Zhejiang Feiyu FY08 EVA Film

Zhejiang Feiyu FY08 EVA Film is an ethylene-vinyl acetate copolymer encapsulant supplied as roll stock for photovoltaic module lamination. The product is positioned for glass/EVA/cell/EVA/backsheet, glass/glass, and transparent-backsheet constructions using monocrystalline or polycrystalline silicon cells. Manufacturer documentation classifies FY08 as a fast-cure grade. Roll width is typically offered up to 2,150 mm, with common thicknesses of 0.40 mm, 0.45 mm, and 0.50 mm; exact width and length tolerances appear in the lot-specific certificate of analysis. The film contains a peroxide thermal initiator, a silane adhesion promoter, and hindered-amine light stabilizers; the exact formulation is proprietary. Storage requirements specify 25 ± 5 °C, relative humidity below 60%, and ultraviolet exclusion. At relative humidity above 60%, pre-drying or desiccant-controlled staging is required because absorbed moisture is released during the vacuum step and can form edge bubbles or reduce post-lamination peel strength.

Published data specific to FY08 is limited; the following descriptions therefore distinguish between manufacturer-declared product positioning and class-typical values for fast-cure EVA encapsulants validated under the cited test methods. Exact lot-specific values for gel fraction, melt mass-flow rate, and adhesion must be taken from the supplier certificate of analysis.

What Distinguishes FY08 from Standard-Cure EVA and Thermoplastic Polyolefin Encapsulants?

Compared with a standard-cure EVA of the same thickness, the FY08 formulation is designed to reach lamination gel content within a shorter dwell window. Class-typical fast-cure peroxide packages reduce the required dwell at 150 °C from approximately 15–18 min to 8–12 min, depending on platen temperature uniformity and laminate thermal mass. The practical consequence on a single-chamber laminator with silicone bladder pressure of 0.08–0.10 MPa is higher throughput without changing the melt-flow and wetting stage. However, the faster cure also narrows the processing window: if platen temperatures exceed 155 °C before the vacuum profile completes, the film can crosslink before gas evacuation, trapping air in the cell gaps.

Relative to thermoplastic polyolefin encapsulants, EVA including FY08 exhibits stronger primerless adhesion to soda-lime float glass through silane coupling, but higher water vapor transmission and higher acetic acid generation potential under damp heat. POE grades used in glass/glass modules generally show lower water vapor transmission at 38 °C / 90% RH and higher volume resistivity after 1,000 h damp heat; published data for this specific configuration is limited because POE formulations vary by supplier. The selection between FY08 and POE therefore depends on bill of materials, warranty requirements, and rear-side moisture sensitivity.

Lamination Cycle Parameters and Crosslinking Kinetics

The crosslinking reaction of FY08-class EVA is initiated by thermal decomposition of an organic peroxide. During the lamination temperature ramp, the film passes through a minimum melt viscosity between 90 °C and 110 °C; this viscosity window must align with the vacuum and bladder pressure stages so that molten polymer flows around cell edges and busbar geometry. If the temperature ramp is too slow, the peroxide half-life at 135–145 °C permits premature crosslinking before full air evacuation. If the ramp is too fast, the film can reach 150 °C while residual air remains between the cell surfaces and the glass, producing local haze and delamination.

Gel fraction after cure is measured by solvent extraction using ASTM D2765-16; values below 70% indicate under-cure and can produce creep in service at module operating temperatures above 85 °C. Values above 90% are not necessarily beneficial because over-crosslinking can increase shrinkage stress and lower impact toughness. On a single-chamber laminator with heated platen dimensions of 3.2 m × 2.6 m, the recommended setpoint is commonly 148–152 °C at a maximum vacuum of 0.1 kPa and a bladder pressure of 0.08–0.10 MPa. Dwell time depends on total layup thickness: a glass/backsheet stack with 0.45 mm FY08 on both sides of 3.2 mm glass may reach gel content above 75% in 10–12 min; a glass/glass stack with the same encapsulant and 2.8 mm glass may require 12–14 min. Exact cycle development must be completed on the production line because platen temperature distribution and vacuum pump capacity differ between laminator models.

Batch-to-batch variation in peroxide concentration, usually controlled to ±0.05 wt%, can shift the gel time by ±90 s. For this reason, incoming material should be sampled and a cure panel prepared on the production laminator before replacement of an existing encapsulant.

Adhesion to glass and backsheet requires a silane coupling agent that migrates to the interface during the lamination dwell. For FY08-class EVA, peel adhesion above 60 N/cm on glass and above 40 N/cm on weather-resistive backsheets is typically achievable when the lamination temperature reaches 150 °C. If the backsheet surface energy is below 38 mN/m, corona or plasma treatment is required; otherwise the silane does not wet the interface and peel strength falls below 30 N/cm. The silane interface is also sensitive to condensation: storage above 60% RH without desiccant staging can hydrolyze the coupling agent and produce non-adhered edge bands. In production, the film should be handled with clean gloves to avoid fatty acid contamination, which migrates to the interface and reduces adhesion.

Volume resistivity is measured on cured film between brass electrodes with a guard ring under IEC 62788-1-2:2016. A value above 1 × 10¹⁴ Ω·cm is necessary to limit leakage current under the module qualification bias of 1,000 V. After 1,000 h damp heat at 85 °C / 85% RH, EVA films may release acetic acid, which reduces glass surface resistivity and increases electrochemical corrosion risk in cells and interconnects. FY08 is positioned by the supplier as a reduced-acetic acid fast-cure grade, but published third-party damp-heat data for this exact product is limited; module qualification should therefore include internal damp-heat and electroluminescence inspection of representative laminates.

When Module Fabricators Substitute FY08 into Existing Glass/Backsheet Stacks

Substitution into an existing lamination process is not a straight material exchange. The vacuum profile must be re-verified because the fast-cure peroxide package responds more quickly to platen temperature overshoot. In a laminator with heated platen temperature uniformity of ±2 °C, the cure window is approximately ±5 °C around the qualified setpoint; outside this band, the edge gel fraction can differ from the center by more than 10%. This is a critical threshold: edge gel content below 70% can cause delamination after 200 thermal cycles in IEC 61215-2:2021 MQT 11, while over-crosslinked center regions above 90% can crack during hail impact testing.

Processors should first qualify a single roll with a cure ladder: 145 °C, 150 °C, and 155 °C at dwell times from 8 min to 14 min. For each laminate, gel fraction, cross-sectional microscopy, and backsheet peel are recorded. If the existing laminator uses a vacuum time longer than 5 min before bladder pressurization, the peroxide may begin crosslinking before the lamination melt phase is complete; in that case, the vacuum time must be reduced to 4 min or the platen temperature lowered by 5 °C. The use of an IR pyrometer on the glass surface is recommended because the actual glass temperature lags the platen setpoint by up to 8 °C during the first 3 min.

The formulation should not be combined with amine-based backsheet primers containing active hydrogen donors; the silane adhesion promoter is prematurely crosslinked by amines and the glass-side peel strength can drop below 30 N/cm. Avoid storing FY08 near diesel exhaust or ozone-generating equipment because the unsaturated vinyl acetate segments are susceptible to ozone-induced surface oxidation.

Compliance, Incoming Inspection, and Production Handling

Incoming rolls of FY08-class EVA require inspection of width, thickness profile, visual gel particles, and surface contamination before release to the lamination line. A thickness variation of ±3% across the web can cause localized pressure nonuniformity: a 0.45 mm film at the upper tolerance can produce squeeze-out at cell edges, while a lower-tolerance film can create voids at busbar crossings. This is observed as a bubble line along the busbar after lamination. The issue is mitigated by adjusting the encapsulant layup to overlap the busbar with a second strip or by specifying a tighter thickness tolerance from the supplier.

For module qualification, the encapsulant must be evaluated within the final module laminate rather than as an isolated film. Typical sequences include visual inspection under IEC 61215-2:2021 MQT 01, insulation and wet leakage current under MQT 03, damp heat under MQT 12 at 85 °C / 85% RH for 1,000 h, and thermal cycling under MQT 11 for 200 cycles between -40 °C and 85 °C. Potential-induced degradation testing is commonly performed under IEC TS 62804-1:2015 at 85 °C / 85% RH, -1000 V, and 96 h for p-type module configurations. POE encapsulants generally provide higher PID resistance for n-type and high-efficiency cell stacks, while EVA remains acceptable for many p-type PERC modules when glass bulk resistivity and cell surface passivation are controlled.

Storage and handling limitations remain operational boundaries. Rolls should be stored horizontally or vertically on clean cores without edge compression. If the storage area exceeds 60% RH for more than 24 h, the roll edges should be dried with desiccant staging at 25 °C for 12–24 h before lamination. Once the film is removed from moisture-barrier packaging, it should be consumed within 72 h in an uncontrolled environment or within 30 days in a controlled cleanroom at 25 ± 5 °C and <50% RH. These limits prevent silane hydrolysis, backsheet adhesion loss, and vacuum-stage bubble formation on production lines.