KR20030060301A - Preparation of precipitated calcium carbonate slurry using a polyacrylate dispersant - Google Patents

Abstract

PURPOSE: Provided is a method for preparing the slurry of calcium carbonate (CaCO3) precipitated from the reaction of Ca(OH)2 and CO2 by using polyacrylate dispersant and water. The resultant CaCO3 slurry for filling agents and paints has high concentration, low viscosity, dispersion stability and long-time storage. CONSTITUTION: The CaCO3 slurry is prepared by the following steps of: reacting Ca(OH)2 and CO2 to form CaCO3; filter pressing to remove water and get filter cakes having the moisture content of 35-40wt.%; adding 0.3-2wt.%(based on the amount of solid CaCO3) polyacrylate dispersant and water to be a CaCO3 slurry (solids:60-65%); stirring at 2000-3000rpm for 0.5-4hrs in dispersed type mixer, then at 3000-4000rpm for 0.5-4hrs in a homo type mixer. The resultant CaCO3 slurry is excellent in mechanical and optical properties, and workability.

Description

Preparation of precipitated calcium carbonate slurry using a polyacrylate dispersant}

The present invention relates to a method for producing a precipitated calcium carbonate slurry using a polyacrylate-based dispersant and to a precipitated calcium carbonate slurry prepared accordingly. More particularly, the present invention provides an economical method for producing a precipitated calcium carbonate slurry in which the polyacrylate-based dispersant is added and stirred after formation of precipitated calcium carbonate particles to improve time stability of the dispersed particles and stabilize the quality thereof. to provide.

Calcium carbonate is inexpensive and has a low specific gravity, so it is widely used in the industrial field. That is, it is used as limestone and marble as various neutralizers such as cement raw material, calcium oxide raw material, steelmaking and building material. In addition, wet powder of clam shells is used for white pigments and water-based paints, and precipitated calcium carbonate is used for pigments, paints, toothpastes, and the like.

Calcium carbonate is industrially obtained by crushing limestone to form a powder, sieving it, and sifting it, or by removing it (manipulating the particle by size or specific gravity by using a difference in speed when solid particles freely settle in the air) (Iii) Calcium carbonate and precipitates produced by blowing carbon dioxide into lime oil are classified into hard calcium carbonate obtained by filtration, drying and fine grinding.

Conventional precipitated calcium carbonate is calcined limestone with high temperature heat to decompose into quicklime (CaO) and carbon dioxide (CO ₂ ), and the resulting quicklime reacts with water to form a calcium hydroxide (Ca (OH) ₂ ) solution, the insoluble matter After filtering off, carbon dioxide is injected to form and precipitate calcium carbonate. The particle size can be adjusted according to the reaction conditions such as reaction temperature and stirring speed, and when the particle size is to some extent, it is precipitated to form an aqueous suspension, which is dehydrated by using a filter such as a filter press, and then used as an attritor, After drying using a dryer such as a paddle dryer, it is generally pulverized and manufactured in powder form.

However, in the method of producing precipitated calcium carbonate as powder, a post-treatment step such as dehydration and drying is required, physical properties due to aggregation of powder are deteriorated, powder properties due to wide particle size distribution are reduced, and during transportation and processing Losses occur and are emitted to the atmosphere in the form of dust, which can cause pollution problems, and the process is complicated, which increases the investment cost.

When the precipitated product of the precipitated calcium carbonate is dehydrated, when the solid concentration is 50% by weight, it has a hard cake form and no fluidity at all. However, hydrous calcium carbonate in cake form is preferred in various fields because it has much less secondary agglomerates than when it is dried once and ground to a powder form. For example, when used in disperse-type pigments, sieving pigments such as water-based pigments, water-based paints and inks, sieving pigments, physical properties such as opacity, glossiness, and printability of these products. In order to make it even better, it is preferable to use a cake-like hydrous calcium carbonate with less secondary aggregates.

Although these non-flowing, hard cake-like hydrous calcium carbonates can be slurried without being processed into powders, they have great advantages in terms of the use of hydrous calcium carbonates, but they are fluid, suspension-stable, highly concentrated and low viscosity. It is difficult to make calcium slurry.

In particular, in the paper industry, a higher concentration of low-viscosity calcium carbonate is urgently developed as a means to reduce the drying cost of the vellum paper and to obtain vellum with good gloss of the shed surface. As a slurry, most commonly anionic surfactants such as sodium hexamethylene, sodium pyrrolate, or polycarboxylic acids such as citric acid or salts thereof, or polymeric polys such as polyacrylic acid or poly (acrylic acid-maleic acid) as dispersion systems It is known to use carboxylic acids or their sodium salts or ammonium salts as dispersants. However, since these dispersants have to be used in large quantities, not only the viscosity is increased, but also the excessive dispersant adversely affects the scratches and beading easily during coating, and the marks on the coated paper are liable to be generated. Brings down.

Meanwhile, a method of preparing a glycol suspension by mixing the prepared precipitated calcium carbonate in the form of a glycol with a dispersing agent such as glycol, and grinding the dispersion using a wet mill is known to obtain a slurry of precipitated calcium carbonate. At this time, it is also proposed to improve the stability of a slurry by using together dispersing agents, such as alkali metal salt or ammonium salt of polycarboxylic acid.

However, the glycol dispersant may be sufficient for the colloidal precipitated calcium carbonate having an average particle diameter of 0.5 μm or less for the effect of obtaining a calcium carbonate slurry having good fluidity at a solid concentration of 60% by weight or more. The use is limited for calcium carbonate having a small hydration layer formation and relatively large particle size on the particle surface of.

Therefore, there has been a great need for the production of precipitated calcium carbonate slurries with excellent dispersion stability and high concentration and low viscosity at a relatively low price.

The inventors of the present invention, when preparing a solid 60-65% precipitated calcium carbonate slurry using a polyacrylate-based dispersant, can make a coating color of high concentration and low viscosity, especially the dispersion effect on precipitated calcium carbonate, which is a fine particle It was found that the excellent and time-lapse stability of the slurry can provide a long time stability and completed the present invention.

1 shows a process flow for making precipitated calcium carbonate slurry.

Figure 2 shows the particle size distribution of the calcium carbonate slurry prepared according to the present invention.

An object of the present invention is to provide a method for producing a precipitated calcium carbonate slurry using a polyacrylate-based dispersant.

Specifically, the method for preparing the precipitated calcium carbonate slurry according to the present invention includes:

(1) calcium hydroxide reacts with carbon dioxide to form calcium carbonate,

(2) dehydration with water content of 35-40%,

(3) supplying a polyacrylate dispersant and water under stirring to form a precipitated calcium carbonate slurry, and

(4) Stirring at 2000-3000 rpm, then 3000-4000 rpm, while maintaining the slurry concentration constant.

It is another object of the present invention to provide a precipitated calcium carbonate slurry thus prepared. Precipitated calcium carbonate slurry according to the present invention is improved in time stability of the dispersed particles and the quality is stabilized.

The configuration of the present invention is described above with reference to FIGS. 1 and 2 attached below, but the present invention is not limited thereto.

1. Firing

After mixing limestone and anthracite at a constant rate, the raw material mixed by the high temperature heat is decomposed and carbon dioxide gas is transferred to the reaction tank after refining process, and quicklime (CaO) is transferred to the hydration tank through the storage tank. Transferred.

2. Hydration

The quicklime transferred through the calcining process reacts with water to produce calcium hydroxide, which is then transferred to the emulsification tank and the concentration control tank, and the sludge (unhydrated component and impurities) generated in the hydrator is discharged to the outside.

3. Oil painting

The coarse particles and impurities of the calcium hydroxide transferred from the hydration tank to the pump are separated and separated into cyclones so that the calcium hydroxide of the fine particles is transferred to the concentration control tank and the coarse particles and the impurities are brought back into the receiver.

4. Concentration control tank

The calcium hydroxide transferred from the emulsifier is stored for aging and concentration control prior to reaction.

5. Reaction

Calcium carbonate (CaCO ₃ ) is produced by the reaction of calcium hydroxide transported from the concentration control tank with carbon dioxide produced in the refining process. The reaction temperature and pressure can be set according to the conventional conditions in the art. The carbon dioxide may be from a separate source.

6. Ripening

Calcium carbonate after the reaction is aged is aged. Aging temperature and time is not particularly limited, it is possible to use conventional conditions in the art.

7. Dehydration

Calcium carbonate transferred from the aging tank is dehydrated with 60 ~ 65% solids (35 ~ 40% water content) using a filter press and the filtrate is transferred to the settling tank. Centrifugal separation etc. can also be used as a dehydration method.

8. Distribution Adjustment

A slurry of 60% solids is prepared by quantitatively adding dispersant and water to a calcium carbonate cake having a solid content of 60 to 65%. The mixing speed is not particularly limited.

The mixed slurry is first agitated at 2000-3000 rpm, for example in a dispersed type mixer. At this time, the concentration and viscosity of the slurry can be determined by analyzing the slurry circulated to the mono pump (Mono Pump).

In order to finely adjust the dispersion of the calcium carbonate slurry, it is possible to stir at a rpm of 3000 to 4000 in a second homo mixer.

In the dispersion tank, as the stirring speed and stirring time increase, the sedimentation speed (emulsification) decreases, but it can be adjusted in consideration of productivity and manufacturing cost. In general, the stirring time is not particularly limited, but 0.5 to 4 hours, preferably 1 to 2 hours in the primary tank, 0.5 to 4 hours, preferably 1 to 2 hours in the secondary tank.

Through the dispersion adjustment as described above, a high concentration / low viscosity precipitated calcium carbonate 60-65%, specifically 60% slurry can be obtained.

In the case where the above dispersion adjustment step was not performed, specifically, when a dispersant and water were simply added to a calcium carbonate cake having a solid content of 60 to 65%, a slurry having satisfactory physical properties and quality was not obtained. On the other hand, in the case of the dispersion adjustment step, when the dispersant is not a polyacrylate-based, it could not produce a low viscosity-high concentration calcium carbonate slurry of desired quality or poor stability over time.

The above-described process steps may be appropriately modified and changed according to the needs of those skilled in the art or according to the manufacturing and use environments, all of which are included in the scope of the present invention without departing from the spirit of the present invention.

The dispersant used in the present invention is a polyacrylate, more specifically, an alkali metal salt of polyacrylate, preferably sodium salt, and a 5% aqueous solution having a pH of 8.0 or more, preferably pH 9.0 or more. do. Polyacrylate sodium salts can be prepared by polymerizing monomeric sodium acrylate. Examples of commercially available products of the dispersant that can be used in the present invention may mention, for example, SN-DISPERSANT 5034 [trade name, Sannovco Korea Co., Ltd., solid content 45%, viscosity 800 cps, pH 9.6 (5% solution)]. Can be.

The amount of dispersant used depends on the desired viscosity of the calcium carbonate or final slurry used, but is not particularly limited. In the present invention, the calcium carbonate is 0.3 to 2.0% (relative to solids), preferably 0.6 to 1.0%.

The powerful stirring device for preparing the calcium carbonate slurry of the present invention usually uses a dispersed type or homo type mixer, but other general mixers such as ribbon mixers, ball mills, homogenizers, and the like are used. It does not depart from the scope of the present invention.

The precipitated calcium carbonate slurry obtained according to the present invention generally has a calcium carbonate solid content of 60-65% by weight, and despite this high concentration, it is low in viscosity and stable in dispersibility and thus can be stored for a long time.

The calcium carbonate slurry of the present invention can be used as a dispersing filler or pigment which imparts excellent mechanical and optical properties to paper, aqueous synthetic resins, paints, inks, adhesives, etc., and makes workability extremely excellent. Depending on the purpose and use, the calcium carbonate slurry of the present invention may be used as a base, and powders or slurries of other fillers, pigments, and other additives may be mixed to form a dispersed dispersion type slurry, which is considered to be very useful.

Examples will now be described in detail.

Example 1

About 15% of the hydrated CaCO ₃ is transferred to a filter press (oil hydraulic system, 50 chamber; model name ZMF2B-WZ; manufactured by Japan Kurita Machinery) using a slurry pump and dewatered. For 70-80 minutes, the waste plate (lid closure), milk grade liquid, pressurized drainage, vacuum drainage, open plate (opening lid), and discharge process were performed in one cycle (cxycle), and 1,300 kg was prepared once based on solid content.

The dehydration cake with 35 ~ 40% water content stored in the hopper is transferred to a double screw feeder equipped with an inverter. While controlling the mixing speed with an inverter, quantitatively input water and SN-DISPERSANT (manufactured by Sannovco Korea, 45% solids, 800 cps viscosity, pH 9.6 (5% solution)).

The mixed slurry is transferred to a primary tank equipped with a distributed mixer and circulated with a mono pump to measure the density of the slurry. The measuring principle of this device is to calculate the specific gravity of the slurry by using the load and pressure difference of the circulator. When the concentration of the slurry is out of the set value, the water input is changed to keep the slurry constant. The mixer speed of the primary tank is set at about 2500 rpm with an inverter installed, and the mixer time of the primary tank is set while analyzing the density and dispersion, but about 1 hour.

The dispersed product in the primary tank is transferred to a secondary tank with a homo mixer using a mono pump. In the homo mixer, the dispersion state of the slurry was analyzed as in the first dispersion mixer, and the rotation speed was controlled by an inverter and stirred at about 3500 rpm to obtain a final 60% slurry (emulsified) product.

The calcium carbonate particle size distribution in the obtained slurry is shown in FIG.

Example 2

In 180 liters of lime oil prepared at 30 ° C. containing 145 g / l of calcium hydroxide, 20 vol% carbon dioxide gas having a carbon dioxide concentration of 20 vol% was supplied at a rate of 1500 l / hr, and the reaction solution was stirred at a stirring speed of 360 rpm. 16 hours after the start of the carbonation reaction, the carbonation reaction was stopped at PH 7.0 and a temperature of 70 ° C. The obtained calcium carbonate aqueous suspension is aged at 50 ° C. for 24 hours, and then dehydrated at a water content of 35 to 40% using a filter press.

After the same procedure as in Example 1 to obtain a precipitated calcium carbonate 60% slurry.

[Comparative Examples 1 to 3]

Proceed in the same manner as in Example 1, but instead of SN-DISPERSANT 5034 as a dispersant, Aron T-40 (Japan Dong-A Synthetic Chemical), HSD-255 R (Sanoff Co., Ltd.), and HSD-5800 (Sanoffco, Korea) Co., Ltd.) was used, respectively.

When the dispersant was used, the prepared precipitated calcium carbonate 60% slurry had a high viscosity and at the time of storage (Example 10 storage), the time for separating solids and water was faster than the slurry of Example 1 using SN-DISPERSANT 5034.

[Comparative Example 4]

Proceed as in Example 1, but did not undergo a dispersion adjustment process after the dispersant was added under stirring. The precipitated calcium carbonate 60% slurry prepared had a viscosity similar to that obtained in Example 1, but upon storage (eg storage for 10 days), solids and water separated very quickly.

Method for producing a precipitated calcium carbonate 60% slurry according to the present invention, First, it is possible to improve the overall quality of the preparation produced by using a precipitated calcium carbonate 60% slurry with improved dispersibility and interfacial properties of the product, process simplification and loss control , Improves the quality of the product, improves the expense and profits of paper companies, improves the whiteness, gloss, opacity, and ink repairability when used as a paper coating agent, and improves the hiding power when used as an aqueous paint filler. And economic effect, and secondly, there is a technical effect of establishing a precipitated calcium carbonate 60% slurry emulsification technique and a technique of improving interfacial properties of the final product of the precipitated calcium carbonate coating agent.

Claims (3)

Method for producing a precipitated calcium carbonate slurry using a polyacrylate-based dispersant, comprising the following steps: (1) calcium hydroxide reacts with carbon dioxide to form calcium carbonate, (2) dehydration with water content of 35-40%, (3) supplying a polyacrylate dispersant and water under stirring to form a precipitated calcium carbonate slurry, and (4) Stirring at 2000-3000 rpm, then 3000-4000 rpm, while maintaining the slurry concentration constant. The method according to claim 1, wherein the polyacrylate-based dispersant is used in an amount of 0.3 to 2.0% (solid content) based on calcium carbonate. A precipitated calcium carbonate slurry comprising a polyacrylate dispersant in an amount of 0.3 to 2.0% (solid content) relative to calcium carbonate.