Adhesion films are usually soft plastic films such as PVC (polyvinyl chloride) or PE (polyethylene) with a very smooth underside, which adhere to smooth, pore-free surfaces such as glass without adhesive. Adhesive films are therefore self-adhesive films, e.g. transparent films from the kitchen. In contrast to normal adhesive film, adhesive film can be removed from the substrate within seconds, even after a longer period of time, without leaving behind any residue. For example, it can be used as a protective film for mobile phone displays, painted or printed as temporary shop window advertising and decoration or window decoration in children's rooms. Adhesive films are particularly suitable for short-term use as an alternative to self-adhesive films.
Application of adhesive films
The popular wet application technique with water film and squeegee
can be used for adhesive films. A squeegee is a tool with which water or air bubbles can be wiped away to the side to create a smooth, bubble-free surface.
But why do adhesive films adhere at all and why can they only do so on smooth surfaces?
Properties of adhesion films
The adhesion of the adhesion films works analogously to the adhesion of geckos. This is where the so-called Van-der-Waals forces work. A gecko can safely climb vertical walls and hang itself upside down from the ceiling. It has several million tiny hairs on the soles of its feet, which in turn are so strongly branched that they form a very large surface that is sufficient to create sufficient attraction between the molecules of the hairs and those of the substrate.
The fact that gecko soles can nevertheless easily detach themselves from the ground with every step is due to the fact that the angle of the hairs changes with the movement of the foot and the Van der Waals bond dissolves. The soft adhesive films can also be easily removed from the substrate using the same principle.
What is behind the Van-der-Waals forces?
One of the main causes of adhesion or attachment forces are the so-called Van-der-Waals forces. These are weak attraction forces that exist between the molecules in the surfaces of two materials. These gravitational forces prevail between all possible surfaces, e.g. even if the hand lies on the table top. The basic idea behind the Van der Waals forces is that the electrons in the molecules are constantly in motion, even if they are so-called solid matter. The movement of the electrons leads to the fact that the charge within a molecule is distributed unevenly for a short time and one side is positively charged, the other negatively. If the positive side of one molecule is now in contact with the negative side of another molecule, they attract each other. In this way, all molecules constantly re-align themselves with their temporary positive or negative partial charges.
The resulting force of attraction between the surfaces of the materials is comparatively weak and decreases the more air is in between. Therefore, the contact surface between the molecules must be as large as possible, which is only possible with really smooth and pore-free surfaces such as the underside of an adhesive film and e.g. glass. We therefore recommend cleaning windows, for example, with degreasing glass cleaner before using the adhesion film. Van-der-Waals forces are not electrostatic forces, which of course can also cause an attraction. Electrostatic forces prevail statically, i.e. permanently between the unevenly charged poles (anion and cation) of molecules. Electrostatic attraction is much stronger and a film that is electrostatically charged should adhere to rougher surfaces.