JPS60253526A - Manufacture of polyester film - Google Patents

Abstract

PURPOSE:To enable to prevent initial break at the time of orientation of a stretched film in a lateral direction which has been stretched in a longitudinal direction already, by making a draw ratio into a regular longitudinal one after the film has been stretched laterally and joined up to a stretching zone and a heat-treating zone which is a downstream side of the stretching zone. CONSTITUTION:In case of manufacture of a polyester biaxially oriented film by performing successively lateral stretching next to longitudinal stretching in relation to a biaxial stretching method, a longitudinally stretched film, whose longitudinal drawn ratio is made more than three times and a longitudinal stretching time (t) is made shorter than a longitudinal-stretching critical time tc as shown by an expression, is fed to a lateral stretching machine wherein T is a longitudinal stretching temperature, and after the film has been stretched laterally and joined up to a stretching zone and a heat-treating zone which is in a downstream side of the stretching zone, stretching terms are restored to regular longitudinal ones and a speed is increased up to a predetermined stretching one. It is capable of eliminating initial break, consequently, by reducing a variation of a birefractive index at the edge of the longitudinally stretched film by shortening the longitudinal stretching time t than the time tc.

Description

[Detailed description of the invention] (Industrial application field) A polyester film produced by biaxially stretching a polyester film formed by the T-die method using a sequential biaxial stretching method or a simultaneous biaxial stretching method has 1 mechanical properties and thermal properties. It has excellent chemical stability, appearance, etc., and is used in a wide range of fields such as industrial and packaging applications, and its market is on the rise. On the other hand, in order to increase the economic efficiency of films, the production speed was increased and the film width was made wider, and in order to achieve this, various improvements were made in machine design and manufacturing, and strict examination of manufacturing conditions was carried out. and is managed.

(Prior Art) When producing a polyester film by the sequential biaxial stretching method, so-called initial cutting poses a serious problem. In other words, when a uniaxially stretched film that has already been stretched in the longitudinal direction is laterally stretched in a tenter-set transverse stretching machine, the longitudinally-axially stretched film is fed into the empty tenter-set transverse stretching machine at a relatively low speed to perform the transverse stretching. After confirming that the film is being stretched continuously, the line speed is increased to a predetermined level. However, after feeding the longitudinally-axially stretched film to the horizontal stretching machine, the film is still stretched in the tenter stretching zone before increasing the speed. is cut without waiting for the end of stretching. A so-called initial cutting phenomenon may occur, and if the initial cutting continues for a long time, yield operability becomes a problem.

(Problems to be Solved by the Invention) The present invention relates to a method for stretching a polyester film using a tenter-set stretching device. Specifically, in a sequential biaxial stretching method, a tenter-set stretching device has already been used in the longitudinal direction (mechanical direction). The present invention relates to a method for preventing initial breakage when stretching a -/axially stretched film in the transverse direction.

(Means for Solving the Problems) We have arrived at the present invention as a result of intensive studies on a method for preventing initial cutting during the production of polyester films by sequential biaxial stretching.

That is, when stretching a longitudinally-axially stretched film in the transverse direction by the sequential biaxial stretching method, the m-axially stretched film is transversely stretched with a longitudinal-axial stretching ratio of 3 times or more and a longitudinal-axial stretching time t of tc seconds or less. Put it into the machine.

where T is the longitudinal-axial stretching temperature, after the film has been stretched and has been connected to the stretching zone and the downstream heat treatment zone.

This is a method for producing a sequentially biaxially stretched polyester film, which is characterized in that the stretching ratio is set to a normal longitudinal stretching ratio and the stretching speed is increased to a predetermined speed.

Here, λ is the longitudinal-axial stretching ratio (unit: double), L is the length of the longitudinal-axial stretching zone, distance from the stretching start point to the stretching end point (unit: m), and V is the length of the longitudinal stretching machine. The longitudinal-axis stretching time can be calculated as the stretched film supply speed (unit: m/sec), and if the film speed is slow, it may be measured or calculated using the following formula.

When calculating the longitudinal-axial stretching time t using the above formula, it is assumed that the -axial stretching speed changes linearly from ■ to λ■ between the stretching start point and end point.

In order to shorten the longitudinal-axial stretching time, it is possible to increase the longitudinal-axial stretching ratio, increase the film feed rate for longitudinal-axial stretching, or shorten the longitudinal-axial stretching zone.

If the stretching ratio in longitudinal-axial stretching is less than 3 times, the polyester film will be stretched in a neck shape, especially in the 2 to 3 times range, and it is practically impossible to carry out the stretching. -Magnification range of neck occurrence depending on axial stretching temperature.

Although the degree of neck occurrence differs, there is no great difference in the neck occurrence magnification and the degree of neck occurrence in the temperature range of about 80° C. to 100° C., which is usually used as the longitudinal-axial stretching temperature for polyester films. This is the main reason why we propose a longitudinal stretching ratio of 3 times or more, but we also need to consider the mechanical performance of the biaxially stretched film and the accuracy of the film thickness.

Other reasons may also be cited.

Next, regarding the point of setting the stretching time in longitudinal-axial stretching to tc seconds or less, if the stretching time in longitudinal-axial stretching exceeds tc seconds, the birefringence profile between the film edges and the film center will change as shown in Figure 1. It looks like this.

(Birefringence-MD refractive index-TD refractive index) That is, the end portion of the longitudinally-axially stretched film during low-speed stretching rapidly increases the degree of vertical orientation. Longitudinal - axial stretching time tc
If it is shorter than seconds, as shown in Figure 1.

(○-・6-♀ in Figure 1) The degree of birefringence change at the film edges becomes smaller, and the stretching time is further shortened (the longitudinal
The difference in birefringence between the ends and the center of the axially stretched film becomes extremely small. The higher the longitudinal/axial stretching temperature, the greater the difference in birefringence between the film edges and the center.

The greater the rise in the degree of orientation at the ends of the longitudinally stretched film, the more likely it is that the film will be cut when the longitudinally and axially stretched film starts being fed during initial transverse stretching. In other words, vertically
- The axially stretched film is gripped by a transverse stretcher clip and stretched in the transverse direction using the transverse stretcher, but the area where the birefringence changes significantly is near the transverse stretcher clip, and the birefringence in this area is high. The longitudinally and axially stretched film in the area with high birefringence is
The central part of the film, which is easily crystallized during the preheating process of the transverse stretching machine and has low birefringence, is easier to stretch, while the edges are less likely to be stretched. Due to this non-uniformity, stretch cuts tend to occur near the clip.

Longitudinal with similar birefringence profile performance once truncation occurs.
- Cutting continues as long as the axially stretched film continues to be supplied. In order to overcome this cutting, the change in birefringence between the edges of the film and the center of the film was reduced as shown in FIG. That is, this can be achieved by supplying a film that has been longitudinally and axially stretched at a longitudinal stretching ratio of 3 times or more and a stretching time of tc seconds or less to a transverse stretching machine.

(Function) Although the reason why the transverse stretchability changes extremely critically after the longitudinal-axial stretching time reaches tc seconds is not clear, the phenomenon is that the longitudinal-axial stretching properties change between the edges of the film, its vicinity, and the center.
Due to changes represented by the birefringence of an axially stretched film, the difference in the degree of crystallization between areas with high and low birefringence during horizontal stretching is caused by the difference in the degree of crystallization during horizontal stretching. It can be said that cuts are likely to occur. By making the longitudinal-axis stretching time shorter than tc, the change in birefringence at the edges of the longitudinally-oriented film can be reduced and, as a result, initial cutting can be eliminated. Here, it is unclear why the birefringence profile increases at the edges of the film and decreases only at the center when the longitudinal-axis stretching time increases. In other words, the birefringence at the center is low.

It is thought that this is due to orientation relaxation due to the long stretching time, but the reason why orientation relaxation occurs only in the central region has not been clearly elucidated. In any case, after the initial cut in the transverse stretching machine is stopped and the film is connected to the stretching zone and the downstream heat treatment zone, the film in the heat treatment zone applies a force that pulls the film in the stretching zone in the longitudinal direction. Because the stress is shared, stress concentration near the clip is alleviated compared to when the film is initially passed through. After that, when returning to normal stretching conditions, depending on the case, the longitudinal-axial stretching time t
Even if the film does not satisfy the longitudinal-axial stretching critical time tc or less, the stress in the vicinity of the clip is relaxed as described above, and the film is continuously stretched.

Here, as a method of shortening the longitudinal/axial stretching time t.

■Method of increasing the stretching ratio λ, ■Method of increasing unstretched film supply speed■, ■Method of shortening the length of the stretching zone,
A method of increasing the standard longitudinal stretching time tc.

That is, method (2) of lowering the stretching temperature can be considered, but method (2) often takes time to return the stretching temperature to its original value. ■It is necessary to change the distance between the stretching rolls.

Adjustment is often troublesome, and in many cases ■ or ■
It is relatively easy to use either alone or in combination.

The term "polyester" used in the present invention refers to polyethylene terephthalate, and other copolymers having a moβ% content of not more than 20% may also be used. Examples of copolymer components are diethylene glycol, propylene glycol, and neopentyl glycol.

Diol components such as tetramethylene glycol 1p-xylylene glycol, 1,4-cyclohexane dimetatool, adipic acid, sepatic acid, phthalic acid.

Isophthalic acid, 2,6-naphthalic dicarboxylic acid.

Examples include bifunctional carboxylic acids such as trimellitic acid, p-oxyethoxybenzoic acid, and the like. It may also be a polymer blend, containing 20wt% of other saturated polyester, polyamide, polypropylene, polyethylene, polystyrene, etc.
They may be mixed to the extent that they do not exceed. It goes without saying that it may further contain inorganic inert substances such as silica, kaolin, calcium carbonate, titanium oxide, etc. to an extent not exceeding 5 ivt%.

As described above, the present invention solves the various problems encountered when producing polyester films using the sequential biaxial stretching method.

It solves the problem of initial cutting, which is a relatively serious problem, and its industrial value is great.

The present invention will be explained below with reference to Examples.

Example 1.2 and Comparative Examples The longitudinal stretching ratio was 3.2 times, the longitudinal stretching temperature was 85°C, and the feeding speed V of the unstretched film to the longitudinal stretching machine was shortened by changing the feeding speed V of the unstretched film to the longitudinal stretching machine. A longitudinally stretched film was drawn in and the initial cutting on a horizontal stretching machine was compared. Transverse stretching preheating temperature is 80°C, 90°C stretching temperature is 90°C, 95°C, 12
The cent temperature was 0°C and 235°C.

Immediately after longitudinal stretching, the sheets were placed in a horizontal stretching machine, and the cutting properties during initial passing were compared. The length of the horizontal stretching machine clip was set to 20 mm. Further, the lateral stretching ratio was 3.4 times.

Example 3.4 Longitudinal stretching temperature: 85°C, feeding speed of unstretched film to the longitudinal stretching machine constant: 0.15 m/5ec
By changing the ratio λ to 3.3 (L 3.5 times), the cutting properties during initial passing were compared under the stretching conditions of a transverse stretching machine not described in Example 1.

(Effect of the invention) Examples 1 and 2 are critical edge-longitudinal stretching time shorter than 1 second.
- It has been stretched for an axial stretching time, has a good birefringence TD profile, and has no initial breakage at all.

Longitudinal-axis stretching supply speed ■Final stretching supply speed 2.5 m/s
The speed increase on the line was completed smoothly up to ec. Comparative Example 1 was stretched with a longitudinal-axial stretching time longer than the critical edge-axial stretching time of 1 second, and its birefringence profile changed significantly at the edges, so that the initial cut during passing through the transverse stretching machine There was no continuous disconnection.

Example 3 was stretched with the same longitudinal-axial stretching time as the critical edge-axial stretching time of 1 second, and Example 4 was stretched with the critical edge-axial stretching time of 1 second.
The longitudinal and axial stretching was performed for 0.9 to 0.95 sec, which is slightly shorter than the second, and in Example 3, the birefringence change at the film edge was slightly larger than that in Example 4. In terms of properties, Example 3 was slightly inferior, with some cutting occurring for about 5 seconds after 9 passes, and the film was then stretched, but in Example 4, there was no initial cutting at all. In both cases, the trailing edge stretching supply speed is ■
The speed increase of the line was completed smoothly up to the final supply speed of 2.5 m/sec without any breakage in between. The longitudinal stretching ratio at the end of the speed increase was 3.3 times in each case, and in Example 4, after the initial passing was completed, the longitudinal stretching ratio was reduced from 3.4 times to 3.3 times, and then the speed increased.

[Brief explanation of the drawing]

FIG. 1 shows an example of the change in the TD direction birefringence profile of a longitudinally-axially stretched film depending on the uniaxial stretching time. The vertical axis shows birefringence, and the horizontal axis shows distance from the film edge. The longitudinal-axial stretching conditions were as in Examples 1 and 2. Same as Comparative Example 1. ○ Comparative Example 1 Critical edge-axial stretching time 1 second, longitudinal-axial stretching time 1.13 seconds6
- Example 1 Critical longitudinal-axial stretching time IJ$>&L-axial stretching Axial stretching time 0.
Gauze 5 Critical edge - axial stretching time 1 second> Longitudinal - axial stretching time 0.50 seconds Patent applicant Unitika 1 Zhu Shiki Company - f1 box

Claims (1)

[Claims] (When manufacturing a polyester biaxially stretched film by vertical-axial stretching followed by horizontal stretching by the 1,1 sequential biaxial stretching method, the longitudinal-axial stretching ratio is set to 3 times or more, A longitudinally-axially stretched film whose axial stretching time is equal to or less than the longitudinally-axially stretched critical time tc shown by the following formula is inserted into a transverse stretching machine. A method for producing a sequentially biaxially stretched polyester film, which is characterized by returning to normal longitudinal stretching conditions and increasing the stretching speed to a predetermined stretching speed.