Definition
A squeegee applicator is a type of laboratory equipment used to prepare uniform wet film coatings on flat substrates. It is widely used in sample preparation and performance testing in coatings, inks, adhesives, battery electrode pastes, ceramic coatings and other fields by controlling the gap between the scraper and the substrate, coating or slurry at a specific thickness.
How it works:
Squeegee coating machines work on the principle of mechanical scraping. The equipment typically consists of a flat base platform, a height-adjustable scraper device, and a clamping system to hold the substrate. During operation, an appropriate amount of sample is placed at the front end of the substrate, and the scraper moves at a constant speed or pressure, so that the sample is stretched into a uniform wet film in the gap between the scraper and the substrate. The thickness of the wet film is mainly determined by the gap distance between the scraper and the substrate, and the relationship can be approximately expressed as:
h ≈ g · k
where h is the thickness of the wet film, g is the set value of the scraper gap, and k is the correction coefficient related to the rheological properties of the material. The actual thickness also needs to consider factors such as material viscosity, scraping speed, and surface properties of the substrate.
Measurement method
The measurement of coating film thickness can be divided into two categories: wet film and dry film. Wet film thickness can be measured by contact using a wet film thickness gauge immediately after application, and the thickness range is determined by comparing the tooth marks on the tooth gauge with the coating on it. The thickness of the dry film needs to be accurately measured by magnetic thickness gauge, eddy current thickness gauge or microscopic cross-sectional method after the coating is completely cured. To obtain reliable data, it is often necessary to take multiple measurements at different locations in the film layer and calculate the average. Thickness uniformity can be assessed by measuring the thickness of multiple points in the transverse and longitudinal directions of the film layer and calculating its standard deviation.
Influencing factors
The quality of the coating film is affected by multiple factors. In terms of material properties, the viscosity, leveling, and thixotropic properties of the sample directly affect the uniformity of the coating and the formation of defects. In the equipment parameters, scraper clearance accuracy, scraping speed stability and knife edge flatness are the key control points. Operating conditions such as ambient temperature and humidity may change the rheological behavior of the material, and the surface energy, roughness and cleanliness of the substrate will also affect the adhesion and apparent quality of the coating. These factors need to be systematically controlled during the experiment to ensure reproducibility of the results.
Applications:
Squeegee coating machines have a wide range of uses in industrial R&D and quality control. In the coatings industry, it is used to prepare standard samples for testing the weathering, adhesion and optical properties of paint films. The field of printed electronics uses it to prepare uniform films of functional materials to study electrical properties. It is commonly used in the field of new energy to coat battery electrode slurries to evaluate the coating process performance of active materials. In addition, this equipment is also an important sample preparation tool in laboratory research on materials such as paper coating, textile handling, optical films, etc.
Selection considerations
When choosing a squeegee coating machine, technical requirements and operating conditions should be comprehensively considered. In terms of equipment accuracy, attention should be paid to the squeegee gap adjustment resolution and linear motion stability, and the gap adjustment range should cover the expected coating thickness requirements. In terms of functional configuration, manual, electric or program-controlled models can be selected as required, and some devices offer heating platforms or vacuum substrate fixation functions to suit special materials. Compatibility is important to ensure that the equipment can handle common substrate sizes and types. Ease of use involves ease of cleaning and maintenance and clarity of the operating interface. In addition, the equipment manufacturing material should have sufficient corrosion resistance and wear resistance to adapt to samples with different chemical properties.