Quartz powder, silicon micropowder and other forms of silica powder used for plastics, rubber and other resins, in order to make the surface compatible with the polymer base material, so as to improve the overall performance and processability of the filling material To be improved and improved, it must be surface treated.
The pulverized quartz powder or other silica powder may appear Si-OH (silanol group), Si-O-Si (silicon ether group) and Si-OH under the action of water and air… Functional groups such as O (surface-adsorbed free water). Therefore, it is easy to accept foreign functional groups, such as amino, epoxy, methacrylic, trimethyl, methyl and vinyl organic functional groups of silane, which lays a solid foundation for the surface modification of silica powder. Base.
1. Modification principle
The surface chemical modification of quartz powder, silica powder or other silica powder mainly uses silane coupling agents, including various silane coupling agents such as amino, epoxy, methacryl, trimethyl, methyl and vinyl. joint agent.
The principle of silane coupling agent modified quartz powder: The -RO functional group of silane coupling agent can be hydrolyzed in water (including free water adsorbed on the surface of the filler) to generate silanol groups, which can be chemically combined with SiO2 or combined with SiO2. The original silyl ether alcohol groups on the surface are integrated into a homogeneous system. In this way, it not only removes the water on the surface of SiO2, but also forms a silicon ether bond with the oxygen atom in it, so that the other end of the silane coupling agent carries the organic functional group-R with good affinity with the polymer. ‘Firmly cover the surface of quartz or silica particles to form a reactive coating.
The organic functional group-R’ and macromolecular materials such as epoxy resin have good affinity, which can reduce the surface energy of quartz or silica powder, improve the wettability with polymer binder, and improve the powder Compatibility with polymeric binders. Furthermore, the formation of this new interfacial layer can improve the rheological properties of the filled composite system.
2. Influencing factors
The main factors that affect the surface treatment effect of quartz powder and other silica powders are: the variety, dosage, use method and treatment time, temperature, pH value of silane coupling agent.
Since the organofunctional group -R’ of silane is selective for materials such as polymers or resins, the type of resin to be filled with quartz powder should be considered when selecting a silane coupling agent.
The dosage of the silane coupling agent can be determined according to the specific surface area of the quartz or silica powder, and the optimum dosage can also be determined according to the experiment.
3. Surface modification process
The wet process is to use appropriate diluents and additives to mix with silane coupling agent to prepare a treatment solution, and to heat and react or soak quartz powder or silica powder in a stirring reaction kettle or reaction tank, and then remove moisture.
When preparing amorphous silica powder by chemical precipitation, wet surface treatment is often used.
The dry process is to add a small amount of diluent and silane to form a treatment agent. Under the condition that the quartz powder is stirred and dispersed at a high speed and heated, the prepared silane treatment agent is sprayed in a mist form, and the material is discharged after a certain time of reaction. It needs to be dehydrated and dried again, and the process is simple.
The dry-wet combination process is to first mix the acidified aqueous solution (deionized water is used when the electrical performance is very high) and an appropriate amount of coupling agent in a strong stirring device to prepare a treatment solution with a certain concentration, and feed according to the quartz powder. Add 8%-10% of the amount to the treatment solution, then mix and grind for 1 hour in a small ball mill with corundum balls or silica balls as the grinding body, and dry the materials at 110 °C, and finally sieve and classify.
In the treatment process, the amount of water added and the mixing time have a great influence on the treatment effect. If the amount of water added is too large, the powder is easy to agglomerate, and the mixing and grinding time is long, which will increase the phenomenon of powder re-grinding and bring in impurities; if the amount of water added is too small, it is not conducive to the full dispersion of the coupling agent and the interaction with the quartz powder. Uniform action.
Meanwhile, the pH of the solution directly controls the degree of hydrolysis of the coupling agent. The powder quartz modified by this method has been tested in resin cement, resin anti-corrosion coating, resin powder coating and PVC artificial leather, and the effect is good.