Standardization is a key part of preventing costly quality-control issues on press.
By Rick Davis
Coating area and procedures
The next work area will be used for coating and drying. Of all the work areas within the screen department, it is here that you need to ensure that dust and garment lint are kept to a minimum. You need sufficient racking to allow for the drying of an adequate screen supply that you can cycle on regular basis to meet production demands. The greatest determining factors here are the number of presses you have to service, run size, and number of colors per graphic.
Screen coating varies from facility to facility—one and one, one and two, two and two—but the process has basically come down to whatever works for each respective printing facility. The most popular costing procedures are one coat on the print side of the screen and one coat on the ink side, or two coats on the print side of the screen and one coat on the ink side. The latter of these two processes is preferred by many, as the initial two coats on the print side of the screen will determine the overall stencil thickness while the remaining coat on the ink side of the screen will transfer the emulsion to the print side of the screen and encapsulate the mesh to ensure durability.
The overall total thickness of the emulsion coating will also depend on the radial edge of the coater, the speed at which the screen is coated, the pressure applied, and the viscosity of the emulsion at the time of application.
Manual vs. automated coating
From the standpoint of consistency and quality, you must also look at the option of automated coaters as opposed to the age-old manual process. Although you can produce a high-quality screen stencil with either process, you cannot surpass the advantage of consistency that an automated coater brings to the process. It is with the automated system that you ensure perfect consistency from screen to screen and run to run (Figure 1).
You can use the same work area for drying the screens prior to imaging or exposure once the screen is coated. The next area is screen imaging. You have two general processes here that are used: film, which has been the industry norm for decades, and DTS imaging (Figure 2), which has taken off in the past decade as the technology has developed.
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