Adhesives offer binding solutions

Written by: Paul Fanning | Published:

It is probably fair to say that the perception of the adhesives market is that not very much tends to change very often. And while it is probably true that change tends more towards the incremental than the cataclysmic, there are nonetheless product improvements that can make a huge difference in both design and, latterly, manufacture.

One such example comes from Henkel. The company's Terostat silane modified polymers are generally used where an elastic bond is required between medium to large bond surfaces. They create friction-locked joints able to withstand dynamic loads. And as the stress is distributed evenly, material fatigue and failure is prevented. As a result, these adhesives are widely used to bond any structures that need to withstand vibration, such as washing machines, buses and trains.

Achieving the bond however, generally requires the elements to be held together in a clamping system or fixture until the adhesive has cured sufficiently for the structure to hold its own weight. While this is perfectly acceptable for many applications, others require a quicker fix and this is where Henkel's Terostat MS 500 hot melt sealant really comes into its own.

This patented adhesive is based on modified silane polymer technology, but takes this class of products into new areas of potential application.

In a matter of seconds this thixotropic adhesive 'grabs' the marrying substrate, creating high initial bond strength that allows immediate handling. As it dries, it cross-links through moisture absorption, curing in as little as 20 or 30 minutes. Terostat MS 500 effectively compensates for the differing thermal expansion characteristics of dissimilar materials and remains flexible over a wide temperature range.

From a manufacturing standpoint, Terostat MS 500 has the ability to reduce production time and costs, while improving product performance and aesthetics. It also saves on the overall weight of the structure, creates an effective seal and generally requires no substrate priming to optimise adhesion.

In common with the majority of Henkel products, Terostat MS 500 was developed to meet the needs of a specific application, bonding and sealing crystalline solar modules. The qualities already described, in combination with resistance to UV and weather extremes, make it extremely well-suited to this task.

Application specialists at Henkel in Hemel Hempstead, however, recognised this product's wider potential. And one of the first UK applications for which it has proved effective is in bonding and sealing caravan panels.

The caravan manufacturer concerned was already using flexible structural bonding technology, but needed to screw panels to struts as a support mechanism during the curing process. As Terostat MS 500 is able to provide an instant bond, the screws are no longer needed. Not only does this eliminate a process and save costs, it also greatly improves the quality of the end product as there are no screw holes to create leak paths.

The need to bond large panels onto struts, to create structures that are exposed to vibration, extends across many manufacturing sectors; building, white goods and transport to name but three. Henkel Terostat MS500 is therefore expected to have wide appeal throughout industry for applications that call for an instant but flexible bond.

Another new adhesive offering valuable properties is Masterbond's FLM36. In an effort to mitigate the more complicated preparation associated with B-staged epoxies, Master Bond developed FLM36 for bonding and sealing applications in the aerospace, electronic, opto-electronic and speciality OEM industries. This B-staged film eliminates mixing and measuring and is easy to handle.

FLM36 can withstand temperatures up to 500°F and retains its high-strength properties upon prolonged exposure to elevated temperature. It bonds well to a variety of substrates, including metals, composites, glass and many plastics. Additionally, thermally-conductive FLM36 is a superior electrical insulator.

Unlike other heat-resistant epoxy systems, FLM36 possesses more flexibility and toughness, which enables it to endure thermal and mechanical shocks as well as thermal cycling. It also has good chemical resistance to water, acids, bases, fuels and oils.

The film has release paper on each side. After the substrates to be bonded are properly prepared, the release paper is removed to expose the adhesive. It's carefully placed onto the part and pressure is applied. The assembly is lightly fixtured and cured for 1-2 hours at 350°F. The bonded parts should be returned to 75°F before removing the fixtures. FLM36 offers uniform bond line thickness and limited 'squeeze-out' during bonding.

This product is offered in three standard sizes: FLM36-4A is 4 x 4 x 0.008 inches, FLM36-8B is 8 x 8 x 0.008 inches and FLM36-12C is 12 x 12 x 0.006 inches. The film can be cut with a pair of sharp scissors into various shapes and sizes. The films are rugged, durable and not prone to cracking. Unlike most thermoset films of this type, FLM36 does not require freezing or refrigeration.

Another innovative product capable of making a big difference in a competitive environment is tesa HAF (Heat Activated Film). Where manufacturers are constantly looking for ways to optimise costs and minimise down-time in their production processes, HAF offers an advanced adhesion technology that allows users to obtain high-quality splices essential in the continuous production process.

HAF  is a thermosetting film based on phenolic resin and nitrile rubber which guarantees maximum adhesive strength and easy processing even under difficult conditions. 

The film is not self-adhesive at room temperature and becomes adhesive at 70oC.  It can withstand temperatures over 500oC but also offers excellent flexibility down to -50oC. With a strength of up to 30N/mm2, it provides an even distribution of stress, offers outstanding resistance to chemicals and ageing, clean easy processing without metering or cleaning and short curing times.

HAF from tesa can be used on virtually all materials (including metal, glass, plastic, wood, paper and textiles) is resistant to common solvents, diluted bases and alkalis and is easily integrated into modern automated production processes.

The product can be used across many applications, including roofing and waterproofing membranes, where various different types of carriers are coated with liquid bitumen at approximately 180oC and splices must be strong and flexible enough to permit uninterrupted production.

With its resistance to high temperatures, tesa HAF increases productivity time as carriers have to change less often.

In the production of fibreglass wall coverings, for instance, the uncoated fibreglass mats have low dimensional stability and strong splices are required.

Lateral contraction must also be avoided to ensure proper processing and high product quality. tesa HAF allows even distribution of stress over the entire spliced seam for all types of fibreglass mats, avoiding lateral contraction and providing strong splices and high product quality.


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