Лако-красочные материалы — производство

Cargo is commonly transported in palletized unit loads, with individual packages stacked on each other on a pallet base. In order to secure the load to the pallet during transport, one solution is to use plastic wraps; however, because this creates much packaging waste, such wraps are being increasingly replaced by palletizing adhesives (Figure 8.32) [32].

The sticky pallet-securing products are usually called ‘adhesives’ and are even made from similar raw materials. However, in fact they basically differ from packaging adhesives on several points, and are better designated as ‘antislipping products’. When a carton, for example, is closed by means of bonding with an adhesive, owing to the strength of the adhesive bond, its material will be destroyed and fibers torn away when the bond is opened. This is due to an intimate contact between the adhesive and the surface of the substrate (adhesion), the adhesive itself having a higher inner strength (cohesion) than the substrate. A pallet-securing product, however, is expected to hold the load units firmly together during transport and storage, yet allow an easy separation of the packages, without damaging their surface. ‘Antislipping products’ must therefore provide either for adhesion failure between the ‘glue’ and the surface of the package, or cohesion failure within the adhesive film when packages are de-palletized. These ‘antislipping products’ can be either waterborne or hot melts.

Waterborne ‘antislipping products’ are usually two-phase systems (dispersions) where the sticky substances (the inner phase) are finely dispersed in water (the outer phase). They are processed at room temperature, their antislipping effect being generated during the drying process. With waterbornes, the cartons and boxes to be palletized must be brought together while the ‘antislipping product’ is still in aqueous condition (‘still wet’). It is of the utmost importance not to exceed the open time of the antislipping product. Waterborne products can be applied either manually (brush, roller, handheld gun) or by means of fully automated nozzles (spray or bead application). Manual application requires a relatively low investment, but dosing is difficult and the pallet-securing quality is not consistent. With automatic equipment, the application process and quantity can be tailored to the individual package, providing for consistent pallet securing quality.

Hot-melt antislipping products are 100% solids that are heated to temperatures ranging between 100 and 180 °C in order to transfer them into the liquid state; this then allows them to be conveyed and processed. Setting takes place by cooling via heat transfer to the substrate and to the environment. As palletizing is generally a slow

operation, the package to be fastened is not placed into the ‘wet’ (liquid) hot melt, but onto a more or less set, solid product. This results in a surface bond with little or no penetration into fiber, and hence little or no fiber tear when separated.

8.5.5