Adhesive tapes, the adhesive resins of which can be cured (and thereby rigidized) by exposure to ultraviolet and/or visible light, are being developed as repair patch materials. The tapes, including their resin components, consist entirely of solid, low-out-gassing, nonhazardous or minimally hazardous materials. They can be used in air or in vacuum and can be cured rapidly, even at temperatures as low as –20 °C. Although these tapes were originally intended for use in repairing structures in outer space, they can also be used on Earth for quickly repairing a wide variety of structures. They can be expected to be especially useful in situations in which it is necessary to rigidize tapes after wrapping them around or pressing them onto the parts to be repaired.
As now envisioned, when fully developed, the tapes would be tailored to specific applications and would be packaged in light- and radiation-resistant, easy-to-use dispensers. The resins in the tapes would be formulated to be curable by low-power light at specific wavelengths that could be generated by light-emitting diodes (LEDs). Each such tape dispenser would be marketed as part of a repair kit that would also include a companion battery-powered LED source operating at the required wavelength.
Each tape consists of a fine-weave fabric impregnated by a resin. On one side of the tape there is a cover ply that prevents the tape from sticking to itself when it is rolled up as in a dispenser. Depending on the specific intended application, the cover ply and resin can be selected such that the cover ply can be either released from the tape or cured in place as an integral part of a repair patch.
The feasibility of the light-curing tapes was demonstrated in experiments in which tapes were made from fiberglass fabric impregnated, variously, with (1) cationic epoxy resins plus a sensitizer that preferentially absorbs light at a wavelength of 380 nm, (2) free-radical curing acrylate resins, or (3) blends of resins of both types. Methods of incorporating adducts into the epoxies to tailor their viscosities were developed. The tapes were applied to aluminum and carbon/epoxy composite substrates that had been prepared by sanding and wiping with alcohol. The resins were cured by 380-nm light from LEDs. The blends of resins of both types were found to be advantageous in that during exposure to the light, their acrylate components contributed rapid buildup of strength, while their epoxy components contributed adhesion and longer-term strength.
Poly(ethylene terephthalate) backing films were shown to pass the needed 380-nm light and, when prepared with corona treatment, to adhere well as parts of cured tapes. Peel tests confirmed generally high degrees of adhesion to aluminum substrates. Demonstrations of repairs were made, including bonding pipes of various materials together, patching burst pipes, and patching punctures. A 1-in. (2.54-cm) patch over a 1/2-in. (1.27-cm)- diameter hole was pressurized to 120 psi (≈0.83 MPa) without failure or delamination.