JP3373063B2 - Surface-treated calcium carbonate for water-based paint - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment for water-based paints, wherein the surface of calcium carbonate is treated with barium sulfate and the surface is further treated with a surfactant. It is about calcium carbonate. More specifically, it solves the problem that the surface gloss is insufficient with calcium carbonate alone, and also solves the problem that the specific gravity is too large and barium sulfate alone must be blended in a large amount, resulting in an increase in weight and cost. The present invention relates to barium sulfate for water-based paint and surfactant-coated calcium carbonate having surface gloss, lightness and low cost. [0002] In general, there are roughly two types of methods for producing calcium carbonate. One is called heavy calcium carbonate, which is obtained by mechanically pulverizing and classifying rough limestone to obtain a desired particle size. There is the other one, co-firing limestone raw stone with coke, etc. to make calcium oxide (quicklime), react it with water to make calcium hydroxide (slaked lime),
It reacts with carbon dioxide gas generated during firing,
Precipitated calcium carbonate called light calcium carbonate or colloidal calcium carbonate in the form of particles. [0003] These calcium carbonates are surface-treated as they are or, if necessary, for the purpose of improving dispersibility and imparting high functionality, are treated with an organic surface treating agent represented by resin acids and fatty acids to form paper, It is used in many industrial fields, including paints. In the field of paints,
Calcium carbonate is used as a partial substitute for titanium oxide used for the purpose of imparting concealing properties, and for the purpose of improving the viscosity of paints. However, when calcium carbonate is used in an aqueous paint, sufficient surface gloss can be obtained. There is a problem that can not be. [0004] On the other hand, barium sulfate is also roughly classified into two types of production methods. One method is to grind a barite raw material called barite.
This is a method of classifying to a desired particle size, and the other is a precipitated barium sulfate obtained by adding sulfate ions to an aqueous solution containing barium ions and reacting in the solution. Barium sulfate obtained by any of these production methods is referred to as invariant white because it has excellent acid resistance and alkali resistance and does not deteriorate with time, and is used in many fields such as papermaking and paints. However, barium sulfate has a specific gravity of 4.
3 to 4.4, which is high and cannot be used in the field of weight reduction. For example, in a paint, in order to increase the thickness of a dry coating film, a large amount must be blended in comparison with calcium carbonate or the like. This is disadvantageous in terms of cost. SUMMARY OF THE INVENTION The present invention solves the problems of calcium carbonate and barium sulfate in the field of water-based coatings as described above, and has a sufficient surface gloss, light weight and low cost. It is intended to provide a surface-treated calcium carbonate for water-based paint which can satisfy the following. [0008] That is, the present invention is characterized in that the surface of calcium carbonate is coated with barium sulfate, and the surface of barium sulfate is further coated with a surfactant. It contains surface-treated calcium carbonate for water-based paints. Although the reason why the surface gloss is improved when the surface-treated calcium carbonate of the present invention is used in an aqueous paint is not necessarily clear, the charge state of the particle surface can be obtained by coating the calcium carbonate surface with barium sulfate. Changes to improve the compatibility with water, and the surface is in a state of surface charge that is more easily dispersed. By further coating the surface with a surfactant, the compatibility with water is further improved, and the dispersion is improved. It is presumed that sex is further enhanced. [0010] The calcium carbonate used in the present invention may be either heavy calcium carbonate or precipitated calcium carbonate, but preferably has good dispersibility. As an index indicating the good dispersion of calcium carbonate, a ratio D ₂₅ / ₂₅ % by weight of particle size D ₂₅ obtained by a particle size distribution measured by a particle size distribution measuring method described below to a ratio of D ₂₅ / ₇₅ % by weight of particle size D _75.
D ₇₅ (dispersion index A).
The larger the value of the dispersion index A, the poorer the dispersibility. Therefore, the calcium carbonate preferably used in the present invention preferably has a dispersion index A of 5 or less, more preferably 3 or less. However, even if calcium carbonate having good dispersibility is used, in the case of coarse particles as a whole, the surface area is small, so that the adsorption power of the surface is weak, and it may be difficult to perform surface treatment of barium sulfate on the calcium carbonate surface. . Therefore, it is desirable that the 50% by weight particle size D ₅₀ obtained from the particle size distribution is 5 μm or less. The concentration of calcium carbonate in an aqueous suspension is 5-6.
A range of 0% by weight is preferred. Small particles of D _50, that is, the case of small particles having an average particle diameter becomes difficult to obtain a uniform suspension becomes high too liquid concentration, is necessary to set the concentration such that the appropriate liquid viscosity is there. As a guide, a Brookfield viscosity of 60 rpm and 2000
cps or less is appropriate. The water-soluble barium compound used in the present invention can be used without any problem as long as it can be dissolved in water at normal temperature. However, barium chloride and barium hydroxide are easily available and advantageous in cost. And the like. The concentration of the water-soluble barium compound to be dissolved is not particularly limited, but is not so high as to be sufficiently dispersed in the calcium carbonate suspension and to allow the reaction with the sulfate compound added later to proceed uniformly on the calcium carbonate surface. It is preferably, for example, 20% by weight or less. The water-soluble sulfate compound to be added can be used without any problem as long as it can be dissolved in water at room temperature. However, like the barium compound, sulfuric acid or sodium sulfate is used from the viewpoint of delivery and cost. Is advantageous. Also, the dissolution concentration is not particularly limited, but when sulfuric acid or the like is used, it is preferable to add it at a low concentration because it may react with calcium carbonate in the suspension before reacting with the barium compound. The amount of the barium compound and the amount of the sulfuric acid compound added to the calcium carbonate are defined as the coating amount of barium sulfate obtained by the reaction of the two, and
The amount is preferably in the range of 0.5 to 100 parts by weight with respect to 0 parts by weight. Therefore, it is preferable to add the barium compound and the sulfate compound so that the barium sulfate amount falls within the above range. If the coating amount as barium sulfate is less than 0.5 parts by weight, the surface of calcium carbonate cannot be completely treated and sufficient gloss cannot be exhibited, while if it exceeds 100 parts by weight, the surface of calcium carbonate The reaction proceeds not only in a completely different part but also in a completely different part, and disadvantages are caused by the production of barium sulfate alone, and it is disadvantageous in terms of cost because the effect corresponding to the large amount cannot be expected to increase. Since the reaction between the barium compound and the sulfuric acid compound proceeds promptly after the addition of the sulfuric acid compound, it is preferable to gradually add the sulfuric acid compound over a long period of time rather than in a short time in a large amount. After the addition of the sulfate compound, dehydration is performed according to a conventional method, followed by washing with water for the purpose of removing a free salt generated by the reaction between the barium compound and the sulfate compound outside the system, and drying and powdering, so that barium sulfate is used. A powder of surface-treated calcium carbonate is obtained. The particle size distribution of calcium carbonate described in the text is measured by the following method. Measurement model: Centrifugal sedimentation light transmission type particle size distribution analyzer SA-CP-2 type (Shimadzu Corporation) Dispersion solvent: 0.2% by weight of sodium hexametaphosphate Dispersion method: Calcium carbonate has a predetermined concentration (usually 2) % By weight) and dispersed by a shaker for 10 minutes. The surfactants used in the present invention may be used alone or in combination of two or more. As the surfactant, for example, at least one kind selected from acrylic acid, methacrylic acid, crotonic acid, etc., at least one kind selected from α, β unsaturated monocarboxylic acid, maleic acid, itaconic acid, fumaric acid, etc. , An alkali metal of a polymer and a copolymer of β-unsaturated dicarboxylic acid, ammonium, a salt of an amine, and the like, and a monomer having copolymerizability with these,
For example, (a) alkyl acrylate and alkyl methacrylate, (b) acrylate and methacrylate having an alkoxy group, (c) acrylate and methacrylate having a cyclohexyl group, (d)
α, β monoethylenically unsaturated hydroxy ester,
(E) polyalkylene glycol monoacrylate and monomethacrylate, (f) vinyl ester, (g) vinyl aromatic, (h) unsaturated nitrile, (i) unsaturated dicarboxylic acid ester, (j) vinyl ether, (k) Examples thereof include salts of conjugated dienes, chain olefins, and copolymers with cyclic olefins, such as alkali metals, ammonium, and amines. Particularly, a surfactant such as polyacrylic acid and a copolymer thereof is preferable. The coating amount of the surfactant was 0.05% with respect to 100 parts by weight of barium sulfate-coated calcium carbonate.
A range of from 10 to 10 parts by weight is preferred. If the amount is less than 0.05 part by weight, the effect of coating with the surfactant becomes insufficient, and even if the surface treatment exceeds 10 parts by weight, the effect corresponding to the increase in the amount of coating cannot be expected, which is disadvantageous in cost. The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which do not limit the present invention in any way. Example 1 D ₂₅ / D ₇₅ = 2.05, D ₅₀ = obtained by the sedimentation method
15% by weight containing 2 kg of 0.40 precipitated calcium carbonate
The slurry was prepared. While stirring the slurry with TK Lab Disper (specialized machine) at 1500 rpm, reagent B
_{a (OH) 2 · 8H 2} O 405.4g of an aqueous solution dissolved in 1 liter of water was added, and after stirring for 10 min, H ₂ SO ₄ 12
An aqueous solution in which 6.0 g was dissolved in 1 liter of water was gradually added, and the mixture was stirred for 30 minutes after completion of the addition. 2 parts by weight of an ammonium salt obtained by copolymerizing 100 parts by weight of acrylic acid with 100 parts by weight of methacrylic acid methyl ester and 100 parts by weight of acrylic acid per 100 parts by weight of the obtained barium sulfate surface-treated calcium carbonate slurry After the surface treatment, the powder was dried and pulverized to obtain a barium sulfate surface-treated calcium carbonate coated with a surfactant. Comparative Example 1 2 kg of heavy calcium carbonate super # 2000 (trade name, manufactured by Maruo Calcium Co., Ltd.) having D ₂₅ / D ₇₅ = 2.89 and D ₅₀ = 1.57 has a solid content of 20% by weight. Was dispersed in water using a stirrer to prepare a slurry. This slurry is used for TK Lab Disper (specialized) 1500rp
The reagent BaCl ₂ .2H ₂ O 209.7 with stirring
g was dissolved in 1 liter of water, and the mixture was stirred for 10 minutes. Then, an aqueous solution of 122.0 g of reagent Na ₂ SO ₄ dissolved in 1 liter of water was gradually added, and the mixture was stirred for 30 minutes after the addition was completed. . After the treatment-completed slurry is dehydrated by Nutsche, the dehydrated cake is re-suspended in 10 liters of water, washed with water, dehydrated again, dried and powdered to obtain about 2 kg of barium sulfate surface-treated calcium carbonate powder. I got The surface coating amount of barium sulfate was 10 parts by weight based on 100 parts by weight of calcium carbonate. Comparative Example 2 D ₂₅ / D ₇₅ obtained by the sedimentation method = 2.05, D ₅₀ =
15% by weight containing 2 kg of 0.40 precipitated calcium carbonate
The slurry was prepared. An aqueous solution containing 126.0g added as an aqueous solution and H ₂ SO ₄ containing 405.4g as _{Ba (OH) 2 · 8H 2} O in the same manner as in Comparative Example 1 into the slurry, dehydration and
After washing with water, the powder was dried and powdered to obtain about 2.2 kg of barium sulfate surface-treated calcium carbonate powder.
The surface coating amount of barium sulfate was 15 parts by weight based on 100 parts by weight of calcium carbonate. Comparative Example 3 Heavy Calcium Carbonate Super # 20 Used in Comparative Example 1
00 was used as is. Comparative Example 4 The calcium carbonate slurry used in Comparative Example 2 was dewatered, dried and powdered without surface treatment with barium sulfate to obtain about 2 kg of untreated calcium carbonate powder. Comparative Example 5 Sedimentary barium sulfate # 100 (Sakai Chemical) was used as a comparative product. Application Example 1, Comparative Application Examples 1 to 5 Using the samples obtained in Example 1 and Comparative Examples 1 to 5 as described above, an emulsion paint was prepared with the following composition,
The surface gloss was measured. Table 1 shows the measurement results. Mixing: (Emulsion paint blended) Water 8.4% by weight sodium hexametaphosphate (10% solution) 0.1 〃 Discoat N-14 (Daiichi Kogyo Seiyaku) 1.2 エ チ レ ン Ethylene glycol 1.2 ノ Nopco 8034L ( San Nopco) 1.0 {Titanium oxide R-930 (Ishihara Sangyo) 7.0} Samples according to Examples and Comparative Examples (surface-treated calcium carbonate) 16.0 {Boncoat EC884 (Dainippon Ink) 58.0} Butyl cellosolve 3. 5 ＣＳ CS-12 (Chisso) 3.5 〃 Adecanol UH420 (Asahi Denka Kogyo) 2.3 〃 As described above, the present invention, when used in water-based paints, imparts appropriate paint viscosity and hiding power, and has a high gloss on the paint surface which cannot be obtained with conventional calcium carbonate. And also achieves the purpose of weight reduction because it does not have a high specific gravity unlike barium sulfate, and its usefulness is extremely large.

Claims (1)

(57) [Claim 1] A water-based paint characterized in that the surface of calcium carbonate is coated with barium sulfate, and the surface of barium sulfate is further coated with a surfactant. For surface treated calcium carbonate.