The solar cell backplane is located at the outermost layer on the back of the module and protects the solar module against moisture in the outdoor environment, generally with a three-layer structure. The outer protective layer has good resistance to environmental corrosion (prevents water vapor erosion, UV resistance, etc.) , The middle layer of PET polyester film has good insulation properties and strength, the inner film PEVA or PE and EVA film has good bonding properties.
First, the thickness
For different materials, the resulting product thickness is not the same, in order to achieve a certain insulating properties, PET thickness of 250μm in general, PVDF film thickness of 25μm, PEVA film thickness of 70μm, the thickness of the two adhesive are So the thickness of solar backplane KPK 320 ± 10μm, KPE thickness of 365 ± 10μm.
Detection method: Thickness gauge material thickness.
Second, tensile strength, elongation at break, peel strength and so on
1, Tensile strength (divided into MD, TD):
The maximum load at the time of breaking of the backplane sample is different, and for different thickness and different materials, the backplane has different tensile strength.
2, elongation at break (divided into MD, TD):
The maximum elongation of the backplane specimen at breakage has different elongation at break for different thickness and different material backsheets.
3, the initial layer of peel strength (points MD, TD and the first and second):
The bond strength between the layers of the test backsheet is most commonly ≥4 N / cm (1 N / cm = 1000 Pa).
4, after boiled layer peel strength (points MD, TD and the first and second):
After placing the backsheet in a boiling water bath for 24 hours, the bond strength between the layers of the backsheet was tested, the most common standard being ≥4 N / cm (1 N / cm = 1000 Pa) , Wrinkles, stratification and other undesirable phenomena.
5, back sheet and EVA film laminated peel strength:
Test backsheet and EVA film laminating bond strength, this test is to simulate the status of the production of components, different back sheet and different EVA adhesive bond strength between a certain gap, but the general standard is ≥ 40N / cm.
Test Method: Take a piece of tempered glass with a length of about 300mm and a width of 150mm, laminate the same size of backsheet and EVA on the toughened glass in the laminating machine, lamination and lamination for 4 hours at room temperature Above, the cured piece was cut into strips of 1 * 300mm. Take a few of them were manually separated from the EVA backplane about 20mm, the sample was fixed on the tensile testing machine, the speed of 100mm / min 180 ° peel , Each stripping 100mm, record the data, the test results to the median data.
Tensile strength, elongation at break, and peel strength were measured by a tensile tester.
Third, the dimensional stability (heat shrinkage)
5%. MD, TD, the back plate baking at 150 ℃ for half an hour after the test its shrinkage in the length and width direction of the more common standard of less than or equal to 1.5%.
Fourth, water vapor transmission rate
Detection methods: There are three detection methods, respectively cup method, electrolysis, infrared method, electrolysis industry is more common photovoltaic.
Electrolytic water vapor transmission rate detection method: the pre-processed sample is fixed in the middle of the test chamber The test chamber points up and down the two chambers, the relative humidity of the gas flow in the upper chamber of the film, the drying gas flow in the lower chamber The water molecules diffuse through the sample to the dry gas on the other side and are carried by the flowing gas to the sensor. The water vapor transmission rate is calculated by analyzing the water vapor concentration measured by the sensor.
Fifth, the light transmittance
According to GB2410-80 "Transparent plastic light transmittance and haze test method" is the standard method for the determination of the transmittance of EVA film, the test equipment selected in this standard is an integrating sphere haze meter, and the other can achieve the same result Test equipment can also be used.
