ISO/PRF 22785-7

ISO/DISPRF 22785-7:2026(en)
ISO/TC 35/SC 9
Secretariat: BSI
Date: 2026-05-2209-30
Paints and varnishes — Coatings on plastics and composites —
Part 7:
Adhesion
© PROOF
ISO/DISPRF 22785-7:2026(en)
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iii
Contents Page
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test specimen characteristics and preparation . 1
4.1 Requirements for test specimens . 1
4.2 Conditioning . 1
5 Influence of the plastics substrate on the adhesion test . 2
6 Test methods . 2
6.1 Pull-off test . 2
6.2 Floating roller method . 3
6.3 Cross-cut test . 5
6.4 X-cut test 1 . 10
6.5 X-cut test 2 . 11
6.6 T-bend test . 11
6.7 Scratch test . 13
6.8 Pressure water jet test . 14
6.9 Scratch test . 17
6.10 Pistol test . 19
6.11 Falling-weight test with large-area indenter . 20
6.12 Falling-weight test with small-area indenter . 26
7 Assessment . 29
Bibliography . 30

iv
ISO/DISPRF 22785-7:2026(en)
Foreword
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General test methods for paints and varnishes.
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v
Introduction
Many of the existing test methods for determining the adhesion of coatings have been developed for metallic
substrates.
This document explains characteristics of plastics and differences between plastics substrates and metallic
substrates, and it shows their potential effect on the behaviour of the coating in different test methods.
It is possible that the substrate has an effect on the behaviour of the coating during the test. It is therefore
sometimes useful to select test conditions that are based, for example, on standards from the plastics sector
and not on standards from the coatings sector, in order to take into account influencing factors such as the
thermal conductivity of the substrate.
vi
DRAFT International Standard ISO/DIS 22785-7:2026(en)

Paints and varnishes — Coatings on plastics and composites — —
Part 7:
Adhesion
1 Scope
This document specifies the testing of adhesion of coatings on plastics, plastics composites and similar
substrates.
It also provides an overview of common test methods.
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, Coatings on plastics and composites — Part 1: General introduction
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and ISO 22785-1 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/
4 Test specimen characteristics and preparation
4.1 Requirements for test specimens
Both coatings on test specimen panels specified in ISO 1514 and coatings on components are tested.
Depending on the selected test method, there are different requirements for the geometry of the test specimen.
It is important that the substrates are free from flaws and damage of any kind that could adversely affect
appearance and properties.
The coating system and the substrate are selected together with the pre-treatment and coating methods so
that a homogeneous coating is achieved. The film thickness is documented in accordance with the technical
requirements relating to the visual appearance and/or coating.
4.2 Conditioning
Conditioning serves to improve the repeatability and reproducibility of test results.
As the properties of plastics substrates depend greatly on humidity levels and conditioning usually takes
longer than for metals, a longer conditioning time is usually required for plastics substrates.
The values and times to be selected depend on the test specimen to be tested.
Unless specified otherwise, the test specimens are conditioned for 16 h under standard climatic conditions
specified in ISO 3270.
5 Influence of the plastics substrate on the adhesion test
The chemical and physical properties of plastics and composites as substrates are very different from those of
metallic substrates.
The hardness and flexibility of the substrate can influence the result of testing stone-chip resistance.
The hardness and flexibility of the substrate depend on temperature. For more details, see ISO 22785-1.
Results obtained with flexible plastics substrates and hard plastics substrates are not comparable.
For methods using cutting tools, care shall be taken not to damage the substrate. This can be achieved by
reduced forces when applying cuts.
6 Test methods
6.1 Pull-off test
Three methods for determining adhesion are described in ISO 4624:
— — Method A: using two dollies for testing on both rigid and deformable plates;
— — Method B: for testing from one side only, using a single dolly (suitable for rigid plates only);
— — Method C: using dollies, one of which is coated with the coating material to be tested.
The test can be carried out on numerous substrates. The method differs depending on whether this involves
a deformable substrate, such as thin metal, plastics and wood, or a rigid substrate, such as thick concrete slabs
and metal plates. The sandwich structure is usually used in order to prevent the substrate from bending during
the adhesion test. With flexible plastics, it shall particularly be ensured that the test specimen does not deflect
during the test. To do this, either the test specimen plate is glued onto a firm surface or the test is carried out
with two dollies glued on using the sandwich method. For special purposes, the coating material may be
applied onto a dolly, for example.
Dollies are glued onto the dried/cured coating.
Once the adhesive has cured, the dollies are pulled off with a tensile tester and the force required to pull off
the dolly is measured.
The test result is the minimum tensile stress that shall be applied in order for the weakest interface (adhesion
failure) or the weakest point (cohesion failure) of the test assembly to fail. Adhesion and cohesion failures can
also occur alongside one another (mixed failures).
A schematic representation of the principle of the pull-off test is shown in Figure 1Figure 1.
ISO/DISPRF 22785-7:2026(en)
Key
1 substrate
2 coating
3 adhesive layer
4 clearance
5 dolly
6 outer ring for supporting the test specimen plate
a
Pull-off direction.
Figure 1 — Principle of the pull-off test
6.2 Floating roller method
The floating roller method is specified in EN 1464.
In accordance with Figure 2Figure 2,, the test specimen is inserted into the retaining device, whereby the non-
glued section of the flexible adherend is clamped into the clamp of the testing machine. Unless otherwise
specified, the test specimens are separated at a constant cross bar advance speed of (100 ± 5) mm/min. If the
rigid adherend bends or warps during the test, the test specimen is designed with a rigid adherend of sufficient
flexural stiffness to ensure uniform peeling. During the peel test, the force counter to the cross-bar movement
(force counter to peeling distance) is recorded over a length of at least 115 mm of the bond line, whereby the
first 25 mm of the peeling distance are disregarded. The results in which a fracture lies outside of the peeling
zone specified in Figure 2Figure 2 are disregarded.
Dimensions in millimetres
Key
ISO/DISPRF 22785-7:2026(en)
1 rigid adherend
2 peeling zone
3 flexible adherend
4 structural steel
5 double roller bearings
Figure 2 — Holder for mounting the test specimens for the peel test
To make separation easier in the starting area, an adhesive tape or fabric can be inserted during the
production process in order to facilitate layer separation on one side.
The average peeling force in Newtons per millimetre (N/mm) test specimen width that is required to separate
the adherends from one another is determined from the automatically recorded curve for a peeling distance
of at least 115 mm (whereby the first 25 mm and the last 25 mm are disregarded).
The average, the maximum and the minimum force are recorded for each test specimen.
6.3 Cross-cut test
The cross-cut test is specified in ISO 2409.
The cross-cut test is a test method for assessing the resistance of coatings to separation from the substrate
when a rectangular grid reaching down to the substrate is cut into the coating. In addition to other factors, a
property determined in accordance with this empirical method is dependent on the adhesion of the coating
on the previously applied layer or on the substrate. However, this method is not a method purely for
measuring adhesion.
Although the method is applicable to coatings on hard and soft substrates, these different substrates
necessitate a different method.
The cut spacing in each direction shall be identical and as follows, depending on the coating layer thickness
and the type of substrate:
1 1)
— — up to 60 µm: 1 mm spacing for hard substrates such as duroplastics (e.g. GRP, CRP ); );
— — up to 60 µm: 2 mm spacing for soft substrates such as thermoplastics, PP/EPDM, polyamides,
2 2)
ABS/PC/PCPBT ; ;
— — 61 µm to 120 µm: 2 mm spacing for hard and soft substrates;
— — 121 µm to 250 µm: 3 mm spacing for hard and soft substrates.
In some specifications, the X--cut test is recommended for hard substra
...