Definition
The masking force assay plate is a special laboratory instrument used to evaluate the masking ability of coatings, inks, pigments and other materials. It typically consists of a set of plates with different areas of contrast in black and white, and its masking performance is quantified by observing how well the material masks the color of the substrate after it has been coated. The instrument plays an important role in quality control, product development, and standard compliance testing, helping users objectively compare the covering effects of different formulations or batches of materials.
Principle
The occlusion force is determined based on the principle of optical contrast. When the material being measured is evenly applied on a base plate with high contrast (usually black and white), the material layer partially absorbs and scatters light, reducing the visual difference between the black and white areas of the base plate. The strength of the masking force depends on the material's ability to block light penetration and mask the underlying color. Occlusion force is typically expressed in terms of the minimum amount of material required to cover a unit area, such as grams per square meter (g/m²), with lower values indicating greater masking efficiency. Its basic relationship can be expressed as:
C = m / A
where C is the covering force, m is the material quality, and A is the area to be covered.
Measurement method
Occlusion force measurements usually follow a standardized operating procedure. First, the sample is evenly coated or scraped onto the black and white grid area of the masking force assay plate. The coating process requires controlling the wet film thickness or coating amount to ensure consistent results. The coating is then observed under the specified lighting conditions, such as in a standard light source, until the black and white grid pattern is completely invisible. In this case, the mass or volume of the material used is determined by weighing or volumetric measurement, and the covering force value is calculated in conjunction with the coating area. Commonly used standards include GB/T 1726, ISO 6504, etc., which specify in detail instrument specifications, coating tools, drying conditions and evaluation methods.
Influencing factors
The measurement results of the occlusion force are affected by a variety of factors. The properties of the material itself, such as pigment concentration, particle size distribution, refractive index, and dispersion state, directly affect its scattering and absorption efficiency of light. Coating process parameters, including coating thickness, uniformity, and drying conditions, can also lead to measurement deviations. Environmental factors such as the type and intensity of the observation light source, the angle of observation, and the difference in the evaluator's visual perception need to be controlled in the test. In addition, the surface flatness of the measuring plate, the reflectivity and contrast of the black and white areas are also the basic conditions to ensure measurement accuracy.
Application
Masking force measuring plates are widely used in coatings, inks, pigments and related chemical industries. During the R&D phase, it is used to optimize formulations and balance coverage performance with cost. In production quality control, it is used to monitor batch consistency and ensure that products meet specifications. In third-party testing institutions, it is used to certify compliance according to national or industry standards. In addition, the assay is also suitable for architectural decoration, automotive painting, printing and packaging, and other fields, helping users choose suitable materials to meet specific covering needs.
Selection
When choosing a masking force plate, there are several aspects to consider. First, the measuring plate should meet the requirements of the target test standard, including size, black and white grid pattern design, and base plate material. Secondly, the durability and surface treatment of the assay plate should be resistant to common solvents and wear to ensure long-term stability. Users also need to match the appropriate coating tools (e.g., scrapers, wire rods) according to the type of material and viscosity of the routine test. For scenarios requiring high-precision measurements, consider equipping a standard light source box to reduce ambient light interference. Finally, the user-friendly design of the operation, such as clear scale markings and easy-to-clean surfaces, can also improve testing efficiency and repeatability.