JP2006083474A - Sheet coated with pigment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet coated with a pigment effectively suppressing the occurrence of minute uncoated parts produced during high-speed coating in a curtain coater and having excellent white paper quality and printing quality. <P>SOLUTION: The sheet coated with the pigment has at least one undercoating layer. In the sheet coated with the pigment, the topmost layer is formed by a curtain coating method using a coating liquid having ≤40 mN/m static surface tension. The pigment in the undercoating layer in contact with the topmost layer is a pigment satisfying specific conditions and ≥90 mass% of the whole pigment in the undercoating layer is the pigment having ≤3 μm average particle diameter. The pigment satisfies the following conditions as the undercoating layer. Conditions: the undercoating layer in contact with the topmost layer has 10-1,000 protruding parts based on 1 mm<SP>2</SP>and the average height h of the protruding parts is 0.1d≤h≤0.8d based on the thickness d of the topmost layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pigment coated sheet that is excellent in white paper quality and printing quality, and relates to a pigment coated sheet that is efficiently produced by effectively suppressing the occurrence of coating defects in a curtain coating method. is there.

  Various methods are known as a coating method of a printing pigment coating sheet used for commercial printing, and a curtain coating method is one form. In the curtain coating method, a free-falling coating liquid film (hereinafter referred to as curtain film) having a uniform flow rate and film thickness in the coating width direction is dropped onto the coating substrate, and the entire amount is transferred to the substrate. Compared with the blade, rod, and roll coating methods that are often used as a method for manufacturing pigment coated sheets, the paint composition does not scrape off and there is almost no change in paint composition, resulting in less quality fluctuations.・ Because it is a lightweight type before the entire amount of paint transferred onto the base material is applied onto the base material, it is easy to manage the coating amount. Excellent coating amount uniformity in the width and flow directions. At the time, the physical contact with the substrate is only the coating solution, and it has many excellent features such as few paper breaks.

  When a coating layer is formed by the curtain coating method, the coating amount is uniform over the entire surface of the resulting pigment coating sheet, and the coating layer thickness is very low because the paint is not pushed into the substrate during coating. Is even. Therefore, for example, in the case of a pigment coated sheet obtained by the blade coating method, the ink absorption unevenness due to the coating layer thickness unevenness is eliminated, and this causes the occurrence of printing defects called eye unevenness / printing mottling. Is effectively suppressed.

  In order to obtain a pigment coating sheet, providing an undercoat layer after providing an undercoat layer, so-called double coating means that an inexpensive coating solution can be used for the undercoat layer, and the same coating amount can be divided into two times. It is possible to improve the white paper gloss and smoothness of the pigment coated sheet obtained by coating, and to provide a pigment coated sheet having different appearances and functions by providing different topcoat layers for the same undercoat layer In recent years, it has become a common technique. It is also possible to perform triple coating for higher quality and lower cost.

  However, at present, the curtain coating method is hardly used in the production of a pigment-coated sheet for general printing. This is because coating speeds exceeding 1000 m / min are becoming common with the recent increase in production speed, whereas curtain coating tends to cause coating defects during high-speed coating. It is thought to be caused.

  The causes of coating defects that occur in the curtain coating methods listed so far can be broadly classified into three. The first is that the free-falling curtain film breaks before it contacts the substrate to be coated, and it is an ellipse that is several cm or more in the width direction and several tens to several m or more in the flow direction on the substrate. This is a phenomenon that produces a relatively large uncoated part with a shape close to the shape. This is because the static surface tension of the coating liquid measured by the Duneuil method or Wilhelmy plate method is 40 mN / It is widely known that by setting it to about m or less, it is possible to effectively suppress film breakage due to air movement in the vicinity of the curtain film and bubbles remaining in the paint. The second is due to a phenomenon called paddling, and a phenomenon in which an uncoated part appears in a unique striped pattern or a faint pattern ranging from a few millimeters to the entire width of coating, and the third is due to the case of paddling due to an air entrainment phenomenon. This is a phenomenon in which a similar pattern or locally a spindle-shaped uncoated portion with a size of several millimeters is generated. These phenomena occur even at a relatively slow coating speed of less than 1000 m / min, and various solutions have been proposed so far.

  On the other hand, with the increase in coating speed, it has become a problem that uncoated parts occur due to a fourth cause which has not been a problem so far. In curtain coating, when the curtain film comes into contact with the base material, the curtain film that has fallen freely in the vertical direction at several tens of meters / minute is several hundred m / minute to 1000 m / minute or more in the base material traveling direction. When the curtain film comes into contact with the substrate when the substrate unevenness is large, such as a paper substrate mainly composed of cellulose fibers having a diameter of several tens of μm as a main component, it is several to several hundred μm. This is the occurrence of a coating defect due to a new cause that breaks in size and leads to the generation of a fine uncoated part (hereinafter referred to as a fine uncoated part).

  Until now, various methods have been proposed to suppress coating defects in the curtain coating method. For example, when two or more coating layers are provided, a method of performing curtain coating on a smooth undercoat layer in which the smoothness of the undercoat layer in contact with the layer provided by the uppermost curtain coating is set to a specific value or less (For example, refer to Patent Document 1), a method of performing curtain coating on a smooth undercoat layer in which the coarse particles of the pigment in the undercoat layer are not more than a specific amount (see, for example, Patent Document 2), in a coating solution A method of adding a specific thickener to the ratio of the curtain film falling speed and the base material traveling speed within a specific range (see, for example, Patent Document 3), and the air accompanying the base material immediately before the curtain film falling point (For example, refer to Patent Document 4) and the like. However, when a smooth undercoat layer is provided, it is effective to suppress the occurrence of fine uncoated parts, but the free-falling coating liquid film that collides with the substrate rapidly As a result, excessive coating liquid accumulates in the vicinity of the dynamic contact line where the coating liquid curtain film that falls freely during high-speed coating contacts the running substrate. As a result, paddling occurs and coating defects occur. In the method of curtain coating on a smooth undercoat layer in which the coarse particles of the pigment in the undercoat layer have a specific amount or less, there is a problem that paddling occurs in the same manner as described above, and further adjustment of the pigment particles to be used. The method of performing the crushing process is illustrated and the production efficiency is inferior. In addition, in a method in which a specific thickener is added and the ratio of the curtain film falling speed and the base material traveling speed is within a specific range, the disclosed thickener has a high viscosity of the coating liquid or is not stretched. The elongation at the time is insufficient, and the curtain film breaks at the μm level due to the abrupt elongation when the curtain film comes into contact with the substrate, leading to generation of a fine uncoated portion. Furthermore, the method of removing the air entrained by the substrate immediately before the curtain film falling point is effective in suppressing the occurrence of coating defects due to air entrainment, but is effective in suppressing the occurrence of paddling and minute uncoated areas. Absent.

  The occurrence of minute uncoated portions hardly changes even when the amount of coating liquid applied on the substrate is changed, and there is a report that a smooth substrate may be used to suppress this (for example, Non-patent document 1). However, it has also been reported that coating defects due to the above-described paddling phenomenon occur when it is over-smoothed, and when using a base paper mainly composed of cellulose fibers with a diameter of several tens of μm, irregularities are specified. Since it is practically difficult to control the narrow area of the substrate, it is difficult to suppress the occurrence of fine uncoated parts only by controlling the unevenness of the base material, and the base material or base material provided with an undercoat layer is smooth. The problem is that the smoothness of the pigment coated sheet is reduced when the smoothness level of the base material or base material provided with an undercoat layer is lowered to avoid paddling. In addition, it is satisfactory as a method for efficiently producing pigment coated sheets with excellent printing quality by effectively suppressing the occurrence of coating defects in the curtain coating method. Law without further improvement in manufacturing technology has been desired.

Japanese Patent No. 3111106 Japanese Patent No. 3257720 JP-A-5-117996 JP 2002-192046 A Kazuaki Ito et al. “Examination of pigment-coated paper by high-speed curtain coating”, Abstracts of the 70th Paper Pulp Research Presentation, 130-133 (June 2003)

  The present invention provides a pigment coated sheet that effectively suppresses the occurrence of fine uncoated portions that occur during high-speed coating in a curtain coater, and is excellent in blank paper quality and printing quality.

In a pigment coated sheet in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one surface of a sheet-like substrate, it has at least one undercoat layer, and the uppermost layer is a static surface. The pigment of the undercoat layer formed by the curtain coating method using a coating liquid having a tension of 40 mN / m or less and in contact with the uppermost layer is a pigment satisfying at least one of the following A or B, 90% by mass or more of the pigment is a pigment having an average particle diameter of 3 μm or less, and C is satisfied as an undercoat layer.
A: A pigment having 90% by mass or more of particles having a particle size of 3.0 μm or less and 55% by mass or more of 1.0 μm or less.
B: Tabular grains having an average particle diameter of 3.0 μm or less and an aspect ratio a / b calculated from the major axis a and the thickness b of 10 to 1,000.
C: The undercoat layer in contact with the uppermost layer has 10 to 1000 convex portions per 1 mm ² , and the average height h of the convex portions is 0.1 d ≦ h ≦ with respect to the uppermost layer thickness d. An undercoat layer that is 0.8d.
In a pigment coated sheet in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one surface of a sheet-like substrate, it has at least one undercoat layer, and the uppermost layer is a static surface. The pigment of the undercoat layer formed by the curtain coating method using a coating liquid having a tension of 40 mN / m or less and in contact with the uppermost layer is a pigment satisfying at least one of the following A or B, 90% by mass or more of the pigment is a pigment having an average particle diameter of 3 μm or less, and C is satisfied as an undercoat layer.
A: A pigment having 90% by mass or more of particles having a particle size of 3.0 μm or less and 55% by mass or more of 1.0 μm or less.
B: Tabular grains having an average particle diameter of 3.0 μm or less and an aspect ratio a / b calculated from the major axis a and the thickness b of 10 to 1,000.
C: An undercoat layer containing 0.5 to 10% by mass of spherical particles having an average particle size of 2.0 to 25.0 μm in the total pigment in the undercoat layer.
As a method for providing an undercoat layer in contact with the uppermost layer, it is preferable to use a blade coating method.
The spherical particles are preferably spherical calcium carbonate.
Further, as the sheet for providing the undercoat layer in contact with the uppermost layer, it is preferable to use a sheet having a convex portion on the surface with spherical particles having an average particle diameter of 5.0 to 40.0 μm, and providing the undercoat layer. As the sheet, a sheet having a convex portion of spherical calcium carbonate on the surface is preferable. The spherical calcium carbonate is more preferably light calcium carbonate which is either calcite crystal or vaterite crystal.

  In order to achieve the above object, the present inventors have intensively studied the cause of problems in curtain coating. As a result, when a coating layer is formed by a curtain coating method after providing a specific undercoat layer, a blank paper is used. It has been found that pigment coated sheets with excellent quality and printing quality can be produced efficiently without the occurrence of coating defects.

The present inventors have at least one undercoat layer in a pigment coated sheet in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one surface of a sheet-like base material. The method of forming the upper layer is a curtain coating method using a coating liquid having a surface tension of 40 mN / m or less, and the undercoat layer in contact with the uppermost layer is A: the pigment in the coating layer is 90% by mass or more. The particles have a particle size of 3.0 μm or less, and 55% by mass or more is 1.0 μm or less. B: The pigment in the coating layer has an average particle size of 3.0 μm or less, and a major axis a and a thickness b. Is a tabular grain having an aspect ratio a / b of 10 to 1000, C: the undercoat layer in contact with the uppermost layer has 10 to 1000 convex portions per 1 mm ² , and The average height h of the convex part is the maximum height formed by curtain coating. Spherical particles having an average particle diameter of 2.0 to 25.0 μm with respect to the upper layer thickness d of 0.1d ≦ h ≦ 0.8d are 0.5 to 10% in the total pigment in the undercoat layer. The pigment of the undercoat layer that is in contact with the uppermost layer is a pigment that satisfies at least one of the following A or B with respect to the four conditions of the undercoat layer containing mass%. It has been found that a pigment coated sheet having a particle size of 3 μm or less and satisfying C or D as an undercoat layer can efficiently produce a pigment coated sheet excellent in white paper quality and print quality. When tabular grains and other grains are used in combination, it is sufficient that tabular grains satisfy the conditions of A or / and B, and grains other than tabular grains satisfy the conditions of A.

  In addition, about the average particle diameter of a pigment, it disperse | distributed with the mixer so that a pigment might become 1% in a 0.1% Nankarin solution, and ultrasonic dispersion was performed for 30 minutes after that. This sample solution was measured with a SediGraph 5100 manufactured by Micromeritics, and the cumulative 50% weight diameter was defined as the average particle diameter of the particles, and the particle diameter ratios of 3.0 μm or less and 1.0 μm or less were also measured.

  The aspect ratio of the tabular grains was determined based on the result of preparing a coating layer containing only tabular grains and observing the major axis a and the thickness b with an electron microscope.

  In pigment-coated paper, it is widely known that by providing an undercoat layer, the smoothness of the coated paper is improved and the quality of blank paper and printing quality are improved. Above all, the coating layer surface provided by blade coating is very different from the pigment coating sheet obtained by other coating methods such as roll coating method and air knife coating method using the same raw materials. Smooth finish. For this reason, when the undercoat layer is provided after the undercoat layer is provided by the blade coating method, the resulting pigment-coated sheet is excellent in white paper gloss and smoothness. In order to improve the glossiness and smoothness of blank paper, it is only necessary to improve the smoothness of the undercoat layer. However, when the overcoat layer is provided by the blade coating method, streaky coating defects called streaks are present. Since it is produced and inferior in production efficiency, there is a limit to smoothing. When an overcoat layer is provided by the curtain coating method, there is an advantage that a coating defect called streak does not occur even if the smoothness of the undercoat layer is very excellent, but as described above, a coating defect called paddling occurs. To do. In order to avoid this, it is necessary to lower the smoothness of the undercoat layer. In this case, however, the glossiness and smoothness of the blank paper of the pigment-coated sheet obtained after the overcoat layer is also reduced.

  The pigment coating sheet according to the present invention is provided with an undercoat layer to smooth the substrate, and preferably uses a blade coating method that can obtain the smoothest coating layer, but after providing the topcoat coating layer In order to improve the white paper gloss and smoothness of the obtained pigment coated sheet, as the pigment in the undercoat layer in contact with the uppermost layer, the pigment in the coated layer is tabular particles, and the average particle size is 3.0 μm or less And the aspect ratio a / b calculated with respect to the major axis a and the thickness b is 10 to 1000, and / or the pigment in the coating layer is other than tabular grains, and 90% by mass or more of grains Is a pigment having a particle diameter of 3.0 μm or less, 55% by weight or more being 1.0 μm or less, and 90% by weight or more being a pigment having an average particle diameter of 3 μm or less in all pigments of the undercoat layer. It is.

However, under these conditions, although smoothness is excellent, coating defects due to paddling occur during curtain coating to provide the uppermost layer, and in order to avoid this, accumulation of excessive coating liquid in the dynamic contact line In order to prevent this, it is necessary to have 10 to 1000 convex portions per mm ^{2 on the} surface of the coating layer after undercoating. Furthermore, in order to prevent the smoothness from being lowered after the uppermost layer is provided, the average height h of the convex portions is 0.1d ≦ h ≦ 0 with respect to the uppermost layer thickness d formed by curtain coating. .8d is required. In addition, in order to form the curtain film stably, it is also necessary to set the static surface tension of the coating liquid to 40 mN / m or less, which is measured by the Duneuling method or the Wilhelmy plate method. is there.

  The pigment coated sheet obtained by the present invention has an effect that, when the curtain film comes into contact with the base material, the projections present on the surface of the undercoat layer in contact with the uppermost layer pull the curtain film in the traveling direction of the base material. Padding caused by accumulation of excessive coating solution in the contact line can be effectively prevented, and by providing an overcoat layer, the convex portion is buried in the overcoat layer, and on the convex portion. Since the coating solution is smoothed by leveling, the finally obtained pigment coated sheet is excellent in smoothness. When spherical particles are used as a method for forming the convex portion, it is preferable because the coating layer smoothing effect by leveling of the coating liquid after curtain coating is excellent.

  When the average particle size of the pigment exceeds 3.0% by mass in all the pigments in the undercoat layer in contact with the uppermost layer, the smoothness of the resulting pigment coated sheet is undesirably lowered. Further, among all the pigments in the undercoat layer, 90% by mass or more satisfies the condition that the pigment has an average particle size of 3 μm or less, and the pigment in the undercoat layer in contact with the uppermost layer has an average particle size of 3.0 μm or less, And when it contains the tabular grain whose aspect ratio a / b calculated with respect to the major axis a and the thickness b is 10 to 1000, as a pigment, 90 mass% or more has a particle diameter of 3.0 μm or less, and Even if the condition that 55% by mass or more is 1.0 μm or less is not satisfied, the smoothness of the resulting coated sheet is excellent, but the average particle diameter exceeds 3.0 μm, or the aspect ratio is 1000 In the case of tabular grains exceeding the above, even if the orientation of the tabular grains present on the coated paper surface is slightly reduced, the smoothness is greatly reduced, and thus the smoothness of the resulting pigment coated sheet tends to decrease. Not good . Further, as a pigment in the undercoat layer in contact with the uppermost layer, in the case of tabular grains having an average particle diameter of 3.0 μm or less and an aspect ratio of less than 10, 90% by mass or more of the pigment has a particle diameter of 3.0 μm or less. And when the particle size distribution condition is not satisfied, even if it is a tabular grain having an average particle size of 3.0 μm or less. The smoothness of the surface of the undercoat layer is impaired, and the quality of the white paper such as the smoothness of the resulting coated paper is deteriorated.

When the number of protrusions on the undercoat layer in contact with the uppermost layer is less than 10 per 1 mm ² , the pulling effect of the curtain film by the protrusions is reduced, and the effect of preventing paddling is reduced. The smoothness of the pigment coated sheet obtained when the properties are too low is inferior. From the viewpoint of achieving both the effect of preventing paddling and the smoothness of the resulting pigment coated sheet, the number of convex portions on the undercoat layer in contact with the uppermost layer is more preferably 100 to 600 per mm ² .

  When the average height h of the convex portion in the undercoat layer in contact with the uppermost layer is less than 0.1 d with respect to the uppermost layer thickness d formed by curtain coating, it is difficult to obtain the effect of preventing paddling, while the other 0 If it exceeds .8d, the height of the convex portion may be too high, which may be inferior in the effect of preventing the occurrence of fine uncoated portions, and the convex portion may be observed even after the overcoat layer is provided. As a result, the smoothness of the resulting pigment coated sheet is lowered, and the thickness of the top coat layer on the convex portion is extremely thin, so that the printing quality is lowered.

  As a method for forming a convex portion in the undercoat layer in contact with the uppermost layer, spherical particles having an average particle size of 2.0 to 25.0 μm in the undercoat coating solution are contained in all pigments in the undercoat layer layer. This can be achieved by adding 0.5 to 10% by mass. It is more preferable that the spherical particles are spherical calcium carbonate because they have good compatibility with other raw materials and are inexpensive. Further, as the calcium carbonate spherical particles, light calcium carbonate is more preferable than heavy calcium carbonate because it can have higher sphericity. Furthermore, among the light calcium carbonates, calcite crystals and vaterite crystals are preferable, and the smoothness of the spherical particles surface is excellent because the smoothness of the surface of the spherical particles finally obtained is excellent. Spherical light calcium carbonate of vaterite crystals having excellent sphericity is more preferred.

  By the way, when the average particle size of the spherical particles contained in the undercoat coating layer contained for forming the convex portion is less than 2.0 μm, the convex portion is formed after the undercoat with a normal coating amount. On the other hand, if it exceeds 25.0 μm, some spherical particles are not coated even after the overcoating layer is provided, and the smoothness of the resulting pigment coated sheet is reduced, or the overcoating on the particles In addition to the extremely thin coating layer, the print quality may be reduced. In the blade coating method preferably used for forming the undercoat layer in contact with the uppermost layer in the present invention, the spherical particles are formed by the blade. It will be scraped off, making it difficult to contain the desired amount in the undercoat layer.

  Further, when the content is less than 0.5% by mass, the number of convex portions is small even when spherical particles having an average particle size of 2.0 to 25.0 μm are added, and the effect of preventing paddling is inferior, and the other is 10% by mass. If it exceeds 1, the smoothness of the pigment coated sheet obtained after providing the top coat layer may be lowered.

  If the average particle size is the same but the particle size distribution is wide, the fine particles have the same effect as other pigments in the coating layer, but the coarse particles cause problems such as reduced smoothness. there is a possibility. For this reason, the particle size distribution of the spherical particles in the undercoat coating layer contained for forming the convex portion is preferably 5% by mass or less, preferably the same proportion of particles exceeding twice the average particle size. Is 1% by mass or less, more preferably, the proportion of particles exceeding 1.5 times the average particle size is 5% by mass or less. In addition, from the viewpoint of the balance between coating suitability and coating defect prevention effect, the average particle size of the spherical particles contained in the undercoat coating layer in contact with the uppermost layer in order to form the convex portion is 5.0. -15.0 micrometers is more preferable.

  The spherical particles referred to in the present invention are organic or inorganic particles, and the ratio da / db between the maximum diameter da and the minimum diameter db of the particles is 1 ≦ da / db ≦ 1.6, preferably 1 ≦ da / db. ≦ 1.2, for example, true spheres and the like, shapes having irregularities on the true sphere, those satisfying the above ratio with egg shape, and satisfying the above ratio with irregularities on the surface Say things.

Moreover, as a sheet before providing the undercoat coating layer in contact with the uppermost layer, it is also possible to use a sheet having a convex portion of spherical particles on the surface in advance, and in this case, an average particle size of 5.0 to 40 An undercoat coating layer in contact with the uppermost layer is provided on the convex portion formed by spherical particles having a thickness of 0.0 μm, and as a result, 10 to 1000 per 1 mm ^{2 on the} surface of the coating layer after the undercoat in contact with the uppermost layer The average height h of the convex portions is 0.1d ≦ h ≦ 0.8d with respect to the thickness d of the topcoat layer coating layer formed by curtain coating. Thus, the desired result of the present invention can be obtained. It is preferable to use a sheet having a convex portion of spherical calcium carbonate on the surface as the sheet.

  In both cases where spherical particles are contained in the undercoat coating layer in contact with the uppermost layer, and when the undercoat coating layer in contact with the uppermost layer is applied to a sheet having a convex portion on the surface in advance, It is preferable that the particles are spherical calcium carbonate because of good affinity with other raw materials, and it is further preferable that the spherical calcium carbonate is light calcium carbonate which is either calcite crystal or vaterite crystal. Since the smoothness of the surface of the spherical particles is excellent in the smoothness of the coating sheet finally obtained, spherical light calcium carbonate of vaterite crystals having excellent smoothness and sphericity of the surface of the spherical particles is preferable.

  The convex portions on the undercoat layer formed in this way can be used to adjust the pigment particle size used in the undercoat layer without the need for crushing treatment, etc. When compared with, spherical particles with a specific particle size can be used for the undercoat layer, which can reduce the variation in height of the convex portion very effectively, and in addition, the height distribution of the convex portion is in contact with the uppermost layer Because it can be adjusted arbitrarily by the above, paddling can be effectively prevented when the overcoat layer is provided by curtain coating, and it occurs due to large unevenness like a paper base material mainly composed of cellulose fibers. Further, it is possible to effectively prevent the occurrence of a minute uncoated portion due to the breakage of the curtain film on the order of μm.

  In curtain coating, there is a concern about the occurrence of coating defects due to air entrainment as the coating speed increases, but in the present invention, various air entrainment suppression devices that have been proposed so far can be used. A method of placing the entrained air shut-off jig in the shape of a roll, blade, etc. in contact with the substrate that is running, or keeping it at a distance of several millimeters or less, and placing it immediately before the dynamic contact line, counter air or decompression device For example, a method of blocking air and a method of replacing entrained air with water vapor can be used.

  As the spherical particles used in the present invention, both inorganic and organic spherical particles can be used. Examples of inorganic particles include light calcium carbonate, magnesium carbonate, solid or hollow glass particles, silica beads, and spherical fine powder silica aggregates. The organic particles are solid, hollow, and through-hole polystyrene resins, styrene-acrylic copolymer resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins, benzoguanamine resins. Examples thereof include resins. One or more kinds of inorganic particles and organic particles are appropriately selected and used as necessary.

  The base material is not particularly limited. A paper base material mainly composed of cellulose fibers, a synthetic paper containing polypropylene or the like and / or containing fine bubbles, a corona treatment on the surface, etc. A polyolefin-based film with improved fixing property can be used.

  The pulp forming the paper substrate is not particularly limited in terms of the production method and type, etc. Chemical pulp such as KP, SP, mechanical pulp such as SGP, RGP, BCTMP, CTMP, ECF pulp, TCF pulp, etc. Waste paper pulp such as chlorine-free pulp, deinked pulp, non-wood pulp such as kenaf, bagasse, bamboo, straw, hemp, etc., organic synthetic fibers such as polyamide fiber, polyester fiber, polynosic fiber, and glass fiber Inorganic fibers such as ceramic fibers and carbon fibers can also be used.

  Moreover, a filler can be mix | blended with a paper base material as needed. The filler in this case is not particularly limited, but various pigments generally used for fine paper, such as kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, zinc oxide, alumina, Mineral pigments such as magnesium carbonate, magnesium oxide, silica, white carbon, bentonite, zeolite, sericite, smectite, polystyrene resin, urea resin, melamine resin, acrylic resin, vinylidene chloride resin and their dense materials Examples thereof include organic pigments that are actual, fine hollow, and through-hole type particles.

  In addition to pulp fibers and fillers, various anionic, nonionic, cationic or amphoteric yield improvers, freeness improvers, paper strength enhancers, fixings are used in the stock. Various papermaking internal additives such as an additive and an internal sizing agent can be appropriately selected and used as necessary. Furthermore, internal additives for papermaking such as dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be appropriately added depending on the use of the paper.

  There is no particular limitation on the paper-making method of the paper base material. For example, an acidic paper-making method having a paper-making pH of around 4.5, and a neutral sizing agent and / or an alkaline filler such as calcium carbonate as a main component. It can be applied to all papermaking methods such as a weakly acidic pH of about 6 to a weakly alkaline neutral papermaking method of about 9 in papermaking. The paper machine can also be a long paper machine, a twin wire paper machine, a round paper machine, Commonly used paper machines such as inclined wire paper machines can be used as appropriate.

  As the pigment in the coating layer used in the pigment coated sheet of the present invention, in addition to the pigment preferably used in the present invention, a pigment generally used so as not to impair the desired effect of the present invention can be used. For example, heavy calcium carbonate, light calcium carbonate, kaolin, calcined kaolin, structural kaolin, deramikaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, magnesium aluminosilicate Mineral pigments such as calcium silicate, white carbon, bentonite, zeolite, sericite, smectite, polystyrene resin, styrene-acrylic copolymer resin, urea resin, melamine resin, acrylic resin, vinylidene chloride resin , Solid type such as benzoguanamine resin, Null type, or it is possible to use also organic pigments such as through-hole type resin, one or more kinds among these are appropriately selected and used.

  As the adhesive, a water-soluble and / or water-dispersible polymer compound can be used. For example, cationic starch, amphoteric starch, oxidized starch, enzyme-modified starch, thermochemically-modified starch, esterified starch, and etherified starch. Starches such as carboxymethylcellulose, hydroxyethylcellulose, etc., natural or semi-synthetic polymer compounds such as gelatin, casein, soybean protein, natural rubber, polydienes such as polyvinyl alcohol, isoprene, neoprene, polybutadiene, polybutene, poly Polyalkenes such as isobutylene, polypropylene, and polyethylene, vinyl halides, vinyl acetate, styrene, (meth) acrylic acid, (meth) acrylic acid esters, (meth) acrylamide, methyl vinyl ether and other vinyl polymers and copolymers, Styling -Synthetic polymer latex such as butadiene-based, methyl methacrylate-butadiene-based synthetic rubber latex, polyurethane-based resin, polyester-based resin, polyamide-based resin, olefin-maleic anhydride-based resin, melamine-based resin, etc. One or more types can be appropriately selected from the above according to the purpose.

  In the coating liquid used in the present invention, in addition to the pigments and adhesives described above, various auxiliary agents such as surfactants, pH adjusters, viscosity adjusters, water retention agents, softeners, gloss imparting agents, waxes, Dispersant, flow modifier, antistatic agent, stabilizer, antistatic agent, cross-linking agent, sizing agent, fluorescent brightener, colorant, ultraviolet absorber, antifoaming agent, water resistant agent, plasticizer, preservative Perfume and the like can be appropriately used as necessary so as not to lose the desired effect of the present invention.

The coating amount after drying of the coating layer of the present invention is not particularly limited, but the coating amount of the undercoat layer is about ² to ²⁰ g / m2, and the coating amount of the topcoat layer is 1 ˜20 g / m ² , and the total coating amount of the undercoat layer and the overcoat layer is generally 3 to 40 g / m ² , preferably 4 to 25 g / m ² with respect to one side of the paper substrate. . When the coating amount is less than 3 g / m ² , the effect of forming the coating layer on the base paper is difficult to appear. On the other hand, when it exceeds 40 g / m ² , rapid drying is required during high-speed coating, resulting in binder migration. This increases the possibility of occurrence of printing troubles such as motoring and a decrease in printing strength, so that the coating amount within the range specified above is preferable.

  The drying method for the coating layer is not particularly limited, and commonly used drying methods such as an air dryer, a cylinder dryer, and an IR dryer can be used.

  As the moisture of the pigment coated sheet, when a paper substrate is used, a coating layer is provided on the paper substrate, and after a normal drying process, or after being smoothed in a surface treatment process or the like as necessary The water content is adjusted to 3 to 10%, preferably about 4 to 8%.

  The smoothing process is performed on-machine or off-machine using a normal smoothing device such as a super calender, gloss calender, or soft calender. The number, heating, etc. are also adjusted as appropriate according to a normal smoothing apparatus.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these ranges. In the examples, “parts” and “%” indicate “parts by mass (solid component)” and “mass%” unless otherwise specified.

Example 1
・ Creation of sheet-like base material 95 parts of LBKP (freeness (CSF) = 400 ml), 5 parts of NBKP (freeness (CSF) = 410 ml), 7 parts of light calcium carbonate (PC: made of calcium Shiraishi) with ash content And using a paper stock to which 1.5 parts of starch per 100 parts of pulp, 0.1 part of alkenyl succinic anhydride, and 0.6 part of sulfuric acid band were added, During the paper making process, the starch is coated and dried with a size press machine so that the dry weight per side is 1 g / m ^2, and the Oken type smoothness is 35 seconds with a machine calendar. Was smoothed to obtain a sheet-like substrate having a basis weight of 67 g / m ² .

・ Preparation of undercoat coating solution FMT-90 (component; heavy calcium carbonate, particle size 3.0 μm or less, 97% by mass, particle size 1.0 μm or less, 64% by mass, manufactured by Pfematech Co., Ltd.) 9 parts in diameter of spherical crosslinked acrylic particles (trade name: MR-10G, manufactured by Soken Chemical Co., Ltd.), 10 parts of starch (trade name; Ace B, manufactured by Oji Cornstarch Co., Ltd.), styrene-butadiene copolymer latex (trade name) 0695 (manufactured by JSR Co.) was added and stirred, and water was further added to prepare an undercoat coating solution having a solid concentration of 64%.

・ Preparation of Topcoat Coating Solution To 90 parts of Milagros 91 (component: Kaolin, Engelhard), 0.1 part of water and dispersant (trade name: Aron A-9, manufactured by Toagosei Co., Ltd.) was added to disperse the core. The kaolin dispersion liquid with a solid content of 72% was obtained. To this dispersion, 10 parts of FMT-97 (component; heavy calcium carbonate, manufactured by Pimatec Co., Ltd.) having a solid content of 75% was added as a solid content to prepare a pigment slurry. For 100 parts of this pigment slurry, 4 parts of starch (trade name; Ace B, manufactured by Oji Cornstarch), 12 parts of styrene-butadiene copolymer latex (trade name: 0619, manufactured by JSR), surface tension adjuster (Product name: DAPRO W-77, manufactured by San Nopco) 0.3 part was added and stirred, and water was further added to prepare an overcoating liquid having a solid content concentration of 58%. The surface tension of this topcoat coating solution was 33 mN / m.

・ Preparation of pigment coating sheet Double-side coating and hot-air drying at 1000 m / min using a roll coater so that the dry coating weight per side is 10 g / m ² on a sheet-like substrate. The top coat coating solution is coated on both sides at 1000 m / min using a curtain coater so that the dry weight per side is 9 g / m ² and dried with hot air to obtain a pigment coated sheet having a basis weight of 105 g / m ^2. Obtained.

Example 2
In Example 1, a pigment coating sheet was obtained in the same manner as in Example 1 except that the coating method of the undercoat coating solution was changed from a roll coater to a blade coater.

Example 3
In Example 2, a pigment coated sheet was obtained in the same manner as in Example 2 except that the coating speed of the undercoat and topcoat coating liquids was 1300 m / min.

Example 4
In Example 3, spherical crosslinked acrylic particles (trade name; MR-10G, manufactured by Soken Chemical Co., Ltd.) in the undercoat coating solution were used as spherical light calcium carbonate (trade name; ED-X, Yonesho lime) having an average particle size of 10 μm. A pigment coated sheet was obtained in the same manner as in Example 3 except that the product was changed to (manufactured by Kogyo Co., Ltd.).

Example 5
In Example 4, 50 parts of FMT-90 in the undercoat coating solution was used, and 50 parts of contrast (component; kaolin, average particle size 0.6 μm, aspect ratio 25, manufactured by Engelhard) and a dispersant (product) Name: Aron A-9) A pigment coating sheet was obtained in the same manner as in Example 4 except that 0.05 part was separately dispersed and added as a kaolin slurry to prepare an undercoat coating solution.

Example 6
In Example 4, FMT-90 in the undercoat coating solution was changed to a contrast and 0.1 part of a dispersant (trade name; Aron A-9) was added to form a kaolin slurry, and then an undercoat coating solution was prepared. A pigment coated sheet was obtained in the same manner as in Example 4 except that.

Example 7
In Example 3, spherical crosslinked acrylic particles (trade name: MR-10G, manufactured by Soken Chemical Co., Ltd.) in the undercoat coating solution were replaced with spherical particles (trade name: MX-1500H, component: crosslinked acrylic particles) having an average particle size of 15 μm. , Manufactured by Soken Chemical Co., Ltd.), the number of added parts was changed from 2 parts to 3 parts, and the basis weight of the pigment coated sheet obtained with an undercoat coating amount of 15 g / m ² and a topcoat coating amount of 14 g / m ² A pigment coated sheet was obtained in the same manner as in Example 3 except that the amount was 125 g / m ² .

Example 8
-Preparation of sheet-like base material In Example 1, 15 parts of spherical light calcium carbonate (trade name; ED-XX, manufactured by Yonejo Lime Industry Co., Ltd.) with an average particle diameter of 20 μm was added to 100 parts of starch with a size press device. the starch coating solution was applied and dried such that the per side 1.5 g / m ² · machine and calender treatment, basis weight to obtain a sheet-like substrate of 68 g / m ^2.

-Preparation of pigment coated sheet 2 parts of spherical cross-linked acrylic particles (trade name: MR-10G, manufactured by Soken Chemical Co., Ltd.) having an average particle size of 9 [mu] m of the undercoat coating solution of Example 1 were added to 0 parts on the sheet-like substrate the undercoating coating solution, a double side coating using a roll coater so that the 10 g / m ² on one surface per dry weight at 1000 m / min, air drying, and then overcoating coating liquid per surface of example 1 Double-side coating and hot-air drying were performed at 1000 m / min using a curtain coater so that the dry weight was 9 g / m ² , thereby obtaining a pigment-coated sheet having a basis weight of 106 g / m ² .

Comparative Example 1
In Example 2, FMT-90 in the undercoat coating solution was changed to FMT-60 (component; heavy calcium carbonate, particle size 3.0 μm or less, 79% by mass, particle size 1.0 μm or less, 42% by mass, PMMA TECH CO., LTD. A pigment-coated sheet was obtained in the same manner as in Example 2 except that the product was changed to (manufactured).

Comparative Example 2
In Example 2, pigment coating was performed in the same manner as in Example 2 except that the number of added spherical crosslinked acrylic particles (trade name; MR-10G, manufactured by Soken Chemical Co., Ltd.) in the undercoat coating solution was changed from 2 parts to 0 parts. A sheet was obtained. Convex portions were not observed on the surface of the obtained undercoat layer, paddling occurred during application of the topcoat coating solution by a curtain coater, and the surface properties of the obtained pigment coated sheet were significantly lowered.

Comparative Example 3
In Example 2, pigment coating was performed in the same manner as in Example 2 except that the number of added spherical crosslinked acrylic particles (trade name; MR-10G, manufactured by Soken Chemical Co., Ltd.) in the undercoat coating solution was changed from 2 parts to 20 parts. A sheet was obtained.

Comparative Example 4
In Example 2, an attempt was made to obtain a pigment-coated sheet in the same manner as in Example 2 except that the number of added parts of the surface tension modifier Dapro W-77 was changed from 0.3 part to 0 part. A large coating defect occurred due to film breakage. At this time, the surface tension of the topcoat coating solution was 52 mN / m.

Comparative Example 5
In Example 4, pigment coating was performed in the same manner as in Example 4 except that ED-X was changed to different spherical particles (trade name: MR-60G, average particle size 60 μm, component: crosslinked acrylic particles, manufactured by Soken Chemical Co., Ltd.). A work sheet was obtained. On the surface of the obtained undercoat layer, almost no convex portions were observed, paddling occurred when the topcoat coating solution was applied by a curtain coater, and the surface properties of the resulting pigment coated sheet were significantly lowered.

  The pigment coated sheets obtained in the above Examples and Comparative Examples were passed through a pressure nip composed of a metal roll and an elastic roll under the same conditions to obtain each evaluation pigment coated sheet. The pigment coating sheet thus obtained was subjected to the following evaluation test, and the results obtained are shown in Table 1. In addition, the measuring method of average particle diameter and particle diameter distribution, the number of undercoat layer surface convex parts, the measuring method of undercoat layer surface convex part average height, and topcoat layer thickness were also described collectively.

-Average particle size and particle size distribution The pigment was dispersed in a 0.1% Nankaline solution so that the pigment would be 1%, followed by ultrasonic dispersion for 30 minutes. This sample solution was measured with SediGraph 5100 manufactured by Micromeritics, the cumulative 50% weight diameter was taken as the average particle diameter of the particles, and the particle diameter ratios of 3.0 μm and 1.0 μm or less were measured as necessary.

-Number of convex portions on the surface of the undercoat layer The surface of the coated paper 100 mm ² was observed with an electron microscope at an observation magnification of 100 times or 500 times, and the number of convex portions per 1 mm ² was collected.

-Undercoat layer surface convex part average height Using a white light interference microscope (Zygo NewView 200 type), the average height per 100 convex parts was determined.

-Topcoat layer thickness About the cross section of the obtained pigment coating sheet, it observed by the observation magnification 1000 times with the electron microscope, and measured the topcoat layer thickness.

-Evaluation of glossiness of blank paper TAPPI test method: In accordance with T480 om-92 (TAPPI Test Method T480 om-92), using a gloss meter (model: GM-26D, manufactured by Murakami Color Research Laboratory) It was measured.

-Evaluation of minute uncoated part The state of minute uncoated part occurrence of coated paper was observed with an electron microscope at an observation magnification of 100 times and evaluated according to the following criteria.
(Double-circle): There is no generation | occurrence | production of a fine uncoated part, and it is excellent.
○: A slight uncoated part is observed, but it is a level with no problem.
(Triangle | delta): The fine uncoated part has generate | occur | produced and it is a level which becomes a problem practically.
X: Many fine uncoated parts are generated, and this is a level that is a serious problem in practical use.

-Printing conditions of the pigment coating sheet It printed on the following conditions using the Mitsubishi Heavy Industries offset 4-color printing machine.
Environment: 20 ° C, 65% RH
Printing speed: 8000 sheets / minute Printing amount: 8000 sheets Drying condition: Adjusted to a paper surface temperature of 150 ° C. using a gas heater Powder: Silicone coated starch, particle size 25 μm

-Print finish The print smoothness and eye unevenness print finish of the offset printed matter obtained as described above were comprehensively evaluated visually. A result is shown by 10-step evaluation, and it shows that the finishing of a printed matter is so favorable that a score is high. As general printing paper, 8 or more points are required in the above evaluation.

Claims (7)

In a pigment coated sheet in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one surface of a sheet-like substrate, it has at least one undercoat layer, and the uppermost layer is a static surface. The pigment of the undercoat layer formed by the curtain coating method using a coating liquid having a tension of 40 mN / m or less and in contact with the uppermost layer is a pigment satisfying at least one of the following A or B, A pigment-coated sheet, wherein 90% by mass or more of the pigment is a pigment having an average particle size of 3 μm or less and satisfies C as an undercoat layer.
A: A pigment having 90% by mass or more of particles having a particle size of 3.0 μm or less and 55% by mass or more of 1.0 μm or less.
B: Tabular grains having an average particle diameter of 3.0 μm or less and an aspect ratio a / b calculated from the major axis a and the thickness b of 10 to 1,000.
C: The undercoat layer in contact with the uppermost layer has 10 to 1000 convex portions per 1 mm ² , and the average height h of the convex portions is 0.1 d ≦ h ≦ with respect to the uppermost layer thickness d. An undercoat layer that is 0.8d. In a pigment coated sheet in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one surface of a sheet-like substrate, it has at least one undercoat layer, and the uppermost layer is a static surface. The pigment of the undercoat layer formed by the curtain coating method using a coating liquid having a tension of 40 mN / m or less and in contact with the uppermost layer is a pigment satisfying at least one of the following A or B, A pigment-coated sheet, wherein 90% by mass or more of the pigment is a pigment having an average particle size of 3 μm or less and satisfies C as an undercoat layer.
A: A pigment having 90% by mass or more of particles having a particle size of 3.0 μm or less and 55% by mass or more of 1.0 μm or less.
B: Tabular grains having an average particle diameter of 3.0 μm or less and an aspect ratio a / b calculated from the major axis a and the thickness b of 10 to 1,000.
C: An undercoat layer containing 0.5 to 10% by mass of spherical particles having an average particle size of 2.0 to 25.0 μm in the total pigment in the undercoat layer.   The pigment coating sheet according to claim 1 or 2, wherein an undercoat layer in contact with the uppermost layer is provided by a blade coating method.   The pigment coating sheet according to claim 2, wherein the spherical particles are spherical calcium carbonate.   The pigment coating sheet according to claim 1 or 3, wherein the sheet provided with the undercoat layer in contact with the uppermost layer is a sheet having a convex portion on the surface made of spherical particles having an average particle diameter of 5.0 to 40.0 µm.   The pigment coated sheet according to claim 5, wherein the spherical particles are spherical calcium carbonate.   The pigment coated sheet according to claim 4 or 6, wherein the spherical calcium carbonate is light calcium carbonate which is either calcite crystal or vaterite crystal.