Heat transfer apparatus for an image bearing member

Information

  • Patent Grant
  • 6393245
  • Patent Number
    6,393,245
  • Date Filed
    Thursday, November 16, 2000
    23 years ago
  • Date Issued
    Tuesday, May 21, 2002
    22 years ago
Abstract
An intermediate transfer member defines a transfer nip with a transfuse member. A cooling platen contacts the intermediate transfer member in the post-transfer nip region. The cooling platen absorbs heat from the intermediate transfer member to evaporate a liquid into a gas. The gas is directed to a heating platen contacting the pre-nip region of the intermediate transfer member. The heating platen condenses the gas to a liquid to heat the intermediate transfer member.
Description




FIELD OF THE INVENTION




This invention relates to printing machines, and more particularly this invention relates to a heat transfer station on an image support surface of a printing machine.




BACKGROUND TO THE INVENTION




Electrostatographic printers are known in which a single color toner image is electrostatically formed on photoreceptive image bearing member. The toner image is transferred to a receiving substrate, typically paper or other print receiving materials. The toner image is subsequently fused to the substrate.




In one arrangement of an electrostatographic printer, a plurality of dry toner imaging systems each having an image bearing member, are used to develop multiple color toner images. Each color toner image is electrostatically transferred from the image bearing members and onto an intermediate transfer member to form a multilayer composite toner image. The composite toner image is electrostatically transferred to a transfuse member and finally transferred and fused to the final substrate. Such systems that use electrostatic transfer to transfer the composite toner image from the image bearing members to the intermediate transfer member, and from the intermediate transfer member to the transfuse member, can have transfer limitations. In operation, the transfuse member is cooled below the glass transition temperature of the toner prior to the transfer nip with the intermediate transfer member. Cooling of the transfuse member requires the transfuse member to be relatively thin. A thin transfuse member however has low conformance therefore providing reduced transfer efficiency in the transfuse nip. The reduced conformance also increases the potential for glossing of the toner image in the transfuse nip. In addition, a thin transfuse member can have a reduced operational life.




SUMMARY OF THE INVENTION




Briefly stated, a heat transfer station in accordance with the invention transfers heat from the post-transfer region of a toner image bearing member to the pre-transfer region of the toner image bearing member. The heat transfer station provides selective cooling and heating of the toner image bearing member.




A preferred printing apparatus employing a heat transfer station in accordance with the invention has a toner image forming station, an intermediate transfer member and a transfuse member. The toner image from the toner image forming station is transferred to the intermediate transfer member at a first transfer nip. The toner image is then transferred from the intermediate transfer member to the transfuse member at a second transfer nip. At a third transfer nip the toner image is transferred from the transfuse member, and generally simultaneously fused, to a substrate to form a document. The transfer from the intermediate transfer member, to the transfuse member is preferably rheologically assisted. The rheological assist is created by maintaining a preestablished temperature differential between the intermediate transfer member and the transfuse member. The transfer can further be electrostatically assisted. Therefor the intermediate transfer member is heated prior to the second transfer nip to heat the toner image supported on the intermediate transfer member.




However, the toner image forming station can be susceptible to excess heat, particularly when the toner image forming station employs a photoreceptor. As a result, a relatively elevated temperature in the first transfer nip can damage the toner image forming station resulting in decreased image quality. In view of the preference to heat the toner image prior to the second transfer nip, and to prevent excessive heat from damaging the toner image forming station, heat on the intermediate transfer member is transferred from the region of the intermediate transfer member intermediate the second and first transfer nips in the process direction to the region of the intermediate transfer member intermediate the first and second transfer nips in the process direction. In other words, the heat transfer station transfers heat from the post-second transfer nip region of the intermediate transfer member to the pre-second transfer nip region of the intermediate transfer member.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic side view of a duplex cut sheet electrostatographic printer having a heat transfer station in accordance with the invention;





FIG. 2

is an enlarged schematic side view of the transfer nips of the printer of

FIG. 1

;





FIG. 3

is an enlarged cross-sectional schematic side view of the heat transfer station of

FIG. 2

;





FIG. 4

is a graphical representation of residual toner as a function of transfuse member temperature; and





FIG. 5

is a graphical representation of crease as a function of transfuse member temperature for given representation of residual substrate temperature.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




With reference to

FIGS. 1 and 2

, a multi-color cut sheet duplex electrostatographic printer


10


has an intermediate transfer belt


12


. The intermediate transfer belt


12


is driven over guide rollers


14


,


16


,


18


, and


20


. The intermediate transfer belt


12


moves in a process direction shown by the arrow A. For purposes of discussion, the intermediate transfer member


12


defines a single section of the intermediate transfer member


12


as a toner area. A toner area is that part of the intermediate transfer member which receives the various processes by the stations positioned around the intermediate transfer member


12


. The intermediate transfer member


12


may have multiple toner areas; however, each toner area is processed in the same way.




The toner area is moved past a set of four toner image producing stations


22


,


24


,


26


, and


28


. Each toner image producing station


22


,


24


,


26


,


28


operates to place a color toner image on the toner image of the intermediate transfer member


12


. Each toner image producing station


22


,


24


,


26


,


28


operates in the same manner to form developed toner image for transfer to the intermediate transfer member


12


.




The image producing stations


22


,


24


,


26


,


28


are described in terms of a photoreceptive system, but it is readily recognized by those of skilled in the art that ionographic systems and other marking systems can readily be employed to form developed toner images. Each toner image producing station


22


,


24


,


26


,


28


has an image bearing member


30


. The image bearing member


30


is a drum or belt supporting a photoreceptor.




The image bearing member


30


is uniformly charged at a charging station


32


. The charging station is of well-known construction, having charge generation devices such as corotrons or scorotrons for distribution of an even charge on the surface of the image bearing member


30


. An exposure station


34


exposes the charged image bearing member


30


in an image-wise fashion to form an electrostatic latent image at the image area. For purposes of discussion, the image bearing member defines an image area. The image area is that part of the image bearing member which receives the various processes by the stations positioned around the image bearing member


30


. The image bearing member


30


may have multiple image areas; however, each image area is processed in the same way.




The exposure station


34


preferably has a laser emitting a modulated laser beam. The exposure station


34


raster scans the modulated laser beam onto the charged image area. The exposure station


34


can alternately employ LED arrays or other arrangements known in the art to generate a light image representation that is projected onto the image area of the image bearing member


30


. The exposure station


34


exposes a light image representation of one color component of a composite color image onto the image area to form a first electrostatic latent image. Each of the toner image producing stations


22


,


24


,


26


,


28


will form an electrostatic latent image corresponding to a particular color component of a composite color image.




The image area is advanced to a development station


36


. The developer station


36


has a developer corresponding to the color component of the composite color image. Typically, therefore, individual toner image producing stations


22


,


24


,


26


, and


28


will individually develop the cyan, magenta, yellow, and black that make up a typical composite color image.




Additional toner image producing stations can be provided for additional or alternate colors including highlight colors or other custom colors. Therefore, each of the toner image producing stations


22


,


24


,


26


,


28


develops a component toner image for transfer to the toner area of the intermediate transfer member


12


. The developer station


36


preferably develops the latent image with a charged dry toner powder to form the developed component toner image. The developer can employ a magnetic toner brush or other well known development arrangements.




The image area having the component toner image then advances to the pretransfer station


38


. The pretransfer station


38


preferably has a pretransfer charging device to charge the component toner image and to achieve some leveling of the surface voltage above the image bearing member


30


to improve transfer of the component image from the image bearing member


30


to the intermediate transfer member


12


. Alternatively the pretransfer station


30


can use a pretransfer light to level the surface voltage above the image bearing member


30


. Furthermore, this can be used in cooperation with a pretransfer charging device. The image area then advances to a first transfer nip defined between the image bearing member


30


and the intermediate transfer member


12


. The image bearing member


30


and intermediate transfer member


12


are synchronized such that each has substantially the same linear velocity at the first transfer nip


40


. The component toner image is electrostatically transferred from the image bearing member


30


to the intermediate transfer member


12


by use of a field generation station


42


. The field generation station


42


is preferably a bias roller that is electrically biased to create sufficient electrostatic fields of a polarity opposite that of the component toner image to thereby transfer the component toner image to the intermediate transfer member


12


. Alternatively the field generation station


42


can be a corona device or other various types of field generation systems known in the art. A prenip transfer blade


44


mechanically biases the intermediate transfer member


12


against the image bearing member


30


for improved transfer of the component toner image. The toner area of the intermediate transfer member


12


having the component toner image from the toner image producing station


22


then advances in the process direction.




After transfer of the component toner image, the image bearing member


30


then continues to move the image area past a preclean station


39


. The preclean station employs a pre clean corotron to condition the toner charge and the charge of the image bearing member


30


to enable improved cleaning of the image area. The image area then further advances to a cleaning station


41


. The cleaning station


41


removes the residual toner or debris from the image area. The cleaning station


41


preferably has blades to wipe the residual toner particles from the image area. Alternately the cleaning station


41


can employ an electrostatic brush cleaner or other well know cleaning systems. The operation of the cleaning station


41


completes the toner image production for each of the toner image producing stations


22


,


24


,


26


, and


28


.




The first component toner image is advanced at the image area from the first transfer nip


40


of the image producing station


22


to the first transfer nip


40


of the toner image producing station


24


. Prior to entrance of the first transfer nip


40


of the toner image producing station


24


an image conditioning station


46


uniformly charges the component toner image to reduce stray, low or oppositely charged toner that would result in back transfer of some of the first component toner image to the subsequent toner image producing station


24


. The image conditioning stations, in particular the image conditioning station prior to the first toner image producing station


22


also conditions the surface charge on the intermediate transfer member


12


. At each first transfer nip


40


, the subsequent component toner image is registered to the prior component toner images to form a composite toner image after transfer of the final toner image by the toner image producing station


28


.




The geometry of the interface of the intermediate transfer member


12


with the image bearing member


30


has an important role in assuring good transfer of the component toner image. The intermediate transfer member


12


should contact the surface of the image bearing member


30


prior to the region of electrostatic field generation by the field generation station


42


, preferably with some amount of pressure to insure intimate contact. Generally, some amount of pre-nip wrap of the intermediate transfer member


12


against the image bearing member


30


is preferred. Alternatively, the pre-nip pressure blade


44


or other mechanical biasing structure can be provided to create such intimate pre-nip contact. This contact is an important factor in reducing high electrostatic fields from forming at air gaps between the intermediate transfer member


12


and the component toner image in the pre-nip region. For example, with a corotron as the field generation station


42


, the intermediate transfer member


12


should preferably contact the toner image in the pre-nip region sufficiently prior to the start of the corona beam profile.




With a field generation station


42


of a bias charging roller, the intermediate transfer member


12


should preferably contact the toner image in the pre-nip region sufficiently prior to the contact nip of the bias charging roller. “Sufficiently prior” for any field generation device can be taken to mean prior to the region of the pre-nip where the field in any air gap greater than about 50 microns between the intermediate transfer member


12


and the component toner image has dropped below about 4 volts/micron due to falloff of the field with pre-nip distance from the first transfer nip


40


. The falloff of the field is partly due to capacitance effects and this will depend on various factors. For example, with a bias roller this falloff with distance will be slowest with larger diameter bias rollers, and/or with higher resistivity bias rollers, and/or if the capacitance per area of the insulating layers in the first transfer nip


40


is lowest. Lateral conduction along the intermediate transfer member


12


can even further extend the transfer field region in the pre-nip, depending on the transfer belt resistivity and other physical factors. Using intermediate transfer members


12


having resistivity nearer the lower end of the preferred range discussed below and/or systems that use large bias rollers, etc., preference is larger pre-nip contact distances. Generally the desired pre-nip contact is between about 2 to 10 mm for resistivities within the desired range and with bias roller diameters between about 12 mm and 50 mm.




The field generation station


42


will preferentially use very conformable bias rollers for the first transfer nips


40


such as foam or other roller materials having an effectively very low durometer ideally less than about 30 Shore A. In systems that use belts for the imaging modules, optionally the first transfer nip


40


can include acoustic loosening of the component toner image to assist transfer.




In the preferred arrangement, “slip transfer” is employed for registration of the color image. For slip transfer, the contact zone between the intermediate transfer member


12


and the image bearing member


30


will preferably be minimized subject to the pre-nip restrictions. The post transfer contact zone past the field generation station


42


is preferentially small for this arrangement. Generally, the intermediate transfer member


12


can optionally separate along the preferred bias roller of the field generation station


42


in the post nip region if an appropriate structure is provided to insure that the bias roller does not lift off the surface of the image bearing member due to the tension forces of the intermediate transfer member


12


. For slip transfer systems, the pressure of the bias roller employed in the field generation station


42


should be minimized. Minimized contact zone and pressure minimizes the frictional force acting on the image bearing member


30


and this minimizes elastic stretch issues of the intermediate transfer member


12


between first transfer nips


40


that can degrade color registration. It will also minimize motion interactions between the drive of the intermediate transfer member


12


and the drive of the image bearing member


30


.




For slip transfer systems, the resistivity of the intermediate transfer member


12


should also be chosen to be high, generally within or even toward the middle to upper limits of the most preferred range discussed later, so that the required pre-nip contact distances can be minimized. In addition, the coefficient of friction of the top surface material on the intermediate transfer member should preferentially be minimized to increase operating latitude for the slip transfer registration and motion quality approach.




In an alternate embodiment the image bearing members


30


, such as photoconductor drums, do not have separate drives and instead are driven by the friction in the first transfer nips


40


. In other words, the image bearing members


30


are driven by the intermediate transfer member


12


. Therefore, the first transfer nip


40


imparts sufficient frictional force on the image bearing member to overcome any drag created by the development station


36


, cleaner station


41


, additional subsystems and by bearing loads. For a friction driven image bearing member


30


, the optimum transfer design considerations are generally opposite to the slip transfer case. For example, the lead in of the intermediate transfer member


12


to the first transfer zone preferentially can be large to maximize the friction force due to the tension of the intermediate transfer member


12


. In the post transfer zone, the intermediate transfer member


12


is wrapped along the image bearing member


30


to further increase the contact zone and to therefore increase the frictional drive. Increased post-nip wrap has a larger benefit than increased pre-nip wrap because there will be increased pressure there due to electrostatic tacking forces. As another example, the pressure applied by the field generation device


42


can further increase the frictional force. Finally for such systems, the coefficient of friction of the material of the top most layer on the intermediate transfer member


12


should preferentially be higher to increase operating latitude.




The toner area then is moved to the subsequent first transfer nip


40


. Between toner image producing stations are the image conditioning stations


46


. The charge transfer in the first transfer nip


40


is normally at least partly due to air breakdown, and this can result in non uniform charge patterns on the intermediate transfer member


12


between the toner image producing stations


22


,


24


,


26


,


28


. As discussed later, the intermediate transfer member


12


can optionally include insulating topmost layers, and in this case non uniform charge will result in non uniform applied fields in the subsequent first transfer nips


40


. The effect accumulates as the intermediate transfer member


12


proceeds through the subsequent first transfer nips


40


. The image conditioning stations


46


“level” the charge patterns on the belt between the toner image producing stations


22


,


24


,


26


,


28


to improve the uniformity of the charge patterns on the intermediate transfer member


12


prior to subsequent first transfer nips


40


. The image conditioning stations


46


are preferably scorotrons and alternatively can be various types of corona devices. As previously discussed, the charge conditioning stations


46


additionally are employed for conditioning the toner charge to prevent re-transfer of the toner to the subsequent toner image producing stations. The need for image conditioning stations


46


is reduced if the intermediate transfer member


12


consists only of semiconductive layers that are within the desired resistivity range discussed later. As further discussed later, even if the intermediate transfer member


12


includes insulating layers, the need for image conditioning stations


46


between the toner image producing stations


22


,


24


,


26


,


28


is reduced if such insulating layers are sufficiently thin.




The guide roller


14


is preferably adjustable for tensioning the intermediate transfer member


12


. Additionally, the guide roller


14


can, in combination with a sensor sensing the edge of the intermediate transfer member


12


, provide active steering of the intermediate transfer member


12


to reduce transverse wander of the intermediate transfer member


12


that would degrade registration of the component toner images to form the composite toner image.




Each toner image producing station positions component toner image on the toner area of the intermediate transfer member


12


to form a completed composite toner image. The intermediate transfer member


12


transports the composite toner image from the last toner image producing station


28


to pre-transfer charge conditioning station


52


. When the intermediate transfer member


12


includes at least one insulating layer, the pretransfer charge conditioning station


52


levels the charge at the toner area of the intermediate transfer member


12


. In addition the pre-transfer charge conditioning station


52


is employed to condition the toner charge for transfer to a transfuse member


50


. It preferably is a scorotron and alternatively can be various types of corona devices. A second transfer nip


48


is defined between the intermediate transfer member


12


and the transfuse member


50


. A field generation station


42


and pre-transfer nip blade


44


engage the intermediate transfer member


12


adjacent the second transfer nip


48


and perform the same functions as the field generation stations and pre-transfer blades


44


adjacent the first transfer nips


40


. However the field generation station at the second transfer nip


48


can be relatively harder to engage conformable transfuse members


50


. The composite toner image is transferred electrostatically and with heat assist to the transfuse member


50


.




The electrical, characteristics of the intermediate transfer member


12


are also important. The intermediate transfer member


12


can optionally be constructed of a single layer or multiple layers. In any case, preferably the electrical properties of the intermediate transfer member


12


are selected to reduce high voltage drops across the intermediate transfer member. To reduce high voltage drops, the resistivity of the back layer of the intermediate transfer member


12


preferably has sufficiently low resistivity. The electrical characteristics and the transfer geometry must also be chosen to prevent high electrostatic transfer fields in pre-nip regions of the first and second transfer nips


40


,


48


. High pre-nip fields at air gaps of around typically >50 microns between the component toner images and the intermediate transfer member


12


can lead to image distortion due to toner transfer across an air gap and can also lead to image defects caused by pre-nip air breakdown. This can be avoided by bringing the intermediate transfer member


12


into early contact with the component toner image prior to the field generating station


42


, as long as the resistivity of any of the layers of the intermediate transfer member


12


are sufficiently high. The intermediate transfer member


12


also should have sufficiently high resistivity for the topmost layer to prevent very high current flow from occurring in the first and second transfer nips


40


,


48


. Finally, the intermediate transfer member


12


and the system design needs to minimize the effect of high and/or non-uniform charge buildup that can occur on the intermediate transfer member


12


between the first transfer nips


40


.




The preferable material for a single layer intermediate transfer member


12


is a semiconductive material having a “charge relaxation time” that is comparable to or less than the dwell time between toner image producing stations, and more preferred is a material having a “nip relaxation time” comparable or less than the transfer nip dwell time. As used here, “relaxation time” is the characteristic time for the voltage drop across the thickness of the layer of the intermediate transfer member to decay. The dwell time is the time that an elemental section of the transfer member


12


spends moving through a given region. For example, the dwell time between imaging stations


22


and


24


is the distance between imaging stations


22


and


24


, divided by the process speed of the transfer member


12


. The transfer nip dwell time is the width of the contact nip created during the influence of the field generation station


42


, divided by the process speed of the transfer member


12


.




The “charge relaxation time” is the relaxation time when the intermediate transfer member is substantially isolated from the influence of the capacitance of other members within the transfer nips


40


. Generally the charge relaxation time applies for regions prior to or past the transfer nips


40


. It is the classic “RC time constant”, that is K


L


ρ


L


e


0


, the product of the material layer quantities the resistivity of a material can be sensitive to the applied field in the material. In this case, the resistivity should be determined at an applied field dielectric constant K


L


times resistivity P


L


times the permitivity of vacuum e


0


. In general corresponding to about 25 to 100 volts across the layer thickness. The “nip relaxation time” is the relaxation time within regions such as the transfer nips


40


. If


42


is a corona field generation device, the “nip relaxation time” is substantially the same as the charge relaxation time. However, if a bias transfer device is used, the nip relaxation time is generally longer than the charge relaxation time. This is because it is influenced not only by the capacitance of the intermediate transfer member


12


itself, but it is also influenced by the extra capacitance per unit area of any insulating layers that are present within the transfer nips


40


. For example, the capacitance per unit area of the photoconductor coating on the image bearing member


30


and the capacitance per unit area of the toner image influence the nip relaxation time. For discussion, C


L


represents the capacitance per unit area of the layer of the intermediate transfer member


12


and C


tot


represents the total capacitance per unit area of all insulating layers in the first transfer nips


40


, other than the intermediate transfer member


12


. When the field generation station


42


is a bias roller, the nip relaxation time is the charge relaxation time multiplied by the quantity [1+(C


tot


/C


L


)].




The range of resistivity conditions defined in the above discussion avoid high voltage drops across the intermediate transfer member


12


during the transfers of the component toner images at the first transfer nips


40


. To avoid high pre-nip fields, the volume resistivity in the lateral or process direction of the intermediate transfer member must not be too low. The requirement is that the lateral relaxation time for charge flow between the field generation station


42


in the first transfer nip


40


should be larger than the lead in dwell time for the first transfer nip


40


. The lead in dwell time is the quantity L/v. L is the distance from the pre-nip region of initial contact of the intermediate transfer member


12


with the component toner image, to the position of the start of the field generation station


42


within the first transfer nip


40


. The quantity v is the process speed. The lateral relaxation time is proportional to the lateral resistance along the belt between the field generating station


42


and the pre-nip region of initial contact, and the total capacitance per area C


tot


of the insulating layers in the first transfer nip


40


between the intermediate transfer member


12


and the substrate of the image bearing member


30


of the toner image producing station


22


,


24


,


26


,


28


. A useful expression for estimating the preferred resistivity range that avoids undesirable high pre-nip fields near the field generation stations


42


is: [L v ρ


L


C


tot


]>1. The quantity is referred to as the “lateral resistivity” of the intermediate transfer member


12


. It is the volume resistivity of the member divided by the thickness of the member. In cases where the electrical properties of the member


12


is not isotropic, the volume resistivity of interest for avoiding high pre-nip fields is that resistivity of the layer in the process direction. Also, in cases where the resistivity depends on the applied field, the lateral resistivity should be determined at a field of between about 500 to 1500 volts/cm.




Thus the preferred range of resistivity for the single layer intermediate transfer member


12


depends on many factors such as for example the system geometry, the transfer member thickness, the process speed, and the capacitance per unit area of the various materials in the first transfer nip


40


. For a wide range of typical system geometry and process speeds the preferred resistivity for a single layer transfer belt is typically a volume resistivity less than about 10


13


ohm-cm and a more preferred range is typically <10


11


ohm-cm volume resistivity. The lower limit of preferred resistivity is typically a lateral resistivity above about 10


8


ohms/square and more preferred is typically a lateral resistivity above about 10


10


ohms/square.




As an example, with a typical intermediate transfer member


12


thickness of around 0.01 cm, a lateral resistivity greater than 10


10


ohms/square corresponds to a volume resistivity of greater than 10


8


ohm-cm.




Discussion below will specify the preferred range of electrical properties for the transfuse member


50


to allow good transfer in the second transfer nip


48


. The transfuse member


50


will preferably have multiple layers and the electrical properties chosen for the topmost layer of the transfuse member


50


will influence the preferred resistivity for the single layer intermediate transfer member


12


. The lower limits for the preferred resistivity of the single layer intermediate transfer member


12


referred to above apply if the top most surface layer of the transfuse member


50


has a sufficiently high resistivity, typically equal to or above about 10


9


ohm-cm. If the top most surface layer of the transfuse member


50


has a somewhat lower resistivity than about 10


9


ohm-cm, the lower limit for the preferred resistivity of the single layer intermediate transfer member


12


should be increased in order to avoid transfer problems in the second transfer nip


48


. Such problems include undesirably high current flow between the intermediate transfer member


12


and the transfuse member


50


, and transfer degradation due to reduction of the transfer field. In the case where the resistivity of the top most layer of the transfuse member


50


is less than about 10


9


ohm-cm, the preferred lower limit volume resistivity for the single layer intermediate transfer member


12


will typically be around greater than or equal to 10


9


ohm-cm.




In addition, the intermediate transfer member


12


should have sufficient lateral stiffness to avoid registration issues between toner image producing stations


22


,


24


,


26


,


28


due to elastic stretch. Stiffness is the sum of the products of Young's modulus times the layer thickness for all of the layers of the intermediate transfer member. The preferred range for the stiffness depends on various systems parameters. The required value of the stiffness increases with increasing amount of frictional drag at and/or between the toner image producing stations


22


,


24


,


26


,


28


. The preferred stiffness also increases with increasing length of the intermediate transfer member


12


between toner image producing stations, and with increasing color registration requirements. The stiffness is preferably >800 PSI-inches and more preferably >2000 PSI-inches.




A preferred material for the single layer intermediate transfer member


12


is a polyamide that achieve good electrical control via conductivity controlling additives.




The intermediate transfer member


12


may also optionally be multi-layered. The back layer, opposite the toner area, will preferably be semi-conductive in the discussed range. The preferred materials for the back layer of a multi-layered intermediate transfer member


12


are the same as that discussed for the single layer intermediate belt


12


. Within limits, the top layers can optionally be “insulating” or semiconductive. There are certain advantages and disadvantages of either.




A layer on the intermediate transfer member


12


can be thought of as behaving “insulating” for the purposes of discussion here if the relaxation time for charge flow is much longer than the dwell time of interest. For example, a layer behaves “insulating” during the dwell time in the first transfer nip


40


if the nip relaxation time of that layer in the first transfer nip


40


is much longer than the time that a section of the layer spends in traveling through the first transfer nip


40


. A layer behaves insulating between toner image producing stations


22


,


24


,


26


,


28


if the charge relaxation time for that layer is much longer than the dwell time that a section of the layer takes to travel between the toner image producing stations. On the other hand, a layer behaves semiconducting in the sense meant here when the relaxation times are comparable or lower than the appropriate dwell times. For example, a layer behaves semi conductive during the dwell time of the first transfer nip


40


when the nip relaxation time is less than the dwell time in the first transfer nip


40


. Furthermore, a layer on the intermediate transfer member


12


behaves semiconductive during the dwell time between toner image producing stations


22


,


24


,


26


,


28


if the relaxation time of the layer is less than the dwell time between toner image producing stations. The expressions for determining the relaxation times of any top layer on the intermediate transfer member


12


are substantially the same as those described previously for the single layer intermediate transfer member. Thus whether or not a layer on the multi-layered intermediate transfer member


12


behaves “insulating” or “semiconducting” during 'a particular dwell time of interest depends not only on the electrical properties of the layer but also on the process speed, the system geometry, and the layer thickness.




A layer of the transfer belt will typically behave “insulating” in most transfer systems if the volume resistivity is generally greater than about 10


13


ohm-cm. Insulating top layers on the intermediate transfer member


12


cause a voltage drop across the layer and thus reduce the voltage drop across the composite toner layer in the first transfer nip


40


. Therefore, the presence of insulating layers requires higher applied voltages in the first and second transfer nips


40


,


48


to create the same electrostatic fields operating on the charged composite toner image. The voltage requirement is mainly driven by the “dielectric thickness” of such insulating layers, which is the actual thickness of a layer divided by the dielectric constant of that layer. One potential disadvantage of an insulating layer is that undesirably very high voltages will be required on the intermediate transfer member


12


for good electrostatic transfer of the component toner image if the sum of the dielectric thickness of the insulating layers on the intermediate transfer member


12


is too high. This is especially true in color imaging systems with layers that behave “insulating” over the dwell time longer than one revolution of the intermediate transfer member


12


. Charge will build up on such insulating top layers due to charge transfer in each of the field generation stations


42


. This charge buildup requires higher voltage on the back of the intermediate transfer member


12


in the subsequent field generation stations


42


to achieve good transfer of the subsequent component toner images. This charge can not be fully neutralized between first transfer nips


40


with image conditioning station


46


corona devices without also causing undesirable neutralization or even reversal of the charge of the transferred composite toner image on the intermediate transfer member


12


. Therefore, to avoid the need for unacceptably high voltages on the back of the intermediate transfer member


12


, the total dielectric thickness of such insulating top layers on the intermediate transfer member


12


should preferably be kept small for good and stable transfer performance. An acceptable total dielectric thickness can be as high as about 50 microns, and a preferred value is <10 microns.




The top most layer of the intermediate transfer member


12


preferably has good toner releasing properties such as low surface energy, and preferably has low affinity to oils such as silicone oils. Materials such as PFA, TEFLON™, and various flouropolymers are examples of desirable overcoating materials having good toner release properties. One advantage of an insulating coating over the semiconductive backing layer of the intermediate transfer member


12


is that such materials with good toner releasing properties are more readily available if the constraint of needing them to also be semiconductive is removed. Another potential advantage of high resistivity coatings applies to embodiments that wish to use a transfuse member


50


having a low resistivity top most layer, such as <<10


9


ohm-cm. As discussed, the resistivity for the intermediate transfer member


12


of a single layer is preferably limited to typically around >10


9


ohm-cm to avoid transfer problems in the second transfer nip


48


if the resistivity of the top most layer of the transfuse member


50


is lower than about 10


9


ohm-cm. For a multiple layer intermediate transfer member


12


, having a sufficiently high resistivity top most layer, preferably >10


9


ohm-cm, the resistivity of the back layer can be lower.




Semiconductive coatings on the intermediate transfer member


12


are advantaged in that they do not require charge leveling to level the charge on the intermediate transfer member


12


prior to and between toner image producing stations


22


,


24


,


26


,


28


. Semiconductive coatings on the intermediate transfer member are also advantaged in that much thicker top layers can be allowed compared to insulating coatings. The charge relaxation conditions and the corresponding ranges of resistivity conditions needed to enable such advantages are similar to that already discussed for the back layer. Generally, the semiconductive regime of interest is a resistivity such that the charge relaxation time is smaller than the dwell time spent between toner image producing stations


22


,


24


,


26


,


28


. A more preferred resistivity construction allows thick layers, and this construction is a resistivity range such that the nip relaxation time within the first transfer nip


40


is smaller than the dwell time that a section of the intermediate transfer member


12


takes to move through the first transfer nip


40


. In such a preferred regime of resistivity the voltage drop across the layer is small at the end of the transfer nip dwell time, due to charge conduction through the layer.




The constraint on the lower limit of the resistivity related to the lateral resistivity apply to the semiconductive top most layer, to any semiconductive middle layers, and to the semiconductive back layer of a multiple layer intermediate transfer member


12


. The preferred resistivity range for each such layer is substantially the same as discussed for the single layer intermediate transfer member


12


. Also, the additional constraint on the resistivity related to transfer problems in the second transfer nip


48


apply to the top most layer of a multiple layer intermediate transfer member


12


. Preferably, the top most semiconductive layer of the intermediate transfer member


12


should be typically >10


9


ohm-cm when the top most layer of the transfuse member


50


is typically somewhat less than 10


9


ohm-cm.




Transfer of the composite toner image in the second transfer nip


48


is accomplished by a combination of electrostatic and heat assisted transfer. The field generation station


42


and guide roller


74


are electrically biased to electrostatically transfer the charged composite toner image from the intermediate transfer member


12


to the transfuse member


50


.




The transfer of the composite toner image at the second transfer nip


48


can be heat assisted if the temperature of the transfuse member


50


is maintained at a sufficiently high optimized level and the temperature of the intermediate transfer member


12


is maintained at a considerably lower optimized level prior to the second transfer nip


48


. The mechanism for heat assisted transfer is thought to be softening of the composite toner image during the dwell time of contact of the toner in the second transfer nip


48


. The toner softening occurs due to contact with the higher temperature transfuse member


50


. This composite toner softening results in increased adhesion of the composite toner image toward the transfuse member


50


at the interface between the composite toner image and the transfuse member. This also results in increased cohesion of the layered toner pile of the composite toner image. The temperature on the intermediate transfer member


12


prior to the second transfer nip


48


needs to be sufficiently low to avoid too high a toner softening and too high a resultant adhesion of the toner to the intermediate transfer member


12


. The temperature of the transfuse member


50


should be considerably higher than the toner softening point prior to the second transfer nip to insure optimum heat assist in the second transfer nip


48


. Further, the temperature of the intermediate transfer member


12


just prior to the second transfer nip


48


should be considerably lower than the temperature of the transfuse member


50


for optimum transfer in the second transfer nip


48


.




The temperature of the intermediate transfer member


12


prior to the second transfer nip


48


is important for maintaining good transfer of the composite toner image. An optimum elevated temperature for the intermediate transfer member


12


can allow the desired softening of the composite toner image needed to permit heat assist to the electrostatic transfer of the second transfer nip


48


at lower temperatures on the transfuse member


50


. However, there is a risk of the temperature of the intermediate transfer member


12


becoming too high so that too much softening of the composite toner image occurs on the intermediate transfer member prior to the second transfer nip


48


. This situation can cause unacceptably high adhesion of the composite toner image to the intermediate transfer member


12


with resultant degraded second transfer. Preferably the temperature of the intermediate transfer member


12


is maintained below or in the range of the Tg (glass transition temperature) of the toner prior to the second transfer nip


48


.




The transfuse member


50


is guided in a cyclical path by guide rollers


74


,


76


,


78


,


80


. Guide rollers


74


,


76


alone or together are preferably heated to thereby heat the transfuse member


50


. The intermediate transfer member


12


and transfuse member


50


are preferably synchronized to have the generally same velocity in the transfer nip


48


. Additional heating of the transfuse member is provided by a heating station


82


. The heating station


82


is preferably formed of infra-red lamps positioned internally to the path defined by the transfuse member


50


. Alternatively the heating station


82


can be a heated shoe contacting the back of the transfuse member


50


or other heat sources located internally or externally to the transfuse member


50


. The transfuse member


50


and a pressure roller


84


define a third transfer nip


86


therebetween.




A releasing agent applicator


88


applies a controlled quantity of a releasing material, such as a silicone oil to the surface of the transfuse member


50


. The releasing agent serves to assist in release of the composite toner image from the transfuse member


50


in the third transfer nip


86


.




The transfuse member


50


is preferably constructed of multiple layers. The transfuse member


50


must have appropriate electrical properties for being able to generate high electrostatic fields in the second transfer nip


50


. To avoid the need for unacceptably high voltages, the transfuse member


50


preferably has electrical properties that enable sufficiently low voltage drop across the transfuse member


50


in the second transfer nip


48


. In addition the transfuse member


50


will preferably ensure acceptably low current flow between the intermediate transfer member


12


and the transfuse member


50


. The requirements for the transfuse member


50


depend on the chosen properties of the intermediate transfer member


12


. In other words, the transfuse member


50


and intermediate transfer member


12


together have sufficiently high resistance in the second transfer nip


48


.




The transfuse member


50


will preferably have a laterally stiff back layer, a thick, conformable rubber intermediate layer, and a thin outer most layer. Preferably the thickness of the back layer will be greater than about 0.05 mm. Preferably the thickness of the intermediate conformable layers and the top most layer together will be greater than 0.25 mm and more preferably will be greater than about 1.0 mm. The back and intermediate layers need to have sufficiently low resistivity to prevent the need for unacceptably high voltage requirements in the second transfer zone


48


. The preferred resistivity condition follows previous discussions given for the intermediate transfer member


12


. That is, the preferred resistivity range for the back and intermediate layer of a multiple layer transfuse member


50


insures that the nip relaxation time for these layers in the field generation region of the second transfer nip


48


is smaller than the dwell time spent in the field generation region of the second transfer nip


48


. The expressions for the nip relaxation times and the nip dwell time are substantially the same as the ones discussed for the single layer intermediate transfer member


12


. Thus the specific preferred resistivity range for the back and intermediate layers depends on the system geometry, the layer thickness, the process speed, and the capacitance per unit area of the insulating layers within the transfer nip


48


. Generally, the volume resistivity of the back and intermediate layers of the multi-layer transfuse member


50


will typically need to be below about 10


11


ohm-cm and more preferably will be below about 10


8


ohm-cm for most systems. Optionally, the back layer of the transfuse member


50


can be highly conductive such as a metal.




Similar to the multiple layer intermediate transfer member


12


, the top most layer of the transfuse member


50


can optionally behave “insulating” during the dwell time in the transfer nip


48


(typically >10


12


ohm-cm) or semiconducting during the transfer nip


48


(typically 10


6


to 10


12


ohm-cm). However, if the top most layer behaves insulating, the dielectric thickness of such a layer will preferably be sufficiently low to avoid the need for unacceptably high voltages. Preferably for such insulating behaving top most layers, the dielectric thickness of the insulating layer should typically be less than about 50 microns and more preferably will be less than about 10 microns. If a very high resistivity insulating top most layer is used, such that the charge relaxation time is greater than the transfuse member cycle time, charge will build up on the transfuse member


50


due to charge transfer during the transfer nip


48


. Therefore, a cyclic discharging station


77


such as a scorotron or other charge generating device will be needed to control the uniformity and reduce the level of cyclic charge buildup.




The transfuse member


50


can alternatively have additional intermediate layers. Any such additional intermediate layers that have a high dielectric thickness typically greater than about 10 microns will preferably have a sufficiently low resistivity such to ensure low voltage drop across the additional intermediate layers.




The transfuse member


50


preferably has a top most layer formed of a material having a low surface energy, for example silicone elastomer, fluoroelastomers such as Viton™, polytetrafluoroethylene, perfluoralkane, and other fluorinated polymers. The transfuse member


50


will preferably have intermediate layers between the top most and back layers constructed of a Viton™ or silicone with carbon or other conductivity enhancing additives to achieve the desired electrical properties. The back layer is preferably a fabric modified to have the desired electrical properties.




Alternatively the back layer can be a metal such as stainless steel.




The transfuse member


50


can optionally be in the form of a transfuse roller (not shown), or is preferably in the form of a transfuse belt. A transfuse roller for the transfuse member


50


can be more compact than a transfuse belt and it can also be advantaged relative to less complexity of the drive and steering requirements needed to achieve good motion quality for color systems. However, a transfuse belt has advantages over a transfuse roller such as enabling large circumference for longer life, better substrate stripping capability, and generally lower replacement costs.




The intermediate layer of the transfuse member


50


is preferably thick to enable a high degree of conformance to rougher substrates


70


and to thus expand the range of substrate latitude allowed for use in the printer


10


.




In addition the use of a relatively thick intermediate layer, greater than about 0.25 mm and preferably greater than 1.0 mm enables creep for improved stripping of the document from the output of the third transfer nip


86


. In a further embodiment, thick low durometer conformable intermediate and top most layers such as silicone are employed on the transfuse member


50


to enable creation of low image gloss by the transfuse system with wide operating latitude.




The use of a relatively high temperature on the transfuse member


50


prior to the second transfer nip


48


creates advantages for the transfuse system. The transfer step in the second transfer nip


48


simultaneously transfers single and stacked multiple color toner layers of the composite toner image. The toner layers nearest to the transfer belt interface will be hardest to transfer. A given separation color toner layer can be nearest the surface of the intermediate transfer member


12


or it can also be separated from the surface, depending on the color toner layer to be transferred in any particular region. For example, if a toner layer of magenta is the last stacked layer deposited onto the transfer belt, the magenta layer can be directly against the surface of the intermediate transfer member


12


in some color print regions or else stacked above cyan and/or yellow toner layers in other color regions. If transfer efficiency is too low, a high fraction of the color toners that are close to the intermediate transfer member


12


will not transfer but a high fraction of the same color toner layers that are stacked onto another color toner layer will transfer. Thus for example, if the transfer efficiency of the composite toner image is not very high, the region of the composite toner image having cyan toner directly in contact with the surface of the intermediate transfer member


12


can transfer less of the cyan toner layer than the regions of the composite toner image having cyan toner layers on top of yellow toner layers. The transfer efficiency in the second transfer nip


48


is >95% therefore avoiding significant color shift.




With reference to

FIG. 4

disclosing experimental data on the amount of residual toner left on the intermediate transfer member


12


as a function of the transfuse member


50


temperature. Curve


90


is with electric field, pressure and heat assist and curve


92


is without electric field assist but with pressure and heat assist. A very low amount of residual toner means very high transfer efficiency. The toner used in the experiments has a glass transition temperature range Tg of around 55° C. Substantial heat assist is observed at temperatures of the transfuse member


50


above Tg. Substantially 100% toner transfer occurs when operating with an applied field and with the transfuse member


50


temperature above around 165° C., well above the range of the toner Tg. Preferential temperatures will vary depending on toner properties. In general, operation well above the Tg is found to be advantageous for the heat assist to the electrostatic transfer for many different toners and system conditions.




Too high a temperature of the transfuse member


50


in the second transfer nip


48


can cause problems due to unacceptably high toner softening on the intermediate transfer member side of the composite toner layer. Thus the temperature of the transfuse member


50


prior to the second transfer nip


48


must be controlled within an optimum range. The optimum temperature of the composite toner image in the second transfer nip


48


is less than the optimum temperature of the composite toner image in the third transfer nip


86


. The desired temperature of the transfuse member


50


for heat assist in the second transfer nip


48


can be readily obtained while still obtaining the desired higher toner temperatures needed for more complete toner melting in the third transfer nip


86


by using pre-heating of the substrate


70


. Transfer and fix to the substrate


70


is controlled by the interface temperature between the substrate and the composite toner image. Thermal analysis shows that the interface temperature increases with both increasing temperature of the substrate


70


and increasing temperature of the transfuse member


50


.




At a generally constant temperature of the transfuse member


50


in the second and third transfer nips


48


,


86


, the optimum temperature for transfer in the second transfer nip


48


is controlled by adjusting the temperature of the intermediate transfer member


12


. The temperature of the intermediate transfer member in the second transfer nip can be adjusted by heat sharing. Heat in the portion of the intermediate member in the post-second transfer nip area, can be transferred to the portion of the intermediate member in the pre-second transfer nip area.




Transfuse in the third transfer nip


86


is optimized by preheating of the substrate


70


. Alternatively, for some toner formulations or operation regimes no preheating of the substrate


70


is required.




The substrate


70


is transported and registered by a material feed and registration system


69


into a substrate pre-heater


73


. The substrate pre-heater


73


is preferably formed a transport belt transporting the substrate


70


over a heated platen. Alternatively the substrate pre-heater


73


can be formed of heated rollers forming a heating nip therebetween. The substrate


70


after heating by the substrate preheater


73


is directed into the third transfer nip


86


.





FIG. 5

discloses experimental curves


94


,


96


of a measure of 5 fix called crease as a function of the temperature of the transfuse member


50


for different pre-heating temperatures of a substrate. Curve


94


is for a preheated substrate and a curve


96


for a substrate at room temperature. The results disclose that the temperature of the transfuse member


50


for similar fix level decreases significantly at higher substrate pre-heating curve


94


compared to lower substrate pre-heating curve


96


. Heating of the substrate


70


by the substrate pre-heater


73


prior to the third transfer nip


86


allows optimization of the temperature of the transfuse member


50


for improved transfer of the composite toner image in the second transfer nip


48


. The temperature of the transfuse member


50


can thus be controlled at the desired optimum temperature range for optimum transfer in the second transfer nip


48


by controlling the temperature of the substrate


70


at the corresponding required elevated temperature needed to create good fix and transfer to the substrate


70


in the third transfer nip


86


at this same controlled temperature of the transfuse member


50


. Therefore cooling of the transfuse member


50


prior to the second transfer nip


48


is not required for optimum transfer in the second transfer nip


48


. In other words the transfuse member


50


can be maintained at substantially the same temperature in both the second and third transfer nips


48


,


86


.




Furthermore, the over layer, the intermediate and topmost layers, of the transfuse member


50


can be relatively thick, preferably greater than about 1.0 mm, because no substantial cooling of the transfuse member


50


is required prior to the second transfer nip


48


. Relatively thick intermediate and topmost layers of the transfuse member


50


allows for increased conformability. The increased conformability of the transfuse member


50


permits printing to a wider latitude of substrates


70


without a substantial degradation in print quality. In other words the composite toner image can be transferred with high efficiency to relatively rough substrates


70


.




In addition, the transfuse member


50


is preferably at substantially the same temperature in both the second and third transfer nips


48


,


86


. However, the composite toner image preferably has a higher temperature in the third transfer nip


86


relative to the temperature of the composite toner image in the second transfer nip


48


. Therefore the substrate


70


has a higher temperature in the third transfer nip


86


relative to the temperature of the intermediate transfer member


12


in the second transfer nip


48


. Alternatively, the transfuse member


50


can be cooled prior to the second transfer nip


48


, however the temperature of the transfuse member


50


is maintained above, and preferably substantially above the Tg of the composite toner image. Furthermore, under certain operating conditions, the top surface of the transfuse member


50


can be heated just prior to the second transfer nip


48


.




The composite toner image is transferred and fused to the substrate


70


in the third transfer nip


86


to form a completed document


72


. Heat in the third transfer nip


86


from the substrate


70


and transfuse member


50


, in combination with pressure applied by the pressure roller


84


acting against the guide roller


76


transfer and fuse the composite toner image to the substrate


70


. The pressure in the third transfer nip


86


is preferably in the range of about 40-500 psi, and more preferably in the range 60 psi to 200 psi. The transfuse member


50


, by combination of the pressure in the third transfer nip


86


and the appropriate durometer of the transfuse member


50


induces creep in the third transfer nip to assist release of the composite toner image and substrate


70


from the transfuse member


50


. Preferred creep is greater than 4%. Stripping is preferably further assisted by the positioning of the guide roller


78


relative to the guide roller


76


and pressure roller


84


. The guide roller


78


is positioned to form a small amount of wrap of the transfuse member


50


on the pressure roller


84


. The geometry of the guide rollers


76


,


78


and pressure roller


84


form the third transfer nip


86


having a high pressure zone and an adjacent low pressure zone in the process direction. The width of the low pressure zone is preferably one to three times, or more preferably about two times the width of the high pressure zone. The low pressure zone effectively adds an additional 2-3% creep and thereby improves stripping. Additional stripping assistance can be provided by stripping system


87


, preferably an air puffing system. Alternatively the stripping system


87


can be a stripping blade or other well known systems to strip documents from a roller or belt. Alternatively, the pressure roller can be substituted with other pressure applicators such as a pressure belt.




After stripping, the document


72


is directed to a selectively activatable glossing station


110


and thereafter to a sheet stacker or other well know document handing system (not shown). The printer


10


can additionally provide duplex printing by directing the document


72


through an inverter


71


where the document


72


is inverted and reintroduced to the pre-transfer heating station


73


for printing on the opposite side of the document


72


.




A heat transfer station


66


(see

FIG. 3

) cools the intermediate transfer member


12


after second transfer nip


48


in the process direction and heats the intermediate transfer member before the second transfer nip


48


. The heat transfer station


66


transfers a portion of the heat on the intermediate transfer member


12


from the exit side or post transfer region of the second transfer nip


48


to the entrance side or pre-transfer region of the second transfer nip


48


. The intermediate transfer member is heated by the transfuse member in the second transfer nip. The intermediate transfer member is preferably cooled before it contacts the photoreceptor of the toner image forming station. Organic photoreceptors in particular can exhibit reduced operational life and other performance degradation when heated to over 50 degrees Celsius. Therefor transfer of heat from the intermediate transfer member prior to the first transfer nip can improve overall printer apparatus performance.




The heat transfer station


66


is a heat exchanger having a cooling platen


268


contacting the intermediate transfer member after the second transfer nip in the process direction. Heating platen


270


is placed in contact with the intermediate transfer member prior to the second transfer nip in the process direction. Heat is preferably transferred between the heating and cooling platen by the evaporation and condensation of a liquid


274


. The liquid


274


can be substantially formed of water, alcohol, or other readily evaporative liquids.




Heat pipes


272


connect the heating and cooling platens to provide passages for the liquid


274


and evaporated liquid


274


. The heat pipes


272


are preferably insulated to prevent or reduce condensation of the evaporated liquid on the walls of the heat pipes


272


. Heat is conductively transferred from the intermediate transfer member to the cooling platen


268


.




The cooling platen defines an inner chamber forming a reservoir for the liquid


274


. The cooling platen


268


after absorbing the heat from the intermediate transfer member, heats the liquid


274


causing the liquid to evaporate. The evaporated liquid then by convection rises through at least one heat pipe to the heating platen


270


. The heating platen forms a chamber to receive the evaporated liquid


274


. The evaporated liquid enters the heating platen


270


and condenses to transfer heat to the heating platen. The intermediate transfer member is then conductively heated by the heating platen


270


. The condensed liquid


274


runs by the inherent force of gravity down through the heat pipes


272


to collect back in the reservoir of the cooling platen


268


.




In the preferred embodiment of the invention, no moving components are required to effectively transfer heat between the heating and cooling platens, and therefor there is an energy saving in the overall system. Where the heating and cooling platens cannot be positioned relative to each other to allow for movement of the evaporated liquid, pumps (not shown) can be employed to circulate the evaporated liquid, or more preferably the liquid without the employment of an evaporative cycle. In this embodiment of the invention, the liquid


274


is circulated by a pump between the heating and cooling platens to transfer heat therebetween.




A moderate temperature at the second transfer nip enables rheologic transfer to occur at a lower transfuse member temperature. Rheologic assisted transfer in the second transfer nip will occur at a lower transfuse member temperature if the intermediate transfer member is run at an above ambient temperature. As an example, the below table shows that the rheologic transfer occurs at 120° C. for a long dwell time of 63 ms (a long dwell time will result in a higher transfer-belt temperature).





















E (V/um)




τ (ms)




Process K




Red




Black




Cyan




Magenta





























(E = 0 V/um)




63 ms




0




0.01




0.11




0.01




0.22






(E = 55 V/um)




63 ms




0




0




0.01




0




0.01






(E = 55 V/um)




13 ms




0.46




0.14




0.2




0.15




0.03














The values in the data table are the optical density of the second transfer residual mass density. The temperature of the transfuse member was 120° C. and the dwell time in the second transfer nip was 63 ms. As the data for long dwell-time shows, rheologic transfer (E=0) contributes significantly to the total toner transfer and 100% rheologic transfer was achieved for process black.




Heating of the intermediate transfer member prior the second transfer nip allows the transfuse member to be operated at a relatively lower temperature. Heating the intermediate member above ambient temperature allows heating of the composite toner image by the intermediate member. Therefor the heat required for rheological assist in the second transfer nip does not have to be entirely provided by the transfuse member. Therefor the transfuse member can be operated at a relatively lower temperature. A lower temperature of the transfuse member will increase the operational life of the transfuse member. In addition, the over all power consumption of the printing apparatus can be reduced by the reduced heating of the transfuse member.




In the addition, the recovery of heat from the post-second transfer nip portion of the intermediate transfer member and transfer of that heat to the pre-second transfer nip portion of the intermediate transfer member by the heat transfer station


66


is a component in the overall reduction of power by the entire printing apparatus. The heat transfer station


66


is applicable to both dry powder toner and liquid ink development systems.




A cleaning station


54


engages the intermediate transfer member


12


. The cleaning station


54


preferably removes oil that may be deposited onto the intermediate transfer member


12


from the transfuse member


50


at the second transfer nip. For example, if a preferred silicone top most layer is used for the transfuse member


50


, some silicone oil present in the silicone material can transfer from the transfuse member


50


to the intermediate transfer member


12


and eventually contaminate the image bearing members


30


. In addition the cleaning station


54


removes residual toner remaining on the intermediate transfer member


12


. The cleaning station


54


also cleans oils deposited on the transfuse member


50


by the release agent management system


88


that can contaminate the image bearing members


30


. The cleaning station


54


is preferably a cleaning blade alone or in combination with an electrostatic brush cleaner, or a cleaning web.




A cleaning station


58


engages the surface of the transfuse member


50


past the third transfer nip


86


to remove any residual toner and contaminants from the surface of the transfuse member


50


.




The transfuse member


50


is driven in the cyclical path by the pressure roller


84


. Alternatively drive is provided or enhanced by driving guide roller


74


. The intermediate transfer member


12


is preferably driven by the pressured contact with the transfuse member


50


. Drive to the intermediate transfer member


12


is preferably derived from the drive for the transfuse member


50


, by making use of adherent contact between intermediate transfer member


12


and the transfuse member


50


. The adherent contact causes the transfuse member


50


and intermediate transfer member


12


to move in synchronism with each other in the second transfer nip


48


. Adherent contact between the intermediate transfer member


12


and the toner image producing stations


22


,


24


,


26


,


28


may be used to ensure that the intermediate transfer member


12


moves in synchronism with the toner image producing stations


22


,


24


,


26


,


28


in the first transfer zones


40


. Therefore the toner image producing stations


22


,


24


,


26


,


28


can be driven by the transfuse member


50


via the intermediate transfer member


12


. Alternatively, the intermediate transfer member


12


is independently driven. When the intermediate transfer member is independently driven, a motion buffer (not shown) engaging the intermediate transfer member


12


buffers relative motion between the intermediate transfer member


12


and the transfuse member


50


. The motion buffer system can include a tension system with a feedback and control system to maintain good motion of the intermediate transfer member


12


at the first transfer nips


40


independent of motion irregularity translated to the intermediate transfer member


12


at the second transfer nip


48


. The feedback and control system can include registration sensors sensing motion of the intermediate transfer member


12


and/or sensing motion of the transfuse member


50


to enable registration timing of the transfer of the composite toner image to the substrate


70


.




A gloss enhancing station


110


is preferably positioned down stream in the process direction from the third transfer nip


86


for selectively enhancing the gloss properties of documents


72


. The gloss enhancing station


110


has opposed fusing members


112


,


114


defining a gloss nip


116


there between. The gloss nip


116


is adjustable to provide the selectability of the gloss enhancing. In particular, the fusing members are cammed whereby the transfuse nip is sufficiently large to allow a document to pass through with out substantial contact with either fusing member


112


,


114


that would cause glossing. When the operator selects gloss enhancement, the fusing members


112


,


114


are cammed into pressure relation and driven to thereby enhancement the level of gloss on documents


72


passed through the gloss nip


116


. The amount of gloss enhancement is operator selectable by adjustment of the temperature of the fusing members


112


,


114


. Higher temperatures of the fusing members


112


,


114


will result in increased gloss enhancement. U.S. Pat. No. 5,521,688, “Hybrid Color Fuser,” incorporated herein by reference, describes a gloss enhancing station with a radiant fuser.




The separation of fixing and glossing functions provides operational advantages. Separation of the fixing and glossing functions permits operator selection of the preferred level of gloss on the document


72


. The achievement of high gloss performance for color systems generally requires relatively higher temperatures in the third transfer nip


86


. It also typically requires materials on the transfuse member


50


having a higher heat and wear resistance such as Viton™ to avoid wear issues that result in differential gloss caused by changes in surface roughness of the transfuse member due to wear. The higher temperature requirements and the use of more heat and wear resistant materials generally result in the need for high oil application rates by the release agent management system


88


. In transfuse systems such as the printer


10


increased temperatures and increased amounts of oil on the transfuse member


50


could possibly create contamination problems of the photoreceptors


30


. Printers having a transfuse system and needing high gloss use a thick nonconformable transfuse member, or a relatively thin transfuse member. However, a relatively nonconformable transfuse member and a relatively thin transfuse member fail to have the high degree of conformance needed for good printing on, for example, rougher paper stock.




The use of the gloss enhancing station


110


substantially reduces or eliminates the need for gloss creation in the third transfer nip


86


.




The reduction or elimination of the need for gloss in the third transfer nip


86


therefore minimizes surface wear issues for color transfuse member materials and enables a high life transfuse member


50


with readily available silicone or other similar soft transfuse member materials. It allows the use of relatively thick layers on the transfuse member


50


with resultant gain in operating life for the transfuse member materials and with resultant high conformance for imaging onto rougher substrates. It reduces the temperature requirements for the transfuse materials set with further gain in transfuse material life, and it can substantially reduce the oil requirements in the third transfer nip


86


.




The gloss enhancing station


110


is preferably positioned sufficiently close to the third transfer nip


86


, so the gloss enhancing station


110


can utilize the increased document temperature that occurs in the third transfer nip


86


. The increased temperature of the document


72


reduces the operating temperature needed for the gloss enhancing station


110


. The reduced temperature of the gloss enhancing station


110


improves the life and reliability of the gloss enhancing materials.




Use of a highly conformable silicone transfuse member


50


is an example demonstrated as one important means for achieving good operating fix latitude with low gloss. Critical parameters are sufficiently low durometer for the top most layer of the transfuse member


50


, preferably of rubber, and relatively high thickness for the intermediate layers of the transfuse member


50


, preferably also of rubber. Preferred durometer ranges will depend on the thickness of the composite toner layer and the thickness of the transfuse member


50


. The preferred range will be about 25 to 55 Shore A, with a general preference for about 35 to 45 Shore A range. Therefore preferred materials include many silicone material formulations. Thickness ranges of the over layer of the transfuse member


50


will preferably be greater than about 0.25 mm and more preferably greater than 1.0 mm. Preference relative to low gloss will be for generally thicker layers to enable extended toner release life, conformance to rough substrates, extended nip dwell time, and improved document stripping. In an optional embodiment a small degree of surface roughness is introduced on the surface of the transfuse member


50


to enhance the range of allowed transfuse material stiffness for producing low transfuse gloss. Especially with higher durometer materials and/or low thickness layers there will be a tendency to reproduce the surface texture of the transfuse member. Thus some surface roughness of the transfuse member


50


will tend toward low gloss in spite of high stiffness. Preference will be transfuse member surface gloss number <30 GU.




A narrow operating temperature latitude for good fix with low gloss in transfuse has been demonstrated at relatively high toner mass/area conditions. Toner of size about 7 microns requiring toner masses about 1 mg/cm2 requires a temperature of the transfuse member


50


between 110-120 C. and preheating of the paper to about 85 C. to achieve gloss levels of <30 GU while simultaneously achieving acceptable crease level below 40. However, low mass/area toner conditions have shown increased operating transfuse system temperature range for fix and low gloss. The use of small toner having high pigment loading, in combination with a conformable transfuse member


50


, allows low toner mass/area for color systems therefore extending the operating temperature latitude for low gloss in the third transfer nip


86


. Toner of size about 3 microns requiring toner masses about 0.4 mg/cm2 requires a temperature of the transfuse member


50


between 110-150 C., and paper preheating to about 85 C., to a while simultaneously achieving acceptable crease level below 40.




The gloss enhancing station


110


preferably has fusing members


112


,


114


of Viton™. Alternatively hard fusing members such as thin and thick Teflon™ sleeves/overcoatings on rigid rollers or on belts, or else such overcoatings over rubber underlayers, are alternative options for post transfuse gloss enhancing. The fusing members


112


,


114


, preferably have an top most fixing layer stiffer than that used for the top most layer of the transfuse member


50


, with a high level of surface smoothness (surface gloss preferably >50 GU and more preferably >70 GU). The topmost surface can be alternatively textured to provide a texture to the documents


72


. The gloss enhancing station


110


preferably includes a release agent management application system (not shown). The gloss enhancing station can further include stripping mechanisms such as an air puffer to assist stripping of the document


72


from the fusing members


112


,


114


.




Optionally the toner formulation may include wax to reduce the oil requirements for the gloss enhancing station


110


.




The gloss enhancing station


110


is described in combination with the printer


10


having an intermediate transfer member


12


and a transfuse member


50


. However, the gloss enhancing station


110


is applicable with all printers having transfuse systems producing documents


72


with low gloss. In particular this can include transfuse systems that employ a single transfer/transfuse member.




As a system example, the transfuse member


50


is preferably 120 C. in the third transfer nip


86


, and the substrate


70


is preheated to 85 C. The result is a document


72


having a gloss value 20-30 GU. The fusing members are preferably heated to 120 C. The temperature of the fusing members


112


,


114


is preferably adjustable so different degrees or levels of glossing can be applied to different print runs dependent on operator choice. Higher temperatures of the fusing members


112


,


114


increase the gloss enhancement while lower temperatures will the reduce the amount of gloss enhancement on the document


72


.



Claims
  • 1. A heat transfer station comprising:a transfuse member; an intermediate transfer member defining a transfer nip with said transfuse member, said intermediate transfer member having a pre-transfer nip region and a post-transfer nip region; a cooling platen contacting said intermediate transfer member at said post-transfer nip region and defining a fluid chamber for evaporation of a liquid; an evaporative liquid in said fluid chamber to cool said cooling platen; a heating platen contacting said intermediate transfer member at said pre-transfer nip region and defining a condensation chamber for condensing a gas to heat to said heating platen; and a gaseous passage to allow passage of an evaporated liquid from said cooling platen to said heating platen.
  • 2. A method for transferring heat on a toner image bearing member comprising:contacting a cooling platen containing liquid to a heated image bearing member; evaporating said liquid to form a gas with said heat from said image bearing member; contacting a heating platen to said image bearing member; and condensing said gas on said heating platen to heat said image bearing member.
  • 3. A method for heating and cooling a toner image bearing member defining a transfer nip with a transfuse member comprising:absorbing heat from a post-transfer nip region of the toner image bearing member to cool said toner image bearing member, wherein said absorbing heat from the post-transfer nip region of the toner image bearing member comprises evaporating a liquid; and transferring absorbed heat to a pre-nip region of the toner image bearing member to heat said toner image bearing member.
  • 4. The method of claim 3 wherein said transferring absorbed heat to the pre-nip region of the toner image bearing member comprises condensing a gas to a liquid.
CROSS REFERENCE TO RELATED APPLICATIONS

Priority is claimed from Provisional Application No. 60/172,460, filed Dec. 17, 1999 by Nancy Y. Jia et al, entitled “Heat Transfer Apparatus for an Image Bearing Member.”

US Referenced Citations (4)
Number Name Date Kind
5835830 Fukuda et al. Nov 1998 A
6002907 Berkes Dec 1999 A
6052551 De Cock et al. Apr 2000 A
6088565 Jia et al. Jul 2000 A
Foreign Referenced Citations (1)
Number Date Country
59-129888 Jul 1984 JP
Provisional Applications (1)
Number Date Country
60/172460 Dec 1999 US