Structural Adhesives and Intermediates

Technology  Functions  Applications  References  Innovations

Technology
Structural Adhesives are used for bonding applications, where the bonded joint must transfer high loads without deformation and creep. For automotive use, also a very high impact resistance is required to replace welding operations. Usually structural adhesives are applied in layers thinner than 1 mm.

Our structural adhesives are based on Epoxy-, Acrylic- and Polyurethane resins and can be formulated as room temperature 2 component- or heat curing 1 component adhesives. For lamination, solvent- or water based dispersions are used.

The development of intermediates leads to new building blocks for structural adhesives based on recycled PET which give new possibilities for formulation of products with exceptional properties at reasonable costs

In addition the durability of adhesives is evaluated and the parameters for calculation of bonded joints are determined.

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Functions
Main function of structural adhesives is bonding of similar or different materials to transfer high loads and replace other joining methods like welding, screwing or riveting. Depending on the design, structural adhesives do not only bond parts together but they fulfil also additional functions:

• strengthening and reinforcing structures with Carbodur strips or with bonded metal sheets. This needs adhesives with shear modulus higher than 1000 MPa
• dampening by increasing stiffness to create stronger structures to shift the resonance frequency towards higher frequencies
• sealing as additional function when bonding metal sheets together thus reducing sealing operations
• protection, since adhesives show excellent adhesion on metal substrates thus preventing corrosion

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Applications
Bonding of Carbodur strips:
With high modulus Epoxy adhesives carbodur strips are bonded on concrete structures and concrete beams at bridges or floors to increase the allowed load or to repair structures with corroded armings.

Anchoring adhesives:
Acrylic adhesives that are used to bond anchors into concrete holes. These adhesives must have very high pull-out strength (break of the concrete) and adhesion on concrete surfaces.

Metal adhesives:
These adhesives are used in automotive, bus and truck industry to bond steel or aluminium metal sheets together thus replacing welding and riveting operations. They are heat curing and show excellent adhesion on oily metal sheets. They cover a wide range of shear modulus depending on the application. The products with the highest performance provide excellent impact resistance even at speeds above 12 m/sec.

For coated metals, structural 2C adhesives based on Polyurethane or Acrylic are used. In this case welding or heat curing is no more possible. The shear modulus and elongation at break must be adapted according to the substrates and the part design. These type of adhesives can also be used for bonding of fibre reinforced plastics and thermoplastic substrates.

Laminating adhesives:
These adhesive are used for bonding of plastic foils and fabrics onto plastic or wooden parts for decorative purposes. Because of the deformation during the application on such three dimensional shaped parts and the required high temperature stability, crosslinkable adhesives based on PUR are used. To achieve high production rates, they build up initial strength through thermoplastic behaviour and crosslink slowly at room temperature.

Warm- and Hotmelt adhesives:
These reactive adhesives based on Polyurethane combine fast initial strenght built up through crystallisation with the high temperature performance of a moisture cured adhesive with adhesion even to difficult substrates.

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References
Epoxy adhesive for concrete strengthening with Carbodur tested at EMPA
Bonding in automotive body shop at VW, BMW, DC
Use of lamination adhesives at Johnson Control
Headlight bonding at Hella

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Innovations
Combination of high strength and elongation by using PUR-Epox hybrid systems for bonding of metals. High impact resistant adhesives. Modulus and elongation at break can be modified according to customers needs.

Acrylic adhesive with high strength, high elongation and excellent adhesion with low odour. Adaptation to different requirements regarding mechanical properties and adhesion possible.

Easy sprayable PUR-Hotmelt adhesive with high process stability.