The Material That Makes Bending Possible Without Breaking
The commercial launch of foldable smartphones, rollable displays, and flexible wearable electronics has created a new requirement for adhesive materials whose performance specifications would have seemed contradictory to adhesive chemists working in conventional electronics assembly a decade ago. A pressure-sensitive adhesive used in a foldable smartphone must bond the display stack layers with sufficient adhesion to prevent delamination under the mechanical stress of hundreds of thousands of fold cycles. It must be optically transparent to the wavelengths of visible light emitted by the OLED display whose image must pass through the adhesive layer without colour shift or haze that the viewer would detect. It must maintain these properties across the temperature extremes that smartphone use environments impose, from the sub-zero temperatures of outdoor winter use to the elevated temperatures of summer automotive dashboard exposure. And it must recover its optical clarity and mechanical integrity after each fold cycle without the stress whitening or void formation that the bending creates in conventional adhesive films whose elastic range does not accommodate the fold radius that commercial foldable devices require.
Pressure-sensitive adhesives are viscoelastic materials that bond to surfaces through the application of light pressure without the activation of chemical crosslinking that structural adhesives require. Their adhesion derives from the intimate contact between the adhesive's viscoelastic surface and the substrate's surface features, with the adhesive's flow at the molecular level under low applied pressure creating the contact area that generates the van der Waals forces whose cumulative strength provides the bond. In conventional electronic assembly, PSA tapes and films serve as the bonding layer between display glass and touch sensor, between protective films and display surfaces, and between component mounting and structural chassis elements in consumer electronics whose assembly relies on PSA bonding rather than mechanical fastening or liquid adhesive application for an increasing proportion of its assembly operations. The transition to foldable electronics has required the development of new PSA formulations whose elastic recovery after deformation substantially exceeds that of the acrylic PSAs that dominate conventional electronics assembly applications.
Optical Clear Adhesive and the Display Stack
Optical clear adhesive is the specific PSA category whose commercial development has been most directly driven by the foldable display market. An OCA film used in the display stack of a foldable smartphone must meet optical specifications that include greater than ninety-nine percent transmittance, less than one percent haze, and refractive index matching to the display cover film and the OLED panel whose optical path it occupies. The mechanical specifications include sufficient elastic modulus to transmit the touch sensor signal through the adhesive layer without signal attenuation, sufficient adhesion to prevent delamination at the fold, and sufficient recovery after bending to return the adhesive layer to its original thickness and optical properties after each fold cycle without residual deformation that would create visible image distortion. Meeting all of these specifications simultaneously in a material that can be manufactured at the dimensional precision and thickness uniformity that display manufacturing requires is the technical challenge that the optical clear adhesive development programmes of 3M, Nitto Denko, Tesa, and Toray have been addressing as the foldable display market has created commercial demand for materials that did not previously exist in commercial production.
The competitive landscape for optical clear adhesive in foldable displays is defined by the depth of co-development relationships between adhesive manufacturers and display panel makers whose process integration requirements determine whether a specific OCA formulation can be adopted in a production display stack. Samsung Display, BOE, and LG Display, whose flexible OLED panels are incorporated in the majority of commercial foldable smartphones, each have specific process requirements for the OCA films used in their display stacks whose validation requires the technical collaboration and process qualification that adhesive manufacturers must invest in before their products can be specified in a production display. The qualification of a new OCA supplier for a display stack that is already in mass production is treated as a significant engineering project whose timeline is measured in months and whose technical risk must be managed carefully to avoid yield impact on a production line whose output is measured in millions of dollars per day.
Beyond Foldables: The Broader Flexible Electronics PSA Market
The foldable smartphone market is the highest-profile application driving flexible electronics PSA development but represents a small fraction of the total flexible electronics adhesive market by volume. Flexible printed circuit boards used in virtually every consumer electronics device as the interconnect between rigid circuit board regions and the connectors, displays, and sensors whose position requires a non-rigid connection use PSA coverlay and bonding films whose volume is measured in billions of square metres annually. Medical wearable sensors including ECG patches, continuous glucose monitors, and wound monitoring devices that must adhere to skin for days at a time use skin-contact PSAs whose biocompatibility, breathability, and gentle removal properties are the design requirements that medical device grade adhesive formulations address. The flexible solar cell market uses encapsulant and lamination adhesives whose UV stability, water vapour barrier performance, and long-term outdoor durability specifications differ from all other flexible electronics applications but whose technical development benefits from the optical clarity and thin film coating expertise that foldable display OCA development has created.
Top 10 Companies in Pressure-Sensitive Adhesives for Flexible Electronics Globally
- 3M: Largest PSA company globally with the broadest portfolio of optically clear adhesives, conductive adhesive films, and specialty electronic assembly tapes; its 3M Optically Clear Adhesive product family and its 3M Electrically Conductive Adhesive Transfer Tape are the reference materials that display and electronics manufacturers specify when establishing new adhesive material standards for their products.
- Nitto Denko: Japanese specialty tape and adhesive company with a major position in optical films and electronics assembly PSAs; its LUCIACS optical clear adhesive for foldable displays and its No.31B base film for flexible electronics are the products whose co-development with Japanese and Korean display manufacturers creates the technical leadership in foldable display adhesive materials.
- Tesa (Beiersdorf): German adhesive tape company with strong positions in electronics assembly and display bonding; its tesa 69401 OCA film and its electronics bonding tape portfolio serve the consumer electronics assembly market where process reliability and thin profile adhesive performance are the primary design requirements.
- Toray Industries: Japanese chemical company with optical film and adhesive products for display applications; its LUMIRROR optical PET base films and its adhesive coating capabilities create the integrated film and adhesive product offering that display manufacturers value for supply chain simplification.
- Henkel: German adhesive company with electronics assembly adhesive products including UV-curable OCA alternatives and conductive adhesive pastes; its Loctite electronics adhesive portfolio and its global technical service network create the application support infrastructure that consumer electronics contract manufacturers depend on for adhesive process development.
- Avery Dennison: US adhesive materials company with specialty adhesive films for electronics and medical device applications; its medical grade skin contact PSAs for wearable sensor attachment and its electronics label and functional film products create the application diversity that distinguishes it from adhesive companies whose portfolio is more narrowly focused on display or structural bonding.
- Lintec Corporation: Japanese adhesive film company with optical adhesive films and semiconductor process tapes for wafer handling; its UV-release dicing tapes for semiconductor packaging and its OCA films for display lamination create the semiconductor and display market positions that Japanese electronics manufacturing supply chain depth sustains.
- Soken Chemical and Engineering: Japanese acrylic adhesive specialist with PSA resins and adhesive products for electronics and optical applications; its acrylic PSA polymer synthesis expertise and its custom adhesive formulation capability create the technical foundation for the specialty performance PSAs that foldable display and flexible electronics applications require beyond what commodity acrylic adhesive chemistry can deliver.
- Mitsubishi Chemical: Japanese chemical company with optical adhesive resin and film products for display applications; its DIANAL acrylic polymer resins and its optical adhesive coating capabilities position it as a raw material and intermediate supplier to the PSA formulation companies whose finished adhesive products reach the display and electronics assembly market.
- Sekisui Chemical: Japanese chemical company with interlayer film and adhesive products for display glass lamination and flexible electronics; its Spulse shock-absorbing adhesive products and its display lamination materials create the specialty adhesive position in the display and automotive glass market whose optical and safety performance requirements are the most demanding in the glass lamination adhesive industry.