1. The role of filling materials
Add fillers such as calcium carbonate, clay, aluminum hydroxide, glass flakes, glass microbeads, and lithopone to polyester resin and disperse them to create a resin mixture. Its function is as follows:
(1) Reduce the cost of FRP materials (such as calcium carbonate and clay);
(2) Reduce the curing shrinkage rate to prevent cracks and deformation caused by shrinkage (such as calcium carbonate, quartz powder, glass microspheres, etc.);
(3) Improve resin viscosity during molding and prevent resin dripping. However, it should be noted that excessive increase in viscosity can sometimes become a disadvantage;
(4) Non transparency of formed products (such as calcium carbonate and clay);
(5) Whitening of formed products (such as barium sulfate and lithopone);
(6) Improve the corrosion resistance of formed products (mica, glass sheets, etc.);
(7) Improve the flame resistance of formed products (aluminum hydroxide, antimony trioxide, chlorinated paraffin);
(8) Improve the hardness and stiffness of formed products (such as calcium carbonate, glass microspheres, etc.);
(9) Improve the strength of formed products (glass powder, potassium titanate fibers, etc.);
(10) Improve the lightweight and insulation properties of molded products (various microspheres);
(11) Provide or increase the thixotropy of resin mixtures (such as ultrafine anhydrous silica, glass powder, etc.).
It can be seen that the purpose of adding fillers to resins is diverse, so it is important to choose suitable fillers according to different purposes to fully utilize the role of fillers.
2. Precautions for the selection and use of fillers
There are various types of fillers. Therefore, it is necessary to choose the appropriate filler brand and grade for the purpose of use, which goes without saying. The general precautions when selecting fillers are not only to choose the variety with predetermined cost and performance, but also to pay attention to the following points:
(1) The amount of resin absorbed should be moderate. The amount of resin absorbed has a significant impact on the viscosity of resin mixtures.
(2) The viscosity of the resin mixture should be suitable for the molding operation. Several adjustments to the viscosity of resin mixtures can be made by diluting with styrene, but adding too many fillers and diluting with styrene will lead to a decrease in FRP performance. The viscosity of resin mixtures is sometimes significantly affected by the mixing amount, mixing conditions, or the addition of filler surface modifiers.
(3) The curing characteristics of the resin mixture should be suitable for the molding conditions. The curing characteristics of resin mixtures are sometimes influenced by the filler itself or the adsorbed or mixed moisture and foreign substances in the filler.
(4) The resin mixture should remain stable for a certain period of time. For the phenomenon of settling and separation of fillers due to standing still, it may sometimes be prevented by endowing the resin with thixotropy. Sometimes, the method of avoiding static and continuous mechanical stirring is also used to prevent the settlement of fillers, but in this case, it is necessary to consider preventing the settlement and accumulation of fillers in the pipeline from the container containing the mixer to the forming site. When certain microbead fillers are prone to upward separation, it is necessary to reconfirm the grade.
(5) The permeability of the resin mixture should be suitable for the operator's technical level. The addition of fillers generally reduces the transparency of the resin mixture and also reduces the ductility of the resin during layering. Therefore, the impregnation, defoaming operation, and judgment during molding have become difficult. These factors should be considered to determine the ratio of the resin mixture.
(6) Attention should be paid to the specific gravity of the resin mixture. When using fillers as incremental materials to reduce material costs, the specific gravity of the resin mixture increases compared to the resin, sometimes not meeting the expected value of intuitively reducing material costs.
(7) The surface modification effect of fillers should be explored. Filler surface modifiers are effective in reducing the viscosity of resin mixtures, and different surface modifiers can sometimes improve mechanical strength in addition to water resistance, weather resistance, and chemical resistance. There are also types of fillers that have undergone surface treatment, and some use the so-called "whole mixing method" to modify the surface of fillers. That is, when mixing resin mixtures, the fillers and modifiers are added together to the resin, sometimes the effect is very good.
(8) The defoaming in the resin mixture should be thoroughly carried out. Fillers are often used in the form of micro powders and particles, with a very large specific surface area. At the same time, there are also many parts where micro powders and particles aggregate with each other. In order to disperse these fillers into the resin, the resin needs to undergo intense stirring, and air is drawn into the mixture. In addition, air is also drawn into the large volume of fillers. As a result, an unimaginable amount of air was mixed into the prepared resin mixture, and in this state, the FRP obtained by supplying it for molding is prone to producing bubbles and voids, sometimes failing to achieve the expected performance. When it is not possible to fully defoaming solely by standing still after mixing, silk bag filtration or pressure reduction can be used to remove bubbles.
In addition to the above points, dust prevention measures should also be taken in the working environment when using fillers. Substances such as ultrafine particulate silica composed of free silica, alumina, diatomaceous earth, frozen stones, etc. are classified as Class I dust, while calcium carbonate, glass powder, glass flakes, mica, etc. are classified as Class II dust. There are also regulations on the controlled concentration of various micro powders in the environmental atmosphere. Local exhaust devices must be installed and labor protection equipment must be strictly used when handling such powdered fillers.
Post time: Feb-18-2024
