Overview
The Masking Force Tester is a critical piece of equipment in the field of coating inspection, used to objectively assess the ability of a coating to mask the underlying color or pattern. Its working principle is mainly based on the measurement of contrast ratio, that is, the ratio of the reflectance of the coating film on the black and white substrate at the specified coating rate. Through sophisticated optical sensors and data processing units, the instrument transforms visual subjective judgment into reproducible quantitative data, providing a scientific basis for coating research and development, quality control and application.
The principle of measurement is with
The quantitative evaluation of occlusion force usually follows the contrast ratio method. The paint is evenly applied on the black and white contrast cardboard that meets the requirements of the standard, and after drying, the coating film is measured separately in the black area (R) using an instrumentb) and white areas (Rw) reflectivity. The formula for calculating the Contrast Ratio (CR) is as follows:
CR = (Rb / Rw) × 100%
Among them, the closer the contrast ratio is to 100%, the stronger the coverage ability of the coating. Widely adopted standards at home and abroad include GB/T 23981.1 (China), ISO 6504-3 (international), and ASTM D2805 (USA). These standards detail applicator types, coating volumes, drying conditions, and instrument calibration procedures, ensuring that test results are comparable across laboratories.
Technical parameters
A typical occlusion force analyzer consists of the following core components: a stabilized light source system, an optical probe with an integrating sphere or specific geometry, a highly sensitive spectral sensor, and data analysis software. To ensure accurate measurements, the instrument needs to be calibrated regularly using a standard whiteboard and blackboard. The following table lists the key operating parameters that affect the measurement results:
| Coating volume control | Use a wire rod or scraper applicator to precisely control the wet film thickness |
| Drying conditions | Cure at standard temperature and humidity until completely dry |
| Measure the aperture | Selected according to the sample size, usually larger than the specified minimum diameter |
| Light source and observation angle | Commonly used D65 light source, 45°/0° or d/8° geometry |
Testing process
The standard test process begins with the preparation of the sample. Use a precision applicator to evenly apply the coating to the black and white cardboard in the specified amount. After the sample is completely dried under standard conditions, it is placed on the instrument measuring table for positioning. The instrument automatically performs multi-point measurements in the black and white area and calculates the average, and finally outputs the pair ratio value. For scientific research or in-depth quality control, reflectance curves can also be analyzed to understand the masking behavior of coatings at different wavelengths.
Applications:
Covering force measurement is widely used in architectural coatings, industrial protective coatings, automotive paints and pigment manufacturing industries. The masking ability of the coating is mainly affected by the following factors: the difference in refractive index between the pigment and the base, the volume concentration of the pigment (PVC), the particle size distribution and the dispersion state of the pigment. By measuring the coverage force, formulation engineers can optimize pigment selection and ratios, while production departments can monitor batch-to-batch consistency to ensure the final coating results meet the desired requirements.
Epilogue
As a key tool for quantifying the occlusion properties of coatings, the standardized test methods provide a common technical language for the industry. By accurately measuring contrast ratios, the instrument helps practitioners go beyond subjective visual evaluation to make data-driven decisions in product development, quality assurance, and cost control. With the advancement of optical sensing and automation technology, the measurement efficiency and data dimension of future instruments are expected to be further improved.
References
GB/T 23981.1-2019, Colored paints and varnishes - Determination of covering force - Part 1: Determination of the ratio of white and light paints.
ISO 6504-3:2019, Paints and varnishes — Determination of hiding power — Part 3: Determination of contrast ratio of light-coloured paints at a fixed spreading rate.
ASTM D2805-11(2018), Standard Test Method for Hiding Power of Paints by Reflectometry.