Patent Application
20060222421
Transfer members are used in printers to transfer printing material, such as toner, representing an image on an electrostatically charged surface to a print medium. The surfaces of such transfer members may be susceptible to being damaged during printing such as being permanently deformed by multiple sheets or thicknesses of media accidentally being brought into contact with the surface or by excessive heat at the surface.
Charger 16 comprises a device configured to electrostatically charge surface 42. In the particular example shown, charger 16 includes 6 corotrons or scorotrons 46. A more detailed description of the exemplary charger 16 may be found in U.S. Pat. No. 6,438,352, the full disclosure of which is hereby incorporated by reference. In other embodiments, other devices for electrostatically charging surface 42 may be employed.
Imager 18 generally comprises any device configured to direct light upon surface 42 so as to form an image. In the example shown, imager 18 comprises a scanning laser which is moved across surface 42 as photoconductor 14 is rotated about axis 48. Those portions of surface 42 which are impinged by the light or laser 50 become electrically conductive and discharge electrostatic charge to form an image (and latent image) upon surface 42.
Although imager 18 is illustrated and described as comprising a scanning laser, imager 18 may alternatively comprise other devices configured to selectively emit or selectively allow light to impinge upon surface 42. For example, in other embodiments, imager 18 may alternatively include one or more shutter devices which employ liquid crystal materials to selectively block light and to selectively allow light to pass through to surface 42. In other embodiments, imager 18 may alternatively include shutters which include individual micro or nano light-blocking shutters which pivot, slide or otherwise physically move between the light blocking and light transmitting states. Examples of such physical shutters described in co-pending U.S. patent application Ser. No. 10/916,690 filed on Aug. 12, 2004 by Dale R. KOPF et al. and entitled IMAGE-FORMING APPARATUS, the full disclosure of which is hereby incorporated by reference.
In still other embodiments, surface 42 may alternatively comprise an electrographic surface including an array of individual pixels configured to be selectively charged or selectively discharged using an array of switching mechanisms such as transistors or metal-insulator-metal (MIM) devices forming an active array or a passive array for the array of pixels. In such an embodiment, charger 16 may be omitted.
Developer units 20 comprise devices configured to apply printing material 54 to surface 42 based upon the electrostatic charge upon surface 42 and to develop the image upon surface 42. In the particular example shown, printing material 54 generally comprises a liquid or fluid ink comprising a liquid carrier and colorant particles. The colorant particles may have a size of less than 2 microns, although in different embodiments the particle size may be different. In the example illustrated, printing material 54 generally includes approximately 2% by weight, colorant particles or solids prior to being applied to surface 42. In one embodiment, the colorant particles include a toner binder resin comprising hot melt adhesive. In one particular embodiment, printing material 54 comprises HEWLETT-PACKARD ELECTRO INK commercially available from Hewlett-Packard.
Each developer unit 20 generally includes a toner chamber 55, a main electrode 56, a back electrode 57, a developer roller 58, a squeegee roller 60, a developer cleaning system 62 and a reservoir 63. Toner chamber 55 comprises a cavity having an inlet (not shown) through which printing material is supplied from reservoir 63 to chamber 55 and to between electrode 56 and developer roller 58. Main electrode 56 and back electrode 57 comprise members situated opposite to developer roller 58 and configured to be electrically charged. In the particular example shown, back electrode 57 has a dielectric tip opposite roller 58 and cooperates with electrode 56 to form toner chamber 55.
Developer roller 58 comprises a roller configured to be rotatably driven and electrically charged to a voltage distinct from the voltage of electrode 56 so as to attract electrically charged ink particles or colorant particles of printing material 54 as roller 58 is rotated. Roller 58 is charged such that the charged ink particles being carried by roller 58 are further attracted and drawn to those portions of surface 42 that are electrostatically charged. Squeegee roller 60 removes excess printing material 54 from the surface of roller 58. In particular embodiments, squeegee roller 60 may be selectively charged to control the thickness or concentration of printing material 54 upon the surface of roller 58. In the example shown, electrode 58 and squeegee roller 60 are appropriately charged so as to form a substantially uniform 6 micron thick film composed of approximately 20% solids on the surface of roller 58 which is substantially transferred to surface 42.
Developer cleaning system 62 removes printing material 54 from developer roller 58 which has not been transferred to surface 42. The removed printing material 54 is mixed and pumped back to a reservoir 63 which colorant particles or solid content of the liquid or fluid is precisely monitored and controlled. One particular example of a developer unit 20 may be found in U.S. Pat. No. 6,438,352, the full disclosure of which is hereby incorporated by reference.
Charge eraser 22 comprises a device situated along surface 42 and configured to remove residual charge from surface 42. In one embodiment, charge eraser 22 may comprise an LED erase lamp. In particular embodiments, eraser 22 may comprise other devices or may be omitted.
Intermediate transfer member 24 comprises a member configured to transfer printing material 54 from surface 42 to print medium 12. Intermediate transfer member 124 includes an exterior surface 66 which is resiliently compressible and which is configured to be electrostatically charged. Because surface 66 is resiliently compressible, surface 66 conforms and adapts to irregularities on print medium 12. Because surface 66 is configured to be electrostatically charged, surface 66 may be charged to a voltage so as to facilitate transfer of printing material 54 from surface 42 to surface 66. As will be described in greater detail hereafter, in some embodiments, surface 66 has a compressibility that may aid in reducing the likelihood of damage caused by permanent deformation of surface 66.
In the particular embodiment shown, intermediate transfer member 24 includes drum 68 and an external blanket 70 which provides surface 66. Drum 68 generally comprises a cylinder supporting blanket 70. In one embodiment, drum 68 is formed from one or more materials having a relatively low thermal conductivity and/or heat resistance. In one embodiment, drum 68 may be formed from one or more polymers. In other embodiments, the cylindrical wall of drum 68 may be formed from a metal such as aluminum.
Blanket 70 wraps about drum 68 and provides surface 66. In one particular embodiment, blanket 70 is adhered to drum 68. In one embodiment, blanket 70 is secured to drum 68 in direct contact with drum 68 without any intervening or intermediate thermal coupling elements such as thermal coupling compounds or thermal coupling adhesives which fill in air gaps, cavities or voids that may exist between blanket 70 and drum 68. In other embodiments, such thermal coupling elements may alternatively be provided between blanket 70 and drum 68. As will be described in greater detail hereafter, some embodiments of blanket 70 include one or more resiliently compressible layers and one or more electrically conductive layers, enabling surface 66 to conform and to be electrostatically charged. Although intermediate transfer member 24 is illustrated as comprising drum 68 supporting blanket 70 which provides surface 66, intermediate transfer member 24 may alternatively comprise an endless belt supported by a plurality of rollers in contact or in close proximity to surface 42 and compressible roller 32. In such an embodiment, the belt may have a configuration substantially similar to blanket 70.
Heating system 26 is external to surface 66 of intermediate transfer member 24 and is configured to apply heat to printing material 54 being carried by surface 66 from photoconductor 14 to media 12. In the example shown, heating system 12 is configured to apply sufficient heat to printing material carried by surface 66 so as to concentrate solids of printing material by at least partially or substantially driving off or evaporating carriers or solvents of the liquid printing material, such as Isopar. In the embodiment shown, heating system 26 is also configured to apply sufficient heat energy to the printing material 54 so as to partially melt and blend solids or colorant particles of printing material 54, forming a hot adhesive liquid plastic. Because heating system 26 is external to surface 66 of intermediate transfer member 24, heat applied by system 26 is directly transmitted to printing material 54, rather than having to pass through intermediate layers, increasing thermal efficiency. Because heating system 26 is external to surface 66 of intermediate transfer member 24, drum 68 may be formed from materials having relatively low thermal conductivity and/or heat resistance. Blanket 70 may also be provided with a greater thickness or improved conformance and may be made from fewer layers and less expensive materials having a lower heat resistance. As a result, surface 66 and blanket 70 are less susceptible to damage from permanent deformation caused by multiple sheets of media accidentally contacting surface 66 and are less susceptible to damage by excess heat at surface 66 resulting from thermal inertia.
In the particular embodiment illustrated, heating system 26 includes heaters 74 and housing 76. Heaters 74 comprise mechanisms configured to generate heat which is transmitted to printing material 54 on surface 66. In the particular example shown, heaters 74 comprise multiple infra-red heaters arranged about surface 66 between photoconductor 14 and impression member 32. Heaters 74 are specifically configured to heat printing material 54 upon surface 66 to a temperature of at least 85° C. nominally 90° and no greater than 110° C. In one example embodiment, heaters 74 may include two individual heaters circumferentially spaced from one another by 2 centimeters and radially spaced from surface 66 by 1 centimeter. In other embodiments, heaters 74 may comprise other heating mechanisms. For example, heaters 74 may alternatively comprise inductive heating devices 74′ (shown in phantom) configured to emit or generate a magnetic field, causing a conductive layer, which is part of blanket 70 and proximate to surface 76, to have eddy currents and to be inductively heated so as to heat printing material 54 upon surface 66. The locations of the heaters shown and described herein are exemplary and may vary.
Housing 76 comprises one or more panels or walls extending partially about heaters 74. In particular embodiments, housing 76 may also partially support heaters 74. As shown by
Dryers 28 and 30 comprise devices configured to facilitate partial drying of printing material 54 upon surface 66. Dryers 28 and 30 are arranged about intermediate transfer member 24 and configured to direct air towards surface 66 and to withdraw air from surface 66. In the particular example shown, dryer 28 forces air through exit slit 80 which forms an air knife and withdraws or sucks air via exit port 82. Similarly, dryer 70 forces air toward surface 66 via chamber 84 and sucks or withdraws air away from surface 66 via chamber 86. One specific example of dryers 28 and 30 may be found in U.S. Pat. No. 6,438,352, the full disclosure of which is hereby incorporated by reference. In other embodiments, other dryers or drying mechanisms may be employed or dryers 28 and 30 may be omitted.
Impression cylinder 32 comprises a cylinder adjacent to intermediate transfer member 24 so as to form a nip 94 between member 24 and cylinder 32. Media 12 is generally fed between intermediate transfer member 24 and impression cylinder 32, wherein printing material 54 is transferred from intermediate transfer member 24 to medium 12 at nip 94. Although impression member 32 is illustrated as a cylinder or roller, impression member 32 may alternatively comprise an endless belt or a stationary surface against which intermediate transfer member 24 moves.
Cleaning station 34 is arranged proximate to surface 66 between the intermediate transfer member 24 and charger 16. Cleaning station 34 comprises one or more devices configured to remove residual ink and electrical charge from surface 66. In particular examples shown, cleaning station 34 flows a cooled liquid, such as a carrier liquid, across surface 66 between rollers 86, 88. Adhered toner particles are removed by roller 88, which is absorbent. Particles and liquids picked up by the absorbent material of roller 88 is squeegeed out by a squeegee roller 90. The cleaning process of surface 66 is completed by station 34 using a scraper blade 92 which scrapes any remaining toner or ink from surface 66 and keeps the carrier liquid from leaving cleaning station 34. One specific example of cleaning station 34 may be found in U.S. Pat. No. 6,438,352, the full disclosure of which is hereby incorporated by reference. In other embodiments, other cleaning stations may be employed or cleaning station 34 may be omitted.
In operation, charger 16 electrostatically charges surface 42. Surface 42 is exposed to light from imager 18. In particular, surface 42 is exposed to laser 50 which is controlled by a raster image processor that converts instructions from a digital file into on/off instructions for laser 50. This results in a latent image being formed for those electrostatically discharged portions of surface 42. Ink developer units 20 develop an image upon surface 42 by applying ink to those portions of surface 42 that remain electrostatically charged. In the embodiment shown, printing material 54 contains approximately 2% solids of colorant particles prior to being applied to developer roller 60 of each developer unit 20. Printing material 54 has an approximately 6 micron thick film with approximately 20% solids on developer roller 60 prior to being applied to surface 42.
Once an image upon surface 42 has been developed, eraser 22 erases any remaining electrical charge upon surface 42 and the ink image is transferred to surface 66 of intermediate transfer member 24. In the embodiment shown, printing material 54 forms an approximately 1.4 micron thick layer of approximately 85% solids colorant particles with relatively good cohesive strength.
Heating system 26 applies heat to printing material 54 upon surface 66 so as to evaporate the carrier liquid of printing material 54 and to melt toner binder resin of the colorant particles or solids of printing material 54 to form a hot melted adhesive. Dryers 28 and 30 partially dry the melted liquid colorant particles. Thereafter, the layer of melted colorant particles forming an image upon surface 66 is transferred to media 12 passing between transfer member 24 and impression cylinder 32. In the embodiment shown, the melted colorant particles are transferred to print media 12 at approximately 90 degrees Celsius. The layer of melted colorant particles freeze to media 12 on contact in the nip formed between intermediate transfer member 24 and impression cylinder 32. Thereafter, any remaining printing material 54 on surface 42 is removed by cleaning station 34.
These operations are repeated for the various colors for preparation in the final image to be produced. In other embodiments, in lieu of creating one color separation at a time on surface 66, sometimes referred to as “multi-shot” process, the above-noted process may be modified to employ a one-shot color process in which all color separations are layered upon surface 66 of intermediate transfer member 24 prior to being transferred to and deposited upon medium 12.
In addition, layer 172 does not need to be thermally bonded or adhered to drum 68 (shown in
In the particular example shown, layer 172 has a thickness of 250 micrometers. The fibers of layers 172 may be in the form of continuous filament, strand or yarn, as a mat, a structure of woven filaments. Examples of fiber materials include carbon, cotton boron, fiberglass, plastics, metals or alloys.
Layer 174 is coupled to layer 172 and is resiliently compressible. For purposes of this disclosure, the term “coupled” shall mean the joining of two members directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate member being attached to one another. Such joining may be permanent in nature or alternatively may be removable or releasable in nature.
Layer 174 includes one or more substantially adjacent layers of resiliently compressible cellular material, such as sponge material. The term “substantially adjacent” encompasses layers that directly contact one another or that directly contact one another but for extremely thin adhesive bonding layer disposed therebetween. Layer 174 provides a mechanical compliance for blanket 170 which typically has a thickness of at least about 500 micrometers. Nominally, in some embodiments, layer 170 has a thickness of at least about 800 micrometers. The thickness of layer 174 enables larger defects (abrupt changes in media thickness) be accommodated by blanket 170 before the elastic limit of layer 174 is reached, reducing the chance of permanent damage to blanket 170. In addition, the enlarged thickness of layer 174 provides a nip 94 (shown in
Layer 174 may be formed from cellular materials and may impart increased compressibility to blanket 170. The cellular material may include open cells or may include closed cells formed with the use of microspheres. In one embodiment, layer 174 is formed by spread coating, calendaring, dipping or otherwise contacting layer 172 with a matrix material which includes microspheres. Suitable matrix materials include plastic and thermosetting resins, polyurethanes and natural synthetic elastomers. Elastomeric materials include acrylonitrile, acrylic rubber, silicon rubber or an elastomer or plastic made from fluorocarbon material. Particular suitable elastomers include hydrogenated nitrile, nitrile or acrylic rubbers applied to layer 172 by a solvent carrier. Microspheres may be formed from materials such as thermoplastic resins, thermosetting resins, ceramics, glass and sintered metals. One example of a thermosetting resin for forming microspheres is a phenolic resin having a density of between about 0.01 and 0.05 grams per cubic centimeter. The microspheres range in diameter between 1 to 200 and nominally 50 to 130 microns. Such microspheres are disbursed relatively uniformly throughout the matrix material.
According to one embodiment, layer 174 is formed by applying a number of thin layers of about 0.002 millimeters in successive applications to layers 172. Microspheres are incorporated into the elastomeric material at a loading of about 4% to 90% and nominally of between about 10% to 70% of the solid contents. As a result, the microspheres are uniformly distributed throughout the elastomer so as to avoid appreciable crushing of the microspheres. Examples of microspheres are found in U.S. Pat. No. 5,754,931, the full disclosure of which is hereby incorporated by reference.
In other embodiments, cells may be formed in the matrix of layer 174 by leeching or by blowing (mechanically inducing air or other gas into the material) before it is applied to layer 172. Mechanical introduction of air or other gas into the matrix of layer 174 may be performed by aerating, stirring or other means. In still other embodiments, cells may be created using chemical blowing agents or foaming agents that are decomposable into gases as they are cured in a compound. One example of a class of blowing agents is CELLOGENS manufactured by Uni-Royal. Other types of blowing agents utilized to form cells within layer 174 are found in U.S. Pat. No. 5,754,931 and U.S. Pat. No. 4,548,858, the full disclosures of which are hereby incorporated by reference.
In still another embodiment, layer 174 may be separately formed and adhered to layer 172. Examples of adhesives that may be used to bond layer 174 to layer 172 include a compounded nitrile rubber or a variety of water and solvent based elastomeric adhesives.
Because printing material 54 is heated upon surface 66 of transfer member 24 by external heating system 26 (shown in
Layer 176 comprises one or more substantially adjacent layers of electrically conductive material which may be electrically connected to a voltage source. In the example shown, layer 176 extends generally adjacent to layer 174 and has a thickness of approximately 100 micrometers. Layer 176 generally has a resistance of less than about 2.5 kilo ohms per square inch. In general, the resistance of layer 176 may be low enough so that current flowing on layer 176 will not cause a substantial variation of voltage along the surface of blanket 170. Resistance of layer 176 and the resistance of an overlying layers including layers 178 and 180, control current flowing through the overlying layers. Layer 176 facilitates the creation of electrostatic charge along surface 66 to transfer printing material 54 from surface 42 (shown in
Layer 178 comprises one or more substantially adjacent layers of resiliently compressible non-cellular materials substantially adjacent to layer 176. Layer 178, sometimes referred to as a compliant or resilient layer, provides local compliance such that printing material 54 is transferred to all surfaces of print media 12 at nip 94 (shown in
In the particular example illustrated, layer 178 is formed from the same material or materials as layer 174 while omitting cells or voids. In one embodiment, layer 178 is formed from nitrile rubber and has a thickness of approximately 100 micrometers. In other embodiments, layer 178 may be formed from other resiliently compressible non-cellular materials and may have other thicknesses.
Layer 180 generally comprises one or more substantially adjacent layers of materials configured to release printing material 54 to media 12 at nip 94 (shown in
Overall, blanket 170 is more durable, less complex and is less expensive. Because layer 174, in some embodiments, has an increased thickness of at least 500 micrometers and nominally at least 800 micrometers, blanket 170 accommodates larger print medium variations without damage or permanent deformation of blanket 170. The increased thickness of layer 174 further allows the same size nip with a lower transfer force, decreasing seam banding. Because blanket 170 may omit thermal coupling to drum 68 (shown in
In one embodiment, layer 278 is formed by applying multiple coatings or layers directly upon layer 174. For example, in one embodiment, the first portion 279 of the coatings may be formed from a material including electrically conductive elements such as electrically conductive carbon black or metal fibers, while the second portion 281 of the coatings may be formed from the same material, such as nitrile rubber, but excluding the electrically conductive elements so as to be electrically insulating. Because layer 278 is coated directly on compressible layer 174, the fabrication of blanket 270 is simpler and less expensive. Moreover, because blanket 270 eliminates layer 176, the fabrication of blanket 270 is further simplified to reduce manufacturing costs. In other embodiments, layer 278 is separately formed with release layer 180 and laminated to layer 174.
Layer 374 is similar to layer 174 except that layer 374 is electrically conductive. As with layer 176 of blanket 170, the electrical conductivity of layer 374 enables layer 374 to be electrically coupled to a voltage source to create an electrostatic charge along surface 66 for adherence of printing materials to surface 66. In the particular example shown, layer 374 has an electrical resistance of no greater than 50 Kohm/square inch. In the particular example shown, layer 374 is made electrically conductive by the incorporation of electrically conductive carbon black or metal fibers. In the particular example shown, layer 374 is spaced from surface 66 by a distance no greater than 200 micrometers and nominally by approximately 105 micrometers. Because layer 374 is electrically conductive so as to eliminate the need for layer 176, blanket 370 is simpler and less expensive to manufacture.
Like blanket 170, blankets 270 and 370 are more durable, less complex and less expensive. Because layers 174 and 274 have increased thicknesses of at least 500 micrometers and nominally at least 800 micrometers. Blankets 270 and 370 accommodate larger print medium variations without damage or permanent deformation. The increased thicknesses further allow the same or larger nip with a lower transfer force, decreasing seam banding. Because blankets 270 and 370 may omit thermal coupling to drum 68 (shown in
Although the present invention has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present invention is relatively complex, not all changes in the technology are foreseeable. The present invention described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.
