GB2309692A

GB2309692A - Preparing colloidal calcium carbonate particles

Info

Publication number: GB2309692A
Application number: GB9702081A
Authority: GB
Inventors: Kyu Jae You
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-02
Filing date: 1997-01-31
Publication date: 1997-08-06
Anticipated expiration: 2017-01-31
Also published as: GB2309692A8; CA2196124C; GB2309692B; KR970061783A; AU1227797A; GB9702081D0; KR0184847B1; CN1163860A; CA2196124A1; AU691437B2; CN1058684C

Abstract

A process for the preparation of colloidal calcium carbonate of particle size 0.04 to 0.08 micrometres comprises (a) adding a sugar or a chelating agent (e.g. EDTA) to an aqueous lime suspension; (b) introducing therein a gas containing carbon dioxide; (c) adding a hydroxide (e.g NaOH or KOH); and (d) heating and agitating the suspension to obtain the calcium carbonate particles in cubic crystal form.

Description

PROCESS FOR PREPARING COLLOIDAL CALCTUM CARBONATE BY PARTICLE SIZE This invention relates to a process for preparing cubic crystals of colloidal calcium carbonate, and more particularly for preparing colloidal calcium carbonates of specific particle size in the range of more than 0.04 tml to less than 0.08 ,an.

Throughout the specification and appended claims, the term "size" of calcium carbonate crystals refers to the length of one edge of the cubic crystal.

Calcium carbonate powders less than 0.1 sm are demanded as a functional filler in various fields of industry such as rubber, plastics, paint, ink and sealant.

Colloidal calcium carbonate powders of 0.04 Mn and 0.08 tan have been heretofore mainly used, however, there is a need for more subdivided particle sizes in the range of more than 0.04 tan to less than 0.08 Sm, i.e., 0.045 tan, 0.050 tan to 0.075 tan, depending on the needs of each industry.

The finer than 0.1 tan the size of colloidal calcium carbonate powders is, the more improved such properties as strength, fluidity and the like are, and vice versa the more strong an aggregation property is. Therefore, when calcium carbonate powders are admixed with matrix or vehicle, the minimum particle size of powders uniformly dispersed by shearing force becomes the most suitable particle size for a specific industry. On the basis of the above fact, there is a necessity for more subdivided particles in the range of more than 0.04 tan to less than 0.08 tan.

According to a conventional process, colloidal calcium carbonate is usually produced by introducing a carbon dioxide-containing gas having a concentration of 20 to 40 % by volume of carbon dioxide and a temperature of 10 to 20 C at a rate of 40 to 100 liters/min. into an aqueous suspension of calcium hydroxide having a concentration of 3 to 10 % by weight of calcium hydroxide and being kept at a temperature of 10 to 20 C, to yield a cubic calcium carbonate of 0.04 tan in particle size.

The cubic calcium carbonate of 0.04 tan in particle size as obtained above is heated up to a temperature of 40 to 80 C, and then ripened with no agitation for 4 to 5 days to yield a cubic calcium carbonate of 0.08 tan in particle size. At that time, the pH of the solution rises from 6.8 + 0.2 to about 11.5, however, if any agitation, even a little, is performed, the process of ripening can not progress.

At that time when the pH thereof becomes stable at about 11.5, after the separation of a supernatant therefrom and the concentration of a resultant suspension up to 10 to 20 % , the latter is neutralized by introducing a carbon dioxide-containing gas thereinto.

By adding an alkali metal solution consisting of a fatty acid or a resin acid, as a surface treatment, to the solution containing the colloidal calcium carbonate of 0.08 tan in particle size as obtained above, powders of colloidal calcium carbonate are produced after dehydrating through a filter press, drying and pulverizing.

However, it takes a long time to ripen the aqueous suspension, for example, five days for the colloidal calcium carbonate of 0.08 tan in particle size. During the period from the first to the fourth day, the particles are in an inconsistent mixture in the range of between 0.04 and 0.08 tan in particle size, thus the colloidal calcium carbonates can not be used for their intended use.

U. S. Patent. No. 4,124,688 (Shibazaki et al.) describes an invention whereby cubic calcium carbonate crystals of uniform size are prepared by contacting with CO2 a starting aqueous suspension containing Ca(OH)2 and cubic CaCO3 crystals less than 0.1 tan in size, and then adding Ca(OH)2 to the suspension resulting from the first step, and finally contacting the resultant mixture with CO2.

U. S. Patent No. 4,133,894 (Shibazaki et al.) describes an invention that precipitated calcium carbonate of uniform particle size is produced by contracting a suspension of calcium hydroxide with a carbon dioxide-containing gas in three steps. The particle size of precipitated calcium carbonate can be optionally selected by suitably adjusting reaction conditions.

US Patent No. 5,075,093 (Tanaka et al.) describes a two-step carbonation method of milk of lime in which partially carbonated milk of lime is admixed with an aqueous carbonating solution containing an alkali metal carbonate or ammonium carbonate and an alkali hydroxide or ammonium hydroxide to complete the carbonation of calcium hydroxide. Particles having a platelet-like configuration of a thickness in the range of oil 0.1 to 0.3 pm, and dimensions within the plane of the platelet from 0.5 to 211m are prepared.

US Patent No. 5,332,564 (Chapnerkar et al.) describes a process for producing rhombic or barrel shaped precipitated calcium carbonate. Quicklime is slaked in an aqueous solution containing about 0.1% to about 2% by weight of a sugar, based upon the weight of CaCO3 to be produced. Carbon dioxide is added to the slaked lime slurry at a preferred temperature of about 50 F-70 "F, until the pH drops from about 11-12 to about 7-8.

None of the above patents addresses the production of colloidal calcium carbonate having a specific particle size depending on its intended use.

An aim of the present invention is to alleviate the drawbacks aforementioned by providing a process for producing uniform particles of colloidal calcium carbonate within the size range of 0.4,um to less than 0.08,um, the particles having low aggregation value.

According to the present invention, there is provided a process for preparing colloidal calcium carbonate of cubic crystals of which the particle sizes are in the range of more than 0.04 to less than 0.081lem, which process comprises: (a) adding sugar or a chelate agent to an aqueous lime suspension prior to the introduction of a gas containing carbon dioxide thereinto; (b) adding a cation-hydroxide to the aqueous lime suspension after the introduction of the gas containing carbon dioxide thereinto, when ripening the aqueous lime suspension; (c) heating and agitating the aqueous lime suspension obtained in step (b) in order to obtain the colloidal calcium carbonate; wherein the introduction of a gas containing carbon dioxide is performed by introducing a gas containing 20 to 40% by volume of carbon dioxide at a rate of 40 to 200 litres per minute per kg of Ca(OH)2 into the aqueous lime suspension having 3 to 8% by weight of Ca(OH)2 and a temperature of 14"C to 18"C.

In a preferred embodiment the particle sizes yielded are 0.045, 0.050, 0.055, 0.060, 0.065, 0.070 and 0.075rim.

In a further preferred embodiment of the present invention, 0.2 to 3.0 part by weight (to be hereinafter referred to briefly as "part") of sugar or EDTA (ethylenediaminetetraacetic acid) per 100 parts of Ca(OH)2 included in the aqueous lime suspension, as a chelate agent, is added to the aqueous lime suspension prior to the introduction of the carbon dioxide-containing gas thereinto, at which time the concentration of calcium ion is increased, as a result of the above process, the colloidal calcium carbonate of 0.0411m is yielded. If the addition amount is below 0.2 part, there may be no effect of accelerating the ripening step and,if it is above 3.0 part, the ripened particles may not become uniform.

In yet a further embodiment of the present invention, 0.1 to 0.8 part of a hydroxide with univalent or bivalent cation per 100 parts of Ca(OH)2 is added to the aqueous suspension at the stage of ripening. Hydroxides with univalent cation are, for example, NaOH, KOH and so on, and those with bivalent cation are Ca(OH), Mg(OH)2, Zn(OH)2 and so on. If an additional amount of hydroxide is below 0.1 part, the addition may have no effect thereof and if it is above 0.8 part, the size distribution of the produced particles may not be uniform. Generally, the size of desired particle is in inverse proportion to a BET surface area, and the pH of the aqueous lime suspension is increased up to about 11.5. However, absolute values of them may change depending on the kind and amount of the hydroxide. Therefore, such elements as above are determined by the relation between the reaction time and the particle size in the real condition of production.

In still a further embodiment of the present invention, the aqueous suspension containing the colloidal calcium carbonate of 0.041lm in particle size is ripened under the conditions of temperature being heated up to 40"C to 95 "C and agitation at the rate of 100 to 5,000 as Reynolds number (Re) to pursue the consistent growth of particles. The Reynolds number can be obtained by the following formula (1). If the agitating rate is under 100 as Reynolds number, the ripening rate may be very low and if it is above 5,000, the produced particles may not be uniform.

Re= pnD2 (1) Wherein Re : Reynolds number p : density of solution n : revolution number of blade (r.p.s.) D: diameter of blade (cm) : viscosity of solution (poise) In yet a further embodiment of the present invention, the aqueous suspension containing the colloidal calcium carbonate in the range of from 0.04 llm to 0.08 pLm in particle size is concentrated to 14 l 1% by weight of colloidal calcium carbonate, and then to treat surfaces thereof with such a surface treatment as fatty acid, resin acid or the like.

By dehydrating, drying and pulverizing the resulting product, powders of colloidal calcium carbonate having uniform particle size and low aggregation property are obtained.

According to the processes mentioned above, one can obtain novel colloidal calcium carbonate by particle size depending on its intended use.

When summarizing the above content, according to the process of the present invention, after the addition of the material to increase the concentration of calcium ion to the aqueous lime suspension, the colloidal calcium carbonate of 0.04 tan in particle size is obtained by introducing the carbon dioxide-containing gas thereinto.Then, by the addition of the hydroxide with univalent or bivalent cation to the resulting suspension and the agitation thereof at the rate of 100 to 5,000 as Reynolds number while the temperature thereof being heated to 40 to 95 OC, thus the colloidal calcium carbonate of 0.04 tan in particle size is ripened and the pH of aqueous suspension rises, as a result, yielding colloidal calcium carbonates of which each length of one edge is increased by 0.005 tan, i.e., cubic crystals of 0.045, 0.050 to 0.075 tan, corresponding to the increased pH ofthe aqueous suspension.

Therein, the above mentioned "ripening" means the phenomenon that a hydrolysis reaction of the colloidal calcium carbonate of 0.04 tan in particle size occurs when its aqueous suspension becomes weakly basic with carbon dioxide gases released from the aqueous suspension neutralized shortly after the first reaction, and finer colloidal calcium carbonates are eluted into the aqueous suspension and then are recrystallized on the lattice defect of other relatively large particles, as a result of that, the surface activity thereof is reduced and stabilized, and thus the aggregation property thereof is reduced and simultaneously the particle thereof becomes larger.

The colloidal calcium carbonate having a specific particle size in the range of more than 0.04,can to less than 0.08 tan according to the process of the present invention is prepared by growing up the colloidal calcium carbonate particle of 0.04 tan in size.

The calcium carbonate powder as obtained above can be used as a good filler to improve the properties of product impregnated therewith and have a good dispersion property due to the stabilized surface activity, the reduced aggregation property and the uniform size which seems to be caused by the adding material and the agitating power.

The present invention will now be described in more detail by way of examples, comparative examples and reference examples. The examples are presented for the illustration purpose only and should not be interpreted in any restrictive way.

(Example 1) After adding 0.5 part of sugar per 100 parts of Ca(OH)2 to an aqueous lime suspension of a concentration of 5% by weight of calcium hydroxide and a temperature of 15 C, and then introducing a gas containing 30% by volume of carbon dioxide thereinto, when the pH of the resulting aqueous suspension became 6.8, an aqueous suspension containing the colloidal calcium carbonate of 0.04 tan in particle size was obtained. KOH having a concentration of 10% by weight was added to the resultant aqueous suspension at an amount of 0.6 part per 100 parts of Ca(OH)2, the aqueous suspension was heated to 80 C, and then the aqueous suspension continued to be agitated at a rate of 2,000 as Reynolds number.

After 2 hours of the above procedure, the carbon dioxide-containing gas was again introduced thereinto when the pH of the aqueous suspension became 8.2, a precipitating agent was added thereto at an amount of 300 ppm, and then a supernatant was separated from the aqueous suspension, as a result, it was obtained an aqueous suspension containing a colloidal calcium carbonate of 0.05 tan in particle size at a concentration of 15% by weight.After pouring the concentrated suspension in a mixer, particle surfaces of colloidal calcium carbonate were treated by adding 3 part of sodium salt of fatty acid, having a concentration of 10% by weight, per 100 parts of CaCO3 to be produced, at a temperature of 90 C. Powders as obtained above were concentrated to 55 % by weight of solids through a filter press, dried at a temperature of 80 C, pulverized and classified to produce colloidal calcium carbonate powders of 0.05 tan in particle size.

(Example 2) Example 1 was repeated except that the time for ripening was 3 hours and the pH of the aqueous suspension was 9.5. The final product was powders of colloidal calcium carbonate having 0.06 tan particle size.

(Example 3) Example 1 was repeated except that the time for ripening was 4 hours and the pH of aqueous suspension was 10.8. The final product was powders of colloidal calcium carbonate having 0.07 tan particle size.

(Comparative Example 1) Example I was repeated except that the agitation of an aqueous suspension was performed at a rate of 8,000 as Reynolds number. Powders of colloidal calcium carbonate, having 0.045 tan particle size, were obtained, however, the pH of a suspension after 2-hour-ripenning was 8.0 and the particle size of the product was not uniform.

(Comparative Example 2) Example 1 was repeated except that the amount of KOH added was 2.0 part per 100 parts of Ca(OH)2. Powders of colloidal calcium carbonate, having 0.05 tan particle size, were obtained, however, the pH of a suspension after 2-hourripenning was 9.2 and the particle size of the product was not uniform.

(Reference Example 1) According to a conventional process to carbonize an aqueous lime suspension, a gas containing 30 % by volume of carbon dioxide was added at a rate of 100 e per minute per kg of Ca(OH)2 to the aqueous lime suspension having a concentration of 5% by weight and a temperature of 15 C. Concentration, surface-treatment, dehydration, drying, pulverization and classification were performed in the same manner as in Example 1 to give a powdery calcium carbonate product. The final product was powders of colloidal calcium carbonate having 0.04 tan particle size.

(Reference Example 2) The aqueous suspension carbonized by the process of Reference Example 1 was maintained and ripened for 100 hours while being heated to a temperature of 80 C. Dehydration, drying, pulverization and classification were performed in the same manner as in Reference Example 1 to give a powdery calcium carbonate product. The final product was powders of colloidal calcium carbonate having 0.08 tan particle size.

(Application Example) According to the formulation given below, each of calcium carbonate powders obtained in Examples 1 to 3, Comparative Examples 1 and 2 and Reference Examples I and 2 was added to DOP, a plasticizer of PVC paste resin, dispersed therein by a conventional method, kneaded by an automatic stirrer for 10 min., and measured with a method of Smm-thickness-slop and a grind gauge to know its grid.

The measured results are listed in Table 1.

Formulation receipt Geon 121 (polyvinylchloride paste resin) 50g DOP (dioctylphthalate) 60g Colloidal calcium carbonate 50g Table 1

Particle BET Size( m) Surface Slope Grid Area ment ment an judge- Dispersity Example 1 0.05 28 7 Oo 3 Oo 0 Example 2 0.06 25 1 # 3 # # Example 3 0.07 22 1 Qo 3 Comparative 0.045 29 60 A 65 A A Example 1 Comparative 0.05 27 70 A 70 A A Example 2 Reference 0.04 30 150 X 90 X X Example 1 Reference 0.08 20 80 X 60 A X Example 2 NOTE: The smaller the values of the slope and the grid are, the better their properties are excellent 0: good A: average X: bad It is evident from the above results that the process according to the present invention provides particles of colloidal calcium carbonate which show lower affinity of aggregation, superior uniformity and dispersity in the end products.

These above examples are set forth to illustrate specific embodiments of the invention and are not intended to limit the scope of the processes of the present invention. Additional embodiments and advantages within the scope of the claimed invention will be apparent to one of ordinary skill in the art.

Claims

CLAIMS:

I. A process for preparing colloidal calcium carbonate of cubic crystals of which the particle sizes are in the range of more than 0.04pm to less than 0.08calm, which process comprises: (a) adding sugar or a chelate agent to an aqueous lime suspension prior to the introduction of a gas containing carbon dioxide thereinto; (b) adding a cation-hydroxide to the aqueous lime suspension after the introduction of the gas containing carbon dioxide thereinto, when ripening the aqueous lime suspension; (c) heating and agitating the aqueous lime suspension obtained in step (b) in order to obtain the colloidal calcium carbonate; wherein the introduction of a gas containing carbon dioxide is performed by introducing a gas containing 20 to 40% by volume of carbon dioxide at a rate of 40 to 200 litres per minute per kg of Ca(OH)2 into the aqueous lime suspension having 3 to 8% by weight of Ca(OH)2 and a temperature of 14"C to 18"C.
2. A process according to claim 1, wherein the amount of sugar or chelate agent added is 0.2 to 3.0 part by weight per 100 parts of Ca(OH)2 included in the aqueous solution.
3. A process according to claim 1, wherein the chelate agent is EDTA.
4. A process according to claim 1, wherein the ripening is performed under the conditions of adding a hydroxide with univalent or bivalent cation to the aqueous suspension at an amount of 0.1 to 0.8 part per 100 parts of Ca(OH)2 to neutralise carboxylic acid ions dissolved in the aqueous lime suspension, containing calcium carbonate of 0.04 ,um in particle size, being at the pH of 6.8.
5. A process according to claim 1 or claim 2, wherein the ripening is performed under the conditions of agitating the aqueous lime suspension at the rate of 100 to 5,000 as Reynolds number while being heated to a temperature of40"C to 95"C.
6. A process according to claim 1 or claim 2, wherein the colloidal calcium carbonate of a specific particle size in the range of between 0.045m and 0.075 Fm is produced by adjusting the pH of the aqueous lime suspension at ripening in step (b).
7. A process according to claim 1 or claim 2, wherein after concentrating the aqueous lime suspension containing colloidal calcium carbonate in the range of more than 0.04pm to less than 0.08m in particle size to a concentration of 14 + 1% by weight thereof, powders of the colloidal calcium carbonate are produced by treating with surfacetreatment, dehydrating, drying and pulverizing.
8. A process of preparing colloidal, calcium carbonate of cubic crystals substantially as described hereinabove with reference to the accompanying examples.