JP7854784B2 - packaging material - Google Patents

Description

This invention relates to a heat-sealable packaging material made of a paper support, and more particularly to a packaging material used in a secondary packaging body in the form of a bag.

Food products such as confectionery displayed in retail stores often consist of packaging that includes a primary packaging containing the food product and a secondary packaging containing one or more of the primary packaging units.
Typically, primary packaging exists to protect food, and secondary packaging exists to protect the primary packaging. Secondary packaging comes in two forms: bags and boxes. Bag-type secondary packaging is generally created by covering the primary packaging with packaging material and heat-sealing the edges of the packaging material. Therefore, the packaging material used for bag-type secondary packaging must be suitable for heat sealing.

Packaging materials suitable for heat sealing are known. For example, there is a known packaging paper having at least one heat-seal layer on at least one surface of a paper substrate, wherein the heat-seal layer contains an ionomer and the dry coating amount of the heat-seal layer is 2 to 10 g/ ^m² for the entire layer (see, for example, Patent Document 1).

Japanese Patent Publication No. 2020-117311

In recent years, due to environmental pollution problems caused by microplastics, plastic films are increasingly being phased out in the field of packaging materials. Paper supports are a promising alternative to plastic films. Patent document 1 also discloses packaging paper that replaces plastic with paper, aiming to reduce plastic usage. However, paper supports lack the smoothness of plastic films. Therefore, to prevent gaps from forming at the heat-sealed areas or to ensure uniform strength at the heat-sealed areas, the packaging material needs to have good adhesion to the heat-sealed surfaces. On the other hand, improving the adhesion of the heat-sealed surfaces in packaging materials can cause blocking between the packaging materials.

A unique challenge with secondary packaging is the heat problem during heat sealing. Specifically, when heat-sealing packaging materials to form a bag, the heat generated during the heat sealing process can damage the food inside the primary packaging. For example, if the food is chocolate, it may melt during heat sealing. When handling food, heat sealing must be achieved at a relatively low temperature and for a short time.

Therefore, the object of the present invention is to provide a packaging material having the following qualities.
(1) The surfaces to be heat-sealed must have good adhesion (adhesion).
(2) The ability to heat seal at a relatively low temperature and in a short time (heat seal suitability).
(3) Ability to suppress blocking between packaging materials (blocking resistance).

The inventors of this invention have conducted thorough research and found that the objective of this invention is achieved as follows:

[1] A packaging material comprising a paper support and one or more coating layers on one side of the paper support, wherein the paper support has a density of 0.83 g/ ^cm³ to 1.03 g/ ^cm³ and an ash content of 2.3% by mass or less, and the outermost coating layer, which is located on the outermost side with respect to the paper support, contains at least an ionomer resin of an ethylene unsaturated carboxylic acid copolymer.

[2] The packaging material according to [1] above, wherein the outermost coating layer is a layer that substantially does not contain inorganic pigments.

The present invention provides a packaging material with excellent adhesion, heat-sealability, and blocking resistance.

The packaging material comprises a paper support and one or more coating layers on one side of the paper support. In the coating layers, the outermost coating layer relative to the paper support is called the outermost coating layer. If there is only one coating layer, this is the outermost coating layer. If there are two or more coating layers, the coating layers between the base paper and the outermost coating layer are not particularly limited. In some embodiments, the coating layers between the base paper and the outermost coating layer are provided to impart various functions to the packaging material as needed. Examples of coating layers include a gas barrier layer containing a gas barrier agent, a water vapor barrier layer containing a water vapor barrier agent, an oil barrier layer containing an oil resistant agent, and an insulating layer containing an insulating material. In some embodiments, for packaging materials used in secondary packaging, there is only one coating layer, including the outermost coating layer. That is, there is only one coating layer. This is because it results in a more cost-effective manufacturing process for packaging materials used in secondary packaging. Furthermore, the coating layer may be present on one or both sides of the paper support. In some embodiments, the packaging material has the outermost coating layer on only one side of the paper support. In some embodiments, in packaging materials where the outermost coating layer is present on only one side of the paper support, a conventionally known printing coating layer or backcoat layer is provided on the opposite side of the paper support for the purpose of improving printability or dimensional stability. For packaging materials used in secondary packaging, the side of the packaging material facing the contents is the side of the packaging material that has the outermost coating layer.

The paper support is a base paper produced by conventionally known papermaking methods under acidic, neutral, or alkaline conditions, using a pulp basil prepared by adding various additives such as fillers, internal sizing agents, fixatives, yield agents, and paper strength agents as needed to a slurry of wood pulp and/or non-wood pulp; a base paper prepared by calendering the said base paper; a fine paper prepared by sizing the said base paper with a sizing liquid containing a surface sizing agent; or a fine paper prepared by calendering the said fine paper.

The above-mentioned paper pulp may be appropriately supplemented with one or more additives selected from the following: pigment dispersants, binders, thickeners, fluidity improvers, bulking agents, defoaming agents, antifoaming agents, mold release agents, foaming agents, penetrating agents, coloring dyes, coloring pigments, fluorescent whitening agents, ultraviolet absorbers, antioxidants, preservatives, anti-fungal agents, water-resistant agents, etc., within a range that does not impair the desired effects of the present invention.

Calendaring is a process that equalizes the smoothness and thickness of paper by passing it between rolls. Examples of calendaring equipment include machine calendars, soft nip calendars, supercalenders, multi-stage calendars, and multi-nip calendars.

Size pressing is a process that imparts water resistance to the surface of paper. Size pressing is performed using size pressing equipment conventionally known in the papermaking field. Examples of size pressing equipment include inclined size presses, horizontal size presses, and film transfer equipment such as rod metering size presses, roll metering size presses, and blade metering size presses. Examples of rod metering size presses include shimsizers, optisizers, and speedsizers. Examples of roll metering size presses include gate roll coaters, bill blade coaters, twin blade coaters, velvapa coaters, tab size presses, and calender size presses.

Wood pulp is conventionally known in the papermaking field. Examples of wood pulp include chemical pulps such as LBKP (Leaf Bleached Kraft Pulp) and NBKP (Needle Bleached Kraft Pulp), mechanical pulps such as GP (Groundwood Pulp), PGW (Pressure Groundwood Pulp), RMP (Refiner Mechanical Pulp), TMP (ThermoMechanical Pulp), CTMP (ChemiThermoMechanical Pulp), CMP (ChemiMechanical Pulp), and CGP (ChemiGroundwood Pulp), and recycled paper pulp such as DIP (DeInked Pulp).
Non-wood pulp is pulp made from non-wood fibers that have been conventionally known in the papermaking field. Examples of raw materials for non-wood fibers include the basts of woody plants such as paper mulberry, mitsumata, and gampi; the basts of herbaceous plants such as flax, hemp, and kenaf; leaf fibers such as Manila hemp, abaca, and sisal; grass plants such as rice straw, wheat straw, sugarcane bagasse, bamboo, and esparto; and seed hairs such as cotton and linter.
The wood pulp and/or non-wood pulp is one or more selected from the group consisting of the wood pulp and the non-wood pulp.

In some embodiments, the base paper for the paper support contains at least NBKP and LBKP as pulp. In some embodiments, the total content of NBKP and LBKP in the base paper for the paper support is 90% by mass or more relative to the pulp in the base paper. This is because it improves the paper strength of the base paper. Paper strength is important for packaging materials used in secondary packaging, as they serve the purpose of protecting the primary packaging during transport.

The filler is an inorganic pigment conventionally known in the papermaking field. Examples of inorganic pigments include light calcium carbonate, heavy calcium carbonate, kaolin, talc, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, silica, aluminum silicate, diatomaceous earth, activated clay, alumina, alumina hydrate, aluminum hydroxide, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide. The filler is one or more selected from the group consisting of the above inorganic pigments.
In some embodiments, the base paper for the paper support contains substantially no filler. This is because it improves the paper strength of the base paper. "Substantially no filler" means that if the amount of filler is such that it does not worsen the paper strength of the base paper, it is considered to contain no filler. In at least one implementation, the amount of filler in the base paper is 3% by mass or less relative to the pulp in the base paper. This is because if the amount of filler is 3% by mass or less relative to the pulp, it does not worsen the paper strength.

The sizing agent is a sizing agent that has been conventionally known in the papermaking field.
Examples of internal sizing agents added to paper stock include rosin-based sizing agents for acidic paper, and alkenyl succinic anhydride, alkyl ketene dimers, neutral rosin-based sizing agents, and cationic styrene-acrylic sizing agents for neutral paper.
Furthermore, the surface sizing agents used in the sizing press fluid are those conventionally known in the papermaking field. Examples of surface sizing agents include starch-based sizing agents, cellulose-based sizing agents, polyvinyl alcohol-based sizing agents, styrene-acrylic sizing agents, olefin-based sizing agents, styrene-maleic acid-based sizing agents, and acrylamide-based sizing agents.
In some embodiments, the paper support is high-quality paper obtained by sizing the base paper with a sizing liquid containing a surface sizing agent. This is because it improves adhesion and heat sealability.

The fixative is a conventionally known fixative in the papermaking field. The fixative improves the fixation of the sizing agent. Examples of fixatives include inorganic salts such as aluminum sulfate.

The yield enhancer is a yield enhancer conventionally known in the papermaking field. The yield enhancer improves the yield of various additives added to the paper pulp. Examples of yield enhancers include organic polymer electrolytes such as polyacrylamide, polyamides, and polyethyleneimine, as well as polyethylene oxide.

Paper strength agents are those conventionally known in the papermaking field. Paper strength agents improve the paper strength of the base paper. Examples of paper strength agents include cationized starch, dialdehyde starch, plant-based gum, urea-formaldehyde resin, polyamide-polyamine-epichlorohydrin polycondensate, and glyoxal-modified polyacrylamide.

The paper support has a density of 0.83 g/ ^cm³ to 1.03 g/ ^cm³ . The density of the paper support is related to its smoothness and therefore affects the formation of the coating layer on which the coating liquid is applied. Higher density increases smoothness, while lower density decreases smoothness. On the other hand, if the density of the paper support is too high, it negatively affects the blocking resistance. The density is measured in accordance with ISO 534:2011 "Paper and board - Determination of thickness, density and specific volume". The density of the paper support is a parameter conventionally known in the papermaking field and can be adjusted by, for example, papermaking conditions such as press part conditions, pulp type and degree of beating, filler type and content, and the presence and condition of calendering. Generally, actions such as increasing the nip pressure in the press section, strengthening the pulp beating, adding fillers, performing size pressing, and calendering increase the density of the paper support. In some embodiments, the density of the paper support is adjusted by size pressing and calendering. This is because it improves the smoothness of the paper support, which positively affects adhesion and heat sealability.

The paper support has an ash content of 2.3% by mass or less. The ash content of the paper support indicates the content of metal components, etc., derived from fillers and inorganic salts contained in the paper support. The ash content of the paper support is related to the permeability of the paper support and therefore affects the formation of the coating layer on which the coating liquid is applied to the paper support. Higher ash content increases permeability, while lower ash content decreases permeability. The ash content is measured according to ISO 1762:2019 "Paper, board, pulses and cellular nanomaterials - Determination of reside (ash content) on ignition at 525 degree C". The ash content of the paper support is a parameter conventionally known in the papermaking field and can be adjusted, for example, by the type and amount of fixatives, which are fillers and/or inorganic salts. In some embodiments, the base paper for the paper support substantially contains no fillers. This is because it is easy to adjust the ash content to 2.3% by mass or less.

The paper support has a density of 0.83 g/ ^cm³ to 1.03 g/ ^cm³ and an ash content of 2.3% by mass or less. Paper supports with densities and ash content within the above ranges have appropriate smoothness and permeability. The packaging material exhibits adhesion, heat sealability, and blocking resistance through the synergistic effect of the paper support having the above physical properties and the outermost coating layer described below. If the density or ash content of the packaging material falls outside the above ranges, at least one of the effects of the present invention cannot be satisfied.

In some embodiments, the paper support has an opacity of 70% to 85%. This is because it improves adhesion, heat sealability, and/or blocking resistance. The opacity is measured according to ISO 2471:2008 "Paper and board - Determination of opacity (paper backing) - Diffuse reflection method".
The opacity of a paper support is a parameter conventionally known in the papermaking field and can be adjusted by, for example, the type and degree of pulp beating, the type and content of fillers, and the presence and condition of calendering. Generally, actions such as reducing the pulp beating, adding fillers, and performing size pressing increase the opacity of the paper support, while calendering decreases it. The opacity of a paper support indirectly represents the void state of the paper support. If voids that exhibit light scattering exist in the paper support, the opacity of the paper support increases. On the other hand, if the voids in the paper support that exhibit light scattering are crushed or filled, the opacity of the paper support decreases. Also, if the thickness of the paper support decreases, the opacity of the paper support decreases.

The outermost coating layer contains an ionomer resin of an ethylene unsaturated carboxylic acid copolymer. The ionomer resin of an ethylene unsaturated carboxylic acid copolymer is a compound represented by the following general formula.

x, y, and z represent the composition ratio of each monomer in the resin. R1 and R2 represent hydrogen atoms or alkyl groups. In some embodiments, the alkyl group is an alkyl group having 1 to 4 carbon atoms. M represents the metal that forms a salt with the carboxyl group. M is, for example, sodium, potassium, calcium, magnesium, zinc, etc. In some embodiments, M is one or more selected from the group consisting of alkali metals and alkaline earth metals. Ionomer resins of ethylene unsaturated carboxylic acid copolymers are commercially available from companies such as Mitsui Chemicals, Mitsui-Dow Polychemicals, and Maruyoshi Chemical Co., Ltd.

Ionomer resins of ethylene unsaturated carboxylic acid copolymers exhibit excellent heat-sealability because the crosslinking bonds of metal ions diffuse upon heat. Furthermore, the inventors hypothesize that the ionomer resin of ethylene unsaturated carboxylic acid copolymers forms a microcrystalline structure with M as the nucleus in the outermost coating layer formed by coating and drying, and that this microcrystalline structure contributes to block resistance. The inventors also believe that a paper support with a density of 0.83 g/ ^cm³ to 1.03 g/ ^cm³ and an ash content of 2.3% by mass or less allows for the successful formation of the microcrystalline structure and the expression of block resistance.

The outermost coating layer may contain conventionally known resins other than ionomer resins of ethylene unsaturated carboxylic acid copolymers. Examples of resins include conjugated diene resins such as styrene-butadiene copolymer resins and acrylonitrile-butadiene copolymer resins, acrylic resins such as polymer resins of acrylic acid esters or methacrylic acid esters or methacrylic acid ester-butadiene copolymer resins, vinyl resins such as vinyl chloride resins, vinylidene chloride resins, ethylene vinyl acetate copolymer resins and vinyl chloride vinyl acetate copolymer resins, thermosetting synthetic resins such as polyurethane resins, alkyd resins, polyester resins, melamine resins and urea resins, starches such as natural rubber, starch, various modified starches and various modified starches, celluloses such as carboxymethylcellulose and hydroxyethylcellulose, natural polymer resins or derivatives thereof such as casein, gelatin and soy protein, polyvinylpyrrolidone, polyvinyl alcohol and modified polyvinyl alcohol, polypropylene glycol, and polyethylene glycol. In some embodiments, the outermost coating layer may contain various conventionally known additives in addition to the ionomer resin of the ethylene unsaturated carboxylic acid copolymer. Examples of additives include viscosity modifiers, defoamers, surfactants, leveling agents, and colorants.
In some embodiments, the outermost coating layer contains 90% by mass or more of an ionomer resin of an ethylene unsaturated carboxylic acid copolymer relative to the dry solid content of the outermost coating layer. This is because it improves adhesion, heat sealability, and/or blocking resistance.

In some embodiments, the outermost coating layer is substantially free of inorganic pigments. This is because it improves heat-sealability. Here, "substantially free" refers to a range where the inorganic pigment content relative to the dry solids content of the outermost coating layer is 2% by mass or less. The inorganic pigments are those conventionally known in the papermaking field and are similar to the inorganic pigments exemplified in the fillers described above.

The coating layer, including the outermost coating layer, can be formed by applying and drying a coating solution to a paper support. For example, the coating and drying method can involve applying and drying the coating solution using coating and drying equipment conventionally known in the field of coated paper. Examples of coating equipment include film press coaters, air knife coaters, rod blade coaters, bar coaters, blade coaters, gravure coaters, curtain coaters, E-bar coaters, and film transfer coaters. Examples of drying equipment include various drying devices such as straight tunnel dryers, arch dryers, air loop dryers, sine curve air float dryers, infrared heating dryers, and microwave dryers.

In some embodiments, the amount of ionomer resin of ethylene unsaturated carboxylic acid copolymer coated in the outermost coating layer is 3 g/ ^m² or more per side of the paper support in terms of dry solids. This is because it improves adhesion and heat sealability. There is no particular upper limit to the coating amount. In some embodiments, the upper limit of the coating amount is 8 g/ ^m² or less, considering the relationship between adhesion, heat sealability, and material cost.

The present invention will be described in further detail below with reference to examples. However, the present invention is not limited to these examples. Here, "parts by mass" and "mass%" represent "parts by mass" and "mass%" of the dry solid content or substantial component content, respectively. The coating amount of each layer represents the dry solid content.

<Paper support>
The following paper pulp was prepared.
LBKP (water filtration rate 630 ml csf) 500 parts by mass NBKP (water filtration rate 470 ml csf) 500 parts by mass Aluminum sulfate (parts listed in Table 1) Light calcium carbonate (parts listed in Table 1) Cationized starch 12 parts by mass Rosin-based sizing agent 5 parts by mass Polyacrylamide-based yield agent 0.1 parts by mass The pulp of the above composition was made on a wire screen paper machine, and a base paper with a basis weight of 54 g/ ^m² was obtained by adjusting the press part conditions of the paper machine. Sizing press was then performed using oxidized starch as a surface sizing agent. The amount of oxidized starch coating was adjusted in the range of 0.8 g/ ^m² to 1.8 g/ ^m² . Next, a supercalendering treatment was performed while adjusting the conditions to obtain a paper support. The density, ash content, and opacity of the obtained paper support are listed in Table 1.

<Coating liquid for the outermost coating layer>
A coating solution for the outermost coating layer containing the following was prepared using water as a medium.
Resin: 100 parts by mass. Calcium carbonate: The amount is listed in Table 1. The solid content concentration of the coating liquid for the coating layer was adjusted to 28% by mass. The resin is listed in Table 1.

The resins listed in Table 1 are as follows:
Resin 1: Ionomer resin of ethylene unsaturated carboxylic acid copolymer (Mitsui Chemicals, Inc., ChemiPearl® S100, average particle size 0.1 μm by microtrac method)
Resin 2: Ionomer resin of ethylene unsaturated carboxylic acid copolymer (Maruyoshi Chemical Co., Ltd., MYE-30MAZ, average particle size 0.3 μm by microtrac method)
Resin 3: Ionomer resin of ethylene unsaturated carboxylic acid copolymer (Mitsui Chemicals, ChemiPearl S300, average particle size 0.5 μm by microtrac method)
Resin 4: Ionomer resin of ethylene unsaturated carboxylic acid copolymer (Mitsui Chemicals, ChemiPearl S500, average particle size 0.7 μm by microtrac method)
Resin 5: Polyethylene resin (Sunopco, SN Coat 287)
Resin 6: Ethylene methyl methacrylate copolymer resin (Sumitomo Chemical Co., Ltd., Aclift® WK307)

<Packaging materials>
A packaging material with an outermost coating layer was obtained by applying the coating solution for the outermost coating layer to one side of a paper support using an air knife coater and drying it in a hot air dryer. The amount of coating is shown in Table 1.

The following evaluations were performed on the obtained packaging materials.

<Adhesion>
Using packaging material, the surfaces with the outermost coating layer were placed facing each other and heat-sealed using a heat sealer under the conditions of a pressure of 2.0 kg/ ^cm² , 130°C, and 1 second.
Ten pieces of heat-sealed packaging material were cut to a width of 15 mm and left to stand at 20°C and 65% RH for 24 hours. The edges of the packaging material were then gently pulled several times by hand to release the heat seals, and the heat-sealed areas were observed. The adhesion was evaluated based on the observation results according to the following criteria. In this invention, packaging material is considered to have good adhesion on the heat-sealed surface if it receives an evaluation of A, B, or C.
A: There are no gaps in the heat-sealed area.
Furthermore, the strength is uniform across the 10 heat-sealed points.
B: There are no gaps in the heat-sealed area.
Furthermore, there is a very slight unevenness in strength at the 10 heat-sealed points.
C: There are no gaps in the heat-sealed area.
Furthermore, there is slight unevenness in strength at the 10 heat-sealed points.
D: There is a gap in the heat-sealed area.
And/or the strength is uneven at 10 heat-sealed points.

<Suitability for heat sealing>
Using packaging material, the surfaces with the outermost coating layer were placed facing each other and heat-sealed using a heat sealer under the conditions of a pressure of 2.0 kg/ ^cm² , a relatively low temperature of 90°C, and a heat seal for 1 second.
Heat-sealable packaging material was cut into 15 mm wide strips and left to stand at 20°C and 65% RH for 24 hours. The peel strength of the heat-sealed area was then measured using a tensile testing machine at a tensile speed of 200 mm/min and a tensile angle of 180 degrees to evaluate its heat-sealability. Measurements were performed on 5 samples, and the average value of these 5 samples was used. Based on the measured values, heat-sealability was evaluated according to the following criteria. In this invention, a packaging material is considered to have heat-sealability if it receives an evaluation of A or B.
A: The value is 16 N/15 mm or higher.
B: The value is 10 N/15 mm or more and less than 16 N/15 mm.
C: Value is 4N/15mm or more and less than 10N/15mm.
D: Value is less than 4N/15mm.

<Blocking resistance>
The packaging material was wound into a roll (500 m in length) on a 150 mm diameter paper tube with the image recording layer facing outwards. The roll was left to stand for 24 hours at 20°C and 65% RH using two methods: placing it directly on the ground and suspending it in mid-air. After standing, the packaging material was unwound (unwinder) from the winding. At this time, the blocking state of the packaging material was visually observed. Based on the observation results, the blocking resistance was evaluated according to the following criteria. In this invention, a packaging material is considered to have blocking resistance if it receives an evaluation of A or B.
A: Blocking is not observed using either direct placement or suspension.
B: Very weak blocking is observed when placed directly on the surface.
Blocking is not permitted using the suspended method.
C: Weak blocking is observed when placed directly on the surface.
Blocking is not permitted using the suspended method.
D: Blocking is permitted using a suspended method.

The evaluation results are shown in Table 1.

Table 1 shows that Examples 1 to 15, which correspond to the present invention, are packaging materials that have adhesion, heat sealability, and blocking resistance. On the other hand, Comparative Examples 1 to 6, which do not satisfy the configuration of the present invention, are packaging materials that cannot satisfy at least one of adhesion, heat sealability, and blocking resistance.
From a comparison mainly between Examples 3, 14, and 15, it can be seen that if the outermost coating layer substantially does not contain inorganic pigments, the heat sealability of the packaging material improves.
From a comparison mainly between Examples 3, 5, 6, 7, and 8 and Examples 9 and 10, it can be seen that when the opacity of the paper support is 70% to 85%, the packaging material exhibits improved adhesion, heat sealability, and/or blocking resistance.

Regarding the embodiments of the present invention described above, the following additional information is disclosed.

<1>
A packaging material comprising a paper support and one or more coating layers on one side of the paper support, wherein the paper support has a density of 0.83 g/ ^cm³ to 1.03 g/ ^cm³ and an ash content of 2.3% by mass or less, and the outermost coating layer, which is located on the outermost side relative to the paper support, contains at least an ionomer resin of an ethylene unsaturated carboxylic acid copolymer.

<2>
The packaging material according to <1> above, wherein the outermost coating layer is a layer that substantially does not contain inorganic pigments.

<3>
The packaging material described in <1> above, wherein the coating layer, including the outermost coating layer, is a single layer.

<4>
The packaging material according to <1> above, wherein the outermost coating layer is a layer that substantially does not contain an inorganic pigment, and the total number of coating layers, including the outermost coating layer, is one.

<5>
The packaging material according to <1> or <4> above, wherein the opacity of the paper support is 70% or more and 85% or less.

Claims (4)

A packaging material comprising a paper support and one or more coating layers on one side of the paper support, wherein the paper support has a density of 0.83 g/ ^cm³ to 1.03 g/ ^cm³ and an ash content of 2.3% by mass or less, the outermost coating layer located on the outermost side relative to the paper support contains at least an ionomer resin of an ethylene unsaturated carboxylic acid copolymer , and the opacity of the paper support is 70% to 85% . The packaging material according to claim 1, wherein the inorganic pigment content is 2% by mass or less relative to the dry solid content of the outermost coating layer. The packaging material according to claim 1 or 2, wherein the coating layer, including the outermost coating layer, is a single layer. The packaging material according to claim 1 or 2, wherein the ionomer resin of an ethylene unsaturated carboxylic acid copolymer accounts for 90% by mass or more of the dry solid content of the outermost coating layer.