Images Digital Edition DEC 2018

KB TIPS & TECHNIQUES www.images-magazine.com 80 images DECEMBER 2018 to air bubbles within the coating trough and in the mesh openings due to incomplete encapsulation of mesh fibres. This is more likely to happen on coarse mesh counts of 77 threads per cm or lower. Conversely, coating emulsions too slowly can lead to high coating thickness from excessive push-through of the emulsion. Coating regime Coating at 1+1 is done by screen printers to save money related to emulsion costs. This creates a false economy as it only creates problems with pinholes and breakdown of the emulsion on press. Increasing the number of coats to 1+2 or 2+2 improves the ink opacity on the garment and the durability of the stencil. Always follow the coating guidelines of your emulsion manufacturer. Whatever coating regime (1+2, 2+1, 2+2, etc) you choose, always start with coating on the print side and finish off from the squeegee side. This will ensure the emulsion is pushed through to the print side, where you want the emulsion build to guarantee the ink deposit and durability of the stencil. If you finish your coating by scraping off the emulsion either on the print side or the squeegee side, you will introduce air into the coating; basically, you should have chosen a different coating regime from the start, ie 1+1 or 2+1. Coating 1+1 can trap air bubbles in the mesh opening that will cause pinholes during printing. One way to avoid air bubbles being trapped in the mesh is to coat from the print side until you see a gloss appearance on the squeegee side of the mesh. This should force any bubbles in the emulsion (from the first coating on the print side) to be forced out of the mesh opening and dispersed when applying the final coats from the squeegee side. www.colenso.co.uk Coating too quickly can lead to air bubbles in the mesh It is important to remember not all emulsions expose at the same time, and all the above factors can influence the correct exposure. A step test exposure is recommended to find your optimum. Dry print side down Additional coats from the squeegee side The emulsion is applied from the print side