Patent Application
20170176929
This application claims priority to Netherlands Patent Application No. 2015973 filed Dec. 16, 2015, the disclosure of which is hereby incorporated in its entirety by reference.
The field of the invention relates to the field of electrophotographic imaging apparatus. Particular embodiments relate to an electrophotographic imaging apparatus with a conditioning unit and/or a fusing unit.
Electrophotographic imaging is well known. In electrophotography, electrophotographic imaging members have a photoconductive surface layer which functions as an insulator so that during the imaging process, electric charges can be retained on its surface. The photoconductive insulating layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of electromagnetic radiation, to create an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly to substrate, such as paper. Such image forming devices include, but are not limited to, printers, copiers, scanners, multi-function devices and other like systems capable of producing and reproducing image data from an original document, data file or the like.
Moisture content in paper substrates has been found to be a major contributing factor to defects in printed images on paper substrates. Moisture in the material matrix of the paper, and in particular a non-uniform distribution of moisture has been found to degrade and impede toner-imaging capabilities. Moisture content difference between different portions of the substrate will cause non-uniformities in the printed image. Further, for thick paper the moisture content should be sufficient, i.e. the paper may not be too dry, in order to have a sufficiently high conductivity of the paper substrate.
It is known to address the above mentioned problems by conditioning, and in particular by heating the paper substrate before printing. In existing embodiments heating rollers are used to heat the paper substrate before printing. Such rollers are typically heated up to a temperature of 100° C. to 200° C. Such rollers have the disadvantage of having a large heat capacity and are therefore difficult to control. Indeed, there will be needed a certain amount of time to heat/cool the rollers. Also, it is difficult to control the distribution of the moisture content using such heating rollers.
Embodiments of the invention aim to provide an electrophotography imaging apparatus with improved conditioning of substrates containing paper.
According to a first aspect of the invention there is provided an electrophotographic imaging apparatus comprising a conditioning unit configured to heat a substrate and an image forming unit configured to develop an image and to transfer the developed image to the heated substrate. The image forming unit is located downstream of the conditioning unit. The conditioning unit is configured to emit radiation having wavelengths between 1 micrometre and 5 micrometre, to the substrate, wherein said conditioning unit comprises at least one infrared radiator which is configured to operate at a temperature between 500 and 2500 degrees Celsius.
Embodiments of the invention are based inter alia on the inventive insight that, above a predetermined threshold wavelength, the radiation absorption of the substrate increases with the wavelength. The specified operation range of the conditioning unit will allow obtaining on the one hand a sufficient amount of total radiated power (proportional with T4, wherein T is the temperature of the IR radiator in Kelvin) with a relatively compact conditioning unit, whilst at the same time achieving a relatively high absorption of the radiation in the substrate. Also, because the conditioning unit can have a radiating body with a relatively small mass and large surface, the heat capacity of the conditioning unit can be very low, so that the time needed to switch on/off the conditioning unit can be very low.
In an exemplary embodiment the conditioning unit is configured to emit radiation having a peak radiation wavelength
between 1.4 micrometre and 5 micrometre, preferably between 2 and 4 micrometre, more preferably between 2.2 and 3.8 micrometre. In this formula T represents the temperature in Kelvin.
In an exemplary embodiment the conditioning unit comprises at least one infrared radiator which is configured to operate at a temperature between 500 and 2500 degrees Celsius, preferably between 500 and 1500 degrees Celsius, and more preferably between 550 and 1000 degrees Celsius.
In an exemplary embodiment the at least one infrared radiator comprises a metal body configured to emit radiation when a voltage is applied over the metal body, i.e. a resistive heater, wherein in operation the temperature of the metal body is as specified above. The metal body may be a metal sheet or a plurality of interconnected sheet strips, lanes or band, optionally coated. In exemplary embodiments the thickness of the metal sheet or strips is smaller than 2 mm, preferably smaller than 1 mm, and more preferably smaller than 0.5 mm. In an exemplary embodiment the metal body comprises a pattern with a plurality of strips connected in series, wherein the plurality of strips has a width between 5 mm and 20 mm, and the total length of the plurality of strips is larger than 1 m. Preferably the pattern is such that the strips create a more or less rectangular radiating surface. The advantage of a metal sheet is that the radiating surface may be relatively large compared to the volume of the metal body. In an alternative embodiment the metal body may be metal wires, optionally coated metal wires. Such embodiments will allow having a relatively small heat capacity per surface area seen by the substrate, so that the temperature of the metal body can decrease fast when switching off the power supply.
In an exemplary embodiment the conditioning unit comprises a converter circuit for converting a mains voltage in an alternating voltage/current for powering the at least one infrared radiator, and a regulator for regulating a duty cycle of the alternating voltage/current.
In an exemplary embodiment the electrophotographic imaging apparatus further comprises at least one sensor configured for measuring a value representative for moisture content in the print substrate before and/or after the print substrate has passed through the conditioning unit, and a controller configured to control the conditioning unit in function of the measured value by the at least one sensor. In that manner the moisture content may be controlled accurately, taking into account the fast response time of the conditioning unit.
According to a second aspect of the invention there is provided an electrophotographic imaging apparatus comprising a conditioning unit configured to heat a substrate, an image forming unit configured to develop an image and to transfer the developed image to the heated substrate, and at least a first sensor and a second sensor configured for measuring values representative for moisture content in the print substrate at a first location and at a second location, respectively. The image forming unit is located downstream of the conditioning unit. The first location is at a distance of the second location seen in a transverse direction perpendicular on a movement direction of the substrate through the electrophotographic imaging apparatus. The conditioning unit comprises at least a first heater and a second heater located adjacently of each other seen in the transverse direction. The apparatus further comprises a controller configured to control the first and second heater in function of the measured values by the first and second sensor.
By providing a first and second infrared radiators adjacent to each other seen in the transverse direction of the substrate, and by providing a controller which can control those infrared radiators independently, differences in moisture content in the substrate can be adequately corrected. The inventors discovered that, e.g. due to storage of substrate rolls in a vertical position, the moisture content may vary significantly in the transverse direction of the substrate. Using embodiments of the invention, these differences between moisture content can be compensated by adjusting the heating by the first and second infrared radiators, such that parts of the substrate with the highest moisture content are heated more than parts of the substrate with the lowest moisture content.
In an exemplary embodiment the first and second sensor are configured for measuring values representative for moisture content in the substrate between the conditioning unit and the image forming unit. In another exemplary embodiment the first and second sensor are configured for measuring values representative for moisture content in the substrate upstream of the conditioning unit. There may also be provided a series of sensors at various locations along the printing substrate path followed by the substrate.
In an exemplary embodiment the conditioning unit is configured to emit radiation having a wavelength between 1 micrometre and 5 micrometre, to the substrate, wherein the first and second heater are a first and second infrared radiator which are configured to operate at a temperature between 500 and 2500 degrees Celsius. In an exemplary embodiment the conditioning unit is configured to emit radiation having a peak radiation wavelength between 1.4 micrometre and 5 micrometre, preferably between 2 and 4 micrometre. In an exemplary embodiment the first and second infrared radiators are configured to operate at a temperature between 500 and 1500 degrees Celsius, preferably between 550 and 1000 degrees Celsius.
In an exemplary embodiment the first and second infrared radiator each comprise a resistive heater with a metal sheet, optionally a coated metal sheet. In other embodiments the first and second infrared radiator each comprise an IR lamp, e.g. a carbon IR lamp or a fast response medium wave (FRMW) IR lamp.
In an exemplary embodiment the conditioning unit comprises a first and second converter circuit for converting a mains voltage in an alternating voltage/current for powering the first and second IR radiator, respectively, and a first and second regulator for regulating a duty cycle of the alternating voltage/current.
According to a third aspect of the invention there is provided an electrophotographic imaging apparatus comprising an image forming unit configured to develop an image and to transfer the developed image to a substrate, and a fusing unit configured to fuse the transferred image on the substrate. The fusing unit is configured to emit radiation having a wavelength between 1 micrometre and 5 micrometre, to the substrate. The fusing unit comprises at least one infrared radiator which is configured to operate at a temperature between 500 and 1200 degrees Celsius.
In that manner a very compact and efficient fusing unit is obtained which is well controllable and can be quickly turned on/off. In the specified operating range the absorption in a paper substrate is good and there are no significant differences between the fusing of different colours. Indeed, for temperatures above 1200 degrees Celsius, the absorption and reflection properties between colour (CMY) and black (K) are different which may lead to deficiencies in the fusing results.
In an exemplary embodiment, the electrophotographic imaging apparatus may have features of the electrophotographic imaging apparatus disclosed in patent application PCT/NL2015/050461 in the name of the Applicant, the content of which is included herein by reference.
In an exemplary embodiment the fusing unit is configured to emit radiation having a peak radiation wavelength
between 1.4 micrometre and 5 micrometre, preferably between 1.9 and 4 micrometre.
In an exemplary embodiment the fusing unit comprises at least one infrared radiator which is configured to operate at a temperature between 500 and 2500 degrees Celsius, preferably between 500 and 1500 degrees Celsius, and more preferably between 550 and 1000 degrees Celsius. The at least one infrared radiator may comprise e.g. a resistive heater with a metal sheet, optionally a coated metal sheet. In other embodiments IR lamps may be used.
In an exemplary embodiment the fusing unit comprises a converter circuit for converting a mains voltage in an alternating voltage/current that is applied over/through a metal body of the infrared radiator; and a regulator for regulating a duty cycle of the alternating voltage/current.
In an exemplary embodiment the electrophotographic imaging apparatus further comprises at least one sensor and a controller. The at least one sensor is configured for measuring a value representative for a property of the print substrate before and/or after the print substrate has passed through the fusing unit, and may be e.g. a temperature sensor and/or a moisture content sensor. The controller is configured to control the fusing unit in function of the measured value by the at least one sensor. In that manner, if the temperature is too high, the controller may control the at least one infrared radiator such that intensity of the at least one infrared radiator may be decreased, and vice versa.
In an exemplary embodiment at least a first and a second sensor configured for measuring values representative for a property of the print substrate, are provided at a distance of each other seen in a transverse direction perpendicular on a movement direction of the substrate through the electrophotographic imaging apparatus; wherein the fusing unit comprises at least a first infrared radiator and a second infrared radiator located adjacently of each other seen in the transverse direction; and wherein the controller is configured to control the first and second infrared radiator in function of the measured values by the first and second sensor.
In an exemplary embodiment the fusing unit comprises at least a first infrared radiator and a second infrared radiator located behind each other seen in a movement direction of the substrate through the electrophotographic imaging apparatus. A controller may then be configured to control the first infrared radiator and the second infrared radiator in function of the measured value by the at least one sensor. Such an embodiment with a number of infrared radiators in series may be advantageous if it is better to fuse with a lower intensity or with a gradually increasing intensity.
In another exemplary embodiment at least a first and a second sensor configured for measuring values representative for a property of the print substrate, e.g. a first and second temperature sensor, are provided at a distance of each other seen in a transverse direction perpendicular on a movement direction of the substrate through the electrophotographic imaging apparatus. The fusing unit comprises at least a first infrared radiator and a second infrared radiator located adjacently of each other seen in the transverse direction. The controller is configured to control the first and second infrared radiator in function of the measured values by the first and second sensor. Yet other variants may use an array of infrared radiators which are independently controllable by the controller in function of values measured by the sensors.
In an exemplary embodiment the at least one infrared radiator of the fusing unit has a heat capacity per surface area seen by the substrate between 50 and 2000 J/m2K, preferably between 50 and 1500 J/m2K, more preferably between 50 and 1000 J/m2K. Such a heat capacity is sufficiently low for allowing a fast switching on and off of the at least one infrared radiator.
According to a fourth aspect of the invention there is provided an electrophotographic imaging apparatus comprising: a fusing unit configured to heat a substrate; an image forming unit configured to develop an image and to transfer the developed image to the heated substrate, said image forming unit being located downstream of the conditioning unit; at least a first sensor and a second sensor; and a controller. The first and second sensor are configured for measuring values representative for a property of the print substrate at a first location and at a second location, respectively, wherein the first location is at a distance of the second location seen in a transverse direction perpendicular on a movement direction of the substrate through the electrophotographic imaging apparatus. The fusing unit comprises at least a first heater and a second heater located adjacently of each other seen in the transverse direction. The controller is configured to control the first and second heater in function of the measured values by the first and second sensor.
In an exemplary embodiment thereof the first and second sensor are configured for measuring values representative for a property in the substrate downstream or upstream of the fusing unit. The first and second sensors may be e.g. temperature sensors and/or moisture content sensors, i.e. sensors configured for measuring a value representative for moisture content in the print substrate.
In an exemplary embodiment thereof the fusing unit is configured to emit radiation having a wavelength between 1 micrometre and 5 micrometre, to the substrate, wherein the first and second heater are a first and second infrared radiator which are configured to operate at a temperature between 500 and 1200 degrees Celsius. More specifically, the fusing unit may be configured to emit radiation having a peak radiation wavelength between 1.4 micrometre and 5 micrometre, preferably between 1.9 and 4 micrometre.
In an exemplary embodiment the first and second infrared radiator each comprise a resistive heater with a metal sheet, or with a plurality of interconnected metal strips or bands, or with a metal wire optionally coated. The metal body may further have the features described above for the metal body of the conditioning unit.
In an exemplary embodiment thereof the fusing unit comprises a first and second converter circuit for converting a mains voltage in an alternating voltage/current for powering the first and second infrared radiator, respectively; and a first and second regulator for regulating a duty cycle of the alternating voltage/current.
In an exemplary embodiment, which may be applicable for the various aspects mentioned above, the image forming unit is configured for using a liquid toner.
In an exemplary embodiment the conditioning unit or the fusing unit may further comprise a blowing unit to cool the one or more infrared radiators when the conditioning unit or the fusing unit is switched off. This will allow to further decrease the time needed to bring the conditioning unit or the fusing unit at a safe temperature.
The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:
The conditioning unit 100 is configured to emit radiation having a wavelength between 1 μm and 5 μm onto the substrate. The conditioning 100 comprises at least one infrared radiator which is configured to operate at a temperature between 500° C. and 2500° C., preferably between 500° C. and 1500° C., more preferably between 550° C. and 1000° C., and even more preferably between 600° C. and 900° C. According to the law of Stefan-Boltzmann the total radiated power is proportional with the surface of the radiator and the temperature T, and more in particular proportional with T4. In other words, the higher the temperature, the higher the total radiated power. However, the spectral energy density is a function of the wavelength, and the peak value for which the spectral density is maximal occurs at a wavelength λmax which is temperature-dependent, as determined by Wien's law:
λmax·T=2900 μm·K
In other words, for 500° C. λmax=3.75 μm, and for 2500° C. λmax=1.05 μm.
Embodiments of the invention are further based on the inventive insight that, above a predetermined threshold wavelength, the radiation absorption of the substrate increases with the wavelength, as illustrated in
In a preferred embodiment, the conditioning unit 100 is configured to emit radiation having a peak radiation wavelength λmax for which the spectral density is maximal, between 1.4 μm and 5 μm, preferably between 2 μm and Sum. As can be seen in
In the exemplary embodiment of
The image forming unit 200 comprises a reservoir 210, a feed member 220, a development member 230, an imaging member 240, an intermediate member 250, and a transfer member 260. The substrate S is transported between intermediate member 250 and transfer member 260. Without loss of generality, the aforementioned members are illustrated and described as rollers, but the skilled person understands that they can be implemented differently, e.g. as belts.
In operation, an amount of liquid toner dispersion, initially stored in the liquid toner dispersion reservoir 210, is applied via feed member 220, to development member 230, imaging member 240, and optional intermediate member 250, and finally to the substrate S. Development member 230, imaging member 240, and intermediate member 250 all transfer part of the liquid toner dispersion adhering to their surface to their successor. The part of the liquid toner dispersion that remains present on the member's surface, i.e. the excess liquid toner dispersion, which remains after selective, imagewise transfer, may be removed after the transfer stage by appropriate removal means such as a scraper and may be recycled. The charging of the toner particles on the development member 230 is done by a charging device (not shown), e.g. a corona or a biased roll. Charging the toner particles causes the liquid toner dispersion to split into an inner layer at the surface adjacent of the development member 230 and an outer layer. The inner layer is richer in toner particles and the outer layer is richer in carrier liquid.
After transfer of the image on the substrate S in the image forming unit 200, fusing is carried out by means of a fusing unit 300. In the example of
Typically, the above described conditioning and imaging process occurs at “high speed”, for instance more than 50 cm/s, and up to 3 m/s or more, so as to enable high-speed printing.
It will be understood that for duplex and multicolour printing several image forming units 200 and fusing units 300 are typically available.
In a preferred embodiment, the fusing unit 300 is similar to the conditioning unit and is also configured to emit radiation having a wavelength between 1 μm and 5 μm to the substrate on which an image has been printed. The fusing unit 300 may comprise at least one infrared radiator which is configured to operate at a temperature between 500° C. and 1500° C., preferably between 500° C. and 1200° C., and more preferably between 550° C. and 1000° C. In the illustrated embodiment, the fusing unit has a lower part 360 and an upper part 350, and the upper part 350 comprises an infrared radiator. In case of duplex printing, and if both sides of the substrate are printed on in the same pass, it may be advantageous to include an infrared radiator in both parts 360, 350. Also the fusing unit 300 may be oriented vertically or under an angle instead of horizontally. A vertical or slanted arrangement may be beneficial for the evacuation of humid air due to the evaporation of moisture from the substrate.
After transfer of images on the substrate S, e.g. images on a both sides of the substrate S, in the image forming unit 200, fusing is carried out by means of a fusing unit 300. In a preferred embodiment, the fusing unit 300 is similar to the conditioning unit 100 and is also configured to emit radiation having a wavelength between 1 μm and 5 μm to the substrate on which an image has been printed. The fusing unit 300 may comprise at least one infrared radiator which is configured to operate at a temperature between 500° C. and 1500° C., preferably between 500° C. and 1200° C., and more preferably between 550° C. and 1000° C. In the illustrated embodiment, the fusing unit has a second part 360 and a first part 350, and both the first and second part 350, 360 comprises an infrared radiator. Alternatively there may be provided a plurality of fusing units 300 in series, and/or a fusing unit 300 may comprise only one infrared radiator in one of the parts 350, 360.
By providing a plurality of infrared radiators 101, 102, 103 adjacent to each other seen in the transverse direction of the substrate S, and by providing a controller 500 which can control those infrared radiators 101, 102, 103 independently, differences in moisture content in the substrate can be adequately dealt with. The inventors discovered that due to storage of substrate rolls in a vertical position, the moisture content between the left and right side of the substrate may vary significantly. In other words, the moisture content may vary significantly in the transverse direction of the substrate S. Using the embodiment of
The implementation of
Now a more detailed exemplary embodiment of a conditioning or fusing unit comprising an infrared radiator will be described with reference to
In exemplary embodiments the thickness of the metal strips 121 is preferably smaller than 2 mm, more preferably smaller than 1 mm, and most preferably smaller than 0.5 mm, e.g between 0.05 mm and 3 mm. The metal sheet 120 may comprise a pattern with a plurality of strips 121 connected in series, wherein the plurality of strips 121 has a width between 5 mm and 20 mm, and the total length of the plurality of strips is larger than 1 m (in the present example five strip each having a length which is larger than 200 mm), preferably larger than 2 m. Preferably the pattern is such that the strips create a more or less rectangular radiating surface.
Such embodiments will allow having a relatively small heat capacity per surface area seen by the substrate, so that the temperature of the metal body can decrease fast when switching off the power supply. Indeed, if it is assumed that e.g. the width is 10 mm, the thickness is 0.25 mm and the total length 2 m, then the heat capacity per surface area seen by the print substrate can be estimated as follows:
total surface area A is approximately 2000 mm*10 mm=0.02 m2;
the weight of the nickel metal sheet with density 8.9 kg/dm3 can be estimated as m=2 dm2*0.25 mm*8.9 kg/dm3=0.0445 kg;
thermal capacity nickel cp=460 J/kg·K;
resulting in a thermal capacity per surface area seen by the print substrate of (m*cp)/A=0.0445 kg*460 J/kgK/(0.02 m2)=1023.50 J/m2K
This value can be further decreased by using thinner metal sheets or by distributing the radiating metal sheet over a larger surface, e.g. by inserting more space between the strips 121. This value may be slightly higher due to the presence of the ceramic substrate 110, but is much lower than the thermal capacity of ceramic tiles used in the prior art embodiments to condition paper substrates.
In other non-illustrated embodiments infrared lamps may be used as the one or more IR radiators. Examples of suitable IR lamps are carbon IR lamps and fast response medium wave (FRMW) IR lamps. Such lamps typically operate at temperature between 1000° C. and 2000° C.
A person of skill in the art would readily recognize that steps performed by a controller in various above-described embodiments can be performed by programmed computers. Herein, embodiments are also intended to cover program storage devices, e.g., digital storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions for performing some or all of the above-described steps. The functions of the various elements shown in the figures, including any functional blocks labelled as “controller”, may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a controller, the functions may be provided by a single dedicated controller, or by a plurality of individual controllers, some of which may be shared.
Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015973 | Dec 2015 | NL | national |
