JP2011012365A - Coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide coated paper that has sufficient paper thickness, excellent whiteness and white paper gloss, printability and rigidity (stiffness) as compared to coated paper having high square meter basis weight of not less than 10 g/min spite of being coated paper having low square meter basis weight in a grade A2 having a square meter basis weight of 85-95 g/m.SOLUTION: The coated paper is obtained by providing base paper with a coating layer containing pigment and an adhesive, has a square meter basis weight of 85-95 g/m, a paper thickness of 75-85 μm, a white paper gloss of not less than 65%, and a maximum value in the range of fiber length of not less than 0.10 mm and less than 0.65 mm in a fiber length distribution curve obtained by classification for every fiber length 0.05 mm of pulp fiber obtained by disintegrating the coated paper by the pulp-disintegrating method JIS-P 8220:1998.

Description

The present invention relates to a coated paper excellent in whiteness, white paper glossiness, rigidity, and printability without deteriorating the appearance even when the coated paper is under 1 kg (about 15 g / m ² reduction). In particular, the present invention relates to thick coated paper having a weight of 85 to 95 g / m ² .

  In recent years, due to efforts to reduce environmental impact and reduce carbon dioxide emissions through resource saving, in the paper field, the quality (whiteness, white paper glossiness, stiffness) of the same level as before, but lighter Paper is sought. In the coated paper field, it is necessary to satisfy printing glossiness and opacity 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 (unit weight) per unit area. However, simply reducing the paper weight of the paper has a problem that particularly the thickness (paper thickness) and rigidity (paper stiffness) of the paper are reduced, and further, the appearance (whiteness and white paper gloss) and printability are also reduced.

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 thick materials in coated paper, for example, using 84.9 g / ^{m 2} as an alternative to the coated paper 104.7 g / ^{m 2,} the basis weight when about 20 g / ^{m 2} to reduce the thickness of the paper described above, the rigidity (the paper (Waist) is likely to be greatly reduced, the appearance (white paper gloss and whiteness), and printability are also reduced.

For this reason, compared to these conventional products, the demand for coated paper with a reduced weight per unit area is high, while having the same thickness, rigidity, appearance (white paper gloss and printing gloss) and printability. However, in the method of simply reducing the rice tsubo while maintaining the above quality, it was the limit to reduce the rice tsubo by about 5 g / m ² .

  As a technology to improve the appearance of coated paper and glossiness of blank paper, the coated surface is flattened (calendar processing) with a flattening facility consisting of metal rolls and elastic rolls to flatten the printed surface of the coated paper. However, according to this method, the coated paper tends to be crushed and not only the paper thickness but also the rigidity is reduced.

  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 papers used for relatively high-grade printing, such as A2 coated papers. In general, blisters are more likely to occur as the US basis weight increases. There is a problem that blisters are likely to occur as compared with A3 coated paper and fine coated paper having a low US tsubo, and it is not preferable to contain a bulking agent. In order to improve the paper thickness, there is a method of including mechanical pulp, but mechanical pulp is stiff, and fuzzing and roughening (fibers rise after printing) are likely to occur, and printability tends to be reduced.

  In order to obtain coated paper with good printability, it is common to increase the coating layer, but the coating layer made of inorganic particles has a higher density and lower bulk than the base paper made of pulp. Difficult to achieve sufficient paper thickness.

As described above, a decrease of about 5 g / m ² was the limit in order to reduce the rice paper weight while maintaining the paper appearance, paper thickness, white paper gloss, printability, and rigidity (waist). . For example, a coated paper that maintains the above-mentioned quality even when the weight of the rice paper is reduced by about 10 g / m ² or more, particularly about 15 g / m ² has not been obtained.

JP 2005-248379 A JP 2009-079327 A

The main problem to be solved by the present invention is a coated paper having a rice tsubo of 85 to 95 g / m ² and a low A2 grade central tsubo, but a tsubo of 10 g / m ² or more (especially 15 g / m ² or more). ) To provide a coated paper that has sufficient paper thickness and good whiteness and white paper gloss compared with high coated paper, and in addition, printability and rigidity (waistness) do not decrease. .

The present invention is a coated paper in which a coating layer containing a pigment and an adhesive is provided on a base paper, having a basis weight of 85 to 95 g / m ² , a paper thickness of 75 to 85 μm, and a blank paper glossiness of 65%. In the fiber length distribution curve obtained by classifying pulp fibers obtained by disaggregating the coated paper according to JIS P 8220: 1998 “pulp-disaggregation method” into fiber lengths of 0.05 mm, fibers The coated paper is characterized by having the largest value in the range of 0.10 mm or more and less than 0.65 mm in length.

  The mass ratio of the coating layer to the base paper is preferably 0.34 to 0.53.

  It is preferable that at least clay is contained as the pigment, and the clay has a maximum value in a range of 0.1 μm or more and less than 1.0 μm and 1.0 μm or more and less than 10.0 μm in the particle size distribution.

  The base paper contains a filler, the blending amount of the filler is 2 to 8% by mass with respect to 100% by mass of the base paper, and the filler is composite particles composed of silica and inorganic particles other than silica. It is preferable.

  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, in a basis weight is 85~95g / ^{m 2} and A2 grade yet basis weight is lower coated paper, basis weight is 10 g / ^{m 2} or more (in particular 15 g / ^{m 2} or more) high coating Compared with paper, it can provide a coated paper that has a sufficient paper thickness, good whiteness and white paper gloss, and in addition, printability and rigidity (waistness) do not deteriorate.

  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 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)
The pulp used in the present invention is a fiber length distribution curve obtained by classifying pulp paper obtained by separating the coated paper by JIS P 8220: 1998 “pulp-disaggregation method” for each fiber length of 0.05 mm. The fiber length needs to have the largest value in the range of 0.10 mm or more and less than 0.65 mm. The range is preferably 0.15 mm or more and less than 0.60 mm, more preferably 0.20 mm or more and less than 0.55 mm. By making the maximum value in the fiber length distribution of the pulp fiber within this range, while maintaining the whiteness, paper thickness, white paper glossiness, printability, and rigidity (waistness) of the paper, the rice basis weight is about 10 g / It can be reduced by about m ² .

  If there are many fibers with a fiber length of less than 0.10 mm, and the fiber length does not have the largest value in the range 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. This is not preferable because sufficient rigidity cannot be obtained. If there are many fibers exceeding the fiber length of 0.65 mm and not having the largest value in the fiber length range of 0.10 mm or more and less than 0.65 mm, the paper thickness tends to increase in part due to the long fibers, It is not preferable because fluffing and roughening occur and printability (appearance after printing) is poor. 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 value in the fiber length distribution range of 0.10 to 0.65 mm in the fiber length distribution curve, 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 are 0.10 to 0.65 mm in terms of fiber length after disaggregation. What is necessary is just to adjust the mixture ratio with other pulp from which fiber length differs so that it may have the maximum value in this range.

In the present invention, the Runkel ratio of the disaggregated pulp is preferably 0.4 to 2.0, 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, the paper thickness, white paper glossiness, and rigidity are high, and printing with less fuzz and roughening is performed. It becomes easy to obtain coated paper excellent in suitability. For example, when the Runkel ratio is less than 0.4 or exceeds 2.0, the appearance does not deteriorate even if the rice basis weight is reduced by about 10 g / m ² , and the whiteness, white paper gloss, stiffness And, coated paper excellent in printability can be obtained. If the Runkel ratio is less than 0.4, the coated paper having a rice basis weight of 85 to 95 g / m ² is not preferable because the paper thickness tends to be less than 75 μm and the rigidity is also lowered. 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 Camellia, Mizunara, Katsura, Harigiri, and Yachidamo have a small Runkel ratio (about 1-2). Even smaller (about 1 or less).

The pulp used in the present invention needs to have the largest value within the range of the fiber length of the disaggregated pulp of 0.10 to 0.65 mm. Furthermore, the Runkel ratio is 0.4 to 2.0, preferably It is preferable to use a conifer having a long fiber length so as to be 0.6 to 1.0. In the present invention, even though the basis weight is low and 85~95g / m ^2, since the paper thickness have 75~85μm sufficient paper thickness, problems strength such as tensile strength and tear strength is likely lowered There is. In order to prevent a decrease in strength, in the present invention, it is preferable to use a pulp having a Runkel ratio of pulp after disaggregation of 0.4 to 2.0 (more preferably 0.6 to 1.0).

  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 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 are easily obtained and the fiber length after disaggregation is likely to be in the range of 0.10 to 0.65 mm. In particular, when thermomechanical pulp or chemithermomechanical pulp is used, there are many fine fibers having a fiber length after disaggregation of 0.10 to 0.65 mm, while there are few shives (binding fibers), and excellent-looking pulp and coated paper Since it is obtained, it is preferable.

  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)
A filler conventionally used for papermaking can be added to the raw material pulp as an internal filler. Examples of the filler include inorganic fillers such as light calcium carbonate, talc, titanium dioxide, clay, calcined clay, synthetic zeolite, and silica, polystyrene latex, urea formalin resin, and the like. In this invention, it is preferable to mix | blend the composite particle which consists of inorganic particles other than a silica and silica as a filler.

(Regenerated particles)
In the present invention, if regenerated particles or regenerated particle aggregates with excellent opacity are used as fillers, and further silica-coated regenerated particle aggregates are used, the amount of filler used can be reduced, and coated paper with higher rigidity can be obtained. preferable.

(Production process of regenerated particles and regenerated particle aggregates)
The recycled particles are obtained by using the deinked floss separated from the pulp fiber in the deinking process of the used paper processing equipment for producing the used paper pulp as a main raw material, and then dehydrating, drying, burning and grinding the main raw material. 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 5 to tens of μm by a known pulverization method. If the particle size is smaller than 5 μm, the yield is poor and it is easy to form foreign matter in the paper machine system, and if it is larger than 10 μm, the formation may be deteriorated and the strength (tensile strength and tear strength) may be reduced. This is not preferable.

  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 or regenerated particle aggregates contain calcium, silicon, and aluminum in 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.

  In the firing process, as the method for adjusting the calcium, silicon and aluminum oxide conversion ratio of the regenerated particle aggregate, the main component is to adjust the raw material composition in the deinking floss, but the drying / classifying process, firing In the process, it is also possible to make adjustments by means of containing a coating floss with a clear origin or an adjustment process floss in the process by spraying or by means of containing incinerator scrubber lime.

  For example, neutral papermaking wastewater sludge and coated paper manufacturing process wastewater sludge are used to adjust calcium in inorganic particle aggregates, and silicon is added in large quantities as an opacity improver. Newspaper manufacturing wastewater sludge can be appropriately used for adjustment of aluminum. Papermaking wastewater sludge such as acidic papermaking system that uses sulfuric acid band and wastewater sludge in high quality papermaking process that uses a lot of talc can be used.

[Attached process]
In order to obtain more stable quality in production facilities, it is preferable to classify the particle size of the regenerated particle agglomerates uniformly in each step, and by feeding back coarse particles and fine particles to the previous step Quality can be 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 the production facility, it is preferable to remove foreign matters other than the aggregates of regenerated particles. For example, sand, plastic foreign matters, metals, etc. are removed with a pulper, screen, cleaner, etc. before reaching the deinking process of the used paper pulp manufacturing process. It is preferable in terms of removal efficiency. 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-coated regenerated particles, silica-coated regenerated particle aggregates]
In the present invention, it is preferable to use fillers generally used in papermaking applications, that is, silica-coated inorganic particles obtained by coating calcium carbonate (heavy and light), clay, talc and the like with silica. Using silica-coated regenerated particle aggregates with the surface of the regenerated particle aggregates coated with silica results in particles that are more bulky and have higher opacity, so the filler content can be reduced, and high paper thickness and rigidity are obtained. be able to. In particular, as in the present invention, in order to prevent a decrease in paper rigidity (waistness), it is necessary to reduce the amount of filler that inhibits interfiber bonding between pulp fibers. However, when the amount of filler decreases, opacity tends to decrease. In addition to this, there is a problem that fluffing and roughening of the pulp fiber occurs and printability tends to be lowered, and it is difficult to achieve both rigidity and printability. However, in the present invention, when silica-coated inorganic particles having excellent opacity are used as the filler, the amount of the filler can be reduced, so that it becomes easy to obtain a coated paper excellent in both rigidity, paper thickness and printability.

  As a suitable measure for precipitating silica on the regenerated particle aggregate, it can be carried out by the methods described in Japanese Patent No. 3907688 and Japanese Patent No. 3935496. However, it is preferable to carry out as follows because silica-coated particles having more excellent opacity can be obtained.

  In the following, a method for coating silica will be described, taking as an example the case where the particles to be coated are aggregates of regenerated particles.

  Mineral acids such as sulfuric acid, hydrochloric acid or nitric acid at a liquid temperature of 70 to 100 ° C. while heating and stirring, after adding / dispersing the regenerated particles or regenerated particle aggregates obtained in the production process to an aqueous alkali silicate solution to prepare a slurry. To produce silica sol, and adjust the pH of the final reaction solution to a range of 8.0 to 11.0 to produce silica sol particles having a particle diameter of 10 to 20 nm on the surface of the regenerated particles. Silica-coated regenerated particles or silica-coated regenerated particle aggregates are obtained. The silica-coated particles can further improve the opacity due to the silica precipitation effect by making calcium, silicon, and aluminum into mass ratios of 30 to 62:29 to 55: 9 to 35 in terms of oxides. .

  Prepare an aqueous solution in which particles to be coated (regenerated particle agglomerates, etc.) and alkali silicate are mixed at a mass ratio of 9: 1, raise the temperature of the solution while heating and stirring, and then add an acid to form a silica sol Thus, silica can be deposited on the surface of the particles to be coated (regenerated particle aggregates).

  The alkali silicate solution to be used is not particularly limited, but a sodium silicate solution (No. 3 water glass) is desirable in view of availability. 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 SiO2). If it exceeds 10% by mass, white carbon is liable to be precipitated, which makes it difficult for silica to precipitate on the surface of the regenerated particle aggregate, and the opacity cannot be sufficiently improved. Moreover, even if it is less than 3 mass%, since silica hardly precipitates on the regenerated particle aggregate, it is not preferable.

  The liquid temperature is preferably 70 to 100 ° C, more preferably 80 to 100 ° C, and most preferably 90 to 100 ° C. If the liquid temperature is less than 70 ° C., the particle diameter does not grow, and it is not preferable because the particles may not become as large as several μm that can be used as a filler. By setting the liquid temperature to 70 ° C. or higher, preferably 80 ° C. or higher, most preferably 90 ° C. or higher, regenerated particles or regenerated particle aggregates pulverized to 1 to 2 μm can be used as an internal filler. It can be grown to about μm.

  When the particle size of regenerated particles or regenerated particle aggregates is larger than 2 μm, the particle size tends to become as large as several tens of μm after regenerating with silica coating, and the resulting coated paper is deteriorated in strength or tensile (tensile strength). Or tear strength) is not preferable. In addition, when the particle before silica coating is as large as 2 μm or more and silica coating is performed at less than 70 ° C., the particle diameter may fall within about 5 to 10 μm, but the generation of silica sol becomes gradual, The obtained silica-coated particles are not preferable because sufficient opacity may not be obtained. In addition, when the particle diameter is mechanically adjusted by pulverization or the like in the subsequent process, the coated state of the silica is broken and the opaque layer is hardly improved.

  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. Usually, in the production of silica particles (white carbon), in order to complete the reaction between hydrated silicic acid and mineral acid, a method of adding mineral acid until pH 5.5 to 7.0 is common, but the pH is 7 When the acid range is as follows, the calcium carbonate contained in the regenerated particles or the regenerated particle aggregates is easily decomposed into calcium hydroxide and carbonic acid, the particle diameter is decreased, and the yield on paper is likely to be decreased. It is not preferable because it is difficult to obtain opacity. If the pH exceeds 11.0, silica is difficult to precipitate and the particles are not easily covered with silica, so that it is difficult to obtain sufficient opacity.

  The silica-coated particles thus obtained can be used as a filler because the surface of the particles is coated with silica, so that the degree of wire wear can be lowered. Inorganic particles added internally to paper, if the particles are hard, the wire (net part) of the paper machine is liable to be damaged, which not only shortens the life of the wire, but is also not preferable because foreign substances are likely to accumulate in the paper machine system. However, as in the present invention, by using inorganic particles coated with silica, preferably silica-coated regenerated particle aggregates, it is possible to obtain 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. In the regenerated particle aggregate having an abrasion degree of about 80 mg, the abrasion degree can be reduced to about 20 mg by silica coating, and particles that can be sufficiently used as an internal filler can be obtained. 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 silica-coated inorganic particles, preferably silica-coated regenerated particle aggregates, as the filler because a coated paper having high opacity can be obtained. In particular, coated papers that require rigidity (waistness) are preferred because even if the filler content is reduced, coated papers that are less prone to fuzzing and roughening and that have excellent blank glossiness can be obtained.

  The content of these fillers is not particularly limited, but is preferably added so as to be 2 to 8% by mass with respect to 100% by mass of the base paper, and more preferably 3 to 7% by mass. When the blending amount of the filler exceeds 8% by mass, not only the binding between pulp fibers is easily inhibited and the rigidity is easily lowered, but also dampening water is absorbed during printing, and paper breakage is likely to occur. . In particular, when silica-coated inorganic particles are contained as a filler, the liquid absorbency of the base paper is likely to be improved, and therefore the paper tends to be easily cut. When the filler content is less than 2% by mass, there is a problem that fuzzing and roughening are 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 pulp fiber needs to have the largest value in the fiber length range of 0.10 to 0.65 mm in the fiber length distribution curve, and in addition, the Runkel ratio is 0.4 to 2.0. (More preferably, it is 0.6 to 1.0). Furthermore, as a filler, the above-mentioned silica-coated inorganic particles are contained in an amount of 2 to 8% by mass (more preferably 3 to 7% by mass) with respect to 100% by mass of the base paper, thereby increasing bulkiness, whiteness and white paper gloss. It is preferable because all of printability, rigidity and opacity can be improved. That is, inorganic particles (regenerated particles, regenerated particle aggregates, etc.) and alkali silicate are mixed at a mass ratio of 9: 1 and heated to 70-100 ° C., preferably 90-100 ° C., and then the pH is 8. The silica-coated inorganic particles having a particle diameter of about 5 to 10 μm obtained by adding acid until the pH is 0 to 9.5, preferably pH 8.5 to 9.0, and without using mechanical means such as grinding. It is preferable to add it as a filler because a coated paper having excellent paper thickness, opacity and rigidity can be obtained. In particular, the basis weight is in coated paper 85~95g / ^{m 2,} a basis weight is 10 g / ^{m 2} or more (in particular 15 g / ^{m 2} or more) as compared to the higher coated paper, whiteness of paper, paper thickness, This is preferable because coated paper having the same level of glossiness, printing suitability, and rigidity (waistness) can be obtained.

  Further, the particles to be coated with silica 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 the present invention, silica-coated inorganic particles obtained by coating these inorganic particles with silica by the method described above 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 base 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 As a result, it is difficult to cause rust stains, so that the rust stains are not noticeable on the entire white paper surface, and a coated paper that does not impair the sense of quality can be obtained. 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 splicing, 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 of the base paper produced as described above, a pigment coating solution containing a pigment and an adhesive is undercoated. 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 12.2 g / m ² , more preferably 8.5 to 11.5 g / m ² , particularly preferably in total on both sides. Is 9.3 to 10.7 g / m ² . When the coating amount of the undercoat coating layer is less than 7.8 g / m ^2, it is preferable because an uncoated part tends to occur on the surface of the base paper, unevenness occurs in smoothness, and the glossiness of the white paper and printability are poor after the topcoat coating. Absent. If it exceeds 12.2 g / m ² , the total coating amount with the top coat layer tends to increase, and the base paper rice tsubo is lowered, so that the rigidity is inferior.

  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 tightness, 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, the fiber length of the disaggregated pulp contains many pulp fibers having a length of 0.10 mm or more and less than 0.65 mm, and in addition, contains many pulp fibers having a Runkel ratio of 0.4 to 2.0. However, the printability is likely to be lowered, but the printability can be improved by providing a topcoat coating layer after the pre-calender treatment after the undercoat coating.

(Top coat coating)
Next, a coating liquid containing a pigment and an adhesive is overcoated on one or both sides of the base paper 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 clay is preferably a combination of fine particles having a small particle size and plate-like particles having a large particle size. By blending small particle size clay, it becomes easier to fill the surface of the coating layer, improving the glossiness of the blank paper and the printability, but on the other hand, the specific gravity of the coated paper that is easily filled is likely to increase. It is difficult to obtain a bulky coated paper. On the other hand, when plate-like particles are blended, the coverage of the coating layer surface tends to be high, and an increase in the tension can be prevented, but on the other hand, the surface is difficult to be filled, and blank glossiness and printability are liable to be reduced. Absent. However, when these small particle size clays and plate-like clays are used in combination, the coverage and filling properties of the coating layer surface can be improved without increasing the tightness of the coated paper, resulting in excellent white paper gloss and printability. Coated paper is obtained.

  The clay having a small particle size preferably has a maximum value in a particle size distribution within a range of 0.1 μm or more and less than 1.0 μm.

  The plate-like clay is not particularly problematic as long as the aspect ratio (the ratio of the plate diameter to the particle thickness) is 5 or more, but it is a maximum value in the range of the particle size distribution from 1.0 μm to less than 10.0 μm. It is preferable to have.

  The particle diameter of the present invention refers to a particle diameter obtained by photographing 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 clay and plate-shaped clay having a maximum value in these ranges are preferably used in a mass ratio of 2: 1 to 1: 2. If the clay with a small particle size is larger than the above range or the plate-like clay is less than the above-mentioned range, in particular, if no plate-like clay is contained, not only the coating property of the coated paper is lowered and the printability is lowered, but also fuzziness and This is not preferable because it is difficult to prevent roughening sufficiently. If the small particle size clay is less than the above range, especially if it does not contain small particle clay, or if the plate-like clay is more than the above range, not only the surface roughness of the coated paper will be reduced and the glossiness of the white paper will be reduced. It is not preferable because it is difficult to prevent fuzzing and roughening sufficiently.

  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 top coat layer is the sum of both surfaces, preferably 13.2 to 20.8 g / m ² , more preferably 14.5 to 19.5 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 20.8 g / m ² , the ratio of the coating layer in the coated paper increases, and not only the rigidity tends to decrease, but also the tenacity and the US basis weight tend to increase, which is not preferable.

The total coating amount of the overcoat coating and underlying coating layer in the coated paper of the present invention (solid content) is preferably from ^{23~31g / m 2, 25~29g / m} 2 is more preferable. If the total coating amount is less than 23 g / m ² , the coating layer surface cannot be sufficiently covered, and not only fuzzing or roughening occurs and printability is deteriorated, but also the glossiness of blank paper is liable to be lowered. If it exceeds 31 g / m ² , the ratio of the coating layer in the coated paper increases, and not only the rigidity tends to decrease, but also the tenacity and the US basis weight tend to increase, which is not preferable.

  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 0.34 to 0.53, and more preferably 0.38 to 0.48. When the ratio is less than 0.34, the ratio of the coating layer decreases, so that not only fuzzing and roughening is not sufficiently prevented, but also the glossiness of the white paper is likely to decrease, and when it exceeds 0.53, the rigidity is likely to decrease. Therefore, 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. 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 fuzzing and roughening sufficiently. Since there are many coating layers, since whiteness falls easily, it is not preferable.

  Particularly when the fiber length of the disaggregated pulp is 0.10 mm or more and less than 0.65 mm as in the present invention, the coating amount is 0.34 to 0.53 (more than the base paper in mass ratio) Preferably it is 0.38 to 0.48) because fuzzing and roughening can be prevented and printability can be improved. In addition to these, as a pigment, preferably clay, on the surface of the coating layer, particles having a maximum value in the particle size distribution range of 0.1 μm or more and less than 1.0 μm, and a particle size distribution of 1. By using particles having a maximum value in the range of 0 μm or more and less than 10.0 μm, the paper thickness, rigidity, blank paper glossiness, and printability can be improved. Furthermore, it is preferable that the mass ratio of these particles is 2: 1 to 1: 2. In addition to these, by using inorganic particles coated with silica as a filler, the rigidity and paper thickness can be further improved, and furthermore, the ratio of the coating amount of the topcoat coating layer to the coating amount of the undercoat coating layer, By setting the mass to 1.5 to 1.9, it is possible to obtain a coated paper that is particularly excellent in paper thickness, whiteness, white paper gloss, stiffness, and printability.

  As described above, in addition to having a fiber length distribution having the largest value in the fiber length range of 0.10 mm or more and less than 0.65 mm, the Runker ratio of the disaggregated pulp is 0.4 to 2.0 (further 0.6). -1.0), and further, as a filler, on the base paper containing 2-8% by mass (preferably 3-7% by mass) of the silica-coated inorganic particles described above with respect to 100% by mass of the base paper. The clay as a coating layer contains 40 to 90 parts by mass (preferably 50 to 80 parts by mass) of the pigment, and two types of clay having a small particle diameter and a plate-like structure are used in combination as a clay. By using it, the surface of the coating layer is made to contain particles having a maximum particle size distribution in the range of 0.1 μm or more and less than 1.0 μm in particle size distribution, and using a plate-like clay With a particle size distribution of 1.0 μm or more The particles having the maximum value in the range of less than 0.0 μm are contained, and the clay and the plate-like clay having a small particle diameter are used in a mass ratio of 2: 1 to 1: 2, and the coating amount is Coating having a mass ratio of 0.34 to 0.53, preferably 0.38 to 0.48 with respect to the base paper, and further comprising at least two coating layers having an undercoat coating layer and an overcoat coating layer In paper, the ratio of the coating amount of the topcoat coating layer to the coating amount of the undercoat coating layer is 1.5 to 1.9 in terms of mass, while the coating weight is low, A coated paper having a paper thickness and excellent in whiteness, white paper gloss, rigidity, and printability can be obtained.

  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 it is not preferable because the above-mentioned particles having a particle diameter of 0.1 to 1.0 μm are not sufficiently adhered. If it exceeds 65%, the amount of latex on the surface of the coating layer will increase, and dirt will adhere to the various rolls in the coated paper manufacturing process, leading to a decrease in operability. 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 an effect of imparting water resistance to the coating layer, the coated paper having a small tension of 1.05-1.20 g / cm ^{3 as in} the present invention absorbs dampening water during printing. From the viewpoint of preventing paper breaks resulting from the above, the above ratio is preferable. In particular, as described above, when silica-coated inorganic particles having a high liquid-absorbing property are contained as a filler, it is preferable to contain 20 to 35% by mass of a styrene component for preventing paper breakage. If the styrene component is less than 20% by mass, the water resistance of the coating layer is inferior. Therefore, in offset printing, in addition to paper breakage, the dampening water is absorbed to reduce the coating layer strength, causing problems such as white spots and paper breakage. 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, printing glossiness, and printability, it is preferable to keep the butadiene component and styrene component in the terrax 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. If the content is less than 5 parts, the coating layer strength decreases, not only white spots occur during printing, but the pigments easily fall off from the coated paper in the manufacturing process, and the system stains the system. Since both paper quality and operability deteriorate, it is not preferable. If 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 the dryer parts, which is performed in a plurality of stages, usually two stages of a pre-dryer part and an after-dryer part. In this coater part, for example, an on-machine coater 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. Among them, even immediately after coating, the coating layer surface has high flatness, and in the subsequent flattening process, the smoothness of the surface can be improved without increasing the glossiness under mild calendering conditions. It is preferable to use a blade coater from the viewpoint that the blank paper glossiness and printability can be improved without reducing the thickness. 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 overcoat using a blade coater. By using the above coating method, high smoothness can be imparted to the surface of the coating layer, so that the calendering process described later can be performed under moderate conditions, and glossy coated paper having a larger paper thickness can be 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 the coated paper having an excellent paper thickness, if the nip pressure is increased to improve the glossiness, the paper thickness may be easily lowered. However, in the present invention, the fiber length is 0.10 to 0.00. In addition to having a fiber length distribution having the largest value in the range of 65 mm, the Runkel ratio of the disaggregated pulp is 0.4 to 2.0, and further 0.6 to 1.0. Even when the flattening treatment is performed at 200 to 500 kN / m), a coated paper having a high paper thickness of 75 to 85 μm and excellent in white paper glossiness, printing glossiness, printability, and rigidity can be obtained.

  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 scorch occurs, or the coated paper itself changes yellow due to heat and pressure ( 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 large-scale equipment is required, and the smoothness of both 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. With the on-machine type, flattening can be performed immediately after coating at a high paper surface temperature, which improves smoothness and minimizes paper thickness reduction while improving blank paper gloss and print gloss. This is preferable.

The coated paper having a basis weight of 85 to 95 g / m ² , which has been flattened under the above conditions, has a high paper thickness of 75 to 85 μm and an excellent bulk even though the glossiness of the white paper is as high as 65% or more. Although it is a coated paper, it is a good-looking coated paper that is less prone to fuzzing and 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 listed in the table are mixed at a ratio (mass ratio) described in the table, and the filler described in the table and 100 parts by mass of this pulp (absolute amount) ), 0.02 parts by mass of internal sizing agent (Part No .: AK-720H, manufactured by Harima Chemicals Co., Ltd.), cationized starch (Part No .: Amilofax T-2600, Abbe Japan Co., Ltd.) )) 1.0 part by mass and 0.02 part by mass of a yield improver (product number: NP442, manufactured by Nissan Eka Chemicals Co., Ltd.) were added to obtain a pulp slurry. The freeness of NBKP was adjusted to 500 ml, the freeness of LBKP was adjusted to 400 ml, and the freeness of BTMP was adjusted to the values shown in the table.

  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. The basis weight of the base paper is as shown in the table.

  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) 8 parts by mass of the undercoat coating liquid was added to both sides, and the coating amount shown in the table ( It was coated with a film transfer type roll coater so that the 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% by mass with respect to 100 parts by mass of the pigments described in the table. %) The top coating solution mixed with 8 parts by mass was applied using a blade coater so that the total coating amount on both sides would be the coating amount (solid content) shown in the table. 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)
-Regenerated particle agglomerates The particles were prepared by adjusting the particle size according to the production method of Japanese Patent No. 3869455. Specifically, the deinking floss discharged from the waste paper treatment process is dehydrated to a moisture content of 60% (dehydration process), dried at 120 ° C. (drying process), and the moisture content at the firing process inlet becomes 3%. And firing at 550 ° C. so that the unburned portion becomes 7% in the first firing step, and firing so that the unburned portion becomes 12 mass% in the second firing step (baking step), and the particle size A 500 μm regenerated particle agglomerate was produced. Thereafter, wet pulverizer (product number: Planetary Mill, manufactured by Seishin Enterprises) using a mean particle diameter (d ₅₀₎ was pulverized so as to be 1.5 [mu] m.

・ Silica-coated regenerated particle agglomerates The regenerated particle agglomerates and alkali silicate obtained in the above production process were mixed at a mass ratio of 9: 1 to prepare a slurry, and then the liquid temperature was raised to 90 to 95 ° C. while stirring. The mixture was warmed and sulfuric acid was added to form a silica sol, and the pH of the final reaction solution was adjusted to 9.0. In this silica-coated regenerated particle aggregate, the ratio of calcium, silicon and aluminum was 31:52:17 in terms of oxide, and the particle diameter (d ₅₀ ) was 8.0 μm.

-Calcium carbonate Light calcium carbonate, product number: TP121-6S, manufactured by Okutama Kogyo 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
・ Plate-like clay Product No .: Century HC, manufactured by Parapigments Co., Ltd., average particle size 2.8 μm
The maximum value of the particle size distribution on the coated paper surface described in the table 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 the clay closest to the point Bcm from the upper side to the lower side of the photograph and Bcm from the left side, and the entire particle being photographed. Here, B is an integer of 1 to 5, and the particle diameter of five clay particles was determined from one sample, and the particle diameter was determined for a total of 100 clay particles. The maximum value was determined by counting the number of clay particles every area particle size of 0.1 μm to obtain a particle size distribution, and determining the presence or absence of the maximum value. 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. The regenerated particles are agglomerated particles composed of calcium, silicon and aluminum derived from deinking floss, calcium carbonate is irregularly shaped spherical particles, and kaolin clay is plate-shaped. The shape can be sufficiently discriminated at a magnification of 12000 times.

  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. The fiber length distribution curve was calculated by counting the number of fibers every 0.05 mm of fiber length, and it was determined in which region the maximum value was included.

The Runkel ratio of the disaggregated pulp was calculated according to the following formula from the average fiber width and 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 the table.

(A) Rice tsubo JISP8124: 1998 It measured based on the method as described in "Paper and paperboard-Basis weight measuring method".

(B) Paper Thickness and Tension This was measured in accordance with the method described in JISP 8118: 1998 “Paper and Paperboard—Test Method for 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 87% or more, the appearance is excellent, if it is 84% or more, the appearance is good, and if it is less than 84%, 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 68% or more, the appearance is excellent, if it is 65% or more, the appearance is good, and if it is less than 65%, the coated paper is inferior in appearance.

(E) Stiffness (vertical)
JISP8143: Measured according to the method described in "Paper-stiffness test method-Clark stiffness tester method" in 1996. In the present invention, if the rigidity is 62 or more, the rigidity is excellent, if it is 60 or more, the rigidity is good, if it is 58 or more, the rigidity is slightly good, and if it is less than 58, the rigidity is inferior. If the stiffness is 58 or more, the coated paper with a weight of 85 to 95 g / m ² can be practically used.

(F) 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 and roughening was observed visually and with a magnifying glass (10 times), and evaluated based on the following evaluation criteria.

(Evaluation criteria)
A: No fuzzing or roughening can be confirmed, and the printability is excellent.
○: Slight fluffing and roughening can be confirmed, and printability is slightly inferior.
Δ: Slight fluffing and roughening can be confirmed, and printability is somewhat inferior.
X: Fluffing and roughening can be clearly confirmed, and printability is poor.
Of the evaluation criteria, ◎, ○, and Δ are judged to be actually usable.

Commercially available A2 coated paper (105 g / m ² ) is shown in Table 1 as Reference Example 1.

  All of the coated papers of the examples are coated papers having excellent whiteness, white paper gloss, rigidity, 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, rigidity, printability, and does not satisfy the object of the present invention.

  According to the present invention, the coating has a sufficient paper thickness, a good whiteness and a good glossiness of white paper, and a printability and rigidity (waistness) are not lowered while having a relatively low weight per square meter. Paper can be provided.

Claims (5)

A coated paper provided with a coating layer containing a pigment and an adhesive on a base paper,
US basis weight is 85 to 95 g / m ² , paper thickness is 75 to 85 μm, blank paper gloss is 65% or more,
In a fiber length distribution curve obtained by classifying pulp fibers obtained by disaggregating the coated paper according to JIS P 8220: 1998 “pulp-disaggregation method” into fiber lengths of 0.05 mm, the fiber length is 0.10 mm. A coated paper having the largest value in a range of 0.65 mm or less.   The coated paper of Claim 1 whose mass ratio of the said coating layer with respect to the said base paper is 0.34-0.53.   3. The pigment according to claim 1, wherein the pigment contains at least clay, and the clay has a maximum value in a range of 0.1 μm or more and less than 1.0 μm and 1.0 μm or more and less than 10.0 μm in a particle size distribution. Coated paper.   The base paper contains a filler, the blending amount of the filler is 2 to 8% by mass with respect to 100% by mass of the base paper, and the filler is composite particles composed of silica and inorganic particles other than silica. The coated paper of any one of Claims 1-3.   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 The coated paper of any one of Claims 1-4 which is 1.9.