ISO INTERNATIONAL STANDARD 12218 Firstedition 1997-08-01 Graphic technology Process control - Offset platemaking Technologie graphique - Maitrise des procedés - Confection des plaques offset ISO Reference number ISO 12218:1997(E) Copyright Intemational Organization for Standardization No reproduction or networking permited without license from IHS Not for Resale ISO 12218:1997(E) Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies (IsO member bodies). The work of preparing International Standards is normally carried out through IsO a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non- governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. ISO/TC 130, Graphic technology. Annex A forms an integral part of International Standard. Annexes B to F are for information only. @ISO1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postale 56.CH-1211 Geneve 20.Switzerland Internet [email protected] X.400 C=ch; a=400net; p=iso; o=isocs; S=central Printed in Switzerland onal Organization for Standardizatior No reproduction or networking permited without license from IHS Not for Resale @ISO ISO 12218:1997(E) Introduction During the production of an offset printing plate, a carrier material is coated with a thin radiation-sensitive film. The plate is referred to as pre. sensitized, if it has been produced by a plate manufacturer rather than at the printing site. The radiation-sensitive coating on the offset printing plate may be either positive-acting (for positive polarity films) or negative-acting (for negative polarity films). Some offset printing plates with positive-acting coatings can be used as convertible plates together with negative polarity inputmaterial. During preparation of the offset printing forme, analogue information is transferred from half-tone film to an offset printing plate by means of a contact exposure step with radiation to which the plate coating has been sensitized. Alternatively, offset printing plates may be exposed using optical projection of reflection or transmission copy or by direct writing techniques. While such alternative processes are not covered by this International Standard, many of the principles included may be applied by analogy. Before the exposure step, the emulsion side of the half-tone film is brought into intimate contact with the sensitized plate coating, usually by means of contain both diffuse and unidirectional components. The benefit of diffuse radiation is that artefacts like film edges of positive polarity films, scratches and dust particles are not rendered on the plate. However, care is required where film and plate are out of contact or where the contact is poor. During the exposure step, the optical spread function of the printing plate and the diffusive component of the radiation cause final detail on a positive acting printing plate to be reduced in width so that the image elements are somewhat smaller than the original on the film. With negative-acting plates, the same physical phenomena result in fine detail on the plate that is somewhat iarger than the original. After the exposure step but before development, the coating usually shows a colour difference between exposed and unexposed areas. The development of