JPH04455B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention relates to a method for producing a biaxially oriented polyethylene terephthalate film, and more specifically to a biaxially oriented polyethylene terephthalate film that has improved mechanical properties in both longitudinal (longitudinal direction of the film) and transverse (width direction of the film) directions. This invention relates to a film manufacturing method. Prior art and its problems Biaxially stretched films made of polyethylene terephthalate (hereinafter abbreviated as PET) resin are used for various purposes due to their excellent thermal stability, dimensional stability, and mechanical properties, but in particular, they are used for magnetic tapes. Its usefulness as a base film is well known. In this application, the better the mechanical properties of the base film, the thinner the film can be used, making it possible to reduce the size and weight of equipment in fields such as magnetic tape. This will result in an increase in capacity and capacity. Conventional biaxially stretched PET film has an F-5 value (tension at 5% elongation) of 10 to 11 kg/
mm ² , but in order to improve this, there is a so-called longitudinal re-stretching method in which a biaxially stretched film that has been stretched in both the longitudinal and transverse directions is further stretched in the longitudinal direction. However, although this method improves the mechanical properties in the longitudinal direction, the mechanical properties in the transverse direction are at the same level or slightly lower than those of conventional biaxially stretched PET films. Therefore, in order to improve the mechanical properties in the transverse direction, a method of re-stretching in the transverse direction after longitudinal re-stretching has been proposed (for example, in Japanese Patent Application Laid-Open No.
133276, 55-22915), this method certainly yields films with improved mechanical properties in both the longitudinal and lateral directions. However, this method of re-stretching horizontally after re-longitudinal stretching requires a re-longitudinal stretching process, a re-transverse stretching process, and a reheat-setting process compared to normal manufacturing equipment, making the manufacturing process extremely long. The drawbacks were low efficiency, increased manufacturing costs, and increased equipment costs. As another method, a method has been proposed in which a biaxially stretched film that has been stretched in both the vertical and horizontal directions is re-stretched in both the vertical and horizontal directions at the same time (for example, Japanese Patent Laid-Open Nos. 55-37305 and 55-27211).
However, this method also has disadvantages in that the manufacturing process is long and complicated stretching equipment for simultaneous biaxial stretching must be used. As a result of intensive research into a method for manufacturing a biaxially stretched PET film that does not have these drawbacks and has high mechanical strength in both longitudinal and transverse directions, the inventors of the present invention have developed a method for producing a biaxially stretched PET film that does not require re-stretching or re-stretching in both the longitudinal and transverse directions. The present invention was achieved by discovering a method for producing a biaxially stretched PET film with improved properties. Purpose of the invention The purpose of the present invention is to provide mechanical strength in both vertical and horizontal directions.
An object of the present invention is to provide a biaxially stretched PET film with a high Young's modulus. Another object is to provide a technique for manufacturing PET film with excellent performance using relatively simple manufacturing equipment. Structure of the Invention The present invention involves stretching a film-like PET in an unstretched state and a substantially amorphous state in at least two stages longitudinally,
This is a method for producing a biaxial PET film, which comprises then transverse stretching and further heat setting. That is, when longitudinally stretching substantially amorphous sheet-like PET, the first stage of longitudinal stretching is carried out at 120 to 150°C.
The yield point magnification is higher than that and the birefringence (△n) is 0.005.
Stretch to ~0.025 and continue to 60 to 110
This is a method for producing a biaxially stretched PET film, which comprises carrying out a second stage of longitudinal stretching at a temperature of 0.degree. To explain the present invention, PET as used in the present invention may be a homopolymer or a copolymer (the copolymer component is preferably 20% or less);
Moreover, its molecular weight may be in a wide range including ordinary ones, and is not particularly limited. Furthermore, at the raw material stage,
Various additives such as heat stabilizing agents, lubricants, ultraviolet absorbers, etc. may be contained. Next, a method for producing a biaxially stretched PET film according to the present invention will be explained. First, the PET polymer is sufficiently dried, then melt-extruded using an extruder, cast through a filter and a die onto a rotating drum, and rapidly cooled and solidified. This rapidly solidified film is substantially amorphous and poorly oriented to unoriented. This film is longitudinally stretched in the first stage at a stretching temperature of 120 to 150° C. at a yield point magnification or higher so that Δn is 0.005 to 0.025. (Hereinafter, this one-step stretched state will be referred to as A film). At this time, the stretching temperature was 120
When the temperature is lower than .degree. C., the biaxially stretched film obtained has low mechanical properties in the machine direction (represented by the F-5 value). on the other hand,
At 150° C. or higher, the stretching becomes substantially flow stretching, which reduces the stretching effect, and the obtained biaxially stretched film has poor thickness unevenness due to high temperature stretching. Furthermore, even if the stretching temperature is within the range of 120 to 150℃, △n is 0.005
If it is less than 0.025, the F-5 value in the longitudinal direction of the biaxially stretched film will be low, and if it exceeds 0.025, the workability (stretchability) in the second stage longitudinal stretching and subsequent transverse stretching will be low.
Particularly in transverse stretching, troubles such as breakage occur more frequently. When performing the first stage longitudinal stretching at 120 to 150°C, if the stretching is below the yield point magnification, △n is 0.005
The stretching ratio must be selected to be equal to or higher than the yield point ratio. Next, heat the A film at 60~110℃, preferably at 70~110℃.
A second stage of longitudinal stretching is carried out at 100°C, more preferably 70 to 90°C (hereinafter, the state after two stages of longitudinal stretching is referred to as a B film). When obtaining this B film, if the stretching temperature is too low, stretching unevenness will occur or the operability and stability of longitudinal stretching will be impaired; if the stretching temperature is too high, although the stretched state is stable, this step
Crystallization progresses significantly in the film, and troubles such as breakage occur frequently in the next horizontal stretching process, making stable production impossible. On the other hand, if the stretching ratio in the second stage of longitudinal stretching is too low, the F-5 value in the longitudinal direction of the biaxially stretched film will be low and the thickness will be uneven. In addition, if the stretching ratio is too high, breakage will occur frequently in the later stage of horizontal stretching, making stable production impossible.
A suitable stretching ratio is 200%. The thus obtained B film was heated to 70 to 120°C, preferably 80 to 100°C using a stenter for 4.3 hours.
The film is laterally stretched at a stretching ratio of at least 4.5 times, preferably at least 4.5 times, then heat set and rolled up. In transverse stretching, if the stretching temperature is too low, the transverse stretchability will deteriorate (occurrence of breakage), and if it is too high, thickness unevenness will worsen. The F-5 value in the lateral direction is low unless the stretching ratio for lateral stretching is 4.3 times or more. In this way, mechanical properties are improved in both the longitudinal and lateral directions by performing longitudinal stretching at a high temperature to give a constant orientation, followed by a second longitudinal stretching in the same direction at a relatively low temperature, and further transverse stretching and heat setting. biaxial stretching
The reason why PET film is obtained is that it has a longitudinally oriented structure due to the second stage of longitudinal stretching at a low temperature in addition to the first stage of longitudinal stretching at a high temperature. It is assumed that the B film has a relaxed structure that is easily horizontally stretched, and that this portion is preferentially horizontally stretched. As a result, it is thought that this is because the longitudinally oriented structure created by longitudinal stretching tends to exhibit physical properties such as mechanical strength in the longitudinal direction. The present invention will be explained below with reference to Examples and Comparative Examples. Examples and Comparative Example 1 When longitudinally stretching substantially amorphous sheet-like PET, the first stage of longitudinal stretching was carried out under the conditions shown in Table 1. The second stage of longitudinal stretching was carried out at a stretching temperature of 90°C and a stretching ratio as high as possible without impairing the transverse stretchability. then laterally
It was stretched 4.6 times at 95°C, heat-set at 210°C, and rolled up.
Table 1 shows the F-5 value of the obtained biaxially stretched film.
It was shown to. As shown in Table 1, the F-5 value in the longitudinal direction is low when the first stage longitudinal stretching temperature is low or when the temperature is appropriate but Δn is too low. Furthermore, even if the temperature is appropriate, if Δn is too high, there will be many breaks during lateral stretching, making stable production impossible. Furthermore, if the temperature is too high, the thickness of the biaxially stretched film will be poor and cannot be put to practical use.

[Table] Example and Comparative Example 2 In longitudinally stretching substantially amorphous sheet-like PET, the first stage of longitudinal stretching was carried out at 140° C. and at 2.5 times. The Δn of this film was 0.0100. This film was subjected to second stage longitudinal stretching at various temperatures as shown in Table 2. The longitudinal stretching ratio in the second stage was increased to the extent that the transverse stretchability was not impaired, and then the transverse direction was stretched 4.6 times at 95°C and then 210°C.
I heat-set it and rolled it up. As shown in Table 2, when the second stage longitudinal stretching temperature is 50°C, the thickness unevenness becomes worse, and at 120°C, the F-5 value is low and the thickness unevenness is also bad.

[Table] Example and Comparative Example 3 When longitudinally stretching substantially amorphous sheet-like PET, the first stage of longitudinal stretching was carried out at 140° C. and at 2.5 times the stretching. The Δn of this film was 0.0100. This film was subjected to a second stage of longitudinal stretching at 90°C and 2.3 times the stretching temperature. Then, it was laterally stretched at the magnification shown in Table 3 (temperature: 95°C). The film was heat-set at 210°C and rolled up. As shown in Table 3, when the transverse stretching ratio is less than 4.3 times, the F-5 value in the transverse direction becomes low.

[Table] As described above, according to the present invention, a biaxially stretched PET film with improved mechanical properties in both the longitudinal and transverse directions can be produced without re-stretching in the longitudinal direction or in the transverse direction. Effects of the Invention According to the manufacturing method of the present invention, F-
A biaxially stretched film with a high 5 value can be obtained. The present invention achieves high physical properties comparable to conventional re-stretched and re-stretched films through two-stage longitudinal and one-stage transverse stretching.
There is an advantage that a PET biaxial film can be obtained.

Claims (1)

[Claims] 1 Film-like polyethylene terephthalate in a substantially amorphous state has a yield point magnification in the longitudinal direction at a temperature of 120 to 150°C and a birefringence of 0.005.
The first stage of longitudinal stretching is carried out so that it becomes ~0.025,
A biaxially stretched polyethylene terephthalate film which is then subjected to a second stage of longitudinal stretching at a temperature of 60 to 110°C, then laterally stretched in the transverse direction at a stretching ratio of 4.3 times or more, and further heat-set. Production method.