JP2009144312A - Method for producing light calcium carbonate slurry produced by caustification process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively and efficiently wet-pulverizing caustified light calcium carbonate after pulverization. <P>SOLUTION: The method for producing a slurry is to feed a slurry containing light calcium carbonate produced in a caustification process in a pulp producing process to a grinding mill 1 which is a continuous medium agitation type grind mill and constituted of a cylindrical grinding vessel 2 having closed both ends, an agitation member 18 rotatably installed inside of the grinding vessel 2 and agitating a grinding medium and a material to be treated locating inside of the grinding vessel 2, and a cylindrical separator 13 installed inside of the grinding vessel 2 and separating the material to be treated in the grinding vessel 2 from the grinding medium. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pulverizer, and is particularly effective for wet pulverization of massive light calcium carbonate having a calcite crystal structure produced in a causticizing step of a pulp production step by a sulfate method or a soda method. The present invention relates to a pulverization method using a medium stirring type wet pulverizer having a ratio of greater than 0.6 and not greater than 1.2.

  In recent years, there is a high demand for high-quality lightweight coated paper having high whiteness, high opacity, and high gloss. In order to meet these requirements, expensive titanium dioxide, plastic pigments, and the like are blended in the coating pigments of high-quality lightweight coated paper, in addition to inorganic pigments such as kaolin, heavy calcium carbonate, and light calcium carbonate.

Calcium carbonate used for the coating pigment is very inexpensive, and the whiteness and opacity of the coated paper can be improved by increasing the blending ratio in the paint, but the glossiness of the white paper is remarkably lowered. For this reason, in order to increase the blending, it is common to atomize by wet pulverization in order to improve the white paper glossiness. However, in order to make fine particles, it is necessary to increase the amount of the dispersant added and pulverize for a long time, so that the pigment production cost increases.
As a general heavy calcium carbonate pulverization method, a pulverization medium (beads) and a slurry in which a material to be pulverized is mixed are filled in a pulverization container, and the rotating shaft in the center of the pulverization container is rotated to rotate the beads and There is an apparatus (bead mill) that performs fine pulverization by colliding a pulverized product. Conventionally, a pass-type horizontal bead mill that receives a slurry treated with a bead mill in a separate tank was used. However, the number of coarse particles and excessively fine particles due to excessive pulverization increased, and the particle size distribution after pulverization did not become sharp.

  For this reason, at present, a multi-pass type bead mill in which slurry is circulated between the bead mill and the circulation tank is often used. As a merit of the multi-pass type pulverizer, it has the feature that the coarse particle size is reduced and the particle size distribution becomes sharp. Among them, a multi-pass medium agitation type wet pulverizer (Patent Document 1) having an L / D ratio of 0.5 or less is particularly large because the pulverization chamber can be devised to reduce the filling rate of beads. It has a feature that enables flow circulation operation.

  In order to compare the pulverization performance of the above-mentioned pass method and multi-pass method, when the heavy calcium carbonate was pulverized under the same conditions by both methods, the multi-pass method has a sharp particle size distribution, Good results were obtained.

  On the other hand, in the causticization process of the pulp manufacturing process by the sulfate method or soda method, the causticizing process is manufactured by causticizing reaction with green liquor after the quick lime is dehydrated with water or weak liquid (causticizing method) Light calcium carbonate (hereinafter referred to as causticized light calcium carbonate). Since this calcium carbonate is a by-product in producing white liquor, which is the main product, existing facilities can be used compared to light calcium carbonate obtained by the conventional method of reaction between lime milk and carbon dioxide, and capital investment There is an advantage that the amount is minimized. However, when causticized light calcium carbonate is highly blended as a coating pigment, the glossiness of the blank paper is remarkably lowered as described above, and it is necessary to atomize by grinding.

  For these reasons, the slurry of causticized light calcium carbonate was pulverized using a multi-pass medium stirring wet pulverizer having an L / D ratio of 0.5 or less. However, the viscosity of the slurry after pulverization is increased, the amount of expensive dispersant used is increased, and the power unit is increased as compared with the pulverization of heavy calcium carbonate, resulting in an increase in cost.

  Therefore, if it is possible to develop a high-quality causticized light calcium carbonate slurry manufacturing technology that can reduce the power cost and suppress the use of expensive dispersant usage, the causticized light calcium carbonate can be highly formulated in the paint. By doing so, high-quality coated paper can be produced without inferior white paper glossiness.

In the pulverization of causticized light calcium carbonate produced by the causticizing method, good results cannot be obtained even if the pulverizer is used. Examples of existing techniques for pulverizing light calcium carbonate include Patent Document 2, Patent Document 3, and Patent Document 4. However, Patent Document 2 is a mixed pulverization of light calcium carbonate and heavy calcium carbonate obtained by the carbon dioxide method, and Patent Document 3 is a mixed pulverization of light calcium carbonate and kaolin, and pulverization and causticization of causticized light calcium carbonate alone. It cannot be applied to mixed grinding of light calcium carbonate and heavy calcium carbonate. Patent Document 4 proposes a highly efficient method for pulverizing light calcium carbonate by directly blowing carbon dioxide gas so that the slurry pH is 8 to 12 when pulverizing light calcium carbonate. Generally, the slurry pH obtained after pulverization of causticized light calcium carbonate is 13 or more, and since the slurry concentration is high, it takes a long time to neutralize to pH 12 or less with carbon dioxide gas. Therefore, the multipass pulverization method in which the slurry is pulverized to the target particle size while circulating the slurry at a large flow rate between the slurry pulverizer and the circulation tank, carbon dioxide neutralization becomes insufficient or impossible, and the expected effect cannot be exhibited.
JP-A-10-230182 JP-A-6-41463 JP2000-110096A JP 2000-239017 A

  In view of the circumstances as described above, an object of the present invention is to solve the above problems and to provide a method for efficiently and wet-grinding causticized light calcium carbonate after grinding.

  In order to solve the above problems, in the present invention, a pulverization container having a cylindrical shape and closed at both ends, and an inside of the pulverization container with the axes substantially coincided with each other, are divided into two in the radial direction. The inner chamber and the outer chamber are formed, and a cylindrical separator in which a plurality of slits communicating between the two chambers are provided in at least a part of the peripheral surface, and a pulverization container and an axis are provided in the inner chamber. A length (L) in the axial direction of the pulverization vessel, comprising a stirring member rotatably provided in a substantially matched state and a supply port for supplying the processed material to the inner chamber. And a diameter (D) ratio (L / D ratio) of 0.6 to 1.2, and using a medium agitation type pulverizer configured to be 1.2 or less, the causticized light calcium carbonate Reduce power consumption during slurry production It is possible to allow that the fluidity can be efficiently atomized in a good condition. The L / D ratio is preferably greater than 0.8 and not greater than 1.0.

  According to the present invention, when a causticized light calcium carbonate high-concentration slurry is atomized, by using a double rotor, the movement of the grinding medium is improved as compared with the prior art, and processing with high grinding efficiency even at low speed rotation. It is possible to reduce power intensity. Further, regarding the physical properties of the causticized light calcium carbonate after pulverization, the specific surface area is reduced and the viscosity is lowered, so that the amount of expensive dispersant used can be reduced.

Hereinafter, the method of the present invention will be specifically described. The light calcium carbonate of this invention uses what was manufactured at the causticizing process of the pulp manufacturing process by a sulfate method or a soda method.
[Method for producing light calcium carbonate]
As a light calcium carbonate production method, (1) a reaction between carbon dioxide-containing gas obtained from a lime baking apparatus and others and lime milk, (2) a reaction between ammonium carbonate and calcium chloride in an ammonia soda method, ( 3) Reaction of lime milk and sodium carbonate, which produces sodium hydroxide by causticization of sodium carbonate, is known. Among these methods, in (2) and (3), the production method for obtaining the main product has been changed to a new method, or because calcium carbonate is a byproduct, the content of impurities is high. Has not been studied much.
[Carbon dioxide method]
On the other hand, (1) has a relatively simple reaction system (water, slaked lime, carbon dioxide), and extensive research has been conducted on methods for producing calcium carbonate suitable for various purposes. Some products are also seen. However, the direct purchase from the manufacturer has the disadvantage that the transportation cost is high and the total cost is high. Further, in the on-site carbon dioxide method, if kiln exhaust gas is used, high-quality calcium carbonate can be produced at a low cost, but there is a problem that the capital investment is enormous.
[Causticization method]
One possible method is to use calcium carbonate, which is a by-product when producing white liquor in the causticizing process for recovering and regenerating cooking chemicals, in the pulp manufacturing process using the sulfate method or soda method. is there. This method has the advantage that existing facilities can be used and the capital investment is minimized.
[Causticization process]
In the pulp manufacturing process by the sulfate method or the soda method, cooking is performed under high temperature and high pressure using a chemical solution in which sodium hydroxide and sodium sulfide are mixed in order to isolate wood fiber. The fiber is separated and purified as a solid layer to become pulp, and the elution components other than the chemical solution and the fiber from the wood are recovered as pulp waste liquid (black liquor) and concentrated to a combustible concentration in the recovery boiler. Further, sodium sulfate is added to replenish sodium and sulfur lost in the series of processes, and then burned in a recovery boiler. At that time, the organic substance in the black liquor is recovered as a heat source, and the inorganic substance is mainly recovered as sodium carbonate and sodium sulfide. These inorganic substances are called smelt and are taken out from the recovery boiler in a molten state. The smelt taken out from the recovery boiler is dissolved in water or a weak liquid (a liquid containing a small amount of white liquor component obtained after washing calcium carbonate with water) to become a green liquid.
[Causticization reaction]
The causticizing process is a process for changing sodium carbonate in green liquor to sodium hydroxide, a cooking chemical. Mixing the slaked lime and green liquor with a hydration reaction (1) to convert quick lime to slaked lime. It consists of a causticizing reaction (2) that produces sodium and calcium carbonate. The liquid obtained by the causticizing reaction is called white liquor, separated from calcium carbonate, clarified, and sent to the cooking process. In the present invention, calcium carbonate that has been separated and recovered and thoroughly washed is used.

CaO + H ₂ O → Ca (OH) ₂ (1): Saturation reaction
Ca (OH) ₂ + Na ₂ CO ₃ → CaCO ₃ + 2NaOH (2): Causticizing reaction [Characteristics of causticizing reaction]
Since this calcium carbonate is a by-product in producing white liquor, which is the main product, existing facilities can be used compared to light calcium carbonate obtained by the conventional method of reaction between lime milk and carbon dioxide, and capital investment There is an advantage that the amount is minimized. Also, by extracting calcium carbonate out of the system from the calcium (quick lime, slaked lime, calcium carbonate) circulation cycle of the causticization process in the conventional closed system, purification in the system and high purity of the circulating lime are achieved. 1) The reactivity improvement of (2), the improvement of the clarity of white liquor, and the reduction of waste can be expected.
[Dehydrated concentration, average particle size]
The light calcium carbonate used in the present invention is in the form of cake or sludge that has been dehydrated and concentrated by a dehydration apparatus such as a squeezing, suction, or centrifugal separation method. In addition, the average particle size of the bulk light calcium carbonate obtained in the causticizing step is not particularly limited as long as it can be concentrated to a concentration of 73% or higher that can be used for pigments. However, a laser transmission particle size distribution analyzer (Mastersizer 2000, Malvern) 10 to 30 μm, preferably 10 to 20 μm.
[Slurry]
As a method of slurrying the causticized light calcium carbonate wet powder obtained in this way, it consists of a cylindrical container and a rod-shaped stirring arm, filled with 3 to 10 mm balls, stirred and dispersed and pulverized. A high-concentration dispersing device equipped with an attritor that can be performed simultaneously or a high-speed stirring blade can be used as appropriate.
[Dispersant]
Moreover, a slurry viscosity and a density | concentration can be adjusted by adding a dispersing agent and dilution water collectively or dividing | segmenting. Examples of the dispersant used in the pigment dispersion include polyacrylates and lignin sulfonates that are generally used for papermaking, and one or more of these are selected and used as necessary. . The average particle size of the light calcium carbonate in this slurry can be adjusted arbitrarily according to the bead size, processing time, etc. The average particle size after this coarse pulverization is determined by a laser transmission type particle size distribution measuring device (Mastersizer 2000, manufactured by Malvern). ) Is preferably 1 to 30 μm, more preferably 1 to 10 μm. The slurry concentration after coarse pulverization is preferably 65 to 80%.

In addition, the present invention can also be applied to a needle-like or columnar causticized light calcium carbonate other than the irregularly shaped causticized light calcium carbonate, when a pulverization treatment is required.
Examples of the dispersant used in the pigment dispersion include polyacrylic acid soda, lignin sulfonic acid soda, phosphates and modified products thereof, which are generally used for papermaking. Can be selected and used as required, and the amount of the dispersant used is preferably 0.7 to 2.0 parts by weight, more preferably 100 parts by weight of the pigment. 0.9 to 1.8 parts by weight are preferred. Causticized light calcium carbonate has higher alkalinity than heavy calcium carbonate, and its cohesiveness and hydrophobicity are extremely high, so the viscosity of the pigment dispersion is very high, and the load on the grinder during grinding is too large. In some cases, problems such as significant cracking and wear of the medium filled in the pulverizer occur. In addition, since the viscosity of the pigment dispersion rapidly increases as pulverization progresses, a larger amount of dispersant is required than when pulverizing heavy calcium carbonate.

If the causticized light calcium carbonate content in the mixed pigment dispersion of heavy calcium carbonate and causticized light calcium carbonate is 50% by weight or less, it can be pulverized without using the pulverizer of the present invention. . In the present invention, the light calcium carbonate as a pigment produced in the causticizing step of the pulp production step, and before being supplied to the medium stirring type pulverizer, is 50 wt. % Or more.
[Crusher]
The pulverizer 1 used in the present invention is a continuous medium agitation type wet pulverizer, which is formed in a cylindrical shape and closed at both ends, and is provided rotatably inside the pulverization container 2. The agitating member 18a and the agitating member 18b for agitating the processed material and the pulverization medium located inside the pulverization container 2 are provided inside the pulverization container 2, and the processed material and the pulverization medium inside the pulverization container 2 are separated. It comprises a cylindrical separator 13.
[Crushing container]
The pulverization container 2 has a cylindrical container body 3 whose one end is closed, and a disk-shaped lid 6 which closes the other end opening of the container body 3.

  A cylindrical boss 4 that communicates the inside and outside of the container main body 3 is integrally provided at the central portion of the closed end of the container main body 3, and the stirring member 18 a and the agitating member 18 a are connected to the inside of the boss 4 via a bearing 8. The stirring member 18b is rotatably supported.

  Although not shown in the drawing, an annular groove is provided along the inner peripheral surface of the container body 3, and the annular groove is not shown in the portion of the lid 6 corresponding to this groove. Is provided. Then, one end of the separator 13 is positioned in a groove (not shown) of the container body 3, and the other axial end of the separator 13 is positioned in a groove (not shown) of the lid 6. Although not shown in the main body 3, the separator 13 is fixed inside the crushing container 2 by fixing with a bolt or the like. Note that the separator 13 may be fixed in the pulverization container 2 by other means, for example, a bolt or the like, without providing the container body 3 and the lid 6 with grooves.

The inside of the pulverization container 2 is divided into two chambers in the radial direction by the separator 13 to form a circular inner chamber 9 and an annular outer chamber 10. A cylindrical supply port 11 that communicates the inside and outside of the inner chamber 9 is integrally provided at the center of the lid 6, and the processed material is supplied into the inner chamber 9 through the supply port 11. The container body 3 is integrally provided with a cylindrical discharge port 12 that communicates the inside and outside of the outer chamber 10, and the processed material that has passed through the separator 13 is discharged from the discharge port 12 to the outside of the pulverization container 2. The
When the treated product is causticized light calcium carbonate, the one in which the L / D ratio of the pulverization container 2 is greater than 0.6 and 1.2 or less is selected. L is the length in the axial direction, and D is the diameter. By setting the L / D ratio to 1.2 or less, the segregation phenomenon of the medium tends to be suppressed. Further, by making the value larger than 0.6, it becomes possible to secure the operating range of the stirring member 18. Preferably, when the L / D ratio is greater than 0.8 and 1.0 or less, each of the above effects becomes more significant.
[Separator]
The separator 13 is composed of a cylindrical inner ring 14, a cylindrical outer ring 15, and a plurality of steel bars 16, 16... The steel bar 16 has a large inner diameter side and is provided between the outer ring 15 and the inner ring 14 at a predetermined interval. By providing a plurality of steel bars 16, 16... Between the inner ring 14 and the outer ring 15, a wedge-shaped slit 17 that gradually increases the distance between the adjacent steel bars 16 from the inner diameter side to the outer diameter side, 17 are formed, and the inner chamber 9 and the outer chamber 10 communicate with each other through the slits 17. The inner ring 14 and the outer ring 15 are provided with a plurality of holes that communicate with the slits 17.

  Then, as described above, the inner ring 14, the outer ring 15, and the steel bar 16 are combined to form a plurality of slits 17, 17..., Thereby providing an effective area sufficient to pass a large amount of processed material. Can be secured. Further, since each slit 17 is formed in a wedge shape in which the interval is gradually increased from the inner diameter side to the outer diameter side, the processed material can flow to the outer chamber 10 side without causing clogging. Furthermore, sufficient strength during operation can be ensured.

In addition, the separator 13 is not limited to the above-mentioned ones. (1) “A sufficient effective area for passing a large flow rate of processed material can be secured”, (2) “Clogging does not occur. ”, (3) Any structure that satisfies the three conditions of“ sufficient strength during operation ”may be used.
[Stirring member]
The stirring member 18 has a cylindrical shape with one end closed, and two stirring members 18a and 18b are provided in the inner chamber 9 of the crushing container 2 so as to be rotatable and in the axial direction. On the outer peripheral side of this portion, concave portions 19 and convex portions 20 are alternately provided over the entire circumference. Each recess 19 is provided with a through hole 21, and the processed material and the grinding medium flow between the inner and outer portions of the stirring member 18 in the radial direction via the through hole 21. A plurality of through holes 22 are provided at one end of the stirring member 18 that is closed. The through holes 22 are concentrically centered around the axis of the stirring member 18 at a predetermined interval, and the processed material and the grinding medium are disposed between the inside and outside of the stirring member 18a and the stirring member 18b through the through hole 22. Flow to each other.

A dispersion member 25 screwed to the tip of the drive shaft 24 is located inside the stirring member 18a on the supply port 11 side, and this dispersion member 25 also serves as a lock nut.
The head of the dispersion member 25 is provided with recesses and projections alternately (not shown) over the entire circumference, and is supplied from the supply port 11 to the inner chamber 9 of the grinding container 2 by the recesses and projections. The processed material and the grinding medium located in the inner chamber 9 are dispersed outward in the radial direction.

  Next, the operation of the above will be described. First, when the drive source 24 is operated to rotate the drive shaft 24, the stirring member 18a and the stirring member 18b connected to the drive shaft 24 rotate, and the dispersion member 25 positioned at the center of the stirring member 18a also Rotate.

  When the processed product is supplied from the supply port 11 to the inside of the inner chamber 9 of the pulverization container 2, the processed product is dispersed in the radially outward direction together with the pulverization medium by the dispersion member 25 and the stirring member 18a, and the stirring member 18a. And it is stirred by the stirring member 18b.

  In this case, since the through holes 21 are provided in the cylindrical portions of the stirring member 18a and the stirring member 18b, a strong centrifugal force acts on the processed material and the pulverization medium by the through holes 21, and the processed material and The grinding medium flows from the through hole 21 to the outer peripheral side of the stirring member 18a and the stirring member 18b.

  Then, the processed material and the pulverization medium that have flowed to the outer peripheral side of the stirring member 18a and the stirring member 18b are stronger on the outer peripheral side of the stirring member 18a and the stirring member 18b by the concave portions 19 and the convex portions 20 of the stirring member 18a and the stirring member 18b. A shearing force is applied to flow in one end direction or the other end direction in the axial direction of the stirring member 18a and the stirring member 18b, and flow to the inside of the stirring member 18a through the gap between the lid 6 and the stirring member 18a. . Further, a part flows through the gap between the stirring member 18b and the container body 3 from the through hole 22 to the inside of the stirring member 18b, and along the series of flows, between the stirring member 18a and the stirring member 18b. Generate a circulating flow.

  Then, the processed material and the pulverizing medium circulate inside the inner chamber 9 as described above, so that the whole is completely mixed, and the processed material is gradually finely pulverized to reach a predetermined particle size. When the processed product having reached a predetermined particle size flows to the outer peripheral side of the stirring member 18, it is separated from the pulverization medium by the separator 13, flows into the slits 17 of the separator, flows there, and flows inside the outer chamber 10. And is discharged from the outer chamber 10 to the outside of the pulverization container 2 through the discharge port 12.

  In the pulverizer 1 according to this embodiment configured as described above, the L / D ratio of the pulverization container 2 is larger than 0.6 and smaller than or equal to 1.2, preferably larger than 0.8 and larger than 1.0. It is formed below, and the volume of the inner chamber 9 (grinding region) is sufficiently secured. Therefore, the grinding efficiency higher than that of the conventional single rotor can be obtained.

  In addition, since the separator 13 for separating the processed material and the grinding medium is formed in a cylindrical shape to form a plurality of slits 17 and the separators 13 are provided inside the grinding container 2 in a state where the axes are substantially coincident with each other. An effective area sufficient to process a flow rate of processed material can be secured. Therefore, the flow of the processed material is not limited by the separator 13, and can sufficiently handle the processing of a large flow rate of processed material.

  Furthermore, since the separator 13 has a configuration in which a plurality of steel bars 16 are provided between the inner ring 14 and the outer ring 15, sufficient strength can be secured even when a large amount of processed material is processed. Therefore, stable performance can be exhibited in the long term.

And while providing the dispersion member 25 in the center part of the stirring member 18a, the closed end of the through-hole 21, the stirring member 18a, and the stirring member 18b which penetrates the inside and outside in the cylindrical part of the stirring member 18a and the stirring member 18b Since the through holes 22 penetrating the inside and the outside are respectively provided in the inner chamber 9, the processed material and the grinding medium can be circulated using the entire inner chamber 9. Therefore, the pulverization medium and the processed product are not shifted to a part of the inside of the pulverization container 2 to affect the operation or make the operation difficult, and good operation characteristics can be obtained in the long term.
[Processing system]
This medium stirring type wet disperser is used in a processing system as shown in FIG. In other words, the processing system 140 is a system in which the disperser 110 is connected to the processing service tank 141 and the circulation pump 142 through the circulation line 143. The processed material put into the service tank 141 is circulated through the circulation line 143 by the circulation pump 142 and repeatedly subjected to the dispersion treatment by the disperser 110. As a result, distributed processing proceeds for the entire processed material in the system.
[Medium filling rate]
The filling rate of the pulverizing medium is preferably as high as possible. However, if the filling rate is too high, the movement of the medium in the pulverizing chamber is limited, which may reduce the pulverizing efficiency. Therefore, the filling rate of the grinding medium is preferably 70 to 90%, and more preferably 75 to 85%.
[Rotor speed]
Also, the rotor (stirring member) rotation speed is preferably as high as possible. However, if the rotor rotation speed is too high, the load on the pulverizer of the pulverizer becomes too large, and in some cases the pulverizer is filled. Media cracking and wear may be significant. Thus the rotor rotational speed, when the rotor outer diameter is 196 mm, preferably 700～1200Min ^-1, still more preferably 800~1000min ^-1.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is of course not limited thereto. In the examples, “parts” and “%” represent “parts by weight” and “% by weight”, respectively, unless otherwise specified.

Lumped light calcium carbonate with a solid content concentration of 73% produced in the causticizing process of Nippon Paper Industries Co., Ltd. A factory was used. In a pigment dispersion obtained by mixing 50 parts of this wet powder and 50 parts of heavy calcium carbonate, or 100 parts of bulk light calcium carbonate, 1.6 to 3.6 parts of a polyacrylic acid-based dispersant is added. Water was added all at once and coarsely pulverized with an attritor (manufactured by Mitsui Mining) to a concentration of 73% and an average particle size of 7 μm. The crude slurry obtained by this treatment was sent to a double rotor type SC mill LSC220 (manufactured by Mitsui Mining Co., Ltd.) having a 7.4 L crushing chamber with a metering pump and wet pulverized.

Zirconia beads (made by Nikkato Co., Ltd.) with a diameter of 0.5 mm are used as the medium, and the bead filling rate (the volume of the grinding medium when closest packed with respect to the void volume in the grinding chamber) is 70 to 90%. The number was set to 800 to 1000 min ⁻¹ and pulverization was performed using the pulverizer of the present invention or a horizontal bead mill pulverizer (manufactured by Mitsui Mining Co., Ltd.) until the average particle size became 0.4 to 1.0 μm. After grinding, the B concentration (60 rpm, manufactured by Tokyo Keiki Co., Ltd.) at 25 ° C. was measured at a slurry concentration of 70%. Moreover, the 50% point of the weight cumulative distribution was calculated as an average particle diameter using Mastersizer 2000 (manufactured by Malvern), and the particle size distribution was also measured using Cedigraph (manufactured by Micromeritex). Further, the BET specific surface area was measured using Micromeritics Gemini 2360 (manufactured by Shimadzu Corporation).
[Example 1]
Polyacrylic acid in a pigment dispersion containing 50 parts of light calcium carbonate produced in the causticizing process (hereinafter referred to as causticized light cal) and 50 parts of heavy calcium carbonate (Sankyo fine powder, average particle size 13 μm) After adding 1.6 parts of a dispersant to a coarse slurry to an average particle size of 7 μm, a double rotor type SC mill LSC220 has a bead filling rate of 90%, an average particle size of 0.4 μm at a rotor speed of 800 min ^−1. Wet pulverized until The power unit at that time is 165 kW · h / t, the B-type viscosity is 3900 mPa · s, and the specific surface area is 15.7 m ² / s.
g.
[Example 2]
After adding 1.6 parts of polyacrylic acid-based dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then a double-rotor SC mill LSC220 is used to fill the beads with 85 %, And wet pulverization was performed until the average particle size became 0.4 μm at a rotor rotation speed of 800 min ⁻¹ . The power unit at that time is 171 kW · h / t, and the B-type viscosity is 4600.
mPa · s, and the specific surface area was 11.1 m ² / g.
Example 3
After adding 1.6 parts of a polyacrylic acid dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then filled with a double rotor type SC mill LSC220 with a bead filling rate of 80 %, And wet pulverization was performed until the average particle size became 0.4 μm at a rotor rotational speed of 900 min ⁻¹ . The power unit at that time is 171 kW · h / t, and the B-type viscosity is 4900.
mPa · s, and the specific surface area was 11.2 m ² / g.
Example 4
After adding 1.6 parts of a polyacrylic acid dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then filled with a double rotor SC mill LSC220 with a bead filling ratio of 70. %, And wet pulverization was performed until the average particle size became 0.4 μm at a rotor rotation speed of 1000 min ⁻¹ . The power unit at that time is 193 kW · h / t, and the B-type viscosity is 500
The specific surface area was 12.4 m ² / g.
Example 5
After adding 1.6 parts of polyacrylic acid-based dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then a double-rotor SC mill LSC220 is used to fill the beads with 85 %, And wet pulverization was performed until the average particle size became 1.0 μm at a rotor rotational speed of 800 min ⁻¹ . The power unit at that time is 111 kW · h / t, and the B-type viscosity is 900 m.
The specific surface area was 7.9 m ² / g.
[Comparative Example 1]
An average particle diameter of 7 μm is obtained by adding 2.6 parts of a polyacrylic acid-based dispersant to a pigment dispersion containing 50 parts of causticized light calcium and 50 parts of heavy calcium carbonate (Sankyo fine powder, average particle diameter of 13 μm). After roughly slurrying to a single rotor type SC mill SC220, the bead filling rate is 90%.
Wet grinding was performed until the average particle size became 0.4 μm at a rotor rotation speed of 800 min ⁻¹ . The power unit at that time was 226 kW · h / t, the B-type viscosity was 7500 mPa · s, and the specific surface area was 18.6 m ² / g.
[Comparative Example 2]
After adding 1.6 parts of a polyacrylic acid dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then a single rotor type SC mill SC220.
Was wet pulverized until the average particle size became 0.4 μm at a bead filling rate of 85% and a rotor rotational speed of 800 min ⁻¹ . The power unit at that time is 238 kW · h / t, and the B-type viscosity is 870.
The specific surface area was 13.1 m ² / g.
[Comparative Example 3]
After adding 1.6 parts of a polyacrylic acid dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then a single rotor type SC mill SC220.
And wet milling until the average particle size is 0.4 μm at a bead filling rate of 80% and a rotor rotation speed of 900 min ⁻¹ . The power unit at that time is 237 kW · h / t, and the B-type viscosity is 820
The specific surface area was 13.8 m ² / g.
[Comparative Example 4]
After adding 1.6 parts of a polyacrylic acid dispersant to a pigment dispersion containing 100 parts of causticized light calcium, the slurry is coarsely slurried to an average particle size of 7 μm, and then a single rotor type SC mill SC220.
Then, wet milling was performed until the average particle size became 0.4 μm at a bead filling rate of 70% and a rotor rotation speed of 1000 min ⁻¹ . The power unit at that time is 285 kW · h / t, and the B-type viscosity is 89
The specific surface area was 13.5 m ² / g.
[Comparative Example 5]
After adding 2.6 parts of polyacrylic acid-based dispersant (1.6 parts in the table) to a pigment dispersion containing 100 parts of causticized light calcium, it is coarsely slurried to an average particle size of 7 μm, and then a single rotor type Wet pulverization was performed with an SC mill SC220 until the average particle size became 0.4 μm at a bead filling rate of 85%, a rotor rotation speed of 1000 min ⁻¹ . The power unit at that time is 247 kW · h / t, the B-type viscosity is 10000 mPa · s or more (unmeasurable), and the specific surface area is 13.7 m ^2.
/ G.
[Comparative Example 6]
After adding 3.6 parts of polyacrylic acid-based dispersant to a pigment dispersion containing 100 parts of causticized light cal, it is coarsely slurried to an average particle size of 7 μm, and then beads are used with a horizontal sand grinder (Mitsui Mining Co., Ltd.). Wet pulverization was carried out at a filling rate of 90% and a rotor rotational speed of 800 min ⁻¹ until the average particle size became 0.4 μm. The power basic unit at that time was 350 kW · h / t, the B-type viscosity was 7100 mPa · s, and the specific surface area was 17.1 m ² / g.
〔Test results〕
1. About B-type viscosity From Examples 1 to 4 in Table 1, according to the pulverizer of the present invention (double rotor having an L / D ratio of 0.9), causticized light cal. Even if wet-pulverized until the particle size reaches 0.4 μm, the B-type viscosity of the slurry is in the range of 3900 to 5000 mPa · s.

  From Comparative Examples 1 to 5, in a conventional pulverizer (single rotor having an L / D ratio of 0.3), causticized light calf is blended in an amount of 50% by weight or more until the average particle size becomes 0.4 μm When wet pulverized, the B-type viscosity of the slurry is in the range of 7500-8900 mPa · s.

From the above, the B-type viscosity of the slurry by the pulverizer of the present invention is about half that of the conventional pulverizer and is excellent in operability. As a matter of course, since the viscosity does not increase, the power unit is also reduced.
2. About the particle size distribution From FIG. 3, the particle size distribution of the solid content of the slurry by the pulverizer of the present invention in Example 2 is narrower than that by the conventional pulverizer even though the average particle size is the same. It is in a range (a state in which the particle diameter is uniform with a so-called sharp particle distribution), and there are few fine particles and large particles, which are good for use as a coating pigment.

  As a factor to be such, in the pulverizer of the present invention of Example 2, since the action of impact force is easily transmitted to the particles, the whole particles tend to be pulverized (so-called volume pulverization). In the conventional pulverizer of No. 6, the effect of the impact force is not transmitted well to the particles, and the action of the frictional force is advanced, so that excessively pulverized particles tend to be generated (so-called surface pulverization).

It is a schematic sectional drawing which shows an example of implementation of the medium stirring type wet disperser of this invention. It is a schematic explanatory drawing which shows the processing system of this invention. It is a graph which shows the relationship between the particle diameter (micrometer) and the abundance ratio (%) of a particle in Example 2 and Comparative Examples 2 and 6 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crusher 2 Crushing container 3 Container body 4 Boss 6 Lid 8 Bearing 9 Inner chamber 10 Outer chamber 11 Supply port 12 Discharge port 13 Separator 14 Inner ring 15 Outer ring 16 Steel bar 17 Slit 18 Stirring member 18a Stirring member 18b Stirring member 19 Recess 20 Convex part 21 Through hole 22 Through hole 24 Drive shaft 25 Dispersing member 110 Medium agitation type wet disperser 140 Processing system 141 Service tank 142 Circulation pump 143 Circulation line

Claims (4)

A slurry manufacturing method for obtaining a coating pigment by wet pulverization of light calcium carbonate manufactured in a causticizing process of a pulp manufacturing process,
A pulverization container having a cylindrical shape and closed at both ends, and provided inside the pulverization container in a state in which the axes substantially coincide with each other, and the inside is divided into two in the radial direction to form an inner chamber and an outer chamber. A cylindrical separator in which a plurality of slits communicating between the chambers are provided in at least a part of the peripheral surface, and a rotation vessel provided in the inner chamber so as to be rotatable in a state in which the axis of the pulverization container is substantially coincided. And a ratio of the length (L) and the diameter (D) in the axial direction of the grinding container (L / The slurry containing light calcium carbonate produced in the causticizing process of the pulp production process is supplied to a medium agitation type pulverizer configured to be a double rotor having a D ratio of greater than 0.6 and less than or equal to 1.2. Characterized by pulverization, Slurry method for producing precipitated calcium carbonate produced by causticizing process the pulp manufacturing process.   Light calcium carbonate as a pigment manufactured in the causticizing step of the pulp manufacturing process, and before being supplied to the medium stirring type pulverizer, the light calcium carbonate is contained in an amount of 50% by weight or more based on the weight of the total pigment. The light calcium carbonate slurry manufacturing method manufactured in the causticizing step of the pulp manufacturing step according to claim 1.   The light calcium carbonate produced in the causticizing step of the pulp producing process is a light calcium carbonate produced in the causticizing step of the pulp producing process according to claim 1 or 2, wherein the light calcium carbonate produced in the causticizing step of the pulp producing process has a lumpy and calcite crystal structure. A method for producing a slurry of calcium carbonate.   The said L / D ratio is larger than 0.8 and 1.0 or less, The slurry manufacturing method of the light calcium carbonate manufactured at the causticizing process of the pulp manufacturing process of Claim 1.

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