Patent Publication Number: US-2006007495-A1

Title: Image-forming method and device utilizing a shim member arrangement

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      Reference is made to commonly-assigned U.S. Patent Applications: Ser. No. 10/722,248 filed Nov. 25, 2003, entitled AN IMAGE FORMING DEVICE HAVING A BRUSH TYPE PROCESSING MEMBER to Alphonse D. Camp et al.; Ser. No. 10/851,886 filed May 21, 2004, entitled AN IMAGE FORMING DEVICE HAVING A BELT TYPE PROCESSING MEMBER WITH MICRO-FEATURES to Zhanjun Gao et al.; Ser. No. 10/874,888 filed Jun. 23, 2004, entitled AN IMAGE FORMING DEVICE AND AN EXPOSURE MEMBER FOR THE DEVICE to Alphonse D. Camp; Ser. No. 11/184,756 filed Jul. 19, 2005 entitled AN IMAGE-FORMING DEVICE HAVING BRUSH/DRUM PROCESSOR to Ralph L. Piccinino, Jr. et al. and Ser. No. ______ (Docket 89571) filed ______ entitled AN IMAGE-FORMING DEVICE HAVING AN EXPOSING/PROCESSING PLATEN to Ralph L. Piccinino, Jr. et al. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to an image forming method and device adapted to develop images on photosensitive media that includes microcapsules that encapsulate material such as coloring material. The device and method of the present invention includes the use of a thin shim member during a pressure develop of the media to minimize artifacts on the media.  
     BACKGROUND OF THE INVENTION  
      Image forming devices are known in which media having a layer of microcapsules containing a chromogenic material and a photohardenable composition, and a developer, which may be in the same or a separate layer from the microcapsules, is image-wise exposed. In these devices, the microcapsules are ruptured, and an image is produced by the differential reaction of the chromogenic material and the developer. More specifically, in these image-forming devices, after exposure and rupture of the microcapsules, the ruptured microcapsules release a color-forming agent, whereupon the developer material reacts with the color-forming agent to form an image. The image formed can be viewed through a transparent support or a protective overcoat against a reflective white support as is taught in, for example, U.S. Pat. No. 5,783,353 and U.S. Publication No. 2002/0045121 A1. Typically, the microcapsules will include three sets of microcapsules sensitive respectively to red, green and blue light and containing cyan, magenta and yellow color formers, respectively, as taught in U.S. Pat. No. 4,772,541. Preferably a direct digital transmission imaging technique is employed using a modulated LED print head to expose the microcapsules.  
      Conventional arrangements for developing the image formed by exposure in these image-forming devices include using spring-loaded balls, micro wheels, micro rollers or rolling pins, and heat from a heat source is applied after this development step to accelerate development.  
      The photohardenable composition in at least one and possibly all three sets of microcapsules can be sensitized by a photoinitiator such as a cationic dye-borate complex as described in, for example, U.S. Pat. Nos. 4,772,541; 4,772,530; 4,800,149; 4,842,980; 4,865,942; 5,057,393; 5,100,755 and 5,783,353.  
      The above-described imaging technology utilizes light sensitive microcapsules incorporated into a photographic coating, and produces a continuous tone digital imaging member. With regard to the media used in this technology, a substrate is coated with millions of light sensitive microcapsules, which contain either cyan, magenta or yellow image forming dyes (in leuco form). The microcapsule comprises a monomer and the appropriate cyan, magenta or yellow photoinitiator that absorb red, green or blue light respectively. Exposure to light, after the induction period is reached, induces polymerization.  
      When exposure is made, the photoinitiator absorbs light and initiates a polymerization reaction, converting the internal fluid (monomer) into polymer, which binds or traps leucodye from escaping when pressure is applied.  
      With no exposure, microcapsules remain soft and are easily broken, permitting all of the contained dye to be expelled into a developer containing binder and developed which produces the maximum color available. With increasing exposure, an analog or continuous tone response occurs until the microcapsules are completely hardened, to thereby prevent any dye from escaping when pressure is applied.  
      Conventionally, as describe above, in order to develop the image, pressure is uniformly applied across the image. As a final fixing step, heat is applied to accelerate color development and to react all un-reacted liquid from the microcapsules. This heating step also serves to assist in the development of available leucodye for improved image stability. Generally, pressure ruptured capsules (unhardened) expel luecodye into the developer matrix.  
      Approximately 100 mega Pascal or 14,500 psi normal pressure was required for capsule crushing as documented in prior art. This application of pressure (high compressive forces) on a small surface area of the media by way of, for example, a stylus or rollers tended to create artifacts such as scratches or surface deformations on the media. As an example, the rollers for conventional pressure development apparatuses utilized hard metallic rollers or balls as the processing rollers (balls) on the media to deliver high stress to the microcapsules. Since the required stress to rupture the microcapsules are rather high, significant stress or deformation are also observed in the media support. As a result of such high stress or deformation, defects in the media support can be seen on the image side of the media as random patterns that compromise the quality of the image. More specifically, the compression forces required for processing may make an “image” of the fiber pattern in the print, thus making the print corrupt.  
      It would be advantageous to provide a means or method of processing that utilized pressure application members such as rollers or styluses but minimized or eliminated the creation of artifacts on the media from the compressive forces.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to eliminate or reduce unwanted random patterns from an image caused by compressive forces of a pressure development member by reducing the stress on the media support while maintaining the required high stress on the microcapsule. The present invention provides for an image-forming device having a pressure application member that utilizes a shim member between the media and the pressure application member. The arrangement of the present invention enables the application of pressure to develop a latent image on microencapsulated media in a manner in which the stress on the media support is reduced while the pressure on the imaging side of the media is sufficient to enable the development of the latent image.  
      The present invention therefore relates to an image forming method that comprises exposing a photosensitive medium comprising a plurality of microcapsules which encapsulate imaging material to form a latent image; placing a thin member over an imaging surface of the photosensitive medium; and applying a pressure to the medium by pressing on the thin member, with the pressure being sufficient to cause a compressive force to be applied to the imaging side of the photosensitive medium to rupture selected microcapsules, and cause a release of imaging material from the microcapsules to develop the latent image on said photosensitive medium. The thin member is adapted to protect the imaging surface of the photosensitive medium during the applying step to minimize artifacts on the photosensitive medium from the compressive force.  
      The present invention further relates to an image forming device that comprises an imaging member adapted to expose a photosensitive medium to form a latent image on the photosensitive medium, with the photosensitive medium comprising a plurality of microcapsules which encapsulate imaging material; a shim member arrangement configured to locate a thin member over the imaging side of the photosensitive medium; and a processing member adapted to develop the latent image, with the processing member comprising a pressure application member adapted to contact the thin member and apply a compressive force to the imaging side of said photosensitive medium that is sufficient to rupture selected microcapsules and cause a development of the latent image on the photosensitive medium, and the thin member being adapted to protect the imaging side of said photosensitive medium to minimize artifacts on said photosensitive medium from the compressive force. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  schematically shows an image-forming device;  
       FIG. 1B  schematically shows an example of a pressure applying system that can be used in the image-forming device of  FIG. 1 ;  
       FIG. 2  is a schematic illustration of an image-forming device in accordance with the present invention;  
       FIG. 3  is a side view of the image-forming device of  FIG. 2 ;  
       FIG. 4  is a schematic view of an image-forming device in accordance with a second embodiment; and  
       FIG. 5  is a side view of the device of  FIG. 4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to the drawings, wherein like reference numerals represent identical or corresponding parts throughout the several views,  FIG. 1A  is a schematic view of an image-forming device  15  pertinent to the present invention. Image forming device  15  could be, for example, a printer that includes an opening  17  that is adapted to receive a cartridge containing photosensitive media. As described in U.S. Pat. No. 5,884,114, the cartridge could be a light tight cartridge in which photosensitive sheets are piled one on top of each other. When inserted into image forming device  15 , a feed mechanism that includes, for example, a feed roller  21   a  in image forming device  15 , working in combination with a mechanism in the cartridge, cooperate with each other to pull one sheet at a time from the cartridge into image forming device  15  in a known manner. Although a cartridge type arrangement is shown, the present invention is not limited thereto. It is recognized that other methods of introducing media into to the image-forming device such as, for example, individual media feed or roll feed are applicable to the present invention.  
      Once inside image forming device  15 , photosensitive media travels along media path  19 , and is transported by, for example, drive rollers  21  connected to, for example, a driving mechanism such as a motor. The photosensitive media will pass by an imaging member  25  in the form of an imaging head that could include a plurality of light emitting elements (LEDs) that are effective to expose a latent image on the photosensitive media based on image information. After the latent image is formed, the photosensitive media is conveyed past a processing assembly or a development member  27 . Processing assembly  27  could be a pressure applicator or pressure assembly, wherein an image such as a color image is formed based on the image information by applying pressure to microcapsules having imaging material encapsulated therein to crush the microcapsules. The pressure could be applied by way of spring-loaded balls, micro wheels, micro rollers, rolling pins, etc.  
       FIG. 1B  schematically illustrates an example of a pressure applicator  270  for processing assembly  27  which can be used in the image-forming device of  FIG. 1A . In the example of  FIG. 1B , pressure applicator  270  is a crushing roller arrangement that provides a point contact on photosensitive medium  102 . More specifically, pressure applicator  270  includes a support  45  that extends along a width-wise direction of photosensitive medium  102 . Moveably mounted on support  45  is a crushing roller arrangement  49  that is adapted to move along the length of support  45 , i.e., across the width of photosensitive medium  102 . Crushing roller arrangement  49  is adapted to contact one side of photosensitive medium  102 . A beam or roller type member  51  is positioned on an opposite side of photosensitive medium  102  and can be provided on a support or spring member  57 . Beam or roller type member  51  is positioned so as to contact the opposite side of photosensitive medium  102  and is located opposite crushing roller arrangement  49 . Beam or roller type member  51  and crushing roller arrangement  49  when in contact with photosensitive medium  102  on opposite sides provide a point contact on photosensitive medium  102 . Crushing roller arrangement  49  is adapted to move along a width-wise direction of photosensitive material  102  so as to crush microcapsules and release coloring material. Further examples of pressure applicators or crushing members that can be used in the image-forming device of  FIG. 1A  are described in U.S. Pat. Nos. 6,483,575 and 6,229,558.  
      Within the context of the present invention, the imaging material comprises a coloring material (which is used to form images) or material for black and white media. After the formation of the image, the photosensitive media is conveyed past heater  29  ( FIG. 1A ) for fixing the image on the media. In a through-feed unit, the photosensitive media could thereafter be withdrawn through an exit  32 . As a further option, image-forming device  15  can be a return unit in which the photosensitive media is conveyed or returned back to opening  17 .  
      An image-forming device  150  in accordance with one embodiment of the present invention is illustrated in  FIG. 2 . More specifically, as shown in  FIG. 2 , image-forming device  150  includes a processing assembly or development member  270  that is in the form of a pressure applicator or a pressure assembly. Processing assembly  270  includes a pressure application member or pressure roller arrangement that comprises a first rotatably mounted pressure roller  270   a  and an opposing backing member that can be a rotatably mounted pressure roller  270   b . Pressure roller  270   a  is rotatably mounted via a shaft  272  on a frame or mount  276 , while roller  270   b  is rotatably mounted via a shaft  274  on frame  276 . Each of the rollers  270   a  and  270   b  are mounted so as to define a nip portion  270 ′ there-between for the passage of media  152  and to provide a pressure or a compressive force to media  152  that is conveyed through the nip portion  270 ′. Pressure rollers  270   a ,  270   b  can be mounted in a manner where a predetermined pressure is applied at the nip portion based on the mounting of the rollers on the frame  276 , or a well known adjustment member can be provided to control the pressure applied by the pressure rollers  270   a ,  270   b  by varying the position of at least one of the rollers  270   a ,  270   b  relative to the other.  
      In a feature of the present invention, a shim member arrangement  154  is located at the processing assembly and comprises a shim in the form of a thin piece of plastic or film  154   a  that is wrapped around first and second support shafts or rollers  280  and  282 , as well as pressure roller  270   b . Therefore, as shown, the portion of the plastic or film  154   a  that is wrapped around the pressure roller  270   b  passes through the nip portion  270 ′ between the rollers  270   a ,  270   b , so that in essence, the nip portion  270 ′ is formed between roller  270   a  and the portion of plastic or film  154   a  that faces roller  270   a . With the arrangement of the present invention, the plastic or film  154   a  is provided so as to completely cover the imaging side of media  152  as the media passes through the nip portion  270 ′.  
      As illustrated in the schematic view of  FIG. 2  and the side view of  FIG. 3 , in order to develop an image on microencapsulated media  152 , the media  152  is conveyed in direction  400  past an exposing device  250  where a latent image on the media is exposed. The media  152  is then conveyed to nip portion  270 ′ where pressure through pressure rollers  270   a ,  270   b  provides a compressive force on at least the imaging side of the media  152 . This compressive force is sufficient to apply pressure to the microcapsules on the imaging side of the media having imaging material encapsulated therein to crush the microcapsules and develop the image.  
      Since plastic or film member  154  is wrapped around pressure roller  270   b , the pressure or compressive force is applied to the imaging side via the portion of the plastic or film member that faces the imaging side of the media  152 . Accordingly, the imaging side of the media  152  is protected by the plastic or film member  154  during the pressure application step.  
      With the arrangement of the present invention, the pressure applied by pressure rollers  270   a ,  270   b  should be of a sufficient force to quickly and rapidly crush selected microcapsules of the media  152  and develop the image. At the same time, shim member arrangement  154  having plastic or film  154   a  is sufficient to protect the media  152  and specifically, the imaging side of the media, so that any stress and deformation applied by the pressure roller  270   a  will not effect the resulting image and, more specifically, will not cause any defect, image patterns or other artifacts on the media from the compressive forces.  
      Additionally, the arrangement as shown in  FIGS. 2 and 3  is compact since the plastic or film member  154   a  of the shim member arrangement  154  is wrapped around pressure roller  270   b  and therefore provides for a reduced footprint. Also, since plastic or film member  154   a  is wrapped around rollers  280  and  282 , as well as pressure roller  270   b , the film or plastic member  154   a  can be rotated about the rollers  280 ,  282 ,  270   b  in either direction  402   a ,  402   b  as the plastic or film member is degraded or worn over time in order to present a new portion of the plastic or film member  154   a  at the nip portion  270 ′.  
      Further, plastic or film member  154   a , along with rollers  270   a ,  270  generally have a width the matches a width of the media  152 , so as to enable the processing along the full width of the media, while at the same time, as noted above, the shim member arrangement  154  protects the imaging side of the media by providing a cushioning effect to prevent any unwanted artifacts on the media and reduce the stress in the media support or base layer of the media.  
      After the development of the image at image processing assembly  270 , the media is transported pass a roller heating arrangement  160  that includes rollers  160   a , and  160   b  rotatably mounted on a frame  162 . At least one of the rollers  160   a ,  160   b  respectively includes a heating element such as a thermocouple ( 164   a ,  164   b ) therein to heat the rollers  160   a ,  160   b . Roller heating arrangement  160  also acts as a drive roller arrangement for the media. As the media passes between rollers  160   a  and  160   b , the media is heated to fix the image on the media and thereafter driven to an output of the image-forming device.  
       FIGS. 4 and 5  illustrate a further embodiment of an image-forming device in accordance with the present invention. As in the embodiment of  FIGS. 2 and 3 , image forming device  150 ′ of  FIGS. 4 and 5  includes and exposing device  250  the exposes a latent image on media  152  that is conveyed in direction  400 . After the exposing device  250 , the media is driven by way of a drive roller arrangement  800  having drive rollers  800   a ,  800   b  to a processing assembly  270 ′. Each of the rollers  800   a ,  800   b  are preferably mounted on a frame  800 ′ via shafts  802 ,  804 . One or both rollers  800   a ,  800   b  can be driven by a known arrangement such as a motor that drives circular gears, a rack gear etc. In the embodiment of  FIGS. 4 and 5 , drive rollers do not apply a compressive or crushing force to the media but deliver the media to processing assembly  270 ′ where a compressive or crushing force is applied to the imaging side of the media.  
      Processing assembly  270 ′ includes a pressure application member  870  that comprises a plurality of pressure applying members or elements  872  which could be stylus-like members or alternatively can be rollers, balls or other types of configurations that are sufficient to apply a pressure onto media. Pressure application member  870  can be adapted to move in directions  300   a ,  300   b  which are directions that are perpendicular to the direction of conveyance or movement  400  of the media, and basically is adapted to be conveyed along the widthwise direction of the media. In a preferred embodiment, this conveyance can be achieved by a motor  900  that is adapted to rotate a gear  902 . Gear  902  meshes with a rack gear  904   a  that includes a platform  904   b  that is attached or mounted to pressure application member  870 . Therefore, actuation of motor  900  causes a linear movement of rack gear  904   a  that provides for the linear movement of pressure application member along the width-wise direction of the media. This structure is one example of achieving a movement of pressure application member in a linear direction as shown and the present application is not limited thereto. It is recognized that other linear movement devices such as belts, pneumatics, etc. can also be used. Pressure application member  870  is also adapted to move down towards the media as the media passes between the pressure application member  870  and a backing member  860  as will be described. This downward movement again can be achieved by a variety of known mechanism such as gears, motor, belts, solenoids, air pressure, etc. that can be adapted to move the application member  870  and the driving arrangement down towards the media and upwardly away from the media.  
      Image-forming device  150 ′ of  FIGS. 4 and 5  also comprises a shim member arrangement  154 ′ which includes a shim in the form of a thin piece of plastic or film  954  that is wrapped or attached to opposing holding rollers  954   a ,  954   b . Rollers  954   a ,  954   b  are provided on opposing ends of backing member  860  and plastic or film member  954  extends between the rollers  954   a ,  954   b  so as to pass between the pressure application members  872  and the backing member  860 .  
      Therefore, after the latent image is formed, the photosensitive media  152  is driven by drive roller arrangement  800  between pressure applicator  870  and backing member  860 , and more specifically, between the film or plastic member  954  and the backing member  860 . It is noted that nip portions are defined between each of the individual pressure-applying members  872  which apply pressure to the media via the plastic or film member  954  and the outer surface of the backing member  860 . With the arrangement of the present invention, when the media  152  passes between pressure applicator  870  and backing member  860 , pressure applicator  870  can be operated to move downward toward the film or plastic member  954 . This causes each of the pressure application members  872  to apply a pressure on the plastic or film member  954  that is converted to a compressive force on the media  152 . This compressive force is sufficient to apply pressure to the microcapsules having imaging material encapsulated therein to crush the microcapsules and develop the image.  
      With the arrangement of the present invention, the pressure applied by pressure applicator  870  and specifically the pressure application members  872  should be of a sufficient force to quickly and rapidly crush selected microcapsules of the media  152  and develop the image. At the same time, film or plastic member  954  of shim member arrangement  154 ′ is sufficient to protect the media  152  and specifically, the imaging side of the media, so that any stress and deformation applied by the pressure applicator members  872  will not effect the resulting image and, more specifically, will not cause any defect, image patterns or other artifacts on the media from the compressive forces.  
      Pressure applicator  870  with pressure application members  872  as noted above, is adapted to crush the microcapsules, and also move in a widthwise direction to ensure that all of the selected microcapsules are crushed. At the same time, as noted above, the plastic or film member  954  of shim member arrangement  154  that protects the imaging side of the media provides a cushioning effect to prevent any unwanted artifacts on the media and reduce the stress in the media support or base layer of the media. Further, the placement of the plastic or film member  954  on opposing rollers as shown in  FIGS. 4 and 5  permits the movement of the plastic or film member in a direction transverse to the direction of movement of the media, such that as the plastic or film member becomes worn or time, a new portion of the plastic or film member can be presented by movement of the rollers  954   a ,  954   b.    
      After the development of the image at image processing assembly  270 ′, the media is transported pass a roller heating arrangement  160  that includes rollers  160   a , and  160   b  rotatably mounted on frame  162  as described above with reference to  FIGS. 2 and 3 . Also as described above with reference to  FIGS. 2 and 3 , at least one of the rollers  160   a ,  160   b  respectively includes a heating element such as a thermocouple ( 164   a ,  164   b ) therein to heat the rollers  160   a ,  160   b . Roller heating arrangement  160  also acts as a drive roller arrangement for the media. As the media passes between rollers  160   a  and  160   b , the media is heated to fix the image on the media and thereafter driven to an output of the image-forming device.  
      Therefore, the present invention provides for an image-forming device having a pressure development member that can be adapted to provide the necessary pressure to crush selected microcapsules on microencapsulated media, so as to release coloring material and develop an image. The arrangement of the present invention provides for a shim member arrangement that includes a thin piece of plastic or film member that can be located over the imaging side of the media The plastic or film member is effective to provide enough of a cushioning effect so as to reduce the stress in the media from the application of pressure and prevent the occurrence of unwanted artifacts or defects.  
      The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.