KENGO VISUAL Super Clear EVA Film

KENGO VISUAL Super Clear EVA Film is an ethylene-vinyl acetate copolymer encapsulant and interlayer supplied in roll form for vacuum-bag lamination of photovoltaic modules, glass-glass laminates, and laminated safety glass. The product model designation is the grade name KENGO VISUAL Super Clear EVA Film; no alphanumeric subtype is substituted here because the converter’s certificate of analysis governs lot-level performance. Published data for this specific configuration is limited. The numerical ranges and test methods that follow describe transparent high-clarity EVA encapsulants of the same optical class and should not be read as a product-specific datasheet. Representative super clear EVA grades contain vinyl acetate in the range 28–33 wt%, a silane adhesion promoter, an organic peroxide crosslinking agent, and a stabiliser package selected for low initial yellowness. Common roll thicknesses are 0.45 mm, 0.50 mm, 0.65 mm, and 0.80 mm; roll width is slit to module dimensions, and width tolerance is typically held to ±2 mm. Melt mass-flow rate before cure, measured to ASTM D1238 at 190 °C/2.16 kg, is commonly in the range 12–30 g/10 min for fast-lamination encapsulants. The film is formulated for lamination plateaus near 145 °C and is not suitable for high-temperature extrusion or injection moulding. Slit widths in photovoltaic conversion lines are often 970 mm, 1015 mm, or 1300 mm, but these are converter-specific and must be confirmed for each purchase order.

What optical and mechanical performance ranges are reported for high-clarity EVA encapsulant films?

Optical values are determined on cured glass/encapsulant/glass or glass/encapsulant/backsheet structures. Transmittance and haze are measured according to ASTM D1003-21; super clear EVA grades in this class typically show luminous transmittance of at least 90.0% and haze below 2.5% after lamination. Product-specific haze below 1.5% depends on vacuum soak time, absence of entrapped air, and the optical quality of the front glass. The ultraviolet cut-off is not a fixed material constant; it shifts with the UV absorber package. Standard EVA often cuts off near 380 nm, whereas super clear formulations may shift the cut-off to 360–370 nm to increase short-wavelength photon delivery to a photovoltaic cell. Yellowness index after lamination, evaluated using ASTM E313-20, is typically 1.0–2.5 for fresh samples in this optical class. Yellowness above 3.0 before damp-heat exposure usually indicates cure nonconformity, stabiliser depletion, or contamination.

Mechanical properties are reported on cured free films. Tensile strength and elongation at break are measured to ASTM D638-14 Type IV; representative values for crosslinked super clear EVA are tensile strength above 15 MPa and elongation at break above 400%. Gel content after xylene extraction by ASTM D2765-16 is commonly controlled between 70% and 90%. The lower bound is significant because gel content below 65% is associated with creep and cell displacement under sustained mechanical load. Shrinkage of EVA film after exposure to lamination temperature is evaluated with an internal free-shrink method; typical values are below 5% in machine direction and below 3% in transverse direction.

The refractive index of cured EVA is approximately 1.49–1.50, providing optical coupling to soda-lime glass with a refractive index near 1.52. This reduces interfacial reflection relative to an air gap, but the optical gain is reduced when low-iron patterned glass or anti-reflective-coated glass is used. Haze measurement should therefore separate bulk film haze from surface contributions induced by glass texture.

The representative ranges in this table are not a certification of the KENGO VISUAL grade. They reflect publicly available technical literature for EVA encapsulants with similar vinyl acetate content and optical class. Lot-to-lot variation in gel content and adhesion is controlled by the converter’s statistical process-control limits rather than by a single-point specification.

Thermal processing window and peroxide decomposition kinetics in vacuum-bag lamination

The film is processed in single-chamber or double-chamber photovoltaic laminators with silicone membrane pressure applied after vacuum evacuation. A representative cycle consists of vacuum soak at 3–6 min before membrane release, followed by a cure plateau at 140–150 °C for 6–10 min. The exact dwell time is a function of encapsulant thickness, glass heat capacity, string spacing, and peroxide half-life. Peroxide systems used in this class are selected for 10-hour half-life temperatures in the range 115–125 °C. At a lamination temperature of 145 °C, the half-life is significantly shorter, and the cure plateau is generally set at three to five peroxide half-lives to reduce residual peroxide. Residual peroxide left after insufficient cure is a known contributor to later acetic acid formation, yellowing, and adhesion loss under damp heat.

Dynamic shear measurements at 100 °C before cure show complex viscosity in the range 2×10³–5×10⁴ Pa·s depending on vinyl acetate content and molecular weight. During crosslinking, storage modulus increases and the material passes through a gel point at which loss tangent falls below unity. On production lines, gel point is inferred from the time at which melt flow stops under membrane pressure. Premature gelation in hot spots above 155 °C can lock in orientation and produce non-uniform adhesion. Heating ramp from 25 °C to 145 °C on a glass-glass stack is often 3–6 °C/min, measured by embedded thermocouples. If the core temperature lags more than 5 °C behind the silicone surface setting, cure time must be extended or the heating profile changed.

The processing window is narrow in high-clarity formulations because prolonged exposure above 155 °C accelerates thermal degradation of the vinyl acetate segments and generates acetic acid, while temperatures below 135 °C may not fully decompose the peroxide within the available cycle. Vacuum removal of air must occur before the crosslinking reaction increases melt viscosity; early membrane pressure or insufficient vacuum creates microbubble haze that cannot be removed after gelation. On production-scale lines, bubble formation is observed as an increase in apparent haze under ASTM D1003-21 after lamination, often with local delamination at cell edges. Laminator loading of double-glass modules with 0.45 mm encapsulant on the cell side and 0.65 mm encapsulant on the back side requires rebalancing of top and bottom silicone membrane temperatures because glass thickness asymmetry changes the heat-up rate.

Thicker films may develop a cure gradient through the cross-section. Gel content measured at the film centre can be 5–10% lower than gel content at the film surface when the cycle is too short. This gradient reduces backsheet adhesion and increases moisture ingress along cell edges. For double-glass modules, the combined effect of glass thermal mass and silicone membrane temperature uniformity is therefore monitored with thermocouple arrays on qualification laminators.

When super clear EVA film replaces standard EVA, PVB, or POE in flat-plate laminators

Replacement of standard EVA with super clear EVA in an existing lamination line does not normally require a change in laminator hardware; however the optical additive package is different. Super clear grades may contain lower levels of metal-oxide UV blocking pigment and therefore transmit more near-ultraviolet radiation in the 360–380 nm band. This increases photon availability for some cell types but also shifts the burden of UV screening to the front glass or backsheet. Process requalification is required because adhesion saturation may occur at a different plateau temperature. In field-scale runs, adhesion to glass is frequently monitored by ASTM D903-98 peel testing; values in the range 30–80 N/15 mm are commonly accepted for EVA encapsulants, but the lower limit for module certification depends on backsheet type and cell string configuration.

Compared with PVB, EVA does not require an autoclave and can be processed in a vacuum-bag laminator at lower pressure; PVB typically requires 12–14 bar autoclave pressure to remove residual air and to homogenise plasticiser distribution. PVB remains a plasticised thermoplastic without a chemical gel network, whereas EVA is peroxide-crosslinked. The modulus and glass-transition behaviour are therefore different. EVA generally has a lower glass transition and a more elastic network at module operating temperature, but PVB may offer higher strength in some architectural laminates. Compared with POE encapsulants, EVA delivers higher polar adhesion to glass without primer but lower volume resistivity. POE formulations using silane-grafted or peroxide-cured networks are often specified for bifacial modules and positive-bias potential-induced degradation resistance; EVA remains more sensitive to acetic acid generation under high positive bias. The following comparative ranges are representative, not lot-specific.

Because high-transparency encapsulants are more sensitive to photochemical yellowing than heavily UV-blocked grades, damp-heat and UV preconditioning tests are used to separate formulation stability from initial clarity. Damp heat is performed at 85 °C/85% RH for 1000 h, with longer 2000–3000 h exposures used for bifacial and glass-glass qualification. After 1000 h, high-clarity EVA encapsulants in this optical class should demonstrate yellowness index shift below 2.0 and retained adhesion above 30 N/15 mm. Reports for KENGO VISUAL Super Clear EVA Film at extended 3000 h damp heat are not publicly available; batch-level qualification data must be obtained from the material converter. The major failure mode is not haze generation alone but acetic acid-induced corrosion of silver grid fingers and degradation of the front-side busbar interface. Therefore gel content and stabiliser depletion must be tracked together with optical loss.

For UV exposure, the film is evaluated through front glass because glass composition and anti-reflective coating control the short-wavelength cut-off. Super clear EVA films with UV cut-off near 360 nm can accumulate yellowing at a slower rate if the front glass blocks the 300–340 nm region and if the hindered amine stabiliser package remains intact. Published data for this specific configuration is limited; qualification should include the exact glass, anti-reflective coating, and backsheet combination used on the production line.

Regulatory compliance is contingent on module-level testing, not film-level certification alone

Film-level compliance statements are commonly issued against RoHS 2011/65/EU and REACH; these address restricted substances and substances of very high concern in the formulated film but do not certify module-level safety. Flammability of thin EVA film is usually classified under UL 94; the typical result for thin encapsulant films is UL 94 HB, but module-level flammability depends on the complete laminate stack and junction box. Electrical insulation of the cured encapsulant is tested using IEC 62788-1-2; volume resistivity is commonly not less than 1×10¹⁴ Ω·cm at 23 °C and 50% RH, decreasing with moisture uptake and temperature. Surface resistivity and tracking resistance are relevant to edge isolation but are less frequently controlled at film level.

Operational boundaries apply during transport, storage, and lamination. Rolls should be stored in sealed desiccant packaging below 25 °C and 60% RH; if a cold roll is opened in a humid environment, condensation on the film surface can produce microvoids and local haze after lamination. Pre-drying is required after exposure above 60% RH; a drying condition of 60 °C for 4–6 h is common for EVA films, but the exact cycle must be validated because excessive drying can migrate stabilisers to the film surface. The film should not be processed above 155 °C or held at cure temperature beyond the validated plateau; extended residence can produce acetic acid and shift yellowness index. Combination with amine-based edge sealants or amine-functional adhesion promoters should be avoided because amine compounds can interfere with silane adhesion chemistry and accelerate local yellowing at the module perimeter. Compatibility with anti-reflective-coated glass and fluoropolymer backsheet layers must be confirmed by batch-level peel testing, because adhesion promotion is surface-specific and not guaranteed by film-level data alone.