JP2001199722A - Method for producing aqueous slurry of calcium carbonate, and aqueous slurry of calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aqueous slurry of calcium carbonate by which the thickening is effectively prevented to provide a high grinding effect by a sand mill even if the slurry exhibits vigorous elution of an alkali, and as a result, the aqueous slurry containing the calcium carbonate particles having small particle diameters and high whiteness is produced. SOLUTION: When producing the aqueous slurry of the calcium carbonate by using the calcium carbonate eluting an alkali component by the dispersion treatment accompanying pulverization, a sodium salt or an ammonium salt of a polycarboxylic acid having <=90%, preferably 50-90% degree of neutralization is used as a disperser in dispersing the calcium carbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aqueous calcium carbonate slurry, and more particularly to a method for producing an aqueous slurry using calcium carbonate having a high alkalinity that elutes an alkali component by a dispersion treatment.

[0002]

2. Description of the Related Art There are various types of commercial products of calcium carbonate, such as powder, semi-dry powder, and slurry. Among them, the slurry is widely used in order to save time for dissolving the pigment.
As a method of slurrying calcium carbonate, there are a method of dispersing powder in water, and a method of dispersing in water water a dehydrated cake or a concentrate obtained by dehydrating and concentrating a low-concentration aqueous calcium carbonate slurry. In applications where whiteness and fine particles are required, such as pigments for papermaking, the dispersion treatment may be multi-staged, or wet grinding using a sand mill or the like may be performed in dispersion. A dispersant or a low-viscosity agent is usually used to effectively perform such a dispersion treatment and to suppress the increase in viscosity due to dispersion.

As a dispersant for calcium carbonate, a polycarboxylic acid dispersant is frequently used. Polycarboxylic acids are
A homopolymer or copolymer of acrylic acid, maleic acid, itaconic acid or the like is used to disperse the particles by adsorbing them on the surface of calcium carbonate particles. In this case, since the charge repulsion of the polycarboxylic acid alone is weak, the one neutralized with a base such as sodium hydroxide or ammonia is usually used.

It is known to use partially neutralized polyacrylic acid as a pulverizing agent for heavy calcium carbonate obtained by pulverizing natural white limestone (Japanese Patent Application Laid-Open No.
No. 59-47265), the precipitated calcium carbonate (PCC) obtained by chemical synthesis has a degree of neutralization of 98 to 100% because of the dispersion effect by expanding the circle of the electric double layer and strengthening the charge repulsion. Used. PCC especially for papermaking
Since the pH required for this application is in the range of 9 to 11, preferably 10 ± 0.5, a dispersant having a high degree of neutralization is used.

[0005] All of these are used as papermaking pigments in the form of an aqueous slurry. Heavy calcium carbonate hardly changes in pH during dispersion treatment, whereas PCC precipitates calcium carbonate in a reaction solution. In some cases, the alkali component is easily coprecipitated, so that the alkali is eluted in the process of producing the above-mentioned aqueous slurry, the pH exceeds the effective range of the dispersant, and the liquid viscosity may increase. Although treatment such as washing of calcium carbonate is performed to prevent coprecipitation, it is difficult to completely remove the alkali component. Particularly, when the dispersion treatment involves grinding using a sand mill or the like, the alkali component is removed. The problem was the increase in liquid viscosity due to elution.

Conventionally, in order to suppress such an increase in the viscosity of the liquid, 1) the dispersion treatment is performed in several steps by lowering the degree of dispersion, and 2) carbon dioxide gas is introduced into the dispersion to neutralize the slurry. 3) Introduce carbon dioxide gas simultaneously with the dispersion at the inlet of the sand mill (JP-A-9-94669)
No. etc.) have been made and proposed.

[0007]

However, among the above-mentioned conventional methods, the method (1) cannot be denied that the processing capacity is greatly reduced. In 2), since it is difficult to uniformly neutralize the slurry, a sharp decrease in local viscosity and accompanying turbulence occur, resulting in a reduction in the pulverization efficiency and a local increase in liquid viscosity. There is a problem that it becomes impossible. 3)
There is a problem that control of pH adjustment is difficult and automatic operation is difficult.

Accordingly, the present invention effectively prevents thickening even in a slurry with a strong alkali elution and provides a high sand mill pulverizing effect. As a result, calcium carbonate particles having a small particle size and a high whiteness can be concentrated at a high concentration. It is an object of the present invention to provide a method for producing an aqueous calcium carbonate slurry capable of obtaining an aqueous calcium carbonate slurry containing the same.

[0009]

According to the present invention, there is provided a method for producing an aqueous calcium carbonate slurry using calcium carbonate which elutes an alkali component by a dispersion treatment accompanied by a pulverization treatment. The present invention provides a method for producing an aqueous calcium carbonate slurry, characterized in that a polycarboxylate having a degree of neutralization of 90% or less is used as a dispersing agent when dispersing calcium carbonate.

[0010] Here, the dispersion treatment accompanied by the pulverization treatment is a dispersion treatment using a sand mill or the like, which means a treatment accompanied by the dispersing and the comminution of calcium carbonate particles. The degree of neutralization is a value obtained by expressing the amount of the base with respect to the carboxylic acid in equivalent% when neutralizing the carboxylic acid with the base.

[0011] By using a polycarboxylate (sodium salt or ammonium salt) having a degree of neutralization of 90% or less, even if hydroxyl ions or calcium ions are eluted in the course of the dispersion treatment, the appropriate pH of the dispersion is adjusted. Is maintained, whereby thickening can be prevented and dispersion and pulverization can be performed effectively.

The present invention also provides an aqueous calcium carbonate slurry produced by the above-mentioned production method.

Hereinafter, the present invention will be described in detail. Calcium carbonate as a raw material is calcium carbonate that elutes an alkali component by a dispersion treatment involving pulverization.Specifically, the pH of the slurry is 0.1 or more due to the dispersion treatment,
Preferably, it means calcium carbonate which rises by 0.5 or more. In particular, 5% of precipitated calcium carbonate (PCC)
Applies to those containing 0% by weight or more.

The precipitated calcium carbonate (PCC) is called light calcium carbonate obtained by injecting carbon dioxide into an aqueous suspension of calcium hydroxide, and quicklime or calcium hydroxide is added to green liquor in the causticizing step of pulp production. There is causticized calcium carbonate obtained by charging the mixture, and any of these may be a mixture. Further, as long as the entire raw material has alkali elution, a mixture of PCC and heavy calcium carbonate may be used.

It is desirable that the PCC be subjected to an alkali coprecipitation prevention treatment in advance. In the case of light calcium carbonate, such treatments include, for example, blowing excess gas during the reaction, removing coarse particles, extending the carbonation reaction time, and washing the generated calcium carbonate. Examples of the causticized calcium carbonate include removal of impurities by filtering green liquor, pulverization of raw lime, and washing of generated calcium carbonate.

These may be in any form of powder, semi-powder, dehydrated cake, and high-concentration slurry. In the case of PCC, a dehydrated cake or a highly concentrated slurry is preferred. Although the particle size of calcium carbonate is not particularly limited, it is preferable to remove coarse particles of 74 μm or more, and usually, those having a particle size of 44 μm or less are used.

As the polycarboxylic acid-based dispersant, a polycarboxylate obtained by polymerizing a monomer having a carboxyl group with another monomer capable of polymerizing or copolymerizing and having a degree of neutralization of 90% or less is used. Examples of polycarboxylates include polyacrylates, acrylic acid-maleate copolymers, acrylic acid-itaconate copolymers, acrylic acid-methacrylate copolymers, and isobutylene-maleate copolymers And polystyrene salts known as dispersants such as styrene-maleate copolymers. Further, a sulfonate group may be partially introduced into the polycarboxylate. The sulfone group is introduced by using an ethylenically unsaturated sulfonic acid monomer such as acrylamide-t-butylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, or vinylsulfonic acid as a comonomer. Can be.

As a counter salt, a sodium salt or an ammonium salt is used. Among these polycarboxylates, those available as dispersants have a degree of neutralization of 98% or more, but in the present invention, by using those having a degree of neutralization of 90% or less, the pH of the slurry can be made uniform. Lowers the effective pH of the dispersant even if a large amount of calcium ions or hydroxide ions elute.
Distributed processing can be performed without departing from the range. As a result, even when PCC having a large amount of residual alkali components is used as a raw material, or when a dispersion treatment with a high degree of dispersion or a pulverization treatment that increases alkali elution is performed, the dispersion efficiency and the pulverization efficiency are improved. It does not drop.

If the neutralization degree is too low, the charge repulsion is weak and a sufficient dispersion effect cannot be obtained, and the pH of the dispersion
Deviates from an appropriate range, so that the degree of neutralization is preferably 50% or more.

The molecular weight of the polycarboxylate is not particularly limited, but is usually in the range of several thousand to several tens of thousands. The amount of the polycarboxylate added to calcium carbonate depends on the type of calcium carbonate as a raw material, but if the amount is too small, the effect cannot be obtained, and if the amount is too large, the viscosity increases. Usually 0.01 to dry weight of calcium carbonate
To 10% by weight, preferably 0.1 to 5% by weight.

The dispersion treatment is carried out by adding the above-mentioned calcium carbonate to water together with the polycarboxylate and mixing the mixture, and a high-speed stirrer such as a coalesce mixer or a homogenizer or a medium mill such as a sand mill, attritor, pin mill, ball mill or the like. Can be carried out using a conventional device using In order to increase the degree of dispersion, it is preferable to increase the number of times of dispersion and to increase the filling rate of the medium mill. By increasing the degree of dispersion, calcium carbonate having a large surface area can be obtained.

When the dispersion is performed a plurality of times, it is preferable to add the dispersant separately for each treatment. This is because, as described above, when a large amount is added in one dispersion treatment, the liquid viscosity is rather increased, and even if there is an excessive dispersant, it is deteriorated by high temperature and shear stress during dispersion.
Also, if the slurry deviates from an appropriate pH due to a large amount of alkali elution or the like in one dispersion, excess polycarboxylate for the next dispersion is consumed.

When the dispersion is performed a plurality of times, it is possible to use another dispersant other than the above-mentioned polycarboxylates in combination. For example, in one dispersion treatment, a normal dispersant is used to disperse, and the degree of neutralization becomes 9 as the degree of dispersion increases.
0% or less of a polycarboxylate may be used.

The aqueous calcium carbonate slurry of the present invention produced by the above-described production method is dispersed with a high dispersion efficiency and has a low viscosity even at a high concentration. For example, the calcium carbonate concentration can be 70% or more, and even in this case, the viscosity (B-type viscosity: 60 rpm) can be 500 cP or less. The aqueous calcium carbonate slurry of the present invention preferably has a particle size of 1.0 μm or less.

[0025]

The present invention will be described below with reference to examples. still,
In the following examples, the solid content concentration was measured at a drying temperature of 105 ° C. using an infrared moisture meter (Mettler LP-16, Mettler). The median diameter was measured using a laser-type particle size distribution analyzer (Horiba, LA-920), and the SEM particle size was the average of 50 to 100 points measured with a digimatic caliper from an SEM photograph. The particle size. The B-type viscosity was measured using a Brookfield viscometer at a rotor speed of 60 rp.
m and a slurry temperature of 25 ° C.

Example 1 A calcite-type spindle-shaped light calcium carbonate aqueous slurry having a solid content of 12%, a median diameter of 2.94 μm, an SEM particle diameter of an average major axis of 1.30 μm, and an average minor axis of 0.35 μm was concentrated and dehydrated with a screw decanter. A concentrated cake having a solid content of 42% by weight was obtained. This was subjected to compression dewatering with a high-pressure squeezing belt press to obtain a dewatered cake having a solid content of 72% by weight.

To the obtained dehydrated cake, a dispersant A (sodium polyacrylate having an average molecular weight of 18,000 and a degree of neutralization of 65% by neutralizing an acrylic acid polymer with sodium hydroxide) was added in an amount of 1.0% by weight in terms of solid content. , Coreless Mixer (6400r
pm, a peripheral speed of 25 m / s) for 5 minutes to obtain a calcium carbonate aqueous slurry having a solid content of 71.5% by weight.

Next, a sand mill (Dynomill KDL-PILO)
T: manufactured by Shinmaru Enterprises Co., Ltd., and secondary dispersion was performed at a filling rate of 85% for glass beads (particle diameter of 1 to 1.4 mm) and a peripheral speed of 14 m / s. Further, the dispersant A was further added at 0.1
% (The second addition of a dispersant), and a sand mill treatment was performed under the same conditions to obtain a calcium carbonate aqueous slurry having a solid content of 71.3% by weight. The first sand mill treatment in the secondary dispersion treatment is called one pass, and the second sand mill treatment is called two passes.

The pH and B-type viscosity of the slurry in each of the above treatment steps (after the first dispersion, immediately after the first pass in the second dispersion, and immediately after the second pass of the dispersant, and immediately after the second pass) were measured. The results are shown in Tables 1 and 2. The median diameter (μm) of the calcium carbonate obtained in each treatment step was measured. Table 3 shows the results.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

Example 2 An aqueous calcium carbonate slurry was produced in the same manner as in Example 1 except that Dispersant B (Table 4) having different degrees of neutralization and pH was used. Also in this example, the pH, the B-type viscosity and the median diameter (μm) of the calcium carbonate obtained in each treatment step were measured. The results are shown in Tables 1 to 3.

[0034]

[Table 4]

Example 3 Using a dispersant C having a different degree of neutralization and a different pH (Table 4), primary dispersion and secondary dispersion were carried out in the same manner as in Example 1. After the two-pass treatment in the secondary dispersion, carbon dioxide gas was introduced into the obtained aqueous calcium carbonate slurry to adjust the pH of the slurry to 10.5. Also in this example, the pH and the B-type viscosity of the calcium carbonate slurry obtained in each treatment step and the median diameter (μm) of the calcium carbonate were measured. The results are shown in Tables 1 to 3.

Comparative Example 1 Primary dispersion and secondary dispersion were carried out in the same manner as in Example 1 except that dispersant D (Table 4) having a different degree of neutralization and pH was used, but the liquid viscosity rapidly increased during two passes. Became impossible to disperse.

Comparative Example 2 Primary dispersion and one-pass treatment were performed in the same manner as in Example 1 using the same dispersant D as in Comparative Example 1, and then the pH was adjusted (10.5) by introducing carbon dioxide into the slurry. . Next, a two-pass treatment was performed in the same manner as in Example 1, and carbon dioxide was further introduced to adjust the pH.
Adjustments (10.5) were made.

After the first dispersion, the first pass, the first introduction of carbon dioxide gas, the second addition of the dispersant, the second pass and the second introduction of carbon dioxide gas, the pH of the aqueous calcium carbonate slurry and the B-form were measured, respectively. The viscosity and the median diameter (μm) of the calcium carbonate were measured. The results are shown in Tables 1 to 3.

Example 4 To the same dehydrated cake of PCC as in Example 1 was added 1.0% by weight of a dispersant A in terms of solid content, and the mixture was subjected to dispersion treatment under the same conditions as in Example 1 using a Cores mixer. In the above, 0.5 parts by weight of a dispersant A and 78 parts by weight of a dispersion were mixed with dry-ground heavy calcium carbonate (Escalon # manufactured by Sankyo Milling Co., Ltd.)
100) 22 parts by weight were added and dispersion treatment was performed for 20 minutes to obtain a primary dispersion having a solid content of 76.5%. Then, Example 1
The secondary dispersion (1 pass + 2 passes) was performed in the same manner as described above.

Also in this example, the pH, the B-type viscosity and the median diameter (μm) of the aqueous calcium carbonate slurry in each treatment step were measured. The results are shown in Tables 1 to 3.

Comparative Example 3 PCC was prepared in the same manner as in Example 4 except that Dispersant A was changed to Dispersant D.
And primary dispersion using heavy calcium carbonate. Thereafter, secondary dispersion (1 pass and 2 passes) including introduction of carbon dioxide gas after one pass was performed in the same manner as in Comparative Example 2, and finally, carbon dioxide gas was introduced again to obtain a calcium carbonate aqueous slurry.

Also in this example, the pH, B-type viscosity and median diameter (μm) of the aqueous calcium carbonate slurry in each treatment step were measured. The results are shown in Tables 1 to 3.

Example 5 Calcite-type angular calcium caustic carbonate having a solid content of 82%, a median diameter of 16.5 μm, and an average particle diameter (SEM particle diameter) of 12.5 μm obtained in the kraft pulp production process was used as a raw material. Except for the above, a calcium carbonate aqueous slurry was obtained in exactly the same manner as in Example 1. Tables 1 to 3 also show the pH, B-type viscosity and median diameter (μm) of the aqueous calcium carbonate slurry in each treatment step for this example.

Comparative Example 4 A dispersion of calcium carbonate aqueous solution was obtained in the same manner as in Comparative Example 2, except that the same causticized calcium carbonate as in Example 5 was used as the raw material and the dispersant D was used. Tables 1 to 3 also show the pH, B-type viscosity and median diameter (μm) of the aqueous calcium carbonate slurry in each treatment step for this example.
Shown in

As can be seen from the results shown in Tables 1 and 2, in Comparative Examples 1 and 2, the pH of the slurry became extremely high immediately after the second pass of the secondary dispersion, and the viscosity also increased. The treatment for increasing the degree of dispersion (2 passes) cannot be performed unless the pH is adjusted by introducing carbon dioxide gas, whereas the increase in pH and viscosity in the second dispersion (1 pass) is effective in Examples 1 to 3. Can be suppressed
It was possible to perform a process for further increasing the degree of dispersion by adding a small amount of a dispersant.

This tendency is the same when heavy calcium carbonate is used in combination with light calcium carbonate as a raw material or when caustic calcium carbonate is used. In particular, when PCC and heavy calcium carbonate are used in combination, when a normal dispersant is used, the viscosity eventually increases even if carbon dioxide gas is introduced after one pass and at the end of the process. ,
By using a dispersant having a low degree of neutralization, an increase in pH and an increase in viscosity could be effectively suppressed, and efficient dispersion could be performed.

As can be seen from the results shown in Table 3, if the raw materials are the same, the particle size distribution after the primary dispersion is not different between the example and the comparative example. However, as the processing in the secondary dispersion progresses, carbon dioxide gas is removed. Calcium carbonate having a smaller particle size than Comparative Examples 2 to 4 used in combination was obtained.

[0048]

As is clear from the above examples, according to the method for producing an aqueous calcium carbonate slurry of the present invention, a polycarboxylate having a degree of neutralization of 90% or less is used as a dispersing agent, whereby dispersion treatment is performed. Suppress the rise in liquid viscosity inside,
Efficient dispersion can be performed. As a result, the amount of the dispersant used for obtaining an appropriate viscosity can be reduced. In addition, in aqueous slurries using PCC, in which alkali elution during dispersion treatment involving milling becomes a problem,
In addition, since the increase in liquid viscosity can be suppressed, efficient pulverization can be performed, and an aqueous slurry having a small particle size of calcium carbonate and low viscosity can be obtained.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4D077 AA05 AB04 AC05 BA01 BA07 BA13 DD08Y DD09Y DD17Y DD19Y DD20Y DE02Y DE04Y DE10Y DE29Y 4G065 AA07 AB13X AB14X BA07 BB06 CA12 DA07 GA01 4G076 AA16 AB06 CA04 BA34 BA46 BA50 BC02 DA30

Claims (3)

[Claims] 1. A method for producing an aqueous calcium carbonate slurry using calcium carbonate that elutes an alkali component by a dispersion treatment involving pulverization, wherein a neutralization degree of 90% is used as a dispersant for dispersing the calcium carbonate. A method for producing an aqueous calcium carbonate slurry, comprising using the following sodium salt or ammonium salt of a polycarboxylic acid. 2. The method for producing an aqueous calcium carbonate slurry according to claim 1, wherein the calcium carbonate as a raw material contains at least 50% of light calcium carbonate and / or causticized calcium carbonate. 3. An aqueous calcium carbonate slurry produced by the production method according to claim 1.