KR100258571B1 - Process for the preparation of biaxially oriented polyester film having good thickness uniformity - Google Patents

Abstract

PURPOSE: A method for producing biaxial orientation polyester film is provided to control orientation crystal in maximum limit and to vertically draw at high ratio while considering regularity of thickness and safety of horizontal processing. CONSTITUTION: Poluester resin is melt and inject-molded, and incompletely combustion sheet is vertically and horizontally drawn. Then, entire drawing ratio of the vertical drawing is over 3.5. The crystallization energy of vertical drawing of first and second stages is separately over 20 J/g and 15 J/g. the vertical drawing of a third stage is parallelly drawn between nip roll while drawing temperature is 110 or 140 deg.C and drawing ratio is 1.5 or 2.5 times. Thereby, the polyester film is used as a base film of self-recording medium demanding safety of travel and flatness of altitude.

Description

PROCESS FOR THE PREPARATION OF BIAXIALLY ORIENTED POLYESTER FILM HAVING GOOD THICKNESS UNIFORMITY

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 use 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 the most important position in the technical level of the current magnetic recording and reproducing apparatus requiring high magnetic recording density and high smoothness in the production of polyester film.

As a conventional method for producing a polyester film, Japanese Patent Publication No. 30-5639 discloses a polyester polymer intermediate product (chip or granule) by polymerizing polyester monomers under reaction conditions such as a constant pressure, temperature, and catalyst. It is disclosed to obtain a biaxially stretched polyester film by drying the substrate so that its water content is below a certain level and then melt extruding in an extruder to obtain an unstretched sheet, which is stretched in the longitudinal direction and then stretched in the transverse direction. In addition, a method of improving the strength and thickness uniformity of a film by uniaxially or biaxially redrawing again after the biaxial stretching process is described in Japanese Patent Laid-Open No. 54-8672.

On the other hand, it is well known that the longitudinal stretching step of initially stretching the unstretched sheet has a significant influence on the thickness uniformity of the final biaxially oriented film. Conventionally, in the longitudinal stretching process, longitudinal stretching could not be carried out at a sufficiently high magnification so that the thickness of the longitudinal stretching sheet was uniform. Even if excessive high magnification longitudinal stretching was performed, the width shrinkage was increased due to excessive orientation crystallization, so that the thickness of both ends of the longitudinal stretching sheet was increased. Not only the defects but also breakage and non-uniform stretching in the lateral stretching process has a limit in producing a polyester film with good thickness uniformity. Therefore, in view of the thickness uniformity of the biaxially oriented film as well as the stability during the lateral stretching process, a method of longitudinally stretching at the highest possible magnification while suppressing the orientation determination to the maximum has been desired.

Recently, a longitudinal multi-stage stretching method for improving the thickness uniformity of the film has emerged. However, Japanese Patent Application Laid-Open Nos. 48-43772, 50-75, 50-139872, 49-42277, 54-56674, 58-78729, The longitudinal multi-stage stretching methods described in subheadings 58-160123 and 60-61233, and Japanese Patent Laid-Open Nos. 57-48377, 57-49377, and 59-36851 are used in the stepwise stretching process. Repeated use of cooling and temperature increases not only the thickness uniformity is lowered but also the longitudinal stretching device is inefficient. In addition, the longitudinal multi-step stretching methods described in U.S. Patent Nos. 4,370,291 and 4,497,865 and Japanese Patent Application Laid-open No. 58-118220 limit the birefringence, or the stretching temperature and the stretching ratio at each stage, and at the final stage. It is characterized by performing diagonal stretching, which is insufficient to realize amorphous high magnification longitudinal stretching and defects on the film surface, which are core technologies of longitudinal multi-stage stretching.

Accordingly, it is an object of the present invention to provide a biaxially oriented polyester film which eliminates the above-mentioned disadvantages of the prior art and has improved thickness uniformity and no defects on the surface of the film.

1 and 2 are schematic views of a three-stage longitudinal drawing apparatus of a biaxially oriented polyester film according to an aspect of the present invention;

3 is a schematic view of a three-stage longitudinal drawing apparatus of a biaxially oriented polyester film according to a comparative example.

In order to achieve the above object, in the present invention, in the method for producing a biaxially oriented polyester film comprising the step of melt-extruding a polyester resin and stretching the resulting unstretched sheet in the longitudinal and transverse directions, the longitudinal stretching The total longitudinal drawing ratio is 3.5 times or more, and is made in three stages, and the crystallization energy of the first and second stage longitudinal drawing sheets is 20 J / g or more and 15 J / g or more, respectively, Provided is a method for producing a biaxially oriented polyester film, characterized in that the longitudinal stretching is carried out by parallel stretching between nip rolls under the conditions of stretching temperature 110 ℃ to 140 ℃, stretching ratio 1.5 to 2.5 times.

Hereinafter, the present invention will be described in more detail.

As the polyester resin of the present invention, a conventional polyester resin can be used, and an intrinsic viscosity measured at a concentration of 0.3 g per 25 ml of orthochlorophenol at 35 ° C. is preferably 0.4 to 0.9 g / dl. If the intrinsic viscosity is less than 0.4 g / dl, breakage occurs frequently during stretching, which leads to a decrease in productivity as well as to a decrease in physical properties such as mechanical strength in the final film. When the viscosity is higher than 0.9 g / dl, the melt viscosity increases significantly. As the extrudeability is lowered, productivity in the post process is lowered.

In this invention, polyester polycondenses the acid component which has aromatic dicarboxylic acid as a main component, and the glycol component which has alkylene glycol as a main component. Specific examples of the aromatic dicarboxylic acid include dimethyl terephthalate, terephthalic acid and isophthalic acid. Naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, anthracenedicarboxylic acid, α, β-bis (2 -Chlorophenoxyethane-4,4'-dicarboxylic acid, and the like, of which dimethyl terephthalate, terephthalic acid and naphthalenedicarboxylic acid are particularly preferred, as alkylene glycol, ethylene glycol, trimethylene glycol, tetramethylene Glycol, pentamethylene glycol, hexamethylene glycol, hexylene glycol, and the like can be used, and among these, ethylene glycol is particularly preferable.

The polyester in the present invention is a homopolyester of at least 60% by weight of polyethylene terephthalate or polyethylenenaphthalate, and copolymerizable within 40% by weight. Specific examples of the copolymer component include dicarboxylic acid components and trimellis such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylene glycol, 1,4-cyclohexanedimethanol, and 5-sodium sulfolezocin Polycarboxylic acid components, such as a triacid and a pyromellitic acid, etc. are mentioned.

According to the method of the present invention, a polyester resin is melt-extruded according to a conventional method to prepare an unstretched sheet, and then longitudinally stretched according to a specific method.

According to the longitudinal stretching method of the present invention, the thickness uniformity of the longitudinally stretched sheet is improved by high magnification stretching of 3.5 times or more in total longitudinal stretching ratio, and longitudinal stretching of the film surface is performed by performing parallel stretching between nip rolls in the third stage longitudinal stretching step. (Scratch) is prevented, and 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 stretch sheet is 20 J / g or more and 15 J / g or more, respectively, and the third However, longitudinal stretching was performed by parallel stretching between nip rolls under the conditions of stretching temperature of 110 ° C to 140 ° C and stretching ratio of 1.5 to 2.5 times, thereby reducing the shrinkage of the longitudinal drawing sheet and lessening the orientation determination, resulting in breakage and non-uniform stretching in the subsequent transverse stretching process. This decreases, and ultimately the thickness of the polyester film becomes uniform in the width and length directions.

As used herein, "parallel stretching between nip rolls" means stretching by the speed difference between two stretching rolls between nip rolls positioned on the vertices of two stretching rolls having the same rotation direction, and "crystallization energy of longitudinal drawing sheet". Means the energy generated during the crystallization process, and the large crystallization energy implies that the longitudinally oriented sheet has little orientation crystallization. In addition, "stretching temperature" means the surface temperature of a stretching roll.

In the present invention, in the first stage and the second stage longitudinal drawing, the crystallization energy of the sheet is adjusted to 20 J / g or more and 15 J / g or more, respectively, by the combination of the draw temperature and the draw ratio of each step. However, it is not limited to the combination of any specific extending | stretching temperature and draw ratio of each step of a 2nd stage longitudinal stretch.

In the longitudinal drawing process, the circumferential speed ratio of each drawing stage roll 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 parallel stretching between the nip rolls is not performed in the final longitudinal stretching step, the breakage of the stretching stress is poor, and the longitudinal scratches on the sheet surface occur due to the difference in speed between the stretching roll surface and the sheet surface, and the first stage longitudinal stretching sheet. When the crystallization energy of is less than 20 J / g, the orientation crystals in the first stage longitudinal drawing process tend to increase, so that the second stage and the third stage longitudinal stretch sheet as well as the first stage become wider and the second stage longitudinal stretch sheet When the crystallization energy of is less than 15 J / g, even though the crystallization energy of the first end longitudinally stretched sheet is 20 J / g or more, many orientation crystals occur during the second stage longitudinal stretch, so that the second and third stage longitudinally stretched sheets The width shrinkage becomes large.

In addition, the specific gravity of the first stage and the second stage longitudinally stretched sheets is 1.345 or less and 1.355 or less, respectively, and when larger than this, the shrinkage or fracture in the subsequent longitudinal stretching process or the transverse stretching process is Occurs.

When the third stage longitudinal stretching is not performed at a stretching temperature of 110 ° C. to 140 ° C. and a stretching ratio of 1.5 to 2.5 times, the longitudinal stretching sheet becomes wider and the thickness uniformity of the longitudinal stretching sheet becomes poor. Breaking and non-uniform stretching are caused in the process. On the other hand, in the case of longitudinal stretching in two or less stages, there is a problem in that the stretching at 3.5 times or more the total longitudinal stretching ratio and the crystallization energy of the first stage and the second stage longitudinal stretching are not more than 20 J / g or 15 J / g, respectively. .

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 used in Examples according to the present invention. In Fig. 1, the rolls 1-3 are one-stage preheating rolls, the four rolls are the first-stage stretching rolls, the fifth roll is the two-stage preheating rolls, and the 6-7 rolls are the two, three-stage stretching rolls, and the eighth roll is Three-stage cooling rolls, rolls 9 and 10 are cooling rolls, and 4 ', 5', 6 ', 7', and 8 'are nip rolls. In producing the polyester film by the longitudinal stretching apparatus configured as described above, the polyester unstretched sheet (F) is subjected to one-stage longitudinal stretching between the fourth and fifth rolls by the circumferential speed difference of the rolls. The longitudinal stretch sheet F 'is produced by performing two steps between burn rolls, and then carrying out three steps of longitudinal stretching between rolls 7 and 8.

In Fig. 2, the rolls 11-14 are preheat rolls, rolls 15, 16, and 17 are rolls 1, 2, and 3, drawing rolls and rolls 18 are cooling rolls, and rolls 19 and 20 are cooled. Rolls 15 ', 16', 17 'and 18' rolls are nip rolls. In the case of using the apparatus shown in Fig. 2, the polyester unstretched sheet (F) is preheated through rolls 11 and 14, and then rolls 15 and 16, between rolls 16 and 17 and 17 The longitudinal stretch sheet F 'is produced 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 and No. 18 roll.

3 is a schematic view of a longitudinal drawing apparatus used in the comparative example, in which the roll configuration is the same as in FIG. 1, but the roll rotation direction after the 28th roll is opposite to that of FIG. 1, between the 27th and 28th rolls. Diagonal longitudinal stretching is performed in a tangential direction.

The longitudinally stretched sheet (F ') is transversely stretched and heat-set by the conventional method to produce the biaxially oriented polyester film of the present invention.

Hereinafter will be described in detail based on the embodiments of the present invention, these examples are provided only to help the understanding of the present invention, the present invention is not limited thereto.

Example 1

The unstretched sheet obtained by melt extruding a polyester chip having an intrinsic viscosity of 0.63 at a temperature of 280 ° C. through a die was produced at a sheet forming speed of 60 m / min. The first roll temperature is 110 ° C, the fifth roll temperature is 110 ° C, the sixth roll temperature is 120 ° C, the eighth roll temperature is 20 ° C, and the unstretched sheet is 2.0 between the fourth and fifth rolls. Following the first stage longitudinal stretching, 1.5 times second stage longitudinal stretching between 6th and 7th rolls, 1.5 times third stage longitudinal stretching between 7th and 8th rolls, the longitudinally stretched sheet is conventionally processed. Lateral stretching and heat setting were performed to obtain a biaxially oriented polyester film having a thickness of 14 µm.

Example 2

The sheet forming speed is 55.6 m / min, the 4-5 roll temperature is 115 ° C in the longitudinal drawing apparatus of FIG. 1, the first stage longitudinal draw ratio is 1.5 times, the second stage longitudinal draw ratio is 1.8 times, and the third A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 1.8 times.

Example 3

The sheet forming speed was 50 m / min, in the longitudinal stretching apparatus of FIG. 1, the roll temperature of 4-5 was 115 deg. C, the roll temperature of 7 was 130 deg. C, and the first stage longitudinal draw ratio was 1.5 times and the second stage. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 1.8 times and the third stage longitudinal draw ratio was 2.0 times.

Comparative Example 1

The longitudinal drawing apparatus of FIG. 1 is used, except that the fourth roll temperature is 100 ° C., the sixth roll temperature is 110 ° C., and one longitudinal stretching is performed at a ratio of 4.5 times the longitudinal draw ratio between the seventh and eighth rolls. The same procedure as in Example 1 was followed to obtain a biaxially oriented polyester film.

Comparative Example 2

In the longitudinal drawing apparatus of FIG. 1, the fourth roll temperature is 100 ° C and the 6-7 roll temperature is 110 ° C, and the longitudinal draw ratio is 3.0 times and 1.5 between rolls 6 and 7, and between rolls 7 and 8, respectively. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the two-stage longitudinal stretching was performed.

Comparative Example 3

The sheet forming speed is 82.3 m / min, the 4th roll temperature is 100 degreeC, the 6th roll temperature is 105 degreeC, the 7th roll temperature is 110 degreeC in the longitudinal drawing apparatus of FIG. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the mystery 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 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 draw ratio is 1.5 times. , The same procedure as in Example 1 was conducted except that the third stage longitudinal draw ratio was 1.5 times to obtain a biaxially oriented polyester film.

Comparative Example 5

The same procedure as in Example 1 was conducted except that the sheet forming speed was 50 m / min, 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. A biaxially oriented polyester film was obtained.

Comparative Example 6

The sheet forming speed is 50 m / min, the roll temperature of the first drawing is 120 deg. C and the roll temperature of the seventh is 100 deg. C, and the first end drawing ratio is 1.5 times and the third end drawing ratio is A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the concentration was 2.4 times.

Comparative Example 7

The sheet forming speed is 50 m / min, the roll temperature of the first drawing is 120 ° C. and the roll temperature of eight is 150 ° C., the first end drawing ratio is 1.5 times and the second end drawing ratio is 1.5 times. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that 1.5 times and the third stage longitudinal draw ratio was 2.4 times.

Comparative Example 8

The sheet forming speed was 50 m / min, and the third longitudinal stretching between the seventh and eighth rolls in the longitudinal stretching apparatus of FIG. The same procedure was followed to obtain a biaxially oriented polyester film.

Examples and Comparative Examples Example conditions, the crystallization energy and specific gravity of the longitudinally stretched sheet, the number of breaks in the transverse stretching process, the thickness uniformity of the final film obtained and whether the surface streaks were evaluated by the following method, which is shown in Table 1 Indicated.

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 the longitudinally stretched sheet was measured according to ASTM D1505 using a density gradient tube.

3. Number of breaks

The number of breaks occurring during 72 hours in the step of transversely stretching the longitudinally stretched polyester film was measured.

4. Thickness uniformity

The thickness uniformity of the film was measured by thickness measuring instrument (Annitsu Co., Ltd.) at a thickness interval of 20mm intervals and the difference between the maximum value and the minimum value was expressed as thickness deviation.

As shown in Table 1, the polyester film prepared in Examples 1 to 3 produced by the method of the present invention, the thickness uniformity than the polyester film of Comparative Examples 1 to 8 manufactured out of the production conditions of the present invention It can be seen that the excellent productivity and good productivity due to the low number of breaks during the transverse stretching process.

Therefore, the polyester film produced according to the present invention can be suitably used for base films of magnetic recording media for video, audio, and computers that require high magnetic recording density, high smoothness, and high driving safety.

Claims (2)

A method for producing a biaxially oriented polyester film comprising melt extruding a polyester resin and stretching the resulting unstretched sheet in a longitudinal direction and a transverse direction, wherein three-stage longitudinal stretching of 3.5 times or more the total longitudinal stretch ratio is performed. The first and second stage longitudinal stretching are performed such 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, and the stretching temperature is 110 to 140 ° C. and the stretching ratio is 1.5 to 2.5. A third stage longitudinal stretching is performed by parallel stretching between nip rolls under bain conditions, wherein the biaxially oriented polyester film is produced. The method of claim 1, And the specific gravity of the first stage and second stage longitudinal stretch sheets is 1.345 or less and 1.355 or less, respectively.

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