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Woodworking

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Misconceptions about PUR adhesive and how they should be run

PUR adhesives for edgebanding

Over the last couple of years, there’s been much publicity about the most appropriate hotmelt adhesives to use for edgebanding and the bonding of various materials to wood-based panel products. It’s universally accepted that EVA is easiest of all to use but comes with disadvantages where the end product is likely to be subjected to steam, heat, or moisture. Polyolefin adhesives fare better and also provide better stability when melting. But, when a watertight, heat resistant bond is required, there is nothing presently on the market to beat the performance of a Polyurethane-based product. Advocates of EVA and PO formulations will always point to the intensive cleaning regimes associated with PUR, the comparatively short pot life of a PUR, and potential health issues, citing these as reasons not to change. Alongside new developments in machinery for larger roller application machines that enable a complete clean down and changeover from EVA or PO to PUR in under eight minutes, there are now PUR adhesives available through the Oldham based adhesive specialist, Kenyon Group, that will suit smaller users – and they won’t render your edgebander inoperable by the following morning if you haven’t used all the product in your gluepot. And if you opt for a Micro Emission PUR product, the risk to users from improper handling, breakdown of the extraction system, or carelessness when cleaning areas that may still contain isocyanate vapours when production has ceased is all but eliminated, since the latest Micro Emission PURs contain less than 0.1% of the potentially harmful product.

Despite the above, there remain a number of misconceptions about PUR adhesive and how it should be run, which, says Ian Kenyon, Managing Director of Kenyon Group, is why he and his team like to spend time discussing the adhesive with customers and training operators. “The main point with PUR is good housekeeping,” says Ian, “And educating the operators how to use these grades to gain the best results is key. When an operator has confidence in the process and understands the basics of PUR, productivity is going to be high and application issues will be reduced.” In the colder months, storage of the core board and the edging material becomes especially important. “Materials stored outside in containers or next to open roller shutter doors where they are exposed to the cold, then introduced immediately into production, cause the PUR adhesive to go off straight away (into shock) on contact with the material. The result is poor adhesion, cold bond and a risk of the edging failing. It is important that the bonded materials are stored above 15 degrees Centigrade for a full cure to take place. Under 15 degrees Centigrade and the curing process is stalled,” advises Ian. For those who, conversely, may be tempted to run the adhesive pot at a lower temperature in the warmer months, believing the reduced pot temperature will offset the higher air temperatures, Ian cautions against: “It’s always best run the adhesive pot at 140 degrees Centigrade,” he says. It may seem like an obvious thing not to do with an adhesive that cures in the presence of moisture, but Ian and his team have often come across operators who “save time” by taking PUR adhesive slugs out of their foil packing the day before and stack them ready for use. “By doing this, the operator has started the curing process. Once cured, PUR cannot be resoftened with heat and adhesive left exposed in this way may cause running issues and blockages. Keep the PUR adhesive in the original manufacturer’s packaging until ready to use,” he says. “This also applies to granules, as packaging left unsealed will cause the curing process to start. If you have PUR adhesive in granular form that may have been exposed to moisture, a quick test for its suitability for use would be to place a granule next to the glue pot. If it melts, all is good; if not, don’t use it.” Arguably one of the biggest issues with users who are new to PUR – particularly those who don’t have a rapid cleaning system on their machines – is lack of good housekeeping when it comes to end-of week cleaning. “PUR adhesives should always be purged with a wax cleaner on a Friday ready for Monday morning,” says Ian. “This will vary from system to system and you should always use the recommend wax cleaner and follow the machine manufacturer’s guidance for cleaning. Make sure the wax cleaner is fully purged through before starting production, otherwise adhesion might be compromised. Purging of the adhesive melt tank and applicator (nozzle/roller) after use with a suitable cleaning agent is very important – and remember PUR adhesives once cured (unlike EVA adhesive), will not re-melt. Good house-keeping is required at all times.”

For more information on the PUR adhesives available through Kenyon Group, or impartial advice on any adhesive problem, visit www.kenyon-group.co.uk or call 0161 627 1001.

Posted in: Woodworking