JP2009114573A - Coated paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated paper having high whiteness and hardly causing troubles such as white spots in printing and roll staining in production while being the coated paper from which staining by friction that is a problem in a matted or dulled pattern can be reduced. <P>SOLUTION: The coated paper is obtained by forming a coated layer comprising a pigment and an adhesive as essential components on a base paper. The coated layer contains calcium carbonate having 0.1-1.0 μm average particle diameter as the pigment, and a latex in which a butadiene component of 40-65 mass% is contained as the adhesive. The density (transfer ink density) of the stain by the friction on a printed surface is ≤0.1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention has been a problem with matte or dull-coated paper, particularly dull-coated paper, which has been a problem in the past (the problem of ink being transferred to the surface of a white paper after ink has been scraped off). It is related with the coated paper which reduced the amount.

  In recent years, with the progress of visualization in the world, the demand for printing paper capable of high-definition printing in full color has increased, and in order to obtain a high-definition printed matter, a coating liquid is applied on the front and / or back side of the base paper. There is an increasing need for coated paper having a coating layer formed in this manner. The coated paper can be used for art paper (A1 grade), coated paper (A2 grade), fine coated paper (depending on the coating amount of the coating liquid, the level of flattening of the coating layer surface, and the required quality. A1 grade coated paper is required to have high-definition printing such as high-quality art books, magazine covers, cutouts, calendars, posters, catalogs, brochures, labels, and cigarette packaging. A2, A3 grade coated paper is used for commercial printing such as leaflets.

  These coated papers are roughly divided into glossy tone, matte tone, and dull tone located between them, and as the classification index, the value of 75 degree blank paper glossiness measured in accordance with JIS-P8142 is used. In general, glossy coated paper has a blank gloss greater than 50%, matte coated paper has a blank gloss of less than 20%, and dull coated paper has a blank gloss of 20% to 50%. % Or less.

  Glossy coated paper is required to reproduce photographic-like gloss and high-definition and high-contrast, and such coated paper can be used to apply unevenness on the front and / or back of the base paper. Cover with a fine structure such as pigment contained in the working liquid to improve the flatness, and apply a flattening process (calendar process) to the coated surface of the coating liquid using a flattening facility consisting of a metal roll or elastic roll. In this way, the printed surface of the coated paper is flattened and the gloss is adjusted to improve the ink coloring property and the halftone dot reproducibility when characters and the like are printed.

  On the other hand, matte coated paper can provide a calm matte printed image by suppressing the glossiness, and can bring out an elegant and high-quality texture. As a technique for suppressing the glossiness, a pigment having a small particle size and low coverage is used, and the glossy coated paper is not subjected to the necessary flattening treatment on the printing surface or in the Z-axis direction (through the paper). It can be obtained by reducing the pressure in the direction) and applying a flattening treatment.

However, with the recent development of an aging society, both existing glossy coated paper and matte coated paper face new problems.
That is, glossy coated paper is unsuitable for reading print information over a long period of time because the surface of the paper is glaring at both the white paper stage and the post-print stage because of its high glossiness. On the other hand, matte coated paper is not sufficiently flattened by pressurization in the Z-axis direction, and printing ink permeation unevenness and transfer unevenness are likely to occur. A printing defect called “elementary omission” occurs, and the print density decreases.

  Accordingly, attention is focused on dull-coated paper having glossiness between glossy and matte. Since this dull-tone coated paper has a white paper gloss of 20% to 50%, the surface is not glaring and printing information can be easily read. In addition, since the coated paper surface is slightly flattened, the white paper has no gloss, but the gloss of the printed part (print gloss) is high, and the gloss contrast between the printed part and the non-printed part is high. , You can make a sharp print.

  On the other hand, however, the dull-tone coated paper has a problem that it is liable to cause a smearing trouble that the ink is scraped off and transferred onto the surface of the blank paper portion after printing. The coated paper printed in the printing process is bound through the bookbinding process. However, when the printing section and the blank section come into contact with each other in the bookbinding process, the printing ink is transferred to the blank section. There is also a problem that the quality of the printed matter is greatly deteriorated because the front cover and the back cover come into contact with each other in the cover after stacking, and the printing ink is transferred to the white paper surface.

  This problem becomes more prominent with matte coated paper and dull coated paper than with glossy coated paper. The reason is that, as a coating pigment for suppressing the glossiness of blank paper, the main content is calcium carbonate, which is a hard pigment, so that the calcium carbonate protruding on the surface of the coating layer can easily scrape the printing ink, Glossy coated paper has a high surface smoothness due to the super calendering process, and it is difficult to scrape ink.

  Since the dull tone coated paper is often used particularly for high-quality printed matter, if it has the above-mentioned cosmetic stain problem, it will not function as a high-quality printing paper.

  In order to eliminate this cosmetic stain trouble, for example, a method of coating a coating composition containing 20 to 80% by mass of delaminated clay having an average particle size of 0.4 to 1.0 μm (for example, Patent Document 1) In the manufacturing method of coated paper in which the coating liquid is applied twice to the base paper, 20% by mass of calcium carbonate having an average particle size of 3 μm or less with respect to 100% by mass of the total pigment in the undercoat coating layer. There is a method (for example, refer to Patent Document 2) in which clay is contained in an amount of 60% by mass or more with respect to 100% by mass of the total pigment in the top coat layer. It could not be reduced sufficiently.

Moreover, 70-85 weight% of heavy calcium carbonate with an average particle diameter of 0.6-1.6 micrometers and 15-30 weight% of kaolin are contained, and the surface property is improved (for example, refer patent document 3). Then, since the polymer latex having a glass transition temperature (Tg) of 10 ° C. or more as an adhesive component is used in an amount of 3 to 25% by weight with respect to 100% by weight of the pigment, the coating layer becomes hard and the cosmetic stain is sufficiently removed. It was not something to reduce. When the glass transition temperature (Tg) of the latex is lowered, the coating layer becomes flexible and the smudge is reduced. However, a latex having a low Tg can be easily transferred by heat or pressure. Since there is a problem of roll dirt that sticks to the roll and latex dirt adheres to the roll, there are restrictions such as using in combination with a special kaolin when used (see, for example, Patent Document 4). Whiteness was not utilized and only low whiteness printing paper was obtained. Further, they have not been able to reduce scumming stains to the extent that they satisfy the quality of high-grade printing paper.
JP 05-005297 A JP 05-214699 A Japanese Patent Laid-Open No. 06-212599 Japanese Patent Laid-Open No. 07-097795

  The main problem to be solved by the present invention is a coated paper with reduced scum stain, which is a problem with matte tone and dull tone, but with high whiteness, white spots during printing and roll stains during production. It is to provide coated paper that does not cause troubles.

The present invention that has solved this problem is as follows.
[Invention of Claim 1]
One or both sides of the base paper is a coated paper provided with at least one coating layer mainly composed of a pigment and an adhesive,
The outermost layer of the coating layer contains calcium carbonate having an average particle size of 0.1 to 1.0 μm as the pigment, and latex having a butadiene component of 40 to 65% by mass as the adhesive. The stain density (transfer ink density) is 0.1 or less.
Coated paper characterized by that.
Here, the cosmetic stain density is a solid color printing on the surface of the coated paper, and after 1 week, a white paper surface is overlapped on the printed surface, and a friction test for dyeing fastness under conditions of a load of 500 g and 20 reciprocations. The density of the black ink transferred to the white paper surface when the printing surface and the white paper surface were rubbed together using a printing machine (manufactured by Toyo Seiki Seisakusho Co., Ltd.) It is a density difference when using the light source: D50 and the viewing angle: 2 ° and measuring the difference from the density of the blank surface before the test.

[Invention of Claim 2]
The coated paper according to claim 1, wherein the latex contains 20 to 35 mass% of a styrene component, and the glass transition temperature (Tg) of the latex is -50 ° C to 0 ° C.

[Invention of Claim 3]
The coated paper according to claim 1 or 2, wherein the latex has an average particle size of 90 to 130 nm.

[Invention of Claim 4]
Content of the said calcium carbonate shall be 15-100 mass parts with respect to 100 mass parts of all the pigments, whiteness shall be 80% or more, and blank paper glossiness shall be 20-50%. 4. The coated paper according to any one of 3 above.

  According to the present invention, the coated paper has reduced white spots, which is a problem with matte tone and dull tone, but has high whiteness and does not cause troubles such as white spots during printing and roll stains during production. It becomes coated paper.

  Hereinafter, the coated paper according to the embodiment of the present invention will be described. In addition, this invention is not necessarily limited to the following embodiment, Of course, the structure can be changed suitably in the range which does not deviate from a claim.

  The coated paper of this embodiment is one in which a coating layer mainly composed of a pigment and an adhesive is provided on the front surface and / or back surface of the base paper.

(material)
The type of raw material pulp is not particularly limited, and one or two or more kinds of raw pulps such as chemical pulp, mechanical pulp, and waste paper pulp can be appropriately selected and used.

  As the chemical pulp, for example, unbleached softwood pulp (NUKP), unbleached hardwood pulp (LUKP), bleached softwood pulp (NBKP), bleached hardwood pulp (LBKP) and the like can be used as raw material pulp, but whiter In order to obtain a highly coated paper, it is preferable to use NBKP and LBKP which are bleached pulp.

  Examples of the mechanical pulp include stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo grand pulp (TGP), ground pulp (GP), Thermo mechanical pulp (TMP), Chemi thermo mechanical pulp (CTMP), refiner mechanical pulp (RMP), etc. are mentioned.

  Waste paper pulp includes, for example, disaggregation / deinked waste paper pulp, disaggregation / deinking / bleached waste paper pulp, etc. produced from magazine waste paper, flyer waste paper, office waste paper, Kami white waste paper, etc., from the viewpoint of environmental protection, It is preferable to blend a large amount of these waste paper pulps.

  The pulp composition is not particularly limited, but NBKP: LBKP = 20 in order that the texture is good, the smoothness after coating of the coating liquid can be improved, and sufficient strength as coated paper is obtained. : It is preferable to mix | blend by 80-50: 50.

  In the present embodiment, the above raw material pulp is mixed to prepare a papermaking raw material (stock slurry). The raw material pulp includes, for example, an internal sizing agent, a paper strength enhancer, a paper thickness improver, and a yield. Various additives such as an improver that are usually blended in coated paper can be internally added by appropriately adjusting the type and blending amount.

  In order to further improve the whiteness of the target matte and dull tone coated paper, JIS P 8148: 2001 “Paper, paperboard and pulp—Measurement method of ISO whiteness (diffuse blue light reflectance)”. The whiteness of the base paper measured according to the standard is preferably 70% or more, and more preferably 80% or more. The coated paper produced from such a base paper can have a whiteness of 80% or more, more preferably 90% or more. For example, compared with a case where the whiteness is less than 80%, the coated paper has a higher definition. Thus, coated paper having high contrast and excellent print information visibility can be obtained. The whiteness of the base paper and the coated paper can be adjusted, for example, by adjusting the raw material pulp composition, papermaking conditions, coating pigment, fluorescent dye, fluorescent dye fixing agent, and the like.

Although there is no particular limitation on the basis weight of the base paper, it is preferable that the basis weight in accordance with JIS P 8124: 1998 “Paper and paperboard—Method for measuring basis weight” of the target coated paper is 30 to 200 g / m ^2. Is preferably adjusted so that the basis weight of the base paper is 25 to 195 g / m ² , preferably 40 to 150 g / m ² . If the basis weight of the coated paper is less than 30 g / m ² , the strength of the paper is low, and there is a possibility that coated paper having the strength required for commercial printing applications cannot be obtained. On the other hand, when the basis weight is larger than 200 g / m ² , the mass increases, which is not practical.

  The papermaking equipment that can be used in the present embodiment is not particularly limited, but is a wire part made of a gap former, a press part made of a straight-through type without an open draw, a dryer part made of a single deck dryer, or a film transfer type roll coating. It is preferable to combine a pre-calender part consisting of a coater part (undercoating) and a soft calendar. With the above configuration, for example, even in high-speed papermaking of 1300 m / min or more, the texture is good, and unevenness in drying in the width direction and the flow direction is reduced. Therefore, the coated base paper is particularly excellent in smoothness. As a result, the coating unevenness in the subsequent overcoating process can be reduced, and as a result of improving the smoothness of the surface of the outermost layer of the coating layer, when the printed surface and the white paper surface overlap after printing, the contact area becomes uniform and local As a result, it is difficult to cause rust stains, so that the rust stains are not noticeable on the entire white paper surface, and a coated paper that does not impair the sense of quality can be obtained. The effects obtained in each part are as follows.

(Wire part)
The wire part can be a long web former, a long web former combined with an on-top former, or a twin wire former, etc., but the paper jets ejected from the head box can be used with two wires. A gap-type gap former that is immediately sandwiched is preferable because there is little difference between the front and back because it dehydrates from both sides, and a difference in front and back is less likely to occur in the cosmetic stain.

(Press part)
The paper layer in the wire part is transferred to the press part and further dewatered. The press machine can be either a straight-through type, an invar type, or a reverse type, and a combination of these can also be used, but the straight-through type with no open draw is easy to hold the paper, This is preferable because there are few operational troubles such as paper breaks. As the dehydration method, a conventional method such as a suction roll method or a grooved press method can be used, but a shoe press capable of improving dehydration and smoothness is more preferable.

(Dryer part)
The wet paper that has passed through the press part is transferred to a single-deck pre-dryer part and dried. The pre-dryer part is preferably a no-open draw type single-deck dryer that has few paper breaks and can be dried efficiently without reducing the bulk. Although it is possible to dry with a double deck method, it is a single deck in terms of operability such as canvas marks, paper breaks, wrinkles, paper splicing, etc., and uniform drying can be obtained in both the width direction and the flow direction Inferior to the method.

(Coater part (undercoating))
Bonded with the surface treatment agent or pigment mainly composed of a water-soluble polymer for the purpose of improving the smoothness of the surface and making the coated surface uniform after top coating. It is preferable to undercoat a pigment coating liquid mainly composed of an agent. The undercoat coating layer may be a single layer or a plurality of layers. Of course, an undercoat coating layer can be omitted.

  As the water-soluble polymer as the main component of the surface treatment agent, for example, those commonly used as surface treatment agents such as oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, etc. Or several types can be mixed and used. In addition to the water-soluble polymer, for example, a paper strength enhancer for the purpose of water resistance and surface strength improvement and an externally added sizing agent for the purpose of imparting sizing should be added to the surface treatment agent. Can do.

The coating amount of the undercoat coating by the surface treatment agent is not particularly limited, it is preferably per side 0.1~4.0g / m ^2, more preferably 0.4~2.5g / m ^2. If it is less than 0.1 g / m ² , the surface coverage is poor, and if it exceeds 4.0 g / m ² , coating unevenness is likely to occur, so both surfaces have low surface smoothness after top coating, Less effective in reducing cosmetic stains.

  There is no restriction | limiting in particular about the pigment in the case of undercoating a pigment coating liquid, Generally what can be used for a papermaking use can be used. For example, kaolin clay, calcium carbonate, talc, satin white, calcium sulfite, gypsum, barium sulfate, white carbon, calcined kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide 1 type or 2 types of inorganic pigments such as zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite, and organic pigments such as polystyrene resin fine particles, urea formalin fine particles, fine hollow particles, and porous fine particles The above may be appropriately selected and blended.

  There are no particular limitations on the type of adhesive blended in the coating solution together with the above pigments, for example, proteins such as casein and soybean protein; styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex Conjugated diene latex such as styrene-methyl methacrylate-butadiene copolymer latex, acrylic latex such as polymer latex or copolymer latex of acrylate ester and / or methacrylate ester, ethylene-vinyl acetate polymer latex, etc. Latexes such as alkali partially soluble or non-soluble latexes obtained by modifying these various latexes with various functional group-containing monomers such as carboxyl groups; polyvinyl alcohol, olefin-maleic anhydride Synthetic resin adhesives such as fats, melamine resins, urea resins, urethane resins; starches such as oxidized starch, positive starch, esterified starch, dextrin; cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, etc. Adhesives used for paper can be mentioned, and one or two or more of these can be appropriately selected and used.

  The ratio of the pigment and the adhesive in the undercoat coating liquid is not particularly limited, but the adhesive is preferably 3 to 17 parts by mass with respect to 100 parts by mass of the pigment, more preferably 5 to 5 parts by mass. 15 parts by mass. If the amount of the adhesive is less than 3 parts by mass, the formability of the undercoat coating layer is lowered, the surface strength is lowered, the paper surface is taken up by ink during printing, and white spots occur. On the other hand, if it exceeds 17 parts by mass, the amount of adhesive is too much and the coating layer becomes hard, so that the cosmetic stain is deteriorated.

  Furthermore, for the undercoat coating liquid (pigment coating liquid), for example, fluorescent whitening agents, fluorescent whitening agent fixing agents, antifoaming agents, mold release agents, coloring agents, water retention agents and the like are usually used. Auxiliary agents can be appropriately blended.

The amount of the pigment coating solution applied to the base paper is preferably 5 to 20 g / m ² , more preferably 8 to 15 g / m ² per side. If the amount of the pigment coating solution is less than 5 g / m ² per side, an uncoated part is likely to occur on the surface of the base paper, unevenness in smoothness may occur, and there is a risk that the cosmetic stain will deteriorate after top coating. If it exceeds 20 g / m ² per side, the surface strength may deteriorate, for example, cracks may occur on the surface of the coating layer after top coating, or the productivity may be reduced and the cost may be increased.

  Although the thickness of the undercoat coating layer to be formed is not particularly limited, it is preferably 5 to 30 μm in consideration of the tightness, smoothness, and printing unevenness after providing the topcoat coating layer.

  Such undercoating is, for example, a two-roll size press coater, a gate roll coater, a blade metering size press coater, a rod metering size press coater, a film transfer type roll coater such as a shim sizer or a JF sizer, or a blade coater. The coating liquid is applied on the base paper in one or more layers by an on-machine coater or an off-machine coater provided with a coating device such as an air knife coater or a curtain coater. However, in order to further improve the surface properties after the undercoating and reduce the cosmetic stain after the overcoating, a film transfer type roll coater that has a high coverage and can be applied uniformly is preferable.

(Pre-calendar part (flattening process))
The base paper after the undercoating is preferably subjected to a flattening process using a precalender before the topcoating. By performing the flattening treatment, unevenness in smoothness after the undercoating can be reduced, and the smoothness after the overcoating can be improved. In particular, in this embodiment, it is necessary to improve the surface property and obtain a coated paper that is less likely to cause scum stains, and it is important to perform a flattening treatment with a pre-calender.

(Top coat coating)
Next, a coating liquid containing a pigment and an adhesive is overcoated on one or both sides of the base paper to provide an overcoating layer. In addition, when this top coat layer is one layer, this top coat layer is the outermost layer regardless of whether or not an undercoat layer is provided, and the top coat layer is two or more layers. In the case, the outermost layer is the outermost layer. Below, the case where the top coat layer is one layer will be described as an example.

  It is essential that the top coating liquid contains calcium carbonate having an average particle size of 0.1 to 1.0 μm and latex having a butadiene component of 40 to 65% by mass.

  The calcium carbonate having an average particle size of 0.1 to 1.0 μm may be heavy calcium carbonate obtained by pulverizing limestone, but light calcium carbonate made of artificially synthesized particles with lower density and softness. preferable. Light calcium carbonate has soft particles, so it is difficult to scrape ink, and it is difficult to cause cosmetic stains. The average particle diameter is a median diameter (D50) and is a value measured using a laser diffraction particle size distribution measuring device (product number: SALD-2200, manufactured by Shimadzu Corporation).

  The average particle size of calcium carbonate is more preferably 0.2 to 0.9 μm, and still more preferably 0.3 to 0.8 μm. When the average particle diameter is less than 0.1 μm, calcium carbonate is likely to sink into the base paper, the surface property of the coating layer is deteriorated, and not only the cosmetic stain is deteriorated, but also the specific surface area of the pigment is increased, and the binder is used. The holding power is reduced, the strength of the coating layer is reduced, and white spots are liable to occur during printing. On the other hand, when the average particle diameter exceeds 1.0 μm, the smoothness of the coating layer is inferior and the cosmetic stain is deteriorated.

  The content of calcium carbonate having an average particle size of 0.1 to 1.0 μm is preferably 15 to 100% (mass basis) of all pigments, more preferably 30 to 100%, and 60 to 100%. More preferably. When the content is less than 15%, high whiteness derived from calcium carbonate cannot be obtained, and not only a coated paper with low whiteness is obtained, but also derived from a clay of pigment generally used in combination with calcium carbonate. High glossiness is imparted to the coated paper, making it impossible to obtain matte or dull coated paper. Moreover, in order to suppress glossiness, it is necessary to loosen the flattening condition, and the surface becomes rough, and a cosmetic stain is likely to occur.

  In the present invention, by using a specific latex described later in combination, a matte-like or dull-like coated paper with sufficiently improved cosmetic stain can be obtained even when the pigment is 100% calcium carbonate. When the calcium carbonate is 100%, the whiteness is high, so that the contrast of the printed matter is high, and a high-quality matte or dull tone coated paper can be obtained.

  Moreover, you may use together pigments other than the said calcium carbonate for the purpose of adjusting the coating-material physical property and whiteness at the time of coating. The pigment to be used in combination is preferably kaolin clay softer than calcium carbonate, more preferably a fine particle type kaolin clay having an average particle diameter of 0.1 to 1.0 μm, particularly 0.1 to 0.5 μm. It is preferable to use kaolin clay in combination because it can impart high flatness while suppressing the gloss of the coated paper, and can improve the scum stain on the matte or dull-coated paper.

  By combining the above, it is possible to sufficiently smooth the surface of the coated paper, and to obtain a matte or dull-like coated paper that is less likely to cause a smudge. As pigments other than those described above, pigments that can generally be used for papermaking can be added as long as the effects of the present invention are not impaired. For example, talc, satin white, calcium sulfite, gypsum, barium sulfate, white carbon, calcined kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, oxidation From inorganic pigments such as zinc, magnesium oxide, bentonite, and sericite, and organic pigments such as polystyrene resin fine particles, urea formalin resin fine particles, fine hollow particles, porous fine particles, etc. You may mix.

  As the above-mentioned pigment adhesive, it is essential to use a polymer latex containing 40 to 65% butadiene as a monomer component, and the butadiene component is preferably 43 to 63%, more preferably 45 to 60%. . If the butadiene component is less than 40%, the adhesion to the pigment is poor, and not only does white-out trouble occur during printing, but also the flexibility of the coating layer is reduced, so that it is likely to cause a smudge. If it exceeds 65%, the amount of latex on the surface of the coating layer increases, and roll contamination is likely to occur. By keeping the butadiene component in the above range, both adhesiveness and cosmetic dirt can be satisfied. Further, by incorporating the latex containing 40 to 65% of the butadiene and the calcium carbonate having the average particle diameter of 0.1 to 1.0 μm in the coating layer, it is a conventional problem with matte or dull tone coated paper. Although it is a coated paper with reduced cosmetic stains, it is possible to obtain a coated paper that has high whiteness and does not cause troubles such as white spots during printing and roll stains during production.

  The monomer component other than butadiene preferably contains 20 to 35% of styrene, more preferably 25 to 30%. The styrene component has an effect of imparting water resistance to the coating layer. On the other hand, since the hardness is increased, it is preferable to keep the blending amount in the above range from the viewpoint of reducing the cosmetic stain. When the styrene component is less than 20%, the water resistance of the coating layer is inferior, and particularly in offset printing, dampening water is sucked to lower the coating layer strength, and troubles such as white spots and paper breakage tend to occur. . When it exceeds 35%, the coating layer becomes hard and the cosmetic stain tends to deteriorate. As described above, in order to effectively reduce cosmetic stains, it is preferable to keep the butadiene component and styrene component in Terrax within a predetermined range, thereby imparting appropriate flexibility and water resistance to the coating layer. In addition, a coated paper with less roll stains and white spots and reduced makeup stains can be obtained.

  In order to further reduce the cosmetic stain, it is preferable to adjust the glass transition temperature (Tg) of the latex to −50 to 0 ° C., more preferably −40 to 0 ° C., and particularly preferably −30 to 0 ° C. By setting the glass transition temperature within a predetermined range, the flexibility of the coating layer can be further improved, and the action of the calcium carbonate on the surface of the white paper scraping off the printed portion at the time of makeup can be alleviated. The glass transition temperature can be easily adjusted by the blending amount of butadiene and styrene, other components (ethylenically unsaturated monomer or vinyl cyanide monomer), the type and amount of polymerization initiator, the degree of polymerization, etc. . If the glass transition temperature is lower than -50 ° C, the coating layer becomes too soft and the predetermined white paper gloss does not come out, and there is a problem of roll contamination that a part of the latex peels off and adheres to the metal roll in the manufacturing process. Occurs, and both paper quality and operability deteriorate. When the glass transition temperature exceeds 0 ° C., the coating layer becomes hard, and a cosmetic stain is likely to occur.

  As described above, by specifying the content of the butadiene and styrene components and the glass transition temperature within a specific range, it was possible to obtain a coated paper with sufficiently reduced cosmetic stains.

  Furthermore, the inventors obtain a coated paper in which the average particle size of the latex is adjusted to 90 to 130 nm, preferably 100 to 120 nm, so that white spots and roll stains do not occur and the makeup stains are sufficiently reduced. I found out that I can. When the average particle size is not within the above range, binder migration occurs in which the latex moves to the surface of the coating layer in the drying process after coating the pigment, and the latex concentrates on the surface of the coating layer, and the coating is performed. There is a tendency for the transfer of latex from the surface of the layer to the metal roll, and this tends to reduce the bond strength inside the coating layer and easily cause white spots. By making the average particle diameter of the latex within the above-mentioned range, the coated paper that reduces the scum stain, suppresses the binder migration of the latex, does not cause white spots and roll stains, and sufficiently reduces the scum stain. Could get. If the average particle diameter of the latex is less than 90 nm, binder migration cannot be prevented, and white spots and roll stains are likely to occur. If the latex particle diameter exceeds 130 nm, roll stains are difficult to occur, but the specific surface area of the latex particles is reduced. Adhesive strength is reduced, and the surface strength of the coating layer is reduced, so white spots are likely to occur.

  In addition, since the latex has excellent coating suitability even at high-speed coating, for example, even when the coating speed is 1300 m / min or more, coating defects such as streak and bleeding are not generated efficiently. Can produce coated paper.

  The ratio of the pigment and the adhesive in the coating solution is preferably 5 to 15 parts by mass, more preferably 7 to 13 parts by mass with respect to 100 parts by mass of the pigment. When the content is less than 5 parts, the coating layer strength is reduced, not only white spots are generated during printing, but the pigment is easily removed from the coated paper in the manufacturing process, and the system is soiled. Since both paper quality and operability deteriorate, it is not preferable. When the content exceeds 15 parts by mass, not only roll stains are generated, but also the coating layer becomes hard and the cosmetic stains deteriorate, which is not preferable.

  In addition to the copolymer latex containing butadiene, an adhesive that can be usually used for coating can be used in combination. For example, proteins such as casein and soybean protein; conjugated diene latexes such as styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, styrene-methyl methacrylate-butadiene copolymer latex, acrylic acid esters and / or Or acrylic latex such as polymer latex or copolymer latex of methacrylic acid ester, vinyl latex such as ethylene-vinyl acetate polymer latex, or these various copolymer latexes containing functional groups such as carboxyl groups Latexes such as alkali partially soluble or insoluble latex modified by the body; synthetic resin adhesives such as polyvinyl alcohol, olefin-maleic anhydride resin, melamine resin, urea resin, urethane resin; oxidized starch, positive Starches such as modified starches, esterified starches, dextrins; and adhesives commonly used in papermaking applications such as cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose. One or more of these may be selected as appropriate. Can be used together.

  In addition, the coating liquid is appropriately blended with various commonly used auxiliaries such as fluorescent brighteners, fluorescent brightener fixing agents, antifoaming agents, mold release agents, colorants, and water retention agents. You can also

  The top coating is preferably performed, for example, in a coater part between the dryer parts, which is performed in a plurality of stages, usually two stages of a pre-dryer part and an after-dryer part. In this coater part, for example, an on-machine coater or an off-machine coater provided with a coating device such as a blade coater, an air knife coater, a transfer roll coater, a rod metering size press coater, a curtain coater, etc. The coating solution is applied in multiple layers. Among them, even immediately after coating, the coating layer surface has high flatness, and in the subsequent flattening process, the smoothness of the surface can be improved without increasing the glossiness under mild calendering conditions. It is preferable to use a blade coater from the viewpoint that dirt can be sufficiently improved. In addition, as a drying method in the dryer part, for example, various heating drying methods such as hot air heating, gas heater heating, and infrared heater heating can be appropriately employed.

The coating amount of the topcoat coating solution on the base paper is preferably 5 to 20 g / m ² , more preferably 8 to 15 g / m ² per side. If the amount of the coating liquid is less than 5 g / m ² per side, an uncoated part is likely to occur on the surface of the base paper, and the smoothness may be lowered. By applying 5 g / m ² or more per side, it is possible to obtain a coated paper that has excellent flatness on the surface of the coated paper and suppresses scum stains. If the amount of the coating solution exceeds 20 g / m ² per side, the coating layer may be cracked and the smoothness may be lowered, binder migration may easily proceed, and white spots may be deteriorated.

  Although the thickness of the topcoat coating layer to be formed is not particularly limited, it is preferably 5 to 30 μm in consideration of the smoothness and surface strength of the coated paper obtained by providing the coating layer.

  As a coating method for obtaining the matte or dull-coated paper of the present invention, the undercoating is performed with a film transfer type roll coater, and after pre-calendering, the overcoating is performed with a blade coater. Is preferred. By using the above coating method, high smoothness can be imparted to the surface of the coating layer, so the surface properties can be sufficiently improved by finishing the matte or dull-like coated paper by calendering described later. In addition, a mat-like or dull-tone coated paper that can sufficiently reduce the cosmetic stain can be obtained.

(Calendar part (flattening process))
In this embodiment, for the purpose of imparting glossiness, flatness, and printability to the coating layer, it is preferable to perform a flattening treatment using a hot roll. In general, in the flattening treatment, a coated paper is passed between an elastic roll and a metal roll, a nip pressure is applied to the coated paper, the surface of the coated paper is polished by frictional force, and gloss is imparted. For matte or dull-coated paper, increasing the nip pressure causes the glossiness to exceed the dull tone (glossiness of 20 to 50%), so flattening with medium nip pressure (50 to 200 kN / m) Under these conditions, sufficient smoothness cannot be imparted to the surface of the coated paper, so that the cosmetic stain cannot be sufficiently improved, and there is a tendency that a high-quality printed matter cannot be obtained.

  In order to effectively improve these problems, a flattening step (A) in which the flattening process is performed without applying the nip pressure (linear pressure) and a flattening process is performed by applying the nip pressure (linear pressure). It is preferable that the flattening step (B) is combined with the following predetermined conditions, and coated paper is produced through at least two types of flattening steps including these steps (A) and (B). Since the smoothness of the coating layer surface can be improved by combining these flattening conditions, matte or dull-tone coated paper with reduced scum stain can be obtained efficiently.

  Here, in the flattening step (A), by flattening the coated paper with zero nip pressure, the coated paper surface can be ironed so as to slide, and only the coated layer surface is effectively applied. Can be flattened. More specifically, in the flattening step (A), the paper is brought into contact with the heat roll only by tension without applying linear pressure. The tension is preferably 100 to 400 N / m. When the tension is less than 100 N / m, flattening does not proceed and the cosmetic stain is not sufficiently improved. On the other hand, if it exceeds 400 N / m, the paper cutting rate increases and there is a problem in continuous operability. Moreover, it is preferable that the holding angle of the coated paper to the said heat roll is 155-175 degrees. When the holding angle is less than 155 °, the contact with the roll is large, so that not only roll dirt is likely to occur, but also a flattening effect due to friction is large, and the target glossiness may be exceeded. On the other hand, if it exceeds 175 °, the contact area between the heat roll and the coated paper is small, so that the flattening does not proceed and the scum stain cannot be improved. Furthermore, the surface temperature of the heat roll is preferably 100 to 160 ° C. If it is less than 100 degreeC, planarization does not progress and a cosmetic stain cannot be improved. On the other hand, when it exceeds 160 ° C., yellowing (fading) of the coating layer occurs, and the whiteness decreases.

  Although there is no restriction | limiting about the number of the heat rolls in the above planarization process (A), Preferably it is 1-8, More preferably, it is 3-5. If the number of heat rolls is 2 or less, the desired smoothness is difficult to obtain, and if it is 6 or more, the improvement in smoothness reaches its peak.

  On the other hand, in the flattening step (B), the linear pressure applied to the coated paper is 50 to 400 kN / m and the surface temperature of the hot roll is 100 to 160 ° C. in a 1 to 8 nip process. In the flattening step (A), the smoothness unevenness of the micro area can be improved due to the flattening process at a low nip pressure, but the macro smoothness such as coating unevenness and rice tsubo unevenness is improved. Is difficult. In order to improve these, by combining the flattening step (B), the smoothness of the surface of the coating layer can be improved while suppressing the glossiness to a predetermined level. Paper is obtained.

  The nip pressure in the planarization step (B) is preferably 50 to 400 kN / m. When the nip pressure is less than 50 kN / m, flattening does not proceed and the cosmetic stain cannot be improved. On the other hand, if the nip pressure exceeds 400 kN / m, fiber scorch occurs, or yellowing (fading) of the coated paper occurs due to heat and pressure, so that the predetermined whiteness cannot be obtained, Since the elasticity of the coated paper is lost, the scum stain is also worsened.

  As for the surface temperature of the heat roll (metal roll) of a planarization process (B), 100-160 degreeC is preferable. If the temperature of the hot roll is less than 100 ° C., flattening does not proceed and the cosmetic stain is deteriorated. When the temperature exceeds 160 ° C., fiber scorch occurs, or the coated paper itself is yellowed (discolored) by heat and pressure, so that the predetermined whiteness cannot be obtained, and the elasticity of the coated paper Because of the loss, the cosmetic stains will also get worse.

  Although there is no restriction | limiting about the number of nip steps including the heat roll which performs a planarization process (B), Preferably it is 2-6 steps, More preferably, it is 2-4 steps. Exceeding 6 steps is not preferable because large-scale equipment is required, and the 1st step cannot sufficiently improve the smoothness of both front and back surfaces.

  The order of performing the flattening step (A) and the flattening step (B) is not particularly limited, but the reason for obtaining a coated paper with reduced scum stain is unknown, but the flattening step (B) After that, it is preferable to perform the planarization step (A) and further perform the planarization step (B).

  As equipment for performing the smoothing process, a conventional machine calendar or a soft calendar may be used, but preferably, the flattening step (A) and the flattening step (B) can be processed in one stack. It is preferable to use a multi-nip calender. The multi-nip calender can perform the flattening step (A) and the flattening step (B) at the same time as long as the specific roll can be operated with the nip treatment applied and other rolls released. Is particularly preferred.

  Moreover, as an installation place of a calendar, an on-machine type integrated with a paper machine and a coating machine is preferable. In the on-machine type, flattening treatment can be performed immediately after coating at a high paper surface temperature, so that smoothness is easily improved and it is easy to reduce scum stains.

  Matte or dull tone coated paper that has been flattened under the above conditions can sufficiently improve both the macroscopic surface property and the microscopic surface property, so the glossiness of blank paper is as low as 50% or less. Regardless, the coated paper has a sufficiently reduced amount of scum stain.

  The coated paper obtained as described above has a blank gloss of 50% or less measured according to the method described in JIS P 8142: 2005 “Paper and paperboard—Method of measuring 75 degree specular gloss”. It is excellent in the visibility of print information because it is low, and it has a smooth print surface with high gloss because of high smoothness. On the other hand, the transfer ink density (cosmetic dirt density) is 0.1 or less in the cosmetic dirt test. Low and high-quality coated paper.

  Here, the stain stain density is a solid color printing on the coated paper surface, and after 1 week, a white paper surface is overlaid on the printed surface, and a friction tester for dyeing fastness under conditions of a load of 500 g and 20 reciprocations. When the printed surface and the white paper surface were rubbed together using Toyo Seiki Seisakusho Co., Ltd., the density of the black ink transferred to the white paper surface was measured using a print density measuring device (product number: SpectroEye, GretagMacbeth). This is a density difference when the difference between the light source: D50 and the viewing angle: 2 ° was measured and the difference from the density of the blank paper before the test was obtained.

  The cosmetic stain concentration is 0.1 or less, and the cosmetic stain is not conspicuous and is an excellent coated paper that can be suitably used for high-grade printing, but is more preferably 0.05 or less, particularly preferably 0.03 or less. is there. Since these are almost free of cosmetic stains, they are coated papers that are particularly superior in quality.

  In order to obtain sufficient print information visibility, the blank paper gloss is preferably 20% to 50%, more preferably 25% to 45%, and more preferably 30% to 40%. Particularly preferred. If it is less than 20%, the matte tone is not obtained, and not only the stain stain is not sufficiently improved, but also the printability tends to be inferior, such as a decrease in printing gloss due to uneven penetration of printing ink and the occurrence of printing unevenness. If the white paper gloss exceeds 50%, the surface of the paper is glaring and print information tends to be inferior.

  Next, although the coated paper of this invention is demonstrated still in detail based on an Example, this invention is not limited only to these Examples.

First, as raw material pulp, NBKP, LBKP, MDIP (pulp derived from magazine waste paper) are mixed at a ratio (mass ratio) of 20:30:50, and each 100 parts by mass (absolute dry weight) of this solid is solid. Minutes, 0.02 parts by mass of internal sizing agent (product number: AK-720H, manufactured by Harima Chemicals Co., Ltd.), cationized starch (product number: Amilofax T-2600, manufactured by Abebe Japan Co., Ltd.) 1.0 mass Part and a yield improver (product number: NP442, manufactured by Nissan Eka Chemicals Co., Ltd.) 0.02 parts by mass were added to obtain a pulp slurry. Next, after a paper web was manufactured through a wire part, a press part, and a predryer part, a starch coating solution was applied to the both surfaces with a coating amount shown in Table 1 undercoat. After this undercoating, after drying with an after-dryer part, flattening with a pre-calender part at a nip pressure of 100 kN / m, and subsequently with the coater part, the pigment and adhesive prepared under the conditions described in Table 1 The coating liquid containing the agent was applied to both sides of the base paper so that the amount was 8 g / m ² per side to form a coating layer having a thickness of about 8 μm per side. The details of the pigment and the adhesive are as follows.
(Pigment)
・ Light calcium carbonate (product number: TP-121-6S, manufactured by Okutama Kogyo Co., Ltd., average particle size 1.8 μm)
・ Heavy calcium carbonate (Product No .: Hydrocurve 90, manufactured by Bihoku Powder Chemical Co., Ltd., average particle size 1.3 μm)
・ Kaolin clay (product number: Amazon Plus, manufactured by CADAM, average particle size 0.3 μm)

  Heavy calcium carbonate and light calcium carbonate were pulverized using a wet pulverizer (product number: planetary mill, manufactured by Seishin Enterprise Co., Ltd.), and adjusted to the average particle size shown in Table 1. The average particle diameter (D50) was measured using a laser diffraction particle size distribution measuring device (product number: SALD-2200, manufactured by Shimadzu Corporation).

(adhesive)
As an adhesive, a styrene-butadiene latex (product number: GT-1857, manufactured by Nippon Zeon Co., Ltd.), Tg: -12 ° C, used for a commercial product A (Dao Paper Co., Ltd., dull-coated paper). Based on butadiene: 35% by mass, styrene: 36% by mass, and average particle size: 88 nm, the glass transition temperature, styrene and butadiene content, and average particle size of this latex were changed as shown in Table 1. An example coated paper was produced. Latex components were butadiene, styrene, and methyl methacrylate, and the total amount was adjusted to 100% by mass.

  Next, the base paper with the coating layer formed on both sides was used in an after dryer part to dry the coating layer, and the calendar part was subjected to flattening treatment. In the flattening process, a flattening process (A) for performing the flattening process without applying a nip pressure (linear pressure) and a flattening process (B) for performing the flattening process by applying nip pressure (linear pressure) are performed. Combined. In the flattening step (A), a thermal roll having a surface temperature of 120 ° C. is subjected to a tension of 250 N / m without applying linear pressure, a holding angle of 160 °, and three rolls. Flattening was performed under the condition of one stage by applying a linear pressure of 150 kN / m to a heat roll having a temperature of 120 ° C. In the process order, the planarization process (A) was performed after the planarization process (B), and the planarization process (B) was further performed. Then, it was used for the reel part and the winder part to obtain coated paper.

  Paper was made using a gap former for the wire part, a straight-through type without an open draw for the press part, and a single deck dryer for the dryer part. In the coater part, after undercoating with a film transfer type roll coater, it was flattened with a pre-calender and overcoated with a blade coater. In the calendar part, a flattening process was performed using a multi-nip calendar or a super calendar (SC). In the multi-nip calender, the above flattening steps (B), (A), (B) are carried out in one stack, and in the super calender, the above flattening steps (B), (A), (B) are carried out one stack at a time. Three stacks were implemented.

About the obtained coated paper, each physical property was investigated with the following method. The results are shown in Table 1.
(A) Whiteness Measured according to the method described in JIS P 8148: 2001 “Paper, paperboard and pulp—Method of measuring ISO whiteness (diffuse blue light reflectance)”.
(B) Gloss of white paper Measured according to the method described in JIS P 8142: 2005 "Paper and paperboard-Method for measuring 75 degree specular gloss".
(C) White spot Using an offset printing machine (model number: Lithopia L-BT3-1100, manufactured by Mitsubishi Heavy Industries, Ltd.), color 4 using color ink (product number: ADVAN, manufactured by Dainippon Ink & Chemicals, Inc.) 5000 copies of color offset printing were performed. The printed surface was observed visually and with a magnifying glass (10 times), and the degree of white spots was evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: White spots cannot be confirmed visually or with a magnifying glass, and printability is excellent.
○: White spots cannot be visually confirmed, but can be confirmed with a magnifying glass, and printability is slightly inferior.
(Triangle | delta): A white spot can be confirmed visually and printability is somewhat inferior.
X: White spots can be clearly confirmed visually, and printing is inferior.
Of the evaluation criteria, ◎, ○, and Δ are judged to be actually usable.
(D) Cosmetic dirt

  Among the print samples adjusted with the above white spots, a black colored printed portion was used to conduct a cosmetic stain test using a dyeing fastness friction tester (manufactured by Toyo Seiki Seisakusho). The test was performed one week after printing in order to completely dry the printing ink, and a blank paper surface was superimposed on the printed surface, and the test was performed under a load of 500 g and 20 reciprocations. After the test, the density of the black ink transferred to the white paper part was measured using a printing density measuring machine (product number: SpectroEye, manufactured by GretagMacbeth) under the conditions of light source: D50, viewing angle: 2 °, and the white paper part before the test. The difference from the above was regarded as the cosmetic stain density. The test result was an average value of 10 samples, and the density of the black ink of each sample was a measured value of a portion where the transferred ink density was the highest.

(E) Operability (roll dirt)

The dirt adhesion of the metal roll of the multi-nip calender when the coated paper was continuously produced for 24 hours was evaluated based on the following evaluation criteria.
(Double-circle): Roll stain | pollution | contamination did not generate | occur | produce and operativity was favorable.
○: Roll stains are slightly generated and operability is slightly inferior.
Δ: Some roll dirt is generated, and the operability is slightly inferior.
X: Roll dirt occurs and the operability is inferior.
Of the evaluation criteria, ◎, ○, and Δ are judged to be actually usable.

Each of the coated papers of Examples 1 to 50 is less matte and has a matte tone or dull tone coated paper having a white paper glossiness of 50% or less. It is an excellent coated paper that does not cause problems such as roll contamination during production.
On the other hand, the coated papers of Comparative Examples 1 to 4 and the commercial product A do not satisfy the object of the present invention, in which any one of cosmetic stains, whiteness, white spots during printing, and roll stains during production is bad. It is coated paper.

  The coated paper of the present invention is a coated paper having a high-class feeling that the glossiness is low and the surface of the paper is not glaring, the visibility of the printed information is excellent, and the scum stain is not easily generated. It can be suitably used for commercial printing of magazines, pamphlets and the like.

Claims (4)

A coated paper provided with at least one coating layer mainly composed of a pigment and an adhesive on one or both sides of a base paper,
The outermost layer of the coating layer contains calcium carbonate having an average particle size of 0.1 to 1.0 μm as the pigment, and latex having a butadiene component of 40 to 65% by mass as the adhesive. The stain density (transfer ink density) is 0.1 or less.
Coated paper characterized by that.
Here, the cosmetic stain density is a solid color printing on the surface of the coated paper, and after 1 week, a white paper surface is overlapped on the printed surface, and a friction test for dyeing fastness under conditions of a load of 500 g and 20 reciprocations. The density of the black ink transferred to the white paper surface when the printing surface and the white paper surface were rubbed together using a printing machine (manufactured by Toyo Seiki Seisakusho Co., Ltd.) It is a density difference when using the light source: D50 and the viewing angle: 2 ° and measuring the difference from the density of the blank surface before the test.   The coated paper according to claim 1, wherein the latex contains 20 to 35 mass% of a styrene component, and the glass transition temperature (Tg) of the latex is -50 ° C to 0 ° C.   The coated paper according to claim 1 or 2, wherein the latex has an average particle size of 90 to 130 nm.   Content of the said calcium carbonate shall be 15-100 mass parts with respect to 100 mass parts of all the pigments, whiteness shall be 80% or more, and blank paper glossiness shall be 20-50%. 4. The coated paper according to any one of 3 above.