JP2018188762A - Printing paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printing paper that is suitable for an offset printing machine as well as has uniformity of color density, dot reproducibility and resistance to waviness for an inkjet printing machine.SOLUTION: The printing paper has a base paper and at least one layer of a coating layer on at least one surface of the base paper. In the coating layer, an outermost coating layer located at the outermost position based on the base paper contains at least a pigment, a binder, a lubricant, a dispersant and a cationic resin; the pigment in the outermost coating layer contains kaolin and calcium carbonate; the content of the kaolin and the calcium carbonate is 80 pts.mass or more with respect to 100 pts.mass of the pigment in the outermost coating layer; a content mass ratio of kaolin to calcium carbonate in the outermost coating layer is 1:9 to 6:4; and on the side of the printing paper having the outermost coating layer, a transfer amount of an aqueous solution having a surface tension of 20 mN/m is 5.0 ml/mor more and 12.0 ml/mor less, measured by Bristow method with 1 second contact time.SELECTED DRAWING: None

Description

  The present invention relates to a printing paper that can be printed by an inkjet printing machine while being a printing paper for an offset printing machine.

The ink jet recording method is a method in which ink droplets are ejected from a fine nozzle onto a recording paper and are deposited on the paper to form ink dots for recording.
The ink jet recording method is used for small printers for home use and SOHO, wide format printers used for POP and poster production, and on-demand printers used for production of commercial prints. The printing paper used has various glossy feelings from matte to glossy. Printing paper for producing commercial printed materials such as business documents, DM, books, booklets, flyers, brochures, catalogs, etc., and photographic paper developed as an alternative to silver halide photography in the inkjet recording method, the cost of printed materials, The required quality differs in terms of print productivity and how to handle the print.

At least water for a recording ink, a recording medium, an ink media set, an ink recording, an inkjet recording method, and an inkjet recording apparatus capable of recording a high-quality image close to commercial printing such as offset printing by an inkjet method. An ink containing a colorant and a wetting agent and having a surface tension at 25 ° C. of 20 to 35 mN / m, a support, and a recording medium having a coating layer on at least one surface of the support; The amount of transfer of the ink to the recording medium at a contact time of 100 ms measured with a dynamic scanning absorption meter is 4 to 15 ml / m ² and the recording of the ink at a contact time of 400 ms ink media set transfer amount to use media is 7~20ml / ^{m 2} is known (e.g. See Patent Document 1).

A printing press such as an offset printing press or a relief printing press requires a “plate” on which a printed image is formed. On-demand printers, on the other hand, do not require a “plate”. That is, in the on-demand printing machine, the image forming apparatus directly prints on the paper according to the digital information regarding the image.
There are on-demand printers that use inkjet recording, i.e., inkjet printers. Examples of inkjet printers include TruePressJet from SCREEN Graphic and Precision Solutions, MJP series from Miyakoshi, Prosper and VERSAMARK from Kodak, JetPress from FUJIFILM, and ColorInkjetWebPress from Hewlett-Packard.

  Such an ink jet printer, although depending on printing conditions, has a color printing speed of 10 to several tens of times faster than a small ink jet printer for home use and SOHO, and a wide format ink jet printer, and a printing speed of 15 m. / Min., More than 100 m / min at higher speeds. For this reason, inkjet printers are distinguished from small inkjet printers and wide format inkjet printers for home use and SOHO use.

JP 2007-216664 A

With the widespread use of on-demand printers, printing paper needs to be compatible with on-demand printers as well as printing presses. In particular, it is necessary to be applicable to an offset printing machine and an inkjet printing machine that are often used for production of commercial printed matter.
In an offset printing machine, ink attached to a printing plate is transferred to a printing paper through a blanket and transferred to produce a printed matter. Ink jet printers produce printed matter by ejecting ink droplets onto printing paper from fine nozzles that are not in contact with the paper. Due to such a difference in printing mechanism, the ink of the offset printing press has adhesiveness and has a high colorant content concentration. The ink of an ink jet printer has fluidity and a low color material content concentration.

When printing paper for conventional offset printing machines is used in an inkjet printing machine, as the printing speed increases, there is a partial variation in the ink absorbency of the printing paper, resulting in uneven color density in the printed area. There is. This is because the ink of the ink jet printer has fluidity and the color material-containing concentration is low.
Also, as the printing speed increases, if the ink on the printing paper is not well received, the dot reproducibility may be reduced at the printed portion. When the dot reproducibility decreases, the image quality deteriorates. This is because the paper conveyance speed increases in proportion to the high printing speed, and ink droplets adhering to the surface of the printing paper flow when they land on the paper surface. That is, dots formed by ink droplets that have landed on the surface of the paper have a distorted shape, or the outline of the dots become unclear, causing a reduction in image quality.
Further, when the ink solvent contained in the ink of the ink jet printer reaches the base paper, the base paper may be wavy due to the expansion and contraction of the fibers. The undulation generated by the ink solvent causes a trouble in contact between the print head and the paper in an ink jet printer or a problem in dimensional defects during post-printing processing.

An object of the present invention is to provide a printing paper having the following qualities for an inkjet printer, aiming at being able to print with an inkjet printing machine while being a printing paper having suitability for an offset printing machine.
(1) The color density of the printed portion is uniform (color density uniformity).
(2) The dot reproducibility of the printed portion is excellent (dot reproducibility).
(3) Suppression of undulation of printed part (anti-corrugation)

As a result of intensive studies, the present inventors have achieved the object of the present invention as follows.
[1] A printing paper having a base paper and one or more coating layers on at least one side of the base paper, and the outermost coating layer located on the outermost side with respect to the base paper in the coating layer, The pigment in the outermost coating layer contains at least a pigment, a binder, a lubricant, a dispersant, and a cationic resin. The pigment in the outermost coating layer contains kaolin and calcium carbonate, and the content of kaolin and calcium carbonate is in the outermost coating layer. 80 parts by mass or more with respect to 100 parts by mass of the pigment, and the content ratio of kaolin and calcium carbonate in the outermost coating layer is 1: 9 to 6: 4, and the outermost coating of the printing paper for the side having the layer, the printing paper is transferred amount of the aqueous solution has a surface tension of 20 mN / m is 5.0 ml / ^{m 2} or more 12.0 ml / ^{m 2} or less at a contact time of 1 second sought Bristow method.

[2] On the side having the outermost coating layer of the printing paper, the transfer amount of an aqueous solution having a surface tension of 20 mN / m is measured at a contact time of 0.4 seconds determined by the Bristow method. The transition amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 1 second]-[Transition amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 0.4 seconds determined by the Bristow method] is 0. The printing paper according to [1], which is 5 ml / m ² or more and 2.5 ml / m ² or less.

  According to the present invention, it is possible to provide a printing paper having color density uniformity, dot reproducibility, and undulation resistance for an ink jet printing machine while being a printing paper having suitability for an offset printing machine.

The present invention is described in detail below.
The printing paper of the present invention has a base paper and a coating layer on at least one side of the base paper. The outermost coating layer located on the outermost side with respect to the base paper in the coating layer contains at least a pigment, a binder, a lubricant, a dispersant, and a cationic resin.
In the present invention, “having a coating layer” refers to a paper having a clear coating layer that can be distinguished from a base paper when a cross section of the paper is observed with an electron microscope. For example, a resin component or a polymer component is applied, and the applied component is a small amount that is absorbed by the base paper, and as a result, a clear layer that can be distinguished from the base paper when the cross section of the printing paper is observed with an electron microscope Does not fall under “having a coating layer”.

  Base paper is chemical pulp such as LBKP (Leaf Bleached Kraft Pulp), NBKP (Needle Bleached Kraft Pulp), GP (Groundwood Pulp), PGW (Pressure Ground Wood pulp), RMP (Refiner Mechanical Pulp), TMP (ThermoMechanical Pulp), CTMP (ChemiThermoMechanical Pulp), CMP (ChemiMechanical Pulp), mechanical pulp such as CGP (ChemiGroundwood Pulp), and at least one pulp selected from waste paper pulp such as DIP (DeInked Pulp), light calcium carbonate, heavy calcium carbonate, Various fillers such as talc, clay, kaolin, sizing agent, fixing agent, retention agent, cationizing agent such as cationic resin and polyvalent cation salt, and various additives such as paper strength agent are added as necessary. It is a papermaking paper made from paper stock. Further, the base paper includes high-quality paper obtained by subjecting papermaking paper to calendar treatment, surface sizing treatment with starch or polyvinyl alcohol, or the like. Further, the base paper includes high-quality paper that has been subjected to surface sizing or calendering after surface treatment.

  In paper stock, other additives include pigment dispersants, thickeners, fluidity improvers, antifoaming agents, antifoaming agents, mold release agents, foaming agents, penetrating agents, colored dyes, colored pigments, fluorescent enhancers. One or more of whitening agents, ultraviolet absorbers, antioxidants, antiseptics, antibacterial agents, water resistance agents, wet paper strength enhancers, dry paper strength enhancers, etc. can be used to achieve the desired effects of the present invention. It can mix | blend suitably in the range which is not impaired.

The coating layer can be provided on at least one side of the base paper by coating and drying the coating layer coating solution. The coating layer is one layer or two or more layers. The coating layer located on the outermost side with respect to the base paper in the coating layer is referred to as the outermost coating layer. When the number of coating layers is one, this coating layer becomes the outermost coating layer. The outermost coating layer contains at least a pigment, a binder, a lubricant, a dispersant, and a cationic resin. The coating layer present between the base paper and the outermost coating layer is not particularly limited with respect to the presence or absence and type of each of the pigment, binder, lubricant, dispersant, and cationic resin.
Each coating amount of the coating layer is not particularly limited. A preferable coating amount is in a range of 5 g / m ² or more and 30 g / m ² or less per side in terms of dry solid content. When there are two or more coating layers, the value is the total of them. When there are two or more coating layers, it is preferable that the outermost coating layer occupies 70% by mass of the coating amount per side in terms of dry solid content.

  The coating layer may be provided on one side or both sides of the base paper. Moreover, in the case of a single side | surface, you may have a conventionally well-known backcoat layer on the surface opposite to the side which has a coating layer in a base paper.

  The method of providing the coating layer on the base paper is not particularly limited. For example, a method of coating and drying a coating layer coating solution using a conventionally known coating apparatus and drying apparatus in the papermaking field can be mentioned. Examples of the coating apparatus include a comma coater, 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. Examples of dryers include various dryers such as straight tunnel dryers, arch dryers, air loop dryers, sine curve air float dryers, hot air dryers, infrared heating dryers, dryers using microwaves, etc. Can do.

The coating layer can be calendered.
The calendar process is a process for averaging smoothness and thickness by passing paper between rolls. Examples of the calendar processing apparatus include a machine calendar, a soft nip calendar, a super calendar, a multistage calendar, and a multinip calendar.
The printing paper of the present invention does not include printing paper on which the outermost coating layer has been cast.

In the printing paper, the transfer amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 1 second determined by the Bristow method on the side having the outermost coating layer is 5.0 ml / m ² or more and 12.0 ml / m ^2. It is as follows.
The amount of transfer of the aqueous solution required by the Bristow method is TAPPI No. In accordance with 51-2000, using an aqueous solution with a surface tension of 20 mN / m, using a head with a slit width of 0.5 mm, the water absorption amount at a contact time of 1 second or 0.4 seconds described later (ml / m ² ) Is a measured value.
Recent inkjet printers tend to use inks with low surface tension with the goal of being able to print on traditional offset printing paper. For this reason, it is possible to perform an evaluation in conformity with an actual ink jet printer by measuring the contact angle using an aqueous solution having a lower surface tension than the measurement of the contact angle using ion-exchanged water having a high surface tension.
When the transfer amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 1 second is less than 5.0 ml / m ² on the side having the outermost coating layer of the printing paper, color density uniformity can be obtained. Can not. When the water transfer amount is more than 12.0 ml / m ² , dot reproducibility or wave resistance cannot be obtained.

In a further preferred embodiment of the present invention, the transfer amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 1 second determined by the Bristow method is 5.0 ml / m ² on the side having the outermost coating layer of the printing paper. The amount of transition of an aqueous solution having a surface tension of 20 mN / m at a contact time of 0.4 seconds was measured at 12.0 ml / m ² or less, and the surface tension was 20 mN / m at a contact time of 1 second determined by the Bristow method. The amount of transition of an aqueous solution in which the surface tension is 20 mN / m at a contact time of 0.4 seconds determined by the Bristow method] is 0.5 ml / m ² or more and 2.5 ml / m ^2. It is as follows. This is because the color density uniformity or wave resistance is further improved.

The transfer amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 0.4 seconds determined by the Bristow method on the side having the outermost coating layer of the printing paper is 4.5 ml / m ² or more and 9.5 ml / m ² or less is preferable.

The surface tension of the aqueous solution is a value measured by the Wilhelmi plate method.
The aqueous solution having a surface tension of 20 mN / m used for the measurement of the transition amount may have a surface tension of 20 mN / m by the Wilhelmi plate method. For example, alcohols such as glycerin, polyethylene glycol, propylene glycol, ethanol or ethylene glycol Alternatively, it can be obtained by adding an appropriate amount of a fluorosurfactant such as perfluoroalkylsulfonic acid to ion-exchanged water.

  The transfer amount of the aqueous solution is a conventionally known physical quantity in the papermaking field as described in, for example, Japanese Patent No. 5081592, and can be adjusted by a conventionally known method in the papermaking field. For example, coating amount, pigment type, pigment average particle size, pigment particle size distribution, pigment shape, pigment oil absorption, binder type, molecular weight or degree of polymerization, water-dispersible binder and water-soluble binder This can be achieved by combining various conditions such as the mixing ratio of the pigments and the content ratio of the pigment and the binder. In particular, an increase in hydrophilic pigment, an increase in the water-soluble binder ratio, a decrease in the binder ratio, a blending of an ionic compound such as a dispersant and a cationic resin, and a decrease in the coating amount tend to increase the transfer amount. Increasing the water-dispersible binder ratio, blending a lubricant, blending a relatively hydrophobic surfactant having a long-chain alkyl group, etc. tend to reduce the amount of transfer. Further, since the state of the layer surface is changed after being formed, the transfer amount varies depending on the application of the outermost coating layer coating liquid and the presence or absence of calendar treatment after drying or the calendar treatment conditions. Since the state of the formed layer changes somewhat, the amount of transfer varies depending on the drying method used when the outermost coating layer is provided.

  The outermost coating layer of the printing paper contains at least a pigment, a binder, a lubricant, a dispersant, and a cationic resin. Due to the synergistic effect of the specific material composition and the specific transition amount range in the outermost coating layer, the printing paper has the suitability for the offset printing machine, while maintaining the color density uniformity, dot reproducibility and resistance to the inkjet printing machine. Wave property can be obtained. If a combination of a specific material composition and a specific transition amount range is not satisfied, the printing paper cannot obtain any of color density uniformity, dot reproducibility, and wave resistance for an inkjet printer.

The pigment of the outermost coating layer contains kaolin and calcium carbonate.
The mass ratio of kaolin and calcium carbonate in the outermost coating layer is kaolin: calcium carbonate = 1: 9 to 6: 4. From the viewpoint of printability for an inkjet printer, the calcium carbonate is preferably heavy calcium carbonate.

The outermost coating layer can contain a conventionally known pigment in addition to kaolin and calcium carbonate. Examples of conventionally known pigments include inorganic pigments such as talc, satin white, lithopone, titanium oxide, zinc oxide, silica, alumina, aluminum hydroxide, activated clay, diatomaceous earth, and organic pigments such as plastic pigments. it can. The outermost coating layer can be used in combination with kaolin and calcium carbonate in combination of one or more of these pigments.
The proportion of kaolin and calcium carbonate in the pigment of the outermost coating layer is 80% by mass or more.

The binder of the outermost coating layer is a conventionally known binder. Examples of conventionally known binders include starch and various modified starches thereof, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, natural polymer resins such as casein, gelatin, soy protein, pullulan, gum arabic, karaya gum and albumin or derivatives thereof. , Polyvinyl pyrrolidone, polyvinyl alcohol and various modified polyvinyl alcohols thereof, polypropylene glycol, polyethylene glycol, maleic anhydride resin, acrylic resin, methacrylate ester-butadiene resin, styrene-butadiene resin, ethylene-vinyl acetate resin or Resins modified with functional groups using monomers containing functional groups such as carboxy groups, binders such as thermosetting synthetic resins such as melamine resins and urea resins, polyurethane Fat, unsaturated polyester resins, polyvinyl butyral, can be exemplified alkyd resin latex. The outermost coating layer contains one or more selected from the group consisting of these binders.
The binder of the outermost coating layer is preferably one or more selected from the group consisting of starch and its various modified starches, polyvinyl alcohol and its various modified polyvinyl alcohols, and styrene-butadiene resins.

  The content of the binder in the outermost coating layer is preferably 3 parts by mass or more and 40 parts by mass or less, and more preferably 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the pigment in the outermost coating layer.

The lubricant for the outermost coating layer is a conventionally known lubricant. Examples of conventionally known lubricants include higher fatty acid salts, waxes and organosilicon compounds. Examples of higher fatty acid salts include higher fatty acid metal salts such as laurate, oleate, palmitate, stearate, and myristate (for example, sodium salts, potassium salts, zinc salts, and calcium salts thereof). And higher fatty acid ammonium salts such as ammonium laurate, ammonium oleate, ammonium palmitate, ammonium stearate, ammonium myristate. Examples of waxes include vegetable waxes, animal waxes, montan waxes, paraffin waxes, synthetic waxes (hydrocarbon synthetic waxes, polyethylene emulsion waxes, higher fatty acid esters, fatty acid amides, ketones / amines, hydrogenated oils) Etc.), aliphatic hydrocarbons such as polypropylene and polytetrafluoroethylene polymer, and derivatives thereof. Examples of the organosilicon compound include polyalkylsiloxane and derivatives thereof, dimethyl silicone oil, methylphenyl silicone oil, alkyl modified silicone oil, alkyl / aralkyl modified silicone oil, amino modified silicone oil, polyether modified silicone oil, and higher fatty acid modified. Examples thereof include silicone oil, carboxyl-modified silicone oil, fluorine-modified silicone oil, and epoxy-modified silicone oil. The outermost coating layer contains one or more selected from the group consisting of these lubricants.
The lubricant for the outermost coating layer is preferably a higher fatty acid salt.

The content of lubricant Saisotonuriko layer is per side 0.01 g / ^{m 2} or more 0.3 g / ^{m 2} or less.

The dispersant for the outermost coating layer is a material for dispersing an insoluble substance in water such as a pigment in an aqueous solution, and is a conventionally known dispersant. Examples of conventionally known dispersants include polycarboxylic acid resins such as sodium polycarboxylate, acrylic resins such as sodium polyacrylate, styrene-acrylic resins, isobutylene-maleic acid resins, and sulfonated polystyrene resins. , Polyvinyl alcohol and modified polyvinyl alcohol, and condensed phosphates. The outermost coating layer contains one or more selected from these dispersants.
The dispersant for the outermost coating layer is preferably one or more selected from the group consisting of polycarboxylic acid resins and acrylic resins.

The content of the dispersant in the outermost coating layer is preferably 0.001 g / m ² or more and 0.1 g / m ² or less per one side. The dispersant has a material overlapping with the binder. However, the material used as the dispersant can be distinguished because the content in the outermost coating layer is clearly smaller than that of the binder, and the dispersant has a lower molecular weight than that of the binder. Although the pigment can be dispersed by the presence of the binder, the dot reproducibility can be improved when the outermost coating layer contains a dispersant.

The cationic resin of the outermost coating layer is a conventionally known cationic resin. A preferable cationic resin is a polymer or oligomer containing a primary to tertiary amine or a quaternary ammonium salt that is easily coordinated with protons and dissociates when dissolved in water to exhibit a cationic property. A preferred cationic resin is a low cation having a degree of cationization of more than 0 meq / g or 3 meq / g or a highly cationic resin having a degree of cationization of more than 3 meq / g. Here, the degree of cationization is a value measured by a colloid titration method.
Examples of conventionally known cationic resins include polyethyleneimine, polyamine and modified polyamine, polyvinylpyridine, polyamidoamine, polyvinylamine, modified polyamide, polyacrylamide, polyallylamine, polydialkylaminoethyl methacrylate, polydialkylaminoethyl acrylate, poly Aliphatic monoamines such as dialkylaminoethylmethacrylamide, polydialkylaminoethylacrylamide, polyvinylbenzyltrimethylammonium chloride, polydiallyldimethylammonium chloride, copolymers of allyldimethylammonium chloride and acrylamide, and dimethylamine-epichlorohydrin polycondensates; Polycondensates with epihalohydrin compounds or diethylenetriamine-epic Polycondensates of aliphatic polyamines such as hydrin polycondensates and epihalohydrin compounds, polyamine polyamide epichlorohydrin, dicyandiamide-formalin polycondensate, dicyandiamide diethylenetriamine polycondensate, polyepoxyamine, polyamide-epoxy resin, melamine resin, and urea Resins can be mentioned. The outermost coating layer contains one or more selected from the group consisting of these cationic resins. The average molecular weight of the cationic resin is not particularly limited. The average molecular weight is preferably 500 or more and 100,000 or less, and more preferably 1000 or more and 60000 or less.
The cationic resin of the outermost coating layer is preferably a modified polyamine or a modified polyamide.

The content of the cationic resin of Saisotonuriko layer, per side 0.01 g / ^{m 2} or more 0.5 g / ^{m 2} or less.

  The outermost coating layer may further contain various conventionally known additives in the coated paper field as necessary. Examples of additives include thickeners, fluidity improvers, antifoaming agents, foaming agents, penetrants, color pigments, colored dyes, fluorescent whitening agents, UV absorbers, antioxidants, preservatives, and antibacterial agents. An agent etc. can be mentioned.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to these examples. Here, “parts by mass” and “% by mass” represent “parts by mass” and “% by mass” of the amount of dry solids or the amount of substantial components, respectively. The coating amount of the coating layer represents the dry solid content.

<Base paper>
A paper slurry was prepared by adding 8 parts by weight of calcium carbonate, 1.0 part by weight of amphoteric starch, 0.8 parts by weight of a sulfuric acid band, and an internal sizing agent to a pulp slurry comprising 100 parts by weight of LBKP having a freeness of 400 mlcsf. The paper stock was made with a long paper machine, starch was attached to both sides of the resulting paper with a size press machine, and machine calendering was performed to prepare a base paper.

<Outermost coating layer coating solution>
The outermost coating layer coating solution was prepared according to the following contents.
Kaolin parts listed in Table 1 calcium carbonate parts listed in Table 1 silica parts listed in Table 1 starch parts listed in Table 1 styrene-butadiene resin parts listed in Table 1 lubricant types and parts listed in Table 1 Dispersion Agent type and number of parts are listed in Table 1. Cationic resin type and number of parts are listed in Table 1. Blended as described above, mixed and dispersed with water to adjust the concentration to 48% by mass.

<Printing paper>
A printing paper was prepared by the following procedure.
The outermost coating layer coating solution was coated on the base paper with a blade coater and then dried. Furthermore, the calendar process was performed after drying. The coating amount was 14 g / m ² per side.
The amount of transition of the aqueous solution having a surface tension of 20 mN / m required by the Bristow method was supplementarily adjusted mainly by calendering and time control of the drying temperature by blending the pigment, lubricant, dispersant and cationic resin. An aqueous solution having a surface tension of 20 mN / m was prepared by adding propylene glycol and a fluorosurfactant to ion-exchanged water so that the surface tension by the Wilhelmi plate method was 20 mN / m.

<Evaluation of color density uniformity>
An evaluation image was printed at 6000 m using a water-based pigment ink at a printing speed of 150 m / min using an ink jet printer MJP20MX-7000 manufactured by Miyakoshi. The evaluation image is a solid image part pattern of 7 colors in total of 7 colors (black, cyan, magenta, yellow) and double colors (red, green, blue) in 3 colors other than black. The images were arranged in a horizontal row with no gaps. The color density uniformity was evaluated based on the following criteria by visually observing the printed portion of each solid color image. In the present invention, if the evaluation is 3 to 5, the printing paper has color density uniformity.
5: The color density is uniform.
4: The density is slightly non-uniform depending on the color.
3: The color density is slightly uneven.
2: The color density is partially uneven.
1: The color density is non-uniform throughout the printed portion.

<Evaluation of dot reproducibility>
An evaluation image using standard image data (image name: N5A) published by the Japanese Standards Association was printed with an aqueous pigment ink using an ink jet printer MJP20MX-7000 manufactured by Miyakoshi Co., Ltd. with a printing speed of 150 m / min. . The dot reproducibility was evaluated according to the following criteria by visually observing the degree to which the landed dot shape collapsed from a perfect circle and the sharpness of the dot outline with a microscope. In the present invention, if the evaluation is 3 to 5, the printing paper has dot reproducibility.
5: True circle and clear.
4: Almost perfect circle and clear.
3: Slightly lost from the perfect circle and slightly lacking in clarity. However, there is no practical problem.
2: Disrupted somewhat from the perfect circle and somewhat lacking in clarity.
1: It breaks from a perfect circle and lacks clarity.

<Evaluation of wave resistance>
An evaluation image was printed at 6000 m using a water-based pigment ink at a printing speed of 150 m / min using an ink jet printer MJP20MX-7000 manufactured by Miyakoshi. The evaluation image is a solid image part pattern of a total of 7 colors, black, cyan, magenta, yellow, and a double color (red, green, blue) in three colors other than black, 15cm x 30cm square The images were arranged in a single vertical line with no gaps. The wave resistance was evaluated based on the following criteria by visually observing the printed portion of each color solid portion image. In the present invention, if the evaluation is 3 to 5, the printing paper has wave resistance.
5: The printed part does not become wavy.
4: Immediately after printing, it becomes wavy, but smoothes immediately.
3: The printed part is wavy, but the degree is small and does not cause any practical problem.
2: The printed part is wavy and the degree is large, which may cause a problem in practical use.
1: The printed portion is wavy and the degree is extremely large, resulting in poor printing.

  The evaluation results are shown in Table 1.

From Table 1, it can be seen that Examples 1 to 16 corresponding to the present invention have color density uniformity, dot reproducibility, and wave resistance. On the other hand, it turns out that Comparative Examples 1-18 which do not satisfy the structure of this invention cannot have these effects.
Mainly from the comparison between Examples 1 to 5 and Examples 9 to 14 and Examples 15 to 16, the surface of the printing paper having the outermost coating layer [surface at a contact time of 1 second determined by the Bristow method [Transition amount of aqueous solution having a tension of 20 mN / m]-[Transition amount of aqueous solution having a surface tension of 20 mN / m at a contact time of 0.4 seconds determined by the Bristow method] is 0.5 ml / m ² or more 2 It can be seen that 5 ml / m ² or less is preferable.

Claims (2)

A printing paper having a base paper and one or more coating layers on at least one side of the base paper, wherein the outermost coating layer located on the outermost side with respect to the base paper is a pigment, a binder The pigment in the outermost coating layer contains at least a lubricant, a dispersant and a cationic resin, and the pigment in the outermost coating layer contains kaolin and calcium carbonate, and the content of kaolin and calcium carbonate is 100 in the outermost coating layer. 80 parts by mass or more with respect to parts by mass, and the mass ratio of kaolin and calcium carbonate in the outermost coating layer is 1: 9 to 6: 4, and the outermost coating layer of the printing paper is provided. for the side, the printing paper is transferred amount of the aqueous solution has a surface tension of 20 mN / m is 5.0 ml / ^{m 2} or more 12.0 ml / ^{m 2} or less at a contact time of 1 second sought Bristow method. For the side having the outermost coating layer of the printing paper, the transfer amount of an aqueous solution having a surface tension of 20 mN / m was measured at a contact time of 0.4 seconds determined by the Bristow method, and [contact time determined by the Bristow method 1 The amount of transition of an aqueous solution having a surface tension of 20 mN / m in seconds]-[Transition amount of an aqueous solution having a surface tension of 20 mN / m at a contact time of 0.4 seconds determined by the Bristow method] is 0.5 ml / m. printing paper according to claim 1 ² or more 2.5 ml / ^{m 2} or less.