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1、BRITISH STANDARD BS ISO 12218:1997 Graphic technology Process control Offset platemaking ICS 37.100.20 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12218:1997 This British Standard, having been prepared under the direction of the S
2、ector Board for Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 November 1997 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
3、participation in its preparation was entrusted to Technical Committee PAI/43, Graphic technology, which has the responsibility 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
4、the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European public
5、ations referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International 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 provi
6、sions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the ISO title pa
7、ge, pages ii to iv, pages 1 to 15 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffield
8、un sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12218:1997 BSI 04-2000i Contents Page National forewordInside front cover Forewordiii Text of ISO 122181 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BS
9、I ii blank Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12218:1997 ii BSI 04-2000 Contents Page Forewordiii Introduction1 1S
10、cope3 2Normative references3 3Definitions3 4Requirements7 4.1Colour separation film quality7 4.2Control patches7 4.3Selection of the exposure8 4.3.1Positive-acting plates8 4.3.2Negative-acting plates8 4.4Reproduction limits8 5Test methods9 5.1Tone value on an offset printing forme Reference method9
11、5.2Tone value of a half-tone control patch on a control strip9 Annex A (normative) Determination of quality parameters of half-tone dots on a half-tone film10 Annex B (informative) Secondary test method for positive-acting plates: Tone values on an offset printing forme Microlines10 Annex C (informa
12、tive) Secondary test method: Tone values on an offset printing forme Densitometry12 Annex D (informative) Test method: Platemaking gradation13 Annex E (informative) Factors which may affect tone value transfer from a half-tone film to a printing forme14 Annex F (informative) Bibliography15 Figure B.
13、1 Positive-acting plates: Example for the dependence of positive and negative microline readings on exposure11 Figure B.2 Positive-acting plates: Example for the determination of the exposure latitude12 Figure D.1 Example of a diagram showing the determination of the platemaking gradation, positive-
14、acting plate13 Table 1 Tone value decrease from the half-tone film to the printing forme8 Table 2 Tone value increase from the half-tone film to the printing forme8 Table B.1 Positive microline reading ranges11 Descriptors: Graphic technology, printing, colour printing, offset printing, preparation,
15、 offset plates, process control, specifications, tests, printing tests. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12218:1997 BSI 04-2000iii Foreword ISO (the International Organization for Standardization) is a worldwide federat
16、ion of national standards 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 committe
17、e. 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 techn
18、ical 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. International Standard ISO 12218 was prepared by Technical Committee ISO/TC 130, Graphic technology. Annex A forms an integ
19、ral part of International Standard. Annex B to Annex F are for information only. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c)
20、BSI BS ISO 12218:1997 BSI 04-20001 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 radi
21、ation-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 input materia
22、l. 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 optica
23、l 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 in
24、to 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 artefacts like film edges of positive polarity films, scratches
25、 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 exposure step, the optical spread function of the printing plate and
26、 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 s
27、omewhat 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 removal of the coating in the non-printing areas. These are the ex
28、posed 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, especially vacuum conditions (including drawdown); chemical com
29、position 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 greater than before. Following exposure and processing, baking or
30、 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 added (positive correction). At the gumming stage, a thin coa
31、ting 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 durability of the coating with regard to chemical or mechanical wear.
32、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 the offset printing forme. b) The exposure should not be so str
33、ong 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 half-tone film to the offset printing forme is constant, irre
34、spective of the offset printing plate type and processing conditions. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12218:1997 2 BSI 04-2000 For half-tone screens with screen frequencies of 70 cm1 or less, it has been found in pract
35、ice that it is possible to meet considerations a) and 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 se
36、lected microline reading. For periodic or non-periodic fine screens which contain image elements of less than 25 4m 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 t
37、he second exposure step, the subject areas are protected 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 fro
38、m the half-tone film to the offset printing forme. In 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 condi
39、tions, the graph of the positive microline reading over 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
40、less steep one. Microline targets useful for process 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
41、 line-to-space ratios other than 1 : 1. Usual ratios 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
42、not be appreciably higher than elsewhere on the control 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 pl
43、ates as well as during plate processing, it is a good 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 fo
44、rme. Determination of exposure negative-acting offset 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-
45、tone film to the printing forme or that extreme shadow 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 recommend
46、ation of the plate manufacturer, which is expressed as 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 determina
47、nt. Some users employ weaker exposures than the manufacturer 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 pos
48、t-exposure or heat treatment. In these cases, the manufacturer 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-a
49、cting offset printing plates, a continuous-tone step 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 processing conditions or the coating have changed. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:54:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12218:1997 BSI 04-20003 1 Scope This
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