Governments around the world are enacting myriad policies in an effort to reduce greenhouse gas emissions (GHGs) and combat the growing climate change crisis. As the transportation sector is a leading source of GHGs, much attention is focused on this industry. Car manufacturers are taking various steps toward these goals.

One key effort involves lightweighting (i.e., reducing the vehicle’s weight in order to improve fuel economy and reduce emissions), which can be achieved through materials replacement. One example includes the use of plastics instead of metals. However, these methods can create additional challenges to navigate, such as the need to create strong bonds between plastics and metals. WACKER’s white paper, released earlier this year, talks in detail about design considerations in using adhesives to bond to thermoplastics. In addition to lightweighting, there are other trends affecting how adhesives are used as solutions to improve or enhance automotive components.

TREND ONE: USING MINERAL ADDITIVES TO STRENGTHEN THERMOPLASTICS

While the popularity in using thermoplastics is rising, a new challenge comes hand in hand. Thermoplastics can be strengthened to improve the overall durability and strength by adding materials such as minerals. While reinforced thermoplastics offer enhanced mechanical properties, the added materials can also trap moisture between elements.

When used in bonding with heat-cured adhesives, this creates a challenge since these adhesives are typically used to speed the curing of two component materials and requires temperatures of up to 150^oC. The higher curing temperature forces the trapped moisture to rise to the surfaces of the thermoplastics, causing bubbling or uncured sections in the adhesive. Heat curing of adhesives for thermoplastics cannot exceed 95^oC and can cause assembly limitations.

TREND TWO: FAST-CURING ADHESIVE DESIRED FOR SEALING CONTROL UNITS

As the number of electronics and content inside the electronic casing is increasing, customers are looking at ways to reduce cost and complexity. One solution is to eliminate or reduce the number of screws used to seal a control unit by using an adhesive.

Manufacturers can reduce part complexities, as well as save on the time required to pick and assemble screws. By using an adhesive, the bond will not only need to act as a gasket but also will need to provide the structural support that screws would normally provide. This means the adhesive strength needs to be higher than a traditional cure-in-place or form-in-place type of adhesive. Additionally, the adhesive needs to maintain a strong bond as it cures and while handled during the assembly process.  In short, customers want a fast-cure adhesive that can also provide a structural seal.

TREND THREE: STRONG ADHESIVE WITH FLEXIBLE CURING PROCESSES

Customers want a product that can be tailored to their process – rather than the other way around. In today’s setting, a production process is tailored around the curing mechanism of the adhesive material and often is the bottleneck due to required curing time during batch processing. Customers must wait for the adhesive to achieve green strength or to become fully cured prior to executing a pressure leak test. This often means batch production and waiting up to 24 hours before proceeding.

Manufacturers want customer process flexibility, so a product that can be cured at ambient temperature as well as at varying levels of heat is needed. Ideally, customers want an adhesive that can be applied and immediately leak tested after application without the risk of breaking the seal and ultimately becoming scrap later down the assembly line.

CONCLUSIONS

Many types of adhesives are feasible for automotive assembly applications, with different silicone-based products offering multiple properties such as strength and durability under heat ageing, thermal shock, and environmental conditions. Partnering with a knowledgeable supplier is recommended to ensure the best adhesive product fit to reach optimal end product quality and production levels. When collaborating with WACKER’s technical service and expertise, silicone adhesives can be tailored to ensure the successful bonding of thermoplastics in specific harsh automotive assembly applications. To learn more, visit WACKER’s automotive electronics page or contact WACKER at www.wacker.com/contact.