Printing paper

Abstract

To provide a printing paper of non-coating paper type that, while being a non-coating paper not having a coating layer containing a while pigment, has printability to an inkjet printing machine and has moist glossy feeling and silky touch feeling.SOLUTION: The challenge is achieved by a printing paper characterized in that a base paper that contains at least pulp and filler, and by applying a size press treatment to the base paper, contains at least surface sizing agents and cationic compounds, with a denison wax pick surface strength of 13A or more and 16A or less as required according to JAPAN TAPPI No.1: 2000, a 75-degree gloss of 10% or more and 23% or less as required according to ISO 8254-1: 1999, and a Bekk flatness (second) obtained according to ISO 5627:1995 of 175 sec or more and 370 sec or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a printing paper that does not have a coating layer containing a white pigment, and further relates to a printing paper that does not have a coating layer containing a white pigment, which has printability for offset printing machines and digital printing machines, particularly for inkjet printing machines, which are a type of digital printing machine. [Background technology]

[0002] Printing machines for producing commercial printed matter include digital printing machines or on-demand printing machines (hereinafter collectively referred to as "digital printing machines") capable of handling variable information. A representative example is an inkjet printing machine that uses an inkjet recording method. Inkjet printing machines already exist under names such as TruepressJet (registered trademark) from SCREEN Graphic Solutions, MJP series from Miyakoshi, Prosper (registered trademark) and VERSAMARK (registered trademark) from Kodak, and JetPress (registered trademark) from Fujifilm.

[0003] Although it depends on the printing conditions, inkjet printers have color printing speeds several tens of times faster than general home and SOHO inkjet printers and large-format inkjet printers, with printing speeds of 60 m / min or more, and even faster speeds exceeding 100 m / min. For this reason, inkjet printers are distinguished from general home and SOHO inkjet printers and large-format inkjet printers.

[0004] Many of the printing machines on the market for producing commercial printed materials are still offset printing machines, which existed before the advent of digital printing machines. In other words, the printing machines on the market for producing commercial printed materials are a mixture of digital printing machines, such as inkjet printing machines, and offset printing machines. Therefore, printing paper needs to be suitable for printing on both types of printing machines.

[0005] In the printing industry, commercial printed matter such as magazines, books, art books, photo books, art books, MOOK books, booklets, catalogs, flyers, and pamphlets are commercial products. The printing paper used in the production of commercial printed matter is not limited to glossy paper or matte paper. In recent years, printing paper comes in a variety of textures, such as gloss or matte feel, smoothness, hue, and texture. For expensive commercial printed matter such as art books, photo books, art books, and fine art books, emphasis is placed on collector's value, and heavy, expensive coated printing paper with a thick coating layer that has high whiteness, high gloss, and high smoothness is used. On the other hand, for commercial printed matter such as magazines, books, MOOKs, pamphlets, catalogs, flyers and brochures, there is a trend to use printing paper of a lightly coated type, which has an extremely small amount of a coating layer containing a white pigment, or an uncoated type, which has no coating layer containing a white pigment, in order to reduce paper costs.

[0006] A method for producing uncoated printing paper that has the same gloss as light-weight coated paper (LWC paper) is known (see, for example, Patent Document 1). The printing paper obtained by the production method described in Patent Document 1 is called "supercalender paper." Recently, in Europe and the United States, supercalender paper is used as printing paper for offset printing machines or gravure printing machines for commercial printing applications such as magazines, advertising flyers, and catalogs. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2008-274517 A Summary of the Invention [Problem to be solved by the invention]

[0008] The printing paper described in Patent Document 1 has a white paper gloss of 30% or more, which is somewhat higher than that of ordinary LWC paper. An object of the present invention is to provide a printing paper that does not have a coating layer containing a white pigment, that has printability for offset printing machines, and also for digital printing machines, particularly for inkjet printing machines, which is a type of digital printing machine, and that has a moist gloss and silky touch in which a weak gloss like that of LWC paper is observed as a surface texture of the paper. [Means for solving the problem]

[0009] The present inventors have intensively engaged in development efforts to address the above-mentioned problems, and as a result, have discovered the present invention. The object of the present invention can be achieved as follows.

[0010] [1] A printing paper comprising a base paper containing at least pulp and a filler, and a surface sizing agent and a cationic compound obtained by subjecting the base paper to a size press treatment, the paper having a wax pick surface strength of 13A or more and 16A or less as determined in accordance with JAPAN TAPPI No. 1:2000 using Denison wax, a 75 degree gloss of 10% or more and 23% or less as determined in accordance with ISO 8254-1:1999, and a Bekk smoothness (seconds) of 175 seconds or more and 370 seconds or less as determined in accordance with ISO 5627:1995.

[0011] In some embodiments, the present invention is the following. [2] The printing paper according to [1] above, wherein the surface sizing agent is one or more selected from the group consisting of starches and polyvinyl alcohols. Effect of the Invention

[0012] According to the present invention, the printing paper does not have a coating layer containing a white pigment, and has printability for offset printing machines, printability for digital printing machines, and in particular printability for inkjet printing machines, which is a type of digital printing machine, and the paper surface has a moist gloss and silky touch with a weak gloss like that of LWC paper. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The printing paper of the present invention comprises a base paper containing at least pulp and a filler, and contains at least a surface sizing agent and a cationic compound by subjecting the base paper to a size press treatment. The printing paper can improve its printability on digital printers by including a filler in the base paper. The printing paper can have a moist glossy feel and a silky touch by including a surface sizing agent and a cationic compound through a size press treatment, and can also obtain printability on digital printers.

[0014] In some embodiments, the base paper is made by making a stock containing at least pulp and a filler by a conventionally known papermaking method. As a result, the base paper can contain pulp and a filler. The printing paper is made by subjecting the base paper to a size press treatment. The printing paper can contain a surface sizing agent and a cationic compound because the size press liquid used in the size press treatment contains a surface sizing agent and a cationic compound. The surface sizing agent and cationic compound contained in the printing paper are present in relatively greater amounts near the surface layer of the printing paper when the surface sizing agent and cationic compound are blended in the size press liquid, resulting in the printing paper containing the surface sizing agent and cationic compound, compared to when the surface sizing agent and cationic compound are blended in the stock, resulting in the printing paper containing the surface sizing agent and cationic compound, and therefore these effects are more likely to be exhibited.

[0015] The papermaking method may be, for example, a method using a papermaking machine conventionally known in the papermaking field, such as a Fourdrinier papermaking machine, a twin-wire papermaking machine, a combination papermaking machine, a cylinder papermaking machine, or a Yankee papermaking machine. The size press treatment may be a method using a size press device that is conventionally known in the papermaking field. Examples of size press devices include inclined size press, horizontal size press, and film transfer type rod metering size press, roll metering size press, and blade metering size press, rod metering size presses include shim sizer, opti sizer, speed sizer, and film press, and roll metering size presses include gate roll coater. Other examples of size press devices include bill blade coater, twin blade coater, Belbapa coater, tab size press, and calendar size press.

[0016] The pulp is one or more types selected from wood pulps and non-wood pulps conventionally known in the papermaking field. Examples of wood pulp include chemical pulps such as Leaf Bleached Kraft Pulp (LBKP) and Needle Bleached Kraft Pulp (NBKP); mechanical pulps such as Groundwood Pulp (GP), Pressure GroundWood pulp (PGW), Refiner Mechanical Pulp (RMP), ThermoMechanical Pulp (TMP), ChemiThermoMechanical Pulp (CTMP), and ChemiMechanical Pulp (CMP); semi-chemical pulps such as ChemiGroundwood Pulp (CGP); waste paper pulps such as DeInked Pulp (DIP); and pulp obtained by disintegrating spoilage generated in paper mills. Non-wood pulp is pulp made of non-wood fibers conventionally known in the papermaking field. Examples of raw materials for non-wood fibers include woody bast such as paper mulberry, mitsumata, and gampi, herbaceous bast such as flax, hemp, and kenaf, leaf fibers such as Manila hemp, abaca, and sisal, grasses such as rice straw, wheat straw, sugarcane bagasse, bamboo, and esparto, and seed hairs such as cotton and linter.

[0017] The filler is a pigment that is conventionally known in the papermaking field. Examples of the pigment include inorganic pigments such as 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. Examples of the pigment include organic pigments such as styrene-based plastic pigments, acrylic-based plastic pigments, polyethylene-based plastic pigments, urea resins, melamine resins, and microcapsules. In some embodiments, the filler is one or more selected from the group consisting of the inorganic pigments and the organic pigments.

[0018] The surface sizing agent is one that has been conventionally known in the papermaking field, and examples of the surface sizing agent include alkylketene dimers, melamine formalin resins, acrylamide polymers, acrylic polymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, acrylonitrile-vinyl formal-acrylic acid ester copolymers, styrene-maleic acid copolymers, olefin-maleic acid copolymers, polyvinyl alcohols such as polyvinyl alcohols and various modified polyvinyl alcohols having various degrees of saponification or polymerization, starches such as starch and various modified starches, and carboxymethyl cellulose. In some embodiments, the surface sizing agent is one or more selected from the group consisting of polyvinyl alcohols and starches, for the following reasons (1) and (2). (1): One or more selected from the group consisting of polyvinyl alcohols and starches do not adversely affect printability on offset printing machines and printability on digital printing machines, in particular printability on inkjet printing machines. (2) One or more selected from the group consisting of polyvinyl alcohols and starches are resin-type additives that have no or only a small effect of imparting a glossy feel, and can impart a moist gloss and silky touch to printing paper.

[0019] In some embodiments, the amount of surface sizing agent applied is 0.4 g / m2 in terms of dry solids content per side of the base paper. 2 More than 1.5g / m 2 The reason is that the printability on an offset printing machine is improved.

[0020] The cationic compound is one or more selected from cationic resins and water-soluble polyvalent cation salts. The cationic resin is a cationic polymer or cationic oligomer, and is conventionally known in the field of inkjet printing paper. In some embodiments, the cationic resin is a polymer or oligomer containing primary to tertiary amines or quaternary ammonium salts that are easily proton-coordinated and dissociate when dissolved in water to exhibit cationicity. Examples of the cationic resin include compounds such as polyethyleneimine, polyvinylpyridine, polyamine sulfone, polydialkylaminoethyl methacrylate, polydialkylaminoethyl acrylate, polydialkylaminoethyl methacrylamide, polydialkylaminoethyl acrylamide, polyepoxyamine, polyamine and modified polyamine, polyamide and modified polyamide, polyamidoamine, dicyandiamide-formaldehyde condensate, polyvinylamine, and polyallylamine, and their hydrochlorides, as well as copolymers of polydiallyldimethylammonium chloride and diallyldimethylammonium chloride with acrylamide, polydiallylmethylamine hydrochloride, and polycondensates of aliphatic monoamines or aliphatic polyamines with epihalohydrin compounds, such as dimethylamine epichlorohydrin polycondensates and diethylenetriamine epichlorohydrin polycondensates. In some embodiments, the cationic resin is a polycondensate of an aliphatic monoamine or an aliphatic polyamine and an epihalohydrin compound, because it has some effect not only on printability for digital printers, particularly inkjet printers, but also on improving the strength of printing paper.

[0021] The water-soluble polyvalent cation salt is a water-soluble salt containing a metal polyvalent cation. The water-soluble polyvalent cation salt is a salt that contains a metal polyvalent cation and can be dissolved in water at 20°C at a concentration of 1% by mass or more. The metal polyvalent cation is, for example, a divalent cation such as magnesium, calcium, strontium, barium, nickel, zinc, copper, iron, cobalt, tin, manganese, etc.; a trivalent cation such as aluminum, iron, chromium, etc.; or a tetravalent cation such as titanium, zirconium, etc.; and a complex ion thereof. The anion that forms a salt with the metal polyvalent cation may be either an inorganic acid or an organic acid, and is not particularly limited. Examples of the inorganic acid include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, and hydrofluoric acid. Examples of the organic acid include formic acid, acetic acid, lactic acid, citric acid, oxalic acid, succinic acid, and organic sulfonic acid. However, aluminum sulfate, which has been known as a fixing agent for sizing agents, is excluded from the water-soluble polyvalent cation salt. In some embodiments, the water-soluble polyvalent cation salt is a calcium salt because this improves printability on digital printers, and particularly on inkjet printers.

[0022] In some embodiments, the amount of the cationic compound applied is 0.5 g / m2 in terms of dry solid content per side of the base paper. 2 More than 2g / m 2 The reason is that the printability for offset printing machines is not impaired, and the printability for digital printing machines, particularly the printability for inkjet printing machines, is improved.

[0023] The stock and size press liquid may contain various additives conventionally known in the papermaking field, as necessary, such as internal sizing agents, fixing agents, retention agents, bulking agents, printability improving agents, colorants, coagulants, paper strength agents, pigment dispersants, thickeners, flow improvers, defoamers, foam inhibitors, release agents, foaming agents, penetrating agents, ultraviolet absorbing agents, antioxidants, preservatives, mold inhibitors, water resistant agents, wet strength agents, and dry strength agents.

[0024] The printing paper has a 75° gloss of 10% to 23% as determined in accordance with ISO8254-1:1999 "Paper and board - Measurement of specular gloss - Part-1: 75° gloss with a converging beam, TAPPI method". The printing paper can have a moist gloss and silky touch due to the synergistic effect of the gloss and the wax pick surface strength value and Bekk smoothness value described below.

[0025] The gloss of printing paper is a physical quantity conventionally known in the papermaking field and can be adjusted by conventionally known methods, such as by adjusting the press pressure in the press part of the papermaking process, and the presence or absence of calendaring and its conditions. Calendering is a process for making the smoothness and thickness of paper uniform by passing the paper between rolls. Examples of calendering devices include a machine calender, a soft nip calender, a super calender, a multi-stage calender, and a multi-nip calender.

[0026] The printing paper has a wax pick surface strength of 13A or more and 16A or less, determined according to JAPAN TAPPI No.1:2000 "Paper and board - Determination of surface strength - Wax pick test method" (corresponding to ASTM D2482 "STANDARD TEST METHOD FOR SURFACE OF PAPER (WAX PICK METHOD)" using Denison wax. The printing paper can have a moist gloss and silky touch due to the synergistic effect of the wax pick surface strength, the gloss value above, and the Bekk smoothness value described below. Furthermore, if the wax pick surface strength of the printing paper is less than 13A, the printability of the paper for offset printing presses tends to deteriorate from the viewpoint of blanket piling. Furthermore, if the wax pick surface strength of the printing paper is more than 16A, the printability of the paper for digital printing presses, particularly inkjet printing presses, tends to deteriorate.

[0027] The wax pick surface strength measurement required according to JAPAN TAPPI No.1:2000 is a method to determine the grade of wax from the peeled off state of the paper surface by using wax graded for adhesive strength, adhering heated and melted wax to paper, and peeling off the wax after it solidifies. Denison wax is graded from 2A to 26A for adhesive strength from weakest to strongest. From the measurement principle, it can be said that the wax pick surface strength is influenced by the contact surface state between the paper and the wax, which depends on the fine unevenness and voids present on the paper surface, in addition to the surface strength of the paper. Therefore, the inventors have considered the wax pick surface strength, which is influenced by the above, as an index that indirectly indicates the shape of the paper surface, and have discovered the present invention, which is related to the glossiness and silky touch of paper.

[0028] The wax pick surface strength of printing paper is a physical quantity conventionally known in the papermaking field and can be adjusted by conventionally known methods, such as by adjusting the types of pulp and filler and their content in the stock, the concentration of the stock, the amount of stock supplied, the press pressure of the press part in the papermaking process, the heat amount of the drying zone, and the presence or absence of calendaring and its conditions.

[0029] The printing paper has a Bekk smoothness (seconds) determined in accordance with ISO5627:1995 "Paper and board--Determination of smoothness (Bekk method)" of 175 seconds or more and 370 seconds or less. Due to the synergistic effect of the Bekk smoothness, the gloss value, and the wax pick surface strength value, the printing paper can have a moist gloss and a silky touch while having printability for digital printers, particularly for inkjet printers. If the Bekk smoothness of the printing paper is less than 175 seconds, the printability for digital printers, particularly for inkjet printers, tends to deteriorate in terms of the sharpness of the printed image. If the Bekk smoothness of the printing paper is less than 175, the offset printability of the printing paper that has been subjected to a size press treatment using a size press liquid containing a cationic compound may deteriorate. If the Bekk smoothness of the printing paper is more than 370 seconds, the printability for digital printers, particularly for inkjet printers, tends to deteriorate in terms of the ink absorbency of the printed image.

[0030] The Bekk smoothness of printing paper is a physical quantity conventionally known in the papermaking field and can be adjusted by conventionally known methods, such as adjusting the press pressure in the press part of the papermaking process, the heat amount and time in the drying zone of the papermaking process, and the presence or absence of calendaring and its conditions.

[0031] In some embodiments, the printing paper has an opacity of 91% or more and 95% or less as measured in accordance with ISO2471:1998 "Paper and board-Determination of opacity (paper backing)-Diffuse reflectance method". This is because the print paper has improved resistance to strike-through. The opacity can be adjusted, for example, by the type and content ratio of pulp and filler contained in the base paper, the density of the base paper, etc.

[0032] In some embodiments, the printing paper has a basis weight of 45 g / m 2 More than 90g / m 2 The reason is that it is easy to handle in commercial printed matter such as magazines, books, and MOOKs. EXAMPLES

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Furthermore, "parts by mass" and "% by mass" shown in the examples indicate parts by mass and % by mass calculated as dry solids or of the actual components unless otherwise specified. Furthermore, the amount applied in the size press treatment indicates the amount of dry solids.

[0034] (base paper) The paper stock was prepared as follows: Pulp (LBKP with CSF filtration rate of 430 ml) 1000 parts by weight Filler (light calcium carbonate) 250 parts by weight Fixing agent (aluminum sulfate) 10 parts by weight Paper strength agent (cationized starch) 10 parts by weight Retention agent (acrylamide resin) 0.4 parts by mass

[0035] (Size press fluid) The size press liquid was prepared using water as a medium with the following contents. Surface sizing agent: Type and mass part are shown in Table 1 Cationic compounds: Type and mass parts are listed in Table 1.

[0036] (Printing paper) The paper stock is made into paper using a fourdrinier machine with a basis weight of 60 g / m 2 The base paper was subjected to a size press treatment using a size press device, and then to a super calendar treatment to obtain a printing paper. In the size press treatment, the total amount of the dye applied to one side of the base paper was 2 g / m 2 It was decided. The gloss, wax pick surface strength and Bekk smoothness were adjusted to the desired values ​​by adjusting the concentration of the paper stock, the supply amount of the paper stock, the press pressure of the press part and the drying zone conditions in the papermaking process, and the supercalendering conditions.

[0037] The materials listed in Table 1 are as follows: "PVA": Saponification degree 98-99 mol% and polymerization degree 300-1700 Polyvinyl alcohol "Starch": Oxidized starch "AKD": alkyl ketene dimer "Calcium chloride": Calcium chloride "Salt Mag": Magnesium chloride "DMAEPI": Dimethylamine epichlorohydrin polycondensate "MPA": Modified polyamine

[0038] (Glossy) The gloss of the printing paper was measured in accordance with ISO8254-1:1999 using a digital gloss meter GM-26D from Murakami Color Research Laboratory Co., Ltd., with the incident / reflecting angle set at 75 degrees.

[0039] (Wax pick surface strength) The wax pick surface strength of the printing paper was measured according to JAPAN TAPPI No. 1:2000 using Denison wax.

[0040] (Bekk smoothness) The Bekk smoothness of the printing paper was measured according to ISO5627:1995.

[0041] (Printability for offset printing machines) Using a sheet-fed offset printing machine (Mitsubishi Heavy Industries, Dia 3H-4), four-color printing was performed on one side of the printing paper using lithographic offset process inks. For printing, a 4 cm x 4 cm image of each color was randomly arranged. The printed image was visually observed and evaluated according to the following criteria. In the present invention, a printing paper is considered to have printability for offset printing machines if it is rated A or B. A: Good usable quality. B: Although inferior to A above, it is still of usable quality. C: The quality is not practical.

[0042] (Printability for inkjet printers) The inkjet printer used was a Fujifilm Jet Press 540W (printing speed: 100 m / min). The printed image was a 2 cm x 2 cm square image with a total of seven solid color patterns, consisting of the single colors black, cyan, magenta, and yellow, and the double colors (red, green, and blue) made with the other three ink colors excluding black, arranged in a horizontal row with no gaps. The prints were visually evaluated from the viewpoints of ink absorption, sharpness, color development, fixation, color vividness, uniformity, image visibility on the back side of the printed surface (the less visible the better), etc. In the present invention, printing paper is deemed to have printability for inkjet printers if it is rated A or B. A: Good usable quality. B: Although inferior to A above, it is still of usable quality. C: The quality is not practical.

[0043] (Glossy) The gloss was evaluated by 20 subjects who observed the printed paper under LED white light. The subjects evaluated the intensity of light reflection, which is based on the perception of regular reflected light and diffuse reflected light, and the diffusion and color of reflected light as perceived by humans, according to the following criteria. 2 points: The gloss tends to be perceived as being strong or somewhat strong. 1 point: Feels like a generally moderate level of gloss. 0 points: Feels matte or tends to feel somewhat matte. The glossiness was evaluated by adding up the individual evaluation scores and classifying the total score into the following three levels: In the present invention, printing paper rated A or B is considered to have a moist glossiness. A: More than 15 points and less than 25 points B: More than 10 points and less than 15 points or more than 25 points and less than 30 points. C: 10 points or less or more than 30 points.

[0044] (Silky touch) The silky touch was evaluated by 20 subjects who viewed blank printing paper. The subjects compared the paper with an existing silky touch printing paper (Crown Van Gelder's Crown Letsgo Silk) and rated it according to the following criteria. 2 points: Smooth, no silky touch or somewhat no silky touch. 1 point: Silky touch feeling or generally silky touch feeling. 0 points: Matte, with no or somewhat no silky touch. The silky touch feeling was evaluated by adding up the individual evaluation scores and classifying the total score into the following three levels: In the present invention, a printing paper that is rated A or B is considered to have a silky touch feeling. A: More than 15 points and less than 25 points B: More than 10 points and less than 15 points or more than 25 points and less than 30 points. C: 10 points or less or more than 30 points.

[0045] The results are shown in Table 1.

[0046] [Table 1]

[0047] From Table 1, it can be seen that the printing papers of Examples 1 to 12 corresponding to the present invention are printing papers that do not have a coating layer containing a white pigment, are suitable for printing on an offset printing machine, and are also suitable for printing on an inkjet printing machine, which is a type of digital printing machine, and have a moist gloss and silky touch with a slight gloss reminiscent of LWC paper in terms of the surface feel of the paper. On the other hand, it is found that the printing papers of Comparative Examples 1 to 8, which do not satisfy the configuration of the present invention, do not satisfy at least one of printability for offset printing machines, printability for inkjet printing machines, which is a type of digital printing machine, moist glossiness, and silky touch.

Claims

1. A printing paper comprising a base paper containing at least pulp and a filler, and a surface sizing agent and a cationic compound obtained by subjecting the base paper to a size press treatment, the printing paper having a wax pick surface strength of 13A to 16A as determined in accordance with JAPAN TAPPI No. 1:2000 using Denison wax, a 75 degree gloss of 10% to 23% as determined in accordance with ISO 8254-1:1999, and a Bekk smoothness (seconds) of 175 seconds to 370 seconds as determined in accordance with ISO 5627:1995.

2. 2. The printing paper according to claim 1, wherein the surface sizing agent is one or more selected from the group consisting of starches and polyvinyl alcohols.

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