Laminated film and packaging bag

Abstract

The present invention provides a laminated film having a heat-sealable resin layer, an inorganic thin film layer, and a protective layer in the stated order, the laminated film being characterized in that the heat-sealable resin layer contains a polyester, and the laminated film fulfills the following criteria (a) to (c). (a) The sealing strength when the heat-sealable resin layers of the laminated film are heat-sealed at 160°C and 0.2 MPa for 2 seconds is 8 N / 15 mm or higher. (b) The rate of decrease in the barrier value (Z) after a rubbing treatment, as represented by the formula below, is 200% or less, where (X) is the value of the oxygen permeability measured at a temperature of 23°C and a relative humidity of 65%, and (Y) is the value of the oxygen permeability after the rubbing treatment, which involves subjecting the surface of the protective layer to 25 back-and-forth cycles in a vibration-type friction tester. Barrier value deterioration rate (Z) after rubbing treatment (%) = (Y / X) × 100. (c) The amount of protective-layer adhesion is 0.10 g / m2 or greater.

Description

Laminated film and packaging bags

[0001] The present invention relates to a laminate used in the packaging field of foods, pharmaceuticals, industrial products, etc. More specifically, it relates to an environmentally friendly laminate film that is excellent in gas barrier properties, processability, and toughness, and is convenient to use.

[0002] In recent years, regulations aimed at reducing the use of disposable plastics have been strengthened in Europe and other countries around the world. Behind these trends are growing international awareness of resource recycling and the worsening waste problems in emerging countries. As a result, environmentally friendly products are being sought from the perspective of the 3Rs (recycle, reuse, reduce) for plastic packaging materials required for food, pharmaceuticals, etc.

[0003] One possibility for making packaging materials more environmentally friendly is to make them from a single recyclable material, i.e., to make them mono-material. For example, polyester-based or olefin-based materials are being considered as materials for making mono-materials.

[0004] While there is a demand for packaging materials with a low environmental impact, the current situation is that the properties required of packaging materials themselves are becoming increasingly multifunctional for convenience. For example, retort food pouches that do not use aluminum foil and can be used in microwave ovens require a single packaging bag that simultaneously exhibits gas barrier properties, heat resistance, toughness (bag tear resistance and pinhole resistance), and high sealability. To achieve this, different materials, each with different functions, must be bonded together. A typical bag configuration is one with at least three layers: a vapor-deposited polyester film on the outside, a polyamide film in the middle, and an olefin-based heat-sealable resin dry-laminated with an adhesive on the inside (contents side). While this configuration achieves the desired performance, the bonded materials have poor recyclability, making them less than environmentally friendly, as mentioned above.

[0005] Taking these points into consideration, research is underway to determine whether it is possible to design an ideal packaging material that has the multifunctionality of a bag, as mentioned above, and in particular gas barrier properties, which are important for preserving the contents, even using the same material that can be made into a monomaterial.

[0006] In the design of olefin-based monomaterial packaging materials, laminated bodies composed of olefin-based films with gas barrier properties have been considered (see, for example, Patent Document 1). However, because olefin-based films have significantly poorer oxygen barrier properties than polyester films, the provision of two or more gas barrier layers is necessary, which increases the number of processes and creates problems such as environmental impact and increased costs. Furthermore, the unstretched sealant in this document is aluminum vapor-deposited, which poses issues regarding the visibility of the contents.

[0007] Meanwhile, in the design of polyester-based monomaterial packaging materials, a polyester-based sealant has been disclosed as an alternative to conventional olefin-based sealants, which has improved sealing properties, low adsorption, and heat resistance by co-extrusion of the polyester resins that make up the heat-resistant layer and the sealing layer (see, for example, Patent Document 2). By separating the layer with heat-sealing properties from the other layers and separately controlling the raw material compositions of these layers, heat-sealing properties and heat resistance are satisfied. However, because the sealant does not possess barrier properties, when used as a gas-barrier packaging material, it was necessary to bond a separate polyester film with gas barrier properties to the sealant.

[0008] Furthermore, a common issue for both the aforementioned olefin-based monomaterial and polyester-based monomaterial packaging designs is the recyclability of laminated packaging. To recycle laminated packaging, two options are available: either peeling off the film to create a single unit, or recycling the laminated packaging as is. However, the former can be difficult to peel and separate, while the latter raises concerns that the adhesives and inks used in bonding the components may make recycling difficult. Furthermore, the lamination process is a dry lamination process using organic solvents, which is not environmentally friendly. Furthermore, lamination increases the amount of film used, which is undesirable from the perspective of reducing plastics.

[0009] To address the above-mentioned issues with laminated packaging, attempts have been made to impart gas barrier properties in addition to the sealant properties by laminating an inorganic thin film layer on the base layer side of a polyester-based sealant (see, for example, Patent Document 3). This allows the film to satisfy the required properties as a standalone material without being laminated through a lamination process, and can be an ideal packaging material with excellent recyclability. However, when the above-mentioned barrier PET sealant is used alone, one side serves as a sealing layer and becomes the inner surface of the bag, while the other side, i.e., the side on which the inorganic thin film layer is laminated, is exposed to the outermost surface of the bag. Inorganic thin film layers are generally vulnerable to physical damage such as bending and rubbing, and defects may lead to a decrease in gas barrier performance. For this reason, designs in which the inorganic thin film layer is located on the outermost surface of a bag are not commonly used.

[0010] In order to prevent external damage to the inorganic thin film layer as described above, attempts have generally been made to laminate a protective layer made of a resin composition mainly composed of an organic compound on the inorganic thin film layer. Furthermore, using a material with gas barrier properties for the protective layer itself can also improve the gas barrier performance of the film (see, for example, Patent Document 4). However, in previous packaging, while the role of the inorganic thin film layer as a protective layer when it is used by bonding it to another film on the inside of a bag has been considered, the protective properties of the inorganic thin film layer when it is used on the outside of the bag, i.e., as the outermost layer, have not been considered. Furthermore, protective layers with gas barrier properties are generally highly crystalline and rigid, which poses the problem of poor protection against abrasion and bending.

[0011] JP 2020-040256 A JP 2017-165059 A JP 2017-165060 A JP 2000-43182 A

[0012] In the above patent documents, it is difficult to simultaneously design a packaging material as a single film with excellent recyclability and to achieve the performance required of the packaging material, and as a result, a packaging material that is both environmentally friendly and highly convenient has not been designed.

[0013] The present invention was made in light of the problems of the prior art. That is, an object of the present invention is to provide a laminated film that is made of almost a single polyester resin, has excellent recyclability, can be used in a single film configuration without the need for lamination, and has gas barrier properties and heat sealability required for packaging materials, and further has high protective durability with little degradation of the barrier film even when the barrier layer is on the outside of the bag.

[0014] The present inventors have discovered that by forming a laminate film in which a predetermined protective layer tailored to the required performance is laminated on an inorganic thin film layer, the protective layer can protect the inorganic thin film layer from external damage even when it is on the outside of the bag, i.e., the outermost layer. Furthermore, by providing a sealing layer on the opposite side of the inorganic thin film layer, it has been discovered that a packaging bag can be provided that exhibits barrier performance and heat sealability with a single film without lamination and that has a low environmental impact, and has thus completed the present invention.

[0015] That is, the present invention has the following configuration: 1. A laminate film having a heat-sealable resin layer, an inorganic thin film layer, and a protective layer in this order, wherein the heat-sealable resin layer contains polyester, and wherein the laminate film satisfies the following requirements (a) to (c): (a) The seal strength when the heat-sealable resin layers of the laminate film are heat-sealed together at 160°C, 0.2 MPa, and for 2 seconds is 8 N / 15 mm or more. (b) When the oxygen permeability value of the laminate film measured under conditions of 23°C and 65% RH is (X), and the oxygen permeability value after subjecting the protective layer surface to 25 back-and-forth rubbing treatment using a Gakushin-type friction tester is (Y), the barrier value deterioration rate (Z) after rubbing treatment, expressed by the following formula, is 200% or less: Barrier value deterioration rate after rubbing treatment (Z) (%) = (Y / X) x 100. (c) The protective layer has an adhesion amount of 0.10 g / m ２ 2. The surface hardness of the protective layer surface of the laminated film is 180 to 350 N / mm ２ 3. The laminate film according to 1. or 2., characterized in that the inorganic thin film layer contains aluminum, silicon oxide, or aluminum oxide as a main component. 4. The protective layer has a coating weight of 0.10 to 0.60 g / m ２ 5. The laminate film according to any one of 1. to 3., characterized in that the protective layer is mainly composed of a urethane resin. 6. The laminate film according to any one of 1. to 4., characterized in that the oxygen permeability of the laminate film at 23°C x 65% RH is 50 ml / m ２7. The laminate film according to any one of 1. to 5., characterized in that the modulus of elasticity is d·MPa or less. 7. The laminate film according to any one of 1. to 6., characterized in that the heat-sealable resin layer comprises a seal layer (A) and a heat-resistant layer (B), the seal layer (A) contains a dicarboxylic acid monomer other than terephthalic acid, a diol monomer other than ethylene glycol, or both, in a total amount within the range of 30 mol % to 50 mol %, and the heat-resistant layer (B) contains a dicarboxylic acid monomer other than terephthalic acid, a diol monomer other than ethylene glycol, or both, in a total amount within the range of 9 mol % to 20 mol %. 8. A packaging bag constructed using only the laminate film according to any one of 1. to 7., without bonding any other film thereto.

[0016] Using this technology, the inventors have been able to provide a laminated film that is highly recyclable, is made up of almost a single polyester resin, can be used in a single film configuration without the need for lamination, and has the gas barrier properties and heat sealability required for packaging materials, as well as high protective durability with little degradation of the barrier film even when the barrier layer is on the outside of the bag. Moreover, because the laminated film of the present invention does not require a lamination step, it is excellent in both economy and environmental load, and can provide a gas barrier sealant film with uniform properties.

[0017] The laminate film of the present invention will be described below. The laminate film of the present invention is a laminate film having a heat-sealable resin layer, an inorganic thin film layer, and a protective layer in this order, wherein the heat-sealable resin layer contains polyester, and the laminate film is characterized by satisfying the following requirements (a) to (c): (a) The seal strength when the heat-sealable resin layers of the laminate film are heat-sealed together at 160°C, 0.2 MPa, and for 2 seconds is 8 N / 15 mm or more. (b) The oxygen permeability value of the laminate film measured under conditions of 23°C and 65% RH is (X), and the oxygen permeability value after subjecting the protective layer surface to 25 back-and-forth rubbing treatment using a Gakushin-type friction tester is (Y), where (X) is the oxygen permeability value, and (Y) is the oxygen permeability value after rubbing treatment using a Gakushin-type friction tester, the barrier value deterioration rate (Z) after rubbing treatment, expressed by the following formula, is 200% or less: Barrier value deterioration rate (Z) after rubbing treatment (%) = (Y / X) x 100. (c) The protective layer has an adhesion amount of 0.10 g / m. ２ That's all.

[0018] [Heat-sealable resin layer] The laminate film of the present invention preferably has a heat-sealable resin layer consisting of at least two layers: a heat-sealable seal layer (A) containing a polyester component and a heat-resistant layer (B) containing the highest ethylene terephthalate content. To further impart barrier properties, an inorganic thin film layer (C) is provided on the heat-resistant layer (B) of the heat-sealable resin layer, and a protective layer (D) is provided on the inorganic thin film layer (C). To achieve a desired heat-seal strength, the seal layer (A) must be provided on either of the outermost layers of the laminate. In the following description, layers made of polyester resins, such as the seal layer (A) and the heat-resistant layer (B), are collectively referred to as the "heat-sealable resin layer" to distinguish them from the inorganic thin film layer and the protective layer.

[0019] (Constituent Materials of the Heat-Sealable Resin Layer) The raw material type of the heat-sealable resin layer of the present invention is one that contains ethylene terephthalate units as the main constituent. Here, "mainly containing" refers to a content of 50 mol% or more, where the total amount of constituents is 100 mol%. It is also preferable that the polyester used in the heat-sealable resin layer of the present invention contains one or more components other than ethylene terephthalate. This is because the presence of components other than ethylene terephthalate improves the heat seal strength of the seal layer (A). While it is preferable that the heat-resistant layer (B) contains fewer components other than ethylene terephthalate, the inclusion of components other than ethylene terephthalate can reduce the difference in shrinkage rate with the seal layer (A), leading to reduced curling of the laminate. The content of each component differs between the seal layer (A) and the heat-resistant layer (B), as will be described below. Examples of dicarboxylic acid monomers that can be components other than terephthalic acid that constitute ethylene terephthalate include aromatic dicarboxylic acids such as isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and alicyclic dicarboxylic acids. However, it is preferable not to include trivalent or higher polyvalent carboxylic acids (e.g., trimellitic acid, pyromellitic acid, and anhydrides thereof) in the polyester.

[0020] Furthermore, examples of diol monomers that can be components other than ethylene glycol that constitute ethylene terephthalate include long-chain diols such as neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, hexanediol, and 1,4-butanediol, aliphatic diols such as hexanediol, and aromatic diols such as bisphenol A. However, it is preferable that the polyester does not contain diols having 8 or more carbon atoms (e.g., octanediol, etc.) or trihydric or higher polyhydric alcohols (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.).

[0021] Furthermore, the polyester may contain a polyester elastomer containing ε-caprolactone, tetramethylene glycol, etc. The polyester elastomer has the effect of lowering the melting point of the polyester resin layer, and is therefore particularly suitable for use in the sealing layer.

[0022] Among these, the use of one or more of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol is preferred because it facilitates achieving a heat seal strength of 8 N / 15 mm or more between the seal layers. The use of one or more of neopentyl glycol and 1,4-cyclohexanedimethanol is more preferred, and the use of neopentyl glycol is particularly preferred.

[0023] Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, coloring inhibitors, and UV absorbers, can be added to the heat-sealable resin layer of the laminate film of the present invention as needed. Furthermore, it is preferable to add fine particles as a lubricant to at least the outermost layer of the film to improve the film's slipperiness. Any fine particles can be selected. For example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles can be appropriately selected as needed within the range of 0.05 to 3.0 μm as measured with a Coulter counter.

[0024] As a method for incorporating particles into the heat-sealable resin layer constituting the laminated film of the present invention, for example, they can be added at any stage in the production of a polyester-based resin, but it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the completion of the transesterification reaction and before the start of the polycondensation reaction to proceed with the polycondensation reaction. Other examples include a method of blending a slurry of particles dispersed in ethylene glycol, water, or other solvent with a polyester-based resin raw material using a vented kneading extruder, and a method of blending dried particles with a polyester-based resin raw material using a kneading extruder.

[0025] The preferred components contained in the sealing layer (A) and the heat-resistant layer (B) will be explained below.

[0026] The polyester used in the seal layer (A) constituting the heat-sealable resin layer preferably has a content of "dicarboxylic acid monomers and / or diol monomers" other than "terephthalic acid and ethylene glycol constituting ethylene terephthalate" of 30 mol% or more, more preferably 32 mol% or more, and particularly preferably 34 mol% or more. The upper limit of the content of the monomers other than ethylene terephthalate is 50 mol%. That is, the seal layer (A) preferably contains a dicarboxylic acid monomer other than terephthalic acid, a diol monomer other than ethylene glycol, or both in a total range of 30 mol% to 50 mol%. If the content of the monomers other than ethylene terephthalate contained in the seal layer (A) is less than 30 mol%, even if the molten resin is rapidly cooled and solidified after extrusion through the die, it will crystallize during the subsequent stretching and heat setting steps, making it difficult to achieve a heat seal strength of 8 N / 15 mm or more, which is not preferable.

[0027] On the other hand, if the content of the monomer other than ethylene terephthalate in the seal layer (A) is 50 mol % or more, the heat seal strength of the film can be increased, but the heat resistance of the seal layer (A) becomes extremely low, resulting in blocking around the sealed area during heat sealing (a phenomenon in which a wider area than intended is sealed due to heat conduction from the heating element), making proper heat sealing difficult. The content of the monomer other than ethylene terephthalate is more preferably 48 mol % or less, and particularly preferably 46 mol % or less.

[0028] The polyester used in the heat-resistant layer (B) that can constitute the laminate film of the present invention preferably has a content of "dicarboxylic acid monomers and / or diol monomers" other than "terephthalic acid and ethylene glycol that constitute ethylene terephthalate" of 9 mol% or more, more preferably 10 mol% or more, and particularly preferably 11 mol% or more. The upper limit of the content of the monomers other than ethylene terephthalate is preferably 20 mol%. That is, the heat-resistant layer (B) preferably contains a dicarboxylic acid monomer other than terephthalic acid, a diol monomer other than ethylene glycol, or both in a total range of 9 mol% to 20 mol%. If the content of the monomers other than ethylene terephthalate contained in the heat-resistant layer (B) is less than 9 mol%, the difference in heat shrinkage rate between the heat-resistant layer (B) and the seal layer (A) becomes large, resulting in significant curling of the laminate film, which is undesirable. If the difference in the content of monomers other than the ethylene terephthalate contained in the heat-resistant layer (B) and the sealing layer (A) becomes large, the difference in the thermal shrinkage rate between each layer during heat setting becomes large, and even if cooling after heat setting is intensified, shrinkage toward the sealing layer (A) side becomes large, resulting in significant curling.

[0029] On the other hand, if the content of the monomer other than ethylene terephthalate in the heat-resistant layer (B) is 20 mol% or more, the heat resistance of the sealant will be reduced, such as the occurrence of holes due to the heat applied during heat sealing, which is undesirable. The content of the monomer other than ethylene terephthalate is more preferably 19 mol% or less, and particularly preferably 18% or less. Furthermore, the difference in the content of the monomer other than ethylene terephthalate for controlling curl between the heat-sealable resin layer (A) and the heat-resistant layer (B), in addition to the amount in each of the above layers, is more preferably 20 mol% to 35 mol%, and even more preferably 21 mol% to 34 mol%.

[0030] The thickness of the heat-sealable resin layer is not particularly limited, but is preferably 3 μm or more and 200 μm or less. A thickness of less than 3 μm is undesirable because it may result in insufficient heat-sealing strength or make processing such as printing difficult. The thickness of the laminate may be greater than 200 μm, but this is undesirable because it increases the weight of the film used and increases costs. The thickness of the laminate is more preferably 5 μm or more and 160 μm or less, and even more preferably 7 μm or more and 120 μm or less.

[0031] The layer ratio of the seal layer (A) to the seal layer (A) and the heat-resistant layer (B) is preferably 20% or more and 80% or less. If the layer ratio of the sealable resin layer (A) is less than 20%, the heat seal strength of the heat-sealable resin layer will decrease, which is not preferred. If the layer ratio of the seal layer (A) is higher than 80%, the heat sealability of the heat-sealable resin layer will improve, but the heat resistance will decrease, which is not preferred. The layer ratio of the seal layer (A) is more preferably 30% or more and 70% or less.

[0032] The layer ratio of the heat-resistant layer (B) is preferably 20% or more and 80% or less. If the layer ratio of the heat-resistant layer (B) is less than 20%, the heat resistance of the film will decrease, which is undesirable. If the layer ratio of the heat-resistant layer (B) is higher than 80%, the ratio of the seal layer (A) in the laminated film will decrease accordingly, which is undesirable because the heat sealability will be sacrificed. The layer ratio of the heat-resistant layer (B) is more preferably 30% or more and 70% or less.

[0033] Furthermore, the outermost layer (including the heat-sealable resin layer) of the laminated film of the present invention may be provided with a layer that has been subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve the printability and slipperiness of the film surface, and such a layer may be provided as desired within the scope of the present invention.

[0034] (Production Conditions for Heat-Sealable Resin Layer) The heat-sealable resin layer constituting the laminate film of the present invention can be obtained by melt-extruding the polyester raw material described above using an extruder to form an unstretched laminate film, which is then stretched using the specified method described below. When the film includes a seal layer (A) and a heat-resistant layer (B), or other layers, the timing of laminating the layers may be either before or after stretching. When laminating before stretching, it is preferable to use a method in which the resin raw materials for each layer are melt-extruded using separate extruders and then joined using a feed block or the like midway through the resin flow path. When laminating after stretching, it is preferable to use lamination, in which separately formed films are bonded together with an adhesive, or extrusion lamination, in which a molten polyester resin is poured onto the surface layer of a single or laminated film to laminate it. Among these, the method of laminating the layers before stretching is preferred.

[0035] As described above, the polyester resin raw material can be obtained by polycondensation of the dicarboxylic acid component and the diol component, selecting their types and amounts so as to contain an appropriate amount of monomers other than ethylene terephthalate. Alternatively, two or more types of polyester chips can be mixed and used as the raw material for the polyester-based resin layer. When melt-extruding the raw resin material, it is preferable to dry the polyester raw material for each layer using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester raw material for each layer, it is melted at a temperature of 200 to 300°C using an extruder and extruded into a laminated film. Any existing extrusion method, such as the T-die method or the tubular method, can be used. The extruded molten film can then be quenched to obtain an unstretched film. A suitable method for quenching the molten resin is to cast the molten resin from a die onto a rotating drum and rapidly solidify it to obtain a substantially unoriented resin sheet.

[0036] The film may be produced by any of the following methods: non-stretching, uniaxial stretching (stretching in at least one of the longitudinal (length) direction and the transverse (width) direction), and biaxial stretching. From the viewpoint of the mechanical strength and productivity of the laminate of the present invention, uniaxial stretching is preferred, and biaxial stretching is more preferred. Below, a sequential biaxial stretching method by longitudinal stretching-transverse stretching in which longitudinal stretching is carried out first and then transverse stretching is carried out will be described, but the order may be reversed (transverse stretching-longitudinal stretching), as this only changes the main orientation direction. A simultaneous biaxial stretching method may also be used.

[0037] For longitudinal stretching, the unstretched film may be introduced into a longitudinal stretching machine having multiple roll groups arranged in series. For longitudinal stretching, it is preferable to preheat the film using preheating rolls until the film temperature reaches 65°C to 90°C. A film temperature lower than 65°C is undesirable because it becomes difficult to stretch in the longitudinal direction and is prone to breakage. Furthermore, a film temperature higher than 90°C is undesirable because it tends to stick to the rolls, causing the film to wrap around the rolls and contaminate the rolls during continuous production. Once the film temperature reaches 65°C to 90°C, longitudinal stretching is performed. The longitudinal stretching ratio should be between 1 and 5 times. Since 1 times means no longitudinal stretching, a longitudinal stretching ratio of 1 is required to obtain a transversely uniaxially stretched film, and longitudinal stretching of 1.1 times or more is required to obtain a biaxially stretched film. The upper limit of the longitudinal stretching ratio may be any number of times, but a longitudinal stretching ratio of 5 times or less is preferable because a too high longitudinal stretching ratio makes transverse stretching difficult and prone to breakage.

[0038] Furthermore, by relaxing the film in the longitudinal direction after longitudinal stretching (longitudinal relaxation), the shrinkage rate of the film in the longitudinal direction caused by longitudinal stretching can be reduced. Furthermore, longitudinal relaxation can reduce the bowing phenomenon (distortion) that occurs in the tenter. This is because, during the subsequent transverse stretching and final heat treatment, the film is heated while both ends in the width direction are held, causing only the central portion of the film to shrink in the longitudinal direction. The longitudinal relaxation rate is preferably 0% to 70% (a relaxation rate of 0% indicates no relaxation). The upper limit of the longitudinal relaxation rate is determined by the raw materials used and the longitudinal stretching conditions, and therefore relaxation cannot be performed beyond this limit. In the polyester-based sealant of the present invention, the longitudinal relaxation rate is limited to 70%. Relaxation in the longitudinal direction can be achieved by heating the film after longitudinal stretching at a temperature of 65°C to 100°C and adjusting the roll speed difference. Any heating means, such as a roll, near infrared radiation, far infrared radiation, or hot air heater, can be used. Furthermore, relaxation in the longitudinal direction does not have to be performed immediately after longitudinal stretching; for example, it can be performed during transverse stretching (including the preheating zone) or final heat treatment by narrowing the clip interval in the longitudinal direction (in this case, both ends in the width direction of the film are also relaxed in the longitudinal direction, thereby reducing bowing strain), and can be performed at any timing. After relaxation in the longitudinal direction (or longitudinal stretching if relaxation is not performed), it is preferable to cool the film once, and cooling is preferably performed with a cooling roll having a surface temperature of 20 to 40°C.

[0039] After the longitudinal stretching, the film is preferably transversely stretched at a stretch ratio of about 3 to 5 times at 65°C to 110°C in a tenter while both widthwise edges of the film are held with clips. Before the transverse stretching, the film is preferably preheated, and the preheating is preferably carried out until the film surface temperature reaches 75°C to 120°C.

[0040] After transverse stretching, it is preferable to pass the film through an intermediate zone where no active heating operation is performed. Because the temperature in the final heat treatment zone, which follows the transverse stretching zone of the tenter, is higher than that in the transverse stretching zone, if an intermediate zone is not provided, heat from the final heat treatment zone (hot air itself or radiant heat) will flow into the transverse stretching process. In this case, the temperature in the transverse stretching zone will be unstable, resulting in poor film thickness accuracy and variations in physical properties such as heat seal strength and shrinkage. Therefore, it is preferable to pass the transversely stretched film through the intermediate zone and allow a predetermined time to pass before performing final heat treatment. In this intermediate zone, it is important to block the accompanying flow associated with the running of the film and the hot air from the transverse stretching zone and the final heat treatment zone so that when a strip of paper is hung down without the film passing through the intermediate zone, the paper hangs down almost completely vertically. A passage time of approximately 1 to 5 seconds through the intermediate zone is sufficient. If the intermediate zone is shorter than 1 second, the length of the intermediate zone will be insufficient, resulting in insufficient heat insulation. On the other hand, it is preferable that the intermediate zone is long, but if it is too long, the equipment will become large, so about 5 seconds is sufficient.

[0041] After passing through the intermediate zone, it is preferable to perform heat treatment in the final heat treatment zone at a temperature equal to or higher than the transverse stretching temperature and equal to or lower than 250°C. The heat treatment temperature must be equal to or higher than the transverse stretching temperature in order to achieve the desired effect. In this case, the heat shrinkage of the film may increase, which is undesirable. The higher the heat treatment temperature, the lower the shrinkage of the film. However, if the heat treatment temperature is higher than 250°C, the haze of the film may increase to more than 15% or the film may melt during the final heat treatment step and fall into the tenter, which is undesirable.

[0042] During the final heat treatment, the shrinkage rate in the width direction can be reduced by shortening the distance between the tenter clips by a desired factor (relaxation in the width direction). Therefore, during the final heat treatment, it is preferable to perform relaxation in the width direction within a range of 0% to 10% (a relaxation rate of 0% means that no relaxation is performed). Although the higher the relaxation rate in the width direction, the lower the shrinkage rate in the width direction, the upper limit of the relaxation rate (shrinkage rate in the width direction of the film immediately after transverse stretching) is determined by the raw materials used, the stretching conditions in the width direction, and the heat treatment temperature, and therefore relaxation cannot be performed beyond this limit. In the polyester-based sealant of the present invention, the upper limit of the relaxation rate in the width direction is 10%.

[0043] Furthermore, the passage time through the final heat treatment zone is preferably 2 to 20 seconds. If the passage time is 2 seconds or less, the film passes through the heat treatment zone before the surface temperature of the film reaches the set temperature, making the heat treatment meaningless. The longer the passage time, the more effective the heat treatment, so 2 seconds or more is preferred, and 5 seconds or more is even more preferred. However, if the passage time is increased, the equipment will become larger, so in practice, 20 seconds or less is sufficient.

[0044] After passing through the final heat treatment, the film is preferably cooled in a cooling zone with cooling air at 10°C to 30°C. At this time, it is preferable to improve the cooling efficiency by lowering the temperature of the cooling air or increasing the air speed so that the actual temperature of the film at the tenter exit is lower than the glass transition temperature of either the sealing layer (A) or the heat-resistant layer (B), whichever is lower. The actual temperature refers to the film surface temperature measured with a non-contact radiation thermometer. If the actual temperature of the film at the tenter exit exceeds the glass transition temperature, the film will thermally shrink when both ends of the film held by the clips are released. This is undesirable because the film will curl toward the sealing layer (A), which has a larger thermal shrinkage rate.

[0045] The time for passing through the cooling zone is preferably 2 to 20 seconds. If the time is less than 2 seconds, the film passes through the cooling zone before its surface temperature reaches the glass transition temperature, causing the film to curl. The longer the time for passing through, the greater the cooling effect, so a time of 2 seconds or more is preferred, and 5 seconds or more is even more preferred. However, if the time for passing through is increased, the equipment will become larger, so for practical purposes, a time of 20 seconds or less is sufficient. The film is then wound up while cutting and removing both ends to obtain a film roll.

[0046] [Inorganic Thin Film Layer (C)] In the present invention, an inorganic thin film layer (C) can be provided on the surface of the heat-resistant layer (B) of the heat-sealable resin layer to improve gas barrier performance. The inorganic thin film layer (C) is a thin film made of a metal or inorganic oxide. There are no particular limitations on the material forming the inorganic thin film layer as long as it can be formed into a thin film. However, from the viewpoint of gas barrier properties, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), and mixtures of silicon oxide and aluminum oxide are preferred. In particular, complex oxides of silicon oxide and aluminum oxide are more preferred in terms of achieving both flexibility and density of the thin film layer. In this complex oxide, the mixing ratio of silicon oxide to aluminum oxide is preferably in the range of 20 to 70 mass% Al in terms of the mass ratio of the metal components. If the Al concentration is less than 20 mass%, the water vapor barrier property may be reduced. On the other hand, if the Al concentration exceeds 70 mass%, the inorganic thin film layer tends to harden, and there is a risk that the film will be destroyed during secondary processing such as printing or lamination, resulting in a reduction in gas barrier property. Note that silicon oxide here refers to SiO or SiO ２ and various silicon oxides such as AlO and Al ２ O ３ and the like, or mixtures thereof.

[0047] The thickness of the inorganic thin film layer (C) is usually 1 to 100 nm, preferably 5 to 50 nm. If the thickness of the inorganic thin film layer (C) is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties. On the other hand, even if the thickness is excessively greater than 100 nm, the corresponding improvement in gas barrier properties cannot be obtained and is actually disadvantageous in terms of flex resistance, abrasion resistance, and production costs.

[0048] The method for forming the inorganic thin film layer (C) is not particularly limited, and any known vapor deposition method may be appropriately employed, such as a physical vapor deposition method (PVD method) such as vacuum deposition, sputtering, or ion plating, or a chemical vapor deposition method (CVD method). A typical method for forming the inorganic thin film layer (C) will be described below using a silicon oxide / aluminum oxide thin film as an example. For example, when the vacuum deposition method is employed, SiO ２ and Al ２ O ３ or a mixture of SiO ２ A mixture of Al and Al is preferably used. These deposition materials are typically particles, and the particle size is preferably large enough to prevent pressure changes during deposition, with a preferred particle diameter of 1 mm to 5 mm. Heating can be performed using methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating. It is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, or other reactive gases as reactive gases, or to employ reactive deposition using ozone addition or ion-assisted deposition. Furthermore, film formation conditions can be freely modified, such as by applying a bias to the deposition target (the laminated film to be deposited) or by heating or cooling the deposition target. The deposition materials, reactive gases, bias, heating, and cooling of the deposition target can be similarly modified when using sputtering or CVD.

[0049] The laminated film of the present invention may have an anchor coat layer between the heat-resistant layer (B) and the inorganic thin film layer (C) for the purpose of ensuring stable gas barrier properties and adhesion. A wide variety of organic polymer adhesive resins can be used as the resin composition for the anchor coat layer, with the aim of improving adhesion to the inorganic layer. The method for forming the anchor coat layer is not particularly limited, and conventional methods such as offline coating and in-line coating can be used.

[0050] [Protective Layer (D)] In the present invention, a protective layer is provided on the inorganic thin film layer. When the laminate film of the present invention is used alone, one side serves as a sealing layer and thus becomes the inner surface of the bag, while the other side, i.e., the side on which the inorganic thin film layer is laminated, is exposed to the outermost surface of the bag. In general, inorganic thin film layers are vulnerable to physical damage such as bending and rubbing, and defects can lead to a decrease in gas barrier performance. In particular, inorganic thin films are vulnerable to direct rubbing, so that rubbing between bags or against cardboard during transport can rapidly deteriorate the barrier performance, and therefore their use as the outermost layer has been avoided to date. In contrast, in the present invention, it has been discovered that by laminating a protective layer with specified properties on the inorganic thin film layer, the barrier layer can be protected from damage due to external rubbing, even when it is located on the outside, i.e., the outermost layer, of the bag.

[0051] In the present invention, in order to keep the barrier value deterioration rate after rubbing treatment within a predetermined range, the amount of the protective layer applied is set to 0.10 g / m ２ It is preferable that the density is 0.10 to 0.60 g / m or more. ２ It is more preferable that the coating amount of the protective layer is 0.12 g / m. This makes it easier to apply the coating uniformly, reducing coating unevenness and defects, while enhancing the protection of the inorganic thin film. In addition, the cohesive force of the protective layer itself is improved, strengthening the adhesion between the inorganic thin film layer and the protective layer, and improving water resistance. The coating amount of the protective layer is preferably 0.12 g / m. ２ More preferably, 0.14 g / m ２ More preferably, 0.16 g / m ２ or more, and preferably 0.58 g / m ２ or less, more preferably 0.56 g / m２ More preferably, 0.54 g / m or less ２ The protective layer has a coating weight of 0.60 g / m or less. ２ If the thickness of the protective layer exceeds 0.10 g / m, the cohesive force inside the protective layer may become insufficient, and adhesion may decrease. Furthermore, unevenness or defects may occur in the coating appearance, and gas barrier properties and adhesiveness may not be fully exhibited. Also, from the viewpoint of recyclability, a high adhesion amount is not preferable. On the other hand, if the thickness of the protective layer is 0.10 g / m, ２ If the thickness is less than 1000 nm, the film may be too thin and may not provide sufficient protection and interlayer adhesion.

[0052] In the present invention, in order to keep the barrier value deterioration rate after rubbing treatment within the above-mentioned specified range, it is preferable that the Tg of the resin composition used in the protective layer is 5 to 100°C. This provides flexibility that can alleviate external loads while maintaining the strength of the film, thereby further improving the protective properties of the inorganic thin film. The Tg of the resin composition is preferably 7 to 98°C, more preferably 9 to 96°C, and even more preferably 11 to 94°C. If the Tg of the resin composition exceeds 100°C, the film becomes too hard, and the barrier performance deteriorates due to rubbing. On the other hand, if the Tg of the resin composition is less than 5°C, the cohesive force decreases, reducing the strength of the protective layer itself and making it more susceptible to peeling, and problems such as blocking are also more likely to occur.

[0053] Resin compositions for use in the protective layer formed on the surface of the inorganic thin film layer of the present invention include urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, and polybutadiene-based resins. Urethane resins, in particular, have polar urethane bond moieties, which provide good adhesion to the inorganic thin film layer and allow the resin to easily penetrate into defective areas. Furthermore, the presence of crystalline portions with high cohesive strength due to hydrogen bonds between urethane bonds provides stable protective performance. Furthermore, since highly flexible amorphous portions are also present, controlling the ratio of amorphous to crystalline portions allows the Tg of the resin composition, i.e., the rate of deterioration of the barrier value after rubbing treatment, to be within the specified range. If only barrier performance is desired in the protective layer, a larger number of crystalline portions due to urethane bonds is preferable, but this can result in excessive hardness and a loss of protective properties.

[0054] In the present invention, a crosslinked structure may be introduced by a curing agent to adjust the scratch resistance of the protective layer and further to improve water resistance and adhesion. A thermosetting resin is desirable as the curing type of resin from the viewpoint of production stability. Types of curing agents that can be used include epoxy-based, isocyanate-based, melamine-based, oxazoline-based, and carbodiimide-based curing agents. Among these, carbodiimide-based curing agents are preferred from the viewpoint of being able to form a flexible coating film while having a crosslinked structure.

[0055] The weight ratio of the curing agent to the entire protective layer is preferably 5 to 30%, more preferably 7 to 28%, and even more preferably 9 to 26%. If the weight ratio of the curing agent is less than 5%, the cohesive strength of the film may decrease, making the film itself more susceptible to peeling due to rubbing. On the other hand, if the weight ratio of the curing agent is greater than 30%, the film may become too hard, resulting in a deterioration in the barrier value after rubbing treatment.

[0056] The method for applying the resin composition for the protective layer is not particularly limited as long as it is a method that can apply the resin composition for the protective layer to the surface of a film to form a layer. For example, a conventional coating method such as gravure coating, reverse roll coating, wire bar coating, or die coating can be used.

[0057] When forming a protective layer, it is preferable to apply a protective layer resin composition and then heat-dry it. The drying temperature is preferably 80 to 150°C, more preferably 85 to 145°C, and even more preferably 90 to 140°C. Drying temperatures below 80°C can result in insufficient drying of the protective layer, or the formation of the protective layer cannot proceed, resulting in reduced cohesive strength and adhesiveness. As a result, performance as a barrier protection layer can be impaired, and the barrier value deterioration rate after rubbing treatment can be increased. On the other hand, drying temperatures above 150°C can cause the film to be heated and shrink, resulting in wrinkles and a decrease in the seal strength of the sealing layer. Furthermore, shrinkage can cause the inorganic thin film to crack, resulting in a deterioration in barrier performance after processing. It is particularly preferable to first volatilize the solvent at a relatively low temperature of 50 to 80°C immediately after application of the protective layer, and then dry it at 80°C or higher, since this results in a uniform and transparent film. In addition to drying, additional heat treatment at as low a temperature as possible can be even more effective in facilitating the formation of the protective layer.

[0058] The laminated film of the present invention is characterized by its properties, which allow it to be used as a packaging material as a single film without lamination, but if necessary, a printed layer or at least one other plastic substrate and / or paper substrate may be laminated on the protective layer, although consideration must be given to the effect on recyclability of using other layers or substrates.

[0059] As the printing ink for forming the printing layer, aqueous and solvent-based resin-containing printing inks are preferably used. Examples of resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoamers, crosslinking agents, anti-blocking agents, and antioxidants. The printing method for forming the printing layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. To dry the solvent after printing, known drying methods such as hot air drying, heat roll drying, and infrared drying can be used.

[0060] (Properties of laminated film)

[0061] In the present invention, the surface hardness of the laminated film is 180 to 350 N / mm ２ This provides the hardness necessary for the development of adhesive strength and enables protection of the inorganic thin film layer from external damage. As a result, the barrier deterioration rate after rubbing treatment can be reduced. The surface hardness is preferably 190 N / mm ２ More preferably, 200 N / mm ２ More preferably, 210 N / mm ２ or more, preferably 340 N / mm ２ or less, more preferably 330 N / mm ２ More preferably, 320 N / mm ２ The surface hardness of the laminated film is 350 N / mm ２ If the surface hardness exceeds 180 N / mm, the surface becomes hard and easily scratches are generated when the film is rubbed, and the scratches propagate to the inorganic thin film, resulting in a deterioration of the gas barrier performance. ２ If the thickness is less than this, the cohesive strength of the protective layer will be weak and the entire protective layer may peel off, resulting in the loss of protection for the inorganic thin film.

[0062] The haze of the laminated film of the present invention is preferably 15%, more preferably 12%, and even more preferably 9%. When printing is performed on a film layer having a haze of 15% or less, the quality of the printed characters and images is improved.

[0063] When the heat-sealable resin layers of the laminated film of the present invention are heat-sealed together at a temperature of 160°C, a sealing bar pressure of 0.2 MPa, and a sealing time of 2 seconds, the heat seal strength is preferably 8 N / 15 mm or more and 30 N / 15 mm or less. If the heat seal strength is less than 8 N / 15 mm, the sealed portion will easily peel off, making it impossible to use as a packaging bag. The heat seal strength is preferably 9 N / 15 mm or more, and more preferably 10 N / 15 mm or more. A high heat seal strength is preferable, but the upper limit currently achievable is about 30 N / 15 mm.

[0064] The laminated film of the present invention has an oxygen permeability of 50 ml / m under the conditions of 23°C x 65% RH. ２ In order to achieve good gas barrier properties, it is preferable that the viscosity is 45 ml / m or less. ２ d MPa or less, more preferably 40 ml / m ２ ・d・MPa or less. Oxygen permeability is 50 ml / m ２ If the viscosity exceeds d MPa, it becomes difficult to use the film in applications that require high gas barrier properties.

[0065] The laminated film of the present invention has a water vapor permeability of 5.0 g / m under the conditions of 40°C x 90% RH. ２ Furthermore, by controlling the deposition amount of the inorganic thin film layer components described above, it is possible to achieve a coating amount of preferably 4.5 g / m2·d or less, more preferably 4.0 g / m2·d or less. ２ The water vapor permeability can be 5.0 g / m or less. ２ If d is exceeded, it becomes difficult to use the film in applications that require high gas barrier properties.

[0066] The laminated film of the present invention is characterized in that, when the oxygen permeability measured under conditions of 23°C x 65% RH is (X), and the oxygen permeability measured after subjecting the protective layer surface to 25 back-and-forth rubbing treatment using a Gakushin-type friction tester is (Y), the barrier value deterioration rate (Z) after rubbing treatment, expressed by the following formula, is 200% or less. This prevents a rapid deterioration in barrier performance when the barrier layer is on the outer side of the bag, i.e., the outermost layer, due to rubbing between bags or against cardboard during transport. If the deterioration rate can be kept to 200% or less, the bag will be durable even under harsh transport conditions and can be used as a bag that satisfies the barrier performance originally required for practical use. The deterioration rate is preferably 190% or less, more preferably 180% or less. If the deterioration rate exceeds 200%, the inorganic thin film may be damaged when the bag is rubbed, significantly deteriorating the barrier performance, and the required barrier performance may not be achieved.

[0067] As a criterion for evaluating the mono-material nature of packaging materials made using the laminated film of the present invention, when the ratio of the thickness of the polyester-based material to the total thickness of each film and other layers (e.g., adhesive layer) is calculated as the mono-material (mono-material) ratio, the mono-material ratio is preferably 70% or more. More preferably, it is 80% or more, and even more preferably, it is 90% or more. By keeping the mono-material ratio within this range, a packaging material that is easy to recycle can be obtained. In the present invention, since the film alone can be used as a packaging material, the mono-material ratio can be 100%, making it a material with excellent recyclability. If the mono-material ratio is less than 70%, recycling may be difficult due to foreign matter from other materials.

[0068] As described above, the laminated film of the present invention is made of almost a single resin, which is highly recyclable, and can be used in a single film configuration without the need for lamination.It also has the gas barrier properties and heat sealability required of packaging materials, and further has high protective durability with little deterioration of the barrier film even when the barrier layer is on the outside of the bag.

[0069] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. Various evaluations were carried out by the following measurement methods.

[0070] (1) Thickness of Various Films The thickness was measured using a dial gauge in accordance with JIS K7130-1999 Method A.

[0071] (2) Film Haze: Measured in accordance with JIS-K-7136 using a haze meter (300A, manufactured by Nippon Denshoku Industries Co., Ltd.) The measurement was carried out twice, and the average value was calculated.

[0072] (3) Heat-sealing strength The heat-sealing strength of the laminated film was measured in accordance with JIS Z1707. The specific procedure is briefly described below. The seal layers of the test pieces were bonded together using a heat sealer. The sealing conditions were: upper bar temperature 160°C, lower bar temperature 100°C, and pressure 2 kg / cm. ２The peel strength was measured using a universal tensile tester "DSS-100" (Shimadzu Corporation) at a tensile speed of 200 mm / min. The peel strength is expressed as the strength per 15 mm (N / 15 mm).

[0073] (4) Composition and Thickness of Inorganic Thin Film Layer The laminate films (after lamination) obtained in the Examples and Comparative Examples were measured for film thickness composition using a fluorescent X-ray analyzer ("ZSX100e" manufactured by Rigaku Corporation) based on a previously prepared calibration curve. The excitation X-ray tube conditions were 50 kV and 70 mA.

[0074] (5) Protective Layer Adhesion Amount In each example and comparative example, the laminate film obtained at the stage of laminating a protective layer onto a heat-sealable resin layer was used as a sample. 100 mm x 100 mm test pieces were cut from the sample, and the protective layer was wiped off with 1-methoxy-2-propanol or dimethylformamide. The adhesion amount was calculated from the change in the mass of the film before and after wiping. (6) Method for Measuring the Surface Hardness of Laminated Films The surface hardness of laminated films was measured using a dynamic ultra-microhardness tester ("DUH-211" manufactured by Shimadzu Corporation). Specifically, a diamond triangular pyramid indenter (Berkovich type) with an edge angle of 115° was used to measure hardness in a load-unload test against the protective layer surface of a single laminated film fixed and held on a glass plate with adhesive. The Martens hardness obtained was used as the surface hardness value. The test conditions were a test force of 0.1 mN, a load rate of 0.02 mN / sec, and a hold time of 2 seconds.

[0075] (7) Evaluation Method of Oxygen Permeability The oxygen permeability of the laminated film was measured in accordance with JIS-K7126 Method B using an oxygen permeability measuring device (OX-TRAN (registered trademark) 1 / 50 manufactured by MOCON Corporation) under an atmosphere of a temperature of 23°C and a humidity of 65% RH. The oxygen permeability was measured in the direction in which oxygen permeated from the protective layer side to the sealing layer side of the laminated film.

[0076] (8) Evaluation method of water vapor permeability The water vapor permeability of the laminated film was measured in accordance with JIS-K7129 Method B using a water vapor permeability measuring device ("PERMATRAN-W 3 / 33MG" manufactured by MOCON Co., Ltd.) under an atmosphere of a temperature of 40°C and a humidity of 90% RH. The water vapor permeability was measured in the direction in which water vapor permeated from the protective layer side to the seal layer side of the laminated film.

[0077] (9) Barrier Value Deterioration Rate After Rubbing Treatment A 100 mm x 150 mm test piece of the film was fixed on the test piece stage of a Gakushin-type abrasion tester (Yasuda Seiki Co., Ltd.). Under a test environment of 23°C x 65% RH, a gauze (a 150 mm x 300 mm piece folded in three) was attached to a friction element with a load of 1.96 N, and the abrasion treatment was performed on the protective layer surface (in Comparative Example 1, on the inorganic thin film layer surface) by 25 reciprocations at a speed of 30 reciprocations / min (1 reciprocation = 20 mm, totaling 5000 mm). Using the treated test piece, oxygen permeability was measured in the same manner as in (7). The test piece was set so that the abraded portion was located in the center of the measurement cell of the oxygen permeability measuring device. The oxygen permeability value before the abrasion treatment was (X) and the oxygen permeability value after the abrasion treatment was (Y), and the barrier value deterioration rate (Z) after the abrasion treatment was calculated using the following formula: Barrier value deterioration rate after rubbing treatment (Z) (%) = (Y / X) x 100

[0078] (10) Evaluation Criteria for Mono-Material Formation: Mono-Material Ratio As an evaluation criterion for mono-material formation of the laminated film, the ratio of the thickness of the polyester-based material to the total thickness of the film was calculated as the mono-material (monomate) ratio.

[0079] The details of the heat-sealable resin used in the present examples and comparative examples are described below. It was used in Examples 1 to 7 and Comparative Examples 1 to 4. (Production of Heat-Sealable Resin Layer) [Polyester Raw Material Synthesis Example 1] 100 mol% of dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as the polyhydric alcohol component were charged into a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, so that the molar ratio of ethylene glycol was 2.2 times that of dimethyl terephthalate. Using 0.05 mol% (relative to the acid component) of zinc acetate as the transesterification catalyst, a transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, 0.225 mol% (relative to the acid component) of antimony trioxide was added as a polycondensation catalyst, and a polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to obtain Polyester A with an intrinsic viscosity of 0.61 dl / g. This Polyester A was polyethylene terephthalate. The composition of the polyester is shown in Table 1. [Polyester Raw Material Synthesis Example 2] Polyesters B to D were obtained by changing the monomers using the same procedure as in Synthesis Example 1. The composition of each polyester is shown in Table 1. In Table 1, TPA is terephthalic acid, BD is 1,4-butanediol, and NPG is neopentyl glycol. In addition, when polyester D was produced, SiO ２ (Sylysia 266 manufactured by Fuji Silysia Ltd.) was added at a ratio of 7,000 ppm to the polyester. Each polyester was appropriately cut into chips.

[0080]

[0081] [Film Formation] (Formation of Heat-Sealable Resin Layer) Polyester A, polyester B, polyester C, and polyester D were mixed in a mass ratio of 10:60:24:6 to form the raw materials for the seal layer, and polyester A, polyester B, polyester C, and polyester D were mixed in a mass ratio of 57:31:6:6 to form the raw materials for the heat-resistant layer. The mixed raw materials for the seal layer and heat-resistant layer were each fed into separate twin-screw extruders and melted at 270°C. The molten resins were joined by a feed block midway through the flow path, extruded from a T-die, and cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The flow path for the molten resin was set so that one side of the laminated film was a seal layer and the other side was a heat-resistant layer (a two-layer structure consisting of a seal layer and a heat-resistant layer), and the extrusion rate was adjusted so that the thickness ratio of the seal layer to the heat-resistant layer was 50 / 50.

[0082] The unstretched two-layer film obtained after cooling and solidification was introduced into a longitudinal stretching machine equipped with a series of rolls, preheated on a preheating roll until the film temperature reached 78°C, and then stretched 4.1 times. The film immediately after longitudinal stretching was passed through a heating furnace set at 100°C using a hot air heater, and subjected to a 20% relaxation treatment in the longitudinal direction by utilizing the speed difference between the rolls at the inlet and outlet of the heating furnace. The longitudinally stretched film was then forcibly cooled by a cooling roll set at a surface temperature of 25°C. The relaxed film was introduced into a transverse stretching machine (tenter) and preheated for 5 seconds until the surface temperature reached 105°C, after which it was stretched 4.0 times in the width direction (transverse direction). The transversely stretched film was then introduced directly into the intermediate zone and passed through for 1.0 second. In the intermediate zone of the tenter, the hot air from the final heat treatment zone and the hot air from the transverse stretching zone were blocked so that when a strip of paper was hung down without the film passing through it, the paper would hang down almost completely vertically.

[0083] The film then passed through the intermediate zone and was introduced into the final heat treatment zone, where it was heat-treated at 190°C for 5 seconds. At this time, the clip interval in the film width direction was narrowed simultaneously with the heat treatment, thereby performing a 3% relaxation treatment in the width direction. After passing through the final heat treatment zone, the film was cooled with 30°C cooling air for 5 seconds. At this time, the actual film temperature at the tenter exit was 45°C. Both edges were cut and removed, and the film was taken up into a roll with a width of 500 mm, thereby continuously producing a 30 μm-thick biaxially stretched film (heat-sealable resin layer) (PET1) over a predetermined length.

[0084] The method for preparing the inorganic thin film layer used in each example and comparative example is described below. The inorganic thin film layers used in Examples 1 to 7 and Comparative Examples 1 to 4 are shown in Table 2. (Formation of Inorganic Thin Film Layer M-1) Aluminum oxide was vapor-deposited onto the heat-resistant layer side of the heat-sealable resin layer (PET1) to form the inorganic thin film layer M-1. The aluminum oxide vapor deposition method involved placing the film on the unwinding side of a continuous vacuum deposition machine and running it over a cooled metal drum until the film was wound up. The continuous vacuum deposition machine was then depressurized to 10 Torr or less, and 99.99% pure aluminum metal was loaded into an alumina crucible from below the cooling drum. The aluminum metal was heated to evaporate, and oxygen was supplied to the vapor to cause an oxidation reaction, depositing it on the film and forming a 10 nm thick aluminum oxide film.

[0085] (Formation of inorganic thin film layer M-2) As the inorganic thin film layer M-2, a composite oxide layer of silicon dioxide and aluminum oxide was formed on the heat-resistant layer side of the heat-sealable resin layer (PET1) by electron beam evaporation. The evaporation source was granular SiO 2 of about 3 mm to 5 mm. ２ (Purity 99.9%) and A1 ２ O ３ (purity 99.9%) was used. The inorganic thin film layer (SiO ２ / A1 ２ O ３ The thickness of the composite oxide layer was 13 nm. ２ / A1 ２ O ３ The mass ratio was 60 / 40.

[0086] The protective layer used in Examples 1 to 7 and Comparative Examples 2 to 4 was prepared by the following method, as shown in Table 2.

[0087] (Resin and crosslinking agent used in coating solution for protective layer) [Polyester resin (a)] A commercially available 25% by mass emulsion of polyester resin ("PLASCOAT (registered trademark) Z730" manufactured by GOO Chemical Co., Ltd.) was prepared as the polyester resin. The Tg of this resin was 46°C.

[0088] [Urethane resin (b)] A commercially available polyester urethane resin dispersion ("Takelac (registered trademark) W605" manufactured by Mitsui Chemicals, Inc.; solid content 30%) was prepared as the urethane resin. The Tg of this resin was 100°C. [Urethane resin (c)] A commercially available polyester urethane resin dispersion ("AP201" manufactured by DIC Corporation; solid content 23%) was prepared as the urethane resin. The Tg of this resin was 10°C.

[0089] [Urethane resin (d)] A commercially available polyester urethane resin dispersion (Takelac (registered trademark) WPB341 manufactured by Mitsui Chemicals, Inc.; solid content 30%) was prepared as the urethane resin. The Tg of this resin was 115°C.

[0090] [Polyester resin (e)] As the polyester resin, "AGN201" (solid content 25%) manufactured by Takemoto Oil & Fat Co., Ltd., which is a water-dispersible acrylic graft polyester resin containing self-crosslinking maleic anhydride as a graft chain, was prepared. The Tg of this resin was -20°C.

[0091] [Carbodiimide-based Crosslinking Agent (f)] As a carbodiimide-based crosslinking agent, commercially available "Carbodilite (registered trademark) SV-02" manufactured by Nisshinbo Industries, Inc. (solid content: 40%) was prepared.

[0092] (Coating of coating liquid onto film (lamination of protective layer)) Each coating liquid prepared according to the formulation shown in Table 2 was applied onto an inorganic thin film layer by the bar coating method, pre-dried at 70°C for 4 seconds, and then fully dried at 100°C for 10 seconds to obtain each protective layer having the specified adhesion amount.

[0093] In this manner, a laminate film having an inorganic thin film layer / protective layer on a heat-sealable resin layer was produced. The obtained laminate film was evaluated. The results are shown in Tables 2A and 2B.

[0094]

[0095]

[0096] According to the present invention, it is possible to provide a laminated film that is highly recyclable, is made up of almost a single resin, can be used in a single film configuration without the need for lamination, and has the gas barrier properties and heat sealability required for packaging materials, as well as high protective durability with little degradation of the barrier film even when the barrier layer is on the outside of the bag. Moreover, because the laminated film of the present invention does not require a lamination process, it is excellent in both economy and environmental load, and can provide a gas barrier sealant film with uniform properties.

Claims

1. A laminated film having a heat-sealable resin layer, an inorganic thin film layer, and a protective layer in this order, the heat-sealable resin layer containing polyester, the laminated film being characterized in that it satisfies the following requirements (a) to (c): (a) the seal strength when the heat-sealable resin layers of the laminated film are heat-sealed together at 160°C, 0.2 MPa, and for 2 seconds is 8 N / 15 mm or more; (b) the oxygen permeability value of the laminated film measured under conditions of 23°C and 65% RH is (X), and the oxygen permeability value after subjecting the protective layer surface to a rubbing treatment with a Gakushin-type friction tester is (Y), the barrier value deterioration rate (Z) after the rubbing treatment, expressed by the following formula, is 200% or less: Barrier value deterioration rate (Z) after rubbing treatment (%) = (Y / X) x 100; (c) the adhesion amount of the protective layer is 0.10 g / m ２ That is all.

2. The surface hardness of the protective layer of the laminated film is 180 to 350 N / mm ２ The laminated film according to claim 1 , 3. The laminated film according to claim 1, wherein the main component of the inorganic thin film layer is aluminum, silicon oxide, or aluminum oxide.

4. The coating weight of the protective layer is 0.10 to 0.60 g / m ２ 2. The laminated film according to claim 1, 5. The laminated film according to claim 1, wherein the main component of the protective layer is a urethane resin.

6. The oxygen permeability of the laminated film at 23°C x 65% RH is 50 ml / m ２ 2. The laminated film according to claim 1, characterized in that the modulus of elasticity is .d.MPa or less.

7. The laminate film according to claim 1, characterized in that the heat-sealable resin layer includes a seal layer (A) and a heat-resistant layer (B), the seal layer (A) contains a dicarboxylic acid monomer other than terephthalic acid, a diol monomer other than ethylene glycol, or both in a total amount within the range of 30 mol % to 50 mol %, and the heat-resistant layer (B) contains a dicarboxylic acid monomer other than terephthalic acid, a diol monomer other than ethylene glycol, or both in a total amount within the range of 9 mol % to 20 mol %.

8. A packaging bag constructed using only the laminate film according to any one of claims 1 to 7 without bonding any other film.

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