KR0142039B1 - Manufacturing method of 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 drawing step is performed in three or more stages of multi-stage longitudinal stretching such that the stretching ratio is at least 3.5 times the total longitudinal stretching ratio and the crystallization energy of the longitudinal stretching sheet is 10 J / g or more, and the glass transition temperature (Tg) + 50 ° C. of the sheet is performed. Immediately after the final step longitudinal stretching in the temperature range of 140 to 140 ° C., it is rapidly cooled by 105 ° C. at that temperature, and then transversely stretched at a draw ratio of 3.5 to 4.5 times.

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 and surface smoothness.

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 insulation frames. 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 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 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 and Japan Special Employment 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 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 and rapid cooling, which are core technologies.

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

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, in the longitudinal stretching step. Three or more stages of longitudinal stretching are carried out so that the longitudinal stretching ratio is 3.5 times or more and the crystallization energy of the longitudinal stretching sheet is 10 J / g or more, and the final stage longitudinal stretching is performed at the temperature of the following formula (1) and the following formula (2) Provided is a method for producing a biaxially oriented polyester film, characterized in that the film is rapidly cooled at a cooling temperature and then transversely stretched at a draw ratio of 3.5 to 4.5 times.

Equation (1) Tg + 50 ℃ ≤ final stage longitudinal drawing temperature ≤ 140 ℃

Equation (2) Cooling temperature ≤ Final drawing longitudinal stretching temperature-105 ℃

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 the total longitudinal stretch ratio, and the final stage longitudinal stretching temperature of the sheet is maintained while the crystallization energy of the longitudinal stretch sheet is 10 J / g or more. By performing three or more stages of multi-stage longitudinal stretching in the range of T / g + 50 ° C to 140 ° C, the width shrinkage of the longitudinal stretching sheet is reduced and the orientation determination is less progressed. Rapid cooling by a difference of more than 105 ° C from the temperature improves the smoothness and thickness uniformity of the surface of the sheet, and the transverse stretching in the transverse stretching process is reduced by the transverse stretching in the range of draw ratio 3.5 to 4.5 times, ultimately resulting in poly The thickness of the ester film 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 addition, the final stretching temperature in the final stage refers to the surface temperature of the stretching roll in the final longitudinal stretching stage in the multi-stage longitudinal stretching process, and Tg means glass transition temperature and is about 67 ° C. in the case of polyester.

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 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 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, the orientation crystallization occurs a lot, and thus the shrinkage of the longitudinally stretched sheet is increased. This results in an increase in width shrinkage and orientation determination, with the final longitudinal draw temperature higher than 140 ° C. resulting in uneven stretching resulting in breakage and non-uniformity in the transverse stretching process. In addition, if the surface is not rapidly cooled by a difference of 105 ° C. or more from the stretching temperature of the final stage, surface scratches are caused by poor cooling, molecular orientation is relaxed, and thickness unevenness and a decrease in mechanical strength are caused. It is inefficient because the preheating loss in the lateral stretching process increases. In addition, the specific gravity of the final longitudinal stretch sheet is to be 1.36 or less, respectively, if larger than this, there is a problem that a draw failure and fracture occurs in the transverse stretching process.

Further, after longitudinal stretching, when the lateral fuel ratio is less than 3.5, the thickness uniformity of the film is lowered. When the transverse stretching ratio is larger than 4.5, breakage occurs frequently in the lateral stretching process and thus there is a problem that film production productivity is lowered.

On the other hand, if the multi-stage longitudinal stretching of three or more stages is not satisfied, problems arise in that the total longitudinal stretching ratio is 3.5 times or more and the crystallization energy cannot be 10J / g or more in the longitudinal stretching process.

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

1 and 2 are schematic views of a third stage longitudinal drawing apparatus of a polyester film according to an 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 the 3rd stage stretching roll, the 10-11th roll is a 3-stage cooling roll, and 4 ', 5', 8 ', 9', and 10 'are roll rolls.

When manufacturing a biaxially oriented polyester film using the third stage longitudinal drawing apparatus shown in FIG. 1, the polyester unstretched sheet (F) was preheated in rolls 1-3 and then rolls 4 and 5 The first stage longitudinal stretching is performed according to the circumferential speed of the rolls, and after cooling on the 5th roll, it is preheated again on the 6th roll, and the second stage between the 8th and 9th rolls, and the 9th and 10th. The third stage longitudinal stretching is performed between the burn 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, in turn, 17 ', 18', 19 'and 20' are roll rolls. When using the apparatus shown in FIG. 2, the polyester unstretched sheet (F) is preheated through rolls 12 to 16 and then rolled between rolls 17 and 18, between rolls 18 and 19, and 19 The longitudinal stretch sheet F 'is manufactured by performing the 1st stage longitudinal stretch, the 2nd stage longitudinal stretch, and the 3rd stage longitudinal stretch, respectively, by the circumferential speed difference of a roll between the 1st and 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 to produce a 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 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 stretching apparatus of FIG. 1, the roll temperature of No. 1-3 is 100 ° C, the No. 4 roll temperature is 120 ° C, the No. 5 roll temperature is 30 ° C, the No. 6 roll temperature is 110 ° C, the No. 8 roll temperature is 125 ° C, and Unstretched sheet 2.0 times 1st stage longitudinal stretch between 4th and 5th rolls, 1.5 times 2nd stage longitudinal stretched between 8th and 9th rolls, 1.5 times 3rd stage longitudinal between 9th and 10th rolls After stretching, the longitudinally stretched sheet was rapidly cooled by a roll No. 10 in which the coolant at 20 ° C was internally circulated at a flow rate of 300 l / min, laterally stretched at a draw ratio of 4.0 times, and heat-set by a conventional method. A biaxially oriented polyester film having a thickness of 14 μm was obtained.

Example 2

In Example 1, the sheet forming speed was 61.7 m / min, the fourth roll temperature was 115 deg. C, the 8-9 roll temperatures were 125 deg. C, the first stage longitudinal draw ratio was 1.5 times and the second stage longitudinal draw ratio 1.8. The same procedure as in Example 1 was carried out except that the vessel, the third stage longitudinal draw ratio 1.8 times, and the tenth cooling roll temperature were 18 ° C and the lateral draw ratio 3.6 times.

Example 3

In Example 1, the sheet forming speed was 45.5 m / min, the fourth roll temperature was 115 ° C., the nineth 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, It carried out similarly to Example 1 except having made the 3rd stage longitudinal stretch ratio 2.0 times and the 10th cooling roll temperature 15 degreeC, and the lateral stretch ratio 4.4 times.

Comparative Example 1

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

Comparative Example 2

In Example 1, in the longitudinal drawing apparatus of FIG. 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 It carried out similarly to Example 1 except having extended | stretched by 3.0 time and 1.5 time, respectively, between 9 and 10 rolls.

Comparative Example 3

In Example 1, the sheet forming speed was 82 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 is 100 ° C., the eighth roll temperature is 110 ° C., the nineth roll temperature is 115 ° C., and the first stage longitudinal draw ratio is 2.0 times, the second stage longitudinal draw ratio is 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 is 56.5 m / min, the fourth roll temperature is 100 ° C., the first stage longitudinal draw ratio is 2.5 times, the second stage longitudinal draw ratio is 1.2 times, and the third stage longitudinal draw ratio is 1.6 times. Except that except for the same as in Example 1.

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, the ninth roll owl was 115 ° C, 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 7

In Example 1, it carried out similarly to Example 1 except having set the 10th cooling roll temperature to 25 degreeC.

Comparative Example 8

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

Comparative Example 9

In Example 1, it carried out similarly to Example 1 except having set sheet forming speed to 59.6 m / min and 4.7 times of lateral stretch ratio.

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, the surface smoothness and the thickness uniformity of the finally obtained film were measured and shown in Table 1 below.

Assessment Methods

1. Crystallization Energy

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

2. Specific gravity

Specific gravity of the film was measured by a 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 transverse direction using a thickness gauge (manufactured by Annitsu Co., Ltd.) and expressed as a thickness deviation that is the difference between the maximum value and the minimum value.

5. Surface smoothness

In the light of fluorescent lamps, the presence or absence of longitudinal surface scratches on the surface of the film was visually evaluated.

As shown in the above table, the polyester film of Examples 1-3 prepared by the production method of the present invention has surface smoothness and thickness uniformity compared to the polyester film of Comparative Example 1-9 without using the production method of the present invention. It can be seen that the productivity is good due to the low number of breaks during the transverse stretching process.

Therefore, the manufacturing method of the present invention 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 computer, which requires 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 total stretch ratio in the stretching step is 3.5 times or more and the length of the stretched sheet. Three or more stages of multi-stage longitudinal stretching are carried out so that the crystallization energy is 10 J / g or more, and the final stage longitudinal stretching is carried out at the temperature of the following formula (1) and rapidly cooled at the cooling temperature of the following formula (2), followed by the stretching ratio of 3.5 Method for producing biaxially oriented polyester film, characterized in that it is lateral stretched by 4.5 times: Equation (1) Tg + 50 ℃ ≤ final stage longitudinal drawing temperature ≤ 140 ℃ Equation (2) Cooling temperature ≤ Final drawing longitudinal stretching temperature-105 ℃ Where Tg is the glass transition temperature of the sheet. The method according to claim 1, wherein the longitudinal stretch sheet has a specific gravity of 1.36 or less.