KR20010045447A - Surface treatment of calcium carbonates with fluoro-compounds - Google Patents

Abstract

PURPOSE: Provided is a surface reforming method of CaCO3 using fluorides(HF, H2SiF2), industrial byproducts. The reformed CaCO3 has high acid-resistance, whiteness and sterilization required for fillers, coaters and sterilizers of papers, cosmetics, toothpaste and pigments. CONSTITUTION: The reformed CaCO3 is obtained by mixing 50-90wt.% of CaCO3 suspension(50-90% in concentration) with 10-50wt.% of aqueous fluoride(5-40% in concentration) selected from the group consisting of H2SiF6, HF, MgSiF6 and mixture thereof. drying at 25-105deg.C for 15-40hrs., and then thermal treating at 350-400deg.C for 1-3hrs. Accordingly, the surface of CaCO3 includes SiO2, CaF2 or NaF and the resultant CaCO3 powder has a particle size of 1-5micrometer.

Description

Surface Modification Method of Calcium Carbonate Using Fluorine Compounds {SURFACE TREATMENT OF CALCIUM CARBONATES WITH FLUORO-COMPOUNDS}

The present invention relates to a method for modifying the surface of calcium carbonate using a fluorine compound. Specifically, a mixture of calcium carbonate, which is an industrial by-product, with calcium carbonate, followed by drying and heat treatment, results in silica (SiO ₂ ) and The present invention relates to a method of modifying the surface of calcium carbonate to have excellent acid resistance, whiteness and antibacterial properties by physically and chemically combining fluorite (CaF ₂ ) or sodium fluoride (NaF).

Currently, inorganic fillers for papermaking include clay (Al ₂ O ₃ · 2SiO ₂ · 2H ₂ O), talc (3MgO · 4SiO ₂ · H ₂ O), calcium carbonate, TiO ₂ , Al (OH) _3, or silica (SiO _2). ), And talc and calcium carbonate are the most widely used. Physical, chemical and optical properties that these inorganic fillers should consider include particle size, charge, shape, distribution, specific surface area, whiteness, specific gravity and acid resistance.

On the other hand, while heavy calcium carbonate (natural ground limestone) is a simple manufacturing method and low manufacturing cost, the quality of the product is limited because the quality is absolutely dependent on the type of ore (limestone) or grinding technology. Accordingly, a method of producing calcium carbonate containing 80 or more particles having a spherical ratio of 0.4 or less or 80 or more having a sphere having a spherical ratio of 0.01 to 0.3 using high-quality gemstones has been disclosed in Japanese Patent No. 88-225521. Various studies have been conducted on particle size control of medium and hard calcium carbonate (see Limestone Mining Association of Japan, 84-111 (1986)), but carbonic acid having an average particle size distribution at the nm level using heavy calcium carbonate It was still difficult to produce calcium.

On the other hand, chemically synthesized hard calcium carbonate is preferred as a filler in the papermaking process because it is easier to control particle size and shape and can be manufactured with higher purity than heavy calcium carbonate (see Japanese Patent No. 87-113719). However, due to their poor chemical stability (e.g. acid resistance) and optical properties (e.g. whiteness), they are used as fillers for acidic paper despite the low price under current conditions that depend on the acidic papermaking process of about 60 or more in papermaking. It is not used and is only used as a filler in neutral and alkaline papermaking processes.

W. Augustine reported a study on the yield of fluorite (CaF ₂ ) produced by the reactivity and reaction of calcium carbonate with aqueous fluorine solutions containing NH ₄ F, KF or NaF ("Study"). of the reaction of crystalline calcium carbonate with aqueous solution of NH ₄ F, KF and NaF ", J. of Fluorine Chem., 12 (1978), 281-292), such as improving acid resistance or whiteness of calcium carbonate. The provision of functionality is not covered at all.

Accordingly, the present inventors have diligently researched and treated the calcium carbonate with an industrial by-product fluorine compound to form and combine silica (SiO ₂ ) and fluorite (CaF ₂ ) or sodium fluoride (NaF) on the surface of the calcium carbonate to improve acid resistance. The present invention has been found to be capable of producing surface modified calcium carbonate, which can be used as a filler of acidic paper, as well as having excellent whiteness and antibacterial properties.

It is an object of the present invention to provide a surface modification method of calcium carbonate which can impart excellent acid resistance, whiteness and antibacterial property to the surface of calcium carbonate and can recycle industrial by-products.

FIG. 1A is a scanning electron micrograph of calcium carbonate before surface treatment, and FIGS. 1B to 1D are hydrofluoric acid (H ₂ SiF ₆ ), magnesium silicate (MgSiF ₆ ) and hydrofluoric acid ( Scanning electron micrograph of calcium carbonate surface-treated with HF).

In order to achieve the above object, the present invention is selected from the group consisting of hydrofluoric acid (H ₂ SiF ₆ ), hydrofluoric acid (HF), magnesium silicate (MgSiF ₆ ), and mixtures thereof, which are industrial by-products in a calcium carbonate suspension in water. After mixing the aqueous solution of the fluorine compound, there is provided a method for surface modification of calcium carbonate comprising drying the product mixture by air drying and heat treatment at 350 to 400 ℃.

Hereinafter, the present invention will be described in detail.

According to the calcium carbonate surface modification method of the present invention, hydrofluoric acid (H ₂ SiF ₆ ) or magnesium silicate fluoride (MgSiF ₆ ) generated as an industrial by-product in the production process of phosphoric acid or hydrofluoric acid, or an etching solution for semiconductors Silica (SiO ₂ ) and fluorite (CaF ₂ ) or sodium fluoride on the surface of calcium carbonate through the reaction shown in Schemes 1 to 3 by mixing an aqueous solution of hydrofluoric acid (HF) generated as wastewater in the process with a calcium carbonate suspension (NaF) is formed.

_{xCaCO 3 + H 2 SiF 6 (} aq) → 3CaF 2 · (x-3) CaCO 3 · SiO 2

_{xCaCO 3 + MgSiF 6 (aq)} → 3CaF 2 · (x-3) CaCO 3 · SiO 2 + MgO

According to the method of the present invention, a calcium carbonate suspension in water as a base material and an aqueous solution of a fluorine compound as a surface modifier are mixed at 50 to 90 weight and 10 to 50 weight, respectively, wherein the concentration of the calcium carbonate suspension is 50 to 90, fluorine The concentration of the aqueous solution of the compound may range from 5 to 40.

Specifically, under room temperature conditions, in the reaction schemes 1 and 2, 3 mol of fluorite (CaF ₂ ) by uniformly mixing hydrofluoric acid (H ₂ SiF ₆ ) or magnesium silicate (MgSiF ₆ ) as a reforming agent with calcium carbonate. In the case of 1 mole of silica (SiO ₂ ) and magnesium silicate (MgSiF ₆ ), an additional 1 mole of MgO is formed on the surface of calcium carbonate, and in the case of Scheme 3, industrial water glass (Na ₂ SiO ₃ ) and fluorinated Hydrogen acid (HF) is first reacted to uniformly mix the reaction product with calcium carbonate to form 2 mol of sodium fluoride (NaF), 1 mol of silica (SiO ₂ ), and H ₂ O on the surface of calcium carbonate.

According to the method of the present invention, the resultant reaction mixture is ventilated for 15 to 40 hours at room temperature to 105 ℃ and then heat treated for 1 to 3 hours at 350 to 400 ℃ silica (SiO ₂ ), fluorite (CaF ₂ ) Alternatively, sodium fluoride (NaF) or the like may produce calcium carbonate physically and chemically bound to the surface of calcium carbonate. At this time, when the heat treatment temperature exceeds 400 ℃ calcium carbonate is decomposed into CaO and CO ₂ is not preferable.

Fluorite (CaF ₂ ) bonded to the surface of calcium carbonate has a particle size of several hundreds to several hundred nm, which contributes to improvement of morphology, specific surface area and particle size distribution of calcium carbonate particles, and silica (SiO). ₂ ) is acid-resistant and has high whiteness of 95 or more (about 90 degrees in case of calcium carbonate) to increase acid resistance and whiteness of calcium carbonate, and sodium fluoride (NaF) gives antibacterial properties to calcium carbonate.

As such, the calcium carbonate surface modified by the method of the present invention has a particle size of 1 to 5 μm, has improved acid resistance and whiteness, and is given antibacterial properties such as fillers (particularly acidic paper fillers), coating agents or paper as antibacterial agents, It can be usefully used in toothpaste, cosmetics or pigments, and has the advantage of recycling industrial by-products from the environmental aspects. When used for pigments, the particle size of the calcium carbonate particles is preferably in the range of 1 to 2.5 µm and narrow in particle size distribution.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited only to these examples. Various characteristics of calcium carbonate were evaluated by the following method.

(1) whiteness

The whiteness of the calcium carbonate before and after the surface treatment was measured three times using a powder-based white system C-100 (KETT Laboratories, Japan), which reflects the average value.

(2) acid solubility (acid resistance)

30 g of calcium carbonate sample before or after the surface treatment was added to 100 g of sulfuric acid (H ₂ SO ₄ , pH 4), impregnated for 120 minutes, and filtered. The filter cake was washed with water to remove residual sulfuric acid, dried at 50 ° C. until weighed, and weighed. The reduced weight was obtained by comparing the weight change of the sample before and after sulfuric acid treatment.

Examples 1 to 3

The calcium carbonate suspension in water at a concentration of 50 and an aqueous solution of hydrofluoric acid (H ₂ SiF ₆ ) at concentration 20 were uniformly mixed at room temperature in the weight ratio shown in Table 1, and then the mixture was air dried at 50 ° C. for 24 hours. Heat treatment was carried out at 400 ° C. for 2 hours to obtain calcium carbonate with a modified surface. Physical, chemical and optical properties of calcium carbonate before and after the surface treatment were measured and shown in Table 1 below.

Examples 4-6

Except for using magnesium silicate (MgSiF ₆ ) instead of hydrofluoric acid was carried out in the same manner as in Example 1 to obtain a surface-modified calcium carbonate, its properties are shown in Table 1 below.

Examples 7-9

After mixing industrial water glass (Na ₂ SiO ₃ ) with a hydrofluoric acid (HF) and a reaction product aqueous solution of concentration 5 and a suspension of calcium carbonate in water at a concentration of 50 in a weight ratio shown in Table 1 below, The same method as in Example 1 was carried out to obtain a modified calcium carbonate surface, and the properties thereof were measured and shown in Table 1 below.

division Calcium Carbonate: Fluorine Compound Weight Ratio Characteristics Average particle size (㎛) Particle shape Particle size distribution Whiteness () Dispersion degree (reduction amount) Antimicrobial activity Before surface treatment - 1.25 Hexagonal Plate (smooth surface) Multi-disperse 90.0 6.3 weight X After surface treatment Example 1 86:14 1.53 Very irregular shape Mono-disperse 94.6 1.98 weight X Example 2 72:28 1.74 94.8 1.92 weight X Example 3 58:42 3.46 93.7 1.92 weight X Example 4 86:14 2.45 94.1 2.70 weight X Example 5 72:28 3.84 92.1 2.61 weight X Example 6 58:42 4.15 89.7 2.56 weight X Example 7 86:14 2.70 93.1 2.31 weight O Example 8 72:28 3.12 93.8 2.01 weight O Example 9 58:42 4.02 91.5 1.90 weight O

From Table 1, the calcium carbonate surface-treated with the fluorine compound has all of the physical properties such as particle shape and particle size distribution, optical properties such as whiteness, and chemical properties such as acid resistance and antimicrobial properties, compared to calcium carbonate untreated. It can be seen that the improvement. 1A is a scanning electron micrograph of calcium carbonate before surface treatment, and FIGS. 1B to 1D show hydrofluoric acid (H ₂ SiF ₆ ), magnesium silicate (MgSiF ₆ ), and the examples according to Examples 3, 6, and 9, respectively. As a scanning electron micrograph of calcium carbonate surface-treated with hydrofluoric acid (HF), improvement in particle shape, specific surface area and particle size distribution of calcium carbonate due to surface treatment with fluorine compounds can be confirmed.

The surface modified calcium carbonate according to the present invention can be used in paper, toothpaste, cosmetics or pigments as fillers, coatings or antimicrobial agents to improve the acid resistance and whiteness and impart antimicrobial properties, surface modification of calcium carbonate according to the present invention The method has the advantage of recycling industrial by-products.

Claims (6)

After mixing an aqueous solution of a fluorine compound selected from the group consisting of hydrofluoric acid (H ₂ SiF ₆ ), hydrofluoric acid (HF), magnesium silicate (MgSiF ₆ ) and mixtures thereof, which are industrial by-products, in a calcium carbonate suspension in water, A method of modifying the surface of calcium carbonate, which comprises drying the product mixture with air and drying it at 350 to 400 ° C. The method of claim 1, The concentration of the calcium carbonate suspension is 50 to 90, the concentration of the aqueous solution of fluorine compound is 5 to 40. The method of claim 2, 50 to 90 weight of calcium carbonate suspension and 10 to 50 weight of aqueous solution of fluorine compound. Calcium carbonate whose surface is modified according to the method of claim 1. The method of claim 4, wherein Calcium carbonate, characterized in that silica (SiO ₂ ) and fluorite (CaF ₂ ) or sodium fluoride (NaF) is bonded to the surface. A product selected from paper, toothpaste, cosmetics and pigments comprising the calcium carbonate of claim 5 as a filler, coating or antimicrobial agent.