1 Introduction Due to its unique structure, polyurethane coatings give processed products outstanding properties such as strength, flexibility, wear resistance, moisture permeability, and low temperature resistance; and are widely used in the coatings industry, leather industry, textile industry, construction industry, etc .; but PU Most coatings are solvent-based. With the continuous strengthening of people's awareness of environmental protection, the related labor protection, safety, fire protection, environmental protection and other laws and regulations are increasingly improved, and the price of organic solvents has skyrocketed, so it is inevitable that water-based PU replaces solvent-based PU; and because of pure PU The emulsion is insufficient in terms of stability, self-thickening, solid content, application range, and gloss retention of the film, while the PUA composite emulsion is inexpensive, safe, non-flammable, and non-toxic; not only strong, tough, wear-resistant, water-resistant, and resistant Good chemical properties; and stability, self-thickening, solid content, application range, good gloss retention of the film. Therefore, PA emulsion and PU emulsion have a certain complementarity in nature, so the generation of PUA composite emulsion has become an inevitable trend. 2. Production and development of PU coatings In foreign countries, based on the isocyanate chemistry developed by OttoBayer and others in 1948, linear polyurethane and polyurea were prepared by the reaction of diisocyanate with ethylene glycol and diamine. In 1955, an adduct (DESMODURL) of toluene diisocyanate (TDI) and trimethylolpropane (TMP) was prepared. In 1961, made of diisocyanate (HDI) biuret, based on which can be formulated with excellent performance of various PU coatings. PU coatings have been widely used abroad in recent years because of the excellent performance of PU coatings and the "three prerequisites" (resources, energy, pollution-free) and "four E principles" (economic ECONOMY, efficiency EFFICIENCY, ecological ECOLOGY) of the development of the coating industry. , ENERGY) to meet the requirements of the increasingly strengthened era. It is estimated that in the 1990s, foreign polyurethane coatings will have further development and achieved many results. The development of PU coatings in China began in 1956 when Dalian Dyestuff Factory successfully produced toluene diisocyanate (TDI) for the first time, and then carried out experimental research on PU coatings and trial production of PU coatings in 1958, but until 1956 in Tianjin, Only Shanghai and other places have a small amount of commercial paint production. In the 1980s, after the implementation of reform and opening up, domestic and foreign technological exchanges increased day by day, and the production process and construction technology of PU coatings were progressively improved, ushering in a new era of vigorous development of PU coatings in China in the 1990s. However, due to the poor stability, self-thickening, solid content, and gloss retention of the film, the development of PU coatings has certain limitations. 3. The generation and development of PA coating In 1927, the German Rohm & Hass company began the industrial production of acrylic esters. After 1931, Britain and the United States gradually developed the industrial production of methacrylate, and produced plexiglass. In the early 1950s, DoPont of the United States began to study polyacrylate coatings and test them for automotive coatings. After several years of application and development, in the mid and late 1950s, the excellent performance of acrylate coatings was gradually paid attention to. China's research on acrylate coatings is relatively late. In the 1950s, the Institute of Coatings Industry of the Ministry of Chemical Industry and Beijing, Tianjin, and individual units began to develop, mainly for aircraft coating. In the 1960s and 1970s, acrylic resin coatings have been further developed. Several conventional acrylic resin-modified resin coatings have been successfully developed, such as acrylic modified vinyl chloride resin, nitrocellulose, alkyd resin and other coatings. Achieved industrial application. Since the 1980s, due to the annual output of 38,000 tons of Beijing Dongfang Chemical Plant and the annual production of acrylic monomers of Jilin Chemical Industry Company with an annual output of 40 thousand tons, the development speed of the acrylic coating industry has been greatly promoted. However, due to the poor toughness, wear resistance, water resistance, and chemical resistance of PA coatings, its development also has certain limitations. 4.1 Production and development of water-based PU coatings The water-based PU coating was invented in 1943, and was first industrialized in 1967. In 1972, the German Bayer Company took the lead in developing the imprainil series of PU aqueous emulsions used as leather coating finishing agents. For decades, Europe, America, and Japan have attached great importance to the research and development of water-based PU. Today, there are many types of water-based PU products, which have been successfully used in light textile, printing and dyeing, leather processing, fabric coating finishing, coatings, adhesives, wood Processing construction, paper, rubber and elastic fibers, elastomers and other fields. Especially in recent years, the global environmental protection requirements have become higher and higher, while considering economic savings, the traditional solvent-based PU system has been seriously challenged, and its application has been decreasing year by year. Replacing solvent-based PU with water-based PU will become a 4. The generation and development of the third-generation water-based PU-PUA coating, compared with foreign countries, the domestic research and development of water-based PU is relatively backward, still in the stage of trial production and small batch production. According to incomplete statistics, there are only more than 40 production units for water-based PU research in China, of which more than 20 production units have a total annual production of more than 10,000 tons. Most of the production of leather finishing agent. Domestically produced water-based PU products have few types, poor performance and quality, and have a large gap compared with similar foreign products, which has led many industries to rely on imports for a long time. The urgent demands of the industry are of great significance. [NextPage] 4.2. Production and development of waterborne PUA coatings [7-8] Compared with its solvent-based products, polyurethane (PU) emulsions and polyacrylate (PA) emulsions are inexpensive, safe, non-flammable, non-toxic, and environmentally friendly. Therefore, they are used in coatings, adhesives, leather, and fabric coatings. The layer is widely used. However, the problems with pure PA emulsions are: poor toughness, wear resistance, water resistance, and chemical resistance; while the problems with single PU emulsions are: stability, self-thickening, solid content, application range, and membrane Poor gloss retention. PU and PA have a certain complementarity in nature. PUA composite emulsion can overcome the shortcomings of PU and PA emulsions, exert their respective advantages, and significantly improve the performance of emulsions and films. There is no doubt that the advantages of PU coating are obvious, but its price is relatively high and its application is limited. Therefore, we are committed to the research of water-based PU-PA modified resins in order to reduce costs, and now we have achieved results, and foreign products have come out. PU-PA modified resin combines the best performance of the two materials in one, overcomes the shortcomings of PU and PA, the coating is soft, resistant to bending, tortuous, good printing effect, weather resistance, and hydrolysis resistance. The PU-PA composite aqueous dispersion technology is a new achievement in material research in the world today, and also represents a new trend in the development of PU. In the past ten years, there have been more researches on PUA composite emulsions abroad.For example, the United States, Germany, Japan, etc. have reported PUA composite emulsions for coatings, fabric finishing agents, etc., only a few in China in recent years. Researchers conducted exploratory experiments to prepare PUA composite emulsions, such as Anhui University, Liming Chemical Research Institute, Jiangsu Provincial Institute of Chemical Engineering, Yantai Chemical Research Institute, Henan Institute of Chemical Engineering, Shanghai University of Technology, etc., but PUA composite emulsion commercialization, At present, there are no reports in China. PUA composite emulsion is known as the third generation water-based PU due to its excellent performance. 4.3. Characteristics and synthesis method of water-based PUA coating The PUA compound emulsion has the advantages of PU and PA, and has the characteristics of wear resistance, corrosion resistance, brightness, softness and elasticity, water resistance, good mechanical properties, good weather resistance, etc., so the research of PUA compound emulsion has become the current coating Development trend. The preparation methods of PUA composite emulsion are as follows: â‘ PU emulsion and PA emulsion blend cross-linking method; â‘¡ synthesis of double bond unsaturated urethane monomer and acrylate copolymerization method; â‘¢ composite emulsion polymerization using PU emulsion as seed law. Among them, the composite emulsion polymerization method first prepares a PU containing a hydrophilic group, disperses it in water as a seed, and then performs emulsion composite polymerization with acrylate to obtain a core / shell PUA latex, or by adding a diene monomer. Interpenetrating polymer network (IPN) latex. This method can be divided into: PU seed made by solvent method; PU made directly by using acrylate monomer as solvent; PU made by chain extension in solvent-free water; the prepared PU all contain hydrophilic groups, which can be self-emulsified as seeds for further use of acrylics The monomer undergoes emulsion compound polymerization. This is a popular method at present. 4.4. Application of IPN technology in PUA coatings After the acrylic polyurethane coating agent is applied to the surface of the object, the hydroxyl group of the acrylic component reacts with the isocyanate of the polyisocyanate component to form a film.It is a conversion coating, which has both acrylic and poly The advantages of two kinds of urethane coating agents are good corrosion resistance, abrasion resistance, and strong adhesion.The coating agents made of aliphatic polyisocyanate as raw materials also have excellent weather resistance, but currently aliphatic polyisocyanates The acid is all dependent on imports and is expensive.The coating made with domestic aromatic polyisocyanate has poor weather resistance and the coating turns yellow after being exposed to sunlight.In order to reduce the cost of external acrylic polyurethane coating agent, we use IPN technology Introduce some aromatic polyisocyanate into the coating to replace the aliphatic polyisocyanate, and reduce the amount of the latter under the premise of ensuring the weatherability of the coating agent. IPN (Interpenetrating Polymer Network) is an intermixed system composed of two or more interpenetrating cross-linked polymers. As the main method of polymer blending and compounding, it can be regarded as a chemical method to achieve polymerization A new method of physical and physical blending, if two networks with similar chemical structures are synthesized by a synchronous method, and the forced compatibilization generated by the two networks interpenetrating, it can be expected that the compatibility of the system will be greater The improvement of morphology is shown as a continuous phase structure, and the weather resistance problem caused by the aromatic isocyanate introduced from this can also be solved. Using cross-linked acrylic cyanide made with caprolactone as a chain extender and acrylic resin cross-linked and cured with hexylene diisocyanate as raw materials, the PU / PAIPN obtained has excellent weather resistance and solvent resistance And adhesion, used as car topcoat and furniture coating, have good decorative effect. 5. Conclusion In general, the development of polyurethane coatings from solvent-based to water-based PU to the third-generation water-based PU-PUA composite emulsion fully shows the vigorous vitality of PU coatings; now water-based PUs are all over the coating industry, leather industry, printing industry, In the construction industry, textile industry and other fields, it is reasonable to believe that with the development of society, the environment and the requirements of industrial production, water-based PU products will certainly have a place in China's chemical industry. 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