JPH07106599B2 - Stretch molding method for polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a stretch-molding method for a polyester film, and more particularly to producing a biaxially-stretched polyester film, particularly an asymmetrically-oriented biaxially-stretched polyester film having increased strength in the machine direction. It is intended to provide a production method which is excellent in film formation stability when performing.

(Prior Art) A biaxially stretched film made of a polyester resin such as polyethylene terephthalate is excellent in various properties such as thermal stability, dimensional stability and mechanical strength. However, as the VCR becomes smaller and lighter, it has become necessary to further thin the base film for magnetic tape. Then, in order to satisfy this requirement, conventionally, a re-longitudinal stretching method for increasing the strength in the longitudinal direction by stretching the biaxially oriented film obtained by stretching in the longitudinal direction and the transverse direction in the longitudinal direction, that is, the running direction, Further, a transverse / longitudinal stretching method has been adopted in which transverse stretching is first performed and then longitudinal stretching is performed.

(Problems to be Solved by the Invention) However, the conventional re-longitudinal stretching method and the transverse / longitudinal stretching method are both poor in film stability of the film, and particularly thin films such as 8 mm video base film, and When forming a film that is required to have a high strength in a certain direction, there is a problem that productivity is significantly reduced and quality unevenness due to process instability is large. That is, in the re-longitudinal stretching method, the film is stretched in the machine direction and the transverse direction to significantly advance the orientation and crystallization, and the film whose main orientation direction is the transverse direction is stretched in the longitudinal direction again to align the molecular chains. Since the direction is returned to the longitudinal direction, there has been a problem that a large amount of energy is required for the stretching and the film is easily broken. Further, in the transverse / longitudinal stretching method, since a wide film once stretched in the transverse direction is stretched in the longitudinal direction at a high ratio,
There is a problem that film breakage is likely to occur during the stretching in the machine direction, and the quality of the film is large because the process is unstable.

The present invention is intended to improve operational stability when producing a biaxially stretched film having increased strength in the machine direction.

(Means for Solving the Problems) A biaxially oriented film in which a substantially unoriented film mainly composed of polyethylene terephthalate is sequentially stretched 2.5 to 5.0 times at a temperature of 80 to 130 ° C. in the transverse direction and the longitudinal direction in this order. Then, the film is re-stretched 1.05 to 2.0 times in the longitudinal direction at a temperature of 100 to 180 ° C and heat set at 160 to 240 ° C.

The substantially non-oriented film mainly composed of polyethylene terephthalate is a raw material of a polymer, a copolymer or a mixture thereof, in which 80 mol% or more of the molecular constitution is composed of polyethylene terephthalate units. In the polymer, internal particles and external particles known as a lubricant,
It may also contain stabilizers such as phosphoric acid, phosphorous acid and their esters. And in this invention,
A substantially unoriented unstretched film obtained by melt-extruding the above polyethylene terephthalate raw material by a usual method and cooling and solidifying is used.

In the present invention, the above-mentioned unoriented film is stretched in the transverse direction and then transversely / longitudinally stretched in the longitudinal direction to obtain a biaxially oriented film. The stretching ratio in this case is set to 2.5 to 5.0 times at a temperature of 80 to 130 ° C. in both the transverse direction and the longitudinal direction, but the stretching ratio is slightly different between the transverse direction and the longitudinal direction, and the transverse direction is 80 to 130 ° C. Stretched 2.5 to 4.0 times at 100 ℃, 90 in the machine direction
It is preferable to stretch at a temperature of 130 ° C. to 3.0 to 5.0 times.

In this invention, the biaxially oriented film obtained by the above-mentioned transverse / longitudinal stretching is re-stretched in the longitudinal direction, and the stretching ratio at this time is 1.05 to 2.0 times at a temperature of 100 to 180 ° C., It is preferably set to 1.05 to 1.50 times under a temperature of 120 to 160 ° C. Then, the film re-stretched in the machine direction is heat-treated at a temperature of 160 to 240 ° C., preferably 200 to 220 ° C. for heat setting. The processing time is preferably 2 to 3 seconds. This heat treatment is performed by holding both ends in the length direction of the re-stretched film with clips, but it may be in a relaxed state in the width direction.

(Operation) In this invention, the biaxially stretched film obtained by the transverse / longitudinal stretching method and selectively oriented in the longitudinal direction is continuously re-stretched in the longitudinal direction. In other words, the longitudinal stretching in the conventional transverse / longitudinal stretching method is performed twice. Therefore, the stretching conditions of longitudinal and transverse re-longitudinal stretching are relaxed, and even if the total stretching ratio is set to the same ratio as the conventional one, the film breakage is eliminated and the operation is stable. You can measure the high strength of.

However, if the temperature for transverse / longitudinal stretching is less than 80 ° C, the stress required for stretching will increase significantly and the film will rupture.
If the temperature exceeds 130 ° C, the film will break due to crystallization that occurs during preheating, and the stretching ratio for the above-mentioned transverse and longitudinal stretching will be
If it is less than 2.5 times, good uniformity of thickness cannot be obtained,
On the other hand, when it exceeds 5.0 times, the stress required for stretching remarkably increases and the film breaks. Then, when the conditions of the transverse stretching and the longitudinal stretching are different, the transverse stretching is performed at a temperature of 80 to 100 ° C and a stretching ratio of 2.5 to 4.0 times, and the longitudinal stretching is performed at a temperature of 90 to 130 ° C and a stretching ratio of 3.0 to 5.0 times. Improves the stability of film formation and the uniformity of thickness.

When the re-stretching temperature is lower than 100 ° C, the stress required for stretching remarkably increases and the uniformity of thickness is reduced.
If it exceeds 180 ° C, the mechanical properties cannot be improved and the thickness uniformity is impaired. When the stretching ratio in the re-longitudinal stretching is less than 1.05 times, the desired improvement in mechanical properties cannot be obtained. On the contrary, when the stretching ratio exceeds 1.50 times, the stretching stress remarkably increases and the film breaks.

Also, when the heat treatment temperature during heat setting is less than 160 ° C, the thermal stability becomes insufficient, and conversely, when it exceeds 240 ° C,
The crystallinity increases remarkably and the abrasion resistance of the film decreases, making it unsuitable for magnetic tape.

After the heat-setting treatment, the film is heated to a temperature of 80 to 130 ° C, preferably 90 to 120 ° C in the longitudinal direction.
The dimensional stability can be further improved by performing the relaxation treatment of 0.1 to 1%.

(Example) After sufficiently drying pellets of polyethylene terephthalate having an intrinsic viscosity of 0.60, the pellets were supplied to an extruder and melt-extruded at a temperature of 280 ° C, which was cooled and solidified by contacting with a drum cooled to a temperature of 30 ° C. An unoriented film having a thickness of 160 μm was obtained.
Next, this unoriented film was stretched 3.2 times in the transverse direction at a temperature of 90 ° C. and then stretched 4.5 times in the longitudinal direction at a temperature of 95 ° C. to obtain a biaxially oriented film. Then, this biaxially oriented film was subjected to re-longitudinal stretching at a temperature of 130 ° C. in the longitudinal direction by changing the stretching ratio to four types within the range of 1.1 to 1.3, and at 210 ° C.
After heat setting for 2 seconds, cool and wind the film,
The high strength films (thickness 9 to 10 μm) of Examples 1 to 4 were obtained.

On the other hand, a thickness of 160 obtained in the same manner as in Examples 1 to 4 above.
A film of Comparative Example 1 (final thickness 10 μm) was produced by subjecting the μ-unoriented film to transverse and longitudinal stretching by a conventional method. That is, the unoriented polyethylene terephthalate film was stretched 3.2 times in the transverse direction at a temperature of 90 ° C., and then stretched 4.8 times in the longitudinal direction at 95 ° C. to obtain a biaxially oriented film.
After heat setting at 2 ° C. for 2 seconds, it was cooled and wound. Further, a film of Comparative Example 2 was produced in the same manner as Comparative Example 1 except that the longitudinal stretching ratio of Comparative Example 1 was changed to 5.2 times, and the transverse stretching ratio of Comparative Example 1 was further increased to 2.8 times and the longitudinal stretching was performed. A film of Comparative Example 3 was produced under the same conditions as in Comparative Example 1 except that the temperature was changed to 100 ° C., but in Comparative Examples 2 and 3, the film broke during film formation, and a final product could be obtained. There wasn't.

The production conditions and performances of the above Examples 1 to 4 and Comparative Examples 1 to 3 are shown in the table below. The stress at 5% elongation and heat shrinkage in the table are MD in the film length direction and in the width direction.
Represented by TD, the numerical value is cut in parallel with the film length direction and width direction to obtain a strip sample with a width of 10 mm and a length of 150 mm and using Tensilon manufactured by Toyo Baldwin Co., Ltd. under a deformation rate of 100% / min. The tensile test was carried out and calculated by the usual method. Regarding the heat shrinkage, a strip sample with the same shape as that used in the tensile test was used, left in a gear oven held at a temperature of 105 ° C in a non-tensioned state for heat treatment, and taken out after 30 minutes. Was calculated from the sample length before and after the treatment.

As is clear by comparing Examples 1 to 4 in the above table, the larger the re-longitudinal stretching ratio is set, the more the MD direction (longitudinal direction) becomes 5.
% The stress increases during elongation. That is, the vertical strength is improved. Then, Example 1 in which the total longitudinal stretching ratio is set equal to that of Comparative Example 1 exhibits the same strength as that of Comparative Example 1. Moreover, in Comparative Examples 2 and 3, since the longitudinal stretching ratio was larger than that in Comparative Example 1, many breakages occurred during film formation, and no products were obtained. Although the magnification was about the same as or higher than that of Comparative Examples 2 and 3, there was little film breakage during film formation, and a high-strength film could be commercialized.

(Effect of the Invention) The present invention is characterized in that, when stretch-molding a polyethylene terephthalate film, transverse-longitudinal stretching is followed by re-longitudinal stretching.
In addition, it specifies the conditions and is equivalent to performing the longitudinal stretching of the conventional method of transverse / longitudinal stretching in two steps. The total longitudinal stretching ratio is set to be larger than that of the conventional method to achieve higher strength than ever. A film is obtained, moreover, breakage during film formation by stretch molding is significantly reduced, smooth operation is possible, and product quality is made uniform.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuro Kuze 10-24 Toyo-cho, Tsuruga City, Fukui Prefecture Toyobo Co., Ltd. General Research Laboratory Tsuruga Branch Office (56) Reference JP-A-58-124617 (JP, A) ) JP-A-59-48124 (JP, A) JP-A-50-8869 (JP, A) JP-A-58-205735 (JP, A) JP-A-59-48125 (JP, A) US Patent 3261903 (US , A)

Claims (1)

[Claims] 1. A substantially non-oriented film mainly composed of polyethylene terephthalate having a thickness of 80 to 80 in the horizontal and vertical directions.
Sequentially stretched 2.5 to 5.0 times at a temperature of 130 ° C to form a biaxially oriented film, and then 1.05 to 2.at a temperature of 100 to 180 ° C in the machine direction.
A stretch-molding method for a polyester film, which comprises re-stretching to 0 times and heat-setting at 160 to 240 ° C.