Advantages and disadvantages of waterborne epoxy coatings and their applications
Waterborne epoxy resin coatings have excellent metal adhesion and corrosion resistance, as well as good chemical stability and bonding properties. Waterborne epoxy resin coatings are the focus of the current coatings industry research. At present, there are many kinds of waterborne epoxy coatings, which can be roughly divided into three main types: water dispersion, colloid dispersion and water solubility. The two components of hydrophobic epoxy resin and hydrophilic amine curing agent are widely used in the market. They can be divided into five types according to their physical morphology. There are many methods to classify waterborne epoxy resin. According to the classical classification method, waterborne epoxy resin coatings can be divided into four categories: type I, type II, type III and type IV. Type I waterborne epoxy resin is composed of low molecular weight liquid bisphenol A epoxy resin and water curing agent. Various active diluents were used to adjust the viscosity of epoxy resin and the crosslinking density of cured film. Type II uses high molecular weight solid bisphenol A epoxy resin. Epoxy resin is an oleophilic molecule, and its hydrophilic-lipophilic equilibrium value (HLB) is less than type III. Type III is composed of low molecular weight liquid epoxy resin emulsion and waterborne epoxy curing agent. Low molecular weight liquid epoxy resin emulsion is usually prepared by phase inversion technology. Type IV waterborne epoxy resin type IV is improved from type III. It is composed of waterborne epoxy resin emulsion and polyurethane modified epoxy curing agent. Properties of waterborne epoxy coatings
Because of the epoxy group, ether bond, hydroxyl group and phenyl ring structure in the molecular structure of epoxy resin, the epoxy coatings play an important role in the final performance of the film, so that the epoxy coatings have the following properties:
ring structure. The excellent adhesion of oxygen resin coatings is mainly determined by the molecular structure of epoxy resin and its curing reaction characteristics. There are polar groups in the molecular structure of epoxy resin, such as epoxy terminal group, hydroxyl group and ether bond. The existence of these groups causes electromagnetic adsorption or chemical bond between epoxy resin molecule and its adjacent interface. Therefore, epoxy resin coating film can produce strong bonding force with the surface of metal, wood, concrete and other substrates.
01 Good chemical corrosion resistance
Epoxy resin containing hydrophilic hydroxyl group, ether bond and amino group in curing agent will affect the water resistance of the film, but two phenyl rings and one propylene group in bisphenol A epoxy resin molecule have shielding effect on hydroxyl and ether bond, so that The water resistance of the whole paint film is guaranteed. After curing epoxy resin into film, because of the stable phenyl ring and ether bond in the molecular structure, the molecular structure is relatively close, so the chemical medium has better stability. There are many kinds of epoxy resin and epoxy curing agent, which can be adapted to different construction conditions and application environments by changing the formulation to make epoxy coatings show variety and flexibility of application. The development advantages of waterborne epoxy coatings
02 Environmentally friendly
Water-borne epoxy coatings are conducive to the healthy development of the environment from the source of raw materials to the whole life cycle of production and use. The volatile organic solvents are replaced in the production process, and the coating tools can be washed with water when used, which also reduces the consumption of cleaning solvents. The production of organic solvents needs to consume fossil raw materials. At the present stage of resource shortage, it is a great challenge to resources. The emergence of waterborne epoxy coatings has solved this problem. At the same time, the reduction of solvents greatly reduces the emission of volatile organic compounds in the production and use process, and improves the surrounding atmospheric environment. On the other hand, water-borne coatings only use a small amount of low-toxic alcohol ether organic solvents, which reduces the volatilization of organic solvents, greatly improves the environment of the workplace and benefits staff. Good health.
03 Safety Improvement
Take toluene and xylene as examples: the flash point of toluene is 4 ~C, vapor can form explosive mixture with air, explosive limit is 1.2%~7.0%(volume); the flash point of xylene is 29 ~C, vapor can form explosive mixture with air, explosive limit is about 1%~7%. (Volume). Both are flammable substances. Therefore, the storage and use of flammable and explosive materials in solvent-based coatings are at risk of fire and explosion accidents. The production and use of waterborne epoxy coatings reduce the demand for flammable and explosive raw materials and greatly reduce the risk.
04 Reduces the cost of raw materials
(a). With the increasing demand for resources and energy, there is a shortage of resources and energy in the world, which leads to the rising prices of oil and even downstream products. As an organic solvent for downstream products, it is no exception. Under the pressure of resource price, the price advantage of water as diluent is gradually emerging.
(b) Reduction of environmental costs. Traditional solvent-based coatings produce a large amount of organic waste gas in the production process. 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. Water-borne epoxy coatings emit little organic waste gas, which lightens the burden of enterprises.
(c) Reduction of safety cost. Waterborne epoxy coatings use water as a diluent to make it a safer coating. The potential fire hazards from production to transportation to application are much lower than those of traditional solvent coatings. For managers
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