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Experience in improving the gloss of barium sulfate application
- 2020-06-23-

Experience in improving the gloss of barium sulfate application

Paint industry:

The gloss of the coating refers to the reflection ability of the surface of the coating to the light of the projected light. The stronger the reflection ability, the greater the gloss. The main factors affecting the gloss of barium sulfate powder material after film formation are its particle size and dispersion performance. If the particle size of barium sulfate powder itself is very fine and can be evenly dispersed into the coating, the coating film will be smooth , Dense as a mirror, the gloss will be very obvious; on the contrary, the particle size of barium sulfate is too thick and the uniformity is poor, the coating surface is rough, the gloss will be reduced and the color tone will be dark.

Gloss is an important performance index of ink, and it has a great influence on the appearance quality of printed parts. The traditional precipitated barium sulfate (glauber's salt method) not only has poor dispersibility, but also has low gloss, which cannot be applied to ink formulation systems. A better barium sulfate material is actually added to the ink formulation in the form of a concentrated slurry. The addition amount of barium sulfate is 20wt% to 70wt% 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, barium sulfate with different properties should be selected according to the specific characteristics and requirements of various inks.

1. Evaluation method of gloss

One method is to make dry-based barium sulfate and standard samples into a coating film to compare gloss analysis: barium sulfate samples are uniformly dispersed in alkyd resin by sanding, and formed on aluminum plates under the control of automatic spraying equipment Wet film coating with uniform film thickness and surface characteristics, and then baked into shape. Then use Hunterlab D-48-7 gloss meter to measure the 20° reflectivity, and calculate the gloss ratio with the standard sample. Another system is to mix with Synocyl 9122X resin to make 40% barium sulfate volume concentration water-based acrylic paint, use 100 micron wire rod to automatically coat the film, put it in a dust-free cabinet and dry for at least 5 hours, then use Glossgard II gloss meter to measure 20 °Glossiness.

Domestically, barium sulfate powder material and refined linseed oil are mixed and ground on a flat grinder to make a slurry, and then coated on a glass plate with an automatic wet film preparation device for measurement. Although it is not completely objective to evaluate the gloss of coatings, the visual grading made by different observers usually has a reasonable correlation.

2. The status quo of foreign technology to improve the application gloss of barium sulfate powder materials

High-gloss barium sulfate powder materials are usually coated on the surface of one or more layers of metal oxides, such as silica, alumina or other components, which are incorporated and wrapped on the surface of the barium sulfate particles by neutralizing oxidation or co-precipitation. The addition amount is 0.5wt% to 3wt% of the total barium sulfate. The organic surface coating is coated with carboxylic acid, silane, siloxane, hydrocarbon wax, and the product reacted 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 product B-35, silicon aluminum coated B-30, B-34 and other types of barium sulfate products coated with silicone surface. Among them, the basic B-30 has long occupied my country's high-end ink market.

2.1 Technology to improve the gloss of barium sulfate

Gemme Corp discloses a method for preparing barium sulfate with high gloss and high weather resistance. The surface of the product is coated with porous alumina and dense alumina. The total mass concentration of alumina is (2-6)% 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 kind of alumina containing sulfate ions, in which the sulfate ions are adsorbed in the alumina, and the mass ratio of alumina to sulfate ions is 10:1 to 1.3:1. At (30-65)°C and pH (5.2-6.5), the alumina is contacted and reacted with sulfate ions for a period of time, thereby densifying the alumina. Boehmite is a crystalline form of alumina that contains adsorbed water. Moisture is inserted into the Al(OH)6 octahedral layer in two ways: random and regular. The surface of BaSO4 crystal is coated with dense alumina to improve durability such as light resistance and powdering resistance. The coating of boehmite alumina layer on the surface of BaSO4 crystal improves its gloss and dispersion.

Gemme Corp. Another method for preparing barium sulfate with improved gloss and weather resistance: barium sulfate and a variety of metal salts, such as 1.0% to 3.0% Al2O3 aluminum, zirconium, and phosphorus compounds. At least one metal salt can provide one Valence anion. According to the wet treatment conditions, the general addition amount of aluminum compound is 1.0%~3.0%Al2O3; according to the surface deposition of titanium dioxide, the addition amount of zirconium compound is 0.1%~0.4%ZrO2; the addition amount of phosphorus compound is 0.1%~0.5%P2O5 ; Organic coating 0.2%~0.4% TMP, TME or pentaerythritol. It has been found that the polyvalent anions in soluble metal salts, such as SO42-, will adhere to the barium sulfate crystal surface during the ion exchange process during coating. Conventional water washing cannot remove these polyvalent anions and cause flocculation, reducing dispersion and whiteness of the final product. Degree, gloss and weather resistance. The metal salt containing monovalent anions will effectively reduce this tendency and possibility.

Gemme Corp strictly controls the pH, temperature, silicon and aluminum addition time of the barium sulfate slurry to prepare barium sulfate powder material with improved gloss and weatherability surface treatment: at 75℃, pH=10.0, pH=9.4, pH= 4.9 Add silicon compound separately, stay at least 10-20min in each step; pH=5.5-7.5, add aluminum compound at 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. After organic coating 0.2%~0.8% TMP. The deposition time of silicon and aluminum is 10 to 45 minutes, and the entire continuous process including the residence time does not exceed 120 minutes. The surface treatment barium sulfate has excellent gloss advantages, and at the same time has good compatibility in paints, inks and coatings. Coloring power and Hegman data show that the barium sulfate prepared by this method has good dispersibility and will not agglomerate when used in paints and inks.

2.2 Technology to improve the gloss and dispersion of barium sulfate

Gemme Corp has deposited at least one monoamine salt treatment on the surface of the treated barium sulfate, and the prepared barium sulfate material has significantly improved gloss and dispersibility. Amine salt can be dimethylolpropionic acid DMPA+triisopropanolamine TIPA, DMPA+TIPA+TME, DMPA+TIPA+TMP , DMBA+TIPA, DMBA+TIPA+TME, DMPA+TIPA+TMP. The molar ratio of DMPA or DMBA to TIPA is 1:1 to 1:1.1, so that the neutral salt produced does not have excessive alkanolamine. The ratio of amine salt to TME or TMP is 95:5 to 1:1. The addition amount of the amine salt is 0.2wt% to 0.5wt% of the titanium dioxide mass. Compared with untreated barium sulfate and barium sulfate treated 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 Water-based paint can significantly reduce the amount of dispersant, which is also its big advantage.

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

Gemme Corp uses aluminum oxide to coat barium sulfate powder to improve the gloss and dispersion of its oily system applications. Add alkaline aluminum compound and acidic aluminum compound aqueous solution in sequence, the total amount is 1wt%~4wt% of the volume weight of barium sulfate in the suspension, wherein the aluminum element in the alkaline aluminum compound aqueous solution is the same as the aluminum element in the acid aluminum compound aqueous solution The ratio of addition amount is 1:1~1:3. The method can be used to treat barium sulfate slurry prepared in any form, and each step can be performed batchwise or continuously.