Hiding power
The ability to paint evenly on the surface of an object with color paint so that the base color no longer appears is called hiding power. It is generally expressed in two ways: that is, the minimum amount of paint required to cover a unit area, expressed in g/m², or the minimum wet film thickness required to cover the bottom surface, expressed in μm.
1. Scope and description
This method is applicable to the measurement of the hiding power of paint. Its test principle is to use a black and white grid board to cover the paint evenly until the black and white grid is invisible, and weigh the amount of paint used to obtain the hiding power. g/m2 table (based on wet paint film or dry film).
2. Instruments and Materials
(1) Paint brush: width 25~35mm; (2) Spray gun: nozzle inner diameter 0.75~2mm; (3) Balance: Sensitivity is 0.01g, 0.001g; (4) Black and white grid glass plate (brushing method): as follows As shown in the figure; (5) black and white grid board (spraying method): as shown in the figure below; (6) glass plate (JG 40-62): 100mmX100mmX (1.2~2) mm; (7) blast constant temperature oven (8) Wooden obscura: 600mmX500mmX400mm, inside the box is divided into upper and lower parts by 3mm thick frosted glass, the grinding surface of the frosted glass is downward to make the light even, the upper part of the obscura is parallel with 2 15W mouth lights, and a light shield is installed in front , with the lower front open for inspection, and the inner walls painted with matt black lacquer.
3. Measurement method
(1) Brushing method
①According to the viscosity specified in the product standard, weigh the total weight of the cup containing the paint and the paintbrush on a balance with a sensitivity of 0.01g.
②Use a paintbrush to evenly paint the paint on the black and white grid glass plate, put it into the dark box, 15 to 20 cm away from the frosted glass sheet, and the end with the black and white grid is inclined at an angle of 30 ° to 45 ° with the plane. Observe under a fluorescent lamp until the black and white squares are just invisible.
③Then weigh the cup containing the remaining paint and the paint brush together to find the weight of the paint on the black and white grid board.
Note: If the viscosity is too high to be painted, adjust the sample to the brushing viscosity. However, the amount of thinner should be deducted when calculating the hiding power.
(2) Spraying method
①Adjust the sample to a viscosity suitable for spraying, weigh two glass plates of l100mnX 100mm on a balance with a sensitivity of 0.001g, and spray in layers with a Spray Gun.
②After each spraying, put the glass plate on the black and white grid plank, place it in the dark box, and place it 15~20cm away from the frosted glass sheet. Observation is carried out, and the black and white squares are just invisible as the end point.
③Then wipe off the paint on the back and edge of the glass plate, and bake various spray paints to constant weight according to the curing temperature specified in the solid content.
Note: When observing in the dark box, one sun lamp should be used for light-colored paint, and two fluorescent lamps should be used for dark-colored paint.
4. The results are not shown
(1) Brushing method The covering power of brushing method (g/m²) is calculated according to the following formula (calculated by wet film):
Take two parallel measurements, and if the difference between the results is not more than 5% of the average value, take the average value; otherwise, a new test is required.
(2) Spraying method The covering power of spraying method (g/m²) is calculated according to the following formula (calculated as dry film):
Two parallel measurements, if the difference between the results is not more than 5% of the average value, take the average value, otherwise, a new test is required.
5. Reference standard
National standard GB/T 1726 "Determination of coating hiding power".
