Packaging paper

Abstract

The present invention addresses the problem of providing packaging paper having satisfactory printability and a satisfactory "stiffness feeling".　The problem is solved by packaging paper comprising a paper substrate containing pulp and at least one coating layer on at least one surface of the paper substrate, wherein: the at least one coating layer contains a white inorganic pigment and a binder; the total content of pulp selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp in the paper substrate is 70 mass% or more relative to the total mass of pulp contained in the paper substrate; the thickness of the packaging paper is 70-170 μm; and the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the packaging paper and the thickness B (μm) of the packaging paper satisfies A / B = 18 to 55.

Description

wrapping paper

[0001] The present invention relates to a wrapping paper, specifically to a wrapping paper suitable for secondary packaging that houses individual packages of a primary package that come into direct contact with the contents.

[0002] Most packaging paper on the market is made from kraft pulp produced by the kraft process and generally does not have a coating layer containing white inorganic pigments. Furthermore, one-sided glazed kraft paper, which is made glossy by smoothing one side of the paper, is also available. Kraft pulp includes unbleached kraft pulp and bleached kraft pulp, which has undergone a bleaching process.

[0003] On the other hand, there are kraft papers suitable for packaging that have a coating layer. For example, kraft papers with a basis weight of 50 to 120 g / m2 according to JIS P8124 are ２ A kraft paper is known that satisfies the quality standards for three types of kraft paper specified in JIS P3401, has a coating layer on at least one side of a base paper made of pulp including kraft pulp, and is formed by applying a coating agent whose main components are a pigment containing at least one of heavy calcium carbonate and chestnut-shaped pigments and an adhesive, and has a sliding slope angle of 20 degrees or more on the surface of the coating layer according to JIS P8147 and a Parker Print Surf roughness of 2.0 to 5.0 μm on the surface of the coating layer according to JIS P8151 (ISO8791-4) (see, for example, Patent Document 1). Patent Document 1 states that the kraft paper described in Patent Document 1 has appropriate paper stiffness and is not only excellently suited to bag-making as packaging paper, but also has excellent printability and no slippage during processing, making it suitable for use in, for example, high-speed, high-resolution offset printing. In Patent Document 1, regarding paper stiffness, the feel (volume) of kraft paper when held in the hand is compared with the feel of conventional bleached kraft paper (product name: Snow Queen G, manufactured by Daio Paper Corporation), and papers that have a feel that exceeds that of conventional bleached kraft paper or that is similar to that of conventional bleached kraft paper are evaluated and certified as having adequate paper stiffness.

[0004] Japanese Patent Application Laid-Open No. 2008-297635

[0005] The "stiffness" of paper is also referred to as stiffness, rigidity, or straightness, and well-known examples include the "Clark stiffness" according to JIS P8143 and the "Taber stiffness" according to JIS P8125. However, the "stiffness" of paper expressed numerically by these measurements differs from the "stiffness" of paper, which is dependent on human perception. This difference is particularly pronounced when the paper has a coating layer. Because of this difference, human perception becomes important in evaluating the "stiffness" of paper, as in the evaluation described in Patent Document 1. The hand feel and volume of the paper described in Patent Document 1 depend not on the stiffness or flexibility of the paper, but on the basis weight and weight. Therefore, it can be said that they capture a somewhat different feel from the "stiffness" of paper.

[0006] A new comprehensive standard is needed to evaluate the "stiffness" of paper suitable for use as packaging paper. Packaging paper requires hardness and resilience to force that can somewhat cushion the impacts received during transport and display in stores. At the same time, from the perspective of familiarity with bag-shaped packaging, it is necessary to avoid a stiff, stiff feel and a lack of resilience. Therefore, in this specification, the appropriate hardness and appropriate resilience of paper are collectively referred to as "suitability for packaging paper," and the suitability for packaging paper and the tactile feel of the paper are collectively defined as the "stiffness" of the paper. Specifically, subjects touch the paper with their hands and sensorily evaluate whether the paper has "stiffness" based on the feel of the paper's hardness and stiffness, tension and resilience, and suppleness.

[0007] Furthermore, packaging paper needs to be printed with information about the contents. Paper substrates that do not have a coating layer containing a white inorganic pigment and a binder, which contribute to printability, are inferior in printability. In particular, compared to printed materials made of polypropylene, which are conventionally used for flexible packaging materials, packaging paper that does not have a coating layer containing a white inorganic pigment and a binder is inferior in printability on gravure printing machines that are typically used for printing on packaging materials.

[0008] On the other hand, paper is traded by weight, so it is measured by basis weight (g / m ２) is important. When comparing packaging paper with a coating layer containing a white inorganic pigment and a binder with packaging paper without the coating layer at the same basis weight, the packaging paper with the coating layer is generally inferior in suitability for packaging paper. The reason for this is that the coating layer containing a white inorganic pigment and a binder is inferior in strength to the paper base material.

[0009] In view of the above, an object of the present invention is to provide a packaging material, i.e., packaging paper, having a paper base material and a coating layer containing a white inorganic pigment and a binder, which has good printability and good paper "stiffness."

[0010] As a result of extensive research, the inventors have invented the packaging paper according to the present invention. The object of the present invention is achieved by the following aspects: [1] A packaging paper having a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, the total content of pulp in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulps contained in the paper base, the thickness of the packaging paper is 70 μm or more and 170 μm or less, and the relationship between the modulus of elasticity A (MPa) in the cross direction (CD) of the packaging paper and the thickness B (μm) of the packaging paper is A / B = 18 to 55.

[0011] The present invention also includes the following aspects: [2] The packaging paper according to [1] above, wherein the paper base material contains a surface sizing agent, and the surface sizing agent contains starch.

[0012] The present invention also includes the following embodiments: [3] The packaging paper according to [1] or [2], wherein one of the at least one coating layer is an outermost layer positioned outermost relative to the paper substrate.

[0013] The present invention also includes the following embodiments: [4] The packaging paper according to [3], wherein the outermost layer further contains a hollow organic pigment.

[0014] The present invention makes it possible to provide a packaging material, i.e., a packaging paper, having a paper base material and a coating layer containing a white inorganic pigment and a binder, which has good printability and good paper "stiffness."

[0015] In this specification, the appropriate hardness and appropriate resilience of paper are collectively referred to as "suitability for wrapping paper," and the suitability for wrapping paper and the tactile feel of the paper are collectively defined as the "sensory stiffness" of the paper. Specifically, subjects touch the paper with their hands and sensorily evaluate whether the paper has "sensory stiffness" based on the feel of the paper's hardness and stiffness, its tension and resilience, and its suppleness. In this specification, ranges (including ranges described using the symbol "to") include their endpoints. For example, the range "18 to 55" includes the values ​​18 and 55, as well as any values ​​therebetween.

[0016] The present invention is described in detail below. One embodiment of the present invention is a packaging paper having a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, wherein the total content of pulps in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulps contained in the paper base, wherein the thickness of the packaging paper is 70 μm or more and 170 μm or less, and wherein the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the packaging paper and the thickness B (μm) of the packaging paper is A / B = 18 to 55. This embodiment provides a packaging material, i.e., packaging paper, having a paper base and a coating layer containing a white inorganic pigment and a binder, which has good printability and good paper "stiffness."

[0017] The packaging paper of the present invention has a pulp-containing paper base and at least one coating layer on at least one side of the paper base. In this specification, "at least one coating layer" means "one or more coating layers."

[0018] The paper base comprises a pulp selected from the group consisting of softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (NBKP). In this specification, "the paper base comprises a pulp selected from the group consisting of softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (NBKP)" means that the paper base comprises any one of softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (NBKP), or any combination thereof. Kraft pulp is a type of chemical pulp produced by the kraft process, which is conventionally known in the papermaking field. Bleached kraft pulp is kraft pulp that has been bleached in a bleaching process. Unbleached kraft pulp is kraft pulp that has not been subjected to the bleaching process. In the paper base material, the total content of pulps selected from the group consisting of softwood unbleached kraft pulp, softwood bleached kraft pulp, hardwood unbleached kraft pulp, and hardwood bleached kraft pulp in the paper base material is 70 mass% or more based on the total mass of all pulps contained in the paper base material. In this specification, the "total content of pulps selected from the group consisting of softwood unbleached kraft pulp, softwood bleached kraft pulp, hardwood unbleached kraft pulp, and hardwood bleached kraft pulp" refers to the total content of any one of softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (NBKP), or any combination thereof. The paper base material may contain pulp other than unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), and bleached hardwood kraft pulp (NBKP) (hereinafter, sometimes referred to as "other pulp"). The other pulp may be, for example, kraft pulp derived from plants conventionally known in the papermaking field other than the softwoods and hardwoods.Other kraft pulp raw materials are derived from plants other than the above-mentioned softwoods and hardwoods that are conventionally known in the papermaking field, such as hemp, linter, straw, bamboo, sugarcane, reed, fruit, paper mulberry, Mitsumata, and gampi. Other examples of other pulps include mechanical pulp, deinked waste paper pulp, and pulp obtained by disintegrating broke generated in paper mills. If the total content of pulps selected from the group consisting of softwood unbleached kraft pulp, softwood bleached kraft pulp, hardwood unbleached kraft pulp, and hardwood bleached kraft pulp in the paper base material is less than 70% by mass of the total mass of all pulps contained in the paper base material, not only will good paper "stiffness" not be achieved, but the sufficient strength required for packaging paper will also not be achieved. In some embodiments, the content of pulp selected from the group consisting of unbleached softwood kraft pulp and bleached softwood kraft pulp in the paper base is 10 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the total content of pulps selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp in the paper base. The reason for this is that a good balance can be achieved between the "stiffness" of the paper and the sufficient strength required for packaging paper.

[0019] The paper base can be obtained by using a conventional paper machine to make a paper stock in which pulp is dispersed in water. Examples of paper machines include a Fourdrinier paper machine, a twin-wire paper machine, a combination paper machine, a cylinder paper machine, and a Yankee paper machine. In addition to pulp, the paper stock can optionally contain various additives such as fillers, sizing agents, fixing agents, retention agents, cationizing agents, strength agents, bulking agents, pigment dispersants, thickeners, flow improvers, defoamers, foam inhibitors, release agents, foaming agents, penetrating agents, colorants, fluorescent whitening agents, UV absorbers, antioxidants, preservatives, mildew inhibitors, water-resistant agents, wet strength agents, and dry strength agents. By incorporating various additives into the paper stock, the paper base can contain various additives. In some embodiments, the paper base contains a sizing agent, a fixing agent, a strength agent, and a retention agent. This is because the water resistance and strength of the paper base are improved.

[0020] In some embodiments, the paper substrate contains a surface sizing agent. The paper substrate can contain a surface sizing agent by undergoing a size press treatment with a size press solution containing the surface sizing agent. Surface sizing agents are conventionally known in the papermaking field. Examples of surface sizing agents include starches, alkyl ketene dimer sizing agents, cellulose sizing agents, polyvinyl alcohol sizing agents, styrene acrylic sizing agents, olefin sizing agents, styrene maleic acid sizing agents, and acrylamide sizing agents. In at least one embodiment, the paper substrate contains a surface sizing agent, and the surface sizing agent includes starches. This is because pulp fibers and starches are easily adsorbed to each other, which can improve the "stiffness" of the paper. Furthermore, printability is improved. Starches are conventionally known in the papermaking field. Starches are polysaccharides in which glucose is polymerized via glycosidic bonds, and polysaccharides in which the hydroxyl groups of glucose in the polysaccharides in which glucose is polymerized via glycosidic bonds are modified with various substituents. Examples of starches include starch, oxidized starch, enzyme-modified starch, etherified starch, cationized starch, amphoteric starch, dialdehyde starch, esterified starches such as phosphate-esterified starch and urea-phosphate-esterified starch, hydroxyethylated starch, and hydroxybutylated starch.

[0021] The size press treatment can be achieved using a size press device conventionally known in the papermaking field. Examples of size press devices include an inclined size press, a horizontal size press, and a film transfer type rod metering size press, a roll metering size press, and a blade metering size press. The rod metering size press may further include a shim sizer, an Optisizer, a speed sizer, and a film press. The roll metering size press may further include a gate roll coater. Other examples include a bill blade coater, a twin blade coater, a Belbapa coater, a tab size press, and a calendar size press.

[0022] The paper substrate can be subjected to a calendering process, which is a process of passing paper between rolls to equalize the smoothness and thickness. The calendering device is a conventionally known device in the papermaking field, such as a machine calender, a soft nip calender, a super calender, a multi-stage calender, and a multi-nip calender.

[0023] The packaging paper of the present invention has at least one coating layer containing a white inorganic pigment and a binder on at least one side of the paper substrate. In this specification, a "coating layer containing a white inorganic pigment and a binder" may be simply referred to as a "coating layer." For convenience, in this specification, when the number of coating layers is two or more, the coating layers may be referred to as the first coating layer, the second coating layer, and so on, starting from the coating layer closest to the paper substrate. In some embodiments, the packaging paper has one or two coating layers containing a white inorganic pigment and a binder on at least one side of the paper substrate. This is because it is advantageous in terms of manufacturing costs. In at least one embodiment, the packaging paper has one coating layer containing a white inorganic pigment and a binder on at least one side of the paper substrate. This is because it is even more advantageous in terms of manufacturing costs. In some embodiments, the packaging paper has at least one coating layer containing a white inorganic pigment and a binder on both sides of the paper substrate. This is because, whereas packaging paper is usually printed on only one side, both sides can be used as printing surfaces. In some embodiments, the packaging paper has at least one coating layer containing a white inorganic pigment and a binder on only one side of the paper substrate. This is because it is advantageous in terms of manufacturing costs for the packaging paper. In some embodiments, the packaging paper has at least one coating layer containing a white inorganic pigment and a binder on the front side of the paper substrate, and a backcoat layer conventionally known in the coated paper field on the back side of the paper substrate. The backcoat layer has functions such as anti-curl. In some embodiments, the packaging paper has at least one coating layer containing a white inorganic pigment and a binder on the front side of the paper substrate, and a heat-seal layer conventionally known in the coated paper field on the back side of the paper substrate. The heat-seal layer has heat-sealing properties. In some embodiments, the packaging paper has at least one coating layer containing a white inorganic pigment and a binder on the front side of the paper substrate, and the back side of the paper substrate is subjected to a water-coating and drying process conventionally known in the coated paper field. The water-coating and drying process is effective, for example, in preventing curling of the packaging paper.

[0024] In this specification, the terms "front surface" and "back surface" of a paper substrate are used for convenience to distinguish between the surfaces of the paper substrate and do not refer to the front and back surfaces of a support based on any specific difference. The side of the packaging paper having the outermost coating layer described below is referred to as the "front surface." The packaging paper of the present invention has good printability at least on the front surface.

[0025] In some embodiments, the packaging paper may have a resin layer between the paper substrate and the coating layer and / or between the coating layers when the coating layer is two or more layers, the resin layer improving the adhesion between the paper substrate and the coating layer or providing barrier properties such as oxygen barrier or water vapor barrier. The resin forming the resin layer is a resin conventionally known in the packaging paper field, such as polyolefin resins (polyethylene, polypropylene, etc.), polyamide resins (nylon, etc.), acrylic resins, polystyrene resins, polyvinyl chloride resins, polyvinyl alcohol resins, polyvinylidene chloride resins, polyester resins (polyethylene terephthalate, etc.), polyurethane resins, biodegradable resins (polylactic acid, etc.), and cellulose resins.

[0026] In some embodiments of the packaging paper, one of the at least one coating layer containing a white inorganic pigment and a binder is the outermost layer located on the paper substrate, and no additional layers are present thereon. That is, among the layers present in the packaging paper, at least the outermost layer located on the paper substrate contains a white inorganic pigment and a binder. This is because printability is improved. In this specification, when the outermost layer located on the paper substrate is a coating layer containing a white inorganic pigment and a binder, the coating layer may be referred to as the "outermost coating layer." For example, when there is only one coating layer containing a white inorganic pigment and a binder, the coating layer is located on the outermost side of the paper substrate, and no additional layers are present thereon, the coating layer is the "outermost coating layer."

[0027] In at least one embodiment of the packaging paper, one of at least one coating layer containing a white inorganic pigment and a binder is the outermost layer located outermost relative to the paper substrate, and the outermost layer does not have heat-sealability. This is because printability is improved. Here, "not having heat-sealability" means that the peel strength measured by the following method is less than 2 N / 15 mm. For example, the outermost coating layer does not have heat-sealability if the content of the white inorganic pigment is 80% by mass or more relative to the total mass of the dry solids forming the outermost coating layer.

[0028] (Method for confirming heat sealability) Two sheets of packaging paper of the same construction are placed with the outermost coating layers of the packaging paper facing each other and heat sealed using a heat sealer under conditions of 0.5 MPa pressure, 130°C, and 1 second. The heat-sealed packaging paper is cut into 15 mm widths and left to stand for 24 hours at a temperature of 23°C and a relative humidity of 50%, after which the peel strength of the heat-sealed area is measured using a tensile tester at a pulling speed of 300 mm / min and a pulling angle of 180°. Measurements are conducted on 5 samples, and the average value of the 5 samples is used.

[0029] The white inorganic pigment for the coating layer is a conventionally known pigment in the field of coated paper. Examples of the white inorganic pigment include light calcium carbonate, heavy calcium carbonate, kaolin, talc, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, silica, aluminum silicate, diatomaceous earth, activated clay, alumina, alumina hydrate, aluminum hydroxide, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide. In some embodiments, at least one of the white inorganic pigments is kaolin. This is because it improves printability on printing machines, particularly gravure printing machines.

[0030] The binder for the coating layer is a water-dispersible or water-soluble binder conventionally known in the field of coated paper. Examples of water-dispersible binders include styrene-based resins such as styrene-butadiene-based copolymer resins, conjugated diene-based copolymer resins such as (meth)acrylonitrile-butadiene-based copolymer resins, acrylic resins such as (meth)acrylate-butadiene-based copolymer resins, (meth)acrylate-styrene-based copolymer resins, and (meth)acrylate-based copolymer resins, vinyl-based copolymer resins such as ethylene-vinyl acetate-based copolymer resins and vinyl chloride-vinyl acetate-based copolymer resins, polyurethane-based resins, alkyd-based resins, polyester-based resins, and modified resins using various monomers thereof, as well as thermosetting synthetic resins such as urea-based resins and melamine-based resins. Examples of water-soluble binders include starches, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose, polyvinyl alcohol-based resins such as unmodified polyvinyl alcohol and various modified polyvinyl alcohols, casein or gelatin or modified products thereof, natural polymer resins or derivatives thereof such as soy protein, pullulan, gum arabic, karaya gum, and albumin, sodium alginate, and maleic acid-based resins. In some embodiments, the binder contained in the coating layer may be a combination of a water-dispersible binder and a water-soluble binder. The water-dispersible binder may be one or more types selected from the group consisting of the examples of water-dispersible binders described above. The water-soluble binder may be one or more types selected from the group consisting of the examples of water-soluble binders described above. The reason for this is that printability is improved.

[0031] In some embodiments, one of the at least one coating layer containing a white inorganic pigment and a binder is the outermost layer located on the paper substrate, and the outermost layer further contains a hollow organic pigment. That is, among the layers of the packaging paper, at least the outermost layer located on the paper substrate contains a white inorganic pigment, a binder, and a hollow organic pigment. This is because it improves not only printability but also the "stiffness" of the paper. Hollow organic pigments are pigments that have an air layer inside, such as an internal space, cavity, void, or bubble, and are conventionally known in the field of coated paper. Hollow organic pigments are available from thermosetting resins and thermoplastic resins, depending on the material, and may be either of these. Hollow organic pigments can be produced by various methods. Examples of methods for producing hollow organic pigments include a method disclosed in Japanese Patent Publication Nos. 36-9168 and 37-14327, in which suspension polymerization or emulsion polymerization is carried out in the presence of a non-polymerizable organic solvent that is insoluble in water to obtain organic particles containing the solvent in their internal pores, and then the inclusions are removed from the organic particles; a method disclosed in Japanese Patent Laid-Open No. 61-87734, in which suspension polymerization or emulsion polymerization is carried out in a dispersion in which a hydrophilic monomer, a crosslinkable monomer, and an oily substance coexist, to obtain organic particles containing the oily substance in their internal pores, and then the oily substance is removed from the organic particles; Examples of suitable hollow organic pigments include, but are not limited to, a method of obtaining hollow organic particles by heating microcapsules encapsulating a volatile substance such as butane or pentane to gasify and expand the volatile substance, as disclosed in Japanese Patent Application Laid-Open No. 56-32513, a method of forming hollow particles by applying a basic substance to polymer particles consisting of an alkali-swellable core and a shell covering the core, thereby swelling and expanding the core and forming hollow particles upon drying, as disclosed in Japanese Patent Application Laid-Open No. 2-173101, and a method of hydrolyzing the core of a core / shell polymer whose core is made of a vinyl acetate polymer. Hollow organic pigments are commercially available from, for example, Dow Chemical Japan, JSR Corporation, Nippon Zeon Co., Ltd., Matsumoto Yushi Seiyaku Co., Ltd., Sekisui Chemical Co., Ltd., and Nippon Phillite Co., Ltd.Examples of resins that constitute hollow organic pigments include styrene-acrylic resins, polystyrene-based resins, (meth)acrylic resins, polyethylene-based resins, polypropylene-based resins, polyacetal-based resins, chlorinated polyether-based resins, and polyvinyl chloride-based resins, as well as copolymer-based resins whose main components are vinylidene chloride and acrylonitrile.

[0032] The coating layer containing the white inorganic pigment and the binder may further contain any additives such as a dispersant, a lubricant, a thickener, a flow improver, an antifoaming agent, a foaming agent, a penetrating agent, a coloring pigment, a coloring dye, a fluorescent brightener, an ultraviolet absorber, an antioxidant, a preservative, and an antifungal agent.

[0033] The packaging paper of the present invention can be produced by providing a coating layer containing a white inorganic pigment and a binder, and optionally other layers such as a backcoat layer and a resin layer, on the paper base material obtained as described above. The coating layer and any other layers can be obtained by applying and drying a coating liquid containing predetermined materials. Coating and drying can be performed using, for example, coating and drying devices conventionally known in the coated paper field. Examples of coating devices include a Comma Coater (registered trademark), a film press coater, an air knife coater, a rod blade coater, a bar coater, a blade coater, a gravure coater, a curtain coater, an E-bar coater, and a film transfer coater. Coating can also be performed using a manual wire bar, which is an experimental method. Examples of drying devices include various drying devices such as hot air dryers such as linear tunnel dryers, arch dryers, air loop dryers, and sine-curve air float dryers, infrared heating dryers, and microwave dryers. Furthermore, methods for providing a resin layer include methods using conventionally known laminator devices, such as wet lamination and dry lamination, as well as methods of applying and drying a resin layer coating liquid in which a non-water-soluble resin is dissolved in a solvent medium.

[0034] After the coating layer and any other layers are applied, the wrapping paper can be subjected to a calendering treatment conventionally known in the papermaking field. This improves the final smoothness of the paper substrate. Calendering can be achieved using a calendering device conventionally known in the papermaking field. The calendering device is the same as the example given above for the calendering of paper substrates.

[0035] The thickness of the packaging paper of the present invention is 70 μm or more and 170 μm or less. In this specification, the thickness of the packaging paper is a value determined in accordance with ISO 534:2011 "Paper and board - Determination of thickness, density and specific volume." The thickness of the packaging paper is a physical quantity conventionally known in the papermaking field and can be empirically controlled, for example, by the amount of paper stock supplied in the papermaking of the paper base, the conditions of the wire part and press part in the papermaking process, the calendering conditions, the coating amount of the coating layer, and the calendering conditions.

[0036] In the packaging paper of the present invention, the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the packaging paper and the thickness B (μm) of the packaging paper is A / B = 18 to 55. Here, CD in cross direction (CD) is an abbreviation for "cross direction" and refers to the direction perpendicular to the machine direction (MD) of the paper. Normally, pulp fibers tend to follow the machine direction (MD) of the paper, but the cross direction (CD) is a direction that intersects with the pulp fibers and is the direction in which the paper is prone to distortion. In this specification, the elastic modulus of packaging paper refers to the tensile modulus, determined in accordance with ISO 1924-2:1994 "Paper and board - Determination of tensile properties - Part 2: Constant rate of elongation mryhod." In this specification, the elastic modulus of packaging paper in the cross direction (CD) is referred to as the elastic modulus A (MPa). Paper typically has a linear elastic region and a nonlinear elastic region in its stress-strain curve. When the nonlinear elastic region is reached, irrecoverable strain remains. The linear elastic region of paper depends on a complex set of factors, including the length of pulp fibers, the degree of beating of pulp, the amount of entanglement of pulp fibers, the entanglement strength of pulp fibers, fiber orientation, and density. To improve resilience against force, when using common pulp, increasing the paper basis weight to increase the amount of entanglement of pulp fibers or increasing the paper density to increase the amount and strength of entanglement of pulp fibers is effective. However, simply increasing the basis weight or density makes the paper feel hard and stiff. Furthermore, excessively reducing the paper density is detrimental to the feel and resilience. The inventors have discovered that paper can have good "stiffness" when the thickness is within a specific range and the cross-direction (CD) modulus per unit thickness is within a specific range, and have arrived at the present invention.

[0037] The elastic modulus of packaging paper is a physical quantity conventionally known in the papermaking field, and can be empirically controlled, for example, when pulp is used in common applications, by adjusting the consistency of the stock, the amount of stock supplied, the J / W ratio in the papermaking process, the wire part conditions and dewatering strength in the papermaking process, and the moisture content in the drying zone after papermaking. In particular, the presence of moisture affects the increase in entanglement of pulp fibers. In packaging paper, the contribution of the coating layer containing a white inorganic pigment and a binder to the elastic modulus is smaller than that of the paper substrate.

[0038] In some embodiments, the wrapping paper has a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, the total content of pulps in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulps contained in the paper base, one of the at least one coating layer is the outermost layer located outermost based on the paper base, the thickness of the wrapping paper is 70 μm or more and 170 μm or less, and the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the wrapping paper and the thickness B (μm) of the wrapping paper is A / B = 18 to 55.

[0039] In some embodiments, the wrapping paper has a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, the total content of pulps in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulps contained in the paper base, one of the at least one coating layer is the outermost layer located on the paper base, and the outermost layer further contains a hollow organic pigment, the thickness of the wrapping paper is 70 μm or more and 170 μm or less, and the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the wrapping paper and the thickness B (μm) of the wrapping paper is A / B = 18 to 55.

[0040] In some embodiments, the wrapping paper has a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, the total content of pulps in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulps contained in the paper base, the paper base contains a surface sizing agent, and the surface sizing agent includes starches, one of the at least one coating layer is the outermost layer located outermost based on the paper base, the thickness of the wrapping paper is 70 μm or more and 170 μm or less, and the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the wrapping paper and the thickness B (μm) of the wrapping paper is A / B = 18 to 55.

[0041] In some embodiments, the wrapping paper has a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, the total content of pulps in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulps contained in the paper base, the paper base contains a surface sizing agent, and the surface sizing agent contains starches, one of the at least one coating layer is the outermost layer located outermost relative to the paper base, and the outermost layer further contains a hollow organic pigment, the thickness of the wrapping paper is 70 μm or more and 170 μm or less, and the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the wrapping paper and the thickness B (μm) of the wrapping paper is A / B = 18 to 55.

[0042] The packaging paper of the present invention can be used as packaging paper for packaging contents. The packaging paper of the present invention is particularly suitable for secondary packaging that stores individual packages of primary packaging that come into direct contact with the contents. The packaging paper of the present invention can be made into a bag shape as appropriate depending on the packaging application.

[0043] The packaging paper of the present invention can be printed by various conventionally known printing methods such as gravure printing, offset printing, screen printing, flexographic printing, inkjet printing, UV printing, and EB printing. Printed packaging paper is also included in the packaging paper of the present invention.

[0044] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Here, "parts by mass" and "% by mass" represent the dry solid content or the substantial component amount, respectively. The coating amount of the coating layer represents the dry solid content.

[0045] <Paper base material-1> A stock was prepared by blending 4 parts by mass of a rosin-based sizing agent, 12 parts by mass of a cationized starch as a paper strength agent, 10 parts by mass of an aluminum sulfate fixing agent, and 0.1 parts by mass of an acrylamide-based retention agent with a pulp slurry consisting of 800 parts by mass of LBKP with a CSF freeness of 430 ml and 200 parts by mass of NBKP with a CSF freeness of 570 ml. The stock was then made into paper using a Fourdrinier paper machine to obtain a paper sheet. Both sides of the paper sheet were subjected to a size press using a size press solution containing an acrylamide-based sizing agent as a surface sizing agent, followed by calendering using a machine calender to obtain a paper base material. The amount of surface sizing agent applied was 1 g / m per side. ２ The thickness and modulus of elasticity of the packaging paper were adjusted to the desired values ​​by adjusting the consistency of the stock, the amount of stock supplied, the conditions of the press part and the dryer part of the papermaking process, the moisture content in the drying zone after papermaking, and the calendering process.

[0046] <Paper base material-2> A stock was prepared by blending 4 parts by mass of a rosin-based sizing agent, 12 parts by mass of a cationized starch as a paper strength agent, 10 parts by mass of an aluminum sulfate fixing agent, and 0.1 parts by mass of an acrylamide-based retention agent with a pulp slurry consisting of 800 parts by mass of LBKP with a CSF freeness of 430 ml and 200 parts by mass of NBKP with a CSF freeness of 570 ml. The stock was then made into a paper sheet using a Fourdrinier paper machine. Both sides of the paper sheet were subjected to a size press using a size press liquid containing oxidized starch as a surface sizing agent, followed by calendering using a machine calender to obtain a paper base material. The amount of surface sizing agent applied was 1 g / m per side. ２ The thickness and modulus of elasticity of the packaging paper were adjusted to the desired values ​​by adjusting the consistency of the stock, the amount of stock supplied, the conditions of the press part and the dryer part of the papermaking process, the moisture content in the drying zone after papermaking, and the calendering process.

[0047] <Paper base material-3> A pulp slurry consisting of 500 parts by mass of LBKP with a CSF freeness of 430 ml, 50 parts by mass of NBKP with a CSF freeness of 570 ml, and 450 parts by mass of deinked recycled paper pulp was blended with 4 parts by mass of a rosin-based sizing agent, 12 parts by mass of a cationized starch as a paper strength agent, 10 parts by mass of an aluminum sulfate fixing agent, and 0.1 parts by mass of an acrylamide-based retention agent to prepare a paper stock. The paper stock was made into a paper sheet using a Fourdrinier paper machine. Both sides of the paper sheet were subjected to a size press using a size press solution containing an acrylamide-based sizing agent as a surface sizing agent, and then calendered using a machine calender to obtain a paper base material. The amount of surface sizing agent applied was 1 g / m per side. ２ The thickness and modulus of elasticity of the packaging paper were adjusted to the desired values ​​by adjusting the consistency of the stock, the amount of stock supplied, the conditions of the press part and the dryer part of the papermaking process, the moisture content in the drying zone after papermaking, and the calendering process.

[0048] <First Coating Layer Coating Fluid> The first coating layer coating fluid was prepared from the following ingredients: White pigment (light calcium carbonate) 100 parts by mass Starch phosphate 2 parts by mass Styrene-butadiene resin 9 parts by mass Calcium stearate (lubricant) 0.3 parts by mass Antifoaming agent (2,4,7,9-tetramethyl-5-decyne-4,7-diol) 0.07 parts by mass The above ingredients were blended, mixed and dispersed in water to adjust the concentration to 48% by mass.

[0049] <Outermost coating layer coating liquid-1: no hollow organic pigment> Outermost coating layer coating liquid-1 was prepared from the following ingredients: White pigment (kaolin) 88 parts by mass White pigment (light calcium carbonate) 12 parts by mass Polyvinyl alcohol (saponification degree 98 to 99 mol%, average polymerization degree 400) 1.2 parts by mass Styrene-butadiene resin 11 parts by mass Calcium stearate (lubricant) 0.3 parts by mass Antifoaming agent (2,4,7,9-tetramethyl-5-decyne-4,7-diol) 0.35 parts by mass The above ingredients were blended, mixed, and dispersed in water to adjust the concentration to 60% by mass.

[0050] <Outermost Coating Layer Coating Liquid-2: With Hollow Organic Pigment> Outermost coating layer coating liquid-2 was prepared from the following ingredients: White pigment (kaolin) 88 parts by mass White pigment (light calcium carbonate) 6 parts by mass White pigment (styrene acrylic hollow organic pigment) 6 parts by mass Polyvinyl alcohol (saponification degree 98 to 99 mol%, average polymerization degree 400) 1.2 parts by mass Styrene butadiene resin 11 parts by mass Calcium stearate (lubricant) 0.3 parts by mass Antifoaming agent (2,4,7,9-tetramethyl-5-decyne-4,7-diol) 0.35 parts by mass The above ingredients were blended, mixed, and dispersed in water to adjust the concentration to 60% by mass.

[0051] The wrapping papers of the Examples and Comparative Examples were produced as follows.

[0052] <Wrapping paper - two-layer type> A wrapping paper having two coating layers was produced by the following procedure. A first coating layer coating liquid was applied to the surface of the paper substrate using an air knife coater and dried. Next, an outermost coating layer coating liquid was applied to the obtained first coating layer using a blade coater and dried. After drying, the wrapping paper was subjected to a calendar treatment to obtain the wrapping paper. The coating amount for the first coating layer was 5 g / m2. ２ The outermost coating layer was 8 g / m ２ The types of paper substrates used in each of the examples and comparative examples are shown in Table 1.

[0053] <Wrapping paper - single layer type> A wrapping paper having one coating layer was prepared by the following procedure. The outermost coating layer coating liquid was applied to the surface of the paper substrate using a blade coater and dried. After drying, the paper was subjected to a calendar treatment to obtain a wrapping paper. The coating amount was 9 g / m ２ The types of paper substrates used in each of the examples and comparative examples are shown in Table 1.

[0054] <Wrapping Paper - Layer-less> The wrapping paper of Comparative Example 6 was prepared using paper substrate-1 without a coating layer.

[0055] The thickness B (μm) of the packaging paper was measured in accordance with ISO 534: 2011, and the modulus of elasticity A (MPa) in the cross direction (CD) of the packaging paper was measured in accordance with ISO 1924-2: 1994. The value of A / B was calculated from the thickness B (μm) and modulus of elasticity A (MPa) of the packaging paper.

[0056] <Printability> A gravure printing machine was used to evaluate printability. Printing was carried out on the outermost coating side of the packaging paper using Gravoproof CM (Nissho Gravure Co., Ltd.) with aqueous gravure ink. Printability was evaluated based on the impression of the printed finish of the packaging paper, using a printed matter of corona discharge-treated biaxially oriented polypropylene film, which is conventionally used for packaging materials, as a comparison, and the following criteria were used. In the present invention, packaging paper was considered to have good printability if it was rated A or B. A: Comparable or generally comparable to the comparison, good. B: Somewhat discolored compared to the comparison, but within an acceptable range, generally good. C: Clearly inferior to the comparison, poor.

[0057] <Paper "Stiffness"> Wrapping paper was cut into pieces measuring 27 cm x 30 cm, and two pieces of the cut wrapping paper were used to create a pseudo-package, with two rolled-up balls of newspaper (406 mm x 545 mm) inside, sealed by gluing the four corners. Five subjects evaluated the paper "stiffness" by touching the package with their hands and evaluating the paper's hardness and stiffness, its tension and resilience, and its suppleness using a sensory evaluation system on a five-point scale as shown below. The final evaluation result was calculated as the average of the five subjects' scores, and any decimal point was rounded off. In the present invention, a wrapping paper with a rating of 3 or higher was considered to have good "stiffness." 5 points: extremely good; 4 points: good; 3 points: generally good; 2 points: average; and 1 point: poor.

[0058] The evaluation results are shown in Table 1.

[0059]

[0060] From Table 1, it can be seen that Examples 1 to 11, which correspond to the packaging paper of the present invention, have good printability and good paper "stiffness." On the other hand, it can be seen that Comparative Examples 1 to 6, which do not satisfy the constitution of the present invention, cannot satisfy one of these effects.

[0061] Mainly, the comparison between Example 1 and Example 3, or the comparison between Example 2 and Example 4, shows that a paper base material containing starch, which is subjected to size press treatment using starch as a surface sizing agent, improves the "stiffness" of the paper.

[0062] Mainly, the comparison between Example 1 and Example 2 or the comparison between Example 3 and Example 4 shows that when the outermost coating layer contains a hollow organic pigment, the "stiffness" of the paper is improved.

[0063] The disclosure of Japanese Patent Application No. 2024-108865 (filing date: July 5, 2024) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A packaging paper having a pulp-containing paper base and at least one coating layer on at least one side of the paper base, wherein the at least one coating layer contains a white inorganic pigment and a binder, the total content of pulp in the paper base selected from the group consisting of unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, and bleached hardwood kraft pulp is 70 mass% or more based on the total mass of all pulp contained in the paper base, the thickness of the packaging paper is 70 μm or more and 170 μm or less, and the relationship between the elastic modulus A (MPa) in the cross direction (CD) of the packaging paper and the thickness B (μm) of the packaging paper is A / B = 18 to 55.

2. The wrapping paper of claim 1, wherein the paper substrate contains a surface sizing agent, the surface sizing agent comprising starches.

3. The packaging paper according to claim 1 or 2, wherein one of the at least one coating layer is the outermost layer located outermost relative to the paper substrate.

4. The wrapping paper according to claim 3, wherein the outermost layer further contains a hollow organic pigment.

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