KENGO ET-HIGH EVA Film (for PDLC Smart&Intelligent glass)

For interior switchable privacy partitions, the KENGO ET-HIGH film is inserted on each side of a PDLC polymer-dispersed liquid crystal film in a symmetrical stack: 4 mm low-iron tempered glass / 0.38 mm ET-HIGH / 0.125 mm PDLC carrier / 0.38 mm ET-HIGH / 4 mm low-iron tempered glass. The ET-HIGH film must be de-aired under silicone membrane vacuum below 0.095 MPa at 20–25 °C for 5–8 min before the first heat ramp. Chamber heating at 2.0–2.5 °C/min to 80 °C allows the EVA surfaces to begin wetting the glass and PDLC film without trapping low-volatile moisture at the interface. A second ramp to 115 °C is held for 40–45 min to reach the crosslink plateau without exceeding the thermal budget of the PDLC film. Cooling proceeds under vacuum to 40 °C before release. The centre-to-edge temperature differential on a 1.2 m × 2.4 m flatbed laminator should remain below ±2 °C; larger deviations produce measurable edge creep and haze. Optical acceptance for a finished privacy partition follows ASTM D1003-21 for haze (≤2.5%), ISO 13468-1:2019 for total luminous transmittance in the clear state (≥85%), and ASTM E313-20 for yellowness index after 1000 h of damp-heat exposure (≤1.5). Films stored above 60% relative humidity must be pre-dried at 60 °C for 12 h; residual interface moisture is the dominant cause of post-lamination microvoids at the PDLC-to-EVA boundary. The finished panel is classified under EN ISO 12543-2:2021 for laminated safety glass. The PDLC bus bar is inserted before lamination and must remain conductive after edge trimming; a four-point probe is used to verify that the sheet resistance at the bus bar has not increased by more than 5%.

What Limits Dwell Time at 115 °C for PDLC Film Switching Contrast?

Dwell time is governed by the parallel kinetics of EVA crosslinking and PDLC liquid crystal reorientation damage. Organic peroxide decomposition in EVA interlayers follows first-order kinetics; the half-life at 115 °C is generally between 40 min and 70 min depending on the peroxide package, and this must be verified by differential scanning calorimetry because the ET-HIGH formulation may contain a proprietary peroxide blend. PDLC films tested by the manufacturer typically show contrast ratio loss when held above 110 °C for more than 60 min. The failure mechanism is not film yellowing but irreversible coalescence of liquid crystal domains, which increases off-state clarity and reduces on-state transparency. Temperature mapping with embedded thermocouples at glass edges and centre is required because silicone membrane heating platens can show edge-to-centre skew of up to 8 °C on multi-chamber vacuum laminators. A two-stage cycle with 95 °C pre-cure for 20 min followed by 112–115 °C for 25–30 min frequently yields acceptable peel strength while limiting PDLC thermal exposure. The flow of ET-HIGH under these conditions is low enough to maintain an edge overhang of 1.0–1.5 mm, but the film does not fully encapsulate exposed ITO leads. Electrical continuity must be checked after trimming; any cut that severs or exposes the bus bar produces visible switching lag at the panel edge. Compliance with ISO 12543-4:2021 for high-temperature, humidity, and radiation durability is needed for interior laminated safety glass. Peel adhesion to glass after boiling should not fall below the minimum specified in ISO 12543-4:2021, and the test result is only valid if the PDLC film remains fully functional through 500 switching cycles at 85 °C.

The first production failure observed in refrigerator door lamination trials occurs when the glass panel passes the initial optical inspection but develops edge hazing after 72 h of thermal cycling between −25 °C and +50 °C. This failure is traced to moisture ingress at the trimmed edge, not to bulk interlayer incompatibility. KENGO ET-HIGH film used in these applications is typically 0.25 mm per side, paired with 3.2 mm tempered glass and a 0.1 mm PDLC film. The thinner ET-HIGH profile reduces thermal mass and allows faster cooling, but it also demands tighter edge sealing. The vacuum bag lamination sequence for refrigerator door glass uses a flatbed press rather than an autoclave. De-airing at 0.098 MPa for 6 min is followed by a ramp at 3 °C/min to 105 °C. The hold duration is 50 min at 105 °C, which is below the 115 °C architectural cycle to protect the lower-grade PDLC films used in white goods. A slower ramp rate of 2 °C/min is required if the door glass has a low-E coating, because coated glass reflects radiant heat and creates a top-to-bottom temperature gradient. The finished door panel must resist condensation on the cold side and maintain steady switching at −20 °C. Moisture vapour transmission through the exposed edge is limited by applying a polyisobutylene primary seal and a neutral alkoxy-cure silicone secondary seal. The panel is conditioned for 1000 h at 85 °C and 85% relative humidity per IEC 60068-2-30; the acceptance criterion is no delamination beyond 1.0 mm from the visual edge and no visible change in PDLC off-state scattering. Batch records from refrigerator door lines indicate that edge sealant adhesion to the ET-HIGH surface is the primary variable controlling humid-ageing failure rate.

Autoclave dwell at 1.2 MPa compensates for low melt flow but not for PDLC film creep

Automotive laminated switchable glazing with KENGO ET-HIGH film is processed in an autoclave after a cold pre-press or nip-roller de-airing step. The glass stack for a curved roof panel typically consists of 2.1 mm chemically strengthened outer glass / 0.38 mm ET-HIGH / 0.125 mm PDLC film / 0.38 mm ET-HIGH / 2.1 mm inner glass. Autoclave pressure of 1.2 MPa at 120 °C prevents residual air pockets without requiring high melt flow. However, pressure cannot compensate for the creep of the PET carrier inside the PDLC film when the autoclave temperature exceeds the PET glass transition onset near 78–85 °C. At 120 °C, biaxially oriented PET softens enough to allow thickness redistribution under 1.2 MPa, particularly in the zones directly below autoclave tray supports. Even a thickness deviation of 5 µm across the carrier produces an optically visible shadow in the off state because the electric field gradient changes. Therefore, autoclave dwell is limited to 25–35 min at 118–120 °C, after which the pressure is held while the chamber is cooled to 45 °C before release. The automotive stack must pass ECE R43 impact testing for laminated safety glass and ANSI Z26.1-2017 for the US market. A 227 g steel ball drop is employed under ANSI Z26.1-2017; the panel is considered acceptable only if the glass remains in place and the PDLC film continues to switch across 95% of the visible area after the impact. Edge overhang for OEM mounting is specified below 0.5 mm, which requires automated trimming after autoclave and inspection of edge bus bar continuity. Peel adhesion at the glass interlayer after boiling is verified per ISO 12543-4:2021, and the bus bar peel strength must exceed 2.0 N/mm before electrical connection is made. Autoclave load density should not exceed 70% of chamber free volume, because pressure shadowing from dense loading alters the film flow profile and creates localised optical distortion near tray edges.

Projection display lamination stacks introduce a different set of optical constraints from privacy-only glazing. In a retail storefront or executive presentation window, the ET-HIGH interlayer is bonded between an optical-grade 4 mm soda-lime glass front and a rear glass that may be coated with a projection gain layer. The PDLC film is placed closer to the front glass to minimize the light path through the scattering layer. A typical stack is 4 mm front glass / 0.38 mm ET-HIGH / 0.1 mm PDLC / 0.25 mm ET-HIGH / 3 mm rear glass. Unlike architectural privacy partitions, projection displays require tight control of transmitted wavefront distortion. ET-HIGH film thickness variation must be below ±0.02 mm across a single sheet; values measured by contact gauge at 10 cm grid spacing are recorded before lamination. Vacuum bag lamination is used instead of autoclave because high pressure can induce micro-waviness in the PET carrier and alter rear-projection gain uniformity. The bag cycle begins with 0.096 MPa de-airing for 10 min, then heats at 1.5 °C/min to 105 °C. The long, slow ramp prevents convective unevenness inside the bag, which is a known source of visual mura in projection panels. Hold time is 30 min at 105 °C; cooling to 40 °C occurs under vacuum at 1.5 °C/min. The finished panel must achieve luminous transmittance above 85% per ISO 13468-1:2019, haze below 1.5% per ASTM D1003-21, and no local contrast inversion across a 0.9 m × 1.5 m active area. Projection gain changes by less than 0.1 unit before and after lamination when measured with a 5500 K reference light source. Published data for ET-HIGH film under laser projector wavelengths is limited; qualification tests for infrared blocking or blue-light durability must be run on the finished stack.

If acid-cure silicone edge sealants release acetic acid during PDLC edge potting, what happens to ITO electrode resistivity?

The exposed indium tin oxide (ITO) edge electrodes of a PDLC film are electrochemically sensitive to acid vapour. Acetoxy-cure silicone sealants release acetic acid during room-temperature vulcanisation. When that acid diffuses to the exposed bus bar or ITO surface before full polymerisation, sheet resistance increases and the electric field across the PDLC layer becomes non-uniform. A sheet resistance rise above 10% at the outer 5 mm of the panel is sufficient to produce a visibly slower switching response along the edge. KENGO ET-HIGH film, laminated with an edge overhang of 1.0–1.5 mm, forms a physical barrier over the cut edge only if the trimming line is aligned with the film edge and the laminate has no exposed ITO voiding. This is difficult to guarantee on high-speed production lines. Therefore, edge potting of PDLC modules for facade or partition use must be performed with neutral alkoxy-cure or two-component polyurethane sealants, not acid-cure RTV silicone. The ET-HIGH film itself must be tested for acid number after lamination because residual peroxide by-products can generate a mildly acidic interface. An acid number below 1.0 mg KOH/g is preferred for edge durability. Electrical testing after 500 switching cycles at 85 °C and 85% relative humidity follows IEC 60068-2-30. The panel passes only if the off-state scattering morphology remains uniform and the sheet resistance at the bus bar does not exceed its initial value by more than 15%. This acceptance criterion is tighter than the one used for architectural laminates without edge-sealed PDLC because the edge seal is the primary ingress pathway for moisture and atmospheric sulphur compounds.

Aerospace cabin window qualification for PDLC dimming systems imposes flammability and decompression requirements absent from architectural applications. The laminate stack for a commercial aircraft window must meet the 14 CFR Part 25.853(a) vertical burn test and the 14 CFR Part 25.853(d) heat release rate limit. Standard EVA films, including low-flow ET-HIGH, are generally not formulated with halogen or phosphorous flame retardants and therefore may exceed the 65 kW/m² peak heat release rate limit of 14 CFR Part 25.853(d) unless a fire-blocking interlayer is added. Published data for ET-HIGH film in aerospace PDLC constructions is limited; qualification testing on the specific layup is mandatory. A typical stack would include 3 mm stretched acrylic outer ply / fire-blocking silicone or polycarbonate layer / 0.38 mm ET-HIGH / 0.1 mm PDLC film / 0.38 mm ET-HIGH / 3 mm stretched acrylic inner ply. The vacuum bag process must not exceed 110 °C for more than 30 min, because stretched acrylic begins to release stress and the PDLC film loses contrast at higher thermal loads. Decompression testing under 14 CFR Part 25.775 or equivalent aviation authority standards requires that no interlayer delamination occur after rapid pressure reduction from cabin altitude to 12,000 m equivalent. The ET-HIGH film must be pre-conditioned at 23 °C and 50% relative humidity for 48 h before lamination. Moisture left in the film will cause hazy interfacial bubbles that are unacceptable under aerospace visual inspection criteria. Edge sealants and electrical bus bars must also pass flaming-fluid test requirements if the window is located near engine zones. Because this application sits outside standard architectural or automotive qualification sequences, production-scale data for ET-HIGH film is limited to laboratory panels and small-batch cabin demonstrators.