Polyurethane Flexible Foam Molded Foaming Process

The molded foaming process involves metering pumps dispensing various liquid materials according to the formula proportions. These materials are mixed uniformly through a mixing head and injected into a mold in a measured quantity. Inside the mold, the materials react and foam. After curing, the molded foam product is removed.

Compared with block foaming, molded foaming eliminates the need for post-cutting processes, minimizes edge trimming waste, increases labor productivity, supports automation, and lowers manufacturing costs. This method is particularly suitable for large-scale production of complex-structured products, making it a rapidly developing technology in recent years. The production flow of the molded foaming process is shown in the diagram below.

Schematic of the Molded Foaming Process for Polyurethane Foam Plastics

The formulation principles for the molded foaming process are roughly similar to those for block foaming. However, for polyether-based molded foams, highly active polyether polyols (with a higher primary hydroxyl content) are predominantly used. These polyols shorten molding and curing times and result in foam products with higher compressive load values. While bifunctional polyether enhances tensile strength and elongation properties of the foam, its slower curing and solidification rates mean it is rarely used alone. If required, it can be mixed with polyethers with higher functionality. Currently, most polyethers used for flexible foam plastics are trifunctional polyethers.

When compared to block foaming formulations, producing molded foam products with a density of less than 32 kg/m³ requires slightly higher amounts of silicone-based foam stabilizers or higher-performance stabilizers to enhance foam stability.

Below is an example of a foaming formulation for a polyether-based thermally cured molded flexible polyurethane foam plastic:

• Polyether polyol/polymer polyether polyol: 100
• Crosslinking agent: 1.0–3.0
• Water: 2.3–5.0
• Amine catalyst: 0.4–0.5
• Silicone surfactant: 1.0–1.5
• TDI 80/20 index: 90–110