Wrapping paper

Abstract

To provide wrapping paper which has better printability and folding and cracking resistance against gravure printing than conventional wrapping paper, and has at least further improved one of printability and folding and cracking resistance against gravure printing.SOLUTION: Wrapping paper has kraft paper containing kraft pulp, and one or two or more coating layers on at least one surface of the craft paper, wherein the outermost coating layer positioned at an outermost place based on the kraft paper in the coating layer contains at least kaolin and a binder, and the kaolin has at least peaks within a particle diameter of 0.20 μm or more and 7.00 μm or less in a particle diameter distribution curve relating to a volume-based particle diameter determined by laser diffraction / scattering type particle size distribution measurement.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a packaging paper having a coating layer on at least one side of kraft paper and having printability for gravure printing. [Background technology]

[0002] One type of packaging paper available on the market is kraft paper. Kraft paper is made from kraft pulp produced by the kraft process. There are two types of kraft paper: unbleached kraft paper, which is usually brown in color, and bleached kraft paper, which is made from kraft pulp that has been bleached. There is also one-sided gloss kraft paper, which is made glossy by pressing one side. For example, bleached kraft paper with improved printability is known as kraft paper (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-100623 A Summary of the Invention [Problem to be solved by the invention]

[0004] There has been a growing call to move away from plastic in the field of packaging materials, such as packaging sheets, packaging bags and containers, and carrier bags. As a result, there are efforts to replace packaging materials that use resins such as polypropylene with packaging materials that use paper, i.e., packaging paper. Kraft paper has traditionally been chosen as packaging paper from the viewpoint of paper strength. However, multicolor printing on kraft paper has been rare. The reason for this is as follows: Conventional kraft paper, which is chosen from the viewpoint of paper strength, has problems with printability from the viewpoints of color density, color saturation, and color vividness of the printed finish. Printing on packaging materials is usually done by gravure printing, and kraft paper has the above-mentioned problem of printability for gravure printing in particular. For example, when replacing packaging materials using resins such as polypropylene with packaging paper, the difference is large and becomes an obstacle to replacement. Furthermore, packaging materials require physical strength on their printed surface in terms of processing them into packages or handling the packages in stores, etc. The reasons for this are as follows. For example, if a product displayed in a store in a packaged state has a defect on the printed surface of the package, it leaves a bad impression on customers and reduces the product value. While this is unlikely to be an issue with flexible resins such as polypropylene, folding cracks are an issue with packaging paper.

[0005] The object of the present invention is to provide a packaging paper based on kraft paper, which has printability to gravure printing and resistance to cracking due to folding that is equal to or better than conventional packaging paper, and at least one of the printability to gravure printing and resistance to cracking due to folding that is improved compared to conventional packaging paper. [Means for solving the problem]

[0006] The present inventors have invented the wrapping paper according to the present invention as a result of intensive research.

[0007] [1] A packaging paper comprising kraft paper containing kraft pulp and one or more coating layers on at least one side of the kraft paper, wherein the outermost coating layer located outermost relative to the kraft paper contains at least kaolin and a binder, and the kaolin has at least two peaks in the particle size range of 0.20 μm to 7.00 μm in a particle size distribution curve for volume-based particle size determined by laser diffraction / scattering particle size distribution measurement.

[0008] In some embodiments, the wrapping paper of the present invention is: [2] The packaging paper according to [1] above, wherein in a particle size distribution curve relating to the volume-based particle size of the kaolin obtained by laser diffraction / scattering particle size distribution measurement, peaks in the particle size range of 0.20 μm or more and 7.00 μm or less exist in the particle size range of 0.30 μm or more and 0.60 μm or less and in the particle size range of 2.00 μm or more and 5.00 μm or less, respectively. Effect of the Invention

[0009] According to the present invention, it is possible to provide a packaging paper which has printability to gravure printing and resistance to cracking due to folding which is equal to or greater than conventional paper, and at least one of the printability to gravure printing and resistance to cracking due to folding which is improved compared to conventional paper. [Brief description of the drawings]

[0010] [Figure 1] 1 shows an example of a particle size distribution relating to volume-based particle diameters determined by laser diffraction / scattering particle size distribution measurement, which corresponds to the kaolin of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below. The packaging paper of the present invention comprises a kraft paper containing kraft pulp and one or more coating layers on at least one side of the kraft paper. The layer located outermost relative to the kraft paper is called the outermost coating layer. When there is only one coating layer, this layer is the outermost coating layer. When the coating layer is two or more layers, the coating layer located between the kraft paper and the outermost coating layer is not particularly limited as long as it does not impair the effects of the present invention. Examples of the coating layer located between the kraft paper and the outermost coating layer include a coating layer containing a white pigment and a binder that is conventionally known in the field of coated paper.

[0012] In some embodiments, the wrapping paper has one or more coating layers on both sides of the kraft paper. The reason for this is that, whereas wrapping paper is usually printed on only one side, the kraft paper can be used as a printing surface regardless of the front or back. In some embodiments, the wrapping paper has one or more coating layers only on one side of the kraft paper. The reason for this is that it is advantageous in terms of the manufacturing cost of the wrapping paper. In some embodiments, the wrapping paper has one or more coating layers on the surface of the kraft paper, and has a backcoat layer conventionally known in the field of coated paper on the back side of the kraft paper. The backcoat layer has, for example, a function of improving dimensional stability and / or preventing curling. This improves the dimensional stability and / or curl prevention of the wrapping paper. In some embodiments, the wrapping paper has one or more coating layers on the surface of the kraft paper, and has a water-coating and drying treatment conventionally known in the field of coated paper on the back side of the kraft paper. The water-coating and drying treatment is, for example, effective in preventing curling of the wrapping paper.

[0013] In some embodiments, the wrapping paper has one or more coating layers on the surface of the kraft paper, and has a heat seal layer containing a heat sealable resin conventionally known in the packaging material field on the back side of the kraft paper, because the wrapping paper can be used as a heat seal paper. Examples of heat-sealable resins include polyester-based resins, polyvinyl alcohol-based resins, vinyl-based resins, vinylidene chloride-based resins, (meth)acrylic-based resins, polyurethane-based resins, cellulose-based resins, melamine-based resins, polyamide-based resins, polyolefin-based resins, and polystyrene-based resins.

[0014] In some embodiments, the packaging paper has one or more coating layers on the surface of the kraft paper, and has a barrier layer on the back side of the kraft paper that contains a barrier material conventionally known in the field of packaging materials. This is because the packaging paper can have barrier properties. Examples of the barrier layer include a gas barrier layer such as an oxygen gas barrier layer, a water vapor barrier layer, a moisture permeable barrier layer, and an oil barrier layer. Barrier materials that exhibit these functions are known. Examples of gas barrier materials include polyvinyl alcohol resins such as fully saponified or partially saponified polyvinyl alcohol and modified polyvinyl alcohol, urethane resins, acrylic resins, vinylidene chloride resins, proteins such as casein, soy protein, and synthetic protein, starches such as oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch, celluloses such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose, polyvinylpyrrolidone, and sodium alginate. Examples of water vapor barrier materials and / or moisture permeable barrier materials include olefin-based resins such as polyethylene and polypropylene, acrylic-based resins, vinyl chloride-based resins, styrene-based resins, styrene-butadiene-based resins, olefin-unsaturated carboxylic acid-based resins, styrene-unsaturated carboxylic acid-based resins, vinyl acetate-based resins, styrene-vinyl acetate-based resins, acrylonitrile-styrene-based resins, acrylonitrile-olefin-based resins, maleic acid-based resins, ABS-based resins, AAS-based resins, AES-based resins, vinylidene chloride-based resins, urethane-based resins, vinylidene fluoride-based resins, vinyl fluoride-based resins, fluorine-based resins, polycarbonate-based resins, polyamide-based resins, polyacetal-based resins, polyphenylene oxide-based resins, polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulfide-based resins, polyimide-based resins, polysulfone-based resins, polyethersulfone-based resins, and waxes. Examples of the oil barrier material include polyvinyl alcohol-based resins, styrene-acrylic resins, and fluorine-based resins.

[0015] In this specification, the terms "front side" and "back side" of the kraft paper are expressions for convenience of distinguishing the sides of the kraft paper, and do not mean the front side and back side of the support based on a specific difference. The printability for gravure printing relates to the side having the outermost coating layer of the packaging paper.

[0016] The outermost coating layer contains at least kaolin and a binder. Kaolin is a white pigment that has been conventionally known in the field of coated paper. Kaolin is usually produced by industrially refining and processing naturally occurring kaolin ore, and is produced through processes such as crushing, washing, iron removal, and classification. Kaolin also includes highly processable kaolin, such as delaminated kaolin, which is made into a thin plate shape by applying shear force to improve the aspect ratio, engineered kaolin, which has a narrow particle size distribution range, and calcined kaolin, which has improved cohesiveness.

[0017] The kaolin contained in the outermost coating layer has at least two peaks in the particle size range of 0.20 μm to 7.00 μm in a particle size distribution curve relating to the volume-based particle size determined by laser diffraction / scattering particle size distribution measurement. Figure 1 shows an example of the particle size distribution of the kaolin. In addition to the relatively clear peaks as shown in Figure 1, the peaks also include shoulder peaks. The packaging paper can have improved printability for gravure printing and resistance to cracking when folded compared to conventional papers because the kaolin in the outermost coating layer has the above characteristics related to the particle size distribution curve. If the kaolin in the outermost coating layer does not satisfy the above characteristics related to the particle size distribution curve, the packaging paper cannot have improved printability for gravure printing and / or resistance to cracking when folded compared to conventional papers.

[0018] In some embodiments, in a particle size distribution curve for the volume-based particle size determined by laser diffraction / scattering particle size distribution measurement of kaolin contained in the outermost coating layer, the peaks present in a particle size range of 0.20 μm or more and 7.00 μm or less exist in a particle size range of 0.20 μm or more and 1.10 μm or less and in a particle size range of more than 1.10 μm and 7.00 μm or less, respectively. In at least one embodiment, a particle size distribution curve for the volume-based particle size determined by laser diffraction / scattering particle size distribution measurement of the kaolin contained in the outermost coating layer has two peaks in a particle size range of 0.20 μm or more and 7.00 μm or less, and these peaks are present in a particle size range of 0.20 μm or more and 1.10 μm or less, and in a particle size range of more than 1.10 μm and 7.00 μm or less, respectively. The reason for this is that printability in gravure printing and / or resistance to cracking due to folding are improved.

[0019] In some embodiments, in a particle size distribution curve for the volume-based particle size determined by laser diffraction / scattering particle size distribution measurement of the kaolin contained in the outermost coating layer, the peaks present in a particle size range of 0.20 μm or more and 7.00 μm or less are present in a particle size range of 0.30 μm or more and 0.60 μm or less and in a particle size range of more than 2.00 μm and 5.00 μm or less, respectively. In at least one embodiment, a particle size distribution curve for the volume-based particle size determined by laser diffraction / scattering particle size distribution measurement of the kaolin contained in the outermost coating layer has two peaks in the particle size range of 0.20 μm or more and 7.00 μm or less, and these peaks are present in the particle size range of 0.30 μm or more and 0.60 μm or less, and in the particle size range of more than 2.00 μm and 5.00 μm or less, respectively. The reason for this is that printability in gravure printing and / or resistance to cracking due to folding are improved.

[0020] Kaolin having the above-mentioned particle size distribution characteristics can be prepared, for example, by a classification step during production, or by mixing kaolin having a relatively small average particle size with kaolin having a relatively large average particle size.

[0021] In some embodiments, the peaks present in the particle diameter range of 0.20 μm to 7.00 μm in the particle size distribution curve of the volume-based particle diameter obtained by laser diffraction / scattering particle size distribution measurement of the kaolin contained in the outermost coating layer are present in the particle diameter range of 0.20 μm to 1.10 μm and the particle diameter range of more than 1.10 μm to 7.00 μm, respectively, and the peak present in the particle diameter range of 0.20 μm to 1.10 μm is defined as the first peak, and the peak present in the particle diameter range of more than 1.10 μm to 7.00 μm is defined as the second peak, and the ratio of the vertical axis value (frequency) of the first peak to the second peak is first peak:second peak = 3:1 to 1:1. This is because the printability and / or fold crack resistance for gravure printing is improved. When multiple peaks are observed in each range, the ratio is based on the vertical axis value (frequency) of the maximum peak present in that range. In at least one embodiment, there are two peaks in the particle size distribution curve of the volume-based particle size of kaolin contained in the outermost coating layer, which is determined by laser diffraction / scattering particle size distribution measurement, in the particle size range of 0.20 μm to 7.00 μm, and there is one first peak and one second peak, and the ratio of the vertical axis values ​​(frequency) of the first peak to the second peak is first peak:second peak=3:1 to 1:1. This is because printability in gravure printing and / or resistance to cracking due to folding is improved.

[0022] In some embodiments, the peaks present in the particle diameter range of 0.20 μm to 7.00 μm in the particle size distribution curve of the volume-based particle diameter obtained by laser diffraction / scattering particle size distribution measurement of the kaolin contained in the outermost coating layer are present in the particle diameter range of 0.30 μm to 0.60 μm and the particle diameter range of 2.00 μm to 5.00 μm, respectively, and the peak present in the particle diameter range of 0.30 μm to 0.60 μm is the first peak, and the peak present in the particle diameter range of more than 2.00 μm to 5.00 μm is the second peak, and the ratio of the vertical axis value (frequency) of the first peak to the second peak is first peak:second peak = 3:1 to 1:1. This is because the printability and / or fold crack resistance for gravure printing is improved. When multiple peaks are observed in each range, the ratio is based on the vertical axis value (frequency) of the maximum peak present in that range. In at least one embodiment, there are two peaks in the particle size distribution curve of the volume-based particle size of kaolin contained in the outermost coating layer, which is determined by laser diffraction / scattering particle size distribution measurement, in the particle size range of 0.20 μm to 7.00 μm, there is one first peak and one second peak, and the ratio of the vertical axis values ​​(frequency) of the first peak to the second peak is first peak:second peak=3:1 to 1:1. This is because printability in gravure printing and / or folding crack resistance are improved.

[0023] The particle size distribution curve of kaolin can be prepared by measuring the kaolin used in the packaging paper in advance using a particle size distribution measuring device that uses a laser diffraction / scattering method. Alternatively, the coating layer of the packaging paper can be peeled off, and the kaolin sampled from the coating layer is measured using a particle size distribution measuring device that uses a laser diffraction / scattering method. An example of a particle size distribution measuring device that uses a laser diffraction / scattering method is the Microtrac (registered trademark) MT3000II by Microtrac.Inc.

[0024] The outermost coating layer of the packaging paper may contain a white pigment that is conventionally known in the field of coated paper in addition to kaolin. Examples of the white pigment include inorganic pigments such as heavy calcium carbonate, light calcium carbonate, talc, satin white, lithopone, titanium oxide, zinc oxide, amorphous silica, colloidal silica, alumina, aluminum hydroxide, zinc oxide, activated clay, and diatomaceous earth. Examples of the white pigment include organic pigments such as styrene-based plastic pigments, acrylic-based plastic pigments, styrene-acrylic plastic pigments, polyethylene-based plastic pigments, urea resins, melamine resins, and microcapsules, as well as hollow or solid particles thereof.

[0025] In some embodiments, the outermost coating layer of the packaging paper contains 78% by mass or more of kaolin based on the total white pigments contained in the outermost coating layer, including kaolin. This is because printability for gravure printing is improved. In at least one embodiment, the outermost coating layer of the packaging paper contains 78% by mass or more of kaolin based on the total white pigments contained in the outermost coating layer, including kaolin, and contains a hollow organic pigment as the white pigment. This is because printability for gravure printing is improved.

[0026] The binder is a conventionally known binder in the field of coated paper. Examples of the binder include starches and celluloses, naturally occurring resins such as casein, gelatin, soybean protein, pullulan, gum arabic, karaya gum, and albumin, and modified products thereof, various synthetic resins such as polypropylene glycol, polyethylene glycol, maleic acid resin, acrylic resin, olefin unsaturated carboxylic acid resin, styrene butadiene resin, and ethylene vinyl acetate resin, thermosetting resins such as melamine resin and urea resin, urethane resin, polyester resin, polyvinyl alcohol resins such as fully or partially saponified polyvinyl alcohol and modified polyvinyl alcohol, polyvinyl butyral, and alkyd resin.

[0027] In addition to the white pigment and binder, the outermost coating layer of the packaging paper may contain additives as necessary and within the range that does not impair the effects of the present invention. Examples of additives include printability improvers, fixing agents, dispersants, thickeners, water retention agents, defoamers, lubricants, water resistance agents, colorants, ultraviolet absorbers, fluorescent agents, surfactants, and waxes.

[0028] The coating layers, including the outermost coating layer, can be obtained by applying and drying a coating solution containing a predetermined material. For example, the coating and drying can be performed using a coating device and a drying device that are conventionally known in the field of coated paper. Examples of the coating device 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, etc. Examples of coating include coating using a wire bar for manual coating, which is an experimental method. Examples of the drying device include various drying devices such as hot air dryers such as a linear tunnel dryer, an arch dryer, an air loop dryer, and a sine curve air float dryer, an infrared heating dryer, and a dryer that utilizes microwaves.

[0029] After the application of the coating layers, including the outermost coating layer, the wrapping paper may be subjected to a calendering treatment, which is conventionally known in the papermaking art, since this improves the final smoothness of the kraft paper. Calendering may be achieved using a calendering device conventionally known in the papermaking art, such as the same calendering device as the example given below for the calendering of kraft paper.

[0030] Kraft paper, which is the base material for packaging paper, is made by papermaking a stock in which pulp produced by the Kraft process is dispersed in water. Papermaking can be achieved, for example, by a method using a papermaking machine conventionally known in the papermaking field. Examples of papermaking machines include a Fourdrinier papermaking machine, a cylinder papermaking machine, and a twin-wire papermaking machine. The raw material of the pulp produced by the Kraft process is wood or non-wood conventionally known in the papermaking field. The raw material of the pulp can be, for example, wood of coniferous and broad-leaved trees, and non-wood such as hemp, linter, straw, bamboo, sugarcane, reed, fruit, paper mulberry, Mitsumata and gampi. In some embodiments, the raw material of the pulp is one or more selected from coniferous and broad-leaved trees. In at least one embodiment, the kraft pulp is one or two selected from bleached coniferous kraft pulp (NBKP) and bleached broad-leaved kraft pulp (LBKP). This is because the strength of the packaging paper is improved.

[0031] The above-mentioned paper stock may contain, in addition to kraft pulp, conventionally known pulps such as mechanical pulp, deinked waste paper pulp, and pulp obtained by disintegrating broke generated in paper mills. In some embodiments, the content of kraft pulp in the kraft paper is 900 parts by weight or more based on 1000 parts by weight of the total pulp contained in the kraft paper. In at least one embodiment, the content of kraft pulp in the kraft paper is 1000 parts by weight based on 1000 parts by weight of the total pulp contained in the kraft paper. The reason for this is that the strength of the packaging paper is improved.

[0032] The above-mentioned paper stock may contain, as necessary, additives for papermaking conventionally known in the papermaking field, such as sizing agents, paper strength agents, paper strength enhancers, fixing agents, retention agents, retention improvers, colorants, fillers, waterproofing agents, dispersants, thickeners, flow improvers, defoamers, foam suppressors, release agents, foaming agents, penetrating agents, fluorescent brightening agents, ultraviolet absorbing agents, antioxidants, preservatives, and mold inhibitors.

[0033] The kraft paper can be subjected to a size press treatment with a size press liquid containing a surface sizing agent conventionally known in the papermaking field. The kraft paper can also be subjected to a calendar treatment conventionally known in the papermaking field. The kraft paper can be subjected to a size press treatment and a calendar treatment with a size press liquid containing a surface sizing agent conventionally known in the papermaking field. Here, the order of the size press treatment and the calendar treatment is not particularly limited. In some embodiments, the kraft paper is subjected to a size press treatment with a size press liquid containing a surface sizing agent conventionally known in the papermaking field, and then the calendar treatment. The reason for this is that the final smoothness of the kraft paper is improved.

[0034] Examples of the surface sizing agent include starch-based sizing agents, alkyl ketene dimer-based sizing agents, cellulose-based sizing agents, polyvinyl alcohol-based sizing agents, styrene acrylic-based sizing agents, olefin-based sizing agents, styrene maleic acid-based sizing agents, and acrylamide-based sizing agents.

[0035] The size press treatment can be achieved using a size press device conventionally known in the papermaking field. Examples of the size press device include an inclined size press, a horizontal size press, a rod metering size press, a roll metering size press, and a blade metering size press as film transfer methods, a shim sizer, an opti sizer, a speed sizer, and a film press as rod metering size presses, and a gate roll coater as a roll metering size press. Other examples of the size press device include a bill blade coater, a twin blade coater, a velbapa coater, a tab size press, and a calendar size press.

[0036] Calendering can be accomplished using any calendering device known in the papermaking art, such as a machine calender, a soft nip calender, a super calender, a multi-stage calender, and a multi-nip calender.

[0037] In some embodiments, the density of the wrapping paper is 0.85 g / cm 3 More than 1.10g / cm 3 The reason is that the paper has improved printability for gravure printing and resistance to cracking without compromising the strength required for packaging paper. The density of packaging paper is determined in accordance with ISO534:2011 "Paper and board-Determination of thickness, density and specific volume".

[0038] The density of the packaging paper is a physical quantity conventionally known in the papermaking field, and can be adjusted by a method conventionally known in the papermaking field. The density of the packaging paper can be adjusted, for example, by the type and beating degree of the pulp of the kraft paper, the supply amount of the paper material, the conditions of the press part of the papermaking process, the conditions of the dryer part of the papermaking process, and the presence or absence and conditions of calendaring, and further, the coating amount and the presence or absence and conditions of calendaring for the coating layer. The density of the packaging paper can be reduced, for example, by adopting measures such as low beating of the pulp, reducing the press pressure of the press part, reducing the drying strength of the dryer part, not performing calendaring or performing calendaring with a small number of nips or performing calendaring with a lighter line pressure, and reducing the coating amount of the coating layer.

[0039] In some embodiments, the total coating weight, including the outermost coating layer of the wrapping paper, is 6 g / m2 in terms of dry solids. 2 More than 12g / m 2 In at least one embodiment, the total coating weight, including the outermost coating layer of the wrapping paper, is 6 g / m2 or less in terms of dry solids. 2 More than 12g / m 2 The outermost coating layer accounts for 70% by mass or more of the total coating weight, because this provides a good balance between suitability for gravure printing and resistance to cracking due to folding. EXAMPLES

[0040] 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 amount of dry solids or the amount of substantial components, respectively. The coating amount of the coating layer represents the amount of dry solids.

[0041] <Kraft paper> A pulp slurry consisting of 800 parts by mass of LBKP with a CSF freeness of 470 ml and 200 parts by mass of NBKP with a CSF freeness of 580 ml was mixed with 4 parts by mass of a rosin-based sizing agent, 12 parts by mass of a starch-based 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 size-pressed with a size press liquid containing starch as a surface sizing agent, and then calendered using a machine calender to obtain kraft paper as the base material. The amount of surface sizing agent attached was 1 g / m per side. 2 The density of the packaging paper was adjusted to a predetermined value by adjusting the amount of paper material supplied, the conditions of the press part and the dryer part of the papermaking process, and the calendering process.

[0042] <Coating liquid for the outermost coating layer> The coating solution for the outermost coating layer was prepared according to the following: White pigment (kaolin) Mass parts and peak positions are listed in Table 1 White pigment (light calcium carbonate) Mass parts are listed in Table 1 White pigment (styrene acrylic hollow organic pigment) Mass parts are listed in Table 1 Polyvinyl alcohol (saponification degree 98-99mol%, average polymerization degree 400) 1.2 parts by mass Styrene butadiene resin 11 parts by weight Calcium stearate (lubricant) 0.3 parts by weight Defoamer (2,4,7,9-tetramethyl-5-decyne-4,7-diol) 0.35 parts by mass The above ingredients were mixed and dispersed in water to adjust the concentration to 60% by mass.

[0043] <Kaolin> Kaolin was prepared by combining a commercially available product with a relatively large average particle size and a commercially available product with a relatively small average particle size, while grinding and / or classifying them as necessary, to obtain a particle size distribution curve for the volumetric particle size. Here, the product was prepared so that there was one peak on the small particle size side, and this peak was designated as the first peak, and the product was prepared so that there was one peak on the relatively large particle size side, and this peak was designated as the second peak. For the measurement, Microtrac MT3000II, a particle size distribution measuring device using the laser diffraction / scattering method, manufactured by Nikkiso Co., Ltd. (Microtrac.Inc.) was used. The particle size corresponding to the peak position was obtained from the particle size distribution curve. In addition, when there was a first peak and a second peak, the ratio of the vertical axis values ​​(frequency) of the first peak and the second peak was approximately first peak:second peak=2:1. In Comparative Examples 1 and 2, kaolin was used that has one peak in the particle size distribution curve relating to the volume-based particle size.

[0044] <Wrapping paper> The wrapping paper was prepared according to the following procedure. The coating solution for the outermost coating layer was applied to one side of the above kraft paper using a blade coater, and then dried. After drying, the paper was subjected to a calendaring treatment using a super calendar. The coating amount was 9 g / m per side. 2 It was decided.

[0045] The density of the packaging paper was measured according to ISO534:2011. The density of the packaging paper is listed in Table 1.

[0046] The resulting wrapping paper was evaluated for printability in gravure printing and resistance to cracking when folded.

[0047] <Printability for gravure printing> The printability for gravure printing was evaluated by printing on the outermost coating layer side of the packaging paper using Gravoproof CM (Nissho Gravure Co., Ltd.) with water-based gravure ink. The evaluation was performed using the following criteria based on the impression from the viewpoints of color density, color saturation, and color vividness of the printed finish, with a printed image on a biaxially oriented polypropylene film that had been corona discharge treated as a comparison. A: It doesn't make a bad impression compared to the comparison target. B: Although it is inferior to A above, the impression is not bad overall. C: Inferior to B above, the impression is slightly worse, but still within the acceptable level for practical use. D: Less impressive than C above.

[0048] <Resistance to cracking due to folding> The resistance to fold cracking was evaluated by folding a gravure-printed wrapping paper so that the crease was located on the image area and the outermost coating layer was on the outside. The wrapping paper used for evaluation was A4 size, and the wrapping paper was folded in half by rolling a 2 kg metal roll twice to create a crease in the wrapping paper, dividing the long side in half. The creased folded part was observed with a magnifying glass and evaluated according to the following criteria. A: There are creases in the folded area, but no peeling or cracks in the layers. B: Inferior to A above, Although there is very slight peeling or cracking of layers, it is still at an acceptable level. C: Inferior to B above, Although slight peeling or cracks in the layers are observed, this is still at an acceptable level for practical use. D: Layer peeling or cracks were observed in the layers, and the level was unacceptable for practical use.

[0049] A product that is generally considered to be a conventional product has evaluation results of "C" for both "printability for gravure printing" and "resistance to cracking due to folding." Therefore, in the present invention, if the evaluation results of "printability for gravure printing" and "resistance to cracking due to folding" of a packaging paper are A, B, or C, and at least one of these evaluation results corresponds to A or B, the product has printability for gravure printing and resistance to cracking due to folding that are equal to or greater than conventional products, and at least one of the printability for gravure printing and resistance to cracking due to folding that is improved compared to conventional products.

[0050] The evaluation results are shown in Table 1.

[0051] [Table 1]

[0052] From Table 1, it can be seen that Examples 1 to 16, which correspond to the packaging paper of the present invention, have improved printability for gravure printing and resistance to cracking when folded compared to conventional papers. On the other hand, it can be seen that Comparative Examples 1 to 3, which do not satisfy the configuration of the present invention, cannot improve printability for gravure printing and / or resistance to cracking when folded compared to conventional papers.

[0053] Mainly, by comparing Examples 1, 7, and 8 with Examples 9 to 12, it is understood that when the kaolin contained in the outermost coating layer has a peak in the particle size distribution curve relating to the volume-based particle size obtained by laser diffraction / scattering particle size distribution measurement that is in the particle size range of 0.20 μm or more and 7.00 μm or less, and a peak in the particle size range of 0.30 μm or more and 0.60 μm or less and a peak in the particle size range of 2.00 μm or more and 5.00 μm or less, the printability for gravure printing and / or fold crack resistance is improved.

[0054] Mainly, from the comparison between Example 5 and Examples 13 to 16, the density of the packaging paper is 0.85 g / cm 3 More than 1.10g / cm 3 It is understood that if the thickness is less than this, the printability in gravure printing and / or the resistance to cracking due to folding can be improved.

Claims

1. A packaging paper comprising: a kraft paper containing kraft pulp; and one or more coating layers on at least one side of the kraft paper, wherein an outermost coating layer located outermost relative to the kraft paper among the coating layers contains at least kaolin and a binder, and the kaolin has at least two peaks in a particle size range of 0.20 μm or more and 7.00 μm or less in a particle size distribution curve relating to volume-based particle size determined by laser diffraction / scattering particle size distribution measurement.

2. 2. The wrapping paper according to claim 1, wherein in a particle size distribution curve relating to the volume-based particle size of the kaolin obtained by laser diffraction / scattering particle size distribution measurement, a peak present in a particle size range of 0.20 μm or more and 7.00 μm or less also exists in a particle size range of 0.30 μm or more and 0.60 μm or less and a particle size range of 2.00 μm or more and 5.00 μm or less, respectively.

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