Background
Polyurethane rigid foam for the construction industry is an important branch of the polyurethane industry, which is characterized by its multi-purpose, simultaneous insulation and waterproofing functions, and rigid foam as shown in Figure 1. This type of product has been used in the construction industry in Europe for 40 years since the 1960s, and some countries have adopted legislation to designate polyurethane as a material for insulation and waterproofing in the construction industry. In recent years, with the rapid development of China’s building energy-saving market, polyurethane rigid foam body insulation products have been widely used in the field of building insulation and waterproofing, and have become one of the leading market insulation and energy-saving products.
Polyurethane chemical composition
Polyurethane (i.e. polyurethane, abbreviated as PU) is a polymer compound containing many repeating -NHCOO- groups on the main polymer bond. Polyurethane series products are generally polymer compounds obtained by the polymerization reaction of binary or multi organic isocyanate and polyol under the action of various additives.
Polyurethane rigid foam insulation material raw materials, generally called by the black material and white material of the reactant composition. Among them, the black material refers to the common name of crude MDI, also called polymerized MDI, the chemical name is “polymethylene phenyl polyisocyanate”, the color is generally black, so it is called black material. White material is the common name of polyether polyol, and the color is white.
At the same time, in order to improve the comprehensive performance of polyurethane and adapt to the use conditions in different environments, other additives such as flame retardant, catalyst and foaming agent are generally added to the white material, so the white material is also called combination material.
Performance Analysis
Polyurethane rigid foam breaks the common problem of traditional building materials with single function, waterproof but not heat preservation, heat preservation but not waterproof, and once the waterproof layer leaks, the heat preservation layer then loses its heat preservation function. Compared with other single-function insulation or waterproofing materials, polyurethane rigid foam has obvious advantages: 1.
1. polyurethane rigid foam has the function of multi-purpose, and at the same time has many functions such as heat preservation, waterproof, sound insulation and vibration absorption.
2. Excellent thermal insulation performance, thermal conductivity ≤ 0.024 W/(m?K), only half of EPS foamed polystyrene board; can form a continuous insulation layer to ensure the integrity of the insulation material and the wall and effectively block the thermal bridge.
3. polyurethane rigid foam body continuous dense skin and nearly 100% of the high strength interconnection wall closed pore, with ideal impermeability. It is constructed by spraying method to achieve a continuous waterproof insulation layer without joints, forming a seamless roof cover and overall exterior wall insulation shell with excellent waterproof and impermeability performance.
4. Super strong self-adhesive performance (without any intermediate bonding materials). Under high pressure, the atomized polyurethane molecules directly penetrate into the capillaries of concrete or mortar, plugging the concrete leakage micropores while forming a high strength bonding layer. Firm bonding with roofing and exterior walls, good performance of wind uncovering and negative wind pressure resistance.
5. flexible gradient technology can effectively prevent the waterproof layer from cracking.
6. mechanized operation, automatic batching, uniform quality and fast construction cycle.
7. outstanding fire performance. Polyurethane added flame retardant, is a kind of flame-retardant self-extinguishing material. From the open flame self-extinguishing, and burning only charring not dripping, the size and shape of the carbonized layer is basically unchanged, can effectively isolate the entry of air, to prevent the spread of fire, fire safety performance is good.
Construction process
In general, polyester polyol, polyether polyol, catalyst, flame retardant and foaming agent are pre-mixed in a certain proportion, and the well-mixed mixture is packed in a drum. In the construction process, the combination of materials and black materials in a certain proportion in different storage tanks, mixed by pressure in the mixing head, and quickly produce a chemical reaction, at the same time, the reaction products were under pressure quickly from the gun muzzle spray, the formation of rigid foam, see Figure 2, Figure 3, Figure 4 shown.
Polyurethane rigid foam foaming principle is: the reaction of black material and white material is an exothermic reaction, the heat released to vaporize the foaming Je (such as F-11, 141B) and form foam. The heat of reaction vaporizes the blowing agent and expands the volume of the foaming system. This expansion will cause the internal pressure of the foam system to rise. The pressure generated by polyurethane in the foaming process is 0.5-0.1kg/cm2
In the process of foaming, the raw material temperature and the ambient temperature and the constant or not directly affect the quality of polyurethane rigid foam, the ambient temperature of 20-30 ℃ is appropriate. The temperature of raw material can be controlled in the range of 20-30℃ or a little higher. When the temperature is low, the foaming reaction will be slow and the foam will take a long time. When the temperature is high, the foaming reaction will be fast and the foam time will be short. If the temperature is too high or too low, it is not easy to get high quality products. Therefore, temperature is an important process parameter in polyurethane foam spraying construction.
When polyurethane foaming, the time of black material and white material staying in the mixing room of the foaming machine is very short, generally only a few minutes to a few seconds, mixing efficiency is a very important factor, black material and white material mixed evenly, the foam pore is fine, uniform, good insulation effect. In order to ensure the mixing effect, high pressure foaming machine should be used when polyurethane foaming.
