Common knowledge of coatings: the importance and common difficulties of developing waterborne coatings

Core tip: water borne coating is defined as "the vast majority of volatile substances in the formula are water-based coating" In water-based coatings, the unique physical properties and universal existence of water determine the use of water-based coatings and the development of science and technology With the continuous improvement of people's awareness of environmental protection and the increasingly strict environmental protection laws and regulations, waterborne coatings will become the leading role in the world paint market in the 21st century At present, there is a huge market in China 1 The importance of developing waterborne coatings From “ Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Home of coatings: water borne coatings are defined as "the vast majority of volatile substances in the formula are water-based coatings" In water-based coatings, the unique physical properties and universal existence of water determine the use of water-based coatings and the development of science and technology With the continuous improvement of people's awareness of environmental protection and the increasingly strict environmental protection laws and regulations, waterborne coatings will become the leading role in the world paint market in the 21st century At present, there is a huge market in China 1 The importance of the development of water-based coatings from the word "water-based", we do not see the significance of this, water has become common in our daily life The reason why the importance of water is highlighted here and other components in coatings are often not mentioned or highlighted is that in this kind of coatings, "water" has replaced or largely replaced "organic solvents" in other kinds of coatings Moreover, from the perspective of practical engineering application, the performance of coatings is largely determined by the characteristics of solvents Waterborne coatings have made great progress because of more and more attention The driving force of its scientific and technological progress is the limitation of the emission of organic solvents into the atmosphere, which is also the driving force of the development and progress of powder coatings and high solid content coatings Reducing the volatilization of organic solvents is of environmental and economic significance The earliest environmental protection consideration began in the United States, which first formulated government regulations to restrict the photosensitivity of organic solvents such as olefins, aromatic compounds and branched ketones The first statute was the six six six statute enacted by Los Angeles County in July 1966 The reason is that Losangels is deeply troubled by the environmental problems caused by organic solvents, because of its geographical characteristics, the volatile organic solvents gather in the air over the city for a long time They linger in the sky of the city, often cause the fog of photochemical reaction and bring great trouble to the city As early as 1970, the U.S government enacted nationwide regulations to control hydrocarbon emissions, known as the "Clean Air Act" t In addition to the advantages of environmental protection, waterborne coatings have many other advantages Especially for the construction workers in the coating industry, the widespread use of water-based coating can make them less or less exposed to the potential toxicity of organic coating and avoid the hidden danger of fire In the aspect of waste treatment, the waste produced by general water-based coating is easier to be non-toxic than solvent coating Economically speaking, water-based coatings are more popular, because water is the cheapest and most recyclable solvent in engineering solvents Water is the most economical and stable alternative to organic solvents, which are often affected by oil prices It is reported that a senior engineer in Taiyuan was decorating his home When he went to the construction site one day, he found that three painters had passed out After emergency rescue, one person died It is understood that the painters can't open windows when painting furniture to prevent the paint from cracking At night, the painters feel bad smell, so they hide in another room without painting and sleep Unexpectedly, they are poisoned Especially in the use of paint in the process of the greatest harm, and paint workers are often the biggest victims In addition, 3-6 months after the use of the coating is also the most vulnerable period to harm human health The main harmful substances contained in the coating are volatile benzene and benzene series compounds, which are the main pollutants It is understood that benzene has been identified as a carcinogen by the World Health Organization, which can cause cancer, blood diseases, etc In addition to the pollution in construction, the harm after occupancy should not be underestimated It is because of the advantages of water-based coatings mentioned above, although some conservative coating users are still hesitating, all kinds of water-based coatings have been more and more popular Many researchers in the field of coatings are more and more devoted to the research of waterborne coatings 2 Green recommendation standard and scope of water-based coatings in July 2002, the Secretariat of China Environmental Labeling Product Certification Committee and the State Environmental Protection Administration jointly issued the new technical requirements for water-based coating environmental labeling products, which made mandatory provisions on the environmental protection, green, health, safety and other standards of water-based coatings commonly used in home decoration We are familiar with Dulux, lipang, Fuya, etc as the first batch of coatings to pass the new standard More than 8000 coating enterprises in China only have more than 30 more than 100 kinds of water-based coatings up to the standard First, VOC (volatile organic compound) index Due to the unclear definition, many enterprises think that their products have reached a higher level than international standards This misunderstanding stems from two influential standards, namely, the limit standard of harmful substances in interior wall coating issued by AQSIQ and the safety and health quality evaluation rules issued by Beijing Municipal Bureau of quality supervision, which both define VOC as the VOC content of volatile organic compounds in one liter coating However, the definition of VOC in the world refers to the content of VOC deducted from the dry weight of water in a litre of paint This difference leads to the VOC ≤ 125g / L index in Beijing rules, but it is equivalent to 250G / L in foreign countries, which is the boundary between foreign waterborne paint and solvent paint However, the national compulsory standard of 200g / L is equivalent to more than 410g / L of foreign countries, which has come out of the boundary of waterborne coatings Therefore, it is wrong for many people to say that the 250 g / L limit stipulated in the 1999 environmental labeling standard is wider than the Beijing rules and the national mandatory standards Because of the same VOC measurement standard as the international standard, the environment mark standard in 1999 is actually stricter than the two mandatory standards The environment mark standard in 2002 stipulates that the interior wall coating is ≤ 100g / L, which is the correct VOC value measured and calculated according to the American ASTM method The limit value is the same as the American Standard, and stricter than the two standards, which reflects the high standard and strictness of the green recommended products Ask Secondly, it is not clear to the public about benzene, toluene, xylene, ethylbenzene, halogenated hydrocarbon, formaldehyde and formaldehyde polymer, as well as heavy metal lead, cadmium, chromium, mercury, etc., which are not allowed to be added, so there is no difference between high and low content, only the law-abiding and illegal problem of complying with the rule of "not adding" Many enterprises take these indicators as the basis of healthy coatings, which is not in line with the actual situation of water-based coatings To this end, the State Environmental Protection Administration standard clearly stated that all the above substances are only to control the limits of harmful substances brought by impurities, that is to say, the harmful substances such as pigments, titanium dioxide and emulsions are not allowed to be artificially added The third is the scope of water-based coatings In addition to the widely used interior and exterior wall coatings, water-based wood coatings, water-based anti-corrosion coatings, water-based waterproof coatings and water-based polyurethane coatings have also entered the green recommended standard range Take only one example of water-based wood paint At the 2004 Athens Olympic Games, all venues are designated with water-based wood paint Because for home decoration, Germany and France have stipulated that neighbors cannot smell the smell of organic solvents In order to adapt to this people-oriented trend, more support for all kinds of waterborne coatings is the goal of this new standard 3 Common difficulties of water-based coating water-based coating and organic solvent coating are similar in some places But in some cases, waterborne coatings often have to face some difficulties that are not found in organic solvent coatings The biggest difference between the two systems is the gradual disappearance mechanism of the continuous phase of the volatiles during the film formation However, the film-forming process has a great influence on the final performance of the coating, which has attracted great attention 3.1 the water in the water-based coating has a high boiling point, so the evaporation process is very slow and strongly depends on the humidity of the environment In the case of low humidity, it may dry quickly and sometimes cause cracks In the case of high humidity (for example, humidity of Nicaragua in tropical countries often reaches 78-85%), the film forming process will be very slow, resulting in the sagging of the coating More energy is needed to dry it, even four times as much as solvent based paint, because of the higher specific heat of water 3.2 the water-based coating has high requirements on the cleanliness of the construction process and the material surface Due to the high surface tension of water, it is not easy to infiltrate and moisten, and it is easy to cause shrinkage of the coating film This problem is particularly prominent on greasy surfaces 3.3 the dispersion stability of water-based coating against strong mechanical force is poor When the flow velocity in the pipeline changes rapidly, the dispersed particles are compressed into solid particles, making the coating produce pockmarks Therefore, it is required that the shape of the conveying pipe is good and the pipe wall is free of defects 3.4 the water-based coating is corrosive to the coating equipment, especially to the iron equipment Corrosion resistant lining or stainless steel materials are often used, which leads to high equipment cost Stainless steel pipe is also required for corrosion and metal dissolution of water-based coating to transmission pipeline, which makes dispersed particles precipitate and coating produces pockmarks 3.5 the baking type water-based coating has strict requirements on the construction environment (temperature and humidity), which increases the input of temperature and humidity regulating equipment, and also increases the energy consumption 3.6 the evaporation latent heat of water is large, and the baking energy consumption is large The cathodic electrophoretic coating needs to be baked at 180 ℃, while the latex coating has a long drying time 3.7 organic cosolvent with high boiling point will produce a lot of oil smoke during baking, which will drop on the surface of the coating after condensation and affect the appearance 3.8 the coating layer formed is often sensitive to water, even if the water vapor content in the air increases, the coating will wrinkle Although there are many problems in water-based coatings, some problems are prevented in the process and some problems are improved and improved through the formulation, coating process and equipment 4 Conclusion and prospect as a new "sunrise" type, waterborne coatings have been and will continue to get rapid development In view of the growing concern for environmental protection, energy and health, the development of waterborne coatings should be a sustained and persistent task for the government and scientific and technological workers in the future In terms of technological innovation, water solubility, cross-linking agent and surfactant are the focus of scientific research Recently, the research and development direction of waterborne coatings is devoted to the change and improvement of stress resistance and ambient temperature