IEC 62788-1-6:2017

IEC 62788-1-6 ®
Edition 1.0 2017-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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

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IEC 62788-1-6 ®
Edition 1.0 2017-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-3857-8

– 2 – IEC 62788-1-6:2017 © IEC 2017
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Principle . 7
5 DSC secondary method . 8
5.1 Instrument and equipment for the secondary method . 8
5.1.1 General . 8
5.1.2 Electronic balance . 8
5.1.3 Differential scanning calorimeter . 8
5.1.4 Instrument calibration . 8
5.2 Specimen preparation for the secondary method. 9
5.2.1 Sampling and storage . 9
5.2.2 Preparation procedures . 9
5.3 Test requirements for the secondary method . 9
5.3.1 Environment requirements . 9
5.3.2 Parameter settings (residual enthalpy method) . 10
5.3.3 Parameter settings (melt/freeze method) . 10
5.3.4 Parameter settings (combined enthalpy and melt/freeze method) . 10
5.4 Test procedure for the secondary method . 11
5.5 Calculation and expression of the results for the secondary method . 11
5.5.1 Enthalpy method . 11
5.5.2 Melt/freeze method . 12
5.6 Uncertainty of measurements for the secondary method . 16
6 The primary method . 16
6.1 Principle for the primary method . 16
6.2 Instrument and equipment for the primary method . 17
6.2.1 Electronic balance . 17
6.2.2 Soxhlet extractor . 17
6.2.3 Thimble . 17
6.2.4 Heating apparatus . 17
6.2.5 Handling apparatus. 18
6.2.6 Solvent . 18
6.3 Specimen preparation for the primary method . 18
6.3.1 Sampling and storage . 18
6.3.2 Preparation procedures . 18
6.4 Test requirements for the primary method – Environment requirements . 19
6.5 Test procedure for the primary method . 19
6.6 Calculation and expression of the results for the primary method . 19
7 Test report . 19
Annex A (informative) Limitations of the primary and secondary measurement methods
...................................................................................................................................... 21
Bibliography . 23

Figure 1 – Example result for the DSC residual enthalpy method . 12

Figure 2 – Location of temperatures and temperature ranges used in the melt/freeze DSC
method . 13
Figure 3 – Example of the temperature bounds applied for an automated software
integration algorithm . 14
Figure 4 – Representation of the measurement profile for an EVA test specimen . 16

Table 1 – Summary of the results for the example measurements shown in Figure 2 . 14

– 4 – IEC 62788-1-6:2017 © IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT PROCEDURES FOR MATERIALS USED
IN PHOTOVOLTAIC MODULES –
Part 1-6: Encapsulants – Test methods for determining
the degree of cure in Ethylene-Vinyl Acetate

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in
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6) All users should ensure that they have the latest edition of this publication.
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arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62788-1-6 has been prepared by IEC technical committee 82: Solar
photovoltaic energy systems.
The text of this standard is based on the following documents:
FDIS Report on voting
82/1197/FDIS 82/1231/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62788 series, published under the general title Measurement
procedures for materials used in photovoltaic modules, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 62788-1-6:2017 © IEC 2017
MEASUREMENT PROCEDURES FOR MATERIALS USED
IN PHOTOVOLTAIC MODULES –
Part 1-6: Encapsulants – Test methods for determining
the degree of cure in Ethylene-Vinyl Acetate

1 Scope
This part of IEC 62788 defines the terminology, test equipment, test environment, specimen
preparation, test procedures, and test report for measuring the degree of cure of Ethylene-Vinyl
Acetate (EVA) encapsulation sheet used in photovoltaic (PV) modules. The differential scanning
calorimetry (both residual enthalpy and melt/freeze protocols) and gel content methods are
included herein. This procedure can be used by material- or module-manufacturers to verify that
the cross-linking additive is present and is active. The procedure can also be used to verify the
module manufacturing (lamination) process for the purposes of quality- and process-control.
The procedure can also be used to assess the uniformity of the EVA formulation within a roll as
well as to compare variation of the EVA formulation from roll to roll. This procedure can be
applied to uncured or recently cured EVA sheet as well as uncured or recently cured EVA from
PV modules.
This test procedure can also be applied to cross-linking ethylenic co-polymers other than EVA.
The temperatures identified for the calorimetry measurements in this procedure have been
optimized for EVA. Therefore, if the test procedure is applied to other encapsulation materials,
the range of the test temperatures can have to be adjusted based on the active temperature of
the curing agent and/or the melt/freeze temperature of the base material.
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.
IEC 61215-1, Terrestrial photovoltaic (PV) modules – Design qualification and type approval –
Part 1: Test requirements
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration
laboratories
ISO 291:2008, Plastics – Standard atmospheres for conditioning and testing
ISO 6427:2013, Plastics – Determination of matter extractable by organic solvents
(conventional methods)
ISO 11357-1:2009, Plastics – Differential scanning calorimetry (DSC) – Part 1: General
principles
ISO 10147:2011, Pipes and fittings made of crosslinked polyethylene (PE-X) – Estimation of the
degree of cross-linking by determination of the gel content
ASTM D2765-11, Standard test methods for determination of gel content and swell ratio of
crosslinked ethylene plastics
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
NOTE Calculations related to these definitions are given in 5.5.
3.1
degree of cure
G
unitless parameter that characterizes the extent of cross-linking within EVA
Note 1 to entry: Unlike the cross-link density, which is a physical quantity defined by the theory of rubber elasticity,
the degree of cure in a polymer may be assessed by any experimental method that distinguishes partially cured
specimens with respect to one another or with respect to a reference material. The degree of cure can be correlated
to the gel content, which is the mass percentage of insoluble material (assumed to be cross-linked) within the
specimen.
3.2
heat flow
Q
thermal flux across a specified area in the direction of a temperature gradient, W
–1
Note 1 to entry: The specific heat flow, q, is defined as the thermal flux per unit mass of the specimen, W g .
3.3
differential scanning calorimetry
DSC
thermoanalytical technique described in ISO 11357-1, in which the difference in the amount of
heat flow required to change the temperature of a material specimen and a reference is
measured as a function of temperature or time
Note 1 to entry: Both the specimen and reference are maintained at nearly the same temperature during DSC
characterization. DSC may be applied to quantify the amount of heat generated or absorbed during the processing
(curing) of EVA. The effects of cross-linking, which occur from changes in the molecular structure of the EVA, may also
be examined using DSC at the phase transitions (glass transition, melting point, and crystallization temperature). The
determination of the phase transition temperatures is described in ISO 11357-2 and ISO 11357-3.
3.4
differential scanning calorimeter
instrument used to measure the heat flow difference between the test crucible (containing the
specimen) and reference (typically empty) crucible
3.5
gel content
percentage of mass content of polymer insoluble in a specified solvent after extraction according
to the specified test conditions
Note 1 to entry: The gel is typically composed of insoluble cross-linked material.
4 Principle
The degree of cure of EVA may be quickly inferred using a "secondary method", such as
differential scanning calorimetry (DSC, ISO 11357-1), described in Clause 5. Established
alternative secondary methods, as identified in Annex A, or specialized equipment may also be
used directly for the purpose of manufacturing and quality control. When the results of the

– 8 – IEC 62788-1-6:2017 © IEC 2017
secondary method are to be compared between different institutions, they shall be calibrated
using a slower, more universal "primary" method, the gel content test as described in Clause 6,
similar to the procedures described in ISO 6427, ISO 10147 and ASTM D2765. The primary
method may also be applied for research and development when the results of the secondary
method are to be compared between formulations of EVA. A test procedure for the primary
method is described in Clause 6. The results of the primary or secondary methods may be
correlated to the module qualification tests (IEC 61215 series) or additional field durability data
to identify the minimum degree of cure necessary. Examples correlating between the secondary
and primary methods may be found in the bibliography of Annex A.
The DSC measurements for EVA may be interpreted based on the enthalpy of the cross-linking
reaction or the characteristics of the melt/freeze transition as described in 5.5. Because the
melt/freeze transition does not depend on the concentration of residual peroxide, the DSC
melt/freeze method may be applied to specimens obtained from fielded modules. Limitations of
the primary and secondary methods are discussed in Annex A.
5 DSC secondary method
5.1 Instrument and equipment for the secondary method
5.1.1 General
References for the application of the DSC method are provided in Annex A.
5.1.2 Electronic balance
The micro balance should have a measurement resolution of at least 0,01 mg, and a maximum
range of at least 20 mg.
5.1.3 Differential scanning calorimeter
5.1.3.1 The calorimeter should have a temperature accuracy of at least ±0,1 °C, temperature
precision of at least 0,01 °C, calorimetric accuracy of at least ±0,5 % (or 0,2 mW), calorimetric
sensitivity of at least 2 µW, and calorimetric repeatability of at least ±0,5 %.
–1
5.1.3.2 The oven heating/cooling rate should be adjustable between 5 °C min and
–1 –1
30 °C min measured with a thermometric accuracy of at least ±0,1 °C min .
5.1.3.3 The baseline drift (absolute value of signal change between the two integration limit,
for an empty cell) should be less than 50 µW, for the temperature range from –50 °C to 250 °C.
5.1.3.4 The baseline curvature (the biggest deviation from the integration baseline) should
be less than 50 µW, for the temperature range from –50 °C to 250 °C.
5.1.4 Instrument calibration
The instrument should be calibrated routinely according to the instrument manufacturer’s
specification, using the instrument supplier’s recommended calibration methods. Accuracy
calibration should be performed using standard substances, for example, indium or tin, as the
temperature and heat-flow verification material. Sapphire may be used to quantify the baseline
(curvature) of the instrument drift. The instrument should specifically be recalibrated if the test
rate, type of pan, or test atmosphere has been changed before DSC measurements.
NOTE The importance, performance, and considerations related to DSC instrument calibration are described further
in D. Chen, A. Green, D. Dollimore, "DSC: the Importance of Baseline Calibration", Thermochimica Acta, 284 (2), 1996,
429–433.
5.2 Specimen preparation for the secondary method
5.2.1 Sampling and storage
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 and fabrication batch.
5.2.1.2 Additional experimentation shall be performed using uncured EVA to establish a
baseline for the uncured state (for both the DSC residual enthalpy and melt/freeze methods) and
a previously cured ("maximum cured") EVA used to establish a baseline for the final cured state
(for the melt/freeze method).
If the experiment is intended to monitor a production process, the "maximum cured" samples
should be taken from a laminated module or test sample subjected to the thermal history used in
lamination. If the experiment is intended to monitor the complete consumption of peroxide
(which often does not occur during the lamination of a PV module), additional processing (time
or temperature) may be required.
5.2.1.3 Operators should wear clean gloves when preparing and handling samples.
5.2.1.4 When storage is required, the EVA should be packaged in a marked, sealed bag for
later use.
5.2.1.5 Specimens should be kept dry (stored at below 50 % relative humidity), maintained
at ambient temperature, and not exposed to light.
It is recommended to verify that the results of the secondary method do not change with storage
time.
5.2.2 Preparation procedures
5.2.2.1 Weigh the empty specimen crucible and empty reference crucibles.
The use of aluminium crucibles is recommended for use with EVA.
5.2.2.2 Prepare EVA specimens 5 mg to 9 mg in size (or of a size recommended by the DSC
instrument manufacturer), obtained from a single sheet of material. The accuracy of the
measurement of the specimen mass should be at least 1 %.
5.2.2.3 A minimum of 2 samples shall be used from each roll of EVA for process control.
5.2.2.4 Place each specimen in a separate crucible, and seal the crucible with a lid.
A non-hermetic aluminium crucible meets the requirement for this test.
The final geometry, specifically the flatness of bottom surface of the crucible, can affect its
thermal contact to the instrument, which is critical to the measurement. If the crucible geometry
is compromised during preparation, the specimen should be discarded.
If the specimen or lid is not well seated relative to the crucible, it will affect the measurement,
and the specimen should be discarded.
5.2.2.5 Record the measured mass of each specimen and its crucible.
5.3 Test requirements for the secondary method
5.3.1 Environment requirements
The recommended laboratory environment of (25 ± 2) °C and the relative humidity of (50 ± 5) %
shall be used, as in ISO 291.
– 10 – IEC 62788-1-6:2017 © IEC 2017
DSC tests should be performed using a dry inert carrier gas, such as nitrogen, in the DSC
-1
instrument. The gas flow rate shall be specified by the user, for example, (50 ± 5) ml·min . The
purity of gas should be at least 99,99 %.
5.3.2 Parameter settings (residual enthalpy method)
The following test parameters are recommended for use during the DSC residual enthalpy
method:
–1
Data acquisition rate: 5 Hz (0,2 s⋅point );
Initial temperature: 25 °C;
End temperature: 225 °C;
–1
Heating rate: 10 °C⋅min .
The completion of the peroxide reaction may be verified using a second thermal cycle (cool to
25 °C and reheat to 225 °C). The residual enthalpy for maximum cured EVA should be
–1
< 0,1 J·g during this second thermal cycle.
5.3.3 Parameter settings (melt/freeze method)
The following test procedure is recommended for use during the DSC melt/freeze method:
–1
Data acquisition rate: 5 Hz (0,2 s⋅point );
Initial temperature: 25 °C;
–1
Heat to 100 °C at the rate of 10 °C⋅min ;
–1
Cool to –20 °C at the rate of 10 °C⋅min .
Care should be taken to ensure that the heating used to melt the specimen and erase
structure-related effects is limited to temperatures less than that capable of activating the
peroxide. If a reaction is evident in the data profile for heating, a temperature less than 100 °C
should be used.
5.3.4 Parameter settings (combined enthalpy and melt/freeze method)
The following test procedure (with no dwell time occurring between the separate steps) is
recommended for performing the DSC enthalpy and melt/freeze characterization on the same
specimen, in a single test:
–1
Data acquisition rate: 5 Hz (0,2 s⋅point );
Initial temperature: 25 °C;
–1
Heat to 100 °C at the rate of 10 °C⋅min ;
–1
Cool to –20 °C at the rate of 10 °C⋅min ;
–1
Heat to 225 °C at the rate of 10 °C⋅min .
Additional data obtained after cooling from 225 °C, can be used for the "maximum cured"
reference specimen required for the DSC melt/freeze method. To make use of the combined
DSC method to also obtain data for the maximum cured reference specimen, cooling should be
–1
carried out to –20 °C at the rate of 10 °C⋅min , so that the freeze transition is accurately
characterized after thoroughly curing the test specimen in the calorimeter. If the maximum cured
reference specimen is measured after the combined DSC characterization of a set of EVA
specimens, the specimens with the greatest previous thermal history (temperature and time)
should be used, to ensure that the EVA is thoroughly cured.

5.4 Test procedure for the secondary method
5.4.1 The DSC tests shall be carried out as follows.
5.4.2 The test parameters in 5.3.2 shall be used for the DSC residual enthalpy method; the
test parameters in 5.3.3 shall be used for the DSC melt/freeze method; or the test parameters in
5.3.4 shall be used for the combined DSC residual enthalpy and melt/freeze methods.
5.4.3 Confirm the furnace (flange) temperature for the calorimeter is in a safe temperature
range, and open the lid.
5.4.4 Place the specimen crucible and the empty reference crucible in the oven, and close
the lid.
5.4.5 Specify the mass of the specimen and reference crucible to the calorimeter and initiate
the test. An isothermal hold at the endpoints of the test segments within the method (i.e., initial,
hot, or cold temperatures) shall not be used for the residual enthalpy, melt/freeze, or combined
methods. In order to obtain the most consistent results, it is recommended to use the same test
method (residual enthalpy, melt/freeze, or combined) for the purpose of process control or other
sample comparison.
5.4.6 Remove the crucibles from the calorimeter at the end of test.
It is suggested that the specimen(s) be weighed after the test, which may be compared to the
initial mass to verify the integrity of the crucible. The final weights of the specimen(s) may also
be used to confirm the specimen identity.
5.4.7 Record test data, and calculate the degree of cure according to the method in 5.5.
5.5 Calculation and expression of the results for the secondary method
5.5.1 Enthalpy method
The degree of cure for the DSC residual enthalpy method shall be calculated using Formula (1):
h − h
u t
G = 100
(1)
e
h
u
In the formula, G represents the degree of cure for the enthalpy method, %; h , the measured
e u
–1
specific enthalpy of EVA of an uncured reference specimen, J·kg ; and h , the measured
t
–1
specific enthalpy of EVA of the test specimen, J·kg .
The specific enthalpy shall be determined using the instrument software from the integral of the
measured heat flow, using the limits of integration from 100 °C to 200 °C for the specified
heating rate. The specific enthalpy for the test specimen may include multiple peaks within the
bounds of integration.
An example result is shown in Figure 1, where an offset has been added to q to distinguish the
test and reference data profiles. As in Figure 1, the degree of cure, G , for the test specimen in
e
the figure is 87,6 %.
– 12 – IEC 62788-1-6:2017 © IEC 2017
–100
Reference specimen (uncured)
–200
–300
–3 –1
h = 15,400 × 10 J • kg
u
–400
–500
–3 –1
h = 1,914 × 10 J • kg
t
–600
Test specimen (cured)
–6
–700 × 10
10 20 40 60 80 100 120 140 160 180 200 220 230
T, temperature (°C)
IEC
Figure 1 – Example result for the DSC residual enthalpy method
The data profiles (with an offset added to the specific heat flow to distinguish the data) are
shown for a cured test specimen and an uncured reference specimen.
The presence of contamination (from backsheet or other materials) may be verified from the
data profile. Contamination will result in unexpected peaks within the data profile, which should
be noted in the test report.
5.5.2 Melt/freeze method
5.5.2.1 Determination of the degree of cure
The analysis for the DSC melt/freeze method considers three parameters within the measured
data: the maximum of the crystallization (freeze) temperature, the extrapolated onset of the
crystallization temperature, and the concavity of the data profile below the crystallization
temperature (assessed using a quantitative shape factor). The DSC melt/freeze method may be
applied to any EVA specimen, regardless of its thermal history (including EVA from fielded
modules), to quantify its degree of cure. The degree of cure for the DSC melt/freeze method
shall be calculated from Formulas (2) to (5):
G + G + G
 
c o SF
G =
 
(2)
a
 
T − T
c,u c,t
G = 100
c (3)
T − T
c,u c,m
T − T
o,u o,t
G = 100
o (4)
T − T
o,u o,m
–1
q, specific heat flow (W • kg )

SF − SF
u t
G = 100
(5)
S,F
SF − SF
u m
represents the average value for the degree of cure from the DSC
In the formulas, G
a
melt/freeze method, %; G represents the degree of cure determined for the change in the
c
maximum of the crystallization temperature, %; G represents the degree of cure determined for
o
the change in the temperature extrapolated at the onset of the crystallization, %; and G
SF
represents the degree of cure determined for the change in the concavity of the data profile
below the crystallization temperature, %. In the formulas, the subscript –a refers to the average
(numerical mean); –c, the maximum crystallization temperature; –o, the extrapolated
temperature at the onset of the crystallization; –SF, the concavity of the data profile below the
crystallization temperature (evaluated using a shape factor – See 5.5.2.2); –t, the cured test
specimen; –m, the previously laminated ("maximum cured") reference EVA specimen; and –u,
a reference EVA specimen with no prior thermal history ("uncured").
Figure 2 shows an example, where the applicable temperatures (T and T ) and temperature
c o
range for the shape factor are identified in the figure for the test specimen. The data is shown for
specimens of the same EVA formulation, so that the effects of the curing process are evident. An
offset has been added to q to distinguish the test and reference (uncured and maximum cured)
data profiles.
0,001 5
0,001 4
0,001 3
0,001 2
T
c
0,001 1
Maximum cured
0,001 0
0,000 9
0,000 8
T Test specimen
o
0,000 7
SF
0,000 6
0,000 5
Uncured
0,000 4
0,000 3
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
T, temperature (°C)
IEC
Figure 2 – Location of temperatures and temperature ranges
used in the melt/freeze DSC method
The data profiles (with an offset added to the specific heat flow to distinguish the data) are
shown for test and reference specimens.
The results shown in Figure 2 are summarized in Table 1. The values, determined from
Formulas (2) to (5), are provided as an example. Table 1 formally demonstrates the required
data (temperature and shape factor values) and corresponding results for the DSC melt/freeze
method.
–1
q, specific heat flow (W • kg )

– 14 – IEC 62788-1-6:2017 © IEC 2017
Table 1 – Summary of the results for the example
measurements shown in Figure 2
SPECIMEN T T SF
c o
%
°C °C
MEASUREMENTS
n, uncured reference 42,3 54,4 79,9
f, maximum cured reference 32,0 37,2 63,7
t, test 33,7 40,3 66,4
G G G G
a c o SF
% % % %
RESULTS
83,0 83,4 82,4 83,1
For software equipped DSC instruments, an integration algorithm may be used to automatically
determine T and T . The choice of the upper-limit and lower-limit bounds for the integration
c o
operation can, however, affect the T and T values. To achieve repeatable results, it is
c o
recommended that the user check for repeatability of the T and T values given by the software,
c o
which can be done by manually varying the limits for the integration. The following steps, which
should apply for a broad variety of EVA specimens, are recommended for the automated
determination of T and T .
c o
i) The upper-limit temperature (T , °C) shall be fixed by taking the approximate T value
ul c
(based on visual inspection of the measured thermogram), and adding 15 °C, as shown in
Figure 3. T should fall within the flat region in the thermogram that precedes the
ul
crystallization peak during cooling. After the integration analysis, T , should be greater than,
ul
but located near T .
o
ii) Once T , has been assigned, the lower-limit temperature bound (T , °C) may be determined
ul ll
by using the software to draw a horizontal line from T down to the temperature intersecting
ul
the data profile in the thermogram, Figure 3. For EVA, T will typically fall in the range from
ll
–20 °C to –10 °C.
T = 49,4
c
T = –18
ll
T = T + 15 = 64
ul c
T = 60,1
o
–20 –10 0 10 20 30 40 50 60 70 80
T, temperature (°C)
IEC
Figure 3 – Example of the temperature bounds applied
for an automated software integration algorithm
–1
q, specific heat flow (W • kg )

5.5.2.2 Determination of the concavity
5.5.2.2.1 The empirical shape factor, characterizing the concavity of the crystallization peak
shall be calculated using the following algorithm.
Select all (T, Q) data points between T and (T – 20 °C).
c c
–1
5.5.2.2.2 Calculate the inverse heat flow, Q , for all data points.
–1
5.5.2.2.3 Calculate the product, T·Q , for all data points.
–1
5.5.2.2.4 Identify the coordinates, [T, T·Q ]max, for which the product reaches a maximum.
5.5.2.2.5 Calculate the shape factor from Formula (6):
−1
[T ⋅Q ]max
SF = 100
(6)
 
−1
T ⋅ Q
 
c
 
Tc − 20
Either the heat flow, Q, or specific heat flow, q, may be used in the concavity analysis.
Figure 4 shows an example of the determination of the shape factor. The measurement profile
from the DSC instrument for an EVA test specimen is shown at the top of the figure. The
determination of the shape factor is performed from the analysis in 5.5.2.2.1. The region of
examination of the shape factor (SF) is identified in both parts of the figure. The maximum of the
–1 –1
product of T and Q , [T·Q ] , is labelled in the bottom of the figure, along with: the
max
–1 –1
temperature at [T·Q ] , T ; the inverse heat flow at T , Q ; the
max [T·Q]max [T·Q]max [T·Q]max
–1
maximum crystallization temperature, T ; and the inverse heat flow at (T – 20 °C), Q .
c c T – 20
c
–1 –1
The shape factor of 66,9 % is determined for T = 27,4 °C, Q = 0,336 mW ,
[T·Q]max [T·Q]max
–1 –1
T = 32,1 °C, and Q = 0,429 mW .
c Tc – 20
– 16 – IEC 62788-1-6:2017 © IEC 2017
T = 32,1
c
3,5
2,5
SF
1,5
0 10 20 30 40 50 60 70
T, temperature (°C)
0,5 12
–1
–1 (T • Q )
Q
max
Tc–20
0,45
–1
Q
0,4
–1
Q
(T•Q)max
–1
T • Q
0,35
SF
0,3
T T
(T•Q)max c
0,25 0
0 5 10 15 20 25 30 35
T, temperature (°C)
IEC
Figure 4 – Representation of the measurement profile for an EVA test specimen
5.6 Uncertainty of measurements for the secondary method
When multiple specimens are examined from the same encapsulation sample or module
fabrication batch, the uncertainty of measurements for DSC should be reported for a 95 %
confidence interval.
6 The primary method
6.1 Principle for the primary method
The results from the DSC residual enthalpy and melt/freeze methods may vary according to the
formulation (additives present), molecular weight (M ) or vinyl acetate content (VaC) of the EVA.
w
The DSC residual enthalpy method could also readily vary with the type and concentration of
peroxide originally present in the EVA. A more absolute method of assessing the degree of cure
is desired, because the DSC methods provide "secondary" results, i.e., the results depend on
the make of EVA examined. The method of "gel content analysis" also characterizes the degree
of cure, providing results that may be interpreted more universally. To clarify the gel content
–1 –1
Q , inverse heat flow (mW ) Q, heat flow (mW)
–1 –1
T • Q , Product (°C • mW )
method does not measure the degree of cure directly, but is used to infer the degree of cure
based on the solubility of the material that is not cross linked. The gel content test may be
applied to any EVA specimen, regardless of its thermal history (including EVA from fielded
modules), to quantify its degree of cure. Some of the limitations for the primary method for the
gel content test, described in Annex A, are addressed by the standardized test procedure for the
primary method.
6.2 Instrument and equipment for the primary method
6.2.1 Electronic balance
An electronic balance shall be used with a measuremen
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