Developing adhesive films to help spark industrial innovation

Researcher Kentaro Hoshi of Dai Nippon Printing Co., Ltd. (DNP) vividly remembers the words his boss gave him in 2009 when he was assigned to develop adhesive materials. “We will see more industrial materials, such as resins, which can’t be welded,” the boss told Hoshi. “Wherever welding can’t be applied, adhesive materials will be needed.”

• Words of wisdom from a boss
• Making adhesives using printing technologies
• Making the adhesive business one of DNP’s biggest operations

Moves to substitute metal auto parts with plastic ones to lighten automobile weights have accelerated in recent years, but Hoshi – who had been with DNP only a little over 2 years at that time – did not realize that adhesive materials had huge market potential. Nonetheless, he felt honored to be handpicked to research a new subject and proceeded to research and develop adhesives “with a sense of mission.”

During the past decade, Hoshi developed various adhesive materials for such innovations as the proliferation of electric vehicles and ultralight airplanes and train cars. In May 2019, DNP announced the development of a new type of the DNP Structural Adhesive Film series of products designed to bond different materials, such as resins, carbon fibers and metals, mainly for automobiles.

The new product cures when two types of tapes coated uniformly with different constituents are adhered. After temporarily affixing parts or components made of different materials with the tapes, like sticking them with double-sided tape, the parts are left at room temperature for three days to ensure firm adhesion. Conventional liquid adhesives have shortfalls such as requiring users to mix two kinds of liquids in the right proportion; a tendency to drip or protrude from the gap between the bonded materials before they cure; and low heat resistance. The new product eliminates these problems with the use of two tapes coated with the appropriate mix of required constituents, a process that helps prevent misalignment of components being adhered and thus makes adhesive operations highly efficient.

The new product is one-of-a-kind, according to DNP, in that it uses two kinds of tapes, whose technologies have been patented. Currently, DNP is considering, with automakers and other manufacturers, using this product for adhering resin components to other parts made of different materials and for various other purposes. DNP has also received inquiries from potential clients eager to use the product for adhering road signs. Given its wide range of applications and potential for solving various problems, the product has been tapped within and outside DNP as “one of the company’s biggest businesses in the future.”

At first glance, Hoshi’s research appears monotonous. Adhesives contain various additives, like spices and seasonings in cooking. He changes the combination and proportion of adhesive ingredients, which number from five to 10, to conduct experiments – on 100 samples in 10 days. His experiments depend on “his own experience, earnest desire to get good results and how much he can believe his own intuition.”

While Hoshi tenaciously conducted his research, advice and encouragement by the aforementioned boss helped him stay focused. Hoshi submitted a report several times a week to the boss, who wrote comments on each one with an orange maker before returning them. The comments included “Keep thinking,” “Hang in there” and “Good job,” Hoshi recalled. “He took time out of his busy schedule to read the reports and write comments on them,” Hoshi said. “Every word is still engraved in my mind.”

During one conversation, the boss posed a question that left a strong impression on Hoshi. “Do you know why monaka can be broken into two?” he asked, referring to a Japanese sweet in which anko sweetened bean paste is sandwiched between wafer-like shells. Hoshi’s boss explained that “breaking soft anko into two is difficult, but the hard shells make it possible to do so.”

As soon as Hoshi heard these words, he thought the reverse notion might hold true for adhesives. “If hard materials are put inside soft ones, it will make the product hard to break,” Hoshi said, adding this concept is useful when designing materials for products. For instance, this idea is used for the latest product. When adhering components made with different materials, soft adhesive materials are required to prevent too much strain from accumulating when stress is applied. However, soft materials generally reduce the adhesive strength. “To solve this trade-off, I purposely put hard materials inside soft materials without blending them,” Hoshi said. “It is like having islands (hard materials) positioned inside a sea of soft resins.”

Why is a printing company making adhesives? It is not as crazy as it sounds, because making adhesive films actually involves many precision coating technologies and know-how DNP established to coat inks and other materials in printing processes, Hoshi said. Precisely rolling films into a final product without wrinkles also uses the principles of printing on paper. Furthermore, blending adhesive ingredients is akin to that of ink. “The technologies we have developed and applied elsewhere can be directly utilized for adhesive films,” Hoshi said. “For example, DNP has many experts on how to advance chemical reactions among materials. I can go and ask them about the necessary technologies and expertise involved. Indeed, there is a wealth of unique know-how inside our company.”

Many other excellent products feature in the DNP Structural Adhesive Film lineup. For example, an adhesive film has been developed for honeycomb sandwich panels, which can make building structures much lighter. This film melts into the honeycomb-like panel to adhere the entire panel surface at a uniform thickness. The product has the rare combination of flexibility and excellent adhesive strength. DNP aims to have this product applied to honeycomb panels used in airplanes, train cars and other structures in the future. Moreover, DNP has developed a “first-aid” material that will prevent concrete debris from falling off structures. This product will help disaster preparedness and mitigation efforts.
Some challenges remain. For instance, the new product currently requires the adhesion of two tapes, so Hoshi is developing a tool to easily align these tapes. Moreover, he is devoted to making its bonding strength – which is now as good as general purpose adhesives – two or three times stronger so it can be used for bonding parts in structures such as airplanes.

“Since several years ago, the technology seeds we planted have started to sprout,” Hoshi said. “We mustn’t let them wither. We’d like to grow them into huge trees.” Hoshi, who now works at DNP’s Advanced Business Center, is also eyeing collaboration with other DNP departments that make products and services compatible with the DNP Structural Adhesive Film series of products by combining the strength of each product or service.

Hoshi is a devoted researcher who keenly looks forward to continuing his work each day. But on weekends, he totally switches off from work and enjoys playing tennis, a sport he took up during his high school days. Any fatigue from a day at work evaporates, Hoshi said, when he looks at the lawn and citrus garden of his log house, where he lives with his wife, son – and three cats.

December 13, 2019 by DNP Features Editorial Department