JP2000202904A - Polyester film and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyester film very suitable for various industrial material films such as for a magnetic recording medium, for a capacitor, for a heat transfer ribbon, for a heat sensitive stencil printing stock paper or the like by a method wherein the film is excellent in a rigidity, a toughness, a dimensional stability, electrical characteristics or the like, and, at the same time, has a few uneven thickness and few surface defects. SOLUTION: In the polyester film manufacturing method comprising the step of stretching a film made of a resin mainly consisting of a polyester by using a simultaneous biaxial tenter, the first method includes three times or more of minutely stretching operations with the area draw ratio of the film of 1.0005-3.0 so as to obtain the total area draw ratio of 25-150, while the second method includes 2-10,000 times of a series of operations, each of which consists of the stretching of the film and its successive relaxation so as to obtain the total area draw ratio of 25-150.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film having greatly improved physical properties and quality of a conventional polyester film and a method for producing the same.

[0002] Specifically, rigidity, toughness, dimensional stability,
It has excellent electrical properties, and has little unevenness in thickness and surface defects.Because of these properties, it is very useful as a film for various industrial materials such as for magnetic recording media, capacitors, thermal transfer ribbons, and heat-sensitive stencil printing paper. And a method for producing the film.

[0003]

2. Description of the Related Art Plastic films enable continuous production of large-area films that cannot be obtained from other materials, and can impart strength, durability, transparency, flexibility, and surface characteristics. For magnetic recording media,
It is used in various fields that are in large demand, such as for agriculture, packaging, and building materials.

[0004] Among them, biaxially stretched polyester film has excellent mechanical properties, thermal properties, electrical properties,
It is used in various fields for its chemical resistance.
In particular, its usefulness as a base film for a magnetic tape does not allow other films to follow. In this field, in particular, in recent years, further thinning of the base film has been required in order to reduce the weight, size, and long-time recording of equipment. In recent years, there has been a very strong tendency to reduce the thickness of thermal transfer ribbons, condensers, and heat-sensitive stencil sheets.

However, when a film is made thinner,
Mechanical strength is insufficient, the strength of the film's waist is weakened, or it becomes easy to stretch, for example, for magnetic recording media, it becomes susceptible to tape damage or head touch deteriorates Electromagnetic conversion characteristics may be reduced. Also, when the film is thinned, the flatness of the ribbon at the time of printing cannot be maintained for the thermal transfer ribbon, causing printing unevenness and over-transfer, and the dielectric breakdown voltage decreases for the capacitor use. There is.

[0006] In such a tendency to reduce the thickness, it is desired to further increase the strength by improving mechanical properties such as tensile properties typified by Young's modulus.

For this reason, conventionally, various methods have been studied for increasing the strength of the film.

[0008] As a generally known technique for increasing the strength of a biaxially stretched polyester film, for example, a film stretched in two vertical and horizontal directions is stretched in the vertical direction again to increase the strength in the vertical direction. The so-called re-longitudinal stretching method is generally used (for example, Japanese Patent Publication No. 42-9270, Japanese Patent Publication No.
3040, JP-A-46-1119, JP-A-46-1120, etc.). In order to further impart strength in the horizontal direction, a re-longitudinal re-horizontal stretching method has been proposed in which the above-described re-vertical stretching is performed and then the film is stretched in the horizontal direction again (for example, Japanese Patent Application Laid-Open No. Sho 50/1985). JP-A-133276, JP-A-55-22915). In addition, a longitudinal multi-stage stretching method in which the first stage stretching is performed in two or more stages in the machine direction of the film and subsequently the film is stretched in the transverse direction has been proposed (for example, Japanese Patent Publication No. 52-33666, Japanese Patent Publication No. Sho 52-33666). 57-49377, etc.).

This longitudinal multi-stage stretching method is superior to the above-described re-longitudinal stretching method and the re-longitudinal re-horizontal stretching method in order to increase strength, improve film thickness unevenness, and improve productivity. However, when the strength of the film is increased, the heat shrinkage of the film is also increased, and a problem that is not practically preferred that the film is frequently broken is also the same in the case of this vertical multi-stage stretching method. .

As one of the conventionally known film manufacturing methods similar to the method of the present invention described later, the film is continuously repeated at least three times in at least one of the longitudinal direction and the lateral direction of the film. There is a proposal of a fine stretching repetition method (extreme multi-stage stretching method) in which stretching is carried out by stretching (Japanese Unexamined Patent Publication No. Hei 8-22477).
No. 7, JP-A-9-57845). However, JP-A-8-224777 and JP-A-9-5784 disclose the following.
In the invention described in Japanese Patent Publication No. 5 only, a specific example in the case of sequential biaxial stretching is mainly shown, and effective film forming mechanisms, apparatuses, and process conditions in the case of simultaneous biaxial stretching are described. In addition, it is not specifically mentioned, and in addition, it is also possible to cope with high-magnification stretching, and the effectiveness of the simultaneous biaxial stretching method using a linear motor system which is proposed to be used as a preferable apparatus in the present invention is also described. Not touched at all.

On the other hand, in recent years, a simultaneous biaxial tenter of a linear motor type has been developed and has attracted attention due to its high film forming speed (for example, Japanese Patent Publication No. 51-33590, US Pat. No. 4,853,602). Specification, U.S. Pat.
No. 675582).

That is, in a conventional simultaneous biaxial stretching method, a screw method in which a clip is placed on a screw groove to increase a clip interval, or a pantograph method in which a clip interval is increased by using a pantograph, etc. In any case, there are problems such as a low film-forming speed, difficulty in changing conditions such as stretching ratio, and difficulty in stretching at high magnification. On the other hand, the linear motor simultaneous biaxial stretching method can solve these problems at once.

JP-B-51-33590 discloses that the interval between tenter clips is changed by electric force generated by a linear motor to enable high-efficiency production. Also, the above-mentioned U.S. Pat.
No. 3,602 discloses a stretching system using a linear motor, and the above-mentioned U.S. Pat. No. 4,675,582 discloses a system for controlling a large number of linear motors along a stretching section. An effective system is disclosed. However, these U.S. patents do not mention the stretching method disclosed in the present invention or the high-quality polyester film obtained by the method.

That is, the process conditions for producing a polyester film having excellent physical properties and quality by simultaneous biaxial stretching of the linear motor system are still unknown, and an effective stretching technique has yet to be explored.

[0015]

As described above, there is still room for improvement in the technology that enables the production of a polyester film having high physical properties and quality, and there is a need for the development of a new technology. This is the current state of the art.

An object of the present invention is to provide a high-quality polyester film which is excellent in mechanical strength and thermal dimensional stability and has small thickness unevenness, and a method for producing the same.

An object of the present invention is to provide a high-quality polyester film which is excellent in rigidity, toughness and dimensional stability, has less thickness unevenness and surface defects, and a method for producing the same.

The present inventors have intensively studied a technique for maximizing the physical properties and quality of a polyester film.

[0019]

As a result, a simultaneous biaxial tenter is used to perform three or more times of fine stretching at an area stretching ratio of 0.0005 to 3.0 times, and the total area stretching ratio is 25%. It has been found that the object of the present invention can be achieved by employing the first method for producing a polyester film of the present invention, in which the film is stretched so as to be up to 150 times.

Alternatively, following the stretching, the production of the second polyester film of the present invention is carried out in such a manner that the film is stretched so as to have a total area stretching ratio of 25 to 150 times, comprising two or more and less than 10,000 times a relaxation operation. It has been found that the object of the present invention can be achieved by using the method.

By adopting the first method of the present invention or the second method of the present invention, (1) the Young's modulus of the polyester film is greatly increased, the heat shrinkage is reduced, and (2) stretching. Magnification increases, productivity increases, (3) film thickness unevenness improves, film breakage frequency decreases, (4) film crystallinity tends to increase, even if the temperature of the heat treatment zone is lowered Numerous surprising findings such as that the heat shrinkage rate does not deteriorate have been found, and the present invention has been completed.

That is, the gist of the present invention is as follows:
This is a method for producing a first polyester film or a method for producing a second polyester film.

The first method of the present invention relates to a method for producing a polyester film in which a film composed of a resin containing polyester as a main component is stretched using a simultaneous biaxial tenter, wherein the stretch ratio of the film is from 0.0005 to 3%. A polyester film production method characterized by including an operation of fine stretching at a magnification of 0.0 times three times or more and a total area stretching ratio of 25 to 150 times (hereinafter, this first production method is referred to as , "Production method (I)").

The method (I) for producing a polyester film of the present invention has the following preferred embodiments.

(A) The fine stretching operation is continuously performed three times or more.

(B) Fine stretching is repeated 10 times or more and less than 10,000 times.

(C) For the unstretched film, the fine stretching is performed by (glass transition temperature (Tg) +10) ° C. to (Tg + 1).
20) Perform in a temperature range of ° C.

(D) The fine stretching is continuously repeated with respect to the unstretched film until the crystallinity of the film becomes 3% or more and less than 30%.

The second method of the present invention is a method for producing a polyester film obtained by stretching a film composed of a resin containing polyester as a main component by using a simultaneous biaxial tenter. This is a method for producing a polyester film, comprising a series of relaxing operations of 2 times or more and less than 10000 times, and a total area stretching ratio of 25 to 150 times (hereinafter, this second method is referred to as " Production method (II) ").

The polyester film production methods (I) and (II) of the present invention both have the following preferred embodiments.

(A) The drive system of the clip is a linear motor system.

Further, the polyester film of the present invention comprises:
A polyester film produced by the production method (I) or (II) of the present invention described above.

Further, the polyester film has the following preferred embodiments.

(A) The sum of the Young's modulus in the longitudinal and transverse directions of the film is 8 to 30 GPa, and the sum of the heat shrinkage at 100 ° C. for 30 minutes is 2% or less.

(B) The degree of crystallinity is 30 to 90%.

(C) The polyester is polyethylene terephthalate, polyethylene naphthalate, or a copolymer or modified product thereof.

(D) The intrinsic viscosity is 0.6 or more.

The polyester film according to the present invention is suitable for applications such as a magnetic recording medium, a capacitor, a thermal transfer ribbon, and a base film of a heat-sensitive stencil.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The polyester in the present invention is a polymer containing at least 80% by weight of a polymer obtained by condensation polymerization of a diol and a dicarboxylic acid. Dicarboxylic acids are terephthalic acid, isophthalic acid, phthalic acid,
Those represented by naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like, and the diols represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexane dimethanol and the like.

Specifically, for example, polymethylene terephthalate, polyethylene terephthalate, polypropylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene- 2,6-naphthalate can be mentioned. These polyesters may be homopolymers or copolymers, and as copolymerization components, for example, diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, and isophthalic acid And dicarboxylic acid components such as 2,6-naphthalenedicarboxylic acid, and hydroxycarboxylic acid components such as hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

In the case of the present invention, in particular, polyethylene terephthalate, polyethylene naphthalate (polyethylene-
2,6-naphthalate) and their copolymers and modified products are preferred in that the effects of the present invention can be further enhanced.

In the present invention, the intrinsic viscosity of the polyester is preferably 0.6 or more, more preferably 0.8 or more, and most preferably 1.0 or more. High molecular weight polyesters usually have the disadvantage that the heat shrinkage of the film also increases with an increase in Young's modulus, but according to the production method of the present invention, not only the total area stretching ratio of the film is increased but also Since the relaxation of the fine structure proceeds effectively, the heat shrinkage can be reduced.

The term "stretching" as used in the present invention is an operation for imparting orientation in the longitudinal and lateral directions of the film. The film is conveyed while holding both ends of the film with clips using a simultaneous biaxial tenter. Refers to an operation of pulling in at least one direction selected from a vertical direction and a horizontal direction. The “longitudinal direction” of the film is the longitudinal direction of the film, and the “lateral direction” is the width direction of the film. The “simultaneous biaxial stretching” is an operation in which the stretching in the longitudinal direction and the stretching in the transverse direction are simultaneously performed temporally. Before or after, or before or after this "simultaneous biaxial stretching", it is also possible to perform further stretching, for example, after stretching alone or sequentially in the transverse or longitudinal direction, and then in the longitudinal and transverse directions Methods for simultaneous stretching, and after further simultaneous biaxial stretching, such as a method for further stretching independently or sequentially in the horizontal or vertical direction,
It is not excluded by the present invention.

In the present invention, it is preferable to use a linear motor type simultaneous biaxial tenter as the stretching machine capable of freely changing the stretching direction and the stretching ratio.

As described above, the simultaneous biaxial tenter of the linear motor type is capable of (1) increasing the film forming speed and film width to the level of conventional biaxial stretching or more, and (2) increasing the magnification. (3) Stretching, heat treatment,
In recent years, attention has been paid to the fact that the deformation pattern of the film in the relaxation step can be freely changed.

In the method of the present invention, the super-multi-stage stretching using the simultaneous biaxial tenter of the linear motor system is adopted.
It is particularly preferable to obtain a polyester film having high physical properties and quality at low cost.

Next, the production method (I) of the present invention will be described. In this method, the area stretching magnification of one fine stretching at the time of performing this super-multi-stage stretching is set to be 0.0005 to 3.0 times, the fine stretching is performed three times or more, and the total area stretching magnification is 25 times. It is necessary to be ~ 150 times.

Here, the "area stretching ratio" is the product of the longitudinal stretching ratio and the transverse stretching ratio of the film. In the present invention, `` fine stretching '' refers to stretching in which the stretching ratio is smaller than usual, and generally speaking, the stretching ratio is an area stretching ratio.
It refers to stretching within the range of 3.0 times or less.

In the present invention, fine stretching is repeated as described above. However, if the area stretching ratio by one fine stretching exceeds 3.0 times, the intended effect of the present invention is hardly obtained. It is not a practical requirement that the ratio be less than 1.005 times.

The area stretching ratio in this single fine stretching is as follows:
1.00-2.0 times is more preferable, and 1.01-1.
5 times is more preferred. The number of fine stretching included in the production method (I) is preferably 10 times or more and less than 10,000 times,
More preferably 50 times or more and less than 1000 times. Also,
The fine stretching is preferably performed continuously three times or more. Although the final total area stretching ratio needs to be 25 to 150 times, preferably 30 to 120 times,
More preferably, it is 50 to 100 times. If the total area stretching ratio is less than 25 times, the desired effect of the present invention cannot be obtained, and it is practically difficult to exceed 150 times.

In the present invention, "one fine stretching" means (1) the stretching is stopped after each fine stretching as shown in the manufacturing method (I), and (2) the manufacturing method (II) (3) stretching after stretching, stretching mode, stretching ratio, temperature condition,
An operation such as changing a stretching condition such as a stretching speed is defined as one section.

In the case of the above (3), that is, in the case of continuous stretching, the relationship between the time and the magnification (or clip speed) in the vertical or horizontal direction is linear (monotonic increase). May also be non-linear. In the case of non-linearity, the inflection point in the curve representing the relationship between time and the magnification in the vertical or horizontal direction is used as a break in fine stretching. Here, the “stretching mode” refers to three types of stretching modes of “stretching only in the vertical direction”, “stretching only in the horizontal direction”, and “simultaneous stretching in the vertical and horizontal directions”. In the above (1), when the stretching is stopped, it is preferable to stop the drawing for 1/100 to 4/5 of the time required for the stretching. A more preferred stretching stop time is 1/100 to 3/5, and more preferably 1/10 to 1/2, of the time required for the immediately preceding stretching. In the present invention,
The stretching speed was 200 in each of the longitudinal and transverse directions.
It is preferably 0 to 300,000% / min, more preferably 5 to 30%.
000-200000% / min, more preferably 100
It is 00 to 100000% / min. The final film forming speed in the vertical direction is preferably 200 m / min or more, more preferably 300 m / min or more, and further preferably 4 m / min or more.
00 m / min or more. The stretching stop time in the above (1) may be changed depending on the stretching speed at that time.

In the present invention, the stretching temperature when the fine stretching is performed on the polyester film is not particularly limited.
(Glass transition temperature (Tg) of polyester + 10) ° C.
(Tg + 120) ° C., preferably (Tg + 2
0) ° C to (Tg + 80) ° C is more preferable. If the stretching temperature is lower than (Tg + 10) ° C., the orientation by stretching is so advanced that it is difficult to stretch to a high magnification.

On the other hand, when the stretching temperature exceeds (Tg + 120) ° C., it becomes difficult to give the polymer chains the fine orientation necessary for relaxing the structure, and the oligomers are scattered even in the stretching step. In the present invention, fine stretching is preferably performed at a stretching ratio until the yield point of the stress-strain curve is reached under each stretching temperature condition. Under such conditions, since the stretching tension and the strain correspond one-to-one, the uniformity of the thickness of the film due to stretching hardly deteriorates, and a high-quality polyester film is easily obtained. In order to fix the structure of the film, (Tg + 120) ° C or higher,
In the heat treatment performed at a temperature lower than the melting point, the fine stretching of the present invention is effective. In this case, the preferred area stretching ratio is 1.5 times or less, more preferably 1.2 times or less. Repeated stretching tends to increase the mechanical properties of the film.

In the present invention, fine stretching may be repeated in any step until a biaxially oriented polyester film is obtained by subjecting an unstretched film made of a resin mainly composed of polyester to stretching and heat treatment. It is preferable that the fine stretching is continuously repeated at least three times in the process until the crystallinity of the unstretched film becomes 3% or more and less than 30% or in the heat treatment process described above. Here, the unstretched film is obtained by feeding sufficiently dried raw material pellets to an extruder, extruding them into a sheet shape on a rotating metal casting drum with a T-type die, and cooling and solidifying the raw material pellets, or undried pellets. Is supplied to a vented extruder to obtain a similar product.

It is preferable that the fine stretching is continuously repeated in the initial stretching step before the unstretched film undergoes volume relaxation to increase the crystallinity, but even if the fine stretching is continuously repeated three or more times, When the crystallinity is less than 3%, it is difficult to remove the strain generated in the subsequent simultaneous biaxial stretching, and it is difficult to increase the stretching ratio.
The Young's modulus of the film and the heat shrinkage tend to increase sharply.

The crystallinity of the film after continuously repeating the fine stretching of the present invention with respect to the unstretched film,
More preferably, it is 5% or more and less than 25%.
% Or more and less than 20%. After the crystallinity exceeds 30%, the film may be repeatedly stretched finely, but may be stretched in one step at a high magnification. In particular, in the case of a raw material that is easily crystallized due to the effects of additives and the like, stretching at a high magnification in one step may be preferable to obtaining a film having excellent physical properties and quality, rather than repeating fine stretching. In addition, in the case of a film having a crystallinity of more than 30%, the volume is easily relaxed by fine stretching,
Since it tends to crystallize before being stretched at a high magnification and to have a low Young's modulus, it is necessary to devise a high-magnification stretching in one step in such a case.

Next, the production method (II) will be described.
The method involves stretching the film and then successively relaxing it two or more times and less than 10,000 times, and it is necessary that the total area stretching ratio is 25 to 150 times.

Here, "relaxation" refers to an operation in which the film is conveyed while holding both ends of the film with clips, and the film is relaxed in at least one direction selected from a longitudinal direction and a lateral direction to relax the stress. Say. Further, in the present invention, the film may be relaxed in the other direction while being stretched in one of the vertical direction and the horizontal direction.

In the present invention, when stretching and relaxation are performed at the same time, if the area stretching ratio of the operation is 1 or more, it is called “stretching”, and if it is less than 1, it is called “relaxation”.

Here, the “area stretch ratio” is the product of the vertical dimension change rate and the horizontal dimension change rate, and the “dimensional change rate” is the original length of the length after stretching or relaxation. It is the ratio to the height. When the dimensional change rate is 1 or more, the value indicates the stretching ratio. When the dimensional change rate is less than 1, the difference between the dimensional change rate (%) and 100 is the relaxation rate (%). In the prior art, the relaxation treatment has been mainly performed in the cooling step after the stretching of the film is completed, or after the stretching and heat treatment. However, in the present invention, the unstretched film that has been melt-extruded into a sheet and cast. It is preferable that the film is stretched to impart orientation to the film, and that the film is subjected to a relaxation treatment in the middle of the process until reaching a target final stretching ratio.

The direction of such stretching or relaxation, the stretching ratio,
In the present invention, it is preferable to use a linear motor type simultaneous biaxial tenter as a stretching machine capable of freely changing the relaxation rate. The features when using a linear motor type simultaneous biaxial tenter are as described above, and the film forming speed and film width are the same as those of conventional sequential biaxial stretching,
Alternatively, the deformation pattern of the film in the stretching, heat treatment, and relaxation steps can be freely changed, and the like.
In the present invention, it is particularly preferable to form a film by combining stretching and relaxation using this simultaneous biaxial tenter of the linear motor type in order to obtain a polyester film having high physical properties and quality at low cost.

In the present invention, the stretching step in which the unstretched film is relaxed during stretching to a high magnification is not particularly limited, but includes an operation of stretching and then relaxing 2 times to less than 10000 times. Perform the operation. More preferably,
3 times or more and less than 1000 times, more preferably 5 times
More than 100 times. If the number of operations is only one, the effect of the present invention is small because the number of relaxation operations is small, and if the number of operations is 10,000 or more, it is often difficult in practice, so it is not preferable. Further, the stretching operation and the relaxing operation may be performed simultaneously in the vertical direction and the horizontal direction, or may be performed in only one direction. Further, in the present invention,
In a series of operations repeated more than once, in addition to the operation of simply repeating stretching and relaxation alternately, an operation in which stretching or relaxation further enters at least once between them, for example,
A series of operation modes such as "-stretch-relax-relax-stretch-" or "-relax-stretch-stretch-relax-" are also included.

In the production method (II), the area stretching ratio by one stretching and the relaxation ratio by relaxation are not particularly limited, but the area stretching ratio by one stretching is as follows.
1.005 to 10 times, and the relaxation rate
It is preferably 0.1 to 80% of the length in each lateral direction. The area stretching ratio by one stretching is more preferably 1.05 to 5 times, and further preferably 1.
1 to 3 times. Area stretching ratio by one stretching is 10
If it exceeds twice, it may be difficult to obtain the desired effect of the present invention, or the film may be frequently broken.
Further, it is not an essential requirement for practical use that the area stretching ratio is less than 1.005 times, and it is often difficult to set the apparatus. Therefore, the range of 1.005 to 10 times is preferable. Further, a more preferable range of the relaxation rate is 0.5 to 60%, and further preferably 1 to 40%. Relaxation rate 80
%, The intended effect of the present invention due to stretching may be reduced, or the flatness or productivity of the film may be deteriorated. It is often difficult to set
A range of 80% is preferred.

As described above, when fine stretching as in the production method (I) or stretching and relaxation operations as in the production method (II) are continuously repeated, the entanglement of the polyester chains in the film is released. (1) Acceleration of structure / volume relaxation facilitates the production of films with high Young's modulus and low heat yield. (2) Increases total area draw ratio, improves film productivity, and reduces costs. It is preferable because effects such as down can be obtained. The dimensional change rate of fine stretching (in the case of the manufacturing method (I)) or stretching and relaxation (in the case of the manufacturing method (II)) performed a plurality of times may be the same or different in each time, Further, the stretching ratio and the relaxation ratio in each of the longitudinal direction and the transverse direction can be appropriately selected based on desired film properties. Further, as described above, one of the longitudinal direction and the lateral direction may be slightly stretched. Further, the ratio (vertical / horizontal) of the total stretching ratio in each of the longitudinal direction and the lateral direction is preferably 0.9 to 1.1 in floppy disk applications in order to impart isotropy. For applications such as video tapes used in magnetic recording devices of the
１．０1.0, and the rotation of the magnetic head is 1.0〜
It is preferably 1.3.

The sum of the Young's modulus (YMD) in the machine direction (MD direction) and the Young's modulus (YTD) in the transverse direction (TD direction) of the film of the present invention, that is, the total Young's modulus depends on the raw materials used. , 8 to 30 GPa. If the total Young's modulus is less than 8 GPa, the practicality as a film is poor, and if it exceeds 30 GPa, it may be very difficult. In this case, the film may be frequently broken. A more preferable range of the total Young's modulus is 10 to 25 GPa, particularly preferably 12 to 22 GPa.
Pa. The balance between the Young's modulus in the vertical direction and the horizontal direction can be controlled by appropriately changing the total magnification in each of the vertical and horizontal directions.

The heat shrinkage of the film obtained in the present invention is as follows:
In most cases, vertical (MD) and horizontal (TD)
Is preferably 2% or less at 100 ° C. for 30 minutes. A more preferable range of the sum of the heat shrinkage rates is 1% or less, further preferably 0.5% or less. The sum of heat shrinkage is 2%
If it is larger, wrinkles and poor flatness are likely to occur in, for example, a polyester processing step, for example, a magnetic layer coating step for a magnetic recording medium, a calendaring step, and the like, so that the total heat shrinkage is 2% or less. Is preferred. According to the manufacturing method disclosed in the present invention, the Young's modulus in the vertical and horizontal directions can be easily increased without increasing the heat shrinkage. That is, the sum of the Young's modulus in the vertical direction and the horizontal direction is 8
To 30 GPa, and a polyester film having a total heat shrinkage of 2% or less at 100 ° C. for 30 minutes is easily obtained.

According to the production method of the present invention, since the polyester is easily relaxed in structure, the crystallinity of the film after biaxial stretching and heat treatment is likely to be high. As described above, the crystallinity of the film is 30 to 90% in the present invention, though it depends on the raw material used, the stretching ratio, the temperature condition of the heat treatment, and the like. The degree of crystallinity is 5 depending on the industrially usable production method.
Obtaining a film of 0% or more is usually not easy, but such a film can be obtained relatively easily by the production method of the present invention.

Further, according to the production method of the present invention, since the crystallinity of the film tends to be high, it is not always necessary to perform the heat treatment at a temperature of 200 ° C. or more. When the temperature of the heat treatment is lowered, oligomer contamination and scattering in the tenter,
Since the amount of oligomer on the film surface is reduced, it is advantageous in terms of reduction of surface defects. The preferred range of crystallinity for obtaining a high-quality polyester film having a high Young's modulus and a small heat shrinkage is 40 to 80%, and more preferably 45 to 70%. If the crystallinity is less than 30%, the structure is often insufficiently fixed, and the heat shrinkage of the film becomes high, which is not preferable. On the other hand, when the crystallinity exceeds 90%, the film is frequently torn and the workability in various film applications is reduced.

In the polyester film of the present invention, as long as the effects of the present invention are not impaired, inorganic particles, organic particles, and other various additives such as antioxidants,
An antistatic agent and a crystal nucleating agent may be added. Specific examples of the inorganic particles include oxides such as silicon oxide, aluminum oxide, magnesium oxide, and titanium oxide; composite oxides such as kaolin, talc, and montmorillonite; carbonates such as calcium carbonate and barium carbonate; calcium sulfate; and barium sulfate. Such as sulfates, barium titanate,
A titanate such as potassium titanate, a phosphate such as tricalcium phosphate, dibasic calcium phosphate, and monobasic calcium phosphate can be used, but not limited thereto. In addition, these are 2 depending on the purpose.
More than one species may be used in combination.

Specific examples of the organic particles include polystyrene or crosslinked polystyrene particles, vinyl particles such as styrene / acrylic / acrylic crosslinked particles, styrene / methacrylic / methacrylic crosslinked particles, benzoguanamine / formaldehyde, silicone, and polytetrafluoroethylene. Although particles such as fluoroethylene can be used, the particles are not limited thereto, and any particles may be used as long as at least a part of the particles constituting the particles is organic polymer fine particles insoluble in polyester. The organic particles preferably have a spherical particle shape and a uniform particle size distribution from the viewpoint of smoothness and uniformity of formation of projections on the film surface. The particle size, blending amount, shape, etc. of these particles can be selected according to the application and purpose, but usually, the average particle size is 0.05 μm or more and 3 μm or less, and the blending amount is
The content is preferably from 0.01% by weight to 10% by weight.

Further, the polyester film of the present invention comprises:
A single film may be used, but another polymer layer such as polyester, polyolefin, polyamide, polyvinylidene chloride and an acrylic polymer may be laminated into two or more layers directly or via a layer such as an adhesive. It may be a film. In particular, in the case of a laminated film in which a polyester layer is laminated on the surface layer, the surface roughness of the film surface to be the magnetic recording surface and the surface roughness of the opposite surface thereof, depending on the application, particularly in the base film of the magnetic recording medium whose surface characteristics are important This is useful as a method that can be used for different designs.

The total thickness of the film in the present invention can be appropriately determined depending on the use and purpose of the film.

Normally, for magnetic materials, 1 μm or more and 20 μm
m or less, preferably 2 μm or more and 8 μm or less for digital video coating magnetic recording media, and 3 μm or more and 9 μm for digital video evaporation magnetic recording media.
The following is preferred. Further, among industrial materials, the thickness is preferably 1 μm to 6 μm for thermal transfer ribbons, 0.5 μm to 15 μm for capacitors, and 0.5 μm to 5 μm for heat-sensitive stencil paper.

Next, specific examples of the method for producing the polyester film of the present invention will be described, but it goes without saying that the present invention is not limited to such examples. Here, an example is shown in which polyethylene terephthalate is used as the polyester, but the production conditions differ depending on the polyester used.

The polyester has an intrinsic viscosity of 0.65
Polyethylene terephthalate pellets under vacuum
Heat to 80 ° C and dry under vacuum for 3 hours or more.
It is supplied to an extruder heated to a temperature of 00 ° C. and extruded from a T-type die into a sheet. It is preferable to use various filters, for example, a filter made of a material such as a sintered metal, a porous ceramic, a sand, or a wire mesh in order to remove foreign substances and a degraded polymer. Further, if necessary, a gear pump may be provided in order to improve the quantitative supply property. The melted sheet is brought into close contact with a drum cooled to a surface temperature of 10 to 40 ° C. by electrostatic force and cooled and solidified to obtain a substantially amorphous unstretched cast film. Also,
In the case of a laminated film, a sheet in which a polyester in a molten state is laminated is extruded using two or more extruders, a manifold, or a merging block. At this time, the ratio of the thickness of the end portion to the center portion of the unstretched film (the thickness of the end portion / the thickness of the center portion) is preferably in the range of 1 or more and 10 or less, more preferably 1 or more and 5 or less. Less than, most preferably 1
Above, it is less than 3. If the ratio of the thickness is less than 1 or more than 10, film breakage or clip detachment frequently occurs, which is not preferable. Next, the unstretched film is guided to a simultaneous biaxial stretching tenter of a linear motor type by gripping both ends of the film with clips, and heated to 90 to 150 ° C. in a preheating zone, so that the area stretching ratio of the film is 1. Fine stretching of 0005 to 3 times is continuously performed at least three times or more. Alternatively, as another method, stretching with an area stretching ratio of the film of 1.005 to 10 times and a relaxation rate of 0.
The relaxation of 1 to 80% is repeated at least twice continuously. At this time, in any case, it is preferable to set the temperature of the clip for gripping the edge of the film in a temperature range of 80 to 160 ° C. The stretching temperature in the stretching step is preferably maintained within a temperature range of 90 to 150 ° C., but may be once cooled and then stretched while suppressing crystallization of the film. In addition, in the case of a raw material having a high molecular weight or a raw material that is hardly crystallized, it is preferable to increase the stretching temperature to 200 ° C. In the latter half of the stretching step, that is, in the step of stretching a film having a plane orientation coefficient of 0.15 or more, it is preferable to perform stretching while gradually increasing the stretching temperature in two or more stages. As described above, the film is stretched by the simultaneous biaxial tenter to stretch the film to a total area stretching ratio of 25 to 150 times.

Next, in order to impart flatness and dimensional stability to the biaxially stretched polyester film, 180 ° C.
The heat treatment is performed in a temperature range lower than the melting point, and in the cooling process from the heat setting temperature, preferably in the vertical and horizontal directions in a temperature range of 100 to 220 ° C, preferably 1 to 1 in each direction.
Perform relaxation treatment in the range of 6%. The relaxation treatment may be performed in one stage or in multiple stages, and a change in the temperature distribution may be provided. At this time, it is also preferable to repeat the fine stretching in the heat treatment step in order to increase the crystal size and increase the Young's modulus of the film. Thereafter, the film is cooled and wound up to room temperature, if necessary, while being subjected to a relaxation treatment in the vertical and horizontal directions, to obtain a desired polyester film.

In the present invention, in order to impart surface characteristics of the film, for example, to impart easy adhesion, easy slipping, releasing property and antistatic property, the film is stretched before being stretched in a simultaneous biaxial tenter. Alternatively, it is also preferable to coat a coating material on the surface of the polyester film in a later step.

[Evaluation of Physical Properties] (1) Intrinsic viscosity [η] in orthochlorophenol at 25 ° C.
The value calculated from the following formula from the solution viscosity measured in the above is used. That is, ηsp / C = [η] + K [η] 2 · C, where ηsp = (solution viscosity / solvent viscosity) −1,
C is the weight of the dissolved polymer per 100 ml of solvent (g / 1
00 ml, usually 1.2), and K is the Haggins constant (0.34
3). The solution viscosity and the solvent viscosity were measured using an Ostwald viscometer. The unit is indicated by [dl / g].

(2) Glass transition temperature Tg, melting temperature Tm As a differential scanning calorimeter, “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used. As a data analyzer, “Disk Session” SSC / 52 manufactured by the company was used.
00 was measured. About 5 mg of a measurement sample was collected, and Tg and Tm were determined from a heat curve obtained when the sample was heated from room temperature to 300 ° C. at a rate of temperature increase of 20 ° C./min.

(3) Young's modulus Measured according to the method specified in ASTM-D882. The sample film was pulled at a width of 10 mm, a test length of 100 mm, and a pulling speed of 200 mm / min using an automatic film strength / elongation measuring device “Tensilon AMF / RTA-100” manufactured by Orientec Co., Ltd. The Young's modulus was determined from the slope of the rising tangent of the obtained stress-strain curve. The measurement was performed in an atmosphere of 23 ° C. and 65% RH.

(4) Heat Shrinkage Ratio Heat shrinkage ratio was measured according to the method specified in JIS-C-2318. Two lines are drawn on the film so as to have a width of 10 mm and a measurement length of about 200 mm, and the distance between these two lines is accurately measured, and is defined as L0. 10 samples of this
After leaving it in a 0 ° C oven for 30 minutes under no load,
The distance between the lines of the book is measured, and this is defined as L1, and the heat shrinkage is determined by the following equation.

Heat shrinkage (%) = {(L0−L1) / L0} × 100 (5) Crystallinity The crystallinity was determined from the density gradient according to the method specified in JIS-K-7112. A density gradient tube using an aqueous sodium bromide solution is prepared, and the density of the film at 25 ° C. is measured. From this density d, the crystallinity was determined using the following equation.

Crystallinity (%) = ((d−da) / (dc)
−da)) × 100 where da is an amorphous density, dc is a perfect crystal density,
In the case of polyethylene terephthalate, da =
1.335, dc = 1.455 g / cm ³ .

(6) Plane Orientation Coefficient The refractive index was measured according to the method specified in JIS-K-7105. Using a sodium lamp as a light source, the refractive index of the film (vertical direction: Na, horizontal direction: Nb, thickness direction: Nc) was determined by an Abbe refractometer (manufactured by Atago).
The plane orientation coefficient F was calculated from the following equation. The mounting solution was measured using methylene iodide in an atmosphere of 23 ° C. and 65% RH.

F = [(Na + Nb) / 2] -Nc (7) Breakage frequency Vacuum-dried polyethylene terephthalate is tightly adhered to a casting drum from a T-type die by electrostatic force to cool and solidify to obtain a cast film. The film was broken by the simultaneous biaxial tenter of the linear motor type during film formation, and the film was judged according to the following criteria.

◎: When there is no film tearing ○: When the film tearing occurs very rarely Δ: When the film tearing occurs occasionally ×: When the film tearing occurs frequently (8) Film thickness unevenness in the longitudinal direction manufactured by Anritsu Corporation Film Thickness Tester "KG
601A "and an electronic micrometer" K306C "are used to continuously measure the thickness of a film sampled 30 mm wide and 10 m long in the longitudinal direction of the film. The transport speed of the film was 3 m / min. From the maximum thickness value Tmax (μm) and the minimum value Tmin (μm) at a length of 10 m, R = Tmax−Tmin was determined, and from R and the average thickness Tave (μm) at a length of 10 m, thickness unevenness was determined by the following equation.

Thickness unevenness (%) = (R / Tave) × 100 (9) Creep compliance The film was sampled to a width of 4 mm, and TMA (TM-300 manufactured by Vacuum Riko Co., Ltd.) was set to a test length of 15 mm.
0) and the heating controller TA-1500.

Under conditions of 50 ° C. and 65% RH, 28 MPa
Was applied to the film and kept for 30 minutes, and the film elongation at that time was measured. The amount of expansion and contraction of the film (% display, ΔL) was determined by a personal computer PC-9801 manufactured by NEC Corporation via an AD converter ADX-98E manufactured by Canopus Electronics Co., Ltd., and creep compliance was calculated from the following equation.

Creep compliance (GPa ^-1 ) =
(ΔL / 100) /0.028 (10) High-speed scraping property A film obtained by slitting a film into a tape having a width of 1/2 inch was guided with a guide pin (surface roughness: 100 nm by Ra) using a tape running tester. ) Run on (running speed 2)
50 m / min, 1 pass of the number of runs, winding angle: 60 °, running tension: 90 g). At this time, the guide pin after running the film was observed with the naked eye, and the case where white powder was not observed was evaluated as ○, and the case where white powder was slightly observed was evaluated as Δ,
A sample to which a large amount of white powder was attached was determined to be x.が is desirable, but △ can be used practically.

(11) Electromagnetic Conversion Characteristics (C / N) of Magnetic Tape A magnetic paint and a non-magnetic paint having the following composition are applied on the surface of the polyester film of the present invention in a multi-layered manner by an extrusion coater (the upper layer is coated with a magnetic paint. 0.1 μm,
The thickness of the non-magnetic lower layer was appropriately changed), magnetically oriented, and dried. Next, after forming a back coat layer having the following composition on the opposite surface, a small test calender (steel / steel roll, 5 steps) was used at a temperature of 85 ° C. and a linear pressure of:
After calendering at 200 kg / cm, at 60 ° C,
Cure for 48 hours. The raw tape was slit into a width of 8 mm to prepare a pancake. Next, a 200 m length of this pancake was incorporated into a cassette to form a cassette tape.

[0093] A commercially available Hi8 VTR (S
7MHz using ONY EV-BS3000)
A +1 MHz C / N (carrier to noise ratio) measurement was performed. This C / N was converted to a commercially available Hi8 video tape (SO
Compared with (NY Corp., 120 minutes MP), +3 dB or more was evaluated as ○, +1 or more and less than +3 dB as Δ, and +1 dB or less as X.が is desirable, but △ can be used practically.

(Composition of Magnetic Coating) Ferromagnetic metal powder: 100 parts by weight Na-sulfonate-modified vinyl chloride copolymer: 10 parts by weight Na-sulfonate-modified polyurethane: 10 parts by weight Polyisocyanate: 5 parts by weight Stearic acid: 1.5 parts by weight-Oleic acid: 1 part by weight-Carbon black: 1 part by weight-Alumina: 10 parts by weight-Methyl ethyl ketone: 75 parts by weight-Cyclohexanone: 75 parts by weight-Toluene: 75 parts by weight (nonmagnetic lower layer) Composition of paint) ・ Titanium oxide: 100 parts by weight ・ Carbon black: 10 parts by weight ・ Na sulfonic acid modified vinyl chloride copolymer: 10 parts by weight ・ Na sulfonic acid modified polyurethane: 10 parts by weight ・ Methyl ethyl ketone: 30 parts by weight ・ Methyl Isobutyl ketone: 30 parts by weight ・ Toluene: 30 layers Parts (composition of the back coat) ・ Carbon black (average particle diameter 20 nm): 95 parts by weight ・ Carbon black (average particle diameter 280 nm): 10 parts by weight ・ α-alumina: 0.1 parts by weight ・ Zinc oxide: 0.3 parts by weight Part: Na sulfonate-modified polyurethane: 20 parts by weight-Na sulfonate-modified vinyl chloride copolymer: 30 parts by weight-Cyclohexanone: 200 parts by weight-Methyl ethyl ketone: 300 parts by weight-Toluene: 100 parts by weight (12) Running of magnetic tape Durability and Storage Property A magnetic paint having the following composition is applied to the surface of the polyester film of the present invention so as to have a coating thickness of 2.0 μm, magnetically oriented, and dried. Then, after forming a back coat layer having the following composition on the opposite surface, and then performing a calendering treatment,
Cure at 48 ° C. for 48 hours. 1 for the above tape
/ 2 inch wide slit, magnetic tape, length 6
A 70-minute portion was incorporated into a cassette to form a cassette tape.

(Composition of Magnetic Coating)-Ferromagnetic metal powder: 100 parts by weight-Modified vinyl chloride copolymer: 10 parts by weight-Modified polyurethane: 10 parts by weight-Polyisocyanate: 5 parts by weight-Stearic acid: 1.5 Parts by weight-Oleic acid: 1 part by weight-Carbon black: 1 part by weight-Alumina: 10 parts by weight-Methyl ethyl ketone: 75 parts by weight-Cyclohexanone: 75 parts by weight-Toluene: 75 parts by weight (composition of the back coat)-Carbon black ( (Average particle diameter 20 nm): 95 parts by weight Carbon black (average particle diameter 280 nm): 10 parts by weight α-alumina: 0.1 part by weight Modified polyurethane: 20 parts by weight Modified vinyl chloride copolymer: 30 parts by weight Cyclohexanone: 200 parts by weight-Methyl ethyl ketone: 300 parts by weight-Tolue : 100 parts by weight The created cassette tape is inserted into Magstar manufactured by IBM.
The tape was run for 100 hours using 3590 MODELB1A Tape Drive, and the running durability of the tape was evaluated according to the following criteria. ○ was judged as a passed product.

：: There is no elongation or bending of the tape end face, and no scraping marks are observed.

Δ: There is no elongation or bending of the tape end face, but some scraping marks are observed.

X: A part of the tape end face is elongated, wakame-like deformation is observed, and scraping marks are observed.

Further, the cassette tape created above is stored in the IB
Magstar3590 MODELB1A T made by M company
After reading the data into the ape drive, the cassette tape was stored in an atmosphere of 40 ° C. and 80% RH for 100 hours, and then the data was reproduced to evaluate the preservability of the tape according to the following criteria. ○ was judged as a passed product.

：: Normal reproduction without track deviation.

Δ: There is no abnormality in the tape width, but reading is impossible in some parts.

X: The tape width has changed and reading is impossible.

(13) Tracking Resistance of Floppy Disk A. Tracking deviation test due to temperature change The following method is used as the tracking deviation test. A magnetic recording layer is formed on both sides of a base film by sputtering a metal thin film, and a floppy disk made of a metal thin film punched out in a disk shape is heated at a temperature of 15 ° C. and a humidity of 60 ° C.
Magnetic recording is performed using a ring head at% RH, and the maximum output and the output envelope of the magnetic sheet at that time are measured.
Next, while maintaining the ambient temperature at 40 ° C. and the humidity of 60% RH, the maximum output and the output envelope at that temperature were examined, and the output envelope at a temperature of 15 ° C. and a humidity of 60% RH, and a temperature of 40 ° C. The output envelope at a humidity of 60% RH is compared to determine the tracking state. The smaller the difference, the more excellent the tracking resistance. If this difference exceeds 3 dB, the tracking becomes ×
And those within 3 dB were evaluated as ○.

B. Tracking deviation test due to humidity change A floppy disk created in the same manner as
Recording is performed in an atmosphere of 5 ° C. and a relative humidity of 20%, and the atmospheric conditions are maintained at a temperature of 25 ° C. and a relative humidity of 70%. The output envelopes under both conditions are compared to determine the tracking state. As in the previous section, if the difference exceeds 3 dB, the tracking is evaluated as x, and if the difference is within 3 dB, the evaluation is evaluated as ○.

(14) Scratch resistance of the floppy disk The same track magnetically recorded on the floppy disk obtained in the same manner as in the above (13) is scanned 100,000 times or more at a relative running speed of 6 m / sec. Examined.
The evaluation criteria were as follows: flaws generated on the surface of the magnetic layer were confirmed, and those in which the output envelope became unstable were evaluated as x. A sample having no scratch on the surface of the magnetic layer and having a stable output envelope was evaluated as ○.

(15) Printability of Thermal Transfer Ribbon A thermal transfer ink having the following composition was applied to a polyester film for a thermal transfer ribbon of the present invention having a fusing prevention layer coated on one side by a hot melt coater so that the applied thickness was 3.5 μm. Coating was performed on the surface opposite to the anti-fusing layer to form a thermal transfer ribbon.

(Composition of Thermal Transfer Ink) Carnauba wax: 60.6% by weight Microcrystalline wax: 18.2% by weight Vinyl acetate / ethylene copolymer: 0.1% by weight Carbon black: 21.1% by weight With respect to the thermal transfer ribbon, black solid was printed with a bar code printer (BC-8) manufactured by Oaks Co., Ltd., and printability was evaluated. ○ was judged as a passed product.

：: Clear printing △: Pitch deviation occurs in printing X: Wrinkles are formed on ribbon and printing is disturbed XX: Wrinkles are formed on the film at the time of hot melt coating, and the thermal transfer ink cannot be applied uniformly.

(16) Evaluation of Characteristics for Capacitor Insulation Resistance The surface resistance of one side of the polyester film of the present invention is 2
Aluminum was vacuum-deposited so as to be Ω / □. At this time, vapor deposition was performed in a stripe shape having a margin portion running in the longitudinal direction (width of the vapor deposition portion 57 mm, width of the margin portion 3 mm
Repeat). Next, insert a blade in the center of each vapor deposition part and the center of each margin part, slit, and left or right 1.5 mm
A 30 mm-wide tape-shaped take-up reel having a width margin was used. A pair of the obtained aluminum vapor-deposited films having left-right symmetrical margins were overlapped and wound to a length having a capacity of 1.5 μF. This roll is heated at 120 ° C. and 20 kg /
It was molded by pressing at a pressure of cm ² for 10 minutes. Metallicon was sprayed on both end surfaces to form electrodes, and lead wires were attached to obtain capacitor samples. Next, 1,000 1.5 μF capacitor samples prepared here were used for 23 samples.
The temperature was measured as a 1-minute value at an applied voltage of 500 V with a super insulation resistance meter 4329A manufactured by YHP under an atmosphere of 65 ° C. and 65% RH, and a capacitor sample having an insulation resistance of less than 5000 MΩ was determined as a defective product according to the following criteria. . In addition,
In the present invention, ◎, △, and Δ were regarded as acceptable.

◎: Less than 10 defective products ○: 10 or more and less than 20 defective products △: 20 or more and less than 50 defective products ×: 50 or more defective products Dielectric breakdown voltage According to the method described in JIS-C-2318, except that
Using a film without metal deposition as a test piece, evaluation is made as follows.

A rubber plate having a rubber shore hardness of about 60 degrees and a thickness of about 2 mm is laid on a metal plate of an appropriate size, and 10 aluminum foils of about 6 μm thickness are stacked on the rubber plate. The lower electrode is a brass cylinder having a weight of about 50 g, a round bottom of about 1 mm, a diameter of 8 mm, and a smooth bottom surface with no damage. The test specimens were previously stored at a temperature of 20 ±
Leave in an atmosphere of 5 ° C. and a relative humidity of 65 ± 5% for 48 hours or more. A test piece is sandwiched between the upper electrode and the lower electrode, and a DC voltage is applied between both electrodes by a DC power supply in an atmosphere at a temperature of 20 ± 5 ° C. and a relative humidity of 65 ± 5%. At 0 V until the dielectric breakdown occurs. A test is performed on 50 samples, and an average value obtained by dividing the dielectric breakdown voltage by the thickness of the test piece is determined. A value of 400 V / μm or more is regarded as acceptable (○).

(17) Image properties of heat-sensitive stencil base paper A non-woven fabric obtained by the following method is bonded to the polyester film of the present invention using a vinyl acetate-based adhesive, and a silicone-based non-woven fabric is bonded to the non-woven fabric side of the film. A release material was applied to obtain a heat-sensitive stencil base paper. The base paper was supplied to "RISOGRAPH" GR375 manufactured by Riso Kagaku Kogyo Co., Ltd., and plate making and printing were performed using a black solid as the original. Twenty sheets were printed, and the state of white spots and density unevenness of the twentieth printed image was visually determined based on the following criteria.

(White spots) ：: no white spots Δ: slight white spots ×: noticeable white spots (shading) ○: no spots Δ: slight spots ×: The unevenness is noticeable ○ or Δ is a practically usable level

[Production of Main Fiber] A polyethylene terephthalate chip was melted at 290 ° C., discharged at 285 ° C. through a die having 900 holes, and wound up at a speed of 1000 m / min.

Next, this undrawn yarn was treated at a magnification of 3.8 times with 8
After stretching in hot water at 0 ° C., a tension heat treatment at 200 ° C. and a relaxation heat treatment at 125 ° C., the resultant was cut into 5 mm to obtain a main fiber A having an average fiber diameter of 5 μm and a birefringence of 0.20.

[Production of Undrawn Fiber] On the other hand, a polyethylene terephthalate chip was melted at 290 ° C.
Discharge at 285 ° C through the base of No. 0, cut to 5mm,
An undrawn fiber a having an average fiber diameter of 8 μm and a birefringence of 0.05 was obtained.

[Paper making] The main fiber A and the undrawn fiber a
After thoroughly mixing and dispersing in a pulper at a weight ratio of 80:20, the mixture was heated and dried with a Yankee dryer (surface temperature: 130 ° C.) at a speed of 10 m / min using a circular paper machine. The weight per unit area was 8 g / m ² . Then, using a metal / elastic roll calendering machine, the metal roll surface temperature was 210 ° C and the linear pressure was 1
By pressing under the condition of 5 kg / cm, the thickness is 25 μm.
m of non-woven fabric was obtained.

[0118]

The present invention will be described below based on examples and comparative examples.

Example 1 A pellet of polyethylene terephthalate (containing 0.1% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.65, a glass transition temperature of 75 ° C, a melting point of 255 ° C, and an average diameter of 0.3 µm) was mixed at 180 ° C for 3 hours. After vacuum drying, it is supplied to an extruder heated to 280 ° C., melt-extruded, and discharged from a T-die into a sheet. Further, this sheet is brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force to be cooled and solidified to obtain an unstretched cast film. Both ends of the unstretched film are gripped with clips and guided to a simultaneous biaxial stretching tenter of a linear motor type, the film temperature is heated to 100 ° C., and the area stretching ratio is 1.082 times (longitudinal ratio: 1.04 times). ,
(Bilateral magnification: 1.04 times)
Do it twice. The stretching stop time between the fine stretchings is set to 1/10 of the time required for the immediately preceding fine stretching. Then 210 ° C
The film is heat-set at a temperature of 120 ° C., subjected to a relaxation treatment at a cooling zone of 120 ° C. at a relaxation rate of 2% in the vertical direction and 2% in the horizontal direction, and gradually cooled to room temperature and wound up. The film thickness is adjusted to 9 μm by adjusting the extrusion amount. Note that the clip temperature at the time of stretching is 100 ° C. The film obtained here is a high-quality film having a total area magnification of about 50 times, a high degree of crystallinity of 58%, a high Young's modulus and a low heat shrinkage, and little thickness unevenness.

[0120] It should be noted that film tearing during film formation is small, and a film having high physical properties and high quality can be obtained extremely stably.

Examples 2 to 5, Comparative Examples 1 and 2 A biaxially stretched polyester film is obtained in the same manner as in Example 1, except that the fine stretching ratio, the number of repetitions, and the total area stretching ratio are changed. Here, in the case of Example 2 and Comparative Example 1 in which the number of repetitions of the fine stretching is three and two, the simultaneous biaxial stretching is further performed in one stage after the fine stretching,
The total area stretching ratio of the film is 25 times. When the number of times of fine stretching is repeated three times or more and further increased, the frequency of film tearing decreases and the total area stretching ratio tends to increase. In addition, when the stretching ratio is increased by increasing the number of times of fine stretching, the degree of crystallinity of the film is increased, and a high-quality film having high rigidity, low heat shrinkage and small thickness unevenness is obtained. If the number of repetitions of fine stretching or the total area stretching ratio does not satisfy the range of the present invention, the Young's modulus is small or the heat shrinkage is large (Comparative Examples 1 and 2).

[0122]

[Table 1] Comparative Examples 3 to 5 A biaxially stretched polyester film is obtained in the same manner as in Example 1, except that the film is stretched without fine stretching. When the film temperature is 100 ° C., the film is stretched 4.3 times in the machine direction by a simultaneous biaxial tenter, and then stretched 4.3 times in the transverse direction. When the film is simultaneously biaxially stretched at a magnification of 3 times, only a film having a small Young's modulus and a large heat shrinkage is obtained, and the thickness unevenness of the film is also increased (Comparative Examples 3 and 4). In addition, the film is placed in the longitudinal direction and the lateral direction, respectively.
When the film is simultaneously biaxially stretched at a magnification of 0 times and then simultaneously biaxially stretched at a magnification of 1.3 times each in the machine direction and the transverse direction, the film is frequently torn and the heat shrinkage of the film is large. (Comparative Example 5).

[0123]

[Table 2] Examples 6 to 10 This example shows an example in which a film is formed by changing the ultimate crystallinity after fine stretching. The film formation was performed in the same manner as in Example 1 except that the fine stretching was repeated and the number of repetitions was changed, and then the fine stretching was continuously repeated, followed by simultaneous biaxial stretching in one step and setting the total area stretching ratio to 50 times. To obtain a biaxially stretched polyester film. Here, the magnification in the vertical and horizontal directions by one elongation / fine elongation is made equal. The crystallinity of the film after fine stretching is 2
% And 34%, the Young's modulus decreases and the heat shrinkage increases.

[0124]

[Table 3] Examples 11 to 13 In a simultaneous biaxial tenter, 100
A biaxially oriented polyester film is obtained by forming a film in the same manner as in Example 4 except that temperature zones of 140 ° C., 140 ° C., 210 ° C., and 250 ° C. are provided, and the temperature conditions of the fine stretching are changed. 21
When fine stretching is performed in a high temperature range of 0 ° C. and 250 ° C., the Young's modulus of the film increases, and the heat shrinkage decreases.

[0125]

[Table 4] Example 14 Both ends of the unstretched film obtained in the same manner as in Example 1 were gripped with clips and led to a simultaneous biaxial stretching tenter of a linear motor system, and the film was heated to 100 ° C. After stretching by 2.5 times, the area stretching ratio is 1.4.
Fine stretching of 4 times (vertical magnification: 1.2 times, horizontal magnification: 1.2 times) is continuously performed 6 times. At that time, the temperature range was 150 ° C,
Temperature zones are provided in the order of 180 ° C. and 210 ° C., and fine stretching is performed twice for each. The stretching stop time between the fine stretchings is set to 1/10 of the time required for the immediately preceding fine stretching. Thereafter, heat set at a temperature of 210 ° C.
The film is subjected to a relaxation treatment in a cooling zone at 2 ° C. at a relaxation rate of 2% in the vertical direction and 2% in the horizontal direction, and the film is gradually cooled to room temperature and wound up.
The film thickness is adjusted to 10 μm by adjusting the extrusion amount.
A film having high Young's modulus and low heat shrinkage can be obtained.

Example 15 Both ends of an unstretched film obtained in the same manner as in Example 1 were gripped with clips, and guided to a simultaneous biaxial stretching tenter of a linear motor type, and the film was heated to 115 ° C. After performing fine stretching continuously 20 times in the direction at a magnification of 1.04 times, simultaneous biaxial stretching is performed at 80 ° C. 4 times in the longitudinal direction and 5 times in the transverse direction. The stretching stop time between the fine stretchings is set to 1/10 of the time required for the immediately preceding fine stretching. Then, 210
The film is heat-set at a temperature of 0 ° C., subjected to a relaxation treatment at a cooling zone of 120 ° C. at a relaxation rate of 2% in the vertical direction and 2% in the horizontal direction, and gradually cooled to room temperature and wound up. The film thickness is adjusted to 10 μm by adjusting the extrusion amount. A film having high Young's modulus and low heat shrinkage can be obtained.

Example 16 Both ends of an unstretched film obtained in the same manner as in Example 1 were gripped with clips and led to a simultaneous biaxial stretching tenter of a linear motor type, and the film was heated to 100 ° C. The stretching ratio of 1.082 times (longitudinal ratio: 1.04 times, lateral ratio: 1.04 times) and the fine stretching in the horizontal direction only 1.04 times are alternately performed 10 times (total number of fine stretching operations: 20 times) After that, simultaneous biaxial stretching is performed four times in each of the vertical and horizontal directions. The stretching stop time between the fine stretchings is set to 1/10 of the time required for the immediately preceding fine stretching. Thereafter, the film is heat-set at a temperature of 210 ° C., subjected to a relaxation treatment at a cooling zone of 120 ° C. at a relaxation rate of 2% in the vertical direction and 2% in the horizontal direction, and gradually cooled to room temperature and wound up. The film thickness is adjusted to 10
Adjust to μm. A film having high Young's modulus and low heat shrinkage can be obtained.

[0128]

[Table 5] Example 17, Comparative Example 6 Polyethylene terephthalate having an intrinsic viscosity of 1.0 (containing 0.1% by weight of spherical crosslinked polystyrene particles having a glass transition temperature of 74 ° C., a melting point of 255 ° C. and an average diameter of 0.3 μm) was used as a polyester raw material. The effect of simultaneous biaxial fine stretching is examined. Here, the temperature of the stretching zone was 115 ° C., the temperature of the heat treatment zone was 210 ° C., and a film was formed in the same manner as in Example 1 except that the stretching pattern was changed. A biaxially oriented polyester film having a thickness of 6.5 μm was obtained. obtain. When performing fine stretching, the area magnification by one fine stretching is 1.082 times (longitudinal magnification:
1.04 times, lateral magnification: 1.04 times)
Repeat several times. The stretching stop time between the fine stretchings is set to 1/10 of the time required for the immediately preceding fine stretching. When fine stretching is not performed, simultaneous biaxial stretching is performed in one step at equal magnification in both longitudinal and transverse directions. Unlike the case of Comparative Example 6, in Example 17 in which fine stretching was performed, the total area stretching ratio was increased,
A film having high Young's modulus and low heat shrinkage can be obtained.

Examples 18 and 19, Comparative Examples 7 and 8 Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65 (spherical crosslinked polystyrene particles having a glass transition temperature of 125 ° C., a melting point of 265 ° C. and an average diameter of 0.3 μm) 0.1% by weight) and a copolymer of 90 mol% of ethylene terephthalate and 10 mol% of ethylene-2,6-naphthalate (glass transition temperature: 84 ° C., melting point: 235 ° C., average diameter: 0.3)
A film was formed in the same manner as in Example 17 and Comparative Example 6 except that a stretched temperature was set to the conditions shown in Table 6 except for using 0.1 μ% by weight of spherical crosslinked polystyrene particles having a thickness of μm. A 5 μm biaxially oriented polyester film is obtained. Even when polyethylene-2,6-naphthalate or the above copolymer was used as a raw material, the effect of the fine stretching of the present invention was remarkably observed. When the simultaneous biaxial fine stretching is repeatedly performed, the total area magnification and the crystallinity increase, and a high-quality polyester film having a high Young's modulus and a low heat shrinkage can be stably formed.

[0130]

[Table 6] Example 20 (Tables 7 and 8) Both ends of an unstretched film obtained in the same manner as in Example 1 were gripped with clips and led to a simultaneous biaxial stretching tenter of a linear motor system, and the film temperature was heated to 100 ° C. And the area stretching ratio is 2.25 times (vertical ratio: 1.5 times, horizontal ratio:
A series of operations of performing simultaneous biaxial stretching (1.5 times) and subsequently performing a relaxation treatment (longitudinal relaxation rate: 5%, lateral relaxation rate: 5%) are continuously performed 5 times. Then, after heat setting at a temperature of 210 ° C., a relaxation treatment of 2% in the vertical direction and 2% in the horizontal direction is performed in a cooling zone of 120 ° C., and the film is gradually cooled to room temperature. Take up. The film thickness can be adjusted by adjusting the extrusion amount.
Adjust to 0 μm. In addition, the clip temperature during stretching is 10
0 ° C. The film obtained here is a high quality film having a total area stretching ratio of 34.5 times, achieving both high Young's modulus and thermal dimensional stability, and having less thickness unevenness. In addition, film breakage during film formation is small, and a film having high physical properties and high quality can be obtained extremely stably. By adding a relaxation operation with the same stretching ratio and number of repetitions as in Example 5, the Young's modulus is slightly reduced, but the thermal dimensional stability is improved.

Examples 21 to 23, Comparative Example 9 A film was formed in the same manner as in Example 20, except that the magnification of one fine stretching, the relaxation rate, the number of repetitions, and the total area stretching magnification were changed. Obtain a polyester film. The polyester films obtained in Examples 21 to 23 are
As in Example 20, it is a high-quality film that achieves both high Young's modulus and thermal dimensional stability and has less thickness unevenness. In addition, film breakage during film formation is small, and a film having high physical properties and high quality can be obtained extremely stably. On the other hand, the polyester film obtained in Comparative Example 9 has a small Young's modulus because the total area stretch ratio does not satisfy the range of the present invention.

Example 24 (Tables 7 and 8) An unstretched film obtained in the same manner as in Example 1 was subjected to a simultaneous biaxial tenter at a film temperature of 100 ° C., and the area stretch ratio was 16.0 times. (Simultaneous biaxial stretching of (longitudinal magnification: 4.0 times, lateral magnification: 4.0 times)) and further relaxation treatment (longitudinal relaxation rate: 5%, lateral relaxation rate: 5%)
At a temperature of 170 ° C., an area stretching ratio of 2.25 times (longitudinal ratio: 1.25 times).
Simultaneous biaxial stretching of 5 times and a transverse magnification of 1.5 times, followed by relaxation treatment (longitudinal relaxation rate: 5%, transverse relaxation rate: 5%). Then, after heat setting at a temperature of 210 ° C., 12
The film is subjected to a relaxation treatment in a cooling zone of 0 ° C. at a relaxation rate of 2% in the vertical direction and 2% in the horizontal direction, and the film is gradually cooled to room temperature and wound up. The obtained polyester film is a high-quality film which has both high Young's modulus and thermal dimensional stability and has less thickness unevenness, as in Example 20. In addition, film breakage during film formation is small, and a film having high physical properties and high quality can be obtained extremely stably.

Example 25 An unstretched cast film was obtained in the same manner as in Example 1.
Both ends of the unstretched film are gripped with clips and guided to a simultaneous biaxial stretching tenter of a linear motor type, the film temperature is heated to 100 ° C., and the area stretching ratio is 1.21 times (longitudinal ratio: 1.1 times). , A horizontal magnification of 1.1 times) and a series of operations for performing a relaxation treatment (longitudinal relaxation rate: 5%, horizontal relaxation rate: 5%) successively 10 times. Then, an area stretching ratio of 1.21 times (longitudinal ratio: 1.1 times, lateral ratio:
(1.1 times) is performed twice, and the relaxation treatment is not performed. Subsequently, an area stretching ratio of 1.21 times (longitudinal ratio: 1.
A series of operations for simultaneous biaxial stretching of 1 × and a lateral magnification of 1.1 ×, followed by a relaxation treatment (longitudinal relaxation rate: 5%, horizontal relaxation rate: 5%) are performed 30 times. The total number of repetitions of a series of stretching and relaxation operations is 40, and the total number of stretching-only operations is two. Then, after heat-setting at a temperature of 210 ° C., a relaxation treatment of 2% in the vertical direction and 2% in the horizontal direction is performed in a cooling zone of 120 ° C., and the film is gradually cooled to room temperature and wound up. . The film obtained here is a high-quality film that has both high Young's modulus and thermal dimensional stability and has less thickness unevenness. In addition, film breakage during film formation is small, and a film having high physical properties and high quality can be obtained extremely stably.

Example 26 An unstretched cast film is obtained in the same manner as in Example 1.
Both ends of the unstretched film are gripped with clips and guided to a simultaneous biaxial stretching tenter of a linear motor type, the film temperature is heated to 100 ° C., and the area stretching ratio is 1.21 times (longitudinal ratio: 1.1 times). , A horizontal magnification: 1.1 times), and a series of operations for performing a relaxation treatment (longitudinal relaxation rate: 5%, lateral relaxation rate: 5%) continuously 30 times. Then, a relaxation process (longitudinal relaxation ratio: 5%, horizontal relaxation ratio: 5%) is performed once, and then, a series of operations for performing the same simultaneous biaxial stretching at a temperature of 140 ° C. and further continuing the relaxation process are performed. Perform 5 times. Then, the relaxation process (vertical relaxation rate: 5%, horizontal relaxation rate: 5%) is performed by 1
And a series of operations for performing the same simultaneous biaxial stretching at a temperature of 170 ° C. and further performing a relaxation treatment are performed seven times. The total number of operations of a series of stretching and relaxation operations is 42 times, and the total number of operations of only relaxation operations is 2 times. Then, after heat setting at a temperature of 210 ° C., 12
The film is subjected to a relaxation treatment in a cooling zone of 0 ° C. at a relaxation rate of 2% in the vertical direction and 2% in the horizontal direction, and the film is gradually cooled to room temperature and wound up. The film obtained here is a high-quality film that has both high Young's modulus and thermal dimensional stability and has less thickness unevenness. In addition, film breakage during film formation is small, and a film having high physical properties and high quality can be obtained extremely stably.

[0135]

[Table 7]

[Table 8] Examples 27 and 28 Using two extruders, extruder A heated to 280 ° C. was provided with polyethylene terephthalate (I) (intrinsic viscosity of 0.1).
65, glass transition temperature 75 ° C, melting temperature 255 ° C, 0.16% by weight of spherical silica particles having an average diameter of 0.07 µm)
The pellets were supplied after being vacuum-dried at 180 ° C. for 3 hours and supplied to an extruder B also heated to 280 ° C., where polyethylene terephthalate (II) (intrinsic viscosity: 0.65, glass transition temperature: 75 ° C., melting temperature: 255 ° C.) , Average diameter 0.3μ
m 0.2% by weight of spherical crosslinked polystyrene particles and 0.01% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm
The blended pellets were supplied after being vacuum-dried at 180 ° C. for 3 hours, and joined in a T-die (stacking ratio I / II = 10 /
1) Electrostatically contact with a cast drum having a surface temperature of 25 ° C., solidify by cooling, and create a laminated unstretched film. For this unstretched film, Example 27 was produced under the same stretching conditions as in Example 1;
It is manufactured under the same stretching conditions as described above. Obtained thickness 6.5
A μm film is processed for a magnetic recording medium, and its practical properties as a video tape and a data tape are evaluated.
The results have excellent characteristics as shown in Table 9.

Comparative Example 10 Both ends of the unstretched film obtained in the same manner as in Example 27 were gripped with clips and guided to a linear motor type simultaneous biaxial stretching tenter, and the film was heated to 95 ° C. After simultaneous biaxial stretching at a magnification of 3.5 times in the direction and the transverse direction, the film was further stretched in the longitudinal and transverse directions at a temperature of 110 ° C.
Simultaneous biaxial stretching at a magnification of 3 times, heat-setting at a temperature of 210 ° C, and a relaxation treatment of 2% in the longitudinal direction and 2% in the horizontal direction in a cooling zone at 120 ° C. The film is gradually cooled to room temperature and wound up to obtain a film having a thickness of 6.5 μm. As shown in Table 9, the film obtained by subjecting the obtained film to processing for a magnetic recording medium is inferior in practical characteristics to a magnetic recording medium as compared with the film of the present invention.

[0137]

[Table 9] Examples 29 and 30 Using two extruders, polyethylene terephthalate (I) (having an intrinsic viscosity of 0. 0) was heated at 280 ° C.
65, a glass transition temperature of 75 ° C., a melting temperature of 255 ° C., and no particles) were supplied after being vacuum-dried at 180 ° C. for 3 hours, and the extruder B also heated to 310 ° C. was supplied with polyethylene terephthalate (II) (II). Intrinsic viscosity 0.65,
Glass transition temperature 75 ° C, melting temperature 255 ° C, mean diameter 0.
3 μm spherical cross-linked polystyrene particles (containing 6% by weight) were dried in vacuo at 180 ° C. for 3 hours, and supplied.
They are joined in a die (lamination ratio I / II = 250/1), electrostatically adhered to a cast drum having a surface temperature of 25 ° C., solidified by cooling, and a laminated unstretched film is prepared. Example 29 is manufactured under the same stretching conditions as in Example 1, and Example 30 is manufactured under the same stretching conditions as Example 20. The resulting thickness 7
A 5 μm film is processed for a magnetic recording medium, and the practical characteristics as a floppy disk are evaluated. The results have excellent properties as shown in Table 10.

Comparative Example 11 Both ends of an unstretched film obtained in the same manner as in Example 29 were gripped with clips and led to a simultaneous biaxial stretching tenter of a linear motor type, and the film was heated to 95 ° C. The film is simultaneously biaxially stretched in the direction and the transverse direction at a magnification of 4 times each,
After heat setting at a temperature of 0 ° C., a relaxation treatment of 2% in the vertical direction and 2% in the horizontal direction is performed in a cooling zone of 120 ° C., and the film is gradually cooled to room temperature and wound up. 75 μm thickness
To obtain a film. As shown in Table 10, the film obtained by subjecting the obtained film to processing for a floppy disk has inferior practical characteristics for a floppy disk as compared with the film of the present invention.

[0139]

[Table 10] Examples 31 and 32 A pellet of polyethylene terephthalate (containing 0.25% by weight of silicon dioxide particles having an intrinsic viscosity of 0.65, a glass transition temperature of 75 ° C, a melting point of 255 ° C, and an average diameter of 1.0 µm) was prepared.
After vacuum drying at 0 ° C. for 3 hours, it is supplied to an extruder heated to 280 ° C., melt-extruded, and discharged from a T-die into a sheet. Further, this sheet is brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force to be cooled and solidified to obtain an unstretched cast film. On one side of this unstretched film, a coating having the following composition as a fusion-adhesion layer has a coating thickness of 0.5 after drying.
Coat with a gravure coater to a thickness of μm.

(Composition of Coating Material) Acrylate: 14.0% by weight Amino-modified silicone: 5.9% by weight Isocyanate: 0.1% by weight Water: 80.0% by weight Then, using a simultaneous biaxial tenter Example 31 was manufactured under the same stretching conditions as in Example 1;
Is manufactured under the same stretching conditions as in Example 20. The obtained film having a thickness of 4 μm is processed for a thermal transfer ribbon,
Evaluate practical properties for thermal transfer ribbons. Result is,
As shown in Table 11, it has excellent characteristics.

Comparative Example 12 In the same manner as in Example 31, an unstretched film having one surface coated with an anti-fusing layer was obtained. Thereafter, using a simultaneous biaxial tenter, a film for a thermal transfer ribbon having a thickness of 4 μm is obtained in the same manner as in the stretching conditions of Comparative Example 10. As shown in Table 11, the film processed for the thermal transfer ribbon has inferior practical properties for the thermal transfer ribbon as compared with the film of the present invention.

[0142]

[Table 11] Examples 33 and 34 180 pellets of polyethylene terephthalate (containing 0.15% by weight of aggregated silica particles having an intrinsic viscosity of 0.65, a glass transition temperature of 75 ° C, a melting point of 255 ° C, and an average diameter of 1.2 µm) were mixed.
After vacuum drying at 3 ° C. for 3 hours, the mixture is supplied to an extruder heated to 280 ° C., melt-extruded, and discharged from a T-die into a sheet. Further, this sheet is brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force to be cooled and solidified to obtain an unstretched cast film. This unstretched film was produced using the same biaxial tenter in Example 33 under the same stretching conditions as in Example 1, and Example 34 was produced under the same stretching conditions as in Example 20 with a thickness of 4 μm. The film is processed for a condenser and the practical characteristics are evaluated. Result is,
As shown in Table 12, it has excellent characteristics.

Comparative Example 13 An unstretched film obtained in the same manner as in Example 33 was
A film having a thickness of 4 μm obtained under the same stretching conditions as in Comparative Example 11 is processed for a capacitor, and the practical characteristics are evaluated. As shown in Table 12, the practical properties for capacitors are inferior to those of the film of the present invention.

[0144]

[Table 12] Examples 35 and 36 A pellet of polyethylene terephthalate (containing 0.45% by weight of aggregated silica particles having an intrinsic viscosity of 0.65, a glass transition temperature of 75 ° C, a melting point of 255 ° C, and an average diameter of 1.2 µm) was mixed with 180
After vacuum drying at 3 ° C. for 3 hours, the mixture is supplied to an extruder heated to 280 ° C., melt-extruded, and discharged from a T-die into a sheet. Further, this sheet is brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force to be cooled and solidified to obtain an unstretched cast film. This unstretched film was produced using the same biaxial tenter in Example 35 under the same stretching conditions as in Example 1, and Example 36 was produced under the same stretching conditions as in Example 20 with a thickness of 4 μm. This film is processed for heat-sensitive stencil paper, and its practical characteristics are evaluated. Result is,
As shown in Table 13, it has excellent characteristics.

Comparative Example 14 An unstretched film obtained in the same manner as in Example 35 was
A film having a thickness of 4 μm obtained under the same stretching conditions as in Comparative Example 11 is processed into a heat-sensitive stencil sheet to evaluate its practical characteristics. As shown in Table 13, the practical properties for heat-sensitive stencil printing are inferior to those of the film of the present invention.

[0146]

[Table 13]

[0147]

According to the production method of the present invention, a high-quality polyester film having high rigidity and low heat shrinkage and having little unevenness in thickness and few surface defects can be stably formed with a reduced frequency of tearing. The present invention is for magnetic recording media, for capacitors,
It can be widely used as a method for manufacturing various films such as for thermal transfer ribbons, heat-sensitive stencil printing, and packaging. In addition, according to the present invention, a new polyester film having physical properties and quality far exceeding the mechanical properties of conventional polyester films A polyester film is obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // B29K 67:00 H01G 4/24 331Z B29L 7:00 F term (reference) 2H111 BB06 BB08 4F210 AA24 AE01 AG01 AH33 AH38 AH81 AR06 AR19 AR20 QA02 QC07 QC17 QD13 QG01 QG18 QL03 5D006 CB01 CB07 5E082 AB05 EE05 EE24 EE37 FG06 FG36 FG48 FG54 GG04 JJ04 JJ22 MM22 MM24 PP06 PP08 PP10

Claims (17)

[Claims] In a method for producing a polyester film, in which a film composed of a resin containing a polyester as a main component is stretched by using a simultaneous biaxial tenter, the film is stretched at an area stretching magnification of from 0.0005 to 3.0 times. The stretching operation is performed three times or more, and the total area stretching ratio is 25 to 150.
A method for producing a polyester film, characterized in that the film is doubled. 2. The method for producing a polyester film according to claim 1, wherein the fine stretching operation is continuously performed three times or more. 3. The method according to claim 1, wherein the fine stretching is repeated 10 times or more and less than 10,000 times.
A method for producing the polyester film as described above. 4. The fine stretching of the unstretched film is performed at (glass transition temperature (Tg) +10) ° C. to (Tg + 12
0) The process is performed in a temperature range of 0 ° C.
The method for producing a polyester film according to any one of the above. 5. The non-stretched film according to claim 1, wherein the fine stretching is continuously repeated until the crystallinity becomes 3% or more and less than 30%. Manufacturing method of polyester film. 6. A method for producing a polyester film obtained by stretching a film composed of a resin containing a polyester as a main component using a simultaneous biaxial tenter, a series of operations of stretching the film and subsequently relaxing the film. More than 100
Less than 00 times, total area stretching ratio is 25-15
A method for producing a polyester film, wherein the ratio is 0 times. 7. The stretching ratio in one stretching in the stretching operation is 1.005 to 10 times, and the relaxation ratio in the relaxing operation is 0.1 to 1.0 in the vertical and horizontal directions just before the relaxation. The method for producing a polyester film according to claim 6, wherein the content is 1 to 80%. 8. The method according to claim 1, wherein the clip is driven by a linear motor when extending.
8. The method for producing a polyester film according to any one of 7. 9. A polyester film produced by the method according to claim 1. 10. The film according to claim 9, wherein the sum of the Young's modulus in the longitudinal direction and the transverse direction of the film is 8 to 30 GPa, and the sum of the heat shrinkage rates at 100 ° C. for 30 minutes is 2% or less. Polyester film. 11. The polyester film according to claim 9, wherein the degree of crystallinity is 30 to 90%. 12. The polyester according to claim 9, wherein the polyester is polyethylene terephthalate, polyethylene naphthalate, or a copolymer or modified product thereof.
The polyester film according to any one of the above. 13. The polyester film according to claim 9, which has an intrinsic viscosity of 0.6 or more. 14. A magnetic recording medium comprising the polyester film according to any one of claims 9 to 13. 15. A capacitor comprising the polyester film according to any one of claims 9 to 13. 16. A thermal transfer ribbon comprising the polyester film according to any one of claims 9 to 13. 17. A heat-sensitive stencil comprising the polyester film according to any one of claims 9 to 13.