SIST ISO 24487:2024

INTERNATIONAL ISO
STANDARD 24487
First edition
2023-12
Graphic technology — Processless
lithographic plates — Evaluation
methods for characteristics and
performance
Technologie graphique — Plaques lithographiques sans traitement —
Méthodes d'évaluation des caractéristiques et des performances
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test procedure .2
4.1 General . 2
4.2 Test environment . 2
4.3 Plate imaging . 3
4.3.1 General . 3
4.3.2 Colour test form . 3
4.3.3 Abrasion and scratch resistance test form . 4
4.3.4 Image visibility test form . 5
4.4 Pre-dampening amount . . 6
4.5 Pre-inking amount . 6
4.6 Ink selection . 6
4.7 Substrate selection. 7
4.8 Fountain solution . 7
4.9 Press preparation and control . 7
4.9.1 Press preparation print run . 7
4.9.2 Reference printing aim values . 8
4.10 Printing method . 8
4.11 Plate exposure to light . 8
5 Assessment methods . 8
5.1 General . 8
5.2 On-press development . 9
5.2.1 Number of sheets required for on-press development . 9
5.2.2 Assessment of non-image area. 9
5.2.3 Assessment of solid area . 10
5.2.4 Assessment of intermediate tones. 11
5.3 Abrasion resistance . . . 11
5.4 Scratch resistance . 11
5.5 Resistance to toning .13
5.6 Chemical resistance .15
5.6.1 General .15
5.6.2 Rub test . 16
5.6.3 Drop test . 16
5.7 Plate performance for stop and restart . 16
5.8 Image visibility . 17
5.9 Run length . 17
6 Reporting requirements .19
Annex A (informative) Examples of measurement method and results .20
Annex B (informative) Example of evaluation results and classification .34
Annex C (informative) Examples of quality grade reporting .36
Bibliography .39
iii
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 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
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
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notice of (a) patent(s) which may be required to implement this document. However, implementers are
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constitute an endorsement.
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expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 130, Graphic technology.
This first edition of ISO 24487 cancels and replaces ISO 24487-1:2021, which has been technically
revised.
The main changes are as follows:
— the title and ISO number have been changed to remove the part number;
— the scope has been expanded to include evaluation points both specific to processless indicator and
those common to the conventional indicator:
— scratch resistance (see 5.4, A.7 and C.3);
— image visibility (see 5.8, A.8 and C.7);
— run length (see 5.9, A.9 and C.8)
— new terms have been added to Clause 3.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Processless plates represent a simple way to prepare plates in prepress. Once a plate has been imaged,
it is mounted directly on the press where the plate coating is removed on start-up of the press. This
approach eliminates the plate processor, associated chemistry, energy required to power the processor,
water, and waste from plate preparation.
Perceived benefits of processless plates include ease of use and improved speed of production compared
to traditional plate preparation systems since there is no need for a plate processor or finishing unit.
Processless plates are mounted directly on press once imaged. Since costs associated with processors
and finishing units, including developer and cleaning solution, time and labour are eliminated, printing
using processless plates is perceived as a low-cost method.
The unique characteristic of processless plates is on-press development. After the exposure process
by computer to plate (CTP) exposing equipment, the non-image area of the photosensitive layer is
physically removed along with the ink and the fountain solution of the press.
The removal procedure is as follows.
— When the press is started, fountain solution and ink are applied. The fountain solution permeates
the unexposed (non-image) area of the photosensitive layer. The unexposed photosensitive layer is
then peeled from the base material by the tack of the printing ink.
— This peeled photosensitive layer is finely dispersed into the ink which is discharged on paper from
the press in the usual way. Parts of the peeled layer are also discharged into the fountain solution.
This document specifies evaluation methods for lithographic plate characteristics, on press development
performance, usability and print image quality. These evaluation methods are primarily intended for
processless lithographic plates but some can be used for the evaluation of all classes of lithographic
plate, however, it should be noted that quality and performance may be significantly affected by the
development process and its stability.
v
INTERNATIONAL STANDARD ISO 24487:2023(E)
Graphic technology — Processless lithographic plates —
Evaluation methods for characteristics and performance
1 Scope
This document applies to processless lithographic plates and specifies evaluation methods for
lithographic plate characteristics, on-press development performance, usability and print image quality.
It specifies measurement conditions for materials and equipment and provides guidelines for the
selection of suitable processless lithographic plates by a printing organization and requirements for
comparative assessment tests.
The assessment of waterless lithographic plates is out of scope of this document.
NOTE Some of these methods can be used for the evaluation of all classes of lithographic plate.
This document specifies measurement conditions for materials and equipment and provides guidelines
for the selection of suitable processless lithographic plates by a printing organization and requirements
for comparative assessment tests.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2846-1, Graphic technology — Colour and transparency of printing ink sets for four-colour printing —
Part 1: Sheet-fed and heat-set web offset lithographic printing
ISO 12647-2, Graphic technology — Process control for the production of half-tone colour separations,
proof and production prints — Part 2: Offset lithographic processes
ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts
images
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
processless plate
plate loaded directly on to a printing press following exposure without any intermediate processing
step other than mechanical processes such as plate punching and bending
Note 1 to entry: Intermediate processing steps typically include plate development, cleaning, fixing (or
desensitization) and other treatments.
Note 2 to entry: Strictly speaking, these plates are 'processed' on press using the press fountain solution and ink.
3.2
pre-dampening amount
fountain solution amount used to wet plates prior to printing
Note 1 to entry: The pre-dampening step is part of the printing process.
3.3
pre-inking amount
ink amount applied to plates prior to printing
3.4
plate tone value
percentage area coverage for process and spot colour scales on the printing plate
3.5
printed tone value
apparent intensity of a printed single colour scale or 3-colour neutral
Note 1 to entry: Applies to density tone value, colour tone value, near-neutral CMY tone value.
Note 2 to entry: Adapted from ISO 12647-2.
4 Test procedure
4.1 General
Offset printing machines in use today differ in physical structure, fountain technology and ink delivery
systems. The test conditions in this document are designed to be practical and to show significant
differentiation between performance of different processless plate technologies.
Test conditions have been chosen to control key factors that have an impact on processless plates
performance.
Two categories of testing are anticipated by this document.
a) Individual test: testing by a printer who wishes to choose the most suitable plate for his purpose
and for this category of test, the production methods and materials used for testing should be those
used by the printer for print production.
b) Comparative test: scientific testing to allow the performance of printing plates to be compared
to one another and for this category, the testing requires the use of specified test materials and
methods which in some cases may be specified by the press or plates manufacturer.
Unless explicitly indicated, test procedures described in this document may be used for both individual
testing and comparative testing.
4.2 Test environment
When comparative testing is conducted, the following conditions shall apply. When individual testing
is conducted the temperature and humidity should be held constant and as close to these values as is
possible.
The temperature of the printing room shall be 24 °C ± 2 °C.
The relative humidity of the printing room shall be (55 ± 10) % RH.
Plates should be kept in the test environment for a minimum of four hours for single packs (12 hours
for bulk material) before imaging and subsequent testing is carried out. Plates should not be exposed to
light during this period.
4.3 Plate imaging
4.3.1 General
Printing plates shall be prepared to include the following content. Additional inked content shall be
added in such a way as to ensure approximately equal inking across the plate of between 20 % to 40 %
coverage.
When printing CMYK, all test forms shall be prepared and printed to meet the requirements of
ISO 12647-2 for solid patches. The plate tone value should be adjusted so that the printed tone value is
the same for all plates being evaluated.
Additional content necessary for process control should be added as required.
When conducting individual testing, a halftone ruling and paper type that are typically used by the
printer should be selected, and these same selections should be used when testing multiple times.
−1
When comparative testing is performed, a half-tone screen ruling of 60 cm (approximately 150 lines
per inch) should be used.
Additional strips with different screen rulings and area coverage may be added and where these
are added, details should be provided in the report. A paper conforming to the requirements for the
reference print substrate should be used and the paper used shall be identified in the test report.
4.3.2 Colour test form
A CMYK test form with a set of rectangular or square patches shall be prepared comprising: a solid
(100 %) patch in each process colour, and patches of intermediate tones from 10 % to 70 % tone value
in each process colour. A region of at least 100 mm × 150 mm of the sheet shall be left blank (the non-
image area).
Each patch should have a minimum size of 10 mm × 10 mm and patches should be spaced by a minimum
of 5 mm. Where visual assessment is required, patches should have a minimum size of 40 mm × 40 mm.
The plate image area shall have a large region of approximately half the total image size where no marks
are imaged. An example test form is shown in Figure 1.
NOTE 1 The minimum size for each patch has been specified so that the patches can be measured easily. The
minimum spacing of patches is required to allow visual assessment of toning between printed elements.
a
Preferred printing direction.
Figure 1 — Example CMYK test form
The test form should be imaged in several positions and with different orientations. When oriented in
the press direction, it shall be aligned with the preferred printing direction as indicated.
NOTE 2 Where a subset of the process inks is to be tested, not all plates need to be imaged. For example, to test
the performance with cyan ink, only the cyan plate needs to be imaged.
The plates shall be exposed as recommended by the manufacturer for optimum image sensitivity and
should be adjusted to ensure that the halftone dot area on plate corresponds to patch tone value. If
direct measurements on plate are not possible, indirect measurement via the dot% on the print should
be made.
When printing is not 4-colour (CMYK), for example monochrome printing or printing of spot inks or
varnish, a test chart comprising the set of process colours generally used in print production shall be
used.
4.3.3 Abrasion and scratch resistance test form
For abrasion resistance tests, an abrasion and scratch test form comprising seven sets of the patches
shall be imaged. This test is generally performed on the black plate, but the same monochrome image
may also be used to image the cyan, magenta or yellow plate.
For scratch tests, scratches are applied to the plate after it has been imaged.
An example of a suitable test form is shown in Figure 2. Sets of patches shall be separated sufficiently
to allow abrasion and scratch resistance testing to be performed on one set without affecting any other
set.
This test form may also be used when testing chemical resistance.
Key
1 scratch markers
a
Preferred printing direction.
b
Abrasion and scratch direction.
Figure 2 — Example abrasion and scratch resistance test form
4.3.4 Image visibility test form
When using processless plates, it is important to be able to identify the colour separation imaged
on the plate. This is usually done by marking each plate with text that uniquely identifies the colour
separation. The text imaged as part of the colour test form in Figure 1 may be used for this purpose. A
more extensive text element D is shown in Figure 3.
Where it is important to be able to see more information on the printing plate, the test form in Figure 3
should be used. This form is designed to test image contrast and resolution.
An example of a test chart that may be used to assess visibility of content is shown in Figure 3. This
chart comprises three sections labelled A, B, C and D. Sections A, B and D are used for visual assessment.
Section A comprises 20 sets of concentric square elements each with a different tone value from 100 %
(element 1) to 5 % (element 20) decreasing by 5 % at each step designed to test visual contrast.
Section B comprises 20 sets of concentric square elements each with a different stroke width from
4 points (element 1) to 0,2 points (element 20) decreasing in 0,2 points at each step designed to test
visual resolution.
Section C is not used for visual evaluation. Each patch has the same tone value as the element with the
same number in Section A and can be used when a tone value measurement is needed.
Section D comprises 11 lines of text each with a different point size from 6 to 11 points in 0,5 points
intervals designed to test readability of small text elements.
Figure 3 — Example image visibility test form
4.4 Pre-dampening amount
The pre-dampening amount should be as small as possible and shall be no greater than the recommended
value from the press vendor.
4.5 Pre-inking amount
The pre-inking amount shall be set to the recommended value from the plate manufacturer or press
vendor.
4.6 Ink selection
When individual testing is performed to determine whether the plate is suitable for a printing operation,
the inks used for testing should be the same as are typically used for production.
When comparative testing is performed, inks conforming to ISO 2846-1 shall be used.
For the evaluation of resistance to toning, a low viscosity and low tack ink with a large content of
varnish should be used.
Details of the inks used shall be reported.
NOTE Low viscosity and low tack inks show more differences when comparing processless plates.
4.7 Substrate selection
When individual testing is performed to determine whether the plate is suitable for a printing operation,
the substrates used for testing should be the same as are typically used for production.
When comparative testing is performed, paper for the appropriate ISO 12647-2 printing condition shall
be used. Where possible, an environmentally friendly paper such as recycled paper and FSC certified
paper should be used.
Details of the substrate used shall be reported.
4.8 Fountain solution
When individual testing is performed to determine whether the plate is suitable for a printing operation,
the fountain solution used for testing should be the same as are typically used for production.
When comparative testing is performed, a fountain solution recommended by the press manufacturer
shall be used. Where possible, an environmentally friendly fountain solution should be used. A list of
fountain concentrates tested by Fogra and approved by the printing press manufacturers is given in
Reference [2].
Dilution of the fountain solution shall be made as recommended by the printing press manufacturer.
The fountain solution and dilution amount used shall be reported.
4.9 Press preparation and control
4.9.1 Press preparation print run
The number of sheets required for plate development depends on the press condition when the print
run starts and can vary by more than a factor of two. To avoid this problem, two sets of identical plates
shall be prepared. The first set shall be used for a press preparation print run of at least 300 sheets
during which ink key settings are established and the second set shall be used for the test print run.
During the press preparation press run, the press settings should be established according to the press
and plate manufacturer's recommendation. The blanket shall then be washed and dried before the
plates to be tested are fitted to the press and the testing begins.
NOTE The start-up procedure according to the plate manufacturer’s and the press manufacturer’s
recommendation can be different for each press or plate.
The press shall be adjusted to achieve the printing aims within the deviation tolerances as specified in
ISO 12647-2 for the solid cyan, magenta, yellow and black process colorants and all patches are within
the variation tolerances.
Printing speed shall be the speed generally used for print production or a standard setting as
recommended by the press manufacturer. Press speed shall be reported.
Other press parameters such as fountain solution cooling temperature, ink roller cooling temperature,
blanket, water supply system, slip ratio between dampening form roller and plate cylinder should be
operated as recommended by the press manufacturer. In cases where the press is operated differently
from that recommended by the manufacturer, the differences shall be reported.
Where available, press manufacturer recommended programs for processless plates should be
used. Where no such recommendation exists, the same press condition as is used for printing using
conventional plates shall be used.
All settings and materials necessary to repeat the result of the press preparation print run shall be
reported.
4.9.2 Reference printing aim values
A set of sheets shall be selected from the end of this press preparation print run that are within the
specified tolerance and shall be measured to establish reference aim values for all coloured patches and
for the unprinted substrate.
4.10 Printing method
Using the printing procedure recommended by the printing press manufacturer or, when individual
tests are performed, by the standard printing method used by the printing operation, approximately
100 sheets should be printed after on-press development is observed by the press operator to be
complete.
NOTE Printing procedures include adjustment of ink roller and dampening roller settings, adjustment of
spacing between plate and blanket cylinder, balance between water and ink, and blanket freshening.
Where assessment of toning, chemical resistance and press stop-and-restart is performed, additional
prints shall be made as follows. Print an additional 1 000 sheets using the standard printing procedure
before stopping the press. The last 30 sheets before stopping shall be collected. The press shall be
stopped for one hour. The press shall be restarted and at least 100 additional sheets printed.
The press state during the period where the press is stopped can affect the stop-and-restart testing.
The best result can be different for each press or plate type and so where they exist, the manufacturers'
recommendations for press stop-and-restart should be used.
The last 30 sheets collected before the press is stopped are used to evaluate toning performance.
The last 30 sheets collected before the press is stopped, along with sheets 70 to 100 printed following
the restart, are used to evaluate chemical resistance and stop-and-restart performance.
4.11 Plate exposure to light
The performance of some plates is affected when exposed to light. This can happen when plates are
prepared and placed next to the press during a previous print run as is often done.
In order to test the effect of light exposure on the plates, a set of plates shall be produced and exposed
to typical pressroom lighting for a period of 1 h.
Where comparative testing is performed, the lighting condition of ISO 3664 P2 should be used.
Plates for this test should be new and stored in a dark place before the test begins.
5 Assessment methods
5.1 General
The following test methods are designed to evaluate processless plates. Measurements shall be made in
accordance with ISO 13655. ISO 3664 viewing condition P2 should be used for visual assessment.
NOTE Some of these test methods can also be used to evaluate all classes of lithographic plate.
Examples of reporting of results are shown in Annex B.
5.2 On-press development
5.2.1 Number of sheets required for on-press development
Figure 4 shows the typical relationship between the number of sheets printed and the CIELAB colour
change for each region of the plate.
NOTE The curve shapes shown in Figure 4 can vary significantly from one press to another, can depend on
the processless plates, and can depend on the start-up condition of the press.
Key
X number of sheets
Y ΔE from substrate
ab
1 colour change of solid image area
2 colour change of intermediate tones
3 colour change of non-image area
Figure 4 — Typical colour coordinates and tone values by number of sheets
The press shall be started, and the colour of regions 1, 2 and 3 shall be monitored until:
— the colour of regions 1 and 2 match the printing aim values established in 4.9.1 to within the variation
tolerances of ISO 12647-2,
— no ink is visible on the non-image area (region 3), and
— the colour of the unprinted sheet matches the reference (see 4.9.1) to within the variation tolerance
specified in ISO 12647-2.
The set of sheets printed from the time the press is started shall be numbered and the sheet number
where all conditions are met shall be identified. The number of this sheet is defined as the number of
sheets required for on-press development.
Details of how to print and measure the sheets are provided in Annex A.
5.2.2 Assessment of non-image area
Assessment of the non-image area provides an indication of the effective removal of the photosensitive
layer. The maximum density of the non-image area generated during the on-press development period
affects the toning in the printing press and the quality of the prints and provides a measure of the
effectiveness of on-press development.
Sheets shall be assessed by visual inspection using a loupe to ensure that no ink is visible on the
unprinted region. Care shall be taken to check that the edges of the printed region are sharply defined
with no residual ink beyond the edge.
The number of sheets required to reach the point where the printed matter does not have any visible
ink shall be recorded along with the maximum CIELAB76 colour difference between the print area and
the unprinted substrate colour on any of the sheets printed from the time the press is started.
When the ink spreads over the entire surface of the plate, excess ink contaminates the printing press
and can cause various quality failures. The maximum ink density in the non-image area provides a
measure of the effectiveness of on-press development.
Key
1 exposed plate
2 plate covered with fountain solution
3 plate covered with ink
4 plate with ink remaining only on halftone dots
Figure 5 — Fountain solution and ink spread
Figure 5 shows the steps in the formation of the non-image area. The exposed plate is completely
covered by fountain solution and is then covered by ink which removes the non-image region to leave
the plate ready to print. When printing ink should only remain on the image area and no ink should be
present on the non-image area.
The set of sheets from the press preparation print run (see 4.9.1) shall be measured at multiple non-
printing area positions on the sheets. The mean value of these measurements shall be recorded as the
reference paper colour and the maximum colour difference between all measurements and this mean
value shall be calculated and recorded as the expected maximum paper colour variation.
Multiple measurements of the non-printing area of selected sheets from subsequent print runs shall be
made and the mean value calculated. The maximum colour difference between all measurements of the
sheet and this mean value shall be calculated. This maximum ΔΕ colour difference should not exceed
ab
the expected paper variation by more than 0,2. Details of this procedure are given in Annex A.
NOTE Measurement variation can be as much as ΔE ±0,2.
ab
5.2.3 Assessment of solid area
The number of sheets printed before the point where the ink is evenly distributed on the sheet with no
visible mottle provides a measure of the effectiveness of on-press development.
The colour of solid areas shall be measured, and the number of sheets printed before a stable colour is
reached shall be recorded. The printing colour shall be considered stable when the variation in colour
is within the tolerance ΔE < 2.
ab
NOTE This variation tolerance is lower than that specified in ISO 12647-2.
Visual inspection of the sheets shall be performed and any non-uniformity in the solid tones shall be
noted.
Reference print samples are collected from the press preparation print run and comparison is
performed against that.
Details of the assessment of the solid patches are given in Annex A.
5.2.4 Assessment of intermediate tones
Effective and consistent printing of intermediate tones is a measure of print quality and so effective
removal of the photosensitive layer around halftone dots in the intermediate tone area provides an
effective measure of on-press development.
The tone value of each of the intermediate tone patches shall be measured and the number of sheets
printed before a stable printed tone value is reached for all intermediate tone patches shall be recorded.
Visual inspection of the sheet where stable printing density is reached shall be performed and any
nonuniformity in intermediate tones shall be recorded. Inspection of dot formation in intermediate
tones shall be performed using a loupe and any missing or malformed dots shall be noted.
Details of the assessment of intermediate tones are provided in Annex A.
5.3 Abrasion resistance
This test provides an indication of abrasion resistance of the plate surface. Abrasion resistance as
described here is a qualitative test for cases where plates are rubbed against each other or the edge
of one plate scratches another when handling the plates. This test is not for wear during the print run.
Abrasion can occur, for example, during plate feeding, sorting, shipping, and transportation of a stack
of plates from a plate making site to a printing site. Plate abrasion reduces the print image quality.
NOTE 1 This test can be used for the evaluation of all classes of lithographic plate.
This document specifies a rub test using a commercially available nylon nonwoven fabric to reproduce
the shape and extent of abrasion generated in practical situations. A nonwoven fabric, similar to that
1)
used for the surface of the 3M™ Scotch-Brite™ General Purpose Scuff Sponge 7441 , should be used.
The rub test is generally performed using the black printing plate after the abrasion resistance test
form has been imaged.
The exposed plate is rubbed with the nylon nonwoven fabric in the direction shown in Figure 2. The
size of the nylon nonwoven fabric should be approximately 30 mm × 30 mm. A weight is placed on a
sponge covered by the nylon fabric to ensure a pressure on the plate of 0,1 kPa and the surface of the
plate is rubbed once in one direction over one set of black patches. The test shall be repeated for each
of the black patches increasing the pressure by 0,1 kPa each time so that the last set of patches has a
pressure of 0,7 kPa applied.
NOTE 2 kilopascal (kPa) = 101,97 kg force per metre squared kgf/m .
Following rubbing of the plate, a visual inspection of the plate shall be performed and any damage
recorded. The plate shall be used for a print run until on-press development is complete. Following this
print run, the printed black patches in the region of the plate area rubbed shall be compared with the
printed black patches that have not been rubbed and any differences noted.
5.4 Scratch resistance
This test provides an indication of the scratch resistance of a plate. The test differs from the abrasion
resistance test in the form of damage that is generated: the scratch resistance test evaluates sharp
tip damage caused by plate corners, clamp edges or any other sharp object present in the printing
1) 3M™ Scotch-Brite™ General Purpose Scuff Sponge 7441 is an example of a suitable product available
commercially. This information is given for the convenience of users of this document and does not constitute an
endorsement by ISO of this product.
environment. Plate scratches disturb the final print either by accepting ink in the non-image area or by
altering the way in which ink is applied to the image area introducing image artefacts.
NOTE This test can be used for the evaluation of all classes of lithographic plate.
A straight scratch test with constant load is used. Multiple scratches are made, and the load is reduced
for each scratch. A schematic representation of the test is shown in Figure 6.
Key
1 sample
2 stylus
3 scratch track
a
Movement of sample.
b
Load.
Figure 6 — Example of scratch resistance apparatus
In order to test the scratch resistance of a plate, the plate is scratched following imaging and before
printing. A chart similar to that shown in Figure 2 may be used. A set of scratch tracks are made to the
region where the chart has been imaged using the scratch markers as reference points. The scratch
tracks should cover the entire chart height.
The scratch tracks are applied as follows. The plate is fixed to the top of a movable table. A stylus with
a sharp tip is placed on top of the plate at a 90° angle. A ruby, sapphire, or diamond stylus with the
following tip radii should be used for these tests. Tests with a superfine and coarse stylus shall be
conducted and when possible, a test with the fine stylus should be conducted. The rate movement of the
scratch table should be 20 mm/s ± 5 mm/s.
— superfine stylus radius: 0,05 mm ± 0,005 mm,
— fine stylus radius: 0,2 mm ± 0,05 mm,
— coarse stylus radius: 1,5 mm ± 0,05 mm.
The force applied to the stylus shall be constant as each scratch is made and shall be reduced between
scratches. The starting weight for each test and weight reduction (decrement) between tests are shown
in Table 1. If necessary, it should start with a larger weight or reduce the weight loss between tests. The
weight applied to the stylus is reduced until the scratch is not visible on the plate. Additional scratches
with further reduction in the weight should be made since in some cases the scratch may be visible on
the print even when not easily visible on the plate.
Table 1 — Scratch tests conditions
Test Stylus radius Starting weight Weight decrement
(mm) N (gf) N (gf)
superfine 0,05 0,490 (50) 0,049 (5)
fine 0,2 1,961 (200) 0,196 (20)
coarse 1,5 8,825 (900) 0,981 (100)
Each new scratch is made parallel to the previous scratch with a different force applied. The plate
should be moved by at least 5 mm to the side each time and a maximum of 3 scratches should be applied
to each set of patches. The force applied and the radius of the stylus tip should be recorded for each
scratch.
Following the application of scratches to the plate the plate shall be used for a print run until on-press
development is complete and the prints from that print run assessed.
For each stylus used, all visible scratches are identified and the scratch in this set that was made with
the lowest load is identified and the load used to generate this scratch recorded as the minimum load to
generate a scratc
...