JP2023126163A - Biaxially oriented polyamide-based resin film - Google Patents

Abstract

To provide a biaxially oriented polyamide-based resin film that has a small dimensional change rate due to heat and moisture, and can sufficiently suppress S-shaped curling after bag making.SOLUTION: There is provided a biaxially oriented polyamide-based resin film that is configured in that films that are clock-wisely cut at a 45 degree direction and a 135 degree direction with respect to a machine direction (MD) during film formation have an absolute value of a difference between a shrinkage rate in the 45 degree direction and a shrinkage rate in the 135 degree direction (dry heat diagonal difference) in dry heat treatment at 160°C for 5 minutes of 1.0% or less, and an absolute value of a difference between a dimensional change rate in the 45 degree direction and a dimensional change rate in the 135 degree direction (water absorption slope difference), which are determined from a length measured immediately after water absorption treatment at 30°C for 1 hour and a length measured after a water absorption treatment and after humidity control at 23°C, 50% RH for 24 hours of 1.5% or less.SELECTED DRAWING: None

Description

The present invention relates to a biaxially oriented polyamide resin film.

Biaxially stretched polyamide resin films have excellent mechanical properties such as tensile strength, puncture strength, impact strength, and pinhole resistance, and are also excellent in heat resistance. For this reason, laminated films made of a biaxially oriented polyamide resin film as a base material and a sealant film made of polyolefin resin laminated thereto using methods such as dry lamination or extrusion lamination are suitable for sterilization processing such as boiling and retort packaging. It is used in a wide range of fields, including packaging materials.

However, the dimensions of polyamide resin films may change due to the influence of moisture or temperature. When a polyamide resin film is used in the field of packaging materials, if there is a difference in the rate of dimensional change in the diagonal direction, the corners of the bag tend to curl due to the dimensional change after bag making. If the bag curls, problems may occur during the filling process, such as having to remove two bags or making it difficult to open the bag.

In general, polyamide resin films produced using a tenter method tend to have a difference in dimensional change rate in the diagonal direction due to the bowing phenomenon (a phenomenon in which the film deforms into a bow shape). For example, polyamide resin films have the characteristic of shrinking when exposed to high temperatures due to residual stress during stretching, and this shrinkage is anisotropic, especially at the lateral edges of the film, due to the bowing phenomenon. sex is likely to occur. When this anisotropy increases, the bag tends to shrink and curl during heat sealing during bag manufacturing.

Furthermore, since polyamide resin films have amide groups, they have high water absorption properties and have the property of expanding when containing water. This expansion also tends to cause anisotropy, particularly at the lateral ends of the film, due to the bowing phenomenon. When this anisotropy increases, the bag becomes more likely to curl due to moisture absorption after the bag making process.

To address such problems with polyamide resin films, Patent Document 1 discloses a method that can reduce S-curl caused by moisture absorption after bag making, even for products near the edges of mill rolls, and Patent Document 2 discloses a method that can reduce S-curl caused by moisture absorption after bag making. A method for reducing twisting of a packaging bag using a biaxially oriented polyamide resin film as the film is described.

JP2021-42386A JP2012-254804A

However, even in these conventional techniques, there is still room for improvement as shown below.
In Patent Document 1, even if S-curl can be suppressed in a low-humidity environment such as 20°C and 20% RH, S-curl does not occur in a general humidity environment such as 20°C and 65% RH. was not sufficiently suppressed.
In Patent Document 2, even if it was possible to suppress the S-curl of small-sized bags, it was not sufficient to suppress the S-curl of large-sized bags at a time when the capacity of products is increasing.
As described above, a method for sufficiently suppressing the S-curl of polyamide resin film after bag making has not yet been developed.
Therefore, an object of the present invention is to provide a biaxially stretched polyamide resin film that has a small dimensional change rate due to heat and moisture and can sufficiently suppress S-curl after bag making.

As a result of extensive research in view of the problems of the prior art, the present inventor has found that by adopting a specific manufacturing method, a biaxially oriented polyamide resin film having specific physical properties that can achieve the above objectives can be obtained. This discovery led to the completion of the present invention.
That is, the gist of the present invention is as follows.

(1) Shrinkage rate in the 45 degree direction and 135 degrees during dry heat treatment at 160°C for 5 minutes of films cut out in the 45 degree direction and 135 degree direction clockwise with respect to the machine direction (MD) during film formation. The absolute value of the difference from the shrinkage rate in the degree direction (dry heat diagonal difference) is 1.0% or less,
The dimensional change rate in the 45 degree direction determined from the length measured immediately after water absorption treatment at 30 ° C. for 1 hour and the length measured after the water absorption treatment at 23 ° C., 50% RH, and 24 hours of humidity control. , a biaxially stretched polyamide resin film characterized in that the absolute value of the difference between the dimensional change rate in the 135 degree direction (water absorption diagonal difference) is 1.5% or less.
(2) The biaxially oriented polyamide resin film according to (1), wherein the MD shrinkage rate of the film cut out in MD is 2.0% or less after dry heat treatment at 160° C. for 5 minutes.
(3) (1) or (2) characterized in that the TD shrinkage rate of the film cut out in the transverse direction (TD) during film formation is 1.0% or less when dry heat treated at 160°C for 5 minutes. The biaxially oriented polyamide resin film described above.
(4) The biaxially oriented polyamide resin film according to any one of (1) to (3), wherein the polyamide resin contains a resin regenerated by chemical recycling.
(5) The biaxially oriented polyamide resin film according to any one of (1) to (4), wherein the polyamide resin contains a resin obtained from a plant-derived raw material.
(6) A biaxially oriented polyamide resin laminate film, characterized in that a gas barrier layer is laminated on at least one surface of the biaxially oriented polyamide resin film according to any one of (1) to (5) above. .
(7) A biaxially oriented polyamide resin laminate characterized in that an easily adhesive layer is laminated on at least one surface of the biaxially oriented polyamide resin film according to any one of (1) to (6) above. film.
(8) A laminate film using the biaxially stretched polyamide resin film according to any one of (1) to (7) above.
(9) A bag-made product using the laminate film described in (8) above.
(10) A method for producing a biaxially oriented polyamide resin film according to any one of (1) to (7) above, wherein after the step of biaxially stretching the unstretched film, the biaxially oriented film is A method for producing a biaxially oriented polyamide resin film, characterized in that in the step of relaxing in the machine direction (MD), the deceleration of the film running speed is 0.08 m/s ² or less and the relaxation rate is 8% or less. .
(11) The method for producing a biaxially stretched polyamide resin film according to (10), wherein the biaxial stretching step is a simultaneous biaxial stretching method.

According to the present invention, a biaxially stretched polyamide resin film is obtained which has a small dimensional change rate due to heat and moisture and can sufficiently suppress S-curl after bag making. Therefore, the bag-made product using the biaxially stretched polyamide-based resin film of the present invention has excellent workability because troubles such as double bag removal do not occur during the filling process.

The biaxially oriented polyamide resin film of the present invention is prepared by cutting out the film at 45 degrees and 135 degrees clockwise with respect to the machine direction (MD) at the time of film formation, and dry-heating the film at 160°C for 5 minutes. The absolute value of the difference between the shrinkage rate in the 45 degree direction and the shrinkage rate in the 135 degree direction (dry heat slope difference) determined from the length measured after humidity conditioning for 2 hours at 23° C. and 50% RH is 1. 0% or less, and is determined from the length measured after water absorption treatment at 30°C for 1 hour and the length measured after humidity control at 23°C, 50% RH for 24 hours after the water absorption treatment, in the 45 degree direction. The absolute value of the difference between the dimensional change rate and the dimensional change rate in the 135 degree direction (water absorption diagonal difference) is 1.5% or less.

<Polyamide resin>
The polyamide resin constituting the biaxially stretched polyamide resin film of the present invention includes, for example, a) ring-opening polymerization using lactams as a monomer component, b) ω-amino acids, dibasic acids, diamines, etc. as monomers. Examples include polyamide resins obtained by condensation polymerization or the like as a component.
Examples of lactams include ε-caprolactam, enantlactam, capryllactam, and lauryllactam.
Examples of the ω-amino acids include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, and 11-aminoundecanoic acid.
Examples of dibasic acids include adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecadionic acid, hexadecadionic acid, eicosandioic acid, eicosadienedionic acid, , 2,4-trimethyladipic acid, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, xylylene dicarboxylic acid and the like.
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, metaxylylenediamine, and the like.
Examples of polymers or copolymers obtained by polymerizing these monomers include polyamide 6, 7, 10, 11, 12, 46, 410, 56, 66, 69, 610, 611, 612, 6T, 6I, In addition to polymers such as 810, 9T, 1010, 1012, 10T, MXD6 (metaxylene dipanamide 6), copolymers such as 6/66, 6/12, 6/6T, 6/6I, 6/MXD6, etc. can be mentioned. Among these, it is preferable to include polyamide 6, which has an excellent balance between heat resistance and mechanical properties.
Furthermore, in order to improve the properties of the biaxially stretched polyamide resin film, two or more types of polyamide resins such as these polymers or copolymers may be mixed. For example, a polyamide resin prepared by mixing polyamide 6 and MXD6 at a mass ratio (polyamide 6/MXD6) of 95/5 to 30/70 improves the straight-line cutting properties of the resulting biaxially stretched polyamide resin film. I can do it.

<Recycled resin>
In addition to polyamide resins obtained using conventional fossil fuel-derived raw materials (particularly virgin monomers), the polyamide resin in the present invention preferably includes resins regenerated by chemical recycling from the viewpoint of environmental consideration. . Polyamide resin regenerated by chemical recycling (chemically recycled polyamide resin) is obtained by depolymerizing polyamide resin that has become resin waste and polymerizing the obtained regenerated monomer again.

The content of the chemically recycled polyamide resin in the polyamide resin is not particularly limited, but from the viewpoints of environmental consideration, reduction of dry heat slope difference, and reduction of water absorption slope difference, it is preferably 10% by mass or more, and 30% by mass or more. The content is more preferably 50% by mass or more. Note that the upper limit of the content of the chemically recycled polyamide resin can be, for example, about 100% by mass, but is not limited thereto.

Further, the polyamide resin in the present invention may also contain a material recycled polyamide resin from the viewpoint of considering the environment. Examples of waste materials generated during the production of polyamide resin films include waste materials such as edge trimming waste and slit waste, as well as films that were not commercialized as defective products. These can be crushed or remelted and used as pellets. The content of the material recycled polyamide resin is not limited as long as it does not impair the effects of the present invention.

<Plant-derived resin>
Further, from the viewpoint of considering the environment, the polyamide resin in the present invention preferably contains a resin obtained from plant-derived raw materials, and may contain a polyamide resin containing a plant-derived monomer component. For example, examples of monomer components derived from plants include decanediamine, aminoundecanoic acid, and sebacic acid using raw materials derived from castor oil, and polyamide resins obtained by polymerizing these include polyamide 1010, polyamide 11, and the like.
The content of the plant-derived polyamide resin in the polyamide resin is not limited as long as it does not impair the effects of the present invention, but from the viewpoint of environmental considerations, it is preferably 3% by mass or more, more preferably 5% by mass or more, and 10% by mass. The above is more preferable. Note that the upper limit of the content of the plant-derived polyamide resin can be, for example, about 100% by mass, but is not limited thereto.

<Biaxially oriented polyamide resin film>
The biaxially stretched polyamide resin film of the present invention is obtained by biaxially stretching an unstretched film of the polyamide resin described above. Unstretched films and uniaxially stretched films have low tensile strength and large anisotropy, so they are not suitable as base materials for producing packaging bags.

The biaxially oriented polyamide resin film of the present invention has a dry heat shrinkage rate in dry heat treatment at 160°C for 5 minutes at 45 degrees and 135 degrees clockwise with respect to the machine direction (MD) during film formation. The absolute value of the difference (dry heat slope difference) needs to be 1.0% or less, preferably 0.8% or less, more preferably 0.6% or less, 0.55 % or less is more preferable. When the dry heat slope difference exceeds 1.0%, anisotropy occurs due to heat shrinkage during heat sealing in bag making process, and curling tends to occur.
The above dry heat shrinkage rate is calculated by cutting out a film with a length of 10 cm and a width of 1 cm in the measurement direction, and measuring the length after humidity conditioning at 23°C, 50% RH for 2 hours (before treatment) and after drying at 160°C for 5 minutes. It is determined from the length (after treatment) after heat treatment at 23° C., 50% RH, and humidity control for 2 hours.

The biaxially stretched polyamide resin film of the present invention preferably has a MD dry heat shrinkage rate of 2.0% or less at 160°C for 5 minutes, more preferably 1.9% or less, 1. More preferably, it is 8% or less. If the dry heat shrinkage rate of the MD exceeds 2.0%, the heat shrinkage during heat sealing of the MD during bag-making processing will increase, and the lengths of the sealed and unsealed areas will not match, which may promote curling. be.

The biaxially stretched polyamide resin film of the present invention preferably has a dry heat shrinkage rate of 1.0% or less in the transverse direction (TD) at 160°C for 5 minutes, more preferably 0.9% or less. It is preferably 0.8% or less, and more preferably 0.8% or less. If the dry heat shrinkage rate of the TD exceeds 1.0%, the heat shrinkage during heat sealing of the TD during the bag making process will increase, and the lengths of the sealed and unsealed areas will not match, which may promote curling. be.

The biaxially oriented polyamide resin film of the present invention is determined from the length when water is absorbed and the length when the humidity is adjusted at 23°C and 50% RH after water absorption in the 45 degree direction and 135 degree direction clockwise with respect to the MD. The absolute value of the calculated dimensional change rate difference (water absorption slope difference) must be 1.5% or less, preferably 1.2% or less, and more preferably 1.0% or less. preferable. In a biaxially oriented polyamide resin film, when the water absorption diagonal difference exceeds 1.5%, the anisotropy of dimensional change due to moisture absorption becomes large, and the corners tend to curl after bag making.
The above dimensional change rate is the length measured by cutting out a film with a length of 10 cm and a width of 1 cm in the measurement direction, and after water absorption treatment at 30°C for 1 hour, and the length measured after the water absorption treatment at 23°C, 50% RH, 24 hours after the water absorption treatment. It is determined from the length measured after humidity conditioning.
Note that in biaxially oriented polyamide resin films, residual stress is generally released by water absorption, so in order to determine the pure dimensional change due to water absorption, the measured values after water absorption and the measured values at humidity control after water absorption were used. is adopted.

The thickness of the biaxially stretched polyamide resin film of the present invention is not particularly limited, but is generally 5 to 100 μm, preferably 5 to 50 μm, and more preferably 5 to 30 μm. When the thickness of the polyamide resin film is less than 5 μm, mechanical strength is insufficient, and when it exceeds 100 μm, problems such as increased weight and decreased transparency may occur.

At least one surface of the biaxially stretched polyamide resin film of the present invention is preferably subjected to a known surface treatment such as corona treatment, plasma treatment, or ozone treatment. A surface-treated polyamide resin film has improved adhesion to other films such as a sealant laminated on the film surface.

<Gas barrier layer>
The biaxially stretched polyamide resin film of the present invention may also have a structure in which a gas barrier layer is laminated on at least one side of the film. Examples of methods for laminating the gas barrier layer include a method of vapor depositing an inorganic substance and a method of applying a gas barrier coating liquid. When depositing an inorganic substance, examples of the inorganic substance used include metals such as aluminum, silicon, magnesium, palladium, zinc, nickel, silver, copper, gold, indium, stainless steel, chromium, and titanium, as well as metals such as each of these metals. Examples include oxides or compounds. When applying a gas barrier coating liquid, examples of the gas barrier coating liquid used include a gas barrier coating liquid containing a polyvinylidene chloride copolymer (PVDC) and a gas barrier coating liquid containing an inorganic layered compound and a resin. The oxygen permeability of the film in which the gas barrier layer is laminated is preferably 100 ml/(m ² ·day · MPa) or less, and the closer it is to 0 ml/(m ² ·day · MPa), the better the gas barrier property is.

<Easy adhesive layer>
The biaxially stretched polyamide resin film of the present invention may also have a structure in which an easily adhesive layer is laminated on at least one side of the film. Examples of the method for laminating the easily adhesive layer include a method of applying an easily adhesive coating liquid. Examples of the easy-adhesion coating liquid to be used include easy-adhesion coating liquids containing various synthetic resins such as polyurethane resin, polyester resin, acrylic resin, and epoxy resin.

<Additives>
The biaxially oriented polyamide resin film of the present invention may contain pigments, heat stabilizers, antioxidants, weathering agents, flame retardants, plasticizers, mold release agents, reinforcing agents, etc. within the range that does not impair the characteristics of the present invention. It may also contain an agent. For example, examples of the heat stabilizer or antioxidant include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, and the like.
Further, the biaxially stretched polyamide resin film of the present invention may contain various inorganic lubricants and organic lubricants in order 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 balloon, carbon black, oxidized Examples include zinc, antimony trioxide, zeolite, hydrotalcide, layered silicate, ethylene bisstearamide, and the like.
The amount of these additives added is not limited as long as it does not impede the effects of the present invention, but usually the total amount may be 5% by mass or less.

<Method for producing biaxially oriented polyamide resin film>
Next, a method for producing a biaxially stretched polyamide resin film of the present invention will be explained.
First, a polyamide resin is melted in an extruder, then extruded as a molten sheet through a T-die, and brought into close contact with a cooling drum whose surface temperature is controlled at 0 to 30°C to be rapidly cooled to obtain a continuous unstretched film.

The obtained unstretched film is desirably subjected to water absorption treatment prior to biaxial stretching. The water absorption treatment is carried out by sending the unstretched film to a hot water bath whose temperature is controlled at 20 to 90°C for 10 minutes or less. By this water absorption treatment, the unstretched film is appropriately plasticized and crystallization of the polyamide resin is suppressed, thereby making it possible to prevent the film from being cut during the stretching process.

Although the moisture content of the unstretched film that has absorbed water through the above treatment cannot be determined unconditionally depending on the mixing ratio of the resin, it is preferably 1.0 to 7.0% by mass, and preferably 1.5 to 5.0% by mass. It is more preferable that there be. If the moisture content of the unstretched film is less than 1.0% by mass, crystallization may progress and the film may be cut. On the other hand, if the moisture content of the unstretched film exceeds 7.0% by mass, folds and wrinkles will occur during the water absorption treatment, making it more likely to cause problems such as meandering, and the resulting biaxially stretched film will have a reduced strength. Or, the thickness unevenness of the film in the lateral direction may increase.

The water-absorbed unstretched film is preferably preheated before stretching. The preheating temperature is preferably 200 to 230°C, more preferably 215 to 230°C, although it depends on the proportion of resin used. If the preheating temperature is less than 200°C, the resulting film will have a large bowing phenomenon, and the anisotropy of the moisture absorption elongation rate and hot water shrinkage rate at the edges of the film will become large; on the other hand, if the preheating temperature exceeds 230°C Otherwise, the film may become whitened or cut.

In the present invention, the 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 well-balanced manner. In the sequential biaxial stretching method, since longitudinal stretching and transverse stretching are carried out separately, the anisotropy of the edges of the obtained film may become large.

The simultaneous biaxial stretching is preferably performed by a tenter method from the viewpoint of improving dimensional stability and thickness accuracy by suppressing the elongation rate during moisture absorption.
The tenter type simultaneous biaxial stretching can be performed using a tenter such as a pantograph type tenter, a screw type tenter, or a linear motor type tenter. Among them, the linear motor tenter, in which each clip is driven independently by a linear motor, allows the longitudinal stretching ratio and longitudinal relaxation rate to be set in detail by controlling a variable frequency driver. It has the flexibility to be accurately and smoothly controlled. This simultaneous biaxial stretching method using a linear motor type tenter is the most preferred stretching method because it reduces the bowing phenomenon and provides a biaxially stretched film with improved uniformity of physical properties in the transverse direction.

The simultaneous biaxial stretching of the preheated unstretched film is preferably carried out at 170 to 210°C, more preferably at 190 to 200°C. If the stretching temperature is less than 170°C, the resulting biaxially stretched film may have a large shrinkage stress and a high hot water shrinkage rate. On the other hand, if the stretching temperature exceeds 210°C, the biaxially stretched film may have a non-uniform thickness and poor quality.

In simultaneous biaxial stretching, the stretching ratio of the unstretched film is preferably 2.5 to 4.5 times in each of MD and TD. Further, the area stretching ratio expressed as the product of the longitudinal stretching ratio and the transverse stretching ratio is preferably 7 to 12 times. If the areal stretching ratio is less than 7 times, the resulting biaxially stretched film may have poor mechanical properties. On the other hand, when the area stretching ratio exceeds 12 times, the resulting biaxially stretched film has a high shrinkage stress and a high shrinkage rate during dry heat treatment. When the shrinkage rate during dry heat treatment increases, the dry heat gradient difference increases, making curling more likely to occur during bag making.

Further, during stretching, it is preferable to reduce the bowing phenomenon using a known method. Examples of methods include creating a temperature gradient in the lateral direction by increasing the stretching temperature at the edges of the film relative to the center when stretching an unstretched film, and performing MD stretching first. ,

The biaxially stretched film is preferably heat treated after stretching. The heat treatment temperature is preferably 200 to 225°C, more preferably 210 to 220°C. If the heat treatment temperature is less than 200°C, the resulting biaxially stretched film may have a high dry heat shrinkage rate and may also have high anisotropy. On the other hand, if the heat treatment temperature exceeds 220° C., the biaxially stretched film obtained will have a high water absorption elongation rate, an increased anisotropy, and may have decreased mechanical properties such as tensile elongation or whitening.

The biaxially stretched film is subjected to relaxation treatment after heat treatment. In the MD relaxation treatment, it is necessary to reduce the deceleration of the film running speed to 0.08 m/s ² or less, preferably 0.001 to 0.08 m/s ² , and preferably 0.001 to 0.08 m/s 2. 06 m/s ² is more preferable, and 0.001 to 0.05 m/s ² is even more preferable. If the deceleration of the film running speed exceeds 0.08 m/s ² , the resulting biaxially stretched film may have a high dry heat shrinkage rate and may also have high anisotropy. On the other hand, if the deceleration of the film running speed is less than 0.001 m/s ² , the zone length required for the relaxation treatment becomes too long, which is unrealistic in that it requires a huge amount of space.

In addition, the relaxation rate of the film in the MD relaxation treatment needs to be 8% or less, preferably 1 to 8%, and preferably 1 to 6%, from the viewpoint of reducing the water absorption gradient difference. More preferably, it is 1 to 5%. If the MD relaxation rate exceeds 8%, the resulting biaxially stretched film will have a high water absorption elongation rate, and its dimensional stability may be impaired. On the other hand, if the MD relaxation rate is less than 1%, the resulting biaxially stretched film may have a high dry heat shrinkage rate.

From the viewpoint of reducing the dry heat shrinkage rate, the relaxation rate of the film in the TD relaxation treatment is preferably 1 to 8%.
From the viewpoint of improving the mechanical properties (piercing strength) of the film, the ratio of the MD relaxation rate to the TD relaxation rate (MD/TD) is preferably 0.20 to 1.80, and preferably 0.80 to 1.80. More preferably, it is 20.

<Production method of chemically recycled polyamide resin>
The method for producing the chemically recycled polyamide resin used as a raw material for the biaxially oriented polyamide resin film is not limited, but includes, for example, (1) a step of producing a monomer from the depolymerization raw material (A) (depolymerization step); 2) a step of producing polyamide resin (B) by polymerizing using a raw material containing the monomer (polymerization step); (3) a step of scouring the polyamide resin (B) (scouring step). It can be obtained suitably.

In the depolymerization step, monomers are regenerated from the depolymerization raw material (A) (hereinafter, such monomers are referred to as "regenerated monomers").
As the regenerated monomer, lactams are particularly preferred, and examples thereof include ε-caprolactam, enantlactam, capryllactam, and lauryllactam. Among these, ε-caprolactam is particularly preferred.

The type of depolymerization raw material (A) is not particularly limited, and in addition to various polyamide resins, oligomers of various polyamide resins can also be used. More specifically, various resins mentioned below for polyamide resin (B) can be exemplified. Further, examples of oligomers include chain bodies ranging from dimers to heptamers, cyclic bodies ranging from dimers to nonamers, and the like.
In particular, in the present invention, at least one type of polyamide 6 resin and its oligomer can be suitably used as the depolymerization raw material (A). In particular, since polyamide 6 is a resin consisting essentially of ε-caprolactam alone as a monomer unit, it also has the advantage of being easy to monomerize and purify and separate.
The form of the polyamide resin used as the raw material for depolymerization (A) includes discharged resin waste including the amount changed between brands during polymerization and the amount changed until the commercialization of film products, as well as edge trimming generated during film manufacturing. Examples include scraps, scraps such as slit scraps, and films that were not commercialized as defective products. The use of waste materials can also contribute to environmental conservation.
The form of the oligomer as the depolymerization raw material (A) includes, for example, not only highly water-soluble oligomers recovered from scouring water generated during scouring of polyamide resin, but also dimers to octamers with low water solubility. Examples include residues after filtration.

The method for producing a monomer from the depolymerization raw material (A) is not particularly limited as long as a predetermined monomer can be obtained, but preferably a depolymerization reaction of the depolymerization raw material (A) can be employed. That is, by chemically decomposing the depolymerization raw material (A) through a depolymerization reaction, a recycled monomer can be suitably obtained.
The method and conditions for the depolymerization reaction are not particularly limited, and the depolymerization reaction can be carried out according to known methods. Therefore, for example, a catalyst may or may not be used. Moreover, it may be carried out in the absence of water (dry method) or in the presence of water (wet method). Particularly from the viewpoint of productivity, a method in which depolymerization is carried out in hot steam in the presence of a catalyst is preferred. Cyclic oligomers with low water solubility are difficult to depolymerize directly due to the slow hydrolysis rate of amide bonds. Regenerated monomers can also be suitably obtained from oligomers.

In the polymerization step, the polyamide resin (B) is manufactured by polymerizing using raw materials containing the monomers (regenerated monomers).
The raw material may be a raw material in which all monomers are recycled monomers, but it is preferable to use virgin monomers in combination. 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 a range close to 100% by mass in the monomer raw material. As a monomer other than C-CL, it is preferable to include ε-caprolactam (hereinafter referred to as "V-CL") as a virgin monomer in the monomer raw material. Here, virgin monomer is an antonym of recycled monomer, and refers to a monomer that has not undergone a polymer depolymerization process. As the virgin monomer, for example, commonly commercially available monomers can be used.

Regenerated monomers may contain by-products that are difficult to separate. As a result, the crystallization rate of the polyamide resin obtained using only the recycled monomer as a raw material can be slightly lower than the crystallization rate of the polyamide resin obtained using only the virgin monomer as a raw material. It is possible to further reduce the crystallization rate of the polyamide resin obtained by using in combination.
The crystallization rate can be determined by the half-value width of the crystallization peak obtained by measuring the cooling crystallization temperature (Tc) of the polyamide resin. In the present invention, the half width is usually preferably 10°C or higher, more preferably 11°C or higher, and even more preferably 12°C or higher. The wider the half width, the wider the crystallization rate, and when the film is stretched and crystallized, local unevenness in the crystalline state on the film surface is less likely to occur, and uniformity can be improved. From this point of view, it is preferable to use a polyamide resin polymerized using a combination of recycled monomers and virgin monomers. Note that the upper limit of the half width can be, for example, about 20° C., but is not limited thereto.
The recycled monomer content in the raw material is not particularly limited, but from the viewpoint of widening the half width, it is preferably 90% by mass or less, more preferably 80% by mass or less, and from the viewpoint of increasing the recycling ratio, The content is preferably 5% by mass or more, more preferably 10% by mass or more. In the polymerization step, as mentioned above, it is preferable to use a virgin monomer as a component other than the recycled monomer, and the content of the virgin monomer in the raw material is preferably 10 to 95% by mass, and 20 to 90% by mass. It is more preferable to express it in mass %.

The polyamide resin (B) produced in the polymerization step may be end-capped, if necessary, for the purpose of suppressing monomer production during melting. For this reason, the raw material may contain additives such as a terminal blocking agent, if necessary. The terminal capping agent is not particularly limited, and examples thereof include organic glycidyl esters, dicarboxylic anhydrides, monocarboxylic acids such as benzoic acid, and diamines.

The polymerization method for obtaining the polyamide resin (B) is not particularly limited, and known monomer polymerization methods can also be employed. For example, a method is adopted in which ε-caprolactam, water, and benzoic acid as an end-blocking agent are mixed, heated in a polymerization pot, pressurized, and then subjected to a polymerization reaction while depressurizing and dehydrating until the desired viscosity is reached. I can do it.

In the scouring step, the polyamide resin (B) is scoured. As a result, the monomer contained in the polyamide resin (B) can be removed and the relative viscosity of the polyamide resin (B) can be increased to a desired range, resulting in physical properties suitable for film formation.
Although not limited to scouring, for example, the polyamide resin (B) is formed into pellets or the like so that the relative viscosity (25°C) of the polyamide resin (B) is within the range of about 2.5 to 4.5. It is preferable to immerse the molded product in hot water at 90 to 100° C. for about 15 to 30 hours.
The number of times of scouring treatment in the scouring step is not particularly limited as long as the half width of Tc is 10° C. or more, but it is preferably once or twice. If the refining process is not carried out, by-products will increase, the relative viscosity will fall below the above range, it may become difficult to form a film, and the strength may decrease when formed into a film. On the other hand, when the number of times of scouring is three or more times, the amount of by-products decreases, and the half width may become less than 10°C.
It is preferable that the polyamide resin (B) after the scouring step is dried as necessary. Drying conditions are not particularly limited. For example, hot air drying can be carried out at about 100 to 130° C. for about 10 to 30 hours, but the method is not limited thereto. More specifically, hot air drying can be performed at 110° C. for 20 hours.

<Gas barrier layer stacking method>
As a method for laminating a gas barrier layer on at least one side of the biaxially stretched polyamide resin film of the present invention, a lamination method using polyvinylidene chloride copolymer (PVDC) will be described.

The gas barrier layer can be laminated by coating at least one side of a polyamide resin film using PVDC in the form of latex. PVDC preferably contains vinylidene chloride units in an amount of 60% by mass or more, and more preferably in a range of 70 to 97% by mass. The average particle size of PVDC in the latex is preferably 0.05 to 0.5 μm, more preferably 0.07 to 0.3 μm. PVDC may contain various additives such as an anti-blocking agent, a crosslinking agent, a water repellent, and an antistatic agent within a range that does not impair the effects of the present invention.

The thickness of the gas barrier layer using PVDC is preferably 0.5 to 3.5 μm, more preferably 0.7 to 3.0 μm, and even more preferably 1.0 to 2.5 μm. . When the gas barrier layer is thinner than 0.5 μm, it is difficult to exhibit sufficient gas barrier properties, and when it is thicker than 3.5 μm, not only the effect is saturated but also the physical properties of the film may be impaired.

It is preferable to form the gas barrier layer on the polyamide resin film after the water absorption treatment and before stretching, at a stage where the monomer content is low, thereby improving the adhesion of the gas barrier layer to the polyamide resin film.

The coating method is not particularly limited, and examples include gravure roll method, reverse roll method, air knife method, reverse gravure method, Meyer bar method, inverse roll method, various coating methods using a combination thereof, and various spraying methods. method etc. can be adopted. Immediately before coating, the polyamide resin film may be subjected to corona discharge treatment or the like.

<Lamination method of easy adhesive layer>
As a method for laminating an easily adhesive layer on at least one side of the biaxially stretched polyamide resin film of the present invention, a lamination method using a polyurethane resin will be described.

The easily adhesive layer can be laminated by coating at least one side of the polyamide resin film using an easily adhesive coating liquid containing a polyurethane resin. A polyurethane resin is a polymer obtained by a reaction between a polyfunctional isocyanate and a hydroxyl group-containing compound. More specifically, polyfunctional isocyanates such as aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane isocyanate, and polymethylene polyphenylene polyisocyanate, or aliphatic polyisocyanates such as hexamethylene diisocyanate and xylene isocyanate, and polyether polyols and polyester polyols. Examples include urethane resins obtained by reaction with hydroxyl group-containing compounds such as polyacrylate polyols and polycarbonate polyols.

For the purpose of improving the water resistance, heat resistance, etc. of the above-mentioned easy-adhesion layer, the easy-adhesion layer can contain a curing agent. Examples of the curing agent include melamine, isocyanate, carbodiimide, oxosaline, and epoxy, but it is particularly preferable to include melamine resin or carbodiimide resin, and the content of melamine resin is determined based on 100 parts by mass of the resin used as the easy-adhesion layer. However, it is preferably 1 to 15 parts by mass. Further, the content of the carbodiimide resin is preferably 1 to 30 parts by mass based on 100 parts by mass of the resin used as the easily adhesive layer.

The thickness of the adhesive layer made of polyurethane resin is preferably 0.01 to 0.5 μm, more preferably 0.02 to 0.1 μm. If the thickness of the easily adhesive layer is less than 0.01 μm, it becomes difficult to form an easily adhesive layer with a uniform thickness on the film. On the other hand, if the thickness of the easy-adhesive layer exceeds 0.1 μm, the effect of improving the adhesion between the polyamide resin film and the metal foil is saturated, and this becomes disadvantageous in terms of cost.

The polyamide resin film to which the easy-adhesion coating liquid is applied may be an unstretched film after water absorption treatment and before stretching, or a stretched film after stretching.

The coating method is not particularly limited, and for example, various coating methods such as a gravure roll method, a reverse roll method, a wire bar method, an air knife method, or a combination thereof can be employed.

<Laminate film>
The biaxially stretched polyamide resin film of the present invention can be laminated with a sealant film such as a polyethylene film or a polypropylene film to form a laminate film. Further, this laminate film can be used as a packaging bag by being fused into a bag shape using a known method such as heat sealing or ultrasonic sealing.

<Bag-made products>
Bag-made products such as the above-mentioned packaging bags can be particularly suitably used as packaging bags for foods, beverages, and the like. In particular, the biaxially stretched polyamide resin film that makes up the packaging bag has low anisotropy in dimensional changes due to moisture absorption and heat, so the print will not be distorted due to moisture absorption during or after printing, and the printed design will not shift. , it is possible to make it into a bag. In addition, the bags do not curl even after being made, and problems are less likely to occur when filling the bags.

Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

The evaluation methods for various properties in the Examples and Comparative Examples below are as follows.
(1) Relative viscosity ηR
The relative viscosity of a sample solution (liquid temperature 25° C.) in which raw material polyamide resin was dissolved in 96% sulfuric acid to a concentration of 1.0 g/dl was measured using an Ubbelohde viscometer.

(2) Cooling crystallization temperature Tc and half-value width Using a differential scanning calorimeter (input compensation type DSC8000, manufactured by PerkinElmer), 10 mg of the obtained resin was weighed, and the temperature was raised from room temperature to 260°C at a heating rate of 10°C/min. The temperature was raised to 260° C., held for 10 minutes, and then cooled to 100° C. at a cooling rate of 10° C./min, and the cooling crystallization temperature was measured. In the DSC curve with heat flow (mW) on the vertical axis and temperature on the horizontal axis, the temperature at the top of the peak at the time of cooling is Tc (℃), the baseline is drawn from the high temperature side, and the two points are 1/2 intensity of the absolute value of Tc. The interval between them was defined as the half width (°C).

(3) Oxygen permeability Using an oxygen barrier measuring device (OX-TRAN 2/20) manufactured by Mocon Co., Ltd., measurement area 50 cm ² , nitrogen gas flow rate 10 cc/min, oxygen gas flow rate 20 cc/min, 20 ° C. The oxygen permeability of a biaxially stretched polyamide resin laminate film on which a gas barrier coat layer was laminated was measured in an atmosphere of 65% RH. The measurement was carried out for 20 minutes per cycle, and the measurement was terminated when the rate of variation in oxygen permeability at 3 cycle intervals was within 1%.

(4) Dry heat shrinkage rate and dry heat angle difference The obtained roll-shaped biaxially stretched polyamide resin film was measured at 45 degrees and 135 degrees with respect to MD, TD, and MD in an environment of 23°C and 50% RH. Five samples each having a length of 10 cm and a width of 1 cm were cut out in the direction.
After the sample was conditioned for 2 hours in a 23° C., 50% RH environment, the length was measured and defined as L1 (before dry heat treatment).
After the measurement, the sample was subjected to dry heat treatment in an oven at 160° C. for 5 minutes, and the humidity was adjusted again for 2 hours in an environment of 23° C. and 50% RH, and the length was measured, which was designated as L2 (after dry heat treatment).
The dry heat shrinkage rate of each sample in each direction was calculated using the following formula, and the average value was determined.
Dry heat shrinkage rate A (%) = (L1-L2)/(L1) x 100
In addition, the absolute value of the difference between the dry heat shrinkage rate (A (45 degrees)) of the sample in the 45 degree direction with respect to MD and the dry heat shrinkage rate (A (135 degrees)) of the sample in the 135 degree direction is The slope difference was calculated using the following formula.
Dry heat slope difference (%) = |A (45 degrees) - A (135 degrees) |

(5) Water absorption dimensional change rate and water absorption diagonal difference Regarding the obtained roll-shaped biaxially stretched polyamide resin film, the length was measured in the 45 degree direction and the 135 degree direction with respect to the MD in an environment of 23° C. and 50% RH. Five samples each having a size of 10 cm and a width of 1 cm were cut out.
The sample was immersed in water at 30° C. for 1 hour to absorb water, and the length of the sample immediately after being taken out from the water was measured, and was defined as L3 (at the time of water absorption).
The sample after water absorption was again conditioned for 24 hours in an environment of 23° C. and 50% RH, the length was measured, and the length was determined as L4 (humidity conditioned after water absorption).
For the water-absorbed samples in each direction, the dimensional change rate after humidity conditioning was calculated using the following formula, and the average value was determined.
Dimensional change rate after humidity conditioning of water absorption sample B (%) = (L3-L4)/L3×100
Difference between the dimensional change rate (B (45 degrees)) of a water-absorbed sample after humidity conditioning in a direction of 45 degrees with respect to MD and the dimensional change rate (B (135 degrees)) of a water-absorbed sample after humidity conditioning in a direction of 135 degrees with respect to MD The absolute value of the water absorption slope difference was calculated using the following formula.
Water absorption angle difference (%) = |B (45 degrees) - B (135 degrees) |

(6) S-shaped bag making curl A biaxially stretched polyamide resin film and a sealant film (CP; unstretched polypropylene film manufactured by Tocello Co., Ltd., RXC-22, thickness 50 μm) are bonded together using a urethane adhesive (Takelac manufactured by Mitsui Chemicals, Inc.). A laminate film was produced by dry laminating (adhesive coating amount: 3 g/m ² ) using A-525/A-52 (two-component type).
The obtained laminate film was folded into two along the longitudinal direction, and the fold was heat-sealed at 180°C to a width of 10 mm in the longitudinal direction using a test sealer, and then 200 mm in the vertical direction. Heat sealing was performed intermittently at intervals of 20 mm in width. Thereafter, it was cut in the transverse direction so that the sealed portions on both edges were 10 mm, to produce 10 three-sided sealed bags with a length of 300 mm (TD), a width of 200 mm (MD), and a seal width of 10 mm. The humidity of these 3-side sealed bags was conditioned for 48 hours in an environment of 20°C, 20% RH or 20°C, 65% RH, and then the 10 3-sided sealed bags were stacked to have the same size as the 3-sided sealed bags. Using a weight, apply a load of 9.8 N (1 kgf) to the entire surface of the bag from above, hold it for 24 hours, then remove the load, and measure the height of the warp of the bottom bag from the horizontal surface on which the bag is placed. The degree of S-curl was evaluated using (h) as an index. In addition, 10 three-sided sealed bags with a length of 390 mm (TD) and a width of 260 mm (MD) were made using the same method, and the humidity of these three-sided sealed bags was conditioned for 48 hours in an environment of 20°C and 65% RH. Similarly, the degree of S-curl was evaluated. In the following evaluation, the usable level as a packaging bag is ○ and Δ, with ○ being the most preferable.
○: 0mm≦h≦5mm
△: 5mm<h≦10mm
×: 10mm<h

(7) Thickness accuracy In the obtained biaxially stretched polyamide resin film, there is a position (a) near the center of the winding width and half of the winding amount, and a position (a) near the right end of the winding width, and A biaxially stretched polyamide-based material with a size of 50 cm in length and 50 cm in width from three positions: position (b), which is half of the winding amount, and position (c), which is near the left end of the winding width and near the end of winding. A resin film was cut out as a sample.
Straight lines were drawn every 5 cm in the vertical and horizontal directions on each of the samples cut out from three positions, and the thickness was measured at the points where the straight lines intersected (81 points). From these values, the average thickness of the sample at each position was calculated. Further, the thickness accuracy was calculated and evaluated using the following formula. The thickness was measured using HEIDENHAIN-METOR MT1287 manufactured by HEIDENHAIN. The thickness accuracy is preferably 1.7% or less, more preferably 1.6% or less, and most preferably 1.5% or less.
Thickness accuracy (%) = ((maximum thickness of film - minimum thickness of film) / 2 / average thickness of film) x 100

(8) Straight-line cutting properties A three-sided seal bag with a width of 300 mm (TD), a width of 200 mm (MD), and a seal width of 10 mm was produced using the method described in "(6) S-shaped curl for bag making" above.
Make a 5mm cut notch on the side seal part, tear 100mm in the width direction (MD) of the 3-side seal bag in the right-hand front and left-hand front directions, and pull it from the cut notch part in the width direction (MD) of the 3-side seal bag. The width of the deviation of the tear propagation edge from the straight line was measured. This operation was repeated 5 times, and the case where the average value of the width of the deviation of the tear propagation end was less than 10 mm was evaluated as "○", and the case where it was 10 mm or more was evaluated as "x".

(9) Puncture strength After conditioning the obtained biaxially oriented polyamide resin film for 2 hours in an environment of 23°C and 50% RH, the film was fixed under tension in a circular formwork with an inner diameter of 100 mm. A needle with a curvature radius of 0.5 mm at the tip was applied perpendicularly to the center of the sample surface at a speed of 50 mm/min to measure the strength at which the film was torn. Measurement was performed using 5 samples, and the average value was calculated. In addition, the piercing strength is practically required to be 9.5N or more, preferably 10.0N or more, and most preferably 10.5N or more.

The materials used in the Examples and Comparative Examples below are as follows.
(1) PA6: Polyamide 6, “A1030BRF” manufactured by Unitika
(2) MXD6: Metaxylene dipanamide 6, “MX Nylon 6007” manufactured by Mitsubishi Gas Chemical Co., Ltd.
(3) PA11: Polyamide 11, “Rilsan BESN O TL PA11” manufactured by Arkema
(4) C-PA6: Chemical recycled polyamide resin Manufactured by the following method.
Resin waste (resin waste) containing film scraps or defective products generated during the production of polyamide 6 resin film and oligomers generated during polymerization of polyamide 6 resin was used as the depolymerization raw material (A). Phosphoric acid is added to the depolymerization raw material (A), a depolymerization reaction is performed under heating using a wet method, and after purification by activated carbon treatment, concentration, and distillation, the regenerated ε-caprolactam "C-CL" is recovered. did.
C-CL, water, and benzoic acid as an end-blocking agent were used as raw materials, and after heating, pressurization, depressurization, and dehydration in a polymerization pot, a polymerization reaction was performed until the relative viscosity reached 3.0ηR. After polymerization, it was pelletized and scoured by hot water treatment at 95°C twice in total for 10 hours and 15 hours, and then dried at 110°C for 20 hours. In this way, a chemically recycled polyamide resin (C-PA6) was obtained. The obtained resin had a relative viscosity of 3.0, a Tc of 172.2°C, and a half width of Tc of 10°C.
(5) PVDC latex: "Saran Latex L536B" manufactured by Asahi Kasei Corporation
(6) Easy adhesion coating liquid: urethane resin “Hydran KU-400SF” manufactured by DIC, methylolmelamine resin “Amidia APM (solid content 80% by mass)” manufactured by DIC as a curing agent, polyurethane resin solid content 100% The solid content of the methylolmelamine resin was added to be 10 parts by mass per part by mass, and the resin solid content was adjusted to 10% by mass by diluting with ion-exchanged water.

Example 1
PA6 was melt-extruded from a T-die at 260° C. and cooled on a drum at 15° C. to obtain a substantially non-oriented unstretched film with a thickness of 150 μm.
The obtained unstretched film was immersed in a 40°C hot water tank for 10 seconds, and then immersed in a 60°C hot water tank for 100 seconds to perform water absorption treatment.
The water-absorbed unstretched film is introduced into a simultaneous biaxial stretching machine, preheated at 220°C, and then simultaneously biaxially stretched at a stretching temperature of 195°C, an MD stretching ratio of 3.0 times, and a TD stretching ratio of 3.3 times. Stretched.
Next, the film after simultaneous biaxial stretching was heat-treated for 4 seconds in a heat treatment zone set at 215°C, and then the MD and TD were heated to 200°C, respectively, with a film running speed deceleration of 0.05 m/s ² . A 5.0% relaxation treatment was performed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm.

Examples 2 to 14, Comparative Examples 1 to 3
As shown in Table 1, a biaxially stretched polyamide resin film having a thickness of 15 μm was obtained in the same manner as in Example 1, except that the composition of the polyamide resin and the film manufacturing conditions were changed.

Example 15
Example 1 except that PVDC latex was applied by the air knife method to one side of the unstretched film after water absorption treatment, and preheated drying treatment was performed for 30 seconds using an infrared irradiation machine at 220°C to evaporate and dry the water in the latex. A biaxially stretched polyamide resin laminate film having a thickness of 15 μm and having a gas barrier coating layer having a thickness of 1.5 μm was obtained in the same manner as above. The oxygen permeability of the obtained biaxially stretched polyamide resin laminate film was 65 ml/(m ² ·day · MPa).

Example 16
The process was carried out in the same manner as in Example 1, except that an easy-adhesive coating liquid was applied to one side of the unstretched film after water absorption treatment using the air knife method, and dried in a dryer at 60°C for 10 seconds to obtain a film with a thickness of 0. A biaxially oriented polyamide resin laminated film having a thickness of 15 μm and having a 1 μm thick adhesive coat layer laminated thereon was obtained.

Comparative example 4
PA6 was melt-extruded from a T-die at 270° C. and cooled on a drum at 18° C. to obtain a substantially non-oriented unstretched film with a thickness of 150 μm.
The obtained unstretched film was introduced into a water tank and subjected to water absorption treatment to adjust the water absorption rate to 4.0%.
The water-absorbed unstretched film is introduced into a simultaneous biaxial stretching machine, preheated at 225°C, and then simultaneously biaxially stretched at a stretching temperature of 195°C, an MD stretching ratio of 3.3 times, and a TD stretching ratio of 3.0 times. Stretched.
Next, the film after simultaneous biaxial stretching was heat treated for 5 seconds in a heat treatment zone set at 215°C, and then subjected to a 5.0% relaxation treatment at 200°C in the TD, and biaxially stretched to a thickness of 15 μm. A polyamide resin film was obtained.

Example 17
PA6 was melt-extruded from a T-die at 260° C. and cooled on a drum at 15° C. to obtain a substantially non-oriented unstretched film with a thickness of 180 μm.
The unstretched film was introduced into an MD stretching machine and MD stretched at a stretching temperature of 100° C. and a MD stretching ratio of 3.0 times. Next, this MD stretched film was introduced into a tenter and TD stretched under the conditions of a preheating temperature of 60° C., a stretching temperature of 135° C., and a TD stretching ratio of 4.0 times.
Next, the film after sequential biaxial stretching was heat-treated for 4 seconds in a heat treatment zone set at 220°C, and then, with a film running speed deceleration of 0.05 m/s ² , MD and TD were heated to 200°C, respectively. A 5.0% relaxation treatment was performed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm.

Comparative example 5
As shown in Table 1, a biaxially stretched polyamide resin film having a thickness of 15 μm was obtained in the same manner as in Example 17 except that the film manufacturing conditions were changed.

Example 18
A raw material containing 97% by mass of PA6 and 3% by mass of MXD6 was melt-extruded from a T-die at 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 stretching machine, and the first stage of preliminary MD stretching was carried out under the conditions of a stretching temperature of 80°C and a MD stretching ratio of 1.03 times, and then a stretching temperature of 80°C and a MD stretching ratio of 1.03 times. The second stage of preliminary MD stretching was carried out at 85°C, and then the first stage of main MD stretching was carried out under the conditions of a stretching temperature of 85°C and an MD stretching ratio of 2.1 times. The second stage main MD stretching was carried out under the following conditions. Next, this MD stretched film was introduced into a tenter and TD stretched at a stretching temperature of 130° C. and a TD stretching ratio of 4.0 times.
Next, the film after sequential biaxial stretching was heat-set in a heat treatment zone set at 210°C, and then the MD and TD were set at 210°C, respectively, with a film running speed deceleration of 0.05 m/ ^s2 . A 5.0% relaxation treatment was performed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm.

Comparative example 6
As shown in Table 1, a biaxially stretched polyamide resin film having a thickness of 15 μm was obtained in the same manner as in Example 18 except that the film manufacturing conditions were changed.

Example 19
PA6 was melt-extruded at 260° C. through an annular die and solidified by water cooling to obtain a substantially non-oriented tubular unstretched film with a thickness of 135 μm.
Next, the tube film was stretched in the MD and TD under conditions of a stretching temperature of 80°C, an MD stretching ratio of 3.0 times, and a TD stretching ratio of 3.3 times, using the speed difference between the low-speed nip roll and the high-speed nip roll and the air pressure existing between them. Biaxial stretching was performed at the same time.
Next, the film after tubular stretching was heat treated for 100 seconds in a heat treatment zone set at 210°C, and then the MD and TD were heated at 200°C, respectively, with a film running speed deceleration of 0.05 m/ ^s2 . A 5.0% relaxation treatment was performed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm.

Example 20
A raw material containing 80% by mass of PA6 and 20% by mass of MXD6 was melt-extruded from a T-die at 270°C and cooled on a drum at 20°C to obtain a substantially non-oriented unstretched film with a thickness of 150 μm. .
The obtained unstretched film was immersed in a 60°C hot water tank for 60 seconds, and then in a 90°C hot water tank for 60 seconds to perform water absorption treatment.
The water-absorbed unstretched film is introduced into a simultaneous biaxial stretching machine, preheated at 220°C, and then simultaneously biaxially stretched at a stretching temperature of 195°C, an MD stretching ratio of 3.0 times, and a TD stretching ratio of 3.3 times. Stretched.
Next, the film after simultaneous biaxial stretching was heat-treated for 4 seconds in a heat treatment zone set at 210°C, and then the MD and TD were heated to 200°C, respectively, with a film running speed deceleration of 0.05 m/s ² . A 5.0% relaxation treatment was performed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm.

Examples 21, 22, Comparative Example 7
As shown in Table 1, a biaxially stretched polyamide resin film having a thickness of 15 μm was obtained in the same manner as in Example 20, except that the film manufacturing conditions were changed.

Table 1 shows the structure, manufacturing conditions, and characteristics of the films obtained in Examples and Comparative Examples.

The biaxially stretched polyamide resin films of Examples 1 to 22 had small dry heat gradient differences and water absorption gradient differences, and were able to sufficiently suppress S-curl after bag making. In particular, the biaxially stretched polyamide resin films of Examples 7 to 10 and 21 contained the chemically recycled polyamide resin, so the dry heat gradient difference and the water absorption gradient difference tended to be smaller.
In addition, the biaxially stretched polyamide resin films of Examples 1 to 3, 5, and 7 to 22 were formed under conditions in which the ratio of the MD relaxation rate to the TD relaxation rate (MD/TD) was in a more preferable range. , had excellent piercing strength.
Furthermore, the biaxially oriented polyamide resin films of Examples 20 to 22 had excellent straight-line cuttability.
On the other hand, the biaxially stretched polyamide resin films of Comparative Examples 1 to 7 had a large dry heat gradient difference, water absorption gradient difference, or both, and could not sufficiently suppress S-curl after bag making.

Claims (11)

The shrinkage rate in the 45 degree direction and the shrinkage rate in the 135 degree direction in dry heat treatment at 160 ° C. for 5 minutes of the film cut in the 45 degree direction and 135 degree direction clockwise with respect to the machine direction (MD) during film formation. The absolute value of the difference from the shrinkage rate (dry heat slope difference) is 1.0% or less,
The dimensional change rate in the 45 degree direction determined from the length measured immediately after water absorption treatment at 30 ° C. for 1 hour and the length measured after the water absorption treatment at 23 ° C., 50% RH, and 24 hours of humidity control. , a biaxially stretched polyamide resin film characterized in that the absolute value of the difference between the dimensional change rate in the 135 degree direction (water absorption diagonal difference) is 1.5% or less. 2. The biaxially oriented polyamide resin film according to claim 1, wherein the MD shrinkage rate of the film cut out in MD is 2.0% or less when subjected to dry heat treatment at 160°C for 5 minutes. The biaxial stretching according to claim 1 or 2, wherein the film cut in the transverse direction (TD) during film formation has a TD shrinkage rate of 1.0% or less in dry heat treatment at 160° C. for 5 minutes. Polyamide resin film. The biaxially oriented polyamide resin film according to claim 1 or 2, wherein the polyamide resin contains a resin regenerated by chemical recycling. The biaxially oriented polyamide resin film according to claim 1 or 2, wherein the polyamide resin contains a resin obtained from a plant-derived raw material. A biaxially oriented polyamide resin laminate film, characterized in that a gas barrier layer is laminated on at least one surface of the biaxially oriented polyamide resin film according to claim 1 or 2. A biaxially oriented polyamide resin laminate film, characterized in that an easily adhesive layer is laminated on at least one surface of the biaxially oriented polyamide resin film according to claim 1 or 2. A laminate film using the biaxially stretched polyamide resin film according to claim 1 or 2. A bag-made product using the laminate film according to claim 8. 3. A method for producing a biaxially stretched polyamide resin film according to claim 1 or 2, wherein the step of relaxing the biaxially stretched film in the machine direction (MD) after the step of biaxially stretching the unstretched film. A method for producing a biaxially stretched polyamide resin film, characterized in that the deceleration of the film running speed is 0.08 m/s ² or less and the relaxation rate is 8% or less. 11. The method for producing a biaxially stretched polyamide resin film according to claim 10, wherein the biaxially stretching step is a simultaneous biaxially stretching method.