The first use of two-component polyurethane adhesives within the automotive sector, occurred in America in 1967. Since the mid 80’s, several of the European body parts manufacturers have ventured into the use of two component polyurethane adhesives for several applications including bonding wind deflectors, trims, body panels etc. These adhesives have found their niche in the automotive sector due to their property of having both rigid and soft domains within the polymer, thus giving a reasonably good balance of flexibility and high cohesive strength. Due to a range of factors, the continued research & development of two component polyurethane adhesives has somewhat plateaued in the last decade. Among then factors may be cited the further development of methacrylate chemistry and the increasing use of composite materials within the sector as a whole.
Why are thermoset composite materials used in ever increasing automotive applications? Apart from the obvious weight saving which composites materials offer, they do not rust and they allow vehicle designers to fabricate unique design shapes which would be difficult or impossible to create using metals. Composite materials may also offer cost benefits for low volume applications and in the production of individual parts for high volume applications. Over the decades, bonded thermoset composite parts, such as complete body panels, doors, roof’s, spoilers and fenders etc, have become very common in automotive assembly. So, what are the negative aspects of using two-component polyurethane adhesives to bond thermoset composite materials?
In order to form an adhesive boundary layer & the required molecular interaction between the adhesive and substrate, often stringent surface preparation (including priming) is required.
Whilst primers do improve adhesion of two component polyurethanes, they often negatively effect the appearance of Class A surfaces if applied directly and subsequently coated.
On certain composite materials, including several grades of sheet moulding compound (SMC), bond failure does occur if the correct surface preparation is not carried out.
Once opened, the ‘B’ side of a cartridge of two component polyurethane can react with atmospheric moisture, possibly leading to bond failures.
During the often time consuming surface preparation stage, composite fibres may be damaged.
Application can be complicated in that the mixing ratio must be precise and exact.
They have limited storage shelf life & often limited service temperature.
Contain isocyanate monomers which cause health issues.
Luckily for the automotive sector, the shortcomings of older polyurethane technology has been successfully
addressed with very unique, cutting edge, high performance structural methacrylate adhesives which are formulation optimised. Methacrylate’s have proved themselves in a host of automotive applications including assembling bonded aluminium roof panels, plastic and composite panels, to name a few.
What benefits do methacrylate adhesives offer over older polyurethane technology? Quite a few actually….
Primerless bonding on most materials.
Higher temperature resistance.
Excellent strength & elongation properties.
Excellent substrate wetting.
Finely balanced rheology which gives excellent sag resistance, critical in vertical bonding applications.
Choice of open times & ambient cure response.
Low exotherm with very greatly reduced chances of bond-line read-through (ideal for Class ‘A’ surfaces).
Can bond dissimilar materials such as metal to metal, composite to metal and composite to composite.
Excellent mechanical properties thus may be used in structural applications.
Excellent resistance to fatigue, shock, impact and overall excellent environmental resistance.
Excellent shelf life.
Lower health hazard than polyurethanes.
One of the worlds leading formulators & manufacturers of structural adhesives, is Scigrip Structural Adhesives. As a global manufacturer and supplier of speciality methacrylate’s, Scigrip offer a very wide range of tailored , high performance structural adhesives which are eminently suitable for use in automotive bonding applications.
Due to the diversity of composite materials and their distinct properties, a general statement as regards adhesive grade selection is not possible, however, we are confident that there is a Scigrip methacrylate adhesive to suit most applications.
All of these adhesives are available in a range of working times, which enables our engineers to specify the correct working time to suit the component size & geometry, thus allowing fabricators to optomise production schedules and reduce bonding cycle times.
SG200 is a non sag, tough but flexible structural adhesive with exceptional environmental resistance. The ideal choice for non level surfaces. Specifically developed for bonding composites and plastics.
SG300 is the definitive adhesive for primerless bonding on a very wide range of metals, composites and plastics. The product offers permanent toughness, combined with excellent shock and impact resistance. It has an excellent tack free cure profile and requires minimal surface preparation.
SG600 is a novel non-sag adhesive offering all of the toughness & required with a very low exotherm. Requires minimal surface preparation. Exceptionally low chance of bond line read-through and exceptional flow & wetting characteristics. A good choice for cross bonding metals with composites.
SG805 is the newest technology offering. A unique adhesive, designed for primerless bonding composites, metals & thermoplastics, it offers a permanently tough glue-line with high fatigue, shock and impact resistance. Combined with high thermal resistance & excellent flow characteristics, it also boasts supreme environmental resistance. Excellent choice for bonding a range of composite materials including polyester & vinyl ester.
SG5000 is a novel adhesive offering exceptionally high tensile strengths for most composite and metal bonding applications. It possesses very high environmental and chemical resistance. The proven choice for structurally bonding thermoplastics such as ABS to itself and crossbonding with metal components or structural assemblies.
Due to the increased use of lightweight thermoset composite materials in the transportation sector, the unique performance characteristics which structural methacrylate adhesives offer, will find an ever broadening field of automotive applications and will in time, transform the sector.
Here at W.I Polymers, we are the leaders in composite bonding. Combined with Ireland’s leading team of adhesive chemists & materials engineers, we are at the forefront of utilising the range of Scigrip structural methacrylate’s, in the most demanding automotive bonding applications.
Using both our research laboratories & those of our supply partner Scigrip, we are capable of undertaking the most demanding technical enquiries. Using customer supplied substrates, we will carry out the full range of adhesive screening tests which will allow us to select the correct adhesive for the specific application. We also give the customer the confidence in knowing, that we can advise on the best production environment conditions that will guarantee reproducible bond quality time and time again.
We can provide the perfect bonding solutions for your automotive bonding needs.