Definition
A heated squeegee coater is a precision coating equipment that evenly applies the coating solution to the surface of the substrate and dries or cures the coating layer through a heating system. The equipment integrates squeegee coating and heating functions, and is designed to realize the preparation of functional layers on the surface of materials by controlling the coating thickness and temperature conditions. Its core is to use the scraper gap to adjust the thickness of the coating solution, and remove solvents or promote the physical and chemical transformation of the coating through heat transfer, which is suitable for continuous or intermittent coating operations in a variety of non-medical fields.
How it works:
The working principle of the heated scraper coater is based on the synergy of fluid mechanics and thermodynamics. The coating liquid is delivered to the surface of the substrate or coating roller through the feeding system, and the scraper uses a set gap to evenly scrape off the excess liquid, forming a wet film with a controllable thickness. The substrate then carries a wet film into the heating area, and a heat source (such as a hot plate, infrared radiator, or hot air system) transfers energy to the coating through conduction, convection, or radiation, promoting solvent evaporation or resin curing. The heating temperature should be matched with the coating speed to avoid crusting on the coating surface due to too high temperature or insufficient drying caused by too low temperature. The formula describes the heating power requirement per unit area that can be expressed as:
\( Q = \rho \cdot c_p \cdot v \cdot (T_t - T_0) \cdot h \)
Among them, \( Q \) is the thermal power per unit area, \( \rho \) is the coating density, \( c_p \) is the specific heat capacity, \( v \) is the coating speed, \( T_t \) is the target temperature, \( T_0 \) is the initial temperature, and \( h \) is the thickness of the wet film. This calculation helps to determine the heating parameter configuration in the experiment.
Measurement method
In a heated squeegee coater, key measurement parameters include coating thickness, temperature uniformity, and coating quality. Thickness measurement usually uses non-contact laser displacement sensor or real-time film thickness monitor, and continuously tracks the dry and wet film behind the scraper and after heating, and the error is controlled within ±2%. Temperature uniformity is acquired at multiple points in the heated area by thermocouple array or infrared thermal imager to assess whether temperature differences affect coating performance. Coating quality inspection relies on optical microscopy to observe surface topography and validate it in combination with adhesion testing (e.g., grid method) and solvent residue analysis (e.g., gas chromatography). In the standard operation, the data should be recorded after calibration, and the relevant requirements of the coating film preparation method should be regularly compared with the reference national standards such as GB/T 1727-2021.
Influencing factors
There are many factors that affect the coating effect of the heating scraper coating machine, which can be classified into three categories: process parameters, material characteristics and equipment status. In the process parameters, the scraper gap directly determines the thickness of the wet film, and the reduction of the gap can reduce the coefficient of variation of coating uniformity. Coating speeds can easily introduce bubbles or streaks at high speeds, while low speeds can extend drying time. In terms of material properties, the viscosity, surface tension and solid content of the coating solution have a significant effect on the spreading performance, and the high viscosity is easy to cause scraper peeling marks, while too high solids content may cause cracking of the coating. Coating defects can also be caused by equipment conditions such as scraper edge wear, aging heating elements, and substrate tension fluctuations. In practice, it is recommended to optimize these parameters through orthogonal experiments or response surface methods to establish a stable process window.
Application:
Heated squeegee coaters have a wide range of uses in numerous non-medical fields. In the new energy industry, it is used for the coating of lithium battery electrode slurry, which improves the consistency of the distribution of electrode active substances by precisely controlling the thickness and drying rate. In the field of electronic materials, it is used in the preparation of dielectric layers and conductive adhesive layers for flexible circuit boards to ensure uniform coverage in small structures. In the packaging and printing industry, equipment can handle functional coatings for food packaging such as barrier films and UV-curable varnishes. In terms of optical materials, such as anti-reflective films and polarizer coatings, mass production can also be achieved through this equipment. In addition, functional materials research and development laboratories often use small heated squeegee coating machines to screen material formulas and verify the feasibility of the coating process.
Key points of selection
The selection should be comprehensively evaluated according to the experimental purpose and sample characteristics. In terms of substrate adaptability, it should be confirmed that the equipment can be adapted to the width, thickness range and curling characteristics of the target substrate (e.g., film, metal foil, paper). The heating method should be selected according to the solvent type and coating requirements, the water-based slurry should be heated by hot air or infrared to control the volatilization rate, and the solvent-based system should be heated by contact heating plate to reduce odor escape. The coating accuracy requirements are judged by the resolution of the scraper adjustment mechanism and the servo drive system, and the adjustable gap is suitable for high-precision scenarios at the micron level. If the temperature control accuracy is required to be ± 1°C, it needs to be equipped with a PID controller and an independent temperature section. In addition, equipment safety requires attention to explosion-proof design and exhaust gas discharge channel configuration, especially when dealing with organic solvents.