JP2012180604A - Coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide coated paper that attains high opacity although produced at low cost.SOLUTION: Coated paper comprises: base paper; and a coating layer provided on the base paper and including, as principal components, a pigment and an adhesive. The base paper includes composite particles compounded at least with inorganic particles. The pigment is at least one of kaoline clay and calcium carbonate. The kaoline clay or the calcium carbonate satisfies the following: (A) it is contained in a ratio of 20 to 100 mass% in the whole pigment; (B) it includes particles with a particle size of 0.5 to 2.0 μm in a ratio of 15 to 80 mass%; and (C) a ratio of a total mass of particles with a particle size smaller than 2.0 μm to a total mass of particles with a particle size smaller than 0.5 μm is 1.3 to 10.0 in it.

Description

  The present invention relates to coated paper, and more particularly to the technical field of coated paper having high opacity.

  In recent years, coated paper has been required to be lighter in order to reduce transportation and mail costs. However, the weight-reduced, that is, low basis weight coated paper tends to cause a phenomenon (back-through) in which printing on the front surface can be seen through from the back surface. Therefore, there is an increasing demand for coated paper having high opacity even with a low basis weight.

In response to the above requirements, Patent Document 1 discloses a technique for achieving high 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.

  Patent Document 3 discloses a technique for improving opacity by internally adding agglomerated calcium carbonate having high opacity as a filler as a filler. In Patent Document 4, regenerated particles derived from paper sludge, regenerated particle aggregates derived from deinking floss, or silica-coated regenerated particle aggregates obtained by coating regenerated particle aggregates derived from deinking floss with silica are used as fillers. Although a technique for improving the opacity by adding is disclosed, these fillers have a large variation in particle diameter, and the paper strength is reduced due to the filler particles having a large particle diameter, so the paper strength is not stable. There's a problem.

JP 2004-003083 A JP 2003-082599 A JP 2008-274523 A JP 2009-242980 A

  However, both organic pigments and titanium dioxide are expensive, resulting in high production costs. Inexpensive kaolin clay and calcium carbonate do not provide sufficient opacity, and even if the particle size of the pigment particles is reduced to improve the scattering property, light scattering properties similar to those of organic pigments and titanium dioxide can be obtained. Therefore, sufficient opacity cannot be achieved.

  In addition, it is possible to classify and remove fillers with a large particle size to make the particle size distribution uniform and prevent high paper strength while maintaining high opacity, but in this case, a classification process occurs. In other words, it is not practical because filler particles having a large particle size that has been classified and removed cannot be used, and the manufacturing cost deteriorates.

  In order to solve the above-described problems, an object of the present invention is to provide a coated paper having high opacity at a low cost.

In order to achieve the above object, the present invention has the following features.
A first invention is a coated paper comprising a base paper and a coating layer mainly composed of a pigment and an adhesive provided on the base paper, wherein at least inorganic particles are combined in the base paper The composite particles are contained, and at least either kaolin clay or calcium carbonate is contained as the pigment, and the kaolin clay or calcium carbonate satisfies the following.
(A) 50 to 100% by mass of all pigments (B) particles having a particle size of 0.5 to 2.0 μm occupy 25 to 80% by mass (C) particles having a particle size of less than 0.5 μm The ratio of the total mass of particles having a particle diameter of less than 2.0 μm to the total mass is 1.3 to 10.0.

  2nd invention is invention which is subordinate to 1st invention, Comprising: The said adhesive agent contains water-soluble polymer, and said water-soluble polymer is 0.1-10 mass with respect to 100 mass parts of said pigments. Partly contained.

  A third invention is an invention subordinate to the first or second invention, wherein the composite particles are regenerated particles obtained by dehydration, drying, firing and pulverization using paper sludge as a raw material, and calcium carbonate. It is characterized by at least one of silica composite calcium carbonate particles composited with silica and silica composite regenerated particles composited with regenerated particles and silica.

  According to the first aspect of the invention, the composite paper that efficiently scatters visible light inside the particle is contained in the base paper, and the coating layer of the coated paper has a high visible light scattering effect of 150 to 400 nm. Since many pores having a pore diameter of 5 are provided, a coated paper having high opacity can be obtained.

  According to the second invention, it is difficult for the pigment particles in the topcoat coating liquid to sink into the base paper, and a coated paper with improved printing opacity can be obtained.

  According to the third invention, a coated paper having higher opacity can be obtained at a low cost.

  The coated paper according to the present embodiment is a coated paper including a base paper and a coating layer mainly composed of a pigment and an adhesive provided on the base paper. More specifically, the coated paper according to this embodiment contains composite particles in which inorganic particles are combined in the base paper, and a pigment having a sharp particle size distribution is used as the pigment.

(Base paper)
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). Examples of the waste paper pulp include disaggregation / deinking waste paper pulp, disaggregation / deinking / bleached waste paper pulp, etc. produced from magazine waste paper, flyer waste paper, office waste paper, and the like. One or more of these raw material pulps can be appropriately selected, and the ratio can be adjusted and used.

  In particular, in the present embodiment, the mechanical pulp is preferably contained in an amount of 5 to 60% by mass, more preferably 10 to 40% by mass of the raw material pulp. When the ratio of the mechanical pulp in the raw material pulp is less than 5% by mass, the tendency of the white paper opacity of the coated paper to decrease becomes remarkable. When the ratio of the mechanical pulp in the raw material pulp exceeds 60% by mass, the opacity of the coated paper is improved, but the white paper gloss and the print gloss are lowered.

  Moreover, in this embodiment, it is preferable that the Runkel ratio of the pulp obtained by dissociating the coated paper is 0.78 to 2.70, and more preferably 0.84 to 1.48. When the Runkel ratio is less than 0.78, the fiber wall thickness of the pulp is so thin that the pulp fiber tends to be crushed and tends to be coated paper having poor rigidity. When the Runkel ratio exceeds 2.70, the fiber wall thickness of the pulp is thick and excellent in rigidity, but the tendency of the base paper surface to become rough becomes remarkable, and the white paper glossiness and printing glossiness of the coated paper are lowered. Further, since the pulp fibers are not easily crushed, the entanglement between the fibers is weak, and the tendency of blister resistance to decrease is remarkable. Note that the Runkel ratio used in this specification is R.I. O. H. Runkel in 1940 on Wachbl. Papierfabr. This is a parameter published in the magazine, and is obtained by dividing twice the fiber wall thickness by the fiber lumen diameter. A larger Runkel ratio indicates a stiffer fiber.

  When the Runkel ratio is 0.78 to 2.70, it is preferable to combine with a filler to be described later because a coated paper excellent in opacity can be obtained. The filler used in the present invention is composite particles, and the surface shape is indefinite. For this reason, the binding between the pulp fibers tends to be hindered, and the paper strength tends to decrease. However, as described above, the pulp fibers having a Runkel ratio of 0.78 to 2.70 have moderate flexibility and are not suitable. It is preferable because a fiber-to-fiber bond is easily formed across the regular composite particles, and the opacity can be improved while preventing a decrease in paper strength. In particular, as composite particles, it is preferable to use a silica composite filler such as silica composite regenerated particles and / or silica composite calcium carbonate described later. Since silica has pores, the adsorbed water and the pulp fibers are more likely to be electrostatically bonded, and it is easier to obtain a bond between the pulp fibers across the filler. It becomes easier to obtain craft paper.

The Runkel ratio can be adjusted by selecting the wood species used as the raw material of the pulp.
In conifers, black and pine have a small fiber width and a large wall thickness, so the Runkel ratio is large (about 4 or more), while fir, todomatsu, red pine, and himekomatsu have a large fiber width and small wall thickness, so the Runkel ratio is small ( About 1-2), larch, spruce, cedar, hinoki and hiba are even smaller (about 1 or less).
In broad-leaved trees, the beech and red oak have a large Runkel ratio (about 4 or more); Even smaller (about 1 or less).

(Filler)
In order to improve the opacity of the coated paper, it is conceivable to contain a filler having a high refractive index in the base paper and to scatter incident visible light efficiently. In general, titanium dioxide is used as a filler having a high refractive index. In this embodiment, composite particles are used instead of titanium dioxide as a filler. Visible light scattering occurs when visible light is refracted at the boundary surface between two substances. If the two substances are two substances having different refractive indexes, the scattering effect is further increased. In the present invention, since composite particles in which two or more particles are combined, preferably composite particles in which two or more particles having different refractive indexes are combined, visible light scattering occurs inside the composite particles. Therefore, a coated paper excellent in opacity can be obtained by incorporating composite particles in the base paper.
Examples of the composite particles include regenerated particles made of clay, talc, calcium carbonate and the like, silica composite particles obtained by subjecting the particles to composite treatment with silica, and aggregated calcium carbonate obtained by agglomerating calcium carbonate. The kind of particles that can be used as a raw material for silica composite particles is not particularly limited. For example, inorganic particles such as calcium carbonate, clay, talc, kaolin, calcined kaolin, titanium dioxide, and aluminum hydroxide, and the above regenerated particles are used. Take as an example. The inorganic particles and the regenerated particles are hereinafter referred to as inorganic particles.

  Among the above composite particles, silica composite particles are preferable because they are excellent in opacity improvement effect. The refractive index of fillers generally used for papermaking is talc (1.54-1.59), calcium carbonate (1.55-1.57), clay (1.56-1.58), white carbon and silica. (Refractive index of 1.44 to 1.50). Among these, a combination having a large difference in refractive index and a high effect of improving opacity is silica composite particles in which white carbon or silica having the smallest refractive index is combined with the other three types. That is, they are silica composite talc, silica composite calcium carbonate, and silica composite clay. On the contrary, in the composite particles in which two kinds of talc, calcium carbonate, and clay having similar refractive indexes are combined, the higher opacity improvement effect is difficult to obtain as the above-mentioned silica composite particles. Titanium dioxide has a refractive index of 2.55 to 2.75.

  The composite particles preferably have a sharp particle size distribution in which 70% or more of the composite particles are contained in a particle size of 2 to 10 μm, and more preferably 75% or more. When the particle size is 70% or more, there is little variation in the particle size of the composite particles. Therefore, when the composite particles are uniformly contained in the base paper, the absorbability of the printing ink tends to be uniform on the paper surface, and the local ink Can be obtained, and a coated paper excellent in printing opacity (difficult to see through) can be obtained. If it is less than 70%, even if the composite particles are uniformly contained in the base paper, uneven printing ink absorption due to variations in the particle diameter of the composite particles is likely to occur, and printing opacity (difficult to see through) is likely to occur. Is not preferred because it tends to decrease. If the particle size distribution is sharp, the tendency to improve the printing opacity becomes remarkable when composite particles composed of two or more kinds of particles are used. That is, since the composite particles have a gap between two or more kinds of particles, the printing ink is easily retained in the gap, and the particles alone exhibit high ink absorbability. For this reason, the fact that the particle diameter of the composite particles is uniform and the ink absorbability is not uneven greatly affects the printing opacity.

  As described above, it is preferable to use silica composite particles as a filler, and the particle size distribution of the filler to be sharp, but as composite particles in which particle diameters of 2 to 10 μm include 70% or more of the composite particles, silica composite carbonic acid is used. It is preferable to use calcium or silica composite regenerated particles because the effect of improving opacity is particularly excellent. This is because silica composite calcium carbonate and silica composite regenerated particles are hard to break due to the high hardness of calcium carbonate and regenerated particles. For example, in a paper machine system, the composite particles are not broken by the shearing force of the screen or pump. This is because it is easily contained in the expected opacity improvement effect. On the other hand, clay and talc are softer than calcium carbonate and regenerated particles, so the composite particles break down in the paper machine system and fine particles are generated, which not only reduces the visible light scattering effect but also decreases the yield. Fine particles are accumulated in the paper machine system and foreign matter is easily generated, and the appearance of the resulting coated paper is likely to be deteriorated.

  On the other hand, since fillers generally used conventionally (for example, talc, clay, calcium carbonate, white carbon, etc.) other than the composite particles are single-particle substances, visible light scattering hardly occurs inside the particles. Therefore, the coated paper using the single particle filler generally used conventionally is inferior in opacity.

  In addition, although titanium dioxide has a high refractive index, titanium dioxide is expensive as described above, which increases the production cost of coated paper. However, by using composite particles consisting of relatively low-cost particles such as clay, talc, calcium carbonate, and silica as fillers, high opacity can be achieved while lowering production costs than using titanium dioxide as fillers. The coated paper which has can be obtained. When using composite particles instead of titanium dioxide, it is not always necessary to replace the total amount of titanium dioxide with composite particles, and a part of titanium dioxide may be replaced with composite particles in consideration of production costs and the like.

(Composite particle production technology)
(Regenerated particles)
The regenerated particles used as the pigment in this 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.

(Silica composite particles)
The silica composite particles used as a pigment 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. All of these known techniques are for producing composite particles in batch mode. As a more preferable example of the production technology of silica composite particles, the following technology for continuously producing silica composite particles can be mentioned.

<Continuous production method of silica composite particles>
The manufacturing method of the silica composite particle of this embodiment uses inorganic silicate etc. aqueous solution of alkali silicate and mineral acid as main raw materials, and combines silica with inorganic particle etc. to make silica composite particle. Specifically, first, the inorganic particles and the alkali silicate are supplied to the first tank, and the slurry in which the inorganic particles and the like in the first tank are dispersed is transferred from the first tank to the second tank. It shall flow from a 2nd tank to a 3rd tank, and this 3rd tank to a 4th tank. In addition to adding the mineral acid R2 to the slurry HC in the third tank, the mineral acid R1 is added in advance to the slurry HA in the first tank to continuously produce silica composite particles. This will be described in more detail below.

(First tank)
In the present embodiment, the inorganic particles or the like and the alkali silicate can be supplied to the first tank separately, and stirred and mixed in the first tank to form a slurry. However, after supplying inorganic particles, alkali silicate (or an aqueous solution thereof), and water as appropriate to the mixing tank preceding the first tank, stirring and mixing in the mixing tank, It is preferable to supply. When the inorganic particles and the like and the alkali silicate are previously stirred and mixed and then supplied to the first tank, the inorganic particles and the like are more uniformly dispersed, so that the homogeneity of the produced silica composite particles is improved.

(Alkali silicate)
The type of alkali silicate is not particularly limited. For example, sodium silicate (Na ₂ O.nSiO ₂ .nH ₂ O) such as sodium silicate glass (water glass), which is a liquid, powdered anhydride, or flaky sodium orthosilicate. ), Potassium silicate aqueous solution for general industrial use, potassium silicate (K ₂ O.nSiO ₂ ) such as high-purity potassium silicate used as a fluorescent material binder for cathode ray tubes, and the like can be used.

The alkali silicate can be supplied as an aqueous solution, for example, and the silicic acid (SiO ₂ ) concentration of the aqueous alkali silicate solution is preferably 6 to 18 g / L, more preferably 8 to 16 g / L. It is particularly preferably 10 to 14 g / L.

(Inorganic particles, etc.)
The kind of inorganic particles that can be used as a raw material is not particularly limited. For example, known inorganic particles such as calcium carbonate, clay, talc, kaolin, calcined kaolin, titanium dioxide, and aluminum hydroxide are preferably used as a filler for papermaking. Calcium carbonate, clay and talc which are preferably used as pigments and pigments can be used. Moreover, since the problem of paper sludge disposal etc. is solved at the same time, recycled particles can be used. Inorganic particles and the like preferably have an average particle size of 1.4 to 3.2 μm, more preferably 1.7 to 2.9 μm, and particularly preferably 2.0 to 2.6 μm. .

(Mineral acid)
The mineral acid R1 is added in advance to the slurry HA in the first tank. This mineral acid R1 is added separately from the mineral acid R2 added to the slurry HC in the third tank, and is different in technical meaning from the addition of the mineral acid R2.

  That is, it is the same in that the silica sol is generated by adding the mineral acids R1 and R2 in both the first tank and the third tank. However, the silica sol generated in the third tank is a silica sol to be combined with inorganic particles or the like in the fourth tank. On the other hand, the silica sol produced in the first tank is glued to the other inorganic particles, so to speak, so that the small-sized inorganic particles are adhered to the other inorganic particles in the second tank. It is a silica sol for making (gluing function). Therefore, the characteristics required for each silica sol are different, and the addition conditions of the mineral acids R1 and R2 are also different. That is, the mineral acid R1 and the mineral acid R2 are added separately in a plurality of stages in order to uniformly disperse the mineral acids R1 and R2 in the slurry HA, HB, HC, and HD. Is different.

  The kind of mineral acid R1 is not particularly limited, and for example, a dilute solution of mineral acid such as dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and the like can be used.

  The concentration of the mineral acid R1 is preferably 0.50 to 4.00 mol / L (1 to 8N (normality)), and more preferably 1.00 to 3.00 mol / L (2 to 6N). It is preferably 1.75 to 2.25 mol / L (3.5 to 4.5 N).

  The addition amount of the mineral acid R1 is not particularly limited, but the slurry HD in the fourth tank has a pH of 7.0 to 8.5 by adjusting the total addition amount of the mineral acid R2 added in the third tank. It is preferable to set the amount to be pH 7.5 to 8.5, and it is particularly preferable to set the amount to be pH 7.8 to 8.2.

(Stirring)
In order to further improve the homogeneity of the silica composite particles to be produced, it is preferable to stir the slurry HA in the first tank. The strength of the stirring is not particularly limited, but the stirring is preferably performed so that the Reynolds number (Re) of the slurry HA is 4000 to 16000, and the stirring is performed so as to be 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

(Passing time)
In relation to setting the Reynolds number of the slurry HA in the first tank to 4000 to 16000, the passing time of the slurry HA in the first tank is preferably 2 to 20 minutes, and 4 to 18 minutes. More preferably, it is particularly preferably 8 to 12 minutes. Note that the passage time of the slurry HA is a calculated time from the addition of the mineral acid R1 to the outflow from the first tank, and does not include the time before the mineral acid R1 is added.

(temperature)
Although the temperature of slurry HA in a 1st tank is not specifically limited, It is preferable that it is 50-100 degreeC, It is more preferable that it is 70-100 degreeC, It is especially preferable that it is 90-100 degreeC.

(Slurry transfer)
The method for moving the slurry HA in the first tank to the second tank is not particularly limited, but as an example, there is a method of overflowing the slurry HA in the first tank and moving it into the second tank. It is done. That is, a partition wall that does not reach the bottom surface is provided in the first tank, and the slurry HA in the first tank is passed between the bottom surface of the first tank and the partition wall, and then raised and overflowed. The method of moving to 2 tanks is mentioned.

(Second tank)
In this embodiment, the slurry HB in the second tank is composed only of the slurry HA in the first tank that has moved, and no new inorganic particles, alkali silicate, sulfuric acid, or the like is added.

  In the second tank, the silica sol generated and grown in the first tank glues small-diameter inorganic particles etc. to other inorganic particles etc., so that the particle size distribution of the manufactured silica composite particles is Sharpens on the small diameter side.

(Stirring)
In the present embodiment, it is preferable to stir the slurry HB in order to advance the gluing uniformly. The strength of the stirring is not particularly limited, but stirring is preferably performed so that the Reynolds number (Re) of the slurry HB is 4000 to 16000, and stirring is preferably performed to 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

(Passing time)
Slurry HB in the second tank in relation to the fact that the slurry HA is stirred so that the Reynolds number is 4000 to 16000 and the passage time is 2 to 20 minutes in the first tank. The passage time is preferably adjusted to 20 to 50 minutes, more preferably 25 to 45 minutes, and particularly preferably 30 to 40 minutes. The passage time of the slurry HB is a calculated time from when the slurry HB (HA) flows into the second tank until it flows out into the third tank.

(temperature)
Although the temperature of the slurry HB in a 2nd tank is not specifically limited, Preferably it is 50-100 degreeC, More preferably, it is 70-100 degreeC, Most preferably, it is 90-100 degreeC.

(Slurry transfer)
The method for moving the slurry HB in the second tank to the third tank is not particularly limited, and for example, the same method as the method for moving the slurry HA in the first tank to the second tank can be mentioned.

(Third tank)
Mineral acid R2 is added to the slurry HC in the third tank. Addition of this mineral acid R2 produces a silica sol as in the first tank. However, the silica sol is a silica sol for compounding with inorganic particles or the like in the fourth tank, and in the first tank to paste the small-diameter inorganic particles or the like to other inorganic particles or the like in the second tank. The technical meaning is different from the silica sol to be formed. Therefore, as will be described below, since the characteristics required for the silica sol are different, the addition conditions of the mineral acid R2 are also different.

(Mineral acid)
The kind of the mineral acid R2 is not particularly limited, and for example, a dilute solution of mineral acid such as dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and the like can be used. The mineral acid R2 may be the same type as the mineral acid R1 used in the first tank or may be a different type.

  The concentration of the mineral acid R2 is preferably 0.50 to 4.00 mol / L (1 to 8N (normality)), more preferably 1.00 to 3.00 mol / L (2 to 6N), and particularly preferably 1 .75 to 2.25 mol / L (3.5 to 4.5 N).

(Stirring)
In the present embodiment, it is preferable to stir the slurry HC in the third tank in order to further increase the homogeneity of the silica composite particles to be produced. The strength of the stirring is not particularly limited, but stirring is preferably performed so that the Reynolds number (Re) of the slurry HB is 4000 to 16000, and stirring is preferably performed to 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

(Passing time)
In relation to the Reynolds number of the slurry HC in the third tank being in the range of 4000 to 16000, it is preferable to adjust the passage time of the slurry HC in the third tank to be 2 to 20 minutes. It is more preferable to adjust so that it may become 4-18 minutes, and it is especially preferable to adjust so that it may become 8-12 minutes. In the present embodiment, the slurry HC continuously flows from the second tank into the third tank, and the addition of the mineral acid R2 is also continuously performed. Therefore, the slurry HC flows during the passage time. It is the same as the time from the beginning to the outflow. In addition, the passage time of the slurry HC is a calculated time from the addition of the mineral acid R2 to the outflow from the third tank.

  In this embodiment, the addition rate of the mineral acid R2 is not particularly limited, and the total addition amount of the mineral acid R1 and the mineral acid R2 (pH of the slurry HD in the fourth tank), the mineral acid R2 It can be appropriately determined from the addition ratio, the passage time of the slurry HC, and the like.

(temperature)
In this embodiment, the temperature of the slurry HC in the third tank is not particularly limited, but is preferably 50 to 100 ° C, more preferably 70 to 100 ° C, and particularly preferably 80 to 100 ° C.

(Slurry transfer)
In the present embodiment, the method for moving the slurry HC in the third tank to the fourth tank is not particularly limited. For example, the method is similar to the method for moving the slurry HA in the first tank to the second tank. A method is mentioned.

(4th tank)
In the present embodiment, the slurry HD in the fourth tank is composed only of the slurry HC in the third tank that has moved, and no new inorganic particles, alkali silicate, sulfuric acid, or the like is added.

  In the present embodiment, silica is composited with inorganic particles or the like by the silica sol generated in the third tank to form silica composite particles.

(Stirring intensity)
In the present embodiment, it is preferable to stir the slurry HD in order to promote the silica composite uniformly. The strength of the stirring is not particularly limited, but stirring is preferably performed so that the Reynolds number (Re) of the slurry HD is 4000 to 16000, and stirring is preferably performed to 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

(Passing time)
In the present embodiment, in relation to limiting the total addition amount of mineral acid R1 and mineral acid R2 to the above-mentioned pH range and setting the amount of mineral acid R2 to 52 to 82% by volume of the total addition amount, The passage time of the slurry HD in the fourth tank is preferably adjusted to be 20 to 50 minutes, more preferably adjusted to 25 to 45 minutes, and adjusted to be 30 to 40 minutes. It is particularly preferable to do this. The passage time of the slurry HD is a calculated time from when the slurry HD (HD) flows into the fourth tank until it flows out.

(temperature)
In the present embodiment, the temperature of the slurry HD in the fourth tank is not particularly limited, but is preferably 50 to 100 ° C, more preferably 60 to 100 ° C, and particularly preferably 70 to 100 ° C.

(Slurry transfer)
In this embodiment, the method of moving the slurry HD in the fourth tank from the fourth tank to other equipment such as a dehydrator is not particularly limited. For example, the fourth tank and other equipment And the slurry HD can be moved through the pipe.

(Other processes)
The slurry HD that has flowed out of the fourth tank is suitably controlled in terms of average particle size, particle size distribution, degree of wear, and the like. Therefore, according to the above production method, it is suitable for use as a filler or pigment for papermaking. Silica composite particles will be obtained continuously.

(Silica composite particles)
The silica composite particles of the present embodiment are obtained by adhering a plurality of particulate silicas of about 10 to 20 nm on the surface of inorganic particles or the like. The particle diameter of the silica can be adjusted, for example, by adjusting the stirring strength, temperature, etc. of the slurry HA, HB, HC, HD.

(Particle size)
The silica composite particles obtained by the above production method have a volume average particle diameter of preferably 2.0. It is-10.0 micrometers, More preferably, it is 3.0-5.0 micrometers, Most preferably, it is 3.4-4.3 micrometers. When the volume average particle diameter of the silica composite particles is less than 2.0 μm, the effect of the silica composite is not sufficiently exhibited. For example, when used as a filler for papermaking, the effect of improving the opacity of the coated paper is sufficient. May not be obtained. On the other hand, when the volume average particle diameter of the silica composite particles exceeds 10.0 μm, when used as a filler for papermaking, it leads to a decrease in tensile strength, a decrease in tearing strength, etc. There is a possibility that the equipment will be polluted.

Further, in the silica composite particles produced by the production method of the present embodiment, the proportion of small particles having a particle size of 1 μm or less is preferably 0 to 2%, more preferably 0 to 1.5%, particularly preferably 0 to 0%. 1.0%. On the other hand, the ratio of large particles having a particle size of 10 μm or more is preferably 4 to 16%, more preferably 6 to 14%, and particularly preferably 8 to 12%.
As described above, in the present invention, the particle diameter of 2 to 10 μm preferably has a sharp particle size distribution in which 70% or more of the composite particles are contained, and more preferably 75% or more. Composite particles having such a particle size distribution cannot be produced by a conventional batch method, and in the case of a batch method, it is necessary to classify the composite particles to make the particle size distribution uniform. In this method, a classification process is required and the process becomes complicated, the composite particles are broken by the classification process and fine particles are easily generated, and the composite particles removed by the classification are not used as a filler. It is inferior and has a high environmental impact. However, when the above-mentioned continuous production method is used, small-sized inorganic particles and the like are glued to other inorganic particles and the like in the first tank, so that the number of small-sized silica composite particles is reduced and the particle size distribution is sharp. Composite particles can be produced. That is, it is possible to obtain composite particles having a sharp particle size distribution in which the composite particles having a particle size of 2 to 10 μm are 70% or more, further 75% or more. In addition, the silica composite regenerated particles produced in batch mode and having the same particle size by classification are easy to break the composite particles in the classification process, and the opacity decreases quickly.Even if the particle size distribution is sharp, sufficient opacity is achieved. Improvement effect is difficult to obtain. In contrast, the silica composite particles produced by the continuous production method have not undergone the classification process, and the composite particles are not subject to excessive mechanical stress, so the composite particles are difficult to break and a particularly high opacity improvement effect is obtained. Therefore, it is preferable.

(Ratio of silica component)
In the silica composite particles of the present embodiment, the ratio of the silica component is preferably 10.0 to 50.0% by mass, more preferably 41.0 to 49.0% by mass, and particularly preferably 42.0 to 48.0%. % By 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.

  This completes the description of the technology for continuously producing silica composite particles. By using silica composite particles produced by this technology as a filler for the base paper, composite particles with a particle size of 2 to 10 μm become 70% or more, and more than 75%, so the printing opacity of coated paper is further improved. Can be made.

  Although the compounding quantity of the filler in a base paper is not specifically limited, 11-25 mass% is preferable with an ash content in paper, and 13-22 mass% is more preferable. If the ash content in the paper is less than 11% by mass, the tendency of the opacity of the resulting coated paper to be difficult to improve becomes significant. If the ash content in the paper exceeds 25% by mass, the rigidity of the resulting coated paper tends to decrease, such being undesirable. The ash content of the present invention is a value measured according to JISP8251 “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method”.

  In the present embodiment, various additives may be internally added to the raw material pulp. For example, normal coatings such as internal sizing agents, paper strength improvers, paper thickness improvers, yield improvers (water-soluble polymers such as various synthetic polymers and starches), and fixing agents for raw pulp Various additives to be blended with the base paper of the working paper can be internally added by adjusting the kind and blending amount thereof.

(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. Examples of the twin wire former include a hybrid former and a gap former. Among these, the gap former that immediately sandwiches the paper jet ejected from the head box with two wires can be dehydrated without destroying the formation of the wet paper. This is preferable because a coated paper having uniform bulkiness can be obtained.

In addition, the gap former is characterized in that the fine fibers in the wet paper are easily removed because it dehydrates rapidly from both sides of the wet paper. Since the strength of the base paper is reduced when the fine fibers are removed, the feature of the gap former that the fine fibers in the wet paper are easily removed is generally a demerit. However, the feature of the gap former that the fine fibers in the wet paper are easily removed is advantageous in the present embodiment for the following reasons. That is, in this embodiment, as will be described later, when a sealing layer mainly composed of a water-soluble polymer is provided, the fine fibers are removed by the gap former and the water absorption due to the capillary phenomenon is reduced, so that the water-soluble property is reduced. The polymer is less likely to penetrate into the base paper. As a result, since the surface of the base paper can be covered with the water-soluble polymer, the effect of the pigment to be applied next and the coating liquid containing the water-soluble polymer as a main component is less likely to penetrate into the base paper. Is obtained. As a result, the effect of the pigment particles of the coating layer covering the surface of the coated paper (hereinafter referred to as the covering effect) is improved, so that the flatness of the coated paper is improved and the white paper glossiness and printing glossiness are improved. Can be improved.
In general, when fine fibers are removed, the network between the fibers increases and the yield of the filler decreases, but the filler used in the present invention is a composite particle, and the particle surface has more irregularities than a general filler. The composite particles are easily caught in the network between the fibers. For this reason, even if a fine fiber falls out, a filler yield can be maintained high, while the above-mentioned covering effect can be obtained.

It should be noted that the effect of the present embodiment is noticeable in coated paper having a paper thickness of 60 μm or less, particularly 30 to 60 μm. The coated paper having a paper thickness of 30 to 60 μm is less likely to obtain opacity because the paper thickness is lower than that of the coated paper exceeding 60 μm, and the effect of improving opacity appears remarkably when the composite filler of the present invention is used. .
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 the present embodiment, the basis weight measured in accordance with “Paper and paperboard—basis weight measuring method” described in JIS P 8124: 1998 is 60 g / m ² or less, particularly 30 to 60 g / m. It is preferable to adjust so as to be ² . Coated paper having a basis weight of 30 to 60 g / m ² is, 60 g / m ² as compared to coated paper exceeded due to the low basis weight hardly opacity obtained, opacity using the composite filler of the present invention The improvement effect appears remarkably.
If the paper thickness exceeds 60 μm or the basis weight exceeds 60 g / m ² , the opacity increases in the first place. Therefore, there is a possibility that the necessary and sufficient opacity may be achieved without using this embodiment. .

(Sealing layer)
You may provide the sealing layer which has a water-soluble polymer as a main component as an adhesive agent on both surfaces of the said base paper. When a sealing layer mainly composed of a water-soluble polymer is provided on a base paper containing composite particles that has been made using a gap former, the composite particles in the base paper are fixed by the water-soluble polymer, so that It becomes difficult for the composite particles to fall off from the mesh. For this reason, even if the subsequent top coating liquid is applied, the composite particles do not move due to the migration of the paint, and high opacity is obtained, which is preferable.
In addition, if the coating layer contains a water-soluble polymer as an adhesive, the pigment will not easily penetrate into the base paper and the sealing coating layer, so it has excellent white paper gloss, printing gloss, and printing opacity. Coated paper can be obtained. This is particularly noticeable when the coating layer and the sealing layer are provided with an on-machine coating machine. In other words, in the on-machine coating machine, the sealing layer is dried in the drying process, and the coating layer is applied in a state where the paper surface temperature is high and the sealing layer is softened. It is because it penetrates easily.

A method for applying a coating liquid for providing a sealing layer (hereinafter referred to as a sealing liquid) is not particularly limited, and for example, a film transfer coating method, a gate roll coating method, or the like can be used. In the present embodiment, the coating amount of the sealing layer is not particularly limited, but the coating amount of the sealing layer is preferably about 0.1 to 5.0 g / m ^{2 on} both sides, and further on both sides. It is more preferable to set it as 0.2-2.0 g / m < ² >. If the coating amount of the sealing layer is less than 0.1 g / m ² per both sides, it becomes difficult to obtain the sealing effect of the sealing layer, and the covering effect is lowered, so that the printing glossiness is lowered. If the coating amount of the sealing layer exceeds 5.0 g / m ² per both sides, the fluidity of the sealing liquid is deteriorated, which may make uniform coating difficult, which is not preferable.

  The sealing layer preferably contains 95% by mass or more of a water-soluble polymer. The sealing layer in the present embodiment uses a water-soluble polymer having a high sealing effect as a main component, thereby improving the covering effect and improving the printing gloss. When the ratio of the water-soluble polymer is less than 95% by mass, the sealing effect of the sealing layer is difficult to be obtained, and the covering effect is likely to be lowered, so that the printing glossiness is likely to be lowered. Further, when a water-insoluble polymer such as latex is used as a main component, the sealing effect of the sealing layer is difficult to be obtained, and the covering effect tends to be lowered, so that the printing glossiness is likely to be lowered.

  There is no restriction | limiting in particular in the water-soluble polymer contained as a main component in the said sealing liquid, The thing generally used for a papermaking use can be used. Examples of water-soluble polymers used in the above-mentioned sealing 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 starch. , Starch such as hydroxyethyl starch, cationized starch, acetylated starch and oxidized starch, and starches (hereinafter referred to as starch and the like). 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 sealing base paper) after the sealing layer mainly composed of the water-soluble polymer is provided, the sealing base paper is It is preferable to perform a flattening process (hereinafter referred to as a flattening process). Since the surface roughness of the sealing base paper can be reduced by planarizing the sealing base paper before providing the coating layer, the sealing effect is further enhanced. In particular, when a sealing layer is provided by a film transfer method, a peeling pattern (split pattern) is likely to occur when peeling from a roll, and even if a coating layer is provided thereon, it is difficult to obtain a sufficient covering effect. For this reason, by performing the flattening process on the sealing base paper, it is possible to further improve the covering effect and the print glossiness, and to further reduce the breakthrough of ink during printing. The conditions for the flattening treatment of the sealing base paper are not particularly limited. However, the nip pressure is preferably 10 to 80 kN / m and the temperature is preferably 20 to 150 ° C., and the nip pressure is 50 kN / m and the temperature is 50 ° C. Is more preferable.
In general, when a pressurizing process using a calendar is performed, the gap between pulp fibers is reduced, so that the diffusion of visible light is suppressed and the opacity tends to decrease. However, as described above, silica composite calcium carbonate and silica composite regenerated particles are harder than silica composite clay and silica composite talc as composite particles, so that composite particles are not easily broken even when pressed by a pre-calender. Since transparency is obtained, it is preferable.

(Coating layer)
A coating layer mainly composed of a pigment and an adhesive is provided on the surface of the sealing base paper. The coating layer is provided by applying a coating liquid mainly composed of a pigment and an adhesive (hereinafter referred to as a top coating liquid) to the surface of the sealing base paper. 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 coating layer contains at least either kaolin clay or calcium carbonate, and the kaolin clay or calcium carbonate satisfies the following.
(A) 50 to 100% by mass of all pigments (B) particles having a particle size of 0.5 to 2.0 μm occupy 25 to 80% by mass (C) particles having a particle size of less than 0.5 μm The reason why this kaolin clay or calcium carbonate in which the ratio of the total mass of particles having a particle diameter of less than 2.0 μm to the total mass is 1.3 to 10.0 will be described below.

  The wavelength of visible light is 380 to 750 nm. If particles having a particle diameter of less than 380 nm (0.38 μm) are used as a pigment, visible light is transmitted without colliding with the particles depending on the phase, and thus 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 opacity of the coated paper does not improve as the pigment particle size increases. As a result of intensive research, the inventors have found that when the pore diameter of the coating layer of the coated paper is about half the wavelength of visible light (150 to 400 nm), the scattering of visible light can be particularly improved. I found it. That is, by providing a coating layer having many pore diameters of 150 to 400 nm on the surface of the coated paper, the scattering of visible light was particularly improved, and a coated paper having high opacity could be obtained.

  The reason why the opacity of the coated paper does not improve as the pigment particle size is increased is that when the pore diameter is larger than half the wavelength (400 nm), the visible light may pass through the pores. Although high, the size of the pores on the surface of the coated paper increases and the number of pores decreases, so that visible light scattering hardly occurs. For this reason, it is considered that the opacity of the coated paper is not sufficiently improved. As a factor that the pore diameter becomes larger than 400 nm, it is considered that pigment particles having a large particle diameter are used. For example, when many particles having a particle diameter exceeding 2.0 μm are contained, the pore diameter is considered to be too large. .

  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. For this reason, it is considered that the opacity of the coated paper is not sufficiently improved. A coating layer having a pore diameter smaller than 150 nm is considered to be easily generated when a pigment having a particle diameter smaller than 500 nm is used. Therefore, in the present invention, as described above, the particle diameter is 0.5 μm to 2. A particle having a particle size of 0 μm is 25 to 80% by mass, preferably 30 to 60% by mass, based on the whole particle. If the particle diameter of the pigment is less than 380 nm (0.38 μm), as described above, visible light is transmitted without colliding with the particle depending on the phase, and it is difficult for visible light to scatter. The opacity of the coated paper decreases.

  In this embodiment, in order to provide a coating layer having many pore diameters of 150 to 400 nm on the surface of the coated paper, the particle size distribution is a specific range (hereinafter referred to as the optimum particle size range), A pigment having a ratio of the total mass of particles within the optimum particle diameter range (hereinafter referred to as a “particle mass ratio”) within a specific range and a sharp particle size distribution is used. The reason will be described in detail below.

In this embodiment, the sharpness of the particle size distribution is “the particle size is less than the maximum value of the particle size optimum range” relative to “the total mass m _min of the particles whose particle size is less than the minimum value of the particle size optimum range”. total mass m _max ratio of "of a particle, i.e.," particle size, the total mass m _max "of less than the maximum value of the particle size optimum range particles" particle size, less than the minimum particle size optimum range It is defined by a value obtained by dividing by the “total mass m _min of a certain particle” (hereinafter referred to as particle mass ratio). The particle mass ratio is preferably 1.3 or more and 10.0 or less, and more preferably 1.5 or more and 5.0 or less. When a coated paper is produced using a pigment having a particle mass ratio of 1.3 or more (that is, a pigment having a sharp particle size distribution), variation in the size of pores on the surface of the coating layer can be suppressed. On the other hand, when a coated paper is produced using a pigment having a particle mass ratio of less than 1.3 (that is, a pigment having a particle size distribution that is not sharp), the tendency of the pore size size on the coated paper surface to vary becomes significant. . When the particle mass ratio exceeds 10.0, the particle size distribution becomes sharp, and the tendency to reduce the variation in the size of the pore diameter on the coated paper surface becomes prominent. Inferior in terms.

  Moreover, the size of the pore diameter of the coated paper surface can be adjusted by defining the optimum range of particle diameter and the particle mass ratio. That is, the surface of the coated paper is made fine by producing the coated paper using a pigment having the particle mass ratio adjusted as described above and the particle size optimum range and the particle mass ratio adjusted to an arbitrary range. It is possible to suppress variation in pore size and adjust the pore size to an arbitrary range. In the present embodiment, the optimum particle size range is preferably 0.5 μm or more and less than 2.0 μm. And the pigment whose particle | grain mass ratio is 70 mass% or more is preferable, and the pigment which is 75 mass% or more is more preferable. That is, a coated paper using a pigment having a particle mass ratio of 1.3 or more, an optimum particle size range of 0.5 μm or more and less than 2.0 μm, and a particle mass ratio adjusted to 70% by mass or more. By producing a coated paper, a coated paper having a large pore diameter of 150 to 400 nm can be obtained.

(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, kaolin clay is preferable because the ink set can be made relatively gentle and the printing glossiness is easily improved. On the other hand, amorphous silica having a relatively large pore volume has a tendency that the ink gloss is too early and print gloss and print opacity are lowered. These effects are particularly remarkable when the kaolin clay is 50 to 100% by mass, preferably 65 to 80% by mass, among the pigments used in the coating layer.

  In this embodiment, it is preferable to contain a water-soluble polymer as an adhesive in the coating layer. As described above, this is because the pigment does not easily penetrate into the base paper and the sealing coating layer, and a resin (for example, latex, etc.) that increases the fluidity of the coating liquid is used as an adhesive in the overcoating liquid. Even if it is used, the fine pigment particles in the topcoat coating liquid are difficult to penetrate into the filler layer and the base paper, and the printing glossiness is hardly lowered. In the present invention, by adding 0.1 to 10 parts by mass of a water-soluble polymer as an adhesive in the topcoat coating liquid with respect to 100 parts by mass of the pigment, the fine pigment particles in the topcoat coating liquid are used as a filler layer. In addition to preventing penetration into the base paper, it is also easy to prevent sinking of pigment particles having an optimum particle size range of 0.5 μm or more and 2.0 μm and a particle mass ratio of 70% by mass or more. Printing gloss can be improved.

  The water-soluble polymer that can be used as the adhesive in the topcoat coating liquid is not particularly limited, and those that can be generally used for papermaking can be used. Examples of water-soluble polymers that can be used as an adhesive in the top coating liquid include starches such as oxidized starch, urea phosphated starch and hydroxyethylated starch, and cellulose-based water-soluble such as carboxymethylcellulose. A functional polymer. One or more of these water-soluble polymers can be appropriately selected and used.

The blending ratio of the water-soluble polymer used as the adhesive in the topcoat coating solution is preferably 0.1 to 10 parts by weight, and 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the pigment in the coating layer. Part is more preferred. As an adhesive for the coating layer, the viscosity of the coating liquid can be improved by adding 0.1 to 10 parts by mass of the water-soluble polymer to the pigment, and the B-type viscosity is 3,000 to 5, Since it can be adjusted to 000 cps and thereby a coating layer having many pores of 150 to 400 nm can be formed, a coated paper excellent in opacity can be obtained. It is preferable to contain a water retention agent in this topcoat coating solution and adjust the water retention to 200 g / m ² or less, preferably 150 g / m ² or less, particularly preferably 100 g / m ² or less. In this case, the water in the topcoat coating liquid is difficult to be absorbed by the sealing base paper, and the penetration of fine pigment particles into the sealing base paper accompanying the movement of moisture can be suppressed, and the opacity is easily improved.
In addition, when the blending ratio of the water-soluble polymer used as the adhesive in the topcoat coating solution is less than 0.1 parts by mass, the tendency to decrease the printing opacity becomes remarkable. If the blending ratio of the water-soluble polymer used as the adhesive in the topcoat coating solution exceeds 10 parts by mass, the viscosity of the coating solution will increase excessively, so that coating unevenness is likely to occur, and blank paper glossiness Since the tendency to decrease becomes remarkable, it is not preferable. Similarly, when the viscosity of the coating liquid is outside 3,000 to 5,000 cps, uneven coating tends to occur.
The concentration of the top coating liquid is preferably 60.0 to 71.0% by mass, more preferably 65.0 to 70.5% by mass, and particularly preferably 67.0 to 70.0% by mass. When coating is performed at this concentration, a coating layer having many pores of 150 to 400 nm can be formed, and thus coated paper having excellent opacity can be obtained.

The coating amount (solid content) of the coated paper according to this embodiment is not particularly limited, but in order to obtain an opacity improvement effect by a coating layer having many pores of 150 to 400 nm, the coating amount is one side. It is preferably 5 g / m ² or more per unit. If it is less than 5 g / m ² , not only the coating layer has few pores and the effect of improving opacity is difficult to obtain, but the coating layer cannot sufficiently cover the base paper, and the base paper-derived pores are coated. There is a possibility that printability on the surface of paper will be reduced. The upper limit of the coating amount is not particularly limited, but if it exceeds 20 g / m ² per side, the effect of improving opacity reaches its peak, and 20 g / m ² or less is preferable.
In general, the opacity increases as the coating layer increases. Therefore, if the coating amount is increased and the coating layer is thickened, there is a possibility that the necessary and sufficient opacity can be achieved without depending on this embodiment. However, if the coating amount is excessively increased, coating unevenness occurs or the cost is increased. Therefore, by using the pigment according to the present embodiment, it is possible to obtain coated paper having high 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 to 70% or more, and it is more preferable to adjust the coated paper which concerns on this embodiment to 75% or more with the said various adjuvants. This is because if the whiteness is 70% or more, visible light is easily transmitted and it is difficult to improve the opacity, and the opacity improvement effect of the present invention becomes remarkable. If the whiteness is less than 70%, the opacity becomes high in the first place, so that there is a possibility that the necessary and sufficient opacity can be achieved without using this embodiment. In addition, the whiteness said here is the value measured based on JISP8148: 2001 "The measuring method of paper, paperboard, and pulp-ISO whiteness (diffuse blue light reflectance)".

(Manufacturing procedure)
First, NBKP, LBKP, and BTMP were mixed as raw pulps at the ratios shown in Table 1 or Table 2. 100 parts by mass (absolute dry amount) of this pulp, each with a solid content, the type and amount of filler described in Table 1 or Table 2, and internal sizing agent (Product No .: AK-720H, manufactured by Harima Chemicals Co., Ltd.) 0 0.05% by mass, cationized starch (product number: Amilofax T-2600, manufactured by Abebe Japan) 1.0% by mass, and yield improver (product number: NP442, manufactured by Nissan Eka Chemicals) 0.02% by mass Thus, a pulp slurry was obtained. Silica composite regenerated particles used as a filler were produced by the method described in Production Example 1 of Japanese Patent Application No. 2010-077671. Silica composite calcium carbonate and silica composite talc were produced by the same method as the continuous production method of silica composite regenerated particles described above, except that heavy calcium carbonate and talc were used for inorganic particles and the like. The regenerated particles used in Example 16 were produced by the method of Japanese Patent No. 4087431 and Production Example 1. The silica composite regenerated particles used in Examples 18 and 19 were produced in a batch manner by the method described in Japanese Patent No. 4087431 and Production Example 1. In Example 19, classification treatment was further carried out so that particles having a particle diameter of 2 to 10 μm were adjusted to 70% by mass. In Examples 23 to 30, classification treatment was carried out after continuous production, and the treated silica composite regenerated particles were mixed so that the particle size ratio shown in the table was obtained.

Paper making the pulp slurry in the wire part, and then to produce a press part, base paper having a basis weight of about 39~41g / m ² was subjected to the pre-dryer part. In the wire part, paper was made by the gap former method. Next, in the undercoater part, the sealing solution was applied by a film transfer coating method so that the sealing layer mainly composed of oxidized starch was 1.0 g / m ² per side.

  Next, the base paper provided with a sealing layer on both sides is provided to an after dryer part, and after this sealing base paper is dried, a flattening treatment (pre-treatment is performed under conditions of a nip pressure of 25 kN / m and a roll temperature of 70 ° C. Calendar).

Next, in the top coater part, a coating layer containing the pigment described in Table 1 or Table 2 and oxidized starch (adhesive) having an amount described in Table 1 or Table 2 with respect to 100 parts by mass of the pigment is provided. The top coating solution was applied by a blade coating method so as to be 7 g / m ² per side to produce a coated paper having a basis weight of 44 g / m ² and a paper thickness of 47 μm. The pigment of the coating layer was made to contain kaolin clay in the content ratio shown in the table, calcium carbonate was used as the remaining pigment, and the total amount was 100 parts by mass. In Example 22, calcium carbonate was contained in the content ratio shown in the table, and kaolin clay was used as the remaining pigment so that the total amount was 100 parts by mass.

  The adhesives and pigments shown in Table 1 or Table 2 are as follows.

<Filler>
Calcium carbonate (Product number: Hydro curve 90, manufactured by Omiya Korea, average particle size: 1.3 μm)
・ Talc (Product number: Talc NTL, manufactured by Nippon Talc Co., Ltd., average particle size: 12 μm)
-Aggregated calcium carbonate (Product No .: TP-NPF, manufactured by Okutama Kogyo Co., Ltd.)
<Seamless layer>
(adhesive)
・ Oxidized starch (Product No .: Mermaid M-200, manufactured by Sankisha)

<Coating layer>
(adhesive)
・ Oxidized starch (Product No .: Mermaid M-200, manufactured by Sankisha)
(Pigment)
・ Calcium carbonate (Product No .: Hydro Curve 60, manufactured by Omiya Korea)
・ Kaolin clay (Product number: Contour Xtreme, manufactured by Imeris)
Since the above pigment has a particle diameter of 0.5 μm to 2.0 μm and less than 25% by mass, using a sieving and wet pulverizer (product number: planetary mill, manufactured by Seishin Enterprise), less than 0.5 μm described in the table And a particle ratio of less than 2.0 μm.

(Evaluation methods)
(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) Runk ratio JIS P 8220: For the pulp fibers obtained by releasing the coated paper in accordance with 1998 “pulp fiber disaggregation method”, the cell wall thickness was measured using a fiber length distribution measuring device (trade name: FiberLab) manufactured by Kajaani. The fiber lumen diameter was determined, and the Runkel ratio was calculated by the following formula.
Runkel ratio = 2 × fiber wall thickness / fiber lumen diameter

(D) Stiffness Measured in the longitudinal direction (paper making direction) in accordance with JIS P 8143: 1996 “Paper—Stiffness Test Method—Clark Stiffness Tester Method”.
A rigidity of 7.5 or higher is excellent in rigidity, 7.0 or higher is good in rigidity, and 6.5 or higher is a lower limit level that can be used although it has rigidity.

(E) Opacity (blank paper)
Measured according to JIS P 8149: 2000 “Paper and paperboard—Opacity test method (backing of paper) —Diffusion illumination method”.
An opacity of 85% or more is excellent in opacity, 80% or more is good in opacity, and less than 80% is inferior in opacity.

(F) Opacity (printing)
Printing was performed on the coated paper under the following conditions to produce a print test specimen.
・ Printing machine: RI-3 type, manufactured by Meisei Seisakusho Co., Ltd. ・ Ink: WebRexNouverHIMARK process, 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.
An opacity of 73% or more is excellent in opacity, 70% or more is good in opacity, 67% or more is opacity but is a lower limit level that can be used, and less than 67% is inferior in opacity.

(G) Glossiness (blank paper)
Measured according to JIS P 8142: 2005 “Paper and paperboard—Measurement method of 75 degree specular gloss”.
A glossiness of 18% or more is excellent in glossiness, 15% or more is good in glossiness, 12% or more is glossy, but is a lower limit level that can be used, and less than 12% is inferior in glossiness.

(H) Glossiness (printing)
About the above-mentioned printing test body, it measured based on JISP8142: 2005 "The measuring method of paper and paperboard -75 degree specular gloss".
A glossiness of 35% or more is excellent in glossiness, 30% or more is good in glossiness, 25% or more is glossy, but is a lower limit level that can be used, and less than 25% is inferior in glossiness.

(I) Blister resistance An oil bath (silicon oil) adjusted to 200 ° C. after preparing the above-mentioned printing test specimen in a flow direction of 2 cm and a width direction of 10 cm, adjusting the humidity under conditions of 23 ° C. and 50% RH for 24 hours. ) For 4 seconds. This test was performed three times, and the occurrence of blisters was visually evaluated as follows.
A: There is no generation of blisters and the appearance is excellent.
○: Although blisters are slightly generated, actual use is possible.
Δ: The lowest level at which actual use is possible although some blistering occurred.

(J) Particle size and particle size distribution The particle size distribution was measured with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200 type” manufactured by Shimadzu Corporation). 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.

  ADVANTAGE OF THE INVENTION According to this invention, the coated paper which has high opacity can be provided at low cost, For example, it can utilize for the coated paper for printing used by offset printing, gravure printing, etc.

Claims (3)

A coated paper comprising a base paper and a coating layer mainly composed of a pigment and an adhesive provided on the base paper,
The base paper contains composite particles in which at least inorganic particles are combined,
As the pigment, at least either kaolin clay or calcium carbonate is contained, and the kaolin clay or calcium carbonate satisfies the following:
(A) 50 to 100% by mass of all pigments (B) particles having a particle size of 0.5 to 2.0 μm occupy 25 to 80% by mass (C) particles having a particle size of less than 0.5 μm The ratio of the total mass of particles having a particle diameter of less than 2.0 μm to the total mass is 1.3 to 10.0.   2. The coating according to claim 1, wherein the adhesive contains a water-soluble polymer, and the water-soluble polymer is contained in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the pigment. Craft paper.   The composite particles are regenerated particles obtained by dehydrating, drying, firing and pulverizing paper sludge, silica composite calcium carbonate particles in which calcium carbonate and silica are combined, and the regenerated particles and silica are combined. The coated paper according to claim 1, wherein the coated paper is at least one kind of silica composite regenerated particles.