JP6200245B2 - Coated paper for web offset printing - Google Patents

Description

  The present invention relates to coated paper for rotary offset printing.

  In recent years, in the printing industry, the printing method has shifted from conventional letterpress printing to offset printing or the like with the full color and high quality of advertisements and magazines. This offset printing is excellent in photographic gradation reproducibility, and multicolor printing is possible on many types of paper. Therefore, simultaneously with the shift of the printing method, there is a demand for improving the quality of paper used for offset printing. In particular, offset rotary printing places emphasis on productivity, resulting in a higher printing speed, and accordingly, a technique for dealing with troubles such as so-called wrinkles is required.

  The above-mentioned wrinkles are wrinkles that are generated when the ink on the paper is subjected to forced heating and drying at a high temperature after the ink and fountain solution are adhered to the coated paper with an offset rotary printing press. That is, the non-image area where ink does not adhere during printing has a higher moisture evaporation rate than the image area where ink adheres, and therefore shrinkage starts first, and the flow direction (papermaking direction) appears in the image area. Will occur. This crease is particularly noticeable on paper having a low basis weight, which is a major obstacle to weight reduction of coated paper. Many technologies have been developed to control this bloating. For example, as an improvement measure by a production facility, a technique of adding an organic compound or amorphous silicate that inhibits inter-fiber bonding of pulp to raw pulp, and processing with a shoe calender after drying (see JP 2006-132030 A), coating As a measure for improving the characteristics of the layer, a technique of incorporating hollow resin particles having an average particle diameter of 0.5 to 3.0 μm as a pigment component in the lowermost layer of the coating layer (see JP 2007-21357 A) ), A technique for suppressing shrinkage by using pulp fibers having a lumen width and a fiber width within a specific range as means for imparting characteristics to the base paper has been reported (see JP-A-10-226979).

  However, the above-mentioned improved manufacturing equipment coated paper requires capital investment, and the coated paper using the hollow resin particles is expensive in the hollow resin particles. Rises. Moreover, it cannot be said that the coated paper which selected the said pulp fiber has fully suppressed wrinkles.

JP 2006-132030 A Japanese Patent Laid-Open No. 2007-212357 Japanese Patent Laid-Open No. 10-226979

  The inventors of the present invention have made a hypothesis that the fluctuation of moisture in the base paper is closely related to the problem of wrinkles, and as a result of intensive studies, the ink on the paper is subjected to forced heating drying at a high temperature. Obtained knowledge that suppressing moisture fluctuations in the base paper effectively works to improve creases, and by incorporating ingredients that suppress moisture fluctuations into the base paper, coated paper for offset rotary printing with a high crease suppression effect. Found that you can get.

  The present invention has been made based on the above-described circumstances, and an object of the present invention is to provide a coated paper for offset rotary printing that can effectively suppress generation of wrinkles in offset rotary printing.

The invention made to solve the above problems is
A coated paper for rotary offset printing comprising a base paper and a coating layer laminated on the base paper and containing a pigment and an adhesive,
Silica composite heavy calcium carbonate particles are internally added as a filler to the base paper,
The silica composite heavy calcium carbonate particles contain adsorbed moisture that volatilizes at 110 ° C. and bound moisture that volatilizes when heated from 110 ° C. to 525 ° C.,
The silica composite heavy calcium carbonate particles have a binding water content of 0.1% by mass or more and 1% by mass or less.

  The coated paper for rotary offset printing contains silica composite heavy calcium carbonate particles that release a certain amount of water when heated at 110 ° C., and as a result, generation of wrinkles can be suppressed. That is, when the paper surface temperature is 90 to 130 ° C. when it is normally dried by offset rotary printing, the energy of hot air applied from the dryer of the printing press is consumed for drying and solidifying the ink and is included in the base paper. The fluctuation of the generated moisture is suppressed by volatilization of the adsorbed moisture of the silica composite heavy calcium carbonate. As a result, the shrinkage of the base paper is suppressed, and the difference in shrinkage between the image line portion and the non-image line portion that causes wrinkles does not occur, and as a result, the occurrence of wrinkles is considered to be suppressed. The effect of suppressing the moisture fluctuation of the silica composite heavy calcium carbonate particles depends on the following characteristics. Silica composite heavy calcium carbonate particles are composed of silica in an irregular shape caused by heavy calcium carbonate particles, and the water content is high due to the synergistic effect of the amorphous form of heavy calcium carbonate and the silica composite. There is little fluctuation in moisture. In addition, in the present invention, by adjusting the content of bound water that volatilizes when heated from 110 ° C. to 525 ° C. to the above range, the water that volatilizes in the paper making stage and the drying process after printing is in a suitable range. Can be. As a result, the coated paper for rotary offset printing has less fluctuation of the base paper having a particularly large expansion / contraction rate, and can suppress generation of wrinkles.

  In addition, the silica composite heavy calcium carbonate particles used in the offset rotary printing coated paper is uniform because the broad heavy calcium carbonate particles generally have a relatively sharp particle size distribution by combining silica. Particles are easily present and particles are easily present in the paper layer without bias. Moreover, this silica composite heavy calcium carbonate particle has the characteristic that it is easy to retain in the gap | interval of a fiber resulting from an amorphous property. By using such silica composite heavy calcium carbonate as a filler, it is possible to reduce the drying speed of the entire paper surface, maintain uniform moisture, and more effectively prevent the generation of wrinkles. Furthermore, since the coated paper for rotary offset printing contains silica composite heavy calcium carbonate particles, it has high opacity, whiteness, oil absorption, etc., and excellent writing characteristics.

  The average particle diameter (D50) measured by the laser diffraction scattering method of the silica composite heavy calcium carbonate particles is preferably 2 μm to 15 μm, and the ash content of the base paper is preferably 5% to 16%. By making the average particle diameter of the silica composite heavy calcium carbonate particles within the above range and the ash content of the base paper within the above range, the basis weight change rate after heating at 100 ° C. for 1 minute can be easily and reliably 3% or less. The moisture retention performance and ash content of the offset rotary printing coated paper can be adjusted to an appropriate range. In addition, the silica composite heavy calcium carbonate having the above average particle diameter has a uniform dispersibility with respect to the raw material pulp when it is contained in the raw material pulp. Can be further improved.

The density of the base paper is preferably 0.7 g / cm ³ or more and 1.5 g / cm ³ or less, and the content ratio of softwood kraft pulp and hardwood kraft pulp in the raw material pulp of the base paper is 0: 100 to 35:65. Preferably, the freeness of the raw pulp is preferably 360 ml or more and 580 ml or less, and the water content is preferably 4% or more and 7% or less. When the density of the base paper is within the above range, for example, using a soft calender consisting of a combination of a metal roll and an elastic roll, the nip width is wider than that of a conventional calender so that the glossiness is the same as that of a conventional calendered product. When the treatment is performed, the pressure applied to the paper is dispersed, and the paper layer can be manufactured without being crushed as much as possible. In other words, by adjusting the base paper to a predetermined density, the base paper does not become excessively dense, and by configuring the base paper layer without using a so-called bulking agent that promotes separation between fibers, Since it becomes possible to suppress a change in moisture in the thickness direction of the base paper, the effect of suppressing wrinkles of the coated paper for offset rotary printing can be further enhanced. Moreover, the raw material pulp which comprises a base paper contains softwood kraft pulp (NBKP) and hardwood kraft pulp (LBKP) in the ratio within the said range, and mainly LBKP with a high wrinkle suppression effect and high printability is mainly used. For this reason, generation | occurrence | production of the wrinkle of the said coating paper for rotary printing can be further suppressed, and formation can be improved. Furthermore, by setting the freeness of the raw pulp within the above range, it is possible to suppress fluctuations in moisture in the pulp fibers due to fluffing of pulp fibers and internal fibrils caused by excessive beating treatment, As a result, the dimensional stability and wrinkle suppression effect of the offset rotary coated coated paper can be enhanced. Further, by setting the moisture content of the offset rotary printing coated paper within the above range, it is possible to further suppress creases, maintain the touch, prevent static electricity and accidental paper breakage during high-speed offset rotary printing, and the like. .

  In the coated paper for rotary offset printing, it is preferable that aluminum oxide is combined with the silica composite heavy calcium carbonate particles. In this way, by combining cationic aluminum oxide with silica composite heavy calcium carbonate particles in addition to silica, the silica composite has a sufficiently large particle size and high dispersibility, and is self-fixing to anionic pulp raw materials. Since heavy calcium carbonate particles can be obtained, it becomes a filler with higher water content, and it can further improve the yield improvement effect of silica composite heavy calcium carbonate particles, the effect of suppressing generation of wrinkles, opacity, whiteness, oil absorption, etc. it can.

The coated paper for offset rotary printing may have a basis weight of 45 g / m ² or more and 105 g / m ² or less. By setting the basis weight of the offset rotary printing coated paper within the above range, the effect of the present invention can be effectively expressed. The offset rotary printing coated paper is used for offset printing for color printing pages such as catalogs. It can be suitably used as a coated paper for printing.

  Here, “content of bound water volatilized when heated from 110 ° C. to 525 ° C.” means silica composite when the silica composite heavy calcium carbonate particles are left in a 110 ° C. environment and become a constant weight. When the mass of heavy calcium carbonate particles is W1, and the mass of silica composite heavy calcium carbonate particles when the silica composite heavy calcium carbonate particles are heated from 110 ° C. to 525 ° C. to become a constant weight is W2 (W1− It is the water | moisture content calculated | required from W2) / W1 * 100. “The ash content of the base paper” is a value measured by means specified in JIS-P8251 (2003). “Density” is a value measured according to JIS-8118 (1998). “Drainage” refers to the standard freeness test method described in JIS-P8121 (1995) for disaggregated pulp obtained by disaggregating coated paper for web offset printing in accordance with JIS-P8220 (1998). It is a measured value. “Moisture content” is moisture measured according to JIS-P8127 (1998). “Basis weight” is a value measured in accordance with JIS-P8124 (2011).

  As described above, the coated paper for offset rotary printing according to the present invention can effectively suppress generation of wrinkles in offset rotary printing.

It is a typical schematic diagram which shows the apparatus used for one Embodiment of the manufacturing method of the silica composite heavy calcium carbonate particle used for this invention.

  Hereinafter, embodiments of coated paper for rotary offset printing according to the present invention will be described in detail.

  The coated paper for rotary offset printing of the present invention has a base paper and a coating layer laminated on at least one side of the base paper.

<Base paper>
Silica composite heavy calcium carbonate particles are internally added as a filler to the base paper for offset rotary printing coated paper of the present invention. The base paper for offset rotary printing coated paper is obtained by papermaking a pulp slurry containing pulp and filler.

<Pulp>
As said pulp, a well-known thing can be used, A virgin pulp, a used paper pulp, or what combined these can be used suitably.

  Examples of virgin pulp include hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood semi-bleached kraft pulp (LSBKP), Chemical pulp such as softwood semi-bleached kraft pulp (NSBKP), hardwood sulfite pulp, softwood sulfite pulp, stone grand pulp (SGP), pressed stone grand pulp (TGP), chemi-ground pulp (CGP), ground wood pulp (GP), Various well-known pulps such as mechanical pulps such as thermomechanical pulp (TMP); pulps chemically or mechanically produced from non-wood fibers such as kenaf, hemp, and straw can be used.

  NBKP and LBKP are preferable as the pulp that can be suitably used in the present invention, and the mass ratio of NBKP and LBKP is preferably 0: 100 to 35:65, and more preferably 12:88 to 18:82. By using LBKP as the main component, it is possible to improve the wrinkle suppression effect and the printability. When the mass ratio of NBKP with respect to the total amount of pulp exceeds the above upper limit, NBKP having low dimensional stability of pulp fibers increases, so that the formation deteriorates and printability may be deteriorated. Conversely, when the mass ratio of NBKP to the total amount of pulp is less than the above lower limit, the stiffness is lowered, and the effect of suppressing elbows may be lowered.

  Used paper pulp used in the present invention is manufactured from, for example, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, upper white waste paper, Kent waste paper, imitation waste paper, old paper waste paper, etc. Examples thereof include disintegrated waste paper pulp, disaggregated / deinked waste paper pulp (DIP), and disaggregated / deinked / bleached waste paper pulp.

  However, since the ionic variation (anionization) of raw material pulp due to mechanical pulp derived from waste paper pulp has an adverse effect on the yield and dispersibility of silica composite heavy calcium carbonate particles, 30 mass% or less is preferable and it is especially preferable not to contain. By making the content of the used paper pulp in the raw material pulp below the above upper limit or not using the used paper pulp, uniform dispersibility of the silica composite heavy calcium carbonate particles used in the coated paper for offset rotary printing and the ground And the generation of wrinkles can be suppressed. In addition, the dimensional stability and printability of the offset rotary coated coated paper can be improved, and the offset rotary coated coated paper having excellent workability can be obtained along with improvement of elbows.

  The freeness of the raw pulp used for the offset rotary printing coated paper is preferably 360 ml or more and 580 ml or less, preferably 410 ml or more and 560 ml or less, and more preferably 430 ml or more and 500 ml or less. When the freeness is less than the above lower limit, the fibrillation rate of the pulp fiber is high, and the silica composite heavy calcium carbonate particles may not be uniformly dispersed. On the other hand, when the freeness exceeds the above upper limit, the moisture fluctuation rate of the raw pulp becomes large, and there is a possibility that the effect of improving the wrinkle of the coated paper for offset rotary printing cannot be obtained sufficiently.

The density of the base paper of the offset rotary coated coated paper is preferably 0.7 g / cm ³ or more and 1.5 g / cm ³ or less, more preferably 0.9 g / cm ³ or more and 1.2 g / cm ³ or less. . When the density of the base paper is less than the above lower limit, there is a possibility that a back-through occurs when printing on the coated paper for offset rotary printing. On the other hand, when the density of the base paper exceeds the above upper limit, the stiffness is lowered and printability may be lowered.

<Filler>
The base paper of the offset rotary printing coated paper contains silica composite heavy calcium carbonate particles as a filler. In addition to the silica composite heavy calcium carbonate particles, the base paper of the coated paper for the paper can contain a filler generally used for papermaking in general, and the base paper of the coated paper for offset rotary printing. For example, talc, light calcium carbonate, heavy calcium carbonate, kaolin, titanium dioxide, white carbon, regenerated particles, deinked floss as raw materials, regenerated particles obtained by dehydration, combustion, and pulverization, regenerated particles combined with silica Silica composite regenerated particles may also be included.

  When the silica composite heavy calcium carbonate particles are used as a filler, the content of the silica composite heavy calcium carbonate particles with respect to the total amount of the filler is preferably 50% by mass to 100% by mass, and more preferably 60% by mass to 100%. The mass% or less is more preferable. When the addition amount of the silica composite heavy calcium carbonate particles is less than the above lower limit, there is a possibility that the effect of suppressing wrinkles due to moisture retention due to the silica composite heavy calcium carbonate particles and the effect of improving the dispersibility of the raw material pulp may be reduced.

The ash content of the base paper of the offset rotary printing coated paper is preferably 5% to 16%, and more preferably 7% to 13%. When the ash content of the base paper is less than the above range, the penetration into the base paper when the coating solution is applied is remarkable, resulting in uneven coating of the paint after coating, which may cause deterioration of the printing surface feeling. In addition, by making the base paper ash content 5% or more, the filler fills the voids on the surface of the base paper, and for example, the coating amount is 0.5-5 g / m ² and the base paper coverage is maintained. Coating suitability is improved even under difficult conditions. On the other hand, when the ash content of the base paper exceeds the above range, the base paper density may increase and the strength may decrease.

<Silica composite heavy calcium carbonate particles>
The silica composite heavy calcium carbonate particles have heavy calcium carbonate particles and silica that covers at least a part of the surface of the heavy calcium carbonate particles. As described above, the silica composite heavy calcium carbonate particles can improve the yield and dispersibility with respect to the raw material pulp, and have a sharp particle size distribution. The front / back difference can be reduced. When silica composite heavy calcium carbonate particles are not included, the yield of the filler to the raw material pulp becomes poor and it is easy to come out of the wire during paper making, and the dispersibility to the raw material pulp does not improve. Becomes larger, and it becomes a cause of the generation of elbows.

  The silica composite heavy calcium carbonate particles may be composited only with silica, but it is preferable that aluminum oxide is composited in addition to silica. Since aluminum oxide is cationic, silica composite heavy calcium carbonate particles combined with aluminum oxide are self-fixing to anionic pulp raw materials, and silica composite heavy calcium carbonate particles when added to pulp raw materials The yield is easy to improve. Moreover, since the average particle diameter of silica composite heavy calcium carbonate particle becomes a sharp particle size distribution, it is easy to disperse | distribute uniformly. Therefore, the anisotropy of the degree of drying of the offset rotary coated coated paper can be suppressed, and the generation of wrinkles can be effectively suppressed. Moreover, the manufacturing method of the silica composite heavy calcium carbonate particle | grains which compounded this aluminum oxide is explained in full detail behind.

  The silica composite heavy calcium carbonate particles contain adsorbed moisture that evaporates at 110 ° C. The lower limit of the adsorbed moisture content is preferably 0.7% by mass, more preferably 1% by mass, and even more preferably 1.5% by mass. On the other hand, the upper limit of the content of adsorbed moisture is preferably 8% by mass, more preferably 5% by mass, and still more preferably 3% by mass. If the adsorbed moisture content is less than the above lower limit, the volatilization of moisture at the time of offset rotary printing is insufficient, and there is a risk that the effect of suppressing elbowing will be insufficient. On the other hand, if the content of adsorbed water exceeds the above upper limit, the volatilization of water during offset rotary printing becomes excessive, and printability may be reduced. The “adsorbed water content” means the silica composite heavy carbonate when the humidity is adjusted to a constant weight in an environment of standard conditions (temperature 23 ° C., humidity 50%) as defined in JIS-P8111 (1998). Moisture obtained from (W3−W2) / W3 × 100 when the mass of the calcium composite heavy calcium carbonate particles is W2 and the mass of the silica composite heavy calcium carbonate particles when the mass is kept constant in an environment of W3 and 110 ° C. It is.

  The silica composite heavy calcium carbonate particles contain bound moisture that evaporates when heated from 110 ° C to 525 ° C. The lower limit of the bound moisture content is 0.1% by mass, more preferably 0.2% by mass, and still more preferably 0.3% by mass. On the other hand, the upper limit of the bound moisture content is 1% by mass, more preferably 0.8% by mass, and even more preferably 0.7% by mass. If the content of bound water is less than the above lower limit, the water content of silica composite heavy calcium carbonate particles will be too small, and there will be insufficient volatilization of water during offset rotary printing, and the effect of suppressing wrinkles may be insufficient. There is. On the other hand, if the content of bound water exceeds the above upper limit, the water holding amount of the silica composite heavy calcium carbonate particles is excessive, and the volatilization of water at the time of offset rotary printing becomes excessive, and printability may be reduced. is there. In addition, when it heats exceeding 525 degreeC, the weight loss by decomposition | disassembly of a calcium carbonate will generate | occur | produce.

  The volume average particle diameter (D50) measured by the laser diffraction scattering method of the silica composite heavy calcium carbonate particles (hereinafter also including aluminum oxide composite) is preferably 2 μm or more and 15 μm or less, preferably 3 μm or more and 10 μm. The following is more preferable, and 3.5 μm or more and 8 μm or less is more preferable. When the average particle diameter of the silica composite heavy calcium carbonate particles is less than the above lower limit, the yield improving effect of the silica composite heavy calcium carbonate particles is not sufficiently exhibited, and there is a possibility that the effect of suppressing the wrinkle is hardly exhibited. Conversely, when the volume average particle size of the silica composite heavy calcium carbonate particles exceeds the above upper limit, the large particle size decreases the uniform dispersibility in the slurry, and also reduces the effect of suppressing the generation of wrinkles. There is a possibility that opacity and oil absorption may not be sufficiently obtained.

  The silica ratio in terms of oxide in the silica composite heavy calcium carbonate particles is preferably 1% by mass to 30% by mass, and more preferably 5% by mass to 20% by mass. Heating from 110 ° C. to 525 ° C. with adsorbed water volatilized by heating at 110 ° C. by adjusting the silica ratio in terms of oxide in the silica composite heavy calcium carbonate particles to 1% by mass to 30% by mass. It is possible to obtain silica-composite heavy calcium carbonate particles having a bound moisture content of 0.1 mass% to 1 mass%. When the ratio of silica is less than the above lower limit, the surface of the silica composite heavy calcium carbonate particles is not sufficiently coated, so the porosity of the silica composite heavy calcium carbonate particles is reduced, the water retention is reduced, and There is a possibility that the effect of suppressing the generation is reduced, and there is a possibility that the whiteness and oil absorption are lowered. On the contrary, when the ratio of silica exceeds the above upper limit, it becomes difficult to obtain an irregular shape due to heavy calcium carbonate particles or a sharp particle size distribution due to silica composite, and the effect of suppressing wrinkles, which is a problem of the present invention, is reduced. There is a fear.

  As a more effective configuration in the present invention, the aluminum oxide content in the case where aluminum oxide is combined with the silica composite heavy calcium carbonate particles is preferably 8% by mass or more and 38% by mass or less, and more preferably 10% by mass or more and 20% by mass. The mass% or less is more preferable. When the content of aluminum oxide is less than the above lower limit, the effect of improving the cationic property of silica composite heavy calcium carbonate particles combined with aluminum oxide is hardly obtained, and the effect of improving dispersibility is reduced, and the effect of suppressing generation of wrinkles is reduced. In addition, there is a possibility that the yield improvement effect upon addition of silica composite heavy calcium carbonate particles may not be sufficiently obtained. Conversely, when the content of aluminum oxide exceeds the above upper limit, not only is the cost high, but the original effect of the silica composite heavy calcium carbonate particles is hindered and the dispersibility with respect to the raw material pulp decreases, and the pulp raw material is reduced. The fixing effect may be reduced. In addition, the content rate of aluminum oxide can be measured by, for example, an X-ray analysis method.

  The above base paper includes other paper strength enhancers such as starches, polyacrylamide, epichlorohydrin, rosin, alkyl ketene dimer, ASA (alkenyl succinic anhydride), internal sizing agent such as neutral rosin, sulfate band, It can contain a coagulant such as polyethyleneimine, an aggregating agent such as polyacrylamide or a copolymer thereof, and the like.

<Undercoat>
It is preferable that a clear coating solution used in combination with a surface sizing agent or a paper strength improver is coated on both sides of the base paper as an undercoat coating. By performing such an undercoat coating, it is possible to suppress penetration of the latex of the coating layer into the base paper. Thereby, the fall of the permeability | transmittance of the water vapor | steam resulting from the film-forming of latex can be suppressed to the minimum, and generation | occurrence | production of a wrinkle can be suppressed. Moreover, the softness | flexibility, printability, etc. of the said paper for offset rotary printing can be improved.

  The surface sizing agent is not particularly limited, and examples thereof include starch, styrene sizing agent, acrylate sizing agent, alkyl ketene dimer, etc. Among them, starch, styrene sizing agent and acrylate sizing An agent is preferable, and starch is particularly preferable. Among them, oxidized starch, hydroxyethylated starch, cationized starch, cationized oxidized starch, acetylated starch, esterified starch, heat-modified starch, enzyme-modified starch, aldehyde-modified starch, etc. Among the modified starches, it is preferable to select and use a starch having a B-type viscosity of 60 rpm of 100 mPa · s or less at a concentration of 10% and a liquid temperature of 30 ° C. Alternatively, these generally available modified starches are further subjected to low molecular weight treatment by known methods such as enzyme modification and oxidation modification, and the B-type viscosity at 60 rpm is 100 mPa · s or less when the concentration is 10% and the liquid temperature is 30 ° C. In addition, the present invention provides a coated paper for offset rotary printing that can effectively suppress generation of wrinkles, which is an object of the present invention, without inhibiting the properties of silica composite heavy calcium carbonate particles. Is preferable.

  The paper strength improver is not particularly limited. For example, polyacrylamide (PAM), polyvinyl alcohol (PVA), acrylic resin, polyamide / polyamine resin, urea / formalin resin, melamine / formalin resin, polyethyleneimine. Among them, among these, PAM, acrylic resin and PVA are preferable, and PAM is more preferable. Polyacrylamide is not limited to ionicity, polymerization degree, carboxyl group content, etc., but when used as a clear coating liquid with the above surface sizing agent, the ratio of the surface sizing agent to the paper strength improver is 2: 1. From 4: 1, the combined use at a ratio of 4: 1 suppresses the film properties caused by PAM while maintaining the effects of PAM, and does not hinder the properties of silica composite heavy calcium carbonate particles. This is preferable in providing a coated paper for rotary offset printing capable of effectively suppressing the occurrence.

The coating amount of the coating solution in the undercoat coating is not particularly limited, but is preferably 0.1 g / m ² or more and 1 g / m ² or less per side in terms of solid content, and 0.3 g / m ² or more and 0. 0.7 g / m ² or less is more preferable. When this coating amount is less than the above lower limit, the effect of the above-mentioned coating is not sufficiently exhibited, the effect of suppressing the generation of wrinkles is reduced, or unevenness occurs in the moisture retention of the base paper due to coating unevenness or The printability may be reduced. On the contrary, when this coating amount exceeds the above upper limit, the coating property of the surface of the base paper is increased by this coating, the water retention property of the base paper is deteriorated, and the effect of suppressing the generation of wrinkles is reduced, In some cases, the surface strength increases, flexibility decreases, and printability decreases.

<Coating layer>
The coating layer contains a pigment and an adhesive as main components, and is laminated on both surfaces of the base paper by applying a coating liquid (top coating). That is, the coating liquid contains the pigment and the adhesive as main components.

  The pigment is not particularly limited. For example, kaolin, delaminated kaolin, talc, clay, calcium carbonate (light calcium carbonate, heavy calcium carbonate), satin white, calcium sulfite, gypsum, barium sulfate, white carbon, baking Kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, silica, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite, and other inorganic pigments and polystyrene resin fine particles And urea formalin resin fine particles, fine hollow particles, and porous fine particles.

  Among these, it is preferable to use calcium carbonate from the viewpoint of increasing whiteness. Further, the oil absorption amount of this calcium carbonate is preferably 40 ml / 100 g or less, more preferably 10 ml / 100 g or more and 30 ml / 100 g or less. By using calcium carbonate having a low oil absorption in this way, it is possible to suppress the printing ink from being absorbed and to reduce the occurrence of mottling. In addition, the absorption of dampening water is also suppressed, and the elongation of the coating layer is suppressed, so that the printability can be improved. In addition, although the combined use of white carbon with a large amount of adsorbed moisture is also considered, white carbon is originally fine and has a problem of low yield in the paper layer.

  As content of the said calcium carbonate with respect to the said pigment, 45 mass% or more is preferable, and 50 mass% or more and 100 mass% or less are more preferable. Thus, the whiteness of the coated paper for offset rotary printing can be increased by increasing the content of calcium carbonate.

  The pigment used together with calcium carbonate in the pigment is not particularly limited, but clay having excellent ink acceptability is preferable.

  The adhesive is not particularly limited, and known ones can be used. Examples include proteins such as casein and soybean protein; styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, styrene-methyl. Conjugated diene latex such as methacrylate-butadiene copolymer latex; acrylic latex such as polymer latex or copolymer latex of acrylate ester and / or methacrylate ester; vinyl latex such as ethylene-vinyl acetate polymer latex Latexes such as alkali partially soluble or insoluble latex obtained by modifying these various copolymer latexes with a functional group-containing monomer such as a carboxyl group; olefin-maleic anhydride resin, melamine resin, urea resin, Urethane resin Synthetic resin-based adhesive; can be mentioned carboxymethyl cellulose, cellulose derivatives such as hydroxyethyl cellulose; oxidized starch, positive starch, esterified starch, starches such as dextrin.

  Among these, a latex adhesive is preferable, and the latex adhesive preferably contains a polymer obtained from a monomer containing acrylonitrile. When acrylonitrile is included as a monomer, the symmetry of the resulting polymer is increased, so that the melting point is increased. Therefore, when such a coating layer is used, the flexibility of the coating layer increases, so that the flexibility of the coated paper for offset rotary printing can be increased and the effect of suppressing wrinkles can be increased. Moreover, printability can also be improved by using a polymer containing acrylonitrile as a monomer.

  The proportion of acrylonitrile in the monomer is preferably 21% by mass or more, and preferably 22% by mass or more and 30% by mass or less. Thus, by relatively increasing the ratio of acrylonitrile, it is possible to increase the flexibility, printability, and the effect of suppressing wrinkles of the coated paper for offset rotary printing. Furthermore, on the base paper having an average cross-sectional area within a predetermined range as described above, starch is used as a surface sizing agent and PAM is used in combination as a paper strength improver, and the proportion of acrylonitrile is 21% by mass or more. When latex is used in combination, the effect of suppressing flexibility and wrinkles can be enhanced.

  Furthermore, the polymer obtained from the monomer containing acrylonitrile preferably contains styrene as the monomer. The polymer obtained by copolymerizing the monomer containing acrylonitrile and styrene in this way is not clear for reasons, but has high adhesion to calcium carbonate and can firmly fix the pigment even in a small amount. . Therefore, by using such a polymer, the amount of the adhesive can be reduced, and the flexibility of the offset rotary printing coated paper and the effect of suppressing wrinkles can be enhanced. In this case, the proportion of styrene in all the monomers is preferably 20% by mass or more and 40% by mass or less in order to suitably exhibit the above function.

  As content of the adhesive agent in the said coating layer (solid content in a coating liquid), 10 mass% or less is preferable, and 3 mass% or more and 8 mass% or less are more preferable. Thus, by reducing the content of the adhesive, a flexible coating layer can be obtained, and the flexibility of the offset rotary printing coated paper can be increased. When content of an adhesive agent is less than the said minimum, there exists a possibility of reducing the surface strength of a coating layer. On the other hand, if the content of the adhesive exceeds the above upper limit, the glossiness and ink absorbability may not be balanced. In addition, by using the above-mentioned oil absorption amount of calcium carbonate as a pigment and using the above-mentioned acrylonitrile and styrene as monomers as an adhesive, even if the content of the adhesive is reduced in this way, The fixing property is high and the printability can be improved.

  For the coating layer (coating liquid), in addition to pigments and adhesives, for example, fluorescent whitening agents, dyed substances of fluorescent whitening agents, antifoaming agents, mold release agents, colorants, water retention agents It can contain various commonly used auxiliaries such as

Examples of the coating amount of the coating layer, preferably per side 5 g / ^{m 2} or more 18 g / ^{m 2} or less, more preferably 7 g / ^{m 2} or more 12 g / ^{m 2} or less. When the coating amount is less than the above lower limit, it may be difficult to exhibit sufficient printability. On the contrary, if the coating amount exceeds the above upper limit, the effect of suppressing wrinkles by the silica composite heavy calcium carbonate particles added to the base paper may be reduced, and the coated paper for offset rotary printing may be caused by the coating layer. When the surface of the resin is cured, the flexibility tends to be lowered.

<Method for producing coated paper for offset rotary printing>
A method for producing the coated paper for offset rotary printing is not particularly limited, and a known method for producing a coated paper for offset rotary printing may be used. Specifically, for example, a raw pulp slurry is made, and subjected to a press part and a pre-dryer part to produce a base paper for the offset rotary printing coated paper, and then subjected to a surface treatment in an undercoater part, followed by drying and Examples of the method include a method of applying a coating liquid to the base paper for the offset rotary printing coated paper and performing a calendar process after the flattening process.

  As a coating apparatus for coating the coating liquid, for example, a size press, a blade metering size press, a rod metalling size press, a blade coater, a bar coater, a gate roll coater, a rod coater, an air knife coater, etc. are used. Can do.

  As a calendar device for calendar processing, for example, various calendars using a combination of a metal and a drum and an elastic roll such as a super calendar, a gloss calendar, and a soft compact calendar can be appropriately used in on-machine or off-machine specifications.

  In addition, you may apply the said coating liquid several times to the said paper for offset rotary printing.

<Quality etc.>
The basis weight of the offset rotary coated coated paper is preferably 45 g / m ² or more and 105 g / m ² or less, and 55 g / m ² or more and 80 g / m ² or less effectively exhibits the effect of suppressing wrinkles based on the present invention. It is further preferable in making it. When the basis weight is less than the above lower limit, the problem of wrinkles hardly occurs, but the feel of paper becomes soft and workability may be reduced. On the other hand, when the basis weight exceeds the above upper limit, the coated paper for rotary offset printing becomes tough and the effect of the present invention is hardly exhibited, and it goes against the recent weight reduction and resource saving.

  As the ash content after coating of the offset rotary printing coated paper, the ash content measured at a combustion temperature of 525 ° C. is preferably 20% or more and 40% or less, and 25% or more and 36% or less based on JIS-P8251: 2003. Further preferred. When the ash content is less than the above lower limit, the effect of the silica composite heavy calcium carbonate particles in the present invention cannot be effectively expressed, and the print opacity may be lowered, or the water retention property may be lowered and the wrinkle suppressing effect may be impaired. There is. On the other hand, if the ash content exceeds the above upper limit, the printing opacity increases, but in the base paper, there is a risk that the strength of the paper will decrease due to a decrease in the adhesion between the pulp fibers, and the silica composite weight in the raw pulp The uniform dispersion of the calcium carbonate particles is impaired, the water retention becomes uneven, the effect of suppressing the wrinkle is impaired, and if there are many pigment components in the coating layer, the printability may be lowered.

  The paper thickness of the offset rotary printing coated paper is preferably 40 μm or more and 90 μm or less. If the paper thickness is less than the above lower limit, the tensile strength may decrease. On the other hand, when the paper thickness exceeds the above upper limit, there is a risk that it is against the request for weight reduction. The paper thickness is a value measured according to JIS-P8118 (1998).

  The water content of the offset rotary printing coated paper is preferably 4% or more and 7% or less, and preferably 4.5% or more and 6.5% or less by adjusting the content of silica composite heavy calcium carbonate particles as a filler. It is more preferable to adjust so that it becomes. When the moisture content is less than the above lower limit, the touch of the offset rotary printing coated paper may be deteriorated, or static electricity or paper breakage may occur during offset rotary printing. On the other hand, when the moisture content exceeds the above upper limit, wrinkles are likely to occur on the coated paper for offset rotary printing, and blisters may be generated.

  The whiteness of the offset rotary coated coated paper is preferably 80% or more and 95% or less, more preferably 83% or more and 95% or less, and more preferably 84% or more and 95% so as not to cause eye strain of the subscriber. The following is more preferable. The whiteness is a value measured according to JIS-P8148 (2001).

  The lower limit of the printing opacity of the offset rotary coated coated paper is preferably 83%, more preferably 84%, and even more preferably 85%. In the present invention, a coated paper for offset rotary printing having such printing opacity can be obtained by uniform dispersibility of silica composite heavy calcium carbonate particles. On the other hand, the upper limit of the printing opacity of the offset rotary coated coated paper is preferably 96%. If the printing opacity is less than the above lower limit, there is a risk that show-through is likely to occur. On the other hand, when the printing opacity exceeds the above upper limit, the necessary pigment increases, and the surface strength of the coated paper for offset rotary printing becomes weak, which may increase paper dust at the time of printing due to dropping of the pigment, There is a possibility that the appearance of coated paper for offset rotary printing is deteriorated. The printing opacity is determined by JAPAN TAPPI No. It is a value measured according to 45.

<Method for producing silica composite heavy calcium carbonate particles>
Hereinafter, the manufacturing method of the silica composite heavy calcium carbonate particle used for the base paper for the coated paper for offset rotary printing will be described in detail.

  The silica composite heavy calcium carbonate particles used for the offset rotary printing coated paper is a composite of heavy calcium carbonate particles and silica, specifically, heavy calcium carbonate particles with alkali silicate and mineral acid. It is obtained by the process of combining silica with the silica.

  Further, it is preferable that the silica composite heavy calcium carbonate particles are further combined with aluminum oxide using an aluminum salt. Silica composite heavy calcium carbonate particles combined with aluminum oxide have a self-fixing property with respect to an anionic pulp raw material, and are easily dispersed uniformly when added to the pulp raw material. Therefore, by combining aluminum oxide, wrinkles can be suppressed more effectively, while suppressing the increase in the viscosity of the pulp slurry, the yield to paper is high, and the whiteness and the like can be improved. Aluminum oxide composite heavy calcium carbonate particles can be obtained. Although it does not specifically limit as this aluminum salt, For example, a sulfuric acid band (aluminum sulfate), sodium aluminate, etc. can be used. Among these, sodium aluminate that does not decompose heavy calcium carbonate particles to generate calcium oxide and can reduce the viscosity of the slurry when added to the pulp slurry is particularly preferable.

  The inventors of the present invention contain adsorbed moisture that volatilizes by heating at 110 ° C., which is the structure of the present invention, and bound moisture that volatilizes when heated from 110 ° C. to 525 ° C. The present invention has found that the problem can be solved by incorporating silica composite heavy calcium carbonate, in which silica is composited so that the content of 0.1% by mass or more and 1.0% by mass or less, is contained in the base paper as a filler. Has been completed.

Silica composite heavy calcium carbonate particles that can be suitably used for the base paper for coated paper for offset rotary printing are, for example,
(1) Particle condensing step for condensing heavy calcium carbonate particles with a coagulant,
(2) A slurry preparation step for obtaining a slurry containing heavy calcium carbonate particles and an alkali silicate salt,
(3) A first reaction step of adding a mineral acid to the slurry, and (4) a second reaction step of adding sodium aluminate and a mineral acid to the slurry.

  The apparatus of FIG. 1 used in the method for producing silica composite heavy calcium carbonate particles includes a condensation reaction tank 1, a first silica composite reaction tank 2, a second silica composite reaction tank 3, a first aluminum treatment reaction tank 4, A dialuminum treatment reaction tank 5 and a storage tank 6 are provided in this order.

  As the heavy calcium carbonate particles X1, which are the raw materials for the silica composite heavy calcium carbonate particles, heavy calcium carbonate particles ground in advance into fine particles are used. The heavy calcium carbonate particles X1 may be combined with silica as it is, but it is preferable that the heavy calcium carbonate particles X1 are aggregated by the coagulant G in the condensation reaction tank 1 to form the heavy calcium carbonate particle aggregate X2. The heavy calcium carbonate particle aggregate X2 is subjected to the first reaction step in the first silica composite reaction vessel 2 and the second silica composite reaction vessel 3 after the slurry adjustment step is performed in the first silica composite reaction vessel 2. It becomes the silica composite heavy calcium carbonate particle X3 in which the silica is composited. Thereafter, the silica composite heavy calcium carbonate particles X3 are subjected to the second reaction step in the first aluminum treatment reaction tank 4 and the second aluminum treatment reaction tank 5, and the silica composite heavy calcium carbonate particles X4 composited with aluminum oxide. And stored in the storage tank 6.

  As the heavy calcium carbonate particles X1, heavy calcium carbonate particles obtained by mechanically pulverizing natural limestone dry or wet are used. Heavy calcium carbonate is inexpensive to produce, but because it is manufactured by physical pulverization, it has an irregular and broad particle size distribution, so it has high wire wear and is used as a filler for internal addition. However, by using composite particles, it is possible to reduce the wear of the wire in the paper making process, and it can be suitably used as a filler for the base paper for the offset rotary printing coated paper.

  In this production method, it is preferable to perform a particle size adjusting step for adjusting the volume average particle size of the heavy calcium carbonate particles X1 to a range suitable for condensation and silica and aluminum oxide composite. In this particle size adjusting step, pulverization, classification, and the like are performed so that the volume average particle size of the heavy calcium carbonate particles X1 falls within a suitable range. As a pulverizer used as a means for pulverizing the heavy calcium carbonate particles X1, for example, a dry pulverizer such as a jet mill or a high-speed rotary mill, or a wet pulverizer such as an attritor, a sand grinder or a ball mill can be used. .

  The volume average particle diameter of the heavy calcium carbonate particles X1 is not particularly limited, but the lower limit is preferably 0.2 μm, and more preferably 1.0 μm. On the other hand, the upper limit of the volume average particle diameter of the heavy calcium carbonate particles X1 is preferably 10.0 μm, and more preferably 5.0 μm. When the volume average particle size of the heavy calcium carbonate particles X1 is less than the above lower limit, in order to obtain a coagulation having a sufficient particle size, agglomeration with a large number of particles is necessary and the coagulation becomes brittle. There is a possibility that the aggregates collapse and the yield of the composite particles cannot be obtained sufficiently. On the contrary, when the volume average particle diameter of the heavy calcium carbonate particles X1 exceeds the above upper limit, the particle size distribution of the heavy calcium carbonate particles X1 becomes broad, and a sharp particle size distribution cannot be obtained even when condensation is performed. As a result, there is a possibility that the silica composite effect and the aluminum composite effect due to the aluminum salt may be insufficient, and the paper containing the silica composite heavy calcium carbonate particles obtained by this production method due to the presence of coarse particles is added. There is a risk that the quality may not be sufficient. In addition, the volume average particle diameter of the heavy calcium carbonate particles X1 is a sample (heavy calcium carbonate particles X1) using a laser diffraction particle size distribution meter (manufactured by Nikkiso Co., Ltd., model number: Microtrack MTII-3000). The particle size distribution is measured, the particle diameter (D50) when the cumulative volume with respect to the volume of all particles is 50% is determined, and this particle diameter is defined as the volume average particle diameter.

[(1) Particle condensation step]
(1) In the particle condensation step, the heavy calcium carbonate particles X1 are obtained by coagulating the heavy calcium carbonate particles X1 with the coagulant G in the condensation reaction tank 1.

  The coagulant G used in the present production method is not particularly limited, and a known synthetic coagulant can be used, but it is cationic that easily causes the heavy calcium carbonate particles X1 to coagulate to an appropriate particle size. A coagulant is preferred. As this cationic coagulant, for example, diallyldimethylammonium chloride, cationic polyacrylamide and the like can be used.

  The lower limit of the mass average molecular weight of the coagulant G is preferably 100,000, and more preferably 200,000. On the other hand, the upper limit of the mass average molecular weight of the coagulant G is preferably 1.5 million, and more preferably 800,000. By setting the molecular weight of the coagulant G within the above range, the heavy calcium carbonate particles X1 can be suitably coagulated. When the mass average molecular weight of the coagulant G is less than the above lower limit, sufficient coagulation force may not be obtained. On the contrary, when the mass average molecular weight of the coagulant G exceeds the above upper limit, a heavy calcium carbonate particle aggregate X2 having an excessively large particle size is formed, and the particle size distribution may be broadened to reduce the yield, When the coagulant G is added to the slurry of the heavy calcium carbonate particle aggregate X2, the viscosity becomes too high and workability and yield may be reduced. In particular, when the viscosity of the slurry of the heavy calcium carbonate particle aggregate X2 exceeds 500 cps, the load of the pump for transferring the slurry of the heavy calcium carbonate particle aggregate X2 may increase, There is a possibility that the miscibility with the pulp raw material is lowered. In addition, there is a possibility that inconveniences in which dirt in the papermaking system becomes obvious. The mass average molecular weight is a numerical value measured using a gel permeation chromatography method (GPC method).

  Further, the lower limit of the cationic charge density of the coagulant G is preferably 3 meq / g, more preferably 5 meq / g. On the other hand, the upper limit of the cation charge density is preferably 25 meq / g, more preferably 20 meq / g. By setting the cationic charge density of the coagulant G within the above range, the heavy calcium carbonate particles X1 can be suitably coagulated. When the cationic charge density of the coagulant G is less than the above lower limit, there is a possibility that sufficient coagulation force cannot be obtained. On the contrary, when the cationic charge density of the coagulant G exceeds the above upper limit, the entire surface of the heavy calcium carbonate particles X1 has a cationic charge, which may make it difficult for condensation to occur due to repulsion due to charge. There is a risk that the heavy calcium carbonate particle aggregate X2 having a large particle size is formed, the particle size distribution becomes broad, and the yield decreases. In addition, this cation charge density says the cation charge density as the whole coagulant, when using a some component as a coagulant.

In the present invention, the cationic charge density is a value measured by the following method. First, after adjusting the sample to an aqueous solution of pH 4.0, the amount of anion required by titration using a 1/1000 normal aqueous potassium potassium sulfate solution with a particle charge measuring device (Muteck PCD-03) based on the streaming potential method. Measure. The cation charge density (meq / g) per 1 g of sample is calculated by the following formula (1) using the obtained anion demand.
Cationic charge density = A / B × 1000 (1)
A: Anion requirement of the aqueous coagulant solution adjusted to pH 4.0 (μeq / l)
B: Solid content concentration of coagulant aqueous solution (g / l)

  In this way, in the coagulation of the heavy calcium carbonate particles X1, it is possible to use the coagulant G having the above-mentioned preferable ranges in both the mass average molecular weight and the cation charge density. It is preferable because both of the above and the thickening suppression of the slurry can be suitably achieved. The reason for this is not clear, but for example, the reason for the aggregation is that there is variation in the charge distribution on the surface of the heavy calcium carbonate particles X1, so that a cationic synthetic polymer having a molecular weight and a cation charge density within a predetermined range is used. It is thought that it is because an electric coagulation action can be exhibited by using.

  The method for coagulating the heavy calcium carbonate particles X1 with the coagulant G is not particularly limited. For example, the heavy calcium carbonate particles X1 are dispersed in water to form a heavy calcium carbonate particle slurry. A method in which the coagulant G is added to the fine calcium carbonate particle slurry and stirred can be used. As a stirring device used at this time, for example, a propeller blade, a turbine blade, a paddle blade, or the like can be used.

  When using the method of adding the coagulant G to the heavy calcium carbonate particle slurry described above, the solid content concentration of the heavy calcium carbonate particle X1 in the heavy calcium carbonate particle slurry is not particularly limited, 10 mass% or more and 30 mass% or less are preferable. By making the density | concentration of a heavy calcium carbonate particle slurry into the said range, coexistence with efficiency improvement of the heavy calcium carbonate particle X1 and suppression of a raise of slurry viscosity can be aimed at. When the concentration of the heavy calcium carbonate particle slurry is less than the above lower limit, even if the coagulant G is added, the heavy calcium carbonate particle X1 may not be condensed to a suitable size. Conversely, when the concentration of the heavy calcium carbonate particle slurry exceeds the above upper limit, the viscosity is too high and workability is reduced, or the particle size distribution of the heavy calcium carbonate particle aggregate X2 becomes broad, Yield may be reduced.

  The coagulant G is preferably added as an aqueous solution to the heavy calcium carbonate particle slurry. Further, the amount of the coagulant G added is preferably 100 ppm or more and 3000 ppm or less in terms of solid content with respect to the solid content of the heavy calcium carbonate particles X1. When the addition amount of the coagulant G is less than the lower limit, the heavy calcium carbonate particles X1 cannot be sufficiently aggregated, and the yield improvement effect may not be exhibited. On the contrary, when the addition amount of the coagulant G exceeds the above upper limit, the thickening of the slurry may occur remarkably, and tertiary and quaternary aggregation may occur, and the silica composite heavy calcium carbonate particles obtained by this production method may be reduced. The paper strength of the added paper may be reduced.

  The volume average particle diameter of the heavy calcium carbonate particle aggregate X2 obtained through the particle aggregation step is preferably 1.1 to 10.0 times the volume average particle diameter of the heavy calcium carbonate particle X1. 2 times or more and 8.0 times or less are more preferable, and 1.3 times or more and 6.0 times or less are particularly preferable. Further, the lower limit of the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 is preferably 0.45 μm, more preferably 1.0 μm, and particularly preferably 1.2 μm. On the other hand, the upper limit of the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 is preferably 10.5 μm, more preferably 8.4 μm, and particularly preferably 6.2 μm. By making the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 in the above range, the yield of the silica composite heavy calcium carbonate particles obtained in the present production process in the paper making process can be efficiently improved. When the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 is less than 1.1 times the volume average particle diameter of the heavy calcium carbonate particle X1 or less than 0.45 μm, the particle size sufficient when combining silica and aluminum oxide In addition to the possibility of being obtained, there is a risk of clogging in the form of glass when silica is combined. Conversely, when the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 exceeds 10.0 times the volume average particle diameter of the heavy calcium carbonate particle X1, the aggregate becomes brittle. There is a possibility that the yield of the silica composite heavy calcium carbonate particles obtained by this production method may not be sufficiently obtained. Moreover, when the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 exceeds 10.5 μm, the particle diameter of the silica composite heavy calcium carbonate particles obtained by this production method is increased and enters the gaps between the pulp fibers. Otherwise, the opacity of the added paper may be reduced. In addition, the volume average particle diameter of the heavy calcium carbonate particle aggregate X2 can be adjusted by the addition amount of the coagulant G, the volume average particle diameter of the heavy calcium carbonate particle X1, and the like.

[(2) Slurry preparation step]
(2) In the slurry preparation step, a slurry containing the heavy calcium carbonate particle aggregate X2 and the alkali silicate is prepared. This slurry may be prepared, for example, by adding the alkali silicate solution L to the slurry containing the heavy calcium carbonate particle aggregate X2 obtained in the above-described particle condensing step. You may prepare by adding the body X2 to the alkali silicate solution L, and making it disperse | distribute.

  The alkali silicate solution L used in this production method is not particularly limited, but it is preferable from the viewpoint of availability to use a sodium silicate solution (No. 3 water glass).

  As a minimum of silicic acid concentration in silicic acid alkali solution L, 6 g / L is preferred, 8 g / L is still more preferred, and 10 g / L or less is especially preferred. On the other hand, the upper limit of the silicic acid concentration is preferably 18 g / L, more preferably 16 g / L, and particularly preferably 14 g / L. When the silicic acid concentration is less than the above lower limit, the silica sol is not sufficiently formed, and there is a possibility that a heavy calcium carbonate particle aggregate X2 in which silica is not combined is generated. On the contrary, when the silicic acid concentration exceeds the above upper limit, white carbon is generated instead of silica sol, and the heavy calcium carbonate particle aggregate X2 is coated with white carbon, so that the porous calcium carbonate particle aggregate X2 is porous. Therefore, the whiteness, opacity and oil absorption of the silica composite heavy calcium carbonate particles obtained by this production method may be reduced.

  In this step, the lower limit of the concentration of the heavy calcium carbonate particle aggregate X2 in the slurry containing the heavy calcium carbonate particle aggregate X2 and the alkali silicate is preferably 95 g / L, more preferably 100 g / L, and 105 g. / L is particularly preferred. On the other hand, the upper limit of the concentration of the heavy calcium carbonate particle aggregate X2 is preferably 125 g / L, more preferably 120 g / L, and particularly preferably 115 g / L. When the density | concentration of the heavy calcium carbonate particle aggregate X2 is less than the said minimum, there exists a possibility that a silica production | generation reaction may become dull and the productivity of a composite particle may deteriorate. On the other hand, when the concentration of the heavy calcium carbonate particle aggregate X2 exceeds the upper limit, the viscosity of the slurry may increase and the dispersibility of the heavy calcium carbonate particle aggregate X2 may decrease.

As the silicic acid concentration in the slurry (SiO ₂ conversion) is preferably 5 mass% to 15 mass%. When the silicic acid concentration is less than the lower limit, the silica composite effect is weakened, and the effect of improving the whiteness, opacity and oil absorption of the silica composite heavy calcium carbonate particles obtained by the present production method may be reduced. On the contrary, when the silica concentration exceeds the upper limit, the absorption capacity of the paper coating liquid to which the silica composite heavy calcium carbonate particles obtained by this production method are added is increased, and thus a coating layer is provided. In addition, the flatness of the coating layer surface may be reduced.

  The temperature of the alkali silicate solution L when the alkali silicate solution L is added to the heavy calcium carbonate particle aggregate X2-containing slurry or when the heavy calcium carbonate particle aggregate X2 is added to the alkali silicate solution L is particularly limited. Although not, it is preferably 50 ° C. or higher. When the heavy calcium carbonate particle aggregate X2 is mixed in a state where the alkali silicate solution L is heated to 50 ° C. or higher, the slurry can be easily homogenized by improving the fluidity.

[(3) First reaction step]
(3) In the first reaction step, silica composite heavy calcium carbonate in which mineral acid N is added to the slurry, the pH of the slurry is lowered, and silica is precipitated on the surface of the heavy calcium carbonate particle aggregate X2. Particle X3 is obtained.

  Specifically, in this step, while heating and stirring so that the liquid temperature of the slurry is 50 to 90 ° C., the slurry is held at a predetermined pressure in a sealed container, and the alkali silicate solution L contained in the slurry is 20 to 50. % Mineral acid N is added in an amount to be neutralized. As a result, alkali silicate, which is a raw material of silica, reacts with a dilute solution of mineral acid N such as sulfuric acid, hydrochloric acid, and nitric acid at high temperature, and silica sol fine particles are generated by hydrolysis reaction and polymerization of silicic acid. It precipitates on the surface of the calcium particle aggregate X2. The particle size of the silica sol fine particles can be adjusted by the stirring conditions during the reaction, the addition conditions of the mineral acid N, and the like. Then, by attaching the silica sol fine particles of about several nanometers so as to cover the entire surface of the heavy calcium carbonate particle aggregate X2, silica sol crystals grow, and the silica sol on the surface of the heavy calcium carbonate particle aggregate X2 is grown. Bonding occurs between the fine particles and the calcium contained in the heavy calcium carbonate particle aggregate X2, and silica can be deposited on the surface of the heavy calcium carbonate particle aggregate X2. In this production method, since the silica is coated on the surface of the heavy calcium carbonate particle aggregate X2, the calcium oxide contained in the heavy calcium carbonate particle aggregate X2 reacts with calcium hydroxide in water. It is considered that the viscosity of the slurry can be suppressed by suppressing.

  The mineral acid N used in this production method is not particularly limited, and for example, sulfuric acid, hydrochloric acid, nitric acid and the like can be used. Among these, sulfuric acid is particularly preferable from the viewpoint of cost and handling.

  As a density | concentration of the mineral acid N used in this manufacturing method, 0.1 mol / L or more and 5.0 mol / L or less are preferable. When the concentration of the mineral acid N is less than the above lower limit, the generation rate of silica is slow, and there is a possibility that the silica is not sufficiently formed. On the other hand, when the concentration of the mineral acid N exceeds the above upper limit, a local reaction occurs, the silica is unevenly distributed, and there is a possibility that the effect of suppressing the wrinkles may be reduced. The resulting silica composite heavy carbonate The yield improvement effect of calcium particles may be reduced.

  The temperature of the slurry during stirring in this step is preferably 50 ° C. or higher and 90 ° C. or lower. Since the temperature of the slurry affects the generation and growth of the silica sol, if the temperature of the slurry is less than the lower limit, silica may not be generated, or the generation and growth rate of the silica sol is slowed down and the silica has sufficient strength. Since it is not combined with the heavy calcium carbonate particle aggregate X2, silica may be peeled off during papermaking. On the contrary, when the temperature of the slurry exceeds the above upper limit, it becomes difficult to produce, and since silica is densely formed on the surface of the heavy calcium carbonate particle aggregate X2, oil absorption of the silica composite heavy calcium carbonate particles The degree may decrease.

  The pH of the slurry in this step is preferably 8 or more and 11 or less. When pH is less than the said minimum, a silica precipitates heterogeneously and there exists a possibility that the whiteness, opacity, and oil absorption of the silica composite heavy calcium carbonate particle obtained by this manufacturing method may fall. On the other hand, when the pH exceeds the above upper limit, the reaction between the alkali silicate salt and the mineral acid becomes dull and it becomes difficult for silica to be precipitated on the surface of the heavy calcium carbonate particle aggregate X2. The opacity of the composite heavy calcium carbonate particles may be reduced.

  In this step, it is preferable to add mineral acid N to the slurry in two stages in order to suppress precipitation of white carbon and more uniformly precipitate silica on the surface of the heavy calcium carbonate particle aggregate X2. In this case, mineral acid N is added in such an amount that the alkali silicate solution L contained in the slurry is neutralized by 20 to 50% in the first stage, and then the liquid temperature is raised by 10 ° C. or more than in the first stage. By adding the mineral acid N so that the pH of the reaction solution is 8 or more and 11 or less, homogeneous silica composite heavy calcium carbonate particles X3 can be obtained.

[(4) Second reaction step]
(4) In the second reaction step, sodium aluminate A and mineral acid N are added to the slurry, and aluminum oxide is precipitated on the surface of the silica composite heavy calcium carbonate particles X3, thereby combining the aluminum oxide with the silica composite. Heavy calcium carbonate particles X4 are obtained. In addition, when obtaining the silica composite heavy calcium carbonate particle which compounded only silica, this process can be omitted.

  Specifically, in this step, as in the first reaction step, while the slurry is heated and stirred, the slurry is maintained at a predetermined pressure in a sealed container, and sodium aluminate A and mineral acid N are added. As a result, aluminum oxide is deposited on the outer layer of silica deposited on the surface of the silica composite heavy calcium carbonate particles X3 obtained in the first reaction step. As a result, silica composite heavy calcium carbonate particles X4 in which the surface is composited with cationic aluminum oxide are obtained.

  In this step, it is preferable to add mineral acid N after adding sodium aluminate A to the slurry. Thus, by adding sodium aluminate A first and then neutralizing by adding mineral acid N, aluminum oxide can be uniformly deposited on the outer layer of silica. Further, it is more preferable to add the mineral acid N to the slurry in two stages in order to precipitate aluminum oxide more uniformly on the surface of the silica composite heavy calcium carbonate particles X3.

  The second reaction step is preferably performed after about 5 to 20 minutes have elapsed after the addition of the mineral acid N in the first reaction step. By providing the reaction holding period in this manner, silica can be uniformly deposited on the surface of the heavy calcium carbonate particle aggregate X2 in advance before the second reaction step, and the adsorbed water volatilized at 110 ° C. and 110 It is easy to obtain silica composite heavy calcium carbonate particles containing bound moisture that evaporates when heated from ℃ to 525 ° C, and the content of the bound moisture is 0.1 mass% or more and 1 mass% or less. Become.

  As a minimum of the addition amount of sodium aluminate A, 10 mass parts is preferable with respect to 100 mass parts of heavy calcium carbonate particles, 12 mass parts is further more preferable, and 15 mass parts is especially preferable. On the other hand, as an upper limit of the addition amount of sodium aluminate A, 30 mass parts is preferable, 25 mass parts is more preferable, and 22 mass parts is especially preferable. When the amount of sodium aluminate A added is less than the lower limit, aluminum oxide is not sufficiently combined with the silica composite heavy calcium carbonate particles X3, the binding strength with the pulp raw material is weakened, and the yield improvement effect is not exhibited. There is. Conversely, when the amount of sodium aluminate A added exceeds the above upper limit, the production cost is increased and the yield improvement effect may reach its peak.

  The final reaction solution in this step is preferably in the neutral to weakly alkaline range, and the pH is preferably 8 or more and 11 or less. When the pH is less than the above lower limit, the whiteness, opacity and oil absorption of the silica-composite heavy calcium carbonate particles obtained by this production method are deteriorated due to excessive addition of mineral acid, resulting in deterioration of the heavy calcium carbonate particles. There is a fear. Conversely, when the pH exceeds the above upper limit, the reaction between sodium aluminate A and mineral acid N becomes dull and it becomes difficult for aluminum oxide to precipitate on the surface of heavy calcium carbonate particles. There is a possibility that the opacity of the silica composite heavy calcium carbonate particles combined with aluminum may decrease.

  The slurry preparation step, the first reaction step, and the second reaction step can be performed by a batch method in which these steps are repeated for each predetermined processing amount, or in a continuous method in which each step is continuously performed. From this point of view, it is preferable to adopt a continuous type.

  When the slurry preparation step, the first reaction step, and the second reaction step are performed in a continuous manner, for example, the silica composite heavy calcium carbonate particles X4 combined with aluminum oxide can be manufactured according to FIG. 1 according to the following procedure. it can. In this procedure, mineral acid N is added in two stages in the first reaction step and the second reaction step. First, the heavy calcium carbonate particle aggregate X2, the alkali silicate solution L and the mineral acid N are continuously supplied to the first silica composite reaction tank 2, and these are stirred under a predetermined temperature and pressure, Part of the first reaction step is performed simultaneously. The slurry obtained in the first silica composite reaction tank 2 is continuously transferred to the second silica composite reaction tank 3. The mineral acid N is further added to the slurry transferred to the second silica composite reaction tank 3 and continuously transferred to the first aluminum treatment reaction tank 4. Since the second silica composite reaction tank 3 has a constant volume, generation and growth of silica proceeds until the slurry is transferred to the first aluminum treatment reaction tank 4, and the heavy calcium carbonate particle aggregate X2 Are continuously supplied to the first aluminum treatment reactor 4 as silica composite heavy calcium carbonate particles X3. Next, sodium aluminate A and mineral acid N are continuously supplied to the first aluminum treatment reaction tank 3, and these are mixed with the slurry of the silica composite heavy calcium carbonate particles X3 to produce the second reaction. Part of the process is performed. This slurry is continuously transferred to the second aluminum treatment reaction tank 5 and further added with the mineral acid N and then transferred to the storage tank 6. Since the second aluminum treatment reaction tank 5 has a certain volume, the reaction proceeds and aluminum oxide is deposited on the surface of the silica composite heavy calcium carbonate particles X3 until the slurry is transferred to the storage tank 6. Then, silica composite heavy calcium carbonate particles X4 composited with aluminum oxide are formed. The slurry containing the silica composite heavy calcium carbonate particles X4 combined with aluminum oxide is stored in a storage tank 6 and supplied to a papermaking production line as a filler, a pigment and the like.

  In addition, in this manufacturing method, addition of the mineral acid N is not performed in the 2nd silica composite reaction tank 3 and the 2nd aluminum treatment reaction tank 5, but addition of the mineral acid N in the 1st reaction process and the 2nd reaction process is 1 It may be done in stages. When the mineral acid N is added in one stage in the first reaction step, the mineral acid N may be added simultaneously with the alkali silicate solution L in the first silica composite reaction tank 2, or after the addition of the alkali silicate solution L, the second Mineral acid N may be added in the silica composite reaction tank 3. Similarly, when adding the mineral acid N in one stage in the second reaction step, the mineral acid N may be added simultaneously with the sodium aluminate A or the sodium aluminate A in the first aluminum treatment reaction tank 4. The mineral acid N may be added later in the second aluminum treatment reactor 5.

  Further, a slurry containing heavy calcium carbonate particles, alkali silicate solution and sodium aluminate may be prepared, and mineral acid may be added to the slurry to combine silica and aluminum oxide with the heavy calcium carbonate particles.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

  In addition, each measured value in a present Example is the value measured with the following method.

[Pulp freeness (unit: ml)]
The disaggregated pulp which disaggregated the coated paper for offset rotary printing based on JIS-P8220 (1998) was measured according to the Canadian standard freeness test method described in JIS-P8121 (1995).

[Adsorption moisture]
Silica composite heavy calcium carbonate particles made constant in a constant temperature dryer at 100 ° C. were conditioned in a standard condition (temperature 23 ° C., humidity 50%) specified in JIS-P8111 (1998) to become constant weight. The mass of the silica composite heavy calcium carbonate particles at the time and the mass of the silica composite heavy calcium carbonate particles when set to a constant weight in an environment of 110 ° C. were measured, and the difference was taken as the adsorbed moisture.

[Moisture content (unit:%)]
The mass W1 of the silica composite heavy calcium carbonate particles when the silica composite heavy calcium carbonate particles are allowed to stand in an environment of 110 ° C. and become constant, and the silica composite heavy calcium carbonate particles are heated from 110 ° C. to 525 ° C. The mass of the silica-composite heavy calcium carbonate particles when the amount became constant was measured as W2 and obtained from (W1-W2) / W1 × 100.

[Volume average particle diameter of filler (unit: μm)]
A 10 mg sample of the filler for measuring the volume was dispersed for 3 minutes with an ultrasonic disperser (output: 80 W). Using this solution, the average particle size (D50) was measured with a laser particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., model number: Microtrack MTII-3000).

[Basis weight (unit: g / m ² )]
It was measured according to “Paper and paperboard—basis weight measurement method” described in JIS-P8124 (2011).

[Base paper density (unit: g / cm ³ )]
The density of the base paper was measured in accordance with “Paper and paperboard—Test method of thickness and density” described in JIS-P8118 (1998).

[Ash content in base paper (unit:%)]
The ash content of the base paper was measured according to “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method” described in JIS-P8251 (2003).

[Filling yield (unit:%)]
For the stock inlet raw material and white water that had fallen under the wire (described as white water under the wire), the solid content concentration and the ash concentration were measured, respectively, and the ash content (filler) yield was measured by the following formula (2). In addition, the measurement of ash content ashed the solid content at 525 degreeC about the stock inlet raw material and the white water under a wire, and measured mass.
Ash content yield = 100 × (A−B) / A (2)
A: Ash concentration (g / l) of stock inlet raw material
B: Ash concentration of white water under the wire (g / l)

  In this example, the following qualities were evaluated.

(1) Printability Using a rotary offset printing press (manufactured by Komori Corporation, model number: LR-435 / 546SII) and color ink (Tokyo Ink Co., Ltd., product number: WEB ACTUS MAJOR), four-color offset printing. Went 17,000 meters. The print surface of the print sample was visually observed for print unevenness, and the degree thereof was evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): There is no printing nonuniformity and it is especially excellent in printability.
○: Print unevenness slightly occurred but excellent printability.
Δ: Some printing unevenness occurs and printability is somewhat inferior, but it can be used in practice.
X: Printing unevenness occurs, printability is poor, and actual use is impossible.

(2) Evaluation of Hijiwa In printing performed in the above-described evaluation of printability, the degree of wrinkles on the printed surface was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: No wrinkles and excellent print quality.
○: Slight wrinkles were generated, but the print quality was excellent.
Δ: Some wrinkles occurred, but actual use is possible.
X: Many wrinkles are generated, print quality is inferior, and actual use is impossible.

(Manufacture of silica composite heavy calcium carbonate particles)
Using coarsely crushed limestone, a bead mill was used to finely pulverize the volume average particle diameter (D50) to 4.0 μm to obtain a raw material heavy calcium carbonate slurry.

  A coagulant (Himax SC-100, manufactured by Hymo Co., Ltd.) was added to the heavy calcium carbonate particle slurry in an amount of 200 ppm in terms of solid content with respect to the solid content of the heavy calcium carbonate particles. The volume average particle diameter (D50) of the heavy calcium carbonate particles after the addition of the coagulant was 4.6 μm.

Next, a sodium silicate solution (silicic acid concentration 12 g / L) is added to the heavy calcium carbonate particle slurry to which a coagulant is added so that the silicic acid concentration (SiO ₂ equivalent) in the heavy calcium carbonate particle slurry becomes 8% by mass. To prepare a slurry. To this slurry, dilute sulfuric acid having a concentration of 0.1 to 5 mol / L and a pH of 9 after reaction was added in two stages, and the slurry was stirred using a mixer to perform the first reaction step. The liquid temperature of the slurry was 70 ° C. in the first stage of dilute sulfuric acid addition and 80 ° C. in the second stage. Moreover, the addition of the mineral acid at the first stage in the first reaction was performed simultaneously with the addition of the sodium silicate solution. Thereafter, the liquid temperature of the slurry is raised to 95 ° C., 8 parts by mass of sodium aluminate is added to 100 parts by mass of heavy calcium carbonate particles, and the dilute sulfuric acid in such an amount that the pH becomes 8 is again divided into two stages. In addition, the slurry was stirred to obtain silica composite heavy calcium carbonate particles. In addition, the addition of the mineral acid in the first stage in the second reaction step was performed simultaneously with the addition of sodium aluminate.

[Example 1]
As raw material pulp, virgin pulp softwood bleached kraft pulp and hardwood bleached kraft pulp were blended at a mass ratio of 15:85. Silica composite heavy calcium carbonate particles obtained by the above-described production method as a filler (additional aluminum oxide in Example 1) were added to the pulp (absolute amount), respectively, as a filler. A pulp slurry was obtained.

  Next, a winder part is used using a papermaking system including a wire part, a press part, a pre-dryer part, an undercoater part, an after-dryer part, a pre-calender part, a top coater part, a scuff dryer part, a calendar part, and a reel part. Thus, coated paper for offset rotary printing was obtained.

Specifically, the pulp slurry was first made with a wire part and then subjected to a press part and a predryer part to produce a base paper with a basis weight of 44.0 g / m ² . Next, in the undercoater part, both sides of the undercoat coating liquid containing starch as an external sizing agent and PAM as a paper strength improver at a mass ratio of 3: 1 are adjusted to 0.5 g / m ² per side. The undercoat was applied and dried in an after dryer part. Thereafter, it was flattened with a pre-calender (linear pressure 20 kN / m), and coated with a coating liquid (calcium carbonate having an oil absorption of 25 ml / 100 g as a pigment and clay in a mass ratio of 70:30 at the top coater part, A latex containing a polymer obtained by polymerizing a monomer containing 22% by mass of acrylonitrile and 25% by mass of styrene (the coating liquid containing 48% butadiene and 5% carboxylic acid) containing 9% of polymer on each side. Both sides were overcoated so as to be 0.5 g / m ² . Next, the calender part is flattened at a linear pressure of 200 kN / m and a speed of 1,500 m / min, and is applied to a winder part to obtain a coated paper for offset rotary printing having a basis weight of 64.0 g / m ^2. It was. The wire part was made with a gap former, the size press part was a rod metering size press coater, and the top coater part was a blade coater. In the calendar part, a multi-nip calendar was used. All the above parts used an on-machine papermaking system.

  The silica composite heavy calcium carbonate particles used had a volume average particle diameter of 6 μm, and the content of aluminum oxide in the silica composite heavy calcium carbonate particles was 15% by mass.

[Examples 2 to 20]
A coated paper for rotary offset printing was produced in the same manner as in Example 1 above using the pulp and filler conditions shown in Table 1. However, in Examples 8 and 9, the silica composite heavy calcium carbonate particles (filler A) and the heavy calcium carbonate not filled with silica (filler B) were included as fillers in the ratios shown in Table 1, respectively. In Example 10, silica composite heavy calcium carbonate particles not composited with aluminum oxide were used as the silica composite heavy calcium carbonate particles.

[Comparative Example 1]
In the same manner as in Example 1, a coated paper for offset rotary printing was produced using silica composite light calcium carbonate particles instead of silica composite heavy calcium carbonate particles as a filler. As the silica composite light calcium carbonate, silica composite light calcium carbonate particles not composited with aluminum oxide were used.

[Comparative Example 2]
In the same manner as in Example 1, a coated paper for rotary offset printing was produced using white carbon (manufactured by Elle Paper Chemical Co.) instead of silica composite heavy calcium carbonate particles as a filler.

[Comparative Example 3]
In the same manner as in Example 1, coated paper for rotary offset printing was produced using heavy calcium carbonate particles (manufactured by Elle Paper Chemical Co.) as a filler instead of silica composite heavy calcium carbonate particles.

[Comparative Example 4]
In the same manner as in Example 1, coated paper for rotary offset printing was produced using light calcium carbonate particles (TP-121 manufactured by Okutama Kogyo Co., Ltd.) instead of silica composite heavy calcium carbonate particles as a filler.

[Comparative Example 5]
In the same manner as in Example 1, a coated paper for rotary offset printing was produced using clay (manufactured by Imeris) instead of silica composite heavy calcium carbonate particles as a filler.

About the coated paper for offset rotary printing of Examples 1-20 and Comparative Examples 1-5, basic weight, base paper density, ash content in the base paper, and filler yield were measured by the method described above, and evaluation of printing suitability and hijiwa Went. The measurement results are shown in Table 1.

  As shown in Table 1, the coated paper for rotary offset printing of the present invention has an effect of reducing wrinkles and is excellent in printability.

  The coated paper for rotary offset printing of the present invention can effectively suppress generation of wrinkles in offset printing.

DESCRIPTION OF SYMBOLS 1 Condensation reaction tank 2 1st silica composite reaction tank 3 2nd silica composite reaction tank 4 1st aluminum treatment reaction tank 5 2nd aluminum treatment reaction tank 6 Storage tank X1 Calcium carbonate particle X2 Calcium carbonate aggregate X3 Silica composite calcium carbonate particle X4 Silica composite heavy calcium carbonate particle G coagulant L silicate alkali solution N mineral acid A sodium aluminate

Claims (4)

A coated paper for rotary offset printing comprising a base paper and a coating layer laminated on the base paper and containing a pigment and an adhesive,
Silica composite heavy calcium carbonate particles are internally added as a filler to the base paper,
The silica composite heavy calcium carbonate particles contain adsorbed moisture that volatilizes at 110 ° C. and bound moisture that volatilizes when heated from 110 ° C. to 525 ° C.,
The silica composite heavy der content of 1 mass% 0.1 mass% or more of bound water of the calcium carbonate particles is,
Web offset printing coated paper of aluminum oxide on the silica composite heavy calcium carbonate particles, characterized that you have been combined. The average particle diameter (D50) measured by the laser diffraction scattering method of the silica composite heavy calcium carbonate particles is 2 μm or more and 15 μm or less,
The coated paper for offset rotary printing according to claim 1, wherein the ash content of the base paper is 5% or more and 16% or less. The density of the base paper is 0.7 g / cm ³ or more and 1.5 g / cm ³ or less,
The raw material pulp of the base paper contains softwood kraft pulp and hardwood kraft pulp in a ratio of 0: 100 to 35:65,
The freeness of the raw pulp is 360 ml or more and 580 ml or less,
The coated paper for offset rotary printing according to claim 1 or 2, wherein the water content is 4% or more and 7% or less. The coated paper for offset rotary printing according to claim 1, wherein the basis weight is 45 g / m ² or more and 105 g / m ² or less.

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