Packaging paper manufacturing method

Abstract

To provide a packaging paper sheet which reduces the amount of plastic used and has good heat sealability and water resistance.SOLUTION: This invention relates to a method for manufacturing a packaging paper sheet having a heat seal layer containing one or more of ionomer, ethylene copolymer or thermoplastic urethane on at least one side of a paper base material, and includes a step of applying the heat seal layer on the paper base material, continuously from a papermaking step of the paper base material, by an on-machine method.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing packaging paper that uses less plastic and has good heat sealability and water resistance. [Background technology]

[0002] 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 container 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 plastics.

[0003] As a countermeasure, it has been proposed to replace plastic with paper. However, even when replacing plastic with paper, when processing the paper into bags or containers, a large amount of polyethylene or polypropylene is laminated and used as a heat seal agent. The amount of lamination of these plastics varies depending on the product concept, but is generally 20 to 50 g / m 2 and 300 g / m 2 In some cases, the amount of plastic used can be large. Therefore, even in packaging containers where plastic is replaced with paper, the amount of plastic used is still not sufficiently reduced, and there is an urgent need for a means to directly reduce the use of plastic. Furthermore, these laminated papers have not only heat sealability but also barrier properties such as moisture resistance, water resistance, and oil resistance, and packaging papers that use less plastic are required to have barrier properties equivalent to those of conventional laminated papers, although the required quality level varies depending on the application.

[0004] Thus, the challenge is to develop packaging paper that uses less plastic than laminated paper and has both heat sealability and barrier properties.

[0005] Such a wrapping paper is a wrapping 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 dry coating weight of the heat seal layer is 2 to 10 g / m2 in total. 2 It has been proposed that the amount of plastic used can be reduced and heat sealability can be imparted by using such a material (see Patent Document 1). 2 There has been proposed a method for producing a heat-sealable water vapor barrier paper having a water vapor transmission rate of 1 / 24 h, in which at least one coating layer containing at least one thermoplastic film-forming polymer is applied in-line to a precoat layer on a papermaking machine, the precoat layer is applied in-line to a fibrous substrate, and then the coating layer is applied to the precoat layer to impart moisture resistance and heat sealability (see Patent Document 2).

[0006] However, the packaging paper described in Patent Document 1 has a plastic reduction effect and heat sealability, but its barrier properties are insufficient and it may not achieve the same level of barrier properties as conventional laminated paper. The manufacturing method for heat-sealable barrier paper described in Patent Document 2 has the effect of imparting moisture resistance, but because it uses polyvinylidene chloride or styrene-acrylic copolymer as the thermoplastic resin, its heat sealability is insufficient and there is a risk that the heat-sealed part will not adhere when molded into a bag or cup, or that the sealed part will peel off before or during use of the container. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6580291 [Patent Document 2] Patent No. 6681891 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for producing packaging paper which reduces the amount of plastic used and has good heat sealability, water resistance, material tear resistance and other barrier properties. [Means for solving the problem]

[0009] In the present invention, at least one of ionomer, ethylene-based copolymer, and thermoplastic urethane is used to reduce the amount of plastic contained in conventional plastic-laminated paper (hereinafter sometimes abbreviated as "polylaminated paper"). That is, the method for producing packaging paper according to the present invention is a method for producing packaging paper having a heat seal layer containing at least one of ionomer, ethylene-based copolymer, and thermoplastic urethane on at least one surface of a paper base material, and is characterized in that it includes a process for on-machine coating the heat seal layer on the paper base material, continuous from the papermaking process of the paper base material. It is possible to obtain packaging paper that reduces the amount of plastic contained in the heat seal layer and has good heat sealability and water resistance.

[0010] It is preferable to have an underlayer between the paper substrate and the heat seal layer. With such a configuration, the underlayer has a sealing effect to prevent the heat seal layer coating liquid from penetrating into the paper substrate, thereby making it possible to obtain a packaging paper with better water resistance.

[0011] In the present invention, the under layer preferably contains at least a pigment and a binder. By using such a constitution, a wrapping paper having better water resistance can be obtained due to the sealing effect of the under layer.

[0012] In the present invention, it is preferable that the under layer contains 5 to 200 parts by mass of binder per 100 parts by mass of pigment. With such a configuration, the under layer can obtain a higher sealing effect, and a packaging paper having better water resistance can be obtained. Furthermore, the strength of the under layer is increased, and a packaging paper having excellent heat seal strength can be obtained. In the present invention, it is preferable that the binder contained in the under layer contains a styrene-butadiene copolymer latex, and the particle diameter of the styrene-butadiene copolymer latex is 70 nm or more. With such a configuration, a packaging paper having excellent adhesion to the heat seal layer can be obtained.

[0013] The present invention relates to a heat seal layer comprising at least one of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane on at least one surface of a paper substrate; A wrapping paper having an underlayer between the paper base material and the heat seal layer, the underlayer contains at least a pigment and a binder, The binder contained in the under layer contains a styrene-butadiene copolymer latex having a particle diameter of 70 nm or more and a Cobb water absorption of 3.0 g / m 2 The present invention relates to the wrapping paper described below. The wrapping paper of the present invention has a reduced amount of plastic contained in the heat seal layer and has good heat sealability and water resistance. The wrapping paper can be obtained by including a step of on-machine coating the heat seal layer on the paper base material as described above. Effect of the Invention

[0014] According to the present invention, it is possible to produce packaging paper that reduces the amount of plastic used and has good heat sealability and water resistance. If a container product uses the packaging paper of the present invention, even if it is inappropriately released into the natural world as garbage, it is possible to reduce the adverse effect of plastic garbage on the natural environment, which helps to solve the plastic garbage problem. The packaging paper of the present invention can be processed into general packaging containers such as primary and secondary bags for food packaging, food cups for ice cream, etc., lids for cup containers, beverage cups for coffee, etc., food containers for hot snacks, etc., and trays, boxes, cases, containers, envelopes, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0016] In this embodiment, the heat seal layer is characterized by including at least one of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane. Here, the ionomer refers to a synthetic resin in which a polymer is aggregated by utilizing the cohesive force of metal ions, and includes all aggregates in which a resin and a metal cation are intermolecularly bonded to each other. For example, metal salts of ethylene-methacrylic acid copolymers, metal salts of ethylene-acrylic acid copolymers, metal salts of ethylene-urethane copolymers, and metal salts of ethylene-fluorine polymer copolymers are included. In the present invention, among the ionomers, metal salts of ethylene-acrylic acid or ethylene-methacrylic acid copolymers are preferred. A relatively small amount of dry coating can provide sufficient heat seal strength. In addition, the ethylene-based copolymer is preferably any one of an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-acrylic acid ester copolymer, an ethylene-methacrylic acid ester copolymer, and an ethylene-vinyl acetate copolymer. The adhesion to the underlayer is particularly excellent. The thermoplastic urethane is not particularly limited, but is preferably any of ester, ester-ether, carbonate, and aromatic isocyanate thermoplastic urethanes. The adhesiveness to the underlayer is particularly excellent. The packaging paper of the present invention may contain resins other than these, and may further contain a mixture of multiple resins, as long as it does not affect the heat seal performance.

[0017] In this embodiment of the present invention, a heat seal layer can be provided by applying a coating liquid for a heat seal layer containing an aqueous emulsion containing one or more of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane to at least one surface of a paper substrate and drying the coating liquid. The resin containing one or more of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane used in the heat seal layer is preferably an aqueous emulsion. By using an aqueous emulsion, it is possible to control the coating amount to a relatively low level, and further, VOC emissions are eliminated, thereby reducing the burden on the natural environment. The coating amount of the heat seal layer is 1 to 10 g / m2 in terms of solid content per one side of the paper substrate. 2 and preferably 2 to 6 g / m2 1g / m 2 If it is less than 10 g / m, sufficient quality cannot be obtained in terms of heat seal strength. 2 If it exceeds this value, sufficient heat seal strength is obtained, but the amount of plastic used also increases, resulting in little effect in reducing plastic. In the packaging paper of the present invention, the heat seal layer is usually provided not only on a part of the surface of the paper base material, but on the entire surface. In other words, it is preferable that the heat seal layer is provided so as to cover the entire surface of the paper base material, rather than being provided only on the part required for adhesion by heat sealing, such as in a net, island, or line shape.

[0018] In addition to the aqueous emulsion containing one or more of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane, various auxiliaries may be added to the coating liquid for the heat seal layer. For example, viscosity modifiers, defoamers, leveling agents such as surfactants and alcohols, coloring pigments, coloring dyes, etc. However, the addition of these auxiliaries tends to reduce the heat seal strength, so it is preferable to add them in small amounts when they are added. In this embodiment, it is preferable that the coating liquid for the heat seal layer is composed of only an aqueous emulsion containing one or more of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane.

[0019] The process of applying the heat seal layer coating liquid includes a process of coating the heat seal layer on the paper substrate on-machine, following the paper substrate papermaking process. The process of applying the heat seal layer on-machine refers to a process of continuously applying the heat seal layer on the paper substrate that has been made and dried on a papermaking machine. By applying the heat seal layer on-machine to the paper substrate, the heat seal layer coating liquid is applied to the paper substrate that still has heat after the papermaking process and is then dried, so that the heat seal layer coating liquid is more likely to be subjected to a drying load. By applying the drying load, the heat seal layer coating liquid is sufficiently dried, and the aqueous emulsion containing at least one of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane is sufficiently dissolved and formed into a film, forming an excellent resin film with few defects. Such a resin film has improved air permeability and is more likely to block air that penetrates through the paper surface of the packaging paper. In addition, it is difficult for water and oil to pass through, so that a packaging paper with good water resistance can be obtained. In addition, the water-repellent substance contained in the pulp slurry does not bleed onto the surface of the paper substrate immediately after it is made and dried. By applying the heat-seal layer to the paper substrate in this state on-machine, the coating liquid for the heat-seal layer is easily applied evenly to the surface of the paper substrate, and a resin film with few repelling pinholes can be formed. When the heat-seal layer is applied to the paper substrate off-machine, the water-repellent substance contained in the pulp slurry bleeds onto the surface of the paper substrate over time, the coating liquid for the heat-seal layer is repelled by the water-repellent substance on the surface of the paper substrate, and repelling pinholes are generated, resulting in a packaging paper with poor water resistance.

[0020] Furthermore, an underlayer may be provided between the paper substrate and the heat seal layer. In this case, when manufacturing a packaging paper having an underlayer between the paper substrate and the heat seal layer, it is preferable to coat the underlayer on the paper substrate continuously from the papermaking process of the paper substrate, and then continuously coat the heat seal layer on the paper substrate on which the underlayer is provided. In the underlayer immediately after coating and drying the coating liquid for the underlayer, the water-repellent substance contained in the coating liquid for the underlayer, such as a dispersant for dispersing the pigment or an emulsifier contained in the binder, does not bleed onto the surface of the underlayer. By coating the heat seal layer on the paper substrate having the underlayer in this state, the coating liquid for the heat seal layer is easily coated uniformly on the surface of the underlayer, and a resin film with few repelling pinholes can be formed. On the other hand, when a heat seal layer is applied off-machine to a paper substrate provided with an under layer, the water-repellent substance contained in the under layer coating liquid bleeds onto the under layer surface over time, and the heat seal layer coating liquid is repelled by the water-repellent substance on the under layer surface, causing pinholes in the form of repelling, resulting in a packaging paper with poor water resistance. The method of applying the heat seal layer coating liquid is not particularly limited, and any commonly used coating device can be used. For example, various known coating devices 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 can be used.

[0021] The present invention also relates to a packaging paper having excellent heat sealability and water resistance. In one embodiment, the packaging paper has a heat seal layer containing one or more of an ionomer, an ethylene copolymer, or a thermoplastic urethane on at least one surface of a paper substrate, and an underlayer between the paper substrate and the heat seal layer, the underlayer containing at least a pigment and a binder, the binder contained in the underlayer containing a styrene-butadiene copolymer latex having a particle size of 70 nm or more, and a Cobb water absorbency of 3.0 g / m 2 The present invention relates to the above-mentioned packaging paper. The packaging paper has a reduced amount of plastic contained in the heat seal layer and has good heat sealability and water resistance. The packaging paper can be obtained, for example, by a manufacturing method including a step of on-machine coating the heat seal layer on the paper base material as described above.

[0022] In this embodiment, the heat seal layer may be 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 resistance, oil resistance, and moisture resistance can be imparted, and a barrier property of the same level as that of polylaminated 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 resistance, oil resistance, and moisture resistance can be further improved. When the heat seal layer has two or more layers, the total coating amount of the heat seal layer is 1 to 15 g / m2 in terms of solid content per one side of the paper substrate. 2 and preferably 2 to 10 g / m 2 It may be.

[0023] In this embodiment, the process of coating two or more heat seal layers may include a process of coating the first heat seal layer on the paper substrate on-machine, which is continuous from the paper substrate papermaking process, and may further continuously coat the second and subsequent heat seal layers on-machine. The paper substrate with heat remaining after drying the first heat seal layer is further coated with the coating liquid for the second and subsequent heat seal layers and dried, so that the coating liquid for the heat seal layer is easily subjected to a drying load, and a resin film with few defects can be formed. Alternatively, the process may include a process of coating the first heat seal layer on the paper substrate on-machine, which is continuous from the paper substrate papermaking process, and may further coat the second and subsequent heat seal layers off-machine. Any coating device can be selected without modifying a conventional papermaking device.

[0024] In this embodiment, an underlayer may be provided between the paper substrate and the heat seal layer, but for example, an underlayer containing at least one of a pigment and a binder or both may be provided. Furthermore, it is preferable that the underlayer contains a pigment and a binder. In the case of a paper substrate having only a paper substrate and a heat seal layer, the paper substrate absorbs the coating liquid for the heat seal layer, so in order to impart water resistance, it is necessary to increase the coating amount of the heat seal layer. Packaging paper with a large coating amount of the heat seal layer increases the amount of plastic used, so that the effect of reducing plastic is poor. However, in the case of packaging paper having an underlayer between the paper substrate and the heat seal layer, the underlayer creates a sealing effect that prevents the coating liquid for the heat seal layer from penetrating the paper substrate, so that even a heat seal layer with a small coating amount can easily form a resin film with few defects, and packaging paper with better water resistance can be obtained. In addition, since the underlayer itself has the effect of preventing the penetration of water and oil, excellent water resistance can be obtained by a synergistic effect with the heat seal layer.

[0025] The pigment in the under layer may be a known pigment used in the coating layer of a general coated printing paper, such as kaolin clay, calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), 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, or organic pigments obtained by copolymerizing these (so-called plastic pigments (hereinafter sometimes abbreviated as "PP particles")). In this embodiment, it is preferable to include at least one or more of kaolin clay, calcium carbonate, titanium dioxide, and PP particles. A packaging paper with excellent adhesion to the heat seal layer can be obtained.

[0026] In this embodiment, the kaolin clay ratio of the pigment contained in the under layer is preferably 80 parts by mass or less relative to 100 parts by mass of the pigment. The kaolin clay ratio of the pigment contained in the under layer is preferably 80 to 20 parts by mass relative to 100 parts by mass of the pigment. If it exceeds 80 parts by mass, a sufficient filling effect can be obtained, but the adhesion to the heat seal layer may be poor. If it is less than 20 parts by mass, a sufficient filling effect cannot be obtained. For example, examples of the pigment contained in the under layer include 10 to 90 parts by mass of kaolin clay and 90 to 10 parts by mass of heavy calcium carbonate or light calcium carbonate, and further, 10 to 70 parts by mass of kaolin clay and 90 to 30 parts by mass of heavy calcium carbonate or light calcium carbonate.

[0027] The binder may be a known binder used in the coating layer of a general printing coated paper, and examples of the binder 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, soy protein, and polyvinyl alcohol, synthetic resins such as vinyl acetate, ethylene-vinyl acetate, polyurethane resins, acrylic resins, polyester resins, polyamide resins, ionomers, and other ethylene copolymers. In this embodiment, the binder preferably contains styrene-butadiene copolymer latex (hereinafter, sometimes abbreviated as "SBR"). More preferably, the binder contains styrene-butadiene copolymer latex having a particle diameter of 70 nm or more. Even more preferably, the binder contains styrene-butadiene copolymer latex having a particle diameter of 100 nm or more. By including styrene-butadiene copolymer latex, it is possible to provide the under layer with flexibility and the effect of preventing penetration of water and oil. In addition, by having a particle diameter of 70 nm or more of the styrene-butadiene copolymer latex, a packaging paper having excellent adhesion to the heat seal layer of the under layer can be obtained. In this embodiment, a combination of multiple binders other than the styrene-butadiene copolymer latex can be used. In this embodiment, the particle diameter is measured by the average particle diameter in the scattering intensity distribution by dynamic light scattering (analysis method is the cumulant method) in accordance with JIS Z 8828:2013. Furthermore, it is preferable to include 50 parts by mass or more, preferably 80 parts by mass or more of styrene-butadiene copolymer latex having a particle diameter of 70 nm or more in the binder component. In practice, for example, it is preferable to use 3 to 40 parts by mass of styrene-butadiene copolymer latex having a particle diameter of 70 nm or more and 1 to 5 parts by mass of phosphated starch as a binder relative to 100 parts by mass of the pigment in the under layer.

[0028] In this embodiment, the under layer preferably contains 5 to 200 parts by mass of binder per 100 parts by mass of pigment. More preferably, it is 20 to 100 parts by mass. If it exceeds 200 parts by mass, a sufficient sealing effect is obtained, but water resistance and heat seal strength are not improved any further. In addition, if a water-repellent substance such as an emulsifier contained in the binder remains on the surface of the under layer, the coating liquid for the heat seal layer is repelled by the water-repellent substance on the surface of the under layer, causing repelling pinholes, and the uniformity of the heat seal layer surface may be deteriorated, resulting in a deterioration in the barrier property of the obtained packaging paper. Furthermore, the binder is expensive, which is economically disadvantageous. If it is less than 5 parts by mass, a sufficient sealing effect is not obtained, and the strength of the under layer is also reduced, so that the heat seal strength may be inferior.

[0029] In this embodiment, the coating amount of the under layer is, for example, 1 to 40 g / m2 in terms of solid content per one side of the paper base material. 2 It is preferable that the range is 1 g / m 2 If it is less than 40g / m, sufficient sealing effect cannot be obtained. 2 If the thickness exceeds this range, a sufficient sealing effect can be obtained, but the water resistance and heat seal strength do not improve any more, and the cost increases, which is economically disadvantageous.

[0030] The under layer may contain various auxiliary agents within the range not impairing the intended effects of the present invention. For example, the under layer may contain a viscosity adjusting agent, a softening agent, a gloss imparting agent, a water resistant agent, a dispersing agent, 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.

[0031] The process of applying the coating liquid for the underlayer may be a process of applying the underlayer to the paper substrate on-machine, which is continuous from the paper substrate papermaking process, and drying the underlayer, and then applying a smoothing treatment to the paper substrate on which the underlayer is provided, which is continuous from the paper substrate papermaking process. By applying the underlayer to the paper substrate on-machine, the coating liquid for the underlayer is applied to the paper substrate with heat remaining after the papermaking process and dried, so that the drying load is easily applied, and the coating liquid for the underlayer is sufficiently dried, and the binder in the coating liquid for the underlayer is sufficiently dissolved, forming a film and filling the gaps, resulting in an underlayer with a high sealing effect. In addition, the underlayer immediately after the coating liquid for the underlayer is applied and dried does not have the water-repellent substance contained in the coating liquid for the underlayer bleeding onto the surface of the underlayer. By applying the heat-seal layer to the paper substrate having the underlayer in this state on-machine, the coating liquid for the heat-seal layer is easily applied uniformly to the surface of the underlayer, and a resin film with few repelling pinholes can be formed.

[0032] The method for applying the underlayer coating liquid is not particularly limited, and any commonly used coating device 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, or lip coater.

[0033] In this embodiment, the method may include a step of smoothing the paper substrate and the under layer. The method of smoothing the paper substrate and the under layer is not particularly limited, and a commonly used calendaring device can be used. For example, various known smoothing devices such as a machine calendar, a soft calendar, a super calendar, a gloss calendar, and a shoe nip calendar can be used. In addition, a step of transferring the mirror surface of a Yankee dryer, as used for one-sided gloss kraft paper, may be included. By applying the heat seal layer after the smoothing treatment, the coating liquid for the heat seal layer is easily applied uniformly to the paper substrate and the under layer surface, and the smoothing treatment also leads to the voids remaining in the under layer being crushed, so that a higher sealing effect can be obtained and a packaging paper with better water resistance can be obtained. 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.

[0034] The paper base material used in this embodiment is not particularly limited, and a known paper base material containing pulp as a main component can be used. As the pulp that is the main component of the paper base material, chemical pulp such as LBKP (hardwood bleached kraft pulp) and NBKP (softwood bleached kraft pulp), mechanical pulp 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 pulp such as DIP (deinked pulp), and non-wood pulp 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").

[0035] The paper base material may contain a filler. Examples of the filler include kaolin clay, calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), calcined clay, talc, 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.

[0036] In addition to the pulp and the filler, the paper base material may contain various known papermaking additives. Examples of papermaking additives include internal paper strength enhancers such as sizing agents, bulk enhancers, retention improvers, drainage improvers, coloring dyes, coloring pigments, fluorescent brighteners, fluorescent decolorizers, and pitch control agents. Water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide may also be applied. If the paper base material contains a wet strength enhancer, the recyclability of the packaging paper will be poor, so it is preferable that the paper base material does not contain a wet strength agent.

[0037] The method for making the paper base material is not particularly limited, and the paper base material can be produced by various paper machines such as a Fourdrinier paper machine, a multi-layer Fourdrinier paper machine, a cylinder paper machine, a multi-layer cylinder paper machine, a multi-layer Fourdrinier cylinder combination paper machine, a twin-wire paper machine, etc. In the present invention, the paper base material may be a single-layer or multi-layer paper machine.

[0038] 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 wrapping paper that has high water resistance and can be used for flexible packaging is 30 to 500 g / m 2 is preferable, and 50 to 300 g / m 2 is more preferred. EXAMPLES

[0039] 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 a solid content.

[0040] Example 1 (Preparation of base paper) A paper stock was prepared by adding 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: Neotack 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.) with water, and the paper stock was made into a paper with a basis weight of 248 g / m using a fourdrinier multi-cylinder papermaking machine. 2 A base paper of 2 g / m2 was prepared. Oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to this base paper by a gate roll coater in a dry coating amount of 2 g / m2 on both sides. 2 Apply the paint so that the thickness becomes 250g / m2, then dry and smooth using a calendar. 2 A base paper of the above formula was obtained.

[0041] (Preparation of Coating Solution for Under Layer) 20 parts of kaolin clay (trade name: Contour 1500, manufactured by Imerys) and 80 parts of heavy calcium carbonate (trade name: Carbilux, manufactured by Imerys) were mixed with 0.2 parts of a dispersant (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.), and water was added and dispersed in water using a Coles disperser to prepare a pigment slurry. 2 parts of phosphated starch (trade name: MS4600, manufactured by Nihon Shokuhin Kako Co., Ltd.) and 20 parts of styrene-butadiene copolymer latex (trade name: L-1432X, manufactured by Asahi Kasei Chemicals Co., Ltd., particle size 182 nm) were added as binders to this pigment slurry, and further water was added and dispersed to prepare a coating liquid for a pigment coating layer with a solid content concentration of 50%.

[0042] (Preparation of paper substrate) Continuously from the papermaking process of the base paper, a coating solution for an underlayer was applied on both sides of the base paper obtained above, on the machine, to a dry coating amount of 20 g / m on one side. 2 The coating was applied using a blade coater so that the surface had a basis weight of 290 g / m2 and then dried. 2 A paper substrate was prepared.

[0043] (Making wrapping paper) On the surface of the paper base material obtained above on which the underlayer was provided, an aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, Inc.) was applied on-machine in a dry coating amount of 5.0 g / m2, continuously from the papermaking process of the paper base material. 2 The mixture was then dried to provide a heat seal layer, thereby preparing a packaging paper.

[0044] Example 2 On one side of the paper base material obtained in Example 1, an aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, Inc.) was applied in a dry coating amount of 4.0 g / m on-machine, continuously from the papermaking process of the paper base material. 2 The first heat seal layer was then coated with the same aqueous ionomer emulsion using an air knife coater so that the dry coating amount was 1.0 g / m2 and dried to form the first heat seal layer. 2 A wrapping paper was produced in the same manner as in Example 1, except that the second heat seal layer was provided by coating using an air knife coater so as to obtain a coating layer having a thickness of 100 μm or more and then drying the coating layer.

[0045] Example 3 A packaging paper was produced in the same manner as in Example 1, except that the amount of styrene-butadiene copolymer latex contained in the under layer coating liquid was changed to 5 parts.

[0046] Example 4 A packaging paper was produced in the same manner as in Example 1, except that the amount of styrene-butadiene copolymer latex contained in the under layer coating liquid was changed to 7 parts.

[0047] Example 5 A packaging paper was produced in the same manner as in Example 1, except that the amount of styrene-butadiene copolymer latex contained in the under layer coating liquid was changed to 30 parts.

[0048] Example 6 A packaging paper was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer latex contained in the coating liquid for the underlayer was changed to a styrene-butadiene copolymer latex (product name: PB7648, manufactured by Nippon A&L Co., Ltd., particle size 99 nm).

[0049] Example 7 A packaging paper was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer latex contained in the coating liquid for the under layer was changed to a styrene-butadiene copolymer latex (product name: L-1535, manufactured by Asahi Kasei Chemicals Corporation, particle size 113 nm).

[0050] Example 8 A packaging paper was produced in the same manner as in Example 1, except that the amount of kaolin clay and the amount of ground calcium carbonate contained in the under layer coating liquid were changed to 60 parts and 40 parts, respectively.

[0051] Example 9 A packaging paper was produced in the same manner as in Example 1, except that the amount of kaolin clay and the amount of ground calcium carbonate contained in the under layer coating liquid were changed to 80 parts and 20 parts, respectively.

[0052] Example 10 In Example 1, the coating amount of the heat seal layer was 1.0 g / m 2 A wrapping paper was produced in the same manner as in Example 1, except that the above-mentioned change was made.

[0053] Example 11 In Example 1, the coating weight of the heat seal layer was 10.0 g / m 2 A wrapping paper was produced in the same manner as in Example 1, except that the above-mentioned change was made.

[0054] Example 12 A wrapping paper was prepared in the same manner as in Example 1, except that the resin used in the heat seal layer was changed to an aqueous ethylene-acrylic acid copolymer emulsion (product name: MICHEM FLEX P1883, manufactured by Michelman Co.).

[0055] (Example 13) A packaging paper was prepared in the same manner as in Example 1, except that the resin used in the heat seal layer was changed to an aqueous ethylene-vinyl acetate copolymer emulsion (product name: Aquatex AC-3100, manufactured by Japan Coating Resins Co., Ltd.).

[0056] Example 14 A packaging paper was produced in the same manner as in Example 1, except that the resin used in the heat seal layer was changed to a water-based polyhydroxyurethane emulsion (product name: Takelac WPB-341, manufactured by Mitsui Chemicals, Inc.).

[0057] Comparative Example 1 An aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, Inc.) was applied off-machine to one side of the paper substrate obtained in Example 1 in a dry coating amount of 5.0 g / m 2 A wrapping paper was prepared in the same manner as in Example 1, except that the coating was performed using an air knife coater so that the thickness became 100 mm and then dried to provide a heat seal layer.

[0058] Comparative Example 2 In Example 1, the coating amount of the heat seal layer was 0 g / m 2 A wrapping paper was produced in the same manner as in Example 1, except that the above-mentioned change was made.

[0059] Comparative Example 3 A wrapping paper was prepared in the same manner as in Example 1, except that the resin used in the heat seal layer was changed to an aqueous styrene-acrylic copolymer emulsion (product name: Saibinol EK-754, manufactured by Saiden Chemical Industry Co., Ltd.).

[0060] Comparative Example 4 An aqueous styrene-acrylic copolymer emulsion (product name: Saibinol EK-754, manufactured by Saiden Chemical Industries, Ltd.) was applied off-machine to one side of the paper substrate obtained in Example 1 in a dry coating amount of 5.0 g / m 2A wrapping paper was prepared in the same manner as in Example 1, except that the coating was performed using an air knife coater so that the thickness became 100 mm and then dried to provide a heat seal layer.

[0061] Comparative Example 5 A packaging paper was produced in the same manner as in Example 1, except that the resin used in the heat seal layer was changed to an aqueous polyvinylidene chloride emulsion (product name: Dio FAN A050, manufactured by Solvay).

[0062] Comparative Example 6 An aqueous polyvinylidene chloride emulsion (product name: Dio FAN A050, manufactured by Solvay) was applied off-machine to one side of the paper substrate obtained in Example 1 in a dry coating amount of 5.0 g / m 2 A wrapping paper was prepared in the same manner as in Example 1, except that the coating was performed using an air knife coater so that the thickness became 100 mm and then dried to provide a heat seal layer.

[0063] The wrapping papers obtained in each of the Examples and Comparative Examples were evaluated by the methods described below. The results are shown in Tables 1 and 2.

[0064] (1) Uniformity of the heat seal layer It is preferable that the packaging paper produced in the present invention has a barrier property equivalent to that of conventional laminated paper. Since defects or pinholes in the heat seal layer can deteriorate the barrier property, the surface uniformity of the heat seal layer was evaluated visually. ⊚: No defects or pinholes at all, suitable for practical use. ○: Almost no defects or pinholes, suitable for practical use. △: There are a few defects or pinholes, but they are not noticeable and can be used. ×: Defects and pinholes are noticeable and not suitable for practical use.

[0065] (2) Heat seal material breakage resistance The obtained wrapping paper was cut into two pieces with a width of 8 mm and a length of 15 cm, the front and back sides of the wrapping paper were overlapped, and the pieces were heat-sealed under fixed conditions (adhesion width: 4 mm, temperature: 180°C, pressure: 0.4 MPa, pressing time: 0.5 seconds, pitch: 4 mm) using a heat-sealing device (Palmec, model number: PTS-100).The heat-sealed sample was then peeled under fixed conditions (peel speed: 100 mm / min, peel length: 10 cm) using a peel strength tester (Shimadzu, model number: Autograph AGS-X), and the peeled surface was visually evaluated. ⊚: The entire seal portion is broken away from the base paper of the paper substrate and can be used. ◯: A part of the seal portion is torn from the base paper of the paper substrate, and it is usable. △: The seal portion is torn from the underlayer of the paper base material, and is usable. ×: The sealed portion is peeled off at the interface of the heat seal layer or is not adhered, and is not usable.

[0066] (3) Cobb absorbency The 120-second Cobb water absorbency of the heat seal layer surface was evaluated in accordance with JIS P8140:1998. The lower the value, the higher the water resistance (the less likely the material is to absorb water). In the present invention, a Cobb water absorbency of 3.0 g / m 2 It can be said that the material is water resistant below this value.

[0067] [Table 1]

[0068] [Table 2]

[0069] As is clear from Tables 1 and 2, the packaging papers of Examples 1 to 14 were clearly superior in the uniformity of the heat seal layer, the heat seal material tear resistance, and the water resistance, compared to Comparative Examples 1 to 6. As the experimental results show, the present invention can provide a method for producing packaging paper that has good heat sealability and water resistance while significantly reducing the amount of plastic used in the heat seal layer compared to the amount of conventional polyethylene laminate, and contributing to the reduction of plastic waste.

Claims

1. A method for producing packaging paper having a heat seal layer containing one or more of an ionomer, an ethylene-based copolymer, or a thermoplastic urethane on at least one surface of a paper base material, and an under layer containing a pigment and a binder between the paper base material and the heat seal layer, characterized in that the method includes a process for coating the under layer on-machine onto the paper base material, continuous from a papermaking process for the paper base material, and then a process for coating the heat seal layer on-machine onto the paper base material with the under layer.

2. The manufacturing method described in claim 1, characterized in that the underlayer does not contain polyacrylamide resin.

3. 3. The method according to claim 1, wherein the under layer contains a pigment and a binder as main components.

4. 4. The method according to claim 1, wherein the under layer contains 5 to 200 parts by weight of a binder based on 100 parts by weight of a pigment.

5. 5. The method according to claim 1, wherein the binder contained in the under layer contains a styrene-butadiene copolymer latex, and the particle size of the styrene-butadiene copolymer latex is 70 nm or more.

6. A manufacturing method described in any one of claims 1 to 5, characterized in that the paper base material is mainly composed of pulp and LBKP (broadleaf bleached kraft pulp) is used alone as the pulp.

7. A heat seal layer comprising at least one of an ionomer, an ethylene-based copolymer, and a thermoplastic urethane on at least one surface of the paper substrate; and A packaging paper having an underlayer between the paper base material and the heat seal layer, the underlayer contains at least a pigment and a binder, The binder contained in the under layer contains a styrene-butadiene copolymer latex having a particle diameter of 70 nm or more, and has a Cobb water absorption of 3.0 g / m ２ The packaging paper, which is as follows:

8. The packaging paper described in claim 7, characterized in that the underlayer does not contain polyacrylamide resin.

9. A packaging paper as described in claim 7 or 8, characterized in that the under layer contains a pigment and a binder as main components.

10. A packaging paper according to any one of claims 7 to 9, characterized in that the paper base material is composed mainly of pulp, and LBKP (broadleaf bleached kraft pulp) is used alone as the pulp.

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