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Polyurethane rigid foam

MAY. 15, 2020

Polyurethane is the best thermal insulation and energy-saving material at present, and each performance index is superior to the traditional XPS and EPS external thermal insulation system. This kind of external insulation system technology has been paid attention to by the relevant leaders and experts of various provinces and cities. The science and Technology Department of the Ministry of construction has established the polyurethane building energy saving application promotion working group, and held the "international exchange meeting on polyurethane wall energy saving application technology" in Beijing in mid of October 2005. Nearly 100 representatives from the energy saving wall reform office and design and development units of the science and technology Department (Construction Committee) of the construction department (Construction Committee) of all provinces, cities, autonomous regions and municipalities directly under the central government attended the meeting. Dr. David Evans, an international expert in building energy conservation, told reporters that polyurethane material is the best thermal insulation material in the world at present. Rigid polyurethane plastic has excellent properties such as light weight, low thermal conductivity, good heat resistance, aging resistance, easy to bond with other materials, no droplet produced by combustion and so on. About 49% of the thermal insulation materials in Europe, America and other developed countries are polyurethane materials, while the proportion in China is less than 10%. Therefore, the Ministry of construction will promote polyurethane materials as a substitute of traditional thermal insulation materials from this year.


Advantages of polyurethane rigid foam external insulation system technology


1. Polyurethane rigid foam


Polyurethane rigid foam is referred to as rigid polyurethane foam, or PU. It is made of isocyanate and polymer polyol, which are pressurized and heated by a special two-component foaming machine, transported to the spray gun through equipment pipeline for high-speed mixing, and then sprayed on the surface of thermal insulation object with compressed air to form a hard foam instantly.


2. Polyurethane rigid foam performance:


1) Strong adhesion: it can be bonded firmly on the surface of concrete, wood, steel, asphalt, rubber, etc;


2) Good thermal insulation: the thermal conductivity can reach 0.017-0.022w/m.k, and the thickness of each centimeter is equivalent to the insulation effect of 40cm red brick;


3) Good waterproof performance: because the closure rate is more than 90%, it has excellent waterproof function.


4) It is sealed as a whole, no cavity and seamless bonding, which can adapt to various shapes of base surface and effectively improve the insulation effect


5) The size stability is less than 1%, it has certain toughness, the elongation is more than 5%, and it will not crack;


6) Density ≥ 35kg / m3, compressive strength > 300kPa, tensile strength > 400kPa, with strong wind resistance, able to bear the weight of 30kg / m2 of external facing without falling off;


7) Good flame retardancy: 3S from fire, self-extinguishing and carbonization, no melting.


The above properties determine the incomparable advantages of polyurethane rigid foam insulation.


3、 Comparison with EPS foam and XPS external insulation


1. Thermal insulation performance: the thermal conductivity of polyurethane rigid foam is 0.022w/m.k, EPS is 0.041w/m.k, and XPS is 0.028w/m.k. The thermal conductivity of rigid polyurethane foam is the lowest.


2. Sealing performance: EPS panel and XPS are sealed with gaps and cavities, and the external air can easily flow through the gaps and cavities, affecting the insulation performance.


In terms of the southern region, the shape coefficient of 24cm light block wall is more than 0.3, achieving 65% energy saving, and the heat transfer coefficient of the wall is 0.57. If Pu insulation is used, the thickness of the insulation layer is 30mm, eps80mm and xps60mm (considering the factors of the cavity gap).


3. Wind resistance and bearing capacity of facing brick layer: Pu density is 35kg / m3, tensile bond strength is 0.3MPa, fully able to bear high-rise building.


The negative pressure load capacity of building exterior wall due to wind and the weight of facing brick 30-35kg / m2. However, the tensile strength of EPS foam panel is only 0.1MPa in dry state, and the bond tensile strength after immersion is lower. Therefore, EPS foam panel cannot be used in high-rise buildings generally. If facing bricks of high-rise buildings are pasted, steel wire mesh and plastic nails are also needed.


4. Anti cracking performance: Pu system adopts overall spraying, Pu's insulation stability is ± 30 ℃, and the size change rate is less than 1%. In addition, thin plastering elastic anti cracking layer is adopted, the surface will not crack. EPS foam and XPS are required to be degraded for 40 days before they can be used in construction, which is difficult to be achieved in practical application. Therefore, many cracks, cold penetration and halogen return of walls appear in EPS insulation projects nationwide.


5. Waterproof performance: PU Rigid Foam closure rate of 90%, self-skinning closure rate of 100%, especially the overall foaming of doors and windows, blocking all voids and EPS, XPS for cavity paste, and water, condensation water is easy to penetrate through cracks and cavities into the room.


6. Flame retardant performance: Pu rigid foam self-extinguishing carbonization. When XPS and EPS meet with fire and high temperature, the molten droplets will cause the wall to fall off and the fire will spread.


7. Pu system can be used for roof insulation and waterproof integration, from the original seven- layer method to three-layer method, simplifying the process and reducing the construction period by two times.


It can be seen from the comparison that the on-site polyurethane rigid foam external wall insulation system has obvious advantages over the previous EPS and XPS external wall insulation system.


1. Definition:


EPS is formed by physical foaming after EPS particles (pre foaming) are heated by steam, and there is a gap between the particles.


XPS uses PS particles, which are heated under pressure in the extruder. After the particles melt, the foaming agent is added, and then the particles are cooled and foamed under reduced pressure, so there is no gap between the particles.


Polyurethane rigid foam panel (PU sandwich panel) has the characteristics of high bulk density, low water absorption, good stability at low temperature or high temperature, long service life, excellent insulation performance and so on. In particular, polyurethane rigid foam board is more widely used, easy to use, good insulation effect.


2. Comparison:


Heat preservation effect: polyurethane foam is the best, the Extrusion board is second, and the eps foam panel is the worst;

Cold and heat resistance: polyurethane foam is the best, the extruded plate is second, and the eps foam panel is the worst;

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