Introduction

About Haze and Light Transmittance

First, it’s important to clarify that the RIM process primarily uses opaque polyurethane (PU) resin. Its core application is in the manufacture of strong, lightweight structural parts and housings, such as medical device cases and automobile bumpers, rather than optical lenses or transparent covers.

Therefore, we generally don’t discuss the “haze” and “light transmittance” of RIM materials, as the process is not designed for transparent parts.

RIM’s Core Advantage: Excellent Surface Quality

The RIM process’s greatest cosmetic advantage lies in its ability to produce a high-quality surface. Because RIM uses precision aluminum alloy molds with double-sided sealing, both the interior and exterior surfaces of the parts achieve a perfectly smooth, flat, Class-A surface finish. This means that after removal from the mold, the parts require little to no additional sanding or leveling and can proceed directly to post-processing.

Common Appearance Finishing Methods

Painting
Painting is the most common and valuable finish for RIM parts. Because of its excellent original surface quality and excellent paint adhesion, it easily creates a uniform, detailed, and high-quality finish, perfectly capturing the color and gloss desired by product designers.

In-Mold Painting
This is a more advanced RIM-exclusive technology. Before injecting the PU liquid raw material, a special paint is sprayed onto the inner wall of the mold. Once the PU material is injected and cures, the paint chemically bonds with the part surface, forming a single component. The paint finish achieved through in-mold painting boasts adhesion and abrasion resistance far exceeding traditional post-painting, achieving automotive-grade durability.

Conclusion

In summary, the strength of RIM in appearance lies not in optical clarity, but in its ability to deliver unparalleled Class-A surface quality when producing large parts. This high-quality surface makes it an excellent substrate for painting, easily achieving sophisticated and durable finishes. It is an ideal solution for achieving both aesthetics and performance when manufacturing high-end equipment and instrument housings.