JPH0796544A - Biaxially oriented polyester film and its manufacture - Google Patents

Abstract

PURPOSE:To achieve a good strength in the lateral direction, electromagnetic exchanging properties and slit properties of a film by a method wherein the ratio between the F-5 value in the longitudinal direction and the F-5 value in the lateral direction is specified and the ratio between the refractive index in the longitudinal direction and the refractive index in the lateral direction are also specified. CONSTITUTION:The F-5 value in the lateral direction of a film is more than 14kg/mm<2>, the ratio between the F-5 value in the longitudinal direction and that in the lateral direction is less than 1.1 and the ratio (MD/TD) between the refractive index in the longitudinal direction and that in the lateral direction is more than 0.975. Polyethylene terephthalate is preferable especially as polyester. In a manufacture, the material is melted and extruded in a filmy state by an extruding machine, made into an amorphous state by quenching and solidifying, stretched and oriented in two steps in a longitudinal direction. The stretching temperature is a glass temperature (Tg)-Tg+60 deg.C and the second step stretching is performed at a temperature lower by at least 5 deg.C than the stretching temperature of the first step. Then the two step stretching and orientation is performed in the lateral direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film suitable for magnetic recording media, capacitors and packaging.

[0002]

2. Description of the Related Art Polyester films represented by polyethylene terephthalate have hitherto been widely used as magnetic recording media, capacitors, packaging films and the like. In recent years, thinning has progressed in various applications, and there is an increasing demand for improvement in mechanical strength of films. Especially in magnetic media applications, the tape thickness tends to become thinner as the recording time becomes longer and the cassette size becomes more compact, and the rigidity of the tape decreases as the film becomes thinner and the head touch of the tape becomes defective.
There is a problem that recording may be lost or image quality may be deteriorated. In order to improve the head touch of the magnetic tape, it is effective to improve the mechanical strength of the base film in the width direction, and in recent years, the strength of the base film in the width direction has been improved. However, if the strength in the width direction of the film is improved, the life of the slitting cutter will be shortened or the cut portion (edge) of the tape will be shortened when the tape is slit to the required width in the slitting step of the magnetic tape processing process. There is a problem that the tape edge is deformed into a wakame shape if it is wound up on a reel after slitting and left to stand, and it becomes unusable as a product in a severe situation.

A conventional technique is, for example, Japanese Patent Laid-Open No. 54-54.
There are polyester films, etc., which have improved slitting property by defining the longitudinal and lateral Young's modulus of the film as shown in 11179, but such a polyester film has insufficient slitting property and becomes severer year by year. It is becoming impossible to adapt to severe processing conditions and usage conditions as products.

The present invention has solved the above problems, has high mechanical strength in the film width direction, has good electromagnetic conversion characteristics (especially RF output) when used as a magnetic tape, and has a cutter life during slitting during the film processing process. It is an object of the present invention to provide a biaxially oriented polyester film having a long length and good slitting property without causing edge rise.

[0005]

The present invention has an F-5 value in the film width direction (TD) of 14 kg / mm ² or more, and a ratio of the F-5 value in the film longitudinal direction (MD) to the width direction (MD / T).
D) is 1.1 or less, and the ratio (MD / TD) of the refractive index in the longitudinal direction and the width direction of the film is 0.975 or more, or a biaxially oriented polyester film, or a film width direction Ratio of F-5 value of (TD) and tear resistance (EL) in the longitudinal direction (MD) of the film (F-5 value T
D / ELMD) is 50 or more and 300 mm ⁻¹ or less, and the main point is a biaxially oriented polyester film.

The polyester in the present invention is not particularly limited, and polyethylene terephthalate, polyethylene-
Examples thereof include 2,6-naphthalate, and among them, polyethylene terephthalate is particularly preferable. Further, other polymers or various additives may be blended or copolymers with other polymers may be used as long as the effects of the present invention are not impaired.

Although not particularly limited, it is more preferable that the biaxially oriented polyester film of the present invention contains inert particles such as inorganic particles and organic particles. Examples of the inorganic particles include silicon dioxide, calcium carbonate, aluminum oxide, and examples of the organic particles include ethylvinylbenzene-divinylbenzene copolymer and polymethylmethacrylate. These inert particles may be used alone or in combination of two or more. By containing these inert particles, the slipperiness of the film is improved, and the handling property in the film forming and processing steps and the running property when used as a product such as a magnetic tape are improved.

The biaxially oriented polyester film according to claim 1 of the present invention has an F-5 value in the width direction (TD) of 14 kg / mm.
² or more, preferably 15 kg / mm ² or more, the ratio of the F-5 value in the longitudinal direction (MD) to the width direction (TD) is 1.1 or less,
Preferably, it should be in the range of 0.3 or more and 1.05 or less. If the F-5 value in the width direction is not within the above range,
Since the mechanical strength in the width direction of the film is insufficient, when the magnetic tape is used, the head touch with the magnetic head becomes defective, and good electromagnetic conversion characteristics cannot be obtained. Further, when the ratio of the F-5 value in the longitudinal direction and the width direction is not within the above range, the slit property is deteriorated, which is not preferable.

Furthermore, the biaxially oriented polyester film has a refractive index ratio (MD / TD) of 0.97 in the longitudinal and width directions.
It should be 5 or more, preferably 0.98 or more and 1.5 or less. If the refractive index ratio is out of the above range, the electromagnetic conversion characteristics and the slit property cannot be compatible when the magnetic tape is the object of the present invention. By setting the ratio of the refractive index in the longitudinal direction to the width direction of the film in the above range, a biaxially oriented polyester film having good slitting property can be obtained even if the F-5 value in the film width direction is high.

The biaxially oriented polyester film of claim 2 of the present invention has a ratio (F-) of F-5 value in the film width direction (TD) and tear resistance (EL) in the film longitudinal direction (MD).
5-value TD / ELMD) is 50 or more and 300 mm ⁻¹ or less,
It is preferably 55 or more and 250 mm ^-1 or less, more preferably 60 or more and 200 mm ^-1 or less. When the ratio of the F-5 value in the width direction and the tear resistance in the longitudinal direction of the film deviates from the above range, the electromagnetic conversion characteristics and the slit property of the magnetic tape, which is the object of the present invention, cannot be satisfied at the same time.

The biaxially oriented polyester film according to claim 2 of the present invention has an F-5 value in the film width direction of 14 kg /
When it is at least ² mm ² , it is particularly effective and preferable for improving the electromagnetic conversion characteristics of a magnetic tape, which is one of the effects of the present invention.

Next, a method for producing the biaxially oriented polyester film of the present invention will be described. As the polyester of the present invention, those obtained by a conventionally known method can be used. After the polyester is sufficiently dried, it is supplied to a known extruder, passed through a filter selected if necessary, and melt-extruded in a film form from a die.
This film polyester is rapidly cooled and solidified on a casting drum controlled to a temperature of 20 to 60 ° C. to be in an amorphous state. At this time, it is more preferable to improve the adhesion between the drum and the polyester film by using a known electrostatic applying device.

The obtained amorphous polyester is first stretched and oriented in the longitudinal direction. The polyester film is passed through a sufficiently heated roll to be preheated, and the stretching temperature in the longitudinal direction is the glass transition temperature (Tg) to Tg + of the polyester.
At a temperature range of 60 ° C., preferably Tg + 20 ° C. to Tg + 50 ° C., after 1.2- to 4-fold, preferably 1.5 to 3-fold, one-step stretching, at a temperature 5 ° C. or more lower than the first-stage stretching temperature. 2 to 5 times, preferably 2.5 to 4 times, the second stage stretching is performed. Performing such a two-stage stretching is particularly suitable for setting the ratio of the refractive index of the film, the ratio of F-5 value in the film width direction and the tear resistance in the film longitudinal direction within the range of the present invention.

Next, stretch orientation is performed in the width direction. Stretching in the width direction is performed by a well-known stenter at a temperature of Tg or more of the obtained uniaxially stretched film at a draw ratio of 2 to 5 times in the first stage, and then 170 ° C. or more, preferably 170 to 220.
The second stage stretching is performed 1.1 to 3 times at a high temperature of ° C. In this way, the stretching in the width direction is divided into two stages, and the stretching temperature in the second stage is set to a high temperature of 170 ° C. or higher, so that the biaxially oriented polyester film of the present invention has a high value in the width direction F-5 value. Is particularly preferable in order to improve the electromagnetic conversion characteristics when used as a magnetic tape. In addition, heat treatment is performed if necessary. The heat treatment is below the melting point of the polyester either under a fixed length or in a relaxed state, and 18 for polyethylene terephthalate.
It is performed for 0.5 to 60 seconds in the temperature range of 0 to 240 ° C.

[0015]

[Measurement method of physical properties and evaluation method of effect]

(1) Refractive index of film Abb using sodium D ray (wavelength 589 nm) as a light source
e The refractive index in the longitudinal direction (MD) and the width direction (TD) of the film is measured by a refractometer, and the MD / TD ratio of the refractive index is calculated. Methylene iodide is used as the mount solution. (2) F-5 value of film A sample film with a width of 10 mm is set in a tensile tester so that the length between chucks is 100 mm, and the temperature is 23 ° C. and 65 ° C.
A tensile test was performed at a tensile speed of 200 mm / min under the condition of% RH to measure the strength of the film at 5% elongation, and the strength was F-
It was set to 5 values. The F-5 value was measured in the longitudinal direction and the width direction of the film, and the longitudinal direction (MD) and the width direction (T
The ratio (MD / TD) of D) is calculated.

(3) Tear resistance (EL) For example, an Elmendorf tear tester manufactured by Toyo Seiki Seisaku-sho, Ltd. is used. 63.5m in the longitudinal direction of the sample film
m, 50.8 mm in the width direction is sampled, a 12.7 mm cut is made in the longitudinal direction at a right angle at the center of both grips along the width direction, and the tearing force (g) for the remaining 50.8 mm is obtained. This force was divided by the thickness of the film to obtain the tear resistance in the machine direction (MD). Unit is g / m
m. The ratio of the F-5 value in the width direction obtained in (1) and the tear resistance obtained here (F-5 value TD / ELMD) is obtained.

(4) RF Output After kneading and dispersing the magnetic coating composition having the following composition into the film, 5 parts of Coronate L from Nippon Polyurethane Industry was added to obtain a magnetic coating, which was coated with a gravure roll, magnetically oriented and dried. Furthermore, using a calendering device (steel roll / nylon roll, 5 steps), temperature 75 ° C, linear pressure 220 kg / cm.
After calendering, cure at 70 ° C for 48 hours. This raw magnetic tape was slit into a 1/2 inch width to prepare a magnetic tape pancake. A tape is stored in the cassette from this pancake to make a video cassette. A test signal was recorded on this cassette using a home-use VCR, and the RF output was measured using a color video noise measuring device.

Ferromagnetic powder Co-γ-Fe ₂ O ₃ : 100 parts α-alumina: 5 parts Metal sulfonate-containing vinyl chloride resin: 10 parts Polyester polyurethane resin: 5 parts Carbon black: 1 part Mistyric acid: 1 part Stearin Acid: 1 part Butyl stearate: 1 part Cyclohexanone: 100 parts Methyl ethyl ketone: 100 parts

(5) Slitting property The magnetic tape stock prepared in the above manner is slit into a 1/2 inch width and a length of 3000 m is wound up as a pancake. This pancake is observed from the direction shown in FIG. The state of the edge portion was judged according to the following criteria, and ◯ and Δ were regarded as good characteristics.

There is no swelling at the edge part: ○ There is a little swelling at the edge part: △ The swelling at the edge part can be seen at a glance: ×

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the invention of claim 1 will be described based on embodiments.

Example 1 (Tables 1 and 2) Polyethylene terephthalate pellets obtained by a known method were dried at 180 ° C. under vacuum for 5 hours, fed to an extruder, melted at a temperature of 280 ° C. and extruded from a die. A film in an amorphous state was obtained by cooling and solidifying on a casting drum having a surface temperature of 25 ° C. by using the electrostatic application method. This film was stretched in the longitudinal direction and the width direction under the conditions shown in Table 1. First, using a longitudinal stretching machine in which several rolls are arranged, two-stage stretching is performed in the longitudinal direction by utilizing the peripheral speed difference of the rolls, and then two-stage widthwise stretching is performed with a stenter to achieve a constant length of 210.
Heat treatment was performed at 4 ° C. for 4 seconds to obtain a biaxially oriented polyester film having a thickness of 10 μm. F- in the width direction of the obtained film
The 5-value was 20 kg / mm ² , the ratio of the F-5 value in the longitudinal direction to the width direction was 0.6, and the ratio of the refractive index in the longitudinal direction to the width direction was 0.99. When the RF output of this film was measured as a magnetic tape by the method shown above, it was +1.8.
A very high value of dB was obtained. In addition, the edge of the pancake was not swollen and the slitting property was good.

Examples 2 to 6, Comparative Examples 1 to 5
(Table 1 and Table 2) Using the same pellet, extruder and stretching device as in Example 1, biaxially oriented polyester films were obtained. The stretching conditions and the properties of the obtained film are shown in Tables 1 and 2.
When the F-5 value in the film width direction, the ratio of the F-5 value in the longitudinal direction to the width direction, and the ratio of the refractive index in the longitudinal direction to the width direction all satisfy the range of the present invention, it is high when used as a magnetic tape. RF
The output and the good slitting property could be satisfied at the same time, but if even one of these characteristics was out of the range of the present invention, both the RF output and the slitting property could not be made good at the same time.

Next, the invention of claim 2 will be described based on embodiments.

Example 7 (Tables 3 and 4) Polyethylene terephthalate pellets obtained by a known method were dried at 175 ° C. under vacuum for 3.5 hours, then fed to an extruder and melted at a temperature of 285 ° C. It was further extruded and cooled and solidified on a casting drum having a surface temperature of 25 ° C. by using an electrostatic application method to obtain an amorphous unstretched film. This film was stretched in the longitudinal direction and the width direction under the conditions shown in Table 3. First, by using a longitudinal stretching machine in which several rolls are arranged, two stages are stretched in the longitudinal direction by utilizing the peripheral speed difference of the rolls, and then two stages in the width direction are stretched by a stenter to obtain a uniform length of 200. Thickness is 8.5μm after heat treatment at ℃ for 3 seconds.
A biaxially oriented polyester film of was obtained. The ratio of the F-5 value in the width direction and the tear resistance in the longitudinal direction of the obtained film was 85 × 10 ⁻³ , and the F-5 value in the width direction was 19 kg / mm.
There were ^two . When the RF output of this film was evaluated as a magnetic tape by the method described above, it was good at 1.5 dB. In addition, the edge of the pancake was not swollen and the slitting property was good.

Examples 8 to 11 and Comparative Examples 6 to 9 (Tables 3 and 4) Biaxially oriented polyester films were obtained using the same pellets, extruder and stretching device as in Example 7. The stretching conditions and the properties of the obtained film are shown in Tables 3 and 4.
When the ratio of the F-5 value in the film width direction and the tear resistance in the longitudinal direction was within the range of the present invention, both RF output and slit property could be satisfied at the same time. However, when the ratio of the F-5 value in the film width direction and the tear resistance in the longitudinal direction is out of the range of the present invention, the RF output and the slit property could not be made good at the same time.

[0027]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[0028]

The biaxially oriented polyester film according to claim 1 of the present invention has an F-5 value in the film width direction, a ratio of the F-5 value in the longitudinal direction to the width direction, and a refractive index in the longitudinal direction and the width direction. The ratio is within a specific range, and the biaxially oriented polyester film of claim 2 has a ratio between the F-5 value in the film width direction and the tear resistance in the longitudinal direction within a specific range, both of which are processed into products. Conventionally, it is a biaxially oriented polyester film that has the opposite characteristics at the same time that the swelling (high edge) of the tape edge at the time of slitting is small and the electromagnetic conversion characteristics when it is made into a magnetic tape are good, especially these characteristics Is very useful in magnetic media applications where is required. Further, it can be widely used not only for magnetic media applications but also for applications requiring strength in the width direction of a film and cutting properties such as slits.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method of determining a slit property in the present invention.

[Explanation of symbols]

 1: Observation direction of pancake 2: Model diagram when slitting property is poor 3: Model diagram when slitting property is good

Claims (4)

[Claims] 1. The F-5 value in the film width direction (TD) is 1.
4 kg / mm ² or more, F-5 value film longitudinal direction (M
D) and the ratio in the width direction (MD / TD) is 1.1 or less,
In addition, the ratio of the refractive index in the longitudinal direction to the width direction of the film (MD /
A biaxially oriented polyester film having a TD) of 0.975 or more. 2. The ratio (F-5 value TD / ELMD) of the F-5 value in the film width direction (TD) and the tear resistance (EL) in the film longitudinal direction (MD) is 50 or more and 300 mm ^−1.
A biaxially oriented polyester film characterized by being: 3. The F-5 value in the film width direction is 14 kg /
The biaxially oriented polyester film according to claim 2, wherein the biaxially oriented polyester film is at least ² mm ² . 4. A substantially amorphous unstretched polyester film is stretched in two or more stages in the longitudinal direction, then stretched in the width direction by one stage, and then stretched in a second stage at a temperature of 170 ° C. or more. The method for producing a biaxially oriented polyester film according to any one of claims 1 to 3, wherein: