Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Infrared energy
Reexamination Certificate
2000-10-13
2002-06-11
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Infrared energy
C034S267000, C034S269000, C034S273000, C034S420000, C034S446000, C034S611000, C034S575000
Reexamination Certificate
active
06401358
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method and an apparatus for drying a substance that is being rapidly transported in a conveyor apparatus, in particular for drying layers of printing ink on rapidly conveyed paper. The invention relates in particular to rapidly conveyed paper with a transport velocity between 2 and 25 m/s.
When a rapidly conveyed substance is to be dried, it is extremely important that the drying operation take effect quickly. For example, the direction of movement of the material carrying a substance to be dried is changed by passage over several deflecting rollers, at a given one of which either one side or the other of the carrier material may make contact with the roller. If, for instance, in an apparatus for printing paper a layer of ink is applied to the paper and then the printed paper passes around a deflecting roller with its printed surface touching the roller, the layer of ink must be sufficiently dry before the paper reaches the roller. For other steps of the process subsequent to printing, as well, adequately dry ink is a prerequisite. Examples include the stacking of printed single pages, one over another, or the rolling up of a printed strip of paper. A similar situation is encountered in the manufacture of paper, when strips of paper that are wet throughout are rapidly conveyed for further processing.
The object of the invention is to disclose a method and an apparatus of the kind mentioned above with which drying of the substance to be dried can be accomplished quickly.
SUMMARY OF THE INVENTION
The method in accordance with the invention for drying an substance that is being rapidly conveyed in a conveyor direction, in particular for drying layers of printing ink on rapidly conveyed paper, electromagnetic radiation is directed into a drying zone so as to separate a moisture component, in particular a solvent, from the substance to be dried and the separated moisture component is transported out of the drying zone by a transport gas current. Electromagnetic radiation, in particular infrared radiation, has proved especially useful and efficient for drying. Even when the carrier material is being conveyed at high velocities, only one drying zone is needed, the length of which is short in the conveyor direction.
During separation of the moisture component from the substance to be dried, the separated moisture component can form a boundary layer that covers the substance and prevents further drying. In particular, a dynamic equilibrium becomes established at the surface of the substance to be dried, in which approximately as many moisture particles emerge from the substance as re-enter it from the boundary layer. In accordance with the invention, therefore, the separated moisture component is removed from the drying zone by a transport gas current. In particular when the transport gas is introduced continuously into the drying zone, the production of a boundary layer that would hinder drying is prevented, because the particles of the separated moisture component are transported away only a short time after they have emerged from the substance to be dried.
The electromagnetic radiation is preferably adjusted to the absorption properties of the moisture component in such a way that the radiation energy is substantially absorbed only by the moisture component and not by the remaining components of the substance to be dried and/or by a carrier material that is not moist. As a result, the moisture component is not vaporized in the strict sense, but instead the particles of the moisture component are specifically activated and expelled from the substance to be dried.
Preferably the transport gas current (D) flows into the drying zone through a region oriented transverse to the conveyor direction, from a direction that encloses an angle of 60 to 90°, preferably about 80°, with the perpendicular to the surface of the substance to be dried, thus striking the substance like a knife. As a result, the transport gas can carry along the moisture particles that emerge from the substance without transferring a substantial fraction of its kinetic energy to the substance. A mechanical deformation of the substance to be dried, which for example could cause blurring of the sharp edges of an ink imprint, is thus avoided.
Preferably the transport gas current exerts a close-range action in the region where it flows into the drying zone, inasmuch as it strikes the surface of the substance to be dried directly, so that a surface layer formed by the separated moisture component is raised away from the substance as though sliced by a knife. The sharp angle of incidence, in particular, enhances this knife-like action.
In particular the combination of the close-range effect with the orientation of the region within which the transport gas current flows into the drying zone, namely elongated in the direction perpendicular to the conveyor direction, results in an advantageously rapid drying effect over the entire extent of the region. It is also advantageous that the velocity of the transport gas current is the same over the entire width of the region occupied by the substance to be dried.
It is favourable for the transport gas current to flow along the surface of the substance to be dried either in the same direction as the substance is being conveyed or in the opposite direction, for a certain distance. This distance can in particular be longer than the length of the drying zone within which the electromagnetic radiation is incident on the substance. Thus it is ensured that the moisture particles will be transported away over the entire drying zone and even beyond it.
So as to cool the substance to be dried, if it is warmed by the electromagnetic radiation, the temperature of the transport gas current is lower, at least before it strikes the moisture component, than the temperature of the substance to be dried. This is advantageous in particular in the case of a heat-sensitive carrier material, because by the cooling of the substance to be dried, heat transfer from the substance to the carrier material can be reduced or prevented.
It is useful for the transport gas current to be formed of expanded pressurized air.
In particular if the moisture component of the substance to be dried is water, the incident electromagnetic radiation has a spectral intensity maximum in the near infrared, in particular in the wavelength range 0.8 to 2.0 &mgr;m. As a result a substantial proportion of the radiation energy is introduced into the substance specifically as excitation energy for particles of the moisture component, in particular water. In the specified wavelength range there are several absorption bands of water. However, other moisture components, in particular solvents, also have absorption bands in this wavelength range.
For reasons of efficiency of the relevant thermodynamic processes, in particular to raise the overall efficacy when the method in accordance with the invention is employed, after leaving the drying zone the transport gas current flows to the source of the electromagnetic radiation in order to cool this source. In particular when the latter takes the form of a thermal radiator operated at a temperature above 2500 K, cooling is required. When the transport gas current is used in this way, it is possible either to do without another, supplementary form of cooling or such supplementary cooling means can have correspondingly smaller dimensions.
To ensure that specified temperature conditions are maintained, the temperature of the dried substance and/or the temperature of the separated moisture component and/or the temperature of the carrier material is regulated by adjusting the radiation flux density of the electromagnetic radiation incident in the drying zone according to a further development of the method. Preferably the temperature to be regulated is measured by means of a pyrometer.
It is useful to use as radiation source for the electromagnetic radiation an electric incandescent bulb, in particular a halogen bulb, and to adjust the radiation f
Bär Kai K. O.
Gaus Rainer
Advanced Photonics Technologies AG
Marshall Gerstein & Borun
LandOfFree
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