IEC TS 62788-2:2017

IEC TS 62788-2 ®
Edition 1.0 2017-08
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –
Part 2: Polymeric materials – Frontsheets and backsheets
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IEC TS 62788-2 ®
Edition1.0 2017-08
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –

Part 2: Polymeric materials – Frontsheets and backsheets

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-4673-3

– 2 – IEC TS 62788-2:2017 © IEC 2017
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 13
4 Test procedures . 16
4.1 General . 16
4.2 Mechanical characteristics . 17
4.2.1 General . 17
4.2.2 Thickness . 17
4.2.3 Area weight . 18
4.2.4 Tensile strength / elongation at break . 19
4.2.5 Curling . 22
4.3 Adhesion testing . 22
4.3.1 Purpose . 22
4.3.2 General . 22
4.3.3 Sample preparation . 23
4.3.4 Sample conditioning . 24
4.3.5 Apparatus and procedure . 24
4.3.6 Adhesion tests for interfaces of backsheet and frontsheet . 24
4.3.7 Reporting requirements . 27
4.4 Thermal characteristics . 28
4.4.1 Thermal endurance . 28
4.4.2 Dimensional stability . 28
4.4.3 Relative thermal expansion (CTE) . 30
4.4.4 Thermal conductivity . 31
4.5 Electrical characteristics . 31
4.5.1 Breakdown voltage . 31
4.5.2 Distance through insulation (dti) . 32
4.5.3 Comparative Tracking Index (CTI) . 37
4.5.4 Volume resistivity . 38
4.6 Optical characteristics . 39
4.6.1 General . 39
4.6.2 Specimen preparation . 40
4.6.3 Visual Inspection . 40
4.6.4 Optical transmittance of frontsheets and backsheets . 41
4.6.5 Optical reflectance of backsheets . 42
4.6.6 Yellowness index (YI) . 42
4.6.7 Colour measurement (L*, a*, b*) . 43
4.6.8 Surface gloss. 44
4.7 Diffusion characteristics . 45
4.7.1 Permeability of water vapour . 45
4.7.2 Permeability of oxygen . 46
4.8 Chemical characteristics . 46
4.8.1 Resistance to solvents . 46

4.9 Other characteristics . 48
4.9.1 Ignitability – Purpose . 48
4.9.2 Flammability – Purpose . 48
4.10 Accelerated ageing tests . 48
4.10.1 Purpose . 48
4.10.2 Damp Heat (DH) testing at elevated heat and moisture . 49
4.10.3 Weathering at elevated levels of temperature and moisture . 50
5 Uniform characterization form (UCF) . 55
5.1 General . 55
5.2 Layer stack description . 55
5.3 Material test results and reporting requirements. 56
6 Data sheet . 58
6.1 Purpose . 58
6.2 Reporting requirements . 58
7 Product identification sheet (label) . 58
Annex A (informative) Overview of adhesion testing of frontsheet and backsheet . 59
A.1 Type of adhesion failure . 59
A.2 Characteristics of adhesion peel tests . 60
A.3 Characteristics of pluck and lap-shear tests . 60
A.4 Cross-hatch tape testing . 61
A.5 Other caveats . 61
A.6 Overview . 61
Annex B (normative) Adhesive bond strength test procedures in PV context . 64
B.1 180°peel adhesion test . 64
B.1.1 Specimens . 64
B.1.2 Procedure . 64
B.1.3 Measurement . 65
B.2 T-peel adhesion test . 66
B.2.1 Sample preparation . 66
B.2.2 Procedure . 67
B.2.3 Measurement . 67
B.3 Dynamic tensile (T-pluck). 68
B.3.1 Purpose . 68
B.3.2 Principle . 68
B.3.3 Specimens . 68
B.3.4 Measurement procedure . 69
B.3.5 Final measurements . 69
B.4 Dynamic overlap shear . 70
B.4.1 Purpose . 70
B.4.2 Principle . 70
B.4.3 Specimens . 70
B.4.4 Measurement procedure . 72
B.4.5 Final measurements . 72
B.5 Cross-hatch tape test . 73
B.5.1 Apparatus . 73
B.5.2 Procedure . 74
B.5.3 Final measurements . 74

– 4 – IEC TS 62788-2:2017 © IEC 2017
Annex C (normative) DC breakdo
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