JP7698701B2 - wrapping paper - Google Patents

Description

The present invention relates to packaging paper that uses a reduced amount of plastic.

In recent years, the problem of plastic waste has become more serious. It is said that the world's plastic production exceeds 400 million tons per year, of which a large amount is produced in the packaging sector, which is the cause of plastic waste. Plastic does not decompose for a long time, and the waste turns into microplastics in the natural environment, causing serious damage to the ecosystem. The most commonly used plastics for packaging containers are polyethylene terephthalate (PET), which is used for beverage bottles, and polyethylene (PE) and polypropylene (PP), which are used for plastic bags and container lamination. Ocean pollution is particularly severe, and it is said that the plastic waste is impossible to recover. In the future, it will be necessary for the global environment to reduce the use of plastic.

On the other hand, the use of biodegradable plastics that can be completely decomposed by microorganisms has been proposed around the world as a measure against plastic waste. Biodegradable plastics decompose in nature within a certain period of time, but until they decompose they are still waste, and unless their usage and disposal amounts are reduced, this cannot be considered an immediate solution (see Patent Documents 1 and 2).

As an immediate solution, it has been proposed to replace plastic with paper, but when processing paper into bags and containers, a large amount of polyethylene or polypropylene is laminated as a heat sealant. The amount of plastic laminate varies depending on the product concept, but is generally 20 to 50 g/ ^m2 , and can be as much as 300 g/ ^m2 . Therefore, even in packaging containers where plastic has been replaced with paper, there is still the problem that the amount of plastic used is not sufficiently reduced, and a means to directly reduce the use of plastic is urgently needed.

JP 2012-148444 A JP 2013-141763 A

The objective of the present invention is to provide packaging paper that can reduce the amount of plastic used.

In the present invention, an ionomer is used to reduce the amount of polyethylene or polypropylene used in conventional plastic laminated paper (hereinafter sometimes abbreviated as polylaminated paper). That is, the packaging paper according to the present invention is a packaging paper having at least one heat seal layer on at least one side of a paper base material, the heat seal layer containing an ionomer, and the coating amount of the heat seal layer is 2 to 10 g/ ^m2 . Compared to the amount of polyethylene or polypropylene laminate used in the heat seal layer of conventional polylaminated paper exceeding 20 g/ ^m2 , the amount of plastic used for the heat seal layer can be reduced to about 10 to 50% of the conventional amount. Here, an ionomer is a synthetic resin that uses the coagulation force of metal ions to make a polymer into an aggregate, and is a synthetic resin that combines acrylic acid or methacrylic acid with ethylene or the like. For example, it is produced by adding a metal cation such as sodium or zinc to an acrylic polymer and ethylene to form an intermolecular bond.

In the present invention, the heat seal layer may be formed in two or more layers on at least one side. With this configuration, it is possible to obtain a wrapping paper with high air permeability, water repellency, and oil repellency.

In the present invention, the air permeability of the wrapping paper may exceed 10,000 seconds. By adopting such a configuration, the wrapping paper has high barrier properties in terms of blocking air, and further has improved water repellency and oil repellency.

In the present invention, the ionomer may be a metal salt of an ethylene-methacrylic acid copolymer. This makes it possible to obtain a wrapping paper with excellent heat sealability.

The method for producing packaging paper in the present invention is characterized by comprising the steps of preparing a coating liquid for a heat-seal layer containing an ionomer emulsion, and coating at least one surface of a paper substrate with the coating liquid for a heat-seal layer in an amount of 2 to 10 g/ ^m2 in terms of solid content. In particular, by using an aqueous ionomer emulsion as the ionomer emulsion, it is possible to control the coating amount to a relatively low level, and since there is no VOC emission, packaging paper with a low environmental impact can be obtained.

In the present invention, it is preferable to apply the coating liquid for the heat seal layer to the surface of the paper substrate having a smoothness of 10 seconds or more. This is preferable because the heat seal layer tends to be a uniform thin film layer without becoming island-like or net-like, and there is less variation in the heat seal strength, which results in a higher heat seal strength of the packaging paper. Note that heat seal strength is the most highly desired characteristic when processing packaging containers using packaging paper.

In the present invention, the ionomer emulsion may be a self-emulsifying emulsion. This makes it possible to obtain a packaging paper having a heat seal layer that is thin but uniform in thickness.

The present invention makes it possible to manufacture packaging paper with reduced plastic usage. If a container product uses the packaging paper of the present invention, it is possible to reduce the adverse impact of plastic waste on the natural environment, even if it is inappropriately released into the natural world as waste, and this helps to solve the plastic waste problem. The packaging paper of the present invention can be processed into general packaging containers, such as bags, food cups for ice cream, beverage cups for coffee, etc., food containers for hot snacks, etc., and trays, boxes, cases, containers, envelopes, etc.

Next, the present invention will be described in detail with reference to an embodiment, but the present invention should not be interpreted as being limited to these descriptions. Various modifications of the embodiment may be made as long as the effects of the present invention are achieved.

In this embodiment, ionomer is a general term for synthetic resins in which polymers are aggregated by utilizing the cohesive force of metal ions, and is a resin in which acrylic acid or methacrylic acid is combined with ethylene or the like. That is, metal salts of ethylene-methacrylic acid copolymers, metal salts of ethylene-acrylic copolymers, metal salts of ethylene-urethane copolymers, metal salts of ethylene-fluorine polymer copolymers, etc. are all called ionomers. Examples of metals that form salts include alkali metal ions and alkaline earth metal ions, specifically, sodium, potassium, calcium, magnesium, and zinc ions. In the present invention, it is preferable that the ionomer is a self-emulsifying emulsion of a metal salt of ethylene-methacrylic acid copolymer. A heat seal layer having sufficient heat seal strength can be provided even if the coating amount of the heat seal layer is relatively small.

In this embodiment, a heat seal layer can be provided by applying a coating liquid for a heat seal layer containing an ionomer emulsion to at least one side of a paper substrate and drying it. By using an ionomer emulsion, it is possible to control the coating amount to a relatively low level, and further, by using an aqueous ionomer emulsion, VOC emissions are eliminated, and the burden on the natural environment can be reduced. The coating amount of the heat seal layer is 2 to 10 g/m ² , preferably 3 to 8 g/m ² , calculated as solid content per one side of the paper substrate. If it is less than 2 g/m ² , sufficient heat seal strength cannot be satisfied. Conversely, if it exceeds 10 g/m ² , the quality is excessive in terms of heat seal strength and the effect of reducing plastics is poor. In the packaging paper of the present invention, the heat seal layer is usually provided on the entire surface of the paper substrate, not only on a part of the surface of the paper substrate. In other words, the heat seal layer is preferably provided so as to cover the entire surface of the paper base material, rather than being provided only in areas required for adhesion by heat sealing, such as in a net, island or line shape.

In addition to the ionomer emulsion, various auxiliary agents may be added to the coating liquid for the heat seal layer. For example, viscosity adjusters, defoamers, leveling agents such as surfactants and alcohols, color pigments, color dyes, etc. However, the addition of these auxiliary agents tends to reduce the heat seal strength, so it is preferable to add them in small amounts, if at all. In this embodiment, it is preferable that the coating liquid for the heat seal layer consists of only an ionomer emulsion.

The method for applying the coating liquid for the heat seal layer is not particularly limited, and any commonly used coating device can be used. For example, various known coating devices can be used, such as an air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray coater, gate roll coater, and lip coater.

In this embodiment, it is preferable that the heat seal layer is formed of two or more layers. By forming two or more layers, the air permeability of the packaging paper can be increased, and further, water repellency and oil repellency can be imparted, and properties similar to or close to those of plastic film laminated paper can be obtained. When the heat seal layer has two or more layers, it is preferable that the coating amount of the lowermost heat seal layer closest to the paper substrate is greater than the total coating amount of the other heat seal layers. This is because the air permeability of the packaging paper can be further improved, and the water repellency and oil repellency can be further improved.

In this embodiment, it is preferable that the air permeability of the wrapping paper exceeds 10,000 seconds. More preferably, it is 12,000 seconds or more, and even more preferably, it is 15,000 seconds or more. By making the air permeability of the wrapping paper 10,000 seconds or more, the barrier property in terms of blocking air is further increased, and the water repellency and oil repellency are further improved. The method of making the air permeability of the wrapping paper 10,000 seconds or more is not particularly limited, but can be achieved, for example, by using a paper base material with high air permeability. Furthermore, the air permeability of the wrapping paper can be increased by increasing the smoothness of the surface on which the heat seal coating liquid is applied. This is because pinholes and cracks can be further reduced in the heat seal layer formed thereafter. For example, the smoothness of the surface on which the heat seal coating liquid is applied can be increased by providing a pigment coating layer and then performing a calendaring process or the like. In addition, applying two or more heat seal layers also has the effect of increasing the air permeability. It is believed that the two-layer coating of the heat seal layer increases air permeability by covering minute pinholes and cracks present in the first coating layer (lower layer) with the second coating layer (upper layer) applied on top of the first layer. Increasing the coating weight of the heat seal layer is also effective in improving air permeability. In terms of film formation of the heat seal layer, air permeability is easily improved by setting the drying temperature after coating of the heat seal layer coating liquid to a temperature equal to or higher than the melting point of the ionomer.

In this embodiment, the smoothness of the surface of the paper substrate to which the heat seal coating liquid is applied is preferably 10 seconds or more. More preferably, it is 20 seconds or more. The higher the smoothness of the paper substrate, the more uniform the thickness of the heat seal layer applied (the less likely fine irregularities are to occur), and as a result, the less variation in heat seal strength is likely to occur, and uniform heat seal strength can be imparted to the flat surface. The method for increasing the smoothness of the paper substrate is not particularly limited, and examples include calendaring using known calendaring devices such as super calendaring, gloss calendaring, shoe nip calendaring, and soft calendaring. In addition, paper to which the mirror surface of a Yankee dryer, such as one-sided gloss kraft paper, is also suitable as a paper substrate with high smoothness. Note that the heat seal layer may have pinholes or cracks that are invisible to the naked eye, but if they are to that extent, they do not adversely affect the heat sealability. In addition, a leveling agent for preventing pinholes can be added to the heat seal layer coating liquid as long as it does not impair the effects of the present invention.

The paper base material used in this embodiment is not particularly limited, and any known paper base material containing pulp as the main component can be used. As the pulp that is the main component of the paper base material, chemical pulps such as LBKP (hardwood bleached kraft pulp) and NBKP (softwood bleached kraft pulp), mechanical pulps such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP (thermo-mechanical pulp), CTMP (chemi-thermo-mechanical pulp), CMP (chemi-mechanical pulp), and CGP (chemi-ground pulp), wood pulps such as DIP (deinked pulp), and non-wood pulps such as kenaf, bagasse, bamboo, and cotton can be used. These can be used alone or mixed in any ratio. For example, 90 to 100 parts by mass of LBKP (hardwood bleached kraft pulp) can be used as the pulp. In addition, synthetic fibers can be further blended within a range that does not impair the intended effect of the present invention. From the viewpoint of environmental conservation, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, waste paper pulp, and pulp obtained from planted trees are preferred. In addition, for example, the appropriate beating degree of pulp is 200 to 700 ml CSF, for example 450 to 620 ml CSF in Canadian Standard Freeness (JIS P 8121: 1995 "Testing Method for Pulp Freeness").

The paper base material may contain a filler. Examples of fillers include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, and aluminum hydroxide. The filler content in the paper base material is, for example, 1 to 30 parts by mass per 100 parts by mass of the dry mass of the pulp. For example, it is preferable to include 1 to 10 parts by mass of light calcium carbonate per 100 parts by mass of the dry mass of the pulp.

In addition to the pulp and filler, the paper base material may contain various known papermaking additives. Examples of papermaking additives include sizing agents, internal paper strength enhancers such as wet strength agents, bulking agents, retention improvers, drainage improvers, coloring dyes, coloring pigments, fluorescent brighteners, fluorescent decolorizers, and pitch control agents. The paper base material may also be coated with water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide.

The method for making the paper base material is not particularly limited, and the paper base material can be made using various papermaking machines such as a Fourdrinier papermaking machine, a multi-layer Fourdrinier papermaking machine, a cylinder papermaking machine, a multi-layer cylinder papermaking machine, a multi-layer Fourdrinier cylinder papermaking machine, and a twin-wire papermaking machine. In addition, in the present invention, the paper base material may be a single layer or multi-layer papermaking machine, or a laminated product of multiple layers.

The paper substrate may have one or more coating layers other than the heat seal layer, for example, a pigment coating layer containing a pigment and an adhesive. The pigment in the pigment coating layer may be a known pigment used in the coating layer of a general printing coated paper, for example, calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), kaolin (including clay), calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, magnesium hydroxide, or other inorganic pigments, or acrylic, styrene, vinyl chloride, nylon itself, or organic pigments obtained by copolymerizing these (so-called plastic pigments). For example, a combination of 20 to 40 parts by mass of kaolin and 60 to 80 parts by mass of heavy calcium carbonate may be used as the pigment. The adhesive may be a known adhesive used in the coating layer of a general coated printing paper, and examples of such adhesives include starches such as butadiene-based copolymer latex, crosslinker-modified starch, oxidized starch, enzyme-modified starch, esterified starch, cationic starch, and amphoteric starch, water-soluble polymers such as gelatin, casein, soybean protein, and polyvinyl alcohol, and synthetic resins such as vinyl acetate, ethylene vinyl acetate, polyurethane resins, acrylic resins, polyester resins, and polyamide resins. The blending ratio of the pigment and adhesive in the pigment coating layer is not particularly limited, but it is preferable to use 5 to 50 parts by mass of the adhesive per 100 parts by mass of the pigment. For example, the adhesive may be a combination of 1 to 5 parts by mass of phosphated starch and 5 to 15 parts by mass of styrene butadiene latex per 100 parts by mass of the pigment. The pigment coating layer may contain various auxiliaries within the range that does not impair the intended effect of the present invention, such as a viscosity regulator, a softener, a gloss imparting agent, a water resistant agent, a dispersant, a flow modifier, an ultraviolet absorbing agent, a stabilizer, an antistatic agent, a crosslinking agent, a sizing agent, a fluorescent brightening agent, a colorant, a pH adjusting agent, an antifoaming agent, a plasticizer, and a preservative. The coating amount of such a pigment coating layer is, for example, 2 to 40 g/ ^m2 in terms of solid content per one side of the base paper. In one embodiment of the packaging paper of the present invention, the heat seal layer may be provided on such a pigment coating layer, and in another embodiment, the heat seal layer may be provided on the side of a paper base material having a pigment coating layer on only one side, on which the pigment coating layer is not provided.

In this embodiment, the basis weight of the packaging paper is not particularly limited, but is, for example, 10 to 1000 g/m ^2. The basis weight of packaging paper that has high barrier properties, water repellency, and oil repellency and can be used for flexible packaging is preferably 30 to 500 g/m ² , and more preferably 50 to 300 g/m ² .

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of parts added is a value calculated as the solid content.

Example 1
(Preparation of base paper)
A stock was prepared by adding water to 100 parts of hardwood bleached kraft pulp with a Canadian Standard Freeness of 520 mlcsf, 5 parts of light calcium carbonate (product name: TP-121, manufactured by Okutama Kogyo Co., Ltd.), 0.2 parts of cationic starch (product name: Neotac 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.), and 0.2 parts of neutral rosin size (product name: CC167, manufactured by Seiko PMC Co., Ltd.), and a base paper with a basis weight of 58 g/ ^m2 was produced using a fourdrinier multi-cylinder papermaking machine. Oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to this base paper by a gate roll coater so that the dry coating amount on each side was 2 g/ ^m2 , and then dried to obtain a base paper with a weight of 60 g/ ^m2 .

(Preparation of coating liquid for pigment coating layer)
A pigment slurry was prepared by adding 0.2 parts of a dispersant (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) to 30 parts of kaolin (trade name: Contour 1500, manufactured by Imerys Co., Ltd.) and 70 parts of heavy calcium carbonate (trade name: Carbilux, manufactured by Imerys Co., Ltd.), adding water, and dispersing the mixture in water using a Coles disperser. To this pigment slurry, 2 parts of phosphated starch (trade name: MS4600, manufactured by Nihon Shokuhin Kako Co., Ltd.) and 8 parts of styrene butadiene latex (trade name: PA0372, Nippon A&L Co., Ltd.) were added as binders, and further water was added thereto to disperse the mixture, thereby preparing a coating liquid for a pigment coating layer having a solids concentration of 50%.

(Preparation of paper substrate)
The coating solution for the pigment coating layer was applied to both sides of the base paper obtained above using a blade coater so that the dry coating amount per side was 10 g/ ^m2 , and then dried. Then, a calendaring process was performed to produce a paper base material (coated paper) with a basis weight of 80 g/ ^m2 . The smoothness of the coated surface (the surface on which the heat seal layer will be provided in a later process) was 400 seconds.

(Making wrapping paper)
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to one side of the paper base material obtained above using an air knife coater so that the dry coating amount was 5 g/ ^m2 , and then dried to provide a heat seal layer, thereby producing packaging paper.

Example 2
A packaging paper was prepared in the same manner as in Example 1, except that the coating amount of the heat seal layer was changed to 10 g/ ^m2 .

Example 3
A packaging paper was prepared in the same manner as in Example 1, except that the coating amount of the heat seal layer was changed to 9 g/ ^m2 .

Example 4
A packaging paper was prepared in the same manner as in Example 1, except that the coating amount of the heat seal layer was changed to 2 g/ ^m2 .

Example 5
A packaging paper was prepared in the same manner as in Example 1, except that the coating amount of the heat seal layer was changed to 3 g/ ^m2 .

Example 6
A base paper was prepared in the same manner as in Example 1. Next, the same coating liquid for the pigment coating layer as in Example 1 was applied as a lower layer to both sides with a gate roll coater at a dry coating amount of 10 g/ ^m2 per side. Next, the same coating liquid for the coating layer as in Example 1 was applied as an upper layer to both sides with a blade coater at a dry coating amount of 10 g/ ^m2 per side, and the resulting paper was treated with a super calendar to prepare a paper substrate (coated paper) with a basis weight of 100 g/ ^m2 . The smoothness of the coated surface (the surface on which the heat seal layer will be provided in a later process) at this time was 2500 seconds. Next, a heat seal layer was provided on one side of the paper substrate obtained above in the same manner as in Example 1 to prepare a packaging paper.

( Reference example 7)
(Preparation of paper substrate)
A paper stock was prepared by adding water to 100 parts of hardwood bleached kraft pulp with a Canadian Standard Freeness of 580 mlcsf, 5 parts of light calcium carbonate (trade name: TP-121, manufactured by Okutama Kogyo Co., Ltd.), 0.2 parts of cationic starch (trade name: Neotac 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.), and 0.2 parts of neutral rosin size (Size Pine NT-78: manufactured by Arakawa Chemical Industries Co., Ltd.), and a base paper with a basis weight of 188 g/ ^m2 was produced using a fourdrinier multi-cylinder papermaking machine. Oxidized starch (trade name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to this base paper by a size press so that the dry coating amount per both sides was 2 g/ ^m2 , and dried to obtain a paper base material of 190 g/ ^m2 . The smoothness of the surface of the paper base material (the surface on which a heat seal layer was provided in a later process) was 10 seconds.

(Making wrapping paper)
An aqueous ionomer emulsion (product name: Chemipearl S-100, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.1 μm) was applied to one side of the paper base material obtained above using an air knife coater so as to give a dry coating amount of 6 g/ ^m2 , and then dried to provide a heat seal layer, thereby producing packaging paper.

( Reference example 8)
A wrapping paper was prepared in the same manner as in Reference Example 7, except that the base paper was subjected to a calendaring treatment after coating with oxidized starch. The smoothness of the surface of the base paper (the surface on which a heat seal layer was to be formed in a later step) was 20 seconds.

( Reference example 9)
(Preparation of paper substrate)
A paper stock was prepared by adding water to 100 parts of hardwood bleached kraft pulp with a Canadian Standard Freeness of 580 mlcsf, 5 parts of light calcium carbonate (trade name: TP-121, manufactured by Okutama Kogyo Co., Ltd.), 0.2 parts of cationic starch (trade name: Neotac 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.), and 0.2 parts of neutral rosin size (Size Pine NT-78: manufactured by Arakawa Chemical Industries Co., Ltd.), and a base paper (three-layer paper) with a basis weight of 298 g/ ^m2 was produced using a three-layer four-cylinder papermaking machine. Oxidized starch (trade name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to this base paper by a size press so that the dry coating amount per both sides was 2 g/ ^m2 , and the base paper was dried and soft calendared to obtain a paper base material with a basis weight of 300 g/ ^m2 . The smoothness of the surface of the paper base material (the surface on which a heat seal layer is provided in a later process) was 100 seconds.

(Making wrapping paper)
An aqueous ionomer emulsion (product name: Chemipearl S-500, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.7 μm) was applied to one side of the paper base material obtained above using an air knife coater so as to give a dry coating amount of 4 g/ ^m2 , and then dried to provide a heat seal layer, thereby producing packaging paper.

(Example 10)
The same coating liquid for the pigment coating layer as in Example 1 was applied to one side of the paper substrate obtained in Reference Example 9 using an air knife coater so that the dry coating amount was 20 g/ ^m2 , and the paper substrate was treated with a soft calendar to produce a paper substrate of 320 g/ ^m2 . The smoothness of the uncoated side of this paper substrate (the side of the paper substrate on which the pigment coating layer was not provided) was 150 seconds. Next, a heat seal layer was provided on the uncoated side of the paper substrate obtained above in the same manner as in Example 1, and a packaging paper was produced.

( Reference example 11)
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to one side of the paper substrate obtained in Reference Example 9 using an air knife coater so that the dry coating amount was 5 g/ ^m2 , and then dried to provide a heat seal layer (lower layer). Next, the same aqueous ionomer emulsion was applied to the surface of the heat seal layer (lower layer) using an air knife coater so that the dry coating amount was 2 g/ ^m2 , and then dried to provide a heat seal layer (upper layer), thereby producing a packaging paper.

Example 12
On the non-coated surface of the paper substrate prepared in Example 10 (the surface on which the pigment coating layer of the paper substrate is not provided), an aqueous ionomer emulsion (product name: MYE-30ER, manufactured by Maruyoshi Chemical Co., Ltd., composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, microtrack method average particle size 0.2 μm) was applied using an air knife coater so that the dry coating amount was 3 g / m ² , and dried to provide a heat seal layer (lower layer). Next, on the surface of the heat seal layer (lower layer), an aqueous ionomer emulsion (product name: MYE-30MAZ, manufactured by Maruyoshi Chemical Co., Ltd., composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, microtrack method average particle size 0.3 μm) was applied using an air knife coater so that the dry coating amount was 1 g / m ² , and dried to provide a heat seal layer (upper layer), and a packaging paper was prepared.

Example 13
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to the uncoated surface of the paper substrate prepared in Example 10 (surface of the paper substrate not provided with a pigment coating layer) using an air knife coater so that the dry coating amount was 5 g/ ^m2 , and then dried to provide a heat seal layer (lower layer). Next, the same aqueous ionomer emulsion was applied to the surface of the heat seal layer (lower layer) using an air knife coater so that the dry coating amount was 1 g/ ^m2 , and then dried to provide a heat seal layer (upper layer), thereby producing a packaging paper.

(Example 14)
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to the uncoated surface of the paper substrate prepared in Example 10 (surface of the paper substrate not provided with a pigment coating layer) using an air knife coater so that the dry coating amount was 1 g/ ^m2 , and then dried to provide a heat seal layer (lower layer). Next, the same aqueous ionomer emulsion was applied to the surface of the heat seal layer (lower layer) using an air knife coater so that the dry coating amount was 9 g/ ^m2 , and then dried to provide a heat seal layer (upper layer), thereby producing a packaging paper.

(Example 15)
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to the uncoated surface of the paper substrate prepared in Example 10 (surface of the paper substrate not provided with a pigment coating layer) using an air knife coater so that the dry coating amount was 9 g/ ^m2 , and then dried to provide a heat seal layer (lower layer). Next, the same aqueous ionomer emulsion was applied to the surface of the heat seal layer (lower layer) using an air knife coater so that the dry coating amount was 1 g/ ^m2 , and then dried to provide a heat seal layer (upper layer), thereby producing a packaging paper.

( Reference example 16)
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to one side of the paper substrate prepared in Reference Example 7 using an air knife coater so that the dry coating amount was 5 g/ ^m2 , and then dried to provide a heat seal layer (lower layer). Next, the same aqueous ionomer emulsion was applied to the surface of the heat seal layer (lower layer) using an air knife coater so that the dry coating amount was 1 g/ ^m2 , and then dried to provide a heat seal layer (upper layer), thereby preparing a packaging paper.

( Reference example 17)
An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size by Microtrack method: 0.5 μm) was applied to both sides of the paper substrate prepared in Reference Example 7 using an air knife coater so that the dry coating amount per side was 5 g/ ^m2 , and then dried to provide a heat seal layer (lower layer). Next, the same aqueous ionomer emulsion was applied to both sides of the upper substrate using an air knife coater so that the dry coating amount per side was 1 g/ ^m2 , and then dried to provide a heat seal layer (upper layer), thereby preparing a packaging paper.

(Comparative Example 1)
A heat seal layer was formed by laminating low-density polyethylene (Petrothene DLZ19A, manufactured by Tosoh Corporation) to a coating amount of 30 g/ ^m2 using an extrusion coater (melt extruder) on one side of the paper base material prepared in Example 1, thereby preparing a packaging paper.

(Comparative Example 2)
One side of the paper base material prepared in Example 1 was laminated with polypropylene (Novatec FL03H, manufactured by Japan Polypropylene Corporation) using an extrusion coater (melt extruder) to a coating amount of 30 g/ ^m2 to provide a heat seal layer, thereby preparing a packaging paper.

(Comparative Example 3)
A wrapping paper was prepared in the same manner as in Example 1, except that the aqueous ionomer emulsion in Example 1 was changed to an aqueous polyethylene emulsion (SN Coat 287, manufactured by San Nopco Ltd.).

(Comparative Example 4)
A wrapping paper was prepared in the same manner as in Example 1, except that the aqueous ionomer emulsion in Example 1 was changed to an aqueous polypropylene emulsion (Hitec P-5300, manufactured by Toho Chemical Industry Co., Ltd.).

The wrapping papers obtained in each of the Examples , Reference Examples , and Comparative Examples were evaluated by the methods described below. The results are shown in Tables 1 to 3. For the sake of convenience, when there was only one heat seal layer, the coating amount was recorded in the column for the coating amount of the upper layer of the heat seal layer.

(1) Smoothness In accordance with JIS P 8155:2010, the smoothness (seconds) of the surface adjacent to the heat seal layer of the paper substrate (the surface on which the heat seal layer is formed) before providing the heat seal layer was measured using a digital Oken type air permeability smoothness tester (manufactured by Asahi Seiko Co., Ltd., model number: EYDO-6-2M). A higher value indicates a smoother surface of the paper substrate.

(2) Air permeability The air permeability (sec) of the packaging paper was measured using a digital Oken type air permeability smoothness tester (manufactured by Asahi Seiko Co., Ltd., model number: EYDO-6-2M) in accordance with JIS P 8117: 2009. A higher value indicates lower air permeability (higher barrier properties).

(2) Heat seal strength The obtained wrapping paper was cut into two pieces with a width of 8 mm and a length of 15 cm, and the front and back sides of the wrapping paper were overlapped and heat sealed under certain conditions (adhesive width: 4 mm, temperature: 180°C, pressure: 0.4 MPa, pressing time: 0.5 seconds, pitch: 4 mm) using a heat sealer (manufactured by Palmec, model number: PTS-100). Next, the heat-sealed sample was subjected to a peel strength test under certain conditions (peel speed: 100 mm/min, peel length: 10 cm) using a peel strength tester (manufactured by Shimadzu Corporation, model number: Autograph AGS-X) to measure the peel strength, which was determined as the heat seal strength (gf/4 mm). The higher the value, the better. In addition, when both sides are heat seal layers, this is the adhesive strength between the heat seal layers.

(3) Water repellency: The water repellency of the heat seal layer surface was evaluated according to JIS K 6768:1999 (Plastics - Films and sheets - Wetting tension test method). The lower the number, the higher the water repellency (the less likely it is to get wet). When there are heat seal layers on both sides, the average value of both sides was used.

(4) Oil repellency The oil repellency of the heat seal layer surface was evaluated according to TAPPI T-559cm-02 (kit method). A higher value (kit value) indicates higher oil repellency. When heat seal layers were present on both sides, the average value of both sides was used.

As is clear from Tables 1 to 3, the wrapping papers of Examples 1 to 6, 10, and 12 to 15 had the same or higher heat seal strength as Comparative Examples 1 and 2, despite the amount of the heat seal layer being significantly reduced. Also, the wrapping papers were clearly superior in heat seal strength to Comparative Examples 3 and 4. As the experimental results show, the present invention can provide wrapping papers that have excellent barrier properties, water repellency, and oil repellency while significantly reducing the amount of heat seal layer used compared to the amount of conventional polyethylene laminate, and contributing to reducing plastic waste.

Claims (13)

A packaging paper consisting of only a paper base material, a heat seal layer, and a pigment coating layer, the heat seal layer being provided on one or more pigment coating layers, and having at least one heat seal layer on at least one side of the paper base material, the heat seal layer containing an ionomer, the dry coating weight of the heat seal layer being 2 to 10 g/ ^m2 in total, and the ionomer being a metal salt of an ethylene-methacrylic acid copolymer. A packaging paper consisting of only a paper base material, a heat seal layer, and a pigment coating layer, the paper base material having a pigment coating layer only on one side thereof, and the paper base material having a heat seal layer on the side thereof on which the pigment coating layer is not provided, the heat seal layer containing an ionomer, the dry coating amount of the heat seal layer being 2 to 10 g/ ^m2 in total, and the ionomer being a metal salt of an ethylene-methacrylic acid copolymer. The wrapping paper according to claim 1 or 2, characterized in that the heat seal layer is formed in two or more layers on at least one side. The wrapping paper according to any one of claims 1 to 3, characterized in that the air permeability exceeds 10,000 seconds. The wrapping paper according to any one of claims 1 to 4, characterized in that the heat seal layer is made of only ionomer. The wrapping paper according to any one of claims 1 to 5, characterized in that the wrapping paper has a basis weight of 10 to 1000 g/ ^m2 . A pigment coating layer is applied to at least one side of the paper substrate, and then
A step of preparing a coating liquid for a heat seal layer containing an aqueous ionomer emulsion;
and applying the heat seal layer coating liquid to at least one surface of a paper substrate in an amount of 2 to 10 g/ ^m2 in terms of solid content;
the ionomer in the aqueous ionomer emulsion is a metal salt of an ethylene-methacrylic acid copolymer;
A method for manufacturing packaging paper consisting of only a paper base material, a heat seal layer, and a pigment coating layer. A pigment coating layer is applied to one side of the paper base, and then
A step of preparing a coating liquid for a heat seal layer containing an aqueous ionomer emulsion;
and applying the heat seal layer coating liquid to a surface of the substrate layer on which no pigment coating layer is provided, in an amount of 2 to 10 g/ ^m2 calculated as a solid content.
the ionomer in the aqueous ionomer emulsion is a metal salt of an ethylene-methacrylic acid copolymer;
A method for manufacturing packaging paper consisting of only a paper base material, a heat seal layer, and a pigment coating layer. The method for manufacturing packaging paper according to claim 7 or 8, characterized in that the coating liquid for the heat seal layer is applied to a surface of the paper base material having a smoothness of 10 seconds or more. The method for producing packaging paper according to any one of claims 7 to 9, characterized in that the aqueous ionomer emulsion is a self-emulsifying emulsion. The method for manufacturing packaging paper according to any one of claims 7 to 10, characterized in that the heat seal layer is made of only ionomer. The method for manufacturing packaging paper according to any one of claims 7 to 11, characterized in that the heat seal layer is formed in two or more layers on at least one side. The method for manufacturing a packaging paper according to any one of claims 7 to 12, characterized in that the packaging paper has a basis weight of 10 to 1000 g/ ^m2 .