Tell you how to measure the spreading rate (with formula)

Scope and description

This method is suitable for determining the theoretical spreading rate (theoretical spreading rate) of various coatings. Spreading rate refers to the average area that can cover the specified substrate per unit volume of paint when one coat is applied according to the prescribed method under certain construction conditions, expressed in m²/L.

Instruments and Materials

(1) Balance: the sensitivity is 0.lg, 0.01lg, 0.00lg; (2) Paint brush: width 25~35mm; (3) Paint film scraper: gap 100μm; (4) Wet Film Thickness Gauge ( Wheel gauge): 0~100μm, as shown in the figure below; (5) Magnetic Thickness Gauge: 0~300μmm; (6) Lever micrometer: accuracy 2μm; (7) Spray gun; (8) Steel plate; (9) Polyester film.

test methods

(1) Brushing method
① After brushing a paint film of a certain thickness and a certain area on an unpolished flat steel plate, immediately use the decrement method to weigh the brush coating on a balance with a sensitivity of 0.1g, and press Formula to calculate the amount of paint used:

②According to the density of the liquid coating, the spreading rate is calculated by the following formula:

③ After the sample is dry, use a magnetic Thickness Gauge to measure the average thickness of the paint film on the sample, and calculate the theoretical coating rate under the required dry film thickness according to the following formula:

④ Three parallel measurements were taken, and the arithmetic mean of the two close results was taken.
(2) Spraying method
①Weigh the mass of the steel plate on a balance with a sensitivity of 0.01g, then spray the diluted sample to form a plate, dry it under the conditions specified in the product standard, weigh the mass, and press Formula to calculate the amount of paint used:

② Then calculate the theoretical coating rate under the required dry film thickness according to the same conversion steps as the above-mentioned brushing method. The test is also measured three times on average, and the arithmetic mean of the two close results is taken.

(3) Scrape coating method
① Prepare a paint film on the polyester film with a scraper applicator, cut a certain area of the test piece with a cutting knife after it dries, and weigh it on a balance with a sensitivity of 0.001g to obtain m². At the same time, measure the average thickness H of the dry paint film on the polyester film with a lever micrometer, remove the paint film with a solvent that has no effect on the dry quality of the polyester film, and weigh the polyester film after it is completely dry. Calculate the surface density of the dry paint film using the formula:

 ②Based on the known dry paint film surface density and other data, the wet film thickness can be calculated according to the following formula:

③ Spreading rate R is the reciprocal of wet film thickness, namely:

(4) Volume solid content method
① Take a flat steel plate with a large area (about 0.5~1.0m²), spray the sample evenly on it according to the construction requirements, and immediately use a wet film thickness meter (wheel gauge) on the upper, middle, and Measure the wet film thickness at the next three parts and take the average value. After hard drying, measure the dry film thickness with a magnetic Thickness Gauge, at least 10 points, take the average value, and calculate the volume solid content (SV,%) as follows:

② Calculate the theoretical spreading rate under the required dry film thickness according to the following formula: