paper

Abstract

To provide paper that has a texture similar to medium-grade paper but contains a minimum amount of mechanical pulp. [Solution] The paper contains 90 parts by weight or more of chemical pulp and less than 10 parts by weight of mechanical pulp per 100 parts by weight of pulp of the base paper, and the difference between the PPS smoothness (soft backing, 2000kPa) and the PPS smoothness (soft backing, 500kPa) as determined in accordance with ISO 8791-4:1992 is 1.1 μm or more. The paper of the present invention is suitable for book paper, paperback paper, and comic book paper.

Description

[Technical Field]

[0001] This invention relates to paper having a texture similar to medium-grade paper, with a minimum mechanical pulp content. More specifically, it relates to paper with good cushioning properties and suitable for letterpress and offset printing. [Background technology]

[0002] Medium-grade paper has been favored for use as comic book paper and paperback paper due to its texture, color, and workability. Medium-grade paper generally contains 10-60% mechanical pulp, which has the characteristics of being rigid and having low whiteness. Therefore, medium-grade paper containing 10-60% mechanical pulp is characterized by high rigidity, low whiteness, and a tendency to be bulky.

[0003] Book and comic book paper is often printed using either offset or letterpress printing, and is required to possess both offset and letterpress printing suitability. Letterpress printing is a printing method that uses a plate made by combining movable type, i.e., typesetting. It is a printing method in which ink is applied to the raised parts of a plate (image areas: raised, non-image areas: recessed) and transferred to the paper by applying pressure. In offset printing, it is easy to change the pressure applied by the plate and impression cylinder, so the degree of ink transfer can be changed by adjusting the printing pressure even on paper with low cushioning. However, in letterpress printing, from the perspective of workload and other factors, printing pressure adjustment is generally not performed, and the paper itself is required to have some cushioning. Furthermore, in order to obtain fine prints, the paper needs to have a suitable degree of smoothness.

[0004] Furthermore, since book paper is printed on both sides, it needs to be resistant to bleed-through (where printed text or images show through to the other side) and also stiff enough to make turning pages easy by hand. As an example of such medium-quality book paper, the technology described in Patent Document 1 is known.

[0005] Furthermore, a technique described in Patent Document 2 is known, which involves adding bulking agents, sizing agents, and calcium carbonate to obtain bulky paper similar to medium-grade paper without using mechanical pulp. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-026985 [Patent Document 2] Japanese Patent Publication No. 2006-052482 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The invention described in Patent Document 1 is a technology based on the use of mechanical pulp. However, in light of the recent global trend towards reducing greenhouse gas emissions, there is an urgent need to reduce the amount of mechanical pulp used, which relies on petroleum fuels, and there is a demand for book paper with a low mechanical pulp content. Furthermore, the suitability of book paper for letterpress printing has not been studied to date.

[0008] In view of these circumstances, the present invention aims to provide a paper that has a medium-grade paper-like texture with high opacity and good cushioning properties, even with a low mechanical pulp content. [Means for solving the problem]

[0009] The present invention is not limited to these, but encompasses the following embodiments. [1] Paper containing 90 parts by weight or more of chemical pulp and less than 10 parts by weight of mechanical pulp per 100 parts by weight of base paper pulp, wherein the difference between the PPS smoothness (soft backing, 2000 kPa) and the PPS smoothness (soft backing, 500 kPa) as required in accordance with ISO 8791-4:1992 is 1.1 μm or more. [2] The paper according to [1], wherein the base paper contains a bulking agent. [3] The paper as described in [1] or [2], where the difference between the PPS smoothness (soft backing, 500 kPa) and the PPS smoothness (soft backing, 2000 kPa) is 1.5 μm or more. [4] The paper as described in [1] or [2], where the PPS smoothness (soft backing, 500 kPa) is 3.0 μm or more and 7.0 μm or less. [5] The paper as described in [1] or [2], where the specific scattering coefficient calculated based on the formula defined in TAPPI T425 (ISO 9426) is 55 m 2 / kg or more. [6] The paper as described in [1] or [2], where the ISO whiteness is 50% or more and 70% or less. [7] The paper as described in [1] or [2], where the ash content in the paper is 20% by weight or less. [8] The paper as described in [1] or [2], where the ash content in the paper is 5% by weight or more. [9] The paper as described in [1] or [2], where the base paper contains two or more colorants with different hues.

[10] The paper as described in [1] or [2], where the base paper contains a black colorant and a colorant other than black. [Effect of the Invention]

[0010] According to the present invention, it is possible to provide a paper having a content of mechanical pulp of at least a medium paper-like texture with high opacity and good cushioning properties. In particular, the paper of the present invention is suitable for book paper, paperback paper, and comic paper printed by letterpress printing and offset printing. [Embodiments for Carrying Out the Invention]

[0011] Base paper The base paper used in the present invention contains 90 parts by weight or more of chemical pulp, preferably bleached kraft pulp, out of 100 parts by weight of total pulp. It is preferable to use at least bleached hardwood kraft pulp (LBKP) or bleached softwood kraft pulp (NBKP) as the bleached kraft pulp. Other raw materials that can be used include unbleached hardwood or softwood kraft pulp (UKP), sulfite pulp, recycled paper pulp, linter pulp, non-wood pulp such as hemp, bagasse, kenaf, esparto grass, and straw, semi-synthetic fibers such as rayon and acetate, and synthetic fibers such as polyolefins, polyamides, and polyesters, all mixed in any proportion. Furthermore, of 100 parts by weight of total pulp, it contains less than 10 parts by weight of mechanical pulp such as wood pulp (GP), refined wood pulp (RGP), thermomechanical pulp (TMP), chemothermetic pulp (CTMP), chemigland pulp (CGP), and semi-chemical pulp (SCP). It is more preferable that the mechanical pulp content be 5 parts by weight or less. It is preferable that the deinked recycled paper pulp derived from recycled newspaper, which contains a large amount of mechanical pulp, be 10 parts by weight or less, more preferably 5 parts by weight or less, and most preferably not contained at all. Since the base paper used in the present invention uses chemical pulp as the main raw material, it is possible to obtain paper that has excellent color development when colorants are added, has high opacity, and is resistant to bleed-through. Furthermore, by limiting the mechanical pulp content to less than 10 parts by weight out of 100 parts by weight of total pulp, it is possible to obtain paper that has good cushioning properties, a texture similar to medium-grade paper, and is environmentally friendly, while suppressing impurities on the paper surface caused by coloring components such as lignin from trees contained in mechanical pulp.

[0012] Smoothness and cushioning The paper of the present invention has moderate smoothness and cushioning properties, so the Parker PrintSurf smoothness (hereinafter also referred to as PPS smoothness (soft / 500kPa)) measured under soft backing / clamping pressure of 500kPa is preferably 7.0μm or less, more preferably 6.5μm or less. The lower limit is preferably 3.0μm or more, more preferably 5.0μm or more. Similarly, the Parker PrintSurf smoothness (hereinafter also referred to as PPS smoothness (soft / 2000kPa)) measured under soft backing / clamping pressure of 2000kPa is preferably 5.0μm or less, more preferably 4.5μm or less. The lower limit is preferably 2.5μm or more, more preferably 3.0μm or more. When the PPS smoothness (soft / 500kPa) and PPS smoothness (soft / 2000kPa) are within the above ranges, the paper of the present invention has moderate smoothness and therefore excellent ink transfer during printing.

[0013] Furthermore, cushioning can be indicated by the value of [PPS smoothness (soft / 500kPa)] - [PPS smoothness (soft / 2000kPa)]. [PPS smoothness (soft / 500kPa)] - [PPS smoothness (soft / 2000kPa)] is preferably 1.0 μm or more, more preferably 1.1 μm or more, and even more preferably 1.5 μm or more. There is no particular upper limit, but it is 5.0 μm or less, more preferably 3.0 μm or less. If the difference in PPS smoothness at different clamp pressures exceeds 5.0 μm, the PPS smoothness value measured at a clamp pressure of 500 kPa may become too high, potentially resulting in paper with poor smoothness.

[0014] PPS smoothness is a value determined in accordance with ISO 8791-4:1992 "Paper and board - Determination of roughness / smoothness (air leak methods)". PPS smoothness can be measured in accordance with ISO 8791-4:1992 "Paper and board - Determination of roughness / smoothness (air leak methods)", for example, using a Messmer Parker Printsurf Roughness Tester. Here, a smaller PPS smoothness value indicates less unevenness in the paper.

[0015] The Parker PrintSurf measurement principle involves measuring the amount of compressed air leaking between a narrow, ring-shaped measuring surface and the sample surface. During measurement, the sample is pressed against the measuring surface by a pressure plate. Therefore, the measured value takes into account the compressibility of the sample. If the distance between the measuring surface and the sample surface is G, the value is calculated as the cube root of the average spatial spacing using the following formula and expressed in μm units. G=(12ηbQ / w△P) 1 / 3 η: Viscosity of air at room temperature b: width of the measuring ring Q: Air volume flowing per unit time w: Effective length of the measuring ring △P: Pressure difference between measuring rings

[0016] Based on the measurement principle described above, PPS smoothness indicates the surface irregularity of the paper. Furthermore, the difference in ParkerPrintSurf smoothness measured at different clamping pressures represents the difference between the surface irregularities when light pressure is applied and when strong pressure is applied, indicating the paper's cushioning properties. A larger difference indicates better cushioning properties. Because the paper of this invention has excellent cushioning properties, it is possible to obtain paper suitable for printing in letterpress printing methods where cushioning properties are required.

[0017] Bulking agent The paper of the present invention preferably contains a bulking agent to achieve stiffness, tactile feel, and cushioning properties similar to medium-grade paper containing a large amount of mechanical pulp, even with a low mechanical pulp content. The bulking agent content is 1.0% by weight or less, preferably 0.9% by weight or less, more preferably 0.8% by weight or less, and more preferably less than 0.7% by weight, based on 100% by weight of pulp. When the bulking agent content is 1.0% by weight or less, a relatively bulky paper can be obtained even if only a small amount of bulky pulp such as mechanical pulp is used. Furthermore, it is possible to obtain paper suitable for letterpress printing because it has excellent cushioning properties, tactile feel when used as a book, and stiffness. In addition, by increasing the bulk of the paper, it is possible to obtain paper with higher opacity. If the bulking agent content is greater than 1.0% by weight, the hydrophobicity of the fibers progresses and interfiber bonding does not progress, which may lead to a decrease in strength, such as a decrease in wet paper strength during manufacturing and a decrease in the interlayer delamination strength of the product. As a lower limit, it is preferable that it be 0.1% by weight or more in order to obtain a sufficient bulking effect.

[0018] Colorants The paper of the present invention preferably contains two or more colorants of different hues, and more preferably contains a black colorant and a colorant other than black. By containing the above-mentioned colorants, it is possible to obtain paper with a subdued color tone, similar to medium-grade paper containing a large amount of mechanical pulp or recycled paper pulp, even while containing a large amount of bleached kraft pulp with high whiteness. Furthermore, the opacity is improved, which reduces print show-through when used as book paper with printing areas on both sides. Examples of black colorants include carbon black pigments such as furnace black, lamp black, acetylene black, channel carbon, and thermal black; magnetic fine particles such as magnetite and ferrite; aniline black, titanium black, copper oxide, iron oxide, and phthalocyanine black. In the present invention, from the viewpoint of dyeing efficiency, it is preferable to include the colorants as internal additives. The two or more colorants of different hues may be dyes or pigments, and examples include colorants having red, yellow, brown, green, blue, and purple hues.

[0019] Relative scattering coefficient The relative scattering coefficient of the paper of this invention is 55m 2 It is 90m² or more. The relative scattering coefficient can be calculated based on the formula specified in TAPPI T425 (ISO 9426). The relative scattering coefficient represents the scattering ability per unit basis weight and can represent the opacity of the paper regardless of the basis weight. Therefore, paper with a high relative scattering coefficient is less prone to show-through. There is no upper limit to the relative scattering coefficient, but it is usually 90m². 2 It would be around / kg. Considering the balance with ash content and strength, 70m 2 A value of less than / kg is more preferable. The specific scattering coefficient can be adjusted as appropriate depending on the type and amount of pulp and filler mainly used.

[0020] Opacity The opacity of the paper of the present invention can be measured in accordance with JIS-P8149:2000. The upper limit of opacity is not limited, but considering its use as book paper, it is preferably 80% or higher, more preferably 85% or higher, even more preferably 90% or higher, and even more preferably 92% or higher. Furthermore, in the present invention, it is preferable that the bleed-through value is 85% or higher. Here, the bleed-through value is the value obtained by measuring the reflectance of the back surface of the printed surface using X-Rite520 (manufactured by X-Rite Corporation) and dividing the reflectance of the back surface of the printed surface by the reflectance of the back surface of the unprinted surface. A larger value indicates less bleed-through.

[0021] Generally, paper with a reduced mechanical pulp content tends to be less bulky and has poorer show-through compared to medium-grade paper at the same basis weight. However, the paper of the present invention can be made highly opaque and less show-through by adjusting the basis weight, specific scattering coefficient, density, and colorant addition rate. Furthermore, by including a small amount of mechanical pulp, it is possible to achieve bulkiness and opacity that cannot be achieved with bulking agents alone, while suppressing the decrease in whiteness caused by mechanical pulp.

[0022] Other internally added medications Various internal additives may be added to the pulp of the present invention, as long as they do not hinder the effects of the present invention. These internal additives are not limited to, but may include: polyacrylamide polymers, polyvinyl alcohol polymers, oxidized starch, esterified starch, cationized starch, various other modified starches, adhesives such as styrene-butadiene copolymers, latex, and vinyl acetate; cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; internal paper strength enhancers such as urea-formaldehyde resin and melamine-formaldehyde resin; internal sizing agents such as rosin-based sizing agents, AKD-based sizing agents, ASA-based sizing agents, petroleum-based sizing agents, and neutral rosin-based sizing agents; aluminum sulfate, yield enhancers, UV inhibitors, fade inhibitors, water drainage enhancers, coagulants, pH adjusters, and slime control agents. From the viewpoint of improving paper strength, it is preferable that the paper of the present invention contains paper strength enhancers. Furthermore, from the viewpoint of adjusting the dampening water absorption during offset printing, it is preferable that the paper has appropriate sizing properties, and therefore, it is preferable that it contains internal sizing agents. Since book paper is preferably manufactured using a neutral papermaking process that minimizes yellowing and deterioration during long-term storage, it is preferable to use an AKD-type sizing agent that exhibits its effects easily in the neutral range. Furthermore, in order to produce paper with a subdued color tone similar to medium-grade paper, it is preferable that the paper of this invention does not contain a fluorescent whitening agent.

[0023] filler The paper of the present invention can be filled with a filler, but the filler used is not particularly limited and can be appropriately selected from known fillers. Examples of such fillers include talc, kaolin, clay, calcium carbonate such as light calcium carbonate and heavy calcium carbonate, titanium dioxide, silica, and organic fillers such as plastic pigments, but calcium carbonate is preferred. Using calcium carbonate as an internal filler in the paper of the present invention is preferable because it has the effect of improving print quality such as opacity and printability. Among calcium carbonates, light calcium carbonate is particularly preferred because it has a high specific scattering coefficient and imparts high opacity. When printing on paper, especially when used as book paper, double-sided printing is often performed, and opacity is an important quality item in order to prevent bleed-through after printing.

[0024] ash In the paper of the present invention, the ash content in the paper is preferably 5% to 35% by weight, more preferably 7% to 30% by weight, and more preferably 10% to 20% by weight, relative to the oven-dry weight of the paper. If the ash content in the paper is less than 5% by weight, the opacity and smoothness may be insufficient. If the ash content in the paper is higher than 20% by weight, the bonding between fibers may be inhibited by the filler in the paper, which may result in insufficient stiffness and cushioning properties of the paper, and reduced sizing properties when an internal sizing agent is added. Furthermore, insufficient stiffness can lead to problems such as poor workability, poor page-turning properties when processed into books, and poor tactile feel. Moreover, from the viewpoint of balancing opacity, stiffness, and cushioning properties like medium-grade paper, if the ash content in the paper is within the above range, it is possible to produce a medium-grade paper-like paper that provides sufficient opacity while suppressing the reduction in stiffness and cushioning properties due to ash content. In particular, paper containing a bulking agent and more than 5% by weight of calcium carbonate can be made to have the same bulk and opacity as book paper containing a large amount of mechanical pulp.

[0025] Paper making process In the present invention, the pulp prepared as described above is appropriately diluted, and after removing foreign matter from the pulp with a screen or cleaner as needed, it is sprayed onto the papermaking wire from the headbox of the papermaking machine. The present invention is manufactured using various papermaking machines, such as halftone, cylinder, short-wire, and twin-wire papermaking machines. The paper of the present invention is suitable for use as book paper with printing on both sides, so it is preferable to use a twin-wire papermaking machine that minimizes the difference between the front and back sides, and examples of twin-wire papermaking machines include gap formers and on-top formers. The press line pressure after papermaking is used appropriately within the range of the density described later, but a low press line pressure is preferable to obtain the bulkiness effect of the present invention. Furthermore, the papermaking method may be neutral papermaking or acidic papermaking, but neutral papermaking is preferable. Specifically, in the present invention, the pH of the pulp during papermaking is preferably 5.0 to 9.0, and more preferably 6.0 to 8.0.

[0026] Surface treatment process In the present invention, it is preferable to apply a surface treatment liquid to the base paper obtained above to provide a clear coating layer in order to improve surface strength, impart water resistance, and improve printability. The type of adhesive used in the surface treatment liquid is not particularly limited, but it is preferable to include starches such as raw starch, oxidized starch, esterified starch, cationized starch, and auto-modified starch produced in a paper mill by thermochemical or enzymatic modification using acetylated tapioca starch as raw materials, as well as modified starches such as aldehyde starch and hydroxyethylated starch. It is also possible to use cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and cellulose nanofiber, modified alcohols such as polyacrylamide, polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, and acetoacetylated polyvinyl alcohol, latex, styrene-butadiene copolymer, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, and polyacrylic acid ester in combination, but from the viewpoint of imparting rigidity to the paper, it is preferable to use a starch-based adhesive. Oxidized starch is more preferable.

[0027] Also, for the purpose of enhancing sizing properties, it is also possible to use surface sizing agents in combination, such as AKD sizing agents, rosin sizing agents, styrene sizing agents, olefin sizing agents, acrylate sizing agents, styrene-acrylic sizing agents, cationic sizing agents, etc. When using surface sizing agents in combination, the solid content concentration in the surface treatment liquid is preferably 0.005% by weight or more and 1% by weight or less, more preferably 0.01% by weight or more and 0.5% by weight or less, and even more preferably 0.015% by weight or more and 0.1% by weight or less. Since the surface sizing agent is effective in reducing friction and developing sizing properties with a small amount compared to the internal sizing agent, sufficient effects can be obtained with the above addition amount. From the perspective of processing during cutting and printing, the surface sizing agent to be used is preferably a styrene-acrylic sizing agent.

[0028] Furthermore, when performing surface treatment in the present invention, various auxiliaries usually incorporated in normal surface treatment liquids, such as dispersants, thickeners, water retention agents, defoaming agents, water resistance agents, colorants, conductive agents, etc., are appropriately used as required. Since the paper of the present invention contains color materials such as black color materials, its whiteness is not too high, and it is not easy to cause eye fatigue when used as book paper.

[0029] The coating amount of the surface treatment liquid is not particularly limited as it is appropriately determined according to the required surface strength, etc., but it is preferably 1.0 g / m 2 or more and 3.0 g / m 2 or less on both sides, and more preferably 1.5 g / m 2 or more and 2.5 g / m 2 or less. By setting it within the above range, sufficient surface strength can be imparted for offset printing.

[0030] The apparatus for applying the surface treatment liquid is not particularly limited, and it can be applied by known coating machines such as two-roll size presses, pond size presses, gate roll coaters, rotogravure size presses, blade coaters, spray coaters, curtain coaters, etc. However, from the perspective of efficiently enhancing the surface strength with a small coating amount for the paper of the present invention, it is preferable to apply it with a gate roll coater or a rotogravure size press, which are film transfer type coating facilities.

[0031] The resulting paper may be passed through known finishing equipment, such as a supercalender, gloss calender, soft calender, or high-temperature soft nip calender, to finish the product, or it may be left untreated or bypassed to achieve the density range described later. However, from the viewpoint of producing paper with bulkiness and cushioning properties similar to medium-grade paper, it is preferable not to perform calendering. When calendering is performed, the processing line pressure is appropriately adjusted to achieve a density similar to medium-grade paper.

[0032] The paper obtained in this invention may be used as a base paper for pigment coating.

[0033] Basis weight The paper of this invention has a basis weight of 40 g / m², as measured in accordance with JIS P 8124. 2 More than 150g / m 2 The following is preferable, and more preferably 45 g / m² 2 More than 140g / m 2 The present invention is particularly suitable for paper with a low basis weight because it can achieve high rigidity even with a low basis weight.

[0034] density The paper of the present invention has a paper density of 0.40 g / cm³ as measured in accordance with JIS P 8118. 3 Preferably, it is 0.45 g / cm³ or more, and more preferably 0.45 g / cm³. 3 The above is more accurate, and more preferably 0.50 g / cm³ 3 That's all. The upper limit is 0.90 g / cm³. 3 The following, and more preferably 0.80 g / cm³ 3 The following, and more preferably 0.75 g / cm³ 3 The following, and more preferably 0.70 g / cm³ 3 The following applies: By setting the density within the aforementioned range, it is possible to obtain a paper that is bulky, has a tactile feel, and is more opaque, similar to medium-grade paper containing a large amount of mechanical pulp. 0.40 g / cm² 3 If the weight is less than 0.80 g / m², the surface may become noticeably rough, potentially impairing its suitability for offset printing. 3In the case of ultra-high quality paper, there is a risk that the medium-quality paper-like texture may be lost.

[0035] stiffness The paper of the present invention preferably has a stiffness (Clark formula) of 30 or more in the longitudinal (MD: machine flow) direction, measured in accordance with JIS-P8143, more preferably 35 or more, and more preferably 40 or more. The upper limit is preferably 210 or less, more preferably 200 or less, and more preferably 190 or less. If the stiffness is lower than the above range, the paper may be too soft when used in a paperback book, or the pages may stick together due to electrostatic discharge, making it difficult to turn the pages. On the other hand, if the stiffness is higher than the above range, the paper at both ends of the pages may not align well when the book is opened, and the paper may stand up, making it difficult to read.

[0036] Hue The paper of the present invention preferably has L*a*b* values ​​under a light source including ultraviolet light according to JIS P8150, where L* is 80 to 98, a* is -5 to 3, and b* is -3 to 20, more preferably L* is 82 to 96, a* is -4.5 to 2, and b* is -2 to 19, and even more preferably L* is 83 to 95, a* is -4 to 1.5, and b* is 0 to 18. Within the above range, a paper with a natural texture similar to medium-grade paper can be obtained. Furthermore, when used as book paper, it is possible to obtain book paper that is less tiring on the eyes even when reading for long periods of time.

[0037] ISO whiteness The ISO whiteness of the paper of the present invention, measured in accordance with JIS P8148, is preferably 80% or less, more preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less, in order to reproduce the texture of medium-grade paper. The lower limit is 50% or more from the viewpoint of color development during printing. In order to make the paper of the present invention have a texture similar to medium-grade paper, the above range can be achieved by adding a black colorant or the like to a pulp slurry that uses a large amount of chemical pulp such as kraft pulp. Furthermore, the higher the whiteness of the paper, the better the color reproduction during printing, making it preferred for multi-color printing where accurate reproduction of photographs and illustrations is required. [Examples]

[0038] The present invention will be described in more detail below with specific examples, but the present invention is not limited to these examples. In this specification, unless otherwise specified, concentrations and the like are given on a weight basis, and numerical ranges are given including their endpoints. In the following description, "parts" means "parts by weight" and "%" means "weight percent".

[0039] <Pharmaceuticals> The chemicals used in the examples and comparative examples are as follows: AKD-type sizing agent: Manufactured by Seikou PMC, AD-1614 Cationic starch: National Starch Co., Ltd., CATO304 Oxidized starch: Manufactured by Nippon Corn Starch Co., Ltd., SK-20 Internal paper strength enhancer: Harima Chemicals Co., Ltd., Hermid EX-283 Bulking agent: Kao Corporation, KB-130 Filling: TP-121 (light calcium carbonate), manufactured by Okutama Kogyo Co., Ltd. Aluminum sulfate: Manufactured by J.O. Chemical Co., Ltd., liquid band Black dye: Direct Paper Black NWS Liquid, manufactured by Nippon Chemical Industries, Ltd. Yellow dye: Direct Paper Yellow RSL, manufactured by Nippon Chemical Industries, Ltd. Red dye: Kayafect Red, manufactured by Nippon Kayaku Co., Ltd. Blue dye: Manufactured by Toa Chemical Co., Ltd., TOA Basic Blue BS (L)

[0040] (Example 1) To a slurry of 90% by weight of bleached hardwood kraft pulp (LBKP, filtration degree 390 mM LCSF) and 10% by weight of bleached softwood kraft pulp (NBKP, filtration degree 620 mM LCSF), 1.1% by weight of aluminum sulfate, 0.4% by weight of internal paper strength enhancer, 0.9% by weight of cationized starch, 0.05% by weight of AKD-based sizing agent, 0.075% by weight of black dye, 0.093% by weight of yellow dye, 0.017% by weight of red dye, and 0.5% by weight of bulking agent were added per 100% by weight of pulp and thoroughly mixed to form the papermaking raw material. Furthermore, light calcium carbonate was added as a filler, targeting a paper ash content of 15% by weight. Subsequently, base paper was made using an on-top former. Dewatering was performed at the press line pressure described in Table 1. The resulting base paper was coated using a gate roll coater, resulting in a total coating weight of 1.6 g / m² on both sides. 2 A surface treatment solution containing oxidized starch was applied to the base paper to create a clear coating layer. After drying, no calendering was performed, and the target basis weight was 43 g / m². 2 It is manufactured to achieve the following, with an actual basis weight of 47.6 g / m². 2 I obtained the paper.

[0041] (Example 2) Paper was manufactured in the same manner as in Example 1, except that the blending ratio of bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP) was changed as shown in Table 1.

[0042] (Example 3) Paper was manufactured in the same manner as in Example 2, except that light calcium carbonate was added as a filler with a target ash content of 17% by weight in the paper.

[0043] (Example 4) Paper was manufactured in the same manner as in Example 1, except that the blending ratio of bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP) was changed as shown in Table 1, light calcium carbonate was added as a filler with a target ash content of 17.5% by weight in the paper, and the black dye was set to 0.057% by weight, the yellow dye to 0.00% by weight, the red dye to 0.004% by weight, and the blue dye to 0.002% by weight.

[0044] (Example 5) Paper was manufactured in the same manner as in Example 2, except that 5% by weight of the bleached hardwood kraft pulp (LBKP) in the paper was replaced with 5% by weight of bleached thermomechanical pulp (bleached TMP).

[0045] (Comparative Example 1) A slurry consisting of 65% by weight bleached thermomechanical pulp (bleached TMP), 20% by weight recycled paper pulp (DIP), and 15% by weight bleached softwood kraft pulp (NBKP) was mixed with 1.2% by weight aluminum sulfate, 0.1% by weight internal paper strength enhancer, 0.5% by weight cationized starch, 0.02% by weight AKD-based sizing agent, and 0.044% by weight black dye per 100% by weight of pulp. The mixture was thoroughly mixed to form the papermaking raw material. Furthermore, light calcium carbonate was added as a filler, targeting a paper ash content of 10% by weight. Subsequently, base paper was produced using an on-top former. Dewatering was performed at the press line pressures listed in Table 1. The resulting base paper was coated using a gate roll coater, resulting in a total coating weight of 1.3 g / m² on both sides. 2 A surface treatment solution containing oxidized starch was applied to the base paper to create a clear coating layer. After drying, calendering was performed to achieve a target basis weight of 43 g / m². 2 It is manufactured to achieve the following, with an actual basis weight of 47.0 g / m². 2 I obtained the paper.

[0046] (Comparative Example 2) Paper was manufactured in the same manner as in Example 1, except that a calendering process was performed.

[0047] (Comparative Example 3) To a slurry of 90% by weight of bleached hardwood kraft pulp (LBKP, filtration efficiency 340 mM LCSF) and 10% by weight of bleached softwood kraft pulp (NBKP, filtration efficiency 480 mM LCSF), 1.7% by weight of aluminum sulfate, 0.9% by weight of cationized starch, and 0.09% by weight of AKD-based sizing agent were added per 100% by weight of pulp and thoroughly mixed to form the papermaking raw material. Furthermore, light calcium carbonate was added as a filler, targeting a paper ash content of 21% by weight. Subsequently, base paper was produced using a wireframe paper machine. Dewatering was performed at the press line pressures listed in Table 1. The resulting base paper was coated using a pound-type size press, resulting in a total coating weight of 2.7 g / m² on both sides. 2 A surface treatment solution containing oxidized starch was applied to the base paper to create a clear coating layer. After drying, calendering was performed to achieve a target basis weight of 64 g / m². 2 It is manufactured to achieve the following, with an actual basis weight of 64.7 g / m². 2 I obtained the paper.

[0048] (Comparative Example 4) Paper was manufactured in the same manner as in Comparative Example 1, except that the blending ratio of bleached thermomechanical pulp (bleached TMP) was changed to 45% by weight, the blending ratio of recycled paper pulp (DIP) was changed to 40% by weight, and 0.1% by weight of a bulking agent was used.

[0049] (Comparative Example 5) A slurry consisting of 56% by weight bleached thermomechanical pulp (bleached TMP), 17% by weight recycled paper pulp (DIP), and 27% by weight bleached softwood kraft pulp (NBKP) was mixed with 2.0% by weight aluminum sulfate, 0.4% by weight internal paper strength enhancer, 1.0% by weight cationized starch, and 0.13% by weight AKD-based sizing agent per 100% by weight of pulp. The mixture was thoroughly mixed to form the papermaking raw material. Light calcium carbonate was then added as a filler, targeting a paper ash content of 20% by weight. Subsequently, base paper was produced using an on-top former. Dewatering was performed at the press line pressures listed in Table 1. The resulting base paper was coated using a gate roll coater, with a total coating amount of 1.4 / m² on both sides. 2 A surface treatment solution containing oxidized starch was applied to the base paper to create a clear coating layer. After drying, calendering was performed to achieve a target basis weight of 43 g / m². 2 It is manufactured to achieve the following, with an actual basis weight of 43.1 g / m². 2 I obtained the paper.

[0050] (Comparative Example 6) Paper was manufactured in the same manner as in Example 5, except that 5% by weight of the bleached softwood kraft pulp (NBKP) in the paper was replaced with 5% by weight of bleached thermomechanical pulp (bleached TMP).

[0051] The book paper obtained in the above examples and comparative examples was subjected to various performance measurements and evaluations using the methods described below. The results are shown in Tables 1 and 2. Note that the mechanical pulp content per 100 parts by weight of pulp in Table 2 includes mechanical pulp contained in bleached thermomechanical pulp (bleached TMP) as well as mechanical pulp contained in recycled paper pulp (DIP).

[0052] 1. Various paper quality measurements Basis weight: Measured in accordance with JIS P 8124. Paper thickness and density: Measured in accordance with JIS P 8118. Ash content: Measured according to ISO 1762-1974. ISO Opacity: Measured according to ISO 2471. Whiteness: Measured in accordance with JIS P 8148. Relative scattering coefficient: Calculated based on the formula specified in TAPPI T425 (ISO 9426). PPS smoothness was measured according to ISO 8791-4:1992 under conditions of soft backing, clamp pressure of 500 kPa, and soft backing, clamp pressure of 2000 kPa.

[0053] 2. Evaluation of cushioning properties In accordance with ISO 8791-4:1992, the difference in PPS smoothness measured under two conditions—soft backing, clamp pressure of 500 kPa, and soft backing, clamp pressure of 2000 kPa—was evaluated on a three-point scale. ○: The PPS smoothness (soft / 500kPa) - PPS smoothness (soft / 2000kPa) is 1.5μm or more and 3.0μm or less, providing sufficient cushioning. △: PPS smoothness (soft / 500kPa) - PPS smoothness (soft / 2000kPa) is 1.0μm or more and less than 1.5μm, and has cushioning properties. ×: The PPS smoothness (soft / 500kPa) - PPS smoothness (soft / 2000kPa) is less than 1.0 μm, and there is no cushioning effect.

[0054] 3. Evaluation of texture The texture of medium-grade paper was evaluated on a three-point scale based on the following criteria, considering its color and density. ○: It has a yellowish color, sufficient bulk, and a texture similar to medium-grade paper. △: It has a yellowish tint and is not very bulky, and has a texture similar to medium-quality paper. ×: It lacks a yellowish tint, bulkiness, and the texture of medium-grade paper.

[0055] 4. Evaluation of suitability for offset printing Surface strength and smoothness, which are required for offset printing, were evaluated in two stages according to the following criteria. For surface strength, a solid color of cyan ink was printed on an A3 size sample using a Roland R202 sheet-fed printing press. The number of pulp fibers that peeled off the surface was then visually observed, and samples with fewer peels were judged to have superior surface strength. ○: Possesses moderate surface strength and smoothness, and is suitable for offset printing. ×: Poor surface strength or smoothness, unsuitable for offset printing.

[0056] 5. Evaluation of suitability for letterpress printing The cushioning and smoothness required for letterpress printing were evaluated in three stages according to the following criteria: A PPS smoothness (soft / 500kPa) of 5.0μm to 6.5μm was considered good smoothness, while a smoothness of 3.0μm to less than 5.0μm or greater than 6.5μm was considered adequate. ○: Possesses sufficient cushioning and good smoothness, and is suitable for letterpress printing. △: Although its cushioning or smoothness is somewhat inferior, it can be printed using letterpress printing. ×: Poor cushioning or smoothness, unsuitable for letterpress printing.

[0057] 6. Evaluation of environmental considerations The degree of environmental consideration was evaluated in two stages based on the amount of mechanical pulp used. ○: The amount of mechanical pulp, which is a major source of greenhouse gas emissions during manufacturing, is low at less than 10 parts by weight per 100 parts by weight of pulp in the base paper, demonstrating environmental consideration. ×: This product contains 10 parts by weight or more of mechanical pulp, which has high greenhouse gas emissions during manufacturing, per 100 parts by weight of the base paper pulp, and is not environmentally friendly.

[0058] 7. Evaluation of back-through The opacity was used as an indicator and evaluated on a three-point scale according to the following criteria. ○: The opacity is 90% or higher, making it less likely to bleed through to the other side. △: Opacity is between 80% and 90%, so there is a slight risk of bleed-through. ×: The opacity is less than 80%, which may cause show-through.

[0059] [Table 1]

[0060] [Table 2]

Claims

1. A paper containing 90 parts by weight or more of chemical pulp and less than 10 parts by weight of mechanical pulp per 100 parts by weight of base paper pulp, Paper in which the difference between the PPS smoothness (soft backing, 2000 kPa) and the PPS smoothness (soft backing, 500 kPa) required in accordance with ISO 8791-4:1992 is 1.1 μm or more.

2. The paper according to claim 1, wherein the base paper contains a bulking agent.

3. The paper according to claim 1 or 2, wherein the difference between the PPS smoothness (soft backing, 500 kPa) and the PPS smoothness (soft backing, 2000 kPa) is 1.5 μm or more.

4. The paper according to claim 1 or 2, wherein the PPS smoothness (soft backing, 500 kPa) is 3.0 μm or more and 7.0 μm or less.

5. The relative scattering coefficient calculated based on the formula specified in TAPPI T425 (ISO 9426) is 55 m ２ The paper according to claim 1 or 2, which is 1 kg or more.

6. The paper according to claim 1 or 2, wherein the ISO whiteness is 50% or more and 70% or less.

7. The paper according to claim 1 or 2, wherein the ash content in the paper is 20% by weight or less.

8. The paper according to claim 1 or 2, wherein the ash content in the paper is 5% by weight or more.

9. The paper according to claim 1 or 2, wherein the base paper contains two or more colorants of different hues.

10. The paper according to claim 1 or 2, wherein the base paper contains a black colorant and a colorant other than black.

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