JP2020200564A - Coated paper for printing - Google Patents

Abstract

To provide coated paper for printing, which is fine coated paper, has excellent ink absorbability and ink transferability, and suppresses occurrence of mottled defect.SOLUTION: Coated paper for printing has base paper containing pulp and a filler, and one or two or more coated layers on at least one surface of the base paper, in which the outermost coated layer located most outside based on the base paper in the coated layer contains a white pigment and a binder, the white pigment contains at least calcium carbonate of which cumulative frequency of particles having a diameter of 2 μm or smaller in a particle size distribution based on volume is 90 vol% or larger and kaolin which has a cumulative frequency of particle size of 5 μm or smaller in a particle size distribution based on volume is 40 vol% or larger and a particle size (D50) of cumulative frequency 50 vol% in a particle size distribution based on volume is 4.5 μm or larger and 7.0 μm or smaller, and a total coating amount of the coated layer containing the outermost coated layer is 2.5 g/m2 or larger 4 g/m2 or smaller.SELECTED DRAWING: None

Description

The present invention relates to a coated paper for printing used in an offset printing machine, and more particularly to a coated paper for printing with a fine coating amount of 4 g / m ² or less per side.

While printing press manufacturers are announcing digital printing presses, the printing industry is still using offset printing presses to produce commercial printed matter such as magazines, books, art books, photo books, MOOK books, booklets, catalogs, leaflets and pamphlets. use. Paper used for commercial printed matter is not limited to glossy paper and matte paper. Paper in recent years has various qualities such as glossiness and matteness, degree of smoothness, color tone, and texture. On the market, heavy-duty coated paper for printing with a high glossiness is preferred. On the other hand, in magazines, MOOK books, booklets and catalogs, coated paper for printing having a rough texture with suppressed glossiness and smoothness is also popular.

In general, the price of paper depends on the weight of the paper. Therefore, in order to keep costs down, printers tend to demand finely coated paper with a small amount of coating and / or bulky paper with a small density.

Despite the low coating amount, it has a pigment and an adhesive on the base paper as a coating paper for printing that is bulky, has high whiteness, has an excellent print surface feeling, has high opacity, and has good printing workability. A coated paper for printing which has one or more coating layers and satisfies the following conditions (1) to (5) is known (see, for example, Patent Document 1).
(1) The base paper contains kraft pulp in an amount of 50% by weight or more based on the dry weight of the total pulp. (2) The base paper contains an organic compound having an action of inhibiting the interfiber bond of pulp.
(3) The amount of one-sided coating of the coating layer is 0.5 to 5 g / m ² .
(4) The density of the coated paper for printing is 0.70 g / cm ³ or less.
(5) The ash content of the coated paper for printing is 10% by weight or more.

Japanese Unexamined Patent Publication No. 2014-07212

A finely coated printing coated paper having a coating amount of 4 g / m ² or less per side is inferior in ink absorbability because the amount of coating for receiving ink is small. If the plain paper does not have a coating layer, ink absorbability can be obtained by the voids of the base paper constituting the plain paper. If the coated paper for printing has a relatively large amount of coating, ink absorbability can be obtained by a thick coating layer. If the coated paper for printing is inferior in ink absorbency, the drying of the ink is delayed, and ink stains such as set-off occur on the resulting printed matter.
In particular, a finely coated printing coated paper having a rough texture is inferior in ink transferability because the coating property of the base paper by the coating layer is inferior. If the coated paper for printing is inferior in ink transferability, the amount of ink transferred from the blanket of the offset printing press to the coated paper for printing will be different, resulting in a color difference in the resulting printed matter.
In addition, a finely coated printing coated paper having a rough texture is often not subjected to calendar processing after a coating layer is provided in order to obtain a rough texture. Therefore, in the coated paper for printing, the components of the coating layer may adhere to the blanket of the offset printing machine. When adhesion occurs, the resulting printed image has speckled defects.

In view of the above, an object of the present invention is to provide a finely coated paper, which has good ink absorbency and ink transfer property, and which suppresses the occurrence of spot-like defects on an image portion. That is.

As a result of diligent research to solve the above problems, the present inventors achieve the object of the present invention by the following.
[1] A base paper containing pulp and a filler, and a coating layer having one or more layers on at least one side of the base paper, and the outermost coating in the coating layer located on the outermost side with respect to the base paper. The working layer contains a white pigment and a binder, and the white pigment has a particle size of 2 μm or less in a volume-based particle size distribution and a cumulative frequency of 90% by volume or more is calcium carbonate and a particle size of 5 μm or less in a volume-based particle size distribution. A coating containing at least kaolin having a cumulative frequency of 40% by volume or more and a particle size (D50) of 50% by volume in a volume-based particle size distribution of 4.5 μm or more and 7.0 μm or less, and including the outermost coating layer. A coated paper for printing in which the total coating amount of the layers is 2.5 g / m ² or more and 4 g / m ² or less per side.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a finely coated paper for printing, which has good ink absorbency and ink transfer property and suppresses the occurrence of spot-like defects on an image portion.

The present invention will be described in detail below.
The coating paper for printing has a base paper containing pulp and a filler, and one or more coating layers on at least one side of the base paper.

The pulp is conventionally known in the field of papermaking. Examples of pulp include chemical pulps such as LBKP (Leaf Bleached Kraft Pulp) and NBKP (Needle Bleached Kraft Pulp), GP (Groundwood Pulp), PGW (Pressure GroundWood pulp), RMP (Refiner Mechanical Pulp), and TMP (ThermoMechanical Pulp). ), CTMP (ChemiThermoMechanical Pulp), BCTMP (Bleached ChemiThermoMechanical Pulp), CMP (ChemiMechanical Pulp), mechanical pulp such as CGP (ChemiGroundwood Pulp), and used paper pulp such as DIP (DeInked Pulp). Examples of the raw material for pulp include conifers and hardwoods, as well as hemp, linter, straw, bamboo, sugar cane, phragmites, fruit, mulberry, mitsumata and ganpi.

The base paper pulp is one or more selected from the group consisting of the above pulps. The base paper pulp preferably contains LBKP and BCTMP. The total content of LBKP and BCTMP with respect to the pulp in the base paper is preferably 70% by mass or more. When the total content of LBKP and BCTMP is less than 100% by mass with respect to the pulp in the base paper, it contains one or more selected from the group consisting of the above pulp excluding LBKP and BCTMP. The mass ratio of LBKP to BCTMP in the base paper is preferably 1.2 or more and 2.5 or less. The drainage degree (CSF) of LBKP is preferably 320 ml or more and 390 ml or less. Here, the drainage degree (CSF) is a value measured according to a Canadian standard drainage degree test method based on JIS P8121: 2012.

The filler is a white pigment conventionally known in the papermaking field. Examples of fillers are calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, active clay, diatomaceous soil, silica, alumina, hydroxide. Examples of white inorganic pigments such as aluminum, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide include white organic pigments such as styrene-based plastic pigments, acrylic-based plastic pigments, polyethylene, microcapsules, urea resins, and melamine resins. The filler is preferably one or more selected from the group consisting of these.

The base paper filler preferably contains talc and calcium carbonate. Further, the calcium carbonate is preferably light calcium carbonate. The total content of talc and calcium carbonate is preferably 80% by mass or more with respect to the filler in the base paper. When the total content of talc and calcium carbonate is less than 100% by mass with respect to the filler in the base paper, it contains one or more selected from the group consisting of the above fillers excluding talc and calcium carbonate. Further, the mass ratio of talc to calcium carbonate in the base paper is preferably [talc: calcium carbonate] = 1: 9 to 5: 5.

The base paper contains pulp and filler, and further contains various additives such as sizing agent, binder, fixing agent, yield agent, cationizing agent such as cationic resin and polyvalent cation salt, and paper strength agent as required. It is a papermaking product obtained by making a paper material mixed with the above. Further, the base paper includes high-quality paper obtained by subjecting papermaking to calendar treatment, surface size treatment with starch, polyvinyl alcohol, or the like, or surface treatment. Further, the base paper includes high-quality paper that has been subjected to surface size treatment or surface treatment and then calendered.
Other additives in paper materials include pigment dispersants, thickeners, fluidity improvers, defoamers, defoamers, mold release agents, foaming agents, penetrants, coloring dyes, coloring pigments, and UV absorption. One or more selected from the group consisting of agents, antioxidants, preservatives, antibacterial agents, water resistant agents, wet paper strength enhancers, dry paper strength enhancers, etc., impairs the desired effect of the present invention. It can be appropriately blended within the range not specified.

The base paper preferably has an ash content of 9% by mass or more and 15% by mass or less. The ash content is a value obtained in accordance with JIS P8251: 2003 "Paper, paperboard and pulp-ash content test method-525 ° C. combustion method". The principle of measurement is as follows. The test piece is placed in a heat-resistant crucible, the mass is measured, and the test piece is burned and incinerated in a muffle furnace at 525 ° C. ± 25 ° C. In addition, the water content is measured with another test piece. The ash content (mass%) is calculated as the mass ratio of the combustion residue to the mass of the test piece in the absolutely dry state determined from the moisture content of the sample. The ash content can be adjusted by the content of the filler contained in the base paper.

Paper making is performed by adjusting the paper material to acidic, neutral or alkaline and using a conventionally known paper machine. Examples of the paper machine include a long net paper machine, a twin wire paper machine, a combination paper machine, a circular net paper machine, and a Yankee paper machine.

The coating layer can be provided on at least one side of the base paper by applying and drying the coating layer coating liquid. The coating layer is one layer or two or more layers. Of the coating layers, the coating layer located on the outermost side of the base paper is called the outermost coating layer. The outermost coating layer contains a white pigment and a binder. When there is only one coating layer, the coating layer is the outermost coating layer. When the number of coating layers is two or more, the coating layer existing between the base paper and the outermost coating layer is not particularly limited with respect to the presence or absence of each of the white pigment, the binder and various additives described later, and their types.
Since the coated paper for printing is a fine coating, the coating amount of the coating layer is 2.5 g / m ² or more and 4 g / m ² or less per side. When there are two or more coating layers, it is the total value of them.
The coating layer is preferably one layer from the viewpoint of manufacturing cost.

The coating layer may be provided on one side or both sides of the base paper. In the case of one side, a conventionally known backcoat layer may be provided on the side of the base paper opposite to the side having the coating layer.

The method of providing the coating layer on the base paper or the existing coating layer is not particularly limited. For example, a method of applying and drying a coating layer coating liquid using a coating device and a drying device conventionally known in the papermaking field can be mentioned. Examples of the coating device include a comma coater, a film press coater, a rod coater, an air knife coater, a rod blade coater, a bar coater, a blade coater, a gravure coater, a curtain coater, an E bar coater, and a size press. Examples of drying devices include hot air dryers such as straight tunnel dryers, arch dryers, air loop dryers, and sine curve air float dryers, infrared heating dryers, and various drying devices such as microwave dryers. Can be done.

Examples of size presses are Inclined Size Press, Horizontal Size Press, Rod Metering Size Press, Roll Metering Size Press, Blade Metering Size Press as film transfer method, Simsizer, Optimizer, etc. for Rod Metalling Size Press. Speed sizers and film presses, and roll metering size presses include gate roll coaters. Other examples include bill blade coaters, twin blade coaters, velva papa coaters, tab size presses, and calendar size presses.

The coating layer can be calendared. In many cases, the coated paper for printing is not subjected to calendar processing after the coating layer is provided in order to obtain a rough texture.
The calendering process is a process of averaging the smoothness and thickness by passing paper between rolls. Examples of the calendar processing device include a machine calendar, a soft nip calendar, a super calendar, a multi-stage calendar, and a multi-nip calendar. The printed coated paper of the present invention does not include the printed coated paper having the outermost coating layer cast.

The outermost coating layer contains a white pigment and a binder.
White pigments are conventionally known in the field of coated paper. Examples of white pigments are calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, active clay, diatomaceous earth, silica, alumina, water. Examples of white inorganic pigments such as aluminum oxide, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide include white organic pigments such as styrene-based plastic pigments, acrylic-based plastic pigments, polyethylene, microcapsules, urea resins, and melamine resins. .. The outermost coating layer is one or more selected from the group consisting of these pigments.

The white pigment in the outermost coating layer contains at least calcium carbonate and kaolin. In the outermost coating layer, the content of calcium carbonate and kaolin is preferably 80% by mass or more with respect to the white pigment in the outermost coating layer. When the total content of calcium carbonate and kaolin is less than 100% by mass with respect to the white pigment in the outermost coating layer, one or more selected from the group consisting of the above white pigments excluding calcium carbonate and kaolin. Contains. In the outermost coating layer, the content mass ratio of calcium carbonate and kaolin is preferably calcium carbonate: kaolin = 40:60 to 20:80.

The cumulative frequency of the particle size of 2 μm or less in the volume-based particle size distribution of calcium carbonate is 90% by volume or more. As such calcium carbonate, heavy calcium carbonate is preferable.
In addition, the kaolin has a particle diameter (D50) of 4.5 μm or more and 7.0 μm with a cumulative frequency of 40% by volume or more and a cumulative frequency of 50% by volume in the volume-based particle size distribution. It is as follows. “The cumulative frequency of particle diameters of 5 μm or less in the volume-based particle size distribution is 40% by volume or more” means that the number of particles having a particle diameter of 5 μm or less increases. The upper limit of the "cumulative frequency of particle diameters of 5 μm or less in the volume-based particle size distribution" is determined by the relationship with D50. The cumulative frequency of kaolin having a particle size of 5 μm or less in a volume-based particle size distribution is preferably 65% by volume or less.

Kaolin is a clay mineral whose main component is hydrous aluminum silicate mineral. Examples of such kaolin include conventionally known kaolins such as commercially available grade kaolins, structural kaolins and delaminated kaolins.

Calcium carbonate with a particle size of 2 μm or less accumulating 90% by volume or more in the volume-based particle size distribution, and a cumulative frequency of 40% by volume or more with a particle size of 5 μm or less in the volume-based particle size distribution Kaolin having a particle size (D50) of 50% by volume of 4.5 μm or more and 7.0 μm or less can be obtained from commercially available calcium carbonate and kaolin having a relatively large particle size by dry pulverization and / or wet pulverization and sizing. Obtainable.

The particle size distribution of calcium carbonate and the particle size distribution of kaolin can be obtained from the state of the coated paper. For the particle size distribution of each white pigment, for example, an electron microscope photograph of the surface of the coating paper for printing is taken using a scanning electron microscope with an element analysis function such as an energy dispersion type X-ray spectroscope, and the photographed particles are taken. It can be obtained by calculating the particle size by regarding it as a spherical shape having an approximate area and measuring the particle size for each of 100 particles existing in the captured image. Cumulative frequency with a particle size of 2 μm or less based on the particle size distribution obtained using particle image analysis software from particle size data measured from 100 particles with the vertical axis representing frequency (%) and the horizontal axis representing particle size (μm). , The cumulative frequency of the particle diameter of 5 μm or less, and the particle diameter (D50) at which the cumulative frequency is 50% by volume can be calculated.

The particle size distribution of calcium carbonate and the particle size distribution of kaolin can also be obtained by measurement using a laser diffraction / scattering method or a dynamic light scattering method. In that case, the particle size distribution is a particle size distribution based on the volume measured by a laser diffraction / scattering particle size analyzer. From the obtained particle size distribution, it is possible to calculate the cumulative frequency of the particle diameter of 2 μm or less, the cumulative frequency of the particle diameter of 5 μm or less, and the particle diameter (D50) at which the cumulative frequency is 50% by volume. As an apparatus, for example, a laser diffraction / scattering type particle size distribution measuring instrument Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd. can be mentioned.

The binder is a water-dispersible binder and a water-soluble binder conventionally known in the field of coated paper. Examples of dispersible binders include conjugated diene copolymers such as styrene-butadiene copolymers and acrylonitrile-butadiene copolymers, acrylate or methacrylic acid ester polymers or methyl methacrylate-butadiene copolymers. Carboxylyl of acrylic copolymers, vinyl copolymers such as ethylene-vinyl acetate copolymers, vinyl chloride-vinyl acetate copolymers, polyurethane resins, alkyd resins, unsaturated polyester resins, or various copolymers thereof. Examples thereof include a functional group-modified copolymer using a functional group-containing monomer such as a group, and a heat-curable synthetic resin such as a melamine resin and a urea resin. Examples of water-soluble binders include starch derivatives such as starch, oxidized starch, etherified starch, and phosphate esterified starch, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose, and polyvinyl alcohols such as polyvinyl alcohol or silanol-modified polyvinyl alcohol. Derivatives, casein and gelatin or their modifications, soybean protein, purulan, arabic rubber, Karaya rubber, natural polymer resins such as albumin or derivatives thereof, vinyl polymers such as sodium polyacrylate, sodium alginate, maleic anhydride or the like. Examples thereof include copolymers. The binder of the outermost coating layer is one or more selected from the group consisting of the water-dispersible binder and the water-soluble binder. The binder of the outermost coating layer is preferably a styrene-butadiene copolymer, starch or starch derivative.
The content of the binder in the outermost coating layer is preferably 10 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the white pigment in the outermost coating layer.

In addition to the white pigment and the binder, the outermost coating layer can further contain various additives conventionally known in the field of coated paper, if necessary. Examples of additives include thickeners, fluidity improvers, defoamers, foaming agents, lubricants, penetrants, color pigments, color dyes, optical brighteners, UV absorbers, antioxidants, preservatives, etc. Examples thereof include antibacterial agents and printability improvers.

Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to these examples. Here, "parts by mass" and "% by mass" represent "parts by mass" and "% by mass" of the amount of dry solids or the amount of substantial components, respectively. The coating amount indicates the amount of dry solid content.

For each Example and each Comparative Example, a coated paper for printing was prepared by the following procedure.

<Base paper>
The paper charges were prepared according to the following contents.
LBKP (Drainage degree (CSF) 360 ml) 54 parts by mass NBKP (Drainage degree (CSF) 450 ml) 20 parts by mass BCTMP 26 parts by mass Calcium carbonate (light calcium carbonate) 9 parts by mass Talk 4 parts by mass Size agent (alkyl keten dimer) System) 0.15 parts by mass Cationic starch 1.2 parts by mass

<Coating layer coating liquid of the outermost coating layer>
The coating layer coating liquid was prepared according to the following contents.
Calcium carbonate (heavy calcium carbonate) Type and number of copies are listed in Table 1. Kaolin Types and number of copies are listed in Table 1. Styrene-butadiene copolymer 10 parts by mass Phosphoric acid esterified starch 10 parts by mass Lubricants 0.4 parts by mass Printability 0.5 parts by mass of improver The above contents were blended and mixed and dispersed with water to adjust the concentration to 49% by mass.

The volume-based particle size distribution of heavy calcium carbonate and kaolin was prepared by measurement using a laser diffraction / scattering type particle size distribution measuring device Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd. From the obtained particle size distribution, the cumulative frequency of the particle diameter of 2 μm or less, the cumulative frequency of the particle diameter of 5 μm, and the particle diameter (D50) at which the cumulative frequency is 50% by volume were calculated.

<Making finely coated paper>
The above paper material was made with a long net paper machine to obtain a base paper having a basis weight of 81 g / m ² . Then, using the film transfer coater equipped on the on-machine coater, apply the coating liquid of the outermost coating layer on both sides so that the coating amount is 4 g / m ² per side. It was dry. After drying, a coated paper for printing was obtained without calendar treatment.

The obtained coated paper for printing was evaluated for ink absorbability, ink transfer property, and spot-like defects according to the following procedure.

<Ink absorbency>
Using an offset printing machine (Diamond 3H-4 manufactured by Mitsubishi Heavy Industries, Ltd.), four-color printing was performed on one side of the coated paper for printing using a lithographic offset process ink. For printing, an image in which solid images of each color of 4 cm × 4 cm were randomly arranged was used. The printed matter after printing was sequentially stacked, 1000 sheets were stacked on a bar, and a 0.5 kg or 2 kg iron plate was further laminated on the rod. Twenty-four hours after stacking the ink, the ink set-off state was visually observed and evaluated according to the following criteria.
In the present invention, it is assumed that the coated paper for printing has good ink absorbency if it is evaluated as A or B.
A: No set-off is observed, which is good.
B: On a 2 kg iron plate, a slight set-off is observed, but it is generally good.
C: It is inferior to B above, and even a 0.5 kg iron plate shows a slight set-off.
Practical range.
D: Inferior to C above and set-off is observed, which is not practically acceptable.

<Ink transferability>
Using an offset printing machine (Diamond 3H-4 manufactured by Mitsubishi Heavy Industries, Ltd.), four-color printing was performed on one side of the coated paper for printing using a lithographic offset process ink. For printing, the repetition of the color chart diagram was used for the image. Twenty-four hours after printing, the color charts repeatedly printed were visually observed for color differences between the color charts and evaluated according to the following criteria.
In the present invention, it is assumed that the coated paper for printing has good ink transfer property if it is evaluated as A or B.
A: Good with no color difference.
B: There is a slight difference in color locally, but it is generally good.
C: Inferior to B above and a slight color difference is observed locally, but it is within a practical range.
D: Inferior to C above and a color difference is observed, which is not practically acceptable.

<Spotted defects>
Using an offset printing machine (Diamond 3H-4 manufactured by Mitsubishi Heavy Industries, Ltd.), four-color printing was performed on one side of the coated paper for printing using a lithographic offset process ink. For printing, an image in which solid images of each color of 4 cm × 4 cm were randomly arranged was used. The solid image part of the printed matter was visually observed with a magnifying glass and evaluated according to the following criteria.
In the present invention, it is assumed that the coated paper for printing suppresses the occurrence of speckled defects if it is evaluated as A, B or C.
A: No speckled defects were observed with a magnifying glass and visual inspection, which was good.
B: Only with a magnifying glass, there are some spot-like defects, but they are generally good.
C: Visually, a slight speckled defect is observed, but it is within a practical range.
D: Inferior to C above, defects are observed, and it is not practically acceptable.

The evaluation results are shown in Table 1.

From Table 1, it can be seen that Examples 1 to 7 corresponding to the present invention are coated papers for printing, which have good ink absorbency and ink transfer property, and suppress the occurrence of spot-like defects. On the other hand, Comparative Examples 1 to 5 which do not correspond to the configuration of the present invention can be found to be coated paper for printing which cannot satisfy at least one of the defects of ink absorbency, ink transferability and spots.

Claims (1)

A base paper containing pulp and a filler and a coating layer having one or more layers on at least one side of the base paper, and the outermost coating layer located on the outermost side of the base paper in the coating layer The cumulative frequency of the white pigment containing a white pigment and a binder and having a particle size of 2 μm or less in a volume-based particle size distribution is 90% by volume or more and a cumulative frequency of a particle size of 5 μm or less in a volume-based particle size distribution. The total number of coating layers containing at least kaolin having a particle size (D50) of 40% by volume or more and a cumulative frequency of 50% by volume in a volume-based particle size distribution of 4.5 μm or more and 7.0 μm or less, and including the outermost coating layer. A coated paper for printing with a coating amount of 2.5 g / m ² or more and 4 g / m ² or less per side.