JP7314512B2 - gas barrier film - Google Patents

Description

The present invention relates to gas barrier films.

Packaging materials used for packaging foods, pharmaceuticals, etc. are required to have the property (gas barrier property) to block the entry of water vapor, oxygen, and other gases that alter the contents in order to suppress deterioration and putrefaction of the contents and maintain their functions and properties.
Therefore, conventionally, these packaging materials have a gas barrier layer.

As the gas barrier layer, a metal foil, a metal deposition film, a resin film, a composite film, and the like are used (see Patent Documents 1 to 5, for example). Examples of the metal foil and metal deposition film include those made of metal such as aluminum. Examples of resin films include those made of water-soluble polymers such as polyvinyl alcohol and ethylene-vinyl alcohol copolymers, and resins such as polyvinylidene chloride. The composite film includes a composite film of the water-soluble polymer and an inorganic layered mineral.

For the purpose of improving the gas barrier property, Patent Document 6, for example, proposes a means of providing a third layer such as a flattening layer or an adhesion layer between the resin substrate and the gas barrier layer.

JP 2001-287294 A JP-A-11-165369 JP-A-6-93133 JP-A-9-150484 Japanese Patent No. 3764109 WO2016/158794

Metal foils and vapor-deposited metal films are excellent in gas barrier properties. However, since the metal foil and the metal deposition film are opaque, the contents cannot be confirmed. In addition, since metal foils and vapor-deposited metal films are inferior in stretchability, cracks occur with elongation of several percent, resulting in deterioration of gas barrier properties. Furthermore, metal foils and vapor-deposited metal films have various problems, such as the need to dispose of them as incombustibles after use.
Resin films made of water-soluble polymers such as polyvinyl alcohol and ethylene-vinyl alcohol copolymer exhibit high gas barrier properties in a low-humidity atmosphere. However, gas barrier properties are dependent on humidity. The gas barrier property of the resin film deteriorates as the humidity increases. In particular, in a high humidity atmosphere, for example, in a humidity of 70% RH or more, the gas barrier property is lost, so there are restrictions on use.
A resin film made of polyvinylidene chloride exhibits low humidity dependence and excellent gas barrier properties. However, since polyvinylidene chloride contains chlorine, disposal is complicated.
Composite films of water-soluble polymers and inorganic layered minerals are superior in transparency to metal foils and vapor-deposited metal films. However, although the gas-barrier property in a high-humidity atmosphere is superior to that of a resin film made of a water-soluble polymer, it is still unsatisfactory.

If a third layer such as a flattening layer or an adhesion layer is provided between the resin base material and the gas barrier layer, the process of producing the gas barrier film becomes complicated, and the material of the third layer and the process of providing the third layer are costly, which is undesirable.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas barrier film having a simple structure and better oxygen barrier properties.

The present invention has the following aspects.
[1] having a resin base material and an oxygen barrier coating positioned in contact with at least one surface of the resin base material,
The gas barrier film, wherein the one surface has a luminance mode value of 95 or more as measured by the following measuring method.
<Measurement method>
An arbitrary area of 52.4 mm square on one surface of the resin base material is irradiated with telecentric illumination at an incident angle of 45.75°, reflected light with a reflection angle of 45° is captured by a camera with a telecentric lens to obtain a captured image, an analysis image of 1024 pixels × 1024 pixels is cut out from the captured image, the analysis image is converted to a 256-gradation monochrome image, and the luminance mode value in the monochrome image is used as the luminance mode value.
[2] The gas barrier film of [1], wherein the oxygen barrier film is a film formed from a coating agent containing a water-soluble polymer (A).
[3] The gas barrier film according to [2], wherein the water-soluble polymer (A) is a polyvinyl alcohol resin, the degree of saponification of the polyvinyl alcohol resin is 95% or more, and the degree of polymerization of the polyvinyl alcohol resin is 300 or more.
[4] The gas barrier film according to [2] or [3], wherein the coating agent further contains an inorganic layered mineral (B), and the content of the inorganic layered mineral (B) is 3 to 50% by mass relative to the mass of the solid content of the coating agent.
[5] The gas barrier film according to any one of [2] to [4], wherein the coating agent further comprises an aqueous polyurethane resin (C), and the aqueous polyurethane resin (C) comprises an acid group-containing polyurethane resin and a polyamine compound.

According to the gas barrier film of the present invention, the structure can be simplified and the oxygen barrier property can be improved.

1 is a cross-sectional view of a gas barrier film according to one embodiment of the present invention; FIG. It is a schematic diagram explaining a measuring device for measuring a luminance mode. It is an example of a histogram used when obtaining the brightness mode. 1 is a photographed image of one surface of a resin base material of a gas barrier film according to one embodiment of the present invention.

An embodiment of the gas barrier film of the present invention will be described below with reference to FIG. It should be noted that the present embodiment is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified.

[Gas barrier film]
As shown in FIG. 1, the gas barrier film 100 of this embodiment has a resin base material 20 and an oxygen barrier film 30 . The oxygen barrier coating 30 is positioned in contact with one surface 21 of the resin substrate 20 .

Although the thickness T ₁₀₀ of the gas barrier film 100 is not particularly limited, it is preferably 3.1 μm to 205 μm, more preferably 5.2 μm to 122 μm, even more preferably 6.3 μm to 31 μm. When the thickness _T100 is at least the above lower limit, the strength of the gas barrier film 100 is likely to be increased. When the thickness _T100 is equal to or less than the above upper limit, the flexibility of the gas barrier film 100 is enhanced and handling is facilitated.

<Resin base material>
The resin base material 20 contains resin. Examples of the resin constituting the resin base material 20 include olefin resins such as polyethylene, polypropylene, olefin polymers having 2 to 10 carbon atoms, and propylene-ethylene copolymers; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyamide resins such as aliphatic polyamides such as nylon 6 and nylon 66, and aromatic polyamides such as poly-metaxylylene adipamide; acrylic resins such as homo- or copolymers of (meth)acrylic monomers such as polymethyl methacrylate and polyacrylonitrile; cellophane; engineering plastics such as polycarbonate and polyimide. These resins may be used individually by 1 type, and may use 2 or more types together.

Examples of the resin substrate 20 include a single-layer film made of a single resin, a single-layer or laminated film using a plurality of resins, and the like. Also, a laminated substrate obtained by laminating the above resin on another substrate (metal, wood, paper, ceramics, etc.) may be used.
The resin base material 20 may be a single layer or two or more layers.
As the resin substrate 20, a polyolefin resin film (especially a polypropylene film), a polyester resin film (especially a polyethylene terephthalate resin film), a polyamide resin film (especially a nylon film), or the like is preferable.

The resin substrate 20 may be an unstretched film or a uniaxially or biaxially stretched oriented film.
As the resin base material 20, a biaxially oriented polypropylene film (OPP) is particularly preferable from the viewpoint of excellent water vapor barrier properties.
The OPP may be a film made of at least one polymer selected from homopolymers, random copolymers and block copolymers. A homopolymer is a polypropylene consisting of propylene alone. Random copolymers are polypropylenes in which the main monomer, propylene, and a small amount of comonomers different from propylene are randomly copolymerized to form a homogenous phase. A block copolymer is a polypropylene that forms a heterogeneous phase by block copolymerization or rubber-like polymerization of propylene, which is the main monomer, and the above comonomer.
When the resin base material 20 is OPP, the OPP may have one layer or two or more layers.

The surface 21 of the resin substrate 20 on which a film formed from a coating agent is laminated (the surface on which the coating agent is applied) may be subjected to chemical treatment, solvent treatment, corona treatment, low-temperature plasma treatment, ozone treatment, or other surface treatment in order to improve wettability with the coating agent and adhesion strength to the film.

The resin base material 20 may contain additives such as fillers, antiblocking agents, antistatic agents, plasticizers, lubricants, and antioxidants. Any one of these additives may be used alone, or two or more thereof may be used in combination.

When the resin base material 20 contains an anti-blocking agent (hereinafter also referred to as "AB agent"), unevenness derived from the AB agent is formed on one surface 21 of the resin base material 20 .
By containing the AB agent, the resin base material 20 can give irregularities to the surface of the film, which is the raw material of the resin base material 20, and can suppress adhesion between the films. Therefore, the film can be easily wound, and the processability of the film can be improved.
On the other hand, if unevenness is formed on the one surface 21 of the resin base material 20, when forming the oxygen barrier film (hereinafter also simply referred to as "film") 30, the film 30 is likely to have defects that serve as gas permeation paths. Therefore, the oxygen barrier property of the gas barrier film 100 may deteriorate.

The resin base material 20 may consist of two or more resin layers. When forming unevenness derived from the AB agent on one surface 21 of the resin substrate 20, the resin substrate 20 is composed of two or more resin layers, and the resin layer on the outermost surface (one surface 21 or the resin layer constituting the other surface 22) preferably contains the AB agent. By doing so, projections can be efficiently formed on one surface 21 or the other surface 22 of the resin base material 20 by adding a small amount of the AB agent. On one surface 21 and the other surface 22, the AB agent may be exposed or covered with resin.
The AB agent produces irregularities on the surface of the resin substrate 20 or the gas barrier film 100, suppresses the occurrence of blocking of the resin substrate 20 or the gas barrier film 100, and can improve the processability of the resin substrate 20 or the gas barrier film 100.

The AB agent is solid particles, including organic particles and inorganic particles. Examples of organic particles include polymethyl methacrylate particles, polystyrene particles, and polyamide particles. These organic particles are obtained by, for example, emulsion polymerization or suspension polymerization. Examples of inorganic particles include silica particles, zeolite, talc, kaolinite, and feldspar. Any one of these AB agents may be used alone, or two or more thereof may be used in combination.

Considering the appearance and transparency of the gas barrier film 100, the ability of the AB agent to fall off, and the anti-blocking performance, the average particle size of the AB agent is preferably, for example, 0.1 to 5 μm.
The average particle size of the AB agent is the weight average particle size measured by the Coulter method.

When the resin base material 20 contains the AB agent, the content of the AB agent is preferably 0.05 to 0.5% by mass with respect to 100% by mass of the resin layer constituting the resin layer constituting the resin base material 20 and constituting the one surface 21 or the other surface 22.
The AB agent content is specifically determined by the following formula (1).
AB agent content [% by mass]={(i)/100}×{(ii)/100}×100 (1)
(1) In the formula, (i) represents the concentration (% by mass) of the AB agent in the masterbatch resin chips formed into pellets by adding the AB agent to the resin, stirring, putting the mixture into an extruder and kneading, and melt extruding.
In the formula (1), (ii) represents the concentration (% by mass) of the masterbatch resin chips containing the AB agent with respect to the total mass of the resin pellets in the resin layer constituting the one surface 21 or the other surface 22 when the masterbatch resin chips containing the AB agent are blended with the resin that does not contain the AB agent.
When the content of the AB agent is equal to or more than the above lower limit value, the processing suitability of the film, which is the raw material of the resin base material 20, is likely to be improved. When the content of the AB agent is equal to or less than the above upper limit, it is easy to suppress deterioration of the oxygen barrier properties of the gas barrier film 100 .

One surface 21 of the resin base material 20 has a luminance mode of 95 or more, preferably 97 or more, and more preferably 100 or more in a 256-gradation monochrome image. When the luminance mode is equal to or greater than the above lower limit, unevenness formed on the one surface 21 of the resin base material 20 is small, and the film 30 is likely to be formed with a uniform thickness. Therefore, defects such as defects and cracks are less likely to occur in the coating 30, and the oxygen barrier properties of the gas barrier film 100 can be improved. The upper limit of the brightness mode value is 255.
When unevenness is formed on the one surface 21 of the resin base material 20, the area where the unevenness is formed looks dark in a photographed image, which will be described later. Therefore, the brightness of the captured image is low. As the number of areas where unevenness is formed increases, the number of areas with low luminance in the captured image increases, and the luminance mode value decreases. Conversely, a large brightness mode value means that there are few locations with low brightness, and that there are few portions where unevenness is formed on the one surface 21 of the resin base material 20 .
The unevenness formed on the one surface 21 of the resin base material 20 may be derived from the AB agent or may be caused by other factors, and is not particularly limited.
In this specification, the luminance mode is a value measured by the following measuring method.

<Measurement method>
An arbitrary area of 52.4 mm square on one surface 21 of the resin base material 20 is irradiated with telecentric illumination at an incident angle of 45.75°. A camera with a telecentric lens captures reflected light at a reflection angle of 45° to obtain a captured image. An analysis image of 1024 pixels×1024 pixels is cut out from the captured image. The clipped image for analysis is converted into a 256-gradation monochrome image. The converted monochrome image is analyzed by image analysis software, and the mode of brightness (the most distributed value) in the monochrome image is defined as the mode of brightness.

A method for measuring the luminance mode will be described below with reference to the drawings.
First, a measuring device for measuring the luminance mode will be described.

(measuring device)
As shown in FIG. 2, the measuring device 1 for measuring the luminance mode includes a sample holder 2, a light source 4, and a color line camera 7. As shown in FIG.
The sample holder 2 is installed on the transport device 10 and can move horizontally. A hole 3 is formed in the central portion of the sample holder 2 .
A light source 4 is positioned above the sample holder 2 and the light source 4 is connected to a telecentric illumination lens 5 . A light source control device 6 is connected to the light source 4 .
A color line camera 7 is positioned above the sample holder 2 and is equipped with a bilateral telecentric lens 8 . An image processing device 9 is connected to the color line camera 7 .
A transport control unit 11 is connected to the image processing device 9 .
The transport controller 11 is connected to the transport device 10 .

The sample holder 2 is not particularly limited as long as it is flat and horizontal, and a known holder may be used.
As the light source 4, a visible light white LED light source is preferable.
The telecentric illumination lens 5 includes a bilateral telecentric lens, an object-side telecentric lens, and an image-side telecentric lens. From the viewpoint of facilitating highly accurate measurement, the telecentric illumination lens 5 is preferably a bilateral telecentric lens.
A telecentric lens is a lens whose principal ray is parallel to the optical axis.

The color line camera 7 preferably has 4096 pixels and a sensor size of 7.04 μm per pixel. The sensor of the color line camera 7 preferably has a sensitivity of about 20 DN/nJ/cm ² at R, G, and B peaks. The color line camera 7 is preferably controlled by the image processing device 9 via a standard interface such as camera link or USB.
The image processing device 9 is composed of, for example, a personal computer equipped with a frame grabber or the like connected to the color line camera 7, and image processing software or the like for controlling the frame grabber.
Personal computers equipped with frame grabbers and the like and image processing software for controlling the frame grabbers are widely distributed or commercially available, and these can be used as the image processing device 9 . Image processing software includes, for example, the public domain software “ImageJ” developed by the National Institutes of Health (NIH).

A uniaxial stage or the like driven by a stepping motor is preferably used as the transport device 10 . The transport control unit 11 controls the transport speed, the start of transport, the stop of transport, and the like.

(Sample preparation)
Next, a method for measuring the luminance mode will be described.
As shown in FIG. 2, first, the resin base material 20 is fixed to the sample holder 2 so that one surface 21 of the resin base material 20 faces the light source 4 side and no difference in height occurs in the plane. When fixing the resin base material 20, it is preferable to fix the end portion of the resin base material 20 using OPP tape, masking tape, or the like. The resin base material 20 is fixed to the sample holder 2 so that the image measurement position 12 of the resin base material 20 is aligned with the punched hole 3 . An antireflection sheet or the like is preferably provided on the back surface of the image measurement position 12 on the other surface 22 of the resin base material 20 .

(Acquisition of photographed image)
Next, light from the light source 4 enters the telecentric illumination lens 5 . Incident light L1 is incident from a spot LED illumination or light guide light source using an optical fiber light guide. The light amount of the light source 4 can be adjusted by the light source control device 6 . The light intensity of the incident light L1 is preferably adjusted using the light source control device 6 so that the light intensity at the image measurement position 12 is 442 lux. At this time, the F value of the telecentric illumination lens 5 is assumed to be eight.
The incident light L1 from the telecentric illumination lens 5 has an incident angle 13 of 45.75° with respect to one surface 21 . The reflected light L2 is reflected at the image measurement position 12 . At this time, the color line camera 7 is installed at a position where the reflection angle 14 of the reflected light L2 is 45°. That is, the angle of reflection 14 has an angular difference of 0.75° from the angle at which the angle of incidence 13 is specularly reflected. The reflected light L2 is measured and photographed by the color line camera 7 via the telecentric lens 8 on both sides.
At this time, it is assumed that the F value of the both-side telecentric lens 8 is 8, the magnification is 0.55, and the spatial resolution is 12.8 μm. The measurement range of the color line camera 7 at the image measurement position 12 is a 52.4 mm square area, and the effective illumination range of the telecentric illumination lens 5 is a 52.4 mm square area or more.

The measurement range of the reflected light L2 is a 52.4 mm square area on one surface 21 . The conveying device 10 is moved so that the measurement range is the above region.
If the conveying device 10 is a stepping motor or the like, the image processing device 9 receives a pulse signal indicating the conveying speed. The transport speed at which the transport device 10 is moved is preferably set equal to the product of the spatial resolution and the capture frequency.
The spatial resolution is determined from the sensor size (7.04 μm) of the color line camera 7 and the magnification (0.55 times) of the telecentric lens 8 on both sides.
The capturing frequency is the capturing frequency of one line of the color line camera 7 . The conveying speed is set equal to the product of the spatial resolution and the capturing frequency, and the resin substrate 20 is continuously conveyed at the image measuring position 12 of the color line camera 7 . At the image measuring position 12 , an image of the resin base material 20 is measured and photographed by the color line camera 7 .

Assume that the exposure time of the color line camera 7 is 400 μs. Set the acquisition frequency period to be longer than the exposure time. The gain of red, green, and blue is set to 2.8 times, 2 times, and 3.8 times so that the luminance values of the red, green, and blue channels image-measured by the color line camera 7 are uniform when the spectral characteristics of the white LED of the light source 4 are incident. The resin base material 20 is conveyed, and a photographed image of 1024 pixels or more is obtained in the conveying direction of the resin base material 20 .

(Image analysis)
In the captured image obtained, 1024 pixels at the center corresponding to the direction in which the sensors of the color line camera 7 are arranged (the direction orthogonal to the direction of conveyance of the resin base material 20) and 1024 pixels in the direction of conveyance are cut out and used as an analysis image. By cutting out the center 1024 pixels in the width direction of the resin base material 20 (direction orthogonal to the conveying direction of the resin base material 20), the influence of unevenness occurring in the peripheral portion of the double telecentric lens 8 can be eliminated. It is also possible to widen the measurement range by cutting out 1024 pixels or more in the transport direction. The clipped image for analysis is analyzed by image analysis software and converted into a 256-gradation monochrome image. Find the mode of brightness (the most distributed value) in a monochrome image.
The mode obtained in this manner is set as the brightness mode of the one surface 21 of the resin base material 20 .

FIG. 3 shows an example of a histogram of a monochrome image. A value P at which the frequency of luminance is distributed most frequently in FIG.

FIG. 4 shows a photographed image of one surface 21 of the resin substrate 20 of the gas barrier film 100 . Areas that appear black in the photographed image have unevenness on the surface of the resin base material and represent areas with low luminance (dark).

The brightness mode value of the one surface 21 of the resin base material 20 serves as an index representing the degree of unevenness formed on the one surface 21 of the resin base material 20 . The brightness mode value of the one surface 21 of the resin base material 20 can be adjusted by, for example, the material, average particle diameter, content, etc. of the AB agent contained in the resin base material 20 .

The thickness T20 of the resin base material ₂₀ is not particularly limited, and is appropriately selected depending on the price and application while considering the suitability as a packaging material and the lamination suitability of other films. Practically, the thickness _T20 is preferably 3 μm to 200 μm, more preferably 5 μm to 120 μm, even more preferably 6 μm to 30 μm.

<Oxygen barrier film>
The oxygen barrier coating 30 is positioned in contact with one surface 21 of the resin substrate 20 . The oxygen barrier coating 30 may be a known oxygen barrier coating formed by a wet coating method (wet coating method).
The oxygen barrier film 30 is obtained by forming a coating film made of a coating agent on one surface 21 of the resin base material 20 by a wet coating method, and drying the coating film. A coating film is a wet film, and a film is a dry film.

The thickness T ₃₀ of the oxygen barrier coating 30 is set according to the required gas barrier properties, preferably 0.1 μm to 5 μm, more preferably 0.2 μm to 2 μm, even more preferably 0.3 μm to 1 μm. When the thickness _T30 is at least the above lower limit, sufficient gas barrier properties are likely to be obtained. When the thickness _T30 is equal to or less than the above upper limit, it is easy to form a uniform coating film surface, and the drying load and manufacturing cost can be suppressed.
The thickness _T30 of the oxygen barrier coating 30 is measured with a scanning electron microscope (SEM).

[Method for producing gas barrier film]
The gas barrier film 100 can be produced by forming the oxygen barrier film 30 on one surface 21 of the resin substrate 20 .
As the resin base material 20, a commercially available product may be used, or a product manufactured by a known method may be used.

The oxygen barrier film 30 can be formed by applying a coating agent to one side (one side 21) or both sides of the resin substrate 20 to form a coating film, and drying the coating film (removing the aqueous medium).
As a method for applying the coating agent, a known wet coating method can be used. Wet coating methods include roll coating, gravure coating, reverse coating, die coating, screen printing, and spray coating.
As a method for drying a coating film made of a coating agent, a known drying method such as hot air drying, hot roll drying, infrared irradiation, or the like can be used. The drying temperature of the coating film is preferably 50 to 200° C., for example. The drying time varies depending on the thickness of the coating film, the drying temperature, etc., but is preferably, for example, 1 second to 5 minutes.

<Coating agent>
Components contained in the coating agent forming the oxygen barrier film 30 are described below. The coating agent of this embodiment contains a water-soluble polymer (A).

(Water-soluble polymer (A))
A "water-soluble polymer" refers to a polymer that is soluble in water. The term "dissolution" as used herein refers to a state in which the solute polymer is dispersed in the solvent water at the molecular chain level to form a homogeneous system. More specifically, it refers to a state in which the intermolecular force with water molecules is stronger than the intermolecular force between the polymer chains, the entanglement of the polymer chains is broken, and the particles are evenly dispersed in water.
As used herein, a polymer refers to a compound having a mass average molecular weight of 10,000 or more. The weight average molecular weight can be measured by GPC and determined using polystyrene as a standard.

Specific examples of the water-soluble polymer (A) include, for example, polyvinyl alcohol resins such as polyvinyl alcohol and derivatives thereof; vinyl polymers such as polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid or esters thereof, salts and copolymers thereof, polyhydroxyethyl methacrylate and copolymers thereof; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; starches such as oxidized starch, etherified starch and dextrin; Polymerized polyester; urethane-based polymers other than the water-based polyurethane resin (C) described later, or functional group-modified polymers obtained by modifying the carboxyl groups of these various polymers.
The water-soluble polymer (A) preferably has a degree of polymerization of 200 or more in consideration of film cohesive strength.

The water-soluble polymer (A) contained in the coating agent may be one kind or two or more kinds.
The water-soluble polymer (A) preferably contains at least one polyvinyl alcohol resin selected from the group consisting of polyvinyl alcohol-based polymers and derivatives thereof, and more preferably contains a polyvinyl alcohol resin having a degree of saponification of 95% or more and a degree of polymerization of 300 or more. The polymerization degree of the polyvinyl alcohol resin is preferably 300-2400, more preferably 450-2000.
The higher the degree of saponification and the degree of polymerization of the polyvinyl alcohol resin, the lower the hygroscopic swelling property. When the degree of saponification of the polyvinyl alcohol resin is 95% or more, it is easy to obtain sufficient gas barrier properties. When the degree of polymerization of the polyvinyl alcohol resin is 300 or more, it tends to be excellent in oxygen barrier properties and film cohesive strength. When the degree of polymerization of the polyvinyl alcohol resin is 2400 or less, the increase in the viscosity of the coating agent is suppressed, it is easily mixed with other components uniformly, and problems such as deterioration of gas barrier properties and adhesion strength are easily suppressed.
The degree of saponification and degree of polymerization of polyvinyl alcohol resin can be measured by the method described in JIS K 6726:1994.

The content of the water-soluble polymer (A) contained in the coating agent is preferably 25 to 92% by mass, more preferably 30 to 87% by mass, and even more preferably 35 to 82% by mass, based on the mass of the solid content of the coating agent. When the content of the water-soluble polymer (A) is at least the above lower limit, the inorganic layered mineral (B) is easily dispersed. When the content of the water-soluble polymer (A) is equal to or less than the above upper limit, it is easy to mix a large amount of the water-based polyurethane resin (C).

(Inorganic layered mineral (B))
The coating agent of the present embodiment preferably further contains an inorganic layered mineral (B).
The term “inorganic layered mineral” refers to an inorganic compound in which very thin (for example, 10 to 500 nm thick) unit crystal layers are stacked to form one layered particle. Since the oxygen barrier film 30 formed from the coating agent contains the inorganic layered mineral (B), it exerts a maze effect that lengthens the gas permeation path, and it is easy to obtain good oxygen barrier properties even in a high-humidity atmosphere.
As the inorganic layered mineral (B), compounds having both or one of properties of swelling and cleaving in water are preferred. Among these compounds, clay compounds having swelling property in water are particularly preferred. More specifically, the inorganic layered mineral (B) is preferably a clay compound that coordinates water between ultrathin unit crystal layers and has properties of absorption and/or swelling. Such a clay compound is generally a compound in which a layer in which Si ⁴⁺ is coordinated to O ^2- to form a tetrahedral structure and a layer in which Al ³⁺ , Mg ²⁺ , Fe ²⁺ , Fe ³⁺ etc. are coordinated to O ^2- and ^OH- to form an octahedral structure are combined in a one-to-one or two-to-one ratio and stacked to form a layered structure. This clay compound may be a natural compound or a synthetic compound.

Representative examples of the inorganic layered minerals (B) include hydrous silicates such as phyllosilicate minerals. Examples include kaolinite group clay minerals such as halloysite, kaolinite, endelite, dickite, and nacrite; antigorite group clay minerals such as antigorite and chrysotile; montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, stevensite, and other smectite group clay minerals; miculite group clay minerals; mica or mica group clay minerals such as muscovite, phlogopite, margarite, tetrasilylic mica and teniolite; and the like. These inorganic layered minerals (B) are used singly or in combination of two or more.
Among these inorganic layered minerals (B), smectite group clay minerals such as montmorillonite and mica group clay minerals such as water-swellable mica are particularly preferred.

As for the size of the inorganic layered mineral (B), it is preferable that the average particle size is 10 μm or less and the thickness is 500 nm or less. When the average particle size and thickness are each equal to or less than the above upper limit values, the inorganic layered mineral (B) tends to be uniformly aligned in the oxygen barrier coating 30 formed from the coating agent, resulting in high gas barrier properties and high cohesive strength.
The average particle size of the inorganic layered mineral (B) is measured with a laser diffraction particle size distribution meter.
The thickness of the inorganic layered mineral (B) is measured with an atomic force microscope (AFM).

The inorganic layered mineral (B) preferably contains at least water-swellable synthetic mica. The mean particle size of the water-swellable synthetic mica is, for example, preferably 1 to 10 μm, more preferably 3 to 8 μm. When the average particle size of the water-swellable synthetic mica is at least the above lower limit, the gas barrier properties are likely to be improved. When the average particle size of the water-swellable synthetic mica is equal to or less than the above upper limit, the particles are easily aligned uniformly in the oxygen barrier film 30 .
The thickness of the water-swellable synthetic mica is, for example, preferably 10-100 nm, more preferably 10-80 nm. When the thickness of the water-swellable synthetic mica is at least the above lower limit, the gas barrier properties are likely to be improved. When the thickness of the water-swellable synthetic mica is equal to or less than the above upper limit, it tends to be uniformly aligned in the oxygen barrier film 30 .

The water-swellable synthetic mica has high compatibility with the water-based polyurethane resin (C) and the water-soluble polymer (A), and contains less impurities than natural mica. Therefore, when water-swellable synthetic mica is used as the inorganic layered mineral (B), deterioration of gas barrier properties and film cohesion due to impurities can be easily suppressed.
In addition, since the water-swellable synthetic mica has fluorine atoms in its crystal structure, it also contributes to reducing the humidity dependence of the gas barrier properties of the oxygen barrier film 30 formed from the coating agent.
In addition, since the water-swellable synthetic mica has a higher aspect ratio than other water-swellable inorganic layered minerals, the labyrinth effect works more effectively, and the oxygen-barrier film 30 formed from the coating agent exhibits particularly high gas barrier properties.
The content of the water-swellable synthetic mica is, for example, preferably 50% by mass or more, more preferably 70% by mass or more, and may be 100% by mass, relative to the total mass of the inorganic layered mineral (B).

The content of the inorganic layered mineral (B) in the coating agent is preferably 3 to 50% by mass, more preferably 5 to 35% by mass, and even more preferably 7 to 20% by mass, based on the mass of the solid content of the coating agent. When the content of the inorganic layered mineral (B) is at least the above lower limit, it is easy to effectively exhibit oxygen barrier properties in a high-humidity environment. When the content of the inorganic layered mineral (B) is equal to or less than the above upper limit, the cohesive strength of the oxygen barrier coating 30 is easily maintained.

(Aqueous polyurethane resin (C))
The coating agent of the present embodiment preferably further contains an aqueous polyurethane resin (C).
The aqueous polyurethane resin (C) preferably contains a polyurethane resin having an acid group (hereinafter also referred to as "acid group-containing polyurethane resin") and a polyamine compound.
Since the coating agent contains the aqueous polyurethane resin (C), the wettability of the coating agent to the resin substrate 20 and the adhesion strength of the oxygen barrier film 30 formed from the coating agent to the resin substrate 20 tend to be excellent.
Furthermore, since the water-based polyurethane resin (C) contains an acid-group-containing polyurethane resin and a polyamine compound, it is easy to develop good oxygen barrier properties even in a high-humidity atmosphere.

The water-based polyurethane resin (C) is used to impart flexibility and gas barrier properties, particularly oxygen barrier properties, to the oxygen barrier film 30 . In the water-based polyurethane resin (C), the acid group of the acid group-containing polyurethane resin is combined with a polyamine compound as a cross-linking agent to exhibit gas barrier properties.
The bond between the acid group of the acid group-containing polyurethane resin and the polyamine compound may be an ionic bond (e.g., an ionic bond between a carboxyl group and a tertiary amino group) or a covalent bond (e.g., an amide bond).

The acid-group-containing polyurethane resin constituting the water-based polyurethane resin (C) has acid groups, and therefore has anionicity and self-emulsifying properties, and is also called an anionic self-emulsifying polyurethane resin.
A carboxyl group, a sulfonic acid group, etc. are mentioned as an acid group. The acid groups may be located at the terminals or side chains of the polyurethane resin, but are preferably located at least at the side chains. This acid group can usually be neutralized with a neutralizing agent (base), and may form a salt with the base. Incidentally, the acid group can bond with the amino group (imino group or tertiary nitrogen atom) of the polyamine compound that constitutes the aqueous polyurethane resin (C).

The acid value of the acid group-containing polyurethane resin can be selected within a range that can impart water solubility or water dispersibility. The acid value of the acid group-containing polyurethane resin is preferably 5 to 100 mgKOH/g, more preferably 10 to 70 mgKOH/g, even more preferably 15 to 60 mgKOH/g. When the acid value of the acid group-containing polyurethane resin is at least the above lower limit, the uniform dispersibility of the water-based polyurethane resin (C) and other materials and the dispersion stability of the coating agent are likely to be improved. When the acid value of the acid group-containing polyurethane resin is equal to or less than the above upper limit, it is easy to suppress deterioration of the water resistance and gas barrier properties of the oxygen barrier film 30 .
The acid value of the acid group-containing polyurethane resin is measured by a method according to JIS K0070.

The sum (total concentration) of the urethane group concentration and the urea group (urea group) concentration of the acid group-containing polyurethane resin is preferably 15% by mass or more, more preferably 20 to 60% by mass, from the viewpoint of gas barrier properties. When the total concentration is at least the above lower limit value, the gas barrier properties are likely to be improved. When the total concentration is equal to or less than the above upper limit, it is easy to prevent the oxygen barrier coating 30 from becoming rigid and brittle.
The urethane group concentration means the ratio of the molecular weight of the urethane group (59 g/equivalent) to the molecular weight of the repeating structural unit of the polyurethane resin. The urea group concentration means the ratio of the molecular weight of the urea group (primary amino group (amino group): 58 g/equivalent, secondary amino group (imino group): 57 g/equivalent) to the molecular weight of the repeating structural unit of the polyurethane resin.
When a mixture of two or more kinds of polyurethane resins is used, the urethane group concentration and the urea group concentration can be calculated based on the charged base of the reaction components, that is, the usage ratio of each component.

The acid-group-containing polyurethane resin preferably has at least rigid units (units composed of hydrocarbon rings) and short-chain units (eg, units composed of hydrocarbon chains). That is, the repeating structural unit of the acid group-containing polyurethane resin is derived from a polyisocyanate component, a polyhydroxy acid component, a polyol component, or a chain extender component (in particular, at least the polyisocyanate component), and preferably contains a hydrocarbon ring (at least one of aromatic and non-aromatic hydrocarbon rings).
The proportion of units composed of hydrocarbon rings in the repeating structural units of the acid group-containing polyurethane resin is preferably 10 to 70% by mass, more preferably 15 to 65% by mass, and even more preferably 20 to 60% by mass. When the ratio of the unit composed of a hydrocarbon ring is equal to or higher than the above lower limit, deterioration of gas barrier properties can be easily suppressed. If the ratio of the units composed of hydrocarbon rings is equal to or less than the above upper limit, it is easy to prevent the oxygen barrier coating 30 from becoming rigid and brittle.

The number average molecular weight of the acid group-containing polyurethane resin can be selected as appropriate, but is preferably 800 to 1,000,000, more preferably 800 to 200,000, even more preferably 800 to 100,000. When the number average molecular weight of the acid group-containing polyurethane resin is at least the above lower limit, deterioration of gas barrier properties can be easily suppressed. When the number average molecular weight of the acid group-containing polyurethane resin is equal to or less than the above upper limit, it is easy to suppress the increase in the viscosity of the coating agent.
The number average molecular weight of the acid group-containing polyurethane resin is a value converted to standard polystyrene measured by gel permeation chromatography (GPC).

The acid group-containing polyurethane resin may be crystalline in order to improve gas barrier properties.
The glass transition temperature of the acid group-containing polyurethane resin is preferably 100 to 200°C, more preferably 110 to 180°C, even more preferably 120 to 150°C. When the glass transition temperature of the acid-group-containing polyurethane resin is at least the above lower limit, deterioration of gas barrier properties can be easily suppressed. The glass transition temperature of the acid group-containing polyurethane resin is typically not higher than the above upper limit.
The glass transition temperature of the acid group-containing polyurethane resin is measured by differential scanning calorimetry (DSC).

The aqueous polyurethane resin (C) preferably contains a neutralizing agent and is formed by dissolving or dispersing the acid group-containing polyurethane resin in an aqueous medium.
The aqueous medium includes water, a water-soluble solvent, a hydrophilic solvent, or a mixed solvent thereof, preferably water or a water-soluble solvent containing water as a main component.
The content of water in the aqueous medium is preferably 70% by mass or more, more preferably 80% by mass or more.
Examples of hydrophilic solvents include alcohols such as ethanol and isopropanol; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran; cellosolves; carbitols;

The aqueous polyurethane resin (C) may be in the form of an aqueous solution in which an acid group-containing polyurethane resin is dissolved in an aqueous medium, or an aqueous dispersion in which an acid group-containing polyurethane resin is dispersed in an aqueous medium.
In the aqueous dispersion, the average particle size of dispersed particles (polyurethane resin particles) is not particularly limited, and is preferably 20 to 500 nm, more preferably 25 to 300 nm, even more preferably 30 to 200 nm. When the average particle size of the dispersed particles is at least the above lower limit, the gas barrier properties are likely to be improved. When the average particle size of the dispersed particles is equal to or less than the above upper limit, deterioration of uniform dispersibility between the dispersed particles and other materials and deterioration of dispersion stability of the coating agent can be easily suppressed, and deterioration of gas barrier properties can be easily suppressed.
The average particle size of the dispersed particles is a value measured with a concentrated particle size analyzer (FPAR-10 manufactured by Otsuka Electronics Co., Ltd.) (diluted with water) at a solid content concentration of 0.03 to 0.3% by mass.

The polyamine compound constituting the water-based polyurethane resin (C) is not particularly limited as long as it can bond with acid groups and improve gas barrier properties, and various compounds having two or more basic nitrogen atoms can be used.
A basic nitrogen atom is a nitrogen atom that can bond with an acid group of an acid group-containing polyurethane resin, and includes, for example, a nitrogen atom in an amino group such as a primary amino group, secondary amino group, or tertiary amino group.
The polyamine compound is preferably a polyamine compound having at least one amino group selected from the group consisting of primary amino groups, secondary amino groups and tertiary amino groups.

Specific examples of polyamine compounds include alkylenediamines, polyalkylenepolyamines, and silicon compounds having a plurality of basic nitrogen atoms. Examples of alkylenediamines include alkylenediamines having 2 to 10 carbon atoms such as ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,4-butanediamine and 1,6-hexamethylenediamine. Polyalkylenepolyamines include, for example, tetraalkylenepolyamine. Examples of silicon compounds having multiple basic nitrogen atoms (including nitrogen atoms such as amino groups) include silane coupling agents having multiple basic nitrogen atoms, such as 2-[N-(2-aminoethyl)amino]ethyltrimethoxysilane and 3-[N-(2-aminoethyl)amino]propyltriethoxysilane.

The amine value of the polyamine compound is preferably 100 to 1900 mgKOH/g, more preferably 150 to 1900 mgKOH/g, still more preferably 200 to 1900 mgKOH/g, particularly preferably 200 to 1700 mgKOH/g, most preferably 300 to 1500 mgKOH/g. When the amine value of the polyamine compound is at least the above lower limit, gas barrier properties are likely to be improved. When the amine value of the polyamine compound is at most the above upper limit, the aqueous polyurethane resin (C) has excellent water dispersion stability.
The amine value of a polyamine compound is measured by the following method.

Accurately weigh 0.5 to 2 g of the sample (sample amount Sg). 30 g of ethanol is added to the precisely weighed sample to dissolve it. Bromophenol blue is added to the resulting solution as an indicator, and titration is performed with a 0.2 mol/L ethanolic hydrochloric acid solution (potency f). The point at which the color of the solution changes from green to yellow is taken as the end point, the amount of titration (AmL) at this time is measured, and the amine value is determined using the following formula 1.
Formula 1: Amine value = A x f x 0.2 x 56.108/S [mgKOH/g]

In the water-based polyurethane resin (C), the content of the polyamine compound is such that the molar ratio (acid group/basic nitrogen atom) of the acid group-containing polyurethane resin to the basic nitrogen atom of the polyamine compound is preferably 10/1 to 0.1/1, more preferably 5/1 to 0.2/1. When the acid group/basic nitrogen atoms are within the above numerical range, a cross-linking reaction between the acid group of the acid group-containing polyurethane and the polyamine compound occurs appropriately, and the oxygen barrier film 30 tends to exhibit good oxygen barrier properties even in a high-humidity atmosphere.

As the water-based polyurethane resin (C), a commercially available one may be used, or one produced by a known production method may be used.
The method for producing the water-based polyurethane resin (C) is not particularly limited, and conventional techniques for making water-based polyurethane resins, such as the acetone method and prepolymer method, are used. In the urethanization reaction, urethanization catalysts such as amine-based catalysts, tin-based catalysts and lead-based catalysts may be used as necessary.
For example, an aqueous polyurethane resin (C) can be prepared by reacting a polyisocyanate compound, a polyhydroxy acid, and, if necessary, at least one of a polyol component and a chain extender component in an inert organic solvent such as ketones such as acetone, ethers such as tetrahydrofuran, and nitriles such as acetonitrile. More specifically, a polyisocyanate compound, a polyhydroxy acid, and a polyol component are reacted in an inert organic solvent (particularly, a hydrophilic or water-soluble organic solvent) to produce a prepolymer having terminal isocyanate groups, neutralized with a neutralizing agent, dissolved or dispersed in an aqueous medium, then added with a chain extender component to react, and the organic solvent is removed to prepare an aqueous solution or aqueous dispersion of an acid group-containing polyurethane resin.
An aqueous polyurethane resin (C) in the form of an aqueous solution or dispersion can be prepared by adding a polyamine compound to the aqueous solution or dispersion of the acid group-containing polyurethane resin obtained in this manner and heating if necessary. When heating, the heating temperature is preferably 30 to 60°C.

When the coating agent contains the aqueous polyurethane resin (C), the content of the aqueous polyurethane resin (C) is preferably 5 to 30% by mass, more preferably 10 to 20% by mass, based on the mass of the solid content of the coating agent. When the content of the water-based polyurethane resin (C) is at least the above lower limit, the adhesion strength of the oxygen barrier film 30 to the resin substrate 20 tends to be excellent. When the content of the water-based polyurethane resin (C) is equal to or less than the above upper limit, the cohesive strength of the oxygen barrier film 30 can be easily increased.

When the coating agent contains the water-based polyurethane resin (C), the solid mass ratio of the water-based polyurethane resin (C) and the water-soluble polymer (A) in the coating agent (hereinafter also referred to as the (C)/(A) ratio) is preferably 85/15 to 5/95, more preferably 75/25 to 10/90, and even more preferably 70/30 to 15/85.
When the (C)/(A) ratio is within the above numerical range, the coating agent can be evenly applied, and the oxygen barrier film 30 with good appearance and gas barrier properties can be easily formed. When the content of the water-based polyurethane resin (C) is less than the (C)/(A) ratio of 85/15, it is easy to suppress the possibility of unevenness during coating. Since unevenness during coating leads to deterioration of appearance and deterioration of gas barrier properties, suppressing unevenness during coating tends to suppress deterioration of appearance and deterioration of gas barrier properties. When the content of the water-based polyurethane resin (C) is greater than the (C)/(A) ratio of 5/95, deterioration of wettability to the resin substrate 20 is suppressed, and uneven repellency during coating is easily suppressed, thereby easily suppressing deterioration of barrier properties.

In the coating agent that forms the oxygen barrier film 30, the total content (solid content) of the water-soluble polymer (A), the inorganic layered mineral (B), and the water-based polyurethane resin (C) is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the mass of the solid content of the coating agent. The upper limit of the total content is not particularly limited, and may be 100% by mass.

(other ingredients)
The coating agent of the present embodiment may contain components (other components) other than the water-soluble polymer (A), the inorganic layered mineral (B), and the aqueous polyurethane resin (C) within a range that does not impair the effects of the present invention.
Other components include additives such as antioxidants, weathering agents, heat stabilizers, lubricants, crystal nucleating agents, UV absorbers, plasticizers, antistatic agents, coloring agents, fillers, and surfactants.

The coating agent preferably has a viscosity at 23° C. of 10 to 80 mPa·s, more preferably 10 to 50 mPa·s.
The viscosity of the coating agent is a value measured with an E-type viscometer.

The coating agent of the present embodiment can be prepared by mixing a water-soluble polymer (A), optionally an inorganic layered mineral (B), an aqueous polyurethane resin (C), an additive, an additional aqueous medium, and the like. The mixing order of each component is not particularly limited.

The gas barrier film of the present invention may further have a printed layer, an anchor coat layer, an overcoat layer, a light-shielding layer, an adhesive layer, a heat-sealable heat-sealable layer, other functional layers, and the like, if necessary.
When the gas barrier film of the present invention has a heat-sealable heat-sealable layer, this heat-sealable layer is arranged on at least one outermost layer of the gas barrier film. Since the gas barrier film has a heat-sealable layer, the gas barrier film can be sealed by heat sealing (for example, a package or a lid).
The heat-sealable layer can be laminated by, for example, a known dry lamination method, an extrusion lamination method, or the like using a known adhesive such as a polyurethane-based, polyester-based, or polyether-based adhesive to a laminate obtained by forming a film on one or both sides of a resin substrate with the coating agent of the present embodiment.

<Effect>
In the gas barrier film of the present invention, a film formed from a coating agent containing a water-soluble polymer (A) is laminated on at least one surface of a resin substrate having a luminance mode value of 95 or more at 256 gradations measured by image.
Since the gas barrier film of the present invention forms a film on the surface of a resin base material having a brightness mode of 95 or more, defects are less likely to occur in the film, and oxygen barrier properties can be improved.
In addition, the gas barrier film of the present invention does not require a flattening layer or an adhesion layer, and has a simple structure because the coating agent is directly applied to the surface of the resin substrate to form the oxygen barrier film.
Therefore, by using the gas barrier film of the present invention as a packaging material, it is possible to inexpensively improve the quality retention of contents.

The gas barrier film 100 of this embodiment has an oxygen barrier film 30 positioned in contact with one surface 21 of the resin substrate 20 .
However, the gas barrier film may have oxygen barrier coatings on both sides of the resin substrate.
From the viewpoint of simplifying the structure, the gas barrier film preferably has an oxygen barrier film on one surface of the resin substrate.

EXAMPLES The present invention will now be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples.
Materials used in the following examples are shown below.

[Materials used]
<Resin base material>
α1: Biaxially oriented polypropylene film (trade name: VPH2011, thickness 20 μm, manufactured by AJ Plast).
α2: Biaxially oriented polypropylene film (trade name: TSB, thickness 20 µm, manufactured by POLO).
α3: Biaxially oriented polypropylene film (trade name: TIMCP, thickness 19 µm, manufactured by Max Specialty Films Limited).
α4: Biaxially stretched polypropylene film (trade name: TIV, thickness 18 μm, manufactured by Max Specialty Films Limited).
α5: Biaxially oriented polypropylene film (trade name: TSSE, thickness 20 μm, manufactured by Tenoval).
α6: Biaxially oriented polypropylene film (trade name: MNH, thickness 20 μm, manufactured by Treofan).

<Water-soluble polymer (A)>
A1: Polyvinyl alcohol having a degree of saponification of 98 to 99% and a degree of polymerization of 500 (trade name: Poval PVA-105, manufactured by Kuraray Co., Ltd.).
A2: Carboxylmethylcellulose (CMC).

<Inorganic layered mineral (B)>
B1: Water-swellable synthetic mica (trade name: Somasif (registered trademark) MEB-3, manufactured by Co-op Chemical Co., Ltd.).
B2: Purified montmorillonite (trade name: Kunipia (registered trademark)-F, manufactured by Kunimine Industries Co., Ltd.).
B3: sodium hectorite (trade name: NHT-sol B2, manufactured by Topy Industries, Ltd.).

<Aqueous polyurethane resin (C)>
C1: Water-based polyurethane resin containing a polyurethane resin having an acid group and a polyamine compound, Mitsui Chemicals, Inc.'s water-based polyurethane dispersion "Takelac (registered trademark) WPB-341".
C2: Polyester polyurethane resin aqueous solution "Hydran (registered trademark) HW350" manufactured by DIC Corporation.

<Examples 1 and 2, Comparative Examples 1 and 2>
The water-based polyurethane resin (C) and the 8% by mass aqueous solution of the water-soluble polymer (A) were blended so as to have the types and solid content blending ratios shown in Table 1. Thereafter, the mixture was diluted with ion-exchanged water and isopropanol so that 10% by mass of the entire aqueous medium was isopropanol and the solid content concentration was 8.2% by mass. Thus, coating agents of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared. Here, the parentheses in the column of coating agents represent the types of materials used, and the numerical values represent the compounding ratios. The blending ratio is the ratio (% by mass) of each component in solid content to the total solid content, and the same applies hereinafter. "0" in the table indicates that the component is not included.

Using a gravure printing machine, the coating agent shown in Table 1 was applied to the corona-treated surface of the resin substrate of the type shown in Table 1 by the gravure coating method, passed through an oven at 90°C for 10 seconds and dried to form an oxygen barrier film, thereby obtaining a gas barrier film.
The cross section of the obtained gas barrier film was observed with a scanning electron microscope (SU8020, manufactured by Hitachi High-Technologies Corporation) to measure the thickness of the film formed.

<Examples 3-12, Comparative Examples 3-4>
The water-based polyurethane resin (C) and the 8% by mass aqueous solution of the water-soluble polymer (A) were blended so as to have the types and solid content blending ratios shown in Table 2. Next, an 8% by mass aqueous dispersion of the inorganic layered mineral (B) was added, followed by dilution with ion-exchanged water and isopropanol so that 10% by mass of the entire aqueous medium was isopropanol and the solid content concentration was 8.2% by mass. Thus, coating agents of Examples 3-12 and Comparative Examples 3-4 were prepared.

Using a gravure printing machine, the coating agent shown in Table 2 was applied to the corona-treated surface of the resin substrate of the type shown in Table 2 under the same conditions as in Examples 1 and 2 to form an oxygen barrier film and obtain a gas barrier film.
The cross section of the obtained gas barrier film was observed with a scanning electron microscope in the same manner as in Examples 1 and 2, and the thickness of the film formed was measured.

<Example 13, Comparative Examples 5-6>
An 8% by mass aqueous solution of the water-soluble polymer (A) was blended so as to have the types and solid content blending ratios shown in Table 3. Next, an 8% by mass aqueous dispersion of the inorganic layered mineral (B) was added, followed by dilution with ion-exchanged water and isopropanol so that 10% by mass of the entire aqueous medium was isopropanol and the solid content concentration was 8.2% by mass. Thus, coating agents of Example 13 and Comparative Examples 5 and 6 were prepared.

Using a gravure printing machine, the coating agent shown in Table 3 was applied to the corona-treated surface of the resin substrate of the type shown in Table 3 under the same conditions as in Examples 1 and 2 to form an oxygen barrier film and obtain a gas barrier film.
The cross section of the obtained gas barrier film was observed with a scanning electron microscope in the same manner as in Examples 1 and 2, and the thickness of the film formed was measured.

<Evaluation>
(1) Brightness mode The brightness mode of each resin substrate was measured by the above-described measurement method. The measurement results are shown in Tables 1-3.

(2) Oxygen gas barrier property (OTR)
For the gas barrier film obtained in each example, the oxygen permeability (OTR, cm ³ /(m ² day MPa)) was measured using an oxygen permeability measuring device (trade name: OXTRAN-2/20, manufactured by MOCON) in an atmosphere of 30°C dry, 30°C, and 70% RH. The measurement results are shown in Tables 1-3.

(3) Water vapor barrier property (WVTR)
The gas barrier film obtained in each example was measured for water vapor permeability (WVTR, g/(m ² ·day)) in an atmosphere of 40°C and 90% RH using a water vapor permeability measuring device (trade name: PERMATRAN-W-3/33, manufactured by MOCON). The measurement results are shown in Tables 1-3.

From the results shown in Table 1, the gas barrier films of Examples 1 and 2 had both good oxygen barrier properties in a dry atmosphere at 30°C and oxygen barrier properties in a 70% atmosphere at 30°C compared to the gas barrier films of Comparative Examples 1 and 2 using resin substrates having a luminance mode of less than 95.
From the results shown in Table 2, the gas barrier films of Examples 3 to 12 had both good oxygen barrier properties in a dry atmosphere at 30°C and oxygen barrier properties in a 70% atmosphere at 30°C compared to the gas barrier films of Comparative Examples 3 to 4 using a resin substrate having a luminance mode of less than 95.
From the results shown in Table 3, the gas barrier film of Example 13 had better oxygen barrier properties in a dry atmosphere at 30°C and in an atmosphere of 30°C and 70% compared to the gas barrier films of Comparative Examples 5 and 6 using resin substrates having a luminance mode of less than 95.

The gas barrier film of the present invention has good oxygen barrier properties. Therefore, when the contents are accommodated as a packaging material, deterioration of the contents due to oxygen can be sufficiently suppressed. Therefore, the gas barrier film of the present invention is useful as a packaging material.

The gas barrier film of the present invention can also be used for applications other than packaging materials. Applications other than packaging materials include, for example, electronic device-related films, solar cell films, various functional films for fuel cells, and substrate films.

20 Resin substrate 30 Oxygen barrier film 100 Gas barrier film

Claims (4)

Having a resin substrate made of a polyolefin resin film and an oxygen barrier coating positioned in contact with at least one surface of the resin substrate,
The oxygen barrier film contains a water-soluble polymer (A), contains at least one of an inorganic layered mineral (B) and an aqueous polyurethane resin (C), and is a film formed from a coating agent that does not contain a polyisocyanate curing agent,
The gas barrier film, wherein the one surface has a brightness mode value of 95 or more and 133 or less as measured by the following measuring method.
<Measurement method>
An arbitrary area of 52.4 mm square on one surface of the resin base material is irradiated with telecentric illumination at an incident angle of 45.75°, reflected light with a reflection angle of 45° is captured by a camera with a telecentric lens having 4096 pixels and a sensor size of 7.04 μm per pixel to acquire a captured image, an analysis image of 1024 pixels × 1024 pixels is cut out from the captured image, the analysis image is converted to a monochrome image of 256 gradations, and the above is performed. The mode of luminance in a monochrome image is set as the mode of luminance. 2. The gas barrier film according to claim 1 , wherein the water-soluble polymer (A) is a polyvinyl alcohol resin, the degree of saponification of the polyvinyl alcohol resin is 95% or more, and the degree of polymerization of the polyvinyl alcohol resin is 300 or more. 3. The gas barrier film according to claim 1 , wherein the coating agent contains the inorganic layered mineral (B), and the content of the inorganic layered mineral (B ) is 3 to 50% by mass relative to the mass of the solid content of the coating agent. The gas barrier film according to any one of claims 1 to 3 , wherein the coating agent comprises the aqueous polyurethane resin (C), and the aqueous polyurethane resin (C) comprises an acid group-containing polyurethane resin and a polyamine compound.

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