Heated roll system for drying printed media

Information

  • Patent Grant
  • 6679599
  • Patent Number
    6,679,599
  • Date Filed
    Thursday, January 31, 2002
    22 years ago
  • Date Issued
    Tuesday, January 20, 2004
    20 years ago
Abstract
A system and method for drying a printed medium includes a heated roll and a transport mechanism which moves the printed medium against the heated roll to dry the printed medium.
Description




TECHNICAL FIELD




The present invention relates to inkjet printing, and more particularly to a method and system for drying a printed document.




BACKGROUND OF THE INVENTION




Inkjet printing has commonly been used for printing conventional documents, but is increasingly common in printing color photographs as well. Many inkjet printouts remain wet for several seconds, and even several minutes or hours, after printing, making them vulnerable to smearing. This relatively long drying time requires the printed medium to be handled carefully before it is completely dry to avoid damage.




SUMMARY OF THE INVENTION




Accordingly, the present invention is directed to a system for drying a printed medium, comprising a heated roll and a transport mechanism for moving the printed medium against the heated roll to dry the printed medium.




The invention is also directed to an inkjet printing mechanism having a system for drying a printed medium comprising a heated roll, a backing roll, and a transport mechanism for moving the printed medium between the heated roll and the backing roll to dry the printed medium.




The invention is further directed to a method for drying a printed medium, comprising the steps of disposing a heated roll in a medium transport path and transporting the printed medium along the medium transport path against the heated roll to dry the printed medium.




Further aspects and embodiments of the invention will be apparent from the description and claims set forth below.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a representative diagram illustrating one embodiment of the inventive system;





FIG. 2

is a representative diagram illustrating another embodiment of the inventive system during a drying process;





FIG. 3

is a representative diagram of the system shown in

FIG. 2

during a repositioning process;





FIG. 4

is a representative diagram of the system shown in

FIG. 2

during a fusing process;





FIG. 5

illustrates yet another embodiment of the inventive system.











DETAILED DESCRIPTION OF THE EMBODIMENTS




To improve image quality, durability, and permanence, a thermal transfer overcoat (“TTO”) is often applied as a laminate to printed inkjet media, such as plain office paper or photo media, although other medias may also be overcoated in some implementations, such as fabric media. However, the TTO should not be applied to the image until the ink is sufficiently dry; otherwise, the application process may compromise image quality. The ink drying time depends on both the type of media used in the printed document and the amount of ink saturation in the printed image. For some papers, such as plain office papers or porous photo media, the drying process occurs quickly enough to allow for almost immediate application of the TTO. But for other papers, such as swellable media, the ink will not be dry enough for TTO application on the order of minutes or even hours. Although it is possible to simply wait for the ink to dry before applying the TTO, the long drying period makes the total printing process slow and inconvenient for some users.




The illustrated embodiments of the invention generally involve using a heated roll


100


to dry printed media. Although the examples discussed below focus on drying inkjet printed media, the illustrated drying system may be incorporated into any printing system or method where a drying mechanism is desired.




The heated roll


100


may be made from any material having a high specific heat, such as a metal, to optimize heat retention and heat transfer to the printed medium. Fuser rolls, which may be similar to those used in laser printers, may be incorporated into an inkjet printing mechanism, such as printer


90


, to carry out the drying process. A variety of different inkjet printing mechanisms may employ the system described herein, such as plotters, cameras, facsimile or multi-function hardcopy devices, as well as auxiliary devices for use in conjunction with such printing mechanisms, but for convenience, a printer


90


is illustrated and described. The illustrated printer


90


defines a printzone


92


in which ink


94


is selectively deposited by one or more printheads


96


of one or more inkjet cartridges


98


. A variety of different suitable ink application systems are known to those skilled in the art, such as those employing reciprocating printheads which scan across the printzone


92


or those that are stationary during printing and span the entire printzone


92


, known in the art as page-wide-array print bars, which for diagrammatic purposes may also be illustrated by cartridge


98


. Other heated roll


100


characteristics, such as size, hardness and applied pressure, may be adjusted according to desired printing and drying characteristics and will be described in greater detail below.





FIGS. 1 through 5

illustrate possible system configurations


101


,


200


and


300


respectively, incorporating the heated roll


100


for drying printed media. The systems


101


,


200


,


300


may use any known paper transport mechanism to move the paper along its paper path, such as drive roller systems or belt transport systems with or without a vacuum hold-down assist.

FIG. 1

is a representative diagram of a system


100


that includes a drying slot


102


and a separate overcoating slot


104


. In this example, a sheet of media


106


first receives a printed image in printzone


92


. The backside


92


′ of the media


106


may either be a blank surface or a surface that has already been printed and dried. Following printing, the printed sheet


106


is first placed in the drying slot


102


and travels along a transport path


103


through a nip


108


formed between the heated roll


100


and a backing roll


110


. Further, in this particular example, the sheet


106


′ travels through the nip


108


with its printed side against the heated roll


100


and its back side against the roll


110


so that the contact and heat from the heated roll


100


will dry the ink. Note that the printed side does not necessarily need to contact the heated roll


100


step and that the printed media may have any orientation that allows the heated


100


to dry the ink.




Allowing the sheet


106


′ to travel along the transport path


103


through the nip


108


while the ink is still wet does create some risk of damaging the image, but the nip area and pressure in the nip


108


may be adjusted to accommodate different paper and ink characteristics to minimize this risk. For example, if the sheet contains a photographic image printed on swellable media, the desired nip characteristics would be different than if the sheet had simple text printed on conventional paper (e.g., simple text tends to be insensitive to nip characteristics) because photographic images, in general, are more saturated with ink and require a longer drying time than plain text.




In this and other embodiments, the area in the nip may be increased by increasing the roll pressure and/or decreasing the roll hardness. For example, vulcanized rubber may be used to decrease the roll hardness, while steel or another metal may be used to increase roll hardness. A larger nip area


108


distributes the pressure from the heated roll


100


over a greater surface area on the printed sheet


106


′. At first glance, allowing contact between the heated roll


100


and the sheet


106


′ would appear to increase the likelihood that the image will be damaged during the drying process. However, the combined heat and pressure in the nip over a larger area actually promotes rapid drying and reduces or eliminates potential damage to the image for certain ink/paper types, which is an unexpected result.




Alternatively, increasing the heated roll


100


hardness and/or reducing the roll pressure using a pressure adjustment mechanism


111


that moves in the direction of vertical arrow


111


′ reduces the nip area, creating a system that is gentler to the printed sheet


106


′. The system shown in

FIG. 1

may even be constructed without the nip roll


110


to eliminate the nip altogether; in this case, the sheet


106


′ preferably travels through the drying slot


102


printzone side


92


up, with its back side


92


′ against the heated roll


100


, allowing the sheet


106


′ to dry through heat absorption. Reducing or eliminating nip pressure on the sheet does reduce the risk of damage, but it also tends to increase drying time and also may potentially complicate the paper path when the drying system is incorporated into a printer. Alternatively, the nip roll


110


may be constructed as a series of star-wheel rollers mounted on a common shaft, similar to hose used in the output path of some inkjet printing mechanisms.




Regardless of the specific nip characteristics, the heated roll


100


may be coated with a non-wetting material to further reduce possible damage to the image from the roll's surface. The non-wetting material may be, for example, a polyethylene, polypropylene, silcone rubber or Teflon(R). An optional heater or fan


107


may also be included to further aid the drying process. For instance, if the heater or fan


107


moved upwardly from the view of

FIG. 1

as indicated by the vertical arrow


107


′, an air flow (heated or unheated) could be directed toward the nip


108


to assist in drying and/or removing moisture in the air adjacent the nip


108


.




After the entire sheet has been dried by the heated roll


100


, it may be ejected out of the drying slot


102


as indicated by arrow


103


′. At this point, the dried sheet


106


″ should be dry enough for safe handling without damaging the printed image. If thermal transfer overcoat (TTO) material application is desired, the dried sheet


106


″ may be inserted into a separate overcoating slot


104


, in the system


101


of

FIG. 1

with its back (unprinted) side


92


′ preferably facing the heated roll


100


. The dried sheet


106


″ and a TTO sheet


112


travel inwardly together along a second transport path


113


through a second nip


114


formed by the heated roll


100


and a second nip roll


116


. Transport path


113


′ indicates the direction of travel for the sheet traveling back out or exiting through the second nip


104


following processing. The TTO sheet


112


used in this embodiment includes TTO material


118


disposed on a carrier substrate or backing layer


120


and is dispensed from a dispenser roll


122


. The second nip roll


116


may be a conventional backing roll or a heated roll as long as the total amount of generated heat and the nip pressure is sufficient to melt the TTO material


118


away from the substrate


120


and deposit the overcoat


118


onto the printed side of the sheet


106


, with the overcoated sheet then being indicated as


106


′″. After the TTO material


118


is removed from the substrate


120


, the empty substrate


120


may be rolled onto a take-up roll


124


for easy disposal.




As can be seen in

FIG. 1

, the second nip


114


presses the TTO composite sheet


112


and printed sheet


106


together. The heat from the heated roll


100


combined with the nip pressure releases the TTO coating


118


from the substrate


120


and fuses the TTO coating


118


to the printed side of the sheet


106


″, emerging as coated sheet


106


′″. Once the combined heat and nip pressure fuses the TTO coating


118


to the image surface, preferably the second nip roil


116


moves away from the heated roll


100


under the power of a roll movement mechanism


125


, shown schematically in FIG.


1


and which may be constructed as described above for mechanism


111


, or using other movement mechanisms known in the art. Element


125


′ illustrates the direction of travel of nip roll


116


movement towards (and away from) the heated roll


100


. This action then opens the second nip


114


and frees the coated sheet


106


′″ for ejection. In the configuration shown in

FIG. 1

, the same heated roll


100


dries the printed sheet


106


′ and fuses the TTO coating


118


onto the sheet


106


″, reducing the number of components in the system


101


. Optionally, the fan or heater unit


107


may move downwardly to assist in the overcoating process.




As noted above, however, allowing contact between the freshly printed sheet


106


and the heated roll


100


may potentially damage the printed image because the roll


100


needs to touch the image before it is completely dry to complete the drying process. Because of this potential risk, the configuration shown in

FIG. 1

may be more appropriate where a compact system is a higher priority than minimal image damage risk.





FIGS. 2 through 4

illustrate an alternative embodiment


200


where the drying process occurs without any contact between the heated roll


100


and the printed portion of the sheet


106


′. This configuration may be used in cases where the paper and/or ink characteristics makes early contact between the image and the heated roll


100


undesirable. In this embodiment, the sheet


106


′ passes between the same heated roll


100


and nip roll


110


twice, once to dry the image and once to apply the TTO


108


. Of course, if the image does not require TTO application, the sheet


106


′ passes between the rolls


100


,


110


only once to dry the image.





FIG. 2

illustrates the system configuration


200


during the drying step. The transport path


201


in this embodiment first passes the sheet


106


over the heated roll


100


, with its back side


92


′ against the heated roll


100


and its printed side


92


facing the nip roll


110


. Further, this embodiment incorporates a duplexer


202


that flips the printed sheet


106


′ between drying and coating steps, as will be explained in greater detail below. During this first pass, the nip roll


110


is spaced apart from the heated roll


100


so that the printed surface does not contact any roll surface. In this embodiment, heat absorbed by the sheet


106


′ and heat convection surrounding the sheet


106


dries the printed surface on the sheet


106


′. To improve convection and further decrease the drying time, an optional dryer


204


, such as a fan, may circulate air near the space between the heated roll


100


and the nip roll


110


. Once the sheet


106


″ is sufficiently dry, it may either be removed from the system


200


or recirculated through the system


200


for TTO application, as described below with respect to FIG.


3


.





FIG. 3

illustrates a repositioning process that flips and positions the sheet


106


for TTO application. After the drying process shown in

FIG. 2

, the sheet


106


in this example is transported along a transport path


201


′ between a guide roll


130


and the duplexer


202


by way of a second guide roll


131


, with the duplexer


202


further guiding the dried sheet


106


″ in the direction of transport path arrow


201


′. Element


202


′ illustrates a possible path of travel associated with duplexer


202


. Note that the duplexer


202


can reposition the sheet


106


″ in ways other than that illustrated in FIG.


3


. Once the entire entire sheet


106


″ clears the nip formed by the duplexer


202


and its associated guide roll


130


, the printzone


92


will be facing the heated roll


100


during the TTO application process, as shown in FIG.


4


. Although

FIG. 3

illustrates one method for flipping the dried sheet


106


″, any duplexer can be incorporated into this embodiment to flip the sheet


106


″ in any manner.





FIG. 4

illustrates the system configuration of

FIGS. 2 and 3

during the TTO application process. As shown in

FIG. 3

, the nip roll


110


and the heated roll


100


move closer to each other to form a nip


206


through which both the dried printed sheet


106


″ and the TTO sheet


112


travel. Before starting the second pass over the heated roll


100


, the printed sheet


106


″ is inverted using any known paper-flipping mechanism so that the printed side


92


, rather than the back side


92


′, faces the heated roll


100


. This arrangement allows the TTO material


118


to contact the printed side of the sheet


106


″ (the printzone


92


) in the nip


206


. As the TTO sheet


112


and the printed sheet


106


″ pass through the nip


206


together along a transport path


201


′″, the nip pressure and heat releases the TTO material


118


from its supporting substrate


120


and fuses the TTO material


118


onto the printed side


92


of the sheet


106


″, resulting in coated sheet


106


′″. Like the configuration shown in

FIG. 1

, the TTO sheet


112


may be unrolled from a dispensing roll


122


and the bare substrate


120


rolled into a take-up roll


124


for easy disposal. Once the TTO material


118


is fused onto the printed side of the sheet


106


″, the coated sheet


106


′″ is ready to be removed from the system


200


.




Because the printed sheet


106


′ passes through the same system


200


for both the drying and the TTO application process, a user does not have to reinsert the sheet


106


′ into the system through two different slots as is required in the embodiment shown in FIG.


1


. The embodiment shown in

FIGS. 2

,


3


and


4


do allow the sheet


106


′ to travel the same transport path


201


twice, decreasing the number of pages that may be printed, dried and coated per minute as well. Further, drying the sheet


106


′ without allowing contact between the printzone


92


and the heated roll


100


tends to increase drying time, decreasing the page per minute rate even further. Despite these potential disadvantages, the lack of contact between the heated roll


100


and the freshly-printed image greatly reduces the risk of image damage and ensures consistent, high-quality TTO coated images in applications where image quality is a higher priority than print speed and minimized system size.




The configuration


300


shown in

FIG. 5

optimizes both printing speed and reduced space. In this embodiment, the sheet


106


is printed by the printer


90


as shown in the Figure. The printed sheet


106


′ then travels along the transport path


301


over the heated roll


100


with its back surface


92


′ against the heated roll


100


to dry the printed image. An optional fan or a supplemental heater


204


disposed near the heated roll


100


circulates air around the sheet


106


′ to improve drying efficiency. Because the system


300


in

FIG. 5

transports the dried printed sheet


106


″ only about halfway around the heated roll


100


before TTO application begins, the fan or heater


204


ensures that the sheet


106


″ is dry enough to prevent the TTO application process from damaging the printed image.




During TTO application, the dried printed sheet


106


″ continues to travel along the transport path


301


, without retracing any previous path portions, through a nip


302


formed by the heated roll


100


and a second heated roll


204


. The TTO medium


112


is also trapped between the two heated rolls


100


,


304


, causing the TTO material


118


to melt away from the substrate


120


and fuse to the printed side


92


of the sheet


106


″. As in the other embodiments, the TTO material


118


may be dispensed from a dispensing roll


122


and the substrate may be collected onto a take-up roll


124


. The coated sheet


106


′″ may then continue along its transport path until it is ejected from the system


300


. The dual functionality of the heater roll


100


and the continuous paper path in this embodiment provides a compact system design that dries and coats sheets quickly.




Note that any roll combination may be used in the inventive system


101


,


200


,


300


as long as it contains at least one heated roll


100


. For example, the system


101


,


200


,


300


may incorporate two heated rolls to form the nip, thereby heating the printed sheet


106


′ simultaneously on its printed side


92


and its back side


92


′ to increase drying efficiency. Using two heated rolls also facilitates melting and transfer of the TTO material onto the printed and dried sheet


106


″. The residual heat from the drying process also helps improve TTO application. Also, although the illustrated embodiments show systems acting as both a dryer and a fuser, the TTO sheet


112


may be omitted from these embodiments to operate the system as a dryer only.




Allowing the heated roll


100


to contact the wet image surface without damaging the image is an unexpected result of the invention. Further, using the heated roll


100


in an inkjet printer is a novel approach to drying inkjet printed images because heated rolls


100


are normally used as fuser rolls in laser printers. In one embodiment, incorporating a laser printer fuser roll into an inkjet printer as a dryer roll uses an existing component in a novel manner.




The optimum parameters for the wait time between printing and fusing, the amount of nip pressure, transport speed through the system, and the heated roll temperatures for drying and fusing may all be varied to ensure that the system dries and coats printed media without compromising print quality. Experimental results have shown that a heated roll temperature between 90° C. and 160° C. dries the printed media without damaging image quality. The delay between the printing and the overcoating steps also affects the final print image quality; during testing, a 10 second delay tended to smear most images, while a 20 second delay resulted in varying print quality. A wait time of 40-60 seconds virtually eliminated smearing, although some there was dye migration in some cases. The optimum parameters may be different in different printing systems, for differing amounts of ink laid on the sheet


106


and for different media, and these specific parameters can be deduced by those of skill in the art without undue experimentation.




As a result, the invention leverages a fuser assembly, which is normally used in laser printers, into a drying system for drying an inkjet-printed document. The invention also may use the fuser assembly to apply the TTO overcoat, providing an efficient way to apply the overcoat to slow-drying print media without adding a separate heating and drying element to the printer. Even though the heated roll


100


contacts the printed image while it is still wet, the invention unexpectedly decreases the image drying time without damaging the image. The inventive system may be incorporated into existing print engine mechanisms to lower the cost and complexity of the TTO engine and the drying engine. Further, by using the same nip to both dry the printed image and to fuse the TTO material


118


, as shown in FIGS.


2


,


3


, and


4


, the system simplifies the paper transport path and keeps the system relatively compact.




Note that any of the embodiments described may be used as solely as a dryer or as a fuser without departing from the scope of the invention. For example, the invention may be used to apply TTO material to a document printed by a different printer, or even printed using a system other than an inkjet system.




It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.



Claims
  • 1. A system for drying a printed medium, comprising:a heated roll; a transport mechanism which moves the printed medium against the heated roll to dry the printed medium; a first backing roll and a second backing roll, wherein the heated roll and the first backing roll form a first nip, the heated roll and the second backing roll form a second nip, the print medium passes between the first nip and the second nip; and the first nip dries the printed medium and the second nip presses and fuses a separate thermal transfer overcoat sheet to the printed medium.
  • 2. The system of claim 1, wherein the transport mechanism includes a first transport path that moves the printed medium into the first nip and a second paper path separate from the first transport path that moves the printed medium and the thermal transfer overcoat into the second nip.
  • 3. The system of claim 1, wherein the backing roll is selectably movable between a first position where the backing roll and heated roll are at a first distance from each other, and a second position where the backing roll and the heated roll are a second distance away from each other to form a nip, with the second distance being smaller than the first distance.
  • 4. The system of claim 3, wherein the backing roll is at the first position to dry the printed medium in a drying process and at the second position to fuse a thermal transfer overcoat material to the printed medium in a fusing process.
  • 5. The system of claim 4, wherein the transport mechanism transports the printed medium such that a back surface of the printed medium faces the heated roll during the drying process and inverts the printed medium such that a printed surface of the printed medium faces the heated roll during the fusing process.
  • 6. The system of claim 1, wherein the backing roll is heated.
  • 7. The system of claim 1, wherein the transport mechanism wraps the printed medium around the heated roll before passing the printed medium between the heated roll and the backing roll.
  • 8. The system of claim 7, wherein the printed medium and a thermal transfer overcoat sheet travel into a nip formed by the heated roll and the backing roll to fuse the thermal transfer overcoat to the printed medium.
  • 9. The system of claim 1, further comprising a dryer that generates at least one of heat convection and air convection and is disposed along a transport path of the printed medium.
  • 10. The apparatus of claim 1, wherein at least one of the heated roll and the backing roll is coated with a non-wetting material.
  • 11. An inkjet printing mechanism having a system for drying a printed medium, comprising:a heated roll; a first backing roll; a second backing roll; and a transport mechanism which moves the printed medium between the heated roll and the backing roll to dry the printed medium; wherein the heated roll and the first backing roll form a first nip that dries the printed medium, and the heated roll and the second backing roll form a second nip that presses and fuses a separate thermal transfer overcoat sheet to the printed medium.
  • 12. The inkjet printing mechanism of claim 11, wherein the backing roll is selectably movable between a first position where the backing roll and heated roll are at a first distance from each other to dry the printed medium in a drying process and a second position where the backing roll and the heated roll are a second distance away from each other to form a nip, the second distance being smaller than the first distance, to fuse a thermal transfer overcoat material to the printed medium in a fusing process.
  • 13. The inkjet printing mechanism of claim 12, wherein the transport mechanism transports the printed medium such that a back surface of the printed medium faces the heated roll during the drying process and inverts the printed medium such that a printed surface of the printed medium faces the heated roll during the fusing process.
  • 14. The inkjet printing mechanism of claim 11, wherein the transport mechanism wraps the printed medium around the heated roll before passing the printed medium between the heated roll and the backing roll.
  • 15. The inkjet printing mechanism of claim 14, wherein the printed medium and a thermal transfer overcoat sheet travel into a nip formed by the heated roll and the backing roll to fuse the thermal transfer overcoat to the printed medium.
  • 16. A method for drying a printed medium, comprising:disposing a heated roll in a medium transport path; transporting the printed medium along the medium transport path through a first nip formed by the heated roll and a first backing roll and in communication and against the heated roll to dry the printed medium; and transporting the printed medium through a second nip formed by the heated roll and a second backing roll to fuse a separate thermal transfer overcoat sheet to the printed medium.
  • 17. The method of claim 16, further comprising:selectively moving the heated roll and a backing roll between a first position where the heated roll and the backing roll are at a first distance from each other, and a second position where the heated roll and the backing roll are at a second distance smaller than the first distance from each other, the second position forming a nip; and drying the printed medium by transporting the printed medium between the heated roll and the backing roll at the first position.
  • 18. The method of claim 17, further comprising:fusing a thermal transfer overcoat material to the printed medium by transporting the printed medium and a thermal transfer overcoat sheet in the nip formed at the second position.
  • 19. The method of claim 18, further comprising:inverting the printed medium before applying the thermal transfer overcoat such that a back surface of the printed medium faces the heated roll during the drying step and a front surface of the printed medium faces the heated roll during the fusing step.
  • 20. The method of claim 16, further comprising:wrapping the printed medium around the heated roll before passing the printed medium between the heated roll and the backing roll; and fusing a thermal transfer overcoat material to the printed medium by transporting the printed medium and a thermal transfer overcoat sheet into a nip formed by the heated roll and the backing roll.
  • 21. An inkjet printing apparatus, comprising: means for transporting a printed medium along a medium transport path, the printed medium including a first side and a second side; means for drying the printed medium in the medium transport path, the drying means including a heated roll and a first backing roll for heating the second side of the medium and an additional heating means for heating the first side of the medium; and means for introducing a separate thermal transfer overcoat sheet to the printed medium at a nip formed between said heated roll and a second backing roll and fusing the thermal transfer overcoat sheet to the first side of the printed medium.
  • 22. The inkjet printing apparatus of claim 21, wherein the transporting means wraps the printed medium around the heated roll before passing the printed medium between the heated roll and the backing roll, and wherein the fusing means is a nip formed by the heated roll and the backing roll.
  • 23. The inkjet printing apparatus of claim 21, further comprising means for selectively moving the heated roll and a backing roll between a first position where the heated roll and the backing roll are at a first distance from each other, and a second position where the heated roll and the backing roll are at a second distance smaller than the first distance from each other to form a nip.
  • 24. A printer comprising: a heated roll; a transport mechanism that moves a first side of a printed medium against the heated roll; a heater that heats a second side of the printed medium; a first backing roll that forms a first nip with the heated roll; a means for supplying a thermal transfer overcoat to a second nip formed by the heated roll and a second backing roll; a means for transporting the printed medium to the second nip such that the printed medium passes through the second nip and the overcoat sheet is fused to the second side of the printed media.
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