With the implementation of increasingly stringent environmental standards, water-based coatings have been widely used and developed as environmentally friendly coatings. For example, all of our interior and exterior paints, metal paints, automotive paints, etc. have corresponding water-based paint products. As a relatively new type of coating in the current coatings market, many people do not have a correct understanding of it. We should learn more about the characteristics of waterborne coatings and the requirements of spraying construction in order to better use them in daily life.
1. Introduction to waterborne coatings
Any coating that uses water as a solvent or as a dispersion medium can be called a waterborne coating. Water-based coatings include water-soluble coatings, water-reducible coatings, and water-dispersible coatings (latex coatings). The water-soluble paint is a water-soluble resin as a film-forming material, and is represented by polyvinyl alcohol and various modified products thereof, in addition to water-soluble alkyd resin, water-soluble epoxy resin, and inorganic polymer water-based resin.
2. Characteristics of water-based paint
Water-based paints use water as a solvent in production and construction applications, and the equipment used can be washed with water; the solid content is increased to lower the price; the pigment dispersion in water-based paints is worse than the solvent type, which affects the weather resistance; The solvent type is high, the wettability and spreadability of the surface of the workpiece are poor, and the coating film is prone to pinholes, shrinkage cavities, bubbles and sag; the water evaporation of the waterborne coating is slower than the solvent-based coating, and the flashing time is long or needs Low temperature baking. The water-based coating film with higher water content needs to be dried and heated at a temperature lower than 100 °C, and can be baked until the moisture is basically removed; the shearing force has an effect on the stability of the water-based paint in the circulation system. Different viscosities and flow rates occur with different shear forces.
Waterborne coatings are a relatively new type of coating on the coatings market today, as opposed to solventborne paints, as follows:
2.1 Advantages of waterborne coatings
(1) Water-based paint uses water as solvent, which saves a lot of resources; water-based paint eliminates fire hazard during construction; reduces pollution to the atmosphere; water-based paint uses only a small amount of low-toxic alcohol ether organic solvent to improve the working environment condition. The general water-based coating organic solvent (accounting for coating) is between 10% and 15%, and the current cathodic electrophoretic coating has been reduced to less than 1.2%, which has a significant effect on reducing pollution and saving resources.
(2) Water-based paint can be directly applied on wet surface and humid environment; water-based paint has good adaptability to material surface and strong coating adhesion.
(3) Water-based paint coating tools can be cleaned with water, greatly reducing the consumption of cleaning solvents.
(4) The waterborne coating electrophoretic coating film is uniform and flat. Good flattening; inner cavity, weld seam, edge and edge parts can be coated with a certain thickness of coating film, which has good protection; electrophoretic coating film has the best corrosion resistance, thick film cathodic electrophoretic coating Salt spray resistance up to 1200h.
2.2 Problems with waterborne coatings
(1) The water-based paint has high requirements on the cleanliness during the construction process and the surface of the material. Due to the large surface tension of the water, the dirt tends to cause shrinkage of the coating film.
(2) The dispersion stability of the water-based paint against the strong mechanical force is poor, and when the flow velocity in the conveying pipe changes abruptly, the dispersed fine particles are compressed into solid particles, causing the coating film to produce pitting. The conveying pipe is required to have a good shape and the pipe wall is free from defects.
(3) Water-based paints are highly corrosive to coating equipment, and need to be made of anti-corrosion lining or stainless steel, and the equipment cost is high. The water-based paint corrodes the conveying pipe, the metal dissolves, the dispersed particles are precipitated, and the coating film produces pitting, and a stainless steel pipe is also required.
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