Electric heating – Microwave heating – With diverse device
Reexamination Certificate
2001-12-04
2004-02-03
Van, Quang T. (Department: 3742)
Electric heating
Microwave heating
With diverse device
C219S692000, C399S336000
Reexamination Certificate
active
06686573
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for fusing toner on a carrier or on a printing material, particularly on a sheet-type or a tape-type printing material, preferably for a digital printer.
Furthermore, the invention relates to a device for heating printing material and/or toner, particularly to fuse toner on a carrier or printing material, particularly a sheet-type or tape-type, preferably for a digital printer, preferably for performing the above-mentioned process.
BACKGROUND OF THE INVENTION
With digital printing, particularly electrostatic or electrophotographic printing, a latent electrostatic image is produced, which is developed by the loaded toner particles, which, on their part, are transferred onto a printing material receiving the image, e.g. paper. There the image transferred to the printing material is fused by heating and softening of the toner and/or heating of the printing material. By, and during, this process the toner particles are fused on the printing material and, if necessary, also on each other.
The use of microwaves is known for the fusing of toner on the printing material. Since the absorption of microwave energy in the toner is usually at least one order of magnitude smaller than that in the printing material, the printing material is preferably heated by the microwaves and the printing material heats on its behalf the toner found thereupon, and indeed up to a temperature that fuses the toner on the printing material. It is well known that, with the use of microwaves for fusing the toner, characteristic values of the printing material used, such as weight, moisture and composition are critical and must be taken into consideration.
Thus, for example, an image-fusing device is known from U.S. Pat. No. 4,511,778, which fuses a toner image on a printing material, particularly a sheet of paper, by high frequency waves, particularly microwaves. One aspect of the known device is the possibility of producing the microwaves as a function of the size of the printing material, so that, by taking this size into consideration as a characteristic value of the printing material, an appropriate melting and fusing of the toner is ensured. This is a process that is quite general and only takes into consideration an immediately obvious size of the printing material, which is determined prior to the fusing thereof for the operation of the device, possibly according to a consideration that a larger piece to be heated, due to its greater heating capacity, requires all in all more energy than a smaller piece to be heated.
Due to this general guideline, however, other critical aspects for the use of microwaves for fusing the toner are ignored. Thus, for example, the cited process is only applicable to black and white printing with a paper weight within only a small range of widths, while the possibly different behavior of a multicolor toner with different paper weights, which may also have different water contents, are not taken into consideration in this general process, which is determined by the size of the printing material. With color printing, the toner may, for example, have four different toner layers. Here, the maximum thickness of each toner layer on the image-carrying substrate or printing material is 100%, whereby a maximum total weight of the toner layers in the toner image is 400%. The thickness of a single color customarily lies in the range of 0% to 100% thickness, and a color toner image is in the range of 0% to 290%.
Furthermore, with the use of sheet-type printing material, the problem may arise that the edge of the sheet that has been irradiated with microwaves may be energetically processed in a different manner than the middle section of the sheet. This may result in a printed product that is uneven.
In addition, the fusing of conventional toner using only microwaves under such conditions only results in an incomplete melting of the toner, depending on its layer thickness, or it results in heating with blistering in areas of the toner. In addition, the fusing of the toner on the printing material is insufficient under the circumstances, because, for example, the fusing of the toner on the printing material is insufficient due to the fact that viscosity of the melted toner is too high. Problems can occur then, especially if a printing material is printed in two successive printing processes on both sides.
Due to the possible occurrence of the problems described, the use of microwave irradiation is usually not trusted for fusing the toner, but the toner is in practice heated without microwave irradiation and is fused on the printing material with a pair of heated, pressurized rollers. However, contact-free fusing is principally desired for preservation of the printed image. Other advantages of the contact-free fusing are the prevention of adhesive wear and tear and the increased service life of the device used as well as ensuring a better reliability of the device.
SUMMARY OF THE INVENTION
The desire of this invention is to make adequate fusing of the toner on a printing material, or its preparation, using microwaves possible, preferably also for multicolor printing on sheet-type printing material and preferably with adjustment to the prevailing special conditions.
With respect to the process, it is provided according to the invention, that the printing material with toner is irradiated with microwaves from at least one microwave conductor, which is heated to melt the toner and that a toner is used that shows a quick transition from its solid state to its liquid state when heated.
In this process according to the invention, a dry toner can be used, for example, that is still quite solid at a medium temperature of some 50° C. to 70° C., so that, by a conventional process, it can be ground to a desired medium toner size of 8-4 micrometers. For example, said dry toner is not yet sticky and does not melt at development temperatures, but already flows very easily and has a lower viscosity at higher temperatures of some 90° C. Thus, if used with capillaries, the dry toner can be fused and adheres without outside pressure and contact-free on the printing material, and when cooled, it becomes hard again and is fused. It has indeed a good surface luster suitable for the printing material, and, in particular, without developing grain boundaries. The latter already also plays a significant roll in the color saturation with color toner.
With this process, in connection with the toner according to the invention, the ratio of the values of the elastic modulus G′ at the reference temperature value can be calculated from the initial temperature at the beginning of the glass transition of the toner plus 50° C. to the value of the elastic modulus at the initial temperature itself <1E-5, preferably even <1E-7, whereby E represents the exponent on base 10. The initial temperature at the beginning of the glass transition of the toner is preferably determined as that temperature value at which the tangents to the functional behavior of the elastic modulus G′ intersect as a function of the temperature before and after the glass transition. The glass transition of the toner from its hard state to its liquid state preferably takes place in a temperature interval or temperature window of approximately 30° C. to 50° C. order of magnitude. This range should lie above 60° C., preferably between approximately 70° C. to 130° C., and most preferably between 75° C. and 125° C.
Another embodiment of the process according to the invention is distinguished in its adaptation to special ratios, in that at least one physical process parameter is controlled and/or regulated as a function of a parameter correlating to the energy charge in the printing material with toner. According to this aspect of the invention, a simple general guideline is thus not envisaged, but advantageously a control regulated to the actual, preferably measured ratio. Here the abovementioned energy charge basically corresponds to a microwave power received from the total system o
Bartscher Gerhard
Behnke Knut
Krause Hans-Otto
Morgenweck Frank-Michael
Preissig Kai-Uwe
Kessler Lawrence P.
Van Quang T.
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