What Is Polyurethane Foam for Packaging?

1. What Is Polyurethane Foam for Packaging？

Polyurethane foam for packaging, also known as ultra-low-density polyurethane foam, typically refers to PU foam with a density lower than 10 kg/m³ used in packaging applications. Its characteristics include:

*Extremely low density, less than 1/100 of water's density

*Certain mechanical strength, with minimal compression deformation

*Good resilience after impact or vibration

*Mold-resistant and moisture-proof

*Convenient to use, simple to shape, safe and hygienic

*Low cost with minimal packaging expense

2. Technical Route and Formulation

Given the characteristics of polyurethane for packaging, the materials are applied on-site and must offer cushioning and recovery functions.

For polyether selection, high reactivity and high molecular weight types are preferred.

Polymeric MDI is the main isocyanate used. Mixed physical blowing agents are typically selected.

Catalysts are primarily tertiary amine-based. Due to the high water content in the formulation, metal catalysts are not suitable. Different formulations require adjustments in catalyst type and dosage.

Foam stabilizers must:

Be stable in the presence of large amounts of water and resist hydrolysis

Ensure open-cell structure for reduced shrinkage

Sample Formulation:

*High-activity, high molecular weight polyether polyol (Mn 5000): 90 parts

*Crosslinker: 10 parts

*Water: 6 parts

*Catalyst: 0.8 parts

*Dichloromethane: 30 parts

*Foam stabilizer Q5307: 2.0 parts

*Polymeric isocyanate (NCO content 30.5%): 121 parts

Foaming Process Conditions:

*Cream time: 7 s

*Rise time: 20 s

*Tack-free time: 70 s

*Cell structure: Open-cell

*Foam density: 9.7 kg/m³

Effect of Raw Material Ratio and Temperature:

3. Influencing Factors:

Multiple factors affect the synthesis and physical properties of ultra-low-density polyurethane foam for packaging, including raw material composition, process conditions, and component storage stability.

(1) Effect of Raw Materials:

Polyether is one of the main raw materials for foam synthesis. It affects miscibility, uniformity, viscosity, and foam mechanical properties.

Low molecular weight polyether results in brittle foam.

Low-reactivity, high molecular weight polyether has poor miscibility with water, slows curing, and increases foam density.

Thus, high-reactivity, high molecular weight polyether (PO-EO copolyether) is required to enhance reactivity and reduce solubility.

(2) Effect of Catalysts:

While general PU catalysts are usable, the special characteristics of polyether systems and the high water content make standard catalysts like T9 or T12 unsuitable.

Strong base amine catalysts such as A33 or A1 cause high closed-cell content, shrinkage, and degrade during storage.

Moderately active tertiary amine catalysts like PC-8, DMEA, and methyldiethanolamine ether are preferred.

Catalysts significantly influence foaming and cell structure. Dosage and type must be adjusted per formulation.