How to Choose and Use Fillers?

(1) How Plastic Manufacturers Choose Fillers
Fillers are an important type of additive, generally in powder form and inert to polymers. Because there are many types, the following points should be noted when selecting fillers:

1. Do not reduce the processing performance of the product
   Resin undergoes plasticizing and injection molding; after adding fillers, these processes should be facilitated rather than hindered.
2. Ideally, enhance certain properties of the resin
   If fillers can improve or strengthen specific properties of the resin, the quality of the plastic products will be higher.
3. Good dispersibility
   After adding fillers, they should quickly blend and disperse uniformly with the resin and other components, ensuring consistent plasticity and uniform quality of the molded parts.
4. Have good heat resistance and corrosion resistance
   injection molding involves a heating and melting process at temperatures reaching 200–300°C. Fillers should remain stable under these conditions and resist corrosion from other materials.
5. Do not reduce the effectiveness of other additives
   Each plastic product requires several additives, each with its own specific function. The addition of fillers should not diminish these special functions.
6. Fillers should be added as much as possible without affecting the overall plastic performance to reduce the amount of expensive resin used
   Additionally, fillers themselves should be inexpensive to help reduce the overall cost of the plastic.

(2) How to Use Fillers
When producing Plastic Products with fillers, important issues include what type of filler to add and how much to add. Improper filling can cause defects in manufacturing processes, color, physical properties, tactile feel, etc., and can also adversely affect production equipment.
The quality of fillers primarily depends on the surface condition of the filler. Resin is an organic macromolecule, while filler is an inorganic small molecule. A strong bond between them requires a bridging connection. The more uneven the surface of filler particles, the more micropores they have, and the greater their specific surface area, the stronger the bond with the resin will be. A common method to achieve this is mechanical grinding of the filler, which not only improves the filler’s surface structure but also alters its chemical structure. During grinding, mechanical forces create new surfaces as the regular bonding of surface atoms is disrupted, resulting in localized surface charges or free radicals.
In addition to mechanical grinding, coupling agents can be added. These multifunctional substances act as excellent bridging agents; one end has groups that interact with the polymer, while the other end has groups that interact with inorganic filler molecules. The presence of coupling agents thus effectively binds the filler and resin together.
Furthermore, filler surface modifiers can be added. These increase the affinity between filler and resin, enhance adhesion, and improve flow properties. Common types of filler surface modifiers include higher fatty acids and their esters, phenol amines, metal salts, higher alcohols, and alkanoic acids.
With these treatments, the bonding force between filler and resin is greatly improved, and the quality of the final products is significantly enhanced.