Definition
The wire rod scraper integrated coating machine is an integrated precision coating equipment that integrates the traditional wire rod coating and scraper coating process units in the same system. The equipment forms a uniform liquid film through the pre-coating of the wire rod, and then the squeegee pre-adjusts the film thickness for the second time, so that the coating process has both the efficient initial coating ability of the wire rod and the accurate final control characteristics of the scraper. This composite structure is suitable for lab-scale coating preparation, especially for uniform coating requirements for high viscosity or particulate slurries.
How it works:
The operation of the equipment is divided into two successive stages. In the first stage, the wire rod is immersed in the slurry tank with a fixed gap and rotated, and the slurry is transferred to the surface of the substrate with a preset film thickness. The surface of the wire rod is usually processed with precision grooves, and the initial liquid film thickness is controlled by the wire diameter and groove depth. In the second stage, the substrate passes through the scraper unit at a constant speed, and the scraper uses hardened metal sheets or polymer materials with micron-level adjustable gaps to shear or compress the pre-coated film, removing the excess slurry from the liquid film, and finally forming a uniform coating of the target thickness on the substrate. Adjusting the relative distance of the scraper to the substrate allows for precise control of the final film thickness, often with micrometer mechanisms with micron-level accuracy.
Measurement method
Film thickness measurement is usually done offline or online. Offline measurement is standardized by sampling using a laser confocal microscope or dry film thickness gauge. The online measurement integrates precision displacement sensors into the scraper module, provides real-time feedback of coating pressure and clearance data, and automatically compensates for mechanical fluctuations through the control system. Monitoring of slurry viscosity is pre-calibrated prior to coating using a rotary viscometer to ensure process repeatability. Surface tension measurements are aided in assessing coating wettability with a contact goniometer, which is especially important for uniformity control in high-viscosity non-Newtonian fluid systems.
Influencing factors
The key variables affecting the uniformity of coating include the rheological properties of the slurry (such as shear dilution behavior and elastic modulus), the surface energy of the substrate (hydrophobic difference), the coating speed (the shear rate directly affects the stability of the liquid film), the tip morphology of the scraper (sharpness, wear state), and the ambient temperature and humidity (affecting the evaporation rate and viscosity of the solvent). Gap fit errors between the wire rod and the scraper can cause coating streaks or thickness fluctuations, so calibration should be prioritized. In addition, the size distribution of particles in the slurry beyond the scraper gap can lead to surface scratches and defects.
Applications:
In the research and development of functional coatings, the equipment is widely used for pre-production verification of new energy electrode coatings, optical film layers, printed electronic conductive layers and flexible sensor functional films. For example, the uniformity control of the primary coating thickness of lithium-ion battery electrode paste on the electrode current collector, and the development of multi-layer coating process for capacitive films. It is also used to optimize the initial ratio of barrier or adhesive layers on substrates such as paper and plastic film, and to replace manual coating methods in materials science laboratories to improve data repeatability.
Selection guide
Laboratory selection prioritizes the evaluation of coating width and substrate length limits, with common coating widths ranging from 100 mm to 400 mm. The type of wire rod should match the viscosity range of the slurry: the low-viscosity system (less than 1000 mPa·s) is suitable for fine wire diameter wire rods, and the thick wire diameter spiral groove wire rod should be selected for high-viscosity or large particle slurry. The scraper material and hardness should be selected according to the chemical characteristics of the slurry, and the PTFE coated scraper should be used for acidic slurry, and the tungsten carbide steel scraper can be used for inorganic systems. The equipment drive system should have speed control capabilities, usually with a speed adjustment range of 1 mm to 400 mm per minute, to ensure the feasibility of low-speed high-shear tests. The control system should support digital memory of coating parameters to facilitate multi-recipe switching.