JP2022039670A - Biaxially oriented polyester film for packaging - Google Patents

Abstract

To provide a biaxially oriented polyester film for packaging which is excellent in bag-tearing resistance even if the film is thin, and is excellent in transparency.SOLUTION: A biaxially oriented polyester film for packaging contains 80-100 mass% of a polyethylene terephthalate resin (A), and 0-20 mass% of a polyester resin (B) other than the polyethylene terephthalate resin (A), and has a plane orientation degree of 0.17 to 0.20 and a piercing strength of 0.76-1.00 N/μm, and a ratio a/b of tensile elongation at break (a) in a longitudinal direction of a film to tensile elongation at break (b) in a width direction thereof of 0.65-1.50.SELECTED DRAWING: None

Description

The present invention relates to a polyester film used in the packaging field of foods, pharmaceuticals, industrial products and the like. More specifically, the present invention relates to a biaxially oriented polyester film having excellent bag resistance and less burden on the environment even if it is thin.

Polyethylene terephthalate (hereinafter sometimes abbreviated as PET) is used in a wide range of fields such as food packaging and industrial products due to its excellent transparency, dimensional stability, mechanical properties, electrical properties, chemical resistance, etc. There is.
However, mechanical strength such as piercing strength and pinhole resistance may be insufficient. For example, packaging for relatively heavy foods and packaging for sharp contents may have insufficient piercing strength and pinhole resistance. It was sometimes used by laminating it with a nylon film or the like having excellent hole properties.

Polybutylene terephthalate (hereinafter, may be abbreviated as PBT) has been conventionally used as an engineering plastic because it has excellent mechanical properties, impact resistance, gas barrier properties, and chemical resistance. PBT has been used as a useful material as an engineering plastic because of its high productivity due to its high crystallization rate. However, when it is used as a stretched film, for example, crystallization deteriorates stretchability and transparency. rice field.

For example, in Patent Document 1, the weight ratio (a / b) of the PET resin (a) and the PBT resin (b) is 20 to 60/80 to 40, and the tensile elastic modulus in the longitudinal direction and the width direction of the film is 2. A polyester film for an inner bag of a can, which is characterized by having a modulus of 3 to 3.5 GPa, is disclosed.

However, since the stretch ratio of the polyester film is relatively low, it is expected that the piercing strength is insufficient. Therefore, for example, in the case of packaging for relatively heavy foods or packaging for sharp contents, there is a high possibility that the bag will be easily torn.

In Patent Document 2, the weight ratio (a / b) of the polyester resin (a) other than the PBT resin and the PBT resin (b) is 0 to 40/60 to 100, and the winding hardness of the surface layer of the film roll is 20 or more and 80. A biaxially oriented polyester film roll characterized by the following is disclosed.

The piercing strength is high, and it is expected that the bag will not tear easily and can be suitably used even in packaging for relatively heavy foods and packaging for sharp contents. However, it is considered that the PBT resin composition in the film is high and crystallization is likely to occur during film formation. Therefore, there is a high possibility that the transparency of the film will deteriorate and the printability will deteriorate.

Patent No. 6195765 JP-A-2020-12086

The present invention has been made against the background of the problems of the prior art. That is, an object of the present invention relates to a polyester film used in the packaging field of foods, pharmaceuticals, industrial products and the like. More specifically, it is an object of the present invention to obtain a biaxially oriented polyester film for packaging, which is thin but has excellent bag resistance and transparency.

As a result of diligent studies to achieve such an object, the present invention sets the blending ratio of PET resin and PBT resin in the film within the specified range and the surface orientation within the specified range, so that the bag is resistant to breakage even if it is thin. It has been found that a biaxially oriented polyester film for packaging having excellent properties and transparency can be obtained.

The present invention has the following configuration.
[1] The polyethylene terephthalate resin (A) is contained in an amount of 80 to 100% by mass, the polyester resin (B) other than the polyethylene terephthalate resin (A) is contained in an amount of 0 to 20% by mass, and the plane orientation is 0.17 to 0.20. Yes, the piercing strength measured in the piercing test according to JIS-Z1707 is 0.76 to 1.00 N / μm, and the tensile elongation at break (a) in the longitudinal direction and the tensile elongation at break in the width direction of the film. A biaxially oriented polyester film for packaging, wherein the ratio a / b of (b) is 0.65 to 1.50.
[2] The biaxially oriented polyester film for packaging according to [1], wherein the film thickness is 6 to 10 μm.
[3] The haze value is 2% or less, and the dynamic friction coefficient value when the front surface and the back surface of the film are brought into contact with each other and slid is 0.25 to 0.95 [1] or. The biaxially oriented polyester film for packaging according to [2].
[4] A laminated film in which a sealant film is laminated on the biaxially oriented polyester film for packaging according to any one of [1] to [3].
[5] The laminated film according to [4], wherein the sealant film is a polyolefin film.
[6] A packaging material using the laminated film according to [4] or [5].

The biaxially oriented polyester film for packaging of the present invention has a compounding ratio of PET resin and PBT resin in the film, and the film surface orientation is within a specified range under specific film forming conditions, so that the film surface orientation is within the specified range, so that even if it is thin, it is resistant to bag breakage. A biaxially oriented polyester film for packaging with excellent transparency and excellent transparency can be obtained.

Schematic diagram of a four-way seal bag for evaluation of openability

Hereinafter, the present invention will be described in detail.
The biaxially oriented polyester film for packaging of the present invention contains PET resin as a main component, and the content of PET resin is 80% by mass or more, preferably 85% by mass, and more preferably 90% by mass. Is. When the content is 80% by mass or more, the transparency of the biaxially oriented polyester film obtained becomes good, the film can be suitably used for printing, and the relatively inexpensive PET resin is the main constituent component, so that the cost is high. It is also cheaper in terms of.

The polyester resin (B) other than the PET resin (A) used in the biaxially oriented polyester film for packaging of the present invention can be contained for the purpose of adjusting the mechanical properties and stretchability of the biaxially oriented polyester film.
Examples of the polyester resin (B) other than the PET resin (A) include polyester resins such as PBT, polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT), and isophthalic acid, orthophthalic acid, and naphthalene. Polyester resin in which dicarboxylic acids such as dicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid are copolymerized, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl Examples thereof include polyester resins in which diol components such as glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol and polycarbonate diol are copolymerized.
Among them, PBT has excellent mechanical properties, and the stretchability is improved by adding a small amount. Further, it is preferable because it has good compatibility with PET resin and is excellent in transparency.

The amount of the polyester resin (B) other than the PET resin (A) added is 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. When the content is 20% by mass or less, the transparency of the biaxially oriented polyester film obtained becomes good, and it can be suitably used for printing. Further, as described above, by adding a small amount, the stretchability is improved, and stable film formation is possible even if the film is stretched at a high magnification.

The lower limit of the intrinsic viscosity of the PET resin (A) is preferably 0.45 dl / g, more preferably 0.50 dl / g, and most preferably 0.55 dl / g. By setting the content to 0.45 dl / g or more, the intrinsic viscosity of the obtained biaxially oriented polyester film can be maintained high, and the mechanical properties such as piercing strength can be enhanced.
The upper limit of the intrinsic viscosity of the PET resin (A) is preferably 0.80 dl / g, more preferably 0.75 dl / g, and most preferably 0.70 dl / g. By setting the content to 0.80 dl / g or less, it is possible to suppress the stress during stretching of the film from becoming too high, and to obtain good film forming properties.

In addition to the polyester resin composition, the biaxially oriented polyester film for packaging of the present invention contains conventionally known additives such as lubricants, stabilizers, colorants, antioxidants, antistatic agents, and ultraviolet absorbers. You may be doing it.

When the total content of the biaxially oriented polyester film for packaging of the present invention 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, and most. It is preferably 99.7% by mass.

The lubricant can adjust the dynamic friction coefficient of the film, and examples thereof include inorganic lubricants such as silica, calcium carbonate, and alumina, as well as organic lubricants. Silica and calcium carbonate are preferable, and porous silica is most preferable from the viewpoint of achieving both transparency and slipperiness.

The lower limit of the lubricant content in the biaxially oriented polyester film for packaging of the present invention is preferably 100 mass ppm, more preferably 300 mass ppm, and most preferably 500 mass ppm. When the amount is 100 mass ppm or more, the slipperiness of the film can be improved.
The upper limit of the lubricant content in the biaxially oriented polyester film for packaging of the present invention is preferably 10,000 mass ppm, more preferably 6000 mass ppm, and most preferably 2000 mass ppm. By setting the content to 10,000 mass ppm or less, the transparency of the film can be improved.

The method for obtaining the biaxially oriented polyester film for packaging of the present invention is not particularly limited, but the T-die method is preferable from the viewpoint of thickness accuracy. In the inflation method, the draw ratio is difficult to increase due to the manufacturing method, and thickness defects in the width direction may occur.

The upper limit of the resin melting temperature in the extruder is preferably 310 ° C, more preferably 300 ° C. When the temperature is 300 ° C. or lower, decomposition of the resin can be suppressed, the film can be prevented from becoming brittle, and deterioration of film quality due to heat-deteriorated substances can be prevented.
The lower limit of the resin melting temperature in the extruder is preferably 230 ° C, more preferably 240 ° C. When the temperature is 230 ° C. or higher, the resin can be extruded, the discharge is stable, and the thickness accuracy is good.

The upper limit of the cooling roll temperature is preferably 40 ° C., more preferably 20 ° C. or lower. When the temperature is 40 ° C. or lower, the degree of crystallization of the melted polyester resin composition when it is cooled and solidified does not become too high, stretching becomes easier, and deterioration of transparency due to crystallization can be suppressed.
The lower limit of the cooling 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. 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.

The thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm. It is more preferably 500 μm or less, and most preferably 300 μm or less.

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 in that respect, sequential biaxial stretching is preferable.

The lower limit of the stretching temperature in the longitudinal direction (hereinafter, also referred to as MD direction) is preferably 90 ° C, more preferably 95 ° C, and particularly preferably 100 ° C. When the temperature is 90 ° C. or higher, breakage can be further suppressed.
The upper limit of the stretching temperature in the MD direction is preferably 140 ° C., more preferably 135 ° C., and particularly preferably 130 ° C. When the temperature is 140 ° C. or lower, the degree of surface orientation can be increased and the piercing strength can be increased.

The lower limit of the draw ratio in the MD direction is preferably 2.8 times, more preferably 2.9 times, and particularly preferably 3.0 times. When it is 2.8 times or more, the degree of surface orientation can be increased and the piercing strength can be increased. Further, when it is 2.8 times or more, unevenness in thickness can be suppressed and loosening of the film roll can be prevented.
The upper limit of the draw ratio in the MD direction is preferably 4.5 times, more preferably 4.4 times, and particularly preferably 4.3 times. When it is 4.5 times or less, the effect of improving the mechanical strength and the thickness unevenness can be sufficiently obtained.

The lower limit of the stretching temperature in the width direction (hereinafter, also referred to as the TD direction) is preferably 100 ° C., more preferably 105 ° C., and particularly preferably 110 ° C. When the temperature is 100 ° C. or higher, fracture is less likely to occur.
The upper limit of the stretching temperature in the TD direction is preferably 140 ° C., more preferably 135 ° C., and particularly preferably 130 ° C. When the temperature is 140 ° C. or lower, the degree of surface orientation can be increased and the piercing strength can be increased.

The lower limit of the draw ratio in the TD direction is preferably 3.8 times, more preferably 3.9 times, and particularly preferably 4.0 times. When it is 3.8 times or more, the degree of surface orientation can be increased and the piercing strength can be increased.
The upper limit of the draw ratio in the TD direction is preferably 5.0 times, more preferably 4.9 times, and particularly preferably 4.8 times. When it is 5.0 times or less, the effect of improving the mechanical strength and the thickness unevenness can be sufficiently obtained.

The lower limit of the heat fixing temperature is preferably 170 ° C, more preferably 180 ° C, and particularly preferably 190 ° C. When the temperature is 170 ° C. or higher, the heat shrinkage rate can be made smaller.
The upper limit of the heat fixing temperature is preferably 240 ° C., more preferably 225 ° C., and particularly preferably 210 ° C. When the temperature is 240 ° C. or lower, the film can be prevented from melting, the degree of surface orientation can be increased, and the piercing strength can be increased.

The lower limit of the relaxation rate is preferably 0.5%, more preferably 1.0%, and particularly preferably 2.0%. 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%, more preferably 8%, and particularly preferably 6%. If it is 10% or less, it is possible to prevent slackening and the like, and it is possible to improve the flatness.

The lower limit of the thickness of the biaxially oriented polyester film for packaging of the present invention is preferably 3 μm, more preferably 5 μm, and particularly preferably 7 μm. The strength of the film can be maintained by setting it to 3 μm or more.
The upper limit of the thickness of the biaxially oriented polyester film for packaging of the present invention is preferably 40 μm, more preferably 20 μm, and particularly preferably 10 μm. By setting the thickness to 40 μm or less, it can be used as a packaging material for which the present invention is intended.
The biaxially oriented polyester film for packaging of the present invention can have an appropriate thickness depending on the type of packaging material, but can be thinner than the conventional polyester film.

The lower limit of the degree of surface orientation of the biaxially oriented polyester film for packaging of the present invention is preferably 0.170, more preferably 0.173, and particularly preferably 0.175. When the value is 0.170 or more, the piercing strength of the film can be increased, and for example, it can be suitably used for packaging for relatively heavy foods and packaging for sharp contents.
The upper limit of the degree of surface orientation of the biaxially oriented polyester film for packaging of the present invention is preferably 0.200, and more preferably 0.190. By setting it to 0.200 or less, heat shrinkage can be suppressed, and processing troubles due to film shrinkage in processes such as vapor deposition and printing can be reduced.

The lower limit of the puncture strength of the biaxially oriented polyester film for packaging of the present invention is 0.76 N / μm, preferably 0.78 N / μm, and more preferably 0.80 N / μm. When the content is 0.76 N / μm or more, for example, it can be suitably used for packaging for relatively heavy foods and packaging for sharp contents.
The upper limit of the puncture strength of the biaxially oriented polyester film for packaging of the present invention is preferably 1.00 N / μm, more preferably 0.97 N / μ, and particularly preferably 0.94 N / μm. By setting the temperature to 1.00 N / μm or less, heat shrinkage can be suppressed, and processing troubles due to film shrinkage in processes such as vapor deposition and printing can be reduced.

The lower limit of the ratio a / b of the tensile elongation at break (a) in the longitudinal direction and the tensile elongation at break (b) in the width direction of the biaxially oriented polyester film for packaging of the present invention is 0.65, preferably 0. It is 75, more preferably 0.85. When the value is 0.65 or more, for example, when the bag is opened from the notch of the bag-making product, the straightness of the tear is improved and the contents can be prevented from spilling.
The upper limit of the ratio a / b of the tensile elongation at break of the biaxially oriented polyester film for packaging of the present invention is 1.50. By setting the value to 1.50 or less, for example, when the bag is opened from the notch of the bag-making product, the straightness of the tear is improved and the contents can be prevented from spilling.

The upper limit of the haze of the biaxially oriented polyester film for packaging of the present invention is preferably 2.0%, more preferably 1.5%, and particularly preferably 1.0%. When it is 2.0% or less, the contents can be seen well and the printing can be seen clearly when it is made into a package, which is preferable.

The lower limit of the dynamic friction coefficient of the biaxially oriented polyester film for packaging of the present invention is preferably 0.2, more preferably 0.35. When it is set to 0.25 or more, the film slips appropriately and the winding quality of the film roll becomes good.
The upper limit of the dynamic friction coefficient of the biaxially oriented polyester film for packaging of the present invention is preferably 0.55, more preferably 0.53, and particularly preferably 0.51. By setting the value to 0.90 or less, the transparency can be increased as a result and the appearance is improved.

The lower limit of the heat shrinkage in the MD direction of the biaxially oriented polyester film for packaging of the present invention is preferably 1.0%, more preferably 1.2%, and particularly preferably 1.4%. By setting it to 1.0% or more, the piercing strength can be increased.
The upper limit of the heat shrinkage in the MD direction of the biaxially oriented polyester film for packaging of the present invention is preferably 5.0%, more preferably 4.8%, and particularly preferably 4.6%. By setting the content to 5.0% or less, it is possible to reduce processing troubles due to film shrinkage in processes such as vapor deposition and printing.

The lower limit of the heat shrinkage in the TD direction of the biaxially oriented polyester film for packaging of the present invention is preferably -1.0%, more preferably -0.8%, and particularly preferably -0.6%. be. The piercing strength can be increased by setting it to -1.0% or more.
The upper limit of the heat shrinkage in the TD direction of the biaxially oriented polyester film for packaging of the present invention is preferably 4.0%, more preferably 3.8%, and particularly preferably 3.6%. By setting the content to 4.0% or less, it is possible to reduce processing troubles due to film shrinkage in processes such as vapor deposition and printing.

A printing layer may be laminated on the biaxially oriented polyester film for packaging of the present invention. 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 additives such as antistatic agents, light blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoamers, cross-linking agents, blocking agents, antioxidants, etc. The agent may be contained.

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.

The biaxially oriented polyester film for packaging of the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment as long as the object of the present invention is not impaired, and known anchors. It may be coated, printed, decorated or the like.

The biaxially oriented polyester film for packaging of the present invention may be provided with a gas barrier layer such as an inorganic thin film layer or a metal foil such as an aluminum foil as long as the object of the present invention is not impaired.

When an inorganic thin film layer is used as the gas barrier layer, 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 oxides such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide. Is preferably mentioned. 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% in terms of mass ratio of metal content. On the other hand, if it is 70% or less, the inorganic thin film layer can be softened, and it is possible to prevent the thin film from being destroyed during secondary processing such as printing or laminating to reduce the gas barrier property. 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 _{AL2O 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. When the film thickness of the inorganic thin film layer is 1 nm or less, a more satisfactory gas barrier property can be easily obtained. On the other hand, if it is 100 nm or less, it is advantageous 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 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 particle size is preferably 1 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 film to be vapor-deposited (laminated film to be subjected to vapor deposition) or heating or cooling the film 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. Further, a print layer may be laminated on the inorganic thin film layer.

In the present 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 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 compatible 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.

Examples of the protective layer include urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, and polybutadiene-based resins to which epoxy-based, isocyanate-based, and melamine-based curing agents are added. .. Examples of the solvent used for 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 butyl acetate. Etc., and examples thereof include polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

A layer of another material may be laminated on the biaxially oriented polyester film for packaging of the present invention, and as a method thereof, the biaxially oriented polyester film can be bonded after production or during film formation.

The biaxially oriented polyester film for packaging of the present invention can be used as a packaging material by forming a heat-sealing resin layer (also referred to as a sealant layer) called a sealant on the biaxially oriented polyester film, for example. The heat-sealing resin layer is usually formed by an extrusion laminating method or a dry laminating method. As the thermoplastic copolymer forming the heat-sealable resin layer, any material may be used as long as it can sufficiently exhibit the sealant adhesiveness, and HDPE and LDPE can be used. Polyethylene resins such as LLDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-α-olefin random copolymers, ionomer resins and the like can be used.

The sealant layer may be a single-layer film or a multilayer film, and may be selected according to the required function. For example, in terms of imparting moisture resistance, a multilayer film in which a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene is interposed can be used. Further, the sealant layer may contain various additives such as a flame retardant, a slip agent, an anti-blocking agent, an antioxidant, a light stabilizer, and a tackifier.
The thickness of the sealant layer is preferably 10 to 100 μm, more preferably 20 to 60 μm.

The biaxially oriented polyester film for packaging of the present invention can be used in the packaging field of foods, pharmaceuticals, industrial products and the like. In particular, it can be used as a base film (base material layer) for a laminated film for packaging. As for the layer structure of the laminated film for packaging, when the boundary between the layers is represented by /, for example, a base material layer / sealant layer, a base material layer / gas barrier layer / protective layer, a 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 material layer / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, Base material layer / gas barrier layer / protective layer / printed layer / adhesive layer / sealant layer, base material layer / printed layer / gas barrier layer / protective layer / adhesive layer / sealant layer. Base material 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 / Print layer / Gas barrier layer / Protective layer / Adhesive layer / Resin layer / Adhesive layer / Sealant layer, Base material layer / Print layer / Adhesive layer / Resin layer / Gas barrier layer / Protective layer / Adhesive layer / sealant layer, base material layer / adhesive layer / resin layer / gas barrier layer / protective layer / printing layer / adhesive layer / sealant layer, and the like.

The laminated film obtained by laminating a sealant film on a biaxially oriented polyester film for packaging of the present invention can be suitably used for packaging materials such as packaging products, various label materials, lid materials, sheet molded products, and laminated tubes. In particular, it is used for packaging bags (for example, pillow bags, pouches such as standing pouches and 4-way pouches). The thickness of the laminated film can be appropriately determined according to the application. For example, it is used in the form of a filmless sheet having a thickness of about 5 to 500 μm, preferably about 10 to 300 μm.

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

[Film surface orientation]
According to the JIS K 7142-1996 A method, the refractive index (Nx) in the longitudinal direction, the refractive index (Ny) in the width direction, and the refractive index in the thickness direction of the film are measured by the Abbe refractive index meter using diiodomethane as the contact liquid using the sodium D line as the light source. The refractive index (Nz) was measured, and ΔP was calculated by the following formula.
Surface orientation = [(Nx + Ny) / 2] -Nz

[Film piercing strength]
The value measured by the test method conforming to JIS-Z1707 was calculated by the following formula in terms of 1 μm.
Puncture strength (N / μm) = Measured puncture strength / Film thickness

[Tension breaking elongation of film]
A sample having a width of 15 mm and a length of 180 mm was cut out from the film. The cut out sample was left to stand in an atmosphere of 23 ° C. and 65% RH for 12 hours, and then measured under the conditions of a distance between chucks of 100 mm and a tensile speed of 200 mm / min under an atmosphere of 23 ° C. and 65% RH, and 5 times. The average value of the measurement results was used. An Autograph AG-1 manufactured by Shimadzu Corporation was used as the measuring device.

[Film haze]
According to JIS K7361-1, a film was cut into a square shape with a side of 10 cm, and haze measurement was performed using a haze meter NDH2000 manufactured by Nippon Denshoku Co., Ltd. It was carried out at three places, and the average value was used as the measured haze value.

[Film dynamic friction coefficient]
In accordance with JIS K-7125, a tensile tester (Tencilon RTG-1210 manufactured by A & D Co., Ltd.) was used to determine the coefficient of dynamic friction when the front surface and the back surface of the film were bonded under a 23 ° C. 65% RH environment. The weight of the thread (weight) around which the upper film was wound was 1.5 kg, and the size of the bottom area of the thread was 39.7 mm ² . The tensile speed at the time of measuring the friction coefficient was 200 mm / min.

[Heat shrinkage of film]
The heat shrinkage was carried out by a dimensional change test method based on JIS-C-2318, except that the test temperature was 150 ° C. and the heating time was 15 minutes.

[Evaluation of bag resistance]
A urethane-based two-component curable adhesive (Mitsui Chemicals Co., Ltd. "Takelac (registered trademark) A525S" and "Takenate (registered trademark) A50" is mixed on a polyester film in a ratio of 13.5: 1.0 (mass ratio). Then, an unstretched polypropylene film (“P1147” manufactured by Toyo Boseki Co., Ltd.) having a thickness of 70 μm was bonded as a heat-sealing resin by a dry laminating method, and aged at 40 ° C. for 4 days to obtain a laminated laminate. The thickness of the adhesive layer formed of the urethane-based two-component curable adhesive after drying was about 4 μm.
The above-mentioned laminated laminate is cut into a size of 15 cm square, two sheets are stacked so that the sealant is on the inside, and the three sides are heat-sealed at a sealing temperature of 160 ° C and a sealing width of 1.0 cm. A 13 cm 3-way seal bag was obtained.
After filling 250 mL of water in the obtained three-way seal bag, the fourth mouth was closed with a heat seal to prepare a four-way seal bag filled with water.
The obtained 4-way seal bag was subjected to a moist heat treatment by holding it in hot water at 130 ° C. for 30 minutes, and then the concrete plate was placed at a height of 100 cm under an environment of room temperature of 5 ° C. and humidity of 35% RH. I dropped it up and counted the number of drops until it broke.
Number of drops 30 or more: 〇 Number of drops less than 30: ×

[Evaluation of openness]
The above-mentioned laminated laminate is cut into a size of 15 cm square, two sheets are stacked so that the sealant is on the inside, and the four sides are heat-sealed at a sealing temperature of 160 ° C and a sealing width of 1.0 cm to achieve internal dimensions. A 13 cm 4-way seal bag was obtained.
As shown in FIG. 1, two types of four-way seal bags in the longitudinal direction and the width direction of the film were cut and opened by hand 10 times each. The straight line extending from the tip of the notch was used as the reference line, and the case where all the crevices at the time of opening were within 4 cm from the reference line was marked with 0, and the case where even one was separated from the reference line was marked with x.

[Example 1]
Using a uniaxial extruder, PET resin (intrinsic viscosity 0.62 dl / g, containing silica particles) is melted at 280 ° C, cast from a T-die at 280 ° C, and electrostatically adhered to a cooling roll at 10 ° C. Further adhered to obtain an unstretched sheet. The content of silica particles in the resin composition was 0.1% by mass as the silica concentration.
Next, the obtained unstretched sheet was stretched 4.0 times in the MD direction at a temperature of 115 ° C., then passed through a tenter and stretched 4.2 times in the TD direction at 110 ° C., and heated at 200 ° C. for 3 seconds. A fixing treatment and a relaxation treatment of 5% for 1 second were carried out to obtain a biaxially oriented polyester film having a thickness of 9 μm. Table 1 shows the resin composition of the biaxially oriented polyester film and the film forming conditions. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

[Examples 2 to 5]
In Example 1, a biaxially oriented polyester film having a thickness of 9 μm was obtained by forming a film in the same manner as in Example 1 except that the raw material composition, stretching conditions, and heat treatment conditions were changed as shown in Table 1. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

[Comparative Example 1]
The same procedure as in Example 1 was carried out except that the raw material composition and stretching conditions were changed as shown in Table 1 in Example 1. Since the obtained film has low piercing strength, it lacks bag resistance.

(Comparative Example 2)
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and stretching conditions were changed to the biaxially oriented polyester film shown in Table 1. Since the obtained film has low piercing strength, it lacks bag resistance.

(Comparative Example 3)
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and stretching conditions were changed to the biaxially oriented polyester film shown in Table 1. Since the obtained film has low piercing strength, it lacks bag resistance.

(Comparative Example 4)
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and stretching conditions were changed to the biaxially oriented polyester film shown in Table 1. Since the obtained film has low piercing strength, it lacks bag resistance. Further, since the ratio of the tensile elongation at break in the MD direction to the TD direction is high, the tear straightness is insufficient.

(Comparative Example 5)
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and stretching conditions were changed to the biaxially oriented polyester film shown in Table 1. Since the obtained film has low piercing strength, it lacks bag resistance. Further, since the ratio of the tensile elongation at break in the MD direction to the TD direction is high, the tear straightness is insufficient.

The biaxially oriented polyester film for packaging of the present invention is excellent in piercing strength and bag tear resistance even if it is thin, and can be used as various packaging substrates. It is useful because it can be used for packaging in fields that could not be used because the conventional PET film lacks bag resistance. In addition, by using a thinner film, resources can be saved and the burden on the environment can be reduced.

Claims (6)

It contains 80 to 100% by mass of the polyethylene terephthalate resin (A) and 0 to 20% by mass of the polyester resin (B) other than the polyethylene terephthalate resin (A), and has a plane orientation of 0.17 to 0.20. The piercing strength measured in the piercing test according to JIS-Z1707 is 0.76 to 1.00 N / μm, and the tensile elongation at break (a) in the longitudinal direction and the tensile elongation at break in the orthogonal width direction of the film. A biaxially oriented polyester film for packaging, wherein the ratio a / b of (b) is 0.65 to 1.50. The biaxially oriented polyester film for packaging according to claim 1, wherein the film thickness is 6 to 10 μm. The invention according to claim 1 or 2, wherein the haze value is 2% or less, and the value of the dynamic friction coefficient when the front surface and the back surface of the film are brought into contact with each other and slid is 0.25 to 0.95. Biaxially oriented polyester film for packaging. A laminated film in which a sealant film is laminated on the biaxially oriented polyester film for packaging according to any one of claims 1 to 3. The laminated film according to claim 4, wherein the sealant film is a polyolefin film. A packaging material using the laminated film according to claim 4 or 5.

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