A laboratory film coater is a precision instrument used to prepare uniform, controllable thickness coatings on substrates. Its core function is to mechanically drive the coating tool to evenly coat various slurries on the target substrate surface at a set speed and pressure. The equipment has a wide range of application value in the fields of material research and development, coating testing, new energy battery electrode preparation and functional film research.
Coating principle
Coating machines usually work on the principle of a squeegee or winding rod. The squeegee coating controls the thickness of the wet film by adjusting the gap between the knife edge and the substrate, and the dry film thickness d can be determined by the formulad = k × h × cIt is estimated that h is the thickness of the wet film, c is the solid content of the slurry, and k is the correction coefficient related to the rheological properties of the slurry. The coating of the wire winding rod uses the diameter of the metal wire wrapped around the rod to determine the coating amount, and the larger the wire diameter, the larger the thickness of the reserved wet film.
Key operating parameters include coating speed, coating pressure, substrate temperature, and ambient temperature and humidity. These parameters need to be coordinated according to the rheological properties of the slurry (e.g., viscosity, thixotropy) to obtain a defect-free continuous coating.
Coating adaptability
Laboratory applicators are capable of handling water-based, solvent-based (oil-based) and solvent-free slurries. Different systems of slurry have specific requirements for coating processes due to their different physical and chemical properties.
| Slurry type: | Typical characteristics and coating precautions |
| Water-based slurry | The volatilization mechanism is mainly water evaporation, and the drying rate is significantly affected by environmental humidity. When coating, attention should be paid to controlling the ambient humidity to avoid cracking the coating due to too fast water volatilization or sagging caused by too slow moisture. |
| Oily slurry | It usually contains volatile organic solvents, has a fast drying rate, and is easy to form a dense film. When coating, pay attention to the matching of the solvent volatilization rate with the coating speed, and ensure good ventilation. |
| High solids slurry | The viscosity is high and leveling may be limited. Adjustments to coating gaps or pressures may be necessary, and consideration of heating the substrate to reduce apparent viscosity. |
| Low viscosity slurry | Easy to flow, need to prevent sagging and edge shrinkage. This can be improved by reducing the coating speed, using a higher wire diameter winding rod, or adjusting the surface tension of the substrate. |
Operation process
To ensure reproducibility and comparability of coating results, it is recommended to follow a standardized operating procedure. First, the substrate needs to be cleaned and pretreated to ensure that its surface can be consistent. Secondly, the slurry should be fully dispersed and defoamed, and left to achieve a stable rheological state. Before coating, it is necessary to accurately set and calibrate the coating gap or select the winding rod of the corresponding wire diameter. During the coating process, it is crucial to keep the speed constant and the substrate flat and fixed. After coating, it needs to be dried or cured according to the conditions specified by the slurry supplier or relevant test standards.
For process optimization of specific slurries, parametric studies are recommended. For example, a simple single-factor experiment can be designed to investigate the effect of coating speed on coating thickness uniformity to determine the optimal process window for the slurry.
FAQs
Regular maintenance is the basis for ensuring the long-term stable operation of the coating machine. Immediately after each use, the coating tool (e.g., scraper, winding rod) should be thoroughly cleaned with a cleaning agent compatible with the slurry solvent to prevent the slurry from curing residue. The guide rail and transmission parts should be lubricated regularly. Common coating defects include streaks, uneven thickness, pinholes, etc. Streaks may be due to damage to the coating tool or the presence of large particles in the slurry; Uneven thickness may be related to uneven substrate, uneven coating pressure or speed fluctuations; Pinholes are often caused by incomplete defoaming of the slurry or poor wettability of the substrate. Targeted inspection of relevant links can usually effectively solve problems.
Summary
Laboratory film coating machines are a critical tool for achieving high-quality coating film preparation. By deeply understanding its working principles, mastering the characteristics of different slurries such as water-based and oil-based, and strictly implementing standardized operation and maintenance procedures, researchers can efficiently and reliably prepare coating samples that meet various experimental requirements, laying a solid foundation for subsequent performance testing and evaluation.