JP2006336158A - Cast-coated paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cast-coated paper having a back-coating layer, having excellent whiteness and aging stability of color in spite of the use of satin white in the back-coating layer, exhibiting excellent surface smoothness (free from unevenness), preventing the staining of the drum surface and producible in high efficiency. <P>SOLUTION: A back-coating layer composed mainly of a pigment and an adhesive is applied to one surface of a base paper, and a primer coating layer composed mainly of a pigment and an adhesive is applied at need to the other surface of the base paper. A cast-coating layer composed mainly of a pigment and an adhesive is formed on the base paper and the paper is pressed against a hot mirror-face drum while the cast-coating layer is still in a wet state to effect the drying of the layer and the glaze finishing of the paper. The back-coating layer contains calcium trisulfoaluminate (satin white) having a pH of ≤12.0. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cast coated paper having a coating layer on the back surface.

  Cast coated paper has a very high surface gloss, excellent smoothness, and excellent printability. As a high-grade printing paper, it covers not only the cover of ordinary books, but also high-grade labels, fashion bags, etc. Widely used. There are three typical methods for producing such cast coated paper having high gloss and high smoothness. That is, a wet cast method in which a wet coating layer is pressed onto the surface of a heated drum that has been mirror-finished, dried, and released to give a gloss finish, and once the wet coating layer is dried, Wet and plasticize again, press contact with heated cast drum surface, rewet cast method to finish by mold release, further gelate wet coating layer, press contact with heated cast drum surface, It is a gelled cast method that is finished by releasing. These cast finishing methods are common in that the coating layer in a wet and plasticized state is pressed against the surface of the heated drum, dried, and released from the heated drum, and the mirror surface is copied.

  The coated paper produced according to these cast finishing methods has a strong glossy surface that is cast on one side and the back side is a so-called single-sided cast coated paper that has a high-quality paper-like surface. Some cast coated papers have a coating layer. This is because cast coated paper is used as a cover for books and magazines, or as text paper, while the gloss and smoothness of printed coated paper are increasing with the recent visualization, colorization, and upgrading. This is because the back surface quality is strongly demanded to have the same white paper quality and print quality as other text sheets.

  As a method for obtaining such a cast coated paper having a coating layer on the back surface, the basic method of the cast finish described above is not changed, and a pigment and an adhesive are previously applied to the back surface (non-cast surface) of the base paper. A coating layer as a main component is provided. Furthermore, if necessary, the base paper is smoothed by applying a calender treatment, and the surface of the base paper is coated with an aqueous coating liquid for casting mainly composed of a pigment and an adhesive, and the cast coating layer is in a wet state. It is pressed against a heated mirror drum and dried to give a high gloss finish. In some cases, the cast coated paper thus obtained may be subjected to a calendar process.

Also, in the production of such cast coated paper, the moisture in the cast coating layer provided on the surface cannot evaporate on the mirror drum side because the coating layer is in close contact with the mirror drum, Unlike the usual drying of coated paper, all of the paper passes through the base paper layer and escapes to the back and evaporates. For this reason, in the production of cast coated paper, the current situation is that it is forced to operate at an extremely low speed compared to the production of general art paper or coated paper dried from both sides of the coated paper. . In particular, in the production of a cast coated paper having a back coating layer, moisture in the cast coating layer is evaporated and dried through the base paper layer and further through the back coating layer. Since the permeability is remarkably reduced, the production speed is greatly reduced as compared to single-sided cast coated paper having no coating layer. Moreover, in the cast coated paper having the back surface coating layer, when the cast coated paper is manufactured using the base paper having the back surface coating layer smoothed by the calendar process, the water vapor permeability is further deteriorated. There is a problem to do.
Note that rapid evaporation of water causes the back coating layer to swell and soften, resulting in a decrease in smoothness and gloss, resulting in a decrease in print quality and printability, as well as a part of the back coating layer being peeled off. May adhere to the surface of the press roll and gradually accumulate. When press roll contamination occurs, the quality of the cast coated surface also deteriorates. That is, a part of the back coating layer adheres and accumulates on the surface of the press roll, resulting in a decrease in the smoothness of the press roll surface and non-uniform adhesion of the surface coating layer to the mirror drum. The so-called drum pick is generated in which the gloss of the surface is partially reduced or unevenness of drying occurs and a part of the surface coating layer adheres to the mirror drum. Therefore, the operation must be temporarily stopped to clean or replace the press roll, resulting in a significant reduction in productivity.

  Also, once the cast finish is complete, calendering is generally performed to smooth the coating layer on the back surface. However, this calendering causes unevenness in the cast surface that has been finished with a high smoothness. The current situation is that calendar processing cannot be performed under strong conditions because it may deteriorate.

  In order to solve the above problems, various proposals have been made. For example, as one method, there is an approach from the viewpoint of equipment, such as a calendar processing method after cast finishing. That is, in the calendering process, the surface temperature of the metal roll, the Shore D hardness and the surface roughness of the resin roll are finished under specific conditions (Patent Document 1), and when the first nip is passed, the cast coat surface is made of metal. A method (Patent Document 2) has been proposed in which the roll and the back surface are calendered so as to contact a resin roll having a specific Shore D hardness. Moreover, when casting, a method of pressing an elastic roll from the back surface (Patent Document 3) has also been proposed. However, in these methods, it is necessary to cope with the equipment and depending on the material used for the back surface. May not provide satisfactory quality.

  As another method, there is a method of approaching from the material side of the back coating layer. Generally, in order to improve white paper gloss and surface smoothness on the back surface, plate-like crystal kaolin is used as a main pigment as a pigment in the coating layer. In this case, kaolin used as a pigment tends not only to be oriented on the surface of the coating layer but also to be oriented in the same manner in the coating layer. Sexuality gets worse. Therefore, aluminum hydroxide, titanium dioxide, barium sulfate, calcium sulfite, zinc oxide, which have better water permeability than kaolin, or rice grains, spindles, spheres, amorphous light calcium carbonate, heavy calcium carbonate, etc. Is known to be used in combination with kaolin or alone.

  However, the cast coated paper using such a pigment has a problem that gloss and surface smoothness are remarkably lowered although moisture permeability is remarkably improved as compared with kaolin alone.

  In order to solve the above problems, a method (Patent Document 4) has been proposed in which specific light calcium carbonate is used for the undercoat coating layer and the back coating layer of the cast. However, with this method, although the water permeability at the time of cast finishing is improved, it is difficult to obtain satisfactory quality for the back surface. In addition, a method of using a hollow plastic pigment for an undercoat coating layer and a back coating layer of a cast has been proposed (Patent Document 5). However, even with this method, it is necessary to blend a large amount of expensive plastic pigments in order to obtain a satisfactory quality on the back surface, which is a problem in manufacturing cost.

  In addition, when calcium trisulfoaluminate (hereinafter satin white) is blended in the coating layer as a pigment, the coating layer surface is characterized by high surface smoothness, and is used for the coating layer of general art paper and coated paper. It is known that high white paper gloss and high surface smoothness can be obtained (Patent Documents 6 to 9), and a satin white or / and plastic pigment is blended on the back surface, and a specific calendar is applied after the cast finish as described above. A method of performing processing (Patent Document 10) has been proposed. In this method, when plastic pigment is used, there is a problem of manufacturing cost as described above, and when satin white is blended, the following problems occur.

  In other words, the coated paper is generally coated with a pulp fiber and coated with a coating composition on a base paper obtained by paper making and then dried with a dryer, followed by pressure smoothing with a super calender. However, the coated paper coated with a coating composition containing strong alkaline satin white (usually around pH 12.5) is subject to color reversal by drying with a dryer or heat treatment such as a thermal supercalender. It has been confirmed to encourage. Also, it is well known that a decrease in whiteness after storage for a long period of time is observed compared to that immediately after production, and the paper is yellowed, that is, a color return phenomenon due to an alkali component is observed. Discoloration of objects over time has become a major problem. In addition, when a coating liquid containing satin white is applied, in order to make the fluorescent whitening dye added to increase the whiteness the same whiteness as the coating liquid not containing satin white There is also a drawback that more must be added.

As a method of preventing the whiteness and hue of a coated paper with an alkaline coating layer containing satin white from fading over time, bleached chemical pulp with a specific copper value is used for the base paper of the coated paper. Method for suppressing decrease in whiteness of coated paper by specifying dynamic wetting value (Patent Document 11), chlorine content related to organochlorine compound contained in pulp fiber is 400 ppm or less, and interphase strength (TAPPI) of base paper -RC308) is 50 × 10 ⁻³ ft / lb / in ² to improve whiteness and hue fade over time (Patent Document 12), and an alkaline coating layer containing satin white was applied and dried. A method for producing a coated paper excellent in stability over time of whiteness and long-term storage by producing a paper surface temperature at 60 ° C. or less both immediately after and after calendering (Patent Document 13) Have been introduced.

  However, the above publication is a method obtained by improving the base paper and the manufacturing method, and is a manufacturing method different from normal coated paper manufacturing. Therefore, there are new sequences, installation of devices, and restrictions on operations. Applying a coating solution containing satin white, which has excellent white paper quality such as surface smoothness and white paper gloss, to general coated paper bases, and with excellent whiteness and hue stability over time even after drying and calendering Paper is desired.

  From the above, cast coated paper with a coating layer on the back side has excellent gloss and surface smoothness (brightness) on the surface of cast coated paper, no occurrence of uneven gloss and pinholes, and high productivity It is very difficult to maintain the actual condition, and the actual condition is manufactured at some sacrifice of either the quality of the cast coated paper or the productivity.

Japanese Patent Laid-Open No. 02-229293 Japanese Patent Laid-Open No. 04-300385 Japanese Patent Laid-Open No. 02-259187 JP 2001-81693 A JP 09-268493 A JP-A-11-247097 JP 09-256295 A JP 09-67794 A Japanese Patent Laid-Open No. 02-14098 Japanese Patent Laid-Open No. 02-14093 Japanese Patent No. 2834782 Japanese Patent No. 3027875 Japanese Patent Application Laid-Open No. 07-279097

  The present invention provides a cast coated paper having a back surface coating layer, which has satin white in the back surface coating layer, has excellent whiteness and hue temporal stability, and has a smooth surface (bokeh surface) of the cast surface. And a cast coated paper that can be produced with high efficiency without contamination of the drum surface.

The present invention provides a back coating layer mainly composed of a pigment and an adhesive on one side of a base paper, and an undercoat coating mainly composed of a pigment and an adhesive, if necessary, on the other side of the base paper. A cast coating layer mainly composed of a pigment and an adhesive is formed on a base paper provided with a coating layer, and is pressed against a heated mirror drum while the casting coating layer is in a wet state, and then dried. Then, in the cast coated paper to be finished with high gloss, the back coated layer is a cast coated paper containing satin white, and when the cast coated paper is heat-treated under the following conditions: The cast coated paper is characterized in that a difference in whiteness (according to JIS-P8148) before and after heat treatment on the back coated layer surface is less than 2.8.
Heat treatment conditions: heat treatment for 24 hours under conditions of 70 ° C. and 90% RH A back coating layer mainly composed of a pigment and an adhesive is provided on one side of the base paper, and necessary on the other side of the base paper According to the above, a cast coating layer mainly composed of a pigment and an adhesive is formed on a base paper provided with an undercoat layer mainly composed of a pigment and an adhesive, and the cast coating layer is wet. A cast coated paper which is pressed against a heated mirror drum while being in a state, dried and has a high gloss finish, and is a cast coated paper containing satin white in the back coating layer, When the coated paper is heat-treated under the following conditions, the cast coated paper is characterized in that the difference in b ^* (according to JIS-Z8722) in the hue before and after the heat treatment on the back surface coated layer surface is less than 1.3. is there.
Heat treatment conditions: heat treatment for 24 hours under conditions of 70 ° C. and 90% RH The satin white has a pH of 12.0 or less.
A back coating layer mainly composed of pigment and adhesive is provided on one side of the base paper, and an undercoat coating layer mainly comprising pigment and adhesive is provided on the other side of the base paper as required. A cast coating layer mainly composed of a pigment and an adhesive is formed on the base paper, and pressed and dried on a heated mirror drum while the cast coating layer is in a wet state, In the cast coated paper to be glossy finished, the back coated layer contains satin white having a pH of 12.0 or less.
It is preferable that pH of the satin white is 8.5 or more and 11.0 or less.
It is preferable that pH of the coating liquid for back surface coating layers containing the satin white is 11.0 or less.
It is preferable that the average particle diameter of the satin white is 0.1 to 1.5 μm.
In the case where the base paper is a base paper having a paper surface pH of 5.5 or more, the effect of excellent temporal stability such as whiteness and hue is more exhibited.
The satin white is preferably contained in an amount of 2 to 30% by mass in the total pigment in the coating layer.
The satin white of the back coating layer used in the present invention was produced by reacting (A) a calcium hydroxide suspension and (B) an aqueous aluminum sulfate solution, and (A) a calcium hydroxide suspension. (B) Aluminum sulfate aqueous solution is added to the liquid in a plurality of stages, and (A) At least one of the (B) aluminum sulfate aqueous solution added to the calcium hydroxide suspension is continuously transferred. It is preferable to be performed by continuous addition in which (B) an aqueous solution of aluminum sulfate is continuously added to the (A) calcium hydroxide suspension.
In the method for producing satin white of the present invention, it is preferable that 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.
In the method for producing satin white according to the present invention, the subsequent addition, which is the second and subsequent additions among the plurality of additions, has a pH of 11. It is preferable to carry out at 0 or more.
For the satin white of the present invention, the ratio (a / b) of (A) the number of moles a of the calcium hydroxide suspension to the number of moles b of the total amount of (B) the aqueous solution of aluminum sulfate added in multiple stages, It is preferable that it is 5.5-7.0.
About the manufacturing method of satin white of the present invention, in the first addition which is the first stage addition among the plurality of stages, (A) the number of moles is 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 a reference mole number is added, and the second addition and the first addition (the second addition among the plurality of additions) ( B) The total number of moles of the aluminum sulfate aqueous solution is preferably 98% or less of the reference mole number.
About the satin white of this invention, it is preferable that at least one of the density | concentration of (A) calcium hydroxide suspension and the density | concentration of (B) aluminum sulfate aqueous solution is 12 mass% or less.

  The cast coated paper according to the present invention has a coating layer on the back surface, and contains satin white in the back surface coating layer, while being excellent in the whiteness of the back surface and the temporal stability of the hue, and on the cast surface. It has excellent surface smoothness (brightness) and can be manufactured with high efficiency without contamination of the drum surface.

  From the actual situation as described above, the present inventors have conducted intensive research to obtain a cast coated paper that has a pigment coated layer on the back surface, and has excellent operability and quality. As a result, we found that cast coated paper with the desired characteristics can be obtained efficiently (at high speed) by using specific satin white as a pigment in the back coating layer, and the present invention was completed. It came to do.

  In general, base papers used for cast coated papers include two types of paper making methods: acid paper making methods and neutral paper making methods. However, since the 1980s, due to the increasing demand for long-term storage of paper, most of the coated paper base papers currently used are base papers produced by the neutral papermaking method. In addition, a base paper by a neutral papermaking method is used because of the ease of waste paper processing that occurs during the manufacture of coated paper.

  In general, when adding satin white having a pH exceeding 12.0 to about 12.5 to 12.7 in the coating liquid, the coating before blending the satin white to improve the stability of the coating liquid. Sodium hydroxide is added to the liquid, and as a result, the pH of the coating liquid containing satin white generally exceeds 11.0.

  When the alkaline coating liquid is applied to the base paper, the coating liquid penetrates into the bleached chemical pulp in the base paper, and the color of the pulp is regenerated by the alkaline component in the coating liquid. This is presumed to involve carbonyl group, carboxyl group and hydroxyl group in the pulp. In the case of base paper by the acid papermaking method, sulfate ions present in the paper neutralize the alkaline components of the coating solution, so it has the effect of suppressing the color return of the pulp and changes over time such as the whiteness of the coated paper Is not clarified. However, since the base paper produced by the neutral papermaking method has few acidic substances in the paper, the color of the pulp is returned due to the alkali component of the coating solution, and the change over time in the whiteness of the coating solution is large. In particular, when the pH of the coating solution is high, the color return of the pulp is remarkably accelerated by heat, and the decrease in whiteness and hue over time becomes extremely large.

  Specifically, when satin white is included in the coating solution, the whiteness and hue of the coated paper between the coater and the super calender and between the super calender and the cutter and winder greatly change over time. It has dropped significantly.

  In the cast coated paper containing satin white in the back surface coating layer of the present invention, the pH of the back surface coating layer coating solution that causes a change in the whiteness and hue of the back surface of the cast coated paper is lowered. That is, the color return due to the alkali component is suppressed by setting the pH of satin white, which is the cause of increasing the pH of the coating solution, to 12.0 or less.

  As a result, the cast coated paper containing satin white in the back surface coating layer of the present invention is subjected to a heat treatment for 24 hours under the conditions of 70 ° C. and 90% RH. The difference in whiteness (according to JIS-P8148) before and after heat treatment was less than 2.8, and it became possible to obtain a coated paper having excellent temporal stability such as whiteness and hue.

Similarly, the cast coated paper containing satin white in the back surface coating layer of the present invention has a back surface coating layer surface when heat-treated for 24 hours at 70 ° C. and 90% RH. The difference in b ^* (according to JIS-Z8722) in the hue before and after the heat treatment was less than 1.3, and it became possible to obtain a coated paper having excellent temporal stability such as whiteness and hue.

  In order to satisfy the above quality characteristics, the pH of satin white contained in the back surface coating layer needs to be 12.0 or less, and the pH is preferably 8.5 or more and 11.0 or less, More preferably, the pH is 9.2 or more and 10.5 or less.

  When the pH of satin white exceeds 12.0, the temporal change in whiteness and hue due to the alkali component increases. In order to suppress changes in whiteness and hue over time, it is preferable to lower the pH of satin white as much as possible. However, when the pH is less than 8.5, the crystal shape of satin white collapses, and aluminum hydroxide or Since reaction by-products of calcium sulfate are mixed, it is not preferable because blank paper quality such as the surface smoothness and blank gloss of satin white is deteriorated. Further, satin white having a pH of 11.0 or less has an advantage that it can be treated in the same manner as a general pigment because a coating solution can be prepared without adding or adding a small amount of sodium hydroxide for coating solution stability.

  For the above reasons, the pH of the coating solution for the back surface coating layer containing satin white of the present invention is preferably 11.0 or less, and 10.0 which is the pH of a coating solution similar to general coated paper. More preferably, it is as follows.

  It does not specifically limit whether the back surface coating layer containing satin white having a pH of 12.0 or less according to the present invention is a single layer or a multilayer. In addition, in the case of multiple layers, all coating layers may contain satin white, but when containing satin white in the coating layer in contact with the base paper, about the effect of suppressing changes in whiteness and hue over time In the case of satin white having a pH of 12.0 or less as compared with conventional satin white (around pH 12.5), this becomes remarkable. This is because the strongly alkaline coating solution does not directly contact the base paper, and therefore, the color reversal of the pulp is prevented from proceeding in a relatively short time.

  Further, the satin white used in the present invention is preferably in the range of an average particle diameter of 0.1 to 1.5 μm by a sedimentation method from the viewpoint of white paper gloss, surface smoothness and releasability on a cast drum, In particular, a range of an average particle size of 0.3 to 0.8 μm is more preferable. Incidentally, when the average particle size of satin white exceeds 1.5 μm, the effect of white paper gloss and surface smoothness on the coating layer is small. Further, when the average particle diameter is smaller than 0.1 μm, it is effective for the white paper glossiness and surface smoothness of the coated paper, but the strength required for the coated paper for printing is exhibited. This is not preferable because the amount of adhesive required for the increase in the amount of the adhesive and the releasability on the cast drum may deteriorate.

The details of the average particle size measurement by the precipitation method are as follows. Using a Sedigraph 5100 manufactured by Micromeritics, Inc. in the United States, the particle size distribution of the composition containing the produced satin white was measured, and the average particle size (d50) corresponding to 50 cumulative mass% was determined. In addition, the composition containing satin white used for the measurement was 0.1% of the phosphate dispersant (sodium pyrophosphate) with respect to the dispersion liquid of the composition containing satin white obtained after completion of the reaction. It was obtained by diluting and dispersing in an aqueous solution so that the pigment solid content concentration was about 4%. As measurement conditions, the specific gravity of satin white was 1.77 g / cm ³ , and the measurement temperature was 35 ° C.

  Further, the content of satin white in the back surface coating layer in the present invention is not particularly limited, but it is preferable to contain 2 to 30% by mass in the total pigment in the coating layer, and particularly 3 to 20%. It is preferable to make it contain in the range of mass%.

  Inclusion of satin white in the coating layer improves white paper quality such as smoothness of the coating layer and glossiness of the white paper. However, if the content of satin white is less than 2% by mass of the total pigment, white paper is used. On the other hand, if the content of satin white exceeds 30% by mass, it is effective for improving the quality of the white paper of the coating layer, but for the strength expression as coated paper. This is not preferable because the amount of the adhesive required for the process increases and is uneconomical.

  The satin white used for the back surface coating layer of the present invention is based on the production method described in Japanese Patent Application No. 2005-123687.

That is, it is produced by reacting (A) a calcium hydroxide suspension and (B) an aluminum sulfate aqueous solution, and (A) a plurality of (B) aluminum sulfate aqueous solutions are added to the calcium hydroxide suspension. (A) Calcium hydroxide suspension to which at least one of (B) addition of a plurality of stages of aqueous solution of aluminum sulfate is continuously transferred to (A) calcium hydroxide suspension (B) It is performed by continuous addition of continuously adding an aqueous aluminum sulfate solution.
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.

That is, first, this method is characterized in that an aqueous aluminum sulfate solution added to a calcium hydroxide suspension is added in a plurality of 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 this method, in addition to the above-described divided addition of the aqueous aluminum sulfate solution, (A) at least one of the steps of adding the aqueous aluminum sulfate solution (B) to the calcium hydroxide suspension is continuously performed. (A) It is characterized by performing by the continuous addition which adds (B) aluminum sulfate aqueous solution continuously to the calcium hydroxide suspension.
This is because, in the present invention, for the addition of the aqueous aluminum sulfate solution divided into a plurality of stages, the aqueous aluminum sulfate solution is gradually added to a predetermined amount of calcium hydroxide suspension over a long period of time. The “batch” method may be used, but regarding the fine and uniform control of the particle size of the generated satin white, the calcium hydroxide suspension that is continuously transferred than the “batch” method is used. Thus, the “continuous addition” method in which the aqueous aluminum sulfate solution is continuously added is superior, so in the satin white used in the present invention, in any addition of the aqueous aluminum sulfate solution performed in multiple stages, The addition by the “continuous addition” method is performed at least once.

  In addition, in the present method, for the addition of the aqueous aluminum sulfate solution by the “continuous addition” method of the present invention, among the additions of the aqueous aluminum sulfate solution divided into a plurality of stages, the first stage addition is “continuous addition”. In addition, 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 of the present invention, 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, The subsequent 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, in this method, 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 stages, is carried out. The pH of the composition to be added may be 11.0 or more.
“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, in the present invention, the pH of the mixed composition before adding aluminum sulfate is preferably 11.0 or more, more preferably 12.0 or more, and the reactivity of calcium hydroxide is increased. In order to recover to a completely stable 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.

  In this method, when producing satin white, (A) the number of moles a of the calcium hydroxide suspension added in multiple stages and added in multiple stages (B) the number of moles of the total amount of aluminum sulfate aqueous solution added The ratio (a / b) to b is preferably 5.5 to 7.0.

(A) The ratio (a / b) between 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 added in multiple stages (a / b) Specifically, a / b = 6.0, which indicates that 6 mol of calcium hydroxide and 1 mol of aluminum sulfate are required to produce 1 mol 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, since the reactivity of calcium hydroxide is very dull, it is extremely difficult to complete the reaction at the 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. Further, the upper limit of the reaction molar ratio (a / b) between calcium hydroxide and aluminum sulfate is more preferably 7.0 or less, and particularly preferably 6.0 (usually calcium hydroxide and aluminum sulfate). The range of the reaction molar ratio (a / b) is preferably a / b = 5.5 to 7.0, particularly preferably a / b = 5.8 to 7.0.) . 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 Since reaction by-products such as calcium are generated in large quantities, it is not preferable, and it is not preferable that the reaction molar ratio exceeds 7.0 because it becomes difficult to obtain satin white having a pH of 12.0 or less.

  Here, as a measuring method of “pH of the composition containing (C) satin white”, at least 10 minutes or more after the final addition of the aqueous aluminum sulfate solution is completed in order to stabilize the state of the remaining calcium hydroxide. The pH measurement is preferably performed after 5 hours or more have elapsed, and for the pH measurement, it is preferable to use a pH meter calibrated with a pH standard calibration solution at least once on the day of measurement. For example, you may make it measure pH of the composition containing (C) satin white of 25 degreeC after progress for 24 hours after completion | finish of the last stage addition of aluminum sulfate aqueous solution. Moreover, as a measuring instrument, a Lacom tester pH meter (pHScanWPBN type / manufactured by ASONE) is used, and (C) a pH electrode is directly immersed in a dispersion of a composition containing satin white to adjust the pH of the composition. taking measurement. In addition, about the pH meter used for pH measurement, after performing pH calibration using NIST reference | standard calibration liquid (pH 6.86 and two types of pH 9.18), pH measurement is performed.

  Regarding the production method of satin white, in the conventional method, the occurrence of reaction by-products of aluminum oxide and calcium sulfate is prevented by maintaining a state where calcium hydroxide is always excessive with respect to aluminum sulfate. However, in order to maintain the excessive state of calcium hydroxide, unreacted calcium hydroxide remains in the generated satin white, and in the satin white where the remaining calcium hydroxide is generated. Therefore, the pH of the conventional satin white suspension is strongly alkaline (pH 12.5 to 12.7).

However, in this method, by adding a predetermined amount of an aluminum sulfate aqueous solution divided into a plurality of stages to the calcium hydroxide suspension having a low reactivity, the aqueous aluminum sulfate solution is added to the reaction end point, Since residual unreacted calcium hydroxide in the satin white suspension can be suppressed, high-quality satin white with low alkalinity can be stably produced.

Therefore, by optimizing the addition amount of the aluminum sulfate aqueous solution by this method, it becomes possible to adjust the pH of the composition containing satin white to be generated to 12.0 or less. By further optimizing, it became possible to obtain a preferable value of 11.0 or less and a more preferable value of 10.5 or less. P
As a lower limit of H, the pH is preferably 8.5 or more, and particularly preferably 9.2 or more.

  This pH can be adjusted by the amount of the aluminum sulfate aqueous solution added. Specifically, (A) the total number of (B) aluminum sulfate aqueous solutions added in multiple stages (a) in the number of moles a of the calcium hydroxide suspension. The pH can be adjusted by changing the ratio (a / b) of the addition amount to the number of moles b. If the ratio (a / b) is increased, the pH increases, and if the ratio (a / b) is decreased, the pH decreases. Therefore, the ratio (a / b) is set to 5.5 so that the predetermined pH is obtained. Adjustment may be made within a range of ˜7.0.

When the pH of the composition containing satin white exceeds 12.0, as described above, a large amount of unreacted calcium hydroxide remains, which is not preferable. On the other hand, a composition containing satin white If the pH of the product is less than 8.5, beyond the reaction end point,
Since an aqueous aluminum sulfate solution is added excessively, the crystal form of the produced satin white is destroyed, and reaction byproducts of aluminum hydroxide and calcium sulfate are generated, which is not preferable.

  Further, in order to increase the average particle size of (C) satin white produced by this method, (A) the number of addition stages of (B) aluminum sulfate aqueous solution to the calcium hydroxide suspension is increased, The flow rate in continuous addition in which (B) the aqueous solution of aluminum sulfate is continuously added to the (A) calcium hydroxide suspension to be transferred may be decreased (that is, the residence time in continuous addition is increased). Conversely, in order to reduce the average particle size of (C) satin white produced by this method, (A) the number of steps of addition of (B) aluminum sulfate aqueous solution to the calcium hydroxide suspension can be reduced or continuously (A) to increase the flow rate in continuous addition (ie, to reduce the residence time in continuous addition) in which (A) the aqueous solution of calcium sulfate is continuously added to the calcium hydroxide suspension (A) The addition amount of the (B) aluminum sulfate aqueous solution in the first addition among the additions of the (B) aluminum sulfate aqueous solution to the calcium hydroxide suspension may be reduced. For this reason, what is necessary is just to change these conditions suitably so that it may become a desired average particle diameter.

  In this method, (B) the number of moles of the calcium hydroxide suspension in the first addition, which is the first stage addition, of the addition of the aqueous aluminum sulfate solution (B) carried out in a plurality of stages. (B) an aqueous solution of aluminum sulfate that is 85% or less of the reference number of moles, which is 1/6 of the number of moles, and the second addition that is the second stage addition among the plurality of stages of addition And (B) the total addition amount of the aluminum sulfate aqueous solution in the first addition may be 98% or less of the reference mole number (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 (ie, before the reaction in the first stage of 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 mass% 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, in this method, 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. It is more preferable that the concentration is not more than mass%, and it is most preferable that both (A) the concentration of the calcium hydroxide suspension and (B) the concentration of the aqueous aluminum sulfate solution are not more than 6 mass%.

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 aluminum sulfate aqueous solution is 0.1% by mass or more, and at least one is 1% by mass or more. It is particularly preferred.

  In the present invention, the reason why the surface smoothness of cast coated paper is improved by using satin white for the back surface coating layer is estimated as follows. That is, the back coating layer is generally subjected to a smoothing process using a super calendar or the like in order to improve the printing quality. At this time, due to the influence of the base paper formation, the cast surface is blurred, and the surface smoothness of the cast surface is deteriorated, but the back coating layer contains satin white to form a highly smooth coating layer. This is because the smoothing process can be reduced. Furthermore, a bulky cast-coated paper can be obtained by reducing the smoothing process using a super calendar or the like.

  In addition, in the production of cast coated paper, when conventional satin white having a pH of about 12.5 to 12.7 is used for the back coating layer, the cast coating liquid is affected during long-time operation. In some cases, the releasability on the drum deteriorates and drum picking occurs. Although the reason for this is not clear, calcium ions are eluted from the calcium hydroxide remaining in the back surface coating solution in a long-time operation and mixed into the aqueous coating solution for casting. As a result, it is presumed that this calcium ion is adsorbed on the surface of the cast drum or the release agent in the coating solution, and the release effect cannot be exhibited.

  In the present invention, the specific pigment other than satin white contained in the back coating layer includes, for example, kaolin, talc, clay, calcined kaolin, heavy calcium carbonate, light calcium carbonate, titanium dioxide, calcium sulfite, gypsum, sulfuric acid Of inorganic pigments such as barium, white carbon, amorphous silica, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite In addition, organic pigments such as urea formalin resin fine particles and fine hollow particles can be exemplified, and these can be used in combination.

  In the present invention, as the adhesive on the back coating layer, proteins such as casein and soy protein, styrene-butadiene copolymer, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer Latex, vinyl polymer latex such as ethylene-vinyl acetate copolymer and other vinyl polymers, or alkali-solubilities obtained by functionally modifying these polymers with monomers containing functional groups such as carboxyl groups Or alkali-insoluble polymer latex, polyvinyl alcohol, olefin-maleic anhydride resin, synthetic resin adhesive such as melamine resin, starches such as positive starch, oxidized starch, esterified starch, carboxymethyl cellulose, hydroxy For general coated paper such as cellulose derivatives such as methylcellulose The adhesive known can be used alone or in combination. In addition, the usage-amount of an adhesive agent is 5-50 mass parts with respect to 100 weight part of pigments, Preferably 10-30 mass parts is mix | blended.

  In the coating composition for the back surface coating layer of the present invention, for the purpose of improving the water resistance and blocking resistance of the coating layer, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, polyethylene glycol diester is used. Polyfunctional epoxy compounds such as glycidyl ether, polypropylene glycol diglycidyl ether, or adipic acid diglycidyl ester, zirconium compounds such as ammonium zirconium carbonate and zirconium acetate, urea-formaldehyde, melamine-formaldehyde, and polyamide urea-formaldehyde Various water-resistant agents and printability improvers such as resins such as resins, glyoxal, water-soluble polyamine resins, and water-soluble polyamide resins can be appropriately added. And the addition ratio in that case is adjusted in 0.01-10 mass parts with respect to 100 mass parts of pigments. Further, as long as the effect of the present invention is not hindered, blue or purple dyes, colored pigments, fluorescent dyes, thickeners, water retention agents, antioxidants, anti-aging agents, conductive treatment agents, antifoaming agents, ultraviolet rays Various auxiliaries such as an absorbent, a dispersant, a pH adjuster, a mold release agent, a water-proofing agent, and a water repellent can be appropriately mixed.

The back coating layer composed of the above materials is generally prepared after the solid content concentration is adjusted to about 45 to 65% by mass, and then dried on a base paper or a porous film of about 35 to 400 g / m ² . When the weight is about 3 to 50 g / m ² per side and emphasis is placed on improving productivity, about 3 to ²⁰ g / m ² is applied. Of course, when forming the back surface coating layer, it is also possible to carry out multilayer coating of two or more layers.

  The coating apparatus for providing the back surface coating layer on the base paper is not particularly limited, and is used in the ordinary coated paper manufacturing field, for example, a blade coater, an air knife coater, a roll coater, Known and publicly used apparatuses such as a brush coater, a Chanplex coater, a bar coater, and a gravure coater are appropriately used.

  Next, the base paper used for the cast coated paper in the present invention will be described. The base paper used for the cast coated paper of the present invention is not particularly limited, and is appropriately selected and used as long as the following materials do not interfere with the desired effects of the present invention.

  Examples of the pulp include generally used bleached chemical pulps such as LBKP and NBKP, ground wood pulp (GP), pressurized ground wood pulp (PGW), refined ground wood pulp (RGP), and thermomechanical pulp (TMP). Pulp, deinked waste paper pulp (DIP), waste paper, and the like are appropriately mixed and used. Moreover, 1 type, or 2 or more types, such as a pulp fiber obtained from non-wood fiber raw materials, such as kenaf, a synthetic pulp, an inorganic fiber, can also be mix | blended with a base paper. Mechanical pulp and DIP can be used after being bleached if necessary, and the degree of bleaching can be arbitrarily performed. For bleaching pulp, it is preferable to use a bleaching process that does not use molecular chlorine such as chlorine gas or chlorine compounds such as chlorine dioxide from the viewpoint of environmental conservation. Pulp that has undergone such bleaching process is used. Examples thereof include ECF pulp and TCF pulp.

  Examples of fillers internally added to the base paper include heavy calcium carbonate, light calcium carbonate, calcium sulfite, gypsum, talc, kaolin, clay, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, diatomaceous earth, carbonic acid. Examples include inorganic pigments such as magnesium, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide, and organic pigments such as urea formalin resin fine particles and fine hollow particles, and are included in waste paper and waste paper. The filler can also be reused. Two or more fillers can be used in combination. The blending amount of the filler is generally added so that the paper (base paper) ash content is in the range of 3 to 20% by mass.

  In addition to pulp and fillers, various types of papermaking exemplified by an internal sizing agent, anionic, nonionic, cationic or amphoteric yield improver, drainage improver, paper strength enhancer, etc. The internal additive aid can be added as necessary. Specific examples of the internally added sizing agent include alkyl ketene dimer, alkenyl succinic anhydride, styrene-acrylic, higher fatty acid, petroleum resin sizing agent, rosin sizing agent and the like. Specific examples of yield improvers, drainage improvers, and paper strength enhancers include, for example, polyvalent metal compounds such as aluminum (specifically, sulfate bands, aluminum chloride, sodium aluminate, basic aluminum compounds). Etc.), various starches, polyacrylamide, urea resin, polyamide / polyamine resin, polyethyleneimine, polyamine, polyvinyl alcohol, polyethylene oxide and the like.

In general, the basis weight of the base paper used for the cast coated paper of the present invention is appropriately adjusted within a range of about 30 to 400 g / m ² . Moreover, the papermaking conditions of the base paper are not particularly limited. As the paper machine, for example, a commercial paper machine such as a long paper machine, a gap former paper machine, a circular paper machine, or a short paper machine can be selected and used as appropriate according to the purpose. . The papermaking method may be any of acid papermaking, neutral papermaking, weak alkaline papermaking, etc., but when using a base paper by neutral-alkali papermaking, the conventional pH is around 12.5 as described above. The difference from the coated paper having a coated layer containing satin white is remarkable. It is also possible to perform size processing on the base paper using various size press machines and roll coaters using natural adhesives such as starch and synthetic adhesives such as polyvinyl alcohol. When performing size processing with the base paper of the present invention Means the base paper after size processing.

Next, the undercoat coating layer of the cast coating layer will be described. In the present invention, the undercoat coating layer is not essential and is formed as necessary. As a coating composition in the case of forming an undercoat coating layer, the undercoat coating layer is not particularly limited, and those generally known in the field of coated paper are used. Is determined as appropriate according to the final quality specification. Of course, the specific satin white defined in the present invention can be contained in the cast coating composition, and the addition ratio in that case is adjusted to 1% by mass or more with respect to 100% by mass of the pigment. . The undercoat coating composition is generally prepared so that the solid content concentration is about 45 to 65% by mass, and the weight after drying is about 3 to 50 g / m ² , as with the back surface coating composition. When emphasizing the improvement of productivity, about 3 to ²⁰ g / m ² is applied. Of course, when forming the undercoat coating layer, it is also possible to carry out multilayer coating of two or more layers.

Next, the cast coating composition used for the cast coating layer will be described. The coating composition for casting is not particularly limited, and those commonly known in the field of cast coated paper are used, and the composition of the composition is appropriately determined according to the final quality specification intended. is there. The cast coating composition is generally prepared so that the solid content concentration is about 45 to 65% by mass, and the weight after drying is 3 to 30 g per side on the base paper provided with the above-mentioned undercoat coating layer. / M ² , more preferably 10 to 20 g / m ² .

  The coating apparatus for coating the cast coating composition is not particularly limited, and includes, for example, trailing, flexible, roll application, fountain application, and short dwell commonly used in the cast coated paper field. Known coating devices such as bevel type and vent type blade coaters, air knife coaters, bar coaters, rod blade coaters, champ flex coaters, gate roll coaters, gravure coaters, curtain coaters, die coaters and spray coaters can be used as appropriate. . After that, while the cast coating layer is in a wet state, it is pressed against a heated mirror drum and dried to give a high gloss finish.

Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% in an example show a solid content mass part and solid content mass%, respectively.
The cast coated paper obtained in each Example and Comparative Example was evaluated by the following method, and the results are shown in Table 1.

(Average pigment particle size)
Disperse the pigment in a 0.1% solution of sodium pyrophosphate with an ultrasonic wave for 5 minutes, and perform precipitation using an X-ray transmission particle size distribution analyzer (model name: Cedygraph 5100, manufactured by Micromeritics). It was measured. The average particle size is shown by the particle size at the point where the cumulative mass from the coarse particles corresponds to 50%.

(PH measurement method)
In the following examples and comparative examples, the pH of the satin white slurry and the coating solution was measured by the following method.
Using a Lacom Tester pH meter (pHScanWPBN type, manufactured by ASONE), pH electrodes were directly immersed in various dispersions and coating solutions to measure the pH of the pigment dispersion and the coating solution. In addition, about the pH meter used for pH measurement, after performing pH calibration using NIST reference | standard calibration liquid (pH 6.86 and two types of pH 9.18), pH measurement was performed.

(Page pH)
Using a tape, the coated paper is divided to expose the base paper surface. According to 49-2, the measurement was performed using a pH meter for measuring the paper surface of Kyoritsu Riken Co., Ltd., MPC type.

Example 1
-Preparation of satin white (1) Addition of first-stage aluminum sulfate aqueous solution to calcium hydroxide suspension 6% water as described above for in-line mixer (pipeline homomixer, mixing means) rotated at 9000 rpm 300 g / min of calcium oxide suspension and 185 g / min of 6% aluminum sulfate aqueous solution (80% of the standard mole number. The calculation method of the standard mole number will be described later) simultaneously and continuously. The injection was performed continuously 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 (intermediate tank as referred to in the present invention) and allowed to stand for 30 minutes for pH recovery. The pH of the mixed composition after the pH recovery (hereinafter referred to as “first composition”) was 12.8.

  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, 185 g / min of 6% aluminum sulfate aqueous solution contains 185 g × 6% = 11.1 g / min of aluminum sulfate, which is 11.1 g / min × 1 / 342.16 in terms of moles. = 0.0324 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 (0.0324 mol / min) / (0.0405 mol / min) = 80%.

(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 injected simultaneously and continuously at 485 g / min and a 6% aqueous solution of aluminum sulfate at 35 g / min (15% of the reference mole number), and the injection was continued 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 (intermediate tank as referred to in the present invention) and allowed to stand for 30 minutes for pH recovery. The pH of the mixed composition after the pH recovery (hereinafter referred to as “second composition”) was 12.4.

(3) Addition of third-stage aluminum sulfate aqueous solution (end of reaction)
In the same manner as in (2) above, 520 g / min of the mixed composition (second composition) and 6% aluminum sulfate aqueous solution with respect to the in-line mixer (pipeline homomixer, mixing means) rotated at 9000 rpm Were simultaneously and continuously injected at 11 g / min (5% of the reference mole number), and the injection was continuously carried out 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 10.6.

The method for 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 231 g / min × 10 minutes = 2310 g, the solid content contained in it is 138.6 g, and Al ₂ (SO ₄ ) is ₃ moles b. Is 0.405 mol. Therefore, the molar ratio (Ca (OH) ₂ / Al ₂ (SO ₄ ) ₃ = a / b) is 6.0. Moreover, the total addition rate of aluminum sulfate was 100% (= 80% + 15% + 5%) 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 dispersant (trade name: Aron T-50, manufactured by Toa Gosei Chemical Co., Ltd.) is previously added to water in an amount of 0.5 part 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 0.49 μm.

-Preparation of coating solution for back surface coating layer 70 parts of kaolin (trade name: UW-90, manufactured by Engelhard), 23 parts of light calcium carbonate (trade name: Tama Pearl TP-123CS, manufactured by Okutama Kogyo Co., Ltd.), the above satin 7 parts of white (in terms of solid content) and 0.5 part of sodium polyacrylate were dispersed in water using a Coreless disperser to prepare a pigment slurry having a solid content concentration of 65%. To this pigment slurry, 4 parts of oxidized starch and 15 parts of styrene-butadiene copolymer latex (both in terms of solid content) are added as an adhesive to 100 parts of pigment, and the back surface coating has a solid content concentration of 60%. A layer coating solution was prepared.

-Preparation of casting undercoat coating solution Kaolin (trade name: UW-90, manufactured by Engelhard) 70 parts, light calcium carbonate (trade name: Tama Pearl TP-123CS, manufactured by Okutama Kogyo Co., Ltd.), sodium polyacrylate 0.5 parts was dispersed in water using a Coreless disperser to prepare a pigment slurry having a solid content concentration of 65%. To this pigment slurry, 4 parts of oxidized starch and 15 parts of styrene-butadiene copolymer latex (both in terms of solid content) are added as an adhesive to 100 parts of pigment, and an undercoat coating with a solid content concentration of 60% is added. A liquid solution was prepared.

-Preparation of coating solution for casting Kaolin (trade name: UW-90, manufactured by Engelhard) 85 parts, light calcium carbonate (trade name: PX, manufactured by Shiraishi Kogyo Co., Ltd.), 15 parts, sodium polyacrylate 0.5 part Was dispersed in water using a Coreless disperser to prepare a pigment slurry having a solid concentration of 65%. To 100 parts of the pigment slurry, 1.0 part of ammonium stearate as a release agent and 10 parts of a 15% casein aqueous solution dissolved in ammonia as an adhesive (in terms of solid content) and styrene-butadiene 15 parts of polymer latex (in terms of solid content) was added to prepare a coating solution for casting having a solid content concentration of 54%.

・ Preparation of base paper 85% LBKP (CSF 430 ml) bleached in multiple steps in the process of oxygen-ozone-sodium hydroxide-hydrogen peroxide-chlorine dioxide and oxygen-ozone-sodium hydroxide-hydrogen peroxide-chlorine dioxide After adding light calcium carbonate (Tama Pearl TP-121 / Okutama Kogyo Co., Ltd.) as a filler to a pulp slurry consisting of 15% of NBKP (CSF 450 ml) bleached in multiple stages in the process, the pulp becomes 10%. Aluminum sulfate 0.5% based on solid content, cationic starch (Ace K-100 / Oji Cornstarch) 0.5%, alkyl ketene dimer sizing agent (Size Pine K-287 / Arakawa Chemical Co.) 0.1 % And polyacrylamide (Polystron 851 / Arakawa Chemical Co., Ltd.) 0.02% were added sequentially to prepare the paper stock. Made. Papermaking obtained stock with on-top twin wire paper machine, further a gate roll size press apparatus oxidized starch (Ace A / Oji Cornstarch Co., Ltd.) in both 1.5 g / m 2 ^(solid content) coated and dried Then, a smoothing process was performed using a machine calendar to obtain a base paper having an actual amount of 119 g / m ² , a tightness of 0.75 g / cm ³ , and a paper surface pH of 7.6.

Cast coated of the paper manufactured using a blade coater on a base paper, coating the cast undercoat coated liquid to be 13 g / m ² on a dry weight on one side to be, dried, on the opposite surface thereof, the dry weight The coating solution for the back surface was applied and dried so as to be 14 g / m ² . Next, the cast coating solution is applied onto the cast undercoat coating layer with a roll coater so that the dry weight becomes 10 g / m ^2, and the paper is immediately cast with a press roll at a surface temperature of 80 ° C. After pressing and drying the drum, it was cast from the cast drum and released from the cast drum. Furthermore, using a super calender, the coated surface was smoothed by passing the paper so that the cast surface was in contact with the metal roll under the conditions of a speed of 500 m / min and a linear pressure of 200 kN / cm to obtain a cast coated paper.

Example 2
-Preparation of satin white The first stage aluminum sulfate aqueous solution addition amount in Example 1 was added at 104 g / min (45% of the reference mole number), and in addition of the second stage aluminum sulfate aqueous solution, the mixed composition The product (first composition) was added at 404 g / min, the aluminum sulfate aqueous solution was added at 81 g / min (35% of the reference number of moles), and in addition of the third stage aluminum sulfate aqueous solution, The composition after completion of the reaction was obtained in the same manner as in Example 1 except that the reaction was terminated by adding 485 g / min of the composition) and 34 g / min of the aqueous aluminum sulfate solution (15% of the reference mole number). . At this time, the pH after recovery of the pH of each mixed composition (first composition, second composition) before the addition of the second-stage and third-stage aluminum sulfate aqueous solutions is 12.7, and 12.5. Moreover, the pH of the composition after completion | finish of reaction was 11.5. The average particle size was 0.44 μm.

In addition, 6% calcium hydroxide finally used is 300 g / min × 10 min = 3000 g, the solid content included in the 6% calcium hydroxide 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% of the reference mole number.

-Manufacture of cast coated paper A cast coated paper was obtained in the same manner as in Example 1 except that the above satin white was used in the preparation of the coating liquid for the back surface coating layer in Example 1.

Example 3
-Preparation of satin white The first stage aluminum sulfate aqueous solution addition amount of Example 1 was added at 58 g / min (25% of the reference number of moles), and in addition of the second stage aluminum sulfate aqueous solution, the mixed composition The product (first composition) was added at 358 g / min, the aqueous solution of aluminum sulfate was added at 162 g / min (70% of the reference number of moles), and in addition of the aqueous solution of aluminum sulfate in the third stage, The composition after completion of the reaction was obtained in the same manner as in Example 1 except that the composition was added at 520 g / min and the aqueous aluminum sulfate solution was added at 11 g / min (5% of the reference mole number) to terminate the reaction. . At this time, the pH of each mixed composition (first composition, second composition) before the addition of the second and third stage aluminum sulfate aqueous solutions is 12.8, and 12.4. Moreover, the pH of the composition after completion | finish of reaction was 9.7. The average particle size was 0.46 μm.

In addition, 6% calcium hydroxide finally used is 300 g / min × 10 min = 3000 g, the solid content included in the 6% calcium hydroxide 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 231 g / min × 10 minutes = 2310 g, the solid content contained in it is 138.6 g, and Al ₂ (SO ₄ ) is ₃ moles b. Is 0.405 mol. Therefore, the molar ratio (Ca (OH) ₂ / Al ₂ (SO ₄ ) ₃ = a / b) is 6.0. The total addition rate of aluminum sulfate was 100% of the reference mole number.

-Manufacture of cast coated paper A cast coated paper was obtained in the same manner as in Example 1 except that the above satin white was used in the preparation of the coating liquid for the back surface coating layer in Example 1.

Example 4
In the preparation of the coating liquid for the back surface coating layer of Example 1, the number of kaolin blended parts was changed to 70 parts, the light calcium carbonate blended part number to 27 parts, and the satin white blended part number to 3 parts. In the same manner as in No. 1, a cast coated paper was obtained.

Example 5
In the preparation of the coating solution for the back surface coating layer of Example 1, the number of kaolin blended parts was changed to 70 parts, the light calcium carbonate blended part number to 10 parts, and the satin white blended part number to 20 parts. In the same manner as in No. 1, a cast coated paper was obtained.

Example 6
-Preparation of coating solution for casting Kaolin (trade name: UW-90, manufactured by Engelhard) 55 parts, light calcium carbonate (trade name: PX, manufactured by Shiraishi Kogyo Co., Ltd.) 35 parts, heavy calcium carbonate (trade name: Hydrocurve 90 (manufactured by Bihoku Powder Chemical Co., Ltd.) and 10 parts of sodium polyacrylate were dispersed in water using a Coreless disperser to prepare a pigment slurry having a solid content concentration of 65%. To 100 parts of the pigment slurry, 1.0 part of ammonium stearate as a release agent and 10 parts of a 15% casein aqueous solution dissolved in ammonia as an adhesive (in terms of solid content) and styrene-butadiene 15 parts of polymer latex (in terms of solid content) was added to prepare a coating solution for casting having a solid content concentration of 45%.

-Production of cast coated paper Using a blade coater on the same base paper as in Example 1, the back surface coating layer coating liquid of Example 1 was coated on one side so that the dry weight was 14 g / m ² . Then, using the air knife coater on the opposite surface, the casting coating solution was coated and dried so that the dry weight was 20 g / m ² . Next, after rewetting the cast coating layer surface with a rewetting liquid consisting of 1% polyethylene emulsion aqueous solution and 1% sodium citrate, it was pressed against a cast drum with a surface temperature of 105 ° C, dried and then peeled off from the drum. Cast finished. Further, using a super calendar, smoothing treatment was performed under the same conditions as in Example 1 to obtain cast coated paper.

Example 7
-Preparation of casting coating solution Kaolin (trade name: UW-90, manufactured by Engelhard) 60 parts, light calcium carbonate (trade name: PX, manufactured by Shiraishi Kogyo Co., Ltd.), heavy calcium carbonate (trade name: Hydrocurve 90 (manufactured by Bihoku Powder Chemical Co., Ltd.) and 10 parts of sodium polyacrylate were dispersed in water using a Coreless disperser to prepare a pigment slurry having a solid content concentration of 65%. To 100 parts of the pigment slurry, 1.0 part of ammonium stearate as a release agent and 10 parts of a 15% casein aqueous solution dissolved in ammonia as an adhesive (in terms of solid content) and styrene-butadiene 15 parts of polymer latex (in terms of solid content) was added to prepare a coating solution for casting having a solid content concentration of 50%.

Cast coating using a blade coater on the same base paper of the manufacturing example 1 of the paper, the back surface coated liquid of Example 1 so that 14 g / m ² by dry weight coated on one surface and dried, the following Using a roll coater on the opposite surface, apply the coating solution for casting to a dry weight of 15 g / m ² , dry it, and then contact with the coagulation solution consisting of 0.5% calcium formate. The cast coating layer was gelled. This coating layer was cast-finished by pressing and drying on a cast drum having a surface temperature of 98 ° C. and then peeling off from the drum. Further, using a super calendar, smoothing treatment was performed under the same conditions as in Example 1 to obtain cast coated paper.

Comparative Example 1
-Preparation of satin white The first stage aluminum sulfate aqueous solution addition amount in Example 1 was added at 104 g / min (45% of the reference mole number), and in addition of the second stage aluminum sulfate aqueous solution, the mixed composition The product (first composition) was added at 404 g / min, the aluminum sulfate aqueous solution was added at 81 g / min (35% of the reference number of moles), and in addition of the third stage aluminum sulfate aqueous solution, The composition after completion of the reaction was obtained in the same manner as in Example 1 except that the composition was added at 485 g / min and the aqueous aluminum sulfate solution was added at 11 g / min (5% of the reference mole number) to terminate the reaction. . At this time, the pH of each mixed composition (first composition, second composition) before the addition of the second and third stage aluminum sulfate aqueous solutions is 12.8, and 12.4. Moreover, the pH of the composition after completion | finish of reaction was 12.5. The average particle size was 0.44 μm.

In addition, 6% calcium hydroxide finally used is 300 g / min × 10 min = 3000 g, the solid content included in the 6% calcium hydroxide 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 196 g / min × 10 minutes = 1960 g, the solid content contained in the 6% aluminum sulfate is 117.6 g, and Al ₂ (SO ₄ ) is ₃ moles b. Is 0.405 mol. Therefore, the molar ratio (Ca (OH) ₂ / Al ₂ (SO ₄ ) ₃ = a / b) is 7.1. Further, the total addition rate of aluminum sulfate was 85% of the reference mole number.

  A cast coated paper was obtained in the same manner as in Example 1 except that the above satin white was used in the preparation of the coating solution for the back surface coating layer in Example 1.

Comparative Example 2
Cast coated paper in the same manner as in Example 1 except that commercially available satin white (trade name: Sachin White BL, manufactured by Shiroishi Kogyo Co., Ltd.) was used in the preparation of the coating liquid for the back surface coating layer of Example 1. Got. The pH of satin white used was 12.5, and the average particle size was 0.49 μm.

Comparative Example 3
In the preparation of the coating solution for the back surface coating layer of Example 1, casting was performed in the same manner as in Example 1 except that satin white was changed to light calcium carbonate (trade name: Tama Pearl TP-123CS, manufactured by Okutama Kogyo Co., Ltd.). Coated paper was obtained.

Comparative Example 4
In the preparation of the coating solution for the back surface coating layer of Example 1, the satin white was changed to light calcium carbonate (trade name: Tama Pearl TP-123CS, manufactured by Okutama Kogyo Co., Ltd.), and the super calender treatment condition was set to 250 kN / cm. A cast coated paper was obtained in the same manner as in Example 1 except for the change.

Comparative Example 5
Cast coated paper in the same manner as in Example 6 except that commercially available satin white (trade name: Sachin White BL, manufactured by Shiroishi Kogyo Co., Ltd.) was used in the preparation of the coating liquid for the back surface coating layer of Example 6. Got.

Comparative Example 6
Cast coated paper in the same manner as in Example 7 except that commercially available satin white (trade name: Sachin White BL, manufactured by Shiroishi Kogyo Co., Ltd.) was used in the preparation of the coating solution for the back surface coating layer of Example 7. Got.

  The cast coated paper obtained in each Example and Comparative Example was evaluated by the following method, and the results are shown in Table 1. In addition, about the measurement and evaluation of the cast coated paper in this invention, unless otherwise indicated, it performed in 23 degreeC and 50% RH environment.

・ Evaluation test of thermo-fading property After heat treatment for 24 hours under the conditions of 70 ° C. and RH 90% using a thermo-hygrostat, the whiteness difference and color difference of the back and front surfaces before and after the treatment were measured by the following method. The fading property was evaluated.

-Measurement of whiteness difference The whiteness of the back surface before and after heat treatment was measured according to JIS-P8148, and the difference in whiteness (ΔW) was determined by the following equation. The smaller the value, the better the thermal fading.
ΔW = (Whiteness before heat treatment) − (Whiteness after heat treatment)

・ (△ b ^* difference)
According to JIS-Z8722, the hue of the back surface before and after the heat treatment was measured, and Δb ^* was measured.

-Measurement of color difference According to JIS-Z8722, the hue of the back surface before and after heat treatment was measured. The color difference (ΔE) was determined from a color difference formula based on the L ^* a ^* b ^* color system in accordance with JIS-Z8730. The smaller the value, the better the thermal fading.

・ Glossiness of white paper Gloss meter (model: GM-26D, Murakami color technology) according to TAPPI test method: T 480 om-92 (TAPPI Test Method T 480 om-92) Measured using a laboratory).

-Surface smoothness The surface smoothness of the cast surface of cast coated paper was visually evaluated according to the following criteria.
A: Surface smoothness is very good.
○: The surface smoothness is good.
(Triangle | delta): Surface smoothness is inferior and there exists a problem practically.

-Dirt on the surface of cast drum The surface of the cast drum after continuously producing 5000 m cast coated paper was visually observed to evaluate the stain on the drum surface.
○: The drum surface is not dirty, and continuous operation is possible.
Δ: The surface of the drum is very dirty, and it is necessary to stop the operation and wipe the surface of the drum again.

・ Production speed When creating cast coated paper, we evaluated the casting speed at which it can be stably operated without sticking to the cast drum or drum pick.

Claims (15)

A back coating layer mainly composed of pigment and adhesive is provided on one side of the base paper, and an undercoat coating layer mainly comprising pigment and adhesive is provided on the other side of the base paper as required. A cast coating layer mainly composed of a pigment and an adhesive is formed on the base paper, and pressed and dried on a heated mirror drum while the cast coating layer is in a wet state, In a cast coated paper to be glossy finished, the back coated layer is a cast coated paper containing calcium trisulfoaluminate, and when the cast coated paper is heat-treated under the following conditions, A cast coated paper characterized in that the difference in whiteness (according to JIS-P8148) before and after heat treatment on the coated layer surface is less than 2.8.
Heat treatment conditions: heat treatment for 24 hours under conditions of 70 ° C. and 90% RH A back coating layer mainly composed of pigment and adhesive is provided on one side of the base paper, and an undercoat coating layer mainly comprising pigment and adhesive is provided on the other side of the base paper as required. A cast coating layer mainly composed of a pigment and an adhesive is formed on the base paper, and pressed and dried on a heated mirror drum while the cast coating layer is in a wet state, In a cast coated paper to be glossy finished, the back coated layer is a cast coated paper containing calcium trisulfoaluminate, and when the cast coated paper is heat-treated under the following conditions, A cast coated paper, wherein the difference in b ^* (according to JIS-Z8722) in hue before and after heat treatment on the coated layer surface is less than 1.3.
Heat treatment conditions: heat treatment for 24 hours under conditions of 70 ° C. and 90% RH   A back coating layer mainly composed of pigment and adhesive is provided on one side of the base paper, and an undercoat coating layer mainly comprising pigment and adhesive is provided on the other side of the base paper as required. A cast coating layer mainly composed of a pigment and an adhesive is formed on the base paper, and pressed and dried on a heated mirror drum while the cast coating layer is in a wet state, A cast coated paper having a gloss finish, wherein the back coated layer contains calcium trisulfoaluminate having a pH of 12.0 or less.   The cast coated paper according to claim 1 or 2, wherein the calcium trisulfoaluminate has a pH of 12.0 or less.   The cast coated paper according to any one of claims 1 to 4, wherein the calcium trisulfoaluminate has a pH of 8.5 to 11.0.   The cast coated paper according to any one of claims 1 to 5, wherein the pH of the coating liquid for the back surface coating layer containing the calcium trisulfoaluminate is 11.0 or less.   The cast coated paper according to any one of claims 1 to 6, wherein an average particle size of the calcium trisulfoaluminate is 0.1 to 1.5 µm.   The cast coated paper according to any one of claims 1 to 3, wherein the base paper has a paper surface pH of 5.5 or more.   The cast coated paper according to any one of claims 1 to 8, wherein the calcium trisulfoaluminate is contained in an amount of 2 to 30% by mass in the total pigment in the back coating layer.   The calcium trisulfoaluminate was produced by reacting (A) a calcium hydroxide suspension and (B) an aqueous aluminum sulfate solution, and (A) the calcium hydroxide suspension was converted into (B) The aqueous solution of aluminum sulfate is added in a plurality of stages, and (A) at least one of the addition of a plurality of stages of the aqueous solution of aluminum sulfate (B) to the calcium hydroxide suspension is continuously transferred (A). The cast coated paper according to any one of claims 1 to 9, which is carried out by continuous addition of continuously adding (B) an aqueous solution of aluminum sulfate to a calcium hydroxide suspension.   The cast coated paper according to claim 10, wherein the subsequent addition, which is the second and subsequent additions among the plurality of additions, is performed after a predetermined time has elapsed from 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 12. A cast coated paper according to item 10 or 11.   (A) 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 is 5.5 to 7.0. The cast coated paper according to any one of claims 10 to 12, which 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 cast coated paper according to any one of claims 10 to 13, wherein the number of moles is 98% or less of the reference number of moles.   The cast coating according to any one of claims 10 to 14, 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.