JP2019060042A - Newsprint paper - Google Patents

Abstract

To provide a newsprint paper having high saturation color reproduction and high opacity when printed using offset printing ink consisting of the four processing colors of yellow, red, amber and black.SOLUTION: The present invention provides a newsprint paper in which a filler is internally added to pulp, and the whiteness is 70% or more to 80% or less, the lightness is 85 or more to 95 or less, and its "a" value is -0.7 or more to -0.5 or less, its color tone "b" value is 0.2 or more to 1.8 or less, and a basis weight is 45 g/mor more to 60 g/mor less. The content of hardwood bleached kraft pulp in the pulp is 20% or more by mass to 40% or less by mass, the content of waste paper pulp is 20% or more by mass to 30% or less by mass, and the content of mechanical pulp is 30 mass% or more by mass to 50 mass% or less by mass, it is preferable to contain calcium carbonate having a volume average particle diameter of 1.0 μm or more to 2.0 μm or less as the filler.SELECTED DRAWING: None

Description

  The present invention relates to newsprint.

  In recent years, newsprint for offset printing has rapidly progressed to color printing, speeding up, digital variable printing, towering, and the like. Accordingly, there is a need for better color print quality and printability for newsprint. However, in the case of lithographic offset printing consisting of four colors (CMYK) of yellow, red, amber and black, which are currently mainstream, the hue is a color mixture due to reduced color mixing. It also narrows. For this reason, in the conventional low whiteness newsprint paper, a difference in color reproducibility between digital data and printed matter tends to occur.

  The subtractive color mixing refers to a phenomenon in which a new color is perceived as a result of color light passing through two or more objects. This is a phenomenon that occurs as each object absorbs light in different wavelength ranges and the color light decreases. Subtractive mixing is mixing by absorbing light, whereas additive mixing is mixing by adding light. The three primary colors Y (yellow), M (magenta) and C (cyan) of the subtractive color mixture become K (black). In printing, each color is thereby created.

  In order to ensure color reproducibility in printing, Patent Document 1 proposes an ink for penetration drying type offset printing. However, improvement of printing ink alone is still insufficient in securing color reproducibility in application to newsprint with low whiteness, and it is possible to print variable information by digital printing machine, which has been further developed in recent years. There is a demand for the development of newsprint for handling, color printing, speeding up, and the like.

  In addition, as a technology for high-white newsprint paper, in Patent Document 2, the ash content in newsprint paper and predetermined raw material pulp are used, and the oil absorption, air permeability, and whiteness are set to the desired ranges. In addition to the appearance of color printing with whiteness, highly white newsprint paper has been proposed which is less likely to cause re-dislocation of undried ink and less likely to cause printing defects even during high-speed printing. According to this technology, although it can be expected that color printing will look good by designing the whiteness of newsprint paper itself high, the oil absorption is high, and furthermore, the air permeability is kept low, so undried paper of ink As the amount of penetration into the layer increases, it becomes difficult to secure a sufficient ink density, and the opacity, which is a problem in high whitening of newsprint, needs to be further studied. In addition, Patent Document 2 describes that the opacity required for newsprint can be maintained by using bleached mechanical pulp, but the problem is that the opacity decreases with increasing whiteness. , The frequent use of mechanical pulp causes improvement in oil absorption due to the fine fiber characteristic of mechanical pulp and it is easy to reveal the problem of strike-through, combined with low air permeability and sufficient opacity in high speed rotary printing It is feared that it is difficult to secure

  On the other hand, as a technique for enhancing the opacity, a pigment coated layer is provided, and a newsprint sheet having an ash content of 7 to 25% by weight derived from the base paper and the pigment coated layer (Patent Document 3), polyhydric alcohol, fatty acid By adding a bulking agent such as an ester compound of an ester compound of (A) and a polyhydric alcohol and a fatty acid, which is an ester compound selected from an ester compound (B) having an oxyalkylene group, A method (Patent Document 4) for providing transparent newspaper has also been proposed. Although such means of using pigments and bulking agents is a method of improving opacity, further improvement is required to provide newsprint excellent in color reproduction with high saturation corresponding to color printing and speeding up. Be

2009-12292 2008-196090 gazette 2009-84734 gazette Publication No. 2000-314091

  The present invention has been made based on the above circumstances, and an object thereof is to provide high saturation color reproduction when printed using an offset printing ink consisting of four processes of yellow, red, yellow and black. It is to provide newsprint which has a high quality and high opacity.

The invention made to solve the above-mentioned problems is newsprint paper in which a filler is internally added to pulp, and the whiteness is 70% to 80%, the lightness is 85 to 95, and the a value is -0. 7 or more and 0.5 or less, b is a color tone of 0.2 or more and 1.8 or less, and the basis weight is 45 g / m ² or more and 60 g / m ² or less.

  The newsprint has high saturation color reproducibility and high opacity when printed using an offset printing ink consisting of four yellow, red, amber and black processes. Although the reason why the newsprint paper has high color saturation is not clear, it is not clear that the color tone of newsprint paper has less influence on the appearance of the color printed by the offset printing etc. It is presumed that the repeatability is increasing.

  The softwood bleached kraft pulp content in the pulp is 16% by mass to 24% by mass, the hardwood bleached kraft pulp content is 18% by mass to 26% by mass, and the recycled paper pulp content is 24% by mass to 32% It is preferable that the content of the mechanical pulp is 26% by mass or more and 34% by mass or less, and calcium carbonate having a volume average particle diameter of 1.0 μm or more and 2.0 μm or less is contained as the filler. In this way, it is possible to ensure high opacity and high printability in high speed offset rotary printing while using high white newsprint.

  The mechanical pulp is chemithermomechanical pulp (CTMP), the ash content is preferably 7% by mass to 20% by mass, and the dripping water absorption is preferably 15 seconds to 40 seconds. By doing this, even if high-speed offset rotary printing is performed, high-definition printing without color misregistration corresponding to visualization can be performed. In addition, color reproducibility and opacity in high-speed offset rotary printing can be further enhanced. It is presumed that this is because, in this way, the permeability, drying property, etc. of the offset printing ink are optimized.

  According to the present invention, it is possible to provide newsprint paper having high color reproducibility and high opacity when printed using offset printing ink consisting of four processes of yellow, red, amber and black. it can.

  Hereinafter, newspaper according to an embodiment of the present invention will be described in detail.

  The said newsprint is a newsprint in which a filler is internally added to pulp. The said newsprint paper can be obtained by paper-making (paper-making) the stock slurry containing a pulp and a filler, and preferably coating of a surface treatment agent, a calendar process, etc.

<Pulp>
Pulp (raw material pulp) used for the newsprint preferably contains softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), waste paper pulp and mechanical pulp. The softwood bleached kraft pulp content in the pulp is 16% by mass to 24% by mass, the hardwood bleached kraft pulp content is 18% by mass to 26% by mass, and the recycled paper pulp content is 24% by mass to 32% The content of mechanical pulp is preferably 26% by mass or more and 34% by mass or less.

(Conifer bleached kraft pulp)
In the newsprint paper, pine trees typified by radiator pine are preferably used as tree species to improve the color reproducibility of high saturation, which is a problem, and also to pull and tear strength in high speed rotary printing equivalent to conventional newsprint paper. It is preferable to blend softwood bleached kraft pulp that has a long fiber length, and it is possible to secure the strength of the paper obtained by blending a predetermined amount, and further to improve cushioning properties and freeness. It can be planned.

  Although the said effect is acquired by mix | blending softwood bleached kraft pulp 16 mass% or more, in the compounding quantity which exceeds 24 mass%, since a fiber length is long, the printability which is a subject may be reduced. As a minimum of content of this softwood bleached kraft pulp, 18 mass% is more preferred, and 20 mass% is still more preferred. On the other hand, 23 mass% is more preferable as an upper limit of this content.

  The Canadian standard freeness (CSF) of softwood bleached kraft pulp to be blended is preferably adjusted to 300 ml or more and 650 ml or less. Here, the freeness is a value represented by the Canadian standard freeness (C.S.F.) defined in JIS P8121, and the beating of the pulp (the pulp is mechanically hit and ground in the presence of water) Value indicating the degree of processing). Generally, the smaller the freeness value, the stronger the degree of beating, and the greater the degree of fiber damage due to the beating, the more fibrillation progresses. NBKP whose freeness is in the above range is such that fibers are easily entangled because fibrillation progresses, and therefore, it is configured by achieving recent reduction in basis weight (weight reduction) of newsprint paper from the viewpoint of improving liquid permeability. Even if the number of fiber-to-fiber bond points is reduced, the strength of each fiber-to-fiber bond is higher than that of NBKP in which the degree of freeness exceeds 650 ml and fibrillation has not progressed relatively. Thus, if the freeness is less than or equal to 650 ml, newsprint based on NBKP may have good strength properties. The freeness of softwood bleached kraft pulp is more preferably 300 to 650 ml, particularly preferably 450 to 550 ml, and still more preferably 480 to 530 ml. If the freeness is less than 300 ml, the strength improvement effect by the entanglement of the fibers is saturated, and the cutting of the fibers is accelerated, and the permeation time may be delayed.

(Hardwood bleached kraft pulp)
In the newsprint paper, hardwood bleached kraft pulp manufactured from eucalyptus or acacia wood is suitably used, and when 18% by mass or more and 26% by mass or less of hardwood bleached kraft pulp is blended, the texture becomes good and the paper quality is stable. And printability is better. If the bleached hardwood kraft pulp is less than 18% by mass, the texture for obtaining high color reproducibility may not be secured. If it is more than 26% by mass, the problem of insufficient strength occurs in recent high-speed rotary printing. There is a case. As a minimum of content of this hardwood bleached kraft pulp, 20 mass% is more preferred, and 21 mass% is still more preferred. On the other hand, as a maximum of this content, 24 mass% is more preferred, and 23 mass% is still more preferred.

  Akashiya wood is a material that has little shrinkage due to drying, is resistant to impact, and is strong and hard, and the pulp obtained from acacia wood retains its original properties, and has a small amount of short fibers, and it has dimensions in the manufacture of newsprint. It is a useful raw material pulp having high stability and high ink absorption and drying property in high speed rotary printing. Eucalyptus belongs to the genus Eucalyptus, and especially Eucalyptus globulus, Eucalyptus grandis, Eucalyptus europhora, Eucalyptus nitense, Eucalyptus lignans etc. have long been widely used as raw material pulp materials for paper production, and the pulp obtained is Fiber lumens (lumens) are hard to crush and are rigid, and by incorporating this pulp fiber, it is possible to obtain a bulky low density newsprint.

  The Canadian standard freeness (CSF) of the hardwood bleached kraft pulp to be blended is preferably adjusted to 300 ml or more and 450 ml or less. If the Canadian standard freeness of hardwood bleached kraft pulp is lower than 300 ml, the freeness is poor, which leads to the deterioration of productivity in high speed papermaking of 1000 m / m or more using a gap former in recent years. On the other hand, if the standard freeness of Canada is higher than 450 ml, the tensile strength is low, and paper breakage is likely to occur during paper making or high speed rotary printing.

(Waste pulp)
In the said newsprint paper, when waste paper pulp is mix | blended 24 mass% or more and 32 mass% or less, it contributes to the effective use of a resource, and can attain cost reduction. The lower limit of the content of this waste paper pulp is more preferably 25% by mass. On the other hand, 30 mass% is more preferable, and, as for the upper limit of this content, 28 mass% is more preferable. As waste paper pulp, deinked pulp is suitably used. The deinked waste paper pulp is roughly divided into high quality and medium quality, and it is preferable to use high quality waste paper pulp in order to obtain newsprint having high color reproducibility and excellent color reproducibility. Examples of high-quality wastepaper pulp include pulps prepared from wastepaper such as white, creased, curd, imitation, on color, Kent, white art, milk carton and the like. As a representative of medium-grade wastepaper pulp, pulp prepared from newspaper, magazines, cuttings, medium-quality anti-corrosion, tea imitation, cardboard, mount / base ticket, cardboard and the like can be mentioned. In addition, newspaper paper has a high recovery rate as waste paper and is said to be an excellent resource for recycling, and by using it as the newspaper paper of the present invention as its application, it becomes possible to further promote circulation use of newspaper paper. . Newspaper waste paper deinking pulp is a pulp obtained by mixing magazine waste paper etc. mainly with newspaper waste paper, and subjecting it to deinking treatment, and these pulps are each composed of chemical pulp such as NBKP, LBKP, and mechanical pulp as a fiber composition. Although mixed, since the fiber composition of the pulp becomes almost constant, it can be used as a stable raw material pulp with a Canadian standard freeness of waste paper pulp of about 150 ml.

  In particular, high-quality wastepaper pulp, which uses high-quality wastepaper as a starting material, has a coating layer containing a large amount of inorganic fine particles, and is removed by removing the printing ink printed on the attendance layer and the coating layer in the deinking treatment step. The raw material pulp having a relatively high whiteness, which constitutes the base paper, can be recovered and reused effectively, so it is optimum for the reason to the present invention, and the inorganic filler derived from waste paper (still after the deinking treatment step and the raw material pulp There is also a large content of the inherent filler), and since the waste paper-derived inorganic filler is fixed to the raw material pulp, it does not fall off even when high-speed offset rotary printing is performed, causing paper dust, and thus high. Uncertainty can be secured.

(Mechanical pulp)
In the newsprint paper, when mechanical pulp is blended in an amount of 26% by mass or more and 34% by mass or less, high-speed offset rotary printing using offset printing ink consisting of four processes of yellow, red, amber, and black is performed. Printability such as better ink dryness, color reproducibility and high opacity. The mechanical pulp does not include waste paper pulp. 27 mass% is more preferable, and, as for the lower limit of the content of mechanical pulp to total pulp, 28 mass% is more preferable. When the content is less than the lower limit, the high-speed full-color offset rotary printing suitability for the newsprint may be deteriorated. On the other hand, 32 mass% is more preferable, and, as for the upper limit of content of mechanical pulp, 31 mass% is further more preferable. If the content exceeds the above upper limit, there is a possibility that generation of paper dust due to fine fibers and deterioration of printability may occur in high speed offset rotary printing of the newsprint. In addition, by setting the mechanical pulp content in the above-mentioned range, it is possible to achieve both printability and opacity, and appropriate stiffness (stiffness) required by a newspaper reader.

  Examples of mechanical pulps include ground pulp (GP), pressurized groundwood pulp (PGW), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc. TMP) Chemothermomechanical pulp (CTMP) is preferably used.

  Thermomechanical pulp (TMP) is a pulp obtained by preheating a raw wood chip at a temperature (above 100 degrees C) below the glass transition temperature of lignin for several minutes and then refining it with a pressurized refiner. It has been used for paper since the latter half of the 1960s and has become the main means of producing mechanical pulp. The CTMP is a mechanical pulp obtained by the same method as the thermomechanical pulp after subjecting a raw wood chip to chemical processing at a low concentration for a predetermined time. First of all, as a characteristic of thermomechanical pulp, it is excellent in strength by heat treatment, and it is possible to secure high opacity, although optical properties such as opacity are slightly smaller than those of ground pulp. It is a preferred means of production to determine the high opacity that can be achieved. Furthermore, although chemithermomechanical pulp is slightly inferior in optical characteristics to thermomechanical pulp by chemical treatment in advance, the high whiteness, printability, and digital printer represented by the ink jet printer are required for the newsprint paper of the present invention. It is possible to secure the correspondence to the variable printing by the above, and also to suppress the production cost of the raw material pulp.

  The pulp of the newsprint paper may contain softwood sara kraft pulp, hardwood bleached kraft pulp, waste paper pulp, and pulp other than mechanical pulp. Other pulps include non-wood pulp and the like. However, the total content of softwood bleached kraft pulp, hardwood bleached kraft pulp, used paper pulp and mechanical pulp in the pulp used in the newsprint is preferably 80% by mass or more, more preferably 90% by mass or more, and 99% by mass The above is more preferable. Thus, the effects of the present invention can be more sufficiently exhibited by appropriately combining and using substantially only four types of softwood bleached kraft pulp, hardwood bleached kraft pulp, waste paper pulp and mechanical pulp.

  The post-disintegration freeness (degree of freeness) of all pulps used for the newsprint paper is a sample of high-white newsprint paper cut into a size of 10 cm × 10 cm according to the present invention, and this sample is prepared in water at 20 ° C. It is a value of freeness measured according to JIS P 8121 (1995) after being immersed for a minute and disintegrated according to JIS P 8220 (1998).

  It is preferable that the post-disintegration freeness (freeness) in the newsprint paper be in the range of 280 ml or more and 350 ml or less. If it is less than 280 ml, it may be difficult to make bulky, which may affect the opacity and the like. The lower limit of the freeness is more preferably 300 ml, still more preferably 320 ml, and even more preferably 330 ml. On the other hand, if it exceeds 450 ml, the liquid absorption amount of the size liquid in the size press will increase to lower the papermaking speed, and the printed finish of the newsprint may also deteriorate. The lower limit of the freeness is more preferably 340 ml and even more preferably 335 ml.

<Filler>
(Calcium carbonate)
The newsprint paper preferably contains calcium carbonate having a volume average particle diameter of 1.0 μm or more and 2.0 μm or less as a filler to be internally added. The lower limit of the volume average particle diameter of the calcium carbonate is preferably 1.2 μm. On the other hand, the upper limit is preferably 1.8 μm. By internally adding calcium carbonate particles of such a particle diameter, even if calcium carbonate having originally high whiteness is combined with the inorganic filler derived from waste paper pulp blended as raw material pulp, the filler is highly blended even There is little generation of paper dust and falling off at the time of printing, it is possible to increase the ash content in the paper, it becomes possible to obtain high whiteness while using waste paper pulp, and it is possible to improve the strike through at the time of printing.

  In addition, by filling the filler in the external fibrils of the raw material pulp by compounding mechanical pulp, high opacity can be obtained in combination with the property of mechanical pulp that can obtain high opacity originally. Further, since the ink absorption and drying properties can be enhanced, good printability and color reproducibility can be exhibited.

  Examples of the calcium carbonate include light calcium carbonate and ground calcium carbonate, but it is preferable to use amorphous calcium carbonate. Amorphous heavy calcium carbonate is more easily contained physically in the raw material pulp than light calcium carbonate and silica, etc., and has a relatively broad particle size distribution, so that various gaps of the raw material pulp can be filled. As a result, the filler yield can be improved. In addition, when using a relatively small particle size calcium carbonate with a particle diameter of 1.0 μm or more and 2.0 μm or less as a volume average particle diameter, use an offset printing ink consisting of four processes of yellow, red, amber and black. Even if high speed offset rotary printing is performed, print aptitude such as good ink drying property, color reproducibility, and white paper feeling are positively affected.

  As a minimum of the compounding quantity of the above-mentioned calcium carbonate, as an amount to pulp, for example, 50 kg / pulp t is preferable, and 80 kg / pulp t is more preferable. On the other hand, as an upper limit of this compounding quantity, 200 kg / pulp t is preferable, for example, and 150 kg / pulp t is more preferable. In addition, "kg / pulp t" means the amount to 1 tons of bone-dry pulp.

(Regeneration charge)
As the above-mentioned filler, in addition to calcium carbonate, it is preferable to use a regeneration filler, more preferably a silica-coated regeneration filler in combination. The regenerating filler is, for example, particles obtained using deinking floss as a main raw material, and having been subjected to a dehydration step, a drying step, a firing step and a grinding step. Silica-coated reclaimed fillers are particles in which the surface of such reclaimed fillers is coated with silica. Coating of silica can be carried out by depositing silica on the surface of the regenerated filler, and the like.

  Since such recycled fillers and silica-coated recycled fillers can be recycled and obtained by calcining deinked floss, disposal such as landfill as waste is not required, and the environmental load is reduced. It greatly contributes to resource saving. In addition, when the raw material is deinking floss generated in the waste paper treatment process, the cost is low, the amount of use of new inorganic particles can be suppressed, and the production cost can be sufficiently reduced. Furthermore, by using the recycled filler, the ash retention during paper making is high, and unlike calcium carbonate, for example, there is no wear deterioration of the paper making equipment such as wire wear, etc. By adsorbing, it prevents pitch trouble due to aggregation of resin and hardly causes contamination of printing equipment, and paper can be manufactured at low cost and high operability, and it has excellent opacity equivalent to conventional one or more. The paper strength is imparted to the paper, and the slip-through and breakage of paper are also reduced.

  In addition, when the silica-coated regenerating filler is internally added, the whiteness, opacity, surface strength, ink drying property, ink absorption unevenness, bulkiness of the paper are more than in the case of using the regenerating filler not coated with the silica. Each effect can be improved. In the deinking floss, the content of calcium carbonate tends to increase with the recent progress of neutral papermaking, and the proportion of calcium in the obtained regenerated filler also tends to increase. When the recycled filler with a high proportion of calcium is internally added to the pulp, the opacity of the paper may decrease slightly, but the silica-coated recycled filler having silica precipitated on the surface is used as a recycled filler for papermaking applications. The functionality is very high and the opacity of the newsprint obtained by internally adding the silica-coated reclaimed filler to the pulp is significantly improved.

  Furthermore, since the regenerated filler used in the present embodiment has a soft and porous property in which fine particles are secondarily agglomerated, it contributes to the formation of a bulky paper layer, and is obtained by internally adding the regenerated filler to the pulp as a filler. Newsprint has low density and good stiffness.

  The particle size of the regenerated filler used in the present embodiment is, for example, an average particle size of 0. 2 as a secondary particle in which primary particles are aggregated, from the viewpoint of the retention in the raw material pulp and the loss of the regenerated filler into white water. The average particle diameter is preferably not more than 16 μm, more preferably not more than 15 μm, from the viewpoint of maintenance of printability and prevention of clogging of the blade tip. The average particle size of the regenerated filler can be determined by measuring the methanol dispersion solution with a Coulter counter particle size distribution analyzer (TA-II, manufactured by COULTERELECTRONICS).

  Moreover, as a minimum of the compounding quantity of the said reproduction | regeneration filler, 1 mass part is preferable with respect to 100 mass parts of calcium carbonate, and 5 mass parts is more preferable. On the other hand, as an upper limit of this compounding quantity, 50 mass parts is preferred to 100 mass parts of calcium carbonate, and 30 mass parts is more preferred.

(Other filler)
In the newsprint, other fillers besides calcium carbonate and reclaimed fillers can be used. Other fillers include, for example, at least one filler selected from inorganic fillers such as white carbon, talc, clay, titanium dioxide, synthetic silica, aluminum hydroxide, etc., synthetic polymer fine particles such as polystyrene resin, urea formaldehyde resin, etc. Can also be used in combination. Among these, white carbon is preferable from the viewpoint of enhancing whiteness, opacity and the like.

  However, as an upper limit of the total blending amount of other fillers, 50 parts by mass is preferable with respect to 100 parts by mass of calcium carbonate, and 30 parts by mass may be more preferable. By setting the blending amount of the other fillers to the upper limit or less, the effect of incorporating calcium carbonate can be further enhanced. On the other hand, 1 mass part is preferable with respect to 100 mass parts of calcium carbonates in order to fully exhibit the effect made to be incorporated as a lower limit of the compounding quantity of other fillers, especially white carbon suitably, and 5 mass parts Is more preferred.

<Other internal additives>
The stock slurry is a slurry containing pulp, filler and water, but other internal additives (auxiliary agents) may be added. As additives to be added to the slurry, those which are compounded (internally added) to ordinary paper can be used, for example, starches, vegetable gums, aqueous cellulose derivatives, paper strength agents such as sodium silicate; rosin Internal sizing agents such as starch, CMC (carboxymethylcellulose), polyvinyl alcohol, alkyl ketene dimer, ASA (alkenyl succinic anhydride), neutral rosin, etc .; Yield improvers such as polyacrylamide and copolymers thereof, sodium silicate And colorants such as dyes and pigments.

<Surface treatment>
In the said newsprint paper, after preparing a paper stock slurry from pulp and making it into a paper, surface treatment agents, such as polymer materials, such as starches, PVA (polyvinyl alcohol), a polyacrylamide, and surface sizing agent, are apply | coated on the surface. You may

(Starch)
Among the above-mentioned polymer materials, it is preferable to use starches from the viewpoints of further enhancing the effects of the present invention and improving the printing suitability and the like. As said starches, a starch, modified starch, etc. are mentioned, A modified starch is preferable. The modified starch is not particularly limited, and a common starch raw material is used, and examples thereof include oxidized starch obtained by subjecting corn, potato, tapioca, wheat, rice and the like to oxidation treatment, enzyme treatment and the like. Also, etherified starch, esterified starch, cationized starch, hydroxyethylated starch (HES) and the like can be used.

  In particular, it is preferable to use oxidized starch and HES in combination. In the said newsprint paper, when what contains oxidized starch and hydroxyethylated starch in this way as a surface treatment agent apply | coated on both surfaces of a base paper, the said 2 types of starch will be base paper at the time of application of this surface treatment agent. It does not penetrate to the inside and forms a strong film on the surface. For this reason, the surface strength is high, and the generation of paper dust can be suppressed, so that it is possible to obtain newsprint paper excellent in printing workability. In addition, the occurrence of slump problems during printing is also suppressed. By using the above two types of starch, the starch does not penetrate to the inside of the base paper, and the reason for forming a strong film on the surface is not clear, but the carboxyl group etc. possessed by oxidized starch and the hydroxyl group possessed by hydroxyethylated starch It is conceivable that by bonding (esterification reaction and the like) and crosslinking, the polymer is made to be hard to penetrate to the inside. In addition, it is thought that the viscosity becomes appropriate by mixing these two types of starch, and the esterification lowers the affinity between the starch and the cellulose that constitutes the pulp fiber, making it difficult to penetrate. Be The decrease in viscosity is also considered to be caused by the reaction of two types of starch. Furthermore, it is considered that suppression of the occurrence of nappy trouble is also due to the decrease in the hydrophilicity of starch due to the esterification and the like. The content ratio of the oxidized starch and the hydroxyethylated starch is preferably 1: 9 to 9: 1, and more preferably 4: 6 to 6: 4 on a mass basis.

  When using these starches, the amount in the surface treatment agent should be adjusted so that the content of the starches is 40% by mass or more and 95% by mass or less in the total solid content to obtain a desired effect. Is preferred.

(Surface sizing agent)
As the surface treatment agent, styrenic sizing agents, olefinic sizing agents, alkyl ketene dimers, alkenyl succinic anhydride, rosin and the like can be used, but high sizing properties, compatibility with ink, and loss prevention of fillers are possible. Styrene-based sizing agents are preferred in terms of effects and the like.

  As a styrene sizing agent, styrene acrylic acid copolymer, styrene (meth) acrylic acid copolymer (note that (meth) acrylic acid means "acrylic acid and / or methacrylic acid"), styrene (Meth) acrylic acid (meth) acrylic acid ester copolymer, styrene maleic acid copolymer, styrene maleic acid half ester copolymer, styrene maleic acid ester copolymer, etc. may be mentioned.

  In addition, a surface sizing agent becomes easy to remain on the surface by using together said 2 types of starch (oxide starch and HES), and the addition amount of a surface sizing agent can be reduced. Moreover, the paper surface dirt in the offset printing machine which generate | occur | produces by excess addition of a surface sizing agent can be suppressed.

  The blending ratio of the surface sizing agent to the starch is preferably 5 parts by mass to 30 parts by mass with respect to 100 parts by mass of the starch in solid content. By setting the compounding ratio of the surface sizing agent to 5 parts by mass or more, the effect of improving the size and surface strength of the paper can be sufficiently obtained. On the other hand, by setting the compounding ratio of the surface sizing agent to 30 parts by mass or less, an increase in the manufacturing cost can be suppressed, and the opacity and the ink drying property can be made more sufficient.

(Other surface treatment agents etc.)
To the surface treatment agent, other adhesives can be added as appropriate, for example, various additives such as pigments such as kaolin and calcium carbonate, antifoaming agents, water resistance agents, surface sizing agents, preservatives and the like. Moreover, solid content concentration of a surface treating agent is not specifically limited, It is preferable to adjust to about 2-25 mass%, for example according to a coating device and the application quantity.

  In addition, when the surface treatment agent is used in too much amount, not only the cost becomes high, but also, when the paper surface is in a wet state, the adhesiveness of the paper surface called naveliness tends to be developed. If the navelness becomes large, there is a risk that the blanket piping especially in the non-image area may be increased in reverse, or the paper may stick to the blanket at the time of printing, resulting in running problems such as wrinkles and broken paper. Unfavorable because there is. In addition, when the amount of the surface treatment agent used is increased, the transparency of the target paper may be increased, that is, the opacity may be decreased, or the drying property of the ink may be deteriorated. Among these surface treatment agents, starch and polyacrylamide are widely used because they have relatively low neparability, but all have high solubility in water, so they are easily dissolved in dampening water during printing to be used as fillers. Deposit on the blanket, and blanket piling tends to occur. In addition, the eluted surface treatment agent is transferred to the printing plate via the blanket and accumulated, whereby the non-image area of the printing plate is oil-sensitized and the ink contamination of the non-image area, that is, the soiling of the paper surface called soiling It is not preferable to use a large amount because it becomes easy to induce.

  The surface treatment agent may be a coating device generally used in the papermaking field, such as a size press, blade metering size press, rod metering size press, gate roll coater, blade coater, bar coater, rod coater, air knife coater, etc. It can be applied.

In order to sufficiently improve the surface strength of the paper, the coating amount of the surface treatment agent is preferably adjusted so as to be 0.4 g / m ² or more per one side in dry mass. Further, in order to prevent the cost increase and the deterioration of the opacity and the ink drying property, the dry weight is preferably adjusted to 3.0 g / m ² or less per one side. More preferably, it is preferable to adjust to 0.5 g / m ² or more and 1.0 g / m ² or less per one side.

  Incidentally, by making the coated amount of the surface treatment agent provided on the front and back surfaces larger on the back surface side which is roughened than the front surface side, it is possible to obtain more flat and bulky news paper and to obtain a high-impact newsprint. it can.

<Colorant: Dye and pigment>
In the said newsprint paper, you may coat coloring agents, such as dye and a pigment, as a surface treatment agent on the surface. In addition, such a coloring agent may be internally added. By using a coloring agent, it is possible to adjust the color tone, whiteness and the like of newsprint paper obtained. The present invention is directed to high whiteness newsprint paper having a basis weight of 45 g / m ² or more and 60 g / m ² or less and a whiteness of 70% or more and 80% or less, and preferably contains hardwood bleached kraft pulp Therefore, opacity is a problem in high-speed rotary offset printing using offset printing ink consisting of four colors of yellow, red, amber and black processes, which have low opacity and especially absorption-drying properties. In the present invention, mechanical pulp and waste paper pulp are preferably used as a measure for securing the opacity, but mechanical pulp is susceptible to discoloration when read by the reader outdoors like newsprint, and it is used in utilization of waste paper pulp. It has been found that there is a problem that the whiteness is lower than that of the bleached kraft pulp, and it is preferable to adjust the color tone to a predetermined color tone with a dye or dye in order to improve the opacity, the color change and the appearance whiteness.

According to the findings of the present inventors, basic dyes having high lightness and capable of vividly expressing colors are preferably used as a measure for enhancing the dyeability to waste paper pulp and mechanical pulp having relatively strong anionicity, and further desired. It has been found that it is preferable to use two or more types of dyes and dyes and pigments in order to secure the color tone of the above. According to the findings of the present inventors, in order to obtain high chroma color reproducibility when reading detailed information of newsprint and printing using offset printing ink consisting of four processes of yellow, red, black and black and black. The color tone is adjusted to a whiteness of 70% to 80%, a lightness of 85 to 95, an a value of −0.7 to −0.5, and a b value of 0.2 to 1.8. Need to be prepared by combining a purple dye and a green dye and / or a yellow dye, and the content of softwood-bleached kraft pulp suitably used in the present invention is 16% by mass to 24% by mass, The opacity of hardwood bleached kraft pulp is 18% to 26% by mass, the content of waste paper pulp is 24% to 32% by mass, and the content of mechanical pulp is 26% to 34% by mass High speed rolling stock DOO in formulation of raw material pulp to ensure the tensile strength in the printing, for example, purple dye 0.05 g / ^{m 2} and a green dye 0.02 0.05 g / ^{m 2} 0.02, and / or a yellow dye It is preferable to adjust at a content of 0.01 to 0.03 g / m ² .

  In the case where the coloring agent is surface-coated instead of internally added, coloring unevenness can be suppressed with a small amount of dye. Generally, colored dyes and pigments are used alone or in combination to adjust the color tone, but since the pulp or white pigment used usually exhibits a slightly yellowish color, this yellowish color is also used. In order to make it look white and even slightly white, blue or violet-based coloring agents (blowing agents) are only used in very small amounts.

  Dyes for paper use have higher dyeability to regenerated fillers than conventionally used clay and calcium carbonate exhibiting anionicity, and cationic direct dyes or basic dyes are dyed according to the specifications of regenerated fillers Is different. Therefore, when these dyes having different dyeability are used in combination in the coating agent, the felt surface with high dye fine fiber ratio and filler ratio is colored with cationic direct dye and basic dye, and the wire surface with high pulp ratio is mainly used It is colored with an anionic direct dye. Therefore, the hue front and back difference can be reduced by adjusting the use ratio of the same color anionic direct dye and the cationic direct dye or the basic dye, and depending on the degree of adjustment, the hue front and back difference becomes zero. It is also possible.

  As the type of the dye, a basic dye is suitably used, but one or two or more kinds may be suitably selected from acid dyes other than basic dyes, anionic direct dyes, cationic direct dyes, nonionic dyes, etc. Can be used in an appropriate combination that contributes to the solution of the problems of the present invention.

  In addition, when a dye is blended in a coating agent together with a surface sizing agent and a paper strengthening agent, the paper strengthening agent relates to the paper strengthening agent from the viewpoint that aggregation with the surface sizing agent hardly occurs and handling is easy. In many cases, anionic starch is used. In this case, the incorporation of a cationic dye may result in the formation of aggregates with anionic starch. Therefore, in this case, it is more preferable to use an anionic direct dye as the dye.

The following can be illustrated as a specific dye.
(Basic dye)
M1: purple basic dye Hodogaya Chemical Industry Co., Ltd. product name: methyl violet G1: green basic dye Nippon Kayaku Co., Ltd. product name: Kayafect green Y1: yellow basic dye Japanization Medicine (trade name): Brand name: Yellow SP

(Anionic direct dye)
M2: purple direct dye, manufactured by Nippon Kayaku Co., Ltd., trade name: violet BC
G2: Green direct dye Nippon Kayaku Co., Ltd. product name: Green G
Y2: yellow direct dye, manufactured by Nippon Kayaku Co., Ltd., trade name: Kayafect Yellow KHC
・ B2: Blue direct dye Nippon Kayaku Co., Ltd., trade name: Kayafect Blue F
R2: Red Direct Dye Nippon Kayaku Co., Ltd., trade name: Kayafect Red P

(Cationic direct dye)
Y3: yellow direct dye Nippon Kayaku Co., Ltd., trade name: yellow CG

  In the said newsprint, if it is an aqueous dye which is hydrophilic and can be dissolved in water, the lightness is 85 or more and 95 or less, a value is -0.7 or more and -0.5 or less, which is the color tone of the present invention. In order to adjust the b value to 0.2 or more and 1.8 or less, any other than the above may be used in combination. For example, acid dyes, direct dyes, basic dyes, etc. are used along the color index. Be

  As a basic dye to be particularly preferably used, for example, two or more kinds of methyl violet, bassazole green, crystal violet, methylene blue, chrysoizone, victoria green, rhodamine and the like are added.

<Calendar>
Paper manufactured can be passed through a calender as needed, subjected to pressure and smoothing treatment, and finished into newsprint. As a calendering device, use a soft calender with a combination of a metal roll and a resin roll rather than a machine calender with a combination of a normal metal roll and a metal roll, and smooth the paper layer without strongly pressing it. It is more preferable because the strength of the paper layer can be sufficiently suppressed.

  In the use of the soft calender, by passing the paper so that the back side corresponding to the rough side of the newsprint paper comes first in contact with the metal roll surface of the soft calender, the flatness and the bulkiness can be further improved. In high speed papermaking at 1000 m / min or more, it is possible to obtain news paper having high flatness and less front and back difference.

<Ash content>
The lower limit of the ash content in the newsprint paper is preferably 7% by mass, and more preferably 10% by mass. By setting the ash content to the above lower limit or more, whiteness and opacity can be enhanced, and good color reproducibility can be exhibited. On the other hand, the upper limit of the ash content is preferably 20% by mass, and more preferably 17% by mass. By setting the ash content to the upper limit or less, it is possible to suppress the decrease in paper strength and to improve the printability, the hand-feeling in a newspaper reader, and the like. The ash content can be measured by the ash content measurement method defined in JIS P-8251 (2003).

<Whiteness>
The lower limit of the whiteness of the newsprint is 70%, preferably 74%, more preferably 76%. By setting the whiteness to the above lower limit or more, it becomes a newsprint paper having high whiteness and excellent color reproducibility with high saturation. On the other hand, the upper limit of this whiteness is 80%. In addition, whiteness is the value measured based on "the Hunter whiteness test method of paper and pulp" of JISP8123. The whiteness can be adjusted by the type and amount of pulp, fillers and colorants.

<White Paper Opacity>
As a minimum of the white paper opacity (opacity) of the said newsprint paper, 90% is preferable and 92% is more preferable. On the other hand, the upper limit of the white paper opacity is preferably 95%, more preferably 94%. By setting the white paper opacity to the above-mentioned range, it is possible to further enhance the effect that the color reproducibility of high saturation is excellent while suppressing the occurrence of the strike-through at the time of printing. The white paper opacity is a value measured in accordance with the “paper opacity test method” described in JIS P8138. The white paper opacity can be adjusted by the type and amount of filler, color tone and the like.

<Color tone>
Methods of measuring and displaying color tone of paper etc. include methods defined in JIS Z-8722 and JIS Z-8730. In this method, the color tone is represented by L * (Elster), a * (Aester) and b * (Beaster). L * represents the lightness, and the larger the value, the higher the lightness. The a * (a value) indicates reddishness, and the larger the numerical value, the stronger the reddishness, and the negative value indicates that the greenishness becomes stronger. The b * (b value) indicates yellowishness, the larger the value, the stronger the yellowishness, and the negative the bluishness. In general, the color tone is represented by the position of the graph in which a * is taken on the horizontal axis and b * is taken on the vertical axis. When both a * and b * are 0, the color is expressed as colorless, in which case the L * value represents the degree of whiteness (blackness). In general, the color tone of the paper to which the filler is added is slightly yellowish at a * of about −2 to +1 and b * of about +5 to +8.

  In the newspaper, the lightness (L *) is 85 or more and 95 or less. Moreover, a value (a *) is -0.7 or more and -0.5 or less, and b value (b *) is 0.2 or more and 1.8 or less. When it is in this range, it is possible to adjust the color reproducibility of high saturation without making a large change in color tone, that is, making it feel white. When the value of a is larger than -0.5, paper becomes reddish, and when smaller than -0.7, greenishness becomes too strong. When the b value is greater than 1.8, the yellowish color is too strong, and when it is smaller than 0.2, the bluish color is too strong. It can be adjusted by the type, amount, etc. By adjusting to the above-mentioned color tone, the color tone change of high speed offset rotary printing using offset printing ink consisting of 4 processes of yellow, red, amber and black is suppressed even in the exposure outdoors, and good color reproducibility Can be maintained. The lower limit of the a value is preferably −0.65, and the upper limit is preferably −0.55. The lower limit of the b value is preferably 0.6, more preferably 1.0, and still more preferably 1.2. On the other hand, 1.6 is preferable and, as for this upper limit, 1.3 is more preferable.

<Drip water absorption>
The lower limit of the dripping water absorption degree in the newsprint paper is preferably 15 seconds, more preferably 20 seconds. The upper limit is preferably 40 seconds, more preferably 35 seconds, still more preferably 30 seconds, and even more preferably 25 seconds. Color reproducibility can be improved by setting the dripping water absorption of the newspaper to the above range. In addition, drip water absorption degree is Japan TAPPI No. A value measured with 1 μl of dropping water according to the method described in 33 (Test method for water absorption rate of absorbent paper). The water absorption degree of the drip can be adjusted by the kind and amount of pulp, filler, sizing agent, other surface treatment agent and internal additive to be used.

<Basic weight>
The lower limit of the basis weight of the newsprint is ^{45g / m 2, 50g / m} 2 is preferred. By setting the basis weight to the above lower limit or the like, it is possible to ensure sufficient opacity, secure paper strength and the like in high speed rotary printing, and the like. On the other hand, the upper limit of the basis weight is ^{60g / m 2, 55g / m} 2 is preferred. Weight reduction, resource saving, etc. can be achieved by setting the basis weight to the above upper limit or less. In addition, a basis weight says the value measured based on "the basis weight measurement method" of JISP8124.

<Density>
As a lower limit of the density of the said newsprint paper, 0.70 g / cm ³ is preferable, and 0.72 g / cm ³ is more preferable. On the other hand, the upper limit of this density is preferably ^{0.80g / cm 3, 0.78g / cm} 3 is more preferable. By setting the density to the above-mentioned range, it is possible to obtain newsprint which can be maintained in weight and weight as well as strength can be maintained. In addition, a density says the value measured based on "the test method of paper and paper board-thickness and density" of JISP8118.

<Stiffness (stiffness, hand-feeling)>
The lower limit of the rigidity of the MD direction of the newsprint, preferably ^{30cm 3/100, 32cm 3/} 100 are more preferred. On the other hand, the upper limit of the stiffness is preferably 55cm ^3/100, more preferably 50 cm ^3/100. By setting the stiffness in the above range, for example, a waist suitable for high-speed rotary printing can be provided. In addition, a rigidity means the value measured based on the "stiffness test method by the paper Clark stiffness tester" of JISP8143.

<Cobb size and oil absorption>
In transfer of dampening water and printing ink in newsprint paper having a basis weight of 45 g / m ² or more and 60 g / m ² or less according to JIS P8124, the present inventors 10 seconds based on JIS P8140 of the newsprint paper. It has been found that it is preferable to have a relationship in which the Cobb size degree is 30 g / m ^{2 to} 80 g / m ² and the oil absorption degree based on JIS P3001 is 50 seconds to 150 seconds. By suppressing the relationship between the so-called hydrophilicity and the lipophilicity within a predetermined range, it becomes possible to further improve the offset rotary printing appropriateness together with the flattening processing.

<RI evaluation>
The surface strength of the newsprint is preferably at least 3 in the minimum grade as measured by an RI tester (manufactured by Akira Mfg. Co., Ltd.). In such a case, the paper quality strength in high speed rotary printing of the newspaper is increased.

  The newsprint has high saturation color reproducibility and high opacity when printed using an offset printing ink consisting of four yellow, red, amber and black processes. In addition, the printing paper has good whiteness. Furthermore, the said newsprint paper is less likely to be wrinkled during printing, ink absorption unevenness, paper powder accumulation on a blanket and strike through, and is excellent in ink drying property. The newsprint is excellent in various characteristics at the time of printing, particularly at the time of color printing, and can be suitably used, for example, for high-speed rotary offset color printing such as about 12 to 170,000 copies / hour.

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.
Various measurements and evaluations were performed by the following methods.

(A) Proportion of Each Pulp in Pulp Measured according to “Fiber composition test method” described in JIS P8120.

(B) Freeness (CSF) (Freeness after disintegration)
A sample of newsprint paper cut into a size of 10 cm × 10 cm is prepared, and this sample is immersed in water at a water temperature of 20 ° C. for 3 minutes, disintegrated according to JIS P 8220 (1998), and JIS P 8121 (1995) Canadian standard freeness (CSF) was measured according to the freeness test method ".

(C) Basis Weight Measured in accordance with “Method for measuring basis weight” described in JIS P8124.

(D) Ash content It measured based on "a paper, a paperboard, and a pulp-ash content test method" of JISP8251.

(E) Whiteness Measured in accordance with “Test method for Hunter whiteness of paper and pulp” described in JIS P8123.

(F) Color tone A lightness (L *), a hue (a *, a value) and a hue (b *, b value) in accordance with JIS Z8722, a colorimetric color difference meter (ZE2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.) It measured using.

(G) White Paper Opacity Measured in accordance with the “paper opacity test method” described in JIS P8138.

(H) Stiffness (MD direction)
It measured based on "the stiffness test method by the Clark stiffness tester of paper" as described in JISP8143.

(I) Cobb water absorption (size)
It was measured in 10 seconds according to "paper and paper board-water absorption test method-cobb method" described in JIS P8140.

(J) Drip water absorption Japan TAPPI No. It measured by dripping water amount 1microliter based on 33 (water absorption rate test method of absorptive paper).

(K) Oil absorption degree It measured by the light oil No. 1 based on the "oil absorption degree test method" as described in JISP3001 (1976).

(L) Bleeding The surface of the newsprint paper was printed five times repeatedly using a RI printing aptitude testing machine (manufactured by Akira Seisakusho Co., Ltd.) with the rubber roll to which the test ink was not applied. The surface of the paper web was visually observed in the range of 100 mm × 100 mm using a loupe and evaluated based on the following evaluation criteria.
(Evaluation criteria)
◎: There is very little standing.
○: There is not much standing.
:: There are a lot of cramps.
X: There are very many people standing up.

(M) Ink absorption unevenness Using an offset color printing machine (model number: SYSTEM C-20, manufactured by Komori Corporation), at a printing speed of 160,000 copies / hour, four colors in the order of yellow, red, yellow and black I did color printing. The ink density unevenness of the dark blue / red heavy color portion was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
◎: No unevenness in ink density observed, uniform and clear image, very high in saturation.
Good: Almost no unevenness of ink density observed, uniform image, high saturation.
Fair: Uneven ink density observed, slightly non-uniform image, slightly poor in saturation.
×: Uneven ink density is apparent, the image is nonuniform, and the saturation is bad.

(N) Paper Powder Deposition on Blanket Using the same offset color printing machine as the above evaluation of ink absorption unevenness, four-color color printing was performed in the order of 藍, red, yellow, and black at the same printing speed. After printing 10000 parts, the degree of accumulation of paper dust on the blanket non-image area was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
◎: No generation of paper dust observed.
○: Slight generation of paper dust is recognized, but there is no problem in practical use.
Fair: generation of paper dust is clearly recognized.
X: A large amount of paper dust is deposited on the blanket, and the blanket is white.

(O) Ink drying property Using the same offset color printing machine as the above evaluation of ink absorption unevenness, at the same printing speed, ink for newspaper printing with 45% vegetable oil content is selected in the order of red, yellow, yellow 4 Color Color printing was done. After overlapping 500 parts of the printed matter so that the printed surface and the white sheet overlap, after leaving it for 1 day under a load of 5 kgf (about 49 N), the degree of dirt on the white sheet was visually observed, and based on the following evaluation criteria It evaluated.
(Evaluation criteria)
◎: Almost no stains observed, and the saturation is very high.
○: Only a few stains were observed, and the saturation was high.
Δ: Staining is observed, and the saturation is a little low.
X: Staining is remarkable and saturation is bad.

(P) Color Reproduction The yellow, red, amber, and black four-color multicolor printing of the offset ink is performed using RI-I type printing machine (manufactured by Akira MFG. Co., Ltd.), and the printed surface is visually observed Evaluation was performed as follows. ○ I passed the above.
◎: There is no influence of the color tone of the paper, and it has excellent color reproducibility with very high saturation.
Good: Although the influence of paper is observed, the color saturation is high and the color reproducibility is good.
Δ: The influence of the color tone of the paper is observed, and the color reproducibility is somewhat poor.
X: The influence of the color tone of paper is seen and the color reproducibility is very bad.

(Q) Strikethrough A black-and-white single color printing was performed at a printing speed of 900 rpm using an offset rotary press (Toshiba offset rotary press, manufactured by Toshiba Corporation). After printing 60,000 parts, the black solid surface was visually observed from the back surface, and evaluated based on the following evaluation criteria.
(Evaluation criteria)
◎: Almost no strike-through is observed.
○: A few strikethroughs are recognized.
Fair: strike-through is observed.
X: Strikethrough is remarkable.

Example 1
Hardwood bleached kraft pulp (NBKP) 24% by mass, Hardwood bleached kraft pulp (LBKP) 18% by mass, disintegrated / deinked used paper pulp (DIP) 28% by mass as waste paper pulp, Chemo-mechanical mechanical pulp (CTMP as mechanical pulp) 30% by mass was added to obtain a pulp slurry whose freeness was adjusted by a refiner. Further, as a dye, a purple basic dye, Hodogaya Chemical Industry Co., Ltd., trade name: methyl violet 0.01 kg / t, a blue direct dye, Nippon Kayaku Co., Ltd., trade name: Kayafect Blue 0.2 kg / t of F, Nippon Kayaku Co., Ltd., which is a red direct dye, manufactured by Nippon Kayaku Co., Ltd., trade name: Kayafectred P 0.50 kg / t was incorporated. To this pulp slurry, calcium carbonate having a volume average particle diameter of 1.5 μm was added as calcium carbonate so that the ash content was 8%, and the pH of papermaking was adjusted to 7.5 with a sulfate band. Using this pulp slurry, a base paper for newsprint was formed by a twin wire paper machine.

Next, a starch solution obtained by mixing 50 parts by mass of oxidized starch (mass-average molecular weight 700,000 manufactured by Japan Food Processing Co., Ltd.) and 50 parts by mass of hydroxyethylated starch (HES, mass-average molecular weight 1,550,000 manufactured by Penford) as a surface treatment agent In addition, 20 parts by mass of a styrene-based sizing agent (SS2712, manufactured by Starlight PMC Co., Ltd.) was blended in solid content with respect to 100 parts by mass of starch. The surface treatment agent was applied on both sides of the base paper having a surface temperature of 50 ° C. at a dry weight of 0.6 g / m ² per one side. The newsprint paper of Example 1 was thus obtained.

[Examples 2 to 13, Comparative Examples 1 to 13]
The type and blending ratio of the pulp, and the type and particle size of the filler are as described in Table 1, and adjusted to be the basis weight and ash content described in Table 2, and Examples 2 to 13 and Comparative Examples 1 to 13 I got each newspaper paper. Ash adjustment was adjusted with the amount of filler. Further, in order to adjust the color tone, the type and amount of the dye were appropriately changed. In addition, when the ratio of each pulp was measured by the said method about the mixed pulp used, it was the same as the compounding ratio of Table 1.

[Evaluation]
Freeness, basis weight, ash, whiteness, color tone (L *, a *, b *), white paper opacity, stiffness, cobb water absorption, drip water absorption of each newsprint paper obtained by the method described above And oil absorption was measured. The results are shown in Table 2.

  Further, with respect to each of the newsprint papers obtained by the above-described method, evaluations were made regarding fluffing, ink absorption unevenness, paper powder deposition on a blanket, ink drying property, color reproducibility and strikethrough. The evaluation results are shown in Table 3.

  As shown in Tables 1 to 3, in particular, in Table 3, each newsprint of Examples 1 to 13 has high evaluation of color reproducibility, and an offset printing ink consisting of yellow, red, amber, and black process four colors It can be seen that it has high saturation color reproducibility when printed using. In addition, each of the newsprint papers of Examples 1 to 13 has high opacity and sufficient whiteness. Furthermore, it can be seen that each of the newsprint papers of Examples 1 to 13 has little paper dust accumulation on the blanket and can sufficiently withstand high-speed printing by a rotary press. Further, each of the newsprint papers of Examples 1 to 13 has less ink absorption unevenness and is excellent in ink drying property. In addition, it can be seen that each of the newsprint papers of Examples 1 to 13 has less fuzz and less penetration. That is, it is understood that each of the newsprint papers of Examples 1 to 13 has excellent printability.

  The newsprint paper of the present invention is suitably used as newsprint paper having high chroma color reproducibility and high opacity when printed using offset printing ink consisting of four processes of yellow, red, amber and black. be able to.

Claims (3)

Newspaper paper with filler internally added to pulp,
Whiteness is 70% or more and 80% or less,
It has a lightness of 85 to 95, an a value of −0.7 to −0.5, and a b value of 0.2 to 1.8,
Newsprint characterized by having a basis weight of 45 g / m ^{2 to} 60 g / m ² . The softwood bleached kraft pulp content in the pulp is 16% by mass to 24% by mass, the hardwood bleached kraft pulp content is 18% by mass to 26% by mass, and the recycled paper pulp content is 24% by mass to 32% % Or less, the mechanical pulp content is 26% by mass or more and 34% by mass or less,
The newsprint paper according to claim 1, containing calcium carbonate having a volume average particle diameter of 1.0 μm or more and 2.0 μm or less as the filler. The mechanical pulp is chemithermo mechanical pulp,
The ash content is 7% by mass or more and 20% by mass or less,
The newsprint according to claim 1 or 2, wherein the dripping water absorption is 15 seconds or more and 40 seconds or less.