Definition
A lacquer frame applicator is a laboratory tool used to prepare wet film coatings of specified thicknesses on the surface of a leveled substrate. It is typically made of corrosion-resistant metal material with a hollow rectangular frame with a precision-machined bottom edge that creates a void of a specific depth in the middle area when in contact with the substrate. When a material containing a paint or similar fluid is scraped through this area, a uniform thickness and area-determining wet film coating is formed, providing a standardized sample for subsequent paint performance testing.
Principle
The working principle of the paint film frame applicator is based on gap coating technology. At its heart is the physical gap between the bottom of the applicator frame and the plane of the substrate. The height of this gap (i.e., the thickness of the frame) directly determines the thickness of the prepared wet film. During operation, place an appropriate amount of fluid to be measured on the substrate in front of the applicator, and use a scraper to smoothly scrape the applicator through the fluid at a constant speed and pressure. The fluid is filled with scraper and passes through the gap at the bottom of the frame, and the excess fluid is scraped off, leaving a wet film coating on the substrate with a uniform thickness equal to the gap height. The relationship between wet film thickness (WFT) and applicator gap depth (d) is equal in ideal conditions, and the relationship can be expressed as: WFT = d.
Measurement method
The process of preparing the coating film using a lacquer film frame applicator is a standardized manual operation. First, choose a clean, flat, and test standard substrate (e.g., tinplate, glass plate, etc.) and secure it horizontally. According to the target wet film thickness, select the appropriate specification of the applicator. Pouring a sufficient amount of paint to be tested at one end of the substrate, in front of the applicator. Hold the scraper in close contact with the upper edge of the applicator and scrape the applicator over the coating area at once with even, moderate force and speed (usually around 10 cm per second) without pause or tilt. After scraping is completed, immediately lift the applicator vertically upwards to obtain a wet film with a fixed area and uniform thickness on the substrate. Subsequently, it is dried or cured under the conditions specified by the relevant product standards to form a dry film for testing.
Influencing factors
The quality of the coating film prepared using a frame applicator is influenced by several factors. Operating factors include the speed and force of scraping, and uneven scraping can cause film thickness fluctuations or streaks. The surface flatness, cleanliness, and fixation stability of the substrate are also crucial, as uneven substrates can lead to uneven clearance. The rheological properties of the coating itself, such as viscosity, thixotropy, and leveling, can affect the uniformity and final appearance of the wet film after application. Environmental conditions such as temperature and humidity can alter the paint's workability. In addition, the manufacturing accuracy of the applicator itself, including the accuracy of gap depth and the straightness and smoothness of the cutting edge, is the basis for ensuring the accuracy of film thickness. The cleanliness of the applicator should not be overlooked, as residual dry paint can change the actual clearance height.
Applications
Paint frame applicators are widely used in fields where standardized evaluation of the physical and chemical properties of coatings is required. In the coatings and inks industry, it is a key tool for laboratory R&D and quality control to prepare and test the adhesion, hardness, flexibility, impact resistance, gloss, color, and corrosion and weather resistance of paint films. It is also used in the development of printing, adhesives, composite coatings, electronic materials (such as conductive coatings), and functional coatings for paper and textiles, as well as to prepare uniform film samples. Its applications run through the entire process from raw material screening, formulation optimization to final product performance verification.
Key points of selection
Choosing the right paint frame applicator requires a comprehensive consideration of multiple technical parameters. The primary parameter is the applicator's nominal wet film thickness, i.e., its gap depth, which should be selected based on the film thickness range required by common testing standards or R&D goals, and laboratories are typically equipped with a range of applicators of different thicknesses. The size of the applicator (i.e., the length and width of the wet film area being prepared) needs to match the commonly used substrate size and testing requirements. In terms of materials, wear-resistant, corrosion-resistant, and non-deformable metals such as stainless steel are usually selected to ensure the accuracy of long-term use. Manufacturing accuracy is key, and attention should be paid to the tolerance range of its gap depth and the machining quality of the cutting edge. Additionally, the applicator's structure should be designed for easy hand-holding, scraping operations, and thorough cleaning after use. When purchasing, you can refer to the requirements of relevant industry standards at home and abroad (such as ASTM, ISO, etc.) for coating preparation tools.