Latest self-adhesive tape makes pretreating aluminum quicker, easier

September 2013 - Pretreating large metal components before repair takes time. In Germany, researchers are exploring how to simplify the pretreatment process of aluminum (and other metals), moving away from pickling pastes and sprays in favor of tape.

Repairing vehicles and devices—anything from railcars to aircrafts—requires a pretreatment process to remove contaminants before any fabrication work. Traditionally, pickling sprays and pastes are used to treat metal. In order to make this work, fabricators must mask the areas of the metal that are not to be repaired, taking time and manpower. To remove the pickling agent, the surface needs to be rinsed with water, resulting in large amounts of contaminated waste water, which then needs to be collected and disposed. 

“For the pickling tape, all pickling agents are included in the adhesive,” says Dr. Malte Kleemeier, researcher at Fraunhofer Institute for Manufacturing Technology and Advanced Materials, adhesives and polymer chemistry, Bremen, Germany, and Dr. Malte Burchardt, researcher for Fraunhofer IFAM’s adhesion and interface research. “There is no masking and no excessive rinsing necessary, making the process simpler and safer.” Fraunhofer IFAM researches and develops products for shaping and functional materials and adhesive bonding technology and surfaces.

Other possible advantages include the pickling tape’s ability to effectively remove oxide layers, conversion coatings and accumulation layers. “Hydrophobic contaminants, such as deep-drawing lubricants, are not removed,” says Kleemeier and Burchardt. “They need to be removed prior to application of the pickling tape. We expect that repair of painted aluminum or bonded repair will benefit most from the pickling tape.”

Preparing for commercial availability

Kleemeier and Burchardt found that for pickling, using acid and water was necessary within the adhesive. So only water-based polymers were used as opposed to what is used in pressure sensitive adhesive tapes, such as Scotch tape, which use solvent-based adhesives. Water-based polymers have limited availability and Fraunhofer IFAM conducted a number of tests to find the best formulation. The trick was to find the right amount of stickiness that could be removed without leaving residue. The tape would have to be sufficiently fast and provide consistent pickling action on the metal surface, according to Fraunhofer IFAM.

Once applied, the treatment time is comparable to sprays or pastes, but both Kleemeier and Burchardt note that a significant amount of time is saved because preparation is simplified. There is no need to mask areas not being treated or protecting the part from contaminated wastewater. “The subsequent rinsing is replaced by a simple wiping with a damp cloth.”

Both Kleemeier and Burchardt expect that repair of painted aluminum or bonded repair will benefit the most from pickling tape, such as needed to repair light aircraft. As aircraft fleets around the world age and deteriorate, repair and maintenance are particularly important. “A simple and safe way to pretreat metal surfaces locally prior to repainting or bonding will make life easier for the repair shops and increase the quality of the repaired parts,” says Kleemeier and Burchardt.

Initially, the tape will be available for aluminum applications. Applications for stainless steel or other metals are in the works. A price point is not yet available because development of the tape is ongoing. “It can be expected that the price will be slightly higher compared to conventional pastes or sprays,” says Kleemeier and Burchardt. “But the savings in time and the improved usability will likely compensate for that.” 

Researchers had to look beyond the practical applications of the tape. “Seeing the effort of reducing the ecological footprint in many industries, disposal was one of the considerations during the development [of the tape],” says Kleemeier and Burchardt. Minimizing wastewater during the rinsing of the treated metal was a major concern.

Going forward, research at Fraunhofer IFAM will continue, further exploring the functions of pickling tape to make it useable as an anodizing tape. Kleemeier and Burchardt believe expanding these functions will further enhance the quality of pretreatment. MM