ISO 22785-3:2026

International
Standard
ISO 22785-3
First edition
Paints and varnishes — Coatings on
2026-06
plastics and composites —
Part 3:
Constant climate and alternating
climate testing
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Characteristics of plastics substrates . 2
4.1 General .2
4.2 Thermal conductivity of the substrate .2
4.3 Specific heat capacity of the substrate .2
4.4 Sample thickness .2
4.5 Substrate deformation .2
4.6 Phase transitions .2
4.7 Substrate ageing .2
4.8 Additive migration .3
4.9 Barrier effect of the substrate .3
4.10 Thermal expansion .3
4.11 Water absorption and release .3
4.12 Adhesive strength . .3
4.13 Density .3
4.14 Elasticity .3
5 Overview on test methods . 3
5.1 General .3
5.2 Constant climate .4
5.2.1 Wet climate (hydrolysis) .4
5.2.2 Dry climate .4
5.2.3 Condensation atmosphere with constant humidity .4
5.3 Alternating climate .5
5.3.1 Condensation alternating climate .5
5.3.2 Cold/warm climate .5
5.3.3 Warm and humid/cold climate .5
5.4 Immersion in water .5
6 Evaluation . 6
6.1 General .6
6.2 Visual assessment of the surface condition .6
6.3 Assessment of gloss and colour .6
6.4 Assessment of adhesive strength.6
Bibliography . 7

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee SC 9,
General test methods for paints and varnishes.
A list of all parts in the ISO 22785 series can be found on the ISO website.
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
The ISO 22785 series explains the characteristics of plastics and the differences between plastics substrates
and metallic substrates.
This document gives an overview of the common climate test methods used in particular for coatings of
automotive exteriors and interiors. Many of the existing test methods have been developed for coatings on
metals. This document specifies the test methods that can lead to a deviating behaviour of the coating on
plastics substrates and the measures that can be taken, where appropriate. It is possible that the substrate
has an effect on the behaviour of the coating during the test. At times, it can be useful to select test conditions
which are based on standards from the plastics sector and not on standards from the coating sector, in order
to take into account the thermal conductivity of a plastics substrate which is normally lower.
The methods listed in this document refer to simple, flat test specimens, but also components. For three-
dimensional samples, different results can be obtained during the exposure; therefore, the installation
position or test position are specified in advance or taken from a sampling plan.

v
International Standard ISO 22785-3:2026(en)
Paints and varnishes — Coatings on plastics and
composites —
Part 3:
Constant climate and alternating climate testing
1 Scope
This document specifies the constant climate and alternating climate testing of coatings on plastics, plastics
composites and similar substrates, hereinafter collectively referred to as plastics.
This document shows the potential effect of plastics on the behaviour of the coating during climate testing.
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 4618, Paints and varnishes — Vocabulary
ISO 22785-1, Paints and varnishes — Coatings on plastics and composites — Part 3: General introduction
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618, ISO 22785-1 and the
following 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
constant climate
environment with constant climatic conditions
3.2
wet climate
environment with a relative humidity of usually > 90 %, non-condensing
3.3
dry climate
environment with a relative humidity of usually < 20 %
3.4
condensation atmosphere with constant humidity
environment with condensing humidity

3.5
alternating climate
cyclic succession of phases with different climatic conditions
3.6
condensation alternating climate
alternating climate (3.5) with at least one phase with condensing air humidity
3.7
immersion in water
partial or complete immersion of the sample in water
4 Characteristics of plastics substrates
4.1 General
Plastics-specific characteristics for pure plastics can be taken from Reference [33]. For recyclates or plastics
mixtures, the characteristics can deviate from the information in Reference [33].
4.2 Thermal conductivity of the su
...