JP7365569B2 - Biaxially oriented polyester film and method for producing biaxially oriented polyester film - Google Patents

Description

The present invention relates to a biaxially oriented polyester film and a method for producing a biaxially oriented polyester film.

Polybutylene terephthalate (hereinafter abbreviated as PBT) resin has better impact resistance than polyethylene terephthalate (hereinafter abbreviated as PET) resin, so it is used as an exterior material for food packaging films and vacuum insulation materials. Applications are also being considered in fields such as , film for drawing, and film for inner bags of cans.

For example, in Patent Document 1, PBT resin is 40 to 80% by weight with respect to PET resin, and the tensile modulus in the longitudinal direction and width direction is 2.3 to 3.5 GPa, so that a polyester film for inner bags of cans is produced. It is disclosed that it can be suitably used as a.

In Patent Document 2, the tensile strength at break in four directions (0° (longitudinal direction), 45°, 90° (width direction), 135°) is 215 MPa or more, 228 MPa or more, 240 MPa or more, and 221 MPa or more, and 4 Two pieces made of PBT resin with a ratio of the maximum value to the minimum value of the tensile strength in the directions (0° (longitudinal direction), 45°, 90° (width direction), 135°) are 1.12 or less. An axially oriented film is disclosed. Further, a packaging material is disclosed in which the biaxially stretched film is used as a base material layer and has a structure of a base material layer, a gas barrier layer, and a sealant layer from the outside. By making the number of pinholes in the packaging material 3 or less when bent 1000 times under conditions of 5°C x 40% RH, it can be suitably used as a packaging material for liquid filling with excellent fragrance retention. It has been disclosed that it is possible.

In Patent Document 3, PBT resin is 60% by mass or more, the yield stress in the longitudinal direction and the width direction is 70 MPa or more, the breaking strength is 160 MPa or more, and the breaking elongation is 100% or more, so that nylon films and other flexible films can be prepared. It is disclosed that it can be suitably used for various purposes.

Patent No. 6195765 Patent No. 6347499 Patent No. 5994864

Since PBT resin has a fast crystallization speed, crystallization progresses even during casting. In particular, the edges of a film obtained by casting tend to be thicker than the center for manufacturing reasons. Therefore, crystallization becomes more noticeable at the edges of the film obtained by casting.
In Patent Documents 1 and 3 mentioned above, quenching treatment using a cooling roll is performed during casting, but since the cooling conditions are the same for the center and edges of the film, the thicker edges are slowly cooled compared to the center. , crystallization progresses more. Therefore, it is presumed that the stretching stress at the ends increases in the subsequent stretching step, which tends to lead to breakage. Furthermore, in Patent Document 2, since the cooling water is at a relatively high temperature of 20°C, it is assumed that the cooling is insufficient and crystallization is progressing, and the stretching stress increases in the subsequent stretching process, which is likely to lead to breakage. It is assumed that

The present invention has been made in view of the above-mentioned problems. That is, an object of the present invention is to provide a biaxially oriented polyester film that has good bag tear resistance and excellent film formability. Another object of the present invention is to provide a method for producing a biaxially oriented polyester film, which makes it possible to obtain the biaxially oriented polyester film.

The present inventors conducted extensive studies on biaxially oriented polyester films. As a result, they found that by employing the following configuration, a biaxially oriented polyester film having good bag breakage resistance and excellent film formability could be obtained, and the present invention was completed.

That is, the biaxially oriented polyester film according to the present invention is
A polyester resin composition containing 75 to 100% by mass of polybutylene terephthalate resin (A),
It is characterized by satisfying the following requirements (1) to (3).
(1) The puncture strength of the biaxially oriented polyester film measured by a puncture test according to JIS-Z1707 is 0.50 N/μm or more.
(2) In the width direction of the biaxially oriented polyester film, samples were taken at positions 10 mm from the left and right edges toward the center, and the highest value of the densities measured according to JIS-K7112 was 1. .40g/ ^cm3 or less.
(3) The intrinsic viscosity of the biaxially oriented polyester film is 0.7 dl/g or more.

According to the above configuration, since the bag includes a polyester resin composition containing 75% by mass or more of polybutylene terephthalate resin (A), puncture strength can be improved and bag breakage resistance can be made good. .
Furthermore, since the puncture strength is 0.50 N/μm or more, the bag can have good resistance to breakage.
Further, since the density is 1.4 g/cm ³ or less, crystallization at the edges is suppressed. As a result, it is possible to suppress excessive stress at the end portions in the stretching step when producing the biaxially oriented polyester film, and film formability can be improved.
In addition, since the intrinsic viscosity is 0.7 dl/g or more, crystallization of the unstretched sheet is suppressed when the resin composition for producing a biaxially oriented polyester film is cast onto a cooling roll to obtain an unstretched sheet. In particular, the yield stress at the thick end portions can be prevented from becoming too high. As a result, it can be made difficult to break during the stretching process.

Note that the biaxially oriented polyester film of the present invention is assumed to be a film after production (after casting and stretching treatment), that is, a film that has not been subjected to slit treatment or the like (a film in a mill roll state). However, as long as the biaxially oriented polyester film of the present invention contains a polyester resin composition containing 75 to 100% by mass of polybutylene terephthalate resin (A) and satisfies the above requirements (1) to (3), the shape of the film is is not particularly limited, and includes, for example, a film made into a small roll by slitting or the like, or a sheet film.

In the above configuration, the polyester resin composition preferably contains a polyester resin (B) other than the polybutylene terephthalate resin (A).

When the polyester resin composition contains a polyester resin (B) other than the polybutylene terephthalate resin (A), the film formability during biaxial stretching and the mechanical properties of the obtained film can be adjusted.

In the above configuration, sampling was performed at a position 10 mm from the left and right edges toward the center in the width direction of the biaxially oriented polyester film, and the total reflection method using the Fourier transform infrared spectroscopy spectrum intensity was used. When the ratio A/B of the resulting absorption intensity A of the peak at 1450±10 cm ⁻¹ and the absorption intensity B of the peak 1410±10 cm ⁻¹ is determined, the highest value is preferably 0.62 or less.

The absorption intensity A is an absorption originating from the methylene group of the α-type crystal of PBT, the absorption intensity B is an absorption originating from the carbon bond of the benzene ring, and the value of the absorption intensity ratio A/B indicates the orientation coefficient. , the smaller the orientation coefficient, the lower the crystallinity, and the higher the orientation coefficient, the higher the crystallinity.
When the highest value of the ratio A/B is 0.62 or less, crystallinity does not become too high, stress during stretching is suppressed, and breakage becomes difficult.

In the above configuration, it is preferable that the degree of plane orientation ΔP of the biaxially oriented polyester film is 0.145 to 0.160.

When the degree of planar orientation ΔP is 0.145 or more, the planar orientation is suitably high, the puncture strength is sufficient, and the bag tear resistance is more excellent.
When the plane orientation degree ΔP is 0.160 or less, the thermal shrinkage rate can be maintained low and the thermal stability can be made better.

Furthermore, the method for producing a biaxially oriented polyester film according to the present invention includes:
Step A of casting a resin composition for producing a biaxially oriented polyester film onto a cooling roll to form an unstretched sheet;
a step B of blowing wind on the unstretched sheet on the cooling roll,
In the step B, when the total width of the unstretched sheet is 100%, the temperature of the wind blown at the center is X, and the temperature blown at both ends is Y, the above X is 15 ° C. or less, and , said Y is at a lower temperature than said X,
The edge portion is characterized in that it includes at least an area within 10% of the edge.

According to the above configuration, the degree of crystallinity can be adjusted by blowing air at a temperature of 15° C. or lower onto the unstretched sheet on the cooling roll and rapidly cooling the B side (the surface opposite to the surface in contact with the cooling roll) of the unstretched sheet. can be made small and film formability can be improved.
Further, the thickness of the end portions of the unstretched sheet is often thicker than the center portion. Therefore, by rapidly cooling the edges (at least a region within 10% of the edge) more strongly than the center, crystallization at the edges can be suppressed to the same extent as the center, and film formability can be improved.

In the above configuration, it is preferable that the temperature of Y is 10° C. or less. When the temperature of Y is 10° C. or less, the degree of crystallinity at the B-side edge of the unstretched sheet does not become too high, and film formability becomes better.

According to the present invention, it is possible to provide a biaxially oriented polyester film that has good bag tear resistance and excellent film formability. Furthermore, it is possible to provide a method for producing a biaxially oriented polyester film that allows the biaxially oriented polyester film to be obtained.

FIG. 3 is a schematic front view for explaining a method of blowing cooling air from a multi-duct onto the B side of an unstretched sheet on a cooling roll. FIG. 2 is a side view of FIG. 1; It is a bottom view showing an example of a multi-duct.

Embodiments of the present invention will be described below.

The biaxially oriented polyester film according to this embodiment is
A polyester resin composition containing 75 to 100% by mass of polybutylene terephthalate resin (A),
A biaxially oriented polyester film characterized by satisfying the following requirements (1) to (3).
(1) The puncture strength of the biaxially oriented polyester film measured by a puncture test according to JIS-Z1707 is 0.50 N/μm or more.
(2) In the width direction of the biaxially oriented polyester film, samples were taken at positions 10 mm from the left and right edges toward the center, and the highest value of the densities measured according to JIS-K7112 was 1. .40g/ ^cm3 or less.
(3) The intrinsic viscosity of the biaxially oriented polyester film is 0.7 dl/g or more.

[Composition of biaxially oriented polyester film]
The polyester resin composition has PBT resin (A) as a main component, and the content of PBT resin (A) in the polyester resin composition is 75% by mass or more. Preferably it is 85% by mass or more, more preferably 90% by mass or more. By setting the content to 75% by mass or more, sufficient puncture strength can be achieved, and bag tear resistance can be improved.
The PBT resin (A) 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 Preferably it is 100 mol%. The glycol component preferably contains 1,4-butanediol in an amount of 90 mol% or more, more preferably 95 mol% or more.

The lower limit of the intrinsic viscosity of the PBT resin (A) is preferably 0.80 dl/g, more preferably 0.95 dl/g, and even more preferably 1.0 dl/g. By setting the intrinsic viscosity of the PBT resin (A) to 0.80 dl/g or more, it is possible to increase the intrinsic viscosity of the film obtained by forming the film, and it is possible to improve the bag tear resistance and film forming properties. can.
The upper limit of the intrinsic viscosity of the PBT resin (A) is preferably 1.3 dl/g. By setting it to 1.3 dl/g or less, stress during film stretching can be suppressed from becoming too high, and film formability can be improved. Furthermore, when a PBT resin with a high intrinsic viscosity is used, the melt viscosity of the resin increases, so the extrusion temperature needs to be raised to a high temperature. This eliminates the need for high-temperature extrusion and suppresses the generation of decomposed products.

The polyester resin composition preferably contains a polyester resin (B) other than the PBT resin (A) for the purpose of adjusting film formability during biaxial stretching and mechanical properties of the obtained film.
Examples of the polyester resin (B) include polyester resins such as PET, polyethylene naphthalate, polybutylene naphthalate, and polypropylene terephthalate, or isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, cyclohexane dicarboxylic acid, adipic acid, and azelain. PBT resin copolymerized with at least one dicarboxylic acid selected from the group consisting of acids and sebacic acid, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5- PBT resin copolymerized with at least one diol component selected from the group consisting of pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, and polycarbonate, isophthalic acid, orthophthalic acid , PBT resin copolymerized with at least one dicarboxylic acid selected from the group consisting of naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid, or 1,3-butanediol, From the group consisting of 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol and polycarbonate At least one resin selected from PET resins copolymerized with at least one selected diol component may be used.

Among them, resins whose main component is PET have a high melting point and excellent heat resistance, good compatibility with PBT resin, and excellent transparency, so PET resins or copolymerized PET resins are preferred, and PET resins are particularly preferred.

The amount of the polyester resin (B) added is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less, based on the entire polyester resin composition. % by mass or less. When the amount of the polyester resin (B) added is 25% by mass or less, the puncture strength can be further increased and the bag tear resistance is more excellent. Moreover, high transparency can be maintained.
The amount of the polyester resin (B) added can be 0% by mass or more, 5% by mass or more, 10% by mass or more based on the entire polyester resin composition.

The lower limit of the intrinsic viscosity of the polyester resin (B) is preferably 0.5 dl/g, more preferably 0.6 dl/g, and still more preferably 0.8 dl/g. The upper limit of the intrinsic viscosity of the polyester resin (B) is preferably 1.3 dl/g. By setting the intrinsic viscosity of the polyester resin (B) within the above numerical range, it becomes possible to mix it better with the PBT resin (A).

The biaxially oriented polyester film contains conventionally known additives such as lubricants, stabilizers, colorants, antioxidants, antistatic agents, ultraviolet absorbers, etc., in addition to the polyester resin composition. You can.

When the entire biaxially oriented polyester film is 100% by mass, the content of the polyester resin composition is preferably 99.5% by mass or more, more preferably 99.6% by mass or more, and 99.7% by mass or more. is even more preferable.
The content of the polyester resin composition is preferably 100% by mass or less, more preferably 99.9% by mass or less, and further preferably 99.8% by mass or less, when the entire biaxially oriented polyester film is 100% by mass. preferable.

The lubricant can adjust the coefficient of dynamic friction of the film, and includes inorganic lubricants such as silica, calcium carbonate, and alumina, and organic lubricants. Silica and calcium carbonate are more preferred, and silica is particularly preferred since it reduces haze. These can provide transparency and slipperiness.

The lower limit of the lubricant content in the biaxially oriented polyester film is preferably 100 mass ppm, more preferably 800 mass ppm. By setting the content to 100 mass ppm or more, slipperiness can be improved.
The upper limit of the content of the lubricant is preferably 20,000 mass ppm, more preferably 1,000 mass ppm, and particularly preferably 1,800 mass ppm. Transparency can be maintained by controlling the content to 20,000 mass ppm or less.

[Characteristics of biaxially oriented polyester film]
As described above, the biaxially oriented polyester film satisfies the following requirement (1).
(1) The puncture strength of the biaxially oriented polyester film measured by a puncture test according to JIS-Z1707 is 0.50 N/μm or more.
The puncture strength is preferably 0.55 N/μm or more, more preferably 0.60 N/μm or more. Since the puncture strength is 0.50 N/μm or more, good bag breakage resistance can be achieved.
Further, the piercing strength is preferably 0.90 N/μm or less, more preferably 0.85 N/μm or less, and even more preferably 0.80 N/μm or less. When it is 0.9 N/μm or less, the thermal shrinkage rate is suppressed and the thermal stability is excellent.
In addition, in this specification, "the puncture strength is 0.50 N/μm or more" means that "the puncture strength is 0.50 N/μm or more" in any part of the biaxially oriented polyester film.

Further, as described above, the biaxially oriented polyester film satisfies the following requirement (2).
(2) In the width direction of the biaxially oriented polyester film, samples were taken at positions 10 mm from the left and right edges toward the center, and the highest value of the densities measured according to JIS-K7112 was 1. .40g/ ^cm3 or less.
The density (the highest value among the densities) is preferably 1.39 g/cm ³ , more preferably 1.38 g/cm ³ . Since the density is 1.4 g/cm ³ or less, crystallization at the edges is suppressed. As a result, it is possible to suppress excessive stress at the end portions in the stretching step when producing the biaxially oriented polyester film, and film formability can be improved.
Further, the density is preferably 1.28 g/cm ³ or more, more preferably 1.29 g/cm ³ or more, and even more preferably 1.30 g/cm ³ or more. If it is 1.28 g/cm ³ or more, the crystallinity will be moderately high and the mechanical strength will be better.
In addition, if the density of the edge (the density of the part sampled at a position 10 mm from the left and right edges toward the center) is 1.4 g/ ^cm3 or less, it is natural that the density is closer to the center than the sampling point. The density satisfies 1.4 g/cm ³ or less.

Further, as described above, the biaxially oriented polyester film satisfies the following requirement (3).
(3) The intrinsic viscosity of the biaxially oriented polyester film is 0.7 dl/g or more.
The intrinsic viscosity is preferably 0.75 dl/g or more, more preferably 0.80 dl/g or more. Since the intrinsic viscosity is 0.7 dl/g or more, crystallization of the unstretched sheet is suppressed when the resin composition for producing a biaxially oriented polyester film is cast on a cooling roll to obtain an unstretched sheet. This makes it possible to prevent the yield stress from becoming too high, especially at the thick end portions. As a result, it can be made difficult to break during the stretching process.
Further, the intrinsic viscosity is preferably 1.20 dl/g or less, more preferably 1.15 dl/g or less, even more preferably 1.10 dl/g or less. When the intrinsic viscosity is 1.20 dl/g or less, stress during stretching does not become too high and film formability becomes better.

The biaxially oriented polyester film was sampled at a position 10 mm from the left and right ends toward the center in the width direction of the biaxially oriented polyester film, and the total reflection method using the Fourier transform infrared spectroscopy spectrum intensity was performed. When calculating the ratio A/B of the absorption intensity A of the peak at 1450 ± 10 cm ^-1 and the absorption intensity ^B of the peak 1410 ± 10 cm -1 obtained using is preferred.
The ratio A/B (the highest value of the ratio A/B) is more preferably 0.61 or less, and even more preferably 0.60 or less. When the ratio A/B is 0.62 or less, crystallinity does not become too high, stress during stretching is suppressed, and breakage becomes difficult.
The ratio A/B is preferably 0.52 or more, more preferably 0.53 or more, and still more preferably 0.54 or more. If it is 0.52 or more, the crystallinity will not be too low and the mechanical strength will be better.
Incidentally, if the ratio A/B of the B side of the biaxially oriented polyester film is 0.62 or less, the ratio A/B of the F side naturally also satisfies 0.62 or less.

The biaxially oriented polyester film preferably has a plane orientation degree ΔP of 0.145 to 0.160. The plane orientation degree ΔP is more preferably 0.1455 or more, and still more preferably 0.146 or more. When it is 0.145 or more, the planar orientation is suitably high, the puncture strength is sufficient, and the bag tear resistance is excellent.
The plane orientation degree ΔP is more preferably 0.157 or less, still more preferably 0.154 or less. When it is 0.160 or less, the thermal shrinkage rate can be maintained low and the thermal stability can be improved.

The lower limit of the heat shrinkage rate after heating the biaxially oriented polyester film at 150° C. for 15 minutes in the MD direction is preferably 0.5%. More preferably it is 0.8%, still more preferably 1.2%. When the content is 0.5% or more, puncture strength can be increased and bag tear resistance can be maintained at a high level.
The upper limit of the heat shrinkage rate of the biaxially oriented polyester film after heating at 150° C. for 15 minutes in the MD direction is preferably 3.5%. More preferably it is 3.0%, still more preferably 2.5%. When it is 3.5% or less, it is possible to suppress the film from shrinking significantly when heat is applied in post-processing, and processing becomes easier.

The lower limit of the thickness of the biaxially oriented polyester film is preferably 5 μm. More preferably, it is 7 μm, and still more preferably 9 μm. When the thickness is 5 μm or more, the film can have sufficient strength.
The upper limit of the thickness of the biaxially oriented polyester film is preferably 40 μm. More preferably, it is 30 μm, and still more preferably 20 μm.

The biaxially oriented polyester film preferably has the same composition throughout the film.

A printed layer may be laminated on the biaxially oriented polyester film.
As the printing ink forming the printing layer, aqueous and solvent-based resin-containing printing inks can be preferably used. Examples of resins used in the printing ink include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink contains known antistatic agents, light blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, antifoaming agents, crosslinking agents, anti-blocking agents, antioxidants, etc. It may also contain additives.

The printing method for providing 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, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

In addition, the biaxially oriented polyester film 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, or a known anchor coating. It may also be treated, printed, decorated, etc.

A gas barrier layer such as an inorganic thin film layer or a metal foil such as aluminum foil can be provided on at least one side of the biaxially oriented polyester film.

When an inorganic thin film layer is used as a gas barrier layer, the inorganic thin film layer is a thin film made of a metal or an inorganic oxide. The material 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 oxides such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide are used. Preferred examples include In particular, a composite oxide of silicon oxide and aluminum oxide is preferred from the standpoint 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 such that Al is in a range of 20 to 70% by weight of the metal content. When the Al concentration is 20% or more, water vapor gas barrier properties can be further improved. On the other hand, when it is 70% or less, the inorganic thin film layer can be made soft, and it is possible to prevent the film from being destroyed and the gas barrier properties from decreasing during secondary processing such as printing or lamination. Note that silicon oxide herein refers to various silicon oxides such as SiO and SiO ₂ or mixtures thereof, and aluminum oxide refers to various aluminum oxides such as AlO and Al ₂ O ₃ or mixtures thereof.

The thickness of the inorganic thin film layer is usually 1 to 100 nm, preferably 5 to 50 nm. When the thickness of the inorganic thin film layer is 1 nm or more, more satisfactory gas barrier properties can be easily obtained. On the other hand, a thickness of 100 nm or less is advantageous in terms of bending resistance and manufacturing cost.

There are no particular restrictions on the method for forming the inorganic thin film layer, and known vapor deposition methods such as vacuum evaporation, sputtering, physical vapor deposition (PVD) such as ion plating, or chemical vapor deposition (CVD) may be used. Laws may be adopted as appropriate. Hereinafter, a typical method for forming an inorganic thin film layer will be explained using a silicon oxide/aluminum oxide thin film as an example. For example, when employing a vacuum evaporation method, a mixture of SiO ₂ and Al ₂ O ₃ or a mixture of SiO ₂ and Al is preferably used as the evaporation raw material. Particles are usually used as these vapor deposition raw materials, and in this case, the size of each particle is preferably such that the pressure during vapor deposition does not change, and the preferable particle size is 1 mm to 5 mm. For heating, methods such as resistance heating, high frequency induction heating, electron beam heating, laser heating, etc. can be adopted. It is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc. as a reactive gas, or to adopt reactive vapor deposition using means such as ozone addition or ion assist. Furthermore, the film forming conditions can also be changed arbitrarily, such as by applying a bias to the object to be deposited (the laminated film to be subjected to vapor deposition), heating or cooling the object to be deposited. The evaporation material, reaction gas, bias of the evaporation target, heating/cooling, etc. can be similarly changed when sputtering or CVD is employed. Furthermore, a printed layer may be laminated on the inorganic thin film layer.

In this embodiment, it is preferable to provide a protective layer on the gas barrier layer. The gas barrier layer made of metal oxide is not a completely dense film, but is dotted with minute defects. By coating a specific protective layer resin composition described below on the metal oxide layer to form a protective layer, the resin in the protective layer resin composition penetrates into the defective parts of the metal oxide layer, As a result, the effect of stabilizing gas barrier properties can be obtained. In addition, by using a material with gas barrier properties for the protective layer itself, the gas barrier performance of the laminated film can be greatly improved.

Examples of the protective layer include urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, polybutadiene-based resins, etc., to which curing agents such as epoxy-based, isocyanate-based, and melamine-based resins are added. . Examples of solvents used in forming the protective layer 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 acetic acid. Examples include ester solvents such as butyl; polyhydric alcohol derivatives such as ethylene glycol monomethyl ether, and the like.

The above-mentioned urethane resin has flexibility because the polar groups of the urethane bond interact with the inorganic thin film layer and the presence of an amorphous part, so it suppresses damage to the inorganic thin film layer even when bending load is applied. This is preferable because it can be done.
The acid value of the urethane resin is preferably within the range of 10 to 60 mgKOH/g. It is more preferably within the range of 15 to 55 mgKOH/g, and even more preferably within the range of 20 to 50 mgKOH/g. When the acid value of the urethane resin is within the above range, the liquid stability improves when it is made into an aqueous dispersion, and the protective layer can be deposited uniformly on the highly polar inorganic thin film, resulting in a good coat appearance. becomes.

The urethane resin described above 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 moist heat treatment process (temperature raising, temperature retention, and temperature cooling).

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

In this embodiment, the proportion of aromatic or araliphatic diisocyanate in the urethane resin is preferably in the range of 50 mol% or more (50 to 100 mol%) based on 100 mol% of the polyisocyanate component. The proportion of the total amount of aromatic or araliphatic 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. When the total amount of aromatic or araliphatic diisocyanate is 50 mol% or more, better gas barrier properties can be obtained.

The urethane resin preferably has a carboxylic acid group (carboxyl group) from the viewpoint of improving 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 or dimethylolbutanoic acid may be introduced as a copolymerization component as a polyol component. Moreover, if a carboxylic acid group-containing urethane resin is synthesized and then neutralized with a salt forming agent, an aqueous dispersion of the urethane resin can be obtained. Specific examples of salt forming agents include ammonia, trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine; -alkylmorpholines, N-dialkylalkanolamines such as N-dimethylethanolamine, N-diethylethanolamine, and the like. These may be used alone or in combination of two or more.

A layer of another material may be laminated on the biaxially oriented polyester film, and this can be done by laminating the biaxially oriented polyester film after it is produced or by laminating it during film production.

The biaxially oriented polyester film can be used as a packaging material, for example, by providing an inorganic vapor deposited layer on the biaxially oriented polyester film and further forming a heat-sealable resin layer called a sealant (also referred to as a sealant layer). . The heat-sealable resin layer is usually formed by extrusion lamination or dry lamination. The thermoplastic polymer forming the heat-sealable resin layer may be any one that can sufficiently exhibit sealant adhesive properties, such as polyethylene resins such as HDPE, LDPE, and LLDPE, and polypropylene resins. Ethylene-vinyl acetate copolymer, ethylene-α-olefin random copolymer, ionomer resin, etc. can be used.

The sealant layer may be a single layer film or a multilayer film, and may be selected depending on the required function. For example, in terms of imparting moisture resistance, a multilayer film in which a resin such as ethylene-cyclic olefin copolymer or polymethylpentene is interposed can be used. The sealant layer may also contain various additives such as flame retardants, slip agents, anti-blocking agents, antioxidants, light stabilizers, and tackifiers.
The thickness of the sealant layer is preferably 10 to 100 μm, more preferably 20 to 60 μm.

The biaxially oriented polyester film can be used in the packaging field of foods, medicines, industrial products, and the like. In particular, the biaxially oriented polyester film can be used as a base film (base layer) of a packaging laminate. The layer structure of the packaging laminate is, for example, base material layer/gas barrier layer/protective layer, base material layer/gas barrier layer/protective layer/adhesive layer/sealant layer, base material Layer / Gas barrier layer / Protective layer / Adhesive layer / Resin layer / Adhesive layer / Sealant layer, base layer / Adhesive layer / Resin layer / Gas barrier layer / Protective layer / Adhesive layer / Sealant layer, Base layer / Gas barrier layer/protective layer/printed layer/adhesive layer/sealant layer, base layer/printed layer/gas barrier layer/protective layer/adhesive layer/sealant layer, base layer/gas barrier layer/protective layer/adhesive layer/ Resin layer / Printing layer / Adhesive layer / Sealant layer, Base material layer / Adhesive layer / Resin layer / Printing layer / Gas barrier layer / Protective layer / Adhesive layer / Sealant layer, Base material layer / Printing layer / Gas barrier layer / Protective layer / adhesive layer / resin layer / adhesive layer / sealant layer, base material layer / printing layer / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, base material layer / adhesive Examples include layer/resin layer/gas barrier layer/protective layer/printing layer/adhesive layer/sealant layer.

A laminate using the biaxially oriented polyester film can be suitably used for packaging products, various label materials, lid materials, sheet molded products, laminated tubes, and the like. In particular, it is used for packaging bags (for example, pillow bags, pouches such as standing pouches and four-sided pouches). The thickness of the laminate can be appropriately determined depending on its use. For example, it is used in the form of a film or sheet having a thickness of about 5 to 500 μm, preferably about 10 to 300 μm.

[Method for manufacturing biaxially oriented polyester film]
As a suitable method for obtaining the biaxially oriented polyester film, a T-die method is preferable from the viewpoint of thickness accuracy in the width direction. In the inflation method, it is difficult to increase the stretching ratio due to the manufacturing method, and thickness defects in the width direction are likely to occur.
In addition, as a preferred method for obtaining the biaxially oriented polyester film, conventionally, when casting the molten polyester resin composition onto a cooling roll, crystallization is carried out by forming eight or more layers of resin of the same composition using a static mixer or the like. A method has been proposed to obtain a uniform unstretched sheet by suppressing the amount of unstretched sheets. However, from the viewpoint of equipment simplicity and maintainability, the casting method described below to obtain a uniform unstretched sheet has been proposed. It is preferable to have a lamination of less than The number of laminated layers is more preferably three or less. In terms of equipment maintenance, a single layer is most preferred. When it is desired to improve the surface characteristics of the film, a layer structure of two types, two layers, two types, three layers, or three types, three layers is preferable.
Since PBT resin has a fast crystallization rate, the lower limit of the intrinsic viscosity of the resulting unstretched sheet is preferably 0.70 dl/g, more preferably 0.75 dl/g, and even more preferably 0.80 dl/g. and particularly preferably 0.90 dl/g. When it is 0.70 dl/g or more, crystallization during casting is suppressed, and the yield stress of the unstretched sheet becomes low. In particular, the yield stress at the thick edges is reduced. As a result, it tends to be less likely to break during stretching.
The upper limit of the intrinsic viscosity of the resulting unstretched sheet is preferably 1.2 dl/g, more preferably 1.1 dl/g. If it is 1.2 dl/g or less, the stress during stretching will not become too high and the film formability will be better.

The lower limit of the die temperature is preferably 240°C, more preferably 245°C, particularly preferably 250°C. When the temperature is 240° C. or higher, the discharge becomes more stable and the thickness can be made more uniform.
Moreover, when the temperature is 240° C. or higher, it is possible to prevent the PET resin that has remained in the resin melt extrusion process from becoming an unmelted substance and mixing into the film, thereby impairing the quality of the film. The upper limit of the resin melting temperature is preferably 280°C, more preferably 275°C, and most preferably 270°C. When the temperature is 280° C. or lower, decomposition of the resin can be suppressed and the film can be prevented from becoming brittle. Further, the progress of crystallization during casting can be suppressed, and film formability can be improved.
The upper limit of the die temperature is preferably 280°C, more preferably 275°C or less, still more preferably 270°C or less. When the temperature is 280° C. or lower, it is possible to prevent the thickness from becoming non-uniform. Furthermore, it is possible to suppress deterioration of the resin and poor appearance due to die lip stains and the like. Further, it is possible to suppress a decrease in the intrinsic viscosity of the obtained film. Further, the progress of crystallization during casting is suppressed, and film formability becomes better.

The lower limit of the rotation speed of the screw in the resin melt extrusion process is preferably 70 rpm, more preferably 80 rpm, and particularly preferably 90 rpm. When the speed is 70 rpm or more, the discharge becomes more stable and the thickness becomes more uniform. Further, the resin can be mixed more thoroughly, and appearance defects can be further suppressed.
The upper limit of the rotation speed of the screw in the resin melt extrusion process is preferably 150 rpm, more preferably 130 rpm, and particularly preferably 110 rpm. When the speed is 150 rpm or less, progress of decomposition of the molten resin due to shear heat generation can be suppressed, and a decrease in the intrinsic viscosity of the obtained film can be suppressed. Further, the progress of crystallization during casting is suppressed, and film formability becomes better.

The upper limit of the cooling roll temperature is preferably 40°C, more preferably 10°C or less. When the temperature is 40° C. or lower, the degree of crystallinity when the molten polyester resin composition is cooled and solidified will not become too high, making stretching easier. Moreover, the lamination strength can be increased, and the bag breakage resistance can be improved.
The lower limit of the chill roll temperature is preferably 0°C. When the temperature is 0°C or higher, the effect of suppressing crystallization when the molten polyester resin composition is cooled and solidified can be sufficiently exhibited. Further, 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 to prevent dew condensation.

When a molten polyester resin composition is cast on the surface of a cooling roll, the temperature of the surface of the cooling roll increases because the high temperature resin comes into contact with the surface. Normally, chill rolls are cooled by running cooling water through pipes inside them, but the surface of the chill roll can be improved by ensuring a sufficient amount of cooling water, by arranging the pipes, and by performing maintenance to prevent sludge from adhering to the pipes. It is necessary to reduce the temperature difference in the width direction. In particular, when a method of obtaining a uniform unstretched sheet by multilayering (for example, 8 or more layers) is not used, care must be taken because crystallization of the unstretched sheet tends to proceed.
At this time, the thickness of the unstretched sheet is preferably in the range of 15 to 2,500 μm. More preferably, it is 500 μm or less, and still more preferably 300 μm or less.

The time from when the molten polyester resin composition is discharged from the die until it touches the cooling roll (hereinafter also referred to as contact time) is preferably within the range of 0.1 to 1.0 seconds, and 0.2 to 0.5 seconds. More preferably, it is within seconds. The contact time is a value obtained by (air gap)/(discharge speed). Here, the air gap refers to the distance between the discharge port 12 and the surface of the cooling roll 20.

In order to reduce the degree of crystallinity of the unstretched sheet and improve stretchability (film forming properties), after casting the resin composition for producing a biaxially oriented polyester film onto a cooling roll (after step A), cooling is performed. It is preferable that the B side of the unstretched sheet on the roll is also rapidly cooled.
Furthermore, in order to further improve the stretchability, it is preferable to rapidly cool the edges of the B side of the unstretched sheet more strongly than the center. Specifically, when the full width of the unstretched sheet is 100%, the temperature of the wind blown at the center is X, and the temperature blown at both ends is Y, then X is 15 ° C. or less, and , it is preferable that the temperature of the Y is lower than the temperature of the X. If the edge of the unstretched sheet is thicker than the center,
Further, the thickness of the end portions of the unstretched sheet is often thicker than the center portion. Therefore, by rapidly cooling the end portions more strongly than the center portion, crystallization can be suppressed to the same extent as the center portion, and film formability can be improved. Although the method of rapid cooling is not particularly limited, a method of blowing cooling air using a multi-duct is preferred from the viewpoint of equipment simplicity and maintainability.
The temperature of X is more preferably 5°C or lower. The temperature of the above-mentioned X is preferably -5°C or higher. When the above-mentioned X is −5° C. or higher, a sufficient effect of suppressing crystallization of the B side of the unstretched sheet can be obtained.
Preferably, the edge portion is at least a region within 10% of the edge. The edge portion is more preferably an area within 15% of the edge, still more preferably an area within 20% of the edge, and particularly preferably an area within 25% of the edge.

The temperature of Y is preferably 10°C or less, more preferably 5°C or less. When the temperature of Y is 10° C. or less, the degree of crystallinity at the B-side edge of the unstretched sheet does not become too high, and film formability becomes better. The temperature of Y is preferably −5° C. or higher. When the temperature of Y is −5° C. or higher, a sufficient effect of suppressing crystallization of the B side of the unstretched sheet can be obtained.

FIG. 1 is a schematic front view for explaining a method of blowing cooling air from a multi-duct onto the B side of an unstretched sheet on a cooling roll, and FIG. 2 is a side view thereof.
As shown in FIGS. 1 and 2, the die 10 is arranged such that the discharge port 12 faces the surface of the cooling roll 20. The distance (shortest distance) between the discharge port 12 and the surface of the cooling roll 20 is not particularly limited, but is generally about 2 cm to 10 cm.
Further, a multi-duct 30 is arranged on the outer peripheral surface of the cooling roll 20.
The position of the multi-duct 30 is determined by the rotation direction of the cooling roll 20 (clockwise rotation direction in FIG. 2) when the position of the die 10 is set at 0° with respect to the center of the cooling roll 20 in the side view (FIG. 2). It is preferable that the angle is set within a range of 0 to 45 degrees, and more preferably within a range of 10 to 35 degrees. When the multi-duct 30 is arranged within the above range, it becomes possible to cool the B side of the unstretched sheet 40 cast onto the cooling roll 20 immediately after casting.
Further, the time from the time when the resin composition for producing a biaxially oriented polyester film is cast (touched) on the cooling roll until the wind is blown onto the part concerned is preferably within 2.0 seconds.1. The time is more preferably within 0 seconds, and even more preferably within 0.5 seconds. The time from the time when the resin composition for producing a biaxially oriented polyester film is cast (touched) on the cooling roll to when the wind is blown to the part concerned (until the part moves directly under the multi-duct 30) ) is within 2.0 seconds, it becomes possible to cool the B side of the unstretched sheet 40 immediately after casting.

The width of the multi-duct 30 (length in the left-right direction in FIG. 1) is preferably greater than or equal to the width of the unstretched sheet 40 to be cast. By setting the width of the multi-duct 30 to be equal to or greater than the width of the unstretched sheet 40 to be cast, it becomes easy to obtain a sufficient crystallization suppressing effect up to the end of the B side of the unstretched sheet 40.

The multi-duct 30 has a configuration that can make the temperature of the air blown at the center different from the temperature blown at the 20% left end portion and the 20% right end portion when the unstretched sheet full width is 100%. It is preferable that Specifically, there is a method in which the outlet of the multi-duct 30 is divided into a plurality of sections by a partition plate or the like, and air at different temperatures is blown from each outlet. The manner in which the air outlets are divided is not particularly limited, and may be equally divided, or each air outlet may have a different width.

An example of a multi-duct is shown in Figure 3. FIG. 3 is a bottom view (view from the cooling roll surface side) showing an example of the multi-duct. In the multi-duct 30 according to this embodiment, the width is set to be the same as that of the unstretched sheet 40 (FIG. 2), and as shown in FIG. It is divided into 5 parts. Specifically, the air outlet of the multi-duct 30 is divided into air outlets 31-1 to 31-5 in order from the left side to the right side in FIG.

The vertical width (length in the vertical direction in FIG. 1) of the multi-duct 30 is preferably 30 cm or more and 80 cm or less, and more preferably 50 cm or more and 60 cm or less.
Further, the speed at which the unstretched sheet 40 moves on the cooling roll 20 is preferably 20 m/min to 100 m/min, more preferably 40 m/min to 80 m/min.
By setting the vertical width of the multi-duct 30 within the numerical range described above and the speed of the unstretched sheet 40 within the numerical range described above, a suitable amount of cooling air can be blown onto the B side of the unstretched sheet 40.

The upper limit of the height of the multi-duct 30 from the cooling roll 20 is 20 cm or less, more preferably 10 cm or less. When the thickness is 20 cm or less, the cooling efficiency is improved, and the effect of suppressing crystallization at the end portions of the unstretched sheet 40 can be sufficiently obtained.
The lower limit of the height of the multi-duct 30 from the cooling roll 20 is not particularly limited, but a range that does not contact the unstretched sheet 40 is desirable.

The upper limit of the wind speed of the cooling air from the multi-duct 30 is preferably 200 m/min, more preferably 180 m/min or less. When the speed is 200 m/min or less, it is possible to prevent the grounding point from shaking due to the cooling air when casting the molten sheet-forming resin composition.
The lower limit of the cooling air speed is preferably 50 m/min. When the speed is 50 m/min or more, the effect of suppressing crystallization at the end portions of the unstretched sheet 40 can be sufficiently obtained.

Among the above-mentioned methods, the method for producing a biaxially oriented polyester film according to the present embodiment includes:
Step A of casting a resin composition for producing a biaxially oriented polyester film onto a cooling roll to form an unstretched sheet;
a step B of blowing wind on the unstretched sheet on the cooling roll,
In the step B, when the total width of the unstretched sheet is 100%, the temperature of the wind blown at the center is X, and the temperature blown at both ends is Y, the above X is 15 ° C. or less, and , said Y is at a lower temperature than said X,
Preferably, the edge portion includes at least a region within 10% of the edge.

Next, the stretching method will be explained. The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching, and is not particularly limited.

The lower limit of the stretching temperature in the longitudinal direction (hereinafter also referred to as MD direction) is preferably 55°C, more preferably 60°C. When the temperature is 55°C or higher, breakage can be further suppressed. Furthermore, it is possible to prevent the orientation in the longitudinal direction from becoming too strong, and to suppress the thermal shrinkage rate in the MD direction from increasing. The upper limit of the stretching temperature in the MD direction is preferably 100°C, more preferably 95°C. When the temperature is 100° C. or lower, sufficient orientation can be obtained, and the mechanical properties can be further improved.

The lower limit of the stretching ratio in the MD direction is preferably 2.5 times, particularly preferably 2.7 times. When it is 2.5 times or more, sufficient orientation can be provided, and the mechanical properties can be further improved. Moreover, when it is 2.5 times or more, thickness unevenness can be suppressed, and loosening of the film roll can be prevented.
The upper limit of the stretching ratio in the MD direction is preferably 3.8 times, more preferably 3.6 times, particularly preferably 3.4 times. When it is 3.8 times or less, the effect of improving mechanical strength and thickness unevenness can be sufficiently obtained.

The lower limit of the stretching temperature in the width direction (hereinafter also referred to as TD direction) is preferably 55°C, more preferably 60°C. When the temperature is 55°C or higher, breakage can be made less likely to occur. Further, it is possible to prevent the orientation in the lateral direction from becoming too strong and to suppress the thermal shrinkage rate in the TD direction from increasing.
The upper limit of the stretching temperature in the TD direction is preferably 100°C, more preferably 95°C. When the temperature is 100° C. or lower, sufficient orientation can be obtained, and the mechanical properties can be further improved.

The lower limit of the stretching ratio in the TD direction is preferably 3.5 times, more preferably 3.6 times, particularly preferably 3.7 times. If it is 3.5 times or more, the degree of orientation in the width direction can be increased, and the mechanical strength can be increased.
The upper limit of the stretching ratio in the TD direction is preferably 5.0 times, more preferably 4.6 times, particularly preferably 4.3 times. When it is 5.0 times or less, the effect of improving mechanical strength and thickness unevenness can be sufficiently obtained.

The lower limit of the heat setting temperature is preferably 170°C, more preferably 180°C. When the temperature is 170° C. or higher, the thermal shrinkage rate can be further reduced.
The upper limit of the heat setting temperature is preferably 220°C. When the temperature is 220° C. or lower, melting of the film and reduction in puncture strength can be suppressed.

The lower limit of the relaxation rate is preferably 0.5%. When it is 0.5% or more, the heat shrinkage rate in the TD direction can be kept low.
The upper limit of the relaxation rate is preferably 10%. If it is 10% or less, sagging can be prevented from occurring and flatness can be improved.

The lower limit of the temperature in the relaxing step is preferably 130°C, more preferably 150°C. When the temperature is 130° C. or higher, the film will sufficiently shrink when relaxing, making it possible to sufficiently obtain the effect of reducing the thermal shrinkage rate.
The upper limit of the relaxation step temperature is preferably 190°C, more preferably 170°C. When the temperature is 190° C. or lower, deterioration of the flatness of the film due to wrinkles etc. can be suppressed.

The method for manufacturing a biaxially oriented polyester film according to this embodiment has been described above.

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples. The film was evaluated using the following measurement method.
[Film thickness]
It was measured using a dial gauge in accordance with JIS K7130-1999 A method.

[Film puncture strength]
Samples measuring 5 mm in length and 5 mm in width were cut out from the films produced in Examples and Comparative Examples, each having a center position in the width direction of the film and a position 10 mm from the left and right ends toward the center.
The puncture strength of the polyester film was calculated by converting the value measured by the test method described in JIS-Z1707 into 1 μm using the following formula.
Puncture strength (N/μm) = Measured puncture strength / Film thickness

[Fourier transform infrared spectroscopy (total internal reflection method)]
Samples measuring 5 mm in length and 5 mm in width were cut out from the films produced in Examples and Comparative Examples, each measuring 5 mm in length and 5 mm in width, centered at a position 10 mm from the left and right ends in the width direction of the film toward the center.
Using Varian 3100FT-IR manufactured by Varian, a diamond medium crystal was brought into close contact with the surface layer of the film, and the spectral intensity was measured by the total reflection method while incident light parallel to the MD direction. The resolution of the spectrometer was 4 cm ⁻¹ and the number of spectral integrations was 64. The spectral intensity is the absorbance at each wavenumber. Calculated using the formula below. The measurement was performed on the B side.
Absorbance ratio (A/B) = Absorbance A (spectral intensity of the peak at 1450 ± 10 cm ^-1 ) / Absorbance B (spectral intensity of the peak at 1410 ± 10 cm ^-1 )

[Planar orientation degree ΔP of film]
Samples measuring 5 mm in length and 5 mm in width were cut out from the films produced in Examples and Comparative Examples, with the center at the center in the width direction of the film, and 10 mm from the left and right ends toward the center.
Regarding the sample, the refractive index in the longitudinal direction (Nx), the refractive index in the width direction (Ny), and the thickness direction were measured using an Abbe refractometer using sodium D ray as a light source and diiodomethane as a contact liquid according to JIS K 7142-1996 A method. The refractive index (Nz) of was measured, and ΔP was calculated using the following formula.
Planar orientation degree (ΔP) = [(Nx+Ny)/2]-Nz

[Intrinsic viscosity of film]
Samples measuring 5 mm in length and 5 mm in width were cut out from the films produced in Examples and Comparative Examples, with the center at the center in the width direction of the film, and 10 mm from the left and right ends toward the center.
The intrinsic viscosity of the sample was measured using an automatic viscosity measuring device "SS-600-L1" manufactured by Shiyama Scientific Instruments Manufacturing Co., Ltd. As the solvent solution, a mixed solution of p-chlorophenol/1,1,2,2-tetrachloroethane=6/4 (mass ratio) was used.

[Film density]
Samples measuring 5 mm in length and 5 mm in width were cut out from the films produced in Examples and Comparative Examples and centered at a position 10 mm from the left and right ends in the width direction of the film toward the center.
The density of the sample was measured by method D (density gradient method) of JIS K 7112. The measurement conditions were as follows. Table 1 shows the one with the highest measured value among the two samples at the left end and right end.
<Measurement conditions>
Gradient liquid: Calcium nitrate tetrahydrate Temperature inside gradient tube: 30℃
Sample size: 5mm x 5mm
Soaking time: 16 hours

[Preparation of laminate laminate for evaluation]
On the B side of the polyester film, apply a urethane two-component adhesive (Mitsui Chemicals, Inc., "Takelac (registered trademark) A525S" and "Takenate (registered trademark) A50") at a ratio of 13.5:1 (mass ratio). A 70 μm thick unstretched polypropylene film (“P1147” manufactured by Toyobo Co., Ltd.) was laminated as a heat-sealable resin layer by a dry lamination method using a polypropylene resin (formulated in A laminate laminate was obtained. Note that the thickness of the adhesive layer formed of the urethane-based two-component curing adhesive after drying was about 4 μm in all cases.

[Production of retort-processed bag products for evaluation]
Samples measuring 15 cm long and 15 cm wide were cut out from the laminate, centered at the center in the width direction, and 30 cm from the left and right ends toward the center.
Regarding the cut samples, two sheets were overlapped so that the sealant was on the inside, and three sides were heat-sealed at a sealing temperature of 160°C and a seal width of 1.0 cm to obtain a three-sided sealed bag with an inner dimension of 13 cm. .
The three-sided sealed bag was made by pasting together two sheets cut out from the center, pasting together two sheets cut out from the left side, and pasting together two sheets cut out from the right side.
After filling the resulting three-sided sealed bag with 250 mL of water, the fourth opening was closed by heat sealing to produce a four-sided sealed bag filled with water.
The resulting four-sided sealed bag filled with water was immersed in hot water at 130° C. for 30 minutes to obtain a retort-treated bag.

[Evaluation of bag breakage resistance]
The bag filled with the retorted water was dropped 10 times from a height of 100 cm onto a concrete plate with the bag side horizontal at a room temperature of 5°C and a relative humidity of 35%. The bags were dropped 10 times with their sides vertical, and the percentage of bags that did not break was calculated. The number of bags used in the test was 20 in both the horizontal and vertical directions.

[Evaluation of film formability]
When producing the films of each example and comparative example, the case where continuous film formation was possible without breakage for 30 minutes or more was evaluated as ○, and the case where breakage occurred at least once within 30 minutes was evaluated as ×.

[Example 1]
Using a single screw extruder, PBT resin (intrinsic viscosity 1.28 dl/g consisting of terephthalic acid//butanediol = 100//100 (mol%)) and PET resin (terephthalic acid//ethylene glycol = 100//100 ( After melting a resin composition for producing a biaxially oriented polyester film at 290°C, which has an intrinsic viscosity of 0.62 dl/g (mol%) and silica particle formulation), it was cast from a T-die at 250°C, and An unstretched sheet was obtained by blowing cold air from a multi-duct onto the B side while closely adhering it to a cooling roll at 0.degree. C. by electrostatic adhesion. The width of the obtained unstretched sheet was 160 cm. The multi-duct has a structure as shown in Fig. 1, and blows cold air at 10°C from the air outlets 31-1 and 31-5 (hereinafter also referred to as air outlets 1 and 5), and from the air outlets 31-2 to 31-4. Cold air at 15°C was blown from the air outlets (hereinafter also referred to as air outlets 2 to 4).
In this example, the widths of the air outlets 1 and 5 were each 40 cm, and the widths of the air outlets 2 to 4 were each 32 cm.
Of the unstretched sheet, air is blown from air outlet 1 or air outlet 5 up to a position 32 cm from the left and right edges toward the center, and air is blown from air outlets 2 to 4 further toward the center. The wind blew.
At this time, the vertical width of the multi-duct was 50 cm, and the moving speed of the unstretched sheet was 60 m/min.
Moreover, the time from the time when the resin composition for producing a biaxially oriented polyester film was cast on the cooling roll (the time when it touched) until the wind was blown onto the part was 0.5 seconds.
The content of silica particles in the resin composition for producing a biaxially oriented polyester film is 0.16 as a silica concentration when the resin composition for producing a biaxially oriented polyester film is taken as the whole (100% by mass). Mass%.

Next, the obtained unstretched sheet was stretched at a temperature of 70° C. in the longitudinal direction (MD direction) by a factor of 3.3, and then passed through a tenter at 80° C. in the width direction (TD direction) at a factor of 4.0. The film was stretched and subjected to a heat setting treatment at 200° C. for 3 seconds and a relaxation treatment of 9% for 1 second to obtain a biaxially oriented polyester film having a thickness of 15 μm. Table 1 shows the resin composition in the resin composition for producing a biaxially oriented polyester film and the film forming conditions. In addition, Table 1 shows the physical properties and evaluation results of the obtained film.

[Example 2-4]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1 except that the resin composition was changed as shown in Table 1. Table 1 shows the physical properties and evaluation results of the obtained film.

[Example 5]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1 except that the die temperature was changed as shown in Table 1. Table 1 shows the physical properties and evaluation results of the obtained film.

[Example 6]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1 except that the heat treatment temperature was changed as shown in Table 1. Table 1 shows the physical properties and evaluation results of the obtained film.

[Example 7]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 6 except that the resin composition was changed as shown in Table 1. Table 1 shows the physical properties and evaluation results of the obtained film.

[Comparative example 1]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1, except that the temperature of the cold air at the outlets 1 and 5 of the multi-duct was changed to the temperature listed in Table 1. The resulting film had poor film formability because the film edges had a high density and a large difference in crystallinity.

[Comparative example 2]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1, except that the time during which the molten resin was in contact with the cooling roll from the die was changed to the time shown in Table 1. The resulting film had poor film formability because the film edges had a high density and a large difference in crystallinity.

[Comparative example 3]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1 except that the die temperature was changed to the temperature listed in Table 1. The obtained film had a low inherent viscosity, a large density at the edges of the film, and a large difference in crystallinity, resulting in poor film formability and low puncture strength, resulting in poor bag breakage resistance.

[Comparative example 4]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1 except that the heat treatment temperature was changed to the temperature listed in Table 1. The obtained film had low puncture strength and had poor bag breakage resistance.

[Comparative example 5]
A biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a film in the same manner as in Example 1 except that the resin composition was changed to the ratio shown in Table 1. The obtained film had low puncture strength and had poor bag breakage resistance.

[Comparative example 6]
The film was formed in the same manner as in Example 1, except that the resin composition was changed to the ratio listed in Table 1, and the cold air temperature of the multi-duct outlets 1 and 5 was changed to the temperature listed in Table 1. A biaxially oriented polyester film having a thickness of 15 μm was obtained. The resulting film had poor film formability because the film edges had a high density and a large difference in crystallinity.

[Comparative Example 7]
In Example 1, a biaxially oriented polyester film having a thickness of 15 μm was obtained by forming a biaxially stretched film in the same manner as in Example 1, except that the B side of the unstretched film was not cooled by the multiduct. The resulting film had poor film formability because the film edges had a high density and a large difference in crystallinity.

10 Dice 12 Discharge port 20 Cooling roll 30 Multi-duct 31 (31-1, 31-2, 31-3, 31-4, 31-5) Air outlet 32 Partition plate 40 Unstretched sheet

Claims (5)

A polyester resin composition containing 75 to 100% by mass of polybutylene terephthalate resin (A),
A biaxially oriented polyester film characterized by satisfying the following requirements (1) to ( 4 ).
(1) The puncture strength of the biaxially oriented polyester film measured by a puncture test according to JIS-Z1707 is 0.50 N/μm or more.
(2) In the width direction of the biaxially oriented polyester film, samples were taken at positions 10 mm from the left and right edges toward the center, and the highest value of the densities measured according to JIS-K7112 was 1. .40g/ ^cm3 or less.
(3) The intrinsic viscosity of the biaxially oriented polyester film is 0.7 dl/g or more.
(4) In the width direction of the biaxially oriented polyester film, samples are taken at positions 10 mm from the left and right edges toward the center, respectively, and the results are obtained using the total reflection method using the Fourier transform infrared spectroscopy spectrum intensity. When the ratio A/B between the absorption intensity A of the peak at 1450 ±10 cm ^-1 and the absorption intensity B of the peak 1410±10 cm ^-1 was determined, the highest value was 0.62 or less. The biaxially oriented polyester film according to claim 1, wherein the polyester resin composition contains a polyester resin (B) other than the polybutylene terephthalate resin (A). The biaxially oriented polyester film according to claim 1 or 2, wherein the degree of plane orientation ΔP of the biaxially oriented polyester film is 0.145 to 0.160. Step A of casting a resin composition for producing a biaxially oriented polyester film onto a cooling roll to form an unstretched sheet;
a step B of blowing wind on the unstretched sheet on the cooling roll,
In the step B, when the total width of the unstretched sheet is 100%, the temperature of the wind blown at the center is X, and the temperature blown at both ends is Y, the above X is 15 ° C. or less, and , said Y is at a lower temperature than said X,
A method for producing a biaxially oriented polyester film, wherein the edge portion includes at least an area within 10% of the edge. The method for producing a biaxially oriented polyester film according to claim 4 , wherein the Y is 10°C or less.

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