Single-component synthetic resin hotmelt adhesive, based on plyurethane
The base material are polyurethane plastics. These have the property to form networked structures with thermosetting properties by absorption of the ambient humidity. For that reason PU-adhesive has to be stored hermatically sealed.
Properties of the bonding
Thermo-Setting - or duroplastics - means: mechanicallly very durable, it is heat, cold and water resistant.
Due to the high temperature-and humidity-resistant, PU adhesives are used especially for bathroom and kitchen furniture as well as the production of doors. PU gluing is well suited for critical surfaces, such as aluminum edges, and is mandatory for hospital equipment.
The granulate or heated cartridge is melted in an encolsed gluing system and afterwards provided to the workpiece's edge. Preferably glue nozzles are used to ensure the closed nature of the gluing system. After the pressing of the edge the connection reaches a high strength, so it enables further processing. The adhesive reacts with moisture in the workpiece and the ambient air. After about 10 minutes already 70 % of the full strength is achieved. The networking process is finishd after 2 to 5 days. The PU glue has to be removed completely after 20 to 24 hours from the machine in order to prevent hardening. One possibility is the flushing of glue system with wax. The wax remains in the System so that PU residues are enclosed which prevents them from hardening.
Some technical solutions
- Biesse offers rapid-change glue pots. The glue pot is taken out of the machine between the uses and placed in a storage container, that is subsequently filled with nitrogen. The nitrogen prevents the hardening of the PU-glue and can be re-used during the next application. Cleaning with granulate is not necessary and there is no loss of adhesive.
- Small amounts of glue are melted in a conventional glue pot. Immediately after application of the adhesive, the glue pot and the gluing system is cleaned with a PUR-cleaner.
- Under certain restrictions, PUR-adhesives may be processed in Quickmelt glue units.
- When processing larger quantities, special premelters standing beside the machine are used. After use, the glue pot has to be removed and stored in a nitrogen atmosphere.
- The glue system with cartridge and ultra-granupress system with glue nozzles are closed gluing systems in which the processing of PUR-cartridges or granulate are easily possible. At the latest 24 hours after melting, the partly used cartridge must be removed from the melting unit. The gluing unit has to be cleaned with two to three cleaning EVA-based cartridges before color change.
- For the processing of larger amounts of PUR glue, HOLZ-HER offers separate premelters as well.
- Processing of polyurethane pellets in a closed Combimelt glue system. After the gluing process the glue pot is filled with a special granulate and a cleaning process starts. The cleaner liquifies the adhesive completely. After cleaning, the glue roller is metallicly pure.
- When processing larger quantities of glue, a supply of PUR adhesives from the outside through a tube is also possible. The gluing roll is metallically cleanse after cleaning.
- During the processing of bigger glue quantities, the injection of PUR-adhesives is possible from the outside through a hose.
- Cartridge system PU BOX since 2014
Recommended equipment for PUR-Machines
- Release agent spraying device for release agent in front of the joint trimming unit; the release agent prevents the adhesion of pure glue on the panel surface.
- Premilling unit to remove the release agent of the adhesive surface.
- Flat scraper to remove glue from the glue joint
- Release agent spraying device for cleaning liquid in front of the buffing unit
strongly depending on the adhesive
- Temperature resistance, depending on the glue: 80/ 150 to -20/-40 ° C
- Joint thickness of 0.15 to 0.1 mm
- Processing temperature 130 to 180 ° C.
For this solution must be considered the following conditions:
- Nitrogen 5.0 (purity class) has to be used.
- The container has to be perfectly sealed.
- For storage the air must be completely exhausted.
Alternative and related terms