Why Should Talc Powder Undergo Surface Coating

2020-10-07

Talc is a water-containing magnesium silicate mineral. It is one of the dominant minerals in China. It has good electrical insulation, heat resistance, chemical stability, lubricity, oil absorption, hiding power and mechanical processing properties. It is widely used in cosmetics, paint, papermaking, plastics, cables, ceramics, waterproof layer materials and other fields.

1. Why should talc powder undergo surface modification?

Like other non-metallic mineral powder materials, the surface organic treatment of talc is necessary. This is because the surface of talc powder contains hydrophilic groups and has high surface energy. As inorganic fillers and organic polymer molecular materials, there are great differences in chemical structure and physical form, lack of affinity, and need Surface treatment of talc particles is carried out to improve the interfacial bonding force between the talc powder and the polymer, and to improve the uniform dispersion and compatibility of the talc particles and the polymer.

In addition, when ultrafine talc is applied to coatings, due to its large surface area, more wetting dispersions are needed, which is difficult to disperse and affects the performance of coatings. Nowadays, some talcum powders with high oil absorption in latex paint, many manufacturers do not have or only carry out simple surface treatment, so its application is greatly restricted.

Surface modification treatment of talc powder can improve the interface affinity between talc powder and polymer, and improve the dispersion state of talc filler in the polymer base material, so that talc powder not only has an incremental effect in the composite material It can also enhance the modification effect, thereby improving the physical and mechanical properties of the composite material, so that the talc has a better application effect and a wider application field.

In terms of policies, the "Talc Industry Standard Conditions (2017 Edition)" issued by the Ministry of Industry and Information Technology clearly stated: encourage the use of talc powder surface modification technologies, and develop talc masterbatch, microporous ceramics, high-end coating talc powder and other high-added Value product.

2. What are the surface modification methods for talc powder?

The mechanism of surface modification of talc is to use some small molecules or polymer compounds with amphoteric groups to modify one or two of the compounded substances to make the surface change from hydrophobic to hydrophilic , The purpose is to make the two substances better combine.

(1) Surface coverage modification method

The surface coating modification method is to cover the surface of the particle with a surfactant or coupling agent, so that the surfactant or coupling agent is combined with the surface of the particle by adsorption or chemical bond, so that the surface of the particle changes from hydrophilic to hydrophobic, giving the particle The new properties improve the compatibility of particles and polymers.

This method is currently the most commonly used method. It can be roughly understood as: in view of the shortcoming of low affinity between talc and polymer, the surfactant with amphoteric group is covered on the particle, the hydrophilic group faces the surface of the particle, and the lipophilic group faces the outside. When combined, there is good compatibility to achieve the purpose of modification and expand the application range of talc.

For example: adding talcum powder modified by silane coupling agent can significantly improve the mechanical properties of the matrix. As the amount of talc and polypropylene increases, the bending performance of the material improves. When the content of polypropylene in the matrix is 50%, the resistance The tensile strength is basically not affected by filler content.

(2) Mechanochemical method

Mechanochemical method is to make larger particles smaller by crushing, friction and other methods, so that the surface activity of the particles is increased, that is, the surface adsorption capacity is enhanced, the process is simplified, the cost can be reduced, and the quality of the product is easier to control. . Superfine grinding is an important means of deep processing of materials, and its main purpose is to provide high-performance powder products for modern industries. This process is not a simple reduction of the particle size of the material, it includes many complex changes in the properties and structure of the powder material, and mechanochemical changes.

Yang Huaming et al. studied the changes of physicochemical properties during the ultrafine pulverization of talc and discussed the related mechanisms of the changes of physicochemical properties. Studies have shown that after talc powder is superfinely pulverized by agitation mill, the surface activity is enhanced, the thermal effect is improved, and the whiteness is improved. The change of powder properties is closely related to the thermodynamic characteristics of the superfine pulverization process.

(3) Modification method of outer membrane layer

The modification of the outer film layer is to coat a layer of polymer evenly on the surface of the particle, thereby giving the particle surface new properties.

Zuo Jianhua and others used TDI (toluene diisocyanate) and HPA to surface treatment of inorganic particle talc. Compared with conventional talc particle fillers, the maximum tensile strength of coated talc filled with polymer materials was The impact strength is significantly improved, and the improvement rate reaches 136% and 162% respectively. It can be used as a new type of strong and tough filling modifier for PVC cable materials.

(4) Local activity modification

Local activity modification uses chemical reactions to graft some groups or functional groups compatible with polymers on the surface of particles, so that inorganic particles and polymers have better compatibility, so as to achieve the purpose of inorganic particles and polymers. .

(5) High-energy surface modification

High-energy surface modification is to use the huge energy generated by high-energy discharge, plasma rays, ultraviolet rays, etc. to modify the surface of particles to make the surface active and improve the compatibility of particles and polymers.

(6) Modification of precipitation reaction

Precipitation reaction modification uses precipitation reaction for modification. This method is to use the precipitation effect to coat the surface of the particles to achieve the effect of modification.

With the gradual deepening of people's understanding of the properties of talc, the application of talc in coatings, plastics and other industries will continue to expand. Since the production capacity of modified high-grade talc powder is far less than the demand of domestic and foreign markets, the reasonable modification of talc powder has been paid more and more attention. Therefore, while we are familiar with the various physical and chemical properties of talc powder and its application characteristics in various industries, we should continue to summarize in experiments and production applications, continue to explore and innovate, and use current high-tech methods to expand the deep processing of low- and medium-grade products and develop high-end products. Value-added talc products.

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