How to Prepare Microcellular Flexible Foam?

1. Applications of Microcellular Flexible Foam

Microcellular flexible foam refers to a type of polyurethane soft foam sheet with cell diameters ranging from 100–250 μm (ASTM D1622) and densities between 240–480 kg/m³. It differs significantly from microcellular PU elastomers (e.g., used in shoe soles or high-speed rail gaskets) in crosslinking structure and performance:

Chemical Structure: Lower crosslinking degree than elastomers (Asker C hardness < 50), with more flexible molecular chains.

Physical Properties: Compression set (ASTM D3574) ≤ 5%, resilience > 90%.

Typical Applications:

*Electronics: 5G base station seals (resistant to 120°C / IP68 rating), smartphone cushioning pads (thickness 0.3±0.05 mm)

*Medical: Catheter sealing rings (closed-cell rate > 95%, water vapor transmission rate < 0.01 g/(m²·24h))

2. Key Characteristics

High sealing performance, excellent energy absorption (shock buffering), dimensional stability, anti-compression set, water resistance, high-temperature resistance, aging resistance, and environmental safety.

3. Density and Specifications

The foam typically has a density of 240–480 kg/m³ and a pore size of 100–250 μm. Different applications require variations in density, thickness, hardness, and cell structure (open or closed).

*Closed-cell foams offer better sealing, waterproofing, and dust resistance.

*Open-cell foams have better elasticity and lower compression set.

*Thickness ranges from 0.1–6 mm, with multiple specification options available.

4. Materials and Formulation

(1) Hydroxyl Component Composition:

Polyester polyol: 16–30

Polyether polyol: 0–50

Polymer polyether polyol: 20–40

Low molecular polyol: 1.5–16

Surfactant (silicone oil): 0.1–1.0

Color paste (mainly black): 0.5–3.0

Antioxidant: 0.2–0.4

Solid fillers (e.g., silica, aluminum hydroxide): 0–20

Flame retardant: as required

Organometallic catalyst: appropriate amount

Organic amine catalyst: 0–0.5

The ratios of polyols vary depending on the specific product to meet performance demands by adjusting equivalence, molecular chain structure, and reactivity.

(2) Isocyanate Component Composition:

Modified MDI: 30–65

Liquefied MDI: 10–30

Crude MDI: 5–30

Isocyanate index: 1.06

Basic Forming Process:

This process differs from conventional water or physical blowing agents (e.g., dichloromethane). It adopts permanent gas injection foaming. A multi-component low-pressure machine pours the mixture onto release paper on a conveyor, levels it into uniform thickness, and cures it in a constant-temperature oven. The product is rolled up and post-cured.

5. Technical Highlights

*Proper selection of organometallic catalysts to control reaction speed.

*Strict temperature control is critical for stable product quality.

6. Post-Treatment of Microcellular Foam

Mainly uses glossy surface finishers, typically acrylic-based coatings.