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Experience in improving the gloss of barium sulfate applications
- 2019-09-25-

Coating industry:


The gloss of the coating refers to the ability of the surface of the coating to reflect the rays of the projected light. The stronger the reflection, the greater the gloss. The main reason for the glossiness of the barium sulfate powder material after film formation is its particle size and dispersibility. If the particle size of the barium sulfate powder itself is very fine and can be evenly dispersed in the coating, the coating film will be flat. , As dense as a mirror, the gloss will be very obvious; on the contrary, the particle size of barium sulfate is too coarse and the uniformity is poor, the surface of the coating is rough, the gloss will be reduced and the hue will be dull.


Gloss is an important performance index of ink, which has a great impact on the appearance quality of printed parts. The traditional precipitated barium sulfate (Glauber's salt method), not only has poor dispersion, but also has low gloss, which cannot be applied to the formulation system of ink. A better barium sulfate material is actually added to the ink formulation in the form of a concentrated slurry. The amount of barium sulfate added is 20% to 70% by weight of the total slurry. The average particle size of the nano-sized barium sulfate powder material is 10nm ~ 1μm. In ink production, different types of ink products have different quality requirements for barium sulfate materials. In addition, in the ink preparation process, it is necessary to select barium sulfate with different properties according to the specific characteristics and requirements of various inks.


1. Evaluation method of gloss


One method is to make a coating film of dry barium sulfate and a standard sample to make a contrast gloss analysis: the barium sulfate sample is evenly dispersed in the alkyd resin by sanding, and is formed on an aluminum plate under the control of automatic spraying equipment Wet film coating with uniform film thickness and surface characteristics, then baked. Then use Hunterlab D-48-7 gloss meter to measure 20 ° reflectance, and calculate the gloss ratio to the standard sample. The other system is mixed with Synocyl 9122X resin to make a 40% barium sulfate volume concentration water-based acrylic paint. It is automatically coated with a 100-micron wire rod to form a film. It is dried in a dust-free cabinet for at least 5 hours and measured with GlossgardⅡ gloss 20. ° Gloss.


In China, barium sulfate powder material is usually mixed with refined linseed oil on a flat mill to grind it to make a paste, and then the film is coated on a glass plate with an automatic wet film preparation device for measurement. Although the gloss of the evaluation coating is not completely objective, the visual grading made by different observers usually has a reasonable correlation.


2. Technology Status of Improving Application Luster of Barium Sulfate Powder Materials Abroad


High-gloss barium sulfate powder materials are usually coated with one or more metal oxides on the surface, such as silica, alumina, or other components. They are incorporated on the surface of the barium sulfate particles by neutralization to promote oxidation or co-precipitation. The added amount is 0.5 wt% to 3 wt% of the total barium sulfate. The organic surface coating is coated with carboxylic acid, silane, siloxane, hydrocarbon wax, and products that react with the surface of the barium sulfate crystal particles, and the added amount is 0.5 wt% to 1.5 wt% of the total barium sulfate. Commercial products on the market such as Gemme Micron, single aluminum coated products B-35, silicon aluminum coated B-30, B-34 and other types of barium sulfate products coated with silicone surface. The basic B-30 has long occupied the high-end ink market in China.


2.1 Technology for improving the gloss of barium sulfate


Anyi discloses a method for preparing a high-gloss, high-weather-resistant surface-treated barium sulfate. The surface of the product is coated with porous alumina and dense alumina. The total mass concentration of alumina is (2 to 6)% of BaSO4. The mass ratio of dense alumina and boehmite alumina is 8: 1 to 1: 2, and the mass ratio of dense alumina to sulfate ion is 10: 1 to 1.3: 1. Dense alumina is a type of alumina containing sulfate ions, where sulfate ions are adsorbed in the alumina, and the mass ratio of alumina and sulfate ions is 10: 1 to 1.3: 1. At (30-65) ° C and pH value (5.2-6.5), alumina is contacted with sulfate ions for a period of time to make the alumina dense. Boehmite is a crystalline form of alumina and contains adsorbed water. Moisture is inserted into the Al (OH) 6 octahedron layer in two ways, random and regular. The surface of BaSO4 crystal is coated with dense alumina to improve its durability such as light resistance and powdering resistance. Coating a thin layer of gibbsite alumina on the surface of BaSO4 crystals has improved its gloss and dispersibility.


Anyi has another method for preparing barium sulfate with improved gloss and weather resistance surface treatment: barium sulfate is treated with various metal salts, such as 1.0% to 3.0% Al2O3 aluminum, zirconium, and phosphorus compounds. At least one metal salt can provide a Valent anion. According to the conditions of wet treatment, the general addition amount of aluminum compound is 1.0% to 3.0% Al2O3; according to the titanium dioxide surface deposition, the addition amount of zirconium compound is 0.1% to 0.4% ZrO2; the addition amount of phosphorus compound is 0.1% to 0.5% P2O5 ; Organic coating 0.2% ~ 0.4% of TMP, TME or pentaerythritol. It has been found that polyvalent anions in soluble metal salts, such as SO42-, will adhere to the surface of barium sulfate crystals during ion exchange during coating. These polyvalent anions will not be removed by conventional water washing, resulting in flocculation, reducing the dispersion and whiteness of the final product. Degree, gloss and weather resistance. And monovalent anion-containing metal salts will effectively reduce this tendency and possibility.


Anyi prepares barium sulfate powder materials with improved gloss and weather resistance by strictly controlling the pH, temperature, and silicon and aluminum addition time of barium sulfate slurry: at 75 ° C, pH = 10.0, pH = 9.4, pH = 4.9 Add silicon compound separately, stay at least 10 ~ 20min for each step; add aluminum compound under the condition of pH = 5.5 ~ 7.5, 75 ℃. The addition amount of silicon oxide is 2.5% to 3.5% by weight of BaSO4, and the addition amount of alumina is 1.6% to 1.9% by weight of BaSO4. Organically coated 0.2% to 0.8% TMP. The silicon and aluminum deposition time is 10 to 45 minutes, and the entire continuous process includes a residence time not exceeding 120 minutes. The surface treatment barium sulfate has excellent gloss advantages, and has good compatibility in paints, inks and coatings. The tinting strength and Hegman data show that the barium sulfate prepared by this method has good dispersibility and does not appear to agglomerate when used in paints and inks.


2.2 Technology for improving gloss and dispersibility of barium sulfate


At least one monoamine salt is deposited on the surface of Anyi's treated barium sulfate, and the prepared barium sulfate material has significantly improved application gloss and dispersibility. The amine salt can be dimethylolpropionate DMPA + triisopropanolamine TIPA, DMPA + TIPA + TME, DMPA + TIPA + TMP, dimethylolbutyric acid DMBA + TIPA, DMBA + TIPA + TME, DMPA + TIPA + One of the TMP combinations. The molar ratio of DMPA or DMBA to TIPA is 1: 1 to 1: 1.1, so the neutral salt produced does not have excess alkanolamine. The ratio of amine salt to TME or TMP is 95: 5 to 1: 1. The addition amount of the amine salt is 0.2 wt% to 0.5 wt% of the mass of titanium dioxide. Compared with untreated barium sulfate and barium sulfate treated solely with TME or other amine salts, the surface treated barium sulfate prepared by this method has a significant improvement in dispersibility and gloss, especially when it is used in Water-based coatings can significantly reduce the amount of dispersant, which is also its great advantage.


3. The status of other technologies to improve the gloss of barium sulfate applications


Anyi uses aluminum oxide to coat barium sulfate powder to improve the gloss and dispersibility of its oily system. A basic aluminum compound and an acidic aluminum compound aqueous solution are sequentially added, and the total amount is 1 wt% to 4 wt% of the volume weight of barium sulfate in the suspension. The aluminum element in the basic aluminum compound aqueous solution and the aluminum element in the acidic aluminum compound aqueous solution are added in total. The ratio of the added amount is 1: 1 to 1: 3. This method can be used to treat barium sulfate slurry made in any form, and each step can be performed batchwise or continuously.