JP2006214055A - Coating sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated sheet without damaging quality such as sheet appearance and printability while having excellent whiteness and very high lightness. <P>SOLUTION: The coated sheet has one or more coated layers at least on one surface of a sheet-shaped base material. The coated layer contains ≥1.0 mass% polyvinyl alcohols and has ≥14% fluorescence intensity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coated sheet. More specifically, the present invention relates to a coated sheet that does not impair quality such as surface feel and printability even though the whiteness is extremely excellent and the brightness is very high. .

  Commercial printing represented by the four major systems of lithographic printing, letterpress printing, intaglio printing and stencil printing is widely used in the world. Its history is long and technically mature, but it continues to change technically due to changing demand. In recent years, a significant percentage of the printed material is color, and the consumer's eyes have become accustomed to color images. In order to produce a high-quality printed material among these, the whiteness of the sheet itself that becomes the substrate of the printed material must be high. This is because, due to the high whiteness, the color reproducibility of the printed matter is expressed at a high level in addition to human sensations that make it stand out and feel beautiful.

  The whiteness of the coated sheet depends greatly on the material used. Pulp mainly used for the sheet-like substrate largely depends on the degree of whiteness depending on the removal rate of the lignin component, simply speaking, the degree of bleaching. In recent years, as represented by ECF bleaching, environmentally friendly bleaching methods have appeared. For the coated sheet, the sheet-like base material is hidden in the coated layer, but the influence is considerably large. It is better to use a white pulp as much as possible. However, considering the production efficiency and economy, there is a limit to increasing the whiteness of the pulp.

  Of the pigments that are the main component of the coating layer, kaolin is often used because it is a very excellent pigment for improving white paper gloss and imparting printability, but it is basically yellowish. Whiteness can be improved by techniques such as magnetic separation and flotation (see “Coating Pigments and Paper Filling” on pages 113 to 114, published on January 20, 1989 by Uni Publishing Co., Ltd.) It does not reach the level of calcium carbonate or titanium dioxide. Titanium dioxide is extremely excellent in whiteness, but in addition to problems such as high unit price and reduced printing gloss, it absorbs ultraviolet light, so the effect of fluorescent whitening agent disappears, so it should be used as the main pigment. Is difficult. Light calcium carbonate, which is produced by chemically synthesizing in calcium carbonate, has a relatively high gloss like aragonite light calcium carbonate, but has a coating suitability such as streak and scratches. It is inferior and the coating layer strength tends to be low. On the other hand, heavy calcium carbonate, which is calcium carbonate finely divided by pulverization, has a low glossiness. If a large amount is blended, the gloss of the coated paper for printing is lowered.

  From the above situation, the current coated sheet has a yellowish finish due to the influence of lignin remaining in the pulp and kaolin used in the coating layer. To prevent this, add blue or red dye and control it to look white. However, the dye basically has a property of absorbing light, and even if the hue becomes white, the lightness is lowered. Usually, a brightening agent is added to compensate for this lightness decay. The fluorescent whitening agent appears to have increased brightness and whiteness in order to shift light having a wavelength outside the visible light region (in the ultraviolet region) to the visible light region.

  However, the more whitening the fluorescent brightening agent is, the more it becomes whiter. If it is added excessively due to the influence of impurities or the like, the green color will appear and the opposite effect will be obtained. The fluorescent whitening agent can increase its effect under the influence of a hydrophilic binder such as starch. Polyvinyl alcohol, in particular, greatly enhances the effect of the fluorescent agent, but has poor coating suitability and could not be added in a large amount.

In addition to such a general whitening technique, there are techniques for improving whiteness by various methods (for example, Patent Documents 1 to 3). However, any of the existing technologies has some limitations, and it has been impossible to produce a high-quality coated sheet with extremely excellent whiteness with the conventional technology.
JP 07-189189 A JP 2001-081692 A JP 2003-328295 A

  An object of the present invention is to obtain a coated sheet that has excellent whiteness and extremely high brightness, but does not impair quality such as surface feel and printability.

  As a result of intensive studies to solve the above problems, the present inventors have invented the following coated sheet.

  That is, in a coated sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate, the coating layer contains 1.0% by mass or more of polyvinyl alcohol, and the fluorescence intensity is 14% or more. It is a coating sheet characterized by being.

  In the present invention, 60% by mass or more of the pigment contained in the coating layer is preferably calcium carbonate.

  In the present invention, the calcium carbonate particles having a particle size of less than 2.0 μm are 95% by mass or more, the particles having a particle size of less than 1.0 μm are 75% by mass, and the particles having a particle size of less than 0.2 μm are 11% by mass or less. It is preferable that

  Moreover, in this invention, it is preferable that the whiteness of a coating sheet is 103% or more, and the brightness is 96% or more.

  Moreover, in this invention, it is preferable that the whiteness of the pulp used for the coating sheet is 88% or more.

  Moreover, in this invention, it is preferable that the amount of ash content of a sheet-like base material is 5 mass% or more.

  In addition, the present invention is characterized in that the coating sheet is a coating sheet for offset printing.

  Although the coated sheet of the present invention is extremely excellent in whiteness and extremely light, it is possible to obtain a coated sheet that does not impair quality such as surface feel and printability.

  Hereinafter, the coated sheet of the present invention will be described in detail.

  As a result of intensive studies on the technology for increasing the whiteness of the coated sheet, the present inventors have invented the following coated sheet.

  In order to increase the whiteness greatly, it is necessary to enhance the effect of the fluorescent brightener. The effect of the optical brightener can be increased by polyvinyl alcohol. When polyvinyl alcohol is added in an amount of 1.0% by mass or more based on the coating layer, the effect of the fluorescent brightening agent can be exhibited greatly. This is more effective as the amount of the fluorescent brightening agent is larger. When the fluorescent intensity is 14% or more, it is clearly whiter than a general coated sheet without adjusting the hue using a dye or the like. I can feel it.

  The general coating sheet here refers to commercially available A2 coated paper. Since there are various types of commercially available A2 coated paper, in the present invention, a new buoy mat made by Mitsubishi Paper Industries will be referred to in order to clarify the standard.

  The polyvinyl alcohol used in the present invention is not particularly related to the degree of saponification, the degree of polymerization, the presence or absence of a copolymerization monomer, and the presence or absence of chemical modification. In order to improve the effect of the optical brightener, a completely saponified polyvinyl alcohol is preferable. In order not to lower the coating suitability even when 1.0% by mass or more is added, the degree of polymerization is preferably 500 or less. Examples of such polyvinyl alcohol include NL04L manufactured by Nippon Synthetic Chemical Co., Ltd. and PVA-104A manufactured by Kuraray Co., Ltd. Of course, it is not limited to these.

  The fluorescent whitening agent used in the present invention is typically a sulfonic acid derivative system of aminostilbene, but any fluorescent whitening effect may be used. A fluorescent whitening agent of a type that has high purity and does not cause a decrease in whiteness even when added in a large amount is preferable. Furthermore, what strongly exhibits the whiteness improvement effect by polyvinyl alcohol is preferable. Examples of such types of fluorescent brighteners include Sun White CST manufactured by Sunrise Chemical Co., and Blancofer UWLiq manufactured by Bayer. Of course, it is not limited to these.

  The fluorescence intensity referred to in the present invention is a reflectance measured by using a C light source as an illumination light source with “SPECTRO COLOR METER MODEL PF-10” manufactured by Nippon Denshoku Industries Co., Ltd., and a 420 nm cut-off filter placed in the optical path (UVout). And the reflectance (UVin) when no filter is placed. For the measurement, a value obtained by superimposing the same paper so as to have a thickness of 250 μm or more is used. It is assumed that the fluorescence intensity measuring device is adjusted so that the relative ultraviolet light amount included in the illumination light matches CIE illuminant C, as per JIS P8148 Annex B (normative).

  As a pigment used for the coating layer, it is preferable to use as much calcium carbonate as possible. When 60% by mass or more of the pigment is calcium carbonate, the whiteness of the coated sheet is higher than when the calcium carbonate is not, and it starts to feel very white sensuously.

  However, simply increasing the proportion of calcium carbonate does not improve the quality of blank paper and printability. As for calcium carbonate, heavy calcium carbonate is better than light calcium carbonate in view of coating suitability, and it is preferable that particles of 2.0 μm or less exceed 95% by mass in comparison with heavy calcium carbonate. When such fine calcium carbonates are compared, it is better that the particle size distribution is uniform. In particular, heavy calcium carbonate having a particle size distribution in which particles of 2.0 μm or less are 95% by mass or more, particles of 1.0 μm or less are 75% by mass or more, and the ratio of particles of 0.2 μm or less is 11% by mass or less. When the coating layer is 60% by mass or more of the coating layer pigment, it is possible to obtain a coated sheet having not only excellent whiteness but also good white paper surface feeling and excellent printability.

  The blank surface feeling referred to here is uniformity that can be sensed when the coated sheet is viewed, and can be easily determined when the test sheet is viewed obliquely. The printability referred to here generally refers to the suitability for printing. In particular, the printability refers to the degree of ink drop on the printing surface. A coated sheet in which a general heavy calcium carbonate is used at a high ratio tends to enter the inside of the coated layer without ink remaining on the sheet surface. For this reason, there is a strong tendency for the ink concentration to be low (poor walling), low printing gloss, and rough surface, resulting in poor printability.

  This is because the pigment is fine, the coated surface is smooth and uniform, and the white paper feel is improved.In addition, the excessively fine pigment does not excessively block the voids in the coating layer, and the appropriate coating layer structure Can be guessed. Furthermore, since there are few pigments smaller than the wavelength of visible light, the concealing effect of the coating layer is enhanced, reducing the influence of light coming from the opposite side of the coating sheet and the light reflected from the base paper layer, and more It appears to be whiter and more visible.

  When these techniques are appropriately combined and the whiteness of the coated sheet is 103% and the lightness is 96% or more, the whiteness perceives pure whiteness that does not require hue adjustment with a dye. For this reason, it is preferable that the whiteness is 103% or more and the lightness is 96% or more because the whiteness is extremely superior to that of general coated paper.

As used herein, whiteness refers to whiteness defined by ISO 2470. Moreover, it is set as the value measured in the state where ultraviolet light enters. Lightness refers to the value of L ^* when measured using a C / 2 light source with “SPECTRO COLOR METER MODEL PF-10” manufactured by Nippon Denshoku Industries Co., Ltd. Both whiteness and brightness are measured by overlapping the same paper so that the thickness is 250 μm or more.

When the coating liquid made by such a design is applied to a sheet-like substrate, the substrate can be covered if the coating amount is 0.5 g / m ² or more. When the coating amount exceeds 20 g / m ² , there may be a problem of the strength of the coating layer. The coating amount is preferably in the range of 1.0 to 10.0 g / m ² because production efficiency, economy and quality are balanced.

  In addition to the technology for increasing the whiteness of the coating layer, the sheet-like substrate can be made whiter when the whiteness is increased. For this purpose, the whiteness of the pulp used for the sheet-like substrate is preferably 88% or more. In such a region, the apparent whiteness of the coated sheet is very high, and general coated paper appears dark. Even if the sheet-like substrate is made white other than the whiteness of the pulp, the influence on the whiteness of the coated sheet is slight. Since the influence of the coloring component (mainly lignin) contained in the pulp becomes very strong under the conditions covered with the coating layer, it is very important to whiten the pulp itself.

  Pulp whiteness as used herein refers to J.P. TAPPI No. Refers to the Hunter whiteness shown at 69. Various kinds of pulp are used in the sheet-like base material, and in the present invention, these average values are indicated. In addition, when a fluorescent brightening agent is included, it is desirable to measure under conditions that eliminate this influence as much as possible.

  The sheet-like substrate contains ash remaining after burning the sheet-like substrate, but this value is preferably 5% by mass or more. This is because the filler, which is the main component of ash, increases opacity and reduces the effect of light coming from the opposite side of the coated sheet, so the whiteness you feel when you look at a single coated sheet Because it goes up. The material used as the filler has high whiteness such as light calcium carbonate, heavy calcium carbonate, and titanium dioxide, but a filler is preferable. Titanium dioxide is particularly preferred because of its high concealing effect.

  The amount of ash here refers to that measured by the test method shown in JIS P8252.

  As the base material of the coated sheet used in the present invention, plant fibers such as wood pulp, cotton, hemp, bamboo, sugar cane, corn, kenaf, animal fibers such as wool and silk, cellulose regeneration such as rayon, cupra and lyocell Chemical fibers such as fibers, semi-synthetic fibers such as acetate, polyamide fibers, polyester fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polypropylene fibers, polyvinylidene chloride fibers, polyurethane fibers, glass fibers, metal fibers In addition, a sheet-like inorganic fiber such as carbon fiber or a resin film layer provided thereon is used.

  In the case of using a fiber sheet-like base material, as a manufacturing method for making each fiber into a sheet, a general paper making process, a wet method, a dry method, a chemical bond, a thermal bond, a spun bond, a spun lace, a water jet, a melt blow, One or more are appropriately selected from each process such as needle punching, stitch blowing, flash spinning, and tow opening.

  These fibers include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, titanium dioxide, aluminum hydroxide and other fillers, binders, sizing agents, fixing agents, retention agents, paper strength enhancers, etc. These various compounding agents are suitably blended according to each step and each material. Furthermore, a resin coat layer and a coating layer may be provided on these fiber sheets.

  Base materials include high quality paper, medium quality paper, color quality, book paper, cast paper, fine coated paper, lightweight coated paper, coated paper, art paper, medium coated paper, gravure paper, Indian paper, coated ivory, Uncoated ivory, art post, coated post, uncoated card, special board, coated ball, tracing paper, type paper, PPC paper, NIP paper, continuous slip paper, foam paper, copy paper, carbonless paper, thermal paper, Inkjet paper, thermal transfer paper, synthetic paper, and other paper and paperboard, non-woven fabric, or various resins, plastics, and metals formed into a film are also included.

  The substrate before coating may be subjected to various surface treatments and calendar treatments in order to obtain the required density, smoothness, and air permeability.

  In the present invention, the pigment that can be used when the coating layer is provided on the substrate is not particularly limited, and for example, purified natural such as various kaolins, talc, and heavy calcium carbonate (ground calcium carbonate). Mineral pigment, light calcium carbonate (synthetic calcium carbonate), composite synthetic pigment of calcium carbonate and other hydrophilic organic compounds, satin white, lithopone, titanium dioxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, calcined There are kaolin, hollow organic pigments, dense organic pigments, plastic pigments, binder pigments, plastic beads, microcapsules and the like. Of course, it is not limited to these.

  Binders used in the coating layer include starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch and those obtained by flash drying. Cold water soluble starch, natural polysaccharides such as dextrin, mannan, chitosan, arabinogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, hydroxyethylcellulose, oligomers thereof, and modified products thereof.

  Furthermore, natural polymers such as casein, gelatin, soybean protein, and collagen, and modified products thereof, and synthetic polymers and oligomers such as polylactic acid and peptides can be mentioned.

  In addition, copolymer latex such as styrene butadiene, acrylic, polyvinyl acetate, ethylene vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyacrylamide, urea, melamine / formalin resin, polyethylene Examples thereof include water-soluble synthetic compounds such as imine and polyamide polyamine / epichlorohydrin. One or more of these can be used. In addition, the use of a known natural or synthetic organic compound is not particularly limited.

  In addition, as a thickener used in the coating solution, water-soluble polymers such as carboxymethylcellulose, sodium alginate, methylcellulose, hydroxyethylcellulose, casein, and sodium polyacrylate, polyacrylate, styrene maleic anhydride copolymer And synthetic polymers such as silicates and inorganic polymers such as silicates.

  In addition, various auxiliary agents that are usually used such as a dispersant, an antifoaming agent, a water-proofing agent, and a coloring agent, and those obtained by cationizing these auxiliary agents are suitably used as necessary.

  In the present invention, the method for coating the coating layer is not particularly limited, and various film transfer coaters such as size press, gate roll, shim sizer, air knife coater, rod coater, blade coater, direct fountain coater, Each system such as a spray coater or cast coater is appropriately used.

  Furthermore, in order to obtain the density, smoothness, air permeability, and appearance required for coated and dried coated sheets in a series of operations, various finishing processes such as calendering are performed as necessary. The

  Examples of the present invention will be described below, but the present invention is not limited to these examples. Further, “parts” shown in the examples represent parts by mass unless otherwise specified.

(Example 1) to (Example 13) and (Comparative Example 1) to (Comparative Example 2)
According to the following content, the coating sheet of Examples 1-13 and Comparative Examples 1-2 was produced.

<Sheet substrate>
LBKP (freeness 400 mlcsf) 70 parts NBKP (freeness 480 mlcsf) 30 parts light calcium carbonate Commercially available cationized starch shown in Table 1 as ash content in sheet-like substrate 1.0 part Commercially available cationic polyacrylamide yield improver 0. 03 parts pulp and internal chemicals were prepared with the above composition, and a base paper was made with a basis weight of 80.6 g / m ² . The whiteness of the pulp used in each example and comparative example is as shown in Table 1 for both LBKP and NBKP.

A 0.80 g / m ² double-sided oxidized starch was adhered to the sheet-like substrate by a size press to obtain a sheet-like base paper for coating.

<Coating solution>
Heavy calcium carbonate (described as “heavy cal” in the table) and kaolin clay were used as the coating liquid pigments. The blending ratio of heavy calcium carbonate is shown in Table 1. All pigments other than heavy calcium carbonate are kaolin clay. The mass% values shown in Table 1 are values in the pigment component and are not calculated including the binders and auxiliaries shown below. The heavy calcium carbonate of Example 7 is “FMT-100” manufactured by Pfematec, the heavy calcium carbonate of Example 8 is “Hydra Curve 60” of Shiroishi Calcium, and the heavy calcium carbonate of Example 9 is Hyogo Clay. “WH-90” in the other examples and comparative heavy calcium carbonate is “OP-2A” manufactured by Phymatech. Kaolin Clay is “Kao Gross” by Shiraishi Calcium. Polyvinyl alcohol (described as PVA in the table) is shown in Table 1 in terms of mass% with respect to the entire coating layer. The polyvinyl alcohol used here is NL-04L manufactured by Nippon Synthetic Chemical. Other blending components are shown below in parts per 100 parts of pigment. The fluorescent whitening agent was Sun White CST manufactured by Sunrise Chemical Co., and the actual measurement was different, but the solid content was 50% by mass for the convenience of the experiment.
Commercially available fluorescent brightener 3 parts Commercially available styrene butadiene latex binder (average particle size 100 nm, gel content 40% by mass, Tg 5 ° C.) 10 parts Commercially available calcium stearate 0.6 parts Commercially available carboxymethylcellulose thickener (CMC) 0. Adjust to pH 9.6 with 1 part sodium hydroxide

The above coating solution was coated on both surfaces under the same conditions using a fountain / blade coater at 62% by mass and an operation speed of 1000 m / min. The coating amount is 10 g / m ² on one side. After coating, a super calender treatment was performed on each of the front and back nips at two nips at a linear pressure of 80 kN / m and a temperature of 20 ° C.

  About the coating sheet obtained by the said Examples 1-13 and Comparative Examples 1-2, it measured with the following measuring method and put up the evaluation result in Table 1.

1. Whiteness The whiteness was measured using “SPECTRO COLOR METER MODEL PF-10” manufactured by Nippon Denshoku Industries Co., Ltd. using a C / 2 light source. Ultraviolet light was measured “in”. The measurement sheet was measured by being overlapped so as to have a thickness of 250 μm or more.

2. Lightness The value of L ^* when measured using a C / 2 light source with “SPECTRO COLOR METER MODEL PF-10” manufactured by Nippon Denshoku Industries Co., Ltd. was used. For the measurement, the test sheets were overlapped so as to have a thickness of 250 μm or more.

3. Blank paper feeling The evaluation was made in five stages according to the following criteria.
A: Unevenness is hardly confirmed even when the sample is observed with oblique light.
○: When the sample is observed obliquely, there is unevenness depending on the place.
○ Δ: There is some unevenness when the sample is observed under oblique light.
Δ: Unevenness can be clearly confirmed when the sample is observed obliquely.
X: Unevenness can be confirmed even when the sample is viewed vertically.

4). Printability Using a RI printing tester, “FLINT INK RED” manufactured by Kuroda Japan Co., Ltd. was transferred onto the coated sheet in an excessive amount (0.7 ml or more), and after 2 minutes, excess ink was wiped off with gauze. At the time of ink transfer, a new buoy mat <110> manufactured by Mitsubishi Paper Industries Co., Ltd. was simultaneously transferred as a comparison. The degree of ink drop on the coated paper surface was judged visually according to the following criteria.
A: The white part is equal to or less than the comparison.
○: There are slightly more white parts than the comparison.
○ △: There are more white parts than comparison.
(Triangle | delta): There are much more white parts than a comparison.
X: The printed surface is scratched.

5. Sensory whiteness New buoy mat <110> manufactured by Mitsubishi Paper Industries Co., Ltd. was used as a comparison, and 10 people were judged as to which one was white. Subjects chose people who were not as familiar with the paper as possible. Five people were judged under sunlight during the day and the other five were judged under white fluorescent lights at night. The judgment of superiority or inferiority of one specimen was made within 10 seconds. In addition, since the test sample of this example and the comparative example does not use a dye for both the sheet-like base material and the coating layer and has a strong yellowish taste, the comparative product in which the hue is adjusted is whiter in instantaneous judgment. It ’s easy to feel. Table 1 shows the results by the number of people who said the comparison was whiter.

<Evaluation results>
Under the condition that the amount of polyvinyl alcohol is small and the fluorescence intensity is low as in Comparative Examples 1 and 2, it is easy to feel that it is not white than the general coated sheet because of the disadvantage of the hue. However, as in Examples 1 to 3, when the polyvinyl alcohol is within the scope of the present invention and the fluorescence intensity exceeds 14%, it can be said that it is clearly whiter than general coated paper. As can be seen from a comparison of Examples 4 to 6, it is understood that heavy calcium carbonate is preferable because it becomes white when it is 60% by mass or more. When the particle size distribution of heavy kull is in the range specified in claim 3 of the present invention as in Example 3, the blank surface feeling and printability are very good. However, as in Examples 7-9, If it is out of the specified range, the white paper feel and printability will be somewhat deteriorated. As in the case of Example 9, since the surface texture clearly affects the sensory whiteness, it can be said that it is preferable to keep the white paper surface and the printed surface texture high in terms of whiteness that cannot be measured by a machine. As can be seen by comparing Examples 3, 10, and 11, the pulp used for the sheet-like substrate preferably has a whiteness of 88% or more. Under these conditions, all people judge that the test sheet is whiter. As can be seen from a comparison of Examples 2, 12, and 13, it is preferable that the ash content of the sheet-like substrate is 5% by mass or more because the sensory whiteness is improved.

  It can be applied to a coated sheet in the printing area.

Claims (7)

  In a coated sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate, the coating layer contains 1.0% by mass or more of polyvinyl alcohol and has a fluorescence intensity of 14% or more. A coated sheet characterized by that.   The coated sheet according to claim 1, wherein 60% by mass or more of the pigment contained in the coated layer is calcium carbonate.   In the case of calcium carbonate, heavy carbonate in which particles having a particle size of less than 2.0 μm are 95% by mass or more, particles having a particle size of less than 1.0 μm are 75% by mass and particles having a particle size of less than 0.2 μm are 11% by mass or less. The coated sheet according to claim 2, wherein the coated sheet is calcium.   The whiteness of a coating sheet is 103% or more, and the brightness is 96% or more, The coating sheet as described in any one of Claims 1-3 characterized by the above-mentioned.   The coating sheet according to any one of claims 1 to 4, wherein the whiteness of the pulp used in the coating sheet is 88% or more.   The coated sheet according to any one of claims 1 to 5, wherein the ash content of the sheet-like substrate is 5% by mass or more.   The coating sheet according to any one of claims 1 to 6, wherein the coating sheet is a coating sheet for offset printing.