The standard vehicle assembly uses over 33 pounds of adhesives! Most of these are used inside the car to secure liners, trim, carpet, and, of course, seating. In the automotive and truck manufacturing industry, design and production components must meet an overwhelming list of requirements for accuracy, quality, safety, reliability, dependability, and repeatability. That’s why automotive and truck manufacturers choose hot melt adhesives to bond parts. Hot melt adhesive is used extensively in the auto manufacturing industry because it typically creates a strong yet flexible bond that can withstand the wear and tear vehicle parts go through. In addition, hot melt can also withstand the extreme heat and cold that vehicles and their interiors are often out in year after year.
In fact, nearly everything in the interior of your car or truck has, in one way or another, been bonded using some type of hot melt adhesive. Everything, from dashboards to lamps, mirrors, sun shades, and more, is attached to one component or another with hot melt. Vehicle seating, in particular, makes heavy use of hot melt to bond leather, fabric, foam, and metal. Since we spend almost all of our time in our cars seated, the seats are exposed to a lot of stress. In addition to durability and sturdiness, appearance, material quality, and ergonomics are important here as well. There are several types of hot melt that are used for their variety of benefits in the vehicle seating assembly process.
Our Recommended Hot Melt Adhesives for Vehicle Seating
Polyurethane Hot Melt Adhesive
Polyurethane (PUR) hot melts are being used more and more in industries, including automobile assembly. PUR characteristics appeal to a huge set of users because they are non-toxic and quick-setting, sustain load-bearing requirements, offer great temperature and weather resistance, and are affordable at any volume requirement. PUR is comprised of a string of polymers that share a similar chemistry linked together by urethane. It’s a so-called “reactive” adhesive because it forms a strong adhesive bond, thanks to a chemical reaction. Moisture needs to be present to spark this chemical reaction and, thus, the bond. Luckily, sufficient moisture usually exists in the air or the material being glued.
PUR eliminates VOCs—ensuring both a safer work experience and a final product without the need for solvents or formaldehyde. PUR hot melt also works better with substrates that are sensitive to high temperatures and which remains stronger at higher temperatures. PUR’s reactive technology creates a higher strength bond than most other adhesives. PUR’s flexibility, along with its wide temperature tolerance and water and chemical resistance, ensures its effectiveness in a wide range of both indoor and outdoor environments. In fact, we have several outstanding stick, bulk, and sprayable hot melt products we’d recommend for vehicle assembly:
- TEC Bond 430 High Performance Sprayable Hot Melt
- TEC Bond 425 Sprayable Hot Melt
- TEC Bond Sprayable Hot Melt Sample Pack
- Infinity SuperTAC 11 High Performance Bulk Hot Melt
- Infinity SuperTAC 11 Super High Performance Hot Melt Sticks
Polyamide Hot Melt Adhesive
With a bond that sticks to even the most difficult substrates with super-human strength, polyamide hot melt adhesives are a great solution for car seats. Polyamides create a strong bond between standard substrates like paper, wood, and metal, as well as more difficult ones, including treated polypropylene and polyethylene, ABS, and vinyl. Some even bond with PVC, which is known to be difficult to bond. Other types of hot melt adhesives simply lack the chemical bond that forms between polymer chains and hydrogen to make it so secure. Polyamide adhesive bonds are also resistant to peeling and impact, as well as chemicals like fuel, oil, and mold.
However, along with all the benefits come a few notes manufacturers will need to consider when assembling vehicle interiors. Many polyamides are difficult to use with a bulk tank because oxygen and moisture too easily get in and react with the effectiveness of the adhesive. They also have shorter shelf life than other hot melt adhesives—usually needing to be replaced after just a year when most hot melt adhesives can be stored indefinitely. Polyamides also require careful storage again because of their high reactivity with any contaminants. Container seals should be airtight to keep air and moisture out and the adhesive should be kept cool and dry and used quickly.
Pressure-Sensitive Hot Melt Adhesive
Pressure-sensitive adhesive, or PSA, holds two surfaces together by contact. To achieve this type of bond, external pressure needs to be applied to the substrates. PSAs offer a lasting, high-tack, repositionable bond for numerous materials like plastic, paper, metal, glass, wood, and more. Pressure sensitive adhesives are great for assembly. Their application doesn't require elaborate equipment and can be easily automated. Compared to liquid adhesives, they save a ton of time and labor, as they require no setup or long curing time and adhesion is immediate. As well as replacing fasteners for adhesion, PSAs provide an insulating seal and are sound and vibration deadening.
Amorphous-Poly-Alpha-Olefin Hot Melt Adhesive
Amorphous-poly-alpha-olefin (APAO) hot melt adhesive is very popular for use in vehicle assembly as it has a high UV protection rating. APAO polymers are a staple in the manufacturing of hot melt adhesive and sealant systems. The compatibility of APAO polymers with solvents, tackifiers, waxes, some styrene block copolymers, and other polymers makes them highly desirable. These polymers are reactor-produced polyolefins produced with a proprietary process called Liquid Pool. There is a wide range of polymers with different physical and performance properties. When deciding which is best, there are several different factors to consider, including:
Melt Viscosity: This is the most distinctive property. It determines the degree of wetting or penetration of the material by the adhesive and gives an indication of the processability of the adhesive. It is typically determined at 375°F. The measurement of dynamic viscosity ranges from about 200, up to 150,000+ centipoises or cps.
Needle Penetration: This indicates resistance to deformation or hardness. When looking at thermoplastics and elastomers, hardness is often used to measure stiffness. Needle penetration indicates the resistance to deformation of the polymer.
- Ring and Ball Softening Point (RBSP): This indicates resistance to heat and ranges between 175° and 324°F. As is true with most polymers, APAO does not have a well-defined melting point. Instead, as the temperature increases, APAO becomes softer, changing from a solid to a high viscosity fluid over a wide temperature range. A high RBSP means that the polymer softens at a high temperature. A low RBSP means that the polymer softens at a lower temperature.
One of our favorite APAOs is Rextac RT2730, used for load floor, sound deadening, and bonding foam to foam. Performance includes high tack, good cohesion, long open time of 300 seconds, thermal stability at 375°F, and application temperature between 280°F and 375°F. Viscosity is 3000 cps at 375°F and the softening point is 230°F. However, at Hotmelt, we can customize APAO polymers to meet your unique application and manufacturing needs.
As you can tell, there are a variety of hot melt adhesives one can use when it comes to seating and other interior automobile elements. Whether it’s Polyurethane Hot Melt Adhesive, Polyamide Hot Melt Adhesive, Pressure Sensitive Hot Melt Adhesive, or Amorphous-Poly-Alpha-Olefin Hot Melt Adhesive—each has its own set of perks that makes it the perfect pick for your unique needs. Contact our team of hot melt adhesive pros to learn more.