Background
Polyurethane rigid foam used in the construction industry is an important branch of the polyurethane industry. It is characterized by its multi-purpose material and its functions of thermal insulation and waterproofing. The rigid foam is shown in Figure 1. This type of product has been used in the European construction industry for 40 years since the 1960s. Some countries have also passed legislation to use polyurethane as a designated thermal insulation and waterproof material for the construction industry. In recent years, with the rapid development of my country’s building energy-saving market, polyurethane rigid foam insulation products have been widely used in the field of building insulation and waterproofing, and have become one of the leading thermal insulation and energy-saving products in the market.
Chemical composition of polyurethane
Polyurethane (polyurethane, English abbreviation PU) is a polymer compound containing many repeating -NHCOO- groups on the main bond of the polymer. Polyurethane series products are generally polymer compounds obtained by polymerization of binary or polyvalent organic isocyanates and polyols under the action of various additives.
The raw material of polyurethane rigid foam insulation material is generally called the reactant of black material and white material. Among them, 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 for polyether polyol and its 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 retardants, catalysts, and foaming agents are generally added to the white material, so the white material is also called a composite material.
Performance Analysis
Polyurethane rigid foam breaks the common problem of traditional building materials with single function: waterproof but not thermal insulation, thermal insulation but not waterproof. Once the waterproof layer leaks, the insulation layer will lose its insulation function. Compared with other single-function insulation or waterproof materials, polyurethane rigid foam has obvious advantages:
1. Polyurethane rigid foam has a multi-purpose function, and also has many functions such as thermal insulation, waterproofing, sound insulation, vibration absorption, etc.;
2. Excellent thermal insulation performance, thermal conductivity ≤0.024 W/(m?K), only half that of EPS foamed polystyrene board; it can form a continuous thermal insulation layer, ensuring the integrity of the thermal insulation material and the wall and effectively blocking it thermal bridge.
3. The continuous and dense skin of polyurethane rigid foam and nearly 100% high-strength interconnected wall closed cells have ideal water impermeability. The spraying method is used for construction to achieve a continuous and seamless waterproof insulation layer, forming a seamless roof and an overall exterior wall insulation shell with excellent waterproof and impermeability performance;
4. Super self-adhesive performance (no need for any intermediate bonding material). Under the action of high pressure, the mist polyurethane molecules directly penetrate into the capillary pores of concrete or mortar, blocking the leakage micropores of concrete and forming a very strong bonding layer. It is firmly bonded to the roof and exterior walls, and has good resistance to wind lifting and negative wind pressure;
5. Flexible gradient technology can effectively prevent the waterproof layer from cracking;
6. Mechanized operation, automatic batching, uniform quality, fast construction and short cycle;
7. Outstanding fire resistance. Polyurethane is a flame retardant and self-extinguishing material after adding flame retardant. It is self-extinguishing when exposed to an open flame, and only carbonizes without dripping when burning. The size and shape of the carbonized layer remain basically unchanged. It can effectively cut off the entry of air, prevent the spread of fire, and has good fire safety performance.
Construction technology
Generally, polyester polyol, polyether polyol, catalyst, flame retardant and foaming agent are pre-mixed according to a certain proportion, and the fully mixed and even mixture is packaged in a packaging barrel. During the construction process, the combined materials and black materials are installed in different storage tanks according to a certain proportion. They are mixed at the mixing head through pressure, and a chemical reaction occurs rapidly. At the same time, the reaction product is quickly ejected from the nozzle of the spray gun under pressure. It is sprayed out to form a hard foam, as shown in Figure 2, Figure 3 and Figure 4.
The principle of polyurethane rigid foam foaming is: the reaction between black material and white material is an exothermic reaction, and the heat released vaporizes the foaming agent (such as F-11, 141B) to form foam. The heat of reaction vaporizes the foaming agent and creates��The volume of the system expands. This expansion will cause the internal pressure of the foam system to increase. The pressure generated by polyurethane during the foaming process is 0.5-0.1kg/cm2
During the foam molding process, the quality of the rigid polyurethane foam is directly affected by the level and consistency of the raw material temperature and the ambient temperature. The appropriate ambient temperature is 20-30°C. The raw material temperature can be controlled in the range of 20-30℃ or slightly higher. When the temperature is low, the foaming reaction proceeds slowly and the foam takes a long time to form. When the temperature is high, the foaming reaction proceeds quickly and the foam formation time is short. If the temperature is too high or too low, it is difficult to obtain high-quality products. Therefore, temperature is the most important process parameter in polyurethane foam spraying construction.
When polyurethane is foamed, the black material and white material stay in the mixing chamber of the foaming machine for a very short time, generally only a fraction to a few seconds. Mixing efficiency is a very important factor. The black material and white material are mixed evenly. The foam cells are fine, uniform and have good thermal insulation effect. In order to ensure the mixing effect, a high-pressure foaming machine should be used when foaming polyurethane.
