Coating drying performance testing

The process of the paint changing from a liquid coating film to a solid film is called drying. According to the national standard GB/T1728-89, the drying degree of paint is divided into two stages: surface drying and actual drying.

1. Determination of surface drying time

Method A (blowing cotton ball method) Gently put a cotton ball on the surface of the deep film, use your mouth to keep the cotton ball 10-15cm away, and gently blow the cotton ball along the horizontal direction. If it can be blown away, there will be no cotton thread left on the film surface The surface is considered to be dry. Method B (finger touch method) lightly touches the surface of the paint film with a finger. If it feels a little sticky, but no paint sticks to the finger, the surface is considered to be dry. (Related instrument: drying time Tester)

2. Determination of actual drying time

Method A (pressed paper method) put a piece of qualitative paper (15mmX15mm) on the paint film (smooth surface in contact with the paint film), lightly place the dry Tester (weight 200g, bottom area 1c㎡) on the paint film, and start the stopwatch at the same time , After 30 seconds, take away the drying Tester, turn the sample over, and the paper can come out and fall, or weave lightly on the back with your fingers a few times, and the paper can fall freely without paper fibers remaining on the paint film, which is the actual drying .

Method B (pressing cotton ball method) put a degreased cotton ball on the paint film, put the drying Tester on the fine ball, and start the stopwatch at the same time, after 30 seconds, remove the drying Tester and cotton ball, and the sample rotates After 5 minutes, observe the marks of glossy balls on the paint film and the phenomenon of loss of gloss. If there are 1-2 cotton threads left on the paint film, which can be gently flicked off with a cotton ball, it is considered that the paint film is actually dry.

Regarding the division and testing methods of the drying process, there are great differences in the standards of various countries, such as ASTMD1640-05. The drying process is divided into 8 stages: ISO1517 uses the 125-250 µm glass bead falling ball method to measure the surface dryness without imprinting Dry, test with 1000g weight ((GB/T9273-88).

If you want to observe the whole drying process continuously, you can use an automatic drying time measuring instrument. This instrument uses a motor to drive the gear through the reduction box, and walks on the paint film in a straight line at a slow speed of 30mm/h. The whole process takes 24 hours. As the paint gradually dries, the tooth track gradually changes from deep to shallow until it disappears. Recently, the needle moves at a constant speed to make a needle track on the paint film, and the drying process is evaluated according to the change of the track (see Figure 8 2 3).