Squeegee coating machine
A squeegee applicator is a specialized equipment that evenly coats liquid paints, inks, or slurries on flat substrates through precision-machined squeegee elements on a laboratory scale. Unlike the wire winding rod applicator, which relies on trunking metering, the scraper coating machine controls the wet film thickness by adjusting the gap between the blade and the surface of the substrate, which is especially suitable for the preparation of medium to high viscosity fluids, slurries containing functional particles, and thicker coatings. The device is a basic sample preparation tool in the R&D and quality control of coatings, inks, adhesives, lithium pastes and functional films, and its core value is to provide coating samples with accurate thickness, uniform film surface and good reproducibility for subsequent performance tests.
Principle
The working principle of the scraper coating machine is based on the scraping action under relative motion and precise gap control. Its basic components include a flat coating platform, a drive mechanism that can be driven at a uniform speed, and a core component - the scraper coating head. When working, the substrate (such as glass plate, PET film, metal foil) is fixed on the platform, and an appropriate amount of sample is placed at one end of the substrate. The scraper then moves relative to the substrate at a set constant speed, scraping and spreading the accumulated sample into a continuous wet film through the precise vertical gap formed between the blade and the substrate surface.
From a hydrodynamic point of view, the squeegee coating process can be simplified to a lubrication flow model. When the scraper forms a wedge-shaped convergence gap with the substrate, the fluid passes through the slit under a combination of shear and pressure gradients. For specific forms such as comma scrapers, theoretical analysis and numerical simulations show that the coating wet thickness is appliedHwslit height with scraperH0There is a quantitative relationship. Within a certain geometric parameter, by solving the simplified Reynolds lubrication equation, the ratio of the two can be deduced to be close to a constant, for example, it has been studiedHw/H0 ≈ 2/3。 This theoretical relationship reveals the decisive influence of scraper geometric parameters on the final film thickness, and provides a theoretical basis for precise control of coating thickness.
Measurement method
When using a squeegee Coater for standardized sample preparation, accurate measurement and control of key parameters is a prerequisite for obtaining high-quality coatings.
Presetting and calibration of wet film thicknessIt is the primary control goal. Modern scraper coating machines are usually equipped with high-precision adjustment mechanisms, such as digital microscopic split heads or micrometers, and the operator directly sets the vertical gap between the scraper blade and the coating platform through the rotary adjuster, and the setting accuracy can reach the micron level (such as ±0.001mm). For some models, the thickness can be set digitally and feedback via a mechanical limit or a high-precision displacement sensor.
Stability of coating speedIt directly affects the longitudinal uniformity of the coating film. The equipment is driven by servo motors or stepper motors, providing adjustable and stable movement speed (common range 1-300mm/s). Small fluctuations in speed can lead to periodic uneven thickness or lateral streaks in the coating. The operator needs to choose the appropriate coating speed according to the rheological characteristics of the sample to ensure that the sample is fully leveled without defects.
Scraper pressure and angleIn some designs it is adjustable. Although rigid scraper Coaters primarily rely on fixed clearance, the scraper's own gravity, mounting angle, and applied additional pressure can affect the contact between the blade and the substrate, especially if there are minor unevenness. Excessive pressure may cause deformation of the substrate, while insufficient pressure may cause missed coating.
Accessibility controlIt is an important means to improve the accuracy and scope of sample preparation.Vacuum adsorptionThe function can flatten flexible or warping substrates such as paper and film on the platform, eliminating the coating gap error caused by substrate deformation.Heated platformIt is used to control the temperature during the coating process, which is especially important for hot melt materials that need to be coated at a constant temperature or for samples that need to study the effect of the drying process on the properties of the film.
Key factors affecting the quality of coating film
The final quality of the scraper coating film is the result of a multi-factor coupling effect, and any deviation in the link can be magnified as a coating defect.
Accuracy and condition of the scraperIt is the core hardware factor that determines the uniformity of the coating. The flatness, straightness, and surface finish of the scraper edge directly determine the coating reference. Tiny chips, burrs, or abrasions at the edge edge can cause continuous longitudinal streaks on the coating. After long-term use, the passivation or deformation of the cutting edge needs to be repaired or replaced in time. The installation parallelism of the scraper is also crucial, as if the blade is not perpendicular to the coating direction or parallel to the platform, it will lead to uneven lateral thickness.
Rheological properties of the sampleIt is an internal factor that affects the coating behavior. The viscosity, thixotropy, solids content and particle size distribution of the sample together determine its flow behavior in the scraper gap. High viscosity may cause uneven or brushed surfaces after coating; Too low viscosity may cause sagging or edge effects due to excessive fluidity after coating. Bubbles or undispersed agglomerated particles in the slurry can form pinholes or tailing scratches in the coating.
Properties and treatment of substratesIt is the basis of coating. The flatness, surface tension, cleanliness, and absorption of the substrate directly affect the spread and adhesion of the coating. If there is oil and dust on the surface of the substrate, it will cause the coating to shrink holes or poor wetting. For porous substrates such as paper, its absorbency can change the final solid content and surface state of the wet film.
Matching and stability of process parametersIt is an external condition. In addition to the above clearance and speed, the ambient temperature and humidity cannot be ignored. Temperature fluctuations can change sample viscosity, and humidity changes can affect the drying rate and substrate dimensional stability of waterborne coatings. The transmission smoothness of the equipment and the horizontality of the platform constitute the physical basis of the process realization.
Standardization of operation and maintenanceIt determines the sustainability of the precision. Failure to clean the scraper in time after coating causes residue to dry knot on the blade, which is a common cause of subsequent coating streaks. Regularly calibrating clearances and checking for wear on transmission components are necessary measures to maintain equipment accuracy.
Applications in the fields of coatings, inks and new materials
With its wide range of adaptability, squeegee coating machines play a pivotal role in R&D and quality control across multiple industries.
inCoatings & Ink Industry, it is a standard tool for preparing performance test templates. The researchers used it to prepare coatings in different formulations to evaluate key indicators such as hiding power, color, gloss, hardness, adhesion and weather resistance. By preparing highly repeatable coating films, the effects of different raw materials and different ratios on coating properties can be scientifically compared, and the process of formula optimization can be accelerated. Its application meets the requirements of sample preparation methods in a number of domestic and foreign test standards.
inNew energy materialsIn particular, in the preparation of lithium-ion battery electrode sheets, scraper coating is the core means of laboratory research on electrode paste formulation and coating process. Since electrode slurries are typically non-Newtonian fluids with high viscosity and large particle solid phases, winding rods are difficult to apply, while squeegee Coaters with adjustable gaps are ideal for the preparation of active material coatings for subsequent electrochemical performance tests.
inFunctional Films and Electronic MaterialsWith the development of emerging technologies such as perovskite solar cells, OLED, and flexible electronics, scraper coating machines are used to coat functional films such as electron transport layers and photoactive layers on glass or flexible substrates. Combined with the heating platform, the morphological evolution and crystallization behavior of the wet film during the drying process can be studied, which is of great significance for optimizing the performance of the device.
Equipment selection basis
Choosing the right squeegee Coater requires a comprehensive evaluation of your lab's application needs, sample characteristics, and future development direction.
Matching of application targets to coating accuracyis the primary consideration. For the formulation screening and physical properties test of conventional coating inks, general-purpose equipment with basic scraper function and accuracy of about ±0.003mm can be competent. For applications that require extremely high uniformity, such as optical films and functional electronic coatings, equipment equipped with high-rigidity scrapers, high-precision differential adjustment mechanisms, and stable servo drives requires higher thickness control accuracy and repeatability.
Adaptation of sample characteristics to coating rangeCareful evaluation is required. The viscosity range of the sample being handled mainly determines whether an enhanced drive or a special scraper design is required. Conventional scraper Coaters are suitable for medium to high viscosity materials. The coating width and substrate size to be considered determine the platform size and effective stroke of the equipment. Common lab equipment coating widths range from 150mm to 600mm. If you often handle flexible film or easy-to-slide paper,Vacuum adsorption platformis a must-have feature.
Functional scalability and ease of operationIt is about the long-term use value of the equipment. Whether it is neededHeated coating platformTo study drying processes or coat hot melt materials? Whether integration is requiredAutomatic feeding systemTo reduce manual operation errors? Is the user interface user-friendly, and can common process parameters be stored and recalled? Is it easy and fast to clean the scraper? These factors directly affect the efficiency and experience of daily use.
Comply with standards and brand reputationIt is an important reference basis. Knowing whether a device is designed to meet relevant international or national testing standards (such as ASTM D823) can help determine the specification of its design and the commonality of test results. While brand-only theories should be avoided, understanding the industry's general evaluation of equipment durability and after-sales service from a particular manufacturer is a useful reference in selection decisions.
In summary, as a bridge between material formulation and application performance, the selection and application of scraper coating machine need to be based on a deep understanding of the working principle, influencing factors and its own needs. Scientific selection and standardized operation are a solid guarantee for researchers in the fields of coatings, inks and new materials to obtain reliable experimental data and promote technological innovation.