Application status
Since the 1950s, my country began to develop and apply polyurethane coatings. With the continuous improvement and improvement of the material living standards of the general public, the development speed of a series of industries such as automobile processing, furniture manufacturing and processing, petrochemical industry, machinery industry, bridges and ships, etc. has been increasing. With its outstanding performance advantages, polyurethane coatings have begun to enter A new stage of rapid development. According to statistics, from 1980 to 2004, the use of polyurethane coatings in various industries has shown a very rapid development trend, and the total use of polyurethane coatings has achieved a breakthrough development from 0.1700 to 200,000 tons. The output of polyurethane coatings is second only to alkyd resin paint, acrylic resin paint and phenolic resin paint, and has become the fourth largest variety in the coatings field. Rapid development trend.
Among the production and processing enterprises related to polyurethane coatings, most of the companies responsible for the development and application of polyurethane coatings are concentrated in the Pearl River Delta and the Yangtze River Delta. Up to now, more than 60 types of polyurethane coatings have been developed. It should be noted that, affected by factors such as capital investment and technological development, most of the polyurethane coating development companies are mainly joint ventures, wholly foreign-owned enterprises and large-scale domestic manufacturers, and the market positioning is mainly mid-to-high-end products. , The township and village enterprises mostly focus on low-end products.
From the perspective of the development and application of polyurethane coatings, the most mainstream is still two-component polyurethane coatings, which have been continuously expanded and improved in the fields of wood furniture coating and other fields. In addition, one-component polyurethane coatings still have strong application advantages in automotive processing, basement waterproofing and other fields. This type of coating uses polyurethane as the main material and has very good application value in the production of various color paints and varnishes. . The newly developed acrylic polyurethane paint uses biuret as the curing agent, and its application value in automotive repair paint is quite reliable. Especially for light cars, large passenger cars and vans, the coating function in vehicle processing is very worthy of recognition, and the market prospect is considerable. Many new types of polyurethane coatings developed on the basis of acrylic polyurethane coatings can also be used in other manufacturing and processing fields to meet the processing quality requirements of processed objects such as household appliances and trains.
In addition, special polyurethane coatings that can be applied to floor coating, machine tool coating, aerospace equipment surface coating and other fields are in the stage of accelerated development and research. Related reports summarize and analyze the current classification, characteristics and application fields of polyurethane coatings.
R & D progress
(1) Waterborne polyurethane coating
In 1942, Shlack successfully prepared cationic water-based polyurethane for the first time. In the 1970s, the industrial production of water-based polyurethane began. Up to now, the world's annual output of water-based polyurethane resin is about 50,000 to 60,000 tons. Waterborne polyurethane coatings use water as the coating dispersion medium. There are fewer organic solvents in the entire polyurethane coating structure system, which meets the current environmental protection requirements for energy saving and emission reduction in the coating field. Therefore, the application of waterborne polyurethane coatings in related fields is related to Development issues have received increasing attention and attention from industry insiders. Up to now, although the application proportion of polyurethane coatings in my country's entire coatings field is only about 4%, the engineering application of water-based polyurethane coatings has maintained a growth rate of nearly 10% in recent years. Under normal circumstances, waterborne polyurethane coatings do not need to add dispersants or emulsifiers, and the molecular size and molecular structure can be adjusted appropriately according to the situation. In view of this feature, compared with the more widely used latex coatings in the traditional sense, waterborne polyurethane coatings can have better low-temperature film-forming properties, without the need to add plasticizers and film-forming aids in proportion to the profit. Compared with other coatings, waterborne polyurethane coatings not only have a good appearance, but also have a short drying time, which shows a unique advantage in the field of wood coatings. Solvent-based acrylic leather coatings in the traditional sense have gradually been replaced by water-based polyurethane leather coatings. With their advantages in chemical resistance and low temperature resistance, they have attracted the attention and attention of people in the leather coatings field. In addition, this type of material also plays a very precise application value in related fields such as plastics, vehicles, industry, and anti-corrosion, and has a considerable space for development.
The performance of waterborne polyurethane coatings still has certain limitations. Insufficient water resistance is one of the most important factors affecting the application of waterborne polyurethane coatings in practice. In addition, during the construction period, there are also certain problems related to the application of water-based polyurethane coatings. For example, for two-component water-based polyurethane coatings, the drying speed after being incorporated into construction materials is relatively slow and requires a long time for maintenance. . The carbon dioxide bubbles generated during the reaction of the waterborne polyurethane coating with water may remain in the coating film in large quantities and affect its performance. Moreover, the high cost has become one of the main factors affecting the industrial application of waterborne polyurethane coatings. More importantly, in waterborne polyurethane coatings, a large amount of waterborne coatings added may have an impact on iron substrates in engineering buildings, leading to flash corrosion problems, and even affecting the wettability and appearance of surface coatings. In view of the above problems, in order to promote the further development of water-based polyurethane coatings, the follow-up should take the composite modified water-dispersed polyurethane coatings as the development direction and research focus, and try to use some molecular structures with more special functions, such as silicon-containing polymer chains and fluorine-containing The polymer chain is introduced into the polyurethane chain to improve the overall performance of the coating film and give play to its advantages in high temperature resistance, water resistance and weather resistance. Low-VOC and high-performance two-component waterborne polyurethane coatings can also be the focus of research and development, which can reduce the cost of polyurethane coatings and improve the efficiency of use.
(2) Modified polyurethane coating
For a relatively single polyurethane coating, in the process of industrial production and application, its appearance, gloss, water resistance and hardness still have certain limitations, so you can try to develop modified polyurethane coatings to improve its performance level . Under the current technical level, the applicable modification methods of polyurethane materials include two types: the first is through chemical intervention, so that polyurethane coatings can have two or more characteristics; the second is through physical Method intervention is to mix two or more resin materials with complementary characteristics, so that polyurethane coatings can have diversified properties. Among them, for organosilicon materials, the material has a series of characteristics and advantages such as non-corrosion, non-toxicity, flame resistance, ozone resistance, weathering resistance, electrical insulation, etc., and it is very good in the modification of polyurethane coatings. Application value. Bayer took the lead in the basic research and development of polyurethane powder coatings, and successfully developed a closed isocyanate cross-linking system. The commonly used IPDI curing system is caprolactam-enclosed, and its curing temperature is above 170 ℃. This high-temperature curing is beneficial to the coating. The highly leveled product is a product that emits no volatile by-products. Previous reports have also pointed out that trying to combine silicone materials with polyurethane coatings and applying appropriate methods for modification processing can obviously overcome the performance defects of polyurethane materials, which is of great value for expanding the application field of polyurethane materials. At the same time, the chemical structure of polysiloxane is relatively special, showing excellent stability, biocompatibility, electrical insulation, and high and low temperature resistance. Since the 1940s, it has been widely used in industrial production practice. In the research and development process of modified polyurethane materials, you can try to use polysiloxane as the soft segment to synthesize polysiloxane-polyurethane block copolymer to highlight the polyurethane. As well as the advantages of polysiloxane, it demonstrates the outstanding advantages of the modified polyurethane coating in terms of surface enrichment, dielectric properties and biocompatibility, and has a very large application space and development potential.
(3) Environmentally friendly polyurethane coating
Affected by environmental protection requirements and the sustainability requirements of the entire coating industry, relevant personnel in the industry must actively explore and develop environmentally-friendly polyurethane coating products, such as light-cured polyurethane coatings, high-solid low-viscosity polyurethane materials, and powdered polyurethane materials Wait. Polyurethane coatings presented in powder form can have good physical and mechanical properties and chemical resistance, while also showing good appearance and aesthetics. Compared with other structural polymer materials, the waterborne polyurethane dispersion resin material has a lot of advantages, and it meets the requirements of environmental protection. It can be dispersed in water, has no favorable isocyanates, is non-toxic, and has good adhesion to the substrate. The water-based two-component polyurethane coating is composed of -OH group-containing water-based polyol and -NCO group-containing low-viscosity polyisocyanate curing agent. The film performance is mainly determined by the composition and structure of the hydroxyl resin.
One-component waterborne polyurethane coatings are a type of coating that uses waterborne polyurethane resin as the base material and water as the dispersion medium. The waterborne polyurethane coating modified by crosslinking has good storage stability, film mechanical properties, water resistance, solvent resistance and aging resistance, and has similar properties to traditional solvent-based polyurethane coatings. It should be used as an environmentally friendly polyurethane coating. One of the very important development directions. From the perspective of future development trends, polyurethane powder coatings have become one of the most mainstream development directions in the current coatings field, and the proportion in various powder coatings and even polyurethane coatings is increasing. For the automotive coatings processing market, in the development process of coating products, polyurethane powder coatings should be the best choice and development direction. At the same time, through technological innovation and research and development, research and development have good adaptability to low temperature environments and no volatility. A new generation of polyurethane powder coatings produced by by-products. This new type of powder coating has good similarities with two-component solvent-based polyurethane coatings in performance. It can be applied to the manufacturing and processing of new-generation automotive production line coatings, while ensuring coating performance. , Which reflects good environmental benefits and has a very considerable comprehensive benefit.
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