A high-end lab R2R coater normally offer interchangeable heads: (1) Slot-Die Coating: The industry standard for high-precision battery electrodes. It uses a shim and a precision pump to "meter" the slurry. This is ideal for your NMP slurries as it minimizes solvent evaporation at the coating head. (2) Comma Doctor / Reverse Comma: Excellent for high-viscosity slurries. It uses a rotating "comma" roller to set the wet thickness. (3) Micro-Gravure: Best for very thin coatings (like functional ceramic layers on separators or thin ion-exchange membranes). It uses a patterned roller to transfer a precise volume of liquid.
General Introduction of R2R coating methods:
(1). Doctor Blade Coating
In a R2R setup, doctor blade coating is normally called Knife-over-Roll coating. It mainly consists of (1) Web: The aluminum or copper foil is pulled over a high-precision backup roller. (2) Reservoir: A "dam" of slurry is maintained just behind the blade. (3) Metering: As the foil moves, the blade (the "knife") scrapes off excess slurry. The thickness of the wet coating is determined by the gap between the blade edge and the foil surface. The wet thickness T= Gap * K (where K is a factor, that is usually around 0.5 to 0.7, depending on the slurry's viscosity and the web speed.)
(2). Reverse Comma Coating (also called Transfer Comma Coating)
Unlike a standard doctor blade where the foil moves under a stationary knife, a reverse comma system uses a three-roll or two-roll configuration to "transfer" a metered film of slurry onto the foil. The key components and features are: (1) Comma Roller: A high-precision steel cylinder with a "comma-shaped" cross-section. It doesn't move during the coating process; instead, it acts as a high-precision gate. (2) Applicator (Back-up) Roller: This roller rotates in the opposite direction (reverse) to the web travel. It picks up the slurry from a reservoir and carries it toward the comma gap. (3) Transfer: As the foil (web) passes between the rollers, the metered slurry is wiped onto the foil.
(3). Slot Die Coating
While doctor blade and comma coating are "metering" methods (where you scrape off excess), slot-die is a "pre-metered" method. This means the exact volume of slurry pumped into the head is the exact volume that ends up on the foil. Normally slot die coating system consists of three main components: A high-precision pump (usually a syringe or gear pump), a slot-die head, and a back-up roller. The slot die coating head is mainly composed of (1) Reservoir (Manifold): The slurry is pumped into an internal cavity inside the die head designed to distribute the fluid evenly across the entire width. (2) Shim: A thin, precision-cut metal plate determines the width of the coating and the internal gap of the die. The coating bead is critical for the coating film quality, where the slurry emerges from a narrow "slot" and forms a liquid bridge (the "bead") between the die lips and the moving foil.
(3). Microgravure Coating
Microgravure coating is a specialized roll-to-roll (R2R) technique used for extremely thin, high-precision coatings. Unlike standard gravure, which uses large rollers and a doctor blade on the foil, microgravure uses a very small diameter engraved roll that rotates in the opposite direction to the web. The R2R microgravure coating system has a small, engraved "gravure" roll (typically 20mm to 50mm in diameter) that is partially submerged in a slurry reservoir. There are multiple distinct features: (1) Engraving Roll: The roll surface is covered in microscopic cells (patterns like honeycombs or pyramids). The "cell volume" determines exactly how much liquid is picked up. (2) Reverse Rotation: The roll rotates in the opposite direction of the foil (web). This "kiss-coating" action shears the liquid as it transfers, resulting in a much smoother surface than traditional gravure. (3) Doctor Blade: A flexible blade scrapes the excess slurry off the roll before it touches the foil, ensuring only the liquid inside the engraved cells is transferred.
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| Power |
- AC220V±10%, single phase, 50/60Hz, 3550 W
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| General Features |
- Roller width: 200 mm
- Loading substrate width: Max. 180 mm
- Coating width: Max. 160 mm
- Mechanical coating speed: 0.01-1.0m/min (the real coating speed depends on the slurry properties and dry oven length/temperature)
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| Unwinding/Winding Parts |
- Roller diameter: 3", mechanical expansion for tightening the loading roll substrate and collection cardboard.
- Max. winding/unwinding roll diameter: 250 mm
- Alignment Sensors were installed and aligning position resolution could be 0.3 mm.
- Coating Roller: Stainless Steel with surface Cr coating, Ф80mm
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| Coating Parts |
(1) Doctor Blade
- The doctor blade is made of SS with surface Cr coating and its diameter is Ф50mm.
- The coating width is 0-160 mm, which can be adjusted by the blocking foam.
- Slurry Viscosity: 2000-6000 cP (recommended, higher viscosity up to 10000-15000 cP may also work for thicker electrode).
- The slurry feeder EABSFPP2L can be considered.
(2) Reverse Comma
- The coating roller is made of SS with surface Cr coating and its diameter is Ф80mm.
- The backing roller is made of rubber (Ф80mm, pneumatic)
- The comma bar is made of SS with surface Cr coating and its diameter is Ф50mm.
- The coating width is 0-160 mm, which can be adjusted by the blocking foam.
- Slurry Viscosity: 2000-12000 cP (recommended)
- The slurry feeder EABSFPP2L can be considered.
(3) Slot Die
- The coating roller is made of SS with surface Cr coating and its diameter is Ф80mm.
- The coating width is 0-160 mm, which can be adjusted by the opening mouth of shims. The standard shim thickness is 0.2, 0.3, 0.4, 0.5mm.
- Slurry Viscosity: 50-12000 cP. For battery application, slurry viscosity is recommended in 2000-8000 cP.
- The precise screw pump EASDCPSP is the best option for stable slot die coating.
- For intermittent coating (or pattern coating) for cylindrical electrode application, the intermittent valve system is highly recommended. For simultaneous dual-layer coating, a customized dual-channel slot die head (ESAR2RCSDH) can be supplied.
  
(4) Microgravure
- A standard microgravure rod with Ф30mm is included. The parameters, such as coating width, engraved pattern, mesh number and depth can be customized.
- Slurry Viscosity: 20-2000 cP.
- The slurry feeder EABSFPP2L can be considered.
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| Heating Oven Features |
- Heating mode: Convection heating (hot air flow). Other heating methods of IR and UV can be customized upon request. Various heating modules are switchable.
- Heating temperature: Max.130℃
- Heating oven length: 0.5 m (standard version). If customer want to increase the heating oven length to increase the coating speed, the dual-heating-oven design can be supplied.
- Ventilation: air flow: 570m³/h, 5" aluminum pipe
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Tension Control System
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- Tension range: 10-40 N (resolution is ±3 N), which is controlled by swing roller system.
- For low-tension substrate coating (eg: separator and membrane), the specially designed low tension version is highly recommended since its lowest tension can be down to 5 N.
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| Gas Compressor |
- A gas compressor (EUQOFGC) is needed to provide 60-80 psi for pneumatic operation.
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| Certification |
- CE certified
- UL and CSA certification is available upon request at extra cost
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| Dimension |
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| Weight |
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References:
M. Schmitt, et al., Slot-die processing of lithium-ion battery electrodes—Coating window characterization, Chemical Engineering and Processing: Process Intensification, 2013, 68, 32-37
H. Li, et al., High-performance supercapacitor carbon electrode fabricated by large-scale roll-to-roll micro-gravure printing, J. Phys. D: Appl. Phys., 2019, 52, 115501
L. A. Román-Ramírez, et al., Effect of coating operating parameters on electrode physical characteristics and final electrochemical performance of lithium-ion batteries, International Journal of Energy and Environmental Engineering, 2022, 13, 943-953.
