KR0140298B1 - Process for preparing biaxially oriented polyester film - Google Patents

Abstract

The present invention relates to a method for producing a biaxially oriented polyester film having excellent thickness uniformity, and specifically, a biaxially oriented polyester comprising melt extruding a polyester resin and stretching an unstretched sheet in a longitudinal direction and a transverse direction. In the method for producing a film, in the stretching step, two-stage longitudinal stretching of 3.5 times or more the total longitudinal stretching ratio is performed, and the first stage longitudinal stretching is performed such that the crystallization energy of the first longitudinal stretching sheet is 20 J / g or more. The second stage longitudinal stretching is performed at a draw ratio of 2.0 to 3.0 times in the range of a temperature of 95 to 140c, and then transversely stretched to a draw ratio of 3.5 to 5.0 times.

Description

Manufacturing method of biaxially oriented polyester film

1 is a schematic view of a two-stage longitudinal drawing apparatus of a polyester film according to one aspect of the present invention.

The present invention relates to a method for producing a biaxially oriented polyester film having excellent thickness uniformity.

The polyester film has excellent mechanical strength, heat resistance, electrical insulation, and chemical resistance, and its use has been increased for magnetic recording media, food packaging, and electrical insulators. In particular, the polyester film is excellent in mechanical strength and heat resistance, and its utilization value is very high as a base film in the manufacture of video tape and audio tape computer tape. Therefore, the thickness uniformity of the polyester film occupies a very important position in the cardinal level of the current magnetic recording and reproducing apparatus requiring high magnetic recording density and high smoothness.

In the conventional method for producing a polyester film, the polyester monomers are polymerized under predetermined reaction conditions such as a predetermined pressure, temperature, and catalyst to obtain a polyester polymer intermediate product (chip or granule), so that the moisture content is below a certain level. The method for producing a biaxially stretched polyester film, which is dried to a swarm, melt-extruded in an extruder and passed through a die to obtain an unstretched sheet, then stretches in the longitudinal direction and stretches in the transverse direction, is disclosed in Japanese Patent Office 30-5639. In addition, a method of improving the strength and thickness uniformity of a film by uniaxially or biaxially redrawing again after a biaxial stretching process is disclosed in Japanese Patent Laid-Open No. 54-8672.

On the other hand, it is a well-known fact that the longitudinal stretching process of primary stretching an unstretched sheet has an important influence on the thickness uniformity of a final biaxially oriented film. Conventionally, in the longitudinal drawing process, the longitudinal stretching sheet could not be longitudinally stretched at a sufficient high magnification so that the thickness of the longitudinal stretching sheet was uniform, and even if the high longitudinal longitudinal stretching was performed, the width shrinkage was increased due to excessive orientation crystallization, so that the longitudinal stretching sheet had poor thickness at both ends. However, there was a limit in producing a polyester film having a good thickness due to breakage and uneven stretching in the lateral stretching process. Therefore, in consideration of the thickness uniformity of the biaxially oriented film as well as the stability of the lateral stretching process, a method of longitudinally stretching the film as high as possible while suppressing the orientation crystal to the maximum has been desired.

Therefore, in recent years, in order to improve the thickness uniformity of the film compared with the conventional stretching method, the longitudinal multi-stage stretching method has emerged. For example, Japanese Unexamined Patent Publications 48-43772, 50-75, 50-139872, 49-42277, 54-56674, 58-78729, 58-160123, 60-61233 -36851 and the like describe a longitudinal multistage stretching method. However, these methods cause the inefficiency of the longitudinal stretching apparatus as well as the reduction in thickness uniformity by repeating the cooling and the temperature raising process in the middle of the stepwise stretching. In addition, the longitudinal multistage stretching method described in USP 4,370,290, 4,497,865 and Japanese Patent Laid-Open No. 58-118220 is characterized by the specification of the birefringence of each stage or the limitation of the stretching temperature and the stretching ratio as components of the invention. There is an ambiguous point to realize amorphous high magnification longitudinal stretching, a key technology.

Accordingly, an object of the present invention is to provide a method for producing a biaxially oriented polyester film which solves the above-mentioned disadvantages of the prior art and improves thickness uniformity.

In the manufacturing method of the biaxially oriented polyester film comprising the step of melt extrusion of the polyester resin of the present invention and stretching the back side sheet in the longitudinal and transverse directions to achieve the above object, the total longitudinal draw ratio in the stretching step 3.5 times or more two-stage longitudinal stretching, but the first stage longitudinal stretching is performed so that the crystallization energy of the first stage longitudinal stretching sheet is 20 J / g or more, the stretching ratio of 2.0 to 3.0 times in the longitudinal stretching temperature range of 95 to 140c Provided is a method for producing a biaxially oriented polyester film, wherein the longitudinal stretching is performed and laterally stretched at a draw ratio of 3.5 to 5.0 times.

According to the method of the present invention, the first stage longitudinal drawing is performed such that the thickness uniformity of the longitudinal drawing sheet is improved by high magnification stretching of 3.5 times or more, and the crystallization energy of the first longitudinal drawing sheet is 20 J / g or more. In addition, by performing the second stage longitudinal stretching at the stretching ratio of 2.0 to 3.0 times at the stretching temperature of 95 to 140c, the width shrinkage of the longitudinal stretching sheet is reduced and the orientation determination is less progressed, and then the transverse stretching is performed at the stretching ratio of 3.5 to 5.0 times. Since breaking and uneven stretching in the redrawing process are reduced, ultimately, the thickness of the polyester film becomes uniform in the width direction and the longitudinal direction.

Herein, the crystallization energy of the longitudinal stretch sheet of 20 J / g or more means that the energy generated in the crystallization process is above a certain level, and that the energy generated in the crystallization process is above a certain level. It implies that the alignment of sheets is below a certain level. In addition, the longitudinal stretching temperature refers to the surface temperature of the stretching roll.

In the present invention, the first stage longitudinal stretching such that the crystallization energy of the first stage longitudinal stretching sheet is 20 J / g or more is performed by the combination of the first stage stretching temperature and the stretching ratio, and is not limited to any specific stretching temperature and the stretching ratio. No.

In the longitudinal drawing process, the circumferential speed ratio of each drawing step roll is the longitudinal drawing ratio of each step, and the product of the longitudinal drawing ratios of each step is defined as the total longitudinal drawing ratio. When the crystallization energy of the first end longitudinal drawing sheet is less than 20 J / g, since the orientation crystals are generated in the first end longitudinal drawing process, the width shrinkage of the first end and the second end longitudinal drawing sheets increases. In addition, the specific gravity of the first stage longitudinal drawing sheet is 1.35 or less, but when it is larger than this, there is a problem in that stretching is impossible in the lateral stretching process and breakage occurs.

When the second stage longitudinal stretching conditions performed in the stretching temperature range of 95 to 140c and the stretching ratio of 2.0 to 3.0 are not satisfied, not only the width shrinkage of the longitudinal stretching sheet becomes large, but also the thickness of the longitudinal stretching sheet becomes poor and the transverse stretching process is performed. Breaking and non-uniform stretching are caused at. On the other hand, if the two-stage longitudinal drawing conditions are not satisfied, problems arise that the total longitudinal drawing ratio is 3.5 times or more and the crystallization energy cannot be more than 20 J / g in the longitudinal drawing process.

Moreover, after longitudinal stretch, when lateral stretch ratio is less than 3.5, the uniformity of a film will fall, and when larger than 5.0, there exists a problem that fracturing | rupture of lateral stretch process is frequent.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of a two-stage longitudinal drawing apparatus of a polyester film according to one aspect of the present invention. In Figure 1, rolls 1-7 are preheat rolls, roll 8 is a first-stretch drawing roll, roll 9 is a second roll chamber, rolls 10-11 are cooling rolls, and 8 ', 9', 10 'are rolls. Is roll roll. After pre-heating the polyester unstretched sheet (F) through the rolls 1 to 7, the first stage stretching is performed by the circumferential speed difference between the rolls 8 and 9, and the rolls between the rolls 9 and 10 A longitudinal drawing sheet (F ') is produced by two-step drawing.

As described above, the longitudinally stretched sheet (F ') is transversely stretched by 3.5 to 5.0 times the stretch paper in a conventional transverse stretching apparatus to produce the biaxially oriented polyester film of the present invention.

Hereinafter, examples of the present invention will be described. However, these are provided only to assist in understanding the present invention, and the present invention is not limited by these examples.

Example 1

A polyester chip with an intrinsic viscosity of 0.63 dl / g was melt-extruded through a die at a sheet forming speed of 70 m / min at 280c to obtain an undrawn sheet. In the longitudinal drawing apparatus of FIG. 1, roll temperatures 100c, 1-3 roll temperatures 120c, 4-7 roll temperatures 120c, 8-9 roll temperatures 125c, and 10-11 roll temperatures 20c, and the undrawn sheets 8 and 9 After stretching 2.0 times first stage longitudinally between rolls, 1.8 times second stage longitudinally between 9th and 10th rolls, longitudinally stretching sheet is transversely stretched to 4.3 times the lateral stretching ratio, and then heat-setting by the conventional method. A biaxially oriented polyester film having a thickness of 14 was obtained.

Example 2

In Example 1, the sheet forming speed was 77.5 m / min, the roll temperature 8 was 120c in the longitudinal drawing apparatus of FIG. 1, the first stage longitudinal draw ratio 1.8 times, the second stage longitudinal draw ratio 2.1 times, and the lateral stretch ratio. It carried out similarly to Example 1 except having set to 3.78 times.

Example 3

In Example 1, the sheet forming speed was 52.5 m / min, the roll temperature No. 9 was 130c in the longitudinal drawing apparatus of FIG. 1, the first stage longitudinal draw ratio 2.0 times, the second stage longitudinal draw ratio 2.4 times the transverse stretch ratio 4.8 It carried out similarly to Example 1 except having doubled.

Comparative Example 1

In Example 1, the roll temperature of 1-7 in the longitudinal drawing apparatus of FIG. 1 is set to 90c, the 8th roll temperature is 110c, and the 9-11 roll temperature is 20c, The same procedure as in Example 1 was carried out except that the one-step longitudinal drawing ratio was increased to 4.0 times.

Comparative Example 2

In Example 1, the sheet forming speed was set at 77.8 m / min, the roll stretching apparatus of FIG. 1 was set at 4-7 roll temperature at 100c, 8 roll temperature at 105c, 9 roll temperature at 110c, and the first stage. The same procedure was followed as in Example 1 except that the longitudinal draw ratio was 1.8 times and the second stage longitudinal draw ratio was 1.8 times.

Comparative Example 3

In Example 1, in the longitudinal stretching apparatus of FIG. 1, the roll temperature of 1-7 is 90c, the roll temperature of 8 is 120c, the roll temperature of 9 is 150c, the first stage longitudinal draw ratio is 2.0 times and the second stage longitudinal The same procedure as in Example 1 was conducted except that the mystery was 2.0 times higher.

Comparative Example 4

In Example 1, the sheet forming speed was 52.5 m / min, the roll stretching apparatus of FIG. 1 was set to 4-7 roll temperature 110c, 8 roll temperature 110c, 9 roll temperature 120c, and the first stage. The same procedure was followed as in Example 1 except that the longitudinal draw ratio was 1.5 times and the second stage longitudinal draw ratio was 3.5 times.

Comparative Example 5

In Example 1, it carried out similarly to Example 1 except having set the sheet | seat forming speed to 82.4 m / min and the lateral stretch ratio to 3.4 times.

Comparative Example 6

In Example 1, it carried out similarly to Example 1 except having set the sheet forming speed to 53.8 m / min, and making lateral draw ratio 5.2 times.

The working conditions of the above examples and comparative examples, the crystallization energy and specific gravity of the longitudinally stretched sheet, the number of breaks in the transverse stretching process, and the thickness uniformity of the finally obtained film were measured and shown in Table 1 below.

Assessment Methods

1. Crystallization Energy

A differential calorimeter (DSC, manufactured by Perkin-Elmer) was used at a sonic temperature of 20 c / min.

2. Specific gravity

Specific gravity of the film was measured by the density gradient tube according to ASTM D1505.

3. Number of breaks

The number of breaks that occurred during the 72 hours transverse stretching process of the polyester film was measured.

4. Thickness uniformity

The thickness was measured at intervals of 20 mm in the lateral direction using a thickness gauge (manufactured by Annitsu Co., Ltd.) and expressed as a thickness deviation that is a difference between the maximum value and the minimum value.

As shown in the above table, the polyester film of Example 1-3 prepared by the manufacturing method of the present invention has better thickness uniformity than the polyester film of Comparative Example 1-6 without using the manufacturing method of the present invention. In addition, it can be seen that the productivity is good because the number of breaks during the transverse stretching process is small.

Therefore, the manufacturing method of the present invention has a high magnetic recording density and a high

It can be used for the production of polyester film suitable as the base film of the video recording and audio, the magnetic recording medium for the computer which requires the smoothness and the high driving stability.

Claims (2)

A method of manufacturing a biaxially oriented polyester film comprising melt extruding a polyester resin and stretching an unstretched sheet in the longitudinal and transverse directions, wherein in the stretching step, two-stage longitudinal stretching of 3.5 times or more the total longitudinal stretch ratio is performed. The first stage longitudinal stretching is carried out so that the crystallization energy of the first stage longitudinal stretching sheet is 20 J / g or more, and the second stage longitudinal stretching is performed at a stretching ratio of 2.0 to 3.0 times in the range of the longitudinal stretching temperature of 95 to 140c. A biaxially oriented polyester film, characterized in that the film is transversely stretched by 5.0 to 5.0 times. The manufacturing method according to claim 1, wherein the specific gravity of the first end edge stretch sheet is 1.35 or less.