Definition
A laboratory coater is a precision instrument used to prepare uniform, controllable thickness films on the surface of a substrate material. It mechanically coats liquid or paste samples (such as coatings, slurries, adhesives, etc.) on flat substrates such as glass plates, metal foils, plastic films, etc. at a specific thickness to simulate the coating process of industrial production or to prepare experimental test samples. This equipment is a key pretreatment equipment in many R&D and quality inspection fields such as material science, electronics, printing, packaging, and new energy.
Principle
The core working principle of laboratory coaters is based on precision mechanical transmission and clearance control. Its main working mode can be divided into two typical modes: scraper coating and wire rod coating. In scraper coating mode, the instrument scrapes the excess sample placed in front of the substrate as it moves at a uniform speed through a precisely adjustable squeegee or coating head to form a uniform wet film. The thickness of the wet film is mainly determined by the physical gap between the scraper and the substrate, and the relationship can be approximately expressed as:
h ≈ g
where h is the thickness of the wet film, and g is the set gap between the scraper and the substrate. In in-line rod coating mode, a wire wound with a thin wire of a specific diameter is used, and as the rod is rolled, its surface wire diameter gap holds and transfers the quantitative sample to the substrate, and the wet film thickness depends primarily on the geometry of the wire diameter.
Measurement and calibration methods
The measurement of coating thickness is divided into wet film thickness and dry film thickness. Wet film thickness is usually verified by multi-point measurement using a wet film thickness comb gauge immediately after application. The dry film thickness needs to be measured with a micrometer to measure the overall thickness difference of the substrate before and after coating after the coating is completely cured, or directly measured with a special film thickness gauge (such as magnetic, eddy current or ultrasonic thickness gauge). The calibration of the instrument is a key part, and it is necessary to regularly use standard thickness gauges or gauge blocks to check the accuracy of the parallelism and clearance set value of the coating head, and verify the stability of the transmission speed according to the standard operating procedures.
Influencing factors
The uniformity and quality of coating film thickness are affected by multiple factors. Instrument factors include the parallelism and flatness of the coating head, the accuracy of the clearance setting, the stability of the substrate transfer speed, and the flatness of the working platform. In terms of process parameters, the coating speed will affect the leveling of the coating and the possible shear effect. The rheological properties of the sample, such as viscosity, thixotropy, and solids content, directly affect the spreading behavior of the coating and the final film thickness. Environmental conditions such as temperature and humidity can affect sample viscosity and solvent volatilization rate. In addition, the surface energy, cleanliness and flatness of the substrate are also the basis for ensuring uniform adhesion of the coating.
Applications
Laboratory coaters are widely used. In the field of new energy, it is used to prepare lithium-ion battery electrode sheets, fuel cell catalytic layers, or photovoltaic functional layer films. In the field of electronic materials, it is used to coat conductive pastes, optical adhesives, semiconductor packaging materials, etc. In the coatings and inks industry, it is used to develop and test the film-forming properties, coverage and color of new product formulations. In the field of adhesives and composites, it is used to prepare uniform film samples to test adhesive properties. It also plays an important role in the development of functional coatings for paper, textiles and packaging materials.
Selection considerations
Selecting the right laboratory coater requires a systematic evaluation. First, it is necessary to identify the main type of coated sample and its physical properties (e.g., viscosity range) to determine the appropriate coating method (scraper, wire rod, or possible option). Core parameters include coating thickness range, coating width, and adjustable range and accuracy of coating speed. The rigidity of the instrument's construction, the corrosion resistance of the material, and the machining accuracy of critical components, such as scrapers, are crucial. Functional scalability, such as whether it has a heating platform, vacuum adsorption substrate or closed-loop thickness control, should be considered according to R&D needs. The user-friendly design of the operation, compliance with relevant safety standards, and technical support and calibration services provided by the supplier are also important decision-making options.