Classification application of Waterborne Polyurethane
Polyurethane, namely carbamate, is a kind of polymer with repeated carbamate groups, which has excellent mechanical chemical properties. In the past, the oil-soluble polyurethane was the majority. In recent years, the water-based trend of polyurethane has been formed, the water-based polyurethane has become more more mature.
Classification of Waterborne Polyurethane
There are many categories of waterborne polyurethane, generally have the following classification methods.
Classification by appearance: waterborne polyurethane can be divided into polyurethane emulsion, polyurethane dispersion polyurethane aqueous solution. The most practical application is polyurethane emulsion dispersion, its appearance characteristics are shown in Table 1.
According to the curing mode. Waterborne polyurethane can be divided into two components, one component self drying radiation curing.
Radiation curable waterborne polyurethane usually contains double bonds, which can be initiated by photoinitiators under UV irradiation.
The water-based two-component system is the same as the traditional solvent based two-component system, that is, the mixture of a B components is required for crosslinking curing, water-based isocyanate curing agent is generally used.
One component waterborne polyurethane can be cured at room temperature heating conditions.
According to the properties of hydrophilic groups. According to whether there are ionic groups in the side chain main chain of polyurethane, that is, whether it belongs to ionic bond polymer, waterborne polyurethane can be divided into anionic type, cationic type non-ionic type. Anionic cationic waterborne polyurethane is also known as ionomer type waterborne polyurethane. Non ionic waterborne polyurethane is called nonionic waterborne polyurethane.
According to the classification of polyurethane raw materials. According to the main types of oligomer polyols, they can be divided into polyether type, polyester type polyolefin type, which refer to the waterborne polyurethane made by using polyether polyol, polyester polyol polybutadiene glycol as oligomers. There are also polyether polyether blends. Polyurethane isocyanate can be divided into aromatic isocyanate, aliphatic isocyanate alicyclic isocyanate.
According to the water-based methods of polyurethane, it can be divided into self emulsifying method external emulsifying method.
Self emulsification, also known as internal emulsification, means that the polyurethane segment contains hydrophilic components, so that no emulsifier is needed to form a stable emulsion.
External emulsification is also called mandatory emulsification. If the molecular chain contains only a small number of hydrophilic segments groups which are enough to self emulsify contain no hydrophilic components, emulsifiers must be added to obtain the emulsion.
In comparison, the emulsions prepared by external emulsification affect the properties of cured polyurethane film because of the residue of hydrophilic small molecular emulsifiers, the self emulsifying method eliminates the disadvantage. At present, the preparation of waterborne polyurethane is mainly by ionic self emulsifying method.
❤ Key applications Mei
Different types of polyisocyanates react with polyhydroxy compounds to produce coatings with different properties to meet the needs of various application fields. Polyurethane coating has a series of excellent characteristics, the most outstanding advantages are wear resistance, chemical resistance, good toughness, elasticity adhesion to the substrate, can be cured at room temperature low temperature. Therefore, polyurethane coating has been widely used in various fields is considered to be the best paint variety with comprehensive performance
Generally speaking, wood paint should be beautiful, wear-resistant stain resistant. Waterborne polyurethane has the characteristics of abrasion resistance, flexibility strong adhesion. Wood coatings have become an important application field of waterborne polyurethane coatings have broad development prospects.
There are many kinds of automobile coatings, including electrophoretic paint, second coat paint, top coat, original paint, repair paint, etc. With the rapid development of automobile industry, the requirements for automobile coating are higher higher. the perspective of environmental protection, waterborne polyurethane is the development trend of automotive coatings. Waterborne polyurethane can be used for primer, intermediate coat, color paint, finishing paint repair paint of automobile surface. At present, the waterborne polyurethane automotive coatings are mainly two-component.
The loss caused by metal corrosion is very serious, especially the corrosion protection of steel has attracted more more attention at home abroad. Coating antirust coating is one of the main methods to prevent steel corrosion. Water based coatings have gradually become the main development direction of coatings because they can effectively overcome the shortcomings of high price pollution of solvent based coatings.
Architectural coatings require some properties such as light resistance, weather resistance, etc. the comprehensive properties of polyurethane dispersion coatings can fully meet the requirements through component adjustment. Because of its excellent water resistance, durability weather resistance, polyurethane dispersion coating has outstanding advantages for the external decoration of buildings. As a high-grade architectural coating, it is widely used in the economically developed United States European countries.
Polyurethane paint film is plump, bright, with excellent corrosion resistance, adhesion, chemical resistance, weather resistance, etc. it is widely used in adhesive coatings other fields. However, single emulsion is satisfactory in terms of stability, self thickening, solid content water resistance gloss of polyurethane resin film. Acrylic resin has the advantages of high mechanical strength, aging resistance, yellowing resistance good water resistance. However, it has some disadvantages such as poor resistance to organic solvents, poor heat resistance, low softening point poor wear resistance.
Therefore, polyurethane polyacrylate have great complementarity in the performance, the combination of the two can get better polymers. The modification of polyurethane with acrylic resin in aqueous system is one of the important development directions in the future.