The choice of painting method is determined by factors such as the shape of the object, location (on-site or production line), the surface area to be painted, and the desired paint thickness.
The method of painting varies depending on factors such as the desired paint thickness, the surface area to be painted, and the condition or shape of the object to be painted. For immovable objects like buildings, on-site painting is suitable, while large, uniform industrial products are best painted using a production line method. Typically, using paint machines suitable for high-viscosity paints is necessary to achieve a thick paint coating. Various painting methods and their applicable paint viscosities are outlined in Table 1-3.
“Brush painting” and “roller painting” are suitable for small surface areas, while “spray painting” is used for large areas and includes “air spray” and “airless spray,” with airless spray being suitable for high-viscosity paint. In industrial “spray painting,” the rotating atomization method is also common, generating fine particles and being suitable for high-quality coatings. However, because spray painting is not very efficient, electrostatic spray painting, which utilizes static electricity, is widely used.
“Curtain flow painting” and “roll coater painting” are suitable for quickly painting flat surfaces, but they are not suitable for curved objects. On the other hand, “dip painting” is suitable for complex-shaped objects and can also be used with powder coatings.
“Electrodeposition painting” is a type of dip painting where voltage is applied between the electrodes to utilize an electrochemical reaction to create a coating. There are two types: cationic electrostatic painting and anionic electrostatic painting.
An overview of various painting methods and their applicable paint viscosities:
Table 1-3: Painting Methods Painting Method Features Viscosity (mPa·S)
- Brush/Roller Painting: Use brushes or roller brushes to directly apply paint to the object. Craftsman’s skill affects the result. Applicable viscosity ranges from 300 to 1000.
- Air Spray: Use a spray gun to mix paint with high-speed airflow and apply it as a mist to the object. Suitable for large areas and smooth coatings with a viscosity range of 20 to 40.
- Airless Spray: Spray relatively high-viscosity paint at high pressure, creating fine droplets. Can create thick coatings in one go, with a viscosity range of 100 to 1000.
- Rotary Atomization Painting: Supply paint to a rapidly rotating disc or cylinder cup, where centrifugal force creates a thin mist. Viscosity ranges from 60 to 150.
- Curtain Flow Painting: Objects pass through a paint curtain flowing down from a slit. Enables fast painting but is limited to flat objects, with a viscosity range of 100 to 300.
- Roll Coater Painting: Supply paint and apply it to the object using an applicator roll. Suitable for high-speed painting of flat objects with a viscosity range of 100 to 300.
- Dip Painting: Dip the object into a tank filled with paint and raise it or pass it continuously. Viscosity ranges from 2000 to 10000.
- Electrostatic Painting: Immerse the object in water-based paint, apply a direct current voltage between the object and counter electrodes, and precipitate paint through electrochemical reactions. Suitable for complex shapes and hard-to-reach areas with a viscosity range of 1.0 to 40.
Regardless of the chosen painting method, proper pre-treatment of the object is crucial, including removing oil, rust, and foreign particles. Additionally, polishing and chemical treatments may be performed as needed.