Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-12-20
2003-12-09
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C399S069000, C399S328000
Reexamination Certificate
active
06661993
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for controlling the gloss of a toner image which has been transferred to an image carrier substrate and fixed, wherein the degree and/or the duration of melting is set depending on the desired gloss of the toner image.
BACKGROUND OF THE INVENTION
A known digital image recording process is electrostatic printing in which a latent electrostatic image is developed by charged toner particles. They are transferred to an image receiver substrate, hereinafter simply a substrate. Then the developed image, which has been transferred to the substrate, is fixed by melting on the toner particles by supplying heat.
Often dry toners are used having particles with an average diameter of 10 microns. To melt the toner particles onto the substrate, hot rollers are often used which are brought into contact with the toner image. The disadvantage here is that a separating agent, for example silicone oil, is necessary to prevent the toner image from sticking to the roller. For a four-color image at least three toner layers are applied in succession to the image carrier substrate, each of the toner layers consisting of a polymer material can have a thickness of 30 microns. The gloss of these toner layers, which is very important for image quality, is determined by many factors, for example by the surface structure of the hot rollers, the fixing temperature and the toner properties.
In another known process, instead of hot rollers, a heated belt is used to melt the toner image. A high gloss can be achieved with this process. Since the belt is heated over a certain length, the toner image, after it has passed the heated area, can cool and become hard before it is separated from the previously hot surface of the belt. This enables simple and reliable separation of the toner image from the belt. The structure of the toner image surface is through the melting identical with the surface of the belt. In order to achieve a very smooth toner surface that goes along with high gloss, therefore, a very smooth belt must be used.
High gloss of the toner image is not necessary for all applications. For example, in an image carrier substrate formed by matt paper, only low gloss of the toner image is necessary. One possibility for changing the gloss is to use only a few heated rollers with a defined surface roughness. The rollers touch the surface of the toner image and imprint their surface structure into the toner image. In order to change the roughness of the toner image and thus its gloss in this process, therefore rollers with different roughness must be used. Another defect of the hot rollers is that they are subject to wear and after a certain time must be replaced; this is costly. Mechanical contact between the toner image and the image carrier substrate and the rollers furthermore leads to the toner image often sticking to the outside jacket surface of the rollers. In most cases therefore a cleaning system for the rollers is necessary.
SUMMARY OF THE INVENTION
The object of the invention is to devise a process for controlling the gloss of a toner image which has been transferred to an image carrier substrate and fixed, in which it is possible to influence the toner image gloss in a controlled manner, preferably cheaply and easily. Another objective of the invention is to devise a digital image-recording device in which a desired toner image gloss can be precisely set. In addition, the costs of the image-recording device should preferably be low.
To achieve this object, a process is proposed in which first the toner image is transferred in the conventional manner to the image carrier substrate and fixed on it, and only afterwards in a second step either completely, or at least in areas, melted to its surface or in a region near its surface. This is done according to the invention in that heat is supplied to the already fixed toner image at least one more time; this takes place, preferably without contact, by a radiation source. The melting of the toner image fixed on the image carrier substrate on its surface leads to the liquid toner beginning to deliquesce so that it has a very smooth surface and thus high gloss when it has completely deliquesced. The toner image gloss can be precisely influenced by the degree of melting, therefore to the extent that the toner image is melted its surface, and by the duration of melting, therefore how long the toner image is kept in the liquid state so that it can deliquesce. The already fixed toner image need not be completely melted again to influence its gloss, but only its uppermost layer, so that the energy to be expended for this purpose is only low. It is especially advantageous in the process according to the invention that essentially any gloss increment can be set; that is, flat to high gloss, without the need to replace parts of the fixing device each time.
If the fixing device for first-time fixing of the toner image on the image carrier substrate has a heater with at least one hot roller, this hot roller can be used for first-time fixing of almost all toner images, regardless of what gloss the respective toner image is to have when it is completed. If the gloss of the toner image fixed by the hot rollers on the image carrier substrate is to be changed, in a second step the surface of the toner image is re-treated in the desired manner, therefore melted and then cooled again so that depending on how high the degree of melting is and the interval for which the toner image is kept in the liquid phase, the toner image then has a gloss which is greater or reduced compared to the initial state.
The re-heating of the already fixed toner image takes place preferably using a heating/melting process which works without contact. The advantages of the process of the invention of course arise when the actual fixing of the toner image on the image carrier substrate takes place by radiation instead of using hot rollers, therefore without contact, since the radiation exposes the toner image only to electromagnetic radiation and is not brought into mechanical contact with the toner image. Here, in the following processing step, the gloss of the toner image already fixed on the image carrier substrate is also adjusted by a preferably non-contact heating process.
The “degree” of re-melting of the surface of the toner image already fixed on the image carrier substrate can be up to 100%. In this case the toner image surface is completely melted and can deliquesce so that a very smooth surface, and thus a very high gloss, result. The degree of melting can also be less than 100%, i.e. the surface of the toner layer is only partially melted, so that the parts of this toner image still in the solid state are in a “melt”. When this state of the toner image is frozen, for example by the toner image being rapidly cooled, a toner surface with a certain roughness and thus with a correspondingly lower gloss than in a smoother toner image surface results.
In one advantageous embodiment of the process, it is provided that the toner image is exposed to two successive electromagnetic radiation pulses, and the duration of the first radiation pulse can be longer than the second radiation pulse. In conjunction with this invention a “radiation pulse” is defined as a flash of light which acts only briefly on the toner image. The radiation of the light flash is in a certain, preferably adjustable wavelength range, especially in the UV range. The first radiation pulse can be very short for example and can have a very high energy intensity so that the surface of the toner image is melted, while by the second, preferably very short radiation pulse, the gloss of the toner image surface is reduced. The intensity of the two radiation pulses can therefore be varied to influence the gloss. A high intensity of at least the first radiation pulse can therefore lead first of all to a high gloss, and this gloss can be changed in a controlled manner by the second radiation pulse.
According to one development of the invention, it is provided that the toner i
Aslam Muhammed
Bartscher Gerhard
Morgenweck Frank-Michael
Rohde Domingo
Kessler Lawrence P.
Nexpress Solutions LLC
Ngo Hoang
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