Determination of film covering power by reflectivity meter

Scope and description

In this method, the sample is coated on a colorless transparent polyester film, or on a covering power paper with black and half background colors, and the reflectance of the coating film on the black bottom surface is measured with a reflectance meter. The ratio of the reflections on the black and white substrates is the contrast ratio, which is their corresponding coverage.

International standards recommend using a reflectance meter to test the hiding power, which has high accuracy, but this method is mainly used for white paints and light-colored paints.

Instruments and Materials

(l) Wire Bar Coater: specification 100 (that is, wire diameter is 100µm), as shown in Figure 1; (2) Gap paint film Applicator, 100µm; 3) Polyester film: colorless and transparent, with a thickness of 30-50µm ;4) Scratch-coated paper with black and white background colors; (5) Reflectance meter: as shown in the figure, a photoelectric instrument that can give indication readings proportional to the reflected luminosity of the tested surface, and its accuracy is within 0.3%. , its spectral sensitivity is approximately equal to the product of the relative spectral energy distribution of CIE light source C or D65 and the color matching function γ(λ) of the cIE standard observer. Composed of ceramic plates (two each). The probe adopts the principle of 0° irradiation and 1 reflection reception. When the reflected light of the sample acts on the surface of the solar cell, an electrical signal is generated and input to the DC amplifier for amplification, and the reading is displayed. When measuring with a reflectance meter, the reflectance from the standard plate should be (80±2)%, and the reflectance of the black standard plate should not be greater than 1%. The instrument can be used for the determination of the hiding power of the paint film and the measurement of the reflectance.

Determination of paint film hiding power with reflectance measuring instrument with Figure 1

test methods

(1) Use a wire rod or wet film preparer to evenly coat the coating to be tested on polyester film or black and white paper with half and half hiding power. Tested after 24 hours under constant temperature and humidity conditions. Determination of the hiding power of the paint film with a reflectance meter with Figure 2 (2) If the surface film is used as the substrate to prepare the coating film, drop a few drops of No. 200 solvent gasoline (or other suitable solvents) on the black and white working board attached to the instrument. Spread the painted polyester film on it, and ensure that There is no air gap between the polyester film and the black and white work board, and then use a reflectance meter to measure the reflectance at at least four positions. Calculate the average reflectance R B (on the black board) _and R _w (on the white board) respectively.

(3l If black and white paper with half covering power is used to prepare the coating film, measure the reflectance directly on at least four positions on the black base color coating film, and calculate the average reflectance R B (black board) _and R _w (white board) superior).

The result shows

Calculate the contrast ratio according to the following formula: contrast ratio=R _B /R _W

Measure twice in parallel, if the difference between the two results is not greater than 0.02, take the average of the two results, otherwise re-test.