Choose surface modifier, mainly look at these 3 aspects!
Modifiers are the key to achieve the intended purpose of powder surface modification, but there are many types and strong pertinence. From the point of view of the interaction between the surface modifier molecules and the surface of the inorganic powder, the surface modifier that can chemically react or chemically adsorb with the surface of the powder particles should be selected as much as possible, because the physical adsorption is strong in the subsequent application process. Easy to desorb under stirring or squeezing.
However, other factors must also be considered in the actual selection, such as product use, product quality standards or requirements, modification process, cost, environmental protection, etc.
Selection factor 1: The purpose of the product
This is the most important consideration in selecting the variety of surface modifiers, because different application fields have different technical requirements for powder application properties, such as surface wettability, dispersibility, pH value, electrical properties, weather resistance, gloss, antibacterial properties This is one of the reasons for selecting the variety of surface modifiers according to the application.
Inorganic powders (fillers or pigments) used for various plastics, rubbers, adhesives, oil-based or solvent-based coatings, requiring good surface lipophilicity, that is, good affinity or compatibility with organic polymer binders, This requires the selection of surface modifiers that can make the surface of inorganic powder hydrophobic and lipophilic;
When choosing the calcined kaolin as filler for cable insulation, the influence of surface modifier on dielectric properties and volume resistivity should also be considered;
For inorganic pigments used in ceramic blanks, it is not only required to have good dispersibility in dry state, but also to have good affinity with inorganic blanks and to be able to disperse uniformly in the blanks;
For surface modifiers of inorganic powders (fillers or pigments) used in water-based paints or coatings, it is required that the modified powders have good dispersibility, sedimentation stability and compatibility in the water phase.
At the same time, the components of different application systems are different, and the compatibility and compatibility with the application system components must also be considered when selecting the surface modifier, so as to avoid the failure of the functions of other components in the system due to the surface modifier.
Selection factor two: modification process
The modification process is also one of the important considerations in selecting the variety of surface modifiers. The current surface modification process mainly adopts dry method and wet method.
For the dry process, it is not necessary to consider its water solubility; but for the wet process, the water solubility of the surface modifier should be considered, because only water-soluble can fully contact and react with powder particles in a wet environment.
For example, stearic acid can be used for dry surface modification of calcium carbonate powder (either directly or after being dissolved in an organic solvent), but in wet surface modification, such as adding stearic acid directly, it is not only difficult to achieve The expected surface modification effect (mainly physical adsorption), and the utilization rate is low, the surface modifier is seriously lost after filtration, and the organic matter discharge in the filtrate exceeds the standard.
A similar situation exists for other types of organic surface modifiers. Therefore, for surface modifiers that cannot be directly water-soluble but must be used in a wet environment, they must be saponified, ammonium or emulsified in advance so that they can be dissolved and dispersed in an aqueous solution.
In addition, the selection of surface modifier varieties should also consider the application process factors, such as temperature, pressure and environmental factors. All organic surface modifiers will decompose at a certain temperature. For example, the boiling point of silane coupling agent varies between 100-310 °C depending on the variety. Therefore, the decomposition temperature or boiling point of the selected surface modifier is preferably higher than the processing temperature at the time of application.
Choice factor three: price and environmental factors
Finally, the selection of surface modifiers should also consider price and environmental factors. On the premise of meeting application performance requirements or application performance optimization, try to use cheaper surface modifiers to reduce the cost of surface modification. At the same time, attention should be paid to the selection of surface modifiers that do not pollute the environment.