How To Use Surface Modifiers

2023-02-02

Some customers have determined the type of powder surface modifier through multi-screening, but in the actual production process, the modification effect is not very satisfactory, which is often related to the use method of the surface modifier.

The use of surface modifiers mainly includes: dosage, preparation, dispersion, addition method and dosing sequence when using more than two surface modifiers.

(1) The amount of surface modifier

In theory, the amount needed to achieve monomolecular layer adsorption on the particle surface is the optimal amount, which is related to the specific surface area of the powder raw material and the cross-sectional area of the surface modifier molecule, but this amount is not necessarily 100% coverage The amount of the surface modifier, the actual optimal amount should be determined by the modification test and the application performance test, this is because the amount of the surface modifier is not only related to the dispersion and coating uniformity of the surface modifier during surface modification It is also related to the specific requirements of the application system on the surface properties and technical indicators of the powder raw materials.

For wet modification, the actual coating amount of the surface modifier on the surface of the powder is not necessarily equal to the amount of the surface modifier, because there is always a part of the surface modifier that fails to interact with the powder particles and is eliminated during filtration. lost. Therefore, the actual amount used is greater than the amount required to achieve monolayer adsorption.

When carrying out chemical coating modification, there is a certain corresponding relationship between the amount of surface modifier and the coating rate. Generally speaking, at the beginning, with the increase of the amount, the surface coating amount of the powder increases rapidly, but then The growth trend slows down, and after a certain amount is used, the surface coating amount will no longer increase. Therefore, it is unnecessary to use an excessive amount, which increases the production cost from an economic point of view.

(2) Preparation method of surface modifier

Different surface modifiers require different preparation methods. For example, for some silane coupling agents, silanols are used to bond with the powder surface. Therefore, it is best to achieve a good modification effect (chemisorption). Hydrolysis was performed before addition.

For other organic surface modifiers that need to be diluted and dissolved before use, such as titanate, aluminate, stearic acid, etc., corresponding organic solvents should be used, such as absolute ethanol, isopropanol, glycerin, toluene, ether, Dilute and dissolve with acetone, etc.

For organic surface modifiers such as stearic acid, titanate and aluminate used in the wet modification process that cannot be directly dissolved in water, they must be saponified, ammonized or emulsified into water-soluble modifiers in advance. product.

(3) Adding method of surface modifier

The best way to add the surface modifier is to make the surface modifier contact with the powder evenly and fully, so as to achieve high dispersion of the surface modifier and uniform coating of the surface modifier on the particle surface. Therefore, it is best to use the continuous spray or drop (addition) method linked with the powder feeding speed. Of course, only the continuous powder surface modification machine can achieve continuous addition of surface modifiers.

4) Dosing sequence of surface modifiers

Due to the inhomogeneity of the powder surface, especially the surface properties of inorganic fillers or pigments, sometimes the mixed use of surface modifiers is better than the use of a single surface modifier. For example, the joint use of titanate coupling agent and stearic acid to modify the surface of calcium carbonate can not only improve the surface treatment effect, but also reduce the amount of titanate coupling agent and reduce production costs.

However, when two or more surface modifiers are selected to treat powder, the order of dosing has certain influence on the final surface modification effect.

When determining the order of adding surface modifiers, it is first necessary to analyze the respective functions of the two surface modifiers and the mode of interaction with the powder surface (either physical adsorption or chemical adsorption). Generally speaking, the main role and chemical adsorption-based surface modifiers are added first, and then the secondary role and physical adsorption-based surface modifiers are added, but it is finally determined by application tests.