JPS61179723A - Manufacture of biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To improve flatness of a biaxially oriented and thermally settled biaxially stretched film by reducing the itnermediate slack, by a method wherein tentering treatment widening the film in a widthward direction is applied to one side or both side fringes, where the film is not slackened, according to a shape or degree of the intermediate slack at the time of thermal settling of the film in a cooling zone. CONSTITUTION:After a film obtained by melting and extruding material resin such as polyethylene terephthalate resin has been stretched in a biaxial direction and settled thermally, the film is cooled at the temperature of more than the secondary transition point and less than 190 deg.C, in a cooling zone. In this instance, tentering in a widthward direction is applied to one side or both side fringes, where the film is not slackened, according to a shape or degree of the intermediate slack. To carry out the tentering it may be good if a device wherein each of two rolls on both sides, whereon a tenter chip runs, become movable independently each other in a widthward direction is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a co-axis oriented polyester film, and more particularly to a method for producing a U-axis oriented polyester film in which center sag is reduced and flatness is improved.

Co-axially oriented polyester films (hereinafter abbreviated as oriented films) are produced during the manufacturing process by (1) film thickness fluctuation, (2) temperature distribution in the transverse stretching machine, and (3) bowing phenomenon that occurs during transverse stretching and heat setting. , (4) non-uniform tension during cooling, and (5) loss of flatness (that is, sagging occurs) due to the cooling rate after heat setting.

Conventionally known methods for improving this flatness defect can be broadly classified into the following methods.

(1) After coaxial stretching, the film is heat-set and cooled to form an oriented film, which is then reheat-treated.

(2) After y-axis stretching and heat setting, take appropriate cooling means for cooling.

(3) When performing Y-axis stretching, use a film in which the crystallinity of both sides is greater than that of the center.

(4) Coaxial stretching, heat setting and cooling are performed to obtain an oriented film, which is then re-stretched or re-stretched.

However, it is advantageous from the viewpoint of workability and cost to reduce the film forming process as much as possible, and the above (1) and (4)
It is industrially undesirable to add a step to improve sag once an oriented film has been formed.

From this point of view, the present inventors took appropriate cooling means when cooling after U-axis stretching, heat setting, and (2) above.
We conducted improvement research on methods that belong to this category.

However, when producing a co-axially oriented polyester film by the tenter method, due to the bowing phenomenon that occurs within the tenter, so-called sagging occurs in the film, where the center part in the film width direction is longer than the side edges. This has long been known. However, in the process of conducting research to improve the sagging of oriented films, the present inventors discovered that in addition to the sagging centered at the center in the width direction as described above, various forms of sagging such as left-right asymmetrical sagging, It has been found that sag occurs not in the center of the film, but in the side edges of the film that are longer than the center, that is, sag that can be called edge sag.

The state of sagging and the degree of sagging in these various aspects can be measured by the following method.

That is, as shown in FIG. 1, the oriented film is passed across two rolls R3 and - placed in parallel with a spacing of jm. Roll so that the line A-A' in the figure matches the width direction (direction perpendicular to the extrusion direction) during film extrusion molding.
and - put it on top. Then, a load is applied to the roll R1 and the film hanging down from the end thereof downward, that is, in the direction of the arrow T, and the film is pulled. In this tensile force, a tensile force of #/♂ is applied to about 4' so that the film is in a tensioned state without being stretched. In the case shown in Figure 1, what about film F?
The part marked , is under tension, but the part marked F is slack. If there is no slack, are the side edges of the film dotted lines? It comes to the position shown by .

As shown in Fig. 1, parallel light rays are applied to the film F stretched as described above at a normal angle α near the center of the roll horse and the horse, and the reflected light is reflected onto the scale plate M. The light is received and measured. FIG. 3 illustrates a state in which a shadow @R is projected on the scale plate M in the film width direction, that is, at a location corresponding to the person-A' I/C in FIG.

In other words, in this example, the right edge of the film is the slackest;
The distance indicated by t is the "sag amount".

When the sagging state of the oriented film was investigated as described above, it was found that there were various types of sagging as shown in the figures. In these figures, M and A' are respectively.

In FIG. 1, the side edge with reference numeral A' and the side edge with reference numeral A' are shown.

The sagging shown in Figures 1 to 1 is caused by the difference in film length.

The longer parts of the film are not subject to any tension and are rolled up and hang low, creating sag, while the shorter parts have concentrated tension and are elevated.

here! , tlEII~! As shown in the figure, the middle part of the film has one or both side edges shortened, and as shown in Figures 6 and 7, one or both side edges are longer than the center part of the film, making it sagging. Things are called edge sagging.

As mentioned above, the sag in a co-axis oriented polyester film includes a middle sag and an end sag (each of which has a symmetrical sag and an asymmetrical sag). Whether symmetrical or asymmetrical, as shown in the figure.

The purpose of this invention is to provide a method for reducing center sag and improving film flatness, and the gist of the invention is a method for producing a co-axis oriented polyester film with reduced center sag, Coaxially stretched and heat-set coaxially oriented.

When the polyester film is cooled from the heat setting temperature in the cooling zone, the iqo
At temperatures below ℃, depending on the shape of the sag and the degree of sag, one or both side edges that are not sagging,
The present invention relates to a method for producing a co-axis oriented polyester film, which is characterized by performing a tentering process to widen the film in the width direction.

The present invention will be explained in detail below.

The most typical polyester for the film material of the present invention is polyethylene terephthalate, but it also includes polyesters copolymerized with ethylene terephthalate as a main component and other polybasic acids such as inphthalic acid and phthalic acid. It will be done. The resin material may be melt-extruded to form a film, stretched in the co-axial direction, and heat-set by conventionally known methods. After heat setting, the film is cooled in a cooling zone at a temperature above the first transition point of the film resin and below iqo°C. Perform tentering in the film width direction on one or both side edges of the film on the non-sagging side. That is, tentering refers to an operation of stretching the film in the width direction to widen the film width. When this film is tentered in the width direction, the length of the side edge on the tented side (if both edges are tented out, the side edges on both sides) will be longer (the dimension in the length direction of the film) than before tentering. The length is also longer.

The change in film length due to such tentering processing is greatest at the side edges of the film, and the effect only slightly reaches the center of the film. The specific operation for tentering is selected based on the length of the film at the center.

For example, in the case of asymmetrical sag in the middle as shown in Figure 1, the dimension on the A side is shorter when taken from the center of the film in the width direction. Increase the dimension in the direction to reduce sagging. In addition, if the film in Fig. S is centered at the center in the width direction and is sagging symmetrically, the entrance side and A'
Widen both sides to improve sagging.

In other words, if one or both side edges of the film are shortened when viewed in the longitudinal direction (or one or both side edges are located at a higher position than the center of the film), one or both of the side edges is shortened. Adjust the width along the side edges. The amount of width adjustment is determined according to the "sag amount", that is, the size of t shown in FIG. The amount of tentering is usually preferably within the following range. That is, the width adjustment for one side edge is
In other words, the length from the center in the width direction of the film to the side edges is 0.3 to 1.
To choose from within the range of 0, set the width of the side edge on the A side by an amount within the range of 0.3 to 0 for each % of the film width, and in the case of Figure 3 Then, on the side edges of A side and A' side, respectively, 0.3-ko for the length of the film width,
The i value is calculated by an amount within the range of 0. If the amount of tentering is too small, the effect of reducing slack will be weak, and if it is too large, it will warp and have a negative effect on flattening. In order to perform this tentering, it is necessary to gradually reduce the width of the tenter in the cooling zone, that is, the distance between the rails of the tenter clips that grip the film edge. It is sufficient to use a device in which each of the rails can be moved in the width direction independently of each other.

Furthermore, the tentering in the cooling zone must be carried out within a temperature range above the first order transition point of the film resin and below 190 DEG C., preferably within a temperature range of 100 to t AOC. At temperatures below the -th transition point, local deformation occurs and the sag becomes large, and at temperatures higher than 190C, the sag changes during the subsequent cooling process, making it ineffective.

As described above, the sag in the oriented film is reduced by providing width to one or both side edges of the film depending on the form and size of the sag, thereby achieving flattening of the film.

Next, an embodiment of the non-inventive method will be described.

Example 1 Polyethylene terephthalate was melt-extruded, cooled with a casting roll to form a film, and then 3. & times, stretched 3 times in the transverse direction,
An oriented film having a thickness of l-μ was obtained by heat setting at 0C. The sag of the film, which was cooled and wound in the usual manner, shows the pattern shown in Figure D, and the amount of sag is g, z.
It was am.

In the temperature range from tboc to //QT:, in the cooling zone after heat fixation, instead of the normal simple cooling mentioned above,
The sides were tentered, and the amount of tentering was varied to perform cooling. Table 1 shows the changes in the amount of slack.

/ Ot,! −〇, ko tr, iJ
00II Ko, Kuda
0.6 Ko! j'
0.1? ,
? The sagging pattern of the film after cooling treatment is experimental/-J
Up until now, the pattern was as shown in Figure 1, but the experiment was...
Now, the sagging state of the pattern shown in FIG. 5 is shown. In other words, it has been revealed that the sag pattern changes when the amount of tentering is around 0.1%.

Example: The same procedure as in Example 1 was carried out, but the film was stretched 303 times in the longitudinal direction and j, j times in the transverse direction, then heat-set with a co-IOC to form a polyethylene terephthalate film with a thickness of 5 μm, and then cooled in the usual manner. I did it. When the sag condition of the wound film was examined, the sag had a pattern shown in FIG. 1, and the amount of sag was 7.6 cm.

Instead of the above-mentioned normal cooling method, in the temperature range from 1&Oc to 10DC, cooling was carried out by tentering on the A side and varying the amount of the tentering. The results are shown in Table 1.

Table - 6
7.6- 〇、ko
ri, lJ O, dako, j hiroo, b 4. z In the above experiment number /-, J, the sagging of the film after tentering and cooling showed the pattern shown in Figure 3, but in experiment number lI
K'' showed the pattern shown in FIG.

It should be noted that the above examples are illustrative to aid understanding of the present invention, and the method of the present invention is not limited to these examples.

[Brief explanation of drawings]

Figures 1 and 7 are explanatory diagrams showing a method for measuring the sagging state of the film, Figure 3 is a drawing showing a scale plate on which the sagging state of the film is projected, and Figures D to 7 illustrate various forms of sagging of the film. This is a drawing. A'70

Claims (1)

[Claims] A method for producing a biaxially oriented polyester film with reduced center sag, in which a biaxially stretched and heat-set biaxially oriented polyester film is cooled from the heat-setting temperature in a cooling zone to a temperature higher than the secondary transition point of the film resin. , a biaxially oriented polyester characterized by performing tentering treatment to widen the film in the width direction on one or both side edges that are not sagging, depending on the shape of the sag in the center and the degree of sagging, at a temperature of 190° C. or lower. Film manufacturing method.