KR0140299B1 - 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, specifically, a biaxially oriented polyester comprising the step of applying and extruding a polyester resin and stretching the unstretched sheet in the longitudinal and transverse directions. In the method for producing a film, in the longitudinal drawing step, a three-step longitudinal drawing of 3.5 times or more of the total longitudinal drawing ratio is performed, wherein the crystallization energy of the first and second longitudinal drawing sheets is 20 J / g or more and 15 J /, respectively. The first stage and the second stage longitudinal stretching are performed so as to be more than g, and the third stage longitudinal stretching is performed at a stretching ratio of 1.5 to 2.5 times in the stretching temperature range of 110 to 140 ° C.

Description

Manufacturing method of biaxially oriented polyester film

1 and 2 are schematic diagrams of a three-stage longitudinal drawing apparatus of a polyester film, respectively, 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.

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

As a conventional method for producing a polyester film, when the polyester monomers are synthesized under predetermined reaction conditions such as a constant pressure, temperature, and catalyst to obtain a polyester polymer intermediate product (chip or granule), the moisture content is below a certain level. A method for producing a biaxially stretched polyester film, which is dried up to and then melt-extruded in an extruder and passed through a die to obtain an unstretched sheet, is then stretched in the longitudinal direction and stretched in the transverse direction. Further, a method of improving the strength and thickness uniformity of a film by uniaxially or biaxially redrawing again after the biaxial stretching step 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. Even if the high longitudinal stretching was performed, the width shrinkage was increased due to excessive orientation crystallization, resulting in poor thickness of both ends of the longitudinal stretching sheet. In addition, 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 view of the thickness uniformity of the biaxially oriented film as well as the stability of the lateral stretching step, a method of longitudinally stretching the film at the highest possible magnification while suppressing the orientation determination 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. Further, the longitudinal multistage stretching method described in USP 4,370,291, 4,497,865 and Japanese Patent Laid-Open No. 58-11820 is characterized by specifying the birefringence of each stage or limiting the stretching temperature and the stretching ratio as components of the invention. There is an ambiguous point to realize amorphous high magnification longitudinal stretching, which is a core 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 order to achieve the above object, the present invention provides a method for manufacturing a biaxially oriented polyester film comprising melt extruding a polyester resin and stretching an unstretched sheet in a longitudinal direction and a transverse direction. Perform three-stage longitudinal stretching of at least 3.5 times the longitudinal stretching ratio, and perform the first and second stage longitudinal stretching so that the crystallization energy of the first and second stage longitudinal stretching sheets is 20 J / g or more and 15 J / g or more, respectively. It provides a method for producing a biaxially oriented polyester film, characterized in that to perform three-stage longitudinal stretching in the stretching ratio of 1.5 to 2.5 times in the stretching temperature range 110 to 140 ℃.

According to the method of the present invention, the thickness uniformity of the longitudinal stretch sheet is improved by high magnification stretching of 3.5 times or more, and the crystallization energy of the first and second stage longitudinal stretch sheets is 20 J / g or more and 15, respectively. By performing the first stage and the second stage longitudinal stretching to be J / g or more, and performing the third stage longitudinal stretching at the stretching ratio of 1.5 to 2.5 times in the stretching temperature range of 110 to 140 ° C, the width shrinkage of the longitudinal stretching sheet is reduced and the orientation is performed. As the crystal proceeds less, the fracture and uneven stretching in the subsequent lateral stretching process are reduced, and ultimately the thickness of the polyester film becomes uniform in the width direction and the longitudinal direction.

Herein, the crystallization energy of the longitudinally stretched sheet means energy that is generated during the crystallization process, and the large crystallization energy implies that the longitudinally-oriented sheet has little orientation crystallization. In addition, the stretching temperature means the surface temperature of the stretching roll.

In the present invention, the first stage and the second stage longitudinal drawing so that the crystallization energy of the first stage and the second stage longitudinal drawing sheet are 20 J / g or more and 15 J / g or more, respectively. And is not limited to any particular combination of stretching temperatures and stretching ratios.

In the longitudinal drawing process, the rolling speed ratio of each drawing stage is the longitudinal drawing ratio of each stage, and the product of the longitudinal drawing ratios of each stage is defined as the total longitudinal drawing ratio. If the total longitudinal drawing ratio is less than 3.5 times, the thickness uniformity of the longitudinal drawing sheet is not sufficient. If the crystallization energy of the first stage longitudinal drawing sheet is less than 20 J / g, the orientation crystals are generated in the first stage longitudinal drawing process, and thus the width shrinkage of the second stage and the third stage longitudinal drawing sheet becomes large. In addition, when the crystallization energy of the longitudinal drawing sheet of the second longitudinal drawing sheet is less than 15 J / g, even if the crystallization energy of the first longitudinal drawing sheet is 20 J / g or more, a large number of orientation crystals are generated in the second longitudinal drawing process. Therefore, the width shrinkage of the second and third longitudinal drawing sheets increases. In addition, the specific gravity of the first stage and the second stage longitudinal drawing sheet should be 1.345 or less and 1.355 or less, respectively, if larger than this, there is a problem that fracture occurs in the width shrinkage or transverse stretching process in each subsequent longitudinal drawing process. .

When the third stage longitudinal stretching conditions performed in the stretching temperature range of 110 to 140 ° C. and the stretching ratio of 1.5 to 2.5 times are not satisfied, not only the width of the longitudinal stretching sheet is increased but also the thickness of the longitudinal stretching sheet is poor, so the lateral stretching is performed. Breaking and non-uniform stretching are caused in the process. On the other hand, if the three stage longitudinal drawing conditions are not satisfied, the total longitudinal draw ratio is 3.5 times or more in the longitudinal drawing process, and the crystallization energy of each of the first and second stages is 20 J / g or more and 15 J / g or more. A problem arises that cannot be done.

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

1 and 2 are schematic views of a three-stage longitudinal drawing apparatus of a polyester film, respectively, according to one aspect of the present invention. According to FIG. 1, rolls 1 to 3 are preheat rolls, 4 rolls are 1st stage stretching rolls, 5 rolls are 1st stage cooling rolls, and 6-7 rolls are 2nd stage preheat rolls, 8 rolls. Silver 2nd stage extending | stretching roll, 9th roll is 3rd stage extending | stretching roll, 10-11th roll is 3rd stage cooling roll, and 4 ', 5', 8 ', 9', 10 'are roll. In the case of producing a biaxially oriented polyester film using the three-stage longitudinal drawing apparatus shown in FIG. 1, the polyester unstretched sheet (F) was preheated in rolls 1-3, and then, between rolls 4 and 5. The first stage longitudinal stretching is performed by the circumferential speed of the roll, and after cooling on the roll 5, preheated again on the roll 6-7, the second stage between the rolls 8 and 9, and the number 9 and 10 A third stage longitudinal stretching is performed between the rolls to produce a longitudinal stretch sheet F '.

Also, in FIG. 2, rolls 12-16 are preheat rolls, rolls 17, 18 and 19 are first, second and third stage stretching rolls, and rolls 20-21 are cooling rolls, 17 ', 18', 19 ', and 20' are rules. In the case of using the apparatus shown in FIG. 2, the polyester unstretched sheet (F) is preheated by passing through rolls 12 to 16, and then between rolls 17 and 18, between rolls 18 and 19, and 19 The longitudinal stretch sheet F 'is produced by performing the first stage longitudinal stretching, the second stage longitudinal stretching, and the third stage longitudinal stretching, respectively, by the circumferential speed difference between the rolls between the and No. 20 rolls.

The sheet (F ') longitudinally stretched as mentioned above is transversely stretched by the usual transverse stretching apparatus, and the biaxially-oriented polyester film of this invention is manufactured.

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 having an intrinsic viscosity of 0.63 dl / g was melt-extruded through a die at a sheet forming speed of 60 m / min at 280 ° C. to obtain an undrawn sheet. In the longitudinal drawing apparatus of FIG. 1, the roll temperature of 1-3 roll temperature 100 ° C, roll 4 temperature 120 ° C, roll 5 temperature 30 ° C, roll 6-7 roll temperature 110 ° C, roll 8-9 roll temperature 125 ° C, 10- No. 11 roll temperature is 20 ° C. and the unstretched sheet is 2.0 times first stage longitudinal stretch between 4th and 5th rolls, 1.5 times second stage longitudinal stretch between 8th and 9th rolls, 9th and 10th After 1.5 times 3rd stage longitudinal stretch between rolls, the longitudinal stretch sheet was lateral stretched and heat-set in the usual way, and the biaxially-oriented polyester film which is 14 micrometers in thickness was obtained.

Example 2

In Example 1, the sheet forming speed is 55.6 m / min, the fourth roll temperature is 115 ° C., the first stage longitudinal draw ratio is 1.5 times, the second stage longitudinal draw ratio is 1.8 times, and the third stage longitudinal draw ratio is 1.8 times. Except that except for the same as in Example 1.

Example 3

In Example 1, the sheet forming speed was 50 m / min, the fourth roll temperature was 115 ° C, the ninth roll temperature was 130 ° C, the first stage longitudinal draw ratio was 1.5 times, the second stage longitudinal draw ratio was 1.8 times, The same procedure as in Example 1 was conducted except that the third stage longitudinal drawing ratio was 2.0 times.

Comparative Example 1

In Example 1, except that the 4-7 roll temperature is stretched to 100 ° C., the 8 roll temperature is 110 ° C., and the 9-11 roll temperature is 20 ° C., between the 8th and 9th rolls, at 4.5 times the longitudinal draw ratio. Was carried out in the same manner as in Example 1.

Comparative Example 2

In Example 1, the roll temperature of 4-7 is 100 ° C, the roll temperature of 8 is 110 ° C, the roll temperature of 9-11 is 20 ° C, between rolls 8 and 9 and between rolls 9 and 10 Was carried out in the same manner as in Example 1 except that the stretching ratio was 3.0 times and 1.5 times respectively.

Comparative Example 3

In Example 1, the sheet forming speed was 82.3 m / min, the fourth roll temperature was 100 ° C, the eighth roll temperature was 105 ° C, the nineth roll temperature was 110 ° C, the first stage longitudinal draw ratio was 1.3 times, The same procedure as in Example 1 was carried out except that the second stage longitudinal draw ratio was 1.4 times and the third stage longitudinal draw ratio was 1.8 times.

Comparative Example 4

In Example 1, the fourth roll temperature was 100 ° C, the eighth roll temperature was 110 ° C, the nineth roll temperature was 115 ° C, the first stage longitudinal draw ratio was 2.0 times, the second stage longitudinal draw ratio was 1.5 times, and the third stage. It carried out similarly to Example 1 except having made 1.5 times the longitudinal stretch ratios.

Comparative Example 5

In Example 1, the sheet forming speed was 50 m / min, except that the first stage longitudinal draw ratio was 1.5 times, the second stage longitudinal draw ratio was 1.2 times, and the third stage longitudinal draw ratio was 3.0 times. It was done.

Comparative Example 6

In Example 1, the sheet forming speed was 50 m / min, the eighth roll temperature was 120 ° C, the ninth roll temperature was 100 ° C, the first stage longitudinal draw ratio was 1.5 times, the second stage longitudinal draw ratio was 1.5 times, It carried out similarly to Example 1 except having set the 3rd stage longitudinal stretch ratio to 2.4 times.

Comparative Example 7

In Example 1, the sheet forming speed was 50 m / min, the eighth roll temperature was 120 ° C, the ninth roll temperature was 150 ° C, the first stage longitudinal draw ratio was 1.5 times, the second stage longitudinal draw ratio was 1.5 times, It carried out similarly to Example 1 except having set the 3rd stage longitudinal stretch ratio to 2.4 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

Using a differential calorimeter (DSC, manufactured by Perkin-Elmer), the temperature was measured at a temperature increase rate of 20 ° C / min.

2.weight

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 produced by the manufacturing method of the present invention of the present invention has a uniform thickness than the polyester film of Comparative Example 1-7, which is not according to the manufacturing method of the present invention. It can be seen that the productivity is good because the number of breaks during the transverse stretching process is excellent.

Therefore, the manufacturing method of the present invention can be used for the production of polyester film suitable as a base film of video recording, audio recording, and computer magnetic recording media requiring high magnetic recording density, high smoothness and high driving stability.

Claims (2)

In the method of producing a biaxially oriented polyester film comprising the step of application extrusion of the polyester resin and stretching the unstretched sheet in the longitudinal and transverse directions, at least three times the total longitudinal stretching ratio of 3.5 times in the longitudinal stretching step Stretching is carried out, but the first stage and the second stage longitudinal stretching are performed so that the crystallization energy of the first stage and the second stage longitudinal drawing sheet is 20 J / g or more and 15 J / g or more, respectively, and the stretching temperature is 110 to 140 ° C. A third stage longitudinal stretching is performed in the stretching ratio in the range of 1.5 to 2.5 times in the range, the method for producing a biaxially oriented polyester film. And the specific gravity of the first end and second end longitudinal drawing sheets is 1.345 or less and 1.355 or less, respectively.