Glossary / O

Off–machine coating
Coating of paper on a separate coating machine.

Off–machine creping
A method whereby paper is creped in a separate operation rather than by the paper machine–s Yankee cylinder.

Offset
Indirect printing technique with chemical properties flat printing plate. The process is characterised by the fact that there is no difference in relief between the printing and non–printing areas of the plate. Instead they differ in their physical and chemical properties, so that the printing areas are able to attract oilbased inks and repel water, whilst the non–printing area accept water and repel the oil–based inks.
The images is transferred from the inked plate to an intermediate cylinder covered with a rubber coated fabric blanket and from this to the printing substrate.
The benefit of indirect printing is that the printing plate lasts longer, since it does not come into contact with the substrate. Offset presses are rotary machines and can print on sheets or webs, in one or more colors, on just one side of the substrate or on both sides at the same time.

Offset paper
Collective term for printing papers with special properties for offset printing. For instance, the paper must not emit dust during processing and must be pick resistant. Offset paper may be woodfree or mechanical, coated (matt, glossy, embossed) or uncoated and is processed in sheets as well as in reels.

One–side coated paper
One–side coated paper. It is used in all cases where only one coated side is needed: labels, posters etc.

On–machine coating
Coating of paper on the paper machine.

Optical characteristics
Characteristics of the appearance of paper or board. Most important are colour, brightness, opacity and gloss.

Oxygen bleaching
A process in which pulp is initially treated with oxygen followed by 4–5 bleaching stages.

Ozone bleaching
Pulp can be treated with ozone at the start of the bleaching sequence to lower its lignin content. Ozone allows bleaching to high brightness without chlorine chemicals.