What is a bleed in printing?
A bleed in the jargon of offset printing, digital printing or large format printing means that a printed sheet has ink printed right to the edge of the paper. For example, this business card has ink all the way to the edge of the sheet (a bleed):
To produce a bleed, the image needs to extend larger than the final trim size of the sheet. The image is printed on a larger sheet so that the bleed area and crop marks fit completely inside the sheet. After printing, the sheet is then trimmed down to size, cutting off the extra image and crop marks. In this example, the artwork was extended by 1/8" all around, creating a "1/8" bleed", then printed on a larger sheet:
There are two main reasons we need to do this. On a printing press, if we print right to the edge of a sheet, ink will migrate past the edges of sheet and will smudge the reverse side of the sheet. The second and perhaps the most important reason has to do with the mechanical nature of the trimming process. If the image is printed exact size on a larger sheet, and then trim the sheet to size, sheets would trim a hair high, low, left or right inconsistently through the stack of sheets. We would see random and unintended small white (unprinted) areas around the edges of the sheets. This is because mechanical tolerances of industrial paper cutters are not high enough to print exactly where the image ends, and environmental factors will randomly change the size of of sheets in the stack while they're drying prior to final trim.
So, what's that "unsafe area" in the graphic? For the same reasons that we print larger than final size, It's a good idea to keep any important design elements such as type away from the area between the blue and pink boxes, so they don't get partly trimmed off in the final trimming process.
As always it's recommended that if you're designing business cards or any printed material, consult with your priting professional before starting the design process.
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