Лако-красочные материалы — производство

The purpose of a tamper-evident bottle closure is to comply with statutory regulations and to issue a guarantee for producer bottling and product integrity. Either hot melts or waterborne adhesives can be used, as necessary and depending on the bottle material.

Both adhesive systems must meet high demands as to the initial strength, detachabili — ty and removability. Bottle closures are made from either plastic or coated metal (e. g. twist-off caps), on the surfaces of which it is much more difficult to obtain adhesion than, for example, on glass surfaces. The surface that is the more difficult to bond (usually the surface of the closure) determines the adhesive used. Furthermore, as the surfaces available generally have a very small area (a few square millimeters to a few square centimeters), in order to provide a secure positioning of the labels and avoid slipping during the curing process, the adhesives must have a high initial strength.

When opening a tamper-evident closure, a bond must be broken, leaving an obvious visual indication that the bottle has indeed been opened. The bonding must therefore not be easy to detach (e. g. by water). A combination of waterborne systems and hot melts may be necessary to bond a paper strip on bottle closures; self-adhesive tamper-evident closures are another option.

In addition to these requirements, tamper-evident closures for returnable bottles must meet another demand — that they be smoothly removable in the bottle-cleaning machine. This is straightforward with casein-based adhesives, but if special require­ments with regards to the adhesion properties make it necessary to use synthetic, resin-based adhesives, then care must be taken to select an adhesive that can later be

easily removed. For example, if a fast setting rate is required to provide for a rapid and secure fixing of very small tamper-evident labels, then conventional packaging hot melts will not be suited because they are not water-soluble. For this purpose, special hot melts have been formulated that are water-soluble or redispersable so as to be removable during bottle washing.