JP4840002B2 - Coated paper for printing and method for producing the same - Google Patents

Description

  The present invention relates to a coated paper for printing (hereinafter abbreviated as coated paper) in which a coated layer is provided on at least one side of a base paper containing a porous filler, and a method for producing the same.

  In recent years, a high-gloss coated paper has been used as a coated paper to provide a calm and high-class feeling. Demand for coated paper is increasing. In particular, matte or dull matte coated paper provides high appeal, and is widely applied to printed materials that use a lot of photographs and designs and are further colored to improve design.

In printed materials, weight reduction is required from the viewpoint of resource saving, transportation and mail cost reduction, and accordingly, the density of coated paper is required to be reduced.
As a method of reducing the density of the coated paper, a method of reducing the density of the base paper by reducing the press pressure and machine calendar pressure at the time of base paper making is known. However, when the density of the base paper is lowered to a desired level only by this method, there is a problem that the smoothness of the base paper is remarkably lowered, and as a result, the smoothness of the coated paper is also lowered.
Further, as a method for reducing the density of the base paper to reduce the weight of the coated paper, a method has been proposed in which mechanical pulp is blended with pulp to be used and amorphous silica is blended as a filler (Patent Documents 1 and 2). reference). However, ordinary amorphous silica is crushed by the press pressure and machine calender pressure at the time of base paper making, and not only the target density reduction cannot be achieved, but also the surface strength of the coated paper is lowered. Moreover, since mechanical pulp has high rigidity, it was easy to reduce the smoothness of coated paper.

  As a method for increasing the smoothness of paper, a method is known in which a pressure finishing process is performed in which the surface of the paper is pressurized with a super calender or the like. However, when pressure finishing is applied to conventional coated paper, there is a problem that the density of the paper increases.

By the way, as a method for obtaining matte or dull matte coated paper, in Patent Document 3, a delaminated clay having a volume distribution average particle size of 3.5 to 20 μm is 30 to 100 parts by mass of pigment. There has been proposed a method of treating a coating layer containing 90 parts by mass with a soft calender provided with a metal roll having a temperature of 100 ° C. or higher.
Patent Document 4 proposes a method for producing a matte coated paper by passing the coated paper through a calendar composed of a hard roughening roll and an elastic roll having a surface roughness R _{max of 8} to 25 μm. Yes.
In Patent Document 5, a coating layer containing 10 to 30 parts by mass of synthetic resin particles with respect to 100 parts by mass of pigment is formed, and a metal roll having a surface roughness R _z (10-point average roughness) of 2 to 8 μm is used. There has been proposed a method for processing so that the glossiness of blank paper is 40 or less by a calendar made of an elastic roll.
These methods described in Patent Documents 3 to 5 are methods for performing calendar processing under mild conditions in order to prevent high gloss. For this reason, it has been particularly difficult to improve the smoothness of matte coated paper.
JP 2001-214395 A Japanese Patent Laid-Open No. 11-279988 JP 2002-194698 A JP-A-4-119192 JP 7-238493 A

As described above, in the methods described in Patent Documents 1 to 5, it is difficult to obtain a coated paper having high smoothness and high surface strength and high internal bond strength despite the low density. In particular, it has been particularly difficult with matte coated paper with reduced surface gloss.
The present invention has been made in view of the above circumstances, and provides a coated paper having high smoothness, high surface strength and high internal bond strength, and a method for producing the same, despite the low density. Objective.

The present invention includes the following inventions.
[1] A printing coated paper comprising a base paper and a coating layer provided on at least one side of the base paper and subjected to pressure finishing treatment,
The base paper, multi-porous filler is contained 1 to 20 mass%,
The porous filler is prepared by adding a mineral acid solution and a metal salt solution of a mineral acid in an aqueous alkali silicate solution stirred at a peripheral speed of 7 m / sec or more to 0.07 to 7.0 with respect to 100% by mass of silicon oxide. obtained from the mass% of the electrolyte concentration 50 to 120 / L of the porous filler slurry the metal is obtained by adding as additives, include aggregates silicon and metal compound oxide are aggregated, the content of metallic compounds However, 0.10 to 8.0 % by mass in terms of oxide with respect to 100% by mass of silicon oxide , a specific surface area of 10 to 150 m ² / g, a pore size of 0.10 to 0.80 μm, and an average particle size of 16 ~40μm are those of,
A coated paper for printing, wherein the coating layer contains a pigment and an adhesive.
[2] The coated paper for printing according to [1], wherein the pressurizing finishing process is a calendering process for setting the blank gloss of the coated paper for printing to 30 to 55%.
[3] The coated paper for printing according to [1] or [2], having a density of 1.0 g / m ³ or less and a smoothness of 400 seconds or more.
[4] The pigment contained in the outermost coating layer contains an inorganic pigment and 2 to 17 parts by mass of a resin pigment with respect to 100 parts by mass of the inorganic pigment. The coated paper for printing described.
[5] The inorganic pigment contains 50 to 100% by mass of a kaolin component composed of engineered kaolin and / or delaminated kaolin, and the average particle size measured by the sedimentation method in the kaolin component is 0.2 to 1.0 μm. The coated paper for printing according to [4].
[6] A step of applying a coating liquid containing a pigment and an adhesive on at least one side of the base paper and drying to provide one or more coating layers, and press finishing treatment on the base paper and the coating layer A process for producing a coated paper for printing comprising the steps of:
As the base paper, with those containing multi porous filler 1 to 20 mass%,
The porous filler is prepared by adding a mineral acid solution and a metal salt solution of a mineral acid in an aqueous alkali silicate solution stirred at a peripheral speed of 7 m / sec or more to 0.07 to 7.0 with respect to 100% by mass of silicon oxide. It was obtained from a porous filler slurry having an electrolyte concentration of 50 to 120 g / L obtained by adding so that a metal of a mass% was added, and contained an aggregate in which silicon oxide and a metal compound were aggregated. Content is 0.10 to 8.0% by mass in terms of oxide with respect to 100% by mass of silicon oxide, specific surface area is 10 to 150 m ² / g, pore size is 0.10 to 0.80 μm, average particle size A method for producing a coated paper for printing, characterized in that the thickness is 16 to 40 μm .
[7] The method for producing a coated paper for printing according to [6], wherein the pressurizing finishing process is a calendering process for setting the white paper glossiness of the coated paper for printing to 30 to 55%.

The coated paper of the present invention has high smoothness and high surface strength and high internal bond strength despite its low density. Such coated paper can be reduced in weight, and can be matte with a high-class feeling by appropriately selecting the conditions of the pressure finishing treatment, and the design of printed matter can be improved. The coated paper of the present invention has sufficiently high opacity and printing strength.
According to the method for producing a coated paper of the present invention, it is possible to produce a coated paper having high smoothness and high surface strength and high internal bond strength despite its low density. In particular, according to the method for producing a coated paper of the present invention, a matte coated paper having a low density and a high smoothness can be easily produced.

(Coated paper)
An embodiment of the coated paper of the present invention will be described.
The coated paper of this embodiment includes a coated layer provided on at least one side of a base paper and is subjected to a pressure finishing process.

[Base paper]
The base paper constituting the coated paper contains a pulp component and a porous filler as main components.
Pulp components include chemical pulp such as softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP), various mechanical pulps such as ground pulp, and various waste papers (GP, PGW, RGP, TMP). Used paper pulp, etc. made from
The freeness of the pulp component is preferably 300 to 550 CSF from the viewpoint of the balance between strength and stiffness in the base paper.

The porous filler contained in the base paper is composed of an aggregate obtained by aggregating silicon oxide and a metal compound.
The silicon oxide constituting the porous filler is formed from, for example, silicon dioxide and / or silicate. Here, the silicate is a compound represented by the general formulas xM ₂ O · ySiO ₂ , xMO · ySiO ₂ , xM ₂ O ₃ · ySiO ₂ , where M is Al, Fe, Ca, Mg, Na , K, Ti, Zn (x and y are arbitrary positive numerical values).
Usually, silicon oxide is in the form of particles.

Examples of the metal element forming the metal compound contained in the porous filler include barium, titanium, aluminum, magnesium, calcium, nickel, iron, zirconium, and strontium. Specific examples of the metal compound include aluminum oxide, barium sulfate, magnesium carbonate, magnesium oxide, and magnesium hydroxide. Among these, aluminum oxide is preferable because of its excellent cost and handleability.
The shape of the metal compound may be particulate or indefinite.

Content of the metal compound in a porous filler is 0.1-8.0 mass% in conversion of an oxide with respect to 100 mass% of silicon oxides, Preferably it is 0.1-4.3 mass%. As a result of investigations by the present inventors, when the content of the metal compound is 0.1% by mass or more in terms of oxide with respect to 100% by mass of silicon oxide, the viscosity in the slurry state can be lowered and the handling is good. It turned out to be. Further, if the content of the metal compound is 8.0% by mass or less in terms of oxide with respect to 100% by mass of silicon oxide, the bulk effect can be sufficiently exhibited when blended in paper, and the density can be lowered. found.
The metal compound content is determined by tableting a porous filler powder sample, measuring the content of each element with a fluorescent X-ray analyzer using the tableted sample as a measurement sample, It is calculated | required by converting into an oxide amount.

The specific surface area of the porous filler is 10 to 150 m ² / g and the pore diameter is 0.10 to 0.80 μm, preferably the specific surface area is 20 to 100 m ² / g and the pore diameter Is 0.15 to 0.50 μm. When the specific surface area is 10 to 150 m ² / g and the pore diameter is 0.10 to 0.80 μm, the binding strength of the aggregate structure constituting the porous filler can be increased, Even if pressure is applied during the pressure finishing treatment, the aggregated structure is not easily destroyed, so that it can be made sufficiently bulky when blended into the base paper, and the density can be lowered. In addition, since the specific surface area and pore diameter of the porous filler are within the above ranges, excessive aggregation and destruction of the aggregate structure can be prevented, so that a narrow particle size distribution can be maintained, and the internal bond strength and surface strength of the paper can be increased. it can.
The specific surface area in the present invention is a value measured by a mercury intrusion method, and is the surface area of all pores assuming that the pore shape is a geometric cylinder. The pressure in the measurement range and the amount of mercury injected The value obtained from the relationship.
The pore diameter in the present invention is a value measured by a mercury intrusion method and is a median pore diameter obtained from an integral specific surface area curve.

The average particle diameter of the porous filler is 16 to 40 μm. If the average particle size of the porous filler is 16 μm or more, the bulkiness effect when blended in paper can be sufficiently exerted, and if the average particle size is 40 μm or less, the surface is caused by dropping off of coarse particles existing on the paper surface. A reduction in strength can be prevented.
The average particle diameter in the present invention is a value that is 50% in volume integration as measured by a laser diffraction method.
The particle size distribution of the porous filler is preferably narrow, and specifically, the standard deviation (σ) of the particle diameter is preferably 0.490 or less, more preferably 0.400 or less. In such a particle size distribution, since both coarse particles and fine particles are smaller, the surface strength and the internal bond strength can be further increased when blended in paper.

  The content of the porous filler in the base paper is 1 to 20% by mass, preferably 2 to 15% by mass, and more preferably 5 to 10% by mass. When the content of the porous filler is less than 1% by mass, the density of the coated paper cannot be sufficiently lowered, and when it exceeds 20% by mass, the surface strength and the internal bond strength are lowered.

  The base paper may contain other fillers other than the above porous fillers, for example, talc, kaolin, heavy calcium carbonate, light calcium carbonate, titanium oxide, etc., for the purpose of adjusting papermaking suitability and strength characteristics of the base paper. Good.

Preferably the basis weight of the base paper is 30~300g / ^{m 2,} in terms of opacity and bulkiness of the base paper, and more preferably 40~130g / ^{m 2.}

[Coating layer]
The coating layer is a layer containing a pigment and an adhesive.
Examples of the pigment contained in the coating layer include inorganic pigments and resin pigments.
Examples of inorganic pigments include heavy calcium carbonate, light calcium carbonate, satin white, calcium sulfite, gypsum, barium sulfate, talc, kaolin, clay, calcined kaolin, white carbon, delaminated kaolin, engineered kaolin, diatomaceous earth, Examples thereof include magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bendnite, and sericite.

Examples of the resin constituting the resin pigment contained in the coating layer include styrene polymers obtained by polymerizing styrene monomers such as styrene and α-methylstyrene, methyl (meth) acrylate, and (meth) acrylic acid. (Meth) acrylic acid alkyl ester polymers obtained by polymerizing (meth) acrylic acid alkyl ester monomers such as ethyl, (meth) acrylic acid butyl and (meth) acrylonitrile, (meth) acrylic acid, maleic acid, fumaric acid And unsaturated carboxylic acid polymers obtained by polymerizing unsaturated carboxylic acid monomers such as itaconic acid and unsaturated amide polymers obtained by polymerizing unsaturated amide monomers such as (meth) acrylamide. In addition, a copolymer obtained by copolymerizing at least one selected from the group consisting of the above aromatic vinyl monomers, acrylic acid alkyl ester monomers, unsaturated carboxylic acid monomers, and unsaturated amide monomers ( For example, a styrene- (meth) acrylic acid ester copolymer) may be used.
When such a resin pigment is contained, the density of the coating layer becomes lower, which is preferable.

  The resin pigment may be hollow or solid particles, may be a particle having a through hole, or may be a bowl-shaped particle.

The average particle size of the resin pigment is preferably 0.5 to 1.5 μm. If the average particle diameter of the resin pigment is 0.5 μm or more, the opacity can be further improved, and if it is 1.5 μm or less, the surface smoothness can be further improved.
Further, the resin pigment is preferably hollow particles having an average particle diameter in the above range and a porosity of 30 to 60%.

Of the one or more coating layers, the outermost coating layer includes both the inorganic pigment and the resin pigment, and the content of the resin pigment in the coating layer is 100 parts by mass in total of the inorganic pigment. 2 to 17 parts by mass is preferable. If the content of the resin pigment is 2 parts by mass or more, the smoothness after calendering becomes higher, and if it is 17 parts by mass or less, the glossiness of the blank paper can be more easily lowered and the printing strength can be reduced. Decline can be prevented more.
In addition, when a coating layer is one layer, the coating layer becomes the outermost layer.

The inorganic pigment contained in the outermost coating layer contains 50 to 100% by mass of a kaolin component composed of engineered kaolin and / or delaminated kaolin, and the average particle size measured by the sedimentation method in the kaolin component is 0. The thing of 2-1.0 micrometer is preferable. If the content of the kaolin component is 50% by mass or more, the blank paper glossiness and smoothness will be higher. Here, the engineered kaolin is a kaolin processed so that the particle size distribution becomes narrow, and the delaminated kaolin is a thin plate-like kaolin.
In addition, if the average particle diameter measured by the sedimentation method of the kaolin component is 0.2 μm or more, the amount of the kaolin component penetrating into the base paper can be reduced when the coating layer is formed. Can be higher. Further, the glossiness of the white paper can be easily lowered, and matte coated paper can be more easily produced. Moreover, if the average particle diameter is 1.0 μm or less, an excessive decrease in the glossiness of the white paper can be prevented.
In the present invention, the average particle diameter measured by the sedimentation method is an average particle diameter (d ₅₀ ) of 50 cumulative mass%.

When the kaolin component in the inorganic pigment is less than 100% by mass, other inorganic pigments are included. Examples of other inorganic pigments include calcium carbonate, calcium sulfate, satin white, titanium oxide, zinc oxide, aluminum hydroxide, magnesium hydroxide, barium sulfate, silica, and silica-alumina. These other inorganic pigments may be used alone or in combination of two or more.
The other inorganic pigments preferably have an average particle size of 0.2 to 1.5 μm, more preferably 0.2 to 1.0 μm, measured by a sedimentation method. If the average particle size of other inorganic pigments is 0.2 μm or more, the smoothness of the coating layer can be further increased, and if the average particle size is 1.5 μm or less, an excessive decrease in white paper glossiness can be prevented. .

  Inorganic pigments, in terms of securing the fluidity of the coating liquid used when forming the coating layer and improving the surface quality of the resulting coated paper, 50 to 85% by mass of the inorganic pigment is the kaolin. More preferably, it is a component and the rest is another inorganic pigment.

When there are two or more coating layers, the above-described kaolin component may also be included in the coating layer (undercoat coating layer) between the outermost coating layer and the base paper.
Further, the outermost coating layer and the undercoat coating layer may be composed of the same component or different components.
When two or more coating layers are provided, the smoothness of the coated paper becomes higher.

As an adhesive contained in the coating layer, for example, a water-dispersible adhesive or a water-soluble adhesive can be used.
Examples of water-dispersible adhesives include styrene / butadiene copolymers, styrene / acrylic copolymers, ethylene / vinyl acetate copolymers, butadiene / methyl methacrylate copolymers, and vinyl acetate / butyl acrylate copolymers. A copolymer etc. are mentioned.
Examples of water-soluble adhesives include, for example, synthetic adhesives such as polyvinyl alcohol, maleic anhydride copolymer, acrylic acid / methyl methacrylate copolymer; proteins such as casein, soy protein, synthetic protein; oxidized starch, positive Examples include starch, etherified starch such as urea phosphate esterified starch and hydroxyethyl etherified starch, and starches such as dextrin; cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose.
These adhesives may be used individually by 1 type, and may use 2 or more types together.

  The adhesive content in the coating layer is preferably 5 to 50 parts by mass, more preferably 10 to 30 parts by mass with respect to 100 parts by mass of the pigment.

  The total thickness of the coating layer is preferably 5 to 50 μm, and more preferably 8 to 30 μm. If the total thickness of the coating layer is 5 μm or more, ink receptivity can be sufficiently exhibited. Moreover, if the total thickness of the coating layer is 50 μm or less, flexibility can be maintained, the texture as paper can be prevented from being impaired, and the surface state of the base paper can be easily applied to the surface of the coating layer. Will be reflected.

[Pressure finishing]
The pressure finishing process in the coated paper manufacturing method to be described later is applied to the pressure finishing process in the coated paper of this embodiment.

As described above, the coated paper of this embodiment includes a base paper and a coating layer, and the base paper includes a specific porous filler. As a result of investigations by the present inventors, it has been found that the specific porous filler is not easily crushed and maintains the target bulkiness even when subjected to pressure during papermaking or pressure finishing. Since the coated paper of this embodiment uses a base paper containing such a porous filler, it is considered that although the density is low, the smoothness is high and the surface strength and the internal bond strength are high. It is done.
Furthermore, the coated paper of the present invention has sufficient opacity and printing strength because the base paper contains a porous filler with few fine particles and coarse particles.

The coated paper of the present invention preferably has a density of 1.0 g / cm ³ or less and a smoothness of 400 seconds or more. When the density and the smoothness are in the above ranges, the coated paper has a sufficiently high smoothness even though the density is sufficiently low. In addition, the density is preferably 0.80 g / cm ³ or more because sufficient strength can be secured, and the smoothness is preferably 3000 seconds or less because it can easily cope with the high speed of coated paper production. .
Here, the smoothness is the Oken type smoothness. Further, the glossiness of blank paper is measured with an incident angle of light for measurement being 75 °, and the glossiness of printing is a value measured with an incident angle of light for measurement being 60 °.
Examples of the method for setting the density and the smoothness in the above-described range include a method of processing in the same manner as the calendar processing for setting a blank paper glossiness of 30 to 55%, which will be described later.

The basis weight of the coated paper is preferably about 45 to 160 g / m ² , since it becomes a matte coated paper having a better texture.

(Production method of coated paper)
Next, an embodiment of the method for producing a coated paper of the present invention will be described.
The coated paper manufacturing method of the present embodiment is a method for manufacturing the above-described coated paper, in which at least one surface of the base paper is coated with a coating liquid and dried to provide one or more coating layers. It is a method which has a process and the process of giving a pressure finishing process to a base paper and a coating layer.

The base paper used in this production method includes, for example, the above-mentioned porous filler, pulp strength enhancer, sizing agent, fixing agent, antifoaming agent, colorant and the like in a pulp slurry containing a beaten pulp component. It is obtained by adding a paper stock to make a paper stock.
As a papermaking method, for example, a method of performing acidic papermaking, neutral papermaking, or alkaline papermaking using a long net machine including a top wire, a round net machine, a twin wire machine, a machine using them together, a Yankee dryer machine, etc. Etc.
Further, when obtaining the base paper, it is preferable to appropriately adjust the press pressure in the dehydration step and the machine calendar pressure in the smoothing step so that both the smoothness and bulkiness of the coated paper are increased.

As a method for producing a porous filler, for example, a mineral acid solution and a metal salt solution of a mineral acid are added to an agitated alkali silicate aqueous solution, and an aggregate obtained by agglomerating silicon oxide and a metal compound is used. And a method of depositing a porous filler to be obtained in water to obtain a slurry-like porous filler. At that time, the stirring speed of the alkali silicate aqueous solution is set to a peripheral speed of 7 m / second or more, and the addition amount of the metal salt solution of the mineral acid is 0.07 to 7.0% by mass of metal with respect to 100% by mass of silicon oxide. The amount added to the alkali silicate aqueous solution is preferably 50 to 120 g / L in the slurry-like porous filler.
If a porous filler is manufactured by such a manufacturing method, the content of the metal compound is 0.10 to 8.0% by mass in terms of oxide with respect to 100% by mass of silicon oxide, and the specific surface area is 10 to 10%. A porous filler having a diameter of 150 m ² / g, a pore diameter of 0.10 to 0.80 μm, and an average particle diameter of 16 to 40 μm can be produced.

The coating solution applied to the base paper contains the above-described pigment and adhesive. The pigment and the adhesive are prepared, for example, by dispersing and mixing in an aqueous medium. In the coating solution, various auxiliary agents such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistance agent, and a coloring agent may be added as necessary.
The coating amount of the coating liquid is selected according to the intended quality of the coated paper. Taking the case where the basis weight of the base paper is 70 g / m ² as an example, if the dry coating amount per side is about 4 to 15 g / m ² , sufficient coverage, higher smoothness and printing gloss can be obtained. Obtainable.

Examples of the coating apparatus that coats the coating liquid on the base paper include a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a size press coater, and a gate roll coater.
Examples of the drying device for drying the coating liquid include various types of dryers such as a heating cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, an infrared heater dryer, and the like, and these may be used alone or in combination. Can do.

  The base paper may be preliminarily coated with starch, polyvinyl alcohol or the like before applying the coating solution. Examples of the preliminary coating apparatus include a two-roll size press coater, a gate roll coater, and a pre-metering size press coater.

Examples of the pressure finishing process include a super calendar process, a mat calendar process, a roughening calendar process, and a soft calendar process.
When the coated paper is a dull or matte matte coated paper, a calendering process is applied to the press finish to bring the glossiness of the blank paper to 30 to 55 % . When the glossiness of the white paper is higher than 55%, the matte property is insufficient, and when the glossiness of the white paper is less than 30%, the printing gloss tends to be impaired.

The calendering process for setting the glossiness of blank paper to 30 to 55% is a calendering process under the condition that the surface is not excessively smoothed. For example, the calendering process with a low linear pressure (nip pressure), the number of times of paper passing between rolls ( Well-known methods such as calendering with a reduced number of nips) and calendering using a roll having a rough surface may be mentioned. According to these methods, a matte coated paper having both low density and high smoothness can be easily obtained.
As a specific method of calendering to make the blank paper glossiness 30 to 55%, it is super calendering that passes between a metal roll and an elastic roll, and the linear pressure is 25 to 250 kg / cm, preferably An example of the treatment is 50 to 150 kg / cm, and the number of paper passing times is 1 to 8 times, preferably 2 to 8 times. When the linear pressure is less than 25 kg / cm, the smoothness may be low. When the linear pressure exceeds 250 kg / cm, or when the number of paper passes exceeds 8, the glossiness increases. The density tends to increase.
Further, as other calendar processing for setting the glossiness of the white paper to 30 to 55%, mat calendar processing and roughening calendar processing are preferable.

Among the pressurizing finishing treatments, a roughened calendering treatment is preferable because a matte or dull-coated paper can be easily obtained while increasing smoothness.
The roughening calendar process is a process of passing paper between a roughening roll and an elastic roll. As the roughening roll, a roll having a maximum height roughness R _z of 8 to 35 μm defined by JIS B 0601-2001 is preferable, and a roll having a maximum height roughness R _{z of 8} to 20 μm is preferable. More preferred. If a roughening roll with a maximum height roughness _Rz of 8 μm or more is used, the effect of lowering the glossiness of the blank paper is high, and the density of the coated paper is easily achieved while keeping the glossiness of the blank paper within a desired range. The desired matte coated paper can be easily produced. On the other hand, if a roughening roll having a maximum height roughness _Rz of 35 μm or less is used, the smoothness of the resulting coated paper can be reliably increased.
In this roughening calendering process, it is preferable that each surface of the coated paper is in contact with the roughening roll 1 to 8 times, since smoothness and matte properties can be sufficiently obtained.

The method for producing a coated paper according to this embodiment applies a coating liquid to at least one side of a base paper containing a specific range of the specific porous filler described above as a base paper, and after drying, pressurizing finish processing is performed. This is a method for obtaining a paper.
As described above, the specific porous filler contained in the base paper is not easily crushed even when pressure is applied. According to the above production method using a base paper containing such a porous filler, it is possible to produce a coated paper having high smoothness, high surface strength and high internal bond strength despite its low density. Furthermore, according to this manufacturing method, a coated paper having sufficient opacity and printing strength can be manufactured.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples. In the following examples, “part” and “%” mean “part by mass” and “% by mass”, respectively, unless otherwise specified.
Moreover, in the porous filler used in the following examples, the metal compound content, specific surface area, pore diameter, average particle diameter, and slurry viscosity were measured as follows.
(Metal compound content)
The metal compound content (as oxide) in the porous filler is a value measured using a fluorescent X-ray analyzer (Spectras PW2404).
(Specific surface area)
The specific surface area is the surface area of all pores when the pore shape is assumed to be a geometric cylinder using a pore sizer Pore Sizer 9230 (manufactured by Shimadzu Corporation), and the pressure within the measurement range. And the value obtained from the relationship between the amount of injected mercury.
(Pore diameter)
The pore diameter is a median pore diameter measured using a pore sizer 9230 (manufactured by Shimadzu Corporation).
(Average particle size)
The average particle diameter is a 50% volume integrated particle diameter measured using a laser diffraction particle size distribution analyzer (SALD2000J (manufactured by Shimadzu Corporation)). The standard deviation of the particle diameter is a value calculated from the particle diameter obtained by a laser diffraction particle size distribution meter.
(Viscosity of porous filler slurry)
The viscosity of the porous filler slurry is a value measured with a B-type viscometer at a temperature of 20 ° C. with the solid content concentration of the porous filler slurry adjusted to 15%.

Moreover, the average particle diameter of the pigment which comprises a coating layer was measured as follows.
(Measurement of average particle size of pigment by sedimentation method)
The average particle size of the pigment by the precipitation method is measured using a pigment dispersion containing the pigment as a measurement sample, and using Sedigraph 5100 (manufactured by Micromeritics, USA), and an average particle size of 50 cumulative mass% (d ₅₀ ).
The pigment dispersion used for the measurement was a pigment slurry obtained by adding 0.05% of a dispersant (sodium polyacrylate) to 100% of the pigment, and 0% of the phosphate dispersant (nancarin). It was prepared by diluting with a 1% aqueous solution so that the pigment solid content concentration was about 1%.

Example 1
[Preparation of base paper (1)]
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler A made of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. did. Furthermore, with respect to 100 parts of pulp (LBKP and NBKP), 0.01 part of AKD sizing agent (trade name: Size Pine K-902, manufactured by Arakawa Chemical Co., Ltd.) as an internal sizing agent and 0 parts of aluminum sulfate .5 parts (in terms of solid content) was added to prepare a paper stock.
Then, paper is made using this stock, and further subjected to surface size press (oxidized starch coating amount is 2.5 g / m ^{2 on} both sides) using oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch). Thus, a base paper (1) having a basis weight of 70 g / m ² was obtained.

[Preparation of undercoat coating solution]
100 parts of coarse-grained heavy calcium carbonate (trade name: Hydrocurve 60, manufactured by Bihoku Powder Chemical Co., Ltd.) and 5 parts of styrene-butadiene copolymer latex (trade name: Sumatex PA2327, manufactured by Nippon A & L Co., Ltd.) Conversion), 5 parts of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch Co., Ltd.) (in terms of solid content) were added to prepare an undercoat coating solution having a solid content concentration of 62%.

[Preparation of top coat liquid (1)]
First grade kaolin (trade name: Ultra White 90, manufactured by Engelhard, average particle size d ₅₀ ; 0.32 μm), 30 parts, fine heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour Industry Co., Ltd., average particle size _d 50; _0.8μm) 40 parts of light calcium carbonate (trade name: TP-121, Okutama Kogyo Co., Ltd., average particle diameter _d 50; 0.70 .mu.m) to a pigment consisting of 30 parts of the pigment 100 as a dispersing agent 0.1 part of sodium polyacrylate was added to the part and dispersed with a mixer to prepare a pigment slurry having a solid content of 70%. To this pigment slurry, 10 parts of styrene-butadiene copolymer latex (trade name: Sumatex PA2327, manufactured by Nippon A & L Co., Ltd.) and 2 parts of oxidized starch (trade name: Ace A) (solids equivalent) are added. By addition, an overcoating liquid (1) having a solid concentration of 64% was prepared.

[Manufacture of coated paper]
On both sides of the base paper (1), the undercoat coating solution was applied and dried with a blade coater at a coating speed of 800 m / min so that the dry coating amount per side was 6 g / m ² . An undercoat coating layer was formed. Next, the above-mentioned overcoating liquid (1) was applied to each undercoat coating layer with a blade coater at a coating speed of 800 m / min so that the dry coating amount was 6 g / m ^2. It was dried to 5.0% to form a top coat layer, and an intermediate product of coated paper was obtained.
Subsequently, the intermediate product of the coated paper was calendered with a super calender composed of a metal roll and an elastic roll under the conditions of a nip pressure of 100 kg / cm and a nip number of 4 times to obtain a matte coated paper.

Example 2
A pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF) contains 2.9% by mass of a porous filler B made of aluminosilicate shown in Table 1 as a filler. Except that light calcium carbonate (average particle size: 6.1 μm, bulk specific gravity: 0.23 g / cm ³ ) was added so as to be contained in 7% by mass in the base paper. In the same manner as in Example 1, a base paper (2) having a basis weight of 70 g / m ² was obtained.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (2) was used.

Example 3
A pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF) is added with a porous filler A shown in Table 1 as a filler so that the base paper contains 15% by mass. A base paper (3) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (3) was used.

Example 4
40 parts primary kaolin (trade name: Ultra White 90, Engelhard, average particle size d ₅₀ ; 0.32 μm), large particle delaminated kaolin (trade name: New Surf, Engelhard, average particle) diameter _d 50; _2.1μm) 20 parts, fine ground calcium carbonate (trade name: Hydro curve 90, Bihoku Funka Kogyo Co., Ltd., average particle diameter _d 50; 0.8 [mu] m) to the pigment consisting of 40 parts of dispersing agent As a result, 0.1 part of sodium polyacrylate was added to 100 parts of the pigment and dispersed with a mixer to prepare a pigment slurry having a solid content of 70%. To this pigment slurry, 10 parts of styrene-butadiene copolymer latex (trade name: Sumatex PA2327, manufactured by Nippon A & L Co., Ltd.) and 2 parts of oxidized starch (trade name: Ace A) (solids equivalent) are added. By addition, an overcoating liquid (2) having a solid content concentration of 62% was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this topcoat coating solution (2) was applied to the undercoat coating layer.

Example 5
Engineered kaolin (trade name: Contrast 300, manufactured by Engelhard, average particle size d ₅₀ ; 0.5 μm) 55 parts, fine heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour & Chemical Co., Ltd., average particle (Diameter d ₅₀ ; 0.8 μm) To an inorganic pigment consisting of 45 parts, 0.1 part of sodium polyacrylate is added as a dispersant to 100 parts of the pigment, and dispersed with a mixer. An inorganic pigment slurry was prepared.
Into this inorganic pigment slurry, 5 parts of hollow plastic pigment (trade name: Ropeke HP91, average particle size: 1 μm, porosity: 55%, manufactured by Rohm and Haas Co., Ltd.), styrene, with respect to 100 parts of inorganic pigment -Add butadiene copolymer latex (trade name: Sumatex PA2327, manufactured by Nippon A & L Co.) 10 parts (solid content conversion), oxidized starch (trade name: ace A) 2 parts (solid content conversion) to add solid content A topcoat coating solution (3) having a concentration of 58% was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this overcoating liquid (3) was applied to the undercoating layer.

Example 6
In Example 5, an undercoat coating solution and an overcoat coating solution (3) were applied to both sides of the base paper and dried to obtain an intermediate product of the coated paper. Except for calendering under the conditions of a nip pressure of 100 kg / cm and a nip number of 4 with a calender composed of a roughening roll and an elastic roll having a height roughness R _z (JIS B 0601-2001) of 15 to 20 μm. In the same manner as in Example 5, a matt coated paper was obtained.

Example 7
Delaminated kaolin (trade name: Contour 1500, manufactured by Imeris Co., Ltd., average particle diameter d ₅₀ ; 0.46 μm) and 85 parts of fine heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour Industries Co., Ltd., (Average particle diameter d ₅₀ ; 0.8 μm) To 15 parts of an inorganic pigment, 0.1 part of sodium polyacrylate is added as a dispersant to 100 parts of the pigment and dispersed with a mixer to obtain a solid content of 70 % Inorganic pigment slurry was prepared.
Into this inorganic pigment slurry, 3 parts of hollow plastic pigment (trade name: Ropeke HP91, average particle size: 1 μm, porosity: 55%, manufactured by Rohm and Haas Co.) with respect to 100 parts of inorganic pigment, styrene-butadiene copolymer Combined latex (trade name: Sumatex PA2327, manufactured by Nippon A & L Co., Ltd.) 10 parts (in terms of solid content) and 2 parts of oxidized starch (trade name: Ace A) (in terms of solid content) were added to obtain a solid content concentration of 58%. A topcoat coating solution (4) was prepared.
A matte coated paper was obtained in the same manner as in Example 6 except that this topcoat coating solution (4) was applied to the undercoat coating layer.

Example 8
Engineered kaolin (trade name: Contrast 300, manufactured by Engelhard, average particle size d ₅₀ ; 0.5 μm) 85 parts, fine heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour & Chemical Co., Ltd., average particle Diameter of inorganic pigment consisting of 15 parts (d ₅₀ ; 0.8 μm) with respect to 100 parts of inorganic pigment, hollow plastic pigment (trade name: Ropeke HP91, average particle size: 1 μm, porosity: 55%, Rohm and Haas Co., Ltd.) 3 parts), styrene-butadiene copolymer latex (trade name: Sumatex PA2327, manufactured by Nippon A & L Co.) 10 parts (solid content conversion), oxidized starch (trade name: Ace A) 2 parts (solid content conversion) By addition, an overcoating liquid (5) having a solid content concentration of 58% was prepared.
A matte coated paper was obtained in the same manner as in Example 6 except that this topcoat coating solution (5) was applied to the undercoat coating layer.

Example 9
75 parts of delaminated kaolin (trade name: Capim DG, manufactured by RCC, average particle diameter d ₅₀ ; 0.61 μm) and fine heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour Industries Co., Ltd., average (Particle diameter d ₅₀ ; 0.8 μm) 25 parts of an inorganic pigment, 3 parts of hollow plastic pigment (AE-851, average particle diameter: 1 μm, porosity: 55%, manufactured by JSR) with respect to 100 parts of inorganic pigment , 10 parts of styrene-butadiene copolymer latex (trade name: SMATEX PA2327, manufactured by Nippon A & L Co.) (solid content conversion), 2 parts of oxidized starch (trade name: ACE A) (solid content conversion), A top coat solution (6) having a solid content concentration of 58% was prepared.
A matte coated paper was obtained in the same manner as in Example 6 except that this topcoat coating solution (6) was applied to the undercoat coating layer.

Example 10
A matte coated paper was obtained in the same manner as in Example 6 except that the dry coating amount of one surface of the base coating liquid (3) was 12 g / m ² .

Example 11
Matte coated paper in the same manner as in Example 6 except that the top coating liquid (3) was directly coated on both sides of the base paper so that the dry coating amount per side of the base paper was 12 g / m ^2. Got.

Comparative Example 1
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler A shown in Table 1 as a filler is added so that 0.8% by mass is contained in the base paper, Example 1 except that light calcium carbonate (average particle size: 6.1 μm, bulk specific gravity: 0.23 g / cm ³ ) was added so as to be contained in 7% by mass in the base paper, and a paper stock was prepared. Thus, a base paper (4) having a basis weight of 70 g / m ² was obtained.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (4) was used.

Comparative Example 2
A pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF) is added with a porous filler A shown in Table 1 as a filler so that the base paper contains 25% by mass. A base paper (5) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (5) was used.

Comparative Example 3
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler C composed of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. A base paper (6) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (6) was used.

Comparative Example 4
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler D made of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. A base paper (7) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (7) was used.

Comparative Example 5
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler E composed of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. A base paper (8) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (8) was used.

Comparative Example 6
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler F made of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. A base paper (9) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (9) was used.

Comparative Example 7
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler G composed of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. A base paper (10) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (10) was used.

Comparative Example 8
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler H made of aluminosilicate shown in Table 1 is added as a filler so that it is contained in 7% by mass in the base paper. A base paper (11) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (11) was used.

Comparative Example 9
To a pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), a porous filler I composed of aluminosilicate shown in Table 1 is added as a filler so that the base paper contains 7% by mass. A base paper (12) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the paper stock was prepared.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (12) was used.

Comparative Example 10
A pulp slurry containing 75 parts of LBKP (freeness 450 ml / CSF) and 25 parts of NBKP (freeness 450 ml / CSF), and light calcium carbonate (referred to as “charcoal cal” in the table) as a filler, 7% by mass in the base paper. A base paper (13) having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that a paper stock was prepared by adding it to be included.
A matte coated paper was obtained in the same manner as in Example 1 except that this base paper (13) was used.

The matte coated paper obtained in each example and comparative example was evaluated for the following glossiness, smoothness, density, printing glossiness, surface strength, and internal bond strength. The results are shown in Tables 2 and 3.
(Blank gloss)
The resulting matte coated paper was conditioned in an environment of 23 ° C ± 1 ° C and (50 ± 2)% RH, and then the gloss meter (GM-26D, Murakami Color Research Laboratory) Manufactured by ISO 8254-Part 1).
(Smoothness)
The matte coated paper thus obtained was conditioned in an environment of 23 ° C. ± 1 ° C. and (50 ± 2)% RH, and under the same environment, the JAPAN TAPPI paper / pulp test method no. It was measured according to 5-2 “Testing method for smoothness and air permeability of paper and paperboard using an air micrometer type tester”.
(density)
Measured according to JIS P 8118-1998.
(Print gloss)
The resulting matte coated paper was conditioned in an environment of 23 ° C. ± 1 ° C. and (50 ± 2)% RH, and in that environment, the printing ink (Varius G ink N Type, manufactured by Dainippon Ink & Chemicals, Inc.) using 0.3 cm ³ , and after leaving for 1 day, the glossiness meter (GM-26D type, manufactured by Murakami Color Research Laboratory) was used to obtain 60 ° glossiness. It was measured.
(Surface strength)
The matte coated paper thus obtained was conditioned in an environment of 23 ° C. ± 1 ° C. and (50 ± 2)% RH, and in that environment, the printing ink (SD50 for paper test) was printed using an RI printing tester. (Red, manufactured by Toyo Ink Co., Ltd.) was printed using 0.6 cm ³ , and the degree of picking on the printed surface was visually evaluated.
A: Picking did not occur at all, and the surface strength was extremely good.
A: Picking occurred slightly, but it was a good level as coated paper.
Δ: Picking occurred and the surface strength was low.
X: A lot of picking occurred and the surface strength was extremely low.
(Internal bond strength)
J. et al. TAPPI No. It measured according to 18-2.

The coated papers of Examples 1 to 11 in which a specific porous filler is contained in a specific range in the base paper have high smoothness, high surface strength, and high internal bond strength despite its low density. Furthermore, the glossiness of the white paper and the printing glossiness were low.
The coated paper of Comparative Example 1 in which the content of the porous filler in the base paper was less than 1.0% by mass had a high density.
The coated paper of Comparative Example 2 in which the content of the porous filler in the base paper exceeded 20% by mass had low surface strength and internal bond strength.
The coated paper of Comparative Example 3 in which the average particle size of the porous filler was less than 16 μm was high in density.
The coated paper of Comparative Example 4 in which the metal compound content in the porous filler was less than 0.1% by mass in terms of oxide had low surface strength.
The coated paper of Comparative Example 5 in which the metal compound content in the porous filler exceeded 8.0% by mass in terms of oxide had high density and low surface strength.
The coated paper of Comparative Example 6 in which the specific surface area of the porous filler was less than 10 m ² / g had a high density and a low surface strength.
The coated paper of Comparative Example 7 in which the specific surface area of the porous filler exceeded 150 m ² / g also had a high density and a low surface strength.
The coated paper of Comparative Example 8 in which the pore size of the porous filler was less than 0.10 μm had high density and low surface strength.
The coated paper of Comparative Example 9 in which the pore size of the porous filler exceeded 0.80 μm had a high density.
The coated paper of Comparative Example 10 using light calcium carbonate as the porous filler had a high density.

Claims (7)

A coated paper for printing, comprising a base paper and a coating layer provided on at least one side of the base paper and subjected to pressure finishing treatment,
The base paper, multi-porous filler is contained 1 to 20 mass%,
The porous filler is prepared by adding a mineral acid solution and a metal salt solution of a mineral acid in an aqueous alkali silicate solution stirred at a peripheral speed of 7 m / sec or more to 0.07 to 7.0 with respect to 100% by mass of silicon oxide. obtained from the mass% of the electrolyte concentration 50 to 120 / L of the porous filler slurry the metal is obtained by adding as additives, include aggregates silicon and metal compound oxide are aggregated, the content of metallic compounds However, 0.10 to 8.0 % by mass in terms of oxide with respect to 100% by mass of silicon oxide , a specific surface area of 10 to 150 m ² / g, a pore size of 0.10 to 0.80 μm, and an average particle size of 16 ~40μm are those of,
A coated paper for printing, wherein the coating layer contains a pigment and an adhesive.   The coated paper for printing according to claim 1, wherein the pressure finishing treatment is a calendering treatment for setting the glossiness of the white paper of the coated paper for printing to 30 to 55%. The coated paper for printing according to claim 1, wherein the density is 1.0 g / m ³ or less and the smoothness is 400 seconds or more.   The printing coating according to any one of claims 1 to 3, wherein the pigment contained in the outermost coating layer contains an inorganic pigment and 2 to 17 parts by mass of a resin pigment with respect to 100 parts by mass of the inorganic pigment. Paper.   The inorganic pigment contains 50 to 100% by mass of a kaolin component composed of engineered kaolin and / or delaminated kaolin, and the average particle size measured by the precipitation method in the kaolin component is 0.2 to 1.0 μm. Item 5. A coated paper for printing according to item 4. A step of applying a coating solution containing a pigment and an adhesive on at least one side of the base paper and drying to provide one or more coating layers; and a step of applying a pressure finishing treatment to the base paper and the coating layer; A method for producing a coated paper for printing, comprising:
As the base paper, with those containing multi porous filler 1 to 20 mass%,
The porous filler is prepared by adding a mineral acid solution and a metal salt solution of a mineral acid in an aqueous alkali silicate solution stirred at a peripheral speed of 7 m / sec or more to 0.07 to 7.0 with respect to 100% by mass of silicon oxide. It was obtained from a porous filler slurry having an electrolyte concentration of 50 to 120 g / L obtained by adding so that a metal of a mass% was added, and contained an aggregate in which silicon oxide and a metal compound were aggregated. Content is 0.10 to 8.0% by mass in terms of oxide with respect to 100% by mass of silicon oxide, specific surface area is 10 to 150 m ² / g, pore size is 0.10 to 0.80 μm, average particle size A method for producing a coated paper for printing, characterized in that the thickness is 16 to 40 μm . The method for producing a coated paper for printing according to claim 6, wherein the pressure finishing treatment is a calendering process for setting the glossiness of the blank paper for printing to 30 to 55%.