Melts for fridges

Looking for a green adhesive that can bond most any substrate? Maria Harding looks into hot melt adhesives and finds that it’s really hot stuff

In the development laboratory at Beardow Adams, among the various pieces of test equipment and interesting pots of glutinous substances, you will find an eccentric collection of materials and components from a huge range of industries. In this lab up to 20 new products a month are developed to meet the growing market for hot melt adhesives.

Hot melt adhesives will bond almost any substrate, pervious or impervious – typically plastics rubber, metals, ceramics, glass, wood and fibrous materials such as paper, board, non-woven fabrics and leather – rapidly and cost effectively. They are widely used throughout the industrialised world and can speed up production, save factory space and reduce waste and pollution.

Hot melts are a one part, no mix formulation and, generally, have a rapid speed of set. Depending upon the choice of product, they are able to withstand extremes of heat and cold, humidity, chemical attack and be resistant to salt water. Bonds may be subjected to vibration, shock and long term stress.

Hot melts create a rough bond by spreading their strength over the entire bonding surface and, by replacing nails, screws and other forms of fixing, they can enhance product appearance. They are also neither hazardous , toxic nor flammable, do not contain solvents and are 100% solid, so making their handling, storage, transportation and use easy, safe and totally reliable with no harmful effects to the environment.

Hot melts have replaced solvents and other fastening systems for foam and fabric bonding in the bedding and furniture industries as well as for aircraft and automotive seating and a wide range of other automotive applications that include sound deadening, carpet bonding, headlining and the bonding of various car components.

Other examples include the bonding of loud speaker cabinets, filter assemblies, gasketing, bonding and sealing telecommunication cables and a variety of applications in the construction and civil engineering industry.

One of the industries that has found several uses for the properties of hot melt adhesives is the white goods industry.

Hot melts are non toxic and do not contain solvents so are an excellent alternative for industries trying to reduce their solvent use. They also make working environments more pleasant for employees – cutting the amount of solvent in the air without the need for expensive extraction and recovery systems. Hot melts do, of course, need to be heated before application so there is a certain amount of capital investment that must be made but little of the product is wasted. Many modern hot melts can be spray applied.

`The challenge is to replicate the performance of a solvent based adhesive,’ says Nick Beardow sales and marketing director at Beardow Adams. Because hot melt adhesives are essentially a thermoplastic, heat resistance can be a slight problem, but Beardow Adams has developed products that have a softening point of over 1500C – higher than many plastics – and others that give good adhesion down to -600C. Beardow Adams has also developed thermoplastic, non-reactive hot melt adhesives with ambient shear strength of over 1000N/25mm2.

HOT MELTS IN WHITE GOODS

Important in bonding components in fridges is the fact that hot melts are completely safe for direct food contact – this also makes them suitable for use in chlidren’s toys and food manufacturing environments. The white goods industry use hot melts in some assembly operations but some refrigerator manufacturers have found a further use.

Where traditional fastening methods are used the insulating polyurethane foam that is injected into the cavity between the inner and outer carcass of the fridge tends to leak out through the spaces between fasteners before it sets. So before the foam could be injected, gaps had to be filled with putty or tape – a time consuming and labour intensive job. Manufacturers who have switched to use of hot melt adhesives for bonding the carcasses have no spaces through which the foam can leak saving time and improving their scope to automate.

Automation in white goods factories varies.It depends upon a number of factors from cost of labour to demand on the product line. Where companies are keen to automate they have found that hot melt adhesives can help them out in other ways.

The coated sheet metal used in white goods manufacture can be easily damaged during fabrication. Some manufacturers have found that instead of using traditional clamping to hold parts during fabrication, hot melts of the right consistency are less damaging and can be just as easily removed. In addition the initial outlay is less than the cost of hard fixturing.

Beardow Adams’ lab is constantly developing and improving products, one of the more recent developments which may find applications in the white goods industry – dishwashing machines, for example – is the foamed in place gasket.

GASKETING

For example Beardow Adams’ Prodas 1307 is one of the company’s gasketing hot melts. It is a single part hot melt adhesive for producing foamed in place gaskets that cure almost instantly. It is designed to replace moisture curing polyurethanes or moulded gaskets at a fraction of the cost. Traditional gaskets of this type are made from a foamed material which bonds to one surface and has material memory so that it springs back into place after it has been squashed. Moulded gaskets can require a lot of tailoring while the hot melt variety can be applied in any shape without costs of cutting or moulding. This can also reduce the cost of design changes.

Prodas 1307 has a temperature resistance of 800C – below which it will not slump or deform -with preferential adhesion to the surface to which it is applied and a high memory to ensure that it reforms its original shape after compression.

This makes it ideal for lids and panels that require a water or air tight seal that may need to be opened – for example outdoor junction boxes and switch boxes.

It is also replacing Butyl rubber gaskets in modular door and window panels because it is easier and less expensive to apply. The other gasketing melts have specific characteristics to suit various production needs, for example, sealing under bonnet electronics in the automotive market.

Beardow Adams’ current capacity is in the region of 30,000tonnes of hot melt adhesives per year, which is the largest single hot melt plant capacity in Europe. The company invested £1million in new plant in Milton Keynes in the last year which doubled production.

Company chairman, Bob Adams says, `This investment shows our commitment to the growth and future of the hot melt adhesive market and also recognises changes in customer needs. It enables the development and manufacture of product on a large scale to meet the requirements of international customers.