Overhead transparency
An overhead film is a transparent film suitable for daylight projection made of writable or printable polyethylene terephthalate or cellulose acetate . Although more and more computer-aided presentation techniques are used today, overhead transparencies are still important for business and schools . In the presentation computer programs, too, the pages of a presentation are still referred to as transparencies.
Stem, manufacture, types, and related slides
The first part of the word is English for over the head (projected) and the German word Folie in the second part originally came from the Latin folium for sheet .
Like others, the foils are produced in strips, have a thickness of about 0.1 mm and a format of 21 × 29.7 cm (A4). They are usually (depending on quality) available in packs of 10 to 100 pieces.
They are available in different versions: For writing on with special felt-tip pens , heat-resistant for copiers and laser printers , coated (with gelatine, which absorbs the ink) for inkjet printers (or color copiers based on inkjet technology).
A non-heat-resistant film can stick to the fusing unit of a copier and lead to damage or a defect in the device.
Similar - mostly more flexible - foils are used in printing technology , for the thematic "levels" of maps and for the light-sensitive layer of films .
In contrast, packaging or construction films are made of other materials because they have to be weatherproof and more stable against tensile forces .
Application note
To use overhead transparencies, it is necessary that the colors used are also translucent. Color toners are usually not. This means that even if transparencies can be printed with a color laser printer , the projections usually appear in black and white or in shades of gray. The printed part of the film covers the surface during projection in black. Suitable inkjet printers are to be preferred for the production of overhead transparencies / for overhead projectors .