Comparison of properties of water and solvent Replace the solvent in the coating, and water is commonly used as a solvent and a dispersing medium. In water-based coatings, water has significantly different properties compared with ordinary solvents.
① Water freezes at 0°C, water-based paints should be stored above the freezing point, and the technical properties of paints (such as stability, usability, surface properties, etc.) should be checked at any time to see if they change due to solidification.
② Water boils at 100°C, and the volatility of a single water is much lower than that of the solvent. The solvent-containing paint mixed solvent will volatilize uniformly over time to form a smooth paint surface, but it is very difficult to form a good coating surface for water-based paints. agent.
③ The surface tension of water is significantly higher than that of organic solvents, which leads to poor wetting of the coated substrate. Therefore, a clean substrate must be provided when using water-based paints. At the same time, an auxiliary solvent is added to reduce the surface tension of the water.
④ Compared with the solvent, the vaporization heat of water is high, the water-based paint needs more energy to dry, the drying is difficult, and the drying time is long.
⑤ Water is non-combustible, this advantage can reduce insurance costs, it is also conducive to storage and transportation, and it is much safer to contact during use. There is no danger of burning during use.
⑥ Water has completely different solubility parameters from organic solvents. It is significantly more polar than organic solvents and can form much stronger hydrogen bonds. dupont ptfe dispersion The polarity of the binder must be close to that of water, and preferably has strong hydrogen bonds.
⑦ The dipole moment and dielectric constant of water and organic solvents have different values, which can be used to predict the properties of water-based coatings.
⑧ The electrical and thermal conductivity of water is significantly different from that of organic coatings. Contrary to solvents, water used in coatings is not an insulator, so it is difficult to conceive the basic principle of electrostatic spraying of water-based coatings.
The characteristics of water-based coatings Compared with solvent-based coatings, water-based coatings have the following characteristics.
Using water as the solvent, the water source is convenient, easy to purify, and saves a lot of other resources; eliminates the risk of fire during construction; reduces the pollution to the atmosphere; only a small amount of low-toxicity alcohol-based organic solvent is used, which improves the operating environment conditions. The general water-based paint organic solvent (accounting for paint) is between 10% and 15%, and the current cathodic electrophoretic paint 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 applied directly on wet surfaces and in wet environments; it has good adaptability to the material surface and strong coating adhesion.
③ The brushing tool can be cleaned with water, which greatly reduces the consumption of cleaning solvent.
④ The electrophoretic coating is uniform, flat and has good flatness; the inner cavity, welds, edges and corners can be coated with a certain thickness of coating, which has good protection; the electrophoretic coating has good corrosion resistance high resistance to salt spray up to 1200ho for thick film cathodic electrophoretic coatings
In a word, water-based coatings are colorless, odorless, non-toxic, low-viscosity, fast-drying, good in fullness, high in solid content, low in cost, wide in sources, free of organic volatiles, high in hardness, and can be diluted and cleaned with water. Requirements are relatively broad and so on. These are unmatched by other solvent-based coatings. If other additives are added, it can also improve its performance and make it have good gloss, leveling, folding resistance, abrasion resistance and chemical resistance, etc., so it is especially suitable for the surface treatment of food, medicine and other packaging. And post-press glazing; and widely used in water-based metal anti-corrosion coatings, water-based wood furniture coatings.
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