Die Coating

Die Coating Methods - a family of coating methods:

• SLOT-BEAD ("slot", "die", "on-roll slot")
• EXTRUSION
• TENSIONED-WEB SLOT ("off-roll slot", "TWSC")
• SLOT-ON-RUBBER ROLL
• SLIDE-BEAD ("slide", "cascade")
• SLOT-CURTAIN ("curtain", "hopper", "inverted fountain")
• SLIDE-CURTAIN ("multilayer curtain")
• JET COATING

Die Coating Characteristics:

Coating process utilizes a "die" applicator for achieving two sequential flows:

• internal manifold flow - distributes flow across intended coating width
  internal manifold flow is similar for all die coating methods
• external transfer flow -transfers the width-distributed flow to the moving substrate
  different methods are distinguished by their particular transfer flows

Slot-Curtain Coating section displaying Manifold and Transfer Flows

Slot Die section view displaying internal manifold

Operating Windows
Each method must operate within its individual operating window, a composite of operability limits determined by the onset of hydrodynamic instabilities of its transfer flow and in some cases further limited by other practical considerations.

Commercial Advantages

Precision Die Coating allows

• participation in higher-margin markets exclusive to superior product functionality and
• more frugal manufacturing (reduced waste, higher productivity)

when compared with other coatings methods such as roll, blade, gravure, rod, etc.

These commercial advantages are the result of the following die coating process advantages:

• Pre-metered operations - Coating thickness is simply and conveniently determined in advance via liquid delivery flow rate and substrate speed settings.
• Accurate coated thickness is achieved via accurate input flow rate and substrate speed.
• Excellent MD uniformity is achieved through constancy of flow and substrate inputs and appropriate selection of the coating process operating state.
• Excellent TD uniformity is possible through the use of a precision die with an optimized design and appropriate selection of the operating state
• Continually clean, fresh and contamination-free coating
• Most die coating methods have low risk, gentle interaction with substrates and minimal undesired penetration of expensive materials in permeable webs (although penetration of applicable substrates can be achieved by certain die coating methods if desired).
• Many of the die coating methods have simultaneous multilayer capability (especially those utilizing slide format dies) with its obvious productivity and product sophistication advantages.

Specific die coating methods have extensive additional advantages as described in subsequent sections.

Die Coating Applications

Die Coating methods are the technologies of choice whenever an application requires an accurate liquid coating using expensive functional materials. The choice of a specific die coating method starts with matching the method's operating window with the economic requirements for the product application. Specific examples of die coating applications are given in subsequent sections describing individual methods.