KR0140310B1 - 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 melt extruding a polyester resin and stretching the unstretched sheet in the longitudinal and transverse directions. In the method for producing a film, the stretching step is a longitudinal stretching of at least 3.5 times the total longitudinal stretching ratio, but after performing three or more stages of multistage longitudinal stretching so that the crystallization energy of the longitudinal stretching sheet is 10 J / g or more, the stretching ratio is 3.5 to 4.5 times It relates to a method characterized by transverse stretching.

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 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, 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.

In the conventional method for producing a polyester film, when the polyester monomers are polymerized 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 stretched in the longitudinal direction and stretched in the transverse direction, is disclosed in Japanese Patent Application No. 30-5639. Moreover, the method of improving the intensity | strength and thickness uniformity of a film by uniaxially or biaxially redrawing again after a biaxial stretching process is disclosed by Unexamined-Japanese-Patent No. 54-8672.

On the other hand, it is a well-known fact that the longitudinal stretching process of primary stretching the unstretched sheet has a significant influence on the thickness uniformity of the final biaxially oriented film. Conventionally, it was not possible to longitudinally stretch at a high magnification enough to uniformly lengthen the longitudinally stretched sheet in the longitudinal stretching process, and even when high magnification longitudinally stretched, the width shrinkage was increased due to excessive orientation crystallization, resulting in poor thickness at both ends of the longitudinally stretched sheet. In addition to breakage and uneven stretching in the transverse stretching process, there was a limit to producing a polyester film of good thickness. Accordingly, in view 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 Patent Offices 48-43772, 50-75, 50-139872, 49-42277, 54-56674, 58-78729, 58-160123, 60-61233, and Japanese Command Offices 57-48377, 57-49377, 59 A longitudinal multistage stretching method is described in -36851 and the like. 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 4,370,291, 4,497,865 and Japanese Patent Laid-Open No. 58-118220 is characterized by 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, 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 is a method for producing a biaxially oriented polyester film comprising the step of melt-extruding a polyester resin and stretching the unstretched sheet in the longitudinal and transverse directions, wherein the stretching step is the total longitudinal draw ratio Production of biaxially oriented polyester film, characterized in that the longitudinal stretching is performed at 3.5 times or more, but the three or more stages of multi-stage longitudinal stretching are carried out so that the crystallization energy of the longitudinal stretching sheet is 10 J / g or more, and laterally stretched at a draw ratio of 3.5 to 4.5 times. Provide a method.

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 in total longitudinal stretch ratio, and three or more stages of multi-stage longitudinal stretching are performed so that the crystallization energy of the longitudinal stretch sheet is 10 J / g or more. This decreases the width shrinkage of the longitudinal stretch sheet and promotes less orientation determination, and ultimately results in the reduction of rupture and uneven stretching in the transverse stretching process by the transverse stretching in the range of 3.5 to 4.5 times the transverse stretching ratio. The thickness becomes uniform in the width direction and the longitudinal direction.

Herein, the crystallization energy of the longitudinally stretched sheet of 10 J / g or more means that the energy generated during the crystallization process is above a certain level, which implies that the orientation of the longitudinally stretched sheet is below a certain level. .

In the present invention, the multi-stage longitudinal stretching of three or more stages in which the crystallization energy of the longitudinal stretching sheet is 10 J / g or more is performed by the combination of the stretching temperature in each stage and the stretching ratio in each stage, and is not limited to any specific stretching temperature and the combination of the stretching ratios. .

In the longitudinal drawing process, the main speed ratio of each drawing stage roll is the longitudinal drawing ratio of each stage, and the product of the longitudinal drawing ratio 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 longitudinally stretched sheet is less than 10 J / g, many orientation crystals are generated in the longitudinally stretched process, so that the longitudinal shrinkage of the longitudinally stretched sheet is increased, and subsequent lateral stretching process involves breakage and uneven stretching. In addition, the specific gravity of the longitudinally stretched sheet is 1.36 or less, but when it is larger than this, there is a problem that a draw failure and fracture occurs in the transverse stretching process. On the other hand, when the multi-stage longitudinal drawing conditions of three or more stages are not satisfied, problems arise in that the total longitudinal drawing ratio is 3.5 times or more and the crystallization energy cannot be 10 J / g or more in the longitudinal drawing process.

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

1 and 2 are schematic views of a 33 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. The silver second stage stretching roll, the 9th roll is a 3rd stage extending roll, the 10-11 roll is a 3rd stage cooling roll, and the 4 ', 5', 8 ', 9', and 10 'roll are roll rolls. When manufacturing 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 3rd step is performed between rolls and a longitudinal stretch sheet | seat F 'is manufactured.

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, Rolls 17 ', 18', 19 'and 20' are rolls. When 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 the 20th rolls.

The longitudinally stretched sheet F 'as described above is laterally stretched at a draw ratio of 3.5 to 4.5 times in a conventional transverse stretching apparatus, and then heat-set by a conventional method to prepare a biaxially oriented polyester film of the present invention.

Hereinafter, the present invention will be described in detail with reference to Examples, but these Examples are provided only to assist in understanding the present invention, but the present invention is not limited thereto.

Example 1

A polyester chip having an intrinsic viscosity of 0.63 dI / g was melt-extruded through a die at 280 ° C. at a sheet forming rate of 60 m / min to obtain an undrawn sheet. In the longitudinal drawing apparatus of FIG. 1, the roll temperature of 1-3 roll is 100 ° C, the roll number 4 is 120 ° C, the roll number 5 is 30 ° C, the roll number 6-7 is 110 ° C, and the roll temperature 8-9 is set. 125 ° C. and 10-11 roll temperature at 20 ° C., and the unstretched sheet was first stretched 2.0 times between 4 and 5 rolls, and 1st stage stretched between 1.5 and 8 rolls. After stretching and stretching the third stage longitudinally by 1.5 times between rolls 9 and 10, the longitudinally stretched sheet is transversely stretched by 4.0 times the lateral draw ratio, and then heat-set by a conventional method to produce a biaxially oriented polyester having a thickness of 14 μm. A film was obtained.

Example 2

In Example 1, the sheet forming speed was 61.7 m / min, the fourth roll temperature was 115 ° C and the 8-9 roll temperature was 125 ° C, and the first stage longitudinal draw ratio was 1.5 in the longitudinal drawing device of FIG. The same procedure as in Example 14 was carried out except that the vessel was subjected to 1.8 times the second stage longitudinal draw ratio, 1.8 times the third stage longitudinal draw ratio, and 3.6 times the lateral stretch ratio.

Example 3

In Example 1, the sheet forming speed was 45.5 m / min, the fourth roll temperature was 115 deg. C, the eighth roll temperature was 125 deg. C, and the nine roll temperature was 130 deg. The same procedure as in Example 1 was performed except that the first stage longitudinal draw ratio was 1.5 times, the second stage longitudinal draw ratio was 1.8 times, the third stage longitudinal draw ratio was 2.0 times, and the lateral stretch ratio was 4.4 times.

Comparative Example 1

In Example 1, the roll temperature of 4-7 in the longitudinal stretching apparatus of FIG. 1 is 100 ° C, the roll temperature of 8 is 110 ° C, and the roll temperature of 9-11 is 20 ° C, between rolls 8 and 9. Was carried out in the same manner as in Example 1 except that the longitudinal draw ratio was 4.5 times and the longitudinal draw ratio was increased by 4.5 times.

Comparative Example 2

In Example 1, the roll temperature of 4-7 in the longitudinal drawing apparatus of FIG. 1 is 100 ° C, the roll temperature of 8-9 is 110 ° 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 two-stage longitudinal stretching at 3.0 and 1.5 times the longitudinal draw ratio, respectively.

Comparative Example 3

In Example 1, the sheet forming speed was set to 82 m / min, the fourth roll temperature was 100 deg. C, the eighth roll temperature was 105 deg. C, the nineth roll temperature was 110 deg. The same procedure was followed as in Example 1 except that the first stage longitudinal draw ratio was 1.3 times, 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 4th roll temperature in the longitudinal drawing apparatus of FIG. 1 is 100 degreeC, the 8th roll temperature is 110 degreeC, and the 9th roll temperature is 115 degreeC, and the 1st stage longitudinal stretch ratio is 2.0 times, 2nd However, it carried out similarly to Example 1 except having made 1.5 times the longitudinal stretch ratio and 1.5 times the 3rd stage longitudinal stretch ratio.

Comparative Example 5

In Example 1, the sheet forming speed was 56.5 m / min, the fourth roll temperature was 100 ° C, the 8-9 roll temperature was 125 ° C, and the first stage longitudinal draw ratio was 2.5 in the longitudinal drawing device of FIG. The same procedure as in Example 1 was carried out except that the vessel, the second stage longitudinal draw ratio were 1.2 times, and the third stage longitudinal draw ratio was 1.6 times.

Comparative Example 6

In Example 1, the sheet forming speed was 50 m / min, the fourth roll temperature was 100 ° C, the eighth roll temperature was 110 ° C, and the nineth roll temperature was 115 ° C in the longitudinal drawing apparatus of FIG. The same procedure as in Example 1 was conducted except that the first stage longitudinal draw ratio was 1.5 times, the second stage longitudinal draw ratio was 1.8 times, and the third stage longitudinal draw ratio was 2.0 times.

Comparative Example 7

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

Comparative Example 8

In Example 1, it carried out similarly to Example 1 except having set the sheet forming speed to 59.6 m / min, and making lateral draw ratio 4.7 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 final film obtained were measured by the following method and shown in Table 1.

1. Crystallization Energy

The crystallization energy of the longitudinally stretched sheet was measured at a temperature increase rate of 20 ° C./min using a differential calorimeter (DSC, manufactured by Perkin-Elmer).

2. Specific gravity

Specific gravity of longitudinally stretched sheets was measured according to ASTM D1505 using a density gradient tube.

3. Number of breaks

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

4. Thickness uniformity

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

As shown in the above table, the total longitudinal drawing ratio is 3.5 times or more, and the three-stage longitudinal drawing is carried out so that the crystallization energy of the longitudinal drawing sheet is 10 J / g or more, and then the transverse stretching is performed at a draw ratio of 3.5 to 4.5 times. The polyester films of Examples 1 to 3 produced by the present invention had better thickness uniformity than the polyester films of Comparative Examples 1 to 6, which were not based on the production method of the present invention, and had fewer breaks during the transverse stretching process. It can be seen that the productivity is good.

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 for producing a biaxially oriented polyester film comprising melt extruding a polyester resin and stretching the unstretched sheet in the longitudinal and transverse directions, the stretching step is carried out at the longitudinal stretch of at least 3.5 times the total longitudinal stretch ratio, but longitudinal stretch After performing three or more stages of multistage longitudinal stretch so that the crystallization energy of a sheet may be 10 J / g or more, it transversely stretches by draw ratio 3.5-4.5 times. The manufacturing method of the biaxially-oriented polyester film characterized by the above-mentioned. The production method according to claim 1, wherein the specific stretching sheet has a specific gravity of 1.36 or less.