Electric heating – Microwave heating
Reexamination Certificate
2001-12-04
2004-01-27
Van, Quang T. (Department: 3742)
Electric heating
Microwave heating
C219S693000, C399S336000
Reexamination Certificate
active
06683287
ABSTRACT:
FIELD OF THE INVENTION
The invention involves a device and process for fixing a toner onto a substrate or a printed material, especially a sheet-shaped or a band-shaped printed material, preferably for a digital printer.
BACKGROUND OF THE INVENTION
In digital printing, especially electrostatic or electrophotographic printing, a latent electrostatic image is generated, which is developed by charged toner particles. These toner particles are transferred onto a printed material, e.g. paper, that receives the image. The image transferred onto the printed material is fixed there by heating and softening of the toner or heating of the printed material. Through and during this process, toner particles bond to the printed material and, possibly, also to each other.
For the fixing of the toner onto the printed material, the use of microwaves is known. Since the absorption of microwave energy in the toner customarily is at least one order of magnitude less than in the printed material, the printed material is preferably heated up by the microwaves and the printed material for its part heats up the toner located on it, and, to be precise, up to a temperature at which the toner bonds to the printed material. As is known, characteristic values of the printed material used, such as, for example, weight, humidity, and composition, are critical in the use of microwaves for fixing of the toner and must be taken into consideration.
Thus, for example, an image-fixing device is known from U.S. Pat. No. 4,511,778, which fixes an image made of toner using high-frequency waves, in particular, microwaves, onto a printed material, especially a sheet of paper. One aspect of the known device is thus the possibility to output the microwaves depending on the size of the printed material, in order to ensure a proper fusing and fixing of the toner taking into account this size as a characteristic value of the printed material. This is a method that only takes into consideration a size of the printed material that is directly apparent and specifies for the operation of the device, prior to fixing, based on consideration, for example, that a larger piece to be heated requires more energy in total than a smaller piece to be heated, because of its larger heat capacity.
However, additional critical aspects remain unconsidered in the use of microwaves for the fixing of toner. Thus, for example, the cited method can only be used in black-white printing with paper weights of a small variation width, while the possibly different behavior of different colored toner and different paper weights, also with possibly different water content, is not considered in this all-inclusive method that is matched to the size of the printed material. In a color print, the toner image can, for example, have four different toner layers. In the process, the maximum density of each toner layer on the image-receiving substrate or printed material is 100%, whereby a maximum total density of the toner layers in the toner image of 400% results. Customarily, the density of a single-color toner image is in the range from 0% to 100% density, and the density of a color toner image is in the range from 0% to 290%. Moreover, the cited device does not contain a microwave resonator, which is desirable when using the microwave application in regard to a homogenous heating, whereby customarily even at least two resonators arranged offset from each other are used, as is known from the patent U.S. Pat. No. 5,536,921 for a general microwave heating outside of the print area.
In addition, during the use of sheet-shaped printed material, a problem can occur that in the area of the edge area of the sheet irradiated with microwaves, processing is done in an energetically different way than the middle sheet area, so that a non-uniformly created printed product can occur. In addition to this, it occurs that during the fixing of traditional toners, only when using microwaves under certain circumstances, only an incomplete melting of the toner is obtained depending on its layer thickness, or heating occurs with bubble formation in areas of the toner. Also, the adhesion of the toner onto the printed material is insufficient under certain circumstances, because, for example, the bond with the printed material is not created sufficiently by the viscosity of the melted toner, which is too high. Problems can occur especially when a printed material is printed on both sides in two subsequently performed printing operations.
Because of these possible problems depicted, the use of microwave radiation in fixing is traditionally and customarily not relied upon, but instead, the toner is in practice heated without microwave radiation and bonded to the printed material using a heated pair of rollers while being impinged with pressure. A non-contact fixing is in principal, however, desirable for the protection of the printed image. Additional advantages of the non-contact fixing are the avoidance of adhesive abrasion and the resultant increased service lifetime of the device used, and an improved reliability of the device.
SUMMARY OF THE INVENTION
The purpose of this invention is to make possible an adequate fixing of toner onto a printed material using microwaves, preferably also for a multicolor printing on sheet-shaped printed material and using a resonator and preferably by adjusting to the special prevalent conditions. This purpose is achieved according to the invention in regard to the process in that the printed material that has the toner is irradiated with microwaves from at least one microwave emitter and is heated to melt the toner and that a toner is used which has a sharp transition from its solid to its liquid state during heating.
In this way according to the invention, for example, a dry toner can be used which is still quite hard at an average temperature of approximately 50° C. to 70° C., so that it can be powdered via conventional processes into a desired average toner size of, for example, 8-4 micrometers and also does not yet become sticky or does not melt at development temperatures, but at a higher temperature of, for example, approximately 90° C. is already very fluid at low viscosity, so that it, if necessary in using capillarities, also without outside pressure and in a non-contact manner settles on and in the printed material and adheres and upon a cooling down then becomes hard again very quickly and is fixed. To be precise, the fixed toner has a good surface gloss that is matched to the printed material, especially lacking formed grain boundaries. The surface gloss also plays a direct, meaningful role for color saturation in colored toner.
In this process, in connection with the toner according to the invention, the ratio of the value of the modulus of elasticity G′ at the reference temperature value, calculated from the starting temperature at the beginning of the glass transformation of the toner plus 50° C., to the value of the modulus of elasticity at the starting temperature itself can be <1E−5, preferably even <1E−7, whereby E represents the base 10 exponent. The starting temperature of the beginning of the glass transformation of the toner is preferably specified as that temperature value at which the tangents to the function progression of the modulus of elasticity G′, as a function of the temperature before and after the glass transformation, intersect. Preferably, the transformation of the toner from its solid into its liquid state should occur in a temperature interval or temperature window from approximately 30° to 50° C. in size. This range should be above 60° C., preferably approximately between 70° C. to 130° C., quite preferably between 75° C. and 125° C.
An additional further embodiment of the process according to the invention is characterized for adjusting to the special conditions in that at least one physical process parameter is controlled or regulated as a function of a parameter that correlates to the energy input into the printed material that has the toner. In this process, the energy inpu
Bartscher Gerhard
Behnke Knut
Krause Hans-Otto
Morgenweck Frank-Michael
Preissig Kai-Uwe
Kessler Lawrence P.
NexPress Solutions LLC
Van Quang T.
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