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Technical Bulletin TRM/95

The offset blanket is the "heart" of the press because it must quickly and efficiently mirror or transfer the image from the plate to the printed sheet. For the blanket to do this faithfully it must be of good quality and maintained properly.

Types of Blankets

Although there are many different blanket constructions, there are basically two types of offset blankets, a non-compressible or hard blanket and a compressible blanket.

A hard blanket usually has 3 cloth layers and a thick rubber top coat. This type is used for general printing and when smooth solids are required.

A compressible blanket usually has 3 cloth layers, a layer of cork or other cellular material, and a thin rubber top coat. These blankets compress and release, therefore printing better halftones. They are also more resistant to blanket smashes.

Adjusting Blanket Tension
When installing a new blanket, don't take all the stretch out with the first tightening. Draw it up snug, then run 40 or 50 impressions and tighten again. Repeat this procedure 2 or 3 times until the blanket is properly tensioned. Do not overtighten.

Breaking in a New Blanket
To break in a new blanket, scrub the surface with pumice, blanket wash, and water. Wet the surface with water, sprinkle it with pumice and use a clean, soft cloth dampened with blanket wash to scrub the surface until you attain a smooth satin finish. Then remove the pumice with water and wash the blanket again with blanket wash.

Restoring the Blanket Longer blanket life can be achieved by taking the blanket off the press before it is completely worn out. First, wash the blanket with blanket wash and water. Then soak it in room temperature water for a few days. This procedure rests the blanket and removes ink, solvents, and gum. When a used blanket is put back on the press, reverse its position.

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