1、 What is a slit coating machine?
Slit coating machineIt is a high-precision, continuous, large-area film coating equipment mainly used to uniformly coat one or more layers of liquid materials (such as adhesives, coatings, pastes, battery materials, optical film layers, etc.) on the surface of substrates (such as paper, plastic films, metal foils, glass, etc.), forming precise thickness and smooth surface coatings or functional films.
It is one of the core equipment in precision coating technology, widely used in fields such as lithium battery manufacturing, flat panel displays (OLED, LCD), photovoltaics, semiconductors, optical films, decorative materials, medical tapes, etc.
2、 Working principle of slit coating machine (technical and coating process analysis)
✅ Core principle: Through a precisely controlled slit die, the slurry is evenly extruded and coated onto a moving substrate, forming a continuous and uniform coating.
1. Basic coating process
Slit coating belongs to the type of "extrusion coating" or "die coating", and its workflow is roughly as follows:
1) Feeding system: The slurry (liquid material) to be coated is stably transported from the storage tank to the coating die by a pump (such as a gear pump or screw pump);
2) Mold head (slit mold head): The slurry enters a precision mold head with a flat slit outlet, which maintains a very small gap (usually tens to hundreds of micrometers) between the mold head and the substrate;
3) Coating window (coating gap): A moving substrate (such as foil or film) passes under the die at a constant speed, and at the exit of the narrow slit between the die and the substrate, the slurry is uniformly "extruded" and spread on the surface of the substrate;
4) Coating formation: The slurry forms a wet film with uniform thickness and neat edges on the substrate;
5) Drying or curing (subsequent process): The wet film is subjected to oven drying, UV curing, infrared drying, and other methods to remove solvents or cure, ultimately forming a solid functional film.
2. Key principle mechanism
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| The coating die has aLong strip slit opening (width ranging from a few millimeters to tens of centimeters)The slurry is uniformly extruded through this narrow slit, which is the key structure to achieve a "thin and uniform" coating |
| The distance between the mold head and the substrate (referred to asGap between lips and mouth(usually 10-300 μ m) greatly affects the thickness and uniformity of the coating, requiring precise adjustment and control |
| Pressure and rheological control | During the coating process, the slurryViscosity, fluidity, pressure distributionStability must be maintained to ensure the uniformity of the coating and avoid issues such as stripes, missing materials, and thick edges |
| Substrate speed matching | The walking speed of the substrate (usually from a few meters/minute to several hundred meters/minute) is matched with the slurry supply rate and the height of the die opening design, which determines the coating thickness and production efficiency |
| Multi layer coating capability | Slit coating machine can be equipped withMulti mode head system (such as double-layer and three-layer heads), achieveCoating multiple layers of different materials at once, such as positive and negative electrode paste or functional coating in batteries |
3、 The core composition structure of the slit coating machine
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| Including storage tanks, mixing devices, conveying pumps (gear pumps/screw pumps), filters, etc., to ensure stable, bubble free, and uniform delivery of the slurry to the mold head |
| Mold head (slit mold head) | The core component determines the width, thickness, and uniformity of the coating; usuallyStainless steel precision machined parts, internal flow channels optimized through CFD simulation |
| Mold head adjustment mechanism | Used for precise adjustment between the mold head and the substrateGap and horizontal alignment (lip parallelism)Ensure even coating |
| Substrate Conveyor System | Including unwinding machine, rewinding machine, tension control system, guide roller, correction device, etc., to ensure that the substrate passes through the coating area smoothly, wrinkle free, and offset free |
| Drying system (post-treatment) | Such as hot air oven, infrared UV、 Microwave, etc., used for wet film drying or curing to form the final coating |
| Including PLC, touch screen, servo motor, temperature and humidity, tension, speed control, etc., to achieve precise control of coating parameters (speed, gap, pressure, temperature) |
4、 Main technical characteristics and advantages of slit coating machine
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| achievableCoating thickness control at the micrometer level (1-100 μ m)Suitable for high-precision functional film layers |
| ✅Good coating uniformity | Through precision die design and fluid control, coatingHigh uniformity in both horizontal and vertical directionsNo stripes, no vertical flow |
| ✅High coating efficiency | suitableLarge scale, continuous productionHigh substrate speed and large production capacity, suitable for industrial large-scale manufacturing |
| ✅Strong material adaptability | Can be coated with various fluids:High viscosity slurry, low viscosity solution, particle containing slurry (such as battery slurry), UV glue, hot melt adhesive, etc |
| ✅Can be coated in multiple layers | supportSingle layer/double-layer/multi-layer synchronous coatingFor example, lithium battery positive/negative/separator coatings, optical film multilayer structures |
| Compared to immersion coating, spray coating and other methods,Accurate coating, no waste, and neat edgesSuitable for coating precious materials |
| Mold width and coating form (such as comma coating, slit coating, spray coating composite) can be customized according to process requirements |
5、 Typical application areas of slit coating
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| Lithium battery manufacturing | Positive/negative electrode slurry, separator coating | The coating thickness is usually 50-200 μ m, with high precision requirements, which affects battery capacity and safety |
| Flat panel display (OLED/LCD) | Optical film, transparent conductive film (such as ITO), polarizer functional layer | Require uniform and defect free coating for displaying image quality and touch performance |
| Photovoltaic backsheet coating, front panel encapsulation adhesive film, perovskite cell thin film | Used to improve photoelectric conversion efficiency and component weather resistance |
| Photoresist coating and packaging materials | High precision, ultra-thin coating with high requirements for cleanliness and uniformity |
| Brightening film, diffusion film, reflective film, protective film | Used for improving display, lighting, and lens optical performance |
| Decoration and Protection | Decorative coating, waterproof coating, anti fingerprint film | Used for surface treatment of household appliances, mobile phones, cars, etc |
| Medical and Adhesive Tape | Medical pressure-sensitive adhesive, wound dressing coating, electronic tape | High requirements for material safety and coating consistency |
6、 Comparison of slit coating vs other coating methods
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| High precision, good uniformity, suitable for large-area continuous coating, suitable for high viscosity slurries | Manufacturing of lithium batteries, displays, photovoltaics, optical films, etc |
| Suitable for low to medium viscosity coatings through the combination of scraper and roller, the equipment is relatively simple | Tape, labels, packaging materials |
| Spraying liquid through a nozzle is suitable for irregular surfaces, but the uniformity is poor | Architectural coatings, 3C shells, non planar substrates |
| After immersing the substrate in the slurry and pulling it to form a film, it is suitable for simple and uniform coating | Laboratory, functional film prototype |
| Transfer coating through coating roller, suitable for medium to low precision large-area coating | Printing, flooring, paper coating |
7、 Summary
✅ The slit coating machine is an efficient coating equipment based on the principle of precision slit die extrusion. Through stable feeding, precision die control, high-speed substrate transportation, and uniform coating formation, it achieves high-precision, high uniformity, and continuous film coating on the surface of the substrate.
