Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-12-17
2003-04-15
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Fixing
C430S124300
Reexamination Certificate
active
06549746
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for printing and/or coating of a substrate, of paper or cardboard, a device for executing and a device for printing and/or coating a substrate, especially of paper or cardboard.
BACKGROUND OF THE INVENTION
In one known process of electrostatic printing, a latent electrostatic image is developed by charged toner particles. The latter are transferred to an image receiver substrate, which is hereinafter also called a substrate for short. Then the developed image which has been transferred to the substrate is fixed by the toner particles being warmed or heated and melted, and optionally the substrate being heated. To melt the toner particles, contact methods are often used, in which the toner particles are brought into contact with corresponding hot rollers or drums. To fix the toner which has been transferred for example to paper, there are furthermore heaters and processes which work without contact in which the toner particles are melted for example using heat/microwave radiation or hot air so that they stick to the paper.
In the printing or copying process in which the image applied to the substrate or the coating is developed by a toner, the gloss of the fixed toner does not follow the gloss of the paper, as is the case for example in offset printing. This applies both to contactless and also contact-making toner fixing processes. The reason for this is the greater layer thicknesses of the toners compared to the color layers produced in the offset printing process. The relatively thick toner layers fill the porosity of the paper, by which a smoothed surface structure and a certain gloss of the toner layer are formed.
In many cases it is desirable to adapt the gloss of the substrate surfaces covered with one or more fixed toner layers to the gloss of the uncovered surfaces of the substrate. For this purpose there have been gloss variation mechanisms, for example in the form of a calendar, which have a surface which acts with a predetermined force on at least one fixed toner layer or a toner layer in the course of being fixed, in order to vary the gloss of the fixed toner layer. One disadvantage of the known gloss variation mechanism is that the surface acting on the toner layer must be replaced by a surface with another structure when the aforementioned matching of the gloss of the fixed toner to the gloss of the uncovered surfaces of the substrate for different toner types and/or different substrates is to be done. The replacement of the corresponding surface of the gloss variation mechanism or the replacement of the entire gloss variation mechanism is however time-consuming and leads to the undesirable machine downtimes.
SUMMARY OF THE INVENTION
The object of the invention is to devise a process and a device with which the gloss of at least one toner layer fixed on the substrate can be varied without gloss variation mechanisms or parts thereof having to be replaced. Another object of the invention is to improve the printing or copying quality.
To achieve this object, a process is proposed which relates to printing and/or coating of a substrate, especially of paper or cardboard, at least one toner layer being transferred to the substrate and fixed on it. For example, in color printing the toner image can have four differently colored toner layers, conventionally one of the toner layers at a time being black, yellow, magenta and cyan. The liquid or dry toner has at least one polymer and color pigments and other constituents. When at least one toner layer is fixed, the polymer chains are crosslinked, by which a fixed toner layer is formed which is also called a polymer layer. The surface roughness and thus the gloss of this polymer layer depend largely on the density of the toner particles, their theological properties, and the melting process used. To match the gloss of the developed toner layer for example to the gloss of the uncovered surfaces of the substrate, there is a gloss variation device which has a surface which acts upon at least one fixed toner layer or one which is being fixed. To enable matching of the gloss, for example to various substrates, without replacing the gloss variation device or parts thereof, in the process it is provided that depending on the gloss to be achieved the force with which the surface of the gloss variation device acts on at least one toner layer and/or at least one property of the surface of the gloss variation device is changed. In this way, matching of the gloss in many cases can be done even during operation of the corresponding device, by which machine downtimes can be avoided and the throughput can be increased.
Changing at least one property of the surface of the gloss variation device can comprise changing the roughness of the surface of the gloss variation device. The roughness is determined especially by the distribution and the height of the elevations on the surface of the gloss variation device. In this connection it is possible to change the intervals of the elevations which determine the structure of the surface of the gloss variation device. Likewise, embodiments are conceivable in which the height of the elevations is changed, and changes the force with which the surface acts on at least one toner layer, preferably being chosen in this case such that the elevations for varying the gloss extend entirely into at least one toner layer.
One possibility for changing the structure of the surface of the gloss variation device is to elastically change the dimensions of the surface. In this connection rotation of the elastic material, which forms the surface of the gloss variation device leads to the distances between the individual elevations increasing, like the dimensions of the elevations themselves. When the forces which cause stretching of the elastic material which, forms the surface of the gloss variation device are reduced, the distances between the elevations and the dimensions of the elevations themselves decrease, again as a result of the elasticity of the material. The change in the dimensions of the surface of the gloss variation device can take place for example by changing the diameter of the drum, which forms the surface of the gloss variation device. Alternatively or additionally, it can be provided that the distance between and/or the length of at least the two drums around which an elastic belt is guided which forms the surface of the gloss variation device is changed.
In one embodiment of the process, it is provided that the gloss variation device is formed by a fixing device which is designed for fixing at least one toner layer. In this case the surface of the gloss variation device can be formed for example by the surface of a heated drum which is a component of the fixing device. The surface of the gloss variation device then acts on at least one toner layer in the course of fixing. This embodiment of the process is characterized by the space requirement being hardly increased at all relative to known devices without the gloss variation device.
In another embodiment of the process it is provided that there is a gloss variation device separate from the fixing device which is necessary for fixing at least one toner layer. In this case the gloss variation device can carry out final processing of the at least essentially already fixed toner layer. This can be advantageous for example in cases in which the gloss of at least one toner layer after fixing is acquired by measurement in order to match the final processing carried out by the glass variation device to the actual conditions.
In the process, it can furthermore be provided that via changing the force with which the surface of the gloss variation device acts on at least one toner layer, elevations of the surface of the gloss variation device which taper towards its free end can be pressed to different degrees into at least one toner layer. The elevations of the surface of the gloss variation device can have for example a pyramidal or conical shape. When a surface which is provided with these elevat
Kessler Lawrence P.
NexPress Solutions LLC
Pendegrass Joan
LandOfFree
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