JP2000202903A - Manufacture of biaxially stretched polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film, the irregularity of the lateral thickness of which is 5% or less by stretching the film longitudinally and further laterally. SOLUTION: A polyester is discharged through a die equipped with a delivery adjusting means and made into a polyester film and then the irregularity of the thickness of the film is detected so as to adjust the delivery of the film in order to cope with the irregularity of the thickness of the film, resulting in manufacturing a biaxially stretched polyester film. The thickness irregularity is a local irregularity X represented by an equation: X(%)=(TA-TB)/TC×100. If the local irregularity is 0.1% or more, the measured irregularity is judged as abnormal, resulting in adjusting the delivery adjusting means. In the equation, TA is the maximum value of the thickness in the range of the width direction L (mm) of the film, TB is the minimum value of the thickness in the range of the width direction L (mm) of the film, L (mm) is set to be 50-250% of the arrangement pitch of the delivery adjusting means in the width direction of the film, TC is the average value of the thickness in the total width direction (mm) of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially oriented polyester film which has good thickness unevenness in the horizontal direction, uniform physical properties in the horizontal direction, and high strength in the vertical direction.

[0002]

2. Description of the Related Art A biaxially oriented polyester film having a large longitudinal strength is usually stretched at a high magnification in a longitudinal direction.
This film has a high heat shrinkage (heat yield) in the longitudinal direction. Therefore, compared to the type in which the strength in the biaxial direction is almost balanced (balanced type) and the horizontal-stretched film in which the strength in the horizontal direction is greater than in the vertical direction, The phenomenon that the shrinkage is large and the length in the vertical direction of the lateral (widthwise) center portion and the edge portion is different (hereinafter, sometimes referred to as bowing) easily occurs.

[0003] Due to this bowing, the physical properties in the lateral direction of the film become non-uniform, and the heat collection and the mechanical properties of the center part and the edge part in the lateral direction are greatly different, causing various adverse effects.

As a specific example of the adverse effect, for example, in the case of a magnetic recording medium, the physical properties of the film differ depending on the position of the base film in the width direction of the film raw material.
The skew caused by touching the magnetic head and heat absorption is different, and when coating the magnetic paint through the drying process, it runs curved due to the difference in expansion and contraction in the film width direction, affecting productivity. Has occurred.

In order to make the physical properties uniform in the film width direction, it is effective to reduce bowing. As this method, Japanese Patent Application Laid-Open No. 57-57629 and
Japanese Patent Application Laid-Open No. 8-24418 proposes a method of performing fine stretching in a heat setting zone. However, this proposal aims at making the physical properties in the vertical and horizontal directions isotropic, and therefore, the stretching ratio in the vertical and horizontal directions is set to be almost the same, and the type in which the strength in the vertical direction is increased The vertical magnification is 4.
No mention is made of making the physical properties in the width direction uniform in a region where the magnification is 0 or more.

Japanese Patent Application Laid-Open No. 9-57845 proposes a method of fine stretching a number of times in the horizontal direction, but also mentions stretching conditions for increasing the longitudinal magnification to 4.0 times or more. It has not been.

Further, in Japanese Patent Application Laid-Open No. 10-138333, laser Raman is used to define the degree of longitudinal orientation. However, in the detailed description, by setting the transverse magnification to 4.0 times or more, unevenness in lateral thickness is obtained. Is good, and when the lateral magnification is less than 4 times, it indicates that the thickness unevenness needs to be improved.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks, and to obtain an F-5 value of 13 kg in the longitudinal direction of the film.
/ Mm ² or more, the thickness unevenness in the horizontal direction is 5% or less, and the difference in the heat shrinkage in the vertical direction at 105 ° C. in the horizontal direction is 0.2% / m. It is to provide a film.

[0009]

The present inventor has conducted intensive studies to solve the above-mentioned problems. As a result, the vertical magnification, the horizontal magnification, and the bowing are related to each other. Although it is easy to occur, it has been found that the thickness unevenness potential in the lateral direction is increased by using a control device that corrects local unevenness. The film is subjected to toe-out in the heat setting zone, and by adjusting the lateral heat yield by toe-in, the properties in the width direction of the film can be further uniformed, and physical properties that do not adversely affect properties after commercialization. It was found that a film of the formula (1) was obtained, and reached the present invention.

That is, in the present invention, polyester is discharged from a die provided with a discharge amount adjusting means, and after forming a polyester film, unevenness of the film thickness is detected, and the discharge amount is adjusted according to the uneven thickness. In the method for producing a biaxially oriented polyester film, the thickness unevenness is a local unevenness (X) represented by the following formula, and the local unevenness is 0.1%.
% Is determined as an abnormal value, and a discharge amount adjusting means is controlled, thereby producing a biaxially oriented polyester film. Local plaques = X (%) = (T A -T B) / T C × 100 ··· Equation (1) T _A: maximum value of the thickness in the range of the width direction L (mm) of the film T _B: film The minimum value of the thickness in the width direction L (mm) L (mm): a range of 0.5 to 2.5 times the arrangement pitch of the discharge amount adjusting means in the width direction of the film T _C : the entire width direction of the film (mm) According to the present invention, the F-5 value in the longitudinal direction is 13 kg / mm ²
As described above, a polyester film having a thickness unevenness in the horizontal direction of 5% or less and a difference in the heat shrinkage in the vertical direction at 105 ° C. in the horizontal direction of 0.2% / m can be produced.

(Local plaque) The local plaque in the present invention can be represented by the following equation (1). _{X (%) = (T A} -T B) / T C × 100 ···· formula (1) X: local spots T _A: maximum value of the thickness in the range of the width direction of the film L (mm) T _B: The minimum value of the thickness in the range of the film width direction L (mm) L (mm): the range of 0.5 to 2.5 times the arrangement pitch of the discharge amount adjusting means in the film width direction _TC : the total width of the film Average value of thickness in direction (mm)

(Die) The die in the present invention is a polyester film extrusion molding die capable of extruding a film (also called a sheet) from a molten polyester through a slit die. Any material can be used as long as it can form a film, but it has adjusting means for controlling the discharge amount for each predetermined width of the die over the entire width of the die.

(Discharge Amount Adjusting Means) The discharge amount adjusting means in the present invention is provided at predetermined intervals over the entire width of the die.
Any material can be used as long as it can control the discharge amount for each predetermined width of the die, but a heater that adjusts the discharge amount by changing the viscosity distribution of the polymer by adjusting the temperature distribution in the width direction of the die lip of the die is used. However, it is preferable in terms of the structural ease of the die. By adjusting the slit width of the die lip of the die using a heat bolt or the like, the discharge amount for each predetermined width of the die can be adjusted.

(Discharge) Discharge in the present invention refers to discharging by extruding dried polyester pellets from a slit-shaped die of a die with an extruder.

(Thickness unevenness) Thickness unevenness (Y) in the present invention.
Can be expressed by the following equation. Y (%) = (T _D -T _E ) / T _C × 100 Y: Uneven thickness T _D : Maximum value of the thickness in the entire width direction (mm) of the film _TE : Minimum of the thickness in the full width direction of the film (mm) the value T _C: average value of the thickness in the entire width of the film direction (mm)

(Control) The control in the present invention is performed as follows. The thickness of the film is input to the controller from the thickness gauge, the controller performs calculations, and outputs the calculated value to the discharge amount adjusting means via the amplifier circuit. The calculation includes a calculation 1 and a calculation 2, and it is preferable that the respective outputs are added at a predetermined ratio to obtain an output.

In the calculation 1, the measured thickness at the thickness measuring point in the width direction of the film corresponding to the discharge amount adjusting means is calculated by:
The deviation from _C (the average value of the thickness in the entire width direction (mm) of the film) is calculated, and the result is defined as a control output (B) corresponding to the deviation. That is, in the input thickness signal, the thickness measurement point in the width direction of the film corresponding to each of the ejection amount adjusting means is set as a detection end of each control loop, and a predetermined control is performed on the deviation of the measured thickness at each detection end from the average thickness. The control output is calculated by performing a calculation, preferably a PI control calculation, and used as the output of the calculation 1 (control output (B)).

In the operation 2, based on the measured thickness, a local plaque is calculated by the equation (1), and a point where the local plaque is equal to or more than a predetermined threshold value is determined as an abnormal point (local plaque), and Output (control output (A)).

It is preferable that the local spots are arranged in the order of the size, and the ejection amount is adjusted based on only the local spots located at a position where the control does not interfere with the local spots. That is, T _A and T _B within the range where the local plaque is the largest are defined as primary local plaque control points, and T _A within the range where the local plaque is the largest within a range where control of the primary local plaque control point does not interfere. And T _B are the second local spot control points. , T _A and T _B within the maximum range of local plaques in the range where control of the (n−1) th local plaque control point does not interfere with each other are defined as the n-th local plaque control point, and the local plaque control points in the entire width of the film. Ask for. By doing so, there is an effect that the local spot can be controlled with good response as a whole.

It is preferable to make adjustments to the ejection amount adjustment means closest to the local spot control point. This adjustment method is based on T
And a target value the average value of _A and T _B, a predetermined control operation on the deviation from the target value, it is preferable that the output of the operational 2 calculates the control output by performing PI control calculation in this example.

When the nearest discharge amount adjusting means is the same, the output at the closest maximum value or minimum value is set as the output to the discharge amount adjusting means. Outputs by value. In addition, by outputting an output of 50% or less of the output so as to cancel the output on the edge side of each of the outputs, the convergence of the local spot is improved.

(Biaxially Oriented Polyester Film) The biaxially oriented polyester film of the present invention is a longitudinal tensilized type having a high strength in the longitudinal direction, and is effective in producing a film having uniform physical property distribution and uneven thickness in the width direction. It is a target.

The biaxially oriented polyester film has an F-5 value in the longitudinal direction of 13 kg / mm ² or more, preferably 14.0 kg / mm ² or more. The F-5 value is such that the total stretching ratio in the longitudinal direction of the film is 4.0 times or more,
Further, it can be provided by setting it to 4.3 times or more. If the longitudinal magnification is set too high, the longitudinal orientation proceeds in the uniaxial film, the bowing phenomenon easily occurs in the transverse stretching or heat fixing step, and the uniformity of the physical properties in the width direction is inhibited, and
Since the potential for thickness unevenness becomes worse, the longitudinal stretching method is a longitudinal multi-stage stretching of two or more stages, and a total magnification of 4.8.
Times or less, preferably 4.7 times or less,
By using this control method, these restrictions are not applied.

In the biaxially oriented polyester film, the difference in the heat shrinkage in the vertical direction at 105 ° C. in the horizontal direction (width direction) is 0.2% / m or less.

The biaxially oriented polyester film is further heated at a temperature of 100.degree.
It is preferable that the difference in the transverse direction between the elongation rate (TMA elongation rate) in the longitudinal direction of the film when a load of mm ² is applied is 0.1% / m or less.

In order to impart the heat shrinkage characteristics and the TMA elongation, the longitudinal orientation of the uniaxial film is reduced, and the heat-shrink zone in the tenter after the biaxial stretching is 1-2 mm in the transverse direction.
0% fine stretching, then 0-20% in the transverse direction in the cooling zone
Relaxation is preferred. Film sagging and vertical heat collection,
Taking into account the standard of the longitudinal strength as a tensilized type, the fine stretching is more preferably performed in the range of 1 to 10%. The relaxation is more preferably performed in the range of 0 to 10%.

Further, when the above-mentioned fine stretching (toe-out) is performed, the heat yield in the lateral direction increases, so that it is necessary to adjust the heat yield by performing relaxation (toe-in) in the cooling zone. that time,
A slight toe-in may be performed in the latter half of the heat fixing zone after the toe-out. Although a slight return of Boeing is observed due to such toe-in, the effect of fine stretching remains sufficiently. However, when the toe-in amount exceeds 20%, wrinkles of the film at the exit of the stenter increase, which is not preferable because it causes folding wrinkles. These conditions have almost no adverse effect on the thickness unevenness, and the thickness unevenness in the vertical and horizontal directions can be reduced to 5% or less in a variation per 1 m. In order to reduce this heat yield, it is conceivable to increase the heat setting temperature instead of toe-in.However, if the heat setting temperature is too high, the heat yield in the stenter will increase and the bowing will increase. Not preferred.

The biaxially oriented polyester film of the present invention has a variation in thickness unevenness in the lateral direction of 5% or less (per 1 m). If this variation exceeds 8%,
This is not preferable because the winding appearance of the film becomes uneven.

(Polyester) The polyester in the present invention is a linear polyester comprising a dicarboxylic acid component and a glycol component.

Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid and the like. Of these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferred. As the glycol component, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol,
Examples thereof include diethylene glycol and neopentyl glycol. Among these, ethylene glycol,
1,4-butanediol is preferred, and ethylene glycol is particularly preferred.

Naphthalenedicarboxylate or polybutylene terephthalate is preferred, and polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are particularly preferred because the film has excellent mechanical properties and thermal properties.

The polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate or polybutylene terephthalate may be a polyester obtained by copolymerizing a dicarboxylic acid component or a glycol component at a ratio of, for example, 10 mol% or less. It may be a polyester obtained by copolymerizing a small amount of a polyvalent compound having a functionality or higher in a range where the polyester becomes substantially linear (for example, 5 mol% or less).

When the copolymer component is polyethylene terephthalate, isophthalic acid and 2,2 are used as acid components.
Preferable examples include 6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid and the like, and propylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol and the like as glycol components.

The copolymer components of polyethylene-2,6-naphthalenedicarboxylate include terephthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid and the like as an acid component, and 1,4-butanediol as a glycol component. Preferred examples include 1,6-hexanediol, propylene glycol, 1,5-pentanediol, 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol and the like.

The copolymerization components of polybutylene terephthalate include isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid and the like as acid components, and ethylene glycol, 1, and 2 as glycol components.
6-hexanediol, propylene glycol, 1,5
-Pentanediol, 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol and the like can be preferably exemplified.

As the copolymerization component of polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate and polybutylene terephthalate, in addition to the above components, for example, hexahydroterephthalic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, etc. Glycol components such as a dicarboxylic acid component, 1,3-propanediol, polyethylene glycol, polytetramethylene glycol, dipropylene glycol, triethylene glycol, and an alkylene oxide adduct of bisphenol A can be mentioned. As the above polyester, a homopolymer or a copolymer can be used, and a blend of these polyesters can also be used.

It is preferably 0.5 × 10 ⁹ Ω · cm or less under the measurement condition of an AC voltage of 50 Hz. The polyester having such a volume resistivity can be obtained, for example, by compounding a compound having an alkali metal salt or by copolymerizing a small amount of a quaternary phosphonium salt of a sulfonic acid, and thereby obtaining a good adhesion between the film and the cooling drum. Sex can be obtained.

Further, in order to improve the winding property of the polyester film and to provide the surface property required for each application, organic or inorganic fine particles having an average particle size of about 0.001 to 5.0 μm are used. For example, it is preferable to mix and contain at a rate of 0.01 to 2.0 wt%. Such fine particles include, for example, dry silica, wet silica, zeolite,
Inorganic fine particles such as calcium carbonate, calcium phosphate, kaolin, kaolinite, clay, talc, titanium oxide, alumina, zirconia, aluminum hydroxide, calcium oxide, graphite, carbon black, zinc oxide, silicon carbide, silver oxide, and crosslinked acrylic resin particles And organic particles such as crosslinked polystyrene resin particles, melamine resin particles, and crosslinked silicone resin particles.

If necessary, a lubricant, an antioxidant,
Antistatic agents, colorants, pigments, tendency brighteners, plasticizers, ultraviolet absorbers, other resins, and the like can be added.

The film is extruded on a cooling drum, brought into close contact with the rotary cooling drum, and cooled to obtain an unstretched film. At that time, it is preferable that an electrostatic charge is applied in a non-contact manner to the air side (opposite to the cooling drum) surface of the extruded molten film near the rotary cooling drum.
For example, a polyester is supplied to an extruder, melted at a temperature of not less than the melting point of the polymer and up to 350 ° C., the molten polymer is discharged from a die, and an electrostatic charge is further applied to the discharged film to bring the film into close contact with a cooling drum. An unstretched film can be produced by cooling and solidifying while cooling. In addition, it is preferable to dry a polyester raw material before supplying to an extruder.

The unstretched film is further stretched in the longitudinal direction, and then stretched in the transverse direction to form a biaxially stretched film. In order to obtain this biaxially stretched film, a temperature at which the unstretched film can be stretched (for example, Tg of polyester)
(Temperature of -10 ° C. or higher and Tg + 80 ° C. or lower) and stretched in the biaxial direction. In the longitudinal stretching, it is preferable to stretch the film by setting it to 4.0 times or more in the film running direction (longitudinal direction). Lateral stretching is in the transverse direction (width direction) of the film
Set to a magnification of 3.0 times or more and the same as the longitudinal stretching temperature,
It is preferable to stretch at a higher temperature. The area magnification is preferably 12 to 25 times.

The biaxially stretched film is, for example, stretched in an unstretched film in the longitudinal direction and then stretched in the transverse direction, that is, a so-called longitudinal-transverse sequential stretching method. It is preferable and preferable to manufacture by a vertical multi-stage stretching method in terms of uneven thickness. The biaxially stretched film may be further stretched in the longitudinal direction or the uniaxial direction in the transverse direction, or in the biaxial direction in the longitudinal direction and the transverse direction to form a biaxially stretched film. The above biaxially stretched film is further higher than the final stretching temperature, preferably 10
It is preferable to heat-treat (heat-set) at a temperature higher than the melting point (Tm) of the polyester and lower than the melting point (Tm) of the polyester, preferably lower than (Tm-30) ° C, and then cool to room temperature. The biaxially stretched film thus obtained has
For example, JP-B-56-183815 and JP-B-57-183815
Surface activation treatment (for example, plasma treatment, amine treatment, corona treatment, etc.) as disclosed in JP-A-303084
May be applied.

The thickness unevenness adjusting device provided with the control means for local unevenness described in the claims is performed by using the control device disclosed in Japanese Patent Application Laid-Open No. 8-267536, and the variation of the thickness unevenness in the horizontal direction is 5% or less ( Per meter).

The thickness of the polyester film of the present invention is preferably 0.5 to 20 μm, depending on the use. This polyester film has surface defects such as a capacitor film (for example, a film having a thickness of 3 μm or less), a film for a printer ribbon (for example, a film having a thickness of about 5 μm), a film for heat-sensitive stencil printing, and a magnetic recording medium, particularly a base film for QIC. It is useful to use as little as possible for preferable applications. In particular, according to the knowledge of the present inventor, it is important that the magnetic recording medium has a small thermal expansion and contraction characteristic (TMA) under a constant load and a uniform expansion and contraction characteristic in the width direction under heating. The polyester film of the present invention satisfies these characteristics, and can prevent running curvature in the drying step after magnetic coating and trouble in the step of heating the film in the manufacturing process.
It is useful as a base film.

[0045]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value was measured by the following method.

1. F-5 value From the biaxially oriented polyester film, five film pieces having a width of 10 mm and a length of 100 mm were cut out from the biaxially oriented polyester film as long sides, and these film pieces were cut at 100 mm / min using a tensile tester manufactured by Toyo Seiki. Tensile force was measured at 5% strain (n = 5).
-5 value.

2. Heat shrinkage Specimen of width 10mm, length 300mm or more,
Cut out each of the biaxially oriented polyester film in the longitudinal direction and the width direction.
The sample was put in a hot air circulation oven at 105 ° C. in a free state, taken out after 30 minutes, and allowed to cool for 10 minutes. The distance between the scores of this test piece was measured by n = 5,
(Score before heat treatment-Score after heat treatment) x 100
The average value of the evaluation interval [%] before heat treatment is defined as the heat shrinkage.

3. Thickness unevenness A sample film piece of 2 m is cut out from the biaxially oriented polyester film in the width direction, and measured with an electronic micrometer manufactured by Anritsu. The percentage obtained by dividing the difference between the maximum thickness and the minimum thickness by the average thickness is defined as the thickness unevenness.

4. TMA elongation and its difference in the width direction 10 mm in the longitudinal direction from the biaxially oriented polyester film,
A plurality of sample film pieces each having a width of 5 mm were cut out in the film width direction, and these were subjected to a tensile force of 1000 g / mm ² in the longitudinal direction by TM-3000 manufactured by Vacuum Riko, and heated at 10 ° C./min in a nitrogen atmosphere. Measure the elastic properties in the longitudinal direction, divide the elongation at 100 ° C by the sample length,
Elongation rate. Then, the difference between the maximum value and the minimum value of the elongation in the width direction is determined.

[Example 1] Polyethylene terephthalate having an intrinsic viscosity of 0.60 (Tm = 2) in which silica particles having an average particle diameter of 0.6 μm were blended at 0.05 wt% with respect to polyester.
56 ° C., Tg = 68 ° C.)
After drying at 0 ° C. for 3 hours, it was supplied to an extruder, melt-extruded at 280 ° C., and cooled on a metal roll at 30 ° C. to obtain an unstretched film.

Next, the unstretched film was heated at a temperature of 110
First stretching at 2.5 ° C., 2.5 times, and further heating to 90 ° C. by infrared heater, followed by longitudinal direction (longitudinal direction)
After stretching 1.95 times to a total of 4.88 times,
Cooled immediately to 20 ° C. Subsequently, using a tenter transverse stretching device, the film is stretched 4.2 times in the transverse direction at 99 ° C., and then finely stretched 7% in the transverse direction while being thermally fixed at 220 ° C. 2 at 180 ° C after the zone
%, 2% toe-in at 110 ° C. in a cooling zone, and then wound.

For adjusting the thickness, a heater was used as a local spot adjusting means. The heaters were arranged at intervals of 30 mm in the width direction of the die. The width of the die is 500 mm. The thickness was measured using a β-ray thickness gauge before winding the film. Local spots were determined at intervals of 1.5 heaters (129 mm) in the heater of the film (1200 mm wide) after biaxial stretching, and 0.5% or more was judged as an abnormal value and controlled.

[0053] Control by the equation (1) calculates the local spots, corresponding to the deviation between the control output corresponding to the topical plaques (A), the measured thickness and T _C in the width direction of the thickness measuring point of the film The control output (B) obtained above is added to the control output (B), and the sum is used as a control output to the discharge amount adjusting means.

The biaxially oriented polyethylene terephthalate film obtained had an F-5 value of 14.5 kg / mm ² ,
The heat shrinkage in the vertical direction at 5 ° C. is 1.2% and the heat shrinkage in the horizontal direction is almost 0%.
The maximum difference in elongation at 100 ° C. by 1% / m and TMA was 0.05% / m, and all properties were good. Also,
The thickness unevenness in the lateral direction showed a value of 4%, which was no problem.

When this biaxially oriented polyethylene terephthalate film was used for a long play magnetic recording tape, the running in a drying oven in the tape manufacturing process was satisfactory without any curvature.

[Comparative Example 1] Vertical magnification 4.9 times, horizontal magnification 3.9
Thickness control was performed using a control device capable of performing only PID control with a double and 7% toe-out, and the other conditions were the same as in the example.
And the running in the drying oven was curved in the tape manufacturing process, and good results could not be obtained.

[0057]

According to the present invention, by using a manufacturing apparatus capable of improving local spots and combining toe-out and toe-in in a heat-fixing zone, uniform heat properties in the width direction can be obtained in a suitable manner. It became possible to obtain a small film. In addition, since a manufacturing device capable of improving local unevenness is used, the thickness unevenness in the lateral direction can be improved, and when used as a film for a thermal transfer printer ribbon or a film for magnetic recording, heat generated in the manufacturing process can be reduced. In the case of bending for running due to expansion and contraction and magnetic recording, a film having good skew and good productivity and quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for manufacturing a film used in an example.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 67:02 (72) Inventor Hiroshi Tokuda 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Teijin Limited Sagamihara F-term in the research center (reference) 4F071 AA45 AA46 AF14 AF54Y BA01 BB06 BB08 BC12 4F207 AA24 AA26 AB17 AE01 AG01 AP11 AQ02 KA01 KM06 KM15 4F210 AA24 AA26 AB17 AE01 AG01 AP11 AQ02 QA02 QC16 QD04 Q01

Claims (7)

[Claims] 1. After discharging polyester from a die having a discharge amount adjusting means and forming a polyester film,
A method for producing a biaxially oriented polyester film while detecting uneven thickness of a film and adjusting a discharge amount according to the uneven thickness, wherein the uneven thickness is a local unevenness (X) represented by the following formula; A method for producing a biaxially oriented polyester film, wherein a case where the local spot is 0.1% or more is judged as an abnormal value, and a discharge amount adjusting means is controlled. Local plaques = X (%) = (T A -T B) / T C × 100 ··· Equation (1) T _A: maximum value of the thickness in the range of the width direction L (mm) of the film T _B: film The minimum value of the thickness in the width direction L (mm) L (mm): a range of 0.5 to 2.5 times the arrangement pitch of the discharge amount adjusting means in the width direction of the film T _C : the entire width direction of the film (mm) Average thickness at 2. The method according to claim 1, wherein the uneven thickness in the entire width direction of the biaxially oriented polyester film is 5% or less. 3. The method according to claim 1, wherein the polyester is polyethylene terephthalate or polyethylene naphthalate. 4. The method according to claim 1, wherein the local plaques are arranged in order of size, and the ejection amount is adjusted based on only local plaques located at a position where control does not interfere with higher-order local plaques. 5. The method according to claim 1, further comprising controlling the discharge amount adjusting means corresponding to the position of T _A and the discharge amount adjusting means corresponding to the position of T _B. 6. The method according to claim 5, wherein the average value of T _A and T _B is set as a control target value. 7. A control output (A) corresponding to the local spot,
Measurements Thickness in the width direction of the thickness measuring point of the film and T _C
2. The method according to claim 1, wherein the control output (B) corresponding to the deviation from the sum is added to the control output to the discharge amount adjusting means.