Laminated structure

Abstract

To provide a laminate which has a laminate structure composed of almost single resin type mainly containing polyester with less environmental loads while containing an environmentally friendly recycled material, and has required performances such as gas barrier property, heat sealability, toughness and transparency required for a packaging material.SOLUTION: A laminate is formed by laminating a polyester base material film containing 50 wt.% or more of a polyester resin recycled from a PET bottle, and a heat sealable resin layer in this order, wherein the base material film has an inorganic thin film layer (A) and a protective layer (a) containing an urethane resin on one surface, and the heat sealable resin layer is composed of a polyester-based resin containing ethylene terephthalate as a main component, and has piercing strength of 10 N or more and a haze of 20% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to laminates used in the packaging of food, pharmaceuticals, industrial products, and the like. More specifically, it relates to an environmentally friendly laminate that offers excellent gas barrier properties, processability, and toughness, as well as the ability to visualize the contents and the convenience of being suitable for microwave use. [Background technology]

[0002] In recent years, regulations aimed at reducing the use of single-use plastics have been strengthened in Europe and around the world. This is due to a growing international awareness of resource recycling and the worsening waste problem in emerging countries. As a result, there is a demand for environmentally friendly products from the perspective of the 3Rs (recycle, reuse, reduce) for plastic packaging materials used for food, pharmaceuticals, and other products.

[0003] The performance requirements for the aforementioned environmentally friendly packaging materials include: (1) being made from recycled materials, (2) having gas barrier properties that can block various gases and extend the shelf life, and (3) having a laminate structure that has a low environmental impact (for example, not using organic solvents, using a small amount of material, and being able to be made into a single material).

[0004] Regarding (1) above, polyester resin recycled from PET bottles is known as a typical recycled material, and a technology is known to produce polyester film for body wrap labels that is less prone to static electricity problems without compromising productivity or quality from polyester resin derived from PET bottles with a low oligomer content (see, for example, Patent Document 1). With increasing environmental regulations in the future, demand for such films is expected to expand.

[0005] Regarding (2) above, in food applications where the barrier against various gases such as water vapor and oxygen is required, gas barrier laminates are commonly used, which consist of a plastic base film on which a metal thin film made of aluminum or the like, and an inorganic thin film made of inorganic oxides such as silicon dioxide or aluminum oxide are formed on the surface. In particular, those with an inorganic thin film layer made of inorganic oxides such as silicon dioxide, aluminum oxide, or mixtures thereof are transparent, allowing for confirmation of the contents, and can be used in microwave ovens, thus increasing demand from an environmental perspective of eliminating aluminum foil.

[0006] Regarding the aforementioned gas barrier film composed of recycled materials and an inorganic thin film, a laminated film has been proposed that uses polyester resin recycled from PET bottles, exhibiting good gas barrier properties when combined with an inorganic thin film layer and a sealant layer due to its low thermal shrinkage and minimal thickness variation (see, for example, Patent Document 2). However, such conventional technology lacked sufficient barrier performance to replace aluminum foil.

[0007] Regarding (3) above, since pouches that do not use aluminum foil require barrier properties, heat resistance, toughness (resistance to tearing and pinholes), and high sealing performance simultaneously, they generally have a structure of at least three layers, with a vapor-deposited polyester film on the outside, a polyamide film in the middle layer, and an olefin-based heat-sealable resin dry-laminated on the inside (contents side) via an adhesive.

[0008] In the aforementioned retort pouch configuration, achieving monomaterialization from an environmental perspective requires further improvement of the barrier performance of the bag (to the same level as aluminum foil), and the elimination of polyamide film and olefin-based sealants, or their replacement with polyester-based materials. However, such changes were not easily made with conventional technology. Furthermore, when using olefin-based sealants, transparency can be insufficient, posing undesirable problems from the standpoint of visual safety and the appearance after printing.

[0009] As an alternative to polyamide films, the use of biaxially oriented polybutylene terephthalate (hereinafter sometimes abbreviated as PBT) films has been considered (see, for example, Patent Document 3). It was known that a biaxially oriented PBT-based film obtained by simultaneously biaxially stretching a resin composition consisting of at least polybutylene terephthalate resin, or a polyester resin composition in which polyethylene terephthalate (hereinafter sometimes abbreviated as PET) resin is blended with polybutylene terephthalate resin in a range of 30% by weight or less, by 2.7 to 4.0 times in both the longitudinal and transverse directions, was used as the base film layer. According to this technology, a liquid-filling packaging material can be obtained that has resistance to bending pinholes and impact, as well as excellent aroma retention. However, this document did not adequately examine the specific numerical values ​​and effects of barrier performance.

[0010] Furthermore, polyester-based sealants with improved low adsorption and heat resistance have been disclosed as an alternative to olefin-based sealants (see, for example, Patent Document 4). The sealant in Patent Document 4 satisfies both heat-sealability and heat resistance by separating the heat-sealable layer from the other layers and controlling the raw material composition of each layer separately. However, the sealant described in Patent Document 4 does not have the ability to block gases such as oxygen and water vapor (gas barrier properties), and therefore does not contribute to improving the barrier performance of the pouch. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2012-91862 [Patent Document 2] Patent No. 6500629 [Patent Document 3] Japanese Patent Publication No. 2017-094746 [Patent Document 4] Japanese Patent Publication No. 2017-165059 [Overview of the project]

Problems to be Solved by the Invention

[0012] In the above Patent Documents 1 to 4, although the performance of each material is described, the performance required for the above-mentioned environmentally friendly packaging material includes (1) containing a recyclable material as a constituent material, (2) having a gas barrier performance capable of blocking various gases and extending the shelf life, and (3) having a laminate structure that is easy to recycle and has a low environmental load (monomaterialization). Furthermore, the basic performance as a pouch (the compatibility of heat sealability, toughness, and transparency) has not been studied. There has been no polyester-based packaging material that satisfies all of the above configurations and performances in the past.

[0013] The present invention has been made against the background of such problems of the prior art. That is, the problem of the present invention is to provide a laminate structure composed of substantially a single resin type with a low environmental load mainly composed of polyester while containing an environmentally considerate recyclable material, and having necessary performances such as gas barrier properties, sealing properties, toughness, and transparency required for packaging materials.

Means for Solving the Problems

[0014] The inventors of the present invention have greatly improved the gas barrier performance by laminating and bonding an inorganic thin film layer, a coating layer, and a barrier protective layer on each film (resin layer) according to the required barrier performance, and further using a base film made of a polyester resin derived from a PET bottle with a low environmental load and laminating a sealant made of a polyester component to achieve monomaterialization while maintaining toughness, sealing properties, and transparency.

[0015] That is, the present invention has the following configuration. 1. A laminated structure comprising a polyester base film containing 50% by weight or more of polyester resin recycled from PET bottles, and a heat-sealable resin laminated in that order, wherein the base film is a laminated film having an inorganic thin film layer (A) and a protective layer (a) made of urethane resin on one side, and the heat-sealable resin is made of a polyester-based component mainly composed of ethylene terephthalate, and is characterized by having a puncture strength of 10N or more and a haze of 20% or less. 2. The laminate according to 1, characterized in that it has an intermediate layer film between the base film and the heat-sealable resin via an adhesive, and the intermediate layer film is made of a resin composition containing 70% by mass or more of PBT resin. 3. The laminate according to 1. or 2., characterized in that an inorganic thin film layer (B) is laminated on at least one side of the heat-sealable resin. 4. The laminate according to any one of 1 to 3, characterized in that an inorganic thin film layer (C) is laminated on at least one side of the intermediate layer film. 5. The laminate according to any one of 1 to 4, characterized in that a protective layer (b) having a urethane resin is laminated on the inorganic thin film layer (C) of the intermediate layer film. 6. The laminate according to any one of 1 to 5, characterized in that it has a coating layer (Y) between the base film and the inorganic thin film layer (C). 7. The laminate according to any one of 4. to 6., characterized in that it has a coating layer (Y) between the intermediate layer film and the inorganic thin film layer (C). 8. The laminate according to 1 to 7, characterized in that the inorganic thin film layers (A) to (C) are layers made of aluminum oxide or a composite oxide of silicon oxide and aluminum oxide. [Effects of the Invention]

[0016] Through this technology, the inventors have made it possible to provide laminated materials that possess the necessary properties such as barrier properties, sealing properties, and toughness required for packaging materials, while also being environmentally conscious. [Modes for carrying out the invention]

[0017] The present invention will be described in detail below. The laminated structure of the present invention is a laminated structure comprising a polyester base film containing 50% by weight or more of polyester resin recycled from PET bottles, and a heat-sealable resin layer laminated in this order, wherein the base film is a laminated film having an inorganic thin film layer (A) and a protective layer (a) containing urethane resin on one side, and the heat-sealable resin layer is made of a polyester resin mainly composed of ethylene terephthalate, and is characterized by having a puncture strength of 10N or more and a haze of 20% or less.

[0018] [Base film layer] In the present invention, as described below, it is preferable to use recycled polyester resin recovered from PET bottles containing isophthalic acid as an acid component as a raw material for the base film. Therefore, the base film is a mixed resin of recycled polyester resin and virgin raw material, i.e., non-recycled resin, and the intrinsic viscosity of the resin constituting the film means the value obtained by measuring the intrinsic viscosity of the mixed resin constituting the film. The lower limit of the intrinsic viscosity of the resin constituting the film obtained by measuring the base film is preferably 0.58 dl / g, and more preferably 0.60 dl / g. If it is less than 0.58 dl / g, many recycled resins made from PET bottles have an intrinsic viscosity exceeding 0.68 dl / g, and when using it to make a film, reducing the viscosity can result in uneven thickness, which is undesirable. Also, the film may become discolored, which is undesirable. The upper limit is preferably 0.70 dl / g, and more preferably 0.68 dl / g. If it exceeds 0.70 dl / g, the resin may become difficult to extrude from the extruder, which can reduce productivity, which is undesirable.

[0019] The lower limit of the thickness of the base film is preferably 8 μm, more preferably 10 μm, and even more preferably 12 μm. A thickness of less than 8 μm is undesirable because it may result in insufficient film strength. The upper limit is preferably 200 μm, more preferably 50 μm, and even more preferably 30 μm. A thickness exceeding 200 μm may make it too thick and difficult to process. Furthermore, a thick film is undesirable from an environmental impact standpoint, so it is preferable to reduce the volume as much as possible.

[0020] The lower limit of the refractive index in the thickness direction of the base film is preferably 1.4930, and more preferably 1.4940. If it is less than 1.4930, the orientation may not be sufficient, and lamination strength may not be obtained. The upper limit is preferably 1.4995, and more preferably 1.4980. If it exceeds 1.4995, the orientation of the surface may be disrupted, and the mechanical properties may be insufficient, which is undesirable.

[0021] The lower limit of the thermal shrinkage rate of the base film after treatment at 150°C for 30 minutes in the longitudinal (sometimes referred to as MD) and transverse (sometimes referred to as TD) directions is preferably 0.1%, and more preferably 0.3%. A value less than 0.1% is undesirable because the improvement effect saturates and the film may become mechanically brittle. The upper limit is preferably 3.0%, and more preferably 2.5%. A value exceeding 3.0% is undesirable because dimensional changes during processing such as printing may cause pitch misalignment. Furthermore, a value exceeding 3.0% is undesirable because dimensional changes during processing such as printing may cause shrinkage in the width direction.

[0022] It is preferable to use recycled polyester resin made from PET bottles containing isophthalic acid as an acid component as the raw material for the base film. The polyester used in PET bottles undergoes crystallinity control to improve the bottle's appearance, and as a result, polyester containing 10 mol% or less of isophthalic acid may be used. In order to utilize recycled resin, it may be necessary to use materials containing isophthalic acid.

[0023] The lower limit of the amount of terephthalic acid component in the total dicarboxylic acid components constituting the polyester resin contained in the base film is preferably 95.0 mol%, more preferably 96.0 mol%, even more preferably 96.5 mol%, and particularly preferably 97.0 mol%. If it is less than 95.0 mol%, the crystallinity decreases, which may lead to a higher thermal shrinkage rate, and is therefore undesirable. Furthermore, the upper limit of the amount of terephthalic acid component in the polyester resin contained in the film is preferably 99.5 mol%, and more preferably 99.0 mol%. Since recycled polyester resin made from PET bottles often contains dicarboxylic acid components other than terephthalic acid, such as isophthalic acid, if the terephthalic acid component constituting the polyester resin in the film exceeds 99.5 mol%, it becomes difficult to manufacture polyester films with a high proportion of recycled resin, and is therefore undesirable.

[0024] The lower limit of the amount of isophthalic acid component in the total dicarboxylic acid components constituting the polyester resin contained in the base film is preferably 0.5 mol%, more preferably 0.7 mol%, even more preferably 0.9 mol%, and particularly preferably 1.0 mol%. Since recycled polyester resin made from PET bottles sometimes contains a large amount of isophthalic acid, having less than 0.5 mol% of isophthalic acid component in the polyester resin constituting the film is undesirable because it makes it difficult to manufacture polyester films with a high proportion of recycled resin. The upper limit of the amount of isophthalic acid component in the total dicarboxylic acid components constituting the polyester resin contained in the film is preferably 5.0 mol%, more preferably 4.0 mol%, even more preferably 3.5 mol%, and particularly preferably 3.0 mol%. If it exceeds 5.0 mol%, the crystallinity decreases, which can lead to a high thermal shrinkage rate, and is therefore undesirable. Furthermore, setting the isophthalic acid component content within the above range makes it easier to create films with excellent lamination strength, shrinkage rate, and thickness uniformity, which is preferable.

[0025] The upper limit of the intrinsic viscosity of recycled resin made from PET bottles is preferably 0.90 dl / g, more preferably 0.80 dl / g, even more preferably 0.77 dl / g, and particularly preferably 0.75 dl / g. If it exceeds 0.9 dl / g, the resin may become difficult to extrude from the extruder, which can reduce productivity and is therefore undesirable.

[0026] The lower limit of the content of recycled polyester resin from PET bottles in the film is preferably 50% by weight, more preferably 65% ​​by weight, and even more preferably 75% by weight. If the content is less than 50% by weight, the utilization of recycled resin is insufficient and not very desirable in terms of contribution to environmental protection. Since the recycled resin is produced by solid-phase polymerization, it has a low content of oligomers, which can be a cause of film whitening. Therefore, a higher recycled resin content tends to improve film whitening after retort processing. If the recycled resin content is less than 50%, there is a concern that uneven whitening of the film after retort processing will be exacerbated. On the other hand, the upper limit of the content of recycled polyester resin from PET bottles is not particularly limited, but is preferably 95% by weight, more preferably 90% by weight, and even more preferably 85% by weight. If it exceeds 95% by weight, it may not be possible to sufficiently add lubricants and additives such as inorganic particles to improve the functionality of the film, which is not very desirable. Furthermore, when adding lubricants or additives such as inorganic particles to improve the film's functionality, recycled polyester resin from PET bottles can be used as the masterbatch (high-concentration resin).

[0027] As for lubricants, inorganic lubricants such as silica, calcium carbonate, and alumina are preferred, as are organic lubricants, with silica and calcium carbonate being more preferred. These can be used to achieve transparency and lubricity.

[0028] The lower limit of the lubricant content in the base film is preferably 0.01% by weight, more preferably 0.015% by weight, and even more preferably 0.02% by weight. If it is less than 0.01% by weight, the slipperiness may decrease. The upper limit is preferably 1% by weight, more preferably 0.2% by weight, and even more preferably 0.1% by weight. If it exceeds 1% by weight, the transparency may decrease, which is not very desirable.

[0029] The method for manufacturing the base film used in the laminated body of the present invention is not particularly limited, but the following manufacturing method is recommended, for example. The temperature setting for melting and extruding the resin in the extruder is important. The basic idea is that (1) since the polyester resin used in PET bottles contains isophthalic acid components, degradation is suppressed by extruding at the lowest possible temperature, and (2) there are parts that are melted at high temperature and high pressure in order to sufficiently and uniformly melt the intrinsic viscosity and fine highly crystalline parts. The inclusion of isophthalic acid components reduces the stereoregularity of polyester, leading to a decrease in the melting point. Therefore, extrusion at high temperatures results in a significant decrease in melt viscosity due to heat and degradation, leading to a decrease in mechanical strength and an increase in degraded foreign matter. Furthermore, simply lowering the extrusion temperature may not allow for sufficient melting and mixing, which can lead to problems such as increased thickness unevenness and foreign matter such as fish eyes. For the reasons above, recommended manufacturing methods include, for example, using two extruders in tandem, increasing the pressure in the filter section, and using a screw with strong shear force in part of the screw configuration.

[0030] The lower limit of the set temperature for the resin melting section in the extruder (excluding the maximum set temperature for the compression section of the screw in the extruder) is preferably 270°C, and the upper limit is preferably 290°C. Below 270°C, extrusion is difficult, and above 290°C, resin degradation may occur, which is undesirable.

[0031] The lower limit of the maximum set temperature in the compression section of the screw inside the extruder is preferably 295°C. Polyester resin used in PET bottles often contains high-melting-point crystals (260°C to 290°C) for transparency reasons. In addition, additives and crystallization nucleating agents are added, resulting in variations in the fine melting behavior within the resin material. Below 295°C, it becomes difficult to sufficiently melt these crystals, which is undesirable. The upper limit of the maximum set temperature in the compression section of the screw inside the extruder is preferably 310°C. Above 310°C, resin degradation may occur, which is undesirable.

[0032] The lower limit of the time the resin passes through the region of the highest set temperature in the compression section of the screw in the extruder is preferably 10 seconds, more preferably 15 seconds. If it is less than 10 seconds, the polyester resin used for PET bottles cannot be sufficiently melted, which is undesirable. The upper limit is preferably 60 seconds, more preferably 50 seconds. If it exceeds 60 seconds, resin degradation is likely to occur, which is undesirable. By setting the extruder within this range, it is possible to obtain a film with less thickness unevenness, foreign matter such as fisheyes, and discoloration, while using a large amount of polyester resin recycled from PET bottles.

[0033] The resin, thus molten, is extruded into a sheet on a cooling roll and then biaxially stretched. While simultaneous biaxial stretching is acceptable, sequential biaxial stretching is particularly preferred. These methods facilitate achieving both productivity and the quality required for this invention.

[0034] In this invention, the method of stretching the film is not particularly limited, but the following points are important. When stretching a resin containing isophthalic acid with an intrinsic viscosity of 0.58 dl / g or more, the ratios of stretching in the longitudinal (MD) direction and transverse (TD) direction, and the temperature are important. If the MD stretching ratio or temperature is not appropriate, the stretching force will not be applied uniformly, the molecular orientation will be insufficient, and the thickness may become uneven or the mechanical properties may be insufficient. In addition, film breakage may occur in the subsequent TD stretching step, or extreme thickness unevenness may occur. If the TD stretching ratio or temperature is not appropriate, the film will not be stretched uniformly, the balance of longitudinal and transverse orientation will be poor, and the mechanical properties may be insufficient. Furthermore, if the film proceeds to the next heat-setting step with large thickness unevenness or insufficient molecular chain orientation, uniform relaxation may not be possible, leading to problems such as further increase in thickness unevenness and insufficient mechanical properties. Therefore, it is generally recommended that in MD stretching, stretching is performed in stages by controlling the temperature as described below, and in TD stretching, stretching is performed at an appropriate temperature to prevent the orientation balance from becoming extremely poor. The following examples illustrate the principles, although they are not limited to the following embodiments.

[0035] For longitudinal (MD) stretching methods, roll stretching and IR heating methods are preferred.

[0036] The lower limit of the MD stretching temperature is preferably 100°C, more preferably 110°C, and even more preferably 120°C. Below 100°C, even if a polyester resin with an intrinsic viscosity of 0.58 dl / g or higher is stretched and the molecules are oriented in the longitudinal direction, film breakage may occur in the subsequent transverse stretching step, or extreme thickness defects may occur, which is undesirable. The upper limit is preferably 140°C, more preferably 135°C, and even more preferably 130°C. Above 140°C, the orientation of the molecular chains may become insufficient, resulting in insufficient mechanical properties, which is not very desirable.

[0037] The lower limit of the MD stretching ratio is preferably 2.5 times, more preferably 3.5 times, and even more preferably 4 times. If it is less than 2.5 times, even if a polyester resin with an intrinsic viscosity of 0.58 dl / g or higher is stretched and molecular orientation is performed in the longitudinal direction, film breakage may occur in the next transverse stretching step, or extreme thickness defects may occur, which is not very desirable. The upper limit is preferably 5 times, more preferably 4.8 times, and even more preferably 4.5 times. If it exceeds 5 times, the effect of improving mechanical strength and thickness uniformity may saturate, and it will not be very meaningful.

[0038] While the single-stage stretching described above is acceptable as the MD stretching method, it is more preferable to divide the stretching into two or more stages. Dividing the stretching into two or more stages makes it possible to effectively stretch polyester resin made from recycled resin containing isophthalic acid, which has high intrinsic viscosity, resulting in better thickness uniformity, laminate strength, and mechanical properties.

[0039] The preferred lower limit for the first-stage MD stretching temperature is 110°C, and more preferably 115°C. Below 110°C, there is insufficient heat, preventing sufficient longitudinal stretching and resulting in poor planarity, which is undesirable. The preferred upper limit for the first-stage MD stretching temperature is 125°C, and more preferably 120°C. Above 125°C, the orientation of the molecular chains becomes insufficient, which may lead to a decrease in mechanical properties, and is therefore undesirable.

[0040] The preferred lower limit for the first-stage MD stretching ratio is 1.1x, and more preferably 1.3x. A ratio of 1.1x or higher allows for sufficient longitudinal stretching of the polyester resin with an intrinsic viscosity of 0.58 dl / g or higher in the first stage, thereby increasing productivity. The preferred upper limit for the first-stage MD stretching ratio is 2x, and more preferably 1.6x. A ratio exceeding 2x is undesirable because the orientation of the molecular chains in the longitudinal direction becomes too high, making it difficult to stretch in subsequent stages and potentially resulting in a film with uneven thickness.

[0041] The preferred lower limit of the second (or final) MD stretching temperature is preferably 110°C, and more preferably 115°C. A temperature of 110°C or higher allows for sufficient longitudinal stretching of polyester resin with an intrinsic viscosity of 0.58 dl / g or higher, enabling transverse stretching in the next step and resulting in good thickness uniformity in both the longitudinal and transverse directions. The preferred upper limit is preferably 130°C, and more preferably 125°C. Above 130°C, crystallization is promoted, making transverse stretching difficult and potentially leading to greater thickness uniformity, which is undesirable.

[0042] The preferred lower limit of the MD stretching ratio for the second (or final) stage is preferably 2.1 times, and more preferably 2.5 times. If it is less than 2.1 times, even if a polyester resin with an intrinsic viscosity of 0.58 dl / g or higher is stretched and molecular orientation is achieved in the longitudinal direction, film breakage may occur in the next transverse stretching step, or extreme thickness defects may occur, which is not desirable. The preferred upper limit is preferably 3.5 times, and more preferably 3.1 times. If it exceeds 3.5 times, the longitudinal orientation becomes too high, which may prevent stretching in the second and subsequent stages, or result in a film with large thickness variations, which is not desirable.

[0043] The lower limit of the TD stretching temperature is preferably 110°C, more preferably 120°C, and even more preferably 125°C. Below 110°C, the lateral stretching stress increases, which may cause film breakage or extreme thickness unevenness, and is therefore undesirable. The upper limit is preferably 150°C, more preferably 145°C, and even more preferably 140°C. Above 150°C, the orientation of the molecular chains does not increase, which may lead to a decrease in mechanical properties, and is therefore undesirable.

[0044] The lower limit of the transverse (TD) stretching ratio is preferably 3.5 times, and more preferably 3.9 times. If it is less than 3.5 times, the molecular orientation may be weak, resulting in insufficient mechanical strength, which is undesirable. Also, if the orientation of the molecular chains in the longitudinal direction is large, the balance between longitudinal and transverse directions will be poor, leading to greater thickness unevenness, which is also undesirable. The upper limit is preferably 5.5 times, and more preferably 4.5 times. If it exceeds 5.5 times, breakage may occur, which is undesirable.

[0045] To obtain the base film used in the laminated film of the present invention, it is desirable to appropriately set the conditions for heat setting, which is performed in the tenter immediately after the completion of TD stretching, and for lowering the film to room temperature thereafter. Polyester film containing recycled resin made from PET bottles containing isophthalic acid has lower crystallinity, is more easily melted into very small pieces, and has lower mechanical strength compared to ordinary polyethylene terephthalate film that does not contain isophthalic acid. Therefore, if the film is rapidly exposed to high temperatures under tension after the completion of stretching, or rapidly cooled under tension after the completion of high-temperature heat setting, the tension balance in the width direction is disrupted due to the unavoidable temperature difference in the width direction of the film, resulting in uneven thickness and poor mechanical properties. On the other hand, if one tries to address this phenomenon by lowering the heat setting temperature, sufficient laminate strength may not be obtained. In the present invention, it is recommended to perform a slightly low-temperature heat setting 1 and a sufficiently high-temperature heat setting 2 (heat setting 3 if necessary) after the completion of stretching, followed by a slow cooling process to lower the film to room temperature. However, this method is not the only one that can be used. Other methods include controlling the film tension according to the speed of the hot air in the tenter and the temperature of each zone, performing a relatively low-temperature heat treatment with sufficient furnace length after the stretching is complete, and using a heated roll to relax the film after heat setting is complete.

[0046] As an example, the method using temperature control of a tenter is shown below.

[0047] The lower limit of the temperature for heat fixing 1 is preferably 160°C, and more preferably 170°C. Below 160°C, the thermal shrinkage rate will ultimately be large, which may cause misalignment or shrinkage during processing, and is therefore undesirable. The upper limit is preferably 215°C, and more preferably 210°C. Above 215°C, the film will be subjected to a high temperature rapidly, which may result in uneven thickness or breakage, and is therefore undesirable.

[0048] The lower limit of the time for heat setting 1 is preferably 0.5 seconds, and more preferably 2 seconds. If it is less than 0.5 seconds, the film temperature may not rise sufficiently. The upper limit is preferably 10 seconds, and more preferably 8 seconds. If it exceeds 10 seconds, productivity may decrease and is therefore undesirable.

[0049] The lower limit of the temperature for heat fixing 2 is preferably 220°C, and more preferably 227°C. Below 220°C, the thermal shrinkage rate increases, which can lead to misalignment or shrinkage during processing, and is therefore undesirable. The upper limit is preferably 240°C, and more preferably 237°C. Above 240°C, the film may melt, or even if it does not melt, it may become brittle, which is therefore undesirable.

[0050] The lower limit of the time for heat setting 2 is preferably 0.5 seconds, and more preferably 3 seconds. A time of less than 0.5 seconds may increase the likelihood of fracture during heat setting, which is undesirable. The upper limit is preferably 10 seconds, and more preferably 8 seconds. A time exceeding 10 seconds may cause sagging and uneven thickness, which is undesirable.

[0051] If necessary, the lower limit of the temperature when heat fixing 3 is provided is preferably 205°C, and more preferably 220°C. Below 205°C, the thermal shrinkage rate increases, which can lead to misalignment or shrinkage during processing, and is therefore undesirable. The upper limit is preferably 240°C, and more preferably 237°C. Above 240°C, the film may melt, or even if it does not melt, it may become brittle, which is therefore undesirable.

[0052] If necessary, the lower limit of the time for heat setting 3 is preferably 0.5 seconds, and more preferably 3 seconds. A time of less than 0.5 seconds may increase the likelihood of fracture during heat setting, which is undesirable. The upper limit is preferably 10 seconds, and more preferably 8 seconds. A time exceeding 10 seconds may cause sagging and uneven thickness, which is undesirable.

[0053] TD relaxation can be performed at any point during heat fixing. The lower limit is preferably 0.5% and more preferably 3%. Below 0.5%, the thermal shrinkage rate, especially in the lateral direction, becomes large, which can lead to misalignment and shrinkage during processing and is therefore undesirable. The upper limit is preferably 10% and more preferably 8%. Above 10%, sagging and uneven thickness may occur, which is therefore undesirable.

[0054] The lower limit of the slow cooling temperature after TD heat fixation is preferably 90°C, and more preferably 100°C. Below 90°C, because the film contains isophthalic acid, rapid temperature changes can cause shrinkage, leading to uneven thickness or breakage, which is undesirable. The upper limit of the slow cooling temperature is preferably 150°C, and more preferably 140°C. Above 150°C, sufficient cooling effect may not be obtained, which is undesirable.

[0055] The lower limit of the slow cooling time after heat setting is preferably 2 seconds, and more preferably 4 seconds. A time of less than 2 seconds may not provide sufficient slow cooling, so it is not very desirable. The upper limit is preferably 20 seconds, and more preferably 15 seconds. A time exceeding 20 seconds tends to be disadvantageous in terms of productivity, so it is not very desirable.

[0056] In the present invention, the upper limit of haze per unit thickness of the substrate film layer is preferably 0.66% / μm, more preferably 0.60% / μm, and even more preferably 0.53% / μm. When printing is applied to a substrate film layer with a haze of 0.66% / μm or less, the quality of the printed characters and images is improved.

[0057] Furthermore, the base film layer in the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment, etc., as long as the objective of the present invention is not impaired, and may also be subjected to known anchor coating treatment, printing, decoration, etc.

[0058] Furthermore, layers of other materials may be laminated onto the base film layer in the present invention. This can be done by laminating the base film layer after its manufacture or during the film formation process.

[0059] [Inorganic thin film layer] In this invention, the substrate film has an inorganic thin film layer (A) on its surface. The inorganic thin film layer (A) is a thin film made of a metal or an inorganic oxide. The material forming the inorganic thin film layer is not particularly limited as long as it can be made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxides such as silicon dioxide (silica), aluminum oxide (alumina), and mixtures of silicon dioxide and aluminum oxide are preferred. In particular, a composite oxide of silicon dioxide and aluminum oxide is preferred in terms of achieving both flexibility and density of the thin film layer. In this composite oxide, the mixing ratio of silicon dioxide and aluminum oxide is preferably in the range of 20 to 70% by mass of Al in terms of the mass ratio of the metal content. If the Al concentration is less than 20% by mass, the water vapor barrier properties may be low. On the other hand, if it exceeds 70% by 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, reducing the gas barrier properties. Here, silicon dioxide refers to various silicon oxides such as SiO and SiO2 or mixtures thereof, and aluminum oxide refers to various aluminum oxides such as AlO and Al2O3 or mixtures thereof It is an object.

[0060] The thickness of the inorganic thin film layer (A) is typically 1 to 100 nm, preferably 5 to 50 nm. If the thickness of the inorganic thin film layer (A) is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties. On the other hand, if it is made excessively thick beyond 100 nm, the corresponding improvement in gas barrier properties cannot be obtained, and it may even be disadvantageous in terms of flexibility and manufacturing costs.

[0061] There are no particular restrictions on the method for forming the inorganic thin film layer (A). For example, any known deposition method such as vacuum deposition, sputtering, ion plating, or other physical deposition methods (PVD), or chemical deposition (CVD), can be used as appropriate. Below, a typical method for forming the inorganic thin film layer (A) will be described using a silicon oxide / aluminum oxide thin film as an example. For example, when using vacuum deposition, a mixture of SiO2 and Al2O3, or a mixture of SiO2 and Al, is preferably used as the deposition raw material. These deposition raw materials are usually particles, and it is desirable that the size of each particle is such that the pressure during deposition does not change, with a preferred particle size of 1 mm to 5 mm. For heating, methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating can be used. It is also possible to use reactive deposition by introducing oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc. as a reaction gas, or by using means such as ozone addition or ion assistance. Furthermore, the film deposition conditions can be arbitrarily changed, such as by applying a bias to the substrate (the laminated film used for deposition) or by heating or cooling the substrate. These deposition materials, reaction gases, bias, heating / cooling of the substrate can also be similarly modified when using sputtering or CVD methods.

[0062] [Coating layer] The laminate of the present invention may have a coating layer (X) between the base film layer and the inorganic thin film layer (A) for the purpose of ensuring stable gas barrier properties and laminate strength. Examples of resin compositions used for the coating layer (X) provided between the base film layer and the inorganic thin film layer (A) include resins such as urethane, polyester, acrylic, titanium, isocyanate, imine, and polybutadiene, to which curing agents such as epoxy, isocyanate, melamine, oxazoline, and carbodiimide are added. It is preferable that the resin compositions used for these coating layers (X) contain a silane coupling agent having at least one type of organic functional group. Examples of such organic functional groups include alkoxy groups, amino groups, epoxy groups, and isocyanate groups. The addition of the silane coupling agent further improves the laminate strength after retort treatment.

[0063] Among the resin compositions used for the coating layer (X), it is preferable to use a mixture of a resin containing an oxazoline group or a carbodiimide group, an acrylic resin, and a urethane resin. These functional groups have high affinity for inorganic thin films and can react with oxygen-deficient portions of inorganic oxides and metal hydroxides generated during the formation of the inorganic thin film layer, exhibiting strong adhesion to the inorganic thin film layer. Furthermore, unreacted functional groups present in the coating layer can react with carboxylic acid terminals generated by hydrolysis of the substrate film layer and the coating layer, forming crosslinks.

[0064] In this invention, the amount of coating layer (X) attached is 0.010 to 0.200 (g / m²). 2 It is preferable to have a coating layer of 0.015 g / m². This allows for uniform control of the coating layer, resulting in the dense deposition of the inorganic thin film layer. Furthermore, the cohesive force within the coating layer is improved, and the adhesion between each layer of the base film, coating layer (X), and inorganic thin film layer (A) is also increased, thereby improving the water-resistant adhesion of the coating layer. The amount of coating layer (X) attached is preferably 0.015 g / m². 2 ) or more, more preferably 0.020 (g / m³) 2 ) or more, more preferably 0.025 (g / m³) 2)Above, preferably 0.190 (g / m 2 ) or less, more preferably 0.180 (g / m 2 ) or less, still more preferably 0.170 (g / m 2 ) or less. When the coating amount of the coating layer (X) exceeds 0.200 (g / m 2 , the cohesive force inside the coating layer becomes insufficient, and good adhesion may not be exhibited. In addition, since the uniformity of the coating layer also decreases, defects may occur in the inorganic thin film layer, and the gas barrier property may decrease. Moreover, the manufacturing cost increases, which is economically disadvantageous. On the other hand, when the film thickness of the coating layer (X) is less than 0.010 (g / m 2 ), the substrate may not be sufficiently coated, and sufficient gas barrier property and interlayer adhesion may not be obtained.

[0065] The method for forming the coating layer (X) is not particularly limited, and for example, a conventionally known method such as a coating method can be adopted. Among the coating methods, preferred methods include an offline coating method and an inline coating method. For example, in the case of an inline coating method performed in the process of manufacturing a substrate film layer, the drying and heat treatment conditions during coating depend on the coating thickness and the conditions of the apparatus, but it is preferable to feed it immediately after coating into a stretching process in the perpendicular direction and dry it in the preheating zone or the stretching zone of the stretching process. In such a case, the temperature is usually preferably about 50 to 250°C. Examples of the solvent used when using the coating method include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; polyhydric alcohol derivatives such as ethylene glycol monomethyl ether, etc.

[0066] [Protective layer] In this invention, a protective layer (a) is provided on the inorganic thin film layer (A). The inorganic thin film layer, which consists of a metal oxide layer, is not a completely dense film, but has minute defects scattered throughout. By coating the metal oxide layer with a specific protective layer resin composition described later to form the protective layer (a), the resin in the protective layer resin composition penetrates into the defects in the metal oxide layer, resulting in the effect of stabilizing the gas barrier properties. In addition, by using a material with gas barrier properties for the protective layer (a) itself, the gas barrier performance of the laminated film is greatly improved. Furthermore, since the barrier layer prevents hot water from penetrating the substrate, the transparency of the film can also be maintained.

[0067] In this invention, the amount of protective layer (a) attached is 0.10 to 0.40 (g / m²). 2 It is preferable to have a protective layer of 0.13 g / m². This allows for uniform control of the protective layer during coating, resulting in a film with fewer coating inconsistencies and defects. Furthermore, the cohesive force of the protective layer itself is improved, and the adhesion between the inorganic thin film layer and the protective layer becomes stronger. In addition, the protective layer contributes to suppressing oligomer exposure, and the haze after retorting is stabilized. The amount of protective layer (a) attached is preferably 0.13 g / m². 2 ) or more, more preferably 0.16 (g / m³) 2 ) or more, more preferably 0.19 (g / m³) 2 ) or more, preferably 0.37 (g / m³) 2 ) or less, more preferably 0.34 (g / m³) 2 ) or less, more preferably 0.31 (g / m³) 2 ) or less. The amount of protective layer (a) attached is 0.400 (g / m 2 When the thickness exceeds 0.10 (g / m²), the gas barrier properties improve, but the cohesive force within the protective layer becomes insufficient, and the uniformity of the protective layer also decreases, which may result in unevenness or defects in the appearance of the coating, or insufficient gas barrier properties and adhesion. On the other hand, when the thickness of protective layer (a) exceeds 0.10 (g / m²), 2 If the value is less than ), sufficient gas barrier properties and interlayer adhesion may not be obtained.

[0068] The resin composition used for the protective layer (a) formed on the surface of the inorganic thin film layer of the laminate of the present invention has a urethane resin as an essential component, and other resins such as polyester, acrylic, titanium, isocyanate, imine, and polybutadiene can be used, and a curing agent such as epoxy, isocyanate, or melamine may also be added. In particular, the inclusion of urethane resin is preferable because, in addition to the barrier performance due to the high cohesiveness of the urethane bonds themselves, the polar groups interact with the inorganic thin film layer, and the presence of amorphous regions provides flexibility, thus suppressing damage to the inorganic thin film layer even when bending loads are applied. Polyester resin is also preferable because similar effects can be expected.

[0069] (urethane resin) The urethane resin used in this invention preferably has a glass transition temperature (Tg) of 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher, from the viewpoint of improving barrier properties through cohesive force. However, in order to exhibit adhesion, a flexible resin with a Tg of 100°C or lower that has excellent flexibility may be mixed in. In that case, the addition ratio of the flexible resin is preferably in the range of 0 to 80%, more preferably in the range of 10 to 70%, and even more preferably in the range of 20 to 60%. When the addition ratio is within the above range, both cohesive force and flexibility can be achieved, resulting in good barrier properties and adhesion. Note that if the addition ratio exceeds 80%, the film may become too soft, leading to a decrease in barrier performance.

[0070] From the viewpoint of improving gas barrier properties, it is more preferable to use a urethane resin that contains aromatic or aromatic aliphatic diisocyanate components as its main constituents. Among these, it is particularly preferable to contain a metaxylylene diisocyanate component. By using the above resin, the cohesive force of the urethane bonds can be further enhanced by the stacking effect between aromatic rings, resulting in good gas barrier properties.

[0071] In the present invention, it is preferable that the proportion of aromatic or aromatic aliphatic diisocyanate in the urethane resin be in the range of 50 mol% or more (50 to 100 mol%) out of 100 mol% of the polyisocyanate component (F). The total proportion of aromatic or aromatic aliphatic diisocyanate is preferably 60 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 80 to 100 mol%. As such a resin, the "Takelac® WPB" series, commercially available from Mitsui Chemicals, Inc., can be suitably used. If the total proportion of aromatic or aromatic aliphatic diisocyanate is less than 50 mol%, good gas barrier properties may not be obtained.

[0072] The urethane resin used in this invention may contain various silicon-based crosslinking agents, to the extent that they do not impair gas barrier properties, in order to improve the cohesive strength of the film and its resistance to humid heat adhesion. A known method for introducing silanol groups into the protective layer is to add silane coupling agents afterwards. However, this method increases the complexity of the work and increases the possibility of errors in measuring the amount added. On the other hand, pre-containing silanol groups in the polyurethane dispersion skeleton has the advantage of preventing the aforementioned complexity and errors.

[0073] If the amount of silanol groups contained in the polyurethane dispersion is less than 700 mg per kg of resin, the amount of Si element contained in the silanol groups will be insufficient for cross-linking, leading to degradation of the resin itself during retort processing, and causing a decrease in adhesion and gas barrier properties after retort processing. Furthermore, if the amount of silanol groups exceeds 1700 mg per kg of resin constituting the polyurethane dispersion (as the amount of Si element contained in the silanol groups), the cross-linking structure becomes excessive, impairing the flexibility of the protective layer and leading to degradation of the inorganic thin film and reduced flexibility during retort processing. In addition, the increased amount of unreacted silanol groups weakens water resistance, and degradation of the resin itself during retort processing is also possible.

[0074] On the other hand, examples of crosslinking agents that can be added later include silicon-based crosslinking agents, oxazoline compounds, carbodiimide compounds, and epoxy compounds. Among these, silicon-based crosslinking agents can particularly improve water-resistant adhesion to inorganic thin film layers. From this viewpoint, silicon-based crosslinking agents are particularly preferred. Other crosslinking agents such as oxazoline compounds, carbodiimide compounds, and epoxy compounds may also be used in combination.

[0075] As silicon-based crosslinking agents, silane coupling agents are preferred from the viewpoint of crosslinking inorganic and organic substances. Suitable silane coupling agents include hydrolyzable alkoxysilane compounds, such as halogen-containing alkoxysilanes (chloroC2-4 alkyltriC1-4 alkoxysilanes such as 2-chloroethyltrimethoxysilane, 2-chloroethyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, etc.), and alkoxysilanes having epoxy groups [2-glycidyloxyethyltrimethoxysilane, 2-glycidyloxyethyltriethoxysilane, 3-glycidyloxypropyl Glycidyloxy C2-4 alkyl triC1-4 alkoxysilanes such as 3-glycidyloxypropyltriethoxysilane, glycidyloxydiC2-4 alkyldiC1-4 alkoxysilanes such as 3-glycidyloxypropylmethyldimethoxysilane and 3-glycidyloxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-(3,4-epoxycyclohexyl)propyl [(Epoxycycloalkyl)C2-4 alkyltriC1-4 alkoxysilanes such as trimethoxysilane, amino group-containing alkoxysilanes [aminoC2-4 alkyltriC1-4 alkoxysilanes such as 2-aminoethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, etc., aminoC2-4 alkyltriC1-4 alkoxysilanes such as 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, etc., 2-[N-(2-aminoethyl)aminoethyl [N-(2-aminoethyl)amino]propyltrimethoxysilane, 3-[N-(2-aminoethyl)amino]propyltrimethoxysilane, 3-[N-(2-aminoethyl)amino]propyltriethoxysilane, etc. (2-aminoC2-4 alkyl)aminoC2-4 alkyltriC1-4 alkoxysilanes, etc. (aminoC2-4 alkyl)aminodiC2-4 alkyldiC1-4 alkoxysilanes, etc., 3-[N-(2-aminoethyl)amino]propylmethyldimethoxysilane, 3-[N-(2-aminoethyl)amino]propylmethyldiethoxysilane, etc.]Alkoxysilanes having a mercapto group (mercapto C2-4 alkyl triC1-4 alkoxysilanes such as 2-mercaptoethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, etc., mercapto diC2-4 alkyl diC1-4 alkoxysilanes such as 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, etc.), alkoxysilanes having a vinyl group (vinyl triC1-4 alkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, etc.), ethylene Examples of silane coupling agents include alkoxysilanes having an unsaturated bonding group, such as (meth)acryloxy C2-4 alkyltriC1-4 alkoxysilanes like 2-(meth)acryloxyethyltrimethoxysilane, 2-(meth)acryloxyethyltriethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, and (meth)acryloxydiC2-4 alkyldiC1-4 alkoxysilanes like 3-(meth)acryloxypropylmethyldimethoxysilane and 3-(meth)acryloxypropylmethyldiethoxysilane. These silane coupling agents can be used alone or in combination of two or more. Among these silane coupling agents, silane coupling agents having an amino group are preferred.

[0076] The silane coupling agent, a silicon-based crosslinking agent, is preferably added to the protective layer in an amount of 0.25 to 3.00% by mass, more preferably 0.5 to 2.75% by mass, and even more preferably 0.75 to 2.50% by mass. If the amount added exceeds 3.00% by mass, the film hardens and the cohesive force improves, but some unreacted areas may occur, potentially reducing the adhesion between layers. On the other hand, if the amount added is less than 0.25% by mass, sufficient cohesive force may not be obtained.

[0077] (Polyester resin) The polyester resin used in the protective layer of the present invention is produced by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component. The molecular weight of the polyester is not particularly limited as long as it provides sufficient film toughness, coating suitability, and solvent solubility as a coating material, but the number average molecular weight is 1,000 to 50,000, more preferably 1,500 to 30,000. The functional groups at the polyester ends are also not particularly limited; they may be alcohol-terminated, carboxylic acid-terminated, or a combination of both. However, when using an isocyanate-based curing agent in combination, it is necessary to use a polyester polyol primarily composed of alcohol-terminated components.

[0078] [Glass transition temperature (Tg) of polyester] The Tg of the polyester used in this invention must be 15°C or higher. If the temperature is lower than this, the resin will become sticky after the coating operation, making blocking more likely and making the winding operation after coating difficult. If the Tg is below 15°C, it becomes difficult to prevent blocking even with the addition of an anti-blocking agent, and even under high pressure conditions near the winding core. A more preferable Tg temperature is 18°C ​​or higher, and even more preferably 25°C or higher.

[0079] The polyester used in this invention is obtained by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component. [Polyhydric carboxylic acid components] The polycarboxylic acid component of the polyester used in the present invention is characterized by containing at least one ortho-oriented aromatic dicarboxylic acid or its anhydride. Aromatic polycarboxylic acids in which the carboxylic acid is substituted at the ortho position, or their anhydrides, include orthophthalic acid or its anhydride, naphthalene 2,3-dicarboxylic acid or its anhydride, naphthalene 1,2-dicarboxylic acid or its anhydride, anthraquinone 2,3-dicarboxylic acid or its anhydride, and 2,3-anthracenecarboxylic acid or its anhydride. These compounds may have substituents on any carbon atom of the aromatic ring. Examples of substituents include chloro group, bromo group, methyl group, ethyl group, i-propyl group, hydroxyl group, methoxy group, ethoxy group, phenoxy group, methylthio group, phenylthio group, cyano group, nitro group, amino group, phthalimide group, carboxyl group, carbamoyl group, N-ethylcarbamoyl group, phenyl group, or naphthyl group. Furthermore, polyester polyols in which these polycarboxylic acids are used at a rate of 70 to 100% by mass are particularly preferred because they have a high barrier-improving effect and excellent solvent solubility, which is essential for coating materials.

[0080] The polyester used in this invention may be copolymerized with other polycarboxylic acid components, to the extent that it does not impair the effects of the invention. Specifically, as aliphatic polycarboxylic acids, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, etc.; as unsaturated bond-containing polycarboxylic acids, maleic anhydride, maleic acid, fumaric acid, etc.; as alicyclic polycarboxylic acids, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc.; as aromatic polycarboxylic acids, terephthalic acid, isophthalic acid, pyromellitic acid, trimellitic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, diphenic acid and its anhydrides, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid and their anhydrides or ester-forming derivatives; polybasic acids such as p-hydroxybenzoic acid, p-(2-hydroxyethoxy)benzoic acid and their ester-forming derivatives can be used alone or in mixtures of two or more. In particular, succinic acid, 1,3-cyclopentanedicarboxylic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalic acid, and diphenic acid are preferred from the viewpoint of organic solvent solubility and gas barrier properties.

[0081] [Polyhydric alcohol components] The polyhydric alcohol component of the polyester used in this invention is not particularly limited as long as it is possible to synthesize a polyester that exhibits gas barrier replenishment performance. However, it is preferable that the polyhydric alcohol component contains at least one selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, cyclohexanedimethanol, and 1,3-bishydroxyethylbenzene. Among these, it is presumed that the fewer the number of carbon atoms between oxygen atoms, the less the molecular chain becomes excessively flexible and the less oxygen permeable it is, so it is most preferable to use ethylene glycol as the main component.

[0082] In the present invention, it is preferable to use the polyhydric alcohol component described above for the polyester, but other polyhydric alcohol components may also be copolymerized as long as they do not impair the effects of the present invention. Specifically, examples of diols include 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, methylpentanediol, dimethylbutanediol, butylethylpropanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Examples of trihydric or higher alcohols include glycerol, trimethylolpropane, trimethylolethane, tris(2-hydroxyethyl) isocyanurate, 1,2,4-butanetriol, pentaerythritol, and dipentaerythulitol. In particular, among the trihydric alcohols, polyesters using glycerol and tris(2-hydroxyethyl) isocyanurate in combination are especially preferred because they have good organic solvent solubility due to their branched structure and moderately high crosslink density, as well as excellent barrier function.

[0083] Examples of catalysts used in the reaction to obtain the polyester used in the present invention include tin-based catalysts such as monobutyl tin oxide and dibutyl tin oxide, titanium-based catalysts such as tetra-isopropyl titanate and tetra-butyl titanate, and acid catalysts such as zirconia-based catalysts such as tetra-butyl zirconate. It is preferable to use a combination of the above-mentioned titanium-based catalysts, such as tetra-isopropyl titanate and tetra-butyl titanate, which have high activity for esterification reactions, and the above-mentioned zirconia catalyst. The amount of catalyst used is 1 to 1000 ppm relative to the total mass of the reaction raw materials used, and more preferably 10 to 100 ppm. If the amount is less than 1 ppm, the catalytic effect is difficult to obtain, and if it exceeds 1000 ppm, problems may arise in which the urethane formation reaction is inhibited when an isocyanate curing agent is used.

[0084] In this invention, when polyester resin is used as the main component of the coating agent constituting the protective layer, it is necessary to use an isocyanate-based curing agent to form a urethane resin. In this case, the coating layer becomes cross-linked, which has the advantage of improving heat resistance, abrasion resistance, and rigidity. Therefore, it is easy to use for boiling and retort packaging. On the other hand, there are also problems such as the inability to reuse the liquid after mixing with the curing agent and the necessity of a curing (aging) process after coating.

[0085] The polyisocyanate compound used in the protective layer (a) of the present invention reacts, at least partially, with the polyester when it has hydroxyl groups, forming a urethane structure and thus acting as a high-voltage resin component. By curing the polymer and causing the polymer chains to aggregate, the gas barrier function can be further enhanced. Furthermore, if the coating resin is a linear resin, crosslinking it with a trivalent or higher polyisocyanate can impart heat resistance and abrasion resistance. The polyisocyanate compound used in this invention may be diisocyanate, a trivalent or higher polyisocyanate, a low molecular weight compound, or a high molecular weight compound, but it is preferable from the viewpoint of improving the gas barrier function if it contains an aromatic ring or an aliphatic ring as part of its skeleton. For example, examples of isocyanates having an aromatic ring include toluene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and naphthalene diisocyanate; examples of isocyanates having an aliphatic ring include hydrogenated xylylene diisocyanate, hydrogenated toluene diisocyanate, isophorone diisocyanate, norborn diisocyanate, or trimers of these isocyanate compounds; and end-isocyanate group-containing compounds obtained by reacting an excess amount of these isocyanate compounds with low molecular weight active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, and triethanolamine, or high molecular weight active hydrogen compounds such as various polyester polyols, polyether polyols, and polyamides.

[0086] The coating method for the protective layer resin composition is not particularly limited as long as it is a method of coating the film surface to form a layer. For example, conventional coating methods such as gravure coating, reverse roll coating, wire bar coating, and die coating can be used.

[0087] When forming the protective layer (a), it is preferable to apply the protective layer resin composition and then heat-dry it, with a preferred drying temperature of 110 to 190°C, more preferably 130 to 185°C, and even more preferably 150 to 180°C. If the drying temperature is below 110°C, the protective layer may not dry sufficiently, or the protective layer may not form properly, reducing its cohesive strength and water-resistant adhesion, which may result in reduced barrier properties and tear resistance. On the other hand, if the drying temperature exceeds 190°C, the film may become too hot, making it brittle, reducing its puncture strength, or shrinking, resulting in poor processability. In particular, drying at 150°C or higher, preferably 160°C or higher, allows the protective layer to form effectively, increasing the adhesion area between the protective layer resin and the inorganic thin film layer, thereby improving water-resistant adhesion. It is particularly preferable to first evaporate the solvent at a relatively low temperature of 90°C to 110°C immediately after application, and then dry the protective film at 150°C or higher, as this yields a uniform and transparent film. In addition to drying, applying an extra heat treatment at the lowest possible temperature is even more effective in promoting the formation of the protective layer.

[0088] [Intermediate layer film] In this invention, in order to ensure the toughness of the bag while enabling monomaterialization, a polyester film mainly composed of PBT can be used as an intermediate layer. The intermediate layer film used in this invention is a biaxially oriented film made of a resin composition containing 70% by mass or more of PBT. A PBT content of 75% by mass or more is more preferable. If the PBT content is less than 70% by mass, the puncture strength will decrease, and the film properties will not be sufficient. PBT preferably contains terephthalic acid as the dicarboxylic acid component in an amount of 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, and most preferably 100 mol%. The glycol component preferably contains 1,4-butanediol in an amount of 90 mol% or more, more preferably 95 mol% or more, even more preferably 97 mol% or more, and most preferably contains no by-products other than those generated by the ether linkage of 1,4-butanediol during polymerization.

[0089] The resin composition used in the intermediate layer film of the present invention may contain polyesters other than PBT for the purpose of adjusting the film-forming properties during biaxial stretching and the mechanical properties of the resulting film. Polyesters other than PBT include PBT copolymerized with at least one polyester selected from the group consisting of PET, polyethylene naphthalate, polybutylene naphthalate, and polypropylene terephthalate, at least one dicarboxylic acid selected from the group consisting of isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebaic acid, and PBT copolymerized with at least one diol component selected from the group consisting of ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, and polycarbonatediol.

[0090] The upper limit for the amount of polyester resin other than PBT added is preferably 30% by mass or less, and more preferably 25% by mass or less. If the amount of polyester other than PBT added exceeds 30% by mass, the mechanical properties of polybutylene terephthalate will be impaired, resulting in insufficient impact strength, pinhole resistance, or rupture resistance, as well as problems such as reduced transparency and gas barrier properties.

[0091] The lower limit of the intrinsic viscosity of the polybutylene terephthalate (PBT) used in the present invention is preferably 0.9 dl / g, more preferably 0.95 dl / g, and even more preferably 1.0 dl / g. If the intrinsic viscosity of the raw material, polybutylene terephthalate (PBT), is less than 0.9 dl / g, the intrinsic viscosity of the resulting film may decrease, potentially leading to a reduction in puncture strength, impact strength, pinhole resistance, or tear resistance. The upper limit of the intrinsic viscosity of polybutylene terephthalate is preferably 1.4 dl / g. Exceeding this limit can lead to excessively high stress during stretching, potentially worsening film-forming properties. When using polybutylene terephthalate with a high intrinsic viscosity, the melt viscosity of the resin increases, requiring a higher extrusion temperature. However, extruding polybutylene terephthalate at higher temperatures can lead to increased decomposition of the material.

[0092] The polybutylene terephthalate (PBT) resin may, if necessary, contain conventionally known additives such as lubricants, stabilizers, colorants, antistatic agents, and ultraviolet absorbers. As for lubricants, inorganic lubricants such as silica, calcium carbonate, and alumina are preferred, as are organic lubricants, with silica and calcium carbonate being more preferred, and silica being particularly preferred in that it reduces haze. These can be used to achieve transparency and lubricity. The lower limit of the lubricant concentration is preferably 100 ppm, more preferably 500 ppm, and even more preferably 800 ppm. If it is below the above, the slipperiness of the substrate film layer may decrease. The upper limit of the lubricant concentration is preferably 20,000 ppm, more preferably 10,000 ppm, and even more preferably 1,800 ppm. If it exceeds the above, the transparency may decrease.

[0093] In the present invention, the upper limit of the thermal shrinkage rate of the biaxially oriented polyester film constituting the intermediate layer film after heating at 150°C for 15 minutes in the longitudinal (MD) direction and transverse (TD) direction is preferably 4.0%, more preferably 3.0%, and even more preferably 2%. If the upper limit is exceeded, dimensional changes in the intermediate layer film that occur during the formation process of the inorganic thin film layer and protective layer, or during high-temperature processing such as retort sterilization, may cause cracks in the inorganic thin film layer, potentially reducing the gas barrier properties. Furthermore, dimensional changes during processing such as printing may cause pitch misalignment.

[0094] In the present invention, the lower limit of the thermal shrinkage rate of the biaxially oriented polyester film constituting the intermediate layer film after heating at 150°C for 15 minutes in the longitudinal (MD) and transverse (TD) directions is preferably 0%. If the shrinkage rate falls below this lower limit, no further improvement can be obtained (saturation occurs), and the film may become mechanically brittle.

[0095] The lower limit of the impact strength of the biaxially oriented polyester film constituting the intermediate layer film in this invention is preferably 0.05 J / μm. A strength of 0.05 J / μm or higher provides sufficient strength when used as a bag. The upper limit of the impact strength of the biaxially oriented polyester film constituting the intermediate layer film in this invention is preferably 0.2 J / μm. Exceeding this upper limit does not provide any further improvement (saturation occurs).

[0096] The lower limit of the plane orientation (ΔP) of the PBT film, which is the intermediate layer film of the present invention, is preferably 0.144, more preferably 0.148, and even more preferably 0.15. If it is less than the above, the orientation is weak, so sufficient strength cannot be obtained, and the puncture strength may decrease. Moreover, when an inorganic thin film layer (C) is provided on the intermediate layer film to form a laminated film, the inorganic thin film layer may stretch easily due to the tension and temperature applied during its formation, causing the inorganic thin film layer to crack, which may reduce the gas barrier properties. In the present invention, the upper limit of the degree of plane orientation (ΔP) of the intermediate layer film is preferably 0.160, and more preferably 0.158. If it exceeds this value, the orientation becomes too strong, making the film prone to breakage during film formation. Furthermore, increasing the orientation necessitates heat fixing at a high temperature to reduce the thermal shrinkage rate, which may actually decrease the strength of the film due to crystallization.

[0097] The upper limit of the haze per unit thickness of the biaxially oriented polyester film constituting the intermediate layer film in the present invention is preferably 0.66% / μm, more preferably 0.60% / μm, and even more preferably 0.53% / μm. When printing is applied to a substrate layer with a haze of 0.66% / μm or less, the quality of the printed characters and images is improved.

[0098] The upper limit of the intrinsic viscosity (IV) of the biaxially oriented polyester film constituting the intermediate layer film in the present invention is preferably 1.20 dl / g, more preferably 1.15 dl / g, and even more preferably 1.10 dl / g. Exceeding the upper limit improves the strength of the film, but increases the pressure load on the filter during extrusion, making manufacturing difficult. The lower limit is preferably 0.60 dl / g, more preferably 0.65 dl / g, and even more preferably 0.70 dl / g. Exceeding the lower limit may reduce the strength of the film.

[0099] Furthermore, the biaxially oriented polyester film constituting the intermediate layer film in the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment, etc., as long as the objectives of the present invention are not impaired, and may also be subjected to known anchor coating treatment, printing, decoration, etc.

[0100] Next, a specific manufacturing method for obtaining the biaxially oriented polyester film constituting the intermediate layer film of the present invention will be described. However, the invention is not limited to these methods. A manufacturing method for obtaining a biaxially oriented polyester film constituting the intermediate layer film of the present invention comprises the steps of: melting and extruding a polyester raw material resin into a sheet and cooling it on a casting drum to form an unstretched sheet; a longitudinal stretching step of stretching the formed unstretched sheet in the longitudinal direction; a preheating step of preheating the sheet to a temperature at which transverse stretching is possible after the longitudinal stretching; a transverse stretching step of stretching the sheet in a width direction perpendicular to the longitudinal direction; a heat setting step of heating the film after the longitudinal and transverse stretching to crystallize it; a heat relaxation step of removing residual strain from the heat-set film; and a cooling step of cooling the film after heat relaxation.

[0101] [Unstretched Sheet Forming Process] First, the film raw materials are dried or hot-air dried. Next, the raw materials are weighed, mixed, and supplied to an extruder, where they are heated and melted to perform melt casting into a sheet. Furthermore, the molten resin sheet is cooled and solidified by bringing it into close contact with a cooling roll (casting roll) using an electrostatic application method to obtain an unstretched sheet. The electrostatic application method is a method in which a voltage is applied to an electrode placed near the opposite side of the resin sheet from the side that contacts the rotating metal roll, near where the molten resin sheet comes into contact with the rotating metal roll. This charges the resin sheet and brings it into close contact with the rotating cooling roll.

[0102] The lower limit of the resin's heating and melting temperature is preferably 200°C, more preferably 250°C, and even more preferably 260°C. Below this temperature, the extrusion may become unstable. The upper limit of the resin's melting temperature is preferably 280°C, more preferably 270°C. Above this temperature, the resin will decompose, and the film will become brittle.

[0103] When casting molten polyester resin onto a cooling roll by extrusion, it is preferable to minimize the difference in crystallinity in the width direction. Specific methods for achieving this include casting multiple layers of raw materials with the same composition when extruding and casting the molten polyester resin, and further, lowering the cooling roll temperature. Because PBT resin crystallizes quickly, crystallization continues even during casting. In this case, if the resin is cast as a single layer without multilayering, there is no barrier to suppress crystal growth, resulting in the growth of large spherulites. As a result, the yield stress of the resulting undrawn sheet becomes high, making it prone to breakage during biaxial stretching, and the resulting biaxially oriented film has insufficient impact strength, pinhole resistance, or rupture resistance. On the other hand, by laminating multiple layers of the same resin, the stretching stress of the undrawn sheet can be reduced, making it possible to perform subsequent biaxial stretching stably.

[0104] A method for casting by extruding molten polyester resin and creating multiple layers of raw materials of the same composition specifically includes at least the following steps: (1) a step of melting a resin composition containing 70% by weight or more of PBT resin to form a molten fluid; (2) a step of forming a laminated fluid with 60 or more layers from the formed molten fluid; (3) a step of discharging the formed laminated fluid from a die and solidifying it by contacting it with a cooling roll to form a laminated unstretched sheet; and (4) a step of biaxially stretching the laminated unstretched sheet. Other processes may be inserted between process (1) and process (2), and between process (2) and process (3). For example, a filtration process, a temperature change process, etc., may be inserted between process (1) and process (2). Also, a temperature change process, a charge addition process, etc., may be inserted between process (2) and process (3). However, there must be no process between process (2) and process (3) that destroys the layered structure formed in process (2).

[0105] In step (1), the method for melting the polyester resin composition to form a molten fluid is not particularly limited, but a preferred method is to heat and melt it using a single-screw extruder or a twin-screw extruder.

[0106] The method for forming the laminated fluid in step (2) is not particularly limited, but a static mixer and / or a multilayer feed block are more preferred in terms of equipment simplicity and maintainability. Furthermore, a device having a rectangular melt line is more preferred in terms of uniformity in the sheet width direction. It is even more preferable to use a static mixer or a multilayer feed block having a rectangular melt line. The resin composition consisting of multiple layers formed by combining multiple resin compositions may be passed through one or more of the static mixer, multilayer feed block, and multilayer manifold.

[0107] The theoretical number of layers in step (2) is preferably 60 or more. The lower limit of the theoretical number of layers is more preferably 500. If the theoretical number of layers is too low, or if the distance between layers becomes too long and the crystal size becomes too large, the effects of the present invention tend not to be obtained. In addition, the degree of crystallinity increases near both ends of the sheet, making film formation unstable, and the transparency after molding may decrease. The upper limit of the theoretical number of layers in step (2) is not particularly limited, but is preferably 100,000, more preferably 10,000, and even more preferably 7,000. If the theoretical number of layers is made extremely large, the effect may saturate.

[0108] When lamination in process (2) is performed using a static mixer, the theoretical number of layers can be adjusted by selecting the number of elements in the static mixer. A static mixer is generally known as a stationary mixer (line mixer) without a drive unit, and the fluid that enters the mixer is sequentially stirred and mixed by the elements. However, when a high-viscosity fluid is passed through a static mixer, division and lamination of the high-viscosity fluid occur, forming a layered fluid. Each time the high-viscosity fluid passes through one element of the static mixer, it is divided into two parts, then merged and laminated. Therefore, when a high-viscosity fluid is passed through a static mixer with n elements, a layered fluid with a theoretical number of layers N = 2n is formed.

[0109] A typical static mixer element has a structure in which a rectangular plate is twisted 180 degrees, and depending on the direction of the twist, there are right-hand and left-hand elements, with the dimensions of each element being basically 1.5 times the diameter in length. The static mixers that can be used in the present invention are not limited to such types.

[0110] When lamination in process (2) is performed using a multilayer feed block, the theoretical number of layers can be adjusted by selecting the number of divisions and laminations of the multilayer feed block. Multiple multilayer feed blocks can be installed in series. It is also possible to use the high-viscosity fluid supplied to the multilayer feed block as the lamination fluid itself. For example, if the number of layers of high-viscosity fluid supplied to the multilayer feed block is p, the number of divisions and laminations of the multilayer feed block is q, and the number of multilayer feed blocks installed is r, then the number of layers N of the lamination fluid is N = p × qr.

[0111] In step (3), the laminated fluid is discharged from the die and solidified by contacting it with a cooling roll. The lower limit of the cooling roll temperature is preferably -10°C. Below this level, the crystallization suppression effect may saturate. The upper limit of the cooling roll temperature is preferably 40°C. Above this level, the degree of crystallization may become too high, making stretching difficult. The upper limit of the cooling roll temperature is preferably 25°C. When the cooling roll temperature is within the above range, it is preferable to lower the humidity of the environment around the cooling roll to prevent condensation. It is preferable to minimize the temperature difference in the width direction of the cooling roll surface. In this case, the thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm. The multilayered unstretched sheet described above consists of at least 60 layers, preferably 250 layers, and more preferably 1000 layers. If the number of layers is small, the effect of improving stretchability is lost.

[0112] [Longitudinal and transverse stretching processes] Next, we will explain the stretching method. While both simultaneous biaxial stretching and sequential biaxial stretching are possible, sequential biaxial stretching is the most preferable method because it is necessary to increase the degree of surface orientation in order to increase puncture strength, and it also offers a fast film formation speed and high productivity.

[0113] The lower limit of the stretching temperature in the longitudinal direction is preferably 55°C, and more preferably 60°C. Breakage is less likely to occur at temperatures above 55°C. Furthermore, because the longitudinal orientation of the film does not become too strong, shrinkage stress during heat setting treatment is suppressed, resulting in a film with less distortion of molecular orientation in the width direction. The upper limit of the stretching temperature in the longitudinal direction is preferably 100°C, and more preferably 95°C. Below 100°C, the orientation of the film does not become too weak, so the mechanical properties of the film do not deteriorate.

[0114] The lower limit of the stretching ratio in the longitudinal direction is preferably 2.8 times, and particularly preferably 3.0 times. When it is 2.8 times or higher, the degree of surface orientation increases, and the puncture strength of the film improves. The upper limit of the stretching ratio in the longitudinal direction is preferably 4.3 times, more preferably 4.0 times, and particularly preferably 3.8 times. When it is 4.3 times or less, the degree of orientation in the transverse direction of the film does not become too strong, the shrinkage stress during the heat setting treatment does not become too large, the distortion of the molecular orientation in the transverse direction of the film is reduced, and as a result the straight tear resistance in the longitudinal direction is improved. Furthermore, the effect of improving mechanical strength and thickness uniformity saturates within this range.

[0115] The lower limit of the stretching temperature in the transverse direction is preferably 60°C, as temperatures above 60°C may make fracture less likely. The upper limit of the stretching temperature in the transverse direction is preferably 100°C, as temperatures below 100°C increase the degree of orientation in the transverse direction, improving the mechanical properties.

[0116] The lower limit of the stretching ratio in the transverse direction is preferably 3.5 times, more preferably 3.6 times, and particularly preferably 3.7 times. A ratio of 3.5 times or higher prevents the degree of orientation in the transverse direction from becoming too weak, improving mechanical properties and thickness uniformity. The upper limit of the stretching ratio in the transverse direction is preferably 5 times, more preferably 4.5 times, and particularly preferably 4.0 times. A ratio of 5.0 times or less is preferable. In this case, the effect of improving mechanical strength and thickness uniformity is maximized (saturates) within this range.

[0117] [Heat setting process] The lower limit of the heat-setting temperature in the heat-setting process is preferably 195°C, and more preferably 200°C. If the temperature is 195°C or higher, the thermal shrinkage rate of the film decreases, and the inorganic thin film layer is less likely to be damaged even after boiling, thus improving the gas barrier properties. The upper limit of the heat-setting temperature is preferably 220°C, and if the temperature is 220°C or lower, the base film layer does not melt and is less likely to become brittle.

[0118] [Thermal relaxation section process] The lower limit of the relaxation rate in the heat relaxation process is preferably 0.5%. If it is 0.5% or higher, breakage may be less likely to occur during heat fixing. The upper limit of the relaxation rate is preferably 10%. If it is 10% or lower, the longitudinal shrinkage during heat fixing is reduced, resulting in less distortion of molecular orientation at the film edges and improved straight-line tear resistance. In addition, sagging of the film is less likely to occur, and thickness unevenness is less likely to occur.

[0119] [Cooling process] In the cooling process following the relaxation in the heat relaxation section, it is preferable to keep the surface temperature of the edges of the polyester film below 80°C. If the temperature of the film edge exceeds 80°C after passing through the cooling process, the tension applied when winding the film will stretch the edge, resulting in a high thermal shrinkage rate in the vertical direction of the edge. This leads to an uneven distribution of thermal shrinkage rate in the width direction of the roll, and when such a roll is heated and transported for vapor deposition or other processes, streaky wrinkles may occur, resulting in uneven physical properties in the width direction of the final gas barrier film.

[0120] In the aforementioned cooling process, methods to keep the surface temperature of the film edges below 80°C include adjusting the temperature and airflow of the cooling process, selectively cooling the edges by providing a shielding plate on the central side in the width direction of the cooling zone, or locally blowing cold air onto the edges of the film.

[0121] The intermediate layer film of the present invention may be provided with a coating layer (Y), an inorganic thin film layer (C), and a protective layer (b), similar to the base film, in order to ensure sufficient barrier properties and lamination strength. For the coated layer (Y), the composition, amount of adhesion, and method of forming the coating layer described above as the coating layer (X) can be applied. For the inorganic thin film layer (C), the composition, film thickness, and method of forming the inorganic thin film layer described above as the inorganic thin film layer (A) can be applied. For the protective layer (b), the composition, amount of adhesion, and method of forming the protective layer described above as the protective layer (a) can be applied.

[0122] [Heat-sealable resin layer] The laminate of the present invention has a heat-sealable resin layer composed of polyester, and if further improvement of barrier performance is desired, an inorganic thin film layer (B) may be provided on the non-sealing surface of the heat-sealable resin layer, and a protective layer (c) may be provided on the inorganic thin film layer (B). In order to satisfy a predetermined heat seal strength, the sealing surface (the surface opposite to the non-sealing surface) of the heat-sealable resin layer must be provided on one of the outermost layers of the laminate. For the inorganic thin film layer (B), the composition, film thickness, and method for forming the inorganic thin film layer described above as inorganic thin film layer (A) may be applied. For the protective layer (c), the composition, adhesion amount, and method for forming the protective layer described above as protective layer (a) may be applied.

[0123] The heat-sealable resin layer of the present invention preferably has a two-layer structure, consisting of a heat-seal layer that constitutes the sealing surface and a heat-resistant layer. The heat-resistant layer is positioned on the non-sealing side of the heat-sealable resin layer. The constituent requirements for each layer will be described later, but in the case of a structure including a heat-seal layer and a heat-resistant layer, the layer with the highest ethylene terephthalate content becomes the heat-resistant layer. The layer structure of the laminate of the present invention is more preferably composed of three layers in order from the outermost layer (sealing surface side) of either side: heat-seal layer / heat-resistant layer / inorganic thin film layer (B).

[0124] The heat-sealable resin layer of the present invention may also have a protective layer on the outermost surface on the side opposite to the heat-seal layer (the non-seal side). In this case, a configuration in which four layers are laminated in the order of heat-seal layer / heat-resistant layer / inorganic thin film layer (B) / protective layer (c) is preferred. By providing a protective layer, not only is the gas barrier performance improved, but the laminate strength when laminated with other materials is also improved, and the occurrence of cracks due to friction and bending is suppressed, among other advantages.

[0125] The thickness of the heat-sealable resin layer is not particularly limited, but is preferably between 3 μm and 200 μm. A thickness of less than 3 μm in the heat-sealable resin layer may result in insufficient heat seal strength and difficulty in processing such as printing, which is undesirable. While the thickness of the laminate may be greater than 200 μm, this is undesirable because it increases the weight of the laminate and thus the cost. A thickness of 5 μm to 160 μm is more preferable, and 7 μm to 120 μm is even more preferable. The ratio of the heat seal layer to the total heat sealable resin layer is preferably 20% to 80%. If the ratio of the heat seal layer is less than 20%, the heat seal strength of the heat sealable resin layer will decrease, which is undesirable. If the ratio of the heat seal layer is higher than 80%, the heat sealability of the heat sealable resin layer will improve, but the heat resistance will decrease, which is undesirable. A ratio of the heat seal layer between 30% and 70% is more preferable.

[0126] The ratio of the heat-resistant layer is preferably between 20% and 80%. If the ratio of the heat-resistant layer is less than 20%, the heat resistance of the film will decrease, which is undesirable. If the ratio of the heat-resistant layer is higher than 80%, the ratio of the heat-seal layer in the laminate will decrease accordingly, sacrificing heat-sealability, which is also undesirable. A ratio of the heat-resistant layer is more preferably between 30% and 70%.

[0127] Furthermore, the outermost layer (including the heat-seal layer) of the laminate of the present invention may be provided with a layer that has been treated with corona treatment, coating treatment, or flame treatment to improve the printability and slipperiness of the film surface, and can be provided as desired without sacrificing the requirements of the present invention. In the following description, layers made of polyester resin, such as the heat-seal layer and the heat-resistant layer, will be collectively referred to as "polyester resin layer" to distinguish them from inorganic thin film layers and protective layers.

[0128] (Characteristics of the heat-seal layer) In the present invention, the upper limit of haze per unit thickness of the heat seal layer is preferably 0.50% / μm, more preferably 0.40% / μm, and even more preferably 0.30% / μm. When printing is applied to a substrate film layer with a haze of 0.50% / μm or less, the quality of the printed characters and images is improved. It is preferable that the heat seal strength of the laminated structure of the present invention, when heat-sealed at a temperature of 200°C, a seal bar pressure of 0.2 MPa, and a sealing time of 4 seconds, is 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 and cannot be used as a packaging bag. A heat seal strength of 9 N / 15 mm or more is preferable, and 10 N / 15 mm or more is more preferable. A high heat seal strength is preferable, but the upper limit that can be obtained at present is about 30 N / 15 mm.

[0129] Preferably, the laminated material of the present invention has a thermal shrinkage rate in both the width direction and the longitudinal direction of -5% or more and 5% or less when treated in 98°C hot water for 3 seconds. If the shrinkage rate exceeds 5%, it is undesirable because when a bag made using the laminate is subjected to heat treatment such as retort processing, the deformation of the bag becomes large and it is not possible to maintain its original shape, and cracks occur in the inorganic layer, reducing the gas barrier properties. A thermal shrinkage rate of 4% or less is more preferable, and 3% or less is even more preferable. On the other hand, if the thermal shrinkage rate of the thermal shrinkage rate falls below -5%, it means that the laminate stretches, and as with a high shrinkage rate, it is undesirable because it becomes difficult for the bag to maintain its original shape. A thermal shrinkage rate of -4% or more and 4% or less is more preferable, and 3% or more and 3% or less is even more preferable.

[0130] The laminate of the present invention preferably has a folded-holding angle of 20 degrees or more and 70 degrees or less, as measured by the method described later. If the folded-holding angle exceeds 70 degrees, it becomes difficult to fold when it is made into a bag, resulting in a poor appearance, which is undesirable. On the other hand, the smaller the folded-holding angle, the better, but the range covered by the present invention is limited to 20 degrees as the lower limit, and even if the folded-holding angle is 25 degrees or more, it can be said to be practically preferable. The upper limit of the folded-holding angle is more preferably 65 degrees, and even more preferably 60 degrees.

[0131] (Materials that make up the polyester resin layer) The raw material for the polyester resin layer constituting the laminate of the present invention is primarily composed of ethylene terephthalate units. Here, "primary component" means that when the total amount of components is taken as 100 mol%, it contains 50 mol% or more. Furthermore, it is preferable that the polyester used in the polyester 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 heat seal layer. In the heat-resistant layer, it is preferable to have fewer components other than ethylene terephthalate, but including components other than ethylene terephthalate can reduce the difference in shrinkage rate with the heat seal layer, leading to a reduction in curl of the laminate. The content of each component differs between the heat seal layer and the heat-resistant layer and will be described later. 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, as well as 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 polycarboxylic acids with a valency of 3 or higher (for example, trimellitic acid, pyromellitic acid, and their anhydrides) in the polyester.

[0132] Furthermore, examples of diol monomers other than ethylene glycol that constitute ethylene terephthalate include 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, long-chain diols such as 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 with 8 or more carbon atoms (e.g., octanediol) or polyhydric alcohols with a valency of 3 or higher (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin).

[0133] Furthermore, the polyester may contain a polyester elastomer as a component, such as ε-caprolactone or tetramethylene glycol. Since the polyester elastomer has the effect of lowering the melting point of the polyester resin layer, it can be used particularly suitably in the heat seal layer.

[0134] Among these, using one or more of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol is preferable because it makes it easier to achieve a heat seal strength of 8 N / 15 mm or more between heat seal layers. Using one or more of neopentyl glycol and 1,4-cyclohexanedimethanol is more preferable, and using neopentyl glycol is particularly preferable.

[0135] The polyester resin layer constituting the laminate of the present invention may contain various additives as needed, such as waxes, antioxidants, antistatic agents, nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and UV absorbers. Furthermore, it is preferable to add fine particles as lubricants to improve the film's slipperiness, at least to the outermost layer of the film. Any fine particles can be selected. For example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, while 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 within the range of 0.05 to 3.0 μm when measured with a Coulter counter.

[0136] As a method for incorporating particles into the polyester resin layer constituting the laminate of the present invention, for example, they can be added at any stage in the production of the polyester resin. However, it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the esterification stage, or after the completion of the transesterification reaction but before the start of the polycondensation reaction, in order to proceed with the polycondensation reaction. Other methods include blending a slurry of particles dispersed in ethylene glycol, water, or other solvents with the polyester resin raw material using a vented kneading extruder, or blending dried particles with the polyester resin raw material using a kneading extruder. The following describes the preferred components to be included in the heat seal layer and the heat-resistant layer.

[0137] The polyester used in the heat seal layer of the laminate of the present invention preferably contains 30 mol% or more of dicarboxylic acid monomers and / or diol monomers other than terephthalic acid and ethylene glycol that constitute ethylene terephthalate, more preferably 32 mol% or more, and particularly preferably 34 mol% or more. Furthermore, the upper limit of the monomer content other than ethylene terephthalate is 50 mol%. If the monomer content other than ethylene terephthalate in the heat seal layer is lower than 30 mol%, even if the molten resin is rapidly cooled and solidified after being extruded from the die, crystallization will occur in the subsequent stretching and heat setting process, making it difficult to achieve a heat seal strength of 8 N / 15 mm or more, which is undesirable.

[0138] On the other hand, if the amount of monomers other than ethylene terephthalate in the heat seal layer is 50 mol% or more, although the heat seal strength of the film can be increased, the heat resistance of the heat seal layer becomes extremely low. As a result, when heat sealing, blocking occurs around the sealed area (a phenomenon in which a wider area than intended is sealed due to heat conduction from the heating element), making proper heat sealing difficult. It is more preferable that the amount of monomers other than ethylene terephthalate be 48 mol% or less, and particularly preferable that be 46% or less.

[0139] The polyester used in the heat-resistant layer that can constitute the laminate of the present invention preferably contains 9 mol% or more of dicarboxylic acid monomers and / or diol monomers other than terephthalic acid and ethylene glycol that constitute ethylene terephthalate, more preferably 10 mol% or more, and particularly preferably 11 mol% or more. Furthermore, the upper limit of the monomer content other than ethylene terephthalate is 20 mol%. If the monomer content other than ethylene terephthalate in the heat-resistant layer is lower than 9 mol%, the difference in thermal shrinkage rate between the heat-resistant layer and the heat-seal layer becomes large, which is undesirable because it causes the laminate to curl more. If the difference in the monomer content other than ethylene terephthalate in the heat-resistant layer and the heat-seal layer becomes large, the difference in thermal shrinkage rate in each layer during heat setting becomes large, and even if cooling after heat setting is strengthened, shrinkage toward the heat-seal layer becomes large, causing curl to become large.

[0140] On the other hand, if the amount of monomers other than ethylene terephthalate contained in the heat-resistant layer is 20 mol% or more, the heat resistance of the sealant will decrease, such as causing holes to form due to the heat applied during heat sealing, which is undesirable. The amount of monomers other than ethylene terephthalate is more preferably 19 mol% or less, and particularly preferably 18% or less. Furthermore, the amount of monomers other than ethylene terephthalate used to control curling is more preferably 20 mol% to 35 mol% and even more preferably 21 mol% to 34 mol% when the difference between the amount in each layer individually and the heat-seal layer is 20 mol% to 35 mol%.

[0141] (Manufacturing conditions for laminates) The polyester resin layer (hereinafter sometimes simply referred to as "film") constituting the laminate of the present invention can be obtained by melt-extruding the polyester raw material described in 3.1. "Raw material type of polyester resin layer" using an extruder to form an unstretched laminated film, and then stretching it by the predetermined method shown below. If the film includes a heat-seal layer, a heat-resistant layer, or other layers, the timing of laminating each layer may be before or after stretching. When laminating before stretching, it is preferable to melt-extrude the resins that will be the raw materials for each layer using separate extruders and join them using a feed block or the like in the middle of 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 molten polyester resin is poured onto the surface layer of a single or laminated film to laminate it. Among these, the method of laminating each layer before stretching is preferred.

[0142] As described above, polyester resin can be obtained by polycondensing dicarboxylic acid and diol components, selecting the type and amount of these components so that they contain appropriate amounts of monomers other than ethylene terephthalate. Alternatively, two or more types of chip-shaped polyester can be mixed and used as raw materials for a polyester resin layer. When melt-extruding the raw resin, it is preferable to dry the polyester raw material of each layer using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester raw material of each layer in this way, it is melted at a temperature of 200-300°C using an extruder and extruded as a laminated film. Any existing method such as the T-die method or the tubular method can be used for extrusion. Subsequently, an unstretched film can be obtained by rapidly cooling the film melted by extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin from a die onto a rotating drum and rapidly cooling and solidifying it to obtain a substantially unoriented resin sheet can be suitably employed.

[0143] The film may be manufactured using any of the following methods: unstretched, uniaxially stretched (stretched in at least one direction, either longitudinal or transverse), or biaxially stretched. From the viewpoint of 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 using longitudinal stretching followed by transverse stretching will be described, but transverse stretching followed by longitudinal stretching is also acceptable as only the main orientation direction changes. Simultaneous biaxial stretching is also acceptable.

[0144] For longitudinal stretching, it is preferable to introduce the unstretched film into a longitudinal stretching machine that has multiple rolls arranged in a continuous pattern. When performing longitudinal stretching, it is preferable to preheat the film using a preheating roll until the film temperature reaches 65°C to 90°C. If the film temperature is lower than 65°C, it becomes difficult to stretch in the longitudinal direction and is prone to breakage, which is undesirable. Also, if the temperature is higher than 90°C, the film tends to stick to the rolls, which is undesirable as it can lead to the film wrapping around the rolls and the rolls becoming easily soiled during continuous production. When the film temperature reaches 65°C to 90°C, perform longitudinal stretching. The longitudinal stretching ratio should be between 1x and 5x. 1x means no longitudinal stretching has been performed, so to obtain a transversely oriented film, the longitudinal stretching ratio should be 1x, and to obtain a biaxially oriented film, the longitudinal stretching ratio should be 1.1x or higher. While there is no upper limit to the longitudinal stretching ratio, excessively high ratios make transverse stretching difficult and increase the likelihood of breakage, so it is preferable to keep it at 5x or less.

[0145] Furthermore, by relaxing the film in the longitudinal direction after longitudinal stretching (relaxation in the longitudinal direction), the longitudinal shrinkage rate of the film caused by longitudinal stretching can be reduced. In addition, relaxation in the longitudinal direction can reduce bowing (strain) that occurs in the tenter. This is because in subsequent processes such as transverse stretching and final heat treatment, both ends of the film in the width direction are held while heating, so only the central part of the film shrinks in the longitudinal direction. It is preferable that the relaxation rate in the longitudinal direction is between 0% and 70% (a relaxation rate of 0% means no relaxation is performed). The upper limit of the relaxation rate in the longitudinal direction is determined by the raw materials used and the longitudinal stretching conditions, so relaxation cannot be performed beyond this limit. In the polyester sealant of the present invention, the upper limit of the relaxation rate in the longitudinal direction is 70%. Relaxation in the longitudinal direction can be performed by heating the film after longitudinal stretching at a temperature of 65°C to 100°C or lower and adjusting the speed difference of the rolls. Any of the heating means can be used, such as rolls, near-infrared rays, far-infrared rays, or hot air heaters. Furthermore, longitudinal relaxation can be performed not only immediately after longitudinal stretching, but also, for example, during transverse stretching (including the preheating zone) or the final heat treatment by narrowing the clip spacing in the longitudinal direction (in this case, both ends in the film width direction are also relaxed in the longitudinal direction, thus reducing bowing distortion), and can be performed at any time. After longitudinal relaxation (or longitudinal stretching if relaxation is not performed), it is preferable to cool the film once, and it is preferable to cool it with a cooling roll with a surface temperature of 20 to 40°C.

[0146] After longitudinal stretching, it is preferable to perform transverse stretching at a stretching ratio of 3 to 5 times at 65°C to 110°C while holding both ends of the film in the width direction with clips inside the tenter. It is preferable to preheat the film before performing transverse stretching, and preheating should be carried out until the film surface temperature reaches 75°C to 120°C.

[0147] After transverse stretching, it is preferable to pass the film through an intermediate zone where no active heating is performed. Because the temperature in the final heat treatment zone is higher than in the transverse stretching zone of the tenter, without an intermediate zone, heat from the final heat treatment zone (both hot air and radiant heat) will flow into the transverse stretching process. In this case, the temperature in the transverse stretching zone will not be stable, leading not only to a deterioration in the film's thickness accuracy but also to variations in physical properties such as heat seal strength and shrinkage rate. Therefore, it is preferable to pass the transversely stretched film through an intermediate zone for a predetermined time before performing the final heat treatment. In this intermediate zone, it is important to block the accompanying flow associated with the film's movement and the hot air from the transverse stretching zone and the final heat treatment zone so that when a strip of paper is dropped without the film passing through, the strip hangs almost completely vertically. A passage time of 1 to 5 seconds through the intermediate zone is sufficient. Shorter than 1 second results in an insufficient intermediate zone length and inadequate heat blocking effect. On the other hand, a longer intermediate zone is preferable, but if it's too long, the equipment will become too large, so about 5 seconds is sufficient.

[0148] After passing through the intermediate zone, it is preferable to perform heat treatment in the final heat treatment zone at a temperature between the transverse stretching temperature and 250°C. The heat treatment temperature must be above the transverse stretching temperature to be effective. In this case, the 80°C hot water shrinkage rate of the film will be higher than 5%, which is undesirable. The higher the heat treatment temperature, the lower the shrinkage rate of the film, but if it is higher than 250°C, the film haze will be higher than 15%, or the film may melt and fall into the tenter during the final heat treatment process, which is undesirable.

[0149] During the final heat treatment, the shrinkage rate in the width direction can be reduced by shortening the distance between tenter clips by an arbitrary factor (relaxation in the width direction). Therefore, it is preferable to perform relaxation in the width direction within the range of 0% to 10% during the final heat treatment (a relaxation rate of 0% means no relaxation is performed). Although the shrinkage rate in the width direction decreases as the relaxation rate in the width direction increases, the upper limit of the relaxation rate (the 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, so relaxation cannot be performed beyond this limit. In the polyester sealant of the present invention, the upper limit of the relaxation rate in the width direction is 10%.

[0150] Furthermore, the passage time through the final heat treatment zone is preferably between 2 seconds and 20 seconds. If the passage time is less than 2 seconds, the film will pass through the heat treatment zone before its surface temperature reaches the set temperature, rendering the heat treatment ineffective. The longer the passage time, the more effective the heat treatment becomes, so a passage time of 2 seconds or more is preferable, and 5 seconds or more is even preferable. However, increasing the passage time would require larger equipment, so for practical purposes, 20 seconds or less is sufficient.

[0151] After the final heat treatment, it is preferable to cool the film in a cooling zone with cooling air at a temperature of 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 airflow speed so that the actual temperature of the film at the tenter exit is lower than the glass transition temperature of either the heat seal layer or the heat-resistant layer, 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 shrink due to heat when the ends of the film that were held by the clips are released. At this time, the film will curl towards the heat seal layer, which has a high thermal shrinkage rate, resulting in a small radius of curvature, which is undesirable.

[0152] The passage time through the cooling zone is preferably between 2 seconds and 20 seconds. If the passage time is less than 2 seconds, the film will pass through the cooling zone before its surface temperature reaches the glass transition temperature, resulting in a smaller radius of curvature. The longer the passage time, the greater the cooling effect, so it is preferable to have a passage time of 2 seconds or more, and even more preferable to have a passage time of 5 seconds or more. However, increasing the passage time would require larger equipment, so for practical purposes, 20 seconds or less is sufficient. Finally, the film is wound up while cutting and removing both ends to obtain a film roll.

[0153] [Adhesive layer] The adhesive layer used in this invention can be any general-purpose laminating adhesive. For example, solvent-free, water-based, or heat-melt adhesives mainly composed of poly(ester)urethane, polyester, polyamide, epoxy, poly(meth)acrylic, polyethyleneimine, ethylene-(meth)acrylic acid, polyvinyl acetate, (modified) polyolefin, polybutadiene, wax, or casein can be used. Among these, urethane or polyester adhesives are preferred considering their resistance to moisture and heat to withstand retort processing and their flexibility to follow dimensional changes of each substrate. The adhesive layer can be applied by methods such as direct gravure coating, reverse gravure coating, kiss coating, die coating, roll coating, dip coating, knife coating, spray coating, fontein coating, or other methods, and the coating amount after drying is 1 to 8 g / m², as sufficient adhesion is achieved after retort processing. 2 Preferred. More preferably 2-7 g / m 2 More preferably 3-6 g / m 2 The coating amount is 1 g / m². 2 If the amount is less than 8 g / m², it becomes difficult to bond the entire surface, and the adhesive strength decreases. 2 Beyond this point, complete curing of the film takes longer, unreacted material is more likely to remain, and the adhesive strength decreases.

[0154] Furthermore, the laminate of the present invention may have at least one printed layer or other plastic substrate laminated between or outside the inorganic thin film layer or substrate film layer and the heat-sealable resin layer. However, from the viewpoint of monomaterialization, the lamination is limited to polyester-based materials.

[0155] Water-based and solvent-based resin-containing printing inks are preferably used as the printing ink for forming the printed layer. Examples of resins used in the printing ink include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoaming agents, crosslinking agents, anti-blocking agents, and antioxidants. The printing method for forming the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. For drying the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

[0156] [Characteristics of laminated materials] The laminated material of the present invention has an oxygen permeability of 5 ml / m² under conditions of 23°C × 65%RH. 2 A pressure of d·MPa or less is preferable for exhibiting good gas barrier properties. Furthermore, by providing a barrier layer on each film, a pressure of 4 ml / m² is preferably achieved. 2 • d·MPa or less, more comfortably 3 ml / m³ 2 It can be set to d·MPa or less. Oxygen permeability of 5 ml / m³ 2 Above d·MPa, it becomes difficult to meet the requirements for applications demanding high gas barrier properties, such as aluminum foil replacement. On the other hand, if the oxygen permeability is 0.5 ml / m³ in all cases... 2 If the oxygen permeability is less than d·MPa, although the barrier performance is excellent, residual solvent will not easily permeate to the outside of the bag, and the amount transferred to the contents may increase relatively, which is undesirable. The preferred lower limit for oxygen permeability is 0.5 ml / m³. 2 It is d·MPa or higher.

[0157] The laminates of the present invention all exhibit a water vapor transmission rate of 1.0 g / m² under 40°C × 90% RH conditions. 2 A value of d or less is preferable in terms of exhibiting good gas barrier properties. Furthermore, by providing a barrier layer on each film, a value of 0.75 g / m² is preferable. 2 • d or less, more preferably 0.5 g / m 2 It can be less than or equal to d. Water vapor transmission rate of 1.0 g / m³ 2 If the value exceeds d, it becomes difficult to meet the requirements for applications that demand high gas barrier properties, such as aluminum foil replacement. On the other hand, if the water vapor transmission rate is 0.1 g / m³ 2 If the value is less than 0.1 g / m³, while the barrier performance is excellent, residual solvent will not easily permeate to the outside of the bag, which may relatively increase the amount transferred to the contents, so this is undesirable. The preferred lower limit for water vapor permeability is 0.1 g / m³. 2 It is d or higher.

[0158] The laminated material of the present invention preferably has a puncture strength of 10N or more, more preferably 12N or more, and even more preferably 14N or more, as measured in accordance with JIS Z1707. If the puncture strength is less than 10N, when used as a bag, there is a risk that a hole will form when an external load is applied, causing the contents to leak out.

[0159] The laminated material of the present invention preferably has a haze of 20% or less, more preferably 18% or less, and even more preferably 16% or less, as measured in accordance with JIS K7136. If the haze is 20% or more, the transparency is poor when used as a bag, which is undesirable from the standpoint of visibility of the contents from a safety perspective and from the standpoint of appearance after printing.

[0160] It is preferable that the heat seal strength of the laminated structure of the present invention, when heat-sealed at a temperature of 200°C, a seal bar pressure of 0.2 MPa, and a sealing time of 4 seconds, is 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 and cannot be used as a packaging bag. A heat seal strength of 9 N / 15 mm or more is preferable, and 10 N / 15 mm or more is more preferable. A high heat seal strength is preferable, but the upper limit that can be obtained at present is about 30 N / 15 mm. [Examples]

[0161] 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 performed using the following measurement methods.

[0162] (1) Thickness of various films Measurements were taken using a dial gauge in accordance with JIS K7130-1999 Method A.

[0163] (2) Composition and film thickness of the inorganic thin film layer The film thickness composition of the laminated films (after thin film lamination) obtained in the examples and comparative examples was measured using a fluorescent X-ray analyzer (Rigaku Corporation's "ZSX100e") according to a pre-prepared calibration curve. The excitation X-ray tube conditions were set to 50kV and 70mA.

[0164] (3) Amount of protective layer In each example and comparative example, the laminated film obtained at the stage of laminating a protective layer onto the base film was used as a sample. A 100 mm × 100 mm test piece was cut from this sample, and the protective layer was wiped off with 1-methoxy-2-propanol or dimethylformamide. The amount of adhesion was calculated from the change in mass of the film before and after wiping.

[0165] [Fabrication of laminated structures] (4) Preparation of laminated samples for evaluation The base film, intermediate layer film, and heat-seal resin described in the Examples and Comparative Examples were bonded together by dry lamination using a two-component urethane-based curing adhesive (a mixture of Mitsui Chemicals' "Takelac® A525S" and "Takenate® A50" in a ratio of 13.5:1 (mass ratio)), and aged at 40°C for 4 days to obtain an evaluation laminate gas barrier laminate (hereinafter sometimes referred to as "Laminate Laminate A"). The thickness of the adhesive layer formed with the two-component urethane-based curing adhesive after drying was approximately 4 μm in all cases.

[0166] (5) Method for evaluating oxygen permeability For the laminated structures prepared in (4) above, the oxygen permeability was measured in accordance with JIS-K7126 Method B using an oxygen permeability measuring device (MOCON Corporation's "OX-TRAN(registered trademark) 2 / 22") under an atmosphere of 23°C and 65% RH. The oxygen permeability was measured in the direction in which oxygen permeates from the base film side to the heat-sealable resin layer side of the laminated structure.

[0167] (6) Method for evaluating water vapor transmission For the laminated structures prepared in (4) above, the water vapor transmission rate was measured in accordance with JIS-K7129 Method B using a water vapor transmission rate measuring device (MOCON "PERMATRAN-W 3 / 33MG") under an atmosphere of 40°C and 90% RH. The water vapor transmission rate was measured in the direction in which water vapor permeated from the heat-sealable resin layer side of the laminated structure toward the base film side.

[0168] (7) Method for evaluating heat seal strength The laminated material prepared in (4) above was subjected to heat seal strength measurement in accordance with JIS Z 1707. The specific procedure is as follows: The heat seal surfaces of the samples were bonded together using a heat sealer. The heat sealing conditions were: upper bar temperature 200°C, lower bar temperature 30°C, pressure 0.2 MPa, and time 4 seconds. The bonded samples were cut to have a seal width of 15 mm. The peel strength was measured using a universal tensile testing machine "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. The peel strength is expressed as strength per 15 mm (N / 15 mm).

[0169] (9) Method for evaluating puncture strength The laminated material prepared in (4) above was sampled in 5cm squares, and the puncture strength of the film was measured in accordance with JIS Z1707 using an IMADA Corporation digital force gauge "ZTS-500N", an electric measuring stand "MX2-500N", and a puncture jig "TKS-250N".

[0170] (10) Haze of laminated structures The haze of the laminated structures obtained in the examples and comparative examples was measured using a haze meter NDH-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136. (11) Evaluation criteria for monomaterialization For the laminated structures prepared in (4) above, the evaluation criterion for monomaterialization was that structures where the thickness of the polyester-based material was 90% or more of the total thickness were marked as ○ (monomaterial). (12) Visibility and range suitability For the laminated structures prepared in (4) above, those with haze of 20% or less and without the use of aluminum foil were marked with ○, those with haze of 20% or more and without the use of aluminum foil were marked with △, and those with the use of aluminum foil were marked with ×.

[0171] The details of the coating liquid used in these examples and comparative examples are described below. These were used in Examples 1-7 and Comparative Examples 1-7.

[0172] [Carbodiimide-based crosslinking agent (A)] As a carbodiimide-based crosslinking agent, we prepared "Carbodilite (registered trademark) SV-02" manufactured by Nisshinbo Co., Ltd. (solid content 40%). [Resin containing an oxazoline group (B)] As a resin containing oxazoline groups, a commercially available water-soluble oxazoline group-containing acrylate ("Epocross® WS-300" manufactured by Nippon Shokubai Co., Ltd.; solid content 10%) was prepared. The amount of oxazoline groups in this resin was 7.7 mmol / g.

[0173] [Acrylic resin (C)] As the acrylic resin, a commercially available 25% by mass emulsion of acrylic acid ester copolymer ("Movinyl® 7980" manufactured by Nichigo-Movinyl Co., Ltd.) was prepared. The acid value (theoretical value) of this acrylic resin was 4 mg KOH / g.

[0174] [Urethane resin (D)] As the urethane resin, a commercially available polyester urethane resin dispersion (Mitsui Chemicals, Ltd., "Takelac® W605"; solid content 30%) was prepared. The acid value of this urethane resin was 25 mg KOH / g, and the glass transition temperature (Tg) measured by DSC was 100°C. Furthermore, the ratio of aromatic or aromatic aliphatic diisocyanate to the total polyisocyanate component, as measured by 1H-NMR, was 55 mol%. [Silane coupling agent (E)] As a silane coupling agent, we prepared commercially available "(registered trademark) KBM903" manufactured by Shin-Etsu Chemical Co., Ltd. (100% solids content). When using it, we diluted it with water to make a 2% aqueous solution.

[0175] [Urethane resin (F)] In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 143.95 parts by mass of metaxylylene diisocyanate, 25.09 parts by mass of 4,4'-methylenebis(cyclohexyl isocyanate), 28.61 parts by mass of ethylene glycol, 5.50 parts by mass of trimethylolpropane, 12.37 parts by mass of dimethylolpropionic acid, and 120.97 parts by mass of methyl ethyl ketone as a solvent were mixed and stirred at 70°C under a nitrogen atmosphere, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, after the reaction solution was cooled to 35°C, 9.14 parts by mass of triethylamine were added to obtain a polyurethane prepolymer solution. Next, 794.97 parts by mass of water were added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 15°C. The polyurethane prepolymer solution was added and dispersed in water while stirring at 2000 min-1. An aqueous amine solution prepared by mixing 22.96 parts by mass of 2-[(2-aminoethyl)amino]ethanol and 91.84 parts by mass of water was then added. Subsequently, an aqueous amine solution prepared by mixing 2.38 parts by mass of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (trade name: KBM-603, manufactured by Shin-Etsu Chemical Co., Ltd.) and 9.50 parts by mass of water was added to carry out the chain extension reaction. After that, under reduced pressure, methyl ethyl ketone and some of the water were removed to obtain a polyurethane dispersion (E) with a solid content of 25% by mass and an average particle size of 70 nm. The Si content (calculated during the initial setup) of the obtained polyurethane dispersion (D-1) was 1200 mg / 1 kg, and the metaxylylene group content (calculated during the initial setup) was 32% by mass.

[0176] [Polyester resin (G)] As the polyester component, polyester polyol (DIC Corporation's "DF-COAT GEC-004C": solid content 30%) was used.

[0177] [Polyisocyanate crosslinking agent (H)] As the polyisocyanate component, a trimethylolpropane adduct of metaxylylene diisocyanate ("Takenate D-110N" manufactured by Mitsui Chemicals, Inc.: solid content 75%) was used.

[0178] [Silane coupling agent (I)] N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (KBM-603, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the silane coupling agent.

[0179] [Coating liquid 1 for use in the coating layer] The following materials were mixed in the specified proportions to create a coating solution (resin composition for the coating layer). Water 54.40% by mass Isopropanol 25.00% by mass Oxazoline group-containing resin (A) 15.00% by mass Acrylic resin (B) 3.60% by mass Urethane resin (C) 2.00% by mass

[0180] [Coating liquid used for the coating layer 2] The following materials were mixed in the specified proportions to create a coating solution (resin composition for the coating layer). Water 57.80% by mass Isopropanol 25.00% by mass Carbodiimide-based crosslinking agent (A) 2.10% by mass Urethane resin (F) 8.00% by mass Silane coupling agent (E) 7.10% by mass

[0181] [Coating liquid 3 for protective layer coating] The following coating agents were mixed to prepare coating solution 3. The mass ratio of urethane resin (E) in terms of solid content is shown in Table 1. Water 22.00% by mass Isopropanol 30.00% by mass Urethane resin (F) 48.00% by mass

[0182] [Coating liquid used for protective layer coating 4] A silane coupling agent (I) was dissolved in acetone (15% wt), and isocyanate (G) was mixed in the following ratio and stirred with a magnetic stirrer for 10 minutes. The resulting mixture was diluted with methyl ethyl ketone, and polyester resin (G) was added to obtain a coating solution. The mixing ratio is shown below. Polyester resin (G) 4.90% by mass Isocyanate (H) 1.87% by mass Silane coupling agent (I) *Acetone dilution 0.85% by mass Methyl ethyl ketone 92.39% by mass

[0183] The following describes the method for preparing the laminated films used in each example and comparative example. The laminated films used in Examples 1-8 and Comparative Examples 1-7 are shown in Table 2.

[0184] 1. Base film (Processing of polyester resin recycled from PET bottles) After washing away foreign matter such as remaining beverage from PET bottles used for beverages, the resulting flakes were crushed and melted in an extruder. The material was then filtered twice using filters with progressively smaller mesh sizes to remove even finer foreign matter, and finally filtered a third time using the smallest mesh size filter (50 μm) to obtain a polyester recycled material. The composition of the resulting resin was terephthalic acid / isophthalic acid / ethylene glycol = 97.0 / 3.0 / 100 (mol%), and the intrinsic viscosity of the resin was 0.70 dl / g. This was designated as polyester A.

[0185] (Manufacturing of base film) Polyethylene terephthalate resin with an intrinsic viscosity of 0.62 dl / g, consisting of terephthalic acid / ethylene glycol = 100 / 100 (mol%), was prepared as polyester B, and a masterbatch of polyester C was prepared by containing 0.3% amorphous silica with an average particle size of 1.5 μm in polyester B. Each raw material was dried at 125°C for 8 hours under reduced pressure of 33 Pa. These were mixed in a weight ratio of A / B / C = 80 / 10 / 10 and fed into a single-screw extruder. The temperature of the resin from the extruder to the melt line, filter, and T-die was set to 280°C. However, for the first 30 seconds from the start of the compression section of the extruder screw, the resin temperature was set to 305°C, and thereafter it was set back to 280°C.

[0186] The molten material extruded from the T-die was brought into contact with a cooling roll to form an unstretched sheet, which was then stretched 1.41 times in the longitudinal direction on a roll with a peripheral speed difference heated to 118°C (MD1), and then stretched 2.92 times in the longitudinal direction on a roll with a peripheral speed difference heated to 128°C (MD2). The longitudinally stretched sheet was guided to a tenter, and the above coating liquid 1 was coated on one side of the film using the fountain coat method. While drying, it was guided to a tenter, preheated to 121°C, and then stretched 4.3 times transversely at 131°C. Subsequently, for heat setting, it was set at 180°C with no relaxation (0%) for 2.5 seconds (TS1), followed by 231°C with 5% relaxation for 3.0 seconds (TS2), followed by 222°C with no relaxation for 2.5 seconds (TS3). Next, the material was cooled at 120°C for 6.0 seconds in the same tenter, and finally wound up with a winder to obtain a biaxially oriented polyester film with a thickness of 12 μm.

[0187] In preparing the base film layers described in each example and comparative example, laminated films were prepared and evaluated in the same manner, except that the blending amounts of resins A / B / C were changed.

[0188] 2. Interlayer film (Preparation of PBT resin) 1) Polybutylene terephthalate (PBT) resin: The polybutylene terephthalate resin used in the production of the biaxially oriented polyester film described later was 1100-211XG (CHANG CHUN PLASTICS CO.,LTD., intrinsic viscosity 1.28 dl / g). 2) Polyethylene terephthalate (PET) resin: The polyethylene terephthalate resin used in the production of the biaxially oriented polyester film described later was terephthalic acid / / ethylene glycol = 100 / / 100 (mol%) (manufactured by Toyobo Co., Ltd., intrinsic viscosity 0.62 dl / g).

[0189] (Film manufacturing) Using a single-screw extruder, a mixture of 80% by mass of PBT resin and 20% by mass of PET resin was added as inert particles, with an average particle size of 2.4 μm, at a silica concentration of 900 ppm relative to the resin mixture. This mixture was melted at 290°C, and the melt line was introduced into a 12-element static mixer. This allowed for the division and lamination of the polyester resin melt to obtain a multilayer melt made from the same raw materials. The melt was cast from a T-die at 265°C and adhered to a cooling roll at 15°C using an electrostatic adhesion method to obtain an unstretched sheet. Next, the film was roll-stretched 2.9 times in the longitudinal direction at 60°C, and after longitudinal stretching, an adhesive layer resin composition (coating liquid 1) was applied by the fountain coat method. Then, while drying, it was guided to a tenter, and then stretched 4.0 times in the transverse direction at 90°C through the tenter. After a tension heat treatment at 200°C for 3 seconds and a relaxation treatment of 9% for 1 second, the film was cooled by cooling at 50°C for 2 seconds. At this time, the surface temperature of the film edge was 75°C. Next, 9% of the gripping portions at both ends were cut off to obtain a laminated film in which a coating layer of 0.030 g / m2 was formed on a polyester film with a thickness of 15 μm. The physical properties of the obtained film are shown in Table 1.

[0190] 3. Heat-sealable resin layer (Preparation of polyester raw materials) [Synthesis Example 1] In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 100 mol% dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% ethylene glycol (EG) as the polyhydric alcohol component were charged so that the molar ratio of ethylene glycol was 2.2 times that of dimethyl terephthalate. Using 0.05 mol% zinc acetate (relative to the acid component) as a transesterification catalyst, the transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, 0.225 mol% antimony trioxide (relative to the acid component) was added as a polycondensation catalyst, and the polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to obtain polyester (A) with an intrinsic viscosity of 0.75 dl / g. This polyester (A) is polyethylene terephthalate. The composition of the polyester is shown in Table 1. [Synthesis Example 2] Polyesters (B) to (E) were obtained by changing the monomer 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, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and DEG is diethylene glycol. When producing polyester (E), SiO2 (Silysia 266, manufactured by Fuji Silysia Co., Ltd.) was added as a lubricant at a ratio of 7,000 ppm relative to the polyester. Each polyester was made into chips as appropriate.

[0191] [Table 1]

[0192] [Film creation] Polyester A, polyester B, polyester D, and polyester E were mixed in a mass ratio of 10:60:24:6 as the raw material for the heat seal layer, and polyester A, polyester B, polyester D, and polyester E were mixed in a mass ratio of 57:31:6:6 as the raw material for the heat-resistant layer. The mixed raw materials for the heat seal layer and the 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 and extruded from a T-die, and cooled on a chill roll set to a surface temperature of 30°C to obtain an unstretched laminated film. The flow path of the molten resin was set so that one side of the laminated film was the heat seal layer and the other side was the heat-resistant layer (a two-layer structure of two types: heat seal layer / heat-resistant layer), and the extrusion amount was adjusted so that the thickness ratio of the heat seal layer to the heat-resistant layer was 50 / 50.

[0193] The unstretched laminated film obtained by cooling and solidifying was guided to a longitudinal stretcher with multiple rolls arranged in a series. After preheating on a preheating roll until the film temperature reached 78°C, it was stretched to 4.1 times its original length. Immediately after longitudinal stretching, the film was passed through a heating furnace set to 100°C using a hot air heater, and a 20% relaxation treatment was performed in the longitudinal direction using the speed difference between the rolls at the inlet and outlet of the heating furnace. Subsequently, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25°C. After the relaxation treatment, the film was guided to a tenter and preheated for 5 seconds until the surface temperature reached 105°C, and then stretched 4.0 times in the width direction (lateral direction). The stretched film was then guided to an 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 lateral stretching zone were blocked so that when a strip of paper was hung down without the film passing through, the strip of paper would hang almost completely vertically.

[0194] Subsequently, the film that had passed through the intermediate zone was guided to the final heat treatment zone and heat-treated at 190°C for 5 seconds. At the same time as the heat treatment, the clip spacing in the width direction of the film was narrowed, thereby performing a 3% relaxation treatment in the width direction. After passing through the final heat treatment zone, the film was cooled for 5 seconds with 30°C cooling air. At this time, the actual film temperature at the tenter exit was 45°C. By cutting off both edges and winding the film into a roll with a width of 500 mm, a biaxially oriented film with a thickness of 30 μm was continuously produced over a predetermined length.

[0195] The methods for preparing the inorganic thin film layers used in each example and comparative example are described below. These methods were used in Examples 1-8 and Comparative Examples 1-7, and are shown in Table 2. (Formation of inorganic thin film layer M-1) As the inorganic thin film layer M-1, the heat-resistant base film layer, intermediate layer, or heat-sealing resin Aluminum oxide was deposited onto the film layer. The method for depositing aluminum oxide onto the substrate film layer involved setting the film on the unwinding side of a continuous vacuum deposition machine and winding the film through a cooling metal drum. At this time, the pressure of the continuous vacuum deposition machine was reduced to 10⁻⁴ Torr or less, and 99.99% pure metallic aluminum was loaded into an alumina crucible from the bottom of the cooling drum. The metallic aluminum was heated and evaporated, and oxygen was supplied into the vapor to cause an oxidation reaction, depositing it onto the film and forming a 10 nm thick aluminum oxide film.

[0196] (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 substrate film layer, intermediate layer, or heat-resistant layer of the heat-seal resin by electron beam deposition. Particulate SiO2 (99.9% purity) and A12O3 (99.9% purity) of approximately 3mm to 5mm were used as the deposition source. The thickness of the inorganic thin film layer (SiO2 / A12O3 composite oxide layer) in the resulting film (inorganic thin film layer / coating layer-containing film) was 13nm. The composition of this composite oxide layer was SiO2 / A12O3 (mass ratio) = 60 / 40.

[0197] (Coating of coating solution 3 onto the vapor-deposited film (lamination of protective layer)) The coating solution 3 prepared above was applied to the inorganic thin film layer of the obtained vapor-deposited film by gravure roll coating, pre-dried at 110°C, and then fully dried at 160°C to obtain a protective layer of a predetermined amount. Subsequently, it was subjected to a post-heat treatment at 40°C for 2 days.

[0198] (Coating of coating solution 4 onto the vapor-deposited film (lamination of protective layer)) The coating solution 4 prepared above was applied to the inorganic thin film layer of the obtained vapor-deposited film by gravure roll coating, pre-dried at 110°C, and then fully dried at 190°C to obtain a protective layer of a predetermined amount. Subsequently, it was subjected to a post-heat treatment at 40°C for 4 days.

[0199] As described above, film laminates 1 to 3, as shown in Table 2, were prepared by providing a coating layer / inorganic thin film layer / protective layer on each film. In each example and comparative example, films 1 to 3 were used and bonded together by a dry lamination method using an adhesive to produce laminate laminates with the configurations shown in Table 3. For the comparative example, a polyamide film (Toyobo N1100-15μm; NY) was used as the intermediate layer, and a linear low-density polyethylene film (Toyobo L4102-40μm; LLDPE) or an unoriented polypropylene film (Toyobo P1146-70μm; CPP) was used as the heat-seal resin. The configurations of the prepared laminate laminates are shown in Table 3. Furthermore, various evaluations were performed on the obtained laminate laminates. The results are shown in Table 3.

[0200] [Table 2]

[0201] [Table 3] [Industrial applicability]

[0202] This invention significantly improves gas barrier performance by laminating and bonding an inorganic thin film layer, a coating layer, and a barrier protective layer onto each film. Furthermore, by laminating a base film made of polyester resin derived from PET bottles, which has a low environmental impact, with a sealant composed of polyester components, monomaterialization is achieved while maintaining toughness, sealing properties, and transparency. Moreover, since the laminated film of this invention can be manufactured easily with fewer processing steps, it is excellent in both economic efficiency and production stability, and can provide a gas barrier film with homogeneous properties.

Claims

1. A laminated structure comprising a polyester base film containing 50% or more by mass of polyester resin recycled from PET bottles, and a heat-sealable resin layer laminated in this order, wherein the base film is a laminated film having an inorganic thin film layer (A) and a protective layer (a) containing urethane resin on one side, the heat-sealable resin layer is a stretched film layer made of a polyester resin mainly composed of ethylene terephthalate, the laminated structure having a puncture strength of 10 N or more and a haze of 20% or less, an inorganic thin film layer (B) laminated on the heat-sealable resin layer, and the thickness of the polyester material relative to the total thickness being 90% or more.

2. The laminate according to claim 1, wherein an intermediate layer film is provided between the base film and the heat-sealable resin layer via an adhesive, and the intermediate layer film is made of a resin composition containing 70% by mass or more of polybutylene terephthalate resin.

3. The laminated structure according to claim 2, characterized in that an inorganic thin film layer (C) is laminated on the intermediate film.

4. The laminate according to claim 2 or 3, characterized in that a protective layer (b) containing urethane resin is laminated on the inorganic thin film layer (C) of the intermediate layer film.

5. The laminate according to any one of claims 1 to 4, characterized in that it has a coating layer (X) between the base film and the inorganic thin film layer (A).

6. The laminate according to any one of claims 2 to 4, characterized in that it has a coating layer (Y) between the intermediate layer film and the inorganic thin film layer (C).

7. The laminate according to any one of claims 1 to 6, characterized in that the inorganic thin film layers (A) to (C) are all made of aluminum oxide or a composite oxide of silicon oxide and aluminum oxide.

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