Mylar Film
Definition
A thin (approximately 6 micrometre) polyester film stretched over the document under vacuum in the ESDA process; it conforms to the document micro-topography, transmitting the impression geometry to the electrostatic charge pattern.
- Material
- Thin polyester film
- Typical thickness
- About 6 micrometres
- Role
- Stretched over the document under vacuum in ESDA
- Function
- Transmits document micro-topography to the charge pattern
Common questions
Why does the film need to be under vacuum during ESDA processing?+
Vacuum draws the film down tightly against the document surface so it conforms to even faint indentations from prior writing. Without close contact, the film would not pick up the fine topographic differences the toner later reveals as an image.
What happens if the Mylar film is wrinkled or reused?+
A wrinkle or a fold introduces its own topographic feature that can be mistaken for or obscure a genuine indented-writing impression, and reused film may carry residual charge or debris that degrades the toner image. Fresh, flat film is used for each ESDA lift.
Does the film itself hold the final image, or something else?+
The film transmits the surface contour to the electrostatic charge that builds on the document itself; the visible image is then developed by applying charged toner that clings preferentially to the charge pattern, not to the film. The film's job is purely to shape that charge distribution.
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