Clean adhesive application without contact

Sunday, 27 June, 2004

Laminates of the most varied materials are ever more widely applied in numerous industries. More and more composite materials and laminates are used or produced directly online, and this not only for low-cost disposable products such as nappies, sanitary towels or tissue products, but also for special applications such as technical textiles or automotive interiors.

The individual components usually consist of very different raw materials and can only be combined with the aid of adhesives.

All these applications are subject to different requirements as far as the applied technologies are concerned. The surfaces or the material structures are often sensitive to tensile or pressure strains and need most gentle handling. Further criteria may be the breathability or the soft touch of the laminate, which demand a very specific, differentiated adhesive application and impose particular requirements on the process.

High machine speeds may not allow an adhesive application in contact with the product or loose fibres can lead to undesirable deposits. Additionally, standstill times of the production equipment must be kept as short as possible. Apart from a very stable process it must be possible to change the machinery as quickly as possible to altering working widths or different adhesive quantities. The adhesive is another parameter subject to change. Special requirements demand specific adhesives which come in a great variety of viscosities and properties. Spraying of hotmelts has been practised already for years. In com-parison with the development presented here, however, the traditional technologies suffer from major drawbacks. This is also the reason why spraying has found rel-atively few applications to date. The main disadvantages with spraying so far were the inferior process stability and the high cleaning effort required.

One company, Robatech, has found the solution to these problems. The development of the PFC spray nozzles is based on different technologies which have been existing already for a long time and which are well proven in practice.

Like all Robatech systems, the product relies on a modular structure. Each module is 22 mm wide and can be switched on and off individually. They can be dismantled individually and equipped with different nozzle types. This also means that the working width can be altered at any time, at high or low production speeds, without need to stop production.

The nozzles consist of small stainless steel plates which are manufactured analogously to the meltblow spin-die manifold, relying on the most advanced processing technology.

The plates feature an absolutely smooth and perfectly flat surface. In combination with the resistance properties of the stainless steel they greatly simplify the rarely required cleaning job and guarantee a long useful life. This solution permits spraying the adhesive onto the product sheet from a very short distance. Product sheet speeds of up to 300 metres/min can be reached without problems and without generating the interfering 'angel's hair'. The very low spray air consumption in comparison with other systems has a major influence on this criterion and at the same time a positive effect on the operating costs.

To satisfy the different requirements from the various industries Robatech has developed some standard nozzle plates specifically adapted to the intended appli-cations and the adhesives to be processed. Apart from the low-viscosity adhesive hotmelts for hygiene products it is also possible to readily process reacting polyurethane (PUR) or even highly viscous copolymers. By altering the pump output and adjusting the air pressure it is possible to finely tune the process, in particular the applied quantity or the fineness of the spray pattern. This guarantees maximum flexi-bility of the equipment and a wide application spectrum. In addition to all these characteristics the company has also ensured that such a spray beam takes up very little space, so that the technique is not only suitable for new plant, but equally well for retrofitting to existing equipment.

Also of high importance for the overall system, is of course, the melting system with the corresponding pump technology. These devices can be combined to a multitude of systems, suitably optimised to meet particular requirements and adhesives.

Peter Gyger, Eng grad HTL, Product Manager, Robatech AG, Muri/Switzerland

For further information contact Robatech
6 Narabang Way, Belrose 2085

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