- The transparency and visual quality of filmed glass are not equal to the visual quality of unfilmed glass. The following criteria apply only to installed window films, not potential defects in the glass surface.
- The adhesion and drying time of window film are influenced by the water solution used during installation. Although excess water is squeezed out between the film and the glass, some water residue is inevitable between the film and the glass. The complete drying time depends on the thickness of the installed film, and climatic conditions also affect drying time and appearance, making it longer or shorter. The time during complete drying is also referred to as the adhesive curing time.
- Visual inspection can be done before the film is completely dry. Table 1 outlines typical drying times for films of different thicknesses. Note that defects such as water bubbles, water distortions, and film haziness during drying are not considered installation defects.
- Glass covered with film should be viewed from inside the room and at least 2 meters away. Observation must take place during daylight but not in direct sunlight and should include the normal field of vision, excluding a 50 mm wide area along the film’s edge.
- The installation is considered acceptable if, after film installation, the following disturbing visual defects do not occur within 2-3% of the allowed deviation: dust spots, hairs, fibers, adhesive residues, fingerprints, insects, loose corners, spots and tears, dents and scratches, haziness, and air bubbles. Observation can be carried out on the day of film installation. If you notice defects, evaluate them as described in point 4.
- The 50 mm wide edge area is evaluated similarly to points 3 and 4, but a small amount of dust spots is allowed, especially if poor frame conditions prevent achieving usual high installation standards.
- The gap between the frame/seal and the film edge is usually between 1-4 mm. The gap allows excess water to be squeezed out from between the film and the glass, preventing the film edge from rising when in contact with the frame/seal. Leaving excess water unremoved can lead to film detachment, which is considered an installation defect. For security films, a 1-4 mm gap is left, and a 1-5 mm gap is acceptable for films thicker than 175μ. Combined sun protection-security films belong to this class. Up to a 2 mm gap is recommended for dark films (tinted, metallized) to reduce the visible light line between the film and the frame.
- Joining films is necessary when covering large glass surfaces where the glass dimensions are larger than the film width. The connection line on the glass surface is not considered an installation defect. The line must be straight and parallel to the frame. The films must be close together but not overlapping at the joint; the maximum gap at the joint can be up to 1 mm. Films with a thickness less than 50μ may have overlapping or connected joints.
- The installation of window film may increase the reflectivity of the window, especially when a film containing metal or metal compounds is installed. This is not a defect but a natural effect of window film.
Table 1: Time required for film drying
Film thickness μ Drying time in days
up to 100 30
100 – 200 60
200 – 300 100
over 300 140
This text is based on the original document “Visual Quality Standard for Applied Window Film” issued by the Glass and Glazing Federation (44-48 Borough High Street, London, UK).