How to Produce Integral Skin Polyurethane Foam?

1. Formula Selection

Formulation must be tailored to the raw materials used and the end-use of the products. Below are examples of three different semi-rigid integral skin foam formulations:

For high abrasion, chemical, and weather resistance, use high molecular weight, low OH-value polyether. Combine with low molecular chain extenders (e.g., EG, 1,4-BG) and use polymer polyol to increase hardness if crosslinker content is low.

Elastic or Soft Integral Skin Foam Formulas and Properties:

2. Production Process

Steps:
Metering → Mixing → Molding → Covering → Venting → Clamping → Post-curing → Demolding → Trimming → Finished Product → Mold Cleaning → Mold Release Spraying

Details:
Weigh components A and B accurately. Pour B into A while stirring rapidly, then inject into preheated mold. Close mold, allow gas to escape, compress mold, cure at 60–80°C for several minutes, demold, trim, and obtain final product. Clean and recoat mold before next use.

In mechanical foaming, the procedure is similar but more automated with higher efficiency and frequency.

3. Advantages of Integral Skin PU Foam Production

Low investment: One foaming machine can fill many molds, even manual foaming is efficient and economical.

Compact workshop: Less space and equipment required, high efficiency, low pollution.

Aesthetic products: Colorful and complex-shaped products are feasible.

Compared to injection or compression molding: Lower pressure and energy, reduced mold cost.

4. Mold Requirements

Material:
High-volume production requires steel molds (up to 10,000+ pieces). Aluminum molds are suitable for <10,000 pieces. Avoid epoxy and silicone molds due to poor thermal conductivity and short lifespan.

Shrinkage:
Shrinkage of integral skin foam is <0.5%, which should be accounted for in mold design.

Venting Holes:
Must be placed at the highest point of the mold for proper gas release. Improper placement causes surface pores.

Mold Wall Thickness:
Keep below 20 mm; slightly thicker for mechanical foaming to accommodate metal inserts. Avoid mold damage.

5. Mold Release Agents

Two types are available: glossy and matte. Choose based on product requirements. Many manufacturers prepare their own silicone-based release agents for cost savings.

Important: Wait for solvent to fully evaporate before pouring foam to avoid surface defects. Periodically clean mold to remove buildup and restore texture clarity. Flame treatment can be used to remove residual release agent.

6. Factors Affecting Foam Properties

Polyether Polyol:
Lower molecular weight improves mechanical properties, though excessive crosslink molecular weight reduces tensile and tear strength but raises flex modulus.

Polymer Polyol:
Increases compression load, tensile and tear strength when content rises.

Mold Temperature:
Higher temperatures → thicker skin; lower temperatures → thinner skin. Optimal range: 40–60°C.

Blowing Agent:
Higher content increases skin thickness. Increased mold charge raises mold pressure, enhancing skin density and thickness.

Isocyanate:
A key raw material that significantly affects performance; its selection is addressed in the formulas.

7. Troubleshooting Abnormal Phenomena

8. Sample Integral Skin Foam Formulas

Formula 1

Formula 2

Formula 3

Formula 4