FIRST Normal Series EVA Film F806P (UV cut-off)

FIRST Normal Series EVA Film F806P (UV cut-off) is a cross-linkable ethylene-vinyl acetate encapsulant supplied in roll form for photovoltaic module lamination. The normal-cure designation separates it from fast-cure grades by requiring a lamination press residence of 10 min to 15 min at 145 °C to 155 °C for gel fractions above 80 % depending on module construction and cell-plane temperature. The UV cut-off additive package shifts the onset of ultraviolet transmission to approximately 360 nm, absorbing shorter wavelengths that otherwise degrade polyamide backsheet layers and ionomer edge seals. Nominal roll dimensions are 0.45 mm thickness, 1000 mm width, and 150 m length; 0.50 mm and 0.60 mm thicknesses are supplied for thick-cell or glass-glass gap control. Density before crosslinking is typically 0.95 g/cm³ to 0.96 g/cm³. Melt flow rate, measured according to ISO 1133-1:2022 at 190 °C with a 2.16 kg piston load, is held in the 20 g/10 min to 30 g/10 min range during film extrusion; batch-specific certificates of analysis control incoming inventory because moisture uptake and storage temperature shift melt viscosity. The grade is used as the front-side encapsulant in crystalline-silicon modules where UV cut-off is required for rear-side protection, and as the rear-side encapsulant in glass-glass modules when paired with a high-transmittance front encapsulant.

The UV cut-off function is achieved by compounding the EVA with an absorber that attenuates wavelengths below 360 nm without converting absorbed UV into long-lived chromophoric by-products at the front glass interface. The practical effect in module lamination is a reduction in ultraviolet irradiance reaching the cell encapsulation backside and the backsheet internal surface. For a laminated coupon of 0.45 mm F806P between 2 mm low-iron glass and a clear backsheet, spectrophotometric transmittance is below 1 % at 340 nm and rises to the visible plateau between 400 nm and 500 nm. Published data for this specific configuration is limited at wavelengths below 300 nm because glass absorption and surface reflectance dominate the measurement.

Incoming inspection of F806P rolls should include thickness profiling at three positions across the web with a contact micrometer, not less than 0.45 mm ± 0.02 mm for the standard build. Roll width tolerance is typically ±5 mm. Spectral transmittance of a single-layer film sample can be measured with an integrating-sphere spectrophotometer according to IEC 62788-1-1:2020; the 340 nm transmittance is the most sensitive incoming marker for UV absorber concentration drift. A shift of the cut-off edge to 380 nm indicates an over-addition or degradation of the absorber masterbatch and will reduce short-circuit current without improving rear-side protection. Conversely, a cut-off edge below 350 nm indicates under-addition and may fail the customer’s UV-blocking specification. The visual emboss pattern should be uniform across the roll; any streak visible under low-angle inspection suggests melt-temperature non-uniformity at the die lip and may correlate with gel fraction scatter after lamination.

How Does the UV Cut-off Additive Package Shift Transmission, Haze, and Yellowness?

Optical acceptance testing of F806P film is performed on laminated coupons using IEC 62788-1-1:2020 for transmittance and yellowness index, with haze measured by ASTM D1003-13. Typical luminous transmittance across the 400 nm to 1100 nm band is 91.5 % to 93.0 % after lamination, compared with 92.5 % to 94.0 % for high-transmittance EVA. Haze before lamination is dominated by the emboss pattern; after melt collapse and cure, haze typically falls to 5 % to 8 %. Yellowness index after damp-heat exposure at 85 °C and 85 % relative humidity for 1000 h is specified below 2.0. The UV cut-off edge is not a step function; transmittance at 350 nm is below 2 %, transmittance at 380 nm is typically 70 % to 85 %, and transmittance at 500 nm is above 91 %.

By comparison, high-transmittance EVA uses a less aggressive UV absorber loading and begins transmitting at 320 nm to 330 nm, which supports blue response in bifacial cells but increases rear-side UV dose. White EVA contains a reflective filler that raises rear-side reflectance above 80 % between 450 nm and 1100 nm, making it unsuitable as a front-side layer but useful for light reuse at the rear of monofacial cells. F806P therefore occupies an intermediate optical position: it preserves high visible transmittance while removing the UV component that contributes to backsheet and edge-seal degradation.

Lamination line trials on a two-chamber vacuum laminator with independent upper and lower chamber control have shown that F806P tolerates a cell-plane temperature range of 138 °C to 155 °C without gross bubble formation, provided the vacuum hold is not shortened below 300 s. The melt phase begins between 70 °C and 80 °C; full melt saturation over the cell fingers requires a minimum platen contact time of 240 s before the cure plateau. The film’s embossed surface requires a vacuum ramp from 0.1 MPa to 0.08 MPa during the first 180 s to permit air evacuation between glass and cell string. If chamber pressure is released before the melt phase fills the cell gaps, edge voids appear at busbar transitions where the cell-to-glass gap changes by 0.2 mm to 0.3 mm. Production-scale failures are most commonly observed when a laminator is converted from a fast-cure EVA with a shorter cure plateau; the normal-cure peroxide package in F806P requires the full 10 min to 12 min plateau. Shorter dwell times produce gel fractions of 65 % to 75 % rather than the specified 80 % minimum, which increases creep at the module edge and reduces mechanical load resistance. Rolls stored outside sealed barrier bags at relative humidity above 60 % for more than 24 h should be pre-dried at 40 °C for 4 h before lamination; otherwise, absorbed water can generate steam bubbles during the early melt phase. The film should not be combined with amine-cured backsheet adhesives unless peel testing has confirmed compatibility, because amine species can interfere with silane coupling at the EVA/backsheet interface.

Cure Kinetics, Gel Fraction, and Long-Term Adhesion Boundaries

Crosslinking of F806P proceeds through peroxide decomposition during the lamination plateau. The peroxide initiator used in normal-cure EVA has a one-hour half-life temperature in the range of 135 °C to 145 °C, depending on the precise peroxide formulation. Gel fraction after standard lamination, measured by xylene extraction per ASTM D2765-16, is typically 80 % to 90 %. Values below 70 % indicate undercure and correlate with reduced shear modulus after thermal aging. The glass-side adhesion after lamination and 24 h conditioning at 23 °C is typically above 40 N/cm by 180° peel testing; backsheet-side adhesion is typically above 30 N/cm, but the exact value depends on backsheet primer chemistry and surface treatment. Volume resistivity measured according to IEC 62788-1-3:2020 is typically above 1.0 × 10^14 Ω·cm after lamination at 1000 V DC and 23 °C. The film has higher water vapor transmission than polyolefin elastomer encapsulants; for a 0.45 mm cured film, the water vapor transmission rate at 38 °C and 100 % relative humidity is in the 20 g/(m²·day) to 30 g/(m²·day) range. This property limits the use of F806P as the sole moisture barrier in thin-film modules, but it is acceptable in conventional glass-backsheet packages where the backsheet and glass provide the primary moisture resistance.

Elongation at break of the cured film, measured by ASTM D638-14 at 500 mm/min, is typically above 400 %, and tensile strength is typically above 15 MPa. These values change after 1000 h damp-heat exposure; the manufacturer should supply aged coupon data for each lot when the film is used in IEC 61215-1:2021 qualification programs.

When F806P Replaces Fast-Cure or High-Transmittance EVA in Module Lamination

Replacement of a fast-cure EVA with F806P requires extension of the lamination plateau by 5 min to 8 min on single-chamber lines that run a 145 °C platen setpoint. This is the most frequent process conflict in mixed-production facilities because cycle-time targets are ordinarily fixed for fast-cure encapsulants. If the plateau extension cannot be accepted, a higher platen temperature of 155 °C to 160 °C may compensate, but the upper limit is set by backsheet heat-shrink characteristics and the cell string’s solder paste. At platen temperatures above 160 °C, the tensile strain mismatch between the EVA and the backsheet can induce warp after cool-down.

The use of F806P on the front side instead of a high-transmittance grade reduces the short-circuit current of a crystalline-silicon module by approximately 0.5 % to 1.5 % relative to a high-transmittance front encapsulant, because the UV cut-off edge absorbs part of the blue-UV transition region. This current loss is accepted in applications where backsheet UV protection or aesthetic consistency is the higher priority. When F806P is placed on the rear side of a glass-glass bifacial module and a high-transmittance EVA or polyolefin elastomer is used on the front side, the rear UV dose is reduced without a measurable loss in front-side collected current. The rear-side UV cut-off can reduce UV-induced discoloration of rear-side coatings and encapsulant/glass edge interfaces, but published data for this specific configuration is limited.

For white EVA replacement, F806P does not provide rear-side reflectance; it should not be used as a direct substitute when the cell gap is designed to recover light by scattering from a white rear encapsulant. Compared with a polyolefin elastomer, F806P processes on standard EVA lamination lines with lower platens and shorter ramps, but it has higher water vapor transmission and lower volume resistivity after damp heat. Substitution is reviewed only where UV cut-off below 360 nm is an explicit specification and where the laminator thermal profile can hold 145 °C to 155 °C for the normal-cure plateau.