| HS Code | 927108 |
| Material | EVA |
| Type | Low-acid EVA encapsulant film |
| Application | TOPCon double-glass photovoltaic modules |
| Color | Transparent |
| Thickness | 0.5 mm / 0.6 mm |
| Width | Up to 2400 mm |
| Light Transmittance | ≥91% |
| Haze | ≤3% |
| Crosslinking Degree | ≥75% |
| Peel Strength To Glass | ≥60 N/cm |
| Peel Strength To Backsheet | ≥40 N/cm |
| Tensile Strength | ≥16 MPa |
| Elongation At Break | ≥500% |
| Volume Resistivity | ≥1.0×10^15 Ω·cm |
| Breakdown Voltage | ≥30 kV/mm |
| Water Vapor Transmission Rate | ≤30 g/m²·day |
| Uv Cut Off Wavelength | ≤360 nm |
| Thermal Shrinkage | ≤3% |
| Acid Content | Low acid |
| Pid Resistance | Yes |
| Storage Temperature | ≤30°C |
| Shelf Life | 6 months |
| Certifications | TUV, UL, IEC, RoHS, REACH |
As an accredited HIUV TOPCon Double-glass Low-acid EVA Film factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
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HIUV TOPCon Double-glass Low-acid EVA Film is specified for the front and rear encapsulation layers of utility-scale TOPCon bifacial double-glass modules. In this stack-up, a 2.0 mm low-iron heat-strengthened front glass, front low-acid EVA film at 0.50 mm ±10% thickness tolerance, TOPCon cell, rear low-acid EVA film at 0.50 mm, and 2.0 mm rear glass are assembled in a multi-chamber vacuum laminator. The film formulation is based on ethylene-vinyl acetate copolymer with vinyl acetate comonomer at 28 wt%; the peroxide crosslinking agent is added at 0.8 wt% tert-butyl peroxy-2-ethylhexyl carbonate, silane adhesion promoter at 0.35 wt% vinyltrimethoxysilane, UV absorber/hindered amine light stabilizer package at 0.25 wt%, and acid-scavenging/antioxidant masterbatch at 0.3 wt%. Raw film melt mass-flow rate is controlled at 12–20 g/10 min under 190 °C/2.16 kg per ISO 1133-1:2022. Lamination proceeds at 0.5–1.0 mbar evacuation, platen temperature 145–150 °C, cure time 18–22 min, and diaphragm pressure 0.8–1.0 bar. The acceptance window for gel content by xylene extraction per ASTM D2765-16 is 85–95%. Compliance for this application is governed by IEC 61215-1:2021, IEC 61215-2:2021 MQT 11, MQT 13, MQT 14, and IEC 61730-2:2016; procurement specifications typically require maximum power degradation after 1000 h damp heat at 85 °C/85% RH to remain below 5% relative to initial. Finished product is a framed utility-scale 210 mm wafer TOPCon half-cell double-glass module with glass/glass construction and anodized 6063-T5 aluminum frame.
On production-scale laminator lines, the dominant encapsulation failure modes are cell displacement when platen temperature non-uniformity exceeds ±3 °C and edge void formation when diaphragm pressure is applied before gelation is complete. The film is stored at <30 °C and <60% RH; opened rolls are resealed and conditioned at 25 ± 5 °C for 12 h before lay-up to prevent condensation-induced adhesion loss at the glass interface.
Floating photovoltaic installations subject the encapsulant to persistent rear-side moisture, water spray, and chloride ingress. The low-acid EVA film is specified at 0.55 mm front and 0.55 mm rear to increase the diffusion path length for water vapor and to reduce the equilibrium moisture concentration at the TOPCon cell surface. The peroxide crosslinking agent is increased to 0.9 wt% TBEC, silane adhesion promoter to 0.45 wt% vinyltrimethoxysilane, and acid-scavenging masterbatch to 0.5 wt%. Published data for acetic acid evolution in this specific floating formulation is limited; module qualification relies on corrosion testing of cell metallization and glass adhesion after damp heat and salt mist exposure rather than direct acetic acid quantification. Lamination uses a dual-chamber vacuum laminator with platen temperature 150–155 °C, cure time 22–25 min, evacuation 0.5–1.0 mbar, and diaphragm pressure 0.8–1.0 bar. After lamination, a polyisobutylene secondary edge seal is applied to the glass perimeter before frame installation; this process blocks liquid water ingress at the cut edge and is applied only when relative humidity during lay-up is below 60% RH. Qualification standards include IEC 61215-2:2021 MQT 13 run at 2000 h, IEC 61701:2020 salt mist corrosion, and ISO 9227:2017 neutral salt spray for attached hardware. The terminal product is a floating double-glass TOPCon module with corrosion-resistant 6005A aluminum frame, IP68 junction box, and sealed cable gland assembly.
The polyisobutylene edge seal is extruded at 120–130 °C with a bead width of 8–10 mm after the laminated glass has cooled below 40 °C; application before cooling causes edge seal deformation and loss of peripheral adhesion. The lamination line is equipped with a moisture analyzer that rejects lay-ups if film moisture content exceeds 0.3 wt% by Karl Fischer titration.
Building-integrated photovoltaic curtain wall units using TOPCon double-glass laminates impose safety glazing and fire classification requirements not present in ground-mount installations. In this configuration the low-acid EVA film is supplied at 0.76 mm thickness as part of a laminated safety glass build: 2.5 mm tempered outer glass, low-acid EVA, TOPCon cell, low-acid EVA, and 2.0 mm tempered inner glass. The formulation is adjusted to a peroxide crosslinking level of 0.7 wt% TBEC and a silane coupling agent of 0.3 wt% to avoid excessive glass adhesion build-up during autoclave processing. Lamination proceeds in a vacuum bag at 0.85–0.95 MPa and 135–140 °C for 45–60 min; bubble-free edge regions required for structural glazing are achieved through the higher pressure and longer soak time. Contact with amine-containing sealants or cleaning agents before lamination is avoided because free amines accelerate premature crosslinking at ambient temperature. Compliance is anchored to IEC 61215-1:2021 and IEC 61215-2:2021 for PV performance, IEC 61730-2:2016 for module safety, EN 13501-1:2018 for reaction-to-fire classification, and EN 1279-2:2018 for insulating glass unit durability. Published data for the specific combination of TOPCon low-acid EVA and EN 1279-2:2018 gas leakage tests is limited; fabrication is typically validated through façade-specific cut-size testing. The terminal product is a building-integrated photovoltaic insulating glass unit with a semi-tempered laminated inner pane and TOPCon double-glass circuit embedded in the cavity.
In façade production, the autoclave load is ramped through the EVA melting plateau at 65–85 °C before pressure is raised to 0.85 MPa; premature pressure application traps low-molecular-weight silane condensates at the glass interface and produces local delaminations under edge shadow testing.
Greenhouse and agri-voltaic double-glass TOPCon modules operate under sustained inner-surface condensation and periodic exposure to fertilizer-derived ammonia and sulfur-containing agrochemicals. The low-acid EVA film is compounded with a hindered phenolic/phosphite antioxidant system at 0.35 wt%, an acid scavenger at 0.4 wt%, peroxide crosslinking at 0.8 wt%, and silane adhesion promoter at 0.4 wt%. Front and rear film thicknesses are set at 0.45 mm to allow higher visible light transmittance through a semi-transparent module aperture while retaining the moisture-barrier path needed under high relative humidity. Lamination is performed in a single-chamber vacuum laminator at 148–152 °C for 20–24 min with diaphragm pressure 0.7–0.9 bar and evacuation before diaphragm release of 0.5–1.0 mbar. Anti-reflective-coated glass is used on the crop side; the laminator platen is maintained flat within ±0.5 mm across the module area to prevent cell displacement during gelation. Qualification requirements include IEC 61215-2:2021 MQT 13 extended to 1500 h for high-humidity service, IEC 62716:2013 ammonia corrosion, and IEC 61730-2:2016 for electrical safety. The terminal product is a semi-transparent greenhouse roof module with 2.0 mm/2.0 mm glass, visible transmittance configured by TOPCon cell spacing, and drainage-oriented edge clamping.
Condensation cycling inside the greenhouse module accelerates extraction of the acid-scavenger component; field inspection data from ventilated greenhouse installations indicate that frame spacing and edge seal drainage have a larger effect on visual delamination than film formulation drift within the tested concentration window. The laminator platen flattening and edge clamp pressure are inspected after every 500 cycles because condensation-driven edge stress concentrates at frame mounting points.
In high-irradiance desert installations, the critical encapsulant failure modes are UV-assisted acetic acid release, thermomechanical creep, and glass adhesion loss during diurnal thermal cycling. The low-acid EVA film is compounded with a UV stabilizer package at 0.35 wt% comprising a benzotriazole UV absorber and hindered amine light stabilizer, peroxide at 1.0 wt% TBEC to raise gel content to 90–95% after lamination, silane at 0.35 wt%, and antioxidant at 0.25 wt%. The 1.0 wt% peroxide level narrows the lamination processing window to approximately ±5 °C; platen temperature is held at 150 ± 3 °C with cure time 22–25 min to avoid exothermic overshoot and void entrapment. Production-scale laminator logs show that batch-to-batch variation in silane coupling agent hydrolysis rate is a larger source of lamination yield loss than crosslinker variability; film pre-drying at 65 °C for 4 h is required when storage relative humidity exceeds 60% RH. Qualification uses IEC 61215-2:2021 MQT 11 thermal cycling from -40 °C to +85 °C for 200 cycles, MQT 15 UV preconditioning at 15 kWh/m² or extended 60 kWh/m² per desert procurement specifications, and IEC 61730-2:2016. The terminal product is a high-load utility TOPCon double-glass module with 2.0 mm heat-strengthened glass, 210 mm half-cut cells, and glass/glass construction without a backsheet.
The laminator cure profile is monitored with thermocouples embedded between front glass and EVA; the cure index calculated from moving die rheometer data is required to exceed 0.90 before the module exits the cooling stage. Photovoltaic module manufacturers record platen temperature drift of ±2 °C between modules; drift beyond this range shifts gel content below 88% and reduces adhesion retention on the rear glass.
In coastal and marine facilities where salt deposition and high relative humidity occur simultaneously, the low-acid EVA film is laminated into double-glass TOPCon modules with rear-edge ventilation paths and sealed junction boxes. The film formulation uses a methacrylate-functional silane adhesion promoter at 0.40 wt%, peroxide crosslinking at 0.85 wt%, and acid scavenger at 0.45 wt%. Front and rear film thicknesses are 0.50 mm each; the laminated pack is subjected to a pre-lamination drying step at 65 °C for 4 h when relative humidity exceeds 60% RH, then vacuum laminated at 145–150 °C for 20–22 min with diaphragm pressure 0.8–1.0 bar. Compliance requirements combine IEC 61215-2:2021 MQT 13 run at 1500 h, IEC 61701:2020 salt mist corrosion, and ISO 9227:2017 neutral salt spray for attached hardware. The terminal product is a coastal water-treatment or port facility rooftop module with glass/glass construction, anodized aluminum frame, and corrosion-resistant connectors.
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Designated as the HIUV TOPCon Double-glass Low-acid EVA Film, the product is a peroxide-cured ethylene-vinyl acetate copolymer sheet supplied for encapsulation of bifacial TOPCon cells in double-glass photovoltaic modules. The product identifier is used as the ordering model designation, with suffixes that encode roll width and nominal thickness. Available roll widths are 1120 mm and 1300 mm, with thicknesses of 0.50 mm, 0.55 mm, 0.60 mm, and 0.70 mm. The low-acid performance class is obtained through a combination of reduced hydrolysable acetate content and acid-scavenging additives; the formulation is intended to reduce free acetic acid generation under damp-heat exposure while retaining EVA-typical glass adhesion and crosslink behaviour. The product is positioned for front-side use in double-glass TOPCon laminates and may be paired with POE at the rear for high-humidity installation environments.
The following table lists representative values measured on 0.55 mm film under laboratory conditions. They are not batch specifications; release limits are stated on the certificate of analysis and are controlled under GB/T 29848-2018 or customer-specific test plans.
| Property | Test method | Typical value | Unit |
|---|---|---|---|
| Nominal thickness | ASTM D374-16 | 0.55 | mm |
| Density | ISO 1183-1:2019 | 0.96 | g/cm³ |
| Tensile strength at break, MD | ASTM D882-18 | 12–18 | MPa |
| Elongation at break, MD | ASTM D882-18 | 400–600 | % |
| Peel strength to glass after cure | IEC 61215-1:2021 | ≥ 60 | N/cm |
| Gel content after cure | ASTM D2765-16 | 75–90 | % |
| Volume resistivity at 25 °C, 500 V DC | IEC 62631-3-1:2016 | ≥ 1.0×1015 | Ω·cm |
| Weighted solar transmittance, 380–1100 nm after lamination | IEC 60904-3:2019 | ≥ 91 | % |
| Haze after lamination | ASTM D1003-21 | ≤ 3.0 | % |
| Water vapour transmission rate, 38 °C/90% RH | ASTM F1249-20 | 15–25 | g/(m²·day) |
Batch-to-batch variation in melt flow rate is controlled within a narrow band because TOPCon double-glass laminates require consistent fill of the cell-string gap without excessive squeeze-out. Laminators operating with 3.2 mm/3.2 mm glass formats have shown that a change of ±3 g/10 min in melt flow rate at 190 °C/2.16 kg shifts the minimum-viscosity window enough to require 60–90 s adjustment to vacuum dwell to prevent bubble retention at busbar edges. The product's thickness tolerance is typically ±0.03 mm; total thickness variation across a roll width should be verified because double-glass lamination pressure transfers thickness error into cell displacement and glass edge stress.
Incoming inspection should include thickness, width, visual defects, gel content after lamination, volume resistivity, light transmittance, and peel strength on cleaned low-iron glass. Sampling plans may follow ISO 2859-1:1999 or customer-specific AQL. Roll weight and length should be recorded to verify yield. The front-side version contains a UV absorber package with a spectral cutoff below 360 nm; weighted solar transmittance remains above 91% for the 380–1100 nm band to preserve bifacial rear irradiance gain while limiting UV embrittlement of the encapsulant.
Low-acid EVA differs from conventional EVA primarily in the concentration of free acetic acid and hydrolysable acetate available after peroxide crosslinking. In conventional EVA, thermal and hydrolytic deacetylation releases acetic acid during damp-heat exposure; acetic acid can reduce interfacial adhesion and increase metal corrosion on cell grids, interconnect ribbons, and solder joints. The HIUV TOPCon Double-glass Low-acid EVA Film uses a lower vinyl-acetate hydrolysable fraction and acid-scavenging additives; the formulated acid value after lamination is lower than general-purpose EVA grades, and the product is designed to maintain volume resistivity above 1.0×1014 Ω·cm after 85 °C/85% RH exposure for 1000 h. Published data for this specific configuration is limited; qualification should therefore be based on module-level IEC TS 62804-1:2015 PID testing and IEC 61215-2:2021 damp-heat cycling rather than encapsulant coupon data alone.
EVA is a copolymer of ethylene and vinyl acetate. Under hydrolytic conditions, vinyl acetate repeat units can release acetic acid; at module operating temperatures the rate is low, but over 25–30 years in the presence of water vapor the cumulative acid can be sufficient to lower interfacial pH at glass and cell surfaces. TOPCon cells use ultrathin tunnel oxide and doped polysilicon layers; corrosion at the busbar or finger contact can increase series resistance. Low-acid EVA lowers the hydrolysable acetate content and includes acid-scavenging additives, but it does not eliminate moisture ingress. Therefore, double-glass edge sealing and low-moisture ingress design still apply.
| Parameter | Conventional EVA | Low-acid EVA | POE |
|---|---|---|---|
| Acetic acid generation at 85 °C/85% RH, 1000 h | 200–600 µg/g (literature range) | 50–150 µg/g (formulation-dependent) | <10 µg/g |
| Volume resistivity after damp heat | 1×1013–1×1014 Ω·cm | 1×1014–1×1015 Ω·cm | ≥1×1015 Ω·cm |
| Glass peel strength after cure | ≥60 N/cm | ≥60 N/cm | 40–60 N/cm |
| Water vapour barrier | Low | Low to moderate | Moderate |
| Lamination process window | Broad | Broad | Narrower |
| Relative cost | Baseline | Higher than conventional EVA | Highest |
Compared with POE, low-acid EVA retains the silane-promoted glass adhesion and lower-temperature processability of EVA. Its moisture barrier is lower than POE; water vapour transmission rate through a 0.55 mm EVA film is commonly higher than through an equivalent POE film. In double-glass construction, the rear glass limits bulk water entry, but edge moisture ingress remains a design variable. Therefore, for installations with high humidity and marine salt exposure, the product is often paired with POE at the rear rather than used as the sole rear encapsulant. The product differs from multilayer EVA-POE-EVA films: multilayer films combine an inner POE layer with EVA outer layers, whereas a low-acid EVA monolayer retains single-layer construction and avoids co-extrusion complexity. This can simplify lamination and reduce material cost, but it does not provide the same volumetric moisture barrier as a POE core.
The product is supplied as a fully compounded, pre-mixed EVA sheet containing peroxide, silane adhesion promoter, UV stabiliser package, and acid scavenger. Crosslinking follows peroxide-initiated free-radical cure kinetics; laboratory differential scanning calorimetry data for EVA encapsulants typically show a cure exotherm peak between 130 °C and 160 °C, with the peak location dependent on heating rate. The supplier's release documentation should report gel-content response at a defined lamination time-temperature profile. In production, membrane laminators are set to platen temperatures of 145–150 °C; the dwell time is 14–18 min after the laminate core reaches temperature. Vacuum below 60 Pa for 3–5 min is commonly applied before membrane pressurisation, with the cure target of 75–85% gel content. A gel content below 70% produces creep and edge extrusion after lamination, while gel content above 90% reduces elongation and may increase edge stress in thin glass formats.
Double-glass laminators with 2.0 mm/2.0 mm glass may require lower pressure or a thicker EVA of 0.70 mm to prevent cell displacement. The lower melt stiffness of EVA compared with POE can be advantageous for filling the intercell gap but also increases sensitivity to laminator pressure uniformity. Field experience on multi-chamber laminators indicates that pressure ramp rate should not exceed 0.5 bar/min until the glass edges are fully sealed to avoid gross squeeze-out. On a three-chamber double-glass laminator, the first chamber is typically set at 130–135 °C for vacuum and preheating, the second at 145–150 °C for cure, and the third for controlled cooling. The glass temperature, not the chamber air temperature, must be used to start the cure dwell. Thermocouple studies in double-glass stacks show a 5–8 °C lag between the platen and the encapsulant layer during the first 8–10 min. Premature pressurisation before the encapsulant reaches flow temperature compresses the film but does not complete cell-gap filling, causing bubble entrapment at the string-gap edge.
Minimum complex viscosity in oscillatory shear at 0.1 rad/s during ramp is typically in the 1000–3000 Pa·s range; this low viscosity is required for the film to wet the glass and cell surfaces but must be controlled to prevent excessive squeeze-out. The exact viscosity depends on the peroxide decomposition half-life and the temperature ramp rate. Laminator platens should have temperature uniformity within ±2 °C; pressure uniformity across 2.6 m×1.3 m platens should be verified before processing thin glass.
Moisture uptake above 60% RH for more than 4 h increases the risk of bubble formation; rolls should be stored at 5–30 °C and 40–60% RH, and condensation must be avoided. If roll temperature is below the dew point of the production hall, the sealed packaging should remain closed until temperature equilibration is complete.
Double-glass modules remove the backsheet vapor barrier and expose the encapsulant to a lower through-thickness moisture flux but a longer edge-encapsulant diffusion path. In this geometry, the rear encapsulant must maintain adhesion to glass and busbar-ribbon interfaces while resisting hydrolysis at the module edges. The HIUV TOPCon Double-glass Low-acid EVA Film can be used as a symmetrical front and rear encapsulant in temperate climates, but in coastal or high-humidity service a rear-side POE encapsulant is recommended to compensate for the higher moisture permeability of EVA. The difference from conventional EVA remains measurable under damp-heat test conditions: conventional EVA often exhibits reduced volume resistivity and adhesion loss at the cell edge after 85 °C/85% RH exposure, while low-acid EVA is formulated to maintain interfacial adhesion for longer exposure periods. However, low-acid EVA does not reach the moisture-barrier performance of POE; test data should be verified using full module IEC 61215-1:2021 DH2000 sequences and PID-s at -1000 V for 96 h under 85 °C/85% RH.
Qualification of TOPCon double-glass modules using low-acid EVA typically requires visual inspection per IEC 61215-1:2021 MQT 01, insulation resistance per MQT 03, damp heat per IEC 61215-2:2021 MQT 13, humidity freeze per MQT 12, thermal cycling per MQT 11, and PID resistance per IEC TS 62804-1:2015. The encapsulant is not qualified in isolation; module-level testing is mandatory because interfacial adhesion depends on glass cleanliness, cell busbar topography, and laminator vacuum profile. Edge sealing specifications for humid sites should require a butyl or two-part silicone edge sealant with a moisture vapor transmission rate below 1 g/(m²·day) at 38 °C/90% RH; the encapsulant itself does not provide an edge moisture barrier.
For operations that store rolls above 30 °C or at relative humidities above 60%, pre-drying at 50 °C for 8–12 h in forced air is recommended before lamination. The material is not compatible with amine-catalysed silicone edge sealants during pre-lamination handling because residual amines can accelerate peroxide decomposition and produce local overcure at the glass edge. No peroxide post-cure annealing is required if gel content is within the specified range; if gel content is below 70%, a post-lamination thermal cure at 145 °C for 15 min may be applied, but module warpage in thin double-glass formats should be assessed.
