KR19990049685A - Manufacturing method of biaxially oriented polyester film - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a biaxially oriented polyester film method which is excellent in uniformity in thickness and capable of preventing breakage failure.

2. The technical problem to be solved by the invention

The present invention stretches the polyester film through the multi-step longitudinal stretching, transverse stretching, and re-stretching process, but at the time of longitudinal stretching, the stretching temperature, the stretching ratio and the crystallization energy of the film are controlled to have excellent thickness uniformity and subsequent transverse stretching process. It is an object of the present invention to provide a method for producing a biaxially oriented polyester film to prevent the risk of width shrinkage and non-uniform thickness of both ends of the film.

3. Summary of Solution to Invention

The present invention for achieving the above object is "in the method for producing a biaxially oriented polyester film comprising a multi-longitudinal stretching, transverse stretching and graded stretching, the total longitudinal stretching ratio at the time of longitudinal stretching at 3.5 times or more in the final longitudinal stretching step Parallel stretching between nip rolls and multi-stage longitudinal stretching in which the crystallization energy of the longitudinal stretching sheet is 10 J / g or more, followed by transverse stretching and heat setting, followed by longitudinal stretching at a draw ratio of 1.2 times or more. It provides a method for producing an oriented polyester film.

4. Important uses of the invention

The present invention has a use as a base film of a magnetic recording medium.

Description

Manufacturing method of biaxially oriented polyester film

The present invention is directed to a method for producing a biaxially oriented polyester film, and more particularly, to a biaxially oriented polyester film method which is excellent in thickness uniformity and can prevent breakage failure.

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 has excellent mechanical strength and heat resistance, and thus has high utility value as a base film in manufacturing tapes for magnetic recording media such as video tapes, audio tapes, and computer tapes.

In order to meet the technical level of the current magnetic recording and reproducing apparatus which requires high magnetic recording density and high smoothness in the production of such a polyester film, the thickness uniformity and mechanical strength of the polyester film are most important. Of course, it must be considered.

In Japanese Patent Application No. 30-5639, a conventional method for producing a polyester film, polyester monomers are polymerized under a predetermined reaction condition such as pressure, temperature, and catalyst to obtain a polyester polymer intermediate product (chip or granule), After drying the content to a certain level or less, and then melt-extruded in an extruder to obtain an unstretched sheet in the die, the method of producing a biaxially stretched polyester film that stretches the unstretched suit in the longitudinal direction and stretches laterally again There is a bar.

In addition, Japanese Patent Application Laid-Open No. 54-8672 discloses a method of improving the strength and thickness uniformity of a film by performing uniaxial or biaxial re-stretch again after performing the biaxial stretching process as described above.

On the other hand, it is well known that the longitudinal stretching method of first stretching an unstretched sheet in the stretching process significantly affects the thickness uniformity of the final biaxially oriented film.

However, in the conventional drawing process, the longitudinal drawing sheet could not be stretched at a high enough magnification so that the thickness of the longitudinal drawing sheet was uniform, and even if excessive high magnification longitudinal drawing was made, the film was contracted by excessive orientation crystallization, resulting in an increase in the width shrinkage of the film. Not only the thickness is poor, but also the breaking and non-uniform stretching occurs in the lateral stretching process has a limit in producing a polyester film of a good thickness.

In this regard, Japanese Patent Laid-Open Nos. 48-43772, 50-75, 50-139872, 49-42277, 54-56674, 58-78729, 58-16023, Nos. 60-61233 and 57-18377, 57-49377, and 59-36851 provide a method for producing a polyester film comprising a longitudinal drawing process in multiple stages. The repetition of the cooling and heating processes in the middle of the stretching step not only reduces the thickness uniformity but also implies the inefficiency of the longitudinal stretching device.

In addition, the technique known by U.S. Pat.Nos. 4370291, 4497865 and Japanese Patent Laid-Open No. 58-118220 also has a longitudinal multistage drawing method as a main component, which is the birefringence of each longitudinal drawing step. Not only to characterize, limit the draw temperature and draw ratio, but also perform diagonal stretching in the final longitudinal stretching stage, which is insufficient to realize amorphous high magnification longitudinal stretching, rapid cooling and film surface defects, which are core technologies for longitudinal multistage stretching. There was one disadvantage.

The present invention is to solve the drawbacks of the prior art described above is to stretch the polyester film through a multi-stage longitudinal stretching, transverse stretching or longitudinal stretching process to adjust the stretching temperature, the stretching ratio and the crystallization energy of the film during longitudinal stretching It is possible to stretch at high magnification while suppressing the orientation determination, so that the thickness uniformity is excellent and the risk of width shrinkage and thickness non-uniformity at both ends of the film in the subsequent transverse stretching process can be prevented. It is an object of the present invention to provide a method for producing a biaxially oriented polyester film having a large improvement in mechanical properties by adjusting the draw ratio.

1 is a three-stage longitudinal drawing device showing an embodiment of the present invention

Figure 2 is a three-stage longitudinal drawing device showing another embodiment of the present invention

3 is a three-stage longitudinal drawing apparatus of the comparative example.

In order to achieve the above object, the present invention provides a biaxially oriented polyester film comprising a multi-longitudinal stretching, a transverse stretching and a longitudinal stretching, the total longitudinal stretching ratio at the time of longitudinal stretching is 3.5 times or more and the nip roll between the final longitudinal stretching step Biaxial orientation, characterized in that parallel stretching and three or more stages of longitudinal stretching are carried out so that the crystallization energy of the longitudinal stretching sheet is 10 J / g or more, and after transverse stretching and heat setting, the longitudinal stretching is performed at a draw ratio of 1.2 times or more. It provides a method for producing a polyester film.

The present invention also provides a method for producing a biaxially oriented polyester film in a method of transverse stretching at a stretching ratio of 3.5 times to 4.5 times at the time of transverse stretching of the polyester film that has been finished in the longitudinal stretching process.

According to the method of the present invention, the thickness uniformity of the longitudinal drawing sheet is improved by high magnification stretching of 3.5 times or more the total longitudinal drawing ratio, and the longitudinal stretching of the film surface is prevented by parallel stretching between the nip rolls in the final longitudinal drawing step. By carrying out three or more stages of longitudinal stretching so that the crystallization energy of the longitudinally stretched sheet is 10 J / g or more, the shrinkage of the longitudinally stretched sheet is reduced, the orientation determination is less progressed, and the fracture occurs in the subsequent transverse stretching process. And the non-uniformity is reduced, and when it is renewed by more than 1.2 times the draw ratio is improved mechanical properties such as longitudinal tensile strength.

In addition, the breakage and non-uniform stretching in the transverse stretching process by the transverse stretching in the stretching ratio of 3.5 to 4.5 times during the transverse stretching is further reduced, and ultimately the thickness of the polyester film becomes uniform in the width direction and the longitudinal direction.

In this application, "parallel drawing between nip rolls" means stretching by the speed difference between two drawing rolls between nip rolls located on the vertices of two drawing rolls having the same rotation direction, and "crystallization energy of the longitudinal drawing sheet is 10J / 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 addition, "stretching temperature" means the surface temperature of a stretching roll.

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

In the longitudinal drawing process, the circumferential speed ratio of each drawing stage determines the longitudinal drawing ratio of each stage.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 insufficient. Can not do it.

In addition, if the parallel stretching between the nip rolls is not performed in the final longitudinal stretching step, the breaking stress is poor, resulting in longitudinal scratches on the sheet surface due to the speed difference between the stretching roll surface and the sheet surface, and crystallization of the longitudinal stretching sheet. If the energy is less than 10 J / g, many orientation crystals are generated in the longitudinal stretching process, so that the longitudinal contraction sheet becomes wider in shrinkage, and subsequent lateral stretching processes are accompanied by breakage and non-uniform stretching.

In addition, the specific gravity of the longitudinally stretched sheet is 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 stretching of three or more stages is not satisfied, there is a problem that the total longitudinal stretching ratio is 3.5 times or more in the longitudinal stretching process and the crystallization energy of the longitudinal stretching sheet is not more than 10 J / g. do.

In addition, if the draw ratio at the time of transverse stretching after longitudinal stretching is less than 3.5 times, the thickness uniformity of the film may be lowered, and if greater than 4.5 times, breakage is more frequent, resulting in poor film production productivity.

In addition, when the longitudinal stretching of the biaxially oriented polyester film subjected to the longitudinal stretching and transverse stretching process is less than 1.2 times, there is a problem that the mechanical properties such as the desired longitudinal tensile strength is not achieved sufficiently.

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

1 is a longitudinal drawing device used for description of the embodiment, but the present invention is not limited thereto. Therefore, as an example in which the present invention can be implemented, there is a schematic diagram of the three-end drawing apparatus of FIG.

The rolls 1-3 of FIG. 1 are the 1st preheating roll, the 4th roll is the 1st draw roll, the 5th roll is the 2nd preheat roll, the 6-7 rolls are the 2nd and 3rd draw rolls, and the 8th roll is the cooling roll 4 ′, 5 ′, 6 ′, 7 ′, 8 ′ are nip rolls.

In drawing a polyester film by the longitudinal drawing apparatus comprised in this way, in FIG. 1, 1st longitudinal drawing is performed by the circumferential speed difference of a roll between the 4th and 5th rolls of polyester unstretched sheet F, Two-stage longitudinal stretching is carried out between rolls 6 and 7, followed by three-stage longitudinal stretching between rolls 7 and 8, followed by rapid cooling between rolls 8 and 9 to form the longitudinal stretching sheet (F '). Manufacture.

Also, in Fig. 2, rolls 11-14 are preheating rolls, rolls 15, 16 and 17 are one-stage, two-stage and three-stage stretching rolls in turn, roll 18 is a cooling roll, and 15 'and 16' Rolls 17 'and 18' are nip rolls.

In the case of using the apparatus shown in FIG. 2, the polyester unstretched sheet (F) is preheated by passing through 11 and 14 rolls, and then between 15 and 16, between 16 and 17 rolls, and 17 The first stage longitudinal stretching, the second stage longitudinal stretching and the third stage longitudinal stretching are performed by the circumferential speed difference between the rolls and the 18th rolls, and then rapidly cooled between the 8th and 9th rolls to obtain the longitudinal drawing sheet (F '). To prepare.

The longitudinally stretched sheet F 'as described above is transversely stretched and heat set at the draw ratio given above by a conventional method to prepare a biaxially oriented polyester film of the present invention.

In addition, the biaxially oriented polyester film subjected to the longitudinal stretching and transverse stretching process is subjected to a longitudinal stretching at the stretching ratio shown above to prepare a biaxially oriented polyester film of the present invention.

FIG. 3 is a schematic view of the comparative example, which is the same as the roll configuration of FIG. 1, but the roll rotation direction after roll 8 is opposite to that of FIG. 1, and diagonally diagonally crosses between rolls 7 and 8 in a tangential direction. .

Hereinafter, examples and comparative examples of the present invention will be described based on the drawings described above. However, the following examples are provided only to assist in understanding the present invention, and the present invention is not limited thereto.

(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 60 m / min at a temperature of 280 ° C. to obtain an unstretched sheet, and then roll temperatures 1-3 in the longitudinal drawing apparatus of FIG. 100 ° C, roll number 4 at 110 ° C, roll number 5 at 110 ° C, rolls 6-7 at 120 ° C, roll 8 at 20 ° C, and the unstretched sheet at roll 4 2.0 times first stage longitudinal stretching between rolls 5 and 5, second stage longitudinal stretching 1.5 times between 6 and 7 rolls, 1.5 times third stage longitudinal stretching between 7 and 8 rolls, and then After stretching and heat-setting the stretched sheet by a conventional method, a stretch ratio of 1.5 times the grade was obtained to obtain a biaxially oriented polyester film having a thickness of 14 μm. The crystallization energy, specific gravity, The number of breaks, thickness uniformity, and tensile strength were measured and shown in Table 1 below.

Experimental Example

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).

- importance -

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

-Number of breaks-

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

-Thickness uniformity-

The thickness uniformity of the film was measured by thickness measurement at an interval of 20 mm using a thickness gauge (manufactured by Annitsu Co., Ltd.), and the difference between the maximum value and the minimum value was expressed as thickness deviation.

- The tensile strength -

The tensile strength of the film was measured by the method defined in ASTM D882.

(Example 2)

In Example 1, the sheet forming speed was 55.6 m / min, the 4-5 roll temperature was 115 deg. C in the longitudinal drawing apparatus of FIG. 1, the first longitudinal drawing ratio was 1.5 times and the second longitudinal drawing ratio was It carried out similarly to Example 1 except having set 1.8 times and 3rd stage longitudinal stretch ratio to 1.8 times.

(Example 3)

In Example 1, the sheet forming speed was 50 m / min, in the longitudinal drawing apparatus of FIG. 1, the roll temperature of 4-5 was 115 ° C, the roll temperature of 7 was 130 ° C, and the first longitudinal draw ratio was 1.5. The same procedure as in Example 1 was carried out except that the vessel, 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, in the longitudinal drawing apparatus of FIG. 1, the roll temperature of 4-5 is 100 ° C, the roll temperature of 6 is 110 ° C, and the first stage longitudinal draw ratio is 4.5 times between rolls 7 and 8. 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 4-5 is set to 100 ° C and the roll temperature of 6-7 to 110 ° C, between rolls 6 and 7, and between rolls 7 and 8, respectively. The same procedure was followed as in Example 1 except that the first stage longitudinal draw ratio was 3.0 times and the second stage longitudinal draw ratio was 1.5 times.

(Comparative Example 3)

In Example 1, the sheet forming speed was 82.3 m / min, the roll stretching apparatus of FIG. 1 was 4-5 roll temperature at 100 ° C, 6 roll temperature was 105 ° C, 7 roll temperature was 110 ° C, 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 1.4 times, and the third stage longitudinal draw ratio 1.8 times.

(Comparative Example 4)

In Example 1, in the longitudinal drawing apparatus of FIG. 1, the fourth roll temperature is 100 ° C, the sixth roll temperature is 110 ° C, the seventh roll temperature is 115 ° C, the first stage longitudinal draw ratio is 2.0 times, and the second stage longitudinal edge. It carried out similarly to Example 1 except having set to 1.5 times the mystery 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 roll temperature 4 in the longitudinal drawing apparatus of FIG. 1 was 100 ° C., the roll temperature 6-7 was 125 ° C., the first stage longitudinal draw ratio 2.5 times, The same procedure as in Example 1 was carried out except that the second stage longitudinal draw ratio was 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 sixth roll temperature was 110 ° C, the seventh roll temperature was 115 ° C in the longitudinal drawing apparatus of FIG. 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.

(Comparative Example 7)

The sheet forming speed is 50 m / min in Example 1, except that diagonal longitudinal stretching of the third stage longitudinal stretching between rolls 7 and 8 is tangentially staggered in the longitudinal stretching apparatus of FIG. It carried out similarly to Example 1.

(Comparative Example 8)

In Example 1, the sheet forming speed was 81.8 m / min, and the drawing extension ratio was 1.1 times the same as that in Example 1 except that the drawing was stretched.

TABLE 1

※ In Table 1, tensile strength means longitudinal tensile strength.

As shown in Table 1, in the longitudinal drawing process, the total longitudinal drawing ratio is 3.5 times or more, and the final stage longitudinal drawing is made in three stage longitudinal drawing and drawing ratio 1.2 times or more so that the crystallization energy of the longitudinal drawing sheet is 10 J / g or more 1.2 The polyester films of Examples 1 to 3 of the present invention which were carried out twice or more had better thickness uniformity and longitudinal tensile strength than the polyester films of Comparative Examples 1 to 8, which were not based on the production method of the present invention, and also laterally stretched. It can be seen that the productivity is good due to the low number of breaks during the process.

(Example 4)

In the same manner as in Example 1, the longitudinally stretched polyester sheet was transversely stretched at a draw ratio of 4.0 times, and then heat-set by a conventional method, and stretched at a stretch ratio of 1.5 times, and the test determined in the above Experimental Example. Crystallization energy, specific gravity, number of breaks, thickness uniformity, and tensile strength were measured through the method, and are shown in Table 2 below.

(Example 5)

In Example 4, the sheet forming speed was 61.7 m / min, the 4-5 roll temperature was 115 deg. C in the longitudinal drawing apparatus of FIG. 1, the first longitudinal drawing ratio was 1.5 times and the second longitudinal drawing ratio was The same procedure as in Example 4 was conducted except that 1.8 times and the third stage longitudinal draw ratio were 1.8 times and the transverse draw ratio was 3.5 times.

(Example 6)

In Example 4, the sheet forming speed was 45.5 m / min, the roll stretching apparatuses of Fig. 1 were 115 deg. C and 115 roll temperature was made 130 deg. It carried out similarly to Example 4 except having made 1.5 times, 2nd stage longitudinal draw ratio 1.8 times, 3rd stage longitudinal draw ratio 2.0 times, and lateral stretch ratio 4.4 times.

(Comparative Example 9)

In Example 4, in the longitudinal drawing apparatus of FIG. 1, the roll temperature of 4-5 is 100 ° C, the roll temperature of 6 is 110 ° C, and the first stage longitudinal draw ratio is 4.5 times between the rolls 7 and 8. Was carried out in the same manner as in Example 4.

(Comparative Example 10)

In Example 4, in the longitudinal drawing apparatus of FIG. 1, the roll temperature of 4-5 is set to 100 ° C and the roll temperature of 6-7 to 110 ° C, between rolls 6 and 7, and between rolls 7 and 8, respectively. The same procedure was followed as in Example 4 except that the first stage longitudinal draw ratio was 3.0 times and the second stage longitudinal draw ratio was 1.5 times.

(Comparative Example 11)

In Example 4, the sheet forming speed was 82.4 m / min, the roll stretching apparatus of FIG. 1 was 4-5 roll temperature at 100 ° C, 6 roll temperature was 105 ° C, roll 7 was 110 ° C, It carried out similarly to Example 4 except having set the 1st stage longitudinal draw ratio 1.3 times, the 2nd stage longitudinal draw ratio 1.4 times, and the 3rd stage longitudinal draw ratio 1.8 times.

(Comparative Example 12)

In Example 4, in the longitudinal stretching apparatus of FIG. 1, the fourth roll temperature is 100 ° C, the sixth roll temperature is 110 ° C, the seventh roll temperature is 115 ° C, the first stage longitudinal draw ratio is 2.0 times, and the second stage longitudinal edge It carried out similarly to Example 4 except having set to 1.5 times the mystery and 1.5 times the 3rd stage longitudinal stretch ratio.

(Comparative Example 13)

In Example 4, the sheet forming speed was 56.3 m / min, the fourth roll temperature was 100 deg. C and the 6-7 roll temperature was 125 deg. C in the longitudinal drawing apparatus of FIG. The same procedure as in Example 4 was repeated except that the second stage longitudinal draw ratio was 1.2 times and the third stage longitudinal draw ratio was 1.6 times.

(Comparative Example 14)

In Example 4, the sheet forming speed was 50 m / min, the fourth roll temperature was 110 ° C and the seventh roll temperature was 115 ° C in the longitudinal drawing apparatus of FIG. 1, and the first stage longitudinal drawing ratio was 1.5 times and the second stage. The same procedure as in Example 4 was repeated except that the longitudinal draw ratio was 1.8 times and the third stage longitudinal draw ratio was 2.0 times.

(Comparative Example 15)

In Example 4, it carried out similarly to Example 4 except having diagonally extended longitudinal stretch between roll 7 and roll 8 in the longitudinal drawing apparatus of FIG.

(Comparative Example 16)

In Example 4, it carried out similarly to Example 4 except having set sheet forming speed to 70.6 m / min, and lateral stretch ratio to 3.4 times.

(Comparative Example 17)

In Example 4, it carried out similarly to Example 4 except having set sheet forming speed to 51.1 m / min, and lateral stretch ratio to 4.7 times.

(Comparative Example 18)

In Example 4, it carried out similarly to Example 4 except having set sheet forming speed to 81.8 m / min, and grade extension ratio to 1.1 times.

TABLE 2

※ In Table 2, tensile strength means longitudinal tensile strength.

From the Table 2, in the longitudinal drawing process, the total longitudinal drawing ratio is 3.5 times or more, and the final stage longitudinal drawing is a three-step longitudinal drawing method in which the crystallization energy of the longitudinal drawing sheet is 10 J / g or more, and the transverse drawing ratio is 3.5 to 4.5 times. And the polyester film of Examples 4 to 6 of the present invention, which is stretched at a grade drawing ratio of 1.2 times or more, than the polyester film of Comparative Examples 9 to 18, which is not based on the production method of the present invention, and has a longitudinal tensile strength. It can be seen that the excellent productivity, and the number of breaks during the lateral stretching process is good.

As described above, the present invention can be suitably used for the base film of video recording, audio recording, and computer magnetic recording media requiring high magnetic recording density, high smoothness, and high running stability. It is a useful invention to provide a method for producing a biaxially oriented polyester film.

Claims (3)

In the method for producing a biaxially oriented polyester film comprising multi-longitudinal stretching, transverse stretching and graded stretching, the longitudinal stretching ratio is 3.5 times or more during longitudinal stretching, parallel stretching between nip rolls in the final longitudinal stretching stage, and crystallization of the longitudinal stretching sheet. A method for producing a biaxially oriented polyester film, characterized in that the three or more stages of multi-stage longitudinal stretching are performed such that the energy is 10 J / g or more, but the cross-stretching and heat setting are performed, followed by the stretching at a ratio of 1.2 times or more. The method of manufacturing a biaxially oriented polyester film according to claim 1, wherein the stretching ratio during the lateral stretching is 3.5 to 4.5 times. The method for producing a biaxially oriented polyester film according to claim 1 or 2, wherein the longitudinal stretch sheet has a specific gravity of 1.36 or less.