JP2006328570A - Coated white paperboard - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated white paperboard with slight white unevenness on the surface and having excellent smoothness and printing suitability for the coated white paperboard using un-deinked waste paper pulp. <P>SOLUTION: The coated white paperboard is provided with two or more coating layers consisting essentially of a pigment and an adhesive on at least one surface of base paper. The coated white paperboard is characterized as follows. The pigment component of an under coating layer in contact with the outermost coating layer is composed of a mixture of 1-30 mass% of calcium trisulfoalminate having the average particle diameter within the range of 0.1-1.5 μm in determination of particle size distribution by an X-ray transmission-based method with 70-99 mass% of other white pigments having the average particle diameter within the range of 0.1-3.0 μm in the determination of the particle size distribution by the X-ray transmission-based method. The amount of the adhesive component of the under coating layer is within the range of 10-30 pts.mass based on 100 pts.mass of the pigment component. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention particularly relates to coated white paperboard using waste paper pulp.

  White paperboard is usually classified into white balls and manila balls, and manila balls are further classified into high-quality white paperboards and special white paperboards. Further, for white balls, there are a coating type and a non-coating type. White paperboard is usually a cardboard having a multilayer structure of 3 to 9 layers, and is often used for various packaging boxes. Among them, white paper, coated white balls, and special white paperboard use a lot of waste paper pulp from the viewpoint of environment and cost reduction of packaging materials, and undeinked waste paper pulp is used for the middle layer. For example, in a coated white ball, virgin pulp or deinked high whiteness pulp is used for the surface layer, and undeinked waste paper pulp with low whiteness is used for the middle layer and the back layer. In the special white paperboard card, virgin pulp or deinked high whiteness pulp is used for the outermost layer (surface layer, back layer), and deinked waste paper is used for the middle layer.

  In order to conceal the color of the middle layer, the outermost layer needs to have a certain thickness, but if the concealability is required only in the outermost layer, there is a cost problem, so there is an intermediate between the outermost layer and the middle layer. It is usual to provide a layer (front lower layer, back lower layer) to conceal the color of the middle layer in this layer.

  However, as described above, it is difficult to use a pulp having a high whiteness equivalent to that of the outermost layer for the intermediate layer, and a pulp having a lower whiteness than the outermost layer is used, although not as much as the middle layer. . By providing the intermediate layer, it is possible to conceal the intermediate layer, but since it is affected by the whiteness of the intermediate layer, color difference unevenness (white unevenness) of a minute area is seen when the paper surface is viewed directly from above. This causes a decrease in the feeling.

The reason why white unevenness is present in white paperboard using undeinked waste paper pulp with low whiteness is not necessarily clear, but is considered as follows. In other words, the outermost layer of rice is about 30 to 80 g / m ² and has low concealment, and the base paper texture of each layer obtained by a normal paperboard machine is based on the difference in machine structure. It is often inferior compared. Therefore, the difference between the portion with a small amount of pulp (high transparency) and the portion with a large amount of pulp (low transparency) is relatively large and the outermost layer is easily noticeable. When this layer is combined with the inner layer, the surface portion of the intermediate layer is seen through from the portion of the outermost layer where the amount of pulp is low (highly transparent). When the degree difference is large, it is presumed that the portion where the surface of the intermediate layer shows through becomes color difference unevenness (hereinafter, referred to as white unevenness), which causes a reduction in the feeling of blank paper.

  Coated white paperboard with a pigment coating layer for the purpose of imparting printability tends to improve whiteness unevenness by providing a coating layer, but the base paper is multilayered compared to single-layer paper. Since the coverage of the coating layer is greatly inferior due to the unevenness of the base paper of each layer derived from the multilayer structure, as a pigment in the coating layer in order to supplement the coating properties so far, structured kaolin, titanium dioxide and hollow type Although a method using a plastic pigment has been proposed (see Patent Documents 1 and 2), further improvement is desired. A method for reducing the difference in whiteness between the outermost layer and the intermediate layer has also been proposed for the purpose of improving whiteness unevenness from the base paper surface (see Patent Document 3).

By the way, in printing coated paper including coated white paperboard, as a method for improving smoothness, it has been proposed to incorporate calcium trisulfoaluminate (hereinafter referred to as “satin white”) in the coating layer. (See Patent Documents 4 to 7). Satin white is, for example, a needle-like white pigment produced by the reaction of calcium hydroxide and aluminum sulfate, and is an inorganic complex compound represented by the following general formula (1), and a coating layer in which this is blended The surface typically exhibits excellent smoothness.
3CaO · Al ₂ O ₃ · 3CaSO ₄ · 31 to 32H ₂ O (1)

  However, any of the prior art documents merely teaches that satin white is blended in the coating layer of the coated paper that controls ink reception.

Japanese Patent Laid-Open No. 06-166991 JP 2003-306882 A Japanese Patent Application No. 2004-114995 JP-A-11-247097 JP 09-256295 A JP 09-67794 A Japanese Patent Laid-Open No. 02-14098

  The present invention provides a coated white paperboard which is excellent in smoothness and printability with little surface whiteness unevenness in coated white paperboard using undeinked waste paper pulp.

The coated white paperboard according to the present invention is a coated whiteboard paper in which two or more coating layers mainly composed of a pigment and an adhesive are provided on at least one side of a base paper, and the undercoat coating in contact with the outermost coating layer. The pigment component of the layer is 1 to 30% by mass of calcium trisulfoaluminate having an average particle size in the range of 0.1 to 1.5 μm in the X-ray transmission particle size distribution measurement, and the average particle size is 0.1 to 0.1%. It is composed of a mixture with 70 to 99% by mass of other white pigments in the range of 3.0 μm, and the amount of the adhesive component of the undercoat layer is in the range of 10 to 30 parts by mass per 100 parts by mass of the pigment component. It is characterized by being.
The average particle diameter measured by the X-ray transmission type particle size distribution measurement method is a particle size distribution of a pigment composition measured using a Sedigraph 5100 manufactured by Micromeritics, Inc. of the United States. The average particle diameter (d50) corresponding to.

  The pigment component of the outermost coating layer is a white pigment having an average particle diameter in the range of 0.1 to 1.5 μm in X-ray transmission particle size distribution measurement, and the adhesive component of the outermost coating layer The amount is preferably in the range of 10 to 25 parts by weight per 100 parts by weight of white pigment.

  It is preferable that 1-30 mass% of the white pigment contained in the outermost coating layer is satin white.

  Satin white in the undercoat layer and the outermost coat layer was produced by reacting (A) a calcium hydroxide suspension and (B) an aqueous aluminum sulfate solution, and (A) hydroxylated. (B) The aqueous solution of aluminum sulfate (B) is added to the calcium suspension in a plurality of stages, and (A) at least one of the addition of the aqueous solution of (B) the aluminum sulfate solution to the calcium hydroxide suspension is continuous. It is preferable to carry out by continuously adding the (B) aqueous solution of aluminum sulfate to the (A) calcium hydroxide suspension to be transferred.

  It is preferable that the subsequent addition, which is the addition after the second stage among the additions in a plurality of stages, is performed after a predetermined time has elapsed since the addition immediately before the subsequent addition.

  It is preferable that the subsequent addition, which is the second and subsequent additions among the plurality of additions, is performed at a pH of 11.0 or higher in the composition to which (B) the aqueous aluminum sulfate solution is added in the subsequent addition.

  (A) The ratio (a / b) of the total addition amount of the aqueous solution of aluminum sulfate (B) added in multiple stages of the number of moles a of the calcium hydroxide suspension to the number of moles b is 5.5 to 8.0. Preferably there is.

  In the first addition which is the first stage addition among the plurality of stages of addition, (A) a mole of 85% or less of the reference mole number which is 1/6 mole number of the calcium hydroxide suspension. (B) an aqueous solution of aluminum sulfate, and the second addition and the first addition of the second stage of the plurality of stages of addition (B) of the total addition amount of the aqueous aluminum sulfate solution The number of moles is preferably 98% or less of the reference number of moles.

  It is preferable that at least one of (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aluminum sulfate aqueous solution is 12% by mass or less.

  According to the present invention, it has become possible to provide a coated white paperboard with less surface white unevenness and excellent smoothness and printability.

Generally, the coating white paperboard is high pulp constituting the recycled paper rate, sufficiently masked and a high whiteness of the coating surface at one side 10 to 30 g / m ² or less of coating weight, and the base paper surface dullness of It is difficult to obtain a good white paper appearance. Therefore, as a result of intensive studies to solve the above problems, the present inventors, as a pigment of the undercoat coating layer of the coating layer, satin white in the total pigment solid content of the undercoat coating layer, By containing 1 to 30% by mass, it is possible to obtain coated white paperboard having high whiteness on the coated surface, concealing property on the surface of the base paper, that is, excellent white paper appearance with little whiteness unevenness, smoothness and printing A coated white paperboard excellent in suitability was obtained, and the desired object of the present invention could be achieved.

  In the coated white paperboard of the present invention, the pigment component constituting the undercoat coating layer has an average particle size of the satin white in the range of 0.1 to 1.5 μm. Even if it is a kind, the average particle diameter is in the range of 0.1 to 3.0 μm, preferably in the range of 0.3 to 2.5 μm. When the average particle size of white pigments other than satin white and satin white exceeds 1.5 μm and 3.0 μm, respectively, it is difficult to impart excellent smoothness to the undercoat layer itself, and it is less than 0.1 μm. In this case, although it is preferable for imparting smoothness, it is economically disadvantageous because a relatively large amount of adhesive is required to form the undercoat coating layer.

  The pigment component of the undercoat coating layer contains 1-30% by mass, preferably 3-20% by mass of satin white. Incorporating satin white in the undercoat layer, coupled with the fact that the average particle size of the pigment component was specified as described above, in addition to excellent smoothness in the undercoat layer itself, high whiteness, high coverage The present inventors have found that the above is imparted. When the amount of satin white is less than 1% by mass of the pigment component of the undercoat coating layer, it is difficult to impart excellent smoothness, whiteness and covering property to the undercoat coating layer itself. On the other hand, when the amount of satin white exceeds 30% by mass of the pigment component of the undercoat coating layer, although the smoothness, whiteness and coverage of the undercoat coating layer itself are improved, it is relatively easy to form the undercoat coating layer. Since a large amount of adhesive is required, it is disadvantageous in terms of economy.

  In addition, although the manufacturing method of satin white used by this invention is not prescribed | regulated in particular, it is preferable to use satin white obtained by the manufacturing method as described in Japanese Patent Application No. 2004-227553. The satin white obtained by the above manufacturing method has a uniform particle shape, and there is little or no unreacted calcium hydroxide and by-product calcium sulfate. Very preferred for obtaining paper. The said manufacturing method is shown below.

Production method of satin white (A) A calcium hydroxide suspension and (B) an aqueous solution of aluminum sulfate, which are produced by reacting (A) a calcium hydroxide suspension with (B) an aqueous solution of aluminum sulfate. (A) Calcium hydroxide in which at least any one of (B) the addition of a plurality of stages of the aqueous solution of aluminum sulfate to the calcium hydroxide suspension is continuously transferred. (B) The aqueous solution of aluminum sulfate is continuously added to the suspension.
Here, (B) the aqueous solution of aluminum sulfate is added (A) the calcium hydroxide suspension is the first stage of the multi-stage addition (before the addition of the aqueous aluminum sulfate solution). Is a pure calcium hydroxide suspension, but in the second and subsequent stages of the multi-stage addition (after the aluminum sulfate aqueous solution has already been added), calcium hydroxide and aluminum sulfate. Means a mixture.

This method is characterized in that the aqueous aluminum sulfate solution added to the calcium hydroxide suspension is added in multiple stages.
When producing satin white by reacting calcium hydroxide suspension and aluminum sulfate aqueous solution, aluminum sulfate, the reaction raw material of satin white, is completely dissolved in water to form an aqueous solution, and the whole amount can be reacted immediately. On the other hand, calcium hydroxide as the other reaction raw material has a very low solubility in water of 0.2% and is in a suspension state that is hardly soluble in water. It is not ready for reaction.
For this reason, a predetermined amount of aqueous aluminum sulfate solution is not added at once to a calcium hydroxide suspension with low reactivity, but the amount of aluminum sulfate sufficient to meet the amount of calcium hydroxide that can be reacted immediately. By adding a predetermined amount of aluminum sulfate in multiple stages within the range, it avoids excessive aluminum sulfate in the reaction system and suppresses the generation of reaction byproducts of aluminum oxide and calcium sulfate. To do.

Further, in addition to the divided addition of the aqueous aluminum sulfate solution described above, at least one of (B) the addition of multiple aqueous aluminum sulfate solutions to the calcium hydroxide suspension is continuously transferred. (A) It is carried out by continuously adding (B) an aluminum sulfate aqueous solution to the calcium hydroxide suspension.
This is because the addition of the aqueous aluminum sulfate solution divided into a plurality of stages is performed by a so-called “batch” method in which the aqueous aluminum sulfate solution is gradually added to a predetermined amount of calcium hydroxide suspension over a long period of time. However, with regard to finely and uniformly controlling the particle size of the produced satin white, the aqueous aluminum sulfate solution is continuously applied to the calcium hydroxide suspension that is continuously transferred rather than the “batch” method. Since the “continuous addition” method to be added to is superior, in the satin white used in the present invention, in any addition of the aqueous aluminum sulfate solution divided into a plurality of stages, the “continuous addition” method is used. The addition is performed at least once.

  In addition, in this method, regarding the addition of the aluminum sulfate aqueous solution by the “continuous addition” method, the addition of the first step is the “continuous addition” method among the additions of the aluminum sulfate aqueous solution performed in a plurality of stages. Furthermore, among the addition of the aqueous aluminum sulfate solution divided into a plurality of stages, all the additions except the final addition can be made a “continuous addition” method. It should be noted that all additions including the final addition may be a “continuous addition” method.

  Further, in the production of satin white, in order to restore the reactivity of calcium hydroxide and maintain an appropriate satin white production reaction, after a predetermined time interval from the addition immediately before the subsequent addition, An aluminum sulfate aqueous solution is added, and the time required for stabilization is 15 seconds or more, although it depends on the state of the mixed composition.

Further, among the additions of the aqueous solution of (B) aluminum sulfate carried out in a plurality of stages, the subsequent addition, which is the second and subsequent additions, is a composition in which (B) the aqueous aluminum sulfate solution is added in the subsequent addition The pH may be 11.0 or higher.
“Subsequent addition” as used herein refers to each aqueous solution of aluminum sulfate, which is performed in the second stage to the final stage when the aqueous solution of aluminum sulfate is added in multiple stages to the calcium hydroxide suspension. Addition.
The “composition to which (B) an aqueous solution of aluminum sulfate is added in the subsequent addition” mentioned here is a mixture of (A) a calcium hydroxide suspension and (B) an aqueous solution of aluminum sulfate, B) A predetermined amount (total amount) of the aqueous aluminum sulfate solution is not mixed (that is, the final stage is not added), and (B) the composition immediately before the aqueous aluminum sulfate solution is added by the subsequent addition Specifically, it shows a composition in which the produced satin white and unreacted calcium hydroxide remain.

The significance that the pH of the composition to which (B) the aqueous aluminum sulfate solution is added in the subsequent addition is 11.0 or more is considered as follows.
Regarding the production of satin white, as described above, it is important to maintain and recover the reactivity of calcium hydroxide as a raw material when adding an aqueous aluminum sulfate solution. On the other hand, by observing the fluctuation state of the pH of the mixed composition obtained by mixing the aqueous aluminum sulfate solution, it is possible to grasp the recovery state of the reactivity of calcium hydroxide in the mixed composition. In the product, it is essential to sufficiently recover the reactivity (= recovery of the increase in pH) before adding aluminum sulfate.
Therefore, the pH of the mixed composition before the aluminum sulfate is added is preferably 11.0 or more, more preferably 12.0 or more, and the calcium hydroxide reactivity is completely stabilized. In order to recover to a state, it is particularly preferable to adjust to a pH range of 12.5 to 13.0. When the pH of the mixed composition before adding aluminum sulfate is less than 11.0, there is a high possibility that the reactivity recovery of calcium hydroxide in the mixed composition is insufficient, and the mixed composition in this state If an aqueous solution of aluminum sulfate is additionally added, it is difficult to perform a satin white formation reaction in an appropriate and stable manner, and a large amount of reaction by-products such as aluminum oxide and calcium sulfate are generated.

Thus, the ratio (a / b) between (A) the number of moles a of the calcium hydroxide suspension and the number of moles b of the total addition amount of the aqueous aluminum sulfate solution (B) added in multiple stages. Theoretically, a / b = 6.0, indicating that 6 moles of calcium hydroxide and 1 mole of aluminum sulfate are required to produce 1 mole of satin white. Accordingly, it is highly preferable to minimize the waste in the reaction by setting the reaction molar ratio (a / b) between calcium hydroxide and aluminum sulfate (a / b) when the satin white is produced in the present invention.
However, as described above, since the reactivity of calcium hydroxide is very low, it is extremely difficult to complete the reaction at a complete reaction end point. Therefore, the lower limit of the reaction molar ratio (a / b) between calcium hydroxide and aluminum sulfate when the satin white is produced in the present invention is preferably a / b = 5.5 or more. 8 is more preferable, and 6.0 is particularly preferable. The upper limit of the reaction molar ratio (a / b) between calcium hydroxide and aluminum sulfate is preferably 8.0 or less, more preferably 7.0 or less, and particularly preferably 6.0. Preferable (usually, the reaction molar ratio (a / b) of calcium hydroxide to aluminum sulfate is preferably a / b = 5.5 to 8.0, and a / b = 5.8 to 7.0. It is particularly preferable to be within the range.) When the reaction molar ratio (a / b) between calcium hydroxide and aluminum sulfate when producing satin white is less than 5.5, the ratio of aluminum sulfate to calcium hydroxide becomes excessive, and aluminum oxide or sulfuric acid A large amount of reaction by-products such as calcium is undesirable, and the reaction molar ratio exceeding 8.0 is that the ratio of aluminum sulfate to calcium hydroxide is too low and unreacted in satin white. A large amount of calcium hydroxide remains, which is not preferable.

  Of the addition of the aqueous solution of aluminum sulfate (B) carried out in a plurality of stages, in the first addition, which is the first stage addition, (A) 1/6 of the number of moles of the calcium hydroxide suspension (B) an aluminum sulfate aqueous solution having a mole number of 85% or less of the reference mole number, which is the number of moles, is added, and the second addition and the first addition of the second stage among the plurality of stages of addition. The total number of moles of the (B) aluminum sulfate aqueous solution added may be 98% or less of the reference number of moles (addition mole number limiting method).

At least one of (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aqueous aluminum sulfate solution may be 12% by weight or less.
Here, the concentration of the calcium hydroxide suspension is such that the calcium hydroxide aqueous solution is not added at all (that is, before the first stage addition of the aluminum sulfate aqueous solution). It is the concentration of the suspension, and in the calcium hydroxide suspension, calcium hydroxide (f1) in a state dissolved in water and calcium hydroxide (f2) in a state dispersed in water as a solid Is the weight% based on the total content of calcium hydroxide (mass F = f1 + f2).

It is indispensable that satin white mixes the calcium hydroxide suspension that is the base and the aluminum sulfate aqueous solution that is the acid instantly and uniformly, but if the concentration of each reaction raw material is too high, It becomes difficult to mix each reaction raw material instantly and uniformly, and the viscosity of the reaction mixture composition (suspension) becomes so high that it exceeds 2000 mPa · s, thus inhibiting the mixing of the reaction raw materials. Fear will arise.
Therefore, it is preferable that at least one of (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aqueous aluminum sulfate solution is 12% by weight or less, and at least one is 6% or less. More preferably, both (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aqueous aluminum sulfate solution are most preferably 6% or less.

And, in order to mix the reaction raw materials instantaneously and uniformly and to carry out the production reaction of satin white stably, the concentration of each reaction raw material is preferably as low as possible as described above. Is extremely low, the amount of the reaction solution to be handled becomes enormous, and it is necessary to install a production facility having an extremely large processing capacity. Therefore, it is not preferable to reduce the concentration of the raw material more than necessary.
Therefore, it is preferable that at least one of (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aqueous aluminum sulfate solution is 0.1% by weight or more, and at least one is 1% or more. Is particularly preferred.

  The average particle size of satin white used for the undercoat coating layer in the present invention is that the smoothness and glossiness of the coated paper are reduced, and the coarse pigment scratches the coating layer in the coating process. In order to prevent the occurrence of “streaks” and the like, the lower limit of the average particle diameter in the X-ray transmission type particle size distribution measurement is preferably 0.1 μm or more, particularly preferably 0.2 μm or more. The upper limit of the average particle diameter is preferably 1.5 μm or less, more preferably 1.2 μm or less, and particularly preferably 1.0 μm or less (usually, the particle diameter range is 0 .1 to 1.5 μm, more preferably 0.2 to 1.0 μm.)

The composition containing satin white used for the measurement was a 0.1% aqueous solution of a phosphate-based dispersant (sodium pyrophosphate) with respect to the dispersion of the composition containing satin white, and the pigment solid content concentration was Obtained by diluting and dispersing to about 4%. As measurement conditions, the specific gravity of satin white was 1.77 g / cm ³ , and the measurement temperature was 35 ° C.

  In the present invention, pigments other than satin white contained in the undercoat coating layer include heavy calcium carbonate, light calcium carbonate, clay, calcined kaolin, engineered kaolin, deramikaolin, talc, calcium sulfate, barium sulfate, hydroxide Inorganic pigments such as aluminum, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, alumina magnesium silicate, calcium silicate, bentonite, zeolite, sericite, and sukumite, solid type, hollow type, through-hole type Organic pigments such as plastic pigments and binder pigments can be used, and pigments used in the ordinary coated paper field can be used, and one or more of these can be appropriately selected and used. In addition, the average particle diameter of the pigment to be used is in the range of 0.1 to 3.0 μm.

  In the present invention, the adhesive contained in the undercoat coating layer is not particularly limited, and adhesives used in the field of ordinary coated white paperboard, for example, water-soluble adhesives such as oxidized starch and esterified starch. , Various starches such as cold water soluble starch, proteins such as casein, soy protein, synthetic protein, cellulose derivatives such as carboxymethylcellulose and methylcellulose, polyvinyl alcohol and modified products thereof, and styrene- It is possible to use conjugated diene polymer latex such as butadiene copolymer, methyl methacrylate-butadiene copolymer, vinyl polymer latex such as acrylic polymer latex, ethylene-vinyl acetate copolymer, etc. If necessary, select one or more of these as appropriate. To to use.

  Moreover, in this invention, the quantity of the adhesive component of an undercoat coating layer is the range of 10-30 mass parts per 100 mass parts of pigment components, and 10-25 mass parts is more preferable. When printing and processing on coated white paperboard, an adhesive is included in the coating layer in order to express the required printing and processing strength, but the amount of the adhesive component is less than 10 parts by mass Therefore, it is difficult to give sufficient printing and processing strength to the coated paper. On the other hand, if it exceeds 30 parts by mass, the required smoothness cannot be obtained and it is economically uneconomical. Become.

  When a water-soluble adhesive is used in combination as the adhesive component of the undercoat coating layer, the content is preferably 7 parts by mass or less, particularly 4 parts by mass or less, per 100 parts by mass of the pigment component. If it exceeds 7 parts by mass, the smoothness of the undercoat coating layer is inferior, which is not preferable. Use of a small amount of a water-soluble adhesive in combination with a dispersion-type adhesive is effective for increasing the viscosity of the coating liquid for forming the undercoat coating layer and retaining water.

  The undercoat coating layer of the coated white paperboard according to the present invention has 1-30% by weight of satin white having an average particle size in the range of 0.1-1.5 μm and an average particle size of 0.1-3.0 μm. The coating liquid which forms the undercoat coating layer which contains the pigment component comprised with 70-99 mass% of other white pigments in the range, and 10-30 mass parts adhesive agent per 100 mass parts of pigment components Is coated on one side or both sides of the base paper and dried.

  The coating apparatus for applying the coating liquid for the undercoat layer to the base paper is not particularly limited. For example, an air knife coater, a blade coater, a rod coater, a bar coater, a gate roll coater, a roll coater such as a size press. A bill blade coater, a bellbapa coater, etc. are used in appropriate combinations within a range not impairing the effects of the present invention, and a rod coater is preferably used. The reason why the rod coater is preferably used is that it is possible to perform contour coating along the unevenness of the surface of the base paper, and because high-concentration paint can be used, high-speed coating is also possible.

  The outermost coating layer of the coated white paperboard according to the present invention has a white pigment having an average particle diameter in the range of 0.1 to 1.5 μm, preferably in the range of 0.3 to 1.0 μm, and a white pigment. By coating the coating liquid for forming the outermost coating layer containing 10 to 25 parts by mass of the adhesive per 100 parts by mass on the surface of the undercoating coating layer formed on the base paper and drying it It is formed.

A blade coater is preferably used as a coating apparatus for forming an outermost coating layer on a paper provided with an undercoat coating layer. The blade coater is preferably used as the coating device for the coating material for the outermost coating layer, and it is easy to obtain a highly smooth coating surface, and a high-concentration coating material can be used like a rod coater used for undercoating. Therefore, the reason is that high-speed coating is possible. The coating amount of the outermost coating solution is selected in the range of 10 to 30 g / cm ² per one side of the base paper in total with the coating amount of the undercoat coating solution described above.

  The reason for defining the average particle size of the white pigment contained in the outermost coating layer as described above is substantially the same as that for the undercoat coating layer. The white pigment, which is one of the main components of the outermost coating layer, preferably contains satin white in an amount corresponding to 1 to 30% by mass, particularly 3 to 20% by mass of the total amount. The reason is substantially the same as in the case of the undercoat coating layer described above.

  Examples of pigments other than satin white that can be used in the outermost coating layer include, for example, calcium carbonate, calcined kaolin, engineered kaolin, deramikaolin, talc, calcium sulfate, barium sulfate, aluminum hydroxide, titanium dioxide, zinc oxide, Examples thereof include inorganic pigments such as alumina, magnesium carbonate, magnesium oxide, silica, magnesium aluminosilicate, calcium silicate bentonite, zeolite, sericite, and smectite, and solid, hollow, and through-hole type plastic pigments. One or more of these white pigments can be used in the present invention.

  As the adhesive component of the outermost coating layer, a dispersion type adhesive is usually used as in the case of the above-described undercoat coating layer. Dispersion type adhesives include conjugated diene polymer latexes such as styrene-butadiene copolymers and methyl methacrylate-butadiene copolymers, acrylic polymer latexes, and vinyl polymer latexes such as ethylene-vinyl acetate copolymers. Etc., and one or more of these can be used as the adhesive component of the outermost coating layer.

  A small amount of water-soluble adhesive can be used in combination with the above-described dispersion type adhesive. Examples of water-soluble adhesives include various starches such as oxidized starch, esterified starch and cold water soluble starch, proteins such as casein, soy protein and synthetic protein, cellulose derivatives such as carboxymethylcellulose and methylcellulose, polyvinyl alcohol and modified products thereof. Etc. can be exemplified.

  The amount of the adhesive component contained in the outermost coating layer is 10 to 25 parts by mass per 100 parts by mass of the pigment component contained in the outermost coating layer, regardless of whether or not a water-soluble adhesive is used in combination. In particular, it is selected in the range of 10 to 20 parts by mass. When the content of the adhesive component is less than 10 parts by mass, the bonding force is insufficient, and when it exceeds 25 parts by mass, the smoothness may be impaired.

  The coating liquid used for the formation of the undercoat coating layer and the coating liquid used for the formation of the outermost coating layer may be blue or purple dyes, colored pigments, fluorescent dyes, Viscosity retention agent, antioxidant, anti-aging agent, conductivity inducer, antifoaming agent, ultraviolet absorber, dispersant, pH adjuster, mold release agent, water-proofing agent, water repellent, etc. can do.

  Before coating, the base paper can be smoothed in advance using a machine calendar, soft calendar, Yankee dryer or the like. Further, it is desirable to apply a smoothing treatment using a machine calendar, a soft calendar, a super calendar, or the like after coating and drying the outermost layer coating solution.

The base paper is composed of two or more layers, and the pulp to be used is not particularly limited. For example, bleached or unbleached chemical pulp, mechanical pulp, deinked or undeinked waste paper pulp, etc. One kind or two or more kinds are appropriately mixed and used. In addition, a sizing agent, a paper strength agent, a filtering agent, a filler, a dye, and the like can be appropriately added to the base paper as necessary. In addition, the base weight of a base paper is about 150-650 g / m < ² > normally.

  Generally speaking, coated white paperboard is produced by forming a coating layer mainly composed of a white pigment and an adhesive on at least one side of a base paper. According to the present invention, particularly for base paper using undeinked waste paper pulp, by defining the type of pigment component and the amount of adhesive component in the undercoat coating layer, there is little surface white unevenness, smoothness and It has become possible to provide coated white paperboard with excellent printability.

  The present invention will be specifically described below with reference to examples. Of course, the present invention is not limited to these examples. In addition, unless otherwise indicated,% in an example shows "mass%".

Example 1
(1a) Preparation of coating solution for undercoat coating layer As pigment, engineered kaolin (trade name: Exilon, Engelhard, average particle size 0.61 μm) 40% by mass, heavy calcium carbonate (trade name: FMT65) , Phematech Co., average particle size 1.21 μm) 50% by mass, satin white (trade name: Sachin White BL, manufactured by Shiroishi Kogyo Co., Ltd., average particle size 0.5 μm) 10% by mass, and as a dispersant, To all the pigments, 0.2% by mass of sodium polyacrylate was added, and a pigment slurry having a solid content concentration of 65% was prepared using a Coreless disperser. To this slurry, phosphoric esterified starch (trade name: Ace P-F260, manufactured by Oji Cornstarch Co., Ltd.) 3 parts by mass (in terms of solid content) and a styrene-butadiene copolymer latex (trade name: X-) having a solid concentration of 50% 400 A, glass transition temperature: −23 ° C., manufactured by JSR) 15 parts by mass (in terms of solid content) were added, and water was further added to prepare a paint having a solid content concentration of 60%.

(1b) Preparation of coating solution for outermost coating layer Kaolin (trade name: UW-90, manufactured by Engelhard, average particle size 0.32 μm) 60% by mass, light calcium carbonate (trade name: TP) -221-GS, manufactured by Okutama Kogyo Co., Ltd., average particle size 0.49 μm) 35% by mass, titanium dioxide (trade name: Kronos KA-10, manufactured by Titanium Industry Co., Ltd., average particle size 0.41 μm) 5% by mass is used. As a dispersant, 0.2% by mass of sodium polyacrylate was added to all the pigments, and a pigment slurry having a solid content concentration of 65% was prepared using a coreless disperser. To this slurry, phosphoric esterified starch (trade name: Ace P-F260, manufactured by Oji Cornstarch Co., Ltd.) 3 parts by mass (in terms of solid content), 50% solid concentration styrene-butadiene copolymer latex (trade name: L-1825) Glass transition temperature: 8 ° C., manufactured by Asahi Kasei Co., Ltd.) 15 parts by mass (in terms of solid content) were added, and water was further added to prepare a paint having a solid content concentration of 60%.

(1c) Preparation of coated white paperboard Deinked waste paper pulp (outside / back layer: pulp whiteness 76%, front / back lower layer 56%) on the outer layer, undeinked wastepaper pulp (pulp whiteness 50% on the middle layer) ) On a single side of a base paper having a weight of 290 g / m ² , which is made into 5 layers using a rod coater, the dry coating weight of the base coat layer obtained above is 8 g / m ^2. The undercoat coating layer is formed by coating and drying so that the coating solution for the outermost coating layer obtained above is further applied to the surface of the undercoat coating layer on the opposite side using a blade coater. It was coated and dried so as to have a dry weight of 7 g / m ² , thereby obtaining a coated white paperboard of the front two-layer type and the rear one-layer type. Next, two stacks of metal rolls having a surface temperature of 150 ° C. and passing through a two-nip soft calender were used to obtain coated white paperboard having both sides smoothed.

Example 2
In the preparation of the coating solution for the undercoat coating layer of Example 1, heavy calcium carbonate (trade name: FMT65, supra) was replaced with heavy calcium carbonate (trade name: Ace 25, manufactured by Dowa Calfine Co., Ltd., average particle size) A coated white paperboard was obtained in the same manner as in Example 1 except that the thickness was changed to 1.71 μm).

Example 3
In the preparation of the coating solution for the undercoat coating layer of Example 1, heavy calcium carbonate (trade name: FMT65, supra) was replaced with heavy calcium carbonate (trade name: Super 2000, manufactured by Maruo Calcium Co., Ltd., average particle size 2). Coated white paperboard was obtained in the same manner as in Example 1 except that the thickness was changed to .23 μm).

Example 4
In the preparation of the coating solution for the undercoat coating layer of Example 1, satin white (trade name: satin white BL, supra) was replaced with satin white (trade name: satin white B, manufactured by Shiroishi Kogyo Co., Ltd., average particle size: 1. A coated white paperboard was obtained in the same manner as in Example 1 except that the thickness was changed to 0 μm).

Example 5
In the preparation of the coating solution for the undercoat coating layer of Example 1, the pigment was 45% by mass of engineered kaolin (trade name: Eccylon, supra), heavy calcium carbonate (trade name: FMT65, supra) 50% by mass. Satin white (trade name: Sachin White BL, supra) A coated white paperboard was obtained in the same manner as in Example 1 except that the content was changed to 5% by mass.

Example 6
In the preparation of the coating solution for the undercoat coating layer of Example 1, the same procedure as in Example 1 was conducted except that the satin white (trade name: Sachin White BL, supra) was changed to the satin white produced by the following production method. Coated white paperboard was obtained.

(6a) Preparation of 6% Calcium Hydroxide Suspension Calcium hydroxide having a purity of 96.4% as Ca (OH) ₂ (trade name: JIS special name slaked lime, manufactured by Okutama Kogyo) 1.24 kg (Ca (OH) 1.20 kg in ₂ minutes) was dispersed in 18.76 kg of water to make 20.0 kg to prepare a 6% calcium hydroxide suspension. The suspension temperature was adjusted to 40 ° C.

(6b) Determination of purity of aluminum sulfate Precisely weighed a predetermined amount of aluminum sulfate (trade name: aluminum sulfate 13-14 hydrate, manufactured by Kishida Chemical Co., Ltd., reagent) is heated at 500 ° C. for 5 hours to contain crystal water. The purity of the anhydrous aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) was measured. As a result, the concentration of aluminum sulfate anhydride (Al ₂ (SO ₄ ) ₃ ) in the reagent was 58.70%.

(6c) Preparation of 6% aluminum sulfate aqueous solution Aluminum sulfate (trade name: Aluminum sulfate 13-14 hydrate, manufactured by Kishida Chemical Co., Ltd., reagent) 2.04 kg (Al ₂ (SO ₄ ) ₃ anhydrous as measured above 1.2 kg) was dissolved in 17.96 kg of water to make 20.0 kg to prepare a 6% aluminum sulfate aqueous solution. The aqueous solution temperature was adjusted to 40 ° C.

(6d) Preparation of satin white (1) Addition of first-stage aluminum sulfate aqueous solution to calcium hydroxide suspension For the in-line mixer (pipeline homomixer, mixing means) rotated at 9000 rpm, the above 6 % Calcium hydroxide suspension at a rate of 300 g / min and 6% aqueous aluminum sulfate at a rate of 104 g / min (45% of the reference mol number. The calculation method of the reference mol number will be described later) simultaneously and continuously. The injection was continued for 14 minutes. The mixed composition (composition discharged from the in-line mixer) obtained at that time was continuously received in a pH restoration tank and allowed to stand for 30 minutes to recover the pH. The pH of the mixed composition (hereinafter referred to as “first composition”) after the pH recovery was 12.7.

Here, a method for calculating the reference number of moles will be briefly described.
The molecular weights of calcium hydroxide and aluminum sulfate are 74.1 and 342.16, respectively, and 300 g / min of 6% calcium hydroxide suspension has a solid content of 18 g / min. The number of moles charged) is 18 / 74.1 = 0.243. Therefore, the reference number of moles which is 1/6 of the number of moles of the calcium hydroxide suspension is 0.243 × 1/6 = 0.0405 mol / min.
On the other hand, 104 g / min of 6% aluminum sulfate aqueous solution contains 104 g × 6% = 6.24 g / min of aluminum sulfate, which is 6.24 g / min × 1 / 342.16 in terms of moles. = 0.0182 mol / min.
Therefore, the calculation of the ratio of the aqueous aluminum sulfate solution added to the first stage to the reference mole number is calculated as (0.0182 mol / min) / (0.0405 mol / min) = 45%.

(2) Addition of second-stage aluminum sulfate aqueous solution In the same manner as in (1) above, the mixed composition (first composition) was applied to an in-line mixer (pipeline homomixer, mixing means) rotated at 9000 rpm. The product was simultaneously and continuously injected at a rate of 404 g / min and a 6% aluminum sulfate aqueous solution at 81 g / min (35% of the reference mole number), and the injection was continuously performed for 12 minutes. The mixed composition (composition discharged from the in-line mixer) obtained at that time was continuously received in a pH restoration tank and allowed to stand for 30 minutes to recover the pH. The pH of the mixed composition after recovery of pH (hereinafter referred to as “second composition”) was 12.5.

(3) Addition of third-stage aluminum sulfate aqueous solution (end of reaction)
In the same manner as (2) above, the mixed composition (second composition) was 485 g / min and a 6% aluminum sulfate aqueous solution with respect to an in-line mixer (pipeline homomixer, mixing means) rotated at 9000 rpm. Were simultaneously and continuously injected at a rate of 34 g / min (15% of the reference mole number), and the injection was continuously performed for 10 minutes (end of reaction). The mixed composition (composition discharged from the in-line mixer) obtained at that time was continuously received in a cushion tank to obtain a composition after completion of the reaction (hereinafter referred to as “reaction completed composition”). The pH of the reaction finished composition was 11.5.

(A) A method of calculating the ratio (a / b) of the total number of moles a of the calcium hydroxide suspension to the number of moles b of the (B) aqueous solution of aluminum sulfate added in multiple stages will be briefly described.
First, the 6% calcium hydroxide finally used is 300 g / min × 10 min = 3000 g, the solid content contained therein is 180 g, and the Ca (OH) ₂ mol number a is 2.43 mol. is there.
The total amount of 6% aluminum sulfate added in multiple stages is 219 g / min × 10 minutes = 2190 g, the solid content contained in it is 131.4 g, and Al ₂ (SO ₄ ) is ₃ moles b. Is 0.38 mol.
Therefore, the molar ratio (Ca (OH) ₂ / Al ₂ (SO ₄ ) ₃ = a / b) is 6.4. The total addition rate of aluminum sulfate was 95% (= 45% + 35% + 15%) of the reference mole number.

  The composition after completion of the reaction (reaction completed composition) is dehydrated with a filter press to obtain a composition having a solid content of about 32 to 34%, and the dehydrated composition is then added to water so that the solid content becomes 27%. Redispersed. At the time of the redispersion, a polyacrylic acid-based dispersant (trade name: Aron T-50, manufactured by Toa Gosei Chemical Co., Ltd.) is previously added to water in an amount of 0.5% relative to the solid content of the composition (the dehydrated composition). And the amount of the dispersant added was adjusted so that the re-dispersed composition dispersion had a low viscosity of about 10 mPa · s. The average particle size was 0.44 μm.

Example 7
In the preparation of the coating solution for the outermost coating layer of Example 1, kaolin (trade name: UW-90, supra) 60% by mass, light calcium carbonate (trade name: TP-221-GS, supra) 25 Coated in the same manner as in Example 1 except that the content was changed to 5% by mass, titanium dioxide (trade name: Kronos KA-10, supra) 5% by mass, and satin white (trade name: satin white BL, supra) 10% by mass. White paperboard was obtained.

Comparative Example 1
In the preparation of the coating solution for the undercoat coating layer of Example 1, the pigment was engineered kaolin (trade name: Eccylon, supra) 50 mass%, heavy calcium carbonate (trade name: FMT65, supra) 50 mass%. A coated white paperboard was obtained in the same manner as in Example 1 except that it was changed to.

Comparative Example 2
In the preparation of the coating solution for the undercoat coating layer of Example 1, heavy calcium carbonate (trade name: FMT65, supra) was replaced with heavy calcium carbonate (trade name: Whiten SB, manufactured by Shiroishi Kogyo Co., Ltd., particle size 4). Coated white paperboard was obtained in the same manner as in Example 1, except that the thickness was changed to 0.1 μm).

Comparative Example 3
In the preparation of the coating liquid for the undercoat coating layer of Example 1, the same as Example 1 except that the satin white (trade name: Sachin White BL, supra) was changed to the coarse-grained satin white obtained below. Thus, a coated white paperboard was obtained.

(3a) Preparation of coarse-grained satin white pigment slurry 90 kg (90 liters) of water was placed in a reaction tank (coreless stirring tank) having a volume of 250 liters, and classification was not performed while stirring (particle size was A lump of quick lime (CaO, manufactured by Adachi Lime Industry Co., Ltd.) 10.0 kg having a diameter of 1 to 4 cm is mixed. Subsequently, it melt | dissolved, continuing stirring, the temperature of the liquid was raised, and after hold | maintaining in the range of 85-95 degreeC for 1 hour, it cooled to 30 degreeC. Next, 58.3 kg of an aqueous solution of sulfuric acid band (25 kg of Al ₂ (SO ₄ ) ₃ · 18H ₂ O dissolved in 50 kg of water) was fed with about 1 kg / min while further stirring. The solution was gradually added in liquid amount to obtain a satin white suspension.
This suspension was squeezed with a filter press to obtain a cake-like satin white having a solid content concentration of 32%, and then sodium polycarboxylate (trade name: Aron T-40, 100 parts of the solid content of this satin white. (Toa Gosei Co., Ltd.) 3 parts and water were added to give a solid content concentration of 20%, then passed through a sand grinder to obtain a satin white dispersion, and this dispersion was subjected to a screen mesh treatment of 150 mesh to obtain a solid content. A satin white pigment slurry with a concentration of 20% was obtained. The average particle size of the satin white obtained from this pigment slurry by X-ray transmission type particle size distribution measurement was 3.0 μm.

Comparative Example 4
In the preparation of the coating solution for the undercoat coating layer of Example 1, the pigment was engineered kaolin (trade name: Exilon, supra) 40% by mass, heavy calcium carbonate (trade name: FMT65, supra) 50% by mass. Coated white paperboard was obtained in the same manner as in Example 1 except that the content was changed to 10% by mass of titanium dioxide (trade name: Kronos KA10, supra).

Comparative Example 5
In the preparation of the coating solution for the undercoat coating layer of Example 1, the pigment was engineered kaolin (trade name: Exilon, supra) 40% by mass, heavy calcium carbonate (trade name: FMT65, supra) 50% by mass. A coated white paperboard was obtained in the same manner as in Example 1 except that it was changed to 10% by mass of a hollow plastic pigment (trade name: HP1055, manufactured by Rohm & Haas, catalog data particle size 1 μm).

  The 12 types of coated white paperboard obtained as described above were evaluated as follows, and the results obtained are shown in Table 1. The measurement and evaluation in the present invention were performed in an environment of 23 ° C. and 50% RH unless otherwise specified.

1. Whiteness After adjusting the humidity for 6 hours under the conditions based on JIS P8111, the surface was measured using a spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS P-8148: 2001.

2. White unevenness The degree of white unevenness on the surface was visually evaluated.
A: Uniform and no white unevenness.
○: Some white unevenness is recognized, but there is no practical problem.
(Triangle | delta): White unevenness is conspicuous and there is a problem in practical use.
X: White unevenness is very conspicuous.

3. PPS smoothness Using Parker Print Surf (PPS) surface smoothness tester (model name: MODEL M-569, MESSMER BUCHEL, UK), backing disk: soft rubber, clamping pressure: 2 MPa, surface 5 times The smoothness was measured and the average was obtained.

4). Printability (ink fillability and print smoothness)
Printing on the surface of each coated white paperboard with RI printer using 0.1cc of printing ink (trade name: Values-G black S type, manufactured by Dainippon Ink & Chemicals, Inc.) with RI printer The ink transfer surface of the coated white paperboard is observed with the naked eye, and the printability of the coated paper is evaluated in four levels based on the transferred ink density (ink fillability) and density uniformity (print smoothness). did.
A: Printability is particularly excellent.
○: Printability is excellent.
Δ: Printability is slightly inferior.
X: Printability is inferior.

Claims (9)

  In coated white paperboard with at least one coating layer consisting mainly of pigment and adhesive on at least one side of the base paper, the pigment component of the undercoat coating layer in contact with the outermost coating layer is X-ray transmissive 1-30% by mass of calcium trisulfoaluminate having an average particle size in the range of 0.1 to 1.5 μm in the particle size distribution measurement, and other particles having an average particle size in the range of 0.1 to 3.0 μm The coating composition is characterized in that it is composed of a mixture of 70 to 99% by weight of a white pigment, and the amount of the adhesive component in the undercoat layer is in the range of 10 to 30 parts by weight per 100 parts by weight of the pigment component. Crafted white paperboard.   The pigment component of the outermost coating layer is a white pigment having an average particle diameter in the range of 0.1 to 1.5 μm in X-ray transmission particle size distribution measurement, and the adhesive component of the outermost coating layer The coated white paperboard of claim 1, wherein the amount is in the range of 10 to 25 parts by weight per 100 parts by weight of the white pigment.   The coated white paperboard according to claim 2, wherein 1 to 30% by mass of the white pigment contained in the outermost coating layer is calcium trisulfoaluminate.   The calcium trisulfoaluminate in the undercoat layer and the outermost coat layer is produced by reacting (A) a calcium hydroxide suspension and (B) an aluminum sulfate aqueous solution, A) A step of adding a plurality of (B) aqueous solutions of aluminum sulfate to a calcium hydroxide suspension, and (A) At least one of the steps of adding a plurality of (B) aqueous solutions of aluminum sulfate to a suspension of calcium hydroxide. The coating according to any one of claims 1 to 3, wherein the coating is carried out by continuously adding (B) an aqueous aluminum sulfate solution to (A) the calcium hydroxide suspension that is continuously transferred. Crafted white paperboard.   The coated white paperboard according to claim 4, wherein the subsequent addition, which is the second and subsequent additions among the plurality of additions, is performed after a predetermined time has elapsed since the addition immediately before the subsequent addition.   The subsequent addition, which is the second and subsequent additions among the plurality of additions, is performed at a pH of 11.0 or higher in the composition to which (B) the aqueous aluminum sulfate solution is added in the subsequent addition. Item 6. The coated white paperboard according to item 4 or 5.   (A) The ratio (a / b) of the total number of moles a of the calcium hydroxide suspension a to the number of moles b of the (B) aqueous solution of aluminum sulfate added in multiple stages is 5.5 to 8.0. The coated white paperboard according to any one of claims 4 to 6, wherein   In the first addition which is the first stage addition among the plurality of stages of addition, (A) a mole of 85% or less of the reference mole number which is 1/6 mole number of the calcium hydroxide suspension. (B) an aqueous solution of aluminum sulfate, and the second addition and the first addition of the second stage of the plurality of stages of addition (B) of the total addition amount of the aqueous aluminum sulfate solution The coated white paperboard according to any one of claims 4 to 7, wherein the number of moles is 98% or less of the reference number of moles.   The coated white plate according to any one of claims 4 to 8, wherein at least one of (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aqueous aluminum sulfate solution is 12% by mass or less. paper.