JPH03122015A - Chain precipitated calcium carbonate and production thereof - Google Patents

Abstract

PURPOSE:To obtain a precipitated calcium carbonate effective as filler, having long chain, simply and inexpensively in reacting milk of lime with an exhaust gas of a lime kiln containing carbon dioxide gas by specifying an amount of carbon dioxide gas fed. CONSTITUTION:In production of a precipitated calcium carbonate by reacting milk of lime with an exhaust gas containing carbon dioxide gas of a lime kiln, the following operations are carried out. Namely, the amount of carbon dioxide gas fed based on an amount of quick lime in milk of lime is an amount to make >= 7-8 ms/cm electrical conductance at primary dropping point of electrical conductance of milk of lime and the reaction is continued. When electrical conductance of milk of lime drops to 3-6 ms/cm, the reaction is different from acidic clay or tack used as a sizing agent for paper, is neutral, shows higher strength than clay or talc in use as a sizing agent or filler and is usable as n industrial material instead of clay and talc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to chain light calcium carbonate used as a neutral filler in paper, paint, rubber, etc., and a method for producing the same.

[Conventional technology]

It is well known that the conventional method for producing chain light calcium carbonate is to use a chelating agent (an active reaction agent used for analysis, etc.) in milk of lime.
. Japanese Patent Publication No. 56-26613 is one example.9 [Problem to be solved by the invention] However, the chain-like light calcium carbonate produced using the above-mentioned chelating agent has a chain length of 1 μm or less. However, when it is filled into paper or the like, the chains are not sufficiently intertwined, resulting in insufficient tensile and tearing strength.Additionally, chelating agents are expensive and are not suitable for practical use.

[Means for solving problems]

Therefore, the present invention provides a method for producing chain light calcium carbonate that is simple, inexpensive, has a long chain, and is effective as a filler by reacting inexpensive milk of lime with exhaust gas from a lime kiln. In producing light calcium carbonate by reacting lime milk with exhaust gas containing carbon dioxide from a lime kiln, the initial boiling water of lime milk is heated to 15 to 20 ml.
℃, and the amount of carbon dioxide gas introduced in the exhaust gas relative to the amount of quicklime in the milk of lime is adjusted so that the conductivity at the primary drop point of the electrical conductivity of the milk of lime is 7 to sllll5/C11 or more, and the reaction is carried out. The conductivity of lime milk is 3 to 6 m after continuous use.
The reaction is stopped when the temperature reaches s/cm.

In this invention, when milk of lime reacts with carbon dioxide gas in exhaust gas, the electrical conductivity of milk of lime decreases significantly due to the amount of calcium carbonate produced in milk of lime, and then this reaction is carried out. Experiments have shown that if the reaction continues, the electrical conductivity of the milk of lime decreases significantly, and that the crystal structure of the calcium carbonate produced is low (around 10 degrees Celsius). ), the crystals of calcium carbonate formed are plate-shaped crystals, and I learned that when the temperature is raised, they become chain-shaped crystals. In addition, when the reaction is started at a low temperature, the plate-shaped crystals that initially appear will progress and grow as plate-shaped crystals as the reaction progresses, and then when milk of lime is heated, other crystals will form, that is, chain-like crystals. I also learned that crystals appear.

Figure 1 shows that the electrical conductivity changes as the reaction between the milk of lime and the exhaust gas progresses; the electrical conductivity of the milk of lime at the initial stage is 9 ms/cm, and the -th point of descent is 7. , 2ms
/cm, and after rising to -7.8 mSlCm, there is a sharp quadratic fall. This indicates that as the reaction progressed, the chain-like crystals of calcium carbonate initially formed in the milk of lime grew, and the chain-like crystals of calcium carbonate increased. In this figure, the reaction was stopped when the conductivity reached 4 ff1s/CI. In addition, the initial temperature of the milk of lime in this figure is 17°C.
Met.

Based on the above findings, milk of lime containing approximately 5% CaO is kept at a temperature of 17°C, and approximately 1
By introducing CO2/175 g/min into the reaction tank and forcibly stirring the milk of lime, CaO and CO were mixed so that the first-order drop in conductivity of the reaction solution did not fall below 7 to 8 ms/cm. , the reaction rate was adjusted. Thereafter, the reaction was continued and stopped when the conductivity showed 3 to 611 S/Cl.

The crystal structure of the calcium carbonate obtained as a result was a chain crystal as shown in FIG.

〔Effect of the invention〕

As explained above, in producing calcilum carbonate by reacting milk of lime with exhaust gas from a lime kiln, the present invention is capable of determining the temperature at the initial stage of the reaction of milk of lime, the primary drop point of electrical conductivity during the reaction, and the like. Measure and control the secondary descent point, and C
Calcium carbonate having a desired chain crystal structure can be obtained by simply adjusting the reaction ratio of aO and CQ, and the calcium carbonate in the chain crystals produced can be Unlike the acidic clay and talc used as sizing agents, it is neutral, and is much stronger than these when used as a sizing agent and filler, making it an industrial alternative to clay and talc. It can be used as a material.

[Brief explanation of drawings]

Figure 1 is a graph of changes in the electrical conductivity of milk of lime during the reaction between milk of lime and carbon dioxide according to the present invention, and Figure 2 shows the crystal structure of chain light calcium carbonate produced by the method of the present invention. This is an electron micrograph. Figure 2

Claims (2)

[Claims] (1) When producing light calcium carbonate by reacting lime milk with exhaust gas containing carbon dioxide from a lime kiln, the initial temperature of lime milk is set to 15 to 20°C, and the amount of quicklime added is relative to the amount of quicklime in lime milk. The amount of carbon dioxide in the exhaust gas is adjusted so that the electrical conductivity of the milk of lime at the primary drop point is 7 to 8 ms/cm or more, and the reaction is continued so that the electrical conductivity of the milk of lime is 3 to 6 ms/cm. A method for producing chain light calcium carbonate, characterized in that the reaction is stopped when the temperature decreases to . (2) Its crystal structure is columnar, and its crystal length is 1 to 2
The chain light calcium carbonate produced by the method according to claim 1, which has an aspect ratio of 10 to 15 in μm.