Elvax 3170 EVA Copolymer Resin,Photovoltaic Grade

Photovoltaic-grade ethylene-vinyl acetate copolymer resin containing 28 wt% vinyl acetate comonomer and a melt flow rate of 6.0 g/10 min per ASTM D1238 at 190°C/2.16 kg is first converted into extrusion-grade encapsulant film for monofacial glass/backsheet crystalline silicon modules. Compounding is generally performed by feeding resin pellets together with a pre-dispersed additive masterbatch into a twin-screw extruder with L/D of 30:1 to 44:1 and barrel temperatures controlled between 65°C and 90°C; die temperatures are limited to 85–95°C because the peroxide initiator, typically tert-butylperoxy-2-ethylhexyl carbonate, begins to decompose measurably above 110°C and the cast film must retain active peroxide for the subsequent module lamination step. The film is produced at 0.45–0.76 mm nominal thickness and chilled on a textured roll to reduce blocking. For this formulation, silane coupling agent, vinyltrimethoxysilane or methacryloxypropyltrimethoxysilane, is added at 0.3–0.6 phr to promote wet adhesion to soda-lime glass and conventional backsheet. Lamination takes place in a vacuum diaphragm laminator with heated platens at 145–155°C; the recommended vacuum pump-down is 5–7 min to remove air from the cell and ribbon interface, followed by diaphragm compression at 0.1–0.2 MPa and cure time of 12–20 min. The resulting encapsulant gel content is controlled at 75–90% as measured by ASTM D2765-16, with T-peel adhesion to glass normally specified above 40 N/cm per ASTM D1876-15 after lamination and after 1000 h damp heat at 85°C/85% RH according to IEC 61215-1:2021. Terminal products are conventional framed glass/backsheet modules that require no additional edge encapsulation beyond the backsheet lamination seal, but film moisture content before lamination must be maintained below 0.03%; pre-drying at 70°C for 4 h is required whenever storage relative humidity exceeds 60%.

Why Does CdTe and CIGS Module Lamination Demand a Moisture Edge Seal Before EVA Encapsulation Is Viable?

When the same photovoltaic-grade EVA is evaluated for thin-film CdTe or CIGS devices, the encapsulated cell stack is not tolerant of acetic acid generation from vinyl acetate hydrolysis. The lamination formulation is modified by introducing acid-scavenging zinc oxide or hydrotalcite masterbatch at 0.2–0.4 phr, and the peroxide level is reduced to keep gel content between 70% and 85% because high crosslink density reduces stress-relaxation capacity around the brittle transparent conductive oxide layer. Amine-based adhesion promoters are excluded because basic nitrogen species interfere with peroxide decomposition and can leave low gel-content regions at the encapsulant surface. Process temperatures are lowered to 130–145°C and cure time extended to 15–20 min so that the peroxide decomposition profile remains in the safe range below the degradation onset of cadmium telluride or copper indium gallium diselenide junction interfaces. Vacuum laminators for thin-film modules require a two-step pressure profile: 300 s at 50 kPa to remove volatile additives and residual moisture, then 0.1 MPa diaphragm pressure for bonding. Because EVA does not provide a sufficient moisture barrier, the module perimeter must include desiccant-loaded edge tape or butyl edge seal with water vapor transmission rate below 0.01 g/m²·day when tested at 38°C/90% RH; without this, damp heat at 85°C/85% RH per IEC 61215-1:2021 may cause acetic acid accumulation at the TCO interface and series-resistance drift. Terminal thin-film modules using EVA are therefore limited to configurations with fully encapsulated edge seals, and published data for long-term CIGS encapsulation with standard EVA remains limited; polyolefin elastomer or ionomer films are frequently substituted when moisture exclusion is the dominant requirement.

Extending Elvax 3170 into glass-glass bifacial module construction shifts the critical quality variable from rear backsheet adhesion to optical uniformity and gel content balance between the front and rear encapsulant plies. In this architecture, two plies of 0.45–0.76 mm cast film are laid up on either side of the cell string, and the rear side is laminated against heat-tempered or heat-strengthened low-iron glass instead of a composite backsheet. Because the rear side is optically active, the film must retain luminous transmittance above 90% after lamination as measured by integrating-sphere spectrophotometry per ASTM E903, and the additive package replaces light-scattering nucleants with clarifying antioxidants at 0.05–0.15 phr. The lamination program uses a slow ramp from 120°C to 150°C over 8–12 min followed by a cure plateau of 15–22 min; this prevents the glass-to-glass edge void defects that occur when the diaphragm reaches full pressure before the EVA melt front has closed around the cell edges. Diaphragm pressure is staged at 0.06 MPa during the first 5 min, then raised to 0.15 MPa. Cure performance is checked by differential scanning calorimetry residual enthalpy and by gel content per ASTM D2765-16, with front and rear samples required to fall within ±5% absolute gel content of the target 78–92%. Terminal products are glass-glass bifacial modules qualified under IEC 61215-1:2021 and IEC 61730-2:2016; rear-side UV exposure makes UV absorber addition at 0.1–0.3 wt% necessary to prevent ethylene-vinyl acetate photodegradation, but excessive UV absorber must be avoided because it reduces rear-side conversion efficiency in the 300–400 nm band.

Building-code impact resistance and curved glass lamination with EVA encapsulant in BIPV façades

Building-integrated photovoltaic modules in façade and skylight applications use Elvax 3170 encapsulant film not as a single 0.45 mm layer but as multiple plies, typically 0.76–1.52 mm total thickness, to achieve laminated safety-glass behavior under impact and post-breakage retention requirements. The formulation for BIPV includes a silane adhesion promoter at the upper end of the normal range, 0.4–0.6 phr, because peel strength to heat-treated glass and to the rear ceramic frit band must remain above 45 N/cm after simulated weathering. Lamination is carried out in a vacuum-bag autoclave rather than a flat-plate laminator when the glass is curved or oversized; the autoclave profile consists of heating to 135–145°C under 0.8–1.0 MPa nitrogen pressure for 30–60 min, which drives dissolved air back into solution and suppresses bubble formation at the concave glass surface. The peroxide masterbatch is adjusted to a lower initiator loading so that the extended high-pressure cycle produces gel content of 80–95% and a residual peroxide level below 5% of the original loading to prevent post-lamination outgassing inside the building cavity. The encapsulant must remain electrically insulating under wet conditions; insulation resistance is verified per IEC 61215-1:2021 and IEC 61730-2:2016, while the glass structure itself is assessed according to the applicable safety-glass classification in the installation region. Terminal products include curtain-wall modules, spandrel panels, and overhead glazing units in which the EVA layer contributes to load transfer and laminate ductility, but the lower shear modulus of EVA at temperatures above 60°C requires finite-element verification of creep deflection for overhead spans.

In lightweight modules using ETFE front sheets and polymer backsheets, Elvax 3170 is processed as a 0.30–0.45 mm cast film at barrel temperatures not exceeding 90°C and die temperatures of 85–95°C to preserve the peroxide activity required for low-temperature lamination. Because the ETFE front sheet does not tolerate the 145–155°C conventional lamination window, the film is designed to cure at 120–130°C with a cure time of 18–25 min. The lower cure temperature demands a faster peroxide initiation system, and the gel content achievable is limited to 70–80% rather than the 75–90% typical of glass-based modules. Prior to lamination, the ETFE surface is corona-treated to a wetting tension of 48–52 dyn/cm and primed with an aminosilane or acrylic primer; without this surface activation, EVA adhesion to fluoropolymer remains below 20 N/cm and delamination occurs after 500 h of damp heat at 85°C/85% RH per IEC 61215-1:2021. The terminal product is a semi-flexible module without glass, but the operational boundary of this EVA in flexible service is significant: the copolymer exhibits pronounced creep and softening above 50–60°C as measured by dynamic mechanical analysis per ASTM D4065, and flexural cycling under IEC 62715 or internal manufacturer protocols can exceed the strain capacity of the crosslinked vinyl acetate network. Consequently, flexible-module designs using this resin are ordinarily restricted to low-flex, fixed-radius installations, and polyolefin elastomer films are often substituted when high cycle fatigue or hot-spot temperatures above 65°C are specified.

If passivated-contact cell stacks are encapsulated, acetic acid generation and PID susceptibility override the default lamination recipe

The selection of Elvax 3170 for TOPCon and silicon heterojunction cell architectures is governed less by lamination throughput than by hydrolytic stability of the vinyl acetate comonomer. Under damp-heat exposure, vinyl acetate hydrolysis releases acetic acid, which corrodes the transparent conductive oxide and passivation stacks associated with high-efficiency n-type cells; for this reason, the encapsulant formulation is modified with acid-scavenging hydrotalcite at 0.2–0.5 phr and zinc oxide at 0.1–0.3 phr, while film moisture is held below 0.02% before lamination by vacuum drying at 70°C. Lamination temperatures are maintained in the narrower 140–150°C band with cure times of 12–16 min, and gel content is controlled to 80–90% per ASTM D2765-16 so that the encapsulant network restricts ionic transport without becoming so rigid that it transfers thermomechanical stress to thin passivation layers. The terminal module is tested not only for standard damp heat according to IEC 61215-1:2021 but also for potential-induced degradation under IEC TS 62804-1:2015 at system voltages of 1000 V or 1500 V, with leakage current limits defined by the module manufacturer. EVA remains qualified only for designs that pass the specified extended damp-heat and PID protocol; where the cell supplier specifies maximum acetic acid concentration at the cell surface or where the module warranty demands 2000 h damp-heat performance, published process windows for standard EVA are limited and polyolefin encapsulants or hybrid EVA-POE structures are typically required. This constraint is not a resin defect but a boundary condition for vinyl acetate chemistry under photovoltaic service.