Definition
A laboratory scraper is a precision laboratory equipment used to prepare uniform, controllable thickness coatings on substrates. It uses mechanical scraping to evenly spread liquid or paste samples (such as coatings, adhesives, slurries, etc.) on the surface of the flat substrate at a set thickness to simulate the coating process or prepare test samples. This equipment is of great value in the fields of material research and development, quality control, and process optimization.
How it works:
The working principle of laboratory scrapers is based on gap coating technology. Its core components include precision scrapers, leveling substrates, and gap adjustment systems. When working, an appropriate amount of sample is placed at the front end of the substrate, and the scraper moves at a constant speed to control the coating thickness through the preset gap between the knife edge and the substrate. There is a direct correlation between the gap height h and the thickness of the coating wet film, usually the wet film thickness is slightly less than the gap height, and the specific relationship can be approximately expressed by the formula as:
hwet ≈ k · hgap
where hwetis the thickness of the wet film, hgapis the scraper gap height, and k is the coefficient related to the rheological properties of the material. After scraping, the sample is cured or dried to form a uniform coating for subsequent performance testing.
Measurement method
When using a laboratory scraper for coating, follow a systematic procedure to ensure consistent results. First, select the appropriate clearance according to the target thickness and use a micrometer or encoder to set it precisely. Fix the substrate to the equipment platform to ensure it is flat and warping. Take an appropriate amount of sample and place it at the beginning of the scraper travel path, start the equipment for uniform scraping. After the coating is completed, the thickness of the wet film usually needs to be verified, and multi-point measurement can be carried out using a wet film comb gauge. After drying, the coating thickness can be measured by instruments such as micrometers and film thickness gauges, and compared with the set value to calibrate the equipment parameters.
Influencing factors
The quality of the coating is affected by multiple factors. Squeegee clearance is a direct parameter that determines thickness, and its accuracy directly affects coating uniformity. The scraping speed affects the shear rate, which may change the leveling behavior of the material, too fast may cause streaks, and too slow may cause local accumulation of material. The rheological properties of the sample itself, such as viscosity, thixotropy, etc., can affect the leveling and final film thickness after coating. Environmental conditions such as temperature and humidity can alter sample fluidity or drying rate. The surface energy and flatness of the substrate will also affect the adhesion and uniformity of the coating. The technical proficiency of the operator and the maintenance status of the equipment are also factors to consider.
Applications:
Laboratory scrapers are widely used in many industrial and scientific research fields. In the coatings industry, it is used to prepare test paint films to evaluate properties such as adhesion, hardness, and weather resistance. In the field of electronic materials, it is used to prepare thin film samples such as conductive pastes and dielectric layers. In adhesive development, it is used to make a standard thickness adhesive layer to test bond strength. In the field of new energy, it is used for the research of coating process of battery electrode paste. In addition, it is also commonly used in R&D and quality control in the fields of optical films, paper coatings, and textile finishing agents.
Equipment selection considerations
When choosing a laboratory scraper, it is necessary to comprehensively consider the technical parameters and actual needs. The scraping thickness range should cover the required range of the experiment, and common equipment ranges from micron to millimeter. Gap adjustment accuracy is key to ensuring repeatability, often requiring micron-level resolution. The scraping speed range and stability need to meet the requirements of different material properties. The equipment should have good platform flatness and rigidity, as well as a convenient way to fix the substrate. The scraper material (e.g., stainless steel, ceramic) and the type of knife edge should be selected according to the sample corrosiveness and coating requirements. Some devices offer additional features such as adjustable squeegee angle and temperature-controlled platforms to suit specific experimental needs. Ease of operation, safety and ease of maintenance of the equipment are also aspects that need to be evaluated in the selection.