ISO 18935:2018

INTERNATIONAL ISO
STANDARD 18935
Third edition
2018-09
Imaging materials — Colour images —
Determination of water resistance of
printed colour images
Matériaux pour l'image — Images en couleurs sur impressions en
papier — Détermination de la résistance interne de la couleur à l'eau
Reference number
©
ISO 2018
© ISO 2018
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Published in Switzerland
ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Categories of water resistance . 1
4.1 General . 1
4.2 Water resistant . 1
4.3 Moderately water resistant . 1
4.4 Not water resistant . 2
5 Water resistance estimating procedures . 2
5.1 General considerations . 2
5.2 Control sample . 2
6 Test methods . 2
6.1 General . 2
6.2 Method 1 — Standing water evaporation . 3
6.3 Method 2 — Standing water plus wiping effects . 3
6.4 Method 3 — Water soak . 3
6.5 Method 4 — Edge immersion . 3
7 Test pattern preparation . 4
7.1 General considerations . 4
7.2 Example test patterns . 5
8 Test report . 5
Annex A (informative) Determination of resistance to other liquids. 7
Bibliography . 8
Foreword
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This document was prepared by Technical Committee ISO/TC 42, Photography.
This third edition cancels and replaces the second edition (ISO 18935:2016), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— changes in Clauses 6 and 8 and in Annex A.
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iv © ISO 2018 – All rights reserved

Introduction
Water resistance is not an important consideration in the normal storage of colour prints. However, in
a disaster situation, such as floods, earthquakes or water main breaks, this property can be of critical
importance if the print is to be salvaged. A wide variety of materials are used for digital colour prints
and the colorants used in some digital prints are water soluble. The degree of their water resistance
varies depending upon the colorants used and if the print has a water-resistant overcoat. In addition,
the paper or other substrate may be of equal importance. The same colorants may exhibit very good
water resistance on one substrate but can be completely washed off from a different substrate. Even
print systems that use water-insoluble colorants may be damaged by water exposure if the substrate
is not also water resistant. This document provides a standardized method to evaluate the qualitative
water resistance of colour prints.
INTERNATIONAL STANDARD ISO 18935:2018(E)
Imaging materials — Colour images — Determination of
water resistance of printed colour images
1 Scope
This document specifies tests to determine the relative water resistance of printed colour images. This
document is applicable to both digital and analogue prints.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
ambient conditions
environmental conditions of (23 ± 1) °C and (50 ± 5) % RH
3.2
mordant
substance that combines with a dye, used to fix it in a material
4 Categories of water resistance
4.1 General
The water resistance of a print is categorized into one of three categories, i.e. water resistant,
moderately water resistant and not water resistant as defined in 4.2 to 4.4.
4.2 Water resistant
Water-resistant print is print that is not noticeably affected by exposure to liquid water.
NOTE No significant degradation of the colorant (bleeding, smearing, hue change), of the support (curl,
cockle, delamination) or of the image surface (gloss changes, water rings, etc.) is found.
4.3 Moderately water resistant
A moderately water-resistant print is a print that exhibits some change or damage by water but is still
considered usable for its intended application.
NOTE The damage can manifest itself as slight media curl, partial delamination along an edge, or ring-like
watermarks due to gloss changes or a minor amount of colorant migration. This damage can be mitigated by the
rapid removal of the water (careful blotting, shaking off the water, etc.).
4.4 Not water resistant
A print that is not water-resistant is a print that is easily damaged by contact with water, even when
incidental (e.g. a water mist) and is considered unsuitable for applications involving contact with water.
NOTE Such damage can manifest itself as appreciable curl, delamination of the image layer, colorant bleed
into non-imaged areas or from colour to colour, or image degradation (hue and gloss changes, surface marks,
etc.). It is strongly advisable to users of these materials to prevent water contact.
5 Water resistance estimating procedures
5.1 General considerations
Water resistance is the ability of a print to resist water damage which may manifest itself in a number
of ways, such as migration of colorants; changes in the size and/or optical density of image elements;
degradation of the image layer, as well as cockle, curl or loss of gloss. The water resistance of prints
made by current methods varies considerably. For example, some ink-jet prints sustain no observable
damage when the surface is rubbed immediately after water has been poured over the image. While
others that do not show any water damage after soaking for hours, lose a portion of their image layer if
it is wiped off before drying.
For dye-based inkjet, water resistance of many systems is dependent on three interdependent variables:
[1]
ink absorption, coating solubility, and effectiveness of mordant . For other systems where the ink
is not absorbed into the substrate, water resistance is dependent on adhesion of the colorant to the
substrate. In both cases, water-resistant laminates will improve water resistance.
Extensive tests have shown that full characterization of water resistance requires several different
methods. Many attempts were made to quantify the test data generated by these methods in
interlaboratory comparison, but none were successful. It is likely that within a given laboratory, the tests
described in this document are sufficiently reproducible to yield statistically reliable data. However,
this is not enough to adopt fixed evaluation criteria. For these reasons, qualitative analysis of the test
results is prescribed. This entails grouping of the results obtained from different print materials into
water-resistant (no change) or not water-resistant categories. An intermediate level of moderate water
resistance is also recognized, although its boundaries cannot be determined exactly.
This document requires the use of deionized or distilled water for all of the tests. The pH of this water is
not controlled (unless it is certified, which will be at pH 7) but pH will have little effect on the tests. This
is because any water-soluble components in the media coating will dissolve into the water and rapidly
change the pH. The final value of this will depend on the media used.
5.2 Control sample
The evaluation of test results based on qualitative criteria for water resistance (as defined in Clause 4)
requires that untreated control specimens be used for com
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