JP7131194B2 - packaging material - Google Patents

Description

TECHNICAL FIELD The present invention relates to packaging materials, and more particularly to packaging materials including printed layers formed by digital printing.

Conventionally, flexible packaging has been printed mainly by printing methods using plates, such as gravure printing and flexographic printing. In recent years, digital printing that can meet the demand for small-lot printing has attracted attention. With digital printing, there is no need to make plates, nor is there any need for color matching. Therefore, it is possible to reduce the cost especially in the case of small-lot printing (for example, variable printing).In addition, the preparation time can be reduced, which leads to shortening of the lead time.

Japanese Patent Laid-Open No. 2002-200003 discloses a flexible package using liquid electrophotography (LEP) and a method of manufacturing the same. US Pat. No. 5,300,001 discloses a primer composition suitable for printing on flexible packaging by an inkjet method.

WO2016/074716 JP 2016-69654 A

By the way, packaging materials used for food packaging are required to prevent deterioration of contents. Laminated films containing a layer (gas barrier layer) having barrier properties against oxygen and water vapor are widely used as food packaging materials. As food packages suitable for long-term storage, there are also known packages subjected to heat sterilization such as retort treatment and boiling treatment. In recent years, the demand for packaging materials with gas barrier properties has increased due to social issues such as food loss reduction and sustainability. Improving the preservability of foods by packaging materials for retort pouches meets the above requirements. Since retort food is manufactured through a process of pressurized heat sterilization at a temperature of 100° C. or higher, packaging materials used therefor are resistant to such environments.

According to the studies of the present inventors, the ink materials used in each of the digital printing methods described above are limited. The adhesion of the ink (printing layer) to the surface is insufficient. In particular, there is no barrier film on the market for digital printing that can withstand retort processing. One of the reasons for this is that a barrier film including a gas barrier layer differs in printability from a substrate film (eg, polyethylene terephthalate (PET) film).

An object of the present invention is to provide a packaging material that can achieve sufficiently high levels of both adhesion of a digitally printed layer to a surface to which digital printing is applied and gas barrier properties.

The packaging material according to the present invention comprises a substrate film, a gas barrier layer, and a coat layer in this order, the coat layer containing particles having an average particle diameter D of 5 nm to 100 nm, and an atomic force microscope. It has a printing surface with a maximum height roughness Rz of 100 nm to 1000 nm measured by , and a digital printing layer is formed on the printing surface. The coating layer contains particles with an average particle diameter within a predetermined range and has a printing surface having a maximum height roughness Rz within a predetermined range mainly due to this, so that digital printing (e.g., Even in the case of printing by an electrophotographic method and an inkjet method), excellent adhesion between the printed surface and the digitally printed layer can be achieved. The inventors presume that this is due to the anchoring effect.

The content of the particles in the coat layer can be, for example, 50% by mass or more based on the mass of the coat layer. The ratio Ra/D between the arithmetic average roughness Ra of the printed surface measured with an atomic force microscope and the average particle diameter D of the particles is preferably 0.25-4. By setting the ratio Ra/D within this range, it is possible to suppress variations in the thickness of the coat layer due to aggregation of the particles, and it is possible to suppress the shedding of the particles and the accompanying peeling of the printed layer.

In the present invention, the coat layer may have retort odor adsorption performance. Specifically, the coat layer may contain at least one of zinc particles and zinc compound particles as the particles. Protein-constituting amino acids include sulfur-containing amino acids (methionine, cystine, cysteine, etc.). Meat products and egg products containing a large amount of sulfur-containing amino acids generate an unpleasant retort odor after heating such as retorting or boiling. The retort odor originates from sulfur compounds (hydrogen sulfide, methyl mercaptan, etc.) generated by hydrolysis of sulfur-containing amino acids during heat treatment. In general, retort odor refers to a peculiar odor of so-called retort food, but the term retort odor includes the same odor that is also recognized in boiled food.

ADVANTAGE OF THE INVENTION According to this invention, the packaging material which can achieve both the adhesiveness of the digital printing layer with respect to the surface to which digital printing is performed, and gas-barrier property to a sufficiently high level is provided.

FIG. 1 is a cross-sectional view schematically showing an example of a gas barrier laminate used for manufacturing a packaging material according to the present invention. FIG. 2 is a cross-sectional view schematically showing one embodiment of a packaging material including the gas barrier laminate shown in FIG. Fig. 3(a) is a cross-sectional view schematically showing another embodiment of the gas barrier laminate, and Fig. 3(b) schematically shows an embodiment of a packaging material including the gas barrier laminate shown in Fig. 3(a). FIG. 3 is a schematic cross-sectional view; 4(a) to 4(d) are atomic force microscope images of the printed surface of the gas barrier laminate according to the example. 5(a) to 5(d) are atomic force microscope images of the printed surface of the gas barrier laminate according to the comparative example.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

<Gas barrier laminate for digital printing>
As shown in FIG. 1, the gas barrier laminate 10A according to the present embodiment comprises a substrate film 1, an adhesion layer 2, a first gas barrier layer 3a, a second gas barrier layer 3b, and a coating layer 5 which are sequentially laminated. It is characterized by

The base film 1 is not particularly limited, and any known film can be used as long as it is transparent and maintains its shape even at a heating temperature of 200° C. or higher. For example, polyester films (polyethylene terephthalate, polyethylene naphthalate, etc.), polyamide films (nylon-6, nylon-66, etc.), polystyrene films, polyvinyl chloride films, polyimide films, polycarbonate films, polyethersulfone cellulose-based films, acrylic films, cellulose-based films (such as triacetyl cellulose or diacetyl cellulose), and the like. Although not particularly limited, a film having a low heat shrinkage is preferred.

Practically, it is desirable to appropriately select the base film 1 depending on the application and required physical properties, and polyethylene terephthalate, polyamide, etc. can be used for packaging medical supplies, medicines, foods, and the like. Moreover, the thickness of the base film 1 is not particularly limited. A thickness of about 6 μm to 200 μm can be used depending on the application.

Various pretreatments such as corona treatment, plasma treatment, and flame treatment, and a coating layer such as an easy-adhesive layer may be provided on the laminated surface of the base film 1 as long as the barrier performance is not impaired.

The adhesion layer 2 is a layer also called an "anchor layer" or an "anchor coat layer". The adhesion layer 2 is provided on the base film 1 and improves the adhesion performance between the base film 1 and the first gas barrier layer 3a. The object is to obtain two effects of uniformly forming the layer 3a (inorganic vapor deposition layer) without any defects and assisting minute barrier defects of the vapor deposition film to develop high barrier performance. The adhesion layer 2 may not necessarily be provided when sufficient adhesion can be obtained by subjecting the laminated surface of the base film 1 to various pretreatments as described above.

Non-aqueous resins are preferable as the material constituting the adhesion layer 2 that exhibits the above effects. phenol and the like. Considering the hot water resistance of the adhesion layer 2, it is more preferable to contain an organic polymer having at least one urethane bond and one or more urea bonds.

Even if the above urethane bond and urea bond use a polymer introduced in advance at the polymerization stage, polyols such as acrylic and methacrylic polyols and isocyanate compounds having isocyanate groups, or amine resins having amino groups and epoxy groups and glycidyl groups A urethane bond is formed by reacting an epoxy compound with a good too. Among these, the non-aqueous resin constituting the adhesion layer 2 is more preferably a composite of an acrylic polyol, a polyester polyol, an isocyanate compound, a silane coupling agent, or the like.

Acrylic polyol is a polymer compound obtained by polymerizing an acrylic acid derivative monomer or a polymer compound obtained by copolymerizing an acrylic acid derivative monomer and other monomers, and has a terminal hydroxyl group. , reacts with the isocyanate group of the isocyanate compound to be added later. Polyester polyols include terephthalic acid, isophthalic acid, phthalic acid, methylphthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, succinic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, Acid raw materials such as hexahydrophthalic acid and reactive derivatives thereof, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-hexanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, A polyester resin obtained by a well-known production method from alcohol raw materials such as neopentyl glycol, bishydroxyethyl terephthalate, trimethylolmethane, trimethylolpropane, glycerin, and pentaerythritol, and having two or more hydroxyl groups at the inner terminal. and is reacted with the isocyanate group of the isocyanate compound to be added later.

The isocyanate compound is added to enhance the adhesion to the base material and inorganic oxides through urethane bonds formed by reaction with acrylic polyols and polyester polyols, and mainly acts as a cross-linking agent or curing agent. In order to achieve this, the isocyanate compound includes monomers such as aromatic tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI), aliphatic xylene diisocyanate (XDI) and hexadiisocyanate (HMDI), These polymers and derivatives are used, and these are used alone or as a mixture.

As the silane coupling agent, any silane coupling agent containing an organic functional group can be used, such as ethyltrimethoxysilane, vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane. , glycidoxypropyltrimethoxysilane, .gamma.-methacryloxypropyltrimethoxysilane, .gamma.-methacryloxypropylmethyldimethoxysilane, or a hydrolyzate thereof.

The adhesion layer 2 is formed through a process of applying a coating liquid on the surface of the base film 1 . As the coating method, the commonly used casting method, dipping method, roll coating method, gravure coating method, screen printing method, reverse coating method, spray coating method, kit coating method, die coating method, metering bar coating method, chamber doctor combination. Conventionally known methods such as a coating method and a curtain coating method can be used. The adhesion layer 2 is formed by heating and drying the coating film formed by applying the coating liquid. The thickness of the adhesion layer 2 is, for example, about 0.01 μm to 2 μm.

The first gas barrier layer 3a is a layer formed by vapor deposition of an inorganic material. Aluminum oxide (AlOx), silicon oxide (SiOx), magnesium fluoride (MgF ₂ ), magnesium oxide (MgO), indium-tin oxide (ITO), or the like can be used as a material having a high oxygen gas barrier property. Aluminum oxide or silicon oxide, which are inorganic oxides, are preferred in terms of material cost, barrier performance, and transparency.

The thickness of the first gas barrier layer 3a may be appropriately set according to the intended use, preferably 10 nm to 300 nm, more preferably 20 nm to 200 nm. When the thickness of the first gas barrier layer 3a is 10 nm or more, the continuity of the first gas barrier layer 3a can be easily made sufficient, and when it is 300 nm or less, curling and cracking can be sufficiently suppressed. , it is easy to achieve sufficient barrier performance and flexibility.

The first gas barrier layer 3a can be deposited by vacuum deposition means. It is preferable from the viewpoint of oxygen gas barrier performance and film uniformity. Film formation means include known methods such as a vacuum deposition method, a sputtering method, and a chemical vapor deposition method (CVD method), but the vacuum deposition method is preferred because of its high film formation speed and high productivity. Among vacuum evaporation methods, electron beam heating is particularly effective because the film formation rate can be easily controlled by adjusting the irradiation area and electron beam current, and heating and cooling of the evaporation material can be performed in a short period of time. be.

The second gas barrier layer 3b is a layer formed by coating the surface of the first gas barrier layer 3a with a polycarboxylic acid-based polymer. A polycarboxylic acid-based polymer is a polymer having two or more carboxyl groups in its molecule. Specific examples of polycarboxylic acid polymers include homopolymers of α,β-monoethylenically unsaturated carboxylic acids; copolymers of at least two types of α,β-monoethylenically unsaturated carboxylic acids; - Copolymers of monoethylenically unsaturated carboxylic acids and other ethylenically unsaturated monomers; acidic polysaccharides having carboxyl groups in their molecules, such as alginic acid, carboxymethylcellulose, and pectin. These polycarboxylic acid-based polymers are used alone or in combination of at least two.

Specific examples of α,β-monoethylenically unsaturated carboxylic acids are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid. Specific examples of ethylenically unsaturated monomers copolymerizable with α,β-monoethylenically unsaturated carboxylic acids include ethylene, propylene, saturated carboxylic acid vinyl esters such as vinyl acetate, alkyl acrylates, and alkyl methacrylates. , alkyl itaconates, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and styrene.

When the polycarboxylic acid polymer is a copolymer of an α,β-monoethylenically unsaturated carboxylic acid and a saturated carboxylic acid vinyl ester such as vinyl acetate, the polycarboxylic acid polymer is saponified. , the saturated carboxylic acid vinyl ester moiety is converted to vinyl alcohol.

When the polycarboxylic acid polymer is a copolymer of α,β-monoethylenically unsaturated carboxylic acid and other ethylenically unsaturated monomers, from the viewpoint of gas barrier properties and water resistance, α , β-monoethylenically unsaturated carboxylic acid is 60 mol % or more, more preferably 80 mol % or more, still more preferably 90 mol % or more, and most preferably 100 mol %.

When the polycarboxylic acid-based polymer is a polymer consisting only of α,β-monoethylenically unsaturated carboxylic acid, the polymer includes acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and croton. It is obtained by polymerization of at least one polymerizable monomer selected from the group consisting of acids. The polymer is preferably obtained by polymerization of at least one monomer selected from acrylic acid, methacrylic acid and maleic acid. The polymer is more preferably obtained by polymerization of polyacrylic acid, polymethacrylic acid, polymaleic acid and/or mixtures thereof.

When the polycarboxylic acid polymer is an acidic polysaccharide, alginic acid is preferably used as the monomer component. The number average molecular weight of the polycarboxylic acid polymer is not particularly limited. The number average molecular weight is preferably in the range of 2,000 to 10,000,000, more preferably in the range of 5,000 to 1,000,000 from the viewpoint of coatability. Other polymers may be mixed with the polycarboxylic acid-based polymer within a range that does not impair the oxygen gas barrier properties of the packaging material of the present invention.

The resin layer containing the polycarboxylic acid-based polymer may consist of a mixture of the polycarboxylic acid-based polymer and polyalcohols. Polyalcohols include low-molecular-weight compounds having two or more hydroxyl groups in the molecule and alcoholic polymers. Polyalcohols include polyvinyl alcohol (PVA), sugars and starches. Specific examples of low molecular weight compounds having two or more hydroxyl groups in the molecule are glycerin, ethylene glycol, propylene glycol, 1,3-propanediol, pentaerythritol, polyethylene glycol and polypropylene glycol. The degree of saponification of PVA is 95% or more, preferably 98% or more, and the average degree of polymerization of PVA is 300-1500. A vinyl alcohol-poly(meth)acrylic acid copolymer containing vinyl alcohol as a main component is used as the polyalcohol from the viewpoint of compatibility with the polycarboxylic acid-based polymer. Monosaccharides, oligosaccharides and polysaccharides are used as sugars. These sugars include sugar alcohols such as sorbitol, mannitol, dulcitol, xylitol, erythritol, substituted sugar alcohols, and sugar alcohol derivatives described in JP-A-7-165942. Preferred sugars are dissolved in water, alcohol, or a mixed solvent of water and alcohol. Starches are included in polysaccharides. Specific examples of starches are raw starch (unmodified starch) such as wheat starch, corn starch, potato starch, tapioca starch, rice starch, sweet potato starch, sago starch, and various processed starches. Specific examples of modified starch include physically modified starch, enzymatically modified starch, chemically modified starch, and graft starch obtained by graft-polymerizing a monomer to starch. Among these starches, water-soluble processed starch obtained by hydrolyzing potato starch with acid, and sugar alcohol obtained by substituting hydroxyl groups for terminal groups (aldehyde groups) of starch are preferred. The starches may be hydrous. These starches are used alone or in combination of two or more.

The mixing ratio (mass ratio) between the polycarboxylic acid-based polymer and the polyalcohol is preferably 99:1 to 20:80 from the viewpoint of obtaining a molded article having excellent oxygen gas barrier properties even under high humidity conditions. More preferably 95:5 to 40:60, most preferably 95:5 to 50:50.

A coating liquid A containing a polycarboxylic acid-based polymer and a solvent, or a coating liquid B containing a polycarboxylic acid-based polymer, polyalcohols and a solvent is coated on the first gas barrier layer 3a, and then the solvent is evaporated. dried. Through the above steps, a resin layer containing a polycarboxylic acid-based polymer is formed on the first gas barrier layer 3a. In the method of coating the first gas barrier layer 3a with the coating liquid A containing the polycarboxylic acid polymer and the solvent, the coating liquid A containing the monomer is coated on the first gas barrier layer 3a and exposed to ultraviolet rays or electrons. A method in which a layer containing a polycarboxylic acid-based polymer is formed by irradiating with a ray, a monomer is vapor-deposited on a substrate, and an electron beam is irradiated to polymerize the polycarboxylic acid. Included are methods in which a layer comprising a system polymer is formed.

A coating liquid A containing a polycarboxylic acid polymer and a solvent is prepared by dissolving or dispersing a polycarboxylic acid polymer in a solvent. The solvent is not particularly limited as long as it can uniformly dissolve or disperse the polycarboxylic acid polymer. Specific examples of solvents are water, methyl alcohol, ethyl alcohol, isopropyl alcohol, dimethylsulfoxide, dimethylformamide, dimethylacetamide. Non-aqueous solvents or mixtures of non-aqueous solvents and water are preferably used as solvents. A preferable concentration of the polycarboxylic acid-based polymer in the coating liquid is 0.1 to 50% by mass.

The method of obtaining the coating liquid B containing the polycarboxylic acid polymer, polyalcohols and solvent is not particularly limited. Specific examples of the method for obtaining the coating liquid B include a method in which each component is dissolved in a solvent, a method in which solutions of each component are mixed, a method in which a monomer containing a carboxyl group is polymerized in a polyalcohol solution, and, if desired, a It is a method that is neutralized with alkali later. Examples of solvents are water, alcohols, mixtures of water and alcohols. A preferable solid content concentration in the coating liquid is 1 to 30% by mass.

Other polymers, softeners, plasticizers (excluding low-molecular-weight compounds having two or more hydroxyl groups in the molecule), stabilizers, anti-blocking agents, adhesives, inorganic layered compounds such as montmorillonite, etc., can be used in the present invention. It may be added to the coating liquids A and B as appropriate within a range that does not impair the oxygen gas barrier properties of the packaging material.

A compound containing a monovalent and/or divalent metal may be added to the coating liquid A from the viewpoint of oxygen gas barrier properties. Specific examples of monovalent and/or divalent metals are sodium, potassium, zinc, calcium, magnesium, copper. Specific examples of compounds containing monovalent and/or divalent metals are sodium hydroxide, zinc oxide, calcium hydroxide and calcium oxide. A preferred addition amount of the compound containing a monovalent and/or divalent metal is in the range of 0 to 70 mol % of the carboxyl groups of the polycarboxylic acid polymer. A more preferable addition amount of the compound containing a monovalent and/or divalent metal is in the range of 0 to 50 mol % of the carboxyl groups of the polycarboxylic acid polymer.

In order to improve the oxygen gas barrier property of the resin layer containing a polycarboxylic acid polymer and polyalcohols, the film obtained by drying the coating liquid B coated on the first gas barrier layer 3a may be heat-treated. In order to relax the heat treatment conditions, a water-soluble alkali metal compound or a metal salt of an inorganic acid or an organic acid is added as appropriate when preparing the coating liquid B. Specific examples of metals are alkali metals such as lithium, sodium and potassium. Specific examples of metal salts of inorganic or organic acids are lithium chloride, sodium chloride, potassium chloride, sodium bromide, sodium phosphinate (sodium hypophosphite), disodium hydrogen phosphite, disodium phosphate, ascorbic sodium acetate, sodium acetate, sodium benzoate, and sodium hyposulfite. Among these exemplified metal salts, phosphinate metal salts (hypophosphite metal salts) such as sodium phosphinate (sodium hypophosphite) and calcium phosphinate (calcium hypophosphite) are preferably used. be. The amount of inorganic acid and organic acid metal salt added is preferably 0.1 to 40 parts by mass, more preferably 1 to 30 parts by mass, per 100 parts by mass of the solid content in the coating liquid. Further, specific examples of alkali metal compounds are lithium hydroxide, sodium hydroxide and potassium hydroxide. The amount of the alkali metal compound added is within the range of 0 to 30 mol % of the carboxyl groups of the polycarboxylic acid polymer.

The coating liquid A or B is applied onto the first gas barrier layer 3a by an air knife coater, a kiss roll coater, a metering bar coater, a gravure roll coater, a reverse roll coater, a dip coater, a die coater, a sprayer, or the like, or It is coated by the apparatus which combined them. Next, the solvent contained in the coating liquid A or B is sprayed with hot air by a device such as an arch dryer, straight bath dryer, tower dryer, floating dryer, drum dryer, infrared dryer, or a device combining them, infrared It is evaporated by drying means such as irradiation, air drying, drying in an oven. As a result, a film made of a polycarboxylic acid-based polymer is formed on the first gas barrier layer 3a.

When the coating liquid A or B is coated on the first gas barrier layer 3a, the first gas barrier layer 3a and a resin layer containing a polycarboxylic acid-based polymer or a layer containing a polyvalent metal compound (polyvalent metal compound-containing layer), an adhesive may be coated in advance on the first gas barrier layer 3a. The adhesive is not particularly limited. Specific examples of adhesives include solvent-soluble alkyd resins, melamine resins, acrylic resins, nitrocellulose, urethane resins, polyester resins, phenolic resins, amino resins, and fluorine resins, which are used as dry laminates, anchor coats, and primers. It is an adhesive containing resin such as resin and epoxy resin.

The thickness of the second gas barrier layer 3b may be appropriately set depending on the intended use, but is preferably 10 μm or less. By setting the thickness of the second gas barrier layer 3b to 10 μm or less, deterioration of the barrier properties due to cracks can be easily suppressed. The lower limit of the thickness of the second gas barrier layer 3b is, for example, 0.01 μm, and may be 0.03 μm or 0.1 μm, from the viewpoint of the gas barrier property and the film forming property of the coating liquid. .

The coat layer 5 contains particles with an average particle diameter D of 5 nm to 100 nm, and has a printed surface 5f with a maximum height roughness Rz measured with an atomic force microscope of 100 nm to 1000 nm. When the maximum height roughness Rz of the printing surface 5f is 100 nm or more, the ink constituting the digital printing layer 12 (see FIG. 2) sufficiently permeates into the coating layer 5 side, thereby forming the printing surface 5f and the digital printing layer. Excellent adhesion with 12 can be achieved. The lower limit of the maximum height roughness Rz of the printing surface 5f may be 110 nm or 120 nm. On the other hand, when the maximum height roughness Rz of the printing surface 5f is 1000 nm or less, excessive aggregation of particles or uneven coating of the coating layer 5 may cause particles to fall off or cause damage to the digital printing layer 12. Delamination can be sufficiently suppressed. The upper limit of the maximum height roughness Rz of the printing surface 5f may be 900 nm or 800 nm.

When the average particle diameter D of the particles is 5 nm or more, excessive aggregation of the particles can be suppressed. The lower limit of the average particle diameter D may be 6 nm or 7 nm. On the other hand, when the average particle diameter D of the particles is 100 nm or less, the fine particles agglomerate on the coat layer 5 to form a complicated uneven surface, so that a large anchor effect can be produced. The upper limit of the average particle diameter D may be 90 nm or 80 nm. The "average particle size" used herein means a value determined using a laser diffraction/scattering particle size distribution analyzer.

The content of the particles in the coat layer 5 can be, for example, 50% by mass or more based on the mass of the coat layer 5 . When the particle content is 50% by mass or more, the leveling effect of the binder resin or the like can be suppressed, and the maximum height roughness Rz can be increased. The lower limit of the particle content may be, for example, 60% by mass. The upper limit of the particle content may be, for example, 95% by mass or 90% by mass. When the particle content is 95% by mass or less, it is possible to suppress the falling off of the particles.

The ratio Ra/D between the arithmetic average roughness Ra of the printed surface 5f measured with an atomic force microscope and the average particle diameter D of the particles is preferably 0.25-4. By setting the ratio Ra/D within this range, it is possible to suppress variations in the thickness of the coat layer 5 due to aggregation of the particles, and it is possible to suppress the shedding of the particles and the accompanying peeling of the printed layer.

The thickness of the coat layer 5 is preferably 0.05 to 10 μm. By setting the thickness of the coat layer 5 to 0.05 μm or more, it is easy to form the coat layer 5 having a sufficiently uniform thickness. The lower limit of the thickness of the coat layer 5 may be 0.1 μm or 0.2 μm. Cohesive failure of the coat layer 5 can be suppressed by setting the thickness of the coat layer 5 to 10 μm or less. The upper limit of the thickness of the coat layer 5 may be 5 μm or 3 μm.

The coat layer 5 may have retort odor adsorption performance. Specifically, the coat layer 5 may contain at least one of zinc particles and zinc compound particles as particles. Examples of zinc compounds include oxides, hydroxides, carbonates, organic acid salts, and inorganic acid salts of zinc, and preferred specific examples include zinc oxide, zinc hydroxide, zinc carbonate, zinc acetate, and phosphoric acid. zinc. The toxicity of zinc is low, and zinc sulfide (white), which is produced when zinc reacts with hydrogen sulfide, which causes retort odor, has almost no effect on the appearance of the package. When the particles are zinc oxide, the zinc oxide migrates to the second gas barrier layer 3b during retorting, thereby polymerizing the components (eg, polycarboxylic acid polymer) contained in the second gas barrier layer 3b. may proceed further. Hereinafter, zinc particles and/or zinc compound particles are referred to as "zinc-containing particles".

The content of the zinc-containing particles in the coat layer 5 is preferably 32.7 mg/m ^{2 or more, more preferably 65.4 mg/m 2 or} more, as zinc per unit area (1 m ² ) of the coat layer 5. It is more preferably 131 mg/m ² or more, and particularly preferably 196 mg/m ² or more. As the content of the zinc-containing particles increases, the retort odor absorption effect increases, but the flavor of the contents may be impaired. For example, when a food such as a garlic seasoning product in which the flavor derived from a sulfur-containing compound is important is packaged with a packaging material containing a large amount of zinc-containing particles, the flavor of the food tends to be impaired.

<Packaging material including digital printing layer>
FIG. 2 is a cross-sectional view showing an embodiment of a packaging material including the gas barrier laminate 10A shown in FIG. As shown in FIG. 2, the packaging material 20A includes a gas barrier laminate 10A, a digitally printed layer 12 formed on the printed surface 5f of the coat layer 5, an adhesive layer 13, an intermediate resin film 15, and an adhesive layer 16. , and a sealant film 18 in that order. The intermediate resin film 15 is employed for improving impact resistance and puncture resistance. As the intermediate resin film 15, a biaxially oriented nylon (ONY) film, a biaxially oriented polypropylene (OPP), or the like can be used. The sealant film 18 has heat sealability, and a specific example thereof is a non-stretched polypropylene (CPP) film. The digital printing layer 12 and the intermediate resin film 15 are bonded together with the adhesive layer 13 interposed therebetween, and the intermediate resin film 15 and the sealant film 18 are bonded together with the adhesive layer 16 interposed therebetween.

The digital print layer 12 is a layer formed by digital printing. Applicable digital printing methods include liquid electrophotography (LEP) methods and inkjet (IJ) methods. In either method, a digital printing layer is pattern-formed without a plate on the printing surface 5f of the coat layer 5 of the gas barrier laminate 10A. A primer layer may be formed between the coat layer and the digital print layer to improve adhesion between the coat layer and the digital print layer. The primer layer may be patterned or may be formed solid (over the entire surface). Similar to the adhesion layer 2, the film thickness is about 0.02 to 2 μm, and since it is transparent, it does not affect the visibility of the digitally printed layer. As the material, the same material as that of the adhesion layer can be used.

Electrophotographic printing is applied to various fields such as copiers, point-of-sale terminal printers, facsimiles, and small-run printers. Toners used in electrophotographic printing are roughly classified into dry toners and liquid toners (electrophotographic inks). Electrophotographic ink is suitable for high-precision printing because toner particles are less likely to scatter and the toner particles can be finer than dry toner. A system using this electrophotographic ink is called a liquid electrophotographic (LEP) system. Indigo manufactured by Hewlett-Packard Company is known as an LEP digital printing apparatus.

In the case of the LEP method, as the composition of the LEP ink and the primer layer, for example, those exemplified in International Publication No. 2016/074716 can be used. The composition of the LEP ink includes, for example, a colorant such as a pigment or dye, an ionic compound (charge director) for charging the LEP ink, a resin composition such as an acrylic resin, a solvent, and other additives. .

The inkjet (IJ) method is a method of patterning by directly ejecting ink onto a printing object. In this embodiment, the digital print layer 12 may be formed by ejecting ink directly onto the coat layer 5 . UV ink is preferably used as the IJ ink. It is because it is excellent in heat resistance. Compositions of IJ inks include UV inks. The UV ink contains, for example, a polymerizable monomer such as an acrylate compound, a photopolymerization initiator, a colorant such as a pigment or dye, a dispersant, and other additives.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, when the gas barrier laminate is used for applications that do not require a very high gas barrier property, as shown in FIG. good too. A gas barrier laminate 10B shown in this figure is composed of a substrate film 1, a gas barrier layer 3 and a coat layer 5. As shown in FIG. The gas barrier layer 3 may have the same configuration as the first gas barrier layer 3a or the same configuration as the second gas barrier layer 3b. FIG. 3(b) is a cross-sectional view showing an embodiment of a packaging material including the gas barrier laminate 10B shown in FIG. 3(a). As shown in FIG. 3B, the packaging material 20B includes the gas barrier laminate 10B, the digital print layer 12 formed on the print surface 5f of the coat layer 5, the adhesive layer 13, the intermediate resin film 15, and the adhesive A layer 16 and a sealant film 18 are provided in that order. As with the packaging material 20A, the intermediate resin film 15 of the packaging material 20B may be biaxially oriented nylon (ONY) film, biaxially oriented polypropylene (OPP), or the like.

Examples of the present invention will be described below. The invention is not limited to the following examples.

[Example]
<Coating liquid for forming adhesion layer>
Adhesive solution (main agent: Takelac A-525/curing agent: Takenate A-52/solvent: ethyl acetate) manufactured by Mitsui Chemicals, Inc. was used to prepare a coating solution for forming an adhesion layer (solid concentration: 3% by mass). did. In preparing the coating liquid, the weight ratio of A-525:A-52:ethyl acetate was 9:1:165.

<Coating liquid containing polycarboxylic acid>
20 g of an aqueous polyacrylic acid solution having a number average molecular weight of 200,000 (manufactured by Toagosei Co., Ltd., Aron A-10H, solid concentration: 25% by mass) was dissolved in 58.9 g of distilled water. After adding 0.44 g of aminopropyltrimethoxysilane (manufactured by Aldrich) to this, the mixture was stirred to obtain a polycarboxylic acid-containing coating liquid.

<Coating liquid for coating layer formation>
A fine particle zinc oxide dispersion (ZS303 manufactured by Sumitomo Osaka Cement, average particle size: 20 nm, solid concentration: 30% by mass, dispersion solvent: toluene) was prepared as a coating liquid for forming a coating layer.

<Fabrication of gas barrier laminate>
The coating solution for forming an adhesion layer was applied to the corona-treated side of a biaxially stretched polyethylene terephthalate film (PET: Lumirror (registered trademark) P60, thickness 12 μm, manufactured by Toray Industries, Inc.) as a base film. An adhesion layer was formed by coating with a bar coater to a thickness of 0.2 μm and drying at 150° C. for 1 minute.
On this adhesion layer, metal aluminum is evaporated by a vacuum deposition apparatus using an electron beam heating method, oxygen gas is introduced therein, and aluminum oxide is deposited to deposit an inorganic deposition layer (first gas barrier layer) having a thickness of 20 nm. formed.
Next, the polycarboxylic acid-containing coating solution is applied onto the inorganic deposition layer using a bar coater so that the thickness after drying is 1 μm, dried at 80° C. for 5 minutes, and then A polycarboxylic acid-containing layer (second gas barrier layer) was formed by aging treatment at 50° C. for 3 days and further heat treatment at 200° C. for 5 minutes.
Furthermore, a zinc oxide particle-containing coating solution was applied onto the polycarboxylic acid-containing layer using a bar coater so that the thickness after drying was 1 μm, and then dried at 90° C. for 2 minutes to obtain A zinc oxide particle-containing layer (coat layer) was formed. The content of zinc oxide particles in the zinc oxide particle-containing layer was 80% by mass.

[Comparative example]
In place of the gas barrier layer of the above example, an organic-inorganic hybrid film (film containing no particles) was formed by mixing a hydrolyzate of tetraethoxysilane and polyvinyl alcohol to form the gas barrier layer. A gas barrier laminate was produced in the same manner as in the example.

<Measurement of surface roughness of printed surface>
The surface roughness of the coating layer surface (printed surface) of the gas barrier laminates obtained in Examples and Comparative Examples was measured using an atomic force microscope (SPM, MFP-3D (manufactured by Asylum Research)). An atomic force microscope is a type of scanning probe microscope (SPM). 4 and 5 show SPM images (four points N1 to N4) of the printed layers according to the example and the comparative example, respectively. Table 1 shows the measurement results of the arithmetic mean roughness Ra and the maximum height roughness Rz (average values of four points N1 to N4). Note that tilt correction was performed on the measurement results.
・Cantilever: OMCL-AC160TS (manufactured by Olympus)
・Measurement mode: AC mode ・Measurement range: 2 μm×2 μm
・Measurement frequency: 1 Hz (example), 0.5 Hz (comparative example)

<Implementation of digital printing>
Digital printing was performed on the surface (printed surface) of the coat layer of the gas barrier laminates obtained in Examples and Comparative Examples. The digital printing was performed by Hewlett-Packard's Indigo (LEP printing technology using electro-ink).

<Digital printing ink adhesion evaluation>
Ink adhesion in digital printing in Examples and Comparative Examples was evaluated as follows. That is, an adhesive tape (manufactured by Nichiban, width: 15 mm) was attached to the digitally printed surface and pressed three times with a finger. After that, the adhesive tape was peeled off, and the extent to which the ink was transferred to the adhesive tape was visually evaluated according to the following criteria. This evaluation was performed immediately, 3 days and 5 days after digital printing, respectively. Table 1 shows the results.
A: No ink was transferred to the adhesive tape.
B: The ink was slightly transferred to the adhesive tape.
C: About half of the ink was transferred to the adhesive tape.
D: Most of the ink was transferred to the adhesive tape.
E: The ink was completely transferred to the adhesive tape.

DESCRIPTION OF SYMBOLS 1... Base film, 2... Adhesion layer, 3... Gas barrier layer, 3a... First gas barrier layer, 3b... Second gas barrier layer, 5... Coat layer, 5f... Print surface, 10A, 10B... Gas barrier laminate, 12... Digital printing layer, 20A, 20B... Packaging material

Claims (3)

a base film;
a gas barrier layer;
a coat layer;
in this order,
The coat layer contains particles having an average particle diameter D of 5 nm to 100 nm, and has a printed surface having a maximum height roughness Rz measured with an atomic force microscope of 100 nm to 1000 nm,
the particles are at least one of zinc particles and zinc compound particles;
A packaging material, wherein a digitally printed layer is formed on the printed surface. The packaging material according to claim 1, wherein the content of the particles in the coat layer is 50% by mass or more based on the mass of the coat layer. The packaging according to claim 1 or 2, wherein the ratio Ra/D between the arithmetic mean roughness Ra of the printed surface measured with an atomic force microscope and the average particle diameter D of the particles is 0.25 to 4. material.

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