JP2009138319A - Coating newsprint paper for offset printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a coating newsprint paper for offset printing having an excellent printed face, and excellent in printability. <P>SOLUTION: The coating newsprint paper for offset printing is obtained by coating a coating liquid including a pigment principally composed of burn kaolin and an adhesive on a base paper, wherein the mass ratio of the mechanical pulp is 30-70 wt.% by mass of the total pulp; the coated weight of the coating liquid for a single side is 0.3-1.0 g/m<SP>2</SP>as solid content; the coated weight of the pigment for a single side is 0.05-0.7 g/m<SP>2</SP>; and the tension in party wetted state decreases in 3.5-10 sec. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coated newsprint for offset printing used in a cold set type offset printing press.

Background of the Invention

In recent years, the printing color and speed have been rapidly increased, and there has been a demand for offset printing newsprint paper suitable for color printing, that is, offset printing newsprint paper with better printability and printing workability. . With regard to printability, in color printing, the higher the whiteness of the paper, the brighter the print surface, so there is a need for high-whiteness newsprint for offset printing. On the other hand, increasing the whiteness decreases the opacity of the paper. In other words, there is a problem that the ink on the front surface easily penetrates from the back surface of the paper. In particular, in color printing, since a larger amount of ink is applied to the paper surface than black and white printing, the occurrence frequency of back-through is increased.
In addition to the above problems, with the recent progress in paper weight reduction, it is likely that offset printing newsprint paper will also use paper with a smaller basis weight, that is, paper that is thinner (prone to show through) than before. Became. Under such severe printing conditions, news paper for offset printing is required to have a quality that simultaneously satisfies high whiteness and high opacity while having a low basis weight.

In order to increase the whiteness of the paper, there are a method of proceeding bleaching of the raw material pulp and a method of adding a filler. Since the opacity of paper decreases when whiteness is increased by proceeding with bleaching of pulp, a method of adding a filler is usually employed. Adding a filler can increase whiteness and improve opacity.
Fillers used for newsprint for offset printing are used according to their respective characteristics such as white carbon, talc, clay, titanium dioxide, calcium carbonate, urea formalin resin and the like. For example, since titanium dioxide has a very high light scattering coefficient, it is effective for increasing opacity, but is expensive and not frequently used in newsprint for offset printing. In addition, talc, clay, and calcium carbonate, which are relatively inexpensive, have problems related to printing workability, such as increasing the amount of addition to obtain the desired effect, reducing the strength of the paper or causing piling in the printing process. There is.
Therefore, particularly when white carbon or urea formalin polymer having high oil absorption is used, the effect of improving opacity after printing is high with a relatively small addition amount, and among these, white carbon is often used.

Next, color misregistration in color printing related to printing workability will be described.
In a newspaper printing press, offset printing newsprint paper extends in the printing direction when dampening water is applied to the paper surface. Here, there is a difference in the degree of elongation before and after the seam portion of two windings having slightly different physical properties. Since the printing section of the rotary press performs color printing in accordance with the physical properties of the winding before paper splicing, the first color is printed when the newsprint for offset printing is replaced with a new winding, and the image areas for the second and subsequent colors. Misregistration occurs (color misregistration), and then correction is performed by the register adjusting device. Since the printed matter from the occurrence of the color misregistration until the correction is completed is discharged as a defective product, the larger the number of discharged sheets, the worse the printing workability. Also, in color printing compared to black and white printing, the amount of dampening water transferred to the paper surface increases, so that the fibers swell and the fibers are elongated, and color misregistration is likely to occur.

As described above, newsprint paper for offset printing has been produced while maintaining a balance between printability, printing workability, and cost. However, among printability, the user's demand for image clarity has increased more than ever. In addition, there is a strong demand for newsprint for offset printing that simultaneously satisfies high whiteness and high opacity while having a low basis weight and further suppresses the occurrence of color misregistration.
In order to improve the sharpness of an image, the following techniques have been proposed as coated newspaper for offset printing provided with a pigment coating layer.
(1) Newsprint paper for a cold-set newspaper rotary printing press in which a coating layer containing a pigment having an oil absorption of 65 to 150 cc / 100 g is provided on the surface of a base paper mainly composed of mechanical pulp. (Patent Document 1)
(2) The dynamic wetting value of the base paper is -0.32 to 0.20 g, (a) 10 to 90% by weight of kaolin as a pigment of the coating composition, (b) an irregular shape and an average particle size Coated newspaper paper containing 10 to 90% by weight of a pigment of 0.5 μm or more, and further having an air permeability of 300 seconds / 10 cc or less by a high-pressure Gurley permeability tester. Manufacturing method. (Patent Document 2)
(3) Newsprint paper for offset printing in which 50% by mass or more of the pigment is calcium carbonate, the main component of the adhesive (binder) is starch, and the coating amount is 0.3 to 3.0 g / m ² . (Patent Document 3)
(4) A surface treatment agent containing starch and latex as binders and calcium carbonate and kaolin as pigments is applied so as to be 1.4 g / m ² or less per side. (Patent Document 4)

Since the newspapers described in Patent Documents 1 to 4 are coated with pigments that are fine particles on the surface, the smoothness of the surface is increased, and the halftone dots (dots) constituting the marking surface become clear, and the image Can be clarified. However, the prevention of color misregistration has not been studied and has the following problems.
In the invention described in Patent Document 1, the base paper is mainly composed of mechanical pulp. However, since the mechanical pulp has a large fiber diameter, the surface of the base paper becomes rough and uneven coating of the pigment occurs. In order to prevent this, a coating amount of at least about 1 g / m ² is required, but in order to suppress an increase in basis weight, the basis weight of the base paper must be suppressed by the amount applied, and the coating amount As the value increases, the strength decreases. As a result, when the fibers are swollen by the fountain solution in the printing process, the paper is easily stretched and color misregistration occurs.
The invention described in Patent Document 2 describes that the coating amount is desirably 1 to 6 g / m ² per side. Also in this case, since the coating amount is large, the strength is insufficient due to a decrease in the basis weight of the base paper, and color misregistration becomes a problem.
The inventions described in Patent Documents 3 and 4 are newspapers whose main component of the pigment is calcium carbonate. However, since calcium carbonate has a low oil absorption, the ink set is poor, and set-off is likely to occur when printing at high speed. is there.

Further, the following patent documents are available as a study on the strength characteristics of newsprint when wet.
In Patent Document 5, 5 μl of water is attached to the center of a piece of paper, and immediately after the attachment of water, a tensile load is applied from both ends of the piece of paper to measure the tensile strength when the water is attached, A high-speed offset rotary printing paper is described in which the tensile strength of a piece of paper in the previous state) is measured, and the dynamic water resistance determined by the percentage of the tensile strength at the time of water adhesion to the tensile strength at the time of drying is evaluated. According to this evaluation method, it is possible to quantitatively evaluate the resistance of paper breaks during offset printing, but this method evaluates the tensile load at which a piece of paper breaks by a tensile test. It is not an indicator of color misregistration caused by the slight elongation of the paper that sometimes occurs.

Japanese Patent Publication No. 4-9237 Japanese Patent No. 2823941 JP 2006-169706 A JP 2007-2344 A JP 2000-282394 A

  An object of the present invention is to provide a coated newsprint for offset printing having excellent sharpness and good printing workability without causing color misregistration in a multicolor printing system.

The present invention specifies the mass ratio of mechanical pulp in coated newspapers for offset printing, and the coating amount of the coating liquid containing the calcined kaolin, the fluorescence intensity, and the water tension separately defined as a specific range. By finding out that the above-mentioned problems can be solved, the coated newsprint for offset printing of the present invention,
(1) Coated newsprint paper for offset printing in which a base paper is coated with a coating liquid containing a pigment mainly composed of calcined kaolin and an adhesive, and the mass ratio of mechanical pulp is 30% by mass to 70% by mass in the total pulp. %, The coating amount of the coating liquid is 0.3 g / m ² or more and 1.0 g / m ² or less in terms of solid content on one side, and the coating amount of the pigment is 0.05 g / m on one side. Coated newsprint for offset printing, having a value of ^{2 to} 0.7 g / m ² and a water tension measured by the following method of 3.5 to 10 seconds.
"Method of measuring water tension"
A paper piece of 15 mm in the horizontal direction (CD direction) and 250 mm in the vertical direction (MD direction) is sandwiched at an interval of 180 mm, and 15 μl of water is attached to the central portion of the paper piece and at the same time a tensile load of 6.0 N is applied to fix the elongation. The time until the tension of the paper piece drops to 4.0 N is taken as the water resistant tension.
(2) The fluorescence intensity obtained by subtracting the whiteness when measured by placing an ultraviolet cutoff filter in the optical path from the whiteness measured according to JIS P8148 is 0.50 to 2.50%. Coated newsprint for offset printing.
It is.
(3) The coated newsprint for offset printing according to (1) or (2), wherein the ash content measured according to JIS P8251 is 4.0 to 15%.
(4) The coated newspaper for offset printing according to any one of (1) to (3), wherein the coating liquid contains a stilbene fluorescent brightening agent.
(5) The coated newspaper for offset printing according to any one of (1) to (4), wherein the coating liquid contains oxidized starch and / or latex as an adhesive.

  The coated newsprint for offset printing according to the present invention is capable of clearly printing characters and images and obtaining a good printing surface. In addition, the occurrence of color misregistration can be suppressed and deterioration of printing workability can be prevented.

The present invention is a coated newspaper for offset printing in which a base paper is coated with a coating liquid containing a pigment and an adhesive. The base paper is mainly used waste paper pulp (DIP), and the mass ratio of mechanical pulp is 30% of the total pulp. The mass is set to not less than 70% by mass. The reason for this is that increasing the mass ratio of mechanical pulp increases opacity and has the effect of suppressing strikethrough, while mechanical pulp has a large fiber diameter and tends to increase the unevenness of the base paper surface, When the mass ratio exceeds an appropriate range, it is difficult to uniformly apply the pigment to the surface when the amount of the pigment applied is relatively small as in the present invention.
Thermomechanical pulp (TMP), grandwood pulp (GP), refiner grandwood pulp (RGP), pressured groundwood pulp (PGW), and newspapers and magazine waste paper containing these pulps as mechanical pulp The used newspaper deinked pulp (DIP) can be used.
The mass ratio of mechanical pulp can be kept within the range by adjusting the mixing of mechanical pulp and the mixing of DIP. Since DIP is manufactured from newspapers, magazine waste paper, etc., chemical pulp such as softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP) and the above-described mechanical pulp are mixed. However, since the mass ratio of each pulp in DIP is almost stable, the mass ratio of mechanical pulp can be predicted and adjusted even if DIP is blended.
As other pulps, chemical pulps such as NBKP and LBKP can be appropriately blended.

In this invention, after mixing the pulp used as a raw material at a preparation process, a filler can be added in order to improve opacity. Examples of the filler used include white carbon, kaolin, talc, and calcium carbonate.
In the present invention, a saponifying rosin sizing agent, a rosin emulsion sizing agent, an alkyl ketene dimer, an alkenyl succinic anhydride or the like, or a fixing agent such as a sulfuric acid band, a cationic starch or a cationic polyacrylamide resin may be used as necessary. In addition, additives such as a dry paper strength enhancer, a wet paper strength enhancer, a slime control agent, a pitch control agent, an antifoaming agent, and a dye can also be used.

In the coated newsprint for offset printing of the present invention, a base liquid is coated with a coating liquid containing a pigment and an adhesive. As the pigment to be coated, calcined kaolin is used. Usually, the pigment coating layer has less voids than the base paper due to the small voids, but the calcined kaolin used in the present invention has a large number of pores formed on the surface of the particles by the calcining treatment in the production process. The oil absorption is relatively large. Therefore, the use of calcined kaolin to a total pigment in 90 mass% or more, when the coating amount of the pigment per one surface 0.05 g / ^{m 2} or more 0.7 g / ^{m 2} or less fixing of the ink becomes favorable, Occurrence of set-off during printing can be suppressed. Coating amount of the pigment is difficult to coat the paper surface a uniform pigment is less than 0.05 g / m ^2, the coating amount of the pigment is greater than 0.7 g / m ^2, in coldset rotary press In printing, drying of the ink is slow, and set-off is likely to occur. Examples of pigments that can be used in combination with calcined kaolin include heavy calcium carbonate, light calcium carbonate, kaolin, satin white, barium sulfate, aluminum hydroxide, and talc.

  In the coating liquid, an adhesive is used for the purpose of strengthening the adhesion between the pigments described above and between the pigment and the base paper and suppressing the occurrence of piling during printing. Adhesives include oxidized starch, enzyme-modified starch, thermochemically modified starch, phosphate esterified starch, hydroxyethylated starch, etc., cellulose compounds such as carboxymethylcellulose, hydroxyethylcellulose, casein, synthetic protein, soy protein, etc. In addition, polyvinyl alcohol which is a synthetic product can be used. These may be used in combination of two or more kinds, and among them, it is preferable to use oxidized starch from the viewpoint of excellent aging resistance and film forming ability. In addition, synthetic latexes such as a styrene-butadiene copolymer, a methyl methacrylate-butadiene copolymer, and an acrylonitrile-butadiene copolymer can also be used. Synthetic latex is expensive, but has advantages such as improved pigment adhesion, good ink retention, and good water resistance.

The amount of the adhesive used in the coating liquid is desirably 30 parts by mass or more with respect to 100 parts by mass of the pigment. When the amount of the adhesive is less than 30 parts by mass with respect to 100 parts by mass of the pigment, the adhesive force between the pigment and the base paper is weakened, and the printing occurs during printing. The upper limit of the amount of the adhesive in the coating liquid is preferably adjusted so that the coating liquid has a solid content of 0.3 g / m ² or more and 1.0 g / m ² or less with respect to the base paper.
In addition to pigments and adhesives, the coating liquid contains surface sizing agents such as styrene / maleic acid copolymers, styrene / acrylic acid copolymers, olefin / maleic acid copolymers, dyes, and anti-slip agents. Known chemicals such as agents and lubricants can be used.

The coating amount of the coating liquid to be applied to the offset newsprint newspaper of the present invention is 0.3 g / m ² or more and 1.0 g / m ² or less in terms of solid content per side. When the coating amount is less than 0.3 g / m ² per side, it is difficult to uniformly apply the coating liquid onto the paper surface, and uneven coating tends to occur. When the coating amount exceeds 1.0 g / m ² per side, the strength is lowered.
The coated newsprint for offset printing of the present invention reduces the coating amount of the coating liquid,
1) Since the coating amount of the adhesive is small, generation of neppari is suppressed.
2) Since the strength can be maintained without greatly reducing the basis weight of the base paper, the occurrence of color misregistration is suppressed.
There are effects such as.

The coated newsprint for offset printing of the present invention has a water resistance tension described below of 3.5 to 10 seconds.
"Method of measuring water tension"
A paper piece of 15 mm in the horizontal direction (CD direction) and 250 mm in the vertical direction (MD direction) is sandwiched at an interval of 180 mm, and 15 μl of water is attached to the central portion of the paper piece and at the same time a tensile load of 6.0 N is applied to fix the elongation. The time until the tension of the paper piece drops to 4.0 N is taken as the water resistant tension.

  The above-mentioned measurement can be performed using a constant speed extension type tensile tester specified in JIS P8113 (1998). The tensile load of 6.0 N is a load that is comparable to the tension in an offset printing press. There is no limitation on the method of attaching water to a piece of paper, and examples thereof include a method of dropping water with a dropper or pipette, a method of attaching water with a brush (brush) to which a certain amount of water is applied, a method by roll transfer, and the like. Although the amount of water to be attached is 15 μl, it has been confirmed that even if this is changed somewhat, the value of the water resistance tension is not affected.

Color misregistration occurs when fountain solution is applied to the paper surface during printing and a paper feed tension is applied to the paper with reduced strength. Conventionally, as a method for evaluating color misregistration on a base paper before printing, a method for individually measuring the size and strength of paper based on water absorption, contact angle with water droplets, and tensile strength according to JIS P8113, or JIS P8135. A method of measuring the strength of paper immersed in water due to the wet tensile strength of the paper has been adopted. However, in the actual printing process, the amount of fountain solution attached is small, and it is not immersed in water as in the wet tensile strength test, and the accuracy of color misregistration is low. Therefore, it was considered necessary to have a method for evaluating newsprint for offset printing under conditions closer to actual printing.
In the color printing section of a newspaper printing press, the time required for the paper to advance to the fourth cylinder after passing through the first cylinder is short. Therefore, in order to evaluate color misregistration before printing, the paper should not be immersed in water for a long time, but the water penetration in a short time and the strength of the paper immediately after the water should penetrate should be evaluated at the same time. Yes, it should not be evaluated by a large tensile load that causes the paper to break, but should be evaluated for the slight elongation of the paper that occurs during offset printing. The color shift of newsprint can be evaluated.

As a result of examining the correlation between the value of the water-resistant tension and the color misregistration in an actual rotary press, the present inventors have found that the coated newspaper for offset printing having a water-resistant tension of 3.5 to 10 seconds has a color misregistration. Was found to be difficult to occur.
When the water resistance tension is less than 3.5 seconds, the occurrence of color misregistration increases. In addition, even if the water resistance tension is greater than 10 seconds, the effect on color misregistration reaches its peak. To make the water tension within the range of 3.5 to 10 seconds, adjust the jet wire ratio (raw material ejection speed / paper machine wire speed ratio), increase NBKP, advance pulp beating, surface sizing agent , Adding internal sizing agent to the pulp, reducing the coating amount of the coating liquid and increasing the basis weight of the base paper, suppressing the additive amount of filler and increasing the basis weight of the base paper, etc. It is done. Here, the adjustment of the addition amount of the filler and the coating amount of the pigment affects the whiteness. Therefore, in order to balance the optical properties of the paper and the water tension, the ash content measured according to JIS P8251 is set to 4.0-15. 0.0% is preferable.
As the method for adjusting the water-resistant tension, one or more methods are selected in consideration of required quality and the like.

In the present invention, a fluorescent whitening agent is applied to a base paper, and the fluorescence intensity obtained by subtracting the whiteness when measured by placing an ultraviolet cutoff filter in the optical path from the whiteness measured according to JIS P8148 is 0.50 to 2. By setting the ratio to 50%, the whiteness can be improved and the stamp surface can be seen clearly. When the whiteness is improved by the fluorescent whitening agent, the amount of the filler having an effect of increasing the whiteness and the coating amount of the pigment can be suppressed, so that the above-described water tension can be increased and the color can be increased. This leads to prevention of deviation.
Examples of the fluorescent whitening agent include stilbene, coumarin, oxazole, and biphenyl, and the use of a stilbene fluorescent whitening agent is preferred. If the coating amount of the fluorescent brightening agent is too small, the effect cannot be obtained, and if it is too much, the effect reaches a peak. Therefore, in order to make the fluorescence intensity 0.50 to 2.50%, the coating amount of the fluorescent brightening agent is 0.03 to 0.1 g / m ² per side.

In the present invention, the coater for applying the coating liquid to the base paper includes a gate roll size press, a 2 roll size press, a rod metalling size press, a blade metalling size press, a blade coater, a rod coater, a bar coater, and the like. However, a gate roll size press suitable for coating with a low coating amount is preferred.
Further, the paper coated with the coating liquid is subjected to a calendar process through a drying process. As the calendar device used here, a machine calendar in which both surfaces are treated with a metal roll, a soft calendar composed of an elastic roll metal roll, a shoe calendar, and the like are used.
As described above, the coated newsprint for offset printing of the present invention is manufactured.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, a mass part and mass% represent solid content mass unless there is a notice.

(Example 1)
Cationic starch (product name: CATO304) with respect to 100 parts by mass of pulp material in which DIP (Canadian standard freeness 180 ml) is mixed with 80% by mass and TMP (Canadian standard freeness 110 ml) is mixed in a proportion of 20% by mass. / Nippon NSC Co., Ltd.) 0.5 parts by mass, internal sizing agent (product name: CC1404 / Seiko PMC Co., Ltd.) 0.4 parts by mass (as it is), sulfuric acid band 3.0 parts by mass ( Appearance: Al ₂ O ₃ concentration 8%) was added to prepare a stock, and a base paper was made with a gap former type paper machine.
Subsequently, calcined kaolin (product name: HuberteX / Huber) is used as a pigment, and 70 parts by mass of oxidized starch (product name: MS9000 / manufactured by Nippon Shokuhin Kako Co., Ltd.), latex, with respect to 100 parts by mass of the total pigment. (Product name: Smartex PA6006 / manufactured by Nippon A & L Co., Ltd.) A mixture of 30 parts by mass is used as a coating liquid, and is applied to a base paper with a gate roll size press so that the solid content is 1.0 g / m ² per side. Worked. In addition, a stilbene fluorescent whitening agent (product name: Keicol BXNL / manufactured by Nippon Soda Co., Ltd.) was mixed with the coating solution so as to be 0.03 g / m ² (appearance) per side.
After coating, drying and calendar treatment were performed to obtain a coated newspaper for offset printing having a basis weight of 46.0 g / m ² .

(Example 2)
NBKP (Canadian standard freeness 550 ml) 5% by mass, DIP (Canadian standard freeness 180 ml) 75% by mass, and TMP (Canadian standard freeness 110 ml) were mixed at a rate of 20% by mass. In the same manner as in Example 1, coated newspaper for offset printing was obtained.

(Example 3)
Implemented except that NBKP (Canadian standard freeness 550 ml) 10% by mass, DIP (Canadian standard freeness 180 ml) 70% by mass, and TMP (Canadian standard freeness 110 ml) were mixed as pulp raw materials at a rate of 20% by mass. In the same manner as in Example 1, coated newspaper for offset printing was obtained.

Example 4
A coated newsprint for offset printing is obtained in the same manner as in Example 1 except that 20% by mass of NBKP (Canadian standard freeness 550 ml) and 80% by mass of DIP (Canadian standard freeness 180 ml) are mixed as pulp raw materials. It was.

(Example 5)
Implemented except that 5% by mass of NBKP (Canadian standard freeness of 550 ml), 85% by mass of DIP (Canadian standard freeness of 180 ml), and TMP (Canadian standard freeness of 110 ml) were mixed as pulp materials at a rate of 10% by mass. In the same manner as in Example 1, coated newspaper for offset printing was obtained.

(Example 6)
Implemented except that 5% by mass of NBKP (Canadian standard freeness of 550 ml), 55% by mass of DIP (Canadian standard freeness of 180 ml), and TMP (Canadian standard freeness of 110 ml) were mixed as pulp raw materials in a proportion of 40% by mass. In the same manner as in Example 1, coated newspaper for offset printing was obtained.

(Example 7)
Example 2 except that the surface sizing agent (product name: POLYMALON OM-25 / manufactured by Arakawa Chemical Co., Ltd.) was mixed with the coating solution so that the coating amount was 0.02 g / m ^{2 in} terms of solid content per side. Similarly, a coated newspaper for offset printing was obtained.

(Example 8)
A coated newspaper for offset printing was obtained in the same manner as in Example 6 except that the surface sizing agent was mixed with the coating solution so that the coating amount was 0.04 g / m ^{2 in} terms of solid content per side.

Example 9
Calcium carbonate (product name: Tamapearl 121-6S / Okutama Kogyo Co., Ltd.) as a filler is added to the pulp slurry at 5.0% by mass (vs dry pulp), and the amount of fluorescent whitening agent applied is 0.02 g per side. A coated newsprint for offset printing was obtained in the same manner as in Example 1 except that / m ² (appearance) was used.

(Example 10)
Example 8 except that 10.0% by mass (as a dry pulp) of calcium carbonate was added as a filler to the pulp slurry, and the coating amount of the fluorescent brightening agent was 0.01 g / m ² (appearance) per side. Similarly, a coated newspaper for offset printing was obtained.

(Example 11)
The amount of oxidized starch and latex in the coating liquid is 50 parts by mass and 0 part by mass with respect to 100 parts by mass of the total pigment, respectively, and the coating amount of the coating liquid is 0.3 g / m ² per side. In the same manner as in Example 1, coated newsprint for offset printing was obtained.

Example 12
The amount of oxidized starch and latex in the coating liquid is 35 parts by mass and 15 parts by mass with respect to 100 parts by mass of the total pigment, respectively, and the coating amount of the coating liquid is 0.3 g / m ² per side. In the same manner as in Example 1, coated newsprint for offset printing was obtained.

(Example 13)
Offset as in Example 11 except that the coating amount of the optical brightener was 0.06 g / m ² per side (as it was) and the coating amount of the coating liquid was 0.8 g / m ² per side. Coated newspaper for printing was obtained.

(Example 14)
The coating amount of the optical brightener is 0.09 g / m ² (as it is) per side, and the amount of oxidized starch and latex in the coating solution is 30 parts by mass and 13 parts by mass with respect to 100 parts by mass of the total pigment, respectively. The coated newspaper for offset printing was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid was 1.0 g / m ² per side.

(Example 15)
For offset printing as in Example 1 except that the pigment was changed and the mass ratio of calcined kaolin and high white kaolin (product name: Capim DG / Imeris Minerals Japan) was 90% and 10% respectively. Coated newspaper was obtained.

(Comparative Example 1)
Cationic starch (product name: CATO304) with respect to 100 parts by mass of pulp material in which DIP (Canadian standard freeness 180 ml) is mixed with 80% by mass and TMP (Canadian standard freeness 110 ml) is mixed in a proportion of 20% by mass. / Nippon NSC Co., Ltd.) 0.5 parts by mass, internal sizing agent (product name: CC1404 / Seiko PMC Co., Ltd.) 0.4 parts by mass (as it is), sulfuric acid band 3.0 parts by mass ( Appearance: Al ₂ O ₃ concentration 8%) was added to prepare the stock, and the base paper was made with a gap former type paper machine.
Subsequently, calcined kaolin (product name: HuberteX / Huber) is used as a pigment, and 70 parts by mass of oxidized starch (product name: MS9000 / manufactured by Nippon Shokuhin Kako Co., Ltd.), latex, with respect to 100 parts by mass of the total pigment. (Product name: Smartex PA6006 / manufactured by Nippon A & L Co., Ltd.) A mixture of 30 parts by mass is used as a coating solution, and is applied to a base paper with a gate roll size press so that the solid content is 0.2 g / m ² per side. Worked. In addition, the optical brightener (product name: Keicol BXNL / manufactured by Nippon Soda Co., Ltd.) was mixed with the coating solution so as to be 0.03 g / m ² (appearance) per side.
After coating, drying and calendering were performed to obtain a coated newspaper for offset printing having a basis weight of 46.0 g / m ² .

(Comparative Example 2)
The coating amount of the optical brightener is 0.006 g / m ² per side (as it is), and the amount of oxidized starch and latex in the coating solution is 900 parts by weight and 0 parts by weight with respect to 100 parts by weight of the total pigment, respectively. The coated newspaper for offset printing was obtained in the same manner as in Comparative Example 1 except that the coating amount was 0.3 g / m ² per side.

(Comparative Example 3)
Offset as in Comparative Example 1 except that the coating amount of the coating liquid is 1.5 g / m ² per side and the coating amount of the fluorescent brightening agent is 0.09 g / m ² per side (as it is) Coated newspaper for printing was obtained.

(Comparative Example 4)
Offset as in Comparative Example 1 except that the coating amount of the coating liquid is 2.5 g / m ² per side and the coating amount of the fluorescent brightening agent is 0.09 g / m ² per side (as it is) Coated newspaper for printing was obtained.

(Comparative Example 5)
50% by mass of DIP (Canadian standard freeness 180 ml) and 50% by mass of TMP (Canadian standard freeness 110 ml) are mixed as pulp raw materials at a rate of 50% by mass, and the coating amount of the coating liquid is 1.0 g / m per side. ^A coated newspaper for offset printing was obtained in the same manner as in Comparative Example 1 except for ² .

(Comparative Example 6)
A coated newspaper for offset printing is obtained in the same manner as in Comparative Example 5, except that 30% by mass of NBKP (Canadian standard freeness 550 ml) and 70% by mass of DIP (Canadian standard freeness 180 ml) are mixed as pulp raw materials. It was.

  Table 1 shows the mass ratio of the pulp of the coated newspaper for offset printing, the coating amount of the coating liquid, the paper quality, and the evaluation of Examples 1 to 15. Table 2 shows the evaluation results of the obtained offset printing coated newspapers for Comparative Examples 1 to 6.

The evaluation method of the offset printing coated newsprint was as follows.
(Mass ratio of pulp)
According to the TAPPI standard T401 om-82 method, the type of pulp fiber constituting the raw material is identified for the sampled pulp raw material, and then the corresponding fiber weight is obtained by multiplying the number of each type of fiber by the respective weight coefficient. The percentage of the total pulp fiber weight was calculated.

(Water resistance)
A piece of paper of 15 mm in the horizontal direction (CD direction) and 250 mm in the vertical direction (MD direction) is sandwiched between clips of a tensile tester (Autograph AG-I 500N / manufactured by Shimadzu Corporation) at an interval of 180 mm, and placed in the center of the piece of paper. At the same time as applying 15 μl of water, a tensile load of 6.0 N was applied, and the time required for the tension of the paper piece to drop to 4.0 N was measured with the elongation fixed. The same operation was repeated 5 times, and the average value was calculated. In addition, the sample conforms to JIS P8111 (1998) in advance at 23 ° C. ± 1 ° C. and (50 ± 2)% r. h. What was conditioned for 24 hours in the standard state was measured in the standard state.

(Whiteness)
Using a spectroscopic white difference meter PF-10 manufactured by Nippon Denshoku Industries Co., Ltd., a pulse xenon lamp was used as a light source, and measurement was performed according to JIS P8148 (2001).

(Fluorescence intensity)
When using a spectroscopic white difference meter PF-10 manufactured by Nippon Denshoku Industries Co., Ltd., using a pulsed xenon lamp as the light source, and not inserting a 420 nm cut-off filter in the optical path at whiteness measured according to JIS P8148 (2001) The value obtained by subtracting the whiteness when the same filter was inserted was used as the fluorescence intensity.

(ash)
In accordance with JIS P8251 (2003), ash content was measured by a 525 ° C. combustion method.

(Color shift)
Four-color printing was performed in the order of ink, indigo red and yellow at a printing speed of 120,000 copies / hour on both sides. A pester from the old winding to the new winding was performed leaving a winding length of 20 m, and the amount of yellow shift was measured using black as a reference immediately after discharging 50 copies.
Pesting was performed 10 times, an average value of shift amounts was calculated, and color shift was evaluated according to the following criteria.
A: Deviation amount is less than 0.1 mm,
○: Deviation amount is 0.1 mm or more and less than 0.5 mm,
X: Deviation amount is 0.5 mm or more

(Set off)
Printed using 1 g of ink (NEW KING ECO ink / manufactured by Toyo Ink Manufacturing Co., Ltd.) with an RI tester, and the density of the ink transferred onto the white paper after overlaying the printed surface and white paper and niping again with the RI tester Was visually confirmed and evaluated in three stages.
A: Low concentration, no problem.
○: Medium concentration, but no problem in practical use.
X: The density is high and the frequency of set-off occurrence is high in the actual machine.

(Betrayal)
Four-color printing was performed with the newspaper rotary printing press, the degree of ink back-through was judged visually, and back-through evaluation was evaluated in 3 stages.
A: Almost no ink breakthrough is observed.
○: Slight penetration of ink is recognized, but there is no practical problem.
X: There was a problem because the ink was rejected.

(Coating unevenness)
Four-color printing was performed with the newspaper rotary printing press, the unevenness of the ink density of the printed image was visually determined, and the evaluation of the uneven coating was evaluated in three stages.
(Double-circle): It is a uniform and clear image with no or almost no ink density unevenness.
○: Slight unevenness in the ink density is observed, but the image is almost uniform and has no practical problem.
X: Uneven image with uneven ink density is observed.

In the coated newspapers for offset printing shown in Examples 1 to 15, clear images could be obtained, and the color misregistration, set-off, back-through, and coating unevenness were evaluated well.
On the other hand, in Comparative Example 1, a clear image could be obtained, but the coating amount of the coating solution was as small as 0.2 g / m ² per side, resulting in uneven coating and non-uniform images.
In Comparative Example 2, the amount of pigment applied was as small as 0.03 g / m ² per side, resulting in uneven coating, both images becoming non-uniform, and the fluorescence intensity being as low as 0.48%, both clear images. Could not get.
In Comparative Examples 3 and 4, clear images could be obtained, but color misregistration occurred because the water resistance tension was low at 3.4 seconds and 2.1 seconds, respectively. The coating amount per one side 0.75 g ^/ m 2 each pigment, 1.25g / ^{m 2,} coating fluid coating amount per side respectively 1.5 g ^/ m 2 of, 2.5 g / ^{m 2} and most Trouble due to set-off occurred.
In Comparative Example 5, a clear image could be obtained, but the mass ratio of mechanical pulp in the raw material was as high as 72% by mass, the surface of the base paper became rough, and coating unevenness occurred.
In Comparative Example 6, the mass ratio of mechanical pulp was as low as 29% by mass, and ink penetration was observed.

Claims (5)

A newsprint paper for offset printing in which a base paper is coated with a coating liquid containing a pigment mainly composed of calcined kaolin and an adhesive, and the mass ratio of mechanical pulp is 30% by mass or more and 70% by mass or less in the total pulp. There, the coating amount of the coating liquid is at 0.3 g / ^{m 2} or more 1.0 g / ^{m 2} or less in terms of solid per side content, the pigment coating weight of 0.05 g / ^{m 2} or more per one side of the 0 .7g / m ² or less, the offset printing coated newsprint value of water tension is 3.5 to 10 seconds, measured by the following method.
"Method of measuring water tension"
A paper piece of 15 mm in the horizontal direction (CD direction) and 250 mm in the vertical direction (MD direction) is sandwiched at an interval of 180 mm, and 15 μl of water is adhered to the center of the paper piece and at the same time a tensile load of 6.0 N is applied to fix the elongation. The time until the tension of the paper piece drops to 4.0 N is taken as the water resistant tension.   The coating material for offset printing according to claim 1, wherein the fluorescence intensity obtained by subtracting the whiteness when measured by placing an ultraviolet cut-off filter in the optical path from the whiteness measured according to JIS P8148 is 0.50 to 2.50%. Engineering newspaper.   The coated newsprint for offset printing according to claim 1 or 2, wherein the ash content measured according to JIS P8251 is 4.0 to 15%.   Coated newsprint for offset printing according to any one of claims 1 to 3, wherein the coating liquid contains a stilbene fluorescent whitening agent.   Coated newsprint for offset printing according to any one of claims 1 to 4, wherein the coating liquid contains oxidized starch and / or latex as an adhesive.