1、BRITISH STANDARD BS ISO 12218:1997 Graphic technology Process control Offset platemaking ICS 37.100.20BSISO12218:1997 This British Standard, having been prepared under the directionof the Sector Board forMaterials and Chemicals, waspublished under the authorityof the Standards Boardand comes into ef
2、fect on 15November1997 BSI 04-2000 ISBN 0 580 28791 2 National foreword This British Standard reproduces verbatim ISO 12218:1997 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee PAI/43, Graphic technology, which has the respo
3、nsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A l
4、ist of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “Internati
5、onal Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a Brit
6、ish Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi and ii, theISO title page,pages ii to iv, pages1 to 15 and a back cover. This standard has been updated (see copyright date) and may have had
7、amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBSISO12218:1997 BSI 04-2000 i Contents Page National foreword Inside front cover Foreword iii Text of ISO 12218 1ii blankBSISO12218:1997 ii BSI
8、04-2000 Contents Page Foreword iii Introduction 1 1 Scope 3 2 Normative references 3 3 Definitions 3 4 Requirements 7 4.1 Colour separation film quality 7 4.2 Control patches 7 4.3 Selection of the exposure 8 4.3.1 Positive-acting plates 8 4.3.2 Negative-acting plates 8 4.4 Reproduction limits 8 5 T
9、est methods 9 5.1 Tone value on an offset printing forme Reference method 9 5.2 Tone value of a half-tone control patch on a control strip 9 Annex A (normative) Determination of quality parameters of half-tone dots on a half-tone film 10 Annex B (informative) Secondary test method for positive-actin
10、g plates: Tone values on an offset printing forme Microlines 10 Annex C (informative) Secondary test method: Tone values on an offset printing forme Densitometry 12 Annex D (informative) Test method: Platemaking gradation 13 Annex E (informative) Factors which may affect tone value transfer from a h
11、alf-tone film to a printing forme 14 Annex F (informative) Bibliography 15 Figure B.1 Positive-acting plates: Example for the dependence of positive and negative microline readings on exposure 11 Figure B.2 Positive-acting plates: Example for the determination of the exposure latitude 12 Figure D.1
12、Example of a diagram showing the determination of the platemaking gradation, positive-acting plate 13 Table 1 Tone value decrease from the half-tone film to the printing forme 8 Table 2 Tone value increase from the half-tone film to the printing forme 8 Table B.1 Positive microline reading ranges 11
13、 Descriptors: Graphic technology, printing, colour printing, offset printing, preparation, offset plates, process control, specifications, tests, printing tests.BSISO12218:1997 BSI 04-2000 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national sta
14、ndards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International or
15、ganizations, 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
16、 circulated to the member bodies for voting. Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO 12218 was prepared by Technical Committee ISO/TC130, Graphic technology. Annex A forms an integral part of Internatio
17、nal Standard. Annex B to Annex F are for information only.iv blankBSISO12218:1997 BSI 04-2000 1 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
18、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 con
19、vertible plates together with negative polarity input material. 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. Alte
20、rnatively, 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 exposur
21、e step, the emulsion side of the half-tone film is brought into intimate contact with the sensitized plate coating, usually by means of a vacuum contact frame. The radiation used for the exposure step may contain both diffuse and unidirectional components. The benefit of diffuse radiation is that ar
22、tefacts like film edges of positive polarity films, scratches and dust particles are not rendered on the plate. However, care is required because diffuse radiation accentuates any artefacts associated with areas where film and plate are out of contact or where the contact is poor. During the exposur
23、e 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 ph
24、ysical phenomena result in fine detail on the plate that is somewhat larger 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 an offset printing plate normally consists of the remov
25、al of the coating in the non-printing areas. These are the exposed areas of a positive-acting plate and the unexposed areas of a negative-acting plate. The quality of the printing forme produced by the platemaking operation depends in particular on the following process parameters: exposure step, es
26、pecially vacuum conditions (including drawdown); chemical composition and temperature of the developer fluid; condition of rollers and brushes; processing speed (development time); finisher condition. After development, the colour contrast between printing and non-printing areas is usually much grea
27、ter than before. Following exposure and processing, baking or post-exposure treatment may be used prior to correction and gumming. The developed offset printing plate is thus transformed into a press-ready offset printing forme. During correction, image elements are deleted (negative correction) or
28、added (positive correction). At the gumming stage, a thin coating of a colloidal solution is applied to the image side of the plate in order to protect the surface and to prevent toning during the printing operation. Baking or post-exposure treatment is a heat treatment which increases the durabilit
29、y of the coating with regard to chemical or mechanical wear. Determination of the optimum exposure for positive-acting offset printing plates: There are three important considerations. a) The exposure should be strong enough for artefacts like film edges and dust particles to not normally show on th
30、e offset printing forme. b) The exposure should not be so strong that the transfer of fine highlight half-tone dots is impaired. c) Since the exposure also determines tone value, which is very important in process control, the exposure should be controlled such that the tone value decrease from the
31、half-tone film to the offset printing forme is constant, irrespective of the offset printing plate type and processing conditions.BSISO12218:1997 2 BSI 04-2000 For half-tone screens with screen frequencies of70cm 1or less, it has been found in practice that it is possible to meet considerations a) a
32、nd b) with a single exposure step. The exposure used is appreciably stronger than one which would result in the best possible resolution (but where artefacts would also be rendered). Consideration c) can be met in addition by observing a suitably selected microline reading. For periodic or non-perio
33、dic fine screens which contain image elements of less than254m size, conditions a) and b) cannot be met with a single exposure step. Instead, a first exposure step is carried out that yields the best possible resolution or slightly above. During the second exposure step, the subject areas are protec
34、ted by a so-called burnout mask; an extended exposure removes the artefacts. For positive-acting printing plates, it has been found that microline targets can be used to define an exposure range which ensures a reproducible tone value decrease from the half-tone film to the offset printing forme. In
35、 this range, the tone value decrease from the half-tone film to the printing forme is a linear function of the microline reading; the function depends on the platemaking resolution. For a particular plate, under given exposure and processing conditions, the graph of the positive microline reading ov
36、er the logarithm of the exposure thus characterizes the tone value dependence on exposure. The slope of the graph is a measure of the rate of tone value change with exposure change. Therefore, a steep slope indicates less exposure latitude than a less steep one. Microline targets useful for process
37、control of platemaking contain a number of subtargets with graduated linewidths ranging from a few micrometres to several tens of micrometres. As distinct from the targets used for testing the resolving power in photography, microline targets show line-to-space ratios other than 1 : 1. Usual ratios
38、are 1 : 9, 3 : 5 and 1 : 4. Within the usual exposure range the microline reading depends very slightly on the line-to-space ratio. It is important to realize that the microline reading depends on the density level between the microlines. It must not be appreciably higher than elsewhere on the contr
39、ol strip film. As an alternative to a division into subtargets of constant linewidth, a single target with microlines of continuously variable linewidth may also be used. Since there can be directional effects during the manufacture of printing plates as well as during plate processing, it is a good
40、 plan to average over readings taken at right angles or to use targets with circular microlines. It is important to note that microline readings always refer to the width of the microlines on the film, not to the (unknown) width on the printing forme. Determination of exposure negative-acting offset
41、 printing plates: There are three important considerations. 1) The exposure should be strong enough to achieve a sufficient and reliable run length. 2) The exposure should not be so strong that there is excessive tone value increase from the half-tone film to the printing forme or that extreme shado
42、w detail is lost. 3) The tone value increase from the half-tone film to the offset printing forme should be at a specified level. Since the first criterion is overriding, negative-acting offset printing plate exposures usually follow the recommendation of the plate manufacturer, which is expressed a
43、s the reading of a continuous-tone step wedge. Once the optimum exposure has been established, microline targets may be used to additionally monitor the consistency of subsequent exposures. They should not be used as the primary exposure determinant. Some users employ weaker exposures than the manuf
44、acturer recommends, in an effort to obtain a desired tone reproduction in automatic processing systems with plates that have long run-length coatings which require more aggressive processing. With some plates, the run length may be extended by post-exposure or heat treatment. In these cases, the man
45、ufacturer may recommend a lower range of allowable exposures and a post-exposure or baking treatment to extend press life. This may result in a lower tone value increase than otherwise. Apart from its use for determining the exposure of negative-acting offset printing plates, a continuous-tone step
46、wedge may also be used to assess the development process. A useful quantity in this respect is the platemaking gradation; it characterizes the reaction of the plate coating to the amount of radiation under a given processing condition. A change of the platemaking gradation indicates that the process
47、ing conditions or the coating have changed.BSISO12218:1997 BSI 04-2000 3 1 Scope This International Standard establishes unified terminology, test methods and requirements for the process control of the preparation of the offset printing forme. This International Standard applies to pre-sensitized m
48、etal plates; applies to contact exposures whether in a contact frame, step-and-repeat machine or other automated processor; does not apply to optical projection or direct writing techniques, although the principles may be applied by analogy; does not apply to non-periodic half-tone screens, although
49、 the tone value specifications may be applied by analogy. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain register
