JP7006445B2 - Polyester film and gas barrier laminated film - Google Patents

Description

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 where a gas barrier film is manufactured by forming an inorganic thin film layer and a protective layer with a wide roll on the base film layer while having excellent pinhole resistance and bag breakage resistance. The present invention also relates to a biaxially stretched polyester film capable of suppressing streak-like wrinkles generated during heat transfer and making the gas barrier property in the width direction uniform.

Packaging materials used in 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 fats, 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 ELs and electronic parts require higher gas barrier properties than packaging materials such as foods.

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

It has been known that by using a biaxially stretched nylon film as a base film layer, pinhole resistance due to the contents is improved and leakage of the contents when the bag is dropped is eliminated. However, the biaxially stretched nylon film has a large dimensional change during moisture absorption, and has a problem that it curls due to moisture absorption during the processing process and the shape is deformed due to shrinkage when a harsh treatment such as retort sterilization is applied. was there.

On the other hand, a polyethylene terephthalate (hereinafter abbreviated as PET) film on which a thin film (inorganic thin film layer) of an inorganic oxide such as silicon oxide, aluminum oxide, or a mixture thereof is formed is transparent and the contents can be confirmed. Therefore, it is widely used (for example, Patent Document 1 and Patent Document 2).
PET film has excellent heat resistance and dimensional stability, and can be used even when harsh treatment such as retort sterilization is applied. However, since PET film is brittle, a bag made of a laminated film using this is used. The problem remained that the bag was torn or punctured when dropped, and the contents packed in the bag leaked.

As a means for solving these problems, it is considered to use a biaxially stretched polybutylene terephthalate (hereinafter abbreviated as PBT) film.
For example, in Patent Document 3, a polyester resin composition containing at least a PBT resin or a PET resin in a range of 30% by weight or less with respect to the PBT resin is mixed in a vertical direction and a horizontal direction 2.7 to 4.0 times at the same time. It has been known that a biaxially stretched PBT film obtained by axial stretching is used as a base film layer. According to such a technique, it is possible to obtain a liquid filling packaging material having bending pinhole resistance, impact resistance, and excellent fragrance retention.

By the way, in the production of a gas barrier film used for food packaging and the like, it is common to process using a wide roll having a film roll width of about 2000 mm. Therefore, if the heat shrinkage characteristics of the film are non-uniform in the width direction of the roll, the film will change in size non-uniformly in the width direction when the inorganic thin film is processed and when the protective layer is processed thereafter. The gas barrier property of the resulting gas barrier film may be non-uniform.
On the other hand, in Patent Document 3 mentioned above, although the isotropic property of the film is mentioned, the means for improving the dimensional stability in the width direction is not considered. Therefore, when processing a biaxially stretched PBT film in a wide width, a means for obtaining physical properties uniformly in the width direction has not been studied.

Japanese Unexamined Patent Publication No. 6-278240, Japanese Unexamined Patent Publication No. 11-10725 JP-A-2017-09946

The present invention has been made in the background of the problems of the prior art.
That is, it has excellent pinhole resistance and bag breakage resistance, and is heated even in the case where an inorganic thin film layer and a protective layer are formed on a wide roll-shaped base film layer to produce a gas barrier film. It is an object of the present invention to provide a biaxially stretched polyester film capable of suppressing wrinkles generated during transportation and making the gas barrier property in the width direction uniform.

It has excellent pinhole resistance and rupture resistance, and is also heated and transported even when a wide roll is formed on the base film layer to form an inorganic thin film layer and a protective layer to produce a gas barrier film. In order to suppress the streaky wrinkles that sometimes occur, it is important to make the dimensional change characteristics of the base film in the width direction uniform.
As a result of diligent studies to solve such a problem, the present inventors have reduced the difference in heat shrinkage rate in the width direction in the roll of the biaxially stretched PBT film, thereby heating and transporting the wide roll for vapor deposition processing, etc. It was found that the streak-like wrinkles can be suppressed and the gas barrier property in the width direction can be made uniform.

In order to further reduce the difference in heat shrinkage in the width direction of the wide roll, the present inventors further described the unstretched polyester sheet melt-extruded into a sheet in the longitudinal direction (hereinafter, also referred to as the longitudinal direction) and the above. When winding the film by keeping the temperature of the surface of the edge of the polyester film low in the process of stretching in the width direction (hereinafter, also referred to as the horizontal direction) orthogonal to the vertical direction, heat fixing, heat relaxation and cooling. It has been found that the end portion of the stretched film is pulled in the vertical direction due to the tension applied to the film and the heat shrinkage rate can be suppressed from becoming high, and the present invention has been completed.

That is, the present invention has the following configuration.
[1] A polyester film containing 70% by weight or more of polybutylene terephthalate and simultaneously satisfying the following (1) to (5).
(1) The puncture strength measured according to JIS Z 1707 is 0.6 N / μm or more.
(2) The degree of surface orientation of the film is 0.144 to 0.165.
(3) The heat shrinkage of the film after heating at 150 ° C. for 15 minutes is 0 to 4% in the vertical direction and -1 to 3% in the horizontal 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 of the heat shrinkage in the vertical 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 is 0.5 or less.
Y (% / m) = {maximum heat shrinkage (%) -minimum heat shrinkage (%)} / roll width (m) ... (1 formula)
[2] Gas barrier laminated film having an inorganic thin film layer on at least one surface of the polyester film according to the above [1] [3] In the gas barrier laminated film according to the above [2], the polyester film and the inorganic. A gas barrier laminated film characterized by having an adhesive layer between thin film layers.
[4] The gas barrier laminated film according to the above [2] or [3], wherein the gas barrier laminated film has a protective layer on the surface of the inorganic thin film layer.

The present inventors have excellent pinhole resistance and bag breakage resistance by such a technique, and form a wide roll on an inorganic thin film layer and a protective layer on a base film layer to form a gas barrier film. It has become possible to provide a biaxially stretched polyester film capable of suppressing wrinkles generated during heat transfer and making the gas barrier property in the width direction uniform even in the case of manufacturing.

Hereinafter, the present invention will be described in detail.
The polyester film of the present invention contains PBT as a main component, and the content of PBT is preferably 70% by weight or more, more preferably 75% by weight or more. If it is less than 70% by weight, the piercing strength is lowered and the film characteristics are not sufficient.
The PBT used as a main component preferably contains terephthalic acid in an amount of 90 mol% or more, more preferably 95 mol% or more, still more preferably 98 mol% or more, and most preferably 100 mol as a dicarboxylic acid component. %. The 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-butanediol at the time of polymerization. It does not contain anything other than by-products produced by the ether bond of the diol.

The polyester film of the present invention may contain a polyester resin other than PBT for the purpose of adjusting mechanical properties and the like.
As the polyester resin other than PBT, 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, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol in which at least one dicarboxylic acid selected from the group consisting of acid, adipic acid, azelaic acid and sebacic acid is copolymerized. , 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, PBT resin in which at least one diol component selected from the group consisting of polycarbonate diol is copolymerized, etc. Can be mentioned.

The upper limit of the amount of the polyester resin other than the PBT resin added is preferably less than 30% by weight, more preferably 25% by weight or less. If the amount of polyester resin other than PBT resin added exceeds 30% by weight, the mechanical properties of PBT will be impaired, impact strength, pinhole resistance, or bag breakage resistance will be insufficient, and transparency and gas barrier will be insufficient. Sexual deterioration 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, and further 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 a film decreases, 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 it exceeds the above, the stress at the time of stretching becomes too high, and the film forming property may deteriorate. When PBT having a high intrinsic viscosity is used, it is necessary to raise the extrusion temperature to a high temperature because the melt viscosity of the resin becomes high, but when the PBT resin is extruded at a higher temperature, decomposition products may be easily generated.

If necessary, the PBT resin may contain conventionally known additives such as lubricants, stabilizers, colorants, antistatic agents, and ultraviolet absorbers.
As the lubricant type, 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 in that haze is reduced. These can be expressed as transparent and slippery.
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 decrease. The upper limit of the lubricant concentration is preferably 20000 ppm, more preferably 10000 ppm, still more preferably 1800 ppm. If it exceeds the above, transparency may decrease.

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

The upper limit of the heat shrinkage rate after heating the polyester film of the present invention at 150 ° C. in the longitudinal direction for 15 minutes is preferably 4.0%, more preferably 3.0%, still more preferably 2%. .. If the upper limit is exceeded, the inorganic thin film layer may be cracked due to the dimensional change of the base film layer caused by the protective film forming process or the high temperature treatment such as retort sterilization treatment, and the gas barrier property may be deteriorated. Pitch deviation may occur due to dimensional changes during processing.
The upper limit of the heat shrinkage after heating the polyester film of the present invention at 150 ° C. in the lateral direction for 15 minutes is preferably 3.0%, more preferably 2.0%, still more preferably 1%. If the upper limit is exceeded, the inorganic thin film layer may be cracked due to the dimensional change of the base film layer caused by the protective film forming process or the high temperature treatment such as retort sterilization treatment, and the gas barrier property may be deteriorated. Pitch deviation may occur due to dimensional changes in the width direction during processing.

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

The value Y (%) obtained by dividing the difference between the maximum and minimum of the heat shrinkage rate after heating at 150 ° C. in the vertical direction for 15 minutes measured at a pitch of 100 mm in the width (horizontal) direction of the roll of the polyester film of the present invention by the width of the roll. / M) is preferably 0.5 or less.
Y (% / m) = {maximum heat shrinkage (%) -minimum heat shrinkage (%)} / roll width (m) ... (1 formula)
When the value Y obtained by dividing the difference between the maximum and minimum of the heat shrinkage 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 larger than 0.5% / m, a wide roll is used. In the case of producing a gas barrier film by forming an inorganic thin film layer or a protective layer on the film, it is not possible to suppress streak-like wrinkles generated during heat transfer, and the gas barrier property becomes non-uniform in the width direction. It ends up.

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 a roll composed of the film in the center of the film manufacturing apparatus. If the slit roll is made of a film in the center of the film manufacturing apparatus, the film having Y (% / m) of 0.5 or less can be easily manufactured. Even if the polyester film of the present invention is a slit roll made of a film other than the central portion of the film manufacturing apparatus in which the maximum value of the orientation angle of the film is 25 degrees or more, the Y (% / m) of the present invention is 0.5 or less. be.

The orientation angle of the film is measured using a MOA-6004 type molecular orientation meter manufactured by Oji Measurement Co., Ltd. The orientation angle of the main axis of the molecular chain is obtained with reference to the axis in the width (horizontal) direction of the film, and the counterclockwise inclination is plus (+) and the clockwise is minus (-) with respect to the film width (horizontal) direction. And. The measurement is performed at the center of the film roll and at positions separated from the center by 20% on the left and right and 40% on the left and right, and the maximum value of the absolute value in the measurement is taken as the maximum orientation angle. In the case of a general biaxially stretched film, the orientation angle of the film at the center of the film manufacturing apparatus is close to zero, and the absolute value of the orientation angle tends to increase toward the film at the edges.

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

The lower limit of the plane orientation (ΔP) of the polyester film of the present invention is preferably 0.144, more preferably 0.148, and even more preferably 0.15. If it is less than the above, the orientation is weak, so that sufficient strength cannot be obtained and the bag-breaking resistance may be deteriorated. In addition, an inorganic thin film layer and a protective layer are provided on the base film layer to form a laminated film. In some cases, the tension and temperature applied when the protective film is formed make it easy to stretch, and the inorganic thin film layer is cracked, so that the gas barrier property may be deteriorated.
The upper limit of the plane orientation (ΔP) of the polyester film of the present invention is preferably 0.165, more preferably 0.160. If the degree of surface orientation is too large, the effect of improving strength and bag resistance is saturated. Further, in order to further increase the degree of surface orientation, it is necessary to increase the draw ratio, which tends to cause breakage during film formation and reduce productivity.

The upper limit of the haze per thickness of the polyester film of the present invention is preferably 0.66% / μm, more preferably 0.60% / μm, and further preferably 0.53% / μm. When printing is applied to the base film layer having a ratio of 0.66% / μm or less, the quality of the printed characters and images is improved.

Further, the polyester film of the present invention may be subjected to a corona discharge treatment, a glow discharge treatment, a flame treatment, a surface roughening treatment, and a known anchor coating treatment, as long as the object of the present invention is not impaired. It may be printed, decorated, or the like.

Next, a manufacturing method for obtaining the polyester film of the present invention will be specifically described. It is not limited to these.
In order to obtain the polyester film of the present invention, the manufacturing method is a step of melt-extruding a polyester raw material resin into a sheet and cooling it on a casting drum to form an unstretched sheet, and stretching the molded unstretched sheet in the longitudinal direction. After performing the longitudinal stretching step, the preheating step of preheating to a temperature capable of lateral stretching after the longitudinal stretching, the transverse stretching step of stretching in the width (horizontal) direction orthogonal to the longitudinal (longitudinal) direction, the longitudinal stretching and the transverse stretching. It comprises a heat fixing step of heating and crystallizing the film, a heat relaxation step of removing residual strain of the heat-fixed film, and a cooling step of cooling the film after heat relaxation.
[Unstretched sheet molding process]
First, the film raw material is dried or hot air dried. Next, the raw materials are weighed, mixed, supplied to an extruder, heated and melted, and melt-casted in the form of a sheet.
Further, the molten resin sheet is brought into close contact with a cooling roll (casting roll) by an electrostatic application method to be cooled and solidified to obtain an unstretched sheet. The electrostatic application method is to apply a voltage to an electrode installed near the surface opposite to the surface of the resin sheet in contact with the rotating metal roll in the vicinity of the molten resin sheet in contact with the rotating metal roll. This is a method in which the resin sheet is charged and the resin sheet and the rotary cooling roll are brought into close contact with each other.

The lower limit of the heating and melting temperature of the resin is preferably 200 ° C., more preferably 250 ° C., and even more preferably 260 ° C. If it is less than the above, the discharge may become unstable. The upper limit of the resin melting temperature is preferably 280 ° C, more preferably 270 ° C. If it exceeds the above, the decomposition of the resin proceeds and the film becomes brittle.

When casting the molten polyester resin onto an extruded cooling roll, it is preferable to reduce the difference in crystallinity in the width direction. Specific methods for this include extruding the molten polyester resin and casting the raw materials having the same composition in multiple layers at the time of casting, and further lowering the cooling roll temperature to a low temperature.
Since the crystallization rate of PBT resin is high, crystallization proceeds even during casting.
At this time, when cast in a single layer without multi-layering, the spherulite grows into a large-sized spherulite because there is no barrier that can suppress the growth of the crystal. As a result, the yield stress of the obtained unstretched sheet becomes high, and not only is it easy to break during biaxial stretching, but also the impact strength, pinhole resistance, or rupture resistance of the obtained biaxially stretched film is improved. The film will be inadequate. 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 a molten polyester resin and casting by layering raw materials having the same composition at the time of casting is specifically a step of melting a resin composition containing 70% by weight or more of PBT resin to form a molten fluid (a step of forming a molten fluid. 1), a step of forming a laminated fluid having a laminated number of 60 or more composed of the formed molten fluid (2), the formed laminated fluid is discharged from a die and brought into contact with a cooling roll to be solidified to form a laminated unstretched sheet. It has at least a step (3) of forming and a step (4) of biaxially stretching the laminated unstretched sheet.
Another step may be inserted between the steps (1) and the step (2), and between the steps (2) and the step (3). For example, a filtration step, a temperature changing step, or the like may be inserted between the steps (1) and the step (2). Further, a temperature changing step, a charge adding step, or the like may be inserted between the steps (2) and the step (3). However, there must be no step between the step (2) and the step (3) to break the laminated structure formed in the step (2).

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

The method for forming the laminated fluid in the step (2) is not particularly limited, but a static mixer and / or a multilayer feed block is more preferable from the viewpoint of convenience of equipment and maintainability. Further, from the viewpoint of uniformity in the sheet width direction, those having a rectangular melt line are more preferable. It is more preferred to use a static mixer or multi-layer feed block with rectangular melt lines. The resin composition composed of a plurality of layers formed by merging the plurality of resin compositions may be passed through one or more of a static mixer, a multilayer feed block, and a multilayer manifold.

The number of theoretical stacks in the step (2) is preferably 60 or more. The lower limit of the theoretical stacking number is more preferably 500. If the number of theoretical layers is too small, or the distance between the layer interfaces becomes long and the crystal size becomes too large, the effect of the present invention tends not to be obtained. In addition, the crystallinity near both ends of the sheet increases, the film formation becomes unstable, and the transparency after molding may decrease. The upper limit of the number of theoretical stacks in the step (2) is not particularly limited, but is preferably 100,000, more preferably 10,000, and even more preferably 7,000. Even if the number of theoretical stacks is made extremely large, the effect may be saturated.

When the lamination in the step (2) is performed by a static mixer, the theoretical number of laminations 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 drive unit, and the fluid entering the mixer is sequentially stirred and mixed by an element. However, when the high-viscosity fluid is passed through the static mixer, the high-viscosity fluid is divided and laminated, and the laminated fluid is formed. 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 laminated fluid having a theoretical stacking number of N = ²ⁿ is formed.

A typical static mixer element has a structure in which a rectangular plate is twisted 180 degrees, and depending on the direction of twist, there are a right element and a left element, and the dimensions of each element are 1.5 times longer than the diameter. It is basic. The static mixer that can be used in the present invention is not limited to such a static mixer.

When the lamination in the step (2) is performed by the multilayer feed block, the theoretical number of laminations can be adjusted by selecting the number of divisions / laminations of the multilayer feed block. Multiple multilayer feed blocks can be installed in series. Further, the high-viscosity fluid itself supplied to the multilayer feed block can be used as the laminated fluid. For example, when the number of laminated high-viscosity fluids supplied to the multilayer feed block is p, the number of divided / stacked multilayer feed blocks is q, and the number of installed multilayer feed blocks is r, the number of stacked fluids N is N = p. It becomes × ^qr .

In the step (3), the laminated fluid is discharged from the die and brought into contact with the cooling roll to be solidified.
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 cooling roll temperature is preferably 40 ° C. If it exceeds the above, the crystallinity may become too high and stretching may become difficult. The upper limit of the cooling 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 near 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 unstretched sheet having a multilayer structure described above has at least 60 layers or more, 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.

[Vertical stretching and transverse stretching steps]
Next, the stretching method will be described. The stretching method can be either simultaneous biaxial stretching or sequential biaxial stretching, but in order to increase the puncture strength, it is necessary to increase the degree of surface orientation, and the film forming speed is high and the productivity is high. In terms of points, sequential biaxial stretching is most preferable.

The lower limit of the stretching temperature in the longitudinal stretching direction is preferably 55 ° C, more preferably 60 ° C. If the temperature is 55 ° C. or higher, fracture is unlikely to occur. Further, since the degree of vertical orientation of the film does not become too strong, shrinkage stress during the heat fixing treatment can be suppressed, and a film with less distortion of 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 lower, 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 longitudinal stretching direction is preferably 2.8 times, and particularly preferably 3.0 times. When it is 2.8 times or more, the degree of surface orientation becomes large and the piercing strength of the film is improved.
The upper limit of the draw ratio in the longitudinal stretching 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 lateral orientation of the film does not become too strong, the shrinkage stress during the heat fixing process does not become too large, and the distortion of the lateral molecular orientation of the film becomes small, resulting in As a result, the straight tearability in the vertical direction is improved. Moreover, the effect of improving the mechanical strength and the thickness unevenness is saturated in this range.

The lower limit of the stretching temperature in the transverse stretching direction is preferably 60 ° C., and if it is 60 ° C. or higher, fracture may be less likely to occur. The upper limit of the stretching temperature in the transverse stretching direction is preferably 100 ° C., and when it is 100 ° C. or lower, the degree of orientation in the transverse direction increases and the mechanical properties are improved.

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

[Heat fixing process]
The lower limit of the heat fixing temperature in the heat fixing step is preferably 195 ° C, more preferably 200 ° C. When the temperature is 195 ° C. or higher, the heat shrinkage rate of the film is reduced, and the inorganic thin film layer is not easily damaged even after the retort treatment, so that the gas barrier property is improved. The upper limit of the heat fixing temperature is preferably 220 ° C., and when it is 220 ° C. or lower, the base film layer does not melt and is less likely to become brittle.

[Heat relaxation section process]
The lower limit of the relaxation rate in the heat relaxation section step is preferably 0.5%. If it is 0.5% or more, it may be difficult for fracture to occur during heat fixing. The upper limit of the relaxation rate is preferably 10%. When it is 10% or less, the shrinkage in the longitudinal (longitudinal) direction at the time of heat fixing becomes small, and as a result, the distortion of the molecular orientation at the end of the film becomes small, and the straight tearability is improved. In addition, slackening of the film is unlikely to occur, and uneven thickness is unlikely to occur.

[Cooling process]
In the cooling step after relaxing in the heat relaxation section step, the temperature of the surface of the edge portion of the polyester film is preferably 80 ° C. or lower.
If the temperature of the end of the film after passing through the cooling step exceeds 80 ° C., the end is stretched by the tension applied when the film is wound, and as a result, the heat shrinkage rate of the end in the vertical direction becomes high. Therefore, the heat shrinkage distribution in the width direction of the roll becomes non-uniform, and when such a roll is heated and conveyed for vapor deposition processing, streaky wrinkles are generated, and the final gas barrier is obtained. The physical properties of the film may become non-uniform in the width (horizontal) direction.

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

[Inorganic thin film layer]
By providing an inorganic thin film layer on the surface of the biaxially stretched polyester film of the present invention, gas barrier properties can be imparted.
The inorganic thin film layer is a thin film made of a metal or an 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, but from the viewpoint of gas barrier properties, inorganic oxidation such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide. 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 in terms of the weight ratio of the metal content. If the Al concentration is less than 20% by weight, the water vapor barrier property may be lowered. On the other hand, if it exceeds 70% by weight, the inorganic thin film layer tends to be hard, and the film may be destroyed during secondary processing such as printing or laminating, and the gas barrier property may be deteriorated. The silicon oxide referred to here is various silicon oxides such as SiO and SiO ₂ or a mixture thereof, and aluminum oxide is various aluminum oxides such as AlO and Al ₂ O ₃ or a mixture thereof.

The film thickness of the inorganic thin film layer is usually 1 to 100 nm, preferably 5 to 50 nm. If the film thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain a satisfactory gas barrier property. On the other hand, even if the thickness exceeds 100 nm, the corresponding improvement effect of the gas barrier property can be obtained. However, it is disadvantageous in terms of bending resistance and manufacturing cost.

The method for forming the inorganic thin film layer is not particularly limited, and is known, for example, a physical vapor deposition method (PVD method) such as a vacuum vapor deposition method, a sputtering method, or an ion plating method, or a chemical vapor deposition method (CVD method). The method may be adopted as appropriate. Hereinafter, a typical method for forming an inorganic thin film layer will be described using a silicon oxide / aluminum oxide thin film as an example. For example, when the vacuum vapor deposition method is adopted, a mixture of SiO ₂ and Al ₂ O ₃ or a mixture of SiO ₂ and Al is preferably used as the vapor deposition raw material. Particles are usually used as these vapor deposition raw materials, but at that time, it is desirable that the size of each particle is such that the pressure at the time of vapor deposition does not change, and the preferable particle diameter is 1 mm to 5 mm. For heating, methods such as resistance heating, high frequency induction heating, electron beam heating, and laser heating can be adopted. Further, it is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor or the like as the reaction gas, or to adopt reactive vapor deposition using means such as ozone addition and ion assist. Further, the film forming conditions can be arbitrarily changed, such as applying a bias to the material to be vapor-deposited (laminated film to be subjected to thin-film deposition) or heating or cooling the material to be vapor-deposited. Such vapor deposition material, reaction gas, bias of the vapor-film-deposited body, heating / cooling, and the like can be similarly changed when the sputtering method or the CVD method is adopted.

[Adhesive layer]
In the gas via laminating 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 the gas barrier property and the laminating strength after the retort treatment.
The resin composition used for the adhesive layer provided between the base film layer and the inorganic thin film layer includes resins such as urethane, polyester, acrylic, titanium, isocyanate, imine, and polybutadiene, and epoxy. Examples thereof 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 organic functional group. Examples of the organic functional group include an alkoxy group, an amino group, an epoxy group, an isocyanate group and the like. By adding the silane coupling agent, the laminating strength after the retort treatment is further improved.

Among the resin compositions used for the adhesive layer, it is preferable to use a mixture of a resin containing an oxazoline group, 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 to the inorganic thin film layer. .. Further, the unreacted oxazoline group present in the adhesive layer can react with the carboxylic acid terminal generated by the hydrolysis of the base film layer and the adhesive layer to form a crosslink.

The method for forming the adhesive layer is not particularly limited, and a conventionally known method such as a coating method can be adopted. Among the coating methods, the offline coating method and the inline coating method can be mentioned as preferable methods. For example, in the case of the in-line coating method performed in the process of manufacturing the base film layer, the conditions of drying and heat treatment at the time of coating depend on the coating thickness and the conditions of the apparatus, but immediately after coating, they are sent to the stretching process in the right angle direction. It is preferable to dry in the preheating zone or the stretching zone in 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 the coating method is used 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. Etc., and examples thereof include polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[Protective layer]
In the present invention, the protective layer is provided on the inorganic thin film layer. The metal oxide layer is not a completely dense film, but is dotted with minute defects. By applying a specific protective layer resin composition to be described later on the metal oxide layer to form the protective layer, the resin in the protective layer resin composition permeates the defective portion of the metal oxide layer. As a result, the effect of stabilizing the gas barrier property can be obtained. In addition, by using a material having a gas barrier property for the protective layer itself, the gas barrier performance of the laminated film is 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. Examples thereof 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 also has flexibility due to the presence of the amorphous portion, so that damage to the inorganic thin film layer is suppressed even when a bending load is applied. It is preferable because it can be used.
The acid value of the urethane resin is preferably in the range of 10 to 60 mgKOH / g. It is more preferably in the range of 15 to 55 mgKOH / g, and even 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. Will be.

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, the swelling of the protective layer due to molecular motion in the wet heat treatment process (heating to heat retention to temperature lowering) can be reduced.

From the viewpoint of improving the gas barrier property, it is more preferable to use a urethane resin containing an aromatic or aromatic aliphatic diisocyanate component as a main component.
Among them, it is particularly preferable to contain a metaxylylene diisocyanate component. By using the above resin, the cohesive force of the urethane bond can be further enhanced by the stacking effect between the aromatic rings, and as a result, a good gas barrier property can be obtained.

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

The urethane resin preferably has a carboxylic acid group (carboxyl group) from the viewpoint of improving the affinity with the inorganic thin film layer. In order to introduce a carboxylic acid (salt) group into the urethane resin, for example, a polyol compound having a carboxylic acid group such as dimethylolpropionic acid and dimethylolbutanoic acid may be introduced as a copolymerization component as a polyol component. Further, if the carboxylic acid group-containing urethane resin is synthesized and then neutralized with a salt-forming agent, an aqueous dispersion urethane resin can be obtained. Specific examples of the salt forming agent include trialkylamines such as ammonia, trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine and tri-n-butylamine, and N such as N-methylmorpholine and N-ethylmorpholine. -Examples include N-dialkylalkanolamines such as alkylmorpholines, 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; ethylene glycol. Examples thereof include polyhydric alcohol derivatives such as monomethyl ether.

From the above, the polyester film of the present invention is excellent in bag breaking resistance and bending resistance, and a wide roll is formed on the base film layer to form an inorganic thin film layer and a protective layer to produce a gas barrier film. Even in such a case, it is possible to suppress streak-like wrinkles generated during heat transfer and make the gas barrier property in the width direction uniform.

[Packaging material]
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 adhesive layer forming surface). The heat-sealing resin layer is usually formed by an extrusion laminating method or a dry laminating method. The thermoplastic polymer that forms the heat-sealable resin layer may be any as long as it can sufficiently exhibit sealant adhesiveness, and is a polyethylene resin such as HDPE, LDPE, LLDPE, a polypropylene resin, or an ethylene-vinyl acetate copolymer. , Ethethylene-α-olefin random copolymer, ionomer resin and the like can be used.

Further, in the laminated film of the present invention, at least one layer of a printing layer or another plastic base material and / or a paper base material is provided between or outside the inorganic thin film layer or the base film layer and the heat-sealing resin layer. The above may be laminated.

As the printing ink forming the printing layer, water-based and solvent-based resin-containing printing inks can be preferably used. Examples of the resin used for the printing ink include an acrylic resin, a urethane resin, a polyester resin, a vinyl chloride resin, a vinyl acetate copolymer resin, and a mixture thereof. Known printing inks include antistatic agents, light blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoaming agents, cross-linking agents, blocking agents, antioxidants and the like. Additives may be included. The printing method for providing the print layer is not particularly limited, and known printing methods such as an offset printing method, a gravure printing method, and a screen printing method can be used. For drying the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. The film was evaluated by the following measurement method.

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

[Film surface orientation ΔP]
About the sample According to the JIS K 7142-1996 A method, the refractive index (Nx) in the longitudinal (longitudinal) direction, the refractive index (Ny) in the width (horizontal) direction, and the refraction in the thickness direction of the film are refracted by the Abbe refractometer using the sodium D line as the light source. The index (Nz) was measured, and the degree of plane orientation ΔP was calculated by the calculation formula of (Equation 2).
Surface orientation (ΔP) = (Nx + Ny) / 2-Nz (2 equations)

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

[Heat shrinkage of film]
The heat shrinkage of the polyester film was measured by the dimensional change test method described in JIS-C-21151-2006.21 except that the test temperature was 150 ° C. and the heating time was 15 minutes. The test piece was used as described in 21.1 (a).

[Homogeneity of heat shrinkage in the width direction]
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 vertical direction was measured according to the above-mentioned method. From the maximum and minimum values of the obtained heat shrinkage and the width of the film roll, Y (% / m) was determined using the following formula (1 formula).
Y (% / m) = {maximum heat shrinkage (%) -minimum heat shrinkage (%)} / roll width (m) ... (1 formula)

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

[Impact strength of film]
Using an impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., the strength of the film against impact punching in an atmosphere of 23 ° C. was measured. The impact spherical surface used was one with a diameter of 1/2 inch. The unit is J / μm.

The details of the raw material resin and the coating liquid used in this example and the comparative example are described below. 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: As the polybutylene terephthalate resin used in the production of the biaxially stretched polyester film described later, 1100-211XG (CHANGE CHUN PLASTICS CO., LTD., Intrinsic viscosity 1.28 dl / g) was used.
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 having an oxazoline group (B): As a resin having an oxazoline group, a commercially available water-soluble oxazoline group-containing acrylate (“Epocross (registered trademark) WS-300” manufactured by Nippon Shokubai Co., Ltd .; solid content 10%) is prepared. did. 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 (“Mobile (registered trademark) 7980” manufactured by Nichigo Vinyl Co., Ltd.” was prepared. This acrylic resin (B). The acid value (theoretical value) of) was 4 mgKOH / g.

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

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

7) Coating liquid used for the adhesive layer 1
Each material was mixed at the following blending ratio to prepare a coating liquid (resin composition for an adhesive layer).
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 used for coating the protective layer 2
The following coating agents were mixed to prepare a coating liquid 2. Here, the weight ratio of the urethane resin (E) in terms of solid content is as shown in Table 1.
Water 60.00% by weight
Isopropanol 30.00% by weight
Urethane resin (E) 10.00% by weight

[Preparation of laminated laminate]
The protective layer of the gas barrier film 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, which will be described later. On the side, a urethane-based two-component curable adhesive (Mitsui Chemicals, Inc. "Takelac (registered trademark) A525S" and "Takenate (registered trademark) A50" are mixed at a ratio of 13.5: 1 (weight ratio)). Using the dry laminating method, an unstretched polypropylene film with a thickness of 70 μm (“P1147” manufactured by Toyobo Co., Ltd.) is bonded as a heat-sealing resin layer, and aged at 40 ° C. for 4 days to perform laminating for evaluation. A laminate was obtained. The thickness of the adhesive layer formed of the urethane-based two-component curable adhesive after drying was about 4 μm.

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

[Moisture vapor transmission rate after retort of laminated laminate]
The above-mentioned laminated laminate was subjected to a wet heat treatment for 30 minutes in hot water at 130 ° C., dried at 40 ° C. for 1 day (24 hours), and the obtained laminated laminate after the wet heat treatment was described above. The water vapor transmission rate 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 characteristics of the following biaxially stretched polyester film.
<Example 1-1>
Using a uniaxial extruder, 80% by weight of PBT resin and 20% by weight of PET resin are mixed, and silica particles with an average particle size of 2.4 μm as inert particles have a silica concentration of 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, it was rolled 2.9 times in the vertical direction at 60 ° C., then passed through a tenter and stretched 4.0 times in the horizontal direction at 90 ° C., tension heat treatment at 200 ° C. for 3 seconds and relaxation of 9% for 1 second. After performing the treatment, the film was cooled by cooling at 50 ° C. for 2 seconds. The surface temperature of the edge of the film at this time was 75 ° C.
Next, the grips at both ends were cut and removed by 10% each to obtain a roll (hereinafter referred to as a mill roll) of the full width of the polyester film having a thickness of 15 μm and a total width of 4200 mm. The obtained mill roll was slit, and two slit rolls having a roll width of 2080 mm were collected.
Table 1 shows the film forming conditions, physical characteristics and evaluation results of the obtained film.

<Examples 1-2 to 1-8, Comparative Examples 1-1 to 1-5>
In the film forming 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 vertical and horizontal stretching ratio, the relaxation rate and the tenter cooling process zone temperature were shown in Tables 1 and 2. .. However, in Comparative Example 1-2, the extrusion temperature was 270 ° C.

<Example 2-1>
Using a uniaxial extruder, 80% by weight of PBT resin and 20% by weight of PET resin are mixed, and silica particles with an average particle size of 2.4 μm as inert particles have a silica concentration of 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, it was rolled 2.9 times in the vertical direction at 60 ° C., and after the vertical stretching, the resin composition for the adhesive layer (coating liquid 1) was applied by the fountain bar coating method. Then, it is guided to a tenter while drying, then passed through the tenter and stretched 4.0 times laterally at 90 ° C., subjected to tension heat treatment at 200 ° C. for 3 seconds and relaxation treatment of 9% for 1 second, and then 50. The film was cooled by cooling at ° C. for 2 seconds. The surface temperature of the edge of the film at this time was 75 ° C.
Next, the grips at both ends were cut and removed by 10% to obtain a mill roll of a polyester film having a thickness of 15 μm and a total width of 4200 mm. The obtained mill roll was slit, and two slit rolls having a width of 2080 mm were collected.
Table 3 shows the film forming conditions, physical characteristics and evaluation results of the obtained film.

<Example 2-2 to Example 2-8, Comparative Example 2-1 to Comparative Example 2-5>
In the film forming process of the biaxially stretched polyester film, the same procedure as in Example 2-1 was carried out except that the PBT ratio, the longitudinal / horizontal stretching ratio, the relaxation rate and the tenter cooling step zone temperature 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 an electron beam vapor deposition method. As the vapor deposition source, particulate SiO ₂ (purity 99.9%) and A1 ₂ O ₃ (purity 99.9%) having a purity of about 3 mm to 5 mm were used. The film thickness of the inorganic thin film layer (SiO ₂ / A1 ₂ O ₃ 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 SiO ₂ / A1 ₂ O ₃ (weight ratio) = 60/40.

<Formation of protective layer 1 on thin-film vapor deposition film>
The coating liquid 2 was applied onto the inorganic thin film layer of the inorganic thin film layer deposited and formed above by the wire bar coating method, and dried at 200 ° C. for 15 seconds to obtain a protective layer. The coating amount after drying was 0.190 g / m ² (as Dry solid content).
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 end at the outlet of the tenter was set to 80 ° C. or lower. By doing so, it was possible to reduce the difference in heat shrinkage rate in the roll width direction, and it was possible to obtain a film roll having a small difference in physical properties in the width direction.

Further, in Examples 1-1 to 1-8, by cooling the temperature of the film end portion at the tenter outlet to 80 ° C. or lower, the heat shrinkage rate of the obtained mill roll end portion can be suppressed. , It became possible to reduce the difference in heat shrinkage rate in the vertical direction of the slit roll. As a result, the generation of streaky wrinkles was suppressed when the inorganic thin film layer and the protective layer were formed, 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 a harsh wet heat treatment such as a retort sterilization treatment. , High gas barrier property could be maintained.

In Comparative Example 1-1 and Comparative Example 2-1, since the heat fixing temperature is raised to suppress the heat shrinkage rate in the vertical direction, the strain in the width direction of the film is large, and the heat shrinkage rate at the end is large. As a result, the gas barrier property at the end is inferior.
Similar to the above, Comparative Example 1-2 and Comparative Example 2-2 have a large difference in heat shrinkage between the central portion and the end portion of the mill roll, and not only the gas barrier property at the end portion is inferior, but also the ratio of PBT is small, which is sufficient. The piercing strength is not obtained.
In Comparative Example 1-3 and Comparative Example 2-3, Comparative Example 1-4 and Comparative Example 2-4, the puncture strength is improved by increasing the draw ratio and the degree of surface orientation, but Comparative Example 1 As in -1 and Comparative Example 2-1 the heat shrinkage rate of the end portion is high, and the uniformity of the gas barrier property in the width direction becomes insufficient.
In Comparative Example 1-5 and Comparative Example 2-5, as a result of raising the heat fixing 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 non-uniform in the width direction. In addition, the mechanical strength of the film was reduced.

According to the present invention, a gas barrier film is produced by forming an inorganic thin film layer and a protective layer with wide rolls on a base film layer while having excellent pinhole resistance and bag breakage resistance. Even in this case, it has become possible to provide a biaxially stretched polyester film capable of suppressing wrinkles generated during heat transfer and making the gas barrier property in the width direction uniform. 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 is excellent in economic efficiency and production stability because uniform physical properties can be obtained in the width direction even when a wide roll is processed, and it is easy to obtain uniform properties. Therefore, such a gas barrier film has advantages, and is not limited to food packaging, but is also used for packaging applications such as pharmaceuticals and industrial products, as well as industrial applications such as solar cells, electronic papers, organic EL elements, and semiconductor elements. Can be widely used.

Claims (4)

A polyester film containing 70% by weight or more of polybutylene terephthalate and simultaneously satisfying the following (1) to (5).
(1) The puncture strength measured according to JIS Z 1707 is 0.6 N / μm or more.
(2) The degree of surface orientation of the film is 0.144 to 0.165.
(3) The heat shrinkage of the film after heating at 150 ° C. for 15 minutes is 0 to 4% in the vertical direction and -1 to 3% in the horizontal 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 of the heat shrinkage in the vertical 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 is 0.5 or less.
Y (% / m) = {maximum heat shrinkage (%) -minimum heat shrinkage (%)} / roll width (m) ... (1 formula) A gas barrier laminated film having an inorganic thin film layer on at least one surface of the polyester film according to claim 1. The gas barrier laminated film according to claim 2, wherein the gas barrier laminated film has an adhesive layer between the polyester film and the inorganic thin film layer. The gas barrier laminated film according to claim 2 or 3, wherein the gas barrier laminated film has a protective layer on the surface of the inorganic thin film layer.