and in this case, the nip roll is provided with a groove in the center for passing the needle through.

Another method for enclosing gas is to widen the lower pair of nip rolls, insert a tube therethrough, blow in gas, and then quickly close the nip rolls together as soon as the tube is pulled out.

Various ideas have been proposed for heating methods in order to uniformly heat the film and prevent the film from wobbling, including a method of surrounding the outer periphery of the tube with a cover, a method of blowing a laminar flow onto the outer surface of the film by nearing, etc. An improved method has 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 be brought to the nip rolls, making the equipment extremely complicated. Because of this, uneven force is applied to the film in this area, and as a result, stretching does not proceed completely uniformly.
Unevenness in the stretching ratio in the lateral direction could not be avoided.

In addition, in the method of sealing gas from between the lower nip rolls, the stretching ratio is likely to change due to leakage of the trapped gas, and to compensate for the leaked gas, the lower nip rolls must be re-separated. This method requires time and skill, and has the disadvantage that a large amount of film is lost each time the gas is replenished.

In addition, in these gas entrapment methods, for tubular films such as polyvinyl alcohol films that naturally contain some volatile content, the proportion of volatile vapor in the enclosed gas gradually increases, causing the transparent gloss of the film to be impaired. Further, when the temperature drops after stretching, volatile vapor condenses on the surface of the film, which may cause 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 trapping gas inside the tube. The nip roll is a grooved roll, and a double tube is inserted into the groove. Gas is introduced from the inner tube of the double tube like a line gun and continuously discharged from the outer tube. Various attempts were made to use a cutter to cut the folded film after passing through the nip roll into two pieces, the front and the back, and to wind each piece onto separate take-up rolls, but the stretching points of the tube were not consistent and it was not possible to achieve the desired purpose. I couldn't reach it.

However, as a result of further studies, the inventor of the present invention discovered that in this gas introduction/exhaust method, at or near the tip of the inner tube for gas introduction, in a direction perpendicular to the inner tube, the diameter of the tube is the same as or smaller than the diameter of the tube before stretching. When a disk with a slightly smaller diameter is attached and the tip of the inner tube with this disk attached is placed in the center of the tube near the stretching point, biaxial stretching proceeds extremely smoothly, resulting in a high-quality product with even thickness. We discovered that a stretched film can be obtained and that this method can be suitably applied not only to raw material films that do not contain volatile matter, but also to raw material films that contain some volatile matter, such as polyvinyl alcohol films. The invention was completed.

The method and apparatus of the present invention will be explained with reference to the drawings.

1 is a thermoplastic film formed by an inflation bottom shape 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 a saponified ethylene-vinyl acetate copolymer film, a saponified α-olefin-vinyl acetate copolymer film having 3 to 30 carbon atoms, and the like.

This film 1 is supplied to a nip roll 2, and after passing through the nip roll 2, it is expanded into a tube shape by gas introduced through an inner tube 4, while being heated from the outside by a heater 7 provided along the outer circumference of the tube.

At this time, the film may be preheated before or after passing through the nip rolls 2.

The lower nip roll 3 is a grooved nip roll,
A double pipe for introducing and discharging gas is inserted through this groove.

The double-tube inner tube 4 is a tube for blowing gas, and is positioned so that its tip reaches the stretching point of the tubular film.

At the distal end (at or near the distal end) of the inner tube 4, a disk 6 having a diameter comparable to or slightly smaller than the diameter of the tube before stretching is installed.

The diameter of the disk 6 is 0.0, where l is the tube diameter before stretching.
It is preferable that 71≦L≦1.21.

If L is too small, stable stretching will be difficult, whereas if L is too large, the operation of positioning the disk 6 at a predetermined location within the tube at the start of stretching will be complicated.

It is convenient if the inner tube 4 and disk 6 are adjustable in position up and down.

The double tube inner tube 5 is shorter in length than the inner tube 4, and only needs to be inserted slightly into the tube by passing through the groove of the nip roll 3.

The gas sent by 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 moves downward through the space between the disk 6 and the tube. Then, it is discharged to the outside through the outer tube 5.

The stretching location is precisely defined by the disk 6, and the warp of the stretched tube is also kept exactly the same, and as a result, the unevenness in film thickness is reduced to an extent unimaginable in this type of biaxial stretching method.

After the stretching is completed, the tube 8 is placed on a guide roll or guide plate 9.
, 9', and folded flat by the nip rolls 3.

The folded tube is torn into two pieces, front and back, by a cutter 10 (not shown in the drawing), and each of these torn film pieces 11 and 11' is placed on a winding roll 1.
2, 12'.

As is clear from the above description, in this system, the gas continuously blown into the inner tube 4 is continuously discharged from the outer tube 5.

Therefore, even if the film 1 supplied from the nip roll 2 contains some moisture or other volatile matter, it will be dried from the inside, so no trouble will occur during stretching, and it will not cause any trouble during secondary processing later. is not an obstacle either.

Note that the stretching ratio can be controlled to a desired degree by 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 below the nib roll 3, and a detector 16 for detecting the width of the folded film or a detector 16/ for detecting the circumference of the tube before folding is provided below the nib roll 3, and these are controlled by a controller 17. It is practical to connect them and control the stretching ratio in a predetermined manner.

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 3QQW, a thickness of 150μ, and a moisture content of 8wtφ was rolled into a nip roll 2.
The material was fed at a speed of 10 m/m/m, and was fed out at a speed of 30 m/m by the lower grooved nip roll 3 and wound onto winding rolls 12 and 12'.

Then, below the nip roll 2, hot air at a temperature of 180°C is blown onto the outer circumference of the tube from the near ring 7 installed outside the tube, while from inside the tube, hot air at a temperature of 6°C is blown from the inner tube 4.
Heated air at 0°C was blown in at a rate of 27713/*7X.

The inner diameter of the inner tube 4 was 15.2 mm, the wall thickness was 2 m, the inner diameter of the outer tube 5 was 25.4 mm, the wall thickness was 2 m, and the diameter of the disc 6 was 18 ON.

After stretching, the tube 8 is crushed by guide rolls 9 and 91 and folded flat by the nip roll 3, and after passing through the nip roll 3, the tube 8 is crushed by a cutter 10 (not shown in the drawing).
The film was cut into two pieces each having a width of 1 gl, one on the front and the other on the back, and then wound on 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 was measured at many locations on the stretched film manufactured by shading, and the average thickness was 17μ and the deflection ratio was ±5.
He was just a staff member.

Control example 1 A polyvinyl alcohol tube was sandwiched between upper and lower nip rolls, air at a temperature of 180°C was blown from the outer periphery by nearing between both nip rolls, and ventilation was applied from between the upper nip rolls (grooved nip rolls) prior to stretching. Stretching was carried out by a factor of 3 in both length and width using a stretching device that previously introduced air with a needle to enclose air.

However, from about 30 minutes after the start of stretching, the stretching point began to fluctuate rapidly, making stable stretching impossible.

Also, the film thickness of the stretched film at the beginning of stretching has a deflection ratio of ±4.
There was also a 0-50 staff.

Example 2 A polypropylene film having a folding width of 3QQ7ta and a thickness of 200μ was stretched according to Example 1 under the following conditions.

Film supply speed: 5 m/i; winding speed: 15 m/in Tube heating: outside: 210°C; inside: 100°C; air blowing speed within the tube: 2 m8/diameter of ring disk: 180 Stretching ratio: 3 times in length and width. Stretched film thus obtained The film thickness was as follows.

Average thickness: 23μ, thickness deviation ratio: ±5 multi-pair side 2 A polypropylene film was stretched 3 times in length and width using the apparatus of Control Example 1, but the stretching point fluctuated significantly from about 30 minutes after the start of stretching. This made stable stretching impossible.

In addition, the thickness of the stretched film at the beginning of stretching has a thickness deviation ratio of ±4.
There was also a 0-50 staff.

[Brief explanation of drawings]

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

Claims (1)

[Scope of 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 winding side, which has a higher circumferential speed than the nip roll 2, and both nip rolls 2, 3 are rolled. 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 equal to or slightly smaller than the diameter of the tube before stretching is attached to the tip of the inner tube 4, and the outer surface of the square tube is aligned along the outer circumference of the tube. The tube 8, which has been biaxially stretched by this operation, is heated by a heater 7 provided in a guide roll or a guide plate 9.
9', the film is folded flat by a nip roll 3, and then cut into two pieces by a cutter 10, and then each torn film piece 11 and 11' is wound onto a winding roll 12, 12'. A method for producing biaxially stretched film. 2 A nip roll 2 on the supply side for running the flattened 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°3. A double pipe consisting of an inner pipe 4 and an outer pipe 5 shorter than this,
A heater 7 for externally heating the film that has passed through the nip roll 2; a guide roll or guide plate 9, 9' that helps fold the stretched tubular film flat again; a cutter for cutting the folded film. 10, and winding rolls 12 and 12' for winding the film, and the tip of the inner tube 4 is installed so as to be located near the tube stretching point, and the tip of the inner tube 4 is provided with a A device for producing biaxially stretched film, which is equipped with a disk 6 having a diameter similar to or slightly smaller than that of the tube.