JP2007100227A - 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 color printing, etc. <P>SOLUTION: The newsprint paper is obtained by coating at least one side of base paper with a coated layer by a coating agent composed of pigment as a main component, has 35-48 g/m<SP>2</SP>basis weight based on JIS P 8124, is mixed aspect pigment having ≥20 aspect ratio as the pigment. The coating layer is formed in 0.3-3 g/m<SP>2</SP>solid content in an amount of the coating agent on one side of base paper. <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. No color misalignment, excellent ink absorbency, halftone dot reproducibility, color reproducibility, sharpness of printing surface, etc. Suitable for offset printing such as high-speed offset color printing, especially high-definition printing especially in high-speed offset full-color printing It relates to newsprint that can be used.

  For many years, multicolor printing of newspapers has been carried out on a cold set type high-speed rotary printing press using ordinary newsprint paper and penetrating dry ink because of the necessity and cost of mass printing. However, such a combination of ordinary newsprint paper and penetrating dry ink has a great disadvantage that the sharpness of the multicolor printing surface is remarkably inferior.

  Therefore, with the development of osmotic drying ink, we focused on newsprint paper, for example, a cold layer in which a coating layer containing a needle-like pigment and a pigment with a specific oil absorption amount was provided on the surface of a base paper mainly composed of mechanical pulp. Newspaper printing paper for set-type printing machines has been proposed (see Patent Document 1).

  The above-mentioned newspaper printing paper certainly exhibits rapid ink setting, surface strength, opacity, foldability, etc., as well as sharpness in multi-color printing by a cold set type high-speed rotary press, as well as sharpness. Was also good. However, offset printing using satellite-type or tower-press-type offset color printing machines, which are increasingly used in recent years, demands for better printing workability and printing suitability for newsprint as a printing medium. It is increasing. Furthermore, since such dampening paper uses dampening water in offset printing, water resistance of the paper surface is also required, and the above-mentioned newspaper printing paper cannot satisfy these requirements.

  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.

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

  Thus, for example, newsprint paper for rotary offset printing in which titanium dioxide and / or a surface treatment agent mainly composed of a hollow organic pigment and an adhesive is applied to a base paper containing hydrated silicic acid as a filler has been proposed (Patent Document 2). reference).

However, when the base paper containing a specific filler and a surface treatment agent containing a highly opaque pigment are combined as in the newspaper for offset rotary printing, the requirement for opacity after printing can be satisfied. However, the effect of improving the water resistance is still inadequate, and sufficient water resistance against the frequent fountain solution at the time of offset printing is not provided, and the problem that such fountain solution easily permeates the newsprint is solved. No.
JP-A-2-169798 JP 2000-136497 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 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, on at least one surface of the base paper, a newsprint coating layer is formed by coating material mainly composed of pigments, basis weight conforming to JIS P 8124 is in 35~48g / m ² Yes, a high aspect ratio pigment having an aspect ratio of 20 or more is blended as the pigment, and a coating layer is formed with a solid content of 0.3 to 3 g / m ² on the one side of the base paper. It is related with the newsprint characterized by having.

  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, halftone dot reproducibility, color reproducibility, and clearness of the print surface. For example, high-definition printing such as high-speed offset color printing, especially high-speed offset full-color printing. Can be suitably used.

(First embodiment)
As described above, the newsprint of the present invention has a coating layer formed on at least one side of a base paper by a coating agent mainly composed of a pigment, and has a basis weight of 35 based on JIS P 8124. a ~48g / m ^2, the coating as a pigment, the aspect ratio is blended is high aspect pigment more than 20, the coating amount of the coating agent to one surface of the base paper, as 0.3 to 3 g / m ² on a solids A construction layer is formed.

  First, the base paper used in this embodiment will be described. For example, kraft pulp is preferably used as the raw material pulp constituting the base paper. By using kraft pulp in this way, the paper quality strength can be further increased while suppressing the extension of the base paper.

  Examples of the kraft pulp include chemical pulp obtained by the kraft method such as softwood kraft pulp (NBKP) and hardwood kraft pulp (LBKP) and pulp bleached from these, and these are used alone or in combination of two or more. Can be used simultaneously.

  In this embodiment, in addition to suppressing the paper quality required for newsprint and stretching, for example, from the viewpoint of dimensional stability in multicolor printing, paper transportability in high-speed rotary printing, the proportion of kraft pulp in raw pulp is: Measured in accordance with “Fiber composition test method” described in JIS P 8120, it is preferably 40% by mass or more, more preferably 42% by mass or more, and 85% by mass or less, further 80% by mass or less. Preferably there is.

  As the raw material pulp constituting the base paper, as long as the purpose of the present embodiment is not hindered, in addition to the kraft pulp, for example, stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner ground pulp (RGP), Mechanical pulp such as Chemi-Grand Pulp (CGP), Thermo-Grand Pulp (TGP), Groundwood Pulp (GP), Thermo-Mechanical Pulp (TMP), Chemi-thermo Mechanical Pulp (CTMP), Refiner Mechanical Pulp (RMP); Deinking Pulp ( DIP), waste pulp such as West Pulp (WP), and pulp used in ordinary newsprint paper such as pulp bleached from these, one or more are selected as appropriate, and the blending ratio is adjusted for use can do.

  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 at least one side of the base paper will be described. The coating agent used in this embodiment is mainly composed of a pigment.

  In the present embodiment, a high aspect pigment having an aspect ratio of 20 or more is blended as the pigment. One of the major features is that such a specific high aspect pigment is used, and thereby, color misregistration is particularly suppressed and the printed surface is excellent in sharpness. For example, various printings such as offset color printing can be performed. Newspaper with excellent characteristics can be obtained.

  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 can not only obtain a high-definition printing surface by improving the flatness of the newspaper surface during printing such as offset color printing, but also in parallel with the printing surface. In view of further improving the opacity, it is 20 or 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.

  In addition, the characteristics of newsprint paper such as suppression of color misregistration, sharpness of printing surface, water resistance, suppression of wetting and stretching of paper against dampening water, and ink absorbability are further improved. In elemental analysis with an X-ray microanalyzer, the area where the high aspect pigment is present is preferably 0.5% or more, more preferably 0.6% or more in terms of area ratio. In addition, for example, multi-color ink is overprinted by offset color printing at high speed, so that the ink receiving surface is covered with a flat pigment, so that ink inking properties and fine image reproducibility are required. In consideration of the pigment dispersibility and cost effectiveness in adjusting the paint, it is preferable that the area where the high aspect pigment is present is about 15% or less in terms of area ratio. As will be described later, the existence area of the high aspect pigment is the same as the number of high aspect pigments observed by X-ray microanalyzer after photographing 10 different areas of the sample at a constant area of 12000 times. The area calculated by multiplying the average area of 10 pigments was measured, and the total area ratio was calculated.

  The average particle diameter of the high aspect pigment is not particularly limited, but is preferably about 2 to 15 μm as measured by a laser method, for example. If the average particle diameter is less than 2 μm, the effect of improving the flatness and glossiness of the coating layer surface due to having a high aspect ratio is poor, and if it exceeds 15 μm, the ink is absorbed and dried, and the coating agent is prepared. There may be problems with the operability of the system.

  The pigment in the present embodiment is not particularly limited as long as the specific high aspect pigment is blended. For example, the high aspect ratio of the newspaper is further improved at the time of printing such as offset color printing. It is preferable that a composite pigment is blended together with the pigment.

  The composite pigment preferably contains mainly Si, Al, and Ca (forms secondary aggregates), and the total contained amount of these Si, Al, and Ca is the X-ray microscopic value on the surface of the coating layer. In elemental analysis with an analyzer, 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 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.

  Further, the average particle diameter of the composite pigment measured by the laser method is 0.1 μm or more, more preferably, from the viewpoint of yield in a bulky paper layer and countermeasures for paper dust problems in printing such as high-speed offset printing. The thickness is preferably 5 μm or more, and is preferably 10 μm or less, and more preferably 5 μm or less from the viewpoint of obtaining a fine print surface, rapid ink absorption / drying property, and ink fixing property on the paper surface.

  In addition, the coating layer is improved in that it improves the properties of newsprint paper, such as water resistance, suppression of paper wetting and stretching against fountain solution, surface strength, color misregistration, ink absorption, and halftone dot reproducibility. In the elemental analysis by the surface X-ray microanalyzer, the area where the composite pigment exists is preferably 20% or more, more preferably 22% or more in terms of area. 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 85% 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. .

  When composite pigments are used in combination with the above high aspect pigments, newspaper paper properties such as water resistance, suppression of paper wetting and stretching against fountain solution, surface strength, color shift suppression, ink absorption, and halftone dot reproducibility From the viewpoint of further improvement, in the elemental analysis by the X-ray microanalyzer on the surface of the coating layer, the total existence area of the high aspect pigment and the composite pigment is preferably 25% or more, more preferably 27% or more in area ratio. . In consideration of the surface strength of the paper surface and the suppression of paper dust generation in offset printing such as high-speed offset printing, the total existence area of the high aspect pigment and the composite pigment may be about 90% or less in area ratio. preferable. The total area of the high-aspect pigment and the composite 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).

  In addition to the high aspect pigment and composite 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.

  As the whole pigment blended in the coating agent, the average particle diameter measured by the laser method is preferably about 0.1 to 10 μm, for example, and the particle size distribution (volume basis) at 10 μm or less is 55 to 70%. It is preferable that it is a grade. The coating agent contains such a pigment as a main component, and the amount of the pigment in the coating agent is usually preferably about 80% by mass or more.

  In the present embodiment, in addition to the pigment, for example, an adhesive that is usually used when a base paper for newsprint is subjected to a coating process can be blended in the coating agent.

  The adhesive is not particularly limited. For example, starches such as oxidized starch, modified starch, esterified starch and dextrin; synthetic resin adhesives such as polyvinyl alcohol; water-soluble substances such as proteins such as casein, soy protein, and synthetic protein Adhesives and conjugated diene copolymer latex such as styrene-butadiene copolymer; acrylic copolymer latex such as acrylate polymer or copolymer; vinyl such as ethylene-vinyl acetate polymer One of latexes such as an alkali-soluble, alkali-swellable or alkali-insoluble polymer latex in which these various polymer latexes are modified with a functional group-containing monomer such as a carboxyl group. Two or more kinds can be appropriately selected and used.

  The blending ratio of the pigment and the adhesive in the coating agent is 25 masses of the adhesive with respect to 100 mass parts of the pigment so that the effect of improving the characteristics of the newsprint during offset color printing is fully expressed. It is preferable to adjust so that it may become 23 parts weight 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.

  In addition to the pigments and adhesives, the coating agents include various auxiliary agents commonly used in the papermaking field, such as surface sizing agents, antifoaming agents, and thickeners. It can mix | blend suitably in the range which does not carry out.

  There is no particular limitation on the method for preparing the coating agent, and the mixing ratio of the pigment and, if necessary, the adhesive and various auxiliaries is appropriately adjusted, and the mixture is stirred and mixed so that the composition is uniform at an appropriate temperature. That's fine.

  The coating agent is applied to at least one side, preferably 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.

The coating amount of the coating agent when forming the coating layer is preferably 0.3 g / m ² or more in terms of solid content with respect to one side of the base paper, in order to impart sufficient surface strength to the coating layer. Is 0.4 g / m ² or more. Moreover, in order to prevent the trouble such as sticking to the blanket and paper breakage due to the high Nepari property, the coating amount of the coating agent is 3 g / m ^{2 in} terms of solid content on one side of the base paper. Hereinafter, it is preferably 2.9 g / m 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 at least one side of the base paper, and may be about the paper making speed when manufacturing ordinary newsprint paper. .

  In this embodiment, for example, using the coating apparatus, after applying the coating agent in the coating amount on at least one side of the base paper, the coating layer is dried to form a coating layer. The product finish can be performed by applying a chemical treatment.

  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. ) Is preferably applied so as to be 8 μm or less, more preferably 7.9 μm or less under a printing pressure of 1.96 MPa. 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. From the viewpoint of weight reduction, the basis weight is 48 g / m ² or less, preferably 47 g / m ² or less.

  Moreover, it is preferable that the ratio of the ash content of newspaper is, for example, about 2 to 25% in accordance with the “ash test method” described in JIS P8251. Furthermore, the average oil absorption after standing for 24 hours in an environment of 20 ° C. and 60% relative humidity in accordance with the “pigment test method” described in JIS K 5101, the ash obtained in accordance with JIS P 8251 Is preferably 35 mL / g or more, more preferably 40 mL / g or more from the viewpoint of the absorbability of ink such as offset ink and the drying property in high-speed printing, for example, overprinting of ink in color printing, that is, on the ink Although a high oil absorption is required from the point that ink is further applied to the ink, excessive ink absorption ability may lead to deterioration in the clarity and appearance of printed information due to the penetration of ink from the paper surface into the paper layer. Therefore, it is preferably 75 mL / g or less, more preferably 70 mL / g or less.

  As described above, the newsprint according to the present embodiment has a specific basis weight, and a coating agent containing a high aspect pigment is applied in a small coating amount on at least one side of a base paper made of a specific amount of kraft pulp. Since the coating layer is formed, it is lightweight, has high water resistance, suppresses paper wetting and stretching even with frequent fountain solutions, has high surface strength, and is a blanket made of paper dust. There are no stains, and it is excellent in various properties during printing, particularly color printing, 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)
Kraft pulp (conifer kraft pulp (NBKP), hardwood kraft pulp (LBKP)) and other pulp (waste paper pulp) were blended at the ratio shown in Table 1 to prepare a pulp slurry. To this pulp slurry, 10 parts by mass of kaolin and 10 parts by mass of rosin emulsion (product name: SPN-773, manufactured by Arakawa Chemical Co., Ltd.) are added to 100 parts by mass 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 1-20 (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, and diluted with purified water to prepare coating agents 1 to 20 having a solid content concentration of about 53 to 58%. did. 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), and in Table 3, the aspect ratio of the high aspect pigment Table 4 also shows the aspect ratios of pigments other than the composite pigment.

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 1-20.

  Using the coating apparatus shown in Table 5, adjust the coating speed as appropriate, adjust the coating amount (solid content) on one side of the base paper as shown in Table 5, and apply the coating agent on both sides of the base paper, It dried and the coating layer was formed. 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, the ratio of ash content, and the average oil absorption of each newspaper were measured. These results are also shown in Table 5. In addition, for the coating layer on the surface of each newsprint obtained, the composite pigment existing area (area ratio), the high aspect pigment existing area (area ratio), and the total existing area (area ratio) of the composite pigment and high aspect pigment. (Preparation Examples 1 to 10) and the existence region (area ratio) of the used pigments other than the composite pigment (Preparation Examples 11 to 20) were 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) Presence area (area ratio) of high aspect pigment
On the surface of the coating layer, an area of a certain area was photographed at 12000 times and 10 different portions of the sample were photographed, and the average area of 10 high aspect pigments over the number of high aspect pigments visually recognized with the same X-ray microanalyzer as above. The area calculated by multiplying was measured, and the total area ratio was calculated.

(F) Total existence area (area ratio) of composite pigment and high aspect pigment
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).

(G) Presence area (area ratio) of pigments used other than composite pigments
On the surface of the coating layer, 10 areas of a sample with a constant area of 12000 times were photographed, and the average area of 10 pigments multiplied by the number of used pigments visually observed with the same X-ray microanalyzer was multiplied. The area calculated was measured, and the total area ratio was calculated.

(H) 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.

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

(J) Ratio of ash content of newsprint paper Measured in accordance with the “ash content test method” described in JIS P 8251.

(K) Average oil absorption amount of ash content of newspaper paper Based on “pigment test method” described in JIS K 5101, it was measured after being left for 24 hours in an environment of 20 ° C. and a relative humidity of 60%.

  Next, each characteristic was investigated about the newsprint of Examples 1-10 and Comparative Examples 1-10 based on the following test examples 1-6. 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 per hour, and the number of times the sword clog occurred at the folded portion during 6 hours. 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.

Test Example 6 (halftone dot reproducibility)
Using an offset color printing machine (model number: LITHRONE44, manufactured by Komori Corporation), a test pattern document was printed at a printing speed of 800 rpm. About the halftone dot printed part of the obtained test pattern, the size, shape and double state of the halftone dot were observed using an enlargement magnifier of about 200 times, and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: The size and shape of the halftone dots are the same as the original, and no double is recognized.
○: The size and shape of the halftone dots are almost the same as the original, and almost no double is observed.
(Triangle | delta): A halftone dot is partly generated and a double is recognized.
X: Notable halftone dots and burrs.

From the results shown in Table 6, the newspapers of Examples 1 to 10 are lightweight with a basis weight of 40 to 45 g / m ^2, and the coating layer on the surface of the base paper is coated with a high aspect pigment. Since it is formed with a coating amount of 0.5 to 2.8 g / m ^{2 on} one side, there is little or no ink absorption unevenness, paper powder accumulation on the blanket, clogging of the sword, and misregistration. It can be seen that it has excellent suitability and halftone dot reproducibility, and has characteristics very suitable for high-speed offset color printing.

  On the other hand, since the newspapers of Comparative Examples 1 to 10 have a coating layer formed with a coating agent that does not contain a specific high aspect pigment, the basis weight is too much or too little, Ink absorption unevenness, paper powder accumulation on the blanket, color printing suitability, clogging of the sword, register misalignment, and halftone dot reproducibility are almost all bad results, and it can be seen that it does 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 with a coating layer formed on at least one side of a base paper by a coating agent mainly composed of a pigment,
The basis weight according to JIS P 8124 is 35 to 48 g / m ² ,
As the pigment, a high aspect pigment having an aspect ratio of 20 or more is blended,
A newsprint, wherein a coating layer is formed with the coating amount of the coating agent applied to one side of a base paper at a solid content of 0.3 to 3 g / m ² .   The newsprint according to claim 1, wherein the high-aspect pigment having an aspect ratio of 20 or more is clay.   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 high aspect pigment is present is 0.5 to 15% in area ratio. The newspaper according to claim 1, wherein a composite pigment mainly containing Si, Al, and Ca is blended as a pigment together with the high aspect pigment.