Recycled Paper – Printability
Recycled Paper – Printability – 20th January 2010
Given the enormous variation in the paper types that include fibre, and the different uses to which they are put, it is impossible to suggest guidelines for printing which will apply to every paper. In practice, however, the structural changes that cellulose fibres undergo cause some broadly similar changes to physical properties and thus to appearance and printability. Most papers containing a high proportion of recycled fibre have a significantly greater bulk and porosity than similar stocks made from virgin fibre.
Absorbency
Absorbency consistently undergoes substantial change. The relatively low moisture content of most recycled stocks makes them prone to absorption of moisture from the air, and their reduced density gives them a larger volume of air spaces that exert capillary suction on both ink and moisture.
The ink absorbency affects the gloss, the drying characteristics (high absorbency assists drying but also demands high ink weights, which can lead to set-off) and dot gain. As with most papers, smoothness and rigidity fall as bulk increases. Litho and flexo can compensate for surface and roughness to a degree, but lack of rigidity can cause problems with feed and delivery on sheet-fed presses.
Brightness
Brightness is reduced in proportion to the amount of contaminants present, including ink particles and lignin from any mechanical fibre present. Surface strength is reduced owing to the poor bonds between fibres and as a result recycled stocks are prone to linting and picking. Contraries can be present in large numbers in some stocks.
Whiteness is often poor, especially on stocks made from post- consumer waste. It also tends to be inconsistent even on some of the higher grades as the papermaker is unable to control adequately the type and proportion of discolouring contaminants.
Stability
Dimensional stability, as one would expect from low moisture content and high absorbency can be very poor. Since the actual expansion of the sheet takes time, its effect is minimised when printing wet-on-wet on a multi-colour press. On the worst sheets, expansion is not confined to the cross-grain direction and serious register problems can result.
Opacity tends to be higher on recycled stocks when comparing sheets of a similar substance and in combination with the higher bulk makes recycled papers highly suitable for certain applications such as book printing. Interestingly, mechanical fibre suffers less degradation than chemical fibre. When used for newsprint, the maintenance of fibre properties and the inclusion of some wood free fibre from periodical and magazine waste actually results in improvements to smoothness, strength and density, and printers find that drying characteristics are improved.
Peter Harrison is Joint Managing Director of The Printing House Ltd,
and Print Buying Direct of Crewe, Cheshire, UK.
Print Buying Direct are UK market Leaders in Leaflet Printing | Brochure Printing.
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For more information on printing and graphic design please see some of our recent blog articles;
- Recycled paper – Availability
- Recycled paper- uses
- Paper Recycling legislation as it concerns the print industry
- Printing and Recycling- definitions and legislation
- Print and paper industry – Other emissions to water
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January 21st, 2010 at 9:23 am
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