Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-12-18
2004-02-24
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000
Reexamination Certificate
active
06697598
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to heating at least one second material layer, especially a toner layer which has been transferred to an image receiver substrate, wherein heating of at least the second material layer takes place predominately via the quantum tunnel effect.
BACKGROUND OF THE INVENTION
One known printing process is electrostatic printing in which 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. Optionally the substrate can also be heated. To melt the toner particles, contact methods are often used, in which the toner particles are brought into contact with the corresponding mechanisms, for example hot rollers or drums. The disadvantage here is that building and maintaining the contact-making heating mechanisms are complex and thus operating costs are high. Moreover, the use of silicone oil as the separating agent which is designed to prevent adhesion of the melted toner to the heating mechanisms is necessary. Furthermore, the fault rate caused by the contact-making heating mechanisms is relatively high.
To eliminate these disadvantages, processes have been suggested in which toner particles are heated or melted using electromagnetic or acoustic waves, so that they stick to the substrate, for example, paper.
In conjunction with the use of electromagnetic or acoustic waves however the problem arises that it is very difficult to control the penetration depth of the waves into the toner layer and optionally the image receiver substrate, regardless of the material properties. At the conventionally used angles of incidence of the electromagnetic or acoustic waves the penetration depth is in the range between a few multiples of the wavelengths and some dozens of the wavelength. But the penetration depth for the entire heating or toner melting process plays a decisive role and for example influences the image quality of one-page printouts, the frequency of reproduction problems on the pages printed second in duplex printing, the glossiness and the gloss differences of the printouts, the adhesion properties of the toner layer fixed on the image receiver substrate, (unwanted) bubble formation, possible shrinkage of the image receiver substrate and so forth.
SUMMARY OF THE INVENTION
Therefore the object of the invention is to devise a process of the initially mentioned type with which the penetration depth of the electromagnetic and/or acoustic waves into a second material which is to be heated, especially a toner layer, and/or a third material layer, especially an image receiver substrate and/or an image receiver substrate carrier, can be controlled, regardless of the properties of the individual material layers. A further object of the invention is to control the amount of energy delivered to at least the second material layer by the electromagnetic and/or acoustic waves, especially without changing the radiation intensity of the wave source and regardless of the reflection properties of the third layer.
To achieve this object, a process is used especially to heat a second material layer in the form of a toner layer which has been transferred to the image receiver substrate, by delivering energy from electromagnetic and/or acoustic waves. The electromagnetic and/or acoustic waves are incident from a layer which can be formed for example by air, at an angle of incidence a relative to the normal of the second material layer. It is known to one skilled in the art, for example from physics textbooks, that at an angle of incidence in the region of 90°, the reflected part of an electromagnetic or acoustic wave which on the interface strikes the second material layer, with a higher index of refraction, is roughly 100%. If the second material layer has a lower index of refraction than the first material layer, similar conditions arise when the angle of incidence a corresponds to the so-called boundary angle of total reflection. Under these conditions the energy delivery by the normally-refracted wave portion which penetrates the second material layer is negligibly small. The penetration depth of this wave portion is therefore almost meaningless. The invention is characterized in that the angle of incidence a is chosen such that the energy delivery which causes at least the heating of the second material layer takes place at least predominantly via the quantum tunnel effect. The use of this quantum tunnel effect for heating at least one second material layer makes it possible to control the penetration depth of electromagnetic and/or acoustic waves into the second material layer exclusively via the wavelength used, regardless of the material properties, by which for example the above mentioned problems can be eliminated.
Since the quantum tunnel effect is sufficiently known to one skilled in the art, for example from physics textbooks, it is described only briefly here. When an electromagnetic or acoustic wave is incident on the interface between the first material layer and the second material layer with a higher index of refraction at an angle of incidence of roughly 90° to the normal of the interface, the reflected portion of the waves is almost 100%. Under these conditions the energy delivery by the normally-refracted wave portion which penetrates into the second material layer is negligible small, for which reason its penetration depth no longer plays a part. But as a result of the quantum tunnel effect the incident waves upon reflection on the interface penetrate into the second material layer with a penetration depth which corresponds roughly to the wavelength of the electromagnetic or acoustic waves. This penetration depth of roughly one wavelength is essentially independent of the material properties of the second material layer. The path traversed when the waves are reflected in the second material layer is arc-shaped and corresponds likewise to roughly one wavelength. The energy is absorbed along this traversed path and depends on the absorption properties of the second material layer and optionally other material layers into which the waves penetrate upon reflection, based on the quantum tunnel effect. Thus the invention is based on the finding that the penetration depth can be decoupled from the amount of absorption, the amount of power delivered however depending furthermore on the amount of absorption and the absorption properties of the second material layer and optionally the other material layers.
Depending on what proportion the energy delivered into the second layer as a result of normal refraction of the waves is to have relative to the energy delivered via the quantum tunnel effect, the angle of incidence &agr; can be in the range from 60° to 90°. But it is preferred that the angle of incidence &agr; is in the region of 90°.
In the process of the invention, it is preferred that there is a second material layer on the third material layer, especially an image receiver substrate. For example, if a toner layer is to be fixed, the wavelength of the electromagnetic and/or acoustic waves can be chosen such that it is somewhat larger than the layer thickness of the second material layer, so that optionally also the image receiver substrate, for example paper or cardboard, can be heated to the desired amount. In some cases this benefits the result of the fixing process.
In general, in the process of the invention, it holds that the wavelength of the electromagnetic and/or acoustic waves is set to a value which corresponds roughly to the penetration depth with which the electromagnetic and/or acoustic waves are to penetrate at least into the second material layer, as is detailed below using the accompanying drawing.
As mentioned, the path traversed by the electromagnetic and/or acoustic waves upon reflection in the second material layer is relatively short and likewise corresponds to rou
Brase Sandra
Kessler Lawrence P.
NexPress Solutions LLC
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