JP7723966B2 - Polyamide laminated film - Google Patents

Description

The present invention relates to a heat-sealable polyamide-based laminate film.

In recent years, awareness of environmental issues has grown, and there is a demand for laminated films used in packaging to be made from a single material (mono-materialization) to make them easier to recycle. However, because the thermal properties and functions required of each layer of laminated films used in packaging are different, it is difficult to construct them from a single material, and progress in mono-materialization has not progressed to date.

One method for making packaging materials mono-material is to use olefin resins such as polyethylene and polypropylene, which are commonly used as sealant layers, as the resin that constitutes the base material layer.
On the other hand, Patent Document 1 discloses a laminated film in which the resin constituting the substrate layer is polyamide 6 or polyamide 66, and the resin constituting the sealant layer is a copolymer polyamide mainly composed of polyamide 6 or polyamide 66 units. Patent Document 2 discloses a laminated film in which the resin constituting the substrate layer is a polyamide having a melting point of 200°C or higher, and the resin constituting the sealant layer is a copolymer polyamide having a melting point of 150°C or lower.

Special Publication No. 56-009407 Japanese Unexamined Patent Publication No. 58-175657

However, the laminated film of Patent Document 1 does not have sufficient heat sealability for use as a packaging bag.
Furthermore, the laminated film of Patent Document 2 has low heat resistance of the sealant layer, which can cause problems such as wrinkling and delamination during high-temperature sterilization treatments such as retort treatment and boiling treatment required for food packaging, etc., limiting its use as a packaging material. Furthermore, if the sealant layer is made of a resin with a high melting point in order to increase the heat resistance of the sealant layer, the temperature required for heat sealing becomes close to the melting point of the resin that makes up the base layer, which can cause wrinkling and deformation in the base layer during heat sealing.

The object of the present invention is to solve the problems of the prior art described above and to provide a laminate film in which all layers are composed of polyamide resins, which has good heat-sealing properties, maintains excellent heat-sealing properties even after heat treatments such as boiling, is free from wrinkles or deformation in the heat-sealed areas, and also has excellent pinhole resistance.

As a result of research into how to solve the above problems, the inventors discovered that a laminate film in which a specific polyamide resin film is laminated onto a polyamide 6 film as a sealant layer can achieve the above objective, leading to the present invention.

That is, the gist of the present invention is as follows.
(1) A laminated film in which a sealant layer is laminated on a substrate layer,
the substrate layer is a film (A) containing polyamide 6,
The sealant layer is a biaxially oriented film (B) containing a polyamide resin having a melting point of more than 150°C and not more than 210°C,
A polyamide-based laminated film characterized in that the seal strength of the sealed portion when the sealant layers are heat-sealed together at an upper surface temperature of 200°C, a lower surface temperature of 150°C, a sealing pressure of 0.3 MPa, and a sealing time of 3.0 seconds is 1.0 kg/15 mm or more.
(2) The polyamide laminate film according to (1), characterized in that the seal strength of the seal portion when the sealant layers are heat-sealed together at an upper surface temperature of 200°C, a lower surface temperature of 150°C, a sealing pressure of 0.3 MPa, and a sealing time of 3.0 seconds after hot water treatment at 90°C for 30 minutes is 0.8 kg/15 mm or more.
(3) The polyamide laminate film according to (1) or (2), wherein the polyamide resin contains a dimer acid as a copolymerization component.
(4) The polyamide laminate film according to any one of (1) to (3), wherein the polyamide resin contains a plant-derived component as a polymerization component.
(5) A method for producing the polyamide-based laminate film according to any one of (1) to (4) above,
a step of adjusting the moisture content of an unstretched laminate film in which an unstretched base layer and an unstretched sealant layer are laminated;
and biaxially stretching the unstretched laminate film whose moisture content has been adjusted.

The present invention provides a laminate film in which all layers are mono-material polyamide resins, making it easy to recycle. It also has excellent heat seal strength and heat resistance, so it retains excellent heat seal strength even after hot water sterilization treatments such as retort treatment and boiling treatment, and also has excellent pinhole resistance. Because the laminate film of the present invention has excellent heat seal strength and pinhole resistance after hot water treatment, it can be suitably used as a packaging material.

The present invention will be described in detail below.
The polyamide-based laminate film of the present invention is a laminate film in which a substrate layer and a sealant layer are laminated together.

The substrate layer constituting the polyamide-based laminate film of the present invention is a film (A) containing polyamide 6.
Polyamide 6, which has excellent cost performance, is preferred in terms of productivity and performance, and the base layer may use polyamide 6 as the film raw material and contain 30 mass% or less of other polyamide components such as polyamide 66, polyamide 46, polyamide 69, polyamide 610, polyamide 612, polyamide 11, polyamide 12, and polymetaxylylene adipamide (polyamide MXD6) in the form of copolymer, mixture, composite layer, etc.

These polyamide resins that make up the base layer preferably contain end-blocking agents such as organic glycidyl esters, dicarboxylic anhydrides, monocarboxylic acids such as benzoic acid, and diamines to suppress monomer generation during melting.

The relative viscosity of the polyamide resin constituting the substrate layer is not particularly limited, but the relative viscosity, measured using 96% sulfuric acid as a solvent at a temperature of 25°C and a concentration of 1 g/dl, is preferably 1.5 to 5.0, more preferably 2.5 to 4.5, and even more preferably 3.0 to 4.0. If the substrate layer contains a polyamide resin with a relative viscosity of less than 1.5, the mechanical properties are likely to deteriorate significantly. Furthermore, polyamide resins with a relative viscosity of more than 5.0 are likely to interfere with the film formability.

The base layer may contain, as needed, one or more of various additives such as pigments, antioxidants, ultraviolet absorbers, preservatives, antistatic agents, antiblocking agents, inorganic fine particles, etc., within the range that does not adversely affect the performance of the film.
The substrate layer may contain one or more inorganic or organic lubricants to improve the slip properties of the film, etc. 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, hydrotalcite, layered silicates, and ethylene bisstearamide.

The sealant layer constituting the laminate film of the present invention is a biaxially oriented film (B) containing a polyamide resin having a melting point of more than 150°C and not more than 210°C. From the viewpoint of improving heat sealability, the melting point of the polyamide resin constituting the sealant layer must be not more than 210°C, and preferably not more than 200°C. Furthermore, from the viewpoint of heat resistance, the melting point of the polyamide resin must be more than 150°C, and preferably not less than 160°C.

Examples of polyamide resins that make up the sealant layer and have a melting point exceeding 150°C and not exceeding 210°C include polyamides such as polyamide 11, polyamide 12, and polyamide 1010, copolymer polyamides, and mixtures and composites thereof.

Copolymerizing components of copolymerized polyamides include ω-amino acids and their lactams, dibasic acids and diamines, etc. Specific examples of ω-amino acids and their lactams include 6-aminocaproic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and their lactams. Furthermore, examples of dibasic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecadioic acid, hexadecadioic acid, eicosanedioic acid, eicosadienedioic acid, 2,2,4-trimethyladipic acid, and dimer acid. Further examples of diamines include ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, pentamethylenediamine, undecamethylenediamine, 2,2,4 (or 2,4,4)-trimethylhexamethylenediamine, cyclohexanediamine, bis-(4,4'-aminocyclohexyl)methane, etc. Small amounts of aromatic dicarboxylic acids, such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, xylylenedicarboxylic acid, etc., or small amounts of aromatic diamines, such as metaxylylenediamine, etc., may also be included.

In particular, polyamides containing dimer acid as a copolymerization component are preferred in terms of productivity and performance, and the copolymerization amount of dimer acid is preferably 1 to 50 mass%. Examples of copolymerization components other than dimer acid include ω-amino acids and their lactams, and diamines. Examples of ω-amino acids and lactams include 3-aminopropanoic acid, 4-aminobutanoic acid, 5-aminopentanoic acid, 6-aminohexanoic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid, and their lactams. Examples of diamines include tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, decamethylenediamine, and dodecamethylenediamine.
Examples of polyamide resins containing dimer acid as a copolymerization component include copolymers of polyamide 6 and polyamide made from dimer acid and hexamethylenediamine.

When the polyamide resin constituting the sealant layer contains polyamide 6 as a copolymerization component, adhesion to the substrate layer containing polyamide 6 can be improved.

Copolyamides can be produced by copolymerizing the above copolymerization components, or commercially available products can be used. Examples of commercially available products include Ultramid C grade manufactured by BASF and copolyamides manufactured by Ube Industries, Ltd.

In the present invention, the polymer components constituting the sealant layer preferably contain plant-derived components in order to reduce the environmental impact. Examples of plant-derived components include pentamethylenediamine, sebacic acid, 11-aminoundecanoic acid, and dimer acid.

These polyamide resins that make up the sealant layer preferably contain end-blocking agents such as organic glycidyl esters, dicarboxylic anhydrides, monocarboxylic acids such as benzoic acid, and diamines to suppress the generation of monomers when melted.

The sealant layer in the present invention must be a biaxially oriented film. By constructing the sealant layer from a biaxially oriented film, the laminate film of the present invention will have excellent pinhole resistance.

The polyamide-based laminate film of the present invention is a biaxially oriented film (B) in which the sealant layer contains a polyamide-based resin having a melting point exceeding 150°C and not exceeding 210°C. When produced by the method described below, the sealant layers are heat-sealed together at an upper surface temperature of 200°C, a lower surface temperature of 150°C, a sealing pressure of 0.3 MPa, and a sealing time of 3.0 seconds, resulting in a seal strength of 1.0 kg/15 mm or greater. Furthermore, the polyamide-based laminate film of the present invention preferably has a seal strength of 0.8 kg/15 mm or greater after hot water treatment at 90°C for 30 minutes, resulting in a seal strength of 1.0 kg/15 mm or greater when the sealant layers are heat-sealed together under the above conditions.

The polyamide laminate film of the present invention can be produced by the following method.
For example, as will be described later, there are methods in which an unstretched laminated film is stretched, and methods in which stretched films are laminated.

Methods for stretching an unstretched laminate film include, for example, stretching an unstretched laminate film produced by co-extrusion, or stretching an unstretched laminate film produced by dry laminating an unstretched substrate layer and a sealant layer with an adhesive. From the perspective of improving heat seal strength after heat treatment and achieving a mono-material film without the use of adhesive, a method in which an unstretched laminate film is produced by co-extrusion and then stretched is preferred.

Methods for producing an unstretched laminate film by co-extrusion include a method in which the resins constituting each layer are melted using separate extruders, superimposed by a feed block method, and extruded through a die; a method in which two molten resins are superimposed in a multi-manifold die and extruded; or a method in which the resins are extruded through a T-die using a combination of the above methods, and then cooled and solidified on a rotating cooling drum by a known casting method such as air knife casting or electrostatic casting, to form a film.
In addition, the adhesive used in the method of laminating an unstretched substrate layer and an unstretched sealant layer by dry lamination via an adhesive may be any known adhesive, such as an isocyanate-based, polyurethane-based, polyester-based, polyethyleneimine-based, polybutadiene-based, polyolefin-based, or alkyl titanate-based adhesive.
If the unstretched laminate film is oriented, the stretchability may decrease in subsequent steps, so it is preferable that the unstretched laminate film is substantially amorphous and unoriented.

When stretching the resulting unstretched laminate film, it is preferable to adjust the moisture content of the unstretched laminate film before stretching it, in order to improve the heat seal strength of the sealant layer. The moisture adjustment step is preferably carried out after the step of removing the monomer from the unstretched laminate film.

From the perspective of improving the heat seal strength of the sealant layer, the moisture content of the unstretched laminate film is preferably 2 to 10% by mass, and from the perspective of suppressing curling of the unstretched laminate film, it is more preferable to have a moisture content of 2 to 7% by mass. When an unstretched laminate film with a moisture content of less than 2% by mass is stretched, the stretching stress increases, making it more susceptible to problems such as film breakage, and the sealant layer of the resulting laminate film may have insufficient heat seal strength. On the other hand, an unstretched laminate film with a moisture content of more than 7% by mass may curl and cause stretching problems, and even if it can be stretched, the resulting laminate film may have significant thickness unevenness.

In the moisture adjustment process, the temperature of the moisture adjustment tank through which the unstretched laminate film passes is preferably 20 to 80°C, more preferably 40 to 80°C, from the perspective of suppressing curling of the unstretched laminate film after moisture adjustment. If the temperature of the moisture adjustment tank is lower than 20°C, moisture adjustment may take a long time, resulting in poor productivity. On the other hand, if the temperature of the moisture adjustment tank exceeds 80°C, the unstretched laminate film may curl, causing stretching problems.

The moisture content of the unstretched laminate film can be adjusted by adjusting the time for which the unstretched laminate film is passed through the moisture adjustment tank. From the viewpoint of suppressing curling after moisture adjustment, a time of 0.5 to 5 minutes is preferred. If the passing time is shorter than 0.5 minutes, the unstretched laminate film will have a low moisture content, and the stretching stress will increase, making the film more susceptible to problems such as breakage, and the sealant layer of the resulting laminate film may have insufficient heat seal strength. On the other hand, if the passing time exceeds 5 minutes, the unstretched laminate film may curl, causing stretching problems, and the resulting laminate film may have significant thickness unevenness.
Pure water is usually used in the moisture adjustment tank, but if necessary, the treatment liquid may contain dyes, surfactants, plasticizers, etc. Furthermore, the moisture may be adjusted by spraying water vapor.

Next, the moisture-adjusted unstretched laminate film can be stretched using known uniaxial or biaxial stretching methods, with biaxial stretching being preferred from the perspective of improving mechanical properties. Examples of biaxial stretching include sequential biaxial stretching, in which stretching is performed in the longitudinal direction and then the transverse direction, and simultaneous biaxial stretching, in which stretching is performed simultaneously in both the longitudinal and transverse directions. In either stretching method, it is preferable to stretch the film to an areal magnification of 9 or more so that the sealant layer has a planar orientation coefficient of 0.05 or greater. There are no particular limitations on the stretching method, but simultaneous biaxial stretching is preferred because it is efficient and can perform the melt film formation, monomer removal, moisture adjustment, stretching, heat setting, and cooling steps in a single process.

The laminated film that has undergone sequential or simultaneous biaxial stretching is heat-set at a temperature of 150 to 220°C in the tenter where the stretching process was performed, and is then subjected to a relaxation process in the machine direction and/or cross direction, if necessary, within a range of 0 to 10%, preferably 2 to 6%.

The thickness of the polyamide-based laminate film produced by stretching the unstretched laminate film is not particularly limited, but when used for packaging purposes, it is preferably 10 to 150 μm, and from the standpoint of film properties and cost, it is more preferably 20 to 100 μm.

The polyamide-based laminate film of the present invention can be produced by laminating stretched films in addition to the above-mentioned method of stretching an unstretched laminate film.
The stretched substrate layer and the stretched sealant layer can be produced by adjusting the moisture content, stretching, and heat treating the film in the same manner as in stretching the unstretched laminate film.
Examples of methods for laminating stretched films include a method in which a stretched substrate layer and a stretched sealant layer are laminated together by dry lamination using an adhesive. The adhesive may be the same as that used in the dry lamination method for the unstretched laminated film described above.
From the viewpoint of improving the heat seal strength of the sealant layer, it is preferable to laminate an oriented film obtained by stretching an unstretched film whose moisture content has been adjusted in the same manner as above.

There are no particular limitations on the thickness of the polyamide-based laminate film produced by laminating stretched films, but when used for packaging purposes, the thickness of the base layer is preferably 10 to 50 μm, and the thickness of the sealant layer is preferably 10 to 150 μm. From a cost perspective, the thickness of the base layer is more preferably 10 to 30 μm, and the thickness of the sealant layer is more preferably 10 to 100 μm.

The laminated film of the present invention has a base layer laminated with a vapor-deposited layer, which can provide a film with excellent gas barrier properties and few processing defects. The vapor-deposited layer is made of an inorganic or organic compound. Examples of inorganic compounds include metals such as aluminum, and inorganic oxides of aluminum, silicon, magnesium, titanium, and the like.
Methods for forming such an inorganic layer include vacuum deposition, sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), etc. Vacuum deposition is particularly advantageous in practical use.
When the substrate layer is subjected to vapor deposition processing, the substrate layer may be subjected to a corona treatment, a plasma treatment, or a coating treatment with an inorganic or organic compound in advance in order to improve the adhesion between the substrate layer and the vapor deposition layer.
In the case of vacuum deposition, aluminum (Al), _alumina ( _Al2O3 ), silicon (Si), silica ( _SiO2 ), or a combination thereof is used as the deposition raw material. Methods for heating the raw material include resistance heating, high-frequency induction heating, electron beam heating, and laser heating. Furthermore, during heating, a gas such as oxygen may be present, ozone may be added, or an ion-assisted method may be used.
The thickness of the vapor-deposited layer is preferably about 1 to 1,000 nm. If the thickness is less than 1 nm, gas barrier properties are not exhibited, and if it exceeds 1,000 nm, the plasticity of the entire film laminated with the vapor-deposited layer is lost, reducing its practicality.

The laminated film of the present invention may have a configuration in which a gas barrier coating layer is laminated on at least one surface of a base layer. The gas barrier coating layer is not particularly limited, but examples thereof include an ethylene vinyl alcohol copolymer (EVOH) layer, a polyvinyl alcohol (PVA) layer, and a polyvinylidene chloride copolymer (PVDC) layer, with a PVDC layer being preferred.
PVDC is a polymer containing 60% by mass or more, preferably 70 to 97% by mass, of vinylidene chloride units, and is used in the form of a latex to coat at least one surface of the substrate layer. The average particle size of the PVDC in the latex is preferably 0.05 to 0.5 μm, more preferably 0.07 to 0.3 μm. The latex may contain various additives, such as an antiblocking agent, a crosslinking agent, a water repellent agent, and an antistatic agent, within the range that does not impair the effects of the present invention.
The thickness of the PVDC-containing gas barrier coating layer 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. If the gas barrier coating layer is thinner than 0.5 μm, it is difficult to achieve sufficient gas barrier properties. On the other hand, if the gas barrier coating layer is thicker than 3.5 μm, not only will the effect saturate, but the physical properties of the film may also be impaired.
The adhesive strength between the substrate layer and the gas barrier coating layer is preferably 0.8 N/cm or more, more preferably 1.0 N/cm or more, and even more preferably 2.0 N/cm or more. If the adhesive strength is less than 0.8 N/cm, the substrate layer and the gas barrier coating layer may peel off during boiling or retort treatment.
When forming a gas barrier coating layer on a substrate layer, it is important to form the layer on the substrate layer at a stage where the amount of monomer is small, after the monomer removal step and before stretching, in order to improve adhesion to the substrate layer.
The coating method is not particularly limited, and for example, various coating methods such as a gravure roll method, a reverse roll method, an air knife method, a reverse gravure method, a Mayer bar method, an inverse roll method, or a combination of these, and various spray methods can be used.
The substrate layer may be subjected to a corona discharge treatment or the like immediately before coating.
The polyamide-based laminate film thus obtained, which has a structure in which a gas barrier layer is laminated on a base layer and a heat seal layer is also laminated on it, has excellent gas barrier properties in addition to the excellent strength and mechanical properties of a polyamide film, and has excellent adhesion between the base layer and the gas barrier layer, making it suitable for use as a packaging material.

The polyamide laminate film of the present invention can be used as a package such as a bag or a lid material for tray packaging by heat-sealing the sealant layer. Examples of the bag form include three-side sealed bags, four-side sealed bags, pillow bags, standing pouches, rocket packages, etc.
In order to impart functionality to the polyamide-based laminate film of the present invention, for example, an antistatic treatment may be performed to suppress the generation of static electricity, or various functional coating liquids other than the above-mentioned barrier coating liquid may be applied.
The polyamide laminate film may be subjected to physicochemical treatments such as corona discharge treatment, plating treatment, cleaning treatment, and dyeing treatment, if necessary.

The following examples and comparative examples will explain the features of the present invention in more detail. However, the scope of the present invention is not limited to these examples.

(1) Moisture content An unstretched film before stretching was collected, placed in a weighing bottle, and dried at 150° C. for 20 hours. The moisture content was calculated from the change in mass before and after drying.

(2) Melting point of polyamide film Using a Perkin Elmer DSC, the sample weight was 10±1 mg, and the temperature was raised from 50°C at a rate of 20°C/min to measure the melting point of the biaxially oriented polyamide resin film (B). When there were multiple crystalline melting peaks, the temperature at which the absolute value of the heat flow was the largest was taken as the melting point. In the case of a coextruded laminated film, the biaxially oriented polyamide resin film (B) was scraped off and the measurement was performed.

(3) Puncture strength (pinhole resistance)
The obtained polyamide-based laminate film was left for 2 hours in an environmental test room adjusted to 23°C and 50% RH, and then measured in accordance with the puncture strength test of JIS Z 1707. Measurements were carried out on 10 samples, and the average strength value per 1 μm of film thickness was calculated. The pinhole resistance was evaluated according to the following criteria.
〇: Piercing strength is 0.35 N/μm or more ×: Piercing strength is less than 0.35 N/μm

(4) Strong seal (sealing temperature 200°C)
Two laminated films were placed together with the sealant side facing each other and heat-sealed. The heat-sealing was performed at an upper surface temperature of 200°C, a lower surface temperature of 150°C, a sealing pressure of 0.3 MPa, and a sealing time of 3.0 seconds. The presence or absence of wrinkles in the sealed area was then confirmed.
The heat-sealed film was left for 2 hours in an environmental test room adjusted to 23°C and 50% RH, and then measured according to the heat seal strength test of JIS Z 1707, and the heat seal strength was evaluated according to the following criteria.
Good: Tensile strength is 1.0 kg/15 mm or more. Bad: Tensile strength is less than 1.0 kg/15 mm.

(5) Seal strength after hot water treatment (90°C, 30 minutes)
The film heat-sealed under the conditions of (4) above was subjected to a hot water treatment at 90°C for 30 minutes, and then left to stand for 2 hours in an environmental test room adjusted to 23°C and 50% RH. After that, the heat seal strength was measured in accordance with the heat seal strength test of JIS Z 1707, and evaluated according to the following criteria.
◯: Tensile strength is 1.0 kg/15 mm or more △: Tensile strength is 0.8 kg/15 mm or more and less than 1.0 kg/15 mm ×: Tensile strength is less than 0.8 kg/15 mm

(6) Strong seal (sealing temperature 210°C)
A heat-sealed film was produced under the same conditions as in (4) above, except that the upper surface temperature was changed from 200° C. to 210° C., and the occurrence of wrinkles in the sealed portion was confirmed.
The heat-sealed film was left for 2 hours in an environmental test room adjusted to 23°C and 50% RH, and then the heat-seal strength was measured in accordance with the heat-seal strength test of JIS Z 1707, and evaluated according to the following criteria.
Good: Tensile strength is 1.0 kg/15 mm or more. Bad: Tensile strength is less than 1.0 kg/15 mm.

(7) Laminated state after hot water treatment Two sheets of laminated film were used and sealed on all four sides under the heat sealing conditions described in (4) above to prepare five 200 mm x 180 mm bags containing 400 ml of water at 20°C.
The five bags thus produced were subjected to a hot water treatment at 90° C. for 30 minutes, and the presence or absence of delamination at the heat-sealed portion was evaluated according to the following criteria.
◯: No delamination occurred △: Delamination occurred in one bag ×: Delamination occurred in two or more bags

The raw materials used in the following examples and comparative examples are as follows.
[Polyamide 6 (PA6)]
100 parts by mass of ε-caprolactam, 0.12 parts by mass of benzoic acid (10 mmol/kg relative to ε-caprolactam), and 3 parts by mass of water were charged into a sealed reaction vessel equipped with a stirrer, and the temperature was raised to carry out a polycondensation reaction under a pressure of 0.5 MPa at a temperature of 260°C. The mixture was discharged from the reaction vessel, cut into chips, refined, and dried to obtain polyamide 6. The polyamide 6 chips had a terminal carboxyl group content of 46 mmol/kg, a terminal amino group content of 36 mmol/kg, and a relative viscosity of 3.03.

[Master Chip]
A master chip was prepared by melt-mixing 6 parts by mass of inorganic fine particles (Sylysia 310P manufactured by Fuji Silysia Ltd.) with 100 parts by mass of PA6.

[Polyamide 12 (PA12)]
Grilamid L25 manufactured by EMS-CHEMIE was used. The melting point was 178°C.

[Copolymer polyamide-1 (polyamide 6/polyamide 6.36 (copolymer PA-1))]
A copolyamide of polyamide 6 and polyamide 6.36 was produced.
932 kg of caprolactam, 323.2 kg of hydrogenated C36-dimer acid (Croda Pripol 1009), 77.84 kg of an 85% by weight aqueous solution of hexamethylenediamine, and 153 kg of water were mixed in a 1930-liter vessel and blanketed with nitrogen. The vessel's exterior temperature was heated to 290°C, and the mixture was stirred at this temperature for 11 hours. The mixture was stirred under pressure for the first 7 hours and under vacuum for the next 4 hours, while the water produced was distilled off. The resulting copolymerized polyamide was removed from the vessel, extruded, and pelletized. The resulting copolymerized polyamide pellets were extracted four times with hot water at 95°C for 6 hours each, followed by drying in a nitrogen stream at 90-140°C for 10 hours. The resulting copolymerized polyamide had a viscosity of 259 ml/g. The proportion of polyamide 6.36 in the copolyamide was 30.3 mass % based on the total mass of the copolyamide, the density was 1.076 g/ml, and the melting point was 202°C.

[Copolymer polyamide-2 (copolymer polyamide containing polyamide 6 (copolymer PA-2))]
Grilon CCF6S manufactured by EMS-CHEMIE was used. The melting point was 130°C.

Example 1
PA6 and the master chips were blended so that the inorganic fine particles were present in an amount of 0.05% by mass, and the resulting mixture was melted and placed in an extruder having a cylinder temperature of 270° C., and the copolymerized PA-1 was melted and placed in an extruder having a cylinder temperature of 250° C. The mixture was then extruded through a T-die orifice to a thickness ratio (PA6-containing layer/copolymerized PA-1-containing layer) of 15/6, and rapidly cooled by being brought into close contact with a rotating drum cooled to 10° C., to obtain an unstretched laminate film having a thickness of 210 μm.
Next, as a moisture adjustment step, the unstretched laminate film was introduced into a moisture adjustment tank at 60° C. and immersed for 1 minute to absorb moisture.
Next, the water-absorbed unstretched laminated film was introduced into a simultaneous biaxial stretching machine and simultaneously biaxially stretched at a stretching ratio of 3.3 times longitudinally and 3.0 times transversely at 170° C. Subsequently, the film was subjected to a heat treatment at 210° C. for 4 seconds and a relaxation treatment of 5% in the transverse direction to obtain a laminated film in which the base layer (A) was a PA6 film having a thickness of 15 μm and the sealant layer (B) was a biaxially oriented film having a thickness of 6 μm.

Example 2
A laminated film was produced in the same manner as in Example 1, except that the thickness of the sealant layer (B) was changed.

Example 3
A laminated film was produced in the same manner as in Example 2, except that copolymer PA-1 was changed to PA12 and the cylinder temperature was changed from 250°C to 260°C.

Example 4
(Production of base film)
The PA6 and master chips were blended so that the inorganic microparticle content was 0.05% by mass, and the blend was then introduced into an extruder, melted in a cylinder heated to 270°C, extruded into a sheet from a T-die orifice, and rapidly cooled by being brought into close contact with a rotating drum cooled to 10°C, to obtain an unstretched substrate film having a thickness of 150 μm.
Next, as a moisture adjustment step, the unstretched substrate film was introduced into a moisture adjustment tank at 60° C. and immersed for 1 minute to absorb moisture.
Next, the water-absorbed unstretched substrate film was introduced into a simultaneous biaxial stretching machine and simultaneously biaxially stretched at a stretching ratio of 3.3 times in the longitudinal direction and 3.0 times in the transverse direction at 170° C. Subsequently, the film was subjected to a heat treatment at 210° C. for 4 seconds, followed by a 5% relaxation treatment in the transverse direction, to obtain a substrate film having a thickness of 15 μm.
(Production of sealant film)
The copolymerized PA-1 was placed in an extruder, melted in a cylinder heated to 250°C, extruded into a sheet from a T-die orifice, and rapidly cooled by being brought into close contact with a rotating drum cooled to 10°C, to obtain an unstretched sealant film having a thickness of 200 μm.
Next, as a moisture adjustment step, the unstretched sealant film was introduced into a moisture adjustment tank at 60°C and immersed for 1 minute to absorb moisture.
Next, the water-absorbed unstretched sealant film was introduced into a simultaneous biaxial stretching machine and simultaneously biaxially stretched at a stretching ratio of 3.3 times in the longitudinal direction and 3.0 times in the transverse direction at 170° C. Subsequently, the film was subjected to a heat treatment at 210° C. for 4 seconds, followed by a 5% relaxation treatment in the transverse direction, to obtain a sealant film with a thickness of 20 μm.
(dry lamination)
Next, one side of each of the base film and the sealant film was subjected to a corona discharge treatment. A urethane adhesive (Takelac A-525/Takenate A-52 two-component adhesive, manufactured by Mitsui Chemicals Polyurethanes, Inc.) was applied to the corona-treated surface of the base film so that the coating amount after drying was 3 g/ ^m² , and the film was dried for 10 seconds in a hot air dryer at 80°C.
The adhesive-coated surface of the base film and the corona-treated surface of the sealant film were bonded together using a nip roll (nip conditions: 80°C), taken up, and the bonded film was aged for 72 hours in an atmosphere of 40°C to obtain a laminated film in which the sealant layer was laminated onto the base layer.

Example 5
(Production of base film)
A substrate film was prepared in the same manner as in Example 4.
(Production of sealant film)
A sealant film was obtained in the same manner as in Example 4, except that copolymer PA-1 was changed to PA12 and the cylinder temperature was changed from 250°C to 260°C.
(dry lamination)
A film in which a sealant layer was laminated on a substrate layer was obtained in the same manner as in Example 4, except that the resin of the sealant layer was changed to PA12.

Comparative Example 1
A laminated film was produced in the same manner as in Example 2, except that the moisture adjustment step was not carried out.

Comparative Examples 2 and 3
Except for changing the water temperature in the moisture adjustment tank and the immersion time in the moisture adjustment tank, the same procedure was followed as in Example 2. After the moisture adjustment step, curling occurred, making it difficult to grip the film with the clips of the simultaneous biaxial stretching machine, and stretching was not possible, making it impossible to produce a laminated film.

Comparative Example 4
A laminated film was produced in the same manner as in Example 2, except that copolymer PA-1 was changed to copolymer PA-2 and the cylinder temperature was changed from 250°C to 180°C.

Comparative Example 5
(Production of base film)
A substrate film was prepared in the same manner as in Example 4.
(Production of sealant layer)
An unstretched sealant film that had absorbed water was obtained in the same manner as in Example 4, except that copolymer PA-1 was changed to copolymer PA-2 and the cylinder temperature was changed from 250°C to 180°C.
Next, the water-absorbed unstretched sealant film was introduced into a simultaneous biaxial stretching machine and simultaneously biaxially stretched at a stretching ratio of 3.3 times in the longitudinal direction and 3.0 times in the transverse direction at 90° C. Subsequently, the film was subjected to a heat treatment at 140° C. for 4 seconds, followed by a 5% relaxation treatment in the transverse direction, to obtain a sealant film with a thickness of 20 μm.
(dry lamination)
A film having a sealant layer laminated on a substrate layer was obtained in the same manner as in Example 4, except that the resin of the sealant layer was changed to copolymer PA-2.

Comparative Example 6
(Production of base film)
A substrate film was prepared in the same manner as in Example 4.
(Production of sealant film)
The copolymerized PA-1 was placed in an extruder, melted in a cylinder heated to 250°C, extruded into a sheet from a T-die orifice, and rapidly cooled by being brought into close contact with a rotating drum cooled to 10°C to obtain an unstretched sealant film having a thickness of 20 μm.
(dry lamination)
A film in which an unstretched sealant layer was laminated on a substrate layer was obtained in the same manner as in Example 4, except that the sealant film was changed to an unstretched sealant film.

The evaluation results for the laminated films obtained in Examples 1 to 5 and Comparative Examples 1 and 4 to 6 are shown in Table 1.

The laminate films of Examples 1 to 5, all of whose layers were composed of polyamide resin films, had good heat sealing properties, excellent heat sealing properties even after heat treatment, and excellent pinhole resistance. In particular, the laminate films of Examples 1 to 3, which were made by coextrusion and stretching unstretched films after adjusting the moisture content, had excellent heat sealing strength after hot water treatment.
On the other hand, the laminated film of Comparative Example 1 was not subjected to the moisture adjustment step and was therefore inferior in heat sealability.
The unstretched laminate films of Comparative Examples 2 and 3 curled after the moisture adjustment step, and could not be stretched to obtain a laminate film.
In the laminated films of Comparative Examples 4 and 5, the melting point of the resin constituting the sealant layer (B) did not satisfy the range specified in the present invention, and the heat sealability after heat treatment was poor.
The laminated film of Comparative Example 6 had a sealant layer (B) that was not biaxially oriented, and was therefore poor in pinhole resistance.

Claims (9)

A laminated film in which a sealant layer is laminated on a base layer,
the substrate layer is a film (A) containing polyamide 6,
The sealant layer is a biaxially oriented film (B) containing a polyamide resin having a melting point of more than 150°C and not more than 210°C,
A polyamide-based laminate film characterized by having the following property 1 .
Property 1: Two sheets of the polyamide laminate film are stacked together with the sealant layers facing each other, and heat-sealed at an upper surface temperature of 200°C, a lower surface temperature of 150°C, a sealing pressure of 0.3 MPa, and a sealing time of 3.0 seconds. After leaving the laminate film for 2 hours under conditions of 23°C and 50% RH, the seal strength of the laminate film is 1.0 kg/15 mm or more. 2. The polyamide laminate film according to claim 1, further having the following property 2 :
Property 2: Two sheets of the polyamide-based laminate film are stacked together with the sealant layers facing each other, and heat-sealed at an upper surface temperature of 200°C, a lower surface temperature of 150°C, a sealing pressure of 0.3 MPa, and a sealing time of 3.0 seconds. The resulting laminate film is then subjected to a hot water treatment at 90°C for 30 minutes, and then left to stand for 2 hours under conditions of 23°C and 50% RH. After this, the seal strength of the laminate film is 0.8 kg/15 mm or more. The polyamide laminate film according to claim 1 or 2, characterized in that the polyamide resin contains a dimer acid as a copolymerization component. 4. The polyamide laminate film according to claim 1 , wherein the polyamide resin contains a plant-derived component as a polymerization component. 3. The polyamide-based laminate film according to claim 1, wherein the polyamide-based resin is at least one selected from the group consisting of a copolymer polyamide of polyamide consisting of dimer acid and hexamethylenediamine and polyamide 6, polyamide 11, polyamide 12, and polyamide 1010. 3. The polyamide laminate film according to claim 1, wherein the polyamide resin is a copolymer polyamide containing 1 to 50% by mass of a polyamide formed from a dimer acid and hexamethylenediamine. 3. The polyamide laminate film according to claim 1, wherein the polyamide resin is a copolymer of polyamide 6 and a polyamide comprising a dimer acid and a diamine. The polyamide-based laminate film according to any one of claims 1 to 7, wherein the film (A) contains a polyamide component and inorganic particles, and 70 mass% or more of the total amount of the polyamide component is polyamide 6. A method for producing the polyamide-based laminate film according to any one of claims 1 to 8 , comprising:
a step of adjusting the moisture content of an unstretched laminate film in which an unstretched base layer and an unstretched sealant layer are laminated;
and biaxially stretching the unstretched laminate film whose moisture content has been adjusted.