JP2018003215A - Coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated paper having high blank glossiness and high printed glossiness.SOLUTION: In the coated paper having a coating layer containing a pigment and a binder on at least one surface of a base paper, the base paper contains a cellulose nanofiber produced by a mechanically defibrating method.SELECTED DRAWING: None

Description

  The present disclosure relates to a coated paper having excellent printability.

  Coated paper for printing is roughly classified into glossy products having high gloss such as art paper, super art paper, or A2 coated paper, and mat products having relatively low gloss. In any case, with the recent trend toward higher grades, there is a demand for paper having high blank gloss and high print gloss.

  In the conventional technology, in order to improve the printing gloss of the coated paper, measures such as increasing the blending amount of a binder such as styrene-butadiene latex, but the printing gloss is improved, There was a problem that the glossiness of blank paper was lowered.

  As a conventional technique, there is a proposal for improving the blank paper glossiness and printing glossiness by including a plastic pigment in the coating layer (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2008-075200 JP 2012-51991 A Japanese Patent Laid-Open No. 2015-977 JP2013-11026A JP2013-104142A JP 2014-146695 A

  However, even in the case of the technique described in Patent Document 1, binder migration (in the drying step after coating the coating layer coating liquid on the base paper, the binder in the coating layer coating liquid is The phenomenon of movement to the coated paper surface) cannot be suppressed, and the blank paper glossiness and printing glossiness cannot be completely satisfied.

  Then, this indication aims at providing the coated paper which has high white paper glossiness and printing glossiness regarding coated paper.

  The present inventor has found that a coated paper for printing having high blank glossiness and high printing glossiness can be obtained by incorporating the mechanical nanofiber cellulose nanofibers into the base paper. That is, the coated paper according to the present invention is a coated paper having a coating layer containing a pigment and a binder on at least one side of the base paper, and the base paper contains mechanically fibrillated cellulose nanofibers. It is characterized by.

  In the coated paper which concerns on this invention, the said mechanical fibrillation method cellulose nanofiber includes the form which is the range of width 1-300 nm and length 0.1-500 micrometers.

  According to the present disclosure, a coated paper having high blank paper glossiness and printing glossiness can be provided.

  Next, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified.

  The coated paper according to the present embodiment is a coated paper having a coating layer containing a pigment and a binder on at least one side of the base paper. The base paper contains mechanically fibrillated cellulose nanofibers. In the present invention, the white paper glossiness and the print glossiness are increased by incorporating the mechanical nanofiber cellulose nanofibers into the base paper.

  The reason why the coated paper of the present invention is excellent in blank paper glossiness and printing glossiness is that the binder migration of the coating liquid is suppressed by including the cellulose nanofibers for mechanical defibration in the base paper. It can be presumed that the smoothness of the layer is improved and the white paper glossiness and printing glossiness of the coated paper are increased.

  The mechanical defibrating cellulose nanofiber contained in the base paper in the present invention is a fiber having a width of about 1 to 300 nm and a length of about 0.1 to 500 μm obtained by defibrating a cellulose-based raw material. The width and length of the cellulose nanofiber can be measured using a transmission electron microscope (TEM). The width of the mechanical fibrillation method cellulose nanofiber is more preferably 2 to 280 nm. Further, the length of the mechanical defibrating cellulose nanofibers is more preferably 0.5 to 400 μm.

  The base paper may contain TEMPO oxidized cellulose nanofibers in addition to mechanically defibrated cellulose nanofibers. Hereinafter, when simply referred to as “cellulose nanofiber”, it refers to cellulose nanofiber including TEMPO oxidized cellulose nanofiber in addition to mechanical defibrated cellulose nanofiber.

  The TEMPO oxidation method cellulose nanofiber is a cellulose nanofiber obtained by a production method using TEMPO. TEMPO oxidation method As a method for producing cellulose nanofibers, a cellulose-based raw material is converted into an N-oxyl compound such as 4-hydroxy TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxy radical derivative) In the presence of a compound selected from the group consisting of bromide, iodide, and mixtures thereof, the cellulosic raw material is oxidized in water using an oxidizing agent such as sodium hypochlorite and then mechanically defibrated. The method is known. On the other hand, as a method for producing a mechanical nanofiber cellulose nanofiber, a method is known in which cellulose raw materials are directly fibrillated by a powerful disperser such as an ultrahigh pressure homogenizer or a mechanical high shear device. Examples of products that are commercially available as mechanical nanofiber cellulose nanofibers include BiNFi-S (manufactured by Sugino Machine), CNF250 (manufactured by Mori Machinery Co., Ltd.), and serisch KY-100G (manufactured by Daicel Finechem). it can. Moreover, regarding the manufacturing method of the specific mechanical fibrillation method cellulose nanofiber, Unexamined-Japanese-Patent No. 2012-51991 (patent document 2), Unexamined-Japanese-Patent No. 2015-977 (patent document 3), Unexamined-Japanese-Patent No. 2013-11026. No. (Patent Document 4), JP2013-104142A (Patent Document 5) or JP2014-146695A (Patent Document 6).

  As the cellulose nanofiber used in the present invention, the amount of carboxyl groups in 1 g of completely dried cellulose nanofiber is preferably 0.5 mmol / g or less. If it exceeds 0.5 mmol / g, the surface electrification of the cellulose nanofibers tends to be inclined to the minus side, the distribution of the cellulose nanofibers in the paper layer is uneven, and the binder migration suppressing effect of the coating liquid may be poor. The amount of carboxyl groups in 1 g of absolutely dry cellulose nanofiber is more preferably 0.3 mmol / g or less. Further, the lower limit of the amount of carboxyl groups in 1 g of absolutely dry cellulose nanofiber is not particularly limited, but is preferably 0.01 mmol / g or more, and more preferably 0.02 mmol / g or more. In the case of the mechanical fibrillation method cellulose nanofiber, it is approximately 0.1 mmol / g or less.

The amount of the carboxyl group was adjusted by adjusting 100 ml of 0.5% by weight slurry of cellulose nanofibers and adding 0.1M hydrochloric acid aqueous solution to pH 2.5, then adding 0.05N aqueous sodium hydroxide solution dropwise to adjust the pH. The electric conductivity can be measured until it reaches 11, and the amount can be calculated from the amount (X) of sodium hydroxide consumed in the neutralization step of the weak acid where the change in electric conductivity is slow, using the number (1).
Number (1) Carboxyl group amount (mmol / g pulp) = X (ml) × 0.05 / cellulose nanofiber weight (g)

  The raw material pulp constituting the base paper of the coated paper according to the present invention is LBKP (hardwood bleached kraft pulp) or NBKP (softwood bleached kraft pulp) as chemical pulp, GP (crushed wood pulp), PGW (pressure type) as mechanical pulp. Ground wood pulp), RMP (refinery mechanical pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemimechanical pulp) or CGP (chemiground pulp), wood pulp, DIP (deinked pulp) Further, non-wood pulp includes kenaf, bagasse, bamboo or cotton. These can be used alone or in combination at any ratio. Moreover, a synthetic fiber can be further blended within a range that does not impair the object and effect of the present invention. It is desirable to use chlorine-free pulp such as ECF (Elemental Chlorine Free) pulp or TCF (Totally Chlorine Free) pulp with low environmental impact. Furthermore, waste paper pulp can also be mix | blended in the range which does not impair the objective and effect of this invention.

  Moreover, it is preferable to make the pulp which comprises a base paper into the paper stock which has a suitable beating degree as a coated paper. Suitable beating degree is, for example, Canadian standard freeness (freeness) (JIS P 8121: 1995 “Pulp Freeness Test Method”), 350 to 650 ml CSF. More preferably, it is 400-600 ml CSF.

  Examples of the filler used for the base paper include heavy calcium carbonate, light calcium carbonate, magnesium carbonate, titanium dioxide, synthetic silica, alumina, talc, calcined kaolin, kaolin, clay, bentonite, zeolite, aluminum hydroxide or zinc oxide. It is possible to use known fillers. The filler content in the base paper is preferably 2 to 20 parts by mass with respect to 100 parts by mass of the dry mass of the pulp. More preferably, it is 4-15 mass parts. If it is less than 2 parts by mass, the opacity and whiteness may decrease, and the filler effect may not be obtained. When the amount exceeds 20 parts by mass, the strength of the paper is lowered, the load during printing or processing cannot be endured, and it may be difficult to use.

  In the paper stock, in addition to the pulp and filler, an internal paper strength enhancer such as an internal sizing agent or wet paper strength enhancer, a sulfuric acid band, a yield improver, a pitch control agent, a coloring dye, a coloring pigment, or a fluorescent material. Various papermaking chemicals such as dyes can be appropriately used. There are no particular limitations on the method for preparing each paper stock, the formulation, and the method for adding each papermaking chemical, as long as the effects of the present invention are not impaired.

  As a method for incorporating cellulose nanofibers that are mechanically defibrated into the base paper, it may be added to the above-mentioned stock, or it may be added to a size press solution applied by a size press or a gate roll coater coating solution applied by a gate roll coater. Although it may be added, it is preferably added to the size press solution or the gate roll coater coating solution because binder migration is easily suppressed.

  When the mechanical nanofiber cellulose nanofibers are added to the paper stock, the content of the mechanical nanofiber cellulose nanofibers is 0.01 to 5 parts by mass with respect to 100 parts by mass of all raw pulp used in the coated paper. Preferably there is. More preferably, it is 0.2-2 mass parts. If it is less than 0.01 part by mass, binder migration cannot be suppressed and the desired glossiness and printing glossiness may not be achieved. Also, it is difficult to improve the printing strength. When the amount exceeds 5 parts by mass, the drainage on the paper machine becomes remarkably low, and the paper cannot be dehydrated and the actual printing paper base paper may not be manufactured.

Mechanical fibrillation method When cellulose nanofibers are added to a size press solution applied with a size press or a gate roll coater solution applied with a gate roll coater, the amount of mechanical fibrillation cellulose nanofibers applied to the base paper is solid. It is preferable that it is 0.01-5 g / m < ² > by mass. If it is less than 0.01 g / m ² , the blank paper glossiness and the print glossiness may decrease. If it exceeds 5 g / m ² , the coating layer strength may decrease. More preferably, the solid mass is 0.05 to ² g / m ² . In addition, either the mechanical fibrillation method cellulose nanofiber is added to the paper material, or it is applied to either a size press solution applied by a size press or a gate roll coater coating solution applied by a gate roll coater, or The base paper subjected to both can be used as printing paper for non-coated paper.

  The method of making the base paper is not particularly limited, and it is possible to make a paper by applying a known paper machine such as a circular net paper machine, a long net paper machine, or a twin wire paper machine using the above-mentioned stock. It is. Further, the number of makings may be single layer making or multi-layer making of two or more layers.

  A surface sizing solution can be applied to the base paper obtained by the paper making method in order to suppress excessive penetration of the coating layer coating liquid into the base paper. The surface sizing liquid is not particularly limited, and is, for example, an aqueous solution containing a known water-soluble polymer such as polyvinyl alcohol, polyacrylamide or starch.

The basis weight of the base paper according to the present invention is not particularly limited, but is usually 30 to 300 g / m ² . More preferably, it is 40-280 g / m < ² >.

  The pigment used in the coating layer (hereinafter sometimes referred to as an ink receiving layer) includes one or more known pigments, such as kaolin, clay, calcined kaolin, talc, calcium carbonate, magnesium carbonate, Organic pigments such as barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, magnesium hydroxide, silica, alumina, boehmite or plastic pigment Can be mentioned.

  Binders used in the coating layer (hereinafter sometimes referred to as binders) include styrene-butadiene latex, polyvinyl alcohol, polyvinyl acetal, oxidized starch, etherified starch, carboxymethyl cellulose, hydroxyethyl cellulose, casein, gelatin, soybean Protein, Polyethyleneimide resin, Polyvinylpyrrolidone resin, Polyacrylic acid or its copolymer, Maleic anhydride copolymer, Acrylamide resin, Acrylic ester resin, Polyamide resin, Polyurethane resin, Polyester resin, Polymerization of polyvinyl butyral resin, alkyd resin, epoxy resin, epichlorohydrin resin, urea resin, methyl methacrylate-butadiene copolymer, acrylic ester, methacrylic ester Or acrylic polymer latex such as a copolymer, or ethylene - may be a known binder such as vinyl polymer latexes such as vinyl acetate copolymer.

  The blending amount of the binder to be blended in the coating layer is determined in consideration of the blank glossiness of the coated paper, the strength of the coating layer, the printing glossiness, and the coating liquid property. Usually, it may be added in the range of 3 to 60 parts by mass with respect to 100 parts by mass of the pigment. Preferably, it adds in the range of about 5-50 mass parts with respect to 100 mass parts of pigments. If the amount is less than 3 parts by mass, the coating layer strength may decrease. When it exceeds 60 parts by mass, the glossiness of the white paper may be lowered.

  Furthermore, in the present invention, in order to obtain a texture similar to that of general printing coated paper, an ink receiving layer is provided on the base paper, and then calendar processing is performed by a known calendar device such as a super calendar, a machine calendar, or a soft calendar. To give an appropriate gloss.

  The ink receiving layer may be provided not only on one side of the base paper but also on both sides. It can be a duplex printing paper. One or more undercoat layers may be provided under the ink receiving layer.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” and “%” represent “parts by mass” and “mass%”, respectively, unless otherwise specified. The number of added parts is a value in terms of solid content.

Example 1
<Preparation of base paper>
Canadian standard freeness 410ml csf hardwood bleached kraft pulp 100 parts, light calcium carbonate (TP-121, Okutama Kogyo Co., Ltd.) 15 parts, cationized starch 0.3 parts and neutral rosin sizing agent (CC167, Seiko PMC) (Made) It added so that it might become 0.05 parts, and it was set as the paper stock. Using this stock, a base paper having a basis weight of 77 g / m ² was prepared with a long mesh multi-cylinder paper machine. The produced base paper was subjected to a mechanical defibration cellulose nanofiber (product name: CNF250, width 30 to 200 nm, length 1 to 1) using a test sheet-fed size press machine (manufactured by Kumagai Riki Kogyo Co., Ltd.). 300 μm, manufactured by Mori Machinery Co., Ltd.) 0.02%, oxidized starch 1%, TCC starch 3.5%, and alkyl ketene dimer surface sizing agent (SE2360, manufactured by Seiko PMC) 0.05% aqueous solution on both sides. It apply | coated so that it might become 3 g / m < ² > of quantity. Mechanical defibration method The coating amount of cellulose nanofibers on the base paper was 0.013 g / m ² in terms of solid mass.

<Preparation of coating solution for coating layer>
35 parts of kaolin (Ultra White 90, manufactured by Engelhard), 55 parts of heavy calcium carbonate (Carbital-97, manufactured by Imeris Minerals Japan) and 10 parts of light calcium carbonate (TP-123CS, manufactured by Okutama Kogyo) A dispersant (Aron T-50, manufactured by Toa Gosei Co., Ltd.) (0.2 parts) was added to the mixture, and after adding water, it was dispersed in water with a Coreless disperser to obtain a pigment slurry. To this pigment slurry, 3 parts of phosphate esterified starch (MS4600, manufactured by Nippon Shokuhin Kako Co., Ltd.) and 12 parts of styrene bradiene latex (JSR0695, manufactured by JSR) are added as binders, and a printability improver (PA629, cationic). Polymer, 0.1 part by Seiko PMC), lubricant (LB-3200I, fatty acid calcium salt, manufactured by Toho Chemical Industry Co., Ltd.) 0.2 part, coloring dye 0.01 part, coloring pigment 0.01 part, A coating solution having a solid concentration of 50% was prepared by mixing 0.2 part of a fluorescent dye and 0.03 part of a preservative.

<Preparation of coated paper>
The coating solution obtained above was applied on both sides of the base paper with a test sheet-fed bar coater (model number: PM-9040MC, manufactured by SMT) so that the dry coating amount per side was 10 g / m ^2. A coated paper having an amount of 100 g / m ² was prepared.

(Example 2)
In Example 1, coated paper was produced as in Example 1 except that the amount of mechanically defibrated cellulose nanofiber added was 0.05%. Mechanical defibration method The amount of cellulose nanofibers applied to the base paper was 0.033 g / m ² in terms of solid mass.

(Example 3)
In Example 1, a coated paper was prepared as in Example 1, except that the amount of addition of the mechanical fibrillation method cellulose nanofiber was 2%. Mechanical fibrillation method The amount of cellulose nanofibers applied to the base paper was 0.92 g / m ² in terms of solid mass.

(Reference Example 1)
In the production of the base paper of Example 1, 100 parts of hardwood bleached kraft pulp, 99 parts of hardwood bleached kraft pulp and mechanically defibrated cellulose nanofiber (product name: CNF250, width 30 to 200 nm, length 1 to 300 μm, Mori Machinery Inc. Manufactured) 1 part, non-coated paper was prepared as in Example 1 except that the size press solution without adding cellulose nanofibers was applied to the size press, and the coating layer coating solution was not applied. did.

(Comparative Example 1)
In Example 1, a coated paper was prepared as in Example 1 except that the addition amount of the mechanical fibrillation method cellulose nanofiber was 0% (no addition).

Table 1 shows the configuration and evaluation results of the coated paper obtained in each example. The evaluation in the table was carried out by the following method.
(1) Glossiness of white paper: The surface of the coated layer of the coated paper was measured based on JISP8142: 2005 “Paper and paperboard—Measurement method of 75 ° specular gloss” (75 ° glossiness).
The glossiness of blank paper is practical when it exceeds 20%, but is more preferably 23% or more.
(2) Print glossiness: Printing was performed using an RI tester (manufactured by Meisei Seisakusho), and the surface of the obtained printed matter was measured based on JISP8142 (75 ° glossiness). The print glossiness is practical when it exceeds 35%, but more preferably 37% or more. The ink used was a flat printing ink (Fusion G EZ N, red, manufactured by DIC). The printing conditions were an ink amount of 0.6 cc, 30 rotations / minute, and two printings.

  As is clear from Table 1, the coated paper obtained in Examples 1 to 3 was excellent in blank paper glossiness and printing glossiness.

  The coated paper of the present invention can correspond to various printing methods such as offset printing, letterpress printing, and gravure printing.

Claims (2)

In coated paper having a coating layer containing a pigment and a binder on at least one side of the base paper,
The coated paper, wherein the base paper contains mechanically fibrillated cellulose nanofibers.   The coated paper according to claim 1, wherein the mechanical fibrillation method cellulose nanofiber has a width of 1 to 300 nm and a length of 0.1 to 500 µm.