WO2024225339A1 - Stretched multilayer polyolefin resin film, packaging material, packaging bag, and package - Google Patents

Abstract

The present invention addresses the problem of providing: a stretched multilayer polyolefin resin film which is configured from a resin with a low environmental impact, and has gas barrier properties, heat sealability, heat resistance, rigidity, and toughness; a packaging material; a packaging bag; and a package.　The present invention relates to a stretched multilayer polyolefin resin film which is obtained by sequentially stacking a base material layer, an intermediate layer, and a thermally fusible layer that contains a polyolefin resin having a melting point of 150°C or less, and which is characterized by having a gas barrier layer on a surface on the reverse side of the front surface of the thermally fusible layer and satisfying the following requirements (a) to (d). (a) The puncture strength of the film is 10 N or more. (b) The Young's modulus of the film is 1 GPa or more in the MD direction and in the TD direction. (c) The seal strength at the time when the thermally fusible layers of the film are heat-sealed at 150°C and 0.2 MPa for 2 seconds is 8 N/15 mm or more. (d) The shrinkage ratio of the film after being heated at 120°C for 15 minutes is 10% or less both in the MD direction and in the TD direction.

Description

Stretched laminated polyolefin resin film, packaging material, packaging bag, and packaging body

The present invention relates to an environmentally friendly stretched laminated polyolefin resin film, packaging material, packaging bag, and packaging body, which are used in the packaging fields of food, medicine, industrial products, etc.

In recent years, regulations aimed at reducing the use of disposable plastics have been strengthened in Europe and other countries around the world. Behind this lies growing international awareness of resource circulation and the worsening waste problem in emerging countries. For this reason, there is a demand for environmentally friendly products from the perspective of the 3Rs (Recycle, Reuse, Reduce) for plastic packaging materials required for food, pharmaceuticals, etc.

As one of the possibilities for making the aforementioned packaging materials more environmentally friendly, active consideration is being given to making packaging materials from the same recyclable material, i.e., mono-materialization. As materials for mono-materialization, for example, polyester-based or polyolefin-based materials are being developed.

While there is a demand for packaging materials with low environmental impact as mentioned above, the current situation is that the properties required of the packaging materials themselves are becoming increasingly multifunctional for the sake of convenience. For example, retort pouches that can be used in microwave ovens are required to have gas barrier properties, heat resistance, water resistance, toughness (resistance to bag breakage and pinholes), high sealability, etc., all at the same time in a single packaging bag without using aluminum foil.
To achieve these, it is necessary to bond different materials, each with a different function, and the bag generally has a structure of at least three layers, with a vapor-deposited polyester film on the outside, a polyamide film in the middle, and a polyolefin sealant dry-laminated on the inside (contents side) with an adhesive. Although this structure can achieve the desired performance, it is poor in recyclability because different materials are bonded together, and there is a problem that it cannot be said to be an environmentally friendly packaging material as mentioned above.

　Taking these points into consideration, studies are underway to design bags with the aforementioned multi-functionality even using the same material that can be made into a mono-material. However, even if the constituent material is made into a mono-material, there are issues with peeling off each layer and recycling it. To address this, it is conceivable to make the sealant, which accounts for the largest proportion of the constituent materials in terms of its thickness, multi-functional and minimize the number of layers that make up the material. This would provide an ideal packaging material that is most easily recycled, and various studies are being conducted in this regard.

For example, Patent Document 1 discloses a polyester sealant with improved low adsorption and heat resistance as an alternative to conventional polyolefin sealants. The polyester sealant in Patent Document 1 has a layer with heat sealability and other layers separated, and the raw material compositions of these layers are controlled separately to achieve both heat sealability and heat resistance. However, there is a problem in that the heat sealability is somewhat inferior to the seal strength of non-oriented polyolefin sealants.
Also disclosed is a barrier sealant having a gas barrier layer on the opposite side of the sealing layer of a polyester sealant (see, for example, Patent Document 2). Although the polyester sealant in Patent Document 2 has a barrier layer, the improvement in barrier properties is not sufficient, and in particular there is no mention of an improvement in water vapor barrier properties.

On the other hand, for polyolefin sealants, unstretched polypropylene resin films or stretched polypropylene resin films are often used. These resins are known to have sufficient sealing strength. However, when considering polypropylene resin films as mono-material packaging materials, the stiffness and toughness of the films are insufficient. For example, a polypropylene resin film has been disclosed in which a polypropylene resin is laminated with a low-melting point polyolefin resin, co-extruded, and then stretched (e.g., Patent Document 3). This stretched polypropylene resin film has a certain degree of sealing strength, but the stiffness and heat resistance of the film are insufficient.

Furthermore, the gas barrier properties of the polypropylene-based resin film in Patent Document 3 were not examined, and there was a problem that the polyolefin-based sealant had significantly inferior gas barrier properties compared to materials with conventional barrier properties. For example, although polyolefin-based resin films have a certain degree of water vapor barrier properties due to their structure, compared to inorganic vapor-deposited polyester-based resin films, which are generally considered to have excellent water vapor barrier properties, the water vapor barrier properties of polyolefin-based resin films are not sufficient, and there was also a problem that the oxygen barrier properties of polyolefin-based resin films were very poor.

Patent Document 4 describes vapor-depositing a barrier material onto a polyolefin-based sealant. Although this sealant exhibits water vapor barrier properties, there is an issue that the oxygen barrier properties are insufficient. Furthermore, because it is an unstretched polyolefin-based sealant, it is inferior in stiffness and toughness as a film, and there is room for improvement as a desired mono-material packaging material.

JP 2017-165059 A JP 2017-165060 A Patent No. 4120227 Patent No. 3318479

In light of the above, in Patent Documents 1 to 4, it was difficult to achieve both mono-material packaging materials and the various properties required of packaging materials (gas barrier properties, heat seal properties, heat resistance, toughness, and firmness), and it was not possible to design packaging materials that were both environmentally friendly and convenient.

The present invention has been made in view of the above problems in the prior art.
In other words, an object of the present invention is to provide a stretched laminated polyolefin-based resin film, a packaging material, a packaging bag, and a packaging body, which are made of a resin that has a low environmental impact and have gas barrier properties, heat sealability, heat resistance, stiffness, and toughness.

The inventors discovered that by laminating a specific gas barrier layer onto a stretched polyolefin film having a low melting point resin layer (e.g., an intermediate layer or a heat-sealing layer) to form a laminated film, it is possible to greatly improve the gas barrier properties while also ensuring high heat sealability, heat resistance, stiffness and toughness, thereby providing an environmentally friendly and highly convenient packaging material, leading to the completion of the present invention.

That is, the present invention comprises the following:
1. A stretched laminated polyolefin resin film comprising a base layer, an intermediate layer, and a heat-sealing layer containing a polyolefin resin having a melting point of 150°C or less, laminated in that order, the stretched laminated polyolefin resin film having a gas barrier layer on the surface opposite to the surface of the heat-sealing layer, and satisfying the following requirements (a) to (d):
(a) The puncture strength of the film is 10 N or more.
(b) The Young's modulus of the film in both the MD and TD directions is 1 GPa or more.
(c) The heat-sealable layers of the film have a seal strength of 8 N/15 mm or more when heat-sealed at 150° C., 0.2 MPa, and for 2 seconds.
(d) The shrinkage rate of the film after heating at 120°C for 15 minutes is 10% or less in both the MD and TD directions.
2. The stretched laminated polyolefin resin film according to 1., wherein the base layer, intermediate layer and heat-sealing layer are each composed of a polyolefin resin composition containing a propylene homopolymer or a propylene copolymer as a constituent component.
3. The stretched laminated polyolefin resin film according to 1. or 2., wherein the content of the propylene copolymer constituting the intermediate layer is more than 60 mass% in the polyolefin resin composition constituting the intermediate layer.
4. The stretched laminated polyolefin resin film according to any one of 1. to 3., wherein the relationship of thickness of the base layer > thickness of the intermediate layer > thickness of the heat-sealing layer is satisfied.
5. The stretched laminated polyolefin resin film according to any one of 1. to 4., wherein the gas barrier layer is an inorganic thin film layer made of any one of aluminum, aluminum oxide, silicon oxide, and a composite oxide of silicon oxide and aluminum oxide.
6. The stretched laminated polyolefin resin film according to any one of 1. to 5., wherein the gas barrier layer is a coating layer containing at least one of a polyvinyl alcohol resin, a polyester resin, a polyurethane resin, and an inorganic layered compound.
7. The stretched laminated polyolefin resin film according to any one of 1. to 6., wherein an anchor coat layer is laminated between the film and the gas barrier layer.
8. The stretched laminated polyolefin resin film according to any one of 1. to 7., wherein a protective layer is laminated on the gas barrier layer.
9. The stretched laminated polyolefin resin film according to any one of 1. to 8., which has an oxygen permeability of 800 ml/ ^m2 ·d·MPa or less under conditions of 23° C. and 65% RH.
10. The stretched laminated polyolefin resin film according to any one of 1. to 9., having a water vapor permeability of 3.0 g/ ^m2 ·d or less under conditions of 40° C. and 90% RH.
11. The stretched laminated polyolefin resin film according to any one of 1. to 10., which is used for heating in a microwave oven.
12. A packaging material obtained by laminating the film according to any one of 1. to 11.
13. The packaging material according to 12., wherein a barrier adhesive layer is laminated on the gas barrier layer.
14. A packaging bag made from the packaging material described in 12.
15. A package in which an item is packaged in the packaging material according to 12.
16. A package comprising an item packaged in the packaging bag according to 14.

The present invention makes it possible to provide a stretched laminated polyolefin resin film that is made of resin that has a low environmental impact and has gas barrier properties, heat sealability, heat resistance, stiffness, and toughness.

The stretched laminated polyolefin-based resin film of the present invention is a stretched laminated polyolefin-based resin film comprising a base layer, an intermediate layer, and a heat-sealing layer containing a polyolefin-based resin having a melting point of 150°C or less laminated in that order, the stretched laminated polyolefin-based resin film having a gas barrier layer on the surface opposite to the surface of the heat-sealing layer, and characterized in that it satisfies the following requirements (a) to (d):
(a) The puncture strength of the film is 10 N or more (preferably 12 N or more).
(b) The Young's modulus of the film in both the MD and TD directions is 1 GPa or more.
(c) The heat-sealable layers of the film have a seal strength of 8 N/15 mm or more when heat-sealed at 150° C., 0.2 MPa, and for 2 seconds.
(d) The shrinkage rate of the film after heating at 120°C for 15 minutes is 10% or less in both the MD and TD directions.

The present invention will be described in detail below.
[Stretched laminated polyolefin resin film]
The stretched laminated polyolefin resin film of the present invention is formed by laminating in order a substrate layer, an intermediate layer, and a heat-sealing layer containing a polyolefin resin having a melting point of 150° C. or less.
The stretched laminated polyolefin resin film may be a uniaxially stretched film or a biaxially stretched film, and is preferably a biaxially stretched film.
The base layer, intermediate layer and heat-sealing layer are each preferably made of a polyolefin resin composition containing a propylene homopolymer or a propylene copolymer as a constituent component.

The substrate layer is a layer for bonding another substrate film capable of constituting a monomaterial such as a stretched polyolefin resin film, and the substrate film is preferably laminated via an adhesive resin. The substrate layer may be provided with a printing layer.
The substrate layer may be a single layer or two or more layers, and is preferably a single layer.

The substrate layer is preferably made of a polyolefin resin composition containing a propylene homopolymer or a propylene copolymer as a constituent component.
The propylene homopolymer and the propylene copolymer may be any one having a predetermined melt flow rate (MFR) and melting point.

The melt flow rate (MFR) of the propylene homopolymer (230°C, load 2.16 kg) is preferably 1.8 g/10 min or more, more preferably 2.0 g/10 min or more, even more preferably 2.2 g/10 min or more, and preferably 10.0 g/10 min or less, more preferably 8.0 g/10 min or less, even more preferably 6.0 g/10 min or less.
When the melt flow rate of the propylene homopolymer is within the above range, the workability and the strength of the film are good.
The melt flow rate is measured, for example, based on JIS K-7210-1 (measurement conditions: 230° C., load 2.16 kg).

The melting point of the propylene homopolymer is preferably 150°C or higher, more preferably 152°C or higher, even more preferably 154°C or higher, still more preferably 156°C or higher, and is preferably 170°C or lower, more preferably 167°C or lower, still more preferably 164°C or lower.
When the melting point of the propylene homopolymer is within the above range, the heat resistance can be improved. The melting point can be measured, for example, by using a differential scanning calorimeter.

Commercially available propylene homopolymers include, for example, FLX80E4 (MFR 7.5 g/10 min, melting point 164°C) manufactured by Sumitomo Chemical Co., Ltd., F-300SP (MFR 3.0 g/10 min, melting point 160°C) manufactured by Prime Polymer Co., Ltd., and FS2011DG3 (MFR: 2.5 g/10 min, melting point 158°C) manufactured by Sumitomo Chemical Co., Ltd.

The propylene copolymer is preferably a propylene-α-olefin copolymer (containing no α-olefin having 3 carbon atoms), and may be either a block copolymer or a random copolymer.
The α-olefin monomer constituting the propylene-α-olefin copolymer is preferably an α-olefin monomer having 2 or 4 to 10 carbon atoms, and the α-olefin monomer having 2 or 4 to 10 carbon atoms is more preferably ethylene, butene, pentene, hexene, octene, decene, or the like.
The propylene copolymer (preferably a propylene-α-olefin copolymer) is preferably a propylene-ethylene copolymer, a propylene-butene copolymer, a propylene-pentene copolymer, a propylene-methylpentene copolymer, a propylene-hexene copolymer, a propylene-octene copolymer, a propylene-ethylene-butene copolymer, or the like.

The melt flow rate (MFR) of the propylene copolymer (230°C, load 2.16 kg) is preferably 2.0 g/10 min or more, more preferably 2.2 g/10 min or more, even more preferably 2.4 g/10 min or more, preferably 8.0 g/10 min or less, more preferably 7.5 g/10 min or less, even more preferably 7.0 g/10 min or less. If the melt flow rate of the propylene copolymer is within the above range, the workability and film strength will be good.

The melting point of the propylene copolymer is preferably 140°C or higher, more preferably 142°C or higher, even more preferably 144°C or higher, even more preferably 146°C or higher, and is preferably 165°C or lower, more preferably 160°C or lower, even more preferably 155°C or lower.
When the melting point of the propylene copolymer is within the above range, the heat resistance can be improved.

The propylene copolymer (preferably propylene-α-olefin copolymer) preferably contains at least one selected from propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of 1.0 mol% or less and propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of more than 1.0 mol%, and more preferably contains propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of 1.0 mol% or less.

The copolymerization ratio of α-olefin in a propylene-α-olefin copolymer (wherein the number of carbon atoms in the α-olefin is 2 or 4 to 10) having an olefin copolymerization ratio of 1.0 mol% or less is preferably 0.9 mol% or less, more preferably 0.8 mol% or less, even more preferably 0.7 mol% or less, and is preferably 0.1 mol% or more, more preferably 0.15 mol% or more, even more preferably 0.2 mol% or more. By setting the copolymerization ratio within the above range, heat resistance and firmness can be improved.

The resin composition containing the polyolefin resin constituting the base layer is preferably composed of a propylene homopolymer or a propylene-α-olefin copolymer (the number of carbon atoms of the α-olefin is 2 or 4 to 10) having a copolymerization ratio of 1.0 mol % or less, and more preferably composed of a propylene homopolymer. The propylene homopolymer or propylene copolymer may be used alone or in combination of two or more kinds.
The propylene homocopolymer is preferably an isotactic crystalline polypropylene resin which is insoluble in n-heptane.

The resin composition containing the polyolefin resin constituting the base layer contains at least one type of polymer selected from a propylene homopolymer and a propylene copolymer (preferably a propylene-α-olefin copolymer (the α-olefin has 2 or 4 to 10 carbon atoms)) in an amount of 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, still more preferably 95% by weight or more, and particularly preferably 100% by weight.
The resin composition containing a polyolefin resin constituting the substrate layer most preferably contains 100% by weight of a propylene homopolymer.

The stretched laminated polyolefin resin film of the present invention has an intermediate layer between the above-mentioned base layer and the heat-sealing layer. This intermediate layer is provided to improve the interlayer strength between the base layer and the heat-sealing layer and to provide the stretched laminated polyolefin resin film of the present invention with appropriate stiffness and heat seal strength.

The intermediate layer is preferably made of a polyolefin resin composition containing a propylene homopolymer or a propylene copolymer as a constituent component.
The propylene homopolymers or propylene copolymers may be used alone or in combination of two or more.
Furthermore, the polyolefin resin composition constituting the intermediate layer may contain an olefin copolymer (sometimes referred to as olefin copolymer X) other than a propylene homopolymer and a propylene copolymer.
The intermediate layer may be a single layer or two or more layers, and is preferably a single layer.

The propylene homopolymer and propylene copolymer may have a specified melt flow rate (MFR) and melting point.

The melt flow rate (MFR) of the propylene homopolymer (230°C, load 2.16 kg) is preferably 1.8 g/10 min or more, more preferably 2.0 g/10 min or more, even more preferably 2.2 g/10 min or more, preferably 10.0 g/10 min or less, more preferably 8.0 g/10 min or less, even more preferably 6.0 g/10 min or less. When the melt flow rate of the propylene homopolymer is in the above range, the workability and the strength of the film are good.
The melt flow rate is measured, for example, based on JIS K-7210-1 (measurement conditions: 230° C., load 2.16 kg).

The melting point of the propylene homopolymer is preferably 150°C or higher, more preferably 152°C or higher, even more preferably 154°C or higher, still more preferably 156°C or higher, and is preferably 170°C or lower, more preferably 167°C or lower, still more preferably 164°C or lower.
When the melting point of the propylene homopolymer is within the above range, the firmness of the material can be improved. The melting point can be measured, for example, by using a differential scanning calorimeter.

Commercially available propylene homopolymers include, for example, FLX80E4 (MFR 7.5 g/10 min, melting point 164°C) manufactured by Sumitomo Chemical Co., Ltd., F-300SP (MFR 3.0 g/10 min, melting point 160°C) manufactured by Prime Polymer Co., Ltd., and FS2011DG3 (MFR: 2.5 g/10 min, melting point 158°C) manufactured by Sumitomo Chemical Co., Ltd.

The propylene copolymer is preferably a propylene-α-olefin copolymer (containing no α-olefin having 3 carbon atoms), and may be either a block copolymer or a random copolymer, with a random copolymer being preferred.
The α-olefin is preferably an α-olefin monomer having 2 or 4 to 10 carbon atoms, and the α-olefin monomer having 2 or 4 to 10 carbon atoms is more preferably ethylene, butene, pentene, hexene, octene, decene, or the like.
The propylene copolymer (preferably a propylene-α-olefin copolymer) is preferably a propylene-ethylene copolymer, a propylene-butene copolymer, a propylene-pentene copolymer, a propylene-methylpentene copolymer, a propylene-hexene copolymer, a propylene-octene copolymer, a propylene-ethylene-butene copolymer, or the like, more preferably a propylene-ethylene copolymer, a propylene-butene copolymer, or a propylene-ethylene-butene copolymer, and even more preferably a propylene-ethylene-butene copolymer.

The above-mentioned propylene copolymer can be exemplified by a polymer synthesized by the continuous gas phase polymerization method described in JP-A-2003-277412, for example FSX66E8 manufactured by Sumitomo Chemical Co., Ltd.

The melt flow rate (MFR) of the propylene copolymer (230°C, load 2.16 kg) is preferably 2.0 g/10 min or more, more preferably 2.2 g/10 min or more, even more preferably 2.4 g/10 min or more, preferably 8.0 g/10 min or less, more preferably 7.5 g/10 min or less, even more preferably 7.0 g/10 min or less. If the melt flow rate of the propylene copolymer is within the above range, the workability and film strength will be good.

The melting point of the propylene copolymer is preferably 124°C or higher, more preferably 126°C or higher, even more preferably 128°C or higher, even more preferably 130°C or higher, and is preferably 145°C or lower, more preferably 142°C or lower, even more preferably 139°C or lower.
When the melting point of the propylene copolymer is within the above range, the heat sealability and stiffness can be improved.

The propylene copolymer (preferably propylene-α-olefin copolymer) preferably contains at least one selected from propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of 1.0 mol% or less and propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of more than 1.0 mol%, and more preferably contains propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of more than 1.0 mol%.

The copolymerization ratio of alpha olefin in a propylene-alpha olefin copolymer (alpha olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of 1.0 mol% or less is preferably 0.9 mol% or less, more preferably 0.8 mol% or less, even more preferably 0.7 mol% or less, and is preferably 0.1 mol% or more, more preferably 0.15 mol% or more, even more preferably 0.2 mol% or more.

The copolymerization ratio of α-olefins in a propylene-α-olefin copolymer (wherein the carbon number of the α-olefin is 2 or 4 to 10) having a copolymerization ratio of α-olefins exceeding 1.0 mol% is preferably 1.1 mol% or more in total, more preferably 1.5 mol% or more, even more preferably 2 mol% or more, even more preferably 4 mol% or more, and is preferably 16 mol% or less, more preferably 14 mol% or less, even more preferably 12 mol% or less, and even more preferably 10 mol% or less. Having the copolymerization ratio of α-olefins within the above range can improve heat sealability.

The copolymerization ratio of ethylene in the propylene-α-olefin copolymer (α-olefin has 2 or 4 to 10 carbon atoms) is preferably 1 mol% or more, more preferably 1.5 mol% or more, even more preferably 1.7 mol% or more, even more preferably 2 mol% or more, and preferably 7 mol% or less, more preferably 6 mol% or less, even more preferably 5 mol% or less, and even more preferably 4 mol% or less. Having the copolymerization ratio of ethylene within the above range can improve heat sealability.

The copolymerization ratio of butene in the propylene-α-olefin copolymer (α-olefin has 2 or 4 to 10 carbon atoms) is preferably 2 mol% or more, more preferably 3 mol% or more, even more preferably 4 mol% or more, even more preferably 5 mol% or more, and preferably 12 mol% or less, more preferably 11 mol% or less, even more preferably 10 mol% or less, and even more preferably 9 mol% or less. Having the copolymerization ratio of butene within the above range can improve heat sealability.

The polyolefin resin composition constituting the intermediate layer preferably contains only a propylene copolymer, and more preferably contains a propylene homopolymer or a propylene copolymer and an olefin copolymer X that is different from the propylene homopolymer or the propylene copolymer.

Olefin copolymer X is preferably an olefin copolymer having 2 or 4 to 10 carbon atoms that does not contain a propylene monomer, more preferably an ethylene-butene copolymer, an ethylene-pentene copolymer, an ethylene-hexene copolymer, an ethylene-octene copolymer, a butene-pentene copolymer, a butene-hexene copolymer, a butene-octene copolymer, even more preferably an ethylene-butene copolymer, an ethylene-pentene copolymer, and even more preferably an ethylene-butene copolymer.

The olefin copolymer X preferably has a given MFR and melting point.
The melt flow rate (MFR) (230°C, load 2.16 kg) of the olefin copolymer X is preferably higher than the MFR of the propylene homopolymer and the propylene copolymer, more preferably 4 g/10 min or more, even more preferably 5 g/10 min or more, even more preferably 6 g/10 min or more, more preferably 20 g/10 min or less, even more preferably 18 g/10 min or less, and even more preferably 16 g/10 min or less. When the melt flow rate of the olefin copolymer X is within the above range, the MFR of the entire resin constituting the intermediate layer when a mixture with a propylene homopolymer or a propylene copolymer is used can be adjusted.

The melting point of the olefin copolymer X is preferably lower than the melting points of the propylene homopolymer and the propylene copolymer, more preferably 40° C. or higher, even more preferably 45° C. or higher, even more preferably 50° C. or higher, particularly preferably 55° C. or higher, and is preferably 100° C. or lower, more preferably 95° C. or lower, even more preferably 90° C. or lower, and even more preferably 85° C. or lower.
When the melting point of the olefin copolymer X is within the above range, it is possible to adjust the melting point of the entire resin constituting the intermediate layer when a propylene homopolymer or a mixture with a propylene copolymer is used.

When the polyolefin resin composition constituting the intermediate layer contains a propylene copolymer, the content of the propylene copolymer in the polyolefin resin composition constituting the intermediate layer is preferably 50% by weight or more, more preferably 52% by weight or more, even more preferably 54% by weight or more, even more preferably 56% by weight or more, and particularly preferably 58% by weight or more, and is preferably 99% by weight or less, more preferably 97% by weight or less, even more preferably 95% by weight or less, and may be 100% by weight. By achieving the above content, the gas barrier properties, heat resistance, and stiffness of the film can be improved.

When the polyolefin resin composition constituting the intermediate layer contains a propylene copolymer, the content of olefin copolymer X in the polyolefin resin composition constituting the intermediate layer is preferably 0% by weight or more, more preferably 1% by weight or more, even more preferably 5% by weight or more, even more preferably 10% by weight or more, preferably 50% by weight or less, more preferably 48% by weight or less, even more preferably 46% by weight or less, even more preferably 44% by weight or less, particularly preferably 40% by weight or less, 35% by weight or less, 25% by weight or less, or 20% by weight or less. The above contents make it possible to adjust the MFR and melting point of the entire resin constituting the intermediate layer when using a mixture with a propylene copolymer.

When the polyolefin resin composition constituting the intermediate layer contains propylene homopolymer, the content of propylene homopolymer in the polyolefin resin composition constituting the intermediate layer is preferably 1% by weight or more, more preferably 5% by weight or more, even more preferably 10% by weight or more, even more preferably 15% by weight or more, preferably 40% by weight or less, more preferably 35% by weight or less, even more preferably 30% by weight or less.

When the polyolefin resin composition constituting the intermediate layer contains a propylene homopolymer, the content of the olefin copolymer X in the polyolefin resin composition constituting the intermediate layer is preferably 60% by weight or more, more preferably 65% by weight or more, even more preferably 70% by weight or more, even more preferably 75% by weight or more, preferably 99% by weight or less, more preferably 95% by weight or less, even more preferably 90% by weight or less, and even more preferably 85% by weight or less. The above contents make it possible to adjust the MFR and melting point of the entire resin constituting the intermediate layer when using a mixture with a propylene homopolymer.

In one aspect of the present invention, the content of the propylene copolymer constituting the intermediate layer in the polyolefin resin composition constituting the intermediate layer is preferably more than 60 mass%, more preferably 65 weight% or more, even more preferably 70 weight% or more, still more preferably 75 weight% or more, and is preferably 100 weight%, 99 weight% or less, or 95 weight% or less.
If the amount of the propylene copolymer is too small, the adhesive strength between the layers constituting the stretched laminated polyolefin resin film may be insufficient, and sufficient heat seal strength may not be obtained. On the other hand, if the amount of the propylene copolymer is too large, there is no problem. If the content of the propylene copolymer in the intermediate layer is in the upper range, the oxygen barrier property and heat sealability can be improved.

In one embodiment of the present invention, it is particularly preferable that the polyolefin resin composition constituting the intermediate layer contains 100% by weight of a propylene copolymer.
In one embodiment of the present invention, it is particularly preferable that the polyolefin resin composition constituting the intermediate layer contains 100% by weight of the propylene copolymer and the olefin copolymer X.
In one embodiment of the present invention, it is particularly preferable that the polyolefin resin composition constituting the intermediate layer contains 100% by weight of propylene homopolymer and olefin copolymer X.

In one embodiment of the present invention, the polyolefin resin composition constituting the intermediate layer preferably does not contain a propylene-α-olefin copolymer (wherein the α-olefin has 2 or 4 to 10 carbon atoms) in which the copolymerization ratio of the α-olefin is 1.0 mol % or less in the polyolefin resin composition constituting the intermediate layer.

The propylene copolymer used in the intermediate layer has excellent mechanical strength such as impact strength and tear properties, low-temperature properties, and weather resistance, and by blending such components, it is possible to impart excellent properties to the stretched laminated polyolefin resin film. However, since the propylene copolymer has a structure in which different α-olefins are randomly introduced as second and third components into the molecular chain of the main component α-olefin, crystallization is suppressed and the crystallinity is lower than that of α-olefin homopolymers such as homopolypropylene, and blending the propylene copolymer results in a decrease in the stiffness of the film. On the other hand, if the amorphous portion is too small, the film becomes hard and difficult to stretch, making it difficult to obtain sufficient heat seal strength. From these points of view, it is preferable to blend a propylene copolymer in the intermediate layer in order to obtain a laminated film that has an appropriate stiffness and can stretch according to load.

Heat-sealing layer The heat-sealing layer is a layer necessary for producing a package by overlapping two films with the stretched laminated polyolefin resin film on the inside and heat-sealing them.
The heat-sealing layer is made of a polyolefin resin composition containing a polyolefin resin having a melting point of 150° C. or less.
The heat-sealing layer may be a single layer or two or more layers, and is preferably a single layer.

The polyolefin resin having a melting point of 150°C or less preferably contains one or more types of propylene copolymers, more preferably two or more types of propylene copolymers, and even more preferably two types of propylene copolymers.

The melt flow rate (MFR) of the propylene copolymer is preferably 2.5 g/10 min or more, more preferably 2.7 g/10 min or more, even more preferably 3.0 g/10 min or more, preferably 20 g/10 min or less, more preferably 17 g/10 min or less, even more preferably 12 g/10 min or less. When the melt flow rate of the propylene copolymer is in the above range, the heat sealability of the film is good.

In order to provide the laminated film of the present invention with sufficient heat seal strength, the lower limit of the melting point of the polyolefin resin (preferably a propylene copolymer) constituting the heat-sealing layer is preferably 60°C, more preferably 65°C, and even more preferably 70°C. If the lower limit of the melting point is too low, the heat-sealed portion may have poor heat resistance, while if the melting point is too high, improvement in heat seal strength may not be expected. Therefore, the upper limit of the melting point is preferably 150°C, more preferably 140°C, and even more preferably 135°C. If the lower limit of the melting point is too low, the heat-sealed portion may have poor heat resistance, while if the melting point is too high, improvement in heat seal strength may not be expected.

The propylene copolymer is preferably a propylene-α-olefin copolymer, and may be a random copolymer or a block copolymer, with a random copolymer being preferred.
The α-olefin is preferably an α-olefin monomer having 2 or 4 to 10 carbon atoms, and the α-olefin monomer having 2 or 4 to 10 carbon atoms is more preferably ethylene, butene, pentene, hexene, octene, decene, or the like.

The propylene copolymer (preferably a propylene-α-olefin copolymer) is preferably a propylene-ethylene copolymer, a propylene-butene copolymer, a propylene-pentene copolymer, a propylene-methylpentene copolymer, a propylene-hexene copolymer, a propylene-octene copolymer, a propylene-ethylene-butene copolymer, or the like, more preferably a propylene-ethylene copolymer, a propylene-butene copolymer, or a propylene-ethylene-butene copolymer, and even more preferably a propylene-butene copolymer or a propylene-ethylene-butene copolymer.

The above-mentioned propylene copolymer can be exemplified by a polymer synthesized by the continuous gas phase polymerization method described in JP-A-2003-277412, for example, FSX66E8 manufactured by Sumitomo Chemical Co., Ltd. and SP8931 manufactured by Sumitomo Chemical Co., Ltd.

The propylene copolymer preferably contains at least one type selected from propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) in which the copolymerization ratio of α-olefin is 1.0 mol% or less and propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) in which the copolymerization ratio of α-olefin is greater than 1.0 mol%, and more preferably contains propylene-α-olefin copolymers (wherein the α-olefin has 2 or 4 to 10 carbon atoms) in which the copolymerization ratio of α-olefin is greater than 1.0 mol%.

The propylene copolymer preferably contains two or more propylene-α-olefin copolymers (the α-olefin has 2 or 4 to 10 carbon atoms) with a copolymerization ratio of α-olefin exceeding 1.0 mol%, and more preferably contains a propylene-α-olefin copolymer (the α-olefin has 2 or 4 to 10 carbon atoms) with a copolymerization ratio of α-olefin exceeding 1.0 mol% and not exceeding 15 mol%, and a propylene-α-olefin copolymer (the α-olefin has 2 or 4 to 10 carbon atoms) with a copolymerization ratio of α-olefin exceeding 15 mol% and not exceeding 45 mol%.

The copolymerization ratio of α-olefins in a propylene-α-olefin copolymer (wherein the number of carbon atoms in the α-olefin is 2 or 4 to 10) having a copolymerization ratio of more than 1.0 mol% and not more than 15 mol% is preferably 2 mol% or more, more preferably 3 mol% or more, even more preferably 4 mol% or more, even more preferably 5 mol% or more, and is preferably 15 mol% or less, more preferably 13 mol% or less, even more preferably 11 mol% or less, and even more preferably 10 mol% or less.

The copolymerization ratio of ethylene in a propylene-α-olefin copolymer (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin exceeding 1.0 mol% and not exceeding 15 mol% is preferably 1 mol% or more, more preferably 1.5 mol% or more, even more preferably 1.7 mol% or more, even more preferably 2 mol% or more, and is preferably 7 mol% or less, more preferably 6 mol% or less, even more preferably 5 mol% or less, and even more preferably 4 mol% or less.

The copolymerization ratio of butene in a propylene-α-olefin copolymer (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin exceeding 1.0 mol% and not exceeding 15 mol% is preferably 2 mol% or more, more preferably 3 mol% or more, even more preferably 4 mol% or more, even more preferably 5 mol% or more, and is preferably 12 mol% or less, more preferably 11 mol% or less, even more preferably 10 mol% or less, even more preferably 9 mol% or less.

The copolymerization ratio of α-olefins in a propylene-α-olefin copolymer (wherein the number of carbon atoms in the α-olefin is 2 or 4 to 10) having a copolymerization ratio of more than 15 mol% and not more than 45 mol% is preferably 18 mol% or more, more preferably 21 mol% or more, even more preferably 24 mol% or more, even more preferably 27 mol% or more, and is preferably 45 mol% or less, more preferably 40 mol% or less, even more preferably 35 mol% or less, and even more preferably 33 mol% or less.

The copolymerization ratio of butene in a propylene-α-olefin copolymer (wherein the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin exceeding 15 mol% and not exceeding 45 mol% is preferably 15 mol% or more, more preferably 18 mol% or more, even more preferably 21 mol% or more, even more preferably 24 mol% or more, and is preferably 45 mol% or less, more preferably 40 mol% or less, even more preferably 35 mol% or less, and even more preferably 33 mol% or less. There is no particular upper limit to the butene content, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be determined appropriately within a range that does not cause such defects.

The propylene-α-olefin copolymer (α-olefin having 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin exceeding 1.0 mol % and not more than 15 mol % is preferably a propylene-ethylene-butene copolymer.
The propylene-α-olefin copolymer (α-olefin having 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of more than 15 mol % and not more than 45 mol % is preferably a propylene-butene copolymer.

The polyolefin resin composition that constitutes the heat-sealing layer contains 60% by weight or more of a propylene copolymer, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, even more preferably 95% by weight or more, and particularly preferably 100% by weight.

The polyolefin resin composition that constitutes the heat-sealing layer contains a propylene-α-olefin copolymer (the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of more than 1.0 mol% and not more than 15 mol%, preferably from 1 wt% to 50 wt%, more preferably from 5 wt% to 45 wt%, and even more preferably from 10 wt% to 40 wt%.
If the blending amount of the propylene-α-olefin copolymer having a copolymerization ratio of α-olefin exceeding 1.0 mol % and not more than 15 mol % is too high, the fusion strength during sealing will be low and it may be difficult to obtain sufficient heat seal strength. On the other hand, if the blending amount is too low, there will be no particular problem with the heat seal performance, but if the amount of antiblocking agent added is insufficient, there is a concern that the handling properties during use will be poor.

The polyolefin resin composition that constitutes the heat-sealing layer contains a propylene-α-olefin copolymer (the α-olefin has 2 or 4 to 10 carbon atoms) having a copolymerization ratio of α-olefin of more than 15 mol% and not more than 45 mol%, preferably from 50% by weight to 99% by weight, more preferably from 55% by weight to 95% by weight, and even more preferably from 60% by weight to 90% by weight.
If the blending amount of the propylene-α-olefin copolymer having a copolymerization ratio of α-olefin exceeding 15 mol % and not exceeding 45 mol % is too small, the fusion strength during sealing will be low and it may be difficult to obtain sufficient heat seal strength. On the other hand, if the blending amount is too large, there will be no particular problem with the heat seal performance, but if the amount of antiblocking agent added is insufficient, there is a concern that the handling properties during use will be poor.

Various additives and fillers may be added to each layer constituting the stretched laminated polyolefin resin film of the present invention as necessary, provided that the properties of each layer are not impaired. Examples include heat stabilizers, antioxidants, light stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments, dyes, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, zinc oxide, magnesium oxide, aluminum oxide, antibacterial agents, and additives that impart natural decomposition properties. In addition, thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, and petroleum resins other than those mentioned above can also be added to the film, provided that the properties of the laminated film are not impaired.

The stretched laminated polyolefin resin film of the present invention may be subjected to a surface treatment as necessary (e.g., to improve printability) as long as the properties of the film are not impaired. Examples of surface treatment methods include corona discharge treatment, plasma treatment, flame treatment, and acid treatment. Among the above-mentioned methods, corona discharge treatment, plasma treatment, and flame treatment are preferred because they allow continuous treatment and can be easily carried out before the winding process during film production. In particular, corona discharge treatment is recommended as a means of improving wetting tension.

The stretched laminated polyolefin resin film of the present invention preferably satisfies the relationship: film thickness of the base layer > film thickness of the intermediate layer > film thickness of the heat-sealing layer. When the above relationship is satisfied, it is possible to improve heat resistance and stiffness.

In the stretched laminated polyolefin resin film of the present invention, the ratio of the base layer is preferably 30% or more and 94% or less (more preferably 40% or more and 88% or less, even more preferably 50% or more and 82% or less) of the total thickness of the stretched laminated polyolefin resin film, the ratio of the heat-sealing layer is preferably 1% or more and 20% or less (more preferably 2% or more and 15% or less, even more preferably 2% or more and 10% or less, even more preferably 4% or more and 10% or less) of the total thickness of the stretched laminated polyolefin resin film, and the ratio of the intermediate layer is preferably 5% or more and less than 50% (more preferably 10% or more and 45% or less, even more preferably 15% or more and 40% or less) of the total thickness of the stretched laminated polyolefin resin film. If the ratio of the base layer is less than 30%, the ratio of the heat-sealing layer is more than 20%, and the ratio of the intermediate layer is 50% or more, it tends to be difficult to obtain a firm feel in the laminated film, which is not preferable in terms of handling the product. Furthermore, if the ratio of the base layer exceeds 94%, the ratio of the heat-sealing layer is less than 1%, and the ratio of the intermediate layer is less than 5%, it may be difficult to obtain the desired heat seal strength.

In the present invention, the thickness of the film is set arbitrarily according to each application, but the lower limit is preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more. On the other hand, the upper limit of the thickness is preferably 300 μm or less, more preferably 250 μm or less, even more preferably 200 μm or less, and particularly preferably 150 μm or less. If the thickness is thin, handling is likely to be poor. On the other hand, if the thickness is thick, not only is there a problem in terms of cost, but also poor flatness due to rolling tendencies is likely to occur when the film is wound up and stored in a roll. The suitable film thickness range when considering the volume reduction of the film and productivity during processing will be described later.

The stretched laminated polyolefin resin film having no gas barrier layer is preferably transparent.
From the viewpoint of visibility of contents, the haze of the stretched laminated polyolefin resin film of the present invention is preferably 6% or less, more preferably 5% or less, even more preferably 4% or less, and preferably 0.1% or more, 0.5% or more, or 1% or more. Haze tends to deteriorate, for example, when the stretching temperature or heat setting temperature is too high, when the cooling roll (CR) temperature is high and the cooling rate of the stretched raw sheet is slow, or when there is too much low molecular weight, so it can be controlled within the above range by adjusting these.

The configuration of the stretched laminated polyolefin resin film of the present invention is not particularly limited as long as it comprises the above-mentioned base layer, intermediate layer, and heat-sealing layer, and the present invention also includes an embodiment in which a polypropylene resin layer of the same type as the constituent resin of the base layer or another resin layer for imparting various properties to the laminated film (e.g., a gas barrier resin layer such as a saponified ethylene-vinyl acetate copolymer or polyvinyl alcohol) is laminated on the surface of the base layer. In addition, the lamination position of the other resin layer is not limited as long as the properties of the laminated film are not impaired, and for example, the above-mentioned other layers can be provided between the base layer and intermediate layer, or between the intermediate layer and the heat-sealing layer.

Among them, it is preferable that the stretched laminated polyolefin resin film of the present invention comprises a base layer, an intermediate layer, and a heat-sealing layer in this order, with no other layers present between the base layer and the intermediate layer, and no other layers present between the intermediate layer and the heat-sealing layer.

The method for producing the stretched laminated polyolefin resin film of the present invention is not particularly limited, and it can be produced by any conventionally known method. For example, it can be produced by melt laminating using an extruder suitable for the number of layers by a T-die method, inflation method, or the like, and then cooling by a cooling roll method, water cooling method, or air cooling method to produce an unstretched laminated film, which is then stretched by a sequential biaxial stretching method, simultaneous biaxial stretching method, tube stretching method, or the like. Among these, the sequential biaxial stretching method is particularly preferred from the viewpoint of good flatness, dimensional stability, heat resistance, thickness unevenness, etc.

In the sequential biaxial orientation method, for example, polypropylene resin is heated and melted in a single-screw or twin-screw extruder until the resin temperature reaches 200°C or higher and 280°C or lower (preferably 220°C or higher, and more preferably 240°C or higher), formed into a sheet from a T-die, and extruded onto a chill roll at a temperature of 10°C or higher and 100°C or lower (preferably 80°C or lower, more preferably 60°C or lower, and even more preferably 40°C or lower) to obtain an unstretched sheet. Next, the film is roll-drawn in the longitudinal direction (MD direction) at 120° C. or more and 165° C. or less (preferably 120° C. or more and 150° C. or less, more preferably 122° C. or more and 135° C. or less) to 3.0 times or more and 8.0 times or less (preferably 3.5 times or more and 7.5 times or less, more preferably 4.0 times or more and 7.0 times or less), and then, after preheating with a tenter, it can be stretched in the transverse direction (TD direction) at 155° C. or more and 175° C. or less (preferably 157° C. or more and 170° C. or less, more preferably 159° C. or more and 165° C. or less) to 4.0 times or more and 20.0 times or less (preferably 5.0 times or more and 15.0 times or less, more preferably 6.0 times or more and 10.0 times or less). Furthermore, after biaxial stretching, the film can be heat-set at a temperature of 165°C to 175°C (preferably 166°C to 174°C, more preferably 167°C to 173°C) while relaxing by 1% to 15% (preferably 2% to 12%, more preferably 3% to 9%).

[Gas barrier layer]
In the present invention, the film has a gas barrier layer on the surface of the base layer. As the gas barrier layer, it is preferable to laminate either a coating layer (A) mainly composed of an organic substance or an inorganic thin film layer (B) mainly composed of an inorganic substance, which will be described later. Furthermore, in order to support the barrier properties of the gas barrier layer, an anchor coat (C) or a protective layer (D), which will be described later, can also be laminated in combination.

The stretched laminated polyolefin resin film of the present invention preferably has a configuration such as coating layer/substrate layer/intermediate layer/thermal adhesion layer, inorganic thin film layer/substrate layer/intermediate layer/thermal adhesion layer, inorganic thin film layer/anchor coat layer/substrate layer/intermediate layer/thermal adhesion layer, or protective layer/inorganic thin film layer/anchor coat layer/substrate layer/intermediate layer/thermal adhesion layer.
The gas barrier properties of the coating layer are higher than those of the inorganic thin film layer, and the gas barrier properties tend to be higher when a protective layer and/or an anchor coat layer is further provided.

[Coating layer (A)]
In the present invention, it is preferable to provide a coating layer (A) as a gas barrier layer. However, in the present invention, it is necessary to design the coating layer (A) while taking into consideration the environmental load, such as increased costs due to an increase in the number of steps and difficulty in recycling depending on the film thickness.

The gas barrier layer is preferably a coating layer containing at least one of a polyvinyl alcohol resin, a polyester resin, a polyurethane resin, and an inorganic layered compound.
As the resin composition used for the coating layer (A) formed on the surface of the laminated film of the present invention, it is desirable to use any one of polyvinyl alcohol polymers, polyester resins, and polyurethane resins. Among them, polyvinyl alcohol polymers are more preferable from the viewpoint of improving barrier performance. Polyvinyl alcohol polymers are mainly composed of vinyl alcohol units, and a significant improvement in barrier performance due to high cohesiveness caused by a hydrogen bond structure can be expected. The polymerization degree and saponification degree of the polyvinyl alcohol polymer are determined based on the target gas barrier property and the viscosity of the coating aqueous solution. Regarding the polymerization degree, since the aqueous solution has a high viscosity and is prone to gelation, coating becomes difficult, and from the viewpoint of coating workability, it is preferably 2600 or less, more preferably 2500 or less, and even more preferably 2400 or less. Regarding the saponification degree, if it is less than 90%, sufficient oxygen gas barrier property cannot be obtained under high humidity, and if it exceeds 99.7%, it is difficult to adjust the aqueous solution, it is prone to gelation, and it is not suitable for industrial production. Therefore, the saponification degree is preferably 90 to 99.7%, and more preferably 93 to 99%. In the present invention, various copolymerized or modified polyvinyl alcohol polymers, such as polyvinyl alcohol polymers copolymerized with ethylene and silanol-modified polyvinyl alcohol polymers, can also be used within the scope of not impairing processability or productivity.

The coating layer (A) of the present invention may contain an inorganic layered compound. The presence of an inorganic layered compound is expected to provide a labyrinth effect for gases, improving the gas barrier properties. In addition, the addition of an inorganic layered compound can suppress the humidity dependency of the gas barrier properties. Examples of materials include clay minerals (including synthetic products thereof) such as smectite, kaolin, mica, hydrotalcite, and chlorite. Specific examples include montmorillonite, beidellite, saponite, hectorite, sauconite, stevensite, kaolinite, nacrite, dickite, halloysite, hydrated halloysite, tetrasilylic mica, sodium teniolite, muscovite, margarite, phlogopite, talc, antigorite, chrysotile, pyrophyllite, vermiculite, xanthophyllite, and chlorite. Furthermore, scaly silica and the like can also be used as an inorganic layered compound. These may be used alone or in combination of two or more types. Of these, smectite (including its synthetic products) is particularly preferred because it is highly effective in improving water vapor barrier properties.

As the inorganic layered compound, those containing metal ions, particularly iron ions, having redox properties are preferred. Among these, montmorillonite, a type of smectite, is preferred from the viewpoints of coating suitability and gas barrier properties. As the montmorillonite, known compounds that have been used in gas barrier agents can be used.
For example, the following general formula:
(X, Y) _2~3 Z ₄ O ₁₀ (OH) ₂・mH ₂ O・(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. H ₂ O represents interlayer water. m and ω represent positive real numbers.)
Among these, those in which W in the formula is Na are preferred from the viewpoint of cleavage in an aqueous medium.

The size and shape of the inorganic layered compound are not particularly limited, but the particle size (long 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 is poor, and as a result, the coatability and coat appearance of the coating layer (A) may deteriorate. On the other hand, the aspect ratio is preferably 50 to 5000, more preferably 100 to 4000, and even more preferably 200 to 3000.

The compounding ratio of the resin composition and the inorganic layered compound in the coating layer of the present invention (resin composition/inorganic layered compound) is preferably 75/25 to 35/65 (wt %), more preferably 70/30 to 40/60 (wt %), and even more preferably 65/35 to 45/55 (wt %). If the compounding ratio of the inorganic layered compound is less than 25 wt %, there is a risk of insufficient barrier performance. On the other hand, if it is more than 65 wt %, there is a risk of poor dispersibility, which may lead to poor coatability and poor adhesion.

In order to improve the cohesive strength and the heat and moisture resistance adhesion of the film, various crosslinking agents may be blended in the coating layer (A) of the present invention, as long as they do not impair gas barrier properties or productivity. Examples of crosslinking agents include silicon-based crosslinking agents, oxazoline compounds, carbodiimide compounds, epoxy compounds, isocyanate compounds, etc. Among them, by blending a silicon-based crosslinking agent, a crosslinking reaction can be caused with a resin composition having a hydroxyl group or an inorganic thin film layer, and from the viewpoint of improving water-resistant adhesion, a silicon-based crosslinking agent is particularly preferred. Examples of commonly used silicon-based crosslinking agents include metal alkoxides and silane coupling agents. Metal alkoxides are compounds represented by the general formula M(OR) _n (M: Si, metal of Al, R: alkyl groups such as _CH3 , _{C2H5 ,} etc.). Specifically, tetraethoxysilane [Si( _OC2H5 ) ₄ ], _{triisopropoxyaluminum} Al[OCH( _CH3 ) ₂ ] ₃ , etc. can be exemplified. Examples of silane coupling agents include those having an epoxy group such as 3-glycidoxypropyltrimethoxysilane, those having an amino group such as 3-aminopropyltrimethoxysilane, those having a mercapto group such as 3-mercaptopropyltrimethoxysilane, those having an isocyanate group such as 3-isocyanatepropyltriethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate. In addition, oxazoline compounds, carbodiimide compounds, epoxy compounds, etc. may be used in combination as crosslinking agents. However, when emphasis is placed on recyclability, the amount of crosslinking agent to be used must be considered.

When a crosslinking agent is added, its amount in the composition constituting the coating layer is preferably 0.1 to 50% by weight, more preferably 0.5 to 50% by weight, and even more preferably 1.0 to 50% by weight. By keeping it within the above range, the film hardens and the cohesive strength improves, resulting in a film with excellent water-resistant adhesion. If the amount of crosslinking agent added exceeds 50% by weight, the amount of uncrosslinked portions increases, or the film hardens due to excessive hardening, which may in turn reduce adhesion. On the other hand, if the amount added is less than 0.1% by weight, there is a risk that sufficient cohesive strength will not be obtained.

In the present invention, the haze of the film after lamination of the coating layer (A) is preferably 20% or less, more preferably 18% or less, and even more preferably 16% or less, from the viewpoint of visibility of the contents. If the haze is more than 20%, in addition to significantly reducing transparency, there is a concern that it may affect the unevenness of the surface, which may lead to poor appearance in the subsequent printing process. The haze can be adjusted by the composition ratio of the coating layer (A), the solvent conditions, the film thickness, etc. Here, the haze is evaluated in accordance with JIS K7136 using a turbidity meter (NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

The coating layer (A) preferably has a coating weight of 0.10 to 3.0 (g/m ² ). The coating layer (A) is more preferably 0.15 (g/m ² ) or more, even more preferably 0.20 (g/m ² ) or more, even more preferably 0.25 (g/m ² ) or more, and is preferably 2.5 (g/m ² ) or less, more preferably 2.0 (g/m ² ) or less, and even more preferably 1.5 (g/m ² ) or less. If the coating layer (A) has a coating weight of more than 3.0 (g/m ² ), the gas barrier properties are improved, but the cohesive force inside the coating layer is insufficient and the uniformity of the coating layer is also reduced, so that the coat may have unevenness (haze increase, whitening) or defects in the appearance, or the gas barrier properties and adhesive properties may not be fully expressed. In terms of processability, the thick film thickness may cause blocking. Furthermore, there is a concern that this may adversely affect the recyclability of the film, and the environmental impact will be greater due to the increased amounts of raw materials, solvents, etc. On the other hand, if the amount of coating layer (A) is less than 0.10 (g/ ^m2 ), sufficient gas barrier properties and interlayer adhesion may not be obtained.

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

When forming the coating layer (A), it is preferable to apply the resin composition for the coating layer, pre-dry it at a relatively low temperature to evaporate the solvent, and then dry it 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 less than 80°C, there is a risk that the coating layer will not be sufficiently dried. Also, if the pre-drying temperature is higher than 110°C, the drying will proceed before the coating layer has spread wet, which may result in a poor appearance.

On the other hand, the main drying temperature is preferably 110 to 140°C, more preferably 115 to 135°C, and even more preferably 120 to 130°C. If the main drying temperature is less than 110°C, the film formation of the coating layer (A) will not proceed, and the cohesive strength and adhesiveness will decrease, which may result in a negative effect on the barrier properties. If the temperature exceeds 140°C, the film may become too hot, making it brittle and causing large wrinkles due to heat shrinkage.

The preferred drying time for preliminary 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. The preferred drying time for 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, care must be taken as the drying conditions vary depending on the heat transfer medium method and the intake and exhaust conditions of the drying furnace. In addition to drying, additional heat treatment for 1 to 4 days in as low a temperature range as possible, specifically in the temperature range of 40 to 60°C, is also more effective in accelerating the formation of the coating layer (A).

[Inorganic thin film layer (B)]
In the present invention, it is preferable to provide an inorganic thin film layer (B) as a gas barrier layer on the surface of the base layer of the film. The inorganic thin film layer (B) is preferably a thin film made of a metal or an inorganic oxide. There are no particular limitations on the material that forms the layer as long as it can be made into a thin film. From the viewpoint of gas barrier properties, metals such as aluminum, silicon oxide (silica), aluminum oxide (alumina), mixtures of silicon oxide and aluminum oxide, etc. Examples of inorganic oxides include:
That is, the gas barrier layer is preferably an inorganic thin film layer made of any one of aluminum, aluminum oxide, silicon oxide, and a composite oxide of silicon oxide and aluminum oxide. It is more preferable that the inorganic thin film layer is made of any one of composite oxides of aluminum.
In particular, a composite oxide of silicon oxide and aluminum oxide is preferred from the viewpoint of achieving both flexibility and density of the thin film layer. In this composite oxide, the mixture ratio of silicon oxide and aluminum oxide is 1/2 to 1/2 of the metal content. The mass ratio (Al/(Al+Si)×100) of Al is preferably in the range of 20 to 70% by weight, more preferably in the range of 25 to 65% by weight, and still more preferably in the range of 30 to 60% by weight. If the Al ratio is less than 20% by weight, the water vapor barrier property may be reduced. On the other hand, if the Al ratio exceeds 70% by weight, the inorganic thin film layer tends to become hard, which makes it difficult to perform printing or other operations. There is a risk that the film will be destroyed during secondary processing such as lamination, resulting in a decrease in gas barrier properties. Note that silicon oxide here refers to various silicon oxides such as SiO and _SiO2 , or mixtures thereof, and aluminum oxide are various aluminum oxides such as AlO and _{Al2O3 ,} or mixtures thereof.

The thickness of the inorganic thin film layer (B) is usually 1 to 100 nm, preferably 5 to 95 nm, and more preferably 7 to 90 nm. If the thickness of the inorganic thin film layer (B) is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties, while if the thickness is excessively greater than 100 nm, the corresponding improvement in gas barrier properties cannot be obtained, and it is rather disadvantageous in terms of flex resistance and production costs.
In particular, the thickness of the aluminum thin film layer is, for example, 20 to 100 nm, preferably 30 to 90 nm, more preferably 40 to 80 nm, and further preferably 50 to 80 nm.
The thickness of the silicon oxide thin film layer is, for example, 10 to 80 nm, preferably 20 to 70 nm, and more preferably 30 to 60 nm.
The thickness of the silicon oxide and aluminum oxide layers is, for example, 5 to 60 nm, preferably 10 to 50 nm, and more preferably 15 to 40 nm.

The method for forming the inorganic thin film layer (B) 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 (B) 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 changed as desired by applying a bias to the deposition target (a laminated film to be deposited), 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.

[Anchor Coat Layer (C)]
It is preferable that an anchor coat layer is laminated between the film and the gas barrier layer.
In the present invention, it is preferable to provide an anchor coat layer (C) as an auxiliary layer for achieving sufficient gas barrier properties and adhesiveness when the above-mentioned gas barrier layer is laminated. By providing an anchor coat layer, it is possible to suppress the exposure of oligomers and antiblocking materials from the polypropylene resin. Furthermore, when other layers are laminated on the anchor coat layer (C), it is also possible to increase the adhesion between layers. In particular, in the formation of an inorganic thin film layer, not only adhesion but also the effect of promoting the formation of the inorganic layer by smoothing the surface can be expected, which improves the gas barrier properties. In addition, by using a material having a certain degree of gas barrier properties (referred to as gas barrier auxiliary properties) for the anchor coat layer (C) itself, it is possible to greatly improve the gas barrier performance of the film when the above-mentioned gas barrier layer is laminated. Furthermore, the anchor coat layer (C) prevents the intrusion of hot water into the substrate, and as a result, it is possible to reduce the whitening of the film after boiling or retorting.

As for the gas barrier properties of the film when only the anchor coat layer (C) is laminated, it is preferable that the oxygen transmission rate in a 23°C x 65% RH environment is 10000 ml/ ^m2 d MPa or less, from the viewpoint of exhibiting good gas barrier properties after lamination of the above-mentioned gas barrier layer, and more preferably 9000 ml/ ^m2 d MPa or less, and even more preferably 8000 ml/ ^m2 d MPa or less. If the oxygen transmission rate exceeds 10000 ml/ ^m2 d MPa, sufficient barrier performance cannot be obtained even after lamination of the gas barrier layer, and it becomes difficult to meet the needs of applications requiring high gas barrier properties.

In the present invention, the adhesion amount of the anchor coat layer (C) is preferably 0.10 to 1.0 g/m ^2. This allows the anchor coat layer (C) to be uniformly controlled during coating, resulting in a film with few coating unevenness and defects. Furthermore, the anchor coat layer (C) contributes to suppressing oligomer exposure, stabilizing the haze after retort wet heat. The adhesion amount of the anchor coat layer (C) is preferably 0.15 g/m ² or more, more preferably 0.20 g/m 2 or more, and even more preferably 0.35 g/m ² or more, and is preferably 0.950 g/m ² or less, more preferably 0.90 g/m ² or ^less , and even more preferably 0.85 g/m ² or less. If the adhesion amount of the anchor coat layer (C) exceeds 1.0 g/m ² , the gas barrier property is improved, but the cohesive force inside the anchor coat layer becomes insufficient and the uniformity of the anchor coat layer is also reduced, resulting in unevenness and defects in the coat appearance. In terms of processability, a thick film thickness may cause blocking or increase manufacturing costs. Furthermore, there is a concern that the recyclability of the film may be adversely affected, and the amount of raw materials, solvents, etc. used increases, which increases the environmental impact. On the other hand, if the film thickness of the anchor coat layer (C) is less than 0.10 g/ ^m2 , sufficient gas barrier properties and interlayer adhesion may not be obtained.

The resin composition used in the anchor coat layer (C) of the present invention may be a resin such as a urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, or polybutadiene-based resin to which a curing agent such as an epoxy-based, isocyanate-based, or melamine-based curing agent has been added. It may further contain a crosslinking agent such as a silicon-based crosslinking agent, an oxazoline compound, a carbodiimide compound, or an epoxy compound.
In particular, urethane resins are preferred because, in addition to the barrier performance due to the high cohesiveness of the urethane bond itself, the polar group interacts with the gas barrier layer, and the presence of amorphous parts gives flexibility, so that damage can be suppressed even when a bending load is applied. Polyester resins are also preferred because they can be expected to have the same effect. In the present invention, it is particularly preferred to contain polyurethane containing polyester resin and isocyanate curing agent as constituents, and it is more preferred to add a silicon-based crosslinking agent from the viewpoint of improving adhesion.

The urethane resin used in the anchor coat layer (C) of the present invention is preferably a urethane resin containing an aromatic or aromatic aliphatic diisocyanate component as the main constituent component from the viewpoint of gas barrier auxiliary properties. Among them, it is particularly preferable to contain a metaxylylene diisocyanate component. By using the above resin, the cohesive strength of the urethane bond can be further increased due to the stacking effect between the aromatic rings, resulting in good gas barrier auxiliary properties.

In the present invention, the proportion of aromatic or araliphatic diisocyanate in the urethane resin used in the anchor coat layer (C) is preferably in the range of 50 mol % or more (50 to 100 mol %) in 100 mol % of the polyisocyanate component. The total proportion of aromatic or araliphatic diisocyanate is more preferably 60 to 100 mol %, even more preferably 70 to 100 mol %, and even more preferably 80 to 100 mol %. If the total proportion of aromatic or araliphatic diisocyanate is less than 50 mol %, good gas barrier auxiliary properties may not be obtained.

The urethane resin used in the anchor coat layer (C) of the present invention may be blended with various crosslinking agents for the purpose of improving the cohesive strength of the film and improving the wet heat resistance adhesion. Examples of crosslinking agents include silicon-based crosslinking agents, oxazoline compounds, carbodiimide compounds, epoxy compounds, etc. Among these, silicon-based crosslinking agents are particularly preferred from the viewpoint that blending a silicon-based crosslinking agent can improve the water-resistant adhesion, particularly with the inorganic thin film layer. Other crosslinking agents such as oxazoline compounds, carbodiimide compounds, and epoxy compounds may also be used in combination.

As the silicon-based crosslinking agent, a silane coupling agent is preferred from the viewpoint of crosslinking inorganic and organic substances. Examples of the silane coupling agent include hydrolyzable alkoxysilane compounds, such as halogen-containing alkoxysilanes (chloro C2-4 alkyl tri C1-4 alkoxysilanes such as 2-chloroethyl trimethoxysilane, 2-chloroethyl triethoxysilane, 3-chloropropyl trimethoxysilane, and 3-chloropropyl triethoxysilane), alkoxysilanes having an epoxy group [glycidyloxy C2-4 alkyl tri C1-4 alkoxysilanes such as 2-glycidyloxyethyl trimethoxysilane, 2-glycidyloxyethyl triethoxysilane, 3-glycidyloxypropyl trimethoxysilane, and 3-glycidyloxypropyl triethoxysilane, glycidyloxy di C such as 3-glycidyloxypropyl methyl dimethoxysilane and 3-glycidyloxypropyl methyl diethoxysilane, etc. 2-4 alkyl di C1-4 alkoxy silanes, 2-(3,4-epoxycyclohexyl) ethyl trimethoxy silane, 2-(3,4-epoxycyclohexyl) ethyl triethoxy silane, 3-(3,4-epoxycyclohexyl) propyl trimethoxy silane and other (epoxy cycloalkyl) C2-4 alkyl tri C1-4 alkoxy silanes, alkoxy silanes having amino groups (amino C2-4 alkyl tri C1-4 alkoxy silanes such as 2-aminoethyl trimethoxy silane, 3-aminopropyl trimethoxy silane, 3-aminopropyl triethoxy silane, amino di C2-4 alkyl di C1-4 alkoxy silanes such as 3-aminopropyl methyl dimethoxy silane, 3-aminopropyl methyl diethoxy silane, 2-[N-(2-aminoethyl) amino] ethyl trimethoxy silane, 3-[N- (2-amino C2-4 alkyl)amino C2-4 alkyl tri C1-4 alkoxysilanes such as (2-aminoethyl)amino]propyl trimethoxysilane and 3-[N-(2-aminoethyl)amino]propyl triethoxysilane, (amino C2-4 alkyl)amino di C2-4 alkyl di C1-4 alkoxysilanes such as 3-[N-(2-aminoethyl)amino]propyl methyl dimethoxysilane and 3-[N-(2-aminoethyl)amino]propyl methyl diethoxysilane, etc.), alkoxysilanes having a mercapto group (mercapto C2-4 alkyl tri C1-4 alkoxysilanes such as 2-mercaptoethyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane and 3-mercaptopropyl triethoxysilane, 3-mercaptopropyl methyl dimethoxysilane, 3-mercaptopropyl methyl mercaptodiC2-4 alkyldiC1-4 alkoxysilanes such as diethoxysilane), alkoxysilanes having a vinyl group (vinyltrimethoxysilane, vinyltriethoxysilane, etc.), alkoxysilanes having an ethylenically unsaturated bond group [(meth)acryloxyC2-4 alkyltriC1-4 alkoxysilanes such as 2-(meth)acryloxyethyltrimethoxysilane, 2-(meth)acryloxyethyltriethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, (meth)acryloxydiC2-4 alkyldiC1-4 alkoxysilanes such as 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, etc.], etc. These silane coupling agents can be used alone or in combination of two or more. Of these silane coupling agents, silane coupling agents having an amino group are preferred, (2-amino C2-4 alkyl) amino C2-4 alkyl tri C1-4 alkoxy silane is more preferred, and 3-[N-(2-aminoethyl) amino] propyl trimethoxy silane is even more preferred.

The silicon-based crosslinking agent is preferably added in an amount of 0.05 to 4.00% by weight to the composition that constitutes the coating layer, more preferably 0.10 to 3.50% by weight, and even more preferably 0.15 to 3.00% by weight. The addition of a silicon-based crosslinking agent promotes hardening of the film and improves cohesive strength, resulting in a film with excellent water-resistant adhesion, and is also expected to have the effect of preventing the exposure of oligomers. If the amount added exceeds 4.00% by weight, the film will harden and improve cohesive strength, but some unreacted areas will be produced, and there is a risk of reduced adhesion between layers. On the other hand, if the amount added is less than 0.05% by weight, there is a risk that sufficient cohesive strength will not be obtained.

The polyester resin used in the anchor coat layer (C) of the present invention is produced by polycondensation of a polyvalent carboxylic acid component and a polyhydric alcohol component. There are no particular restrictions on the molecular weight of the polyester resin as long as it can provide sufficient film toughness, coatability, and solvent solubility as a coating material, but the number average molecular weight is preferably 1,000 to 50,000, and more preferably 1,500 to 30,000. There are also no particular restrictions on the functional group at the polyester end, and it may be an alcohol end, a carboxylic acid end, or both. However, when an isocyanate-based curing agent is used in combination, it is necessary to use a polyester polyol that is mainly alcohol-terminated.

The Tg of the polyester resin used in the anchor coat layer (C) of the present invention is preferably 10°C or higher. If the temperature is lower than this, the resin will become sticky after the coating operation and will be prone to blocking, making the winding operation after coating difficult. If the Tg is less than 10°C, it will be difficult to prevent blocking even under conditions where the pressure near the winding core is high, even with the addition of an anti-blocking agent. The Tg is more preferably 15°C or higher, even more preferably 20°C or higher, preferably 70°C or lower, and more preferably 60°C or lower.

The polyester resin used in the anchor coat layer (C) of the present invention is a polycondensate of a polyvalent carboxylic acid component and a polyhydric alcohol component. The polyvalent carboxylic acid component of the polyester resin used in the present invention contains, for example, at least one of ortho-oriented aromatic dicarboxylic acids or their anhydrides. The ortho-orientation improves solubility in solvents, making it possible to coat the substrate uniformly. A uniformly coated film reduces the variation in barrier performance, which ultimately contributes to the suppression of oligomer whitening. In addition, the ortho-orientation results in a film with excellent flexibility and improved interfacial adhesion, which reduces damage to the substrate caused by wet heat treatment and leads to the suppression of oligomers.

Aromatic polycarboxylic acids or anhydrides in which the carboxylic acid is substituted at the ortho position include orthophthalic acid or anhydride, naphthalene 2,3-dicarboxylic acid or anhydride, naphthalene 1,2-dicarboxylic acid or anhydride, anthraquinone 2,3-dicarboxylic acid or anhydride, and 2,3-anthracene carboxylic acid or anhydride. These compounds may have a substituent at any carbon atom of the aromatic ring. Examples of the substituent include a chloro group, a bromo group, a methyl group, an ethyl group, an i-propyl group, a hydroxyl group, a methoxy group, an ethoxy group, a phenoxy group, a methylthio group, a phenylthio group, a cyano group, a nitro group, an amino group, a phthalimido group, a carboxyl group, a carbamoyl group, an N-ethylcarbamoyl group, a phenyl group, or a naphthyl group. Furthermore, polyester polyols with a content of 70 to 100 mol% relative to 100 mol% of the total polycarboxylic acid components are particularly preferred because they are highly effective in improving barrier properties and have excellent solvent solubility, which is essential for coating materials.

In the present invention, other polycarboxylic acid components may be copolymerized within the scope that does not impair the effects of the invention. Specifically, examples of aliphatic polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid; examples of unsaturated bond-containing polycarboxylic acids include maleic anhydride, maleic acid, and fumaric acid; examples of alicyclic polycarboxylic acids include 1,3-cyclopentanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid; examples of aromatic polycarboxylic acids include terephthalic acid, isophthalic acid, pyromellitic acid, trimellitic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, diphenic acid and its anhydride, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, and anhydrides or ester-forming derivatives of these dicarboxylic acids; p-hydroxybenzoic acid, p-(2-hydroxyethoxy)benzoic acid, and ester-forming derivatives of these dihydroxycarboxylic acids. These polybasic acids can be used alone or in mixtures of two or more kinds. Among these, succinic acid, 1,3-cyclopentanedicarboxylic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalic acid, and diphenic acid are preferred from the viewpoints of organic solvent solubility and gas barrier properties.

The polyhydric alcohol component of the polyester used in the anchor coat layer (C) of the present invention is not particularly limited as long as it is possible to synthesize a polyester that exhibits gas barrier compensation performance, but it is preferable that the polyhydric alcohol component contains at least one selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, cyclohexanedimethanol, and 1,3-bishydroxyethylbenzene. Among these, it is most preferable to use ethylene glycol as the main component, since it is presumed that the fewer the number of carbon atoms between oxygen atoms, the less flexible the molecular chain is and the less oxygen permeable it is.

In the present invention, it is preferable to use the polyhydric alcohol components described above, but other polyhydric alcohol components may be copolymerized within the scope of the present invention without impairing the effects of the present invention. Specifically, diols include 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, methylpentanediol, dimethylbutanediol, butylethylpropanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol, and trihydric or higher alcohols include glycerol, trimethylolpropane, trimethylolethane, tris(2-hydroxyethyl)isocyanurate, 1,2,4-butanetriol, pentaerythritol, and dipentaerythritol. In particular, polyesters using glycerol and tris(2-hydroxyethyl)isocyanurate in combination among trihydric alcohols are particularly preferred because they have a moderately high crosslinking density due to their branched structure, have good solubility in organic solvents, and have excellent barrier function.

Catalysts used in the reaction to obtain the polyester of the present invention include acid catalysts such as tin-based catalysts such as monobutyltin oxide and dibutyltin oxide, titanium-based catalysts such as tetra-isopropyl-titanate and tetra-butyl-titanate, and zirconia-based catalysts such as tetra-butyl-zirconate. It is preferable to use the above titanium-based catalysts such as tetra-isopropyl-titanate and tetra-butyl-titanate, which have high activity in ester reactions, in combination with the above zirconia catalyst. The amount of the catalyst is preferably 1 to 1000 ppm, more preferably 10 to 100 ppm, based on the total mass of the reaction raw materials used. If the amount is less than 1 ppm, it is difficult to obtain the catalytic effect, and if it exceeds 1000 ppm, a problem of inhibiting the urethane reaction may occur when an isocyanate curing agent is used.

In the present invention, when a polyester resin is used as the main agent of the coating agent constituting the anchor coat layer (C), it is particularly preferable to use an isocyanate-based curing agent to form a urethane resin. In this case, the coating layer becomes a crosslinked system, which has the advantage of improving heat resistance, abrasion resistance, and rigidity. Therefore, it is easy to use for packaging boiled or retorted foods. On the other hand, there is a problem that the liquid cannot be reused after mixing with the curing agent, and a curing (aging) process is necessary after coating. Advantages include, for example, that as a simple overcoat varnish, there is no risk of thickening of the coating liquid, coating production is easy to manage, the coating liquid can be diluted and reused, and in addition, a curing process (so-called aging process) is not required. In this case, the end of the polyester used can be polyol or polycarboxylic acid, or a mixture of these two, without any problems. On the other hand, since the resin of the coating layer is linear, there are cases where the heat resistance and abrasion resistance are insufficient, and problems occur that make it difficult to use for packaging boiled or retorted foods.

When using a hardener in the coating layer, since it is a coating on a film, an isocyanate-based hardener is preferred from the viewpoint of the heat resistance of the film, and in this case the resin component of the coating material needs to be polyester polyol. On the other hand, when an epoxy-based compound is used as a hardener, it needs to be polyester polycarboxylic acid. In these cases, the coating layer becomes crosslinked, which has the advantage of improving heat resistance, abrasion resistance, and rigidity. Therefore, it is easy to use for boiled and retort packaging. On the other hand, there are problems with this, as the liquid cannot be reused after mixing with the hardener, and a hardening (aging) process is necessary after coating.

When the polyester has a hydroxyl group, the polyisocyanate compound used in the present invention reacts at least partially to form a urethane structure, which makes the resin component highly polar, and can further enhance the gas barrier function by aggregating between polymer chains. In addition, when the resin of the coating material is a straight-chain resin, crosslinking with a trivalent or higher polyisocyanate can impart heat resistance and abrasion resistance. The polyisocyanate compound used in the present invention may be any of diisocyanates, trivalent or higher polyisocyanates, low molecular weight compounds, and high molecular weight compounds, but it is preferable to contain an aromatic ring or an aliphatic ring in a part of the skeleton from the viewpoint of improving the gas barrier function. For example, examples of isocyanates having an aromatic ring include toluene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and naphthalene diisocyanate; examples of isocyanates having an aliphatic ring include hydrogenated xylylene diisocyanate, hydrogenated toluene diisocyanate, isophorone diisocyanate, norbornine diisocyanate, or trimers of these isocyanate compounds; and compounds containing terminal isocyanate groups obtained by reacting an excess amount of these isocyanate compounds with low molecular weight active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, and triethanolamine, or high molecular weight active hydrogen compounds such as various polyester polyols, polyether polyols, and polyamides.
The polyisocyanate compound may be an adduct, an allophanate, a biuret, or the like.
Among them, it is preferable to use a trimethylolpropane adduct of metaxylylene diisocyanate as the polyisocyanate compound.

The method for forming the anchor coat layer (C) is not particularly limited, and any conventionally known method such as a coating method can be used. Among the coating methods, the offline coating method and the in-line coating method are preferred. For example, in the case of an in-line coating method carried out in the film manufacturing process, the conditions for drying and heat treatment during coating will vary depending on the coating thickness and the equipment conditions, but it is preferable to send the film to a stretching process in the perpendicular direction immediately after coating and dry it in the preheating zone or stretching zone of the stretching process. In such cases, it is usually preferable to use a temperature of about 50 to 250°C.

The coating method for the resin composition for the anchor coat layer (C) is not particularly limited as long as it is a method that coats the film surface to form a layer. For example, conventional coating methods such as gravure coating, reverse roll coating, wire bar coating, and die coating can be used.

When forming the anchor coat layer (C), it is preferable to apply the resin composition for the anchor coat layer and then heat and dry it. The drying temperature is preferably 100 to 145°C, more preferably 110 to 140°C, and even more preferably 110 to 130°C. If the drying temperature is less than 100°C, the anchor coat layer may not be sufficiently dried. On the other hand, if the drying temperature exceeds 145°C, the film may be too hot, making it brittle or shrinking, resulting in poor processability. In particular, it is particularly preferable to first volatilize the solvent at a relatively low temperature of 80°C to 110°C immediately after application, and then dry at 120°C or higher, since this will result in a uniform film. In addition to drying, additional heat treatment at as low a temperature as possible is also effective in promoting the formation of the anchor coat layer.

[Protective layer (D)]
In the present invention, a protective layer may be laminated on the gas barrier layer, and it is preferable to have a protective layer (D) on the inorganic thin film layer that is the gas barrier layer. The inorganic thin film layer made of a metal or metal oxide layer is not a completely dense film, and minute defects are scattered. By forming a protective layer by applying a specific resin composition for protective layer described later on the metal oxide layer, the resin in the resin composition for protective layer penetrates into the defective parts of the metal oxide layer, and as a result, the barrier property of the gas barrier layer is stabilized. In addition, by using a material having gas barrier property for the protective layer itself, the gas barrier performance of the laminated film is also improved.

The resin composition used in the protective layer (D) of the present invention may be a polyvinyl alcohol-based, urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, polybutadiene-based resin, etc., and may contain a curing agent such as an epoxy-based, isocyanate-based, melamine-based, silanol-based, etc. Furthermore, it may contain a crosslinking agent such as a silicon-based crosslinking agent, an oxazoline compound, a carbodiimide compound, an epoxy compound, etc.
In particular, the protective layer is preferably made of a composition containing a polyvinyl alcohol resin and a silicon-based crosslinking agent, examples of which include the same polyvinyl alcohol resin and silicon-based crosslinking agent as those described above.

In the present invention, the adhesion amount of the protective layer (D) is preferably 0.10 to 0.40 (g/m ² ). This allows the protective layer to be uniformly controlled during coating, resulting in a film with fewer coating irregularities and defects. In addition, the cohesive force of the protective layer (D) itself is improved, and the adhesion between the inorganic thin film layer and the protective layer is also strengthened. The adhesion amount of the protective layer is more preferably 0.13 (g/m ² ) or more, even more preferably 0.16 (g/m ² ) or more, even more preferably 0.19 (g/m ² ) or more, and is preferably 0.37 (g/m ² ) or less, more preferably 0.34 (g/m ² ) or less, and even more preferably 0.31 (g/m ² ) or less. If the amount of protective layer (D) deposited exceeds 0.40 (g/ ^m2 ), the gas barrier properties are improved, but the cohesive force inside the protective layer becomes insufficient and the uniformity of the protective layer also decreases, which may result in unevenness or defects in the coat appearance and insufficient gas barrier properties and adhesiveness. On the other hand, if the amount of protective layer (D) deposited is less than 0.10 (g/ ^m2 ), sufficient gas barrier properties and interlayer adhesion may not be obtained.

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

When forming the protective layer (D), it is preferable to apply the resin composition for the protective layer and then heat and dry it. The drying temperature is preferably 100 to 160°C, more preferably 110 to 150°C, and even more preferably 120 to 140°C. If the drying temperature is less than 100°C, the protective layer may not be sufficiently dried, or the film formation of the protective layer may not progress, resulting in a decrease in cohesive strength and water-resistant adhesion, and as a result, the barrier properties and hand-tearability may be reduced. On the other hand, if the drying temperature exceeds 160°C, the film may become too hot, making it brittle and reducing puncture strength, or shrinking and reducing processability. It is particularly preferable to first volatilize the solvent at a relatively low temperature of 90°C to 110°C immediately after application of the protective layer, and then dry it at 130°C or higher, since this will result in a uniform and transparent film. In addition to drying, additional heat treatment at as low a temperature as possible is also effective in promoting the film formation of the protective layer.

[Other films]
In the present invention, other films may be laminated to the stretched laminated polyolefin resin film mainly composed of a polyolefin resin, within the range satisfying the mono-material ratio to the packaging material described below. The other film used in the present invention is, for example, a film obtained by melt-extruding a plastic and, as necessary, stretching it in the longitudinal direction and/or the width direction, cooling, and heat setting. Examples of the plastic include polyamides represented by nylon 4.6, nylon 6, nylon 6.6, nylon 12, etc., polyesters represented by polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, etc., as well as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene vinyl alcohol, wholly aromatic polyamide, polyamideimide, polyimide, polyetherimide, polysulfone, polystyrene, polylactic acid, etc.

The other films in the present invention can be of any thickness depending on the desired purpose, such as mechanical strength and transparency. There are no particular limitations on the thickness of the other films, but it is usually recommended that the thickness be 5 to 250 μm, and when used as a packaging material, it is desirable that the thickness be 10 to 60 μm. However, it is necessary to take into consideration the mono-material ratio of the packaging material, which will be described later.

The other film in the present invention may be a laminated film of one or more types of plastic films. When a laminated film is used, the type of laminate, the number of layers, the lamination method, etc. are not particularly limited, and can be arbitrarily selected from known methods depending on the purpose.

[Adhesive layer]
In the present invention, it is preferable that a barrier adhesive layer is laminated on the gas barrier layer.
The adhesive layer used in the present invention can be a general-purpose adhesive for lamination. For example, (non-)solvent type, water-based type, or hot melt type adhesives mainly composed of poly(ester)urethane, polyester, polyamide, polyamine, epoxy, poly(meth)acrylic, polyethyleneimine, ethylene-(meth)acrylic acid, polyvinyl acetate, (modified) polyolefin, polybutadiene, wax, casein, or the like can be used. Among these, from the viewpoints of heat resistance, flexibility that can follow the dimensional changes of each substrate, and improvement of the gas barrier properties of the adhesive itself, adhesives obtained by crosslinking polyurethane, polyester, or polyamine resins are preferred. However, caution is required because there is a concern that the barrier performance after bending treatment may decrease if the film becomes too hard due to crosslinking. In addition, it is also effective to add inorganic substances such as particles to improve the barrier performance. The adhesive layer can be laminated by, for example, direct gravure coating, reverse gravure coating, kiss coating, die coating, roll coating, dip coating, knife coating, spray coating, fountain coating, or other methods. In order to develop sufficient adhesiveness, the thickness after drying is preferably 1 to 8 μm, more preferably 2 to 7 μm, and even more preferably 3 to 6 μm. If the coating amount is less than 1 μm, it becomes difficult to bond the entire surface, and the adhesive strength decreases. Also, if it exceeds 8 μm, it takes a long time to completely cure the film, unreacted materials are likely to remain, and the adhesive strength decreases.

[Print Layer]
Furthermore, in the packaging material of the present invention, at least one printed layer may be laminated between the stretched laminated polyolefin resin film and the film to be laminated or on the outside thereof.

As the printing ink for forming the printing layer, water-based and solvent-based resin-containing printing inks can be preferably used. 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. There are no particular limitations on the printing method for providing the printing layer, and known printing methods such as offset printing, gravure printing, and screen printing can be used. To dry the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

[Characteristics of stretched laminated polyolefin resin film]
The stretched laminated polyolefin resin film of the present invention can have any laminated structure as a packaging material. From the viewpoint of environmental load, it is preferable to use the laminated film alone, since it requires the fewest materials and the fewest number of lamination steps. On the other hand, from the viewpoint of further improving the barrier property, printability, toughness, and stiffness, a laminate laminated with another substrate film, for example, can be cited as one of the preferred structures. In this case, by laminating the printing layer on the substrate film on the front side, there is also an advantage that it is not necessary to print on the film having a gas barrier layer. In addition, lamination with a white substrate film to improve the concealing property, or lamination with an ultraviolet-cutting film to block light, etc. are also suitable structures.

The stretched laminated polyolefin resin film of the present invention must have a puncture strength of 10N or more, measured according to JIS Z1707, from the viewpoint of toughness. This range ensures the toughness of the film, and makes it possible to make a packaging material that is less likely to be punctured. The puncture strength is preferably 11N or more, more preferably 12N or more, and preferably 20N or less or 19N or less. If the puncture strength is less than 10N, the toughness is insufficient, and when used as a bag, there is a risk that a hole will be opened and the contents will leak out if an external load is applied. In addition, from the viewpoint of reducing the volume of the plastic film, it is preferable that the above-mentioned puncture strength and the seal strength described below can be expressed with a thinner film. In particular, in the case of a process such as deposition processing, where there is a limit to the winding diameter that can be input per batch, a thinner film increases the amount that can be processed per batch, and therefore productivity can be improved. In that sense, the preferred thickness range of the stretched laminated polyolefin resin film is 45 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less.

The Young's modulus of the stretched laminated polyolefin resin film of the present invention must be 1 GPa or more in both the MD and TD directions. This range allows for a packaging material with excellent firmness, self-supporting ability, and ease of handling. The Young's modulus in the MD and TD directions is preferably 1.2 GPa or more, more preferably 1.4 GPa or more, and is preferably 5 GPa or less, more preferably 4 GPa or less, and even more preferably 3.5 GPa or less. If the Young's modulus is less than 1 GPa, the firmness will be insufficient, and there is a risk of problems with the bag's self-supporting ability and handling.

The stretched laminated polyolefin resin film of the present invention must have a seal strength of 8N/15mm or more when the heat-sealing layers are heat-sealed at 150°C, 0.2MPa, for 2 seconds. If the seal strength is less than 8N/15mm, the sealed portion is prone to peeling, limiting its use as a packaging bag, such as not being usable for applications involving large amounts of contents. The heat seal strength is preferably 9N/15mm or more, more preferably 10N/15mm or more, more preferably 20N/15mm or less, more preferably 19N/15mm or less, and even more preferably 18N/15mm or less. The heat seal strength can be measured, for example, in accordance with JIS Z1707.

In the present invention, the heat shrinkage rate of the stretched laminated polyolefin resin film at 120°C for 15 minutes must be 10% or less in both the MD and TD directions. This ensures the heat resistance required when processing the film and when using it as a package. For example, even if the film is subjected to a thermal load during coating, deposition, printing, and lamination, the film undergoes little dimensional change, and the film is prevented from deteriorating in barrier performance in terms of quality and from developing wrinkles and sagging in terms of quality. In addition, the finish is good when heat-sealing the film at a high temperature of 120°C or more to make a package, the seal strength is stable, and the package is provided with little dimensional change or appearance change when subjected to severe wet heat treatment. The heat shrinkage rate of 120°C for 15 minutes is preferably 9.5% or less, more preferably 9% or less, even more preferably 8% or less, even more preferably 7% or less, preferably 0.1% or more, more preferably 0.5% or more, and even more preferably 1.0% or more. If the heat shrinkage rate exceeds 10%, the barrier property may deteriorate during processing. Additionally, heat wrinkles and sagging can easily occur, which can reduce the quality of the product.

In the stretched laminated polyolefin resin film of the present invention, it is preferable that the oxygen permeability of the film alone under the condition of 23°C x 65% RH is 1000 ml/ ^m2 ·d·MPa or less in terms of exhibiting good gas barrier properties. Within this range, a certain level of barrier performance can be expected even when the film alone is compared with an olefin film, and higher barrier performance can be exhibited by laminating it with another film. The oxygen permeability is more preferably 900 ml/ ^m2 ·d·MPa or less, even more preferably 800 ml/ ^m2 ·d·MPa or less, even more preferably 750 ml/ ^m2 ·d·MPa or less, preferably 1 ml/ ^m2 ·d·MPa or more, more preferably 5 ml/ ^m2 ·d·MPa or more, and even more preferably 10 ml/ ^m2 ·d·MPa or more. If the oxygen permeability exceeds 1000 ml/ ^m2 ·d·MPa, it becomes difficult to meet the needs of applications requiring gas barrier properties. The oxygen permeability can be measured, for example, based on JIS-K7126 B method.

In the stretched laminated polyolefin resin film of the present invention, it is preferable that the oxygen permeability under the condition of 23°C x 65% RH when it is bonded to another film via an adhesive is 60 ml/ ^m2 ·d·MPa or less in terms of exhibiting good gas barrier properties. The oxygen permeability is more preferably 50 ml/ ^m2 ·d·MPa or less, even more preferably 40 ml/ ^m2 ·d·MPa or less, preferably 0.5 ml/ ^m2 ·d·MPa or more, more preferably 1 ml/ ^m2 ·d·MPa or more. If the oxygen permeability exceeds 60 ml/ ^m2 ·d·MPa, it becomes difficult to meet the application requiring high gas barrier properties. On the other hand, if the oxygen permeability is less than 0.5 ml/ ^m2 ·d·MPa, although the barrier performance is excellent, the residual solvent is difficult to permeate to the outside of the bag, and there is a possibility that the amount of migration to the contents increases relatively, which is not preferable.

In the stretched laminated polyolefin resin film of the present invention, the water vapor permeability of the film alone under the conditions of 40°C x 90% RH is preferably 3.0 g/ ^m2 ·d or less in terms of exhibiting good gas barrier properties. The water vapor permeability can be more preferably 2.5 g/ ^m2 ·d or less, even more preferably 2.0 g/ ^m2 ·d or less, preferably 0.1 g/ ^m2 ·d or more, and more preferably 0.2 g/ ^m2 ·d or more. If the water vapor permeability exceeds 3.0 g/ ^m2 ·d, it becomes difficult to meet the needs of applications requiring high gas barrier properties. The water vapor permeability can be measured, for example, based on JIS-K7129 B method.

As an evaluation criterion for mono-materialization in packaging materials made using the stretched laminated polyolefin resin film of the present invention, when the ratio of the thickness of the polyolefin material to the total thickness of each film and adhesive is calculated as the mono-material (mono-mate) ratio, the mono-material ratio is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more. By setting the mono-material ratio in this range, a packaging material configuration that is easy to recycle can be achieved. If the mono-material ratio is less than 70%, there is a risk that recycling will be difficult due to foreign matter from other materials. Note that if all the polyolefin materials used are polypropylene resins, a configuration that is even easier to recycle can be achieved.

In a packaging material made using the stretched laminated polyolefin resin film of the present invention, the total thickness of each film and adhesive is preferably 20 to 140 μm, more preferably 25 to 135 μm, and even more preferably 30 to 130 μm. By keeping the total thickness of the packaging material within this range, a package can be obtained that can exhibit the necessary physical properties, such as the firmness required for the above-mentioned packaging material, as well as toughness and barrier performance. If the total thickness is less than 20 μm, the bag will not have enough firmness and will not stand on its own. Furthermore, the bag will not have enough toughness and may tear or develop holes. On the other hand, if the total thickness exceeds 140 μm, the bag will be too stiff, making it difficult to handle, and will also increase the cost of the package, which is economically undesirable.

The packaging material made of the stretched laminated polyolefin resin film of the present invention has excellent heat sealability, stiffness, strength, heat resistance, and barrier properties as described above, and can be used as various packages. Examples of the packages include those for general food, frozen food, vacuum packaging, boiled retort food, and microwave heating.
In particular, the laminated polyolefin resin film of the present invention is preferably used for heating in a microwave oven.

The shape of the package of the packaging material made using the stretched laminated polyolefin resin film of the present invention is not particularly limited and may take various shapes.
Examples of packaging forms include three-sided and four-sided pouches, standing pouches, and spout pouches.

The present invention also includes a package in which an item is packaged in a packaging material. The contents filled in a packaging bag using the packaging material of the present invention are not particularly limited, and the contents may be liquid, powder, or gel. The contents may also be food or non-food.

This application claims the benefit of priority based on Japanese Patent Application No. 2023-072695, filed on April 26, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-072695, filed on April 26, 2023, are incorporated by reference into this application.

The present invention will now be described in more detail with reference to examples, but the present invention is not limited to the following examples. Various evaluations were carried out by the following measurement methods.
In the examples, the stretched laminated polyolefin resin film will hereinafter be referred to as a laminated film.

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

(2) Composition and thickness of inorganic thin film layer (B) on laminated film The laminated films (after thin film lamination) obtained in the examples and comparative examples were measured for thickness composition using a fluorescent X-ray analyzer (Rigaku Corporation, "Supermini 200") based on a calibration curve prepared in advance. The excitation X-ray tube conditions were 50 kV and 4.0 mA.

(3) Amount of adhesion of coating layer (A), anchor coat layer (C), and protective layer (D) on laminate film In each example and comparative example, each laminate film obtained at the stage where a predetermined coating layer (A), anchor coat layer (C), and protective layer (D) were laminated on the laminate film was used as a sample, and a test piece of 100 mm x 100 mm was cut out from this sample, and the coating layer was wiped off with either water, ethanol, or acetone, and the amount of adhesion was calculated from the change in mass of the film before and after wiping.

(4) Evaluation method of heat seal strength of laminated film Heat seal strength measurement was performed on the laminated films obtained in the examples and comparative examples in accordance with JIS Z1707. Specific procedures are shown below. The heat-sealing layers of the films were bonded together using a heat sealer. The heat seal conditions were upper bar temperature 150°C, lower bar temperature 30°C, pressure 0.2 MPa, and time 2 seconds. The adhesive sample was cut out so that the seal width was 15 mm. The peel strength was measured at a tensile speed of 200 mm/min using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation). The heat seal strength was expressed as the strength per 15 mm (N/15 mm). The seal appearance was evaluated relative to the following: ◯ for seals that were sealed without wrinkles, △ for those with wrinkles in some areas, and × for those with wrinkles over the entire surface.

(5) Puncture strength of laminated film The films obtained in the examples and comparative examples were sampled into 5 cm squares, and the puncture strength of the films was measured in accordance with JIS Z1707 using a digital force gauge "ZTS-500N", an electric test stand "MX2-500N" and a puncture jig "TKS-250N" manufactured by Imada Co., Ltd. The unit of measurement was N.

(6) Evaluation of Heat Shrinkage of Laminated Films Test pieces of 20 mm wide and 300 mm long were prepared so that the measurement direction (MD or TD) of the laminated film prepared in each Example and Comparative Example was the long side, and a gauge was placed at a distance of 200 mm in the center of the test piece. The distance between the gauges was then read to the first decimal place with a metal ruler, and the gauge distance A before heating was obtained. Then, the end of this test piece was clamped with a clip, and the test piece was placed in a heating oven adjusted to 120°C ± 1°C for 15 minutes while hanging from a metal bar. After heating, the gauge distance of the removed test piece was read with a metal ruler in the same manner as before heating, and the gauge distance B after heating was obtained. Based on each value obtained, the heat shrinkage was calculated using the following calculation formula.
Heat shrinkage rate (%) = (A - B) / A x 100

(7) Evaluation of Young's modulus of laminated film The Young's modulus in the longitudinal direction and width direction of the film was measured at 23°C according to JIS K 7127. A sample was cut out from the film to a size of 15 mm x 200 mm, and set in a tensile tester (Instron 5965 dual column tabletop tester manufactured by Instron Japan Co., Ltd.) with a chuck width of 100 mm. A tensile test was performed at a tensile speed of 200 mm/min. The Young's modulus was calculated from the slope of the linear portion at the beginning of elongation from the obtained strain-stress curve.

(8) Evaluation method of oxygen transmission rate (OTR) of laminated film The oxygen transmission rate of the films obtained in the examples and comparative examples was measured in accordance with JIS-K7126 method B using an oxygen transmission rate measuring device ("OX-TRAN (registered trademark) 2/22" manufactured by MOCON Co., Ltd.) under an atmosphere of temperature 23°C and humidity 65% RH. The measurement of oxygen transmission rate was performed in the direction in which oxygen permeates from the substrate film side to the heat seal layer side.

(9) Evaluation method of water vapor transmission rate (WVTR) of laminated film The water vapor transmission rate of the films obtained in the examples and comparative examples was measured in accordance with JIS-K7129 Method B using a water vapor transmission rate measuring device ("PERMATRAN-W 3/33MG" manufactured by MOCON) under an atmosphere of temperature 40°C and humidity 90% RH. The water vapor transmission rate was measured in the direction in which water vapor permeates from the substrate film side to the heat seal layer side.

[Preparation of packaging materials]
(10) Preparation of packaging material for evaluation Adhesive 1 or 2 described below was applied to the surface of various films described below so that the thickness after drying treatment at 80° C. was 3.5 μm, and then the base layer side of the laminated film obtained in the Examples and Comparative Examples was dry laminated on a metal roll heated to 60° C., and aging was performed at 40° C. for 4 days (96 hours) to obtain a laminated product for evaluation. One of the following two types of adhesive was used.
Adhesive 1: Base C: Polyester/Curing agent C: Isocyanate curing adhesive (TM569/cat10L manufactured by Toyo-Morton Co., Ltd.)
Adhesive 2: Base A: Polyamine/Curing agent A: Epoxy curing adhesive (C93/M100 manufactured by Mitsubishi Gas Chemical Company, Inc.)

(11) Evaluation method for oxygen transmission rate (OTR) of packaging material The oxygen transmission rate of the packaging material prepared in (10) above was measured in accordance with JIS-K7126 Method B using an oxygen transmission rate measuring device ("OX-TRAN (registered trademark) 2/22" manufactured by MOCON Corporation) under an atmosphere of temperature 23°C and humidity 65% RH. The oxygen transmission rate was measured in the direction in which oxygen permeates from the base film side of the packaging material to the heat seal layer side.

(12) Evaluation Criteria for Mono-Materialization: Mono-Material Ratio As an evaluation criterion for mono-materialization of the packaging materials produced in (10) above, the ratio of the thickness of the olefin-based material to the total thickness of each film and adhesive was calculated as the mono-material ratio.

The propylene homopolymers or propylene copolymers used in the present examples and comparative examples are listed below. The propylene homopolymers or propylene copolymers used in Examples 1 to 12 and Comparative Examples 1 to 6 are shown in Tables 1 and 2A.

The resins constituting the respective layers used in the following production examples are as follows.
PP-A: Propylene homopolymer: "FS2011DG3" manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5 g/10 min, melting point: 158° C.
PP-B: Propylene-ethylene-butene random copolymer: "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 2.5 mol%, butene content: 7 mol%, MFR: 3.1 g/10 min, melting point: 133°C
PP-C: Ethylene-butene copolymer: "A-4085S" manufactured by Mitsui Chemicals, Inc., MFR: 6.7 g/10 min, melting point: 66°C
PP-D: Propylene-butene copolymer: "SP8931" manufactured by Sumitomo Chemical Co., Ltd., butene content: 33 mol%, MFR: 9.0 g/10 min, melting point: 130° C.

[Production Example 1]
Using three melt extruders, the base material layer (PP-A: 100 parts by weight) was extruded from the first extruder, the intermediate layer (PP-B: 100 parts by weight) was extruded from the second extruder, and the heat-sealing layer (PP-B: 30 parts by weight, PP-D: 70 parts by weight of mixed resin) was extruded from the third extruder at a resin temperature of 260 ° C., and laminated in a T-die to form a base material layer / intermediate layer / heat-sealing layer, which was cooled and solidified by a chill roll at 20 ° C. Next, the obtained unstretched film was stretched 4.5 times in the longitudinal direction at a temperature of 125 ° C., and then stretched 8 times in the transverse direction at a temperature of 163 ° C., and heat-set at 169 ° C. while relaxing by 6.7% in the width direction (TD). A laminated film OPP1 (30 μm) with a base material layer: 21.5 μm, an intermediate layer: 7.5 μm, and a heat-sealing layer: 1 μm was obtained. The surface of the base layer of this biaxially oriented polypropylene film was subjected to a corona treatment using a corona treatment machine manufactured by Softal Corona & Plasma GmbH under the condition of an applied current value of 0.75 A, and then the film was wound up with a winder. Table 1 shows the configuration of the laminated film OPP1.

[Production Examples 2 to 7]
Laminated films OPP2 to OPP7 were produced in the same manner as in Production Example 1, except that the compounding ratio of the resins constituting each layer of the laminated film and the thickness of each layer were changed as shown in Table 1. The compositions of OPP2 to OPP7 are shown in Table 1.

(Other base films)
(OPP-A) Biaxially oriented polypropylene film (P2102-30 μm, manufactured by Toyobo Co., Ltd.)
(CPP) Non-oriented polypropylene film (P1128-30 μm, manufactured by Toyobo Co., Ltd.)

(Coating layer (A))
The coating liquid for forming the coating layer (A) used in the present examples and comparative examples is described in detail below. The coating layer was used in Examples 1 and 2 and is shown in Table 2A.

[Polyvinyl alcohol resin (a)]
To 90 parts by weight of purified water, 10 parts by weight of a fully saponified polyvinyl alcohol resin (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name: G Polymer OKS8049Q (saponification degree 99.0% or more, average polymerization degree 450) was added, and the mixture was heated to 80° C. with stirring, and then stirred for about 1 hour. The mixture was then cooled to room temperature, and a nearly transparent polyvinyl alcohol solution (PVA solution) with a solids content of 10% was obtained.

[Inorganic layered compound dispersion (b)]
5 parts by weight of montmorillonite (trade name: Kunipia F, manufactured by Kunimine Industries Co., Ltd.), which is an inorganic layered compound, was added to 95 parts by weight of purified water while stirring, and thoroughly dispersed with a homogenizer set at 1500 rpm. After that, the mixture was kept at 23° C. for 1 day to obtain an inorganic layered compound dispersion liquid with a solid content of 5%.

[Coating solution 1 used for coating layer 1]
The materials were mixed in the following ratio to prepare a coating liquid (resin composition for coating layer).
Ion-exchanged water 15.00% by weight
Isopropyl alcohol 15.00% by weight
Polyvinyl alcohol resin (a) 30.00% by weight
Inorganic layered compound dispersion (b) 40.00% by weight

[Coating of Coating Liquid 1 on Film (Lamination of Coating Layer 1)]
The above-prepared coating solution 1 was applied onto the corona-treated surface of the substrate film by the gravure roll coating method, pre-dried at 90°C for 4 seconds, and then dried at 120°C for 4 seconds to obtain a coating layer. The coating layer had an adhesion weight of 0.30 g/ ^m2 . Then, a post-heat treatment was performed at 40°C for 2 days (48 hours). In this manner, a laminated film provided with a coating layer 1 was produced.

[Preparation of Coating Solution 2 Used for Coating Layer 2]
A solution obtained by hydrolyzing tetraethoxysilane with 0.02 mol/L hydrochloric acid was added to a 5 wt % aqueous solution of polyvinyl alcohol resin (PVA) having a saponification degree of 99% and a polymerization degree of 2400 in a weight ratio of SiO ₂ /PVA = 40/60 to obtain coating solution 2.

[Coating of Coating Liquid 2 on Film (Lamination of Coating Layer 2)]
The above-prepared coating solution 2 was applied onto the corona-treated surface of the substrate film by the gravure roll coating method, pre-dried at 90°C for 4 seconds, and then dried at 120°C for 4 seconds to obtain a coating layer. The coating layer had an adhesion weight of 1.00 g/ ^m2 . Then, a post-heat treatment was performed at 40°C for 2 days (48 hours). In this manner, a laminated film provided with a coating layer 2 was produced.

(Inorganic thin film layer (C))
The method for producing the inorganic thin film layer (C) used in each of the Examples and Comparative Examples is described below. The inorganic thin film layer was used in Examples 3 to 12 and Comparative Examples 2 to 6, and is shown in Table 2A. (In the table, the inorganic thin film layer is referred to as the inorganic layer.)

(Formation of Inorganic Thin Film Layer 1 (Vapor Deposition 1))
Metallic aluminum was deposited on the base layer or anchor coat layer to form the inorganic thin film layer 1. Using a small vacuum deposition apparatus (VWR-400/ERH, manufactured by ULVAC KIKO Inc.), the pressure was reduced to 10 ⁻³ Pa or less, and then aluminum foil with a purity of 99.9% was placed on a Nilaco deposition source CF-305W from below the substrate, and metallic aluminum was heated and evaporated to form a metallic aluminum film with a thickness of 70 nm on the film.

(Formation of inorganic thin film layer 2 (vapor deposition 2))
Silicon oxide was deposited on the base layer or anchor coat layer to form the inorganic thin film layer 2. Using a small vacuum deposition device (VWR-400/ERH, manufactured by ULVAC KIKO Inc.), the pressure was reduced to 10 ⁻³ Pa or less, and silicon oxide was then placed in a Nilaco deposition source B-110 from below the substrate and evaporated by heating to form a silicon oxide film with a thickness of 40 nm on the film.

(Formation of Inorganic Thin Film Layer 3 (Vapor Deposition 3))
As the inorganic thin film layer 3, a composite oxide layer of silicon dioxide and aluminum oxide was formed on the substrate layer or the anchor coat layer by electron beam deposition. As the deposition source, granular SiO ₂ (purity 99.9%) and Al ₂ O ₃ (purity 99.9%) of about 3 mm to 5 mm were used. The film thickness of the inorganic thin film layer (SiO ₂ /Al ₂ O ₃ composite oxide layer) in the film thus obtained was 20 nm. The composition of this composite oxide layer was SiO ₂ /Al ₂ O ₃ (weight ratio) = 70/30.

(Anchor Coat Layer (B))
The method for producing the anchor coat layer (B) used in each of Examples 8 and 9 will be described below.
[Polyester resin (a)]
As the polyester component, a polyester polyol (DF-COAT GEC-004C manufactured by DIC Corporation: solid content 30%) was used.

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

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

[Coating solution 1 for anchor coat layer 1 (AC1)]
A solution (15% by weight) of silane coupling agent (c) dissolved in acetone and polyisocyanate crosslinking agent (b) were 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 referred to as PGM), and polyester resin (a) was further added to obtain the intended coating solution 1. The mixing ratio is shown below.
Polyester resin (a) 10.62% by weight
Polyisocyanate crosslinker (b) 4.07% by weight
Silane coupling agent (c) *Acetone diluted solution 1.73% by weight
Methyl ethyl ketone 69.55% by weight
PGM 14.03% by weight

(Coating of coating fluid onto film (lamination of anchor coat layer))
The coating layer was formed by applying the coating solution 1 to the corona-treated surface of the substrate film by the gravure roll coating method, pre-drying at 95°C for 4 seconds, and then drying at 115°C for 4 seconds to obtain an anchor coat layer. The adhesion amount of the anchor coat layer at this time was 0.40 g/ ^m2 .
Thereafter, a post-heat treatment was carried out at 40° C. for 4 days (96 hours) to obtain the desired laminated film.

(Protective Layer (D))
The method for producing the protective layer (D) used in Example 9 will be described below.

[Coating solution 1 used for protective layer (D)]
A solution obtained by hydrolyzing tetraethoxysilane with 0.02 mol/L hydrochloric acid was added to a 5 wt % aqueous solution of polyvinyl alcohol resin (PVA) with a saponification degree of 99% and a polymerization degree of 2,400 in a weight ratio of _SiO2 /PVA = 60/40 to prepare a gas barrier protective layer solution (coating solution 1).

(Coating the film with coating fluid (laminating protective layer))
The above-mentioned coating solution 1 was applied onto the inorganic thin film layer of the laminated film by a gravure roll coating method, and dried for 10 seconds in a dry oven at 120°C to obtain a protective layer (protection 1). The amount of adhesion of the protective layer at this time was 0.30 g/ ^m2 . Then, a post-heat treatment was performed at 40°C for 2 days (48 hours). In this manner, a laminated film provided with a protective layer was produced.

In this manner, laminated polyolefin films were produced that had a coating layer, an anchor coat layer, an inorganic thin film layer, or a protective layer on each laminate film.

In each of the Examples and Comparative Examples, each film was used alone or by laminating multiple films together using the dry lamination method with the aforementioned adhesive to produce a packaging material with the configuration shown in Table 2C. In addition, various evaluations were carried out on the resulting packages. The results are shown in Table 2B.

According to the present invention, by laminating a specified gas barrier layer onto a stretched polyolefin film having a low-melting point resin layer to form a laminate film, it is possible to greatly improve the gas barrier performance and ensure high heat sealability, heat resistance, stiffness and toughness, thereby providing an environmentally friendly and highly convenient packaging material.
Moreover, the packaging material of the present invention requires fewer processing steps and can be easily produced, so that it is excellent in both economy and production stability, and can provide packaging products with uniform properties.

Claims (16)

A stretched laminated polyolefin-based resin film comprising a base layer, an intermediate layer, and a heat-sealing layer containing a polyolefin-based resin having a melting point of 150°C or less laminated in that order, the stretched laminated polyolefin-based resin film having a gas barrier layer on the surface opposite to the surface of the heat-sealing layer, and satisfying the following requirements (a) to (d):
(a) The puncture strength of the film is 10 N or more.
(b) The Young's modulus of the film in the MD direction and the TD direction is 1 GPa or more.
(c) The heat-sealable layers of the film have a seal strength of 8 N/15 mm or more when heat-sealed at 150° C., 0.2 MPa, and for 2 seconds.
(d) The shrinkage rate of the film after heating at 120° C. for 15 minutes is 10% or less in both MD and TD. The stretched laminated polyolefin resin film according to claim 1, wherein the base layer, intermediate layer and heat-sealing layer are each composed of a polyolefin resin composition containing a propylene homopolymer or a propylene copolymer as a constituent component. The stretched laminated polyolefin resin film according to claim 1 or 2, wherein the content of the propylene copolymer constituting the intermediate layer is more than 60 mass% in the polyolefin resin composition constituting the intermediate layer. The stretched laminated polyolefin resin film according to claim 1 or 2, which satisfies the relationship: thickness of the base layer > thickness of the intermediate layer > thickness of the heat-sealing layer. The stretched laminated polyolefin resin film according to claim 1 or 2, wherein the gas barrier layer is an inorganic thin film layer made of any one of aluminum, aluminum oxide, silicon oxide, and a composite oxide of silicon oxide and aluminum oxide. The stretched laminated polyolefin resin film according to claim 1 or 2, wherein the gas barrier layer is a coating layer containing at least one of a polyvinyl alcohol resin, a polyester resin, a polyurethane resin, or an inorganic layered compound. The stretched laminated polyolefin resin film according to claim 1 or 2, in which an anchor coat layer is laminated between the film and the gas barrier layer. The stretched laminated polyolefin resin film according to claim 1 or 2, in which a protective layer is laminated on the gas barrier layer. 3. The stretched laminated polyolefin resin film according to claim 1, which has an oxygen permeability of 800 ml/ ^m2 ·d·MPa or less under conditions of 23°C and 65% RH. 3. The stretched laminated polyolefin resin film according to claim 1, which has a water vapor permeability of 3.0 g/m ² ·d or less under conditions of 40° C. and 90% RH. The stretched laminated polyolefin resin film according to claim 1 or 2, which is used for microwave heating. A packaging material formed by laminating the stretched laminated polyolefin resin film according to claim 1 or 2. The packaging material according to claim 12, in which a barrier adhesive layer is laminated on the gas barrier layer. A packaging bag made from the packaging material according to claim 12. A package in which an item is packaged with the packaging material according to claim 12. A package in which an item is packaged in the packaging bag according to claim 14.