Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
1996-08-19
2002-05-14
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S213000
Reexamination Certificate
active
06386696
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for transferring solid or liquid printing ink from an intermediate carrier, such as a transfer cylinder, to a further intermediate carrier or a substrate, such as paper, as well as to a device for performing the method.
In order to be able to transfer liquid printing ink from a cylinder of a printing press onto a further cylinder and a substrate, respectively, the adhesion of the printing ink to the second cylinder or the substrate, a characteristic which is based upon physical interfacial effects, must be greater than the adhesion thereof to the original cylinder. Upon the transfer of liquid ink, however, a cracking or splitting of the liquid film occurs, so that a portion thereof remains on the original cylinder, and it is virtually impossible to achieve anything even remotely close to 100% transfer of liquid printing ink.
The same problem exists in the transfer of solid printing ink which is in a granular state, such as toner powder, for example. To be sure, electrostatic transfer techniques which achieve a transfer efficiency of approximately 95 to 98% maximum have become known heretofore; however, this is only for applications using non-conducting toner. For production presses with an output of many thousands of sheets per hour, this is not sufficient, however, because it would be necessary permanently for the cleaning devices to be replaced and to be cleaned outside the printing press, respectively.
In an article entitled “Offset Quality Electrophotography” in the “journal of Imaging Science and Technology”, Volume 37, No. 5, September/October 1993, p. 458 (hereinafter referred to as “OQE”), various xerographic techniques which are suitable for transferring conductive toner even when the humidity is quite high are described. In one of the techniques, the toner is transferred under pressure onto a substrate and is simultaneously fixed. A further technique calls for a thermal or heat transfer in two temperature stages. In addition, combinations of transfer under pressure and thermal transfer are described therein. Such a combination is presented on page 459 of the aforementioned publication. The toner is transferred by pressure from a first cylinder onto an intermediate cylinder and then by thermal transfer onto paper which runs between the intermediate cylinder and a heated impression cylinder. An efficiency of 95% is supposed to be achieved in the case of transfer by pressure, while an efficiency of 100% is attained in the case of thermal transfer.
In the periodical “The Seybold Report on Publishing Systems”, Volume 24, No. 20, page 20, left-hand column (hereinafter referred to as the “Seybold Report”), a transfer system is described wherein an image is transferred to paper through the intermediary of two belts. One of the belts accepts the toner in a distribution corresponding to the printed image. The image is then transferred to the other belt, which is heated. The latter belt is not hot enough to melt the toner, but the heat thereof is sufficient to cause the toner particles to adhere to one another. The heated belt then transfers the image onto the paper, which is preheated, the image being fixed by means of a hot pressure roller. Consequently, no subsequent melting or fixing of the toner is required.
In the first step, the transfer from a first belt to a second belt, it is not possible at all to achieve a transfer efficiency of 100%. The first belt is, in fact, teflon-coated, and basically exerts at least small adhesion forces on the toner, so that, in the first step at least, a transfer efficiency of less than 100% is to be assumed, as is similar to the situation with the technique described in the aforementioned “Offset Quality Electrophotography” article.
In both of the aforedescribed techniques, the toner is thus not transferred in its entirety from the cylinder and from the first belt, respectively. Particularly with regard to recently developed printing techniques, e.g., the printing technique described in the “Seybold Report”, it is necessary, however, for the remaining printing ink to be entirely removed before new printing ink is applied to the first belt and to the first cylinder, respectively, in order to attain a perfect print. This may be very difficult and costly, particularly if the printing ink is to be reused.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a device for transferring printing ink wherein transfer techniques are used which virtually always have a transfer efficiency of 100%, not only when transferring ink onto paper, but also when transferring ink onto an intermediate carrier.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of transferring printing ink from an intermediate carrier to a printing-ink receiver selected from the group consisting of a further intermediate carrier and a substrate, wherein the printing ink adheres in a granular state to the intermediate carrier, which comprises melting the printing ink at a side thereof facing away from the intermediate carrier before transferring the printing ink to the printing-ink receiver.
In accordance with another aspect of the invention, there is provided a method of transferring printing ink from an intermediate carrier to a printing-ink receiver selected from the group consisting of a further intermediate carrier and a substrate, wherein the printing ink adheres in an at least partially liquid state to the intermediate carrier, which comprises reducing the adhesion of the printing ink to the intermediate carrier with a separating agent at one time at least before and during transfer to the printing-ink receiver.
In accordance with a further mode, wherein the intermediate carrier has an outer elastic layer containing the separating agent, the method according to the invention includes pressing the intermediate layer and the printing-ink receiver against one another so as to drive the separating agent to the surface of the elastic layer.
In accordance with an added aspect of the invention, there is provided a device for transferring printing ink from an inking unit via an intermediate carrier to a printing-ink receiver selected from the group consisting of a further intermediate carrier and a substrate, comprising a heat source disposed opposite a surface of the intermediate carrier, the surface extending between the inking unit and the printing-ink receiver.
In accordance with an additional aspect of the invention, there is provided a device for transferring printing ink from an inking unit, comprising an intermediate carrier for receiving printing ink from the inking unit and for transferring the printing ink to a printing-ink receiver selected from the group consisting of a further intermediate carrier and a substrate, the intermediate carrier having at least one of the properties consisting of being permeable to a separating agent and having a storage capacity for a separating agent.
In accordance with yet another aspect of the invention, there is provided a device for transferring printing ink from an inking unit of a printing press to a substrate being transported through the printing press, comprising a first intermediate carrier adjoining the inking unit and having a surface to which printing ink is transferrable from the printing unit, and a second intermediate carrier disposed so as to be in contact with the first intermediate carrier and the substrate and having a surface extending between the first intermediate carrier and the substrate for transferring printing ink from the first intermediate carrier to the substrate, comprising a first heat source disposed opposite the surface of the first intermediate carrier, and a second heat source disposed opposite the surface of the second intermediate carrier.
In accordance with yet a further aspect of the invention, there is provided a device for transferring printing ink from an inking unit of a printing press to a substrate
Freyer Norbert
Klingel Hans
Rodi Anton
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