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Industrial Adhesive Bonding: Surface Preparation Rules of Thumb

Posted on 1/26/2018 10:53:22 AM By ASC
  

A strong bond is dependent on good surface preparation. What that should consist of will depend on a lot of factors, but 3M answers a few of the most frequently asked questions its customers raise with general tips and techniques for industrial adhesive bonding.

Choosing the Right Adhesive

When materials have a high surface energy, they have higher molecular attraction, allowing adhesives to flow across the surface. There is greater contact with the substrate, and bonding such substrates is relatively easy. However, when substrates have low surface energy, strong bonds can generally be achieved with the help of modified acrylic and synthetic adhesives.

Other factors affecting adhesive choice include the type of assembly, the way an item is manufactured, and the environment in which the adhesive will be used. However, across all bonding applications, the basic principles remain constant: maximize the adhesive’s contact with the surface.

To achieve this, manufacturers must ensure that the surfaces to be bonded are dry and free of contaminants, and consider issues such as exposure to oil or harsh chemicals good reasons for choosing a specialized adhesive.

Preparing the Substrate

When using its high-strength acrylic foam tapes, 3M recommends cleaning the surfaces with a mixture of water and isopropyl alcohol (IPA). However, some surfaces may require other treatments. For example, surfaces contaminated with oils will require degreasing before the final clean with water and IPA. If the surface is oxidized or very dirty, abrasive cleaning may be necessary.Apart from removing grime and oxidization, the scratches left by abraisave cleaning will also increase the surface area and result in a stronger bond. 3M recommends that they be made with a circular motion rather than straight lines. 

Porous materials, on the other hand, require a little extra pre-treatment in the form of a coating while hydrophilic materials that attract water such as glass, stone,and ceramics may need to be prepared with a silane coupling agent.

Materials with a tendency to oxidize may need lacquering, and flexible PVC requires a barrier film to prevent the plasticizers in the PVC from migrating into the tape affecting adhesion. Rubber materials have low surface energy and contain plasticizers and oils, but this can be overcome with an adhesion promoting agent.

Bonding Primers

3M advises the use of primers when using its tapes to bond challenging substrates. These could include painted surfaces, metals, and most plastics. The company produces an isopropyl alcohol-based primer which cleans and primes surfaces simultaneously. It also dries very quickly, reducing downtime.

Films and vinyl graphics such as those used for vehicle decals and wraps may require a purpose-designed primer to promote adhesion to glass, concrete or metal.

Specialized Advice

Using adhesive tapes looks easy, but 3M advises manufacturers to consider surface preparation carefullyin order to get the best bond performance. If they are uncertain of the right adhesive and surface preparation technique, expert help and advice are available.