JP7735869B2 - Metallized paper - Google Patents

Description

The present invention relates to metallized paper.

Paper-based packaging materials with added water vapor barrier properties to block water vapor, gas barrier properties to block gases other than water vapor, and especially oxygen barrier properties to block oxygen, have traditionally been used to package food, medical products, electronic components, and other items to prevent deterioration of the contents.

Metal-deposited paper has a vapor-deposited layer of metal or metal oxide on a paper base material, and taking advantage of its glossy finish, it is widely used for decorative label paper for alcoholic beverages and soft drinks, as well as wrapping paper for confectionery.

For example, Patent Document 1 discloses a metal-deposited paper having, on one side of a paper substrate, a laminate layer of ethylene-alpha-olefin copolymer polymerized using a single-site catalyst and a thin film of inorganic oxide, in that order. Furthermore, Patent Document 2, for example, discloses a sealing sheet for PTP packaging in which, on one side of tissue paper having a basis weight of a specific value or less, a filler coating layer made of a polyolefin-based aqueous dispersion liquid, a thin vapor-deposited layer of inorganic oxide, and a heat-seal resin layer are formed in that order.

Japanese Patent Application Publication No. 10-202781 Japanese Patent Application Publication No. 7-223686

As in Patent Documents 1 and 2, attempts have been made to improve the barrier properties of paper substrates against oxygen and water vapor by forming a vapor-deposited layer, but it has been found that the vapor-deposited paper described in Patent Document 1 and the PTP packaging sealing sheet described in Patent Document 2 have the problem of poor barrier properties (oxygen barrier properties).

Metal-plated paper used as a food packaging material is required to have improved barrier properties (oxygen barrier property and water vapor barrier property) to protect the flavor of food. In addition, improved recyclability is required to reduce the environmental impact of materials. Therefore, the object of the present invention is to provide metal-plated paper with excellent barrier properties and recyclability.

The inventors discovered that the above problems could be solved by adjusting the water absorption and surface properties of the metallized paper, leading to the completion of the present invention.

That is, the present invention relates to the following items <1> to <15>.
<1> A metal-deposited paper having a coating layer, a vapor-deposited layer, and an overcoat layer on one side of a paper base material in this order, wherein the Cobb water absorbency of the surface on the overcoat layer side measured in accordance with JIS P 8140:1998 at a temperature of 23°C for a contact time of 120 seconds is 1.0 g/ ^m2 or less, the Cobb water absorbency of the surface opposite to the overcoat layer side measured in accordance with JIS P8140:1998 at a temperature of 23°C for a contact time of 120 seconds is 10 g/ ^m2 or more, and the surface specific electrical resistivity of the overcoat layer side measured in accordance with JIS C 2139:2008 is 1.0 x ¹⁰¹² Ω or more, and when a 20 μm-thick unstretched polypropylene film is laminated on the overcoat layer of the metal-deposited paper to form a laminate sheet, the metal-deposited paper satisfies JIS K 7126-2:2006, the oxygen permeability of the laminated sheet at a temperature of 23°C and a relative humidity of 50% is 2.0 mL/ ^m2 ·day·atm or less.
<2> The metal-deposited paper according to <1>, which has a water vapor transmission rate of 1.0 g/m ^{2 ·day or less at a temperature of 40°C and a relative humidity of 90%, as measured in accordance with JIS Z 0208:1976} (cup method) B method.
<3> The metal-deposited paper according to <1> or <2>, wherein the coating layer has a clay coating layer and a resin layer in this order from the paper substrate side.
<4> The metal-deposited paper according to <3>, wherein the resin layer and the overcoat layer contain a water-dispersible polymer.
<5> The metal-deposited paper according to <4>, wherein the water-dispersible polymer contained in the resin layer and the overcoat layer includes at least one resin selected from the group consisting of polyester-based resins and polyurethane-based resins.
<6> The metal-deposited paper according to <5>, wherein the polyurethane resin, when formed into a sheet having a thickness of 25 μm, has an oxygen permeability of 100.0 mL/(m ² ·day ·atm) or less at 23° C. and 50% RH.
<7> The metal-deposited paper according to <5> or <6>, wherein the polyurethane resin contains at least one selected from the group consisting of a structural unit derived from metaxylylene diisocyanate and a structural unit derived from hydrogenated metaxylylene diisocyanate.
<8> The metal-deposited paper according to any one of <5> to <7>, wherein the polyurethane resin has a hydroxy group and a hydroxyl value of 50 mgKOH/g or more.
<9> The metal-deposited paper according to any one of <5> to <8>, wherein the polyurethane resin has a total content of meta-xylylene diisocyanate-derived structural units and hydrogenated meta-xylylene diisocyanate-derived structural units of 50 mol% or more relative to the total amount of polyisocyanate-derived structural units.
<10> The metal-deposited paper according to any one of <3> to <9>, wherein the clay coating layer contains an inorganic pigment and a binder, and the inorganic pigment has an aspect ratio of 50 or less and an average particle size of 5 μm or less.
<11> The metal-deposited paper according to <10>, wherein the inorganic pigment is kaolin.
<12> The metal-deposited paper according to <10> or <11>, wherein the binder contained in the clay coating layer comprises at least one selected from the group consisting of a styrene-butadiene resin, a styrene-(meth)acrylic resin, an olefin-unsaturated carboxylic acid copolymer, and a polylactic acid. <13> The metal-deposited paper according to any one of <1> to <12>, wherein the thickness of the overcoat layer is less than 1 μm.
<14> The metal-deposited paper according to any one of <1> to <13>, wherein the metal-deposited layer is a metal-deposited layer containing an inorganic oxide, and the inorganic oxide contains at least one selected from the group consisting of silicon oxide and aluminum oxide.
<15> The metal-deposited paper according to any one of <1> to <14>, wherein the thickness of the metal-deposited layer is 10 to 1000 Å.

The present invention makes it possible to provide metallized paper with excellent barrier properties and recyclability.

The metallized paper of this embodiment has a coating layer, a metallized layer, and an overcoat layer on one side of a paper substrate in this order, and has a temperature of 23°C measured in accordance with JIS P 8140:1998.
the Cobb water absorbency of the surface opposite the overcoat layer side, measured in accordance with JIS P8140:1998, is 10 g/ ^m2 or more at 23°C for a contact time of 120 seconds; the surface opposite the overcoat layer side, measured in accordance with JIS C 2139:2008, has a surface specific electrical resistivity of 1.0 x ¹⁰¹² Ω ^or more; and when a 20 μm-thick unstretched polypropylene film is laminated onto the overcoat layer of the metallized paper to form a laminate sheet, the oxygen permeability of the laminate sheet, measured in accordance with JIS K 7126-2:2006, at 23°C and 50% relative humidity (sometimes referred to as 50% RH), is 2.0 mL/ ^m2 day atm or less. The metallized paper of this embodiment has excellent barrier properties (oxygen barrier properties and water vapor barrier properties) and recyclability. The mechanism by which these effects are achieved is unknown, but is presumed to be as follows.

By setting the Cobb water absorbency of the overcoat layer side surface of the metallized paper to 1.0 g/ ^m2 or less, a water-impermeable film with few defects is formed, thereby achieving high barrier properties. Furthermore, by setting the Cobb water absorbency of the surface opposite the overcoat layer side to 10 g/ ^m2 or more, water penetration during defibration is facilitated, resulting in high recyclability. Furthermore, by setting the surface specific electrical resistivity of the overcoat layer side surface to 1.0 x ¹⁰¹² Ω or more, metallic foreign matter is reduced, resulting in high recyclability. Furthermore, by setting the oxygen permeability at a temperature of 23°C and a relative humidity of 50% to 2.0 mL/ ^m2 ·day·atm or less, high barrier properties suitable for food packaging can be achieved. For these reasons, the metallized paper of this embodiment can exhibit excellent barrier properties and recyclability. Note that the above mechanism is based on speculation, and the mechanism by which the effects of the present invention are achieved is not limited to this.

The structure and physical properties of the waterproof paper of this embodiment are described in more detail below. In this specification, a numerical range represented by "X to Y" means a numerical range with X as the lower limit and Y as the upper limit. When a numerical range is stated in stages, the upper and lower limits of each numerical range can be combined in any combination. Furthermore, "(meth)acrylic" is a generic term that includes both acrylic and methacrylic.

The metallized paper of this embodiment has a coating layer, a vapor deposition layer, and an overcoat layer, in this order, on at least one side of the paper substrate. The coating layer preferably has a clay coating layer and a resin layer, in this order, from the paper substrate side. In this case, the clay coating layer and resin layer may be present, in this order, on one side of the paper substrate, or on both sides. However, from the perspective of production efficiency, it is preferable to have a clay coating layer and a resin layer, in this order, on one side. Furthermore, the vapor deposition layer preferably contains an inorganic oxide, preferably at least one selected from the group consisting of silicon oxide (silica) and aluminum oxide (alumina), and preferably silicon oxide (silica). From the perspective of recyclability, the metallized paper preferably has a coating layer, a vapor deposition layer, and an overcoat layer, in this order, on at least one side of the paper substrate, and more preferably has nothing laminated on the other side of the paper substrate.

<Paper base material>
The pulp constituting the paper base material in this embodiment is preferably primarily composed of plant-derived pulp, and is primarily composed of wood pulp. Examples of wood pulp include hardwood pulp and softwood pulp. Examples of non-wood pulp include cotton pulp, hemp pulp, kenaf pulp, and bamboo pulp. Materials other than pulp fiber, such as synthetic fibers such as rayon fiber and nylon fiber, may also be blended as secondary paper materials as long as they do not impair the effects of the present invention.

The proportion of hardwood pulp in the pulp constituting the paper base material may be 65% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.
When the proportion of hardwood pulp constituting the paper base material is in the above range, the paper base material has excellent recyclability.

Specific examples of paper substrates used in the metallized paper of this embodiment include bleached kraft paper, unbleached kraft paper, fine paper, paperboard, liner paper, coated paper, one-side glazed paper, glassine paper, and graphene paper. Of these, bleached kraft paper, unbleached kraft paper, fine paper, and one-side glazed paper are preferred.

(Size)
The sizing degree of the paper substrate is not particularly limited, but from the viewpoint of improving barrier properties, it is preferable that the Stockigt sizing degree according to JIS P 8122:2004 is 1 second or more. There is no particular upper limit, but it is preferably 100 seconds or less, more preferably 30 seconds or less. The sizing degree of the paper substrate can be controlled by the type and content of the internal sizing agent, the type of pulp, smoothing treatment, etc.

Internal sizing agents include rosin-based, alkyl ketene dimer-based, alkenyl succinic anhydride-based, styrene-unsaturated carboxylic acid-based, higher fatty acid-based, and petroleum resin-based agents. The amount of internal sizing agent is not particularly limited, but is preferably 0 parts by mass or more and 3 parts by mass or less per 100 parts by mass of pulp in the paper base material.

In addition to the internal sizing agent, other known internal additives may be added to the paper base material. Examples of internal additives include fillers, paper strength agents, retention aids, pH adjusters, drainage aids, water-resistant agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, and pigments.

Examples of fillers include titanium dioxide, kaolin, talc, calcium carbonate (heavy calcium carbonate, light calcium carbonate), calcium sulfite, gypsum, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, diatomaceous earth, magnesium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide.

Paper base materials are obtained by papermaking using papermaking raw materials whose main component is pulp slurry. The pulp slurry is obtained from wood or non-wood raw material chips through processes such as cooking, washing, and bleaching. There are no particular restrictions on the methods used in the cooking, washing, and bleaching processes. The pulp slurry obtained through these processes is further beaten in the presence of water.

When making paper substrates, any known wet paper machine can be selected and used as appropriate. Examples of paper machines include Fourdrinier paper machines, gap former paper machines, cylinder paper machines, and short wire paper machines. The paper layer formed by the paper machine is preferably transported on a felt and dried in a dryer. A multi-stage cylinder dryer may also be used as a pre-dryer before drying in the dryer.

The paper substrate obtained as described above may also be subjected to a surface treatment using a calendar to achieve a uniform paper thickness and gloss profile. A known calendaring machine can be appropriately selected and used for the calendaring treatment.

(Basic weight)
The basis weight of the paper substrate is not particularly limited, but is preferably 20 g/ ^m2 or more, more preferably 30 g/ ^m2 or more, even more preferably 40 g/ ^m2 or more, and is preferably 500 g/m2 or ^less , more preferably 400 g/ ^m2 or less, even more preferably 200 g/ ^m2 or less, and even more preferably 100 g/ ^m2 or less. The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011.

(Thickness)
The thickness of the paper substrate is not particularly limited, but is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 75 μm or less. The thickness of the paper substrate is measured in accordance with JIS P 8118:2014.

(density)
From the viewpoint of formability, the density of the paper substrate is preferably 0.5 g/cm or ^more , more preferably ^0.6 g/cm or more, and is preferably 1.2 g/cm or ^less , more preferably 1.0 g/cm or ^less . The density of the paper substrate is calculated from the basis weight and thickness of the paper substrate measured by the above-mentioned method.

(Oken type smoothness)
From the viewpoint of obtaining a uniform vapor-deposited layer, the paper substrate preferably has an Oken smoothness of 5 seconds or more, more preferably 10 seconds or more, even more preferably 100 seconds or more, and even more preferably 300 seconds or more, on at least the surface on which the vapor-deposited layer is to be formed. The upper limit is not particularly limited, but is preferably, for example, 1000 seconds or less. The Oken smoothness of the paper substrate is measured in accordance with JIS P 8155:2010.

<Clay court layer>
The coating layer in the metallized paper of this embodiment preferably has a clay coat layer, and more preferably has the clay coat layer between the paper substrate and the resin layer described below. This allows the paper substrate to be sealed and smoothed, forming a flatter resin layer, which results in the formation of a uniform metallized layer when the metallized paper described below is made, improving the barrier properties.

The clay coat layer preferably contains an inorganic pigment and a binder, and more preferably is composed primarily of an inorganic pigment and a binder. Note that "the clay coat layer is composed primarily of an inorganic pigment and a binder" means that the total content of the inorganic pigment and binder in the clay coat layer is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. There is no particular upper limit, but it is 100% by mass or less. Note that the clay coat layer may further contain optional components in addition to the inorganic pigment and binder.

(inorganic pigments)
The inorganic pigment contained in the clay coating layer is not particularly limited, but examples thereof include kaolin, talc, mica, etc., and kaolin is preferred. The content of the inorganic pigment in the clay coating layer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and is preferably 98% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

<Aspect ratio>
The aspect ratio of the inorganic pigment is preferably 50 or less, more preferably 40 or less, from the viewpoint of forming a uniform and smooth resin layer and of dispersing the inorganic pigment finely in the clay coat layer to improve the disintegration properties of the base paper for metallized paper during recovery. The lower limit is not particularly limited, but is preferably 1 or more, more preferably 20 or more. The aspect ratio can be measured by observation with an electron microscope or X-ray diffraction measurement.

≪Average particle size≫
The average particle size of the inorganic pigment is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less, from the viewpoint of forming a uniform and smooth resin layer and dispersing it finely in the clay coat layer to improve the disintegration properties of the base paper for metallized paper during recovery. There is no particular lower limit, but a value of 0.05 μm or more is preferred, and a value of 0.10 μm or more is more preferred. The average particle size refers to the median diameter (d50) measured by laser diffraction/scattering particle size distribution measurement.

(binder)
The binder contained in the clay coating layer is not particularly limited, but examples thereof include styrene-butadiene resins, (meth)acrylic (co)polymers, styrene-(meth)acrylic resins, olefin-unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, polylactic acid, etc. The binder preferably contains one or more selected from the group consisting of styrene-butadiene resins, styrene-(meth)acrylic resins, olefin-unsaturated carboxylic acid copolymers, and polylactic acid, and more preferably contains one or more selected from the group consisting of styrene-(meth)acrylic resins, ethylene-(meth)acrylic acid copolymers, and polylactic acid.

The (meth)acrylic (co)polymer is a (co)polymer of one or more monomers selected from (meth)acrylic acid and (meth)acrylic acid esters. There are no particular limitations on the (meth)acrylic acid ester, but it is preferable that it be an alkyl ester of (meth)acrylic acid having 1 to 12 carbon atoms.

Styrene-(meth)acrylic resin is a copolymer of styrene and at least one monomer selected from (meth)acrylic acid and (meth)acrylic acid esters.

The binder content in the clay coating layer is preferably 2% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

The coating amount of the clay coating layer is not particularly limited, but is preferably 5 g/m2 or ^more , more preferably 7 g/ ^m2 or more, in terms of solid content, and is preferably 30 g/m2 or ^less , more preferably 20 g/ ^m2 or less.

The method for forming the clay coating layer is not particularly limited, but a preferred method is to apply a dispersion containing an inorganic pigment and a resin binder to a paper substrate and dry it. The dispersion containing an inorganic pigment and a resin binder is preferably one that uses an aqueous medium, such as an aqueous dispersion, as the solvent.

<Resin layer>
In the metallized paper of this embodiment, the coating layer preferably has a resin layer, and more preferably has a resin layer on a clay coat layer. By providing a resin layer, adhesion between the metallized layer of the metallized paper and the paper substrate is improved, improving the barrier properties. Furthermore, since the resin layer has oxygen barrier properties and water vapor barrier properties, it also has the function of improving the barrier properties of the metallized paper.

The resin layer preferably contains a water-suspendable polymer, and more preferably contains primarily a water-suspendable polymer. A water-suspendable polymer is a polymer with a solubility in water at 25°C of 10 g/L or less. Forming the resin layer using a water-suspendable polymer is thought to improve adhesion to the vapor deposition layer and result in a vapor-deposited paper with excellent barrier properties (oxygen barrier property, water vapor barrier property). The phrase "the resin layer primarily contains a water-suspendable polymer" means that the content of the water-suspendable polymer in the resin layer is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit is not particularly limited, but is 100% by mass or less. The resin layer may further contain optional components in addition to the water-suspendable polymer.

(Water-suspended polymer)
The water-dispersible polymer contained in the resin layer is not particularly limited, but examples thereof include alkyd resins; (meth)acrylic (co)polymers, styrene-(meth)acrylic resins; olefin-unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers; vinyl alcohol resins such as polyvinyl alcohol and ethylene-vinyl alcohol copolymers (ethylene-modified polyvinyl alcohol); cellulose resins; polyurethane resins; polyester resins; polylactic acid, etc. Among these, one or more selected from vinyl alcohol resins, polyurethane resins, polyester resins, and polylactic acid are preferred, and from the viewpoint of further improving biodegradability and recyclability, one or more selected from the group consisting of polyester resins, polyurethane resins, and polylactic acid are more preferred, one or more selected from the group consisting of polyurethane resins and polylactic acid are even more preferred, one or more selected from the group consisting of polyester resins and polyurethane resins are even more preferred, and polyurethane resins are even more preferred.

<Polyester resin>
The polyester-based resin contained in the resin layer is not particularly limited, and is preferably one that can be prepared into one or more types selected from the group consisting of polyester-based resin dispersions and emulsions, more preferably one that can be prepared into a polyester-based resin dispersion or emulsion, and even more preferably one that can be prepared into a polyester-based resin dispersion.

Commercially available polyester resins may be used, such as the "Elite KT Series (product name)" manufactured by Unitika Ltd. and the "Landy PL Series (product name)" manufactured by Miyoshi Oil & Fats Co., Ltd. Specific examples include Elite KT-8803 and Landy PL-3000.

<Polyurethane resin>
The polyurethane-based resin contained in the resin layer is not particularly limited, and is preferably one that can be prepared into one or more selected from the group consisting of polyurethane-based resin dispersions and emulsions, more preferably one that can be prepared into a polyurethane-based resin dispersion or emulsion, and even more preferably one that can be prepared into a polyurethane-based resin dispersion.

The polyurethane resin can be produced by a known production method. For example, the polyurethane resin can be obtained by reacting a polyisocyanate compound (e.g., a diisocyanate compound) with a polyhydroxy acid (e.g., a dihydroxy acid). Alternatively, the polyurethane resin can be obtained by reacting the polyisocyanate compound and the polyhydroxy acid with a polyol compound (e.g., a polyester polyol, a polyether polyol) and/or a chain extender.

The polyurethane resin contained in the resin layer preferably contains at least one selected from the group consisting of structural units derived from meta-xylylene diisocyanate and structural units derived from hydrogenated meta-xylylene diisocyanate. A structural unit derived from meta-xylylene diisocyanate refers to a monomer unit in a urethane resin that has reacted with meta-xylylene diisocyanate. A monomer unit refers to the form in which a monomer substance in a polymer has reacted.

When a polyurethane resin contains at least one of a meta-xylylene diisocyanate-derived structural unit and a hydrogenated meta-xylylene diisocyanate-derived structural unit, the total content of the meta-xylylene diisocyanate-derived structural unit and the hydrogenated meta-xylylene diisocyanate-derived structural unit relative to the total amount of polyisocyanate-derived structural units is preferably 50 mol% or more, more preferably 60 mol% or more. There is no particular upper limit, but it is preferably 95 mol% or less, more preferably 90 mol% or less. Such polyurethane resins exhibit high cohesion due to hydrogen bonding and the stacking effect between xylylene groups, and therefore have excellent gas barrier properties. The above content can be determined using known analytical techniques such as ^1H -NMR.

The polyurethane resin contained in the resin layer may contain hydroxyl groups, and its hydroxyl value is preferably 50 mgKOH/g or more, more preferably 100 mgKOH/g or more, and even more preferably 150 mgKOH/g or more. There is no particular upper limit to the hydroxyl value, but it is preferably 1000 mgKOH/g or less, more preferably 800 mgKOH/g or less, and even more preferably 600 mgKOH/g or less. A hydroxyl value of the polyurethane resin within the above range is preferred because it provides excellent oxygen barrier properties. The hydroxyl value is measured in accordance with JIS K0070-1992, and the number of milligrams of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl groups when 1 g of the sample is acetylated is measured.

-Oxygen permeability-
The polyurethane resin contained in the resin layer, when molded into a 25 μm thick sheet, has an oxygen permeability of 100.0 mL / (m ² · day · atm) or less at 23 ° C. and 50% RH, more preferably 50.0 mL / (m ² · day · atm) or less, even more preferably 25.0 mL / (m ² · day · atm) or less, even more preferably 10.0 mL / (m ² · day · atm) or less, particularly preferably 3.0 mL / (m ² · day · atm) or less. In addition, when molded into a 25 μm thick sheet, the oxygen permeability at 23 ° C. and 50% relative humidity may be 0 mL / (m ² · day · atm).
The oxygen permeability when molded into a 25 μm thick sheet is measured using a 25 μm thick sheet formed from the polyurethane resin in question. In this specification, the oxygen permeability is measured using an oxygen permeability measuring device (OX-TRAN2/22, manufactured by MOCON) in accordance with JIS K 7126-2:2006 under conditions of 23°C and 50% RH.

- Glass transition temperature -
From the viewpoint of protecting the vapor-deposited layer of the vapor-deposited paper described below, it is important that the polyurethane resin contained in the resin layer has high film-forming property, and the glass transition temperature is preferably 150° C. or lower, more preferably 140° C. or lower, and particularly preferably 135° C. or lower. The glass transition temperature is measured in accordance with JIS K 7122:2012.

As the polyurethane resin, a synthetic product may be used. For example, the polyurethane resin described in International Publication No. 201
Examples of the polyurethane resin include those described in Japanese Patent Application Publication No. 5/016069.

Commercially available polyurethane resins may be used, such as "Takelac W Series (product name)," "Takelac WPB Series (product name)," and "Takelac WS Series (product name)" manufactured by Mitsui Chemicals, Inc., with Takelac WPB-341 being a specific example. Other commercially available products include "HPU W-003" (hydroxyl value 235 mg KOH/g) manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

(Silane coupling agent)
From the viewpoint of improving the flex resistance of the resin layer, it is preferable that the resin layer contains, in addition to the above-mentioned water-dispersible polymer, a silane coupling agent and/or a reaction product thereof, and it is more preferable that the resin layer is formulated with a silane coupling agent.

A silane coupling agent is a compound that contains at least one alkoxysilyl group and at least one reactive functional group other than the alkoxysilyl group within the molecule. The alkoxysilyl group may be a monoalkoxysilyl group, a dialkoxysilyl group, or a trialkoxysilyl group, but from the perspective of reactivity, a trialkoxysilyl group is preferred.

Examples of reactive functional groups other than alkoxysilyl groups include vinyl groups, epoxy groups, styryl groups, (meth)acryloyloxy groups, amino groups, isocyanato groups, ureido groups, and acid anhydride groups. Of these, amino groups, epoxy groups, and acid anhydride groups are preferred, with amino groups being more preferred.

Examples of epoxy group-containing silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

Examples of amino group-containing silane coupling agents include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane. Of these, 3-aminopropyltriethoxysilane is preferred.

Examples of acid anhydride group-containing silane coupling agents include 3-trimethoxysilylpropylsuccinic anhydride.

Commercially available silane coupling agents may be used, such as KBM-303, KBM-402, KBM-403, KBE-402, KBE-403, KBM-602, KBM-603, KBM-903, KBE-903, KBE-9103P, KBM-573, and X-12-967C, all manufactured by Shin-Etsu Chemical Co., Ltd.

The amount of silane coupling agent in the resin layer is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.2 parts by mass or more, and particularly preferably 0.3 parts by mass or more, per 100 parts by mass of the water-suspendable polymer, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 1 part by mass or less.

The coating amount of the resin layer is not particularly limited, but is preferably 0.1 g/m2 or more, more preferably 1 g/ ^m2 or more, and is preferably 10 g/ ^m2 or ^less , more preferably 5 g/m2 or ^less , in terms of solid content.

The method for forming the resin layer is not particularly limited, but it is preferable to form it by applying an aqueous medium such as an aqueous solution or aqueous dispersion of a water-dispersible polymer and drying it.

<Vapour-deposited layer>
In the metallized paper of this embodiment, the metallized layer is preferably a metallized layer containing an inorganic oxide from the viewpoint of recyclability. The inorganic oxide is not particularly limited, but preferably contains at least one selected from the group consisting of silicon oxide (silica) and aluminum oxide (alumina), and more preferably contains silicon oxide (silica). The metallized layer may contain silicon oxide (silica) and aluminum oxide (alumina). When silicon oxide and aluminum oxide are used in combination, the mixing ratio (silicon oxide:aluminum oxide) is preferably 1:10 to 10:1, and more preferably 1:2 to 2:1, by mass. The metallized layer is more preferably a silicon oxide metallized layer, an aluminum oxide metallized layer, or a metallized layer consisting of a mixture of silicon oxide and aluminum oxide.

From the viewpoint of barrier properties, the thickness of the vapor-deposited layer is preferably 10 Å or more, more preferably 30 Å or more, and more preferably 50 Å or more. On the other hand, from the viewpoint of film-forming properties, the upper limit is preferably 1000 Å or less, more preferably 500 Å or less, and even more preferably 200 Å or less. In other words, the thickness of the vapor-deposited layer is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. On the other hand, the upper limit is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less.

The method for forming the vapor deposition layer is not particularly limited, and it can be formed using known methods such as vacuum deposition.

<Overcoat layer>
The metallized paper of this embodiment has an overcoat layer on top of the metallized layer. By providing the overcoat layer, the water resistance and oxidation resistance of the metallized paper are improved, and the barrier properties are improved. Furthermore, the overcoat layer has oxygen barrier properties and water vapor barrier properties, and therefore also functions to improve the barrier properties of the metallized paper.

The overcoat layer preferably contains a water-suspendable polymer, and more preferably contains primarily a water-suspendable polymer. Forming the overcoat layer using a water-suspendable polymer is believed to improve adhesion to the vapor-deposited layer, resulting in a vapor-deposited paper with excellent barrier properties (oxygen barrier property, water vapor barrier property). The phrase "the resin layer primarily contains a water-suspendable polymer" means that the content of the water-suspendable polymer in the resin layer is, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more. The upper limit is not particularly limited, but is 100% by weight or less. The resin layer may further contain optional components in addition to the water-suspendable polymer. Preferred aspects of the water-suspendable polymer are the same as those described for the resin layer.

(Water-suspended polymer)
The water-dispersible polymer contained in the overcoat layer is not particularly limited, and examples thereof include alkyd resins; (meth)acrylic (co)polymers, styrene-(meth)acrylic resins; olefin-unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers; vinyl alcohol resins such as polyvinyl alcohol and ethylene-vinyl alcohol copolymers (ethylene-modified polyvinyl alcohol); cellulose resins; polyurethane resins; polyester resins, etc. Among these, it is preferable to contain one or more selected from vinyl alcohol resins, polyurethane resins, and polyester resins, and from the viewpoint of further improving biodegradability and recyclability, it is more preferable to contain one or more selected from the group consisting of polyester resins and polyurethane resins, and it is even more preferable to contain a polyurethane resin.

<Polyester resin>
The polyester-based resin contained in the overcoat layer is not particularly limited, and is preferably one that can be prepared into one or more selected from the group consisting of polyester-based resin dispersions and emulsions, more preferably one that can be prepared into a polyester-based resin dispersion or emulsion, and even more preferably one that can be prepared into a polyester-based resin dispersion.

Commercially available polyester resins may be used, such as the "Elite KT Series (product name)" manufactured by Unitika Ltd. and the "Landy PL Series (product name)" manufactured by Miyoshi Oil & Fats Co., Ltd. Specific examples include Elite KT-8803 and Landy PL-3000.

<Polyurethane resin>
The polyurethane-based resin contained in the overcoat layer is not particularly limited, and is preferably one that can be prepared into one or more selected from the group consisting of polyurethane-based resin dispersions and emulsions, more preferably one that can be prepared into a polyurethane-based resin dispersion or emulsion, and even more preferably one that can be prepared into a polyurethane-based resin dispersion.

The polyurethane resin contained in the overcoat layer preferably contains at least one selected from the group consisting of structural units derived from meta-xylylene diisocyanate and structural units derived from hydrogenated meta-xylylene diisocyanate. When the polyurethane resin contains at least one of structural units derived from meta-xylylene diisocyanate and structural units derived from hydrogenated meta-xylylene diisocyanate, the total content of the structural units derived from meta-xylylene diisocyanate and the structural units derived from hydrogenated meta-xylylene diisocyanate relative to the total amount of structural units derived from polyisocyanate is preferably 50 mol% or more, more preferably 60 mol% or more. While there is no particular upper limit, it is preferably 95 mol% or less, more preferably 90 mol% or less. Such polyurethane resins exhibit high cohesion due to hydrogen bonding and the stacking effect between xylylene groups, and therefore have excellent gas barrier properties. The content can be determined using known analytical techniques such as ^1H -NMR.

The polyurethane resin contained in the overcoat layer may contain hydroxy groups, and its hydroxyl value is preferably 50 mgKOH/g or more, more preferably 100 mgKOH/g or more, and even more preferably 150 mgKOH/g or more. There are no particular limitations on the upper limit of the hydroxyl value, but it is preferably 1000 mgKOH/g or less, more preferably 800 mgKOH/g or less, and even more preferably 600 mgKOH/g or less. A hydroxyl value of the polyurethane resin within the above range is preferred because it provides excellent oxygen barrier properties. The hydroxyl value is measured in accordance with JIS K0070-1992, and the number of milligrams of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl groups when 1 g of the sample is acetylated is measured.

-Oxygen permeability-
The polyurethane resin contained in the overcoat layer, when molded into a 25 μm thick sheet, has an oxygen permeability of 100.0 mL/(m ² ·day ·atm) or less at 23 ° C. and 50% RH, more preferably 50.0 mL/(m ² ·day ·atm) or less, even more preferably 25.0 mL/(m ² ·day ·atm) or less, even more preferably 10.0 mL/(m ² ·day ·atm) or less, and particularly preferably 3.0 mL/(m ² ·day ·atm) or less. Note that, when molded into a 25 μm thick sheet, the oxygen permeability at 23 ° C. and 50% relative humidity may be 0 mL/(m ² ·day ·atm).
The oxygen permeability when molded into a sheet having a thickness of 25 μm is measured by forming a sheet having a thickness of 25 μm using the polyurethane resin in question.

- Glass transition temperature -
From the viewpoint of protecting the vapor-deposited layer of the vapor-deposited paper described below, it is important that the polyurethane resin contained in the overcoat layer has high film-forming property, and the glass transition temperature is preferably 150° C. or lower, more preferably 140° C. or lower, and particularly preferably 135° C. or lower. The glass transition temperature is measured in accordance with JIS K 7122:2012.

Synthetic polyurethane resins may also be used, such as those described in WO 2015/016069.

Commercially available polyurethane resins may be used, such as "Takelac W Series (product name)," "Takelac WPB Series (product name)," and "Takelac WS Series (product name)" manufactured by Mitsui Chemicals, Inc., with Takelac WPB-341 being a specific example. Other commercially available products include "HPU W-003" (hydroxyl value 235 mg KOH/g) manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

(Silane coupling agent)
From the viewpoint of improving the flex resistance of the overcoat layer, the overcoat layer preferably contains, in addition to the water-dispersible polymer, a silane coupling agent and/or a reaction product thereof, and is preferably formed by blending a silane coupling agent. Preferred embodiments of the silane coupling agent are the same as those described for the resin layer.

The amount of silane coupling agent in the overcoat layer is preferably 0.03 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 0.2 parts by weight or more, and particularly preferably 0.3 parts by weight or more, per 100 parts by weight of the water-suspendable polymer, and is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, even more preferably 6 parts by weight or less, and particularly preferably 5 parts by weight or less.

The coating amount of the overcoat layer is not particularly limited, but is preferably 0.1 g/m2 or more, more preferably 0.2 g/ ^m2 or more, and is preferably 5 g/ ^m2 or ^less , more preferably 3 g/ ^m2 or less, in terms of solid content.

The thickness of the overcoat layer is not particularly limited, but from the perspective of reducing the amount of resin used and improving recyclability, it is preferably less than 1 μm, and more preferably 0.6 μm or less. The lower limit of the overcoat layer thickness is not particularly limited, but from the perspective of barrier properties, it is preferably 0.1 μm or more, and more preferably 0.3 μm or more.

There are no particular limitations on the method for forming the overcoat layer, but it is preferable to form it by applying an aqueous medium such as an aqueous solution or aqueous dispersion of a water-dispersible polymer and drying it.

<Heat seal layer>
The metal-deposited paper of this embodiment may have a heat-seal layer containing a thermoplastic resin on the overcoat layer. Methods for forming the heat-seal layer include coating a thermoplastic resin solution or a thermoplastic resin dispersion and drying it, and extrusion lamination. Among these, coating a thermoplastic resin solution or a thermoplastic resin dispersion and drying it is preferred.

The thermoplastic resin solution or thermoplastic resin dispersion used here may be a solution using an organic solvent to dissolve the thermoplastic resin, a dispersion using an organic solvent to disperse the thermoplastic resin, or a dispersion using an aqueous medium, with dispersions using an aqueous medium being preferred from the standpoints of coatability and environmental impact.

Methods for applying a thermoplastic resin solution or thermoplastic resin dispersion include bar coating, blade coating, squeeze coating, air knife coating, roll coating, gravure coating, and transfer coating, and a coating machine such as a fountain coater or slit die coater may also be used.

Coated metallized paper coated with a thermoplastic resin solution or thermoplastic resin dispersion can be dried to remove the organic solvent or aqueous medium, yielding a coated metallized paper with a heat seal layer on the overcoat layer.

The thickness of the heat seal layer is not particularly limited, but is preferably between 1 μm and 15 μm. A thickness of 1 μm or more ensures sufficient heat sealability. Furthermore, a thickness of less than 15 μm can impart disintegration properties, resulting in a metallized paper with excellent recyclability.

In order to reduce the amount of resin used and improve recyclability, it is preferable not to provide an additional heat seal layer on the overcoat layer. That is, in the metallized paper of this embodiment, the uppermost layer on one side of the paper substrate is preferably the overcoat layer. Preferably, the metallized paper has a coating layer, a metallized layer, and an overcoat layer formed in this order on one side of the paper substrate.

<Physical properties of metallized paper>
(Cobb absorbency)
The metallized paper of this embodiment may have a Cobb water absorbency of the overcoat layer-side surface (e.g., the overcoat layer surface) of 1.0 g/ ^m² or less, preferably 0.5 g/ ^m² or less, measured in accordance with JIS P 8140:1998 at a temperature of 23°C and a contact time of 120 seconds. By maintaining the Cobb water absorbency of the overcoat layer-side surface within the above range, a water-impermeable film with few defects can be formed, and the resulting metallized paper is thought to be able to exhibit excellent barrier properties. The lower limit of the Cobb water absorbency of the overcoat layer-side surface is not particularly limited, but is, for example, 0 g/ ^m² or more, 0.1 g/ ^m² or more, or 0.2 g/m² or ^more . The Cobb water absorbency of the overcoat layer-side surface can be adjusted to within the above range by adjusting the components and coating amount of the coating layer (e.g., the resin layer) and the overcoat layer.

The metallized paper of this embodiment has a Cobb water absorbency of 10 g/m² or more, preferably 20 g/ ^m² or ^more , on the surface opposite the overcoat layer side (e.g., the paper substrate surface), measured in accordance with JIS P8140:1998 at a temperature of 23°C and a contact time of 120 seconds. Furthermore, by ensuring that the Cobb water absorbency of the surface opposite the overcoat layer side falls within the above range, water can easily penetrate the paper substrate, which is believed to enable the resulting metallized paper to exhibit excellent recyclability. There is no particular upper limit for the Cobb water absorbency of the surface opposite the overcoat layer side, but it is preferably 40 g/ ^m² or less, more preferably 30 g/ ^m² or less. The Cobb water absorbency of the surface opposite the overcoat layer side can be adjusted to fall within the above range by selecting the paper substrate, etc.

(Surface specific electrical resistance)
The metal-deposited paper of this embodiment has a surface resistivity of the overcoat layer side surface, measured in accordance with JIS C 2139:2008, of 1.0×10 ¹² Ω or more, more preferably 2.0×10 ¹² Ω or more, even more preferably 1.0×10 ¹³ Ω or more, and even more preferably 2.0×10 ¹⁴ Ω or more. By setting the surface resistivity of the overcoat layer side surface of the metal-deposited paper within the above range, the incorporation of metallic foreign matter is suppressed and recyclability is improved. The upper limit of the surface resistivity of the overcoat layer side surface is not particularly limited, but is, for example, 1.0×10 ¹⁵ Ω or less. The surface resistivity can be adjusted to within the above range by adjusting the coating weight of the coating layer (e.g., resin layer) and overcoat layer, selecting the components of the coating layer (e.g., resin of the resin layer) and overcoat layer, and selecting the metal-deposited layer.

(Thickness)
The thickness of the metallized paper of this embodiment is preferably 10 μm or more, more preferably 30 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less.

(oxygen permeability)
When a laminate sheet is formed by laminating a 20 μm-thick unstretched polypropylene film (CPP film) onto the overcoat layer of the metallized paper of this embodiment, the oxygen permeability of the laminate sheet measured in accordance with JIS K 7126-2:2006 at a temperature of 23°C and a relative humidity of 50% is 2.0 mL/ ^m² -day-atm or less, preferably 1.0 mL/ ^m² -day-atm or less. There is no particular lower limit, but it is preferably 0 mL/ ^m² -day-atm or more, and 0.05 mL/ ^m² -day-atm or more. An adhesive, for example, is used to bond the metallized paper and the CPP film. The type and amount of adhesive to be applied are not particularly limited as long as the adhesive has gas barrier properties, but are as described in the examples, for example. The oxygen permeability can be reduced, for example, by adjusting the resin layer to the optimum thickness described above, improving the smoothness of the resin layer, or increasing the thickness of the metallized layer. Here, "the adhesive does not have gas barrier properties" means that the adhesive in question is applied at 4 g/ ^m2 to a paper substrate having an Oken air resistance of 100 seconds or less as measured in accordance with JIS P 8117:2009, and a 20 μm thick CPP film is laminated to form a laminate sheet, and the oxygen permeability at a temperature of 23°C and a relative humidity of 50% as measured in accordance with JIS K 7126-2:2006 is 2000 mL/ ^m2 day atm or more.

(Water vapor permeability)
The metallized paper of this embodiment preferably has a water vapor permeability of 1.0 g/( ^m2 ·day) or less, more preferably 0.7 g/(m2·day) or less, at 40°C and 90% RH, as measured in accordance with JIS Z 0208:1976 (cup method) Method B. There is no particular lower limit, but the water vapor permeability is preferably 0 g/( ^m2 ·day) or more, 0.1 g/( ^m2 ·day) or more, or 0.2 g ^/ ( ^m2 ·day) or more. The water vapor permeability can be reduced, for example, by optimizing the resin layer thickness as described above, improving the smoothness of the resin layer, or increasing the thickness of the metallized layer.

There are no limitations on the method for producing the metallized paper of this embodiment, and known methods can be used. For example,
Examples of methods for producing metal-deposited paper having a clay coating layer, a resin layer, a vapor-deposited layer, and an overcoat layer, in this order, on at least one surface of a paper substrate include the following: A preferred production method includes the steps of applying a clay coating layer coating liquid containing an inorganic pigment and a binder onto the paper substrate and drying it to form a clay coating layer, applying a resin layer coating liquid containing a water-dispersible polymer onto the clay coating layer and drying it to form a resin layer, vacuum-depositing a material for the vapor-deposited layer onto the resin layer to form a vapor-deposited layer, and applying an overcoat layer coating liquid onto the vapor-deposited layer and drying it to form an overcoat layer.

The metallized paper of this embodiment can be used effectively as a packaging material for foods such as coffee, confectionery, and milk, as well as pharmaceuticals, medical supplies, and electronic components, taking advantage of its excellent barrier properties, and is also highly recyclable.

The following examples and comparative examples further illustrate the features of the present invention. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, unless otherwise specified, "%" and "parts" represent "% by mass" and "parts by mass," respectively. Furthermore, unless otherwise specified, the operations in the examples and comparative examples were carried out at room temperature (20-25°C) and normal humidity (40-50% RH).

Example 1
A coating solution for a clay coating layer was prepared by mixing 80 parts by mass of kaolin (Contour Xtreme manufactured by Imerys, aspect ratio 33, average particle size d50: 0.26 μm) and 20 parts by mass (solid content) of a styrene-acrylic copolymer binder (JONCRYL HSL-9012 manufactured by BASF). The above clay coating layer coating liquid was applied to the glossy side of one-sided glossy paper (manufactured by Oji F-Tex Co., Ltd., hardwood pulp content: 100% by mass, disintegrated freeness: 420 ml, basis weight: 50 g/ ^m2 , thickness: 60 μm, density: 0.83 g/ ^m3 , sizing degree: 9 seconds, Oken smoothness of glossy side: 499 seconds, Oken smoothness of non-glossy side: 15 seconds) using a Mayer bar and dried at 120°C for 1 minute to form a clay coating layer (12 g/ ^m2 ).
Next, a resin layer coating liquid was prepared by mixing 100 parts by mass of an aqueous dispersion of a polyurethane resin binder (Takelac WPB-341 manufactured by Mitsui Chemicals: glass transition temperature 130°C, solids concentration 30%) having an oxygen permeability (23°C, 50% RH) of 2.0 ml/( ^m2 ·day·atm) when formed into a 25 μm thick sheet with 0.15 parts by mass of aminopropyltriethoxysilane (KBE-903 manufactured by Shin-Etsu Chemical Co., Ltd.) on the clay coating layer using a Mayer bar, and dried at 120°C for 1 minute to form a resin layer (2 g/ ^m2 ), and a base paper for metallized paper was obtained.
A silicon oxide vapor-deposited layer (100 Å (10 nm) thick) was formed on the resin layer of the obtained base paper for metallized paper by vacuum deposition. An aqueous dispersion of a polyurethane resin binder (Takelac WPB-341, manufactured by Mitsui Chemicals, Inc.) with an oxygen permeability (23°C, 50% RH) of 2.0 ml/( ^m2 ·day·atm) when formed into a 25 μm-thick sheet was applied to the silicon oxide vapor-deposited layer with a Mayer bar and dried at 120°C for 1 minute to form an overcoat layer (0.5 g/ ^m2 , thickness: 0.5 μm), yielding a metallized paper with a thickness of 68 μm.
The polyurethane resin used in the resin layer and the overcoat layer was subjected to ^1H -NMR analysis, and the content of metaxylylene diisocyanate-derived structural units relative to the total amount of polyisocyanate-derived structural units was 85 mol%, or 50 mol% or more. The solubility of the polyurethane resin binder in water at 25°C was 10 g/L or less.

Example 2
A metallized paper having a thickness of 67 μm was obtained in the same manner as in Example 1, except that the coating amount of the resin layer was 1 g/m ² .

Example 3
A metallized paper having a thickness of 68 μm was obtained in the same manner as in Example 1, except that a resin layer (2 g/m ² ) was formed using a polylactic acid emulsion (LANDY PL-3000 manufactured by Miyoshi Oil & Fats Co., Ltd., solid content concentration 40%). The solubility of the polylactic acid in water at 25°C was 10 g/L or less.

Example 4
A metallized paper having a thickness of 68 μm was obtained in the same manner as in Example 1, except that a resin layer (2 g/m ² ) and an overcoat layer (0.5 g/m ² , thickness: 0.5 μm) were formed using an aqueous dispersion of a polyurethane resin binder having hydroxy groups (HPU W-003, manufactured by Dainichiseika Color & Chemicals Co., Ltd., hydroxyl value 235 mg KOH/g, solids concentration 30%). The solubility of the polyurethane resin binder having hydroxy groups in water at 25°C was 10 g/L or less.

Example 5
A metallized paper having a thickness of 68 μm was obtained in the same manner as in Example 1, except that a metallized layer (thickness: 10 nm) was formed by vacuum deposition using aluminum oxide instead of silicon oxide.

Example 6
Metallized paper was obtained in the same manner as in Example 1, except that a vapor-deposited layer (thickness 10 nm) was formed by vacuum deposition using silicon oxide and aluminum oxide simultaneously (mass ratio, silicon oxide:aluminum oxide = 50:50) instead of silicon oxide.

<Comparative Example 1>
A metallized paper having a thickness of 68 μm was obtained in the same manner as in Example 1, except that the metallized layer was changed to an aluminum metallized layer (thickness: 500 Å (50 nm)).

<Comparative Example 2>
A metallized paper having a thickness of 68 μm was obtained in the same manner as in Example 1, except that a resin layer (2 g/m ² ) was formed using an aqueous dispersion of an ethylene-acrylic acid copolymer binder (Zaixen AC manufactured by Sumitomo Seika Chemicals Co., Ltd., solid content concentration 29%).

<Comparative Example 3>
In the same manner as in Example 1, a clay coating layer and a resin layer were applied to both sides of a paper substrate, and then a vapor deposition layer and an overcoat layer were formed on only one of the resin layers to obtain a vapor-deposited paper having a thickness of 75 μm.

<Evaluation of metallized paper>
The metallized papers obtained in the examples and comparative examples were evaluated as follows.

[Cobb absorbency]
The test was carried out in accordance with JIS P 8140: 1998. The temperature of the water (distilled water was used) to be brought into contact was 23°C, and the contact time was 120 seconds, with the water being brought into contact with the overcoat layer surface of the metallized paper and the opposite surface (i.e., the paper substrate surface).

[Surface specific electrical resistivity]
The surface specific electrical resistivity of the overcoat layer side surface (overcoat layer surface) was measured in accordance with JIS C 2139:2008.

<Evaluation of metallized paper>
[Oxygen permeability]
The oxygen permeability of the metallized paper was measured using an oxygen permeability measuring device (OX-TRAN2/22, manufactured by MOCON Corporation) at a temperature of 23°C and a relative humidity of 50%. Specifically, 5 g/m2 of an isocyanate-based adhesive (a mixture of 10 parts of DIC Corporation's DIC Dry LX-500 and 1 part of DIC Dry KW-75) was applied to the overcoat layer of the metallized paper obtained in the Examples and Comparative Examples, ^and a 20 μm-thick CPP film (Hokuetsu Chemicals Co., Ltd.'s GP-32) was then attached to form a laminate sheet. The oxygen permeability of the laminate sheet was measured at a temperature of 23°C and a relative humidity of 50% in accordance with JIS K 7126-2:2006. The lower the oxygen permeability value, the better the oxygen barrier property.

[Water vapor permeability]
The water vapor permeability was measured in accordance with JIS Z 0208:1976 (cup method) Method B (temperature 40°C ± 0.5°C, relative humidity 90% ± 2%), with the metallized paper positioned so that the overcoat layer was on the inner side (low humidity side). The lower the water vapor permeability value, the better the water vapor barrier property.

[Suitable for barrier packaging materials]
The metallized papers of the Examples and Comparative Examples were evaluated for suitability as barrier packaging materials based on the oxygen permeability and water vapor permeability measured above.
◯: Oxygen permeability is 2 mL/ ^m2 ·day·atm or less and water vapor permeability is 5 g/ ^m2 ·day or less. ×: Oxygen permeability is greater than 2 mL/ ^m2 ·day·atm, or water vapor permeability is greater than 5 g/ ^m2 ·day.

[Recyclability (pulp recovery rate after re-defibration and visual evaluation)]
The obtained metallized paper was disintegrated in accordance with JIS P 8220-1:2012. Ten minutes after the start of disintegration, the dispersion was treated with a vibrating flat screen equipped with a 6-cut screen, and a sample on the 6-cut screen (mesh size: 0.15 mm) was collected and dried to calculate the mass ratio (%) of the residue. The value obtained by subtracting the mass ratio (%) of the residue from 100% was defined as the pulp recovery rate (%) after redisintegration. The recovered pulp was visually evaluated for the presence or absence of colored foreign matter. Recyclability was evaluated from the pulp recovery rate and the presence or absence of colored foreign matter.
Good: Pulp recovery rate is 80% or more and there is no colored foreign matter.
x: Pulp recovery rate is less than 80% or colored foreign matter is present.

Compared to the metallized papers of Comparative Examples 1 to 3, the metallized papers of Examples 1 to 6 had lower oxygen permeability, superior barrier properties, and also superior recyclability.

Claims (7)

A metal-deposited paper having a coating layer, a metal-deposited layer, and an overcoat layer in this order on one side of a paper substrate,
the Cobb water absorption of the overcoat layer side surface measured in accordance with JIS P 8140:1998 at a temperature of 23°C for a contact time of 120 seconds is 1.0 g/ ^m2 or less;
the Cobb water absorbency of the surface opposite to the overcoat layer side is 10 g/ ^m2 or more at a temperature of 23°C and a contact time of 120 seconds, as measured in accordance with JIS P8140:1998;
the surface specific electrical resistance of the overcoat layer side surface measured in accordance with JIS C 2139:2008 is 1.0×10 ¹² Ω or more;
When a laminate sheet is formed by laminating a 20 μm-thick unstretched polypropylene film on the overcoat layer of the metallized paper, the oxygen permeability of the laminate sheet measured in accordance with JIS K 7126-2:2006 at a temperature of 23°C and a relative humidity of 50% is 2.0 mL/m2 ^day atm or less ,
the coating layer has a clay coating layer and a resin layer in this order from the paper substrate side,
The metal-deposited paper , wherein the resin layer and the overcoat layer contain a water-dispersible polymer, and the water-dispersible polymer contains at least one type selected from the group consisting of polyester-based resins and polyurethane-based resins . 2. The metallized paper according to claim 1, which has a water vapor transmission rate of 1.0 g/m ^<2> day or less at a temperature of 40°C and a relative humidity of 90%, measured in accordance with JIS Z 0208:1976 (cup method) B method. 3. The metal-deposited paper according to claim 1, wherein the water-dispersible polymer contained in the resin layer comprises at least one selected from the group consisting of polyurethane resins and polylactic acid. the clay coating layer comprises an inorganic pigment and a binder;
4. The metal-deposited paper according to claim 1 , wherein the inorganic pigment has an aspect ratio of 50 or less and an average particle size of 5 μm or less. 5. The metal-deposited paper according to claim 4 , wherein the inorganic pigment is kaolin. 6. The metal-deposited paper according to claim 4, wherein the binder contained in the clay coating layer comprises at least one selected from the group consisting of styrene-butadiene resins, styrene-( meth )acrylic resins, olefin -unsaturated carboxylic acid copolymers, and polylactic acid. the vapor-deposited layer is a vapor-deposited layer containing an inorganic oxide,
The metal-deposited paper according to any one of claims 1 to 6 , wherein the inorganic oxide comprises at least one selected from the group consisting of silicon oxide and aluminum oxide.