Windscreens and rear window glass are bonded on the outer edges with liquid PU adhesives as a final bonding step.
However, until the liquid PU adhesive cures (which can take several hours or even one to two days, depending on conditions and bond line), locator pins can hold the glass in position to avoid any misalignments or uneven gaps at the edges.
The DuploLUX 14071 adhesive tape system is applied to those locator pins in a three-step process. First, a user removes an opaque protective liner film from the pre-applied adhesive tape. Second, the exposed tape surface is activated for three seconds with UV light (365nm/UVA LED, at an energy dose greater than 3,000mJ/cm²). Third, the pin is pressed to the glass with a pressure of at least 20N/cm². As a visual aid during assembly, the cyan-coloured tape turns pink as it cures.
Once applied to the glass, the tape is strong enough to be processed further, as handling strength is immediate. Final bonding strength and static shear resistance prevents the windscreen creeping or sliding on the pins, so the window can be positioned in the car body on the final assembly line. Within two hours, the partially-cured adhesive’s shear strength has increased to over 3MPa; after 24 hours its full cure lap shear strength of over 4MPa is reached (see below). Quasi-static tensile strength tests reveal a strain before break of 0.75mm (at forces greater than 1kN).
Previously, pin bonding was often carried out using PSA acrylic foam. In comparison, UV-Lux provides nearly three times the shear strength. In addition, while PSA can withstand one to two hours of static shear, though displacement begins after only a couple of minutes, UV-Lux’s resistance to shear lasts for weeks at least.
Also, compared with liquid adhesives that cure under UV, UV-Lux offers greater variety of add-on part materials, as its cationic curing mechanism does not require any translucent parts. In contrast, liquid UV-cure adhesives’ mechanism requires irradiation through one of the substrates.
Lohmann’s new system is said to be more efficient, stable and repeatable than liquid adhesive alternatives. It offers three particular benefits. First is the potential for post-autoclave assembly, in that it provides a way to equip glass with add-on parts freely after the autoclave process. Second is the ability to reduce weight by swapping metal parts for plastic. Since the process does not introduce heat as does thermal epoxy bonding, it therefore is safe for glass, protecting it from thermal stress. It also supports reducing the thickness of the glass. Third, it can be used in a sustainable process that requires no cool chain, and involves parts that are pre-equipped with die-cuts delivered ready to use.
