There are many types of auxiliary materials for molding plastics, mainly consisting of fillers, reinforcing materials, curing systems, and various functional additives. The matching of auxiliary materials for different resin systems of molding materials can vary greatly. Below, we will explain the common types separately.

Common auxiliary materials classified by function

Filler: The core function is to reduce costs and improve performance. Common ones include calcium carbonate, aluminum hydroxide, talc powder, silica micro powder, wood powder, mica, etc. For example, BMC (bulk molding compound) commonly uses calcium carbonate, and epoxy molding compound (EMC) commonly uses silicon micro powder. ‌‌

Reinforcement material: mainly enhances mechanical strength. The most typical is glass fiber, with a content of 10% -30% in BMC and a length of 3-25mm; some formulations may also use silicate fibers, etc. ‌‌

Curing system: the key to crosslinking thermosetting resin into a network. Phenolic resin is used as a curing agent in epoxy molding compounds, followed by the addition of accelerators; BMC contains peroxide initiators (catalysts). ‌‌

Lubricants/Release Agents: Improve processing fluidity and demolding effect. Commonly used stearic acid and its metal soaps (zinc, calcium, etc.), polyethylene wax, ethylene bis stearamide (EBS), etc., with a dosage generally around 0.5% -1%. ‌‌

Plasticizers: Enhance flexibility and processability. For example, phthalates are commonly used in soft PVC systems, but are less commonly used in many thermosetting molding compounds. ‌‌

Flame retardant: Make the product reach a flame retardant level, such as UL94 V-0. Common types include filler type flame retardants such as aluminum hydroxide, as well as specialized flame retardant additives. ‌‌

Coloring agent (pigment): Adjusting the color of the product. BMC has 75 colors to choose from, and pigments are added during the mixing stage. ‌‌

Other functional additives:

Low shrinkage/low profile additives: control the shrinkage rate of BMC and SMC molding

Coupling agents: such as aluminum ester coupling agents, improve the interface bonding between fillers and resins

Inhibitors/Stabilizers: Control curing speed and extend storage life

Antistatic agents, foaming agents, etc.: added according to special requirements