JP2003286026A - Method for manufacturing calcium carbonate whisker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously manufacture calcium carbonate whisker useful as a functional filler for paper making, plastics, rubber or the like by using caustification reaction. <P>SOLUTION: The calcium carbonate whisker useful as a functional filler for paper making, plastics, rubber or the like is obtained by continuously adding a suspension of calcium hydroxide and an aqueous solution essentially comprising sodium carbonate to a reaction chamber to cause a caustification reaction. The concentration and flow rates for addition of the calcium hydroxide suspension and the aqueous solution essentially comprising sodium carbonate are controlled to bring the product of the calcium ion concentration and carbonate ion concentration [Ca<SP>2+</SP>][CO<SB>3</SB><SP>2-</SP>] in the reaction tank and the ratio of the calcium ion concentration to the carbonate ion concentration [Ca<SP>2+</SP>]/[CO<SB>3</SB><SP>2-</SP>] into specified ranges. The reaction temperature is also controlled. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing calcium carbonate whiskers useful as a functional filler for papermaking, plastics, rubber and the like by a causticizing reaction, and more specifically to a calcium hydroxide suspension and carbonate. An aqueous solution containing sodium as a main component was continuously added to the reaction tank, and the product of calcium ion concentration and carbonate ion concentration in the reaction tank, [Ca ^{2 +} ] [CO ₃ ^2- ], calcium ion concentration and carbonate ion concentration The ratio of [Ca ²⁺ ] / [CO ₃ ²⁻ ] is within the specified range, and the concentration and addition flow rate of the calcium hydroxide suspension and the aqueous solution containing sodium carbonate as the main component are adjusted, and The present invention relates to a method for producing calcium carbonate whiskers useful as a functional filler for papermaking, plastics, rubber and the like by controlling the reaction temperature.

[0002]

2. Description of the Related Art Fillers are used for paper manufacturing, plastics, rubber, etc. in order to reduce product costs. However, in recent years, fillers have been used not only to reduce the cost but also to improve the performance of papermaking, plastics, rubber and the like. Among the fillers for the purpose of improving the performance, the whiskers in the form of fibers are widely used for the purpose of improving the strength especially in the field of plastics because of their large aspect ratio. Whisker type fillers for plastics include potassium titanate, aluminum borate, basic magnesium sulfate, calcium carbonate and the like, but the above-mentioned fillers are expensive and their use is limited. Has already been applied for a patent relating to the production of whisker-like shapes by the carbon dioxide method (Japanese Patent Laid-Open No. 62-278123,
JP-A-3-88714). However, these methods have a drawback that the production cost is high, such as using calcium chloride / magnesium hydroxide or a phosphate, and thus there are limitations in use in the same manner as above.

[0003]

In view of the above situation, in order to inexpensively provide calcium carbonate whiskers useful as a functional filler for papermaking, plastics, rubber, etc., it is possible to reduce the cost by continuous reaction of causticizing reaction. It was an object of the present invention to obtain stable calcium carbonate whiskers.

[0004]

[Means for Solving the Problems] The present inventors have decided to use quicklime or / and slaked lime in quicklime so that the concentration of calcium hydroxide suspension in the causticizing reaction of batch reaction becomes 10 to 30% by weight in terms of quicklime. An alkaline aqueous solution containing 0.1 mol or less of carbonate ions per 1 mol of conversion was added and stirred to prepare a calcium hydroxide suspension, and then an aqueous solution containing sodium carbonate as a main component was continuously added. It was found that whiskers of aragonite crystals of calcium carbonate without aggregation can be obtained by controlling the addition rate and reaction temperature. However, in order to increase the aspect ratio of the whisker-like aragonite crystals to 20 or more, the addition rate of the aqueous solution containing sodium carbonate as a main component is lowered, so that efficient production cannot be performed. In addition, an aqueous solution having a high sodium hydroxide concentration and a low sodium carbonate concentration must be used as the alkaline aqueous solution when preparing the calcium hydroxide suspension, which is unlikely to be an inexpensive manufacturing method.

Therefore, as a result of further intensive studies, the present inventors have found that when a calcium hydroxide suspension and an aqueous solution containing sodium carbonate as a main component are continuously added to the reaction tank, the inside of the reaction tank is always alkaline. It was found that whisker-like aragonite crystals were easily generated. Among them [C
a ²⁺ ] [CO ₃ ^2- ] and [Ca ²⁺ ] / [CO ₃ ^2- ] are within the specified range Concentration of calcium hydroxide suspension and aqueous solution containing sodium carbonate・ Adjust the flow rate of addition,
In addition, by controlling the reaction temperature, there is no need for an alkaline aqueous solution necessary for the preparation of the calcium hydroxide suspension, and the aspect ratio can be maintained without lowering the addition flow rate of the aqueous solution containing sodium carbonate as the main component. It was found that whisker-like aragonite crystalline calcium carbonate having a large size was obtained, and the present invention was completed based on this finding.

According to the method of the present invention, the minor axis of the particles is from 0.3 to
It was found that needle-shaped and columnar calcium carbonate whiskers having a major axis of 5 to 50 μm and a diameter of 1.5 μm were prepared. These are excellent in whiteness, bulkiness, opacity and rigidity when used as a filler for paper making, and can improve bending strength and the like when used as a filler for plastics. Further, in addition to calcium carbonate, the causticizing reaction is a reaction that continuously produces sodium hydroxide, so that sodium hydroxide can be continuously produced, resulting in an even cheaper calcium carbonate. Further, if the green liquor produced in the causticizing step of pulp production by the sulfate method or the soda method is used as the aqueous solution containing sodium carbonate as a main component, it can be produced at a lower cost.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The quicklime used in the preparation of the calcium hydroxide suspension of the present invention is limestone containing calcium carbonate as a main component, and sodium carbonate in the causticizing step of pulp production by the sulfate method or the soda method. What is necessary is just to calcinate the calcium carbonate produced when converting to sodium hydroxide. Regarding the firing equipment at that time, Beckenbach furnace, Meltz furnace, rotary kiln, Kunii furnace, KHD (Car Hardy) furnace, coma furnace, calmatic furnace, fluidized firing furnace, mixed firing furnace, calcium carbonate, etc. It is not particularly limited as long as it is a device for converting lime into quick lime (calcium oxide).

The slaked lime used in the preparation of the calcium hydroxide suspension may be wet hydrated or dry hydrated lime, but the particle size of the calcium carbonate whiskers produced by the dry slaked lime is better. More favorable for distribution.

As a liquid to be added in the preparation of the calcium hydroxide suspension, a neutral to alkaline aqueous solution having a carbonate ion concentration of 0.1 mol or less with respect to 1 mol of quicklime is used. Although it is not particularly necessary to use an alkaline aqueous solution, in consideration of the causticizing reaction, it is also possible to use purified sodium hydroxide produced in the causticizing reaction. When calcium carbonate whiskers are produced in the causticizing step of pulp production by the sulfate method or the soda method, the white liquor produced in the causticizing step can be diluted with water before use.

When an alkaline aqueous solution is used, 1 mol of quick lime is used.
If the amount of carbonate ion is more than 0.1 mol with respect to l, the generated calcium carbonate becomes aggregated aragonite crystals,
It becomes spindle-shaped or lump-shaped calcite crystals.

The calcium hydroxide suspension concentration at the time of preparation of the calcium hydroxide suspension must be 10 to 30% by weight in terms of quicklime. Where the calcium hydroxide concentration is 30
When the content exceeds the weight%, uniform agitation in the reaction tank becomes difficult, and thus aggregation easily occurs. Further, if stirring is intensified to reduce aggregation, it becomes difficult to obtain whiskers having a large aspect ratio. On the other hand, if the concentration of the calcium hydroxide suspension is less than 10% by weight, the volume of the liquid becomes large, and it takes time to separate the calcium carbonate whiskers and the aqueous sodium hydroxide solution, which lowers the productivity and is not practical.

For mixing slaked lime and dissolution of slaked lime, general stirring blade type, pump type, extruders,
A kneading machine or a kneading machine may be appropriately selected and used according to the viscosity of the liquid or slurry at the time of mixing.

As the aqueous solution containing sodium carbonate as a main component in the causticizing reaction of the present invention, an aqueous solution of sodium carbonate in which soda ash is dissolved, or a green liquor generated from the general sulfate method or the causticizing step of the soda method is used. be able to. Solid sodium carbonate can also be used as long as [Ca ²⁺ ] [CO ₃ ²⁻ ] and [Ca ²⁺ ] / [CO ₃ ²⁻ ] in the reaction tank can be controlled within a specified range. Aqueous solution containing sodium carbonate as the main component
Na ₂ CO ₃ concentration 40 to 230 g / L (Na ₂ O conversion, the same below), preferably Na ₂ CO ₃ concentration 60 to 180 g / L, more preferably 80 to 120 g.
Must be done with / L. When the Na ₂ CO ₃ concentration is lower than 20 g / L, the volume of the liquid becomes large, and it takes time to separate the calcium carbonate whiskers and the sodium hydroxide aqueous solution, resulting in poor productivity, which is not practical. on the other hand,
Since a solution with a concentration of 230 g / L is close to the saturation concentration, a solution with a higher concentration cannot be prepared.

The addition flow rate of the calcium hydroxide suspension and the aqueous solution containing sodium carbonate as the main component is [Ca ²⁺ ] [C in the reaction tank.
O ₃ ²⁻ ] and [Ca ²⁺ ] / [CO ₃ ²⁻ ] are appropriately adjusted to fall within the specified range. At this time, if sodium carbonate is less than equimolar to calcium hydroxide in the reaction tank, calcium hydroxide will remain in the aragonite crystals, but
Transfer the whisker-like calcium carbonate slurry in which calcium hydroxide remains to the reaction tank following the tank or another reaction tank, and add sodium carbonate sufficient to eliminate the remaining sodium hydroxide to this Thus, pure whisker-like aragonite crystalline calcium carbonate can be obtained.

In the reaction tank in which the calcium hydroxide suspension and the aqueous solution containing sodium carbonate as a main component are mixed, [Ca
^{2 +} ] [CO ₃ ^2- ] is 0.01 × 10 ^{-3 to} 0.05 × 10 ^-3 (mol ² / l ² ), preferably 0.015 × 10 ^{-3 to} 0.03 × 10 ^-3 , and [Ca ²⁺ ] / [CO ₃ ^2- ]
^{Should be} 2 × 10 ⁻³ or more, preferably 3 × 10 ⁻³ or more. The calcium ion concentration depends almost on the sodium hydroxide concentration, and the higher the sodium hydroxide concentration, the lower it becomes. Therefore, in order to make [Ca ²⁺ ] [CO ₃ ^2- ] lower than 0.01 × 10 ^-3, high hydroxylation Since it is necessary to make the sodium concentration low at the sodium concentration, it is necessary to make the addition flow rate very low, resulting in poor productivity. When [Ca ²⁺ ] [CO ₃ ²⁻ ] is higher than 0.05 × 10 ⁻³ , agglomeration of particles increases, and it becomes difficult to obtain whisker-like calcium carbonate. On the other hand, [Ca ²⁺ ] / [CO ₃ ^2- ]
If it is less than 2 × 10 ⁻³ , the addition flow rate must be lowered, resulting in poor production efficiency.

The reaction temperature is 60 to 95 ° C., preferably
Must be done at 70-90 ° C. If the temperature is higher than 95 ° C, aggregated aragonite crystals will be formed, or spindle-shaped or lump-shaped calcite crystals will not be obtained, and desired needle-shaped or columnar aragonite crystals cannot be obtained. On the other hand, when the temperature is lower than 60 ° C., fine aragonite crystals are generated, and it becomes difficult to obtain whisker-like calcium carbonate.

Stirring during the causticizing reaction was prepared by slaked quick lime and dissolution of slaked lime from general stirring blade type, pump type, extruders, kneading machines and kneading machines. A calcium hydroxide suspension and a sodium carbonate solution that can be uniformly mixed may be appropriately selected and used.

Under the above-mentioned conditions, acicular and columnar aragonite crystalline calcium carbonate having a minor axis of 0.3 to 1.5 μm and a major axis of 5 to 50 μm can be prepared.

The calcium carbonate of aragonite crystals obtained by the present invention is excellent in whiteness, bulkiness and opacity when used as a filler for papermaking, and can improve bending strength and the like when used as a filler for plastics. In addition to these applications, it can also be used for rubber, paint, sealing agents, adhesives, fertilizers and the like.

[0020]

The present invention will be described in more detail below with reference to examples and comparative examples, but it goes without saying that the present invention is not limited to the examples. [Test Method] Measurement of Ca ²⁺ Concentration: The slurry discharged from the flask was replaced with No. The crystals and the solution were separated with 5C filter paper. The solution was neutralized with hydrochloric acid, and the neutralized aqueous solution was measured for Ca ²⁺ concentration using an ICP emission spectrophotometer (SPS-1700R: manufactured by Seiko Instruments Inc.). Measurement of CO ₃ ^2- concentration: The slurry discharged from the flask was replaced with No. The crystals and the solution were separated with 5C filter paper, and the solution was tapped with TAPPI624hm-85, TAPPI625hm.
The Na ₂ CO ₃ concentration was measured at -85, or in accordance with this, and defined as the CO ₃ ^2- concentration. Morphological observation: The product was washed with water, filtered, dried, and then observed with a scanning electron microscope (JSM-840A, manufactured by JEOL Ltd.). Based on the observation here, the minor axis and major axis of each of 50 particles were measured to determine the aspect ratio (major axis / minor axis). Crystal structure: X-ray diffractometer (XD-D1: manufactured by Shimadzu Corp.) was used for measurement. Example 1 A 500 ml separable flask equipped with a jacket having an outlet at the bottom was charged with 10 wt% calcium hydroxide suspension (as CaO) and 100 g / l sodium carbonate aqueous solution (as Na ₂ O). Continuously added, the suspension volume in the flask was kept at 500 ml, and [Ca ²⁺ ] [CO ₃ in the flask
^2- ] is 0.019 × 10 ^-3 , and [Ca ²⁺ ] / [CO ₃ ^2- ] is 4.6 × 10 ^-3 . Adjusting the discharge flow rate, temperature 75 ℃, stirring speed 400 rpm (KYOEI POWER STIR
RER TYPE PS-2N) proceeded the reaction.

Observation of the average particle size and morphology of the reaction product revealed that the average major axis was 15.6 μm and the average minor axis was 0.6 μm.
Aragonite crystals with almost no aggregation were observed. The experimental conditions and results are shown in Table 1. [Example 2] Concentration of calcium hydroxide suspension is 20% by weight
Then, instead of the aqueous solution of sodium carbonate, green liquor (Na ₂ CO ₃ : Na ₂
S = 1.6: 0.5 mol / l) and [Ca ²⁺ ] [CO ₃ ^2- ] in the flask
Is adjusted to 0.03 × 10 ^-3 and [Ca ²⁺ ] / [CO ₃ ^2- ] is 4.2 × 10 ^-3 by adjusting the flow rates of calcium hydroxide suspension and green liquor.
The conditions of Example 1 were followed except that the continuous reaction was carried out at 80 ° C. The product has an average major axis of 13.1 μm and an average minor axis of 0.6 μm,
Aragonite crystals with almost no aggregation were observed. The experimental conditions and results are shown in Table 1. [Comparative Example 1] [Ca ²⁺ ] [CO ₃ ^2- ] in a flask at a temperature of 50 ° C
Was 0.055 × 10 ⁻³ and [Ca ²⁺ ] / [CO ₃ ²⁻ ] was 4.7 × 10 ⁻³ , and the continuous reaction was performed in the same manner as in Example 1. As the product, aragonite crystals having an average short diameter of 0.3 μm and agglomerating in aggregate were obtained. The experimental conditions and results are shown in Table 1. [Comparative Example 2] [Ca ²⁺ ] [CO ₃ ²⁻ ] in the flask was 0.057 × 10 ⁻³
Then, the same procedure as in Example 1 was performed except that the continuous reaction was performed so that [Ca ²⁺ ] / [CO ₃ ²⁻ ] became 0.6 × 10 ⁻³ . The reaction product at this time was particles in which granular and acicular particles were aggregated. The experimental conditions and results are shown in Table 1.

[0022]

[Table 1]

[0023]

As shown in Examples 1 and 2, the calcium carbonate according to the present invention was in the form of whiskers of aragonite crystals with almost no aggregation. It was confirmed that when they were used as a filler for papermaking, they were excellent in whiteness, bulkiness and opacity, and when they were used as a filler for plastics, the bending strength was improved.
Furthermore, since this method can produce whisker-like calcium carbonate as a by-product of sodium hydroxide, the production cost can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a whisker-like shape of the aragonite crystal obtained in Example 1.

FIG. 2 is a diagram showing a result of X-ray diffraction of a product obtained in Example 1.

FIG. 3 is a scanning electron micrograph of aggregated particles obtained in Comparative Example 2.

Claims (2)

[Claims] 1. A method for producing a calcium carbonate whisker useful as a functional filler by a causticizing reaction, wherein the calcium hydroxide suspension concentration is 10 to 30 in terms of quick lime.
A calcium hydroxide suspension prepared by adding water or an alkaline aqueous solution to a substance selected from the group consisting of quick lime and / or slaked lime so that the weight% is reacted with an aqueous solution containing sodium carbonate as a main component. The product of calcium ion concentration and carbonate ion concentration ([Ca ²⁺ ] [CO ₃ ²⁻ ]) in the reaction vessel is 0.01 × 10 ^{-3 to} 0.05 × 10 ^-3 (mo
l ² / l ² ), and the calcium hydroxide suspension and carbonate so that the ratio of calcium ion concentration to carbonate ion concentration ([Ca ²⁺ ] / [CO ₃ ^2- ]) is 2 × 10 ^-3 or more. Adjust the concentration and flow rate of the aqueous solution containing sodium as the main component, and adjust the reaction temperature to 60-95.
A method for producing calcium carbonate whiskers useful as a functional filler, which comprises carrying out a causticizing reaction at ℃ and continuously extracting the suspension in the reaction tank. 2. The method for producing a calcium carbonate whisker according to claim 1, wherein the calcium carbonate whisker is for papermaking, plastic or rubber.