Film and Powder Adhesives Reshaping Automotive Manufacturing

According to the Center for Automotive Research, adhesives are expected to become the most popular way to secure vehicle bonding, replacing spot welding, screws, bolting, rivets and all other joining processes. Researchers anticipate these changes through the mid-to-late 2020s, and say adhesives could make up about half of all vehicle bonding by 2030. Adhesives have the ability to reduce vehicle weight, make the body rigid and evenly distribute pressure better than mechanical fasteners. Better distribution of stress also allows for the use of thinner materials, which can save automotive manufacturers costs.

When automotive manufacturers began using pressure sensitive adhesives, they were once unable to compete with the strength of epoxies, welds and rivets. However, today’s technologies often outlast the vehicle itself, including the use of films and powder coatings. As the vehicle adhesive R&D continues, films and powder coating processes are expected to become more vital bonding options for the automotive industry.

Films are gaining popularity among manufacturers as adhesive solutions, and more development in future years is expected to make this adhesive a high-demand, cost-effective option. The reasons films provide a variety of opportunities include:

Flexibility in usage: Films can be dispensed more easily and accurately than liquid adhesives. They offer the option of being double-sided, as well as supplying specific adhesives on either side for the needed substrate. Films can be die-cut accurately to the shape and dimensions of a part in advance for simple application.

Cost-saving opportunities: There’s no need for expensive ventilation equipment to protect production workers when using films. Total curing times are faster, saving time and money for production lines. It also takes away the headaches with messy materials, mixing and metering. Films can help with sound damping and vibration, which is often an issue manufacturers must address in working with lighter materials. 

How to Use Film Adhesives Successfully

The base polymer of a film will determine its compatibility with certain substrates. For example, a polyester film is likely to bond better to a similar polyester substrate. This is why some substrates may be better suited for a PSA and others may require a heat activated adhesive.

Pressure Sensitive Adhesives (PSA): PSAs do not require heat or equipment for bonding. They have become a go-to, affordable option for automotive manufacturers, as PSAs work well for attachment or mounting in particular. PSAs are thermoplastic, meaning they will be flexible when cured and can bond in various application conditions. For example, PSAs are being used in dashboard screens, sensors and lens bonding applications.

Heat Activated Adhesives: These adhesives must be heated in order to form a bond. Heat activated films can be either processed continuously or cut into sheets to enable precise layer placement before bonding. Heat activated adhesives can be useful in bonding gaskets, weatherstrips, or parts with elastic properties. There are two types of heat activated films:

• Thermoset: This material forms an irreversible chemical bond once it cures. It offers increased strength and higher heat and chemical resistance. Thermoset film can provide increased rigidity due to cross-linking that happens when it is cured. It is commonly used to bond carbon fiber to clutch disks, mounting gear control sensor plates, and attaching brake shims to brake pads.
• Thermoplastic: This material becomes soft when heated, then sets when it’s cooled. The heating and cooling process for thermoplastic film can be repeated numerous times. Thermoplastic is typically used for vehicle liftgates.

Flame Retardancy in Automotive Manufacturing

It is also important for automotive manufacturers to consider the need for flame retardancy. Both PSAs and heat-activated films can be formulated for flame retardancy, which is typically a desirable feature for seat cushions and other automotive interiors. A flame retardant adhesive can often help a finished product pass industry standards, such as FAR or DIN.

Many manufacturers feel it’s not possible to get a successful bond with two-part acrylic adhesives before coating, due to the potential of high temperatures causing degradation during the curing process. However, powder coating after adhesive bonding is not only possible, it can reduce hurdles often associated with mechanical fasteners including:

Reducing corrosion: Welds often cause weathering, but powder coating can help keep the strength of the bond after its application. Manufacturers often see the bonding strength once assembly processes return to room temperature after heat exposure.

Withstanding extreme heat: Powder coating ovens range from 400 to 450° F, and acrylic adhesives can withstand heat of up to 400° F (204° C) for up to 90 minutes, and will not degrade with a powder coating application. Powder coating also helps in assembling large parts faster with fewer steps. This provides manufacturers a simpler alternative to welding and fastening processes, while still getting long-term durability and pleasing surface aesthetics.

How to Use Powder Coating Successfully

If the following procedures are followed properly, the combination of acrylic adhesives with a powder coating can provide a successful, durable bonding alternative to welding or mechanical fastening.

Proper assembly placement: It is important to consider hot tear strength with acrylic adhesives and powder coating. While neither part of this adhesive process will worsen at the higher temperatures, the adhesive will begin to soften around 180° F (82° C). This is why it’s crucial for substrates to be properly placed during assembly, in order to avoid bonded pieces slipping.

Proper racking: Manufacturers should be cautious when racking a part before the powder coating application. The part should be suspended from the solid structure rather than bonded sections, to lower the risk of bonding failure. Automotive parts, especially if they are heavy, should be set to prevent slipping as the adhesives re-harden during room temperature.

The opportunities to implement film adhesives and powder coatings into automotive assembly procedures is expected to expand. Contact a Bostik representative today to find ways to use these products in your manufacturing processes.

Other content relevant to this topic:  

Types of Film Adhesives and When to Use Each One

How the Automotive OEM Landscape is Changing

How the Right Adhesive Helps You Meet NVH Standards