Definition
A micro applicator is a laboratory tool used to prepare uniform wet film thickness on a flat substrate surface. It typically consists of a precision-machined metal or plastic body with gap grooves of a specific depth that spreads liquid samples (such as coatings, inks, adhesives, etc.) into a wet film of a set thickness, typically in the micron range.
How it works:
Micro applicators work on the gap scraping principle. During operation, an appropriate amount of sample is placed at the front end of the substrate, and the applicator scrapes over the surface of the substrate at a constant speed and pressure, and its gap groove controls the size of the section through which the sample passes, leaving a uniform wet film on the substrate. The thickness of the wet film is mainly determined by the gap depth of the applicator, and theoretically, the thickness of the wet film is directly proportional to the gap depth, but it is affected by the characteristics of the fluid. The relationship between wet film thickness and gap depth can be approximately expressed as:
h ≈ k · d
where h is the thickness of the wet film, d is the gap depth of the applicator, and k is the coefficient related to the rheological properties of the fluid.
Measurement method
After using a micro applicator to prepare the wet film, the film thickness needs to be verified. Common methods include direct measurement of wet film comb gauges, that is, when the wet film is not cured, a thickness gauge with a toothed scale is placed vertically on the film surface, and the wet tooth scale is read to determine the thickness. Another way is to measure the thickness of the dry film and convert it with a known volume of solids, the formula is:
Wet film thickness = dry film thickness / volume solids
To ensure accuracy, measurements should be taken at multiple locations and averaged.
Influencing factors
The uniformity of film thickness prepared by micro coaters is affected by various factors. The processing accuracy of the applicator gap depth is key, and gap deviation will directly lead to thickness changes. Operation techniques such as scraping speed and consistency of applied pressure can also affect the results, which may lead to discontinuity of the film layer, and uneven pressure can cause thickness fluctuations. The rheological properties of the sample itself, such as viscosity, thixotropy, etc., can affect the flow behavior of the sample during scraping, thereby changing the actual film thickness. The flatness of the substrate is just as important as the surface energy, with uneven surfaces leading to local thickness differences and low surface energy causing sample shrinkage.
Applications:
Micro applicators are widely used in R&D and quality inspection processes that require precise control of coating thickness. In the coatings industry, it is used to prepare test samples to evaluate properties such as hiding power, gloss, and wear resistance. The field of printing ink is used to simulate the printing process and study the influence of ink layer thickness on color and adhesion. The adhesive industry uses it to prepare uniform adhesive layers to test bond strength. In addition, micro coaters are also important sample preparation tools in laboratory research in fields such as electronic materials, optical films, and textile coatings.
Key points of selection
When choosing a micron applicator, it is necessary to first clarify the desired wet film thickness range, and then choose the model corresponding to the gap depth, and common applicators are available in a variety of specifications from tens of microns to hundreds of microns. In terms of material, the stainless steel coater has good wear resistance and is suitable for long-term use; Plastic applicators are less costly and suitable for disposable or corrosive samples. In terms of structural design, some coaters have adjustable clearances or combined designs, providing more flexible thickness options. The size of the substrate should also be considered to ensure that the applicator width is suitable. Finally, the requirements for coating film preparation in relevant industry standards (such as ASTM D823, etc.) should be referred to to ensure that the selected tool adheres to the standard method.