The advantages and disadvantages of water-based epoxy coatings and their application.

Water-based epoxy coatings have excellent metal attachment and corrosion resistance, but also have good chemical stability and bonding properties, water-based epoxy coatings are the focus of current research in the coating industry.
classification of water-based epoxy coatings
There are a wide variety of water-based coatings, which are broadly divided into three main types: water dispersion type, collosus dispersion type, and water solubility. Widely used in the market is mainly hydrophobic epoxy resin and hydrophobic amine curing agent 2 parts, according to the physical form of 2 parts can be divided into 5 types

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There are many classification methods of water-based epoxy resin, according to the classical classification method of water-based epoxy resin coating into I. type, II type, III.type, IV.type and other 4 categories: I. type water-based epoxy resin body consists of low-molecular liquid biphenol A epoxy resin and water-based curing agent. Various active thinners are used to regulate the viscosity of epoxy resins and the cross-link density of the coated film after curing. Type II uses a high molecular weight solid Bisphenol A epoxy resin. Epoxy resin is an oil-friendly molecule whose hydro-hydro-oil balance value (HLB) is less than type III. Type III. Type consists of a liquid epoxy emulsion with low molecular weight and a water-based epoxy curing agent, and a liquid epoxy emulsion with low molecular weight is generally prepared using reverse trans-technology. Iv. Type water-based epoxy resin IV. Type is improved by Type III. It consists of a water-based epoxy emulsion and a polyurethane modified epoxy curing agent.
Water-based epoxy coating performance
Due to the epoxy base, ether bonds, hydroxyl and benzene ring structure contained in the molecular structure of epoxy resin, the final performance of the coating film plays an important role, so that epoxy coating has the following properties:
01, excellent adhesion
epoxy coating has excellent adhesion is mainly determined by the molecular structure of epoxy resin and its curing reaction characteristics. Epoxy resin molecular structure has epoxy end, hydroxyl and ether bonds and other polar groups, the presence of these groups so that epoxy resin molecules and adjacent interface to produce electromagnetic adsorption or chemical bonds, so epoxy resin coating film and metal, wood, concrete and other substrate surface can produce a strong bonding force.
02, good chemical corrosion resistance
Epoxy resin contains hydrohydroxy, ether bonds and amino in the curing agent and other hydro-hydrogenic groups will affect the water resistance of the coating film, but bisphenol A epoxy resin molecules in the two benzene rings and a subpropanyl hydroxyl and ether bonds have a shielding effect, thus ensuring the water resistance of the entire paint film. After epoxy resin is cured into film, it has better stability to chemical medium because the molecular structure contains stable benzene ring and ether bonds, and the molecular structure is relatively tight.
03, the diversity of coating varieties and a wide range of adaptability
epoxy resin and epoxy curing agent varieties are many, can be changed to adapt to different construction conditions and application environment, so that epoxy coatings show variety and application flexibility.
the development advantages of water-based epoxy coatings
01, environmentally friendly
water-based epoxy coatings from raw material sources to the production and use of the full life cycle, are conducive to the healthy development of the environment. Volatile organic solvents are replaced during the production process, and the use of coating tools can be cleaned with water, reducing the consumption of cleaning solvents. The production of organic solvents needs to consume fossil raw materials, which is a challenge to resources at this stage of resource shortage, and the emergence of water-based epoxy coatings solves this problem. At the same time, solvent reduction, greatly reduce the production and use of volatile organic compounds emissions, improve the surrounding atmospheric environment, on the other hand, water-based coatings only use a small amount of low toxic alcohol ether organic solvents, organic solvent volatility decreased, greatly improve the workplace environment, conducive to the health of staff.
02, safety improvement
to solvents in the more common toluene and xylene as an example: toluene flash point of 4 degrees C, steam can form an explosive mixture with air, explosion limit 1.2% to 7.0% (volume); Both are flammable substances. Therefore, solvent-based coatings of flammable and explosive raw materials storage and use of the site, there is a risk of fire and explosion accidents. The production and use of water-based epoxy coatings reduces the demand for flammable and explosive raw materials and greatly reduces the risk.
03, reduce costs
(a) reduce the cost of raw materials. With the increasing demand for resources and energy, there is a shortage of resources and energy in the world, resulting in the price of oil and even downstream products continue to rise, as downstream products organic solvents are no exception. Under the pressure of resource price, the price advantage of water as a thinner is gradually emerging.
(b) reduce environmental costs. Traditional solvent-based coating production process produces a large number of organic exhaust gases, in order to meet the emission requirements, enterprises need to configure exhaust treatment facilities and related supporting facilities, and bear the cost of daily operation and maintenance. The organic emissions of water-based epoxy coatings are very small, which reduces the burden on enterprises.
(c) reduce security costs. Water-based epoxy coatings use water as a thinner to make them safer coatings, and fire hazards from production to transportation to applications are significantly reduced compared to conventional solvent-based coatings. For managers, the cost of safety inputs will also be reduced accordingly.
04, construction conditions and appearance performance
water-based epoxy coating due to better breathability, water vapor inside the grass-roots can spread outwards, not easy to foam, so in the grass-roots requirements, water-based epoxy coating construction of the grass-roots moisture content should be less than 10%, solvent-based paint construction of the grass-roots moisture content should be less than 8%. Water-based epoxy coating is adaptable to the surface of the material, the coating adhesion is strong, in the humid environment can be directly coated for construction. In general, solvent-based coatings are applied with solids up to 60%-70%, while water-based epoxy coatings are applied with solids of only 20%-30%, thus it can be seen that the smoothness of water-based coatings is relatively good.
The disadvantages of water-based epoxy coatings
(1) because of the large surface strength of water, difficult to immerse the substrate, easy to produce shrink holes, water-based epoxy coatings on the construction process and material surface cleanliness requirements are also high.
(2) the melting point of the two types of coating dispersion medium is very different, the water is 0 degrees C, while the melting point of organic solvents is much lower, toluene is -95 degrees C, xylene is about 25 degrees C. Therefore, for the construction temperature, water-based epoxy coating construction generally requires more than 5 degrees C, and solvent-based coatings at 0 degrees C can be constructed.
(3) spraying water-based epoxy coating on the humidity of the paint room also has certain requirements, water-based paint in the environment relative humidity of more than 85% when the table dry slowly, water solvent in a more saturated humidity environment can not be normally volatile, when the humidity is too high (up to more than 90%), the coating on the coating will flow down. Therefore, it is necessary to have a good air circulation in the paint room to maintain proper humidity.
(4) because of the evaporation potential heat of water, is 5-7 times the general solvent, often need to increase the drying temperature or extend the drying time.
(5) Although water-based epoxy coatings have the protection and decoration functions of ordinary solvent-based coatings, but in high decorative requirements of the occasion, can not achieve a high degree of abundance, the need for solvent-based coatings to achieve.
Water-based epoxy coating application
Due to the excellent performance and characteristics of water-based epoxy resin, it is widely used in roof leakage prevention, airport runway, elevated bridge road reinforcement, parking lot, sports field, plant flooring, walls, ships, decks, basements and warehouses, aircraft carrier aprons, tunnels and other fields.
water-based epoxy coating can be constructed on wet or newly poured concrete surfaces, has good adhesion to concrete surfaces, can close the water vapor of concrete capillary pipes, and can prevent pan-alkali, suitable as a concrete closed primer. Solvent-based or water-based epoxy floor coatings can be constructed on top of closed primers. Wall and industrial floor coating is an important use of water-based epoxy coating. Water-based epoxy resin odor is small, the coating surface is easy to clean, especially suitable for hospital drug rooms and operating rooms, food processing plants, breweries, beverage factories, pharmaceutical plants, supermarkets, dairy and cosmetics factories and other places that need to maintain a high degree of cleanliness and dust, in line with GMP requirements. If the need for secondary decoration, does not affect the re-painting, the old and new coating still maintain good adhesion. It has now been commercialized with water-based iron epoxy red rust-proof paint, water-based zinc epoxy phosphate rust-proof paint, water-based epoxy zinc-rich primer and water-based epoxy mica rust-proof paint. Water-based epoxy anti-corrosion paint than the market common phenyl propylene, ethyl propylene water-based anti-rust paint and water-based epoxy anti-rust paint performance has greatly improved, in foreign countries is the fastest growing water-based paint, and even some countries have included water-based epoxy anti-corrosion paint in the category of heavy anti-corrosion paint. As an adhesive, water-based epoxy resins can be used in bonding of old and new concrete, repair of cement pre-products and adhesives for paper-plastic composite film. Water-based epoxy resin coatings use water as a dispersion medium, do not contain volatile organic solvents or low content, non-combustible, storage, transportation and use of high safety. Because of its curing after the formation of the coating film is easy to remove radioactive pollution, and water-based epoxy good compounding can facilitate the nuclear power plant's multiple decoration, so many foreign countries have approved water-based epoxy resin coating for nuclear power plant internal walls, ceilings, floors.
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