Shear can be damaging to materials if you’re moving plates too fast for the thickness coating. If they’re moving fast but are far apart, it’s also a high shear. If they’re moving slow but are closing together, it’s considered high shear. Shear level is based on speed and on distance between the plates. If you take a plate with wet glue on it sandwich it with another plate then slide one plate but keep the other steady - that’s shearing. The amount of shearing force that’s put onto the fluid when its being coated. For example, the viscosity of water is 1 cps, while motor oil is 200 to 500 cps. The more viscous the material, the less runny it will be. Fluid viscosity is measured in centipoises (cps). This is a measure of the thickness of the material. We’ve already touched on the delivery method above. In the chart below, there are several key terms you’ll need to understand. Now let’s compare the different methodologies. Comparison chart: Choosing what’s right for you The volume of fluid in the engraved patterns is transferred to the substrate ensuring the precise amount of coating is applied.Ĭheck out our post for more on slot die coating. Excess material is removed with a doctor blade. With gravure, the coating fluid is delivered onto a roller with patterns engraved into the face of the roll. With slot die coating, the coating fluid is precisely delivered to the slot die head, then applied directly to the substrate. Volumetric metering allows for the delivery of an exact volume of material to the substrate, which gives you the ability to control the thickness. The knife meters the coating to the required specs.Ī roller applies the coating fluid to the substrate, and then a Meyer bar meters out the correct amount. With comma roll coating, the coating solution is either dispensed directly to the substrate and metered via the comma roll or the coating solution is metered by the comma roll onto an applicator roll then applied to the substrate.Ĭoating fluid is dispensed to the substrate, which then passes through a knife and roller. Its unique feature is the two reverse running nips: An application roller runs in one direction, the support roller in the other.Ĭoating is applied in excess to the surface of the application roller, and the coating is then regulated at the metering nip. Reverse roll coating is considered a roll to roll coating methodology for wet coatings. The following coating methods are used with mechanical metering: Reverse Roll Mechanical metering requires a flooded surface and a mechanical device to wipe away excess and set the thickness of coating. Delivery methodsĪs Scott mentioned in the video, there are essentially two methods of delivering web coating, and within those delivery methods are the coating methods themselves. In this video, Scott Zwierlein of Frontier (a Delta ModTech company) provides us with an overview.īefore we get to the comparison chart, let’s establish some coating definitions. For example, integrate a coater with a drying station at the beginning of the point of the process, and then additional converting stations for die cutting, laser cutting, lamination and/or pouching at the end. Multiple converting functions can take place within an integrated system. Then at the other end of the machine, the material rewind. In the machine below, you see the substrate unwind, solution delivery, coating applicator and drying/curing oven. It’s a complicated and delicate balance of fluid mechanics and interfacial phenomena.Įach web coating machine will have the same basic features: In the converting process, web coating replaces a boundary layer gas at a solid surface with a layer of liquid, then solidifies the liquid layer by drying or curing. If you’re new to the web coating process, let’s start out with an overview of how it works. To simplify the process, we’ve created both an overview of web coating and a coating method comparison chart. As web coating technologies have become more advanced, choosing the right methodology requires more sophisticated analysis.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |