Diazotype Photocopier

an office machine for making single and multiple copies of documents, mainly drawings and blueprints, using the diazo process.

The process of producing a photocopy is accomplished in two steps: exposure and developing. In most diazotype photocopiers exposure is by the contact method. This involves placing a transparent or translucent original, for example, tracing paper, with an image on one side against a photosensitive layer of a diazo compound and subjecting the layer to intense ultraviolet light. This results in the production of a latent image in the diazo-compound layer. The exposed material is developed by the wet, dry, or hot process, depending on the type of diazo compound material used.

Diazotype photocopiers are classified according to the method of treating the diazo-compound material as dry-process, wet-process, and hot-process photocopiers. There are console and table models, and the photocopiers may use individual sheets of paper or roll paper. Some photocopiers have separate developing machines, while others combine exposure and developing. Photocopiers may be classified as semiautomatic or automatic. They may be produced in unit with auxiliary devices, such as paper-cutting, collating, or paper-folding equipment, or without such devices.

Exposure in diazotype photocopiers involves placing the original in contact with the diazo paper and wrapping the two around a transparent cylinder containing ultraviolet light sources, such as mercury-quartz lamps (Figure l,a). A tape-transport moves the diazo paper, and the exposed paper then enters the developing apparatus. Single-component diazo paper is developed by the wet process using alkaline solutions (Figure l,b). Wet-process photocopiers are usually manufactured as table models; they do not require special ventilation and may be installed in design studios or offices. They include the model SKM-22, which produces copies on roll diazo paper up to 460 mm wide at roll speeds of 0.5 to 5.5 m/min, and an office table model that produces copies on 210 x 297 mm sheets (A4 format).

Two-component diazo paper is developed in ammonia vapors by the dry process (Figure l,c). Dry-process photocopiers are usually manufactured as console models and use roll paper. The paper speed of such machines may reach 42 m/min. They are most commonly used in design offices and planning organizations and are frequently produced in unit with paper-cutting and collating devices.

Hot-process diazo paper contains not only diazo and azo components but also compounds that when heated produce alkaline substances required for developing. Such papers are treated in a heating device. The design of hot-process photocopiers is similar to that of dry-process machines.

By 1975, high-quality, high-sensitivity diazo-compound materials had been developed that make it possible for diazotype photocopiers to produce reproduction copies and inexpensive microcopies. As a result of the increase in the photosensitivity of diazo materials and of their sensitivity not only to ultraviolet rays but also to green light, the rate of exposure has increased to more than 50 m/min. This permits projection copying from microfilm.