JPS5922660B2 - Stretching method for polyester film or sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stretching a polyester film or sheet (hereinafter collectively referred to as a polyester film), more specifically, a method for stretching two or more polyester films simultaneously in the transverse direction while stacking them together, The present invention relates to an improvement in a method for producing multiple films at once by separating stacked films after stretching.

Polyester film has excellent mechanical and electrical properties, and is used in magnetic tapes, capacitors, electrical insulation materials,
It is widely used in the production of gold and silver thread.

In order to meet such wide-ranging demands, various studies have been made for the purpose of improving productivity, and as part of these studies, research goal b- has been adopted in the direction of increasing the width and speed.

However, these improvements have limitations in terms of product quality and workability, and the cost of underlayer equipment tends to rise faster than the cost of film, making it difficult to increase production by increasing the number of underlayers. There is a problem with economics in increasing the amount. In order to solve these problems, there is a method in which multiple films are stacked together, stretched simultaneously using a single stretching machine, and after stretching, the stacked films are separated into husbands and wives to produce multiple films at once. For example, JP-A-50-22069, JP-A-51-24678, JP-A-5
1-31775). However, when this method is stretched, there is a problem of adhesion between the films when heated to the stretching temperature, making it extremely difficult to put them into practical use. In other words, when two or more polyester films are overlapped and sequentially biaxially stretched, The film uniaxially stretched in the longitudinal direction is preheated to above the glass transition temperature, usually with hot air, and then stretched in the transverse direction with (.
In this case, the film sticks locally or over the entire surface, especially during preheating, and it becomes impossible to separate the stacked films after transverse stretching. In order to solve the problems that were hindering its practical application, Tatsuta conducted repeated research and completed the present invention.

The present invention provides a method for stacking two or more polyester films and stretching them in at least the lateral direction using an underlayer, and then separating the stacked films without causing the films to stick to each other during the stretching. The object of the present invention is to provide a method that can produce stretched films of the same quality as conventional single-sheet stretched films with high efficiency, and this purpose is to produce polyester films or sheets according to the method of the present invention. The polyester film subjected to the longitudinal uniaxial stretching must have a crystallinity of 2.5% or more and a 10q
This is achieved by using 6 or less.

The method of the present invention will be explained in detail below.

The polyester used in the method of the present invention contains terephthalic acid as an acid component and, if desired, a small amount of other acid components (such as isophthalic acid, phthalic acid, p-oxybenzoic acid, etc.), and ethylene glycol, as a glycol component. Typical examples include homopolymers or copolymers containing a small amount of other glycol components (e.g. trimethylene glycol, hexamethylene glycol, etc.) if desired, and mixtures of two or more of these polyesters or mixtures of these polyesters. Mixtures with other compatible polymers at low temperatures and small amounts can also be used.

In the method of the present invention, a polyester film having a crystallinity within a specific range is used as a raw material polyester film. Methods for controlling the crystallinity of polyester films include adjusting the cooling rate of the melt-extruded and quenched film, or heating the quenched film again under selected conditions (e.g., using an infrared heater). No matter what happens L. By appropriately selecting the conditions, a desired degree of crystallinity can be obtained. For example, in the case of a certain polyethylene terephthalate film (1,
0.616, crystallinity 0.8%, density 1.336. V/
Cd), crystallinity (χc) 1.7% (density 1.337f/Crii) when treated at a temperature of 100°C for 32 minutes
However, the treatment time is longer and 64°C is obtained at the same temperature.
When treated for 1 minute, the χc becomes 2.5% (density 1.338), and when the treatment temperature is increased to 110°C for 8 minutes, the χc becomes 5.0% (density 1.3407/Cd). When treated at 120°C for 1 minute, χc was 2.5% (
Density: 1.338 f/Cd), and when treated at the same temperature for 2 minutes, χc becomes 5.8% (density: 1.342 f/Cd). In this way, the desired degree of crystallinity can be experimentally obtained for each polyester film.
The method for measuring the degree of crystallinity (χc) indicated in the inventive method was based on the density determined by the density gradient tube method, using the relationship of the following formula.

In the above equation, ρ is the density of the sample, and ρa is the density of the amorphous resin (1.335f for polyethylene terephthalate).
/CrA), ρc is the density of complete crystallinity (1,455 f/Cri, in the case of polyethylene terephthalate).

In the method of the present invention, when two or more polyester films within a predetermined range are overlapped and laterally stretched using a tenter, it is possible to subject the films to longitudinal uniaxial stretching before the overlapping of the films, which is performed before the transverse stretching step. Even if the film has a crystallinity within a predetermined range, if it is immediately laterally stretched, adhesion will occur between the overlapping films.

For example, regarding the relationship between the temperature and time of the treatment to achieve the desired crystallinity as described above (for the example film, treatment conditions were 100℃, 64 minutes, χC 2.5%, 110℃).
, 8 minutes, χC5. O%, 110℃, 8 minutes, χC5
．． Two sheets of O9ll, 120° C., 2 minutes, χC 5.8%, and 120° C., 1 minute, χC 2.5% were stacked and stretched horizontally without being uniaxially stretched in the longitudinal direction, but sticking occurred in all of them. However, when the film was uniaxially stretched in the longitudinal direction (90° C., 2.5 times) and then laterally stretched (90° C., 3.0 times), no adhesion was observed in either case. In the method of the present invention, the raw film must have a crystallinity within the range of 2.5 to 10 (:F6), but if the crystallinity is lower than 2.5%, the film must be Adhesion occurs and the stacked films cannot be separated.

When the degree of crystallinity is higher than 10q1), stretching unevenness occurs in the subsequent stretching step, and breakage occurs during transverse stretching, and the film becomes more uneven in thickness. In addition, the longitudinal uniaxial stretching conditions are, for example, 60 to 60 in the case of polyethylene terephthalate.
1.5 to 4.5 times at 110°C, preferably 80 to 90°C
The normally used conditions of 2.5 to 3.5 times may be used.

In principle, the direction of longitudinal uniaxial stretching does not matter; however, in practice, longitudinal uniaxial stretching is selected for equipment reasons. To carry out the method of the present invention, equipment commonly used in the past can be used as is.

That is, it may be of the type in which a conventional tenter follows a longitudinal stretching device. All that is required is to provide a device for crystallizing the film before stretching and a take-off machine for taking over two or more overlapping films after leaving the tenter, depending on the number of sheets.
In this case, the tenter 1 can be used not only for stretching in the horizontal direction, but also for simultaneous stretching in the horizontal and vertical directions. Furthermore, the film that has exited the tenter may be subjected to a longitudinal stretching process if necessary. can be stretched in the lateral direction all at once without causing adhesion, which greatly contributes to improved productivity.

Next, examples of the present invention will be described. Example 1 Polyethylene terephthalate with an intrinsic viscosity (1) of 0.62 was melt-extruded at an extrusion temperature of 290°C and brought into contact with a casting roll to produce a quenched film with a width of 700 mm and a thickness of 150 μm. was crystallized by heat treatment in an oven.

The crystallization conditions are 120° C. for 1.5 minutes in an air atmosphere. The crystallinity of the obtained film was 3.5%, and the crystallinity of the solution base was 2.3%. Next, add this film to 90
The stretched film was longitudinally uniaxially stretched at a magnification of 3.5 times at ℃, and this stretched film was divided into two equal parts with a cutter in the direction of flow, and one of the two equal parts was guided with an inclined roll to separate the other two equal parts. It was stacked on top of the other, introduced into a tenter, and laterally stretched three times at 90°C. The horizontally stretched film was separated and each part was wound up using a take-up machine. The adhesion state of the film and the presence or absence of stretching unevenness are shown in Table 1 below. Example 2 Except that the crystallization conditions were changed to 120° C. for 3 minutes in an air atmosphere to obtain a film with a crystallinity of 8%, which was then used.
The other operations were the same as in Example 1.

The first thing to check is the adhesion state of the film after horizontal stretching and the presence or absence of stretching unevenness.
Shown in the table. Comparative Example 1 Crystallization conditions were set to 120°C in an air atmosphere (at a temperature of 0.5
The procedure was the same as in Example 1 except that a film with a crystallinity of 1.5% was obtained and used.

Table 1 shows the adhesion state of the film after transverse stretching and the presence or absence of stretching unevenness. Comparative Example 2 The procedure was the same as in Example 1 except that the crystallization conditions were 120° C. for 8 minutes in an air atmosphere to obtain a film with a crystallinity of 15%.

Table 1 shows the adhesion state of the film after transverse stretching and the presence or absence of stretching unevenness. In the table above, non-adhesive means that the stacked films are in close contact with each other and do not show any resistance when separated. In itself, there is no abnormality in appearance.

Adhesive means that the overlapping films are in close contact with each other locally or over the entire surface, and when they are separated, there is resistance or breakage occurs, making it impossible to wind them up smoothly.・U.Also, "no stretching unevenness" means that overlapping films are separated, and each film obtained has an appearance (for example, 2
A film that is uniformly stretched and has uniform mechanical, optical, and electrical properties (such as when observed by inserting a film between two orthogonal polarizing plates). The opposite of uneven stretching is L.
cormorant. From the table above, it can be seen that if the crystallinity of the film material to be stretched is within the range of 2.5 to 10%, the stacked films will not stick together during horizontal stretching. Below the lower limit of the range, it indicates that sticking occurs (
・Ru.

Claims (1)

[Claims] 1 Two or more polyester films or sheets are stacked together and stretched simultaneously at least in the transverse direction, and after stretching,
In a method in which stacked films or sheets are separated and a plurality of stretched films or sheets are obtained at once, the films or sheets are subjected to longitudinal uniaxial stretching treatment before stacking, and this longitudinal uniaxial stretching treatment is performed. The crystallinity of the film or sheet before stretching treatment is 2.5% or more, 1
A method characterized by using 0% or less.