Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-12-17
2003-07-01
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
Reexamination Certificate
active
06587665
ABSTRACT:
FIELD OF THE INVENTION
The invention involves a process for fixing a toner image transferred onto an image-carrier substrate, a process for fixing a single-color or multi-color toner image transferred onto an image-carrier substrate, a digital printer or copier machine that has a fixing device for fixing a toner image onto an image-carrier substrate, and a digital printer or copier machine, wherein at least two electromagnetic radiation pulses are applied in a time-delayed manner onto the same area of the image-carrier substrate.
BACKGROUND OF THE INVENTION
A known process is electrostatic printing, in which a latent electrostatic image is developed by charged toner particles. These particles are transferred onto an image-carrier substrate, such as paper, for example, hereinafter referred to simply as “substrate”. Afterwards, the developed image that has been transferred onto the substrate is fixed by the toner particles being heated and fused, and possibly the substrate being heated. In order to fuse the toner particles, contacting processes are often used in which the toner particles are brought into contact with suitable devices, for example, hot rollers or cylinders. It is disadvantageous that the design, the maintenance and the operating costs of these heating devices that operate by contact are expensive and thus cost-intensive. In addition, it is usually necessary to use silicone oil as a separating agent that should prevent an adhesion of the fused toner onto the heating device. Furthermore, the defect rate, especially paper jams, caused by the contacting heating devices, is relatively high.
In order to fix the toner that is transferred onto the paper, for example, heating devices and processes are also known that operate in a non-contact manner, in which for example, the toner particles are fused, for example, using heat radiation and/or microwave radiation or with hot air, so that they adhere to the paper.
A known fixing device has a xenon lamp that is arranged above the transport path of the paper. Using the xenon lamp that is electrically powered by a power supply unit, a flash/radiation pulse or a continuous radiation can be applied onto the paper when the paper is guided past the xenon lamp. The toner image is fused, by the clocked or continuous electromagnetic radiation, and liquefies so that after it has cooled off, it adheres in a desirable manner to the paper surface. Xenon flash lamps emit electromagnetic radiation, mainly in the visible and near infrared wavelength range, in which the toner has a high absorption and the paper has only a low absorption. This known phenomenon leads to a non-uniform heating of the areas of the toner image, which have variably high toner densities. In the areas of the toner image with a low toner density, in which the toner particles are arranged more or less individually, the toner temperature is clearly lower than in the areas with a high toner density, because the areas with the high toner density absorb a large portion of the electromagnetic radiation. This different absorption behavior leads to a non-uniform fusing of the toner image in the areas with varying toner density. If the toner image is impinged with an energy that is so high that the toner is also fused in the areas with a low toner density, the so-called “micro-blistering” frequently occurs in the areas of the toner image with a high toner density, i.e. a bubble forms within the fused toner layer as a result of overheating of the toner and possibly the paper. It is disadvantageous in this that the gloss of the toner image is influenced in an undesirable manner. Furthermore, a partial overheating of the paper can occur, so that it begins to undulate.
Xenon flash lamps for fixing a single color (black) toner image, which emit electromagnetic radiation in the visible and short infrared range, have been known for a long time. The absorption capacity of the toner in the three process colors cyan, magenta, and yellow on the one side and the absorption capacity of black toners on the other side differ considerably in the wavelength range emitted from the xenon flash lamp. The process color-toner portions absorb only in a very narrow wavelength spectrum in the visible range and customarily absorb less than 10% in the near infrared range. Black toners absorb approximately 100% in the aforementioned wavelength ranges. These varying absorption characteristics lead to a non-uniform fusing of the toner image when the light of a xenon flash lamp is used to fix the toner image. A non-uniform fusing of the toner image leads to a non-uniform fixing of the toner, to a non-uniform gloss, to a partial bubble formation in the toner image or to a partial overheating and discoloration of the paper. This effect is especially yielded between the three process colors cyan, magenta, and yellow, which absorb the electromagnetic radiation emitted from the xenon flash lamp differently, but each selectively in a wavelength range between 0.25 &mgr;m and 2 &mgr;m, in particular in the range 0.4 &mgr;m and 1 &mgr;m. In this wavelength range, black toner absorbs approximately 100% of the electromagnetic radiation.
In order to match the absorption capacity of the process color toners to each other, an infrared absorber is added to them, for example, such that they obtain the same absorption characteristic as black toner in a wavelength range between 700 nm and 2 &mgr;m. These types of absorbers, however, are not completely colorless in the visible range, so that they act in a disadvantageous way on the color reproduction. The better the absorption capacities of the process color toners are matched to each other using the infrared absorbers, the greater is their overlap with the visible range.
SUMMARY OF THE INVENTION
The purpose of the invention is to provide a process in which the toner to be fixed is fused using electromagnetic radiation, whereby the areas of the toner image with higher and with lower toner density have at least approximately the same fusing quality. Another purpose of the invention is eliminating defects in the toner image, which result due to a non-uniform energy absorption of the toner image. Another purpose is providing a process in which the process color toners impinged with electromagnetic radiation and the black toner have an improved uniformity in their absorption capacity. Finally, another purpose of the invention is to provide a digital printer or copier machine to perform the process.
In order to achieve the purpose, a process is characterized in that in order to fuse the toner particles at least two electromagnetic radiation pulses are applied onto the same area of the image substrate in a time-delayed manner. The second radiation pulse/flash is then triggered, for example, when the intensity of the first radiation pulse/flash has been reduced to a certain value. The term “time-delayed” is understood here to be the time duration between the triggering of the first radiation pulse/flash and the triggering of the second radiation pulse/flash. It has been revealed that by the time-delayed application of the second radiation pulse, the limit value of the energy, at which the toner image is overheated, increases. According to the invention, it is thus possible that to fuse areas of the toner image with high and low toner density, the same energy can be applied to each, without a bubble formation occurring in the fused toner layer in areas with high toner density. The energy of each individual radiation pulse is in each case below the limit energy at which a bubble formation would occur in the molten mass in the areas of the toner image with high toner density. The total of the energy of all radiation pulses is in any case so high that even areas of the toner image with low toner density are fused in the desired way and in this way fixed onto the image-carrier substrate. With process according to the invention, an at least approximately equivalent fusing quality of the areas of the toner image with high and with low toner density can thus be ensured. In addition, it is a
Bartscher Gerhard
Hauptmann Gerald Erik
Morgenweck Frank-Michael
Rohde Domingo
Schulze-Hagenest Detlef
Kessler Lawrence P.
NexPress Solutions LLC
Ngo Hoang
LandOfFree
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