JP2008127711A - Lightweight coated paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight coated paper having two coating layers composed mainly of a pigment and an adhesive on one surface of a base paper by a blade coating method, having excellent high-speed coating performance at a low coating rate of both of the undercoating layer and the top-coating layer, and having excellent bulkiness, sheet gloss and smoothness of a white paper and a printed paper. <P>SOLUTION: The lightweight coated paper has two coated layers composed mainly of a pigment and an adhesive on one surface of a base paper by a blade coating method. The base paper contains a filler having at least one kind selected from among an amorphous silica and an amorphous silicate in an amount of 1-10 mass% based on the mass of the base paper, the top-coating layer of the coated layer contains a kaolin having a specific average particle diameter and a specific Hercules viscosity as a pigment in an amount of 30-70 mass% based on the total pigment, and a ground calcium carbonate having a specific average particle diameter and particle size distribution in an amount of 30-70 mass% based on the total pigment, and the coating amount in the top-coating layer is 4-7 g/m<SP>2</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light-weight coated paper, and more particularly to a light-weight coated paper that is excellent in high-speed coating properties, bulky, and excellent in white paper gloss, white paper, and smoothness after printing.

  Coated paper for printing is generally manufactured by providing a coating layer mainly composed of pigment and adhesive on the base paper, and is used for cast coated paper, art paper, coated paper, lightweight coated paper, fine coated paper, etc. being classified. These coated papers for printing are mainly used as multicolor printed materials such as posters, catalogs, flyers and other commercial printed materials, books and magazines. In recent years, these printing coated papers have been upgraded and the shift from art papers and coated papers to lightweight coated papers has been progressing due to the trend toward cost reduction. High quality has come to be demanded due to the bulkiness, white paper smoothness, print reproducibility, etc. for printing workability and ease of handling of printed matter.

  For this reason, there are methods for increasing the bulkiness, such as reducing the press pressure and machine calender pressure during papermaking, and reducing the density of the base paper by blending mechanical pulp, etc. There is a drawback that the smoothness of the paper is also greatly reduced.

Also, blade coaters, air knife coaters, bar coaters are used to obtain a coated paper for printing having a coating surface with high smoothness by applying a coating liquid mainly composed of a pigment and an adhesive. Among coating methods using various coaters such as curtain coaters and gate roll coaters, blade coaters are the most excellent. However, the problem of high-speed coating with a blade coater is the generation of solids due to destabilization of the coating liquid at the blade tip and the occurrence of defects such as streaks and scratches. The harder it gets, the harder it gets. In particular, in a light-weight coated paper having a basis weight of 80 g / m ² or less and a single-side single coating amount of about 7 to 10 g / m ^2, about 5 g / m ² by a blade coating method. It is very difficult to uniformly apply a low coating amount by double coating, and there are even more severe ones in high-speed coating at 1000 m / min or more. For this reason, Patent Document 1 proposes a lightweight coated paper manufacturing method in which a low coating amount is applied at high speed by a film transfer coating method different from the blade coating method. In contrast, the covering property of the surface of the base paper is inferior, and in addition to white paper properties such as smoothness and white paper gloss, printing suitability such as printing smoothness and printing gloss is also inferior.

  Patent Document 2 discloses a method of manufacturing a coated paper by scraping a coating solution having a high solid content concentration containing specific kaolin and calcium carbonate in a short time in blade coating. It is insufficient as a proposal for obtaining high-speed coating suitability, gloss, smoothness and the like required in a low coating amount region.

Further, in Patent Document 3, it is proposed to apply a coating liquid having a specific heavy calcium carbonate and a specific latex in order to obtain a high-quality coated paper without uneven gloss in blade coating. Yes. In Patent Document 4, the particle size of the pigment in the coating composition is specified to improve the fluidity under a high shear rate, and to improve the workability in coating at a high solid content concentration. Has been proposed. Further, Patent Document 5 discloses a coating paper for printing having at least two coating layers containing a pigment and an adhesive on a base paper, and the coating layer contains kaolin and calcium carbonate having a specific particle size. There have been proposals that specify the standard deviation of whiteness and glossiness of industrial paper. However, these proposals all improve the high-speed coating property by blade coating in a low coating amount region of 7 g / m ² or less, and are not suitable for obtaining a light-weight coated paper having high bulkiness, glossiness and smoothness. It is enough.

JP-A-9-302596 JP 59-30992 A Japanese Patent Laid-Open No. 11-50390 JP-A-57-176297 JP 2004-91997 A

Conventionally, the coating amount of lightweight coated paper is usually around 7 to 10 g / m ^{2 on} one side, but when a lower coating amount is carried out, the solid content concentration of the pigment coating solution is lowered or the pressure of the blade is pressed. It is necessary to control the coating amount by increasing the thickness. All of these measures deteriorate the coverage of the base paper surface, resulting in a decrease in smoothness and uniformity in the width direction. Further, when a smoothing process such as a multi-stage calendar is strengthened in order to improve smoothness, the density becomes higher than the density of about 1.20 g / m ² and the bulk is reduced, and the rigidity is also lowered. In order to improve the smoothness and print reproducibility of the coated surface, it is effective to add a large amount of kaolin, which is a flat pigment, but the viscosity of the coating liquid increases and high-speed coating properties are improved. descend. For this reason, it is necessary to take measures such as lowering the coating concentration, and the required smoothness and printing gloss cannot be obtained. Accordingly, an object of the present invention is to provide a light-weight coated paper in which two layers of a coating layer mainly composed of a pigment and an adhesive are provided on one side of the base paper. An object of the present invention is to provide a lightweight coated paper that is excellent in high-speed coating by a blade coating method with a low coating amount for both the topcoat layer, bulky, white paper gloss, white paper, and smoothness after white paper printing.

The inventors of the present invention have completed the present invention as a result of repeated studies for improving the bulkiness of the base paper and the high-speed coating suitability in the blade coater, white paper gloss and smoothness, which are the above-mentioned problems. That is, in a light-weight coated paper in which a coating layer mainly composed of a pigment and an adhesive is provided on a base paper by a blade coating method on one side, the base paper is made of amorphous silica or amorphous silicate as a filler. A pigment having at least one kind contained in an amount of 1 to 10% by mass relative to the mass of the base paper, the overcoat layer of the coating layer having a mean particle size of 0.2 to 0.5 μm as a pigment component, and a solid content concentration of 72% by mass Kaolin having a Hercules viscosity of 8 mPa · s or less at a shear rate of 9000 sec ⁻¹ of the slurry is 30 to 70% by mass of the total pigment, and further has an average particle size of 0.5 to 1.0 μm and a particle size of 2 μm or less. Light weight coating characterized in that heavy calcium carbonate having 95% by volume or more is contained in an amount of 30 to 70% by mass of the total pigment, and the coating amount of the overcoat layer is 4 to 7 g / m ^2. Paper. Furthermore, in the present invention, the undercoat layer comprises heavy calcium carbonate having an average particle size of 0.5 to 1.5 μm as a pigment component and 90% by volume or more of a particle size of 2 μm or less of 80 to 100 of all pigments. By coating so that the coating amount of the undercoat layer is 4 to 7 g / m ² , it is possible to obtain a lightweight coated paper that is superior in terms of white paper gloss, white paper, and smoothness after printing. preferable.

  According to the present invention, the base paper contains at least one of amorphous silica or amorphous silicate as a filler to ensure bulkiness, and the top coat of the coating layer provided on the base paper by two blade coating methods. By containing a specific kaolin and heavy calcium carbonate in the layer, and more preferably by providing a specific heavy calcium carbonate in the undercoat layer, it is excellent in high-speed coating property at a low coating amount, and has a gloss of blank paper, a blank paper and A lightweight coated paper having a quality excellent in smoothness after printing can be obtained.

Hereinafter, the present invention will be described in detail.
The base paper used in the present invention comprises a pulp component and a filler as main components. As a pulp component, waste paper pulp made from various waste papers as well as chemical pulps such as softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP) can be appropriately blended and used. However, in order to obtain a coated paper having sufficient smoothness, the pulp component of the base paper is composed only of chemical pulp, or it is classified into old paper (for example, upper white and card) that does not contain mechanical pulp. It is desirable to use waste paper pulp made from used paper (used paper classified as imitation / color). The bleaching method for producing the chemical pulp is not particularly limited, but ECF pulp bleached without using molecular chlorine such as chlorine gas in the bleaching process, and further chlorine-based compounds such as chlorine dioxide. The TCF pulp bleached without using it is preferably used from the viewpoint of environmental protection.

In the present invention, it is important to internally add at least one of amorphous silica or amorphous silicate as a filler for the base paper, and bulkiness can be obtained by this addition. Examples of the amorphous silica used include white carbon and hydrous silicic acid. Amorphous silicates include general formulas xM ₂ O · ySiO ₂ , xMO · ySiO ₂ , xM ₂ O ₃ · ySiO _2, etc. (M is Al, Ca, Mg, Na, etc .: x and y are any positive numbers) The thing which consists of a silicate represented by these and / or silicon dioxide, and a metal oxide is illustrated.

  The average particle diameter of amorphous silica and amorphous silicate is preferably 16 to 40 μm. When the average particle diameter is less than 16 μm, the bulkiness effect when blended into paper is poor, and when the average particle diameter exceeds 40 μm, the surface strength is reduced due to the dropout of coarse particles present on the paper surface. There is. In addition, the average particle diameter said here is a particle diameter in 50% of volume integration of the particle size distribution measured by the laser diffraction method using SALD2100 (made by Shimadzu Corporation).

Furthermore, amorphous silica and amorphous silicate are more preferable if the specific surface area is 10 to 150 m ² / g and the pore diameter is 0.10 to 0.80 μm. Incidentally, if the specific surface area is more than 10 m 2 / ^g and less than 150 meters 2 / ^g, the pressing pressure, easily collapsed calendering pressure, in addition to bulky when internally added to the paper is insufficient, the particle size distribution is poor As a result, fine particles and coarse particles are increased, and the base paper interlayer strength and surface strength are lowered. In addition, when the pore diameter is less than 0.10 μm and exceeds 0.80 μm, it tends to be crushed by the press pressure and calendering pressure, and the bulkiness when internally added to paper becomes insufficient. Here, the specific surface area is the surface area of all pores assuming that the pore shape is a geometric cylinder using a pore sizer 9230 (manufactured by Shimadzu Corporation), and is the pressure in the measurement range and the amount of mercury injected. The value obtained from the relationship. The pore diameter is a median pore diameter obtained from an integral specific surface area curve using a pore sizer 9230 (manufactured by Shimadzu Corporation).

  Amorphous silica and amorphous silicate are preferably those having a bulk specific gravity of 0.3 g / ml or less measured according to JIS K-5101 (static method). When amorphous silica or amorphous silicate having a bulk specific gravity exceeding 0.3 g / ml is used, a base paper having a sufficient paper thickness cannot be obtained. However, since the interlayer strength of the base paper decreases as the bulk specific gravity decreases, it is necessary to take measures against the strength of the base paper, so that the bulk specific gravity is more preferably 0.05 to 0.2 g / ml. In the present invention, when amorphous silica or amorphous silicate satisfies all of the specific surface area, pore diameter, average particle diameter and bulk specific gravity defined here, it is easy to balance the reduction in density of the base paper and the maintenance of the interlayer strength. More preferably used. The amount used as a filler is added so as to be 1 to 10% by mass with respect to the mass of the base paper to prepare the paper stock. Incidentally, if it is less than 1% by mass, a sufficiently low density cannot be obtained. Conversely, if it exceeds 10% by mass, the bond between pulp fibers is weakened and the strength cannot be maintained.

  Here, other than the amorphous silica or the amorphous silicate, other fillers such as talc, kaolin, heavy calcium carbonate, light, for the purpose of adjusting the papermaking suitability and the strength characteristics of the base paper within the range not inhibiting the desired effect of the present invention. At least one of calcium carbonate and titanium oxide may be used in combination.

  In addition, paper-making chemicals that are used for ordinary acid and neutral paper-making materials, such as rosin sizing agent, reinforced rosin sizing agent, emulsion sizing agent, alkyl ketene dimer sizing agent, size fixing agent, drying A paper strength enhancer, a wet strength enhancer, a yield improver, a freeness improver, a water resistance agent, an antifoaming agent, a slime control agent, a dye, and the like are added as necessary.

It is obtained by making paper with a mixture of the above materials with various paper machines such as a long net machine, a round net machine, a long net and round net combination machine, a twin wire machine, an on-top wire machine, and a gap former machine. A base paper having a basis weight of about 30 to 60 g / m ² is used as the support of the present invention. The base paper is a surface made of an adhesive such as starch, polyvinyl alcohol, or polyacrylamide, if necessary, using a blade metering size press, a rod metering size press, a gate roll coater, a bill blade coater, or a two roll size press. A treating agent can be applied. In addition to the above surface treatment agents, surface sizing agents usually used in the papermaking field, antifoaming agents, preservatives, thickeners, and conductive agents such as sodium carbonate, disodium hydrogen phosphate, trisodium phosphate, chloride It is also possible to use a salt such as sodium as appropriate.

In the light-weight coated paper of the present invention, two coating layers mainly composed of a pigment and an adhesive are provided on one side of the base paper, and kaolin which is one of the pigments is contained in the top coating layer of the coated layer. Is essential because it is highly effective in producing orientation and smooth surfaces when applied with a blade, and by smoothing the coated paper with the desired smoothness and gloss. It is. Therefore, as a result of examination together with the knowledge that the fluidity of the coating solution for obtaining the high-speed coating property required in the present invention is greatly influenced by kaolin, a more suitable kaolin was found. That is, the use of kaolin having an average particle diameter of 0.2 to 0.5 μm and a herbless viscosity of 8 mPa · s or less at a shear rate of 9000 sec ⁻¹ in a pigment slurry having a solid content of 72% by mass. . Here, in order to optimize the behavior in higher-speed coating, the average particle size alone is not sufficient, and it is important to consider the Hercules viscosity characteristics at a shear rate of 9000 sec ⁻¹ . Incidentally, when the Hercules viscosity exceeds 8 mPa · s, the fluidity of the coating liquid is remarkably lowered, and it becomes difficult to control the target low coating amount. On the other hand, when the average particle diameter exceeds 0.5 μm, the fluidity is lowered and the glossiness is also lowered. On the other hand, if the thickness is less than 0.2 μm, the strength of the coated surface becomes weak and the printability is poor. The kaolin content in the overcoat layer of the coating layer is 30 to 70% by mass, and desirable high-speed coating properties, gloss and smoothness can be obtained. More preferably, it is 35-65 mass%. Incidentally, if it is less than 30% by mass, satisfactory smoothness cannot be obtained. On the other hand, if it exceeds 70% by mass, the high-speed coating property is adversely affected.

  Furthermore, as a pigment other than the above kaolin used in the overcoat layer, it exhibits excellent fluidity even when the solid content concentration of the pigment slurry is 70% by mass or more, and the viscosity under a higher shear rate can be obtained by mixing with kaolin. It is essential to use heavy calcium carbonate that can reduce the viscosity and obtain stable coating performance. However, since the blending of heavy calcium carbonate lowers the smoothness and glossiness, the average particle diameter is 0.5 to 1.0 μm in order to obtain characteristics excellent in fluidity, smoothness and glossiness. In addition, heavy calcium carbonate having a particle size distribution with a particle diameter of 2 μm or less of 95% by volume or more is used. Incidentally, if the average particle diameter is less than 0.5 μm, the fluidity tends to be inferior, and if it exceeds 1.0 μm, the coarse particles increase, resulting in poor smoothness and gloss. Further, heavy calcium carbonate having a particle diameter of 2 μm or less and less than 95% by volume is inferior in smoothness due to an increase in coarse particles. The content in the topcoat layer is 30 to 70% by mass, and desirable high-speed coating properties, gloss and smoothness can be obtained. More preferably, it is 35-65 mass%. Incidentally, if it is less than 30% by mass, long-term coating stability cannot be obtained, and if it exceeds 70% by mass, sufficient white paper gloss, white paper smoothness and printing smoothness cannot be obtained.

The undercoat layer in the present invention covers high-speed coating suitability such as water retention of the topcoat coating solution, and is effective for ensuring high smoothness and print gloss, which are the quality of the final product, and in terms of cost. is there. Usually, by providing an undercoat layer, the surface smoothness is increased, and defects such as streaks and scratches are likely to occur when the overcoat layer is applied, but this is solved by applying the overcoat layer coating liquid of the present invention. I can do it. Here, the undercoat layer may be applied as it is with the coating solution of the overcoat layer, and is not particularly limited, but the average particle size as a pigment component is 0.5 to 1.5 μm or less and 2 μm or less. By containing 80 to 100% by weight of heavy calcium carbonate having a particle diameter of 90% by volume or more, high-speed coating suitability and superior undercoating effect due to the good fluidity of heavy calcium carbonate can be achieved by blade coating. This is a preferred embodiment because it can be obtained by work. The coating amount of the undercoat layer is preferably 4 g / m ² or more in terms of dry weight per side from the viewpoint of coatability of the coated surface, and is 7 g / m ² or less within a range not departing from the grade of the light coated paper. Preferably there is.

  As the components constituting the undercoat layer and the overcoat layer of the present invention, the above-mentioned specific kaolin and specific heavy calcium carbonate are mainly used. However, other pigment components such as delaminator can be used as long as the characteristics can be maintained. Ted kaolin, talc, satin white, light calcium carbonate, heavy calcium carbonate, calcium sulfite, gypsum, barium sulfate, white carbon, calcined kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide , Magnesium hydroxide, Zinc hydroxide, Zinc oxide, Magnesium oxide, Bentonite, Sericite and other inorganic pigments, Polystyrene resin fine particles, Urea formalin resin fine particles, Hollow plastic pigments, Porous fine particle plastic pigments, etc. Conventional A combination of one or more kinds of various pigments which are al used appropriately can be used.

  Furthermore, examples of the adhesive used together with the pigment component constituting the undercoat layer and the overcoat layer include proteins such as casein and soybean protein, and conjugates such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer. Diene polymer latex, acrylic polymer latex such as acrylic acid ester and methacrylic acid ester polymer or copolymer, vinyl polymer latex such as ethylene-vinyl acetate copolymer, or various types of these polymers Synthetic resins such as alkali-soluble or alkali-insoluble polymer latexes, polyvinyl alcohols, olefin-maleic anhydride resins, melamine resins obtained by functionally modifying copolymers with functional group-containing monomers such as carboxyl groups Adhesive, positive starch, oxidized starch, phosphate esterified starch Starches such as enzyme modified starch, carboxymethyl cellulose, cellulose derivatives such as hydroxyethyl cellulose, various adhesives known for general coated paper is used alone or in combination. The total amount of the adhesive used is about 3 to 15 parts by mass per 100 parts by mass of the pigment.

  In addition to the above-mentioned pigments and adhesives, the coating solution contains a lubricant such as a polyolefin resin, a fatty acid emulsion, a fatty acid salt emulsion, and a wax emulsion as an auxiliary agent, an alkali thickening acrylic emulsion, and a polyacrylate. It is also possible to add water retention agents such as various water resistance agents, printability improvers, antifoaming agents, colorants, mold release agents, flow modifiers, preservatives and the like as necessary.

In the present invention, the coating amount of the topcoat layer on the base paper coated with the undercoat layer and dried is 4 to 7 g / m ² in terms of dry weight per side. Incidentally, if it is less than 4 g / m ² , since there is a smoother undercoat layer than ordinary base paper, it is difficult to control the coating amount, and there is a concern that defects such as deterioration in smoothness and streaks may occur. On the other hand, if it exceeds 7 g / m ² , it is necessary to reduce the basis weight of the base paper, and the paper strength may be reduced, which may cause a paper break at the time of coating or printing.

  The above-mentioned coating composition liquid for the undercoat layer and the overcoat layer is prepared on-machine or capable of high-speed coating of 1000 m / min or more after the solid content concentration is adjusted to about 60 to 70% by mass, preferably 61 to 65% by mass. It is applied with an off-machine blade coater. As the blade coater, various blade coaters such as a bevel or bent type coater, a rod blade, and a short dwell are used. The blade used for coating the coating liquid has a tip wedge part angle of 42 degrees or more, preferably 45 degrees or more, and further has two wedge parts to reduce the coating amount. A machined one with a reduced blade surface length is preferably used. The blade thickness is appropriately selected from 0.5 mm to 0.7 mm depending on the coating amount. As the material of the blade, SK steel is used, but the surface of the coating layer and the surface of the blade coated with a ceramic to increase the life of the blade, and the one subjected to plating treatment are preferably used.

  As a method of drying the coating layer immediately after coating with the blade, for example, various drying methods such as a heating cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, an infrared heater dryer, etc. may be used alone or in combination. Can do.

  The lightweight coated paper thus obtained is smoothed by a multi-stage super calender or a soft calender consisting of a metal roll and a resin elastic roll as necessary. Calendar conditions such as pressure and paper feeding speed are not particularly limited, and are appropriately adjusted according to required quality.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In the examples, “parts” and “%” indicate parts by mass and mass% unless otherwise specified.

Example 1
<Making paper>
Amorphous silicate (average particle size: 18.0 μm, bulk specific gravity: 0.12 g / ml, specific surface area 60 m ² / g, fine as a filler in a pulp slurry consisting of 70 parts LBKP (400 ml freeness) and 30 parts NBKP (500 ml freeness) (A pore size of 0.21 μm) is added so as to be 8% by mass with respect to the mass of the base paper, and further, an alkyl ketene dimer type sizing agent (trade name: Size Pine K-902, manufactured by Arakawa Chemical Industries) 0.1 % And aluminum sulphate 0.2% were added at a paper making speed of 1200 m / min using an on-top wire machine, and polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.) using a gate roll size press coater. ) And starch (trade name: Ace A, manufactured by Oji Cornstarch Co., Ltd.) 4: 1 mixed solution 5%, solid content on both sides is 2 g / Give the base paper of the coated basis weight 45 g / ^{m 2} such that ^{m 2.}

<Preparation of topcoat coating solution>
A fine kaolin having a Hercules viscosity of 6.9 mPa · s at a shear rate of 9000 sec ⁻¹ and a mean particle size of 0.4 μm in a pigment slurry having a solid content of 72% by mass (trade name: Amazon Plus, manufactured by Caddam Corp. Kaolin A) 40 parts, fine heavy calcium carbonate having an average particle size of 0.7 μm and a particle size of 2 μm or less of 99% by volume (trade name: Seta Curve HG, manufactured by Bihoku Flour & Chemical Co., Ltd., Heavy Calcium Carbonate A) 60 Part is added to water in which 0.2 part of sodium polyacrylate (in terms of solid content) is added to the pigment as a dispersant, and dispersed using a Cowles disperser, and the pigment slurry having a solid content concentration of 70% Was prepared. As an adhesive to this slurry, oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstarch Co., Ltd.) 2 parts (in terms of solid content), carboxy-modified styrene-butadiene copolymer latex (trade names: OJ-2000, manufactured by JSR) ) 8 parts (in terms of solid content) were added, and water was further added to prepare a top coat solution having a solid content concentration of 63%.

<Preparation of undercoat coating solution>
As a pigment, 100 parts of heavy calcium carbonate (trade name: FMT-90, manufactured by Pfematech Co., Ltd., Heavy Calcium Carbonate B) having an average particle size of 1.3 μm and a particle size of 2 μm or less of 90% by volume is used as a dispersant. In addition to water added with 0.4 part of sodium polyacrylate (converted to solid content) with respect to the pigment, it was dispersed using a Cowles disperser to prepare a pigment slurry having a solid content concentration of 73%. Oxidized starch (trade name: Oji Ace A: manufactured by Oji Cornstarch Co., Ltd.) 3 parts (solid content conversion), carboxy-modified styrene-butadiene copolymer latex (trade name: OJ-2000, manufactured by JSR) 6 Parts (in terms of solid content) were added, and water was further added to prepare an undercoat coating solution having a solid content concentration of 61%.

<Production of lightweight coated paper>
Using a blade coater using an off-machine ceramic blade, the base coating solution having a basis weight of 45 g / m ² was applied at a coating speed of 1200 m / min. After coating / drying on both sides so as to be / m ² , the above-mentioned top coating solution was further coated and dried on both sides so that the solid content per side was 5.5 g / m ² . After that, using a soft calender consisting of a resin roll with a shore hardness of 94 ° and a metal roll with a surface temperature adjusted to 180 ° C., a linear pressure of 80 kN / m and a smoothing treatment at 2 nips are performed to reduce the weight of the coating. I got paper.

Example 2
A light-weight coated paper was obtained in the same manner as in Example 1 except that in the preparation of the top coat liquid of Example 1, kaolin A was changed to 30 parts and heavy calcium carbonate A was changed to 70 parts.

Example 3
A light-weight coated paper was obtained in the same manner as in Example 1 except that in the preparation of the top coat liquid of Example 1, kaolin A was changed to 70 parts and heavy calcium carbonate A was changed to 30 parts.

Example 4
A light-weight coated paper was obtained in the same manner as in Example 1 except that the light-weight coated paper of Example 1 was made with a coating speed of 1400 m / min.

Comparative Example 1
A light-weight coated paper was obtained in the same manner as in Example 1 except that the amorphous silicate filler was added in an amount of 0.5% by mass based on the mass of the base paper in the papermaking of Example 1.

Comparative Example 2
A light-weight coated paper was obtained in the same manner as in Example 1 except that the amorphous silicate filler was added in an amount of 12% by mass based on the mass of the base paper in the paper making of the base paper of Example 1.

Comparative Example 3
In Example 1, a light-weight coated paper was obtained in the same manner as in Example 1 except that only the topcoat coating solution was applied without applying the undercoat coating solution.

Comparative Example 4
In the production of the base paper of Example 1, a lightweight coating was applied in the same manner as in Example 1 except that the amorphous silicate of the filler was changed to light calcium carbonate (trade name: TP-121, manufactured by Okutama Kogyo Co., Ltd.). I got paper.

Comparative Example 5
In the preparation of the top coat liquid of Example 1, the Hercules viscosity at a shear rate of 9000 sec ⁻¹ of kaolin A having an average particle diameter of 0.4 μm and a solid content concentration of 72% by mass of 9000 sec ⁻¹ is 10.4 mPa · s. A light-weight coated paper was obtained in the same manner as in Example 1 except that it was changed to fine kaolin (trade name: Hydra Gloss 90, Engelhard Corp., Kaolin B). The coating amount of the top coat at this time was 8 g / m ² .

Comparative Example 6
In the preparation of the top coat liquid of Example 1, the Hercules viscosity at a shear rate of 9000 sec ⁻¹ of kaolin A having an average particle diameter of 0.6 μm and a solid content concentration of 72% by mass of 9000 sec ⁻¹ is 11.3 mPa · s. A light-weight coated paper was obtained in the same manner as in Example 1 except that it was changed to fine kaolin (trade name: Kao Fine, manufactured by Seal Co., Ltd., Kaolin C). The coating amount of the top coat at this time was 8 g / m ² .

Comparative Example 7
In the preparation of the top coat liquid of Example 1, the Hercules viscosity at a shear rate of 9000 sec ⁻¹ of kaolin A having an average particle diameter of 1.17 μm and a solid content concentration of 72% by weight of 9000 sec ⁻¹ is 18.6 mPa · s. A light-weight coated paper was obtained in the same manner as in Example 1 except that it was changed to high whiteness fine kaolin (trade name: Milagros J, manufactured by Engelhard, Kaolin D). The coating amount of the top coat at this time was 8 g / m ² .

Comparative Example 8
In the preparation of the topcoat coating solution of Example 1, it was carried out except that Kaolin A was changed to Kaolin D and heavy calcium carbonate A was changed to heavy calcium carbonate B (used in the preparation of the basecoat coating solution of Example 1). A lightweight coated paper was obtained as in Example 1. The coating amount of the top coat at this time was 8 g / m ² .

Comparative Example 9
A light-weight coated paper was obtained in the same manner as in Example 1 except that in the preparation of the top coat liquid of Example 1, kaolin A was changed to 80 parts and heavy calcium carbonate A was changed to 20 parts. The coating amount of the top coat at this time was 8 g / m ² and the coating speed was 900 m / min.

Comparative Example 10
A light-weight coated paper was obtained in the same manner as in Example 1 except that Kaolin A was changed to 10 parts and heavy calcium carbonate A was changed to 90 parts of heavy calcium carbonate B in the preparation of the top coat liquid of Example 1. It was.

  The 14 kinds of lightweight coated papers thus obtained were subjected to the following evaluation tests, and the results are shown in Table 1. In addition, unless otherwise indicated, the measurement and evaluation of the lightweight coated paper in this invention were performed in the ISO environment of 23 degreeC +/- 1 degreeC and (50 +/- 2)% RH.

<Average particle diameter of pigment>
The particle size distribution was measured with a laser sedimentation type particle size distribution meter (trade name: Microtrac X-100, manufactured by Nikkiso Co., Ltd.), and the particle size was determined as 50% of volume integration.

<Hercules viscosity>
The Hercules viscosity of the kaolin slurry prepared to a solid content concentration of 72% by mass is 2200 rpm using a Hercules viscometer (trade name: Hercules type high shear viscometer HR-801CD, manufactured by Kumagaya Riki Kogyo Co., Ltd.) using B Bob The value was (shear rate 9000 sec ⁻¹ ).

<Density>
The basis weight was measured by the method prescribed in JJS P-8124, and the thickness was measured in accordance with JIS P-8118.

<Blank smoothness>
Using a digital Oken type smoothness meter (Asahi Seiko Co., Ltd.), the JAPAN TAPPI paper pulp test method no. Measured according to 5-2.

<Glossiness of blank paper>
The 75 degree glossiness was measured using a gloss meter (trade name: GM-26D, manufactured by Murakami Color Research Laboratory).

<Surface strength>
Printing was carried out using 0.6 ml of offset printing ink (SD50 Beni, manufactured by Toyo Ink Co., Ltd.) with an RI printing tester (manufactured by Ishikawajima Kikai Co., Ltd.), and the degree of paper staining on the printed surface was visually evaluated.
A: Paper smear does not occur.
○: Slight paper smearing occurs, but it is a good level as coated paper.
(Triangle | delta): Paper smear generate | occur | produces and surface strength is inferior.
X: Many paper spots occur and the surface strength is considerably inferior.

<Print smoothness>
With an RI printing tester (manufactured by Ishikawajima Kikai Co., Ltd.), 0.5 ml of offset printing ink (Value-G black: manufactured by Dainippon Ink & Chemicals, Inc.) was printed and visually evaluated.
◎: Very good ○: Good △: Inferior ×: Very inferior

  As shown in Table 1, Examples 1 to 4 are lightweight coated papers that are excellent in high-speed coating properties, bulky, and have high white paper gloss, white paper smoothness, and printing smoothness. Comparative Example 1 is inferior in strength and high bulk density due to a small amount of amorphous silicate, while Comparative Example 2 is inferior in strength due to a large amount of amorphous silicate. Comparative Example 3 is considerably inferior in smoothness and gloss because no undercoat layer is provided. Since Comparative Example 4 uses light calcium carbonate instead of amorphous silicate, it has high density, no bulkiness, and poor gloss. Since Comparative Examples 5 to 10 use a pigment having a particle diameter and / or a Hercules viscosity outside the specified range of the present invention, the coating amount is controllable, white paper gloss, smoothness, etc. Inferior. As described above, according to the present invention, it is possible to obtain a light-weight coated paper that is excellent in high-speed coating property, bulky, and excellent in white paper gloss, white paper, and smoothness after printing.

Claims (2)

In a lightweight coated paper in which a coating layer mainly composed of a pigment and an adhesive is provided on a base paper by using a blade coating method on one side, the base paper is at least one of amorphous silica or amorphous silicate as a filler. A pigment slurry containing 1 to 10% by mass of seeds based on the mass of the base paper, the overcoat layer of the coating layer having a mean particle size of 0.2 to 0.5 μm as a pigment component, and a solid content concentration of 72% by mass The kaolin having a Hercules viscosity of 8 mPa · s or less at a shear rate of 9000 sec ⁻¹ of 30 to 70% by mass of the total pigment, an average particle size of 0.5 to 1.0 μm, and a particle size of 2 μm or less is 95. Lightweight coated paper comprising 30 to 70% by weight of heavy calcium carbonate having a volume% or more of the total pigment, and coated so that the coating amount of the overcoat layer is 4 to 7 g / m ^2. . The undercoat layer of the coating layer has a heavy calcium carbonate having an average particle size of 0.5 to 1.5 μm as a pigment component and a particle size of 2 μm or less of 90% by volume or more and 80 to 100% by mass of the total pigment. ^2. The lightweight coated paper according to claim 1, which is coated so that the coating amount of the undercoat layer is 4 to 7 g / m ² .