Biaxially Extended Polyamide Film

Abstract

This invention provides a biaxially extended polyamide film, which is used to construct packaging bags with excellent straight-line cutting properties and crack resistance. The biaxially stretched polyamide film of the present invention comprises: 70 to 95 parts by weight of aliphatic polyamide, 5 to 30 parts by weight of poly(m-phenylene hexamethylenedimethylamine), and Oxides or hydroxides of Group 2 elements in the periodic table, ranging from 0.01 to 0.20 parts by mass; The shrinkage rates of the end film sheets and the central film sheets cut from the mill roll of the film after steam treatment at 120°C in both the long side direction (MD direction) and the width direction (TD direction) are 2.0% to 7.0%, and the absolute value of the difference between the shrinkage rates of the end film sheets and the central film sheets in the width direction (TD direction) at 45° and 135° after steam treatment at 120°C is less than 1.0. The end film sheet is a square film sheet with 200mm side cut out with the center of the square located 300mm inside the right or left end of the 2000mm wide film roll. The central film is a square film sheet with one side of 200mm cut out with the center of the roll width direction as the center of the square.

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polyamide film, and more particularly to a biaxially stretched polyamide film formed from a raw material composition containing aliphatic polyamide and poly(m-xylylene adipate), which has excellent straight-line cutting properties and is not prone to cracking. Prior Art

[0002] Due to its excellent puncture strength and impact strength, biaxially oriented polyamide films have been used for packaging purposes such as food, medicine, and industrial products. For example, packaging bags using laminated biaxially oriented polyamide films and heat-sealable non-oriented films have been developed.

[0003] Packaging bags made of biaxially oriented polyamide film are particularly required to have pinhole resistance and linear cut resistance. However, because biaxially oriented polyamide film is a tough film, in order to impart linear cut resistance to the biaxially oriented polyamide film, it is necessary to perform perforation or cutting processes, or add tear strips. However, the linear cutting properties imparted by such processing methods are not inherent to the biaxially oriented polyamide film itself, so there are cases where the film cannot be torn straight all the way to the end, or where it gets stuck along the way, causing the contents to fly out.

[0004] To solve the above-mentioned problem, a laminated film has been proposed. The laminated film is formed by melt-extruding a polyamide composition containing an aliphatic polyamide and poly(m-xylylene adipate) (hereinafter also referred to as "MXD6") mixed in a ratio of aliphatic polyamide / MXD6 = 40-85 parts by weight / 15-60 parts by weight. The film is then stretched by an inflation method to form a tearable film having a length of at least 2.8 times in both the longitudinal direction (MD) and the width direction (TD) as one of a plurality of layers (Patent Documents 1 and 2). In addition, a tearable film has also been proposed, which is obtained by melt-extruding a mixed polyamide composition composed of 60-95 parts by weight of aliphatic polyamide, 5-40 parts by weight of poly(m-xylylene adipate), and 0.01-0.50 parts by weight of an oxide or hydroxide of an alkaline earth metal, and stretching it to more than twice its original length using a tubular method (Patent Document 3). [Prior Art Literature] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 5-220837 [Patent Document 2] Japanese Patent Application Laid-Open No. 5-200958 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-193616 Summary of the Invention

[0006] [Technical Problems to be Solved by the Invention]

[0007] This method involves laminating a sealing film such as polyethylene (PE) or polypropylene (PP) onto a biaxially oriented polyamide film with excellent linear cutting properties. The polyamide film is then folded in two parallel to the flow direction, with the three sides heat-welded and cut, creating a three-sided sealed bag with one side open. With the side to be linearly cut facing the flow direction, the bag is filled with the contents, sealed, and then released to the market.

[0008] However, bags made of laminated films including the films described in Patent Documents 1 to 3 have a straight-line tearing property when torn in the MD direction. However, if the tearing is not intentional and deviates from the MD direction, the inner and outer films do not cut in the same straight line, resulting in cracks and difficulty in opening. This problem is particularly prone to occur when making bags from split rolls of film near the end of a mill roll. This is believed to be caused by bowing, a phenomenon in biaxially oriented film where the film's molecular orientation is prone to bending into a bow shape. This bowing makes it more likely to crack when attempting to tear the split roll near the end of the mill roll. In this context, a mill roll refers to the full-width roll of film that is wound around the film-making machine after the ends are trimmed during film production. A split roll refers to the roll of film that is split to reduce its width for printing or lamination.

[0009] The present invention was developed against the backdrop of the above-mentioned problems and aims to provide a laminated film that can be used for packaging bags and has excellent straight-line cutting properties and is crack-resistant, with little cracking even when unintentionally torn in a direction other than the MD; a biaxially oriented polyamide film that constitutes the laminated film; and a method for producing the biaxially oriented polyamide film. [Technical means]

[0010] The present inventors conducted intensive research to address the above-mentioned issues and discovered that a biaxially oriented polyamide film containing 70 to 95 parts by mass of an aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of an element from Group 2 of the periodic table, and having a specific shrinkage ratio after steam treatment at 120°C, can be used as a laminate film for packaging bags having excellent straight-line cutting properties and crack resistance. This led to the completion of the present invention.

[0011] Specifically, the present invention relates to [1]~[8]. [1] A biaxially stretched polyamide film comprising: 70 to 95 parts by mass of an aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of an element from Group 2 of the periodic table; The shrinkage of the end film sheets and the central film sheets cut from the film roll after steam treatment at 120°C in the longitudinal direction (MD direction) and the width direction (TD direction) is 2.0% to 7.0%, and the absolute value of the difference in shrinkage of the end film sheets and the central film sheets after steam treatment at 120°C in the 45° and 135° directions in the width direction (TD direction) is less than 1.0; the end film sheets are square film sheets with a side of 200 mm cut by taking the position 300 mm inside the right end or left end in the width direction of the film roll with a width of 2000 mm as the center of the square; the central film is a square film sheet with a side of 200 mm cut by taking the center position in the width direction of the roll as the center of the square. [2] A biaxially stretched polyamide film as described in [1], wherein the stretching ratio in the MD direction and the TD direction is 2.7 times or more, and the difference between the stretching ratios in the MD direction and the TD direction is 0.2 times or less. [3] The biaxially stretched polyamide film as described in [1], wherein the oxide or hydroxide of the element of Group 2 of the periodic table is magnesium hydroxide or magnesium oxide. [4] The biaxially stretched polyamide film as described in [2], wherein the oxide or hydroxide of the element of Group 2 of the periodic table is magnesium hydroxide or magnesium oxide. [5] A laminated film comprising a plurality of layers and having excellent linear cutting properties, wherein at least one of the plurality of layers is formed from a biaxially stretched polyamide film as described in any one of [1] to [4]. [6] A method for producing a biaxially stretched polyamide film as described in any one of [1] to [4], the method comprising: (A) melt-kneading a raw material composition containing 70 to 95 parts by mass of an aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of an element from Group 2 of the periodic table, followed by cooling to form a film to obtain an unstretched film; and (B) simultaneously biaxially stretching the unstretched film into a tubular shape at a stretching ratio of 2.7 times or more in both length and width. [7] A method for producing a biaxially stretched polyamide film as described in [6], wherein after the aforementioned (B) tubular simultaneous biaxial stretching step, it further includes (C) a heat treatment step of heat-treating the film. [8] A method for producing a biaxially stretched polyamide film as described in [7], wherein the aforementioned (C) heat treatment step is a heat treatment step in which heat treatment is performed using a hot roller, or a heat treatment step in which heat treatment is performed using a tenter oven after the hot roller. [Effects of the Invention]

[0012] According to the present invention, there are provided a laminated film which can be used for packaging bags and has excellent straight-line cutting properties and is crack-resistant, with little cracking even when unintentionally torn in a direction other than the MD; a biaxially oriented polyamide film which constitutes the laminated film; and a method for producing the biaxially oriented polyamide film.

[0013] Furthermore, the present invention provides a biaxially oriented polyamide film for producing packaging bags having excellent straight-line cutting properties and preventing cracking even when unintentionally torn in a direction other than the MD, thereby preventing the film from being difficult to open; and a method for producing the biaxially oriented polyamide film. Simple diagram description

[0014] [Figure 1] Figure 1 is a schematic diagram of a tubular method simultaneous two-axis stretching device. [Figure 2] Figure 2 is a cross-sectional view showing the structure of a laminated film according to one embodiment of the present invention [(a) shows a cross-sectional view showing the structure of a laminated film composed of a two-layer laminate. (b) shows a cross-sectional view showing the structure of a laminated film composed of a three-layer laminate. (c) shows a cross-sectional view showing the structure of a laminated film composed of a four-layer laminate.]. [Figure 3] Figure 3 is a diagram showing the shape of a test piece used for linear cutting performance evaluation. [Figure 4] Figure 4 shows test pieces after the linear cutting performance evaluation [(a) shows a test piece with good linear cutting performance. (b) shows a test piece with poor linear cutting performance.]. [Fig. 5] Fig. 5 is a diagram showing the shape of a test piece used for cracking evaluation. [Figure 6] Figure 6 shows test pieces after cracking evaluation [(a) shows a test piece with good cracking properties. (b) shows a test piece with poor cracking properties.]. Implementation Method

[0015] [Biaxially stretched polyamide film] The biaxially stretched polyamide film of the present invention comprises: 70 to 95 parts by mass of an aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of an element from Group 2 of the periodic table; The shrinkage of the end film sheet and the central film sheet of the film roll in the longitudinal direction (MD direction) and the width direction (TD direction) after 120℃ steam treatment is 2.0%~7.0%, and The absolute value of the difference in shrinkage after 120°C steam treatment between the end film sheet and the central film sheet in the 45° direction and the 135° direction in the width direction (TD direction) (hereinafter also referred to as the 120°C shrinkage strain difference) is 1.0 or less; The end film sheets are square film sheets with a side of 200 mm, each cut from a film roll with a width of 2000 mm, with the position 300 mm inside the right end or left end in the width direction as the center of the square; the central film is a square film sheet with a side of 200 mm, cut from the center position in the width direction of the roll as the center of the square.

[0016] The aliphatic polyamide used in the present invention is not particularly limited, and polyamide 6 (nylon 6), polyamide 66 (nylon 66), polyamide 46 (nylon 46), polyamide 610 (nylon 610), polyamide 12 (nylon 12), etc. can be used. These can be used alone or in combination of two or more. In addition, aliphatic polyamides such as polyamide 6 (nylon 6) can be used with a number average molecular weight of 10,000-30,000 or 22,000-24,000. Using an aliphatic polyamide with a number average molecular weight of 10,000 or higher allows for biaxially oriented polyamide films to possess sufficient impact and tensile strength. Furthermore, aliphatic polyamides with a number average molecular weight of 30,000 or lower exhibit moderate molecular chain entanglement, which suppresses excessive strain during stretching, preventing cracking and puncture during stretching, thereby enabling stable production of biaxially oriented polyamide films.

[0017] Poly(m-xylylenediamine adipate) (MXD6) used in this invention is obtained by the polycondensation reaction of m-xylylenediamine and adipic acid. MXD6 can also be obtained by the polycondensation reaction of m-xylylenediamine, adipic acid, and components that can polymerize with these. Poly(m-xylylenediamine adipate) can be used alone or in combination of two or more.

[0018] The resin component of the biaxially stretched polyamide film of the present invention is composed of 70 to 95 parts by mass of aliphatic polyamide and 5 to 30 parts by mass of poly(m-xylylene adipate). The content is not particularly limited as long as it is within the above range. The lower limit of the aliphatic polyamide content is, for example, 70 parts by mass or more, for example, 75 parts by mass or more, for example, 80 parts by mass or more, for example, 85 parts by mass or more, for example, 90 parts by mass or more, or for example, 95 parts by mass; the upper limit is, for example, 95 parts by mass or less, for example, 90 parts by mass or less, for example, 85 parts by mass or less, for example, 80 parts by mass or less, for example, 75 parts by mass or less, or for example, 70 parts by mass. Furthermore, the lower limit of the poly(m-xylylenediamine) content is, for example, 5 parts by mass or more, for example, 10 parts by mass or more, for example, 15 parts by mass or more, for example, 20 parts by mass or more, for example, 25 parts by mass or more, or for example, 30 parts by mass; the upper limit is, for example, 30 parts by mass or less, for example, 25 parts by mass or less, for example, 20 parts by mass or less, for example, 15 parts by mass or less, for example, 10 parts by mass or less, or for example, 5 parts by mass. By using the above content, the biaxially stretched polyamide film of the present invention can have impact resistance, excellent straight-line cutting properties, and crack resistance. For example, when the content of poly(m-xylylenediamine adipamide) is less than 5 parts by mass, the resulting biaxially oriented polyamide film may lack linear cutting properties and crack resistance.

[0019] In the present invention, in order to make the biaxially stretched polyamide film exhibit sufficient straight-line cutting properties and crack resistance, an oxide or hydroxide of an element from Group 2 of the periodic table is used. The oxide or hydroxide of the element of Group 2 of the periodic table is not particularly limited, and beryllium oxide or hydroxide, magnesium oxide or hydroxide, calcium oxide or hydroxide, strontium oxide or hydroxide, or barium oxide or hydroxide can be used. Specifically, beryllium oxide, beryllium hydroxide, magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, strontium oxide, strontium hydroxide, barium oxide, and barium hydroxide can be mentioned. Magnesium oxide and magnesium hydroxide are particularly preferred, and magnesium hydroxide is more preferred. The oxides or hydroxides of these elements of Group 2 of the periodic table may be used alone or in combination of two or more. Two or more particles of the same type but with different average particle sizes and specific surface areas may be used in combination.

[0020] The content of the oxide or hydroxide of an element from Group 2 of the periodic table is preferably 0.01 to 0.20 parts by mass based on 100 parts by mass of the total of the aliphatic polyamide and poly(m-xylylenediamine) adipamide contained in the biaxially stretched polyamide film. The lower limit is, for example, 0.01 parts by mass or more, for example, 0.03 parts by mass or more, for example, 0.06 parts by mass or more, for example, 0.10 parts by mass or more, for example, 0.12 parts by mass or more, for example, 0.15 parts by mass or more, for example, 0.18 parts by mass or more, or for example, 0.20 parts by mass or more; the upper limit is, for example, 0.20 parts by mass or less, for example, 0.18 parts by mass or less, for example, 0.15 parts by mass or less, for example, 0.12 parts by mass or less, for example, 0.10 parts by mass or less, for example, 0.06 parts by mass or less, or 0.03 parts by mass or less.

[0021] While the specific surface area of ​​oxides or hydroxides of Group 2 elements is not particularly limited, the specific surface area, as determined by the BET method, is ideally 10-500 μm² / g, more preferably 20-300 μm² / g. Using oxides or hydroxides of Group 2 elements with a specific surface area, as determined by the BET method, of 500 μm² / g or less can suppress rapid moisture absorption by the oxides or hydroxides of Group 2 elements, making them easier to handle during thin film production.

[0022] The average particle size of oxides or hydroxides of Group 2 elements of the periodic table is not particularly limited, but is preferably 5 μm or less, more preferably 1 μm or less. The average particle size refers to the particle size at which the cumulative value of the number of particles in a particle size distribution determined by laser diffraction / scattering is 50% (D50).

[0023] The oxides or hydroxides of the elements of Group 2 of the periodic table may be those whose surfaces are not treated, but from the viewpoint of improving the transparency of the biaxially stretched polyamide film, it is ideal to use those whose surfaces are treated. The surface treatment method is not particularly limited, and examples thereof include a wet method in which a surface treatment agent is heated and dissolved in a solvent such as water or alcohol, particles of an oxide or hydroxide of a Group 2 element of the periodic table are added thereto, mixed and stirred, and then the solvent is removed; or a dry method in which particles of an oxide or hydroxide of a Group 2 element of the periodic table and the surface treatment agent are stirred and mixed. Furthermore, the surface treatment agent is not particularly limited, and silane coupling agents, titanium coupling agents, aluminum coupling agents, higher fatty acids, higher fatty acid esters, higher fatty acid metal salts, and the like can be appropriately used.

[0024] The thickness of the biaxially stretched polyamide film of the present invention can be adjusted appropriately according to the intended use, for example, 8 μm to 50 μm, ideally 10 μm to 30 μm.

[0025] Furthermore, the biaxially oriented polyamide film of the present invention may contain conventional additives and modifiers within the scope of not impairing the effects of the present invention. Examples of such conventional additives and modifiers include heat stabilizers, UV absorbers, light stabilizers, antioxidants, antistatic agents, tackifiers, sealant improvers, antifogging agents, crystal nucleating agents, release agents, plasticizers, crosslinking agents, flame retardants, and colorants (pigments, dyes, etc.).

[0026] The biaxially oriented polyamide film of the present invention has shrinkage rates in the longitudinal direction (MD direction) and the width direction (TD direction) of the end film sheets and the central film sheet of the rolled film after steam treatment at 120°C of 2.0% or more, preferably 2.5% or more, and more preferably 3.0% or more; and furthermore, the shrinkage rates are both 7.0% or less, preferably 6.5% or less. When the shrinkage after 120°C steam treatment in the longitudinal direction (MD) and width direction (TD) is less than 2.0%, the straight-line cutting performance of packaging bags made of biaxially oriented polyamide film is reduced, and cracking is likely to occur. In addition, if the shrinkage rate after 120°C steam treatment is greater than 7.0%, the shrinkage caused by the heat during the printing step or the lamination step is likely to cause pitch deviation during the printing step or the lamination step, which poses practical problems.

[0027] Here, the end film sheet refers to a square film sheet with a side of 200 mm cut by taking the position 300 mm inside the right or left end in the width direction of a film roll with a width of 2000 mm as the center of the square; the center film refers to a square film sheet with a side of 200 mm cut by taking the center position in the width direction of a film roll with a width of 2000 mm as the center of the square. Furthermore, the end film sheets and the center film sheet are square film sheets cut with a pair of opposite sides each being parallel to the TD direction or the MD direction of the film roll.

[0028] Shrinkage after 120°C steam treatment is calculated by measuring the dimensional change in a film cut into 200 mm squares in both the TD and MD directions and conditioning the film at 23°C, 50% RH for 2 hours. The film is then exposed to 120°C steam at 0.1 MPa for 30 minutes and then conditioned at 23°C, 50% RH for 2 hours. The resulting length is then measured and calculated using the following formula. Shrinkage after 120℃ steam treatment (%) = (length before treatment - length after treatment) / length before treatment × 100

[0029] In addition, the biaxially oriented polyamide film of the present invention has a shrinkage strain difference of 120°C in the 45° direction and the 135° direction (i.e., the diagonal line of the square film sheet) in the width direction (TD direction) of the end film sheet and the center film sheet of the rolled film of less than 1.0, ideally less than 0.9, more ideally less than 0.8, and even more ideally less than 0.5. If the shrinkage strain difference at 120°C exceeds 1.0, the packaging bag made of biaxially oriented polyamide film will easily crack when it is torn.

[0030] The shrinkage rate after 120°C steam treatment in the 45° and 135° directions is calculated using the above formula. The shrinkage rate after 120°C steam treatment in the 45° direction is compared with the shrinkage rate after 120°C steam treatment in the 135° direction to calculate the 120°C shrinkage strain difference. Shrinkage strain difference at 120°C = |(shrinkage after steam treatment in the 45° direction) - (shrinkage after steam treatment in the 135° direction)|

[0031] The biaxially oriented polyamide film containing an aliphatic polyamide, poly(m-xylylene adipate), and an oxide or hydroxide of an element from Group 2 of the periodic table is believed to contain poly(m-xylylene adipate) stably dispersed in the aliphatic polyamide in the form of elongated islands. Furthermore, when the end and center film sheets exhibit shrinkage rates of 2.0% to 7.0% in the MD and TD directions after steam treatment at 120°C, and a 120°C shrinkage strain difference of 1.0 or less in the 45° and 135° directions, the elongated islands of poly(m-xylylene adipate) are present in the MD direction in the end and center film sheets of the rolled product. Consequently, packaging bags using this biaxially oriented polyamide film are believed to exhibit linear cutting properties and MD crack resistance.

[0032] In this specification, the term "excellent straight-line cutting properties" means that when a cut (notch) is formed at the end of the film by hand or with a knife, the film is torn along its longitudinal direction through the cut, and the tear propagates to the side opposite to the side where the cut was made. For example, this refers to an evaluation value of 8 or above in the straight-line cutting property evaluation test described in paragraph

[0048] . In this specification, "excellent crack resistance" means that cracking hardly occurs, or even if cracking occurs, cracking is unlikely to occur to a degree that would hinder practical use. For example, it means that the maximum width of the deviation in the cracking evaluation test described in paragraph

[0050] is 5 mm or less.

[0033] [Laminating film] The present invention also includes a multi-layer laminated film formed by laminating the biaxially oriented polyamide film of the present invention with other films. The multi-layer laminated film of the present invention may include at least one of the layers being the biaxially oriented polyamide film.

[0034] Hereinafter, examples of the laminated film of the present invention will be described with reference to drawings, but the present invention is not limited thereto. Examples include: a laminated film 201 comprising a two-layer structure of a biaxially stretched polyamide film 21 and a sealing film 22, as shown in FIG2(a); a laminated film 202 comprising a three-layer structure of a biaxially stretched polyamide film 21, a gas barrier layer 23, and a sealing film 22, as shown in FIG2(b); and a laminated film 203 comprising a four-layer structure of a biaxially stretched polyester film 24, a gas barrier layer 23, a biaxially stretched polyamide film 21, and a sealing film 22, as shown in FIG2(c).

[0035] Examples of the sealing film include films made of unstretched polyethylene, unstretched polypropylene, unstretched polyvinyl chloride, ethylene-vinyl acetate copolymer, and ionomer resin. The thickness of the sealing film can be set within a range that does not impair the effects of the present invention, for example, 20 μm to 100 μm, preferably 30 μm to 80 μm. Examples of the gas barrier layer include metal foil layers such as aluminum, or metal vapor-deposited layers such as oxygen-barrier biaxially stretched polybutylene terephthalate (OPBT) films (e.g., alumina vapor-deposited OPBT films or silica vapor-deposited OPBT films). The thickness of the gas barrier layer can be set within a range that does not impair the effects of the present invention, for example, 5 μm to 30 μm, preferably 7 μm to 25 μm. Biaxially stretched polyester films include biaxially stretched polyethylene terephthalate (PET) films, biaxially stretched polyethylene naphthalate (PEN) films, and biaxially stretched polybutylene terephthalate (PBT) films. The thickness of the biaxially oriented polyester film can be set within a range that does not impair the effects of the present invention, for example, 10 μm to 30 μm, preferably 12 μm to 25 μm. As the dry lamination adhesive used for laminating the layers, a well-known adhesive can be used, for example, a two-component curing polyurethane. The thickness of the laminated film can be set within a range that does not impair the effects of the present invention, for example, 35 μm to 160 μm, preferably 50 μm to 130 μm.

[0036] The laminated film of the present invention, comprising the aforementioned biaxially oriented polyamide film layer, exhibits excellent linear cuttability and crack resistance in the longitudinal direction (MD). Therefore, by forming the laminated film of the present invention into a bag with the MD direction of the biaxially oriented polyamide film as the tearing direction, a bag having linear cuttability and crack resistance is obtained. Therefore, the laminated film of the present invention is useful as a packaging film for foods such as soups, jams, and sterilized prep packets, as well as pharmaceuticals, daily necessities, and toiletry products.

[0037] [Method for producing biaxially stretched polyamide film] The method for producing the biaxially stretched polyamide film of the present invention is also an object of the present invention. The biaxially stretched polyamide film can be obtained, for example, by the steps of (A) melt-kneading a raw material composition containing 70 to 95 parts by mass of an aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of an element from Group 2 of the periodic table, followed by cooling to form a film, and (B) The unstretched film is produced by a process of biaxially stretching the unstretched film at a stretching ratio of 2.7 times or more in both its length and width.

[0038] In the present invention, the method of melt-kneading the raw material composition containing 70 to 95 parts by mass of aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of an element from Group 2 of the periodic table can be performed using a well-known melt kneader such as a single-screw extruder or a double-screw extruder. When the above-mentioned conventional additives and modifiers are added to the raw material composition, the additives and modifiers can be added before the raw material composition is melt-kneaded, or the conventional additives and modifiers can be added after the raw material composition is melt-kneaded and then further melt-kneaded. The melt kneading temperature is appropriately selected depending on the aliphatic polyamide and poly(m-xylylene adipate), and is generally above the melting temperature of the aliphatic polyamide and poly(m-xylylene adipate), and ideally within a temperature range where the aliphatic polyamide and poly(m-xylylene adipate) do not discolor due to thermal decomposition, for example, 240°C to 300°C, preferably 245°C to 280°C, and more preferably 250°C to 270°C.

[0039] The cooling film forming method may be a well-known method. The film forming method includes well-known methods such as the T-die method and the ring die method.

[0040] Methods for biaxially stretching an unstretched film include well-known length-width biaxial stretching methods such as simultaneous biaxial stretching using a tubular method, simultaneous biaxial stretching using a tenter method, and sequential biaxial stretching. Simultaneous biaxial stretching is preferred, and tubular simultaneous biaxial stretching is more preferred, as it facilitates uniform length-width stretching and produces a film with excellent isotropic properties.

[0041] The biaxially oriented polyamide film of the present invention has a stretch ratio of 2.7 times or greater in both the MD and TD directions, and more preferably 2.9 times or greater. A stretch ratio of 2.7 times or greater yields a film with desired strength properties, excellent straight-cutting properties, and crack resistance. Furthermore, a stretch ratio of 6.0 times or less ensures stretching stability and prevents problems such as film breakage.

[0042] Furthermore, in the method for producing the biaxially oriented polyamide film of the present invention, the biaxially oriented film obtained through the biaxial stretching step may be subjected to heat treatment in order to improve dimensional stability. Biaxially oriented films can be heat-treated using well-known methods. Ideally, roll heat treatment using heated rollers is used, but a combination of roll heat treatment and tenter heat treatment is also possible. Conventional tenter heat treatment causes bending at the ends and center of the film roll, which can easily cause variations in physical properties across the width of the film. Roll heat treatment, however, allows the film to be heat-treated uniformly by contacting the film with heated rollers. From the viewpoint of production stability, the film is relaxed and heat treated. The temperature of the heat treatment is, for example, 180°C to 220°C, more preferably 190°C to 215°C. The relaxation rate during heat treatment is, for example, 0% to 10%, more preferably 0% to 8%, and even more preferably 0% to 5%.

[0043] The method for producing the biaxial polyamide film of the present invention will be described in more detail with reference to FIG1. ​​However, the present invention is not limited to the following. The raw material composition is melt-kneaded in an extruder, extruded through a ring die into a tubular shape, and temporarily cooled to obtain a tubular unstretched film. This tubular film is then passed between a pair of pinch rolls 2, and air is blown into the tubular film to expand it. While being heated by a heater 3, air is blown out through a cooling ring 4 to cool it. After being folded by a guide roll 5, the film is passed through a pair of pinch rolls 6 to obtain a biaxially stretched polyamide film using the continuous simultaneous biaxial stretching tubular process. [Example]

[0044] The present invention is described in detail below with reference to examples, but the present invention is not limited to these examples.

[0045] In addition, in the examples, the abbreviations have the following meanings. OPET: Biaxially oriented polyethylene terephthalate film (Toyobo Co., Ltd., E5102, thickness 12 μm) AL: Aluminum foil (manufactured by Toyo Aluminum Co., Ltd., 1N30, thickness 9 μm) CPP: Unoriented polypropylene film (Toyobo Co., Ltd., P1146, thickness 50 μm)

[0046] Example 1 (Production of biaxially oriented polyamide film) 70 parts by mass of an aliphatic polyamide [nylon 6: manufactured by Ube Industries, Ltd.] (PA6) having a relative viscosity of 3.5 and 30 parts by mass of poly(m-xylylene adipate) diamine [aromatic polyamide: manufactured by Mitsubishi Gas Chemical Co., Ltd.] (MXD6) having a relative viscosity of 2.7 were mixed, and 0.03 parts by mass of magnesium hydroxide [KISUMA 5B: manufactured by Kyowa Chemical Industry Co., Ltd.] was further added to prepare a raw material composition. The prepared raw material composition was then melt-extruded through an annular die and cooled with internal and external water-cooled mandrels to produce a tubular unstretched film (radius 750 mm) with a thickness of 150 μm. In a tubular simultaneous biaxial stretching apparatus (Figure 1), the unstretched tubular film was simultaneously biaxially stretched in both the MD and TD directions by utilizing the speed difference between the low-speed and high-speed nip rolls and the air pressure present therebetween. The tubular film was then folded and split into two sheets at both ends. The film was then subjected to a hot roll treatment at a maximum temperature of 210°C for several seconds to produce a biaxially stretched polyamide film with a width of 2400 mm and a thickness of 15 μm. The ends of the film were then cut off to form a flat film, which was then wound between two rolls to produce a 2000 mm wide film roll. The raw material composition and manufacturing conditions are shown in Table 1.

[0047] (120℃ steam treatment shrinkage test) Pull out the film from the film roll, and use the center of the film and a position 300 mm inward from the right end of the film roll as the center of the square. Cut the film into square pieces with a side of 200 mm so that the opposite sides are parallel to the TD direction of the film as (A) the center film piece and (B) the end film piece. The center film sheet (A) and the edge film sheets (B) were conditioned at 23°C and 50% RH for 2 hours. The lengths of the center film sheet (A) and the edge film sheets (B) were measured to the second decimal place in the TD (0°), 45°, MD (90°), and 135° directions, with the TD direction at 0°, passing through the center point. This was used as the pre-treatment length. After these measurements, the center film sheet (A) and the edge film sheets (B) were treated in 120°C steam at 0.1 MPa for 30 minutes using an autoclave (HVE-50 manufactured by Hirayama Seisakusho Co., Ltd.). The center film sheet (A) and the edge film sheets (B) were then removed and conditioned at 23°C and 50% RH for 2 hours. After humidity adjustment, measure the film lengths of (A) the center film piece and (B) the end film piece through the center point, with the TD direction at 0°, the TD direction at 0°, the MD direction at 90°, and the 135° direction to the second decimal place. This is the processed length. The following formulas were used to calculate the shrinkage percentages after steam treatment at 120°C in the TD (0°), 45°, MD (90°), and 135° directions of (A) the center film and (B) the end films, as well as the 120°C shrinkage strain difference between (A) the center film and (B) the end films. In the 120°C steam treatment shrinkage test, two film sheets (A) and two film sheets (B) were prepared for each end film sheet and measured, and the average values ​​are shown in Table 1. Shrinkage after 120℃ steam treatment (%) = (length before treatment - length after treatment) / length before treatment × 100 Shrinkage strain difference at 120°C = |(shrinkage after steam treatment in the 45° direction) - (shrinkage after steam treatment in the 135° direction)| The shrinkage after steam treatment in the TD and MD directions is judged to be good when it is 2.0% to 7.0%, and it is judged to be poor when it exceeds 7.0%. Furthermore, a difference in shrinkage strain at 120°C between the 45° direction and the 135° direction of 1.0 or less was judged as good, and a difference exceeding 1.0 was judged as poor.

[0048] (Production of laminated films) A 12μm OPET film, a 9μm AL film, a 15μm biaxially oriented polyamide film obtained by the above-described biaxially oriented polyamide film preparation, and a 50μm CPP film were coated with a dry lamination adhesive (DIC Graphics Co., Ltd.: LX-703VL and KR90 (solvent: ethyl acetate)). The solvent was dried to a solid content of 3.5g / m². A four-layer laminated film with a length of 400mm in the MD direction, a 300mm in the TD direction, and a thickness of 96.5μm was produced. Biaxially oriented polyamide film used in the production of laminated films is drawn from a film roll. A rectangular strip (A') with a length of 400 mm in the MD direction and a length of 300 mm in the TD direction are cut from the center of the film and a rectangular strip (B') with a length of 400 mm in the MD direction and a length of 300 mm in the TD direction, respectively, with the center of the film and a position 300 mm inward from the right end of the film roll facing the film roll being the center of the film.

[0049] (Straight-line cutting performance evaluation test) From the laminated film containing the prepared (A') center film sheet or (B') end film sheet, a rectangular film sheet measuring 205 mm in the MD direction and 20 mm in the TD direction was cut. Ten samples were prepared by cutting a 5 mm long slit in the center of one TD side of the film sheet (see Figure 3). The slit was then torn manually in the MD direction, as shown in Figure 4(a). The number of samples in which the tear propagated to the short side opposite the cut was used as the evaluation value (evaluation value: 0-10). The evaluation values ​​are shown in Table 1. In Table 1, the laminated film containing the (A') center film sheet used in the linear cutting performance evaluation test is abbreviated as the (A') center film sheet, and the laminated film containing the (B') center film sheet is abbreviated as the (B') center film sheet.

[0050] (Production of laminated packaging bags) From the laminated film containing the (A') central film sheet or the (B') end film sheet obtained in the above-mentioned laminated film preparation, two rectangular film sheets with a length of 130 mm in the MD direction and 160 mm in the TD direction were cut. The two film sheets were overlapped with the CPP layer on the inside, and the two TD edges and one MD edge were sealed with a width of 5 mm to produce a three-sided bag.

[0051] (Cracking evaluation test) Samples were prepared by cutting 5 mm long cuts at three locations along the TD edge of one side of the 3-square bag at intervals equal to the length of the TD edge (see Figure 5). The sample was then manually torn from the cut along a 30° angle with the MD direction at 0°, with the tear propagating to the TD edge opposite the cut edge. As shown in Figures 6(a) and (b), the maximum widths of the deviations (cracks) 31 and 32 generated by the tear positions on the two laminated films were used as evaluation values. The evaluation values ​​are shown in Table 1. In Table 1, the 3-square bag containing the laminated film (A') central film sheet used in the cracking evaluation test is abbreviated as the (A') central film sheet, and the 3-square bag containing the laminated film (B') central film sheet is abbreviated as the (B') central film sheet.

[0052] (Example 2 to Example 10) and (Comparative Example 1 to Comparative Example 13) Except for changing the weight percentages of the components in the raw material composition, the stretching ratio, the heat setting method, and the maximum heat treatment temperature according to Table 1, the same procedures as in Example 1 were followed to produce a biaxially oriented polyamide film and perform a shrinkage test after a 120°C steam treatment, produce a laminated film and perform a linear cutting performance evaluation test, and produce a laminated three-square bag and perform a cracking performance evaluation test. The test results are shown in Table 1. However, in Comparative Examples 1 to 13, the production of a laminated three-square bag containing the (A') center film and the cracking performance evaluation test were not performed.

[0053] (Comparative Example 14 and Comparative Example 15) The same procedures as in Example 1 were followed, except that the biaxially oriented polyamide film in Example 1 was replaced with a commercially available film having linear cutting properties (product name: NCBC, manufactured by UNITIKA Co., Ltd.) or product name: TB1010, manufactured by Idemitsu Unitech Co., Ltd.). The following tests were performed: shrinkage test after 120°C steam treatment, preparation of laminated films and linear cutting property evaluation test, and preparation of laminated three-square bags and cracking property evaluation test. The test results are shown in Table 1.

[0054] [Table 1]

[0055] According to the results shown in Table 1, by using the biaxially oriented polyamide films of Examples 1 to 10 containing 70 to 95 parts by mass of aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate diamine), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of a Group 2 element of the periodic table, the shrinkage of the central and end film sheets after 120°C steam treatment in the MD and TD directions was 2.0% to 7.0%, and the difference in 120°C shrinkage strain between the 45° and 135° directions was 1.0 or less. Regardless of whether the central film (A') or the end film (B') was used, laminated films with excellent straight-line cuttability were obtained. Furthermore, using these laminated films, laminated three-sided bags were produced. Even when torn from the MD along a 30° angle, the inner and outer films still tear in the same direction with a deviation of less than 2 mm, preventing problems caused by cracking. On the other hand, it was confirmed that when using the biaxially oriented polyamide films of Comparative Examples 1 to 6 and 10 to 13 containing 70 to 95 parts by mass of an aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate) diamine, and 0.01 to 0.20 parts by mass of an oxide or hydroxide of a Group 2 element of the periodic table, the shrinkage after 120°C steam treatment of the center and end film sheets in the MD and TD directions was 2.0% to 7.0%, and the difference in 120°C shrinkage strain between the 45° and 135° directions exceeded 1.0, a laminated film with excellent straight-line cuttability was obtained regardless of whether the (A') center film or the (B') end film was used. However, when a three-sided bag made from the laminated film containing the (B') end film was torn along a 30° direction from the MD direction, the deviation between the inner and outer films was 5 mm or more, and cracking was likely to occur. Furthermore, it has been confirmed that laminated 3-square bags made with commercially available tenter frame heat-treated film (NCBC) with a 120°C shrinkage strain difference exceeding 1.0 between the 45° and 135° directions, or tenter frame heat-treated film (TB1010) with a shrinkage ratio exceeding 7.0% after 120°C steam treatment in the MD direction, can easily crack when torn at 30° from the MD direction, with a deviation of more than 5mm between the inner and outer films. Furthermore, it was confirmed that when the biaxially oriented polyamide films of Comparative Examples 7 to 9 were used, which contained 70 to 95 parts by mass of aliphatic polyamide, 5 to 30 parts by mass of poly(m-xylylene adipate diamine), and 0.01 to 0.20 parts by mass of an oxide or hydroxide of a Group 2 element of the periodic table, and the difference in shrinkage strain at 120°C between the 45° and 135° directions was 1.0 or less, and the shrinkage after 120°C steam treatment of the central film sheet and the end film sheets in the MD and TD directions was outside the range of 2.0% to 7.0%, it was found that, regardless of whether the central film (A') or the end film (B') was used, a laminated film having excellent straight-line cuttability could not be obtained. Furthermore, when a three-sided bag made of the laminated film including the end film (B') was torn at 30° from the MD direction, the deviation between the inner and outer films was 5 mm or more, and cracking was likely to occur.

[0056] 1: Unstretched film 2: Pinch roller 3: Heater 4: Cooling ring 5: Guide roller 6: Pinch roller 7: Biaxially oriented film 21: Biaxially oriented polyamide film 22: Sealing film 23: Gas barrier layer 24: Biaxially oriented polyester film 201:Laminated film 202:Laminated film 203:Laminated film 31, 32: Deviation of cracking evaluation test

Claims

1. A biaxially extended polyamide film, comprising: 70 to 95 parts by mass of aliphatic polyamide, 5 to 30 parts by mass of poly(m-phenylene glycolide), and 0.01 to 0.20 parts by mass of oxides or hydroxides of Group 2 elements of the periodic table; the shrinkage rates of the end film sheets and the central film sheets cut from the mill roll of the film after steam treatment at 120°C in both the long side direction (MD direction) and the width direction (TD direction) are 2.0% to 7.0%, and the absolute value of the difference between the shrinkage rates of the end film sheets and the central film sheets in the width direction (TD direction) at 45° and 135° directions after steam treatment at 120°C is 1.0 or less; the end film sheets are square film sheets with one side of 200 mm, each cut with the center of a square located 300 mm inside the right or left end of the width direction of the mill roll of the film with a width of 2000 mm. The central film is a square film sheet with one side of 200mm cut out with the center of the roll width direction as the center of the square.

2. The biaxially extended polyamide film as described in claim 1, wherein, It is formed by extending more than 2.7 times in both the MD and TD directions, and the difference between the extension ratios in the MD and TD directions is less than 0.2 times.

3. The biaxially extended polyamide film as described in claim 1, wherein, The oxides or hydroxides of the elements in Group 2 of the periodic table are magnesium hydroxide or magnesium oxide.

4. The biaxially extended polyamide film as described in claim 2, wherein, The oxides or hydroxides of the elements in Group 2 of the periodic table are magnesium hydroxide or magnesium oxide.

5. A laminated film comprising a plurality of layers, wherein at least one of the plurality of layers is composed of a biaxially extended polyamide film as described in any one of claims 1 to 4.

6. A method for manufacturing a biaxially stretched polyamide film as described in any one of claims 1 to 4, the method comprising: (A) melting and mixing a raw material composition containing 70 to 95 parts by mass of aliphatic polyamide, 5 to 30 parts by mass of poly(m-phenylene glycolide), and 0.01 to 0.20 parts by mass of oxides or hydroxides of elements of Group 2 of the periodic table, followed by cooling to form an unstretched film; and (B) simultaneously biaxially stretching the length and width of the unstretched film in a tubular shape at an elongation ratio of 2.7 times or more.

7. A method for manufacturing a biaxially stretched polyamide film as described in claim 6, wherein, Following the (B) tubular simultaneous biaxial stretching step, the process further includes (C) a heat treatment step of heat-treating the film.

8. A method for manufacturing a biaxially stretched polyamide film as described in claim 7, wherein, The heat treatment step (C) is either a heat treatment step performed by a hot roller or a heat treatment step performed by a tenter frame oven after the hot roller.

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