Definition
A multi-sided wet film applicator is a laboratory tool used to prepare a specific thickness of wet film coating on a flat substrate surface. It is usually composed of multiple grooves or gaps of varying depths to form a series of parallel wet film strips with increasing thickness in a single operation, allowing for subsequent comparison or evaluation of coating properties.
How it works:
The applicator works on the principle of mechanical scraping. Its body is usually a precision-machined metal or plastic block with multiple highly accurate stepped grooves or gaps formed by two parallel cutter edges on one side. When the operator pulls the applicator over the substrate coated with the liquid sample at a constant speed and pressure, the excess liquid is scraped off and the space within the groove or gap is filled by the sample, leaving a wet film coating on the substrate that corresponds to the depth of the groove. The wet film thickness depends primarily on the geometric depth of the applicator groove.
Measurement method
After the coating is prepared using a multi-sided wet film applicator, the key measurement object is the wet film thickness. The wet film thickness can be directly determined by the nominal gap depth of the applicator itself, which is usually clearly marked in microns on the side of the applicator. For verification of coating uniformity or actual thickness, instant measurements can be made using a dedicated thickness gauge when the wet film is not cured. The thickness of the dry film formed after the coating is completely cured needs to be calculated by mass and area or measured by the corresponding instruments, and the volumetric solids of the coating can be calculated in combination with the thickness of the wet film. The formula for calculating the volume of solids can be expressed as:
VS= (DFT/WFT) × 100%
Among them,VSrepresents the volume of solids,DFTrepresents the thickness of the dry film,WFTRepresents wet film thickness.
Influencing factors
The coating effect is affected by a variety of factors. Operating factors include pulling speed, applied pressure, and operating angle during application, and uneven speed or pressure fluctuations can lead to inconsistent coating thickness. The rheological properties of the sample itself, such as viscosity, thixotropy, and leveling, directly affect the formation quality and final appearance of the coating. The surface flatness, cleanliness, and material affinity of the substrate can also affect the adhesion and uniformity of the coating. Environmental conditions such as temperature and humidity may act indirectly by changing the volatilization rate or rheology of the sample. In addition, the manufacturing accuracy of the applicator itself, the wear condition of the knife edge, and the cleanliness of the gap are the basis for ensuring thickness accuracy.
Applications:
Multi-sided wet film applicators are widely used in multiple industries and research and development fields. In the coatings industry, it is used to evaluate the leveling, hiding power, color and preliminary film properties of different coatings of coatings. In the field of inks, it is used to test printability and color performance. In the adhesive industry, films of different thicknesses can be prepared to test adhesive properties. In the research and development of functional materials, such as electronic pastes, optical coatings, etc., it can be used to quickly prepare experimental coatings. In addition, it is also a sample preparation tool specified in the relevant standard test methods for standardized pre-test preparation for coating resistance, hardness, gloss and other properties.
Selection considerations
Choosing the right multi-sided wet film applicator requires a combination of aspects. First, it is necessary to clarify the commonly used wet film thickness range, and then select the stepped depth series covered by the applicator. The coating width should be determined based on common substrate sizes or test standard requirements. In terms of material, stainless steel has good wear resistance and is suitable for frequent use or abrasive samples; Anodized aluminum or plastic materials are lightweight and corrosion-resistant. The type of knife edge (e.g., groove or gap) can be selected according to the characteristics of the sample and the operating habits. It is also necessary to pay attention to the processing accuracy of the applicator, and its gap depth tolerance is the key to ensuring the reliability of the results. Finally, consider which specific industry or national standard test method requirements are met or compatible.