ISO 22785-1:2026

International
Standard
ISO 22785-1
First edition
Paints and varnishes — Coatings on
2026-08
plastics and composites —
Part 1:
General introduction
Peintures et vernis — Revêtements sur plastiques et
composites —
Partie 1: Introduction générale
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Plastics substrates . 3
5 Function of coatings on plastics substrates . 3
6 Characteristics of plastics substrates . 3
6.1 General .3
6.2 Thermal conductivity of the substrate .4
6.3 Specific heat capacity of the substrate .4
6.4 Transparency of the substrate .4
6.5 Sample thickness .4
6.6 Substrate deformation .4
6.7 Phase transitions .4
6.8 Substrate ageing .4
6.9 Additive migration .5
6.10 Barrier effect of the substrate .5
6.11 Thermal expansion .5
6.12 Volume changes due to water absorption and release .5
6.13 Adhesive strength . .5
6.14 Density .5
6.15 Elasticity .5
6.16 Electrical conductivity and magnetic properties .5
6.17 Other substrate characteristics .6
7 Conditioning after coating . 6
8 Effect of the differences to metallic substrates . 6
Annex A (informative) Overview of typical plastics and their characteristics (extract) . 7
Bibliography .12

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
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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
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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
Many of the existing test methods for coatings resulting from paints and varnishes have been developed for
metallic substrates and were often applied to plastics substrates in the past.
This document explains characteristics of and differences between plastics and metallic substrates and
shows their possible effect on the behaviour of the coating in various test methods.
It is possible that the substrate has an effect on the behaviour of the coating during tests. Therefore, it can be
useful to select test conditions which are based, for example, on standards from the plastics sector and not
on standards from the coating sector, in order to take into account influencing factors such as the thermal
conductivity of the substrate.
This document provides a general introduction to the particularities and terms and definitions of coatings
on plastics and composites. The test methods for which deviating behaviour of the coating can occur on
plastics substrates and which measures can possibly be taken are dealt with in the other parts of the
ISO 22785 series. The structure of the ISO 22785 series is as follows:
— ISO 22785-2 on weathering and irradiation testing
— ISO 22785-3 on constant climate and alternating climate testing
— ISO 22785-4 on abrasion and scratch testing
— ISO 22785-5 on chemical resistance testing
— ISO 22785-6 on stone-chip resistance testing
— ISO 22785-7 on adhesion
— ISO 22785-8 on film thickness

v
International Standard ISO 22785-1:2026(en)
Paints and varnishes — Coatings on plastics and
composites —
Part 1:
General introduction
1 Scope
This document specifies the applicability of general test methods for coatings resulting from paints and
varnishes (hereinafter referred to as “coatings”) on plastics, plastics composites and similar substrates,
hereinafter collectively referred to under the term “plastics”. It provides a general introduction to the
particularities of coatings on plastics.
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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 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
transparency
property of a material or coating by which a negligible portion of the transmitted radiation undergoes
scattering or absorption, thereby enabling objects or the substrate to be distinguished clearly through the
material
[SOURCE: ISO 472:2013, 2.1200, modified — definition extended to coatings; “light” replaced by “radiation”;
"or absorption" added; "or the substrate" added.]
3.2
opaque
quality whereby materials or coatings are impenetrable
Note 1 to entry: Depending on the thickness, most real materials and paints and varnishes are neither completely
opaque nor completely transparent.

3.3
plastic
material which contains as an essential ingredient a high polymer and which, at some stage in its processing
into finished products, can be shaped by flow
Note 1 to entry: Elastomeric materials, which are also shaped by flow, are not considered to be plastics.
Note 2 to entry: In some countries, particularly the United Kingdom, the term “plastics” is used as the singular form as
well as the plural form.
[SOURCE: ISO 472:2013, 2.702]
3.4
homopolymer
polymer derived from a single species of monomer
[SOURCE: ISO 472:2013, 2.465]
3.5
copolymer
polymer derived from more than one species of monomer
[SOURCE: ISO 472:2013, 2.212]
3.6
composite
solid product consisting of two or more distinct phases, including a binding material (matrix) and a
particulate or fibrous material
[SOURCE: ISO 472:2013, 2.182.1, modified — example omitted]
3.7
recyclate
plastics (3.3) material resulting from the recycling of plastics waste
Note 1 to entry: The terms “secondary raw material”, “recycled plastics” and “regenerate” are sometimes used
synonymously with “recyclate”.
Note 2 to entry: As soon as the used plastics material is treated in such a way that it is ready to replace virgin product,
material or substance in a production process, it loses its characteristics as waste.
[SOURCE: ISO 472:2013, 2.1705]
3.8
ageing
entirety of all irreversible chemical and physical processes occurring in a material in the course of time
Note 1 to entry: For testing purposes, ageing is often artificially induced.
Note 2 to entry: In literature, the term “physical ageing” can also be found, which sometimes refers only to a (thermo-)
reversible change of polymeric materials.
3.9
conditioning
measures which bring the test specimen to a uniform state and thus to a state of equilibrium (temperature
and humidity) within a specified period of time
Note 1 to entry: The conditioning of plastics (3.3) and its coating can have an influence on the result of a test. Therefore,
it is important to indicate how the object to be tested was conditioned before exposure. This can include storage of
the test specimen under standard conditions (see ISO 3270 for coatings and ISO 291 for uncoated plastics) or forced
conditioning. The aim of conditioning is to create the same conditions for all test specimens. Particularly moisture-
sensitive materials, e.g. polyamides (PA), are usually force-dried.

4 Plastics substrates
The plastics substrates used in the test methods of the ISO 22785 series are: homopolymers, copolymers,
composites and recyclates from these materials.
5 Function of coatings on plastics substrates
Coatings on plastics can differ in composition, adhesive strength, pretreatment and other aspects from
coatings on metals. Also, the required functionalities can differ compared to metal substrates. Often, it is
expected that several requirements are met simultaneously, such as for the automotive sector. Depending on
the functionality or functionalities, fulfilling multiple requirements at the same time can affect the ageing
behaviour.
Typical functionalities on plastics substrates are:
a) decorative: colour, gloss, reflection and other optical effects;
b) thermal: thermal insulation and infrared (IR) reflection;
c) mechanical: scratch protection, hardness;
d) adhesive strength;
e) light/ultraviolet (UV) protection;
f) sealing/barrier effect/insulation;
g) adhesion characteristics/wettability (hydrophobic, etc.);
h) burning behaviour.
Major differences between metal and plastics substrates can be found in the thermal characteristics,
the hardness and the proportion of water absorption and release. The influence o
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