JPH11254524A - Polyester film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester film of high quality excellent in rigidity, tenacity and heat shrinkage characteristics and reduced in thickness irregularity and surface defect and a method for producing the same. SOLUTION: In a method for producing a polyester film by biaxially stretching a film comprising a resin based on polyester at the same time by using a simultaneous biaxial tenter of a linear motor system, micro-stretching operation setting the area draw ratio of the film to 1.0005-3.0 times is continuously repeated three times or more to obtain the polyester film.

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. Specifically, it has excellent rigidity, toughness, heat shrinkage properties, electrical properties, etc., and
The present invention relates to a polyester film which has little unevenness in thickness and surface defects and is suitable for films for magnetic recording and various industrial materials, and a method for producing the same.

[0002]

2. Description of the Related Art Plastic films enable continuous production of large-area films that cannot be obtained from other materials, and are characterized by their strength, durability, transparency, flexibility, and imparting surface characteristics. Utilizing this technology, it is used in fields that are in large demand, such as for magnetic recording, agriculture, packaging, and building materials. Among them, biaxially stretched polyester films are used in various fields because of their excellent mechanical properties, thermal properties, electrical properties, and chemical resistance, and are particularly useful as base films for magnetic tape. Is unrivaled by other films. In recent years, further thinning of the base film has been demanded in order to reduce the weight and size of the equipment and to record for a long time, and thus higher strength is desired.
In recent years, there has been a very strong tendency for thin films for thermal transfer ribbons, capacitors, heat-sensitive stencils, and printing stencils, and similarly, higher strength is desired.

As a technique for increasing the strength of a biaxially stretched polyester film, a so-called re-longitudinal stretching method in which a film stretched in two longitudinal and transverse directions is stretched again in the longitudinal direction to increase the strength in the longitudinal direction is generally used. (For example, Japanese Patent Publication No. 42-9270)
JP, JP-B-43-3040, JP-A-46-1
119, JP-A-46-1120). Also,
In order to further impart strength in the horizontal direction, a re-longitudinal re-horizontal stretching method has been proposed in which the film is stretched again in the transverse direction and then stretched in the transverse direction again (for example, JP-A-50-133276, JP-A-55-22915). In addition, there has been proposed a vertical 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 in the transverse direction of the film (for example, Japanese Patent Publication No. 52-33666, Japanese Patent Publication No. 57-57). No. 49377). The vertical multi-stage stretching method is intended to improve strength, improve film thickness unevenness, and improve productivity.
This is a method superior to the above-described re-longitudinal stretching method and the re-longitudinal re-horizontal stretching method. However, when the strength of the film is increased, the heat shrinkage of the film is increased and the film is frequently broken.

Further, as a production method related to the present invention, a fine stretching repetition method (extreme multi-stage stretching method) in which stretching is continuously repeated at least three times in at least one of the longitudinal direction and the transverse direction of the film. (Japanese Patent Application Laid-Open Nos. 8-224777 and 9-57845) have been proposed. However, the super multi-stage stretching method generally requires (1) an extremely complicated apparatus, so that it is difficult to increase the number of fine stretching repetitions, which requires high costs for equipment modification. There is a problem that the method is not practical because it is expensive. In addition, Japanese Patent Application Laid-Open No.
No. 4777, Japanese Unexamined Patent Publication No. 9-57845 only shows specific examples mainly in the case of sequential biaxial stretching,
There is no description about the effective film forming apparatus and process conditions in the case of simultaneous biaxial stretching, and no mention is made of the effectiveness of the simultaneous biaxial stretching of the linear motor system used in the present invention.

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. Conventional simultaneous biaxial stretching method, screw method to put the clip in the groove of the screw to increase the clip interval, pantograph method to increase the clip interval using a pantograph, etc., the film forming speed is slow, Although there were problems such as difficulty in changing the conditions such as the stretching ratio, these problems can be solved at once with the simultaneous biaxial stretching of the linear motor system. However, process conditions for producing a polyester film having excellent physical properties and quality by simultaneous biaxial stretching of this method are still unknown, and an effective stretching method is still being explored.

As described above, there is still room for improvement in the polyester film having high physical properties and high quality and its production technology, and the development of a new technology is required in the present field.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high quality polyester film which is excellent in rigidity, toughness and heat shrinkage, has less thickness unevenness and surface defects, and a method for producing the same.

[0008]

Means for Solving the Problems The present inventors diligently studied a method for maximizing the physical properties and quality of a polyester film. As a result, using the simultaneous biaxial tenter of the linear motor system,
When the 3.0 times fine stretching is continuously repeated 3 times or more, (1) the Young's modulus of the polyester film is greatly increased, the heat shrinkage is reduced, (2) the stretching ratio is increased, and the production is increased. (3) The film thickness unevenness is improved and the film breakage frequency is reduced, (4) The crystallinity of the film is easily increased, and the heat shrinkage does not deteriorate even if the temperature of the heat treatment zone is lowered. And many other surprising facts were found, and the present invention was completed.

That is, 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 simultaneously biaxially stretched using a simultaneous biaxial tenter of a linear motor type. The operation of fine stretching at a magnification of 0.0005 to 3.0 times
The main feature is a method for producing a polyester film, which is repeated continuously at least twice, and a polyester film according to the production method.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester referred to 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,
Examples thereof include phthalic acid, naphthalenedicarboxylic acid, adipic acid, and sebacic acid, and diols include ethylene glycol, trimethylene glycol, tetramethylene glycol, and cyclohexane dimethanol. 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. Of course, these polyesters may be a homopolymer or a copolymer, and as a copolymerization component, for example, diethylene glycol, neopentyl glycol,
Diol components such as polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-
It may contain a dicarboxylic acid component such as naphthalenedicarboxylic acid and a hydroxycarboxylic acid component 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 copolymers and modified products thereof are preferable from the viewpoint of achieving the effects of the present invention. 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 polyester film of the present invention may contain inorganic particles, organic particles, and other various additives such as an antioxidant, an antistatic agent, and a crystal nucleating agent. 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. Sulfates, such as
Barium titanate, titanates such as potassium titanate, and phosphates such as tricalcium phosphate, dicalcium phosphate, and monocalcium phosphate can be used, but are not limited thereto. Absent. These may be used in combination of two or more depending on the purpose. Specific examples of the organic particles include polystyrene or crosslinked polystyrene particles, vinyl particles such as styrene-acrylic and acrylic crosslinked particles, styrene-methacrylic and methacrylic crosslinked particles, benzoguanamine formaldehyde, silicone, polytetrafluoroethylene, and the like. However, the particles are not limited thereto, and any particles may be used as long as at least a part of the constituent parts of 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 of these particles,
The shape and the like can be selected according to the application and purpose, but usually the average particle diameter is 0.05 μm or more and 3 μm or more.
m or less, and the compounding amount is preferably 0.01% by weight or more and 10% by weight or less.

The film of the present invention may be a laminated film having two or more layers. In the case of a laminated film in which two or more layers are laminated, particularly in a base film of a magnetic recording medium, it is an optimal method for designing the surface roughness of the film surface to be a magnetic recording surface and the surface roughness different from each other depending on the application. is there.

Simultaneous biaxial stretching in the present invention refers to stretching in order to simultaneously orient the film in the longitudinal and transverse directions. The film is conveyed while holding both ends of the film with clips using a simultaneous biaxial tenter. Refers to the operation of stretching in the vertical and horizontal directions. Here, the longitudinal direction of the film is the longitudinal direction of the film, and the lateral direction is the width direction of the film. Of course, it is sufficient if there is a portion where the stretching in the longitudinal direction and the stretching in the horizontal direction are simultaneously stretched temporally.Therefore, after stretching in the transverse direction or the longitudinal direction independently first, the stretching in the longitudinal direction and the transverse direction is performed. Are also included in the scope of the present invention, for example, a method of stretching simultaneously and a method of further stretching independently in the horizontal or vertical direction after the simultaneous biaxial stretching. In the present invention, a linear motor type simultaneous biaxial tenter is used as a stretching machine capable of freely changing the stretching direction and the stretching ratio. The drive system of the clip for holding the film may be any of a roller bearing system and a slider system. Using a linear motor type simultaneous biaxial tenter can increase the film forming speed and film width to the level of conventional sequential biaxial stretching or more, and freely change the film deformation pattern in the stretching, heat treatment, and relaxation processes. Has been attracting attention in recent years, but this multi-stage stretching with simultaneous biaxial tenter of linear motor type is
The present invention has been found to be extremely effective in obtaining a polyester film having high physical properties and quality at low cost. In the present invention, the area stretching ratio of one simultaneous biaxial fine stretching at the time of performing this super multi-stage stretching is set to be 0.0005 to 3.0 times,
Fine stretching needs to be repeated continuously three times or more.

Here, the area stretching ratio is the product of the longitudinal stretching ratio and the transverse stretching ratio of the film. If the area stretching ratio by one simultaneous biaxial fine stretching exceeds 3.0 times, it is difficult to obtain the effect aimed at by the present invention, and 1.0
Being less than 005 is not a practical requirement. The area stretching ratio by this one fine stretching is 1.005 to
2.0 times is more preferable, and 1.01 to 1.5 times is still more preferable. The number of repetitions of simultaneous biaxial fine stretching is preferably 10 times or more and less than 10,000 times, and 50 times or more and 10 times or less.
More preferably less than 00 times. If the micro-stretching is continuously repeated in this way, probably because the entanglement of the polyester chains in the film is released, (1) the structure and volume relaxation are accelerated, and a film with high Young's modulus and low heat yield is easily obtained. (2) It is preferable because effects such as an increase in total area stretching ratio, an improvement in film productivity and a reduction in cost can be obtained. The respective magnifications of the fine stretching repeated three or more times may be the same or different, and the respective stretching magnifications in the machine direction and the transverse direction can be appropriately selected based on the desired film properties. Further, as described above, one of the longitudinal direction and the lateral direction may be slightly stretched.

The stretching temperature when performing simultaneous biaxial fine stretching on the film is not particularly limited, but when performing fine stretching on an unstretched film, the glass transition temperature of the polyester Tg + 10) ° C. to (Tg + 120). ) ° C, preferably (Tg + 20) ° C to (Tg + 80) ° C. When the stretching temperature is lower than Tg + 10 ° C., the orientation by stretching is excessively advanced, and it is difficult to stretch to a high magnification, which is not preferable. On the other hand, the stretching temperature is Tg + 120 ° C
If it exceeds, it is difficult to give the polymer chains the fine orientation necessary for relaxing the structure, and the oligomers are liable to scatter in the stretching step, which is not preferable. In the present invention, it is preferable to perform simultaneous biaxial fine stretching at a stretching ratio until the yield point of the tension-strain curve is reached under each stretching temperature condition. Under these conditions, since the stretching tension and the strain correspond one-to-one, the thickness uniformity of the film hardly deteriorates due to the stretching, and a high-quality polyester film is easily obtained. To fix the structure of the film,
In the heat treatment performed under a temperature condition of (Tg + 120) ° C. or higher and lower than the melting point, the simultaneous biaxial fine stretching of the present invention is effective.
This heat-treating fine stretching is preferable from the viewpoint of increasing 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 performing stretching and heat treatment on an unstretched film made of a resin containing polyester as a main component. It is preferable to repeat the fine stretching three or more times continuously in the step until the crystallinity of the unstretched film becomes 3% or more and less than 30% or in the heat treatment step. Here, the unstretched film refers to a sufficiently dried raw material pellet supplied to an extruder,
This refers to a material extruded into a sheet shape on a rotating metal casting drum by a die and cooled and solidified, or a material obtained by supplying undried pellets to a vent-type extruder in the same manner.

It is preferable to repeat fine stretching continuously in the initial stretching step before the unstretched film undergoes volume relaxation to increase the crystallinity, but the simultaneous biaxial fine stretching is continuously repeated in three or more steps. However, when the degree of crystallinity is less than 3%, it is difficult to remove the stress strain generated in the subsequent simultaneous biaxial stretching, which tends to make it difficult to increase the stretching ratio, and the Young's modulus of the film. This is not preferred because the decrease and the increase in the heat shrinkage rate tend to be severe.

The crystallinity of the unstretched film after continuously repeating the fine stretching of the present invention is preferably 5% or more and less than 25%, more preferably 10% 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 the case of a raw material that tends to crystallize due to the effects of additives, it may be preferable to stretch the film at a high magnification in one step to obtain a film having excellent physical properties and quality, rather than repeating fine stretching. Further, a film having a degree of crystallinity of more than 30% tends to undergo volume relaxation due to fine stretching, tends to crystallize before stretching at a high magnification, and tends to have a low Young's modulus. In such a case, it is necessary to devise a method such as stretching at a high magnification in one step.

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 is very difficult. A more preferable range of the total Young's modulus is 10 to 25.
GPa, particularly preferably 12 to 22 GPa.
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 many cases, the sum of the heat shrinkage in the vertical and horizontal directions at 100 ° C. for 30 minutes is less than 2%. A more preferred range of the sum of the heat shrinkage rates is less than 1%, and more preferably less than 0.5%. 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, it is easy to obtain a polyester film in which the sum of the Young's modulus in the longitudinal direction and the transverse direction is 8 to 30 GPa and the sum of the heat shrinkage rates at 100 ° C. for 30 minutes is less than 2%.

According to the production method of the present invention, the structure of the polyester is easily relaxed, so that the crystallinity of the film after biaxial stretching and heat treatment tends 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 films of 0% or more is usually not easy, but such films are relatively easy to obtain according to 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, if the crystallinity exceeds 90%, the film is frequently broken and the workability in various film uses is undesirably reduced.

The total thickness of the film in the present invention can be appropriately selected according to the use and purpose of the film. Usually, for magnetic material applications, it is preferably 1 μm or more and 20 μm or less,
In particular, the thickness is 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 or less for digital video evaporation magnetic recording media. Also, among industrial materials, 1μ for thermal transfer ribbon
m to 6 μm, 0.5 μm to 15 μm for capacitors, and 0.5 μm to 5 for heat-sensitive stencil paper.
It is preferably not more than μm.

Next, specific examples of the method for producing the polyester film of the present invention will be described, but it is needless to say that the present invention is not limited to such examples.

The polyester has an intrinsic viscosity of 0.65
Polyethylene terephthalate pellets under vacuum
The mixture is heated to 80 ° C., dried sufficiently, supplied to an extruder heated to a temperature of 270 to 300 ° C., and extruded from a T-type die into a sheet. This melted sheet is subjected to a surface temperature of 10
It is brought into close contact with a drum cooled to 40 ° C. by electrostatic force and solidified by cooling to obtain a substantially amorphous unstretched cast film. At this time, the ratio of the thickness of the end portion and the center portion of the unstretched film (the thickness of the end portion / the thickness of the center portion) is 1 or more,
0 or less, preferably 1 or more and less than 5, more preferably 1 or more and 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 system by grasping both ends of the film with clips,
The film is heated to 90 to 150 ° C. in the preheating zone, and the simultaneous biaxial fine stretching in which the area stretching ratio of the film is 0.0005 to 3 times is continuously performed at least three times. At this time, it is preferable that the temperature of the clip for gripping the film end is set in a temperature range of 80 to 160 ° C. The stretching temperature in the fine stretching step is preferably kept within a temperature range of 90 to 150 ° C., but the film may be cooled once and finely 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. The simultaneous biaxial stretching is performed as described above, and the total area stretching ratio of the film is 2
It is simultaneously biaxially stretched 0 to 150 times. Next, in order to impart flatness and dimensional stability to the biaxially stretched polyester film, a heat treatment is performed at a temperature in the range of 200 ° C. or higher and lower than the melting point.
The relaxation treatment is carried out in the vertical and horizontal directions in a temperature range of 00 to 200 ° C., preferably in the range of 1 to 6% in each direction.
At this time, the simultaneous biaxial fine stretching in the heat treatment step can be preferably repeated 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 relaxation treatment in the vertical and horizontal directions, to obtain a desired polyester film. In the present invention, in order to impart surface properties of the film, for example, in order to impart easy adhesion, easy slip, release properties, antistatic properties, the process before or after the simultaneous biaxial stretching of the film It is also preferable to coat a coating material on the surface of the polyester film.

[0027]

[Evaluation method of physical properties] (1) Intrinsic viscosity [η] The value calculated from the following formula from the solution viscosity measured in orthochlorophenol at 25 ° C 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 A "Robot DSC-RDC220" manufactured by Seiko Instruments Inc. is used as a differential scanning calorimeter, and "Disk Session" SSC / 52 manufactured by the company is used as a data analyzer.
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 tension-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 being left in an oven at 0 ° C. for 30 minutes under no load, the distance between the two lines is measured again, and this is set to L1, and the heat shrinkage is calculated 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 the casting drum from a T-type die by electrostatic force and cooled and solidified 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) Unevenness in the thickness direction of the film 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) of the 10-m length, thickness unevenness was determined by the following equation.

Uneven thickness (%) = (R / Tave) × 10
0

[0037]

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

Example 1 (Table 1) 180 pellets 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) were mixed. After vacuum drying at 3 ° C. for 3 hours, the mixture was supplied to an extruder heated to 280 ° C., melt-extruded, and discharged from a T-die into a sheet. Further, this sheet was brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force and 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 total area magnification is 1.082 times (vertical magnification: 1.04 times).
(Double magnification, transverse magnification: 1.04 times) at the same time. Thereafter, heat setting is performed at a temperature of 210 ° C., and 2% in the vertical direction and 2% in the horizontal direction in the cooling zone of 120 ° C.
%, And the film was gradually cooled to room temperature and wound up. The film thickness was adjusted to 9 μm by adjusting the extrusion amount. In addition, the clip temperature at the time of extending | stretching was 100 degreeC. The film obtained here was 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. In addition, film tearing during film formation is small,
A film with high physical properties and high quality was obtained very stably.

Examples 2 to 5, Comparative Example 1 (Table 1) A film was formed in the same manner as in Example 1 except that the simultaneous biaxial fine stretching magnification, the number of repetitions, and the total area magnification were changed. A film was obtained. Here, in the case of Example 2 and Comparative Example 1 in which the number of repetitions of fine stretching is three and two, simultaneous biaxial stretching is further performed in one stage after fine stretching, and the total area magnification of the film is 25 times. did. When the number of times of fine stretching was repeated three times or more and further increased, the frequency of film tearing decreased, and the total area stretching ratio tended to increase. Further, when the number of repetitions of the fine stretching was increased and the stretching was performed at a high magnification, the crystallinity of the film was increased, and a high-quality film having high rigidity, low heat shrinkage and small thickness unevenness was obtained.

[0040]

[Table 1] Comparative Examples 2 to 4 (Table 2) A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the film was stretched without performing simultaneous biaxial 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 was simultaneously biaxially stretched at a magnification of 3 times, only a film having a small Young's modulus and a large heat shrinkage was obtained, and the thickness unevenness of the film was also large (Comparative Examples 2 and 3). In addition, the film is placed in the longitudinal direction and the lateral direction, respectively.
After simultaneous biaxial stretching at a magnification of 0, and further, simultaneous biaxial stretching at a magnification of 1.2 times each in the machine direction and the transverse direction, film tearing occurs frequently and the heat shrinkage of the film is large. (Comparative Example 4).

[0041]

[Table 2] Examples 5 to 9 (Table 3) In this example, an example is shown in which a film is formed by changing the ultimate crystallinity after fine stretching. Example 1 except that the magnification and the number of repetitions of the fine stretching were changed, and the fine stretching was continuously repeated, followed by simultaneous biaxial stretching in one stage to set the total area magnification to 50 times.
A biaxially stretched polyester film was obtained in the same manner as described above. Here, the magnification in the vertical and horizontal directions by one simultaneous biaxial stretching was set equal. When the crystallinity of the film after simultaneous biaxial fine stretching was 2% and 34%, the Young's modulus decreased and the heat shrinkage increased.

[0042]

[Table 3] Examples 10 to 12 (Table 4) In a simultaneous biaxial tenter, 100
A film was formed in the same manner as in Example 4 except that temperature zones of ° C, 140 ° C, 210 ° C, and 250 ° C were provided and the temperature conditions for simultaneous biaxial fine stretching were changed to obtain a biaxially oriented polyester film. When simultaneous biaxial fine stretching was performed in a high temperature range of 210 ° C. and 240 ° C., the Young's modulus of the film increased, and the heat shrinkage decreased.

[0043]

[Table 4] Example 13, Comparative Example 5 (Table 5) 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 polyester Using it as a raw material, the effect of simultaneous biaxial fine stretching was investigated. 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 to obtain a biaxially oriented polyester film having a thickness of 6.5 μm. Was. When performing fine stretching, the area magnification by one fine stretching is 1.082 times (longitudinal magnification: 1.times.).
(0.4 times, lateral magnification: 1.04 times) and repeated 50 times continuously. When fine stretching was not performed, simultaneous biaxial stretching was performed in one step at the same magnification in each of the vertical and horizontal directions. Unlike the case of Comparative Example 5, in Example 13 in which fine stretching was performed, the total area magnification was increased, and a film having a high Young's modulus and low heat shrinkage was obtained.

Examples 14 and 15 and Comparative Examples 6 and 7 (Table 5) Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65 (sphere having a glass transition temperature of 125 ° C., a melting point of 265 ° C. and an average diameter of 0.3 μm) A copolymer of 90 mol% of polyethylene terephthalate and 10 mol% of polyethylene-2,6-naphthalate (glass transition temperature: 84 ° C., melting point: 235 ° C., average diameter: 0.3 μm) 0.1% by weight of polystyrene particles
), And a biaxially oriented polyester film having a thickness of 6.5 μm was obtained in the same manner as in Example 13 and Comparative Example 5, except that the stretching temperature was set to the conditions shown in Table 5.
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. By repeating the simultaneous biaxial fine stretching, the total area ratio and the crystallinity were increased, and a high-quality polyester film having a high Young's modulus and a low heat shrinkage could be stably formed.

[0045]

[Table 5]

[0046]

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. INDUSTRIAL APPLICABILITY The present invention can be widely used as a method for manufacturing various films for magnetic recording, electrical insulation, thermal transfer ribbon, thermal stencil printing, packaging, and the like. A novel polyester film having physical properties and quality far exceeding properties can be obtained.

Claims (8)

[Claims] 1. A method for producing a polyester film, comprising simultaneously biaxially stretching a film composed of a resin containing polyester as a main component by using a simultaneous biaxial tenter of a linear motor type, wherein the area stretching ratio of the film is from 0.0005 to 3. .
A process for producing a polyester film, wherein the operation of fine stretching at a magnification of 0 is continuously repeated at least three times. 2. The method for producing a polyester film according to claim 1, wherein said fine stretching is repeated 10 times or more and less than 10,000 times. 3. The fine stretching of the unstretched film is performed at (glass transition temperature Tg + 10) ° C. to (Tg + 120) ° C.
The method for producing a polyester film according to claim 1, wherein the temperature is set in a temperature range of: 4. The method according to claim 1, wherein the fine stretching is continuously repeated with respect to the unstretched film until the crystallinity becomes 3% or more and less than 30%. Manufacturing method of polyester film. 5. A polyester film obtained by stretching a film made of a resin containing polyester as a main component using a simultaneous biaxial tenter of a linear motor type,
A polyester film manufactured by continuously repeating the operation of fine stretching while setting the area stretching ratio of the film to 1.0005 to 3.0 times, three times or more. 6. The film according to claim 5, wherein the sum of the Young's modulus in the machine direction and the transverse direction is 8 to 30 GPa, and the sum of the heat shrinkage rates at 100 ° C. for 30 minutes is less than 2%. Polyester film. 7. The polyester film according to claim 5, wherein the degree of crystallinity is 30 to 90%. 8. The polyester film according to claim 5, wherein the polyester is polyethylene terephthalate, polyethylene naphthalate, or a copolymer or modified product thereof.