Gas barrier film and laminated film using the same

Abstract

The objective is to provide a laminated film that enables weight reduction and volume reduction of packaging materials, has excellent impact resistance and puncture resistance, and possesses barrier properties while also having excellent tear resistance. [Solution] A laminated film comprising a gas barrier film and a sealant film, wherein the gas barrier film is composed of at least a base layer / coating layer, the base layer is a biaxially oriented polyester film containing 30-55% by mass of polybutylene terephthalate resin and 45-70% by mass of polyethylene terephthalate resin, and has a puncture strength of 0.60-1.00 N / μm per unit film thickness, and the laminated film is characterized by satisfying the following conditions (a) to (b). (a) The oxygen permeability is 30 ml / m2·day·MPa or less. (b) The tear strength in both the MD direction and the TD direction is 200 to 1000 mN.

Description

[Technical Field]

[0001] This invention relates to laminated films used in the packaging of food, pharmaceuticals, and the like. More specifically, it relates to a gas barrier film with excellent gas barrier properties, dimensional stability, processability, and tear resistance, and a laminated film using the same. [Background technology]

[0002] In the field of food and pharmaceutical packaging, packaging is required to protect its contents, and high airtightness is crucial to prevent easy opening against external forces such as sterilization processes during food manufacturing, vibrations during transportation, and handling. On the other hand, it is also required to be easy to open when in use, so "easy opening" is required for containers, lids, and packaging. In recent years, due to social factors such as the increased participation of women in the workforce, the rise of nuclear families, and the aging population, there has been a growing demand for convenient and easy-to-open packaging.

[0003] For example, various types of easy-open packaging have been proposed, including containers with easy-open lids that facilitate opening the cup or tray-shaped container body, and easy-open type sealed packaging containers. Among these, packaging called "easy-peel" uses a sealant film that provides opening capabilities and is widely used as a lid for prepared foods, desserts, and dairy products, where a balance between stable sealing and easy opening is important. Furthermore, since these sealed packaging containers are often boxed, transported, and sold in stores in recent years, it is required that they are resistant to tearing even if dropped during the process.

[0004] These easy-open type sealed packaging containers usually have an opening to allow for easy opening. In the case of containers with a fixed shape, such as hard trays or cups, one can grasp the container body with one hand and the opening with the other to open it. However, in the case of trays made of thin sheets, if force is applied to open the container by grasping the container body, the container itself will deform. Therefore, an unsealed section is usually provided at the corner, continuous with the easy-open seal, and the container is opened by grasping both the lid and bottom material of the unsealed section.

[0005] However, because packaging containers are designed with safety in mind, the peel strength of the easy-open seal is almost always set to be quite strong. In the case of surface seals, the peel boundary gradually widens as the seal peels away from the opening, which can cause the lid to tear and prevent a clean opening. If the contents include paste or liquid substances, problems such as the contents spilling out due to the tearing of the lid or deformation of the container can occur, potentially resulting in hands or clothes getting soiled with food contents, or burns if the contents are heated.

[0006] Patent Document 1 discloses a polyester laminated film containing a thermoplastic copolymer polyester resin and a polyolefin resin in the sealing layer. According to this technology, by keeping the crystal melting peak temperature and ratio of the polyethylene terephthalate resin and thermoplastic copolymer polyester resin contained in the sealing layer, and the ratio of the polyolefin resin within a specific range, and laminating a polyester laminated film composed of a support layer made of polyethylene terephthalate resin with a base layer, a package with improved ease of opening and impact resistance can be obtained.

[0007] While using a polyester film as the base layer can provide lids and packaging materials with excellent single-material properties, easy peeling, easy opening, heat-sealability, and aroma retention, the biaxially oriented polyester film used for the base layer has drawbacks such as low impact strength, puncture strength, and pinhole resistance, leaving room for improvement. Furthermore, in order to stably produce polyester laminated films and ensure good handling such as winding, it is necessary to make the support layer thick, making it difficult to reduce the volume of the packaging including the base layer. As the volume of the packaging decreases, the mechanical strength and puncture strength, which are problematic, decrease, and impact resistance becomes insufficient, posing problems in terms of resource conservation and environmental impact.

[0008] On the other hand, biaxially oriented polyester films mainly composed of polybutylene terephthalate resin are known to possess heat resistance and flexibility (Patent Document 2). According to this technology, by using a biaxially oriented polyester film mainly composed of polybutylene terephthalate resin, it can be suitably used in applications requiring toughness, such as those where conventional polyamide films have been used. Furthermore, in applications where polyethylene terephthalate film and polyamide film have been laminated, it becomes possible to replace the polyethylene terephthalate film and polyamide film with a single layer of biaxially oriented polyester film mainly composed of polybutylene terephthalate resin, thereby reducing the volume of packaging material. If the openability of packaging using such a highly flexible film can be improved, it is expected that it will be used for packaging a wider range of contents.

[0009] However, polybutylene terephthalate resin is known to have a faster crystallization rate and a lower final degree of crystallinity compared to other crystalline polymers. Therefore, it is difficult to manufacture biaxially oriented polyester films with polybutylene terephthalate resin as the main component, and it has been challenging to improve puncture strength and ease of opening while increasing the orientation of the film in both the longitudinal and width directions.

[0010] Furthermore, packaging materials used for food, pharmaceuticals, etc., are required to possess gas barrier properties—that is, properties that block gases such as oxygen and water vapor—in order to suppress the oxidation of proteins and fats, maintain taste and freshness, and preserve the efficacy of pharmaceuticals.

[0011] Conventionally, in food applications requiring the blocking of various gases such as water vapor and oxygen, gas barrier films have been commonly used, which consist of a plastic base film with a metal thin film made of aluminum or the like, or an inorganic thin film made of inorganic oxides such as silicon dioxide or aluminum oxide, formed on its surface. Among these, films with a thin film (inorganic thin film layer) of inorganic oxides such as silicon dioxide, aluminum oxide, or mixtures thereof are widely used because they are transparent and allow for confirmation of the contents. (Patent Document 3)

[0012] However, when the above gas barrier film is laminated with a sealant film to form a laminated film, the presence of an inorganic thin film layer between the film layers results in poor tearability, which in turn impairs ease of opening. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2023-9803 [Patent Document 2] Japanese Patent Publication No. 2018-20844 [Patent Document 3] Japanese Patent Application Publication No. 6-278240 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] This invention was made against the backdrop of the aforementioned technical challenges. Specifically, the objective of this invention is to provide a laminated film that enables weight reduction and volume reduction of packaging materials, has excellent impact resistance and puncture resistance, and possesses barrier properties while also having excellent tear resistance.

[0015] As a result of intensive studies to achieve such an object, the present invention has been completed as follows: By devising the blending ratio of the polybutylene terephthalate resin in the film and the stretching conditions during film formation, the orientation in the longitudinal and width directions of the film is enhanced, and a biaxially stretched polyester film having a puncture strength within a specific range can be obtained. By applying a coating layer containing a water-soluble polymer component to the biaxially stretched polyester film, a gas barrier film having good tearability can be obtained.

[0016] 1. A laminated film including a gas barrier film and a sealant film, wherein the gas barrier film is composed of at least a base material layer / a coating layer, the base material layer contains 30 to 55% by mass of a polybutylene terephthalate resin and 45 to 70% by mass of a polyethylene terephthalate resin, and is a biaxially stretched polyester film having a puncture strength of 0.60 to 1.00 N / μm per film thickness, and the laminated film satisfies the following conditions (a) to (b). (a) The oxygen permeability is 30 ml / m 2 ·day·MPa or less. (b) The tear strength in both the MD direction and the TD direction is 200 to 1000 mN. 2. The laminated film according to 1., wherein the coating layer contains a water-soluble polymer having a plurality of hydroxyl groups in the molecule. 3. A package including the laminated film according to 1. or 2. 4. A packaging container including the laminated film according to 1. or 2.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a laminated film that can reduce the weight and volume of packaging materials, is excellent in impact resistance and puncture resistance, has barrier properties, and is excellent in tearability.

Modes for Carrying Out the Invention

[0018] The present invention will be described in detail below. In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0019] (Biaxially oriented polyester film that constitutes the base layer) The biaxially oriented polyester film constituting the base layer of the present invention contains 30 to 55% by weight of polybutylene terephthalate resin (hereinafter sometimes abbreviated as PBT resin) and 45 to 70% by weight of polyethylene terephthalate resin (hereinafter sometimes abbreviated as PET resin), more preferably containing 35 to 50% by weight of PBT resin and 50 to 65% by weight of PET resin. A PBT resin content of 30 to 55% by weight allows for excellent dimensional stability, processability, and the development of tear resistance, chemical resistance, and pinhole resistance at low temperatures. The PBT resin may contain copolymer components, but PBT resin without copolymer components is preferred.

[0020] The intrinsic viscosity of the PBT resin used in this invention is preferably 0.9 to 1.3 dl / g, more preferably 0.95 to 1.3 dl / g, and even more preferably 1.0 to 1.3 dl / g. By setting the intrinsic viscosity of the PBT resin to 0.9 dl / g or higher, it is possible to suppress a decrease in the intrinsic viscosity of the film obtained by film formation, which would otherwise reduce puncture strength, impact strength, and tear resistance. On the other hand, by setting the intrinsic viscosity to 1.3 dl / g or lower, it is possible to suppress excessive stress during film stretching and obtain good film-forming properties. Furthermore, it is possible to suppress the generation of decomposition products during extrusion, which would otherwise be required to raise the extrusion temperature due to a higher melt viscosity.

[0021] The intrinsic viscosity of the PET resin used in the present invention is preferably 0.5 to 1.2 dl / g, and more preferably 0.6 to 1.2 dl / g.

[0022] The biaxially oriented polyester film of the present invention may contain polyester resins other than PBT resin and PET resin. Examples of polyester resins other than PET resin include polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT), as well as polyester resins copolymerized with dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid, and polyester resins copolymerized with diol components such as 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.

[0023] The biaxially oriented polyester film of the present invention may contain, as necessary, lubricants, stabilizers, colorants, antioxidants, antistatic agents, ultraviolet absorbers, and the like.

[0024] As lubricants, inorganic particulate 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.

[0025] The lower limit of the lubricant content in the biaxially oriented polyester film is preferably 100 to 10,000 ppm by mass, more preferably 500 to 6,000 ppm by mass, and even more preferably 800 to 1,800 ppm by mass. A lubricant content of 100 ppm by mass or more allows the film to exhibit slipperiness, while a lubricant content of 10,000 ppm by mass or less allows for good transparency of the film.

[0026] The manufacturing method for obtaining the biaxially oriented polyester film according to the present invention will be described in detail. However, it is not limited to these methods.

[0027] There are no particular limitations on the method for obtaining the biaxially oriented polyester film of the present invention, but the T-die method is preferred from the viewpoint of thickness accuracy. In the inflation method, the stretching ratio is difficult to increase due to the manufacturing method, and thickness defects in the width direction may occur. A typical manufacturing process of the T-die method is described here. The T-die method includes (1) a step of melt-extruding a polyester resin composition into a sheet using an extruder and a T-die, and cooling it on a cooling roll to form an unstretched sheet, (2) a stretching step of stretching the formed unstretched sheet in the MD direction and in the TD direction perpendicular to the MD direction, (3) a heat-setting step of heating the film after stretching to crystallize it, (4) a heat-relaxation step (sometimes called a relaxation step) to remove residual strain from the heat-set film, and (5) a cooling step of cooling the film after heat relaxation.

[0028] The resin melting temperature inside the extruder is preferably 230 to 310°C, and more preferably 240 to 300°C. A temperature of 230°C or higher enables resin extrusion and ensures stable discharge and good thickness accuracy. A temperature of 300°C or lower suppresses resin decomposition, preventing the film from becoming brittle and preventing a decrease in film quality due to thermal degradation.

[0029] The cooling roll temperature in the process of forming the unstretched sheet is preferably 0 to 40°C, and more preferably 0 to 20°C or lower. Setting the temperature above 0°C allows for sufficient suppression of crystallization when the molten polyester resin composition cools and solidifies. Furthermore, 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. On the other hand, setting the temperature below 40°C prevents the degree of crystallization of the molten polyester resin composition from becoming too high when it cools and solidifies, making stretching easier and suppressing a decrease in transparency due to crystallization.

[0030] The thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm. More preferably it is 500 μm or less, and most preferably 300 μm or less.

[0031] In the stretching process, both simultaneous biaxial stretching and sequential biaxial stretching are possible. However, in order to increase puncture strength, it is necessary to increase the degree of surface orientation, and sequential biaxial stretching is preferable because it allows for a faster film formation speed and higher productivity.

[0032] The stretching temperature in the longitudinal direction (also called the MD direction) is preferably 55 to 130°C, and more preferably 60 to 120°C. A temperature of 55°C or higher not only makes fracture less likely, but also strengthens the longitudinal orientation due to low-temperature stretching, which suppresses the increased distortion of molecular orientation in the width direction caused by increased shrinkage stress during heat-setting treatment. A temperature of 130°C or lower enhances surface orientation, thereby increasing puncture strength. Furthermore, it suppresses the deterioration of mechanical properties due to a lack of orientation.

[0033] The stretching ratio in the MD direction is preferably 2.6 to 4.5 times, and particularly preferably 3.4 to 4.4 times. By setting it to 2.6 times or higher, the degree of surface orientation can be increased, and the puncture strength can be increased. In addition, a decrease in mechanical properties and deterioration of thickness uniformity can be suppressed, and sagging of the film roll can be prevented. By setting it to 4.5 times or lower, sufficient effects on improving mechanical strength and thickness uniformity can be obtained. Furthermore, because the orientation in the MD direction becomes stronger, it is possible to suppress the increase in molecular orientation distortion in the width direction due to the increased shrinkage stress during heat fixing treatment.

[0034] The lower limit of the stretching temperature in the width direction (also called the TD direction) is preferably 90 to 130°C, more preferably 95 to 125°C, and particularly preferably 100 to 120°C. Setting it above 90°C makes it less likely for fracture to occur. Setting it below 130°C increases the degree of surface orientation, thereby increasing the puncture strength. In addition, it is possible to suppress the decrease in mechanical properties due to the lack of orientation.

[0035] The stretch ratio in the TD direction is preferably 3.6 to 5.0 times, more preferably 3.8 to 4.8 times, and particularly preferably 4.0 to 4.5 times. By setting it to 3.6 times or higher, the degree of surface orientation can be increased, and the puncture strength can be increased. In addition, deterioration of mechanical properties and thickness uniformity due to lack of orientation can be suppressed. By setting it to 5.0 times or lower, sufficient effects on improving mechanical strength and thickness uniformity can be obtained.

[0036] The heat-setting temperature in the heat-setting process after stretching in the TD direction is preferably 180 to 240°C, more preferably 190 to 225°C, and particularly preferably 200 to 210°C. Setting the temperature above 180°C can reduce the thermal shrinkage rate and suppress misalignment and shrinkage during processing. Setting the temperature below 240°C can suppress the film from melting, prevent the film from becoming excessively brittle, and increase the degree of surface orientation, thereby increasing puncture strength. The processing time in the heat-setting process is preferably 1.0 to 10.0 seconds, more preferably 1.5 to 7.0 seconds, and even more preferably 2.0 to 5.0 seconds. Setting the processing time above 1.0 second can enhance the processing effect of the heat-setting process, while setting it below 10.0 seconds can increase productivity.

[0037] The relaxation rate in the TD direction during the thermal relaxation process is preferably 1 to 12%, more preferably 2 to 11%, and particularly preferably 3 to 10%. Setting it to 1% or more keeps the thermal shrinkage rate in the TD direction low, preventing breakage from occurring during thermal fixing. Setting it to 12% or less prevents uneven thickness due to sagging, improving flatness. The processing time during the thermal relaxation process is preferably 0.3 to 5.0 seconds, more preferably 0.5 to 4.0 seconds, and even more preferably 1.0 to 3.0 seconds. Setting it to 0.3 seconds or more enhances the processing effect of the thermal relaxation process, while setting it to 5.0 seconds or less increases productivity.

[0038] The thickness of the biaxially oriented polyester film in this invention is preferably 8 to 30 μm, and more preferably 10 to 20 μm. A thickness of 8 μm or more maintains the strength of the film. A thickness of 30 μm or less achieves the volume reduction that is the objective of this invention. One of the features of the biaxially oriented polyester film of this invention is that it can be made thinner than conventional polyester films.

[0039] The haze of the biaxially oriented polyester film of the present invention is preferably 10% or less, more preferably 9% or less, and even more preferably 7% or less. A haze of 7% or less is preferable because it allows the contents to be clearly visible when packaged and the printing to look good. The lower limit is not particularly limited, but may be 1% or more, or 2% or more.

[0040] The puncture strength per unit thickness of the biaxially oriented polyester film of the present invention is preferably 0.60 to 1.00 N / μm, more preferably 0.60 to 0.90 N / μm, even more preferably 0.60 to 0.85 N / μm, and particularly preferably 0.60 to 0.80 N / μm. Setting it to 0.60 N / μm or higher can suppress insufficient strength when used as a packaging material, and it can be suitably used, for example, for packaging relatively heavy food products or packaging for sharp contents. Setting it to 1.00 N / μm or lower can suppress thermal shrinkage, and can reduce processing problems caused by film shrinkage in processes such as vapor deposition and printing.

[0041] The static and dynamic friction coefficients of the biaxially oriented polyester film of the present invention are preferably 0.25 to 0.50, more preferably 0.30 to 0.48, and particularly preferably 0.34 to 0.45. By keeping the coefficients within the range of 0.25 to 0.50, the film's slipperiness is appropriate and the winding quality of the film roll can be improved.

[0042] The thermal shrinkage rate of the biaxially oriented polyester film of the present invention after heating at 150°C for 15 minutes in the longitudinal direction is preferably 1.0 to 5.0%, more preferably 1.2 to 4.5%, and even more preferably 1.4 to 4.0%. By setting it in the range of 1.0 to 5.0%, the puncture strength can be increased. On the other hand, the thermal shrinkage rate after heating at 150°C for 15 minutes in the width direction is preferably -1.0 to 1.5%, more preferably -0.8 to 1.2%, and even more preferably -0.6 to 1.0%. By setting it in the range of -1.0 to 1.5%, processing problems such as pitch deviation due to dimensional changes during processing such as printing can be reduced.

[0043] (covering layer) The coating layer in the present invention is formed for the purpose of improving the gas barrier performance of a biaxially oriented polyester film and is characterized by containing a water-soluble polymer having multiple hydroxyl groups in its molecule. Although an inorganic thin film layer may be provided as a means of improving gas barrier performance, it is preferable not to include an inorganic thin film layer because if the inorganic thin film layer is included in the laminate, the stress during tearing may not be transmitted well near the inorganic thin film layer, which may increase the tear strength.

[0044] Examples of the aforementioned water-soluble polymers include polyvinyl alcohol, polyvinylpyrrolidone, starch, methylcellulose, carboxymethylcellulose, and sodium alginate. Polyvinyl alcohol-based polymers are particularly preferred from the viewpoint of barrier properties. Polyvinyl alcohol-based polymers are those whose main component is vinyl alcohol units, and a significant improvement in barrier performance can be expected due to the high cohesiveness resulting from the hydrogen bonding structure. Various copolymerized or modified polyvinyl alcohol-based polymers can also be used, such as polyvinyl alcohol-based polymers copolymerized with ethylene and silanol-modified polyvinyl alcohol-based polymers.

[0045] The degree of polymerization and degree of saponification of the polyvinyl alcohol-based resin are determined based on the desired gas barrier performance and the viscosity of the aqueous solution. The degree of polymerization is preferably 2600 or less, and more preferably 1800 or less. By setting the degree of polymerization to 2600 or less, the viscosity of the aqueous solution can be reduced, making it easier to apply to coating processes. The degree of saponification is preferably 90.0% to 99.7%, and more preferably 93.0% to 99.0%. Setting the degree of saponification to 90% or more increases the degree of resin cohesiveness, allowing for sufficient oxygen gas barrier properties even under high humidity. On the other hand, if the degree of saponification is 99.7% or more, it becomes difficult to prepare the aqueous solution, it is prone to gelation, and the stability of the aqueous solution is poor, making it difficult to apply to coating processes.

[0046] In the coating layer of the present invention, inorganic layered compounds, metal alkoxides, and their hydrolysates may be added to further improve barrier properties. The presence of inorganic layered compounds in the coating layer is expected to create a labyrinthine effect on gas molecules, thereby improving gas barrier properties. Furthermore, the presence of metal alkoxides and their hydrolysates in the coating layer allows for the formation of a dense and strong polymerized film with water-soluble polymers, further improving gas barrier properties.

[0047] Examples of the inorganic layered compound include clay minerals such as smectite, kaolin, mica, hydrotalcite, and chlorite (including their synthetic counterparts). Specifically, examples include montmorillonite, beiderite, saponite, hectorite, souconite, stevensite, kaolinite, nacrite, dickite, halloysite, hydrated halloysite, tetrasilyl mica, sodium teniolite, muscovite, margalite, phlogopite, talc, antigorite, chrysotile, pyrophyllite, vermiculite, xanthophyllite, and chlorite. Furthermore, flaky silica and the like can also be used as inorganic layered compounds. These may be used individually or in combination of two or more. Smectite (including its synthetic counterparts) is particularly preferred due to its high effect in improving water vapor barrier properties.

[0048] Furthermore, as the inorganic layered compound, it is preferable that it contains redox metal ions, particularly iron ions. In addition, montmorillonite, a type of smectite, is preferred from the viewpoint of coating suitability and gas barrier properties. As the montmorillonite, known types that have been conventionally used as gas barrier agents can be used. For example, the following general formula: (X,Y)2~3Z4O10(OH)2·mH2O·(Wω) (In the formula, X represents Al, Fe(III), or Cr(III). Y represents Mg, Fe(II), Mn(II), Ni, Zn, or Li. Z represents Si or Al. W represents K, Na, or Ca. H2O represents intercalated water. m and ω represent positive real numbers.) Among these, those in which W is Na in the formula are preferred because they can be cleaved in an aqueous medium.

[0049] The size and shape of the inorganic layered compound are not particularly limited, but the particle size (longest diameter) is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. If the particle size is larger than 5 μm, the dispersibility will be poor, which may result in deterioration of the coating properties and appearance of the coating layer. On the other hand, the aspect ratio is 50 to 5000, more preferably 100 to 4000, and even more preferably 200 to 3000.

[0050] The blending ratio of the polyvinyl alcohol copolymer to the inorganic layered compound in the coating layer of the present invention is preferably 75 / 25~35 / 65 (wt%), more preferably 70 / 30~40 / 60 (wt%), and even more preferably 65 / 35~45 / 55 (wt%). If the blending ratio of the inorganic layered compound is less than 25%, the barrier performance may be insufficient. On the other hand, if it is more than 65%, dispersibility will be poor, which may lead to deterioration of coating properties and adhesion.

[0051] Examples of the metal alkoxide include alkoxysilanes, such as tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, methyltriethoxysilane, and methyltrimethoxysilane. Tetraethoxysilane is particularly preferred from the viewpoint of being relatively stable in aqueous solvents.

[0052] Examples of hydrolysis products of metal alkoxides include those in which at least one of the alkoxy groups of the metal alkoxide has been replaced with a hydroxyl group. Hydrolysis products of metal alkoxides can be prepared by known methods. For example, they can be prepared by adding an aqueous solution of an acid such as hydrochloric acid to a metal alkoxide and allowing a hydrolysis reaction to occur. Metal alkoxides and their hydrolysates acquire hydroxyl groups through hydrolysis, and these hydroxyl groups undergo dehydration condensation to form a dense and strong polymerized film.

[0053] The blending ratio of the polyvinyl alcohol copolymer, metal alkoxide and its hydrolysate, and water-soluble polymer in the coating layer of the present invention is preferably 80 / 20 to 20 / 80 (wt%), and more preferably 60 / 40 to 40 / 60 (wt%). If the blending ratio of metal alkoxide is less than 20%, the bonding from inorganic elements becomes insufficient, resulting in a coating layer with low water resistance. If it exceeds 80%, the bonding from inorganic elements becomes excessive, resulting in a hard and brittle coating layer, which leads to a decrease in gas barrier properties.

[0054] The amount of coating layer adhering is 0.10 to 1.00 (g / m²). 2 It is preferable to set it to 0.20~0.80 (g / m³). 2 It is more preferable to have a coating layer adhesion amount of 1.00 (g / m²). 2 If the amount of adhesion of the coating layer exceeds 0.10 (g / m²), the cohesive force within the coating layer may become insufficient, potentially preventing it from exhibiting sufficient gas barrier properties and adhesion. 2 If the value is less than ), sufficient gas barrier properties may not be obtained.

[0055] The method for applying the coating layer is not particularly limited, and known methods can be used. For example, dip coating, roll coating, gravure coating, reverse coating, air knife coating, etc., can be used.

[0056] When forming the coating layer, it is preferable to apply the resin composition for the coating layer, pre-dry it at a relatively low temperature to first evaporate the solvent, and then perform the main drying at a high temperature, as this will result in a uniform film. The pre-drying temperature is preferably 80 to 110°C, more preferably 85 to 105°C, and even more preferably 90 to 100°C. If the pre-drying temperature is below 80°C, the coating layer may not dry completely. If the pre-drying temperature is above 110°C, drying may proceed before the coating layer has a chance to spread evenly, potentially resulting in a poor appearance.

[0057] On the other hand, the drying temperature is preferably 110 to 200°C, more preferably 120 to 190°C, and even more preferably 130 to 180°C. If the drying temperature is below 110°C, the formation of the coating layer will not proceed, reducing cohesiveness and adhesion, which may negatively affect the barrier properties. If the temperature exceeds 200°C, the film may be subjected to too much heat, making it brittle or causing large wrinkles due to thermal shrinkage.

[0058] The preferred drying time for pre-drying is 3.0 to 10.0 seconds, more preferably 3.5 to 9.5 seconds, and even more preferably 4.0 to 9.0 seconds. Similarly, the preferred drying time for the main drying is 3.0 to 10.0 seconds, more preferably 3.5 to 9.5 seconds, and even more preferably 4.0 to 9.0 seconds. However, it is important to note that the drying conditions may vary depending on the type of heat transfer medium and the intake and exhaust conditions of the drying oven. In addition to drying, applying an additional heat treatment for 1 to 4 days at the lowest possible temperature range, specifically 40 to 60°C, is also more effective in promoting the formation of the coating layer.

[0059] The gas barrier film may have a printed layer laminated on it. 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, defoamers, crosslinking agents, anti-blocking agents, and antioxidants.

[0060] The printing method for creating 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.

[0061] The gas barrier film may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment, etc., as long as it does not impair the objectives of the present invention, and may also be subjected to known anchor coating treatment, printing, decoration, etc.

[0062] (Sealant film) The sealant film may be a heat-sealable resin layer. Any thermoplastic copolymer that can sufficiently exhibit sealant adhesion can be used to form the sealant film, and examples include polyethylene resins such as HDPE, LDPE, and LLDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-α-olefin random copolymers, and ionomer resins.

[0063] The sealant film may be a single-layer film or a multi-layer film, and the choice should depend on the required function. For example, to provide moisture resistance, a multi-layer film with a resin such as ethylene-cyclic olefin copolymer or polymethylpentene can be used. The sealant layer may also contain various additives such as flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, and tackifiers.

[0064] The thickness of the sealant film is preferably 10 to 100 μm, and more preferably 20 to 60 μm.

[0065] Methods for forming a laminated film by bonding a gas barrier film and a sealant film include extrusion lamination and dry lamination.

[0066] (adhesive layer) For the adhesive layer used in dry lamination, general-purpose laminating adhesives can be used. For example, (solventless), aqueous, or hot-melt adhesives mainly composed of poly(ester)urethane-based, polyester-based, polyamide-based, epoxy-based, poly(meth)acrylic-based, polyethyleneimine-based, ethylene-(meth)acrylic acid-based, polyvinyl acetate-based, (modified) polyolefin-based, polybutadiene-based, wax-based, casein-based, etc. can be used. Among these, considering heat resistance and flexibility to follow the heat elongation of each substrate, urethane-based or polyester-based adhesives are preferred.

[0067] As the lamination method of the above adhesive layer, for example, it can be applied by direct gravure coating method, reverse gravure coating method, kiss coating method, die coating method, roll coating method, dip coating method, knife coating method, spray coating method, fountain coating method, or other methods. In order to exhibit sufficient adhesiveness, the coating amount after drying is preferably 1 - 8 g / m 2 More preferably 2 - 7 g / m 2 Even more preferably 3 - 6 g / m 2 is. When the coating amount is less than 1 g / m 2 , it becomes difficult to bond the entire surface, and the adhesive strength decreases. Also, when it exceeds 8 g / m<…>, it takes time for the film to completely cure, and unreacted substances tend to remain, resulting in a decrease in adhesive strength.

[0068] The oxygen permeability of the laminated film of the present invention is preferably 30 ml / m 2 ·day·MPa or less, more preferably 20 ml / m 2 ·day·MPa or less, and particularly preferably 10 ml / m 2 ·day·MPa or less. By setting the oxygen permeability to 30 ml / m 2 ·day·MPa or less, for example, when used for food packaging bags or lids of packaging containers, it is difficult for the contents to deteriorate, and the expiration date can be extended.

[0069] The tear strength of the laminated film of the present invention is preferably 200mN to 1000mN, more preferably 200mN to 900mN, and particularly preferably 200mN to 800mN. By setting the tear strength to 1000mN or less, for example, when used as a lid material for food packaging bags or packaging containers, the force required to open can be reduced, resulting in excellent ease of opening. If the tear strength is 200mN or less, there is a risk that it may be opened unexpectedly with even a small force.

[0070] The laminated film of the present invention can be suitably used for applications such as packaging bags and containers for food, beverages, and pharmaceuticals, various label materials, and laminate tubes. [Examples]

[0071] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0072] The processing and measurement methods used in each example and comparative example are as follows. Unless otherwise specified, physical property measurements were performed in a measurement room at 23°C and 65% relative humidity.

[0073] (Processing method) [Preparation of laminated films for evaluation] Apply a dry laminating adhesive (Toyo Morton Co., Ltd., TM569, CAT-10L) with a solid content of 3g / m² to each gas barrier film or biaxially oriented polyester film. 2 The film was applied in this manner, and after the solvent was evaporated in an 80°C oven, a 40μm thick unstretched polypropylene film (L4102 manufactured by Toyobo Co., Ltd.) was nipped and bonded to it on a temperature-controlled roll at 60°C, and then aged at 40°C for two days to obtain a laminated film. Apply a dry laminating adhesive (Toyo Morton Co., Ltd., TM569, CAT-10L) with a solid content of 3g / m² to each gas barrier film or biaxially oriented polyester film. 2The material was applied in this manner, and after the solvent was evaporated in an 80°C oven, a 15μm thick biaxially oriented nylon film (N1100, manufactured by Toyobo Co., Ltd.) was nipped and bonded as a bonding film on a temperature-controlled roll at 60°C. Then, a dry laminating adhesive (Toyo Morton Co., Ltd., TM569, CAT-10L) with a solid content of 3g / m² was applied to the biaxially oriented nylon film on the opposite side of the laminated surface. 2 The film was applied in this manner, and after the solvent was evaporated in an 80°C oven, a 40μm thick unstretched polypropylene film (L4102 manufactured by Toyobo Co., Ltd.) was nipped and bonded to it on a temperature-controlled roll at 60°C, and then aged at 40°C for two days to obtain a laminated film.

[0074] (Measurement method) [Film thickness] Measurements were taken using a dial gauge in accordance with JIS K7130:1999 Method A.

[0075] [Film haze] In accordance with JIS K7361-1:1997, the film was cut into 10cm squares, and haze measurements were performed using a NDH2000 haze meter manufactured by Nippon Denshoku Co., Ltd. Measurements were taken at three locations, and the average value was used as the measured haze value.

[0076] [Coefficient of friction and static friction of film] A sample film was prepared by cutting a section of the obtained film with an area of ​​400 mm in the longitudinal direction and 100 mm in the width direction. This was aged for 12 hours in an atmosphere of 23°C and 65% RH, and then divided into a test piece of 300 mm in the longitudinal direction and 100 mm in the width direction for the test table, and a test piece of 100 mm in the longitudinal direction and 100 mm in the width direction for the sliding piece. The test piece for the test table was set on the test table, and the test piece for the sliding piece was attached to the bottom surface (area of ​​39.7 mm², square) of a metal sliding piece with a load of 1.5 kg, with each side facing the other. In accordance with JIS K-7125:1999, a tensile testing machine (Tensilon RTG-1210 manufactured by A&D) was used to measure the coefficient of dynamic friction and the coefficient of static friction of the test piece at a sliding speed of 200 mm / min, under conditions of 23°C and 65% RH, and the average of three measurements was used.

[0077] [Thermal shrinkage rate of the film] The thermal shrinkage rate was measured using a dimensional change test method compliant with JIS C2318:2020, except that the test temperature was 150°C and the heating time was 15 minutes.

[0078] [Puncture strength of the film] The values ​​measured using the test method compliant with JIS-Z1707:2019 were calculated in 1 μm equivalent using the following formula. Puncture strength (N / μm) = Measured puncture strength / Film thickness

[0079] [Tear strength of laminated film] Tear strength was measured in accordance with JIS K7128-1:1998. The laminated film was evaluated. Measurements were taken in the longitudinal and width directions with N=3, and the average value was calculated.

[0080] [Oxygen permeability] The oxygen permeability of the laminated film was measured using an oxygen permeability measuring device (MOCON's "OX-TRAN(registered trademark) 1 / 50") in accordance with JIS-K7126 Method B. The oxygen permeability was measured in the direction in which oxygen permeates from the gas barrier film side.

[0081] [Water vapor transmission rate] The water vapor transmission rate of the laminated film was measured using a water vapor transmission rate measuring device (MOCON "PERMATRAN-W 3 / 33MG") in accordance with JIS-K7129 Method B, under conditions of 40°C and 90% RH. The water vapor transmission rate was measured in the direction in which water vapor permeated from the gas barrier film side.

[0082] The biaxially oriented polyester films and coating layers used in this example and comparative example are described below. These were used in Examples 1-6 and Comparative Examples 1-7, and are shown in Table 2.

[0083] [Preparation of coating liquid for the protective layer] (Coating liquid 1) To a solution prepared by mixing 80 parts by mass of purified water with 10 parts by mass of isopropanol, 10 parts by mass of commercially available polyvinyl alcohol (Kuraray Co., Ltd., "Poval 5-98" (saponification degree 98.0%, average degree of polymerization 500)) was added as a water-soluble polymer compound. The mixture was heated to 80°C while stirring, and then stirred for approximately 1 hour. After that, it was cooled to room temperature to obtain coating solution 1 with a solid content of 10%.

[0084] (Coating liquid 2) 90 parts by mass of purified water were mixed with 10 parts by mass of fully saponified polyvinyl alcohol resin (G Polymer OKS8049Q, manufactured by Nippon Synthetic Chemical Co., Ltd., with a saponification degree of 99.0% or higher and an average degree of polymerization of 450). The mixture was heated to 80°C while stirring, and then stirred for approximately 1 hour. After that, it was cooled to room temperature, yielding a nearly transparent polyvinyl alcohol solution with a solid content of 10%.

[0085] Five parts by mass of montmorillonite (manufactured by Kunimine Industries, "Kunipia F"), an inorganic layered compound, were added to 95 parts by mass of purified water while stirring, and thoroughly dispersed in a homogenizer at a setting of 1500 rpm. The mixture was then incubated at 23°C for one day to obtain a dispersion of the inorganic layered compound with a solid content of 5%.

[0086] Coating solution 2 was prepared by mixing each material in the following proportions. Ion-exchanged water 20.00% by mass Isopropyl alcohol 15.00% by mass Polyvinyl alcohol solution 35.00% by mass Inorganic layered compound separation liquid 30.00% by mass

[0087] (Coating liquid 3) To 87.2 parts by mass of purified water, 10.4 parts by mass of tetraethoxysilane (Shin-Etsu Chemical Co., Ltd., "KBE-04") and 2.4 parts by mass of hydrochloric acid (0.1N) were added, and the mixture was stirred for 3 hours to obtain a hydrolysis solution of tetraethoxysilane with a solid content of 3% (calculated by weight as SiO2).

[0088] To a solution prepared by mixing 90 parts by mass of purified water with 7 parts by mass of isopropanol, 3 parts by mass of commercially available polyvinyl alcohol (Kuraray Co., Ltd., "Poval 5-98" (saponification degree 98.0%, average degree of polymerization 500)) was added as a water-soluble polymer compound. The mixture was heated to 80°C while stirring, and then stirred for approximately 1 hour. After that, it was cooled to room temperature to obtain a polyvinyl alcohol solution with a solid content of 3%.

[0089] Coating solution 3 was prepared by mixing each material in the following proportions. Hydrolyzed solution of tetraethoxysilane, 60.00% by mass Polyvinyl alcohol solution 40.00% by mass

[0090] (Coating liquid 4) A silane coupling agent (Shin-Etsu Chemical Co., Ltd., "KBM-603") was dissolved in acetone (15% by mass), and a polyisocyanate resin (Mitsui Chemicals, "Takenate D-110N": 75% solids) was mixed in the following ratio and stirred for 10 minutes using a magnetic stirrer. The resulting mixture was diluted with methyl ethyl ketone and 1-methoxy-2-propanol (hereinafter PGM), and then polyester resin (DIC Corporation, "DF-COAT GEC-004C": 30% solids) was added in the following ratio to prepare coating solution 4. Polyester resin 10.62% by mass Polyisocyanate resin 4.07% by mass Silane coupling agent diluted with acetone 1.73% by mass Methyl ethyl ketone 69.55% by mass PGM 14.03% by mass

[0091] [Creation of biaxially oriented polyester film] (Base material 1) Using a single-screw extruder, a resin composition containing 40 parts by mass of PBT resin (intrinsic viscosity 1.28 dl / g), 60 parts by mass of PET resin (intrinsic viscosity 0.62 dl / g), and 900 ppm of porous silica particles (average particle size 2.4 μm) was melted. The mixture was then cast from a T-die at 280°C and adhered to a cooling roll at 20°C by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was roll-stretched 3.8 times in the MD direction at a temperature of 80°C, then passed through a tenter and stretched 4.5 times in the TD direction at 110°C, followed by a tension heat treatment at 200°C for 3 seconds and a relaxation treatment of 9% for 1 second to obtain a biaxially oriented film with a thickness of 15 μm.

[0092] (Base material 2) A biaxially oriented film with a thickness of 20 μm was obtained by forming a film using the same method as for substrate 1.

[0093] (Base material 3) A biaxially oriented film with a thickness of 15 μm was obtained by forming a film in the same manner as with substrate 1, except that the raw material composition and stretching conditions were changed to those described in Table 1.

[0094] (Base material 4) A biaxially oriented film with a thickness of 12 μm was obtained by forming a film in the same manner as with substrate 1, except that the raw material composition and stretching conditions were changed to those described in Table 1.

[0095] [Table 1]

[0096] The methods for preparing the inorganic thin film layers used in each example and comparative example are described below. The methods used in Comparative Examples 2, 3, and 6 are shown in Table 2.

[0097] [Creation of an inorganic thin film layer] (M-1) A composite oxide layer of silicon dioxide and aluminum oxide was formed on a biaxially oriented polyester film by electron beam deposition. Particulate SiO2 (99.9% purity) and A12O3 (99.9% purity) with a particle size of approximately 3mm to 5mm were used as the deposition source. The film obtained in this manner (film containing an inorganic thin film layer / coating layer) had a thickness of 13nm of the inorganic thin film layer (SiO2 / A12O3 composite oxide layer). The composition of this composite oxide layer was SiO2 / A12O3 (mass ratio) = 60 / 40.

[0098] The following describes the method for preparing the coating layer used in each example and comparative example. The methods used in Examples 1-6 and Comparative Examples 3, 4, 5, and 7 are shown in Table 2.

[0099] [Creating a coating layer] (OC1~4) Coating solutions 1-4 were applied to the corona-treated surface or inorganic thin film layer of a biaxially oriented polyester film by gravure roll coating. Pre-drying was performed at 100°C for 4 seconds, followed by full drying at 180°C for 10 seconds. Subsequently, a post-heat treatment at 40°C for 4 days (96 hours) was performed to obtain the coating layer. The adhesion amount of the coating layer at this time was 0.20 g / m². 2 That was the case.

[0100] [Table 2A]

[0101] [Table 2B]

[0102] As described above, a laminated film comprising each biaxially oriented polyester film, an inorganic thin film layer, and a coating layer was fabricated.

[0103] As shown in Examples 1 to 6 in Table 2, the laminated films obtained by the present invention exhibit excellent barrier properties and tear resistance. These can be suitably used as food packaging materials.

Claims

1. A laminated film comprising a gas barrier film and a sealant film, wherein the gas barrier film is composed of at least a base layer / coating layer, the base layer is a biaxially oriented polyester film containing 30 to 55% by mass of polybutylene terephthalate resin and 45 to 70% by mass of polyethylene terephthalate resin, and has a puncture strength of 0.60 to 1.00 N / μm per unit thickness, and the laminated film is characterized in that it satisfies the following conditions (a) to (b). (a) Oxygen permeability of 30 ml / m³ ２ It is below day·MPa. (b) The tear strength in both the MD direction and the TD direction is 200 to 1000 mN.

2. The laminated film according to claim 1, characterized in that the coating layer contains a water-soluble polymer having a plurality of hydroxyl groups in its molecule.

3. A packaging body comprising the laminated film according to claim 1 or 2.

4. A packaging container comprising the laminated film according to claim 1 or 2.

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