by Dave Dennings
Screen printers the world over battle with the ubiquitous pinhole. For many years the pinhole has been responsible for increasing screen processing times and reducing the efficiency and profitability of the printing process. When screen printers estimate the price to charge the print buyer, they must factor in the cost of materials used, the cost of labor, and the time required for completing the job. Screen printers who better control these costs and can complete the job more efficiently, will be more profitable and more competitive in this market.
Printers who are continuously plagued with pinholes find they are spending more time and money to complete the job than their competitors who have taken the necessary steps to reduce, if not eliminate, pinholes in their production process.
In this report, we will take a look at the many causes of pinholes, and fisheyes, for that matter, and what steps can be taken during screen preparation to properly prevent pinholes. Let's first define pinhole and fisheye.
The SGIA Glossary of Screen Printing defines a pinhole as an imperfection in the form of tiny transparent dots that appear in printing screens or in process films after development.
The SGIA Glossary of Screen Printing further defines a fisheye as a flaw in the screen printed film of ink consisting of a generally circular defect caused by slight bubbling of the ink with resulting dispersion of the pigment within the immediate area, causing non-uniformity of color. This definition can be expanded to include a flaw in the screens stencil consisting of the same circular defect usually caused by chemical contamination, or oils on the screen.
Often times the term pinhole is used when describing, as mentioned above, an imperfection in the film or screens before the screen leaves the screen-making department.
Other times the term is used in the production department (press room) when press operators will refer to their screens "pinholing on press" when the stencil breaks down either mechanically or chemically and ink begins to leak through the stencil onto the substrate unintentionally.
This report is broken down into two sections: prepress pinholes and on press pinholes. I will identify the contributing factors that cause pinholes one at a time for each section and offer ways of overcoming them.
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