Definition
Laboratory coating machines, simply put, are devices capable of scraping uniform coatings onto small-sized substrates. It is not like the giant on an industrial production line, but a precision tool designed for R&D, prototyping, and quality control. It must be admitted that its core task is to control the thickness and flatness of the coating; the casual application method of manual scraping can't be used here.
Principle
The principle is not complicated; it relies on precise clearance control. Typically, an adjustable squeegee or wire rod (winding rod) is used to slide it over the substrate surface. By setting the gap between the scraper and the platform, or by setting the diameter of the wire wound on the wire rod, the wet film thickness is forcibly controlled. Here is a calculation of wet film thickness: for wire rods, the wet film thickness ≈ wire diameter × 0.2 (an empirical coefficient), but the actual effect is also affected by the coating viscosity and coating speed. For scrapers, adjustment is done directly with a micrometer. Don't be fooled by mechanical actions; even a slight unevenness in the substrate can cause the coating thickness to differ by several microns.
Operation and measurement
In terms of operation, most methods involve placing the substrate, such as PET film or aluminum foil, and securing it with vacuum adsorption or tape. Then pour the paint onto the front end of the substrate and start the squeegee to move it toward the end at a constant speed. You have to keep your speed steady, or the coating will show stripes—it's just like slamming on the brakes while driving. Later, measure the thickness of the dry film by using an electromagnetic induction film thickness meter or microscope for sectional observation, and compare the thickness of the wet film to estimate the solid content. Of course, there are also cases where direct integration with online thickness measurement is available, but offline testing is still more common in laboratories.
Case study
Once, when developing an anti-rust coating, epoxy-modified resin was applied to steel plates in a 20-micron dry film. At first, using a manual squeegee, no matter how you scrape, micron-level ripples appear, which become even more obvious after curing. Later, I switched to a coating machine with a vacuum adsorption platform, leveled the substrate, and ran it again with a double-sided wire rod. The ripples disappeared and the adhesion test was passed. This shows that substrate flatness and coating stability are more critical than anything else. There is also a project for solar backplanes, where the coating thickness allows within ±2 microns, and finally requires adjusting the squeegee clearance and speed parameters to complete the task.
Application:
This machine covers a wide range of surfaces: during coating formulation development, leveling and covering strength are measured; Adhesive prototyping to check coating uniformity; Applying conductive paste to electronic materials; Even primer verification for food packaging laminated films. One thing to note is that it is not suitable for materials with high fluid viscosity or solvent explosions, unless protective devices are added. Overall, wherever rapid confirmation of coating performance is needed, the laboratory may have one installed.
Selection
When choosing a model, first consider the width and material of the substrate, ensuring both softness and rigidity match. For example, PET films should be selected with anti-static functions to prevent dust from being adsorbed. Next is the coating method: wire rods are suitable for low-viscosity coatings, and the squeegee is used for high-viscosity or thick films. In terms of precision, the gap must be adjusted to the 1-micron level; otherwise, the error will snowball. There is also a speed adjustment range; slow speeds are suitable for high-viscosity materials, and fast speeds may introduce bubbles. By the way, let me nag again: don't just look at the specs—it's best to test a few scrapes with your own paint. Some machines claim to have lower precision in practice. That's basically the idea: if you get it right, you can save half the debugging time.