More than adhesives

The robot’s yellow gripper arm silently reaches forwards. Controlled by sensors, the silver robot head works its way along the edge of a section of chassis painted white that will become a front car door. The door sealant, which is sticky on both sides, peels off of a large roll, centimeter by centimeter, and is applied with a pressure roller.
A “rubber anvil” ensures that the sealant is properly positioned on the door’s opening. On the side facing the adhesive strip, the sealant is thicker in the middle and thinner towards the outside to act as a sort of guide rail. In addition, this shape helps spread the pressure evenly over the adhesive strip.
“This is a major breakthrough,” Klaus Malecki, director of 3M’s training and application center in Neuss, Germany, says proudly. Until recently, the U.S. manufacturer’s acrylic foam strips were used to automatically apply sealants on car doors, though the process was tricky on a chassis flange offset at a 90 degree angle. It took a little extra time. The door sealants with double-sided adhesives had to be delivered as a closed ring or in strips of varying lengths that were precut to fit. Now, they can simply be pulled off of a large roll.

Expertise for adhesion solutions

But what does this innovation, which was co-developed with the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) and a rubber manufacturer, have to do with PV applications? “A lot,” says Stefan Dornieden, head of 3M’s new renewable energy department for Europe, Africa and the Middle East. “Our strength is the transfer of our expertise from all kinds of applications to new ones, like photovoltaics.” For instance, experience from the automated adhesion technology in automotive construction could be used for panel production: for example, by optimizing adhesives for frames, back rails (assembly systems), or connection sockets. Dornieden says his firm is working closely with such companies as Solarworld, Applied Materials and Oerlikon.
3M developers recently managed to further automate the cleaning process for the manufacture of chassis by using the roll-to-roll approach. A Scotch-Brite high-performance cleaning cloth was cut into a slender, 1.8 centimeter wide strip and integrated in the robot’s cleaning head; the cloth then runs off the roll and back onto it as with a film projector.

Benefits of automation

As Malecki explains: “This automated cleaning not only helps reduce costs, but also increases process safety.” After all, the cleaning cloth used is always fresh as it continues to roll. Automobile manufacturers use the new process, for instance, to clean the door flanges before they are equipped with an acrylic foam strip. The application in photovoltaics is obvious. Within six months, 3M engineers had further developed the process for module production. Dornieden says that glass thin film module manufacturers now use the new process technology. After production, the metal support profiles in solar panels are coated with zinc deposits, which can automatically be taken off with the Scotch-Brite cloths before the 3M adhesive strips are applied to the back rails. Malecki shows the effect on a demonstration system by marking a metal rail with red lines. With a quick press of a button, the application arm moves downwards, pulls the cloth, and cleans the surface of any residue. A Solar Acrylic Foam Tape, when used for automated, off-the-roll module frame adhesion, is more than 1,000 meters long. The standard length is 66 meters, or 100 meters, with thickness varying from 0.4 to 3 millimeters. Dornieden says the two-sided adhesive strips, along with Scotchshield Film 17 back-protective sheets for crystalline panels, are currently his firm’s most important products for the photovoltaic sector. 3M invented the acrylic foam tape – viscoelastic adhesive strips with a foam adhesive middle – which has been used in industry for more than 25 years, and at least ten years in module production. At EU PVSEC in September 2009, 3M presented the latest innovations in product series 2000, 3000, and 4000. Stefan Dornieden lists the benefits: the closed-cell adhesive core is sealed off against dirt and moisture; it is especially resistant to ultra violet light; provides immediate adhesion; can handle great temperature fluctuations extremely well; compensates for the different expansion rates of the materials used without stress; and it can be quickly and cleanly applied. Furthermore, he says the technology has proven to be reliable in the application of adhesives to high-rise façades.
As demonstrated in an accelerated aging test, the Solar Acrylic Foam Tapes have also proven to be especially weatherproof, with long service lives. Even after 10,000 hours under extreme conditions – intense ultraviolet light, moisture, and heat – the adhesive strip’s performance hardly changes.

Streakless adhesives

At 3M’s training lab in Neuss, a wide range of adhesive approaches undergo technical tests. The attempts to pull the Solar Acrylic Foam Tape by hand off of a number of back rail samples (stainless steel profiles) on the laboratory table fail completely. In contrast, a test specimen with a PE adhesive strip is relatively easy to pull apart.
Then comes a demonstration of a connection socket attached to a glass surface with a pad made of Solar Acrylic Foam Tape. A lab worker pulls the protective sheet off and presses the socket onto the glass by hand. She then applies a roller to the back of the plastic socket to increase the pressure for at least five seconds. Shortly thereafter, Matthias Annas, from 3M’s Renewable Energy Development Department in Neuss, can no longer get the plastic off the glass. A look through the glass at the bottom of the plastic reveals that it was attached without streaks.
What is being demonstrated here on a small scale works on a large scale when automated. For instance, leading manufacturers now use adhesives to connect connection sockets to the back of thin film glass modules. As Annas explains, the adhesion process automatically dries the surface of the glass, which helps the adhesive stick. And the adhesive strips are manufactured just a few kilometers south of Neuss at 3M’s largest German plant in Hilden.

Photovoltaics as growth driver

“Demand is great, and tomorrow morning I have my next appointment for a final inspection at a client’s,” explains Matthias Annas. Like Dornieden, the engineer believes that photovoltaics will provide additional growth potential for 3M’s adhesive products and solutions, especially as the market for thin film glass modules grows.
The company hopes that photovoltaics and other types of renewable energy will help it grow again. After all, analysts forecast a drop in sales revenue for the technology firm down to some 22.9 billion U.S. dollars, 9.5 percent less than in 2008.
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