JP2024051846A - Packaging laminate and packaging bag - Google Patents

Abstract

[Problem] To provide a packaging laminate that has high puncture resistance even for packaging bags in which the paper ratio is increased to reduce the environmental impact. [Solution] A laminate including a biaxially oriented polyamide film, a paper base layer and/or a nonwoven fabric base layer, and a sealant film, in which the weight ratio of the paper base layer and/or the nonwoven fabric base layer is 50% or more relative to the laminate, and the puncture strength of the laminate is 8.0 N or more. [Selected Figure] None

Description

The present invention relates to a packaging laminate, which is mainly composed of paper or nonwoven fabric and is laminated with a biaxially oriented polyamide film, and a packaging bag.

In recent years, from the viewpoint of suppressing environmental loads such as global warming due to _CO2 emissions and marine pollution by microplastics, paper-based packaging bags, including food packaging films, have been attracting attention by changing the material from resin to paper. Patent Document 1 discloses a packaging bag having a paper layer containing a paper component and a resin layer containing a thermoplastic resin provided on at least one side of the paper layer, in which the ratio of the paper component in the packaging bag is 50% or more. This technology is a sheet packaging body that contains sheets such as paper towels and tissue paper, but when the contents are liquid or hard contents such as frozen foods, there is a need for the bag not to break when dropped and not to be punctured by the hard contents, i.e., puncture resistance, so there is room for improvement.

JP 2022-107363 A

The object of the present invention is to provide a packaging laminate that has high puncture resistance, even in packaging bags that have a high paper ratio to reduce environmental impact.

The present invention comprises the following configurations.
[1] A laminate comprising a biaxially oriented polyamide film, a paper base layer and/or a nonwoven fabric base layer, and a sealant film, wherein the weight ratio of the paper base layer and/or the nonwoven fabric base layer to the laminate is 50% or more, and the puncture strength of the laminate is 8.0 N or more.
[2] The laminate according to [1], wherein the biaxially oriented polyamide film has a thickness of 8 to 15 μm.
[3] The laminate according to [1] or [2], wherein the biaxially stretched polyamide film includes a core layer and a skin layer, the core layer includes 80% by mass or more of a polyamide 6 resin and 1 to 20% by mass of an aliphatic polyester copolymer or an aromatic-aliphatic polyester copolymer, and the skin layer includes 70% by mass or more of a polyamide 6 resin.
[4] The laminate according to any one of [1] to [3], wherein the aliphatic polyester resin or aromatic aliphatic polyester resin is at least one polyester resin selected from the group consisting of polybutylene succinate, polybutylene succinate adipate, and polybutylene adipate terephthalate.
[5] The laminate according to any one of [1] to [5], which has a barrier layer between the biaxially oriented polyamide film layer and the paper substrate layer and/or the nonwoven fabric substrate layer.
[6] The laminate according to [5], wherein the barrier layer is an inorganic thin film layer.
[7] The laminate according to [6], wherein the inorganic vapor deposition layer is a layer made of aluminum oxide or a composite oxide of silicon oxide and aluminum oxide.
[8] The laminate according to [5], wherein the barrier layer is a thin metal layer.
[9] A packaging bag using the laminate according to any one of [1] to [8].

The laminate of the present invention uses a thin biaxially oriented polyamide film with excellent puncture resistance and a paper or nonwoven fabric substrate, making it possible to obtain a packaging bag with excellent puncture resistance even when the packaging bag has a high paper or nonwoven fabric ratio.

The present invention is a laminate including at least a biaxially oriented polyamide film, a paper substrate layer and/or a nonwoven fabric substrate layer, and a sealant film. The biaxially oriented polyamide film, the paper substrate layer and/or the nonwoven fabric substrate layer, and the sealant film are preferably arranged in this order.

In the configuration of the laminate of the present invention, it is preferable that the weight ratio of the paper base layer and/or the nonwoven fabric base layer is 50% or more relative to the laminate. When the weight ratio of the paper base layer relative to the laminate exceeds 50%, a paper mark can be used as an identification mark for the material.

As the paper base material is the basic material that constitutes the paper container, it is possible to use one that has shapeability, flex resistance, rigidity, stiffness, strength, etc., and for example, various paper base materials such as highly sizable bleached or unbleached paper base materials, or pure white roll paper, kraft paper, paperboard, processed paper, etc. In the present invention, the above-mentioned paper base material can be one with a basis weight of about 30 to 600 g/ ^m2 , preferably one with a basis weight of about 40 to 450 g/ ^m2 .

For example, polyester, polypropylene, rayon, nylon, biodegradable fibers, pulp, cotton, etc. may be used as the nonwoven fabric substrate, with polypropylene being preferred. As the nonwoven fabric, either short fiber nonwoven fabric or long fiber nonwoven fabric may be used.

The paper substrate and the nonwoven fabric substrate may be used alone or in combination. From the viewpoint of reducing the use of petroleum-derived plastics, it is preferable to use a paper substrate for the laminate.

The puncture strength of the laminate of the present invention is preferably 8.0 N or more. More preferably, it is 8.5 N or more, and even more preferably, it is 9.0 N or more. By making the puncture strength 8.0 N or more, even when filled with solid contents, it is possible to prevent the contents from piercing the packaging bag and creating a hole therein, or to prevent the packaging bag from being pierced by external factors during transportation.

The thickness of the biaxially oriented polyamide film used in the present invention is preferably 8 μm or more and 15 μm or less. More preferably, it is in the range of 8 μm or more and 12 μm or less. One of the features of the present invention is that the thickness of the biaxially oriented polyamide film is reduced, while increasing the weight ratio of the paper substrate layer and/or the nonwoven fabric substrate layer, and yet maintaining the necessary puncture resistance.

The biaxially stretched polyamide film used in the present invention preferably has a heat shrinkage rate at 160°C for 10 minutes in the range of 0.6 to 3.0% in both the machine direction (hereinafter abbreviated as MD direction) and the width direction (hereinafter abbreviated as TD direction), more preferably 0.6 to 2.5%. If the heat shrinkage rate exceeds 3.0%, curling or shrinkage may occur when heat is applied in the next process, such as lamination or printing. Furthermore, the lamination strength with the sealant film may be weakened. Although it is possible to reduce the heat shrinkage rate to less than 0.6%, the film may become mechanically fragile. Furthermore, productivity may be reduced.

The haze value of the biaxially oriented polyamide film used in the present invention is preferably 7.0% or less. More preferably, it is 6.5% or less, and even more preferably, it is 6.0% or less. A haze value of 7.0% or less provides good transparency and gloss, and when used for packaging bags, it allows for beautiful printing and increases the product value.

The static friction coefficient of the biaxially oriented polyamide film used in the present invention is preferably 0.70 or less. More preferably, it is 0.65 or less, and even more preferably, it is 0.60 or less. By having a static friction coefficient of 0.70 or less, the laminated film has good slip properties, prevents wrinkles during processing into packaging bags, and provides good processing characteristics.

One of the preferred embodiments of the biaxially stretched polyamide film used in the present invention is a biaxially stretched polyamide film including a core layer and a skin layer. More preferably, the biaxially stretched polyamide film is configured in the order of skin layer, core layer, and skin layer. Representative examples of the core layer and skin layer are described below.

The core layer is preferably formed from a resin composition containing 80% by mass or more of polyamide 6 resin. The core layer may further contain 1 to 20% by mass of an aliphatic polyester resin or an aromatic aliphatic polyester resin. By containing 1% by mass or more of an aliphatic polyester resin or an aromatic aliphatic polyester resin, it is possible to obtain an improved effect in bending pinhole resistance. If the content exceeds 20% by mass, not only will the film become too soft, reducing the puncture strength and impact strength, but the film will also become more stretchable, making it more likely that pitch deviations will occur during processing such as printing.

The aliphatic polyester resin or aromatic aliphatic polyester resin contained in the core layer preferably has a glass transition temperature (Tg) of -30°C or less. By using a polyester copolymer with a glass transition temperature of -30°C or less, excellent pinhole resistance can be achieved even in a freezing environment. Among these, preferred aliphatic polyester resins are polybutylene succinate and polybutylene succinate adipate, and preferred aromatic aliphatic polyester resins are polybutylene adipate terephthalate, which is preferred due to its flexible properties.

The core layer may contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, anti-fogging agents, UV absorbers, dyes, pigments, etc., as needed.

The skin layer is preferably formed from a resin composition containing 70% by mass or more of polyamide 6 resin. By containing 70% by mass or more of polyamide 6 resin, a biaxially stretched polyamide film having excellent mechanical strength such as impact strength and gas barrier properties such as oxygen can be obtained. As the polyamide 6 resin, the same polyamide 6 resin as that used in the core layer can be used.

When the skin layer is used on the outside of a packaging bag, it needs to be resistant to abrasion and pinholes, so it is undesirable to include soft resins such as polyamide elastomers or polyolefin elastomers or substances that generate a large amount of voids.

The skin layer can contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, anti-fogging agents, UV absorbers, dyes, pigments, etc., depending on the function to be imparted to the surface of the skin layer.

To improve the slipperiness of the film, it is preferable to incorporate fine particles or an organic lubricant into the skin layer as a lubricant. By improving the slipperiness, the film becomes easier to handle and the risk of the packaging bag breaking due to friction is reduced.

The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, and zeolite, and polymeric organic fine particles such as acrylic and polystyrene fine particles. From the standpoint of transparency and slipperiness, it is preferable to use silica fine particles.

The preferred average particle size of the fine particles is 0.5 to 5.0 μm, and more preferably 1.0 to 3.0 μm. If the average particle size is less than 0.5 μm, a large amount is required to obtain good slip properties. On the other hand, if it exceeds 5.0 μm, the surface roughness of the film tends to become too large, resulting in a poor appearance.

As the silica fine particles used in the biaxially oriented polyamide film used as the base layer of the packaging laminate of the present invention, it is preferable to use two or more types of silica particles with different silica pore volumes, generally expressed as oil absorption (mL/100 g).

In general, by using silica particles with a large pore volume, the increase in haze due to voids can be reduced by crushing the aggregated silica due to the stress during film stretching. However, when the thickness of the biaxially stretched polyamide film after stretching is less than 12 μm, the film's stiffness decreases, so with only the silica particles with a large pore volume as described above, it is necessary to add a large amount of silica particles to obtain sufficient slipperiness, which results in an increase in the haze of the film and a deterioration in its appearance. On the other hand, only the use of silica particles that are not easily crushed by the stress during film stretching, i.e., silica particles with a small pore volume, can efficiently impart slipperiness because they are more likely to form surface protrusions, but conversely, the haze of the film can increase due to voids that occur at the interface between the silica and polyamide resin due to the stress during stretching, which may worsen the appearance. Therefore, as a means of solving the above problems, it is preferable to use two or more types of silica particles with different pore volumes in combination.

The oil absorption range (mL/100g) of silica particles with a large pore volume (silica particles A) is preferably 250 to 400 mL/100g, more preferably 270 to 380 mL/g, and most preferably 280 to 370 mL/g. The oil absorption range of silica particles with a small pore volume (silica particles B) is preferably 90 to 240 mL/100g, more preferably 100 to 230 mL/g, and most preferably 100 to 220 mL/100g.

The organic lubricant that can be contained in the skin layer can be fatty acid amide and/or fatty acid bisamide. Examples of fatty acid amide and/or fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, and ethylene bisoleic acid amide. The content of the organic lubricant is preferably 0.01 to 0.40% by mass, and more preferably 0.05 to 0.30% by mass, based on 100% by mass of the resin composition that constitutes the skin layer.

In order to improve the slipperiness of the film, polyamide resins other than polyamide 6, such as polyamide MXD6 resin, polyamide 11, polyamide 12 resin, polyamide 66 resin, polyamide 6-12 copolymer resin, and polyamide 6-66 copolymer resin, can be added to the skin layer. Polyamide MXD6 resin is particularly preferred, and it is preferable to add 1 to 10% by mass. By including 1% by mass or more, it is possible to obtain a slipperiness improving effect. If it is more than 10% by mass, the effect of improving the slipperiness of the film may become saturated.

The thickness of each layer of the biaxially oriented polyamide film used as the substrate layer of the present invention is preferably such that the thickness of the core layer is 50 to 93% of the total thickness of the core layer and the skin layer, and more preferably 60 to 93%.

The laminate of the present invention may have a barrier layer between the biaxially oriented polyamide film layer and the paper substrate layer and/or the nonwoven fabric substrate layer. The barrier layer may be provided to impart gas barrier properties, and an inorganic thin film layer or a metal foil layer may be used as the barrier layer.

The inorganic thin film layer is a thin film made of a metal or an inorganic oxide. There is no particular restriction on the material forming the inorganic thin film layer as long as it can be made into a thin film, but from the viewpoint of transparency and gas barrier properties, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferred from the viewpoint of achieving both flexibility and denseness of the inorganic thin film layer. In this composite oxide, the mixture ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70 mass% Al in terms of the mass ratio of the metal content. If the Al concentration is less than 20 mass%, the water vapor barrier property may be reduced. On the other hand, if it exceeds 70 mass%, the inorganic thin film layer tends to become hard, and the film may be destroyed during secondary processing such as printing or lamination, resulting in a decrease in gas barrier property. Note that silicon oxide here refers to various silicon oxides such as SiO and _SiO2 , or a mixture thereof, and _aluminum oxide refers to various aluminum oxides such as AlO and _Al2O3 , or a mixture thereof.

The thickness of the inorganic thin film layer is usually 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 made excessively thick, exceeding 100 nm, the corresponding improvement in gas barrier properties cannot be obtained, and it is actually disadvantageous in terms of bending resistance and manufacturing costs.

The method for forming the inorganic thin film layer is not particularly limited, and may be any known deposition method such as physical deposition methods (PVD methods) such as vacuum deposition, sputtering, and ion plating, or chemical deposition (CVD). A typical method for forming the inorganic thin film layer will be described below using a silicon oxide/aluminum oxide thin film as an example. For example, when the vacuum deposition method is used, a mixture of SiO ₂ and Al ₂ O ₃ , or a mixture of SiO ₂ and Al, is preferably used as the deposition raw material. Particles are usually used as these deposition raw materials, and in this case, it is desirable that the size of each particle is such that the pressure during deposition does not change, and the preferred particle diameter is 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 introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc. as a reactive gas, or to adopt reactive deposition using means such as ozone addition and ion assist. Furthermore, the film formation conditions can be arbitrarily changed by applying a bias to the deposition target (a laminated film to be subjected to deposition), heating or cooling the deposition target, etc. The deposition material, reactive gas, bias, heating/cooling, etc. of the deposition target can be changed in the same way when the sputtering method or CVD method is adopted.

The metal constituting the metal foil layer used in the barrier layer is not particularly limited, and metal foils composed of aluminum, magnesium, etc. can be used. The thickness of the metal foil is preferably 3 μm or more and 100 μm or less, and more preferably 6 μm or more and 25 μm or less. The metal foil can be laminated via an adhesive layer.

The laminate of the present invention preferably has a sealant film. Examples of the sealant film include unstretched linear low-density polyethylene film, unstretched polypropylene film, and ethylene-vinyl alcohol copolymer resin film.

Examples of layer configurations of the laminated film of the present invention, where the boundary between layers is represented by /, include: ONY/bond/paper/bond/LLDPE, ONY/bond/paper/bond/CPP, ONY/PE/paper/bond/LLDPE, PET/bond/ONY/bond/paper/bond/LLDPE, PET/bond/ONY/bond/paper/PE/LLDPE, PET/bond/ONY/bond/paper/PE/LLDPE, PET/bond/ONY/bond/paper/ LLDPE, PET/adhesive/ONY/adhesive/paper/adhesive/CPP, ONY/adhesive/PET/adhesive/paper/adhesive/LLDPE, ONY/adhesive/PET/adhesive/paper/PE/LLDPE, ONY/adhesive/PET/adhesive/paper/adhesive/CPP, ONY/adhesive/paper/PE/LLDPE, ONY/adhesive/paper/PE/CPP, OPP/adhesive/ONY/adhesive/paper/adhesive/LLDP Examples include E, ONY/adhesive/EVOH/adhesive/paper/adhesive/LLDPE, ONY/adhesive/EVOH/adhesive/paper/adhesive/CPP, ONY/adhesive/aluminum-deposited PET/adhesive/paper/adhesive/LLDPE, ONY/adhesive/aluminum-deposited PET/adhesive/ONY/adhesive/paper/adhesive/LLDPE, ONY/adhesive/aluminum-deposited PET/adhesive/paper/PE/LLDPE, ONY/PE/aluminum-deposited PET/PE/paper/LLDPE, ONY/adhesive/aluminum-deposited PET/adhesive/paper/adhesive/CPP, PET/adhesive/aluminum-deposited PET/adhesive/ONY/adhesive/paper/adhesive/LLDPE, CPP/adhesive/ONY/adhesive/paper/adhesive/LLDPE, ONY/adhesive/paper/adhesive/aluminum-deposited LLDPE, ONY/adhesive/paper/adhesive/aluminum-deposited CPP, etc.
The abbreviations used in the above layer structure are as follows:
Paper: paper base material, ONY: biaxially oriented polyamide film of the present invention, PET: oriented polyethylene terephthalate film, LLDPE: unoriented linear low density polyethylene film, CPP: unoriented polypropylene film, OPP: oriented polypropylene film, PE: extrusion laminate or unoriented low density polyethylene film, EVOH: ethylene-vinyl alcohol copolymer resin, Adhesive: adhesive layer for bonding films together, aluminum vapor deposition means that aluminum is vapor-deposited.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The film was evaluated using the following measurement methods. Unless otherwise specified, measurements were performed in a measurement room with an environment of 23°C and a relative humidity of 65%.

(1) Thickness The film was divided into 10 equal parts in the TD direction (narrow films were divided so that the width was sufficient to measure the thickness), and 10 100 mm films were cut out in the MD direction in layers, and conditioned for 2 hours or more in an environment of 23° C. and 65% relative humidity. The thickness of the center of each sample was measured using a thickness meter manufactured by Tester Sangyo Co., Ltd., and the average value was taken as the thickness.
The thickness of each layer constituting the biaxially stretched polyamide film was calculated based on the ratio of the amount of resin discharged for each layer.

(2) Haze Value: Measured using a direct reading haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS-K-7105.

(3) Static Friction Coefficient The static friction coefficient between the surfaces of the base layers was evaluated in accordance with JIS-C 2151. The test piece had a width of 130 mm and a length of 250 mm, and the test speed was 150 mm/min.

(4) Heat Shrinkage Rate The heat shrinkage rate was measured according to the following formula in accordance with the dimensional change test method described in JIS C2318, except that the test temperature was 160° C. and the heating time was 10 minutes.
Heat shrinkage rate = [(length before treatment - length after treatment) / length before treatment] x 100 (%)

(5) Planar Orientation Degree For a film sample, the refractive index in the film MD direction (n _x ) and the refractive index in the film TD direction (n _y ) were measured using an Abbe refractometer with sodium D line as a light source according to JIS K 7142-1996 A method, and the planar orientation coefficient was calculated according to the following formula.
Plane orientation coefficient (ΔP)=(n _x +n _y )/2−n _z

(8) Puncture strength of film and laminate Biaxially stretched polyamide film and laminate were sampled to 5 cm square, and the puncture strength of the film was measured in accordance with JIS Z1707 using a digital force gauge "ZTS-500N", a motorized test stand "MX2-500N" and a puncture jig "TKS-250N" manufactured by Imada Co., Ltd. The unit of measurement was N.

(9) Density and basis weight of sealant film The density of the sealant film was evaluated according to JIS K7112:1999 D method (density gradient tube). The unit is g/ ^cm3 . The basis weight of the sealant film was calculated from the density and the thickness of the film obtained above. The unit of basis weight is g/ ^m2 .

(10) Basis Weight of Paper Base The basis weight of the paper base was measured in accordance with the provisions of JIS P8124: 2011. The unit of basis weight is g/ ^m2 .

(11) Weight ratio of paper substrate The weight ratio (%) of the paper substrate layer to the laminate was calculated using the following formula.
Weight ratio (%)=100×basis weight of paper component [g/m ² ]/basis weight of laminate [g/m ² ]

(Production example)
(Substrate 1)
An apparatus consisting of two extruders and a 380 mm wide co-extrusion T-die was used, and the layers were laminated in a skin layer/core layer/skin layer configuration by the feed block method. A molten resin of the following resin composition was extruded from the T-die into a film, which was then cast onto a cooling roll whose temperature was controlled at 20°C and electrostatically adhered to obtain an unstretched film with a thickness of 130 μm.

The resin compositions of the core layer and the skin layer are as follows.
Resin composition constituting the core layer: 100 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220° C.).
Resin composition constituting the skin layer: a resin composition consisting of 95 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C), 5.0 parts by mass of polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd., relative viscosity 2.1, melting point 237°C), 0.54 parts by mass of silica particles A (porous silica fine particles, manufactured by Fuji Silysia Chemical Ltd., average particle diameter 3.9 μm, oil absorption 320 ml/100 g), 0.075 parts by mass of silica particles B (porous silica fine particles, manufactured by Fuji Silysia Chemical Ltd., average particle diameter 2.7 μm, oil absorption 170 ml/100 g), and 0.15 parts by mass of fatty acid bisamide (ethene bisstearic acid amide, manufactured by Kyoeisha Chemical Co., Ltd.).

The feed block configuration and extruder output were adjusted so that the biaxially oriented polyamide film had a total thickness of 10 μm, a core layer thickness of 8 μm, and skin layers each 1 μm thick on the front and back.

The unstretched film obtained was introduced into a roll-type stretching machine, and using the difference in peripheral speed of the rolls, it was stretched 1.73 times in the MD direction at 80°C, and then further stretched 1.85 times at 70°C. Subsequently, this uniaxially stretched film was continuously introduced into a tenter-type stretching machine, preheated at 110°C, and then stretched 1.2 times in the TD direction at 120°C, 1.7 times at 130°C, and 2.0 times at 160°C, heat-set at 218°C, and then relaxed by 7% at 218°C. The surface on the side to be dry-laminated with the linear low-density polyethylene film was then corona discharge-treated to obtain a biaxially stretched polyamide film. The evaluation results of the obtained biaxially stretched film are shown in Table 1.

(Substrate 2)
An apparatus consisting of two extruders and a 380 mm wide co-extrusion T-die was used, and the layers were laminated in a skin layer/core layer/skin layer configuration by the feed block method. A molten resin of the following resin composition was extruded from the T-die into a film, which was then cast onto a cooling roll whose temperature was controlled at 20°C and electrostatically adhered to obtain an unstretched film with a thickness of 130 μm.

The resin compositions of the core layer and the skin layer are as follows.
Resin composition constituting the core layer: a polyamide resin composition consisting of 89.5 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C) and 10.5 parts by mass of polybutylene terephthalate adipate (manufactured by BASF under the trade name "Ecoflex", glass transition temperature -31.3°C, melting point 120°C).
Resin composition constituting the skin layer: a resin composition consisting of 95 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C), 5.0 parts by mass of polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd., relative viscosity 2.1, melting point 237°C), 0.54 parts by mass of silica particles A (porous silica fine particles, manufactured by Fuji Silysia Chemical Ltd., average particle diameter 3.9 μm, oil absorption 320 ml/100 g), 0.075 parts by mass of silica particles B (porous silica fine particles, manufactured by Fuji Silysia Chemical Ltd., average particle diameter 2.7 μm, oil absorption 170 ml/100 g), and 0.15 parts by mass of fatty acid bisamide (ethene bisstearic acid amide, manufactured by Kyoeisha Chemical Co., Ltd.).

The feed block configuration and extruder output were adjusted so that the biaxially oriented polyamide film had a total thickness of 10 μm, a core layer thickness of 8 μm, and skin layers each 1 μm thick on the front and back.

The unstretched film obtained was introduced into a roll-type stretching machine, and using the difference in peripheral speed of the rolls, it was stretched 1.73 times in the MD direction at 80°C, and then further stretched 1.85 times at 70°C. Subsequently, this uniaxially stretched film was continuously introduced into a tenter-type stretching machine, preheated at 110°C, and then stretched 1.2 times in the TD direction at 120°C, 1.7 times at 130°C, and 2.0 times at 160°C, heat-set at 218°C, and then relaxed by 7% at 218°C. The surface on the side to be dry-laminated with the linear low-density polyethylene film was then corona discharge-treated to obtain a biaxially stretched polyamide film. The evaluation results of the obtained biaxially stretched film are shown in Table 1.

(Substrates 3 to 7 and Substrates 9 to 10)
A biaxially stretched film was obtained in the same manner as for Substrate 1, except that the raw material compositions of the core layer and the skin layer and the thicknesses of the core layer and the skin layer were changed as shown in Table 1. The evaluation results of the obtained biaxially stretched film are shown in Table 1.

(Substrate 8)
An apparatus consisting of two extruders and a 380 mm wide co-extrusion T-die was used, and the layers were laminated in a skin layer/core layer/skin layer configuration by the feed block method. A molten resin of the following resin composition was extruded from the T-die into a film, which was then cast onto a cooling roll whose temperature was controlled at 20°C and electrostatically adhered to obtain an unstretched film with a thickness of 130 μm.

The resin compositions of the core layer and the skin layer are as follows.
Resin composition constituting the core layer: a polyamide resin composition consisting of 89.5 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C) and 10.5 parts by mass of polybutylene terephthalate adipate (manufactured by BASF under the trade name "Ecoflex", glass transition temperature -31.3°C, melting point 120°C).
Resin composition constituting the skin layer: a resin composition consisting of 95 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C), 5.0 parts by mass of polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd., relative viscosity 2.1, melting point 237°C), 0.54 parts by mass of silica particles A (porous silica fine particles, manufactured by Fuji Silysia Chemical Ltd., average particle diameter 3.9 μm, oil absorption 320 ml/100 g), 0.075 parts by mass of silica particles B (porous silica fine particles, manufactured by Fuji Silysia Chemical Ltd., average particle diameter 2.7 μm, oil absorption 170 ml/100 g), and 0.15 parts by mass of fatty acid bisamide (ethene bisstearic acid amide, manufactured by Kyoeisha Chemical Co., Ltd.).

The unstretched film was then introduced into a simultaneous biaxial stretching machine, where it was preheated at 210°C for 2 seconds, and then subjected to simultaneous biaxial stretching at 195°C for 2 seconds with an MD stretch ratio of 3.2 times and a TD stretch ratio of 3.3 times. This was followed by a heat setting treatment at 220°C for 5 seconds, followed by a 5% relaxation treatment, to obtain a polyamide film with a thickness of 10 μm.

(Formation of inorganic thin film layer)
An inorganic thin film layer of a composite oxide of silicon dioxide and aluminum oxide was formed by electron beam deposition on the corona-treated surface of the substrate 2. The deposition method was to set the film on the unwinding side of a continuous vacuum deposition machine, run it over a cooled metal drum, and wind the film. At this time, the continuous vacuum deposition machine was depressurized to 10-4 Torr or less, and particulate SiO ₂ (purity 99.9%) and A12O3 (purity 99.9%) of about 3 mm to 5 mm were used as deposition sources in an alumina crucible from the bottom of the cooling drum. The thickness of the obtained inorganic thin film layer (SiO ₂ /A1 ₂ O ₃ composite oxide layer) was 13 nm. The composition of this composite oxide layer was SiO ₂ /A1 ₂ O ₃ (mass ratio) = 60/40.

[Preparation of Laminate]
Example 1
The above substrate 1 and unglazed kraft paper with a basis weight of 54 g/m2 were laminated using a dry lamination adhesive (Takelac (registered trademark) A-950 manufactured by Mitsui Chemicals, Inc.) so that the adhesive layer after drying would be 1.5 μm thick. A polyester-based adhesive was further applied to the paper side of the above substrate layer 1/paper laminate, and then a linear low-density polyethylene film (L-LDPE film: L4102 manufactured by Toyobo Co., Ltd.) with a thickness of 40 μm was dry laminated, and aging was performed for 3 days in an environment of 40° C. to obtain a laminate of Example 1. The evaluation results of the obtained laminate are shown in Table 2.

(Examples 2 to 9, Comparative Examples 1 and 2)
Laminates of Examples 2 to 9 and Comparative Examples 1 and 2 were obtained by the method described in Example 1, except that the substrates used in the laminate preparation method of Example 1 were changed to those shown in Table 2.
The evaluation results of the obtained laminate are shown in Table 2.

As shown in Table 2, even though the laminates of the Examples had a high paper ratio, packaging laminates having high puncture resistance were obtained.
In the laminate of Comparative Example 1, the thickness of the biaxially oriented polyamide film was too thin, and therefore the puncture strength of the laminate was poor.
In the laminate of Comparative Example 2, the thickness of the biaxially oriented polyamide film was large and the weight ratio of paper was less than 50%, which was insufficient from the viewpoint of reducing the environmental load.

Example 10
Three-side sealed type and pillow type packaging bags were produced using the biaxially stretched polyamide film produced in Example 2. Packaging bags with good appearance and resistance to tearing in a drop impact test were produced.

Claims (10)

A laminate comprising a biaxially oriented polyamide film, a paper base layer and/or a nonwoven fabric base layer, and a sealant film, in which the weight ratio of the paper base layer and/or the nonwoven fabric base layer to the laminate is 50% or more, and the puncture strength of the laminate is 8.0 N or more. The laminate according to claim 1, wherein the thickness of the biaxially oriented polyamide film is 8 to 15 μm. The laminate according to claim 1, wherein the biaxially stretched polyamide film includes a core layer and a skin layer, the core layer includes 80% by mass or more of polyamide 6 resin and 1 to 20% by mass of an aliphatic polyester copolymer or an aromatic aliphatic polyester copolymer, and the skin layer includes 70% by mass or more of polyamide 6 resin. The laminate according to claim 3, wherein the aliphatic polyester resin or aromatic aliphatic polyester resin is at least one polyester resin selected from the group consisting of polybutylene succinate, polybutylene succinate adipate, and polybutylene adipate terephthalate. The laminate according to claim 1, which has a barrier layer between the biaxially oriented polyamide film layer and the paper substrate layer and/or the nonwoven fabric substrate layer. The laminate according to claim 5, wherein the barrier layer is an inorganic thin film layer. The laminate according to claim 6, wherein the inorganic vapor deposition layer is a layer made of aluminum oxide or a composite oxide of silicon oxide and aluminum oxide. The laminate of claim 5, wherein the barrier layer is a metal foil layer. A packaging bag using the laminate described in any one of claims 1 to 8. A packaging container using the laminate described in any one of claims 1 to 8.