JPH09272148A - Polyester film and heat treating method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester film, which has high strength and favorable flatness and the heat stability and dimensional stability of which are improved, by a method wherein the longitudinal heat shrinkage factor and cystalline size of the polyester film at the specified temperature are respectively set to be specified value or less. SOLUTION: The longitudinal heat shrinkage factor of a polyester film at 80 deg.C is set to be 0.25% or less, preferably 0.23% or less. The crystalline size Xc of the polyester film is set to be 6nm or less, preferably 5.8nm or less. Dimethyl terephthalate and ethylene glycol are polymerized together by the conventional procedure by employing calcium acetate as ester interchange catalyst, antimony trioxide as polymerization catalyst and phosphoric acid as stabilizer. Thus, a polyester film is obtained, which is excellent in dimensional stability through having high strength, at the same time, the amount of unsymmetrical elongation of which is small and the flatness of which is kept favorably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film, and more particularly to a polyester film having high strength, good flatness, heat stability and dimensional stability. More specifically, it relates to a polyester film particularly suitable for a magnetic recording medium having excellent electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Polyester film has excellent strength and dimensional stability and is widely used as a base film for magnetic recording media, capacitors, packaging, and printing materials. Video tapes, audio tapes, computer tapes, and the like are widely known as magnetic recording media using a polyester film as a base film. In these fields of application, digitalization has been rapidly progressing in recent years, and with the increase in density of magnetic recording, there are many demands on the polyester film used for the base film. Among them, especially in the case of digital tape for business use, the environment during data collection is diverse, and the demand for dimensional stability of the tape is increasing. In addition, because the number of tracks in computer backup tapes has increased with the increase in density, the track width has become narrower, and off-track accuracy has become even more stringent, requiring computer tape dimensional stability. It is getting higher and higher.
Along with this, a base film having excellent thermal stability and dimensional stability has been demanded. In addition, the tape running system of video cameras, VCRs, and data recording systems has become extremely strict for high-density magnetic recording, and the demand for higher strength is increasing for tapes. . Various proposals have been made in the past for a base film having high strength and excellent thermal stability (for example, Japanese Patent Publication No. 3-71013), but most of them are based on relaxation heat treatment. Since the relaxation heat treatment is performed while the film is running, it is difficult to apply uniform tension in the width direction of the film, and it is difficult to make the temperature of the film uniform in the width direction. With such a method, although a certain degree of thermal stability is obtained, a difference in physical properties in the width direction of the film occurs during the relaxation heat treatment, and it is very difficult to control the flatness of the film.

[0003]

As described above, the conventional film is a base film whose thermal stability is improved to some extent, but it is difficult to control the flatness of the film and the flatness is deteriorated. For this reason, the film roll may not be usable during the film processing in the subsequent process. For example, if a film with poor flatness is used as a base film for a magnetic recording medium, which requires a strict flatness of the film, uneven coating of the magnetic layer during the magnetic tape manufacturing process or running failure during the drying process may occur, resulting in a significant loss. Reduce the rate. Further, when it is used as a film for capacitors, there are various problems such that a uniform film cannot be laminated and the electrical characteristics are deteriorated.

As a method of preventing such a flatness defect,
Various resin films have been proposed in order to achieve both thermal stability and flatness of the film, but they are still lacking in practicality.

An object of the present invention is to solve the above problems and to provide a polyester film having high strength, good flatness, and excellent heat stability and dimensional stability.

[0006]

The above-mentioned object of the present invention can be achieved by setting the thermal shrinkage of the polyester film at 80 ° C. in the longitudinal direction to 0.25% or less and the crystal size (χ _c ) to 6 nm or less. .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester film of the present invention has a thermal shrinkage in the longitudinal direction at 80 ° C. of 0.25%.
It is below, preferably 0.23% or below. If a polyester film less than the above range is used, the shrinkage due to heat is large and the handling property in the processing step is deteriorated, which is not preferable. In particular, in the processing step of the magnetic tape, wrinkles may be generated in the drying step after applying the magnetic material, and it may become unusable in the subsequent steps such as slitting. The heat shrinkage is preferably as low as possible, that is, close to 0%, but the heat shrinkage is practically 0.1% or more. The method for adjusting the heat shrinkage ratio of the polyester film in the longitudinal direction at 80 ° C. to such a range is not particularly limited, but it can be achieved, for example, by subjecting it to a roll-like heat treatment. A desired heat shrinkage rate can be achieved by appropriately adjusting the temperature, humidity, time and the like of the heat treatment conditions.

The crystal size (χ _c ) of the polyester film in the present invention is 6 nm or less, preferably 5.
It is 8 nm or less. Use of a polyester film which does not fall within such a range is not preferable because the film is likely to be broken and film breakage or pinholes are generated in the processing step. The crystal size is preferably as small as possible, but practically the crystal size is 5.5 nm or more. The method for controlling the crystal size of the polyester film in such a range is not particularly limited, but for example, a desired value can be achieved by appropriately adjusting the heat treatment temperature, the heat treatment time, the tension applied during the heat treatment in the film manufacturing process. .

The Young's modulus in the longitudinal direction of the polyester film of the present invention is preferably 6.3 GPa or more, more preferably 6.8 GPa or more. When a magnetic tape is processed using a polyester film which does not fall within such a range, the tension applied in the video deck may cause deformation such as curling, which may cause troubles such as poor running. In addition, the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the polyester film is 11.7 GP.
It is preferably a or more, and more preferably 12.
It is 7 GPa or more. When a magnetic tape is processed using a polyester film that does not fall within such a range, the adhesion between the magnetic tape and the rotary head may deteriorate, and the electromagnetic conversion characteristics may deteriorate. Practically 9.8 GPa
The method for making the sum of the Young's modulus in the longitudinal direction of the polyester film which is the following and the Young's modulus in the longitudinal direction and the width's Young's modulus practically 13.7 GPa or less is not particularly limited, For example, a desired value can be achieved by appropriately adjusting the stretching ratio, the stretching temperature, the heat treatment temperature, the heat treatment time, the tension applied during the heat treatment and the like in the film manufacturing process.

The breaking elongation in the longitudinal direction of the polyester film of the present invention is preferably 65% or more,
It is more preferably 70% or more. If a magnetic tape is processed using a polyester film that does not fall within such a range, the cutting edge may cause cutting defects when slitting, resulting in cutting when used as a magnetic tape, or chips may cause clogging of the magnetic head. is there.

The main component of the polymer constituting the polyester film of the present invention is polyester. The polyester is not particularly limited, but is at least selected from the group consisting of ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, and ethylene 2,6-naphthalate. There is one having one kind as a main structural unit. Above all, it is particularly preferable when ethylene terephthalate is the main constituent unit, that is, when the polyester film is substantially composed of polyethylene terephthalate. It should be noted that two or more kinds of resins may be mixed for the purpose of increasing the strength or a copolymerized polymer may be used within a range that does not impair the object of the present invention.

Further, in order to improve the handling property of the film, it is common to add inert particles as a lubricant, and the inert particles include colloidal silica, calcium carbonate, titanium dioxide, alumina, aluminum silicate, etc. Inorganic inert particles represented by, and organic inert particles represented by crosslinked polystyrene and silicone are used.

The inert particles may be contained in the resin at any stage before the melt extrusion step, for example, before, during or after the polymerization of the resin polymer. It may also be performed during the melt extrusion preparation step. Further, as a method of incorporating the particles into the resin, for example,
When it is contained in the polyester, it is preferable to disperse the particles in the form of slurry in ethylene glycol which is a diol component and polymerize the ethylene glycol with a predetermined dicarboxylic acid component. When the particles are added, for example, if the water sol or alcohol sol obtained during the synthesis is added without once drying, the dispersibility of the particles is very good and the electromagnetic conversion characteristics can be improved. Also effective is a method in which an aqueous slurry of particles is directly mixed with a predetermined polyester pellet and supplied to a vent type twin-screw kneading extruder and kneaded into polyester. As a method of adjusting the content of particles, it is effective to prepare a high-concentration particle master by the above method, and dilute it with a polyester that does not substantially contain particles during film formation to adjust the content of particles. Is.

In the film of the present invention, a different polymer may be blended for the purpose of increasing the strength, etc., within the range not impairing the object of the present invention, and an antioxidant, a heat stabilizer, and an ultraviolet ray. Organic additives such as absorbers, light-shielding agents and antistatic agents may be added to the extent that they are usually added.

As a method of winding the above polyester film into a roll, there are a center wind method and a surface wind method. To obtain the roll of the present invention, either method may be selected. The surface wind method, which can control the contact pressure at the time of taking, is preferable. The winding conditions are not particularly limited, but the following conditions are generally used. That is, the winding tension 8 to
12 kg / m, winding contact pressure 30-60 kg / m, winding speed 100-
The rate of 200 m / min is preferable in terms of preventing the appearance of the film roll, especially vertical wrinkles and horizontal wrinkles. Especially 1m wide,
When winding a film with a length of 10,000 m, the winding tension should be 10 to 12 kg / m, the winding contact pressure should be 40 to 60 kg / m, and the winding speed should be 130 to 180 m / min. It is preferable in that it prevents wrinkles from occurring.

As a method for producing the polyester film of the present invention, it is effective to apply a roll-like heat treatment to prevent deterioration of the flatness of the film, but the heat treatment condition is 40 ° C. to 65 ° C. Is preferably performed at 45 ° C. to 60 ° C. If the heat treatment is performed under the condition that the heat treatment temperature is higher than 65 ° C., the flatness of the film may deteriorate. 40 ° C
When heat treatment is performed under lower conditions, the thermal shrinkage of the film at 80 ° C. in the longitudinal direction may increase. The humidity during heat treatment is preferably 30% or less, more preferably 25% or less. When heat treatment is performed in an environment where the humidity during heat treatment exceeds 30%, film-to-film adhesion may occur, that is, a so-called blocking phenomenon may occur.

Further, when the polyester film is wound into a roll and subjected to heat treatment, fiber-reinforced plastic, aluminum, iron or the like can be used as the core material. Among them, when the fiber-reinforced plastic core is used, heat treatment is performed. It is preferable in that it is possible to prevent the occurrence of wrinkles due to the winding tightening due to the above, particularly the winding tightening near the core.

The thermal expansion coefficient of the core material is 3 × 10.
It is preferably ⁻⁵ / ° C. or less in order to prevent the deformation of the core during heat treatment of the film roll from being transferred to the film near the core and causing wrinkles, and more preferably 1 × 10 ^−5. / ° C or lower. The method for adjusting the coefficient of thermal expansion of the core material to such a range is not particularly limited,
For example, a desired value can be achieved by appropriately adjusting the molding temperature, the molding time, the annealing temperature, the annealing time in the core manufacturing process.

The axial bending strength of the core material is 19
The pressure is preferably 0 MPa or more, more preferably 210 MPa or more. If a take-up core that is less than this range is used, the take-up core may be deformed due to the tension and contact pressure applied when the film is taken up. Also, the elastic modulus in the axial direction of the core material is preferably 9.8 GPa or more, more preferably 14.7 GPa or more.
If a core material less than this range is used, the winding core may be deformed as described above. The method for setting the strength of the winding core in such a range is not particularly limited,
For example, it can be adjusted by appropriately selecting the amount of carbon fiber yarn in the base material of the fiber reinforced plastic core, and the desired strength can also be obtained by adjusting the thickness of the base material.

The surface roughness (Ra) of the core material is preferably 0.5 μm or less, more preferably 0.3 μm or less. When a core material less than such a range is used, the unevenness of the surface of the core is transferred to the surface of the film, so for example, as a film for a magnetic tape in which the flatness of the film is strictly required, the electromagnetic conversion characteristics are significantly deteriorated. It may end up. Surface roughness of core material (R
The method for setting a) in such a range is not particularly limited, but a desired surface roughness can be obtained by, for example, providing a resin layer on the core surface and precisely grinding the surface.

The surface hardness of the core material is preferably 65 ° Shore or more, more preferably 70 ° Shore.
More than shore. If a winding core less than this range is used, the surface of the winding core may be deformed due to the tension and contact pressure applied when the film is wound, and the deformation may be transferred to the film, resulting in poor planarity. The method for adjusting the surface hardness of the winding core to such a range is not particularly limited, but can be adjusted, for example, by using a hard resin such as an epoxy resin for the core surface and appropriately selecting the thickness thereof.

[0022]

【Example】

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Young's modulus and elongation at break According to the measuring method of JIS K 7127, it was measured at 25 ° C. and 65% RH using an Instron type tensile tester.

(2) Thermal shrinkage in the longitudinal direction at 80 ° C. Five samples each having a width of 10 mm and a length of 300 mm are taken in the longitudinal direction of the film, a line of measurement intervals is put in the sample, and the original length is measured with a cassette meter. After measuring the original length, the sample is put in a hot air circulation type oven maintained at 80 ° C., taken out 30 minutes later, and left to cool for 10 minutes. This sample is again measured with a cassette meter, the average value is calculated, and the heat shrinkage rate is calculated by the formula (1). Thermal shrinkage (%) = {original length (mm) -length after heat treatment (mm)} / original length (mm) x 100 (1)

(3) Crystal size (χ _c ) The diffraction intensity was measured by the reflection method using an X-ray analyzer.
A polyester film having a thickness of 50 μm was used as a sample, and the X-ray irradiation angle was changed in a plane perpendicular to the longitudinal direction of the film, and the measurement was performed under the following conditions.

Target: Cu-Kα ray Filter: Ni Voltage: 30 kV Current: 20 mA Time: 4 min. Scan speed: 1 ° / min. Chart speed: 20 mm / min. Baseline: 32 ° to 18 ° Scattering Slit: 1 ° Divergency Slit: 0.15 mm Crystal size (χ _c ) was calculated by the following formula. χ _c = λ / {(B−b) cos θ} where B: half-width of diffraction peak b = 0.12 λ: Cu-Kα line wavelength (0.15418 nm) θ: diffraction angle of peak

(4) Coefficient of thermal expansion (α _tc ) of the winding core A core having an outer diameter of 167 mm, an inner diameter of 152.5 mm and a length of 50 mm is placed on an L-shaped surface plate tilted 5 ° from the horizontal, and the temperature is 60 °
The test core heated to the above was gradually cooled, and the outer diameter displacement of the test core with respect to the temperature change was measured with a dial gauge.

(5) Surface hardness of winding core TYPE-D according to the measuring method of JIS K7215.
The surface hardness meter was used for the measurement.

(6) Surface roughness (Ra) of winding core In accordance with JIS B 0601, a surface roughness meter Surfcom 111A manufactured by Tokyo Seimitsu Co., Ltd. was used to cut off 0.2.
The center line average roughness was measured at 3 points at 5 mm, and the average value was taken as the surface roughness.

(7) Axial elastic modulus and bending strength of winding core Outer diameter 167 mm, inner diameter 152.5 mm, length 1200 m
The core of m was supported so that the distance between fulcrums was 900 mm, a load was applied to the center of the core, the elastic modulus in the axial direction was obtained from the load-deflection ratio, and the bending strength was obtained from the breaking load.

(8) Evaluation of flatness A film having a width of 1 m and a length of 1 m is attached onto a non-woven fabric (Exeine E type manufactured by Toray Industries, Inc.) while wrinkles are stretched,
The film is left for 30 seconds and 1 minute and observed for the occurrence of tarumi on the film. The evaluation was performed as follows. ○: No tarmi even after left for 1 minute. Δ: Talumi did not occur after being left for 30 seconds, but talumi occurred after being left for 1 minute. ×: Talmi was generated after being left for 30 seconds.

(9) Evaluation of one-sided elongation A film having a width of 1 m and a length of 30 m is placed on a stainless steel plate, and the whole film is attached to the plate while being stretched with a cloth from the center of the film. A thread is stretched over the film edges of 0 and 30 m, and the distance between the film edge at the center of the film (15 m) and the thread is measured and used as the value of one-sided elongation.

Example 1 Dimethyl terephthalate and ethylene glycol were polymerized by a conventional method using calcium acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst and phosphoric acid as a stabilizer. Average particle size of 0.3μ as a lubricant during polymerization
m spherical silica particles synthesized by the water glass method were added so as to be 0.3% by weight to obtain polyethylene terephthalate having an intrinsic viscosity of 0.620 (polyester A).

The above polyester A was dried, supplied to an extruder, melted at 280 ° C., cast on a cooling roll through a slit die and rapidly solidified to obtain an amorphous film having a thickness of 210 μm.

Then, this was placed at 115 ° C. in a longitudinal direction of 3.4.
Double stretching at 95 ° C in the transverse direction at 3.4 times, again at 135 ° C in the longitudinal direction at 1.7 times, again at 205 ° C in the width direction at 1.2 times, and then at 210 ° C at 2 times. Heat treated for seconds,
A biaxially oriented film original film having a thickness of 9 μm was obtained. This film stock has a length of 1200 mm and a thermal expansion coefficient of 1.4 × 1.
0 ^-5 / ° C, axial bending strength 210 MPa, axial elastic modulus 14.7 GPa, surface roughness (Ra) 0.2 μm,
Fiber reinforced plastic with surface hardness of 85 ° shore (FW
P) Core (FWP-10 manufactured by Tenryu Kogyo Co., Ltd.) was wound by a surface center wind type slitter on a film roll having a width of 1 m and a length of 10,000 m and a winding tension of 10 kg /
It was wound up at a winding contact pressure of 50 kg / m and a winding speed of 150 m / min.

This film roll is heated to a temperature of 60 ° C. and a humidity of 1
The film was heat-treated at 0% RH for 40 hours and then left standing at a temperature of 25 ° C. and a humidity of 60% RH for 24 hours to evaluate the physical properties of the film.

The results of measurement and evaluation of the obtained polyester film properties are shown in Table 1 together with those of other Examples and Comparative Examples.

Example 2 The amorphous film of Example 1 was used at 115 ° C. in a longitudinal direction of 3.5.
Double stretching at 95 ° C in the transverse direction 3.3 times, stretching at 135 ° C in the longitudinal direction 1.7 times again, and then heat-treating at 205 ° C for 2 seconds to prepare a biaxially oriented film original film having a thickness of 9 μm. Obtained. The obtained film original fabric was wound into a roll in the same manner as in Example 1, and the film roll was heated at a temperature of 45 ° C. and a humidity of 10%.
Heat treatment at RH for 72 hours, then temperature 25 ℃, humidity 60
The film was allowed to stand for 24 hours at% RH to evaluate the physical properties of the film.

Example 3 An original film film was prepared under the same conditions as in Example 1 except that the heat setting temperature was 210 ° C. when the biaxially oriented film original film having a thickness of 9 μm of Example 1 was obtained. . The obtained film raw fabric was wound into a roll in the same manner as in Example 1, and the film roll was heat treated at a temperature of 60 ° C. and a humidity of 10% RH for 40 hours, and then left at a temperature of 25 ° C. and a humidity of 60% RH for 24 hours. Then, the physical properties of the film were evaluated.

Comparative Example 1 In obtaining the biaxially oriented original film having a thickness of 9 μm of Example 1, the film temperature after heat setting was 120 ° C. and the tension was 250 kg / cm.
Except that for ² at 2 seconds relaxation heat treatment to obtain a film raw under the same conditions as in Example 1. The physical properties of the obtained film were evaluated.

Comparative Example 2 When obtaining the 9 μm thick biaxially oriented film stock of Example 1, the heat setting temperature was set to 210 ° C., the film temperature after heat setting was 100 ° C. and the tension was 250 kg / cm ² for 2 seconds. An original film film was obtained under the same conditions as in Example 1 except that the relaxation heat treatment was performed.
The physical properties of the obtained film were evaluated.

Comparative Example 3 In obtaining the biaxially oriented film roll of Example 3 having a thickness of 9 μm, the winding core was changed to a polyvinyl chloride (PVC) core (manufactured by Showa Marutsu Co., Ltd.) to obtain a film roll. It was
The film roll 6 at a temperature of 70 ° C and a humidity of 10% RH
The film was heat-treated for 0 hour and then left standing at a temperature of 25 ° C. and a humidity of 60% RH for 24 hours to evaluate the physical properties of the film.

Comparative Example 4 In obtaining the 9 μm thick biaxially oriented film stock of Example 1, the heat setting temperature was set to 220 ° C., the film temperature after heat setting was 100 ° C. and the tension was 250 kg / cm ² for 2 seconds. An original film film was obtained under the same conditions as in Example 1 except that the relaxation heat treatment was performed.
The physical properties of the obtained film were evaluated.

The polyester film satisfying the requirements of the present invention has a small amount of one-sided elongation as shown in Table 1 and has good flatness of the film. On the other hand, with the polyester film outside the scope of the present invention, a film in which the amount of one-sided elongation and the flatness of the film were both good could not be obtained.

[0045]

[Table 1]

[0046]

EFFECT OF THE INVENTION The film of the present invention and the heat treatment method thereof have high strength, excellent dimensional stability, small single-sided elongation, and good flatness.

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Claims (14)

[Claims] 1. A polyester film having a heat shrinkage in the longitudinal direction at 80 ° C. of 0.25% or less and a crystal size (χ
A polyester film having _c ) of 6 nm or less. 2. The polyester film according to claim 1, wherein the polyester film has a Young's modulus in the longitudinal direction of 6.3 GPa or more and a sum of Young's modulus in the longitudinal direction and Young's modulus in the width direction is 11.7 GPa or more. 3. The polyester film according to claim 1, wherein the breaking elongation in the longitudinal direction of the polyester film is 65% or more. 4. The polyester film is selected from the group consisting of ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, and ethylene 2,6-naphthalate. At least one of them is a main structural unit.
The polyester film as described in any one of 3 to 3. 5. The polyester film according to claim 4, wherein the polyester film has ethylene terephthalate as a main constituent unit. 6. A polyester film for a digital magnetic recording medium according to claim 1. 7. A heat treatment method for a polyester film, which comprises subjecting the film roll to a heat treatment at a step of producing the polyester film according to any one of claims 1 to 6 or at any stage after the production. 8. The heat treatment method for a polyester film according to claim 7, wherein the heat treatment is performed at a temperature of 65 ° C. or less and a humidity of 30% RH or less. 9. The heat treatment method for a polyester film according to claim 7, wherein the core of the film roll is a fiber reinforced plastic. 10. The heat treatment method for a polyester film according to claim 7, wherein the core of the film roll has a coefficient of thermal expansion of 3 × 10 ⁻⁵ / ° C. or less. 11. The heat treatment method for a polyester film according to claim 7, wherein an axial bending strength of the core of the film roll is 190 MPa or more. 12. The heat treatment method for a polyester film according to claim 7, wherein the core of the film roll has an axial elastic modulus of 9.8 GPa or more. 13. The heat treatment method for a polyester film according to claim 7, wherein the surface roughness (Ra) of the core of the film roll is 0.5 μm or less. 14. The heat treatment method for a polyester film according to claim 7, wherein the surface hardness of the core of the film roll is 65 ° Shore or more.