Polyurethane reactive adhesive, better known as PUR, has been the glue for the printing industry’s transition to digital print technology. Where conventional EVA hot melt glues struggled with digital printed papers, with glossy papers and especially with finishing oils used in the process, PUR would stick just about anything.
It offered a strong highly flexible bind on almost any kind of material. Because it works through a cross linking process on reaction to humidity, only small amounts of adhesive are necessary.
However, PUR is relatively expensive, particularly when unused glue has to be thrown away, application equipment is expensive and needs attention because of the aggressive nature of the product and ideally books should be left to cure before further finishing.
Nevertheless PUR has been a breakthrough product enabling many with no perfect binding experience to begin producing perfect bound books, catalogues and brochures, using single-clamp binders.
Suppliers have adapted, fitting shallower tanks to limit the amount of glue that is wasted, using nozzle systems that do not expose the glue to the air and developing new ways of applying the adhesive.
One supplier has now come up with a much more powerful hot melt adhesive which tackles the problems that PUR avoids while also avoiding the problems that PUR creates. This is Planamelt, developed by German adhesives specialist Planatol, and now coming to the UK.
The glue was first announced last year and has been taken up in Germany, Italy and other countries on mainland Europe. Its reputation has taken it across the Channel and over the summer a number of trials have taken place at different printers and finishing houses to confirm that the glue is easy to use, that the bind is strong and that there are no unforeseen drawbacks. So far none has been found.
The company claims a bind strength of 13N/cm2, a figure at which it will be easier to tear the paper than remove the page from the spine. This has been upheld on a wide range of papers during the testing on a wide range of equipment from single-clamp to high end binders.
“We are delivering now to almost all countries in Europe,” says Nuno Campos, export sales manager for Planatol. “Most of those using it are in digital printing using binders from the likes of Horizon or Duplo.”
The big advantage for those specifying a binder is that there is no need to invest the extra systems needed to cope with PUR he explains. And those systems need to be cleaned carefully to avoid a build up of glue. PUR will also attack valves and nozzles which means maintenance and replacement over time.
In contrast the Planamelt is benign. It can be heated to its operating temperature around 160ºC and cooled and reheated without problem. EVA will over the course of time cook, burn and discolour. Planamelt does not seem to do this.
Philip Lee, managing director of Ace Adhesives, first came across Planamelt when a customer encountered production problems on another job. On a visit the unusual glue was noted and samples taken back to the office.
“We ran page pull tests on this unknown glue and achieved 13N,” says Lee. “Then the next week Steve Giddins from Perfect Bindery Solutions asked if I had heard of Planamelt. It sticks on digital print, on glossy coated papers so I approached Planatol and said I would like to sell it in the UK.
“This is the first big difference in book binding adhesives I have seen, other than PUR, since we started in 1986 – and I have seen a lot of book binding adhesives in 30 years.”
Ace will sell Planamelt as a spine glue in the main to digital printers looking to move away from the inconvenience of PUR. Lee has been asking customers to run trials on anything from “single-clamp to 16-clamp binders”. To date this has focused on roller and slot applicators, but there is no reason for it not to work with nozzles.
“We are aiming at people who don’t have PUR at the moment,” he says, “and who don’t want to invest in PUR. They may have a need for PUR but because they don’t use it all the time and do not want to keep changing, they have stuck with EVA.”
Lee admits that the pull strength on PUR is higher, but points out that using PUR can be like driving a Ferrari on roads where its extra performance is not relevant over an executive car like a Jaguar. “It provides all the performance you need and you can use it every day,” he says.
“If you are a trade binder this can provide the confidence to take on any kind of work without having to turn away digital jobs if you don’t have PUR.”
The finished book can be handled after an hour, though it will take up to 24 hours to go off completely, much faster than a PUR. It has advantages over the standard EVA product he points out: there is greater latitude in temperatures that the glue works out, and there is greater resistance to solvents.
This is even better than the new generation of micro emission PURs where there can be adverse reactions to plasticisers in inks or where there is a limited cure on very dry papers.
If there were such things as maidens in the bindery, Planamelt might be the answer to their prayers.
Planamelt glue has been tested on a number of binders including Horizon BQ470 four-clamp machines.
