Hiding power (hidingp0wer) refers to the ability of the coating film to cover the background color of the coated surface after the paint, ink, etc. are evenly coated, and is the result of the scattering and absorption of light by the pigment. Paint hiding power refers to the minimum amount of paint used to evenly coat the color paint on the surface of the object so that the base color no longer appears, expressed in g/certificate. Pigment coverage refers to the minimum amount of pigment used when pigments and varnishes are ground into color paste and evenly painted on the black and white grid substrate so that the black and white grid is just covered.
The strength of the pigment's hiding power is mainly determined by the following properties: refractive index, the larger the refractive index, the stronger the hiding power; the ability to absorb light, the greater the light absorbing ability, the stronger the hiding power; The covering power of amorphous is weak; the degree of dispersion, the greater the degree of dispersion, the stronger the covering power.
For the same weight of paint products, under the same construction conditions, products with high hiding power can coat more areas than products with low hiding power. In order to overcome the inaccuracy of visually measuring the covering power of black and white grid panels, the covering power was measured with a reflectance meter, and the tested samples were coated on transparent poly film with different thicknesses, and placed on black and white glass plates after drying. Measure the reflectance respectively, and the ratio is the contrast ratio. When the contrast ratio is equal to 0.98, it is full coverage. The hiding power can be obtained according to the thickness of the paint film, which is suitable for white and light-colored paints. The following focuses on the measurement of hiding power by the reflectance method.
1. Scope and Description
In this method, the sample is coated on a colorless transparent polyurethane film, or on cardboard with black and half background colors, and the reflectance of the coating film on the black and white bottom surface is measured with a reflectance meter. The ratio of the reflectance on the white base is the contrast ratio , which is its corresponding opacity. International standards recommend using a reflectance meter to test the hiding power, which has high accuracy, but this method is mainly suitable for white paints and light-colored paints.
2. Apparatus and Materials
Wire Bar Coater, also known as coating rod , specification 100 (that is, wire diameter is 100 m); gap type paint film Applicator, 100 m; polycool film, colorless and transparent, thickness 30-50m; background color black and white Half of the cardboard; reflectance meter, a photoelectric instrument that can give indication readings proportional to the reflected luminosity of the tested surface, its accuracy is within 0.3%, and its spectral sensitivity is approximately equal to that of CIE illuminant C or D65 The product of the relative spectral energy distribution and the color matching function y(in) of the CIE standard observer. The instrument is composed of a probe, a host, black and white standard plates (one for each), and black and white ceramic plates (two for each). The probe adopts the principle of 0· irradiation and diffuse reflection reception. When the reflected light of the sample acts on the surface of the selenium photocell, an electric signal is generated and input to the DC amplifier , and the reading is displayed. When measuring with a reflectance meter, the reflectance of the white standard plate should be (80±2)%' black mark
The reflectivity of the quasi-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.
Note: The instrument should be preheated for more than 15 minutes before use , and zero-adjusted and calibrated repeatedly. During continuous testing, the measuring head should to prevent photoelectric fatigue of the selenium photoelectric cell.
3. Measurement method
(1) Use a wire rod or a gap-type paint film preparer to evenly coat the tested paint ) % of the constant temperature and humidity conditions after 24h test.
(2) If the coating film is prepared by using polyhalo film as the substrate, drop No. 200 solvent gasoline spread the paint polyhalo film on it , and ensure that there is no air gap , then use a reflectance meter to test the reflectance at least four positions, and calculate the average reflectance Rs ( on the blackboard) and Rw (on the whiteboard) .
(3) If the coating film is prepared with half and half black and white cardboard , measure the scene reflectance , and calculate the average reflectance Rs (on the blackboard) and Rw (on the whiteboard) respectively. superior).
4. Results presentation
Measure twice in parallel, if the difference between the two measurement results is not greater than 0.02, take the average of the two measurement results, otherwise re-test.
5. Reference standards
Standard GB/T9755-2001, National Standard-2009, National Standard-2001.
National GB/T9756GB/T9757
