Biaxially oriented polyamide resin film and method for producing the same

Abstract

To provide a polyamide resin film in which elongation due to moisture absorption is more effectively controlled. [Solution] The present invention relates to a biaxially oriented polyamide resin film characterized in that the angular change Δθ obtained by measurement conditions consisting of a specific process is 1.0° or less.

Description

[Technical Field]

[0001] This invention relates to a novel biaxially oriented polyamide resin film and a method for producing the same. [Background technology]

[0002] Biaxially oriented polyamide resin films exhibit excellent mechanical strength, including tensile strength, puncture strength, pinhole strength, and impact strength, as well as superior heat resistance. For this reason, laminated films, which use biaxially oriented polyamide resin films as a base material and laminate them with a sealant film made of polyolefin resin by methods such as dry lamination and extrusion lamination, are used in a wide range of fields, including as packaging materials for sterilization processes such as boiling and retorting.

[0003] However, polyamide resin films have high hygroscopicity due to the presence of amide groups, and the film may stretch when it absorbs moisture. In particular, polyamide resin films produced using the tenter method are affected by the bowing phenomenon (a phenomenon in which the film deforms into a bow shape), resulting in differences in the elongation rate in the diagonal direction. For example, a film that should originally be square or rectangular may deform into a roughly parallelogram shape due to moisture absorption.

[0004] Such deformation of the film due to moisture absorption can cause problems, for example, when manufacturing bags. For instance, when the film is folded in half and stacked to make a bag, the overlapping printed patterns may not align (a so-called "half-fold misalignment" may occur). Also, if the film deforms due to moisture absorption after being folded and made into a bag, the diagonal stretch rate may differ between the front and back surfaces of the bag, causing the edges of the bag to curl. Furthermore, when used as a lid material, problems may arise such as the pattern not aligning with the container.

[0005] Furthermore, the elongation due to moisture absorption in the transverse direction (TD), where no tension is applied during processing, tends to be higher. When polyamide resin films are used in the field of packaging materials, the length may change during the multi-color printing process, which can cause the printed design to not match.

[0006] On the other hand, polyamide resin films produced by the tubular method tend to undergo greater dimensional changes due to moisture absorption compared to those produced by the tenter method, which can lead to misalignment of the print during the multi-color printing process, known as misregistration.

[0007] Recently, the size of pouches has been increasing due to the trend towards larger capacities, as seen in refillable liquid detergents and other similar products. Even if the difference in diagonal elongation is the same, in films with such a wide range of applications, the misalignment that occurs where the edges of the film overlap becomes larger.

[0008] In addition, if moisture absorption progresses after the bag-making process, the four corners of the bag may curl, a phenomenon known as curling. When curling occurs in the bag, it not only spoils the appearance, but it can also cause problems during the subsequent filling process, such as the filling machine picking up two bags at once, a phenomenon known as double-picking.

[0009] To address the problems associated with moisture absorption in polyamide resin films, a biaxially oriented polyamide resin film has been proposed, for example, comprising at least a low-hygroscopic polyamide resin and a bending fatigue-resistant agent, characterized in that the dimensional change rates in the longitudinal and transverse directions of the film for every 60% change in relative humidity are both 2.0% or less, and the number of pinholes generated by bending the film 1000 times at a speed of 40 times / min is 20 or less per 17.78 cm square (Patent Document 1).

[0010] For example, a biaxially oriented polyamide resin film is known, characterized by a moisture shear of 2.0 to 4.0 mm and a boil strain of 2 to 3% (Patent Document 2). [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2010-121136 [Patent Document 2] Japanese Patent Publication No. 2006-88690 [Overview of the project] [Problems that the invention aims to solve]

[0012] However, even these conventional technologies still have room for improvement, as shown below.

[0013] Patent Document 1 does not describe the diagonal moisture-absorbing elongation, which is a particular problem when making bags using film. In other words, Patent Document 1 does not address the anisotropy of moisture-absorbing elongation as a problem. Furthermore, the film described in Patent Document 1 may result in a decrease in practical strength.

[0014] Patent Document 2 aims to reduce the anisotropy of moisture-induced elongation and hot water shrinkage, but recent demands for aesthetically pleasing printed designs or bag shapes necessitate more precise control over moisture-induced elongation.

[0015] As pouches and similar products become larger, dimensional changes due to moisture absorption in polyamide resin films are becoming a more pronounced problem, but a technology to solve this problem has yet to be developed.

[0016] Therefore, the main objective of the present invention is to provide a biaxially oriented polyamide resin film in which elongation due to moisture absorption is more effectively controlled. [Means for solving the problem]

[0017] In light of the problems of the prior art, the inventors conducted extensive research and, as a result, discovered that a biaxially oriented polyamide resin film capable of exhibiting unique physical properties can be obtained by employing a specific manufacturing method. Based on this discovery, the inventors realized that the above objective could be achieved, and thus completed the present invention.

[0018] In other words, the present invention relates to the following biaxially oriented polyamide resin film and a method for producing the same. 1. A biaxially oriented polyamide resin film, comprising the following steps: (1) A first step of conditioning the film for 48 hours in an environment of a temperature of 20°C and a humidity of 95%RH, and then conditioning it for 48 hours in an environment of a temperature of 20°C and a humidity of 40%RH; (2) A second step of cutting out a square sample in an environment of a temperature of 20°C and a humidity of 40%RH after the first step; (3) A third step of conditioning the square sample obtained after the second step for 48 hours in an environment of a temperature of 20°C and a humidity of 90%RH; (4) A fourth step of measuring each angle (θ) formed by the four vertices of the sample after the third step and (5) A fifth step of calculating the angle change [Δθ = |90 - θ|] with respect to the 90° angle formed by the vertices of the sample in the second step A biaxially stretched polyamide-based resin film, wherein the angle change Δθ obtained under the measurement conditions consisting of the above is 1.0° or less. 2. The following steps: (1) A first step of conditioning a square sample cut out from the film in the MD direction and the TD direction for 48 hours in an environment of a temperature of 20°C and a humidity of 95%RH, and then conditioning it for 48 hours in an environment of a temperature of 20°C and a humidity of 40%RH; (2) A second step of measuring the length (L1) of the side in the TD direction of the sample in an environment of a temperature of 20°C and a humidity of 40%RH after the first step; (3) A third step of conditioning the sample for 48 hours in an environment of a temperature of 20°C and a humidity of 90%RH after the second step; (4) A fourth step of measuring the length (L2) of the side in the TD direction of the sample after the third step and (5) A fifth step of calculating the TD moisture absorption elongation rate based on the following formula TD moisture absorption elongation rate (%) = [(L2 - L1) / L1] × 100 The biaxially stretched polyamide-based resin film according to item 1 above, wherein the TD moisture absorption elongation rate obtained under the measurement conditions consisting of the above is 1.3% or less. 3. The biaxially stretched polyamide-based resin film according to item 1 or 2 above, wherein the TD direction of the film is 500 mm or more. 4. A biaxially oriented polyamide resin film according to any one of items 1 to 3, wherein the polyamide resin includes a polyamide resin obtained by chemical recycling. 5. A biaxially oriented polyamide resin film according to any one of items 1 to 4, wherein the polyamide resin includes a polyamide resin obtained from plant-derived raw materials. 6. A biaxially oriented polyamide resin film as described in any of items 1 to 5 above, to be used as the object of printing. 7. A method for producing a biaxially oriented polyamide resin film, (1) A process to obtain an unstretched film by forming a molten mixture containing polyamide resin into a sheet, (2) A stretching step to obtain a biaxially oriented film by stretching the unstretched film using MD stretching and TD stretching, (3) A process of heat-setting and relaxation treatment on the obtained biaxially oriented film and (4) A process of cooling the biaxially oriented film after the relaxation treatment at a cooling rate of 180°C / second or less. A method for producing a biaxially oriented polyamide resin film, characterized by including the following: 8. The manufacturing method according to item 7, wherein the relaxation rate in the MD direction is 8% or less. 9. The manufacturing method according to item 8 or 9, wherein biaxial stretching is performed by a simultaneous biaxial stretching method. 10. The manufacturing method according to any one of items 8 to 10 above, wherein the preheating temperature is 200 to 225°C. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a biaxially oriented polyamide resin film in which elongation due to moisture absorption is more effectively controlled.

[0020] In particular, since the film of the present invention also has suppressed anisotropy in moisture-absorbing elongation, dimensional changes due to moisture absorption during or after the manufacture of the bag are small, and it has excellent suitability for printing and bag-making processes.

[0021] Therefore, the biaxially oriented polyamide resin film of the present invention is less prone to printing misalignment and positional misalignment during bag manufacturing, making it suitable for use as a packaging material to be printed on (especially as a material for manufacturing printed bags). [Brief explanation of the drawing]

[0022] [Figure 1] This figure shows the shape of the sample in "(4) Angle change due to moisture absorption" in Test Example 1. [Figure 2] This figure shows samples for the evaluation of "(6) Printing misalignment" and "(7) Printing misregistration" in Test Example 1. [Modes for carrying out the invention]

[0023] 1. Biaxially oriented polyamide resin film The biaxially oriented polyamide resin film of the present invention (the present invention film) is a biaxially oriented polyamide resin film, and is made up of the following steps: (1) The first step is to humidify the film at a temperature of 20°C and a humidity of 95%RH for 48 hours, and then humidify it at a temperature of 20°C and a humidity of 40%RH for 48 hours. (2) After the first step, the second step is to cut out a square sample under the above conditions. (3) A third step in which the square sample is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90%RH after the second step. (4) The fourth step involves measuring the angles (θ) formed by the four vertices of the sample after the third step, and (5) The fifth step calculates the angular change [Δθ=|90-θ|] relative to the angle of 90° formed by the vertices of the sample in the second step. The measurement conditions are characterized in that the angular change Δθ (absolute value) obtained is 1.0° or less.

[0024] (1) Composition of the film of the present invention The film of the present invention mainly consists of a polyamide resin, and may contain other components as long as they do not hinder the effects of the present invention. The polyamide resin content in the film of the present invention is not limited and can usually be about 90 to 100% by mass, and is particularly preferably 95 to 100% by mass.

[0025] (1-1) Polyamide resin Examples of polyamide resins that constitute the film of the present invention include polyamide resins obtained by a) ring-opening polymerization using lactams as monomer components, and b) condensation polymerization using ω-amino acids, dibasic acids, and diamines as monomer components.

[0026] Examples of lactams include ε-caprolactam, enantractam, capryllactam, and lauryllactam.

[0027] Examples of ω-amino acids include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, and 11-aminoundecanoic acid.

[0028] Examples of dibasic acids include adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandionic acid, dodecadionic acid, hexadecadionic acid, eicosanedionic acid, eicosadienedionic acid, 2,2,4-trimethyladipic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, xylylenedicarboxylic acid, and the like.

[0029] Examples of diamines include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, 2,2,4 (or 2,4,4)-trimethylhexamethylenediamine, cyclohexanediamine, bis-(4,4′-aminocyclohexyl)methane, and metaxylylenediamine.

[0030] Polymers or copolymers obtained by polymerizing these monomers include, for example, polymers such as polyamide 6, 7, 10, 11, 12, 46, 410, 56, 66, 69, 610, 611, 612, 6T, 6I, 810, 9T, 1010, 1012, 10T, and MXD6 (metoxylendipanamide 6), as well as copolymers such as 6 / 66, 6 / 12, 6 / 6T, 6 / 6I, and 6 / MXD6. Among these, it is preferable to include polyamide 6, which has an excellent balance of heat resistance and mechanical properties.

[0031] (1-1-a) Chemically recycled polyamide resin In addition to conventional polyamide resins obtained using fossil fuel-derived raw materials (especially virgin monomers), it is preferable that the polyamide resin contains so-called chemically recycled polyamide resins, which are obtained by depolymerizing polyamide resin waste and then repolymerizing the resulting recycled monomers, from an environmental perspective.

[0032] Chemically recycled polyamide resins can be suitably obtained by a manufacturing method that includes, but is not limited to, (1) a step of generating monomers from a depolymerization raw material (A) (depolymerization step), (2) a step of producing a polyamide resin (B) by polymerization using a raw material containing the monomers (polymerization step), and (3) a step of scouring the polyamide resin (B) (scouring step).

[0033] Depolymerization process In the depolymerization process, monomers are regenerated from the depolymerization raw material (A) (hereinafter, such monomers are referred to as "regenerated monomers").

[0034] As the regenerated monomer, lactams are particularly preferred, such as ε-caprolactam, enantractam, capryllactam, and lauryllactam. Among these, ε-caprolactam is particularly preferred.

[0035] The type of depolymerizing raw material (A) is not particularly limited, and various polyamide resins, as well as oligomers of various polyamide resins, can be used. More specifically, the various resins listed in polyamide resin (B) described later can be used as examples. Examples of oligomers include chain-like structures ranging from dimers to heptamers, and cyclic structures ranging from dimers to nocamers.

[0036] In particular, in the present invention, at least one of polyamide 6 resin and its oligomer can be suitably used as a depolymerization raw material (A). In particular, since polyamide 6 is a resin composed substantially of ε-caprolactam alone as monomer units, another advantage is that monomerization and purification separation are easy.

[0037] Polyamide resins can take various forms, including waste resin from switching between different grades during polymerization and from switching to the final product of film manufacturing, as well as waste materials such as trimming scraps and slitting scraps generated during film production, and defective films that were not commercialized. Furthermore, the use of waste materials can contribute to environmental protection.

[0038] Examples of oligomer forms include not only highly water-soluble oligomers recovered from the scouring water generated during the scouring of polyamide resin, but also filtration residues containing less water-soluble 2-8 mers.

[0039] The method for producing monomers from the depolymerization raw material (A) is not particularly limited as long as the desired monomer can be obtained, but preferably a depolymerization reaction of the depolymerization raw material (A) can be employed. That is, the depolymerization raw material (A) can be chemically decomposed by the depolymerization reaction to suitably obtain regenerated monomers.

[0040] The method and conditions for the depolymerization reaction are not particularly limited and can be carried out according to known methods. Therefore, for example, a catalyst may be used or not. It may also be carried out in the absence of water (dry reaction) or in the presence of water (wet reaction). Particularly from the viewpoint of productivity, a method of carrying out depolymerization in hot water vapor in the presence of a catalyst is preferred. Cyclic oligomers with low water solubility are difficult to depolymerize directly because the hydrolysis rate of the amide bond is slow, but by ring-opening polymerization to form chain molecules and then depolymerizing under the above conditions, recycled monomers can be suitably obtained from cyclic oligomers as well.

[0041] Polymerization process In the polymerization process, polyamide resin (B) is produced by polymerization using raw materials containing the monomer (recycled monomer).

[0042] The above raw materials may consist entirely of recycled monomers, but it is preferable to use virgin monomers in combination. Here, virgin monomers are the opposite of recycled monomers and refer to monomers that have not undergone the depolymerization process of polymers. Commercially available virgin monomers can also be used. For example, commonly available monomers can be used as virgin monomers.

[0043] Recycled monomers may contain by-products that are difficult to separate. This can slightly reduce the crystallization rate of polyamide resins made from recycled monomers alone compared to polyamide resins made from virgin monomers alone, and further reduce the crystallization rate of polyamide resins polymerized using both recycled and virgin monomers. This crystallization rate was measured by determining the cooling crystallization temperature (TC) of the obtained polyamide resin, and the full width at half maximum (FWHM) of the obtained crystallization peak was used as an indicator. In this invention, the FWHM is usually preferably 10°C or higher, more preferably 11°C or higher, and most preferably 12°C or higher. The wider the FWHM, the wider the range of crystallization rates, which reduces localized unevenness in the crystalline state of the film surface as the film is stretched and crystallized, thereby improving uniformity. From this viewpoint, it is preferable to use polyamide resins polymerized using both recycled and virgin monomers. The upper limit of the FWHM can be, for example, around 20°C, but is not limited to this.

[0044] The recycled monomer content in the raw material is not particularly limited, but from the viewpoint of broadening the full width at half maximum, it is preferable to set the upper limit to 90% by mass or less, and more preferably to 80% by mass or less. The lower limit is not particularly limited, but from the viewpoint of increasing the recycling rate, it is preferable to set it to 5% by mass or more, and particularly preferably to 10% by mass or more.

[0045] In addition to recycled monomers, it is preferable to use virgin monomers in combination. In this case, the virgin monomer content in the raw materials is usually preferably about 10 to 95% by mass, and more preferably 20 to 90% by mass.

[0046] For example, it is possible to use ε-caprolactam (hereinafter referred to as "C-CL") regenerated by the depolymerization reaction of polyamide 6 resin in the monomer in a range of nearly 100% by mass, but it is preferable to include ε-caprolactam (hereinafter referred to as "V-CL") as a virgin monomer as a monomer other than C-CL.

[0047] Furthermore, the polyamide resin (B) may be end-capping as needed to suppress monomer formation during melting. For this reason, the raw materials may contain additives such as end-capping agents as needed. End-capping agents are not particularly limited and include, for example, organic glycidyl esters, dicarboxylic anhydrides, monocarboxylic acids such as benzoic acid, and diamines.

[0048] The polymerization method for obtaining polyamide resin (B) is not particularly limited, and known monomer polymerization methods can also be employed. For example, a method can be employed in which ε-caprolactam, water, and benzoic acid as a chelating agent are mixed, heated in a polymerization vessel, pressurized, and then polymerized under reduced pressure and dehydration until the desired viscosity is reached.

[0049] Scouring process In the refining process, the polyamide resin (B) is refined. This removes monomers contained in the polyamide resin, and the relative viscosity of the polyamide resin can be increased to a desired range, resulting in physical properties suitable for film formation.

[0050] The refining method is not limited, but it is particularly preferable to refining the polyamide resin (B) so that its relative viscosity (at 25°C) is in the range of approximately 2.5 to 4.5. Therefore, for example, it is preferable to refining the polyamide resin (B) using hot water at 90 to 100°C for about 15 to 30 hours.

[0051] The refining method itself can employ known methods such as immersing the polyamide resin (B) in hot water. In this case, the polyamide resin (B) can be refined in the form of a molded body, such as pellets.

[0052] The number of times the scouring process is performed is not particularly limited as long as the full width at half maximum (FWHM) of TC is 10°C or higher, but it is preferable to perform it once or twice. If the scouring process is not performed, the amount of by-products will increase, the relative viscosity will fall below the above range, making film formation difficult or potentially reducing the strength of the film. On the other hand, if the number of scouring steps is three or more, the amount of by-products will decrease, and the FWHM may fall below 10°C.

[0053] The polyamide resin after the scouring process is preferably dried as needed. The drying conditions are not particularly limited. For example, hot air drying can be performed at around 100-130°C for 10-30 hours, but is not limited to this. More specifically, hot air drying can also be performed at 110°C for 20 hours.

[0054] The chemically recycled polyamide resin obtained by the above methods is not limited in content as long as it does not impair the effects of the present invention. However, from an environmental perspective, it is generally preferable that the proportion of the chemically recycled polyamide resin in the total polyamide resin be 10% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more. The upper limit of the above blending amount can be, for example, about 100% by mass, but is not limited thereto.

[0055] (1-1-b) Material recycled polyamide resin Furthermore, from an environmental perspective, recycled polyamide resin may also be included. For example, waste materials generated during the manufacture of polyamide resin films include, for instance, trimming scraps from the edges, slitting scraps, and films that were not commercialized as defective products. Pellets made by remelting these materials can be used as remelted resin (raw material). The content of recycled polyamide resin is not limited as long as it does not impair the effects of the present invention.

[0056] (1-1-c) Plant-derived polyamide resin Furthermore, from the perspective of environmental considerations, the polyamide resin may also contain plant-derived monomer components. For example, plant-derived monomer components include decanediamine, aminoundecanoic acid, and sebacic acid, which are derived from castor oil, and polyamide resins obtained by polymerizing these include polyamide 1010 and polyamide 11.

[0057] The content of plant-derived polyamide resin is not limited as long as it does not impair the effects of the present invention, but from an environmental perspective, it is generally preferable that the proportion of plant-derived polyamide resin in the polyamide resin is 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. The upper limit of the above blending amount can be, for example, about 100% by mass, but is not limited thereto.

[0058] (1-2) Other ingredients (additives) The film of the present invention may contain pigments, heat stabilizers, antioxidants, weathering agents, flame retardants, plasticizers, release agents, reinforcing agents, etc., to the extent that it does not impair the properties of the present invention. For example, examples of heat stabilizers or antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, etc.

[0059] Furthermore, the film of the present invention may contain various inorganic or organic lubricants to improve the slip properties of the film. Specific examples of lubricants include clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, magnesium aluminosilicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalside, layered silicates, ethylenebisstearamide, and the like.

[0060] The amount of these additives added is not limited as long as it does not interfere with the effects of the present invention, but it is generally sufficient if the total amount is 5% by mass or less.

[0061] (2) Physical properties of the film of the present invention The film of the present invention has the following physical properties. In particular, it is necessary to satisfy at least the angular change described in (2-1) below.

[0062] (2-1) Angle change The film of the present invention is made by the following steps: (1) The first step is to humidify the film in an environment of 20°C and 95%RH for 48 hours, and then humidify it in an environment of 20°C and 40%RH for 48 hours. (2) After the first step, the second step involves cutting out a square sample in an environment of 20°C and 40% RH. (3) A third step in which the square sample is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90%RH after the second step. (4) The fourth step involves measuring the angles (θ) formed by the four vertices of the sample after the third step, and (5) The fifth step calculates the angular change [Δθ=|90-θ|] relative to the angle of 90° formed by the vertices of the sample in the second step. The measurement conditions are characterized in that the angular change Δθ (absolute value) obtained is 1.0° or less.

[0063] In this invention, the angle change is an indicator of the degree of deformation due to moisture absorption of the film, and a smaller value indicates less deformation due to moisture absorption. This makes it possible to provide films that are more suitable for applications such as bag making and printing.

[0064] As described above, the angle change Δθ is practically 1.0° or less, particularly preferably 0.7° or less, even more preferably 0.6° or less, and most preferably 0.5° or less. If the angle change exceeds 1.0°, when the bag is folded in half during the bag-making process after printing and lamination, misalignment may occur at the point where the ends of the print overlap, potentially damaging the appearance of the bag after bag-making. Furthermore, if the bag absorbs moisture after bag-making, it may curl, potentially causing problems during the filling process.

[0065] While the lower limit of the angle change is most preferably 0°, it can usually be around 0.1°, but is not limited to this value.

[0066] In the first step, the film to be measured is conditioned for 48 hours at a temperature of 20°C and a humidity of 95%RH, and then conditioned for 48 hours at a temperature of 20°C and a humidity of 40%RH.

[0067] Subsequently, in the second step, a square sample is cut out under conditions of 20°C and 40% RH humidity. The method of cutting out the sample is not particularly limited; the square may be cut so that one side is parallel or perpendicular to the MD-TD direction of the stretched film, or it may be cut at any other angle. For example, as in the test example described later, a square sample can be cut so that it is parallel to the MD. A known cutting tool such as a cutter or scissors may be used for cutting. The size of the square is also not particularly limited, but from the standpoint of measurement accuracy, it is preferable to cut it so that, for example, one side parallel to the TD direction is 500 mm or more.

[0068] In the third step, the square sample described above is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90%RH after the second step.

[0069] Next, in the fourth step, the angles (θ) formed by the four vertices of the square sample that was humidity-controlled in the third step are measured. While it is possible to measure these angles directly, since the values ​​of the angle changes are absolutely small, they can also be suitably calculated using the law of cosines, for example, as shown in the test example below. That is, the length of each side can be measured after fixing the sample so that it does not stretch, and the angles of each vertex can be determined based on these measurements.

[0070] In step 5, based on the angles of each vertex obtained in step 4, the angle change [Δθ=|90-θ|] relative to the 90° angle formed by the vertices of the sample is calculated.

[0071] During measurement, the angles of all four vertices of a square sample are measured, and the angle change Δθ (absolute value) from the initial angle (90 degrees) is determined. The requirement is that the angle change at all vertices must be 1 degree or less. In other words, a characteristic of the film of this invention is that the change in all four angles is 1 degree or less.

[0072] Furthermore, it is preferable that each of the above steps be carried out continuously, and no steps that substantially affect the measurement results of the angle change Δθ are included between each step. In other words, it is desirable to move to the next step as quickly as possible after the completion of the previous step.

[0073] (2-2) TD moisture absorption elongation The film of the present invention is made by the following steps: (1) In the first step, square samples cut from the film in the MD direction and TD direction are conditioned for 48 hours in an environment of 20°C and 95%RH, and then conditioned for 48 hours in an environment of 20°C and 40%RH. (2) A second step after the first step, in which the length of the side (L1) in the TD direction of the sample is measured in an environment with a temperature of 20°C and a humidity of 40%RH. (3) In the third step, after the second step, the sample is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90%RH. (4) A fourth step in which the length of the side (L2) of the sample in the TD direction is measured after the third step. (5) The fifth step is to calculate the TD moisture absorption elongation rate based on the following formula. TD moisture absorption elongation rate (%) = [(L2-L1) / L1] × 100 For practical purposes, the TD moisture-absorbing elongation obtained under the measurement conditions is 1.3% or less, preferably 1.2% or less, and more preferably 1.0% or less. If the dimensional change rate in the TD direction exceeds 1.3%, moisture absorption may occur during time-consuming printing processes such as multi-color printing, causing discrepancies in the design, or the planned print size may not match the size of the bag.

[0074] In the first step, a square sample is cut out from the film to be measured. The method of cutting out the sample is not particularly limited; the sample may be cut so that one side of the square is parallel or perpendicular to the MD-TD direction of the stretched film, or it may be cut at any other angle. For example, as shown in the test example below, a square sample can be cut so that it is parallel to the MD. A known cutting tool such as a cutter or scissors can be used to cut the sample. The size of the square is also not particularly limited, but from the viewpoint of measurement accuracy, it is preferable to cut out a square sample such that, for example, one side of the square is parallel to the TD direction and the length of each side is 1 m or more.

[0075] The excised samples are conditioned for 48 hours at a temperature of 20°C and a humidity of 95%RH, and then conditioned for 48 hours at a temperature of 20°C and a humidity of 40%RH.

[0076] Subsequently, in the second step, the length of the side (L1) in the TD direction of the sample is measured under conditions of 20°C and 40%RH humidity.

[0077] Next, in the third step, the above sample is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90%RH.

[0078] After the third step, the fourth step involves measuring the length of the side (L2) in the TD direction of the sample. It is preferable that L2 is measured on the same side as L1, which was measured earlier.

[0079] Next, in the fifth step, the TD moisture absorption elongation is calculated using the following formula based on the L1 and L2 values ​​obtained above. TD moisture absorption elongation rate (%) = [(L2-L1) / L1] × 100

[0080] Furthermore, it is preferable that the above processes be carried out continuously, and no processes that substantially affect the measurement results of the TD moisture absorption elongation rate are included between each process. In other words, it is desirable to move to the next process as quickly as possible after the completion of the previous process.

[0081] (2-3) Film width Furthermore, the film of the present invention preferably has a width of 500 mm or more, more preferably 600 mm or more, and most preferably 700 mm or more. When the width is 500 mm or more, the misalignment between the edges when folded in half begins to increase, which increases the likelihood of damaging the appearance, so the effects of the present invention are more fully realized within that range.

[0082] (2-4) Film thickness The thickness of the film of the present invention is not particularly limited, but is generally about 3 to 100 μm, and is particularly preferably 5 to 50 μm, and more preferably 5 to 30 μm. If the film thickness is less than 5 μm, the mechanical strength will be insufficient, and if it exceeds 100 μm, problems such as increased weight and decreased transparency may occur.

[0083] Furthermore, the thickness accuracy (uniformity of thickness) is generally preferably 1.7% or less, more preferably 1.6% or less, and most preferably 1.5% or less, according to the measurement method described in the test examples below. A lower value indicates greater uniformity of thickness. The lower limit can be, for example, around 0.1%, around 0.5%, or even around 1.0%, but is not limited to these values.

[0084] (2-5) Hayes The film of the present invention is preferably transparent. More specifically, the haze is preferably 12% or less, more preferably 10% or less, even more preferably 8% or less, and most preferably 6% or less. If the haze exceeds 12%, the transparency of the film is lost, which may make it difficult to impart design properties through printing. There is no particular lower limit to the haze, but it is usually around 1.0%.

[0085] (2-6) Strong piercing The puncture strength of the film of the present invention is preferably 6N / 15μm or higher, more preferably 7N / 15μm or higher, and particularly preferably 8N / 15μm or higher. If the puncture strength of the polyamide resin film is less than 6N / 15μm, it will be insufficient in strength, which may cause problems such as pinholes occurring during handling after it has been molded into pouches or the like.

[0086] (3) Other configurations of the film of the present invention Preferably, at least one surface of the film of the present invention is subjected to a known surface treatment such as corona treatment, plasma treatment, or ozone treatment. Laminating another film, such as a sealant, onto the surface-treated polyamide resin film surface improves the adhesion between the film and the polyamide resin film.

[0087] Furthermore, the film of the present invention may consist of the polyamide resin described above alone, or it may be a mixture or multilayer of two or more types.

[0088] The film of the present invention is obtained by biaxially stretching an unstretched polyamide resin film. Unstretched films or uniaxially oriented films have low tensile strength and high anisotropy, and are therefore not suitable as base materials for manufacturing packaging bags.

[0089] 2. Method for manufacturing biaxially oriented polyamide resin film The method for manufacturing the film of the present invention is not limited, but is preferably the following: a method for manufacturing a biaxially oriented polyamide resin film, (1) A process to obtain an unstretched film by forming a molten mixture containing polyamide resin into a sheet (molding process), (2) A step to obtain a biaxially oriented film by MD stretching and TD stretching the unstretched film (stretching step), (3) A process of heat-setting and relaxation treatment on the obtained biaxially oriented film (heat treatment process) and (4) A step to cool the film temperature of the biaxially oriented film after the relaxation treatment at a cooling rate of 180°C / second or less (cooling step) The film of the present invention can be suitably manufactured by a manufacturing method characterized by including [the specified element].

[0090] Molding process In the molding process, an unstretched film is obtained by forming a molten mixture containing polyamide resin into a sheet.

[0091] In addition to the polyamide resin mentioned above, various additives as exemplified above can be added as part of the molten mixture. That is, the molten mixture can be prepared by melting the starting material containing the polyamide resin.

[0092] Therefore, for example, the starting material can be introduced into an extruder and melted, then extruded as a molten sheet from a T-die, rapidly cooled in close contact with a cooling drum with a surface temperature controlled to approximately 0-25°C, and a continuous unstretched film can be obtained.

[0093] Furthermore, in this invention, films that have been formed into a cylindrical shape in advance prior to stretching, such as in the case of stretching using a tubular method, are also included as unstretched films.

[0094] The obtained unstretched film is preferably subjected to a water absorption treatment prior to biaxial stretching, if necessary. The water absorption treatment is carried out by sending the unstretched film to a warm water bath heated to 20-80°C for 10 minutes or less. This water absorption treatment moderately plasticizes the unstretched film and suppresses the crystallization of the polyamide resin, thereby preventing the film from breaking during the stretching process.

[0095] The moisture content of the unstretched film that has absorbed water through the above treatment is preferably 1.0 to 7.0% by mass, and more preferably 1.5 to 5.0% by mass. If the moisture content of the unstretched film is less than 1.0% by mass, crystallization will progress and there is a risk of breakage. On the other hand, if the moisture content of the unstretched film exceeds 7.0% by mass, creases and wrinkles may occur during the water absorption treatment, making it prone to problems such as meandering, and the resulting biaxially oriented film may have reduced strength or increased thickness unevenness in the TD direction.

[0096] Stretching process In the stretching process, a biaxially oriented film is obtained by stretching the unstretched film using MD stretching and TD stretching.

[0097] In this invention, biaxial stretching of the unstretched film is preferably carried out by a simultaneous biaxial stretching method in order to improve the dimensional stability of the resulting film in a balanced manner. Sequential biaxial stretching is performed by carrying out longitudinal stretching and transverse stretching separately, which can result in greater anisotropy at the edges of the resulting film.

[0098] Simultaneous biaxial stretching is preferably carried out using the tenter method. Films obtained using the tubular method have a large elongation rate when absorbing moisture, and the elongation rate tends to be particularly high in the MD direction, resulting in poor dimensional stability. Furthermore, it is difficult to improve thickness accuracy with the tubular method, and in terms of film quality stability and productivity, the tenter-type simultaneous biaxial stretching method is superior.

[0099] Simultaneous biaxial stretching using a tenter is not limited and can be performed using various tenters, such as pantograph-type tenters, screw-type tenters, and linear motor-type tenters. Among these, the linear motor-type tenter, in which each clip is driven independently by a linear motor, has the flexibility to precisely and accurately control the longitudinal stretching ratio or longitudinal slack ratio by controlling a variable frequency driver. This simultaneous biaxial stretching method using a linear motor-type tenter is the most preferred stretching method because it reduces the Boeing effect and produces a biaxially oriented film with improved uniformity of lateral physical properties.

[0100] In particular, if the unstretched film has been treated to absorb water, it is preferable to preheat it before stretching. The preheating temperature is not particularly limited, but is usually preferably 200 to 230°C, and more preferably 215 to 230°C. If the preheating temperature is less than 200°C, the resulting film will exhibit a greater bowing phenomenon, and the angle change at the film edges before and after moisture absorption will be larger. On the other hand, if the preheating temperature exceeds 230°C, the film may whiten or break.

[0101] Simultaneous biaxial stretching of unstretched films is usually preferably carried out at 170-210°C, and more preferably at 190-200°C. If the stretching temperature is below 170°C, the resulting film may have high shrinkage stress and a high hot water shrinkage rate. If the stretching temperature exceeds 210°C, the film may have uneven thickness and be of inferior quality.

[0102] In simultaneous biaxial stretching, the stretching ratios for the unstretched film are preferably 2.5 to 4.5 times for both the longitudinal (MD) and transverse (TD) directions. Furthermore, the area stretching ratio, which is the product of the longitudinal and transverse stretching ratios, is preferably 7 to 12 times. If the area stretching ratio is less than 7 times, the resulting biaxially oriented film may have inferior mechanical properties. On the other hand, if the area stretching ratio exceeds 12 times, the resulting biaxially oriented film may have high shrinkage stress and a high shrinkage rate during hot water treatment.

[0103] Furthermore, it is preferable to reduce the Boeing effect during extension. The method for reducing the Boeing effect is not particularly limited and can be carried out according to known methods.

[0104] Heat treatment process In the heat treatment process, the resulting biaxially oriented film is subjected to heat-setting and relaxation treatments.

[0105] The heat treatment temperature in the heat-setting process is usually preferably 200 to 225°C, and more preferably 210 to 220°C. If the heat treatment temperature is below 200°C, the resulting biaxially oriented film may have a high hydrothermal shrinkage rate, and if the heat treatment temperature exceeds 220°C, the biaxially oriented film may suffer from reduced mechanical properties such as tensile elongation or whitening.

[0106] The biaxially oriented film undergoes a relaxation treatment in the latter half of the heat treatment zone. By performing the relaxation treatment, the hot water shrinkage rate of the biaxially oriented polyamide resin film can be reduced. The relaxation rate of the film in the relaxation treatment is preferably 8% or less in the longitudinal direction (MD), more preferably 6% or less, and even more preferably 5% or less. If it exceeds 8%, the anisotropy of the moisture-absorbing elongation tends to increase.

[0107] Furthermore, the relaxation rate in the transverse direction (TD) is usually preferably 2-8%, more preferably 2-6%, and most preferably 4-6%. If the relaxation rate is less than 2%, the resulting film may have a high hot water shrinkage rate. On the other hand, if the relaxation rate exceeds 8%, the resulting film may have a high moisture-absorbing elongation rate in the TD direction, and it may take a long time to relax, resulting in a decrease in production efficiency.

[0108] cooling process In the cooling process, the film temperature of the biaxially oriented film after the relaxation treatment is cooled at a cooling rate of 180°C / second or less. By cooling the biaxially oriented film that has undergone the specific treatment described above at a cooling rate of 180°C / second or less, deformation of the film due to moisture absorption can be more effectively prevented or suppressed.

[0109] The cooling process refers to the steps taken from immediately after the relaxation treatment until the film is transported to the winding machine. Of these steps, the film is cooled most rapidly when it is discharged from the stretching machine outlet, so it is desirable to control the film temperature at this time.

[0110] Cooling is performed by cooling the biaxially oriented film immediately after it is discharged from the stretching machine (outlet) at the predetermined cooling rate described above, as the film is heated due to the relaxation process. For example, when stretched by a tenter, the heat-treated film is generally discharged from the tenter outlet of the stretching machine and fed into the winding machine. The cooling rate of the film at this time is preferably 180°C / second or less, more preferably 160°C / second or less, even more preferably 140°C / second or less, and particularly preferably 130°C / second or less. If the cooling rate exceeds 180°C / second, the angle change before and after moisture absorption becomes large, increasing the likelihood of problems such as misalignment during half-folding.

[0111] Furthermore, it is preferable that the temperature of the film fed into the winding machine be below the glass transition temperature (Tg) of the film. For this reason, from the viewpoint of production efficiency, it is preferable that the cooling rate be 50°C / second or higher.

[0112] Methods for controlling the temperature of the film include, but are not limited to, adjusting the temperature of the zone after the relaxation process of the stretching machine, or installing a temperature-controlled fan at the outlet of the stretching machine.

[0113] Furthermore, the film temperature when it is discharged from the stretching machine is usually preferably between 100 and 150°C. Lowering the temperature below 100°C would require lowering the temperature in the latter half of the stretching machine, resulting in a large temperature difference with the heat treatment zone and making it difficult to maintain temperature balance. On the other hand, if the temperature is above 150°C, it will take a long time to cool to below the Tg, which may reduce production efficiency.

[0114] Furthermore, the film of the present invention may be subjected to surface treatments such as corona discharge treatment or easy-adhesion treatment, as necessary, to the extent that the effects of the present invention are not impaired.

[0115] The film of the present invention may have a coating layer, provided that it does not impair the effects of the present invention. Examples of coating layers include easy-adhesion coatings such as urethane, and barrier coating layers such as polyvinylidene chloride or polyvinyl alcohol.

[0116] The film of the present invention may have a vapor-deposited layer, provided that it does not impair the effects of the present invention. The vapor-deposited layer is not limited to, but may include, for example, a metal vapor-deposited layer such as aluminum, or a transparent vapor-deposited layer such as an inorganic material.

[0117] The film of the present invention can be printed using ink. That is, the film of the present invention is suitable as a printing surface, and printing can be suitably applied to the film of the present invention. The printing method is not limited to this, and examples of known methods include gravure printing, flexographic printing, and offset printing. Because the film of the present invention has a low moisture elongation rate in the TD direction, it is possible to print without the printed pattern shifting due to moisture absorption during printing. It can be particularly suitably used in multi-color printing, which is time-consuming in the printing process.

[0118] The film of the present invention may be in the form of a single sheet, or in the form of a film roll wound onto a roll, or any other form. In this case, it can also be provided as a film with dimensions of 500 mm or more in the TD direction. Therefore, the present invention also includes, for example, a film roll made by winding the film of the present invention, which is a biaxially oriented polyamide resin film roll having a width direction (TD direction) of 500 mm or more.

[0119] Furthermore, the film of the present invention can be laminated to a sealant film such as polyethylene film or polypropylene film. Additionally, the laminated film can be used to create packaging bags and other bag products by fusing them together using known methods such as heat sealing or ultrasonic sealing.

[0120] The above-described packaging bag can be suitably used as a packaging bag for food, beverages, and the like. In particular, the biaxially oriented polyamide resin film that constitutes the packaging bag has low anisotropy in its moisture-absorbing elongation rate, so the print does not become distorted due to moisture absorption during and after printing, and the misalignment of the design at both ends can be minimized when the bag is folded in half. Furthermore, it is possible to reduce curling of the packaging bag due to moisture absorption after filling with contents, making it suitable for use in the filling process as well. [Examples]

[0121] Examples and comparative examples are shown below to give a more detailed explanation of the features of the present invention. However, the scope of the present invention is not limited to the examples.

[0122] 1. Materials used (1) PA6: Unitika Corporation "A1030BRF" (2) Plant-derived PA11: "Rilsan BESN O TL PA11" manufactured by Arkema. (3) PA6T / 6: BASF "UltramidTKR4350" (4) Chemically recycled polyamide resin: Manufactured by the following method. Film waste or defective products generated during the manufacture of polyamide 6 resin film, and resin waste (resin waste material) including oligomers etc. produced during the polymerization of polyamide 6 resin were used as depolymerization raw material (A). Phosphoric acid was added to depolymerization raw material (A), and a depolymerization reaction was carried out under heating using a wet method. After purification by activated carbon treatment, concentration, and distillation, the regenerated ε-caprolactam "C-CL" was recovered. Using C-Cl, water, and benzoic acid as a chelating agent as raw materials, the mixture was heated, pressurized, depressurized, and dehydrated in a polymerization vessel, and then polymerized until a relative viscosity of 3.0ηR was achieved. After polymerization, the mixture was pelletized and refined twice by hot water treatment at 95°C for 10 and 15 hours, and then dried at 110°C for 20 hours. In this way, a chemically recycled polyamide resin was obtained. The relative viscosity of the obtained resin was 3.0, and the full width at half maximum (TC) was 10°C.

[0123] 2. Examples and Comparative Examples [Example 1] Polyamide 6 (PA6) was melt-extruded from a T-die at a temperature of 260°C and cooled on a drum at 15°C to obtain a substantially unoriented, unstretched film with a thickness of 150 μm. The obtained unstretched film was immersed in a 40°C hot water bath for 10 seconds, and then immersed in a 60°C hot water bath for 100 seconds to perform water absorption treatment. The water-absorbing, unstretched film was fed into a simultaneous biaxial stretcher, preheated to 220°C, and then simultaneously biaxially stretched under the conditions of a stretching temperature of 195°C, an MD stretching ratio of 3.0x, and a TD stretching ratio of 3.3x. Next, the film, after simultaneous biaxial stretching, was heat-treated for 4 seconds in a heat treatment zone set to 215°C, thereby loosening the MD and TD of the film by 5.0%. Next, after the relaxation treatment, the film was cooled to 25°C at a cooling rate of 140°C / second from the tenter outlet of the stretching machine to obtain a biaxially oriented polyamide resin film with a thickness of 15 μm, which was then harvested in roll form.

[0124] [Examples 2-23, Comparative Example 1] As shown in Table 1, a biaxially oriented polyamide resin film with a thickness of 15 μm was obtained by following the same procedure as in Example 1, except that the composition of the polyamide resin and the film manufacturing conditions were changed.

[0125] [Example 24] Polyamide 6 (PA6) was melt-extruded from a T-die at a temperature of 260°C and cooled on a drum at 15°C to obtain a substantially unoriented, unstretched film with a thickness of 180 μm. The unstretched film was introduced into an MD stretching machine and stretched using the MD stretching method at a stretching temperature of 100°C and an MD stretching ratio of 3.0x. Next, this MD-stretched film was introduced into a tenter and stretched using the TD stretching method at a preheating temperature of 60°C, a TD stretching temperature of 135°C, and a TD stretching ratio of 4.0x. Next, the film, after sequential biaxial stretching, was heat-treated for 4 seconds in a heat treatment zone set to 220°C, and a 5.0% relaxation treatment was applied to the film in the TD direction. Next, the film was cooled to 25°C at a cooling rate of 130°C / second from the tenter outlet of the stretching machine to obtain a biaxially oriented polyamide resin film with a thickness of 15 μm, which was then harvested in roll form.

[0126] [Comparative Example 2] As shown in Table 2, a biaxially oriented polyamide resin film with a thickness of 15 μm was obtained by following the same procedure as in Example 27, except that the composition of the polyamide resin and the film manufacturing conditions were changed.

[0127] [Example 25] A substantially unoriented, unstretched film with a thickness of 180 μm was obtained by melt-extruding a T-die with 40% by mass of polyamide 6 (PA6) and 60% by mass of polyamide 6T / 6 at a temperature of 260°C and cooling on a drum at 15°C. The unstretched film was introduced into an MD stretching machine and stretched using the MD stretching method at a stretching temperature of 100°C and an MD stretching ratio of 3.0x. Next, this MD-stretched film was introduced into a tenter and stretched using the TD stretching method at a preheating temperature of 60°C, a TD stretching temperature of 135°C, and a TD stretching ratio of 4.0x. Next, the film, after sequential biaxial stretching, was heat-treated for 4 seconds in a heat treatment zone set to 220°C, and a 5.0% relaxation treatment was applied to the film in the TD direction. Next, after the relaxation treatment, the film was cooled to 25°C at a cooling rate of 140°C / second from the tenter outlet of the stretching machine to obtain a biaxially oriented polyamide resin film with a thickness of 15 μm, which was then harvested in roll form.

[0128] [Comparative Example 3] The procedure was carried out in the same manner as in Example 25, except that the cooling rate from the tenter outlet of the stretching machine was changed to 190°C / second, and a biaxially oriented polyamide resin film with a thickness of 15 μm was obtained.

[0129] [Example 26] Polyamide 6 (PA6) was melt-extruded from a T-die at a temperature of 260°C and cooled on a drum at 30°C to obtain a substantially unoriented, unstretched film with a thickness of 200 μm. The unstretched film was introduced into an MD stretcher and first stretched under the conditions of a first MD stretching temperature of 85°C and a first MD stretching ratio of 2.2x. Subsequently, it was stretched under the conditions of a second MD stretching temperature of 70°C and a second MD stretching ratio of 1.5x. Next, this MD stretched film was introduced into a tenter and TD stretched under the conditions of a preheating temperature of 60°C, a TD stretching temperature of 130°C, and a TD stretching ratio of 4.0x. Next, the film, after sequential biaxial stretching, was heat-treated for 4 seconds in a heat treatment zone set to 210°C, and a 6.1% relaxation treatment was applied to the film in the TD direction. Next, the film was cooled to 25°C at a cooling rate of 140°C / second from the tenter outlet of the stretching machine to obtain a biaxially oriented polyamide resin film with a thickness of 15 μm, which was then harvested in roll form.

[0130] [Comparative Example 4] The procedure was carried out in the same manner as in Example 26, except that the cooling rate from the tenter outlet of the stretching machine was changed to 190°C / second, and a biaxially oriented polyamide resin film with a thickness of 15 μm was obtained.

[0131] [Example 27] Polyamide 6 (PA6) was melt-extruded from an annular die at a temperature of 260°C and solidified with water to obtain a substantially unoriented, tubular, unstretched film with a thickness of 135 μm. Next, the tube film was simultaneously biaxially stretched in both the medium (MD) and tangential (TD) directions under the conditions of a stretching temperature of 80°C, an MD stretching ratio of 3.0x, and a TD stretching ratio of 3.3x, using the speed difference between the low-speed and high-speed nip rolls and the air pressure present between them. Next, the tubularly stretched film was heat-treated for 100 seconds in a heat treatment zone set to 210°C, thereby loosening the TD of the film by 5.0%. Subsequently, the material was cooled to 25°C at a cooling rate of 150°C / second from the outlet of the heat treatment tenter to obtain a biaxially oriented polyamide resin film with a thickness of 15 μm, which was then harvested in roll form.

[0132] [Test Example 1] Table 1 summarizes the film manufacturing conditions and the properties of the obtained films in the examples and comparative examples. The properties were measured using the following method.

[0133] (1) Relative viscosity ηR The relative viscosity of a sample solution (at a temperature of 25°C) prepared by dissolving the raw material polyamide resin in 96% sulfuric acid to a concentration of 1.0 g / dl was measured using an Ubbelohde viscometer.

[0134] (2) Cooling crystallization temperature Tc and full width at half maximum Using a PerkinElmer differential scanning calorimeter (input-compensated DSC8000), 10 mg of the obtained resin was weighed, heated from room temperature to 260°C at a heating rate of 10°C / min, held at 260°C for 10 minutes, and then cooled to 100°C at a cooling rate of 10°C / min to measure the cooling crystallization temperature. In the DSC curve with heat flow (mW) on the vertical axis and temperature on the horizontal axis, the temperature of the peak top during cooling was defined as Tc (°C), and the baseline was drawn from the high-temperature side, with the interval between two points at half the absolute value of Tc defined as the width at half maximum (°C).

[0135] (3) Film temperature and cooling rate Film temperature was measured using a Chino Corporation IR-TA handheld infrared thermometer. Measurements were taken at 500 mm intervals in the MD direction immediately after the relaxation process, and measurements were taken until the temperature dropped below Tg. Film temperature inside the stretching machine was measured from the top of the machine. Three measurements were taken in the TD direction at each measurement position, and the average value was taken as the film temperature. The cooling rate was calculated from the difference in film temperature between adjacent 500 mm intervals and the film's running speed, and the maximum value was taken as the film's cooling rate.

[0136] (4) Angle change due to moisture absorption From the resulting roll of biaxially oriented polyamide resin film, one sample measuring 1.5 m in length in the longitudinal direction (MD) was cut out. This sample was then conditioned for 48 hours in an ESPEC built-in chamber set to a temperature of 20°C and a humidity of 95% RH, and subsequently conditioned for another 48 hours in an environment of 20°C and 40% RH. Subsequently, under conditions of 20°C and 40% RH humidity, samples were cut into 500mm squares with the film edge (MD) as one side. If the film width was 500mm or more, samples were cut from both ends. If the film width was less than 500mm, a sample was created with one side equal to the film width. The outer shape of the samples is shown in Figure 1. The sample in Figure 1 shows the case where one side is parallel to the MD. Next, after conditioning the sample in a chamber set at a temperature of 20°C and a humidity of 90% RH for 48 hours, as shown in Fig. 1, each vertex was designated as ABCD clockwise from the upper left, and the lengths between each vertex, AB, AC, AD, BC, BD, and CD, were measured. The angles of each vertex (θA, θB, θC, θD shown in Fig. 1) were calculated using the law of cosines. cos(θA(°))=(AB , , 2 , ,

[0137] , 2 , , 2 , , , 2 , , , , 2 , , , +AD 2 -BD 2 ) / (2×AB×AD) cos(θB(°))=(AB 2 +BC 2 -AC 2 ) / (2×AB×BC) cos(θC(°))=(BC 2 +CD 2 -BD 2 ) / (2×BC×CD) cos(θD(°))=(AD 2 +CD 2 -AC 2 ) / (2×AD×CD) The angle change was calculated from the obtained angles using the following formula. ΔA(°)=|90 - θA| ΔB(°)=|90 - θB| ΔC(°)=|90 - θC| ΔD(°)=|90 - θD| The maximum value of the angle change of each obtained vertex was taken as the angle change of the biaxially stretched polyamide-based resin film. When two samples were taken from each end, the maximum values of the angle changes at a total of eight locations were adopted.

[0137] (5) TD moisture absorption elongation From the obtained roll-shaped biaxially stretched polyamide-based resin film, a 1 m long square sample in the longitudinal direction (MD) was cut out. After conditioning in an Espec built-in chamber set at a temperature of 20°C and a humidity of 95% RH for 48 hours, it was then conditioned in an environment of 20°C and 40% RH for 48 hours. Thereafter, in an environment of 20°C and 40% RH, the length (L1) in the direction perpendicular to the film end (MD) (TD) was measured. Next, the sample was conditioned for 48 hours in the same chamber set to a temperature of 20°C and a humidity of 90%RH, and then the length (TD) perpendicular to the film edge (MD) (L2) was measured in the same manner. The TD moisture absorption elongation in each direction was calculated using the following formula. TD moisture absorption elongation rate (%) = [(L2-L1) / L1] × 100

[0138] (6) Printing misalignment Using a 10-color gravure printing press (manufactured by Fuji Machinery Industry Co., Ltd.), a single-color print was continuously applied to one side of the obtained polyamide resin film using Sakata Inx gravure ink "Bellcolor" in blue, so that rectangles measuring 600 mm in the MD direction and 400 mm in the TD direction were arranged side by side as shown in Figure 2, thereby obtaining a printing roll. The printing was performed at a speed of 150 m / min and a drying temperature of 60°C. Afterward, one rectangle was cut from the printing roll and conditioned for 24 hours at a temperature of 23°C and a humidity of 50% RH. Subsequently, the conditioned biaxially oriented polyamide resin film was folded along the central printed area. The amount of displacement (mm) at the vertices of the rectangle was measured and evaluated. Ideally, a displacement of 5 mm or less is desired, particularly 2 mm or less, even more preferably 1.5 mm or less, and most preferably 1 mm or less.

[0139] (7) Printing misregistration Using a 10-color gravure printing press (manufactured by Fuji Machinery Industry Co., Ltd.), a polyamide resin film was obtained by continuously printing on one side of the film with Sakata Inx gravure inks "Bellcolor" in blue and white, alternating between the same positions, five times each for a total of 10 prints, so that rectangles measuring 600 mm in the MD direction and 400 mm in the TD direction were arranged horizontally, as shown in Figure 2, to obtain a printing roll. The printing was performed at a speed of 100 m / min and a drying temperature of 60°C. The printed portion was cut out from the resulting printing roll, and the amount of deviation in the TD direction was checked and evaluated. A deviation of 3 mm or less is preferred, 1 mm or less is more preferred, and no deviation is most preferred.

[0140] (8) Evaluation of S-shaped curl in bag making A biaxially oriented polyamide resin film and a sealant film (CP; unoriented polypropylene film, RX-21, 50 μm thick, manufactured by Tohcello Co., Ltd.) were dry-laminated using a urethane adhesive (Takeda Pharmaceutical Company Limited, Takelac A-525 / A-52, two-component type) (adhesive application amount: 3 g / m²). 2 A laminate film was produced by ). The obtained laminate film was folded in half along its longitudinal direction, and both edges were continuously heat-sealed at 180°C for 20 mm intervals using a test sealer. Additionally, 10 mm sections were intermittently heat-sealed perpendicular to the edges at 300 mm intervals to obtain a semi-finished bag approximately 200 mm wide. This semi-finished bag was then cut longitudinally so that the sealed portions at both edges were 10 mm wide. Finally, it was cut perpendicularly at the boundary of the sealed portion to create 10 three-sided sealed bags. These three-sided sealed bags were conditioned for 48 hours at a temperature of 20°C and a humidity of 65% RH. Furthermore, these 10 three-sided sealed bags were stacked, and a load of 9.8 N (1 kgf) was applied to the entire surface of the bags from above. After holding for 24 hours, the load was removed, and the degree of bag curl (S-shaped curl) was observed and evaluated according to the following criteria. ◎: All 10 sheets are not warped. ○: Some show slight curvature. △: Some show clear signs of warping. ×: The curvature is pronounced.

[0141] (9) Thickness accuracy From the obtained biaxially oriented polyamide resin film, samples measuring 50 cm in length and 50 cm in width were cut from three positions: (a) near the center of the winding width and at half the length of the winding; (b) near the right end of the winding width and at half the length of the winding; and (c) near the left end of the winding width and near the end of the winding. For each sample cut from three different locations, straight lines were drawn every 5 cm in the vertical and horizontal directions, and the thickness was measured at the points where these lines intersected (81 points). From these values, the average thickness for each sample was calculated. The thickness accuracy was also calculated and evaluated using the following formula. A HEIDENHAIN-METOR MT1287 manufactured by Heidenhain was used for thickness measurement. A thickness accuracy of 1.7% or less is generally preferred, 1.6% or less is more preferred, and 1.5% or less is the most preferred. Thickness accuracy (%) = ((Maximum film thickness - Minimum film thickness) / 2 / Average film thickness) × 100

[0142] (10) Hayes In this invention, haze was measured using the NDH4000 haze meter manufactured by Nippon Denshoku Industries Co., Ltd. More specifically, a sample of polyamide resin film was conditioned at a temperature of 23°C and a humidity of 50% RH for 2 hours, and then measured under the same temperature and humidity conditions. The number of samples measured was n=10, and the average value was used.

[0143] (11) Strong piercing The obtained polyamide resin film was conditioned for 24 hours at a temperature of 20°C and a humidity of 50%RH. The film was then tensioned and fixed in a circular mold with an inner diameter of 100 mm. A needle with a tip radius of curvature of 0.5 mm was pierced perpendicularly to the sample surface at a speed of 50 mm / min into the center of the sample, and the strength at which the film tore was measured. The strength per 15 μm was calculated. The number of samples measured was n=5, and the average value was used.

[0144] [Table 1]

[0145] The biaxially oriented polyamide resin films of Examples 1 to 27 showed minimal angle change before and after moisture absorption, suppressing printing misalignment during fold and curling after bag making.

[0146] In contrast, the biaxially oriented polyamide resin film of Comparative Example 1, in particular, experienced a large change in angle before and after moisture absorption because the cooling rate from the stretcher outlet exceeded 180°C / second. This resulted in significant printing misalignment during fold and large curling after bag making. Polyamide resin films stretched by sequential biaxial stretching showed particularly large changes in angle before and after moisture absorption.

Claims

1. A biaxially oriented polyamide resin film, comprising the following process: (1) The first step is to humidify the film in an environment of 20°C and 95% RH for 48 hours, and then humidify it in an environment of 20°C and 40% RH for 48 hours. (2) A second step in which a square sample is cut out in an environment with a temperature of 20°C and a humidity of 40% RH after the first step. (3) A third step in which the square sample is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90% RH after the second step. (4) A fourth step in which the angles (θ) formed by the four vertices of the sample after the third step are measured and (5) The fifth step calculates the angle change [Δθ = |90 - θ|] relative to the angle of 90° formed by the vertices of the sample in the second step. A biaxially oriented polyamide resin film characterized in that the angular change Δθ obtained by the measurement conditions having the above characteristics is 1.0° or less.

2. The following steps: (1) A first step in which a square sample cut from the film in the MD direction and TD direction is conditioned for 48 hours in an environment of 20°C and 95% RH, and then conditioned for 48 hours in an environment of 20°C and 40% RH. (2) A second step in which the length of the side (L1) in the TD direction of the sample is measured in an environment with a temperature of 20°C and a humidity of 40% RH after the first step. (3) A third step in which the sample is conditioned for 48 hours in an environment with a temperature of 20°C and a humidity of 90% RH after the second step. (4) A fourth step in which the length of the side (L2) of the sample in the TD direction is measured after the third step and (5) The fifth step of calculating the TD moisture absorption elongation rate based on the following formula. TD moisture absorption elongation rate (%) = [(L2 - L1) / L1] × 100 A biaxially oriented polyamide resin film according to claim 1, wherein the TD moisture-absorbing elongation obtained by the measurement conditions having the above characteristics is 1.3% or less.

3. A biaxially oriented polyamide resin film according to claim 1 or 2, wherein the TD direction of the film is 500 mm or more.

4. A biaxially oriented polyamide resin film according to any one of claims 1 to 3, wherein the polyamide resin includes a polyamide resin obtained by chemical recycling.

5. A biaxially oriented polyamide resin film according to any one of claims 1 to 4, wherein the polyamide resin includes a polyamide resin obtained from plant-derived raw materials.

6. A biaxially oriented polyamide resin film according to any one of claims 1 to 5, to be used as a printing target.

7. A method for producing a biaxially oriented polyamide resin film, (1) A step of obtaining an unstretched film by forming a molten kneaded material containing polyamide resin into a sheet, (2) A stretching step to obtain a biaxially oriented film by stretching the unstretched film by MD stretching and TD stretching. (3) A step of performing a heat-setting treatment and a relaxation treatment on the obtained biaxially oriented film and (4) A step of cooling the biaxially oriented film after the relaxation treatment at a cooling rate of 180°C / second or less. A method for producing a biaxially oriented polyamide resin film, characterized by including the following:

8. The manufacturing method according to claim 7, wherein the relaxation rate in the MD direction is 8% or less.

9. The manufacturing method according to claim 8 or 9, wherein biaxial stretching is performed by a simultaneous biaxial stretching method.

10. The manufacturing method according to any one of claims 8 to 10, wherein the preheating temperature is 200 to 225°C.

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