Biaxially oriented polyamide film and polyamide film mill roll

Abstract

The present invention aims to provide a biaxially oriented polyamide film that has good mechanical and thermal properties despite being a product close to the end of a mill roll, and also has less S-shaped curling due to moisture absorption after elimination. To solve the above problem, the biaxially oriented polyamide film of the present invention is a biaxially oriented polyamide film made of a polyamide resin containing 60 mass% or more of polyamide 6, characterized in that the molecular orientation angle of the film is 20° or more, the hygroscopic deformation is 1.3% or less, the impact strength is 0.8 J / 15 μm or more, and additionally, the thermal shrinkage rate after heating at 160°C for 10 minutes is 0.6 to 3.0% in both the MD direction and the TD direction.

Description

Technology Field

[0001] The present invention relates to a biaxially oriented amide film having excellent impact resistance and pinhole resistance for use in packaging food, etc. In particular, the invention relates to a biaxially oriented polyamide film having less S-shaped curling caused by moisture absorption when a film close to the end in the width direction of a mill roll is processed into a food packaging bag. Background Technology

[0002] Generally, biaxially oriented polyamide films are widely used as packaging materials for various foods and the like due to their excellent mechanical properties, thermal properties, and gas barrier properties. However, conventional biaxially oriented polyamide films have problems such as stretching due to moisture absorption in high-humidity environments, which causes the bags to curl into an S-shape when processed into bags, making it difficult to box-package the bags, or causing malfunctions in the conveying section of the device that fills the bags with contents.

[0003] This problem is likely to occur when producing bags from film on a slit roll near the end of a mill roll. Here, a mill roll refers to a full-width film roll of a film-making device wound after trimming the corners at both ends during the film manufacturing process, and a slit roll refers to a film roll that has been narrowed in width by slitting the mill roll to perform printing or lamination processes.

[0004] The above-mentioned polyamide film used for food packaging is typically printed on its surface, then laminated with a polyolefin-based resin film such as polyethylene (PE) or polypropylene (PP), folded in half parallel to the flow direction with the polyamide film facing outward, heat-seals three sides, and cut to form a three-way sealing bag with one side open. Then, contents are filled into this bag, sealed, and provided to the market.

[0005] Polyamide films used for such food packaging applications are primarily manufactured by the biaxial stretching method. However, biaxially oriented polyamide films manufactured by the biaxial stretching method are prone to variations in physical properties in the width direction. One cause of this variation in physical properties in the width direction is the bowing phenomenon. The bowing phenomenon is thought to be a phenomenon in which the main axis of orientation tilts in an arc shape in the width direction because, when longitudinal shrinkage stress occurs due to high temperatures during the heat-setting process, the ends of the film are held and restrained by clips, whereas the central part of the film shrinks due to weaker restraint.

[0006] Due to the bowing phenomenon, the principal axes (angles exhibiting the largest values) of physical properties such as thermal shrinkage rate, dimensional change rate due to moisture absorption, and refractive index differ in the width direction of the film. Consequently, the difference in physical property values ​​regarding thermal shrinkage rate and dimensional change rate due to moisture absorption increases in the oblique direction.

[0007] In other words, when a bag is made using a biaxially oriented polyamide film for food packaging obtained by the conventional method, the main axis direction of orientation differs on the front and back of the bag when folded in half due to the bowing phenomenon, so the dimensional change also differs on the front and back, causing bending at the corners of the bag. That is, a phenomenon in which two sides of the bag curl into an S shape (hereinafter simply referred to as S-curling) occurs, making it difficult to place the bag into a box when packaging it in a box, or causing functional failure in the conveying section of the device that fills the bag with contents.

[0008] As a countermeasure against the bowing phenomenon, a method has been proposed to reduce misalignment caused by moisture absorption using a polyamide film that satisfies the relationship between a specific boiling water shrinkage deformation and a difference in molecular orientation angle obtained by heat-setting after transverse stretching and cooling (see Patent Document 1). However, in the case of bags produced from a film slit roll near the end of the mill roll, S-shaped curling due to moisture absorption occurred.

[0009] In addition, a method for reducing S-shaped curling after boiling water treatment has been proposed using a biaxially oriented polyamide resin film in which the direction of the orientation principal axis of an α-type crystal is 14 degrees or less with respect to the longitudinal or transverse direction of the film, characterized by stretching in two stages in the longitudinal direction (see Patent Document 2).

[0010] However, even with this method, in the case of bags produced from a film slit roll near the end of the mill roll, S-shaped curling due to moisture absorption occurred. It is believed that this is because the countermeasures in Patent Document 2 are countermeasures for the S-shaped curling phenomenon that occurs after treating the bags with boiling water, and are not countermeasures for the S-shaped curling phenomenon caused by moisture absorption.

[0011] Regarding the problem of S-shaped curling caused by moisture absorption, a packaging bag has been proposed in which the acute angle formed by the main orientation axis direction of the biaxially stretched polyamide film layers on the front and back of the packaging bag is 30° or less (see Patent Document 3). However, in this method, the S-shaped curling caused by moisture absorption is less in a bag made from a film roll slit near the center of the mill roll because the angle formed by the main orientation axis direction of the polyamide film layers on the front and back is small, but in a bag close to the end of the mill roll, the occurrence of S-shaped curling caused by moisture absorption cannot be reduced because the angle formed by the main orientation axis direction of the polyamide film layers on the front and back is large. Prior art literature

[0012] Japanese Patent Publication No. 2623939, Japanese Patent Publication No. 3726304, Japanese Patent Publication No. 2012-254804 The problem to be solved

[0013] The present invention was made against the background of the above problem, and aims to provide a biaxially oriented polyamide film and a film mill roll that have less S-shaped curling due to moisture absorption, even when a packaging bag is made using a film product close to the end of the mill roll. means of solving the problem

[0014] The inventors of this application have conducted diligent research to solve the above-mentioned problem and have finally come to complete the present invention.

[0015] The present invention is composed of the following components.

[0016] [1] A biaxially oriented polyamide film made of a polyamide resin containing 60 mass% or more of polyamide 6, characterized in that the molecular orientation angle of the film is 20° or more, the hygroscopic deformation is 1.3% or less, the impact strength is 0.8 J / 15 μm or more, and the thermal shrinkage rate after heating at 160°C for 10 minutes is 0.6 to 3.0% in both the MD direction and the TD direction.

[0017] [2] A biaxially oriented polyamide film as described in [1], characterized by being a polyamide resin containing 90 mass% or more of polyamide 6.

[0018] [3] A biaxially oriented polyamide film as described in [1] or [2], characterized in that the thermal shrinkage deformation of the film after heating at 160°C for 10 minutes is 2.0% or less.

[0019] [4] A biaxially oriented polyamide film characterized by having an adhesive layer on at least one side of the biaxially oriented polyamide film described in any one of [1] to [3], the adhesive layer being composed of a polyester resin, a polyurethane resin, and / or a polyacrylic resin, with a coating amount as a solid content of 0.01 to 3 g / m².

[0020] [5] A polyamide film mill roll made of a polyamide resin containing 60 mass% or more of polyamide 6, wherein the impact strength of the film at a position 300 mm inward from the right and left ends in the width direction of the film mill roll is 0.8 J / 15 μm or more, the hygroscopic deformation is 1.3% or less, and the thermal shrinkage rate after heating at 160°C for 10 minutes is 0.6 to 3.0% in both the MD direction and the TD direction.

[0021] [6] A polyamide film mill roll described in [5], characterized by having a biaxially oriented polyamide film having an adhesive layer on at least one side of the film made of a polyester resin, a polyurethane resin, and / or a polyacrylic resin, with a coating amount of 0.01 to 3 g / m² as a solid.

[0022] [7] Polyamide film mill roll described in [5] or [6], characterized in that the thermal shrinkage deformation of the film at a position 300 mm inward from the right and left ends in the width direction of the film mill roll is 2.0% or less after heating at 160°C for 10 minutes. Effects of the invention

[0023] The biaxially oriented polyamide film and film mill roll of the present invention, despite being a film near the end of the mill roll, exhibit low anisotropy in stretching under high humidity and low dimensional deformation before and after moisture absorption, thereby reducing S-shaped curling of the processed bag. Consequently, it is difficult for functional failure to occur during bag conveyance when filling the contents into the bag, resulting in good workability. Furthermore, since the deformation due to shrinkage at high temperatures is small, the deformation due to shrinkage after heat sealing the bag is also small. Therefore, it can be suitable for various packaging applications. Brief explanation of the drawing

[0024] Figure 1 is a schematic diagram of a slit roll provided for S-curling evaluation. Figure 2 is a schematic diagram of the S-curling evaluation of a bag. Explanation of the symbols 1: Mill roll of biaxially oriented polyamide film (4,000 mm width) 2: Slit roll on the left (940 mm width) 3: Laminate roll with sealant laminated onto the film of the slit roll on the left. 4: 3-way sealing bag on the left 5: Heat sealing part of the 3-way sealing bag 6: Weight for measuring bending 7: Height of bend indicating the degree of S-curling Specific details for implementing the invention

[0025] Embodiments of the present invention are described in detail below.

[0026] [Raw Material Composition of Biaxially Oriented Polyamide Film]

[0027] The biaxially oriented polyamide film of the present invention is preferably composed of a polyamide resin containing 60 mass% or more of polyamide 6, more preferably 80 mass% or more, and even more preferably 90 mass% or more. If it is less than 60 mass%, it is not desirable because mechanical strength or thermal dimensional stability deteriorates.

[0028] Polyamide 6 in the present invention is typically prepared by ring-opening polymerization of ε-caprolactam. Polyamide 6 obtained by ring-opening polymerization is typically dried and melt-extruded using an extruder after removing the ε-caprolactam monomer with hot water.

[0029] The polyamide 6 used in the present invention may be commercially available from Ube Industries, Inc., BASF, etc. In particular, a polyamide 6 commercially available for film applications having the following relative viscosity, having a residual lactam monomer content of 1 mass% or less, and having terminal blocking or terminal modification that makes it difficult to generate lactam monomers upon melting is preferred.

[0030] In the present invention, the relative viscosity of polyamide 6 is preferably 1.8 to 4.5, and more preferably 2.6 to 3.6. If the relative viscosity is less than 1.8, the impact resistance of the film is insufficient. If it is greater than 4.5, the load on the extruder increases, making it difficult to obtain a sheet before stretching.

[0031] The biaxially oriented polyamide film of the present invention may include other thermoplastic resins in addition to polyamide 6, which is the main component, for the purpose of improving stretchability, pinhole resistance, and ease of cutting. In addition, it may include small amounts of additives such as anti-blocking agents, lubricants, antistatic agents, heat stabilizers, and light-resistant agents.

[0032] Other thermoplastic resins other than polyamide 6 used in the present invention may include, for example, homopolymers or copolymers such as polyamide resins, polyester resins, polyolefin resins, acrylic resins, polycarbonate resins, polyvinyl resins, and urethane resins.

[0033] Nylon MXD6, nylon 6I, etc. may be included to improve elongation.

[0034] To improve pinhole resistance, polyamide elastomers, polyester elastomers, polyolefin elastomers, etc. may be included.

[0035] Examples of anti-blocking agents used in the present invention include inorganic fine particles such as silica, kaolin, and zeolite, and cross-linked polymer fine particles such as acrylic and polystyrene. Additionally, silica fine particles can be suitably used in terms of transparency and slipperiness.

[0036] Examples of lubricants used in the present invention include organic lubricants such as ethylenebisstearamide (EBS) which have the effect of lowering surface energy. They may be included within a range where no problems with adhesion and wettability occur.

[0037] Using an anti-blocking agent and a lubricant in combination is desirable because it allows the film to simultaneously possess excellent slipperiness and transparency.

[0038] [Adhesive layer of biaxially oriented polyamide film]

[0039] In the biaxially oriented polyamide film of the present invention, it is preferable to install an adhesive layer made of any one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin, with a coating amount as a solid content of 0.01 to 3 g / m².

[0040] The above adhesive layer is installed by applying and drying a coating solution before winding the film onto a mill roll during the film manufacturing process.

[0041] The coating solution may be applied to an unoriented film, a uniaxially oriented film, and / or a biaxially oriented film. When the film is manufactured by sequential biaxial stretching, the coating solution is typically applied to a uniaxially oriented film and dried. When the film is manufactured by simultaneous biaxial stretching, the coating solution is typically applied to an unoriented film and dried.

[0042] As for the coating solution for installing the adhesive layer in the present invention, since the coating solution is applied and dried before the film is wound onto a mill roll during the film manufacturing process, it is preferable to use a water dispersion or an aqueous solution of a resin to ensure safety and hygiene during manufacturing.

[0043] [Polyester resin used in this adhesive layer]

[0044] When a polyester resin is installed as the above-mentioned adhesive layer, a copolymerized polyester resin may be selected as the polyester resin. A copolymerized polyester resin is a polycondensate of a dicarboxylic acid component, a diol component, and other ester-forming components. Examples of dicarboxylic acid components included as constituents in copolymerized polyester resins include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenylenedicarboxylic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and tetrahydrophthalic acid.

[0045] In addition to the above dicarboxylic acid component, salts of 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2,6-dicarboxylic acid, and 5(4-sulfophenoxy)isophthalic acid may be used to impart water dispersibility. Among these, it is preferable to use 5-sodium sulfoisophthalic acid in a range of 1 to 10 mol%.

[0046] Examples of diol components contained in copolymerized polyester resins include aliphatic diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and polyethylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol; aromatic diols such as 4,4'-bis(hydroxyethyl)bisphenol A; and bis(polyoxyethylene glycol)bisphenol ether.

[0047] [Polyurethane resin used in this adhesive layer]

[0048] In the present invention, when a polyurethane resin is installed as the adhesive layer, the polyurethane resin may be, for example, obtained by reacting an organic polyisocyanate with a polyol having two or more active hydrogens.

[0049] Examples of polyols include polyols having unsaturated double bonds, such as saturated polyester polyols; polyether polyols (e.g., polyethylene glycol, polytetramethylene glycol, etc.); amino alcohols (e.g., ethanolamine, diethanolamine, triethanolamine, etc.); unsaturated polyester polyols (e.g., obtained by polycondensing an unsaturated polycarboxylic acid alone or a mixture of it and a saturated polycarboxylic acid, and a mixture of a saturated polyalcohol and an unsaturated polyalcohol), polybutadiene polyols (e.g., 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, etc.), and acrylic polyols (acrylic polyols having hydroxyl groups in the side chains, obtained by copolymerizing various acrylic monomers with acrylic acid monomers having hydroxyl groups).

[0050] Examples of organic polyisocyanates include aromatic polyisocyanates (e.g., diphenylmethane diisocyanate, toluene diisocyanate, etc.), aliphatic polyisocyanates (e.g., hexamethylene diisocyanate, etc.), alicyclic polyisocyanates (e.g., isophorone diisocyanate, etc.), aromatic and aliphatic polyisocyanates (e.g., xylylene diisocyanate), and polyisocyanates obtained by reacting these isocyanates with a low molecular weight polyol beforehand.

[0051] This polyurethane resin can be manufactured by known methods. During manufacturing, it is necessary to ensure that at least two unreacted isocyanate groups exist in the resulting prepolymer. It is desirable to block these isocyanate groups, and this blocking is particularly essential when preparing an aqueous coating solution. This blocking is well known as the blocking of isocyanates, which allows for the regeneration of free isocyanate groups by heating. Examples of blocking agents include bisulfites, alcohols, oximes, active methylene compounds, imidazoles, lactams, imine compounds, amide compounds, imide compounds, etc.

[0052] The reaction between these blocking agents and the isocyanate groups in the polyurethane prepolymer can be carried out at a temperature of room temperature to 100°C, and a urethane catalyst may be used as needed. Here, to impart stable water dispersibility and water solubility to the polyurethane prepolymer, hydrophilic groups should be introduced into the molecule. Examples of these hydrophilic groups include -SO3M (where M is an alkali metal or alkaline earth metal), -OH, and -COOR (where R is a residue of ammonia or a tertiary amine). Among these, a carboxyl group neutralized by ammonia or a tertiary amine is particularly preferred. There are methods for introducing carboxyl groups neutralized with ammonia or tertiary amines into a polyurethane prepolymer, such as using a carboxyl group-containing polyhydroxy compound as one of the reaction raw materials during the synthesis of the polyurethane prepolymer, reacting a hydroxyl group-containing carboxylic acid or an amino group-containing carboxylic acid with the isocyanate group of a polyurethane prepolymer having unreacted isocyanate groups, and then adding the reaction product to an ammonia solution or a tertiary amine aqueous solution during high-speed stirring to neutralize it.

[0053] [Polyacrylic resin used in this adhesive layer]

[0054] In the present invention, when a polyacrylic resin is installed as the adhesive layer, the polyacrylic resin may be an acrylic polymer obtained by polymerizing acrylic acid or methacrylic acid, or their salts or esters.

[0055] Examples of acrylic acid ester-based and methacrylic acid ester-based monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, etc. Examples of salts of acrylic acid and methacrylic acid include sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, ammonium acrylate, ammonium methacrylate, etc.

[0056] In addition to these essential components, acrylic acid monomers such as acrylamide, methacrylamide, aminoethyl methacrylate, aminomethyl methacrylate, N-methylolacrylamide, and N-methoxymethylacrylamide may be added.

[0057] In addition to the above, it is also possible to use monomers such as vinyl chloride, vinyl acetate, styrene, vinyl ether, butadiene, isoprene, and sodium vinylsulfonate as copolymer components in the polyacrylic resin. Furthermore, in the acrylic polymer, it is desirable to include hydrophilic components such as acrylate components, methacrylate components, acrylic acid components, acrylamide components, 2-hydroxyethyl acrylic acid components, and N-methylolacrylamide components as copolymer components to enhance the functionality of the coating film. Additionally, it may be a copolymer having functional groups in the molecular side chains. Furthermore, this acrylic polymer can be obtained by using a hard component such as methyl methacrylate or ethyl methacrylate as the main component and copolymerizing a soft component such as an acrylic acid ester as the copolymer component.

[0058] [Acrylic graft copolymer polyester water-based dispersion used in the adhesive layer]

[0059] As the resin used in the adhesive layer of the present invention, an acrylic graft copolymer polyester aqueous dispersion is particularly preferred. It comprises particles of grafted polyester and water, an aqueous solvent, or an organic solvent, exhibiting a translucent to milky white appearance. This grafted polyester has a main chain made of polyester and a graft portion (side chain) formed by a polymer of radical polymerizable monomers, including radical polymerizable monomers having hydrophilic groups.

[0060] The average particle size of grafted polyester particles in an acrylic graft copolymer polyester aqueous dispersion, measured by laser light scattering, is 500 nm or less, preferably 10 nm to 500 nm, and more preferably 10 nm to 300 nm. If the average particle size exceeds 500 nm, the film strength after application decreases.

[0061] The content of acrylic graft copolymer polyester particles in the acrylic graft copolymer polyester aqueous dispersion is typically 1 mass% to 50 mass%, preferably 3 mass% to 30 mass%.

[0062] The particles in the acrylic graft copolymer polyester aqueous dispersion that can be used in the present invention may have a core-shell structure in which a polyester main chain is the core in the aqueous dispersion medium.

[0063] The core-shell structure referred to herein means a two-layer structure in which a core portion, composed of a polymer in an aggregated state insoluble in a dispersion medium, is surrounded by a shell portion, composed of a polymer in a dissolved state soluble in a dispersion medium, as is known in the relevant technical field. This structure is a structure that is characteristic of a dispersion of a composite polymer formed by chemically bonding polymers with different solubility in a dispersion medium, and it is known that this structure cannot be expressed by simply mixing polymers with different solubility in a dispersion medium. Furthermore, a simple mixture of polymers with different solubility in a dispersion medium cannot exist as a dispersion having a particle size of 500 nm or less.

[0064] Since the particles in the acrylic graft copolymer polyester aqueous dispersion used in the present invention have a core-shell structure as described above, the dispersion state of the polymer particles in the dispersion medium is stabilized even without using emulsifiers or organic cosolvents commonly used in conventional dispersions. This is intended to protect the dispersed polymer particles by allowing the resin in the shell portion to form a sufficient hydration layer.

[0065] The coating film obtained from the above acrylic graft copolymer polyester aqueous dispersion has excellent adhesion to polyamide films. In addition, because it has excellent anti-blocking properties, it can be used without problems even on film substrates with relatively low glass transition points. Furthermore, when formed into a laminate, it also has very good adhesion to adhesives used when laminating printing inks or sealant layers. The resulting laminated film (also called a laminate film) can have significantly improved durability during retort processing and boiling water treatment. In addition, if a flexible grafted polyester is used in the copolymer polyester aqueous dispersion, the glass transition temperature of the grafted polyester is 30°C or lower, preferably 10°C or lower, the durability of the laminate is further improved.

[0066] [Polyester main chain of acrylic graft copolymer polyester]

[0067] In the present invention, the polyester that can be used as the main chain of the grafted polyester is suitably a saturated or unsaturated polyester synthesized from at least a dicarboxylic acid component and a diol component, and the resulting polyester may be a single polymer or a mixture of two or more polymers. Furthermore, a polyester that is inherently not dispersed or dissolved in water is preferred. The weight average molecular weight of the polyester that can be used in the present invention is 5,000 to 100,000, preferably 5,000 to 50,000. If the weight average molecular weight is less than 5,000, the physical properties of the coating film, such as post-processability of the dried coating film, deteriorate. In addition, if the weight average molecular weight is less than 5,000, the polyester serving as the main chain is prone to water solubilization, so the resulting grafted polyester cannot form the core-shell structure described later. If the weight average molecular weight of the polyester exceeds 100,000, water oxidation becomes difficult. From the perspective of water oxidation, 100,000 or less is desirable. The glass transition point is 30°C or less, preferably 10°C or less.

[0068] The above dicarboxylic acid component is preferably a dicarboxylic acid mixture comprising at least one aromatic dicarboxylic acid, at least one aliphatic and / or alicyclic dicarboxylic acid, and at least one radical polymerizable dicarboxylic acid having an unsaturated double bond. The aromatic dicarboxylic acid included in the dicarboxylic acid mixture is 30 to 99.5 mol%, preferably 40 to 99.5 mol%; the aliphatic and / or alicyclic dicarboxylic acid is 0 to 70 mol%, preferably 0 to 60 mol%; and the dicarboxylic acid having an unsaturated double bond having a radical polymerizable dicarboxylic acid is 0.5 to 10 mol%, preferably 2 to 7 mol%, more preferably 3 to 6 mol%. When the content of a dicarboxylic acid containing a radical polymerizable unsaturated double bond is less than 0.5 mol%, it is difficult to effectively graft the radical polymerizable monomer onto the polyester, so the dispersion particle size in the aqueous medium tends to increase and the dispersion stability tends to decrease.

[0069] As aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, etc. may be used. Additionally, sodium 5-sulfoisophthalate may also be used as needed.

[0070] As aliphatic dicarboxylic acids, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedionic acid, dimer acid, and their acid anhydrides can be used.

[0071] As cycloaliphatic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and their acid anhydrides can be used.

[0072] As radical polymerizable dicarboxylic acids containing unsaturated double bonds, fumaric acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid may be used as α,β-unsaturated dicarboxylic acids, and 2,5-norbornene dicarboxylic acid anhydride, tetrahydrophthalic anhydride, etc. may be used as alicyclic dicarboxylic acids containing unsaturated double bonds. Among these, fumaric acid, maleic acid, and 2,5-norbornene dicarboxylic acid (end-bicyclo-(2,2,1)-5-heptene-2,3-dicarboxylic acid) are preferred.

[0073] The above diol component consists of at least one of an aliphatic glycol having 2 to 10 carbon atoms, alicyclic glycol having 6 to 12 carbon atoms, and an ether-linked glycol.

[0074] As aliphatic glycols having 2 to 10 carbon atoms, ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol, etc. can be used.

[0075] As a cycloaliphatic glycol having 6 to 12 carbon atoms, 1,4-cyclohexanedimethanol, etc., can be used.

[0076] As ether-linked glycols, diethylene glycol, triethylene glycol, dipropylene glycol, and additionally glycols obtained by adding 1 to several moles of ethylene oxide or propylene oxide to two phenolic hydroxyl groups of bisphenols, for example, 2,2-bis(4-hydroxyethoxyphenyl)propane, may be used. Polyethylene glycol, polypropylene glycol, and polytetramethylene glycol may also be used as needed.

[0077] In addition to the above dicarboxylic acid component and diol component, polycarboxylic acids and / or polyols with three or more functionalities can be copolymerized.

[0078] As polycarboxylic acids with three or more functions, (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid, (anhydrous) benzophenone tetracarboxylic acid, trimesic acid, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), etc. can be used.

[0079] As polyols with three or more functionalities, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, etc. can be used.

[0080] Polycarboxylic acids and / or polyols having three or more functionalities may be used in a range of 0 to 5 mol%, preferably 0 to 3 mol%, with respect to the total polycarboxylic acid component including the dicarboxylic acid component or the total polyol component including the diol component.

[0081] (Graft portion of acrylic graft copolymer polyester)

[0082] The graft portion of the grafted polyester that can be used in the present invention may be a polymer derived from a monomer mixture comprising at least one radical polymerizable monomer having a hydrophilic group or a group that can be later changed to a hydrophilic group.

[0083] The weight-average molecular weight of the polymer constituting the graft portion is 500 to 50,000, preferably 4,000 to 50,000. If the weight-average molecular weight is less than 500, the grafting rate decreases, so the imparting of hydrophilicity to the polyester is not sufficiently achieved, and furthermore, it is generally difficult to control the weight-average molecular weight of the graft portion to be less than 500. The graft portion forms a hydration layer of the dispersed particles. In order to impart a hydration layer of sufficient thickness to the particles and obtain a stable dispersion, it is preferable that the weight-average molecular weight of the graft portion derived from the radical polymerizable monomer be 500 or more. The upper limit of the weight-average molecular weight of the graft portion of the radical polymerizable monomer is preferably 50,000 as described above in terms of polymerization compatibility in solution polymerization. Control of molecular weight within this range can be achieved by appropriately selecting the amount of polymerization initiator, monomer dropping time, polymerization time, reaction solvent, and monomer composition, and, if necessary, appropriately combining a chain transfer agent or a polymerization inhibitor. The glass transition point is 30°C or lower, preferably 10°C or lower.

[0084] As hydrophilic groups possessed by radical polymerizable monomers, carboxyl groups, hydroxyl groups, sulfonic acid groups, amide groups, quaternary ammonium salts, phosphate groups, etc., can be used. As groups capable of being converted into hydrophilic groups, acid anhydrides, glycidyl, chlor, etc., can be used. The dispersibility of the grafted polyester in water can be controlled by the hydrophilic groups introduced into the polyester by grafting. Among the above hydrophilic groups, carboxyl groups are preferred for controlling the dispersibility of the grafted polyester in water because the amount introduced into the grafted polyester can be accurately determined using an acid value known in the relevant art.

[0085] Examples of carboxyl group-containing radical polymerizable monomers include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, etc. Additionally, maleic anhydride, itaconic anhydride, methacrylic anhydride, etc., which readily generate carboxylic acids upon contact with water / amine, may be used. Preferred carboxyl group-containing radical polymerizable monomers are acrylic anhydride, methacrylic anhydride, and maleic anhydride.

[0086] In addition to the above-mentioned radical polymerizable monomer containing a hydrophilic group, it is preferable to copolymerize a radical polymerizable monomer that does not contain at least one hydrophilic group. In the case of the hydrophilic group-containing monomer alone, grafting onto the polyester main chain does not occur smoothly, making it difficult to obtain a good copolymerized polyester aqueous dispersion. Only by copolymerizing a radical polymerizable monomer that does not contain at least one hydrophilic group can highly efficient grafting be performed.

[0087] As a radical polymerizable monomer that does not contain a hydrophilic group, one or more combinations of monomers having an ethylenically unsaturated bond and also not containing a hydrophilic group as described above are used. As such monomers, acrylic acid esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and hydroxypropyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and hydroxylpropyl methacrylate; acrylic acid or methacrylic acid derivatives such as acrylamide, N-methylolacrylamide, and diacetoneacrylamide; nitriles such as acrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetate, vinyl propionate, and vinyl benzoate; vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, etc. Examples include vinyl ethers; vinyl ketones such as vinyl methyl ketone, vinylhexyl ketone, and methyl isopropenyl ketone; N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride; and aromatic vinyl compounds such as styrene, α-methylstyrene, t-butylstyrene, vinyltoluene, and vinyl naphthalene. These monomers may be used individually or in combination of two or more.

[0088] The ratio of the monomer containing hydrophilic groups to the monomer not containing hydrophilic groups is determined by considering the amount of hydrophilic groups introduced into the grafted polyester, and is typically in the range of a mass ratio (monomer containing hydrophilic groups:monomer not containing hydrophilic groups) of 95:5 to 5:95, preferably 90:10 to 10:90, and more preferably 80:20 to 40:60.

[0089] When a carboxyl group-containing monomer is used as the hydrophilic group-containing monomer, the total acid value of the grafted polyester is 600–4,000 eq. / 106 g, preferably 700 to 3,000 eq. / 10 6 g, most preferably 800 to 2,500 eq. / 10 6 It is g. The acid value is 600 eq. / 10 6 When the value is g or less, it is difficult to obtain a copolymer polyester aqueous dispersion with small particle size when the grafted polyester is dispersed in water, and furthermore, the dispersion stability of the copolymer polyester aqueous dispersion decreases. Acid value 4,000 eq. / 10 6 If g or more, the water resistance of the adhesive layer formed from the copolymer polyester water-based dispersion is reduced.

[0090] The mass ratio of the polyester main chain to the graft portion (polyester:radical polymerizable monomer) in the acrylic graft copolymer polyester is in the range of 40:60 to 95:5, preferably 55:45 to 93:7, and more preferably 60:40 to 90:10.

[0091] If the mass ratio of the polyester main chain is 40 mass% or less, the excellent performance of the matrix polyester described above—namely, high processability, excellent water resistance, and excellent adhesion to various substrates—cannot be fully exhibited, and conversely, the undesirable performance of the acrylic resin—namely, low processability, gloss, and water resistance—is added. If the mass ratio of the polyester is 95 mass% or more, the amount of hydrophilic groups in the graft portion that impart hydrophilicity to the grafted polyester is insufficient, so a good aqueous dispersion cannot be obtained.

[0092] [Solvents for the Grafting Reaction of Acrylic Grafted Copolymer Polyesters]

[0093] The solvent for the grafting reaction is preferably composed of an aqueous organic solvent having a boiling point of 50 to 250°C. Here, an aqueous organic solvent refers to an organic solvent having a solubility in water at 20°C of at least 10 g / L, preferably 20 g / L or more. An aqueous organic solvent with a boiling point exceeding 250°C is unsuitable because its evaporation rate is slow, so it cannot be sufficiently removed even by high-temperature seizure of the coating film after film formation. Furthermore, an aqueous organic solvent with a boiling point of 50°C or lower is undesirable because when carrying out a grafting reaction using this solvent, an initiator that decomposes into radicals at a temperature of 50°C or lower must be used, which increases the risk of handling.

[0094] As an aqueous organic solvent (Group 1) that dissolves polyesters well and also dissolves polymerizable monomers containing hydrophilic groups, particularly carboxyl groups, and polymers thereof relatively well, the solvents include esters, e.g., ethyl acetate; ketones, e.g., methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ethers, e.g., tetrahydrofuran, dioxane, and 1,3-dioxolane; glycol ethers, e.g., ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol propyl ether, ethylene glycol ethyl ether, and ethylene glycol butyl ether; carbitols, e.g., methyl carbitol, ethyl carbitol, and butyl carbitol; lower esters of glycols or glycol ethers, e.g., ethylene glycol diacetate and ethylene glycol ethyl ether acetate; ketone alcohols, e.g., diacetone alcohol; and N-substituted Examples of amides include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

[0095] In this regard, water, lower alcohols, lower glycols, lower carboxylic acids, lower amines, etc. are examples of aqueous organic solvents (Group 2) that hardly dissolve polyester but relatively well dissolve polymerizable monomers containing hydrophilic groups, particularly carboxyl groups, and polymers thereof. Preferably, alcohols and glycols having 1 to 4 carbon atoms.

[0096] When the grafting reaction is carried out in a single solvent, one type of aqueous organic solvent of Group 1 may be used. When carried out in a mixed solvent, multiple types of aqueous organic solvents of Group 1 or at least one type of aqueous organic solvent of Group 1 and at least one type of aqueous organic solvent of Group 2 may be used.

[0097] Grafting reactions can be carried out in either a single solvent from the aqueous organic solvents of Group 1 or a mixed solvent consisting of one type each from the aqueous organic solvents of Group 1 and Group 2. However, in terms of the behavior of the grafting reaction, the appearance and properties of the grafting reaction product and the aqueous dispersion derived therefrom, it is preferable to use a mixed solvent consisting of one type each from the aqueous organic solvents of Group 1 and Group 2. This is because, in the grafting reaction of polyester, gelation of the system is prone to occur due to crosslinking between polyester molecules, but gelation can be prevented by using a mixed solvent as described below.

[0098] It was confirmed by measuring the viscosity of the polyester in the solutions that in the solvent of Group 1, the polyester molecular chains are in an extended state with large extensions, whereas in the mixed solvent of Group 1 and Group 2, the polyester molecular chains are in a tangled state with small extensions in a pore shape. When the polyester molecular chains are in an extended state, all reaction sites within the polyester main chain can contribute to the grafting reaction, so the grafting rate of the polyester increases, but at the same time, the rate of intermolecular crosslinking also increases. On the other hand, when the polyester molecular chains are in a pore shape, the reaction sites inside the pores cannot contribute to the grafting reaction, and at the same time, the rate of intermolecular crosslinking also decreases. Therefore, by selecting the type of solvent, the state of the polyester molecules can be controlled, and thereby the grafting rate and intermolecular crosslinking by the grafting reaction can be controlled.

[0099] The compatibility of a high graft rate and inhibition of gelation can be achieved in a mixed solvent system. The optimal mixing ratio of the mixed solvents of Group 1 and Group 2 may vary depending on the solubility of the polyester used, but typically the mass ratio of the mixed solvents of Group 1 and Group 2 is in the range of 95:5 to 10:90, preferably 90:10 to 20:80, and more preferably 85:15 to 30:70.

[0100] [Radical Polymerization Initiators and Other Additives for Acrylic Graft Copolymer Polyesters]

[0101] As radical polymerization initiators that can be used in the present invention, organic peroxides and organic azo compounds known to those skilled in the art may be used.

[0102] Examples of organic peroxides include benzoyl peroxide and t-butyl peroxypivalate, and examples of organic azo compounds include 2,2'-azobis(isobutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile).

[0103] The amount of radical polymerization initiator used to carry out the grafting reaction is at least 0.2 mass%, preferably 0.5 mass% or more, relative to the radical polymerizable monomer.

[0104] In addition to the polymerization initiator, a chain transfer agent to control the chain length of the graft portion, such as octyl mercaptan, mercaptoethanol, 3-t-butyl-4-hydroxyanisole, etc., may be used as needed. In this case, it is preferable to add it in the range of 0 to 5 mass% with respect to the radical polymerizable monomer.

[0105] [Grafting reaction of acrylic graft copolymer polyester]

[0106] The formation of the graft portion proceeds by polymerizing the radical-polymerizable unsaturated double bond in the polyester with the radical-polymerizable monomer and / or by reacting the radical-polymerizable unsaturated double bond with the active end of the polymer of the radical-polymerizable monomer. The reaction product after the completion of the grafting reaction contains, in addition to the desired grafted polyester, a polyester without a graft portion and a polymer of the polyester and the ungrafted radical-polymerizable monomer. If the production ratio of the grafted polyester in the reaction product is low and the ratio of the polyester without a graft portion and the polymer of the ungrafted radical-polymerizable monomer is high, a dispersion with good stability is not obtained.

[0107] Typically, the grafting reaction can be carried out by adding the radical polymerizable monomer and the radical initiator to a solution containing the polyester at once under heating, or by adding them dropwise over a certain period of time and then continuing the reaction under heating for an additional period of time. Alternatively, if necessary, a portion of the radical polymerizable monomer may be added first, followed by adding the remaining radical polymerizable monomer and the polymerization initiator dropwise over a certain period of time, and then continuing the reaction under heating for an additional period of time.

[0108] The mass ratio of polyester to solvent is selected to ensure that the reaction proceeds uniformly during the polymerization process, taking into account the reactivity of the polyester and the radical polymerizable monomer and the solvent solubility of the polyester. Typically, it is in the range of 70:30 to 10:90, preferably 50:50 to 15:85.

[0109] [Water Oxidation of Acrylic Graft Copolymer Polyester]

[0110] The grafted polyester that can be used in the present invention can be water-oxidized by introducing it into an aqueous medium in a solid state, or by dissolving it in a hydrophilic solvent and then introducing it into an aqueous medium. In particular, when a monomer having acidic groups such as sulfonic acid groups and carboxyl groups is used as a radical polymerizable monomer having hydrophilic groups, the grafted polyester can be easily dispersed in water as fine particles with an average particle size of 500 nm or less by neutralizing the grafted polyester with a basic compound, thereby preparing a copolymerized polyester aqueous dispersion.

[0111] As for the basic compound, it is preferable to have a compound that volatilizes during film formation or during baking curing when the curing agent described below is incorporated. As such a basic compound, ammonia and organic amines are preferred. Examples of organic amines include triethylamine, N,N-diethylethanolamine, N,N-dimethylethanolamine, aminoethanolamine, N-methyl-N,N-diethanolamine, isopropylamine, iminobispropylamine, ethylamine, diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyliminobispropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine, triethanolamine, etc.

[0112] The amount of basic compound used is preferably such that it at least partially or completely neutralizes the carboxyl groups contained in the graft portion, thereby making the pH value of the aqueous dispersion range from 5.0 to 9.0.

[0113] As a method for preparing an aqueous dispersion of copolymer polyester neutralized by a basic compound, the solvent is removed from the reaction solution under reduced pressure using an extruder or the like after the grafting reaction is completed to form a melt or solid phase (pellet, powder, etc.), and then this is added to an aqueous solution of a basic compound and heated and stirred, or an aqueous solution of a basic compound is added to the reaction solution immediately after the grafting reaction is completed and additional heating and stirring is continued (one-pot method). The one-pot method is preferred for convenience. In this case, if the boiling point of the solvent used in the grafting reaction is 100°C or lower, part or all of it can be easily removed by distillation.

[0114] [Crosslinking agent added to the coating solution forming the adhesive layer]

[0115] The above coating solution can be used as is as a coating agent to form the adhesive layer, but by additionally mixing a crosslinking agent (curing resin) and performing curing, high water resistance can be imparted to the adhesive layer.

[0116] As crosslinking agents, phenolformaldehyde resins, which are condensates of alkylated phenols, cresols, etc., and formaldehyde; amino resins, such as adducts of formaldehyde, urea, melamine, benzoguanamine, etc., and alkyl ether compounds composed of these adducts and alcohols having 1 to 6 carbon atoms; polyfunctional epoxy compounds; polyfunctional isocyanate compounds; block isocyanate compounds; polyfunctional aziridine compounds; oxazoline compounds, etc. may be used.

[0117] Examples of phenol-formaldehyde resins include condensates of phenols and formaldehyde such as alkylated (methyl, ethyl, propyl, isopropyl or butyl)phenol, p-tert-amylphenol, 4,4'-sec-butylidenephenol, p-tert-butylphenol, o-, m-, p-cresol, p-cyclohexylphenol, 4,4'-isopropylidenephenol, p-nonylphenol, p-octylphenol, 3-pentadecylphenol, phenol, phenyl o-cresol, p-phenylphenol, and xylenol.

[0118] Examples of amino resins include methoxylated methylol urea, methoxylated methylol N,N-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, etc., and preferably, methoxylated methylol melamine, butoxylated methylol melamine and methylolated benzoguanamine, etc.

[0119] As polyfunctional epoxy compounds, for example, diglycidyl ethers of bisphenol A and their oligomers, diglycidyl ethers of hydrogenated bisphenol A and their oligomers, orthophthalic acid diglycidyl esters, isophthalic acid diglycidyl esters, terephthalic acid diglycidyl esters, p-oxybenzoic acid diglycidyl esters, tetrahydrophthalic acid diglycidyl esters, hexahydrophthalic acid diglycidyl esters, succinic acid diglycidyl esters, adipic acid diglycidyl esters, sebacic acid diglycidyl esters, ethylene glycol diglycidyl ethers, propylene glycol diglycidyl ethers, 1,4-butanediol diglycidyl ethers, 1,6-hexanediol diglycidyl ethers and polyalkylene glycol diglycidyl ethers, trimellitic acid triglycidyl esters, Examples include triglycidyl isocyanurate, 1,4-diglycidyloxybenzene, diglycidylpropyleneurea, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol triglycidyl ether, and triglycidyl ether of glycerolalkylene oxide adduct.

[0120] As polyfunctional isocyanate compounds, low or high molecular weight aromatic or aliphatic diisocyanates and polyisocyanates with trivalent or higher valence may be used. As polyisocyanates, there are tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and trimers of their isocyanate compounds. In addition, examples include terminal isocyanate group-containing compounds obtained by reacting an excess amount of these isocyanate compounds with low molecular weight active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, and triethanolamine, or high molecular weight active hydrogen compounds such as polyester polyols, polyether polyols, and polyamides.

[0121] Blocked isocyanates can be prepared by adding the above isocyanate compound and a blocking agent by a suitable conventionally known method. Examples of isocyanate blocking agents include phenols such as phenol, cresol, xylenol, resorcinol, nitrophenol, and chlorophenol; thiophenols such as thiophenol and methylthiophenol; oximes such as acetoxyme, methyl ethyl ketoxyme, and cyclohexanone oxime; alcohols such as methanol, ethanol, propanol, and butanol; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol; tertiary alcohols such as t-butanol and t-pentanol; lactams such as ε-caprolactam, δ-valerolactam, v-butyrolactam, and β-propyllactam; aromatic amines; imides; active methylene compounds such as acetylacetone, acetoacetic acid esters, and ethyl malonicate; mercaptans; imines; ureas; diaryl compounds; and sodium bisulfite. It is possible.

[0122] These crosslinking agents can each be used individually or in a mixture of two or more types. As for the amount of crosslinking agent, 5% to 40% by mass relative to the grafted polyester is preferred.

[0123] As a method for incorporating a crosslinking agent, (1) if the crosslinking agent is water-soluble, a method of directly dissolving or dispersing it in a water-based dispersion, or (2) if the crosslinking agent is oil-soluble, a method of adding the crosslinking agent after the grafting reaction is completed, or before or after water oxidation, to coexist with the polyester in the core. These methods can be appropriately selected depending on the type and properties of the crosslinking agent. In addition, a curing agent or an accelerator may be used in combination with the crosslinking agent.

[0124] The adhesive layer used in the present invention may additionally contain additives such as antistatic agents, inorganic lubricants, and organic lubricants to impart antistatic and slip properties, to the extent that the effects of the present invention are not impaired. When antistatic agents, inorganic lubricants, organic lubricants, etc. are applied to the film surface, it is preferable to include them in the adhesive layer to prevent the separation of these additives.

[0125] In order to form this adhesive layer, known coating methods such as gravure, reverse, die, bar, and dip methods may be used as a method for applying a coating agent containing a copolymer polyester water-based dispersion to a polyamide film substrate.

[0126] The amount of coating agent applied is 0.01 to 3 g / m² as a solid content relative to the polyester film after biaxial orientation. Preferably, it is applied to a value of 0.04 to 0.5 g / m². If the amount of coating is 0.01 g / m² or less, sufficient adhesive strength between this adhesive layer and the other layer is not obtained. If it is 3 g / m² or more, blocking occurs, which is a practical problem.

[0127] This adhesive layer can be prepared by applying a coating agent to a biaxially stretched polyamide film substrate, or by applying a coating agent to an unstretched or uniaxially stretched polyamide film substrate, drying, and, if necessary, performing heat setting after additional uniaxial or biaxial stretching. By drying and heat setting at a drying temperature of 150°C or higher, preferably 200°C or higher, after applying the coating agent, the coating film becomes rigid, and the adhesion between this adhesive layer and the polyamide film substrate is improved.

[0128] When stretching is performed after coating, drying after coating requires controlling the moisture content of the coating film to a range of 0.1 to 2% so as not to impair the stretchability of the coating film. After stretching, drying and heat-setting at 200°C or higher hardens the coating film, thereby dramatically improving the adhesion between the adhesive layer and the polyamide film substrate.

[0129] [Physical properties of biaxially oriented polyamide film]

[0130] The biaxially oriented polyamide film of the present invention has a molecular orientation angle of 20° or more and a hygroscopic deformation of 1.3% or less. A hygroscopic deformation of 1.1% or less is more preferable. If the hygroscopic deformation is greater than 1.3%, the S-shaped curling caused by moisture absorption of the manufactured bag increases, causing problems.

[0131] Since the biaxially oriented polyamide film of the present invention is a film close to the end with respect to the width direction of the mill roll, the molecular orientation angle is 20° or greater. The molecular orientation angle is the angle in the direction of the molecular chain orientation axis, measured using the MOA-6004 molecular orientation angle measuring device manufactured by Oji Measuring Instruments Co., Ltd. The molecular orientation angle is a value calculated by setting the angle in the longitudinal direction of the film to 0 degrees, and determining the difference from 0 degrees when the direction of the molecular orientation axis is less than 45 degrees relative to the longitudinal direction, and the difference from 90 degrees when it is greater than 45 degrees. A larger value indicates a larger bowing phenomenon, and the value increases as the film moves closer to the end from the center of the mill roll. Therefore, in the present invention, it is important to obtain a film with small hygroscopic deformation even if the molecular orientation angle is large.

[0132] The impact strength of the biaxially oriented polyamide film of the present invention is 0.8 J / 15 μm or higher. Preferably, it is 1.0 J / 15 μm or higher. If the impact strength is lower than 0.8 J / 15 μm, the packaging bag may be damaged by impact during transportation when used for packaging. A higher impact strength is preferable because it makes it less likely for the packaging bag to be damaged. However, it is difficult to manufacture to satisfy other characteristics while also making it greater than 2.0 J / 15 μm.

[0133] In addition, the thermal shrinkage rate of the biaxially oriented polyamide film of the present invention after heating at 160°C for 10 minutes is in the range of 0.6 to 3.0% in both the MD direction (longitudinal direction) and the TD direction (width direction). Preferably, it is 0.6 to 2.5%. If the thermal shrinkage rate is greater than 3.0%, the film shrinks during printing, lamination, or binding processes, which is undesirable as it results in poor appearance. If the thermal shrinkage rate is less than 0.6%, moisture absorption deformation may increase.

[0134] In addition, the biaxially oriented polyamide film of the present invention preferably has an orientation angle of 20° or more and a heat shrinkage deformation of 2.0% or less. More preferably, it is 1.8% or less. If the heat shrinkage deformation is greater than 2.0%, shrinkage deformation may occur in the heat-sealed portion when the bag is heat-sealed, which may result in a deterioration of the appearance. In addition, a sufficient S-curling inhibition effect may not be obtained.

[0135] [Method for manufacturing a biaxially oriented polyamide film]

[0136] The biaxially oriented polyamide film of the present invention is obtained, for example, by first pre-longitudinally stretching an unoriented polyamide film in the longitudinal direction at a low magnification, then performing main longitudinal stretching in the longitudinal direction in two or more stages so that the total longitudinal stretching magnification is three or more, then performing transverse stretching, heat-setting treatment, and heat-relaxing treatment, then trimming the clip gripping portion, winding it with a mill roll, and then slitting it to a width for processing.

[0137] The width of the mill roll of the biaxially oriented polyamide film of the present invention is not particularly limited, but is typically 3,000 to 8,000 mm. The winding length of the polyamide film mill roll is not particularly limited, but is typically 5,000 to 70,000 m.

[0138] The width of the slit roll for processing is 400 to 3,000 mm, and the winding length is 3,000 to 10,000 m.

[0139] Recently, with the increase in film size in aluminum vacuum deposition machines, slit rolls have also become larger. Therefore, it does not matter if the slit roll has a larger width and winding length than the above.

[0140] Since the biaxially oriented polyamide film of the present invention is a film close to the end of the mill roll, the orientation angle is 20° or more.

[0141] The biaxially oriented polyamide film of the present invention tends to have a larger orientation angle and larger moisture absorption deformation and heat shrinkage deformation as it gets closer to the end of the mill roll.

[0142] If the film roll contains a biaxially oriented polyamide in which the orientation angle of the film on the right or left end of the slit film roll is 20° or more and the moisture absorption deformation is 1.3% or less, the amount of S-shaped curling caused by moisture absorption of the bag obtained by processing can be suppressed to an amount that does not cause problems.

[0143] A preferred method for obtaining a biaxially oriented polyamide film of the present invention will be described in more detail.

[0144] For example, the biaxially oriented polyamide film of the present invention is preferably produced by pre-stretching an unoriented polyamide film in the longitudinal direction at a low magnification, then performing main longitudinal stretching in the longitudinal direction at a high magnification in two or more stages, continuing transverse stretching, and additionally performing heat-setting and heat-relaxation treatments, thereby winding the biaxially oriented polyamide film to obtain a mill roll.

[0145] The above preliminary longitudinal stretching may be one stage or two or more stages. However, the total stretching ratio obtained by multiplying each stretching ratio of the preliminary longitudinal stretching is preferably 1.005 to 1.15 times.

[0146] It is preferable that the main longitudinal stretching performed after the preliminary longitudinal stretching be divided into two or more stages in the longitudinal direction. The ratio of the first stage of the main longitudinal stretching is preferably 1.1 to 2.9 times. It is preferable that the ratio of the second stage and subsequent stages of the main longitudinal stretching be set so that the total longitudinal stretching ratio, calculated by multiplying each stretching ratio including the preliminary longitudinal stretching ratio, is 2.8 to 5.0 times. It is more preferable to have a ratio of 3.0 to 3.5 times.

[0147] An example of a method for obtaining a biaxially oriented amide film of the present invention will be described.

[0148] First, the raw material having the above polyamide 6 as the main component is dried, then melt-extruded by an extruder, cast from a T-die onto a rotating drum, and rapidly cooled to obtain an unoriented polyamide film.

[0149] This unoriented film is subjected to preliminary longitudinal stretching of 1.005 to 1.15 times at a temperature of [glass transition temperature (hereinafter abbreviated as Tg) + 20]°C or higher and [low-temperature crystallization temperature (hereinafter abbreviated as Tc) + 20]°C or lower.

[0150] Here, Tg and Tc are values ​​obtained by measuring using the method described in the example.

[0151] If preliminary longitudinal stretching is performed at a temperature below (Tg + 20)°C, necking occurs, making it prone to increased thickness non-uniformity. On the other hand, if stretching is performed at a temperature exceeding (Tc + 20)°C, crystallization proceeds, making it prone to fracture during transverse stretching, which is undesirable. A more preferable stretching temperature is (Tg + 30)°C to (Tc + 10)°C. If the stretching ratio in this preliminary longitudinal stretching is excessively low, it is difficult to obtain the effect of improving hygroscopic deformation. Conversely, if it is excessively high, orientational crystallization proceeds excessively, causing the stretching stress in the main longitudinal stretching described later to become excessively high, making it prone to fracture during main longitudinal stretching or transverse stretching. From this perspective, the stretching ratio of the preliminary stretching is preferably 1.005 to 1.15 times. A more preferable stretching ratio is 1.01 to 1.1 times. Preliminary longitudinal stretching may be performed in a single stage or in multiple stages, but it is preferable to keep the total preliminary longitudinal stretching ratio within the above range.

[0152] For preliminary longitudinal stretching, known longitudinal stretching methods such as thermal roll stretching and infrared radiation stretching may be used.

[0153] It is preferable to perform preliminary longitudinal stretching followed by multi-stage main longitudinal stretching (abbreviated as main longitudinal stretching). It is preferable to perform the main longitudinal stretching at a stretching temperature of (Tg + 20)°C or higher and (Tc + 20)°C or lower. It is preferable to perform the first stage of the main longitudinal stretching with a longitudinal stretching ratio of 1.1 to 2.9 times. If this first stage of the main longitudinal stretching is excessively low, no stretching effect is obtained. Conversely, if it is excessively high, orientational crystallization proceeds excessively, causing the stretching stress in the second stage of the main longitudinal stretching to become excessively high, making it prone to fracture during longitudinal or transverse stretching. It is preferable that the stretching temperature in the first stage of the main longitudinal stretching be (Tg + 20)°C to (Tc + 20)°C. If the stretching temperature is below (Tg+20)℃, the stretching stress increases, making it prone to fracture during transverse stretching, and if it exceeds (Tc+20)℃, thickness non-uniformity increases. More preferably, it is (Tg+30)℃ to (Tc+10)℃. For the same reasons as above, the stretching ratio of the first stage of the main longitudinal stretching is preferably 1.1 to 2.9 times. A more preferable stretching ratio is 1.5 to 2.5 times. For the first stage of the main longitudinal stretching, known longitudinal stretching methods such as thermal roll stretching and infrared radiation stretching may be used.

[0154] After the first stage of main longitudinal stretching, the second stage of main longitudinal stretching is performed. For the second stage of main longitudinal stretching, a thermal roll stretching method is preferred. For the second stage of main longitudinal stretching, it is preferable to use a ceramic roll with a surface roughness Ra of 0.2 μm or less. If a roll with a Ra greater than 0.2 μm is used, stretching is performed while the film slides on the roll, which is undesirable as it causes abrasions on the film surface. Furthermore, it is undesirable because the stretching start point on the roll becomes uneven in the width direction or the stretching start point varies, resulting in thickness unevenness. That is, for the second stage of main longitudinal stretching, it is preferable that the film be stretched while in a linear, close contact state in the width direction on the roll, regardless of the width direction thickness profile of the film that underwent the first stage of main longitudinal stretching, thereby achieving uniform thermal stretching in the width direction. Here, Ra refers to the centerline average roughness, which is the average height of irregularities (unit = μm), and is a value specified in JIS B 0601.

[0155] The elongation ratio of the second stage of the main longitudinal stretching is performed such that the sum of the products of each preliminary longitudinal stretching ratio and the main longitudinal stretching ratio is 2.8 times or more. If it is less than 2.8 times, the variation in physical properties in the width direction of the biaxially oriented film is reduced, but the strength in the longitudinal direction decreases. If the total longitudinal stretching ratio becomes excessively large, there may be cases where the effect of reducing the variation in physical properties in the width direction of the biaxially oriented film is not manifested. Considering this, the preferred total longitudinal stretching ratio is 3.0 to 3.8 times, and more preferably 3.0 to 3.5 times. The stretching temperature in the second stage of longitudinal stretching is also (Tg+20)℃ to (Tc+20)℃. If this stretching temperature is below (Tg+20)℃, the stretching stress increases, making it easy to break during transverse stretching, and if it exceeds (Tc+20)℃, thickness non-uniformity increases. More preferably, it is (Tg+30)℃ to (Tc+10)℃.

[0156] The coating solution can be applied to the longitudinally uniaxially oriented film obtained in this way. Known methods such as roll coating (gravure method, reverse method, etc.), knife coating, rod coating, nozzle coating, and air knife coating can be employed for the coating process.

[0157] After application, the coating solution is dried with hot air or the like, and then stretched in the transverse direction using a tenter. Drying of the coating solution may also be performed using a tenter.

[0158] If the transverse stretching temperature is excessively low, the transverse stretching ability may deteriorate (fracture may occur). On the other hand, if it is excessively high, thickness non-uniformity tends to increase. In this regard, the transverse stretching temperature is preferably 100 to 200°C, and more preferably 120 to 160°C. In addition, in order to secure transverse strength, the stretching ratio is preferably 3.0 to 5.0 times, and more preferably 3.5 to 4.5 times. The biaxially oriented polyamide film stretched in this manner is subjected to heat-setting and heat-relaxation treatments, the clip-holding portion is cut off, and then wound onto a mill roll.

[0159] As described above, the biaxially oriented polyamide film of the present invention is preferably obtained by, for example, dividing longitudinal stretching into preliminary longitudinal stretching and main longitudinal stretching, and further dividing the main longitudinal stretching into two or more stages, using a ceramic roll with a surface roughness Ra of 0.2 μm or less as the stretching roll of the second stage of the main longitudinal stretching, then applying a coating solution and drying, then stretching in the transverse direction, heat-setting treatment and heat-relaxation treatment, cutting off the clip-holding portion, and winding it with a mill roll.

[0160] To further improve dimensional stability, the biaxially oriented polyamide film of the present invention may be subjected to additional heat-setting treatment, heat-relaxation treatment, moisture-regulating treatment, etc. In addition, to further improve adhesion and wettability, corona treatment, coating treatment, flame treatment, etc., may be performed.

[0161] The above-mentioned heat-setting treatment, heat-relaxation treatment, humidity control treatment, corona treatment, coating treatment, flame treatment, etc., can also be performed during the manufacturing process of the biaxially oriented polyamide film. In addition, it is also possible to perform the treatment by unwinding a mill roll or a slit roll.

[0162] Examples

[0163] The present invention will be explained in more detail below with reference to examples. In addition, the raw materials used, the physical properties of the film, and the method for evaluating the characteristics are as follows. Unless otherwise specified, measurements were performed in a measurement room with an environment of 23°C and 65% relative humidity.

[0164] <Raw Materials for Biaxially Oriented Polyamide Films>

[0165] [Polyamide 6]

[0166] Polyamide 6 with relative viscosity RV = 2.9 and melting point (Tm): 220°C was used.

[0167] [Polyamide MXD6]

[0168] Polyamide MXD6 with relative viscosity RV = 2.2 and melting point (Tm): 238°C was used.

[0169] [Masterbatch of Silica Microparticles and Ethylenebisstearamide]

[0170] 93.5 mass% of the above polyamide 6, 5 mass% of porous silica fine particles (weight average particle size = 4 μm, pore volume = 1.6 ml / g), and 1.5 mass% of ethylenebisstearic acid amide (Lightamide WE-183 manufactured by Kyoei Chemical Co., Ltd.) were blended, melt-kneaded and extruded using a twin-screw extruder, and cut into pellet shapes to obtain a masterbatch.

[0171] <Coating solution used to form the adhesive layer>

[0172] To form this adhesive layer, the following two types of aqueous dispersion coating solutions were used.

[0173] [Coating solution (A): Water-based dispersion of acrylic graft copolymer polyester]

[0174] 466 parts by mass of dimethyl terephthalate, 466 parts by mass of dimethyl isophthalate, 401 parts by mass of neopentyl glycol, 443 parts by mass of ethylene glycol, and 0.52 parts by mass of tetra-n-butyl titanate were placed in a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, and an ester exchange reaction was carried out at 160–220°C for 4 hours. Subsequently, 23 parts by mass of fumaric acid were added, and the temperature was increased from 200°C to 220°C over 1 hour to carry out an esterification reaction. Then, the temperature was increased to 255°C, the reaction system was gradually depressurized, and the reaction was carried out under a reduced pressure of 0.2 mmHg for 1 hour and 30 minutes while stirring to obtain a polyester. The obtained polyester was pale yellow transparent, with a glass transition temperature of 60°C and a weight average molecular weight of 12,000. The composition obtained by NMR measurement, etc. was as follows.

[0175] · Dicarboxylic acid component

[0176] Terephthalic acid 48 mol%

[0177] Isophthalic acid 48 mol%

[0178] Fumaric acid 4 mol%

[0179] · Diol ingredient

[0180] Neopentyl glycol 50 mol%

[0181] Ethylene glycol 50 mol%

[0182] 75 parts by mass of the polyester resin, 56 parts by mass of methyl ethyl ketone, and 19 parts by mass of isopropyl alcohol were added to a reactor equipped with a stirrer, a thermometer, a reflux device, and a quantitative dispensing device, and the resin was dissolved by heating and stirring at 65°C. After the resin was completely dissolved, a mixture of 17.5 parts by mass of methacrylic acid and 7.5 parts by mass of ethyl acrylate and a solution of 1.2 parts by mass of azobisdimethylvaleronitrile dissolved in 25 parts by mass of methyl ethyl ketone were added dropwise to the polyester solution at a rate of 0.2 ml / min, and stirring was continued for an additional 2 hours after the dispensing was finished. After taking an analytical sample (5 g) from the reaction solution, 300 parts by mass of water and 25 parts by mass of triethylamine were added to the reaction solution, and the mixture was stirred for 1 hour to prepare a dispersion of grafted polyester. Afterwards, the temperature of the obtained dispersion was raised to 100°C, and methyl ethyl ketone, isopropyl alcohol, and excess triethylamine were removed by distillation to obtain a copolymer polyester aqueous dispersion.

[0183] The obtained dispersion was white with an average particle size of 300 nm and a Type B viscosity of 50 centipoise at 25°C. 1.25 g of heavy water was added to 5 g of this dispersion to make the solid content concentration 20 mass%, and then DSS was added, followed by 125 MHz 13C-NMR measurement. The full width at half maximum (FWHM) of the signal of the carbonyl carbon of the polyester main chain (160–175 ppm) was ∞ (no signal detected), and the FWHM of the signal of the carbonyl carbon of the methacrylic acid in the grafted portion (181–186 ppm) was 110 Hz. The solution sampled at the end of the grafting reaction was dried under vacuum at 100°C for 8 hours, and the acid value of the solid was measured, the graft efficiency of the polyester was measured (by NMR measurement), and the molecular weight of the grafted portion by hydrolysis was measured. The acid value of the solids is 2,300 eq. / 10 6It was g. From the measurement of 1H-NMR, no signal of fumaric acid origin (δ = 6.8–6.9 ppm, doublet) was detected, confirming that the graft efficiency of the polyester was 100%. The molecular weight of the grafted portion was a weight-average molecular weight of 10,000.

[0184] After that, the aqueous dispersion obtained as described above was diluted with water to a solid content concentration of 5 mass% to obtain a coating solution (A).

[0185] [Coating solution (B): Water-based dispersion of polyurethane resin]

[0186] (A) Preparation of a polyurethane and an aqueous dispersion; adipic acid was used as the dicarboxylic acid component; and 60 mol% of 1,4-butanediol (glycol component) and 40 mol% of a propylene oxide (1 mol) adduct of bisphenol A were used as the glycol component to obtain a polyester (polyester polyol) with a Tg of -5°C. A urethane polymer was obtained by reacting this polyester with toluene diisocyanate. This was used as a prepolymer, and 1,6-hexanediol was reacted to extend the chain while simultaneously reacting aminocarboxylates at the terminals to obtain a water-insoluble and water-dispersible polyurethane. This was dispersed in hot water while stirring to obtain a 25% aqueous dispersion.

[0187] A coating solution (B) was obtained by adding the above-mentioned aqueous dispersion of polyurethane to an equal mixture of ion-exchanged water and isopropyl alcohol and diluting it so that the solid content is 5 mass%.

[0188] <Measurement Methods, Evaluation Methods>

[0189] Measurement and evaluation of biaxially oriented polyamide films and film rolls were performed using the following methods. The results of the measurement and evaluation are shown in Tables 1 to 6 along with the film formation conditions.

[0190] [Relative Viscosity]

[0191] The relative viscosity of a polyamide solution, prepared by dissolving 0.25 g of the above-mentioned raw material polyamide in 96% sulfuric acid in a 25 ml volumetric flask to a concentration of 1.0 g / dL, was measured at 20°C.

[0192] [Tg, Tc and Tm]

[0193] Using a DSC-60 type differential scanning calorimeter manufactured by Shimadzu Corporation in accordance with JIS K7121, the melting peak temperature Tm was measured as the melting point while heating a pan containing 10 mg of unoriented polyamide film from 30°C to 280°C at a heating rate of 10°C / min in a nitrogen atmosphere, and after reaching 280°C, the pan containing the sample was immersed in liquid nitrogen to rapidly cool it, and then the pan was heated from -10°C to 280°C at a heating rate of 20°C / min, and the glass transition onset temperature Tg and cold crystallization peak temperature Tc, which were added during the heating process, were measured.

[0194] [Amount of this adhesive layer applied]

[0195] A biaxially oriented polyamide film was cut into an area of ​​10 cm × 10 cm, and the adhesive surface of the film was wiped with a cloth soaked in a mixed organic solvent of methyl ethyl ketone / toluene = 1 / 1. The weight before and after wiping was measured using a precision balance (AUW120D manufactured by Shimadzu Corporation). The coating amount (g / m²) was calculated by converting the measured weight difference into a value per square meter.

[0196] [Molecular Orientation Angle]

[0197] A slit roll was slit, and a slit roll with a width of 940 mm was fabricated on the inside, with the corner formed at 150 mm from the left end of the mill roll. A film sample was taken in a square shape with sides of 100 mm, with the center of the square formed at 150 mm from the right and left ends in the width direction of the slit roll, and the molecular orientation angle (angle in the direction of the molecular orientation axis) was measured using a molecular orientation angle measuring device (MOA-6004) manufactured by Oji Measuring Instruments Co., Ltd. For the molecular orientation angle, the angle in the longitudinal direction of the film was set to 0 degrees. When the direction of the molecular orientation axis was less than 45 degrees relative to the longitudinal direction, the difference from 0 degrees was calculated, and when it was greater than 45 degrees, the difference from 90 degrees was calculated; the larger value was shown as the molecular orientation angle in Table 1. In both the examples and comparative examples, the value at the left end, which is closer to the end of the mill roll, was larger.

[0198] [Film Thickness] and [Impact Strength]

[0199] A mill roll was slit to form a corner 15 mm from the left end of the mill roll, and a slit roll with a width of 940 mm was fabricated on the inside. A measurement sample was cut out centered at a position 150 mm inward from the right and left ends in the width direction of the slit roll, and after measuring the thickness using a thickness gauge manufactured by Tester Sangyo, the impact strength of the film was measured using a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., with a hemispherical impact head with a diameter of 1 / 2 inch. The obtained value was expressed as an impact strength equivalent to 15 μm using the formula below. Table 1 shows the values ​​on the left end side, where the molecular orientation angle was large.

[0200] Impact Intensity (J / 15 µm) = Observed Impact Intensity (J) × 15 µm / Thickness (µm)

[0201] For the evaluation of the mill roll, film samples were taken at positions 300 mm inward from the right and left ends in the width direction of the mill roll, and the thickness and impact strength were measured in the same manner. The evaluation results are shown in Table 2.

[0202] [Moisture absorption deformation]

[0203] A mill roll was slit, and a slit roll with a width of 940 mm was fabricated on the inside, with the corner formed at 150 mm from the left end of the mill roll. A measurement sample was taken in the shape of a square with sides of 210 mm, with the center of the square formed at 150 mm from the right and left ends in the width direction of the slit roll. A circle with a diameter of 200 mm was drawn with the center of the sample as the center, and lines passing through the center of the circle were drawn in the 45° and 135° directions with the MD direction set to 0°. Subsequently, the sample was left in an atmosphere of 30° × 80%RH for at least 2 hours, and the diameter in each direction was measured to determine the length under high humidity. Afterward, the sample was left in a room of 20° × 40%RH for at least 2 hours, and the length of the straight line drawn in each diameter direction was measured again to determine the length under low humidity, and the moisture absorption elongation rate was calculated using the following formula. Afterwards, the absolute value (%) of the difference in hygroscopic elongation in the 45° direction and the 135° direction was calculated as hygroscopic deformation, and the value with the larger absolute value was shown in Table 1 as hygroscopic deformation. In the examples and comparative examples, the value on the left was larger, similar to the molecular orientation angle.

[0204] Moisture absorption elongation = [(Length at high humidity - Length at low humidity) / Length at low humidity] × 100 (%)

[0205] For the evaluation of the mill roll, film samples were taken at positions 300 mm inward from the right and left ends in the width direction of the mill roll, and moisture absorption deformation was measured in the same manner. The evaluation results are shown in Table 2.

[0206] [Thermal Shrinkage Rate]

[0207] A mill roll was slit, and a slit roll with a width of 940 mm was fabricated on the inside, with the corner formed at 150 mm from the left end of the mill roll. A measurement sample was cut out centered at 150 mm inward from the right and left ends in the width direction of the slit roll, and the thermal shrinkage rate was measured by the following formula in accordance with the dimensional change test method described in JIS C2318, except that the test temperature was 160°C and the heating time was 10 minutes. Table 1 shows the values ​​on the left side, where the molecular orientation angle was large.

[0208] Thermal shrinkage rate = [(Length before treatment - Length after treatment) / Length before treatment] × 100 (%)

[0209] For the evaluation of the mill roll, film samples were taken at positions 300 mm inward from the right and left ends in the width direction of the mill roll, and the thermal shrinkage rate was measured in the same manner. The evaluation results are shown in Table 2.

[0210] [Thermal Shrinkage Deformation]

[0211] A mill roll was slit, and a slit roll with a width of 940 mm was fabricated on the inside, with the corner formed at 150 mm from the left end of the mill roll. A measurement sample was taken in the shape of a square with sides of 210 mm, with the center of the square formed at 150 mm from the right and left ends in the width direction of the slit roll, and each film was left in an atmosphere of 23° and 65%RH for at least 2 hours. Then, a circle with a diameter of 200 mm was drawn with the center of the sample as the center, and with the MD direction (longitudinal direction) set to 0°, straight lines passing through the center of the circle were drawn in the 45° and 135° directions, and the diameter in each direction was measured and taken as the length before processing. Next, the sample was heat-treated at a test temperature of 160°C for 10 minutes, removed, and left in an atmosphere of 23°C and 65% RH for at least 2 hours. The length of the straight line drawn in each diameter direction was measured again and used as the length after treatment, and the thermal shrinkage rate was calculated by the following formula. Subsequently, the absolute value (%) of the difference in thermal shrinkage rates between the 45° and 135° directions was calculated as the thermal shrinkage deformation, and the value with the larger absolute value was shown in Table 1 as the thermal shrinkage deformation. In the examples and comparative examples, the value on the left was larger, similar to the molecular orientation angle.

[0212] Thermal shrinkage rate = [(Length before treatment - Length after treatment) / Length before treatment] × 100 (%)

[0213] For the evaluation of the mill roll, film samples were taken at positions 300 mm inward from the right and left ends in the width direction of the mill roll, and thermal shrinkage deformation was measured in the same manner. The evaluation results are shown in Table 2.

[0214] [S-curling]

[0215] A mill roll was slit to form a corner 150 mm from the left end of the mill roll, and a slit roll with a width of 940 mm was fabricated on the inside. A polyester-based adhesive [a mixture of TM-569 (product name) and CAT-10L (product name) manufactured by Toyo Motor Inc. at a weight ratio of 7.2 / l (solid content concentration 23%)] was applied to the corona-treated surface of the polyamide film of the slit roll so that the resin solid content after drying was 3.2 g / m². Then, a linear low-density polyethylene film (L-LDPE film: manufactured by Toyo Motor Inc., RIX (registered trademark) L4102) 40 μm was dry-laminated, and aging was performed for 2 days under an environment of 40°C to obtain a laminated film.

[0216] As described above, the laminated film wound as a laminated film roll was folded in half at the center parallel to the winding length direction using a 3-way sealing bag making machine manufactured by Nishibe Kikai Co., Ltd., then cut and stacked so that the polyamide film was on the outside. The ends were heat-sealed at 155°C with a width of 10 mm in the longitudinal direction and a center part with a width of 20 mm, and heat-sealed intermittently at 180°C with a width of 20 mm and a spacing of 170 mm in the vertical direction. After cutting the edges on both sides so that the width of the bag was 220 mm at the center of the central sealing part in the winding length direction, the bag was cut at the center of the sealing part in the vertical direction to produce a 3-way sealing bag (sealing width: 10 mm). Ten samples of the left-side bags of the produced 3-way sealing bags were prepared. Then, 10 three-way sealing bags were treated at 30°C and 60%RH for 24 hours, maintained in an atmosphere of 20°C and 20%RH for 24 hours, and three points—two openings at the four corners and one at the sealing part—were pressed, and the degree of bending (S-curling) of the remaining corner was evaluated as follows.

[0217] 10 points: Less than 40 mm

[0218] 5 points: Less than 40–50 mm

[0219] 1 point: 50 mm or more

[0220] The average of the 10-point evaluation scores was marked as ◎ for 7 points or more, ○ for 3 to 7 points, and × for less than 3 points.

[0221] For bags rated × with less than 3 points, the problem is that there are issues with the bag's box packaging or the return of the charger. If the rating is 3 points or higher, the problem is within an acceptable range.

[0222] [Water Resistance Laminate Strength (Laminate Strength under Water Adhesion Conditions)]

[0223] To evaluate S-curling, a laminated film was cut into a rectangular shape with a width of 15 mm × a length of 200 mm, and one end of the laminated film was peeled at the interface between a biaxially stretched polyamide film and a linear low-density polyethylene film. Using a (manufactured by Shimadzu Corporation, Autograph), the laminate strength was measured three times while dropping water with a dropper onto the peeling interface of the rectangular laminated film under conditions of a temperature of 23°, relative humidity of 50%, a tensile speed of 200 mm / min, and a peel strength of 90°, and the average value was evaluated.

[0224] [Example 1]

[0225] The raw materials were blended to contain 85 mass% of polyamide 6, 3 mass% of polyamide MXD6, and 12 mass% of a masterbatch of silica fine particles and ethylenebisstearamide. After adjusting the moisture content of the blended raw materials to 0.1 mass%, the molten film was extruded from a T-die at a temperature of 260°C by an extruder, electrostatically adhered to a metal roll cooled to 30°C by applying a DC high voltage, and then cooled and solidified to obtain an unoriented film with a thickness of 200 μm. The Tg of this unoriented film was 41°C and the Tc was 69°C.

[0226] Using a roll stretcher, the unoriented film was subjected to a first stage of preliminary longitudinal stretching at a stretching temperature of 80°C by 1.03 times, followed by a second stage of preliminary longitudinal stretching at a stretching temperature of 80°C by 1.03 times, followed by a first stage of main longitudinal stretching at 85°C by 2.1 times, and additionally, a second stage of main longitudinal stretching at a stretching temperature of 70°C by 1.5 times, the longitudinally stretched film was continuously introduced into a tenter, and after transverse stretching at 130°C by 4.0 times, heat-setting treatment was performed at 210°C, and additionally, a 5.0% relaxation treatment was performed in the transverse direction at 210°C. After cooling at 100°C and corona treating one side of the film, the tenter clip gripping portions at both ends were trimmed to a width of 150 mm to obtain a mill roll of a biaxially oriented polyamide film with a thickness of 15 μm and a width of 6,000 mm.

[0227] [Example 2]

[0228] As shown in Tables 1 and 2, a biaxially oriented polyamide film was obtained in the same manner as in the example, except that the temperature and ratio of the preliminary longitudinal stretching and the ratio of the main longitudinal stretching were changed.

[0229] [Example 3]

[0230] As shown in Tables 1 and 2, a mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 2, except that the preliminary longitudinal stretching was set to the first stage and the ratio of Table 1 was set, the ratio of the second stage of the main longitudinal stretching and the thickness of the unoriented film were changed to 180 μm.

[0231] [Example 4]

[0232] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 3, except that the mill roll width was changed to a film-making device with a width of 4,000 mm.

[0233] [Comparative Example 1]–[Comparative Example 6]

[0234] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in the example, except that preliminary longitudinal stretching was not performed as shown in Tables 1 and 2, and main longitudinal stretching was performed in two stages at the temperature and magnification shown in Tables 1 and 2.

[0235] [Comparative Example 7]

[0236] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in the example, except that preliminary longitudinal stretching was not performed as shown in Tables 1 and 2, and main longitudinal stretching was performed in a single stage at the temperature and magnification shown in Tables 1 and 2.

[0237]

[0238]

[0239] As shown in Table 1, the biaxially oriented polyamide films of the present application invention in Examples 1 to 4, despite being slit rolls at the ends of the mill rolls, had an acceptable range of S-shaped curling when encapsulated.

[0240] Meanwhile, in the biaxially oriented polyamide films obtained in comparative examples other than Comparative Examples 3 and 6, the molecular orientation angle was greater than 20° and the hygroscopic deformation was greater than 1.3%, so an unacceptable amount of S-shaped curling occurred when encapsulated.

[0241] In the biaxially oriented polyamide film obtained in Comparative Example 3, the molecular orientation angle was greater than 20° and the hygroscopic deformation was 1.3% or less, but because the heat shrinkage rate after heating at 160°C for 10 minutes was large, an unacceptable amount of S-shaped curling occurred when used as a bag, and at the same time, the heat sealing part shrank and deformed.

[0242] In the biaxially oriented polyamide film obtained in Comparative Example 6, the hygroscopic deformation was 1.3% or less and S-curling was within an acceptable range, but because the impact strength was low, it did not satisfy the characteristics of a polyamide film requiring impact resistance.

[0243] As shown in Table 2, in the polyamide film mill rolls of Examples 1 to 4, even if the end slit roll was used, the occurrence of S-shaped curling when encapsulated was within an acceptable range.

[0244] Meanwhile, in the polyamide film mill rolls obtained in comparative examples other than Comparative Examples 3 and 6, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was greater than 1.3%, so an unacceptable amount of S-shaped curling occurred when encapsulated.

[0245] In the polyamide film mill roll obtained in Comparative Example 3, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was 1.3% or less, but because the heat shrinkage rate after heating at 160°C for 10 minutes was large, an unacceptable amount of S-shaped curling occurred when making a bag, and at the same time, the heat sealing part shrank and deformed.

[0246] In the polyamide film mill roll obtained in Comparative Example 6, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was 1.3% or less, and S-curling was also within an acceptable range, but because the impact strength was low, it did not satisfy the characteristics of a polyamide film requiring impact resistance.

[0247] [Example 5]

[0248] An unoriented film was prepared in the same manner as in Example 1, and a first stage of preliminary longitudinal stretching was performed, followed by a second stage of preliminary longitudinal stretching, a first stage of main longitudinal stretching, and additionally, a second stage of main longitudinal stretching was performed.

[0249] Next, a water-based dispersion coating solution (A) of acrylic graft copolymer polyester was applied to the longitudinally stretched film using a roll coater method and dried with hot air at 70°C.

[0250] Next, the longitudinally stretched film was continuously fed into a tenter, transversely stretched 4.0 times at 130°C, heat-set at 210°C, and additionally relaxed by 5.0% in the transverse direction at 210°C. Subsequently, it was cooled at 100°C, corona-treated one side of the film, and then the tenter clip gripping portions at both ends were trimmed to a width of 150 mm to obtain a mill roll of a biaxially oriented polyamide film with a thickness of 15 μm and a width of 6,000 mm. The coating amount of the acrylic graft copolymer polyester on the obtained biaxially oriented polyamide film was 0.05 g / m² as a solid content.

[0251] [Example 6]

[0252] As shown in Tables 3 and 4, a mill roll of polyamide film was obtained in the same manner as in Example 5, except that the temperature and ratio of the preliminary longitudinal stretching and the ratio of the main longitudinal stretching were changed.

[0253] [Example 7]

[0254] As shown in Tables 3 and 4, a mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 6, except that the preliminary longitudinal stretching was set to the first stage and the ratio of Table 3 was set, the ratio of the second stage of the main longitudinal stretching and the thickness of the unoriented film were changed to 180 μm.

[0255] [Example 8]

[0256] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 7, except that the mill roll width was changed to a film-making device with a width of 4,000 mm.

[0257] [Comparative Example 8]–[Comparative Example 14]

[0258] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 5, except that preliminary longitudinal stretching was not performed as shown in Tables 3 and 4, and main longitudinal stretching was performed in two stages at the temperature and magnification shown in Table 3.

[0259] [Comparative Example 15]

[0260] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in the example, except that preliminary longitudinal stretching was not performed as shown in Tables 3 and 4, and main longitudinal stretching was performed in a single stage at the temperature and magnification shown in Tables 3 and 4.

[0261]

[0262]

[0263] As shown in Table 3, the biaxially oriented polyamide films of the present application in Examples 5 to 8, despite being slit rolls at the ends of mill rolls, exhibited S-shaped curling within an acceptable range when encapsulated. In addition, because there was an adhesive layer made of acrylic graft copolymer polyester, the laminate strength of the sealant film and the polyamide film was also good.

[0264] Meanwhile, in the biaxially oriented polyamide films obtained in comparative examples other than Comparative Example 3-3 and Comparative Example 6, the molecular orientation angle was greater than 20° and the hygroscopic deformation was greater than 1.3%, so an unacceptable amount of S-shaped curling occurred when encapsulated.

[0265] In the biaxially oriented polyamide film obtained in Comparative Example 3, the molecular orientation angle was greater than 20° and the hygroscopic deformation was 1.3% or less, but because the heat shrinkage rate after heating at 160°C for 10 minutes was large, an unacceptable amount of S-shaped curling occurred when used as a bag, and at the same time, the heat sealing part shrank and deformed.

[0266] In the biaxially oriented polyamide films obtained in Comparative Examples 3-6, the hygroscopic deformation was 1.3% or less and S-curling was within an acceptable range, but because the impact strength was low, it did not satisfy the characteristics required for a polyamide film with impact resistance.

[0267] As shown in Table 4, in the biaxially oriented polyamide films of Examples 5 to 8 of this application, even with slit rolls at the ends, the occurrence of S-shaped curling when encapsulated was within an acceptable range. In addition, because there is an adhesive layer made of acrylic graft copolymer polyester, the laminate strength of the sealant film and the polyamide film was also good.

[0268] Meanwhile, in the polyamide film mill rolls obtained in comparative examples other than Comparative Example 11 and Comparative Example 14, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was greater than 1.3%, so an unacceptable amount of S-shaped curling occurred when encapsulated.

[0269] In the polyamide film mill roll obtained in Comparative Example 11, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was 1.3% or less, but because the heat shrinkage rate after heating at 160°C for 10 minutes was large, an unacceptable amount of S-shaped curling occurred when making a bag, and at the same time, the heat sealing part shrank and deformed.

[0270] In the polyamide film mill roll obtained in Comparative Example 14, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was 1.3% or less, and S-curling was also within an acceptable range, but because the impact strength was low, it did not satisfy the characteristics of a polyamide film requiring impact resistance.

[0271] [Examples 9] to [Examples 12]

[0272] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 5, except that the coating solution was changed from (A) to a water-based dispersion of polyurethane resin (B) and the film formation conditions shown in Table 5 were adopted. The amount of polyurethane resin applied to the obtained biaxially oriented polyamide film was 0.05 g / m² as a solid content.

[0273] [Comparative Example 16]

[0274] Except for changing the coating solution from (A) to a water-based dispersion (B) of polyurethane resin, preliminary longitudinal stretching was not performed as in Comparative Example 8, and main longitudinal stretching was performed in two stages at the temperatures and ratios shown in Tables 5 and 6 to obtain a biaxially oriented polyamide film.

[0275] [Reference Example 1]

[0276] A mill roll of a biaxially oriented polyamide film was obtained in the same manner as in Example 5, except that the coating solution was not applied.

[0277]

[0278]

[0279] As shown in Table 5, the biaxially oriented polyamide films of the present application in Examples 9 to 12, despite being slit rolls at the ends of mill rolls, exhibited S-shaped curling within an acceptable range when encapsulated. In addition, because there was an adhesive layer made of polyurethane resin, the laminate strength of the sealant film and the polyamide film was also good.

[0280] Meanwhile, in the biaxially oriented polyamide film obtained in Comparative Example 16, the molecular orientation angle was greater than 20° and the hygroscopic deformation was greater than 1.3%, so an unacceptable amount of S-shaped curling occurred when encapsulated.

[0281] In addition, in the biaxially oriented polyamide film obtained in Reference Example 1, since the molecular orientation angle and hygroscopic deformation were within the range of the present invention, the occurrence of S-shaped curling when encapsulated was within an acceptable range, but the laminate strength of the laminated film of the sealant film and the polyamide film was insufficient because there was no adhesive layer.

[0282] As shown in Table 6, in the polyamide film mill rolls of the present application invention in Examples 9 to 12, even with the end slit rolls, the occurrence of S-shaped curling when encapsulated was within an acceptable range. In addition, because there is an adhesive layer made of polyurethane resin, the laminate strength of the sealant film and the polyamide film laminated together was also good.

[0283] Meanwhile, in the polyamide film mill roll obtained in Comparative Example 16, the moisture absorption deformation at a position 300 mm inward from the right and left ends in the width direction of the film was greater than 1.3%, so an unacceptable amount of S-shaped curling occurred when encapsulated.

[0284] In addition, the polyamide film mill roll obtained in Reference Example 1 had a moisture absorption deformation of 1.3% or less at a position 300 mm inward from the right and left ends in the width direction of the film, and the occurrence of S-shaped curling when encapsulated was within an acceptable range, but the laminate strength of the laminated film of the sealant film and the polyamide film was insufficient because there was no adhesive layer.

[0285] Industrial applicability

[0286] The biaxially oriented polyamide film of the present invention exhibits good mechanical and thermal properties even when the product is near the end of the mill roll. Furthermore, since there is minimal S-shaped curling due to moisture absorption after packaging, it is difficult for functional failure to occur during bag conveyance when filling contents into bags, resulting in good workability. Additionally, since the deformation due to shrinkage at high temperatures is small, the deformation due to shrinkage after heat sealing the bags is also small. Moreover, when an adhesive layer is installed, the lamination strength is strong, making it difficult for the bags to break. Therefore, it can be suitable for various packaging applications.

Claims

Claim 1 A biaxially oriented polyamide film composed of a polyamide resin containing 60 mass% or more of polyamide 6, characterized in that the molecular orientation angle of the film is 20° or more, the hygroscopic deformation is 1.3% or less, the impact strength is 0.8 J / 15 μm or more, and the thermal shrinkage rate after heating at 160°C for 10 minutes is 0.6 to 3.0% in both the MD direction and the TD direction. Claim 2 A biaxially oriented polyamide film according to claim 1, characterized in that it is a biaxially oriented polyamide film made of a polyamide resin containing 90 mass% or more of polyamide 6. Claim 3 A biaxially oriented polyamide film according to claim 1, characterized in that the thermal shrinkage deformation of the film after heating at 160°C for 10 minutes is 2.0% or less. Claim 4 A biaxially oriented polyamide film characterized by having an adhesive layer on at least one side of the biaxially oriented polyamide film described in any one of claims 1 to 3, the adhesive layer being composed of any one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin, with a coating amount as a solid content of 0.01 to 3 g / m². Claim 5 A polyamide film mill roll for a biaxially oriented polyamide film made of a polyamide resin containing 60 mass% or more of polyamide 6, characterized in that the impact strength of the film at a position 300 mm inward from the right and left ends with respect to the width direction of the film mill roll is 0.8 J / 15 μm or more, the hygroscopic deformation is 1.3% or less, and the thermal shrinkage rate after heating at 160°C for 10 minutes is 0.6 to 3.0% in both the MD direction and the TD direction. Claim 6 A polyamide film mill roll according to claim 5, characterized in that it has a biaxially oriented polyamide film having an adhesive layer on at least one side of the film composed of a polyester resin, a polyurethane resin, and / or a polyacrylic resin, with a coating amount as a solid content of 0.01 to 3 g / m². Claim 7 A polyamide film mill roll according to claim 5 or 6, characterized in that the thermal shrinkage deformation of the film at a position 300 mm inward from the right and left ends with respect to the width direction of the film mill roll is 2.0% or less after heating at 160°C for 10 minutes.

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