Calendering is the most common technology used for processing PVC film. The raw mixture, known as the dry blend, is formed into a plastic web by rotating heated rollers. The gap between the rollers determines the film thickness. The surface of the film web is subsequently modified by embossing. High-gloss or satin-finish surfaces can be produced, with or without surface texturing. In the further course of the process the film is cooled and then wound up into a reel.
The extrusion process entails forcing the plastic mixture through a shaping die at high temperatures by means of a screw. The plastic web is drawn off onto a roller and cooled. An embossing or stretching process can then be carried out. The advantage of this technology is that it enables the production of sheets and profiles with complex geometries, in addition to thin film. Extrusion is the most widespread technology for processing plastics.
The lamination process generally involves the two-dimensional bonding of two or three film webs. The films are heated by means of a heated cylinder and simultaneously pressed together. In this way, thicker or multi-layer films can be produced in one or several different plastics. At RENOLIT, this process is applied to bond together PVC films and acrylic films.
The film surface is enhanced with a textured cylinder. High-gloss or matt film surfaces or reliefs can be produced in this manner. The film passes between two rollers, one of which carries out embossing (embossing roller) while the other provides the counterpressure (back roller). The attributes and stability of the embossed finish are determined above all by the embossing pressure and temperature. A clean and smooth-running embossing process is crucial to achieving an excellent and reproducible surface finish.
While there are many technical variants of the printing process, they all follow the same principle of transferring colour (or text) to a surface in a controlled manner. In the area of flat webs, the colour is applied to various roller systems which are engraved as appropriate and transferred to the film surface through contact with the latter. Well-known procedures include offset printing, gravure printing and flexographic printing. Ink-jet printing systems are employed for cutting-edge digitally controlled processes which use ink to print high-resolution images in non-contact mode.
Coating entails applying formless substances to the surface of a substrate in order to produce a bonded, continuous layer. In the case of film, these substances are generally transferred to the surface by means of rollers or a doctor knife. Surplus solvents such as water are expelled in a subsequent drying phase and the surface is homogenised. The layer thickness and adhesion to the substrate are key quality criteria for a coating. Well-known uses include the application of an adhesive layer to self-adhesive film or the coating of a printed surface with a protective lacquer.