JP6018410B2 - Coated paper - Google Patents

Description

TECHNICAL FIELD The present invention relates to coated paper, and more specifically, lightweight coated paper having high opacity, high bulkiness, and rigidity (less than 50 g / m ² ), and further, lightweight coated paper and fine coated paper technology. Related to the field.

  In recent years, coated paper has been required to be lighter in order to reduce transportation and mail costs. However, weight-reduced, that is, light-weight and fine-coated paper is a phenomenon in which the pattern on the lower surface of the paper is seen through a single blank sheet (so-called show-through), and printing ink is applied. There is a tendency that a phenomenon (so-called strike-through) that penetrates from the surface of the paper to the back surface and the surface printing can be seen through (so-called strike-through), and so-called hand feeling and lowering of the waist accompanying weight reduction. Therefore, it is desired to develop a coated paper having high opacity, hand feeling and waist, which does not cause the show-through or strike-through even at a low basis weight.

  In response to the above requirements, Patent Document 1 discloses a technique for improving opacity by using an organic pigment or titanium dioxide having a high refractive index as a pigment.

  Patent Document 2 discloses a technique for improving the opacity of coated paper by using calcium carbonate having a median diameter of 5.5 μm or less as a filler.

  Further, in Patent Document 3, recycled paper obtained by dewatering, drying, firing and pulverization using papermaking sludge as a raw material, and silica composite recycled particles in which silica is fixed on the surface of the recycled particles are used as a base paper. A technique for improving the opacity of a coated paper by containing it in is disclosed.

JP 2004-003083 A JP 2003-082599 A JP 2007-2111374 A

  However, since organic pigments and titanium dioxide are both expensive, when coated paper is produced using organic pigments or titanium dioxide, the cost increases.

  In addition, measures to reduce the particle size of the calcium carbonate filler and improve light scattering properties are also being studied, but simply reducing the particle size does not provide light scattering properties such as organic pigments, and sufficient opacity is not achieved. Cannot be achieved. In addition, the presence of calcium carbonate having a small particle diameter in the paper makes it difficult to obtain a bulk and lowers the hand feeling, and also causes a problem that the rigidity of the paper is lowered and the waist is not easily raised.

In addition, the recycled particles and the silica composite recycled particles are expected to improve opacity in coated paper with a low basis weight (50 g / m ² or less) such as lightweight coated paper and fine coated paper. However, the bulk and stiffness are still insufficient.

  In order to solve the above problems, the object of the present invention is to provide a coated paper that is lightweight but has high opacity, and that suppresses the decrease in bulkiness and rigidity, and further provides a lightweight coated paper and a fine coated paper. There is to do.

  In order to achieve the above object, the present invention has the following features.

The first invention is a coated paper comprising a base paper, and a coating layer provided on the base paper and comprising a pigment and an adhesive as main components,
The base paper comprises calcium carbonate particles having a primary particle diameter of 0.05 μm to 3.0 μm as core particles, the core particles are condensed to form calcium carbonate aggregates, and silica is added to the calcium carbonate aggregates by alkali silicate and mineral acid. 15: 85-50: A silica composite inorganic particle treated body in which an aluminum component is contained in a calcium carbonate aggregate obtained by combining and further combining the silica with an aluminum salt, and inorganic particles other than the silica composite inorganic particles. Containing at a rate of 50,
The volume average particle diameter (D50) of the treated silica composite inorganic particles is 4. 5-6 . 5 is a [mu] m, and wherein the volume average particle diameter of the inorganic particles other than the silica composite inorganic particles (D50) is 3.0 to 10.0, a coated paper.
Here, the volume average particle diameter refers to the volume median particle diameter (D50) in the particle size distribution measured by the laser diffraction scattering method.

  The second invention is an invention subordinate to the first invention, wherein the inorganic particles other than the silica composite inorganic particles are aggregates having a primary particle diameter of 0.05 μm to 0.20 μm, and are contained in the base paper. The total filler component contained is characterized in that it is contained in the base paper in an ash content according to JIS P 8251 in an amount of 10 to 20%.

As Hama fee, silica and silica composite inorganic particles complexed with inorganic particles other than silica, and inorganic particles other than the silica composite inorganic particles 15: 85-50: it contains 50 ratio of said silica composite inorganic The volume average particle diameter (D50) of the particles is 4.3 to 6.0 μm, and the volume average particle diameter (D50) of the inorganic particles other than the silica composite inorganic particles is 3.0 to 10.0 μm. By using silica composite inorganic particles with a sharp distribution in combination with inorganic particles, a large number of voids can be provided between the particles, resulting in a bulky and improved rigidity and a high printing opacity and blank paper opacity. A craft paper can be obtained.

Before SL inorganic particles are aggregates of primary particle diameter of 0.05Myuemu～0.20Myuemu, and the ash-conforming to JIS P 8251 in the base paper, by containing 10-20%, further bulky Thus, the rigidity is improved and more voids can be provided between the particles in the base paper, so that a coated paper having higher printing opacity and white paper opacity can be obtained.

Before SL silica composite inorganic particles treated, the calcium carbonate particles of the primary particle diameter 0.05μm~3.0μm the core particles, said core particles and the calcium carbonate aggregates agglomerated with calcium carbonate by alkali silicate and a mineral acid composite of silica aggregates, further by that contain a aluminum component to the calcium carbonate aggregates complexed with the silica by aluminum salts, can scatter visible light effectively, aluminum component is cationic Therefore, the bondability with the raw material pulp fiber is improved, so that the yield of ash content in the paper is improved, and lightweight coated paper and fine coated paper having higher blank paper opacity can be obtained.

The figure which shows an example of the manufacturing process of a silica composite inorganic particle and a silica composite inorganic particle process body

  The coated paper according to the present embodiment is a coated paper that includes a base paper and a coating layer that is provided on the base paper and mainly includes a pigment and an adhesive. More specifically, the coated paper according to the present embodiment contains at least inorganic particles other than silica composite inorganic particles and silica composite inorganic particles in the base paper, and the ratio thereof is 15:85 to 50:50. Contains. In addition, it may replace with a silica composite inorganic particle, and may use a silica composite inorganic particle process body (it mentions later for details).

(Base paper)
(pulp)
The base paper may be any paper that can be obtained by making a normal raw pulp. The raw material pulp is not particularly limited, and examples thereof include mechanical pulp (MP), chemical pulp (CP), and waste paper pulp. Examples of mechanical pulp include stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo grand pulp (TGP), ground pulp (GP), Examples include refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), and bleached thermomechanical pulp (BTMP). Examples of chemical pulp include unbleached softwood pulp (NUKP), unbleached hardwood pulp (LUKP), bleached softwood pulp (NBKP), and bleached hardwood pulp (LBKP). The above-mentioned paper pulp, once used as a pulp, a pulp obtained by reproducing process after being recovered as waste paper, as an example of waste paper pulp, deinking obtained from magazines waste paper such as pulp (MDIP), Examples include deinked pulp (NDIP) obtained from used newspaper and deinked pulp (FDIP) obtained from fine old paper. One or more of these raw material pulps can be appropriately selected, and the ratio can be adjusted and used.

  In the present embodiment, among the above pulps, it is preferable to contain mechanical pulp or waste paper pulp in the base paper. The fibers contained in the waste paper pulp are cut and shortened due to use in the city and regeneration treatment, and the pulp fibers are loosened and changed into flexible properties. Waste paper pulp having such a short fiber length and high flexibility has a high opacity improvement effect compared to virgin raw material pulp by containing a large amount of waste paper-derived ash while being made and recycled once. Waste paper-derived ash has a characteristic that it does not easily fall off, and has a high opacity while being lightweight, and is suitable as a raw material pulp for a base paper of coated paper that suppresses a decrease in bulkiness and rigidity. In particular, because recycled newspaper has a high recycling rate, pulp contained in newspaper waste paper has been used and recycled several times in the city, so it is particularly flexible and has a high yield of ash content from waste paper. It has become. Therefore, in the present embodiment, among the above-mentioned waste paper pulp, NDIP made from newspaper waste paper having a stable quality and stable carry-in ash derived from waste paper is preferable.

  As a raw material pulp that can be suitably combined with waste paper pulp, bleached thermomechanical pulp (BTMP) is particularly preferable. Bleached thermomechanical pulp (BTMP) has the bulky advantage of mechanical pulp, and the bleaching treatment makes the raw pulp fiber highly flexible with high whiteness, internal fibrils by mechanical beating, and internal by bleaching treatment. The silica composite inorganic particles, which are the points of the present invention, and the inorganic particles other than the silica composite inorganic particles are physically retained in the fibril gaps, contributing to the improvement of the ash yield, and being lightweight and high, which is the subject of the present invention It is effective to provide coated paper having opacity, bulkiness, and reduction in rigidity, and further, lightweight coated paper and fine coated paper.

  In the present embodiment, the waste paper pulp is preferably contained in an amount of 5 to 60% by mass, more preferably 10 to 40% by mass, and more preferably 30% by mass, based on the total raw material pulp of the base paper. Most preferred. When the ratio of the used paper pulp in the raw material pulp is less than 5% by mass, the effect of retaining the filler on the base paper tends to decrease, which is not preferable. When the ratio of the used paper pulp in the raw material pulp exceeds 60% by mass, the whiteness is lowered and the tendency of the stiffness of the coated paper to decrease is not preferable.

  The whiteness in the present invention is preferably 65% to 73%. When the whiteness exceeds 73%, it becomes difficult to satisfy the opacity in the low basis weight coated paper which is the subject of the present invention. If the whiteness is less than 65%, the appearance will be poor, and visual properties will be impaired in information printing such as symbols, which is the main application of the present invention.

  The content ratio of the mechanical pulp in the raw material pulp is preferably 5 to 15% by mass, and more preferably 5 to 10% by mass, based on the total raw material pulp of the base paper. Mechanical pulp is effective for improving bulkiness and rigidity at a ratio of 5% or more. When the content exceeds 15% by mass, the paper strength of the coated paper, which is the object of the present invention, is represented by tension or tearing. This causes a problem that the coating layer strength in offset printing requiring surface strength characteristics is reduced.

  In a more preferred configuration in the present embodiment, the fibrillation rate of the raw paper pulp used is preferably 4.3 to 5.8%, and more preferably 4.5 to 5.5%. preferable. When the fibrillation rate is less than 4.3%, the inorganic particles are hardly retained in the base paper, and the printing opacity and the white paper opacity are likely to decrease. Further, the flexibility of the base paper is lowered, the smoothness of the base paper is lowered, and coating unevenness and gloss reduction are likely to occur. When the fibrillation rate exceeds 5.8%, the pulp fiber becomes too soft and the tendency to decrease the stiffness becomes remarkable. In addition, the fibrillation rate of the raw material pulp fiber of the base paper is, for example, FiberLab. It can be evaluated by the fibrillation rate (Fibrillation) measured using (Kajaani).

<Measuring means of fibrillation rate>
The coated paper obtained by the present invention is disaggregated with a standard disaggregator in accordance with JIS P 8220, and the disaggregated pulp obtained by removing the sediment residue (inorganic matter) is used as a sample. FiberLab (manufactured by Kajaani) Measured with

(Filler)
In this embodiment, as a filler, silica composite inorganic particles obtained by combining silica with inorganic particles other than silica and inorganic particles other than the silica composite inorganic particles are used in combination, which is a problem in lightweight coated paper. The opacity of the coated paper can be improved while maintaining bulkiness and rigidity while reducing the weight. This will be described in detail below.

(Silica composite inorganic particles)
The silica composite inorganic particles used in the present invention are obtained through a silica composite process in which silica is combined with inorganic particles with an alkali silicate and a mineral acid to obtain silica composite inorganic particles.

  The silica composite inorganic particles used as a filler in the present embodiment can be produced using a conventionally known technique. For example, as a known technique for producing silica composite calcium carbonate, there is a technique disclosed in Japanese Patent Application Laid-Open No. 2009-40612. As a known technique for producing silica composite regenerated particles, there is a technique disclosed in Japanese Patent No. 4087431. In addition, all these known techniques are what is called a batch type. As a preferable example of the technology for producing silica composite inorganic particles, a technique for continuously producing silica composite inorganic particles as described below can be mentioned. According to the method for continuously producing silica composite inorganic particles as described below, silica composite inorganic particles having a uniform quality can be produced at a lower cost than conventional batch production methods.

  Drawing 1 is a figure showing an example of a manufacturing process of silica compound inorganic particles and a silica compound inorganic particle processing object. As the inorganic particles X1 which are the raw materials for the silica composite, commercially available or inorganic particles previously pulverized into fine particles are used. Next, the inorganic particles X1 can be used as they are in the next silica composite step. Preferably, the inorganic particles X1 are coagulated by the coagulant G in the coagulation reaction tank 1 to become the inorganic particle aggregate X2. Thereafter, the inorganic particle aggregate X2 becomes silica composite inorganic particles X3 by a silica composite reaction between the alkali silicate solution L and the mineral acid N in the first silica composite reaction tank 2 and the second silica composite reaction tank 3. Preferably, finally, the silica composite inorganic particles X3 are treated with the aluminum salt A in the aluminum salt reaction tank 4 to form a silica composite inorganic particle processed body X4, stored in the storage tank 5, and then supplied as a filler to the papermaking process. .

(Inorganic particles X1)
The inorganic particles X1 used in the method for producing the silica composite are not particularly limited, and for example, calcium carbonate, talc, titanium dioxide, clay, calcined clay, synthetic zeolite, regenerated particles and the like can be used. Among them, calcium carbonate having high whiteness and opacity and relatively low cost is preferable. Among them, heavy calcium carbonate can obtain particles having a sharp particle size distribution while suppressing the generation of coarse particles by the coagulant G. Therefore, it is particularly preferable.

(Recycled particle production technology)
The regenerated particles used as the inorganic particles X1 in the present invention are preferably obtained by dehydrating, drying, firing and pulverizing the deinking floss from the papermaking sludge. The basic method for producing regenerated particles used as a filler in the present embodiment can be produced using a conventionally known technique. Examples of known techniques for producing the regenerated particles include those disclosed in Japanese Patent Application Laid-Open Nos. 2007-112682 and 2005-53984.

  As the above-mentioned calcium carbonate, heavy calcium carbonate obtained by dry or wet mechanical pulverization of natural limestone, or light calcium carbonate (precipitated calcium carbonate) produced by injecting carbon dioxide into quick lime or slaked lime and neutralizing reaction Can be used. Since light calcium carbonate has a uniform crystal structure compared to heavy calcium carbonate, it is possible to reduce wire wear in the paper making process and to impart higher whiteness and opacity to paper. On the other hand, heavy calcium carbonate has a low production cost, but because it is manufactured by physical pulverization, it exhibits an irregular and broad particle size distribution, so the wire wearability is high, and it is used for internal addition. Although it was rarely used as a filler, it is possible to reduce wire wear in the paper making process by using a silica composite in the production method, and further using a silica composite after coagulation treatment with a coagulant in advance. Therefore, it can be suitably used as a raw material for the silica composite.

<Particle size adjustment process>
In the said manufacturing method, it is preferable to perform the particle size adjustment process for making the volume average particle diameter of the inorganic particle X1 into a suitable range for condensation and a silica composite. In this particle size adjustment step, the inorganic particles X1 are pulverized and classified by a pulverizer so that the volume average particle size of the inorganic particles X1 falls within a suitable range. As a pulverizer used as a means for pulverizing the inorganic 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 inorganic particles X1 is not particularly limited, but the lower limit is preferably 0.05 μm, and more preferably 0.1 μm. On the other hand, the upper limit of the volume average particle diameter of the inorganic particles X1 is preferably 3.0 μm, and more preferably 2.8 μm. When the volume average particle size of the inorganic particles X1 is less than the above lower limit, agglomeration becomes brittle because agglomeration with a large number of particles is necessary to obtain an aggregate having a sufficient particle size. It may collapse and the yield of the silica composite may not be sufficiently obtained. On the other hand, when the volume average particle diameter of the inorganic particles X1 exceeds the above upper limit, the particle size distribution of the inorganic particles X1 becomes broad, and a sharp particle size distribution cannot be obtained even when condensed, resulting in a silica composite effect. In addition to the possibility that the surface modification effect of the silica composite inorganic particles by the aluminum salt, which can enhance the expression of the effect, may be insufficient, the silica obtained by the production method due to the presence of coarse particles of inorganic particles There is a possibility that the quality of the paper to which the composite is added deteriorates.

<(1) Inorganic particle condensation step>
(1) In the inorganic particle condensing step, it is preferable to obtain the inorganic particle aggregate X2 by condensing the inorganic particles X1 with the coagulant G in the condensation reaction tank 1.

(Coagulant G)
The coagulant G used in the inorganic particle coagulation step is not particularly limited, and a known synthetic coagulant can be used. As the inorganic particles X1, heavy calcium carbonate is suitably used to have an appropriate particle size. Cationic coagulants that are easy to coagulate are 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 inorganic 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, an inorganic particle aggregate X2 having an excessively large particle size is formed, the particle size distribution may be broadened, and the yield may be reduced. When the coagulant G is added to the slurry of the body X2, the viscosity becomes too high and the workability and the yield may be reduced. In particular, when the viscosity of the slurry of the inorganic particle aggregate X2 exceeds 500 cps, the load on the pump for transferring the slurry of the inorganic particle aggregate X2 may increase, or the mixing property of the silica composite with the pulp raw material may decrease. There is. 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 inorganic 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 inorganic particle X1 has a cationic charge, which may make it difficult for condensation to occur due to repulsion due to charge, and excessively the particle size. Large inorganic particle aggregate X2 is formed, the particle size distribution becomes broad, and the yield may decrease. 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 inorganic 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 cationic charge density to suppress the coagulation property of the inorganic particles X1 and the increase in the viscosity of the slurry. Both are preferable because they can be suitably achieved. The reason for this is not clear, but, for example, the reason for the condensation is that there is variation in the charge distribution on the surface of the inorganic particles X1, so that a cationic synthetic polymer having a molecular weight and a cationic charge density in a predetermined range is used. This is thought to be due to the ability to exert electrical condensation.

(Inorganic particle slurry)
The method of coagulating the inorganic particles X1 with the coagulant G is not particularly limited. For example, the inorganic particles X1 are dispersed in water to form an inorganic particle slurry, and the coagulant G is added to the inorganic particle slurry. The method of stirring 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 the method of adding the coagulant G to the inorganic particle slurry is used, the solid content concentration of the inorganic particles X1 in the inorganic particle slurry is not particularly limited, but is 10% by mass to 30% by mass. preferable. By making the density | concentration of an inorganic particle slurry into the said range, coexistence with efficiency improvement of the inorganic particle X1 and suppression of a raise of slurry viscosity can be aimed at. When the concentration of the inorganic particle slurry is less than the lower limit, even if the coagulant G is added, the inorganic particles X1 may not be condensed to a suitable size. On the other hand, when the concentration of the inorganic particle slurry exceeds the above upper limit, the viscosity is too high and workability may be reduced, or the particle size distribution of the inorganic particle aggregate X2 may be broad, which may reduce the yield. is there.

  The coagulant G is preferably added to the inorganic particle slurry as an aqueous solution. Further, the addition amount of the coagulant G is preferably 100 ppm or more and 3000 ppm or less in terms of solid content with respect to the solid content of the inorganic particles X1. When the addition amount of the coagulant G is less than the above lower limit, the inorganic 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 paper to which the silica composite obtained by the production method is added The paper strength may be reduced.

(Inorganic particle aggregate X2)
The lower limit of the volume average particle diameter of the inorganic particle aggregate X2 obtained through the inorganic particle aggregation step is preferably 3.5 μm, more preferably 3.8 μm, and particularly preferably 4.0 μm. On the other hand, the upper limit of the volume average particle diameter of the inorganic particle aggregate X2 is preferably 5.5 μm, more preferably 5.3 μm, and particularly preferably 5.0 μm. By making the volume average particle diameter of the inorganic particle aggregate X2 in the above range, it is possible to efficiently improve the yield of the silica composite in the paper making process. When the volume average particle size of the inorganic particle aggregate X2 is less than 3.5 μm, the yield improvement effect of the silica composite obtained by the production method may not be exhibited. On the contrary, when the volume average particle diameter of the inorganic particle aggregate X2 exceeds 5.5 μm, there is a possibility that the paper surface deteriorates on the paper to which the silica composite obtained by the inorganic particle aggregate X2 is added. In addition, the volume average particle diameter of the inorganic particle aggregate X2 can be adjusted by the addition amount of the coagulant G, the volume average particle diameter of the inorganic particles X1, and the like.

(Silica composite)
Since the silica composite obtained by the above production method has an appropriate particle size and self-fixing property to a pulp raw material, the yield when added to paper as a filler is high. Moreover, since it has high whiteness, opacity, and oil absorption, the whiteness, opacity, ink drying property, etc. of the added paper can be improved. Moreover, since the silica composite obtained by the said manufacturing method has a small density and bulkiness, it can be used suitably as a filler of bulky paper.

<(2) Silica compound process>
(2) In the silica composite step, silica composite particles X3 are obtained by combining silica with the inorganic particle aggregate X2 obtained in the above step.

(Continuous production method of silica composite inorganic particles and treated silica composite inorganic particles)
The method for producing silica composite inorganic particles of the present embodiment includes inorganic particles, a coagulant, an alkali silicate aqueous solution, a mineral acid, and preferably an aluminum salt as a main raw material. To do. In the method for producing a treated silica composite inorganic particle, the surface of the silica composite inorganic particle is cationized with an aluminum salt. First, the slurry of the inorganic particle aggregate X 2 in which the inorganic particles are condensed in the condensation reaction tank 1 is preferably transferred from the condensation reaction tank 1 to the first silica composite reaction tank 2 to the first silica composite reaction tank 2. Then, a slurry obtained by adding mineral acid and alkali silicate solution to form silica composite inorganic particles is aged in the second silica composite reaction tank 3, and the slurry of silica composite inorganic particles is treated with aluminum salt from the second silica composite reaction tank 3. It shall flow into the reaction tank 4. Further, slurry alkali silicate solution L of the first silica composite reaction vessel 2, a mineral acid of N, and added pressure silica composite inorganic particles continuously addition to producing, but not shown, the second silica composite reaction By adding the mineral acid N to the tank and allowing the slow silica complex reaction to proceed, an inorganic particle aggregate slurry having a more uniform silica coating can be obtained. According to the knowledge of the present inventors, the silica sol generated in the first silica composite reaction tank has a function of further aggregating only the fine inorganic particle aggregates contained in the inorganic particle aggregate slurry obtained through the previous condensation reaction tank. It works to increase the volume average particle size of the inorganic particle aggregates and narrow the particle size distribution range to show a sharp particle size distribution. In the second silica combined reaction tank, the silica composite is maintained while maintaining the sharp particle size distribution. A slurry of silica composite inorganic particles having a uniform silica composite film can be obtained by advancing the reaction and aging.
This will be described in more detail below.

  In the present invention, the method of combining silica with the inorganic particle aggregate X2 is not particularly limited. For example, the following method is preferably used. First, the inorganic particle aggregate X2 is added to and dispersed in the alkali silicate solution L to prepare a slurry. After that, while heating and stirring so that the liquid temperature of this slurry becomes 70 to 100 ° C., the mineral acid N is added while maintaining a predetermined pressure in a sealed container to generate silica sol, and the pH of the final reaction liquid is adjusted. By adjusting to the range of 8.0 to 11.0, silica can be deposited on the surface of the inorganic particle aggregate X2.

  The reaction solution at the time of silica precipitation in this step is preferably in a neutral to weakly alkaline range, and the pH is preferably 8.0 or more and 11.0 or less, more preferably 8.5 or more and 10.5 or less. When pH is less than the said range, the calcium component contained in reproduction | regeneration particle | grains becomes easy to change to calcium hydroxide by excessive addition of a mineral acid, and there exists a possibility that the viscosity of a slurry may increase. Further, white carbon is generated instead of silica sol, and the whiteness, opacity and oil absorption of the composite particles obtained by the production method may be lowered. On the other hand, when the pH exceeds the above range, the reaction between the alkali silicate and the mineral acid becomes dull and it is difficult for silica to precipitate on the surface of the inorganic particle aggregate X2. May decrease. Silica deposited on the surface of the aggregate X2 of inorganic particles is obtained by reacting alkali silicate as a raw material with a dilute solution of mineral acid such as sulfuric acid, hydrochloric acid, nitric acid, etc. at high temperature, and by hydrolysis reaction and polymerization of silicic acid. Made of silica sol fine particles. 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, and the like.

  By attaching silica sol fine particles of about several nanometers produced by adding a mineral acid N such as sulfuric acid to the alkali silicate solution L so as to cover the entire surface of the inorganic particle aggregate X2, the first silica composite reactor 2 In addition, a silica sol crystal grows in the second silica composite reaction tank 3, and a bond is generated between the silica sol fine particles on the surface of the inorganic particle aggregate X2 and calcium contained in the inorganic particle aggregate X2, and the inorganic particle aggregate Silica can be deposited on the surface of X2.

  As a minimum of the density | concentration of the inorganic particle in the slurry which added and disperse | distributed the inorganic particle aggregate X2 in this process to the alkali silicate solution L, 95g / L is preferable, 100g / L is more preferable, 105g / L is especially preferable . On the other hand, the upper limit of the concentration of the inorganic particles is preferably 300 g / L, more preferably 250 g / L, and particularly preferably 200 g / L. When the density | concentration of an inorganic particle is less than the said range, a silica production | generation reaction may become dull and there exists a possibility that productivity of a composite particle may deteriorate. On the other hand, when the concentration of the inorganic particles exceeds the above range, the viscosity of the slurry may increase and the dispersibility of the inorganic particles may decrease.

  The temperature of the slurry during stirring in this step is preferably 70 ° C or higher and 100 ° 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 above range, the silica may not be generated, or the generation and growth rate of the silica sol may be slowed so that the silica has sufficient strength. Since it is not combined with inorganic particles, silica may be peeled off during papermaking. On the other hand, when the temperature of the slurry exceeds the above range, production becomes difficult, and silica is densely formed on the surface of the inorganic particle aggregate X2, which may reduce the oil absorption of the silica composite particle X3. is there.

(Silicic acid alkali solution L)
The alkali silicate solution L used in this step is not particularly limited, but it is preferable in terms 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 range, the silica sol is not sufficiently generated, and there is a possibility that the inorganic particle aggregate X2 in which silica is not combined is generated. Conversely, when the silicic acid concentration exceeds the above range, white carbon is generated instead of silica sol, and the inorganic particle aggregate X2 is coated with white carbon, so that the porosity of the inorganic particles is lost. There is a possibility that the whiteness, opacity and oil absorption of the resulting silica composite may be reduced.

  The addition amount of the alkali silicate solution in this step is preferably such that the silicic acid concentration (in terms of SiO2) in the slurry of the inorganic particle aggregate X2 is 5% by mass or more and 15% by mass or less. When the silicic acid concentration is less than the above range, the silica composite effect is weakened, and the whiteness, opacity and oil absorption of the silica composite obtained by the production method may be lowered. On the contrary, when the silicic acid concentration exceeds the above range, the absorption capacity of the paper coating liquid to which the silica composite obtained by the production method is added becomes large. There is a possibility that the flatness of the material will be lowered.

(Mineral acid N)
The mineral acid N used in this step 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 at this process, 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 range, the generation rate of silica is slow, and the silica may not be sufficiently formed. On the contrary, when the concentration of the mineral acid N exceeds the above range, a local reaction occurs, silica is unevenly distributed, and the yield improvement effect and the like of the resulting silica composite may be reduced. The amount of mineral acid N added in this step is preferably such that the alkali silicate neutralization rate is 50% or more and 75% or less.

  The reaction solution at the time of silica precipitation in this step is preferably in the neutral to weakly alkaline range, and the pH is preferably 8 or more and 11 or less, more preferably 8.5 or more and 10.5 or less. When pH is less than the said range, the calcium component contained in reproduction | regeneration particle | grains becomes easy to change to calcium hydroxide by excessive addition of a mineral acid, and there exists a possibility that the viscosity of a slurry may increase. In addition, white carbon is generated instead of silica sol, and the whiteness, opacity and oil absorption of the silica composite obtained by the production method may be reduced. On the other hand, when the pH exceeds the above range, the reaction between the alkali silicate and nitric acid becomes dull and it is difficult for silica to precipitate on the surface of the inorganic particle aggregate X2, so the opacity of the silica composite obtained by this production method May decrease.

(Silica composite particles X3)
As a minimum of the volume average particle diameter of silica composite inorganic particle X3 obtained through this process, 4.3 micrometers is preferred and 4.5 micrometers is more preferred. On the other hand, the upper limit of the volume average particle diameter of the silica composite inorganic particles X3 is preferably 6.0 μm, and more preferably 5.8 μm. If the volume average particle diameter of the silica composite inorganic particles X3 is less than the above range, the yield improvement effect of the composite particles obtained by the production method may not be sufficiently obtained. On the other hand, when the volume average particle diameter of the silica composite inorganic particles X3 exceeds the above range, there is a possibility that the paper surface deteriorates on the paper to which the composite particles obtained by the production method are added.

  The silica ratio in terms of oxide in the silica composite inorganic particles X3 is preferably 6.0% by mass or more and 42.0% by mass or less. When the ratio of silica is less than the above range, the surface of the inorganic particle aggregate X2 is not sufficiently covered, so that the yield improvement effect of the silica composite inorganic particles obtained by the production method may be reduced. Conversely, when the silica ratio exceeds the above range, the amount of silica precipitated becomes excessive, and the whiteness, opacity and oil absorption of the silica composite inorganic particles obtained by the production method may be reduced.

<(3) Aluminum salt treatment process>
(3) In the aluminum salt treatment step, the silica composite particles are treated with aluminum salt A to obtain aluminum-treated silica composite particles X4.

(Aluminum salt A)
The aluminum salt A used in this step is not particularly limited. For example, a sulfuric acid band (aluminum sulfate), sodium aluminate, or the like can be used. Among these, a sulfuric acid band having an effect of improving the yield of the obtained composite particles and an effect of reducing production costs is particularly preferable.

  The method for treating the silica composite inorganic particles X3 obtained in the above step with the aluminum salt A is not particularly limited. For example, a method of adding the aluminum salt A to the slurry of the silica composite inorganic particles X3 is used. be able to.

  The addition amount of the aluminum salt A is preferably such that the pH at the completion of the reaction is preferably 6.8 to 9.2, more preferably 7.2 to 9.0. As a minimum of the addition amount of the aluminum salt A, 18 mass parts is preferable with respect to 100 mass parts of the silica composite inorganic particle X3, 23 mass parts is further more preferable, and 28 mass parts is especially preferable. On the other hand, the upper limit of the addition amount of the aluminum salt A is preferably 48 parts by mass, more preferably 43 parts by mass, and particularly preferably 38 parts by mass. When the addition amount of the aluminum salt A is less than the above upper limit, the treatment of the silica composite inorganic particles X3 is sufficient, the binding strength with the pulp raw material is weakened, and the yield improving effect may not be exhibited. Conversely, if the amount of aluminum salt A added exceeds the above upper limit, the production cost may increase and the yield improvement effect may reach its peak.

(Aluminum salt-treated silica composite inorganic particle treated body X4)
As a minimum of the volume average particle diameter of silica compound inorganic particle processing object X4 obtained through this process, 4.5 micrometers is preferred and 4.8 micrometers is more preferred. On the other hand, the upper limit of the volume average particle diameter of the silica composite inorganic particle treated body X4 is preferably 6.5 μm, and more preferably 6.2 μm. When the volume average particle diameter of the silica composite inorganic particle treated body X4 is less than the above range, the yield improving effect upon addition of the silica composite inorganic particle treated body X4 may not be sufficiently obtained. On the contrary, when the volume average particle diameter of the silica composite inorganic particle treated body X4 exceeds the above range, the absorption capacity of the paper coating liquid to which the aluminum treated silica composite particle X4 is added is increased. When it is provided, the flatness of the coating layer surface may be lowered, and the strength of the paper to which the silica composite inorganic particle treated body X4 is added may be reduced. Moreover, there is a risk that dirt in the papermaking system and the degree of wear of the wire will increase.

  The lower limit of the oil absorption of the silica composite inorganic particle treated body X4 obtained through this step is preferably 50 ml / 100 g, and more preferably 70 ml / 100 g. On the other hand, the upper limit of the oil absorption of the silica composite inorganic particle treated body X4 is preferably 150 ml / 100 g, and more preferably 100 ml / 100 g. By setting the oil absorption of the silica composite inorganic particle treated body X4 in the above range, it is possible to improve the ink drying property of the paper to which the silica composite inorganic particle treated body X4 is added. When the oil absorption is less than the above range, the effect of improving the ink drying property of the paper to which the silica composite inorganic particle treated body X4 is added may not be obtained. On the contrary, when the oil absorption exceeds the above range, the ink absorbency of the paper to which the silica composite inorganic particle treated body X4 is added becomes too high, and the color developability may be deteriorated due to the sinking of the ink. .

  As a minimum of the aluminum content rate of silica compound inorganic particle processing object X4 obtained through this process, 1 mass% is preferred and 2% mass is still more preferred. On the other hand, the upper limit of the aluminum content of the silica composite inorganic particle treated body X4 is preferably 10% by mass, and more preferably 6% by mass. When the aluminum content is less than the above range, the yield improvement effect of the silica composite inorganic particle treated body X4 may not be sufficiently obtained. On the contrary, when the aluminum content exceeds the above range, the pH of the silica composite inorganic particle treated body X4 is too low, and when the inorganic particles X1 are calcium carbonate, the calcium carbonate is dissolved, and the target silica composite There is a possibility that the inorganic particle treated body X4 cannot be obtained.

  In the present invention, as described above, the silica composite step and the aluminum salt treatment step are performed separately, so that the composite particles having high yield, high whiteness, opacity and oil absorption (silica composite inorganic particle treated body X4) are obtained. ) Can be obtained. When the silica composite step and the aluminum salt treatment step are performed simultaneously, that is, when the aluminum salt A is added simultaneously when the silica is combined with the inorganic particle aggregate X2, the silica aggregates with the aluminum ions as nuclei. Particles in which carbon is formed and silica is combined cannot be obtained.

  In addition, the silica composite step and the aluminum salt treatment step can be performed in a batch method in which these steps are repeated for each predetermined treatment amount, or in a continuous method in which each step is executed continuously, from the viewpoint of production efficiency. Is preferably a continuous type.

  When performing the said silica composite process and an aluminum salt processing process by a continuous type, as shown in FIG. 1, the inorganic particle aggregate X2, the silicate alkali solution L, and the mineral acid N are continuously contained in the 1st silica composite reaction tank 2. As shown in FIG. The slurry obtained by mixing and feeding them under a predetermined temperature and pressure is stirred. The stirred slurry containing the inorganic particle aggregate X2, the silicate alkali solution L, and the mineral acid N is continuously transferred to the second silica composite reaction tank 3. The slurry transferred to the second silica composite reaction tank 3 is continuously transferred to the aluminum salt 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 aluminum salt treatment reaction tank 4, and the inorganic particle aggregate X2 is a silica composite particle. X3 is supplied continuously to the aluminum salt treatment reactor 4. Next, the aluminum salt A is continuously supplied to the aluminum salt treatment reactor 4 and mixed with the silica composite particles X3. In the aluminum treatment reaction tank 4, aluminum ions are bonded to the silanol groups of the silica composite particles X3 to form a silica composite inorganic particle treated body X4. The slurry containing the silica composite inorganic particle treated body X4 is stored in the storage tank 5 and supplied to the papermaking production line as a filler, a pigment, and the like. In addition, when supplying the slurry containing the silica composite inorganic particle body X3 to a papermaking production line, it is not necessary to perform the above-mentioned aluminum salt treatment. That is, the aluminum salt treatment reaction tank 4 may be omitted.

(Composite particles)
The composite particles (silica composite inorganic particle-treated product) obtained by the above production method have an appropriate particle size and self-fixing property to pulp raw materials, and therefore have a high yield when added to paper as a filler. Moreover, since it has high whiteness, opacity, and oil absorption, the whiteness, opacity, ink drying property, etc. of the added paper can be improved. Moreover, since the composite particles obtained by the above production method have a small density and bulkiness, they can be suitably used as a filler for bulky paper.

(Other processes)
The slurry that has flowed out of the aluminum salt treatment reactor 4 is suitably controlled in terms of average particle size, particle size distribution, wear level, etc., and thus has high opacity and high bulkiness, which is the subject of the present invention. Coated paper in which deterioration of the property and rigidity is suppressed, and further, lightweight coated paper and fine coated paper can be obtained.

(Adjustment of particle size)
The silica composite inorganic particles of the present embodiment are formed by adhering particulate silica to the surfaces of the inorganic particles, and the particle diameter of the silica is adjusted by, for example, adjusting the stirring strength or temperature of the slurry. Can be adjusted.

(Ratio of silica component)
In the present embodiment, the silica composite inorganic particles preferably have a silica component ratio of 10.0 to 50.0% by mass, more preferably 41.0 to 49.0% by mass, and 42.0%. Most preferred is ˜48.0 mass%. When the ratio of the silica component is less than 10.0% by mass, there is a possibility that the composite of silica is not sufficiently performed, and when used as a filler or pigment for papermaking, the effect of improving the opacity of the coated paper May not be sufficient. On the other hand, if the proportion of the silica component exceeds 50.0% by mass, silica may be overcombined, and when used as a filler for papermaking, the effect of improving opacity is sufficiently obtained. It may not be possible.

  The above is description about the method of producing continuously a silica composite inorganic particle and a silica composite inorganic particle processed body. According to the method for continuously producing the silica composite inorganic particles and the silica composite inorganic particle treated body as described above, the silica composite inorganic particles and the silica composite inorganic particle treated body having a uniform quality as compared with the conventional batch production method. Can be produced at low cost.

  In addition, although the organic pigment and titanium dioxide have high refractive index, the particles themselves are expensive as described above, and therefore the production cost increases when the organic pigment or the like is used as a raw material for the coated paper. However, in this embodiment, by using composite inorganic particles composed of relatively low-cost particles such as clay, talc, calcium carbonate, and silica as a filler, the production cost is higher than when organic pigments are used as the filler. A coated paper having high opacity can be obtained while lowering the thickness. In using silica composite inorganic particles or silica composite inorganic particle treated bodies instead of organic pigments, it is not always necessary to replace the total amount of organic pigments, etc. with silica composite inorganic particles or silica composite inorganic particle treated bodies. For example, part of the organic pigment may be replaced with silica composite inorganic particles.

(Inorganic particles)
As described above, in this embodiment, together with the silica composite inorganic particles or the silica composite inorganic particle treated body, inorganic particles different from the silica composite inorganic particles are contained in the base paper as a filler. In the present embodiment, aggregated calcium carbonate obtained by agglomerating primary particles into secondary particles is suitably used, and the aggregated light calcium carbonate has a primary volume average particle size of 0.05 μm to 0.20 μm, preferably 0.08 μm to A material having a particle size of 0.15 μm and a secondary volume particle size of 3.0 μm to 10.0 μm, more preferably 4.0 to 8.0 μm is used. The content of the aggregated calcium carbonate is 50% by mass to 85% by mass, more preferably 60% by mass to 80% by mass in terms of solid content with respect to the filler component in the base paper. By incorporating the aggregated calcium carbonate particles having the volume average particle diameter as described above into the base paper, the opacity of the coated paper can be improved.

  If the volume average particle size of the aggregated calcium carbonate particles that have been secondary-aggregated is less than 3.0 μm, it is impossible to fill the large voids formed between the pulp fibers, so printing due to the opacity of the coated paper, especially strike-through, occurs. It is not preferable because the opacity tends to decrease. When the volume average particle diameter is more than 10.0 μm, it becomes easy to form between the pulp fibers, but the aggregated calcium carbonate particles tend to inhibit the interfiber binding of the pulp, so that the stiffness of the coated paper is reduced, Since silica particles are exposed on the surface of the base paper, irregularities are formed, printing unevenness is generated, and glossiness is liable to be lowered.

  If the content of the secondary agglomerated aggregated calcium carbonate particles is less than 50% by mass in terms of the solid content in the proportion of the filler component contained in the base paper, the effect of improving the printing opacity cannot be sufficiently obtained. If the amount exceeds 85% by mass, the particle size is large, so that the binding between pulp fibers inside the base paper is likely to be hindered and the rigidity is likely to decrease, and aggregated calcium carbonate particles appear on the surface of the base paper, resulting in unevenness. Even if a coating layer is provided, printing unevenness occurs due to the unevenness of the base paper, and the glossiness tends to decrease, which is not preferable.

(Silica composite inorganic particles or combined use of silica composite inorganic particles and inorganic particles)
Since both the inorganic particles and the silica composite inorganic particles have a large specific surface area, they easily absorb printing ink. By using such inorganic particles or silica composite inorganic particles as a filler, even if a coating layer is provided, strike-through can be prevented and printing opacity can be improved. However, when only one of inorganic particles and silica composite inorganic particles is used as a filler, the absorption effect of printing ink (hereinafter referred to as ink absorption effect) depends on the specific surface area of silica particles, etc. When using particles or silica composite inorganic particles as a filler, it is a coated paper having a high opacity, which is the subject of the present invention while having a high opacity, and suppressing a decrease in bulkiness and rigidity, and further a lightweight coated paper and In obtaining fine coated paper, it is impossible to obtain a quality satisfying high opacity, bulkiness and rigidity.

  Therefore, in this embodiment, silica composite inorganic particles and inorganic particles having different particle diameters are used in combination. By incorporating a large amount of silica composite inorganic particles that are agglomerated with silica composites or cationic properties into inorganic particles composed of secondary aggregates, the number of contacts between the inorganic particles and silica composite inorganic particles is increased. Many voids are formed between these particles. Since the void has an effect of retaining the printing ink, an ink absorption effect that can be expected from the specific surface area of inorganic particles or the like can be obtained. Thereby, the effect of preventing strike-through at the base paper stage can be further enhanced, and the printing opacity can be further improved. The same applies to the case where a silica composite inorganic particle treated body is used instead of the silica composite inorganic particles.

  Examples of the inorganic particles used in the present embodiment include aggregated calcium carbonate in which primary particles are aggregated and aggregated into secondary particles, and calcium carbonate that exhibits a so-called chestnut-like crystal structure in spite of primary particles. It is preferable to use aggregated calcium carbonate in which primary particles are aggregated and secondary particles are aggregated as inorganic particles. Aggregated calcium carbonate is a secondary particle in which primary particles are aggregated, and therefore there are many irregularities on the particle surface. A larger void is formed by adsorbing silica composite inorganic particles having an ionicity by imparting silica composite or cationicity to the surface of the aggregated calcium carbonate, thereby obtaining a higher ink absorption effect. be able to.

  Also, by using silica composite inorganic particles and inorganic particles having different properties as fillers, silica composite inorganic particles can easily stay between inorganic particles made of secondary aggregates and pulp fibers, improving the filler yield. Therefore, it is possible to protect the wire of the papermaking equipment and to prevent the scale in the equipment (the filler etc. sticking to the piping and becoming a foreign substance).

  In this embodiment, in order to provide more voids between the particles, the total content of the silica composite inorganic particles and the inorganic particles is 50% by mass to 85% by mass as a ratio of the total filler components contained in the base paper. %, More preferably 60% by mass to 80% by mass, and the ash content according to JIS P 8251 as the total filler component in the base paper is preferably 10% to 20%. As a result, the effect of preventing strike-through at the base paper stage can be further enhanced, and the printing opacity can be further improved.

(Other fillers)
In this embodiment, as described above, in order to improve the opacity of the coated paper, the silica composite inorganic particles and the inorganic particles are contained in an ash content based on JIS P 8251 in an amount of 10% to 20%. Fillers generally have a function of inhibiting hydrogen bonding of pulp fibers in paper, so if such fillers are contained in such a large amount, the paper will be cut and produced in the paper making process etc. with only a slight change in the filler content. There is a problem of worsening sex.

  In the present embodiment, as described above, it is preferable for the raw pulp to contain waste paper pulp. However, waste paper pulp contains fillers derived from waste paper. Since the content of fillers derived from used paper in used paper pulp varies depending on the type of used paper, etc., when the base paper is produced by containing used paper pulp, the content of the filler in the used paper greatly fluctuates. There is a problem that the quality varies. Therefore, it is preferable to reduce the variation in the content of the filler in the base paper, and it is preferable to use waste paper pulp derived from newspaper waste paper with stable ash content.

  As an example of a method for reducing the variation in the content of the filler in the base paper, the amount of silica composite inorganic particles and inorganic particles is increased or decreased according to the content of the filler derived from the used paper contained in the used paper pulp, A method for reducing the fluctuation in the content of the filler in the base paper is conceivable.

  However, although this method can reduce the variation in the content of the filler in the base paper, the content of the silica composite inorganic particles and silica particles excellent in the effect of improving the opacity varies. The opacity is not constant and the quality of the coated paper is not uniform.

  Therefore, in this embodiment, the addition amount of the silica composite inorganic particles and the inorganic particles is constant, and the addition amount of the filler other than the silica composite inorganic particles and the inorganic particles (hereinafter referred to as the adjustment filler) A method of reducing the fluctuation in the content of the filler in the paper is preferable. In addition, the filler for adjustment is preferably a filler that easily stays between the pulp fibers in order to protect the wire of the papermaking facility and suppress the generation of scale in the facility. An example of such a filler for adjustment includes spindle-shaped light calcium carbonate which is generally used.

  In the present embodiment, various additives may be internally added to the base paper. For example, on the base paper, for example, internal sizing agents, paper strength improvers, paper thickness improvers, yield improvers (water-soluble polymers such as various synthetic polymers and starches), and fixing agents thereof, Various additives that are usually blended in the base paper of the coated paper can be internally added by adjusting the kind and blending amount.

(Basic paper manufacturing method)
The base paper can be manufactured by a conventionally used manufacturing method. In the wire part in the process of making the base paper, a former generally used for papermaking can be used. Conventional examples of formers generally used for papermaking include a circular net former, a long net former, and a twin wire former.

It should be noted that the effect of the present embodiment is noticeable in coated paper having a paper thickness of 50 μm or less, particularly 30 to 50 μm. This is because if the paper thickness of the coated paper exceeds 50 μm, the opacity increases in the first place, and the necessary and sufficient opacity is achieved regardless of this embodiment. Moreover, in order to adjust the paper thickness of coated paper to the above-mentioned range, it is preferable to prescribe | regulate also basic weight. In the coated paper according to this embodiment, the basis weight measured in accordance with “Paper and paperboard—basis weight measurement method” described in JIS P 8124: 1998 is 50 g / m ² or less, particularly 30 to 50 g / m. It is preferable to adjust so as to be ² . If the basis weight exceeds 50 g / m ² , the paper thickness increases, and the opacity increases in the first place. Therefore, the necessary and sufficient opacity is achieved regardless of this embodiment.

(Undercoat clear coating layer (including impregnation state that does not constitute a layer))
In a more preferred configuration of the present invention, an undercoat clear coating layer mainly comprising a water-soluble polymer as an adhesive is provided on both sides of the base paper. A method for applying a coating liquid for providing an undercoat clear coating layer (hereinafter referred to as an undercoat clear coating liquid) is not particularly limited. For example, a film transfer coating system, a gate roll coating system, or the like is used. be able to. In this embodiment, the coating amount of the undercoat clear coating layer is not particularly limited, but the coating amount of the undercoat clear coating layer is preferably about 0.1 to 1.5 g / m ² per both sides. Furthermore, it is more preferable to set it as 0.2-1.3 g / m < ² > per both surfaces. When the coating amount of the undercoat clear coating layer is less than 0.1 g / m ² per both sides, the pigment in the topcoat coating layer tends to sink into the base paper, and the printing gloss is lowered. When the coating amount of the undercoat clear coating layer exceeds 1.5 g / m ² per both sides, the fluidity of the undercoat clear coating solution is deteriorated, which may cause coating unevenness, which is not preferable.

  There is no restriction | limiting in particular in the water-soluble polymer contained as a main component in the said undercoat clear coating liquid, Generally what is used for a papermaking use can be used. Examples of water-soluble polymers used in the undercoat coating liquid include water-soluble resins such as polyacrylamide and polyvinyl alcohol, cellulose-based water-soluble polymers such as hydroxyethyl cellulose and carboxymethyl cellulose, raw starch, and enzyme-modified Starches such as starch, hydroxyethyl starch, cationized starch, acetylated starch, oxidized starch and the like can be mentioned. One or more of these water-soluble polymers can be appropriately selected and used in combination.

(Pre-calendar)
In the present embodiment, before the coating layer is provided on the base paper (hereinafter referred to as the undercoating paper) after the provision of the clear undercoating layer mainly composed of a water-soluble polymer, the undercoating is performed. It is preferable to perform a process for flattening the paper (hereinafter referred to as a flattening process). The pulp fibers in the undercoat coated paper can be packed by flattening the undercoat coated paper before providing the coating layer. Thereby, the printing glossiness can be further improved, and the printing opacity can be further improved. The conditions for the flattening treatment of the undercoat clear coated paper are not particularly limited by appropriately adjusting the gloss, paper thickness, and opacity of the resulting coated paper as an index, but the nip pressure is 10 to 80 kN / m, and the temperature is 20 ˜150 ° C., nip pressure 50 kN / m, and temperature 50 ° C. are more preferable.

(Top coat layer)
On the surface of the undercoat clear coating layer, a topcoat coating layer mainly comprising a pigment and an adhesive is provided. The coating layer is provided by coating a surface of the undercoat clear coated paper with a coating liquid mainly composed of a pigment and an adhesive (hereinafter referred to as a top coating liquid). The method for applying the top coating solution is not particularly limited, but a blade coating method that is excellent in smoothness of the coated surface is preferable.

(Pigment)
(Pigment particle diameter)
In this embodiment, the pigment used for the top coat layer has a ratio of the total mass of particles having a particle diameter of less than 2.0 μm to 1.3 to 10.0 with respect to the total mass of particles having a particle diameter of less than 0.5 μm. Is used. The reason for using the pigment having the above particle diameter will be described below.

  The wavelength of visible light is 380 to 750 nm. If a particle having a particle diameter of less than 380 nm (0.38 μm) is used as a pigment, visible light is transmitted without colliding with the particle depending on the phase, so that visible light is hardly scattered. On the other hand, when particles having a particle diameter exceeding 750 nm (0.75 μm) are used as the pigment, visible light collides with the particles with a high probability. However, the larger the pigment particle size, the better the white paper opacity of the coated paper. As a result of intensive studies, the inventors have found that when the pore diameter of the top coat layer is about half the wavelength of visible light (150 to 400 nm), the scattering of visible light can be particularly improved. Synergy by using silica composite inorganic particles in which silica is combined with inorganic particles other than silica as a filler and a base paper containing inorganic particles other than silica composite inorganic particles in a ratio of 15:85 to 50:50. As a result, it has been found that it is possible to provide a coated paper that has high opacity, is light in weight, has low bulkiness, and suppresses a decrease in rigidity, and further, a lightweight coated paper and a fine coated paper. That is, 15:85 to 50: Silica composite inorganic particles obtained by combining silica with inorganic particles other than silica in the topcoat layer having many pore diameters of 150 to 400 nm and inorganic particles other than the silica composite inorganic particles. By improving the scattering of visible light by providing it on the base paper contained at a ratio of 50, and further on the surface of the clear undercoat layer, it has high opacity, lightness, low bulkiness and low rigidity. We were able to provide reduced coated paper, as well as lightweight coated paper and fine coated paper.

  In the present invention, the stiffness (lateral) is preferably 0.12 or more, more preferably 0.17 or more. If the stiffness (horizontal) is less than 0.12, the coated paper has a high opacity and a high opacity, and suppresses a decrease in bulkiness and stiffness, which is the subject of the present invention. Insufficient stiffness in providing paper.

  The reason why the opacity of the blank of coated paper does not improve as the particle diameter of the pigment is increased is that, when the pore diameter is larger than half the wavelength (400 nm), visible light may pass through the pore. However, since the number of pores on the surface of the coated paper decreases, visible light scattering hardly occurs. Therefore, it is considered that the white paper opacity of the coated paper is not sufficiently improved.

  On the other hand, when the pore diameter is smaller than half of the wavelength (150 nm), the number of pores in the coating layer increases, but the probability that visible light passes through the pores decreases, and visible light becomes difficult to scatter. Therefore, it is considered that the white paper opacity of the coated paper is not sufficiently improved.

(Pigment component)
As the component of the pigment that can be used in the present embodiment, those conventionally used as a pigment in papermaking applications can be used. Examples of the pigment include calcium carbonate, kaolin clay, calcined kaolin, deramikaolin, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide And inorganic pigments such as zinc hydroxide, and organic pigments such as polystyrene resin fine particles and urea formalin resin fine particles, and one or more kinds can be used in combination as necessary. Further, so-called regenerated particles may be used. Among these pigments, since the inorganic pigment has pores in the particles, the fluidity of the overcoating liquid is relatively poor, so that the fine pigment particles in the overcoating liquid are difficult to sink into the undercoating paper. Therefore, it is preferable because the printing gloss can be improved. Amorphous silica having a relatively large pore volume, for the above-mentioned reasons, makes it difficult for fine pigment particles in the overcoating liquid to sink into the undercoating paper, but the ink set is accelerated due to the large pore volume, The tendency for printing gloss and printing opacity to decrease is prominent. In that respect, kaolin clay and calcium carbonate having an appropriate pore volume are more preferable because the ink set is relatively slow and the printing glossiness is further improved. These effects are particularly remarkable when kaolin clay and calcium carbonate are 80% by mass or more among the pigments used in the top coat layer.

  In this embodiment, it is preferable that the adhesive in the coating layer contains a water-soluble polymer. This is because when a resin (for example, latex) that increases the fluidity of the coating liquid is used as the main component of the adhesive in the overcoating liquid, the fine pigment particles in the overcoating liquid form the undercoating layer. This is because it passes through and easily sinks into the base paper, and the print glossiness decreases. In the present invention, by using a water-soluble polymer as a main component as an adhesive in the top coating liquid, the fine pigment particles in the top coating liquid are prevented from sinking into the base paper, and the printing gloss is improved. Can be made.

The water-soluble polymer that can be used as the main component of the adhesive in the topcoat coating liquid is not particularly limited, and those that can generally be used for papermaking can be used. Examples of water-soluble polymers which can be used as the main component of the overcoat coating solution of the adhesive include water-soluble, high molecular cellulose such as hydroxycarboxylic ethyl starch and carboxymethylcellulose, and starches . One or more of these water-soluble polymers can be appropriately selected and used.

  The preferred printing gloss (surface) of the coated paper in the present invention is preferably 30% or more, more preferably 50% or more.

The mixing ratio of the water-soluble polymer used as the main component of the adhesive in the topcoat coating liquid is not particularly limited, but is preferably 3 to 17 parts by weight with respect to 100 parts by weight of the pigment in the topcoat coating layer. -15 mass parts is more preferable. By containing 3 to 17 parts by mass of a water-soluble polymer with respect to the pigment as an adhesive for the top coating layer, the B-type viscosity of the top coating solution is 3,000 to 5,000 cps, and the water retention is 200 g / Since it can be adjusted to m ² or less, preferably 150 g / m ² or less, particularly preferably 100 g / m ² or less, the water in the overcoating liquid is difficult to be absorbed by the undercoating paper after coating, and accompanying the movement of moisture This is preferable because penetration of the fine pigment particles into the undercoat coated paper can be suppressed. Moreover, it can prevent that a coating nonuniformity arises by making the viscosity of a coating liquid into 3,000-5,000 cps, More preferably, a coating nonuniformity arises further by setting it as 4,000 cps. be able to. If the blending ratio of the water-soluble polymer used as the main component of the adhesive in the topcoat coating solution is less than 3 parts by mass, the tendency to decrease the printing opacity becomes remarkable. If the blending ratio of the water-soluble polymer used as the main component of the adhesive in the topcoat coating liquid exceeds 17 parts by mass, the viscosity of the coating liquid will increase too much, and coating unevenness is likely to occur. Since the tendency to decrease the glossiness of blank paper becomes remarkable, it is not preferable.

  The blank paper glossiness (surface) in the present invention is preferably 15% or more, more preferably 30% or more.

The coating amount (solid content) of the topcoat coating layer of the coated paper according to this embodiment is not particularly limited, but it is a coating having many pore diameters of 150 to 400 nm as long as it is 6 to 18 g / m ² per both sides. A layer can be provided on the surface of the coated paper. If only the white paper opacity of the coated paper is improved, the necessary and sufficient white paper opacity can be achieved regardless of this embodiment if the coating amount is increased and the coating layer is thickened. However, increasing the amount of coating leads to coating unevenness and cost increase. By using the pigment according to the present embodiment as the pigment contained in the coating layer, it is possible to obtain a coated paper having a high blank paper opacity while having a low coating amount.

  In addition to the pigment and the adhesive, the topcoat coating liquid used in the present embodiment includes, for example, a dust preventing agent, a fluorescent dye, a fluorescent dye brightener, an antifoaming agent, a release agent, a colorant, and water retaining agent. Various auxiliary agents generally used in papermaking applications, such as an agent, can be appropriately blended within a range not impairing the object of the present invention. The method for preparing the top coating liquid is not particularly limited, and the pigment, the adhesive, and various necessary auxiliaries may be appropriately adjusted and mixed with stirring so as to obtain a uniform composition at an appropriate temperature. .

  Moreover, it is preferable to adjust the whiteness (surface) to 65 to 73%, and it is more preferable to adjust the coated paper which concerns on this embodiment to 70 to 73% with the said various adjuvants. This is because not only the appearance is lowered if the whiteness is less than 65%, but also the opacity is high in the first place, so that the necessary and sufficient opacity can be achieved without using the coated paper according to the present embodiment. Because it can.

Furthermore, the coated paper according to the present embodiment is preferably adjusted to 85 to 93%, more preferably 90 to 93%, with the above-mentioned various auxiliary agents, etc. Also in the later printing opacity (surface), the printing opacity is preferably 80 to 88%. This is to provide a coated paper having a high opacity while being lightweight, which is the subject of the present invention, and suppressing a decrease in bulkiness and rigidity, and further a lightweight coated paper and a fine coated paper, This is to ensure an opacity equal to or higher than that of a conventional coated paper having a basis weight of 50 g / m ² or more. If the blank paper opacity is less than 85% and the print opacity is less than 80%, the problem of the present invention cannot be solved.

  Examples 1 to 26 are shown in Tables 1 and 2, and Comparative Examples 1 to 9 are shown in Tables 3 and 4.

(Manufacturing procedure)
The raw material pulp used was NDIP and BTMP, and NDIP was contained in the ratios shown in Table 1. With respect to 100 parts by mass (absolutely dry amount) of this pulp, the internal sizing agent (Part No .: AK-720H, manufactured by Harima Chemicals Co., Ltd.) 0.05% by mass, cationized starch (Part No .: Amilofax T) -2600, manufactured by Abebe Japan Co., Ltd.) 1.0 mass%, and a yield improver (product number: NP442, manufactured by Nissan Eka Chemicals Co., Ltd.) 0.02 mass% were added to obtain a pulp slurry. As the silica composite inorganic particles or the silica composite inorganic particle treated body used as the filler, those produced by the continuous production method of the silica composite inorganic particles and the silica composite inorganic particle treated body described above were used.

The pulp slurry was made into a paper and used for a wire part, then a press part and a pre-dryer part to produce a base paper having a basis weight of about 28 g / m ² . In the wire part, paper was made by the gap former method. Next, in the undercoater part, the undercoat coating solution was applied by a film transfer coating method so that the undercoat coating layer containing cationized starch as a main component was 1.0 g / m ² per side.

  Next, the base paper provided with an undercoat coating layer on both sides was provided to an after dryer part, and after drying the undercoat paper, a flattening treatment was performed under conditions of a nip pressure of 25 kN / m and a roll temperature of 70 ° C. Pre-calendar).

Next, in the top coater part, the top coat layer mainly composed of pigment (kaolin clay) and cationized starch (adhesive) is overcoated by a blade coating method so as to be 7 g / m ² per side. The working liquid was applied to produce a coated paper having a basis weight of 44 g / m ² and a paper thickness of 47 μm.

  In addition, details of the adhesive and the pigment are as follows.

<Filler>
Inorganic particles (aggregated light calcium carbonate product number: TP-221BM, manufactured by Okutama Kogyo Co., Ltd., volume average particle size: 5.6 μm)

<Undercoat coating layer>
(adhesive)
・ Cationized starch (Product No .: Amylofax T-2600, manufactured by Abebe Japan)

<Topcoat coating layer>
(adhesive)
・ Cationized starch (Product No .: Amylofax T-2600, manufactured by Abebe Japan)
(Pigment)
・ Kaolin clay (product number: AMAZON, manufactured by Kadam)
The particle diameter of the pigment is determined by sieving the above pigment or using a wet pulverizer (product number: planetary mill, manufactured by Seishin Enterprise Co., Ltd.), and the total number of particles less than 2.0 μm relative to the total mass of particles less than 0.5 μm It adjusted so that the ratio of mass might be 1.3-10.0.

(Evaluation method)
(A) Basis weight Measured according to JIS P 8124: 1998 "Paper and paperboard-Basis weight measuring method".

(B) Paper thickness Measured according to JIS P 8118: 1998 “Paper and paperboard—Test method for thickness and density”.

(C) Ash content Measured according to JIS P 8251: 2003 “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method”.

(D) Stiffness (lateral)
In accordance with the method described in JIS P 8143: 2000 “Rigidity Test Method Using Paper Clark Stiffness Tester”, the transverse direction of the paper was measured.

(E) Whiteness (surface)
Measured according to JIS P 8148: 2001 “Paper, paperboard and pulp—Measurement method of ISO whiteness (diffuse blue light reflectance)”.
Whiteness of 70% or more is excellent in whiteness, 65% or more is good in whiteness, and less than 65% is inferior in whiteness.

(F) Blank paper opacity (surface)
Measured according to JIS P 8149: 2000 “Paper and paperboard—Opacity test method (backing of paper) —Diffusion illumination method”.
Blank paper opacity of 90% or more is excellent in blank paper opacity, 85% or more is good in blank paper opacity, and less than 85% is inferior in blank paper opacity.

(G) Printing opacity (surface)
Using an offset rotary printing press (model: RI-2, manufactured by Ishikawajima Industrial Machinery Co., Ltd.), changing the ink amount of offset rotary printing ink (trade name: News Zeta Naturalis (black), Dainippon Ink & Chemicals, Inc.) The ratio of the back surface reflectance after printing to the back surface reflectance before printing when the printed surface reflectance was 9% was determined. A spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd.) was used for measuring the reflectance. The printing opacity is obtained by the following equation.
Printing opacity (%) = (back surface reflectance after printing / back surface reflectance before printing) × 100
A printing opacity of 88% or more is excellent in printing opacity, a printing opacity of 80% or more is good, and a printing opacity of less than 80% is inferior in printing opacity.

(H) White paper glossiness (surface)
Measured according to the method described in JIS P 8142: 2005 “Paper and paperboard—Measurement method of 75 degree specular gloss”.
Blank paper glossiness of 30 to 44% or more is excellent in blank paper glossiness, 15 to 30% is good in blank paper glossiness, and less than 15% is inferior in blank paper glossiness.

(I) Print glossiness (surface)
A printing test specimen was prepared under the following conditions, and the glossiness was measured by the same method as the blank paper glossiness to obtain the printing glossiness.

Printing machine: RI-3 type, manufactured by Meisei Co., Ltd. Ink: WebRex Nouver HIMARK process (indigo), manufactured by Dainichi Seika Co., Ltd.

  Test method: The ink was kneaded for 3 minutes each with the upper and lower rolls (kneaded for 2 minutes, then the roll was inverted and further kneaded for 1 minute), and two-color simultaneous printing was performed at a rotation speed of 30 rpm.

The print specimen was measured according to JIS P 8142: 2005 “Paper and paperboard—Measurement method of 75 degree specular gloss”.
If the printing gloss is 50-60%, the gloss is excellent, if it is 30-50%, the gloss is good, and if it is less than 30%, the gloss is inferior.

(J) Coating surface (surface)
The coating surface feeling was evaluated based on the following evaluation criteria.
A: Coating unevenness did not occur and coating could be performed stably.
○: Some coating unevenness occurred, but coating was relatively stable.
Δ: Some coating unevenness occurred, and a stable coating could not be obtained.
X: Coating unevenness occurred and coating was not stable.
Of the evaluation criteria, ◎, ○, and Δ are judged to be actually usable.

(K) Particle size and particle size distribution The particle size and particle size distribution were measured with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200 type” manufactured by Shimadzu Corporation). did. The measurement sample was prepared by adding inorganic particles S to a 0.1% sodium hexametaphosphate aqueous solution and dispersing the mixture with ultrasonic waves for 1 minute. The particle diameter of the particle means the diameter when the particle is spherical, and the average value of the major axis and the minor axis when the particle is not spherical.

  Since all of the coated papers of the examples satisfy the configuration of claim 1, good results were obtained in the respective evaluation items. That is, the coated paper which concerns on each Example can solve this application subject.

  On the other hand, since all of the coated papers of the comparative examples do not satisfy the configuration of claim 1, good results cannot be obtained in any of the evaluation items, and the subject matter of the present application cannot always be solved. .

  Although the present invention has been described in detail above, the above description is merely an example of the present invention in all respects and is not intended to limit the scope thereof. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention.

  According to the present invention, it is possible to provide lightweight coated paper and fine coated paper having high opacity at a low cost, and can be used for, for example, printing coated paper used in offset printing, gravure printing, and the like.

DESCRIPTION OF SYMBOLS 1 Condensation reaction tank 2 1st silica composite reaction tank 3 2nd silica composite reaction tank 4 Aluminum salt processing reaction tank 5 Storage tank X1 Inorganic particle X2 Inorganic particle aggregate X3 Silica composite inorganic particle X4 Silica composite inorganic particle processing body G Coagulant L Silica alkali solution N Mineral acid A Aluminum salt

Claims (2)

A coated paper comprising a base paper and a coating layer provided on the base paper and mainly composed of a pigment and an adhesive,
The base paper comprises calcium carbonate particles having a primary particle diameter of 0.05 μm to 3.0 μm as core particles, the core particles are condensed to form calcium carbonate aggregates, and silica is added to the calcium carbonate aggregates by alkali silicate and mineral acid. 15: 85-50: A silica composite inorganic particle treated body in which an aluminum component is contained in a calcium carbonate aggregate obtained by combining and further combining the silica with an aluminum salt, and inorganic particles other than the silica composite inorganic particles. Containing at a rate of 50,
The volume average particle diameter (D50) of the treated silica composite inorganic particles is 4. 5 μm to 6. Coated paper, wherein the volume average particle diameter (D50) of inorganic particles other than the silica composite inorganic particles is 5 to 10.0 μm, and is 3.0 to 10.0. Inorganic particles other than the silica composite inorganic particles are aggregates having a primary particle size of 0.05 μm to 0.20 μm,
2. The coated paper according to claim 1, wherein the base paper contains 10 to 20% of an ash content in accordance with JIS P 8251 as a total filler component contained in the base paper.

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