Multiple Materials Challenge Adhesive Manufacturers

Demand for adhesives of all kinds is going up everywhere, but especially for use in assemblies that join multiple, even completely dissimilar materials. According to a recent report by market research firm Freedonia Group what's fueling this overall growth in demand is some good news: expansions in manufacturing across several industries, such as electronics and automotive. Another driver is the desire to replace or enhance mechanical fasteners. By weight, global demand for adhesives and sealants is expected to grow by 4.5% between 2014 and 2019, and by 2.9% in North America alone, says the report.

This growth, and the changing requirements it puts on adhesive makers, are constant challenges, said Torsten Uske, president of DELO Industrial Adhesives, North America. "Much of the materials changes on the part of the customer, like a move from aluminum to brass in automotive cameras, is driven by costs," he said. "So we need to adjust our adhesive materials accordingly. Most of the time we are working with one- or two-component epoxies, and we may have to adjust their mechanical properties. Sometimes it's a matter of finding new adhesive materials, and sometimes it's changing the product chemistry or process of how an existing adhesive material is applied, such as curing time, curing temperature, or surface geometry."

Many new materials being introduced to the automotive industry are associated with electronics, such as the wide range of cameras now appearing. An example is rearview cameras like this one. Maintaining transparency over time in a wide range of temperatures is also an issue for coatings on an optical die or a camera. Adhesive and coating materials must be continually updated to maintain the correct optical index and refractive index.

(Source: DELO Industrial Adhesives)

The main industries where DELO is seeing an increasing need on the part of customers to join multiple materials are aviation, automotive, and standard consumer electronics, as well as microelectronics. In aviation, the main growth in new materials is happening in interior components, such as overhead compartments and seating. New materials continue to come in, and they must be joined with adhesives that can maintain the same color and transparency levels over time under wide temperature ranges, Uske said. These are issues especially for adhesives that attach materials covering displays, such as those located on the backs of airplane seats.

New Materials and Bonding Methods

Many of the new materials coming into use in the automotive industry are associated with more electronics that are appearing in cars, such as cameras. Maintaining transparency over time in a wide range of temperatures, especially elevated ones, is also an issue for coatings placed over an optical die or over a camera in consumer electronics, as well as for automotive displays. Adhesive and coating materials must be continually updated to maintain the correct optical index and refractive index. "For example, in a mobile phone's flashlight, transparency and yellowing issues are a big deal," said Uske. "So is water resistance, which is becoming more important in consumer electronics. This all has an effect on the adhesive materials used for a given application."

An example of modifying processes for applying adhesives instead of creating new adhesive materials is a new injection bonding technique from Dow Automotive Systems. It helps speed up the bonding of structural automotive adhesives -- a critical factor in high-volume automotive assemblies -- while it also maintains accuracy, especially important for complex parts that can be difficult to join. Dow Automotive invented the highly specialized process for applying its BETAFORCE structural adhesive to car body parts made of multimaterial substrates, such as coated metal and carbon fiber composites. The new method can address a specific customer's production requirements, such as open times and cycle times, without affecting mechanical properties. It also enables wider application of carbon fiber parts in mixed-material assembly with coated steel or coated aluminum to support carmakers' lightweight strategies.

The new injection bonding method can be used in roofing, complete carbon-fiber compartments, or hang-on parts such as doors. In side-frame applications along the roof, for example, the carbon-fiber part is used as an inlay in a metal housing running along the A-pillar into the roof and down the D-pillar. This ensures stability of the passenger compartment in the case of a side-pole impact or rollover, as well as increases vehicle torsional stiffness, while improving subsequent ride-handling and reducing noise, vibration & harshness at the lowest mass.

Dow Automotive Systems has invented an injection bonding method for its BETAFORCE composite bonding adhesives used in volume auto manufacturing. It can be used in roofing, complete carbon-fiber compartments, or hang-on parts, such as doors. In side-frame applications along the roof, for example, the carbon-fiber part is used as an inlay in a metal housing running along the A-pillar into the roof and down the D-pillar. This ensures stability of the passenger compartment in the case of a side-pole impact or rollover, as well as increases vehicle torsional stiffness, while improving subsequent ride-handling and reducing noise, vibration & harshness at the lowest mass.

(Source: Dow Automotive)

One of the newest areas where DELO has seen a need for multimaterials adhesives is in the production of electric motors, Uske said. The company's new adhesive material for this application, DELO DUOPOX SJ8665, is stable up to 180C, which is high for a two-component epoxy. This impact-resistant epoxy resin gives both reliability and flexibility for electric motor production. Since it can be used in a medium temperature range, it's especially suitable for bonding surface magnets that are subject to sudden loads, and for fixing stator laminations to housings.

Compared to standard two-component epoxy resins, SJ8665 also has double the tensile shear strength. Bond strength remains the same, even after 1,000 hours of being stored at 85C with 85% humidity and it's resistant to chemicals such as gasoline or gear oil. It cures to functional strength in five minutes, with full curing in 10 minutes, both at 80C. The epoxy reaches a strength of 16 MPa on aluminum at 80C. That lower temperature means it can be used to bond temperature-sensitive materials such as plastics and magnetized metals. When induction cured at 100C, it reaches a strength of 10 MPa within one minute, with final curing at room temperature.

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