ADHESIVES IN SIGN MANUFACTURE
30 September 2002 - Huntsman Araldite

In the high street the retailer battles to attract the next person through the door, on the forecourt the battle for business is forever competitive, in the office
corporate image is a high priority. Signs and livery are a vital part of the process of
image building; they have seconds to make an impression, which could last for years.

Freedom of design has helped to increase the impact which a sign can have, and
allows greater scope for the designers. But how often does the reality of manufacture ruin the promise of design? Traditional joining methods and materials often limit the creativity of the designer. So an alternative has to be found.

How can the use of adhesives help?
Modern structural adhesives such as Araldite® are so versatile that there are almost no materials which cannot be joined together with their help. Compared with other joining methods, the benefits of using adhesives are:

· Reduced assembly times
· Reduced costs
· Improved appearance and greater design freedom
· Low initial investment and ease of use
· Lower corrosion and longer life
· Reduced weight

Reduced Assembly Times
The use of adhesives to join materials in the sign industry requires fewer operations than some conventional methods such as riveting or bolting. For example, operations such as drilling and sealing, which are necessary when using rivets or bolts, become completely redundant since with adhesives the joint is sealed when the two components are brought together. By removing these and other operations, such as grinding down post-weld beads, the overall assembly time can be significantly reduced. In some cases this can mean a reduction of up to 50% in the assembly time of a sign.

Paste adhesives also offer the advantage of flexibility of cure speed. Rapid- cure
adhesives can give handling strength in less than 5 minutes, which can allow for
small areas to be bonded very quickly, but with still enough time to position the parts in exactly the right place, whereas longer-cure materials allow larger areas to be bonded safely and efficiently. This means that complex shapes and parts can be assembled in one operation and it eliminates the need for any re-working or
repetition!

Reduced Costs
By reducing the assembly time of a product the labour costs for each job are also
reduced. This allows manufacturers to be more competitive. Costs can further be
reduced through the use of lighter, cheaper substrates. For example, because
adhesives can join different materials, costly metals such as aluminium, steel and
brass can be replaced with plastics and composites such as GRP and acrylics, which
in turn can result in cost savings. The flexibility offered by adhesive joining can also
contribute to a reduction in production costs. The same adhesive can be used to join metals and plastics, which means that expensive joining methods such as aluminium welding are eliminated.

Gap-filling structural adhesives, such as those in the Araldite 2000 range, also help
to save costs by filling any gaps in joints caused by poor tolerances. A good
example for this can be found in the manufacture of box-like signs.

Once the relevant mitred corners have been cut in the aluminium profiles, the joint is formed by bonding a simple angled gusset bracket into the reverse section. Any gap in the mitre is then taken up by the adhesive and cannot be seen after painting.

Improved Appearance and Increased Design Flexibility
Adhesive joining can open up possibilities for sign manufacturers to explore the use
of new substrates and give greater design freedom. Unlike welding and brazing for
example, different substrates can be joined together, allowing materials like
aluminium, coated steels, Dibond and Perspex to be used in the design and
construction of signs.

The use of adhesives can also improve the appearance of the design. Mirroring
effects caused by welding are eliminated and rivet and bolt heads removed, which
allows for an unspoilt, smooth appearance.

Ease of Use and Low Initial Investment
Many modern structural adhesives come ready to use in two-pack cartridge systems.

By simply attaching a mixer nozzle to the cartridge and using the relevant gun,
manufacturers can be up and running for as little as £50. The flexibility of adhesives also means that one joining system can be used for most of the materials that a sign maker would wish to join together, thus reducing the need for high levels of capital investment.

Increased Life and Reduced Corrosion
Because of the way adhesives work, they offer other advantages over traditional
joining methods. As no holes are drilled there are no places for water to leak
through. Furthermore, as the joint consists of a continuous bead of adhesive, the joint is also sealed in the same operation. This leads to reduced corrosion and a better looking sign for longer.

The fact that there are no holes along the joint gives an additional benefit to the sign manufacturer. With mechanical fixing methods, any stress on a joint is usually
concentrated around the holes. This can lead to failures around these concentrations. Adhesive bonding creates a continuous joint, which means that
stress concentrations are eliminated resulting in a longer lasting sign.

Reduced Weight
By removing mechanical fasteners not only are holes eliminated from the structure
giving a longer life, but the dead weight of these fasteners is also removed. This
allows cheaper, less robust fastening mechanisms to be used to attach the finished
sign to walls, roofs or columns, again saving money.

How to Choose the Right Adhesives
Adhesive selection depends upon the materials to be bonded together, the required
cure time and the desired bond strength. Generally a high-strength adhesive is
required, with the ability to bear the load generated not only by the weight of the
materials used but also the load caused by external forces such as the weather.
Often signs are required to be powder coated or painted. The adhesive should
therefore be able to withstand these processes and have some heat and chemical
resistance.

Depending upon the size of the sign the adhesive needs to have a long or short cure time, for example using a rapid-cure adhesive means that only small areas can be joined. The area to be bonded also needs to be taken into consideration. If some degree of flexibility is required then an adhesive with some elasticity is needed.

However, the use of very flexible adhesives should be avoided as these materials are prone to creep and the sign will eventually fall apart under its own weight. Therefore for joints which require high strength, creep resistance, weather, chemical and heat resistance, structural adhesives are the only choice.

How to use them
Appropriate pre-treatment is critical to the success of a bonded assembly - this does not mean a surgically clean workshop though! However it does mean that the
surfaces have to be wiped with a suitable degreasing agent before the adhesive is
applied. Degreasing may be followed by abrading and subsequent removal of loose
particles, a process, which will add significant strength to the bonded joint.

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  • For September 2002
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