Low Pressure Molding (LPM) with polyamide and polyolefin (hot-melt) materials

Key to this process are the raw materials and specialized molding equipment. Dimer acid based polyamide materials, better known as hot-melts, are used as molding compounds. They are thermoplastics i.e. the material, when heated, becomes less viscous and is able to re-shaped, then hardens to keep the desired form upon cooling down. These polyamide materials differ from other thermoplastics in two main areas: One: Viscosity: At processing temperature (410F/210C) the viscosity is very low, typically around 3,000 centipoise (similar to pancake syrup). Low viscosity materials require low injection pressure in order to inject into a cavity. In fact it is normal to use a simple gear pump to inject the polyamide material. Low injection pressure is paramount, when over-molding relatively fragile electronic component. Two: Adhesion: Polyamide materials are basically high performance hot-melt adhesives. The adhesive properties of polyamide is what seals a chosen substrate. The type of adhesion is purely mechanical i.e. no chemical reaction takes place.