| HS Code | 881911 |
| Thickness | 0.45 mm |
| Width | 1000-2200 mm |
| Length | 200 m |
| Density | 0.95 g/cm³ |
| Melt Flow Index | 25 g/10 min |
| Melting Point | 70 °C |
| Crosslinking Degree | ≥ 75% |
| Gel Content | ≥ 75% |
| Light Transmittance | ≥ 91% |
| Uv Transmittance | ≥ 80% |
| Uv Cut Off Wavelength | ≤ 300 nm |
| Haze | ≤ 2% |
| Tensile Strength | ≥ 16 MPa |
| Elongation At Break | ≥ 500% |
| Peel Strength | ≥ 60 N/cm |
| Volume Resistivity | ≥ 1×10^15 Ω·cm |
| Breakdown Voltage | ≥ 30 kV/mm |
| Water Absorption | ≤ 0.1% |
| Shrinkage | ≤ 3% |
As an accredited FIRST Normal Series EVA Film F406P (UV transmittance) factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
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In a standard glass-backsheet photovoltaic lamination line, the normal-cure EVA film F406P is positioned as the front encapsulant where the UV transmittance value is used as an incoming optical QC gate. The incoming roll data are measured by UV-Vis spectrophotometry in the 280–380 nm band against an air reference following ASTM E903-20; a shift of more than 2 % absolute transmittance at 340 nm is sufficient to alter the total solar transmittance calculation used for module power prediction under IEC 60904-3. The layup is low-iron tempered glass / 0.45 mm F406P film / cell matrix / 0.45 mm F406P film / weatherable PET-fluoropolymer backsheet. Cell spacing is maintained at 2.0–2.5 mm to reduce ribbon stress after crosslinking. Lamination is executed on flat-bed laminators with platen setpoints of 145–150 °C. The vacuum stage is held for 4–6 min at ≤2 mbar absolute pressure to remove air from the cell gaps before the pneumatic chamber applies 0.08–0.10 MPa during the 8–10 min press stage.
Crosslinking is monitored by gel fraction per ASTM D2765-16. A gel fraction below 75 % produces hot-creep elongation above 150 % and increases the risk of creep delamination in subsequent thermal cycling, while values above 90 % reduce fracture toughness and make modules more sensitive to hail impact. On production lines with 3.2 m × 2.2 m platens, batch-to-batch variation in melt flow index exceeding ±3 g/10 min under ISO 1133-1:2022 has required dwell-time offsets of 90–120 s to maintain adequate cell embedding. Edge void formation has been traced to vacuum leak rates greater than 8 mbar/min during pull-down, which prevents the film from conforming to the interconnect ribbon geometry. The terminal product is a IEC 61215-2:2021 qualified c-Si module, with peel strength to glass checked by ASTM D903-98 and typical acceptance at ≥60 N/cm.
Replacing the backsheet with a second layer of low-iron semi-tempered glass removes the rear-side heat drain that a polymer backsheet provides, and the thermal mass of the glass sandwich slows the temperature ramp at the cell plane. In this configuration F406P is used on both sides of the cell string, typically 0.45 mm per layer, with peripheral butyl sealing tape applied at 12–15 mm width before lamination. The platen setpoint is raised to 150–155 °C, and the press stage is extended to 12–15 min so that the gel fraction reaches the same 78–88 % target as the glass-backsheet build. A vacuum stage shorter than 3 min produces bubble clusters at the glass-EVA interface near the cell edges because the higher glass stiffness delays rubber conformity.
UV transmittance data for F406P are relevant in glass-glass modules when the rear-side junction receives albedo light; however UV exposure is not the primary bifacial gain driver. The more immediate process risk is differential thermal expansion between the upper and lower glass sheets. When the upper and lower platen temperatures diverge by more than 4 °C, the laminate exhibits residual bow after cooling, and the resulting non-uniform pressure during the next module causes seal width variation. Crosslinked F406P is checked by ASTM D2765-16 gel fraction and by peel adhesion to glass per ASTM D903-98 after damp heat preconditioning per IEC 61215-2:2021. The terminal product is a glass-glass bifacial module qualified to IEC TS 62915:2018 and IEC 61730-2:2016.
| Process variable | Glass-backsheet c-Si line | Glass-glass bifacial line |
|---|---|---|
| Platen setpoint | 145–150 °C | 150–155 °C |
| Vacuum stage | 4–6 min | 3–5 min |
| Press stage | 8–10 min | 12–15 min |
| Total laminator cycle | 14–18 min | 18–22 min |
| Gel fraction after cure, ASTM D2765-16 | 75–88 % | 78–88 % |
EVA-based interlayers differ from PVB in that the crosslinking reaction permits lamination without a pressurized autoclave, making the process suitable for architectural fabricators with vacuum-bag ovens. F406P is introduced as a two-layer interlayer pack, commonly 0.45 mm per sheet, between two panes of 3–6 mm heat-strengthened glass. Lamination is performed at 135–140 °C under vacuum for 30–45 min, followed by slow cooling at 2–3 °C/min to avoid thermal stress. Moisture content in the EVA is controlled before lamination; rolls stored at relative humidity above 60 % require pre-drying at 60–65 °C for 4 h because residual moisture above 0.2 % creates bubble defects along the cut edges.
UV transmittance in this safety-glass segment is a process-critical input. Where the laminated pane carries a UV-cured edge sealant or bonded profile, the F406P transmittance in the 300–380 nm window must be confirmed to permit sufficient cure energy through the glass. Where UV blocking is required for interior fading protection, a UV absorber film must be added in the build-up; F406P alone cannot be assumed to act as a UV screen. The terminal product is laminated safety glass evaluated to EN ISO 12543-2:2021 and ANSI Z97.1, with adhesion measured by ASTM D903-98 and impact classification by EN 12600.
For building-integrated spandrel panels, F406P is processed simultaneously as the cell encapsulant and the glass-to-glass interlayer, which eliminates the need for a separate PVB interlayer. The layup is a ceramic-fritted outer glass sheet, a 0.45 mm F406P front sheet, the cell circuit, a second 0.45 mm F406P sheet, and a clear inner glass sheet. Lamination is carried out at 145–150 °C with a total cycle of 16–20 min; the ceramic frit layer is pre-dried to reduce outgassing from organic ink vehicles, which otherwise migrate into the F406P and reduce interfacial adhesion. Cells are placed with 20–30 mm clear edges to satisfy facade electrical isolation requirements.
The UV transmittance specification of F406P is used in BIPV not as an efficiency claim but as a compatibility check for the surrounding building system. UV-curable structural silicone joints, butyl tapes, and edge profiles may require a known UV dose at the sealant interface; the laminate transmittance curve determines whether cure time must be extended. Compliance for the resulting module is assessed to EN 50583-1:2016 for building integration and IEC 61215-2:2021 for photovoltaic performance. The terminal product is a spandrel panel that replaces conventional non-solar glass in curtain wall assemblies.
Flexible module production using transparent ETFE front sheets instead of rigid glass operates with lower platen setpoints because the front sheet has lower thermal conductivity and cannot tolerate prolonged exposure to 150 °C without surface flow. In this configuration a single 0.45 mm F406P layer is used as the front encapsulant over the cell matrix, and a second layer is placed between the cells and the PET backsheet. The process window is 140–145 °C platen temperature, 8–12 min press stage, and 4–5 min vacuum stage; the shorter cycle reduces the risk of PET backsheet shrinkage above 1.5 %, which causes curling and rear-side delamination.
The UV transmittance of F406P becomes a critical boundary condition in flexible modules because the ETFE front sheet transmits a higher UV fraction than low-iron glass. Incoming ETFE-F406P combinations are checked by ASTM E903-20 across the 280–380 nm band to ensure that the UV dose reaching the encapsulant does not exceed the value used in the UV preconditioning portion of IEC 61215-2:2021. If the combined transmittance exceeds the qualification baseline by more than 5 % integrated UV, the outer adhesive layer and the F406P film are re-qualified before production release. The terminal product is a semi-flexible photovoltaic module for marine, RV, and portable applications, with peel strength measured by ASTM D903-98 and torsional durability validated by on-roof exposure rather than a single laboratory standard; published data for this specific F406P configuration is limited, and batch-level optical testing is required.
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FIRST Normal Series EVA Film F406P (UV transmittance) is a peroxide-curable ethylene-vinyl acetate encapsulant sheet produced for flat-plate photovoltaic modules and laminated glass assemblies where ultraviolet radiation in the 320–400 nm UVA band must be transmitted to underlying functional layers. The F406P designation belongs to the normal-cure segment of the FIRST Normal Series, separating it from fast-cure EVA grades and from standard UV-blocking EVA sheets that contain benzotriazole or hydroxyphenyl triazine absorbers. The film is supplied as an unprinted, tacky sheet with a nominal thickness range of 0.40–0.65 mm, roll widths to 2,000 mm, and slit tolerances of ±1.5 mm. The base resin is an EVA copolymer with a vinyl acetate comonomer content typically between 26 wt% and 30 wt%, selected to balance optical clarity, low-temperature flexibility, and crosslinking efficiency. The crosslinking package is compounded to achieve a gel content above 75% after lamination at 150 °C for 15 min, determined by solvent extraction in xylene or decalin according to ASTM D2765-16. The film is intended for applications where UVA radiation must penetrate the encapsulant to cure edge sealants, primers, or UV-active coatings after lamination, and where spectral transmission requirements are not met by standard UV-blocking EVA grades.
| Property | Test method | Typical value | Unit |
|---|---|---|---|
| Thickness tolerance | ISO 4593-1993 | ±0.05 | mm |
| Width tolerance | ISO 4591:2002 | ±1.5 | mm |
| Vinyl acetate content | Manufacturer internal method | 26–30 | wt% |
| Melt mass-flow rate at 190 °C, 2.16 kg | ISO 1133-1:2022 | 3–5 | g/10 min |
| Total luminous transmittance | ASTM D1003-21 | ≥90.5 | % |
| Haze | ASTM D1003-21 | ≤1.2 | % |
| Spectral transmittance at 365 nm | ISO 13468-2:2021 | ≥80 | % |
| Spectral transmittance at 385 nm | ISO 13468-2:2021 | ≥88 | % |
| Yellowness index after cure | ASTM E313-20 | ≤1.5 | — |
| Gel content after 150 °C/15 min | ASTM D2765-16 | ≥75 | % |
| Tensile strength at break | ASTM D638-14 | ≥14 | MPa |
| Elongation at break | ASTM D638-14 | ≥500 | % |
| Peel strength to glass at 180° | ASTM D903-98 | ≥60 | N/cm |
| Dimensional stability at 120 °C, 3 min | ASTM D2732-14 | ≤3 | % |
The values in the table are not separate low-specification claims; they represent the combined cure state after lamination. The UV-transmittance properties are measured on cured glass/EVA/glass laminates with low-iron glass of 3.2 mm thickness, because surface reflection and glass absorption must be included. Integrating sphere geometry per ISO 13468-2:2021 is required to capture forward-scattered radiation and avoid underestimating transmittance from haze. A standard D65 illuminant and 2° observer are used for colorimetric values. The exact guaranteed limits should be obtained from the current manufacturer’s technical datasheet for F406P.
In standard UV-blocking EVA formulations, the spectral cut-on is deliberately steepened between 350 nm and 390 nm by the addition of substituted benzotriazole UV absorbers or hydroxyphenyl triazine compounds at concentrations of 0.10–0.30 wt%. These additives dissipate absorbed UVA as heat through excited-state intramolecular proton transfer. The molar extinction coefficient of a typical benzotriazole absorber at 365 nm is high enough that a 0.50 mm EVA sheet containing 0.20 wt% absorber exhibits spectral transmittance below 10% at that wavelength. F406P eliminates or sharply reduces this absorber loading, so the cut-on is governed by the EVA polymer matrix itself. The vinyl acetate carbonyl group contributes n→π* absorption below approximately 300 nm, while the aliphatic backbone is relatively transparent across the UVA range. After lamination, residual peroxide decomposition products and trace co-curing agents can produce a weak absorption tail extending to 320–330 nm. As a result, the spectral transmittance of F406P at 365 nm is typically not less than 80%, but the film should not be treated as a deep-UV or UVB-transmitting material. The exact transmittance depends on glass composition: low-iron patterned solar glass with an anti-reflective coating can raise total UVA transmission, whereas conventional soda-lime glass containing iron oxide reduces the transmitted UVA flux and shifts the usable cut-on upward. Process validation should therefore be performed on the specific glass stack rather than on a free film alone. The UV-transmittance designation does not degrade visible-light performance: total luminous transmittance remains above 90%, and haze remains below 1.2% after curing.
For lamination, the melt flow behavior of F406P is determined by the base resin and the peroxide cure package. A melt mass-flow rate between 3 g/10 min and 5 g/10 min at 190 °C, 2.16 kg per ISO 1133-1:2022 is typical for normal-cure EVA. The film softens sufficiently to fill cell gaps and busbar steps but does not promote excessive cell movement. On production-scale flat-bed laminators with heated platens, the recommended cure window is 150 ± 5 °C at the glass surface with a diaphragm pressure of 0.06–0.10 MPa and a total cycle of 15–22 min. The laminator vacuum should pull to less than 80 Pa residual pressure before pressurization. Inadequate vacuum leaves air at busbar edges, producing bubble defects in the cured laminate. Excessive pressure above 0.12 MPa can crush cells, especially with thin 0.40 mm encapsulant film. A curing plateau at 145 °C may require an extension of 3–5 min compared with 155 °C processing.
The processing window for F406P is controlled by temperature lag through the glass and solar-cell stack. At a platen setting of 152 °C, the glass top surface can reach 140–145 °C within 6–8 min for standard monocrystalline or polycrystalline module constructions, while the back-side encapsulant may lag by an additional 3–5 min. The cure package is formulated with an alkoxyalkyl peroxide whose 10-h half-life temperature is typically near 120–130 °C; at 150 °C the half-life is approximately 5–8 min. A curing hold of 12–18 min therefore provides between 2 and 3 peroxide half-lives at the coolest portion of the laminate. If the edge or corner temperature remains below 135 °C, gel content measured by ASTM D2765-16 can fall below 70%, producing a film with low creep resistance and reduced peel adhesion. If the platen temperature exceeds 165 °C or the hold exceeds 30 min, excess peroxide decomposition can increase crosslink density but also increases radical recombination by-products that contribute to post-lamination yellowness. In accelerated testing, laminates cured above 165 °C show yellowness index values measured by ASTM E313-20 that are 0.5–1.0 units higher than equivalent laminates cured at 150 °C. This is particularly significant for a UV-transmittance grade because the same optical pathway that transmits UVA also makes yellowness more visible in the final module.
Production-scale lamination trials with F406P on flat-bed laminators show that the most common defect is void formation at busbar edges when the vacuum dwell is shortened below 4 min or when residual pressure remains above 100 Pa before diaphragm pressurization. The second common issue is cell displacement when the film is over-thick or the pressurization ramp is too rapid. At 0.65 mm thickness, the molten film can hydraulically shift cells during the first 60 s of pressure. A two-step pressure ramp mitigates this: 0.03 MPa for 2 min, followed by full pressure of 0.08–0.10 MPa. Laminates made with F406P at 0.50 mm show lower edge air entrapment than 0.40 mm film when glass surface roughness is high. Wetting is acceptable on textured solar glass with surface roughness Ra up to 0.8 µm; beyond that, bubble traps may require alternative layup sequencing.
| Property | F406P UV-transmittance normal cure | Standard UV-blocking EVA | Fast-cure EVA |
|---|---|---|---|
| Spectral transmittance at 365 nm | ≥80% | ≤15% | ≥80% |
| UV absorber loading | Minimal or absent | 0.10–0.30 wt% benzotriazole or triazine | Minimal or absent |
| Time at 150 °C to reach ≥75% gel content | 12–18 min | 12–18 min | 6–10 min |
| Primary use condition | UV-through-glass curing, UV-stable architectures | UV protection for cells and backsheets | High-throughput lamination |
Specifying F406P is appropriate when a subsequent manufacturing step uses UVA radiation through the front glass to cure a silicone edge seal, a UV-cationic encapsulant, or a UV-free-radical coating. A 365 nm LED exposure with irradiance of 200 mW/cm² through low-iron glass and 0.50 mm F406P film can deliver sufficient UVA dose to cure many thin-film UV resin formulations, although published data for this specific configuration is limited and hardness and adhesion must be confirmed by the end user. In building-integrated photovoltaic and bifacial glass-glass modules, the UV-transmittance encapsulant can prevent UV-stable coatings from being starved of the radiation needed for cure. However, F406P should not be selected when the module contains a UV-sensitive backsheet, a non-UV-stabilized PET interlayer, or cell surfaces requiring UV blocking below 380 nm. In those cases a standard UV-blocking EVA or a two-layer structure with a UV-blocking rear encapsulant should be used. Long-term UV exposure testing under IEC 61215-2:2021 MQT 10 conditions may show greater yellowness in F406P than in UV-blocking grades because the UV absorber package is reduced. This is not necessarily a product failure if the optical requirement is UVA transmission. The acceptable yellowness index after UV exposure is a module-level specification and must be agreed with the certifying body.
F406P must be stored in sealed, desiccated polyethylene packaging at temperatures between 0 °C and 30 °C and relative humidity below 60%. Moisture content should remain below 0.20 wt% before lamination; higher levels produce steam bubbles during vacuum release. If the film is exposed to RH 60–80% for more than 24 h, the rolls should be re-dried at 55–60 °C for 6–8 h in a forced-air oven before use. Contact with amine-based silane primers, amine antioxidants, or heavy-metal salts should be avoided because these species can interfere with peroxide decomposition or accelerate premature crosslinking. Shelf life is typically 6 months from the date of manufacture in original packaging. During slitting, the film should be processed at 10–35 °C; above 40 °C tackiness increases and may cause blocking on rewound rolls. Below 5 °C the film becomes stiff and may crack during unwind. The material is not intended to be used as a UV-blocking layer; users requiring a strong spectral cutoff below 380 nm should select a UV-blocking EVA grade or combine F406P with a UV-blocking back layer.
