JPS5836924A - Growing method for crystal of aragonite type prismatic calcium carbonate - Google Patents

Abstract

PURPOSE:To grow crystals of aragonite type prismatic CaCO3 suitable for use as a coating pigment for paper making by reacting Ca(OH)2 with CO2 under specified conditions using seed crystals of aragonite type prismatic CaCO3. CONSTITUTION:A slurry of seed crystals of aragonite type CaCO3 having <=about 2mum major axis size and <=about 0.2mum minor axis size is mixed with a Ca(OH)2 emulsion so as to make the molar ratio of Ca(OH)2/CaCO3 1-5, and the concn. after the mixing is adjusted to 50-250g/l. While stirring this slurry, a gas contg. >=about 10vol% CO2 is blown into the slurry at a rate adjusting the amount of CO2 in the gas to 0.5-10Nl/min per 1kg CaCO3, and they are reacted at about 5-80 deg.C to grow crystals of aragonite type prismatic CaCO3. The resulting CaCO3 crystals are suitable for use in a field of the paper making industry and can enhance printing luster, printing strength, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for growing crystals of arabnite columnar calcium carbonate suitable as a coating pigment for paper manufacturing.

Ordinary white paper for printing is coated with paper coating pigments to improve the optical properties, smoothness, ink receptivity, etc. of the paper. Traditionally, kaolin clay has been mainly used as this pigment, but in recent years it has been difficult to supply them, so synthetic and naturally produced calcium carbonate has been attracting attention as an alternative material.

By the way, synthetic calcium carbonate is generally produced in Japan by the reaction of calcium hydroxide emulsion with carbon dioxide, but when the calcium carbonate crystals obtained by this method are used as a coating pigment for paper manufacturing, the whiteness and ink Although it produces better results than kaolin clay in terms of acceptability, it has inferior print gloss and print strength, so kaolin clay is currently used in applications where these properties are important.

Therefore, in the field of paper manufacturing, there is a demand for calcium carbonate crystals that have improved printing gloss and printing strength while retaining the advantages of calcium carbonate itself, namely, whiteness and excellent ink receptivity.

As a result of various studies to meet these demands, the present inventors have found that by using aragonite-based columnar calcium carbonate seed crystals and reacting calcium hydroxide and carbon dioxide under specific conditions, the desired results can be obtained. It was discovered that calcium carbonate crystals can be obtained, and based on this knowledge, the present invention was completed.

That is, in producing calcium carbonate by the reaction of calcium hydroxide and carbon dioxide, the present invention uses aragonite-based columnar calcium carbonate seed crystals and calcium hydroxide in a molar ratio of calcium hydroxide to calcium carbonate of 1 to 5. A carbon dioxide-containing gas is contained in an aqueous slurry in which the concentration after mixing is in the range of 50 to 25 ny/l. The present invention provides a method for growing crystals of aragonite-based columnar calcium carbonate by carrying out a blowing reaction at a rate of 1 ONt.

In the method of the present invention, the particle size of the aragonitic columnar calcium carbonate crystals used as seed crystals is not particularly limited as long as it is smaller than that of the target calcium carbonate crystal, but preferably the major axis is 2 μm or less and the minor axis is 2 μm or less. 0.2 μm or less, more preferably major axis 0.5 to 1 μm
m and the short axis is in the range of 0.05 to 0.1 μm.

The proportion of seed crystals and calcium hydroxide in the aqueous slurry in the method of the invention must be selected such that the molar ratio of calcium hydroxide to calcium carbonate is from 1 to 5. The growth rate of this seed crystal depends on the mixing ratio of calcium hydroxide; as the ratio of calcium hydroxide increases, the degree of growth increases, and as the ratio of calcium hydroxide decreases, the degree of growth decreases. Therefore, if the molar ratio of both is outside the above range, calcium carbonate crystals with desired physical properties cannot be obtained.

In addition, the slurry concentration after mixing the seed crystal and calcium hydroxide is 50 to 250 f/Ls, preferably 100 to 20
09/l, and this slurry concentration is 50 to 250f.
/t is outside the range, it becomes difficult to form calcium carbonate crystals with desired physical properties, which is unfavorable in terms of productivity and workability.

In the method of the present invention, a carbon dioxide-containing gas is blown into the aqueous slurry having the above composition at a rate such that the carbon dioxide in the gas is 0.5 to IOt, particularly 1 to 3t, per Ikg of calcium hydroxide per minute under standard conditions. Preferably. If the carbon dioxide blowing rate is less than 0.5, the growth rate of the crystal will be slow and impractical, and if it exceeds 10 tons, crystals with desired physical properties will not be obtained.

The carbon dioxide concentration in the carbon dioxide-containing gas used in this reaction is desirably 10% by volume or more, more preferably 25% by volume or more.
~35% by volume.

In the method of the present invention, the temperature of the aqueous slurry at the start of blowing the carbon dioxide-containing gas is 5 to 80°C, preferably 25 to 35°C.
selected within the range. Further, the reaction time is about 1 to 10 hours.

The aragonite-based columnar calcium carbonate crystals thus obtained are subjected to mechanical solid-liquid separation according to a conventional method, and the obtained calcium carbonate slag is used as a product as it is or after being dried.

Calcium carbonate obtained by the method of the present invention has a major axis of 1
．． It is an aragonite-based columnar crystal with a length of 4 to 4.5 μm and a minor axis of 0.12 to 0.6 μm. When used as a coating pigment for papermaking, it exhibits gloss and printing strength comparable to -grade kaolin clay, and - Provides a white paper exhibiting superior whiteness, opacity and ink receptivity to grade kaolin clay.

Next, the present invention will be explained in more detail with reference to Examples.

Note that the paper quality test in the Examples was conducted according to the method shown below. That is, using coated base paper (basis weight 68 t/n?, high-quality paper), apply the coating liquid prepared under the following conditions to 16 to 20 f.
A coated paper was prepared by applying 9 coats of coach-in-blonde so as to give a coating of /-, and then supercalendering the coated paper under the following conditions.

Preparation of coating liquid (a) Binder; Starch/SDR=7/13, binder level 2
0 parts by weight Starch (made by Nippon Shokuhin ■+46oo) SBR (0692 made by Nippon Synthetic Rubber ■) (b) Additive; Lubricant (Doff922 B made by Nissin Chemical ■) 1.5 parts by weight (c) Sample calcium carbonate ilO' (in parts by weight) Solid content concentration; 45wt% WB Super calender asthma conditions (a) Linear pressure 100Kf/cIn (b)
Temperature: 55°C (c) Number of paper passes: 3 times) Calender speed: 8 m/min The coated paper thus obtained was subjected to a paper quality test by the following measurements or evaluations. Amount: Difference in weight measurement before and after coating (2) Whiteness: Measured using a Hunter set day color meter (3) Opacity: Measured using a Hunter set day color meter (4) White paper gloss: 75 measured using a gloss meter °-75° measurement (5) Print gloss 1 75°-75° by gloss meter
Measurement (Ink used: TKUG Red-Kuchi 0.4 Go) (6) K&N ink acceptability; Measured by No. 1 whiteness meter (K&H 2-minute value) (7) Surface strength i By 1GT printability tester measurement(
Ink used: SMXJITKU20) Example 1 Columnar calcium carbonate seed crystal slurry with a major axis of 1 μm and a minor axis of 0.1/Jm and calcium hydroxide emulsion were mixed with Ca(OH
)2/CaCO3 molar ratio is 1 to 4,
After adjusting the concentration of both after mixing to xoof/z, the mixture was supplied to a reaction tank and maintained at 30°C.

While stirring this slurry, add 30% carbon dioxide by volume.
A carbonation reaction was carried out by blowing a gas containing carbon dioxide at a rate of 2Nt carbon dioxide per minute per 111g of calcium hydroxide. The particle size of the calcium carbonate crystals thus obtained is shown in Table 1, and enlarged photographs of the crystals are shown in Figs. Figures 5 and 5 show experimental results, respectively.
-1.1-2.1-3.1-4 This is a microscopic photograph of the calcium carbonate crystals obtained. show. In addition, blanks in Table 2 are as follows:
These are the paper quality test results for seed crystals.

Table 1 Table 2 Example 2 Same as Example 1 except that the Ca(OH)2/CaCO3 molar ratio in Example 1 was changed for each experiment number within the range of 1 to 5. A carbonation reaction was carried out to obtain calcium carbonate crystals, which were used to test the quality of coated paper. Table 3 shows the particle size of the calcium carbonate crystals obtained, and Table 4 shows the paper quality test results.

Table 3 As is clear from this table, the changes in the molar ratio of Example 1. The degree of crystal growth is different compared to .

Table 4 Example 3 Using the same columnar calcium carbonate seed crystals as in Example 1, a carbonation reaction was carried out according to the conditions shown below.

Concentration reaction start temperature after combination of columnar calcium carbonate seed crystals and 50 flt calcium hydroxide: 5°C 0a (OH)
2/CaCO3 molar ratio 1 to 5 blown carbon dioxide gas amount 0.5Nt-C! 02Af-Ca(OH)
Table 5 shows the particle size of the calcium carbonate crystals obtained at 2-minute carbon dioxide concentration of 10% by volume, and Table 6 shows the paper quality test results.

Table 5 Table 6 Example 4 Using the same columnar calcium carbonate seed crystals as in Example 2, a carbonation reaction was carried out under the conditions shown below.

Mixed concentrated columnar calcium carbonate and slaked lime 250t/l Reaction initiation temperature 80℃Ca(OH)2
/CaCO3 molar ratio 1 to 5 Injected carbon dioxide gas amount 1ONt-CO2/15-C! a(OH)2・
The particle size of the calcium carbonate crystals obtained with a carbon dioxide concentration of 100% by volume is shown in Table 7, and the paper quality test results are shown in Table 8.

As shown in Table 7, the slurry viscosity was high and sufficient stirring was not performed, resulting in a relatively low crystal growth rate.

Table 8 Comparative Example A carbonation reaction was carried out under the same conditions as in Example 1 without using calcium carbonate seed crystals. The obtained calcium carbonate crystals were spindle-shaped calcium carbonate having a major axis of 2 to 3 μm% and a void diameter of 0.5 μm. The paper quality test results of coated paper using this calcium carbonate crystal were compared with commercially available nokaolin clay (manufactured by Engel Nord, USA, UW90) and calcium carbonate (
The results are shown in Table 9 along with the paper quality test results for Okutama Kogyo ■, 0.2-0.4 μm square). Further, a microscopic photograph of this crystal is shown in FIG.

Table 9

[Brief explanation of the drawing]

Figure 1 shows calcium carbonate as a seed crystal used in Example, Figure 2, Figure 3, Figure 42, Figure 5 and Figure 6 respectively show experimental cliff 1-1.1-2 in Example 1. .1-3.
5 and 6 are micrographs (x 100 times) of calcium carbonate crystals obtained in 1-4 and Comparative Example.

Claims (1)

[Scope of Claims] l In producing calcium carbonate by the reaction of calcium hydroxide and carbon dioxide, arabinite columnar calcium carbonate seed crystals and calcium hydroxide are used in a manner in which the molar ratio of calcium hydroxide to calcium carbonate is Contained in a ratio of 1 to 5, and the concentration after mixing the two is 50 to 25.
A carbon dioxide-containing gas is added to an aqueous slurry in the range of 0 y/l, and the carbon dioxide in the gas is
A method for growing crystals of aragonite-based columnar calcium carbonate, characterized by carrying out a blowing reaction at a rate of 0.5 to 1 ON4 per kg/min. 2. The method according to claim 1, wherein the aragonite-based columnar calcium carbonate seed crystal is a columnar crystal with a major axis of 2 μm or less and a minor axis of 0.2 μm or less. 3. The method of claim 1, wherein the carbon dioxide concentration in the carbon dioxide-containing gas is at least 10% by volume. 4. The method according to claim 1, wherein the temperature of the aqueous slurry at the start of blowing the carbon dioxide-containing gas is in the range of 5 to 80°C.