EVATHENE UE2828 EVA resina de copolímero, grau de encapsulação de células solares

EVATHENE UE2828 EVA Copolymer Resin, Solar Cell Encapsulation Grade, is an ethylene-vinyl acetate base resin supplied as translucent pellets for photovoltaic module lamination. The manufacturer-reported vinyl acetate content is 28 wt%, placing the grade in the high-VA class used to reduce crystalline light scattering and to increase polar adhesion to module glass. Melt flow rate is 25 g/10 min when measured at 190 °C under a 2.16 kg load in accordance with ASTM D1238 and ISO 1133-1. The resin is an uncompounded base material; it is not supplied with organic peroxide, silane coupling agent, UV absorber, or crosslinking coagent. Formulation, compounding, and film production are downstream operations. Packaging is usually multilayer paper or polyethylene-lined bags to limit moisture ingress, and bulk handling should use dried compressed air to avoid condensation.

The table states manufacturer-reported typical values; the luminous transmittance value is for a fully compounded and cured film, not for the neat pellet. Published multi-laboratory verification data for this specific configuration is limited, so incoming resin certification and laminated-film testing under the module maker’s lamination profile remain necessary.

How Does the Vinyl Acetate Distribution Influence Crystallinity and Optical Transmission?

The 28 wt% vinyl acetate content reduces the ethylene sequence length and depresses crystallinity relative to 18 wt% VA extrusion grades. Differential scanning calorimetry per ASTM D3418 shows a broad melting endotherm near 62 °C and a lower heat of fusion than low-VA resins, which is consistent with a thinner lamellar population. Lower crystallinity reduces haze and increases luminous transmittance. In cured 0.45 mm encapsulant films, ASTM D1003 transmittance of 90 % to 92 % and haze below 5 % are typical acceptance ranges for EVA encapsulants. The VA ester also increases surface polarity and contributes to wetting on glass before silane condensation. FTIR peak ratios at 1740 cm⁻¹ for the carbonyl and 1240 cm⁻¹ for the acetate C–O stretch are used for lot release VA content verification. Solar encapsulation grades are further screened for gel particles and contaminant specks because a fish-eye or black speck in the film can create local light scattering at the cell margin.

Formulation with a silane coupling agent, commonly vinyltrimethoxysilane at 0.3 wt% to 0.5 wt%, is required to convert the inherent VA polarity into durable interfacial adhesion. The silane methoxy groups hydrolyze and condense with silanol groups on glass, while the vinyl group participates in the peroxide-initiated EVA network. Peel adhesion measured per ASTM D903 on laminated glass is typically between 40 N/cm and 80 N/cm for a well-cured film, depending on silane addition, glass cleaning, and lamination cycle. Without the silane or with insufficient silane condensation, adhesion can fall below 20 N/cm after damp heat.

When the Melt Flow Rate Is Set at 25 g/10 min, What Processing Trade-offs Appear in Cast Film Production?

The 25 g/10 min MFR lowers melt viscosity and enables lamination temperatures from 140 °C to 150 °C to fill cell gaps without excessive hydraulic pressure. In vacuum laminators, the cure cycle is typically divided into a first stage at 120 °C to 130 °C under vacuum to wet the glass and backsheet, and a second stage at 145 °C to 150 °C to decompose peroxide. Vacuum pressure below 1 mbar during the first stage removes air and volatile by-products. The high MFR reduces extruder torque in compounding and can raise throughput on 30:1 L/D twin-screw extruders. The associated trade-off is lower melt strength. On chill-roll cast film lines, the film can draw down at the edges or oscillate in thickness when the draw ratio between die lip and chill roll is too high. Melt strength can be managed with electrostatic pinning, vacuum box stabilization, die gap control between 0.5 mm and 1.0 mm, and chill roll temperatures between 15 °C and 25 °C. Published data for UE2828-specific melt strength versus line speed is limited; line trials are required to set air gap and roll speed for a given die width.

A compounder typically blends the resin with 1.0 wt% to 1.5 wt% organic peroxide, 0.1 wt% to 0.3 wt% hindered phenolic antioxidant, and 0.3 wt% to 0.5 wt% silane coupling agent in a co-rotating twin-screw extruder with L/D ratio 30:1 or longer. Melt temperature is maintained below 120 °C during compounding to prevent premature peroxide decomposition; low-shear screw elements and barrel cooling zones are used. The compounded pellets are then dried before film extrusion. Water cooling sections are controlled to avoid pellet moisture above 0.1 % because moisture in the compound can hydrolyze silane during storage.

During film extrusion, barrel zone temperatures are set between 190 °C and 230 °C. Sustained melt temperatures above 240 °C accelerate deacetylation, producing acetic acid, yellowing, and reduction in VA content. Pre-drying in desiccant hoppers at 60 °C to 70 °C for 4 h to 6 h is recommended when storage RH exceeds 60 %. A closed-loop thickness gauge should hold film thickness within ±5 % of nominal because thickness variation affects both optical transmission and lamination melt distribution.

UE2828 differs from general-purpose extrusion EVA grades in gel specification and optical cleanliness. General-purpose EVA with the same nominal 28 wt% VA content may have wider gel and contamination tolerances that produce visible defects in a thin encapsulant film. Relative to 18 wt% VA EVA, UE2828 has lower crystallinity and lower tensile modulus, which reduces stress on cells during thermal cycling but increases chain mobility and water uptake. Water absorption for EVA encapsulant films tested per ISO 62 typically ranges from 0.1 % to 0.3 % after 24 h immersion. Relative to a 33 wt% VA EVA solar grade, 28 wt% VA may reduce ester hydrolysis sites but also reduces the total polarity available for glass wetting. Selection between 28 wt% and 33 wt% VA is made after ASTM D903 peel testing and damp heat retention at 85 °C/85 % RH. Compared with polyolefin elastomer encapsulants, EVA has a wider commercial lamination window but greater potential for acetic acid generation under damp heat. Polyolefin elastomers do not contain ester groups and therefore avoid acetic acid formation, but they generally require different primer or adhesion-promoter chemistry.

Acetic Acid Generation, Damp Heat Aging, and Module Qualification

During damp heat exposure at 85 °C/85 % RH per IEC 61215, EVA slowly hydrolyzes and releases acetic acid. The acid can corrode solder coatings, increase series resistance, and degrade the interfacial adhesion between encapsulant and glass/backsheet. Encapsulant formulations based on 28 wt% VA EVA are therefore compounded with hydrolysis-resistant packages and cured to gel content above 70 % when measured by xylene extraction per ASTM D2765. A dense crosslinked network reduces ion mobility and acetic acid diffusion. Adhesion retention after 1000 h damp heat should remain above 50 % of initial ASTM D903 peel values. Volume resistivity measured per IEC 60093 or ASTM D257 should remain above 1 × 10¹⁴ Ω·cm for module insulation. UV stabilizers are added in the compounded film because the base resin itself has limited UV stability; UV exposure without stabilizer leads to chain scission, yellowing, and loss of transmission. Published UE2828-specific damp heat data is limited in public literature; the recited acceptance ranges are industry-class baselines for EVA encapsulants and not a product-specific guarantee.

Regulatory screening of EVA encapsulant films under RoHS uses IEC 62321 methods for restricted substances. REACH registration and Safety Data Sheet obligations sit with the resin supplier, importer, or compounder according to tonnage and regional role. Incoming resin should be sampled for moisture content, melt flow rate, and VA content; batches exceeding the supplier certificate tolerance for MFR or showing pellet discolouration should be quarantined. Storage below 30 °C in sealed packaging away from UV is required to prevent oxidation and moisture uptake. Incompatibility with unneutralized amine-based additives is noted because amine species can accelerate ester hydrolysis or interfere with peroxide cure; slip agents or anti-static packages containing free amines should be avoided in direct contact with the compounded resin.