JP2010133050A - Coated paper causing suppressed picking trouble - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated paper for printing, suppressing generation of picking and blister even by printing by a high-speed rotary offset printing machine, especially a rotary offset printing machine having a printing speed of as high as &ge;1,200 rpm, and giving printed matter having good appearance and excellent finish. <P>SOLUTION: The coated paper includes base paper and at least two coating layers containing a pigment and an adhesive and formed on the base paper. The pigment in the undercoating layer contacting with the base paper contains clay and/or calcium carbonate, and the pigment in the undercoating layer has a particle diameter distribution having peaks in both of a range of &ge;0.8 &mu;m and &lt;1.3 &mu;m and a range of &ge;1.3 &mu;m and &lt;2.2 &mu;m in the area diameter distribution of particles totaled for every 0.1 &mu;m. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to coated paper. More specifically, the present invention relates to a coated paper for printing that suppresses the occurrence of paper smearing in offset printing, has high whiteness, and has a good printed appearance.

  In recent years, with the increase in the speed of printing presses, offset rotary printing presses are more likely to cause paper mess troubles in which the coated paper surface is removed by the printing ink and the coating layer is peeled off. Paper scraps are mainly generated when a part of the coating layer is peeled off from the coated paper in the coating layer, between the coating layer and the base paper, or in the base paper. This peeling is particularly likely to occur when the coated paper absorbs dampening water supplied from a printing press and the surface strength of the coated paper surface decreases. Various proposals have been made to suppress the occurrence of such paper smears.

  For example, a technique that uses kaolin as a pigment and regulates the particle size of latex as an adhesive (see Patent Document 1), a technique that uses calcium carbonate in an undercoat coating layer and a specific polyvinyl alcohol as an adhesive (Patent Document) 2), a technology that contains calcium carbonate of a specific shape in the base paper and a latex of specific properties in the topcoat and undercoat coating layers (see Patent Document 3), and a technology that characterizes the latex of the topcoat coating layer (Refer to Patent Document 4), technology for containing a wet paper strength enhancer having a specific shape (see Patent Document 5), technology for including a specific paper strength enhancer in the undercoat coating layer (see Patent Document 6) Has been proposed.

Although the occurrence of paper scraping can be reduced to some extent by the above technique, in recent high-speed rotary offset printing, the printing speed (the rotational speed of the blanket cylinder) has been increased from about 600 to 800 rpm to 1200 rpm or more, and according to this, After the ink is transferred from the blanket cylinder of the printing machine to the paper, the ink is abruptly peeled off from the coated paper, and a part of the coating layer is taken to the blanket cylinder side together with the ink. Printing defects are likely to occur. Also, the drying temperature after printing, which was conventionally around 105 to 110 ° C. on the paper surface, becomes as high as 120 to 130 ° C., and blisters that occur when moisture in the base paper evaporates (blister) There is a problem that defects tend to occur. For this reason, even if the above-described technique is used, there is a problem that paper smears and blisters cannot be sufficiently suppressed, and a printed matter having a high level and good appearance cannot be obtained as required.
Japanese Patent Laid-Open No. 10-140498 JP-A-11-279991 Japanese Patent Laid-Open No. 11-279992 JP 2000-265396 A JP 2003-286585 A JP 2000-282395 A

  An object of the present invention is to provide a printed matter obtained by printing with a high-speed rotary offset printing machine, in particular, even when printing is performed using a high-speed rotary offset printing machine with a printing speed of 1200 rpm or more, and generation of paper smears and blisters is suppressed. The object of the present invention is to provide a coated paper for printing that has a good appearance and excellent finish.

  As a result of the study by the present inventor to solve the above-mentioned problems, in the coated paper having at least two coating layers, by limiting the kind of pigment used in the undercoat coating layer and the particle size distribution, And it discovered that generation | occurrence | production of a blister was suppressed and completed this invention.

  That is, the coated paper of the present invention is a coated paper having at least two coating layers containing a base paper and a pigment and an adhesive on the base paper, and is an undercoat coating in contact with the base paper. The pigment of the layer contains clay and / or calcium carbonate, and the pigment of the undercoat coating layer has a distribution of area particle diameters counted every 0.1 μm, 0.8 μm or more and less than 1.3 μm and 1.3 μm or more It has a particle size distribution having a maximum value in each range of less than 2.2 μm.

  The coated paper of the present invention can suppress the occurrence of paper smears and blisters even when printing is performed using a high-speed rotary offset printer, particularly a high-speed rotary offset printer with a printing speed of 1200 rpm or more, and the whiteness is low. High, the appearance of the printed matter obtained by printing is improved and the finish is excellent.

  The present invention is a coated paper having at least two coating layers containing a base paper and a pigment and an adhesive on the base paper, wherein the pigment of the undercoat coating layer in contact with the base paper is clay and / or In the distribution of the area particle diameter that contains calcium carbonate and the pigment of the undercoat coating layer is counted every 0.1 μm, each of 0.8 μm or more and less than 1.3 μm and 1.3 μm or more and less than 2.2 μm It is a coated paper characterized by having a particle size distribution having a maximum value in the range.

<Paper making>
First, the base paper which comprises the coated paper which concerns on this embodiment is demonstrated.

  The base paper should just be obtained by papermaking a normal raw material pulp. The raw material pulp is not particularly limited. For example, chemical pulp such as unbleached softwood pulp (NUKP), unbleached hardwood pulp (LUKP), bleached softwood pulp (NBKP), bleached hardwood pulp (LBKP), etc .; Stone Grand Pulp (SGP) ), Pressurized Stone Grand Pulp (PGW), Refiner Grand Pulp (RGP), Chemi Grand Pulp (CGP), Thermo Grand Pulp (TGP), Grand Pulp (GP), Thermo Mechanical Pulp (TMP), Chemi Thermo Mechanical Pulp ( CTMP), refiner mechanical pulp (RMP) and other mechanical pulp; magazine waste paper, leaflet waste paper, waste paper pulp manufactured from office waste paper, etc., waste paper pulp such as disaggregation, deinking, bleached waste paper pulp, etc. , Select one or more of these as appropriate, It can be used to adjust the focus.

  A filler conventionally used for papermaking can be added to the raw material pulp as an internal filler. Examples of the filler include inorganic fillers such as light calcium carbonate, talc, titanium dioxide, clay, calcined clay, synthetic zeolite, and silica, polystyrene latex, urea formalin resin, and the like. Although the compounding quantity of a filler is not specifically limited, It is preferable to add so that it may become 8 mass% or less by paper ash content, and 6 mass% or less is more preferable. If the ash content in the paper exceeds 8% by mass, hydrogen bonds between the pulps are likely to be hindered, resulting in paper having no internal strength, and paper scumming during printing tends to occur, which is not preferable. If the internal ash content is reduced, the internal strength tends to improve, but the opacity of the coated paper decreases, so the printed part may be seen through, which may result in a poor-looking coated paper. There is sex. The ash content of the present invention is a value measured according to JISP8251 “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method”.

  It is preferable to add an internal sizing agent to the raw material pulp. In the present invention, it is preferable to increase the sizing degree of the base paper by adding an internal sizing agent in order to suppress dampening water absorption and prevent paper smearing during printing.

  In the present embodiment, in addition to the internal sizing agent, the raw material pulp includes, for example, a paper strength improver, a paper thickness improver, and a yield improver (water-soluble polymers such as various synthetic polymers and starches). In addition, various additives such as these fixing agents that are usually blended into the base paper of the coated paper can be internally added by appropriately adjusting the kind and blending amount thereof.

  After making the papermaking raw material as described above in the wire part and then supplying it to the press part and the pre-dryer part to produce the base paper, and then coating the base paper with the coating liquid described later in the coater part It can be used for an after dryer part, a calendar part, a reel part, a winder part and the like to obtain a desired coated paper.

  In addition, when the coating liquid containing clay is top-coated in a top coating layer to be described later, it is difficult to obtain high whiteness coated paper. Therefore, in order to further improve the whiteness of the target coated paper, the whiteness of the base paper is measured by a color analyzer (model number: color i5, manufactured by Macbeth Gretag), 70% or more, and further 75. % Or more is preferable. When the coated paper for printing is manufactured from such a base paper, the whiteness can be set to 80% or more, for example, as will be described later. When such a coated paper for printing having a whiteness of 80% or more is used, for example, a high-quality printed material with higher definition and high contrast can be obtained compared to a coated paper for printing with a whiteness of less than 80%. It is done.

Although there is no particular limitation on the basis weight of the base paper, as will be described later, the basis weight of the target coated paper is preferably 40 to 100 g / m ^2. Usually, it is preferable to adjust so that it may become about 20-70 g / m < ² >.

<Undercoat>
The base paper is provided with an undercoat coating layer mainly composed of a pigment and an adhesive before providing an overcoating layer to be described later.

(Pigment)
The undercoat coating layer must contain calcium carbonate and / or clay. When neither calcium carbonate nor clay is included, sufficient surface strength cannot be obtained. For example, when high-speed offset printing at 1200 rpm or more is performed, a problem of paper smearing occurs.

  When calcium carbonate is used, it is preferable because the pigment is indeterminate, the coating layer is easily clogged, and it is easy to prevent the occurrence of paper smears in which a part of the coating layer peels from the inside of the coating layer. Further, since calcium carbonate has high whiteness, the whiteness of the coated paper obtained is easily improved. Examples of calcium carbonate include those having an average area particle size of about 5 μm or less obtained by dry pulverization or wet pulverization of white crystalline limestone.

  When clay is used, the flatness after undercoating can be improved, and the dampening water will not easily penetrate into the base paper. This is preferable because it is possible to effectively suppress the occurrence of paper smears in which a part of the coating layer peels off together with a part of the base paper.

  By defining the particle size distribution of the calcium carbonate and clay contained in the undercoat coating layer, the effect of preventing paper smearing of the present invention can be obtained. The particle size distribution needs to have a maximum value in each range of 0.8 μm or more and less than 1.3 μm and 1.3 μm or more and less than 2.2 μm in the area particle size distribution counted every 0.1 μm, By adopting the configuration, for example, even in a high-speed offset printing machine having a printing speed of 1200 rpm or more, paper smearing can be sufficiently prevented.

  When pigments having local maximum values are used in the range of 0.8 μm or more and less than 1.3 μm and 1.3 μm or more and less than 2.2 μm in the area particle size distribution, the pigments tend to be more densely clogged and there are fewer voids. A high-density undercoat coating layer is obtained. This makes it difficult for the fountain solution to pass through the undercoat coating layer and to reach the base paper, making it difficult for the fountain solution to absorb water. It is possible to reduce paper troubles in which the undercoat coating layer peels from between the coating layers or a part of the coating layer peels from the inside of the base paper.

  The area particle diameter referred to in the present invention is the diameter of the smallest circle (particle circumscribed circle) that can enclose the particles of pigment particles photographed with an electron microscope. For the maximum value, the number of pigment particles was counted for each area particle size of 0.1 μm to obtain a particle size distribution, and the presence or absence of the maximum value was determined.

  As the pigment of the undercoat coating layer, calcium carbonate and clay having a specific area particle diameter range are used, and preferably by pre-calendering, the surface of the undercoat coating layer is improved in smoothness as described later. be able to. This prevents dampening water that has passed through the topcoat coating layer from penetrating deeper than the undercoat coating layer, especially by preventing it from penetrating into the base paper, further suppressing paper smudges during printing. can do.

  In particular, when two types of calcium carbonate having different average area particle diameters are used as pigment particles, the coating layer is denser than when clay is used, and it is easier to prevent paper scumming. Paper scum and blister resistance These are particularly preferable, and the whiteness of the resulting coated paper is as high as 87% or more. However, since the flatness of the surface after the top coat is lowered and the printability is liable to deteriorate, when two types of calcium carbonate having different average area particle sizes are used for the undercoat layer, the top coat described later is used. In the layer, it is preferable to add clay capable of improving printability.

  The types of clay are kaolin, dickite, nacrite, halloysite, antigolite, chrysotile, pyrophyllite, montmorillonite, hectorite, tetrasilic mica, sodium teniolite, margarite, talc, vermiculite, xanthophyllite, green mud Among them, kaolin clay is preferable.

  In the undercoat coating layer, in addition to calcium carbonate and clay, pigments generally used for papermaking can be used in combination. Examples of such pigments include titanium dioxide, zinc oxide, silicon oxide, amorphous silica, magnesium carbonate, barium carbonate, aluminum hydroxide, alumina, calcium hydroxide, magnesium hydroxide, and zinc hydroxide. One or more types can be used in combination as required.

  As described above, calcium carbonate and / or clay is used as the pigment of the undercoat coating layer, and the distribution of the area particle diameter obtained by counting the pigments every 0.1 μm is 0.8 μm or more and less than 1.3 μm and 1.3 μm or more 2 By setting the maximum value in each range of less than 2 μm, it is possible to obtain coated paper that prevents paper smearing. In particular, in a high-speed offset rotary printing press with a printing speed of 1200 rpm or more, the occurrence of paper scraps and blisters can be effectively prevented by having the maximum value as described above.

(adhesive)
As an adhesive for the undercoat coating layer, an adhesive that can be generally used for papermaking can be used. For example, proteins such as casein and soybean protein; conjugated diene latex such as methyl methacrylate-butadiene copolymer latex and styrene-butadiene copolymer latex, polymer latex or copolymer of acrylate ester and / or methacrylate ester Acrylic latex such as latex, vinyl latex such as ethylene-vinyl acetate polymer latex, or various types of copolymer latex modified with a functional group-containing monomer such as a carboxyl group. Latexes such as latex; synthetic resin adhesives such as polyvinyl alcohol, olefin-maleic anhydride resin, melamine resin, urea resin, urethane resin; starches such as oxidized starch, positive starch, esterified starch, dextrin; Carboxymethyl Cellulose, such as cellulose derivatives such as hydroxyethyl cellulose, are adhesives exemplified usually used for coated paper can be used in combination one or more from among the appropriately selected and.

  As the adhesive for the undercoat coating layer, styrene-butadiene copolymer latex is particularly preferable among the adhesives because of its high adhesiveness and thermal stability. The styrene-butadiene copolymer latex is a latex obtained by copolymerizing at least styrene and butadiene, and is obtained by copolymerizing methyl methacrylate and acrylonitrile in addition to styrene and butadiene. -Acrylonitrile copolymer latex is more preferred. In particular, when the styrene component in the latex is 40 to 60% by mass, the butadiene component is 25 to 45% by mass, the methyl methacrylate component is 5 to 15% by mass, and the acrylonitrile component is 1 to 10% by mass, the adhesiveness is high. Paper dipping and blisters are less likely to occur, which is preferable. In particular, in a high-speed offset rotary printing press of 1200 rpm or higher, the paper surface temperature during drying increases to around 120 ° C., so the thermal stability of the undercoat coating layer can be improved by blending a large amount of styrene with good thermal stability, Blister properties can be improved. If the styrene component is less than 40% by mass, sufficient blister resistance cannot be obtained, and if it exceeds 60% by mass, the adhesiveness derived from the butadiene component is likely to be lowered, and the pigment cannot be sufficiently fixed, and paper scumming tends to occur. Therefore, it is not preferable. Adhesion can be obtained by increasing the butadiene component, so if the butadiene component is less than 25% by mass, it is difficult to prevent paper smearing. If it exceeds 45% by mass, the coating layer becomes too soft and blister resistance decreases. Therefore, it is not preferable.

  If the average particle size of the styrene-butadiene copolymer latex is as large as 150 to 210 nm, water vapor can easily escape from the base paper in the drying stage after printing, and blister resistance can be improved. Especially when using a pigment having a small particle diameter as the undercoat coating layer as in the present invention, and forming a high density undercoat coating layer, it is difficult for water vapor to escape from the base paper. It is preferable to prevent a decrease in blister resistance. If the average particle size is less than 150 nm, the blister resistance is poor, and if it exceeds 210 nm, a sufficient coating layer strength cannot be obtained, and paper smearing tends to occur, which is not preferable. In addition, by reducing the gel content of the styrene-butadiene copolymer latex to 30 to 60% by mass, not only the blister resistance can be prevented from being lowered, but also the adhesiveness to the pigment is enhanced, and the effect of preventing paper scumming is also achieved. Since it is obtained, it is preferable. If the gel content is less than 30% by mass, sufficient coating layer strength cannot be obtained, and peeling inside the undercoat coating layer tends to occur, and if it exceeds 60% by mass, it is applied with dampening water. This is not preferable because not only peeling within the construction layer is likely to occur but also blistering is likely to occur. If the glass transition temperature of the latex is −20 to 10 ° C., the thermal stability of the coating layer can be improved, and the blistering can be reduced even when the paper surface temperature is as high as 120 to 130 ° C. during drying after printing. preferable.

  The blending ratio of the pigment and the adhesive in the undercoat coating solution is preferably 4 to 12 parts by mass, more preferably 6 to 10 parts by mass with respect to 100 parts by mass of the pigment in the undercoat coating layer. preferable. If the blending amount of the adhesive is less than 4 parts by mass, the pigment cannot be fixed, the internal strength of the coating layer is likely to be lowered, and paper scumming is likely to occur. When the blending amount of the adhesive exceeds 12 parts by mass, the porosity in the undercoat coating layer is likely to decrease, and paper scumming is likely to occur, which is not preferable.

  The undercoat coating solution can be applied by various known methods in the size press process during the paper making process, but is preferably applied by a film transfer method. The film transfer method is a method in which the paint is transferred to paper after the coating paint is applied to the roll, so that a uniform coating layer can be formed on the surface of the base paper, so uniform and good surface strength can be obtained. preferable. For example, in a method of forming a coating liquid pool such as a two-roll size press, a pigment with a small particle size can easily enter the inside of the base paper, while a pigment with a large particle size is applied to the surface of the coating layer. It is difficult to obtain a dense coating layer. In the case of the blade coating method, a coating layer having a uniform thickness cannot be obtained, so that dampening water easily permeates from a thin portion of the coating layer, and paper damage caused by delamination inside the base paper. Is difficult to suppress.

The concentration of the undercoat coating solution is not particularly limited, the coating amount preferably per side 4~10g / m ^2, more preferably to be in the range of 5-6 g / m ^2, it may be appropriately adjusted. For example, the concentration may be 60 to 70% by mass, and 62 to 68% by mass is preferable because more uniform coating can be performed within the above coating amount range. When the concentration is less than 60% by mass, moisture in the coating liquid is easily absorbed by the base paper, and the tensile strength of the paper is lowered, and the paper is easily cut during undercoating. If the concentration exceeds 70% by mass, it is difficult to obtain a uniform coating, and not only the hand feeling is lowered, but also the flatness after the undercoating and hence the printability after the overcoating are unfavorable.

Subbing coating layer, the coating amount per one surface at a solids coating weight, preferably 4~10g / ^{m 2,} and more preferably is applied such that 5-6 g / ^{m 2.} If the solid content is less than 4 g / m ^2, it is difficult to obtain uniform coatability and sufficient coverage, and it is not only possible to sufficiently prevent the dampening water from being absorbed into the base paper, but also to flatten the base paper. It is difficult to form, and printability after top coating is reduced. If the amount of the top coat is increased by setting the amount of the undercoat to less than 4 g / m ² to obtain uniform coatability and sufficient coverage, it is necessary to increase the amount of coat excessively. This is not preferable because the internal strength of the construction layer is likely to be lowered and paper scumming is likely to occur. This is the same even when the undercoat coating amount exceeds 10 g / m ² .

<Pre-calendar>
The coated base paper after the undercoating is preferably subjected to a pre-calendering flattening process before the topcoating (pigment coating) because the density of the undercoating layer is easily improved. As the pre-calender, a soft calender combining a metal roll and an elastic roll is preferable because the effect of improving the density is high. The pre-calendar can be performed in one stage or a combination of two or more stages as required. The linear pressure of the pre-calender is preferably 10 to 80 kN / m, more preferably 10 to 50 kN / m. When the density is less than 10 kN / m, the density of the undercoat coating layer is difficult to improve, and when it exceeds 80 kN / m, the base paper is pressed more than necessary, and thus delamination easily occurs inside the undercoat coating layer. It is not preferable because it is inferior in preventing paper smearing.

<Topcoat coating>
An undercoating layer is formed, and an overcoating layer mainly composed of a pigment and an adhesive is provided on a base paper that has been preferably flattened with a pre-calender.

(Pigment)
The pigment in the top coat layer is not particularly limited, and those generally usable for papermaking can be used. Specifically, the pigment of the undercoat coating layer described above can be used as appropriate.

  Among the pigments, kaolin clay is preferable because the occurrence of paper smearing tends to decrease. Kaolin clay is a plate-like pigment that covers the surface of the coating layer widely, making it easy to suppress the absorption of dampening water, delamination inside the overcoating layer, and the interlayer between the overcoating layer and the undercoating layer. Peeling, delamination inside the undercoat coating layer, delamination between the undercoat coating layer and the base paper, and paper smearing due to delamination inside the base paper are easily prevented, which is preferable. Further, use of kaolin clay is preferable because glossiness and smoothness of the coated paper are easily improved and printing suitability is further improved. As in a preferred embodiment of the present invention, when calcium carbonate having low printability is used for the undercoat coating layer, particularly when two types of calcium carbonate having different average area particle sizes are used, kaolin clay is used in the topcoat coating solution. By blending, printability is easily improved.

  As the kaolin clay, those conventionally used for papermaking can be used. For example, large particle size clay, fine particle clay, calcined clay, high white clay and the like can be mentioned. Among these, when using kaolin clay in which particles having an area particle size of 0.5 to 2.0 μm occupy 80 to 100% by mass, more preferably 85 to 95% by mass, covering of the top coat layer is good. It is preferable because the coating amount can be reduced, the surface strength of the top coating layer is hardly lowered, and paper smearing is easily suppressed. When particles of less than 0.5 μm occupy 80% by mass or more of the whole, the amount of liquid absorption increases because the number of pores increases, so that dampening water easily penetrates into the undercoat coating layer, and paper scumming tends to occur. . When particles exceeding 2.0 μm account for 80% by mass or more of the whole, the flatness of the surface of the top coat layer is lowered, and it becomes difficult to obtain good printability.

  The blending amount of kaolin clay in the top coat layer is preferably 30 to 70% by mass with respect to the total amount of pigment blended in the top coat layer. When it is less than 30% by mass, it is not preferable because it is inferior in white paper gloss and printing gloss. In addition, since the voids in the coating layer increase, the amount of dampening water absorbed increases, and it is difficult to suppress the occurrence of paper scumming. In addition, sufficient printability cannot be obtained. When it exceeds 70 mass%, since whiteness will fall, it may become a coated paper inferior in appearance.

  By using calcium carbonate having high whiteness as a pigment in the topcoat coating layer together with kaolin clay, it is possible to prevent paper smearing. As calcium carbonate, particles having an area particle diameter of 0.2 to 1.0 μm occupy 80 to 100% by mass, preferably 85 to 95% by mass. When there are many particles of less than 0.2 μm and particles with an area particle size of 0.2 to 1.0 μm are less than 80% by mass of the total pigment, the amount of liquid absorption increases because the number of pores increases, and dampening water is undercoated. It becomes very easy to penetrate into the coating layer, and paper smearing is likely to occur. When the number of particles of 1.0 μm or more is large and the particles having an area particle size of 0.2 to 1.0 μm are less than 80% by mass of the total pigment, the flatness of the surface of the top coat layer is remarkably lowered. Can't get.

  Calcium carbonate has a high whiteness and is easy to improve the whiteness of the coated paper obtained, but it is preferably used in combination with kaolin clay because the surface properties after coating are reduced and the printability is poor. In this case, it is preferable to set it as 30 to 70 mass% with respect to the whole quantity of the pigment mix | blended with a top coat layer as a compounding quantity of a calcium carbonate.

  The whiteness of the coated paper varies slightly depending on the application, but from the viewpoint of obtaining a sufficiently satisfactory aesthetic appearance as a printed matter or recorded matter, it is measured with a color analyzer (model number: i5, manufactured by Macbeth Gretag). It is preferably 83% or more, more preferably 85% or more. Setting the blending amount of calcium carbonate to 30 to 70% by mass as described above is preferable because a coated paper with good whiteness can be obtained while suppressing the occurrence of paper scraping.

  The top coat layer having the above-described structure, that is, kaolin clay in which particles having an area particle size of 0.5 to 2.0 μm occupy 80 to 100% by mass, 30 to 70 parts by mass of the entire pigment, and area particle size of 0.2 The above-mentioned undercoat layer, that is, calcium carbonate and kaolin clay, containing 30 to 70 parts by mass of the total pigment of calcium carbonate in which particles of ~ 1.0 μm account for 80 to 100% by mass is contained. However, when it is provided on an undercoat coating layer having a particle size distribution having two maximum values, a coated paper that can sufficiently suppress paper smearing while maintaining good printability can be obtained. In addition, the adhesive used for the undercoat coating layer is a styrene-butadiene-methyl methacrylate-acrylonitrile copolymer latex, the components of which are 40-60 mass% of styrene component and 25-45 mass% of butadiene component. In addition, it is preferable that the methyl methacrylate component is 5 to 15% by mass and the acrylonitrile component is 1 to 10% by mass because not only paper scraps but also blisters can be sufficiently reduced.

  As the adhesive used for the topcoat coating layer, the same material as the undercoat coating layer can be used, but a styrene-butadiene copolymer latex that has high blister resistance and can effectively prevent paper smearing is used. It is preferable to use a styrene-butadiene-methyl methacrylate-acrylonitrile copolymer latex. More preferably, when the latex used in the topcoat layer has a butadiene component of 35 to 60% by mass, and more preferably 40 to 55% by mass, the adhesiveness to the pigment of the undercoat coating layer is increased, and the primer coating is performed. The adhesiveness between the layer and the top coat layer is improved, and it is preferable because it is easy to prevent paper smearing. In particular, as in the present invention, when the molecular weight distribution of the pigment in the undercoat layer has two maximum values, the surface of the undercoat layer is easily flattened because the undercoat layer is densely packed, There is a tendency that the top coat layer does not easily adhere to the surface of the coating layer, and delamination occurs between the undercoat layer and the top coat layer, which tends to cause paper scraping. If the butadiene component is less than 35% by mass, the adhesiveness between the undercoat coating layer and the topcoat coating layer is reduced, and paper smearing is likely to occur. If it exceeds 60% by mass, the coating layer becomes too soft and blister resistant. Since it is inferior in property, it is not preferable. For this reason, it is preferable to make a butadiene component into the above-mentioned range. That is, it is preferable that the butadiene component of the latex used for the topcoat coating layer is 5% by mass, and even 10% by mass more than the butadiene component used for the undercoat coating layer, because it is easy to effectively prevent paper smearing. If the butadiene component used in the topcoat coating layer is more than 25% by mass compared to the butadiene component used in the undercoat coating layer, the blister resistance is lowered, which is not preferable.

  Moreover, it is preferable that the styrene component of the latex used for a top coat layer is 10-50 mass%, and also 15-35 mass%. In other words, if the styrene component of the topcoat coating layer is 5% by mass or more, further 10% by mass or more, and especially 15% by mass or more less than the styrene component of the undercoat coating layer, as described above, paper scumming is prevented. It is preferable because it is easy. If the styrene component of the topcoat layer is less than 40% by mass compared to the styrene component of the undercoat layer, a sufficient surface strength cannot be obtained, and paper scumming occurs, which is not preferable.

  Further, in the present invention, it is preferable to contain kaolin clay in the overcoating layer in order to reduce the absorbability of dampening water. However, since the whiteness is decreased at 70 parts by mass or more, the pigment has a high whiteness. It is preferable to contain calcium carbonate, and under such conditions, the ink setting property is high, while the ink set is fast and the printing gloss tends to be lowered. For this reason, it is preferable that the latex used for the top coat layer has a small amount of methyl methacrylate component that improves the inking property and a large amount of acrylonitrile component that improves the printing gloss. Specifically, the methyl methacrylate component contained in the latex used for the top coat layer is preferably 1 to 10% by mass, and more preferably 3 to 8% by mass. The acrylonitrile component is preferably 5 to 29 mass%, more preferably 10 to 27 mass%.

  Further, the average particle size of the latex used in the topcoat coating layer is 0.7 times or less, more preferably 0.5 times or less of the average particle size of the latex of the undercoat coating layer. The adhesive strength is high, so that not only is paper not easily generated, but also high printing gloss is obtained, which is preferable. In particular, as in the present invention, when the undercoat coating layer is dense and peels from between the undercoat coating layer and the topcoat coating layer, and the paper coating is likely to occur, the topcoat coating layer has strong adhesive strength. It is preferable to use latex. Similarly, when the gel content of the latex used for the topcoat coating layer is 1.7 times or more, and further 2.0 times or more than the gel content of the latex used for the undercoat coating layer, strong adhesive strength can be obtained. It is preferable because delamination between the undercoat coating layer and the topcoat coating layer hardly occurs and it is easy to prevent paper smearing.

  The blending ratio of the pigment and the adhesive in the top coating liquid is preferably 4 to 10 parts by mass, and more preferably 6 to 8 parts by mass with respect to 100 parts by mass of the pigment in the top coating layer. It is more preferable to adjust so. If the blending amount of the adhesive is less than 4 parts by mass, it is not preferable because the coating layer is easily smeared with a metal roll when performing a flattening process with a super calender or the like. On the other hand, if the blending amount of the adhesive exceeds 10 parts by mass, the adhesive is formed in the coating layer, the smoothness of the surface of the coating layer is lowered, and paper smearing is likely to occur during printing, which is not preferable. .

  In addition to pigments and adhesives, the top coating liquid used in the present embodiment includes, for example, dust preventing agents, fluorescent dyes, fluorescent dye brighteners, antifoaming agents, mold release agents, colorants, water retention agents, and the like. Various auxiliary agents generally used in papermaking applications can be appropriately blended within a range not impairing the object of the present invention.

  There is no particular limitation on the method for preparing the topcoat coating solution, and the mixing ratio of pigments, adhesives, dust inhibitors, and various auxiliary agents as necessary is adjusted appropriately, and a uniform composition at an appropriate temperature. What is necessary is just to stir and mix so that it may become. In addition, the solid content concentration of the topcoat coating liquid is not particularly limited, and is preferably adjusted to, for example, about 60 to 75% by mass according to the coating apparatus and the coating amount.

The top coat layer is preferably applied to both sides of the base paper at a solid content of 6 to 10 g / m ² per side of the base paper, and more preferably 7 to 9 g / m ^2. More preferred. If the coating amount is less than 6 g / m ² per side, the coating layer is not sufficiently flattened, and dampening water is likely to penetrate into the undercoating coating layer and the base paper, and paper scumming is likely to occur. Absent. If it exceeds 10 g / m ² , the penetration of the fountain solution will decrease, but the internal strength of the coating layer will decrease, making it difficult to sufficiently suppress the occurrence of paper smears.

  For the purpose of further improving the printability, the overcoating layer formed as described above may be subjected to a flattening process using a flattening facility that combines an elastic roll and a metal roll, such as a super calender or a soft calender. it can. Unlike conventional machine calenders, such flattening equipment treats the paper surface with a wide surface at a high temperature, thereby enabling flattening without excessively increasing the density of the base paper or the coating layer. For example, a suitable printing surface can be formed in offset printing, electrophotographic printing, and the like. Among them, a multi-nip calender, more preferably a 6-stage, 8-stage, or 10-stage multi-nip calender is preferable because the nip pressure can be easily adjusted. In particular, when two types of calcium carbonate are used in combination in the undercoat coating layer, or when calcium carbonate is contained in the topcoat coating layer, it is difficult to obtain white paper glossiness compared to kaolin clay, so the linear pressure can be adjusted appropriately. The use of a multi-nip calender is particularly preferable because the glossiness of blank paper is easily improved as compared with other calender equipment.

  Moreover, as an installation place of a calendar, an on-machine type integrated with a paper machine and a coating machine is preferable. The on-machine type is preferable because it can be flattened immediately after coating at a high paper surface temperature, so that the glossiness of the white paper is easily improved, and high white paper glossiness can be obtained while preventing the occurrence of paper smearing.

  The linear pressure, temperature, and speed of the flattening treatment using various calendar facilities are not particularly limited. To improve the smoothness of the coated layer after the treatment and improve the hand feeling, for example, the linear pressure is 100. It is preferable to adjust so that it may become -300 kN / m, a metal roll temperature may be 100-200 degreeC, and a speed | rate may be 1,000-2,000 m / min.

The basis weight of the coated paper thus obtained is 30 to 100 g / m ^{2 as} measured according to the method described in JISP 8124 “Basis weight measurement method” from the viewpoint of ensuring printability and hand feeling. preferably, it is preferred that even at ^{50g / m 2 ~80g / m 2} . When the basis weight is less than 30 g / m ² , for example, it may be difficult to ensure the paper quality strength at the same time while ensuring printability. When the basis weight exceeds 100 g / m ² , it has recently been required. There is a risk that it will be difficult to achieve the weight saving and resource saving.

  Like this invention, it consists of two layers comprised from the undercoat coating layer which touches a base paper, and the overcoat coating layer formed on the said undercoat coating layer, and calcium carbonate and / or as a pigment of an undercoat coating layer Or, the pigment of the undercoat coating layer that contains clay and is in contact with the base paper is 0.8 to 1.3 μm and 1.3 to 2.2 μm, respectively, in the distribution of area particle diameters counted every 0.1 μm. By having a particle size distribution having a maximum value in the range, paper smearing can be prevented.

  Furthermore, when the adhesive is a styrene-butadiene copolymer latex and the butadiene component of the styrene-butadiene copolymer latex used for the top coat layer is 35 to 60% by mass, the above particle size distribution is obtained. Even the undercoat coating layer is preferable because it improves adhesion with the topcoat coating layer and easily prevents paper smearing. In addition, when the styrene component of the latex used for the topcoat coating layer is 10% by mass or more, and further 15% by mass or less, compared to the styrene component used for the undercoat coating layer, it is possible to further prevent paper smearing.

  Moreover, in order to obtain sufficient printing gloss, the methyl methacrylate component contained in the latex used for the top coat layer is preferably 1 to 10% by mass, more preferably 3 to 8% by mass, and the acrylonitrile component is 5 to 5%. 29 mass% is preferable and 10-27 mass% is more preferable.

  In addition, in order to further prevent paper smearing, the latex of the top coat layer should have a particle size of 0.7 times or less, more preferably 0.5 times or less, compared with the latex of the undercoat coating layer. The gel content is preferably 1.7 times or more, more preferably 2.0 times or more. In addition, the smoothness of the surface of the undercoat coating layer can be improved by applying a precalender after applying the undercoat coating layer, so that the absorbency of dampening water can be reduced and the occurrence of paper smudges is suppressed. It is preferable because it is easy to do. In particular, in the case of printing with a high-speed rotary offset printing machine having a printing speed of 1200 rpm or more, the paper surface is easy to be removed when the ink is peeled off from the paper surface, and paper smearing is more likely to occur. As a result, paper smear can be effectively suppressed even in a high-speed offset rotary printing press.

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

Examples and Comparative Examples Undercoating and topcoating were performed in the types and proportions shown in Tables 1 and 2, and coated paper was obtained. The pigments, raw materials and chemicals used are as follows.

(1) Undercoat coating (pigment)
・ Calcium carbonate Super 4S: Heavy calcium carbonate (Product number: Super 4S: Maruo Calcium Co., Ltd., area particle size: 2.42 μm)
Charcoal Cal # 60: Heavy Calcium Carbonate (Part No .: Hydro Curve 60, manufactured by Omiya Korea, area particle size: 2.13 μm)
Charcoal Cal # 75: Heavy Calcium Carbonate (Part No .: Hydrocurve 75, manufactured by Omiya Korea, area particle size: 1.59 μm)
Super: Heavy calcium carbonate (Product number: Super # 2300: Maruo Calcium Co., Ltd., area particle size: 1.30 μm)
Charcoal Cal # 90: Heavy Calcium Carbonate (Part No .: Hydro Curve 90, manufactured by Omiya Korea Co., Ltd., area particle size: 1.25 μm)
Escalon: Heavy calcium carbonate (Product No .: Escalon # 2300: Sankyo Flour Mills, area particle size: 0.84 μm)
Charcoal Cal # 15: Heavy calcium carbonate (Product No .: Brilliant 15: Shiraishi Kogyo Co., Ltd., area particle size: 0.75 μm)
・ Kaolin clay capim DG (Product number: Capim DG, manufactured by Imeris Co., Ltd., area particle size: 1.15 μm)
Capim NP (Part No .: Capim NP, manufactured by Imeris Corporation, area particle size: 2.20 μm)
Silica (Product number: Carplex # 80, manufactured by Kanematsu Chemical Co., Ltd., area particle size: 1.12 μm)
Alumina (Product No .: Sumiko Random AA-2, manufactured by Sumitomo Chemical Co., Ltd., area particle size: 1.27 μm)
Silica and alumina are pulverized using a wet pulverizer (product number: planetary mill, manufactured by Seishin Enterprise Co., Ltd.), and the area particle size distribution counted every 0.1 μm is maximized in the range of 0.8 μm to less than 1.3 μm. A pigment having a value was prepared and used.

  In addition, the area particle diameter of this invention was measured as follows. The coated paper was cut out to A4 size, and a sample of 5 mm square was cut out at a point of Acm from the upper side to the lower side and Acm from the left side, with the short side of the paper as the upper side. Here, A is an integer of 1 to 20, and a total of 20 samples were collected. The surface of the cut out sample was photographed at a magnification of 12000 using a scanning electron microscope (model number: S-2150, manufactured by Hitachi, Ltd.). The area particle diameter was measured for the pigment that was closest to the point Bcm from the upper side to the lower side of the photograph and Bcm from the left side, and the entire particle was photographed. Here, B is an integer of 1 to 5, and the area particle diameter of 5 particles was determined from one sample, and the area particle diameter was determined for a total of 100 pigment particles. Since the pigment particles are not perfect circles, the diameter of the smallest circle that can enclose the pigment particles is defined as the area particle size.

  The average area particle diameter of each pigment used was a coated paper for evaluation coated with an undercoat coating layer in the same manner as in Example 1 except that the pigment was used alone, and an area of 100 points was obtained by the method described above. The particle diameter was measured and taken as the median value.

  The distribution of the area particle diameter of the total pigment contained in the undercoat coating layer was determined by measuring the area particle diameter of the coated paper coated with the undercoat coating layer obtained in each Example by the above-described method, and calculating the number of particles. The particle size distribution was calculated by summing up for each area particle size of 0.1 μm. With respect to the pigment group classified for each 0.1 μm, the presence or absence of a maximum value was determined.

(adhesive)
・ Styrene-butadiene copolymer latex (Part No .: PA-5118, manufactured by Japan A & L)
In Examples 9-20, the latex of the undercoat used in Example 1 with the components, gel content, and particle size changed as shown in Table 1 was used.

  The latex gel content and average particle size were determined as follows.

  Gel content of latex: About 0.3 g of latex is spread thinly on a slide glass, and dried with a dryer at 50 ° C. until a film is formed. The latex film is soaked in about 50 ml of toluene all day and night, filtered through a glass filter, the filtrate is dried with a dryer at 105 ° C., and the weight of toluene-soluble matter is measured. From the toluene soluble weight obtained here, the gel content is calculated according to the following formula.

Gel content (%) = (dry film weight−toluene soluble weight) × 100 / dry film weight Latex average particle diameter: Prepare a sample diluted to a concentration of 0.05 to 0.2%, and measure the absorbance at a wavelength of 525 nm. Measured and determined with a calibration curve prepared in advance.

(2) Top coating (pigment)
-Calcium carbonate: Heavy calcium carbonate Product number: Hydrocurve 90, manufactured by Omiya Korea)): 50 parts by mass-Kaolin clay: Product number: Kao Fine, manufactured by Imeris: 50 parts by mass (adhesive)
-Styrene-butadiene copolymer latex Examples 1 to 20 Item No .: F1558.02, manufactured by Asahi Kasei Corporation In Examples 21 to 32, the latex of the top coat used in Example 1 was classified into components, gel content, and particle size, respectively. Were used as shown in Table 2.
Example 33 Part No .: PA-6082, Japan A & L Example 34 Part No .: T-2748F, JSR Example 35 Part No .: HT-3022, Nippon Zeon Example 36 Part No .: T-2736A, JSR Example 37 Article No .: T-2730P, manufactured by JSR Corporation ・ Acrylonitrile-butadiene polymer latex (NBR)
Example 38 Article number: Nipol 1562, manufactured by Nippon Zeon Co., Ltd. Carboxy-modified methyl methacrylate-butadiene polymer latex (MBR)
Example 39 Article number: MR-171, manufactured by Japan A & L Co. (manufacturing procedure)
LBKP and NBKP are blended as raw material pulp at a mass ratio of 80:20, and the internal sizing agent (Product No .: AK-720H, manufactured by Harima Chemicals Co., Ltd.) is solid for each of these pulps (absolutely dry). ) 0.02% by mass, cationized starch (product number: Amilofax T-2600, manufactured by Abebe Japan Co., Ltd.) 1.0% by mass, and yield improver (product number: NP442, manufactured by Nissan Eka Chemicals Co., Ltd.) 0 0.02 mass% was added to obtain a pulp slurry.

  Next, in the winder part using the paper making system including wire part, press part, pre-dryer part, undercoater part, pre-calender part, after-dryer part, top coater part, scuff dryer part, calendar part, reel part Finished product.

First, the pulp slurry is made with a wire part, then subjected to a press part and a pre-dryer part to produce a base paper having a basis weight of 36 g / m ² , and then, as a pigment described in Table 1 in an undercoater part. Mix both the pigment and 8 parts by mass of latex with respect to 100 parts by mass of the pigment, and prepare a primer coating solution prepared at a concentration of 65% on both sides with a film transfer system (Shimsizer) so that the amount is 6 g / m ² per side. The undercoat was applied and dried in an after dryer part. Then, it planarized with the pre-calender (linear pressure 50kN / m).

Next, 50 parts by mass of calcium carbonate, 50 parts by mass of kaolin clay, and 6 parts by mass of the latex shown in Table 2 were mixed in the top coater part, and the top coating solution prepared to a concentration of 65% by mass was 9 g / m per side. ² was coated on both sides to produce a coated paper for printing having a basis weight of 64 g / m ² .

  Next, the calender part was subjected to a flattening treatment at a linear pressure of 200 kN / m and a speed of 1,000 m / min, and was applied to a winder part to obtain a coated paper for printing.

  In addition, paper was made using a gap former in the wire part, a rod metering size press coater was used in the undercoater part, and a blade coater was used in the top coater part. In the calendar part, a super calendar was used.

  About the obtained coated paper, whiteness, the generation | occurrence | production temperature (blister resistance) of blister, the paper swelling generated at the time of rotary printing, the glossiness of the obtained printed matter, and the ink set were investigated by the following methods. The results are shown in Table 2.

(A) Whiteness It measured about the unprinted coated paper according to the method of JISP8148: 2001 "Paper, paperboard, and a pulp-ISO whiteness (diffuse blue reflectance) measuring method".

(B) Blister generation temperature An oil bath (silicon oil) adjusted to a constant temperature after conditioning a test sample (2 cm in the flow direction and 10 cm in the width direction) of the coated paper for printing for 24 hours under conditions of 23 ° C. and 50% RH. ) For 4 seconds. This test was performed three times, and the lowest temperature among the temperatures at which blisters were generated was defined as the blister generation temperature. The temperature of the oil bath was increased from 160 ° C. in 10 ° C. increments, and when blisters were generated at that temperature, the blister generation temperature was determined. If the blister generation temperature is 170 ° C. or higher, it can withstand actual use, and if it is 180 ° C. or higher, blisters are less likely to be generated, and if it is 200 ° C. or higher, the coated paper has particularly excellent blister resistance. Become.

・ Preparation of printing sample Using offset printer (model number: LITHOPIA MAX BT2-1000, manufactured by Mitsubishi Heavy Industries, Ltd.), color ink (product number: ADVAN, manufactured by Dainippon Ink & Chemicals, Inc.) 5,000 copies were printed at a speed of 1,200 rpm. The paper surface temperature was set to 115 ° C.

(C) Paper Smudge The degree of occurrence of paper scum on the print sample was visually evaluated according to the following criteria.
A: There is no paper smearing and it can be used in practice.
○: Paper blurring occurs slightly and looks slightly inferior, but can be used in practice.
Δ: Paper blurring occurs slightly, and the appearance is somewhat inferior, but it can be used in practice.
X: Paper blurring occurs, the appearance is inferior, and actual use is impossible.

(D) Print Glossiness The print surface of the print sample was measured for glossiness according to JISP8142: 2005 "Paper and paperboard-Method for measuring 75 degree specular gloss". If the printing glossiness is 77% or more, there is no problem in actual use. If the printing glossiness is 80% or more, the appearance is excellent, and if it is 83% or more, the coated paper is particularly excellent in printing glossiness.

(E) Ink set Immediately after preparation of the print sample, the coated surface of the coated paper of each example was superimposed on the printed surface, and pressure-bonded at a pressure of 20 N for 1 minute. After pressure bonding, the state of ink transfer to the coated surface was visually observed and evaluated based on the following evaluation criteria.

(Evaluation criteria)
(Double-circle): The stain | pollution | contamination does not arise at all on the coated paper surface.
○: Slight dirt is generated on a part of the coated paper surface, but there is no problem in actual use.
Δ: Slight stains occur on a part of the coated paper surface, but there is no problem in actual use.
×: The entire coated paper surface is very dirty and cannot be used in practice.

  The coated paper of the present invention can be suitably used as a printing coated paper used in offset printing.

Claims (3)

A coated paper having at least two coating layers containing a base paper and a pigment and an adhesive on the base paper,
The pigment of the undercoat coating layer in contact with the base paper contains clay and / or calcium carbonate,
Particles in which the pigment of the undercoat coating layer has a maximum value in each range of 0.8 μm or more and less than 1.3 μm and 1.3 μm or more and less than 2.2 μm in the distribution of area particle diameters counted every 0.1 μm Coated paper characterized by having a diameter distribution. The adhesive is a styrene-butadiene copolymer latex;
The styrene-butadiene copolymer latex used for the top coat layer of the outermost layer has 5 to 40% by mass less styrene component and 5 butadiene components compared to the styrene-butadiene copolymer latex used for the undercoat coat layer. The coated paper according to claim 1, wherein the coated paper is ˜25% by mass.   The styrene-butadiene copolymer latex of the top coat layer has a gel content of 1.7 times or more and an average particle size of 0.7 times or less compared to the styrene-butadiene copolymer latex of the undercoat layer. The coated paper according to claim 2, wherein the coated paper is provided.