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n the world of slot die coating, thin is in. Or, to be precise, thin and accurate is in. According to Scott
Zwierlein of Frontier, “roll-to-roll slot die coating has become the industry standard for extremely thin and extremely accurate coating.” Just how thin can slot die go? With a
slot die, Zwierlein explains you can achieve an attainable wet coating thickness of <2 micron. To put that in perspective, a micron, which is the abbreviated term for micrometres, is one millionth of a metre (or one thousandth of a millimetre, 0.001mm, or about 0.000039-inches. A human hair is about 75 microns across. Although this article will focus on thin, slot die can also be used to coat thick as well. And how accurate is accurate? Accuracy in the coating world is flatness. Or, in other words, how much the thickness varies from your target. The attainable transverse web accuracy with a slot die is <2 per cent.
EXTREMELY THIN As Zwierlein notes, 2 microns is the “Holy Grail of liquid coatings.” Many traditional methods exist, but only slot die can achieve this level. Why? It is the nature of the equipment design. Other methods will flood a large amount of coating, and then wipe it away. Slot die does the opposite. It applies the exact amount to the substrate. Everything the pump delivers is applied to the substrate – there is no waste.
STRIPE COATING In battery and capacitor applications, for example, stripe coating is the preferred method when you are producing a narrow strip with exposed foil along one or both edges. One requirement for good stripe coating is uniform coating thickness - proper cavity design is essential. You need proper die shim thickness for optimised die pressure; that produces the right uniformity for cross web production. It is also essential to have accurate width control and good edge quality - accurate shim
design and fabrication is important to maintain the proper alignment. A die vacuum is used to fine-tune the width and to ensure there is no saw tooth or waviness.
you cannot match the accuracy of slot die. With other coating methods the gap set for the blade, or the bar is fixed and the substrate and coating fluid pass through it. If the substrate thickness varies, the thickness will vary. “The substrate you coat on is never that flat,” he says.
THE IMPORTANT ATTRIBUTES OF SLOT DIE COATING A number of attributes need to be present
to help slot die deliver on its promise. These attributes result in significant benefits over traditional methods in terms of functionality and cost savings. 1. Precision pre-metered fluid delivery 2. Extremely flat and straight die surfaces 3. High-precision backing roll 4. Accurate and precise positioning of die to the substrate 5. Contamination-free environment
Stripe coating delivers precision for battery applications.
INDUSTRIES FOR SLOT DIE COATING Slot die is becoming increasingly necessary in a number of industries. Here are just a few applications: Micro-electronics (flat panel displays, thin circuits), batteries and capacitors (lithium-ion battery electrodes, multilayer ceramic capacitors), barrier films (food and medical packages), solar photovoltaic (solar cells require thin coatings), and medical diagnostics. Variations in thickness can lead to differing
results. The more accurate you coat the transdermal, the more accurate the dosage.
PROVE > DESIGN > BUILD Frontier is committed to helping you streamline the process of determining the right coating application for your company and your product. Contact Frontier today to learn how to improve your coating quality and production.
www.frontiercoating.com
Visit Frontier at the Battery Show Europe Other methods, such as reverse roll, knife
over roll, and comma coating, use a device to wipe away excess coating leaving just the thickness desired. In this scenario you are requiring a blade or bar to be positioned 2 microns away from a substrate. According to Zwierlein that is almost impossible.
EXTREMELY ACCURATE Accuracy is based on the amount of material you want to put down, how close you are, and how uniform you want it to be. Zwierlein explains that you might be able to achieve 2 microns with other methods, but
8 April 2018
Visit Frontier at The Battery Show Europe in Hannover, Germany, on May 15-17, 2018. Engineers will be available at Booth 165 to discuss your project requirements. Find out more about the variety of solutions Frontier
can offer. From lab scale to total manufacturing solutions, Frontier can help you develop the best equipment for your specific application. The Frontier engineering team will be available to discuss your project requirements and the capabilities of our equipment offerings, its compact, modular pilot coating system, for example. This completely self-contained coating system sets the industry standard for coating process optimisation. Available coating technologies include slot die, patch and pattern coating, gravure, direct/offset coating, mayer rod, knife-over-roll, comma coating, screen printing and extrusion.
Slot die coating is the perfect solution for products that rely on precision
www.convertermag.co.uk
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