JP2010090500A - Coated paper for printing and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated paper for printing, which has a coated layer containing calcium carbonate as a pigment in a high mixing ratio to total pigments of &ge;90 mass% and has a high brightness and excellent surface feeling and printability and a method for producing the same. <P>SOLUTION: A coating solution useful for coating on at least an outermost layer of coated layer has a calcium carbonate content in the pigment of &ge;90 mass% and contains a hydroxyethyl starch as an adhesive. The doctor blade of a blade coater is equipped with a surface hardened part so as to cover the vicinity of the tip part of rake face side of a base material and the surface hardened part of the rake face side is equipped with two or more bent parts. A length (S1) from the tip of the rake face to a first bent part closest to the tip of the rake face is made shorter than the total (S2) of a length from the first bent part to the final bent part farthermost from the tip of the rake face. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a coated coated paper for printing excellent in surface feel and printability while containing 90% by mass or more of heavy calcium carbonate as a pigment in a coating layer coating material, and a method for producing the same.

  The coated paper for printing is required to have higher whiteness, better surface feeling and printability. The decrease in printability is considered to be mainly caused by coating unevenness. In particular, if a lot of minute coating unevenness occurs, the transfer amount of the printing ink onto the paper tends to be non-uniform, and the printing suitability tends to decrease, for example, the printing unevenness decreases. When the printability is lowered, for example, in a solid print portion such as a black color, unevenness occurs in the transfer amount of the printing ink, and a uniform image cannot be obtained, resulting in a poor-looking printed matter.

  The surface feeling indicates the uniformity of appearance, and represents the degree of minute unevenness of whiteness or white paper glossiness. The surface feeling is likely to be improved by a flattening process such as calendering. On the other hand, when sufficient flattening conditions are not obtained, the coated paper has a low flatness and a poor surface feeling. For example, in a printed matter with a high black-and-white contrast, there is a slight unevenness in the whiteness and white paper glossiness of the white portion that is the ground color, even if the black portion is evenly printed, if the surface texture is poor. As a result, the printed matter will not look neat and look bad.

  In particular, matte and dull coated papers cannot be sufficiently flattened by a flattening facility such as a soft calender or a supercalender to suppress the glossiness of blank paper, and it is difficult to improve the surface feeling. In order to improve the surface feeling in matte and dull coated paper, it is necessary to improve the flatness without increasing the gloss under milder flattening conditions. In order to achieve this, kaolin clay (see Patent Document 1) with high flatness and a plastic pigment (see Patent Document 2) that easily breaks and improves the gloss of white paper are available as pigments. Since the whiteness is lower than calcium, there is a problem that it is difficult to improve the whiteness of the coated paper obtained.

  As a method for improving the whiteness, there are a method of blending calcium carbonate and titanium dioxide, which are high white pigments, or adding a fluorescent dye to improve the whiteness by a fluorescent whitening effect. When titanium dioxide is used, since it is an expensive pigment, it is disadvantageous in terms of cost, and the fluorescent whitening effect by the fluorescent dye has a problem of high fading.

  When calcium carbonate, which is a high white pigment, is used, the whiteness is improved, but it is a pigment that is less likely to be crushed than clay. There was a problem. A technique for applying a coating solution containing 80 to 100% by mass of calcium carbonate as a pigment for the coating layer with a roll transfer type coater is already known (see Patent Document 3). Since it is processed, there exists a problem inferior to the flatness and surface feeling of the coated paper obtained.

  In addition, a technique of coating at a coating speed of 1500 m / min or more is known (see Patent Document 4), but there is a problem that sufficient surface feeling and printability cannot be obtained. Even if coating is performed using the above technique with the blade coating method, the paint near the blade is likely to be sheared (shearing force), and minute coating unevenness is likely to occur. It becomes.

  Although the technique which devised the shape of a blade is also known (refer patent documents 5 and 6), when a coating liquid containing 90 mass% or more of heavy calcium carbonate is applied, sufficient surface feeling and Printability could not be obtained.

A coated paper having a coating layer with a high blending ratio of calcium carbonate as a pigment, particularly a blending ratio of 90% by mass or more of all pigments, is easy to obtain a coated paper with high whiteness, but has excellent surface feel. Even when a coating layer was coated on a paper substrate by the blade coating method, a sufficient surface feeling could not be obtained at a high coating speed of 1500 m / min or more. In particular, in matte and dull-tone coated paper, an excessive linear pressure of the calendar is required for flattening, the surface gloss cannot be improved while suppressing the glossiness of the white paper, and its manufacture is difficult.
Japanese Patent Laid-Open No. 2004-091997 JP 2006-193864 A JP 2006-257590 A JP 2005-194660 A JP 2006-124863 A JP 2006-124864 A

  Providing a coated paper for printing having a coating layer containing calcium carbonate as a pigment at a high blending ratio of 90% by mass or more of all pigments, having high whiteness and good surface feel and printability, and a method for producing the same. Objective.

  As a result of repeated investigations on a coating paper for printing and a method for producing the same, a coating liquid is applied to the surface of a paper substrate using a blade coater. When the coating solution to be used has a calcium carbonate content of 90% by mass or more in the pigment and contains hydroxyethyl starch as an adhesive, by using a doctor blade of a specific form, it is possible to achieve high speed coating. The present inventors have found that a coated paper excellent in feeling and printability can be obtained, and have completed the present invention.

Specifically, the present invention
A coated paper for printing in which a coating liquid containing a pigment and an adhesive is applied to the surface of a paper substrate to provide a coating layer,
The coating liquid used for the coating of at least the outermost layer of the coating layer has a ratio of calcium carbonate in the pigment of 90% by mass or more, and contains hydroxyethyl starch as the adhesive,
The coating layer is provided by a blade coater,
The doctor blade of the blade coater is provided with a surface hardened portion so as to cover the vicinity of the tip portion on the rake face side of the base material,
The surface hardened portion on the rake face side is provided with two or more bent portions,
The length (S1) from the tip portion of the rake face to the first bent portion closest to the tip portion of the rake face is from the first bent portion to the final bent portion farthest from the rake face tip portion. Longer than the total length (S2),
The present invention relates to a coated paper for printing.

The present invention also provides:
A method for producing a coated paper for printing in which a coating liquid containing a pigment and an adhesive is applied to the surface of a paper substrate to provide a coating layer,
The coating liquid used for the coating of at least the outermost layer of the coating layer has a ratio of calcium carbonate in the pigment of 90% by mass or more, and contains hydroxyethyl starch as the adhesive,
The coating layer liquid is provided by a blade coater,
The doctor blade of the blade coater is provided with a surface hardened portion so as to cover the vicinity of the tip portion on the rake face side of the base material,
The surface hardened portion on the rake face side is provided with two or more bent portions,
The length (S1) from the tip portion of the rake face to the first bent portion closest to the tip portion of the rake face is from the first bent portion to the final bent portion farthest from the rake face tip portion. Longer than the total length (S2),
The present invention relates to a method for producing a coated paper for printing.

  In the coated paper for printing and the method for producing the same according to the present invention, the doctor blade used in blade coating is made into a special form so that the coating liquid having a calcium carbonate content of 90% by mass or more can be homogeneously made into a paper substrate Since it can be coated on top, it is possible to obtain a coated paper for printing with high surface feel and high printability.

  The adhesive further contains a styrene-butadiene latex, and the mass ratio in terms of solid content of the styrene-butadiene latex with respect to hydroxylethyl starch is preferably 1.4 or more and 7.0 or less.

  The (S1) is preferably 300 μm or more and 400 μm or less.

  The (S2) is preferably 100 μm or more and 200 μm or less.

  The coated paper for printing and the method for producing the same of the present invention are particularly useful for high-speed coating with a coating speed of 1500 m / min or more.

  According to the coated paper for printing and the method for producing the same of the present invention, it is possible to apply the coated paper for printing with high whiteness, high surface feeling and high printability at high speed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, this invention is not limited to the following description.

<Doctor blade>
FIGS. 1 and 2 are diagrams showing a main configuration of a doctor blade used in the coated paper for printing and the method for producing the same according to the present invention, FIG. 1 is a top view, and FIG. 2 is a cross-sectional view taken along line AA in FIG. FIG. 1 and 2, the doctor blade 1 includes a base material 2 indicated by a hatched portion and a surface hardened portion 3 provided on the base material 2.

  The surface hardened portion 3 is formed so as to cover the vicinity of the tip of the rake face (the face that contacts and faces the paper base material) of the base material 2, and in FIGS. 1 and 2, the doctor blade 1 is a paper base material. It is provided in the part which contacts the upper coating liquid. Unlike FIGS. 1 and 2, the surface hardened portion 3 may be provided on the entire rake face side of the base material 2.

  The doctor blade 1 is fixed by a blade coater clamp (not shown) in a state where the left end (free end) side in FIGS. 1 and 2 is allowed to be deformed, and the right end side in the figure is fixed. .

The doctor blade 1 is arranged on the backing roll so as to face the paper base material (base paper) that runs in the direction of the two-dot chain line in the figure by the rotation of the backing roll. The doctor blade 1 has a coating amount of the solid content of the coating liquid of 6 to 12 g / per side when the rake face 4 of the surface hardened portion 3 comes into contact with the paper base coated with the coating liquid. The amount of coating on the base paper is adjusted so that m ^2, and a coated paper for printing on which a smooth coated surface is formed is produced.

  The doctor blade 1 is attached to the blade coater so that the contact pressure (blade linear pressure) of the surface hardened portion 3 to the paper substrate can be controlled, and the coating amount can be easily adjusted by adjusting the blade linear pressure. It can be changed.

  An enlarged view of the contact portion between the doctor blade and the paint on the paper substrate in the blade coater is shown in FIG. In FIG. 3, the paper substrate 12 is on the backing roll 11, and the coating liquid 13 is applied on the substrate 12. Since the backing roll 11 moves from the right side to the left side in FIG. 2, the paper base 12 and the coating liquid 13 also move in the same direction. The doctor blade 1 is fixed so that the first inclined portion 4d and the coating liquid 13 on the paper substrate 12 come into contact with each other.

  Excess coating liquid 13 on the paper substrate 12 is scooped off by the first inclined portion 4 d, and a coating layer 14 made of a coating liquid having a reduced thickness is formed downstream of the doctor blade 1. Excess coating liquid 13 hits the second inclined portion 4 e of the doctor blade 1 and is scraped off along the upper surface 3 a of the surface hardened portion 3. At this time, a liquid pool of the coating liquid 13 is generated between the paper base 12 and the second inclined portion 4e.

  The base material 2 has a suitable hardness (for example, Rockwell hardness C scale 22 or more) and a material having a certain degree of elasticity so that the contact pressure with the paper substrate can be easily controlled. preferable. For example, carbon tool steel (SK material), alloy tool steel, stainless steel and the like are preferable. The base material 2 includes a flat lower surface 2a, a land surface 2b orthogonal to the lower surface 2a, a base material scooping surface 2c inclined to the land surface 2b, and a flat surface formed in parallel to the lower surface 2a. An upper surface 2d is provided, and a lower surface 2a and an upper surface 2d configured in parallel with each other are connected to the clamp. The hardness of the base material 2 is preferably about 240 Hv to 940 Hv in terms of Vickers hardness from a practical and economical viewpoint.

  The surface hardened portion 3 is made of a material harder than the base material 2 and preferably has a Vickers hardness of 1000 Hv or more and 1700 Hv or less. By setting the hardness within the above range, even in high-speed coating at 1500 m / min or higher, the effect of improving the coating surface feeling can be reliably exhibited while imparting appropriate wear resistance to the surface hardened portion 3. When the Vickers hardness is less than 1000 Hv, the surface hardened portion 3 is likely to be worn, and the life of the doctor blade may be reduced. On the other hand, when the Vickers hardness is higher than 1700 Hv, it becomes difficult to form the bent portion, and it may take time and labor to form the surface-hardened portion and thus the doctor blade, and may increase the cost.

  In particular, as in the present invention, when a paint having a heavy calcium carbonate ratio of 90% by mass or more is provided by a blade coater, the Vickers hardness of the surface-hardened portion is set to 1000 Hv or more and 1700 Hv or less, as described above. This is preferable because a coated paper with little wear and good surface feel can be obtained. Furthermore, since the increase in the viscosity of the coating liquid can be suppressed by including hydroxyethyl starch as an adhesive, it is possible to obtain a coated paper for printing particularly excellent in surface feel.

  It is preferable that the surface hardening part 3 is comprised from the material etc. which have tungsten as a main component, for example. The surface hardened portion 3 includes an upper surface 3a formed parallel to the lower surface 2a of the base material 2, and a land surface 3b continuously provided on the base material land surface 2b so as to be orthogonal to the base material lower surface 2a, A rake surface (bevel surface) 4 is formed between the upper surface 3a and the land surface 3b.

  The surface hardened portion 3 is formed by depositing, for example, a material obtained by adding aluminum oxide to tungsten, which is a main component, on the base material rake face 2c and the upper face 2d of the base material 2 by plasma spraying. can do. Instead of aluminum oxide, a material obtained by adding a small amount of chromium, titanium, or the like to tungsten may be used.

  By forming the surface hardened portion 3 using a material containing tungsten as a main component, it is possible to increase the toughness while ensuring sufficient wear resistance and to easily improve the coating surface feeling by the bent portion. Can be obtained. That is, tungsten is a material excellent in wear resistance, and it is possible to easily extend the life of the surface hardened portion, and thus the doctor blade. Further, since the particles of tungsten are fine, it is possible to easily obtain a good coated surface feeling, and it is possible to suppress the deterioration of the coated surface feeling as much as possible even when the surface hardened portion is worn.

  Other than materials mainly composed of tungsten, one or more metal oxides, metal carbides or metal nitrides, or ceramic materials such as cermets in combination thereof, cemented carbide containing tungsten carbide or chromium carbide, chromium You may comprise the surface hardening part 3 with plating metals, such as plating.

  As a method of forming the surface hardened portion 3 on the base material 2, other than the plasma spraying method, other spraying methods, vapor deposition methods such as PVD, CVD, and the like may be used. However, it is possible to increase the toughness of the surface-hardened portion 3 while sufficiently securing the wear resistance of the surface-hardened portion 3 when using the above-described material containing tungsten as a main component as compared with the case of using another material. In addition, it is preferable in that the effect of improving the coating surface feeling by the first bent portion 4b and the second bent portion 4c can be easily obtained.

  When the hardened surface portion 3 having a Vickers hardness greater than 1500 Hv is formed using a metal nitride ceramic material or a material with relatively low toughness such as chrome plating, the hardened surface portion 3 May become short and the life of the doctor blade 1 may be shortened. Therefore, when the surface hardened part 3 is formed using such a material, even when high-speed coating of 1500 m / min or more is performed, the life reduction of the doctor blade 1 can be sufficiently suppressed. More preferably, the Vickers hardness is 1500 Hv or less so that the bending portion 4 c and the like can be relatively easily formed and the coating surface feeling can be enhanced.

  The surface hardened portion 3 is formed on the base material 2 so as to have a thickness of about 0.2 μm to 0.4 μm. Further, it is not necessary to cover the entire upper surface 2d of the base material 2, and it is sufficient if it covers at least a portion that may come into contact with the coating liquid during use. In that case, only the upper surface 2d of the base material is connected to the clamp. Will be.

  On the rake face 4, from the free end (left end in FIGS. 1 and 2) side of the doctor blade 1 to the fixed end (right end in FIGS. 1 and 2) side, the rake face tip 4a, the first bent part 4b, Two bent portions 4c are sequentially provided, and the rake face 4 includes a first inclined portion 4d and a second inclined portion 4e.

  In the doctor blade shown in FIGS. 1 and 2, since there are two bent portions, the second bent portion 4c is the final bent portion, but the bent portions may be three or more. When there are three bent portions, the rake face tip 4a and the first bent from the free end (left end in FIGS. 1 and 2) side of the doctor blade 1 toward the fixed end (right end in FIGS. 1 and 2). The portion 4b, the second bent portion 4c, and the third bent portion (not shown) are sequentially provided, and the third bent portion becomes the final bent portion.

  The plurality of bent portions can be formed by performing grinding or the like on the inclined portion 4 of the surface hardened portion 3 formed on the base material 2 by the plasma spraying method.

  By providing a plurality of bent portions on the rake face 4, an appropriate liquid pool of the coating liquid can be formed between the paper base and the second inclined portion 4e, and the coating surface feeling can be improved. Furthermore, in order to obtain a coated paper with higher whiteness, coating with a calcium carbonate content of 90% by mass or more, preferably 100% by mass, results in a high concentration paint with a coating concentration exceeding 68% by mass. In this case, the length (S1) in the longitudinal direction from the rake face tip 4a to the first bend 4b that is the bend closest to the rake face tip 4a is determined from the first bend 4b to the rake face tip. By making it longer than the total length (S2) in the longitudinal direction to the final bent portion (second bent portion 4c in FIG. 1) which is the farthest bent portion from the portion 4a, the first inclined portion 4d and coating The contact area with the liquid 13 is increased, it is possible to improve the effect of flattening the coating liquid, and the coating surface feeling is likely to be improved.

  Here, the length of S1 and S2 refers to the length in the direction perpendicular to the land surface of the doctor blade (direction perpendicular to the doctor blade width direction). In FIGS. 1 and 2, the free end of the doctor blade 1 is used. The length in the direction connecting the (left end in FIGS. 1 and 2) side and the fixed end (right end in FIGS. 1 and 2) side. In FIG. 2, when a perpendicular is drawn from the first bent portion 4b and the second bent point 4c to the lower surface 2a, the distance between the points P and Q is S1, and the distance between the points Q and R is S2. .

  The rake face tip portion 4a, the first bent portion 4b, and the second bent portion 4c may be provided with an R processed portion after grinding. Applying R processing is preferable because initial familiarity of the blade is improved and the coating profile is stabilized at an early stage, and the catching of the coating liquid can be reduced, so that streaks are less likely to occur. The specific dimension of R processing is preferably 0.1 ± 0.02 mm.

  S1 needs to be longer than S2. If S1 is shorter than or equal to S2, the action of the paint being flattened by the S1 portion of the blade is reduced, resulting in minute coating unevenness and flatness of the coating layer surface. On the other hand, the liquid pool becomes large and uniform coatability is difficult to obtain, and the surface feeling is lowered.

  S1 is preferably 300 μm or more and 400 μm or less, and more preferably 320 μm or more and 380 μm or less. When S1 is less than 300 μm, the flatness of the coating layer surface by the blade cannot be improved, and the surface feeling tends to deteriorate. On the other hand, if it exceeds 400 μm, even if the pressing force is excessive, the set coating amount will not be reduced, and a blade share will be applied to the coated surface, so that minute coating unevenness is likely to occur and printability may be reduced. is there. In this respect, the blade shape of Patent Document 6 in which S1 is 500 μm and S2 is 400 μm is different from the preferable blade shape of the present invention.

  S2 is preferably from 100 μm to 200 μm, and more preferably from 120 μm to 180 μm. When the thickness is less than 100 μm, the liquid pool of the coating liquid in the second inclined portion 4e becomes small, and minute coating unevenness is likely to occur, and printability may be reduced. On the other hand, if it exceeds 200 μm, the liquid pool in the second inclined portion 4e becomes large, and a uniform coating cannot be obtained, and printability may be reduced.

  By specifying the lengths of S1 and S2 on the rake face (bevel face) 4, as described later, a coating liquid having a calcium carbonate content of 90% by mass or more in the pigment can be coated with uneven coating. Since the coating can be performed while suppressing the surface, the surface feeling is more likely to be improved after the flattening process using a calendar. As a result, the resulting coated paper has a good appearance on the white paper portion, and also has a good appearance on the printed portion because of its high printability. Especially for matte and dull tone coated papers, the line pressure on the calender required for flattening is lower than before, and as a result, it is possible to improve printability while suppressing gloss, so a high-quality mat A tone and dull tone coated paper is obtained. Furthermore, by setting the Vickers hardness of the surface hardened portion of the doctor blade to 1000 Hv or more and 1700 Hv or less, a coated paper having a good surface feel can be obtained even in high-speed coating at a coating speed of 1500 m / min or more.

  The thickness (S3) of the base material 2 on the fixed end side is preferably 0.5 mm or more and 0.7 mm or less. Moreover, it is preferable that the thickness (S4) of the surface hardening portion 3 on the fixed end side is 0.2 mm or more and 0.4 mm or less. This is because, if S3 and S4 are within the above ranges, it is easy to obtain an effect of improving the surface feeling and the printability due to the pool of coating liquid generated by the first rake face 4d and the second rake face 4e.

<Component 1 of coating liquid: Pigment>
Calcium carbonate is used for the pigment which is the main component of the paint. Calcium carbonate is preferable in that the whiteness is high and the whiteness of the coated paper obtained is high. Calcium carbonate has low water retention compared to kaolin clay, so if it is highly blended as a pigment in the coating solution, the coating tends to immobilize and difficult to apply uniformly, and a uniform coating layer cannot be obtained. was there. In addition, when the calcium carbonate concentration is high, the coating concentration increases, coating unevenness is likely to occur, and printability is liable to deteriorate. However, in the coated paper for printing and the method for producing the same of the present invention, since the hydroxyethyl starch described later is used as the adhesive, the above-mentioned problems can be suppressed, and a coated paper having excellent surface feel and printability can be obtained. Obtainable.

  As calcium carbonate, either heavy calcium carbonate or light calcium carbonate can be used. However, the shape of heavy calcium carbonate is indefinite, whereas light calcium carbonate has a specific shape such as spindle shape, column shape, needle shape, etc., so the proportion of light calcium carbonate in the total pigment is If it is 80% by mass or more, the coatability is deteriorated, and it becomes difficult to obtain a uniform coating layer surface, so that the printability tends to be lowered. However, when light calcium carbonate is used, it is a pigment that tends to be crushed compared to heavy calcium carbonate, so that flatness is improved and surface texture is easily improved. It is preferable to use light calcium carbonate together with heavy calcium carbonate as appropriate depending on the feeling and printability.

  As the heavy calcium carbonate, for example, a dry crystalline or wet pulverized white crystalline limestone having a number average particle size of about 5 μm or less can be used, but the number average particle size is 0.3 μm or more and 2.0 μm or less. It is preferable to use wet heavy calcium carbonate having a particle ratio of 10% or less. When the number average particle size of heavy calcium carbonate is smaller than 0.3 μm, the heavy calcium carbonate particles are likely to re-agglomerate in the coating solution, and foreign matter is generated and defects such as streaks are likely to occur. May be. On the other hand, when the number average particle size is larger than 2.0 μm, the coating surface feel is poor, or even when the hardness of the surface-cured portion is increased, the wear at the surface-cured portion is likely to progress, It becomes difficult to increase speed etc. In addition, when the proportion of particles having a particle size larger than 2.0 μm is larger than 10%, even when the surface-cured portion is made relatively hard, wear at the cured portion is likely to proceed and the coating speed is increased. Etc. may be difficult to raise.

  The number average particle diameter can be measured with a general particle size measuring instrument. In the examples described later, the particle size distribution measuring instrument (equipment name: MICROTRAC PARTICLE-SIZE ANALIZER, manufacturer: LEEDS & NORTHRUP INSTRUMENTS) is used. did.

  As the light calcium carbonate, for example, one produced by baking limestone and having a number average particle size of about several μm or a number average particle size of about 0.02 μm to 0.10 μm can be used. Examples of the shape of the light calcium carbonate include a columnar shape, a needle shape, and a spindle shape, and a chestnut shape in which crystal structures having these shapes are aggregated and crystallized.

  The blending amount of calcium carbonate needs to be 90% by mass or more of the whole pigment, preferably 95% by mass or more, and most preferably 97% or more. If the calcium carbonate is less than 90% by mass, the whiteness tends to decrease, such being undesirable. As the high white coated paper, the whiteness is preferably 85% or more, and more preferably 87% or more. In order to obtain these whitenesses, it is preferable to increase the calcium carbonate content within the above range. In order to uniformly apply the calcium carbonate highly blended paint in the above range, it is preferable to use a doctor blade having two or more bent portions and having S1 longer than S2, as described above. It is more preferable to use a doctor blade having a surface hardened portion having a Vickers hardness of 1000 Hv to 1700 Hv, S1 of 300 μm to 400 μm, and more preferably S2 of 100 μm to 200 μm. A craft paper can be obtained.

  In the coated paper for printing and the method for producing the same according to the present invention, since calcium carbonate is highly blended with 90% by mass or more of the total pigment, a coated paper having a whiteness of 87% or more and high whiteness can be obtained. Furthermore, by containing hydroxyethyl starch as a water-soluble polymer, which will be described later, even when a paint containing a high amount of calcium carbonate is applied, the surface feel and printability can be improved.

  As pigments other than calcium carbonate, those generally used as papermaking pigments can be used in combination. For example, kaolin clay, delaminated kaolin, talc, white carbon, titanium dioxide, calcium sulfate, satin white, calcium sulfite, gypsum, barium sulfate, diatomaceous earth, magnesium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, water Inorganic pigments such as zinc oxide, zinc oxide, magnesium oxide, bentonite, and sericite, and organic pigments such as polystyrene resin fine particles, urea formalin fine particles, fine hollow particles, and porous fine particles can be used. One type or two or more types can be appropriately selected and blended in the coating solution.

<Component 2 of coating agent: adhesive>
A water-soluble polymer is used as the adhesive. Hydroxyethyl starch (HES) can be used as a water-soluble polymer to reduce the viscosity of the coating solution, so even in highly blended paints containing 90% or more by weight of calcium carbonate after the blade coating, This is particularly preferable because the flatness of the film becomes high and the surface feeling is easy to improve, and since the uniform coating layer surface can be obtained, the printability tends to be high.

  When the total pigment is 100 parts by mass, the HES blending part is preferably 1 part by mass or more and 5 parts by mass or less, and more preferably 2 parts by mass or more and 3 parts by mass or less. If the amount is less than 1 part by mass, the pigment cannot be sufficiently fixed and coating unevenness occurs, resulting in a decrease in surface feel.If the amount exceeds 5 parts by mass, the coating concentration decreases and not only uniform coating is possible, but also a minute amount. Coating unevenness is likely to occur, and the printability tends to deteriorate, which is not preferable. Further, the formation of starch on the surface of the coating layer is not preferable because the surface feel and printability may be easily lowered.

  In the coated paper for printing and the method for producing the same according to the present invention, high whiteness coated paper can be obtained because calcium carbonate is highly blended at 90% by mass or more, and further, HES is used in combination as an adhesive. Therefore, even if a high calcium carbonate coating liquid is applied, the surface of the resulting coating layer is highly flat and easy to improve the surface, and a uniform coating layer surface can be obtained. Tends to be higher. Furthermore, by adding latex in addition to HES as an adhesive, it is possible to more effectively improve the surface feel and printability.

  As an adhesive, it is preferable to use latex which is a synthetic resin in addition to HES. As described above, when starches are formed on the surface of the coating layer, local unevenness in white paper glossiness is likely to occur, and the surface feel and printability are likely to be reduced. For this reason, it is preferable to minimize the amount of HES, which is a water-soluble polymer, and to supplement necessary pigment fixation with latex.

  As the latex, styrene-butadiene latex (SBR) is preferable in terms of good thermal stability. In particular, when a gradient latex having a composition different between the inside and the outside of the latex particles is used, a high strength can be obtained with a low blending part compared to a conventional single structure latex. In addition, using a gradient latex that can achieve higher strength makes it easier to fix the pigment to the coating layer, making it difficult for minute coating unevenness to occur, reducing water-soluble polymers and hydroxyethyl starch, It is preferable because the surface feeling and printability are easily improved.

  In particular, for coated paper for printing that has a coating layer with high blending of heavy calcium carbonate with a low printability of 90% by mass or more of the total pigment, the amount of latex that tends to lower the printability should be reduced. Is preferred. As the latex, it is preferable to use an inclined latex having a stronger adhesive force. In particular, it is preferable to use HES in combination with a doctor blade having two or more bent portions and having S1 longer than S2, because a coated paper with better printability can be obtained. More preferably, a doctor blade having a surface hardened portion having a Vickers hardness of 1000 Hv to 1700 Hv, S1 of 300 μm to 400 μm, and more preferably S2 of 100 μm to 200 μm is used.

  In the case of the gradient latex, the blending part is preferably 4 parts by mass or more and 10 parts by mass or less, and more preferably 6 parts by mass or more and 8 parts by mass or less when the total pigment is 100 parts by mass. If the amount is less than 4 parts by mass, unevenness in the fixation of the pigment will occur, and a uniform flattening effect will not be obtained, and the surface feeling will deteriorate, and if it exceeds 10 parts by mass, the coating concentration will decrease and a uniform coating will be obtained. Therefore, the printability may be easily deteriorated.

  As a ratio of HES and latex, latex is preferably 1.4 or more and 7.0 or less, and more preferably 2.3 or more and 4.0 or less with respect to HES1 in mass ratio.

  In the coated paper for printing and the method for producing the same according to the present invention, calcium carbonate is blended as high as 90% by mass or more, and HES is used as an adhesive to obtain a coated paper excellent in surface feeling and printability. be able to. Furthermore, when a styrene-butadiene latex is used at a mass ratio of 1.4 to 7.0 with respect to HES1, it is preferable because the surface feel and printability are more likely to be improved. In particular, a gradient latex is used as the latex. Thus, it is possible to apply the calcium carbonate high-blending coating liquid while preventing deterioration in surface feeling and printability. In addition, in order to uniformly apply the paint having the above-described configuration, a doctor blade having a surface hardened portion having two or more bent portions, S1 longer than S2, and Vickers hardness of 1000 Hv to 1700 Hv is used. It is preferable. More preferably, when S1 is 300 μm or more and 400 μm or less, and more preferably, S2 is 100 μm or more and 200 μm or less, it is possible to obtain a coated paper with excellent surface feeling.

  As an adhesive other than the above, an adhesive that can generally be used for papermaking can be used in combination. For example, (1) proteins such as casein and soy protein; (2) conjugated diene latexes such as methyl methacrylate-butadiene copolymer latex and styrene-methyl methacrylate-butadiene copolymer latex, acrylate esters and / or methacrylic esters Acrylic latex such as acid ester polymer latex or copolymer latex, vinyl latex such as ethylene-vinyl acetate polymer latex, or these various copolymer latexes with functional group-containing monomers such as carboxyl groups Latexes such as modified alkali partially soluble or insoluble latex; (3) Synthetic resin adhesives such as polyvinyl alcohol, olefin-maleic anhydride resin, melamine resin, urea resin, urethane resin; (4) Oxidation Starch, positive starch, esterified starch, deki Starches such as string; (5) Cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose can be used, and one or more of these can be appropriately selected and used.

  The ratio of the pigment and the adhesive in the paint is preferably adjusted so that the adhesive is 5 parts by mass or more and 15 parts by mass or less, and is 7 parts by mass or more and 11 parts by mass or less with respect to 100 parts by mass of the pigment. It is more preferable. When the blending amount of the adhesive is less than 5 parts by mass, unevenness occurs in fixing the pigment, so that the pigment tends to fall off from the surface of the coating layer, and sufficient flatness cannot be obtained. On the other hand, if the amount of the adhesive exceeds 15 parts by mass, the adhesive is formed in the coating layer, which is not preferable because printability is deteriorated.

<Other auxiliaries>
There is no particular limitation on the method for preparing the coating agent, and in addition to pigments and adhesives, it is generally used in papermaking applications such as dust prevention agents, fluorescent dyes, antifoaming agents, mold release agents, colorants, water retention agents, etc. Various auxiliary agents can be blended as appropriate.

<Coating amount>
In the coated paper for printing and the method for producing the same according to the present invention, the coating liquid is preferably applied to one side of the paper base at 6 g / m ² or more and 12 g / m ² or less per side of the paper base, 8 g The coating is more preferably carried out at a rate of not less than / m ^{2 and not} more than 10 g / m ² . If the coating amount is less than 6 g / m ² per side of the paper substrate, the printability is likely to deteriorate due to uneven coating, and if the coating amount exceeds 10 g / m ² , the coating amount increases. Since unevenness is likely to occur, it is not preferable because printability tends to be lowered.

In the coated paper of the present invention, since HES as an adhesive and preferably styrene-butadiene latex are used in combination, a high blending coating liquid containing calcium carbonate as a pigment, particularly containing 90% by mass or more of the total pigment is used. Even if it is applied at a rate of about 6 to 12 g / m ² per side of the paper substrate, it is possible to obtain coated paper with good surface feel and excellent printability.

Conventionally, when a coating liquid containing 90% by mass or more of calcium carbonate in a pigment is applied at a coating amount of about 6 to 12 g / m ² , the surface texture cannot be sufficiently improved and the printability is improved. There was a problem of lowering. However, in the present invention, since this problem can be solved, a coating paper containing a large amount of pigment such as calcium carbonate can be applied with a good feel to obtain a coated paper having good printability. In addition, by using a blade with a specific shape, a coating with a high blending ratio of calcium carbonate of 90% by mass or more of the total pigment can be applied to the blade with a good feel and applied at a high speed of 1500 m / min or more. Can be applied.

<Planarization treatment>
After coating the coating liquid on a paper substrate, flattening a combination of an elastic roll and a metal roll, such as a super calender or soft calender, for the purpose of further improving the gloss, smoothness and printability of the coating layer Depending on the equipment, the coated paper for printing can be flattened. Unlike conventional machine calenders, such flattening equipment treats the surface of the paper with a wide surface at a high temperature so that it can be flattened without excessively increasing the density of the base paper or the coating layer. For example, a suitable printing surface can be formed in offset printing, electrophotographic printing, and the like.

  Among them, a multi-nip calender (especially, a multi-nip calender with 6 steps, 8 steps or 10 steps) is optimal because it is easy to adjust the nip pressure and the gloss and flatness of the coated surface. Moreover, as an installation place of a calendar, an on-machine type integrated with a paper machine and a coating machine is preferable. With the on-machine type, flattening can be performed immediately after papermaking and coating with a high paper surface temperature. Is preferable because of a low decrease in paper strength.

  In particular, in the matte tone and dull tone coated paper having a coating layer in which heavy calcium carbonate is highly blended with 90% by mass or more of the total pigment, in order to improve the flatness without improving the white paper glossiness, When HES and styrene-butadiene latex are blended in the coating solution and flattened with a multi-nip calender immediately after papermaking and coating, a matte and dull-coated paper with superior surface feel can be obtained. Since it is obtained, it is preferable.

  The linear pressure, temperature, and speed of the flattening process with a soft calender are not particularly limited, but the smoothness of the coated layer after the treatment is sufficiently improved, and the final strength of the coated paper is not excessive. In order to achieve this, for example, it is preferable to adjust the linear pressure to 10 to 100 kN / m, the metal roll temperature to 100 to 200 ° C., and the speed to 1500 m / min to 2000 m / min.

  In addition to the above, the manufacturing system may use an off-machine coater in which the paper machine and the coater part are separated, or a system including an off-machine calendar in which the paper machine and the soft calendar are separated.

The basis weight of the coated paper for printing thus obtained is measured in accordance with the method described in JIS P8124 `` Method for measuring basis weight '' from the viewpoint of ensuring the paper quality strength, and is 30 g / m ² or more and 200 g / m ² or less. It is preferably 50 g / m ² or more and 170 g / m ² or less. When the basis weight is less than 30 g / m ² , it is difficult to ensure the paper strength, and there is a possibility that an operation trouble such as a paper break at the time of printing may occur. On the other hand, if the basis weight exceeds 200 g / m ² , it will be difficult to achieve weight reduction and resource saving that have been required in recent years.

  In the coated paper for printing and the method for producing the same of the present invention, only one coating layer composed of a pigment and an adhesive may be applied on the paper substrate, or two or more layers may be applied. In the case of two or more layers, it is preferable that both the undercoat coating layer and the topcoat coating layer are the coating method of the present invention. The undercoat coating layer may be provided by a coating method other than the present invention, but at least the outermost coating layer needs to be the coating method of the present invention. As the paper substrate, uncoated paper or base paper coated with a water-soluble polymer such as starch or polyvinyl alcohol, or coated paper coated with an adhesive and a pigment may be used.

[Example]
(Doctor blade)
The doctor blade of the blade coater has the shape shown in FIG. 1 and FIG. 2 and has a surface hardened portion mainly composed of tungsten by thermal spraying on a base material made of carbon tool steel (SK material). used. On the rake face of the surface hardened portion, a tip portion and two bent portions (first bent portion and second bent portion) were provided, and the tip portion and the first bent portion were subjected to R processing of 0.1 mm. The Vickers hardness of the surface hardened portion was 1000 Hv. S1 and S2 are as shown in Table 1 described later, S3 is 0.635 mm, and S4 is 0.300 mm.

(Coating fluid)
The coating liquid prepared at the ratio shown in Table 1 was applied so as to have the coating amount shown in Table 1. The pigments and chemicals used are as follows.

(1) Pigment ・ Heavy calcium carbonate (Product number: Hydro curve 90K, manufactured by Omiya Korea)
・ Light calcium carbonate (Product number: Tama Pearl TP-121-6S, manufactured by Okutama Kogyo Co., Ltd.)
・ Fine granulated kaolin clay (Product number: Kaofine, manufactured by Imeris)
(2) Adhesive-Styrene-butadiene copolymer latex Tilted structure: (Part number: PA-6082, manufactured by Nippon A & L Co., Ltd.)
Single structure: (Part number: PA-2070, manufactured by Nippon A & L)
・ Water-soluble polymer HES: Hydroxyethyl etherified starch (Product No .: K96F, manufactured by GPC)
Phosphoric acid: Phosphate esterified starch (Product No .: MS4600, manufactured by Nippon Food Processing Co., Ltd.)
PVA: Polyvinyl alcohol (Product number: PVA-110, manufactured by Kuraray Co., Ltd.)

(Manufacturing procedure)
LBKP (hardwood bleached kraft pulp) and NBKP (softwood bleached kraft pulp) are blended at a mass ratio of 80:20 as raw material pulp, and the internal additive sizing agent (part number) : AK-720H, manufactured by Harima Chemicals Co., Ltd.) 0.02% by mass, cationized starch (Product No .: Amilofax T-2600, manufactured by Abebe Japan Co., Ltd.) 1.0% by mass, and yield improver (Product No .: NP442, Nissan) A pulp slurry was obtained by adding 0.02% by mass of Eka Chemicals Co., Ltd.

  Next, coating for printing at the winder part using a papermaking system including wire part, press part, pre-dryer part, undercoater part, afterdryer part, top coater part, scuff dryer part, calendar part, reel part Finished on paper.

First, the pulp slurry was made with a wire part, and then subjected to a press part and a pre-dryer part to produce a paper base having a basis weight of 37 to 55 g / m ² . Next, undercoater part, sizing agent (Harsize AK720H, manufactured by Harima Kasei Co., Ltd.) was undercoated on both sides of the paper substrate so as to be 0.5 g / m ² per side, and dried with an after dryer part. Thereafter, the top coater shown in Table 1 was applied at the top coater part using a blade coater having a doctor blade having the shape shown in Table 1 described later. In Comparative Example 7 and Comparative Example 8, a blade without a bent portion was used.

The coating layer was coated on both sides so that the coating amount (g / m ² ) shown in Table 1 per side was produced, and a coated paper for printing having a basis weight of 60 g / m ² was produced. Drying equipment was performed using IRT (infrared dryer) and hot air drying (scuff dryer).

  Next, the calender part was flattened at a linear pressure of 50 kN / m and at a speed of 1800 m / min, and used for a winder part to obtain a coated paper for printing. However, the flattening process was performed only at Example 30 at a speed of 1500 m / min.

  In addition, paper was made using a gap former in the wire part, a rod metering size press coater was used in the undercoater part, and a blade coater was used in the top coater part. In the calendar part, a multi-nip calendar was used. In the examples and comparative examples, an on-machine system in which the wire part to the calendar part were integrated was used. For this reason, the flattening speed of the calendar part becomes the paper making speed and the coating speed.

  The thus-obtained printing papers of Examples and Comparative Examples were examined for whiteness, texture, and printability by the following methods. The results are shown in Tables 1 and 2.

(A) Whiteness
Measured according to JIS P8148 (2001) “Paper, paperboard and pulp—Method of measuring ISO whiteness (diffuse blue reflectance)”.

(B) Surface feeling The minute coating unevenness generated on the coated paper surface was evaluated based on the following evaluation criteria.
◎: Minute coating unevenness does not occur, surface feeling is particularly good and can be used practically ○: Small coating unevenness slightly occurs, but surface feeling is sufficiently good and practical use △: Minute coating Some unevenness has occurred, but the surface feel is good and can be used practically ×: Small coating unevenness has occurred, the surface feeling is poor and cannot be used in practice

(C) Printing suitability For printing with color ink (Part No .: ADVAN, manufactured by Dainippon Ink & Chemicals, Inc.) using an offset printer (model number: Lithopia L-BT3-1100, manufactured by Mitsubishi Heavy Industries, Ltd.) 5000 copies of 4-color printing were performed on the coated paper. About 5000 parts of the printed surface, the printing unevenness of the printed surface was observed visually and with a magnifying glass (10 times), and the degree thereof was evaluated based on the following evaluation criteria.
◎: No printing unevenness ○: Printing unevenness slightly occurred but practical use △: Printing unevenness slightly occurred and slightly poor printability, but practical use possible ×: Actual use because many printing unevenness occurred impossible

  In Table 1 and Table 2, the mass% of the pigment indicates the ratio of heavy calcium carbonate, light calcium carbonate and fine kaolin clay to the whole pigment. For example, “calcium carbonate 80, clay 20” means “the pigment is a mixture of 80% by mass of heavy calcium carbonate and 20% by mass of fine kaolin”. In Tables 1 and 2, heavy calcium carbonate is indicated as “heavy cal”, and light calcium carbonate is indicated as “light cal”.

  Further, in the doctor blades used in Comparative Example 7 and Comparative Example 8 shown in Table 2, the rake face of the surface hardened portion is a single flat surface, and there is no bent portion in the rake face.

  As is clear from Tables 1 and 2, in each example, a blade having a specific shape is used. Even when coating was performed at the above coating speed, coating unevenness hardly occurred and a uniform coating was obtained. The obtained coated paper for printing had high whiteness, good surface feel, and good printability. However, in Comparative Examples 1 to 8, the above effects were not obtained.

  In addition, when S1 was set to 1, it was also confirmed that S2 is preferably 0.25 or more and 0.67 or less, and more preferably 0.32 or more and 0.56 or less.

It is a top view of the doctor blade used with the manufacturing method of the coated paper for printing based on one Embodiment of this invention. It is AA sectional drawing of FIG. It is an enlarged view of the contact part of the doctor blade and the coating material on a paper base material in a blade coater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Doctor blade 2 Base material 2a Lower surface of base material 2b Land surface 2c Rake surface 3 Surface hardening part 3a Upper surface of surface hardening part 3b Land surface of surface hardening part 4 Bevel surface 4a Tip part 4b First bending part 4c First Two bent portions 4d First inclined portion 4e Second inclined portion S1 Length from the leading end portion to the first bent portion S2 Total length from the first bent portion to the final bent portion 11 Backing roll 12 Paper base material 13 Coating Liquid 14 Coating surface 15 Liquid pool

Claims (5)

A coated paper for printing in which a coating liquid containing a pigment and an adhesive is applied to the surface of a paper substrate to provide a coating layer,
The coating liquid used for the coating of at least the outermost layer of the coating layer has a ratio of calcium carbonate in the pigment of 90% by mass or more, and contains hydroxyethyl starch as the adhesive,
The coating layer is provided by a blade coater,
The doctor blade of the blade coater is provided with a surface hardened portion so as to cover the vicinity of the tip portion on the rake face side of the base material,
The surface hardened portion on the rake face side is provided with two or more bent portions,
The length (S1) from the tip portion of the rake face to the first bent portion closest to the tip portion of the rake face is from the first bent portion to the final bent portion farthest from the rake face tip portion. Longer than the total length (S2),
The coated paper for printing characterized by the above-mentioned.   The coated paper for printing according to claim 1, wherein the adhesive further contains a styrene-butadiene latex, and a mass ratio in terms of solid content of the styrene-butadiene latex with respect to hydroxylethyl starch is 1.4 or more and 7.0 or less.   The coated paper for printing according to claim 1 or 2, wherein (S1) is 300 µm or more and 400 µm or less.   The coated paper for printing according to any one of claims 1 to 3, wherein (S2) is 100 µm or more and 200 µm or less. A method for producing a coated paper for printing in which a coating liquid containing a pigment and an adhesive is applied to the surface of a paper substrate to provide a coating layer,
The coating liquid used for the coating of at least the outermost layer of the coating layer has a ratio of calcium carbonate in the pigment of 90% by mass or more, and contains hydroxyethyl starch as the adhesive,
The coating layer is provided by a blade coater,
The doctor blade of the blade coater is provided with a surface hardened portion so as to cover the vicinity of the tip portion on the rake face side of the base material,
The surface hardened portion on the rake face side is provided with two or more bent portions,
The length (S1) from the tip portion of the rake face to the first bent portion closest to the tip portion of the rake face is from the first bent portion to the final bent portion farthest from the rake face tip portion. Longer than the total length (S2),
A method for producing a coated paper for printing.

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