ISO/TR 21555:2019

TECHNICAL ISO/TR
REPORT 21555
First edition
2019-08
Paints and varnishes - Overview of
test methods on hardness and wear
resistance of coatings
Reference number
ISO/TR 21555:2019(E)
©
ISO 2019

---------------------- Page: 1 ----------------------
ISO/TR 21555:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TR 21555:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Hardness tests . 2
4.1 Indentation tests with resting indenter . 2
4.1.1 Indentation test with Buchholz indenter. 2
4.1.2 Indentation test with Knoop indenter . 5
4.1.3 Indentation test with Pfund indenter . 6
4.1.4 Indentation test with Vickers indenter . 8
4.2 Indentation tests with oscillating indenter .10
4.2.1 Oscillation damping test with König pendulum .10
4.2.2 Oscillation damping test with Persoz pendulum .11
4.2.3 Oscillation damping test with rocker .13
5 Wear resistance tests .14
5.1 Single-scratch tests .14
5.1.1 Scratch test with pencils .14
5.1.2 Scratch test with ball stylus 1 .17
5.1.3 Scratch test with ball stylus 2 .20
5.1.4 Scratch test with conical stylus 3 .22
5.1.5 Scratch test with conical stylus 4 .25
5.1.6 Scratch test with conical stylus 5 .28
5.1.7 Scratch test with conical stylus 6 .31
5.1.8 Scratch test with disc-shaped stylus .33
5.1.9 Scratch test with U-shaped stylus .37
5.2 Multiple scratch tests .39
5.2.1 Multiple scratch test with locked abrasive wheel .39
5.2.2 Multiple scratch test with abrasive cylinder .40
5.2.3 Multiple scratch test with rotating abrasive wheels .42
5.2.4 Multiple scratch test with rotating brush .43
5.3 Dry abrasion tests .45
5.3.1 Abrasion test with locked abrasive wheel .45
5.3.2 Abrasion test with rotating abrasive wheels 1 .47
5.3.3 Abrasion test with abrasive wheels 2 .48
5.3.4 Abrasion test with rotating abrasive wheels 3 .50
5.3.5 Abrasion test with rotating abrasive wheels 4 .51
5.4 Wet abrasion tests .53
5.4.1 Scrub test with brush .53
5.4.2 Scrub test with non-woven web 1 .55
5.4.3 Scrub test with non-woven web 2 .57
5.5 Falling-sand tests .60
5.5.1 Falling-sand test with corundum granulate .60
5.5.2 Falling-sand test with quartz sand .62
Annex A (informative) Overview on test methods on hardness and wear resistance of coatings .64
Bibliography .69
© ISO 2019 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TR 21555:2019(E)

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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
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 35, Paints and varnishes, Subcommittee
SC 9, General test methods for paints and varnishes.
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 © ISO 2019 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/TR 21555:2019(E)

Introduction
The determination of the hardness and of the wear resistance is one of the most important preconditions
for evaluating the resistance of coatings to mechanical stress.
The procedures and numerical data given in this document provide a rough overview; detailed
information is found in the applicable standards.
For all of the methods for the evaluation of the hardness and of the wear resistance the visco-elastic
properties have a wide influence on the test result. Consequently, the time between testing and
evaluation are agreed and observed.
Mechanical properties of coatings depend on, among others, temperature and moisture content.
Consequently, the tests should be carried out immediately after the conditioning phase.
The tests are preferably carried out in the climatic chamber.
Each method has its specific application. An unsuitable method may lead to false conclusions. All of the
test methods require a certain expertise of the test person. For most of the test methods the test results
depend on, among others, the film thickness of the coating to be tested.
© ISO 2019 – All rights reserved v

---------------------- Page: 5 ----------------------
TECHNICAL REPORT ISO/TR 21555:2019(E)
Paints and varnishes - Overview of test methods on
hardness and wear resistance of coatings
1 Scope
This document provides an overview for selecting the most suitable test method regarding the
evaluation of the hardness and the wear resistance of coatings.
Annex A gives a summarized list of test methods for the evaluation of the hardness and of the wear
resistance of coatings for different stresses.
Methods for testing cross-linking (wear test in connection with solvents) and abrasion tests with
multiple impacts are not covered by this document.
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 — Terms and definitions
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 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
hardness
ability of a dry film or coat to resist indentation or penetration by a solid object
[SOURCE: ISO 4618:2014, 2.136]
3.2
wear
irreversible change of a coating which is caused by the mechanical impact of moved objects
3.3
stylus
scratching tool with specified geometry
[SOURCE: ISO 22557:2019, 3.1]
3.4
scratch
line-shaped damage of a coating which is caused by the impact of a loaded object being moved over
the coating
© ISO 2019 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/TR 21555:2019(E)

3.5
mar
blemish on the surface of a coating, extending over a particular area of the coating and visible due to
the difference in the light-reflection properties of the area affected compared with the light-reflection
properties of adjacent areas
[SOURCE: ISO 4618:2014, 1.152]
3.6
abrasion
wear (3.2) which is caused by removal of coating material on a surface
3.7
repeatability conditions
conditions where independent test results are obtained with the same method on identical test items
in the same laboratory by the same operator using the same equipment within short intervals of time
[SOURCE: ISO 5725-1:1994, 3.14]
3.8
repeatability limit
r
the value less than or equal to which the absolute difference between two test results obtained under
repeatability conditions (3.7) may be expected to be with a probability of 95 %
[SOURCE: ISO 5725-1:1994, 3.16]
3.9
reproducibility conditions
conditions where test results are obtained with the same method on identical test items in different
laboratories with different operators using different equipment
[SOURCE: ISO 5725-1:1994, 3.18]
3.10
reproducibility limit
R
the value less than or equal to which the absolute difference between two test results obtained under
reproducibility conditions (3.8) may be expected to be with a probability of 95 %
[SOURCE: ISO 5725-1:1994, 3.20]
4 Hardness tests
4.1 Indentation tests with resting indenter
4.1.1 Indentation test with Buchholz indenter
— Description
An indenter made of hardened steel, the shape and dimensions of which are specified in accordance
with Buchholz, impacts the coating under a load (500 g, corresponding to 4,96 N) for 30 s and
produces an indentation. After a resting time of 35 s the indentation length (mm) is determined
under specified lighting conditions using a measuring microscope (×20 magnification).
Figure 1 shows the test device and Figure 2 shows the Buchholz indenter. Figure 3 illustrates the
microscopic measurement of the indentation.
2 © ISO 2019 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/TR 21555:2019(E)

Key
1 steel block
2 indenter
3 tip
Figure 1 — Indentation tester in accordance with Buchholz
Dimensions in millimetres
Key
1 indentation edge
2 indenter
3 coating
4 substrate
Figure 2 — Buchholz indenter
© ISO 2019 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO/TR 21555:2019(E)

a) Arrangement of the light source and of the microscope
b) Image of the Buchholz indentation
Key
1 light source
2 microscope
3 indentation
4 coating
5 substrate
l indentation length
Figure 3 — Measuring the Buchholz indentation
— Application
The indentation test with Buchholz indenter is generally applicable.
— Calibration
A calibration method is not specified.
— Procedure
— Condition test panel (23 °C / 50 % relative humidity / ≥ 16 h)
— First, lower the tips of the test device onto the coating, and then carefully lower the indenter.
— Leave the loaded indenter on the coating for 30 s and remove in reverse order.
— 35 s after removal of the load determine the indentation length (mm) using a measuring
microscope (see Figure 3).
— Evaluation
Test result is the indentation length (mm), as mean value of five determinations.
— Precision
The repeatability limit r is 0,23 mm.
The reproducibility limit R is 0,45 mm.
4 © ISO 2019 – All rights reserved

---------------------- Page: 9 ----------------------
ISO/TR 21555:2019(E)

— Reference
The indentation test with Buchholz indenter is specified in ISO 2815.
4.1.2 Indentation test with Knoop indenter
— Description
A diamond indenter, the shape and dimensions of which are specified in accordance with Knoop,
impacts the coating under a load (25 g, corresponding to 0,245 N) for 18 s and produces an
indentation. Immediately after removal of the load the length (mm) of the long diagonal of the
indentation is determined using a measuring microscope. From this, the “Knoop Hardness Number”
2
KHN (kg/mm ) is calculated.
Figure 4 shows the dimensions of the Knoop indenter. Figure 5 shows the top view of the Knoop
indentation.
Key
α angle of the longitudinal edge (172,5°)
β angle of the transverse edge (130°)
Figure 4 — Dimensions of the Knoop indenter
Key
l indentation length
Figure 5 — Top view of the Knoop indentation
— Application
The indentation test with Knoop indenter is generally applicable.
— Calibration
On a reference block the KHN value is determined and compared to the nominal value.
— Procedure
— Condition test panel (23 °C / 50 % relative humidity / ≥ 24 h).
— Lower the test device onto the coating in a plane area.
© ISO 2019 – All rights reserved 5

---------------------- Page: 10 ----------------------
ISO/TR 21555:2019(E)

— Lower the indenter and apply the specified test load.
— Leave the loaded indenter on the coating for 18 s.
— Immediately after the removal of the load, determine the indentation length l (mm) using a
measuring microscope (see Figure 5).
— Evaluation
2
Calculate the KHN value using the measured length l: KHN = 0,356 / l . (Factor 0,356 results from
the test load and the shape factor of the indenter.)
Test result is the KHN value (kg/mm), as mean value of n determinations. (The number n is agreed.)
NOTE In accordance with ISO 4545-1, the Knoop hardness is expressed in HK, which is different from
the KHN used here.
— Precision
The repeatability (in accordance with ASTM D1474/D1474M) is 9 %.
The reproducibility (in accordance with ASTM D1474/D1474M) is 24 %.
— Reference
The indentation test with Knoop indenter is specified in ASTM D1474/D1474M-13, Method A: Knoop
Indentation Hardness.
A general method for the determination of the Knoop hardness HK is specified in ISO 4545-1.
For testing automobile coatings, the method is also described in References [47] and [56].
4.1.3 Indentation test with Pfund indenter
— Description
A transparent quartz or sapphire indenter (hemisphere Ø 0,318 mm), the shape and dimensions of
which are specified in accordance with Pfund, impacts the coating under load (1 kg, corresponding
to 9,8 N) for 60 s and produces an indentation. Immediately after that the diameter (mm) of the
indentation under load by the transparent indenter is determined using a measuring microscope.
2
From this, the “Pfund Hardness Number” PHN (kg/mm ) is calculated.
Figure 6 shows the principle of the indentation test with Pfund indenter.
6 © ISO 2019 – All rights reserved

---------------------- Page: 11 ----------------------
ISO/TR 21555:2019(E)

Key
1 test panel
2 stop
3 load arm
4 transparent indenter
5 pivot
6 tare weight
7 load weight
8 light source
9 semi-transparent mirror
10 measuring microscope
11 microscopic image (Pfund indentation and scale)
Figure 6 — Principle of the indentation test
— Application
The indentation test with Pfund indenter is generally applicable.
— Calibration
On a reference block the PHN value is determined and compared to the nominal value.
— Procedure
— Condition test panel (23 °C / 50 % relative humidity / ≥ 24 h).
— Lower the test device onto the coating in a plane area.
— Lower the indenter and apply the specified test load.
— Leave the loaded indenter on the coating for 60 s.
— After that, still loaded, determine diameter d (mm) of the indentation through the transparent
indenter using a measuring microscope.
— Evaluation
2
Calculate the PHN value using the measured diameter d: PHN = 1,27 / d . (Factor 1,27 results from
the test load and the shape factor of the indenter.)
2
Test result is the PHN value (kg/mm ), as mean value of at least 5 determinations.
© ISO 2019 – All rights reserved 7

---------------------- Page: 12 ----------------------
ISO/TR 21555:2019(E)

— Precision
The repeatability (in accordance with ASTM D1474/D1474M) is 18 %.
The reproducibility (in accordance with ASTM D1474/D1474M) is 36 %.
— Reference
An indentation test with Pfund indenter is specified in ASTM D1474/D1474M-13, Method B: Pfund
Indentation Hardness.
4.1.4 Indentation test with Vickers indenter
— Description
A diamond indenter, the shape and dimensions of which are specified in accordance with Vickers, is
2
pressed into the coating under increasing, controlled load. The Martens hardness HM (N/mm ) in
dependence of the indentation depth is calculated from the measured indentation depth (µm) and the
respective test load (N).
Figure 7 shows the dimensions of the indenter and Figure 8 shows the test principle.
Key
α pyramid angle (136°)
Figure 7 — Schematic diagram of the Vickers indenter
8 © ISO 2019 – All rights reserved

---------------------- Page: 13 ----------------------
ISO/TR 21555:2019(E)

Key
1 substrate
2 coating
3 distance measuring device for the indentation depth
4 indenter with Vickers geometry
h indentation depth
F test load
Figure 8 — Principle of the indentation test with Vickers indenter
— Application
The indentation test with Vickers indenter is generally applicable.
— Calibration
On a certified calibration panel (e.g. glass of the BK 7 type) an indentation test with a specified load
is carried out. From the load-indentation curve the HM value is determined and compared to the
certified value.
— Procedure
— Agree the test parameters:
— The number and the values of the test load levels (N) [the test load levels are normally
1/2
selected proportionally (test load) ].
— Position the test panel in the test device and set the agreed test parameters.
— Start the test procedure and record the indentation depth h (µm) in dependence of test load F (N).
— Evaluation
2 2
Calculate the values for the Martens hardness HM = F/26,43 h (N/mm ) from the h-values and the
corresponding F-values. (Factor 26,43 results from the shape factor of the indenter.)
2
Test result is the Martens hardness HM (N/mm ) for an agreed indentation depth h (µm) and/or
the hardness profile (HM as a function of h).
— Precision
No precision data are currently available.
© ISO 2019 – All rights reserved 9

---------------------- Page: 14 ----------------------
ISO/TR 21555:2019(E)

— Reference
An indentation test with Vickers indenter is specified in ISO 14577-1 and ISO 14577-4.
For testing automobile coatings slightly deviating procedures are described in
References [42] and [45].
4.2 Indentation tests with oscillating indenter
4.2.1 Oscillation damping test with König pendulum
— Description
A pendulum, the shape, mass and dimensions of which are specified in accordance with König,
together with its two integrated tungsten-carbide balls (Ø 5 mm) is lowered on the coating,
displaced by 6°, and released. The damping duration (s) of the pendulum swing until reaching the
specified final displacement (3°) is determined.
Figure 9 shows the test principle.
Key
1 angle scale
2 König pendulum
3 tungsten-carbide ball
4 test panel
5 adjusting weight
Figure 9 — Principle of the test with König pendulum
10 © ISO 2019 – All rights reserved

---------------------- Page: 15 ----------------------
ISO/TR 21555:2019(E)

— Application
The oscillation damping test with König pendulum is generally applicable.
— Calibration
On a polished, plane glass panel the duration of a pendulum swing and the damping duration are
determined and compared to the corresponding nominal values.
— Procedure
— Condition test panel (23 °C / 50 % relative humidity / ≥ 16 h).
— Position the test panel in the test device.
— Lower the pendulum with the integrated hard-metal balls onto the coating so that the tip of the
pendulum is aligned with the zero point of the scale.
— Displace pendulum by 6° and release.
— Determine the damping duration (s) until reaching the final displacement (3°) by using a
stop watch.
— Evaluation
Test result is the damping duration (s), as mean value of three determinations.
— Precision
The repeatability limit r is 7 s, corresponding to 5 swings.
The reproducibility limit R is 14 s, corresponding to 10 swings.
— Reference
The oscillation damping test with König pendulum is specified in ISO 1522 and ASTM D4366.
For testing automobile coatings a slightly deviating method is described in Reference [61].
4.2.2 Oscillation damping test with Persoz pendulum
— Description
A pendulum, the shape, mass and dimensions of which are specified in accordance with Persoz,
together with its two integrated tungsten-carbide balls (Ø 8 mm) is lowered on the coating,
displaced by 12°, and released. The damping duration (s) of the pendulum swing until reaching the
specified final displacement (4°) is determined.
Figure 10 shows the principle.
© ISO 2019 – All rights reserved 11

---------------------- Page: 16 ----------------------
ISO/TR 21555:2019(E)

Key
1 angle scale
2 Persoz pendulum
3 tungsten-carbide ball
4 test panel
Figure 10 — Principle of the test with Persoz pendulum
— Application
The oscillation damping test with Persoz pendulum is generally applicable.
— Calibration
On a polished, plane glass panel the duration of a pendulum swing and the damping duration are
determined and compared to the corresponding nominal values.
— Procedure
— Condition test panel (23 °C / 50 % relative humidity / ≥ 16 h).
— Position the test panel in the test device.
— Lower the pendulum with the integrated hard-metal balls onto the coating so that the tip of the
pendulum is aligned with the zero point of the scale.
— Displace pendulum by 12° and release.
— Determine the damping duration (s) until reaching the final displacement (4°) by using a
stop watch.
— Evaluation
Test result is the damping duration (s), as mean value of three determinations.
12 © ISO 2019 – All rights reserved

---------------------- Page: 17 ----------------------
ISO/TR 21555:2019(E)

— Precision
The repeatability limit r is 3 %.
The reproducibility limit R is 8 %.
— Reference
The oscillation damping test with Persoz pendulum is specified in ISO 1522 and ASTM D4366.
4.2.3 Oscillation damping test with rocker
— Description
A rocker, the shape, mass and dimensions of which are specified in accordance with Sward, together
with its two races is lowered on the coating, displaced by 22° and released. The number of swings
until reaching the specified final displacement (16°) is determined.
Figure 11 shows the test arrangement.
Key
1 race
2 level for final displacement
3 level for initial displacement
4 adjustment apparatus
5 levelling level
6 adjustable foot
7 test panel
8 clamp mask
9 glass panel
Figure 11 — Arrangement of the oscillation damping test with rocker
— Application
The oscillation damping test with rocker is generally applicable.
— Calibration
On a glass panel the number of swings within a time period of 60 s is determined and compared to
the nominal value.
© ISO 2019 – All rights reserved 13

---------------------- Page: 18 ----------------------
ISO/TR 21555:2019(E)

— Procedure
— Condition test panel (23 °C / 50 % relative humidity / ≥ 24 h).
— Secure the test panel with the clamp mask on the levelled glass plate (see Figure 11).
— Lower the rocker with the two races onto the coating, displace by 22° and release.
— Determine the number of swings until reaching the final displacement (16°).
— Evaluation
Test result is the number of swings, multiplied by two, within the specified angle range, as mean
value of four determinations.
— Precision
No precision data are currently available.
— Reference
The oscillation damping test with rocker is specified in ASTM D2134.
5 Wear resistance tests
5.1 Single-scratch tests
5.1.1 Scratch test with pencils
— Description
A pencil lead with specified geometry is pushed over the coating at an angle of 45° and a test load
of 7,5 N. The hardness degree
...