JPH03183618A - Production of spindle-shaped calcium carbonate - Google Patents

Abstract

PURPOSE:To efficiently obtain spindle-shaped calcium carbonate particles having good dispensability and uniform particle size by adding a water suspension of partly carbonated calcium hydroxide into a lime slurry to a specified carbide ratio and allowing the slurry to react with carbon dioxide gas. CONSTITUTION:In the production process of spindle-shaped calcium carbonate by the reaction of water suspension of calcium hydroxide and a gas containing carbon dioxide gas, water suspension of colloid particles of calcium hydroxide which is partly carbonated is added into the reaction system to obtain 50% carbonate ratio. In this process, with low concn. of the lime slurry as low as <5wt.%, productivity is poor, while it is not preferably to add the slurry over 10wt.% concn. since the product shows high cohesive property and bad dispersibility. If addition of the preliminary carbonated calcium hydroxide is continued to exceed 50% carbonation ratio, the product will become two components, one is grown colloid particles and the other is large-size spindle- shaped particles.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing spindle-shaped calcium carbonate suitable as a filler or pigment for paper manufacturing, and more specifically to a method for producing spindle-shaped calcium carbonate suitable for use as a filler or pigment for paper manufacturing. In the process of producing spindle-shaped calcium carbonate by reaction with The present invention relates to a method for producing spindle-shaped calcium carbonate having a long diameter of 1 to 5 μm and having a uniform and good dispersibility.

Conventional technology As a method for producing precipitated calcium carbonate, the carbon dioxide method, in which carbon dioxide gas is blown into milk of lime and reacted, is currently widely used industrially. Particles of various sizes, from heavy particles to coarse particles weighing several tens of micrometers in weight, are produced, and particles of various shapes such as spindle, square, columnar, and needle-like are produced. ing.

As described above, there are various particle forms, and it is quite difficult to control the particle size for each. However, for spindle-shaped calcium carbonate, a calcium hydroxide suspension is preliminarily dispersed in a wet continuous fine dispersion machine for 2 to 10 minutes. A method of carrying out a carbonation reaction by wet grinding, activating calcium hydroxide into fine particles, and adjusting the temperature and concentration (Japanese Patent Publication No. 54-28399);
Ultrafine calcium carbonate with little secondary agglomeration is dispersed into almost single particles with an average primary particle size of 0.1 to 0, oi μm.
- Supply subcarbonated lime milk, and while stirring and mixing at a pH of 10.0 or higher in the reaction system, conduct a carbonation reaction by introducing carbon dioxide-containing gas, and convert the reactant into ultrafine calcium carbonate crystal nuclei. The crystal is grown as 0.11- depending on the supply amount.
A method for obtaining calcium carbonate having a desired particle size of 1p has been proposed (Japanese Patent Publication No. 58-43331).

However, in the former method, an aqueous suspension of calcium hydroxide with a concentration of 10-15% is processed with a sand grinder, so the operation is complicated, and there is a risk that the whiteness of the reaction product will decrease due to contamination with glass beads. In addition, the latter has the disadvantage that it requires a large number of steps and is complicated to operate, and that it is time-consuming and inefficient, as it requires stirring for more than 8 hours to achieve the desired viscosity in the dispersion treatment process of carbonated slurry. has.

In addition, ultrafine calcium carbonate I of less than 0.1 μm and uncarbonated lime milk were added, and carbon dioxide gas was blown into the mixed suspension.
Crystals grow using the original ultra-fine calcium carbonate as a core,
Although there is a known method for obtaining calcium carbonate having a particle size of 0.11-1p, this method inevitably generates a large amount of secondary nuclei and the particles become non-uniform.

Problems to be Solved by the Invention The present invention overcomes the drawbacks of the conventional method for producing spindle-shaped calcium carbonate, and makes it possible to easily and efficiently produce spindle-shaped calcium carbonate with uniform particles with good dispersibility on an industrial basis. The purpose of this study was to provide a manufacturing method.

Means for Solving the Problems The present inventors have conducted various studies to develop an industrial method for producing spindle-shaped calcium carbonate having the above-mentioned preferable characteristics. As a method to freely control the particle size, it is possible to more easily react the calcium hydroxide aqueous suspension with the carbon dioxide-containing gas without going through the process of processing the raw materials or the process of stirring and mixing to disperse. It has been discovered that the purpose can be achieved by adding a partially carbonated colloidal particulate calcium hydroxide aqueous suspension until a predetermined carbonation rate is reached,
Based on this knowledge, we have completed the present invention.

That is, in producing spindle-shaped calcium carbonate by reacting a calcium hydroxide aqueous suspension (hereinafter referred to as lime slurry) with a carbon dioxide gas-containing gas, the present invention uses colloidal particulate hydroxide that is partially carbonated. Calcium aqueous suspension (hereinafter referred to as subcarbonated lime slurry) was prepared with a carbonation rate of 5.
The present invention provides a method for producing spindle-shaped calcium carbonate that is uniform and has good dispersibility and has an average major axis of 1 to 5 μm, characterized in that the amount of calcium carbonate is added until the amount reaches 0%.

The present invention will be explained in detail below.

In the method of the present invention, the -subcarbonated lime slurry is preferably produced before the carbonation rate reaches 50% during the reaction between the lime slurry and the carbon dioxide-containing gas, that is, at the reaction stage when the carbonation rate is 50% or less. is added at the beginning of the reaction, more preferably just before introducing the carbon dioxide-containing gas into the reaction system.

To produce the primary carbonated lime slurry used in this case, an aqueous suspension of calcium hydroxide, preferably having a concentration of 2 to 5% by weight, is adjusted to a temperature in the range of 5 to 20°C, and slaked lime, i.e., hydroxide Carbonation rate is 20 to 50%, preferably 30 to 40% by blowing carbon dioxide containing gas at a rate of 3 to 12 NM per kg of calcium, preferably 4 to 4 g NQ/min.
This is done by stopping gas blowing when it reaches %.

The reaction in the method of the present invention (hereinafter referred to as the reaction of the present invention) is preferably performed at a concentration of 5 to IO% by weight and a temperature of 40 to 60°C.
Add subcarbonated lime slurry in an amount not exceeding 5% in terms of slaked lime weight ratio to the lime slurry adjusted to the range of
3-12 per kg of slaked lime at reaction temperature 40-60°C
This is carried out by blowing a carbon dioxide-containing gas at a rate of NQ/min, preferably from 4 to 8 NI2/min, and by blowing a constant amount of gas until the carbonation rate reaches 110%.

If the temperature during the production of the primary carbonated lime slurry is less than 5°C, colloid particles will be produced but will tend to form aggregates,
In the reaction of the present invention, it tends to be difficult to control the particle size, and when the temperature exceeds 20°C, spindle-shaped particles tend to be mixed in, resulting in a two-component system. Furthermore, if the carbonation rate of the subcarbonated lime slurry is less than 20%, it will be difficult to control the particle size in the reaction of the present invention, and if it exceeds 50%, agglomerated secondary particles will easily grow, and the In order to obtain colloid particles with a low degree of fractionation, it is desirable that the carbonation rate be 20 to 50%, preferably 30 to 40%.

In the reaction of the present invention, if the reaction temperature exceeds 60°C, aragonite will be produced and the reactants will tend to become two components, and if the reaction temperature is below 40°C, the spindle shape will be divided into two components, one large and one small. It becomes difficult to obtain uniform products. Further, if the concentration of the lime slurry is less than 5% by weight, the concentration is low and productivity is poor, and if it exceeds 10% by weight, the agglomeration becomes strong and the dispersibility becomes poor, which is not desirable.

Furthermore, if the addition of the subcarbonated lime slurry is continued even after the carbonation rate exceeds 50%, it will result in a 2C system consisting of grown colloid particles and large spindle-shaped particles, which is undesirable. If the addition rate exceeds 5% by weight, the reactant will not form a spindle shape, but will simply form an aggregate of colloid particles that have grown as crystals, which is not desirable.

Effects of the Invention According to the method of the present invention, spindle-shaped calcium carbonate having an average major axis of 1 to 5 pm and having good dispersibility can be obtained.

This spindle-shaped calcium carbonate has high dispersibility, so it is made into a highly concentrated slurry and used for filling or coating paper, giving it high opacity and hiding properties, and it can also be used for surface treatment using an appropriate surface modifier. By applying this, it has various advantages such as providing excellent mechanical properties when used as a filler for rubber or resin.

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

Example 1 30g10. Calcium hydroxide slurry 30Q with a concentration of
was charged into a reactor, and the carbon dioxide concentration was 30 at a temperature of 15°C.
% carbon dioxide-containing gas was blown into the reactor to stop the reaction at a carbonation rate of 35% to obtain a sub-carbonated lime slurry.

85 mQ of this slurry was added to a reactor containing hydroxide slurry 304 with a concentration of 85 g/Q and adjusted to a temperature of 50°C, and the reaction temperature was 50°C! A carbon dioxide-containing gas with a carbon dioxide concentration of 30% was blown into the reactor to cause a reaction until the carbonation rate reached 110%. SE the reaction product
When the particle size was measured using a digimatic caliper from the M photograph, it was found to be uniform spindle-shaped particles with an average major axis of 4.5 μm and an average minor axis of 1.4 μm.

Example 2 A reaction was carried out in the same manner as in Example 1 except that the amount of primary carbonated lime slurry added was 0.8512. The obtained reaction product was uniform spindle-shaped particles with an average major axis of 2.5 μm and an average minor axis of 0.6 μm.

Example 3 A reaction was carried out in the same manner as in Example 1 except that the amount of primary carbonated lime slurry added was 2.6C. The obtained reaction product was a uniform spindle-shaped particle having an average major axis of 1.5 μm and an average minor axis of 0.4 μm.

Example 4 A reaction was carried out in the same manner as in Example 1 except that the amount of secondary carbonated lime slurry added was 4.3Q. The obtained reaction product was uniform spindle-shaped particles with an average major axis of 1.2 μm and an average minor axis of 0.3 μm.

Comparative Example A reaction was carried out in the same manner as in Example 1, except that the amount of primary carbonated lime slurry added was 6.0Q. The obtained reaction product was an aggregate of spherical or angular particles with an average major diameter of 1.0 μm or less.

Table 1 shows the addition rate of subcarbonated lime slurry and the measured particle size for Examples 1 to 4.

Application Example 1 The calcium carbonate obtained in Examples 1 to 4 was dehydrated using a filter press, dried, pulverized, and classified.

To the obtained powder, a polyacrylic acid Na-based dispersant (Aron manufactured by Toagosho Co., Ltd.) was added in an amount of 1.0% by weight based on calcium carbonate to obtain a slurry with a solid content concentration of 60%. The viscosity of this slurry is shown in Table 1.

Next, 110 parts by weight of each calcium carbonate, 10 parts by weight of a binder made by mixing starch (eclipse #4610) and SBR (JSR0692) at a weight ratio of 1:4, and 1.5 parts by weight of a lubricant (calcium stearate) were added. parts by weight, and water to give a solid content concentration of 45! A paper property test was conducted using the slurry expressed as % by weight as a coating liquid. The results are shown in Table 2.

In addition, each physical property in Table 1 and Table 2 was measured as follows.

(1) Average major axis and minor axis: The major axis and minor axis were measured using a digimatic caliper from the SEM photograph, and the average value was determined.

(2) Viscosity: Using a B-type viscometer, the rotor rotation speed is 60゛.
The measurement was performed under conditions of rpm and slurry temperature of 25°C.

(3) Whiteness: Measured according to JIS P 8123.

(4) White paper gloss: Measured according to JIS P 8142.

(5) Printing gloss: TKUG-mouth 0.4rn as ink
Measured according to JIS P 8142 using Q.

(6) K&N ink acceptability: The dichotomous value of K&N was measured using a Hunter whiteness meter.

(7)! nk Set: Measurement of ink transfer after printing using a Hunter whiteness meter.

Application Example 2 The calcium carbonate obtained in Examples 1 to 4 was dehydrated using a filter press, dried, pulverized, and classified.

Next, this calcium carbonate was blended into the pulp (LBKP110%) at a ratio of 20% by weight, and a neutral sizing agent was added at an amount of 0.2% by weight based on the calcium carbonate. f, s) 310 cc, paper with a metric basis weight of 40 g/+1" was hand-made to obtain paper filled with calcium carbonate.

The paper thus obtained was subjected to a paper quality test.

The results are shown in Table 3.

In addition, each physical property in Table 3 was measured as follows.

(1) Yield: Calculated according to JIS P 8129.

(2) Whiteness: Measured according to JIS P 8123.

(3) Opacity: Measured according to JIS P 8136.

(4) Tensile strength 2 Measured according to JIS P 8113.

Claims (1)

[Claims] 1. In producing spindle-shaped calcium carbonate by reacting an aqueous calcium hydroxide suspension with a carbon dioxide-containing gas,
Uniform and spindle-shaped with an average major axis of 1 to 5 μm with good dispersibility, characterized by adding a partially carbonated colloidal particulate calcium hydroxide aqueous suspension until the carbonation rate reaches 50%. Method for producing calcium carbonate. 2. The method for producing spindle-shaped calcium carbonate according to claim 1, wherein the colloidal particulate calcium hydroxide aqueous suspension according to claim 1 has a carbonation rate of 10 to 50%. 3. Claim 1 or 2, wherein the amount of the colloidal calcium hydroxide aqueous suspension according to claim 1 added does not exceed 5% by weight in terms of calcium hydroxide based on the calcium hydroxide aqueous suspension. A method for producing spindle-shaped calcium carbonate. 4.Claim 1, 2 or 3, wherein the addition of the colloidal particulate calcium hydroxide aqueous suspension according to claim 1 is completed at the beginning of the reaction.
The method for producing spindle-shaped calcium carbonate as described.