JP5571927B2 - Coated paper - Google Patents

Description

The present invention does not deteriorate the appearance even when the coated paper is 1 kg (reduced by about 6 to 16 g / m ² ), and is excellent in whiteness, white paper gloss, opacity, stiffness and printability. Regarding paper. In particular, the present invention relates to a coated paper having a basis weight of 111 to 121 g / m ² .

  In recent years, due to efforts to reduce environmental impact and reduce carbon dioxide emissions through resource conservation, in the paper field, while maintaining the same level of quality (whiteness, white paper glossiness, stiffness, opacity), more There is a need for lightweight paper. In the coated paper field, it is necessary to satisfy the printing gloss level in order to obtain a high-definition printed matter.

  The coated paper can be used for art paper (A1 grade), coated paper (A2 grade), lightweight coated paper (depending on the amount of coating liquid applied, the degree of flattening of the coating layer surface, and the required quality. A3 grade), finely coated paper, and A1 grade coated paper is required for high-definition printing such as high-quality art books, magazine covers, pictures, calendars, posters, labels, and cigarette packaging. A2 grade coated paper is used for commercial printing etc. that need to look good in catalogs, brochures, etc., A3 grade coated paper and fine coated paper are used for commercial printing such as flyers, etc. Has been used.

  Under the recent recession, the demand for cheaper coated paper is increasing. Cheaper paper is paper that has less weight (basis weight) per unit area. However, simply reducing the basis weight of the paper has the problems of reducing the paper thickness (paper thickness) and appearance (whiteness and white paper gloss), as well as opacity, stiffness (paper stiffness), and printability. Also decreases.

In particular, A2 grade coated paper, currently ^{84.9g / m 2, 104.7g / m} 2, although the basis weight of ^{127.9g / m 2, 157g / m} 2 is typical, these coating in the paper, for example, using 104.7 g / ^{m 2} as an alternative to the coated paper 127.9 g / ^{m 2,} a basis weight when about 23 g / ^{m 2} to reduce the thickness of the paper described above, appearance (whiteness and (Glossiness of white paper) is easily reduced, and opacity, stiffness (paper stiffness), and printability are also reduced.

Therefore, compared with these conventional basis weight products, paper thickness, appearance (whiteness and white paper glossiness), rigidity and opacity are good, and printability is similar, but basis weight is reduced. Although the demand for coated paper is increasing, the method of simply reducing the basis weight while maintaining the above-mentioned quality has the limit of reducing the basis weight by about 5 g / m ² .

  As a technique to improve the glossiness of the coated paper, the printing surface of the coated paper is flattened by applying a flattening process (calendar process) to the coating layer using a flattening facility consisting of a metal roll or elastic roll. Although the method is general, according to this method, the coated paper is liable to be crushed and not only the paper thickness but also the stiffness is lowered.

  As a technique for preventing a decrease in paper thickness, there is a method of improving the paper thickness by adding a bulking agent (see Cited Document 1), but the bulking agent is a chemical that inhibits fiber-to-fiber bonding. There is a problem that blisters are likely to occur during printing. In particular, blisters are a serious quality defect in coated paper used for relatively high-grade printing such as A2 coated paper, and generally blisters are more likely to occur as the basis weight increases. There is a problem that blisters are likely to occur as compared to A3 coated paper and fine coated paper with low basis weight, and it is not preferable to contain a bulking agent. There is a method to contain mechanical pulp to improve paper thickness and opacity, but mechanical pulp is rigid, and if it is contained in a large amount of about 35% by mass or more of the total pulp, fluffing and roughening (fibers emerge after printing) Is likely to occur, and printability is likely to deteriorate.

In order to obtain coated paper with good printability, it is common to increase the coating amount, but the coating layer made of inorganic particles has a higher density and lower bulk than the base paper made of pulp, It is difficult to achieve a sufficient paper thickness.
In order to obtain coated paper with high opacity, it is common to increase the filler content. However, since the filler inhibits the entanglement of the pulp fibers, the internal strength of the base paper decreases as the content increases. As a result, there are problems such as blister defects at the time of printing, and printing omission (picking) in the printed matter due to weakened strength of the coated paper surface.

As mentioned above, especially to reduce the basis weight while maintaining the paper thickness, appearance (blank gloss and print gloss), opacity, printability, and stiffness, a decrease of about 5 g / m ² is the limit. Met. For example, a coated paper that has maintained the above-mentioned quality even if the basis weight is reduced by about 6 g / m ² or more, further 10 g / m ² or more, particularly about 16 g / m ² has not yet been obtained.

JP 2005-248379 A JP 2009-079327 A

The main problem to be solved by the present invention is that the basis weight is 111 to 121 g / m ² and the coated paper has a low basis weight, but the basis weight is 6 g / m ² or more, more preferably 10 g / m ² or more. Compared with coated paper as high as 16 g / m ² or more, a coated paper having sufficient paper thickness, good white paper gloss, and in which whiteness, opacity, printability and rigidity are not reduced. Is to provide.

The present invention is a coated paper provided with a coating layer containing a pigment and an adhesive on a base paper, and has a basis weight of 111 to 121 g / m ² , a paper thickness of 90 to 110 μm, JIS P 8142: 2005. Paper and paperboard-Pulp fibers having a blank paper glossiness of 70% or more in "Measurement method of 75-degree specular gloss" and disaggregating the coated paper according to JIS P 8220: 1998 "Pulp-Disaggregation method" The weight-weighted fiber length distribution is obtained, tabulated every 0.05 mm fiber length, and has a maximum value in the fiber length range of 0.10 mm to less than 0.65 mm, and the base paper is a silica composite regenerated particle as a filler Or it is a coated paper characterized by including a silica composite reproduction | regeneration particle | grain aggregate.

  The mass ratio of the coating layer to the base paper is preferably 0.23 to 0.34.

  The pigment contains at least clay and calcium carbonate, and the clay and calcium carbonate have a particle size distribution in the range of 0.1 μm or more and less than 1.0 μm, and 85% or more, preferably 90% or more of the total pigment. It is preferable to contain 15% or less, preferably 10% or less of the total pigment in the range of 0 μm or more and less than 10.0 μm.

  The base paper contains a filler, the blending amount of the filler is 2 to 10 parts by mass with respect to 100 parts by mass of the total pulp contained in the base paper, and the filler is composed of silica and inorganic particles other than silica. The composite particles are preferably.

  The coating layer is at least two layers, and the mass ratio of the coating amount of the outermost coating layer farthest from the base paper to the coating amount of the undercoat coating layer in contact with the base paper is 1.5 to It is preferable that it is 1.9.

According to the present invention, though it is coated paper having a basis weight of 111~121g / ^{m 2,} a basis weight of 6 g / ^{m 2} or more, further 10 g / ^{m 2} or more, especially 16g / ^{m 2} or more high 127.9g To provide a coated paper having sufficient paper thickness and good white paper gloss as compared with coated paper of / m ² , and in addition, whiteness, opacity, printability and rigidity are not reduced. Can do.

1 is a schematic diagram of a production facility for regenerated particles or regenerated particle aggregates preferably used in the present invention. It is a schematic diagram of a 2nd combustion furnace, (a) is a longitudinal cross-sectional view, (b) is an expanded view of an inner surface.

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

The coated paper of this embodiment is one in which a coating layer mainly composed of a pigment and an adhesive is provided on the front surface and / or the back surface of the base paper.
In the present invention, the fiber fibers obtained by disaggregating the coated paper according to JIS P 8220: 1998 “pulp-disaggregation method” are referred to as FiberLab. The centerline fiber length measured using (Kajaani) was defined as the fiber length.

  The Runkel ratio is also calculated using FiberLab. It is calculated from the fiber width and the fiber wall thickness measured by Kajaani. The Runkel ratio used in the present invention is R.K. O. H. Runkel in 1940 on Wachbl. Papierfabr. This is a parameter published in the magazine, and is calculated as (Runkel ratio) = (twice the fiber wall thickness) / (fiber lumen diameter). A larger Runkel ratio indicates a stiffer fiber.

(pulp)
For the pulp used in the present invention, the weight-weighted fiber length distribution is obtained for pulp fibers obtained by disaggregating the coated paper by JIS P 8220: 1998 “pulp-disaggregation method”, and the fiber length is determined every 0.05 mm. It is essential that the fiber lengths are aggregated and have a maximum value in a range of fiber length of 0.10 mm or more and less than 0.65 mm. The maximum value is preferably in the range of 0.15 mm or more and less than 0.60 mm, more preferably in the range of 0.20 mm or more and less than 0.55 mm. By setting the maximum value in the fiber length distribution of the pulp fiber within this range, the basis weight is 6 g / m while maintaining the white paper glossiness and paper thickness as well as printability, rigidity, whiteness and opacity. ² or more, further it can be 10 g / ^{m 2} or more, to reduce particularly 16g / ^{m 2} or more.

  If there are many fibers with a fiber length of less than 0.10 mm and the maximum value is not in the range of fiber lengths of 0.10 mm or more and less than 0.65 mm, the base paper is densely packed and the paper thickness is reduced because there are many fine fibers. Not only is it easy, but it is not preferable because sufficient rigidity is difficult to obtain. When there are many fibers with a fiber length of 0.65 mm or more and the maximum value is not in the range of fiber lengths of 0.10 mm or more and less than 0.65 mm, the paper thickness tends to increase partially due to many long fibers, Since roughening occurs and printing suitability (appearance after printing) tends to be inferior, it is not preferable. In addition, since the long fibers are easily raised on the surface of the coating layer, the glossiness of the white paper tends to be lowered.

  In order to suitably obtain a pulp fiber having a maximum fiber length distribution in the range of 0.10 mm or more and less than 0.65 mm, the freeness may be adjusted using a conventionally used beating method. For example, beater Conical refiners, cylindrical refiners, and disc refiners (SDR, DDR) can be used. For example, the freeness may be beaten to about 30 to 300 ml using DDR. The pulp fibers obtained by beating can also be used by mixing with other pulps having different fiber lengths, in which case the pulp fibers after mixing have a fiber length after disaggregation of 0.10 mm or more and 0.65 mm. What is necessary is just to adjust a compounding ratio with the other pulp from which fiber length differs so that it may have a maximum value in the range below.

In the present invention, the Runkel ratio of the disaggregated pulp is preferably 0.4 to 2.0, and more preferably 0.6 to 1.0. The larger the Runkel ratio (the larger the wall thickness), the more rigid the paper and the higher the paper thickness. On the other hand, the fuzzing and roughening deteriorates, the printability and white paper glossiness tend to decrease, and the Runkel ratio is small ( When the wall thickness is small, it is difficult to obtain sufficient paper thickness and rigidity. In the present invention, when the Runkel ratio is preferably 0.4 to 2.0, more preferably 0.6 to 1.0, paper thickness, opacity, white paper glossiness, and rigidity are high, and fluffing and roughening are performed. Therefore, it becomes easier to obtain a coated paper with less printability. For example, even if the Runkel ratio is less than 0.4 or exceeds 2.0, the basis weight may be reduced by 6 g / m ² or more, further 10 g / m ² or more, particularly 16 g / m ² or more. In addition, the appearance is not deteriorated, the paper thickness and the white paper glossiness are excellent, and furthermore, coated paper excellent in whiteness, opacity, rigidity and printability is easily obtained. If the Runkel ratio is less than 0.4, the coated paper having a basis weight of 111 to 121 g / m ² is not preferable because the paper thickness tends to be less than 90 μm and the rigidity tends to decrease. If the Runkel ratio exceeds 2.0, the paper thickness tends to increase, but it is not preferable because fuzzing or roughening tends to occur on the surface of the coating layer.

  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), and the beech, mizunara, wig, sharpness, and yachidamo have a small Runkel ratio (about 1-2), and the drunk, linden, gill, aspen, birch, and maple are Even smaller (about 1 or less).

It is essential that the pulp used in the present invention has a maximum value in the range where the fiber length of the pulp fiber obtained by disaggregation is 0.10 mm or more and less than 0.65 mm, and preferably the Runkel ratio is 0.4 to 2. It is preferable to use a conifer having a long fiber length so as to be 0.0, more preferably 0.6 to 1.0. In the present invention, even though the basis weight is 111 to 121 g / m ² , the paper thickness is 90 to 110 μm and has a sufficient paper thickness, so the strength such as tensile strength and tear strength is low. It becomes easy to become. In order to prevent the strength from being lowered, in the present invention, it is preferable to use a pulp having a Runker ratio of 0.4 to 2.0 (more preferably 0.6 to 1.0) after pulping.

  As a method for producing pulp from the above tree species, a method generally used for papermaking can be used, and chemical pulp, mechanical pulp, or the like can be used as pulp.

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

  Examples of the mechanical pulp include stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo grand pulp (TGP), ground pulp (GP), Thermo mechanical pulp (TMP), Chemi thermo mechanical pulp (CTMP), refiner mechanical pulp (RMP), etc. are mentioned. Among these, the use of thermomechanical pulp is preferable because there are few foreign matters and the strength (rigidity) of the paper is high.

  In addition, waste paper pulp regenerated from waste paper using chemical pulp or mechanical pulp can also be used, for example, disaggregated / deinked waste paper pulp manufactured from magazine waste paper, flyer waste paper, office waste paper, upper white waste paper, etc. Examples include disaggregation, deinking and bleached waste paper pulp.

  Among the above pulps, it is preferable to use mechanical pulp because short fiber lengths can be easily obtained and the fiber length after disaggregation tends to be in the range of 0.10 mm or more and less than 0.65 mm. In particular, when thermomechanical pulp or chemithermomechanical pulp is used, pulp and coated paper that have excellent fine appearance due to a large number of fine fibers having a fiber length after disaggregation of 0.10 mm or more and less than 0.65 mm but a small number of shives (binding fibers). Is preferable because it is easily obtained.

  In the raw material pulp of the present invention, for example, various additives that are usually blended in coated paper, such as an internal sizing agent, a paper strength enhancer, a paper thickness improver, a yield improver, etc. The amount can be adjusted appropriately and added internally.

(Filler)
The raw pulp preferably contains composite particles composed of silica and inorganic particles other than silica as an internal filler. The composite particles composed of silica and inorganic particles other than silica are different from the conventional calcium carbonate, talc, and clay in their constituent components and shape, and have excellent opacity, so the opacity of the coated paper is maintained. The amount of filler used in the base paper can be reduced. By reducing the filler content, the entanglement between the pulp fibers in the base paper becomes good, so that the rigidity and paper thickness of the resulting coated paper can be improved.
In addition to composite particles composed of silica and inorganic particles other than silica, fillers conventionally used in papermaking applications can be added as long as the effects of the present invention are not impaired. Examples of the filler include inorganic fillers such as light calcium carbonate, talc, titanium dioxide, clay, calcined clay, synthetic zeolite, and silica, polystyrene latex, urea formalin resin, and the like.

(Regenerated particles)
In the present invention, as the filler, it is preferable to use composite particles composed of silica having excellent opacity and inorganic particles other than silica. When inorganic particles other than silica are used as regenerated particles or regenerated particle aggregates, the use of filler is more preferable. The amount can be reduced, and in particular, a coated paper excellent in paper thickness, opacity and rigidity can be obtained, which is preferable.

(Production process of regenerated particles and regenerated particle aggregates)
Recycled particles are deinked floss separated from pulp fibers in the deinking process of waste paper processing equipment that produces waste paper pulp, and paper sludge separated from paper mill wastewater as the main raw material, and the main raw material is dehydrated and dried. It is obtained through a combustion and pulverization process. For example, the manufacturing method described in Japanese Patent No. 3869455 can be used as the manufacturing method. When used as an internal filler, it is preferable to adjust the particle size by pulverizing the particle size to 0.5 to tens of μm by a known pulverization method. If the particle size is smaller than 0.5 μm, the yield is poor and it is easy to form a foreign substance in the paper machine system, which is not preferable. If the particle size is larger than 10 μm, the formation deteriorates and the strength (tensile strength and tear strength) decreases. This is not preferable because there is a possibility.
Here, the particle diameter of the regenerated particles is a volume average particle diameter measured by a laser analysis type particle size distribution measuring apparatus “SALD-2200 type” manufactured by Shimadzu Corporation.

  The regenerated particles produced by the above method form a regenerated particle aggregate in which several individual particles are aggregated, and have an irregular shape such as a lump-like mass. Due to this irregular shape, when it is contained in the base paper, the paper thickness is likely to be obtained, and since it is a highly opaque particle, the filler content can be reduced and the rigidity tends to be high, which is preferable.

  These regenerated particles contain calcium, silicon, and aluminum at a mass ratio of 30 to 82: 9 to 35: 9 to 35 in terms of oxides. The mass ratio is preferably 40 to 82: 9 to 30: 9 to 30, more preferably 60 to 82: 9 to 20: 9 to 20.

  As a method for adjusting the calcium, silicon, and aluminum oxide conversion ratio of regenerated particles or regenerated particle aggregates in the firing step, the main component is to adjust the raw material composition in the deinking floss, but drying and classification In the process and the baking process, it is possible to adjust the coating floss and the adjustment process floss with a clear origin by means of including in the process by spraying or by means of containing the incinerator scrubber lime.

  For example, neutral papermaking wastewater sludge and wastewater sludge from the coated paper manufacturing process are used to adjust calcium in recycled particles and inorganic particle aggregates, and white carbon as an opacity improver is used to adjust silicon. Wastewater sludge from newsprint manufacturing systems that contain a large amount of additives, papermaking drainage sludge that uses sulfuric acid bands such as acidic papermaking to adjust aluminum, and wastewater from high-quality papermaking processes that often use talc. Sludge can be used as appropriate.

[Attached process]
In order to obtain more stable quality in production facilities, it is preferable to classify the particle size of regenerated particles and regenerated particle aggregates uniformly in each step, and feed back coarse and fine particles to the previous step. In this way, quality can be further stabilized.

  In addition, it is preferable to granulate the deinked floss that has been subjected to dehydration in the previous stage of the drying process, and it is more preferable to classify the granulated product to have a uniform particle size. It is possible to further stabilize the quality by feeding back the granulated particles to the previous process. In granulation, a known granulation facility can be used, and facilities such as a rotary type, a stirring type and an extrusion type are suitable.

  In production facilities, it is preferable to remove foreign substances other than regenerated particles and regenerated particle aggregates. For example, sand, plastic foreign materials, metals, etc. with pulpers, screens, cleaners, etc., before the deinking process of the used paper pulp manufacturing process It is preferable from the viewpoint of removal efficiency to remove. In particular, iron contamination is a substance that reduces the whiteness of fine particles due to oxidation, so it is recommended to avoid iron contamination and selectively remove it. Design or lining each process with materials other than iron, It is preferable to prevent iron from being mixed into the system due to abrasion or the like, and to further remove iron selectively by installing a high magnetic material such as a magnet in the drying / classifying equipment.

[Silica composite regenerated particles, silica composite regenerated particles aggregate]
In the present invention, it is preferable to use fillers generally used for papermaking, that is, silica composite inorganic particles in which calcium carbonate (heavy and light), clay, talc and the like are combined with silica. Preferably, the use of silica composite regenerated particles or silica composite regenerated particle aggregates in which the surfaces of the above regenerated particles or regenerated particle aggregates are combined with silica results in more bulky and highly opaque particles. This makes it easy to obtain a coated paper having a high paper thickness and opacity. In order to prevent a decrease in paper stiffness in the present invention, it is preferable to reduce the amount of filler that inhibits interfiber bonding between pulp fibers. However, if the amount of filler decreases, opacity tends to decrease. It was difficult to balance stiffness. However, preferably in the present invention, the amount of filler can be reduced by using composite particles composed of silica and inorganic particles other than silica as filler, particularly silica composite regenerated particles or silica composite regenerated particle aggregates excellent in opacity. A coated paper excellent not only in paper thickness and white paper gloss, but also in opacity, rigidity, and printability is easily obtained.

  As a suitable measure for precipitating silica on the regenerated particles or regenerated particle aggregates, the method described in Japanese Patent No. 3907688 or Japanese Patent No. 393596 can be used. However, it is preferable to carry out as follows because silica composite regenerated particles or silica composite regenerated particle aggregates having better opacity can be obtained.

<Silica composite particles>
Next, the silica composite particles of the present invention will be described in more detail while taking the silica composite regenerated particles as an example and showing the production method.

(Silica composite treatment process)
As described above, regenerated particles mainly made of paper sludge and deinking floss are added to and dispersed in an alkali silicate aqueous solution, and a mineral acid is added in a temperature range of 50 ° C. to 100 ° C. while stirring. . More preferably, it is added in at least two stages to carry out a silica composite reaction.

  A suitable particle size of the regenerated particles of this embodiment for use as a filler is a particle size of 0.5 μm to several tens of μm, preferably 1.0 to 3.0 μm. The particle diameter of the regenerated particles after the pulverization step is a volume average particle diameter measured by a laser analysis type particle size distribution measuring apparatus “SALD-2200 type” manufactured by Shimadzu Corporation.

  If the particle diameter of the regenerated particles is excessively smaller than 0.5 μm, a sufficient particle size may not be obtained at the time of silica composite, and there is a possibility of clogging into a glass state when silica is composited. Within the scope of the present invention, the silica composite reaction can be sufficiently promoted. On the other hand, if the particle size is excessively large, excessively regenerated silica composite particles are likely to be produced, and the opacity may be lowered.

  Silica composite is a reaction operation for generating silica sol particles having a particle diameter of 10 to 20 nm (measured particle diameter by a scanning electron microscope) on the surface of regenerated particles. The particle size of the silica sol particles can be controlled by the stirring conditions during the reaction, the addition conditions of the mineral acid, and the like.

  The present inventors have surpassed the knowledge that the pore volume of all fine pores of the internally added fine particles has been regarded as an index of oil absorption and opacity, and the actual oil absorption is only the pore volume of inorganic fine particles. In addition, the silica composite regenerated particles that can be suitably used in the present invention have been found to have a high contribution of the ability to retain oil between the particles of inorganic fine particles. It has been found that pores of 1,000 angstroms or less greatly contribute to the substantial oil absorption.

  The pore volume of the silica composite regenerated particles obtained in the present invention is a value measured using a mercury intrusion porosimeter (“PASCAL 140/240” manufactured by Terumo), and the pore volume in the region of 10,000 mm or less is 0.00. 30 to 1.10 cc / g, preferably 0.43 to 1.03 cc / g, more preferably 0.47 to 1.00 cc / g.

  If the pore volume of the pores in the region of 10,000 mm or less is less than 0.30 cc / g, sufficient oil absorption cannot be expressed, and if it exceeds 1.10 cc / g, the oil absorption is improved. Decrease in opacity is likely to occur.

  In a preferred embodiment of the present invention, the particle diameter of the obtained silica composite regenerated particles is in the range of 1.0 to 10.0 μm, and further the ratio of silica in terms of oxide contained in the silica composite regenerated particles is set. By setting the content to 6.0 to 42.0% by mass, a high oil absorption amount and an opacity improving effect can be obtained.

Although it does not specifically limit regarding alkali silicate aqueous solution, A sodium silicate solution (No. 3 water glass) is desirable at the point which is easy to acquire. The concentration of the alkali silicate solution is preferably 3 to 10% by mass in terms of the silicic acid content in the aqueous solution (in terms of SiO ₂ ). If the amount exceeds 10% by mass, the regenerated particles are not a composite of regenerated particles and silica, but the regenerated particles are covered with white carbon, and the porosity and optical characteristics of the regenerated particles in the core may not be exhibited. There is sex. On the other hand, if the amount is less than 3% by mass, the silica component in the composite particles is lowered, so that it is difficult to form silica composite regenerated particles.

  The slurry concentration in the case where a regenerated particle or regenerated particle aggregate is added to and dispersed in an alkali silicate aqueous solution to prepare a slurry is preferably 8 to 14% by mass. By adjusting the slurry concentration, the particle size of the silica composite regenerated particles of the regenerated particles to be formed is controlled, and at the same time, the composition ratio of the regenerated particles and silica is determined. Mineral acids used in the present invention include dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and other mineral acids, and dilute sulfuric acid is most desirable from the viewpoint of price and handling. Furthermore, when using diluted sulfuric acid, it is preferable to add the mineral acid at a concentration of about 4 to 10 N from the viewpoint of improving production efficiency and homogeneity of the composite silica. If it is less than 4N, the reaction is slow, and if it exceeds 10N, a local reaction occurs, and there may be a problem that amorphous composite particles that are unevenly distributed are likely to be generated. Moreover, since silica precipitates in a short time, so that there is much mineral acid addition amount, it is desirable to adjust an addition rate according to those conditions. Addition within 5 minutes makes the structure of the uniform reaction system insufficient.

  Since the regenerated particles or regenerated particle aggregates preferably used in the present invention contain calcium, aluminum, and silica as constituent elements, addition of an excessive concentration of mineral acid may cause alteration of the regenerated particles.

  As described above, in the present invention, an aqueous alkali silicate solution is added and dispersed at a solid content ratio of 100: 5 to 100: 15 with respect to regenerated particles or regenerated particle aggregates to form a slurry, while stirring. In the temperature range of 50 to 100 ° C., the mineral acid is added in at least two stages to perform a silica composite reaction.

  When the ratio of the alkali silicate aqueous solution to the regenerated particles or the regenerated particle aggregates is less than 100: 5 in terms of solid content, the silica composite effect of the obtained silica composite regenerated particles is low and the effect of improving opacity is difficult to obtain. When the ratio exceeds 15, the tendency to increase the oil absorption becomes remarkable, so that the penetration of the coating liquid into the base paper becomes excessive when used as the base paper of the coated paper suitably used in the present invention, The flatness of the coated surface and the covering property of the base paper surface are impaired, and a problem that printability is deteriorated easily occurs.

  In the step of adding the regenerated particles to the alkali silicate aqueous solution, the temperature of the alkali silicate aqueous solution can be heated to a temperature of 50 ° C. or higher, and then heated. When the porous regenerated particles are added in a state where the temperature of the aqueous alkali silicate solution is heated to 50 ° C. or higher in advance, the fluidity by heating is improved, so that the slurry can be easily homogenized. A homogeneous mixed slurry of alkali silicate and regenerated particles can be obtained.

On the other hand, after preparing a homogenized alkali silicate and regenerated particle slurry, the mixture can be heated and stirred. As a heat source in this case, a known heat source can be used. For example, by blowing live steam (for example, 13 kg / m ² , 120 ° C.) in the factory, the temperature raising time can be shortened, and the regenerated particle slurry can be used. It is possible to prevent the temperature from being reduced when added, and to rapidly increase the temperature and the reaction, thereby improving the production efficiency.

  Regarding the reaction temperature during the production of the silica composite regenerated particles in the present invention, a slurry temperature range of 50 to 100 ° C., particularly a slurry temperature range of 50 to 98 ° C. is desirable. As a result of intensive studies by the present inventors, the reaction temperature with the regenerated particles used in the present invention affects the formation of silica, the crystal growth rate, and the mechanical strength of the formed silica composite regenerated particles. When the reaction temperature is less than 50 ° C., the rate of silica formation / growth does not occur or is slow, the silica composite regenerated particles have poor silica composite properties, are difficult to combine sufficiently, and the composite is formed by the shearing force applied during the making of the filler-added paper. Fragile. If it exceeds 100 ° C., the reaction process becomes complicated because an autoclave must be used because it is an aqueous reaction. In addition, the reaction proceeds excessively to form a dense silica composite regenerated particle form, and the opacity of the obtained silica composite regenerated particle is lowered, so that the intended product is difficult to perform.

  In the present invention, it is desirable to add at least two stages of mineral acid and to control the temperature at that time. That is, the slurry temperature at the time of adding the mineral acid in the first stage is 50 to 75 ° C., and the slurry temperature at the time of adding the mineral acid after the second stage is at least 10 ° C. higher than that at the first stage. Is desirable. Specifically, the desirable temperature conditions are that the liquid temperature in the first stage is 50 to 75 ° C., the temperature in the second stage is 70 to 100 ° C. in accordance with the number of mineral acid addition stages, and 90 in the final stage of the reaction. The temperature is set to a temperature of not lower than 98 ° C. and not higher than 98 ° C. Under these temperature conditions, more uniform silica composite regenerated particles can be obtained.

  The pH of the final reaction solution is preferably 8.0 to 11.0, more preferably 8.3 to 10.0, and most preferably 8.5 to 9.0.

  In the production of white carbon obtained by reacting a conventional alkali silicate with a mineral acid, in order to complete the reaction between the alkali silicate and the mineral acid, the mineral acid is added to the alkali oxalate until the pH reaches 5.5 to 7.0. Addition method is adopted, but when mineral acid is added until the pH reaches 7.0 or less, the calcium component contained in the regenerated particles easily changes to calcium hydroxide, and the resulting silica composite regeneration This is not preferable because the particle diameter of the particles is excessively decreased, the shape is not uniform, the yield on paper is reduced, the generation of paper dust, and sufficient opacity are difficult to obtain. When the pH exceeds 11.0, the reaction between the alkali oxalate and the mineral acid becomes dull and it becomes difficult for silica to be combined with the surface of the regenerated particles.

  When the mineral acid is added in one stage, it is preferable to set the addition amount of the mineral acid so that it takes 40 minutes or more for the pH to decrease by one.

  In the present invention, as described above, the mineral acid is preferably added in two or more stages. In this case, in order to obtain a homogeneous silica composite, it is preferable to uniformly add the mineral acid in each stage. In addition, after one stage of addition (addition until the mineral acid reaches a neutralization rate of 20 to 50% with respect to the aqueous alkali oxalate solution), a holding time of about 5 minutes to 20 minutes is made, so that the silica complex reaction In addition, the silica is homogeneously compounded on the surface of the regenerated particles, and the addition of the mineral acid in the second stage can further promote the formation of a composite layer of silica, which makes the surface of the regenerated particles more uniform. Silica can be composited with.

  The addition amount of the mineral acid for one stage is preferably set so that it takes 10 minutes to 45 minutes in order to uniformly combine silica on the surface of the regenerated particles. Even when the mineral acid is added in two or more stages, it is homogeneous to set the addition amount so that it takes about 10 to 120 minutes for the pH of the mineral acid to decrease by 1 in the fluctuation of the pH. Preferred for silica composites.

  In the agitation in this reaction step, for example, an unreacted zone is not formed. Therefore, it is preferable to employ an agitation means such as generating a turbulent flow by reversing the agitation blade or providing a baffle plate in the agitation tank.

  The obtained silica composite regenerated particles have a particle size of 0.5 to 10.0 μm, and the silica composite regenerated particles preferably have calcium, silicon and aluminum in an oxide conversion of 40 to 83: 6 to 42: 7 to 18. The mass% ratio. This component analysis is a value obtained by performing elemental analysis at an acceleration voltage (15 KV) using an X-ray microanalyzer manufactured by Horiba, Ltd., and converting the component to oxide.

  The more preferable particle diameter of the obtained silica composite regenerated particles is 0.6 to 9.7 μm, the most preferable range is 1.3 to 9.0 μm, and more preferably 2.0 to 8.8 μm.

  When the particle diameter of the silica composite regenerated particles is less than 0.5 μm, the effect of silica composite cannot be sufficiently exhibited, and the effect of improving the oil absorption and opacity is difficult to obtain. When the particle diameter of the silica composite regenerated particles exceeds 10.0 μm, the filler used for the base paper for the coated paper becomes excessive in the absorption capacity of the coating liquid, and it simply inhibits the flatness of the coating layer surface. However, problems such as pulling, tearing, and so-called decrease in paper quality, paper dust, and papermaking equipment are likely to occur.

  Printing of coated paper using silica composite regenerated particles obtained by making the ratio of silica (silicon) in terms of oxide after compounding the silica component 6.0 to 42.0% by mass The effect of improving transparency can be obtained.

  The ratio of the silica component is preferably 38.0 to 42.0% by mass, and more preferably 39.0 to 42.0% by mass. If the ratio of the silica component is less than 6.0% by mass, the silica composite is not sufficiently performed. Therefore, it is difficult to improve the oil absorption and opacity. If the ratio of the silica component exceeds 42.0% by mass, the silica component is fine. There may be a problem that the silica particles are excessively filled, resulting in a decrease in oil absorption and opacity.

  As an incidental effect of the silica composite, the whiteness is improved by the silica composite. Although white paper opacity tends to decrease due to whiteness improvement, by using silica composite recycled particles with high oil absorption, offset ink used for coated paper can be absorbed inside the paper, further increasing printing opacity Can be improved.

  By combining the silica with the regenerated particles, the interfiber bonding is moderately inhibited by the cationic property of the regenerated particles and the anionic property of the silica, and the bulkiness is exhibited.

(Use or application)
The silica composite regenerated particles of the present invention have a large specific surface area because the surface of porous regenerated particles is originally composited with silica, and when this is used as a filler for internal addition, the paper thickness, whiteness, Highly transparent coated paper can be obtained.

  Furthermore, the oil absorption amount of the silica composite regenerated particles is preferably in the range of 50 to 180 ml / 100 g. This is because when the silica composite regenerated particles in this range are used as an internal filler, the silica composite regenerated particles in the paper layer absorb the ink, the organic solvent, etc. impregnated in the paper layer. This is because a decrease in printing opacity is suppressed, and the effect of preventing ink drying and blurring becomes conspicuous by absorbing the ink and the organic solvent. On the other hand, when the oil absorption is less than 50 ml / 100 g, the above effect is not sufficient, and the silica composite regenerated particles may tend to inhibit the ink absorption and drying properties. On the other hand, when the oil absorption exceeds 180 ml / 100 g, there is a case where the ink sinks and the so-called color developability is inferior due to high ink absorbability.

  The oil absorption amount of the silica composite particles can be adjusted by adjusting the reaction temperature, the addition time, the holding time, the pH, the viscosity, the combustion means of the regenerated particles used, the particle diameter, etc. in the silica composite reaction step. When adjusted so that the pore volume of 1,000 Å or less is 0.30 to 1.10 cc / g, it is possible to obtain silica composite regenerated particles that exhibit high oil absorption and can improve paper opacity. High opacity can be obtained in the silica composite regenerated particle-containing paper containing regenerated particles.

As mentioned above, the production method of the silica composite regenerated particles has been described in detail by taking regenerated particles as an example. Recycled particle aggregates instead of regenerated particles, and calcium carbonate conventionally used as a filler for papermaking applications (heavy and light) Silica composite inorganic particles can be produced using talc, clay or the like and internally added to the coated paper.
Thus, the particle | grains which combined the silica can make a wire wear degree low, since the particle | grain surface is compounded with the silica, and can be used suitably as a filler. Inorganic particles added internally to paper, if the particles are hard, the wire (net part) of the paper machine is liable to be damaged, and the life of the wire is shortened. However, as in the present invention, the life of the wire can be extended by using inorganic particles composited with silica, preferably silica composite regenerated particles or silica composite regenerated particle aggregates, which are soft inorganic particles that do not easily damage the wire.

  The degree of wire wear can be evaluated by a Filcon type wire wear degree test. When a regenerated particle aggregate having an abrasion degree of about 80 mg is used as inorganic particles to be combined with silica, the abrasion degree can be reduced to about 20 mg by silica combination, and particles that can be sufficiently used as an internal additive are obtained. be able to. In addition, the wire wear degree of heavy calcium carbonate is 100 mg or more, light calcium carbonate is about 50 mg, and white carbon is about 15 mg. If it is about 50 mg or less, it can be used as an internal filler.

  As described above, it is preferable to use composite particles made of silica and inorganic particles other than silica, preferably silica composite regenerated particle aggregates, as the filler because a coated paper having high opacity can be obtained. Especially for coated papers that require high opacity and stiffness, even if the filler content is reduced, fluffing and roughening hardly occur, and coated papers with excellent opacity and white paper gloss can be obtained. preferable.

  The content of these fillers is not particularly limited, but is preferably added so as to be 2 to 10% by mass, and more preferably 3 to 8% by mass with respect to 100% by mass of the base paper. When the blending amount of the filler exceeds 10% by mass, the binding between the pulp fibers tends to be hindered, and the stiffness tends to decrease. When the filler content is less than 2% by mass, not only the opacity is not improved, but the bulk (paper thickness) becomes too high, and the paper becomes inflexible and fuzzing or roughening is likely to occur. In addition, content of the said filler is ash content measured according to JISP8251 "Paper, paperboard, and a pulp-ash content test method-525 degreeC combustion method."

  In the present invention, as described above, the fiber length distribution obtained by classifying the pulp fibers obtained by disaggregating the coated paper according to JIS P 8220: 1998 “pulp-disaggregation method” for each fiber length of 0.05 mm. The fiber length is 0.10 mm or more and less than 0.65 mm, so that the paper thickness and white paper glossiness are excellent, and further, opacity, whiteness, printability, and rigidity are all improved. Can do. Preferably, silica composite inorganic particles composed of silica and inorganic particles other than silica as a filler, preferably silica composite regenerated particles composed of silica and regenerated particles, or silica composite regenerated particle aggregates composed of silica and regenerated particle aggregates, The silica composite particles are contained in an amount of 2 to 10% by mass (more preferably 3 to 8% by mass) with respect to 100% by mass of the base paper. It is added at a ratio of 100: 15, and is obtained by carrying out a silica coating reaction by adding a mineral acid preferably in two stages in a temperature range of 50 to 100 ° C., particularly 50 to 98 ° C. More preferably, the mineral acid of the first stage is added at 50 to 75 ° C., and after a holding time of about 5 to 20 minutes, the temperature is raised by 10 ° C. or more, preferably 70 to 100 ° C., particularly preferably 90 The mineral acid from the second stage is added at a temperature of from ℃ .degree. C. to 98.degree. C. and the pH of the final reaction solution is 8.0 to 11.0, preferably 8.3 to 10.0, more preferably 8.5. By setting the value to 9.0, the particle size is 0.5 to 10.0 μm, preferably 0.6 to 9.7 μm, more preferably 1.3 to 9.0 μm, and particularly preferably 2.0 to 8.8 μm. It is possible to obtain silica composite inorganic particles having a high oil absorption and an effect of improving opacity, in which the ratio of silica in terms of oxide contained in the silica composite regenerated particles is 6.0 to 42.0% by mass. .

As described above, the pulp fiber has a fiber length distribution and has a maximum value in a range of fiber length of 0.10 mm or more and less than 0.65 mm, so that the coated paper has excellent opacity and rigidity as well as paper thickness and white paper gloss. Is obtained. In particular, in addition to the fiber length distribution described above, the Runkel ratio of the disaggregated pulp is 0.4 to 2.0 (more preferably 0.6 to 1.0), and silica composite inorganic particles are contained as a filler. in coated paper having a basis weight of 111~121g / ^{m 2,} a basis weight of 6 g / ^{m 2} or more, further 10 g / ^{m 2} or more, in particular coating of 16g / ^{m 2} or more and high 127.9 g / ^{m 2} Since it is easy to obtain coated paper having the same degree of opacity, whiteness, paper thickness, white paper glossiness, printability, and rigidity as paper, it is preferable.

  Further, the particles to which the silica composite is applied are not limited to regenerated particles and regenerated particle aggregates, and conventionally used fillers generally used for papermaking can be used. That is, calcium carbonate (heavy and light), clay, talc and the like may be used. In this invention, the silica composite inorganic particle obtained by carrying out the silica composite of these inorganic particles by the above-mentioned method can be used.

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

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

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

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

(Undercoating)
For the purpose of improving the smoothness and whiteness of the surface, it is possible to undercoat a pigment coating solution containing a pigment and an adhesive on the base paper produced as described above. The undercoat coating layer may be a single layer or a plurality of layers.

  The pigment used for the undercoat coating layer is not particularly limited, and those generally usable for papermaking can be used. For example, clay (kaolin, wax), calcium carbonate, talc, satin white, calcium sulfite, gypsum, barium sulfate, white carbon, calcined kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, hydroxide From inorganic pigments such as calcium, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, and sericite, and organic pigments such as polystyrene resin fine particles, urea formalin resin fine particles, fine hollow particles, and porous fine particles One or two or more may be appropriately selected and blended.

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

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

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

The coating amount (solid content) of the undercoat coating layer on the base paper is preferably 7.8 to 11.5 g / m ² , more preferably 8.5 to 11.1 g / m ² , particularly in terms of the total on both sides. Preferably it is 9.3-10.7 g / m < ² >. If the coating amount of the undercoat coating layer is less than 7.8 g / m ² , an uncoated portion is likely to occur on the surface of the base paper, unevenness in smoothness is likely to occur, and the white paper glossiness and printability are likely to be inferior after top coating. Therefore, it is not preferable. If it exceeds 11.5 g / m ² , the total coating amount with the top coat layer tends to increase, and the basis weight of the base paper tends to decrease, which is not preferable.

  Although the thickness of the undercoat coating layer to be formed is not particularly limited, it is preferably 8 to 12 μm in consideration of the density, smoothness, and printing unevenness after providing the topcoat coating layer.

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

(Pre-calendar part (flattening process))
The base paper after the undercoating is preferably subjected to a flattening process using a precalender before the topcoating. By performing the flattening treatment, unevenness in smoothness after the undercoating can be reduced, and the smoothness after the overcoating can be improved. In particular, in this embodiment, since the fiber length of the disaggregated pulp contains many pulp fibers of 0.10 mm or more and less than 0.65 mm, fluffing in the coated paper after the top coating is performed by performing a precalender treatment after the undercoating. And roughening are preferable. Further, when a lot of pulp fibers having a Runkel ratio of 0.4 to 2.0 are included, it is preferable because printability can be further improved.

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

  As the pigment used in the topcoat coating layer, the pigments exemplified in the undercoat coating layer can be used, but if a large amount of clay is included among these, a coated paper with more excellent white paper gloss and printability can be obtained. preferable.

  The content of clay is preferably 40 to 90 parts by mass, more preferably 50 to 80 parts by mass, out of 100 parts by mass of the pigment contained in the topcoat coating layer. If it is less than 40 parts by mass, there is a possibility that sufficient blank paper glossiness and printability may not be obtained. If the amount exceeds 90 parts by mass, the fluidity of the coating tends to deteriorate, coating unevenness occurs, and it is difficult to prevent fuzzing and roughening sufficiently, such being undesirable.

  The pigment particles are preferably used in combination with a small particle size pigment having an average particle size of 0.1 μm or more and less than 1.0 μm and a large particle size pigment having an average particle size of 1.0 μm or more and less than 10.0 μm. By blending a small particle size pigment, the surface of the coating layer can be easily filled, and the glossiness of the blank paper and printability are improved. On the other hand, the specific gravity of the coated paper that is easily filled can easily be increased. Bulky coated paper is difficult to obtain. On the other hand, when particles having a large particle diameter are blended, the coverage of the coating layer surface tends to be high, and the coating amount can be reduced, thereby preventing an increase in density. On the other hand, it is not preferable because the surface is difficult to be filled, and the glossiness of white paper and the printability are liable to decrease. However, when these small particle size pigments and large particle size pigments are used in combination, the coverage and filling properties of the coating layer surface can be improved without increasing the density of the coated paper. Easy to obtain industrial paper.

  As the pigment having a small particle diameter, a pigment having a maximum value in a range of particle diameter distribution of 0.1 μm or more and less than 1.0 μm is preferable. Examples of such pigments include KAOFINE (manufactured by Shiraishi Calcium Co., Ltd.), HYDRAGLOSS (manufactured by Huber), and AMAZON SB (manufactured by Kadam).

  As the pigment having a large particle diameter, a pigment having a maximum value in the range of 1.0 μm or more and less than 10.0 μm in the particle diameter distribution is preferable. A clay having an aspect ratio (ratio of the particle thickness to the diameter of the plate-like particle) of 5 or more is particularly preferable because higher white paper glossiness can be obtained. Examples of such clays include HYDRASPERS (manufactured by HUBBER, average particle diameter 1.8 μm, aspect ratio 6), UW-90 (manufactured by Engelhart, average particle diameter 1.6 μm, aspect ratio 5), KAPIM NP ( Examples include Rio Capim, average particle size 2.2 μm, aspect ratio 20), KCS (Imeris, average particle size 2.7 μm, aspect ratio 14), and the like. In the case of calcium carbonate, for example, Tama Pearl TP121-6S (Okutama Kogyo Co., Ltd., average particle size 1.8 μm), Hydrocurve 90 (Bihoku Fuka Kogyo Co., Ltd., average particle size 1.3 μm), FMT-90 (Phimatec Corporation) Manufactured, average particle diameter of 1.2 μm).

  The particle diameter of the coating pigment refers to the particle diameter obtained by photographing the pigment particles on the surface of the coating layer with an electron microscope and measuring the diameter of the photographed particles.

The small particle size pigment and the large particle size pigment having the maximum values in these ranges are preferably used in a mass ratio of 4: 6 to 2: 8. If the small particle size pigment is larger than the above range or the large particle size pigment is less than the above range, and particularly not containing the large particle size pigment, not only the coating property of the coated paper is lowered and the printability tends to be lowered, This is not preferable because the density of the coating layer increases and the opacity tends to decrease, and it is difficult to prevent fuzzing and roughening sufficiently. If the small particle size pigment is less than the above range, especially if it does not contain small particle clay, or if the large particle size pigment is more than the above range, the surface roughness of the coated paper will decrease and the white paper gloss will tend to decrease. In addition, it is not preferable because it is difficult to prevent fuzzing and roughening sufficiently.
Moreover, the coated paper which can solve the subject of this invention by using together the small particle diameter pigment and the large particle diameter pigment which have the maximum value in these ranges in the ratio of 4: 6 to 2: 8 is suitable. Can get to. If the mass ratio is outside of 4: 6 to 2: 8, the effects of the present invention, that is, sufficient paper thickness, white paper glossiness, and printability may be difficult to obtain.
In addition, when the surface of the coating layer is photographed with an electron microscope by setting the above range, 85% or more of all pigments, preferably 90% or more, in a range of particle diameter of 0.1 μm or more and less than 1.0 μm, A coated paper containing 15% or less, preferably 10% or less of the total pigment in a range of 1.0 μm or more and less than 10.0 μm is preferable because it is easy to obtain a coated paper.

  In addition to the above, the above-mentioned pigments can be added as long as the effects of the present invention are not impaired.

The coating amount (solid content) of the topcoat coating layer is the sum of both surfaces, preferably 13.2 to 19.5 g / m ² , more preferably 14.5 to 18.9 g / m ² , and particularly preferably 15. 7 to 18.3 g / m ² . If the coating amount of the top coating layer is less than 13.2 g / m ² , the coating layer surface cannot be sufficiently covered, and not only fuzzing or roughening occurs but printability is deteriorated, and the glossiness of blank paper also decreases. It is not preferable because it is easy. If it exceeds 19.5 g / m ² , the ratio of the coating layer in the coated paper increases and the stiffness tends to decrease, and the density and basis weight tend to increase, such being undesirable.

The total coating amount (solid content) of the top coating layer and the undercoat coating layer in the coated paper of the present invention is preferably 21 to 31 g / m ^{2 on} both sides, more preferably 23 to 30 g / m ² , and 25 to 25. 29 g / m ² is more preferable. If the total coating amount is less than 21 g / m ^2, it is not preferable because the coating layer surface cannot be sufficiently covered, and not only fuzzing or roughening occurs and printability tends to be inferior, but also the glossiness of blank paper tends to be lowered. If it exceeds 31 g / m ² , the ratio of the coating layer in the coated paper increases and the stiffness tends to decrease, and the density and basis weight tend to increase.

  In addition, the total coating amount (solid content) of the undercoat coating layer and the top coating layer, or when the coating layer is one layer, the coating amount (solid content) of that one layer is based on the base paper. The mass ratio is preferably 0.23 to 0.34, more preferably 0.26 to 0.33, and particularly preferably 0.28 to 0.32. When the ratio is less than 0.23, the ratio of the coating layer is decreased, so that not only fuzzing and roughening are not sufficiently prevented, but also the glossiness of the white paper is easily lowered. Since the ratio of the coating layer to occupy is large and the rigidity tends to decrease, it is not preferable.

  In addition, the ratio of the coating amount of the top coating layer to the coating amount of the undercoat coating layer is preferably 1.5 to 1.9 in terms of mass, and preferably 1.6 to 1.8. Is more preferable. If the amount of undercoating is large, or the amount of overcoating is small and the ratio is less than 1.5, not only is it difficult to obtain the glossiness of the blank paper, but also the linear pressure of the calendar etc. is increased to give more gloss. This is not preferable because the paper thickness and stiffness are likely to decrease. When the ratio exceeds 1.9, it is difficult to obtain a flattening effect by the undercoat coating layer and the pre-calendering process, and it becomes difficult to prevent fuzz and roughening sufficiently. Since there are many topcoat coating layers, since whiteness falls easily, it is not preferable.

In particular, as in the present invention, when the fiber length of the disaggregated pulp contains many pulp fibers of 0.10 mm or more and less than 0.65 mm, the coating amount is 0.23 to 0.34 (more It is preferably 0.26 to 0.33, particularly preferably 0.28 to 0.32) because fuzzing and roughening can be prevented and printability can be improved. Furthermore, as a pigment on the surface of the coating layer, a small particle diameter pigment having an average particle diameter in a range of 0.1 μm or more and less than 1.0 μm, and a large particle having an average particle diameter in a range of 1.0 μm or more and less than 10.0 μm. By using the particle size pigment in a weight ratio of 4: 6 to 2: 8, the particle size distribution on the surface of the coating layer is 85% or more, preferably 90% in the particle size distribution of 0.1 μm or more and less than 1.0 μm. %, And a coated paper having a particle diameter of 1.0 μm or more and less than 10.0 μm of 15% or less, preferably 10% or less can be obtained. Further, it is preferable because rigidity, opacity, and printability are easily improved. Furthermore, by making the ratio of the coating amount of the topcoat coating layer to the coating amount of the undercoat coating layer 1.5 to 1.9 in terms of mass, especially the paper thickness, white paper glossiness, whiteness, This is preferable because a coated paper excellent in opacity, rigidity and printability can be easily obtained.
Such an effect is achieved by adding 2 to 10% by mass of composite particles composed of silica and inorganic particles other than silica as a filler to 100% by mass of the base paper, thereby further improving the paper thickness, opacity and stiffness. It is preferable because it is easy to make.

As described above, when the fiber length of the disaggregated pulp contains a large amount of pulp fibers having a length of 0.10 mm or more and less than 0.65 mm, composite particles composed of silica and inorganic particles other than silica are used as a filler, based on 100% by mass of the base paper. 2 to 10% by mass (preferably 3 to 8% by mass), and the Runker ratio of the disaggregated pulp is preferably 0.4 to 2.0 (more preferably 0.6 to 1.0). . In the coating layer on the base paper, a small particle size pigment having an average particle size of 0.1 μm to 1.0 μm and a large particle size pigment having an average particle size of 1.0 μm to 10.0 μm are used in a weight ratio of 4: 6. By using together at a ratio of ˜2: 8, the surface of the coating layer has a particle diameter in the range of 0.1 μm or more and less than 1.0 μm, 85% or more, preferably 90% or more of the pigment particles, and a particle diameter of 1 In the range of 0.0 μm or more and less than 10.0 μm, the pigment particles can be contained in an amount of 15% or less, preferably 10% or less. In particular, clay is used as a pigment in an amount of 40 to 90 parts by mass (preferably 50 to 80 parts by mass). In addition, the coating amount is 0.23 to 0.34, preferably 0.26 to 0.33, particularly preferably 0.28 to 0.32, in terms of mass ratio with respect to the base paper. At least two coating layers having a coating layer and a top coating layer In the coated paper having, the ratio of the coating amount of the top coating layer to the coating amount of the undercoat coating layer is 1.5 to 1.9 in terms of mass, and the basis weight is 111 to 121 g / Although it is m ² coated paper, it is preferable because it is easy to obtain coated paper having high paper thickness, good white paper glossiness, and excellent opacity, whiteness, rigidity and printability.

  As an adhesive used for the top coat layer, it is preferable to use a polymer latex containing 40 to 65% by mass of a butadiene component as a monomer component, more preferably 43 to 63% by mass, and still more preferably 45 to 60% by mass. It is. When the butadiene component is less than 40% by mass, the adhesion to the pigment is inferior, and the above-mentioned small particle size pigment having a particle size of 0.1 to 1.0 μm is difficult to adhere sufficiently. If it exceeds 65% by mass, the amount of latex on the surface of the coating layer increases, and dirt is attached to various rolls in the coated paper manufacturing process, so that the operability tends to decrease. By keeping the butadiene component in the above range, both adhesiveness and operability can be satisfied. In addition, by adding a latex containing 40 to 65% by mass of the butadiene component and clay having an average particle size of 0.1 to 1.0 μm to the coating layer, the coating layer has excellent white paper gloss and printing gloss. A construction layer can be obtained.

  As monomer components other than butadiene, it is preferable to contain 20-35 mass% of styrene components, More preferably, it is 23-30 mass%. Since the styrene component has the effect of imparting water resistance to the coating layer, if the styrene component is less than 20% by mass, the dampening water is absorbed during offset printing and the coating layer strength decreases, and printing omission (picking) troubles occur. Tend to occur. When it exceeds 35% by mass, the coating layer becomes hard and printability tends to deteriorate. As described above, in order to effectively improve the whiteness, white paper glossiness, print glossiness, and printability, it is preferable to keep the butadiene component and styrene component in the latex within a predetermined range.

  The ratio of the pigment and the adhesive in the top coat layer is preferably 5 to 15 parts by mass, more preferably 7 to 13 parts by mass with respect to 100 parts by mass of the pigment. When the content is less than 5 parts, the coating layer strength is reduced, not only white spots are generated during printing, but the pigment is easily removed from the coated paper in the manufacturing process, and the system is soiled. This is not preferable because both the paper quality and the operability are likely to deteriorate. When the content exceeds 15 parts by mass, not only roll contamination occurs but also troubles such as blisters are likely to occur, which is not preferable.

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

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

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

  As a coating method for obtaining the coated paper of the present invention, it is preferable to perform undercoating with a film transfer type roll coater, pre-calendering, and then overcoating with a blade coater. By using the above coating method, it is easy to impart high smoothness to the surface of the coating layer, so that a calendering process described later can be performed under moderate conditions, and glossy coated paper having a larger paper thickness is easily obtained.

(Calendar part (flattening process))
In this embodiment, for the purpose of imparting glossiness, flatness, and printability to the coating layer, it is preferable to perform a flattening treatment using a hot roll. In general, in the flattening treatment, a coated paper is passed between an elastic roll and a metal roll, a nip pressure is applied to the coated paper, the surface of the coated paper is polished by frictional force, and gloss is imparted. In a coated paper excellent in paper thickness, if the nip pressure is increased in order to improve the glossiness, the paper thickness may be easily lowered. However, in the present invention, the fiber length is 0.10 mm or more and 0.0. In addition to having a fiber length distribution having a maximum value in a range of less than 65 mm, it is preferable that the Runkel ratio of the disaggregated pulp is 0.4 to 2.0, more preferably 0.6 to 1.0. Even if the flattening treatment is performed at a pressure (200 to 500 kN / m), it is easy to obtain coated paper having a high paper thickness of 90 to 110 μm and excellent blank paper gloss, print gloss, printability, and rigidity.

  The surface temperature of the heat roll (metal roll) is preferably 100 to 160 ° C. If the temperature of the heat roll is less than 100 ° C, flattening may not proceed and the glossiness of the white paper may be inferior. If the temperature exceeds 160 ° C, fiber burn and yellowing (fading) are likely to occur due to heat and pressure, and high whiteness May not be obtained.

  Although there is no restriction | limiting about the number of nip steps including the heat roll which performs a planarization process, Preferably it is 2-10 steps, More preferably, it is 2-8 steps. Exceeding 10 steps is not preferable because a large facility is required, and it is not preferable that the smoothness of both the front and back surfaces cannot be sufficiently improved with one step.

  As the equipment for performing the smoothing treatment, a conventional machine calendar or a soft calendar may be used, but it is preferable to use a multi-nip calendar capable of adjusting the linear pressure for each nip.

  Moreover, as an installation place of a calendar, an on-machine type integrated with a paper machine and a coating machine is preferable. In the on-machine type, flattening can be performed immediately after coating at a high paper surface temperature, so it is easy to improve smoothness and improve blank glossiness and printing glossiness while minimizing the decrease in paper thickness. It is preferable because it is easy.

The coated paper having a basis weight of 111 to 121 g / m ² , which has been flattened under the above conditions, is a coated paper having a high paper thickness of 90 to 110 μm and an excellent bulk, and a blank paper glossiness of 70% or more. It is preferable because it is easy to obtain a coated paper that is high in appearance and does not easily generate fuzz or roughening.

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

  First, as raw material pulp, NBKP, LBKP, and BTMP produced from the tree species shown in Table 4 were mixed at a ratio (mass ratio) shown in Table 4, and the filler shown in Table 4 and 100 parts by mass of this pulp ( In each case, the amount of the internal sizing agent (product number: AK-720H, manufactured by Harima Chemical Co., Ltd.) 0.02 parts by mass, cationized starch (product number: amylofax T-2600, Abebe) A pulp slurry was obtained by adding 1.0 part by mass of Japan Co., Ltd. and 0.02 part by mass of a yield improver (product number: NP442, manufactured by Nissan Eka Chemicals Co., Ltd.). The NBKP freeness was adjusted to 500 ml, the LBKP freeness was 400 ml, and the BTMP freeness was adjusted to the values shown in Table 4.

  Next, a base paper was manufactured through a wire part made of a gap former, a straight-through press part without an open draw, and a pre-dryer part made of a single deck dryer. Table 4 shows the basis weight of the base paper.

  On both sides of the base paper, an adhesive (styrene-butadiene latex, product number: PA) with respect to 100 parts by weight of heavy calcium carbonate (product number: Hydrocurve 90, manufactured by Bihoku Flour Industry Co., Ltd., average particle size 1.3 μm). -6082, manufactured by Japan A & L, Tg: −6 ° C., butadiene: 46% by mass, styrene: 25% by mass) Undercoat coating liquid mixed with 8 parts by mass, the coating amount shown in Table 4 in total on both sides It was coated with a film transfer type roll coater so as to be (solid content). Then, it dried with the after-dryer part which consists of a single deck dryer, and planarized by the nip pressure of 100 kN / m by the pre-calender part.

  Subsequently, the adhesive (styrene-butadiene latex, product number: PA-6082, manufactured by Japan A & L Co., Tg: -6 ° C., butadiene: 46% by mass, styrene: 25 with respect to 100 parts by mass of the total pigment described in Table 4. (Mass%) The top coating solution mixed with 8 parts by mass was coated using a blade coater so that the coating amount (solid content) shown in Table 4 would be the total of both surfaces. After drying, a multi-nip calender was used to perform a flattening treatment at a nip pressure of 250 kN / m and a roll temperature of 80 ° C. to obtain a coated paper. Details of the filler and the pigment are as follows.

(Filler)
[Production of regenerated particles]
As the material to be processed (raw material), papermaking sludge or deinking floss is used in advance, and after the dehydration process, the manufacturing equipment shown in FIGS. 1 and 2 performs the organic component heat treatment process under the conditions shown in Table 1. A wet pulverization process was performed sequentially using the 1st combustion process and the 2nd combustion process as appropriate to obtain regenerated particles. The internal heat kiln used in the heat treatment process of the organic components in Production Examples 2 and 3 and Production Examples 6 and 7 is an internal heat kiln furnace in which the main body is placed horizontally and rotates around the central axis. The paper flow sludge was supplied from the raw material supply port and hot air was blown into it.

  The internal heat kiln used in the first combustion process is an internal heat kiln furnace in which the main body is placed horizontally and rotates around the central axis. Furthermore, the external heat kiln furnace used in the second combustion process is an external heat kiln furnace in which the main body is placed horizontally and rotates around the central axis. An electric kiln furnace was adopted. The wet pulverization process was performed using a ceramic ball mill. The deinking floss in Production Example 4 was used by separating it before the high-grade used paper deinking floss was mixed in the papermaking sludge.

  As the primary combustion temperature, the primary combustion furnace outlet temperature was measured. The secondary combustion temperature was measured at the secondary combustion furnace outlet temperature. As for the oxygen concentration, the primary combustion furnace outlet oxygen concentration and the secondary combustion furnace outlet oxygen concentration were measured.

[Production of silica composite regenerated particles]
Under the conditions shown in Table 2, 38% concentration of sodium silicate solution (No. 3 water glass) and 20% concentration of regenerated particle slurry were mixed as an aqueous solution of alkali silicate, diluted water was added, and it was composed of alkali silicate and regenerated particles as shown in Table 2. After adjusting the slurry to a predetermined reaction initiation concentration and reaction initiation pH, sulfuric acid having a prescribed degree was added as a mineral acid and stirred to produce silica composite regenerated particles. A known mixer is used for stirring the slurry. The pH of the slurry was measured with a pH meter manufactured by Horiba, and the reaction temperature was measured with a known thermometer. In the primary reaction step, the mineral acid was added so that the neutralization rate between the alkali silicate aqueous solution and the mineral acid was as shown in Table 2.

  The holding time refers to the time from the completion of the addition of the mineral acid performed in the primary reaction step to the re-addition of the mineral acid in the secondary reaction step.

  In the secondary reaction step, the same mineral acid as in the primary reaction step was added over a predetermined time so that the reaction completion pH was reached. As shown in Table 2, the 10% concentration slurry viscosity of the finished raw material is a B-type viscometer obtained by subjecting the silica composite regenerated particle slurry that has undergone the reaction through the secondary reaction step to dehydration filtration and adjusting the solid content concentration to 10%. (Measurement temperature 25 ° C.).

[Measurement of regenerated particles and silica composite regenerated particles]
Tables 1 and 3 show the component analysis results of the regenerated particles and the silica composite regenerated particles. The inorganic constituents in each step were subjected to elemental analysis at an acceleration voltage (15 KV) using an X-ray microanalyzer manufactured by Horiba, Ltd., and converted into oxides from the constituents.

  The specific surface area and pore volume were measured using a mercury intrusion porosimeter (“PASCAL 140/240” manufactured by Terumo Corporation) after filtration of the sample and vacuum drying.

The amount of oil absorption is based on the kneading method described in JIS K 5101-13-2. That is, 2 g to 5 g of a sample dried at 105 ° C. to 110 ° C. for 2 hours is taken on a glass plate, and refined linseed oil (oxidized 4 or less) is dropped from the buret little by little to the center of the sample and kneaded with a spatula each time. The dripping and kneading operations are repeated, and the amount of refined linseed oil dripped is determined with the end point when the whole is first assembled into a single rod shape, and the oil absorption is calculated by the following equation.
Oil absorption amount = [linseed oil amount (ml) × 100] / sample (g)

  The particle size is measured when the particle size distribution is measured with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200 type” manufactured by Shimadzu Corporation), and the cumulative volume with respect to the volume of all particles is 50%. It is determined as the particle diameter (d50). For the preparation of the measurement sample, silica composite regenerated particles were added to a 0.1% sodium hexametaphosphate aqueous solution and dispersed with an ultrasonic wave for 1 minute.

  An X-ray diffraction apparatus (Rigaku Denki, RAD2X) was used for the measurement of the hard substance. Measurement conditions: Cu-Kα-curved monochromator 40 KV-40 mA, diverging slit 1 mm SS 1 mm RS 0.3 mm, scanning speed 0.8 ° / min, scanning range 2 theta = 7 to 85 degrees, sampling 0.02 degrees.

  The productivity shown in Table 3 indicates that the yield of the silica composite reaction converted from the amount of unreacted chemical contained in the filtrate of the obtained silica composite regenerated particles is ◎ at a yield of 95% or more, and from 80% to less than 95%. 70% or more and less than 80% was evaluated as Δ, and less than 70% as ×.

  In Table 4, the regenerated particles used as the internal filler are Production Example 1-1 described in Table 1, and the silica composite regenerated particles (referred to as silica composite in Table 4) are Production Example 1-1 described in Table 3. .

The following were used for the calcium carbonate and white carbon described as fillers in Table 4.
・ Calcium carbonate (light calcium carbonate, product number: TP121-6S), manufactured by Okutama Kogyo Co., Ltd.
White carbon (secondary particle size: 15.5 μm, oil absorption: 203 ml / 100 g), manufactured by Eliere Paper Chemical Co., Ltd.

(Pigment)
-Charcoal Cal Heavy calcium carbonate, product number: Hydrocurve 90, manufactured by Bihoku Powder Chemical Co., Ltd., average particle size 1.3 μm
-Fine clay product number: Amazon Plus, manufactured by CADAM, average particle size 0.3 μm
・ Large particle size pigment Product No .: Century HC, manufactured by Para-Pigments, average particle size 2.8 μm

The maximum value of the particle size distribution on the coated paper surface described in Table 5 was measured as follows. The coated paper was cut out to A4 size, and a sample of 5 mm square was cut out at a point of Acm from the upper side to the lower side and Acm from the left side, with the short side of the paper as the upper side. Here, A is an integer of 1 to 20, and a total of 20 samples were collected. The surface of the cut out sample was photographed at a magnification of 12000 using a scanning electron microscope (model number: S-2150, manufactured by Hitachi, Ltd.). The particle diameter was measured for a pigment which was closest to the point Bcm from the upper side of the photograph and Bcm from the left side and was photographed to such an extent that the entire particle was understood. Here, B is an integer of 1 to 5, and the particle diameter of five pigment particles was determined from one sample, and the particle diameter was determined for a total of 100 pigment particles. In addition, the maximum value is obtained by calculating the particle size distribution by counting the number of pigment particles up to an area particle size of 0.1 μm up to a particle size of 1.0 μm, and counting the particles exceeding 1.0 μm every 1.0 μm. The presence or absence of a value was judged. In addition, “0.1 to 1.0” described in Table 5 refers to particles in the range of 0.1 μm or more and less than 1.0 μm, and “1.0 to 10.0” means 1.0 μm or more. Refers to particles in the range of less than 10.0 μm.
When a plurality of types of pigments such as regenerated particles, calcium carbonate, kaolin clay, and the like are used in combination, it is possible to determine which particle is which pigment. Regenerated particles are aggregated particles composed of calcium, silicon and aluminum derived from deinked floss, heavy calcium carbonate is amorphous spherical particles, light calcium carbonate is spindle-shaped particles, and kaolin clay is plate-shaped. Particles. The shape can be sufficiently discriminated at a magnification of about 12,000.

  The maximum value of the fiber length distribution of the disaggregated pulp was measured as follows. The pulp fibers obtained by disaggregating the coated paper according to JIS P 8220: 1998 “pulp-disaggregation method” are described in FiberLab. The centerline fiber length was measured using (Kajaani Co., Ltd.) and defined as the fiber length. A weight-weighted fiber length distribution was obtained and tabulated for each fiber length of 0.05 mm to determine in which region the maximum value was included. In addition, the maximum value “0.50 to 0.55” described in Table 5 indicates that the maximum value is in a range of 0.50 mm or more and less than 0.55 mm. The same applies to the other numerical ranges.

The Runkel ratio of the disaggregated pulp was calculated according to the following formula from the number average fiber width and the number average fiber wall thickness obtained by measuring the fiber length distribution described above.
(Runkel ratio) = (twice the fiber wall thickness) / (fiber lumen diameter)
(Fiber lumen diameter) = fiber width-(twice the fiber wall thickness)

  About the obtained coated paper, each physical property was investigated with the following method. The results are shown in Table 5.

(A) Basis weight It measured based on the method of JISP8124: 1998 "Paper and paperboard-Basis weight measuring method".

(B) Paper thickness and density It measured based on the method as described in JISP8118: 1998 "Paper and paperboard-Test method of thickness and density".

(C) Whiteness Measured according to the method described in JIS P 8148: 2001 “Paper, paperboard and pulp—Method of measuring ISO whiteness (diffuse blue light reflectance)”. In the present invention, if the whiteness is 88% or more, the appearance is excellent, if it is 85% or more, the appearance is good, and if it is less than 85%, the coated paper is inferior in appearance.

(D) White paper glossiness Measured according to the method described in JIS P 8142: 2005 “Paper and paperboard—Measurement method of 75 ° specular gloss”. In the present invention, if the glossiness of white paper is 75% or more, the appearance is excellent, if it is 73% or more, the appearance is good, and if it is 70% or more, the appearance is slightly good and can be used practically. If it is less than this, the coated paper is inferior in appearance. If the white paper glossiness is 70% or more, it is practically used as a coated paper having a basis weight of 111 to 121 g / m ² .

(E) Stiffness (vertical)
Measured in the longitudinal direction according to the method described in JIS P 8143: 1996 “Paper-stiffness test method—Clark stiffness tester method”. In the present invention, if the stiffness is 95 or more, the stiffness is excellent, if it is 93 or more, the stiffness is good, if it is 90 or more, the stiffness is slightly good, and if it is less than 90, the stiffness is inferior.

(F) Opacity Measured according to the method described in JIS P 8149: 2000 “Paper and paperboard—Opacity test method (backing of paper) —diffuse illumination method”. In the present invention, if the opacity is 96% or more, the opacity is excellent, if it is 95% or more, the opacity is good, and if it is 93% or more, the opacity is slightly better, less than 93%. If so, the opacity is inferior.

(G) Printability Using an offset printing machine (model number: Lysopia L-BT3-1100, manufactured by Mitsubishi Heavy Industries, Ltd.), color 4 (color: product number: ADVAN, manufactured by Dainippon Ink & Chemicals, Inc.) 5000 copies of color offset printing were performed. About this printing surface, the degree of fluffing, roughening, and picking was observed visually and with a magnifying glass (10 times), and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: No fluffing, roughening or picking can be confirmed, and the printability is excellent.
○: Slight fluffing, roughening and picking can be confirmed, and printability is slightly inferior.
(Triangle | delta): Fluffing, roughening, and picking can be confirmed a little, and printability is somewhat inferior.
X: Fluffing, roughening and picking can be clearly confirmed, and the printability is poor.
Of the evaluation criteria, ◎, ○, and Δ are judged to be actually usable.

Commercially available A2 coated paper (S Utrilo Coat 127.9 g / m ² , manufactured by Daio Paper Co., Ltd.) is shown in Table 4 and Table 5 as Reference Example 1.

  All of the coated papers of the examples are coated papers having excellent whiteness, white paper gloss, stiffness, opacity, and printability. On the other hand, the coated paper of the comparative example is a coated paper that is inferior to any one or a plurality of items of whiteness, white paper glossiness, stiffness, opacity, and printability and does not satisfy the object of the present invention.

According to the present invention, while a basis weight of coated paper 111~121g / ^{m 2,} has a sheet thickness substantially equal to that of 127.9 g / ^{m 2,} a white paper glossiness is excellent, whiteness, A coated paper having an opacity, printability, and rigidity equivalent to 127.9 g / m ² can be provided.

  DESCRIPTION OF SYMBOLS 10 ... Raw material, 12 ... Storage tank, 14 ... 1st combustion furnace (internal heat kiln furnace), 20 ... Hot-air generating furnace, 22 ... Recombustion chamber, 26 ... Heat exchanger, 28 ... Induction fan, 30 ... Chimney, 31 ... External heat jacket, 32 ... second combustion furnace (external heat kiln furnace), 34 ... cooler, 36 ... particle size sorter, 42 ... heat treatment furnace (internal heat kiln furnace), 43 ... hot air generating furnace.

Claims (4)

A coated paper provided with a coating layer containing a pigment and an adhesive on a base paper, having a basis weight of 111 to 121 g / m ² , a paper thickness of 90 to 110 μm, JIS P 8142: 2005 “paper and paperboard— The weight of the pulp fiber obtained by disaggregating the coated paper according to JIS P 8220: 1998 “pulp-disaggregation method” having a white paper glossiness of 70% or more in the “75-degree specular gloss measurement method”. The fiber length distribution is calculated and tabulated every 0.05 mm fiber length, and has a maximum value in the range of fiber lengths from 0.10 mm to less than 0.65 mm,
Look containing silica composite playback particles or silica composite reproduction agglomerate the base paper as a filler,
Said coating layer has a top coat coating and underlying coating layer, the total coating amount of the overcoat coating and underlying coating layer (solid content) is characterized in that it is a 21~31g / m ² Coated paper. The pigment contains at least clay and calcium carbonate, and the clay and calcium carbonate have a particle size distribution in the range of 0.1 μm or more and less than 1.0 μm, 85% or more of all pigments, 1.0 μm or more and less than 10.0 μm. The coated paper according to claim 1 , which is contained in an amount of 15% or less of the total pigment. The coated paper according to claim 1 or 2 , wherein the blending amount of the filler is 2 to 10% by mass with respect to 100% by mass of the total pulp contained in the base paper. For coating amount of the undercoat coating layer in contact with the base paper, the mass ratio of the farthest outermost layer coating layer from the base paper, characterized in that it is a 1.5 to 1.9, according to claim 1, The coated paper of Claim 2 or Claim 3 .

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