JPH0410919A - Manufacture of polyethylene-2,6-naphthalate film - Google Patents

Abstract

PURPOSE:To manufacture a film with a high elastic modulus at a low cost in industrial scale by performing lateral and longitudinal drawing under specific conditions when a biaxially stretched film is manufactured by drawing first in lateral direction, then longitudinal direction depending on the differences in circumferential velocities between rolls and thereafter applying heat treatment. CONSTITUTION:A substantially unoriented polyethylene-2,6-naphthalate film is first drawn in a lateral and then in a longitudinal direction depending on the differences in circumferential velocities between rolls and thereafter heat treatment is applied thereto to manufacture a biaxially stretched film, in which the lateral drawing, a first stage, is performed at a temperature of 130-190 deg.C to achieve a drawing ratio of 3.0-6.0 so that the double refraction of the film in the width and thickness direction is in the range of 0.2-0.32. Thereafter, the longitudinal drawing, a second stage, is performed at a temperature of the low crystallization temperature or lower of the film having been laterally drawn, in which the temperature of said film is kept at a temperature of the primary dispersion peak temperature (Talpha) or higher and lower then Talpha+40 deg.C to achieve a drawing ratio of 4.5 or larger using a noncontact heating device. As a result, a biaxially stretched PEN film having longitudinal Young's modulus of 800kg/mm<2> or larger and lateral modulus of 550kg/mm<2> or larger can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing polyethylene-2,6-naphthalate film. More specifically, the present invention relates to a method for producing a polyethylene-2°6-naphthalate film suitable for fields requiring a high elastic modulus in the longitudinal direction, such as base films for magnetic recording media.

(Prior Art) In the field of magnetic recording media, particularly magnetic tapes, base films containing polyethylene terephthalate (PET) as a main component are widely used, and their range of application tends to further expand. On the other hand, as technology becomes more sophisticated, devices and tapes are required to be smaller, and therefore base films are also required to be thinner. In order to achieve this, it is essential to increase the elastic modulus of the base film.
2,6-naphthalene (PEN) films are beginning to be used as base films. It is known that a Young's modulus of -800 kg/, 1 - can be obtained with PEN film (JP-A-50-100174, JP-A-50-102303, JP-A-63-
80731). However, in all of these methods, complicated multi-stage stretching methods are adopted in which the film is stretched sequentially in the order of length-to-width or length-to-width-to-width, resulting in high film production costs (and PEN Considering that the raw material cost is much higher than that of PET, PEN film did not necessarily have superior industrial value.In addition, in order to reduce manufacturing costs, a relatively simple vertical film was developed. Transverse stretching method or transverse-longitudinal stretching method Method of stretching PEN (Japanese Patent Publication No. 48-29541, Japanese Patent Publication No. 56-50693, Japanese Patent Application Laid-open No. 50-13
3279, Japanese Patent Publication No. 53-11996) have also been proposed, but these methods only exemplify a maximum longitudinal stretching ratio of about 4.5 times, and at most 800 kg/-culm. The limit was to obtain a Young's modulus of .

(Problems to be Solved by the Invention) The present invention seeks to solve the drawback of the prior art, namely, that it is extremely difficult to produce PEN films with high elastic modulus at low cost on an industrial scale. It is something.

(Means for Solving the Problems) A specific means for solving the above problems, that is, the present invention is to first stretch a substantially unoriented polyethylene-2,6-naphthalate film in the transverse direction, and then roll it out. In the method of producing a biaxially oriented film by stretching in the longitudinal direction with a difference in circumferential speed and then heat-treating, the first stage of transverse stretching is 130 to 190
Stretched 3.0 to 6.0 times at a temperature of ℃ to make the film width direction and thickness direction birefringence in the range of 0.2 to 0.32,
In the second stage of longitudinal stretching, the stretching roll temperature is set below the low-temperature crystallization start temperature of the film after transverse stretching, and a non-contact heating device is used to adjust the film temperature to the main dispersion peak temperature (T) of the film after transverse stretching.
4.5 times the amount 1- as a temperature higher than α) and lower than Tα+40℃
It is characterized by stretching at a magnification of .

In the present invention, polyethylene-2,6-naphthalate is a polymer in which 80 mol% or more is composed of ethylene-2゜6-naphthalene dicarboxylate units.
It refers to copolymers and mixtures, and can be produced by known methods.

In the present invention, the PEN film is stretched sequentially in the horizontal and vertical directions. If the stretching order is reversed and the stretching is carried out in the vertical and horizontal directions, it is extremely difficult to obtain a Young's modulus in the vertical direction of 800 kg/mj or more, even if the stretching ratio in the vertical direction is 4.5 times or more. It is.

In the lateral stretching in the present invention, the stretching is performed by 3.0 to 6.0 times at a temperature of 130 to 190°C. If the transverse stretching temperature is less than 130° C., it is not preferable because it tends to be in a cold stretched state and causes stretching unevenness and whitening. Conversely, the transverse stretching temperature was set to 19
If the temperature is 0° C. or higher, flow stretching tends to occur, resulting in insufficient orientation or breakage. Further, when the stretching ratio is 3.0 degrees or more, unevenness in thickness in the film width direction is likely to occur, and conversely, when the stretching ratio is 6.0 degrees or more, whitening and breakage are likely to occur.

In the present invention, it is necessary that the birefringence (refractive index in the width direction - refractive index in the thickness direction) of the film after horizontal stretching is in the range of 0.2 to 0.32, preferably 0.22 to 0.30. be. This is because even if the temperature and magnification of the transverse stretching are within the above range, if the birefringence is less than 0.2, the orientation will be insufficient and breaks and uneven thickness will easily occur. This is because if the birefringence exceeds 0.32, not only will whitening and breakage be likely to occur, but also the next step of longitudinal stretching will be difficult. In order to bring the birefringence within this range, the temperature and magnification of the transverse stretching may be adjusted within the above ranges.

Further, in the present invention, heat treatment or relaxation treatment may be performed between the horizontal stretching and the next longitudinal stretching.

In the second stage of longitudinal stretching in the present invention, the stretching roll temperature is set to be lower than the low-temperature crystallization start temperature of the film after transverse stretching, and a non-contact heating device is used to adjust the film temperature to the main dispersion peak temperature (Tα) of the film after transverse stretching. Stretching is carried out at a magnification of 4.5 times or more at a temperature below Fτα+40°C. The inventive step of the present invention lies in this point.According to the present invention, it is possible to perform longitudinal stretching at a high magnification that was not possible in the past, and it is possible to increase the Young's modulus in the longitudinal direction to 800 kg/nJ or more. easily possible.

That is, the method of stretching in the horizontal and vertical directions is a method that can produce particularly remarkable effects in PEN under certain conditions.

The temperature of the longitudinal stretching in the present invention is τα+
It is less than 40°C and less than 200°C. This is because longitudinal stretching of 4.5 times or more is difficult when longitudinal stretching is performed at a temperature lower than Tα, and Tα+40°C or higher or 200°C
This is because if the stretching is above, flow stretching occurs, making it difficult to obtain the desired elastic modulus.

In the present invention, as a method of adjusting the film temperature during longitudinal stretching to below Tα or hTa+40°C, the temperature of the heating roll is preferably 150°C below the low temperature crystallization temperature after finishing the transverse stretching.
The method is as follows, and non-contact heating using an infrared heater etc. is also used. This is to prevent the film from sticking to the stretching rolls and to perform uniform longitudinal stretching. Only by adopting such a film heating method can longitudinal stretching be carried out uniformly and stably at a high magnification, which was previously unimaginable.

Further, a relaxation treatment may be performed subsequent to the longitudinal stretching.

In the present invention, the heat treatment after biaxial stretching is performed at 180 to 2
It may be carried out at a temperature of 80°C. Further, relaxation treatment or re-stretching may be performed during or before or after the heat treatment.

〔Example〕

Hereinafter, before explaining the present invention using examples, the evaluation method used in the examples will be explained.

(1) Transverse Stretching Ratio Markers were written on the unstretched film in advance, and evaluation was made from the ratio of the marker width before lateral stretching to the marker width after lateral stretching.

■Longitudinal stretch ratio Evaluation was made based on the speed ratio between the low speed roll and the high speed roll.

(3) Longitudinal Stretching Temperature The film temperature was measured using an infrared radiation thermometer manufactured by Burns.

(2) Low-temperature crystallization temperature 20°C per minute using Seiko Electronics Co., Ltd. DSC100
The temperature was raised at a rate of , and the temperature at which the DSC time differential coefficient was maximum in the low-temperature crystallization region was defined as the low-temperature crystallization temperature.

■Main dispersion peak temperature■Orientic Rheopybron DI) V-I
Using I-EP, heating rate 2 for 7 minutes, frequency 110Hz
The temperature change in the loss modulus was measured in the longitudinal direction of the film, and the peak temperature was used.

(6) Birefringence (refractive index in the width direction - refractive index in the thickness direction) The method described in the Journal of the Fiber Science Society, Vol. 28, No. 11, Section 431 was used. Namely, ■ Nikon polarizing microscope and Letter Zone 1
using a standard plate and a universal stage.
Birefringence (ro) in the film plane and the average birefringence (r
) was sought.

Then, the birefringence (Δn) in the width direction and the thickness direction was calculated from the obtained birefringence value using the following formula.

Δn=n-(((n-Ae)'n2・5in2θ)÷(
n”(n-Ae)2・cos2θ)]μ2 However, Ae
” ro re * (7=IO' T n=
1.8■Young's modulus・Tensilon UTM-11-500 made by Soorientic
The measurement was carried out using a mold at a temperature of 23° C. and a relative temperature of 65%. The shape of the sample was 10 cm long and 1 cm wide, and the pulling speed was 100%/min.

(Example 1.2) After drying polyethylene-2,6-naphthalate pellets with an intrinsic viscosity of 0.59 for 10 minutes, they were fed to an extruder and melt-extruded at 300°C. It is cooled and solidified by contacting it with a drum that has been cooled to a thickness of 180 mm.
An unoriented film of jJ was obtained.

This unoriented film is then introduced into a stenter and at a temperature of 1
Stretched 3.7 times (transversely) at 45°C.Subsequently stretched at 135°C.
The film was heated to 163°C using a roll heated to 900°C and a non-contact infrared heater heated to a surface temperature of 900°C.
It was longitudinally stretched twice. Thereafter, the biaxially stretched PEN films of Example 1 and Example 2 were obtained by introducing the film into a stenter again and heat-treating it under the conditions shown in Table 1. Table 1 shows the stretching conditions and film properties.

(Example 3.4) Example 3 and Example 4 were carried out in the same manner as in Example 1 except that the transverse stretching conditions and longitudinal stretching conditions were as shown in Table 1.
A biaxially stretched PEN film was obtained.

Table 1 shows the stretching conditions and film properties.

(Comparative Examples 1 and 2) Biaxially stretched PEN films were produced in the same manner as in Example 1 except that the longitudinal stretching conditions were as shown in Table 1. In addition, in Comparative Example 2, a biaxially stretched film could not be obtained because many breaks occurred during longitudinal stretching.

Table 1 shows the stretching conditions and film properties.

(Comparative Examples 3 to 5) Laterally uniaxially stretched films were created under the conditions shown in Table 1 for the lateral stretching conditions. However, these films all had noticeable unevenness and frequent breakage, so longitudinal stretching was omitted. The stretching conditions and film properties are shown in Table 1.

Margin below (Name of the invention) According to the present invention, a biaxially stretched PEN film having a Young's modulus in the longitudinal direction of 800 kg/- or more and a Young's modulus in the transverse direction of 550 kg/- or more is produced by a simple method called the horizontal and longitudinal stretching method. It can be seen that this method is extremely useful for applications such as base films for magnetic recording tapes, since it is possible to produce a PEN film having a high elastic modulus at low cost.

Claims (1)

[Claims] In a method for producing a biaxially oriented film by first stretching a substantially unoriented polyethylene-2,6-naphthalate film in the transverse direction, then stretching it in the longitudinal direction by a difference in circumferential speed between rolls, and then heat-treating the film, the method comprises: The horizontal extension of the stage is 130 to 19
The film is stretched 3.0 to 6.0 times at a temperature of 0°C to make the birefringence in the film width direction and thickness direction within the range of 0.2 to 0.32, and the second stage longitudinal stretching is performed at the stretching roll temperature. is below the low-temperature crystallization start temperature of the film after horizontal stretching, and using a non-contact heating device, the film temperature is adjusted to the main dispersion peak temperature of the film after horizontal stretching (
A method for producing a biaxially oriented polyethylene-2,6-naphthalate film, which comprises stretching at a temperature of Tα) or higher and lower than Tα+40° C. at a stretching ratio of 4.5 times or higher.