Laminated film

Abstract

The objective is to provide a laminated film that exhibits excellent puncture resistance even without a coating layer, and also maintains excellent barrier properties after retort processing. [Solution] A laminated film comprising a gas barrier film and a sealant film, wherein the gas barrier film is composed only of a base layer and an inorganic thin film layer, the base layer contains 30-55% by mass of polybutylene terephthalate resin and 45-70% by mass of polyethylene terephthalate resin, the puncture strength per unit film thickness is 0.60-1.00 N / μm, and the oxygen permeability after retort treatment at 130°C for 30 minutes is 100 ml / m². 2 A laminated film characterized by having a pressure of less than or equal to / day / MPa.

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 and a laminated film using the same, which have excellent barrier properties, dimensional stability, processability, and pinhole resistance, and also possess excellent gas barrier properties in applications subject to harsh moist heat treatment such as retort sterilization, and in applications where the contents are prone to damage from hard materials such as dry goods packaging. [Background technology]

[0002] 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.

[0003] 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 other materials, 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. (See, for example, Patent Document 1)

[0004] However, the above-mentioned gas barrier films have a problem in that, during moist heat sterilization processes in food manufacturing, such as boiling and retorting, the inorganic thin film layer suffers physical damage due to bending loads, which deteriorates its adhesion to the substrate layer and thus its gas barrier properties.

[0005] To address the above problem, attempts have been made to provide a coating layer between the substrate layer and the inorganic thin film layer. For example, a method has been proposed in which a polyester resin aqueous dispersion and methylated melamine are coated onto a polyester substrate to provide an adhesive modification layer, and an inorganic thin film layer is formed on the adhesive modification layer (see, for example, Patent Document 2). According to this technique, good gas barrier properties can be maintained even when subjected to the moist heat sterilization treatment described above. However, biaxially oriented polyethylene terephthalate film, which is the most commonly used substrate for gas barrier films, is brittle, and problems remain such as leakage of contents due to physical damage such as punctures by the contents.

[0006] On the other hand, a technique was known in which a film with good pinhole resistance and no leakage of contents when the bag is dropped can be obtained by laminating a vapor-deposited layer onto a biaxially oriented nylon film (for example, Patent Document 3). However, this conventional technique had the problem of large dimensional changes when moisture is absorbed and curling during processing.

[0007] Furthermore, a technology has been proposed for a retort pouch characterized by sequentially laminating a base film made of a biaxially oriented polyester resin film, a gas barrier substrate having an inorganic thin film layer on one side of a resin film made of a biaxially oriented polyamide resin film, and a heat-sealable resin layer, via a laminating adhesive layer, resulting in good dimensional stability and tear resistance (for example, Patent Document 4). However, in such a configuration, the process is complicated because it includes a lamination step between the polyamide film and the polyester film, and there are limitations in terms of reducing film weight and waste.

[0008] As a way to solve these problems, a technique was known in which a laminated film can be obtained that has gas barrier properties usable even under harsh retort conditions of 130°C or higher, while also having excellent pinhole resistance, by sequentially forming a coating layer, an inorganic thin film layer, and a protective layer on a polyester film substrate obtained by biaxially stretching a resin composition containing at least 60% by mass of polybutylene terephthalate (for example, Patent Document 5). However, the laminated films disclosed in such conventional technologies employ coating and protective layers, and because the processing steps are numerous, they suffer from problems such as variations in properties due to process variations, such as slight temperature differences in drying and heat treatment in the film width direction during coating, and are at a significant disadvantage in terms of cost. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 6-278240 [Patent Document 2] Japanese Patent Publication No. 2005-097560 [Patent Document 3] Japanese Patent Application Publication No. 6-278240 [Patent Document 4] Japanese Patent Publication No. 2013-154605 [Patent Document 5] WO2017-126563 publication [Overview of the project] [Problems that the invention aims to solve]

[0010] This invention was made against the backdrop of the problems of the prior art. Specifically, the objective of this invention is to provide a laminated film that has excellent pinhole resistance while maintaining excellent gas barrier properties even after moist heat sterilization treatment, without having a resin layer that is applied by a coating process such as a coating layer or protective layer.

[0011] In order to achieve the above objective, the present invention was developed through diligent research. By optimizing the blending ratio of polybutylene terephthalate resin and polyethylene terephthalate resin in the film and the stretching conditions during film formation, it was possible to improve the orientation of the film in the longitudinal and width directions and obtain a biaxially oriented polyester film with a specific range of puncture strength. Furthermore, by applying an inorganic thin film layer to the above biaxially oriented polyester film as a base layer, a gas barrier film with excellent gas barrier properties was obtained. Moreover, it was found that a laminated film obtained by laminating the above gas barrier film and a sealant film exhibits excellent adhesion and gas barrier properties even after moist heat sterilization treatment, leading to the completion of the present invention as exemplified below.

[0012] The present invention has the following configuration. 1. A laminated film comprising a gas barrier film and a sealant film, wherein the gas barrier film consists only of a base layer and an inorganic thin film layer, the base layer contains 30-55% by mass of polybutylene terephthalate resin and 45-70% by mass of polyethylene terephthalate resin, the puncture strength per unit film thickness is 0.60-1.00 N / μm, and the oxygen permeability after retort treatment at 130°C for 30 minutes is 100 ml / m². 2 Laminated film characterized by having a pressure of / day / MPa or less. 2. The laminated film according to claim 1, characterized in that the inorganic thin film layer is an inorganic thin film layer selected from the group consisting of aluminum, aluminum oxide, silicon oxide, or a mixed oxide of aluminum oxide and silicon oxide. 3. The laminated film according to 1, characterized in that the lamination strength between the gas barrier film and the sealant film is 3.0 N / 15 mm or more after retort treatment at 130°C for 30 minutes. 4. A package containing the laminated film described in any of items 1 to 3 above. 5. A packaging container containing the laminated film described in any of items 1 to 3 above. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a laminated film excellent in pinhole resistance while maintaining excellent gas barrier properties even after wet heat sterilization treatment, without having a resin layer imparted by coating processing such as a coating layer or a protective layer. MODE FOR CARRYING OUT THE INVENTION

[0014] Hereinafter, the present invention will be described in detail. In the present specification, a numerical range represented by using "~" means a range including the numerical values described before and after "~" as the lower limit and the upper limit.

[0015] (Base Material Layer) The base material layer of the present invention is preferably a stretched polyester film, more preferably a biaxially stretched polyester film. Hereinafter, the base material layer will be described with a biaxially stretched polyester film as a representative example. The biaxially stretched polyester film constituting the base material layer of the present invention comprises 30 to 55 mass% of polybutylene terephthalate resin (hereinafter sometimes abbreviated as PBT resin) and 45 to 70 mass% of polyethylene terephthalate resin (hereinafter sometimes abbreviated as PET resin). The content of the PBT resin is preferably 30 to 55 mass%, more preferably 35 to 50 mass%. This provides excellent dimensional stability and processability, and can develop bag breakage resistance, chemical resistance, and pinhole resistance at low temperatures.

[0016] The intrinsic viscosity of the PBT resin used in the present invention is preferably 0.9 to 1.3 dl / g, more preferably 0.95 to 1.3 dl / g, still more preferably 1.0 to 1.3 dl / g. By setting the intrinsic viscosity of the PBT resin to 0.9 dl / g or more, it is possible to suppress a decrease in the intrinsic viscosity of the film obtained by film formation, and suppress the decrease in puncture strength, impact strength, bag breakage resistance and the like. On the other hand, by setting the intrinsic viscosity to 1.3 dl / g or less, it is possible to prevent the stress during film stretching from becoming too high, and obtain good film formability. In addition, since an increase in melt viscosity makes it necessary to set the extrusion temperature to a high temperature, it is possible to suppress the tendency for decomposition products to be easily generated during extrusion.

[0017] 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.

[0018] The biaxially oriented polyester film of the present invention may contain polyester resins other than PBT resin and PET resin. Examples of PET resin and polyester resins other than PET resin include homopolyester resins such as polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT), as well as polyester resins copolymerized with dicarboxylic acids such as terephthalic acid, 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, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, 1,4-cyclohexanedimethanol, polyethylene glycol, polytetramethylene glycol, and polycarbonatediol.

[0019] The biaxially oriented polyester film of the present invention may contain, as necessary, lubricants, stabilizers, colorants, antioxidants, antistatic agents, ultraviolet absorbers, and the like.

[0020] As 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 lubricants can be used to achieve transparency and slipperiness.

[0021] The lower limit of the lubricant content 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 content of 100 ppm by mass or more allows the film to exhibit slipperiness, while a content of 10,000 ppm by mass or less allows for good transparency of the film.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The cooling roll temperature is preferably 0 to 40°C, and more preferably 0 to 20°C or lower. Setting it above 0°C allows for sufficient suppression of crystallization when the molten polyester resin composition cools and solidifies. 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 it 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.

[0026] 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.

[0027] While both simultaneous biaxial stretching and sequential biaxial stretching are possible methods for stretching, sequential biaxial stretching is preferable because it is necessary to increase the degree of surface orientation in order to increase puncture strength, and it also offers a faster film formation speed and higher productivity.

[0028] The stretching temperature in the longitudinal direction (also called the MD direction) is preferably 70 to 130°C, and more preferably 70 to 120°C. A temperature of 70°C or higher not only makes fracture less likely, but also strengthens the longitudinal orientation due to stretching at low temperatures, 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.

[0029] 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.

[0030] The stretching temperature in the width direction (also called the TD direction) is preferably 100 to 120°C, and more preferably 105 to 115°C. A temperature of 100°C or higher makes fracture less likely. A temperature of 120°C or lower increases the degree of surface orientation, thereby increasing puncture strength. Furthermore, it suppresses the decrease in mechanical properties due to a lack of orientation.

[0031] 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.

[0032] The thermal setting temperature in the TD direction is preferably 180 to 240°C, more preferably 190 to 225°C, and particularly preferably 200 to 210°C. Setting it above 180°C can reduce the thermal shrinkage rate and suppress misalignment and shrinkage during processing. Setting it 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.

[0033] The relaxation rate in the TD direction 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 thickness unevenness due to sagging, improving flatness.

[0034] 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.

[0035] 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.

[0036] The puncture strength per unit thickness of the biaxially oriented polyester film of the present invention is 0.60 to 1.00 N / μm, preferably 0.60 to 0.90 N / μm, more preferably 0.60 to 0.85 N / μm, and particularly preferably 0.60 to 0.80 N / μm. By setting the puncture strength to 0.60 N / μm or higher, insufficient strength when used as a packaging material can be suppressed, and it can be suitably used, for example, for packaging relatively heavy food products or packaging for sharp contents. By setting the puncture strength to 1.00 N / μm or lower, thermal shrinkage can be suppressed as described later, and processing problems due to film shrinkage in processes such as vapor deposition and printing can be reduced.

[0037] 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.

[0038] 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.

[0039] (Inorganic thin film layer) The laminated film of the present invention has an inorganic thin film layer on at least one surface of the base layer (base film). The two layers have good adhesion even without a coating layer formed by a coating process between the base layer and the inorganic thin film layer, and excellent gas barrier properties can be maintained even after moist heat sterilization treatment.

[0040] An inorganic thin film layer is a thin film made of a metal or an inorganic oxide. While there are no particular restrictions on the material used to form the inorganic thin film layer, 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 because it allows for both flexibility and density in the thin film layer. In this composite oxide, the mixing ratio of silicon dioxide and aluminum oxide is preferably in the range of 20-70% Al by mass ratio of the metal content. If the Al concentration is less than 20%, the water vapor barrier properties may be low. On the other hand, if it exceeds 70%, the inorganic thin film layer tends to harden, and there is a risk that the film will be damaged during secondary processing such as printing or lamination, reducing its 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.

[0041] The thickness of the inorganic thin film layer is typically 1 to 100 nm, preferably 5 to 50 nm. If the thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties. On the other hand, if the thickness is excessively increased 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.

[0042] There are no particular restrictions on the method for forming an inorganic thin film layer; for example, any known deposition method such as vacuum deposition, sputtering, ion plating (physical vapor deposition methods (PVD)), or chemical vapor deposition (CVD) can be used as appropriate. Below, a typical method for forming an inorganic thin film layer will be described using a silicon oxide / aluminum oxide thin film as an example. For example, when 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 formation conditions can be arbitrarily changed, such as by applying a bias to the substrate (laminated film to be deposited) or by heating or cooling the substrate. These deposition materials, reaction gases, bias of the material to be deposited, heating / cooling, etc., can be similarly modified when using sputtering or CVD methods.

[0043] The gas barrier film of the present invention 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, defoaming agents, crosslinking agents, anti-blocking agents, and antioxidants.

[0044] 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.

[0045] The gas barrier film of the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment, etc., as long as it does not impair the purpose of the present invention, and may also be subjected to known anchor coating treatment, printing, decoration, etc.

[0046] (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.

[0047] 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.

[0048] The thickness of the sealant film is preferably 10 to 100 μm, and more preferably 20 to 60 μm.

[0049] Methods for forming a laminated film by bonding a gas barrier film and a sealant film include extrusion lamination and dry lamination.

[0050] (adhesive layer) For the adhesive layer used in dry lamination, general-purpose laminating adhesives can be used. For example, solvent-free, water-based, and 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, and casein can be used. Among these, urethane or polyester adhesives are preferred considering heat resistance and flexibility to follow the thermal expansion of each substrate.

[0051] The above adhesive layer can be applied using methods such as direct gravure coating, reverse gravure coating, kiss coating, die coating, roll coating, dip coating, knife coating, spray coating, fontein coating, and others, and will exhibit sufficient adhesion. The coating amount after drying is 1 to 8 g / m². 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.

[0052] In the laminated film of the present invention, the lamination strength between the gas barrier film and the sealant film is preferably 1.5 N / 15 mm or more, more preferably 2.0 N / 15 mm or more, and particularly preferably 3.0 N / 15 mm or more. By setting it to 1.5 N / 15 mm or more, the adhesion between the substrate layer and the inorganic thin film layer becomes strong, and the deterioration of the gas barrier properties can be minimized.

[0053] The lamination strength between the gas barrier film and the sealant film in the laminated film of the present invention is preferably 1.5 N / 15 mm or more, more preferably 2.0 N / 15 mm or more, and particularly preferably 3.0 N / 15 mm or more after retort treatment at 130°C for 30 minutes. By setting the strength to 3.0 N / 15 mm or more, the adhesion between the base material layer and the inorganic thin film layer becomes strong, and the deterioration of gas barrier properties can be reduced.

[0054] The oxygen permeability of the laminated film of the present invention after retort treatment at 130°C for 30 minutes is 100 ml / m 2 ·day·MPa or less, more preferably 90 ml / m 2 ·day·MPa, and particularly preferably 80 ml / m 2 ·day·MPa. By setting the oxygen permeability to 100 ml / m 2 ·day·MPa or less, for example, when the laminated film is used as a food packaging bag or a lid material for a packaging container, deterioration of the contents is less likely to occur, and the expiration date can be extended.

[0055] The water vapor permeability of the laminated film of the present invention after retort treatment at 130°C for 30 minutes is 10.0 g / m 2 ·day or less, more preferably 8.0 g / m 2 ·day, and particularly preferably 5.0 g / m 2 ·day. By setting the water vapor permeability to 5.0 g / m 2 ·day or less, for example, when the laminated film is used as a food packaging bag or a lid material for a packaging container, deterioration of the contents is less likely to occur, and the expiration date can be extended.

[0056] The laminated film of the present invention can be suitably used for applications such as food and beverage packaging bags and packaging containers, various label materials, and laminated tubes. [Examples]

[0057] Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples by any means.

[0058] 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.

[0059] (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.

[0060] [Retort processing method] The laminated film obtained as described above was subjected to retort treatment at 130°C for 30 minutes using a hot water spray type retort sterilization device (RCS-60SPXTG, manufactured by Hisaka Works Co., Ltd.). After that, it was dried in a 40°C room for one day.

[0061] (Measurement method) [Film thickness] Measurements were taken using a dial gauge in accordance with JIS K7130:1999 Method A.

[0062] [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.

[0063] [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.

[0064] [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.

[0065] [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

[0066] [Lamination strength] Laminated films were cut into 15 mm wide and 200 mm long specimens to form test pieces, and the laminate strength was measured using a Tensilon universal material testing machine (Tensilon UMT-II-500 model, manufactured by Toyo Baldwin Co., Ltd.). The laminate strength was measured at a tensile speed of 200 mm / min, and the gas barrier film and sealant film of each laminated film obtained in the examples and comparative examples were peeled at a peel angle of 90 degrees.

[0067] [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.

[0068] [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.

[0069] The biaxially oriented polyester films and coating layers used in this example and comparative example are described below. These were used in Examples 1-4 and Comparative Examples 1-4, and are shown in Table 2.

[0070] [Preparation of coating liquid for the protective layer] (Coating liquid 1) As the oxazoline group-containing resin, a commercially available water-soluble oxazoline group-containing acrylate (Nippon Shokubai Co., Ltd. "Epocross® WS-300"; solid content 10%) was used. The oxazoline group content of this resin was 7.7 mmol / g. As the acrylic resin, a commercially available 25% by mass emulsion of acrylic acid ester copolymer (Nichigo Movinyl Co., Ltd. "Movinyl® 7980") was used. The acid value (theoretical value) of this acrylic resin (B) was 4 mg KOH / g. As the urethane resin, a commercially available polyester urethane resin dispersion (Mitsui Chemicals, Inc. "Takelac® W605"; solid content 30%) was used. The acid value of this urethane resin was 25 mg KOH / g, and the glass transition temperature (Tg) measured by DSC was 100°C. 1 The proportion of aromatic or aromatic aliphatic diisocyanates to the total polyisocyanate component, as measured by 1H-NMR, was 55 mol%.

[0071] Coating solution 1 was prepared by mixing each material in the following proportions into a solution of water and isopropanol. Water 54.40% by mass Isopropanol 25.00% by mass Oxazoline group-containing resin 15.00% by mass Acrylic resin 3.60% by mass Urethane resin 2.00% by mass

[0072] [Preparation of biaxially oriented polyester film and coating layer] (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.

[0073] (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.

[0074] (Base material 3) Except for changing the raw material composition of substrate 1 to the conditions listed in Table 1, the film was prepared in the same manner as for substrate 1 to obtain a biaxially oriented film with a thickness of 15 μm.

[0075] (Base material 4) Except for changing the raw material composition of substrate 1 to the conditions listed in Table 1, the film was prepared in the same manner as for substrate 1 to obtain a biaxially oriented film with a thickness of 15 μm.

[0076] (Base material 5) 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.

[0077] (Base material 6) 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.

[0078] (Base material 5) In the film-forming process of the substrate 5, coating solution 1 was applied by fountain coat method after MD stretching. Then, it was guided to a tenter while drying, and the solvent was evaporated and dried at a preheating temperature of 70°C. Next, it was stretched transversely, heat-treated, and relaxed to obtain a 15 μm thick biaxially oriented polyester film with a coating of 0.030 g / m² on one side. 2 A material with a coated layer was obtained.

[0079] (Base material 6) In the film-forming process of the substrate 6, coating solution 1 was applied by fountain coat method after MD stretching. Then, it was guided to a tenter while drying, and the solvent was evaporated and dried at a preheating temperature of 70°C. Next, it was stretched transversely, heat-treated, and relaxed to obtain a 15 μm thick biaxially oriented polyester film with a coating of 0.030 g / m² on one side. 2 A material with a coated layer was obtained.

[0080] [Table 1]

[0081] The methods for preparing the inorganic thin film layers used in each example and comparative example are described below. The methods used in Examples 1-4 and Comparative Examples 1-4 are shown in Table 2.

[0082] [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 using electron beam deposition. The deposition source was particulate matter of approximately 3mm to 5mm in size.i O2 (99.9% purity) and A12O3 (99.9% purity) were used. In the film obtained in this manner (film containing inorganic thin film layer / coating layer), the inorganic thin film layer (S i The thickness of the O2 / A12O3 composite oxide layer was 13 nm. The composition of this composite oxide layer was S i The O2 / A12O3 (mass ratio) was 60 / 40.

[0083] [Table 2]

[0084] As described above, a laminated film comprising each biaxially oriented polyester film, a coating layer, and an inorganic thin film layer was fabricated.

[0085] As shown in Examples 1-4 in Table 2, the laminated film obtained by the present invention exhibits excellent barrier properties even after retort processing, despite the absence of a coating layer. These can be suitably used as packaging materials for foods requiring heat sterilization. [Industrial applicability]

[0086] The present invention provides a laminated film that maintains excellent gas barrier properties even after moist heat sterilization treatment, while also exhibiting excellent pinhole resistance, without having a resin layer that is applied by a coating process such as a coating layer or protective layer.

Claims

1. The laminated film includes a gas barrier film and a sealant film. The gas barrier film consists only of a base layer and an inorganic thin film layer. The base layer contains 30-55% by mass of polybutylene terephthalate resin and 45-70% by mass of polyethylene terephthalate resin. The puncture strength per unit film thickness is 0.60-1.00 N / μm, and the oxygen permeability after retort treatment at 130°C for 30 minutes is 100 ml / m². ２ A laminated film characterized by having a pressure of / day / MPa or less.

2. The laminated film according to claim 1, characterized in that the inorganic thin film layer is an inorganic thin film layer selected from the group consisting of aluminum, aluminum oxide, silicon oxide, or a mixed oxide of aluminum oxide and silicon oxide.

3. The laminated film according to claim 1, characterized in that the lamination strength between the gas barrier film and the sealant film is 3.0 N / 15 mm or more after retort treatment at 130°C for 30 minutes.

4. A packaging body comprising the laminated film according to any one of claims 1 to 3.

5. A packaging container comprising a laminated film according to any one of claims 1 to 3.

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