JP7310876B2 - Polyester film and gas barrier laminated film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially stretched polyester film used in the packaging field of foods, pharmaceuticals, industrial products and the like. More specifically, in the case of producing a gas barrier film that has excellent pinhole resistance and bag breakage resistance and that is formed by forming a wide roll on a base film layer, an inorganic thin film layer and a protective layer. Also, it relates to a biaxially stretched polyester film that suppresses streak-like wrinkles that occur during heating and transportation and that can provide uniform gas barrier properties in the width direction.

Packaging materials used for foods, pharmaceuticals, etc. must have the property of blocking gases such as oxygen and water vapor, that is, gas barrier properties, in order to suppress the oxidation of proteins and oils, maintain the taste and freshness, and maintain the efficacy of pharmaceuticals. It has been demanded. Further, gas barrier materials used for electronic devices such as solar cells and organic EL, electronic parts, etc. require higher gas barrier properties than packaging materials for foods and the like.

Conventionally, in food applications that require blocking of various gases such as water vapor and oxygen, metal thin films such as aluminum and inorganic oxides such as silicon oxide and aluminum oxide are applied to the surface of a base film layer made of plastic. A gas barrier laminated film having an inorganic thin film formed thereon is generally used.

It has been known that the use of a biaxially oriented nylon film as the base film layer improves the pinhole resistance of the contents and eliminates the leakage of the contents when the bag is dropped. However, biaxially oriented nylon film undergoes a large dimensional change when it absorbs moisture, causing it to curl due to moisture absorption during the processing process. was there.

On the other hand, a polyethylene terephthalate (hereinafter abbreviated as PET) film with a thin film of inorganic oxide such as silicon oxide, aluminum oxide, or a mixture thereof (inorganic thin film layer) is transparent and allows confirmation of the contents. Therefore, it is widely used (for example, Patent Literature 1 and Patent Literature 2).
PET film has excellent heat resistance and dimensional stability, and can be used even when subjected to severe treatment such as retort sterilization. There was still the problem that the bag was torn or punctured when dropped, and the contents packed in the bag leaked out.

As a means for solving these problems, the use of biaxially stretched polybutylene terephthalate (hereinafter abbreviated as PBT) film has been investigated.
For example, in Patent Document 3, at least a PBT resin or a polyester resin composition obtained by blending a PET resin in a range of 30% by weight or less with respect to the PBT resin is simultaneously doubled 2.7 to 4.0 times in the longitudinal direction and the lateral direction. It has been known to use a biaxially stretched PBT film obtained by axial stretching as a base film layer. According to this technique, it is possible to obtain a liquid-filled packaging material having bending pinhole resistance, impact resistance, and excellent aroma retention.

By the way, in the production of gas barrier films used for food packaging and the like, it is common to use wide rolls with a width of about 2000 mm for film roll processing. For this reason, if the heat shrinkage characteristics of the film are uneven in the width direction of the roll, the dimension of the film will change unevenly in the width direction during the processing of the inorganic thin film and the subsequent processing of the protective layer. In some cases, the gas barrier properties of the gas barrier film obtained are non-uniform.
On the other hand, although the above-mentioned Patent Document 3 refers to the isotropy of the film, it does not consider means for improving the dimensional stability in the width direction. Therefore, when processing a biaxially stretched PBT film in a wide width, no means for obtaining uniform physical properties in the width direction have been studied.

JP-A-6-278240, JP-A-11-10725 JP 2017-094746 A

The present invention has been made against the background of such problems of the prior art.
That is, it has excellent pinhole resistance and bag breakage resistance, and even in the case of producing a gas barrier film by forming an inorganic thin film layer and a protective layer on a wide roll-shaped base film layer, heating is possible. To provide a biaxially stretched polyester film capable of suppressing wrinkles generated during transportation and having uniform gas barrier properties in the width direction.

In addition to having excellent pinhole resistance and bag breakage resistance, it can be heated and transported even in the case of manufacturing a gas barrier film by forming an inorganic thin film layer and a protective layer on a base film layer with a wide roll. In order to suppress the streak-like wrinkles that sometimes occur, it is important to make the dimensional change characteristic in the width direction of the substrate film uniform.
As a result of intensive studies by the present inventors in order to solve such problems, the roll of biaxially stretched PBT film, by reducing the difference in heat shrinkage in the width direction, heats and conveys a wide roll to carry out vapor deposition processing, etc. The inventors have also found that streak-like wrinkles can be suppressed and the gas barrier property in the width direction can be made uniform even when performing.

The present inventors have further found that in order to reduce the difference in heat shrinkage in the width direction of a wide roll, the unstretched polyester sheet melt-extruded into a sheet is stretched in the longitudinal direction (hereinafter also referred to as the machine direction) and in the above-mentioned direction. In the process of stretching in the width direction perpendicular to the machine direction (hereinafter also referred to as the transverse direction), heat setting, thermal relaxation and cooling, by keeping the surface temperature of the end of the polyester film low, when winding the film The inventors have found that it is possible to prevent the ends of the stretched film from being stretched in the longitudinal direction due to the tension applied to the stretched film, thereby suppressing an increase in the thermal shrinkage rate, thereby completing the present invention.

That is, the present invention consists of the following configurations.
[1] A polyester film containing 70% by weight or more of polybutylene terephthalate and simultaneously satisfying the following (1) to (5).
(1) Puncture strength measured according to JIS Z 1707 is 0.6 N/μm or more.
(2) The plane orientation degree of the film is 0.144 to 0.165.
(3) The thermal shrinkage of the film after heating at 150° C. for 15 minutes is 0 to 4% in the longitudinal direction and −1 to 3% in the transverse direction.
(4) The maximum orientation angle of the film is 25 to 50 degrees.
(5) The value Y (%/m) obtained by dividing the difference between the maximum and minimum thermal shrinkage in the longitudinal direction after heating at 150 ° C. for 15 minutes measured at a pitch of 100 mm in the width direction of the film roll by the width of the film roll. 0.5 or less.
Y (%/m) = {maximum thermal shrinkage (%) - minimum thermal shrinkage (%)}/roll width (m) (1 formula)
[2] A gas barrier laminate film comprising the polyester film of [1] and an inorganic thin film layer on at least one surface thereof.
[3] The gas-barrier laminated film according to [2] above, characterized by having an adhesive layer between the polyester film and the inorganic thin film layer.
[4] The gas-barrier laminated film according to [2] or [3], wherein the inorganic thin film layer has a protective layer on its surface.

The inventors of the present invention have developed a gas barrier film having excellent pinhole resistance and bag breakage resistance by forming an inorganic thin film layer and a protective layer on a base film layer by forming a wide roll on the base film layer. It has become possible to provide a biaxially stretched polyester film that suppresses wrinkles that occur during heating and transportation even in the case of production and that can have uniform gas barrier properties in the width direction.

The present invention will be described in detail below.
The polyester film of the present invention contains PBT as a main component, and the PBT content is preferably 70% by weight or more, more preferably 75% by weight or more. If it is less than 70% by weight, the puncture strength will be lowered and the film properties will not be sufficient.
PBT used as a main component preferably contains 90 mol% or more of terephthalic acid as a dicarboxylic acid component, more preferably 95 mol% or more, still more preferably 98 mol% or more, and most preferably 100 mol%. %. 1,4-Butanediol as a glycol component is preferably 90 mol % or more, more preferably 95 mol % or more, still more preferably 97 mol % or more, and most preferably 1,4-butane during polymerization. It does not include by-products other than by-products produced by ether bonds of diols.

The polyester film of the present invention may contain a polyester resin other than PBT for the purpose of adjusting mechanical properties.
Polyester resins other than PBT include at least one polyester resin selected from the group consisting of PET, polyethylene naphthalate, polybutylene naphthalate and polypropylene terephthalate, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and cyclohexanedicarboxylic acid. PBT resin copolymerized with at least one dicarboxylic acid selected from the group consisting of acid, adipic acid, azelaic acid and sebacic acid, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol , 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol and PBT resin copolymerized with at least one diol component selected from the group consisting of polycarbonate diol, etc. is mentioned.

The upper limit of the added amount of the polyester resin other than the PBT resin is preferably less than 30% by weight, more preferably 25% by weight or less. If the amount of the polyester resin other than the PBT resin added exceeds 30% by weight, the mechanical properties of the PBT are impaired, resulting in insufficient impact strength, pinhole resistance, or bag breakage resistance, transparency and gas barrier properties. A decrease in sexuality may occur.

The lower limit of the intrinsic viscosity of the PBT resin used in the present invention is preferably 0.9 dl/g, more preferably 0.95 dl/g, still more preferably 1.0 dl/g.
When the intrinsic viscosity of the PBT resin as a raw material is less than 0.9 dl/g, the intrinsic viscosity of the film obtained by forming the film is lowered, and the puncture strength, impact strength, pinhole resistance, bag breakage resistance, etc. may decrease.
The upper limit of the intrinsic viscosity of the PBT resin is preferably 1.4 dl/g. If the above is exceeded, the stress during stretching may become too high, resulting in deterioration of the film formability. When PBT with a high intrinsic viscosity is used, the melt viscosity of the resin increases, so it is necessary to raise the extrusion temperature.

If necessary, the PBT resin may contain conventionally known additives such as lubricants, stabilizers, colorants, antistatic agents, and ultraviolet absorbers.
As lubricant species, in addition to inorganic lubricants such as silica, calcium carbonate and alumina, organic lubricants are preferable, silica and calcium carbonate are more preferable, and silica is particularly preferable from the viewpoint of reducing haze. Transparency and lubricity can be expressed by these.
The lower limit of the lubricant concentration is preferably 100 ppm, more preferably 500 ppm, still more preferably 800 ppm. If it is less than the above, the slipperiness of the base film layer may be lowered. The upper limit of the lubricant concentration is preferably 20000 ppm, more preferably 10000 ppm, still more preferably 1800 ppm. If the above is exceeded, the transparency may be lowered.

The lower limit of the thickness of the polyester film of the present invention is preferably 3 μm, more preferably 5 μm, still more preferably 8 μm. When the thickness is 3 μm or more, the strength as a base film layer is sufficient.
The upper limit of the thickness of the polyester film of the present invention is preferably 100 µm, more preferably 75 µm, still more preferably 50 µm. When the thickness is 100 μm or less, processing for the purpose of the present invention becomes easier.

The upper limit of the thermal shrinkage after heating at 150° C. for 15 minutes in the longitudinal direction of the polyester film of the present invention is preferably 4.0%, more preferably 3.0%, and still more preferably 2%. . If the upper limit is exceeded, cracks may occur in the inorganic thin film layer due to dimensional changes in the base film layer that occur in the process of forming the protective film or in high-temperature processing such as retort sterilization, and the gas barrier property may decrease. Due to dimensional changes during processing, pitch deviation and the like may occur.
The upper limit of the heat shrinkage after heating at 150° C. for 15 minutes in the lateral direction of the polyester film of the present invention is preferably 3.0%, more preferably 2.0%, and still more preferably 1%. If the upper limit is exceeded, cracks may occur in the inorganic thin film layer due to dimensional changes in the base film layer that occur in the process of forming the protective film or in high-temperature processing such as retort sterilization, and the gas barrier property may decrease. Dimensional changes in the width direction during processing may cause pitch deviation.

The lower limit of the thermal shrinkage after heating at 150° C. for 15 minutes in the longitudinal direction of the polyester film of the present invention is preferably 0%. Even if it is less than the above, the effect of improvement cannot be obtained anymore (saturation), and it may become mechanically fragile.
The lower limit of the thermal shrinkage after heating at 150° C. for 15 minutes in the transverse direction of the polyester film of the present invention is preferably 1.0%. Even if it is less than the above, the effect of improvement cannot be obtained any more (saturation), and there are cases where it becomes mechanically fragile.

Value Y (% /m) is preferably 0.5 or less.
Y (%/m) = {maximum thermal shrinkage (%) - minimum thermal shrinkage (%)}/roll width (m) (1 formula)
If the value Y obtained by dividing the difference between the maximum and minimum heat shrinkage rates in the vertical direction measured at a pitch of 100 mm in the width (horizontal) direction of the roll by the width of the roll is greater than 0.5% / m, using a wide roll In the case of producing a gas barrier film by forming an inorganic thin film layer or a protective layer on a film, streaky wrinkles that occur during heating and transportation cannot be suppressed, resulting in non-uniform gas barrier properties in the width direction. put away.

The maximum absolute value of the orientation angle of the polyester film of the present invention is 25 to 50 degrees. This indicates that the slit roll of the film of the present invention is not the roll of the film in the central portion of the film manufacturing apparatus. A film having a Y (%/m) of 0.5 or less can be easily produced by a slit roll composed of a film in the central portion of the film production apparatus. Even with a slit roll made of a film other than the central portion of a film manufacturing apparatus in which the maximum value of the orientation angle of the film is 25 degrees or more, the polyester film of the present invention has a Y (%/m) of 0.5 or less. be.

The orientation angle of the film is measured using a MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd. Based on the axis in the width (horizontal) direction of the film, the orientation angle of the main axis of the molecular chain is obtained. and The measurement is made at the center of the film roll and at positions 20% left and right and 40% left and right of the entire width from the center, and the maximum absolute value among them is taken as the maximum orientation angle. In the case of a general biaxially stretched film, the orientation angle of the film at the central portion of the film manufacturing apparatus is a value close to zero, and the absolute value of the orientation angle tends to increase toward the end portion of the film.

The lower limit of the puncture strength of the polyester film of the present invention is preferably 0.6 N/μm. If it is 0.6 N/μm or more, the strength of the bag may be insufficient when used as a bag.

The lower limit of the impact strength of the polyester film of the present invention is preferably 0.05 J/μm. When it is 0.05 J/μm or more, the strength is sufficient when used as a bag.
The upper limit of the impact strength of the base film layer in the invention is preferably 0.2 J/μm. Even at 0.2 J/μm or less, the effect of improvement may be maximized.

The lower limit of the degree of plane orientation (ΔP) of the polyester film of the present invention is preferably 0.144, more preferably 0.148, still more preferably 0.15. If it is less than the above, the orientation is weak, so sufficient strength cannot be obtained, and not only the bag breakage resistance may be reduced, but also the inorganic thin film layer and the protective layer are provided on the base film layer to form a laminated film. In some cases, the tension and temperature applied during the formation of the protective film make it easier to stretch and crack the inorganic thin film layer, which may reduce the gas barrier properties.
The upper limit of the degree of plane orientation (ΔP) of the polyester film of the present invention is preferably 0.165, more preferably 0.160. If the degree of plane orientation is too large, the effect of improving the strength and bag breakage resistance is saturated. Further, in order to increase the degree of plane orientation, it is necessary to increase the draw ratio, which tends to cause breakage during film formation and reduce productivity.

The upper limit of haze per thickness of the polyester film of the present invention is preferably 0.66%/μm, more preferably 0.60%/μm, still more preferably 0.53%/μm. When the substrate film layer having a density of 0.66%/μm or less is printed, the quality of printed characters and images is improved.

Further, the polyester film of the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment as long as the object of the present invention is not impaired. Printing, decoration, etc. may be applied.

Next, the production method for obtaining the polyester film of the present invention will be specifically described. It is not limited to these.
The production method for obtaining the polyester film of the present invention includes a step of melt extruding a polyester raw material resin into a sheet, cooling on a casting drum to form an unstretched sheet, and stretching the unstretched sheet in the longitudinal direction. A longitudinal stretching step, a preheating step of preheating to a temperature at which transverse stretching is possible after the longitudinal stretching, a lateral stretching step of stretching in a width (horizontal) direction perpendicular to the longitudinal (longitudinal) direction, and after the longitudinal stretching and transverse stretching A heat setting step for heating and crystallizing the film, a heat relaxation step for removing the residual strain of the heat set film, and a cooling step for cooling the film after heat relaxation.
[Unstretched sheet forming step]
First, the film raw material is dried or dried with hot air. Next, the raw materials are weighed, mixed, supplied to an extruder, heated and melted, and melt-cast into a sheet.
Further, the molten resin sheet is brought into close contact with a cooling roll (casting roll) using an electrostatic application method and solidified by cooling to obtain an unstretched sheet. In the electrostatic application method, a voltage is applied to an electrode placed in the vicinity of the surface of the resin sheet opposite to the surface of the resin sheet in contact with the rotating metal roll in the vicinity of the contact of the molten resin sheet with the rotating metal roll. In this method, the resin sheet is charged and the resin sheet and the rotating cooling roll are brought into close contact with each other.

The lower limit of the heat melting temperature of the resin is preferably 200°C, more preferably 250°C, still more preferably 260°C. If it is less than the above, ejection may become unstable. The upper limit of the resin melting temperature is preferably 280°C, more preferably 270°C. If the above is exceeded, the decomposition of the resin will proceed and the film will become brittle.

When casting the molten polyester resin onto the extrusion cooling roll, it is preferable to reduce the difference in crystallinity in the width direction. Specific methods for this include extruding and casting a molten polyester resin to cast multiple layers of raw materials of the same composition, and further reducing the cooling roll temperature to a low temperature.
Since the PBT resin has a high crystallization speed, crystallization proceeds even during casting.
At this time, if a single layer is cast without forming multiple layers, there is no barrier that can suppress the growth of crystals, so that they grow into large spherulites. As a result, the yield stress of the obtained unstretched sheet increases, and not only is it easy to break during biaxial stretching, but also the impact strength, pinhole resistance, or bag breakage resistance of the obtained biaxially stretched film is improved. Inadequate film. On the other hand, by laminating the same resin in multiple layers, the stretching stress of the unstretched sheet can be reduced, and the subsequent biaxial stretching can be stably performed.

A method of extruding and casting a molten polyester resin to form a molten fluid by melting a resin composition containing 70% by weight or more of a PBT resin ( 1) Step (2) of forming a layered fluid composed of the formed molten fluid having a number of layers of 60 or more, discharging the formed layered fluid from a die, contacting a cooling roll and solidifying to form a layered unstretched sheet. It has at least a step (3) of forming and a step (4) of biaxially stretching the laminated unstretched sheet.
Other steps may be inserted between steps (1) and (2) and between steps (2) and (3). For example, a filtration process, a temperature change process, etc. may be inserted between the process (1) and the process (2). Further, a temperature changing process, a charge adding process, etc. may be inserted between the process (2) and the process (3). However, between the steps (2) and (3), there should be no step of destroying the laminated structure formed in the step (2).

In step (1), the method of melting the polyester resin composition to form a molten fluid is not particularly limited, but a suitable method includes a method of heating and melting using a single-screw extruder or a twin-screw extruder. can be done.

The method of forming the layered fluid in step (2) is not particularly limited, but a static mixer and/or a multilayer feed block are more preferable from the viewpoints of facility simplicity and maintainability. Further, from the viewpoint of uniformity in the sheet width direction, it is more preferable to have a rectangular melt line. More preferably, static mixers or multi-layer feedblocks with rectangular melt lines are used. In addition, a resin composition having a plurality of layers formed by joining a plurality of resin compositions may be passed through any one or more of a static mixer, a multilayer feed block and a multilayer manifold.

The theoretical lamination number in step (2) is preferably 60 or more. The lower limit of the number of theoretical laminations is more preferably 500. If the number of theoretical laminations is too small, or the distance between layer interfaces becomes too long and the crystal size becomes too large, the effect of the present invention tends to be unobtainable. In addition, the degree of crystallinity increases in the vicinity of both ends of the sheet, resulting in unstable film formation and reduced transparency after molding. Although the upper limit of the number of theoretical layers in step (2) is not particularly limited, it is preferably 100,000, more preferably 10,000, and even more preferably 7,000. Even if the theoretical lamination number is extremely increased, the effect may be saturated.

When the lamination in step (2) is performed with a static mixer, the theoretical number of lamination can be adjusted by selecting the number of elements of the static mixer. A static mixer is generally known as a static mixer (line mixer) without a driving part, and fluids entering the mixer are sequentially stirred and mixed by elements. However, when a high-viscosity fluid is passed through a static mixer, division and lamination of the high-viscosity fluid occur to form a laminated fluid. Each time it passes through one element of the static mixer, the high-viscosity fluid is split into two and then merged and laminated. Therefore, when a high-viscosity fluid is passed through a static mixer having n elements, a layered fluid having a theoretical number of layers N=2n is formed.

A typical static mixer element has a structure in which a rectangular plate is twisted 180 degrees. Depending on the direction of twist, there are right and left elements. Each element measures 1.5 times its diameter. Basic. Static mixers that can be used in the present invention are not limited to these.

When lamination in the step (2) is performed using a multi-layer feedblock, the number of theoretical lamination can be adjusted by selecting the number of times of division and lamination of the multi-layer feedblock. Multiple multilayer feedblocks can be installed in series. It is also possible to use the high-viscosity fluid itself supplied to the multilayer feedblock as the laminated fluid. For example, if the number of layers of the high-viscosity fluid supplied to the multilayer feedblock is p, the number of divisions and layers of the multilayer feedblock is q, and the number of the multilayer feedblocks installed is r, the number of layers N of the layered fluid is N=p. xqr.

In step (3), the lamination fluid is discharged from the die and brought into contact with chill rolls to solidify.
The lower limit of the cooling roll temperature is preferably -10°C. If it is less than the above, the effect of suppressing crystallization may be saturated. The upper limit of the chill roll temperature is preferably 40°C. When the above is exceeded, the degree of crystallinity becomes too high, and stretching may become difficult. The upper limit of the chill roll temperature is preferably 25°C. When the temperature of the cooling roll is within the above range, it is preferable to lower the humidity of the environment around the cooling roll in order to prevent dew condensation. It is preferable to reduce the temperature difference in the width direction of the cooling roll surface. At this time, the thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm.
The above unstretched sheet having a multilayer structure has at least 60 layers, preferably 250 layers or more, and more preferably 1000 layers or more. If the number of layers is small, the effect of improving stretchability is lost.

[Longitudinal Stretching and Lateral Stretching Processes]
Next, the stretching method will be explained. The stretching method can be simultaneous biaxial stretching or sequential biaxial stretching, but in order to increase the puncture strength, it is necessary to increase the degree of plane orientation, and the film formation speed is fast and productivity is high. Sequential biaxial stretching is the most preferable in terms of point.

The lower limit of the stretching temperature in the machine direction is preferably 55°C, more preferably 60°C. When the temperature is 55°C or higher, breakage is less likely to occur. In addition, since the degree of longitudinal orientation of the film does not become too strong, the shrinkage stress during heat setting treatment can be suppressed, and a film with less distortion in molecular orientation in the width (horizontal) direction can be obtained. The upper limit of the stretching temperature in the longitudinal stretching direction is preferably 100°C, more preferably 95°C. When the temperature is 100° C. or less, the orientation of the film does not become too weak, so that the mechanical properties of the film do not deteriorate.

The lower limit of the draw ratio in the machine direction is preferably 2.8 times, particularly preferably 3.0 times. When it is 2.8 times or more, the degree of plane orientation increases, and the puncture strength of the film improves.
The upper limit of the draw ratio in the machine direction is preferably 4.3 times, more preferably 4.0 times, and particularly preferably 3.8 times. When it is 4.3 times or less, the degree of orientation in the horizontal direction of the film does not become too strong, the shrinkage stress during heat setting treatment does not become too large, and the distortion of the molecular orientation in the horizontal direction of the film becomes small. As a result, the straight tearability in the vertical direction is improved. Further, the effect of improving the mechanical strength and thickness unevenness is saturated within this range.

The lower limit of the stretching temperature in the lateral stretching direction is preferably 60°C, and if it is 60°C or higher, breakage may hardly occur. The upper limit of the stretching temperature in the lateral stretching direction is preferably 100° C. If the temperature is 100° C. or less, the degree of orientation in the lateral direction increases, resulting in improved mechanical properties.

The lower limit of the draw ratio in the transverse direction is preferably 3.5 times, more preferably 3.6 times, and particularly preferably 3.7 times. When it is 3.5 times or more, the degree of orientation in the horizontal direction does not become too weak, and the mechanical properties and thickness unevenness are improved. The upper limit of the draw ratio in the transverse direction is preferably 5 times, more preferably 4.5 times, and particularly preferably 4.0 times. If it is 5.0 times or less, the effect of improving the mechanical strength and thickness unevenness is maximized (saturated) even in this range.

[Heat setting process]
The lower limit of the heat setting temperature in the heat setting step is preferably 195°C, more preferably 200°C. When the temperature is 195° C. or higher, the heat shrinkage of the film is reduced, and the inorganic thin film layer is less likely to be damaged even after retort treatment, thereby improving gas barrier properties. The upper limit of the heat setting temperature is preferably 220° C. When the temperature is 220° C. or less, the base film layer does not melt and is less likely to become brittle.

[Thermal relaxation part process]
The lower limit of the relaxation rate in the thermal relaxation step is preferably 0.5%. If it is 0.5% or more, it may become difficult to break during heat setting. The upper limit of the relaxation rate is preferably 10%. If it is 10% or less, shrinkage in the longitudinal (vertical) direction during heat setting is reduced, resulting in reduced molecular orientation distortion at the film ends and improved linear tearability. In addition, sagging of the film is less likely to occur, and thickness unevenness is less likely to occur.

[Cooling process]
In the cooling step after relaxing in the thermal relaxation step, the temperature of the surface of the end portion of the polyester film is preferably 80° C. or less.
If the temperature of the edge of the film after passing through the cooling process exceeds 80°C, the edge is stretched by the tension applied when winding the film, and as a result, the heat shrinkage rate of the edge in the longitudinal direction increases. As a result, the distribution of the heat shrinkage rate in the width direction of the roll becomes uneven. The physical properties of the film may become non-uniform in the width (horizontal) direction.

In the cooling process, as a method of setting the surface temperature of the film edge to 80 ° C. or less, in addition to adjusting the temperature and air volume in the cooling process, a shielding plate is provided at the center side in the width direction of the cooling zone to select the edge. A method of locally cooling the film or a method of locally blowing cold air against the edge of the film can be used.

[Inorganic thin film layer]
Gas barrier properties can be imparted by providing an inorganic thin film layer on the surface of the biaxially stretched polyester film of the present invention.
The inorganic thin film layer is a thin film made of metal or inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as it can be made into a thin film. things are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferable from the viewpoint of achieving both flexibility and denseness of the thin film layer. In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70% by weight of Al based on the weight ratio of metal. If the Al concentration is less than 20% by weight, the water vapor barrier properties may deteriorate. On the other hand, if it exceeds 70% by weight, the inorganic thin film layer tends to become hard, and there is a risk that the film will be destroyed during secondary processing such as printing and lamination, resulting in a decrease in gas barrier properties. Here, silicon oxide means various silicon oxides such as SiO and SiO2 or mixtures thereof, and aluminum oxide means various aluminum oxides such as AlO and Al2O3 or mixtures thereof.

The film thickness of the inorganic thin film layer is usually 1 to 100 nm, preferably 5 to 50 nm. If the thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties. It is rather disadvantageous in terms of bending resistance and manufacturing cost.

The method for forming the inorganic thin film layer is not particularly limited, and known vapor deposition methods such as physical vapor deposition (PVD method) such as vacuum vapor deposition, sputtering, and ion plating, or chemical vapor deposition (CVD method). Laws should be adopted accordingly. A typical method for forming an inorganic thin film layer will be described below using a silicon oxide/aluminum oxide thin film as an example. For example, when a vacuum deposition method is employed, a mixture of SiO2 and Al2O3, a mixture of SiO2 and Al, or the like is preferably used as the deposition raw material. Particles are usually used as these vapor deposition raw materials, and in this case, the size of each particle is desirably such that the pressure during vapor deposition does not change, and the preferred particle diameter is 1 mm to 5 mm. Methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating can be employed for heating. It is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor, etc. as reaction gases, or adopt reactive vapor deposition using means such as addition of ozone and ion assist. Furthermore, film formation conditions can be arbitrarily changed, such as applying a bias to the object to be vapor-deposited (laminated film to be vapor-deposited) or heating or cooling the object to be vapor-deposited. Such vapor deposition material, reaction gas, bias of the object to be vapor-deposited, heating/cooling, etc. can be similarly changed when adopting the sputtering method or the CVD method.

[Adhesion layer]
In the gas-via laminated film of the present invention, an adhesive layer can be provided between the base film layer and the inorganic thin film layer for the purpose of ensuring gas barrier properties and lamination strength after retort treatment.
As the resin composition used for the adhesive layer provided between the base film layer and the inorganic thin film layer, urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, polybutadiene-based resins, epoxy Examples include those to which a curing agent such as a system, an isocyanate system, or a melamine system is added. The resin composition used for these adhesive layers preferably contains a silane coupling agent having at least one or more organic functional groups. Examples of the organic functional groups include alkoxy groups, amino groups, epoxy groups, and isocyanate groups. Addition of the silane coupling agent further improves the lamination strength after retorting.

Among the resin compositions used for the adhesive layer, it is preferable to use a mixture of an oxazoline group-containing resin, an acrylic resin, and a urethane resin. The oxazoline group has a high affinity with the inorganic thin film, and can react with the oxygen-deficient portion of the inorganic oxide generated during the formation of the inorganic thin film layer and the metal hydroxide, and exhibits strong adhesion with the inorganic thin film layer. . In addition, unreacted oxazoline groups present in the adhesive layer can react with carboxylic acid terminals generated by hydrolysis of the base film layer and the adhesive layer to form crosslinks.

The method for forming the adhesive layer is not particularly limited, and conventionally known methods such as a coating method can be employed. Suitable methods among the coating methods include an off-line coating method and an in-line coating method. For example, in the case of the in-line coating method performed in the process of manufacturing the base film layer, the conditions for drying and heat treatment during coating depend on the thickness of the coat and the conditions of the equipment, but immediately after coating, the film is sent to the stretching process in the perpendicular direction. It is preferable to dry in the preheating zone or stretching zone of the stretching step, and in such a case, the temperature is usually preferably about 50 to 250°C.
Examples of the solvent (solvent) used when using the coating method include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ethyl acetate and butyl acetate. ester-based solvents such as ethylene glycol monomethyl ether; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[Protective layer]
In the present invention, a protective layer is provided on the inorganic thin film layer. The metal oxide layer is not a completely dense film, and is dotted with minute defects. By forming a protective layer by applying a specific resin composition for protective layer to be described later on the metal oxide layer, the resin in the resin composition for protective layer permeates into the defective portions of the metal oxide layer, As a result, the effect of stabilizing the gas barrier property is obtained. In addition, by using a material with gas barrier properties for the protective layer itself, the gas barrier properties of the laminated film are greatly improved.

The resin composition used for the protective layer formed on the surface of the inorganic thin film layer of the laminated film of the present invention includes urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, polybutadiene-based resins, and epoxy resins. Examples include those to which a curing agent such as a system, an isocyanate system, or a melamine system is added.
In the urethane resin, the polar group of the urethane bond interacts with the inorganic thin film layer, and the presence of the amorphous part also provides flexibility, so even when a bending load is applied, damage to the inorganic thin film layer can be suppressed. It is preferable because
The acid value of the urethane resin is preferably in the range of 10-60 mgKOH/g. It is more preferably in the range of 15 to 55 mgKOH/g, still more preferably in the range of 20 to 50 mgKOH/g. When the acid value of the urethane resin is within the above range, the liquid stability is improved when it is made into an aqueous dispersion, and the protective layer can be uniformly deposited on the highly polar inorganic thin film, so that the coat appearance is good. becomes.

The urethane resin preferably has a glass transition temperature (Tg) of 80° C. or higher, more preferably 90° C. or higher. By setting the Tg to 80° C. or higher, it is possible to reduce swelling of the protective layer due to molecular movement during the wet heat treatment process (temperature increase, heat retention, and temperature decrease).

As the urethane resin, it is more preferable to use a urethane resin containing an aromatic or araliphatic diisocyanate component as a main component from the viewpoint of improving gas barrier properties.
Among these, it is particularly preferable to contain a meta-xylylene diisocyanate component. By using the above resin, the cohesive force of the urethane bonds can be further increased due to the stacking effect of the aromatic rings, and as a result, good gas barrier properties can be obtained.

In the present invention, the proportion of the aromatic or araliphatic diisocyanate in the urethane resin is preferably in the range of 50 mol% or more (50 to 100 mol%) in 100 mol% of the polyisocyanate component (F). The proportion of the total amount of aromatic or araliphatic diisocyanates is preferably 60-100 mol %, more preferably 70-100 mol %, still more preferably 80-100 mol %. As such a resin, the "Takelac (registered trademark) WPB" series commercially available from Mitsui Chemicals, Inc. can be suitably used. If the total amount of aromatic or araliphatic diisocyanates is less than 50 mol %, good gas barrier properties may not be obtained.

From the viewpoint of improving affinity with the inorganic thin film layer, the urethane resin preferably has a carboxylic acid group (carboxyl group). In order to introduce a carboxylic acid (salt) group into a urethane resin, for example, a polyol compound having a carboxylic acid group such as dimethylolpropionic acid or dimethylolbutanoic acid may be introduced as a copolymerization component. Further, after synthesizing a carboxylic acid group-containing urethane resin, neutralization with a salt-forming agent makes it possible to obtain an aqueous dispersion of the urethane resin. Specific examples of the salt-forming agent include ammonia, trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine and tri-n-butylamine; -alkylmorpholines, N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These may be used alone or in combination of two or more.
Examples of the solvent (solvent) include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; Examples include polyhydric alcohol derivatives such as monomethyl ether.

As described above, the polyester film of the present invention is excellent in bag breakage resistance and flex resistance, and a wide roll is formed on the base film layer to form the inorganic thin film layer and the protective layer to produce a gas barrier film. Even in such a case, it is possible to suppress streaky wrinkles that occur during heating and transportation, and to make the gas barrier properties uniform in the width direction.

[Packaging materials]
When the laminated film of the present invention is used as a packaging material, it is preferable to form a heat-sealing resin layer called a sealant. The heat-sealable resin layer is usually provided on the inorganic thin film layer, but may be provided on the outside of the base film layer (the surface opposite to the surface on which the adhesive layer is formed). Formation of the heat-sealable resin layer is usually carried out by an extrusion lamination method or a dry lamination method. The thermoplastic polymer forming the heat-sealable resin layer may be any polymer that can exhibit sufficient sealant adhesiveness, and includes polyethylene resins such as HDPE, LDPE, and LLDPE, polypropylene resins, and ethylene-vinyl acetate copolymers. , ethylene-α-olefin random copolymers, ionomer resins, and the like can be used.

Furthermore, in the laminated film of the present invention, at least one layer of a printed layer or other plastic substrate and/or paper substrate is provided between or outside the inorganic thin film layer or base film layer and the heat-sealable resin layer. You may laminate|stack above.

As the printing ink for forming the printing layer, water-based and solvent-based resin-containing printing inks can be preferably used. Examples of resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. Antistatic agents, light shielding agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, antifoaming agents, cross-linking agents, anti-blocking agents, antioxidants, and the like are known to the printing ink. may contain additives. The printing method for forming the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. For drying the solvent after printing, a known drying method such as hot air drying, hot roll drying, or infrared drying can be used.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. In addition, evaluation of the film was performed by the following measuring method.

[Film thickness]
It was measured using a dial gauge in accordance with JIS K7130-1999 A method.

[Plane orientation degree ΔP of film]
About the sample According to JIS K 7142-1996 A method, the refractive index (Nx) in the film longitudinal (longitudinal) direction, the refractive index (Ny) in the width (horizontal) direction, and the refractive index (Ny) in the thickness direction with an Abbe refractometer using sodium D line as a light source The ratio (Nz) was measured, and the plane orientation degree ΔP was calculated by the formula (2).
Planar orientation degree (ΔP) = (Nx + Ny) / 2-Nz (2 formulas)

[Orientation angle of film]
The film was cut into a size of 100 mm×100 mm, and the orientation angle of the main axis of the molecular chain was determined using a MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd., based on the axis in the width (horizontal) direction of the film. At this time, a counterclockwise tilt with respect to the width (horizontal) direction of the film is positive (+), and a clockwise tilt is negative (-). The measurement was made at the center of the film roll and at positions 20% left and right and 40% left and right of the full width from the center, and the maximum absolute value among them was taken as the maximum orientation angle.

[Thermal shrinkage of film]
The heat shrinkage of the polyester film was measured by the dimensional change test method described in JIS-C-2151-2006.21 except that the test temperature was 150° C. and the heating time was 15 minutes. Specimens were used as described in 21.1(a).

[Wide direction uniformity of heat shrinkage]
The obtained film roll was sampled at a pitch of 100 mm in the width (horizontal) direction of the roll, and the heat shrinkage rate in the longitudinal direction was measured according to the method described above. Y (%/m) was determined using the following formula (1) from the obtained maximum and minimum values of thermal shrinkage and the width of the film roll.
Y (%/m) = {maximum thermal shrinkage (%) - minimum thermal shrinkage (%)}/roll width (m) (1 formula)

[Film puncture strength]
The obtained polyester film was sampled in a 5 cm square, and a digital force gauge "ZTS-500N" manufactured by Imada Co., Ltd., an electric measurement stand "MX2-500N", and a piercing jig "TKS-250N" were used, according to JIS Z1707. was used to measure the puncture strength of the film. The unit is N/μm.

[Film impact strength]
An impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd. was used to measure the strength of the film against impact punching in an atmosphere of 23°C. A 1/2 inch diameter impact sphere was used. The unit is J/μm.

Details of raw material resins and coating liquids used in Examples and Comparative Examples are described below. In addition, it was used in Examples 1-1 to 1-8 and Comparative Examples 1 to 5, and is shown in Tables 1 and 2.
1) PBT resin: 1100-211XG (CHANG CHUN PLASTICS CO., LTD., intrinsic viscosity 1.28 dl/g) was used as a polybutylene terephthalate resin used in the production of a biaxially stretched polyester film described later.
2) PET resin: The PET resin used in the production of the biaxially stretched polyester film described later is terephthalic acid // ethylene glycol = 100 // 100 (mol%) (manufactured by Toyobo Co., Ltd., intrinsic viscosity 0.62 dl / g). board.

3) Resin (B) having an oxazoline group: As a resin having an oxazoline group, a commercially available water-soluble oxazoline group-containing acrylate (manufactured by Nippon Shokubai Co., Ltd. "Epocross (registered trademark) WS-300"; solid content 10%) is prepared. bottom. The amount of oxazoline groups in this resin was 7.7 mmol/g.

4) Acrylic resin (C)]: As an acrylic resin, a 25% by weight emulsion of a commercially available acrylic acid ester copolymer ("Movin (registered trademark) 7980" manufactured by Nichigo Movinyl Co., Ltd. was prepared. This acrylic resin (B ) had an acid value (theoretical value) of 4 mgKOH/g.

5) Urethane resin (D): As a urethane resin, a dispersion of commercially available polyester urethane resin (“Takelac (registered trademark) W605” manufactured by Mitsui Chemicals, Inc.; solid content: 30%) was prepared. This urethane resin had an acid value of 25 mgKOH/g and a glass transition temperature (Tg) of 100° C. as measured by DSC. Also, the ratio of the aromatic or araliphatic diisocyanate to the entire polyisocyanate component measured by 1H-NMR was 55 mol %.

6) Urethane resin (E): As a urethane resin, a dispersion of a commercially available metaxylylene group-containing urethane resin (“Takelac (registered trademark) WPB341” manufactured by Mitsui Chemicals, Inc.; solid content 30%) was prepared. This urethane resin had an acid value of 25 mgKOH/g and a glass transition temperature (Tg) of 130° C. as measured by DSC. The ratio of aromatic or araliphatic diisocyanate to the entire polyisocyanate component measured by 1H-NMR was 85 mol%.

7) Coating liquid 1 used for adhesive layer
A coating liquid (resin composition for adhesive layer) was prepared by mixing each material in the following mixing ratio.
Water 54.40% by weight
Isopropanol 25.00% by weight
Oxazoline group-containing resin (A) 15.00% by weight
Acrylic resin (B) 3.60% by weight
Urethane resin (C) 2.00% by weight

8) Coating liquid 2 used for coating the protective layer
A coating solution 2 was prepared by mixing the following coating agents. Table 1 shows the weight ratio of the urethane resin (E) in terms of solid content.
Water 60.00% by weight
Isopropanol 30.00% by weight
Urethane resin (E) 10.00% by weight

[Preparation of laminated laminate]
Protective layers of gas barrier films shown in Examples 1-1 to 1-8, Examples 2-1 to 2-8, Comparative Examples 1-1 to 1-5 and Comparative Examples 2-1 to 2-5 described later On the side, a urethane-based two-liquid curing adhesive ("Takelac (registered trademark) A525S" and "Takenate (registered trademark) A50" manufactured by Mitsui Chemicals, Inc. are blended at a ratio of 13.5: 1 (weight ratio)) Using a dry lamination method, a 70 μm thick unstretched polypropylene film (“P1147” manufactured by Toyobo Co., Ltd.) is laminated as a heat-sealable resin layer, and aged at 40 ° C. for 4 days to obtain a laminate for evaluation. A laminate was obtained. In addition, the thickness of the adhesive layer formed from the urethane-based two-liquid curing adhesive after drying was about 4 μm.

[Water vapor permeability of laminated laminate]
According to the JIS-K7129-1992 B method, the above-mentioned laminate laminate is measured using a water vapor permeability measuring device (“PERMATRAN-W1A” manufactured by MOCON) under an atmosphere of a temperature of 40 ° C. and a relative humidity of 90 RH%. , the water vapor transmission rate in the normal state was measured. The water vapor transmission rate was measured in the direction in which water vapor permeates from the base film layer side to the sealant side.

[Water vapor permeability after retorting of laminated laminate]
The above-mentioned laminate laminate is subjected to a wet heat treatment in which it is held in hot water at 130 ° C. for 30 minutes, dried at 40 ° C. for 1 day (24 hours), and the obtained laminate laminate after the wet heat treatment is described above. Water vapor permeability was measured in the same manner.

The method for producing the biaxially stretched polyester film used in each example and comparative example is described below. Table 1 shows the physical properties of the following biaxially stretched polyester film.
<Example 1-1>
Using a single screw extruder, a mixture of 80% by weight of PBT resin and 20% by weight of PET resin is added with silica particles having an average particle size of 2.4 μm as inert particles so that the silica concentration is 900 ppm with respect to the mixed resin. After melting at 290° C., the melt line was introduced into a 12 element static mixer. As a result, the polyester resin melt was divided and laminated to obtain a multilayer melt made of the same raw material. It was cast from a T-die at 265°C and adhered to a cooling roll at 15°C by an electrostatic adhesion method to obtain an unstretched sheet.
It is then roll-stretched 2.9 times in the machine direction at 60° C., then passed through a tenter and stretched 4.0 times in the transverse direction at 90° C., tension heat treated at 200° C. for 3 seconds and relaxation of 9% for 1 second. After treatment, the film was cooled by cooling at 50°C for 2 seconds. At this time, the surface temperature of the edge of the film was 75°C.
Next, 10% of the gripped portions at both ends were cut off to obtain a full-width roll (hereinafter referred to as a mill roll) of a polyester film having a thickness of 15 μm and a full width of 4200 mm. The obtained mill roll was slit to obtain two slit rolls having a roll width of 2080 mm.
Table 1 shows the film-forming conditions, physical properties and evaluation results of the obtained film.

<Examples 1-2 to 1-8, Comparative Examples 1-1 to 1-5>
In the film formation process of the biaxially stretched polyester film, the same procedure as in Example 1-1 was carried out, except that the ratio of the PBT resin, the longitudinal and transverse stretch ratio, the relaxation rate, and the zone temperature of the tenter cooling process were shown in Tables 1 and 2. . However, in Comparative Example 1-2, the extrusion temperature was 270°C.

<Example 2-1>
Using a single screw extruder, a mixture of 80% by weight of PBT resin and 20% by weight of PET resin is added with silica particles having an average particle size of 2.4 μm as inert particles so that the silica concentration is 900 ppm with respect to the mixed resin. After melting at 290° C., the melt line was introduced into a 12 element static mixer. As a result, the polyester resin melt was divided and laminated to obtain a multilayer melt made of the same raw material. It was cast from a T-die at 265°C and adhered to a cooling roll at 15°C by an electrostatic adhesion method to obtain an unstretched sheet.
Then, the film was rolled 2.9 times in the longitudinal direction at 60° C. After the longitudinal stretching, the adhesive layer resin composition (coating liquid 1) was applied by a fountain bar coating method. After that, it was led to a tenter while drying, then stretched 4.0 times in the transverse direction at 90 ° C. through the tenter, and after performing tension heat treatment at 200 ° C. for 3 seconds and 9% relaxation treatment for 1 second, 50 C. for 2 seconds to cool the film. At this time, the surface temperature of the edge of the film was 75°C.
Then, 10% of the gripped portions at both ends were cut off to obtain a mill roll of a polyester film having a thickness of 15 μm and an overall width of 4200 mm. The obtained mill roll was slit to obtain two slit rolls having a width of 2080 mm.
Table 3 shows the film-forming conditions, physical properties and evaluation results of the obtained film.

<Examples 2-2 to 2-8, Comparative Examples 2-1 to 2-5>
In the process of forming a biaxially stretched polyester film, the same procedure as in Example 2-1 was carried out, except that the ratio of PBT, the longitudinal and transverse stretch ratio, the relaxation rate, and the zone temperature in the tenter cooling process were shown in Tables 3 and 4. However, in Comparative Example 2-2, the extrusion temperature was 270°C.

The method of forming the inorganic thin film layer in each example and comparative example is described below.
<Formation of inorganic thin film layer M-1>
As the inorganic thin film layer M-1, a composite oxide layer of silicon dioxide and aluminum oxide was formed by electron beam evaporation. As a vapor deposition source, particulate SiO2 (purity 99.9%) and A12O3 (purity 99.9%) of about 3 mm to 5 mm were used. The film thickness of the inorganic thin film layer (SiO2/A12O3 composite oxide layer) in the film (inorganic thin film layer/adhesive layer-containing film) thus obtained was 13 nm. The composition of this composite oxide layer was SiO2/A12O3 (weight ratio)=60/40.

<Formation of Protective Layer 1 on Deposited Film>
The coating liquid 2 was applied on the inorganic thin film layer formed by vapor deposition above by a wire bar coating method and dried at 200° C. for 15 seconds to obtain a protective layer. The coating weight after drying was 0.190 g/m2 (as Dry solids).
As described above, a gas barrier laminated film having an adhesive layer/metal oxide layer/protective layer on the base film layer was produced.

As shown in Tables 1 and 3, in Examples 1-1 to 1-8 and Examples 2-1 to 2-8, the surface temperature of the film edge at the exit of the tenter was 80°C or less. By doing so, the difference in heat shrinkage in the width direction of the roll could be reduced, and a film roll with a small difference in physical properties in the width direction could be obtained.

Further, in Examples 1-1 to 1-8, by cooling the temperature of the film end to 80° C. or less at the exit of the tenter, the heat shrinkage rate of the end of the obtained mill roll can be suppressed. , it is possible to reduce the difference in heat shrinkage in the longitudinal direction of the slit roll. As a result, the generation of streaky wrinkles was suppressed during the formation of the inorganic thin film layer and the protective layer, and the gas barrier property in the width direction was made uniform. Further, in Examples 2-1 to 2-8, by having an adhesive layer between the base film layer and the inorganic thin film layer, even after severe wet heat treatment such as retort sterilization treatment, , a high gas barrier property could be maintained.

In Comparative Examples 1-1 and 2-1, the heat setting temperature is increased to suppress the heat shrinkage in the longitudinal direction, so the film has a large distortion in the width direction and the heat shrinkage at the ends. As a result, the gas barrier property of the edge is inferior.
In Comparative Examples 1-2 and 2-2, similarly to the above, the difference in thermal contraction rate between the central portion and the end portion of the mill roll is large, and the gas barrier property at the end portion is inferior. sufficient piercing strength is not obtained.
In Comparative Examples 1-3 and 2-3, and in Comparative Examples 1-4 and 2-4, the piercing strength is improved by increasing the degree of plane orientation by increasing the draw ratio, but Comparative Example 1 As in -1 and Comparative Example 2-1, the heat shrinkage rate at the ends is high, and the uniformity of the gas barrier properties in the width direction becomes insufficient.
In Comparative Examples 1-5 and 2-5, as a result of increasing the heat setting temperature in order to suppress the heat shrinkage rate in the vertical direction, the heat shrinkage rate at the central portion is small, but the difference from the end portion is large. , the gas barrier property was uneven in the width direction. Moreover, the mechanical strength of the film was lowered.

According to the present invention, it has excellent pinhole resistance and bag breakage resistance, and is such that a wide roll is formed on a base film layer, an inorganic thin film layer and a protective layer to produce a gas barrier film. Even in this case, it has become possible to provide a biaxially stretched polyester film that suppresses wrinkles that occur during heating and transportation and that can have uniform gas barrier properties in the width direction. Since it can be widely applied as a food packaging material, it is expected to greatly contribute to the industrial world.
The biaxially stretched polyester film obtained by the present invention can obtain uniform physical properties in the width direction even when processing a wide roll, so it is excellent in economic efficiency and production stability, and it is easy to obtain uniform properties. Therefore, such a gas barrier film is not limited to food packaging, but is also used for packaging pharmaceuticals, industrial products, etc., as well as for industrial applications such as solar cells, electronic paper, organic EL elements, semiconductor elements, etc. Can be used widely.

Claims (6)

A step of melt extruding a polyester raw resin into a sheet and cooling it on a casting drum to form an unstretched sheet, a longitudinal stretching step of stretching the unstretched sheet in the longitudinal direction, and a process perpendicular to the longitudinal (longitudinal) direction. Lateral stretching step of stretching in the width (horizontal) direction, heat setting step of the film after performing the longitudinal stretching and horizontal stretching, heat relaxation step of the heat set film, and cooling the film after heat relaxation In the cooling step , a shielding plate is provided on the center side of the cooling zone in the width direction to selectively cool the edge of the film so that the temperature of the surface of the edge of the film is 80 ° C. or less. A method for producing a polyester film, characterized by: 2. The method for producing a polyester film according to claim 1, wherein the cooling step includes a step of locally blowing cold air onto the edge of the film. The method for producing a polyester film according to claim 1 or 2 , wherein the heat setting temperature in the heat setting step is 195°C or higher and 220°C or lower. The method for producing a polyester film according to any one of claims 1 to 3 , wherein the relaxation rate in the thermal relaxation step is 0.5% or more and 10% or less. The method for producing a polyester film according to any one of claims 1 to 4 , wherein the polyester film contains polybutylene terephthalate. The method for producing a polyester film according to claim 5 , wherein the polyester film contains polybutylene terephthalate and polyethylene terephthalate.