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.
The new mold is mounted in the vac-form press and we’re ready to begin. From this point forward, consistency is the prime objective. First, we must determine where on the sheet to print the image. Because of the way the sheet will sag during its heat cycle in the vac-form press, simply positioning the image in the middle of the sheet may not be adequate. Using Adobe Illustrator, we’ll create a new art file, sized to match the dimensions of the PETG sheet. Next, we create a grid with horizontal and vertical lines spaced 0.25 in. apart. The grid will cover the same area as the mold, which is about 2 in. less than the sheet size in each direction. The grid file is downloaded to the screen department, where it is used to create one stencil. The grid image is printed on four PETG sheets, with white ink for maximum visibility. We used Sericol’s 3-D series UV ink for this job because it’s designed for vacuum-forming applications. One gridded sheet is retained in our graphics/prepress department. Exact guide points used on the screen press are marked on the remaining sheets, which are then sent to the vac-form department.
At the vac-form press, the guide points are transferred from the gridded sheets to the pneumatic clamps surrounding the mold. This ensures that both machines will guide to the same three points relative to the sheet.
We then bring the mold up to operating temperature by cycling scrap material until the coolant (water) being circulated through the mold’s cooling tubes reaches its target temperature—about 170°F, depending on the substrate. We keep the water within a 5-8° range by using a temperature-controlling machine called a chiller. We also manage external influences that contribute to misaligned images, such as changes in ambient room temperature, humidity, and even stray breezes created by fans in the vicinity of the vac-form press. These factors must be noted at the beginning of the process and kept as consistent as possible throughout the production run.
The gridded sheets are vacuum formed as soon as the mold reaches operating temperature. After cooling, the formed sheets are sent back to the prepress department so the image can be properly located on the sheet. One of the sheets is sent off-site to aid in steel-rule-die fabrication.
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