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IEC 62788-1-6
Edition 1.0 2020-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
Measurement procedures for materials used in photovoltaic modules –
Part 1-6: Encapsulants – Test methods for determining the degree of cure
in Ethylene-Vinyl Acetate
Procédures de mesure des matériaux utilisés dans les modules
photovoltaïques –
Partie 1-6: Encapsulants – Méthodes d'essai pour déterminer le degré
de durcissement dans l'éthylène-acétate de vinyle
IEC 62788-1-6:2017-01/AMD1:2020-05(en-fr)
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IEC 62788-1-6
Edition 1.0 2020-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
Measurement procedures for materials used in photovoltaic modules –
Part 1-6: Encapsulants – Test methods for determining the degree of cure
in Ethylene-Vinyl Acetate
Procédures de mesure des matériaux utilisés dans les modules
photovoltaïques –
Partie 1-6: Encapsulants – Méthodes d'essai pour déterminer le degré
de durcissement dans l'éthylène-acétate de vinyl
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-8209-0
– 2 – IEC 62788-1-6:2017/AMD1:2020
© IEC 2020
FOREWORD
This amendment has been prepared by IEC technical committee 82:Solar photovoltaic energy
systems.
The text of this amendment is based on the following documents:
FDIS Report on voting
82/1691/FDIS 82/1720/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
_____________
2 Normative references
Add the following new references:
ISO 6721-1, Plastics – Determination of dynamic mechanical properties – Part 1: General
principles
ISO 14577-1, Metallic materials – Instrumented indentation test for hardness and materials
parameters – Part 1: Test method
3 Terms and definitions
Add the following new term:
3.6
degree of cure
G
i
parameter that correlates with the extent of cross-linking within the EVA
using the indentation method
Note 1 to entry: Unit: dimensionless.
5.2.1 Sampling and storage
Replace the existing subclause 5.2.1.1 with the following:
© IEC 2020
5.2.1.1
Because the results for the secondary method may depend on the make of EVA, test results
may only be directly compared for the same formulation of EVA. Therefore, test specimens
should come from the same manufacturer(s) for the same fabrication lay-up configuration
(backsheet/EVA combination). Changes in the encapsulant that affect the curing process,
including but not limited to a change of the material supplier, would require validating the
correlation between G and the degree of cure. For example, if the percentage vinyl acetate
%
and the degree of cure (from
content in the EVA resin changes, a new correlation between G
%
a secondary method) should be obtained because the percentage vinyl acetate content is
known to significantly affect the viscoelastic-dependent cure characteristics of the
encapsulant.
7 Test report
Replace the existing item h) with the following:
h) identification of test method used and test instrument and other equipment used, including
the laminator and the temperature, pressure, and time settings used, when applicable. In
the case of the indentation secondary method (per correlation or usual use of method), the
test temperature, tip material, tip geometry, and tip size, maximum indentation load,
maximum indentation depth, and frequency of modulation (if applicable) shall also be
reported;
Replace the existing item i) with the following:
i) reference to sampling procedure, where relevant, including the number of tests per
specimen;
Replace the existing item k) with the following:
k) measurements (associated and their uncertainty), examinations and derived results
supported by tables, graphs, sketches and photographs as appropriate including degree of
cure, specimen mass, measured enthalpy, graphs of the enthalpy/temperature data,
graphs of the crystallization peaks, and gel content;
Add the following new clause:
8 Indentation secondary method
8.1 General
An alternative secondary method, using indentation to characterize the degree of cure of EVA,
has emerged from the PV industry. The method is presently being used by module
manufacturers and has been demonstrated in in-line application. A general description of the
principle, related equipment, and use of the method is given herein.
G is obtained using an indentation instrument, where the result may follow from the analysis
i
of the applied load, penetration depth, use of a modulated applied load (such as harmonic
stiffness, storage modulus, loss modulus, or tan[δ]), and/or the specimen viscoelastic
response (including the relaxation or recovery response). G may be obtained from a more
i
complicated dimensionless fit, including a fit applied to the specimen's viscoelastic response
(e.g., using a Maxwell model) or a combination of characteristics monitored during
indentation. G may be obtained from a dimensionless fit of the response of the specimen (for
i
example
CC−
tn
G=
i
CC−
mn
– 4 – IEC 62788-1-6:2017/AMD1:2020
© IEC 2020
where
C is the characteristic of interest,
C is the test specimen;
t
C is the reference specimen with the greatest thermal history (“maximum correlated”, e.g.,
m
most-cross-linked); and
C is the reference specimen with minimal or no thermal history (“minimum correlated”, i.e.,
n
not-laminated or not-cured).
NOTE A suitable apparatus is supplied by LayTec AG in Germany. For this presently available commercial
equipment, G can range from 0,3 to 2,5.
i
The terminology and definitions related to dynamic indentation, including harmonic stiffness,
storage modulus, loss modulus may be found in ISO 14577-1. The terminology and definitions
related to tan[δ] may be found in ISO 6721-1.
8.2 Principle
The indentation method probes the mechanical response (viscoelastic characteristics) of
cured EVA layers, which change due to the cross-linking of the EVA during the curing
process. In the method, a probe tip (connected to a force transducer) is pressed against the
flexible back-sheet affecting the EVA. The corresponding reaction force acting on the tip
during indentation and subsequent relaxation is recorded by the force transducer and
analyzed, giving a figure of merit (G ) describing the viscoelastic properties of the material.
i
The principle of the indentation method is described in the related references in the
bibliography.
A correlation between the degree of cure and the gel content can be established by a series
of measurements on samples, each with a different degree of cure. Indentation can thus be
used as a secondary method to quantify the degree of cure. To enable more widespread
comparison, the same set of sample materials shall be characterized using the gel content
method (Clause 6 of IEC 62788-1-6) after indentation to establish a correlation between gel
content and the degree of cure. The indentation method is valid for the specific combination of
EVA and back-sheet examined.
This test procedure may also be applied to cross-linking ethylenic co-polymers other than
EVA. The maximum tip displacement, maximum applied load, and temperatures identified for
the indentation measurements in this procedure have been optimized for EVA. For other
materials, the optimum temperature depends on the stack of materials subject to indentation,
including the encapsulant and backsheet.
The method and instrumentation is designed for non-destructive examination of PV modules
with a flexible back-sheet for the purpose of manufacturing process control. The method may
not be applied to modules with a glass/glass laminated construction. The indentation method
may be used for quality control in production lines. The variation of the method (one standard
deviation) is typically ≤ ±3 % (see Kunath et al.).
8.3 Instrument and equipment for the indentation method
Equivalent instruments that contain the following components and can be shown to provide
repeatability and reproducibility of ≤ ±5 % for two standard deviations for correlation of G as
i
defined in Section 3.6 may be used.
The instrument consists of:
__________
This information is given for the convenience of users of this International Standard and does not constitute an
endorsement by IEC of the product named.
© IEC 2020
– a rigid probe;
– a force transducer connected to the probe, measuring the reaction force acting on the
probe during indentation;
– a temperature regulation system, to maintain the test specimen (module) at a designated
temperature;
– a mechanically rigid linear stage that may be used to move the probe and force transducer
for site-specific indentation.
8.4 Instrument calibration
The tip, force transducer, and temperature
...