Coating drying methods are divided into three categories: natural drying, drying and radiation curing.
It is suitable for white-drying paints such as volatile paints, air-drying paints, and curing agent-cured paints. They are dried into films . The drying speed is greatly affected by the environmental conditions, requiring good ventilation and less dust, which is conducive to solvent volatilization and the safety of the work site, and reduces the adhesion of dust.
When the ambient humidity is high, the evaporation of the solvent is inhibited, the drying is slow, and it causes defects such as whitening of the coating film. Therefore, the humidity of the working environment should be low rather than high. When the temperature is high, the solvent volatilizes quickly, the curing reaction is fast, and the drying is also fast, which is beneficial to reduce dust adhesion, but it may make the leveling property worse. The thinner should .
Drying is divided into low temperature drying, medium temperature drying and high temperature drying. Below 100°C is called low-temperature drying. It is mainly to carry out forced drying of self-drying paint or dry the coating film on the surface of the material with poor heat resistance. The drying temperature is usually 60~80 ℃ , so that the drying time is greatly shortened to meet the industrial production line.
For example: Nitro paint takes 1.5 hours to dry at room temperature, but only 10-30 minutes at 60-80 ℃ ; the drying time of two-component polyurethane paint at room temperature is 12 hours, 30 minutes at 60 ℃ , and only 15 minutes at 80 ℃ .
Medium temperature drying is below 150 ℃ , mainly used for drying and filming of top coats. When the temperature exceeds 150 °C , the coating film will turn yellow and become brittle, and it is usually baked between 120 °C and 140 °C .
The suitable drying temperature for various coatings is as follows:
| Acrylic baking varnish | 120-140℃ | 30-60min |
| Amino baking varnish | 120-140 °C | 30-60 minutes |
| Alkyd paint | 100-120 °C | 20-30 minutes |
| Aqueous Amino | 140 °C | 20-40min _ |
| Baking Lacquer (Acid Catalyzed) | 130-150 ℃ | 20-40min _ |
| Synthetic resin secondary paste | 120-140 °C | 20-30 minutes |
| amino acid | 100-120 °C | 30-60 minutes |
| Zinc Yellow Primer | 120-140 °C | 20-40min _ |
Light-colored paint generally adopts a lower drying temperature (such as 120°C, which can cure the coating film for a longer time to avoid yellowing; dark-colored paint adopts a higher drying temperature to shorten the drying time and increase productivity.
Above 150 ℃ belongs to high temperature drying. Such as epoxy phenolic primer, water-based phenolic, cathodic electrophoretic paint , etc. , generally at a high temperature of 180~200 ℃ to fully cross-link and cure the coating film to improve the anti-corrosion performance of the coating film. Since the primer only requires protective properties and has no requirements on the color of the coating film, it is dried at .
In order to prevent defects such as pinholes and orange peels in the coating film during the drying process, the wet coating film should be pre-dried for 3~8 minutes according to the thickness of the coating film before .
Radiation curing is the use of ultraviolet rays or electron beams to rapidly initiate and polymerize unsaturated resin paints, and the curing speed is very fast. Ultraviolet rays can only cure varnishes, and the hardening time generally does not exceed 3 minutes; electron beam radiation can be used for rapid hardening of colored paints because of its high energy and strong penetrating power, and the hardening time only takes a few seconds . Electron beam radiation curing equipment has a large investment, strict safety management, and less use; while ultraviolet curing is widely used for curing coatings on flat surfaces such as wood, plastic, paper, and leather.
In addition to the above three main drying methods, there are also electric induction drying and microwave drying, but they are mainly used for rapid curing of adhesives. Inductive drying is also called high-frequency heating. When a metal workpiece is put into the coil, the coil is energized with 300~400Hz/s alternating current, and a magnetic field is generated around it to heat maximum temperature can reach 250~280 ℃ , which can be Adjust according to the current intensity. Since the energy is directly applied to the workpiece, the resin film is heated and dried from the inside out, the solvent can be quickly and effectively released and the coating film is cured, the bonding strength is very high, and it is better used in the bonding field.
Microwave drying is a specific material molecule vibrating under the action of microwave (1mm~1m) to obtain energy and produce thermal effect. Microwave drying is limited to the coating film on the surface of non-metallic substrates, which is just opposite of high-frequency heating. Microwave drying is selective to the object to be dried, and the equipment investment is large, but its drying is uniform and fast, and the drying time is only 1/10~1/100 of the conventional method.