JP2009221636A - Newsprint paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide newsprint paper can carry out high-speed papermaking at 1,300 m/min paper velocity without causing voids, without producing edge dust due to deterioration of surface strength, without deteriorating printing operation efficiency, and print suitability such as color drift, and without deteriorating printing opacity, using a cold-setting type ink, and suitable for high-speed web offset printing at 170,000-200,000 copies/h. <P>SOLUTION: The newsprint paper is characterized by internally adding hydrated silicic acid as a filler, and having 36-50 g/m<SP>2</SP>basis weight according to JIS P 8124, 7-17 mass% ash content measured according to JIS P 8251, and ≤7.5 mass% content of magnesium (content of magnesium in terms of oxides) in the ash content. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to newsprint. More specifically, the present invention relates to newsprint that is particularly suitable for high-speed offset rotary printing using, for example, cold set ink.

In order to reduce the burden of delivery work, to reduce delivery costs, and to make effective use of resources, it is desirable to reduce the weight of printing paper such as newspaper and free paper that are used in large quantities every day. A lightweight one having a basis weight of 36 to 50 g / m ² is mainly used.

  However, with the reduction in weight and the effective use of resources, the used ratio of used paper increases, resulting in a decrease in blank paper opacity and printing opacity of the resulting newspaper. Therefore, as a measure for reducing the opacity, an inorganic filler is usually blended in the raw material pulp. However, due to the increased distribution of the inorganic filler, troubles such as a decrease in the surface strength of newsprint and generation of paper dust have occurred.

  In general, waste paper pulp such as deinked waste paper pulp is pulp that has been paper-made, calendered, and recycled from waste paper collected after use in the market. Therefore, the pulp fiber is damaged, the fiber is short, and the cushioning property is low. It has become. For this reason, newsprints containing a large amount of waste paper pulp have high density and low cushioning properties. In addition to the occurrence of paper dust due to a decrease in ink setting properties and ink inking properties and a decrease in surface strength, inks resulting from these The concentration is lowered. In newsprint, in particular, the constituent materials are approximate, and a large amount of used newspaper that is most efficient in terms of resource recycling is likely to cause such problems.

  Deinked wastepaper pulp derived from used newspaper contains a large amount of fine inorganic substances derived from fillers contained in newsprint, and is finely fixed firmly to the raw pulp fibers even after deinking and washing processes in the deinking process. Inorganic fine particles remain. In the recycling process that has been repeated many times in recent years, the content ratio of such residual inorganic particles is further increased, and printing suitability such as white spots, generation of paper dust due to a decrease in surface strength, printing operability, color misregistration, etc. This is a cause of problems such as a decrease in printing opacity.

  Therefore, as a technique for solving such a problem, for example, in Patent Document 1, a conventional calendar formed of a metal roll is replaced with a soft calendar including a combination of an elastic roll and a metal roll, and a metal roll (heat roll) is used. ) Is adjusted to 20 to 150 ° C. and flattened to produce a newspaper for offset printing with a small amount of paper dust. However, such a physical flattening process lowers the rigidity of the paper, deteriorates the handling as newsprint, makes it difficult for the reader to handle the newsprint, and makes the newsprint surface more precise. This impedes the absorption and drying properties of the ink, and causes ink stains and set-off problems.

On the other hand, in the technique of simply applying starch (surface treatment agent) to the surface of the base paper, for example, a starch application amount exceeding 2.0 g / m ² is required. As a result, there is a problem that nepari occurs, and it becomes difficult for the newsprint to be peeled off from the blanket and the workability is lowered.

Therefore, as a technique for solving such a problem, for example, Patent Document 2 discloses that a high-speed printing with a cold-set ink is performed by applying a newsprint coating composition containing a specific polymer latex to a newsprint base paper. In color offset rotary printing, newspapers are excellent in offset printing suitability such as surface strength, ink fillability, ink setability, etc. and tensile strength (especially wet tensile strength), and a good balance between these offset printing suitability and tensile strength. Techniques for obtaining a paper coating composition and newsprint are disclosed. This is because latex generally has high film properties, so the strength of the newsprint surface is increased, and when printing is performed using cold-set ink, the ink is retained on the newsprint surface, so that the ink setting properties and ink setting properties are improved. Thus, it is intended to obtain offset printing aptitude. However, newsprint with a latex film that has a much higher film-forming property than conventional newsprint, can reduce the amount of cold set ink applied during offset printing (reduce the amount applied). If it is not carried out by a machine, the ink setting property of the cold set type ink in newspaper printing does not sufficiently progress and warps, and causes problems such as rubbing stains and ink back-off. Therefore, it is necessary to set a printing machine different from the conventional conventional high-speed multi-color offset rotary printing, and there is a problem that the printing workability is deteriorated and printing defects are caused.
Japanese Patent Laid-Open No. 2002-285496 JP-A-6-123099

  The present invention has been made in view of the above-described background art, and is capable of high-speed papermaking, for example, at a papermaking speed of 1300 m / min or more. The occurrence of paper dust due to white spots and a decrease in surface strength, printing operability, color Conventional problems such as poor printability such as misalignment and low print opacity have been improved, and the use of cold set ink, which has become the mainstream in recent years, for example, at a high speed of 170 to 200,000 copies / hour An object of the present invention is to provide a newsprint suitable for offset rotary printing.

The present invention
A newsprint with a basis weight of 36-50 g / m ² in accordance with JIS P 8124, with hydrated silicic acid added internally as a filler,
The ash content measured according to JIS P 8251 is 7 to 17% by mass, and the magnesium content (magnesium content in terms of oxide) in the ash content is 7.5% by mass or less. , Newsprint.

According to the present invention, for example, a high speed papermaking of, for example, a paper making speed of 1300 m / min or more is possible, and although a basis weight is as small as 36 to 50 g / m ² and light, a cold set type ink is used. Even when it is subjected to multicolor offset rotary printing at a high speed of 170 to 200,000 copies / hour, the printing operability is good, and the ink setting property is also good while having high ink density and ink setting properties. Thus, there is provided a newsprint that not only has excellent printability without causing color misregistration, but also does not generate white spots or paper dust due to a decrease in surface strength, and maintains high printing opacity.

(Embodiment)
The newsprint of the present invention contains hydrated silica as a filler and has a basis weight of 36 to 50 g / m ² .

  First, the raw material pulp used in the present invention will be described. The pulp constituting the base paper of the newsprint of the present invention is not particularly limited. For example, it is preferable to use at least deinked waste paper pulp.

  The use of deinked waste paper pulp is preferable from the viewpoint of environmental conservation, and in newsprint paper, in particular, the use of deinked waste paper pulp and high blending have been demanded from the viewpoint of effective use of resources. On the other hand, increasing the amount of deinked waste paper pulp generally makes it difficult to ensure a predetermined surface strength, and lowers the printability such as ink setting properties and ink fillability. In other words, deinked waste paper pulp is pulp that has been paper-made, calendered, and recycled from used paper collected after use in the market, so that the pulp fibers are damaged, the fibers are short, and the cushioning properties are low. . For this reason, newsprint paper containing a large amount of deinked waste paper pulp has high density and low cushioning properties, resulting in paper dust due to a decrease in ink setting and ink inking properties and a decrease in surface strength. Causes a decrease in ink density.

  In particular, among the deinked waste paper pulp, the use of deinked waste paper pulp from which newspaper wastepaper has been deinked is similar in constituent materials and is most efficient in terms of resource recycling. Deinked waste paper pulp that has been recycled repeatedly exists, and the pulp fiber deteriorates due to repeated recycling, which not only reduces the opacity of newsprint, but also makes it brittle, paper dust and powder, and the paper surface The problem arises that the fibers are taken up by an offset printing blanket.

  However, the newsprint of the present invention contains hydrated silica, and the area ratio of the hydrated silicate particles having a specific particle diameter is adjusted to be high on the paper surface, and the ash in the paper Since the amount of magnesium and the content of magnesium in the ash (magnesium content in terms of oxide) are adjusted within a specific range, the ink set even when a large amount of deinked waste paper pulp is blended In addition to the generation of paper dust due to the deterioration of the ink property and the ink inking property and the reduction of the surface strength, the conventional problems such as the reduction of the ink density caused by these are solved, and the high printing opacity is maintained.

  As the deinked waste paper pulp used in the present invention, for example, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, reprint waste paper, flyer waste paper, office waste paper, corrugated waste paper, upper white waste paper, Kent waste paper, imitation waste paper, ground Disaggregated / deinked waste paper pulp, disaggregated / deinked / bleached deinked waste paper pulp, etc. produced from ticket waste paper and the like can be used, and one or more of these can be appropriately selected and used.

  In the present invention, the deinked waste paper pulp is 30 to 100% by mass, preferably 50 to 100% by mass, more preferably 70 to 100% based on the total pulp components, from the viewpoint of weight reduction of newsprint and effective use of resources. It is desirable to be contained by mass%.

  In addition to the deinked waste paper pulp, for example, Stone Grand Pulp (SGP), Pressurized Stone Grand Pulp (PGW), Refiner Grand Pulp, as a pulp that is a constituent of newsprint, as long as the object of the present invention is not impaired. Mechanical pulps such as (RGP), Chemi-Grand Pulp (CGP), Thermo-Grand Pulp (TGP), Grand Pulp (GP), Thermo-Mechanical Pulp (TMP), Chemi-thermo Mechanical Pulp (CTMP), Refiner Mechanical Pulp (RMP); Hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood semibleached kraft pulp (LSBKP), coniferous semibleached kraft pulp (NSBKP) ), Hardwood Acid pulp, such as chemical pulp such as soft wood sulfite pulp, be mentioned various known pulps, select one or more from among these can be appropriately used by adjusting the ratio.

  The bleaching method for producing the chemical pulp is not particularly limited, but chlorine-free bleached (ECF) pulp bleached without using molecular chlorine such as chlorine gas in the bleaching process, and further chlorine dioxide Chlorine-free bleached (TCF) pulp bleached without using any chlorine compound is preferred from the viewpoint of environmental protection.

  In order to obtain the base paper constituting the newsprint of the present invention, a filler is used together with the raw material pulp, and hydrated silicic acid is internally added as the filler.

  Conventionally, a method has been adopted in which hydrated silicic acid, which has a particularly high opacity improving effect, is agglomerated and fixed to the raw pulp fiber as an aggregating agent or a coagulant. It has been found that transparency and printability with cold set inks are impaired. Therefore, in the present invention, hydrated silicic acid having a high effect of improving opacity is internally added to the raw material pulp as a filler.

  In the present invention, for example, a mineral acid is added to an alkali silicate aqueous solution to neutralize the alkali silicate aqueous solution, and the precipitated hydrated silicic acid has at least the same mol or more as the particles initially dispersed in the alkali silicate aqueous solution. Hydrated silicic acid produced by adding an acid and not undergoing a post-reaction drying step can be suitably used.

  In the present embodiment, the hydrated silicic acid not subjected to the drying step after the reaction is used, the ash content measured according to JIS P 8251 is 7 to 17% by mass, and the magnesium content in the ash content (oxide) By making the magnesium content in terms of conversion 7.5% by mass or less, even when it is subjected to multi-color offset rotary printing at high speed, printing operability is good, and high ink density and ink inking properties. In addition, the ink setability is good, the problem of color misregistration does not occur, and the printability is excellent. In addition, white spots and paper dust due to a decrease in surface strength are not generated, and high printing opacity is maintained. Newspapers can be obtained.

More specifically, for example, an alkali silicate aqueous solution (sodium silicate aqueous solution or potassium silicate aqueous solution) in which SiO ₂ / R ′ ₂ O (molar ratio, R ′ represents Na or K) is in the range of 2.0 to 3.4. Further, a mineral acid such as sulfuric acid is added to neutralize the alkali silicate aqueous solution. The mineral acid may be added at once or divided into a plurality of parts. When adding by dividing into a plurality of times, the first addition of the mineral acid is carried out in the temperature range of the alkali silicate aqueous solution in the range of 20 to 60 ° C., and the amount of mineral acid required to neutralize the alkali silicate aqueous solution is 10 to 10. 50% by weight is added. Further, after raising the temperature of the alkali silicate aqueous solution to a range of 85 ° C. or higher and lower than the boiling point of the aqueous solution, an aging time is provided as necessary, and then the second and subsequent mineral acids are added at once or continuously. After the addition, an aging time may be provided as necessary.

  Mineral acid may be further added to the hydrated silicic acid produced by the method as described above. At this time, it is preferable to adjust the pH of the slurry containing the hydrated silicic acid to a range of 4-6.

Hydrated silicic acid is present in the form of primary particles in the stable period after reaction, although the primary particles of hydrated silicic acid are small and the particle size is relatively uniform in the process where the reaction is completed in the production process. They are not agglomerated and form secondary particles. In addition, when a drying process is performed in the product production process, secondary particles may form aggregates, and coarse particles may be generated. The reason is not clear, but the hydrated silicic acid in the slurry state does not have some silica atoms and is liberated in the form of -SiOH, and the two-dimensional structure becomes a network tube and the surface is porous. Yes. On the other hand, the dried hydrated silicic acid has a basic structure of SiO ₂ tetrahedron and shares a three-dimensional network structure sharing oxygen. Therefore, when the hydrated silicic acid is once dried, the bonding force with the cellulose fibers due to -SiOH on the surface decreases, so that the hydrated silicic acid that has finished the reaction remains in a slurry state and is not subjected to a drying treatment. It is possible to perform high-speed papermaking at a speed of 1300 m / min or more, for example, by adding wet pulverization to the secondary pulp as a filler after subdividing the excessive secondary aggregates produced in the stable period. In addition, the newspaper according to the present invention, which is lightweight, free of paper dust and excellent in opacity, particularly in printing opacity, is compatible with high-speed offset rotary printing such as 170 to 200,000 copies / hour, for example. It is suitable to obtain.

  Water having a volume average particle diameter of hydrated silicic acid of, for example, 3 to 10 μm and a particle diameter of 1 to 30 μm by laser analysis is used to remove excessive agglomerates of hydrated silicic acid remaining after the wet pulverization. In order to easily adjust the ratio of the Japanese silicate particles to, for example, 80% by mass or more, it is preferable to perform a classification treatment after the wet pulverization.

  If the volume average particle size of hydrated silicic acid by laser analysis is less than 3μm, the loss of dehydration in the papermaking process will increase, it will remain in the white water, and it will combine with other foreign substances to cause damage and damage to the equipment. There is a risk of becoming. On the other hand, when the volume average particle diameter exceeds 10 μm, it appears to be scattered as aggregates on the newspaper paper surface, resulting in reduced strength of the newspaper paper, generation of paper dust, opacity, especially printing opacity. There is a fear. Therefore, the hydrated silicic acid used as a filler in the present invention preferably has a volume average particle diameter of 3 μm or more, more preferably 4 μm or more, more preferably 10 μm or less, further 9 μm or less by laser analysis. High speed papermaking at a speed of 1300 m / min or more is possible, and while supporting high-speed offset rotary printing such as 170 to 200,000 copies / hour, for example, it is lightweight, does not generate paper dust, and has an opacity. This is preferable for obtaining newsprint with excellent printing opacity.

  Furthermore, the ratio of the hydrated silicate particles having a particle size of 1 to 30 μm by laser analysis is preferably 80% by mass or more, more preferably 82% by mass or more, that is, by sharpening the particle size, The dispersibility of the hydrated silicic acid in the layer can be increased, and a homogeneous paper layer can be formed. Thereby, the intensity | strength of the newspaper paper surface can be improved, generation | occurrence | production of paper dust can be suppressed, and opacity, especially printing opacity can be improved simultaneously. Although it is preferable that the ratio of hydrated silicic acid particles having a particle size of 1 to 30 μm by laser analysis is as close as possible to 100% by mass, hydrated silicic acid, which is an aggregate of fine primary particles, is produced industrially. In doing so, it is difficult to adjust to 100% by mass. From the viewpoint of production cost, the proportion of hydrated silicic acid particles having a particle diameter of 1 to 30 μm is at most about 95% by mass.

  In this specification, the laser analysis method refers to a particle size distribution measuring device (laser method) for a dispersion solution in which 10 mg of a sample is added to 8 ml of a methanol solution and dispersed for 3 minutes by an ultrasonic disperser (output: 80 W). The analysis method using a Microtrac particle size analyzer (manufactured by Nikkiso Co., Ltd.).

  In addition, the hydrated silicic acid not subjected to the post-reaction drying step used in the present invention is described in JIS K 5101-13-1, “Pigment Test Method—Part 13: Oil Absorption—Section 1: Refined Sesame Oil Method Is preferably 150 ml / 100 g or more, more preferably 160 ml / 100 g or more, more preferably 250 ml / 100 g or less, and even more preferably 240 ml / 100 g or less. If the oil absorption amount of the hydrated silicic acid is less than 150 ml / 100 g, the opacity may decrease and bleeding in offset printing may increase. On the other hand, if it exceeds 250 ml / 100 g, the vehicle component in the printing ink will be paper. Produce newsprint paper that penetrates inside and is lightweight, free of paper dust and excellent in opacity, especially in printing opacity, while supporting high-speed rotary printing such as 170 to 200,000 copies / hour In this case, it is difficult to obtain an excellent printing density.

  In the present invention, for example, hydrated silicic acid obtained without passing through the drying step after the reaction as described above is diluted to a concentration of 3% by mass or less in advance, and the diluted solution is internally added to the raw material pulp to make paper. It is preferable.

  Hydrated silicic acid obtained without passing through the drying stage after the reaction has the property of reducing the apparent viscosity at high shear rate (thixotropic property) and shears the secondary aggregates and aggregates of the hydrated silicic acid. When force is applied, the agglomeration breaks down and becomes smaller one after another. In order to obtain small agglomerates by this shearing force and not to cause problems due to secondary agglomerates or agglomerates of hydrated silicic acid, the hydrated silicic acid is preferably 3 mass% or less in advance, more preferably Is preferably diluted and dispersed to a concentration of 2.8% by mass or less and then internally added to the raw material pulp. In addition, the concentration of the hydrated silicic acid is 1% by mass or more from the viewpoint of effectively imparting the dispersion capacity of the existing equipment, the shearing force to the secondary aggregate, and preventing the particle size distribution of the hydrated silicic acid after dispersion from being broad. It is preferable to dilute in advance so that, for example, in high speed papermaking at a papermaking speed of 1300 m / min or more.

  Further, in order to prevent such agglomeration of small agglomerated grains, it is preferable to add a dilute solution of hydrated silicic acid which does not undergo a post-reaction drying step to the raw pulp before the screen.

  In the present invention, in addition to the hydrated silicic acid, as a filler, for example, calcium carbonate such as calcite calcium carbonate or aragonite calcium carbonate aggregated or crystallized in a chestnut shape, such as calcium carbonate, clay, talc, titanium dioxide, Usual paper-making fillers such as inorganic fillers and organic fillers such as zeolite, barium sulfate, zinc oxide, aluminum oxide, silicic acid, colloidal silica, colloidal alumina, and satin white can be used. Among these, for example, when waste paper pulp is used as the raw material pulp, the calcium chloride calcium carbonate is easy to provide a gap between fibers due to its unique shape, and easily stays between the fibers. It is preferable in high speed papermaking such as / min.

When calcium carbonate is used as a filler, the paper surface pH is 7-9 due to its buffer effect, and when the paper surface pH is neutral or alkaline, each fiber is sufficiently stretched compared to the acidic case. The area where the fibers form hydrogen bonds increases. Therefore, when the ash content is about the same as that of acid newsprint, neutral newsprint paper has a higher paper strength. As a result, even if the newsprint paper has a low basis weight of 36 to 50 g / m ² , high speed Sufficient strength to withstand offset rotary printing can be obtained, but in particular, when calcium chestnut calcium carbonate is used as a filler together with hydrated silicic acid, the paper structure becomes more bulky and cushioning is imparted to newsprint, for example In addition to the improvement in the cold setting ink, there is an advantage that the blank paper opacity, printing opacity, printability, etc. are further improved.

  Further, the whiteness of the hydrated silicic acid alone has a relatively low contribution in the base paper of ordinary newsprint, but the combined use of the calcium carbonate of the chestnut improves the whiteness of the newsprint.

  In the process of obtaining calcium carbonate having a stable calcite type crystal structure such as a spindle type or a columnar shape, or a calcium carbonate having a metastable aragonite type crystal structure by reacting calcium hydroxide with a carbon dioxide-containing gas. When the carbon dioxide-containing gas supply method is adjusted, or when dehydration, drying, and heat treatment are performed, for example, an additive such as condensed phosphoric acid or a metal salt thereof is added to agglomerate the spindle or columnar crystal structure. Obtained by crystallization.

In the case of calcite-based calcium carbonate, calcite is produced more naturally than limestone because it is more stable than other crystal structures. In addition, artificially, for example, natural limestone is decomposed into calcium oxide and carbon dioxide at high temperatures (impurities are removed), and calcium oxide is put into water to form calcium hydroxide (soaking). The calcite calcium carbonate can be obtained by blowing carbon dioxide while controlling the conditions (temperature, concentration, degree of stirring) as in the following reaction formula.
Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O

Aragonite-based calcium carbonate is almost the same as the method for producing calcite-based calcium carbonate, and aragonite-based calcium carbonate can be obtained by adjusting the reaction conditions during the production. For example, as shown in the following reaction formula, using slaked lime and water in a causticization reaction tank, stirring and mixing with a stirrer equipped with a stirring blade to prepare lime milk, the sodium carbonate addition rate, addition time, and temperature conditions are appropriately set It is obtained by adjusting to cause a causticizing reaction.
Na ₂ CO ₃ + CaO + H ₂ O → CaCO ₃ + 2NaOH

The chestnut calcium carbonate used in the present invention has an oil absorption of 150 to 250 ml / 100 g, a BET specific surface area of 50 to 150 m ² / g, and a volume average particle diameter based on the method described in JIS K 5101-13-1. The (secondary particle diameter) is preferably 1.0 to 10.0 μm.

  If the amount of oil absorption of Hashikari calcium carbonate is less than 150 ml / 100 g, for example, there may be a decrease in white paper opacity and bleeding in cold-set offset printing, while if it exceeds 250 ml / 100 g, the vehicle in the printing ink The components may penetrate into the paper and make it difficult to obtain an excellent printing density. Therefore, the amount of oil absorption of Oguri calcium carbonate is preferably 150 ml / 100 g or more, more preferably 160 ml / 100 g or more, and preferably 250 ml / 100 g or less, more preferably 240 ml / 100 g or less.

In addition, if the BET specific surface area of Oguri calcium carbonate is less than 50 m ² / g, the voids in the aggregated structure decrease, so that the ink absorbability may be lowered. On the other hand, if it exceeds 150 m ² / g, the filler dispersion The dilution viscosity of the ink becomes high, so that the operability is lowered, for example, the drying property of the cold-set type offset ink taken in is lowered, and there is a possibility that rubbing stains and printing print-off occur. Therefore, the BET specific surface area of the chestnut calcium carbonate is preferably 50 m ² / g or more, more preferably 70 m ² / g or more, and 150 m ² / g or less, further 130 m ² / g or less. High speed papermaking at a speed of 1300 m / min or more is possible, and while supporting high-speed offset rotary printing such as 170 to 200,000 copies / hour, for example, it is lightweight, does not generate paper dust, and has an opacity. This is preferable in providing newsprint with excellent printing opacity.

  In addition, in this specification, the BET specific surface area of Oguri calcium carbonate means the value measured with the fully automatic BET specific surface area measuring device (model number: Frosorb 2300, Shimadzu Corporation make).

  Further, the calcium chloride calcium carbonate has a primary particle of, for example, 100 nm or less, and when its volume average particle diameter (secondary particle diameter) is less than 1.0 μm, when added as a filler, This makes it easier to enter the gaps between the pulp fibers that make up, making it difficult to exert the bulky effect of the paper chestnut calcium carbonate, resulting in a decrease in printability. The amount decreases and it becomes difficult to hold the ink. If the ink penetrates into the base paper or in the extreme case, the ink may penetrate into the back surface, resulting in a decrease in print density or print back-through. On the other hand, when the volume average particle size (secondary particle size) of the calcium chloride calcium carbonate exceeds 10.0 μm, the contact area with the pulp fiber decreases, and as a result, paper dust is generated at the paper making stage and the printing stage. In addition to the possibility of a decrease in printability, there is a risk of paper dust and printing failure due to the drop of calcium chloride. Therefore, the volume average particle diameter of the potato chestnut calcium carbonate is preferably 1.0 μm or more, more preferably 1.8 μm or more, and is preferably 10.0 μm or less, more preferably 9.6 μm or less.

  In addition, in this specification, the volume average particle diameter of Higurashi calcium carbonate means the value measured by the said laser analysis method.

  Further, the aspect ratio (the ratio of the major axis to the minor axis (major axis / minor axis)) of the calcium chestnut calcium carbonate is 3.5 or less, and further 3 from the viewpoint of further improving the opacity and printability of newspaper. .4 or less, and 1.5 or more, more preferably 2.0 or more, from the viewpoint of sufficiently suppressing deterioration in quality of newsprint.

  In particular, when calcium carbonate such as calcium chestnut calcium carbonate is used as a filler, in order to efficiently disperse it in paper, the calcium carbonate is previously adjusted to a concentration of 7.5% by mass or less, and further 7.0% by mass or less. After dilution, it is preferably added internally to the raw material pulp, and from the viewpoint of yield to paper, the concentration of calcium carbonate is 5.5% by mass or more, more preferably 6.0% by mass or more. It is preferable to dilute in advance.

  If the diluted concentration of calcium carbonate exceeds 7.5% by mass, uniform dispersion in the raw material pulp becomes difficult, and conversely if less than 5.5% by mass, the amount of filler dispersion in the raw material pulp increases. As a result, the operability deteriorates and the frequency of contact with the raw material pulp decreases, resulting in a decrease in yield.

  In addition, depending on the concentration of the raw material pulp slurry to be added, excessive physical dispersion force is added to the filler agglomerate by the raw material pulp fiber, such as a bead mill, in the mixing with the raw material pulp. The concentration is preferably low, and the filler is preferably added in an environment in which the filler itself is easily dispersed. Therefore, in the present invention, the raw pulp slurry is preferably 0.5 to 5.0% by mass in line with the finished chest, the fan pump suction side before the seed box, and most preferably the fan pump suction before the seed box. It is desirable to add a filler at a concentration of 1.5 to 3.0% by mass.

  In the present invention, as a filler, the total amount (100% by mass) is preferably hydrated silicic acid as described above in terms of improving printing transparency, but as described above, other examples such as calcium chestnut calcium carbonate, etc. It is also possible to use a filler in combination. When hydrated silicic acid and calcium chloride calcium carbonate are used in combination, the ratio of hydrated silicic acid and calcium chloride calcium carbonate can be reduced in order to further improve printability, bulkiness, and paper strength in a balanced manner. : Calcium calcium carbonate (mass ratio) is preferably 20:80 or more, more preferably 40:60 or more, and preferably 95: 5 or less, more preferably 80:20 or less.

  In actual paper production, due to the use of waste paper pulp and the circulation of machine white water, fillers derived from waste paper, for example, other than the filler added to the raw pulp, are inevitably incorporated into the paper. It is. The average particle size of the filler in the paper is smaller than the average particle size in the slurry before addition. The reason is that in the preparation process before papermaking, the papermaking process, and the drying process, it is influenced by stirring force and shrinkage due to drying. Therefore, in the present invention, as will be described later, the particle diameter and particle size distribution on the surface of the newsprint after completion of papermaking are controlled within a certain range.

In the present invention, the amount of filler added to the raw material pulp is sufficient to express the effect of improving printing operability and printing suitability while maintaining opacity, particularly printing opacity, by using the filler. Is a newspaper paper having a basis weight of 36 to 50 g / m ² according to JIS P 8124, in addition to the ash content from waste paper so that the ash content measured according to JIS P 8251 is 7 to 17% by mass, It is preferable to newly add a filler.

  In order to obtain the base paper constituting the newsprint of the present invention, the raw material pulp is preliminarily filled with a filler containing hydrated silicic acid, preferably hydrated silicic acid obtained without passing through the drying step as described above. Add a filler containing a dilute solution diluted to a concentration of not more than mass%, and adjust the conditions such as pH so that it is preferably neutral to alkaline, for example, pH 6.0 to 10.0. It is possible to adopt a paper making method using a normal paper machine such as a machine or a twin wire type paper machine.

  Further, when making the paper, for example, normal paper making chemicals such as a sizing agent, a dry paper strength enhancer, a wet paper strength enhancer, a yield improver, a drainage improver, an antifoaming agent, a slime control agent, and a dye. Can be added as needed.

  In the present invention, when obtaining newsprint base paper, it is possible to add a coagulant in the raw pulp preparation stage, and further add a flocculant to the pulp slurry before the paper making process following the raw pulp preparation stage. Promotes agglomeration of fine inorganic particles mixed in the suspension and further improves the filler yield by attaching inorganic particles to the raw pulp, improving drainage and obtaining wet-end stability. Therefore, it is preferable.

  In particular, when mechanical pulp or used paper pulp having a high ratio of the mechanical pulp is used as a raw material pulp, since the pulp surface exhibits a relatively high anionic property, a coagulant is added at the pulp preparation stage, and further, Adding a flocculant before the papermaking process following the preparation stage improves the yield of the filler by physically and chemically adhering the filler between the pulp fibers, and improves the wet end stability by improving the drainage. For example, it is preferable because high-speed papermaking such as a papermaking speed of 1300 m / min or more is possible.

  As a coagulant preferably added in the raw material pulp preparation stage as described above, for example, polyacrylamide (PAM), polyvinylamine (PVAm), polydiallyldimethylammonium chloride (polydadomac, PDADMAC), polyamine (PAm), polyethyleneimine Examples thereof include organic polymer coagulants such as (PEI), and inorganic coagulants such as sulfuric acid bands and polyaluminum chloride. Among these, it is preferable to use at least one of PAM, PDADMAC, PAm, and PEI.

  For example, when the organic polymer coagulant is used in combination with hydrated silicic acid and calcium carbonate as an aggregate of secondary particles (particle diameter is less than 100 nm), the hydrated silicic acid is retained in the pulp, and the drainage The charge density is preferably 3 meq / g or more, more preferably 10 meq / g or more. When the charge density is less than 3 meq / g, it is necessary to increase the amount of the organic polymer coagulant to increase the cation requirement of the pulp to a predetermined value. The sheet formation may be reduced. The average molecular weight of the organic polymer coagulant is preferably 700,000 to 1.3 million, more preferably 800,000 to 1,200,000. When the average molecular weight is less than 700,000, the cohesive force is weak, and for example, hydrated silicic acid or calcium chloride calcium carbonate is insufficiently fixed on the wet paper, and as a result, the intended effect may not be improved. If it exceeds 1.3 million, the cohesive force is too strong, so the paper fit of the newsprint decreases, and in order to maintain the paper fit well, the amount of addition must be reduced, which also improves the intended effect. There is a fear that I can not hope.

  The addition amount of the organic polymer coagulant is preferably adjusted so that the cation requirement reduction rate and the cation requirement of the paper filtrate after the addition of the organic polymer coagulant are satisfied. Therefore, the addition amount of the organic polymer coagulant depends on the addition amount of the inorganic coagulant described later, but is preferably 1000 to 4000 ppm, more preferably 1200 to 3800 ppm in solid content with respect to the pulp. . If the amount of the organic polymer-based coagulant added is less than 1000 ppm, the effect may be insufficient. On the other hand, if it exceeds 4000 ppm, the paper texture may be lowered and the cost may be increased.

  Moreover, it is preferable that the addition amount of an inorganic type coagulant is 0.1-5.0 mass% with solid content with respect to a pulp, Furthermore, it is preferable that it is 0.1-3.0 mass%.

  In addition, when using a cationic coagulant especially among the said coagulants, it is preferable that the addition amount is 50-400 ppm with a pure part with respect to a pulp, Furthermore, it is preferable that it is 100-300 ppm. As such a cationic coagulant, a polymer compound similar to the aggregating agent described later, that is, a cationic water-soluble polymer or copolymer, can be used, but those having a small molecular weight are preferably used. That is, as the cationic coagulant, a cationic water-soluble polymer having an average molecular weight of 1,000,000 to 1,200,000 and a ratio of the cationic monomer of 5 to 100 mol%, further 10 to 100 mol%, or Copolymers can be used. Representative examples of such cationic coagulants include PAm, PEI and the like. If the average molecular weight of the cationic coagulant is less than 1 million, the effect of using the cationic coagulant may not be sufficiently exhibited. However, there is a risk of high costs.

  In the present invention, as described above, it is preferable to add a coagulant in the raw pulp preparation stage. For example, the pulp and filler, and, if necessary, a filler treatment agent, an internal sizing agent, a fixing agent, Various paper making aids such as a yield improver, a cationizing agent, a paper strength enhancer, and an antifoaming agent are mixed in a compounding chest to become a finished raw material. Therefore, it is preferable that a coagulant is added between the compounding chest and the machine chest, and in order to sufficiently mix the coagulant with the finished raw material, it is more preferable to add the coagulant to the compounding chest.

  Next, when a cationic flocculant described later is used as the flocculant, it is preferable to add the coagulant at an initial stage of raw material pulp preparation, that is, at an early stage with respect to the pulp slurry. After that, it is optimal to add the flocculant to the pulp slurry before the paper making process, that is, in the head box before the paper making net. When such an addition procedure is employed, in the slurry solution state before the papermaking raw material is placed on the papermaking net, the adhesion between the pulp fiber and the hydrated silicic acid or the calcium carbonate calcium carbonate suitably used increases due to the aggregation effect of the coagulant. At the same time, the paper net has a stronger adhesion between the pulp fiber and the hydrated silicic acid or calcium chloride calcium carbonate due to the coagulation effect of the coagulant. As a result, the yield of these hydrated silicic acid and calcium chloride calcium carbonate in paper is further improved. And when such an addition procedure is employ | adopted, the effect that smooth paper-making work progresses also with the further improvement of the yield of hydrated silicic acid or the calcium carbonate calcium carbonate used together suitably.

  As the flocculant, a cationic flocculant is particularly suitable for an anionic pulp and filler. As such a cationic flocculant, for example, the average molecular weight is 8 million to 12 million, more preferably 8.5 million to 11 million, and the proportion of the cationic monomer is 5 to 100 mol%, further 10 to 100 mol%. Cationic water-soluble polymers or copolymers can be used. Typical examples of such cationic flocculants include PAM. If the average molecular weight of the cationic flocculant is less than 8 million, the effect using the cationic flocculant may not be sufficiently exhibited. On the other hand, if the average molecular weight is larger than 12 million, the desired effect can be hardly improved. However, there is a risk of high costs.

  As described above, the addition of the flocculant is particularly preferably performed in the head stage before the paper making process, that is, in the head box before the paper making net. Thereby, the quantity of the hydrated silicic acid lacking in a paper-making net | network and the calcium chloride of a chestnut can be reduced markedly.

  Moreover, it is preferable that the addition amount of a flocculant is 100-150 ppm with a pure part with respect to a pulp, Furthermore, it is preferable that it is 120-140 ppm. If the addition amount of the flocculant is less than 100 ppm, the yield improvement effect of hydrated silicic acid or calcium chloride calcium carbonate may not be sufficiently obtained. On the other hand, if it exceeds 150 ppm, the formation of newsprint may be lowered. .

  Further, when producing the newsprint of the present invention, before preparing a plurality of stocks and supplying them to a seed box, the slurry of each stock is subjected to a cation demand measurement value measured using an on-line cation demand measurement device. Based on this, the amount of the coagulant added in the preparation stage can be controlled.

  Thus, by controlling the addition amount of the coagulant on-line, it is possible to control the potential according to the optimum cation demand. In particular, it is possible to feed back and control the rapid cation demand measurement value, stabilize the drainage at the wire part of the paper machine, and only reduce the paper breakage at the wet part. In addition, it is possible to satisfactorily maintain the resulting newspaper.

  The cation demand is the total charge of the anionic substance. An anionic substance (anionic trash) is a negatively charged substance, and includes pulp (including fine fibers), filler (hydrated silicic acid and calcium carbonate calcium carbonate suitably used), and various wet ends. Papermaking aids (other fillers, filler processing agents, internal sizing agents, antifoaming agents, etc.), resin pitch, elution lignin and the like.

  By adding a cationic coagulant to the anionic substance and adding the anionic (or cationic) flocculant to the coagulated substance, the coagulated anionic substance aggregates to form a floc. Under such a mechanism, the pitch concentration can be reduced mainly by adsorbing the pitch to the pulp and passing the process together with the paper stock in a minimal state, or discharging the process out of the system. Thereby, dirt, a defect, a paper break, etc. can be reduced and productivity can be further improved. Further, the yield can be further improved by neutralization with an anionic substance, and when the anionic substance aggregates and forms a floc, the drainage state is improved. For this reason, it is preferable that the cation demand (or the amount thereof) is low with respect to the drainage state.

  A typical example of an apparatus for measuring an online cation demand as described above is a cation demand measuring apparatus (model number: PCT15 or PCT20, manufactured by Mutek). In the cation demand measuring apparatus, when the stock is introduced into the cell of the tester, the sample liquid flows between the cell cylinder and the piston by the operation of the upper and lower pistons, and electricity is generated by the distortion of the surface charge of the colloidal particles. Arise. The colloidal dissolved substance particles in the pulp suspension are charged with ions, and the charge requirement is measured by measuring the polymer electrolyte by using this.

  Thus, the newsprint of the present invention is obtained through the paper making process. In the present invention, it is preferable that a surface treatment agent made of, for example, a water-soluble polymer compound is further applied to the front and back surfaces of the newsprint.

  In this way, the surface treatment agent is applied to the front and back sides of the paper, so that for example, the cold set type offset ink vehicle is quickly absorbed, and the printing ink amount can be increased by increasing the speed of the rotary press and using a double-sided color tower press. Even if it increases, sufficient absorption drying property is expressed, and it is possible to ensure excellent printing opacity, printability and the like.

  A combination of a hydrated silicic acid or calcium carbonate and water-soluble polymer compound used as a filler in the present invention is preferably a water-soluble polymer compound such as starch and / or polyvinyl alcohol (hereinafter referred to as PVA). This is because, for example, gate roll coating suitability is excellent, aging resistance is high, and film forming ability is excellent.

  Furthermore, since hydrated silicic acid and calcium chloride calcium carbonate that can be suitably used in the present invention have a large specific surface area and high oil absorption, the ink remains on the paper surface when cold set offset ink is used. The cold-set offset ink, which is easy to absorb and dry, may cause a problem of ink see-through on the opposite paper surface when it is overlapped. The effect of improving the problem of dryness and set-off is also manifested.

  Examples of the water-soluble polymer compound suitable for the present invention include starch and PVA, and these can be used alone or simultaneously.

  The type of starch is not particularly limited. For example, modified starch has an effect of improving tensile strength and surface strength while penetrating into paper, but exhibits neutrality or anionic property, and thus exhibits anionic property. The fixability to the pulp fiber surface is low and the coating property is low. Therefore, in the present invention, it is preferable to use a cationic starch having high fixability to the surface of an anionic pulp fiber. In the case of cationic starch, the fixability to pulp fibers is high, the coating property is excellent, and the surface strength is also improved.

  Furthermore, as said starch, esterified starch is more preferable. When esterified starch is used, the ink density and ink setting properties are dramatically improved. Examples of the raw material starch for obtaining such esterified starch include various starch-containing materials in addition to untreated starch and treated starch. Representative examples of such raw material starch include, for example, untreated starch such as wheat starch, potato starch, corn starch, sweet potato starch, tapioca starch, sago starch, rice starch, waxy corn flour, high amylose content corn starch; And starch-containing materials such as tapioca starch, corn flour, rice flour, etc., and processed starch obtained by subjecting it to oxidation, acid treatment and the like. Among these, tapioca starch is preferable in that the ester-modified product is superior to other cereal starches in terms of viscosity, coating properties, elasticity, and extensibility.

  In the esterified starch, the degree of esterification is not particularly limited, but the average number of ester bonds introduced is preferably 1 to 3, more preferably 1 to 2, per glucose unit. Among them, it is optimal to use a hydrophobic group-containing ester-modified tapioca starch in which a hydrophobic group is introduced into the end group of the ester-modified starch.

  Furthermore, the esterified starch that can be preferably used in the present invention has a carboxylic acid “—COOH” structure in the terminal group and is ionized like “—COO—” in the neutral region to form hydrogen bonds. The ester-modified starch, which exhibits thixotropic behavior based on rebound without being able to secure the connection due to the penetration, penetrates into the paper after application while showing fluidity when applied to the surface of newsprint paper. This is preferable from the viewpoint of exhibiting a high film property on the paper surface. In particular, when used in combination with PVA or the like having a high coating property, which will be described later, even if a large amount of hydrated silicic acid, which is a filler added to the raw material pulp, is used, ink concentration and ink setting properties can be further improved. As such esterified starch, 1-octenyl succinic esterified starch obtained by ester-modifying tapioca starch as a main raw material is particularly preferable. 1-Octenyl succinate esterified starch is particularly excellent in terms of viscosity, film elasticity, and coatability. For example, when used in combination with PVA described later, printing operability and coatability, ink concentration, and ink setability Can be further improved.

  The starch used in the present invention has an average molecular weight of 600,000 to 3,000,000, more preferably 800,000 to 2.8 million, and the solvent component is used as a paper while keeping the paper surface coverage and the ink component on the paper surface. It is preferable from the point of taking in and improving absorption drying property.

As the starch, those having a viscosity (10%) of 30 × 10 ⁻³ Pa · s or less, more preferably 15 × 10 ^{−3 to} 25 × 10 ⁻³ Pa · s have a high viscosity on the paper surface. From the point that it can not penetrate into the paper and can remain on the paper surface.

  As described above, examples of the water-soluble polymer compound include PVA in addition to starch. In general, when PVA is applied to the front and back surfaces of newsprint paper alone, the surface strength is approximately three times that of the case where starch is applied alone, and the coating property is excellent, but the coating property is high. If a printing ink is used that penetrates into the paper and dries like a cold set ink, the ink absorbability of the printing ink is low, and sufficient ink setting properties may not be obtained. In addition, when a certain amount of PVA is applied alone, the treatment liquid containing the PVA has a high viscosity. For example, in the film transfer method, paper breakage, papermaking equipment stains, wrinkles, and paper surface stains may occur. However, when such PVA is used in combination with starch, the coating property for retaining the ink filler component on the paper surface is improved and the ink setting property is lowered while appropriately promoting the penetration of the printing ink solvent into the paper. Is also sufficiently suppressed.

  There is no particular limitation on the type of PVA, and the PVA that can be used in the present invention has PVA having a terminal cation-modified or an anionic group in addition to normal PVA obtained by hydrolysis of polyvinyl acetate. Modified PVA such as anion-modified PVA is also included.

  As normal PVA obtained by hydrolyzing polyvinyl acetate, those having an average degree of polymerization of 300 to 3000, more preferably 1000 to 2400, and particularly 1700 to 2000 are excellent in compatibility with starch and have a uniform film. It is preferable from the viewpoint of being easily obtained.

  Moreover, as normal PVA, a thing with a saponification degree of 80-100 is preferable, and the complete saponification PVA with a saponification degree of 90-100 is more preferable. When completely saponified PVA is used, a film having water resistance and heat resistance is more easily obtained on the newspaper paper surface than when partially saponified PVA is used.

  When such PVA is used, the affinity with starch is good, and it is possible to blend starch and PVA in a short time, further improving the operability and reducing the occurrence of mist in the coating equipment. be able to.

  By using PVA having the above characteristics, it is possible to realize high ink setting properties of offset ink while obtaining a high ink concentration. In addition, when newspaper sheets are stacked after printing, ink transfer to the back surface can be sufficiently prevented.

  When starch and PVA are used in combination, the ratio of the two (starch: PVA (solid content mass ratio)) is 10: 0.8 to 10: 2.0, and further 10: 0.9 to 10: 1.2. It is preferable that If the ratio of PVA to starch exceeds 10: 2.0, the viscosity of the surface treatment agent containing both will rise rapidly, resulting in coating unevenness and mist, resulting in poor coating quality and contamination around the equipment. On the other hand, if the ratio is less than 10: 0.8, there is no problem with the compatibility between starch and PVA, but when applied to the newspaper surface, the synergistic effect between starch and PVA cannot be obtained. There is a risk of penetration into the paper and uneven coating. Therefore, by setting the ratio of both in this range, a synergistic effect between starch and PVA can be ensured, and at the same time a high ink concentration is expressed by retaining the filler component in the ink on the newspaper surface, It is possible to quickly absorb the solvent in the ink into the newspaper, and to express the ink setting property quickly.

When the starch and PVA are used together as a surface treatment agent to be applied to the front and back surfaces of newsprint, these starch and PVA are 0.2 to 2.0 g / m ² per side on the front and back of newsprint, It is preferably applied (unevenly distributed) in an amount of 0.5 to 1.5 g / m ² . If the amount of starch and PVA is less than 0.2 g / m ² , it will be difficult to obtain sufficient film properties with these starch and PVA, and it will be difficult for the filler component in the ink to stay on the surface of the newsprint, resulting in a sufficiently high ink concentration. On the other hand, if it exceeds 2.0 g / m ² , a large amount of mist of the surface treatment agent containing starch and PVA will be generated around the coating equipment, and the peripheral equipment will be soiled and caused by dirt. This may cause paper breaks and paper defects.

  In the present invention, even when a large amount of deinked waste paper pulp is used as the pulp, the hydrated silicic acid is used as a filler, and a surface treatment agent comprising a water-soluble polymer compound such as starch or PVA is applied to the front and back surfaces. Then, the shortcomings based on a large amount of deinked waste paper pulp are covered, and at the same time, a synergistic effect that ink density and printability are further improved is expressed.

  When a surface treatment agent composed of a water-soluble polymer compound such as starch or PVA is applied to the front and back surfaces of newsprint, it is preferable to employ a film transfer system such as a gate roll coater or a blade. In particular, coating with a gate roll coater is optimal when applying contour coating with a high coverage on a newspaper paper surface with a low coating amount, unlike other coating methods, and does not apply a rapid shearing force to the surface treatment agent. Therefore, the surface treatment agent to be circulated is excellent in stability, and a uniform film can be obtained at high speed. In particular, when thixotropic ester-modified starch is used, it exhibits fluidity when applied to the surface of newsprint paper, but after application, the fluidity is suppressed and the surface treatment agent does not easily penetrate into the paper. High film properties are imparted to the newsprint while staying on the surface.

  In addition, when applying a surface treatment agent mainly composed of starch and PVA as a water-soluble polymer compound to the front and back surfaces of newspaper paper, for example, a size press or a rod metering size may be used without adopting the film transfer method. Conventionally known coating means such as a press can also be employed. However, if the contour coating along the unevenness of the newspaper paper surface is not applied, the coverage with starch and PVA becomes insufficient. For example, when multicolor offset rotary printing is performed using cold set ink, the ink density, ink There is a risk that it is difficult to obtain newsprint paper that is sufficiently excellent in printability such as setability and ink fillability. Therefore, in order to apply the surface treatment agent mainly composed of starch and PVA to the front and back of the newsprint at a low concentration and a low coating amount, it is optimal to adopt the film transfer method.

  In the present invention, newspaper paper after paper making or newsprint paper coated with a surface treatment agent can be finished by passing through a calender device and applying pressure and smoothing as necessary. As the calender device, a machine calender with a combination of a normal metal roll and a metal roll may be used, but the paper layer is more strongly pressed when a soft calender with a combination of a metal roll and a resin roll is used. It is more preferable because it can be smoothed without further reducing the decrease in paper layer strength.

  In addition, in the use of the soft calendar, by passing the paper so that the back side corresponding to the rough side of the newsprint is in contact with the metal roll surface of the soft calendar first, it is possible to further improve the flatness and bulkiness, For example, in high-speed papermaking at 1300 m / min or higher, newsprint paper having high flatness and little difference in front and back can be obtained. Furthermore, with respect to the coating amount of the surface treating agent, by increasing the back surface side rather than the front surface side, better flatness and bulkiness can be obtained, and a firm newsprint can be obtained.

The newspaper of the present invention thus obtained has a basis weight measured in accordance with the “basis weight measurement method” described in JIS P 8124 of 36 g / m ² or more, preferably 37 g / m ² or more, and 50 g. / M ² or less, preferably 46 g / m ² or less. When the basis weight is less than 36 g / m ² , the opacity and the paper quality strength are insufficient, and in recent high-speed web offset printing, which is in the range of 170 to 200,000 copies / hour, there is a problem that paper breakage is likely to occur. . On the other hand, if the basis weight exceeds 50 g / m ² , it becomes easy to ensure sufficient opacity, but it is difficult to handle as lightweight newsprint. The newsprint of the present invention having such a basis weight is used for high-speed printing of 170 to 200,000 copies / hour, such as paper breakage, white spots, generation of paper dust due to reduced surface strength, printing operability, and color. This solves problems such as poor printability such as misalignment and low print opacity.

  Further, the ash content in the newsprint is 7% by mass or more, preferably 8% by mass or more, measured according to “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method” described in JIS P 8251. Moreover, it is 17 mass% or less, Preferably it is 15 mass% or less. In the newsprint of the present invention, the magnesium content in the ash (magnesium content in terms of oxide) is 7.5% by mass or less, preferably 6% by mass or less, more preferably 4% by mass or less. is there.

  The content of ash and the composition of the ash in newspapers enable high-speed papermaking, white spots, generation of paper dust due to reduced surface strength, printing operability, reduced printability such as color misregistration, printing opacity It is an important factor in solving the conventional problems such as lowering of the ash content. Thus, the ash content is 7 to 17% by mass, and the magnesium content in the ash content (magnesium content in terms of oxide) By adjusting the amount) to 7.5% by mass or less, it is possible to realize the newsprint of the present invention in which the conventional problems are solved.

  If the ash content in the newspaper is less than 7% by mass, sufficient opacity is difficult to be obtained, and there is a risk that it will cause the show-through. Especially in the case of high whiteness, the show-through tends to be noticeable if the ash content is too low. . On the other hand, if the ash content exceeds 17% by mass, as described above, the paper strength is liable to be lowered, causing a paper-cutting trouble in the paper making process, resulting in a decrease in productivity, contamination in the system, and high-speed offset rotation. Paper breakage troubles easily occur in printing, and printing operability decreases.

  The ash content in the newsprint is preferably adjusted as appropriate according to the desired optical properties of the newsprint, the required surface strength, and the like. Appropriately adjust the amount of filler to be included. When the addition rate of the filler containing the hydrated silicic acid is too small, the effect of using the filler is not sufficiently exhibited, and conversely, when the amount is too large, the paper strength may be lowered. Is preferably contained in the paper as a paper ash content of 7 to 17% by mass, and more preferably 8 to 15% by mass.

Magnesium in ash (magnesium in terms of oxide) is usually mostly inorganic material or talc derived from so-called talc (hydrated Mg ₂ SiO ₃ ). For example, when using waste paper pulp as a raw material, It is included in flyers and high-quality papers that are processed by being mixed with waste recovered medium. Magnesium inhibits the drying property of offset ink in offset rotary printing, causes partial ink transfer and set-off, and makes the contaminants slippery. It is considered to be a causative substance that causes double feeding and paper dust.

  That is, among the fine inorganic fine particles derived from deinked waste paper, the presence of magnesium, which is thought to be derived from talc (talc), is a fine particle derived from deinked wastepaper, but it is due to the plate-like crystal structure that is its property. Inhibiting the entanglement of the fibers and reducing the binding strength of the pulp fibers at the paper making stage. At the same time, magnesium has a low refractive index and a high oleophilic property, which reduces the opacity, particularly the printing opacity, and reduces the printability of the cold set ink.

  Therefore, by adjusting the magnesium content in the ash (magnesium content in terms of oxide) to 7.5% by mass or less, preferably 6% by mass or less, more preferably 4% by mass or less, The newspaper paper obtained can be further imparted with excellent web offset printing aptitude.

  The content of magnesium in the ash (magnesium content in terms of oxide) is preferably closer to 0% by mass, and the magnesium can be added to or subtracted from the amount of deinked floss extracted during deinking such as flotation. Although a method of removing by a selective process using a specific gravity difference utilizing a large target particle size has been proposed, it is not practical in practice. Considering that magnesium is often mixed from flyers and high-quality paper contained in city-used recovered paper, when using deinked wastepaper pulp as the raw material pulp, it is preferable to select the deinked wastepaper. Is the most efficient and effective in adjusting.

  In addition, it is considered that the magnesium contained is mainly derived from talc, and talc is inferior in hydrophilicity to other fillers and has lipophilicity. By using a high deinking agent, it can be efficiently removed outside the system.

  As the defoaming agent with high foaming property, an anionic surfactant has been used for a long time, but since anionic surfactants are mainly foaming and inferior in deinking properties, the type of hydrophobic group is selected. It is preferable to do. As a selectable hydrophobic group, as sulfate ester type, for example, higher alcohol sulfate ester salt, higher alkyl ether sulfate ester salt, sulfated oil, sulfated fatty acid ester, sulfated olefin, etc., as sulfonate type, For example, alkylbenzene sulfonate, alkyl naphthalene sulfonate, paraffin sulfonate, succinic acid diester sulfonate, and the like, and examples of the phosphoric acid ester salt type include higher alcohol phosphoric acid ester salts.

  In addition, a method in which the anionic surfactant and the nonionic surfactant are used in combination to efficiently remove talc and maintain the deinking property can be employed.

  In this specification, the content of magnesium in the ash (magnesium content in terms of oxide) is the X-ray microanalyzer (model number: E-MAX · S-) for the ash measured in accordance with JIS P 8251. 2150, manufactured by Hitachi, Ltd./manufactured by Horiba, Ltd.), and a value obtained by component analysis in terms of oxide.

  In this way, the amount of ash in the paper and the content of magnesium in the ash (magnesium content in terms of oxide) are adjusted within a specific range, so even if a large amount of deinked waste paper pulp is blended Even in this case, the newsprint of the present invention suffers from the conventional problems such as a decrease in ink setting property and ink inking property, generation of paper dust due to a decrease in surface strength, and a decrease in ink density due to these. And high printing opacity is maintained.

  Further, in the newsprint of the present invention, an X-ray microanalyzer (model number: E-MAX, manufactured by Hitachi, Ltd.) is used to measure the surface of the paper under the condition that the X-ray acceleration voltage is 8 kV and the diffusion region is 1 μm. In the area analysis, the area ratio in the predetermined area of the aggregate particles having a particle diameter of 6 to 20 μm according to the detection area is 80% or more in the size of the detection area of the silicon to be analyzed with the aggregate particles of hydrated silicic acid. Preferably there is.

  In the size of the detection area of the hydrated silicic acid aggregate particles and the silicon to be analyzed, which is one of the characteristics of the present invention, the area ratio in the predetermined area of the aggregate particles having a particle diameter of 6 to 20 μm according to the detection area As a means to make 80% or more, the means using the hydrated silicic acid obtained without passing through the drying step after the reaction described above, preferably diluted to a predetermined concentration before adding to the raw pulp, physical shear force In addition to means for adding hydrated silicic acid with improved dispersibility to the raw material pulp, there are means for adding hydrated silicic acid that has been previously treated with a filler treatment agent to the raw material pulp.

  As the filler treating agent suitably used in the present invention, an alkyl group or an alkenyl group (hereinafter, this alkyl group or alkenyl group may be simply referred to as a hydrophobic group) and a hydrophilic group are an amide bond or an ester bond. And a compound bonded by at least one selected from the group consisting of ether bonds, for example, chemical name FM8170 and chemical name FM8171 (both are acrylamide polymers) manufactured by Hoshimi PMC Co., Ltd. The name FM8173 (styrene acrylate-based polymer) is mentioned, and among these, the chemical name FM8173 has good dispersibility of hydrated silicic acid and calcium carbonate and fixability to raw material pulp, and can be suitably used.

Conventionally, map analysis of existing inorganic substances has been performed from elemental analysis of the paper surface using an X-ray microanalyzer, but each element is comprehensively detected in general elemental analysis using an X-ray microanalyzer. Therefore, the X-ray acceleration voltage is set to 15 kV or higher, and more preferably 20 kV or higher. However, with such a high acceleration voltage, the diffusion region by the following formula exceeds 1 μm, and even the presence of inorganic particles in the thickness direction of the paper is detected, so that only the paper surface can be accurately analyzed. Can not.
ρR = 0.0276E ₀ ^1.67 A / Z ^8/9
(Where R is the X-ray diffusion region, ρ is the average density, E ₀ is the acceleration voltage, A is the average molecular weight of the analysis site, and Z is the average atomic number)

  Accordingly, in the present invention, in view of the relationship between the X-ray acceleration voltage and the diffusion region, the surface analysis of the paper surface using the X-ray microanalyzer under the conditions that the X-ray acceleration voltage is 8 kV and the diffusion region is 1 μm. Thus, in the size of the detection area of the silicon to be analyzed as the hydrated silicic acid aggregate particles, the area ratio of the aggregate particles having a particle diameter of 6 to 20 μm according to the detection area is preferably 80% or more. By adjusting so that it becomes, the target newsprint can be realized more easily.

  When the area ratio of the 6 to 20 μm aggregate particles in a predetermined region is less than 80%, for example, when the paper is produced at a high speed of 1300 m / min or more, the obtained newspaper is, for example, 170 to 200,000 copies / When subjected to high-speed offset rotary printing such as time, the papermaking equipment is worn and paper dust is generated, and in particular, the printing opacity may be reduced. Therefore, the area ratio is 80% or more, preferably 85% or more, and more preferably 90% or more. In addition, it is desirable for the area ratio in the predetermined area | region of the aggregate particle | grains of 6-20 micrometers to be as large as possible.

  The newspaper pH of the newsprint of the present invention is preferably 6.0 or more, more preferably 6.5 or more, and is preferably 10.0 or less, more preferably 9.5 or less. For example, in high-speed offset rotary printing such as 170 to 200,000 copies / hour, since the dampening water applied to the paper surface before printing varies depending on the newspaper company, it is almost neutral. In consideration of this, it is preferable to adjust to such a paper surface pH range in order to reduce the risk of printing failure. In order to obtain newsprint having such a paper surface pH, conditions such as papermaking pH may be adjusted as appropriate.

  In the present specification, the pH of the paper is measured with a reagent (MPC-BCP: pH 4.8 to 6.8, MPC-CR: pH 6.8 to 8.8) using a pH measurement kit for paper (manufactured by Kyoritsu Riken). ) And the value measured visually with a discoloration standard meter.

  Further, the newsprint of the present invention preferably has a formation index by a sheet formation tester of 5% or more, more preferably 6% or more, and preferably 10% or less, more preferably 9.5% or less. The newsprint of the present invention requires a predetermined tensile strength because it is mainly printed on a rotary press. Therefore, in order to obtain a predetermined tensile strength in the longitudinal direction, it is preferable from experience that a formation unevenness having a formation index of about 5% occurs. On the other hand, when the formation index exceeds 10%, it is difficult to obtain sufficient longitudinal tensile strength, and for example, in offset printing, particularly in color printing, uneven absorption of ink along uneven formation occurs, and printability, in particular, There is a risk of reducing the printing opacity.

  In addition, in this specification, the formation index of newsprint means a value measured by a sheet formation tester (manufactured by Toyo Seiki Seisakusho). The formation index is a value obtained by using a sheet formation tester which is a light transmission type ground total. The measuring principle of this measuring instrument is that the light transmitted through the base paper is decomposed into each pixel with a CCD camera, and the standard deviation, which is the variation in absorbance of each pixel, is divided by the average absorbance. "". That is, the larger the formation index, the worse the formation.

  In the newsprint of the present invention, a surface treatment agent made of, for example, the water-soluble polymer compound is applied to the front and back surfaces of the paper whose water content is adjusted to 5 to 15% by mass, and the surface treatment agent is applied. It is preferable that the water content is adjusted to 8 to 10% by mass. That is, for example, when the surface treatment agent is applied to the front and back surfaces of the paper, the water content before application is adjusted to 5 to 15% by mass, and the final water content after passing through the dryer part (after application) is 8 It is preferable to make the paper so that it becomes 10% by mass. Newspaper paper that has come out of the dryer part passes through the calendar part, and after the calendar, it is wound up at the outlet (reel) of the papermaking machine. For finishing.

  In order to adjust the moisture content before coating to preferably 5 to 15% by mass, more preferably 7 to 12% by mass, for example, the water content is 50 to 58% by mass mechanically squeezed with a press part. It is possible to adopt a method in which the wet paper that has reached the degree is guided to the predryer part, and the amount of steam, the steam temperature, and the like inside the cylinder constituting the predryer part are appropriately set.

  In order to make paper so that the final moisture content after papermaking is preferably 8 to 10% by mass, more preferably 8.5 to 9.5% by mass, for example, the conditions in the after dryer part are: As with the predryer part, a method of changing as appropriate can be adopted.

  In addition, as a method of managing the moisture of the paper discharged from the paper machine and the moisture of the paper discharged from the after dryer, for example, a method of measuring with an on-line BM meter, a moisture from the paper machine and an after dryer A method of actually measuring moisture can be employed.

  In the present invention, for example, high speed papermaking is possible at a paper making speed of 1300 m / min or more, and it is lightweight while generating high speed offset rotary printing at 170 to 200,000 copies / hour, for example, and generation of paper dust is also possible. The purpose is to provide newsprint with excellent opacity, especially printing opacity. Needless to say, it satisfies the basic quality required for original newsprint, The ink density of the printed part measured with a Macbeth densitometer is preferably 1.25 or more, more preferably 1.27 or more, and preferably 1.36 or less, more preferably 1.34 or less. If the ink density is less than 1.25, it may be difficult to obtain a desired ink density, for example, in printing on an actual rotary press in a newspaper company. Conversely, if it exceeds 1.36, the ink density is sufficient. This can result in reduced print opacity and set-off problems.

  The ink concentration can be adjusted, for example, by appropriately adjusting the degree of saponification and degree of polymerization of the water-soluble polymer compound such as starch and PVA used as a surface treatment agent, and the amount of use thereof.

  In addition, in this specification, the ink density | concentration of the printing site | part after printing means the value calculated | required in the following ink density | concentration tests.

(Ink density test)
Using an RI printing aptitude tester (model number: RI-2 type, manufactured by Ishikawajima Industrial Machinery Co., Ltd.), offset printing ink (trade name: Newsz Naturalis (black), large, between the metal roll and rubber roll. After applying Nippon Ink Chemical Co., Ltd., ink usage: 0.85 ml), printing was performed at a speed of 30 rpm (test piece: CD direction 50 mm, MD direction 100 mm), and a constant chamber state (described in JIS P 8111) (Paper, paperboard and pulp-standard conditions for humidity conditioning and testing)) for 24 hours. About this print sample, the ink density of 25 printing parts selected at random is measured with a Macbeth densitometer, and these average values are calculated.

  Further, the whiteness of the newsprint is 55% or more, more preferably 55.5 to 58, as measured according to “Pulp—Diffusion Blue Light Reflectance (ISO Whiteness) Measurement Method” described in JIS P 8212. % Is preferred. When the whiteness is less than 55%, not only the white paper appearance before printing is degraded, but also the appearance of the printed matter after offset printing, particularly after color printing, may be degraded.

  The blank paper opacity of the newsprint is 88% or more, and further 90 to 94%, as measured in accordance with “Paper and paperboard—Opacity test method (paper backing)” described in JIS P 8149. It is preferable. If the blank paper opacity is less than 88%, not only the appearance of the blank paper before printing is deteriorated but also the appearance of the printed matter after the offset printing may be lowered.

  The printing opacity after printing on the newsprint of the present invention is preferably 0.5% or more, more preferably 0.8 to 2.0% higher than the blank paper opacity.

Further, the newsprint of the present invention has a density of about 0.63 to 0.90 g / cm ³ measured in accordance with “Test method of thickness and density” described in JIS P 8118. The Beck smoothness measured in accordance with the described “paper and paperboard—smoothness test method using a Beck smoothness tester” is about 41 to 65 seconds. It is preferable in that it can be further improved.

  Next, the newspaper of the present invention will be described in more detail based on the following examples, but the present invention is not limited to these examples.

Preparation Examples 1-13 and Comparative Preparation Examples 1-4 (Preparation of hydrated silicic acid)
2500 L of sodium silicate aqueous solution adjusted to a concentration of 195 g / L in terms of silicon dioxide (silica), 4800 L of fresh water, and 130 kg of anhydrous sodium sulfate were charged into a reaction tank having a volume of 10 m ³ .

  After the temperature of the solution in the reaction vessel was 50 ° C., while stirring, 410 L of sulfuric acid (concentration: 20% by mass) corresponding to 32.5% by mass of the total amount of sulfuric acid necessary for neutralizing sodium silicate was added. Added continuously over a period of minutes. After the addition of sulfuric acid, the reaction solution was heated to 90 ° C. over 35 minutes with stirring, and then aged for 10 hours at 90 ° C.

  Next, the remaining 850 L of sulfuric acid (concentration: 20% by mass) was continuously added over 25 minutes. Further, aging was performed for 20 minutes while maintaining the temperature. Thereafter, sulfuric acid was continuously added to adjust the pH of the slurry to 5.2. The slurry with adjusted pH was filtered and washed, and then wet pulverization and classification were sequentially performed to obtain hydrated silicic acid (secondary aggregate).

  In addition, while following the above manufacturing means, the concentration of the initial sodium silicate aqueous solution, the molar ratio of sodium silicate and sulfuric acid, the reaction temperature, the addition rate and amount of the chemical to be added were appropriately changed and adjusted, and the numbers shown in Table 1 1 to 13 and ratio 1 to ratio 4 of hydrated silicic acid were obtained. In Comparative Preparation Examples 1 to 4, a hydration silicic acid (secondary agglomerate) was further subjected to a drying process using a spray-drying type dryer.

  The obtained hydrated silicic acid composed of secondary aggregates was analyzed by the laser analysis method, and the ratio of hydrated silicate particles having a volume average particle diameter and a particle diameter of 1 to 30 μm (shown as the particle ratio in Table 1). Was measured. The results are shown in Table 1.

  Moreover, the oil absorption amount of the obtained hydrated silicic acid was measured based on JISK5101-13-1. The results are shown in Table 1.

  Furthermore, the obtained hydrated silicic acid was diluted with fresh water to prepare diluted water having the concentrations shown in Table 1.

Examples 1 to 13 and Comparative Examples 1 to 4 (Manufacture of newsprint)
Deinked waste paper pulp (disaggregation / deinked waste paper pulp) and mechanical pulp (TMP) are blended in the proportions shown in Table 2, and the fillers (variety A and variety B) shown in Table 3 are mixed in Table 3 per ton of pulp. Was added in the amount shown in. Further, a coagulant (variety a and variety b) shown in Table 4 was added to obtain a pulp slurry.

  Next, the flocculant shown in Table 4 was added to the obtained pulp slurry, and paper was produced at a paper making speed of 1300 m / min using a long net paper machine to produce a paper. The water-soluble polymer compound shown in Table 5 was applied to the front and back surfaces of this paper by the coating method shown in Table 5 so that the coating amount on one side (total amount of water-soluble polymer compound) shown in Table 5 was reached. Got the paper.

  The ratio of the filler shown in Table 3 (variety A: variety B (mass ratio)) is not a 500-fold image obtained by electron beam probe microanalysis using an ash obtained in accordance with JIS P 8251 as a sample. About 10 places selected for the purpose, the ratio of silica and calcium in terms of oxide was measured, and the measurement results at these 10 places were averaged. The measurement was performed using an X-ray microanalyzer (model number: E-MAX, manufactured by Hitachi, Ltd.) and an electron microscope (manufactured by Shimadzu Corporation) under the condition of an acceleration voltage of 8 kV.

Moreover, the filler shown in Table 3, the coagulant | flocculant and flocculant shown in Table 4, and the water-soluble polymer compound shown in Table 5 are as follows, respectively.
(Filler)
Chestnut: Chestnut calcium carbonate Heavy: Heavy calcium carbonate Spindle type: Spindle type calcium carbonate (coagulant)
PEI: Polyethyleneimine PVAm: Polyvinylamine PDADMAC: Polydiallyldimethylammonium chloride PAm: Polyamine (flocculating agent)
PAM: Polyacrylamide (water-soluble polymer compound)
Esterified starch: 1-octenyl succinate esterified starch

  Each physical property of the obtained newspaper was measured by the following method. These results are shown in Table 6.

Further, commercially available newsprints A to C were used as Comparative Examples 5 to 7, and each physical property was measured in the same manner. These results are also shown in Table 6. In addition, the kind of filler currently mix | blended with these commercially available newsprints AC is as showing below.
Filler Type Newspaper A: Hydrated Silica Newspaper B: Spindle Type Calcium Carbonate Newspaper C: Hydrated Silicic Acid

(A) Basis weight It measured based on JISP8124.

(B) Paper surface pH
Using a reagent (MPC-BCP: pH 4.8 to 6.8, MPC-CR: pH 6.8 to 8.8) with a pH measurement kit for paper (manufactured by Kyoritsu Riken), visually check with a discoloration standard meter Measured with

(C) Ash content It measured based on JISP8251.

(D) Magnesium content in ash (magnesium content in terms of oxide)
The ash content measured in accordance with JIS P 8251 is subjected to elemental analysis with an X-ray microanalyzer (model number: E-MAX S-2150, manufactured by Hitachi, Ltd./manufactured by Horiba, Ltd.), and oxidized. It calculated | required by the component analysis of conversion.

(E) Geometric index Measured with a sheet formation tester (manufactured by Toyo Seiki Seisakusho).

(F) Whiteness Measured according to JIS P 8212.

(G) Printing Opacity JAPAN TAPPI Paper Pulp Test Method No. 45 (2000) in accordance with "Newspaper-Testing method for opacity after printing", using an offset rotary printing press (model number: RI-2, manufactured by Ishikawajima Industrial Machinery Co., Ltd.) Product name: News Zet Naturalis (black), Dainippon Ink Chemical Co., Ltd.), changing the ink amount, printing at a speed of 180,000 copies / hour, and when the printed surface reflectance is 10%, Ratio of back surface reflectance after printing to back surface reflectance before printing:
(Back side reflectance after printing / Back side reflectance before printing) × 100 (%)
Asked. A spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd.) was used for measuring the reflectance.

(H) Ink Concentration Using an RI printing aptitude tester (model number: RI-2 type, manufactured by Ishikawajima Industrial Machinery Co., Ltd.), offset printing ink (trade name: News Zet Naturalis) in the gap between the metal roll and the rubber roll. (Black), Dainippon Ink & Chemicals, Inc., ink usage: 0.85 ml), and printing at a speed of 30 rpm (test piece: CD direction 50 mm, MD direction 100 mm) (According to JIS P 8111) for 24 hours. About this print sample, the ink density | concentration of 25 printing parts selected at random was measured with the Macbeth densitometer, and these average values were calculated | required. If the ink density is less than 1.25, there may be a problem that the desired ink density does not occur, for example, in web offset printing in a newspaper company. Conversely, if it exceeds 1.36, the ink density is sufficient. However, there may be a decrease in printing opacity and a problem of set-off.

(I) Area ratio of aggregate particles having a particle diameter of 6 to 20 μm X-ray using an X-ray microanalyzer (model number: E-MAX, manufactured by Hitachi, Ltd.) and an electron microscope (manufactured by Shimadzu Corporation) The surface of the paper is subjected to surface analysis under the conditions of an acceleration voltage of 8 kV and a diffusion region of 1 μm, and in the size of the detection area of the silicon to be analyzed for the hydrated silicic acid aggregate particles, the particle size corresponding to the detection area is 6 The area ratio of the aggregate particles of ˜20 μm in the predetermined area (area ratio in the analysis area of 1 cm ² combined with the elemental analysis mapping photograph of the paper surface photographed at 500 times) was determined.

(J) Water content The water content of the paper before the application of the water-soluble polymer compound and the final water content of the newsprint after the application are described in “Paper and paperboard-water test” described in JIS P 8127. Measured in accordance with “Method (Method Using Dryer)”. The moisture content before coating is shown in Table 5, and the moisture content after coating is shown in Table 6 (in Table 6, indicated as product moisture content).

  Next, each characteristic was investigated about the newsprint of Examples 1-13 and Comparative Examples 1-7 based on the following test examples 1-5. The results are shown in Table 7.

Test Example 1 (Ink setting property)
Using an RI printing aptitude tester (model number: RI-2 type, manufactured by Ishikawajima Industrial Machinery Co., Ltd.), newspaper ink (trade name: Newsjet Naturalis (black), manufactured by Dainippon Ink & Chemicals, Inc.) After solid printing with, the coated paper was stacked on the printing surface and pressure-bonded at a constant pressure. The state of ink transfer to the coated paper was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): The smear does not arise at all on the coated paper surface.
○: Slight dirt is generated on a part of the coated paper surface, but there is no practical problem.
Δ: Stain is observed on the entire coated paper surface.
X: Stain on the entire coated paper surface is remarkable.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

Test example 2 (ink inking property)
Using an offset printing machine (model number: Komori SYSTEMC-20, manufactured by Komori Corporation), using newspaper ink (trade name: Newsz Naturalis (black), manufactured by Dainippon Ink & Chemicals, Inc.), 18 Continuous 10,000 copies were printed at a speed of 10,000 copies / hour. About the obtained printed matter, the clearness and the shading unevenness of an image were observed visually, and it evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): The image is clear, there is no unevenness in density, and the ink deposition property is excellent.
A: The image is clear, there is almost no unevenness in density, and the ink deposition property is good.
Δ: Some portions have unclear images and unevenness in density, and ink inking property is not good.
X: Overall, the image is unclear, the density unevenness is remarkable, and the ink deposition property is inferior.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

Test example 3 (surface strength)
Ink tack 18 using a color change tester (model number: RI-1 type, manufactured by Ishikawajima Sangyo Co., Ltd.) in accordance with “lithographic ink—Part 1: test method” described in JIS K5701-1. The printing was performed under the conditions of the first printing. The newspaper paper surface was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: The entire surface of the newsprint is not removed.
○: Slightly removed on a part of the newspaper surface, but there is no practical problem.
Δ: Taken over the entire newspaper surface.
X: Significant removal on the entire newspaper surface.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

Test Example 4 (Ink absorption unevenness)
Using an offset printing machine (model number: Komori SYSTEMC-20, manufactured by Komori Corporation), using newspaper ink (trade name: Newsz Naturalis (black), manufactured by Dainippon Ink & Chemicals, Inc.), 18 Printing was performed at a speed of 10,000 copies / hour. The obtained printed matter was visually observed for ink density unevenness and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: There is no unevenness in the ink density, and the image is uniform and clear.
◯: There is almost no ink density unevenness and the image is uniform.
(Triangle | delta): The ink density nonuniformity is recognized in part, and there exists a location where an image is unclear.
X: Overall, the ink density unevenness is remarkable and the image is unclear.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

Test Example 5 (printing operability)
(1) Cutter tip clogging Using an offset rotary printing press (model number: LITHOPIA BTO-N4, manufactured by Mitsubishi Heavy Industries, Ltd.), printing was performed at a rate of 180,000 copies / hour on 50-roll newspapers. The presence or absence of clogging of the sword tip was examined and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: No sword clogging occurred.
○: A sword clog occurred only once with one winding.
Δ: Claw tip clogging occurred 2 to 3 times with one winding.
X: Sword tip clogging occurred 4 times or more with one winding.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

(2) Blanket paper dust piling Using an offset printer (model number: Komori SYSTEMC-20, manufactured by Komori Corporation), continuous 4-color printing of 5000 parts was performed at a speed of 180,000 parts / hour. The presence or absence of paper dust generation / deposition in the blanket non-image area was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): Generation | occurrence | production of paper dust is not recognized at all.
○: Slight generation of paper dust is observed, but no deposition on the blanket is observed.
(Triangle | delta): Generation | occurrence | production of paper dust is recognized and it has accumulated on the blanket.
X: Accumulation of paper dust on the blanket is remarkable.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

(3) Neppari (Blanket adhesive)
Two samples obtained by cutting newspaper paper into a size of about 4 cm in width and about 6 cm in length were prepared, immersed in water for 10 seconds, and then these two samples were quickly brought into close contact with each other. This was passed through a calendar at a linear pressure of 100 kg / cm, dried at room temperature for 24 hours, and then manually peeled off two samples (T peel peel test imitation sensory test). Based on the evaluation.
(Evaluation criteria)
(Double-circle): It did not peel and it did not adhere | attach at all.
○: Although partly adhered, it could be easily peeled off.
(Triangle | delta): There existed a part which has adhere | attached and was hard to peel.
X: Adhered as a whole, and fluffing of fibers from the adhesion surface was observed at the time of peeling.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

  In each of the newsprints of Examples 1 to 13, hydrated silicic acid is internally added to the raw material pulp in a low-concentration diluted solution, the amount of ash is adjusted within a specific range, and magnesium in the ash is contained. Content (magnesium content in terms of oxide) is adjusted to be as low as 7.5% by mass or less.

  Therefore, as shown in Tables 6 and 7, the newsprint papers of Examples 1 to 13 are not only lightweight, but also have high whiteness and maintain high printing opacity. Recognize. Moreover, all the newspapers of Examples 1 to 13 have a high ink concentration, but also have good ink setability and ink fillability and excellent printability, as well as high surface strength and generation of paper dust. It can be seen that it is completely or hardly present, has excellent printing operability, and has excellent characteristics particularly suitable for high-speed offset rotary printing.

  On the other hand, all the newspapers of Comparative Examples 1 to 4 have a magnesium content (magnesium content in terms of oxide) in ash of more than 7.5% by mass. Therefore, it can be seen that all the newspapers of Comparative Examples 1 to 4 have insufficient whiteness and low printing opacity. Moreover, all the newspapers of Comparative Examples 1 to 4 are suitable for high-speed offset rotary printing such as inferior ink setting properties and ink inking properties, uneven ink coloring, low surface strength, and poor printing operability. It can be seen that it does not have the necessary characteristics.

  Further, the newspapers of Comparative Examples 5 to 7 have an ash content of less than 7% by mass, and the magnesium content in the ash (magnesium content in terms of oxide) is greater than 7.5% by mass. It can be seen that the ink does not have the characteristics necessary for high-speed offset rotary printing, such as inferior ink setability and ink fillability, uneven ink coloring, low surface strength, and poor printing operability.

  The newsprint of the present invention can be suitably used for offset rotary printing such as high-speed offset rotary printing such as 170 to 200,000 copies / hour using a cold set type ink.

Claims (3)

A newsprint with a basis weight of 36-50 g / m ² in accordance with JIS P 8124, with hydrated silicic acid added internally as a filler,
The ash content measured according to JIS P 8251 is 7 to 17% by mass, and the magnesium content (magnesium content in terms of oxide) in the ash content is 7.5% by mass or less. , Newspaper.   Using the X-ray microanalyzer, in the surface analysis of the paper surface under the condition that the acceleration voltage of X-ray is 8 kV and the diffusion region is 1 μm, The newspaper according to claim 1, wherein the area ratio of the aggregate particles having a particle diameter of 6 to 20 μm according to the detection area in a predetermined region is 80% or more.   A dilute solution obtained by diluting the hydrated silicic acid obtained without passing through the drying step after the reaction into a concentration of 3% by mass or less in advance. The newsprint according to claim 1, wherein the newspaper is internally added to the raw pulp at a stage preceding the screen, and the flocculant is added to the pulp slurry at a stage prior to the paper making process.