Photocopying – Contact printing – Light boxes
Patent
1989-04-14
1991-05-14
Grimley, A. T.
Photocopying
Contact printing
Light boxes
354321, 354322, 355282, G03G 1520
Patent
active
050160583
DESCRIPTION:
BRIEF SUMMARY
The invention is directed to a method for fixing toner images applied to a web-shaped recording medium and to an arrangement for the implementation of the method according to the preamble of patent claims 1 and 2.
German Patent 28 38 864 discloses an apparatus of the species initially cited. For fixing toner powder applied to a recording medium, for example a paper web, in electrostatic copier or recording devices, the recording medium is transported through a fixing station in which the toner is joined fast to the recording medium. The fixing station contains a container through which the recording medium is conducted loop-shaped. Solvent vapor is generated at the underside of the container. A deflection means around which the recording medium is conducted is arranged in the region of the container enriched with solvent vapor. The recording medium is thereby exposed to the solvent vapor. After fixing, the recording medium departs the fixing region and is in turn conducted out of the container via an upper deflecting roller. The fixing region is limited in that cooling coils are arranged in the container wall in the upper region of the container. A cooled region in which solvent vapor emerging from the fixing region condenses thereby arises in the container. The lower deflection means can be removed from the container for introducing the recording medium.
Such non-mechanical copier or printer devices operating on the cold-fixing method are based on the principle that toner can be dissolved or, respectively, volatilized under the influence of solvent vapor and, thus, can penetrate into the surface of the recording medium. The degree of softening or, respectively, volatilization of the toner material depends critically on the concentration of the solvent vapor and on its influencing time.
The recording medium is thereby drawn through the vapor region of the fixing means with constant speed in the form of a loop. The reaction time between toner and solvent thus becomes a constant quantity in system-conditioned fashion.
In order to achieve the goal of a uniform fixing quality, the concentration of the solvent or, respectively, fixant vapor must be exactly held to a corresponding value.
To this end, German Patent 31 11 970 discloses a circuit arrangement in a means for monitoring the concentration of an air-vapor mixture in a toner image fixing station working with solvent vapor.
Fluctuations in the fixing strength, as may nonetheless still occur, can no longer be eliminated even by an improvement of the control outlay for the vapor concentration. The reason lies therein that the solvent (fixing means) is replenished in liquid form when the rated concentration is fallen below and must then be evaporated. The evaporation speed therefore led to a thermically conditioned dead time for the control system. A further dead time arises given an excess of vapor, i.e. an excessively high concentration of the solvent vapor. This is dismantled essentially only as a consequence of condensation at a cold trap arranged in the container for the solvent vapor and cannot be influenced in control-oriented terms.
The fixing strength decreases given a decrease in the vapor concentration. Given an increasing concentration, the toner dissolves to a more intense degree. The time span that elapses from the emergence of the recording medium from the fixing station up to deposit on a fanfold deck is available for the subsequent drying process.
When printed paper is deposited in the form of a fanfold deck without an adequate quantity of solvent vapor having dried, this leads thereto that the tonered (inked) regions of the paper web stick to one another. This particularly occurs when the deck part stacked thereabove compresses the region that lies lower. The residue of solvent that is still effective in this case allows the toner adhering to the paper web to harden only gradually. The more or less pasty consistency of the toner harbors the risk that the toner layers touching one another will fuse to one another. This must be avoided under
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Dang T. A.
Grimley A. T.
Siemens Aktiengesellschaft
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