KENGO SOLAR EVA Film

In monofacial PERC module production using 3.2 mm tempered low-iron rolled glass and a weathering-resistant polyamide backsheet, KENGO SOLAR EVA Film is processed as a crosslinkable thermoplastic interlayer. The laminate stack enters a 3-chamber oil-heated flatbed laminator with the sequence glass / EVA / cell string / EVA / backsheet. The film is fed from roll stock with a slit width matched to the glass area plus a 5–8 mm perimeter overhang. Roll storage outside desiccant-sealed bags at relative humidity above 60% requires re-drying at 70 °C for 4–6 h because absorbed moisture increases void formation at the cell-ribbon interface.

Formulation parameters in this segment typically include a vinyl acetate content between 28 wt% and 33 wt%, a silane adhesion promoter, and a peroxide curing agent selected to reach a gel fraction of 78–88% after lamination. The exact peroxide concentration is normally in the 1.0–1.5 wt% range for standard cure films and is not independently adjusted by the module maker. Cure state is verified by solvent extraction per ASTM D2765-16, while adhesion to glass is evaluated by 180° peel testing adapted from IEC TS 62788-2:2017, with a minimum cohesive failure requirement. Compliance for this architecture follows IEC 61215-1:2021, IEC 61215-2:2021, IEC 61730-1:2023, and IEC 61730-2:2023, with North American certification under UL 1703.

Lamination is conducted at a platen setpoint of 150 ± 3 °C for 12–16 min. Melt phase vacuum is held at −95 kPa gauge for 2–4 min, followed by a pressure phase at 0.4–0.6 bar chamber overpressure. The belt speed is adjusted so that the module exits below 120 °C to minimise backsheet curl. Post-lamination gel fraction below 75% indicates undercure and predicts reduced damp-heat durability; gel fraction above 90% may embrittle the film at low temperature and increase cell microcracking risk during mechanical load cycles. In-line electroluminescence after trimming identifies cell edge microcracks associated with film shrinkage, which is typically specified below 3% in machine direction after thermal conditioning at 150 °C for 20 min.

The terminal product for this segment is a glass-backsheet monofacial PERC module, typically in 144-half-cell or 120-half-cell formats with a junction box and aluminium frame. The encapsulant function is mechanical decoupling, UV absorption, and moisture barrier assistance, while the backsheet remains the primary humidity barrier. Final module quality is verified by damp heat 85 °C / 85% RH for 2000 h with power loss below 5% and backsheet adhesion retention above 80% of initial.

What Changes When a Transparent Backsheet Replaces an Opaque Polyamide Backsheet in a Glass-Glass Stack?

Glass-glass bifacial modules replace the rear opaque polyester backsheet with 2.0 mm heat-strengthened transparent glass. This architecture removes the rear-side humidity sink and raises total laminate weight, requiring the rear EVA film to carry both adhesion and optical transmittance duties. The front film may be 450 µm thick; the rear film is often reduced to 350–400 µm because the rear glass contributes mechanical stiffness. If the rear surface receives albedo irradiance, the rear encapsulant must contain an additional UV absorber package to protect the cell rear passivation. Published data for specific stabilizer loading in KENGO SOLAR EVA Film for rear-side albedo above 200 W/m² is limited; incoming film UV cut-off data per IEC 61215-2:2021 MQT 10 UV preconditioning should be reviewed before qualification.

Bifacial glass-glass formulations are adjusted with a higher crosslink density target to prevent rear-side creep in wind loading. Gel content is measured at 80–90%. The rear film may be specified with a melt flow index of 20–30 g/10 min at 190 °C / 2.16 kg per ISO 1133-1:2022 to allow rapid bubble evacuation without excessive flow into the cell gaps. Unlike opaque backsheet stacks, the edge seal is the only moisture path, so the laminated edge is trimmed with a 2–3 mm EVA overhang and then sealed with butyl or silicone tape.

Lamination occurs in a flatbed laminator with oil-heated platens at 140–150 °C and a longer press-cure cycle of 14–18 min. The symmetric glass / EVA / cell / EVA / glass layup requires a membrane press capable of ±5 °C platen uniformity to avoid wedge bond defects. Vacuum is drawn to −90 kPa gauge before platen contact; the chamber is vented at 1.0–1.2 bar during cure. After lamination, edge bubble density is inspected by optical scanner, and the module is annealed at 100 °C for 1 h to reduce interfacial stress.

The finished product is a frameless or framed dual-glass bifacial module with front and rear transparent encapsulation. Electrical safety and performance are assessed under IEC 61215-2:2021 bifacial nameplate irradiance conditions and IEC/TS 60904-1-2:2019. The laminated glass assembly must pass IEC 61730-2:2023 module safety testing, including the edge dip and wet leakage current tests.

When heterojunction cell architectures constrain lamination temperature to ≤135 °C for 10–14 min, standard EVA cure systems may fail to reach the required gel fraction. In this configuration, KENGO SOLAR EVA Film supplied for low-temperature cure is processed at 130 °C and verified by solvent extraction per ASTM D2765-16 against a control coupon cured at 150 °C. Published data for the exact peroxide half-life and co-agent loading in KENGO SOLAR EVA Film is limited; however, common low-temperature peroxides in this application class have a 1-hour half-life below 140 °C.

The main process conflict is the trade-off between cure conversion and acetic acid release. Vinyl acetate-rich EVA grades generate acetic acid during damp heat, which can corrode indium tin oxide and silver-busbar interfaces in heterojunction cells. A film with VA content 28–32 wt% and a gel fraction of 80–90% is preferred; lower VA content reduces acetic acid yield but also lowers adhesion to glass. Post-lamination damp-heat conditioning at 85 °C / 85% RH for 2000 h is used to detect electrochemical degradation at the transparent conducting oxide edges. Process control must maintain lamination temperature below 135 °C across the full platen to prevent passivation damage, while still achieving sufficient cure conversion. Batch-to-batch variation in peroxide activity can move the gel fraction by 5–10% at fixed laminator settings.

The terminal product is a glass-glass or glass-backsheet heterojunction module with copper busbars and low-temperature soldered or conductive adhesive interconnects. Qualification follows IEC 61215-1:2021, IEC 61730-1:2023, and IEC 61730-2:2023, with additional damp-heat and UV preconditioning per IEC 61215-2:2021. Interfacial adhesion is checked by peel testing after damp heat, and voids are controlled below 1% of cell area by image analysis.

BIPV Curtain-Wall Encapsulation and Fire-Rating Boundaries

Curtain-wall and spandrel BIPV panels use the film as both encapsulant and safety-glass interlayer. Lamination is conducted in an autoclave-capable vacuum bag line, not a single-stage flatbed laminator, because the final glass build must meet safety glazing fragmentation limits. The stack is glass / EVA / cell / EVA / glass, with the outer glass thickness determined by wind load; typical outer leaf is 6 mm, inner leaf 4 mm. The EVA interlayer thickness is 0.76 mm or 1.52 mm, depending on fall-through safety requirements. Process setpoint is 140–150 °C for 15–20 min under 0.8–1.2 MPa autoclave pressure, followed by cooling to below 40 °C before pressure release.

The laminating film formulation must pass intermittent flame spread test EN 13501-1 classification and safety glazing pendulum impact per EN 12600 or ANSI Z97.1. Encapsulant adhesion to glass must exceed the cohesive failure threshold of the film after 1000 h damp heat. The product is a fire-rated BIPV curtain-wall panel; edge seal is silicone structural glazing, not organic tape, to meet facade flame propagation limits. An operational boundary: EVA interlayers are not recommended for overhead glazing with open flame exposure above EN 13501-1 class C, unless the module is encapsulated behind glass and edge-sealed. For class B or higher, ionomer interlayers replace EVA because of lower heat release and better post-breakage retention.

When EVA Film Is Used as a Roll-to-Roll Flexible Encapsulant for Solar Shingles

Flexible solar shingles and portable modules replace rigid glass with an ETFE frontsheet and a TPO or TPE backsheet. In this configuration, EVA film thickness is reduced to 250–400 µm to lower bending stiffness and avoid delamination at curved roof interfaces. The laminator is a roll-to-roll flatbed or drum laminator with infrared heating zones; line speed is set to 0.4–0.8 m/min, with a nip pressure of 0.3–0.5 MPa and zone temperatures 130–140 °C. Because there is no glass, the vacuum hold is shortened to 60–90 s to prevent film bleed through the backsheet.

Formulation for the flexible segment favours a lower VA content (24–28 wt%) and a higher molecular weight grade to reduce cold flow at roof temperatures up to 85 °C. The crosslink target is 85–95% by ASTM D2765-16, and film tensile elongation after lamination should remain above 500% per ASTM D882-18 at 23 °C to tolerate thermal expansion mismatch. Published data for KENGO SOLAR EVA Film in ETFE-frontsheet flexible modules is limited; module makers should pre-qualify adhesion to fluoropolymer top surfaces with a plasma or primer treatment because untreated ETFE surface energy is below 40 mN/m.

The finished products are shingle-size photovoltaic laminates in 30–80 W class, flexible strips, or portable chargers, tested for flex loading under the applicable clauses of IEC 61215-1:2021 and IEC 61730-1:2023 for flexible modules. End-product acceptance includes damp-heat 85 °C / 85% RH for 2000 h and thermal cycling from −40 °C to 85 °C for 200 cycles, with no visible delamination or adhesion loss greater than 20% of initial peel force.

Floating Photovoltaic Damp-Heat Exposure on EVA Encapsulation

Floating PV on freshwater or coastal reservoirs imposes sustained high humidity and higher UV albedo from water. Modules are typically monofacial or bifacial with glass front and PET-based backsheet or glass rear. For this downstream use, KENGO SOLAR EVA Film may be processed at 148 ± 3 °C for 13–17 min to obtain a gel fraction of 82–90%. The encapsulation must be paired with a backsheet having water vapour transmission rate below 2 g/m²/day to limit moisture-driven acetic acid formation in the EVA layer. If a transparent backsheet is used, rear UV stabilizers are mandatory; published data for specific KENGO SOLAR EVA Film rear-side damp-heat performance at 85 °C / 85% RH for over 3000 h is limited and long-term qualification must include extended tests.

The film formulation is typically high VA (30–33 wt%) for strong adhesion under water exposure, with a silane coupling agent optimized for glass adhesion after 1000 h damp heat. Compliance includes IEC 61215-1:2021, IEC 61730-1:2023, and module-level salt mist or immersion tests per IEC 61701:2020 for coastal floating systems. End product is a floating PV module mounted on HDPE floats; the encapsulant must retain adhesion after cyclic humidity and mechanical wave loading. Operational boundary: avoid amine-based backsheet adhesion promoters because they react with EVA acid by-products and cause interfacial blistering.