JP2005171401A - Coated paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide coated paper having folding and cracking resistance suitability and excellent printing suitability. <P>SOLUTION: The coated paper is provided with a paper substrate and a coating layer consisting essentially of a pigment and an adhesive and provided on at least one surface thereof. In the coated paper, the ratio (=T/Y) of the tensile strength (T) in the machine direction to the tensile strength (Y) in the cross direction by JIS P 8113 is ≥1.5, an internal bonding strength by JAPAN TAPPI No. 18 is ≤2.0 kgf×cm, and the coated paper has ≥2.5% elongation when the tensile strength in the machine direction is exhibited, 50-80% 75° specular glossiness by JIS P 8142 and ≤7,000 sec air permeability by JIS P 8117. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to coated paper. In particular, the present invention relates to a coated paper that has resistance to cracking, has high gloss of white paper, and does not generate blisters.

  Glossy coated paper is increasingly used for booklets, brochures, etc. as printed materials become more visual, more colored, and more sophisticated. In addition, thick coated paper is often used for the cover of various books, shopping bags and fashionable paper bags.

  To finish the coated paper after printing into a booklet or pamphlet, the printing process is followed by a folding process such as bi-folding or tri-folding, or in the manufacture of shopping bags, paper bags, etc. The bag making process is performed. However, in such a process, the coating layer at the crease part of the coated paper may crack, or the coating layer may tear and the base paper layer may be exposed. There was a problem of deteriorating the appearance and reducing the commercial value. In addition, this problem of cracking is more noticeable with thicker coated paper than with thin coated paper, and when the moisture content in the coated paper is small during folding, for example, with an ink drying device in the printing process. This was conspicuous when the moisture of the paper was lost or when folding was performed in a dry environment.

  Therefore, the appearance of coated paper having excellent folding processability, that is, resistance to folding cracking, which prevents cracking and tearing of the coated paper (coating layer) is desired.

Various attempts have already been proposed as a method for imparting resistance to folding.
Japanese Patent Application Laid-Open No. 7-216792 (see Patent Document 1) discloses a styrene-butadiene copolymer substance having a glass transition temperature of 0 ° C. or less as a binder and a pigment mainly composed of kaolin on a base paper. And a method of printing on a coating layer composed of phosphate esterified starch and / or acetylated starch and forming an overprint varnish coating layer on the printed surface.

  However, the method of selecting and using a flexible styrene-butadiene copolymer material having a low glass point transfer Tg and an adhesive for the coating layer has not been sufficient in improving the crackability. In addition, the coated paper manufactured by such a method has poor air permeability, and when printing of such coated paper is performed by a rotary method in which ink drying is performed instantaneously by high heat such as an oven, the ink is dried. There was a problem that a blister (hereinafter referred to as “blister”) occurred in the image area and the appearance was remarkably deteriorated. In addition, since the overcoat varnish application is a separate process, the number of processes is increased, workability is not only inferior, and cost is also disadvantageous.

  Japanese Patent Laid-Open No. 5-287597 (see Patent Document 2) discloses that a Tg of −10 ° C. to −45 as an adhesive in a coating composition used for under (lower layer) coating of coated white paperboard for double coating. The combined use of a latex in the range of 0 ° C. and a water-soluble copolymer obtained from a specific monomer as a water retention agent is described.

  However, even if a latex having a low glass transition point Tg and a soft latex or a water retention agent is used, if the water content in the coated paper is reduced by using an ink drying device, The crackability cannot be improved.

  Japanese Patent Laid-Open No. 6-341096 (see Patent Document 3) discloses a cover and cover of books and magazines by applying a coating liquid mainly composed of a pigment and an adhesive onto a base paper surface and transferring the mirror surface. A glossy paper printed for a cover is described as a high-gloss paper with gloss and fold strength by applying an ultraviolet curable resin or a radiation curable resin to the polished surface and irradiating with ultraviolet rays or radiation. ing. However, since the method described in the publication applies UV curable resin after printing and is cured by irradiating it with UV rays, the number of processes is increased, workability is inferior, and cost is satisfactory. It is not possible.

  Japanese Patent Laid-Open No. 2001-316999 (see Patent Document 4) discloses a paper machine according to JIS P 8113 as an effort related to the tensile strength of printing paper, when the paper is divided into 12 in the width direction. The ratio T / Y between the measured value T of the tensile strength in the direction of travel (MD) and the measured value Y of the tensile strength in the direction perpendicular to the direction of travel of the paper machine (CD) is in the range of 1.5 to 2.8. And a book paper in which the absolute value of the T / Y difference is within 0.6.

  However, even if curling and undulation after binding can be suppressed by adjusting the T / Y ratio of the tensile strength of the paper to a range of 1.5 to 2.8 by this method, the anti-folding is improved. In addition, because it is a high-quality paper having no coating layer, the glossiness is low and a high-quality printed matter cannot be obtained.

JP 7-216792 A (second page)

Japanese Patent Laid-Open No. 5-287597 (page 2)

Japanese Patent Laid-Open No. 6-341096 (page 2)

JP 2001-316999 A (second page)

  An object of the present invention is to provide a coated paper which has an ability to break, has a high gloss of white paper, and does not generate blisters. .

The present invention includes the following embodiments.
(1) In a coated paper comprising a paper base material and a coating layer mainly composed of a pigment and an adhesive on at least one surface thereof, the longitudinal strength of the coated paper according to JIS P 8113 The ratio of the direction (ST) to the horizontal direction (SY) (= ST / SY) is 1.5 or more, the elongation at break in the longitudinal direction is 2.5% or more, and JAPAN TAPPI No. The coated paper characterized by having an internal bond strength by 18 of 2.0 kgf · cm or less.

(2) The coated paper according to (1), wherein the surface of the coating layer has a 75 ° specular glossiness of 50% or more according to JIS P 8142.

(3) The coated paper according to (1) or (2), wherein the air permeability according to JIS P 8117 is 7000 seconds or less.

(4) The ratio (= VT / VY) of the longitudinal direction (VT) and the transverse direction (VY) of the ultrasonic propagation velocity measured by the sound velocity method of the coated paper is 1.4 or more (1) to The coated paper according to any one of (3).

(5) The coated paper according to any one of (1) to (4), wherein the density of the coated paper is 0.9 g / cm ^{3 to} 1.2 g / cm ³ .

  The coated paper according to the present invention is a coated paper that has resistance to folding, has high gloss of white paper, and does not generate blisters, and is extremely useful in practice.

  In order to achieve the above-mentioned object, the present inventors have studied in detail the phenomenon of cracking of coated paper, and as a result of earnestly examining the relationship with the physical properties of the coated paper, the tensile strength in the machine direction of the coated paper has been determined. The ratio of the tensile strength in the transverse direction, the elongation at break, and the internal bond strength were found to be deeply related to the occurrence of cracking, and the present invention was completed.

The paper base material of this invention is demonstrated.
The coated paper of the present invention comprises a paper substrate and a coating layer mainly composed of a pigment and an adhesive provided on at least one surface thereof.

The paper base material is a sheet base material mainly composed of pulp.
Longitudinal and transverse tensile strength ratio (ST / SY) of coated paper, longitudinal elongation at break, internal bond strength, and longitudinal acoustic wave velocity measured by sound velocity method The ratio of the direction of sound wave propagation speed (VT / VY) is greatly influenced by the characteristics of the paper substrate used. Therefore, it is important to adjust the characteristics of the paper substrate in advance so that the desired characteristics are exhibited in the coated paper. The adjustment of the above characteristics is, for example, the selection of the paper machine used for the production of the paper base material and the adjustment of the operating conditions, for example, the jet / wire ratio of the raw material in the wet part of the paper machine (the raw material jet speed / the paper machine's wire speed ), Optimization of the dehydration process in the wire part, and adjustment of the tension balance in the dryer part. In particular, with respect to the improvement of the internal bond strength, for example, adjustments such as appropriately selecting the type of pulp or promoting beating to increase the bond between fibers are effective. In addition, the above characteristics can also be adjusted by adjusting the type of filler and the amount of the filler, and adjusting the type and amount of the paper strength enhancer.

The elongation at break in the longitudinal direction can be measured based on JIS P8113.
As a method for measuring the sound propagation velocity, for example, the SONIC SHEET TESTER manufactured by Nomura Corporation is widely used, but the ratio of the sound propagation velocity in the vertical direction and the sound propagation velocity in the lateral direction of the present invention is also this method. Can be measured.

  The manufacturing method and type of the pulp to be used are not particularly limited. Hardwood pulp, softwood pulp, chemical pulp such as KP, SP, mechanical pulp such as GP, SGP, RGP, TMP, BCTMP, CTMP, waste paper pulp such as deinked pulp, or kefna, bamboo, straw, hemp Such non-wood pulp, polyamide fibers, polyester fibers, polynosic fibers, and other organic synthetic fibers, and glass fibers, ceramic fibers, carbon fibers, and other inorganic fibers can also be used. Among the chemical pulps, pulps produced without using chlorine in the bleaching step, that is, ECF pulp and TCF pulp are preferably used.

  Moreover, a filler can be mix | blended in a paper base material as needed. The filler is not particularly limited, but various pigments generally used for fine paper, such as kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, zinc oxide, alumina, magnesium carbonate, oxidation Mineral pigments such as magnesium, silica, white carbon, bentonite, zeolite, sericite, smectite, polystyrene resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins and their hollow micro particles Organic pigments are listed, and one or more of them can be selected and blended. Although the compounding quantity of a filler is not specifically limited, Usually, it is the range of 5 mass% thru | or 30 mass%. If it is less than 5% by mass, the opacity of the paper substrate is low, and the opacity of the finished coated paper may be low. On the other hand, if it exceeds 30% by mass, the paper substrate may be less rigid, or the internal bond strength of the paper may be excessively reduced.

  Furthermore, in addition to pulp and filler, the paper base material has various anionic, nonionic, cationic or amphoteric yield improvers, and improved drainage, as long as the effects of the present invention are not impaired. Various paper making aids such as an agent, a paper strength enhancer, and an internal sizing agent can be appropriately selected and used as necessary. Furthermore, internal additives for papermaking such as dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like may be appropriately added depending on the application.

  The papermaking method is not particularly limited. For example, it is applicable to all papermaking methods such as acidic papermaking with a papermaking pH of around 4.5 and weakly acidic neutral papermaking with a papermaking pH of about 9 including weakly acidic papermaking pH of about 9 including alkaline fillers such as calcium carbonate. can do. As the paper machine, a long net paper machine, a twin wire paper machine, a round net paper machine, a Yankee paper machine, and an inclined wire paper machine can be used as appropriate.

  Paper substrate is a paper machine size press process, starch, polyvinyl alcohol, polyacrylamide, polyethylene glycol, sulfonated styrene resin, quaternary ammonium chloride, calcium oxide, sodium chloride, sodium nitrate, calcium chloride, various surface sizing agents A size press solution containing the above is applied to the paper base by a known method.

  The paper base material of the present invention preferably has a Beck smoothness of 50 seconds or less and an air permeability of 40 seconds or less. If the Beck smoothness exceeds 50 seconds, the operability may be deteriorated, for example, streak may occur in the coating process or the adhesion of the paint may worsen. On the other hand, if the air permeability exceeds 40 seconds, the air permeability after providing the coating layer and smoothing becomes too high, and the generation of blisters cannot be completely prevented. A preferred Beck smoothness is 30 seconds or less, and a preferred air permeability is 30 seconds or less.

  The Beck smoothness and air permeability of the paper substrate are adjusted by selecting the pulp and filler to be used and adjusting the conditions of a smoothing processing apparatus such as a machine calender or soft nip calender. Or, paper strength enhancer such as polyamide, acrylamide, amine compound, amide, epoxy and melamine compound, water repellent of natural wax, olefin, zirconium or fluorine wax, and polyvinyl alcohol, fluorine resin, acrylic It can be adjusted by impregnation with water-soluble resin or water-dispersible resin such as resin, styrene resin, acrylic-styrene copolymer resin, amide resin, urethane resin, epoxy resin, and size press coating. .

  Next, the coating layer of the present invention will be described. The coating layer of the present invention is mainly composed of a pigment and an adhesive.

  Examples of the pigment used include heavy calcium carbonate, light calcium carbonate, kaolin, calcined kaolin, structural kaolin, delaminated kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide. Mineral pigments such as silica, magnesium aluminosilicate, particulate calcium silicate, particulate magnesium carbonate, particulate light calcium carbonate, white carbon, bentonite, zeolite, sericite, smectite, polystyrene resin, styrene-acrylic copolymer Organic pigments such as solid, through-hole, and hollow types such as system resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins, and benzoguanamine resins can also be used. 1 type or More species appropriately selected and used.

  In particular, blending kaolin having an aspect ratio of 5 to 15 and an average particle size of 0.3 to 1.0 μm with respect to 100% by mass of pigment in an amount of 60% by mass or more provides gloss while suppressing an increase in air permeability. Since it can obtain, it is preferable.

  Furthermore, a hollow organic pigment having an average particle size of 0.5 to 1.5 μm can be appropriately blended. Examples of the hollow organic pigment material include polystyrene resins, styrene-acrylic copolymer resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins, and benzoguanamine resins. Alternatively, two or more types can be appropriately selected and used.

  As the adhesive, a water-soluble and / or water-dispersible polymer compound can be used. For example, cationic starch, amphoteric starch, oxidized starch, enzyme modified starch, thermochemically modified starch, esterified starch, etherified starch and other starches, carboxymethylcellulose, cellulose derivatives such as hydroxyethylcellulose, gelatin, casein, soybean Proteins, natural or semi-synthetic polymer compounds such as natural rubber, polyvinyl alcohol, isoprene, neoprene (registered trademark), polydienes such as polybutadiene, polyalkenes such as polybutene, polyisobutylene, polypropylene and polyethylene, vinyl halides, vinyl acetate, Synthetic rubbers such as styrene, (meth) acrylic acid, (meth) acrylic acid ester, (meth) acrylamide, and vinyl polymers and copolymers such as methyl vinyl ether, styrene-butadiene and methyl methacrylate-butadiene. Tex, polyurethane resins, polyester resins, polyamide resins, olefin - maleic anhydride resins, synthetic polymer compounds such as melamine resins and the like. Among these, one or more kinds are appropriately selected and used according to the purpose.

  The blending ratio of the pigment and adhesive in the coating layer of the present invention is preferably in the range of 5 to 50 parts by mass (solid content) with respect to 100 parts by mass (solid content) of the pigment. If it is less than 5 parts by mass, the strength of the coating layer of the coating layer is weak, and the coating layer may be peeled off and deposited on the printing plate of the rotary press, which may cause damage to the printing plate. On the other hand, if it exceeds 50 parts by mass, the coating layer becomes dense and the air permeability may be remarkably increased, causing blistering.

  In addition to the pigments and adhesives described above, various auxiliary agents such as surfactants, pH regulators, viscosity modifiers, softeners, gloss-imparting agents, waxes, dispersants, flow modifiers, anti-conductive agents Agents, stabilizers, antistatic agents, cross-linking agents, sizing agents, fluorescent brighteners, colorants, UV absorbers, antifoaming agents, water-resistant agents, plasticizers, lubricants, preservatives, fragrances, etc. as required Can be used as appropriate.

The coating amount of the coating layer of the present invention, 8~20g / m ^2, it is necessary to preferably from 10 to 20 g / m ^2. If the coating amount is less than 8 g / m ² , the unevenness on the surface of the paper substrate cannot be sufficiently covered, and the acceptability of the printing ink may be significantly reduced. On the other hand, if it exceeds 20 g / m ² , inconveniences such as reduced operability such as poor drying properties during coating and high production costs occur.

  As a coating method for forming a coating layer, generally known coating apparatuses such as blade coaters, air knife coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, gravure coaters, Champlex coaters, A brush coater, a two-roll or metering blade type size press coater, a bill blade coater, a short dwell coater, a gate roll coater, a slide bead coater and the like can be used as appropriate.

  The coating layer is formed on at least one surface of the paper substrate, and it is possible to provide a multilayer structure by providing one layer or two or more intermediate layers as necessary. In the case of double-sided coating or multilayer structure, it is not necessary that each coating liquid has the same composition or the same coating amount, and it may be appropriately adjusted according to the required quality level and is particularly limited. It is not a thing.

  In addition, when a coating layer is provided on one side of a paper base, a synthetic resin layer, a coating layer made of pigment and adhesive, etc. on the back side, an antistatic layer, etc. are provided to prevent curling, impart printability, and feed / discharge It is also possible to impart aptitude and the like. Further, it is of course possible to use the paper base material with application suitability by subjecting the back surface of the paper substrate to various processing such as adhesion, magnetism, flame retardancy, heat resistance, water resistance, oil resistance, and slip resistance.

  The coated paper of the present invention is provided with a coating layer on a paper substrate, and then smoothed by a normal drying step, surface treatment step, etc., and has a moisture content of 3 to 10%, preferably 4 to 8%. It is finished by adjusting to a degree.

  The smoothing processing is performed by a smoothing processing device such as a normal super calendar, gloss calendar, or soft calendar. The surface smoothing device may be incorporated in the coating machine (on machine) or separately (off machine). The form of the smoothing pressure device, the number of pressure nips, and the heating conditions are appropriately adjusted according to a normal smoothing device.

  The coated paper subjected to the smoothing treatment is preferably adjusted to 50 to 80% of the white paper glossiness at an incident / light receiving angle of 75 degrees based on JIS P8142 so as to have a texture of gloss type printing paper. If the gloss level is less than 50%, the appearance of white paper and the desired gloss may not be obtained. A more preferable range is 60 to 80%.

  Further, the air permeability is preferably adjusted to 7000 seconds or less according to JIS P 8117 in order to prevent the generation of blisters in the printing process. More preferably, the air permeability is 5000 seconds or less, and further preferably 3000 seconds or less, so that it can be adapted to various printing machines, printing conditions, and printing environments. When the glossiness is higher than 80%, it is generally difficult to adjust the air permeability to 7000 seconds or less, and macro blisters or micro blisters may be generated.

The coated paper of the present invention is preferably coated paper having a basis weight of 80 g / m ^{2 to} 250 g / m ² , particularly 127 g / m ² or more where the problem of cracking becomes remarkable. The density is preferably in the range of 0.9 g / cm ^{3 to} 1.2 g / cm ³ . When the density is less than 0.9 g / cm ^3, it is generally difficult to achieve glossiness, and when it exceeds 1.2 g / cm ³ , it is generally difficult to adjust the air permeability according to JIS P 8117 to 7000 seconds or less. .

  The coated paper of the present invention obtained by the above-mentioned method is used as an image recording paper for non-impact printing methods such as an electrophotographic method and a thermal transfer method due to its high smoothness and high air permeability on the surface as well as suitability for offset rotary printing. It can also be used.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited thereto.
In the examples, “parts” and “%” indicate “parts by mass (solid content)” and “mass%” unless otherwise specified.

Example 1
[Preparation of paper substrate]
LBKP (freeness (CSF) = 450 ml) 100 parts of pulp slurry, polyacrylamide resin (trade name: PS117, manufactured by Arakawa Chemical Industries) 0.1% as a paper strength enhancer, and polyacrylamide resin (trade name) : PS460, manufactured by Arakawa Chemical Co., Ltd.) 0.3%, 1 part of a sulfuric acid band was added, and these mixtures were diluted with white water to prepare a paper stock having a pH of 5.3 and a solid content concentration of 1.1%. This stock is made using a long paper machine, the ratio of the jet speed of the raw material to the wire speed of the paper machine (jet / wire ratio), and the tension in the dryer drying process are adjusted, and the test of JIS P 8113 According to the method, the tensile strength of the coated paper was adjusted so as to obtain a predetermined ratio (ST / SY) between the vertical direction and the horizontal direction.

Next, a mixed solution of 80 parts by mass of oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstarch Co., Ltd.) and 20 parts by mass of a polyacrylamide resin (trade name: Polymer Set 531, manufactured by Arakawa Chemical Industries, Ltd.) as a size press solution. Was adjusted to a concentration of 2%, and applied with a size press apparatus so that the coating amount was 2.0 g / m ² in terms of dry mass, and dried.

A paper substrate having a basis weight of 81 g / m ² was obtained by smoothing with a machine calendar so that the Beck smoothness was 30 seconds. Table 1 shows the Beck smoothness of the paper substrate and the air permeability according to JIS P 8117.

[Preparation of coating solution]
Kaolin (trade name: Astra Plus, manufactured by Huber, average particle size: 0.5 μm, aspect ratio: 10) as a pigment in 95 parts, polyacrylic acid soda (trade name: Aron A-9, Toa Gosei Co., Ltd.) as a dispersant 0.2 parts) was added and dispersed in water using a Coreless disperser to prepare a pigment slurry. To this pigment slurry, 5 parts of hollow organic pigment (trade name: HP91, manufactured by Rohm & Haas), as an adhesive, 3.0 parts of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch), styrene-butadiene series 10 parts of copolymer latex (trade name: OX1060, manufactured by Nippon Zeon Co., Ltd.) was added and stirred, and water was further added to prepare a coating solution having a solid content concentration of 50%.

[Formation of coating layer]
The obtained coating solution was coated on both sides using a blade coater so that the dry weight per side of the paper substrate was 12 g / m ² and passed through a pressure nip composed of a metal roll and an elastic roll. A coated paper having a basis weight of 105 g / m ² was obtained by adjusting the white paper glossiness of an incident / light-receiving angle of 75 ° based on JIS P8142 to 75%.

About the obtained coated paper, the ratio (ST / SY) of the longitudinal direction of a tensile strength and a horizontal direction (ST / SY) followed the test method of JISP8113, and an internal bond strength is JAPAN TAPPI No.2. According to 18 test methods, the air permeability was obtained by measuring each according to the test method of JIS P 8117.
Tensile strength and elongation at break in the longitudinal direction were measured in accordance with the method of JIS P8113 by cutting out a paper specimen having a width of 15 mm and a length of 200 mm in the longitudinal or lateral direction of the coated paper and setting the gripping distance of the measuring jig to 180 mm. .
The aspect ratio of the sound wave propagation speed was measured using a SONIC SHEET TESTER manufactured by Nomura Shoji Co., Ltd., and the coated paper was cut into 30 cm squares, and the sound wave propagation speeds in the vertical and horizontal directions were measured.
Table 1 shows the numerical values, glossiness, and density obtained for the coated paper.

Example 2
A coated paper was obtained in the same manner as in Example 1 except that the basis weight of the paper substrate was 104 g / m ² .

Example 3
A coated paper was obtained in the same manner as in Example 1 except that the basis weight of the paper substrate was 134 g / m ² .

Example 4
A coated paper was obtained in the same manner as in Example 1 except that the basis weight of the paper substrate was 196 g / m ² .

Example 5
A coated paper was obtained in the same manner as in Example 3 except that the paper slurry was made into 75 parts of LBKP (freeness (CSF) = 450 ml) and 25 parts of NBKP (freeness (CSF) = 420 ml). .

Example 6
As a size press solution, oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstarch Co., Ltd.) 60 parts by mass, polyvinyl alcohol (trade name: K17, manufactured by Denki Kagaku Kogyo Co., Ltd.), 20 parts by mass, polyacrylamide resin (trade name: Polymer set 531 (manufactured by Arakawa Chemical Co., Ltd.) 20 parts by mass of the mixed solution was adjusted to a concentration of 2% and applied with a size press so that the coating amount was 1.5 g / m ^{2 in} dry mass. In the same manner as in Example 5, a coated paper for printing was obtained.

Example 7
A coated paper is obtained in the same manner as in Example 6 except that the paper slurry is made into 85 parts of LBKP (freeness (CSF) = 450 ml) and 15 parts of NBKP (freeness (CSF) = 420 ml). It was.

Comparative Examples 1 and 4
When making paper, adjust the ratio of the jet speed of the raw material and the wire speed of the paper machine (jet / wire ratio) and the tension balance in the dryer drying process so that the aspect ratio of the specified tensile strength is obtained. Otherwise, coated paper was obtained in the same manner as in Example 3.

Comparative Example 2
As a paper strength enhancer, 0.2% polyacrylamide resin (trade name: PS117, manufactured by Arakawa Chemical Industries) and 0.5% polyacrylamide resin (trade name: PS460, manufactured by Arakawa Chemical Industries) are blended. Further, a paper substrate was produced in the same manner as in Example 2 except that the coating amount of the size press was 4.0 g / m ² in terms of dry mass to obtain a coated paper.

Comparative Example 3
Coated paper was obtained in the same manner as in Comparative Example 2 except that the basis weight of the paper substrate was 134 g / m ² .

[Print evaluation method]
The printing machine uses “Komori System C-20” manufactured by Komori Corporation, in an environment of temperature 20 ° C. and humidity 65% RH, printing speed: 250 m / min, printing length: 6000 m, drying condition: using a gas heater. Printing was carried out by adjusting the paper surface temperature to 150 ° C.

[Evaluation of cracking suitability]
The printed coated paper is cut into A4 size, folded in half with a paper folding machine (made by Horizon) in an environment of temperature 20 ° C and humidity 30% RH, and the bent part is observed with an enlarged loupe. Evaluation was performed according to the following evaluation criteria.

(Double-circle): The coating layer of a bending part does not have a crack and a tear, and a favorable thing.
○: Some cracks are observed in the coating layer at the bent portion, but there is no practical problem.
(Triangle | delta): A crack and a tear are seen in the coating layer of a bending part, and there exists a problem practically.
X: Cracks and tears were observed in the coating layer at the bent part, the pulp fiber of the paper base material was exposed, and there was a problem in practical use.

[Macro Blister Evaluation]
The state of occurrence of macro blisters was confirmed with an enlarged loupe (30 times) and evaluated according to the following evaluation criteria.

A: Macro blister is not seen. There are no practical problems and the quality is excellent.
○: Some macro blisters can be seen. There is no problem in practical use.
Δ: Macro blisters are frequently observed. There are practical problems.
X: Macro blisters were remarkably observed. There is a problem in practical use and the quality is remarkably inferior.

  Examples 1 to 7 of the present invention are excellent in cracking suitability and practically useful. On the other hand, in Comparative Example 1, it is difficult to disperse the stress generated by folding because the aspect ratio of the tensile strength is small. In Comparative Example 2 and Comparative Example 3, since the internal bonding force is large, it is difficult to relieve the stress inside the paper base in the bent portion. In Comparative Example 4, the aspect ratio by the speed of sound method is small, that is, the pulp fibers forming the paper base material are close to random orientation, so that it is difficult to disperse the stress in the same manner as in Comparative Example 1. Is inferior. Comparative Example 5 has high gloss, but is inferior in blister due to high density and air permeability.

Claims (5)

  In a coated paper in which a paper base material and a coating layer mainly composed of a pigment and an adhesive are provided on at least one surface thereof, the longitudinal direction of the tensile strength of the coated paper according to JIS P 8113 (ST ) And the transverse direction (SY) (= ST / SY) is 1.5 or more, the elongation at break in the longitudinal direction is 2.5% or more, and JAPAN TAPPI No. The coated paper characterized by having an internal bond strength by 18 of 2.0 kgf · cm or less.   The coated paper of Claim 1 whose 75 degree specular glossiness by JISP8142 is 50% or more of the said coating layer surface.   The coated paper according to claim 1 or 2, wherein the coated paper has an air permeability according to JIS P 8117 of 7000 seconds or less.   The ratio (= VT / VY) of the longitudinal direction (VT) and the horizontal direction (VY) of the ultrasonic propagation velocity measured by the sound velocity method of the coated paper is 1.4 or more. The coated paper of any one of these. The coated paper according to any one of claims 1 to 4, wherein the density of the coated paper is 0.9 g / cm ^{3 to} 1.2 g / cm ³ .