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An In-Depth Look at Distortion Printing

(November 2009) posted on Thu Oct 22, 2009

Some of the most impactful display graphics owe much of their appeal to the painstaking process of distortion printing. This article uses an actual job to describe the demanding workflow.

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By Andy Wood, Rick Turner

Take a walk through any large grocery store, mega-mart or shopping mall, and you are likely to see examples of printed and formed plastic used as key components in P-O-P displays and other types of product merchandising. Distortion forming is the name of the process used to create these displays, and the P-O-P industry has relied on it for decades. Liquor sales, sporting goods, fast-food, video games, and even Hollywood blockbusters—all have benefitted from the use of distortion forming. 

Distortion forming is the process of printing an image onto a sheet of plastic and strategically vacuum-forming the sheet on a mold so that specific areas of the printed image appear in corresponding areas of the resulting three-dimensional part. Computer software has made the process quicker and more repeatable, but overall manufacturing techniques have changed little over the years. To understand how the process works, we need to start in the middle. Let’s begin with a basic overview of vacuum forming.

Vacuum forming
Joliet Pattern, Inc. produces distortion-formed parts via screen printing and cut-sheet vacuum forming. In this method, individual pre-printed sheets (as opposed to roll stock), are delivered to the vacuum-form press. 

During the vacuum-forming process, a thermoplastic sheet is clamped tightly in a frame and heated until it becomes soft and pliable. At this point, known as the glass transition temperature (Tg), the sheet actually begins to sag (Figure 1). The sagging sheet is brought in contact with the mold, which contains minute holes (vac-holes) drilled through its outer surface, to a cavity beneath the surface. Vacuum is applied to the cavity, which, via the vac-holes, evacuates air trapped between the mold and the pliable sheet coming in contact with its surface. Surrounding air pressure forces the compliant sheet to conform to the mold’s every detail (Figure 2). After forming on the mold, the sheet is left in place to cool. Coolant, running through copper tubes embedded in the mold, carries heat away from the sheet, accelerating its cooling time. As the sheet cools, it re-hardens and retains the shape imparted to it by the mold. The sheet is pulled off of the tool and removed from the frame, completing the forming cycle. 

