JP4868907B2 - Printing paper - Google Patents

Description

  The present invention relates to printing paper. More specifically, the whiteness is high, the color fading property is excellent, the printability is excellent despite the fact that it is light and bulky, almost no paper dust is generated, and the touch feeling is good, for example, offset printing, rotary printing. It is related with the printing paper which can be used conveniently for the above.

  In recent years, research has been promoted to reduce printing paper weight and improve bulkiness with the aim of reducing the number of pages with respect to thickness and creating an apparent volume feeling by reducing the transportation cost of printed materials and increasing the bulkiness. ing.

  Also, in terms of printing technology, for example, offset printing, color printing, high-speed mass printing, and automation have made great progress. Improvement is required from the aspect.

  For example, various types of printing paper are used according to the type of printed matter such as advertisements, direct mail, various magazines, catalogs, manuals, and books. Among them, comic paper is mainly composed of mechanical pulp and deinked pulp. In printing on paper as well, demands for higher printing speed, color paper, automation, etc., as described above, have increased, and in conjunction with the introduction of computer systems for printing paper, the shift from letterpress printing to offset printing has rapidly progressed. Yes. Furthermore, especially for comic paper, the amount of circulation as an old book is large, and in the display at an old book store, printing with good fading is caused by the problem that the product value of the appearance decreases due to the color unevenness due to the fading of the cut surface of each book. Paper is required.

  Due to the widespread use of offset printing, for example, (1) it is bulky and lightweight, (2) it has high whiteness and good fading, and (3) water absorption resistance. Is maintained moderately and has wet strength, (4) high reproducibility of printing, and (5) no generation of paper dust. Of these, the demands for high whiteness, good fading, bulkiness, and light weight are particularly high.

  The weight reduction of printing paper is considered to reduce the basis weight of the base paper, using raw pulp with high drainage with as little beating as possible, or using a specific shape such as spindle shape, column shape, needle shape, etc. It has been studied to internally add light calcium carbonate having a shape. However, the reduction of the basis weight reduces the paper quality strength of the base paper itself, which causes problems such as paper breakage during printing operations, generation of paper dust during offset printing, and ink breakthrough due to a decrease in opacity.

  On the other hand, as measures for improving the bulkiness of printing paper, the use of bulking agents and the high blending of mechanical pulp that is rigid and easily forms voids between fibers are being studied. However, since the bulking agent is expensive and has the property of inhibiting or separating the bonds between the fibers, it has a problem of reducing not only the surface strength but also the paper quality strength in the Z-axis (thickness) direction. Moreover, although high blending of mechanical pulp makes it possible to obtain bulkiness at low cost, mechanical pulp has inherently low whiteness and a large amount of fluorescent whitening agent must be used. However, the frequent use of the fluorescent brightening agent significantly deteriorates the fading property of the printing paper over time and causes a decrease in whiteness. Furthermore, the heavy use of mechanical pulp is not only due to the above-mentioned whiteness problem, but also the paper surface flatness is impaired, causing paper dust generation during offset printing, and due to a decrease in wet paper strength due to dampening water in rotary printing. Various problems also occur in printing suitability such as paper breakage.

  Therefore, various technologies have been developed to provide printing paper with good whiteness and fading, lighter weight and improved bulkiness, and excellent printability with no paper dust generation or paper breakage. Has been.

For example, Patent Document 1 discloses a printing paper containing hardwood mechanical pulp having a density of 0.45 g / cm ³ or less of handmade paper produced using 100 ml of pulp with Canadian Standard Freeness (hereinafter referred to as CSF). Has been. Such hardwood mechanical pulp is obtained by impregnating hardwood wood chips with an alkaline hydrogen peroxide aqueous solution and then subjecting to normal pressure or pressure refining treatment, and has a large Runkel ratio of 4.0 or more and is a rigid hardwood machine By containing 5 to 96% by weight of pulp in the base paper, an attempt is made to obtain a printing paper that maintains optical characteristics such as opacity and whiteness, and is bulky and excellent in printability.

  However, since the printing paper disclosed in Patent Document 1 uses hardwood mechanical pulp, as described above, the raw pulp has a very low CSF of 100 ml. Printing paper made from such pulp does not only cause paper breaks and paper dust during bookbinding, but also has poor surface properties and fading due to its rigid hardwood mechanical pulp, and is particularly poor in flatness and suitable for printing. Inferior, high-definition printing cannot be performed.

  Patent Document 2 discloses a coated printing paper containing mechanical pulp having an opacity of 89% or more, a whiteness of 65% or more, a surface roughness of less than 4.5 μm, and 90% by weight or more of the total fiber amount. Has been. In such coated printing paper, mechanical pulp of 90% by weight or more of the total fiber amount is used to give opacity and firmness, and within a relatively bulky range, it is adjusted to the desired volume by calendering, so that it is suitable for printing. In addition, the production cost is reduced by reducing the amount of chemical pulp used.

  However, since the coated printing paper disclosed in Patent Document 2 is a coated paper, the manufacturing cost is not only higher than that of the non-coated paper, but also the density is high due to the coating and the hand feeling is high. It ’s bad.

Further, in Patent Document 3, a starch-based paper strength agent is applied to a base paper using at least hardwood mechanical pulp and bulking agent produced by chemical treatment, and the density is 0.35 to 0.50 g / cm. ^Three bulky medium printing papers are disclosed. In such a bulky medium-sized printing paper, hardwood mechanical pulp having a single fiber density index of 0.20 or more is used in an amount of 10 to 60% by weight of the total pulp, and the amount of bulking agent added is 0.1 to 1.2%. By setting the coating amount of the surface paper strength agent to 0.3 to 3.0 g / m ² , the whiteness is improved, the density is reduced, and the flexibility (low rigidity) is improved. It is intended to improve the printing suitability and suppress the occurrence of bleeding.

However, since the bulky medium-sized printing paper disclosed in Patent Document 3 uses hardwood mechanical pulp as well as the printing paper disclosed in Patent Document 1, the raw material pulp has an extremely low CSF of 100 ml, and bookbinding. Not only are the paper torn and paper dust generated during processing, but the rigid hardwood mechanical pulp is poor in surface properties, fading properties, particularly flatness, and is inferior in printability, so that high-definition printing cannot be performed.
JP 2003-49386 A JP 2004-525284 A JP 2005-163253 A

  The present invention has been made in view of the above-mentioned background art, and has high whiteness, excellent fading, excellent printability despite being lightweight and bulky, almost no generation of paper dust, and feel to the touch. Is intended to provide a good printing paper.

That is, the present invention relates to a printing paper characterized in that the whiteness according to JIS P 8123 is 75% or more, the density according to JIS P 8118 is 0.50 g / cm ³ or less, and the fading property is 6 or less. .

  The printing paper of the present invention is high in whiteness, excellent in fading, excellent in printability despite being light and bulky, has almost no generation of paper dust, and has a good touch feeling, for example, offset printing. It can be suitably used for rotary printing and the like.

(First embodiment)
As described above, the printing paper of the present invention has a whiteness according to JIS P 8123 of 75% or more, a density according to JIS P 8118 of 0.50 g / cm ³ or less, and a fading property of 6 or less. is there.

  First, raw material pulp used for printing paper according to the present embodiment will be described. In the present embodiment, as long as the printing paper has the desired whiteness, density, and fading as described above, the raw material pulp is not particularly limited, but, for example, mechanical pulp can be suitably used.

  As mechanical pulp that can be suitably used in the present embodiment, for example, pine, spruce, fur, etc., which are softwood materials, are used as raw materials in order to obtain bulky printing paper. , Refiner grandwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), pressurized groundwood pulp (PGW), and the like, among them, TMP and PGW are particularly It is preferable in terms of obtaining a printing paper that is bulky and has high opacity, high whiteness, and high strength. In particular, PGW is obtained by grinding softwood wood under pressure in the same way as grandwood pulp (GP), and does not contain bundling fibers that cause paper scumming during offset printing even when used as a raw material pulp. In terms of fiber length distribution, it contains more intermediate fibers than GP and TMP. Moreover, since PGW is fibrillated, it has characteristics that it has high strength and is easy to express smoothness, and has low fading properties among mechanical pulps. Therefore, it can be suitably used for printing paper according to this embodiment. it can.

  In addition, when higher whiteness is calculated | required according to the intended purpose etc. of the printing paper obtained, one or more well-known bleaching processes can be given to the said mechanical pulp, and a pulp can also be bleached further. In this case, for example, an oxidizing agent such as hydrogen peroxide, ozone or peracetic acid or a reducing agent such as hydrosulfite (sodium dithionite), sodium hydrogen sulfate, sodium borohydride, formamidine sulfinic acid (FAS) or the like. Can be used. In particular, when bleaching is performed using a reducing agent, the reason is not clear, but high fading is exhibited.

  In this embodiment, in addition to the mechanical pulp, for example, kraft pulp such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), waste paper pulp such as deinking pulp (DIP), and West pulp (WP). Can be used without limitation. Among these, it is preferable to use kraft pulp, particularly hardwood kraft pulp having straight and short fibers, from the viewpoint that the bulk, weight reduction, and printability of the obtained printing paper can be further improved.

  In addition, in order to more fully improve the bulk and weight reduction of the obtained printing paper, the “pulp” described in JIS P 8121 of the raw pulp after disaggregation based on “pulp-disaggregation method” described in JIS P 8220 is used. It is preferable that the CSF based on the “freeness test method” is 340 ml or more, more preferably 350 ml or more. When the CSF is less than 340 ml, the density change easily occurs in the flattening process in the manufacturing stage, and the bulkiness may be impaired. In addition, from the viewpoint of securing the strength of printing paper, it is necessary to apply an appropriate beating treatment to the raw pulp, and the beating degree that can obtain a good formation that ensures the strength without reducing the bulkiness. Therefore, the CSF is preferably 370 ml or less.

  In the present embodiment, when, for example, the mechanical pulp is used as the raw pulp, the paper, board and pulp-fiber composition test method described in JIS P 8120 is used for the raw pulp after disaggregation according to JIS P 8220. The proportion of mechanical pulp by the dyeing method is to ensure the bulkiness by the rigidity of the fibers while suppressing the discoloration and yellowing caused by the mechanical pulp, and to reduce the weight compared to the printing paper of the same thickness From the point that it is possible, it is preferable that it is 25 mass% or more, and also 27 mass% or more. Further, in order to prevent the discoloration and yellowing caused by mechanical pulp from being difficult, or to prevent the printing paper itself from becoming brittle and reducing bookbinding processing suitability, the proportion of the mechanical pulp is 50% by mass or less. Is preferably 48% by mass or less.

  Also, when using kraft pulp, especially hardwood kraft pulp, together with the mechanical pulp, as raw material pulp, in order to ensure fine printability on printing paper and to obtain a desired whiteness of 75% or more, conform to JIS P 8220 The ratio of hardwood kraft pulp by the dyeing method based on JIS P 8120 in the raw pulp after disaggregation is preferably 50% by mass or more, and more preferably 52% by mass or more. In addition, the hardwood kraft pulp ratio is 75% by mass or less, in order to prevent the increase in density and difficulty in securing bulkiness and light weight from the straight and short fiber structure inherent in hardwood. It is preferable that it is 73 mass% or less.

  In order to obtain the printing paper according to the present embodiment, the pulp slurry composed of the raw material pulp, if necessary, various kinds of fillers, internally added sizing agents, fixing agents, yield improvers, cationizing agents, paper strength enhancing agents, etc. For example, a method of adding an additive as appropriate and adjusting a condition such as a pH value and making paper with a normal paper machine such as a long net paper machine or a twin wire paper machine can be employed.

  Examples of fillers include light calcium carbonate, heavy calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, silica White inorganic pigments such as magnesium acid, synthetic silica, aluminum hydroxide, alumina, lithopone, zeolite, magnesium carbonate, magnesium hydroxide; styrene plastic pigment, acrylic plastic pigment, polyethylene, microcapsule, urea resin, melamine resin, etc. And organic pigments.

  Examples of internally added sizing agents include rosin sizing agents for acidic papermaking, modified rosin sizing agents for neutral papermaking, alkenyl succinic acid sizing agents, alkyl ketene dimer sizing agents, alkenyl succinic anhydride sizing agents, and wax sizing agents. Styrene resin sizing agent, olefin resin sizing agent, styrene-acrylic resin sizing agent, higher fatty acid sizing agent, cationic polymer sizing agent, oxidized starch and the like.

  In addition to the above-mentioned various additives, a method of adding a bulking agent to the raw pulp slurry and improving the bulk of the resulting printing paper has been tried, but the bulking agent is mainly based on the Z-axis strength of the paper. In order to reduce the paper strength, it is preferable to refrain from using it. In addition, when mechanical pulp is frequently used to obtain a desired bulkiness, the mechanical pulp itself has low whiteness, and therefore, a fluorescent whitening agent can be mainly used in combination. Among these fluorescent brighteners, there is a fear of carcinogenicity, as well as those that impair the fading and reduce the whiteness. 8) and the one that does not show elution of fluorescent substances as defined in Shokugan Kikai No. 0107001 (January 7, 2004) is effective in maintaining high whiteness of printing paper Is.

  Note that when the printing paper according to the present embodiment is applied to, for example, offset printing in particular, since dampening water is used in such offset printing, it is preferable to appropriately impart size characteristics (water absorption resistance) to the printing paper. . By maintaining such sizing properties satisfactorily, it is possible to more sufficiently suppress fears such as an increase in the amount of dampening water transfer, paper elongation, poor wet inking, and color misregistration.

  In order to control the sizing property, the internal sizing agent as described above is added to the raw pulp slurry, and the internal sizing agent is added to the inside of the printing paper at the same time as paper making, or after paper making, a two-roll size press, gate It is preferable to apply a surface sizing agent to the surface of the printing paper using a coating machine such as a roll coater, or at least one of them. As the surface sizing agent, for example, those exemplified as the internal sizing agent can be used.

  For example, in the case of using the internal additive sizing agent, in order to impart sufficient sizing properties to the resulting printing paper and to further improve the moisture resistance and water resistance, 0.1 parts by mass or more with respect to 100 parts by mass of the raw material pulp, It is preferable to be 0.3 parts by mass or more, and in order to prevent the absorption and drying properties of the ink on the surface of the printing paper from being lowered and the printing operability from being deteriorated, the amount of the raw material pulp is 100 parts by mass. It is preferably 1 part by mass or less, more preferably 0.8 part by mass or less.

For example, when the surface sizing agent is used, in order to impart sufficient sizing properties to the obtained printing paper and to improve moisture resistance and water resistance, the coating amount on the printing paper is 0.04 g / m per side. ² or more, and more preferably 0.06 g / m ² or more. In order to prevent the ink from drying and drying on the surface of the printing paper from being deteriorated and the printing operability from being deteriorated, the printing paper is used. The coating amount on one side is preferably 0.20 g / m ² or less, more preferably 0.18 g / m ² or less per side.

The printing paper according to the present embodiment thus obtained satisfies specific whiteness, density, and fading properties at the same time. That is, the printing paper according to the present embodiment has a whiteness degree of 75% or more conforming to JIS P 8123, a density conforming to JIS P 8118 of 0.50 g / cm ³ or less, and a fading property of 6 or less.

  In the present embodiment, in order to ensure the cosmetics of the target printing paper, in consideration of ensuring the whiteness of appearance compared to conventional printing paper, “Paper and Pulp” described in JIS P 8123. The whiteness measured in accordance with the “hunter whiteness test method” is 75% or more, preferably 76% or more. For example, when mechanical pulp is used as the raw material pulp, the original whiteness of the mechanical pulp is at most about 70%, and preferably whiteness of 75% or more is applied to the printing paper by bleaching with a reducing agent such as ozone or FAS. The printing paper can be produced at low cost. The whiteness is slightly different depending on the purpose of use of the printing paper to be obtained, and the upper limit is not particularly limited. In the application development to comic paper that can be expected to be particularly effective in the present invention, While the whiteness is about 70%, the whiteness is 75% or more, and it can be suitably used for comic paper by recent flow color and high-definition offset printing.

The density of the printing paper according to the present embodiment measured in accordance with “Test method for thickness and density” described in JIS P 8118 is 0.50 g / cm ³ or less. For example, the Beck smoothness measured according to the “Smoothness test method using a Beck smoothness tester” described in JIS P 8119 is set to 3 seconds or more, so that high-definition printing suitability can be achieved. Obtainable. Furthermore, the density is preferably 0.48 g / cm ³ or less, and the Beck smoothness is preferably 4 to 20 seconds. When the Beck smoothness is 20 seconds or more, it is difficult to maintain bulkiness and avoid an excessive decrease in density, and it is easy to generate paper dust due to physical flattening of the surface of the printing paper, resulting in a feeling of touch. May fall. In consideration of adhesion between the offset printing plate and the printing paper (cushioning property), touch feeling, and securing of paper quality strength, the density is preferably 0.42 g / cm ³ or more.

  The printing paper according to the present embodiment has a fading property of 6 or less, preferably 5 or less in consideration of, for example, quality maintenance for long-term use outdoors. As will be described in detail later, the fading property referred to here is a process corresponding to sunlight irradiation in summer using a fade meter, and the whiteness before and after the treatment is described in “Paper, paperboard and pulp-ISO” described in JIS P 8148. The measurement is performed according to the “whiteness test method”, and the difference in ISO whiteness of the outermost surface of the printing paper before and after processing is calculated. The smaller the value, the better the fading. Such fading varies slightly depending on the purpose of use of the obtained printing paper, but it is usually preferable to be close to zero.

  By the way, printing on a conventional rotary offset printing press, particularly comic paper, is accelerated to 800 to 1000 rpm, and the maximum speed is 1500 rpm, taking the case of a half-size size B plate. .

  As the printing speed increases in this way, the printing paper needs to be managed with a higher sizing degree (water absorption resistance), so sufficient quality improvement can be achieved only by controlling the paper strength in the conventional dry or wet state. Is not done. In addition, it is not sufficient to measure only the sizing degree measurement method and the water drop method (drip water absorption degree method), which are current sizing degree management methods. In other words, the Cobb sizing measurement method and drip water absorption method capture only static liquid absorption, and although it is an index of water absorption, printing is performed at high speed and contact with dampening water is instantaneous. It is insufficient to observe the water absorption behavior of the process.

  For this reason, it is necessary to perform quality control in a state close to actual printing conditions, and it is necessary to manage water absorption of paper instantaneously (that is, dynamically in a state where printing is actually performed). Under such circumstances, in view of the demand for higher quality printing paper, the dynamic water absorption test value is measured in the present embodiment.

  The dynamic water absorption test value is measured using a size tester (trade name: EST, manufactured by Emtec). First, a measurement paper piece (75 mm × 50 mm) is fixed to a folder with a double-sided tape, and is submerged in a test container filled with a solvent (350 ml of water). Here, the folder is sunk between the ultrasonic wave transmitting element and the receiving element provided in the test container. The measurement is started 0.025 seconds after the paper piece comes into contact with the solvent. Since the transmission intensity of the ultrasonic wave changes as the solvent penetrates into the paper piece, a graph of the dynamic water absorption test value (%) and the elapsed time (s) is displayed on the monitor of the size tester. And a dynamic water absorption test value can be calculated | required by reading this graph. The ultrasonic frequency for measurement is 2 MHz.

  For example, in offset printing, fountain solution is applied prior to printing, and as a result, the strength of the printing paper is partially reduced by the fountain solution in a state where tension is applied by the printing press, resulting in sheet breakage. it is conceivable that. Here, when the dynamic water absorption test value is 100%, water permeation into the surface of the printing paper is started. For example, in the case of conventional printing paper having poor surface water resistance, 0.025 seconds to 0.2 seconds from the start of measurement. In less than a second, water penetration into the printing paper starts, and in less than 0.3 seconds, the dynamic water absorption test value reaches 50%. On the other hand, in the printing paper according to the present embodiment, the time required for the dynamic water absorption test value to reach 50% is preferably 0.30 seconds or more, more preferably 0.32 seconds or more. The water resistance of the surface of the printing paper is sufficiently improved, and the dimensional change and paper breakage due to water absorption and drying are suppressed. The time required for the dynamic water absorption test value to reach 50% varies slightly depending on the purpose of use of the obtained printing paper, but in consideration of securing the absorbability and drying property of the offset ink, It is preferably about 0.45 seconds or less.

  In the printing paper according to the present embodiment, for example, in order to satisfy the time required for the dynamic water absorption test value to reach 50% as described above, a blend of raw material pulp, particularly mechanical pulp and hardwood kraft pulp is used. It is useful to adjust the ratio, or to use the internal sizing agent and / or surface sizing agent, and the blending amount and coating amount thereof.

As described above, the printing paper according to this embodiment has a whiteness of 75% or more, a density of 0.50 g / cm ³ or less, and a fading of 6 or less, preferably dynamic water absorption. The time required for the property test value to reach 50% is 0.3 seconds or more, but in addition to these, it is preferable to have the following physical properties, for example.

For example, the basis weight measured in accordance with the “basis weight measurement method” described in JIS P 8124 is about 52 to 78 g / m ² from the viewpoint of securing suitable paper quality strength and opacity as well as weight reduction in transportation. It is preferable that

  The thickness measured in accordance with “Test method for thickness and density” described in JIS P 8118 is 125 to 125 from the viewpoint of securing suitable paper quality strength and opacity and imparting good printing workability. It is preferably about 150 μm.

  The wet tensile strength measured in accordance with “Paper and paperboard—wet tensile strength test method” described in JIS P 8135 gives, for example, sufficient paper quality strength to dampening water during offset printing. Moreover, it is preferable that it is about 0.08-0.15 kN / m from the point of maintaining sufficient printing appropriateness.

  The opacity measured in accordance with “Paper and paperboard—Opacity test method (paper backing)” described in JIS P 8149 may be appropriately adjusted according to the intended use of the printing paper. It is preferably about 95%.

Stiffness (longitudinal) measured in accordance with “Paper Clark Stiffness Testing Method” described in JIS P 8143 gives good printing workability and touch feeling, and maintains sufficient printing suitability. terms, is preferably about 20 to 30 cm ^3/100.

  As described above, the printing paper according to the present embodiment has specific whiteness, density, and fading, is light and bulky, has excellent printing suitability, and has a good touch feeling.

  Next, although the printing paper of this invention is demonstrated still in detail based on the following Examples, this invention is not limited only to these Examples.

Examples 1 to 10 and Comparative Examples 1 to 6 (Manufacture of printing paper)
Hardwood kraft pulp (LBKP), mechanical pulp (PGW) and softwood kraft pulp (NBKP) were blended at the ratio shown in Table 1 to prepare a raw material pulp slurry. After adding 1 part by mass of clay to 100 parts by mass of pulp solids, 0.1 g of oxidized starch as a surface sizing agent is used as a surface sizing agent in a gate roll coater using a long net type paper machine. / M ² coating was performed to obtain a printing paper.

  In Table 1, CSF based on JIS P 8121 of raw pulp after disaggregation based on JIS P 8220 is also shown. Moreover, the compounding quantity of each raw material pulp of Table 1 is calculated | required by the dyeing | staining method based on JISP8120.

Each physical property of the obtained printing paper was measured by the following method. These results are shown in Table 2. Further, a commercially available printing paper having an actually measured basis weight of 69 g / m ² was used as Comparative Example 7, and each physical property was measured in the same manner. The raw pulp and CSF of this commercially available printing paper are as shown in Table 1.

(A) Whiteness Measured according to “Hunter whiteness test method for paper and pulp” described in JIS P 8123.

(B) Density The density was measured in accordance with “Test method of thickness and density” described in JIS P 8118.

(C) Discoloration Fading meter (trade name: light resistance tester FAL-5, UV long life fade meter, manufactured by Suga Test Instruments Co., Ltd.) performs 10-hour treatment corresponding to about one month of sunlight irradiation in summer. It was. The whiteness before and after this treatment was measured in accordance with “Paper, Paperboard and Pulp-ISO Whiteness Test Method” described in JIS P 8148, and the difference in ISO whiteness on the outermost surface of the printing paper before and after the treatment was calculated. In addition, the calculated numerical value is smaller, and the closer to 0, the better the fading property.

(D) Time required for the dynamic water absorption test value to reach 50% Using a size tester (trade name: EST, manufactured by Emtec), a piece of paper (75 mm × 50 mm) was fixed to a folder with a double-sided tape. The folder was sunk between an ultrasonic wave transmitting element and a receiving element provided in a test container filled with 350 ml of water. The measurement starts 0.025 seconds after the paper piece comes into contact with water. From the graph of the dynamic water absorption test value and the elapsed time displayed on the monitor of the size tester, the dynamic water absorption test value is 50%. The time required to reach the value (indicated as “EST size degree” in Table 2) was read. The ultrasonic frequency for measurement was 2 MHz.

(E) Basis weight It measured based on the "basis weight measuring method" described in JISP8124.

(F) Thickness Measured according to “Test method of thickness and density” described in JIS P 8118.

(G) Wet tensile strength Measured according to “Paper and paperboard—wet tensile strength test method” described in JIS P 8135.

(H) Opacity Measured in accordance with “Paper and paperboard—Opacity test method (backing of paper)” described in JIS P 8149.

(I) Stiffness (vertical)
It was measured in accordance with “A stiffness test method using a paper Clark stiffness tester” described in JIS P 8143.

  Next, each characteristic was investigated about the printing paper of Examples 1-10 and Comparative Examples 1-7 based on the following test examples 1-2. The results are shown in Table 2.

Test example 1 (suitable for printing)
Using an RI printing test machine (Ishikawajima Industrial Machinery Co., Ltd.), 1.0 g of ink for offset printing (trade name: TK High Echo Black, manufactured by Toyo Ink Co., Ltd.) was developed and printed. After 5 minutes from the start of printing, the coated paper was adhered to the printing surface with a constant pressure, the state of ink transfer to the coated paper was examined, and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: The set is very fast, can be used for high-speed printing with offset sheet-fed printing, and there is no problem of set-off.
○: Level is fast and there is no problem of set-off.
Δ: Standard level.
×: Level of setting is slow and unusable for offset printing.

Test Example 2 (Occurrence of paper dust)
Using an offset color printer (model number: LITHRONE44, manufactured by Komori Corporation), continuous 5000 copies of indigo, red, yellow, and black ink were printed. Thereafter, the accumulation state of the paper powder in the blanket non-image area was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: Paper dust is not recognized.
○: Paper dust is slightly recognized, but there is no problem in actual operation.
(Triangle | delta): Paper dust is recognized and there exists a problem in actual operation.
X: A lot of paper dust is deposited on the blanket.

  From the results shown in Table 2, each of the printing papers of Examples 1 to 10 has high whiteness, low density and fading, and further reaches a dynamic water absorption test value of 50%. It can be seen that the required time is long and excellent in water resistance. Further, it is found that the printing properties are excellent, paper dust is hardly generated, and excellent properties suitable for printing such as offset printing are provided.

  On the other hand, the printing papers of Comparative Examples 1 to 7 have insufficient whiteness, high density and fading, and further the time required until the dynamic water absorption test value reaches 50%. It turns out that it has problems, such as being short and inferior in water resistance. In addition, it can be seen that it does not have excellent characteristics suitable for printing such as offset printing, such as poor printing suitability and remarkable generation of paper dust.

  The printing paper of the present invention can be suitably used for, for example, offset printing and rotary printing.

Claims (3)

The Canadian standard freeness according to JIS P 8121 of the raw pulp after disaggregation according to JIS P 8220 is 340 ml or more,
The ratio of the mechanical pulp by the dyeing | staining method based on JISP8120 in the raw material pulp after this disaggregation is 25-50 mass%,
Containing mechanical pulp of conifer as mechanical pulp,
The ratio of the hardwood kraft pulp by the dyeing method based on JIS P 8120 in the raw pulp after the disaggregation is 50 to 75% by mass,
The surface sizing agent is applied at 0.04 g / m ² or more and 0.20 g / m ² or less per side, or the internal sizing agent is added at 0.3 parts by mass or more and 1.0 part by mass with respect to 100 parts by mass of the raw material pulp. is applied contained and surface sizing agent per side 0.04 g / m ² or more 0.20 g / m ² or less or less,
In the dynamic water absorption test, the time required for the dynamic water absorption test value to reach 50% is 0.30 seconds or more, the whiteness according to JIS P 8123 is 75% or more, and the density according to JIS P 8118 is 0. Offset printing paper, characterized in that it is 50 g / cm ³ or less and the fading property is 6 or less.   The offset printing paper according to claim 1, wherein the mechanical pulp of the conifer is PGW.   The offset printing paper according to claim 1 or 2, wherein the Beck smoothness according to JIS P8119 is 4 to 20 seconds.