KR0140295B1 - 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 longitudinal drawing step is carried out longitudinal stretching of at least 3.5 times the total longitudinal stretching ratio, characterized in that the three or more stages of multi-stage longitudinal stretching so that the crystallization energy of the longitudinal stretching sheet is 10 J / g or more. It is about a method.

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 embodiment 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.

As a conventional method for producing a polyester film, the polyester monomers are synthesized under predetermined reaction conditions such as a constant pressure, temperature, and catalyst to obtain a polyester composite intermediate product (chip or granule) so that the water content is below a certain level. A method for producing a biaxially stretched polyester film, which is dried until then, is melt-extruded in an extruder and passed through a die to obtain an unstretched sheet, which is stretched in the longitudinal direction and stretched in the transverse direction, is disclosed in Japanese Patent Application No. 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 well known that the longitudinal stretching step of primary stretching the unstretched sheet has a significant effect on the thickness uniformity of the 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 when the high longitudinal longitudinal stretching was performed, the width shrinkage 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 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 a film compared with the conventional stretching method, the longitudinal multistage 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. Further, 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 specifying the birefringence of each stage or limiting the stretching temperature and the stretching ratio as the components of the present invention. There is an ambiguous point to realize amorphous high magnification 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 producing a biaxially oriented polyester film comprising melt extruding a polyester resin and stretching an unstretched sheet in a longitudinal direction and a transverse direction, wherein the total stretching in the longitudinal stretching step is performed. Provided is a method for producing a biaxially oriented polyester film, characterized in that longitudinal stretching is performed 3.5 times or more, and three or more stages of multi-stage longitudinal stretching are performed such that the crystallization energy of the longitudinal stretching sheet is 10 J / g or more.

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 the 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 results in reduced width shrinkage of the longitudinal stretch sheet and less orientation determination, resulting in reduced fracture and non-uniform stretching in the subsequent transverse stretching process, resulting in uniform thickness of the polyester film in the width and length directions.

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, and implies that the orientation determination of the longitudinally stretched sheet is below a certain level.

In the present invention, the multi-stage longitudinal stretching of three or more stages for the crystallization energy of the longitudinal stretching sheet to be 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 rolling speed ratio of each drawing stage 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 smaller 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 width shrinkage of the longitudinally stretched sheet is increased, and breakage and nonuniformity are involved in the subsequent transverse stretching process. In addition, the specific gravity of the longitudinally stretched sheet is to be 1.36 or less, but when larger than this, there is a problem that a draw failure and fracture occurs in the transverse stretching process. On the other hand, if 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 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 preheated rolls, 4 rolls are 1st stage drawing rolls, 5 rolls are 1st stage cooling rolls, and 6-7 rolls are 2nd stage preheating 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 fifth roll, it is preheated again on the 6th roll and the second stage between the 8th and 9th rolls, and the 9th and 10th A third stage longitudinal stretching is performed between the rolls to produce a longitudinal stretch sheet F '.

In addition, in FIG. 2, rolls 12-16 are preheat rolls, rolls 17, 18 and 19 are first, second and third stage drawing rolls, and rolls 20-21 are cooling rolls, Rolls 17 ', 18', 19 'and 20' are rolls. In the case of using the apparatus shown in FIG. 2, the polyester unstretched sheet (F) was preheated by passing through rolls 12 to 16, 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 transversely stretched and heat set according to a conventional method to produce 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 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 rolls is 100 ° C, the roll number 4 is 120 ° C, the roll number 5 is 30 ° C, the roll temperature 6-7 is 110 ° C, and the roll temperature 8-9 is set. At 125 ° C and 10-11 roll temperatures to 20 ° C, the unstretched sheet was first stretched 2.0 times between rolls 4 and 5, first stage stretched and 1.5 times between rolls 8 and 9 After extending | stretching and extending | stretching 3rd stage longitudinally 1.5 times between rolls 9 and 10, a longitudinal stretch sheet was transversely stretched and heat set by the conventional method, and the biaxially-oriented polyester film which is 14 micrometers in thickness was obtained.

Example 2

In Example 1, the sheet forming speed was 56.3 m / min, the fourth roll temperature was 115 ° C. in the longitudinal drawing apparatus of FIG. 1, the first stage longitudinal draw ratio was 1.5 times and the second stage longitudinal draw ratio was 1.8 times. And it carried out similarly to Example 1 except having made the 3rd stage longitudinal stretch ratio 1.8 times.

Example 3

In Example 1, the sheet forming speed was 50 m / min, the fourth roll temperature was 115 deg. C, the 9th roll temperature was 130 deg. C, and the first stage longitudinal draw ratio was 1.5 times. The same procedure as in Example 1 was conducted except that the second stage longitudinal draw ratio was 1.8 times and the third stage longitudinal draw ratio was 2.0 times.

Comparative Example 1

In Example 1, the roll on No. 4-7 in the longitudinal drawing apparatus of FIG. 1 is set to 100 ° C., the roll temperature of 8 is 110 ° C., the roll temperature of 9-11 is 20 ° C., and between rolls 8 and 9. It carried out similarly to Example 1 except having carried out single stage longitudinal stretch at 4.5 times longitudinal stretch ratio.

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 longitudinal stretching was performed at 3.0-fold and 1.5-fold, respectively.

Comparative Example 3

In Example 1, the sheet forming speed was set at 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 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 draw ratio is 2.0 times, and 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 in the longitudinal drawing apparatus of FIG. 1 was set at 100 ° C, the 8-9 roll temperature was set at 125 ° C, and the first stage longitudinal draw ratio was It carried out similarly to Example 1 except having set 2.5 times, 2nd stage longitudinal draw ratio 1.2 times, and 3rd stage longitudinal draw ratio 1.6 times.

Comparative Example 6

In Example 1, the sheet forming speed was 50 n / min, the fourth roll temperature was 100 deg. C, the eighth roll temperature was 110 deg. C, and the nine roll temperature was 115 deg. The same procedure was followed as in Example 1 except that the 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.

The conditions of the above examples and comparative examples, the crystallization energy and specific gravity of the longitudinally stretched sheets, 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.

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 represented by 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 draw 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. It can be seen that the polyester film has better thickness uniformity than the polyester films of Comparative Examples 1 to 6, which are not based on the production method of the present invention, and the productivity is good because the number of breaks during the transverse stretching step is small.

Therefore, the manufacturing method of the present invention can be used for the production of a 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 running stability.

Claims (2)

A method for producing a biaxially oriented polyester film comprising melt extruding a polyester resin and stretching an unstretched sheet in a longitudinal direction and a transverse direction, wherein the two-stage longitudinal stretching of 3.5 times or more the total longitudinal stretch ratio in the longitudinal stretching step. Performing a two-stage longitudinal stretching so that the crystallization energy of the longitudinal stretching sheet is 15 J / g or more. The method according to claim 1, wherein the longitudinal stretch sheet has a specific gravity of 1.35 or less.