Packaging paper and method for manufacturing the same

Abstract

The present invention aims to provide a method for manufacturing packaging paper that can reduce plastic waste. [Solution] The present invention relates to packaging paper having at least one heat-seal layer on both sides of a paper substrate, characterized in that the heat-seal layer on one side is a part-coat layer (also referred to as a heat-seal part-coat layer or simply a part-coat layer). Furthermore, a method for manufacturing packaging paper having at least one heat-seal layer on both sides of a paper substrate, characterized in that a heat-seal layer is provided on one side by part-coating a heat-seal layer coating liquid using a gravure printing method.

Description

[Technical Field]

[0001] This invention relates to packaging paper that reduces plastic waste and a method for producing the same. [Background technology]

[0002] In recent years, the plastic waste problem has become increasingly serious. Global plastic production is said to exceed 400 million tons per year, with the packaging sector accounting for a large portion and contributing significantly to plastic waste. Plastic does not decompose semi-permanently, and its waste breaks down into microplastics in the natural environment, severely impacting ecosystems. The most commonly used plastics in packaging are polyethylene terephthalate (PET), used in beverage bottles, and polyethylene (PE) and polypropylene (PP), used in shopping bags and container laminations. Marine pollution, in particular, is severe, and the resulting plastic waste is considered impossible to recover. Reducing plastic use is essential for the global environment.

[0003] On the other hand, the application of biodegradable plastics, which can be completely decomposed by microorganisms, is being proposed worldwide as a measure against plastic waste. Although biodegradable plastics decompose in nature within a certain period of time, they are still waste until they decompose, and unless their usage and disposal amounts are reduced, it cannot be said to be an immediate solution (see Patent Documents 1 and 2).

[0004] As an immediate solution, replacing plastic with paper has been proposed. However, when paper is processed into bags and containers, large amounts of polyethylene or polypropylene are laminated as a barrier layer. The amount of these plastics laminated varies depending on the product concept, but is generally around 20-50 g / m². 2 It is 300g / m 2In some cases, the amount of plastic used can be quite large. Therefore, even with packaging containers that replace paper with plastic, the amount of plastic used is still not sufficiently reduced, and there is an urgent need for direct measures to reduce the use of plastic.

[0005] To address these problems, various methods have been proposed, such as applying barrier agents or heat sealants to paper substrates using a coater. However, this method is more expensive than laminated products, and a manufacturing method that reduces costs is needed. Furthermore, when heat-sealing products coated with the above-mentioned coater (heat sealant) have the problem of reduced processing efficiency compared to laminated products. As a measure to reduce manufacturing costs, a manufacturing method has been proposed in which a heat seal layer coating liquid is applied to the opposite side (paper substrate) of the gravure printed surface using a gravure plate (see Patent Document 3). However, in order to align the part-coat layer, it was necessary to introduce a control device to the printing press or to add a registered trademark mark to the printed material. Moreover, when a heat sealant is applied to only one side and processed by overlapping it with the side without a heat seal layer, the heat seal strength is still insufficient with conventional lamination processing machines. This is thought to be because the heat seal layer is conceptually thinner than the laminate layer, and its heat seal adhesion cannot keep up with high-speed processing machines. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-148444 [Patent Document 2] Japanese Patent Publication No. 2013-141763 [Patent Document 3] Japanese Patent Publication No. 2022-22688 [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide a method for manufacturing packaging paper that can reduce plastic waste. With the present invention, it is possible to obtain packaging paper that has excellent heat sealing efficiency and cost performance. [Means for solving the problem]

[0008] The present invention relates to packaging paper having at least one heat-seal layer on both sides of a paper substrate, characterized in that the heat-seal layer on one side is a part-coat layer (also referred to as a heat-seal part-coat layer or simply a part-coat layer). Furthermore, the present invention relates to a method for manufacturing packaging paper having at least one heat-seal layer on both sides of a paper substrate, characterized in that the heat-seal layer on one side is coated with a heat-seal coating liquid using a gravure printing method. In the present invention, cost reduction is possible by making one side a part-coat layer. Furthermore, by using a gravure printing machine for heat-seal layer coating, it is possible to apply a part-coat only to the parts where a heat-seal layer is needed, eliminating the need to coat the entire surface with a heat-seal layer and thus reducing costs. Moreover, because the heat-seal layer is present on both sides of the paper substrate, when the front and back surfaces of the packaging paper are heat-sealed together, sufficient heat-seal strength can be obtained even in processes such as the molding of paper cups, resulting in excellent packaging material processing efficiency. Furthermore, it is possible to perform the heat-seal coating liquid part-coat and design printing with printing ink in a single process, which can reduce manufacturing costs.

[0009] In a preferred embodiment of the present invention, the heat-seal layer on the side opposite the part-coated surface has barrier properties. A barrier-type packaging paper can be obtained by having a barrier-type heat-seal layer (hereinafter also referred to as the barrier layer). Furthermore, the packaging paper can be manufactured in a single process without requiring a new barrier layer, thereby reducing manufacturing costs.

[0010] In the present invention, the heat-sealing layer (barrier layer) having barrier properties is provided by coating using a gravure printing method. In the gravure printing method, it is preferable to use a honeycomb plate as the plate of the coating roll for the barrier layer. By using a honeycomb plate, the leveling property of the coating liquid for the barrier agent is improved, and it becomes possible to obtain a barrier layer with fewer pinholes compared to conventional lattice plates and diagonal line plates, etc. Further, it is preferable to add alcohol to the coating liquid for the barrier layer. By adding alcohol, the leveling property of the coating liquid is improved and the barrier property is improved. Also, it is preferable to form two or more layers of the barrier layer on at least one surface. It is possible to maintain the barrier property at a higher level. Furthermore, in the present invention, it is preferable that the moisture content of the paper base material conforming to JIS P8127 is 5 to 9%. Variation in the dimensions of the paper base material in the gravure machine can be suppressed, and control of the application position of the part coat layer becomes easy.

Effects of the Invention

[0011] According to the present invention, it is possible to manufacture packaging paper that can reduce plastic waste with high efficiency and at low cost. In addition, as the uses of the packaging paper manufactured by the present invention, for example, it can be used for all packaging containers such as bags, cartons, cups, trays, boxes, cases, containers, etc.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a preferred embodiment of the packaging paper of the present invention. [Figure 2] FIG. 2 is a view showing a schematic top view of a honeycomb plate.

Modes for Carrying Out the Invention

[0013] Next, embodiments of the present invention will be shown and described in detail, but the present invention is not construed as being limited to these descriptions. As long as the effects of the present invention are achieved, the embodiments may be variously modified.

[0014] The present invention provides a packaging paper having at least one heat-seal layer on both sides of a paper substrate, characterized in that the heat-seal layer on one side is a part-coat layer. Here, a part-coat layer refers to a layer in which the heat-seal layer is applied only to a specified portion, rather than to the entire surface of one side of the paper substrate. The heat-seal layer generally contains a substance that imparts heat-sealability. Examples include synthetic resins such as vinyl acetate, ethylene vinyl acetate (EVA), polyurethane resins, acrylic resins, styrene acrylic resins, ionomer resins, polyvinylidene chloride resins (PVDC), ethylene copolymer resins, polylactic acid (PLA), and polybutylene succinate (PBS). More preferably, from the viewpoint of heat-seal strength, ionomer resins and ethylene copolymer resins are used. As mentioned above, applying aqueous dispersions of these is preferable from the viewpoint of environmental considerations.

[0015] In this embodiment, ionomer is a general term for synthetic resins in which polymers are aggregated using the cohesive force of metal ions, and is a resin obtained by combining acrylic acid or methacrylic acid with ethylene or the like. That is, metal salts of ethylene-methacrylic 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 are alkali metal ions, 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 which is a metal salt of ethylene-methacrylic copolymer. A heat seal layer with sufficient heat seal strength can be provided even with a relatively small amount of heat seal layer coating.

[0016] The part-coat layer of the present invention may be manufactured by any manufacturing method. On the other hand, in the method for manufacturing packaging paper having at least one heat-seal layer on both sides of the paper substrate of the present invention, the heat-seal layer is provided on one side by part-coating a heat-seal layer coating liquid using a gravure printing method. If a gravure printing machine is used, roll winding and movement are not required, and for example, design printing with printing ink can be performed without going through multiple processes.

[0017] Furthermore, the packaging paper of the present invention is preferably a packaging paper having barrier properties. These barrier properties include, for example, gas barrier properties such as water vapor barriers and oxygen barriers, odor barriers, heat barriers, water repellency, and oil repellency. Examples of barrier agents include butadiene copolymer latex (SBR), starch, gelatin, casein, soy protein, water-soluble polymers such as polyvinyl alcohol (PVA) and butenediol vinyl alcohol copolymer (BVOH), vinyl acetate, ethylene vinyl acetate (EVA), polyurethane resins, acrylic resins, styrene acrylic resins, ionomer resins, polyvinylidene chloride resins (PVDC), polyester resins (PET), polyamide resins, ethylene copolymer resins, polylactic acid (PLA), polybutylene succinate (PBS), and other synthetic resins. Among these, it is preferable to use one or more resins selected from ethylene vinyl acetate (EVA), acrylic resins, styrene acrylic resins, ionomer resins, and ethylene copolymer resins, as these readily provide good heat sealability along with water vapor barrier, water resistance, and oil resistance. Furthermore, in this invention, it is preferable to use a water-based barrier agent because it eliminates VOC emissions and reduces the environmental burden. In addition, pigments (e.g., light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin clay, calcined clay, titanium dioxide, aluminum hydroxide) may be added to the barrier layer as long as they do not impair the barrier properties. Furthermore, an anti-blocking agent (such as a wax-based lubricant) may be added to the heat seal layer coating liquid as long as it does not impair the heat sealability.

[0018] In one embodiment of the packaging paper of the present invention, barrier properties can be imparted by having a barrier layer having barrier properties on the inside of the heat-seal layer. Furthermore, preferably, in the packaging paper of the present invention, as shown in Figure 1, it is preferable to provide a heat-seal layer having barrier properties as the heat-seal layer on the side opposite to the part-coated surface. That is, it is preferable to make the heat-seal layer on the opposite side the barrier layer. This eliminates the need to provide a separate barrier layer and makes it possible to obtain packaging paper with barrier properties without increasing the manufacturing process. Here, it is preferable to use a substance that imparts heat-seal properties and also acts as a barrier agent in the barrier layer. Furthermore, the substance that imparts heat-seal properties used in the heat-seal layer as described above also acts as a barrier agent. Therefore, in the present invention, for example, synthetic resins such as vinyl acetate, ethylene vinyl acetate (EVA), polyurethane resins, acrylic resins, styrene acrylic resins, ionomer resins, polyvinylidene chloride resins (PVDC), ethylene copolymer resins, polylactic acid (PLA), and polybutylene succinate (PBS), as described above, can also be included in the heat-seal layer having barrier properties (in the barrier layer).

[0019] In this embodiment, the amount of heat-seal layer, which is a part-coat layer, and the amount of heat-seal layer (barrier layer) having barrier properties applied is 15 g / m² in terms of solid content per side of the paper substrate. 2 The following is preferable. More preferably, the coating amount of the barrier layer is 2 to 13 g / m². 2 It is 2g / m 2 If the density is less than 15 g / m², the coating liquid for the barrier heat seal layer will be absorbed by the paper layer, reducing the density of the coating layer and preventing sufficient barrier properties from being obtained. Conversely, if the density is 15 g / m², the coating liquid for the barrier heat seal layer will be absorbed by the paper layer, reducing the density of the coating layer and preventing sufficient barrier properties from being obtained. 2 If it exceeds this amount, the plastic reduction effect will be diminished. The coating amount for the part coat layer should be 0.5 to 10 g / m². 2 This is preferable. Note that the coating amount for the part-coat section is the coating amount for the coated section only.

[0020] In the present invention, the barrier layer, that is, the heat-sealing layer having barrier properties, is preferably applied by gravure printing, and it is preferable that the plate of the coating roll at that time is a honeycomb plate. The plate used for gravure printing is based on a metal roll (base cylinder) made of iron or aluminum, and its surface is plated, and a small concave depression called a "cell" that becomes the pattern to be printed is made to form the plate. A schematic diagram of the honeycomb plate is shown in FIG. 1. The honeycomb plate is a plate in which hexagonal cells are arranged two-dimensionally as shown in FIG. 1 (hexagonal concave depressions are arranged). The coating liquid for the barrier layer enters this cell and is transferred to the paper substrate. By using the honeycomb plate, the leveling property of the coating liquid for the barrier agent is increased, and it is possible to obtain a barrier layer with fewer pinholes compared to conventional lattice plates and diagonal plates. The pitch of the honeycomb plate cells is preferably 80 lines / inch to 200 lines / inch. Further, since the coating device is a gravure printing machine, it is possible to provide a plurality of layers of barrier layers in one step without requiring the processes of winding and moving the roll. Further, for the same reason, it is also possible to perform design printing on the opposite side of the barrier layer coating in one step. Therefore, it is possible to reduce the product cost with higher efficiency than the conventional manufacturing method.

[0021] In the present invention, the Cobb water absorption (120 seconds) of the barrier layer conforming to JIS P8140 is 10 g / m 2 or less, which is preferable. The water repellency becomes good and the barrier property is excellent. Preferably 5 g / m 2 or less, and more preferably 2 g / m 2 or less. However, there is no absolute standard for water repellency, and it varies depending on the product concept. It is only necessary to control the Cobb water absorption to the required level. Also, in the case of a paper substrate, unlike a film substrate, since the barrier layer paint is absorbed by the paper substrate, by optimizing the pitch of the honeycomb plate, pinholes are reduced, the barrier property is improved, and the water repellency is improved. Also, by containing a sizing agent in the paper substrate, it is possible to lower the value of Cobb water absorption and improve the water repellency. The addition amount of the sizing agent is preferably 0.05 parts by mass or more in terms of dry pulp. More preferably, it is 0.1 parts by mass or more.

[0022] In the present invention, it is preferable to add alcohol to the barrier layer coating solution from the viewpoint of barrier properties. Commercially available alcohols such as methanol, ethanol, isopropyl alcohol (IPA), and propanol can be used as the alcohol, but isopropyl alcohol (IPA) is preferred from the viewpoint of barrier properties. The amount added is preferably 1 to 15% by mass relative to the barrier layer coating solution, for example, 2 to 8% by mass. Furthermore, the drying temperature after coating with the barrier layer coating solution is preferably 100 to 200°C. If the drying temperature is below 100°C, the barrier properties of the coating layer will decrease, and if the drying temperature exceeds 200°C, the moisture content of the paper will decrease, making the barrier layer coating layer prone to cracking.

[0023] The paper substrate used in this embodiment is not particularly limited, and known paper substrates mainly composed of pulp can be used. As the pulp that serves as the main component of the paper substrate, chemical pulps such as LBKP (bleached hardwood kraft pulp) and NBKP (bleached softwood kraft pulp), mechanical pulps such as GP (groundwood pulp), PGW (pressure-processed groundwood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemothermetic pulp), CMP (chemimechanical pulp), and CGP (chemigland pulp) can be used, as well as wood pulps such as DIP (deinking pulp) and non-wood pulps such as kenaf, bagasse, bamboo, and cotton. These can be used individually or mixed in any proportion. Furthermore, unbleached pulp that has not been bleached can also be used. For example, as pulp, a combination of 70 to 100 parts by mass of LBKP (bleached hardwood kraft pulp) and 30 to 0 parts by mass of NBKP (bleached softwood kraft pulp) can be used. Preferably, as pulp, a combination of 75 to 98 parts by mass of LBKP (bleached hardwood kraft pulp) and 25 to 2 parts by mass of NBKP (bleached softwood kraft pulp) can be used. Furthermore, synthetic fibers can be further blended within a range that does not impair the effects intended for this invention. From the viewpoint of environmental protection, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, recycled paper pulp, and pulp obtained from plantation trees are preferred. Furthermore, for example, an appropriate degree of pulp beating is 200-700 mlCSF, or 450-620 mlCSF, according to the Canadian standard freeness (JIS P 8121:1995 "Test Method for Pulp Freeness").

[0024] Paper substrates containing fillers can also be used. 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 substrate is preferably 1 to 30 parts by mass per 100 parts by mass of dry pulp. For example, it is preferable to include 1 to 10 parts by mass of light calcium carbonate per 100 parts by mass of dry pulp.

[0025] Furthermore, the paper substrate may contain various known papermaking additives in addition to pulp and fillers. Examples of papermaking additives include sizing agents, internally added paper strength enhancers such as wet paper strength enhancers, bulk enhancers, yield enhancers, water drainage enhancers, coloring dyes, coloring pigments, fluorescent whitening agents, fluorescent decolorizing agents, and pitch control agents. In addition, water-soluble polymers such as starch (e.g., cationized starch), polyvinyl alcohol, and polyacrylamide may be coated. For example, it is preferable to include 0.1 to 0.5 parts by mass of cationized starch per 100 parts by mass of dry pulp. The papermaking method for the paper substrate is not particularly limited and can be manufactured using various papermaking machines such as wire screen machines, wire screen multilayer paper machines, cylinder screen machines, cylinder screen multilayer paper machines, wire screen and cylinder screen combination multilayer paper machines, and twin wire paper machines. Furthermore, in the present invention, the paper substrate may be single-layer, multilayer, or a laminated product of multiple layers.

[0026] Furthermore, it is preferable that the paper substrate contains 0.01% by mass or more of a sizing agent. If the sizing agent content is less than 0.01% by mass, the barrier layer coating liquid penetrates the paper substrate more than necessary, reducing leveling properties and thus lowering barrier performance. Preferably, it is 0.02% by mass or more. Examples of main sizing agents include rosin-based, alkyl ketene dimer (AKD)-based, alkenyl succinic anhydride (ASA)-based, polyvinyl alcohol (PVA)-based, styrene-acrylic copolymer (copolymer)-based, and styrene-methacrylic copolymer-based sizing agents. The content of the sizing agent can be quantified using a gas chromatograph-mass spectrometer (GC-MS). For example, it is preferable to include 0.1 to 0.5 parts by mass of neutral rosin sizing agent per 100 parts by mass of dry pulp.

[0027] The paper substrate may have one or more pigment coating layers other than the barrier layer, for example, a pigment coating layer containing a pigment and an adhesive may be provided. As the pigment in the pigment coating layer, known pigments used in the coating layers of general printing coated paper can be used, for example, inorganic pigments such as 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 organic pigments (so-called plastic pigments) obtained by copolymerizing these, such as acrylic, styrene, vinyl chloride, nylon itself, or copolymers thereof. For example, as the pigment, a combination of preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass of kaolin and preferably 70 to 95 parts by mass, more preferably 80 to 90 parts by mass of heavy calcium carbonate can be used. Furthermore, known adhesives used in the coating layers of general printing coated paper can be used as adhesives. Examples include starches such as butadiene copolymer latex, crosslinking agent modified starch, oxidized starch, enzyme modified starch, esterified starch, etherified starch, cationic starch, and amphoteric starch; water-soluble polymers such as gelatin, casein, soy protein, and polyvinyl alcohol; and synthetic resins such as vinyl acetate, ethylene vinyl acetate, polyurethane resins, acrylic resins, polyester resins, and polyamide resins. The mixing ratio of pigment to adhesive in the pigment coating layer is not particularly limited, but it is preferably 5 to 50 parts by mass of adhesive per 100 parts by mass of pigment, and more preferably 10 to 20 parts by mass. For example, as an adhesive, a combination of 0.1 to 3 parts by mass of phosphate esterified starch and 10 to 20 parts by mass of styrene-butadiene latex can be used per 100 parts by mass of pigment. The pigment coating layer may contain various auxiliary agents to the extent that they do not impair the effects intended for the present invention. For example, it may contain colorants, viscosity modifiers, softeners, gloss enhancers, water-resistant agents, dispersants, flow modifiers, UV absorbers, stabilizers, antistatic agents, crosslinking agents, sizing agents, pH adjusters, defoamers, plasticizers, and preservatives.Furthermore, the amount of such a pigment coating layer applied is, for example, 2 to 40 g / m² in terms of solid content per side of the paper substrate. 2 The pigment coating layer is preferably provided on the inside of the heat-seal layers on both sides. In one embodiment of the packaging paper of the present invention, the barrier layer may be provided on such a pigment coating layer, and in another embodiment, the pigment coating layer may be provided on only one side, a heat-seal part-coat layer may be provided on the outermost surface thereof, and a barrier layer may be provided on the opposite side.

[0028] In this embodiment, the basis weight of the packaging paper is not particularly limited, but for example, 10 to 500 g / m² 2 Therefore, considering the coating and processing suitability of the barrier layer, it is preferably 20 to 400 g / m². 2 It is preferable.

[0029] In this embodiment, it is preferable that the moisture content of the paper substrate is 4 to 10% according to JIS P8127. If the moisture content is less than 4%, the paper substrate will absorb moisture in the gravure machine, causing it to expand and misalign the part-coat area. If the moisture content exceeds 10%, the paper substrate will release moisture in the gravure machine, causing it to shrink and misalign the part-coat area. Preferably, the moisture content of the paper substrate is 5 to 9%. [Examples]

[0030] Next, the present invention will be described more specifically 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. Note that the number of added parts is the value on a solid content basis.

[0031] (Example 1) (Preparation of paper substrate) A pulp was prepared by adding water to 80 parts of Canadian Standard Freeness 530ml csf bleached hardwood kraft pulp, 20 parts of Canadian Standard Freeness 500ml csf bleached softwood kraft pulp, 2.5 parts of light calcium carbonate (product name: TP-121, manufactured by Okutama Kogyo Co., Ltd.), 0.3 parts of cationized starch (product name: Neotack 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.), and 0.35 parts of neutral rosin sizing agent (product name: CC167, manufactured by Seikou PMC Co., Ltd.). The resulting pulp was then processed using a three-layer, long-wire, multi-cylinder papermaking machine to achieve a basis weight of 248 g / m². 2 A base paper was prepared (three-layer papermaking). Oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to this base paper using a gate roll coater at a dry coating rate of 2g / m² per side. 2 Apply so that it becomes 250g / m² and let it dry. 2 A paper substrate was obtained.

[0032] (Preparation of coating solution for pigment coating layer) Fifteen parts of kaolin (product name: Contour 1500, manufactured by Imerys) and eighty-five parts of heavy calcium carbonate (product name: Carvilax, manufactured by Imerys) were mixed with 0.15 parts of a dispersant (product name: Aron T-50, manufactured by Toagosei Co., Ltd.), water was added, and the mixture was dispersed in a Koles disperser to prepare a pigment slurry. To this pigment slurry, one part of phosphated starch (product name: MS4600, manufactured by Nippon Shokuhin Kako Co., Ltd.) and fifteen parts of styrene-butadiene latex (product name: PA0372, manufactured by Nippon A&L Co., Ltd.) were added as binders, and water was further added and dispersed to prepare a coating solution for a pigment coating layer with a solid content of 50%.

[0033] (Preparation of coated paper substrate) Apply the pigment coating solution to both sides of the base paper obtained above, with a dry coating amount of 10 g / m² per side. 2 The surface was coated using a blade coater and dried to achieve the desired finish. Afterwards, it underwent calendering treatment, resulting in a basis weight of 270 g / m². 2 A coated paper substrate was prepared. The moisture content of the coated paper substrate at this time was 5.5%.

[0034] (Formation of a barrier layer in packaging paper) On one side of the coated paper substrate obtained above, a water-based ionomer polymer emulsion (product name: Chemipearl S300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size 0.5 μm by microtrac method) was diluted with isopropyl alcohol (IPA) to a solid content concentration of 33% (IPA addition rate 5.7%), and the total dry coating amount was 8 g / m². 2 To achieve this, the gravure printing press honeycomb plate (175 lines / inch) was used to apply two coats of coating (total coating amount after two coats: 8 g / m²). 2 The material was dried at 120°C to create a barrier layer, and packaging paper was produced.

[0035] (Partial coating on the heat-sealed layer of packaging paper) On the opposite side of the surface where the barrier layer described above is applied, a water-based ionomer polymer emulsion (product name: Chemipearl S300, manufactured by Mitsui Chemicals, Inc.) is diluted with isopropyl alcohol (IPA) to a solid content concentration of 30% (IPA addition rate 5.7%), resulting in a total dry coating weight of 3 g / m². 2 To achieve the desired coating amount (for the part-coated area only), the necessary parts (heat-sealed areas) were partially coated in one pass using a gravure printing machine, dried at 120°C to create a heat-sealed layer, and the packaging paper was manufactured.

[0036] (Example 2) In Example 1, the coating amount of the barrier layer was 15 g / m². 2 Except for the change made, the packaging paper was prepared in the same manner as in Example 1.

[0037] (Example 3) In Example 1, the coating amount of the barrier layer was 4 g / m². 2 Except for the change made, the packaging paper was prepared in the same manner as in Example 1.

[0038] (Example 4) Similar to Example 1, after applying the barrier layer, UV 4-color printing was performed on the side opposite the barrier layer in a single step. Then, a heat seal layer part-coat was applied to the side opposite the barrier layer in a single step, similar to Example 1, to produce the packaging paper.

[0039] (Example 5) In Example 1, the dry coating amount of the heat seal layer part coat was 1 g / m². 2 The packaging paper was prepared in the same manner as in Example 1, except for the difference mentioned above.

[0040] (Example 6) In Example 1, the dry coating amount of the heat seal layer part coat was 8 g / m². 2 The packaging paper was prepared in the same manner as in Example 1, except for the difference mentioned above.

[0041] (Example 7) In Example 1, packaging paper was prepared in the same manner as in Example 1, except that a pigment coating layer was not provided.

[0042] (Example 8) (Preparation of paper substrate) A pulp was prepared by adding water to 95 parts of Canadian Standard Freeness 520ml csf bleached hardwood kraft pulp, 5 parts of Canadian Standard Freeness 520ml csf bleached softwood kraft pulp, 0.2 parts of cationized starch (product name: Neotack 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.), 3 parts of light calcium carbonate (product name: TP-121, manufactured by Okutama Kogyo Co., Ltd.), and 0.3 parts of neutral rosin sizing agent (Sizing Pine NT-78, manufactured by Arakawa Chemical Industries Co., Ltd.). The resulting pulp was then processed using a multi-cylinder, long-wire paper machine to achieve a basis weight of 128 g / m². 2 A base paper was prepared (single-layer papermaking). Oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to this base paper using a gate roll coater at a dry coating rate of 2g / m² per side. 2 Apply so that it becomes 130g / m² and let it dry. 2 A paper substrate was obtained. The moisture content of the paper substrate at this time was 8.5%.

[0043] (Formation of a barrier layer in packaging paper) On one side of the coated paper substrate obtained above, a water-based acrylic polymer emulsion (product name: AQUENCE EPIX BC 900F, manufactured by Henkel) was diluted with water to a solid content concentration of 25%, resulting in a total dry coating weight of 8 g / m². 2To achieve this, the gravure printing press honeycomb plate (175 lines / inch) was used to apply two coats of coating (total coating amount after two coats: 8 g / m²). 2 The material was dried at 120°C to create a barrier layer, and packaging paper was produced.

[0044] (Partial coating on the heat-sealed layer of packaging paper) On the opposite side of the surface where the barrier layer described above is applied, a water-based ionomer polymer emulsion (product name: Chemipearl S300, manufactured by Mitsui Chemicals, Inc.) is diluted with isopropyl alcohol (IPA) to a solid content concentration of 35% (IPA addition rate 5.7%), resulting in a total dry coating amount of 2 g / m². 2 To achieve the desired coating amount (for the part-coated area only), the necessary parts (heat-sealed areas) were partially coated in one pass using a gravure printing machine, dried at 120°C to create a heat-sealed layer, and the packaging paper was manufactured.

[0045] (Example 9) In Example 8, the dry coating amount of the heat seal layer part coat was 8 g / m². 2 The packaging paper was prepared in the same manner as in Example 8, except for the difference mentioned above.

[0046] (Example 10) Similar to Example 8, after applying the barrier layer, UV 5-color printing was performed on the side opposite the barrier layer in a single step. Then, a heat seal layer part-coat was applied to the side opposite the barrier layer in a single step, similar to Example 8, to produce the packaging paper.

[0047] (Example 11) Packaging paper was prepared in the same manner as in Example 8, except that the moisture content of the paper substrate was set to 4.0%.

[0048] (Example 12) Packaging paper was prepared in the same manner as in Example 8, except that the moisture content of the paper substrate was set to 10%.

[0049] (Comparative Example 1) In Example 1, packaging paper was prepared in the same manner as in Example 1, except that a heat-seal layer part-coating was not performed.

[0050] (Comparative Example 2) In Example 8, packaging paper was prepared in the same manner as in Example 8, except that a heat-seal layer part-coating was not performed.

[0051] The packaging paper obtained in each example and comparative example was evaluated using the method described below. The results are shown in Table 1.

[0052] (1) Processing suitability in paper cup processing and molding machines The packaging paper obtained in the above examples and comparative examples was cut using a flat cutting process and then die-cut to predetermined dimensions to form paper cup bodies. The packaging paper obtained in Comparative Example 1 was used as the bottom paper for Examples 1-7 and Comparative Example 1, and the packaging paper obtained in Comparative Example 2 was used as the bottom paper for Examples 8-12 and Comparative Example 2. Furthermore, paper cups were molded using the above materials with a commercially available paper cup molding machine. The processing speed was set to a relatively high 110 cups / minute. The heat-sealed portion of the body paper of the molded paper cups was peeled off by hand, and the material breakage resistance was evaluated visually. In this invention, material breakage refers to the paper layer tearing and peeling off when the heat-sealed adhesive portion is peeled off by hand. The stronger the adhesive strength, the more it peels off at the paper layer. ◎: The entire heat-sealed area of ​​the cardboard body is damaged, but it is still at a usable level. ○: There are a few small areas on the heat-sealed surface of the cardboard body that are not torn, but it is still at a usable level. △: A large portion of the heat-sealed area of ​​the cardboard body is not damaged, making it unsuitable for practical use. ×: A significantly large portion of the heat-sealed area of ​​the cardboard body is not damaged, making it unsuitable for practical use.

[0053] (2) Evaluation of misalignment in the part coat area The packaging paper obtained in the above examples and comparative examples was cut using a flatbed cutting process and then die-cut to the predetermined dimensions to form paper cup bodies. The misalignment of the part-coated portion from the predetermined position was visually evaluated as follows. ◎: There is absolutely no miscalculation, and it is at a practical level. ○: There is a slight miscalculation, but it is at a practical level. ×: The accuracy is significantly off and not practical.

[0054] [Table 1]

[0055] As is clear from Table 1, the packaging papers produced in Examples 1 to 12 showed superior suitability for heat sealing compared to Comparative Examples 1 and 2. In particular, Examples 4 and 10 demonstrated that the number of processes in the production of printed packaging paper could be reduced, thereby enabling cost reduction.

Claims

1. Packaging paper having at least one heat-seal layer on both sides of a paper base material, characterized in that the heat-seal layer on one side is a part-coat layer.

2. The heat-seal layer on the opposite side of the part-coated surface has barrier properties. The packaging paper according to claim 1, characterized by the above.

3. The packaging paper according to claim 1 or 2, characterized in that the moisture content of the paper substrate is 5 to 9% in accordance with JIS P8127.

4. A method for manufacturing packaging paper having at least one heat-seal layer on both sides of a paper substrate, characterized in that a heat-seal layer is provided on one side by partially coating a heat-seal layer coating liquid using a gravure printing method.

5. A method for manufacturing packaging paper according to claim 4, characterized in that a barrier heat seal layer is provided as a heat seal layer on the side opposite to the part-coated surface.

6. A method for manufacturing packaging paper according to claim 5, characterized in that the barrier heat seal layer is provided by coating it using a gravure printing method, and in the gravure printing method, a honeycomb plate is used as the plate for the coating roll for the barrier heat seal layer.

7. A method for manufacturing packaging paper according to any one of claims 4 to 6, characterized in that printing with printing ink is applied to the same surface as the part-coated surface.

8. A method for manufacturing packaging paper according to any one of claims 4 to 6, characterized in that the moisture content of the paper substrate is 5 to 9% in accordance with JIS P8127.

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