Definition
A wet film preparer is a laboratory instrument used to apply and form a wet film coating of a specific thickness on the surface of a flat substrate. It ensures uniform and controlled thickness of the coating through a precise mechanical structure, providing a standardized initial sample for subsequent coating performance tests such as drying time, adhesion, gloss, and color evaluation. At the heart of this work is the preparation of wet films with known and consistent thickness, which is the basic premise for quantitative testing of many coatings.
Principle
The working principle of wet film preparers is based on gap coating. The body of the instrument is usually a precision-machined metal frame with two parallel support feet on either side of the bottom and a scraper with a specific clearance height in the middle. When an appropriate amount of paint is placed on the substrate in front of the scraper and the operator pushes the preparer forward at a constant speed and pressure, the scraper scrapes the paint away, and the excess paint is carried away by the scraper, leaving a wet film on the substrate whose thickness is determined by the height of the scraper gap. The thickness of the wet film formed by it is approximately equal to the physical gap height of the scraper under ideal conditions, i.e., H ≈ h. This process ensures accuracy and repeatability of film thickness.
Measurement method
After coating with a wet film preparer, the thickness of the wet film should be verified or the thickness of the dry film should be calculated. Wet film thickness can be measured directly by a wet film thickness gauge while the coating is not dry. And the dry film thickness FtThen it can pass through the wet film thickness WtSolids and coating volumevThe formula is: Ft = Wt × (Sv / 100)。 In practice, the uniformity and integrity of the wet film are usually checked immediately after coating, and after it is fully cured, multi-point measurements are carried out using the corresponding dry film thickness gauge to evaluate the stability and accuracy of the coating process.
Influencing factors
The effect of wet film preparation is affected by various factors. Operating factors include the uniformity of the push speed, the stability of the applied pressure, and the initial amount of coating. Substrate factors involve surface flatness, cleanliness, and material. The rheological properties of the coating itself, such as viscosity and thixotropy, can significantly affect the uniformity of the coating and the final film thickness. Environmental conditions, such as temperature and humidity, can affect the results by altering the paint's viscosity and drying speed. In addition, the accuracy of the preparer scraper, the wear condition, and the cleanliness of the knife edge are also key to ensuring the accuracy of film thickness.
Main application areas:
Wet film preparers are widely used in areas where standardized coating samples are required. In the coatings and inks industry, it is used for R&D and quality control, testing formulation properties. In the automotive industry, test plates are used to prepare colored paints, varnishes to evaluate appearance and durability. In the field of building materials and anti-corrosion coatings, it is used to prepare test coatings to evaluate weather resistance and corrosion resistance. In the electronics industry, it can be used to prepare test samples for conductive coatings or optical films. In addition, it is an essential tool for performing relevant national or international standard tests in academic research and standard testing institutions.
Key points to consider in selection
When choosing a wet film preptor, it is necessary to consider multiple aspects. The primary factor is the thickness range of the desired wet film, and models that cover this range should be selected, with common preparers offering a range of fixed or adjustable clearances. The scraper material needs to be wear-resistant and corrosion-resistant, usually stainless steel. The processing accuracy of the instrument, especially the accuracy and parallelism of the gap, directly affects the reliability of the results. Choose a preparer of the appropriate width according to the substrate size. Ease of operation, such as handle design, should also be taken into account. Finally, it is necessary to confirm that the instrument meets the specific standard specifications referenced for the target test.