JP2007100226A - Newsprint paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain newsprint paper that is lightweight, has high water resistance, controls wetting and extension of paper even against dampening water of high frequency, has surface strength, no blanket stain by edge dust, excellent various properties in color printing, for example, is favorably used in highly fine printing in offset printing such as high-speed offset printing, etc. <P>SOLUTION: The newsprint paper is obtained by coating both sides of base paper with a coated layer by a coating agent composed of pigment and an adhesive as main components, has 35-50 g/cm<SP>2</SP>basis weight based on JIS P 8124 and is mixed with composite pigment mainly containing Si, Al and Ca as the pigment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to newsprint. More specifically, it is lightweight, has high water resistance, suppresses paper wetting and stretching even with frequent fountain solutions, has high surface strength, is free from blanket stains due to paper dust, and is clogged with a sword. Newspaper paper that is excellent in ink absorption, color reproducibility, print surface clarity, etc. without color misalignment, and can be used suitably for offset printing such as high-speed offset color printing, especially high-definition printing in high-speed offset full-color printing About.

  In recent years, offset printing has been frequently used as a newspaper printing method, and in such offset printing, satellite type or tower press type offset color printing machines have become widespread.

  The demand for better printing workability and printability in the offset printing is also increasing for newsprint as a printing medium. Furthermore, since such dampening paper uses dampening water in offset printing, water resistance of the paper surface is also required.

  Here, offset color printing, for example, four-color printing of indigo, red, yellow, and black, is performed four times on the same paper surface. The problem of poor inking property such as insufficient printing density is likely to occur. In other words, the problem of poor inking property is a problem of ink inking property when the newspaper is wet, and is particularly remarkable in the case of the satellite type offset color printing machine.

  It is considered that the cause of the poor ink depositability as described above is that the newspaper paper absorbs dampening water, the fibers swell, and the paper surface becomes wet. Furthermore, the wetness of the paper surface reduces the surface strength and causes blanket contamination due to paper dust. Therefore, for example, a surface treatment agent mainly composed of starch and a copolymer (surface sizing agent) composed of a monomer containing at least (meth) acrylic acid ester and an ethylenically unsaturated carboxylic acid is applied to newsprint base paper. In addition, a newsprint for offset printing has been proposed in which penetrating water during offset printing is transferred to paper and the permeability is reduced within 1 second (see Patent Document 1).

  However, when a surface treatment agent containing starch and a surface sizing agent is applied (externally added) as in the newspaper for offset printing, the effect of the surface sizing agent is obtained, although there is an effect of suppressing the generation of paper dust. However, the water resistance against dampening water at the time of offset printing is not sufficiently improved, and the problem that such dampening water easily permeates newspaper is not solved.

  On the other hand, as newsprint, base papers mainly made of mechanical pulp and waste paper pulp are used, but recently there has been a demand for paper weight reduction (low basis weight). Opacity after printing on the paper is also required.

  Therefore, for example, a coating layer mainly composed of a recycled pigment obtained by carbonizing a mixture of an organic substance and white inorganic particles and further whitened is provided on the surface of the base paper, and the opaqueness of the paper after printing is provided. An improved coated paper for printing has been proposed (see Patent Document 2).

However, the coated paper for printing certainly has good opacity after printing and is excellent in print back-through. However, particularly when applied to the satellite-type offset color printing machine, the coated paper for printing is used at the time of offset printing. There is a tendency that the regenerated pigment tends to be leached out of the coating layer due to frequent fountain solution, and there is a problem that water resistance to the fountain solution during offset printing is insufficient.
JP 2003-253598 A JP 2003-119695 A

  The present invention has been made in view of the background art described above, and is lightweight, highly water-resistant, prevents paper from being wet and stretched even with frequent fountains, has high surface strength, It is an object of the present invention to provide a newsprint that is free from blanket stains and has excellent various characteristics during color printing, and can be suitably used for high-definition printing in offset printing such as high-speed offset color printing.

That is, the present invention is a newsprint in which a coating layer is formed on both sides of a base paper with a coating agent mainly composed of a pigment and an adhesive, and has a basis weight of 35 to 50 g / gram according to JIS P 8124. m ^2, and as the pigment, Si, about newsprint mainly including composite pigment of Al and Ca is characterized in that it is formulated.

  The newsprint of the present invention is lightweight, has high water resistance, suppresses paper wetting and stretching against frequent fountains, has high surface strength, and is free from blanket stains caused by paper dust. There is no clogging of the sword or color misalignment, and it has excellent ink absorption, color reproducibility, sharpness of the printed surface, etc. To get.

(First embodiment)
As described above, the newsprint of the present invention has a coating layer formed on both sides of a base paper by a coating agent mainly composed of a pigment and an adhesive, and is based on JIS P 8124. The amount is 35 to 50 g / m ² , and as such a pigment, a composite pigment mainly containing Si, Al and Ca is blended.

  First, the base paper used in this embodiment will be described. There are no particular limitations on the type of raw material pulp that constitutes the base paper, and pulp used in ordinary newsprint can be used as appropriate.

  Examples of the raw material pulp include stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo ground pulp (TGP), ground wood pulp (GP), and thermo. Mechanical pulp (TMP), Chemi-thermo mechanical pulp (CTMP), refiner mechanical pulp (RMP) and other mechanical pulp; Deinking pulp (DIP), waste pulp such as West pulp (WP); conifer kraft pulp (NBKP), hardwood Chemical pulps such as kraft pulp (LBKP), pulps bleached from these, and the like can be mentioned, and one or more of them can be selected and used.

  In this embodiment, from the viewpoint of ensuring the opacity required for newsprint, ink absorption and drying properties according to information recording means such as offset ink, hand feeling and readability when reading newsprint, The proportion of mechanical pulp is preferably 60% by mass or less, more preferably 58% by mass or less, and 15% by mass or more, as measured in accordance with “Fiber composition test method” described in JIS P 8120. Preferably there is.

  Furthermore, in view of the transportability of paper in recent high-speed rotary printing and the paper quality strength in handling, and the dimensional stability in multicolor printing, the ratio of chemical pulp in raw pulp is described in “Fiber composition” described in JIS P 8120. It is preferably 10 to 65% by mass, more preferably 12 to 63% by mass, measured according to “Test method”.

  The method for producing the base paper used in the present embodiment is not particularly limited. For example, the raw pulp is filled with fillers such as kaolin, calcium carbonate, talc, titanium dioxide, and urea formaldehyde resin; sizing agent such as rosin emulsion; starch and modified starch. Paper strength agents such as plant gum, carboxymethyl cellulose, polyacrylamide; yield improver; freeness improver; and paper making agents such as UV inhibitors, etc., and then adjusting conditions such as pH value as appropriate, for example, It is possible to adopt a paper making method in a normal paper making process using a twin wire type paper machine.

  Next, a coating agent for forming a coating layer on both sides of the base paper will be described. The coating agent used in the present embodiment is mainly composed of a pigment and an adhesive.

  In the present embodiment, a composite pigment mainly containing Si, Al, and Ca is blended as the pigment. One of the major features is that such a specific composite pigment is used. This makes it particularly high in water resistance and suppresses the wetting and stretching of the paper even with frequent fountain solutions. Newspaper having excellent characteristics during printing such as color printing can be obtained.

  The composite pigment used in the present embodiment can be produced by appropriately adjusting the incinerated ash obtained by incinerating a known papermaking sludge. For example, the composite pigment can be suitably used by the method described in JP-A-2002-275785. It is possible to manufacture.

  The composite pigment only needs to mainly contain Si, Al, and Ca (form secondary aggregates), and the total inclusion amount of these Si, Al, and Ca is X-rays on the surface of the coating layer. In elemental analysis with a microanalyzer, it is usually preferably about 90% or more. In addition, composite pigments (regenerated pigments) composed of secondary aggregates of these pigments having Si, Al, and Ca include Al, Si, and Ca in terms of oxides in the surface analysis of the coating layer surface by an X-ray microanalyzer. However, it is preferable that it is the structure of the inclusion ratio of 8-40: 10-40: 20-82 (mass ratio) by elemental analysis, and in order to obtain the porosity of a pigment, the sum total of Si and highly cationic Al Raw material for papermaking sludge in a composition of 8 to 30:10 to 30:40 to 82 (mass ratio) of Al, Si and Ca in terms of oxide so that the ratio is larger than the ratio of Ca It is more preferable to adjust the configuration.

  The average particle diameter of the composite pigment measured by the laser method is 1 μm or more, and further 1.1 μm or more in terms of yield in a bulky paper layer and countermeasures against paper dust problems in printing such as high-speed offset printing. In view of obtaining a fine print surface, quick ink absorption / drying property, and ink fixing property on the paper surface, it is preferably 6 μm or less, more preferably 5.9 μm or less.

  In addition, the X-ray microscopic properties of the surface of the coating layer are improved in terms of water resistance, suppression of wetting and stretching of the paper against dampening water, surface strength, suppression of color misregistration, and ink absorbency. In elemental analysis by an analyzer, the area where the composite pigment is present is preferably 30% or more, more preferably 32% or more in terms of area ratio. Further, considering that such a composite pigment is a flexible secondary aggregate and excessive blending causes generation of paper dust in high-speed rotary printing and a decrease in paper quality strength, the area where the composite pigment exists is 90% in area ratio. It is preferable that it is below a grade. In addition, as will be described later, the composite pigment is present in a region having a constant area of 12,000 times, photographing 10 different portions of the sample, and performing elemental analysis in each region with an X-ray microanalyzer. The part detected by overlapping Si, Al and Ca is selected as a composite pigment, and the area ratio of the part detected by overlapping Si, Al and Ca is calculated by an image analyzer. .

  The pigment in the present embodiment is not particularly limited as long as the specific composite pigment is blended. For example, from the point that the characteristics of newsprint at the time of printing such as offset color printing are further improved, together with such a composite pigment. It is preferable that a high aspect pigment having an aspect ratio of 20 or more is blended.

  Examples of the high aspect pigment include high aspect clays such as kaolin clay and delaminated clay, and other examples include clays having an aspect ratio of about 50, and an aspect ratio of up to 100 at the laboratory level. Calcium carbonate has been developed. Such a pigment having an aspect ratio close to 100 has a problem that a pigment having a large particle diameter cannot be produced and is expensive, so that a pigment having an aspect ratio of about 50 may be exemplified. it can. The aspect ratio of such a high aspect pigment is not only able to obtain a high-definition printed surface by improving the flatness of the newspaper surface during printing such as offset color printing, but also in parallel to the printed surface. In view of further improving the opacity, it is preferably 20 or more, more preferably 21 or more. In consideration of the price and the quality obtained, the aspect ratio of the high aspect pigment is preferably 30 or less.

  When high-aspect pigments are used in combination with the above composite pigments, the properties of newsprint such as water resistance, suppression of paper wetting and stretching against dampening water, surface strength, suppression of color misregistration, and ink absorption are further improved. Therefore, in the elemental analysis by the X-ray microanalyzer on the surface of the coating layer, the total existence region of the composite pigment and the high aspect pigment is preferably 45% or more, more preferably 48% or more in terms of area ratio. In consideration of the surface strength of the paper surface in printing such as high-speed offset printing and the suppression of paper dust generation, the total area of the composite pigment and the high aspect pigment is preferably about 90% or less in area ratio. . The total area of the composite pigment and the high-aspect pigment is the same as the area where the composite pigment is present. The area of the constant area is 12000 times and 10 different parts of the sample are photographed, and an X-ray microanalyzer is used. Perform elemental analysis in each region, measure the area (A) where Si, Al, and Ca are detected by overlapping with an image analyzer, and count the number of high-aspect pigments as viewed with an X-ray microanalyzer. The area (B) calculated by multiplying the average area of 10 is measured, and the total area ratio is calculated from the area (A) and the area (B).

  Further, as the pigment, in addition to the composite pigment and the high aspect pigment, for example, light calcium carbonate, heavy calcium carbonate, talc, clay, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white , Aluminum silicate, Diatomaceous earth, Calcium silicate, Magnesium silicate, Synthetic amorphous silica (white carbon), Colloidal silica, Colloidal alumina, Pseudoboehmite, Aluminum hydroxide, Alumina, Lithopone, Zeolite, Hydrous halloysite, Magnesium carbonate Inorganic pigments such as magnesium hydroxide, porous synthetic amorphous silica, porous magnesium carbonate, porous alumina; styrene plastic pigments, acrylic plastic pigments, polyethylene, microcapsules, urea resin Such organic pigments such as melamine resins, among pigments which are commonly incorporated into coating agents can be selected and used one or more suitably.

  In addition, when using pigments other than the said composite pigment, it is preferable that the average particle diameter measured by the laser method is about 2-15 micrometers, for example. Moreover, as the whole pigment mix | blended with a coating agent, it is preferable that the average particle diameter measured by the laser method is about 0.1-10 micrometers, for example, and the particle size distribution (volume basis) of 15 micrometers or less is 55-55. It is preferably about 70%.

  There are no particular limitations on the adhesive compounded in the coating agent together with the pigment. For example, starches such as oxidized starch, modified starch, esterified starch, and dextrin; synthetic resin adhesives such as polyvinyl alcohol; casein, soy protein, Water-soluble adhesives such as proteins such as synthetic proteins, conjugated diene copolymer latex such as styrene-butadiene copolymer; acrylic copolymer latex such as acrylate polymer or copolymer; ethylene -Vinyl-based polymer latex such as vinyl acetate polymer; Latex such as alkali-soluble, alkali-swellable or alkali-insoluble polymer latex obtained by modifying these various polymer latexes with a functional group-containing monomer such as a carboxyl group One type or two or more types can be appropriately selected and used from among the classes.

  The blending ratio of the pigment and the adhesive in the coating agent is such that, for example, the effect of improving the characteristics of the newsprint at the time of printing such as offset color printing can be expressed sufficiently with respect to 100 parts by mass of the pigment. It is preferable to adjust so that an agent may be 25 mass parts or less, Furthermore, 23 mass parts or less. Further, in order to prevent the amount of the adhesive from being too small and insufficient adhesion of the coating agent to the base paper, the adhesive is 10 parts by mass or more, further 12 parts by mass or more with respect to 100 parts by mass of the pigment. It is preferable to adjust so that.

  The coating agent is mainly composed of a pigment and an adhesive, and the total amount of these pigment and adhesive in the coating agent is usually preferably about 90% by mass or more.

  In this embodiment, in addition to the pigment and the adhesive, the coating agent includes various auxiliary agents that are usually used in the papermaking field, such as a surface sizing agent, an antifoaming agent, and a thickener. It can mix | blend suitably in the range which does not inhibit the objective.

  There is no particular limitation on the method for preparing the coating agent, and the mixing ratio of pigments and adhesives, and various auxiliary agents as necessary is adjusted as appropriate, and the mixture is stirred and mixed so that the composition is uniform at an appropriate temperature. do it.

  The coating agent is applied to both sides of the base paper to form a coating layer. There is no particular limitation on the coating apparatus used for coating, for example, a two roll size press, a blade metalling size press, a rod metalling size press, a gate roll coater, a blade coater bar coater, a rod blade coater, an air knife coater, etc. It can be used as appropriate. Among these, a gate roll coater can be particularly preferably used. When forming the coating layer, it is preferable to adopt a film transfer method so that the fibers of the raw material pulp constituting the base paper are not exposed as much as possible. By adopting, there is an advantage that it is possible to achieve printing surface coating with a uniform coating layer over a wide range without being affected by the protrusion of the paper surface.

When the coating amount of the coating agent is too small, there is a possibility that sufficient surface strength may not be imparted to the coating layer. Therefore, 0.3 g / m ² or more per side, and further 0.5 g / m. ^Two or more are preferable. Also, if the amount of dry coating is too large, the Nepari property becomes high and there is a risk of problems such as sticking to a blanket, paper breakage, etc., so 10 g / m ² or less per side, and even 9 g / m. It is preferable to set it to ² or less.

  Further, the coating speed at which the coating agent is applied to the base paper is not particularly limited as long as a desired coating layer is formed on both sides of the base paper, and may be about the paper making speed when manufacturing ordinary newsprint paper.

  In this embodiment, the coating agent is applied to both surfaces of the base paper using, for example, the coating apparatus, and then dried, for example, the coating layer is formed so as to have the dry coating amount. The surface can be flattened to finish the product.

  In the flattening process, a calendar is usually used. However, a soft calender having a large flattening effect can be suitably used without increasing the pressure condition. Such flattening treatment improves the surface smoothness Rp value of the coating layer (Parker print surf roughness (air leakage method)) from the point that the characteristics of the resulting newsprint during printing such as offset color printing are further improved. ) Under a printing pressure of 1.96 MPa is preferably 8.2 μm or less, more preferably 8 μm or less. In consideration of the instantaneous contact between the plate cylinder and the surface of the printing paper in high-speed rotary printing (the printing pressure applied to the paper is instantaneous), the surface smoothness Rp value of the coating layer is under a printing pressure of 1.96 MPa. It is preferable that it is 3.8 μm or more.

The basis weight of the newsprint thus obtained is in accordance with the “basis weight measurement method” described in JIS P 8124 in terms of weight reduction in delivery and transportation, securing of paper quality strength in high-speed rotary printing, and securing of printing opacity. Measured to be 35 g / m ² or more, preferably 38 g / m ² or more. Moreover, from the point of the weight reduction, this basic weight is 50 g / m < ² > or less, Preferably it is 48 g / m < ² > or less.

  Further, the ash content of the newsprint is not particularly limited, but it is preferably about 2 to 25% in accordance with, for example, the “ash content test method” described in JIS P 8251.

  As described above, the newsprint according to this embodiment has a specific basis weight, and a specific composite pigment mainly including Si, Al, and Ca is included in the coating layer formed on both surfaces of the base paper. Therefore, it is lightweight, highly water-resistant, prevents paper from wetting and stretching even with frequent fountain solutions, has high surface strength, and is free from blanket stains caused by paper dust. It is also excellent in various characteristics at the time, and can be suitably used for high-speed offset color printing such as about 1 to 170,000 copies / hour.

  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.

Production Examples 1 to 20 (Preparation of base paper)
Compounding mechanical pulp (bleached pressed stone ground pulp (BPGW)), chemical pulp (conifer kraft pulp (NBKP), hardwood kraft pulp (LBKP)) and other pulp (newspaper pulp) at the ratio shown in Table 1, A pulp slurry was prepared. To this pulp slurry, 10 parts by weight of kaolin and 10 parts by weight of rosin emulsion (product name: SPN-773, manufactured by Arakawa Chemical Industries, Ltd.) are added to 100 parts by weight of pulp solids, and a twin wire type paper machine is used. Papermaking was performed to obtain base papers 1 to 20 having a basis weight of 36 to 43 g / m ² .

Preparation Examples 1-10 and Comparative Preparation Examples 1-10 (Preparation of coating agent)
The pigments and adhesives shown in Tables 2 to 4 are stirred and mixed at room temperature until a uniform composition is obtained, diluted with purified water, and the solid content concentration is about 53 to 58%. Coating agents 1 to 10 were prepared. In Table 2, the average particle diameter of the composite pigment, the ratio of Si, Al, Ca and other elements included in the composite pigment (as oxides) are shown in Tables 3 to 4 except for the composite pigment. The aspect ratio and average particle diameter of the pigment are also shown.

Examples 1-10 and Comparative Examples 1-10 (Preparation of Newspaper)
As shown in Table 5, newsprint paper was produced by combining base papers 1-20 and coating agents 1-10 or comparative coating agents 1-10.

Using the coating device shown in Table 5, the coating speed is appropriately adjusted, and the coating agent or comparative coating agent is applied to both sides of the base paper so that the dry coating amount per side is about 4 to 5 g / m ^2. It was applied and dried to form a coating layer. When applying the coating agent, a film transfer method was adopted. This was subjected to a flattening process with a soft calender, and newspaper paper was prepared with the surface smoothness Rp value of the coating layer as shown in Table 5.

  The basis weight and ash content of each newspaper were obtained. These results are also shown in Table 5. Moreover, about the coating layer of each obtained newspaper paper surface, the presence area (area ratio) of a composite pigment and the total presence area (area ratio) of a composite pigment and a high aspect pigment (Preparation Examples 1 to 10), The existence region (area ratio) (Comparative Preparation Examples 1 to 10) was also measured. These results are shown in the said Tables 2-4.

  In addition, the various measured values shown to Tables 1-5 were measured with the following method.

(A) The ratio of each pulp in raw material pulp It measured based on the "fiber composition test method" of JISP8120.

(B) Average particle diameter of composite pigment Measurement was performed by a laser method using a laser diffraction particle size distribution measuring device (model number: Microtrac particle size distribution measuring device, manufactured by Nikkiso Co., Ltd.).

(C) Ratio of Si, Al, Ca and other elements included in the composite pigment (as oxide)
Elemental analysis was performed on the surface of the coating layer with an X-ray microanalyzer (model number: E-MAX, manufactured by Horiba, Ltd.).

(D) Presence area (area ratio) of composite pigment
On the surface of the coating layer, 10 areas of a sample with a constant area of 12000 times were photographed, and elemental analysis was performed in each area using the same X-ray microanalyzer as described above, and an image analysis apparatus (model number: Luzex, ( The part detected by overlapping Si, Al, and Ca in Nireco Co., Ltd. was selected as a composite pigment, and the area ratio of the part detected by overlapping Si, Al, and Ca was calculated using an image analyzer.

(E) Total area of composite pigment and high aspect pigment (area ratio)
On the surface of the coating layer, 10 areas of a sample with a constant area at a magnification of 12000 were photographed, elemental analysis was performed in each area using the same X-ray microanalyzer, and Si was analyzed using the same image analysis apparatus as described above. The area (A) detected by overlapping Al and Ca was measured, and the area calculated by multiplying the number of high aspect pigments visually recognized by an X-ray microanalyzer by the average area of 10 high aspect pigments ( B) was measured, and the total area ratio was calculated from the area (A) and the area (B).

(F) Presence area (area ratio) of pigment used in comparative preparation examples
On the surface of the coating layer, 10 areas of a constant area were photographed at 12000 times and 10 different parts of the sample were photographed, and the average area of 10 pigments in the number of pigments used in the comparative preparation example visually observed with the same X-ray microanalyzer The area calculated by multiplying was measured, and the total area ratio was calculated.

(G) Surface smoothness Rp value of coating layer It was measured under a printing pressure of 1.96 MPa with a smoothness tester (Parker Print Surf, manufactured by Lorentzen & Wettre) due to air leakage.

(H) Basis Weight of Newspaper Paper Measured according to the “basis weight measuring method” described in JIS P 8124.

(I) Ash content of newspaper paper Measured according to “ash content test method” described in JIS P 8251.

  Next, each characteristic was investigated about the newsprint of Examples 1-10 and Comparative Examples 1-10 based on the following test examples 1-5. The results are shown in Table 6.

Test example 1 (ink absorption unevenness)
Using an offset color printer (model number: SYSTEM C-20, manufactured by Komori Corporation), four-color printing was performed in the order of indigo, red, yellow, and black at a printing speed of 160,000 copies / hour. The ink density unevenness of the deep blue / red color portion was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: Ink density unevenness is not recognized at all, and the image is uniform and clear.
○: Ink density unevenness is hardly recognized, and the image is uniform.
Δ: Ink density unevenness is recognized and the image is slightly non-uniform.
X: Ink density unevenness is obvious and the image is non-uniform.

Test Example 2 (Paper dust accumulation on blanket)
Using the same offset color printing machine as in Test Example 1, four-color printing was performed in the order of indigo, red, yellow, and black at the same printing speed. After printing 5000 parts, the degree of paper powder accumulation on the blanket non-image area was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: Generation of paper dust is not recognized.
○: Slight generation of paper dust is observed, but there is no practical problem.
Δ: The occurrence of paper dust is clearly recognized.
X: A lot of paper dust is accumulated on the blanket, and the blanket is white.

Test Example 3 (Color printing suitability)
Using an offset rotary press (for newsprint, manufactured by Tokyo Machine Works, Ltd.), four-color printing was performed in the order of indigo, red, yellow, and black at a printing speed of 150,000 copies / hour. The print surface density and density unevenness of the fourth black single color part and the uniformity of the printed image of the heavy color part where the four colors were superimposed were visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): The printing surface density | concentration of a black monochrome part is very high, and there is no density nonuniformity. In addition, a very uniform image is obtained in the heavy color area.
◯: The printed surface density of the black single color portion is high and there is almost no density unevenness. In addition, a uniform image is obtained in the heavy color area.
(Triangle | delta): The printing surface density | concentration of a black monochrome part is a little low, and a density nonuniformity is recognized. In the heavy-colored area, an image that is uneven and slightly sharp is obtained.
X: The printing surface density of the black monochrome portion is low, and density unevenness is clearly recognized. In the heavy color area, an image that is uneven and lacks clarity is obtained.

Test example 4 (number of blade clogs)
Using a newspaper offset rotary press (model number: DIAMONDSTAR, manufactured by Mitsubishi Heavy Industries, Ltd.), printing was performed at a printing speed of 150,000 copies / hour on both sides. It was measured.

Test Example 5 (Register misalignment)
Using the same newspaper offset rotary press as in Test Example 4, four-color printing was performed in the order of indigo, red, yellow, and black at a printing speed of 120,000 copies per hour. The difference in the width direction of the registration mark position between the first color and the fourth color was measured immediately before the paster (automatic paper splicing) and at the 100th copy after the paster, respectively, and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: The difference between before and after the paster is less than 0.1 mm.
○: The difference between before and after the paster is 0.1 mm or more and less than 0.2 mm.
(Triangle | delta): The difference before and behind a paster is 0.2 mm or more and less than 0.3 mm.
X: The difference before and after the paster is 0.3 mm or more.

From the results shown in Table 6, the newspapers of Examples 1 to 10 are lightweight with a basis weight of 45 / m ² or less, and the coating layers on both sides of the base paper are blended with a specific composite pigment. Because it is formed with a chemical, there is no or little ink absorption unevenness, accumulation of paper dust on the blanket, clogging of the sword tip and misregistration, excellent color printing suitability, and very suitable for high-speed offset color printing. You can see that

  On the other hand, since the newspapers of Comparative Examples 1 to 10 are those in which a coating layer is formed with a coating agent in which a specific composite pigment is not blended, uneven ink absorption, paper dust on the blanket It can be seen that most of the deposits, color printing suitability, sword clogging and misregistration are bad results and do not have characteristics suitable for high-speed offset color printing.

  The newsprint of the present invention can be particularly suitably used for high-speed offset color printing in, for example, a satellite type or tower press type offset color printing machine.

Claims (4)

Newspaper paper in which a coating layer is formed on both sides of a base paper by a coating agent mainly composed of a pigment and an adhesive,
The basis weight according to JIS P 8124 is 35 to 50 g / m ² ,
Newsprint paper, wherein a composite pigment mainly containing Si, Al, and Ca is blended as the pigment.   The newsprint according to claim 1, wherein in the elemental analysis with an X-ray microanalyzer on the surface of the coating layer, the area where the composite pigment is present is 30% or more by area ratio.   The newsprint according to claim 1, wherein a high aspect pigment having an aspect ratio of 20 or more is blended as the pigment together with the composite pigment. The newspaper according to claim 3, wherein the total area of the composite pigment and the high-aspect pigment is 45% or more in area ratio in elemental analysis with an X-ray microanalyzer on the surface of the coating layer.