Helping to improve efficiency of conventional print by using preferred plate sizes
ISO 12635 Graphic technology — Plates for offset printing — Dimensions
Article by W Craig Revie and David W Penfold, ISO TC130 UK experts
For metal lithographic printing plates to be used in computer-to-plate (CtP) applications, not only is it necessary to specify the width, length and thickness of the plates, but also flatness, edge straightness and burr requirements. ISO 12635 specifies all these parameters as they apply to unprocessed plates.
This standard has now been revised and includes a set of preferred plate sizes that can be used by printers to guide their selection of conventional printing plates. This article explains some of the rationale behind this revision and shows how this standard can be used not only to improve the efficiency of conventional print but also to reduce the environmental impact of a large number of different sizes.
On 18 April 2018 a group of experts met at DIN's offices in Berlin and discussed ways to streamline the supply chain for both conventional print and CtP applications. The group noted the very large numbers of plate sizes and identified this as one area that could be improved.
The project work was done by an ad hoc group of experts representing manufacturers of both plates and printing presses.
In 2018 over 2000 different sizes of plates were in use. Some of these plate sizes differed from others by less than 1 mm in each dimension. The preferred plate size list in the revised ISO 12635 has just over 200 sizes.
In recent years, conventional printing has been squeezed on two fronts: print runs are becoming shorter for most kinds of printed matter and the quality of digital printing has been steadily improving.
It is, however, recognised that it will not be possible to use these preferred plate sizes in every print run and that there will still be a need for other sizes. For this reason, it remains possible to order sizes that are not on the list of preferred plate sizes.
How is the standard expected to be used?
ISO 12635 includes an Excel spreadsheet with the preferred plate sizes grouped in size intervals; this can be used directly when plate sizes are chosen. It is anticipated that the information from this spreadsheet will also be provided by plate manufacturers on their web sites. Figure 1 shows a part of this spreadsheet. The top image shows the sizes grouped, while the lower one shows them ordered. How these sizes were determined is explained below.
Figure 1: Excel spreadsheet for preferred plate sizes
What problems does it solve?
Preferred plate sizes have been introduced with two objectives:
• to reduce the environmental impact; and
• to improve the competitiveness of conventional offset printing systems relative to that of digital printing.
The manufacture of printing plates involves cutting plates to size from a roll of aluminium. Where many different plate sizes must be cut from these rolls (which have a fixed width), there is a high percentage of waste aluminium, which can have significant environmental impact.
Furthermore, the use of large numbers of plate sizes has a significant impact on the conventional print supply chain, affecting both inventory management and storage of the plates. Reducing the number of sizes should reduce the costs associated with these aspects and so improve the overall cost-effectiveness of conventional print.
Finally, the manufacture, distribution, storage and use of large numbers of different plate sizes is inherently inefficient and wasteful. Using preferred plate sizes is one way to start to address these problems and keep conventional print competitive.
How were the preferred plate sizes selected?
The preferred sizes were identified by plate manufacturers and press manufacturers from an ad hoc group formed of experts in ISO TC130 Working Group 4. The goal was to ensure that commonly used plate sizes and plate sizes recommended by press manufacturers were included.
Figure 2 shows graphically the current situation. Each circle represents a plate size interval of 10 mm in each direction and the colour and density indicate the number of plate sizes currently supplied within this range. Thus, a green circle indicates that only one size is supplied within this interval, yellow that between two and six sizes are supplied and red more than six (with the red getting darker the more sizes are supplied). So, the enlarged example shown and circled in green on the right-hand side is for the interval 520–530 mm by 650–660 mm and the numbers within the circle show the number of sizes supplied by three different manufacturers within this range.
Figure 2: Identifying the hot spots
For each of the hot spots identified in Figure 2, clusters of plate sizes that vary by a small difference can be seen and some possible groupings of sizes is shown schematically in Figure 3. The group agreed that if a suitable size were selected in each cluster, for many applications it would be possible to use this in place of the other sizes in the cluster. These sizes are the preferred plate sizes.
Figure 3: Identification of clusters
The following rules were used to select the most useful set of sizes within each format interval using the obvious clustering as a guide.
Rule1: Format size was identified as a preferred plate size by at least one press manufacturer and at least one plate manufacturer from the ad hoc group,
Rule2: Format size was identified as a preferred plate size by at least two plate manufacturers or by at least two press manufacturers in the ad hoc group,
Rule3: Where a preferred plate size from a press manufacturer did not exactly match a preferred plate size from a plate manufacturer but there was a closely matching size (within √2 mm), the size from a press manufacturer was selected as the preferred size,
Rule4: Where the preferred plate sizes from the plate manufacturers were close to each other or sizes from press manufacturers are close to each other the largest size was selected.
This selected preferred plate size was also applied to sizes within √2 mm.
Where no manufacturer or only one manufacturer (press or plates) selected a preferred plate size in an interval this is indicated as ‘no preferred plate sizes for this interval’.
What if your work requires a plate size that is not a preferred plate size?
These sizes are intentionally called 'preferred' plate sizes and are recommended by ISO 12635, but where these sizes cannot be used, other sizes can be selected as long as they conform to the additional requirements of ISO 12635 for sheet presses (width and height multiples of 5 mm) and web presses (width multiple of 5 mm, height multiple of 2 mm). It is likely that plate manufacturers will continue to supply plate sizes for which there is a demand.
What about plates with different thickness (gauge) or orientation?
The preferred plate sizes apply to all plate thicknesses and the sizes are listed with the shorter dimension first.
Traditionally, plates have been cut so that the grain of the plate material is oriented around the plate cylinder. With advances in plate production technology, consideration of the grain orientation is usually no longer necessary.
Will the preferred sizes apply to both sheet-fed and web presses?
Preferred sizes apply to both types of press and the preferred sizes list does not distinguish between sizes for sheet-fed presses and sizes for web presses.
No reason to treat these separately has been identified but if necessary, this aspect will be considered in the next revision.
Will it be necessary to modify presses or plate processing equipment to use the preferred sizes?
For all cases considered when making the revision, sizes can be selected from the preferred sizes list that will not need modification of the press or plate processing equipment.
No specific case where a modification is required has been identified but in case of doubt, refer to the user manual to determine whether modification is necessary and if so, how to make the adjustment. Contact the equipment manufacturer if necessary.
It remains possible to order sizes that are not on the list of preferred plate sizes.
Will the preferred plate sizes have any effect on the sizes of paper to be used?
Paper sizes matching the preferred plate size should be used or alternatively a preferred size should be chosen that can be used with the size of the paper you wish to use. There is a preferred plate size for use with all standard sizes of paper.
Cutting services are able to respond to orders of many variations for both sheet and roll media and preferred plate sizes should be referred to when considering the use of non-standard paper sizes.
What if a press will not take a preferred size of plate?
As part of the process of selecting preferred plate sizes the ad hoc group of experts considered press sizes currently in use. For most existing presses it is possible to use plate sizes from the preferred plate size list. There may still be some special cases where other plate sizes are required and for this reason, we have not made preferred plate sizes mandatory. Over time the number of these special cases should be reduced.
Designers of new presses and those involved in their marketing and design are encouraged to refer to the preferred plate sizes list to reduce the number of size variations. This may reduce marketing, design and other cost related to plate size.
Will this save (or cost) printers money and/or increase (or decrease) their competitiveness?
Members of the ad hoc group of experts believe that this approach helps to save costs and improve competitiveness throughout the print supply chain including print production. Specific benefits for printers include the need to store and manage fewer plate sizes and the ability to use the same plate size for multiple presses.
There may also be savings as the cost-per-plate reduces when larger numbers of plates of the same size are ordered.
ISO 12635 endorsements from industry leaders
Environmental protection has always been of great importance to HEIDELBERG. Standardizing plate sizes can help to improve the eco-balance of offset printing.
Nikolaus Pfeiffer, Senior Project Engineer, Heidelberg
The ISO12635 revision, has a new annex with recommended dimensions of preferred plate sizes. This annex addresses the problem that in some cases plate dimensions are slightly different for each printing machine even where such differences are not needed. We hope that specifying preferred plate sizes will result in improved efficiency for traditional printing.
Masaaki Matsuo, Japanese Committee for Printing Industry Standardization
Many plate sizes are used by one single printer in the world. Such situations, often historically grown by for instance conversions from the metric to the imperial system, where sizes then only differ by 1 mm, will now be avoided by the introduction of the new standard.
Guy Desmet, Head of Marketing - Business Division Offset Solutions, Agfa
This revision of ISO 12635 (Plate sizes) is a great step towards improving efficiency in our industry and helping to secure our strong partnership with our valued customers in this challenging environment.
Sven Freyer, WW Director Plate & Chemical Operation - TRADITIONAL PRINT, Kodak Graphic Communications GmbH
As the demand for offset printing declines, the entire printing industry needs to be more efficient. We believe that the standardization of plate sizes will lead to inventory reductions in the supply chains of plate makers, press makers, and printing companies.
Shuichiro Yamada, Senior Manager, Graphic Systems Business Div. FUJIFILM Corporation