What Are The Applications Of Semi-rigid Polyurethane Foam In Other Automotive Components?

Automotive linings can use special thermoformable polyurethane foam boards. Compared with traditional materials, this foam has unique characteristics due to its special linear molecular structure combined with some hard segments, giving it partial thermoplastic properties. As shown in the shear modulus chart, this material's thermal performance can be compared with typical rigid polyurethane foam. "Thermoplastic" foam can be thermoformed or vacuum-formed, while still maintaining high thermal stability.

These foam boards are either cut from block foam or produced using lamination machines, with widths up to 1.3 meters, thicknesses of 10–40 mm, and densities between 50–80 kg/m³. Combined with soft foam or fiberglass fabric, they serve as surface layers on both sides of the car body. These materials may also be used together for specialized reinforcement applications.

The finished products are manufactured using semi-automatic or fully automatic equipment. The foam boards are fed into a multi-layer heater and heated to a molding temperature of about 200°C. After heating, they are placed in molds between the press plates of a molding machine. The molding pressure is below 0.5 MPa.

Demolding time depends on the product’s thickness, density, thermal stability, and geometry—especially on the heat transfer properties of the mold. For example, molding a 100 mm thick product from a 20 mm thick, 50 kg/m³ board takes about 40 seconds.

Thermoformed components should include decorative surfaces for use as linings. These decorative layers can be applied either before or after forming. Before forming, thermoplastic films, high-temperature-resistant fabrics (films, fabrics, or polyethylene gel coatings) are used; after forming, films, fabrics, or flocks are applied. For cost efficiency (saving materials, easy decoration changes, and fine surfaces), in-process lamination is preferred. For large-deformation materials, decorative layers must be held in the mold using vacuum. Sometimes, thermoforming is required using special devices or the mold itself before pressing. These decorative thermoplastic films or fabrics are bonded with hot-melt adhesives.

Thermoplastic PU foam is mainly used for car headliners. Due to its lightweight nature, design flexibility, decorative surface, simple and fast installation using inlay methods instead of adhesives, thermal stability below 110°C, and improved interior safety, it meets the requirements of the automotive industry.

Another structure involves spraying rigid polyurethane foam onto the car roof and laminating it with a PVC-PU soft foam composite film. The film has micro-perforations less than 1 mm in diameter, serving as sound-absorbing headliner material. The insulation and soundproofing performance of side wall panels can be enhanced by on-site spraying of rigid polyurethane foam. Rigid PU foam can also be used to seal cavities between automotive components. Integral-skin PU rigid foam is used in interior trim, such as brackets, door panels, and headliners. Structural rigid polyurethane foam is suitable for rear cover plates.

Flexible polyurethane foam is used in automotive filters. It can also partially replace microporous PU elastomers for lightweight and energy-absorbing parts, such as bumpers. Other major PU applications in cars include sun visors, sleeves, bushings, spring seats, lock parts, dust covers, and engine insulation components.

Semi-rigid polyurethane foam is particularly effective in absorbing and dispersing impact energy. This foam has high compressive hardness, with 50% compression hardness ranging from 300–600 kPa. It is used to make bumpers with a thickness of 7–10 cm, mounted on certain chassis components and encapsulated with soft integral-skin PU foam or thermoplastic film. These lightweight impact-absorbing components, with a foam density of 100–140 kg/m³, can withstand impacts at speeds around 8 km/h without permanent deformation and recover to their original shape. SRIM (Structural RIM) materials can be used to produce large parts such as floor bases and body panels.