The principle of all-water foaming is:
Water reacts with polyisocyanates to form CO2, and C02 remains in the cells as a foaming agent for foams.
The ODP value of the system is zero, non-toxic, environmentally friendly, simple process, no special requirements for equipment, and low cost, which is an important route for CFC-11 replacement.
All-water foamed PU rigid foam can be used for non-thermal insulation purposes, such as high-density structural foam (imitation wood), packaging materials, filling materials, etc., as well as a few thermal insulation materials with low thermal insulation requirements, such as sprayed thermal insulation rigid foam, metal veneer sandwich panels;It is used for pipe insulation, building materials;Automotive interior materials, water heater insulation, etc.
In conventional foaming systems, the physical blowing agent has a solvent dilution effect;It can greatly reduce the viscosity of foam materials, which is conducive to the mixing of various components, and high-viscosity polyether polyols can be used.
And the all-water foaming systemNo physical blowing agent is addedPolyether polyols with low viscosity and good miscibility with water and additives must be used. In the preparation of low-density rigid foam, due to the large water consumption, the foam is brittle, the strength, dimensional stability, and thermal insulation performance are poor, and the polyisocyanate is consumed more.
The high thermal conductivity of foams is a major disadvantage of all-water foaming technology. The thermal conductivity of C02 is as high as 16 at 253mw/m.K, which is higher than CFC-11 and other alternatives. C02 gas molecules are small and easy to escape through the wall of the polyurethane rigid foam, resulting in a decrease in the pressure inside the pores and the air slowly penetrating into the pores. Whereas, the thermal conductivity of air is 27mwm?k。
Therefore, the all-water foamed polyurethane rigid foamPoor thermal insulationIt cannot be used in situations where high thermal insulation performance is required. To achieve the same thermal insulation, the thickness of the foam in the CO2 foam system must be increased by more than 30%.
In addition, C02 diffuses outward from the foam pores 1.1 faster than air enters the foam pores0 times, in order to prevent foam shrinkage, the density of polyurethane must also be increased, and the cost is therefore greatly increased. However, after formula improvement, the density of hard foam can be appropriately reduced.