Definition
The Vacuum Adsorption Scraper Coating Tester is a precision equipment used to prepare uniform films or coatings in a laboratory setting. Its core function is to evenly spread the fluid material on the surface of the substrate through a mechanical scraper and use a vacuum adsorption system to fix the substrate to control coating thickness and uniformity. The equipment is widely used in process development and performance verification in the fields of energy materials, electronic devices, functional coatings and composite materials, aiming to simulate the continuous coating process and provide a parameter basis for large-scale production.
How it works:
The workflow of the vacuum adsorption squeegee coating tester is divided into four key steps: substrate fixation, slurry feeding, squeegee coating, and drying forming. First, the substrate (such as film, glass, or metal sheet) is placed on a porous vacuum platform and adheres smoothly through negative pressure adsorption, preventing warping or shifting during the coating process. Second, a preset volume or ratio of slurry is applied to the front end of the substrate. The squeegee then translates along the surface of the substrate with an adjustable gap height, typically set by a micron-scale spiral micrometer, to push the slurry flow and create a wet film of uniform thickness. The scraper movement speed, gap size, and slurry rheological characteristics all determine the initial thickness of the coating. Finally, the wet film enters the hot air drying channel or infrared drying area with the substrate, and the solvent volatilizes after heating, leaving a solid functional layer. The vacuum system works continuously throughout the process to ensure the stability of the substrate.
The coating thickness can be preliminarily estimated based on the scraper gap and slurry concentration. Assuming that the gap between the scraper and the substrate is \( h \ (in meters) and the solid content of the slurry is \( \phi \) (dimensionless), then the theoretical dry film thickness \( d \) after drying can be expressed as:
\( d = h \times \phi \)
The actual thickness also needs to consider factors such as scraper pressure, substrate surface energy and slurry thixotropy, so it needs to be calibrated experimentally.
Measurement method
The evaluation of coating quality and performance relies on several measurement techniques. Thickness measurement typically uses a contact probe profiler or a non-contact optical thickness gauge that takes a multi-point average over the coating area and records uniformity and standard deviation. Surface topography is observed by atomic force microscopy or laser confocal microscopy to analyze micropores, cracks, or orange peel defects. Adhesion testing uses the grid method or peel method to determine the physical match based on the bond strength between the substrate and the coating. The rheological properties of the slurry (e.g., viscosity, yield stress) are measured by a rotary rheometer to provide input for the adjustment of the coating process parameters. The drying efficiency is monitored by differential scanning calorimetry or thermogravimetric analyzer.
Influencing factors
The coating results of the vacuum adsorption squeegee coating tester are constrained by the following main factors:
Substrate properties: The surface roughness, hydrophilicity and thermal stability of the substrate directly affect the adhesion and uniformity of the coating. High surface energy substrates help the slurry spread, while low surface energy substrates are prone to shrinkage or dehumidification.
Rheological properties of slurry: The viscosity, thixotropy and solid content of the slurry determine its fluidity under the scraper. Low-viscosity slurry is easy to spread evenly due to gravity and shear force, but may cause edge effect due to surface tension. High-viscosity slurries require more scraper pressure and are prone to streaking.
Process parameters: The scraper clearance, moving speed and vacuum pressure need to be coordinated and optimized. Too small a gap will cause a thin coating or a worn scraper, and a large gap will waste material; Too fast speed may introduce bubbles or shear thinning effects; Insufficient vacuum pressure can cause the substrate to move away from the platform, causing thickness deviations.
environmental conditions: Ambient temperature and humidity affect the volatilization rate of solvents and the viscosity of the slurry. Excessive humidity may cause mist bleaching of the coating, and temperature fluctuations will change the viscosity dynamics, and the temperature should be controlled from 20°C to 25°C and relative humidity below 60% under reasonable conditions.
Scraper material and condition: The flatness, hardness and corrosion resistance of scrapers (commonly stainless steel or ceramic) are crucial. Worn edges or with microscopic defects can leave scratches or bands on the surface of the coating.
Applications:
The Vacuum Adsorption Squeegee Coating Tester has a wide range of uses in several non-medical fields:
Energy materials: For slurry coating of lithium battery electrodes, the effect of positive and negative coating thickness on energy density and cycle life is studied. In addition, in the field of solar cells, it is used in the uniform preparation of perovskite absorbing layers and electron transport layers to optimize the photoelectric conversion efficiency.
Electronics: In flexible display panels, it is used to coat conductive polymers or insulating layers as interlayers for organic light-emitting diodes or electronic paper. In the field of printed electronics, it is used to prepare transparent conductive films (such as silver nanowire networks).
Functional coating: In the field of optics, anti-reflective film or anti-fog coating is applied to a glass or polyester substrate; In the field of anti-corrosion, epoxy resin or polyurethane protective film is prepared and its salt spray resistance is evaluated.
Composite materials: Used to prepare thermal management materials (such as graphene thermal conductive films) or electromagnetic shielding coatings, achieving gradient structures through multi-layer coating. In the textile industry, waterproof or flame-retardant finishes are applied to enhance functionality.
Key points of selection
When choosing a vacuum adsorption scraper coating tester, the following parameters should be evaluated in combination with the experimental objectives and cost constraints:
Coating width and substrate size: The testing machine often provides adjustable widths from 100 mm to 400 mm, and it is necessary to confirm whether it is compatible with the length and width of the target substrate. Larger sizes are suitable for bulk sample preparation, but increase equipment footprint and energy consumption.
Clearance adjustment accuracy: The gap adjustment between the scraper and the substrate should reach the micron level (e.g., 1 micron resolution) to meet the needs of precision coating. Some models support automatic positioning of servo motors to improve repeatability; Manual adjustment is less costly.
Coating speed range: Typical speed range is 1 mm/s to 100 mm/s, low speed is conducive to the spread of high-viscosity slurry, and high speed is suitable for simulating rapid manufacturing rhythms. It is necessary to match the requirements of the experiment for uniformity and periodicity.
Vacuum system capabilities: The vacuum level is at least 0.6 megapascals (negative pressure), and the platform should be designed with porous areas to evenly adsorb the substrate. Larger substrates require higher pumping rates.
Drying and temperature control system: The testing machine is usually equipped with a drying channel or infrared module, with an operating temperature range of 50°C to 200°C, and needs to have independent temperature zone control. For heat-sensitive materials, the ability to adjust the low temperature section is particularly important.
Ease of operation and data interface: The user interface should support parameter preset, real-time display and data export (such as USB or network port) to facilitate integration into the laboratory data management system. In addition, the ease of cleaning and maintenance (e.g., removable scraper, vacuum table cleaning) directly affects the efficiency of the experiment.