Contact copier
A contact copier (also known as contact printer) is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface (film, paper, plate, etc.). The more common processes are negative, where clear areas in the original produce an opaque or hardened photosensitive surface, but positive processes are available. The light source is usually an
Commercial contact printers or
Uses
The contact copying process was used in the early days of photography and sunlight-exposed blueprints; it is still used in amateur photography, silkscreen printing, offset printing, and photochemical machining, such as the manufacture of Printed circuit boards. By the early 20th century, blueprinting (producing white lines) or diazo blue line printing used contact-rollers rather than flat-glass exposure.[citation needed]
Silkscreen printing and photochemical machining originally were based on
Photography
The contact copier is used for duplication of negative or positive prints obtaining what are called contact prints, that is, to reproduce on paper or film, a photographic negative or positive of exactly the same size of the original. (With normal photographic non inverting processes, black generates white on the target while white generates black). It was the common mode to make prints until it began the use of the alternative
The reproduction is done by placing the negative on top of the glass and then the photo paper with the
Whiteprint
In the process of
Silkscreen
In
The
Offset
In
The process shares some fundamental principles with the photographic processes, since the pattern engraved on the plate is generated by exposure to light with an image created in a contact copier using an optical mask. This procedure is comparable to the high-precision method of the version used to make printed circuit boards.
Printed circuits
The contact copier is used today, particularly in the areas hobbyist, for the photoengraving of prototype printed circuit boards (PCBs) before being sent to production (artisanal creation ). Substantially similar to the contact printer used in photography, this variant usually uses ultraviolet lamps to impress a copper base specifically pre-sensitized.
Burned by exposure to light parts reproduce patterns drawn on a transparent photolith film on a pre-sensitized plate (epoxy or Bakelite). This pre-sensitized plate comprises an insulating plate (epoxy resin or bakelite), adhered with a layer of copper, and coated with a varnish layer sensitized. The varnish is sensitive to UV rays, which weaken or strengthen its structure depending on whether a "positive" or "negative" process. Photolith film printed parts (usually black), inserted between the light source and the pre-sensitized plate, protect the varnish from the UV. The base copper impressed must then be engraved in a specific bath (usually ferric chloride FeCl3), that removes the excess copper.
See also
- Lightbox
- Azo compound
- Blueprint
- Ozalid
- Heliographic copier
- Thermal copier
- Verifax copier
- Diatype (machine)
References
- ^ ISSN 0032-4558.
- ISBN 978-0-7897-3504-1.
- ISBN 978-81-7833-087-7.