How Acrylic Processing Aids Improve Quality in Rigid PVC Injection Molding

PVC injection compounds have diverse applications, spanning from appliance components to electrical enclosures and the construction industry. The manufacturing of injection-molded products faces challenges in effectively managing both long-flow and compact channels, achieving proper mold filling, and producing intricate shapes—all while adhering to stringent standards for physical properties, appearance, and, ultimately, cost. The three key factors that can impact the quality of injection-molded products, including fittings, are:

 A meticulously formulated PVC compound is crucial for achieving optimum processability and seamless melting in injection molding. Certain additives, particularly processing aids, can assist in resolving issues associated with inexperienced or worn-out machinery.

Low Levels, High Impact:

Acrylic processing aids primarily consist of polymethyl methacrylates (PMMA) but occasionally include copolymers with styrene. The molecular weight or viscosity is often regarded as a crucial parameter for specific application requirements. (Nevertheless, it is more prudent to consider the length of the polymer chain rather than the molecular weight.) Despite their concentration, typically ranging from 0.5 to 2.0 phr, acrylic processing aids markedly improve processability. Their influence extends across various aspects, including:

• Accelerating the fusion/gelation: Their longer chain (than the chain length of PVC) increases physical entanglements which is crucial for PVC fusion. Here’s how processing aids contribute to PVC fusion:

The longer chain of processing aid (in the Figure above) creates numerous entanglements (depicted as yellow dots), forming a stronger network of PVC.

• Influencing melt flow in molds: Acrylic processing aids’ chains enhance melt elasticity, thereby influencing the reduction of welding line, jetting and gate blushes. In other words, they make compound flow smoother and more consistent. Another outstanding aspect of it is glossier surfaces.
• Reducing adhesion to metal surfaces: Some grades of processing aids are specially designed to improve the lubricating effect. These are the copolymers with styrene. While both traditional external lubricants and lubricating processing aids contribute to metal release in rigid PVC injection molding, the key distinction lies in their molecular weight and the associated impact on potential deposit formation, plate-out, and equipment cleaning requirements. As a result, lubricating processing aids optimise the metal release and the downtimes.

“Processing aids not only have a significant effect on quality and process enhancement but also reduce the cost of production by minimizing reworks and cleaning times.”

Understanding the specific functions and benefits of processing aids is crucial during raw material selection. The correlation between function and molecular weight of processing aids is summarized in the provided table.

Baumann offers a well-balanced one-pack stabilizer for fittings, along with exceptional processing aids promoting fusion, enhancing compound elasticity, and avoiding the flow marks. Contact us to eliminate product defects and enhance quality—our experts are ready to assist you, regardless of location!