3.Machining and processing HPL
The bonding of HPL is particularly important, as it has a significant influence on the subsequent properties. There are adhesives on the market which feature good adhesive strength and resistance to temperature as well as humidity. They are therefore very suitable for bonding HPL. The materials to be bonded as well as transport and application conditions must be taken into account when selecting a suitable adhesive system. Follow the health and safety regulations and accident prevention regulations when working with adhesives! In addition, ensure that the surfaces, front and back, are completely clean and free of residue. Particular attention should be paid to the suitability of the cleaning agents used.
Processing and storing adhesives require special care. The guidelines and data sheets of the adhesive manufacturers are therefore to be complied with in all details.
If you have any questions about bonding and for new applications please contact the adhesives manufacturer.
The following types of adhesives are suitable: Dispersion adhesives (e. g. PVAc glues = white glues), condensation adhesives (e.g. urea, resorcinol and phenolic), contact adhesives (e. g. polychloroprene adhesives), reactive adhesives (e. g. epoxy, unsaturated polyester, polyurethane) and hot melt adhesives (e. g. polyurethane hot melt).
The expected moisture load of the bonding joints is classified as follows as per EN 204 (Classification of thermoplastic wood adhesives for non-structural applications):
| D 1: | Interior areas, maximum wood moisture content 15% |
| D 2: | Interior areas, with occasional short-term exposure to running or condensed water or to occasional high humidity, with the moisture content of the wood not exceeding 18 % |
| D 3: | Interior areas, with frequent short-term exposure to running or condensed water and/or heavy exposure to high humidity. Exterior areas not exposed to weather |
| D 4: | Interior areas with frequent long-term exposure to running or condensed water. Exterior areas exposed to the weather, but with suitable surface protection |
The information on temperature resistance shown in the following tables applies only for short-term exposure of the glue joint. They must not be confused with long-term exposure of the composite elements (consisting of HPL, adhesive and substrate). The long-term durability of the composite element rather depends on type and class of the HPL, the substrate as well as on humidity and ambient temperature. Proper processing is always crucial. The manufacturer must always be contacted for special applications because the adhesives within the stated group have different properties and are under continuous further development.
Table 7: Application of adhesives
| Adhesive type | Processing method | Comment | Typical application |
|---|---|---|---|
| Dispersion adhesives: | |||
| PVAc adhesives Two-component PVAc adhesives |
| Pressing using a stationary press or clamp | Surface, edge |
| Condensation resin adhesives: | |||
| Urea resin with high filler content Melamine/urea resin Phenol/resorcinol resin |
| Pressing using a stationary press while applying heat | Surface |
| Contact adhesives: | |||
| Contact adhesives without hardener Contact adhesives with hardener Contact adhesives withintegrated resin hardeners |
| Pressing with short, high pressure using a roller | Surface, edge |
| Reaction adhesives: | |||
| 1-component systems Polyurethane adhesives |
| 1-component systems require moisture from the surrounding materials. Use of heat shortens the processing time | Surface, edge |
| 2-component systems Epoxy and polyurethane adhesives | 2-component systems do not require moisture from the surrounding materials. Use ofheat may be required depending on the system | Primarily surface | |
| Hot melt adhesives: | |||
| EVA PO |
| Application: Residential rooms | Edge |
| PUR | Application: Mainly in areas with high levels of humidity and heat | Surface, edge | |
The guide values in the following table refer only to the adhesive gap.
Table 8: Durability of the adhesives (based on experience)
| Adhesive type | Temperature resistance (approximate values) (1) | Stress resistance based on DIN EN 204* (2) |
|---|---|---|
| Dispersion adhesives: | ||
| PVAc adhesives | - 20 °C to + 100 °C | D 2 / D 3 |
| 2-component PVAc adhesives | - 20 °C to + 100 °C | D 3 / D 4 |
| Condensation resin adhesives: | ||
| Urea resin with high extender content | - 20 °C to + 150 °C | D 3 |
| Melamine/urea resin | - 20 °C to + 150 °C | D 3 |
| Phenol/resorcinol resin | - 20 °C to + 150 °C | D 3 / D 4 |
| Contact adhesives: | ||
| Contact adhesives without hardener | - 20 °C to + 70 °C | – |
| Contact adhesives with hardener | - 20 °C to + 100 °C | – |
| Contact adhesives with integrated resin hardeners | Request from manufacturer | Request from manufacturer |
| Reactive adhesives: | ||
| Epoxy, unsaturated polyester and polyurethane adhesives | - 20 °C to + 100 °C | D 3 / D 4 |
| Hot melt adhesives: | ||
| EVA | - 20 °C to + 90 °C | D 2 |
| PO | - 20 °C to + 110 °C | D 2 |
| PUR | - 30 °C to + 140 °C | D 3 / D 4 |
