Patent Publication Number: US-2005143240-A1

Title: Polymer sleeve member for an image cylinder or a blanket cylinder

Description:
FIELD OF THE INVENTION  
      This invention relates to a polymer sleeve for an image cylinder or a blanket cylinder having a Young&#39;s Modulus of Elasticity from about 0.5 to about 10,000 and a Tg lower than about 20° C.  
     BACKGROUND OF THE INVENTION  
      In electrophotographic processes requiring an image cylinder and a blanket cylinder to produce electrophotographic copies, the image cylinder typically receives a charge, an image and a toner coating on the image area and then transfers the toner image to a blanket cylinder. The blanket cylinder transfers the toner image to a substrate, such as paper or the like, which passes via a web between the blanket cylinder and a back pressure roller to transfer the toner image to the substrate with the substrate thereafter being fused, as well known to the art.  
      In such processes, the image cylinder is a cylinder that typically includes a mandrel, which may be of aluminum, steel or any other suitably durable metal or conductive polymer of a suitable thickness to produce a noncompliant member that may be about 10 millimeters (mm) in thickness. The mandrel may include reinforcing structure internally and includes a very smooth, low out-of-round tolerance exterior. The image cylinder includes a mandrel and a sleeve positioned over the outside of the mandrel and is used for production and transfer of the images to the blanket cylinder. The image cylinder has a photosensitive layer on the exterior of the sleeve. The mandrel also includes bearings connected to each of its ends for positioning it in an electrophotographic copying machine and has an air inlet into an interior of the mandrel for an air discharge through a plurality of holes placed around one end of the mandrel near a tapered end of the mandrel.  
      In such processes, the blanket cylinder comprises a cylinder that typically includes a mandrel, which may be of aluminum, steel or any other suitably durable metal or conductive polymer of a suitable thickness to produce a noncompliant member that may be about 10 millimeters (mm) in thickness. The mandrel may include reinforcing structure internally and includes a very smooth, low out-of-round tolerance exterior. The blanket cylinder includes a mandrel and a sleeve positioned over the outside of the mandrel and is used for transfer of the images from the blanket cylinder to a substrate. The mandrel also includes fittings connected to each of its ends for positioning it in an electrophotographic copying machine and has an air inlet into an interior of the mandrel for an air discharge through a plurality of holes placed around one end of the mandrel near a tapered end of the mandrel.  
      The sleeves have been produced by use of a metal core, which is typically a noncompliant metal member, such as nickel or the like, which is produced by plating. The core must be seamless and must provide a very low variation surface outer diameter. The polymer layer has been positioned around the outside of the metal core, the metal core is mounted on a mandrel or the like, and the polymer layer is machined to a desired thickness. Additional exterior coatings have been applied by techniques such as ring coating and the like. The completed sleeve will have an internal diameter slightly less (typically about 100 microns) than the outer diameter of the mandrel upon which it is to be placed. This interference fit allows the sleeve to be firmly positioned on the outside of the mandrel after it is installed. The sleeve must have a smooth exterior and a closely controlled wall thickness.  
      The sleeve is typically installed by urging it toward and onto the tapered end section of the mandrel while air is ejected through the holes at the end of the mandrel near the tapered section. The air injection permits the positioning of the sleeve on the mandrel by an air bearing technique as known to those skilled in the art. The interference fit between the sleeve and the mandrel is accomplished and the sleeve is retained snugly and firmly in position on the outside of the mandrel. The outside of the mandrel, including the sleeve, must have an outside diameter variation within a range of about +/−12.5 microns. This close tolerance is necessary to ensure accurate receipt of images from the image cylinder and accurate transmission of the images to the substrate by the blanket cylinder.  
      There are various other specific requirements for the blanket cylinder and it has been previously considered necessary to meet these other requirements as well as those discussed above by the use of a metal core in the sleeve. This is a relatively expensive, time-consuming step and the cores are relatively expensive. As a result, a continued effort has been directed to the development of methods for producing sleeves more economically that will meet the demanding requirements for the blanket cylinder sleeves.  
     SUMMARY OF THE INVENTION  
      The present invention provides an improved sleeve member having no metal core. The sleeve member is adapted for mounting on a mandrel to form an image cylinder or a blanket cylinder for use in an electrophotographic process, the sleeve member has a sidewall of a polymer selected from the group consisting of thermoplastic, thermoset and elastomeric polymers, the sleeve member having an inner diameter from about 1 to about 20 percent less than the outer diameter of the mandrel and a Young&#39;s Modulus of Elasticity from about 0.5 to about 10,000 mega paschal (Mpa). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows an embodiment of a process and system wherein a blanket cylinder and/or imaging cylinder according to present invention is used;  
       FIG. 2  is a schematic diagram of a mandrel and a sleeve, with the sleeve being positioned for installation on the mandrel;  
       FIG. 3  is a schematic diagram of a sleeve positioned on the mandrel;  
       FIG. 4  is a schematic diagram of a mold positioned for rotation and injection of polymer material to form a polymer sleeve according to the present invention;  
       FIG. 5  shows a mold body that has been coated by a ring coating process; and  
       FIG. 6  shows an apparatus for producing a polymer sleeve having an exterior coating and a polymer layer positioned in a mold. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      In the description of the figures, the same numbers will be used to refer to the same or similar components throughout in the discussion of the figures.  
      In  FIG. 1 , an electrophotographic process and system  10  are shown. The process includes an image cylinder  12  positioned in engagement with a blanket cylinder  14 , which is positioned in engagement with a web  16  and a back pressure roller  18 . A substrate  20 , which may be paper or the like, is passed along a web  16  between blanket cylinder  14  and back pressure roller  18 . The substrate, now bearing an image, is passed along web  16  to a fuser section  26  where it is fused as known to those skilled in the art. The direction of travel of the substrate is shown by arrow  22 . A sensor  24  is positioned to ensure that substrate  20  passes in contact with blanket cylinder  14  at a proper time so that the image is properly positioned on substrate  20 .  
      In the operation of the process, image cylinder  12  rotates in a direction shown by arrow  36  and blanket cylinder  14  rotates in a direction shown by arrow  42 . Back pressure roller  18  turns in a direction as shown by arrow  19 . A nip  38  is formed between image cylinder  12  and blanket cylinder  14 . The nip is typically about 4.5+/−1 mm in width. Similarly, a nip  44  is formed between blanket cylinder  14  and back pressure roller  18 . This nip is about 4 to about 10 mm in width. A cleaning station  28  is positioned to contact the surface of image cylinder  12  after it passes nip  38 . The clean image cylinder surface then passes a charger station  30 , a writer station  32  where an electrostatic image is placed on the surface of cylinder  12  and a toner station  34  that applies toner to the electrostatic image, which is then transferred at nip  38  to blanket cylinder  14 . Blanket cylinder  14  transfers the image to substrate  20  and is thereafter cleaned by a cleaner  40  to ensure that a clean surface is provided on blanket cylinder  14  for transfer of an additional image from image cylinder  12 .  
      The image cylinder and blanket cylinder are of similar construction, although their outer coatings are different.  
      As shown in  FIG. 2 , blanket cylinder  12  includes a mandrel  50  that has side walls  54  and ends  52  and includes a tube  60  which supports a bearing  62  in operative engagement with one end of mandrel  50  and a shaft  64  which supports a second bearing  66  in operative engagement with the other end of mandrel  50 .  
      Tube  60  is adapted for the injection of air into mandrel  50 , which includes near one of its ends, a taper  56 , and a plurality of air holes  58 . These air holes are used for the ejection of air during the installation of a sleeve over mandrel  50 . Mandrel  50  has an outside diameter  68 , which is somewhat larger than the inner diameter  72  of a sleeve  70 . Sleeve  70  as shown, is a polymer sleeve according to the present invention. Its end  74  is urged into engagement with tapered section  56  of mandrel  50  and the sleeve is placed over an outside diameter  68  of mandrel  50  by an air step process using the ejection of air through holes  58 .  
      In  FIG. 3 , an installed sleeve, according to the present invention, is shown on mandrel  50 . The mandrel and sleeve that comprise blanket cylinder  14  are now assembled.  
      The blanket cylinder may have an outer diameter from about 40 mm to about 600 mm. While the diameter may vary widely, the variations in diameter or the out of round run out must be limited to +/−12.5 microns. This is necessary to ensure that the proper nip is achieved between the blanket cylinder and the pressure roller and that good image transfer from the image cylinder to the blanket cylinder and from the blanket cylinder to the substrate is accomplished.  
      The image cylinder may have a diameter from about 40 mm to about 600 mm. While the diameter may vary widely, the variations in diameter or the out of round run out must be limited to +/−12.5 microns. This is necessary to ensure that the proper nip is achieved with the blanket cylinder and that good image transfer is accomplished.  
      Desirably the outside of the image cylinder sleeve  70  has a Shore A hardness of about 90+/−10. The hardness is readily varied by changing the formulation of the polymer, as well known to those skilled in the art. The thickness of the sleeve wall may be from about 125 to about 1000 microns. The sleeve wall is polymer and is rigid enough to handle. Further the polymer desirably has a conductivity of at least 10 10  ohms·cm. As known to those skilled in the art, the polymer can be somewhat more conductive if desired. To produce an acceptable exterior surface on image cylinder  12 , it is necessary that the wall thickness of the sleeve be held to a thickness variation of +/−2.5 microns.  
      The blanket cylinder may have a diameter from about 40 mm to about 600 mm. While the diameter may vary widely, the variations in diameter or the out of round run out must be limited to +/−12.5 microns. This is necessary to ensure that the proper nip is achieved with the blanket cylinder and the pressure roller and that good image transfer from the image cylinder to the blanket cylinder and from the blanket cylinder to the substrate is accomplished.  
      Desirably the outside of the blanket cylinder sleeve has a Shore A hardness of about 65+/−5. The hardness is readily varied by changing the formulation of the polymer, as well known to those skilled in the art. The thickness of the sleeve wall may be from about 0.01 to about 40 mm and preferably from about 0.5 to about 20 mm. The sleeve wall is polymer and is rigid enough to handle. Further the polymer desirably has a conductivity of at least 108 to 10 14  ohms·cm. Generally the conductivity of the blanket cylinder sleeve is less than for the image cylinder sleeve, although the charge on the blanket cylinder is typically higher than that on the image cylinder. To produce an acceptable exterior surface on blanket cylinder  14 , it is necessary that the wall thickness of the sleeve be held to a wall thickness variation of +/−2.5 microns. Generally the blanket cylinder sleeve exterior is more compliant than the exterior of the image cylinder sleeve.  
      Sleeves have been formed in the past by positioning the sleeves on a seamless metal core typically formed by plating. The metal core provided support for the positioning of the polymer around the metal core and then the polymer was machined to the required size. Both the requirement for the metal core and the requirement for machining represent expensive and time consuming operations that have been required to achieve the precision necessary to produce the sleeves for the blanket cylinder. Recently methods for producing such sleeves without a metal core have been proposed.  
      As well known to those skilled in the art, an image-accepting layer is required on the outside of the image cylinder. This layer has been applied by processes, such as ring coating, dipping and the like. It is also known that inorganic or organic layers may be applied over the image-accepting layer to modify surface properties such as surface energy. The use and application of outer layers is not considered to constitute part of the present invention, which is directed to the production of a sleeve for an image cylinder meeting the exacting requirements for such a sleeve.  
      Typically the wall of the sleeve is at least partially includes thermoplastic, thermoset or elastomeric polymers or combinations thereof and particularly, polyurethanes are preferred. Polysiloxanes and fluorocarbon polymers and copolymers may also be used. The properties of the polymers may be varied as known to those skilled in the art to produce the desired properties in the sleeve member. The polymers may contain selected additives, fillers and the like as known to the art and may be used as blends of a plurality of the polymers.  
      As well known to those skilled in the art, a thin hard release layer such as a sol-gel, a ceramer or a fluoropolymer may be placed on the outside of the sleeve for the blanket cylinder. This layer has been applied by processes such as ring coating, dipping and the like. It is also known that inorganic or organic layers may be applied over the outside of the sleeve to modify surface properties such as surface energy. The use and application of such outer layers is not considered to constitute part of the present invention, which is directed to the production of a sleeve for a blanket cylinder meeting the exacting requirements for such a sleeve.  
      Such sleeves are readily produced by a method wherein a quantity of polymer precursors, a suitable liquid polymer, or a liquefiable polymer are positioned in a mold with the mold then being heated by a heater  90  to a suitable temperature to result in the presence of the polymer in the mold in a liquid form. A suitable mold is shown schematically in  FIG. 4 . The mold has a mold having a wall  78  and ends  82 . Openings  84  are generally left in the ends.  
      While the polymer could be introduced in a number of ways, it is shown as being introduced through a tube  86  that supplies a quantity of polymer suitable to form a sleeve of the desired thickness and of uniform thickness in the mold. The uniformity is achieved by spinning the mold while the polymer is heated and as the polymer moves through a molten phase. The molding may be done with a thermoplastic material, which after liquefying is allowed to cool back into a hardened phase. In any event, the formation of the solid sleeve is accomplished with rotation of the mold at a rate sufficient to produce a centrifugal force equal to at least five and preferably at least about 10 and desirably from about 5 to about 100 times the force of gravity at the inside of the mold until the polymer has solidified.  
      Suitable polymers include thermoplastic, thermoset and elastomeric polymers and particularly polyurethanes are preferred. With polyurethanes, polymer precursors may be placed into the mold and allowed to polymerize, cross-link and otherwise react to form the desired polymers as the mold spins. In any event, it has been found that when the inside of the mold is formed to have a surface within the required variations for the outside of the sleeve, that the inside of the sleeve and the sleeve wall thickness can be produced to sufficiently close tolerances by this method to enable its positioning over a mandrel and use on the blanket cylinder.  
      The heating and cooling of the mold may be at rates deemed suitable for the particular polymer used and desirably the rotation of the mold is continued until the polymer has reached a temperature of about 100° C. and thereafter until the polymer is cooled to a temperature selected for convenience in handling and the like. After cooling, the sleeve typically releases from the inside of the mold by contraction of the polymer so that the sleeve is readily removed from the mold by simply removing one of ends  82  and removing the sleeve. The sleeve is then ready for use or for coating with additional materials that may be desired on its exterior. A heater  90  is shown but it will be understood that any suitable type of heater can be used.  
      While sleeves can be produced by the molding process described above, the sleeves can also be produced by use of a mandrel with the sleeve being formed of a suitable polymer material positioned on the mandrel with the mandrel then being rotated to machine the polymer material to a desired configuration and thickness on a production mandrel. The sleeve is then removed from the production mandrel and can be used without a core. The polymer material can be placed on the production mandrel by any of a variety of known methods, such as extrusion casting, injection casting, ribbon casting and the like. In all instances the production mandrel must have an outer diameter the same as the desired inner diameter of the sleeve.  
      In either case, the use of the sleeve without the nickel core achieves certain advantages. Particularly, the nickel cores used in the sleeves for the blanket cylinder must be formed very precisely at a high cost. In addition, the handling of the nickel sleeve during the manufacturing process is high due to the intensive cleaning and priming steps required. Elimination of the use of a nickel core represents a substantial cost savings.  
      While the sleeves of the present invention may be formed by either process, they still require the positioning of an outer coating such as a ceramer, a sol-gel or a fluorocarbon polymer or copolymer or an image-accepting coating on the exterior of the sleeve. As indicated previously, such coatings can be applied readily by ring coating, dipping and the like. If the molding process is used, the exterior coating may be applied as a layer either inside the mold prior to positioning the polymer body of the sleeve or as one constituent of the mixture placed in the mold prior to rotation.  
      Such sleeves can be produced much more economically and more efficiently than with previously used methods. The sleeves produced consist essentially of a polymer sleeve for use by positioning it over an outer diameter of a mandrel. The polymer sleeve has a wall thickness from about 1 to about 20 mm, an inner diameter smaller than the outer diameter of the mandrel, a Shore A hardness of about 65+/−5 for a blanket cylinder and about 90+/−10 for an image cylinder and a wall thickness variation of no more than about +/−2.5 mm from the average wall thickness. These sleeves are highly desirable as replacement sleeves around the outside of mandrels in image cylinders and blanket cylinders. These sleeves are also much more economically produced while providing sleeves of an equivalent or superior quality to those produced by prior art methods.  
      While these sleeves are beneficial because they are more economical and provide adequately controlled wall thicknesses and surface properties, they must be produced at a size somewhat less than the outer diameter of the mandrel upon which they are to be placed. The undersizing is greater than that typically used with sleeves that contain a nickel core. For instance, a sleeve including a nickel or other metal core may be about 100 microns smaller than the outer diameter of a mandrel upon which it is to be placed. It has been found with the sleeves containing no nickel or other metal core that typically the undersizing must be in the range from about 1 to about 20 percent of the outer diameter of the mandrel, and preferably from about 4 to about 12 percent of the outer diameter of the mandrel.  
      This difference is primarily the result of the fact that the nickel or other metal core is relatively unexpandable whereas the polymer functions as a more elastomeric material. Since the polymer is more elastic, a greater expansion is necessary in order to obtain a desired friction between the inside of the sleeve and the outside of the mandrel. The amount of difference will depend upon a variety of factors such as the particular polymer used, the thickness of the sidewall of the sleeve and the like. These factors exert quantifiable effects upon the friction between the inside of the sleeve and the outside of the mandrel.  
      Such sleeves, since they are retained in position on the outside of the mandrel by the elasticity of the sleeve, have more stringent elasticity requirements than does the polymer sleeve that includes a metal core. As noted previously, the metal core is smaller, but not substantially smaller, than the outer diameter of the mandrel. The polymer sleeve without a metal core is typically 1 to 20 percent smaller than the outside of the mandrel. The friction between the polymer and the mandrel surface holds the polymer sleeve in place on the outside of the mandrel.  
      Accordingly, it is desirable that the polymer has a Young&#39;s Modulus of Elasticity from about 0.5 to about 10,000 MPa. Preferably, the Young&#39;s Modulus of Elasticity is from about 1 to about 10 MPa.  
      While the sleeves used for either the image cylinder or the blanket cylinder will require certain characteristics in common, the sleeve for the image cylinder will typically have a Shore A hardness of about 90+/−10. Typically the sleeve for the image cylinder has a conductivity of at least 10 10  ohm·cm.  
      The sleeve for use with a blanket cylinder typically will have a Shore A hardness of 65+/−5 with a conductivity of at least 10 7  to 10 14  ohm·cm.  
      By selecting a material for use as a sidewall polymer that has a Young&#39;s Modulus of Elasticity within the desired range and selecting a material that has a Tg well removed from the operating temperature, the desired elasticity in the sleeve sidewall can be obtained and maintained over extended periods of time. In the event that the Tg is near the operating temperature, it is to be anticipated that shorter service life from the sleeve may be realized because of the loss of elasticity as a result of polymer material fatigue and the like. Preferably the sidewall polymer is a rigid polyurethane, although other materials selected from thermoplastic and thermoset resins can also be used.  
      As also well known to those skilled in the art, different coating materials are placed on the outside of the sleeve for use on the image cylinder and on the blanket cylinder.  
      While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments.