Coated Paper

Abstract

To provide a coated paper having excellent ink dry property, ink impression property, and print brightness.SOLUTION: Provided herein is a coated paper including a pigment coating layer on a base paper, in which its coating weight per single side is 5.0 g / m2 or over, Oken type smoothness degree is 65 s or under, and ISO whiteness is 70% or over.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to coated paper having good ink drying properties. [Background technology]

[0002] In recent years, with the decline in the number of newspapers sold as paper media, efforts have begun to utilize newspaper rotary presses for purposes other than newspapers. Generally, printing with newspaper rotary (offset) presses using penetration-drying cold set ink does not have a drying process, but dries the ink by penetrating the ink into the paper, and the paper is required to have good ink absorption. If the paper has poor ink absorption, problems such as staining of the printing press and the paper surface and a decrease in printing speed occur, causing a deterioration in printing quality and a decrease in operability. In such printing methods, uncoated paper without a pigment coating layer, especially newsprint that contains a large amount of recycled paper pulp, has generally been used. However, although the ink drying properties are good when uncoated paper or newsprint is used, there are problems such as insufficient ink adhesion and printing gloss, which have been a major obstacle when using cold set offset printing for printing information other than text. To solve this problem, Patent Document 1 describes a method for printing a paper with a density of 0.5 g / m per side. 2 More than 4.0g / m 2 A lightly coated paper suitable for newspaper inks has been proposed, which has a pigment coating layer of less than 1000 μm. This lightly coated paper can achieve excellent printability with ink drying and clarity comparable to that of newsprint paper. Patent Document 2 also describes a paper that uses a surface treatment agent containing a plastic pigment and a synthetic adhesive at 4 g / m per side. 2 A cold-set offset printing paper coated with the above-mentioned coating has been proposed. This printing paper is said to have high print gloss, color printability, and little drag staining. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-31927 A [Patent Document 2] JP 2012-117174 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a coated paper having excellent ink drying properties, ink acceptance and printing gloss. [Means for solving the problem]

[0005] The above problems are solved by the present invention described below. [1] A coated paper having a pigment coating layer on a base paper, The coating weight of the pigment coating layer is 5.0 g / m per side. 2 That's all. Oken smoothness is 65 seconds or less. Coated paper with an ISO brightness of 70% or more. [2] The coated paper according to [1], wherein the total amount of calcium carbonate and clay in the pigment coating layer is 80 parts by weight or more per 100 parts by weight of pigment. [3] Coated paper according to [1] or [2], which has a 75° gloss of 30% or more when printed in a solid state with a print density of 1.6 using coldset news ink. [4] The coating amount is 8.0 g / m per side. 2 The coated paper according to any one of [1] to [3] below. [5] The basis weight of the coated paper is 45 to 75 g / m 2 The coated paper according to any one of [1] to [4], [6] The density of the coated paper is 0.5 to 1.0 g / cm 3 The coated paper according to any one of [1] to [5], [7] 5.0 g / m per side on base paper with an Oken smoothness of 20 seconds or less 2 A method for producing coated paper according to any one of [1] to [6], comprising the step of providing a pigment coating layer as described above. Effect of the Invention

[0006] The present invention can provide coated paper having excellent ink drying properties, ink receptivity and printing gloss. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present invention will be described in detail below. In the present invention, "X to Y" includes the extreme values ​​X and Y.

[0008] 1.Coated paper In the present invention, a coated paper is a paper having a specific amount of pigment coating on a base paper. The coated paper of the present invention is particularly suitable for offset printing with coldset inks such as news inks.

[0009] (1) Pigment coating layer The pigment coating layer is a layer that contains a white pigment as a main component. The coated paper of the present invention has a coating weight of 5.0 g / m 2 The coating weight is 5.5 to 8.0 g / m per side. 2 The upper limit is preferably 7.0 g / m 2 The following is more preferable: Examples of white pigments include commonly used pigments such as calcium carbonate, kaolin, clay, calcined kaolin, amorphous silica, zinc oxide, aluminum oxide, satin white, aluminum silicate, magnesium silicate, magnesium carbonate, titanium oxide, and plastic pigments.

[0010] When the pigment coating layer contains calcium carbonate or clay, the smoothness of the coated paper is improved, so that a printed image with fine detail and good color development can be obtained. From this viewpoint, the total amount of calcium carbonate and clay per 100 parts by weight of pigment in the pigment coating layer is preferably 80 parts by weight or more, more preferably 90 parts by weight or more. There is no upper limit to the total amount, and it is 100 parts by weight or less.

[0011] The average particle size of calcium carbonate is preferably 0.5 to 1.0 μm. The average particle size can be measured by a laser diffraction particle size distribution measuring instrument such as Malvern's Mastersizer, and D50 can be defined as the average particle size. The content of particles of calcium carbonate having a particle size of 2.0 μm or less is preferably 90% by volume or more, more preferably 93% by volume or more, and even more preferably 95% by volume or more. Examples of calcium carbonate include heavy calcium carbonate and light calcium carbonate. Light calcium carbonate (causticized light calcium carbonate) described in Japanese Patent No. 5274077 may also be used as the light calcium carbonate.

[0012] The average particle size of the clay is preferably 6.0 μm or less. If the clay particle size is small, fine voids can be formed in the coating layer, improving the drying properties of the ink. The average particle size of the clay can also be measured using a laser diffraction particle size distribution measuring device or the like, and D50 can be used as the average particle size. There is no lower limit to the average particle size, but it is preferably 1.0 μm or more. From the viewpoint of whiteness, the clay content in the total amount of calcium carbonate and clay is 50% by weight or less. % Less than 40% by weight is preferred % The following is more preferred:

[0013] The pigment coating layer contains an adhesive. Examples of the adhesive include etherified starch such as oxidized starch, cationic starch, urea phosphate esterified starch, hydroxyethyl etherified starch, and various starches such as dextrin, proteins such as casein, soybean protein, and synthetic protein, cellulose derivatives such as polyvinyl alcohol, carboxymethyl cellulose, and methyl cellulose, conjugated diene polymer latex such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer, acrylic polymer latex, and vinyl polymer latex such as ethylene-vinyl acetate copolymer. These can be used alone or in combination of two or more. It is preferable to use a mixture of a starch-based adhesive and a latex-based adhesive, since it provides an excellent balance between the coating suitability of the pigment coating liquid and the printing suitability such as surface strength. The total amount of adhesive in the pigment coating layer is preferably 1 to 15 parts by weight, more preferably 2 to 14 parts by weight, and even more preferably 3 to 13 parts by weight, based on 100 parts by weight of the pigment. If the amount of adhesive is less than 1 part by weight, the adhesive will be insufficient and the coating layer will be weak, which may result in many defects such as white spots during printing.On the other hand, if the amount is more than 15 parts by weight, the voids in the pigment coating layer will be insufficient, making it difficult for the penetrating cold set ink to penetrate the paper, which may result in poor drying properties.

[0014] The pigment coating layer may contain various auxiliary agents such as dispersants, thickeners, defoamers, colorants, antistatic agents, preservatives, etc., which are generally used in the paper manufacturing field.

[0015] The pigment coating layer can be provided by applying a coating liquid to one or both sides of the base paper by a known method. The solid content concentration in the coating liquid is preferably about 30 to 70% by weight from the viewpoint of coating suitability. The pigment coating layer may be one or more layers, but since it is a lightly coated paper, one layer is preferred. The coating amount of the pigment coating layer is 5.0 g / m2 in total per side. 2 More than 5.5 g / m 2 The upper limit of the coating amount is 8.0 g / m or more. 2 Preferably, the thickness is 7.0 g / m or less. 2 More preferably, the coating weight is less than 5 g / m 2If the coating weight is less than this, the base paper cannot be sufficiently covered by the coating layer, resulting in poor ink color development, whereas if the coating weight is too high, the ink does not penetrate well and the ink dries poorly.

[0016] (2) Base paper The pulp raw material of the base paper used in the present invention is not particularly limited, and mechanical pulps such as ground pulp (GP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), and chemical pulps such as waste paper pulp (deinked pulp (DIP)), softwood kraft pulp (NKP), and softwood kraft pulp (LKP) can be used. As the waste paper pulp, those derived from sorted waste paper such as fine paper, medium-quality paper, low-quality paper, newspapers, flyers, and magazines, or unsorted waste paper in which these are mixed can be used, but waste paper pulp containing medium-quality paper, low-quality paper, and newspapers containing mechanical pulp as raw materials is preferable. The printing paper of the present invention contains 30 parts by weight or more of chemical pulp per 100 parts by weight of pulp. By containing a large amount of chemical pulp, the density of the printing paper can be improved and the ink can be prevented from excessively penetrating deep into the base paper, thereby improving the ink color development. From this viewpoint, the lower limit of the chemical pulp content is preferably 40 parts by weight or more, and more preferably 50 parts by weight or more. On the other hand, since the paper is required to have a suitable stiffness in the printing process, processing process, or when made into a book, it is preferable that the paper contains a certain amount of mechanical pulp or recycled paper pulp that contains mechanical pulp as a raw material. Therefore, the upper limit of the chemical pulp content is preferably 90 parts by weight or less, and more preferably 80 parts by weight or less.

[0017] The coated paper of the present invention preferably contains 10 parts by weight or more of mechanical pulp or recycled paper pulp containing mechanical pulp, more preferably 20 parts by weight or more, in total, per 100 parts by weight of pulp. The upper limit of this total amount is preferably 50 parts by weight or less. If the total amount exceeds this value, the density may decrease, leading to a decrease in ink color development, and further the whiteness may decrease, leading to a decrease in image quality.

[0018] Known fillers can be added to the base paper. Examples of fillers include inorganic fillers such as heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, delaminated kaolin, magnesium carbonate, barium carbonate, barium sulfate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, and amorphous silica produced by neutralizing sodium silicate with a mineral acid, and organic fillers such as urea-formaldehyde resin, melamine resin, polystyrene resin, and phenol resin. These may be used alone or in combination. Among these, calcium carbonate and light calcium carbonate-silica composite, which are typical fillers in neutral papermaking and alkaline papermaking and can provide high opacity, are preferred.

[0019] As the internal additives, bulking agents, dry strength improvers, wet strength improvers, drainage improvers, dyes, neutral sizing agents, etc. may be used as necessary. Examples of the dry strength improvers include polyacrylamide and cationic starch, and examples of the wet strength improvers include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the formation or runnability. Examples of the neutral sizing agents include alkyl ketene dimers, alkenyl succinic anhydrides, neutral rosin sizing agents, etc. Bulking agents may be used, but since there is a possibility that the paper becomes too bulky, it is preferable to use a small amount, and it is more preferable not to use any bulking agents. When using a bulking agent, it is preferable to adjust the paper thickness by calendaring or the like so that the paper density falls within the range of the present invention. These internal additives can be used together with pulp and filler as necessary to form paper stock.

[0020] The base paper is preferably a single-ply paper, and is manufactured by a known papermaking method. For example, it can be manufactured using a Fourdrinier papermaking machine, a gap former type papermaking machine, a hybrid former type papermaking machine, an on-top former type papermaking machine, a cylinder papermaking machine, etc., but is not limited thereto. The coldset offset printing paper of the present invention may be manufactured by an on-machine method in which the papermaking process and the pigment coating process are successively performed, or it may be manufactured by an off-machine method in which coating is performed in the pigment coating process after the papermaking process. The papermaking and coating speeds are preferably 400 to 2000 m / min.

[0021] The Oken smoothness of the base paper is preferably 20 seconds or less. If the smoothness is 20 seconds or less, the surface smoothness of the base paper will be at a relatively low level, but if the base paper has this level of smoothness, the ink drying properties can be improved even if the coating weight of the pigment coating layer is increased. The reason for this is not clear, but it is presumed that if the smoothness of the base paper is in the above range, the specific surface area of ​​the coated paper after the pigment coating layer is provided will be high, and the low smoothness will result in low base paper coverage during coating, and ink will be easily absorbed by the exposed base paper, which will improve ink absorption. There is no lower limit for the Oken smoothness, but it is preferably 5 seconds or more, and more preferably 10 seconds or more. Furthermore, the coated paper of the present invention has a surface smoothness of 5 g / m 2 The presence of the above pigment coating layer provides good ink receptivity and printing gloss, and the paper combines ink drying properties, ink receptivity and high printing gloss.

[0022] (3) Other processing The coated paper of the present invention may further have a clear coating layer, mainly composed of an adhesive, on one or both sides of the base paper. The clear coating layer is preferably adjacent to the base paper layer, but may be provided as the outermost layer furthest from the base paper. The adhesive used in the clear coating layer is as described above. When the clear coating layer is provided adjacent to the base paper, it is preferable because it is possible to suppress the penetration of the pigment coating liquid into the base paper and the base paper coverage of the pigment coating layer is improved, and starch is preferably used as the adhesive. Furthermore, the strength of the base paper is improved by the penetration of the clear coating liquid into the base paper. From the above, the coating amount of the clear coating layer is 0.5 to 5.0 g / m on both sides. 2is preferable, and 1.0 to 4.5 g / m 2 More preferably, 2.0 to 4.0 g / m 2 is more preferred.

[0023] The coated paper of the present invention may be subjected to a surface treatment, such as a soft calender, a super calender, a gloss calender, a heat calender, or a shoe calender.

[0024] (4) Characteristics of the coated paper of the present invention 1) Oken type smoothness The coated paper of the present invention has an Oken smoothness (JIS P8155) of 65 seconds or less, preferably 60 seconds or less. If this value exceeds the upper limit, the ink penetration speed slows down and drying properties deteriorate. There is no lower limit, but from the viewpoint of surface properties such as printing gloss, it is preferable that the value be 30 seconds or more.

[0025] 2) ISO whiteness The coated paper of the present invention has an ISO whiteness (JIS P8148) of 70% or more, preferably 75% or more, and more preferably 80% or more. If the whiteness is less than 75%, the whiteness of the blank areas decreases, and the appearance of the printed image also decreases.

[0026] 3) Print gloss The coated paper of the present invention preferably has a 75° gloss of 30% or more, and more preferably 35% or more, when solid printed with coldset news ink to a print density of 1.6. If the gloss is less than 30%, the printed matter will lack luster and the appearance of the printed image may also be impaired.

[0027] 4)Basic weight, density The basis weight of the coated paper of the present invention is preferably 45 g / m 2 More preferably, it is 50 g / m 2 More preferably, it is 55 g / m 2 The upper limit of the basis weight is preferably 75 g / m 2 More preferably, it is 70 g / m 2Less than 65 g / m, more preferably 2 From the viewpoint of ease of turning pages when made into a book, it is most preferable that the basis weight is 63 g / m2 or less. 2 If it is less than 75 g / m, the paper will not be stiff enough when used in a book, and the texture may be poor. 2 If it exceeds 1.0 g / cm, it may be difficult to make a single layer of paper from the viewpoint of drainage, etc. Also, the density of the paper is preferably 0.5 to 1.0 g / cm 3 and more preferably 0.6 to 0.9 g / cm 3 It is.

[0028] 2. Manufacturing method of coated paper of the present invention The coated paper of the present invention is preferably manufactured by a step of providing a pigment coating layer of the above-mentioned coating amount on one or both sides of the base paper by blade coating. The pigment coating layer can also be provided by roll coating, but blade coating is a coating method in which the coating liquid is applied and then scraped off with a blade, so that a highly smooth coated surface can be obtained, and printing paper with good ink color development can be obtained.

[0029] 3.Applications The coated paper of the present invention is suitable for coldset offset printing because it exhibits excellent ink drying, ink adhesion, and print gloss in coldset offset printing. In particular, by using the coated paper in coldset offset printing using a rotary press, a large amount of high-quality printed matter can be efficiently produced at high speed. Therefore, the coated paper of the present invention is suitable for applications in which printing with coldset inks is used, and is useful as, for example, newsprint paper, book paper, comic paper, textbook paper, etc. Furthermore, because the coated paper of the present invention has good ink drying properties, it can also be used in on-demand printing methods such as inkjet printing, which require ink drying and color development. EXAMPLES

[0030] [Example 1] The base paper was made from a stock containing 30% by weight of NBKP, 23% by weight of LBKP, 27% by weight of deinked pulp, 20% by weight of GP, and 12% by weight of light calcium carbonate as a filler. The density was 0.56 g / cm. 3 , basis weight 54g / m 2 Base paper 2 was prepared as follows. 82 parts by weight (solids) of heavy calcium carbonate (manufactured by Fimatec Corporation, product name: FMT97, proportion of particles with a particle size of 2 μm or less by sedimentation method: 97%, D50=0.64 μm) and 18 parts by weight (solids) of second-class clay (manufactured by IMERYS, product name: KCS, D50=4.9 μm) were used as pigments, and 5 parts by weight of styrene-butadiene copolymer latex and 7.5 parts by weight of oxidized starch were blended as adhesives, and water was further added to obtain coating liquid 1 with a solids concentration of 55% by weight. The pigment coating liquid was applied to one side of the base paper with a blade coater until the dry coating amount was 5.5 g / m 2 The coated paper was evaluated by the method described below.

[0031] [Example 2] Coated papers were obtained and evaluated in the same manner as in Example 1, except that the coating amount was changed as shown in Table 3.

[0032] [Example 3] Except for using 100 parts by weight (solid content) of second-grade clay (manufactured by IMERYS, product name: KCS, D50=4.9 μm) as the pigment, Coating Liquid 2 was obtained in the same manner as Coating Liquid 1. Except for changing Coating Liquid 1 to Coating Liquid 2, coated paper was obtained and evaluated in the same manner as in Example 1.

[0033] [Comparative Examples 1 and 2] Target coating weight: 4.0g / m 2 , 3.0g / m 2 Except for these changes, coated papers were obtained and evaluated in the same manner as in Example 1.

[0034] [Comparative Examples 3 and 4] Base paper 2 was calendered at a linear pressure of 20 kg to obtain base paper 1, and coated papers were obtained and evaluated in the same manner as in Example 2 and Comparative Example 1, except that this was used.

[0035] [Comparative Example 5] The coated paper obtained in Comparative Example 3 was calendered at a linear pressure of 60 kg, and a coated paper was obtained in the same manner as in Comparative Example 3 and evaluated.

[0036] [Table 1]

[0037] [Table 2]

[0038] [Table 3]

[0039] As shown in Table 3, it is clear that the coated paper of the present invention has excellent ink drying properties, ink acceptance and printing gloss in coldset offset printing.

[0040] The evaluation method is described in detail below. (1) Paper gloss Measurements were performed based on JIS P8142. (2)Basic weight The measurement was performed in accordance with the "Basis Weight Measurement Method" described in JIS P8124. (3) Paper thickness and density Measurements were made in accordance with "Paper and paperboard -- Test methods for thickness and density" described in JIS 8118. (4) Oken type smoothness Measurements were performed based on JIS P8155. (5) Whiteness ISO whiteness measurement method: Based on JIS P8148, using a color difference meter CM manufactured by Murakami Color Co., Ltd. Measurements were taken using an S-35SPX with a light source including ultraviolet light. (6) Ink drying Coldset offset printing (Media Shine ink, manufactured by DIC Graphics Corporation) was performed using a manual RI printing machine (manufactured by Akira Manufacturing Co., Ltd.), and the printout was transferred to coated paper one minute after printing, and the degree of staining on the coated paper was evaluated visually and numerically. Numerical evaluation was performed using an X-Rite (manufactured by X-Rite Corporation) to evaluate the Y value difference (white paper - ink transferred area). A: There is little ink transfer and it dries quickly. B: There is some ink transfer, but it does not affect use. C: The ink is not dry and cannot be used. (7) Ink density The print density of the sample printed in (6) above was measured 1 hour after printing using X-Rite ( The measurements were performed using a fluoroscopy (manufactured by X-Light). A: Over 1.50, good ink adhesion. B: 1.40 to 1.50, ink adhesion is somewhat good. C: Less than 1.40, poor ink adhesion. (8) Print gloss The print gloss of the sample printed in (6) above, after being left for one day in an environment of 23°C and 50% relative humidity, was measured according to JIS P-8142. The print gloss corresponds to the 75° gloss when solid printing is performed using coldset newspaper ink so that the print density is 1.6. A: Over 35% and the print gloss is quite good. B: 30-35% and printing gloss is somewhat good. C: Less than 30% and poor print gloss.

Claims

1. A coated paper having a pigment coating layer on a base paper, The coating amount of the pigment coating layer is 5.0 g / m per side. ２ That's all. the pigment coating layer contains calcium carbonate and clay in a total amount of 90 parts by weight or more per 100 parts by weight of pigment, provided that the content of clay per 100 parts by weight of the total of calcium carbonate and clay is 50 parts by weight or less, and does not contain a plastic pigment; The Oken smoothness is 65 seconds or less. The ISO brightness of the base paper is 70% or more. Coated paper.

2. 2. The coated paper of claim 1, which has a 75° gloss of at least 30% when solid printed with a coldset news ink to a print density of 1.

6.

3. The coating amount is 8.0 g / m per side. ２ 3. The coated paper according to claim 1 or 2, wherein:

4. The basis weight of the coated paper is 45 to 75 g / m ２ The coated paper according to any one of claims 1 to 3,

5. The density of the coated paper is 0.5 to 1.0 g / cm ３ The coated paper according to any one of claims 1 to 4,

6. 6. The coated paper according to claim 1, wherein the base paper contains 40 parts by weight or more of chemical pulp per 100 parts by weight of pulp, and the chemical pulp contains LBKP (hardwood pulp) and NBKP (softwood pulp).

7. On the base paper, 5.0 g / m per side ２ A method for producing coated paper according to any one of claims 1 to 6, comprising the step of providing a pigment coating layer as described above.

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