JPH03228819A - Production of wet powdery calcium carbonate - Google Patents

Abstract

PURPOSE:To improve centrifugal dehydration property of wet powder of calcium carbonate without losing its quality when used as a filler of paper by introducing gaseous CO2 under specified conditions into a lime suspension to produce light CaCo3 slurry and subjecting this slurry to centrifugal dehydration. CONSTITUTION:Gaseous CO2 is introduced into a lime suspension having >=5wt.% concn. at >=30 deg.C under conditions of >=25vol.% CO2 gas concn., 20-100 Nl/min.kg Ca(OH)2 gas flow and >=1.0kg/cm<2> gas gauge pressure at the exit of the reaction tower till pH of the suspension becomes <=8 so as to obtain a spindle-like light CaCo3 slurry. Then a lime suspension by 0.2-2 molar ratio is added to this slurry, into which gaseous CO2 having >=25vol.% CO2 gas concn. is introduced with <=40Nl/min.kg Ca(OH)2 flow rate to obtain a light CaCO3 slurry comprising uniform flocculation of 2-5mu particle size. Then, this process is repeated for several times as necessary so as to obtain flocculated light CaCO3 slurry of 3-10mu particle size and the obtd. slurry is subjected to centrifugal dehydration at >=3000m/min peripheral velocity to obtain wet powdery CaCO3 containing <=35% water.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a light calcium carbonate for use in neutral paper making, which is made by using a combination of pulp fiber, AKD or ASA sizing agent, cationic starch, polyacrylamide, etc. This relates to a manufacturing method.

[Conventional technical background, problems]

In recent years, paper making methods have been shifting from acid paper making to neutral paper making due to problems such as paper storage stability and closed drainage.

In neutral paper making, it became possible to use calcium carbonate, which is abundantly produced in Japan, as a filler, and at first, cheap heavy calcium carbonate was focused on and used. However, this heavy calcium carbonate suffers from high wire abrasion in papermaking wires and does not fully satisfy the required qualities of paper (whiteness, opacity, smoothness, ink receptivity, etc.). However, some studies have begun to consider the use of light calcium carbonate, which is superior in these properties.

Light calcium carbonate has been manufactured in Japan for a long time,
Spindle-shaped paper is generally used as a filler in neutral papermaking, and provides excellent paper quality due to its properties such as uniform particle size distribution, high whiteness, bulk, and high oil absorption.

However, since this light calcium carbonate is a synthetic product, it is more expensive than the talc that has traditionally been used in acidic papermaking or the above-mentioned heavy calcium carbonate, and its introduction into neutral papermaking is currently at a standstill. Met.

In view of the current situation, the present inventors have conducted intensive studies to produce a low-cost neutral light calcium carbonate for papermaking, and have completed the present invention.

[Problem that the invention seeks to solve]

Conventionally, light calcium carbonate is supplied to paper mills in one of three forms:

a) Slurry product with a concentration of 15 to 30%...The compound slurry is transported as it is or by a concentration lorry.

b) Slurry product with a high concentration of 50 to 65%: After mechanically dehydrating the compound slurry, a dispersant is used to make a high concentration slurry, and the product is transported by tank truck or liquid container bag.

1) Dry powder: Compound slurry is mechanically dehydrated, dried, and then crushed, and then supplied in paper bags or container bags.

However, the above-described product form and manufacturing process increase costs and cause various adverse effects, making it impossible to maintain prices comparable to conventional talc.

That is, in case (a), since it is a low-concentration slurry, the transportation cost increases significantly, and the transportation range is limited to an extremely short distance. For this reason, production facilities for light calcium carbonate have to be built near paper manufacturing companies, making it impossible to supply to many paper manufacturing companies.

Regarding b), the use of expensive dispersants increases costs, and the use of strong anionic dispersants increases the chemical consumption rate in the papermaking process, which also has a negative impact on paper quality. . Furthermore, transporting highly concentrated slurry requires the use of tank trucks or liquid containers, which increases transport costs.

In the case of (1), the cost will increase significantly due to the equipment, heavy oil, labor costs, etc. required for the drying process.

In order to solve the cost increase caused by the above-mentioned causes and provide inexpensive light calcium carbonate, the inventors of the present invention have dehydrated a compound slurry into a dehydrated cake after centrifugal dehydration without drying it or making it into a highly concentrated slurry. To make the product as it is,
investigated. However, since the light calcium carbonate slurry produced by the conventional compounding method has a small particle size, it does not have good dehydration properties using a centrifuge, and has a high water content and the cake is lumpy, so it is difficult to fill it in a paper bag or hang a container and leave it. This caused problems such as solidification, which caused problems in the user's extraction or re-slurry in water.

[Means for solving problems]

After that, through repeated studies, we found that by manufacturing light calcium carbonate under specific compounding conditions, we can obtain light calcium carbonate in the form of a wet powder with low water content and good centrifugal dehydration properties without impairing the quality of paper filling. I discovered that.

That is, in the compounding process, [first step] when passing carbon dioxide gas through milk of lime, the concentration of carbon dioxide gas is 25% by volume or more, the gas flow rate is 20 to 100 N1/min・kg calcium hydroxide, and the concentration of calcium hydroxide at the outlet of the reaction tower is Gas gauge pressure 1.0kg/
Gas is passed in the range of cm2 or more until the pH becomes 8 or less. The temperature of the milk of lime is not particularly limited as long as it is 30°C or higher, and the milk of lime concentration may be 5% by weight or higher, but in order to improve the dehydration efficiency, it should be used as much as possible. Preferably, the concentration is high. Carbon dioxide flow rate is 2
ONl/min·kg calcium hydroxide or less, or when the carbon dioxide concentration is less than 25% by volume, or when the gas gauge pressure at the outlet of the reaction tower is less than 1.0 kg/cm2, it is possible to obtain spindle-shaped calcium carbonate with good uniform dispersibility. First, it becomes non-uniform and has many agglomerates, making it difficult to obtain a uniform secondary agglomerate in the second step. Also, the carbon dioxide flow rate is 1
If the amount exceeds 00 Nl/min.kg calcium hydroxide, the gas absorption efficiency becomes extremely poor, resulting in poor economic efficiency.

It has been found that by the first step, it is possible to obtain spindle-shaped light calcium carbonate having a primary particle diameter of about 1 μm and having almost no agglomeration.

[Second step] Add milk of lime to the compound slurry obtained in the first step at a molar ratio of 0.
．． It is added in a range of 2 to 2 mol, and then gas is passed through until the carbon dioxide gas flow rate is less than 4ONl1min.kg slaked lime and less than pl+8. When the molar ratio of milk of lime added is 0.2 mo1 or less, there is too little milk of lime to form a uniform secondary aggregate, and a portion of calcium carbonate remains.

When the molar ratio of milk of lime added is 2 mo1 or more, the added amount is too large, so that a part of the added milk of lime does not work as a flocculating effect, and free and dispersed calcium carbonate is generated. Furthermore, when the carbon dioxide gas flow rate exceeds 4ONl1min.kg slaked lime, new nuclei due to the added milk of lime begin to form, resulting in extremely non-uniform agglomerated particle diameters. The milk of lime to be used may have a concentration of 5% by weight or more, but it is preferable to have as high a concentration as possible. By the second step, light calcium carbonate having a uniform agglomerated particle size of 2 μm to 5 μm can be obtained. The size of the aggregated particle size depends on the molar ratio of milk of lime added, and the larger the molar ratio of added milk, the larger the particle size can be obtained.

Even if the slurry obtained in the second step is subjected to centrifugal dehydration as it is, it can be sufficiently converted into a wet powder product with a water content of 35% or less, which is the object of the present invention. However, if you want to further increase the particle size to reduce dehydration properties and water content, milk of lime is added again to the calcium carbonate slurry obtained in the second step, and carbon dioxide gas is passed in the same manner, resulting in aggregated particles with a diameter of 3 μm or more. l
Light calcium carbonate having a uniform particle size of Oμ can be produced. The second step may be performed two or more times in order to obtain aggregated light calcium carbonate having a desired aggregated particle size.

[Third Step] The spindle-shaped agglomerated light calcium carbonate slurry obtained in the first and second steps above was heated at a circumferential speed of 100 m/min.
By performing centrifugal dehydration at a speed of 1 minute or more, it is possible to obtain wet powder calcium carbonate with extremely low water content (35% by weight or less on a wet basis).

〔Effect of the invention〕

(Cost effectiveness) The light calcium carbonate obtained by the present invention can be supplied to paper manufacturing users by being packed in container bags after centrifugal dehydration without drying or turning into a slurry, and compared to slurry form, dry powder form, etc. This enables significant cost reductions.

(Other effects) The centrifuge-dehydrated light calcium carbonate produced by the method of the present invention has an extremely low water content and is powder-like in appearance, and does not solidify at all even when stored in a container bag for a long period of time. It maintains its fluidity and can be easily discharged from the container bag.

Also, when re-slurrying on the paper manufacturing user side,
It has better dispersion in water than dry powder, and also has less scattering when added, making it extremely easy to handle. For high quality paper when packed into papermaking, it has a uniform three-dimensional agglomerated structure, so it has excellent whiteness and opacity, and is also superior in terms of paper strength compared to conventional light calcium carbonate. It is something.

The invention is further illustrated by the following examples.

Example 1 [First step] A compound group was filled with 10 m3 of milk of lime with a concentration of 10% by weight, and a gas with a carbon dioxide concentration of 30 to 35% discharged from a lime furnace was added to the mixture at a rate of 4ONm3 per minute at a gas gauge at the outlet of the reaction tower. Pressure 1.
The carbonation reaction was carried out at 3 kg/cm2. 32 minutes after the start of the compounding, the slurry pl+ reached 7.8 and the compounding was stopped. The particle size distribution of the obtained calcium carbonate was measured by a sedimentation light transmission method, and the average particle size was 1.2 μm. When observed using an electron microscope, it was found to be a uniform spindle-shaped light calcium carbonate without any agglomeration.

This slurry was subjected to centrifugal dehydration at a circumferential speed of 3500 m for 7 minutes for 10 minutes, and the cake formed on the furnace cloth was scraped and discharged using an automatic scraper. The resulting cake has a water content of 3
The content was 8% by weight (wet haze), and the appearance was not clay-like but rather lump-like.

This material was filled into a container bag, a constant load was applied from the top, and the container was left for a long period of time, but this caused the container to become stuck and could no longer be discharged from the container bag.

[Second step] To 7 m3 of the calcium carbonate slurry obtained in the first step, 3.3 ml of milk of lime with a concentration of 10% by weight is added, and gas with a carbon dioxide concentration of 30 to 35% is passed through at a rate of 9 NII + 3 per minute for a carbonation reaction. After 42 minutes, the pl became +7.0 and the compounding was stopped. The average particle diameter of the obtained Calcilla carbonate J1 was 2°5μ.
Met. When observed using an electron microscope, the particles were found to be uniform three-dimensional aggregates.

The obtained slurry was subjected to centrifugal dehydration at a circumferential speed of 3500 m for 7 minutes for 10 minutes, and the cake was scraped off. The resulting cake had a moisture content of 32% by weight (wenotose),
It was powdery and fluid. This material was filled into a container hang and left for a long period of time under a constant load, but it did not solidify and maintained its original fluidity, and could be easily discharged from the container bag.

Example 2 To slurry 71113 obtained in the same manner as in Example 1, three or three times milk of lime with a concentration of 10% by weight was added, and gas with a carbon dioxide concentration of 30 to 35% was passed through it at a rate of 9 Nm'/min. Carbonation was performed and the reaction was stopped at pH 7.2 after 39 minutes.

The average particle size of the obtained calcium carbonate was 4. 1JM, and when observed using an electron microscope, it was found to be uniform three-dimensional agglomerated particles, and no coarse particles or primary dispersed particles were observed.

The obtained slurry was subjected to centrifugal dehydration at a circumferential speed of 3300 m/min for 10 minutes, and after dehydration, it was scraped off and discharged. The resulting cake had a moisture content of 27% by weight (wet basis), and was powdery and fluid. The long-term storage stability when filled into a container bag was also good, and no solidification was observed.

(Comparative Example 1) Under the same conditions as Example 1, only the gas flow rate was 15 NI1 per minute.
Carbonation was carried out at 13 and the compound was stopped after 85 minutes at p++7.9. The average particle diameter of the obtained calcium carbonate was 1.
The particle size was 9μ, and when observed using an electron microscope, many aggregated particles were observed in addition to the primary dispersed particles.

(Comparative Example 2) Additive compounding was performed to the calcium carbonate slurry obtained in Comparative Example 1 in the same manner as in Example 2. The average particle size of the obtained calcium carbonate was 3.0 μm, and observation using an electron microscope revealed extremely non-uniform secondary agglomerated particles with a particle size of 2 μm to 6 μm.

(Comparative Example 3) In the same operation as in Example 2, only the gas flow rate was changed to 1/min.
Carbonation was carried out at 5Nm'', and after 23 minutes pif −'+
The compounding was stopped at step 1. The obtained calcium carbonate had an average particle diameter of 2.3 μm, and observation using an electron microscope showed that many primary dispersed particles were observed.

hand Continued N11 Positive book 1990 March 15th

Claims (1)

[Claims] 1. Carbon dioxide concentration 25% by volume or more, carbon dioxide flow rate 20~
A first step of producing a spindle-shaped light calcium carbonate slurry by introducing carbon dioxide gas into milk of lime at a gauge pressure of 100 Nl/min.kg calcium hydroxide and a gas at the outlet of the reaction tower of 1.0 kg/cm^2 or more; Adding milk of lime in an amount of 0.2 to 2 in molar ratio to the calcium carbonate slurry obtained in step 1,
Carbon dioxide with a carbon dioxide concentration of 25% by volume or more at a gas flow rate of 40%
A second step of producing a slurry of flocculated light calcium carbonate with a uniform particle size by introducing at a rate of Nl/min·kg calcium hydroxide or less, and optionally carrying out the second step a desired number of times, the flocculated light calcium carbonate obtained A method for producing wet powder calcium carbonate, comprising a third step of centrifugally dehydrating the slurry to remove water in the cake. 2. The method for producing wet powder calcium carbonate according to claim 1, wherein the spindle-shaped calcium carbonate obtained in the first step has an average particle diameter of 2 μ or less and has a spindle shape with good dispersibility. 3. The method for producing wet powdered calcium carbonate according to claim 1, wherein the aggregated particle size of the aggregated light calcium carbonate obtained in the second step is in the range of 2 to 5μ. 4. The method for producing wet powdered calcium carbonate according to claim 1, wherein in the third step, centrifugal dehydration is performed at a circumferential speed of 3000 m/min or more to reduce the moisture content in the cake to 35% or less. .