Patent Application
20110102491
The process and device described below relate to inkjet imaging devices and, more particularly, to inkjet imaging devices that condition an image receiving substrate for ink image formation.
Drop on demand inkjet technology for producing printed media has been employed in products such as printers, multifunction products, plotters, and facsimile machines. Generally, an inkjet image is formed by selectively ejecting ink drops from a plurality of drop generators or inkjets, which are arranged in a printhead or a printhead assembly, onto an image receiving substrate. For example, the printhead assembly and the image receiving substrate may be moved relative to one other and the inkjets may be controlled to emit ink drops at appropriate times. The timing of the inkjet activation is performed by a printhead controller, which generates firing signals that activate the inkjets to eject ink. The image receiving substrate may be an intermediate image member, such as a print drum or belt, from which the ink image is later transferred to a print medium, such as paper. The image receiving substrate may also be a moving continuous web of print medium or sheets of a print medium onto which the ink drops are directly ejected. The ink ejected from the inkjets may be liquid ink, such as aqueous, solvent, oil based, UV curable ink, or the like, which is stored in containers installed in the printer. Alternatively, the ink may be loaded in a solid or a gel form and delivered to a melting device, which heats the ink to generate liquid ink that is supplied to a printhead.
Typically, ink drops deposited on an obverse side of a print medium should be affixed to the obverse side without bleeding through or penetrating to a reverse side of the print medium. Penetration of an ink drop through the thickness of a print medium is referred to as “show-through”, because the ink originally deposited on the obverse side is visible on the reverse side of the print medium. Show-through may also occur when an ink drop only partially penetrates the thickness of a print medium, but is still visible on the reverse side. Show-through reduces the image quality of duplex printing operations, which form an image on both sides of the print medium. Specifically, ink deposited on an obverse side of a print medium may at least partially penetrate the print medium and blur or distort an image formed with ink deposited on a reverse side of the print medium. Show-through also affects simplex printing operations, which form an image on only the obverse side of the print medium, because the obverse image density is reduced, and the reverse side of a print medium should generally remain free from ink deposits.
Show-through is related to the properties of the print medium and the ink ejected onto the print medium. For instance, some print mediums have a porous structure that permits an ink to penetrate the print medium before the ink stabilizes, cures, or hardens. Additionally, the viscosity of the ink ejected onto the print medium may result in show-through. For example, inks having a low viscosity are more likely to be absorbed by the print medium than inks having a high viscosity. For these reasons and others, efforts to reduce show-through have been directed to either the properties of the ink or the print medium onto which the ink is deposited.
Processes for reducing show-through are effective, but often limit the type of print medium or ink that may be used by an inkjet printer. For instance, show-through may be reduced or eliminated by coating a print medium with a polymer that makes the print medium have a nonporous surface. The nonporous surface prevents ink deposited onto the print medium from penetrating to a reverse side of the print medium. Polymer coated papers, however, are expensive and certain inks cannot effectively adhere to them. Additionally or alternatively, a printer may be configured to eject only inks having a high viscosity. Many inks, however, do not have a viscosity great enough to prevent the effects of show-through completely, especially on porous print mediums. Accordingly, further developments to reduce show-through are desirable.
An inkjet printer has been developed that reduces the effects of show-through by depositing ink onto a cooled print medium. The inkjet printer includes a printhead and a cooler. The printhead is configured to eject ink onto an ink receiving member as the ink receiving member is transported along a portion of a media path through the inkjet printer. The cooler is positioned proximate the media path to cool the ink receiving member to a temperature less than an ambient temperature prior to the printhead ejecting ink onto the ink receiving member.
A printing system has been developed that forms an image on a cooled ink receiving member. The printing system includes a support frame, a printhead, a platen, and a cooling device. The support frame is configured to define a media path through the printing system. The printhead is configured to eject ink onto an ink receiving member as the ink receiving member is transported along a portion of the media path. The platen is coupled to the support frame and is configured to cool the ink receiving member to a temperature less than an ambient temperature prior to the printhead ejecting ink onto the ink receiving member. The cooling device is coupled to the support frame and thermally coupled to the platen to remove heat from the platen.
A method for forming and fixing a printed image on a cooled image receiving member has been developed. The method includes cooling an image receiving member to a first predetermined temperature and ejecting ink droplets onto the cooled image receiving member with a printhead.
The foregoing aspects and other features of the present disclosure are explained in the following description, taken in connection with the accompanying drawings.
The device and method described herein make reference to a printer. The term “printer” refers, for example, to reproduction devices in general, such as printers, facsimile machines, copiers, and related multi-function products. While the specification focuses on an inkjet printer, the device and method described herein may be used with any printer that ejects ink onto an image receiving surface. Furthermore, the device and method described herein may be used with printers that form printed images with either aqueous ink, phase change ink, or gel ink, as described below.
As shown in
As shown in
The cooling device 116 is any type of device capable of cooling the platen 120. In particular, the cooling device 116 may be a refrigeration unit configured to cool a fluid such as, but not limited to, water, glycol, ethylene glycol, diethylene glycol, propylene glycol, or mixtures of such fluids. The fluid cooled by the cooling device 116 is coupled to the platen 120 through a conduit 124. The conduit 124 channels the fluid cooled by the cooling device 116 into thermal contact with the platen 120 to remove heat from the platen 120. The conduit 124 may be connected to the platen 120 in a serpentine configuration, among other configurations, to remove heat evenly from the platen 120.
The platen 120 is positioned adjacent to a portion of the media path 104 prior to the printhead 112. In particular, the platen 120 may be coupled to the support frame of the printer 100 proximate to or in contact with the substrate 114. For instance, the platen 120 may be positioned to contact directly the substrate 114. Alternatively, the platen 120 may be positioned approximately 0.5 to 2.0 centimeters below the substrate 114. In another embodiment, the platen 120 is connected to a lower surface of the media path 104 to cool an upper surface of the media path 104 on which the substrate 114 is transported. Although the platen 120 and cooling device 116 are depicted as being located below the substrate 114, in other embodiments, the platen 120 and/or cooling device 116 may be positioned above the substrate 114 to cool directly the surface of the substrate 114 configured to receive ink.
The platen 120 may have an irregular surface configured to be positioned proximate to the substrate 114. The irregular surface may include channels or valleys for diverting condensation that may form on the platen 120 into a collection tank or a drain. Positioning the platen 120 below the substrate 114 reduces the possibility of condensation falling onto or otherwise contacting the substrate 114; however, the platen 120 may be positioned above the substrate 114 without causing condensation to contact the substrate 114. The platen 120 may also have an approximately planar surface configured to contact the substrate 114. The platen 120 is formed of a thermally conductive material, including, but not limited to, aluminum, copper, or any other thermally conductive metal or alloy of materials having similar thermal properties.
The platen 120 cools each type of substrate 114 transported on the media path 104. In particular, as shown in
The platen 120 is configured with a length L that enables the cooling device 116 to reduce sufficiently the temperature of the substrate 114 for a range of speeds used to transport the substrate 114 along the media path 104. The printer 100 may adjust the speed at which the substrate 114 is moved along the media path 104 for different types of print jobs. Consequently, the substrate 114 is exposed to the platen 120 for different periods of time. The platen 120, therefore, is configured with a length L that enables the substrate 114 to be cooled sufficiently even when the substrate 114 is moving at a maximum print speed.
To address further variations in substrate temperatures and time periods for platen 120 exposure, the printer 100 may adjust the temperature of the platen 120. To implement temperature variations of the platen 120, in one embodiment, a temperature sensor 140 may be coupled to the platen 120 to generate an electronic signal indicative of the temperature of the platen 120, as shown in
The controller 144 may include a first selector (not illustrated) for controlling whether the platen 120 is cooled to a set point temperature or is cooled within a temperature range. Additionally, the cooler 108 may include a second selector (not illustrated) for adjusting the temperature range and/or the set point temperature. The temperature range and/or the set point temperature may also be adjusted and determined with a computer (not illustrated), which is electrically coupled to the controller 144. Coupling a computer to the controller 144 permits a user to monitor and to control remotely the cooling device 116. Furthermore, coupling a computer to the controller 144 permits a computer program to calculate the temperature range and/or the set point temperature in response to a plurality of factors, such as, but not limited to, print speed, substrate type, ink type, humidity levels, ambient temperature, and the particular image being printed. In other embodiments, the temperature range and/or the set point temperature may be empirically determined or manually calculated in response to print speed, substrate type, ink type, humidity levels, ambient temperature, and the particular image being printed, among other factors.
In some embodiments, the platen 120 is formed of multiple sections referred to herein as sub-platens 128. As shown in
In another embodiment, illustrated in
As shown in
Additionally or alternatively, the cooler 108 may impinge cooled air or another gas against the substrate 114 to cool the substrate 114. The apparatus and methods described above for controlling the temperature of the platen 120 may also be configured in a manner useful for controlling the temperature and flow of a cooled gas against the substrate 114. For example, a heat exchanger may be used to cool a gas sufficiently that a flow of the cooled gas directed against the substrate 114 regulates the temperature of the substrate 114 in a predetermined range.
In operation, the printer 100 prevents show-through by cooling the substrate 114 prior to the printhead 112 ejecting ink onto the substrate 114. An exemplary method of operating the printer 100 is illustrated by the process of
Next, the controller 144 receives from the temperature sensor 140 a signal indicative of the temperature of the platen 120 (block 508). If the temperature of the platen 120 is greater than the set point temperature, the controller 144 activates the cooling device 116 to cool the platen (blocks 512 and 516). In response to the controller 144 determining that the cooling device 116 has cooled the platen 120 to at least the set point temperature, the printer 100 may begin moving the substrate 114 along the media path 104 (block 520). The cooled platen 120 removes heat from the substrate 114 before the printhead 112 ejects ink onto the substrate 114 (block 524). In response to contacting the cooled substrate 114, the ink bonds to the obverse surface of the substrate 114 without penetrating the substrate 114 sufficiently to cause show-through. In particular, even a radiation curable gel ink does not have sufficient thermal energy to raise the temperature of the substrate 114 above a temperature that permits the ink to penetrate the substrate 114, as described below.
The printer 100 may be configured to form printed images with phase change ink or gel ink. The term “phase change ink” encompasses inks that remain in a solid phase at an ambient temperature and that melt into a liquid phase when heated above a threshold temperature, referred to as a melt temperature. Phase change ink is ejected onto the substrate 114 in the liquid phase. An exemplary range of melt temperatures is approximately seventy to one hundred forty degrees Celsius; however, the melt temperature of some types of phase change ink may be above or below the exemplary temperature range. The terms “gel ink” or “gel-based ink” encompass inks that remain in a gelatinous state at the ambient temperature and that may be altered to have a different viscosity suitable for ejection by the printhead 112. In particular, gel ink in the gelatinous state may have a viscosity between 105 and 107 centipoise (“cP”); however, the viscosity of gel ink may be reduced to a liquid-like viscosity by heating the ink above a threshold temperature, referred to as a gelation temperature. An exemplary range of gelation temperatures is approximately thirty to fifty degrees Celsius; however, the gelation temperature of some types of gel ink may be above or below the exemplary temperature range.
Some inks, including gel inks, may be cured during the printing process. Radiation curable ink becomes cured after being exposed to a source of radiation. Suitable radiation may encompass the full frequency (or wavelength) spectrum including, but not limited to, microwaves, infrared, visible, ultraviolet, and x-rays. In particular, ultraviolet-curable gel ink, referred to herein as UV gel ink, becomes cured after being exposed to ultraviolet radiation.
As shown in
As described above, the printer 102 of
The main reservoir 158 and the ink reservoir 164 of the printer 102 may be configured to remain connected to the printer 102 during normal usage and servicing of the printer 102. Specifically, when the ink level in the ink reservoir 164 falls below a predetermined level, the printer 102 refills the ink reservoir 164 with ink (either phase change ink, gel ink, or another type of ink) from the main reservoir 158. Similarly, when the ink level in the main reservoir 158 falls below a predetermined level, the printer 102 is configured to fill the main reservoir 158 with additional ink from the ink loader 150. Accordingly, in one embodiment, neither the main reservoir 158 nor the ink reservoir 164 are disposable units configured to be replaced when the printer 102 exhausts an ink supply.
The cooler 108 prevents show-through that may result from heated phase change ink contacting the substrate 114. Some types of phase change ink when ejected onto an un-cooled substrate 114 may locally heat the substrate 114 and at least partially penetrate a thickness of the substrate 114 causing show-through. The cooler 108, however, causes the phase change ink ejected onto the substrate 114 to freeze into the solid phase before show-through occurs.
The cooler 108 also prevents show-through which may result from UV gel ink contacting the substrate 114. In one embodiment, UV gel ink may be heated to a temperature of approximately eighty five degrees Celsius and the substrate 114 may be cooled to approximately fifteen degrees Celsius. Upon contacting the cooled substrate 114, droplets of the UV gel ink ejected by the ink ejectors 166 freeze to the gelatinous state. In particular, the UV gel ink cools to a temperature that increases the viscosity of the ink and prevents the ink from penetrating a thickness of the substrate 114 to a depth that results in show-through or that results in an objectionable level of show-through. The set point temperature of the platen 120 may be selected to ensure that any heat generated by the leveling device 148 and/or the source of ultraviolet radiation 152 does not heat the ink and/or the substrate 114 to a temperature that produces show-through or that increases show-through to an objectionable level.
In one embodiment, the printer 102 of
Referring to
Show-through may be quantitatively determined by subtracting a front density from a back density. In particular, back density may be determined by directing a reflection densitometer at the reverse side of a substrate having ink affixed to the obverse side. Front density may be determined by first placing an ink-free section of substrate directly on top of an ink covered section of substrate. Next, a reflection densitometer may be directed at the ink-free section of substrate to determine a front density value. Values of show-through quantitatively determined may be scaled to a suitable range by multiplying the values of show-through by a proportionality constant.
Those skilled in the art will recognize that numerous modifications may be made to the specific implementations described above. Therefore, the following claims are not to be limited to the specific embodiments illustrated and described above. The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
