SLOT DIE COATING
Slot die coating was originally developed in the early 1950s, and in 1951 Eastman Kodak Co. filed the first patent principles for Slot Die coating. Slot Die coating has a low operational cost and is an easily scaled processing technique for depositing thin and uniform films rapidly, while minimizing material waste. Slot die coating technology is used to deposit a variety of liquid chemistries onto substrates of various materials such as glass, metal and polymers by precisely metering the process fluid and dispensing it at a controlled rate while the coating die is precisely moved relative to the substrate.
Slot-die coating technology allows for precise, repeatable and scalable deposition of liquid thin films from almost any material onto a wide variety of surfaces and substrates. It is a technique that has traditionally been used in industrial-scale manufacturing processes due to its reliability, high throughput, and extremely low waste production. Some of the world’s most important commercial products are made using
slot-die coating techniques, including LCD displays, chemical release patches, touchscreens, food packaging, Li-ion batteries and multi-layer ceramic capacitors among many other applications. Additional benefits include is its non-destructive nature and deterministic thickness
control. These properties combine to afford significant process control and scaling advantages over common R&D coating techniques such
as spin coating and blade coating.
SLOT DIE HEAD
Slot-die systems achieve their coatings by delivering the desired coating fluid (often referred to as “ink”) onto the desired substrate through a highly precise deposition vessel known as the “slot-die head.” The slot-die head lies at the core of any slot-die coating system, as its design and position relative to the substrate significantly influence the quality and stability of the resulting thin film. A fully assembled Slot Die head consists of several key components. Namely, the front plate, back plate, shim, and meniscus guide. The front and back plates are the exterior metal blocks that receive the ink from the delivery system and secure all of the Slot Die head components in place. The shim and meniscus guide are two thin sheets of metal between the front and back plate that serve to guide the ink to the coating edge of the Slot Die head.
The interior design of a Slot Die head can vary, though typically the coating ink is pumped into the head via tubing connected to an inlet on either the front or back plate. Upon entering the Slot Die head, the ink travels into a hollow cavity, often referred to as the ink reservoir, manifold or distribution chamber. The ink is then guided downwards from this reservoir to the coating edge of the Slot Die head by the shim, whose cutout shape determines the coating width or stripe pattern of the ink on the substrate. The meniscus guide protrudes slightly from the bottom of the Slot Die head in an inverted pattern with respect to the cutout pattern of the shim. This serves to guide the ink uniformly onto the substrate to improve coating quality and stability.
The process of Slot Die coating is often described as being “pre-metered.” This means that the thickness of the final coating is a function of the rate at which the ink passes through the system. More specifically, it means that the wet film coating thickness can be easily calculated from the pump rate (the rate at which ink enters the system), the substrate motion speed (the rate at which the substrate absorbs ink from the system), and the coating width (the width across which the ink is dispersed upon the substrate).
While coating thickness is often the primary parameter of interest for users of slot-die coating equipment, control over the quality of this coating must also be carefully considered. The quality of coating is generally discussed in terms of the “stable coating window” of a process. This stable coating window is defined by all of the possible combinations of upstream pressure versus the gap-to-thickness ratio that result in a reliable coating process without defects (e.g. clumps, splotches or pinholes) in the coated layer. In practical terms, this means that achie-ving a defect-free film of a desired thickness is often a matter of balancing the ink pump rate and the substrate motion speed. However, the precise boundaries of the stable coating window vary depending on the nature of the ink and substrate being used for a given coating process, and uniformity of coating always remains directly related to the machining precision of the slot-die head and motion system.
By optimizing processes and designing equipment to exert greater control over these parameters, slot-die coating affords precise and repeatable coating of thin films ranging from tens of nanometers to hundreds of microns in thickness. For these reasons, slot-die coating has seen greatly increased use in lab-scale materials R&D, as researchers aim to achieve more consistent experimental results, exert greater control over their coating processes, and demonstrate the scalability of their work for industrial roll-to-roll and sheet-to-sheet manufacturing. As a result, FOM Technologies coating equipment is now supporting cutting edge research into 3rd generation photovoltaics, OLED displays, fuel cells, batteries, membranes, printed electronics, conductive thin films and more.
ENABLING FUNCTIONAL MATERIALS R&D
At FOM Technologies we aim to bring industry-grade coating solutions to the R&D environment. We pride ourselves on providing high quality hardware, user-friendly process control, and a researcher-focused design mentality across our all of our products. Whether you are conducting fundamental research, establishing a pilot process, or moving into full-scale production, it is our mission to support you with a premium, precise and scalable coating platform to elevate your coating research and production initiatives.