Modern thermoplastic hot melt adhesives based on polyolefin from Jowat bond wood-based materials as well as a wide variety of different plastics with relatively low surface tension, such as PE and PP, and also metallic surfaces. Special formulations and the purely physical adhesion mechanism of the adhesives facilitate a mechanical removal of the cold adhesive from the bonding surface with virtually no residues. Therefore, the formwork elements can be reused several times for casting concrete parts.
Jowat-Toptherm® 233.10 and Jowat-Toptherm® 233.20 are applied using hot melt guns which are either filled with a cartridge or supplied with adhesive from a melting tank – filled with granulate – through a heatable hose.
The two adhesives are characterised by a very fast build-up of strength during cooling, and the formwork can already be filled with adhesive a few minutes after bonding. Controlled ambient conditions are not necessary for bonding.
The adhesives Jowat-Toptherm® 233.10 (all-purpose) and Jowat-Toptherm® 233.20 (especially for low processing temperatures) have been optimised for this particular application. They are flexible enough to absorb vibrations and hard enough for a relatively easy removal. The tried and proven PO-based hot melt adhesives from Jowat have been used for many years and are available – adapted to the established applicator systems – in granulate form (only Jowat-Toptherm® 233.10) as well as in cartridges.
For flexible bonding of temperature insensitive materials. Good adhesion to plastics, such as PE, PP, PS and PC, as well as to wood, and steel. Ideal assembly hot melt adhesive with a wide range of applications, also on non-absorbent surfaces. Flexible bondline which can absorb vibrations.
The hot melt is adapted for use in the production of precast concrete parts due to its special characteristics. This application not only requires a good adhesion of the adhesive to the substrates. A reliable bond also has to ensure resistance against the vibrations occurring when the concrete in the formwork is compacted with plate compactors. In addition, these thermoplastic adhesives leave no residues when removed after cooling from the formwork panels. This is especially important for a superior appearance of precast béton brut parts, and also allows to reuse the formwork panels as well as other relevant parts used in the manufacture of precast concrete.
Directions for use
The PO adhesives are usually supplied in block or granulate form and are heated in standard melting units to a temperature of approx. 180 – 200 °C and applied onto one substrate as beads using a hot melt gun or sprayed onto the full surface. Adhesive cartridges are processed the same way. To ensure an optimum adhesion, the surface to be bonded has to be clean, dry and free of oil.
To achieve a sufficient bond strength, the part with the adhesive only has to be pressed firmly onto the formwork panel for a few seconds. On cooling, the adhesive will build up its cohesive strength as well as the adhesion between the bonded parts. The wide range of adhesion of the adhesives facilitates a reliable bonding of many, different materials. The specified open time indicates the maximum processing time of the hot adhesive, directly after application onto the substrate until fastening, e.g. on a formwork panel.
When the adhesives are heated again, they become soft and liquid and facilitate a repositioning of the bonded parts without any significant loss of adhesion.
In cold environments, it may be advantageous to use an adhesive with a longer open time (Jowat-Toptherm® 233.20) to maintain a processing period which is long enough in spite of a faster cooling of the hot melt. The adhesive application amount should always be high enough to ensure a sufficient adhesive coating, i.e. the surface to be bonded should be fully wetted.