JP4191943B2 - Method for producing calcium carbonate whisker - Google Patents

Description

【００２３】
【発明の効果】
実施例１〜2に示す如く、本発明による炭酸カルシウムは凝集のほとんどないアラゴナイト結晶のウィスカー状であった。これらを製紙用填料として用いると白色度、嵩、不透明度に優れ、プラスチック用充填材として用いると曲げ強度の向上などが認められた。さらに、本法は水酸化ナトリウムの副生成物としてウィスカー状の炭酸カルシウムを製造することができるため、製造コストが非常に低減できた。
【図面の簡単な説明】
【図１】 実施例１で得られたアラゴナイト結晶のウィスカー状形状の走査型電子顕微鏡写真である。
【図２】 実施例１で得られた生成物についてのＸ線回折の結果を示す図である。
【図３】 比較例2で得られた凝集粒子の走査型電子顕微鏡写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a calcium carbonate whisker useful as a functional filler for papermaking, plastics, rubber and the like by causticizing reaction, and more particularly, an aqueous solution mainly composed of calcium hydroxide suspension and sodium carbonate. Is continuously added to the reaction vessel, and the product of calcium ion concentration and carbonate ion concentration in the reaction vessel, the ratio of [Ca ²⁺ ] [CO ₃ ^2- ] and calcium ion concentration to carbonate ion concentration, [Ca ²⁺ By adjusting the concentration and flow rate of the aqueous solution mainly composed of calcium hydroxide suspension and aqueous sodium carbonate so that] / [CO ₃ ^2- ] is within the specified range, and controlling the reaction temperature The present invention relates to a method for producing calcium carbonate whiskers that are useful as functional fillers such as papermaking, plastics, and rubbers.
[0002]
[Prior art]
Fillers are used in papermaking, plastic, rubber, etc. to reduce product costs. However, in recent years, fillers have been aimed not only for cost reduction but also for improving the performance of papermaking, plastics, rubber, and the like. Among such fillers for improving performance, whiskers in the form of fibers are widely used for the purpose of improving strength, particularly in the field of plastics, because of their large aspect ratio. Whisker type plastic fillers are (1) potassium titanate, (2) aluminum borate, (3) basic magnesium sulfate, (4) calcium carbonate, etc. Fillers are expensive and their use is limited. Regarding (4), patents relating to the production of whisker-like shapes by the carbon dioxide method have already been filed (Japanese Patent Laid-Open Nos. 62-278123 and 3-88714). However, these methods have a drawback that the production cost is high, for example, using calcium chloride / magnesium hydroxide and phosphate, and the use is limited in the same manner as in the above (1) to (3).
[0003]
[Problems to be solved by the invention]
In view of the above situation, in order to provide calcium carbonate whiskers useful as functional fillers such as papermaking, plastics, rubbers, etc. at low cost, it is important to obtain inexpensive calcium carbonate whiskers by a continuous reaction of causticizing reaction. The subject of the invention.
[0004]
[Means for Solving the Problems]
The present inventors have added 0.1 mol to 1 mol in terms of quicklime to quicklime or / and slaked lime so that the calcium hydroxide suspension concentration is 10 to 30% by weight in terms of quicklime in the causticization reaction of the batch reaction. Add an aqueous alkaline solution containing the following carbonate ions and stir to prepare a calcium hydroxide suspension, then add an aqueous solution containing sodium carbonate as the main component, and control the rate of addition and reaction temperature. It was found that whisker-like calcium carbonate aragonite crystals without aggregation were obtained. However, if the whisker-like aragonite crystal has an aspect ratio of 20 or more, the addition rate of an aqueous solution containing sodium carbonate as a main component is lowered, so that efficient production cannot be achieved. In addition, when preparing a calcium hydroxide suspension, an aqueous solution having a high sodium hydroxide concentration and a low sodium carbonate concentration must be used as an alkaline aqueous solution, which is unlikely to be an inexpensive production method.
[0005]
Therefore, as a result of further earnest studies, the inventors have continuously added an aqueous solution mainly composed of calcium hydroxide suspension and sodium carbonate to the reaction tank, the inside of the reaction tank always becomes alkaline, and whisker-like It was found that aragonite crystals are easily formed. Among them, calcium hydroxide suspension and sodium carbonate aqueous solution are the main components so that [Ca ²⁺ ] [CO ₃ ^2- ] and [Ca ²⁺ ] / [CO ₃ ^2- ] are within the specified range. By adjusting the concentration / addition flow rate of the aqueous solution and controlling the reaction temperature, there is no need for an alkaline aqueous solution necessary for preparing the calcium hydroxide suspension, and an aqueous solution mainly composed of sodium carbonate. The present inventors have found that whisker-like aragonite crystalline calcium carbonate having a large aspect ratio can be obtained without lowering the flow rate of the addition of, and based on this finding, the present invention has been made.
[0006]
It was found that needle-like and columnar calcium carbonate whiskers having a minor axis of 0.3 to 1.5 μm and a major axis of 5 to 50 μm were prepared by the method of the present invention. These are excellent in whiteness, bulk, opacity and rigidity 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 calcium carbonate, the causticizing reaction is a reaction that continuously produces sodium hydroxide, so that sodium hydroxide can be continuously produced, resulting in a cheaper calcium carbonate. Moreover, if the green liquor produced | generated at the causticizing process of the pulp manufacture by a sulfate method or a soda method is used as aqueous solution which has sodium carbonate as a main component, it can manufacture more cheaply.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The quicklime used in the preparation of the calcium hydroxide suspension of the present invention converts limestone mainly composed of calcium carbonate, and sodium carbonate into sodium hydroxide 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 | generated in the case. Regarding the firing equipment at that time, Beckenbach furnace, Melz furnace, rotary kiln, Kunii-type furnace, KHD (Kerhardy) furnace, Koma-type furnace, Kalmatic furnace, fluidized firing furnace, mixed baking stand, etc., calcium carbonate If it is an apparatus which converts lime into quicklime (calcium oxide), it will not be restricted in particular.
[0008]
In addition, the slaked lime used in the preparation of the calcium hydroxide suspension may be a hydrated dry hydrated lime, but for the calcium carbonate whisker particle size distribution produced by the dry hydrated slaked lime. More preferred.
[0009]
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 per 1 mol of quicklime is used. Although it is not particularly necessary to use an alkaline aqueous solution, it is possible to use a purified sodium hydroxide produced by the causticizing reaction in consideration of the causticizing reaction. Moreover, when manufacturing a calcium carbonate whisker in the causticization process of the pulp manufacture by a sulfate method or a soda method, it is also possible to dilute and use the white liquor produced | generated at a causticization process.
[0010]
When an alkaline aqueous solution is used, if the carbonate ion is more than 0.1 mol per mol of quicklime, the calcium carbonate that is formed becomes an aggregated aragonite crystal or a spindle-shaped or massive calcite crystal.
[0011]
The calcium hydroxide suspension concentration during preparation of the calcium hydroxide suspension needs to be 10 to 30% by weight in terms of quicklime. Here, when the calcium hydroxide concentration exceeds 30% by weight, uniform stirring in the reaction tank becomes difficult, and aggregation tends to occur. Further, if the agitation is increased in order to reduce aggregation, it becomes difficult to obtain whiskers having a large aspect ratio. On the other hand, when the calcium hydroxide suspension concentration is less than 10% by weight, the volume of the liquid increases, and it takes time to separate the calcium carbonate whisker and the sodium hydroxide aqueous solution.
[0012]
For mixing with quick lime slaked and slaked lime dissolved, use the general stirring blade type, pump type, extruders, kneaders, and kneaders to match the viscosity of the liquid or slurry during mixing. Can be selected and used as appropriate.
[0013]
As the aqueous solution containing sodium carbonate as a main component in the causticizing reaction of the present invention, an aqueous sodium carbonate solution in which soda ash is dissolved, or a green liquor generated from a causticizing step of a general sulfate method or soda method can be used. . If [Ca ²⁺ ] [CO ₃ ²⁻ ] and [Ca ²⁺ ] / [CO ₃ ²⁻ ] in the reaction vessel can be controlled within a specified range, sodium carbonate solid can also be used. An aqueous solution containing sodium carbonate as a main component has a Na ₂ CO ₃ concentration of 40 to 230 g / L (in terms of Na ₂ O, hereinafter the same), preferably a Na ₂ CO ₃ concentration of 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 increases, and it takes time to separate the calcium carbonate whisker from the sodium hydroxide aqueous solution. 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 produced.
[0014]
The addition flow rate of the aqueous solution mainly composed of calcium hydroxide suspension and sodium carbonate is defined by [Ca ²⁺ ] [CO ₃ ^2- ] and [Ca ²⁺ ] / [CO ₃ ^2- ] in the reaction vessel. Adjust appropriately to be within the range. At this time, if sodium carbonate is less than an equimolar amount with respect to calcium hydroxide in the reaction tank, calcium hydroxide remains in the aragonite crystal, but in the reaction tank following the first tank or another reaction tank. The whisker-like calcium carbonate slurry in which calcium hydroxide remains is transported, and pure whisker-like aragonite crystalline calcium carbonate is added by adding sodium carbonate sufficient to eliminate the remaining sodium hydroxide. Obtainable.
[0015]
In the reaction vessel 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 changed to 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 There is. The calcium ion concentration is almost dependent on the sodium hydroxide concentration, and the higher the sodium hydroxide concentration, the lower the concentration. To reduce [Ca ²⁺ ] [CO ₃ ^2- ] below 0.01 × 10 ^-3, high hydroxide Since it is necessary to use a low sodium carbonate concentration with a sodium concentration, the flow rate must be very low, resulting in poor productivity. When [Ca ²⁺ ] [CO ₃ ²⁻ ] is higher than 0.05 × 10 ⁻³ , particle aggregation increases, making it difficult to obtain whisker-like calcium carbonate. On the other hand, in order to make [Ca ²⁺ ] / [CO ₃ ²⁻ ] less than 2 × 10 ⁻³ , the addition flow rate must be lowered, resulting in poor production efficiency.
[0016]
About reaction temperature, it is necessary to carry out at 60-95 degreeC, Preferably it is 70-90 degreeC. When the temperature is higher than 95 ° C., it becomes an aggregated aragonite crystal, or a spindle-like or massive calcite crystal, and the desired needle-like or columnar aragonite crystal cannot be obtained. On the other hand, when it is lower than 60 ° C., fine aragonite crystals are formed, and it becomes difficult to obtain whisker-like calcium carbonate.
[0017]
For the stirring during the causticizing reaction, calcium hydroxide prepared by dehydration of quick lime and dissolution of slaked lime from general stirring blade type, pump type, extruders, kneaders, kneaders A suspension and a sodium carbonate solution that can be uniformly mixed may be appropriately selected and used.
[0018]
Under the above 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 adjusted.
[0019]
The aragonite crystal calcium carbonate obtained by the present invention is excellent in whiteness, bulk 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 uses, it can also be used for rubber, paints, sealing agents, adhesives, fertilizers and the like.
[0020]
【Example】
The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the examples.
[Test method]
(1) Measurement of Ca ²⁺ concentration: The slurry discharged from the flask is The crystals and the solution were separated with 5C filter paper. This solution was neutralized with hydrochloric acid, and the Ca ²⁺ concentration of the neutralized aqueous solution was measured using an ICP emission spectroscopic analyzer (SPS-1700R: manufactured by Seiko Instruments Inc.).
( ² ) Measurement of CO ₃ ^2- concentration: The slurry discharged from the flask is The crystals were separated from the solution with 5C filter paper, and the solution was measured for TAPPI 624hm-85, TAPPI 625 hm-85, or a Na ₂ CO ₃ concentration according to this to obtain a CO ₃ ²⁻ concentration.
(3) Morphological observation: The product was washed and filtered with water, dried, and then observed with a scanning electron microscope (JSM-840A manufactured by JEOL Ltd.). Based on this observation, the minor axis and major axis of each of the 50 particles were measured, and the aspect ratio (major axis / minor axis) was determined.
(4) Crystal structure: Measured with an X-ray diffractometer (XD-D1: manufactured by Shimadzu Corporation). [Example 1]
10% by weight calcium hydroxide suspension (as CaO) and 100 g / l sodium carbonate aqueous solution (as Na ₂ O) were continuously added to a 500 ml separable flask with a jacket with an outlet at the bottom. The suspension volume in the flask is kept at 500 ml, and [Ca ²⁺ ] [CO ₃ ^2- ] in the flask is 0.019 × 10 ^-3 and [Ca ²⁺ ] / [CO ₃ ^2- ] is 4.6. Adjusting the addition flow rate of calcium hydroxide suspension and sodium carbonate aqueous solution and the discharge flow rate from the bottom of the flask so that it becomes × 10 ^-3 , at a temperature of 75 ° C and a stirring speed of 400 rpm (KYOEI POWER STIRRER TYPE PS-2N) The reaction was allowed to proceed.
[0021]
As a result of observation of the average particle size and morphology of the reaction product, aragonite crystals having an average major axis of 15.6 μm and an average minor axis of 0.6 μm and almost no aggregation were observed. Experimental conditions and results are shown in Table 1.
[Example 2]
When the concentration of the calcium hydroxide suspension is 20% by weight, green solution (Na ₂ CO ₃ : Na ₂ S = 1.6: 0.5 mol / l) is used instead of the sodium carbonate aqueous solution, and [Ca ²⁺ ] in the flask is used. Adjust the flow rate of calcium hydroxide suspension and green liquor so that [CO ₃ ^2- ] is 0.03 × 10 ⁻³ and [Ca ²⁺ ] / [CO ₃ ^2- ] is 4.2 × 10 ⁻³ , The reaction was performed under the same conditions as in Example 1 except that the continuous reaction was performed at a temperature of 80 ° C. The product had an average major axis of 13.1 μm and an average minor axis of 0.6 μm, and aragonite crystals with little aggregation were observed. Experimental conditions and results are shown in Table 1.
[Comparative Example 1]
At a temperature of 50 ° C, the [Ca ²⁺ ] [CO ₃ ^2- ] in the flask is 0.055 × 10 ^-3 and the [Ca ²⁺ ] / [CO ₃ ^2- ] is 4.7 × 10 ^-3 The same procedure as in Example 1 was performed except that a continuous reaction was performed. The product was an aragonite crystal with an average minor axis of 0.3 μm and agglomerated. Experimental conditions and results are shown in Table 1.
[Comparative Example 2]
The continuous reaction was carried out so that [Ca ²⁺ ] [CO ₃ ^2- ] in the flask was 0.057 × 10 ^-3 and [Ca ²⁺ ] / [CO ₃ ^2- ] was 0.6 × 10 ^-3. The procedure was the same as in Example 1 except that. The reaction product at this time was particles in which granular and acicular particles were aggregated. Experimental conditions and results are shown in Table 1.
[0022]
[Table 1]

[0023]
【The invention's effect】
As shown in Examples 1 and 2, the calcium carbonate according to the present invention was in the form of whisker of aragonite crystals with little aggregation. When these were used as fillers for papermaking, they were excellent in whiteness, bulk and opacity, and when used as fillers for plastics, improvements in bending strength were recognized. 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 the drawings]
1 is a scanning electron micrograph of whisker-like shapes of aragonite crystals obtained in Example 1. FIG.
2 is a graph showing the results of X-ray diffraction for the product obtained in Example 1. FIG.
3 is a scanning electron micrograph of aggregated particles obtained in Comparative Example 2. FIG.

Claims (2)

Calcium carbonate whisker that is useful as a functional filler by causticization reaction , wherein the short diameter is 0.3 to 1.5 μm, the long diameter is 5 to 50 μm, and the aspect ratio is 20 or more. There,
A calcium hydroxide suspension prepared by adding water or an aqueous alkaline solution to a substance selected from the group consisting of quicklime and / or slaked lime so that the calcium hydroxide suspension concentration is 10 to 30% by weight in terms of quicklime. A suspension and an aqueous solution containing sodium carbonate as a main component are continuously added to the reaction vessel, and the product of the calcium ion concentration and the carbonate ion concentration in the reaction vessel ([Ca ²⁺ ] [CO ₃ ²⁻ ]) is reduced to 0. 01 × 10 ^{−3 to} 0.05 × 10 ⁻³ (mol ² / l ² ), and the ratio of calcium ion concentration to carbonate ion concentration ([Ca ²⁺ ] / [CO ₃ ²⁻ ]) is 2 × 10 ^−3. As described above, the concentration and addition flow rate of the aqueous solution mainly composed of calcium hydroxide suspension and sodium carbonate are adjusted, causticizing reaction is performed at a reaction temperature of 60 to 95 ° C., and the suspension in the reaction vessel Unplug continuously Method for producing useful calcium carbonate whisker as a functional filler consisting Succoth.   The method for producing calcium carbonate whiskers according to claim 1, wherein the calcium carbonate whiskers are for papermaking, plastics or rubber.

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