JPH02104795A - coated paper for printing - Google Patents

Abstract

PURPOSE:To obtain the subject coated paper, excellent in white paper and printing paper glossiness though with high opacity and rigidity by containing specific precipitated calcium carbonate as a filler and providing a coating layer on a base paper with a specified ash content thereof. CONSTITUTION:The objective coated paper obtained by providing a pigment coating layer on a base paper, containing calcite-based precipitated calcium carbonate containing a filler having an average particle particle diameter within the range of 0.3-2.0mu in an amount of >=4wt.% based on the weight of the base paper and having >=10wt.% total ash content thereof, drying the coating layer and bringing the coated surface into pressure contact with a soft calender. Furthermore, in bringing the above-mentioned coated surface into pressure contact with the soft calender having 6 number of nips, the hardness of the soft calender elastic rolls is preferably >=75 (Shore D hardness) and an index (L) preferably satisfies conditions of formula I (DO is the outside diameter of the elastic rolls; DB is the outside diameter of rigid rolls; Di is the outside diameter of the iron core in the elastic rolls; PL is the nip linear pressure; SD is the hardness of the elastic rolls; V is the line treating speed; K is formula II; 100<=PL<=550).

Description

DETAILED DESCRIPTION OF THE INVENTION A) Industrial Field of Application The present invention relates to a coated paper for printing, and particularly to a coated paper for printing that is excellent in opacity, whiteness, and rigidity, and has excellent white paper gloss and printing gloss. It is.

B) Prior Art and Problems In recent years, it has become increasingly desirable for coated paper for printing to be lightweight and to visualize printed matter.

In addition, as printing speeds increase, coated paper that can withstand these speeds is becoming necessary.

On the other hand, from the standpoint of producing coated paper, the most important issue now more than ever is how to increase production efficiency. Under these circumstances, in order to reduce the weight of coated paper, the qualities that require particular attention are opacity and rigidity. Rigidity is also important from the viewpoint of high-speed printing workability.

When considering the visualization of printed matter, it is important to have whiteness, smoothness, and high gloss in addition to opacity. Is there any known method for obtaining high opacity?
There are some. For example, choosing mechanical pulp as the pulp to be used, or adding a high filler content to the base paper, and processing at a relatively lower linear pressure than the super calender, which has a high linear pressure, in the finishing process. For example, use a gloss calendar.

In addition, in terms of whiteness, it is necessary to use many raw materials with high whiteness, and in terms of stiffness, the same measures as opacity measures are effective except for high ash base paper.

However, when attempting to take such measures when actually producing coated paper, the accompanying drawbacks also appear, making it difficult to make the desired coated paper a reality.

For example, the quality, opacity, stiffness, gloss, and smoothness of the coated paper obtained vary greatly depending on the finishing method, but in the case of machine calender finishing, the web is usually passed between two unheated steel rolls under high linear pressure. Because it passes through, it produces smoothness, but almost no gloss can be obtained.

The supercalender is composed of multiple rolls of steel and elastic material alternately, and its linear pressure is 180~45Q kgl/a.
n, = tube pressure 140 to 300 kgt/Ci,
The roll temperature is usually 70 to 80°C.

Although the resulting coated paper has high gloss and smoothness, it inevitably collapses, which is disadvantageous in obtaining high opacity and stiffness. Another finishing method is gloss calendering, which uses heated finishing rolls to give coated paper or board a longer pass through the nip without finishing at the higher linear pressures of supercalendering. Produces luster.

Linear pressure of the device is 90-180 kgt/am, nip pressure 7
0 to 140 kgt/cd1 Temperature of 100 to 150°C, particularly as high as 230°C, is the usual manufacturing condition. This relatively low linear pressure finish does not densify the paper too much, resulting in relatively good opacity, while the relatively high temperature softens the coating and allows for improved gloss. However, this finishing effect is limited to the top side of the web.

Therefore, the surface of this coated paper does not have the smoothness that can be obtained with a supercalender, and it is generally difficult to obtain high quality.

Also, as seen in Publication No. 63-500188,
Nip pressure, roll linear pressure, web residence time in the nip,
However, even in this case, the preferred nip width is 1.
．． The nip width is 27 to 2.54 ann, which is much wider than the nip width of the super calender, which is 0.6 to 1.20, and is an operational problem when using a gloss calender. roll durability,
There is no improvement in drum dirt. Another recent finishing method is to use a soft calendar.

The soft calender method combines a metal roll and an elastic roll and calenders with a small number of nips.

The elastic roll uses a special synthetic resin-coated roll with a hardness comparable to or higher than that of a supercalender, but the key point lies in the material of this roll. That is, it is necessary to select a special material that has excellent heat resistance, abrasion resistance, and is resistant to scratches under high nip pressure. For this reason, this finishing method is mainly applied to matte finishes that do not place a relatively large load on the roll.

On the other hand, if high opacity is to be obtained in the formulation, for example, when mechanical pulp is used as the pulp, its whiteness will be low, and if it is attempted to achieve this by increasing the ash content of the base paper, its rigidity will decrease. For this reason, the reality is that it is not possible to produce coated paper with excellent opacity, whiteness, rigidity, white paper gloss, and printing gloss at low cost and with good operability, especially as lightweight coated paper. The realization of this has become a major challenge for coated paper manufacturers.

In view of this current situation, the inventors of the present invention have conducted intensive research to develop a coated paper that has unprecedented high opacity and rigidity, as well as high white paper gloss and printing gloss. Contains certain light lucium carbonate as
Moreover, by applying a special finish to coated paper, which has a pigment coating layer on base paper containing a specific amount of ash, they discovered an effect that had not been seen in the past, leading to the completion of the present invention.

The purpose of the coated paper produced in this manner is to be able to achieve both contradictory physical properties of coated paper, which are not available in the past, and to provide an excellent coated paper.

C) Means for Solving the Problems The present invention is characterized in that the filler content contains 4% by weight or more of calcite-based light calcium carbonate having an average particle diameter in the range of 0.3 to 2.0μ based on the weight of the base paper, and , the total ash content of the base paper is 10% by weight or more, more preferably the base paper is not subjected to size press treatment, and a pigment coating layer is provided on the base paper, and after drying, the coated surface is pressed onto a soft calender. Coated paper for printing.

Furthermore, the treatment with the soft calender satisfies the following three conditions for press-bonding the coated surface to the soft calender with a nip number of 6 or less.

a: The hardness of the soft calender elastic roll is 75 or more (Shore D hardness).

b - The index defined by the following formula satisfies the following conditions.

(K・Do・D,・pL) 0.333L= −11111−−−−−−−−−−−−11−−−−−−
---Vt(Do + DB)・(1,48cxp(
0,ll5o ) )l ” ”33L≦0.002 *However, D. : Elastic roll outer diameter cm DB; Rigid roll outer diameter Dl; Elastic roll iron core outer diameter PL; Nip line pressure kg f/amSD+elastic roll hardness (Shore D) V; Line processing speed cm/5 e( K=3 (
D, -D, ) J Roff million C: Nip linear pressure satisfies the following conditions.

100≦Pt≦550 In the present invention, as mentioned above, a specific light calcium carbonate is used, but the light calcium carbonate referred to in the present invention refers to raw coal obtained by burning coal stone and carbon dioxide gas. Synthesized by the carbonation method, which involves refining raw coal and dissolving it in water to make coal milk, and then blowing carbon dioxide gas into it, or by a carbonate solution, which is created by reacting coal milk or calcium chloride solution with soda carbonate. It refers to precipitated calcium carbonate, and its crystal form (calcite-based or argonite-based potash, size, shape, etc.) can be adjusted depending on conditions such as synthesis reactions.

In the case of calcite-based crystals, the shapes are usually spindle-like, bur-like in which these crystals are aggregated, and cube-like (cubic and dumpling). In addition, aragonite usually has a shape called rod-like or needle-like.

The internal filler used in the present invention is light calcium carbonate, and its shape is such that the average particle size is 0. 3μm or more2.
It is a calcite crystal with a size of 0 μm or less. Particularly preferred is one with rounded corners. Compared to those having the particle shape of the present invention, for example, aragonite-based particles, the proportion of interfiber bonds being inhibited is particularly small, and therefore the strength is less reduced. However, the rate of improvement in opacity is correspondingly small, but the present invention is based on the premise of soft calender finishing with a coating machine, and the rate of decrease in opacity due to calendering affects the final opacity.

The light calcium carbonate having the particle shape of the present invention has a lower rate of decrease in opacity due to calendering than other shapes, and the opacity of the final product is high. The reason for this is not certain, but if we consider that the decrease in opacity due to calendering is a decrease in optically effective voids, it is possible that the particle shape of light calcium carbonate, such as the average particle size, crystal shape, external shape, etc. This is thought to be due to the fact that this affects the reduction rate of optically effective voids.

In addition, when the average particle size is smaller than 0.3 μm, the paper strength decreases significantly with respect to the internal addition ratio;
If it is more than m, the improvement rate of opacity will be low (this is not preferable).

Further, the blending ratio of the filler containing the above-mentioned light calcium carbonate to the base paper must be 10% by weight or more as ash, and more preferably in the range of 12 to 20% by weight. If the filler content is less than 10% by weight, sufficient physical properties of the coated paper cannot be obtained by the soft calendering treatment described below, and if the filler content is 20% by weight or more, the strength of the base paper is insufficient for offset printing. In addition, the required content ratio of light calcium carbonate in the filler is 40 to 1% of the total ash content.
00%, and if it is less than 40%, sufficient opacity cannot be obtained.

In the present invention, the average particle diameter refers to the average particle size measured by dispersing the filler aqueous dispersion in an ultrasonic dispersion machine for 5 minutes, then using a light transmission particle size distribution measuring machine (
Measured using SKN method (manufactured by Seishin Enterprise Co., Ltd.), cumulative weight%
It refers to the particle diameter when 50% of the particle diameter reaches 50%, which is the so-called weight average particle diameter.

The ash content of the present invention can be determined by taking an arbitrary amount of a sample from 1 to Log, drying it at 105° C. for 1 hour, and measuring the dry weight. After that, it was incinerated at 500° C. for 3 hours, and the absolute dry weight of the residue is expressed in weight % with respect to the absolute dry weight of the sample.

In the present invention, fillers commonly used in paper making, such as kaolin, clay, heavy calcium carbonate, titanium dioxide, calcined kaolin, and talc for paper making, may be used in combination.

It is also commonly used in paper making as sizing agents, antifoaming agents, slime control agents, dyes, colored pigments, optical brighteners, dry paper strength agents, wet paper strength agents, freeness improvers, and retention improvers. Additive chemicals can also be included if necessary.

Furthermore, it is possible to apply starch, polyvinyl alcohol, paint, and various surface sizing agents to the surface of the base paper using a size press, gate roll, or bill blade device, but the size press process hardens the base paper, resulting in the finishing described below. In order to fully exhibit the treatment effect, it is preferable to use base paper that has not been subjected to size treatment.

The base paper used in the present invention is general pulp (NBKP).
, LBKP), high yield pulp (GP.

TMP, CTMPSCMP, etc.) and waste paper pulp.

In the present invention, a pigment coating layer is provided on the above-mentioned base paper, and the coating layer is coated on one or both sides of the base paper using an on-machine coating device such as a size press, gate roll, bill blade, or a commonly used blade coater or air. It refers to the coating applied with an off-machine coater such as a knife coater, and the coating amount is 3 to 25 glrd, more preferably 5 to 15 g/rIK.

Generally known pigments, binders, dispersants, thickeners, etc. can be used in the coating liquid that can be used in the present invention.

As pigments, kaolin, calcium carbonate, clay, satin white, talc, titanium oxide, aluminum hydroxide, silica, zinc oxide, activated clay, silicon earth, lake, plastic pigments, etc., or sand milled products of these pigments can be used as appropriate. As the dispersant, polycarboxylic acids such as acrylic acid polymers and copolymers of acrylic acid and maleic acid, or their soda salts, ammonium salts,
One or more of phosphoric acid-based surfactants such as sodium hexametaphosphate and sodium pyrophosphate, anionic surfactants such as lignosulfonate and naphthylsulfonate, citric acid, malic acid, or salts thereof can be used as appropriate.

Binders include various copolymers such as styrene/butadiene, styrene/acrylic, vinyl acetate, acrylic, ethylene/vinyl acetate, butadiene/methyl methacrylate, vinyl acetate/butyl acrylate, polyvinyl alcohol, and maleic anhydride. Synthetic binders such as acid/styrene copolymers, isobutyne/maleic anhydride copolymers, acrylic acid/methyl methacrylate copolymers, oxidized starches, enzyme-modified starches, and cold water-soluble starches obtained by flash drying them. , generally known binders such as natural binders such as casein and soybean protein.

The present invention is characterized in that the coating machine is processed under special conditions in the soft calender.

As mentioned above, soft calenders have a smaller number of nips than super calenders, 2 to 6 nips, and elastic rolls have a hard iron core thinly covered with synthetic resin (75-97 degrees Shore D hardness). ing. For this reason, the nip width becomes narrower. Furthermore, the rigid rolls are composed of chilled rolls and forged steel rolls, and have a heating mechanism, allowing paper webs to be processed even at high temperatures exceeding 100°C.

In supercalendering, the density of the paper increases rapidly due to the wider nip width and higher number of nips (8 to 14 nips) compared to soft calendering, resulting in a decrease in opacity and stiffness. Both are damaged. In this way, what characterizes calendar processing is the nip passage time.

However, in order to grasp the nip passage time during paper passing processing, it is necessary to clarify the nip width. In the above-mentioned Publication No. 63-500188, the width of the nip created by the deformation of the elastic roll in a static state is calculated from the values of the elastic modulus (E), Poisson's ratio (σ), etc. of the elastic roll using formula '6. <
Shown (TAL'P11, October 1987
(pages 5 to 118) and are shown below.

214(1-cr2)Do'DB"PL"5
Nip width = □ (πE (Do + DB) 0.s *However, Do: Elastic roll outer diameter RoD: Rigid roll outer diameter Opening: Nip linear pressure kg [/am However, if there is paper between the nip In other words, when processing a web, the elastic modulus of the web during processing must be considered.The elastic modulus of the web changes not only depending on the raw material composition and manufacturing conditions of the web, but also on the basis weight. .

Therefore, the inventor has developed a base paper coated with a coating liquid having pressure-sensitive characteristics, which has a basis weight of 25 to 100 g/rrf and a coating of 413 to 30 g/rIf.
As a result of examining the relationship between the nip passage time and calendar conditions using the coating liquid of As mentioned above, we found that when the factors satisfy the following relationship, high smoothness and gloss can be obtained with low density, high opacity, and stiffness. When exceeded, an increase in density occurs,
The value of L is 0.0 because the rigidity and opacity are significantly reduced.
It must be kept within a range not exceeding 0.02.

As mentioned above, since the value of L in the soft calender is suppressed to a small value, as a result, a high nip surface pressure can be obtained at the same linear pressure.

For this reason, if too high a linear pressure is applied, the density of the paper web will increase, so a linear pressure exceeding 550 (kgf/cm) should not be applied. In addition, in order to obtain gloss and smoothness of the coating surface,
It is necessary to apply a linear pressure of at least 100 (kgf/Cm) or more.

Naturally, an increase in the number of nips leads to an increase in density (
Therefore, it is necessary to suppress the number of nips to 6 or less.

The processing conditions of the soft calender in the present invention increase the nip surface pressure, but keep the nip passage time short, so
If the coated paper to be treated, especially the base paper layer, is not flexible, the smoothness and gloss of the coated layer surface cannot be obtained.

Although the flexibility of the coated base paper can be significantly increased by increasing the filler content, the most effective filler is light calcium carbonate. For clay for drilling, etc., 0
．． If the L value is less than 002, the necessary smoothness and gloss cannot be obtained.

D) Examples In the following, the present invention will be explained in more detail using examples.

Example 1 - Commercially available LBKP (freeness 350ml csf):
30 parts/Commercially available NBKP (Freeness 420ml/csf
) : In Examples and Comparative Examples of 70 parts or less, unless otherwise specified, the pulp compositions described above are prepared.

・Light calcium carbonate: 13 parts (*) (average particle size: 1 μm, 1 calcite type) *Displayed as atomic weight in base paper.

<Internally added chemicals> ・Commercially available alkyl ketene dimer-based internally added sizing agent (AKD
): Q, 03 parts・Commercially available cationized starch: 0,2 parts・Commercially available cationic polyacrylamide retention improver: O
, Oa parts In the Examples and Comparative Examples below, unless otherwise specified, the internally added chemicals are prepared according to the above formulations.

A base paper with a basis weight (bone dry) of 37 g/nf was made using the above formulation, and a coating solution having the following formulation was coated on both sides using a blade coater at a coating weight of 7 g/rrf per side.

・Commercially available primary kaolin: 50 parts ・Commercially available secondary kaolin: 50 parts ・Commercially available polyacrylic acid dispersant: 0.05 parts ・Commercially available phosphoric acid starch: 4 parts ・Commercially available styrene/butadiene latex = 12 parts ・Stear calcium phosphate
:O, 3 parts/sodium hydroxide :0.
In Examples and Comparative Examples containing 15 parts or less, unless otherwise specified, coating liquids are prepared with the above formulation.

Further, the base paper basis weight and coating amount are also adjusted to the above values.

The smeared paper processed under the above conditions was smeared and immediately after drying, soft calender treatment was performed under the following conditions.

Soft calendar specification> - Number of nips: 2 (form a nip so that the rigid roll surface hits the front and back sides of the smeared paper once) - Rigid roll: diameter 80anΦ, forged steel roll - Elastic roll: diameter 70anΦ, synthetic Resin coating, Shore D hardness = 80 degrees, <Soft calender processing conditions> ・Processing speed: 1000 m/min ・Rigid roll surface temperature: 120°C ・Linear pressure: 150 kg/cm ・L value
:0. OOl The characteristics of the product of Example 1 are summarized in Table 1, and satisfactory characteristic values were obtained.

Example 2 The same base paper as in Example 1 was coated under the same coating conditions as in Example 1, except that the amount of light calcium carbonate was changed to 11 parts (base paper ash content), and the treatment was also carried out. .

The characteristics of the product of Example 2 are summarized in Table 1.
Although the opacity is slightly lower than that of , satisfactory characteristics are obtained.

Example 3 A base paper with the same composition as in Example 1 was coated under the same coating conditions as in Example 1, except that the amount of light calcium carbonate was changed to 16 parts (base paper ash content). The treatment was carried out under the same soft calendar conditions as in Example 1.

The characteristics of the product of Example 3 are summarized in Table 1.
Compared to , the density is slightly higher and the pick strength is slightly lower, but all other properties are improved.

Example 4 The filler to be blended was light calcium carbonate (crystal system is calcite, average particle size 1 μm), the blending amount was 5 parts, and other fillers were mixed into clay (average particle size was 1 μm, 8 parts (base paper) except for the ash content), on the base paper with the same composition as in Example 1,
Coating was performed under the same coating conditions as in Example 1, and treatment was also performed under the same soft calender conditions as in Example 1.

The characteristics of the product of Example 4 are summarized in Table 1.
Compared to , the density is slightly lower, and other than the pick strength being slightly improved, all other properties are lower, but this is not at a level that poses a problem.

Example 5 A base paper having the same formulation as in Example 1 was coated under the same coating conditions as in Example 1, except that the average particle size of the light calcium carbonate was 0°5μ. The treatment was carried out under the same soft calendar conditions as in Example 1.

The characteristics of the product of Example 5 are summarized in Table 1.
Compared to , the density is slightly higher and the pick strength is slightly lower, but all other properties are improved.

Example 6 A base paper with the same formulation as in Example 1 was coated under the same coating conditions as in Example 1, except that the average particle size of the light calcium carbonate was 2 μm. Processing was carried out under the same soft calendar conditions.

The characteristics of the product of Example 6 are summarized in Table 1.
Compared to this, the density is lower and the pick strength is improved, but all other properties are slightly lower, but characteristic values that are acceptable for practical use are obtained.

Example Fine line size press (ISP: A base paper is passed between two rubber rolls, a pool of water-soluble binder solution is created on the nip entrance side, and the base paper is immersed in it.A 4% oxidized starch aqueous solution is used as the water-soluble binder here. Except for this point, Example 1 was applied to the base paper having the same composition as Example 1.
Coating was performed under the same coating conditions as in Example 1, and treatment was also performed under the same soft calender conditions as in Example 1.

The product characteristics of Example 7 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but other characteristics are considerably lower and remain at a level that does not cause any problems. .

Comparative Example 1 The filler to be blended was made from commercially available clay (average particle size: 1 μm).
) A base paper prepared under the same manufacturing conditions as in Example 1 was coated with the same coating conditions as in Example 1, except that the amount was changed to 13 parts, and the treatment was also carried out under the same soft calender conditions as in Example 1.

The product characteristics of Comparative Example 1 are summarized in Table 1, and compared to Example 1, the density is lower and the pick strength is improved, but all other characteristics are significantly lower, and satisfactory characteristic values cannot be obtained. do not have.

Comparative Example 2 The filler to be blended was light calcium carbonate (crystal system is calcite, average particle size 1 μm), the blending amount was 3 parts, and other fillers were added to make clay (average particle size 1 μm) 7 parts. A base paper with the same formulation as in Example 1 except for the base paper ash content was coated under the same coating conditions as in Example 1, and also treated under the same soft calender conditions as in Example 1.

The product characteristics of Comparative Example 2 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other characteristics are significantly lower and unsatisfactory (characteristic values are not obtained). I can't.

Comparative Example 3 The filler to be blended was light calcium carbonate (crystal system is calcite, average particle size 1 μm), the blending amount was 4 parts, and other fillers were added to make clay (average particle size 1 μm) 4 parts. A base paper with the same formulation as in Example 1 except for the base paper ash content was coated under the same coating conditions as in Example 1, and also treated under the same soft calender conditions as in Example 1.

The product properties of Comparative Example 3 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other properties are significantly lower, and satisfactory property values cannot be obtained. do not have.

Comparative Example 4 The crystal system of light calcium carbonate to be blended is aragonite (
Coating was performed on base paper with the same formulation as in Example 1 under the same coating conditions as in Example 1, except that the average particle size was 1 μm) and the blending amount was 13 parts (base paper ash content). The treatment was carried out under the same soft calendar conditions as in Example 1.

The product characteristics of Comparative Example 4 are summarized in Table 1, and compared to Example 1, the density is significantly higher and the pick strength is significantly lower, making it impossible to obtain satisfactory characteristic values.

Comparative Example 5 The average particle size of light calcium carbonate (crystal system is calcite) to be blended was 0.2 μm, and the blending amount was 13 parts (
A base paper with the same composition as in Example 1 was coated with the same coating conditions as in Example 1, except for the base paper ash content, and the coating was applied under the same coating conditions as in Example 1.
Processing was carried out under the same soft calendar conditions.

The product characteristics of Comparative Example 5 are summarized in Table 1, and compared to Example 1, the density is significantly higher and the pick strength is significantly lower, making it impossible to obtain satisfactory characteristic values.

Comparative Example 6 The average particle size of light calcium carbonate (crystal system is calcite) to be blended was 2.5 μm, and the blending amount was 13 parts (
A base paper with the same composition as in Example 1 was coated with the same coating conditions as in Example 1, except for the base paper ash content, and the coating was applied under the same coating conditions as in Example 1.
Processing was carried out under the same soft calendar conditions.

The product properties of Comparative Example 6 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other properties are significantly lower, and satisfactory property values cannot be obtained. do not have.

Comparative Example 7 A smeared paper obtained by coating base paper with the same formulation as in Example 1 under the same coating conditions as in Example 1 was subjected to supercalender treatment under the following conditions.

Super calendar specifications> ・Number of stages: 10 stages ・Rigid roll: Chilled roll, outer diameter 400 mm medium ・Elastic roll: Cotton roll, outer diameter 420 mm medium Super calender processing conditions> ・Processing speed: 600 m/min ・Line Pressure: 200 kg/cm - Hollow roll temperature: 265°C The product characteristics of Comparative Example 7 are summarized in Table 1, and the density is significantly higher than that of Example 1, making it impossible to obtain satisfactory characteristic values.

Example 8 A base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the same conditions as Example 1 were applied except that the nip linear pressure of the soft calender was 250 kg/cmh. Processed with.

The characteristics of the product of Example 8 are summarized in Table 1.
Compared to this, except for the density being slightly higher, all other characteristics were improved, and satisfactory characteristic values were obtained.

Example 9 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the same procedure as in Example 1 was performed except that the nip linear pressure of the soft calender was 500 kg/ai+. The treatment was carried out under the following conditions.

The characteristics of the product of Example 9 are summarized in Table 1.
Compared to this, except for the density being slightly higher, all other characteristics were improved, and satisfactory characteristic values were obtained.

Example 10 A base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the same procedure as Example 1 was performed except that the nip linear pressure of the soft calender was 100 kg/an. The treatment was carried out under the following conditions.

The characteristics of the product of Example 9 are summarized in Table 1.
Compared to , except for the density being slightly lower, all other properties are slightly lower, but characteristic values that pose no problem in practical use are obtained.

Example 11 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the nip linear pressure of the soft calender was set to 150 kg/am, the same conditions as in Example 1. The conditions were the same as in Example 1, except that two soft calenders with the specifications shown in Example 1 were passed in series (a nip was formed so that the rigid roll surface touched the front and back sides of the smearing paper twice). Number of whelks treated with: 4).

The characteristics of the product of Example 11 are summarized in Table 1. Compared to Example 1, except for the slightly higher density, all other characteristics were improved, and satisfactory characteristic values were obtained.

Example 12 A base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the same procedure as Example 1 was performed except that the elastic roll hardness of the soft calender was set to 89°. The treatment was carried out under the following conditions.

The characteristics of the product of Example 12 are summarized in Table 1, and as compared to Example 1, there is no change in density, and there are no major differences in other characteristics, and satisfactory characteristic values are obtained.

Example 13 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the same procedure as in Example 1 was carried out, except that the elastic roll hardness of the soft calender was set to 96°. The treatment was carried out under the following conditions.

The properties of the product of Example 13 are summarized in Table 1. Compared to Example 1, the density remains unchanged and the smoothness is improved, but the gloss is slightly reduced. However, overall, satisfactory characteristic values were obtained.

Example 14 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the nip linear pressure of the soft calender was set to 11001 C/am, the same conditions as in Example 1. The conditions were the same as in Example 1, except that three soft calenders having the specifications shown in Example 1 were passed in series (a nip was formed so that the rigid roll surface touched the front and back sides of the smearing paper twice). The number of whelks treated with = 6).

The properties of the product of Example 14 are summarized in Table 1. Although the density is considerably higher than that of Example 1, it is at an acceptable level, and the properties such as smoothness and gloss are improved, and the properties are satisfactory. value is obtained.

Comparative Example 8 A base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the same conditions as Example 1 were applied except that the nip linear pressure of the soft calender was 50 kg/cm. Processed with.

The characteristics of the product of Comparative Example 8 are summarized in Table 1.
Compared to this, except for the density being slightly lower, all other properties are significantly lower, making it impossible to obtain satisfactory characteristic values.

Comparative Example 9 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the conditions were the same as in Example 1 except that the nip linear pressure of the soft calender was 600 kg/cm. Processed with.

The characteristics of the product of Comparative Example 9 are summarized in Table 1, but those of Example 1
Compared to , the density is significantly higher and satisfactory characteristic values cannot be obtained.

Comparative Example 10 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, with a soft calender nip line pressure of 5501■/■ and an elastic roll hardness of 60°.
The treatment was carried out under the same soft calender conditions as in Example 1, except for the following.

The characteristics of the product of Comparative Example 10 are summarized in Table 1. Compared to Example 1, not only the density increased significantly, but also the white paper gloss and print gloss decreased slightly, and the overall characteristic values were satisfactory. I can't get it.

(The following is a blank space) E) Effects of the invention By carrying out the present invention, it is possible to produce coated paper that has high opacity and high rigidity, as well as high smoothness, white paper gloss, and printing gloss. .

1. Indication of the incident 1988 Patent Application No. 257641 2
, Coated paper for printing the name of the invention 3, Person making the amendment Relationship with the case Patent applicant a (600) 2481 (1) Amend the scope of the claims as shown in the attached sheet.

(2) Lines 12-13 of page 4 of the specification, "180 to 450 kgt/cmJ, r Corrected to 180 to 450 kg1/anJ.

(3) Same page 4, line 13, r 14-0~300kgj/cJj is
00 kgl/a (corrected to J.

(4) Same page 5, line 3, r90-180 kgt/cmj, r90-180
Correct to kgf/aoJ.

(5) Same page 5, lines 3-4, r 7 'O~14 Qkgl/cnrJ is changed to "70~
Corrected to 140 kgl/cJJ.

(6) Same, page 8, line 17, "Diameter measurement" Correct to "rigidity".

(7) “Coal” on page 9, line 7.8.9.10.
Correct each to "lime".

(8) Line 4 of page 10 of the specification, "Comparative angle" Correct to "relatively square".

(9) Same, page 10, line 9, "Coating Machine Soft Calendar" Correct to "soft calendar on coating machine".

(10) Same page 15, line 5, "For coating machines" Correct to "coated paper".

(11) Same page 16, line 4, "Poisson" Correct to "Poisson".

(12) Same page 16, line 6, rl 987J, Correct to rl 978J.

(13) Same page 16, line 10, r (πE(DO+DB) 05J
+DIl) ) ” Correct to 5J.

(14) Page 17, line 1 of the specification, "Coating fluid J, Correct to “coated paper”.

(15) Same page 17, line 7, "I did" Correct it to "I did."

(16) Same page 21, line 3, "The same base paper" Correct to "base paper with the same composition".

(17) On page 21, line 5, "Processed." is corrected to "Processed under the same soft calendar conditions as in Example 1."

(18) Same page 23, line 12, "Incline size press" Correct to "inclined size press".

(19) Ibid., page 23, line 16. ``Except for this point,'' is corrected to ``Except for the point that was processed.''

(20) Page 24, line 6 of the specification, “I made it to 13 parts” Corrected to "13 copies (based on base paper ash content)."

(21) Same page 31, line 9, "twice" Corrected to "3 times".

2. Scope of Claims (1) Calcite-based light calcium carbonate with a filler content in the range of average particles 0.3 to 2.0 μm to 4 mm of base paper.
% by weight or more, and the total ash content of the base paper is 10% by weight.
A coated paper for printing, characterized in that a pigment coating layer is provided on the above-mentioned base paper, and after drying, the coated surface is pressed against a soft calender.

(2) The coated paper for printing according to claim 1, characterized in that the following three conditions are satisfied as conditions for press-bonding the coated surface to a soft calender with a nip number of 6 or less.

a: The hardness of the soft calender elastic roll is 75 or more (Shore D hardness).

b = The index defined by the following formula satisfies the following conditions.

(K 'Do 'DB 'PL) ``333L=□VlfDo +Do)' (1,48exp(fl,
11So))lo333L≦0.002 *However, D. 1 Elastic roll outer diameter -]), : Rigid roll outer diameter - Dl: Elastic roll iron core outer diameter - PL: Nip line pressure kgl/an SD 1 Elastic roll hardness (Shore D) ■Niline processing speed /sec.

K = 3 (Do-DI) (Do /D+)
C: Nip linear pressure satisfies the following conditions: 100≦PL
≦550 (3) The coated paper for printing according to claim 1 or 2, wherein the base paper is a base paper that has not been subjected to size press treatment.

Procedural amendment letter 1, case description 1988 patent application No. 257641 2
, Name of the invention Coated paper for printing 3, Relationship with the case of the person making the amendment Patent applicant address 4-2 Shiratama-chome, Maruno, Chiyoda-ku, Tokyo Name (59g) Mitsubishi Paper Mills Co., Ltd. Contact information 125
Mitsubishi Paper Mills Co., Ltd., 4-1 Toganemachi-chome, Katsushika-ku, Tokyo
Patent Department ffi (60012481 Specification, Table 1 on page 34 is amended as shown in the attached sheet.

Procedural amendment (formerly υ 1. Indication of the case 1988 Patent Application No. 257641 2,
Name of the invention Coated paper for printing 3, Relationship with the case of the person making the amendment Patent applicant address 4-2, Marunoshiratama-chome, Chiyoda-ku, Tokyo Contact information 4-1-chome, Togane-cho, Katsushika-ku, Tokyo 125 Patent Department, Mitsubishi Paper Mills Co., Ltd. (60012481 4, Full text of the specification subject to amendment 1, Name of the invention Coated paper for printing 2, Claims (1) Filler content is 0.3 to 0.3 average particles Contains at least 4% by weight of calcite-based light calcium carbonate in the range of 2.0 μm based on the weight of the base paper, and the total ash content of the base paper is 10
A coated paper for printing, characterized in that a pigment coating layer is provided on a base paper of at least % by weight, and after drying, the coated surface is pressed against a soft calender.

(2) The coated paper for printing according to claim 1, characterized in that the following three conditions are satisfied as conditions for press-bonding the coated surface to a soft calender with a nip number of 6 or less.

a: The hardness of the soft calender elastic roll is 75 or more (Shore D hardness).

b: The index defined by the following formula satisfies the following conditions.

(K・Do・D,・PL)0333 L=□ Y((Do + DB)・(1,48exp(0,
ll5o))l' 333L≦0.002 *However, D. : Elastic roll outer diameter ω Ds: Rigid roll outer diameter ■ Dl: Elastic roll iron core outer diameter Mouth PL: Nip linear pressure kg/an SD: Elastic roll hardness (Shore D) V Niline processing speed an/B (K=3 (Do-D, ) - (Do /D, )
'-'C: Nip linear pressure satisfies the following conditions100
≦PL≦550 (3) The coated paper for printing according to claim 1 or 2, wherein the base paper is a base paper that has not been subjected to size press treatment.

3. Detailed Description of the Invention A) Industrial Application Field The present invention relates to a coated paper for printing, and particularly to a coated paper for printing that is excellent in opacity, whiteness, and rigidity, and has excellent white paper gloss and printing gloss. It is.

B) Prior Art and Problems In recent years, there has been an increasing desire for coated paper for printing to be lighter in weight and to visualize printed matter.

In addition, as printing speeds increase, coated paper that can withstand these speeds is becoming necessary.

On the other hand, from the standpoint of producing coated paper, the most important issue now more than ever is how to increase production efficiency. Under these circumstances, in order to reduce the weight of coated paper, the qualities that require particular attention are opacity and rigidity. Rigidity is also important from the viewpoint of high-speed printing workability.

When considering the visualization of printed matter, it is important to have whiteness, smoothness, and high gloss in addition to opacity. There are several known methods for obtaining high opacity. For example, choosing mechanical pulp as the pulp to be used, or incorporating high filler properties into the base paper, and processing at a relatively lower linear pressure than the super calender, which has a high linear pressure in the finishing process. For example, using a gloss calendar.

In addition, in terms of whiteness, it is necessary to use many raw materials with high whiteness, and in terms of stiffness, the same measures as opacity measures are effective except for high ash base paper.

However, when attempting to take such measures when actually producing coated paper, the accompanying drawbacks also appear, making it difficult to make the desired coated paper a reality.

For example, the quality, opacity, stiffness, gloss, and smoothness of the coated paper obtained vary greatly depending on the finishing method, but in the case of machine calender finishing, the web is usually passed between two unheated steel rolls under high linear pressure. Because it passes through, it produces smoothness, but almost no gloss can be obtained.

Super calender is composed of multiple rolls of steel and elastic material alternately, and its linear pressure is 180 to 450 kg/alt.
1. The nip pressure is usually 140 to 300 kg/ad, and the roll temperature is usually 30 to 80°C.

Although the resulting coated paper has high gloss and smoothness, it inevitably collapses, which is disadvantageous in obtaining high opacity and stiffness. Another finishing method is gloss calendering, which uses heated finishing rolls to give coated paper or board a longer pass through the nip without finishing at the higher linear pressures of supercalendering. Produces luster.

Linear pressure of the device is 90-180 kg/cm, nip pressure 7
The normal production conditions are 0 to 140 kg/cnr and a temperature of 100 to 150°C, particularly as high as 230°C. This relatively low linear pressure finish does not densify the paper too much, resulting in relatively good opacity, while the relatively high temperature softens the coating and allows for improved gloss. However, this finishing effect is limited to the top side of the web.

Therefore, the surface of this coated paper does not have the smoothness that can be obtained with a supercalender, and it is generally difficult to obtain high quality.

Also, as seen in Publication No. 63-500188,
Nip pressure, roll linear pressure, web residence time in the nip,
However, even in this case, the preferred nip width is 1.
．． The nip width is 27 to 2.54 cm, which is much wider than the super calender's nip width of 0.6 to 1.2 marks, and it does not improve roll durability or drum stains, which are operational problems when using a gloss calender. . Another recent finishing method is to use a soft calendar. The soft calender method combines a metal roll and an elastic roll and calenders with a small number of nips.

The elastic roll uses a special synthetic resin-coated roll with a hardness comparable to or higher than that of a supercalender, but the key point lies in the material of this roll. That is, it is necessary to select a special material that has excellent heat resistance, abrasion resistance, and is resistant to scratches under high nip pressure. For this reason, this finishing method is mainly applied to matte finishes that do not place a relatively large load on the roll.

On the other hand, if high opacity is to be obtained in the formulation, for example, when mechanical pulp is used as the pulp, its whiteness will be low, and if it is attempted to achieve this by increasing the ash content of the base paper, its rigidity will decrease. For this reason, the reality is that it is not possible to produce coated paper with excellent opacity, whiteness, rigidity, white paper gloss, and printing gloss at low cost and with good operability, especially as lightweight coated paper. The realization of this has become a major challenge for coated paper manufacturers.

In view of this current situation, the inventors of the present invention have conducted intensive research to develop a coated paper that has unprecedented high opacity and rigidity, as well as high white paper gloss and printing gloss. By applying a special finish to coated paper, which is a base paper that contains a specific light calcium carbonate and a specific amount of ash, and a pigment coating layer, we can create effects that have not been seen before. This discovery led to the completion of the present invention.

The purpose of the coated paper produced in this manner is to be able to achieve both contradictory physical properties of coated paper, which are not available in the past, and to provide an excellent coated paper.

C) Means for solving the problem The present invention is characterized in that the filler content contains 4% by weight or more of calcite-based light calcium carbonate having an average particle size in the range of 0.3 to 2.0 μm based on the weight of the base paper, and , the total ash content of the base paper is 10
This coated paper for printing is characterized in that it has a weight of 96 or more and is preferably not subjected to size press treatment, and is provided with a pigment coating layer, and after drying, the coated surface is pressed against a soft calender.

Further, in the treatment with the soft calender, it is desirable that the following three conditions be satisfied in order to press the coated surface to the soft calender with a nip number of 6 or less.

a: The hardness of the soft calender elastic roll is 75 or more (Shore D hardness).

b: The index defined by the following formula satisfies the following conditions.

(K・Do・Dll・PL)0・333L=V((Do + De)(1,48exp(0,1I
So))l”333L≦0.002 *However, D.: Elastic roll outer diameter DB = Rigid roll outer diameter Cl1l D.: Elastic roll iron core outer diameter Country PL: Nip linear pressure kg/cm So: Elastic roll hardness (Shore D)V Niline processing speed cm/secK=3 (Do -D
, ) −(Do /D, ) 05C: The nip linear pressure satisfies the following conditions.

100≦PL≦550 In the present invention, as mentioned above, a specific light calcium carbonate is used, but the light calcium carbonate referred to in the present invention refers to quicklime obtained by burning limestone and purified carbon dioxide gas. It is synthesized by the carbonation method, which is made by dissolving quicklime in water to make milk of lime, and then blowing carbon dioxide gas into it, or by the carbonate solution, which is made by reacting milk of lime or calcium chloride solution with soda carbonate. It refers to precipitated calcium carbonate, and its crystal form (calcite type, argonite type, etc.) and size can be adjusted depending on the conditions of the synthesis reaction.

In the case of calcite-based crystals, the shapes are usually spindle-like, bur-like in which these crystals are aggregated, and cube-like (cubic and dumpling). In addition, aragonite usually has a shape called rod-like or needle-like.

The internal filler used in the present invention is light calcium carbonate, and its shape has an average particle size of 0.3 μm or more and 2.0 μm or more.
It is a calcite-based crystal with a size of μm or less. Particularly preferred is one with relatively rounded corners. Compared to particles having the particle shape of the present invention, for example, aragonite-based particles, the rate of inhibiting interfiber bonding is particularly small (therefore, there is little decrease in strength. However, the rate of improvement in opacity is small accordingly). The present invention is based on the premise that soft calender finishing is performed on a coating machine, and the rate of decrease in opacity due to calendering affects the final opacity.

The light calcium carbonate having the particle shape of the present invention has a lower rate of decrease in opacity due to calendering than other shapes, and the opacity of the final product is high. The reason for this is not clear, but if we consider that the decrease in opacity due to calendering is a decrease in optically effective voids, the optical This is thought to be because it affects the effective void reduction rate.

In addition, when the average particle size is smaller than 0.3 μm, the paper strength decreases significantly with respect to the internal addition ratio;
If it is more than m, the rate of improvement in opacity decreases, which is not preferable.

Further, the blending ratio of the filler containing the above-mentioned light calcium carbonate to the base paper must be 10% by weight or more as ash, and more preferably in the range of 12 to 20% by weight. If the filler content is less than 10% by weight, sufficient physical properties of the coated paper cannot be obtained by the soft calendering treatment described below, and if the filler content is 20% by weight or more, the strength of the base paper is insufficient for offset printing. In addition, the required content ratio of light calcium carbonate in the filler is 40 to 1% of the total ash content.
00%, and if it is less than 40%, sufficient opacity cannot be obtained.

In the present invention, the average particle diameter refers to the average particle size measured by dispersing the filler aqueous dispersion in an ultrasonic dispersion machine for 5 minutes, then using a light transmission particle size distribution measuring machine (
Measured using SKN method (manufactured by Seishin Enterprise Co., Ltd.), cumulative weight%
It refers to the particle diameter when 50% of the particle diameter reaches 50%, which is the so-called weight average particle diameter.

The ash content of the present invention can be determined by taking an arbitrary amount of 1 to 10 g of a sample, drying it at 105° C. for 1 hour, and measuring the dry weight. After that, it was incinerated at 500° C. for 3 hours, and the absolute dry weight of the residue is expressed in weight % with respect to the absolute dry weight of the sample.

In the present invention, fillers commonly used in paper making, such as kaolin, clay, heavy calcium carbonate, titanium dioxide, calcined kaolin, and talc for paper making, may be used in combination.

It is also commonly used in paper making as sizing agents, antifoaming agents, slime control agents, dyes, colored pigments, optical brighteners, dry paper strength agents, wet paper strength agents, freeness improvers, and retention improvers. Additive chemicals can also be included if necessary.

Furthermore, it is possible to apply starch, polyvinyl alcohol, paint, and various surface sizing agents to the surface of the base paper using a size press, gate roll, or bill blade device, but the size press process hardens the base paper, resulting in the finishing described below. In order to fully exhibit the treatment effect, it is preferable to use base paper that has not been subjected to size treatment.

The base paper used in the present invention is monolaminar pulp (NBKP).
, LBKP), high yield pulp (GP.

TMP, CTMP, CMP, etc.) and waste paper pulp.

In the present invention, a pigment coating layer is provided on the above-mentioned base paper, and the coating layer is coated on one or both sides of the base paper using an on-machine coating device such as a size press, gate roll, bill blade, or a commonly used blade coater or air. It refers to what is provided with an off-machine coater such as a knife coater, and the coating amount is preferably 3 to 25 g/rrf, more preferably 5 to 15 g/d.

Generally known pigments, binders, dispersants, thickeners, etc. can be used in the coating liquid that can be used in the present invention.

As pigments, kaolin, calcium carbonate, clay, satin white, talc, titanium oxide, aluminum hydroxide, silica, zinc oxide, activated clay, silicon earth, lake, plastic pigments, etc., or sand milled products of these pigments can be used as appropriate. . As the dispersant, polycarboxylic acids such as acrylic acid polymers and copolymers of acrylic acid and maleic acid, or their soda salts, ammonium salts,
One or more of phosphoric acid-based surfactants such as sodium hexametaphosphate and sodium pyrophosphate, anionic surfactants such as lignosulfonate and naphthylsulfonate, citric acid, malic acid, or salts thereof can be used as appropriate.

As a binder, various copolymers such as styrene/butadiene type, styrene/acrylic type, vinyl acetate type, acrylic type, ethylene/vinyl acetate type, butadiene/methyl methacrylate type, vinyl acetate/butyl acrylate type, polyvinyl alcohol, maleic anhydride etc. Synthetic binders such as acid/styrene copolymers, isobutyne/maleic anhydride copolymers, acrylic acid/methyl methacrylate copolymers, oxidized starches, enzyme-modified starches, and cold water-soluble starches obtained by flash-drying them; Generally known binders such as natural binders such as casein and soybean protein may be used.

The present invention is characterized in that coated paper is treated under special conditions in a soft calender.

As mentioned above, soft calenders have a smaller number of nips than super calenders, 2 to 6 nips, and elastic rolls have a hard iron core thinly covered with synthetic resin (75-97 in Shore D hardness). There is. For this reason, the nip width becomes narrower. Furthermore, the rigid rolls are composed of chilled rolls and forged steel rolls, and have a heating mechanism, allowing paper webs to be processed even at high temperatures exceeding 100°C.

In supercalendering, the density of the paper increases rapidly due to the wider nip width and higher number of nips (8 to 14 nips) compared to soft calendering, resulting in a decrease in opacity and stiffness. Both are damaged. In this way, what characterizes calendar processing is the nip passage time.

However, in order to grasp the nip passage time during paper passing processing, it is necessary to clarify the nip width. The above-mentioned Publication No. 63-500188 also provides a formula for calculating the width of the nip created by the deformation of an elastic roll in a static state from values such as the elastic modulus (E) and Poisson's ratio (σ) of the elastic roll. (TAPPl October 1978 No. 115~
11g page), so it is shown below.

2f4(1-cy")Do IDB'PL)"
'Nip width = □ (πE(Do +t+B) ) O, s * However, Do
: Outer diameter of elastic roll Country: Outer diameter of rigid roll Country PL : Nip linear pressure kg/an However, if there is paper between the nip, that is, if a web is being processed, then the elastic modulus of the web during processing is must be taken into consideration. The elastic modulus of the web changes not only depending on the raw material composition and manufacturing conditions of the web, but also on the basis weight.

Therefore, the inventor proposed that the basis weight of base paper coated with a coating liquid with pressure-sensitive properties is 25 to 100 g/rrf coating fit 3 to 30 g/rr.
As a result of examining the relationship between nip passage time and calendar conditions using coated paper of As mentioned above, it has been found that when the following factors are satisfied, high smoothness and gloss can be obtained with low density, high opacity, and rigidity.

L≦0.002 When the value of L exceeds 0.002, an increase in density occurs;
The value of L is 0.0 because the rigidity and opacity are significantly reduced.
It must be kept within a range not exceeding 0.02.

As mentioned above, since the soft calender has a small shear value, it is possible to obtain a high nip surface pressure at the same linear pressure.

For this reason, if too high a linear pressure is applied, the density of the paper web will increase, so it is not desirable to apply a linear pressure exceeding 550 kg/cml.Also, in order to obtain gloss and smoothness of the coated surface, It is desirable to apply a linear pressure of at least 100 (kg/cm) or more.

As mentioned above, if the elastic roll hardness is too low, it becomes necessary to apply a significantly high linear pressure, so a Shore D hardness of less than 75 is not desirable.

Naturally, an increase in the number of nips leads to an increase in density, so it is desirable to suppress the number of nips to 6 or less.

The processing conditions of the soft calender in the present invention increase the nip surface pressure, but keep the nip passage time short, so
If the coated paper to be treated, especially the base paper layer, is not flexible, the smoothness and gloss of the coated layer surface cannot be obtained.

Although the flexibility of the coated base paper can be significantly increased by increasing the filler content, the most effective filler is light calcium carbonate. For clay for drilling, etc., 0
．． If the L value is less than 002, the necessary smoothness and gloss cannot be obtained.

D) Examples In the following, the present invention will be explained in more detail using examples.

Example 1 - Commercially available LBKP (freeness 350ml esf):
70 parts/Commercially available NBKP (Freeness 420ml/csf
) : 3 parts or less In Examples and Comparative Examples, unless otherwise specified, the above pulp formulations are used.

・Light calcium carbonate = 13 parts (*) (Average particle size: 1 μm 1 calcite type) *Displayed as atomic weight in base paper.

Internal additive chemicals> ・Commercially available alkyl ketene dimer internal sizing agent (AKD
): 0.03 parts, commercially available cationized starch = 0.2 parts, commercially available cationic polyacrylamide retention improver: 0
．． In the Examples and Comparative Examples below, unless otherwise specified, the internally added chemicals are prepared according to the above-mentioned formulations.

A base paper with a basis weight (absolutely dry) of 37 g/J was made using the above formulation, and a coating liquid having the following formulation was coated on both sides using a blade coater at a coating weight of 7 g/d per side.

・Commercially available primary kaolin: 50 parts ・Commercially available secondary kaolin: 50 parts ・Commercially available polyacrylic acid dispersant: 0.05 parts ・Commercially available phosphoric ester starch: 4 parts ・Commercially available styrene/butadiene latex: 12 parts ・Stear calcium phosphate
=0.3 parts・Sodium hydroxide: 0
．． In Examples and Comparative Examples containing 15 parts or less, unless otherwise specified, coating liquids are prepared with the above formulation.

Further, the base paper basis weight and coating amount are also adjusted to the above values.

The smeared paper processed under the above conditions was smeared and immediately after drying, soft calender treatment was performed under the following conditions.

<Soft calendar specification> - Number of nips = 2 (form a nip so that the rigid roll surface hits the front and back sides of the smeared paper once) - Rigid roll: diameter 80cmφ, forged steel roll - Elastic roll: diameter 70anφ, synthetic Resin coating, Shore D hardness = 80 Soft calender processing conditions> ・Processing speed: 1000 m/min ・Rigid roll surface temperature: 120°C ・Linear pressure: 150 kg/cm ・L value
:0. OOl The characteristics of the product of Example 1 are summarized in Table 1, and satisfactory characteristic values were obtained.

Example 2 A base paper with the same composition as in Example 1 was coated under the same coating conditions as in Example 1, except that the amount of light calcium carbonate was 11 parts (base paper ash content). The treatment was carried out under the same soft calendar conditions as in Example 1.

The characteristics of the product of Example 2 are summarized in Table 1.
Although the opacity is slightly lower than that of , satisfactory characteristics are obtained.

Example 3 Example 1 was applied to base paper having the same composition as Example 1, except that the amount of light calcium carbonate was 16 parts (base paper ash content).
Coating was performed under the same coating conditions as in Example 1, and treatment was also performed under the same soft calender conditions as in Example 1.

The characteristics of the product of Example 3 are summarized in Table 1.
Compared to , the density is slightly higher and the pick strength is slightly lower, but all other properties are improved.

Example 4 The filler to be blended was light calcium carbonate (crystal system is calcite, average particle size 1 μm), the blending amount was 5 parts, and other fillers were mixed into clay (average particle size was 1 μm, 8 parts (base paper) except for the ash content), on the base paper with the same composition as in Example 1,
Coating was performed under the same coating conditions as in Example 1, and treatment was also performed under the same soft calender conditions as in Example 1.

The characteristics of the product of Example 4 are summarized in Table 1.
Compared to , the density is slightly lower, and other than the pick strength being slightly improved, all other properties are lower, but this is not at a level that poses a problem.

Example 5 A base paper having the same formulation as in Example 1 was coated under the same coating conditions as in Example 1, except that the average particle size of the light calcium carbonate was 0°5μ. The treatment was carried out under the same soft calendar conditions as in Example 1.

The characteristics of the product of Example 5 are summarized in Table 1.
Compared to , the density is slightly higher and the pick strength is slightly lower, but all other properties are improved.

Example 6 A base paper with the same formulation as in Example 1 was coated under the same coating conditions as in Example 1, except that the average particle size of the light calcium carbonate was 2 μm. Processing was carried out under the same soft calendar conditions.

The characteristics of the product of Example 6 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other characteristics are slightly lower, but there are no problems in practical use. value is obtained.

Example Finclined size press (ISP: A base paper is passed between two rubber rolls, a pool of water-soluble binder solution is created on the nip entrance side, and the base paper is immersed.The water-soluble binder here is a 4% oxidized starch aqueous solution. Coating was performed on base paper with the same formulation as in Example 1, except for the treatment, under the same coating conditions as in Example 1, and also under the same soft calender conditions as in Example 1. Processed with.

The product characteristics of Example 7 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but other characteristics are considerably lower and remain at a level that does not cause any problems. .

Comparative Example 1 The filler to be blended was made from commercially available clay (average particle size: 1 μm).
)13 parts (based on base paper ash content), base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and also under the same soft calender conditions as in Example 1. processed.

The product characteristics of Comparative Example 1 are summarized in Table 1, and compared to Example 1, the density is lower and the pick strength is improved, but all other characteristics are significantly lower, and satisfactory characteristic values cannot be obtained. do not have.

Comparative Example 2 The filler to be blended was light calcium carbonate (crystal system is calcite, average particle size 1 μm), the blending amount was 3 parts, and other fillers were added to make clay (average particle size 1 μm) 7 parts. A base paper with the same formulation as in Example 1 except for the base paper ash content was coated under the same coating conditions as in Example 1, and also treated under the same soft calender conditions as in Example 1.

The product properties of Comparative Example 2 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other properties are significantly lower, and satisfactory property values cannot be obtained. do not have.

Comparative Example 3 The filler to be blended was light calcium carbonate (crystal system is calcite, average particle size 1 μm), the blending amount was 4 parts, and other fillers were added to make clay (average particle size 1 μm) 4 parts. A base paper with the same formulation as in Example 1 except for the base paper ash content was coated under the same coating conditions as in Example 1, and also treated under the same soft calender conditions as in Example 1.

The product properties of Comparative Example 3 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other properties are significantly lower, and satisfactory property values cannot be obtained. do not have.

Comparative Example 4 The crystal system of light calcium carbonate to be blended is aragonite (
Coating was performed on base paper with the same formulation as in Example 1 under the same coating conditions as in Example 1, except that the average particle size was 1 μm) and the blending amount was 13 parts (base paper ash content). The treatment was carried out under the same soft calendar conditions as in Example 1.

The product characteristics of Comparative Example 4 are summarized in Table 1, and compared to Example 1, the density is significantly higher and the pick strength is significantly lower, making it impossible to obtain satisfactory characteristic values.

Comparative Example 5 The average particle size of light calcium carbonate (crystal system is calcite) to be blended was 0.2 μm, and the blending amount was 13 parts (
A base paper with the same composition as in Example 1 was coated with the same coating conditions as in Example 1, except for the base paper ash content, and the coating was applied under the same coating conditions as in Example 1.
Processing was carried out under the same soft calendar conditions.

The product characteristics of Comparative Example 5 are summarized in Table 1, and compared to Example 1, the density is significantly higher and the pick strength is significantly lower, making it impossible to obtain satisfactory characteristic values.

Comparative Example 6 The average particle size of light calcium carbonate (crystal system is calcite) to be blended was 2.5 μm, and the blending amount was 13 parts (
A base paper with the same composition as in Example 1 was coated with the same coating conditions as in Example 1, except for the base paper ash content, and the coating was applied under the same coating conditions as in Example 1.
Processing was carried out under the same soft calendar conditions.

The product properties of Comparative Example 6 are summarized in Table 1. Compared to Example 1, the density is lower and the pick strength is improved, but all other properties are significantly lower, and satisfactory property values cannot be obtained. do not have.

Comparative Example 7 A smeared paper obtained by coating base paper with the same formulation as in Example 1 under the same coating conditions as in Example 1 was subjected to supercalender treatment under the following conditions.

Super calendar specifications> - Number of stages = 10 stages - Rigid roll: chilled roll, outer diameter 400 mm φ - Elastic roll: cotton roll, outer diameter 420 mm φ Super calender processing conditions> - Processing speed: 600 m/min - Linear pressure: 200 kg /an - Hollow roll temperature = 65° C. The product characteristics of Comparative Example 7 are summarized in Table 1, and the density is significantly higher than that of Example 1, making it impossible to obtain satisfactory characteristic values.

Example 8 A base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the same procedure as Example 1 was performed except that the nip linear pressure of the soft calender was 250 kg/cm. The treatment was carried out under the following conditions.

The characteristics of the product of Example 8 are summarized in Table 1.
Compared to this, except for the density being slightly higher, all other characteristics were improved, and satisfactory characteristic values were obtained.

Example 9 A base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the same procedure as Example 1 was performed except that the nip linear pressure of the soft calender was 500 kg/an. The treatment was carried out under the following conditions.

The characteristics of the product of Example 9 are summarized in Table 1.
Compared to this, except for the density being slightly higher, all other characteristics were improved, and satisfactory characteristic values were obtained.

Example 10 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the process was the same as in Example 1 except that the nip linear pressure of the soft calender was 100 kg/cm. The treatment was carried out under the following conditions.

The characteristics of the product of Example 9 are summarized in Table 1.
Compared to , except for the density being slightly lower, all other properties are slightly lower, but characteristic values that pose no problem in practical use are obtained.

Example 11 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the nip linear pressure of the soft calender was set to 150 kg/an, the same conditions as in Example 1. The conditions were the same as in Example 1, except that two soft calenders with the specifications shown in Example 1 were passed in series (a nip was formed so that the rigid roll surface touched the front and back sides of the smearing paper twice). Number of whelks treated with: 4).

The characteristics of the product of Example 11 are summarized in Table 1. Compared to Example 1, except for the slightly higher density, all other characteristics were improved, and satisfactory characteristic values were obtained.

Example 12 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the conditions were the same as in Example 1 except that the elastic roll hardness of the soft calender was set to 89. Processed with.

The characteristics of the product of Example 12 are summarized in Table 1, and as compared to Example 1, there is no change in density, and there are no major differences in other characteristics, and satisfactory characteristic values are obtained.

Example 13 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the same conditions as in Example 1 were applied except that the elastic roll hardness of the soft calender was set to 96. Processed with.

The properties of the product of Example 13 are summarized in Table 1. Compared to Example 1, the density remains unchanged and the smoothness is improved, but the gloss is slightly reduced. However, overall, satisfactory characteristic values were obtained.

Example 14 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the nip linear pressure of the soft calender was set to 100 kg/am, the same conditions as in Example 1. The conditions were the same as in Example 1, except that three soft calenders with the specifications shown in Example 1 were passed in series (a nip was formed so that the rigid roll surface touched the front and back sides of the smear paper three times). The number of whelks treated with 6).

The properties of the product of Example 14 are summarized in Table 1. Although the density is considerably higher than that of Example 1, it is at an acceptable level, and the properties such as smoothness and gloss are improved, and the properties are satisfactory. value is obtained.

Example 15 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, and the conditions were the same as in Example 1 except that the nip linear pressure of the soft calender was 50 kg/cm. Processed with.

The properties of the product of Example 15 are summarized in Table 1. Compared to Example 1, the density was slightly lower, but the other properties were slightly lower.

Example 16 Same as Example 1, except that base paper prepared under the same manufacturing conditions as Example 1 was coated under the same coating conditions as Example 1, and the nip linear pressure of the soft calender was 600 kg/an. The treatment was carried out under the following conditions.

The properties of the product of Example 16 are summarized in Table 1. Compared to Example 1, the density is significantly higher, but both the white paper gloss and print gloss are increased.

Example 17 A base paper prepared under the same manufacturing conditions as in Example 1 was coated under the same coating conditions as in Example 1, with a soft calender nip linear pressure of 550 kg/cm and an elastic roll hardness of 60.
The treatment was carried out under the same soft calender conditions as in Example 1, except for the following.

The characteristics of the product of Example 17 are summarized in Table 1. Compared to Example 1, the density is higher, but both white paper gloss and print gloss are increased.

(The following is a blank space) E) Effects of the invention By carrying out the present invention, it is possible to produce coated paper that has high opacity and high rigidity, as well as high smoothness, white paper gloss, and printing gloss. .

Claims (3)

[Claims] (1) Calcite-based light calcium carbonate with a filler content in the average particle size range of 0.3 to 2.0μ is added to
% by weight or more, and the total ash content of the base paper is 10% by weight.
A coated paper for printing, characterized in that a pigment coating layer is provided on the above-mentioned base paper, and after drying, the coated surface is pressed against a soft calender. (2) The coated paper for printing according to claim 1, characterized in that the following three conditions are satisfied as conditions for press-bonding the coated surface to a soft calender with a nip number of 6 or less. a: The hardness of the soft calender elastic roll is 75 or more (Shore D hardness). b: The index L defined by the following formula satisfies the following conditions. L=[{K・D_O・D_B・P_L}^0^. ^3^
3^3]/[V{(D_O+D_B)・(1.48ex
p(0.11S_D))}]^0^. ^3^3^3L≦
0.002*However, D_O: Elastic roll outer diameter cm D_B: Rigid roll outer diameter cm D_i: Elastic roll iron core outer diameter cm P_L: Nip linear pressure kgf/cm S_D: Elastic roll hardness (Shore D) V: Line treatment Speed cm/sec. K=3(D_O-D_i)√(D_O/D_i) c: Nip linear pressure satisfies the following conditions 100≦P_L≦550 (3) The coated paper for printing according to claim 1 or 2, wherein the base paper is a base paper that has not been subjected to size press treatment.