Coating knowledge: advantages and problems of Waterborne Coatings

Core tips: [Abstract] compared with solvent based coatings, the development advantages of water-based coatings in environmental protection, risk reduction, cost reduction, etc are introduced Meanwhile, problems such as thorough oil removal, poor fullness and poor recognition are summarized Suggestions for basic research and improvement of service performance are put forward [Key words] water based coatings; solvent based coatings; latex [Chinese classification No.] tu56 [document code] a [Article No.] 1001 – 523X (2015) 02 – 0066 – 03 with the rapid growth of national economy, China's coating production Which is the price of Dajin diatom mud Recommended brief introduction: which is the price of Dajin diatom mud? How to buy genuine diatom mud? Guangdong diatom mud agent suggests placing a basin of cold water in the air conditioning room, so that the diatom mud wall can breathe effectively The feature of the breathing wall is obvious When the indoor air is dry, the diatom mud wall will release the absorbed water quickly Put it out to help regulate the indoor dry humidity It is suggested to place a basin of cold water in the air conditioning room, so that the wall of diatom mud can breathe effectively The feature of the wall that can breathe is obvious When the indoor air is relatively dry, the wall of diatom mud will absorb the water Home of coatings: [Abstract] compared with solvent based coatings, this paper introduces the development advantages of water-based coatings in environmental protection, risk reduction, cost reduction, etc., at the same time, it sums up the problems faced by water-based coatings, such as thorough oil removal, poor fullness and poor awareness, and puts forward suggestions for basic research and improvement of service performance [Key words] water based coatings; solvent based coatings; latex [classification no of Chinese library] tu56 [document code] a [article number] 1001 – 523X (2015) 02 – 0066 – 03 with the rapid growth of national economy, the production and consumption of coatings in China is growing at an alarming rate, becoming the world's largest coating production and consumption country during the 11th Five Year Plan period However, compared with developed countries, China's coating consumption structure is not reasonable, high pollution solvent coating accounts for a considerable proportion A lot of volatile organic compounds (VOC) are released during the production and use of solvent based coatings, which will have a serious impact on human health According to statistics, the amount of VOC released from coating processing and production accounts for 20% ~ 25% of the total emission, ranking second only to the emission of automobile exhaust and the VOC pollution [1] In the face of increasingly severe environmental problems and huge resource and energy consumption, many countries have formulated strict laws, regulations and environmental protection emission standards to limit the emission of volatile organic compounds, so as to encourage and promote the use of green, energy-saving and material-saving new products In China, the guidance on promoting joint prevention and control of air pollution to improve regional air quality (GBF [2010] No 33), the 12th Five Year Plan for prevention and control of air pollution in key regions and other documents have been implemented successively, which requires that joint prevention and control measures be taken to control key pollutants such as volatile organic compounds and nitrogen oxides, and the prevention and control of volatile organic compounds is in the environment The importance of environmental management is gradually highlighted In the 12th Five Year Plan for China's coating industry, the production of environmentally friendly coatings (waterborne wood coatings, waterborne industrial coatings, waterborne marine coatings, radiation curing coatings, and coatings that do not cause pollution to the environment or improve the environmental quality in the production, use, construction and post-treatment processes) that meet the standards is encouraged Therefore, environment-friendly coating is the development trend of coating industry Among them, water-based coating has become the research focus because of its innocuity, easy purification, low cost, low viscosity, non stimulation, non combustion and other characteristics [2] 1 Brief introduction of water-based coating water-based coating refers to the coating using water as solvent or dispersion medium, including water-soluble coating, water dilutive coating and water dispersive coating (emulsion coating) The water-soluble coating is based on water-soluble resin as film-forming material, mainly including polyvinyl alcohol and its various modifiers, water-soluble alkyd resin, water-soluble epoxy resin and inorganic high polymer water-based resin Water diluent coatings mainly use emulsion emulsion as the film-forming material to dissolve the resin Then, with the help of the emulsifier, the resin is dispersed in water to form emulsion by strong mechanical agitation It is called post emulsified emulsion, and the coating made of it can be diluted with water in construction Water dispersive coating mainly refers to the coating made of synthetic resin emulsion as film forming material Solvent based coatings are composed of pigments, fillers, resins, solvents and various additives The composition of water-based coating is almost the same as that of solvent-based coating, but water-based coating needs more auxiliaries, and its formula is more complex, mainly composed of water-based resin, pigment and filler auxiliaries, neutralizer, water, etc 2 Development advantages of water-based coatings 2.1 the whole life cycle of environmentally friendly water-based coatings from raw materials to production and use is conducive to the healthy development of the environment It can not only replace the volatile organic solvent in the production process, but also clean the coating tools with water and reduce the consumption of cleaning solvent The production of organic solvents needs to consume fossil raw materials At this stage of resource shortage, it is a big challenge to resources The emergence of water-based coatings solves this problem At the same time, the reduction of solvents greatly reduces the emissions of VOCs in the process of production and use, and makes a positive contribution to improving the surrounding atmospheric environment Ma Chunqing [3] et al Compared the VOC emissions of different coating systems, the results showed that the VOC emissions of the process system of "solvent based intermediate coating + solvent based paint + single component varnish" were 120g / m3, while the VOC emissions of the process system of "water based intermediate coating + water based paint + water based varnish" were only 28g / m3, which greatly reduced the emissions On the other hand, the water-based coating only uses a small amount of low toxic alcohol ether organic solvent, which reduces the volatile amount of organic solvent, greatly improves the environment of the workplace, and is conducive to the health of the staff The organic solvent of general water-based coating is between 10% and 15%, while the current cathodic electrophoretic coating has dropped below 1.2%, which has a significant effect on reducing pollution and saving resources 2.2 risk reduction take toluene and xylene, the most common solvents, as an example: the flash point of toluene is 4 ℃, the vapor can form an explosive mixture with air, and the explosion limit is 1.2% - 7.0% (volume); the flash point of xylene is 29 ℃, the vapor can form an explosive mixture with air, and the explosion limit is about 1% - 7% (volume) Both are flammable substances Therefore, the place where the flammable and explosive raw materials of solvent based coatings are stored and used has the risk of fire and explosion accidents In China, the accidents of fire and explosion occurred in the solvent tank of paint factory are often reported The production and use of water-based coatings reduce the demand for flammable and explosive raw materials, greatly reducing the risk 2.3 cost reduction 2.3.1 with the increasing demand for resources and energy, there is a shortage of resources and energy in the world, which leads to the continuous increase of the price of oil and even downstream products, including organic solvents as downstream products Under the pressure of resource price, the price advantage of water as diluent is gradually emerging [4] 2.3.2 in order to meet the emission requirements, enterprises need to configure tail gas treatment facilities and related supporting facilities, and bear the daily operation and maintenance costs The discharge of organic waste gas from waterborne coatings is very little, which reduces the burden for enterprises 2.3.3 safety cost water-based coating uses water as diluent to make it a safer coating The fire hazard from production to transportation and application is greatly reduced compared with traditional solvent based coating For managers, the cost of safety investment will be reduced accordingly Considering the cost of raw materials, equipment, safety and occupational diseases, waterborne coatings are competitive in the market 2.4 construction conditions and appearance performance due to good air permeability, the water vapor inside the base can diffuse outwards; However, the film-forming of solvent-based coating is compact, such as the high moisture content of the base course, water vapor can not be volatilized from the coating film, and it is easy to bubble Therefore, in terms of the requirements for the base course, the moisture content of the base course for the construction of water-based coating shall be less than 10%, and the moisture content of the base course for the construction of solvent-based coating shall be less than 8%, which is stricter than that for the water-based coating The water-based coating has good adaptability to the material surface and strong adhesion It can be applied directly in humid environment The volatilization of water in water-based coatings is mainly controlled by temperature and humidity, while solvent based coatings can adjust the evaporation rate of diluent to adjust the solid content Generally, the solid content of solvent coating is as high as 60% ~ 70%, while the solid content of water-based coating is only 20% ~ 30% Therefore, the smoothness of water-based coating is relatively good 3 Difficulties in the popularization of water-based coatings 3.1 although the requirements of water-based coatings on environmental humidity and moisture content of the base are better than solvent based coatings, their applicability in other aspects is not as good as solvent based coatings (1) Due to the high surface tension of water, it is difficult to infiltrate the base material, and it is easy to produce shrinkage cavity The water-based coating also has high requirements on the construction process and material surface cleanliness Whether it is solvent coating or water-based coating, the quality of oil removal on the surface of workpiece will affect the quality of coating For the spraying of solvent based coating, the oil removal on the surface of the workpiece is not complete, which is not easy to appear immediately on the appearance; however, for the spraying of water-based coating, if the oil removal on the surface of the workpiece is not complete, it is difficult to form a complete paint film on the surface (2) The melting points of the two types of paint dispersion media are very different The melting points of water are 0 ℃, while the melting points of organic solvents are much lower The melting points of toluene and xylene are - 95 ℃ and - 25 ℃ respectively Therefore, for construction temperature, water-based coating construction is generally required to be above 5 ℃, while solvent based coating can also be constructed at 0 ℃ This requirement seriously limits the scope of application of waterborne coatings (3) Spraying water-based coating also has certain requirements for humidity of spray booth When the relative humidity of water-based coating is more than 85%, the surface drying is slow, and the water solvent cannot volatilize normally under the relatively saturated humidity When the humidity is too high (more than 90%), the coating film on the coating will flow down [5] Therefore, it is necessary for the spray booth to have good air circulation and maintain proper humidity (4) Because of the great latent heat of water evaporation, which is 5-7 times of the general solvent, it is often necessary to increase the drying temperature or extend the drying time 3.2 at present, the water-based coating has the protection and decoration functions of common solvent based coating, but in the occasion of high decorative requirements, it can not achieve high fullness, which needs solvent based coating to achieve 3.3 thinking inertia at present, there is no mandatory requirement for the use of water-based coatings, while traditional solvent based coatings are widely rooted in all aspects of social production and life, and professionals have long been familiar with their performance, so they have to be handy in both production and use To master this new thing, it needs to spend extra energy to understand and be familiar with its characteristics Because of the influence of using inertia, most people are not willing to give up the solvent coating which has been used stably and take some investment risk to use water-based coating, which is also a big obstacle to the popularization and application of water-based coating 4 It is expected that the VOC content of water-based coatings is significantly lower than that of solvent based coatings, which is environmentally friendly and healthy for constructors and users