JP6905967B2 - How to make cast coated paper - Google Patents

Description

The present disclosure relates to a method for producing cast coated paper. More specifically, the present invention relates to a method for producing cast-coated paper by the rewet method, and relates to a method for producing cast-coated paper having high glossiness, high smoothness, and high water repellency.

Due to the high gloss and smoothness of its surface, cast coated paper is used for posters, catalogs, pamphlets, book covers, food labels, inkjet printing paper, marking sheets, release paper, or It is used in various fields such as industrial applications such as processed paper base paper. Further development such as packaging is expected by imparting water repellency.

As a method for producing cast-coated paper, a coating liquid containing a pigment and an adhesive as a main component is applied to the surface of a support to form a coating layer, and the surface of the coating layer is in a wet state. It is manufactured by pressure-welding a cast drum with a mirror gloss and drying it.

Specifically, the treatment method for obtaining a cast coat layer and performing a gloss finish is roughly classified into a wet method (direct method), a gelation method (solidification method), and a rewet method (rewetting method). That is, after applying a cast coating liquid containing a pigment and an adhesive as a main component to the support, pressure bonding (pressure welding) is performed on the surface of a mirror-finished heating drum (cast drum) while the coating layer is in a wet state. Wet method to dry and gloss finish, gelling method to gel the wet cast coating layer and press-weld it to the heated drum surface to gloss finish, and after drying the wet cast coating layer once, A rewetting method, in which the surface of a heating drum is pressure-welded and dried after being plasticized with a re-wetting liquid, is generally known.

In general cast-coated paper, a pigment and an adhesive are contained in the coating layer in order to develop high glossiness. Flat pigments such as kaolin are often used as the main pigments, and the adhesive components are mainly casein, polyvinyl alcohol, styrene-butadiene copolymer latex, etc. in order to gel or plasticize the cast coat layer. Used as an adhesive. In order to form a cast coat layer having uniform and high gloss, a relatively large amount of coating layer is required. If the amount of coating is too small, a uniform coated surface and high glossiness cannot be obtained due to the influence of the unevenness of the support, and there is a problem that uneven gloss occurs. Further, as described above, since the cast coat layer is gelled, a water-soluble adhesive such as casein or polyvinyl alcohol is used, and a large amount of silica is used as a pigment component of the cast coat for inkjet recording, so that the cast coat layer is made water resistant. There is a scarce problem.

As such a cast-coated paper, a cast-coated paper having a coating amount of the cast coat layer of 8 to 30 g / m ² is disclosed (see, for example, Patent Document 1). Further, a cast-coated paper for inkjet recording provided with an ink receiving layer containing a pigment containing cellulose nanofibers and colloidal silica and a binder is disclosed (see, for example, Patent Document 2). Further, a cast coated paper containing a novolak type epoxy resin in a water resistant cast coated layer is disclosed (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2012-197542 Japanese Unexamined Patent Publication No. 2011-733668 JP-A-2010-70888

However, in the cast-coated paper of Patent Document 1, the glossiness tends to decrease as the coating amount of the coating layer decreases, and a high glossiness cannot be obtained ^{when the coating amount is about 9 g / m 2.} Further, the cast-coated paper for inkjet recording disclosed in Patent Document 2 contains cellulose nanofibers in the ink receiving layer, but in order to obtain high glossiness, the influence of unevenness of the paper support is reduced. A pigment coating layer is provided as an under layer so as to be possible. Since the ink receiving layer is provided on the under layer, it is necessary to increase the amount of coating in order to increase the substantially high glossiness. Further, when the amount of the cellulose nanofibers added is large, there is a problem that the coating unevenness becomes remarkable and the glossiness and the suitability for inkjet are lowered. The cast coated paper disclosed in Patent Document 3 has a hard coating layer, improved water resistance, and improved adhesion between cast surfaces, but has a problem that the cast surface is easily wetted with water. Further, although there is a method such as adding a sizing agent to the base paper to impart water resistance to the cast coated paper, it was not possible to impart water repellency to the glossy surface.

Therefore, an object of the present disclosure is to provide a method for producing a cast-coated paper having high glossiness, high smoothness, and high water repellency even when the amount of the pigment coating layer applied is relatively small.

Other purposes and effects of the present disclosure will be readily appreciated by those skilled in the art by reference to the following description herein.

In the method for producing cast-coated paper according to the present invention, at least one surface of a support containing pulp as a main component is coated with a coating liquid for a pigment coating layer containing a pigment and an adhesive, followed by coating. A step of drying to provide a pigment coating layer and a coating liquid for a nanocellulose coating layer containing nanocellulose having a number average fiber diameter of 1 nm or more and less than 70 nm are applied to the surface of the pigment coating layer. Subsequently, a step of drying to provide the nanocellulose coating layer and a rewetting liquid containing zirconium chloride are applied to the surface of the nanocellulose coating layer, and then the nanocellulose coating layer is in a wet state. It is characterized by having a step of performing a casting process by pressure-welding to a mirror-finished drum heated in between.

In the method for producing cast-coated paper according to the present invention, it is preferable that the coating amount of the pigment coating layer is 5 to ^{20 g / m 2 in terms of solid content per one side of the support.} According to such a configuration, the glossiness and smoothness can be increased even with such a small amount of the pigment coating layer applied.

In the method for producing cast-coated paper according to the present invention, the coating amount of the nanocellulose coated layer is preferably ^{0.29 to 7.0 g / m 2 in terms of solid content per one side of the support.} According to such a configuration, uneven gloss is less likely to occur, and water repellency can be suitably exhibited while maintaining smoothness.

The method for producing cast-coated paper according to the present invention is defined in JIS P 8155: 2010 "Paper and Paperboard-Smoothness Test Method-Oken-type Smoothness Specified by the Oken Method" on the surface subjected to the cast treatment. The Oken type smoothness is preferably 11000 seconds or more. With such a configuration, cast-coated paper having high smoothness can be obtained, so that printing such as offset printing and resin letterpress printing or post-processing such as extrusion lamination such as polyethylene can be preferably performed. In addition, it can be expected to be applied to various applications such as electronic parts and packaged products.

In the method for producing cast-coated paper according to the present invention, the 20-degree mirror gloss specified in JIS Z 8741: 1997 "Mirror gloss-measurement method" of the cast-treated surface may be set to 40% or more. preferable. According to such a configuration, it is possible to obtain a cast-coated paper having higher reproducibility.

In the method for producing cast-coated paper according to the present invention, it is preferable that the water repellency of the cast-treated surface is R4 or higher as defined in JAPAN TAPPI No. 68: 2000 "Paper and Paperboard-Water Repellent Test Method". .. With such a configuration, it is less likely to be affected by dew condensation and the like, so that it can be used outdoors.

In the method for producing cast-coated paper according to the present invention, it is preferable that the coating liquid for the nanocellulose coating layer contains a blocked isocyanate compound and / or a compound having an oxazoline group as a functional group. With such a configuration, high water repellency can be maintained due to the synergistic effect with the water resistance of the coating layer, and the adhesion to the pigment coating layer is also improved.

In the method for producing cast-coated paper according to the present invention, it is preferable that the nanocellulose coated layer does not contain a pigment and an adhesive. According to such a configuration, since nanocellulose is easily oriented, glossiness and smoothness can be preferably obtained.

In the method for producing cast-coated paper according to the present invention, the nanocellulose is preferably at least one of TEMPO-oxidized cellulose nanofibers, underwater counter-collision-type cellulose nanofibers, and cellulose nanocrystals. According to such a configuration, a cast-coated surface having few paper defects can be obtained, so that a cast-coated paper having higher glossiness, smoothness, and high water repellency can be produced.

In the method for producing cast-coated paper according to the present invention, the coating amount of the nanocellulose coated layer is 0.29 to 3.0 g / m ² in terms of solid content per one side of the support, and the rewetting is performed. The wet coating amount of the liquid is preferably ^{10 to 15 g / m 2.} During the casting process, defects called pits due to steam rupture are less likely to occur, and a more uniform cast-coated surface can be formed.

In the method for producing cast coated paper according to the present invention, the rewetting liquid preferably has a pH of 3.5 or less. Since the nanocellulose coated layer aggregates and easily gels during the casting process, it is possible to produce cast-coated paper having higher glossiness, higher smoothness, and higher water repellency.

According to the present disclosure, it is possible to produce a cast-coated paper having high glossiness, high smoothness and high water repellency even if the amount of coating of the pigment coating layer is relatively small. Further, the obtained cast coated paper has high glossiness, high smoothness and high water repellency.

Next, the present invention will be described in detail by showing embodiments, but the present invention is not construed as being limited to these descriptions. The embodiments may be modified in various ways as long as the effects of the present invention are exhibited.

(Support)
The support used in this embodiment contains pulp as a main component. Here, the main component of pulp means that pulp is 50% by mass or more among the fibers of the support. Preferably, it is 70% by mass or more. Examples of the pulp used here include chemical pulps such as LBKP (broadwood bleached kraft pulp) and NBKP (coniferous bleached kraft pulp), TMP (thermomechanical pulp), GP (crushed wood pulp), and CTMP (chemithermomechanical pulp). , RMP (Refiner Mechanical Pulp), and other mechanical pulps, DIP (Deinked Pulp) and other wood pulps, and cotton, Kenaf, bamboo, Bagas and other non-wood pulps. These can be used alone or in admixture in any proportion. In addition, synthetic fibers can be further blended as long as the desired effect of the present invention is not impaired. From the viewpoint of environmental protection, it is preferable to contain ECF (Elemental Chlorine Free) pulp and TCF (Total Chlorine Free) pulp.

A filler can be added to the support to improve whiteness and opacity. Examples of the filler used include talc, kaolin, calcined clay, light calcium carbonate, heavy calcium carbonate, titanium dioxide, and clay. The filler content in the paper is preferably 1 to 25 parts by mass with respect to 100 parts by mass of the dry mass of the pulp. More preferably, it is 2 to 20 parts by mass. More preferably, it is 3 to 18 parts by mass. If it is less than 1 part by mass, effects such as improvement of whiteness and improvement of opacity may not be obtained. If it exceeds 25 parts by mass, the strength of the support itself may be insufficient to withstand printing and processing, and it may not be practically usable.

In addition to pulp and filler, the support includes internal paper strength enhancers such as internal sizing agents and wet paper strength enhancers, pitch control agents, fluorescent whitening agents, coloring dyes, coloring pigments, and fluorescent decoloring agents. Various auxiliary agents such as the above can be appropriately blended within a range that does not impair the desired effect of the present invention. Various known sizing agents can be used, and the internal sizing agent is not particularly limited, and examples thereof include AKD, ASA, a strengthened rosin sizing agent, a weakly acidic rosin sizing agent, and an acidic rosin sizing agent. As the internal paper strength enhancer, a conventionally known paper strength enhancer can be used. For example, a starch-based paper strength enhancer, a polyvinyl alcohol-based paper strength enhancer, and a polyacrylamide-based paper strength enhancer can be used. Is.

The method for making the support is not particularly limited, and is not particularly limited, and is a twin wire paper machine, a long net paper machine, a circular net multi-layer paper machine, a long net multi-layer paper machine, a circular net paper machine, and a long net circular net combination multi-layer paper machine. It can be manufactured with various devices such as machines.

A known water-soluble polymer such as polyvinyl alcohol, starch, or polyacrylamide may be coated on the surface of the support. The basis weight of the support is not particularly limited, but is usually 40 to 500 g / m ² .

(Pigment coating layer)
In the present embodiment, a coating liquid for a pigment coating layer containing a pigment and an adhesive is applied to at least one surface of the support. After applying the coating liquid for the pigment coating layer, it is dried to provide the pigment coating layer. The pigment used here is not particularly limited, and one or more known pigments can be mixed. For example, synthetic amorphous silica, colloidal silica, alumina, pseudo-bemite, aluminum hydroxide, light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide. , Zinc carbonate, satin white, aluminum silicate, siliceous soil, calcium silicate, magnesium silicate, magnesium hydroxide and other inorganic pigments. In addition, organic pigments such as styrene-based plastic pigments, acrylic-based plastic pigments, polyethylene, microcapsules, urea resins, and melamine resins can be used in combination as needed. In the present embodiment, it is advantageous that the pigment coating layer can be made highly smooth. Therefore, among these pigments, flat plate pigments such as talc and kaolin can be preferably used. Among the kaolins, delaminated kaolin (delaminated kaolin) is particularly preferable.

The adhesive contained in the coating liquid for the pigment coating layer is not particularly limited, and includes, for example, polyvinyl alcohol (including modified polyvinyl alcohol such as carboxyl-modified polyvinyl alcohol and silanol-modified polyvinyl alcohol) and polyvinyl acetal. , Oxidized starch, etherified starch, carboxymethyl cellulose, hydroxyethyl cellulose, casein, gelatin, soybean protein, polyethyleneimide-based resin, polyvinylpyrrolidone-based resin, polyacrylic acid or its copolymer, maleic anhydride copolymer, acrylamide-based resin , Acrylic acid ester resin, polyamide resin, acrylic resin, styrene-acrylic resin, polyurethane resin, polyester resin, polyvinyl butyral resin, alkyd resin, epoxy resin, epichlorohydrin resin, styrene-butadiene co-weight Acrylic polymer latex such as coalescence, methyl methacrylate-butadiene copolymer, acrylic acid ester, methacrylic acid ester polymer or copolymer, vinyl polymer latex such as ethylene-vinyl acetate copolymer, A composite resin of colloidal silica and an acrylic resin, a composite resin of colloidal silica and a styrene-acrylic resin, or the like can be used alone or in combination. The amount of the adhesive used is preferably in the range of 2 to 200 parts by mass with respect to 100 parts by mass of the pigment. More preferably, it is added in the range of 3 to 100 parts by mass, and further preferably 4 to 80 parts by mass, for example, 5 to 10 parts by mass. If it is less than 2 parts by mass, the surface strength of the pigment coating layer may decrease. If it exceeds 200 parts by mass, the smoothness of the pigment coated layer may be impaired, and as a result, the glossiness of the cast-coated paper may be impaired.

In the present embodiment, the coating liquid for the pigment coating layer contains a dispersant, a thickener, an antiseptic, an antifoaming agent, a coloring dye, and a coloring pigment as long as the effect intended by the present invention is not impaired. , Fluorescent whitening agents, water resistant agents, antioxidants, ultraviolet absorbers and other various auxiliaries can be appropriately selected and added.

In the present embodiment, the coating liquid for the pigment coating layer is applied to the support, but the coating method is not particularly limited, and the curtain coater, die coater, air knife coater, flexible, and roll application are not particularly limited. , Fountain application, bevel type or vent type blade coater such as short duel, bar coater, gravure coater, spray coater, rod blade coater, champlex coater, gate roll coater, spray coater, etc. You may use the thing.

The pigment coating layer can be dried by appropriately selecting from general drying methods such as a hot air drying method, an infrared drying method, and a drum drying method. Among them, hot air using an air dryer or the like can be appropriately selected. The drying method is preferred. By drying with hot air from the surface layer of the coating layer, it becomes easy to form a uniform pigment coating layer.

The amount of the pigment coating layer applied is not particularly limited, but it is preferably 5 to ^{20 g / m 2 in terms of solid content per side of the support.} More preferably 6-10 g / ^{m 2,} still more preferably 6-8 g / ^{m 2.} According to this embodiment, it is possible to obtain a relatively high glossiness when the coating amount of the pigment coating layer is relatively high, but when the coating amount of the pigment coating layer is less ^{than 5 g / m 2} , the unevenness of the support is uneven. May not be sufficiently coated, and the smoothness of the surface of the pigment coating layer may not be satisfied, and as a result, the glossiness of the cast-coated paper may not be satisfied. Further, since the coating of the pigment coating layer is not sufficient, the coating liquid for the nanocellulose coating layer permeates more, and the coating amount of the nanocellulose coating layer may become more than necessary. If the coating amount of the ^{pigment coating layer exceeds 20 g / m 2} , the strength of the pigment coating layer may be impaired. Further, since the coating of the pigment coating layer is thick, the penetration of the coating liquid for the nanocellulose coating layer becomes poor, and a uniform nanocellulose coating layer may not be obtained. The pigment coating layer does not have an under layer and is preferably one layer.

In the present embodiment, after the pigment coating layer is provided on the support, calendar processing may be performed by a calendar device such as a machine calendar, a soft calendar, or a super calendar. In the present embodiment, the higher the smoothness of the surface of the pigment coated layer, the more advantageous it is to improve the glossiness of the cast-coated paper. Therefore, it is preferable to set the smoothness of the surface of the pigment coated layer to 200 to 2000 seconds. It is preferable to perform calendering so as to have a range, preferably in the range of 400 to 1000 seconds.

(Nanocellulose layer)
In the present embodiment, a coating liquid for a nanocellulose coating layer containing nanocellulose having a number average fiber diameter of 1 to 50 nm is applied to the surface of the pigment coating layer, dried, and nanocellulose coated. Provide a layer. The coating liquid for the nanocellulose coating layer is obtained by dispersing cellulose nanofibers and / or cellulose nanocrystals in water. The solid content concentration of nanocellulose in the coating liquid for the nanocellulose coating layer is preferably 80% by mass or more, more preferably 95% by mass or more, and further preferably 99% by mass or more. Various auxiliary agents such as sizing agents, water repellents, surfactants, and cross-linking agents may be used in the coating liquid for the cellulose nanofiber coating layer as long as the intended effect of the present invention is not impaired. However, it is preferable not to contain pigments and adhesives that are added to the coating liquid for the pigment coating layer. When a pigment and an adhesive are contained, it becomes difficult for the nanocellulose to be oriented, and it may be difficult to obtain glossiness and smoothness.

In the present embodiment, the coating liquid for the nanocellulose coating layer contains nanocellulose. Here, nanocellulose is cellulose microfibrils obtained by chemically and / or physically defibrating a cellulosic raw material, and is called cellulose nanofibers or cellulose nanocrystals. Here, in the present embodiment, it is preferable to use a cellulosic raw material in which the functional group of cellulose remains as it is, but in some cases, a tetramethylpiperidinyloxy radical (hereinafter referred to as TEMPO), an acid anhydride, or the like. A cellulosic raw material may be used in which the surface of the cellulosic raw material is chemically modified with an acid halide to improve dispersibility.

In the present embodiment, the number average fiber diameter of nanocellulose contained in the coating liquid for the nanocellulose coating layer is 1 nm or more and less than 70 nm. 1 to 65 nm is preferable, 1 to 60 nm is more preferable, 1 to 50 nm is more preferable, 2 to 30 nm is more preferable, 3 to 20 nm is further preferable, and 3 to 9 nm is particularly preferable. Within this range, it is considered that the distribution of the fiber width is relatively uniform, the nanocelluloses are likely to be closely entangled with each other, and a nanocellulose coating layer having few voids can be formed. Further, the coating liquid for the nanocellulose coating layer can also be expected to have stable water retention, so that the coating property can be satisfied. When the number average fiber diameter exceeds 50 nm, the number of cellulose fibers having a large fiber width increases, so that the distribution of fibers tends to be non-uniform, and the surface of the nanocellulose coating layer is less likely to gel, so that a uniform coating layer can be obtained. Hateful. On the other hand, when the number average fiber diameter is less than 1 nm, the viscosity of the coating liquid increases remarkably, coating cannot be performed unless the nanocellulose concentration of the coating liquid is significantly reduced, and the drying load after coating increases. Wrinkles and waviness are likely to occur on the support, and productivity is also reduced.

Here, the number average fiber diameter is calculated according to the following. Nanocellulose cast on a carbon film-coated grid is observed by an electron microscope image using a transmission electron microscope (TEM, Transmission Electron Microscope). For the obtained observation image, two random axes are drawn vertically and horizontally for each image, and the fiber diameters of the fibers intersecting the axes are visually read. At this time, observation is performed at a magnification of 5000 times, 10000 times, or 50,000 times depending on the size of the constituent fibers. The sample or magnification is a condition in which 20 or more fibers intersect the shaft. In this way, at least three images of the non-overlapping surface portion are taken with an electron microscope, and the value of the fiber diameter of the fiber intersecting each of the two axes is read. Therefore, information on at least 20 fibers × 2 × 3 = 120 fibers can be obtained. The number average fiber diameter is calculated from the fiber diameter data thus obtained. Regarding the branched fiber, if the length of the branched portion is 50 nm or more, it is incorporated into the calculation of the fiber diameter as one fiber. Further, the number average fiber diameter may be calculated according to the following. The aqueous dispersion of nanocellulose is lyophilized and observed with an electron microscope image using a scanning electron microscope (SEM). For the obtained observation image, two random axes are drawn vertically and horizontally for each image, and the fiber diameters of the fibers intersecting the axes are visually read. At this time, observation is performed at a magnification of 5,000 to 50,000 times depending on the size of the constituent fibers. Images of multiple non-overlapping surface parts are taken with an electron microscope, and the value of the fiber diameter of the fiber intersecting each of the two axes is read. The number average fiber diameter is calculated from the fiber diameter data of at least 120 fibers. Regarding the branched fiber, if the length of the branched portion is 50 nm or more, it is incorporated into the calculation of the fiber diameter as one fiber. The sample is conductively coated in advance in order to obtain a distortion-free observation image, but the influence of the coating film thickness is also taken into consideration. For example, when ion sputtering (E-1045, manufactured by Hitachi High-Technology Co., Ltd.) is used, the coating film thickness is 12 nm when the discharge current is 15 mA, the sample-target distance is 30 mm, the degree of vacuum is 6 Pa, and the coating time is 2 minutes. However, when measuring the fiber diameter, the coating film thickness is halved because the deposition direction of the coating film is perpendicular to the assumed direction. That is, when coated under the above conditions, the coating film thickness of 12 nm (= 6 nm + 6 nm) at both ends is excluded from the fiber diameter obtained from the SEM.

The number average fiber length of nanocellulose is not particularly limited, but is preferably 0.01 to 20 μm. More preferably, it is 0.05 to 10 μm. More preferably, it is 0.08 to 7.0 μm. Particularly preferably, it is 0.7 to 1.0 μm. When the number average fiber length is less than 0.01 μm, the nanofibers become close to particles, and a film may be formed but the coating layer strength may be weakened. If the number average fiber length exceeds 20 μm, the cellulose nanofibers are entangled with each other more easily, and the fibers are likely to aggregate with each other, so that a uniform film may not be obtained. The number average fiber length is calculated by observing nanocellulose with an electron microscope image using a scanning electron microscope (SEM). For the obtained observation image, 10 independent fibers are randomly selected for each image, and the fiber lengths are visually read. At this time, the magnification is one of 1000 to 30,000 times depending on the length of the constituent fibers. The sample or magnification shall be one in which the start point and end point of the fiber are within the same image. In this way, at least 12 non-overlapping surface image images are taken by SEM and the fiber length is read. Therefore, information on at least 10 fibers x 12 fibers = 120 fibers can be obtained. The number average fiber length can be calculated from the fiber length data thus obtained. For branched fibers, the length of the longest portion of the fiber is defined as the fiber length.

In the present embodiment, the nanocellulose preferably has a viscosity of 5000 mPa · s or more at a B-type viscosity (60 rpm, 20 ° C.) at a concentration of 2.0% by mass of the slurry dispersed in water. More preferably, it is 6000 to 20000 mPa · s. By using such nanocellulose, coating becomes easy, and a nanocellulose coating layer having few voids can be formed. The viscosity can be measured with a Brookfield viscometer (BM type of Brookfield viscometer manufactured by TOKIMEC).

In the present embodiment, as the nanocellulose, cellulose nanocrystals prepared by a chemical method such as acid hydrolysis with sulfuric acid, hydrochloric acid, hydrobromic acid or the like can be used. Of these, cellulose nanocrystals prepared by hydrolysis with sulfuric acid are preferable. Sulfuric acid is the most common strong acid and is non-volatile and therefore easy to handle. Furthermore, since it is added as a sulfuric acid ester, the anionic property becomes stronger and it becomes difficult to aggregate. In the present embodiment, the cellulose nanocrystal is preferably an anionic cellulose nanocrystal, more preferably a sulfate esterified cellulose nanocrystal. If necessary, cellulose nanocrystals may be prepared by combining the above-mentioned defibration methods. Cellulose nanocrystals are subjected to a chemical treatment such as acid hydrolysis of a cellulosic raw material, and the chemically treated cellulose raw material is chemically and / or physically deflated in the form of crystals, or a cellulosic type. There is a crystalline form in which the raw material is chemically and / or physically defibrated to form microfibrils, and the microfibrils are chemically treated such as acid hydrolysis. The number average fiber diameter of the cellulose nanocrystal is 1 nm or more and less than 70 nm, and the number average fiber length is about 25 to 3000 nm. The average value of nanocellulose (number average fiber diameter, number average fiber length) in the present embodiment is an average value when nanocellulose in the field of view of an electron microscope is measured as described above.

In the present embodiment, the cellulose nanofibers used as nanocellulose include unmodified cellulose nanofibers in which the functional group of the cellulose molecule is not chemically converted, and modified in which the functional group of the cellulose molecule is chemically converted. There are cellulose nanofibers. Examples of the unmodified cellulose nanofibers include underwater facing collision type cellulose nanofibers, homogenized cellulose nanofibers, and grinder type cellulose nanofibers. Examples of the modified cellulose nanofibers include TEMPO oxidation method cellulose nanofibers and phosphoric acid esterification method cellulose nanofibers. In the present embodiment, the cellulose nanofibers are preferably cellulose nanofibers having many hydroxyl groups on the surface, and are, for example, underwater facing collision type cellulose nanofibers and TEMPO oxidation method cellulose nanofibers. In particular, TEMPO-oxidized cellulose nanofibers containing a large amount of carboxyl groups can preferably form a coating layer.

In the method for producing cast-coated paper according to the present embodiment, the nanocellulose is preferably at least one of TEMPO-oxidized cellulose nanofibers, underwater counter-collision-type cellulose nanofibers, and cellulose nanocrystals. That is, preferable forms of nanocellulose are TEMPO-oxidized cellulose nanofibers, underwater counter-collision cellulose nanofibers, cellulose nanocrystals, TEMPO-oxidized cellulose nanofibers and underwater counter-collision cellulose nanofibers, and TEMPO-oxidized cellulose. One of a mixture of nanofibers and cellulose nanocrystals, a mixture of underwater facing collision method cellulose nanofibers and cellulose nanocrystals, and a mixture of TEMPO oxidation method cellulose nanofibers and underwater facing collision method cellulose nanofibers and cellulose nanocrystals. Can be one. According to the configuration such as these forms, it is possible to obtain a cast-coated surface having few paper defects, so that it is possible to produce a cast-coated paper having higher glossiness, smoothness, and high water repellency.

The coating device for applying the coating liquid for the nanocellulose coating layer is not particularly limited, and bevel type such as curtain coater, die coater, air knife coater, flexible, roll application, fountain application, short duel, etc. Known coating devices such as bent type blade coaters, bar coaters, gravure coaters, spray coaters, rod blade coaters, champlex coaters, gate roll coaters, and spray coaters can be appropriately used. Among them, the air knife coater is preferable.

The method for drying the nanocellulose coated layer can be appropriately selected from general drying methods such as hot air drying method, infrared drying method, and drum drying method, and among them, an air dryer or the like was used. The hot air drying method is preferable. By drying with hot air from the surface layer of the coating layer, it becomes easy to form a uniform coating layer.

The amount of the nanocellulose coating layer applied is not particularly limited, but is preferably in the range ^{of 0.29 to 7.0 g / m 2 in terms of solid content per side of the support, preferably 0.3 to 5.0 g.} The range of / m ² is more preferred, and the range of 0.6 to 3.0 g / m ² is even more preferred. If the coating amount is ^{less than 0.29 g / m 2} , it is difficult to form a uniform cast-coated surface, uneven gloss may occur, and stable water repellency may not be obtained. On the other hand, if ^{it exceeds 7.0 g / m 2} , the drying load of the coating device before the casting process becomes high, and defects due to steam burst called pits occur finely, resulting in uneven gloss and impairing smoothness. In some cases. In addition, the water-repellent effect may be poor due to the drawback.

In the present embodiment, it is preferable that the coating liquid for the nanocellulose coating layer contains a blocked isocyanate compound or a compound having an oxazoline group as a functional group. These function as cross-linking agents in relation to nanocellulose. By containing a blocked isocyanate compound or a compound having an oxazoline group as a functional group (hereinafter, also referred to as a cross-linking agent), water repellency is improved, and the adhesiveness between the nanocellulose coating layer and the pigment coating layer is also improved. Improves and increases durability.

(Cast processing)
In the present embodiment, a coating layer is provided on the support, then a nanocellulose coating layer is provided, and then a cast treatment is performed by a rewet method. First, a rewetting liquid (rewetting liquid) is applied to the surface of the dried nanocellulose coating layer to swell the nanocellulose coating layer. Next, while the nanocellulose coating layer is in a wet state, it is pressed against a heated mirror surface drum (cast drum). The cast-treated surface of the cast-coated paper thus obtained has high glossiness, high smoothness, and high water repellency.

The rewetting liquid is a treatment liquid (aqueous solution) for rewetting that has the effect of swelling the once dried nanocellulose coating layer and appropriately adhering the coating layer to the heated mirror-finished drum. This rewetting liquid contains zirconium chloride. The rewetting liquid preferably contains 0.5 to 7.0% by mass of zirconium chloride, preferably 1.0 to 5.0% by mass. If it is less than 0.5% by mass, the swelling of the coating layer is poor, the cross-linking of the coating surface does not proceed, and water repellency may not be exhibited. On the other hand, swelling and cross-linking of the coating layer exceeding 7.0% by mass proceed more than necessary, and adhesion to the mirror surface drum or formation of a non-uniform surface may result in unstable quality. In addition, acids such as formic acid and hydrochloric acid, phosphates such as hexametaphosphate, hydroxyates such as citrate, sulfates, zinc sulfate, dicyandiamide, urea and the like may also be contained, and among these, formic acid. And acids such as hydrochloric acid are preferred. In addition, a mold release agent, a fixing agent, and a cross-linking agent can be added to the re-wetting liquid as long as the desired effect of the present invention is not impaired.

By applying such a rewetting liquid, the nanocellulose coating layer aggregates and gels. Only the surface of the nanocellulose coating layer needs to be gelled, but the nanocellulose coating layer can relatively reduce the amount of coating, so even if the entire coating layer is gelled. The amount of the rewetting liquid applied can be relatively small. That is, since the amount of water retained in the coating layer during the casting process can be reduced, the defect of vapor burst called a pit is unlikely to occur during the casting process, and a uniform cast-coated surface can be formed.

Zirconium chloride refers to a substance that has zirconium and chlorine in its chemical formula. Specifically, for example, the chemical formulas ZrCl ₄ , Zr (OH) Cl ₃ , Zr (OH) ₂ Cl ₂ , Zr (OH) ₃ Cl, ZrBrCl ₃ , ZrBr ₂ Cl ₂ , ZrBr ₃ Cl, Zr (NO ₃ ). Cl ₃ , Zr (NO ₃ ) ₂ Cl ₂ , Zr (NO ₃ ) ₃ Cl, Zr (CH ₃ COO) Cl ₃ , Zr (CH ₃ COO) ₂ Cl ₂ , Zr (CH ₃ COO) ₃ Cl, Zr ( NO ₃ ) BrCl ₂ , Zr (OH) BrCl ₂ , Zr (CH ₃ COO) BrCl ₂ , Zr (NO ₃ ) (OH) Cl ₂ , Zr (CH ₃ COO) (NO ₃ ) Cl ₂ , Zr (CH ₃₎ COO) (OH) Cl ₂ , Zr (NO ₃ ) Br ₂ Cl, Zr (OH) Br ₂ Cl, Zr (CH ₃ COO) Br ₂ Cl, Zr (NO ₃ ) ₂ BrCl, Zr (NO ₃ ) ₂ ( OH) Cl, Zr (CH ₃ COO) (NO ₃ ) ₂ Cl, Zr (OH) ₂ BrCl, Zr (NO ₃ ) (OH) ₂ Cl, Zr (CH ₃ COO) (OH) ₂ Cl, Zr (CH) ₃ COO) ₂ BrCl, Zr (CH ₃ COO) ₂ (OH) Cl, Zr (CH ₃ COO) ₂ (NO ₃ ) Cl, Zr (NO ₃ ) (OH) BrCl, Zr (CH ₃ COO) (NO ₃₎ ) (OH) Cl, Zr (CH ₃ COO) (OH) BrCl, Zr (CH ₃ COO) (NO ₃ ) BrCl, ZrCl ₃ , Zr (OH) Cl ₂ , Zr (OH) ₂ Cl, ZrBrCl ₂ , ZrBr ₂ Cl, Zr (NO ₃ ) Cl ₂ , Zr (NO ₃ ) ₂ Cl, Zr (CH ₃ COO) Cl ₂ , Zr (CH ₃ COO) ₂ Cl, Zr (NO ₃ ) BrCl, Zr (OH) BrCl, Zr (CH ₃ COO) BrCl, Zr (NO ₃ ) (OH) Cl, Zn (CH ₃ COO) (NO ₃ ) Cl, Zr (CH ₃ COO) (OH) Cl, ZrOCl ₂ , ZrO (OH) Cl, ZrO (NO ₃ ) Cl, ZrOBrCl, ZrO (CH ₃ COO) Cl, Zr (SO ₄ ) Cl ₂ , Zr (SO ₄ ) BrCl, Zr (SO ₄ ) (NO ₃ ) Cl, Zr (SO ₄ ) (OH) ) Cl or Zr (SO ₄ ) (CH ₃ COO) Cl Examples thereof include a compound, a hydrate or ammine salt of the compound, or a complex of the compound and an arbitrary compound.

The form of the rewetting liquid containing zirconium chloride includes, for example, a rewetting liquid prepared by adding zirconium chloride to water, zirconium sulfate, zirconium sulfate, zirconium nitrate, zirconium nitrate, zirconium bromide, and odor. A water-soluble zirconium compound such as zirconium oxide or zirconium acetate or zirconium acetate was added to water, and a compound having a chloride ion such as hydrochloric acid was further added to prepare the compound so as to substantially contain the chloride of zirconium. Wetting liquid and the like can be mentioned.

The pH of the rewetting liquid is preferably 3.5 or less. When the pH exceeds 3.5, the aggregation of the nanocellulose coating layer becomes weak and the gelation strength decreases. Therefore, even if the nanocellulose coating layer is pressed against the cast drum, uneven gloss occurs, and smoothness and water repellency are less likely to be exhibited. Therefore, the desired cast-coated surface may not be obtained. The amount of the rewetting liquid applied is not particularly limited, and for example, the amount of wet coating is 5 to 25 g / m ² , preferably 10 to 20 g / m ² , and more preferably 10 to 15 g / m ² . can do.

In the present embodiment, the coating amount of the nanocellulose coating layer is 0.29 to 3.0 g / m ² in terms of solid content per one side of the support, and the wet coating amount of the rewetting liquid is 10. It is preferably ~ 15 g / m ^2. By minimizing the coating amount of the nanocellulose coating layer, the coating amount of the rewetting liquid can be minimized, and the amount of water retained in the coating layer during the casting process is also minimized. be able to. Therefore, defects due to steam burst called pits are less likely to occur during the casting process, and a more uniform cast-coated surface can be formed.

By obtaining the cast-coated paper in this way, JIS P 8155: 2010 "Paper and paperboard-Smoothness test method-Oken-type smoothness specified by the Oken method" of the cast-treated surface of the cast-coated paper. The specified Oken-type smoothness can be set to 11000 seconds or more. The upper limit of the smoothness is, for example, 70,000 seconds, preferably 60,000 seconds, considering the amount of the nanocellulose coating layer applied and the amount of the rewetting liquid applied. Further, the 20-degree mirror surface gloss specified in JIS Z 8741: 1997 "Mirror gloss-measurement method" of the cast surface can be set to 40% or more. Further, it is preferable that the 60-degree mirror glossiness is 65% or more. The upper limit of the 20-degree mirror glossiness is, for example, 75%, preferably 70%, in consideration of the coating amount of the nanocellulose coating layer and the coating amount of the rewetting liquid. Further, the water repellency specified in JAPAN TAPPI No. 68: 2000 "Paper and Paperboard-Water Repellent Test Method" of the cast surface can be set to R4 or higher. The upper limit of the water repellency is, for example, R10, preferably R9, in consideration of the coating amount of the nanocellulose coating layer and the coating amount of the rewetting liquid.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Further, "parts" and "%" in the example indicate "solid mass parts" and "solid mass%", respectively, unless otherwise specified. The cellulose nanofibers will also be referred to as CNF hereafter. Cellulose nanocrystals will also be referred to as CNC below.

<Nanocellulose and carboxymethylcellulose>
The nanocellulose and carboxymethyl cellulose used in each Example and Comparative Example are as follows. Each CNF is a commercially available product and is in a state of being dispersed in water.
CNF (A): TEMPO oxidation method cellulose nanofiber (product name Leocrysta I-2SP, number average fiber length 750 nm, number average fiber diameter 4 nm, concentration 2.0% by mass, B-type viscosity (60 rpm, 20 ° C) 15,000 mPa · s , Made by Daiichi Kogyo Seiyaku Co., Ltd.)
CNF (B): Underwater facing collision type cellulose nanofiber (product name BiNFi-s IMa-1002, number average fiber length 3100 nm, number average fiber diameter 35 nm, concentration 2.0% by mass, B-type viscosity (60 rpm, 20 ° C.) 6800 mPa · s, manufactured by Sugino Machine Limited)
CNF (C): Mechanical defibration method cellulose nanofiber (product name CNF250, number average fiber length 5600 nm, number average fiber diameter 70 nm, concentration 2.0% by mass, B-type viscosity (60 rpm, 20 ° C.) 2050 mPa · s, Made by Mori Machinery Co., Ltd.)
CNC (A): Cellulose nanocrystal NBSP (coniferous bleached sulfite pulp) pulp sheet was coarsely pulverized by a dry method to obtain cotton-like fibers. The fibers were added to a 64% aqueous sulfuric acid solution, suspended, and hydrolyzed at 45 ° C. for 45 minutes so that the solid content concentration was 5% by mass. Ion-exchanged water was added to this suspension to dilute it 5-fold, and the suspension was filtered and dehydrated to recover solids. After that, ion-exchanged water was added to the solid to obtain a suspension having the same solid content as when diluted, and the operation of filtering and dehydrating to recover the solid was repeated twice. Ion-exchanged water was added to the solid and neutralized with sodium hydroxide to make 2.0% by mass. The suspension was defibrated with an ultrasonic homogenizer (US300E, manufactured by Nissei Tokyo Office) for 10 minutes (hereinafter referred to as operation M). The obtained CNC (A) had a number average fiber length of 250 nm, a number average fiber diameter of 10 nm, a concentration of 2.0% by mass, and a B-type viscosity (60 rpm, 20 ° C.) of 100 mPa · s.
CNC (B): In the cellulose nanocrystal operation M, CNC (B) was obtained in the same manner as in the operation M except that the defibration treatment time by the ultrasonic homogenizer was changed from 10 minutes to 60 minutes. The obtained CNC (B) had a number average fiber length of 100 nm, a number average fiber diameter of 4 nm, a concentration of 2.0% by mass, and a B-type viscosity (60 rpm, 20 ° C.) of 500 mPa · s.
CNC (C): In the cellulose nanocrystal operation M, CNC (C) was obtained in the same manner as in the operation M except that the defibration treatment time by the ultrasonic homogenizer was changed from 10 minutes to 2 minutes. The obtained CNC (C) had a number average fiber length of 350 nm, a number average fiber diameter of 70 nm, a concentration of 2.0% by mass, and a B-type viscosity (60 rpm, 20 ° C.) of 50 mPa · s.
CMC: Carboxymethyl cellulose (product name SG cellogen PR, non-fiber (non-nanocellulose), water-soluble, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)

<Preparation of rewetting liquid (rewetting liquid)>
The concentration of zirconyl chloride (chemical formula ZrO (OH) Cl, zircozole ZC-2, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.) became 1.0% by mass, and the release agent (R-053D, fatty acid derivative, Nissin Chemical Laboratory) A rewet solution having a pH of 2.1 was obtained by dispersing and dissolving in water so that the concentration of (manufactured by the company) was 0.05% by mass.

(Example 1)
<Preparation of support>
To a pulp slurry in which 100 parts by mass of L-BKP (broad-leaved bleached kraft pulp) beaten to 530 mL of Canadian Standard Freeness (CSF) was dispersed in water, 5 parts by mass of talc (T-light 83: manufactured by Taihei Taruku) was used as a filler. Add 1.0 part by mass of sulfuric acid band, 0.25 part by mass of acidic rosin sizing agent (AL-1200: manufactured by Seikou PMC), and 1.0 part by mass of cationized starch (Neotack 40T: manufactured by Nippon Food Processing Co., Ltd.). It was dispersed to obtain a raw material slurry. The obtained raw material slurry was used for papermaking using a long net paper machine to obtain paper shavings. Then, oxidized starch (MS # 3800: manufactured by Nihon Shokuhin Kako Co., Ltd.) was applied to both sides of the paper with a size press so that the ^{amount applied in terms of solid content was 1.0 g / m 2 per side, and dried.} , A high-quality paper having a basis weight of 170 g / m ^{2 was obtained.}
<Preparation of coating liquid for pigment coating layer>
As a pigment, 100 parts by mass of Delamicre (CAPIM-NP: manufactured by Imeris Minerals Japan Co., Ltd.) is mixed with 15 parts by mass of styrene-butadiene latex (L-1537: manufactured by Asahi Kasei Chemicals Co., Ltd.) and water, and the solid content concentration is 70% by mass. The coating liquid for the pigment coating layer of No. 1 was obtained.
<Pigment coating layer coating process>
The coating liquid for the pigment coating layer is applied to one side of the woodfree paper with an air knife coater so that the coating amount in solid form is 10 g / m ^2, and the pigment coating layer is dried with hot air. Formed. Subsequently, a soft calendar process was performed to set the Oken-type smoothness of the surface of the pigment coating layer to 600 seconds.
<Preparation of coating liquid for nanocellulose coating layer>
CNF (A) was hydrated and dispersed by an ultrasonic homogenizer to obtain a coating liquid for a nanocellulose coating layer having a solid content concentration of 0.5% by mass.
<Nanocellulose coating layer coating process>
The coating liquid is coated on the pigment coating layer with an air knife coater so that the coating amount in solid form is 0.69 g / m ² , dried with hot air, and the nanocellulose coating layer (NC coating). (Also called a work layer) was formed.
<Casting process>
Next, the nanocellulose coated layer is coated with a dip coater so that the wet coating amount of the rewet liquid is 20 g / m ^2, and this surface is immediately pressed on a cast drum having a surface temperature of 105 ° C. with a press roll. After pressure welding and drying, it was peeled off from the cast drum by a take-off roll to obtain cast coated paper.

(Example 2)
A cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 1.26 g / m 2.}

(Example 3)
A cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 0.29 g / m 2.}

(Example 4)
In Example 1, the same as in Example 1 except that CNF (A) was changed to CNF (B) and the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 0.89 g / m 2.} I got a cast coated paper. However, the dispersion after water addition to CNF (B) was performed by a three-one motor, and the solid content concentration was adjusted to 0.5% by mass.

(Example 5)
A cast-coated paper was obtained in the same manner as in Example 4 except that the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 2.03 g / m 2.}

(Example 6)
A cast-coated paper was obtained in the same manner as in Example 4 except that the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 4.50 g / m 2.}

(Example 7)
In Example 1, cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the pigment coating layer was 6 g / m ^2.

(Example 8)
In Example 4, cast-coated paper was obtained in the same manner as in Example 4 except that the coating amount of the pigment coating layer was 6 g / m ^2.

(Example 9)
A cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the pigment coating layer was set to 8 g / m ^2.

(Example 10)
In Example 1, cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the pigment coating layer was 20 g / m ^2.

(Example 11)
A cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 7.00 g / m 2.}

(Example 12)
Cast coated paper was obtained in the same manner as in Example 1 except that the concentration of zirconyl chloride used in the rewet solution was changed from 1.0% by mass to 0.5% by mass (pH 2.4) in Example 1. ..

(Example 13)
Cast coated paper was obtained in the same manner as in Example 1 except that the concentration of zirconyl chloride used in the rewet solution was changed from 1.0% by mass to 5.0% by mass (pH 1.2) in Example 1. ..

(Example 14)
In Example 1, the same as in Example 1 except that CNF (A) was changed to CNC (A) and the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 2.41 g / m 2.} I got a cast coated paper. However, the dispersion after water addition to CNC (A) was performed by a three-one motor, and the solid content concentration was adjusted to 0.5% by mass.

(Example 15)
Example 2 except that CNF (A) was changed to nanocellulose (number average fiber diameter 22.5 nm) in which CNC (A) and CNF (B) were mixed at a solid content ratio of 1: 1. Cast coated paper was obtained in the same manner as in 2. However, the dispersion after water addition to the mixed nanocellulose was performed by a three-one motor, and the solid content concentration was adjusted to 0.5% by mass.

(Example 16)
In Example 1, 0.25 parts by mass of a compound having an oxazoline group (Epocross K2020E: manufactured by Nippon Catalyst Co., Ltd.) was added to 100 parts by mass of the coating liquid for the nanocellulose coating layer. Cast coated paper was obtained in the same manner.

(Example 17)
In Example 1, the same procedure as in Example 1 was carried out except that 0.25 parts by mass of blocked isocyanate (SU-315V: manufactured by Meisei Kagaku Co., Ltd.) was added to 100 parts by mass of the coating liquid for the nanocellulose coating layer. I got a cast coated paper.

(Example 18)
In Example 1, the CNF (A) was changed to a CNF (number average fiber diameter 19.5 nm) in which CNF (A) and CNF (B) were mixed at a solid content ratio of 1: 1 to change the nanocellulose coated layer. A cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid for application ^{was changed to 0.79 g / m 2.} However, the dispersion after water addition to the mixed CNF was performed by an ultrasonic homogenizer (US300E, manufactured by Nissei Tokyo Office) to adjust the solid content concentration to 0.5% by mass.

(Example 19)
In Example 1, CNF (A) was changed to nanocellulose (number average fiber diameter 7 nm) in which CNC (A) and CNF (A) were mixed at a solid content ratio of 1: 1 for a nanocellulose coated layer. A cast-coated paper was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid ^{was changed to 1.55 g / m 2.} However, dispersion after water addition to the mixed nanocellulose was performed with an ultrasonic homogenizer (US300E, manufactured by Nissei Tokyo Office) to adjust the solid content concentration to 0.5% by mass.

(Example 20)
Example 1 except that the coating amount of the nanocellulose coating layer coating liquid ^{was changed to 0.35 g / m 2} and the wet coating amount of the rewet liquid was changed to 11 g / m ^2. Cast coated paper was obtained in the same manner as above.

(Example 21)
A cast-coated paper was obtained in the same manner as in Example 1 except that the rewet solution having a pH of 2.1 was changed to the rewet solution having a pH of 3.5. The rewet solution having a pH of 3.5 was obtained by adding caustic soda to the rewet solution having a pH of 2.1 in Example 1 to adjust the pH to 3.5 and dissolving the solution.

(Example 22)
In Example 1, the same as in Example 1 except that CNF (A) was changed to CNC (B) and the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 2.41 g / m 2.} I got a cast coated paper. However, the dispersion after water addition to CNC (B) was performed by a three-one motor, and the solid content concentration was adjusted to 0.5% by mass.

(Comparative Example 1)
In Example 1, the same as in Example 1 except that CNF (A) was changed to CNF (C) and the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 1.60 g / m 2.} I got a cast coated paper. However, the dispersion after water addition to CNF (C) was performed by a three-one motor, and the solid content concentration was adjusted to 0.5% by mass.

(Comparative Example 2)
Same as in Example 1 except that CNF (A) was changed to CMC, which is a non-fiber, and the coating amount of the coating liquid for the CMC coating layer ^{was changed to 2.30 g / m 2.} I tried to obtain cast coated paper, but I could not perform the cast process. The CMC was diluted with water and dispersed by a three-one motor to adjust the solid content concentration to 0.5% by mass to prepare a coating liquid.

(Comparative Example 3)
A cast-coated paper was obtained in the same manner as in Example 2 except that the rewet liquid was changed to pure water in Example 2.

(Comparative Example 4)
In Example 2, an attempt was made to obtain cast-coated paper in the same manner as in Example 2 except that the coating liquid for the nanocellulose coating layer was applied and then the rewet liquid was applied without drying. The process could not be performed.

(Comparative Example 5)
In Example 2, cast-coated paper was obtained in the same manner as in Example 2 except that the pigment coating layer was not provided.

(Comparative Example 6)
In Example 1, cast-coated paper was obtained in the same manner as in Example 1 except that the nanocellulose layer was not provided.

(Comparative Example 7)
In Example 1, the same as in Example 1 except that CNF (A) was changed to CNC (C) and the coating amount of the coating liquid for the nanocellulose coating layer ^{was changed to 2.41 g / m 2.} I got a cast coated paper. However, the dispersion after water addition to CNC (C) was performed by a three-one motor, and the solid content concentration was adjusted to 0.5% by mass.

The cast-coated papers obtained in Examples 1 to 22, Comparative Example 1, Comparative Example 3 and Comparative Examples 5 to 7 were evaluated for glossiness, smoothness, and water repellency. These evaluations were performed according to the following method after humidity control at 23 ° C. and 50% RH, and the results are shown in Table 1.

(1) Glossiness The mirror surface glossiness with an incident angle of 20 ° on the cast-processed surface was measured by adopting the mirror surface glossiness measuring method specified in JIS Z 8741: 1997.

(2) Smoothness The smoothness of the cast surface was measured by adopting the Oken-type smoothness measuring method specified in JIS P 8155: 2010.

(3) Water repellency The water repellency of the cast surface was measured by adopting JAPAN TAPPI No. 68: 2000 "Paper and Paperboard-Water Repellent Test Method".

As is clear from Table 1, the cast-coated papers obtained in Examples 1 to 22 had high glossiness, smoothness, and water repellency, and had a good cast-coated surface. In Examples 15, 18 and 19, even when different types of nanocellulose were mixed, the glossiness, smoothness and water repellency were all high, and a good cast coat was obtained. Examples 1 and 20 are examples in which the coating amount of the nanocellulose coating layer and the coating amount of the rewetting liquid are changed, but the coating amount of the nanocellulose coating layer should be minimized. As a result, even if the amount of the rewetting liquid applied was minimized, the glossiness, smoothness, and water repellency were all high, and a good cast coat was obtained.

On the other hand, in the cast-coated paper obtained in Comparative Example 1, it is considered that the number average fiber diameter of the cellulose nanofibers is too large and many cellulose nanofibers having a large fiber width are present, which makes it difficult to gel. , The desired water repellency was not obtained. In Comparative Example 2, the carboxymethyl cellulose coating layer was difficult to gel, and the cast treatment could not be performed as in each example in which the nanocellulose coating layer was provided. In the cast-coated paper obtained in Comparative Example 3, the nanocellulose coated layer did not gel, and although the cast treatment was possible, water repellency could not be obtained. Comparative Example 4 is a so-called gelling method, and although gelation of the entire coating layer was observed, the amount of water used was large, so that it was difficult to be supported on the support and the casting process could not be performed. In the cast-coated paper obtained in Comparative Example 5, the nanocellulose layer penetrated quickly, and the desired performances in terms of glossiness, smoothness, and water repellency could not be obtained. Since the cast-coated paper obtained in Comparative Example 6 did not have a nanocellulose layer, there was no gelation, and desired performances could not be obtained in terms of glossiness, smoothness, and water repellency.

Claims (11)

A step of applying a coating liquid for a pigment coating layer containing a pigment and an adhesive to at least one surface of a support containing pulp as a main component, and then drying to provide a pigment coating layer.
A coating liquid for a nanocellulose coating layer containing nanocellulose having a number average fiber diameter of 1 nm or more and less than 70 nm is applied to the surface of the pigment coating layer, and then dried to provide a nanocellulose coating layer. Process and
After applying a rewetting liquid containing zirconium chloride to the surface of the nanocellulose coating layer, the nanocellulose coating layer is pressed against a heated mirror surface drum while the nanocellulose coating layer is in a wet state to perform a casting process. A method for producing cast-coated paper, which comprises a process. The method for producing cast-coated paper according to claim 1, ^{wherein the coating amount of the pigment coating layer is 5 to 20} g / m 2 in terms of solid content per one side of the support. The cast-coated paper according to claim 1 or 2, wherein the coating amount of the nanocellulose coated layer is 0.29 to 7.0 g / m ^{2 in terms of solid content per one side of the support.} Production method. The Oken-type smoothness specified in JIS P 8155: 2010 "Paper and paperboard-Smoothness test method-Oken-type smoothness specified by the Oken method" of the cast surface shall be 11000 seconds or more. The method for producing cast-coated paper according to any one of claims 1 to 3. Any one of claims 1 to 4, wherein the 20-degree mirror surface gloss specified in JIS Z 8741: 1997 "Mirror gloss-measurement method" of the cast-treated surface is 40% or more. The method for manufacturing cast coated paper according to the above. Any one of claims 1 to 5, wherein the water repellency specified in JAPAN TAPPI No. 68: 2000 "Paper and Paperboard-Water Repellent Test Method" of the cast-treated surface is R4 or more. The method for producing cast coated paper according to. The cast-coated paper according to any one of claims 1 to 6, wherein the coating liquid for the nanocellulose coating layer contains a blocked isocyanate compound and / or a compound having an oxazoline group as a functional group. Manufacturing method. The method for producing cast-coated paper according to any one of claims 1 to 7, wherein the nanocellulose coated layer does not contain a pigment and an adhesive. The invention according to any one of claims 1 to 8, wherein the nanocellulose is at least one of a TEMPO oxidation method cellulose nanofiber, an underwater counter-collision type cellulose nanofiber, and a cellulose nanocrystal. How to make cast coated paper. The coating amount of the nanocellulose coating layer is 0.29 to 3.0 g / m ² in terms of solid content per one side of the support, and the wet coating amount of the rewetting liquid is 10 to 15 g / m. The method for producing a cast-coated paper according to any one of claims 1 to 9, wherein the size is ^{m 2.} The method for producing cast-coated paper according to any one of claims 1 to 10, wherein the rewetting liquid has a pH of 3.5 or less.