Calcium carbonate for paint having high hiding property and paint with high hiding property containing calcium carbonate

Abstract

To provide calcium carbonate for paints, capable of synthesizing calcium carbonate having high whiteness and high hiding properties, and paints having high hiding properties containing the calcium carbonate.SOLUTION: Calcium carbonate for paints having high hiding properties has: an average particle size (D50) of 2 to 20 μm; a particle size distribution D10 of 1 to 13 μm; a particle size distribution D90 of 3 to 30 μm; and a cuboidal shape.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to calcium carbonate for paints having high hiding properties and paints containing the calcium carbonate and having high hiding properties, and in particular to calcium carbonate for paints having high hiding properties that can be used as a filler for various paints and the like, and paints containing the calcium carbonate and having high hiding properties. [Background technology]

[0002] Calcium carbonate and titanium oxide are used in a wide range of industrial fields as fillers for plastics, resins, rubber, paper, paints, cosmetics raw materials, etc., and are used to improve various physical properties. In particular, calcium carbonate, which has a small refractive index, is mainly used as an "extender pigment," and titanium oxide, which has a large refractive index, is mainly used as a "white pigment," as fillers in paints. Calcium carbonate includes ground calcium carbonate, which is prepared by crushing high-purity natural limestone and classifying it to adjust the particle size. In addition, calcium carbonate is calcined to form lime, which is then reacted with water to form slaked lime, which is then reacted with carbon dioxide to form calcium carbonate again, which is then recovered, dried, crushed, and classified to produce light calcium carbonate.

[0003] However, limestone (heavy calcium carbonate), which is crushed calcium carbonate, has the problem that it does not have a high hiding power and is insufficient in hiding power. In addition, titanium oxide is expensive as a filler compared to calcium carbonate, and when it is filled into resin or the like, there is a problem that the applied surface deteriorates when exposed to sunlight.

[0004] Japanese Patent Laid-Open Publication No. 2008-156204 (Patent Document 1) discloses a method for producing fine-particle aggregated precipitated calcium carbonate, which comprises a step (1) of obtaining milk of lime by wet slaking quicklime, a step (2) of blowing carbon dioxide gas into a calcium hydroxide suspension obtained by suspending calcium hydroxide in water to obtain a colloidal particulate calcium hydroxide suspension by carbonation to a carbonation rate of 20% or less, and a step (3) of adding the colloidal particulate calcium hydroxide suspension obtained in step (2) to the milk of lime obtained in step (1), blowing in carbon dioxide gas, and reacting until the carbonation rate reaches 100%, and thereby producing a fine-particle aggregated precipitated calcium carbonate having a BET specific surface area of ​​10 to 25 m. 2 / g or less, and the pore volume of 0 to 1000 Å by nitrogen adsorption method is 0.05 cm 3 It is described that the resulting fine particle aggregated light calcium carbonate has a pore volume ratio of 250 Å or less to the total pore volume of 25% or more and an oil absorption by liquid paraffin of 100 cc / 100 g or more. It is further described that when the resulting calcium carbonate is used as a filler for printing paper, the printing paper can be given excellent ink absorbency and opacity (especially opacity after printing).

[0005] Furthermore, JP2012-207346A (Patent Document 2) discloses a calcium carbonate slurry having an average particle size of 0.5 to 1.5 μm and a gradient coefficient (D30 / D70) (wherein DX represents a finer equivalent spherical diameter when X weight % of the particles corresponds to this diameter) of 40 or more, and a coated paper having a coating layer containing the calcium carbonate, for the purposes of providing a calcium carbonate slurry that can provide a coating layer having concealing properties and providing a coated paper having a coating layer containing calcium carbonate and having concealing properties.

[0006] Furthermore, Japanese Patent Laid-Open Publication No. 2002-233851 (Patent Document 3) discloses that, for the purpose of using calcined ash to provide light calcium carbonate-coated particles having high whiteness and low abrasion properties and paper using the same, the calcined ash is pulverized to an average particle size of 3 μm or less, the calcined ash particles after pulverization are mixed into an aqueous suspension containing calcium hydroxide, carbon dioxide or a gas containing carbon dioxide is passed through the aqueous suspension to coat the periphery of the calcined ash particles with light calcium carbonate, and the light calcium carbonate-coated particles thus produced are used as a filler for filler-containing paper or as a pigment for coated paper.

[0007] However, the above-mentioned conventional calcium carbonate does not have sufficient hiding power even when blended in a paint, and calcium carbonate with higher hiding power is desired. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2012-96975 A [Patent Document 2] Patent Publication No. 2021-79377 [Patent Document 3] JP 2002-233851 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a calcium carbonate for paint that solves the above-mentioned problems and has high purity and high whiteness with almost no impurities, and is excellent in hiding property, and a paint having high hiding property that contains the calcium carbonate. [Means for solving the problem]

[0010] In order to solve the above problems, the calcium carbonate for paint of the present invention and the paint having high hiding power containing said calcium carbonate have mainly the following technical features. (1) The calcium carbonate for paint having high hiding power of the present invention has an average particle size (D50) of 2 to 20 μm, a particle size distribution of D10 of 1 to 13 μm, and a particle size distribution of D90 of 3 to 30 μm, and has a cubic shape.

[0011] (2) The calcium carbonate described in (1) above further has a whiteness color value measured by a color difference meter of L * is 95.0~99.9, a * is -1.0 to 1.0, and b* is -1.0 to 1.0.

[0012] (3) The calcium carbonate described in (1) or (2) above has a crystal system that is calcite as measured by X-ray diffraction (XRD).

[0013] (4) A paint having high hiding power according to the present invention is a paint containing any one of the above calcium carbonate for paints. Effect of the Invention

[0014] The calcium carbonate for paint of the present invention has a cubic shape, a sharp and narrow particle size distribution, high purity, and high whiteness, and when used as a filler for paint, it can exhibit excellent hiding power. In particular, even if the calcium-containing waste material used as the raw material contains heavy metals and magnesium, the calcium carbonate of the present invention can be made into a cubic calcium carbonate with high whiteness because the heavy metals and magnesium are removed from the calcium carbonate. Therefore, by blending the calcium carbonate for paint of the present invention with various paints, high hiding power can be imparted to the paints. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is an electron microscope photograph showing the shapes of the calcium carbonate for paint of the present invention and other calcium carbonates. [Diagram 2] FIG. 1 is a diagram showing particle size distributions of calcium carbonate for paint of the present invention and other calcium carbonates. [Diagram 3] FIG. 2 is a diagram obtained by X-ray analysis of the calcium carbonate for paint of the present invention and other calcium carbonates. [Figure 4] FIG. 2 shows the color of particles of calcium carbonate obtained according to the invention and other calcium carbonates. [Diagram 5] FIG. 2 is a photograph showing an example for measuring the hiding ratio of a paint containing the calcium carbonate of the present invention and other calcium carbonates. [Figure 6] FIG. 2 is a photograph of another example for measuring the hiding ratio of a paint containing the calcium carbonate of the present invention and another calcium carbonate. [Figure 7] FIG. 2 is an electron microscope photograph showing the state of each calcium carbonate contained in a paint containing the calcium carbonate of the present invention and another calcium carbonate when the paint is applied. [Figure 8] FIG. 1 is a flow diagram of an example of a production method for producing calcium carbonate for paint of the present invention. [Figure 9] FIG. 9 is a schematic diagram of an example incorporating a process for fixing carbon dioxide and producing alkali carbonate. [Figure 10] FIG. 1 is an electron microscope photograph showing the shape of calcium carbonate obtained when the pH in a calcium carbonate production step is changed in producing calcium carbonate for paint. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The calcium carbonate for coating of the present invention will be described below with reference to the drawings. The calcium carbonate having high hiding power of the present invention is a calcium carbonate for paint having high hiding power, which has an average particle size (D50) of 2 to 20 μm, a particle size distribution D10 of 1 to 13 μm, a particle size distribution D90 of 3 to 30 μm, and a cubic shape.

[0017] The calcium carbonate of the present invention has a cubic shape, and a photograph of the shape of the calcium carbonate for paint of the present invention observed with an electron microscope is shown in Figure 1. For comparison, electron microscope photographs of the shapes of commercially available heavy calcium carbonate (heavy carbon) and light calcium carbonate (light carbon (1)) are also shown in Figure 1. As shown in FIG. 1, the calcium carbonate of the present invention has a cubic shape with almost no variation in particle size, while calcium bicarbonate has a mixture of large and small particles, and precipitated calcium carbonate has small primary particles but secondary aggregates.

[0018] The particle size distribution of the calcium carbonate for a paint of the present invention is such that the average particle size (D50) is 2 to 20 μm, preferably 4 to 16 μm, and more preferably 6 to 10 μm, the D10 of the particle size distribution is 1 to 13 μm, preferably 2 to 10 μm, and more preferably 4 to 7 μm, and the D90 of the particle size distribution is 3 to 30 μm, preferably 6 to 20 μm, and more preferably 10 to 15 μm. The particle size distribution of the calcium carbonate for paint of the present invention shown in Figure 1 is shown in Figure 2. For comparison, the particle size distributions of the commercially available heavy calcium carbonate and light calcium carbonate shown in Figure 1 are also shown in Figure 2. The particle size distribution was measured using a particle size distribution measuring device (MT-3000, manufactured by Microtrac-Bell). The median diameter (average particle size) D50 means the diameter below which half of the population in the particle size distribution falls. Similarly, D90 is defined as the diameter below which 90% of the population falls, and D10 is defined as the diameter below which 10% of the population falls.

[0019] 2, it is clear that the calcium carbonate for paint of the present invention has a particle size distribution within the above-mentioned numerical range, and the shape is sharp and narrow. On the other hand, it is clear that the commercially available heavy calcium carbonate and light calcium carbonate have a wide particle size distribution, and the particle sizes vary.

[0020] The calcium carbonate of the present invention shown in FIG. 2 and commercially available heavy calcium carbonate and light calcium carbonate were measured by XRD (X'PertPro MPD, manufactured by Malvern Panalytical), and the results are shown in FIG. From these results, it is clear that the crystal system of the calcium carbonate and calcium bicarbonate of the present invention is calcite, while the precipitated calcium carbonate contains calcium hydroxide.

[0021] Preferably, the calcium carbonate for paint of the present invention has a color value measured by a color difference meter of L * is 95.0~99.9, a * The whiteness is excellent, with a being -1.0 to 1.0 and b* being -1.0 to 1.0. The whiteness of the calcium carbonate of the present invention (e.g., SOC-CR-001) and commercially available heavy calcium carbonate and light calcium carbonate was measured using a Konica Minolta colorimeter (CR-400 / 410). The state and results are shown in FIG. 4 and Table 1.

[0022] [Table 1]

[0023] Preferably, the calcium carbonate of the present invention can be blended as a hiding filler in various paints to obtain paints having high hiding properties. Examples of paints include various types of paints available on the market, such as acrylic paints, urethane paints, silicon paints, radical paints, fluorine paints, photocatalyst paints, and inorganic paints.

[0024] As an example, the calcium carbonate for paint of the present invention (shown as SOC-CR-001 in FIG. 5) was mixed with an aqueous acrylic emulsion (Lionbond A, manufactured by Sumitomo Osaka Cement Co., Ltd.) in a mass ratio of 5:6, and the mixture was mixed until it became uniform. In accordance with JIS 5600-4-1, a coating film was formed on a hiding rate test paper (a piece of paper with adjacent white and black parts printed and coated with varnish, which is easily wetted with paint diluted with solvent or water but does not penetrate) with the same thickness (the same thickness in the range of 50 to 100 μm) (FIG. 5). The tristimulus values ​​on the white and black parts of the hiding rate test paper were measured with a colorimeter (CR-400 / 410, manufactured by Konica Minolta) to determine the hiding rate. The results are shown in Table 2. For comparison, the same experiment was carried out except that the commercially available heavy calcium carbonate (special grade heavy carbon in FIG. 5) in FIG. 1 was used instead of the calcium carbonate of the present invention, and the results are also shown in Table 2 below.

[0025] [Table 2]

[0026] As another example, the calcium carbonate of the present invention (SOC-CR-002 in FIG. 6) was mixed with an aqueous acrylic emulsion (Lionbond A, manufactured by Sumitomo Osaka Cement Co., Ltd.) in a mass ratio of 7:6, and the mixture was mixed until it became uniform. In accordance with JIS5600-4-1, a coating film was formed on a hiding rate test paper (a piece of paper with adjacent white and black parts printed and coated with varnish, which is easily wetted with paint diluted with solvent or water but does not penetrate) with the same thickness (the same thickness in the range of 50 to 100 μm) (FIG. 6). The tristimulus values ​​on the white and black parts of the hiding rate test paper were measured with a colorimeter (CR-400 / 410, manufactured by Konica Minolta) to obtain the hiding rate. The results are shown in Table 3. For comparison, the same experiment was carried out except that the commercially available light calcium carbonate (light carbon (1) in FIG. 6) in FIG. 1 was used instead of the calcium carbonate of the present invention, and the results are also shown in Table 3 below.

[0027] [Table 3]

[0028] As can be seen from Fig. 4 and Table 1, the whiteness of the calcium carbonate of the present invention is superior to that of the compared heavy calcium carbonate and light calcium carbonate. Also, as can be seen from Fig. 5 and Table 2, and Fig. 6 and Table 3, the calcium carbonate for paint of the present invention blended into a paint has a higher hiding power than the cases in which heavy calcium carbonate or light calcium carbonate is blended into a paint.

[0029] In addition, when the state of the applied coating film in Fig. 6 is observed by an electron microscope photograph, it is in the state shown in Fig. 7, and in the coating film containing the calcium carbonate for paint of the present invention, the calcium carbonate particles are uniformly arranged in the coating film, and maintain high hiding power. On the other hand, in the coating film coated with the paint containing light calcium carbonate, the particle size of the calcium carbonate contained varies and is irregularly arranged. In addition, in the coating film in which another commercially available light calcium carbonate (light carbon (2): spherical calcium carbonate) was used instead of the light calcium carbonate (light carbon (1)), the gaps between the spherical particles (acrylic resin parts) were increased, as shown in FIG. 7. Therefore, the calcium carbonate for paint of the present invention has excellent hiding power when blended as a filler in a paint.

[0030] The above results for the calcium carbonate for coating of the present invention are summarized in Table 4 below.

[0031] [Table 4]

[0032] From these results, it is evident that the calcium carbonate of the present invention has a uniform cubic morphology, a sharp and narrow particle size distribution, and a high purity, and therefore has a high whiteness, and when used as a filler, it is a calcium carbonate that can have excellent hiding power.

[0033] An example of the method for preparing the calcium carbonate for coating of the present invention will be described below. The calcium carbonate for paint of the present invention having high hiding power can be produced by mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, adjusting the pH of the mixture to 11.5 to 13, and producing cubic calcium carbonate.

[0034] The aqueous solution containing calcium ions is not particularly limited as long as it is an aqueous solution containing calcium ions. For example, an aqueous solution containing calcium ions obtained by using calcium-containing waste and adding hydrochloric acid water to the calcium-containing waste to dissolve calcium can be exemplified.

[0035] An example of producing calcium carbonate of the present invention will be described with reference to, for example, Figs. FIGS. 8 and 9 show an example of a method for producing calcium carbonate for paint of the present invention, and are schematic diagrams illustrating a method for producing calcium carbonate for paint, comprising a step of mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, such as potassium carbonate and / or sodium carbonate, and adjusting the pH to 11.5 to 13, preferably 12 to 12.5, to prepare calcium carbonate for paint.

[0036] 8 shows an example of a method for producing calcium carbonate from calcium (Ca)-containing waste, and the method includes a calcium dissolving step of adding hydrochloric acid water to calcium-containing waste to dissolve calcium and produce an aqueous solution containing calcium ions. Preferably, the method then includes a separation step of adjusting the hydrogen ion concentration index of the aqueous solution containing calcium ions, and separating a component containing at least one selected from the group consisting of Si, Al, Mg, and heavy metals from the aqueous solution, and particularly for the Mg component, adjusting the pH to 11.5 to 12.5 to separate the component, and then mixing the aqueous solution containing calcium ions with an aqueous solution containing potassium carbonate and / or sodium carbonate to adjust the pH to 11.5 to 13, preferably 12 to 12.5, to prepare calcium carbonate. This is a schematic diagram illustrating an example of a method for producing calcium carbonate. In addition, in Figs. 8 and 9, double line arrows indicate the flow of solids, single line arrows indicate the flow of liquids, and dotted lines indicate the flow of gas.

[0037] The calcium material used to prepare the aqueous solution containing calcium ions is not particularly limited as long as it is a material containing calcium, and for example, calcium (Ca)-containing waste can be used. Examples of such waste include incineration ash from general waste and industrial waste, fly ash discharged from thermal power plants, slag, waste concrete, ready-mix concrete sludge, and bio-ash.

[0038] The particle size of the Ca-containing waste is adjusted to 1000 μm or less, more preferably 500 μm or less and 100 μm or more, which makes it easier to extract Ca.

[0039] In the Ca dissolution step, hydrochloric acid water is added to the Ca-containing waste whose particle size has been adjusted, and the hydrogen ion concentration index is preferably adjusted to a range of less than pH 2.5. In this case, washing water may be added as necessary. Washing is carried out in order to replace the liquid contained in the solids with clean water during solid-liquid separation. The reaction time required for extracting Ca from Ca-containing waste is 120 minutes or less, more preferably 30 minutes or more and 60 minutes or less. It is also possible to carry out dissolution extraction in multiple stages, particularly in a multi-stage countercurrent flow.

[0040] The temperature of the aqueous solution containing hydrochloric acid when extracting Ca is preferably room temperature or higher, and more preferably in the range of 20°C or higher and 70°C or lower.

[0041] In the Ca dissolution process, the residue is separated from the aqueous solution, and the residue can be used as a cement raw material, for example, in a cement manufacturing facility.

[0042] The aqueous solution containing Ca ions obtained in the Ca dissolution process contains impurity ions other than Ca, and in the separation process, the impurity ions can be separated by adjusting the hydrogen ion concentration exponent. The pH of the aqueous solution containing Ca ions obtained from the Ca dissolution step can be adjusted to, for example, pH 5 to 6 using sodium hydroxide or potassium hydroxide, thereby removing Si and Al ions contained in the aqueous solution containing Ca ions as hydroxides. If necessary, it is also possible to add washing water such as fresh water to wash the solid content. These gels can be used as cement raw materials.

[0043] Next, the pH of the Ca ion-containing aqueous solution after removing the Si and Al ions is adjusted to, for example, pH 7 to 10 using sodium hydroxide or potassium hydroxide, thereby separating heavy metals such as Pb and Cr ions derived from the calcium-containing waste. If necessary, cleaning water such as fresh water can be added, and the solid content is washed by such cleaning.

[0044] In addition, before removing heavy metals, it is possible to add a flocculant to the Ca ion-containing aqueous solution as necessary. For example, polymer flocculants or inorganic flocculants can be used. Inorganic flocculants include iron salts such as polyferric sulfate, and aluminum salts such as aluminum sulfate and polyaluminum chloride. Polymer flocculants can be anionic, nonionic, cationic, or other suitable ones depending on the pH and particle properties, and examples of such polymer flocculants include polyacrylamide, sodium polyacrylate, and polyacrylic ester.

[0045] Furthermore, by adjusting the pH of the Ca ion-containing aqueous solution from which the heavy metal ions have been removed to 11.5 to 12.5 using sodium hydroxide or potassium hydroxide, it becomes possible to remove the Mg ions contained in the aqueous solution derived from the calcium-containing waste as a gel. If necessary, it is also possible to add washing water such as fresh water, and the solid content is washed by such washing.

[0046] An aqueous solution containing potassium carbonate and / or sodium carbonate is added to the aqueous solution obtained by separating and removing the unnecessary impurities from the Ca ion-containing aqueous solution, and the pH of the mixed solution is adjusted to 11.5 to 13, preferably 12 to 12.5. As a result, high-purity cubic calcium carbonate is produced, and calcium carbonate is recovered by separating it into calcium carbonate and an aqueous solution of potassium chloride and / or sodium chloride. In fact, when the purity of calcium carbonate was calculated from the weight loss at 550°C to 800°C using a thermal analyzer (TG), a value of 95.7% was obtained.

[0047] This method can produce calcium carbonate that is free of impurities such as magnesium carbonate, has a high purity, is cubic, and has a uniform narrow particle size distribution, and the calcium carbonate thus obtained can be blended with various paints to produce paints with high hiding power. It can also be used as a filler for plastics, paper, etc., or as a cosmetic raw material, and can be applied to various fields where high hiding power is desired.

[0048] FIG. 9 is a schematic diagram of FIG. 8, incorporating the process of fixing carbon dioxide to produce alkali carbonate (K2CO3 / Na2CO3). The hydrochloric acid used in the Ca dissolution step as an example for preparing an aqueous solution containing calcium ions is not particularly limited as long as it is hydrochloric acid, but for example, hydrochloric acid produced by subjecting an aqueous solution containing potassium chloride and / or sodium chloride to a bipolar membrane electrodialysis (BMED) treatment (BMED treatment means) can also be used (not shown). As the potassium chloride and / or sodium chloride, an aqueous solution containing potassium chloride and / or sodium chloride produced in the calcium carbonate production step of FIG. 8 can also be used.

[0049] As shown in FIG. 9, carbon dioxide is brought into contact with an aqueous solution containing potassium hydroxide and / or sodium hydroxide to absorb the carbon dioxide, thereby producing an aqueous solution containing potassium carbonate and / or sodium carbonate. This aqueous solution containing potassium carbonate and / or sodium carbonate is applied to the calcium carbonate recovery step of FIG. 8 and used for producing calcium carbonate. The carbon dioxide used may be, for example, carbon dioxide contained in combustion exhaust gas from thermal power generation facilities or exhaust gas from cement manufacturing facilities. It is also possible to directly absorb carbon dioxide in the atmosphere and use it.

[0050] Moreover, in the above-mentioned example of the method for producing calcium carbonate of the present invention, the pH in the calcium carbonate production step was changed from pH 11.5 to 13 to pH 3, 6, and 9, respectively, and calcium carbonate obtained was observed under an electron microscope, and the results are shown in FIG. 10.

[0051] As can be seen from FIG. 10, when producing the calcium carbonate of the present invention, if the pH in the above steps is set outside the pH range of 11.5 to 13, the calcium carbonate prepared will have not only cubic calcite but also spherical vaterite, and therefore, in order to obtain the calcium carbonate of the present invention, the pH is preferably 11.5 to 13.

[0052] The calcium carbonate for paint of the present invention thus obtained can be blended into various paints available on the market. The blending method is not particularly limited as long as it can be uniformly mixed into the paint, and any known blending method can be applied, making it possible to produce a paint with high hiding power. [Industrial Applicability]

[0053] As described above, the calcium carbonate of the present invention has a narrow particle size distribution with little variation in particle size and a uniform cubic shape, and when blended as a filler in a paint, it has high hiding power and can be effectively used as a filler for various synthetic resin paints.

Claims

[Claim 1] Calcium carbonate for paints having high hiding power, characterized in that the average particle size (D50) of the particle size is 2 to 20 μm, the D10 of the particle size distribution is 1 to 13 μm, the D90 of the particle size distribution is 3 to 30 μm, and the calcium carbonate for paints has a cubic shape.

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